CONTENTS

ArticlesPage ampPaper

Study of the effect of fluorescence increasing of N-ARYL-3-aminopropionic acids in the presence of zinc and cadmium ions

EV Dedyukhina NV Pechishcheva LK NeudachinaKYu Shunyaev AA Belozerova

4

Synthesis and microstructure design of metal and ceramic matrixcomposites using mechanical milling of the reactantsconstituents

D V Dudina O I Lomovsky

11

Modern methods of rhenium determination

OV Evdokimova NV Pechishcheva KYu Shunyaev14

The determination of the kinetic function structure for the high-temperature synthesis in the mechanically activated mixture 3Ni-Al

VYu Filimonov MA Korchagin EV Smirnov NZ Lyakhov

34

The preparation of mechanicomposites tungsten-metal and sinteringmaterials

T Grigoreva L Dyachkova A Barinova S Tsibulya N Lyakhov

37

Non-carbon preparation of Silicon by mechanically activatedthermal synthesis

TF Grigorieva TL Talako AI Letsko V Sepelak VG ScholzMR Sharafutdinov IA Vorsina AP Barinova PA VitiazNZ Lyakhov

53

Spin-crossover in the pentanuclear bypiramidal Co2Fe3 andFe2Fe3 compounds

S Klokishner S Ostrovsky A Palii K Dunbar B Tsukerblat

65

Self-propagating high-temperature synthesis of nanograined TiN-TiB2 composites

MA Korchagin BB Bokhonov

76

the standard enthalpy and entropy of formation OF GASEOUSAND LIQUID POLYCHLORINATED BIPHENYLSPOLYCHLORINATED DIBENZO-n-DIOXINS ANDDIBENZOFURANS

TV Kulikova AV Mayorova KYu Shunyaev

78

Preparation of composites CuZrO2 and CuTiO2 by MA SHS

AI Letsko TL Talako AF Ilyushchenko TF Grigoreva SVTsybulya IA Vorsina NZ Lyakhov

89

Zinc ions reduction on solid metal electrodes in chloride melts

A Lugovskoy Z Unger M Zinigrad D Aurbach104

Effect of hardening temperature on the structural-morphologicalcharacteristics of metal cements based on mechanosynthesizedcopper compounds

NZ Lyakhov PA Vityaz SA Kovaleva TF Grigoreva VGLugin AP Barinova SV Tsybulya

118

Phase states of mechanoactivated manganese oxides

SA Petrova RG Zakharov AYa Fishman LI Leontiev138

Chemical-thermal treatment in carbon manganese steel at induction-heating in various borating conditions

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

153

Wear-resistant detonation sprayed coatings based on the compositemechanically activated SHS-materials

AA Sitnikov VI Yakovlev MA Korchagin DM Skakov AAPopova ME Tatarkin

159

Microstructure studies of the coatings produced by arc deposition ofthe mechanoactivated SHS-composite TiC+XME (R6M5 PR-N70H17S4R4-3) powders

AA Sitnikov VI Yakovlev MA Korchagin MN SeidurovME Tatarkin

161

Morphological study of detonation sprayed coatings of calciumhydroxyapatite deposited on a nanostructured titanium substrate

AA Sitnikov VI Yakovlev YuP Sharkeev EV LegostaevaAA Popova

162

Fabrication and modification of metallic nanopowders by electricaldischarge in liquids

NV Tarasenko AA Nevar NA Savastenko EI Mosunov N ZLyakhov TFGrigoreva

164

Basalt plastics of enhanced heat and chemical stabilities

OS Tatarintseva NN Ноdakova VV Samoilenko182

Repair compound modified by nano particles of ferrous oxide

OS Tatarintseva SN Novosyolova TK Uglova184

Cathode processes in KCl-PbCl2 melt

YuP Zaikov PA Arkhipov YuRKhalimullina VVAshikhin186

186

CATHODE PROCESSES IN KCl-PbCl2 MELT

YuP Zaikov1 PA Arkhipov1 YuRKhalimullina2 VVAshikhin2

1The Institute of High Temperature Electrochemistry Ural Branch ofRussian Academy of Sciences

S KovalevskayaAcademicheskaya St 2220 620990 Yekaterinburg e-maildirihteuranru

2Open Joint-Stock Company ELECTROMED Scientific ResearchCentre Lenin St 1 624091 Verkhnyaya Pyshma

Technology of crude lead refining is developed in the Institute ofHigh-temperature Electrochemistry The crude lead was obtained fromthe car battery wastes While organizing the refinement in the moltensalts it is important to know deposition mechanisms [1] of lead ions inthe chloride melts containing oxychloride complexes It is necessary tostudy kinetics of electrode processes to understand this mechanism

Many authors studied kinetics of electrode processes of leadelectroreduction from chloride melts [2 ndash 10] Diffusion coefficients ofions in molten salts were measured by using radioactive isotopes [10]and with the help of electrochemical parameters [2 -9]

VPYurkinskyi DV Makarov [2 3] studied the mechanism anddetermined kinetic parameters of Pb(II) ion at electrochemicalreduction process in various individual melts (NaCl KCl и CsCl) aswell as in mixtures with various component content using linearvoltamperometry chronopotentiometry and chronoamperometrymethods Studies of lead ions reduction in lithium sodium potassiumand cesium chlorides showed that cation composition causes significantinfluence on the process Electrochemical reduction is limited by Pb2+

diffusion in LiCl and NaCl melts when in the potassium and cesiumchlorides by chemical reaction of complex ion [PbCln]

2-n dissociationDiffusion coefficient value was found to decrease and lead(II) iondiffusion activation energy to increase in the LiClndashCsCl row

YM Rybuhin EA Ukshe [4] measured lead ions diffusioncoefficients in molten chlorides by chronopotentiometry methodMeasurements were carried out under the argon atmosphere Therectangular polished platinum plate about 1 cm2 square was used as theworking electrode Molten lead placed into the quartz tube connected bycapillary with the bulk melt was the anode and reference electrode

187

NaCl KCl PbCl2 salts of chemically pure grade were used in the workThey were melted under vacuum before the experiment According tothe results of these studies the validity of the Stocks-Einstein equationto ion diffusion in molten salts is limited by the systems where theprocess of complex formation is absent that is why the significantdeviations from the equation take place in KCl ndash NaCl and especially inthe pure KCl

D=KT(6r) (1)where - viscosity r ndash ion radius according to Goldschmidt

Using oscillographic method II Naryshkin and VP Yurkovskyidetermined lead silver and cadmium ions diffusion coefficientsdepending on temperature against the equimolar mixtures NaCl-KCland LiCl-KCl Platinum microelectrode the platinum wire butt with 06mm diameter soldered into a quartz capillary was used 400 mm2

platinum foil was used as anode Chloride-silver electrode was used asthe reference electrode Short circuit during two minutes was used torenovate the electrode surfaces after each observation For obtaining themore reliable results each curve was observed several times and theresults were averaged out Authors showed the direct dependence of thepeak current from the investigated ions concentration This fact confirmsthe conclusion of Hills Ocsley and Terner [11] about the possibility ofthe oscilligraphic voltamperometry for the rapid quantitative analysis inthe molten salts Dependence of the peak potential from the logarithm ofinvestigated ion concentration for cadmium lead and silver was foundIndependence of the peak potential from the concentration logarithm forcadmium and lead chlorides corresponds to the dissolved matterdeposition Linear dependence observed for the silver chloridedemonstrates the absence of solubility in the process of silver depositionThe following valence values were found for silver 116 for lead 24

In the works [7-9] diffusion coefficients of lead zinc andcadmium ions in the LiCl ndash KCl и NaCl ndash KCl melts were determinedRaymond J Heus and James JEgan [7] used polyrophic method to studyprocesses of lead zinc cadmium ions electroreduction in the moltenchlorides Dropping bismuth electrode was a cathode Silver chloridecontaining 2 mass of AgCl in KCl ndash LiCl (eutectics) was a referenceelectrode Authors obtained linear dependencies of the concentration of

188

the investigated chlorides from the diffusion current densities Diffusioncoefficients were calculated with the Ilkovich equation

Richard B Stein [8] investigated the ion reduction reaction ofdivalent lead in the NaCl ndash KCl melt with oscillographic polyrographymethod Platinum microelectrode with 05 mm diameter soldered intothe quartz tube with 189х10-3 cm2 square was a cathode Referenceelectrode was silver chloride and the auxiliary electrode was graphiteAuthor founded out that the lead ion diffusion coefficients obtained bythe experimental data differ from calculated according to the equation ofStocks-Einstein He derived the conclusion that the cation structure ismore complex than just a single ion

HA Laitinen HCGaur [9] investigated lead cobalt and thalliumion reduction in the molten potassium and lithium chlorides withchronopotenciometry method Authors fixed the value of the transitiontime for melts containing the control values of ions under investigationAccording to the experimental data empiric dependences ofconcentrations and transitional time were determined Coefficients ofcadmium cobalt lead and thallium ion diffusion were calculated withSandrsquos equation (208 242 218 38810-5 cm2s correspondingly)

Cathode processes in chloride melts containing lead ions werestudied by chronopotentiometric and stationary galvanostaticpolarization curves methods

Experiments were carried out in the cell made of quartzhermetically closed fluoroplastic cover (2) with the holes for electrodesand thermocouple with accordance to the Fig1

Glassy-carbon was a working electrode (cathode) Glassy-carboncontainer played a role of a counter electrode Melted equimolar mixtureof lead lithium and potassium chlorides was used as the electrolyte forthe reference and working electrodes Electrolytes of the workingelectrode and reference electrode were separated by the diaphragm fromthe Gooch asbestos (7) Measurements were conducted relatively to thelead reference electrode that is a metal lead of C1 grade being in contactwith the melt containing 5 mass of lead chloride

Potassium chloride lithium chloride chemically pure grade andlead chloride of pure for analysis grade were used for electrolytepreparation Glassy-carbon container (4) was placed on the cell bottomon the special fireproof brick support (8)

189

Current lead to liquid-metal reference electrode was realized in aform of molybdenum rod and to glassy-carbon crucible through graphitebar Current leads were protected from the contact with melt by alundumtubes closed with the rubber plugs (1) to keep the cell hermeticallyclosed

Fig 1 Electrolytic cell 1 ndash rubber plugs 2 ndash fluoroplastic cover 3 ndash thermo-couple 4 ndash glassy-carbon container 5 ndash quartz-glass sell 6 ndash workingelectrode 7 ndash diaphragm 8 ndash fireproof brick support 9 ndash current leads toelectrodes 10 ndash electrolyte 11 ndash reference electrode

4

1

2

5

6

8

93

10

11

Vacuum

7

Ar

190

The cell was pumped out and fullfilled with purified argon Laterit was put into the resistance furnace and heated until the giventemperature under the abundant pressure of the inert gas

The setup was equipped with the automatic system of temperaturestabilization Temperature measurement was performed with the help ofchromyl-aluminum thermocouple Content of components in electrolytewere being controlled before and after the experiment with the atomic-absorption method

Stationary polarization measurementsLead ion deposition processes in eutectic melt of lithium and

potassium chlorides were studied at 04 to 30 mol lead chloride intemperature range from 673 to 823 К Polarization curves are given onthe fig 2 and 3 Two characteristic areas are observed on thepolarization curves On the first area little potential deviations from theequilibrium value takes place with cathode current density increasing to008 Acm2

Experimental points on the area with 04 mol lead chlorideconcentration are on straight lines described by equationsE = - 00703lgi - 01203 and E = - 00775lgi - 0091 for 673 and 773 Кcorrespondingly

At temperature 673 К tg is 0070 мВ and at 773 К - 0078 мВAccording to the equation

Ftg

RT23

n (2)

we have n=19 for 673 К and n=20 for 773 КAt lead chloride concentration 30 mol experimental points on

the first area of the polarization curve is described by the equationE= - 00779lgi - 00877

Amount of electrons in the reaction calculated on the equation (2)is equal 2

Reaching current densities 011 012 020 и 032 Асm2 on thefig3 for 673 723 773 823 К temperatures correspondingly Potentialis greatly shifted to the negative area to the values -084 -084 -106and -110 correspondingly

At small values of cathode current density there is one wavecorrespondingly to the fig 4 In some time after current rise potential

191

reaches its stationary value at current density 0045 Асm2 for 35 s forcurrent density 0060 Асm2 for 30 s After current disconnectionpotential comes back to its equilibrium value

Fig 2 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

(04 mol ) melt

192

Fig 3 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

melt at 823 К depending on the lead chloride concentration Concentration oflead chloride in mol per cents 1 - 04 2 - 05 3 ndash 30

193

Fig 4 Engaging curves at 823 К temperature and the different current density

On the engaging curves at current density values corresponding tothe second characteristic area on the polarization curves on the figures 2and 3 two waves on figure 5 are seen Time of reaching stationarypotential tst decreases with the current density increasing (for currentdensity 012 Асm2 tst equals 85 s for current density 017 Асm2 tst -45 s)

Fig 5 Engaging curves at 04 mol lead chloride concentration currentdensity 012 013 017 Асm2 and 823 К

194

Processes taking places on the electrode can be described in thefollowing way On the first characteristic area of the polarization curvelead ion deposition happens

Pb2+ + 2e = Pb0 (3)The limiting current density of lead reduction increases with the

temperature and lead chloride concentration At 30 mol of leadchloride concentration and 823 K limiting current density ilim is 12Acm2

On the second characteristic area of the polarization curvedeposition of the alkaline metal is possible on the reaction

K+ + e = K0 (Pb) (4)Low values of the alkaline metal reduction potentials might be

connected with the process of alloy formation of alkali metal with leadK + 4Pb = KPb4 (5)

Chronopotentiometric measurements at lead deposition from LiClndash KCl (45-55 mol ) ndash PbCl2 melt at 04 mol lead chlorideconcentration were performed at 823 K and current density range from010 to 017 Acm2 There is only one wave on chronopotentiometriccurves under these conditions Values of product i12 depending oncurrent density are given in the table 1 where - transition time

Table 1 Values of product i12 at diverse current density

s i mAcm2 i12 mAcm2s12

095 170 165161 130 165181 120 162

262 102 165

It is seen that the product i12 does not depend on current

density at constant concentration of depolarizator 0OxC In the table 2

potential values Е4 at time equaling the forth of the correspondingvalues of transition time are given

195

Table 2Values of Е4 potential of different current density

i Acm2 s 4 s Е4 V

010 264 0660 -0061

012 181 0453 -0600

013 161 0403 -0061

017 095 0238 -0062

It is seen that the potential Е4 does not depend on the experimentconditions the current density in this case

Equation for the reversible process can be as follows

1ln

nF

RT21

4t

ЕЕ

(6)

for irreversible process

2100

1lnlnnF

RT

t

nF

RT

i

knFCЕ

fhOx (7)

where E ndash electrode potential 4E - measurement potential at frac14

of transition time R ndash gas constant F ndash Faraday number n ndash number

of electrons T ndash temperature - transition time 0OxC - depolarizator

concentration 0fhk - deposition speed constant

On the figure 6 dependencies Е -

1ln

21

t

and Е -

21

1ln

t at 04 mol of lead chloride concentration current

density 01 Acm2 and 823 K are given

196

y = -00835x + 00654

0002

0022

0042

0062

0082

0102

0122

0142

0162

-115 -065 -015 035 085

- E В

1 2

Fig 6 Dependencies 1ndashЕ=f

1ln

21

t

and 2-Е =f

21

1ln

t

From the analysis of given graphic dependencies follows that the

experimental points in coordinates E -

1ln

21

t

are in a straight line

with the confidence interval 095 The can be described by equation

08300650 E

1ln

21

t

(8)

The amount of electrons in the electrode reaction was calculatedfrom the equation

F

RTn

0830 (9)

hence n=2

197

It follows from the experimental conditions on lead ion (II)deposition that the process is reversible ie it is controlled by the speedof divalent lead ions mass transfer from the volume of melt to theelectrode surface

Diffusion coefficient of lead dichloride at 823 K was calculated onSandrsquos equation

20

2

)(

)(2D

oxnFC

i

(10)

Lead ions (II) diffusion coefficient are equal to 23310-

5сm2s It is in good accordance with the data obtained by other authors[5 6]

References1 Yurkinsky V Makarov D Electrochemical reduction of lead ions in

halide melts Russian J Applied Chem 1994 67 p 1283-12862 Yurkinsky V Makarov D The influence of cation composition on

kinetics of lead electrochemical reduction in chloride melts RussianJ Applied Chem 1994 68 p 1474-1477

3 Ryabukhin Yu And Ukshe E The diffusion coefficients of lead inmolten chlorides DAN SSSR 1962 145 p 366-368

4 Naryshkin I Yurkinsky V Oscillographic investigation oftemperature coefficients for some chlorides diffusion in LiCl-KClRussian J Electrochemistry 1968 4 p 871-872

5 Naryshkin I Yurkinsky V Voltammetry in molten salts Russian JElectrochemistry 1968 2 p 856-866

6 Raymond J Heus James J Egan Fused Salt Polarography Using aDropping Bismuth Cathode ndash J of the Electrochemical SocietyOctober 1960 p 824-828

7 Richard B Stein The Diffusion Coefficient of Lead ion in FusedSodium Chloride Eutectic ndash J Electrochem Soc 1959 vol 106 p528

8 Laitinen H A Gaur H C Chronopotentiometry in Fused LithiumChloride-potassium Chloride - Anal Chem Acta 1958 vol 18 p1-13

9 Hills GI Oxley I E Turner D W Silicates Ind 1961 vol 26 p559

184

REPAIR COMPOUND MODIFIED BY NANO PARTICLES OFFERROUS OXIDE

OS Tatarintseva SN Novosyolova TK UglovaInstitute for Problems of Chemical and Energetic Technologies SB RAS

Biysk Altai region Russia labmineralmailru

The results of influence study of nano-dispersed ferrous oxide oncharacteristics of the composite material developed earlier (compound)and intended to repair and recover engineering structures and massifshave been presented in this paper The compound consists ofmulticomponent polymer matrix including epoxy oligomer low-molecular synthetic rubber plasticizer and process additives filler and alow-temperature amine hardener Microcalcite with particle size lessthan 50 μm has been used as filler

The composite has been modified with nano powder of ferrousoxide (II) (manufactured by MACH I Inc USA) consisting of needle-like crystalline particles with average size 4 nm and having specificsurface area 2379 m2g

Experiments have shown that even distribution of nano particlesin epoxy resin is caused with a high-velocity mechanical device underthe additional influence of ultrasonic field

The most important things for low-viscosity repair compositionsapplied to recover the integrity of natural materials are high flowabilitydetermining the ability to fill narrow-opened fractures and stability ofstrength properties for a long time

The positive effect of ultra-dispersed modifier is seen within therange of 030-035 of its percentage in the composition as shown byresults of the study given in the Table At these amounts the maximumvalues of flowability and mechanical characteristics have been providedThe logical increase in samples density indicates the optimality of thepacking developed and reduction in the porosity of a composite materialthat is important while using it in conditions on high humidity

The compound developed is environmentally friendlyincombustible waterproof stable to heat vibration and long mechanicalloads and can be used to perform repair work in construction industrypublic service stone mining and processing industries and architecture

185

Table Percentage influence of ferric oxide nano powder on technicalcharacteristics of the composite material

Value at modifier percentage Characteristics

0 010 020 030 035 040

Dynamic viscosityat T = 20 oC Pamiddots

210 212 225 262 266 288

Flowability cm 48 48 48 52 53 45

Density gm3 141 141 143 145 146 146

Compressive forceMPa

79 78 79 82 86 74

Relative deformation

023 021 021 025 025 020

182

BASALT PLASTICS OF ENHANCED HEAT AND CHEMICALSTABILITIES

OS Tatarintseva NN Ноdakova VV SamoilenkoInstitute for Problems of Chemical and Energetic Technologies

of the SB RAS Biysk Russialabmineralmailru

The experience of the application of metal pipes for chemicalproductions cool and hot water supply systems transportation ofpetroleum products and other aggressive fluids has shown that they aregreatly subjected to corrosion that reduces their lifetimes to severalyears Therefore natural is the observed worldwide tendency ofreplacing steel and cast iron by composite materials of high chemicalstability and durability to which glass-reinforced plastic having acomplex of high service properties should primarily be relatedHowever requirements for composites have presently increasedespecially with regard to their heat and chemical stabilities andresistance to microorganisms ground and waste waters

The paper demonstrates the study results with respect to thedevelopment of a composite material for filament-wound pipe productswhich is superior in its basic parameters to analogous ones in the field ofglass-reinforced plastic application As a reinforced material basaltroving with higher strength characteristics and resistance to aggressiveenvironments as compared to a glass one was chosen the polymermatrix was a heatproof binder TS developed on the basis of nitrogen-containing epoxy resin synthesized Having rheological properties andstrength characteristics similar to those that are widely used in themanufacture of filament-wound glass-reinforced plastic products of thebinders EDI and EChDI the binder TS possesses enhanced heat stabilityand low viscosity at room temperature which permits the reduction ofpower inputs for its processing

The obtained data on advantages of both basalt fiber and thebinder developed have to the full extent been realized in laboratorysamples of the reinforced composite and in basalt plastic pipes producedindustrially (see Table below)

183

Table Temperature dependence of elastic modulus E of basalt plasticpipes

Еmiddot103 MPa at Т degСBinder 20 85 125 155 200

EDI 11701 11263 4363 3528 -EChDI 11277 10951 9944 6217 -

TS 19960 19336 19179 17557 9096

The 9-fold strength reserve of the basalt plastic pipes determinedwhen hydro-tested under extreme conditions (150degC 15 MPa) hasconfirmed the possibility of creating composite polymer materialsoperating under high-temperatures and humidity

164

FABRICATION AND MODIFICATION OF METALLICNANOPOWDERS BY ELECTRICAL DISCHARGE IN LIQUIDS

NV Tarasenko1 AA Nevar1 NA Savastenko2 EI Mosunov3 NZ Lyakhov4 TFGrigoreva4

1 Institute of Physics NAS B Minsk Belarus2 Leibniz-Institute for Plasma Science and Technology Greifswald Germany

3 The Institute of Machine Mechanics and Reliability NAS B Minsk Belarus4Institute of Solid State Chemistry and Mechanochemistry SB RAS

18 Kutateladze Str Novosibirsk 630128 Russia grigsolidnscru

Electrical-discharge technique was developed for preparation ofmetallic and metal-containing nanoparticles as well as for modificationof metal micropowders in liquids The morphology and composition ofthe nanopowders formed under various discharge conditions wereinvestigated by means of transmission electron microscopy and X-raydiffraction analysis The optimal conditions for the production oftitanium carbide and copper nanoparticles embedded in carbon layerswere found

IntroductionA synthesis of metallic and metal-containing nanopowders is of a

great interest due to their potential applications as super hard materials[1] environmentally friendly fuel cells with highly effective catalysts[23] and so on Transition metal carbides have been widely studied aselectrocatalysts because of their electrochemical properties andelectrical conductivities Nanosized carbon particles are suitable supportmaterials for certain types of catalysts Of particular interest for futurecatalytic applications are carbon-based materials with embeded metalnanoparticles [4] As long as carbon nanoparticles are relatively inertsupports many studies have been conducted in order to find which pre-treatment procedures are needed to achieve optimal interaction betweenthe support and metal species [5]

For any application of nanoparticles to be commercially viablelow-cost production methods have to be developed A low-temperatureand non-vacuum synthesis of nanoparticles via discharge in liquid(submerged discharge) provides a versatile choice for economicalpreparation of various nanostructures in a controllable way An arc

165

discharge in liquid nitrogen has firstly been reported as a cost-effectivetechnique for the production of carbon nanotubes in 2000 by Ishigamy etal [6] Since that time many efforts have been devoted to develop thismethod Sano et al proposed to submerge electrodes in water instead ofliquid nitrogen [78] They reported synthesis of carbon onions [78] andsingle-walled carbon nanohorns (SWNHs) [9] In latter case carbonnanoparticles were produced via discharge in water method with thesupport of gas injection Parkansky et al reported nanoparticlessynthesis via a pulsed arc submerged in ethanol Ni W steel andgraphite electrodes were used [1011] The particles composition variedfrom carbon to pure metal including various intermediate combinationsof these materials Bera et al employed an arc-discharge in a palladiumchloride solution to produce carbon nanotubes decorated with in situgenerated Pd nanoparticles [10] Importantly the synthesized materialcontained no chlorine

In this paper methods based on electrical-discharges in liquids forproduction of tungsten and titanium carbide as well as coppernanoparticles embedded in carbon nanostructures is reported Thecapabilities of arc and spark discharges submerged in liquids forsynthesis of nanoparticles as well as electrical-discharge modification ofmetallic powders were studied

Experimental detailsThe experimental reactor (Fig 1) consisted of four main

components a power supply system (pulse generator) the electrodes aglass vessel and a water cooling system outside the beaker A pulseddischarge was generated between two electrodes being immersed in 100ml of liquid (pure (995) ethanol or 0001 M CuCl2 aqueous solution)The appropriate combinations of pairs of metallic (tungsten titanium orcopper) and graphite electrodes were used The choice of ethanol wasmotivated by the fact that organic compounds play a role of a carbonsource to produce nanoparticles in discharge-in-liquid system [7 12]Addition of the copper chloride salt into double distilled water favoredthe activation of discharge process Metal (tungsten titanium or copper)and graphite rods with diameters of 6 mm were employed as electrodesAn optimum distance between the electrodes was kept constant at 03mm to maintain a stable discharge The discharge was initiated byapplying a high-frequency voltage of 35 kV The power supply

166

provided several different types of discharges Both direct current (dc)and alternating current (ac) arc and spark discharges were generatedwith repetition rates of 100 and 50 Hz respectively Current I(t) wasrecorded during the discharge as a function of time by means of anoscilloscope The peak current of the arc discharge was 9 A with a pulseduration of 4 ms The peak current of the pulsed spark discharge was 60A with a pulse duration of 30 μs

The synthesized products were obtained as colloidal solutionsAfter 15 min presedimentation the large particles precipitated at thevessel bottom The top layer contained the small nanoparticles wascarefully poured off into a Petry dish These suspended nanoparticleswere characterized by UV-Visible optical absorption spectroscopytransmission electron microscopy (TEM) and X-ray diffraction analysis(XRD) for their size morphology crystalline structure and composition

The optical absorption spectra of colloids were measured by UVndashVisible spectrophotometer (CARY 500) using 05 cm quartz cuvetteTransmission electron microscopy was performed by LEO 906E (LEOUK Germany) microscope operated at 120 kV A drop of solution putonto the amorphous carbon coated copper grid for TEM measurementsThereafter the liquid was evaporated at the temperature of 80 C Afterthe drying of colloidal solution the deposit obtained on the bottom ofPetri dish was examined by XRD Powder composition and itscrystalline structure were characterized by using X-ray diffraction atCuK (D8-Advance Bruker Germany)

Synthesis of carbide nanopowdersPromising capabilities of the developed technique for synthesis of

tungsten and titanium carbides (WC TiC) as well as carbon-encapsulated copper nanoparticles were demonstrated using theappropriate combinations of pairs of metallic and graphite electrodessubmerged into the appropriate solution Also physical and chemicalprocesses induced by the electrical discharges in liquids were studied tooptimize the process of nanoparticles synthesis

The results of nanoparticles preparation are summarized in theTable1 The synthesis rate varied in range of 2 ndash 40 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofmetal and graphite electrodes The synthesis rate increased withincreasing of discharge current and decreasing of pulse duration The

167

composition and morphology of nanoparticles were also found to dependon discharge parameters It should be noted that there is a possibility toscale-up the process

Table 1 summarized the variation in synthesis rate andcomposition of tungsten nanopowders with the discharge parameters Asa general tendency the synthesis rate was order of magnitude higher forspark discharge than that of arc discharge It may be due to thedifference in current value [13] For both arc and spark discharges itwas found that the synthesis rate is lower when tungsten was acting as acathode This result is consistent with literature data For example Beraet al reported that the consumption of anode is higher than that ofcathode [13]

Table 1 Summary of nanopowder synthesis conditions andresults of nanopowder characterization by XRD

XRD-analysisDischargetype

Electrodes Powdersyield

mgminW2Cvol

WC1-xvol

Cvol

Wvol

1 ac arc W C 02 71 781 147 -2 dc arc W(cathode)C(anode) 01 62 901 37 -3 dc arc W(anode)C(cathode) 02 66 715 219 -4 ac spark W C 25 58 328 614 -5 dc spark W(cathode)C(anode) 12 570 307 89 336 dc spark W(anode)C(cathode) 21 56 325 618 -

As it can be seen from the Table 1 the synthesized nanopowder isa mixture of hexagonal W2C face centered cubic WC1-x and graphite Nopeaks corresponding to WO were observed Nanopowder contained alsosmall amount body centered cubic W when synthesis was performed bydc current spark discharge with tungsten rod acting as cathode Here theparticular behavior of this discharge should be stressed showing ratherhigh ability to synthesize W2C Moreover in contrast to the other sparkdischarges synthesized material contained relatively small amount ofgraphite On the other hand applying tungsten as a cathode materialappears to reduce C content in nanopowder prepared via arc dischargetoo Generally the content of C is higher and content of WC1-x is lowerwhen synthesis was performed by spark discharge

168

Nanoparticles prepared by arc discharge were observed in theiragglomerated form The agglomerated nanoparticles were surrounded bythe grey regions which were probably graphite layers This typical viewwas seen everywhere in TEM images of product synthesized by arc forboth ac and dc current discharges irrespective of electrodes polarityThat fact implies that the morphology of synthesized nanopowders wasgoverned rather by the current pulse duration and value of peak currentthan the polarity of the electrodes Since nanoparticles were observed inthe agglomerated form it was difficult to measure their size correctlyWe suppose that approximately 4 nm nanoparticles are formed duringthe arc discharge in ethanol

Fig1 shows the TEM image of titanium carbide nanopowdersynthesized by spark discharge in ethanol As can be see from the Fig1the nanoparticles were also surrounded by graphite layers Fig 1demonstrates that the nanoparticles synthesized by spark were nearlyspherical with a mean diameter of ~ 7 nm The particle size distributionwas rather narrow (plusmn 2 nm) The XRD pattern of synthesized sample isshown in Fig 1 (right picture) The diffraction peaks at 60deg 418deg605deg 724deg 765deg and 407deg 504deg 590deg 667deg 741deg correspond tothe formation of cubic face-centered titanium carbide TiC and cubicprimitive TiC2 respectively There are some diffraction peaks with 2θvalue of 407deg 504deg 590deg 667deg and 741deg which can be assigned tothe hexagonal C The amount of TiC reached 887 vol The quantitiesof TiC2 and C in samples detected by XRD corresponded to ca 47 vol and ca 67 vol respectively

Fig 1 TEM image (left picture) of titanium carbide nanopowder synthesizedby ac spark discharge and XRD-pattern (right picture) of the sample

169

Synthesis of copper-carbon composite nanostructuresNumerous studies have focused on synthesis of metal-containing

carbon nanocapsules (CNCs) via submerged discharge method[89141516] Because of the carbon sheets surrounding the metal corethe CNCs are protected from the environment and from degradation Thecarbon coatings mean that nanoparticles are biocompatible and stable inmany organic media Thus carbon encapsulated nanoparticles arecandidate for bioengineering application high-density data storagemagnetic toners for use in photocopiers [81718] The metal containingcarbon nanostructures were prepared by using the electrode frommixture of graphite and metal precursor [16 1920] Recently Xu et aldemonstrated a possibility to synthesize Ni- Co- and Fe-containingCNCs by an arc discharge between carbon electrodes in aqueoussolution of NiSO4 CoSO4 and FeSO4 respectively [15] In contrast tothe data reported by Bera et al the synthesized material consisted of Oand S due to SO4

-2 ionic precursors in the solution Since the metal core-forming material was supplied by liquids the production rate of CNCswas limited by the salt concentration [4] This restriction may cause alimit to apply the submerged discharge method to the large-scaleproduction of CNCs

In this paper Cu-based nanoparticles were prepared viasubmerged discharge of bulk copper and graphite electrodes in a copperchloride (CuCl2) aqueous solution Thus material of copper electrode aswell as Cu from solution was supposed to be incorporated into theresulting nanoparticles The effect of discharge parameters and electrodecomposition on the morphology and composition of final products havebeen investigated Additionally synthesized material was modified bylaser irradiation The changes in nanoparticles morphology andcomposition were examined by transmission electron microscopy(TEM) X-ray diffraction (XRD) and UV-Vis spectroscopy

The six types of nanoparticles suspension were prepared underdifferent discharge parameters The synthesis parameters aresummarized in Table 2 As it can be seen the weight change of eachelectrode was generally higher when spark discharge was generatedThe anode consumption rate was higher than that of cathode irrespectiveto a discharge type and electrode material However in contrast to theliterature data [4] there was no cathode gain in weight As a generaltrend the nanopowder synthesis rate was higher for spark discharge than

170

that of arc discharge It may be explained by the difference in currentvalue [21] For both arc and spark discharges it was found that thesynthesis rate was higher when copper was acting as an anode There isa discrepancy between nanopowder synthesis rate and materialconsumption rate The values of discrepancy D listed in the Table 2were calculated as follows

100()

CCu

syn

RR

RD (1)

Here Rsyn is the synthesis rate of nanopowder RCu is theconsumption rate of the copper electrode and RC is the consumptionrate of the graphite electrode The discrepancy D depended ondischarge parameters For ac-discharges the value of discrepancy washigher for spark discharge than that for arc discharge For dc-discharges this trend remained if the polarity of electrodes was takeninto account It is worth to notice here that the discrepancy betweenmaterial consumption rate and nanopowder synthesis rate may be causednot only by separation of sediment fraction but by the reaction of carbonatoms with water resulting in the production of gaseous compounds [9]

Table 2 Summary of nanopowder synthesis parametersType of

dischargepeak currentpulse duration

Electrodes materialRCu and RC

mg min-1RSyn

mg min-1D

Cu 671 ac1) spark60 A 30 micros C 48

59 49

Cu 122 ac arc10 A 4 ms C 26

25 34

Cu (cathode electrode) 473 dc2) spark60 A 30 micros C (anode electrode) 61

21 81

Cu (anode electrode) 664 dc spark60 A 30 micros C (cathode electrode) 46

69 38

Cu (cathode electrode) 115 dc arc10 A 4 ms C (anode electrode) 25

19 47

Cu (anode electrode) 286 dc arc10 A 4 ms C (cathode electrode) 21

33 33

1) Alternating current pulsed discharge2) Direct current pulsed discharge

171

This coincides with the fact that the largest discrepancy (morethan 80) was observed in sample with the largest graphite electrodeconsumption rate (sample 3) For all samples the synthesized powderseparated into three phases one floating in suspension one settling atthe bottom as sediment and one as a layer of film-like material floatingon the liquid surface

The aqueous solutions of CuCl2 were discharge treated for only 20s to acquire yellowish suspensions The transparency of the suspensionsdecreased with the time during the discharge treatment The liquidsturned to dark yellow after treatment by ac-discharge for 10 min Thesuspensions resulting from dc-discharge treatment were conspicuouslydarker when C electrode was acting as an anode The nanoparticlessuspension produced by spark and arc discharges were dark brown anddark grey respectively It might be due to the presence of relatively largeamount of carbon particles in suspension (see Table 3) The dc-dischargetreated solutions were olive-green when Cu was used as the anodeelectrode Yellow or green colour of suspension may indicate theoxidation of copper nanoparticles [22] The presence of Cu2Onanoparticles was further confirmed by XRD analysis No changes incolour were observed after laser irradiation of suspensions

Figure 2 shows the absorption spectra of as prepared (a) and laserirradiated (b) suspended nanopowders synthesized by dischargetreatment of aqueous solution of CuCl2 (2) for 1 min The spectra werecorrected to the contributions of solvents The optical density increasedwith decrease in wavelength Generally the optical density ofsuspensions prepared by spark discharge was higher than that ofsuspension prepared by arc discharge This is consistent with the factthat the nanoparticles production rate was higher when the solution wastreated by spark discharge In the spectral range of 200 ndash 500 nm theoptical density of the samples 1 4 6 was higher than that of samples 23 and 5 This seems to suggest that the main parameter in determiningthe optical properties of suspensions was concentration of Cu-basednanoparticles For the samples number 1 and 4 a weak absorption peakwas observed at very short wavelength According to the literature data[2324] a surface plasmon peak at wavelength of 289 nm may beattributed to the presence of very small separated Cu nanoparticles (lt 4nm in size) Though TEM examination confirmed the presence of smallnanoparticles in sample 1 there were no nanoparticles with diameter less

172

than 4 nm in sample 4 Moreover there were no copper nanoparticles insample 1 as revealed by the XRD (see below) More likely theexistence of weak absorption peak at 280 nm implied formation of liquidbyproducts We did not observe in the absorption spectra surfaceplasmon band around 570 nm Missing of the plasmon band can beexplained by copper oxidation on the particle surface [23] Thissuggestion was further confirmed by XRD analysis (see below) Thesuspensions exhibited the same colours after laser irradiation butabsorption intensity increased for samples 3 1 and to the less extent forsample 5 as illustrated in Figure 2b TEM analysis revealed themorphological similarity of irradiated samples 1 3 and 5 (see below)

Figure 3 depicts the corresponding TEM images for thesuspensions shown in curves 1-6 of Figure 2 Parts (a) and (b) representthe TEM views of the as-prepared and irradiated samples respectivelyThree distinct structures were observed dark small spherical particlesdark particles surrounded by a gray shell and gray flake-like structureshaving diffuse contours The small dark particles with diameter 2-5 nmwere observed in samples 1 2 3 and 5 (marked with black ellipses inFigure 3) Some dark particles notable when using ac spark dischargefor synthesis were bigger than 20 nm indicating coalescence Thenanoparticles synthesized by ac arc discharge (sample 2) were

Fig 2 Absorption spectra for the as-prepared (a) and laser modified (b)suspended nanoparticles produced by ac- (12) and dc- pulsed discharges(3456) The following electrode pairs were used Cu and C for the ac-spark(1) and ac-arc (2) discharges Cu as a cathode electrode and C as an anodeelectrode for the dc-spark (3) and dc-arc (5) Cu as an anode electrode and C asa cathode electrode for the dc-spark (4) and dc-arc (6)

173

surrounded by the arrowed gray regions which were probably carbonshells as shown in Figure 3a

Fig3 TEM images of nanoparticles from as-prepared (a) and irradiated (b)suspensions produced by ac- (12) and dc- pulsed discharges (3456) Thefollowing electrode pairs were used Cu and C for the ac-spark (1) and ac-arc(2) discharges Cu as a cathode electrode and C as an anode electrode for thedc-spark (3) and dc-arc (5) Cu as an anode electrode and C as a cathodeelectrode for the dc-spark (4) and dc-arc (6)

174

As we did not have any direct evidence that the shells consisted ofcarbon these nanostructures will be referred further as core-shellnanoparticles The core-shell nanoparticles were also observed in colloidprepared by dc arc discharge between copper cathode and graphiteanode (sample 5) It can be seen that core-shell nanoparticles rangedfrom 20 to 50 nm in diameter while the cores within the nanoparticlesvaried from 8 to 25 nm The cores were non-spherical They seemed tocompose of small particles clustered together The flake-like structureswith diffuse contours were 50 nm in size They were observed in allsamples Samples 4 and 6 consisted mostly of structures with diffusecontours On the basis of the above observations the ac arc dischargeand dc arc discharge with copper anode electrode seemed to be moresuitable for synthesis of nanoparticles with core-shell structure

It is clear seen that many smaller particles with sizes around 2-7nm were generated after the irradiation of samples 2 4 and 6 Theparticles larger than 10 nm completely disappeared The micrographrevealed that after the irradiation these suspensions consisted ofparticles with circular cross-section whereas before the irradiation theparticle shape was not spherical The nanoparticles were dispersed verywell No small nanoparticles were observed in suspensions 1 3 and 5after the irradiation Though as can be seen by comparing Figure 1(a)3(a) and 5(a) with 1(b) 3(b) and 5(b) the shape of nanoparticleschanged after the irradiation The laser induced morphology change mayoccur through heating of the nanoparticles because of the absorption ofthe laser light [25] According to the mechanism proposed by Takami etal the morphology of irradiated nanoparticles was determined by therelationship between temperature of nanoparticles their melting andboiling point

The laser induced change in shape and size occurred if thetemperature of nanoparticles was at the boiling point If the temperaturewas lower than the melting point no changes took place If thetemperature was between melting point and boiling point only thechange in shape occurred Thus the difference in morphology of theirradiated samples can be attributed to the difference in theircomposition Even being irradiated with the same laser light intensitythe nanoparticles of different composition changed their morphology indifferent ways as they have different melting and boiling points

175

X-ray diffraction data were collected to identify synthesizedsamples The diffraction peaks at 432deg and 503deg correspond to theformation of faced-centered-cubic Cu There are three diffraction peakswith 2θ value of 365deg 423deg and 614deg which can be assigned to theprimitive cubic Cu2O Besides there are two peaks at 240deg and 265degwhich can be assigned to the hexagonal C XRD revealed that dischargetreatment of aqueous solution of CuCl2 led to the formation of Cu2

(OH)3Cl and Cu2OCl2 because of a strong affinity between chlorine andthe metal (peaks with a value of 2θ around 165deg 19deg 31deg 323deg 327deg330deg 387deg 398deg 401deg 503deg 505deg 538deg and 178deg 360degrespectively) For comparison the XRD patterns of initial solution ofCuCl2 are also plotted at the top of Fig 4 Non-treated aqueous solutionof copper chloride was allowed to evaporate and than analyzed by XRDThe diffractogram of this sample showed peaks at about 2θ around162deg 220deg 240deg 267deg 289deg 328deg 340 348deg 352deg 409deg 430deg448deg 453deg 490 and 573deg which are characteristics of CuCl2middot2H2O

XRD data were used to semi-quantitatively determine thepercentage of constituents The semi quantitative analysis of phasecomposition is shown in Table 3 The nanopowder composition wasstrongly dependent on the synthesis parameters It should be noted herethat metallic copper was only formed by dc-discharge treatment whencopper was acting as an anode electrode (samples 4 and 6) Synthesizedmaterial contained copper mostly in form of oxide (Cu2O) copperhydroxychloride (Cu2(OH)3Cl) and copper oxychloride (Cu2OCl2)Difference in Cu2O and C contents among all samples was significantSamples 2 and 5 contained no copper oxide while sample 6 had thelargest percentage of copper oxide (ca 80 vol) On the other handsample 6 contained no carbon The carbon contain in sample 4 exceeded80 vol The quantities of Cu2(OH)3Cl in samples ranged from lessthan 2 vol to ca 30 vol Only three samples contained Cu2OCl2

(samples 12 and 5) The maximal amount of Cu2OCl2 detected by XRDcorresponded to ca 30 vol In spite of high copper electrodeconsumption rate sample 4 contained unexpectedly small quantities ofCu and Cu-containing compound It might be due to the formation ofrelatively large and heavy copper microparticles They precipitated fromcolloid quickly after synthesis Therefore they were not collected andanalyzed by XRD (see experimental section) A correlation was

176

observed between low copper electrode consumption rate and absence ofCu and Cu2O fractions in nanopowder composition for samples 2 and 5

It should be stressed here that the core-shell structures wereobserved for only samples 2 and 5 Taking into account firstly thatsamples 2 5 and 6 were prepared by arc treatment secondly that thesample 6 contained no C and assuming that the shells consisted ofcarbon we can suggest that arc discharge was more suitable forsynthesis of core-shell nanoparticles On the other hand the chemicalcomposition of final product was governed by different competingreactions As they have different equilibrium constants they may form anetwork where the ratios of the products are sensitive to concentrationsof each of the many components Therefore the slight difference ininitial concentration might results in significant difference incomposition and morphology of synthesized material (compare samples5 and 6)

Although the exact mechanism for formation of nanoparticles viadischarge in solution process is not clear the following possibility may

Table 3 Semi-quantitative analysis of synthesized powder by XRD

XRD-analysisType of

dischargeElectrodesmaterial Cu

volCu2Ovol

Cvol

Cu2(OH)3Clvol

Cu2OCl2vol

1 ac1) sparkCuC

- 135 403 165 297

2 ac arcCuC

- - 646 300 54

3 dc2) sparkCu (cathode)C (anode)

- 391 370 239 -

4 dc sparkCu (anode)C (cathode)

78 83 825 14 -

5 dc arcCu (cathode)C (anode)

- - 339 336 325

6 dc arcCu (anode)C (cathode)

74 775 - 151 -

1) Alternating current pulsed discharge2) Direct current pulsed discharge

177

be considered During discharge treatment of the liquid copper andgraphite electrodes were heated melted and vaporized in the region ofthe discharge generated In the vicinity of electrodes the liquid was alsovaporized rapidly due to extremely high temperature Hence the plasmaregion produced by the discharge adjacent to the electrodes wassurrounded by a gas bubble Following Sano et al [8] the gas mixturemay comprise CO and H2 formed as follows

22 HCOOHC (2)

This reaction might cause the discrepancy between electrodeconsumption rate and nanopowder synthesis rate since some of carbonatoms formed gaseous CO Sano et al reported that gas bubbles didnot comprise water vapor since no condensation occurred [8] Howeverwe should consider that water vapour also existed in the discharge zoneas we did not obtain any evidence of its absence

Copper chloride is an anionic compound that dissociates inaqueous solution and may form different ionic species such as Cu2+ Cl-or complex ions such as CuCl2

- CuCl32- CuCl4

2-[26] The reduction ofcopper ions into copper atoms was likely taking place in plasma regionduring discharge treatment of the liquid as shown in Eq 3

02 2 CueCu (3)

As the temperature in the vicinity of the electrodes was estimatedto be around 4000 K [8] the thermal decomposition of complex ions tometallic copper possible took place in discharge zone (Eq (4-6))

20

2 ClCuCuCl (4)

20

3 322 ClCuCuCl (5)

202

4 2ClCuCuCl (6)

The nanoparticles were then formed from the complex gasmixture through different transformation stages namely nucleationgrowth condensation and coalescence Both the evaporated copper fromelectrode and Cu produced by reduction of ions from solutions were

178

supposed to be incorporated into the resulting nanoparticles Becausewater vapor existed in gas bubble the copper nanoparticles were easilyoxidized Reduction of copper oxide by carbon monoxide and hydrogenwas possible the subsequent step (Eq (7) and (8))

OHCuCOOCu 22 2 (7)

222 2 COCuHOCu (8)

According to the XRD measurements (see Table 3) copper oxidewas only partially reduced into copper in sample 4 and 6 The data ofXRD analysis implied also reaction of chlorine with copper andorcopper oxide to form Cu2Cl(OH)3 and Cu2OCl2 These reactions mightinvolve hydrogen produced via reaction (2)

It should be noted that there was no direct evidence to support theabove-mentioned formation sequence and the true mechanism may bemore complicated

ConclusionsFrom the results and discussion presented above the following

conclusions can be madeThe electrical discharge between two electrodes immersed in

ethanol is a suitable method to produce in a controllable waynanoparticles with different contents of metal and carbon By varyingthe current value and its pulse duration morphology of nanoparticlesand their composition can be changed The average diameters of theprepared nanoparticles were in the range of 3-7 nm

Cu-based nanoparticles with different morphologies wereprepared via submerged electrical discharge of bulk copper and graphiteelectrodes in a CuCl2 aqueous solution Synthesized material wassubjected to laser-induced modification It was found that core-shellnanoparticles were formed by treatment of CuCl2 aqueous solution bythe arc pulsed discharge with pulse duration of 4 ms and peak current of10 A

The synthesis rate varied in range of 19 ndash 69 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofcopper and graphite electrodes The synthesis rate was found to behigher when copper was acting as an anode electrode The synthesis rate

179

increased with increasing of discharge current and decreasing of pulseduration The composition and morphology of nanoparticles were alsofound to depend on discharge parameters The copper nanoparticleswere only formed by dc-discharge treatment when copper was acting asan anode electrode The maximum diameter of nanoparticles did notexceed 50 nm while the minimum diameter was around 2 nm Theresults of the experiments imply that plasma treatment with longer pulseduration and lower current leads to the formation of carbon embeddednanoparticles TEM confirms the formation of encapsulatednanoparticles

Irradiation of nanoparticles in aqueous solution by a pulsedNdYAG laser at 532 nm was found to cause the shape change and sizereduction of the particles

AcknowledgementsThe work has been supported by the Integral Program of the

Siberian Branch of RAS under the Grant 138-T-09-CO-014 Authorsare thankful to KV Scrockaya for carrying out the TEM investigations

References

1 I Zalite S Ordanyan G Korb (2003) Synthesis of transition metalsnitridecarbonitride nanopowders and application of them formodification of structure of hardmetals Powder Metallurgy Journal46 2143 ndash 147

2 XG Yang and CY Wang (2005) Nanostructured tungsten carbidecatalysts for polimer electrolyte fuel cells Appl Phys Lett 8624104-1 -224104-3

3 M Rosenbaum F Zhao U Schroder F Scholz (2006) InterfacingElectrocatalysis and Biocatalysis with Tungsten Carbide A High-Performance Noble- Metal-Free Microbial Fuel Cell Angew Chem118 1-4

4 D Bera S C Kuiry M McCutchen S Seal(2004) In situ syntesis ofcarbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method J Appl Phys 96 5152-5157

5 P Serp M Corrias P Kalck Carbon nanotubes and nanofibers incatalysis Applied Catalysis A General ndash 2003 ndash Vol 253 ndash P337-358

180

6 Ishigami M Cummings J Zettl A Chen S (2000) A simple method forthe continuous production of carbon nanotubes Chem Phys Lett319 457-459

7 Sano N Wang H Alexandrou I Chhowalla M Amaratunga G A J(2001) Nanotechnology Synthesis of carbon ldquoonionsrdquo in waterNature (London) 414 506-507

8 Sano N Wang H Alexandrou I Chhowalla M Teo K B KAmaratunga G A J (2002) Properties of carbon onions produced by anarc discharge in water J Appl Phys 92 2783 ndash 2788

9 Sano(a) N (2004) Low-cost synthesis of single-walled carbonnanohorns using the arc in water method with gas injection J PhysD 37 L17-L20

10 Parkansky N Alterkop B Boxman R L Goldsmith S Barkay ZLereah Y (2005) Pulsed discharge production of nano- andmicroparticles in ethanol and their characterization PowderTechnology 150 36-41

11 Parkansky N Goldsmith S Alterkop B Boxman R L Barkay ZRosenberg Yu Frenkel G (2006) Features of micro and nano-particlesproduced by pulsed arc submerged in ethanol Powder Technology161 215-219

12 P Muthakarn N Sano T Charinpanitkul W TanthapanichakoonT Kanki Characteristics of Carbon Nanoparticles Synthesized by aSubmerged Arc in Alcohols Alkanes and Aromatics Phys Chem Bndash 2006 ndash Vol 110 37 ndash P 18299 -18306

13 D Bera G Johnston H Heinrich S Seal A parametric study on thesynthesis of carbon nanotubes through arc-discharge in water Nanotechn ndash 2006 ndash Vol 17 ndash P 1722-1730

14 Hsin Y L Hwang K C Chen R-R Kay J J (2001) Production and insitu metal filling of carbon nanotubes in water Adv Mater 13 830-833

15 Xu B Guo J Wang X Liu X Ichinose H (2006) Synthesis of carbonnanocapsules containing Fe Ni or Co Carbon 44 2631-2634

16 Lange X Sioda M Huezko A Zhu Y Q Kroto H W Walton D R M(2003) Nanocarbon prodction by arc discharge in water Carbon 411617 ndash 1623

17 Sergienko R Shibata E Akase Z Suwa H Nakamura T Shido (2006) Carbon encapsulated iron carbide nanoparticles synthesized in

181

ethanol by an electric plasma discharge in an ultrasonic cavitationfield Mater Chem Phys 98 34-38

18 Leo G H Jeong S H J W Ri H C (2002) Excelent magnetic propertiesof fullerene encapsulated ferromagnetic nanoclusters J Magn Mater246 404 ndash 411

19 Ang K H Alexandrou I Mathur N D Amaratunga G A J Hag S(2004) The effect of carbon encapsulation on the magnetic propertiesof Ni nanoparticles produced by arc discharge in de-ionized waterNanotechnology 15 520 ndash 524

20 Sano(c) N Nakano J Kanki T (2004) Synthesis of single-walledcarbon nanotubes with nanohorns by arc in liquid nitrogen Carbon42 686-688

21 Bera(c) D Jonston G Heinrich H Seal S (2006) A parametric studyon the synthesis of carbon nanotubes through arc-discharge in waterNanotechnology 171722-1730

22 Yeh M-S Yang Y-S Lee Y-P Yeh Y-H Yeh C-S (1999) Formationand characteristics of Cu colloids from CuO powder by laserirradiation in 2-propanol J PhysChem B 103 6851-6857

23 Aslam M Gopakumar G Shoba T L Mulla I S Vijayamohanan K(2002) Formation of Cu and Cu2O nanoparticles by variation of thesurface ligand preparation structure and insulating-to-metallictransition J Colloid Inter Sci 25579-90

24 Salkar R A Jeevanandam P Kataby G Aruna S T Koltypin YPalchik O Gedanken A (2000) Elongated copper nanoparticlescoated with a zwitterionic surfactant J Phys Chem B 104 893-897

25 Takami A Kurita H Koda S (1999) Laser-induced size reduction ofnoble metal particles J Phys Chem B 1031226-1232

26 Brown JB (1948-1949) The constitution of cupric chloride inaqueous solution Transaction of the Royal Sociaty of New Zeland 7719-23

162

MORPHOLOGICAL STUDY OF DETONATIONSPRAYED COATINGS OF CALCIUM HYDROXYAPATITE

DEPOSITED ON A NANOSTRUCTURED TITANIUMSUBSTRATE

AA Sitnikov VI Yakovlev YuP Sharkeev 1EV Legostaeva 1 AA Popova

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1Institute of Strength Physics and Materials Science SB RASTomsk

Biocompatible coatings are effectively formed by spraying ofcalcium hydroxyapatite Са10(РО4)(ОН)2 powders on a titanium substrateRecently along with the composition macro- and microstructuredevelopment the surface morphology of the coatings has receivedincreasing attention In a number of studies the roughness of thecoatings has been shown to significantly influence the inductionprocesses of cells As a substrate material titanium VT1-0 has beenchosen which has several advantages being highly biocompatiblebioinert practically non-toxic corrosion-resistant and possessing lowthermal conductivity and low coefficient of thermal expansion Themorphology of the gas-detonation sprayed calcium phosphate coatingsdeposited on ultrafine-grained and nanostructured titanium substratesand implant imitations has been studied The substrates and implantimitations were produced in the Institute of Strength Physics andMaterials Science SB RAS Tomsk

It was shown that the detonation sprayed hydroxyapatite powderswith particles ranging from 1 to 20 microm formed coatings non-uniform inthickness and phase composition The roughness of the coatings wasRa=365-472 microm (class 5) When hydroxyapatite particles of 20-100microm in size are sprayed coatings more uniform in thickness and phasecomposition are formed (Fig1) with an average roughness of Ra = 624microm (class 4) Preliminary treatment of the titanium substrate by sandingand chemical etching allows increasing the adhesive strength of thecoating up to 20MPa

163

Fig1 SEM images hydroxyapatite powder (a) detonation sprayedhydroxyapatite coating (b) XRD pattern of the coating (c)

Biological studies have demonstrated biocompatibility andbioactivity of the coatings It was found that the calcium phosphatedetonation sprayed coatings induce growth of tissue cells with 100probability which indicates that the relief of the coatings is optimal forfixation and aging of the cells Comparative studies of calciumphosphate coatings produced by detonation spraying and those producedby micro-arc in an electrolyte containing phosphoric acidhydroxyapatite and calcium carbonate have shown the advantages ofdetonation spraying for providing the required phase composition of thecoating This opens up a possibility of making two-phase coatings(hydroxyapatite and beta-calcium phosphate) ensuring the closest matchin composition to the bone tissue

ва б

100

200 20 30 40 50 60 70 80 90 10

(1

10) (002

) (2

10)

(2

11)

(

300

)

(3

10)

(

222

)

312

)

(3

20)

(

511

)

(

432

)

(5

22)

(

100

)

161

MICROSTRUCTURE STUDIES OF THE COATINGSPRODUCED BY ARC DEPOSITION OF THE

MECHANOACTIVATED SHS-COMPOSITE TIC+XME(R6M5 PR-N70H17S4R4-3) POWDERS

AA Sitnikov VI Yakovlev MA Korchagin1MN Seidurov ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

One of the main challenges in the development of new materialsfor arc deposition using flux-cored wires is to design materials of specialinterest using cost-effective and ecologically friendly technologies Asmaterialstechnologies meeting these requirements we can proposelayered composites produced by self-propagating high-temperaturesynthesis (SHS) in mechanically activated powder mixtures

The samples of SHS-mechanocomposites of TiC+XMe (R6M5PR-N70H17S4R4-3) composition arc-deposited on steel 45 substrateswere selected for investigations Microstructure of the arc-depositedcoatings was studied using a Carl Zeiss AxioObserver A1m OpticalMicroscope For observations cross-sections of the samples wereprepared and etched with a solution containing 20 potassiumferricyanide К3[Fe(CN)6] 20 КОН and 60 H2O Finemicrostructure and composition of the deposited layers were analyzedusing a Carl Zeiss EVO50 Scanning Electron Microscope equipped withan EDS X-ACT laquoOXFORDraquo device

The investigations show that the microstructure of the depositedlayers is uniform with submicron titanium carbide reinforcing phase inthe form of separate inclusions or chains of particles in the matrix

159

WEAR-RESISTANT DETONATION SPRAYED COATINGSBASED ON THE COMPOSITE MECHANICALLY ACTIVATED

SHS-MATERIALS

AA Sitnikov VI Yakovlev MA Korchagin 1DM Skakov AA Popova ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

The application of titanium carbide as a material for thermalspraying is rather difficult mainly due to its high melting temperatureand high hardness

A technology has been developed abroad for the production of thecomposite powders for spraying The production of these compositepowders is a laquoknow-howraquo of MBN Nanomaterialia (Italy)

An approach to the development of TiC-containing coatings canbe based on the technology of mechanocomposites with metallic orintermetallic matrices reinforced with nanosized particles of a ceramicphase [1] The technology of the powder preparation consists of 3 stagesAt the first stage the mixture of initial reactants which in this particularcase are titanium carbon and nichrome is mechanically activated (MA)in a planetary ball mill At the second stage self-propagating hightemperature synthesis (SHS) is conducted resulting in the formation ofTiC particles uniformly distributed in the metallic matrix AdditionalMA of the products of SHS at the third stage along with dispersingtitanium carbide particles creates a principally new state of the matrixwhich experiences grain refinement and shows high internal stresses andhigh concentrations of non-equilibrium defects In addition thesubsequent mechanical activation can be advantageously used forcompositions with higher matrix contents that are not possible to makethrough the SHS special additives can be also introduced into thecomposites at this stage

In order to compose the initial mixtures the following powderswere used titanium PTM lampblack PM-15 and nichrome PR-N70H17S4R4-3 Mechanical activation of the powder mixtures and theSHS-products was carried out in a planetary ball mill AGO-2M

160

Detonation spraying was performed using the laquoKatun-Mraquo set-upIt was found that the chemical composition did not change duringspraying

Wear resistance of the sprayed coatings was evaluated using afriction machine 2168 UMT in the laquoshoe-on-diskraquo mode A coating 02mm thick was deposited on a steel 40 shoe Prior to deposition the shoewas rubbed against the disk until a contact spot was formed over thewhole surface of the shoe After the coating was deposited the workingsurfaces were subjected to abrasive diamond treatment to reduce theirroughness

Tribological tests showed that with increasing metallic matrixcontent from 20 to 60 wt the weight losses under dry friction at 950 Nincreased almost twice Comparative tests of the coatings and thesamples of hardened steel revealed that the wear of the coatings obtainedfrom the mecahnocomposite powders was 8 times lower than that ofsteel 40H

References1 MAKorchagin DVDudina Application of self-propagating high-

temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007 v43 2 p176-187

153

CHEMICAL-THERMAL TREATMENT IN CARBONMANGANESE STEEL

AT INDUCTION-HEATING IN VARIOUS BORATINGCONDITIONS

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

Ural Federal University Ekaterinburg RussiaAltay State Agrarian University Barnaul Russia

Abstract Processes of borating of high-carbon manganese steel65Mn by carbide of boron and amorphous boron in conditions of fluxwith additives of various activators of borating are investigated at high-speed induction-heating It is shown that the nature of the boratingagent the additive of flux activators CaF2 and NH4Cl have influence onstructure and properties which are formed on a surface of boroneutectics

Keywords boron carbide of boron induction heating chemical-thermal processing

Among modern processes of chemical-thermal treatment (CTT)production engineering of saturation of surface layer constructional andalloy steels with boron ndash the borating occupy a special place In boratingit is possible to obtain the extended beds distinguished by high hardnessand strength corrosion-resistance abrasive durability and highreceptivity to wear on a surface of a steel detail [1 2] However themajority of known processes of borating are prolonged and are badlybuilt in into flow diagrams of state of productions

Intensification of CTT processes and in particular borating canbe carried out with application of technology of short-term high-speedheating of steel detail surface with the borating composition put on herrf currents (RFC) up to temperatures of formation of new phases andeutectics (1100-1350 оС) in systems Fe-B Fe-B-C and Fe-Me-B-Cwhere Ме - is an alloy element from group Cr Mn Ni etc [3] Unlikewell investigated processes of borating of alloy steels by mediums anddaubing at temperatures up to 950оС [4] there are open generalquestions of peculiarities of chemical interaction of components in suchsystems phase condition and properties of formed products

154

In the present work chemical-thermal treatment of carbonmanganese 65Mn steel combined with RFC-heating of its surface invarious borating conditions has been investigated

Experimental partAs the basic subject of research 65Mn (GOST 4543-71) alloy

carbon steel was chosen from the group of the same kind manganesechromos chromos-nickel and chromos-manganese steels from group 70U8А 50CrMnА 30CrMnSiА 45Cr 70Mn etc with similar propertiesand composition

Technical carbide of boron B4С in accordance with GOST 5744-85 and reactive amorphous boron of qualification reagent-grade weretaken as borating agents of different nature Known composition for theinduction deposition (F1) consisting of borax glass the boric anhydridecalcium silica and welding flux АN-348А (30 Na2B4O7 20 B2O310 CaSi2 and 40 flux АN-348А) was used as flux Reagent-gradeCaF2 and NH4Cl served as activators

RFC-heating of samples was carried out in a loopback water-cooled copper inductor by diameter of 160 mm connected to RF-lampgenerator VCG 7-600066 The adjustment of a contour and geometryof an inductor provided heating of researched samples to the temperatureof 1300-1350оС during 40-60 sec with the subsequent stabilizationAfter holding at the specified temperature during from 1 up to 2 minsamples were pulled out from an inductor and cooled down loosely

Microstructure of the coverings formed has been investigated andthickness of borated bed has been determined (МIМ-7 Neophot-30)hardness has been measured (PМТ-3 by 50 100 g) phase composition(DRON-2 radiation Co-Kα speed of angular moving of a sample of 1grads min) has been determined

Results and discussionIt is known that classical production engineering of kiln borating

are based on gradual (during 05-6 h) saturation of a surface of a steelproduct by boron from various pastes daubings liquid or a gaseous fluidat temperatures of process from 750 up to 950 оС Thus in the capacityof sources of boron its various compounds (В2О3 В4С ВF3 Na[BF4]etc) are applied capable to decay on active elements at temperatures ofprocess Depending on a phase condition of the borating agent hardness

155

and liquid borating are distinguished and also borating from a gas phase[4] We investigated six variants of mixes for high-speed borating atRFC-heating steel 65Mn Mixes differed in the nature of the boratingagent e borating agent composition presence fluxes componentsactivators and technological additions Compositions of the mixes usedare given in table 1

Table 1

Mixes Boratingagent

Activator Flux

Iа B4C (84) NH4Cl (6) F1 (10)II B4C (84) ndash F1 (16)

IIIа B (90) CaF2 (5) F1 (5)

Mixes I Iа II and IIа used as borating agent contained carbide ofboron mixes III IIIа - amorphous boron in mix Iа activator chloride ofammonium and in mix IIIа - fluoride of calcium has been added allmixes contained melted flux as a fluxing component for inductiondeposition F1

With decrease of density of a borating phase and increase intemperature of process its speed in the interval of temperatures from 800up to 950 оС increases insignificantly therefore for their intensificationcollateral saturation of a surface by several elements at once or thermocycling are applied [5] If the temperature of the process exceeds 1100-1300 оС in an aspect of beginning processes of high-temperaturestructural reorganization in steel speeds of borating sharply increase in2-4 min with the increase in temperature at every 15-20 оС thus theprocess passes from a diffusive zone to a zone of chemical reaction Soat the temperature of 1200-1300 оС according to the data[6] it ispossible to obtain in a few minutes the thickness of the single-phaseboron-bed up to 02-04 mm thus heating of a detail is carried out by thespecial thermo reaction mix

At RFC-heating of the steel 65Mn covered by researched boratingcompositions with chosen parameters of process fig 1 adamantinecoverings are formed on all samples resembling bed covered hard metalX-ray analysis of a material of coverings has shown presence of Fe

156

borides FeB and Fe2B carbon-borides Fe3(C B) and Fe23(C B)6 variousmeta- and orto-borates of iron (Fe3BO3 Fe3BO6 Fe3BO5) traces FeOand FeOFe2O3 Thus at RFC-heating of alloy carbon steels under bedof flux F1 containing from 84 up to 90 of borating agents complexboron-phases are formed on their surfaces hardening a surface of a detailand it is strongly linked with it and oxide films are removed togetherwith slag

To find out the characteristics and structure of received beds andthe conditions of borides in them photomicrography of micro sectionswas taken Typical structures of boron-beds are given in fig 1

a b C

Fig 1

As it is seen from fig1 with the chosen heating environments andthe time of borating the structure and the condition of boundary line ofreceived wear-resistant beds differ but in all cases as against classicalboron two-phase beds on a surface of samples the eutectic with stronglypronounced or with the diffusive boundary line separating it from anoriginal material is formed faster in conditions of heavy abrasive sign-variable and shock wear boron-plate Apparent changes in structure ofparent metal caused by its short-term overheat were not observed

For the mixes containing in the capacity of borating agent equalquantity of carbide of boron similar quantity of fluxes-component anddistinguished only by the presence of activator NH4Cl promoting areinforcement of convertible diffusive and transport reactions especiallyat low temperatures right at the beginning of the process of borating (Т

157

lt300 оС) formation of fine grained structure of eutectic turnings on withhardness not above 700-750 HV thickness of bed of 016 mm and withlegibly discernible interface with parent metal (fig 1а) is observed

For the analogous mix II without this activator the expressedpropagation of dendrites islands and druses of boron-phases withhardness up to 1050-1120 HV thickness of bed of 028 mm and adiffuse interface boron bed with parent metal (fig 1b) is observed Themixes on the basis of amorphous boron (fig 1c) appeared to be the mostreactive thus in mix IIIа containing follow-up 5 of activator CaF2 and5 of fluxes component beyond chosen relationships for 1 minthickness of bed on steel of 65Mn has made 088 mm at its hardness in2200-2300 HV The structure represents the remote eutectichomogenized iron ndash boron formed with such speed that from a melt atits solidification balls of slag had not time to bleed up to the end

Thus amorphous boron which at the presence of flux F1 andactivator CaF2 under the chosen conditions of experiment forms denseclose-grained beds on a surface of alloy steels with depth up to 800microns with hardness up to 2400-2500 HV (fig 2) appeared to be themost efficient borating agent at RFC-heating

Fig 2

It is interesting to note that the structure of the wear-resistantcovering obtained at high-speed 1 min borating steel 65Mn a mix II ismetastable and at borating during 2 min like in picture 1а with hardness2300-2400 HV turns to the fine grained structure and thickness of a

158

covering does not change and the interface with parent metal becomesdiscernible

References1 Methods of raise of longevity of machine components Red VN

Tkacheva M 19712 Belyj AV Karpenko GD Myshkin KN Structure and methods of

formation of wear-resistant surface layers M 19913 Tkachev VN Fishtejn BM Kazintsev NV Aldyrev DA

Induction overlaying welding of hard metals M 19704 Voroshnin LG Lyahovich LS Borating of steel M 19785 Guryev АМ Kozlov EV Ignatenko LN Popova NA Physical of

a basis of thermal-cycle borating Barnaul 2000

138

PHASE STATES OF MECHANOACTIVATED MANGANESEOXIDES

SA Petrova RG Zakharov AYa Fishman LI LeontievInstitute of Metallurgy Ural Division of RAS Ekaterinburg 620016

Russian Federation

An investigation of structural characteristics of the manganeseoxides in order to understand these characteristics affected bymechanochemical treatment conditions has been undertaken Chemicallypure manganese (II III IV) oxides were used as the initial componentsIt is shown that the properties of the mechanoactivated oxides differgreatly from those of initial materials Relationships among structuralcharacteristics of the mechanoactivated oxides and their prehistory wayand conditions of producing have been detected

IntroductionStudy of phase states of mechanoactivated oxides makes it

possible to analyze the patterns of expression of the mechanochemicaleffect in redox processes to determine the mechanism of the effect ofactivation processes on the type and parameters of the structural phasetransitions to establish the role of higher oxides in the redox processesAs one of the consequencies of the intensive mechanical activation is theappearance of nanodisperse states specificity of phase transformationsin nanocrystalline oxides is considered at the same time

It is known now that the decrease in the crystallite size inmechanoactivated systems causes a decrease of structural phasetransition temperatures In metallic alloys reducing of crystallites size isaccompanied by suppression of martensitic transitions [1-2] Completeinhibition occurs when the grain size becomes smaller than that of thecritical nucleus of a new phase It can be regarded as established that theparameters of phase transitions in oxides with relatively lowtemperatures of phase transitions also depend strongly on the grain sizeFor example in barium titanate BaTiO3 transition from cubic to low-symmetry phase is completely suppressed when the grain size is about10 nm [3] Changes in the crystal structure and the effects of reduction(the change of temperature and phase transition heat) in the structuralphase transitions with decreasing grain size also occurred for the oxides

139

Al2O3 Fe2O3 PbTiO3 PbZrO3 La1-xSrxCuO4 YBa2Cu3O7-δBi2CaSr2Cu2O8 [4] and several other oxides [5-6] Besides for the oxidesin nanoscale state the coexistence of two different structuralmodifications [7] was observed The processes of mechanoactivationmay also lead to new types of metastable phase states due to theredistribution of cations between the crystallographically inequivalentsublattices [8]

In the present work the main attention is paid on the analysis ofthe effects associated with the evolution of metastable structures underconditions of temperature increase and oxide interaction with anaggressive environment So far the main contribution to theinvestigation of these issues has made the study of metallic alloys (seefor example [9-10]) The behavior of the activated oxide materials ismuch less studied Study of structural phase transitions in the systemMn-O subjected to mechanochemical activation and structuralcharacteristics of the crystalline phases allows us to test how general arepreviously established patterns for systems with different types ofchemical bonds

The effect of mechanical activation on structural phase transitionsboth of martensate type (from cubic to tetragonal modification Mn3O4)and those accompanied by redox processes (between phases withdifferent degrees of oxidation etc) is investigated The choice of Mn-Ooxides as the object of study is largely connected with the fact that atleast two structural phase transitions observed in the considered crystalswith temperature changes involved the cooperative Jahn-Teller (JT)phase The value of the JT deformation in it is determined by theconcentration of JT ions in octahedral sites that allows to get additionalinformation about the structural changes caused by themechanoactivation of oxide

1 Production and structural properties of themechanoactivated oxides

11 Mechanoactivation of manganese oxidesPure manganese oxides MnO2 Mn2O3 and Mn3O4 annealed at

200deg 900deg and 1250degC respectively were used as the initial materialsFor the mechanical treatment of oxides which was described in

detail in [1112] a planetary mill AGO-2 with water-cooled drums (V =

140

150ml) and a centrifugal factor up to g = 60 [3] was used Download ofballs was 203g the material - from 5g Milling was made dry Theprocessing of powders was carried out after preliminary lining in acontinuous mode or with periodic stops of the mill According toestimates (performed by XPES) contamination by iron was not morethan 02 Previously [14] we found that prolonged continuousmechanical treatment leads to the fact that within the grains matureduring the first seconds along with a further (slow) reduction ofcoherent scattering blocks chemical processes begin leaking Because atthis stage the main purpose was to obtain single-phase samples theduration of continuous grinding was restricted by 30s The temperatureinside the drums during grinding did not exceed 320K which ensuredthe preservation of initial metastable phases During stops of mill thedrums where opened and powder was manually stirred but samplingwas not performed

To be able to conduct magnetic research on the mechanicallyactivated samples and to investigate the effect of intensity ofmechanoactivation (the degree of deformation) on the redox processesand the stability of weakly activated oxides the part of samples wasobtained as a result of mechanical activation in the vario-planetary millPulverizette 4 (Fritsch) in glasses of tungsten carbide Volume of drumwas equal to 250ml loading of crushing balls was 800g and a materialmass was 20 g Milling was made dry the duration was 3 min

12 Attestation of mehanoactivated manganese oxides andmethods of their experimental study

The phase composition of obtained substances the size ofcoherent scattering domains (CSD) and microstresses were determinedby X-ray diffractometer D8 ADVANCE (Bruker) (radiation CuKα Ni-filter position-sensitive detector VANTEC1) High-temperature X-raystudies of the stability of mechanoactivated oxides was carried out usinghigh-temperature chamber HTK1200N (Anton Paar)

The particle size of powders obtained was assessed by dynamiclight scattering using a laser analyzer DelsaNanoC (Beckman Coulter)and an atomic force microscope Solver-Next (NT-MDT) Surface ofoxides was studied by XPES and STEM (Omicron Multiprob)

High-temperature X-ray studies were performed in the range 30-1200degC in air The rate of heating and cooling was 05degCmin Step of

141

the temperature during heating and cooling was 5deg and 10degCrespectively Exposure in the point was 17s (the time of isothermal delayshooting diffractogram was 150s) For the analysis of diffractionpatterns the software package DIFFRACplus [15] was used

13 Results and discussionThe results of the attestation of the initial and mechanoactivated

oxides are presented in Table 1

Table 1 Treatment conditions and characteristics of the manganeseoxides

Cell parameters Initial phasetreating mode

Finalcomposition аAring сAring

Samplename

1 Mn2O3- initial Mn2O3 9412 M232 Mn2O3- AGO 30s Mn2O3 9410 M23A303 Mn2O3- AGO 60s Mn2O3 9410 M23A604 Mn2O3- AGO

10minMn2O3 9410

M23A10

5 Mn2O3- P4 3min Mn2O3 9403 M23P46 Mn2O3-

P4(3min)+USD(70s)Mn2O3 9403

M23P4U

7 Mn3O4-initial Mn3O4 5760 9474 M348 Mn3O4- AGO 30s Mn3O4 5762 9442 М34А309 Mn3O4- AGO 60s Mn3O4 5762 9431 M34A60

5787 950810 Mn3O4- AGO10min

Mn2O3+ Mn3O4

9410M34A10

11 MnO2-initial MnO2 4396 2869 M1212 MnO2- AGO 30s MnO2+Mn2O3(tr) 4397 2872 М12А3013 MnO2- AGO 60s MnO2+Mn2O3(tr) 4397 2872 M12A6014 MnO2- AGO 10min Mn2O3 9408 M12A10

AGO-High-energy planetary mill (60g) P4-Pulverisette 4 (~20g)USD-Ultrasound disintegrator

Since the analysis of the results of mechanoactivation of oxidesMn2O3 showed little difference between the samples activated in theAGO within 30 and 60 seconds further investigation of oxides Mn3O4

and MnO2 was performed on 60-second samples However it is

142

necessary to note that in the case of oxide MnO2 samples after 30 and60-second milling contained different amounts of Mn2O3

According to X-ray phase analysis data chosen mode ofmechanochemical treatment allowed to preserve essentially thecomposition of the initial oxides The exceptions were oxides MnO2which after grinding contained 5 of oxide Mn2O3 and Mn3O4 whichafter grinding for 10 minutes contained a few of Mn2O3

Data on grain size and the coherent scattering domains arepresented in Table 2 It is obvious that even a relatively weakmechanical treatment leads to a decrease in grain size in 2-3 times Inthis case the comparison of grain size and the CSD (comparison of thedynamic light scattering data and X-ray diffraction (XRD) results)shows that the mechanical treatment with a small degree of deformationallows to obtain defect-free grains while increasing of the centrifugalacceleration leads to the appearance and rise of the defects in the grainA tendency to agglomeration of grains with increasing time of intensemechanoactivation should be noted

Table 2 The characteristics of coherent-scattering domains and averagegrain size

Sample nameCoherent-scattering domain

nmGrain size nm

M23 gt200 1026plusmn95M23A30 30 436plusmn168M23A60 23 344plusmn155M23A10 24 939plusmn175M23P4 44 386plusmn50

M23P4U 44 336plusmn22M34 gt200 400plusmn801300plusmn300

M34A60 15 529plusmn340

M34A10 1913 795plusmn104

M12 gt200 428plusmn78M12A60 61 1133plusmn167M12A10 22 565plusmn343

XRD-dataDynamic light-scattering

data

143

Changes in phase composition during heating and cooling ofinitial and mechanically activated manganese oxides are presented inTables 3-4 and Fig 1-2

Comparison of the temperature behavior of the initial unactivatedoxide Mn2O3 and that of grinded for 3 minutes with a force of less than20g shows that mechanoactivation treatment with a small amount ofcentrifugal factor and short times can save not only the phasecomposition but apparently and generally does not alter the propertiesof the powder While increasing the degree of exposure (eg use of millssuch as AGO-2 with acceleration 60g) even at short times leads to achange in system characteristics (the appearance and growth of defectsredox processes) that affect later on behavior of oxide For examplemechanoactivation treatment leads to a shift of phase transitiontemperaures at thermal processing as well as to change of the structuralcharacteristics of the phases formed In particular to different degrees oftetragonal distortion of hausmannite formed during heating Mn2O3 (Fig4)

Table 3 The phase composition of the initial andmechanoactivated manganese oxides at different temperatures

Heating CoolingSample MnO2 Mn2O3 Mn3O4 Spinel Mn3O4 Mn2O3 Phase

1 2 3 4 5 6 7 8- + 920 1140 1120 - appearanceM23

- 955 1170 1010 + - disappear

- + 950 950 1010 - appearanceM23A30

- 995 1105 730 + - disappear

- + 950 950 1040 - appearanceM23A60

- 1000 1120 840 + - disappear

- + - 950 840 840 appearanceM23A10

- 1000 - 290 + 770 disappear

- + 940 1140 1120 - appearanceM23P4

- 980 1165 1080 + - disappear

- + 935 1140 1120 - appearanceM23P4U

- 980 1170 1050 + - disappear

144

1 2 3 4 5 6 7 8

- 685 + 1125 1090 - appearanceM34

- 945 1160 1010 + - disappear

- + appearance370

655

970 1050 -

disappear

900 appearance

M34A60

-

970

1130

880 + -

disappear

- + + 930 880 - appearanceM34A10

- 1005 655 600 + - disappear

+ 550 950 1155 1120 870 appearanceM12

595 1025 1170 1070 + + disappear

+ + 940 985 1110 750 appearanceM12A60

535 985 1165 840 + + disappear

- + 960 960 1000 790 appearanceM12A10

- 1005 1075 630 + + disappear

Table 4 The temperature boundaries of the phases during heating andcooling

Heating CoolingSample Phase

from to from to

1 2 3 4 5 6

Mn2O3 30 955 - -

Mn3O4 920 1170 1120 30

M23

Spinel 1140 1200 1200 1010

Mn2O3 30 995 - -

Mn3O4 950 1105 1010 30

M23A30

Spinel 950 1200 1200 730

Mn2O3 30 1000 - -

Mn3O4 950 1120 1040 30

M23A60

Spinel 950 1200 1200 840

Mn2O3 30 1000 840 770

Mn3O4 - - 840 30

M23A10

Spinel 950 1200 1200 290

145

1 2 3 4 5 6

Mn2O3 30 980 - -

Mn3O4 940 1165 1120 30

M23P4

Spinel 1140 1200 1200 1080

Mn2O3 30 980 - -

Mn3O4 935 1170 1120 30

M23P4U

Spinel 1140 1200 1200 1050

Mn2O3 685 945 - -

Mn3O4 30 1160 1090 30

M34

Spinel 1125 1200 1200 1010

Mn2O3 370 970 - -

Mn3O4 30 655

Mn3O4 900 1130

1050 30

M34A60

Spinel 970 1200 1200 880

Mn2O3 30 1005 - -

Mn3O4 30 655 880 30

M34A10

Spinel 930 1200 1200 600

MnO2 30 595 - -

Mn2O3 550 1025 870 30

Mn3O4 950 1170 1120 30

M12

Spinel 1155 1200 1200 1070

MnO2 30 535 - -

Mn2O3 30 985 750 30

Mn3O4 940 1165 1110 30

M12A60

Spinel 985 1200 1200 840

Mn2O3 30 1005 790 30

Mn3O4 960 1075 1000 30

M12A10

Spinel 960 1200 1200 630

146

a d

be

c fFig 1 The temperature boundaries of the phases during heating and coolingof initial and mechanoactivated Mn2O3 a - original b - M23P4 c -M23P4U d-M23A30 e-M23A60 f-M23A10

147

a

b

cFig 2 The temperature boundaries of the phases during heating and cooling of

initial and mechanoactivated Mn3O4 a-initial b-M34A60 c-M34A10

148

a

b

cFig 3 The temperature boundaries of the phases during heating and cooling ofinitial and mechanically activated MnO2 a - initial b - M12A60 c - M12A10

149

Fig 4 Temperature dependence of the degree of hausmannite tetragonaldistortion for samples with different prehistories

The growth of the crystallite size of mechanoactivated phase withtemperature is shown in Fig 5 Data are shown for the initial phasebelow the temperature of the corresponding phase transition

It is obvious that prolonged treatment in the high-energy millalmost did not give reduction of coherent scattering domains butessentially affected the thermal stability of investigated oxide

150

Fig 5 Temperature dependences of coherent scattering domain size in oxideMn2O3 with varying degrees of mechanoactivation

ConclusionThe main results of investigations are the followingI The conditions of mechanochemical treatment enabling to make

the transfer of Mn-O system to single-phase nanosized state withoutsignificant changes in composition of the initial oxide are found Theexception was oxide MnO2 which after grinding contained a smallamount of oxide Mn2O3

II It is shown that the use of mill of the type AGO-2 with 60gacceleration even at short times of activation treatment of oxides leadswhile maintaining the single-phase of sample to an appreciable changeof lattice parameters growth of stresses and the appearance of defects

III It is found that despite the relaxation character of the evolutionof these metastable structures in the face of rising temperatures there is ashift of phase transition temperatures and changes in structuralcharacteristics of the newly formed phases in comparison with the initialoxides Including marked changes in the parameters of the JT strain (ca

151

- 1) at high-temperature transitions between cubic and tetragonal phasesof oxide Mn3O4

IV It is shown that more prolonged mechanical activation ofoxides MnnOm activates redox processes in these materials theemergence of two-phase states with different degrees of oxidation andeven a complete change of the manganese oxidation degree

V The temperature boundaries of existence of phases duringheating and cooling were determined for the initial andmechanoactivated oxides MnnOm Not only noticeable quantitativedifferences in the position of phase boundaries but also qualitativedifferences in the constructed phase state diagrams were found

This work was supported by RFBR (grant 10-03-96016-p_ural_a) the Program of fundamental research of Presidium ofRussian Academy of Sciences N 27 ldquoFoundations of fundamentalresearch of nanotechnology and nanomaterialsrdquo and the Federal TargetProgram Scientific and scientific-pedagogical staff of innovationRussia (contract 02740 110641)

References1 Glezer AM Blinov EN Pozdnyakov VA Martensitic

transformations in microcrystalline ferro-nickel alloys Izvestiya Aseries of Physical 2002 V66 N9 pp1263-1275

2 Andrievsky PA RAGULYA AV Nanostructured materialsMoscow Academy 2005 192p

3 Polotai AV Ragulya AV Skorohod VV Nanocrystalline BaTiO3

synthesis sintering and size effect Science o Sintering CurrentProblems and New Trends Beograd Kluwer Academic Publishers2003 pp119-125

4 PAyyub VRPalkar SChattopadhyay et al Effect of Crystal SizeReduction on Lattice Symmetry and Cooperative Properties PhysRev B 1995 V51 N9 pp6135-6138

5 Parathasarathi Mondal Dipten Bhattacharya Pranab ChoudhuryDielectric anomaly at orbital order-disorder transition inLaMnO3+ J Phys Condens Matter 2006 V 18 p6869

6 Nandini Das Parathasarathi Mondal Dipten BhattacharyaPartical size dependence of orbital order-disorder transition inLaMnO3 Phys Rev B 2006 V74 p 014410

152

7 VYa Shevchenko OL Khasanov GS Yuriev etc The coexistence ofcubic and tetragonal structures in the nanoparticle of ZrO2Y2O3

oxides Neorg Mater 2001 V37 N9 pp1117-11198 AYa Fishman MA Ivanov SA Petrova et al Specific Features of

Jahn-Teller Structure Phase Transitions in NanocrystallineMaterials Defect and Diffusion Forum 2009Vols 283-286 pp53-58

9 Grigorieva ТF Barinova AP Lyakhov NZ Some features of themechanical alloying in the systems Cu-Bi and Fe-Bi J Metastableand Nanocryst Mater 2003 V15-16 pp475-478

10 Lyakhov N Grigorieva T Barinova A Lomaeva S Yelsukov EUlyanov A Nanosized mechanocomposites and solid solution inimmiscible metal systems J Mater Sci 2004 V39 N 16-17pp5421-5423

11 Zyryanov VV Journal of Structural Chemistry 2004 V45 pp135-143

12 Zyryanov VV Lapina OB Neorg Mater 2001 V37 N3 pp331-337

13 Zyryanov VV Sysoev VF Boldyrev VV Korosteleva TVCertificate of authorship of USSR N 1375328-BI-1988 N 7 p39

14 Fishman AYa Ivanov MA Petrova SA Zakharov RGStructural Phase Transitions in Mechanoactivated ManganeseOxides Defect and Diffusion Forum 2010 Vols 297-301 pp 1306-1311

15 DiffracPlus TOPAS Bruker AXS GmbH OstlicheRheinbruckenstraszlige 50 D-76187 Karlsruhe Germany 2008

118

EFFECT OF HARDENING TEMPERATURE ON THE STRUC-TURAL-MORPHOLOGICAL CHARACTERISTICS OF METAL

CEMENTS BASED ON MECHANOSYNTHESIZED COPPERCOMPOUNDS

NZ Lyakhov1 PA Vityaz2 SA Kovaleva2 TF Grigoreva1VG Lugin3 AP Barinova1 SV Tsybulya4

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS630128 Novosibirsk Kutateladze str 18 grigsolidnscru

2 United Institute of Mechanical Engineering NAS Minsk Belarus3 Belarussian State Technological University Minsk Belarus

4 G K Boreskov Institute of Catalysts SB RAS Novosibirsk Russia

IntroductionMetal cements may be used in many branches of industry due to

good adhesion to the materials of different types (glass ceramics metalsetc) and the metal character of thermal and electric conductivity Theformation of metal cements occurs through the interaction of copper(nickel) alloys with liquid metals and alloys Interactions of a solid metalwith liquid one in particular copper with gallium are known [1 2] tohave diffusion character they are substantially affected by temperatureand the area of contact between the reagents

The use of mechanically synthesized copper compounds allowsone to increase the contact surface between the components and to intro-duce doping elements (Bi In) that improve wettability during gluing andthe strength properties of the alloys to be formed This causes a changeof the kinetics of interaction between a solid metal and a liquid one dueto the acceleration of diffusion processes and due to the formation ofadditional phases

The goal of the present work is investigation of the effect of hard-ening temperature on the structural-morphological characteristics ofmetal cements obtained on the basis of CuBi mechanocomposites andsupersaturated solid solutions Cu(In)

Methods and materialsCopper powder PMS-1 (GOST 4960ndash75) granulated bismuth (TU

6-09-3616ndash82) indium (GOST 10297ndash94) were used in the work Me-chanical activation of the powders was carried out for 15 min in the

119

high-energy ball planetary mill AGO-2 with water cooling in argon at-mosphere (cylinder volume 250 cm3 ball diameter 5 mm loaded wt200 g the weighed portion of the sample under treatment 10 g the fre-quency of rotation of the cylinders around the common axis about 1000rpm) Mechanocomposites having the composition Cu 10 wt Bisolid solutions Cu-12 wt In were obtained [3] Diffusion-hardeningalloys were prepared by mixing the mechanosynthesized copper com-pounds with gallium melt followed by exposure at a temperature of 20C during the whole process of alloy formation To study the effect oftemperature on the structure and morphology of metal cements harden-ing was carried out at 90 С 120 С and 160 С

Surface examination was carried out with the NT-206 atomicforce microscope (Microtestmachines Gomel) using standard commer-cial V-type probes NSC11 (Mikromasch) in the contact mode

The structure of the resulting samples was studied using Mikro200 optical microscope and high-resolution scanning electron micro-scope (SEM) MIRATESCAN with an attachment for micro-X-ray spec-tral analysis (MXSA) The diameter of the electronic probe was 52 nmexcitation region was 100 nm Images were obtained in the mode of re-cording secondary and backward scattered electrons which allowed usto investigate the distribution of chemical elements over the surface andto establish its composition non-homogeneity

The phase composition of powders after mechanical activationand the final products of their interaction with liquid gallium were de-termined with the help of X-ray diffraction techniques X-ray structuralanalysis and semi-quantitative examination of the products were carriedout with the D8 Advance Bruker diffractometer (Germany) by means ofpowder X-ray diffraction in the θ-2θ configuration with a step of 01Phase identification was performed using the diffraction patterns re-corded in CuKα radiation (154051 Aring)

Calorimetric measurements were carried out with Netzsch STA409 PCPG instrument in argon atmosphere in a crucible made ofAl2O3 within the temperature range from room temperature up to 290 Cwith the heating rate of 20 min

120

Results and discussionIt was established in the previous diffraction studies of alloy for-

mation dynamics in CuBi + Ga and Cu(In)+Ga that the formation ofnew phases takes place within a broad time interval During the interac-tion of CuBi mechanocomposite in Bi that is insoluble in copper and ingallium the formation and crystallization of the intermetallic compoundCuGa2 and bismuth take place simultaneously [4]

For the case of Cu(In) solid solution in which the doping elementis soluble in gallium the formation of the phase of solid solution of in-dium has an incubation period of about 210 minutes which is determinedby its concentration in the system with gallium [5]

The interaction processes are described with the following chemi-cal reactions

CuBi + 2 Ga rarr CuGa2 + BiCu(In) + 2 Ga rarr CuGa2 + In(Ga)

1 Effect of the temperature of interaction of CuBimechanocomposites with liquid gallium on the structure andmorphology of the formed metal cementsIt is known that the resulting mechanocomposites are nanosized

copper surrounded by a thin bismuth layer [6] Bismuth is mainly com-posed of the particles less than 5 nm in size

According to the data of AFM topography the size of mechano-composite particles is 150divide250 nm (Fig 1)

Fig 1 Mechanocomposite Cu + 10 wt Bi after activation for 15 mina ndash SEM image b ndash AFM c ndash TEM

121

At first we studied the interaction of CuBi with liquid gallium atroom temperature

The X-ray structural analysis of the resulting cement carried outafter the interaction for 4 and 48 hours showed that the size of the crys-tallites of the intermetallic compound increases from ~ 200 nm to ~ 550nm The size of bismuth crystallites increases up to 100 nm It should benoted that this is accompanied by a decrease in the size of copper crys-tallites down to ~ 10 nm The final phase composition is determined asCuGa2 Bi and unreacted copper (Fig 2)

Fig 2 Diffraction patterns of the product of interaction Cu 10 Bi + Ga

Figure 3 shows the high-resolution SEM images of the micro-structure of the surface of the final interaction product The SEM imageof sample surface after hardening without the mechanical treatment ofthe surface is shown in Fig 3a The image of the surface obtained in thebackward scattered electrons after sample polishing is shown in Fig 3bBecause bismuth is the heaviest element in this system it will be distin-guished by the maximal brightness in the SEM image

The data obtained by means of microscopy show that the structureof the surface of final product is facetted tetragonal crystals СuGa2 withthe size up to 4 μm Bismuth is localized at the faces of crystals and at

122

the boundaries of CuGa2 grains as disperse formations 70-250 nm insize and also forms separate grains with a size up to 10 μm

a bFig 3 Topography of the surface of CuGa2 +Bi alloy after the interaction for48 hours a ndash SEM image of non-polished sample in direct electrons b ndash SEM

image of the polished sample in backward-scattered electrons

The use of AFM allowed us to study the microstructure of facet-ted tetragonal CuGa2 crystals The presence of screw dislocations inthem may be stressed as a result the crystalline layer grows by windingcontinuously on itself so the step takes the shape of a spiral (Fig 4) Thelayer-by-layer growth of crystallographic facets should also be men-tioned The edges of incomplete layers or steps move along the facetwhile they grow The step height that is the thickness of the depositinglayer varies within the range 4 to 200 nm The appearance of highgrowth steps may cause trapping of the melt drops and precipitation ofinsoluble bismuth admixture on the surface of steps of the growing crys-tals which is indeed observed in Fig 4 b Bismuth is adsorbed on facetssteps and along the grain boundaries

It should be stressed that the growth of faceted crystals requiresspecial conditions supersaturation or supercooling of the mother me-dium small number of appearing nuclei We suppose that the localthermal supercooling arises as a consequence of the chemical interactionof copper with gallium melt on the interface between the solid phase andthe liquid one with the formation of chemical compound CuGa2 withcrystallization temperature higher than the temperature of the melt Theconditions of substantial supercooling are created for this compound soits crystallization starts In this process bismuth particles get released

123

into the melt Thee particles are insoluble in liquid gallium and may actas the centres of crystallization and also they may brake down thegrowth of intermetallide particles by getting adsorbed on their surfaceThe latent heat of melting released during crystallization raises the tem-perature of the melt (so gallium remains in the liquid state during reac-tion at 20 C) and decreases the degree of overcooling thus creating theconditions for the growth of larger facetted intermetallide crystals fromthe melt

а b

Fig 4 AFM image of the surface of resulting alloy CuGa2 + Biа - Torsion-image of bismuth on facets and growth steps of CuGa2 (the contrastis formed due to the difference in tribological characteristics of the phases of

intermetallide and bismuth) b ndash layered spiral growth of CuGa2 crystals alongthe screw dislocation (marked with arrows) The upper part shows a scheme ofcrystal growth along the screw dislocation and the shape of the step formed inspiral growth [7]

At room temperature the final product of the interaction of CuBimechanocomposite with liquid gallium is a matrix composed of CuGa2

intermetallide particles 1ndash4 μm in size with bismuth particles distrib-uted in it (from 70 to 250 nm) which form local agglomerations up to 10μm in size

X-ray studies of the alloys obtained at hardening temperature of90 and 120 C showed that an increase in temperature to 120 C does notaffect the phase composition Similarly to the case of room temperature

124

the product is composed of intermetallide CuGa2 (PDF-2 No 25-0275)bismuth (PDF-2 No 44-1246) and residual copper (PDF-2 No 04-0836)(Fig 5)

Fig 5 Diffraction patterns of CuGa2 + Bi samples obtained at temperature 40(a) 90 (b) and 120 (c) C Unmarked peaks relate to CuGa2 intermetallide

With an increase in the interaction temperature the lattice pa-rameters of copper and CuGa2 phases remain almost unchanged Thesize of copper crystallites is about 35 nm Bismuth undergoes tempera-ture-caused changes An increase in the size of bismuth crystallites from100 nm at 20 C to 180 nm at 90 C and to more than 500 nm at 120 C

Alloys obtained by mixing the CuBi mechanocomposite with liq-uid gallium have a composite structure after hardening Their structuremay be described as an intermetallic shell with the unreacted part ofcopper in its centre The СuGa2 intermetallide has a shape of facetedtetragonal crystals up to 4 μm in size With an increase in reaction tem-perature to 90 C the size of het particles of intermetallic compund in-creases to 6-8 μm and remains almost the same at a temperature of 120C In the lateral contrast mode the facets of crystals obtained at 90 and120 C exhibit local accumulations of bismuth as well as substantial de-formation distortions of crystals due to the arising stretching strain inthe crystal in the direction lt001gt (Fig 6) Intermetallide crystal starts to

125

have layered structure The facets of the intermetallide obtained at ele-vated temperatures also exhibit deformation distortions that are likelyconnected with bismuth adsorption on the facets The appearance ofthese lines is due to the development of local fluidity They arise in thecases when the material possesses a distinct yield point even insignifi-cant concentration of strain promotes the appearance and developmentof these figures [8] Change of the straight character of the glide lines islikely to be connected with the effect of boundary volumes intra-grainstructural strain caused by differences in the volumes of the intermetal-lide and bismuth as well as by glide in different systems and with thetransition from one system to the other

а

b

Fig 6 AFM images of CuGa2 + Bi alloys obtained at a temperature of 90 (a)and 120 (b) С

126

Metallographic in-vestigation of the alloysurface after polishing(Fig 7) showed that thenumber of macrodefectssuch as pores and discon-tinuity flaws decreaseswith an increase in crystal-lization temperature Mi-crohardness of the inter-metallide increases fromHV 70 to 125

Investigation of thedistribution of chemicalelements over the sampleby means of SEM involv-ing X-ray spectral analysisrevealed nonuniformity ofthe distribution of insolu-ble bismuth

Bismuth is not ob-served in the regions withthe intermetallic com-pound which may be con-nected with the fine distri-bution of disperse particlesover the boundaries of theintermetallide Local ac-cumulations of bismuth upto 10 μm in size are ob-served mainly in the siteswhere macrodefects (poresgrain boundaries) get ac-cumulated With an in-crease in the temperature ofinteraction up to 120 Сthe number of local bis-muth accumulations de-

а

b

cFig 7 Optical images of the structure of

CuGa2 + Bi alloys obtained at 20 (a) 90 (b)and 120 (c) С

127

creases but their size increases to 20 μm (Fig 8)

а b

Fig 8 SEM images (in backward scattered electrons) of CuGa2 + Bi alloyHardening temperature а ndash 20 С b ndash 120 C

Thermal investigation of the alloys with different hardening tem-perature points showed that the curves of differential scanning calo-rimetry (DSC) exhibit definite differences only during heating the alloyswith hardening temperature 20 C and 90 C The DSC curves of the al-loys with hardening temperature 90 and 120 С are identical Duringheating the alloy with hardening temperature 20 С exhibits the exother-mal heat effect at a temperature of 120-150 С This effect may be con-nected with the occurrence of recrystallization processes in bismuthThis exo-peak is absent during the repeated heating

Thus investigation showed that an increase in the temperature ofthe interaction of CuBi mechanocomposite with liquid gallium leads toan increase in the size of the formed intermetallide as well as to a de-crease in macrodefects in the form of pores discontinuity flaws cracksThe hardness of the intermetallide thus increases

2 Effect of the temperature of interaction of mechanochemi-cally prepared solid solution Cu (In) with liquid gallium onthe structure and morphology of metal cementThe use of mechanochemically prepared powders of Cu-In system

as the solid phase in the reactions with liquid gallium increases the num-

128

ber of interacting systems due to the solubility of indium in gallium Ac-cording to the state diagram of the system GandashIn [9] the solubility of Inin Ga in the solid state is less than 03 at while the solubility of Ga inIn is 31 at At a temperature of 60 С indium may be dissolved in liq-uid gallium up to 48 wt

Mechanochemically synthesized powder in the system Cu + 12wt In was used as the initial solid-phase component The X-ray phaseanalysis of the products of mechanochemical synthesis (Fig 9) showedthat the solid solution of indium in copper in formed during mechanicalactivation of copper powder with 12 wt indium As a result the latticeparameter of copper increases to а = 36659 Ǻ (аref = 36150 Ǻ) The size of copper crystallite is about 30 nm

Fig 9 X-ray diffraction patterns of the powder Cu-12 wt In after mechanicalactivation (for 20 min) in argon

Mechanical activation of the system Cu + 12 wt In leads to theformation of fine particles of the solid solution of indium in copper (150ndash 230 nm) (Fig 10) Recrystallization of the solid solution of copper andthe formation of grains larger than 15 μm are also possible

129

Fig 10 Topography of the ultrafine powder of the solid solution Cu(In)

A decrease in the size of precursor powder is known to providelarger area of contact between the components of the solid phase and theliquid one and therefore shorter diffusion distances during subsequentinteractions with metal melts Because both copper and nickel are solu-ble in liquid gallium one may expect that the rate of dissolution of themechanocomposites of the system Cu-In would be significant

X-ray phase analysis of the final products of the interaction of thesolid solution Cu(In) with gallium at room temperature revealed thepresence of three phases intermetallide CuGa2 indium and unreactedcopper (Fig 11)

Fig 11 Diffraction patterns of the alloys obtained through the interac-tion of Cu 12 wt In + Ga CuGa2 - In - Cu

130

For the initial powder with indium concentration 12 wt theproduct of the interaction exhibits a decrease in the indium unit cell pa-rameter с in the alloy under formation to с = 49306 Ǻ (cref = 49459 Ǻ) The size of copper crystallites is about 7 nm while the size of indiumcrystallites is about 30 nm Slight changes in the unit cell volume of in-dium may be related to the formation of the solid solution of gallium inindium

During the interaction indium gets dissolved in the liquid phaseof gallium gets concentrated and crystallizes at the interfaces betweenthe solid phase and the liquid one The alloys with the 12 indium con-tent are characterized by a large range of the dimensions of tetragonalparticles of the intermetallic compound CuGa2 (from 05 to 8 μm) TheAFM image (Fig 12) exhibits coarse crystals their crystallographicshape is uncharacteristic of the intermetallide CuGa2 Comparing the X-ray data and the results of AFM we may assume that they are a solidsolution of gallium in indium

Fig 12 AFM topography of the surface of CuGa2+ In(Ga) alloy

A decrease in the AFM scanning pitch and simultaneous acquisi-tion of the image of distribution of normal (topography) and lateral (tor-sion) forces allowed us to distinguish the structural features of the phaseof the solid solution of gallium in indium (Fig 13) A specific distin-guishing feature is the presence of strands in the crystals of the solid so-lution of gallium in indium connected with layering of the solid solutioninto the regions with larger and smaller concentration of the componentwhich is well seen in the image of torsion (Fig 13b) The size of separate

131

grains of the solid solution of gallium in indium reaches more than 10μm

Fig 13 AFM topography of the surface of samples of CuGa2+ In(Ga) alloy (а)image of torsion (b)

Fig 14 The SEM image in direct (а) and back-scattered electrons (b) of thealloy CuGa2+ In(Ga) In the upper part the data chart of the quantitative spec-

tral analysis carried out in the indicated points

To investigate the microstructure of the surface of alloys we car-ried out the examination with the scanning electron microscope and ob-tained the images of the surface of resulting alloy for the interaction Cu12 wt In + Ga in direct (Fig 14а) and back-scattered (Fig 14 b) elec-trons The application of imaging in back-scattered electrons allow one

132

to investigate the composite surface non-uniformity with which the in-tensity distribution over the image depends on the atomic number of anelement One can see in Fig 14 b that the contrast in the BSE images isdetermined by the topographic features of the surface and the distribu-tion of intensities is uniform In addition local X-ray spectral analysiscarried out in different points of the alloy surface revealed the presenceof indium in concentrations 01 to 7 This fact allows us to concludethat indium is present on the surface of CuGa2 intermetallic crystals inthe form of thin films

Another characteristic feature of the surface of samples obtainedin the interaction of solid solutions Cu(In) with liquid gallium is thepresence of fine dispersed formations on the surface of crystals andgrains of CuGa2 that are more clearly seen in the AFM images (Fig 13a) and are detected in the SEM images (Fig 15 b) The formation of thestructures of this kind on the surface of the intermetallide may be con-nected with indium crystallization on the surface of the growing crystals

Fig 15 AFM (a) and SEM images (b) of the face of CuGa2 intermetallic ob-tained by the interaction of Cu 20 In + Ga

So on the basis of X-ray spectral data obtained and the results ofAFM and SEM we may assume that indium gets crystallized not only inthe form of large grains of the phase of the solid solution of gallium inindium but also on the faces of the intermetallide thus forming a nano-meter-sized film of indium about 10 nm thick

133

In order to establish the effect of temperature on the structure andmorphology we carried out alloy hardening at temperature of 60 120and 160 C

X-ray structural investigation of the final phase composition (Fig16) of the alloys showed that no changes in the phase composition of themetal cement are observed with an increase in hardening temperature to160 C The parameters of intermetallic compound CuGa2 remain almostunchanged The values of lattice parameters of the indium phase underformation are also insignificantly differing from the reference ones

Fig 16 Diffraction patterns ofCu-In-Gа samples obtained at

different temperatures

Investigation of the microstructure of alloys obtained at 20 Cshowed that indium is well adsorbed on the surface of intermetallidecrystals and crystallizes not only as separate crystals of the solid solutionof gallium in indium but also as the film formations with grained anddendrite structure on the faces of the intermetallide The occurrence ofintercrystal films of indium or the solid solution of indium may be re-sponsible for a decrease in strength characteristics of the alloy and be areason of both the intra-crystal and inter-crystal fractures (Fig 17 b) It

134

is assumed that an increase in hardening temperature causes substantialformation of the film structures of the solid solution of indium

The AFM investigation of the topography of alloys obtained attemperatures 90-160 C showed that the alloys are characterized by alarge size range of the intermetallic compound CuGa2 At the interactiontemperature of 20 C the size of CuGa2 particles was 05 to 8 μm Withan increase in reaction temperature to 90 C the crystal size increases upto 11 μm Crystal concretions are also formed (Fig 17) One can see inFig 17 b that cracks are formed in the grain plastoelastic deformationson the intermetallide face occur which is likely to be due to the differ-ence in interfacial surface tension of the intermetallide and indium film

ab

Fig 17 AFM image of the surface of CuGa2 + In(Ga) alloy obtained at 90 C a- topography b ndash distribution of lateral forces (arrows show cracks deforma-

tion distortions)

At a temperature of 120 and 160 C the contrast of the surface re-lief decreases due to the formation of a continuous film (Fig 18) on thesurface

Investigation of the phase transitions in the alloys was carried outby means of DSC For heating the products of the interaction betweenthe solid solution of indium in copper and liquid gallium at a rate of30Cmin an endothermic effect is observed on the DSC curves of all thealloys at a temperature about 254 C and an exothermic effect at 290 Con cooling the exothermic peak appears at a temperature of 210-220 С

135

а b

Fig 18 AFM topography of the CuGa2 + In(Ga) alloy a ndash 120 C b- 160 C

According to the Cu-Ga state diagram these effects are connectedwith the peritectic transformations of the main phase of intermetallideCuGa2 during heating and cooling The cooling curves exhibit no ther-mal effect due to the phase transition of indium The DSC curve of thealloy obtained at 20 C contains an endothermic peak at about 130 Cwhich gives much smaller heat effect in the second heating cycle Tak-ing into account the fact that the formation of indium films and the solidsolution of indium with the grained and dendrite structures occurs on thesurface of the intermetallide it may be assumed that heating to 130 C isaccompanied by melting of the indium film (taking into account a de-crease in melting temperature for thin films) [10] and the solid solutionIn(Ga) At the temperature of the peritectic transformation 254 C in-dium gets dissolved in the formed liquid Ga(Cu) with subsequent for-mation of the ternary compound Cu-Ga-In during cooling For coolingthe temperature of the peritectic reaction for the obtained compound de-creases to 210-220 C

ConclusionAs a result of the investigation of the structure and morphology of

metal cements prepared on the basis of mechanosynthesized coppercompounds CuBi and Cu(In) the structure and morphology in the reac-tions with liquid gallium are determined by the degree of interaction of

136

the doping component with gallium In the case of the CuBi mechano-composite in which Bi does not interact with gallium an intermetallidewith particle size up to 4 μm and local accumulations of bismuth areformed With an increase in hardening temperature to 120 C intermetal-lide growth to 8 μm occurs

When using the solid solutions Cu(In) in which indium is solublein liquid gallium and the incubation period for the crystallization of thesolid solution In(Ga) the formed particles of intermetallide CuGa2 havea broad size range from 05 to 8 μm With an increase in hardening tem-perature to 160 C the size of intermetallide particles increases to 11 μmredistribution of indium occurs along with an increase in the number ofits film structures that are formed on the faces of the intermetallide andcause a decrease in its strength properties thus providing intra-crystaland inter-crystal fracture A decrease in the melting temperature for in-dium to 130C and a decrease in the heat effect at this temperature in thealloys obtained at the alloy formation temperature of 90 120 and 160 Cmay be connected with an increase of indium film amount

The work is carried out under the Integration Project of SB RASNo 138 and BRFFI Т09СО-014 laquoDevelopment of Fundamental Basisof the Action of Activation on Regulation of the Processes of Interactionof Solid Metals and Their Comopunds with Metal Melts for the Purposeof Obtaining Functional Materials with Required Structure and Proper-tiesraquo

References1 Tikhomirova OI Ruzinov LP Pikunov MV Marchukova ID

Investigation of mutual diffusion in the system gallium ndash copperFiz metallov I metallovedenie 1970 vol 29 issue 4 p 796-802 (inRussian)

2 Glushkova LI Konnikov SG Interaction between components inthe solder paste based on gallium Pressure treatment of metals andwelding Proceedings of the Leningrad Polytechnical Institute1969 No 308 p 205-208 (in Russian)

3 Grigorieva TF Barinova AP Lyakhov NZ Mechanochemicalsynthesis in metal systems Novosibirsk 2008 (in Russian)

4 Ancharov AI Grigorieva TF Barinova AP Lyakhov NZ Investi-gation of the interaction of liquid metals with nanocomposites by

137

means of diffraction of the synchrotron radiation Nuclear Instru-ments amp Methods in Physics Research 2007 v A 575 p 130-133

5 Ancharov AI Grigorieva TF Tsybulya SV Boldyrev VVNeorganicheskie Materialy 2006 V 42 No 9 p 1164-1170 (inRussian)

6 N Lyakhov T Grigorieva A Barinova Nanosized mechanocom-posites and solid solution in immersible metal systems Journal ofmaterials science 39(2004) 5421-5423

7 Chernov AA Crystallization processes Modern CrystallographyMoscow 1980 vol 3 p 5-12 (in Russian)

8 Bernshtein ML Zaymovsky VA Mechanical properties of metalsMoscow Metallurgy 1979

9 State diagrams of binary metal systems Ed by NP Lyakishev1997 vol 2 p 636ndash637 (in Russian)

10 Gromov DG Gavrilov SA Redichev EN Klimovitskaya AVAmmosov R M Factors determining melting temperature of thinfilms of Cu and Ni on inert surfaces Zhurnal Fizicheskoy KhimiiV 80 No 10 2006 p 1856-1862 (in Russian)

104

ZINC IONS REDUCTION ON SOLID METAL ELECTRODES INCHLORIDE MELTS

Alex Lugovskoy 1a Zeev Unger 12b Michael Zinigrad 1cDoron Aurbach 2d

1Material and Chemical Engineering Department Ariel UniversityCenter of Samaria Ariel 40700 Israel

2Department of Chemistry Bar-Ilan University Ramat-Gan 52900Israel

alugovsaarielacil bzevikitoarielacil сzinigradarielacildaurbachmailbiuacil

keywords electrodeposition chloride melts cyclic voltammetry high-temperature electrochemistry

AbstractThe reduction of zinc ions on solid tungsten and platinum

electrodes in chloride melts at the temperatures 700 ndash 750 degC wasstudied by cyclic voltammetry chronoamperometry and energydispersion spectroscopy It was established that no zinc is reduced onplatinum electrodes As for the reduction of zinc ions on tungstenelectrodes the process has a complex character it starts as anirreversible two-electron zinc ion reduction and after the new phase isformed the process of saturation of the electrode surface with lithium orsodium begins As the second process develops the alkaline metalbecomes essentially the only constituent on the electrode surface

GeneralSince zinc is industrially recovered from sulfate solutions rather

than from melts and because its melting temperature (4195 degC) is lowerthan the temperatures of most molten chloride compositions thereduction of zinc ions on solid electrodes in chloride melts has beeninvestigated relatively poorly There are quite a few papers devoted tothe electrolysis of zinc containing chloride melts (1 2) and these coveronly some details of the electrochemistry of this metal However zinc isnot only an engineering metal It can often be a component of moltenchloride systems in which various processes of synthesis or purification

105

are performed Therefore the detailed electrochemical behavior of zinccan be of great importanceThe study of electro-reduction processes of zinc ions on solid tungstenand platinum electrodes in eutectic NaCl ndash KCl and LiCl ndash KCl melts inthe temperature range of 700 ndash 750 degC is presented in this work Thesetemperatures are somewhat higher than the eutectic points of NaCl ndashKCl (646 degC ) and LiCl ndash KCl (628 degC) and the melts are thereforeliquid enough to be used in technologically important processes oflanthanides and actinides separation reduction and rectification On theother hand these temperatures are significantly lower than the boilingpoint of zinc (907 degC) and there is essentially no loss of the metal due toevaporation

ExperimentalThe electrochemical experiments were performed using a three-

electrode cell made of sintered alumina placed in an alumina crucibleunder nitrogen atmosphere Tungsten (9995 1 mm diameter) andplatinum wires (9995 05mm diameter) were used as the workingelectrodes and their surface area was controlled by immersion depth(typically 6ndash12mm) and by measuring their diameter before and aftereach experiment A 1mm tungsten wire served as a pseudo-referenceelectrode and a flat spiral tungsten wire set perpendicular to theworking and reference electrodes close to the bottom of the cell servedas the counter electrode The area of the counter electrode was ~ 20 foldas large as that of the working electrode ZnCl2 LiCl NaCl and KCl(990 +ACS grade Alfa Aesar) were used for the preparation meltswithout further purification

Zinc chloride was mixed with alkaline metals chlorides usingmortar and pestle in a glove-bag in dry nitrogen atmosphere Themixture was then placed into a crucible the electrode cell was mountedand transferred into the furnace (single-zone Carbolite 1600 degC STF tubefurnace) In the furnace the mixture was first dried under vacuum at 40ndash50 degC for an hour After completing the drying dry nitrogen wasbubbled through the electrolyte during its heating up to the temperatureof the experiments (700ndash750 C) for another hour The temperature wascontrolled by a type S thermocouple placed next to the cell andprotected by an alumina capillary thus maintaining a precision of plusmn1 degCin measuring and controlling the temperature Dry nitrogen atmosphere

106

(1 bar) was maintained in the furnace during the measurements and thepost-experimental cooling The electrochemical measurements werecarried out using an Autolab PGStat-12 potentiostat SEM images andelement analysis by EDS were performed with a SEM system fromJEOL Inc Model JSM 7000F

Results and discussion

Deposition of zinc on a tungsten electrodeSome typical voltammograms for the electrochemical reduction ofZn(II) are shown in Fig 1

-02

-01

0

01

02

03

04

-1 -05 0

iA

cm

2

E V vs W

C

A

QaQ

c~ 1

0502005 Vsec

-0680-0650-0600E

p V

(peak C)

164141110Qc Ccm

2

177150113Qa Ccm

2

Fig 1 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0163 mol L) in equimolar NaCl-KCl melt on a W electrode at 700degC Scanrates are 50 mV sec (solid line) 200 mV sec (slashed line) and 500 mV sec(dotted line) Each charge density was calculated as the sum of areas limited bythe baseline and the appropriate current density curves for the forward andbackward semi-cycles

107

As follows from Fig 1 a single cathodic peak C corresponds toone anodic peak A The potential shape and behavior of the cathodicpeak are typical for the metal deposition on a solid electrode (2-4) Nodifference is observed between the reduction of zinc ions in NaCl ndash KCland in LiCl ndash KCl melts Peak A is assigned to the reoxidation of zincBoth peaks are clearly not independent on the scan rate Rather peak Cis shifted to more negative potentials and peak A moves to more positivepotentials as the scan rate increases The dependence of the cathodicpeak potential on the scan rate is shown in Fig 2 Such voltammetricresponse is typical for irreversible processes

055

06

065

07

075

0 01 02 03 04 05 06

-Ep

V

Vs

Fig 2 Dependence of the cathodic peak potential on the scan rate for thereduction of Zn2+ (0163 mol L) at 710degC on a W electrode

The cathodic peak C appears at about -06 V vs tungsten electrodefor the scan rate of 50 mVsec and at -07 V for 500 mVsec Such asignificant shift is a clear indication that the process is irreversible Thecathodic peak not only is shifted as the scan rate grows but it becomes

108

broader so that the difference |Ep ndash Ep2| grows from 01 V for 005 Vsecto 015 V for 05 Vsec Values of n calculated by equation 23 are inthe range of 156 for low scan rates to 104 for high scan rates The mostlogical interpretation of this finding is that the charge-transfer is of two-electrons which is not surprising in the case of Zn2+ ions reduction Thevalue of is then 078 for 005 Vsec and 052 for 05 Vsec This isevident that the rate determining step is the Faradaic process

Zn2+ + 2e- Znwhen the system is close to the steady state Note that at low enoughpotential scanning rates diffusion limitations may be less influencingwhile at higher scan rates the diffusion limitations are more importantRandles-Sevcik dependencies for the zinc (II) ions reductiondemonstrate linearity but their intercepts are apparently non-zero (Fig3)

0

01

02

03

04

05

06

07

0 02 04 06 08 1

i pA

cm

2

12 V12s-12

Fig 3 Randles-Sevcik plots for Zn2+ ions reduction on W in a NaCl-KCl meltat 700 degC different concentration of the ions (peak C in Figure 39) 900x10-5

molmL Zn2+ 163x10-4 molmL Zn2+ 177x10-4 molmL Zn2+

109

It is evident that the process Zn2+ + 2e- Zn is complicated bysomething else Despite the irreversible character of the depositionprocess it is still reasonable to roughly evaluate the diffusion coefficientof Zn2+ according equation 1

ip = 06105 (nF)32(RT)12D12C12 (11)

where ip is the peal current density (A cm2) n is the number ofelectrons F is Faraday constant (96500 C) R is the gas constant (8314Jmol∙K) T is the absolute temperature (K) D is the diffusion coefficient(cm2 sec) C is the bulk concentration of a Red (Ox) species (mol cm3) and is the scan rate (V sec)

Thus calculated diffusion coefficients are shown in Table 1

Table 1 Diffusion coefficients of Zn2+ to a tungsten electrode in NaCl-KCl melt

C105 mol L D 105 cm2 sec900 955n

163 1020n

177 1364n

Given that the value of n for the reduction of Zn2+ cannot exceed 2 and0 le le 1 ( asymp 05 for most cases) reasonable values of n must beclose to 1-2 Therefore the values of the diffusion coefficients fromTable 2 lie in the range of 1-6∙10-4 cm2sec Available literature data forthe diffusion coefficients of most metal ions lie in the range 10-5-10-4

cm2sec Particularly T Stoslashre G M Haarberg and R Tunold found thatthe values of the diffusion coefficients for Zn2+ in KCl-LiCl melts at400degC lie in the range 06 ndash 106∙10-5 cm2sec (2) Delimarski providesthe value of the diffusion coefficient of Zn2+ in NaCl-KCl at 710degCwhich is 23∙10-5 cm2sec (5) The deviation of our results from theliterature data can hint that that the process cannot be treated as simplezinc ion reduction on the surface of tungsten

110

It is worth to mention that the fact that the diffusion coefficientfor zinc ions in the chloride melt lay in the range 10-4 ndash 10-5 cm2sec mayserve as an indirect argument in the discussion about the existence ofcomplex species described by the general formula [ZnxCly]

z+ in chloridemelts While some authors argue in favor of the formation of complexions (6 ndash 10) other studies give evidence for the existence of individualzinc ions as the key reacting species (11 ndash 12) The relatively highvalues of the diffusion coefficients found in our experiments hint that thecharge is transferred by individual ions rather than by more massivecomplex moieties

005

01

015

02

025

03

035

04

02 03 04 05 06 07 08 09 1

700oC

750oC

740oC

720oC

i pA

cm

2

12

V12

s-12

Fig 4 Randles-Sevcik plots for Zn2+ reduction on W in a NaCl-KCl melt fordifferent temperatures [Zn2+] = 900x10-5 molmL

Another intriguing aspect of the zinc ions deposition process ona tungsten electrode can be seen in the temperature dependence of

111

Randles-Sevcik plots (Fig 4) As seen from Fig 4 Randles-Sevcik plotsdo not change (to the accuracy of the experiment) as the temperaturerises from 700degC to 750degC

The lack of dependence of Randles-Sevcik plots on thetemperature is really surprising A plausible explanation to this could bean additional process in the system which occurs simultaneously withthe observed process but does not involve charge-transfer and cannot bedetected electrochemically Such a process could compensate for theexpected increase of the slope of Randles-Sevcik plots as thetemperature grows and thus distort the temperature dependence

The most probable candidates for such competing processes area coupled chemical (not charge-transfer) reaction or a process of phase-formation However cyclic voltammetry alone cannot discriminatebetween these two possibilities

Fig 5 A chronoamperometric plot for the deposition of Zn2+ on a tungstenelectrode Temperature 725degC [Zn2+] = 900x10-5 molmL The potential was

stepped from OCV to -055 V

A further insight on the nature of the deposition process can beprovided by chronoamperometry As seen from Fig 5 the current fallsin the course of the first 11 seconds of the experiment and then risesreaches a peak and gradually declines as expected with time until theend of the experiment (300 seconds)

The initial falling and rising of the current can be attributed tothe nucleation of the deposits fluctuations of current for more advanced

112

reaction times as seen in Fig 5 may indicate to a very active charge-transfer process which cannot be explained by a simple zinc depositionprocess

Even more surprising information is provided by EDS analysisof the working electrode after a 3000 second deposition experiment at ndash055 V (Fig 6 Table 2) The most striking result of the analysis is theunexpectedly high content of sodium on the electrode surface Thisamount of sodium cannot be accounted for melt adhesion or penetrationbecause the percentage of potassium and chlorine is much smaller Infact the working electrode looks as it was made of sodium withmoderate inclusions of tungsten and zinc rather of tungsten

Fig 6 An EDS spectrum of tungsten working electrode after 3000 seconddeposition at ndash 055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Table 2 Element composition of the tungsten working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Element Na K Cl W ZnAt 6084 580 2861 224 191

113

A somewhat similar phenomenon was reported by Thus T StoslashreG M Haarberg and R Tunold for the deposition of Zn2+ on a glassycarbon electrode in KCl-LiCl melts at 400degC (2) They observed aldquosubstantial residual current observed prior to the Zn(II) reductionpeakrdquo This current was attributed by them to lithium intercalation intothe lattice of the glassy carbon electrode

Unfortunately the data about standard reduction potentials ofmany important ions in molten chlorides are lacking The only source inwhich suitable potentials were found is the book of Yu DelimarskildquoElectrochemistry of Ionic Meltsrdquo (5) The values of standard potentialstabulated in this book were calculated on the base a few assumptionsand are far from being strictly thermodynamical However they arehelpful from the practical point of view The potentials relevant for thisdiscussion are summarized in Table 3

Table 3 Standard reduction potentials in molten chlorides (adopted fromref [5])

Half-Element Li+|Li Na+|Na K+|K Zn2+|Zn Fe2+|FeEH2 (700degC) V - 239 - 236 - 250 - 040 - 007

As seen from Table 3 the standard potentials of lithium andsodium are very close to each other Therefore it is not surprising thatthe interference from sodium in the deposition of zinc ions is similar tothat of lithium as reported by T Stoslashre G M Haarberg and R TunoldOf course it is not intercalation that serves as the moving force of theprocess of sodium penetration into the surface layers of zinc deposit onthe tungsten electrode

The large amounts of sodium in the deposits obtained in the studyof the Zn2+ ions reduction on tungsten electrodes cannot be explained asthe formation of a W-Na alloy because such a process is not observedby the cyclic voltammograms of NaCl-KCl on tungsten electrodes in theabsence of zinc ions (3) Therefore it is zinc which triggers thedeposition of sodium Moreover the data obtained bychronoamperometry at E = ndash 055 V vs W (Fig 5) indicate that there aretwo sequential faradaic processes The first of them is relatively weak

114

and is completed after ~ 11 seconds Then the second process starts andits current only grows with time The first process can be related to thereduction of zinc ions and the formation of zinc deposits As theelectrode surface is covered by a layer of zinc the interaction of thislayer with Na+ ions begins Apparently sodium ions are absorbed by theliquid zinc (Tm = 419 degC) and this facilitates their reduction at thepotential so much more positive than the sodium reduction potential inthe absence of zinc ( - 11 V vs W) Both lithium and sodium are liquidat the temperature of the experiment and these two metals form on theelectrode surface a liquid solution with zinc which continues to absorbnew portions of the lithium or sodium ions

The following speculation may account for the phenomenonobserved in our system

1 Zinc ions are discharged on the surface of the tungstenelectrode As the surface concentration of zinc atoms grows nucleationoverpotential starts to dump the overall process This dumping isobserved in the course of the first 11 seconds in Fig 5

2 Zinc (or zinc-tungsten) phase is formed This phase triggers theprocess of sodium-zinc exchange

Zn + Na+ Zn+ + Na or Zn + 2Na+ Zn2+ + 2Na3 The process (2) becomes the main process on the electrode

surface

Deposition of zinc on a platinum electrodeSome typical voltammograms for the electrochemical reduction

of Zn(II) are shown in Fig 7 Again no difference is observed betweenthe processes in NaCl ndash KCl and in LiCl ndash KCl melts and two melts arefurther described on the instance of in NaCl ndash KCl alone

As seen from Fig 7 the voltammogram is completely anomalousas compared to the other studied systems No cathodic peaks areobserved in the range -11V to + 09V ie in the limits of theelectrochemical window The peaks ndash 125V and at +09 V are the sameas for the ldquoblankrdquo melt NaCl-KCl These are the limits of theelectrochemical window

A very poorly pronounced anodic peak A at about ndash 028 V issimilar to the anodic peak A which appears for the zinc deposition on atungsten electrode (Fig 1) However the cathodic branch of thevoltammogram contains a continuous transition to the cathodic limit of

115

the windows rather than a peak It is obvious that zinc deposition ismasked by another process whose nature cannot be studied in theframework of this research

Fig 7 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0176 mol L) in equimolar NaCl-KCl melt on a Pt electrode at 700degC Scanrate is 300 mVsec

Fig 8 An EDS spectrum of a platinum working electrode after 3000 secondcathodic polarization at ndash 07 V vs W at 725degC in equimolar NaCl-

KCl melt containing 176x10-4 molmL of Zn2+ ions

116

An attempt of obtaining a sample of zinc deposit by holding thesystem at ndash 07 V (that is at such a potential which is considerably morepositive than the cathodic limit but more negative than the potential atwhich zinc is deposited on a tungsten electrode) for 3000 seconds wasmade However the analysis (Fig 8) demonstrated that essentially nozinc is found on the surface of the electrode (Table 4) since the value098 At is comparable with the sensitivity of the method The richcontent of potassium (5857 At ) in the surface layers can hint thatpotassium sorption is the process which masks the deposition of zincHowever this information alone is not sufficient for making positiveconclusions

To try to understand the essence of the process other moltenchloride systems containing no potassium could be studied Howeversuch a study is far beyond the framework of the current work

Table 4 Element composition of the platinum working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 176x10-4 molmL

Element Na K Cl Pt ZnAt 555 5857 3426 618 098

ConclusionsThe deposition of zinc on a tungsten electrode starts as an

irreversible two-electron zinc ion reduction Zn2+ + 2e- Zn After anobvious initial nucleation step a new phase is formed This phasecatalytically launches the process of saturating the electrode surface withsodium After the onset of the process of sodium deposition the latterbecomes essentially the only constituent on the electrode surface

The attempts of studying the deposition of zinc ions on a platinumelectrode were unsuccessful because this process is masked by anotherprocess which can result in the saturation of the electrode by potassiumThe exact nature of the latter process demands a separate study

117

References1 Fray D J J Appl Electrochem 3 103 (1973)2 Stoslashre T Haarberg GM Tunold R J Appl Electrochem 30 1351

(2000)3 Lugovskoy A Zinigrad M Aurbach D Israel Journal of

Chemistry 47 (3-4) 409 (2007)4 Lugovskoy A Zinigrad M Aurbach D and Unger Z

Electrochimica Acta 54 (6) 1904 (2009)5 Delimarski Yu K Electrochemistry of Ionic Melts Metallurgiya

Moscow 1978 (in Russian)6 Mackenzie J D and Murphy W K J Chem Phys 33 366 (1960)7 Irish D E and Young T F J Chem Phys 43 1765 (1965)8 Allen DA Howe RA Wood ND Howells WS J Phys

Condens Matter 4 1407 (1992)9 Price D L Saboungi M-L Susman S Volin K J Wright A C J

Phys Condens Matter 3 9835 (1991)10 Bassen A Lemke A Bertagnolli H Phys Chem Chem Phys 2

1445 (2000)11 Biggin S and Enderby J E J Phys C Solid State Phys 14 3129

(1981)12 Badyal Y S and Howe R A J Phys Condens Matter 5 7189

(1993)

89

PREPARATION OF COMPOSITES CuZrO2 AND CuTiO2

BY MA SHS

AI Letsko1 TL Talako1 AF Ilyushchenko1 TF Grigoreva2SV Tsybulya3 IA Vorsina2 NZ Lyakhov2

1 Powder Metallurgy Institute of NAS B Minsk Belarus2 Institute for Solid State Chemistry and Mechanochemistry of SB RAS

18 Kutateladze str Novosibirsk Russia grigsolidnscru3 GK Boreskov Catalysis Institute of SB RAS Novosibirsk Russia

IntroductionMetaloxide composites are quite perspective materials for

application in machine industry instrument engineering and electricalengineering in comparison to pure metals due to their improvedchemical and physical properties (heat resistance strength hardnesserosion resistance) Chemical mixing salt mixture decompositionhydrogen reduction in solutions chemical precipitation from solutionsinternal oxidation are well-known methods of preparing such materialshaving application in industry [1] The above-mentioned technologiesallow attaining metaloxide composites but they are quite expensive andlong-term Based on this a very topical issue is elaboration of newapproaches to production of metal-ceramic materials

In this work we explored possibilities of preparation ofcopperoxide composites (CuZrO2 and CuTiO2) by methods ofmechanochemical synthesis (MS) in planetary mills and of mechanicallyactivated self-propagating high-temperature synthesis (MA SHS)

ExperimentalCopper copper oxide CuO and zirconium M-41 titanium PTOM

were used in this work as raw materials Mechanical activation (MA)was carried out in planetary ball mills with water cooling [2] (the drumvolume ndash 250 cm3 the balls diameter ndash 5 mm the load ndash 200 g sampleweight ndash 10 g the drums rotation speed about the general axis ~ 1000rpm) After MA the activated mixture was compacted (under a load of4ndash6 t) in the mould up of 17 mm diameter and ~25 mm in height (tillstrength sufficient for the sample transfer to the reactor) SHS wascarried out in the argon atmosphere the combustion was initiated withan electrically heated tungsten coil The temperature and burning

90

velocity were evaluated by a thermocouple method (C-A thermocouplesOslash asymp 02 mm) using an outer 2-channel 24-charge analog-to-digitalconverter ADSC24-2T

X-ray diffraction research was conducted with diffractometersXrsquoTRA (Thermo ARL Switzerland) with application of CoK radiation(λ = 1 789 Aring) and URD-63 with application of CuK radiation (λ = 15418 Aring) Evaluation of effective sizes of coherent scattering area wascarried out in compliance with the Scherer formula with the strongestpeaks of phases analysed

The high-resolution scanning electronic microscope (SEM)MIRATESCAN equipped with an INCA 350 accessory for EDXanalysis was used for the structure research The electron probe diameterwas 52 nm excitation area was 100 nm Images in direct electrons andback-scattered electrons were attained and it allowed studying chemicalelements distribution over the surface Brightness distribution in theimage depends on the average atomic element number in eachmicroarea

IR absorption spectra were registered by spectrometer IFS-66The samples were prepared to the exposure by standards methods

Results and discussion

Cu-O-Zr systemMechanochemical reduction of copper oxide with metallic

zirconium was initially investigated in this system This reaction is quitehigh-exothermic (∆H (2 CuO + Zr = 2 Cu + ZrO2) asymp -188 kcalmol) ieit can be implemented under mechanical activation conditions IRspectroscopic investigations have shown that the original copper oxideCu-O band is considerably widened at 505 cm-1 after 20 s of MA ofCuO + Zr mixture of stoichiometric composition This widening (Fig1b) can testify some structural failures After 30 s of activation thefollowing bands are present in the IR-spectrum of the product 505 cm-1

(original oxide CuO) 615 cm-1 (the lowest copper oxide Cu2O) [3] and415 585 735 cm-1 (zirconium oxide (Fig 1c) [4 5] X-ray-phaseanalysis shows the presence of certain amount of Cu2O already after 20 sof activation The 30-second activation product diffractogram showsclear copper (coherent scattering area asymp 80 nm) and zirconium oxide

91

(coherent scattering area asymp 100 nm) reflection and two copper oxidereflections ie mechanochemical reduction of copper oxide takes placeat such activation duration This reaction speed shows that the reactionpresumably takes place in the thermal explosion mode when especiallyhigh heat dissipation speed is needed what is very difficult to performeven in the most effectively cooled highly-energy planetary ball millsAs such a process dimensional scaling seems to be absolutely impossiblein conditions of mechanochemistry an attempt to produce compositeCuZrO2 by the SHS method was made

Fig 1 IR-spectra of mixture CuO + Zr before (a) and after MA for 20 (b) and30 s (c)

At first CuOZr mechanocomposite was used as the SHS-precursor This mechanocomposite formed after 20 s of MA ofstoichiometric composition mixture has a small amount of cuprous oxideCu2O beside original copper oxide and zirconium SHS process proceedsin the heat explosion mode in this system Burning parameters fixingfailed in this case because of the inertia of the equipment applied

92

Not pure metal but solid solutions intermetallic compounds ornano-composites where metal-reducer (zirconium in our case) isdistributed in the inert matrix can be used as a reducing agent todecrease the system reaction capability At the same components ratiochemical energy of the raw mixture would be considerably lower and asa consequence heat release would reduce

In this work mechanocomposite formed during mechanicalactivation of mixture Cu + 20 wt Zr for 20 min with zirconium hadbeen pre-dispersed for 4 minutes (zirconium coherent scattering areasize ~ 20 nm) was used for copper oxide reduction This compositediffractogram shows the widened intensive copper (coherent scatteringarea asymp 20 nm) reflection and very vague zirconium reflection coherentscattering area of which cannot be evaluated (Fig 2) Since copperreflections havenrsquot changed their position we can conclude thatzirconium hasnrsquot become a part of copper crystal lattice ie CuZrmechanocomposite and not solid solution is attained

Fig 2 Diffractograms of Cu + 20 Zr mixture before (a) and after 20 minof MA (b)

93

This is confirmed by the SEM results (Fig 3) The electronmicroscopy data more clearly show zirconium distribution Zr elementalmapping testifies that local zirconium areas are much diffused

Fig 3 SEM-images of sample Cu + 20 Zr after MA for 20 min

94

X-ray research of the product of joint activation of mixture CuO +mechanocomposite Cu + 20 Zr (the mixture composition correspondsto the stoichiometric ratio of copper oxide and zirconium) for 2 and 4minutes show that copper oxides diffraction reflections are retained inall cases although they are substantially widened (Fig 4) Thezirconium oxide reflection is not observed ie mechanochemical copperoxide reduction does not take place in this time gap CuOCuZrmechanomposite formed as a result of joint mechanical activation ofmixture CuO + mechanical composite Cu 20 Zr for 4 min was usedas a precursor for SHS

Fig 4 Diffractogram of sample CuO + CuZr after MA for 4 min

Usage of mechanocomposite CuOCuZr instead of CuOZr one asthe SHS precursor changes a mechanism of interaction between thereactants during the SHS process from the thermal explosion mode (forCuOZr mechanocomposite) to the steady-state combustion with the

95

burning velocity asymp 2 mms temperature rise speed about 730 Cs andburning temperature 1044 C The combustion temperature record (Fig5) shows 2 isothermal plateaus The first one is fixed at temperaturemaximum and most probably points out melting process The secondone is fixed at 580 ndash 590 C and accounts for post-processes in the after-burning zone of combustion wave

Fig 5 Temperature record of the SHS process from mechanical compositeCuOCuZr

X-ray-phase analysis has shown that SHS product consists ofcopper and zirconium oxide with Cu2O traces (Fig 6) Electronicmicroscopy with the EDX analysis confirms composite structureformation (Fig 7 Table 1)

96

Fig 6 Diffractogram of the SHS product from mechanical compositeCuOCuZr

Fig 7 SEM-image of the SHS product from mechanical composite CuOCuZr

97

Table 1 Results of the EDX analysis (from Fig 7)

Number ofspectrum

O Cu Zr

1 382 8744 8742 714 8152 11343 2803 2747 44504 1653 4640 37065 2314 2914 4772

Cu-O-Ti systemChemical reduction of CuO with titanium is also high-exothermic

(∆H (2 CuO + Ti = 2 Cu + TiO2) asymp -151 kcalmol) Mechanicalactivation of equimolar mixture of copper oxide with titanium powderfor 4 minutes did not result in titanium oxide formation Longeractivation is not reasonable since it contaminates the reaction mixturewith balls and drums material That is why the composites formedduring the short-term MA were used as precursors for SHS

After 30 s MA composite structure CuOTi with a small additiveof cuprous oxide reduced from CuO (Fig 8) is formed The SHS processfrom such mechanocomposites proceeds with a very high speed andtemperature (on a levels typical for the thermal explosion mode) andwith the substances scatter

Fig 8 Diffractogram of mixture CuO + Ti after MA for 30 s

98

To decrease combustion temperature and velocitymechanocomposite CuTi containing 20 wt of titanium was used as areducing agent in the next experiment Figure 9 shows the diffractogramof the mechanocomposite formed after 10 min mechanical activation ofthis mixture It shows that metals reflections especially that of titaniumare widened testifying substantial increase of their dispersivityAccording to the X-ray data analysis the titanium coherent scatteringarea size is ~ 10 nm in this composite

Fig 9 Diffractogram of mixture Cu + 20 Ti after 10 min of MA

Mixture of copper oxide and CuTi mechanocomposite (thecomposition corresponds to the stoichiometric ratio of titanium andcopper oxide for its full reduction) was subjected to activation for 4minutes Only a band of valence vibrations of vCu-O copper oxide (Fig10a) is present in the IR-spectrum of the activated mixture like in theoriginal one but its intensity slightly decreases X-ray research alsoindicates that the titanium oxide reflections are absent in the 4-minuteactivation product diffractogram (Fig 11)

99

Fig 10 IR-spectra of sample CuO + CuTi after 4 min of MA (a)and after SHS (b)

Fig 11 Diffractogram of sample CuO + CuTi after 4 min of MA

100

SHS process from CuOCuTi mechanocomposite takes place inthe steady-state combustion mode with burning velocity higher than 20mms and burning temperature ~2000 ordmC A band (~730 cm-1)corresponding to valence vibrations of rutile vTi-O (Fig 10b) [2]appears in the IR-spectrum of the SHS product from CuOCuTimechanicocomposite Diffraction reflections (Fig 12) also correspond toreflections of rutile and copper

Fig12 Diffractogram of the SHS product from CuOCuTi mechanocomposite

Electron-microscopy exposure in back-scattered electronsindicates the partial phase separation of TiO2 and Cu (Fig 13 a) thoughcomposite particles containing TiO2 inclusions with size from 30 nm till1 5 m (Fig 13 c) are also formed The elemental mapping in thetitanium characteristic radiation confirms this fact (Fig 13d)

101

a

b cFig 13 SEM-images of the SHS-product from CuOCuTi mechanocomposite

102

Table 2 The EDX analysis results (from Fig 13 a)

Number ofspectrum

O Ti Cu

1 191 052 9757

2 235 051 9714

3 2230 2094 5676

4 1586 1295 7118

5 180 108 9712

6 336 228 9436

7 4335 4685 980

8 3297 2738 3966

9 4978 4645 377

ConclusionThus our investigations have shown that copper oxide can be

mechanochemically reduced with zirconium resulting in formation ofzirconium oxide and copper but the reaction goes in the thermalexplosion mode

To produce composite CuZrO2 by the method of MASHS usageof mechanocomposite CuZr instead of pure zirconium seems to be morepromising The MASHS product is a copper-based composite withinclusions of ZrO2 and some amount of Cu2O

Mechanical activation of equimolar mixture of copper oxide withtitanium powder for 4 minutes did not result in titanium oxide formationThat is why the composites formed during the short-term MA were usedas precursors for the following SHS

Reduction of CuO with CuTi mechanocomposite can beimplemented by the method of MASHS Partial phase separation of TiO2

and Cu takes place during the synthesis process along with the formationof copper-based composite particles with inclusions of titanium oxidesized from 30 nm up to 15 m

103

References1 PA Vityaz Mechanically alloyed alloys on the basis of aluminum

and copper PA Vityaz FG Lovshenko GF Lovshenko ndashMinsk Belnauka 1998 ndash 351 p

2 YG Avvakumov AP Potkin OI Samarin Authorrsquos certificate ofUSSR 975068 Planetary mill BI 1982 No 43

3 SS Batsanov VPBokarev YVLazareva On CuO interaction withcopper Inorganic Chemistry Journal 1977 V 22 issue 4 P 888ndash 892

4 AI Boldyrev Infrared spectra of minerals M Nedra 19765 BT Kaminsky AS Plygunov GN Prokofyeva Infrared spectra of

oxides of titanium zirconium and hafnium Ukrainian ChemicalJournal 1973 V 35 No 9 P 946 ndash 977

78

THE STANDARD ENTHALPY AND ENTROPY OFFORMATION OF GASEOUS AND LIQUID

POLYCHLORINATED BIPHENYLS POLYCHLORINATEDDIBENZO-n-DIOXINS AND DIBENZOFURANS

TV Kulikova AV Mayorova KYu ShunyaevInstitute of Metallurgy Ural Branch RAS

Yekaterinburg RussiaE-mail kulikogmailcom

AbstractThe study deals with analysis and systematization of the known

and calculation of the unknown thermodynamic characteristics (thestandard enthalpy of formation the standard entropy of formation) ofwidespread hazardous isomers of gaseous and liquid compounds ofpolychlorinated biphenyls (PCBs) polychlorinated dibenzo-n-dioxins(PCDDs) and polychlorinated dibenzofurans (PCDFs) Thecomparison of results obtained in different studies reveals aconsiderable discrepancy between values reported by highlyrespected investigators In this connection laquoindependentraquo results ofthe thermodynamic characteristics have been calculated

IntroductionUnique technological and physicochemical properties of

polychlorinated biphenyls (PCBs) a huge volume of theirproduction considerable volatility and solubility and extremechemical inertness have led to the world-wide spread of PCB-containing equipment and materials resulting in the universalcontamination with these substances The most common method usedin Russia for destruction of PCBs is their incineration with theformation of polychlorinated dibenzo-n-dioxins (PCDDs) anddibenzofurans (PCDFs) which are among the most hazardouschemical substances known to the mankind

As often happens the hazard of PCBs has long beenunderestimated With respect to their severe toxicological effectPCBs are identical to substances that are referred to the high class ofhazard Since these substances are especially toxic they have beenassigned low toxicological standards which necessitate special

79

requirements on the organization of processes assuming formation ofthese substances (the so-called dioxinogenic processes) so thatindustrial emissions meet the norms Instrumental investigations ofthese substances are very expensive and in this connection interestis attracted to calculation methods for simulation of processes by thedata on their thermochemical properties

A quality thermodynamic simulation requires the knowledge ofthermodynamic and thermochemical properties of all reliablycertified compounds of the system under study in the gaseous orcondensed state Therefore the present study deals with the analysisand systematization of the known and calculation of the unknownthermochemical properties (the standard enthalpy and entropy offormation) of most toxic and hazardous isomers of gaseous PCBsPCDDs and PCDFs and liquid PCBs

Calculation of thermochemical propertiesIt is known that there are 209 individual PCB congeners 420

polychlorinated dibenzo-n-dioxins and polychlorinateddibenzofurans which differ by the number and positions of chlorineatoms in a molecule The most widespread PCB compoundscontaining up1 to 10 chlorine atoms were chosen for the study Indeciding on isomers preference was given to ortho-unsubstitutedPCBs because they are most toxic and their effect is similar to theeffect of PCDDs and PCDFs Congeners which do not have chlorineatoms in ortho-positions of molecules (ortho-unsubstituted PCBs)can acquire the planar configuration which is more favorable inenergy terms Such congeners are isostereoisomeric to PCDDs andPCDFs and present the greatest hazard As to the PCDD and PCDFisomers of special hazard to humans and the environment are tri-tetra- penta- and hexa-substituted dioxins and furans containinghalogen atoms in lateral positions 2 3 7 and 8

In this study we analyzed the known and calculated theunknown thermodynamic properties of 17 most widespread andhazardous isomers of PCBs PCDDs and PCDFs in the gaseous stateand 11 compounds of liquid PCBs

80

Gaseous PCBs PCDDs and PCDFsThe literature survey showed that studies dealing with

estimation of the thermochemical properties of gaseous PCB PCDDand PCDF compounds are few Most of them are based oncalculations or are semi-empirical For example Saito and Fuwa [1]calculated thermodynamic functions of all PCBs and some PCDDsand PCDFs on the basis of semi-empirical calculations in terms ofthe PM3 model OV Dorofeeva et al [2-4] used statistical methodsTable 1 presents the literature data on standard enthalpies andentropies of formation of gaseous and liquid PCBs PCDDs andPCDFs The comparison of results obtained in different studiesreveals a considerable discrepancy between values reported by highlyrespected investigators who did very arduous work In particularvalues of the formation enthalpy [1] are 8-70 larger and the entropyis 11-15 smaller than the corresponding values in [2-4] thediscrepancy grows with the number of chlorine atoms in a moleculeSo we thought it reasonable and topical to attempt an independentresult

Bensons method [5] was used to calculate thermodynamiccharacteristics (the standard enthalpy of formation ΔНdeg298 thestandard entropy of formation ΔSdeg298) of the gaseous PCBs PCDDsand PCDFs We shall dwell briefly on this method

Bensons method is the group additivity method involvinganalysis of the molecule structure Atomic or molecular groups areseparated and the nearest neighbors of the atom or the group areconsidered Table 2 gives the number of groups necessary fordetermination of group increments in structural formulas of PCBsPCDFs and PCDDs Values of the thermodynamic characteristics ofgroup increments were determined from available reference andliterature data [5 6] Information about the energy contribution ofeach group (see Table 3) and the number of groups was used tocalculate thermochemical properties of the PCBs PCDDs andPCDFs

81

Table 1 Standard enthalpies (∆Нo298 kJmole) and entropies (∆So

298Jmole K) of formation of gaseous and liquid PCBs PCDDs andPCDFs

Gaseous state Liquid state

Compo-unds Saito Fuwa [1]

the given work

OV Dorofeeva etal

[2-4]

∆Нo298

[7 8 121617]

So298

[781014 16 17]

∆Нo298

the givenwork and

[814]

So298

thegivenworkand[14]

1 2 3 4 5 6 7 8 9

C12H10

(biphenyl)

1986[1]

1797

3454[1]

4104

1820[3]

3908[3]

1819[8]

1814[16]

3927[16]

11711162[8]11710

[14]

257402574[14]

C12H9Cl(3-mono-

chlor-biphenyl)

1705[1]

1500

3851[1]

4413

1561[2]

4323[2]

1548[8]

15088[16]

4214[16]

7629 2840

C12H8Cl2

(44rsquo-dichlor-biphenyl)

1422[1]

1202

3992[1]

4721

1260[2]

4518[2]

1276[8]

12004[16]

4492[16]

3584 3106

C12H7Cl3

(344rsquo-trichlor-biphenyl)

1194[1]

905

4240[1]

5030

1041[2]

4923[2]

1004[8]

892[16]

4780[16]

-452 3372

C12H6Cl4

(33rsquo44rsquo-tetrachlor-biphenyl)

969[1]

608

4444[1]

5338

899[2]

5216[2]

732[8]

5836[16]

5068[16]

-4488 3638

C12H5Cl5

(33rsquo44rsquo5-penta-

chlorbiphenyl

748[1]

310

4620[1]

5647

569[2]

5502[2]

460[8]

2752[16]

5356[16]

-8524 3904

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlor-

biphenyl)

529[1]13

4615[1]

5956

314[2]

5675[2]

190[8]

-332[16]

5644[16]

-12558 4170

C12H3Cl7

(233rsquo44rsquo55rsquo-hepta-

chlor-biphenyl)

400[1]

-284

4842[1]

6264

152[2]

6077[2]

-84[8]

-416[16]

5932[16]

-16596 4436

82

1 2 3 4 5 6 7 8 9

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-

octachlor-biphenyl)

241[1]

-581

4886[1]

6573-90[2]

6342[2]

-356[16]-650[8]

6220[8]

-20632 4702

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-

nanochlor-biphenyl)

873[1]

-878

5048[1]

6881

-153[2]

6607[2]

-628[16]-958[8]

6508[8]

-24668 4968

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlor-biphenyl)

-67[1]

-1176

5034[1]

7190

-247[2]

6757[2]

-901[16]

-1267[8]

6796[8]

-28604 5234

C12H8O2

(dibenzo-n-dioxin)

-402[1]

-448

3764[1]

-592[4]

3965[4]

-592[12]-592[7]

-550[17]

3951[7]

3880[17]

- -

C12H4Cl4O2

(2378-tetrachlor-dibenzo-n-

dioxin)

-1372[1]

-1592

4553[1]

-1640[4]

4781[4]

-1345[7]

-158[17]

5136[7]

4784[17]

4781[10]

4784[9]

- -

С12H3Cl5O2

(12378-pentachlor-dibenzo-n-

dioxin)

-1532[1]

-1900

4931[1]

-1900[4]

54035[4]

-1162[7]

-196[17]

5531[10]

5010[17]

- -

С12H2Cl6O2

(123478-hexachlor-dibenzo-n-

dioxin)

-1691[1]

-2164

4841[1]

-2196[4]

56912[4]

-1224[7]

57559[7]

5236[17]

- -

С12HCl7O2

(1234678-hepta-chlor-

dibenzo-n-dioxin)

-1848[1]

-2472

5005[1]

-2460[4]

59789[4]

-1196[7]

61031[7]

5462[17]

- -

C12H8O(dibenzo-

furan)

1061[1]

518

3787[1]

553[4]

3759[4]

552[17]

3744[17]

- -

C12H4Cl4O(1234-

tetrachlor-dibenzo-furan)

203[1]

-625

4505[1]

-500 [4]49098

[4]-528[17]

4648[14]

- -

83

1 2 3 4 5 6 7 8 9

С12H3Cl5O(12378-pentachlor-

dibenzo-furan)

-123[1]-934

4592[1]

-759[4]

51975[4]

-748[17]

4874[14]

- -

С12H2Cl6O(123478-

hexachlor-dibenzo-furan)

-283[1]

-12424713[1]

-1051[4]

54852[4]

-1043[17]

5100[14]

- -

С12HCl7O(1234678heptachlor-

dibenzo-furan)

-441[1]

-1550

4833[1]

-1315[4]

57729[4]

-1313[17]

5326[14]

- -

Table 2 Number of groups for determination of group increments instructural formulas of PCBs PCDFs and PVDDs

Number of groupsCompound Св-H Св-Cl Св-O Св-Св

Number ofchlorine atoms

in a molecule (n)

PCBs 10 - n n - 2 1 ndash 10

PCDFs 8 - n n 2 2 1 ndash 8

PCDDs 8 - n n 4 - 1 ndash 8

Св is the carbon atom in an aromatic ring

Values presented in Table 1 show the thermodynamiccharacteristics of PCBs PCDDs and PCDFs calculated in this studyand by other investigators

It is seen for example ( Table 1) that the formation enthalpy

(o298H ) of biphenyl (C12H10) equals (kJmole) 1986 [1] 1820 [3]

1819 [7] and 1814 [8] while the formation entropy (o298S ) of

2378-tetrachlordibenzo-n-dioxin (C12H4Cl4O2) is (J(mole K))4553 [1] 4781 [4] 4784 [9] and 4781 [10]

84

Table 3 Values of the thermodynamic characteristics determined bythe method of group increments[58]

(gas) (liquid)Group

o298H

kJmole

o298S

J(moleК)

o298H

kJmole

o298S

J(moleK)

Св-H 1381[8]1382[5]

4831[8]4827[5]

816[8] 2887[8]

Св-Св 2166[8]2077[13]

-3657[8]-3618[5]

1721[8] -

Св-Cl -1703[8]-1591[5]

7708[8]7913[5]

-3220[8] 5547[8]

(Св)2-O -7766[8]-8834[5]

--

- -

orto corrCl-Cl

950[8]921[5]

- 1400[5] -

meta corrCl-Cl

-500[8] - 400[5] -

In this study the values of the standard entropy of formationobtained by using statistical methods (OV Dorofeeva et al [2-4 9])for 17 isomers of PCBs PCDDs and PCDFs are in good agreementwith the values calculated by other investigators [8 10 12 13] andwith the values calculated by us

Liquid PCBsIt should be noted that ample literature data on the

thermochemical properties of liquid ecotoxicants is only available forbiphenyl (C12H10) [8 14] dibenzo-n-dioxin (C12H8O2) [11 15] anddibenzofuran (C12H8O) [5 17] The only study dealing withcalculation of thermodynamic functions for the whole series of liquidPCDD and PCDF homologues was published by VS Iorish et al[11] As to liquid PCB compounds the literature data on theirthermochemical properties are scarce [8 14]

The thermochemical properties namely the standard enthalpyand entropy of formation of liquid PCBs were calculated using thegroup additivity method due to Domalski [8] Values of the groupincrements (Table 3) were adopted from [8] It is seen from Table 3

85

that the energy contribution of the group Св-Св is unavailable for the

entropy calculation However if one uses known values ofo298S for

liquid biphenyl (C12H10) [14] and the data on the contribution of the

Св-H and Св-Cl groups [8] it is possible to calculateo298S for the

whole series of PCBs

o298S (PCB) =

o298S (BP) - (10-n)

o298S (Св-H) + n

o298S (Св-Cl) +

+(morto corr Cl- Cl ) +(pmeta corr Cl- Cl) (1)

where n is the number of chlorine atoms in a PCBs moleculem (p) - spatial amendments number Cl (from two and more) beingin orto - (meta-) position rather each other

The enthalpy of formation (o298H ) for the PCBs series

compounds was calculated by two options using the group additivitymethod due to Domalski [8] and from the equation

o298H (PCB) =

o298H (BP) - (10 - n)

o298H (Св-H) +

+ no298H (Св -Cl) +(morto corr Cl-Cl )+(pmeta corr Cl-Cl) (2)

Table 4 lists values of the standard enthalpy of formation forthe series of liquid PCBs compounds as calculated by the groupadditivity method [8] and the equation (2) It is seen that the values of

o298H which were calculated by the two methods are in good

mutual agreementThe thermochemical properties which were taken as reliable

were added to the TERRA database and were used forthermodynamic simulation of the thermal stability of PCBs PCDDsand PCDFs

86

Table 4 Calculated enthalpy of formation (∆Нo298) for liquid PCBs

compounds∆Нo

298 kJmole

CompoundGroup

incrementsmethod

Eq (5)δ

C12H9Cl(3-monochlorbiphenyl)

7584 76742 12

C12H8Cl2

(44rsquo-dichlorbiphenyl)3530 36382 30

C12H7Cl3

(344rsquo- trichlorbiphenyl)-506 -3978 2138

C12H6Cl4

(33rsquo44rsquo-tetrachlorbiphenyl)-4542 -44338 238

C12H5Cl5

(33rsquo44rsquo5-pentachlorbiphenyl)-8578 -84698 126

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlorbiphenyl)-1261 -125058 083

C12H3Cl7

(233rsquo44rsquo55rsquo-heptachlorbiphenyl)-1665 -165418 065

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-octachlorbiphenyl)-20686 -205778 052

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-nanochlorbiphenyl)-24722 -246138 044

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlorbiphenyl)

-28758 -286498 038

Conclusions1The literature data on the thermochemical properties of 17

most widespread and hazardous isomers of PCBs PCDDs andPCDFs in the gaseous state and 11 compounds of liquid PCBs havebeen analyzed and systematized for the first time

2Methods have been developed for calculating of thethermodynamic characteristics of organic compounds Values of thethermodynamic functions (standard enthalpy and entropy offormation) of liquid PCBs PCDDs and PCDFs have been calculatedfor the first time

87

3The comparison of the calculated values of thethermodynamic functions with the known literature datademonstrated their good mutual correlation

4The obtained data were added to the TERRA database andwere used for thermodynamic simulation of the thermal stability ofPCBs PCDDs and PCDFs

5The obtained data can be used for simulating of the behaviorof complex heterogeneous systems including ecotoxicants over awide interval of temperatures and initial compositions

This study was supported by RFBR (project No 08-03-00362-a)

References1 Nagahiro Saito Akio Fuwa Chemosphere 2000 vol40 p

131-1452 OV Dorofeeva NF Moiseeva VS YungmanLV JPhys

Chem A 2004 vol 108 p 8324-83323 OV Dorofeeva Thermodynamica Acta2001 vol374 p7-114 OV Dorofeeva VS Iorish NF Moiseeva J Chem Eng

Data 1999 vol 44 p 516-5235 SW Benson FR Cruickshank DM Golden GR Haugen

HE OrsquoNeal AS Rodgers R Shaw and R Walsh Chem Rev1969 vol69 p 279 -324

6 HK Eigenmann DM Golden and SW Benson J PhysChem 1973 vol 77 1687-1691

7 Jung Eun Lee and Wonyong Choi J PhysChem A 2003vol 107 p 2693-2699

8 Domalski E S and Hearing E D J of Phys and Chem RefData 1993 vol 22 p 805-1159

9 LV Gurvich OV Dorofeeva VS Iorish Zh Fiz Khimii 1993vol67 No 10 p 2030-2032

10 W-Y Shiu and K-C Ma J Chem Ref Data 2000 vol29No 3 p 387-462

11 VS Iorish OV Dorofeeva NF Moiseeva J Chem Eng Data2001 vol46 p 286-298

12 VA Lukyanova VP Kolesov Zh Fiz Khimii1997 vol 71No 3 p 406-408(in Russian)

88

13 P Reid J Prausnitz T SherwoodLeningrad Khimiya 1982592 p(in Russian)

14 Richard Laurent and Helgeson Harold C Geochimica etCosmochimica Acta 1998 vol 62 No 2324 p 3591 ndash 3636

15 I Barin ldquoThermochemical Data of Pure SubstancesrdquoWeinheim Federal Republic of Germany VCHVerlagsgesellschaft mbH 1997

16 Cambridgesoft database ver 806 December 31 200317 Thompson D Thermochim Acta 1995 vol261 p7-20

76

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OFNANOGRAINED

TiN-TiB2 COMPOSITES

MA Korchagin BB BokhonovInstitute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirsk Russiakorchagsolidnscru

Titanium nitride is known to exhibit high oxidation resistancehigh thermal conductivity and hardness as well as high corrosionresistance in acids Titanium diboride is also very hard possessing highstrength at elevated temperatures and anomalously high electricalconductivity among other ceramic materials

Composite materials based on the mixture of these twocompounds have been widely used in a variety of applications Highperformance parts have been also developed Thus ceramics containing40-50 molTiN shows high oxidation resistance [1] However untilvery recently TiN and TiB2 have been produced separately by twodifferent routes At present new methods are being developed tosynthesize mixtures of these two compounds in a single process One ofthese methods is based on self-propagating high-temperature synthesis(SHS) The use of SHS eliminates the need of having furnace equipmentto synthesize the desired products The possibility of SHS in the systemis due to the high enthalpies of formation of the products serving as aninternal chemical source of energy

In order to simultaneously obtain TiN and TiB2 by SHS the initialreactants can be either the powder mixtures of Ti-BN [3] or Ti-B-BN[4] The products of the reactions consist of highly porous well meltedsintered pieces with the minimum grain size of 1-10 microm [4] Hightemperatures developed in the combustion wave in the traditional SHSdo not allow finer grains of the products to retain

In order to overcome this problem short mechanical activationof the mixtures of reactants is proposed followed by the SHS in anatmosphere of argon or nitrogen

In the previous investigations preliminary mechanical activationhas been shown to significantly reduce the combustion temperatures

77

which to a great extent determine the grain size of the products of SHS[6 7]

Experiments were performed on the stoichiometric mixtures 3Ti +2BN The time of preliminary mechanical activation in a planetary ballmill (AGO-2 type) did not exceed 10 min The influence of the durationof mechanical activation on the combustion rate temperature and phasecomposition of the products was studied

The milled mixtures and the products of SHS were studied usingXRD analysis and Electron Microscopy The experimental conditionshave been found favoring the formation of the two-phase mixtures ofTiN of TiB2 with the grain size ranging from 20 to 50 nm [7]

References1 GV Samsonov Nitridy (Nitrides) Kiev laquoNaukova Dumkaraquo 19692 AG Merzhanov Tverdoplamennoe gorenie (Solid State

Combustion) Chernogolovka ISMAN 2000 224 p3 AEGrygoryan ASRogachev Combustion of titaniumwith

nonmetal nitridesCombustion explosion and shock waves 2001v37 2 p168-172

4 R Tomoshige A Murayma T Matsushita Production of TiB2-TiNcomposites by combustion synthesis and their properties J AmCeram Soc 1997 80[3] 761-764

5 MAKorchagin TFGrigorrsquoeva BBBokhonov MRSharafutdinovAPBarinova NZLyakhov Solid-state combustion in mechanicallyactivated SHS systems Combustion explosion and shock waves2003 v39 1 p43-58

6 MAKorchagin DVDudina Application of self-propagating high-temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007v43 2 p176-187

7 MAKorchagin BBBokhonov Combustion of mechanicallyactivated 3Ti+2BN mixtures Combustion explosion and shockwaves 2010 v 46 2 p170-177

65

SPIN-CROSSOVER IN THE PENTANUCLEAR BYPIRAMIDALCo2Fe3 AND Fe2Fe3 COMPOUNDS

Sophia Klokishner Sergei Ostrovsky Andrei PaliiInstitute of Applied Physics Academy of Sciences of Moldova

Kishinev MoldovaKim Dunbar

Department of Chemistry Texas AampM UniversityCollege Station TX USA

Boris TsukerblatChemistry Department Ben-Gurion University of the Negev

Beer-Sheva Israel

In this article we report a model for a spin-crossover phenomenonin pentanuclear bypiramidal [M(III)(CN)6]2[M(II)(tmphen)2]3 (MM=CoFe FeFe) cluster compounds The spin-crossover phenomenonis considered as a phase transformation accompanied by a change of theground state spin The model takes into account cooperative interactionsin the crystal network local crystal fields and spin-orbit coupling actingwithin the degenerate metal sites Magnetic properties and Moumlssbauerspectra are analyzed and compared to the experimental data

1 IntroductionSpin-crossover compounds have been a subject of many

experimental and theoretical studies [1-6] Till now only a fewexperimental reports on spin crossover in cluster compounds [7-11] havebeen reported Recently FeII ions were introduced into the equatorialmetal sites of discrete cyano-bridged pentanuclear clusters[MIII(CN)6]2[MII(tmphen)2]3 (MM =CoFe(1) FeFe(2) ) [12] with atrigonal bipyramidal (TBP) structure The octahedral nitrogensurrounding of FeII ions facilitates the spin-crossover behavior Theoccurrence of the ls-hs transition in compounds 1 and 2 was proved bythe combination of Moumlssbauer spectroscopy magnetic measurementsand single-crystal X-ray studies For both types of clusters[FeII(tmphen)2]3[M

III(CN)6]2(M=FeCo)7 the T product increases by

~9emumiddotKmol between 150 K and 375 K thus indicating the ls ndashhstransition at the FeII sites The TBP FeII

3CoIII2 cluster due to its electronic

66

structure represents an ideal system for studying the effects ofintracluster short-range and intercluster long-range interactionsfacilitating spin-crossover In the (FeIII)2 (FeII)3 cluster the hs-FeII and ls-FeIII ions are coupled by exchange interaction In spite of the fact that theexchange interaction of the hs-FeII and ls-FeIII ions through the cyanidebridge is sufficiently weak as compared with that in oxide clusters it isinterestingly to understand whether this interaction may affect the spintransformation The effects of orbital degeneracy on the spin-crossovertransformation in the [FeII(tmphen)2]3[FeIII(CN)6]2 crystal will beexamined as well In the present article a microscopic approach to theproblem of spin crossover in crystals containing metal clusters isdeveloped

2 The modelIn the basic structural unit of compounds 1 and 2 two MIII ions

surrounded by six carbon atoms occupy the apical positions and threeFeII ions coordinated by the nitrogen atoms reside in the equatorial plane[12] In a strong crystal field of carbon atoms the ground terms of the

CoIII and FeIII ions are the low-spin orbital singlet )( 621

1 tA ( 0S ) and

the orbital triplet )( 421

3 tT respectively The ground state of a FeII -ion in

the crystal field induced by the nitrogen atoms can be either low-spin

(ls)- term )( 621

1 tA or high spin (hs) ndashterm 2422

5 etT Both magnetic

measurements and Moumlssbauer spectroscopy for water containing crystals[12] demonstrate the presence of some amount of FeII ions in the hsconfiguration even at very low temperatures Further on we consider inthe model two types of FeII ions and denote by x the fraction of FeII -ions which are in the hs ndashstate at all temperatures while theconcentration of those ions which undergo the ls-hs transition is (1-x)The number pi of trigonal bypiramidal clusters in which i (i=0123) ofthree FeII ions are in the hs configuration in the whole temperature range

is estimated as iiii xxCp 33 1 where rllrC r

l

The Hamiltonian of intraion interactions can be written in the form

67

Hg

gllsH

kkB

kkB

kZkk

)(

32)(

211

02

0

H

lsH

(1)

where numbers theIIFehs ions in the k-th bypiramidal cluster the

first term is the spin-orbit (SO) coupling in the cubic )( 2422

5 etT - term of

theIIFehs -ion the second term describes the axial crystal field

splitting the 125 lT term into an orbital singlet ( 0lm ) and an

orbital doublet ( 1lm ) the third term refers to the Zeeman

interaction for hs-FeII ions and contains both the spin and orbitalcontributions B is the Bohr magneton and g0 is the spin Lande factorFinally the fourth term represents the interaction of the ground Kramersdoublets of two ls-FeIII ions in the cluster with the external magnetic

field i is the matrix of the pseudo -spin frac12 of the ls-FeIII ion g1 =173

is the Lande factor Up to room temperature the ls-FeIII can be regardedas an ion with the pseudo-spin frac12 because the ground Kramers doubletand the excited quadruplet arising from the splitting of the 2T2 term by

the spin-orbital interaction are separated by the gap 173023 cm

( 1486 cm [13] for a free ls-FeIII) that is large enough from the

thermal population of the excited quadruplet at room temperatureThe superexchange interaction (several cm-1 [1415]) in the

[FeII(tmphen)2]3[FeIII(CN)6]2 through the cyanide bridges couples the hs-FeII ions in equatorial and ls-FeIII ndashions in axial positions Further on wewill neglect the essentially anisotropic orbitally dependent terms andretain only the isotropic part of the exchange interaction between the hsndashFeII and ls ndashFeIII ions in a cluster The Hamiltonian of exchangeinteraction for the thk cluster looks as follows

kkkex

k

exJH

212 σσs (2)

where 2s is the spin of the hs-FeII ion the summation in (2) takes

into account the hs-FeII ions appearing in the thk cluster due to thespin transition and those which are in the hs-state in the whole

68

temperature range As in [16-18] we suppose that the mechanismresponsible for the ls-hs transition is the interaction of FeII ions with thespontaneous all-round full symmetric lattice strain Applying theprocedure suggested in [16-18] we obtain the Hamiltonian of electron-deformational interaction

2k kkk

kkst

nm

JBH (3)

where 21AB 21AJ

01021

2

ccc

cA n

(n=123) is the number of FeII ions which undergo the ls-hs transition ina complex m is the number of TBP MIII

2MrsquoII3 complexes whose FeII ions

are involved in the spin conversion =1n k=1m 0 is thevolume that falls at a Fe ion and its nearest surrounding and is the unit

cell volume per one iron respectively In the basis of the states 25T and

11A the 1616 matrix k is diagonal and has 15 eigenvalues equal to 1

and one eigenvalue equal to -1 Finally 2)(1 lshs

2)(2 lshs hs and ls are the constants of interaction of the

FeII ion with the full symmetric strain1A in the hs and ls states

respectively The first term in (3) acts as an additional field applied toeach spin-crossover ion and redefines the effective energy gap 0

between the hs and ls states of the FeII in the cubic crystal field Thesecond term in (3) represents an infinite range interaction between theFeII ions which undergo the spin conversion This interaction arises fromthe coupling to the strain The model of the elastic continuum introducedabove satisfactorily describes only the long-wave acoustic vibrations ofthe lattice Therefore the obtained intermolecular interactioncorresponds to the interaction via the field of long-wave acousticphonons

Due to the proximity of the FeII ions in the clusters short-rangeinteractions between these ions inside the cluster are relevant Thelargest is the effect of the exchange arising from the optic phonons [19]

69

The Hamiltonian describing short-range interactions between FeII ionswithin the trigonal bipyramid can be written as

0

kkk

sr JH (4)

The Hamiltonian (4) takes into account the interaction between the FeII

ions participating in the spin transitions the interaction of these ionswith those FeII ions which are in the hs-state in the whole temperaturerange as well as the interaction between the latter It should bementioned that eq (3) as compared with eq(4) only accounts for FeII

ions participating in spin conversion The Hamiltonian for the wholecrystal can be written as

k

kexstsr HHHHH

2

00 (5)

where k

k

exex HH In the molecular field approximation the full

Hamiltonian H can be written as a sum of one-cluster Hamiltonians

)(32)(

)2

(~

211101

2

1

0

0

kkB

kkkB

k

ex

kkZ

kkkkkkk

gIgHIl

IlsJBJH

HlsH

(6)

where in the basis of the states 25T and 1

1A kI1

is a diagonal 1616 -

matrix with 15 eigenvalues equal to 1 and one vanishing eigenvalue is the order parameter In fact the Hamiltonians kH

~describe clusters

with different numbers of spin-crossover FeII ions and k as beforenumbers the clusters in the crystal For calculation of the temperaturedependence of the order parameter the self-consistent procedure wasapplied The calculations of the magnetic properties were based on theHamiltonian given in Eq(6)

3 Results and discussionThe estimation of the parameters J and B was performed

according the procedure suggested in paper [16-18] For characteristicfor compounds 1 and 2 parameters =1026Aring3 0 =8Aring3

c2 (005divide01)c1211

2 10 cmdynec 1046 141

cm 142 1087 cm the

70

parameters J and B take on the values 20divide80 cm-1 and -95 divide -24 cm-1respectively

Fig1 shows the experimental data for compound 1 together withthe calculated T vs T curves The result of the best fit procedure in

the model above developed is presented by curve 1 The best fitparameters are the part of the figure caption One can see that a quitegood agreement with the experimental data is obtained At temperaturesbelow 100 K the T values show that the FeII ions are mainly in the ls ndashstate However some small admixture of hs ions is present In thetemperature range 150-300 K the T product gradually increases thusindicating the ls - hs transition in the FeII ions

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30 35

04

06

08

10

3

2

1

T

cm

3K

mo

l-1

Temperature K

23

1

T

cm

3K

mo

l-1

Temperature K

Fig1 Temperature dependence of the T product for 1 Circles-experimentaldata [12] The solid lines represent a theoretical fit with =-103 cm-1 x=10and (1) hs-ls =640 cm-1 J =35 cm-1 J0=45 cm-1 =180 cm-1 =10 (2) hs-

ls=620 cm-1 = -136 cm-1 J=0 J0=0=06 (3) hs-ls=630 cm-1 =168 cm-1J=0 J0=0 =06

The parameter J of long -range cooperative electron-deformationalinteraction obtained from the best fit procedure falls inside the limits

71

estimated above Relatively small values of the parameters J and J0 ascompared with the gaps hs-ls= 0-2B and are also in agreement withthe observed gradual temperature dependence of T and noticeable

increase of T at temperatures higher than 150K Finally the estimated

from the best fit procedure percentage of FeII ions (x=10) which are inthe hs-state at any temperature is very close to that obtained from theMoumlssbauer spectra [12] For comparison in the same figure (curves 23)the results of fitting of the T curve in neglect of long- and short-

range interactions are shown for the cases of 0 and 0 It isseen that in this approximation the calculated curves 2 and 3 differsignificantly from the experimental one both at low and hightemperatures besides this the obtained value 60 is too small forhs-FeII-ions

For compound 2 the variation of the observed magneticsusceptibility as a function of temperature is presented in Fig2

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

321

T

cm

3K

mo

l-1

Temperature K

Fig2 Temperature dependence of the T product for 2 Circles experimentaldata [12] Curves 1- 3 were calculated with the following parameter values hs-

ls =690 cm-1 J=30 cm-1 J0=40 cm-1 =100 cm-1 =-103 cm-1 =10 x=9and (1) Jex = 3 cm-1 (2) Jex = 0 (3) Jex = -3 cm-1

72

First the magnetic behavior of complex 2 was analyzed withneglect of intracluster Heisenberg exchange interaction between FeII andFeIII ions The result of the best fit procedure is presented by curve 2 inFig2 The best fit parameters are the part of the figure caption One cansee that the values of the key parameters are close to those for complex1 However the obtained energy gap hs-ls between the ls and hsconfigurations for complex 2 is a bit larger than the corresponding gapfor compound 1 while the parameters of short-range and long-rangeinteractions are smaller Namely this difference in the characteristicparameters leads to lower values of T for compound 2 as compared

with compound 1 at temperatures higher than 150K The effect ofexchange interaction on the magnetic behavior is illustrated in Fig2 bycurves 1 and 3 Since typical values of the exchange parameters incyanide bridged complexes are of several cm-1 we calculated the Tproduct with the set of the best fit parameters and Jex = -3 cm-1 and 3cm-1 One can see that at temperatures higher than 50K the smallexchange interaction has no effect on the magnetic properties ofcomplex 2

Moumlssbauer spectra provide direct information about the populationof the hs and ls states and serve a reliable test for the theoreticalbackground of the SCO phenomenon The total Moumlssbauer spectrum(ie the observable spectrum) was obtained by summing up the spectrayielded by different cluster electronic states in the molecular field withdue account for their equilibrium populations for a given (at a certaintemperature) value of the molecular field In calculations theexperimental values for the parameters of the quadrupole splttings andisomeric shifts were taken from [12] The calculated and experimentalspectra are shown in Fig3

Quite good agreement between the experimental data andtheoretical calculations is obtained It should be underlined that themodel takes into account the main effect inducing the temperaturedependence of the Moumlssbauer spectra and this is the temperaturedependence of the cluster energies in the molecular field Namely thiseffect is responsible for the transformations of the Moumlssbauer spectrawith temperature

73

The proposed model gives a good fit to the observed temperaturedependence of the static magnetic susceptibility and the Moumlssbauerspectra The last clearly illustrates the cooperative nature of SCOtransformations in TBP compounds that leads to a crossing of the ls andhs levels due structural phase transition induced by the ordering of thelocal deformations through the field of the acoustic phonons

Fig3 Moumlssbauer spectra for compound 1 calculated at T=42 220 and 300Kwith the set of the best fit parameters (thick solid lines) Contributions from ls -FeII and hs -FeII ions are shown in dash and dot lines respectively The half-width of the individual lines Г=016 cm-1(42 К) Г=018 cm-1(220К)Г=024cm-1(300К)

74

AcknowledgmentsFinancial support of the STCU (project N5062) is highly

appreciated BT and KD gratefully acknowledge financial support ofthe Binational US-Israel Science Foundation (BSF grant no 2006498)BT thanks the Israel Science Foundation for the financial support (ISFgrant no 16809)

References1 Guumltlich P Goodwin H A Spin Crossover in Transition Metal

Compounds Springer-Verlag 20042 Hauser A Light-Induced Spin Crossover and the High-Spin rarrLow-

Spin Relaxation Springer-Verlag 20043 P Guumltlich J Jung Nuovo Cimento D 1996 18 1074 P Guumltlich A Hauser H Spiering Angew Chem Int Ed Engl

1994 33 20245 J Zarembowitch New J Chem 1992 16 2556 A B Gaspar V Ksenofontov M Serdyuk P Guumltlich Coord

Chem Rev 2005 249 26617 JA Real AB Gaspar MC Munoz P Guumltlich V Ksenofontov H

Spiering TopCurrChem2004 2331678 G Vos RAG De Graaff JGHaasnoot AM van der Kraan De

PVaal JReedijk InorgChem 1984 23 29059 EBreuning MRuben JMLehn FRenz YGarcia VKsenofontov

P Guumltlich E Wegelius KRissanen AngewChemIntEd 2000 392504

10 M Nihei MYi MYokota LHan AMaeda HKushida HOkamoto HOshio AngewChem IntEd 2005 446484

11 D-Y Wu O Sato Y Einaga C-Y Duan Angew Chem Int Ed2009 48 1475 ndash1478 2009

12 MShatruk ADragulescu-Andrasi KEChambers SAStoianELBominaar CAchim KRDunbar J Am Chem20071296104

13 AAbragam BBleaney Electron Paramagnetic Resonance ofTransition Ions Clarendon Press Oxford 1970

14 A V Palii SM Ostrovsky S I Klokishner B S Tsukerblat C PBerlinguette K R Dunbar J R Galaacuten-Mascaroacutes JAmChemSoc2004 126 16860

15 HWeihe H Gudel H Comments Inorg Chem 2000 22 75

75

16 SI Klokishner F Varret J Linares ChemPhys 2000 255 31717 SI Klokishner JLinares PhysChemC 2007 111 1064418 SI Klokishner J Linares F Varret Journal of Physics

Condensed Matter 2001 13 59519 JM Baker Rep Prog Phys 1971 341 109

53

NON-CARBON PREPARATION OF SILICON BYMECHANICALLY ACTIVATED THERMAL SYNTHESIS

TF Grigorieva1 TL Talako2 AI Letsko2 V Šepelaacutek3 VG Scholz4MR Sharafutdinov1 IA Vorsina1 AP Barinova1 PA Vitiaz2

NZ Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry Kutateladzestr 18 Novosibirsk 630128 Russia grigsolidnscru

2 Powder Metallurgy Institute Platonov str 41 Minsk 220005 Belarus3 Inst of Nanotechnology KIT Eggenstein-Leopoldshafen 76344 Germany

4 Inst of Chemistry Humboldt Univ Berlin 12489 Germany

IntroductionIn industrial processes the production of Si is based on the

reduction of silicon dioxide by carbon at a temperature of about 1800 C[1] However the coke applied to the reduction can be hardly refinedfrom the most dangerous for silicon impurities like boron phosphorusarsenic and antimony That is why development of non-carbon routes forsilicon production is a topical problem of a silicon industry Reductionof oxides with magnesium and aluminum by the method of self-propagating high-temperature synthesis (SHS) has been used in industryfor a long time [2] As such reactions are highly exothermal they can bealso organized with the use of mechanochemistry for instance reductionof the copper oxide by aluminum Mechanochemical reduction of ironoxide by aluminum aimed at obtaining precursors with differentcompositions for intermetallideoxide SHS composites has been alsoconsidered [3ndash6]

SiO2 + Al reaction is not high exothermic enough to organize theSHS without preliminary heating [7] Mansurov et al [8] reportedcreation of ceramic composites in several stages first the silicon oxidewas mechanochemically treated in an organic compound environmentthen the resultant material was annealed (carbonized) at ~ 850 C andfinally the mixture of the carbonized silicon oxide with aluminum wassubjected to SHS However as-formed product included silicon carbide

The objective of activities described in this paper is to study thepossibility of using mechanochemical treatment for obtainingsiliconaluminum oxide composites by the SHS and thermal synthesis atconsiderably lower temperatures with the following removal of alumina

54

Sample preparation and examination proceduresThe PA-4 aluminum powder and the silicon oxide with a particle

size of ~ 3 nm were used in our experimentsA stoichiometric mixture of the silicon oxide with aluminum was

processed in a high energy planetary ball mill (drum volume 250 cm3ball diameter 5 mm mass of the balls 200 g mass of the sample 10 gand velocity of rotation of the drums around a common axis ~1000 rpm)

The IR spectra were recorded by a Specord IR 75 spectrometerthe samples for this study were pressed with annealed potassiumbromide

The 27Al (I = 52) NMR spectra were recorded on a BrukerAdvance 400 spectrometer corresponding to a 27Al resonance frequencyof 782 MHz MAS experiments were realized with a high speed probeusing 25 mm zirconia rotor The spinning speed was 20 KHz Themagnetic field strength (in frequency unit) was set to 104262 MHz Theexcitation pulse duration was chosen equal to 1 s The recycling delaybetween each acquisition was fixed to 1 s To see weak signals in the Al-O region in mechanically activated samples we applied accumulationsnumbers up to 56000 (ie measurement time of 15 hours)

The dynamics of the SHS process was studied with the use ofdiffraction of synchrotron radiation and an OD-3 single-coordinatedetector The samples for SHS were prepared in the form of pellets 20mm in diameter and 1ndash2 mm thick by pressing at a pressure of 200 atmThe resultant samples were placed onto a ceramic plate so that they werein the center of the goniometer The process was initiated by a nichromespiral The OD-3 detector was triggered to operate in the ldquofast filmingrdquomode simultaneously with the beginning of pellet burning The time ofone ldquoframerdquo was 05 sec and the number of ldquoframesrdquo was 128 Theradiation wavelength was 1527 Aring

For investigation of mechanically activated thermal synthesis thesamples were heated up to 650 C in the reaction chamber XRK 900 inair with a heating rate 10 min The OD-3 detector was also used forstudying the process dynamics though time of one ldquoframerdquo was 1 min

55

Results and discussionFirst we made an attempt of direct mechanochemical reduction of

the silicon oxide by aluminum The study of this process showed that thechemical reaction of SiO2 reduction does not occur within 6 min ofmechanical activation The IR spectrum of the initial mixture containsclear absorption bands with the maximums at 1005 and 480 cmminus1

(valence and deformation oscillations of the SindashO bond of the SiO4

tetrahedra of the siliconndashoxygen skeleton) and two maximums in therange of 900ndash670 cmminus1 due to oscillations of the SindashOndashSi bridges Thephenomena observed in the course of mechanical activation were agradual decrease in intensityand broadening of the characteristic bands of the SindashO bond (Fig 1)

An electron-microscopy study of the SiO2Al composite obtainedafter 1 min of mechanical activation in characteristic radiation revealed a

Fig 2 Microphotograph of themechanocomposite after 1 minactivation in Si characteristic

radiation

Fig 1 IR spectra of the SiO2 + Al mixturebefore mechanical activation (1) and aftermechanical activation during 05 (2) 1 (3)

and 6 (4) min

56

very small grain size and a very uniform distribution of the componentsin the mechanocomposite (Fig 2)

Based on the data of the differential thermal analysis (DTA) evenshort-time activation of this mixture appreciably affects its thermalcharacteristics For the initial mixture the real chemical interactionoccurs at a temperature T gt 1000 C (Tmax = 10836 C) (Fig 3 a) iesubstantially higher than the melting point of aluminum whereas thesituation is different for the mixture subjected to mechanical activationduring 20 sec Two clearly expressed exothermal peaks appear the firstpeak at 6217ndash6486 C (Tmax = 6327 C) and the second peak at 9921ndash10759 C (Tmax = 10292 C) (Fig 3 b) For the mixture activated for 40sec the first peak is at 6045ndash6366 C (Tmax = 612 C) and the secondpeak is extremely broad and smeared in the range of 8161ndash11117 C(Tmax = 10381 C)

These observations can be explained by the fact that a tightcontact is created between some part of the ultrafine non-plastic siliconoxide and plastic aluminum already within 20 sec of mechanicalactivation the silicon oxide is ldquowettedrdquo by aluminum as a result somepart of the silicon oxide starts to interact with aluminum at a temperatureT = 6217C which is lower than the melting point of the latter Asmechanical activation is continued aluminum becomes also dispersed tonanoparticles greater amounts of the components of the mixture areinvolved into the contact and the temperature of the interactionbeginning decreases after 1 minute of activation the interaction beginsat T = 5399 C and ends at T = 6303 C (Fig 3 c)

The curve for this sample obtained by the method of differentialscanning calorimetry (DSC) has only one exothermal peak ie theentire process proceeds at a temperature lower than the melting point ofaluminum Longer activation further decreases the temperature ofreaction beginning (Table 1) but there are no any further significantchanges in the system parameters determined by DSC

The duration of mechanochemical treatment was limited to 6 minfor the following reasons- the IR spectra are so smeared already after 4 min that do not provide

any new information (see Fig 1)- the DTA study does not reveal any significant changes in the thermal

characteristics after 1 min of mechanical activation (see Table 1)

57

- mechanochemical actions should be always minimized to ensure theminimum possible contamination of the products by milling

Fig 3 Results of differential scanning calorimetry (DSC) and thermogravimetry(TG) studies of the SiO2 + Al mixture before (a) and after mechanical activation

during 20 (b) and 60 sec (c)

58

Table 1 Parameters of Exothermal Peaks on DTA Curves of SiO2 + AlSamples after Mechanical Activation

Temperature CDuration of activation

beginning of thereaction

end of the reaction

1 min 5930 6303

2 min 5871 6243

4 min 5867 6291

6 min 5870 6258

27Al MAS NMR spectra of the nanostructured SiO2Almechanocomposites are dominated by a broad resonance associated withthe presence of nanostructured Al matrix (Fig 4) The interestingobservation is that additional resonance lines appear in the spectra ofmechanoactivated samples corresponding to AlO4 AlO5 and AlO6

polyhedra Their content is slightly increasing with increasing millingtime however the relative intensity of AlOx polyhedra compared withthe Al matrix spectral intensity is even after the longest milling periodvery low It can be assumed that these nonequilibrium localcoordinations of aluminium atoms are located on the SiO2-Al interfaces[9] The intensity of the resonance lines belonging to various polyhedrarelative to the total spectral intensity allows us to calculate the volumefraction of interface regions in the nanocomposites Furthermoreassuming a spherical shape of SiO2 nanoparticles the thicknees of theinterface regions was calculated their known volume fraction

Thus the study of mechanically activated SiO2+Al mixturesshows that silicon reduction does not occur during mechanical activationstep except formation of some AlOx species at the interfaces but anexothermal reaction in activated mixtures can proceed at substantiallylower temperatures

In the subsequent step the nanostructured SiO2Almechanocomposites were used as precursors for the preparation ofSiAl2O3 composites via self-propagating high-temperature synthesisOur experience shows that combustion initiation requires sample

59

preheating approximately to 200 C (as compared with 650-860 Сreported in [7])

Fig 4 27 Al MAS NMR spectra of non-activated sample (a) the samplemechanoactivated for 1 (b) and 6 (c) minutes

60

The overall pattern of phase transformations is illustrated in Fig 5a To analyze them however it is more convenient to use the projectiononto the diffraction angle (β)ndashtime plane (Fig 5 b) As the silicon oxideused in these experiments is amorphous to x-ray radiation onlyaluminum peaks are observed

Fig 5 Dynamics of phase transformations in the Al + SiO2 mechanocompositein the SHS mode (a) three-dimensional image (b) projection onto thediffraction anglendashtime plane

61

It is clearly seen thataluminum becomes heatedas the combustion waveapproaches the peaks areshifted toward smallerangles ie greaterdistances between theplanes After that theintensity of these peaksdrastically decreaseswhich is apparently due tomelting No crystallinephases are observed in thetwo frames (~ 1 sec) Inour opinion corundum(Al2O3) peaks appearslightly earlier than siliconpeaks A possible reason isthe lower melting point ofsilicon (1410 C) as compared with corundum (2050 C) An electron-microscopic study of the SHS product of the SiO2 + Al system subjectedto mechanical activation during 1 min in characteristic radiation (Fig 6)shows a fairly uniform distribution and small size of all elements in thesystem including silicon being formed

Previously it was shown that chemical interaction between SiO2

and Al in the mechanocomposites formed during the mechanicalactivation starts at essentially (~ 500 C) lower temperatures as comparedwith the non-activated mixtures

In the final step we used as-formed mechanocomposites asprecursors for the preparation of SiAl2O3 composites via thermalsynthesis The samples after mechanical activation for 6 min wereplaced into cuvette and gently prepressed to get the plane surface Thenthe cuvette with the sample was sited in the furnace The thermocouplewas directly close to the registration area Recording of diffractogramswas started at temperature 230 С Dynamics of phase transformation inAl SiO2 composites during heating from 590 up to 660 C is presentedin Fig7

Fig 6 Microphotograph of the SHS productin Si characteristic radiation

62

As can be seen from the Fig 7 the reaction products (silicon andalumina) start to form at about 590 С It is interesting that corundum isformed during the SHS and thermal synthesis after low activation time

Fig 7 Dynamics of phase transformation in Al SiO2 composites duringheating from 590 up to 660 C

Fig 8 XRD-pattern of the thermal synthesis product from the mechanocompositesactivated for 6 min and heated up to 660 C

63

while -Al2O3 is identified in the product of thermal synthesis afterlonger MA durations (Fig 8)

ConclusionsThus though the silicon oxide is not reduced by aluminum

directly by mechanical activation the use of the mechanocomposite as aprecursor for both SHS and thermal synthesis allows a fine-grainsiliconaluminum oxide composite to be obtained In both caseschemical interaction starts at essentially lower temperatures as comparedwith the non-activated mixtures

AcknowledgementsThis work was supported by the joint project No 5 ldquoNon-carbon

preparation of Si by mechanically activated thermal synthesisrdquo of NASBand SB RAS

References1 Denisov VM Istomin SA Podkopaev OI Serebrjakova LI

Pastuchov EA Beletsky VV Silicon and its alloys EkaterinburgPublishing house of Ural Branch of the Russian Academy ofSciences 2005 467 p (in Russian)

2 AG Merzhanov Forty Years of SHS Happy Life of a ScientificDiscovery (in Russian) Chernogolovka (2007)

3 TF Grigoryeva SA Petrova IA Vorsina et alldquoMechanochemical reduction of a copper oxiderdquo in TheOptimization of the Composition Structure and Properties ofMetals Oxides Composites Nano and Amorphous Materials Proc6th IsraelindashRussian Bi-National Workshop Jerusalem (2007) pp197ndash204

4 TF Grigoryeva TL Talako AA Novakova et al ldquoMA and MASHS production of nanocomposites metaloxides andintermetallicsoxidesrdquo ibid pp 139ndash148

5 NZ Lyakhov PA Vityaz TF Grigorieva et alldquoMechanochemically synthesized SHS precursors for obtainingintermetallideoxide nanocompositesrdquo Dokl Akad Nauk 406 No6 776ndash778 (2005)

64

6 5 T Talaka T Grigorieva P Vitiaz et al ldquoStructure peculiaritiesof nanocomposite powder Fe40AlAl2O3 produced by MA SHSrdquoMater Sci Forum 534ndash536 1421ndash1424 (2007)

7 Maltsev VM Gafiyatulina GP Tavrov AV Spreading of thecombustion wave in SiO2-Al systems Proc SPIE Vol 3172(111997) p 724-727

8 ZA Mansurov RG Abdulkarimova NN Mofa et al ldquoSHS ofcomposite ceramics from mechanochemically treated and thermallycarbonized SiO2 powdersrdquo Int J SHS 16 No 4 213ndash217 (2007)

9 V Sreeja TS Smitha Deepak N Ajithkumar TG and PA JoySize dependent coordination behavior and cation distribution inMgAl2O4 nanoparticles from 27 Al solid state NMR studies J PhysChem C 112 14737-14744 (2008)

37

THE PREPARATION OF MECHANICOMPOSITESTUNGSTEN-METAL AND SINTERING MATERIALS

T Grigoreva1 L Dyachkova2 A Barinova1 S Tsibulya3 N Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS 18Kutateladze str 630004 Novosibirsk Russia grigsolidnscru

2 Institute of Powder Metallurgy NAS B Minsk Belarus3 Boreskov Institute of Catalysis SB RAS Novosibirsk Russia

Tungsten-based materials are used for manufacture of electro-technical items spot welding electrodes spraying cathodes etc

The preparation of the high-melting materials is powerconsumptive as two-stage high-temperature sintering is used tungstenpre-sintering temperature is 1150 ndash 1300 C final tungsten sinteringtemperature is 2900 - 3000 C [1]

Metal additives with a lower melting temperature are introducedinto the high-melting material for sintering temperature reduction andsince the tungsten powder has a bad moldability level more plasticmetals such as copper nickel iron are introduced for the moldabilityimprovement

Tungsten ndash copper mixture has been studied the best so farThe mixture W-Cu sintering process research has shown [2] that

the product density depends on the initial powders dispersion degree andthe mixture composition So at the tungsten particles size 10-15 m themaximum densification is observed at the copper weight ration 50 The blend density sharply decreases with the copper content decrease(less than 35 ndash 40 wt) At the same time mixtures with the coppercontent not higher than 10 are needed Special methods have to beused for the preparation of the tungsten alloys

The active densification (from 44 till 12 ) is known to take placeat 1100 - 1200 C at sintering of mixtures W-20 vol Cu with tungstenparticles size lower than 1 m [3] Even higher densification speed isobserved in a blend attained with copper tungsten reduction whencomponents mixing practically achieves a molecular level [4] ie thesecond element concentration reduction is possible at tungsten particlessize decrease and homogeneous distribution of the both componentsThe original blends mechanical activation process [5ndash7] is very

38

perspective in this trend since grinding and formation of larger contactsurface between the original components take place during mechanicalactivation This process is especially effective at mechanical activationof solid and liquid metals and plastic ndash non-plastic metals pair Thecomposite nucleus (non-plastic component) ndash cover (plastic metal) canbe created in this case The possibility of chemical interaction onbetween tungsten and plastic metal the contact surface duringmechanical activation should be considered here

The work aim is to study structure and morphology of thecomposites formed at mechanochemical activation of the tungsten witha small content (till 10 ) of plastic metals both interacting (nickel iron)with it and not interacting (copper) with it The influence of the structureand morphology of the mechanocomposites on the processes of formingand sintering was studied

Powders of tungsten nickel iron copper were used forpreparation of mechanocomposites Mechanical activation of themixtures was carried out in a high energy planetary ball mill with watercooling in argon atmosphere (drum volume ndash 250 cm3 balls diameter ndash5 mm the load ndash 200 g the sample - 10 g the velocity of rotation of thedrums around a common axis 1000 rpm)

X-ray analysis was carried out with diffractometer D8 AdvanceBruker (Germany) at the CuK radiation Research of the structure andmorphology of the mechanocomposites was carried out with thescanning electronic microscope (SEM) ldquoMira LMHrdquo with the add-ondevice for micro-x-ray analysis The electronic probe comprised 5 2 nmthe actuation area comprised 100 nm The research was carried out inmodes of registration of absorbed (AE) and backscattered (BSE)electrons and also of characteristic radiation of tungsten copper nickeland iron The sintered materials research is carried out with themetallographic microscope MEF-3 (Austria) at zoom times200 and times950

The compressibility was determined via density in compliancewith the ISO 3927-1985 of cylindrical samples with diameter 10 mmheight 12 mm pressed in a steel die-mold at pressure 200 400 600 and800 MPa The pressed samples were sintered in vacuum at temperatureof 1100 ndash 1450 C

Compression strength of mechanically activated blends wasdetermined via the samples of diameter 10 mm height 12 mm

39

transverse strength ndash via prismatic samples with height 5 mm width 10mm length 55 mm The tests were preformed on the testing machineldquoInstronrdquo with the loading speed 2 mmmin

Sintered samples microstructure was studied on metallographicsections etched with solution (10 g K3Fe(CN)6 10 g KOH 100 mlH2O) via metallographic microscope MEF-3 of the company ldquoReihertrdquo(Austria)

Mechanical activation was carried out in two stages for attainingmechanical composites tungsten ndash metal (Cu Ni Fe) The first stagesaw grinding only tungsten for 4 min At the second stage 7 ndash 10 copper (nickel iron) was added and joint mechanical activation wascarried out for 1 ndash 2 min

In compliance with the x-ray data the initial tungsten sample is awell-crystallised powder (Fig 1a) The intensity of the diffraction peaksshows the texture (of the preferred orientation) presence in trend 110The X-ray pattern of the tungsten samples activated during 4 min (Fig1b) has widened peaks The X- ray analysis shows that widening ismostly caused because of micro-defects in the tungsten structure (at thelarge particles sizes retaining) It should be also noted that thedistribution intensity of the peaks shows the texture absence (the equalparticles distribution in powder from the point of view of theircrystallographic orientation)

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

Ia

u

2 Theta degree

110

200

211

220

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

Ia

u

2 Theta degree

a bFig 1 X-Ray patterns for initial W (a) and activated for 4 min (b)

40

During the mechanical activation in a high energy planetary ballmills plastic metals tend to stick to balls and the drums walls even atshort-time activation because of that they were introduced to the blendsinto the already activated for 4 minutes tungsten and the mixture wastreated for 2 minutes more

The different X-Ray patterns were received for the samples withCu Ni Fe additives (Fig 2) The second metal phase is seen to bepresent in a well-crystallised form besides the phase W in all cases thecopper picks relative intensity is however considerably higher than thenickel picks intensity that in turn exceeds the iron reflection intensityFormation of intermetallic compounds in the X-ray-amorphous state oncontact surface WNi WFe can be supposed to be possible forchemically interacting metal pairs (tungsten ndash nickel tungsten ndash iron)X-Ray research data are indirect confirmation of this supposition Thesedata have shown that mechanochemical efforts donrsquot allow to receivehomogeneous distribution of copper in the tungsten matrixMechanocomposites W + 10 Cu is arranged in compliance with theldquosandwichrdquo principle where copper phase of micrometric size is locatedin the tungsten die (Fig 3)

The second metal phase is seen to be present in a well-crystallisedform besides the phase W in all cases the copper picks relative intensityis however considerably higher than the nickel picks intensity that inturn exceeds the iron reflection intensity Formation of intermetalliccompounds in the X-ray-amorphous state on contact surface WNiWFe can be supposed to be possible for chemically interacting metalpairs (tungsten ndash nickel tungsten ndash iron) X-Ray research data areindirect confirmation of this supposition These data have shown thatmechanochemical efforts donrsquot allow to receive homogeneousdistribution of copper in the tungsten matrix Mechanocomposites W +10 Cu is arranged in compliance with the ldquosandwichrdquo principle wherecopper phase of micrometric size is located in the tungsten die (Fig 3)Electron microscopy and X-Ray research of mechanocomposites forinteracting metals (W + 10 Ni) has shown homogenous nickeldistribution

41

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Ia

u

2 Theta degree

Cu

а

40 50 60 70 80 90

0

1000

2000

3000

4000

Ia

u

2 Theta degree

Ni

b

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Iau

2 Theta degree

Fe

c

Fig 2 X-Ray patterns for mechanocomposites W (4 min) + additives Cu(a) Ni (b) Fe (c) (2 min)

The received result allows to suggest that metals distributionhomogeneity depends on the thermodynamical parameters of theirmixture (Нmix(W-Ni) = - 2 kJmol Нmix(W-Cu) = + 10 kJmol [8])and on a possibility of the chemical interaction between them The thinlayers of intermetallic compounds form on the continuously renewingcontact surface in the systems W-Ni and W-Fe for this time period (1-2min) and because of distance these thin layers do not manage to form acrystalline phase that could be fixed in X-Ray way

42

а bFig 3 Micrographs of the mechanocomposites W-Cu (a) W-Ni (b) in

characteristic radiation Cu and Ni

The research of compressibility of various mechanocompositeshas shown that non-interaction metals (W-Cu) couldnrsquot compressed andthe compressibility of the interaction metals (W-Ni W-Fe) depends ofthe contents of additives Research of compressibility of mechanicallyactivated powders of various composition has shown that tungsten ndash10 iron mixture powder has the best compressibility level andtungsten ndash 7 nickel mixture powder has the least compressibility level(Fig 4)

But it should be noted that mechanically activated powderscompressibility level is not high moreover some mechanocompositesdo not have compressibility at specific pressure 200 ndash 300 MPa and thesamples layering is observed at pressure higher than 600 MPa Therelative density of the pressed samples is 50 ndash 78 It indicates at thenecessity of the additional lubricants introduction into the mechanicallyactivated powders for their compressibility increase

43

Fig 4 Tungsten-based mechanocomposites compressibility curve

For the powders compressibility improvement the lubricants areintroduced directly into initial mixture or plated to the press-mouldsurface for decrease of friction between the powder and the press-mouldwall and also between the powder particles The lubricant removaltemperature depends on the lubricant melting or dissociationtemperature The melting and boiling temperature or the lubricantsdissociation temperature generally used in powder metallurgy are givenin table 1 [9]

Stearates especially zink stearates have the leading place Therest lubricants have not got such a wide use since residual remains aftertheir removal [10]

Nowadays nylon-binding-based lubricant has been developedabroad This nylon binder is introduced during the charge mixingprocess and needs warm pressing [11-14] Such a lubricant allowsattaining high (θ is no less than 95 ) density of iron-based materials

The lubricant addition as a rule retains ~1 wt as higher contentleads to the pressing growth if the lubricant is present in the sinteringprocess till the sintering temperature

The lubricant burning-out process is carried out in the protective-reducing atmosphere in separate furnaces or in a sintering furnace (in thearea separated from the sintering area) The lubricant burning-outtemperature is as a rule not high and comprises 600 ndash 800 C

44

Table 1 Temperature of melting and dissociation of solid lubricants

Lubricant Lubricant formulaMeltingpoint С

Boiling ordissociation

point СZink stearate Zn(C18H35O2)2 140 335Calcium stearate Ca(C18H35O2)2 180 350Aluminium stearate Al(C18H35O2)2 120 360Magnesium stearate Mg(C18H35O2)2 132 360Plumbum stearate Pb(C18H35O2)2 116 360Lithium stearate LiC18H35O2 221 320Stearinic acid CH3(CH2)16CООH 694 360Oleinic acid С8Н17СНСН-

(СН2)7СООН13 286

Benzol acid С6Н5СООН 122 249Hexoic acid СН3(СН2)4СООNН2 -4 205Paraffin From С22Н46 till

С27Н56

40-60 320-390

Molybdenum disulfide MoS2 1185 -Tungsten disulfide WS2 1250 -Manganous sulphide MnS 1655 -Graphite С (crystalline) 3500 -Molybdenum trioxide MoO3 795 -

During one-component materials heating till 100 ndash 150 C thechange of the contact character between the particles connected withwater evaporation and elastic stress relief tale place As a result somecontact areas rupture and as a consequence general inter-particlecontact surface decrease are possible

The elastic stress relief is ended the further gases are removedand burning-out of the lubricants and binders introduced to the powdertake place during heating from 150 C till the temperature comprising 40ndash 50 of the metal melting temperature The oxide films reduction andnon-metal contact replacement with a metal one take place at highertemperatures although visible pressings density change does not takeplace

45

This work saw lubricants introduction during mechanicalcomposite formation zink stearate stearinic acid and lauric acid wereused The lubricants were introduced in amount of 0 1 0 2 0 3 0 5wt During mechanical activation metal ndash organic acid the latter ismelted (the melting temperature is lower than 70 C) and thus it wets themetal surface and flows with the formation of a larger contact surface Incase of good wettability and sufficient amount of the low-meltingconstituent all the solid-phase surface becomes contact ie mixturenucleus (metal) ndash cover (organic substance) is formed [15] Thecompressibility level has to be naturally higher in this case andmechanochemical approach allows a substantial reduction of plasticizingagentsrsquo concentration

Research of compressibility of powders with lubricants has shownthat Zink stearate has the least influence in comparison to otherlubricants used (Fig 5)

Fig 5 The compressibility curves of the mechanocomposites W-Fe with thelubricant 1 ndash zink stearate 2 ndash lauric acid

The lubricant content increase leads to the mechanically activatedpowders compressibility improvement (Fig 6) but at the lubricantcontent more than 0 3 the samples destruction takes place at sinteringbecause of intensive gas release Plasticizing agents introduction hasallowed mechanical composites formation also for non-interactingmetals (tungsten ndash copper) (Fig 6 7)

46

Fig 6 The compressibility curve of the mechanically activated blend W-Cuwith stearinic acid 1 ndash 0 1 2 ndash 0 3 3 ndash 0 5

Fig 7 The compressibility curves of the mechanically activated blend W-Cuwith lauric acid 1 ndash 03 2 ndash 05

Lauric and stearinic acids additives allow the pressings densityincrease by 25 ndash 40 (Fig 5 8)

Research of density of sintered samples of mechanocomposite hasshown that the density of the samples from mixtures tungsten ndash ironpressed at 400 and 600 MPa does not practically change after sinteringat 1250 C (Fig 9 line 2 5) and at 1450 C the samples density decreases(Fig 9 line 3 6) Mixtures tungsten ndash nickel are subject to a substantial

8

9

10

11

12

200 400 600

De

nsi

ty g

сm

3

Pressure МPа

1

2

11

115

12

125

13

200 300 400 500 600

10Fe+W

10Ni+W

De

nsi

tyg

cm

3

Compacting pressure MPa

47

shrinkage (Fig 10) and density of the samples of W-Ni pressed at 400MPa is 146 gcm3 after sintering at 1250 C and 147 gcm3 at 1350 CSintering temperature increase till 1450 C leads to samples shrinkinglevel reduction and density does not exceed 117 gcm3

Fig 8 The compressibility curves of blends W + 10 Fe and W-10 Ni withaddition of 1 of stearinic acid

Fig 9 Relation of density of mechanically activated blends W + 10 1 ndash afterpressing at 400 MPa 2 ndash pressing at 400 MPa sintering at 1250 ordmC 3 ndashpressing at 400 MPa sintering ndash at 1450 ordmC 4 ndash after pressing at 600 MPa 5 ndashpressing at 600 MPa sintering at 1250 ordmC 6 ndash pressing at 600 MPa sintering at1450 ordmC

10

11

12

13

14

200 400 600

Pressure МPа

Density

gс

m3

1

2

3

0

2

4

6

8

10

W+Fe

De

nsityg

cm

3

12 3

4 5 6

48

0

3

6

9

12

15

400 МPа 600 МPа

De

nsity g

сm

3

Fig 10 Relation of density of mechanically activated blend W + 10 Ni 1 ndashafter pressing 2 ndash pressing sintering at 1250 C 3 ndash pressing sintering at 1350C 4 ndash pressing sintering at 1450 C

Moulding pressure increase till 600 MPa practically does not

influence the sintered samples density Density reduction of the samples

sintered at 1450 C is apparently explained with dissociation of oxides

and other compounds of tungsten and nickel

Sintering at 1450 ordmC of blends W-Ni leads to meltback and

samples form loss thus sintering should be carried out at temperature

not higher than 1350 ordmC

Tungsten-based mechanocomposite strength research has shown

that strength has a direct relation to their density (Fig 11) The blend

tungsten ndash iron (870 MPa) has the minimal strength

The microstructure analysis has shown that in case of sintering at

temperature 1250 C tungsten ndash nickel have a very fine dispersed

structure (Fig 12) Coagulation of nickel insertions located at the base

grains boundaries in tungsten ndash nickel grains growth take place with

sintering temperature increase

49

0

100

200

300

400

500

600

700

800

900

1000

1100

1 2

Ela

stic

lim

it of

com

pre

ssio

n

МP

а

I - pressure 200 МPа

II - pressure 400 МPа

III - pressure 600 МPа

1 - sintering temperature 1250оС 2 - sintering temperature 1350

оС

I

II

III

Fig 11 Influence of attaining modes of samples from mechanically activatedblend tungsten + 10 nickel on their strength

Substantial grain growth large porosity formation nickel phase

particles growth take place in blends sintered at 1450 C eutectic that is

more visible in the blend tungsten ndash nickel is formed at tungsten grains

boundaries

Conclusions

The conducted research has shown that homogenous copper

distribution is failed to be carried out in tungsten with short-term

mechanical activation method for interacting metals of W-Cu system

These mechanically activated samples can be not compacted (moulded)

50

a b

c dFig 12 Microstructure of mechanically activated blends W-Ni sintered at 1250C (a b) and 1350 C (c d) a c ndash times200 b d ndash times950

Homogenous distribution of nickel and iron in tungsten is ensuredwith short-term mechanical activation in systems from interactingmetals The attained samples are formable mechanically activatedpowders compressibility has however been found to be not high therelative density of the pressed samples is 50 ndash 78 and that points atnecessity of additional lubricants introduction into powders for theircompressibility improvement Lubricants introduction allowed ensuringmoldability of immiscible system tungsten ndash copper and densification ofpressings by 25 ndash 40 - for interacting metals

Density of samples from blends tungsten ndash iron does notpractically change after sintering at 1250ordmC and is decreased at 1450 ordmCBlends tungsten ndash nickel are subject to a substantial shrinkage during

51

sintering Sintering temperature increase till 1450 ordmC also leads to theshrinkage level decrease Strength of sintered blends from mechanicallyactivated tungsten-based powders depends on density and kind of theadditive Grain size dispersivity and type of additive location in theblend structure from mechanically activated powders depend on thesintering temperature

AcknowledgementsThe work was carried out within the framework of Fundamental

Research Programme of Russian Academy of Sciences ldquoElaboration ofchemical substances attaining methods and new materials creationrdquoproject No 1821 ldquoElaboration of tungsten mechanical composites-basedhigh-density alloys creation basicsrdquo

References1 IM Fedorchenko IN Francevich ID Radomyselskiy at al

Powder Metallurgy Materials technologies properties andapplications Kiev Naukova dumka ndash 1985 ndash 624 P

2 VN Eremenko JV Najdich IA Lavrinenko Sintering in thepresence of liquid metal phase Kiev Naukova dumka ndash 1968 ndash 122P

3 VV Panichkina MM Sirotuk VV Skorohod Powder Metallurgyndash 1982 - 6 ndash P27-31

4 VV Skorohod YuM Solonin NI Filippov at al PowderMetallurgy ndash 1983 - 9 ndash P9-13

5 Kim JС Moon IН Nanostruct Mater 1998 Vol 10 No 2 P283-290

6 Moon IH Kim EP Petrow G Powder Metallurgy 1998 Vol41 No 1 P 51-57

7 Kim JC Ryu SS Kim YD Moon IH Scripta Mater 1998 Vol39 No 6 P 669-676

8 FR de Boer R Boom WCM Mattens AR Miedema andAK Niessen Cohesion in metals (Cohesion and structurevol 1) (Elsevier Amsterdam 1988) pp 758

9 Hausner H Handbook of Powder Metallurgy Chemical PublishingCo New York 1973

10 Moyer KH Intern J Powder Met 1971 - 7 Р 33

52

11 US patent В 22 F 100 5368630А Powder Metallic Blend with abinder for densification at the set temperature Journal Inventions ofcountries worldwide 1996 1

12 US patent В 22 F 100 5429792 Metal powder content containing a binder for pressing at elevated temperatures JournalInventions of countries worldwide 1996 7

13 US patent В22F 100 (11) 52980555 (40) 940329 laquoIron-basedpowder mixtures with a binding lubricantraquo 1995

14 US patent В 22 F 100 95372138 (5484469А) laquoMetal powder content and a method of a sintered part manufacture from itraquo 1995

15 TF Grigoryeva AP Barinova NZ Lyahov Mechanochemicalsynthesis of metal systems Novosibirsk Parallel ndash 2008 ndash 311 P

34

THE DETERMINATION OF THE KINETIC FUNCTIONSTRUCTURE FOR THE HIGH-TEMPERATURE SYNTHESIS IN

THE MECHANICALLY ACTIVATED MIXTURE 3Ni-Al

VYu Filimonov1 MA Korchagin2 EV Smirnov1NZ Lyakhov2

1Altai State Technical University Barnaul2Institute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirskvyfilimonovramblerru

The peculiarities of heating-up and phase formation in themechanically activated powder mixture 3Ni + Al reacting in the thermalexplosion mode have been experimentally investigated The self-heatingin the mixtures was studied using a specially designed SHS-reactorusing a technique presented in [1] Tungsten-rhenium thermocouples of100 microm diameter were used to control the temperature and to recordthermograms Preliminary mechanical activation was carried out using aplanetary ball mill of AGO-2 type in an atmosphere of argon under theenergy of 40g (centrifugal acceleration of balls 400 ms2) with varyingtime of the activation process The reactant mixtures were preparedusing the aluminum powder PAndash4 particle size 5 divide 60 microm and thecarbonyl nickel powder PNK-1L5 particle size 1 divide 10 microm

The primary goal of this work was to determine the activationenergy and the structure of the kinetic function during the heat evolutionin the system as a result of the phase formation At the adiabatic stage ofheating a system of equations of the temperature increase and thedynamics of the degree of transformation was considered [2]

0 expdT E

k fdt RT

(1)

f

RT

Ek

dt

d

exp1

(2)

The initial conditions are as follows 00 t 0TT where

T temperature of the reacting mixture degree of transformation

t time 0k 1k exponential factors E activation energy f -

35

kinetic function The search for )(f was performed in the known class

of functions [3]

exp

1nm

f

(3)

At the first step of analysis of the experimental thermograms theeffective activation energy of the phase formation was determined from

the curvature of the experimental plot ln 1dT dt f T Based on the

results of 6 measurements and using the slope of the fitting curvepassing through the point of the minimum curvature the effectiveactivation energy was determined which turned out to be anomalouslylow and equal to E = 95plusmn2 kJmol It was found that the experimental

results are best fitted with a function 1n

f where

09 015n [4] Fig1 shows the results of integration of (11) with the

determined parameters

Fig1 Results of integration of (11) -1 experimental thermogram -2

Since the interaction of the reactants is described by the law ofhomogeneous kinetics we suggest that during thermal explosion in themechanically activated mixture of the composition under study thesynthesis occurs through homogeneous regrouping of atoms of the initialreactants without formation of dense diffusional layers hindering thereaction The latter is possible due to high concentrations of defects andinternal stresses formed as a result of intensive plastic deformation of theinitial reactants during mechanical activation

36

References1 Filimonov VY Evstigneev VV Afanasev AV and Loginova MV

Thermal Explosion Ti + 3Al Mixture Mechanism of PhaseFormation International Journal of Self-Propagating High ndashTemperature Synthesis-2008- vol 17-2рр 101-105

2 Aldushin AP Martemyanova T M Merzhanov A G Propagationof the front of an exothermic reaction in condensed mixtures withthe interaction of the components through a layer of high-meltingproduct Composition Combust Explos Shock Waves19728(2)159

3 M I Shilyaev V Е Borzykh A R Dorokhov and V EOvcharenko Determination of thermokinetic parameters from theinverse problem of an electrothermal explosion Combust ExplosShock Waves 1992 28(3)258

4 MA Korchagin VYu Filimonov EV Smirnov NZ LyakhovThermal explosion of a mechanically activated 3Ni + Al mixture Combustion explosion and shock waves 2010 v 46 1 pp41-46

14

MODERN METHODS OF RHENIUM DETERMINATION

OV Evdokimova NV Pechishcheva KYu ShunyaevInstitute of Metallurgy of UB RAS

101 Amundsen st Ekaterinburg Russiashunuralru

IntroductionRhenium due to its unique properties is the promising metal

widely used in various industries At present day the main areas ofapplication of rhenium is the production of catalysts for the petroleumrefining industry and refractory alloys used for turbines manufacturing[1]

The great demand for this element requires large amounts of itsproduction There is a need extracting rhenium even from industrialwaste water from plants [2] due to the high cost and its low content innatural materials

This situation stimulates the development (or modification) ofmethods of analytical control of various nature materials

The content of rhenium in rhenium-containing materials bothnatural and technogenic and contect of accompanying to rheniumelements vary in a wide range of concentrations from 10-7 to tens ofpercent

Earlier the following methods were used for the determination ofrhenium spectrophotometry gravimetry kinetic electrochemicalextraction-fluorimetric methods X-ray fluorescence analysis [3] Themain disadvantages of mostly methods for determining rhenium are thelow sensitivity the bad reproducibility of results the influence ofaccompanying elements Ag W Mo Pt Cu Fe and etc

In modern analytical practice the following methods for therhenium determination are used inductively coupled plasma atomicemission spectroscopy (AES ICP) inductively coupled plasma - massspectrometry (ICP-MS) [4] electrochemical methods [1] X-rayfluorescence analysis and spectrophotometric methods do not lose theirrelevance [1] they have undergone significant modifications recently

15

Inductively coupled plasma atomic emission spectroscopy(AES ICP) is widely used for the rhenium determination in mineral rawmaterials and products of metallurgy production This method allows todetermine up to 10-4 rhenium The advantage of AES ICP is the highstability and reproducibility of results absence of chemical influences

However analysis of more complex objects such as metallurgicalproducts is a not easy task because the lines of rhenium emission areoverlaped with the lines of accompanying elements in samples So thelines of Mo (221427 nm) W (221431 nm) Fe (227519 nm) whichmay be present in the samples in large quantities are overlaped to themost intense lines of rhenium (221426 nm and 227525 nm) Thisproblem requires the development of new methods of samplepreparation and selection of optimal conditions for determination ofrhenium by atomic emission spectrometres

Also a significant disadvantage of this method is the small rangeof certificated reference materials So there are a limited number ofRussian rhenium standard materials with certified value of the rheniumcontent It is molybdenum and copper-molybdenum ores andconcentrates in which the rhenium content is in the range ofconcentrations from 000047 to 00221

In most cases analysts develop the synthetic mixture to monitorthe rhenium content in the analysis of specific samples of complexcomposition This mixture is similar to composition to the matrix of theanalyzed samples consisting of rhenium ions and other ions with agiven concentration For example the authors [5] to develop a techniquefor rhenium determining together with platinum and palladium in thesamples of spent catalysts by AES-ICP applied a synthetic mixtureprepared on the basis of aluminum oxide and standard solutions of Pt(IV) Pd (II) Re (VII)

One of modern methods and the most sensitive methods for thedetermination of rhenium is inductively coupled plasma - massspectrometry (ICP MS) [4 6 7 8] These days ICP MS withseparation and concentration allows to measure rhenium at lower thanseveral ngg However ICP MS performance in analyses of complexsamples is commonly affected by matrix effects and polyatomicinterference and signal drift High levels of salt solutions content cause

16

plugging of sampling orifice with decrease in analytical signal inaddition many spectral interferences may occur [6]

For the rhenium determination in molybdenite by ICP MS shouldbe use large dilution of sample to reduce the matrix influence and reducethe salts influence However this approach is not feasible in the case ofhigh levels of molybdenum and relatively low levels of rhenium in theanalyzed objects The most effective way to minimize the matrix effectsis separation of rhenium from the matrix Often for this purposeextraction by organic solvents [6] sorption by anion-exchangers [8] areused

Recently X-ray fluorescence analysis becomes more popular Itis rapid and is often used for mass analysis The advantage of thismethod is the possibility of direct determination of rhenium in the solidsamples in water solutions [9 10] in the biological samples (plants) [2]

However the method is not without disadvantages firstly thedetection limit of rhenium by X-ray fluorescence analysis is low and isonly 005-01 secondly there are only few the standard materials witha high rhenium content and thirdly the influence of interfering elementsin the sample related to determination of rhenium

Using the concentration can not only reduce the detection limitbut also in the same time solve and reduce the influence of interferingions For the concentration of rhenium in X-ray fluorescence analysis isoften used sorption of rhenium in the form of perrhenate-ions [9 10]

The authors [11] describes a problem related to the developmentof rhenium-containing standard materials by traditional hightemperature approach for X-ray fluorescence analysis Thus high-temperature studies of MoO3-ReO3 which could be served ascomparison materials for the rhenium determination by X-rayfluorescence analysis showed that 50-90 of rhenium is lost duringcalcination of mixtures it indicates the impossibility to use them fordevelopment of standard materials In the paper [11] the method ofpreparing rhenium glassy reference samples (10 - 50) on the basis ofBi2O3 and B2O3 is described The developed method allows to determinerhenium in the range of 001-10 [11]

17

Electrochemical methods in particular the electrostrippingvoltammetry (ESV) occupy a significant place in the analyticalchemistry of rhenium [12 13] This method allows to determine up to10-6-10-5 of rhenium

To avoid the effects of many electropositive components (Mo WCu Ag Au) which may interfere to the rhenium determination by ESVit has been proposed the sorption concentration of perrhenate ions on thesurface of activated charcoal (BAU) [12 13]

The most widely used techniques determine the 10-2 - 10-5 ofrhenium is spectrophotometric method The advantages of this methodare simplicity low cost equipment and a relatively high sensitivitySpectrophotometric method is based on the formation of coloredcomplex compounds of rhenium with organic and inorganic ligands [1]Photometric methods with thiocyanate ion thiourea are widely spread[14 15 16] Development of spectrophotometric methods for rheniumdetermination is largely due to the searching and using of new reagentsIn [17] for the extraction-photometric determination of perrhenate ionsin the form of ion associates the basic polymethine dyes derivatives of133-trimethyl-3H-indole have been offered but the influence ofoxyanions of tungsten and molybdenum is not excluded [17]

The disadvantage of the spectrophotometric methods is the needfor prior separation of rhenium from a number of interfering elements(Mo W Cu) that it is achieved by concentrating perrhenate-ions bysorption or extraction

Over the past decade main changes in the methods of rheniumdetermination related with the improvement stadium of samplepreparation transfer the sample into an analytical form modification ofknown methods and reagents (eg creation of new facilities developmentof new reagents for measurements) and conditions of analysis

In general in the literature a large number of works are relatedwith the separation of rhenium from the analyzed solutions and theseparation of rhenium (VII) from interfering elements by using newtypes of extractants and new sorbents is given Used extractants andsorbents as well as the optimal conditions for extraction and sorption ofrhenium are presented in Table 1 and 2 respectively

18

Extraction plays a dominant role in the methods of separationand concentration of rhenium

In most cases in the hydrometallurgical processing of rhenium-containing products in the acidic solutions ReO4

- are formed Forperrhenate ions extraction the anion-exchange reagents or extractants ofneutral type are often used The literature contains information on theextraction of rhenium (VII) by various amines and quaternaryammonium compounds [18 19 20] Efficient extractants of rheniumfrom acidic solutions are neutral organophosphorus compounds (tributylphosphate alkylphosphineoxides their derivatives) [21 22] a variety ofsolvent mixtures (tributyl phosphate + trioctylamine [23]) theextractants of neutral type such as ketones and aliphatic alcohols [1624 25]

Alcohols ketones and ethers are more selective having higherspeed separation of organic and aqueous phases as well as higherchemical resistance and lower cost compared with amines andorganophosphorus compounds but inferior to them in the extractioncapacity for rhenium (VII) [16]

Thus for perrhenate ions extraction aliphatic alcohols with 7-10carbon atoms in the aliphatic chain are well proven that can extractmore than 98 of rhenium from sulfuric acid and hydrochloric acidsolutions In the case of alcohol there is no need to use solvents andmodifiers what simplifies their use in extraction processes [16]

The efficiency of rhenium extraction into organic phase by aminesdecrease as follow quaternarygt tertiarygtsecondarygtprimary Amongthem secondary and tertiary amines are widely used as efficientextractants of rhenium from acidic solutions Perrhenate ions areextracted by amines in a wide range of pH For systems of amine - low-polar diluent - H2SO4-ReO4-H2O the formation inverse micelles istypical in the organic phase Acid ions and anionic complexes arelocated inside the aqueous core of the micelle with the metal ioncoordinates the polar functional group of amine [19 20]

It should be noted that the extraction by amines is complicated bythe use of solvents the nature of which depends on the solubility ofamines and their extraction capacity So low-polarity solvent toluene incontrast to the non-polar kerosene enhances the polarity of anionic saltsof amine which increases the reactivity of the extractant to the anion

19

exchange of inorganic acid to extractable anionic rhenium complexes[18]

Tertiary amines are the most effective extractants for rhenium(VII) However in paper [18] it is shown that the secondary amine(diisododecylamine) gives advantage to the tertiary amines on therhenium extraction efficiency from sulfuric acid media It can beexplained by the influence of steric factors and smaller rival extractionof mineral acids by secondary amines [1]

Most papers are related to the rhenium extraction from acidicsolutions but the extraction of rhenium from alkaline medium whichare formed after leaching of ores concentrates also represents a difficultproblem In the paper [23] rhenium extraction from alkaline solutionscontaining also molybdenum by solvent extraction using a mixture oftributylphosphate (TBP) and trioctylamine (N235) is describedMolybdenum which is also extracted by solvents in small amountsinterferes to the extraction of rhenium

Over the last decade most works refer to the development offundamentally new classes of extractants for perrhenate ions [26 2728 29] such as encapsulating ligands (cryptands and podands)macrocycles crown ethers These ligands can interact with ReO4

minus byboth the electrostatic interaction between ReO4

minus and protonated ligandand the hydrogen bond formation compared with simple open-chainligands If the complex between ReO4

minus and ligand has highhydrophobicity ReO4

minus in an aqueous solution may be separatedeffectively by a solvent extraction technique [30]

Crown ethers extract rhenium (VII) in the presence of potassiumor sodium in the form of K(Na)LReO4 (L-crown-ether) into the organicphase (12 - dichloroethane chloroform) [31 32] In the paper [31] theextraction perrhenate-ions by 3m-crown-m-ethers (m = 56) ether and itsmono-benzo-derivatives in 12-dichloroethane are described

Podands are analogues of crown ethers containing terminalphosphoryl ligands in their polyether chains they are used for theextraction of rhenium (VII) The efficiency of extraction by phosphorylpodands depends of the following factors the number of oxygen atomsin the polyether chain molecules the number of donor centers in themolecule of podands hydrophobicity of the reagent molecule the size offorming cycles the nature of substituent at the phosphorus atom Studies

20

have shown that phosphoryl podands with three oxygen atoms in thearomatic polyether chain combined with the phosphoryl group bydimetilen or o-phenylene fragments have high extraction ability forrhenium from sulfuric acid solutions [32]

In the paper [30] authors mark another type of podands such aspodands with nitrogen donor ligand -N N N `N`-tetrakis (2-pyridymethyl) -12-ethylendiamine (TREN) and its hydrophobicanalogs which also allow to extract perrhenate ions from highly acidicenvironments

Perrhenate is characterized by its ability to undergo a change ingeometry specifically from tetrahedral to hexagonal in the presence ofdonor ligands (eg acetonitrile triphenylphosphine) Protonationchanges the electron density present on the oxygen atoms Beer et al[33] suggested that the tripodal ligand L1 would be suitable for thebinding and extraction of perrhenate anion This ligand (Fig 1) basedon the combination of tris(2-aminoethyl)amine and crown ether motifswas found to complex sodium cations and to extract perrhenate anionsfrom aqueous solutions into an organic phase

Atwood and co-workers developed calixarene-type ligand L2(Fig 1) that specifically extracts perrhenate from water solution into anorganic phase The selectivity for extractions decreases as followTcO4

minus ge ReO4minus gt ClO4

minusgtNO3minus gtSO4

2minus gtClminus This selectivity pattern isattributed to a combination of charge size and shape Efficientextraction is observed at high and neutral pH the molar ratio ofligandperrhenate ion = 14 [33]

L1 L2Fig 1 Tripodal ligand L1 and calixarene-type ligand L2 for perrhenateextraction

21

Schiff-base macrocycles are used as a new conjugatedmacrocycles for perrhenate ions Thus a series of amino-azacryptands(L3ndashL16) for encapsulation and extraction of the oxoanions perrhenate(Fig 2) from aqueous solution were proposed by the authors [34]Thecomplexation amino-azacryptands L to ReO4

- is via hydrogen-bondedinteractions

Fig2 Amino-azacryptands (L3ndashL16) for encapsulation and extraction of theoxoanions perrhenate

Thus the main characteristics of the compounds for the effectiveperrhenate ions extraction as follows

Energy coordination of ligand with ReO4- should be higher than

the energy of perrhenate ion hydrationThe interaction between the ligand and perrhenate ions an

electrostatic interaction or the formation of hydrogen bonds Functional ligands to be a suitable size (volume of the cavity

should be more than 736 Aring3) shape electronegativity andhydrophobicity

Ligand should be protonated

22

Table 1 Characteristics of extractants for rhenium extraction

Extractant

Analysis objectComposition of

the initialsolution

Extractonconditions

Interferinginfluences

Aliphatic alcoholswith C 7-10

1-Heptanol 4-Heptanol 1-octanol 1-decanol 4-decanol 2-Heptanol 3-Heptanol

3-octanolback-extractant

NH4OH

Solutions HCland H2SO4

Т=293КTime of phase

contacttex = 5 min

organic phase toaqueous

(OL = 11)4 steps of

extraction 2stripping

Coextractionof mineral

acidsincomplete

re-extractionof Re (VII)

1

OctanolSolutions ofHNO3 and

H2SO4

Т=286-290Кtex = 10 min OL

= 11

Coextractionof HNO3

H2SO4

2

Basic polymethinedyes (derivatives of133-trimethyl-3H-

indole) astrazon violet

Aqueous andaqueous-organic

solution

Т=293КрН=6

tex = 10-30 secextractant mixture

toluene +dichloroethane

(1 1)

do notinterfere

3000-5000fold excess ofS04

2- CO32-

300- HPO42-

MoO42-

WO42-

10-20 S2O32-

Cr2O72- IO3

-metal ions as

sulfates

3

Secondary(diisododecylamine)and tertiary amines

(dioctylamin andtrioctylamine)

Solutions H2SO4

Т=293КA wide range of

pH

tex=5-7 mindiluent - toluene

-

4N-benzoyl-N ndashphenyl-

hydroxylamine

Molybdenitedissolved inHCl HNO3

HCl 05 molltex=15 min

diluent chloroform-

23

Table 1 (continued)

Extractant

Analysisobject

Compositionof the initial

solution

Extractonconditions

Interferinginfluences

5

Phosphoryl podands

back-extractant H2O

СReinitial=2middot105 moll

aqueoussolutions of

salts of alkalimetals

solutions ofmineral acids

Т=286-291КОL=11

tex= 60 mindiluent

nitrobenzene12-

dichloroethanechloroform

toluene

-

6Triotylamine (N235)+

tributyl phosphate(TBP)back-extractant18 NH4OH

Alkalinesolutions

afterleaching

containingMo

СRe 01-165gl

T=293 КрН =90 OL=11

tex=10 мин20

triotylamine+30 tributylphosphate

diluentkerosene

-

7

Podand-type nitrogendonor ligand ndashNNN`N`-tetrakis(2-pyridymethyl)-

12-ethylendiamine (TREN)

Aqueoussolution

NH4ReO4

С =10-4 M

Ionic strength01M

pH=1-65diluent

chloroformОL=11tex=24 h

-

8

3m-crown-m-ethers(m=56) mono-benzo-

derivates12-dichloroethane

СReO4-=

0057-0060М

T=291-295Ktex=2h

-

24

Table 1 (continued)

The range of Re concentrations

RecoveryMethods for determination Ref

Recovery gt99

Determination from back-extractSpectrophotometric method with

thiourea reductant-Sn (II)wavelength of 390 nm

[16 24]

1

gt98 Spectrophotometric method [25]

2The range of Re concentrations

001-550 mcgml

Determination from extractSpectrophotometric method

wavelength of 540 nm[17]

3 -AES-ICP

Spectrophotometric methodwith thiourea

[18 1920]

4Mo W Fe are extracted 97

into the organic phase

Determination from aqua phaseafter extraction

ICP-MS[6]

5 -AES-ICP

Spectrophotometric method[21 22]

6 968Spectrophotometric method with

butyl rhodamine[23]

7 - AES-ICP [30]

8 -AES-ICP

Spectrophotometric method[31]

9 - ICP-MS [32]

25

Table 2 Characteristics of sorbents for rhenium sorption

Sorbent

Analysis objectComposition of the

initial solutionConditions of

sorptionInterferinginfluences

1

Activated carbons(BAU)

Eluenthot soda solution

nitrate media

gold ore raw

static conditionsа)рH =2-3

б) рH =15-25

volume ofsolution 10 mlmass of sorbent

03 g(SL=1333)t=10 min UV

a) electro-positive

components(Mo W Cu

Ag Au)b)1000 fold

excess ofMo W do

not interfere

2

Activated carbons- CN-G CN-PCU developed

from waste woodand grain

processingindustries

sulfuric acidsolutions with CRe= 002 gl pH =2

solid phasesliquid SL==105

t=5-7 days-

3

2 Carbon fibrousmaterials

modified withchitosan

neutral aquasolutions of

rhenium

static conditionsТ=286-289 КSL=11000

-

4

3 Weakly basicanion-exchangersАН-105 Purolite

A 170

mineralizedsulphite solutionsimulating rinsing

water(С Re=001-002

gl Mo Cu Fe As)

static anddynamic

conditionsSL = 1500

t = 150-200 min

-

5

Strongly-basicanion-exchangers

АВ-17(sorbent PAN-АВ-

17)

neutral or slightlyacid

solutions

dynamicconditionst = 20 min

The disks ofpolyacrylonitrilefiber filled resin

1000 foldexcess of

Fe Cu ZnPb Cd do

not interfere

6Lignin anion-

exchangerssolutions NH4ReO4

static conditionsSL=1400

t=15min-2 h-

26

Table 2 (continued)

NotesMethods for

determinationRef

1

а) Sorption capacity of BAU forRe СЕ=14175 mgg AC

Detectionlt 10

б) СЕ=00763 mmolg or 142mgg

The concentrations range of Re050 100 mgL in standard

solutions025 50 mgl in the presence

of Mo and W (11000)

a) Electrostrippingvoltammetry

b) X-ray fluorescenceanalysis

a) [12]b) [9 10]

2 -Spectrophotometric

method [35]

3 СЕ=179-185mggSpectrophotometric

method with ammoniumthiocyanate

[38 39]

4Full dynamic exchange capacity

114 mgg

Spectrophotometricmethod with ammonium

thiocyanatekineticmethod

[36]

5 -

Determination of Re bythe diffuse reflectance

spectra at 420 nmrhenium thiocyanate

complex in the presenceof tin (II)

[15]

6 СЕ=3427-2328 mgg Traditional polarography [37]

Sorption is one of the methods for separation of rhenium fromvarious solutions

Sorption of rhenium or perrhenate-ions often occurs on solidsorbents from the liquid phase The presence of a large specific surfacearea and a large number of functional groups of the sorbent determinesits high sorption properties with respect to rhenium (VII) Sorbentscontain the same functional groups (amino groups hydroxyl groups

27

phosphorus groups) as extractants for the selective extraction ofrhenium but these groups are fixed on solid carriers or support

Activated carbons (AC) of various brands are used the mostwidely [9 10] The use of activated carbons as sorbents due to the factthat they have a whole set of valuable properties highly polydisperseporous structure a complex but relatively easily controlled surfacechemistry and specific physical properties Activated carbons like manyother carbon materials exhibit high selectivity to perrhenate ions thatexplains the increased interest to this type of sorbents [12]

The characteristic distinction of carbonaceous materials is that thesorption of rhenium is not only due to complexation with surfacefunctional groups (containing oxygen nitrogen sulfur atoms) but alsodue to the interaction with carbon matrix

AC can act as anion-exchanger in acidic media and themechanism can be described by the following scheme

[C2+ OH-] + ReO4-= [C2+ ReO4

-] + OH-On the other hand the AC have significant reduction properties

the reaction of the electrochemical reduction of perrhenate ions in themethods of rhenium determination by voltammetry is based on this it[12]

It has been established [9 10] that ReO4- is sorbed from nitric

acid solutions almost entirely (95-99) by 10 minutes of UV irradiationwhile without irradiation this process takes up to 60 minutes Increasedsorption by UV authors attribute to the fact when UV radiationsolutions of rhenium (VII) salts rhenium (VI) and rhenium (V) areformed which are considerably faster adsorbed on AC

Extensive use of the AС is also associated with their low costActivated carbons - CN-G CN-P CU developed from waste wood andgrain processing industries have a low cost and their capacitance andkinetic characteristics slightly inferior to conventional AC (FAC) [35]

However from acid solutions together with rhenium molybdenumcan also be sorbed by the AC Furthermore perchlorates nitrates andother oxidants can reduce the adsorption capacity of coals by oxidationThe disadvantage of rhenium sorption by activated carbons is as followsa decreasing in their activity after 4-6 cycles of sorption-desorption [1]low mechanical strength [35]

28

Anion-exchange resin is the next width of use which havegreater selectivity and capacity compared with activated carbons Theseanion-exchangers synthesized on the basis of the gel and porouscopolymer of styrene and divinylbenzene From the neutral and acidicsolutions rhenium is adsorbed by low-basicity anion-exchangers with thefunctional groups of primary and tertiary amines In recent studiesconducted on the use of weakly basic macroporous anion-exchangerswith a more developed specific surface area (20-100 m2g) such asPurolite A170 with secondary amino groups [36]

Sorption by strongly-basic anion-exchangers compared to weaklybasic anion-exchangers has several advantages firstly they are almostquantitatively and selectively extract rhenium from solutions andsecondly work in a wide range of pH [15]

The rapid technique for perrhenate ions determination isdeveloped which allows to find their content directly on the site ofsampling for example in lake water using strongly-basic anion-exchangers AB-17 with the sensitivity of the technique is 2-3 orderslower than the best conventional spectrohotometric methods withthiocyanate [15]

Recently the authors of paper [37] synthesized new highlypermeable lignin anion-exchangers on the basis of lignin a naturalpolymer a component of terrestrial plants It is noted that the exchangecapacity of anion-exchangers for rhenium in lignin is much higher (EC =3427-2328 mgg) compared with conventional anion-exchangersHowever the time to reach equilibrium sorption by some anion-exchangers can reach from 2 up to 12 hours

Carbon fibrous materials modified with chitosan haveimproved kinetic (time and rate of sorption) characteristics comparedwith activated carbon and ion-exchange resins [38 39] Carbon fibrousmaterials modified with chitosan contain amino groups includingprotonated The increasing of the number of protonated groupscauses the increasing of sorption capacity of the material withrespect to the negatively-charged perrhenate-ions However thesorption capacity for rhenium (179-185 mgg) still yields to ligninanion in addition investigations were carried out of neutral aquasolutions of rhenium without interfering influences

29

ConclusionIn this review the methods for rhenium determination which over

the last decade have acquired great fame are presented A large numberof works related to improving methods for rhenium determining pointsto the increased interest to this metal The majority of the studies aimedto the selective extraction of rhenium from the analyzed complex objectsand the separating it from interfering elements in the matrix to increasethe sensitivity of the methods Most of the work related to the searchingof various organic reagents selective to rhenium (V VII) ions and usedin extraction and sorption processes In general the development ofrapid selective methods that can determine the content of rhenium in awide range of concentrations in various materials remains an actualproblem nowadays

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

Reference1 AA Palant ID Troshkina AM Chekmarev Metallurgy of

rhenium Science Moscow 2007 298 p2 LV Borisova YuV Demin NG Gatinskaya VV Ermakov

Determnation of rhenium in plant materials Journal of AnalyticalChemistry 2005 V60 1 P 97-103

3 LV Borisova AN Ermakov Analytical chemistry ofrhenium 1974 Science Мoscow 318 p

4 S Uchidaa KTagamia K Tabei Comparison of alkaline fusionand acid digestion methods for the determination of rhenium in rockand soil samples by ICP-MS Analytica Chimica Acta 2005 V535P 317ndash323

5 VI Manshilin EK Vinokurova SA Kapelushniy Determinationof Pt Pd Re mass fraction in dead catalyst samples using ICPatomic emission spectrometry method Methods and objects ofchemical analysis 2009 V41 P 97-100 (in Russian)

6 Jie Li Li-feng Zhong Xiang-lin Tu Xi-rong Liang Ji-feng XuDetermination of rhenium content in molybdenite by ICPndashMS afterseparation of the major matrix by solvent extraction with N-benzoyl-N-phenylhydroxalamine Talanta 2010 V81 P 954ndash958

30

7 T Meisel J Moser N Fellner Wo Wegscheider R SchoenbergSimplified method for the determination of Ru Pd Re Os Ir and Ptin chromitites and other geological materials by isotope dilutionICP-MS and acid digestion Analyst 2001 V126 P 322ndash328

8 K Shinotsuka K Suzuki Simultaneous determination of platinumgroup elements and rhenium in rock samples using isotope dilutioninductively coupled plasma mass spectrometry after cation exchangeseparation followed by solvent extraction Analytica chimica acta2007 V603 P129ndash139

9 NA Kolpakova AS Buinovsky IA Jidkova Determinationof rhenium by X-ray fluorescence analysis Proceedings ofuniversities Physics 2004 12 P147-149 (In Russian)

10 AS Buinovsky NA Kolpakova IA Melnikov Determinationof rhenium in the ore material by X-ray fluorescence analysis News polytechnic university 2007 V311 3 P92-95 (InRussian)

11 DV Drobot AV Belyaev VA Kutvitsky Development of aunified X-ray fluorescence method for the determination ofrhenium in multicomponent oxide compositions News highereducational institutions Non-ferrous metallurgy 1999 4 P23-24 (in Russian)

12 LG Goltz NA Kolpakov Sorption preconcentration anddetermination by voltammetry perrhenate ions in the mineralraw materials Proceedings of the Tomsk PolytechnicUniversity 2006 V 309 6 P77-80 (in Russian)

13 NA Kolpakova LG Gol`ts Determination in mineral rawmaterials by stripping voltammetry Journal of AnalyticalChemistry 2007V62 4 Р418-422

14 Wahi A Kakkar LR Microdeterminaton of rhenium withrhhodamine-B and thiocyanate usng ascorbic acid as the reductant Analytical sciences 1997 august V 13 P657-659

15 LV Borisova SB Gatinskaya SB Savvin VA RyabukhinAdsorbtion-spectrophotometric determination of rhenium fromdiffuse reflectance spectra of its complexes on a PAN-AV-17adsorbent Journal of Analytical Chemistry 2002 V572 P 161-164

31

16 AG Kasikov AM Petrova Extraction of rhenium (VII) byaliphatic alcohols from acid solutions Journal of AppliedSpectroscopy2009 V82 2 P 203-209 (in Russian)

17 ZhA Kormosh YaR Bazel` Extraction of oxyanions with basicpolimethine dyes from aqueous and aqueous-organic solutionsextraction-photometric determination of rhenium (VII) and Tungsten(VI) Journal of Analytical Chemistry 1999 V54 7 P 690-694

18 AA Palant NA Yatsenko VA Petrova Extraction of rhenium

(VII) from sulfuric acid solutions by diisododecylamine

Journal of Inorganic Chemistry 1998 V43 2 P 339-343 (inRussian)

19 NA Yatsenko AA Palant Micelle formation in theextraction of ions W (VI) Mo (VI) Re (VII) from sulfuric acidmedia diisododecylamine dioctylamine and trioctylamine Journal of Inorganic Chemistry 2000 V45 9 P 1595-1599 (in Russian)

20 N Latsenko AA Palant SR Dungan Extraction of tungsten (VI)molybdenum (VI) and rhenium (VII) by diisododecylamine Hydrometallyrgy V 55 Issue 1 Febr 2000 P 1-15

21 AV Antonov AA Ischenko The use of extraction in thedetermination of rhenium in the presence of molybdenumChemistry and chemical technology 2007V50 9113-116 (in Russian)

22 VF Travkin AV Antonov VL Kubasov AA IshchenkoExtraction of rhenium (VII) and molybdenum (VI)hexabutyltriamid phosphoric acid from the acidic environment Journal of Applied Chemistry 2006 V78 6P 920-924 (inRussian)

23 Cao Zhang-fang Zhong Hong Qiu Zhao-hui Solvent extraction ofrhenium from molybdenum in alkaline solution Hydrometallurgy2009 V 97 3-4 P 153-157

24 AG Kasikov AM Petrova Influence the structure of octanolon their extraction ability in acid solutions with respect to

32

rhenium (VII) Journal of Applied Chemistry 2007 V80 4 P689-690 (in Russian)

25 VF Travkin YM Glubokov Extraction of molybdenum andrhenium by aliphatic alcohols Metallurgiya2008 7 P21-25 (in Russian)

26 EA Kataev GV Kolesnikov VN Khrustalev MYu AntipinRecognition of perrhenate and pertechnetate by a neutralmacrocyclic receptor J radioanal Nuclchem 2009 2 V282 P 385-389

27 Bambang Kuswandi Nuriman Willem Verboom David NReinhoudt Tripodal Receptors for Cation and Anion Sensors Sensors 2006V 6 P 978-1017

28 Lagili O Abouderbala Warwick J Belcher Martyn G BoutellePeter J Cragg Jonathan W Steed Cooperative anion binding andelectrochemical sensing by modular podands PNAS April 162002 V 99 8 P 5001ndash5006

29 EA Kataev GV Kolesnikov EK Myshkovskaya Newmacrocyclic ligands based bipyrroles to bind perrhenate andpertechnetate ions radiation safety 2008 4 P16-22(inRussian)

30 Takeshi Ogata Kenji Takeshita Kanako Tsuda Solvent extractionof perrhenate ions with podand-type nitrogen donor ligands Separation and Purification Technology 2009V68 P288ndash290

31 Yoshihiro Kudo Ryo Fujihara Shoichi Katsuta Yasuyuki TakedaSolvent extraction of sodium perrhenate by 3m-crown-m ethers(m=5 6) and their mono-benzo-derivatives into 12-dichloroethane

32 Elucidation of an overall extraction equilibrium based oncomponent equilibria containing an ion-pair formation in water Talanta V 71 2007 656ndash661

33 AN Turanov VK Karandashev VE Baulin Extraction ofrhenium (VII) by phosphorylated podands Russian journal ofinorganic chemistry 2006 V514 P676-682 (in Russian)

34 E A Katayev Yu A Ustynyuk J L Sessler Receptors fortetrahedral oxyanions Coordination Chemistry Reviews 2006V250 P3004ndash3037

33

35 Leroy Cronin Macrocyclic and supramolecular coordinationchemistry Annu Rep Prog Chem Sect A 2004V100 P 323ndash383

36 ID Troshkina ON Ushakova VM Mukhin Sorption ofrhenium from sulfuric acid solutions by activated carbon News of higher educational institutions Non-ferrousmetallurgy 2005 3 P38-41 (in Russian)

37 AA Abdusalomov Sorption of rhenium from sulfuric acidsolutions of molybdenum Sorption and ChromatographicProcesses 2006 Vol6 V 6P 893-894 (In Russian)

38 NN Chopabaeva EE Ergozhin ATasmagambet AI NikitinaSorbtion of perrenate-anons by lignin anion exchangers Chemistry of solid fuel 2009 2 P 43-47 (in Russian)

39 AV Plevaka ID Troshkina LA Zemskova AV Voit Sorption ofrhenium chitosan-fiber materials Journal of InorganicChemistry 2009V54 7 P1229-1232 (in Russian)

40 LA Zemskova AV Voit YuMNikolenko ID Troshkina AVPlevaka Sorption of rhenium on carbon fibrous materials modifiedwith chitozan Journal of nuclear and radiochemical sciences2005 V6 3 P221-222

11

SYNTHESIS AND MICROSTRUCTURE DESIGN OF METALAND CERAMIC MATRIX COMPOSITES USING

MECHANICAL MILLING OF THEREACTANTSCONSTITUENTS

Dina V Dudina Oleg I LomovskyInstitute of Solid State Chemistry and Mechanochemistry

Siberian Branch of Russian Academy of Sciences Kutateladze 18Novosibirsk 630128 Russia

E-mail dina1807gmailcom

Mechanical milling greatly alters the state of a powder mixtureintroducing plastic strain and defects into the components andcreating new interfaces and mutual configurations of nano-sizedgrains This opens up a possibility to design microstructures of thecomposite to be synthesized by modifying the initial state of reactingpowder mixtures In certain mechanically milled reactive systemsone can observe microstructure refinement of the product [1-2] anincrease in the yield of the reaction [3] improved distribution of thephases [3 4] and lower reaction onset and developed temperatures[1-2] The presentation intends to demonstrate several successfulexamples of this approach for synthesizing composites by self-propagating high-temperature synthesis (SHS) shock compressionand electric-current assisted sintering

SHS in the mechanically milled Ti-B-Cu powder mixtures wassuccessfully performed and resulted in a TiB2-Cu composite [1-2]Compared to untreated powders in the mechanically milled mixturestitanium and boron started reacting at a reduced ignition temperaturewhile lower combustion temperatures developed in the combustionwave favored formation of submicron grains of TiB2

The powder particles brought to react with each other by shockcompression of the mixture may not fully transform into the productsif the loading is too short and the temperatures developed during thepressure rise and the post-loading period are not high enough In themechanically milled mixture the yield of the reaction can beincreased as a result of the decreased grain size of the initial reactants

12

and shorter diffusion distances (example Ti-Cu-B system partial andcomplete reaction of Ti and B [3])

When the sintering process ensures temperatures and timesufficient for the completion of the reaction in the mechanicallymilled mixture one can expect more uniform microstructure and finergrains of the products (example Ti-B-C system forming B4C-TiB2

phases during electric-current assisted sintering [4])Ball milling can refine the microstructure of the as-synthesized

composites and can be used to introduce additional quantities of theconstituents in the composite This was applied in order to develophighly conductive Cu-based composites One of the possible reasonsfor low conductivity of in-situ dispersion strengthened copper may bethe incompleteness of the reaction between the initial reactantswhich form solid solutions with the copper matrix In this regard weconducted an in-situ synthesis of TiB2-Cu composites starting fromthe powder mixtures with the limited content of copper ensuring ahigh probability of contact between the particles of titanium andboron and as a result their full conversion into the TiB2 phase Thenanoparticles were formed in a self-propagating mode in the ballmilled Ti-B-Cu powder mixture corresponding to the 57 volTiB2-Cu composition Afterwards in order to adjust the composition thecomposite was ldquodilutedrdquo with the required amount of copper usingsubsequent ball milling [5]

The consolidated nano- and microcomposite materialsdeveloped on the basis of the described systems were tested for theirenhanced mechanical properties (fracture tough composites B4C-TiB2

[4]) electric erosion resistance [6] and electric conductivity [5] Inthis presentation each property is discussed as resulting from thephase and microstructure evolution during the synthesis of thematerial by the selected processing method

AcknowledgementsParts of this work were carried out by DVD at the University

of California Davis USA during her postdoctoral appointment Theauthors greatly appreciate the collaboration with DrKorchagin(ISSCM SB RAS) Dr VIMali and Dr AGAnisimov (Institute of

13

Hydrodynamics SB RAS Novosibirsk Russia) and Prof JSKim(University of Ulsan South Korea)

References1 DVDudina OILomovsky MAKorchagin VIMali Chem

Sust Dev 12 (2004) 319-3252 MAKorchagin DVDudina Comb Expl Shock Waves 43 (2)

(2007)176-1873 DVDudina VIMali AGAnisimov OILomovsky Mater Sci

Eng A 503 (2009) 41-444 DVDudina DMHulbert DJiang CUnuvar SJCytron

AKMukherjee JMaterSci 43 (2008) 3569-35765 JSKim DVDudina JCKim YSKwon JJPark CKRhee J

Nanosci Nanotech 10 (2010) 252-2576 J-SKim Y-SKwon DVDudina OILomovsky MAKorchagin

VIMali JMaterSci 40 ( 2005)3491 - 3495

4

STUDY OF THE EFFECT OF FLUORESCENCE INCREASINGOF N-ARYL-3-AMINOPROPIONIC ACIDS IN THE PRESENCE

OF ZINC AND CADMIUM IONS

EV Dedyukhina1 NV Pechishcheva1 LK Neudachina2KYu Shunyaev1 AA Belozerova1

1 ndash Institute of Metallurgy of UB RAS 101 Amundsen st Ekaterinburgshunuralru

2 ndash Ural State University 51 Lenin av Ekaterinburg Russia

Earlier the effect of increasing of phosphorescence intensity in thefrozen solutions with excess of metal chlorides and sulphates has beenreported Ions оf these metals have filled electronic shells and largevalue of electric field intensity - Li(I) Be(II) Ca(II) Mg(II) Cd(II)Zn(II) Al(III) In(III) and Ga(III) For example this effect was found forbenzene aniline phenol amino acids ndash tyrosine tryptophanephenylalanine [1]

The same effect have been found for fluorescence of onerepresentative of N-aryl-3-aminopropionic acids (AAPA) - NN-di(2-carboxyethyl)-p-anisidine - in the presence of cadmium(II) and zinc(II)ions at Т=77 К [2] Increasing of fluorescence intensity (Ifl) in frozeninorganic matrix is expected for other representatives of AAPA whichnot have electron acceptor groups in structure and demonstrate theconsiderable fluorescence intensity of the protonated form

Fluorescence of some AAPA in frozen inorganic matrixNN-di(2-carboxyethyl)aniline (I) NN-di(2-carboxyethyl)-34-

xylidine (II) NN-di(2-carboxyethyl)-3-methyl-aniline (III) andN-(2-carbamoylethyl)-о-anisidine (IV) are representatives of a class ofAAPA Figure 1 presents structures of the AAPA In the present workthe fluorescence of aqueous solutions of this AAPA with molar excess ofcadmium and zinc sulphates at рH 1-6 and Т=77 К have beeninvestigated

The fluorescence spectra of solutions were measured using aFluorat-02-Panorama spectrofluorometer (Lumex Russia) Fluorescencespectra at T=77 K was excited and recorded using a fiber-optic cablewith a special optical connector

5

It have been established that the Ifl of the protonated form of I-IV(СR=1middot10-4 moldm3) is increased in the presence of cadmium(II) andzinc(II) ions at Т=77 К Figure 2 presents spectra of II We suggest thatcause of this effect is interaction enhancement of reagent with metal inconsequence of isolation from water and micro concentration (waterform ice crystals impurities are displaced in intercrystal area)

CH3

N

O

OHO

OH

1 2 3 4

Fig 1 Structures of AAPA 1 - NN-di(2-carboxyethyl)aniline2 - NN-di(2-carboxyethyl)-34-xylidine 3- NN-di(2-carboxyethyl)-3-

methyl-aniline 4 - N-(2-carbamoylethyl)-о-anisidine

The increasing Ifl of protonated reagent form of I-IV also isobserved at Т=293К but is not as strong as at T=77 K

0

1

2

3

4

5

6

7

240 260 280 300 320 340 360

wavelength nm

Ia

u

1

2

3

Fig 2 Spectra of fluorescence II (СR=1middot10-4 moldm3) in the presence andabsence of Cd(II) и Zn(II) ions (СZn(II)= СCd(II)= 560 mgdm3) рН=60 Т=77 К

λex = 214 nm 1 - II 2 - II+Zn(II) 3 - II+Cd(II)

The fluorescence increasing is observed only when concentrationof metal ions in dozens of times more than concentration of fluorophor

6

This indicate that Ifl increasing is occured due to reagent solvation byions of inorganic salts but not chelation

We have obtained the Ifl of solutions of I-IV as functions of theconcentration of cadmium(II) and zinc(II) ions at Т=77 К pH=6 (table1) The largest increasing of Ifl in the presence of metal ions have beenobserved for IV But the most correlation coefficient R value of linearfunction Ifl=f(CMe) with wider concentrations range has been obtainedfor II

Table 1 The Ifl of I-IV as functions from concentration of metal ions Т=77 КCCd(II)= CZn(II)= 200 mgdm3 СR=10-4 moldm3 рН=6

Metalion

ReagentConcentrationsrange mgdm3 I R+MeIR R Slope

I 11 090 321

II 11 098 494III

25-760

13 092 456Cd(II)

IV 25-245 80 092 2997

I 3 095 82

II 8 098 414

III

30-845

11 096 437Zn(II)

IV 30-560 70 090 1542

In addition we have studied the fluorescence of aniline and naturalamino acids (tyrosine tryptophane phenylalanine) in frozen inorganicmatrix Structures of amino acids are presented on figure 3 thiscompounds are not belong to class of substituted anilines Thiscompounds similarly of investigated AAPA not have electron acceptorgroups in structure tyrosine phenylalanine and AAPA have the samebenzene fluorophore Besides this amino acids are commerciallyavailable reagents

Investigations have been shown that present amino acids alsodisplay the effect of Ifl increasing of protonated reagent form in thepresence of cadmium(II) and zinc(II) ions at Т=77 К But is not asstrong (12ndash5 times) as AAPA Ifl increasing Metal ions at T=298 K havelittle effect on a fluorescent spectra of amino acids

7

1 2 3

Fig 3 Structure of amino acids1 - phenylalanine 2 - tyrosine 3 - tryptophane

Thus we can deduce that the presence of substituted amino groupin benzene ring (especially in combination with others electron donorgroups) allow to observe more effective increasing of Ifl in salt solutionat 77 К Replacement benzene fluorophore to indole one (intryptophane) result to decreasing of observing effect extent

The fluorescence of II in the presence of Mg(II) ions at Т=77 Кwas investigated We tried to find the II0 fluorescence of II functionfrom z2r ratio for two-charged cations where z - ionic charge (+2) r -ionic radius nm [3] Data is presented in table 2

Table 2 Characteristiс of the functions II0 = f(z2r) for II Т=77 К рН=6λexλem= 214286 nm СII =10-4 М

Ion z2r SlopeI I0

CMe= 200 mgdm3

Cd(II) 412 494 107

Zn(II) 541 414 85

Mg(II) 615 352 74

The functions II0=f(z2r) of fluorescence II in frozen inorganicmatrix from are presented in figure 4 they are linear Also linearfunctions of Ifl=f(CMe) slope on z2r ratio have been obtained

N

NH2

OH

O

H2N

OHO

OH

8

y = -016x + 174

R2 = 099

6

7

8

9

10

11

40 45 50 55 60 65

z2r

IIo

Zn

Cd

Mg

Fig 4 Functions II0=f(z2r) of fluorescence II in the presence of metal ions [3]CCd(II)= CZn(II)= CMg(II)= 200 mgdm3 λexλem= 214286 nm Т=77 К

Study of fluorescence of some reagents in glycerolwater andethanolwater mixtures and micellar solutions at Т=298 КWe have studied a fluorescence II and tryptophane in

glycerolwater (11) and ethanolwater (11) mixtures in the presence ofzinc(II) ions at 77 К It was done for proving hypothesis about reducinginteraction fluorophore with water in aqueous media at freezing Wesuggest that interaction between of the solute and solvent molecules arepreserved in nonaqueous solutions

Corresponding spectra of II are presented on figure 3 similarsituation is observed for tryptophane We can see effect of increasing Ifl

is not observed in glycerolwater and ethanolwater mixtures in contrastto aqueous solutions

Isolation reagent from water at room temperature is possible in thepresence of surfactants

Fluorescence II have been study in the presence of surfactants ofdifferent nature in acidic media at Т=298 К The Ifl increasing ofprotonated form II is occured in the presence of Triton Х-100 (non-ionicsurfactant) and sodium dodecylsulphate (anionic surfactant)Fluorescence II is decreased by cetyltrimethylammonium bromide(CTAB cationic surfactant)

Fluorescence of II in the presence of surfactants and excess ofmetal ions have been study at рН=1-6 Zinc and cadmium ions increaseIfl of II at рН 50-65 with CTAB Thus metal ions and CTAB at

9

Т=298 К have same Ifl increasing effect as the effect at Т=77 К withoutsurfactants

0

5

10

15

20

25

240 260 280 300 320 340 360 380

wavelength nm

Ia

u

1

2

3

Рис 5 Fluorescence of II (СII=1middot10-4 moldm3) in ethanolwater (11)mixtures in the presence and absence of Zn(II) pH=60 Т=77 К λex=214 nm

1 - II 2 - II + Zn(II) (44middot10-4 moldm3) 3 - II+ Zn(II) (86middot10-3moldm3)

We have obtained under these conditions the Ifl of II solutions asfunction of the concentration of Cd and Zn ions with variousconcentrations of CTAB (table 3) The plots are linear and have thegreatest slope value at СCTAB=14middot10-3 moldm3 Cadmium ions have agreater influence on the fluorescence of the II than zinc ions

The fluorescence investigations in the presence of CTAB andmetal cations have been carried out on other AAPA (I III and IV)aniline and tyrosine (table 4) It was found that zinc ions increase offluorescence of protonated reagent form of I and III cadmium ions ndashIII

Table 3 Characteristiс of the functions Ifl=f(CMe) of II with addition of CTAB

exem = 218286 Т=298 К

Range of concentrationsCation

С CTABmoll moldm3 mgdm3 tg α

96middot10-4 2middot10-4 ndash 4middot10-3 45-450 18Cd(II)

14middot10-3 2middot10-4 ndash 8middot10-3 45-900 3696middot10-4 4middot10-4 ndash 15middot10-2 25-850 055

Zn(II)14middot10-3 4middot10-4 ndash 11middot10-2 25-850 10

10

Table 4 Fluorescence of reagents in the presence of zinc and cadmium ions(СMe=560 mgdm3) and CTAB (С= 96middot10-4 moldm3) рН=6

Zn(II) Cd(II)

Reagentexem

nm II0 I (R+Zn+CTAB)au

II0I (R+Cd+CTAB)

au

aniline 253278 11 07 10 06I 222300 62 16 08 02II 218286 73 44 85 51III 217288 65 34 33 15IV 218304 10 32 12 12

tyrosine 222302 10 480 11 462

The resulting functions will be used for developing of thefluorescent techniques of zinc and cadmium determination

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

References1 AV Karyakin n-electrons of heteroatoms in hydrogen bonding and

luminescence (in Russian) Nauka Мoscow 1985 135 p2 LK Neudachina EV Dedyukhina OV Evdokimova

NV Pechishcheva EV Osintseva KYu Shunyaev Fluorescenceof NN-di(2-carboxyethyl)-p-anisidine in solution and crystallinestate Journal of Applied Spectroscopy 2010 V 77 2 P 206-212

3 Lurie YuYu Hand-book of analytical chemistry (in Russian)Khimiya Мoscow 1989 447 p

Zinc ions reduction on solid metal electrodes in chloride melts

A Lugovskoy Z Unger M Zinigrad D Aurbach104

Effect of hardening temperature on the structural-morphologicalcharacteristics of metal cements based on mechanosynthesizedcopper compounds

NZ Lyakhov PA Vityaz SA Kovaleva TF Grigoreva VGLugin AP Barinova SV Tsybulya

118

Phase states of mechanoactivated manganese oxides

SA Petrova RG Zakharov AYa Fishman LI Leontiev138

Chemical-thermal treatment in carbon manganese steel at induction-heating in various borating conditions

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

153

Wear-resistant detonation sprayed coatings based on the compositemechanically activated SHS-materials

AA Sitnikov VI Yakovlev MA Korchagin DM Skakov AAPopova ME Tatarkin

159

Microstructure studies of the coatings produced by arc deposition ofthe mechanoactivated SHS-composite TiC+XME (R6M5 PR-N70H17S4R4-3) powders

AA Sitnikov VI Yakovlev MA Korchagin MN SeidurovME Tatarkin

161

Morphological study of detonation sprayed coatings of calciumhydroxyapatite deposited on a nanostructured titanium substrate

AA Sitnikov VI Yakovlev YuP Sharkeev EV LegostaevaAA Popova

162

Fabrication and modification of metallic nanopowders by electricaldischarge in liquids

NV Tarasenko AA Nevar NA Savastenko EI Mosunov N ZLyakhov TFGrigoreva

164

Basalt plastics of enhanced heat and chemical stabilities

OS Tatarintseva NN Ноdakova VV Samoilenko182

Repair compound modified by nano particles of ferrous oxide

OS Tatarintseva SN Novosyolova TK Uglova184

Cathode processes in KCl-PbCl2 melt

YuP Zaikov PA Arkhipov YuRKhalimullina VVAshikhin186

186

CATHODE PROCESSES IN KCl-PbCl2 MELT

YuP Zaikov1 PA Arkhipov1 YuRKhalimullina2 VVAshikhin2

1The Institute of High Temperature Electrochemistry Ural Branch ofRussian Academy of Sciences

S KovalevskayaAcademicheskaya St 2220 620990 Yekaterinburg e-maildirihteuranru

2Open Joint-Stock Company ELECTROMED Scientific ResearchCentre Lenin St 1 624091 Verkhnyaya Pyshma

Technology of crude lead refining is developed in the Institute ofHigh-temperature Electrochemistry The crude lead was obtained fromthe car battery wastes While organizing the refinement in the moltensalts it is important to know deposition mechanisms [1] of lead ions inthe chloride melts containing oxychloride complexes It is necessary tostudy kinetics of electrode processes to understand this mechanism

Many authors studied kinetics of electrode processes of leadelectroreduction from chloride melts [2 ndash 10] Diffusion coefficients ofions in molten salts were measured by using radioactive isotopes [10]and with the help of electrochemical parameters [2 -9]

VPYurkinskyi DV Makarov [2 3] studied the mechanism anddetermined kinetic parameters of Pb(II) ion at electrochemicalreduction process in various individual melts (NaCl KCl и CsCl) aswell as in mixtures with various component content using linearvoltamperometry chronopotentiometry and chronoamperometrymethods Studies of lead ions reduction in lithium sodium potassiumand cesium chlorides showed that cation composition causes significantinfluence on the process Electrochemical reduction is limited by Pb2+

diffusion in LiCl and NaCl melts when in the potassium and cesiumchlorides by chemical reaction of complex ion [PbCln]

2-n dissociationDiffusion coefficient value was found to decrease and lead(II) iondiffusion activation energy to increase in the LiClndashCsCl row

YM Rybuhin EA Ukshe [4] measured lead ions diffusioncoefficients in molten chlorides by chronopotentiometry methodMeasurements were carried out under the argon atmosphere Therectangular polished platinum plate about 1 cm2 square was used as theworking electrode Molten lead placed into the quartz tube connected bycapillary with the bulk melt was the anode and reference electrode

187

NaCl KCl PbCl2 salts of chemically pure grade were used in the workThey were melted under vacuum before the experiment According tothe results of these studies the validity of the Stocks-Einstein equationto ion diffusion in molten salts is limited by the systems where theprocess of complex formation is absent that is why the significantdeviations from the equation take place in KCl ndash NaCl and especially inthe pure KCl

D=KT(6r) (1)where - viscosity r ndash ion radius according to Goldschmidt

Using oscillographic method II Naryshkin and VP Yurkovskyidetermined lead silver and cadmium ions diffusion coefficientsdepending on temperature against the equimolar mixtures NaCl-KCland LiCl-KCl Platinum microelectrode the platinum wire butt with 06mm diameter soldered into a quartz capillary was used 400 mm2

platinum foil was used as anode Chloride-silver electrode was used asthe reference electrode Short circuit during two minutes was used torenovate the electrode surfaces after each observation For obtaining themore reliable results each curve was observed several times and theresults were averaged out Authors showed the direct dependence of thepeak current from the investigated ions concentration This fact confirmsthe conclusion of Hills Ocsley and Terner [11] about the possibility ofthe oscilligraphic voltamperometry for the rapid quantitative analysis inthe molten salts Dependence of the peak potential from the logarithm ofinvestigated ion concentration for cadmium lead and silver was foundIndependence of the peak potential from the concentration logarithm forcadmium and lead chlorides corresponds to the dissolved matterdeposition Linear dependence observed for the silver chloridedemonstrates the absence of solubility in the process of silver depositionThe following valence values were found for silver 116 for lead 24

In the works [7-9] diffusion coefficients of lead zinc andcadmium ions in the LiCl ndash KCl и NaCl ndash KCl melts were determinedRaymond J Heus and James JEgan [7] used polyrophic method to studyprocesses of lead zinc cadmium ions electroreduction in the moltenchlorides Dropping bismuth electrode was a cathode Silver chloridecontaining 2 mass of AgCl in KCl ndash LiCl (eutectics) was a referenceelectrode Authors obtained linear dependencies of the concentration of

188

the investigated chlorides from the diffusion current densities Diffusioncoefficients were calculated with the Ilkovich equation

Richard B Stein [8] investigated the ion reduction reaction ofdivalent lead in the NaCl ndash KCl melt with oscillographic polyrographymethod Platinum microelectrode with 05 mm diameter soldered intothe quartz tube with 189х10-3 cm2 square was a cathode Referenceelectrode was silver chloride and the auxiliary electrode was graphiteAuthor founded out that the lead ion diffusion coefficients obtained bythe experimental data differ from calculated according to the equation ofStocks-Einstein He derived the conclusion that the cation structure ismore complex than just a single ion

HA Laitinen HCGaur [9] investigated lead cobalt and thalliumion reduction in the molten potassium and lithium chlorides withchronopotenciometry method Authors fixed the value of the transitiontime for melts containing the control values of ions under investigationAccording to the experimental data empiric dependences ofconcentrations and transitional time were determined Coefficients ofcadmium cobalt lead and thallium ion diffusion were calculated withSandrsquos equation (208 242 218 38810-5 cm2s correspondingly)

Cathode processes in chloride melts containing lead ions werestudied by chronopotentiometric and stationary galvanostaticpolarization curves methods

Experiments were carried out in the cell made of quartzhermetically closed fluoroplastic cover (2) with the holes for electrodesand thermocouple with accordance to the Fig1

Glassy-carbon was a working electrode (cathode) Glassy-carboncontainer played a role of a counter electrode Melted equimolar mixtureof lead lithium and potassium chlorides was used as the electrolyte forthe reference and working electrodes Electrolytes of the workingelectrode and reference electrode were separated by the diaphragm fromthe Gooch asbestos (7) Measurements were conducted relatively to thelead reference electrode that is a metal lead of C1 grade being in contactwith the melt containing 5 mass of lead chloride

Potassium chloride lithium chloride chemically pure grade andlead chloride of pure for analysis grade were used for electrolytepreparation Glassy-carbon container (4) was placed on the cell bottomon the special fireproof brick support (8)

189

Current lead to liquid-metal reference electrode was realized in aform of molybdenum rod and to glassy-carbon crucible through graphitebar Current leads were protected from the contact with melt by alundumtubes closed with the rubber plugs (1) to keep the cell hermeticallyclosed

Fig 1 Electrolytic cell 1 ndash rubber plugs 2 ndash fluoroplastic cover 3 ndash thermo-couple 4 ndash glassy-carbon container 5 ndash quartz-glass sell 6 ndash workingelectrode 7 ndash diaphragm 8 ndash fireproof brick support 9 ndash current leads toelectrodes 10 ndash electrolyte 11 ndash reference electrode

4

1

2

5

6

8

93

10

11

Vacuum

7

Ar

190

The cell was pumped out and fullfilled with purified argon Laterit was put into the resistance furnace and heated until the giventemperature under the abundant pressure of the inert gas

The setup was equipped with the automatic system of temperaturestabilization Temperature measurement was performed with the help ofchromyl-aluminum thermocouple Content of components in electrolytewere being controlled before and after the experiment with the atomic-absorption method

Stationary polarization measurementsLead ion deposition processes in eutectic melt of lithium and

potassium chlorides were studied at 04 to 30 mol lead chloride intemperature range from 673 to 823 К Polarization curves are given onthe fig 2 and 3 Two characteristic areas are observed on thepolarization curves On the first area little potential deviations from theequilibrium value takes place with cathode current density increasing to008 Acm2

Experimental points on the area with 04 mol lead chlorideconcentration are on straight lines described by equationsE = - 00703lgi - 01203 and E = - 00775lgi - 0091 for 673 and 773 Кcorrespondingly

At temperature 673 К tg is 0070 мВ and at 773 К - 0078 мВAccording to the equation

Ftg

RT23

n (2)

we have n=19 for 673 К and n=20 for 773 КAt lead chloride concentration 30 mol experimental points on

the first area of the polarization curve is described by the equationE= - 00779lgi - 00877

Amount of electrons in the reaction calculated on the equation (2)is equal 2

Reaching current densities 011 012 020 и 032 Асm2 on thefig3 for 673 723 773 823 К temperatures correspondingly Potentialis greatly shifted to the negative area to the values -084 -084 -106and -110 correspondingly

At small values of cathode current density there is one wavecorrespondingly to the fig 4 In some time after current rise potential

191

reaches its stationary value at current density 0045 Асm2 for 35 s forcurrent density 0060 Асm2 for 30 s After current disconnectionpotential comes back to its equilibrium value

Fig 2 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

(04 mol ) melt

192

Fig 3 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

melt at 823 К depending on the lead chloride concentration Concentration oflead chloride in mol per cents 1 - 04 2 - 05 3 ndash 30

193

Fig 4 Engaging curves at 823 К temperature and the different current density

On the engaging curves at current density values corresponding tothe second characteristic area on the polarization curves on the figures 2and 3 two waves on figure 5 are seen Time of reaching stationarypotential tst decreases with the current density increasing (for currentdensity 012 Асm2 tst equals 85 s for current density 017 Асm2 tst -45 s)

Fig 5 Engaging curves at 04 mol lead chloride concentration currentdensity 012 013 017 Асm2 and 823 К

194

Processes taking places on the electrode can be described in thefollowing way On the first characteristic area of the polarization curvelead ion deposition happens

Pb2+ + 2e = Pb0 (3)The limiting current density of lead reduction increases with the

temperature and lead chloride concentration At 30 mol of leadchloride concentration and 823 K limiting current density ilim is 12Acm2

On the second characteristic area of the polarization curvedeposition of the alkaline metal is possible on the reaction

K+ + e = K0 (Pb) (4)Low values of the alkaline metal reduction potentials might be

connected with the process of alloy formation of alkali metal with leadK + 4Pb = KPb4 (5)

Chronopotentiometric measurements at lead deposition from LiClndash KCl (45-55 mol ) ndash PbCl2 melt at 04 mol lead chlorideconcentration were performed at 823 K and current density range from010 to 017 Acm2 There is only one wave on chronopotentiometriccurves under these conditions Values of product i12 depending oncurrent density are given in the table 1 where - transition time

Table 1 Values of product i12 at diverse current density

s i mAcm2 i12 mAcm2s12

095 170 165161 130 165181 120 162

262 102 165

It is seen that the product i12 does not depend on current

density at constant concentration of depolarizator 0OxC In the table 2

potential values Е4 at time equaling the forth of the correspondingvalues of transition time are given

195

Table 2Values of Е4 potential of different current density

i Acm2 s 4 s Е4 V

010 264 0660 -0061

012 181 0453 -0600

013 161 0403 -0061

017 095 0238 -0062

It is seen that the potential Е4 does not depend on the experimentconditions the current density in this case

Equation for the reversible process can be as follows

1ln

nF

RT21

4t

ЕЕ

(6)

for irreversible process

2100

1lnlnnF

RT

t

nF

RT

i

knFCЕ

fhOx (7)

where E ndash electrode potential 4E - measurement potential at frac14

of transition time R ndash gas constant F ndash Faraday number n ndash number

of electrons T ndash temperature - transition time 0OxC - depolarizator

concentration 0fhk - deposition speed constant

On the figure 6 dependencies Е -

1ln

21

t

and Е -

21

1ln

t at 04 mol of lead chloride concentration current

density 01 Acm2 and 823 K are given

196

y = -00835x + 00654

0002

0022

0042

0062

0082

0102

0122

0142

0162

-115 -065 -015 035 085

- E В

1 2

Fig 6 Dependencies 1ndashЕ=f

1ln

21

t

and 2-Е =f

21

1ln

t

From the analysis of given graphic dependencies follows that the

experimental points in coordinates E -

1ln

21

t

are in a straight line

with the confidence interval 095 The can be described by equation

08300650 E

1ln

21

t

(8)

The amount of electrons in the electrode reaction was calculatedfrom the equation

F

RTn

0830 (9)

hence n=2

197

It follows from the experimental conditions on lead ion (II)deposition that the process is reversible ie it is controlled by the speedof divalent lead ions mass transfer from the volume of melt to theelectrode surface

Diffusion coefficient of lead dichloride at 823 K was calculated onSandrsquos equation

20

2

)(

)(2D

oxnFC

i

(10)

Lead ions (II) diffusion coefficient are equal to 23310-

5сm2s It is in good accordance with the data obtained by other authors[5 6]

References1 Yurkinsky V Makarov D Electrochemical reduction of lead ions in

halide melts Russian J Applied Chem 1994 67 p 1283-12862 Yurkinsky V Makarov D The influence of cation composition on

kinetics of lead electrochemical reduction in chloride melts RussianJ Applied Chem 1994 68 p 1474-1477

3 Ryabukhin Yu And Ukshe E The diffusion coefficients of lead inmolten chlorides DAN SSSR 1962 145 p 366-368

4 Naryshkin I Yurkinsky V Oscillographic investigation oftemperature coefficients for some chlorides diffusion in LiCl-KClRussian J Electrochemistry 1968 4 p 871-872

5 Naryshkin I Yurkinsky V Voltammetry in molten salts Russian JElectrochemistry 1968 2 p 856-866

6 Raymond J Heus James J Egan Fused Salt Polarography Using aDropping Bismuth Cathode ndash J of the Electrochemical SocietyOctober 1960 p 824-828

7 Richard B Stein The Diffusion Coefficient of Lead ion in FusedSodium Chloride Eutectic ndash J Electrochem Soc 1959 vol 106 p528

8 Laitinen H A Gaur H C Chronopotentiometry in Fused LithiumChloride-potassium Chloride - Anal Chem Acta 1958 vol 18 p1-13

9 Hills GI Oxley I E Turner D W Silicates Ind 1961 vol 26 p559

184

REPAIR COMPOUND MODIFIED BY NANO PARTICLES OFFERROUS OXIDE

OS Tatarintseva SN Novosyolova TK UglovaInstitute for Problems of Chemical and Energetic Technologies SB RAS

Biysk Altai region Russia labmineralmailru

The results of influence study of nano-dispersed ferrous oxide oncharacteristics of the composite material developed earlier (compound)and intended to repair and recover engineering structures and massifshave been presented in this paper The compound consists ofmulticomponent polymer matrix including epoxy oligomer low-molecular synthetic rubber plasticizer and process additives filler and alow-temperature amine hardener Microcalcite with particle size lessthan 50 μm has been used as filler

The composite has been modified with nano powder of ferrousoxide (II) (manufactured by MACH I Inc USA) consisting of needle-like crystalline particles with average size 4 nm and having specificsurface area 2379 m2g

Experiments have shown that even distribution of nano particlesin epoxy resin is caused with a high-velocity mechanical device underthe additional influence of ultrasonic field

The most important things for low-viscosity repair compositionsapplied to recover the integrity of natural materials are high flowabilitydetermining the ability to fill narrow-opened fractures and stability ofstrength properties for a long time

The positive effect of ultra-dispersed modifier is seen within therange of 030-035 of its percentage in the composition as shown byresults of the study given in the Table At these amounts the maximumvalues of flowability and mechanical characteristics have been providedThe logical increase in samples density indicates the optimality of thepacking developed and reduction in the porosity of a composite materialthat is important while using it in conditions on high humidity

The compound developed is environmentally friendlyincombustible waterproof stable to heat vibration and long mechanicalloads and can be used to perform repair work in construction industrypublic service stone mining and processing industries and architecture

185

Table Percentage influence of ferric oxide nano powder on technicalcharacteristics of the composite material

Value at modifier percentage Characteristics

0 010 020 030 035 040

Dynamic viscosityat T = 20 oC Pamiddots

210 212 225 262 266 288

Flowability cm 48 48 48 52 53 45

Density gm3 141 141 143 145 146 146

Compressive forceMPa

79 78 79 82 86 74

Relative deformation

023 021 021 025 025 020

182

BASALT PLASTICS OF ENHANCED HEAT AND CHEMICALSTABILITIES

OS Tatarintseva NN Ноdakova VV SamoilenkoInstitute for Problems of Chemical and Energetic Technologies

of the SB RAS Biysk Russialabmineralmailru

The experience of the application of metal pipes for chemicalproductions cool and hot water supply systems transportation ofpetroleum products and other aggressive fluids has shown that they aregreatly subjected to corrosion that reduces their lifetimes to severalyears Therefore natural is the observed worldwide tendency ofreplacing steel and cast iron by composite materials of high chemicalstability and durability to which glass-reinforced plastic having acomplex of high service properties should primarily be relatedHowever requirements for composites have presently increasedespecially with regard to their heat and chemical stabilities andresistance to microorganisms ground and waste waters

The paper demonstrates the study results with respect to thedevelopment of a composite material for filament-wound pipe productswhich is superior in its basic parameters to analogous ones in the field ofglass-reinforced plastic application As a reinforced material basaltroving with higher strength characteristics and resistance to aggressiveenvironments as compared to a glass one was chosen the polymermatrix was a heatproof binder TS developed on the basis of nitrogen-containing epoxy resin synthesized Having rheological properties andstrength characteristics similar to those that are widely used in themanufacture of filament-wound glass-reinforced plastic products of thebinders EDI and EChDI the binder TS possesses enhanced heat stabilityand low viscosity at room temperature which permits the reduction ofpower inputs for its processing

The obtained data on advantages of both basalt fiber and thebinder developed have to the full extent been realized in laboratorysamples of the reinforced composite and in basalt plastic pipes producedindustrially (see Table below)

183

Table Temperature dependence of elastic modulus E of basalt plasticpipes

Еmiddot103 MPa at Т degСBinder 20 85 125 155 200

EDI 11701 11263 4363 3528 -EChDI 11277 10951 9944 6217 -

TS 19960 19336 19179 17557 9096

The 9-fold strength reserve of the basalt plastic pipes determinedwhen hydro-tested under extreme conditions (150degC 15 MPa) hasconfirmed the possibility of creating composite polymer materialsoperating under high-temperatures and humidity

164

FABRICATION AND MODIFICATION OF METALLICNANOPOWDERS BY ELECTRICAL DISCHARGE IN LIQUIDS

NV Tarasenko1 AA Nevar1 NA Savastenko2 EI Mosunov3 NZ Lyakhov4 TFGrigoreva4

1 Institute of Physics NAS B Minsk Belarus2 Leibniz-Institute for Plasma Science and Technology Greifswald Germany

3 The Institute of Machine Mechanics and Reliability NAS B Minsk Belarus4Institute of Solid State Chemistry and Mechanochemistry SB RAS

18 Kutateladze Str Novosibirsk 630128 Russia grigsolidnscru

Electrical-discharge technique was developed for preparation ofmetallic and metal-containing nanoparticles as well as for modificationof metal micropowders in liquids The morphology and composition ofthe nanopowders formed under various discharge conditions wereinvestigated by means of transmission electron microscopy and X-raydiffraction analysis The optimal conditions for the production oftitanium carbide and copper nanoparticles embedded in carbon layerswere found

IntroductionA synthesis of metallic and metal-containing nanopowders is of a

great interest due to their potential applications as super hard materials[1] environmentally friendly fuel cells with highly effective catalysts[23] and so on Transition metal carbides have been widely studied aselectrocatalysts because of their electrochemical properties andelectrical conductivities Nanosized carbon particles are suitable supportmaterials for certain types of catalysts Of particular interest for futurecatalytic applications are carbon-based materials with embeded metalnanoparticles [4] As long as carbon nanoparticles are relatively inertsupports many studies have been conducted in order to find which pre-treatment procedures are needed to achieve optimal interaction betweenthe support and metal species [5]

For any application of nanoparticles to be commercially viablelow-cost production methods have to be developed A low-temperatureand non-vacuum synthesis of nanoparticles via discharge in liquid(submerged discharge) provides a versatile choice for economicalpreparation of various nanostructures in a controllable way An arc

165

discharge in liquid nitrogen has firstly been reported as a cost-effectivetechnique for the production of carbon nanotubes in 2000 by Ishigamy etal [6] Since that time many efforts have been devoted to develop thismethod Sano et al proposed to submerge electrodes in water instead ofliquid nitrogen [78] They reported synthesis of carbon onions [78] andsingle-walled carbon nanohorns (SWNHs) [9] In latter case carbonnanoparticles were produced via discharge in water method with thesupport of gas injection Parkansky et al reported nanoparticlessynthesis via a pulsed arc submerged in ethanol Ni W steel andgraphite electrodes were used [1011] The particles composition variedfrom carbon to pure metal including various intermediate combinationsof these materials Bera et al employed an arc-discharge in a palladiumchloride solution to produce carbon nanotubes decorated with in situgenerated Pd nanoparticles [10] Importantly the synthesized materialcontained no chlorine

In this paper methods based on electrical-discharges in liquids forproduction of tungsten and titanium carbide as well as coppernanoparticles embedded in carbon nanostructures is reported Thecapabilities of arc and spark discharges submerged in liquids forsynthesis of nanoparticles as well as electrical-discharge modification ofmetallic powders were studied

Experimental detailsThe experimental reactor (Fig 1) consisted of four main

components a power supply system (pulse generator) the electrodes aglass vessel and a water cooling system outside the beaker A pulseddischarge was generated between two electrodes being immersed in 100ml of liquid (pure (995) ethanol or 0001 M CuCl2 aqueous solution)The appropriate combinations of pairs of metallic (tungsten titanium orcopper) and graphite electrodes were used The choice of ethanol wasmotivated by the fact that organic compounds play a role of a carbonsource to produce nanoparticles in discharge-in-liquid system [7 12]Addition of the copper chloride salt into double distilled water favoredthe activation of discharge process Metal (tungsten titanium or copper)and graphite rods with diameters of 6 mm were employed as electrodesAn optimum distance between the electrodes was kept constant at 03mm to maintain a stable discharge The discharge was initiated byapplying a high-frequency voltage of 35 kV The power supply

166

provided several different types of discharges Both direct current (dc)and alternating current (ac) arc and spark discharges were generatedwith repetition rates of 100 and 50 Hz respectively Current I(t) wasrecorded during the discharge as a function of time by means of anoscilloscope The peak current of the arc discharge was 9 A with a pulseduration of 4 ms The peak current of the pulsed spark discharge was 60A with a pulse duration of 30 μs

The synthesized products were obtained as colloidal solutionsAfter 15 min presedimentation the large particles precipitated at thevessel bottom The top layer contained the small nanoparticles wascarefully poured off into a Petry dish These suspended nanoparticleswere characterized by UV-Visible optical absorption spectroscopytransmission electron microscopy (TEM) and X-ray diffraction analysis(XRD) for their size morphology crystalline structure and composition

The optical absorption spectra of colloids were measured by UVndashVisible spectrophotometer (CARY 500) using 05 cm quartz cuvetteTransmission electron microscopy was performed by LEO 906E (LEOUK Germany) microscope operated at 120 kV A drop of solution putonto the amorphous carbon coated copper grid for TEM measurementsThereafter the liquid was evaporated at the temperature of 80 C Afterthe drying of colloidal solution the deposit obtained on the bottom ofPetri dish was examined by XRD Powder composition and itscrystalline structure were characterized by using X-ray diffraction atCuK (D8-Advance Bruker Germany)

Synthesis of carbide nanopowdersPromising capabilities of the developed technique for synthesis of

tungsten and titanium carbides (WC TiC) as well as carbon-encapsulated copper nanoparticles were demonstrated using theappropriate combinations of pairs of metallic and graphite electrodessubmerged into the appropriate solution Also physical and chemicalprocesses induced by the electrical discharges in liquids were studied tooptimize the process of nanoparticles synthesis

The results of nanoparticles preparation are summarized in theTable1 The synthesis rate varied in range of 2 ndash 40 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofmetal and graphite electrodes The synthesis rate increased withincreasing of discharge current and decreasing of pulse duration The

167

composition and morphology of nanoparticles were also found to dependon discharge parameters It should be noted that there is a possibility toscale-up the process

Table 1 summarized the variation in synthesis rate andcomposition of tungsten nanopowders with the discharge parameters Asa general tendency the synthesis rate was order of magnitude higher forspark discharge than that of arc discharge It may be due to thedifference in current value [13] For both arc and spark discharges itwas found that the synthesis rate is lower when tungsten was acting as acathode This result is consistent with literature data For example Beraet al reported that the consumption of anode is higher than that ofcathode [13]

Table 1 Summary of nanopowder synthesis conditions andresults of nanopowder characterization by XRD

XRD-analysisDischargetype

Electrodes Powdersyield

mgminW2Cvol

WC1-xvol

Cvol

Wvol

1 ac arc W C 02 71 781 147 -2 dc arc W(cathode)C(anode) 01 62 901 37 -3 dc arc W(anode)C(cathode) 02 66 715 219 -4 ac spark W C 25 58 328 614 -5 dc spark W(cathode)C(anode) 12 570 307 89 336 dc spark W(anode)C(cathode) 21 56 325 618 -

As it can be seen from the Table 1 the synthesized nanopowder isa mixture of hexagonal W2C face centered cubic WC1-x and graphite Nopeaks corresponding to WO were observed Nanopowder contained alsosmall amount body centered cubic W when synthesis was performed bydc current spark discharge with tungsten rod acting as cathode Here theparticular behavior of this discharge should be stressed showing ratherhigh ability to synthesize W2C Moreover in contrast to the other sparkdischarges synthesized material contained relatively small amount ofgraphite On the other hand applying tungsten as a cathode materialappears to reduce C content in nanopowder prepared via arc dischargetoo Generally the content of C is higher and content of WC1-x is lowerwhen synthesis was performed by spark discharge

168

Nanoparticles prepared by arc discharge were observed in theiragglomerated form The agglomerated nanoparticles were surrounded bythe grey regions which were probably graphite layers This typical viewwas seen everywhere in TEM images of product synthesized by arc forboth ac and dc current discharges irrespective of electrodes polarityThat fact implies that the morphology of synthesized nanopowders wasgoverned rather by the current pulse duration and value of peak currentthan the polarity of the electrodes Since nanoparticles were observed inthe agglomerated form it was difficult to measure their size correctlyWe suppose that approximately 4 nm nanoparticles are formed duringthe arc discharge in ethanol

Fig1 shows the TEM image of titanium carbide nanopowdersynthesized by spark discharge in ethanol As can be see from the Fig1the nanoparticles were also surrounded by graphite layers Fig 1demonstrates that the nanoparticles synthesized by spark were nearlyspherical with a mean diameter of ~ 7 nm The particle size distributionwas rather narrow (plusmn 2 nm) The XRD pattern of synthesized sample isshown in Fig 1 (right picture) The diffraction peaks at 60deg 418deg605deg 724deg 765deg and 407deg 504deg 590deg 667deg 741deg correspond tothe formation of cubic face-centered titanium carbide TiC and cubicprimitive TiC2 respectively There are some diffraction peaks with 2θvalue of 407deg 504deg 590deg 667deg and 741deg which can be assigned tothe hexagonal C The amount of TiC reached 887 vol The quantitiesof TiC2 and C in samples detected by XRD corresponded to ca 47 vol and ca 67 vol respectively

Fig 1 TEM image (left picture) of titanium carbide nanopowder synthesizedby ac spark discharge and XRD-pattern (right picture) of the sample

169

Synthesis of copper-carbon composite nanostructuresNumerous studies have focused on synthesis of metal-containing

carbon nanocapsules (CNCs) via submerged discharge method[89141516] Because of the carbon sheets surrounding the metal corethe CNCs are protected from the environment and from degradation Thecarbon coatings mean that nanoparticles are biocompatible and stable inmany organic media Thus carbon encapsulated nanoparticles arecandidate for bioengineering application high-density data storagemagnetic toners for use in photocopiers [81718] The metal containingcarbon nanostructures were prepared by using the electrode frommixture of graphite and metal precursor [16 1920] Recently Xu et aldemonstrated a possibility to synthesize Ni- Co- and Fe-containingCNCs by an arc discharge between carbon electrodes in aqueoussolution of NiSO4 CoSO4 and FeSO4 respectively [15] In contrast tothe data reported by Bera et al the synthesized material consisted of Oand S due to SO4

-2 ionic precursors in the solution Since the metal core-forming material was supplied by liquids the production rate of CNCswas limited by the salt concentration [4] This restriction may cause alimit to apply the submerged discharge method to the large-scaleproduction of CNCs

In this paper Cu-based nanoparticles were prepared viasubmerged discharge of bulk copper and graphite electrodes in a copperchloride (CuCl2) aqueous solution Thus material of copper electrode aswell as Cu from solution was supposed to be incorporated into theresulting nanoparticles The effect of discharge parameters and electrodecomposition on the morphology and composition of final products havebeen investigated Additionally synthesized material was modified bylaser irradiation The changes in nanoparticles morphology andcomposition were examined by transmission electron microscopy(TEM) X-ray diffraction (XRD) and UV-Vis spectroscopy

The six types of nanoparticles suspension were prepared underdifferent discharge parameters The synthesis parameters aresummarized in Table 2 As it can be seen the weight change of eachelectrode was generally higher when spark discharge was generatedThe anode consumption rate was higher than that of cathode irrespectiveto a discharge type and electrode material However in contrast to theliterature data [4] there was no cathode gain in weight As a generaltrend the nanopowder synthesis rate was higher for spark discharge than

170

that of arc discharge It may be explained by the difference in currentvalue [21] For both arc and spark discharges it was found that thesynthesis rate was higher when copper was acting as an anode There isa discrepancy between nanopowder synthesis rate and materialconsumption rate The values of discrepancy D listed in the Table 2were calculated as follows

100()

CCu

syn

RR

RD (1)

Here Rsyn is the synthesis rate of nanopowder RCu is theconsumption rate of the copper electrode and RC is the consumptionrate of the graphite electrode The discrepancy D depended ondischarge parameters For ac-discharges the value of discrepancy washigher for spark discharge than that for arc discharge For dc-discharges this trend remained if the polarity of electrodes was takeninto account It is worth to notice here that the discrepancy betweenmaterial consumption rate and nanopowder synthesis rate may be causednot only by separation of sediment fraction but by the reaction of carbonatoms with water resulting in the production of gaseous compounds [9]

Table 2 Summary of nanopowder synthesis parametersType of

dischargepeak currentpulse duration

Electrodes materialRCu and RC

mg min-1RSyn

mg min-1D

Cu 671 ac1) spark60 A 30 micros C 48

59 49

Cu 122 ac arc10 A 4 ms C 26

25 34

Cu (cathode electrode) 473 dc2) spark60 A 30 micros C (anode electrode) 61

21 81

Cu (anode electrode) 664 dc spark60 A 30 micros C (cathode electrode) 46

69 38

Cu (cathode electrode) 115 dc arc10 A 4 ms C (anode electrode) 25

19 47

Cu (anode electrode) 286 dc arc10 A 4 ms C (cathode electrode) 21

33 33

1) Alternating current pulsed discharge2) Direct current pulsed discharge

171

This coincides with the fact that the largest discrepancy (morethan 80) was observed in sample with the largest graphite electrodeconsumption rate (sample 3) For all samples the synthesized powderseparated into three phases one floating in suspension one settling atthe bottom as sediment and one as a layer of film-like material floatingon the liquid surface

The aqueous solutions of CuCl2 were discharge treated for only 20s to acquire yellowish suspensions The transparency of the suspensionsdecreased with the time during the discharge treatment The liquidsturned to dark yellow after treatment by ac-discharge for 10 min Thesuspensions resulting from dc-discharge treatment were conspicuouslydarker when C electrode was acting as an anode The nanoparticlessuspension produced by spark and arc discharges were dark brown anddark grey respectively It might be due to the presence of relatively largeamount of carbon particles in suspension (see Table 3) The dc-dischargetreated solutions were olive-green when Cu was used as the anodeelectrode Yellow or green colour of suspension may indicate theoxidation of copper nanoparticles [22] The presence of Cu2Onanoparticles was further confirmed by XRD analysis No changes incolour were observed after laser irradiation of suspensions

Figure 2 shows the absorption spectra of as prepared (a) and laserirradiated (b) suspended nanopowders synthesized by dischargetreatment of aqueous solution of CuCl2 (2) for 1 min The spectra werecorrected to the contributions of solvents The optical density increasedwith decrease in wavelength Generally the optical density ofsuspensions prepared by spark discharge was higher than that ofsuspension prepared by arc discharge This is consistent with the factthat the nanoparticles production rate was higher when the solution wastreated by spark discharge In the spectral range of 200 ndash 500 nm theoptical density of the samples 1 4 6 was higher than that of samples 23 and 5 This seems to suggest that the main parameter in determiningthe optical properties of suspensions was concentration of Cu-basednanoparticles For the samples number 1 and 4 a weak absorption peakwas observed at very short wavelength According to the literature data[2324] a surface plasmon peak at wavelength of 289 nm may beattributed to the presence of very small separated Cu nanoparticles (lt 4nm in size) Though TEM examination confirmed the presence of smallnanoparticles in sample 1 there were no nanoparticles with diameter less

172

than 4 nm in sample 4 Moreover there were no copper nanoparticles insample 1 as revealed by the XRD (see below) More likely theexistence of weak absorption peak at 280 nm implied formation of liquidbyproducts We did not observe in the absorption spectra surfaceplasmon band around 570 nm Missing of the plasmon band can beexplained by copper oxidation on the particle surface [23] Thissuggestion was further confirmed by XRD analysis (see below) Thesuspensions exhibited the same colours after laser irradiation butabsorption intensity increased for samples 3 1 and to the less extent forsample 5 as illustrated in Figure 2b TEM analysis revealed themorphological similarity of irradiated samples 1 3 and 5 (see below)

Figure 3 depicts the corresponding TEM images for thesuspensions shown in curves 1-6 of Figure 2 Parts (a) and (b) representthe TEM views of the as-prepared and irradiated samples respectivelyThree distinct structures were observed dark small spherical particlesdark particles surrounded by a gray shell and gray flake-like structureshaving diffuse contours The small dark particles with diameter 2-5 nmwere observed in samples 1 2 3 and 5 (marked with black ellipses inFigure 3) Some dark particles notable when using ac spark dischargefor synthesis were bigger than 20 nm indicating coalescence Thenanoparticles synthesized by ac arc discharge (sample 2) were

Fig 2 Absorption spectra for the as-prepared (a) and laser modified (b)suspended nanoparticles produced by ac- (12) and dc- pulsed discharges(3456) The following electrode pairs were used Cu and C for the ac-spark(1) and ac-arc (2) discharges Cu as a cathode electrode and C as an anodeelectrode for the dc-spark (3) and dc-arc (5) Cu as an anode electrode and C asa cathode electrode for the dc-spark (4) and dc-arc (6)

173

surrounded by the arrowed gray regions which were probably carbonshells as shown in Figure 3a

Fig3 TEM images of nanoparticles from as-prepared (a) and irradiated (b)suspensions produced by ac- (12) and dc- pulsed discharges (3456) Thefollowing electrode pairs were used Cu and C for the ac-spark (1) and ac-arc(2) discharges Cu as a cathode electrode and C as an anode electrode for thedc-spark (3) and dc-arc (5) Cu as an anode electrode and C as a cathodeelectrode for the dc-spark (4) and dc-arc (6)

174

As we did not have any direct evidence that the shells consisted ofcarbon these nanostructures will be referred further as core-shellnanoparticles The core-shell nanoparticles were also observed in colloidprepared by dc arc discharge between copper cathode and graphiteanode (sample 5) It can be seen that core-shell nanoparticles rangedfrom 20 to 50 nm in diameter while the cores within the nanoparticlesvaried from 8 to 25 nm The cores were non-spherical They seemed tocompose of small particles clustered together The flake-like structureswith diffuse contours were 50 nm in size They were observed in allsamples Samples 4 and 6 consisted mostly of structures with diffusecontours On the basis of the above observations the ac arc dischargeand dc arc discharge with copper anode electrode seemed to be moresuitable for synthesis of nanoparticles with core-shell structure

It is clear seen that many smaller particles with sizes around 2-7nm were generated after the irradiation of samples 2 4 and 6 Theparticles larger than 10 nm completely disappeared The micrographrevealed that after the irradiation these suspensions consisted ofparticles with circular cross-section whereas before the irradiation theparticle shape was not spherical The nanoparticles were dispersed verywell No small nanoparticles were observed in suspensions 1 3 and 5after the irradiation Though as can be seen by comparing Figure 1(a)3(a) and 5(a) with 1(b) 3(b) and 5(b) the shape of nanoparticleschanged after the irradiation The laser induced morphology change mayoccur through heating of the nanoparticles because of the absorption ofthe laser light [25] According to the mechanism proposed by Takami etal the morphology of irradiated nanoparticles was determined by therelationship between temperature of nanoparticles their melting andboiling point

The laser induced change in shape and size occurred if thetemperature of nanoparticles was at the boiling point If the temperaturewas lower than the melting point no changes took place If thetemperature was between melting point and boiling point only thechange in shape occurred Thus the difference in morphology of theirradiated samples can be attributed to the difference in theircomposition Even being irradiated with the same laser light intensitythe nanoparticles of different composition changed their morphology indifferent ways as they have different melting and boiling points

175

X-ray diffraction data were collected to identify synthesizedsamples The diffraction peaks at 432deg and 503deg correspond to theformation of faced-centered-cubic Cu There are three diffraction peakswith 2θ value of 365deg 423deg and 614deg which can be assigned to theprimitive cubic Cu2O Besides there are two peaks at 240deg and 265degwhich can be assigned to the hexagonal C XRD revealed that dischargetreatment of aqueous solution of CuCl2 led to the formation of Cu2

(OH)3Cl and Cu2OCl2 because of a strong affinity between chlorine andthe metal (peaks with a value of 2θ around 165deg 19deg 31deg 323deg 327deg330deg 387deg 398deg 401deg 503deg 505deg 538deg and 178deg 360degrespectively) For comparison the XRD patterns of initial solution ofCuCl2 are also plotted at the top of Fig 4 Non-treated aqueous solutionof copper chloride was allowed to evaporate and than analyzed by XRDThe diffractogram of this sample showed peaks at about 2θ around162deg 220deg 240deg 267deg 289deg 328deg 340 348deg 352deg 409deg 430deg448deg 453deg 490 and 573deg which are characteristics of CuCl2middot2H2O

XRD data were used to semi-quantitatively determine thepercentage of constituents The semi quantitative analysis of phasecomposition is shown in Table 3 The nanopowder composition wasstrongly dependent on the synthesis parameters It should be noted herethat metallic copper was only formed by dc-discharge treatment whencopper was acting as an anode electrode (samples 4 and 6) Synthesizedmaterial contained copper mostly in form of oxide (Cu2O) copperhydroxychloride (Cu2(OH)3Cl) and copper oxychloride (Cu2OCl2)Difference in Cu2O and C contents among all samples was significantSamples 2 and 5 contained no copper oxide while sample 6 had thelargest percentage of copper oxide (ca 80 vol) On the other handsample 6 contained no carbon The carbon contain in sample 4 exceeded80 vol The quantities of Cu2(OH)3Cl in samples ranged from lessthan 2 vol to ca 30 vol Only three samples contained Cu2OCl2

(samples 12 and 5) The maximal amount of Cu2OCl2 detected by XRDcorresponded to ca 30 vol In spite of high copper electrodeconsumption rate sample 4 contained unexpectedly small quantities ofCu and Cu-containing compound It might be due to the formation ofrelatively large and heavy copper microparticles They precipitated fromcolloid quickly after synthesis Therefore they were not collected andanalyzed by XRD (see experimental section) A correlation was

176

observed between low copper electrode consumption rate and absence ofCu and Cu2O fractions in nanopowder composition for samples 2 and 5

It should be stressed here that the core-shell structures wereobserved for only samples 2 and 5 Taking into account firstly thatsamples 2 5 and 6 were prepared by arc treatment secondly that thesample 6 contained no C and assuming that the shells consisted ofcarbon we can suggest that arc discharge was more suitable forsynthesis of core-shell nanoparticles On the other hand the chemicalcomposition of final product was governed by different competingreactions As they have different equilibrium constants they may form anetwork where the ratios of the products are sensitive to concentrationsof each of the many components Therefore the slight difference ininitial concentration might results in significant difference incomposition and morphology of synthesized material (compare samples5 and 6)

Although the exact mechanism for formation of nanoparticles viadischarge in solution process is not clear the following possibility may

Table 3 Semi-quantitative analysis of synthesized powder by XRD

XRD-analysisType of

dischargeElectrodesmaterial Cu

volCu2Ovol

Cvol

Cu2(OH)3Clvol

Cu2OCl2vol

1 ac1) sparkCuC

- 135 403 165 297

2 ac arcCuC

- - 646 300 54

3 dc2) sparkCu (cathode)C (anode)

- 391 370 239 -

4 dc sparkCu (anode)C (cathode)

78 83 825 14 -

5 dc arcCu (cathode)C (anode)

- - 339 336 325

6 dc arcCu (anode)C (cathode)

74 775 - 151 -

1) Alternating current pulsed discharge2) Direct current pulsed discharge

177

be considered During discharge treatment of the liquid copper andgraphite electrodes were heated melted and vaporized in the region ofthe discharge generated In the vicinity of electrodes the liquid was alsovaporized rapidly due to extremely high temperature Hence the plasmaregion produced by the discharge adjacent to the electrodes wassurrounded by a gas bubble Following Sano et al [8] the gas mixturemay comprise CO and H2 formed as follows

22 HCOOHC (2)

This reaction might cause the discrepancy between electrodeconsumption rate and nanopowder synthesis rate since some of carbonatoms formed gaseous CO Sano et al reported that gas bubbles didnot comprise water vapor since no condensation occurred [8] Howeverwe should consider that water vapour also existed in the discharge zoneas we did not obtain any evidence of its absence

Copper chloride is an anionic compound that dissociates inaqueous solution and may form different ionic species such as Cu2+ Cl-or complex ions such as CuCl2

- CuCl32- CuCl4

2-[26] The reduction ofcopper ions into copper atoms was likely taking place in plasma regionduring discharge treatment of the liquid as shown in Eq 3

02 2 CueCu (3)

As the temperature in the vicinity of the electrodes was estimatedto be around 4000 K [8] the thermal decomposition of complex ions tometallic copper possible took place in discharge zone (Eq (4-6))

20

2 ClCuCuCl (4)

20

3 322 ClCuCuCl (5)

202

4 2ClCuCuCl (6)

The nanoparticles were then formed from the complex gasmixture through different transformation stages namely nucleationgrowth condensation and coalescence Both the evaporated copper fromelectrode and Cu produced by reduction of ions from solutions were

178

supposed to be incorporated into the resulting nanoparticles Becausewater vapor existed in gas bubble the copper nanoparticles were easilyoxidized Reduction of copper oxide by carbon monoxide and hydrogenwas possible the subsequent step (Eq (7) and (8))

OHCuCOOCu 22 2 (7)

222 2 COCuHOCu (8)

According to the XRD measurements (see Table 3) copper oxidewas only partially reduced into copper in sample 4 and 6 The data ofXRD analysis implied also reaction of chlorine with copper andorcopper oxide to form Cu2Cl(OH)3 and Cu2OCl2 These reactions mightinvolve hydrogen produced via reaction (2)

It should be noted that there was no direct evidence to support theabove-mentioned formation sequence and the true mechanism may bemore complicated

ConclusionsFrom the results and discussion presented above the following

conclusions can be madeThe electrical discharge between two electrodes immersed in

ethanol is a suitable method to produce in a controllable waynanoparticles with different contents of metal and carbon By varyingthe current value and its pulse duration morphology of nanoparticlesand their composition can be changed The average diameters of theprepared nanoparticles were in the range of 3-7 nm

Cu-based nanoparticles with different morphologies wereprepared via submerged electrical discharge of bulk copper and graphiteelectrodes in a CuCl2 aqueous solution Synthesized material wassubjected to laser-induced modification It was found that core-shellnanoparticles were formed by treatment of CuCl2 aqueous solution bythe arc pulsed discharge with pulse duration of 4 ms and peak current of10 A

The synthesis rate varied in range of 19 ndash 69 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofcopper and graphite electrodes The synthesis rate was found to behigher when copper was acting as an anode electrode The synthesis rate

179

increased with increasing of discharge current and decreasing of pulseduration The composition and morphology of nanoparticles were alsofound to depend on discharge parameters The copper nanoparticleswere only formed by dc-discharge treatment when copper was acting asan anode electrode The maximum diameter of nanoparticles did notexceed 50 nm while the minimum diameter was around 2 nm Theresults of the experiments imply that plasma treatment with longer pulseduration and lower current leads to the formation of carbon embeddednanoparticles TEM confirms the formation of encapsulatednanoparticles

Irradiation of nanoparticles in aqueous solution by a pulsedNdYAG laser at 532 nm was found to cause the shape change and sizereduction of the particles

AcknowledgementsThe work has been supported by the Integral Program of the

Siberian Branch of RAS under the Grant 138-T-09-CO-014 Authorsare thankful to KV Scrockaya for carrying out the TEM investigations

References

1 I Zalite S Ordanyan G Korb (2003) Synthesis of transition metalsnitridecarbonitride nanopowders and application of them formodification of structure of hardmetals Powder Metallurgy Journal46 2143 ndash 147

2 XG Yang and CY Wang (2005) Nanostructured tungsten carbidecatalysts for polimer electrolyte fuel cells Appl Phys Lett 8624104-1 -224104-3

3 M Rosenbaum F Zhao U Schroder F Scholz (2006) InterfacingElectrocatalysis and Biocatalysis with Tungsten Carbide A High-Performance Noble- Metal-Free Microbial Fuel Cell Angew Chem118 1-4

4 D Bera S C Kuiry M McCutchen S Seal(2004) In situ syntesis ofcarbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method J Appl Phys 96 5152-5157

5 P Serp M Corrias P Kalck Carbon nanotubes and nanofibers incatalysis Applied Catalysis A General ndash 2003 ndash Vol 253 ndash P337-358

180

6 Ishigami M Cummings J Zettl A Chen S (2000) A simple method forthe continuous production of carbon nanotubes Chem Phys Lett319 457-459

7 Sano N Wang H Alexandrou I Chhowalla M Amaratunga G A J(2001) Nanotechnology Synthesis of carbon ldquoonionsrdquo in waterNature (London) 414 506-507

8 Sano N Wang H Alexandrou I Chhowalla M Teo K B KAmaratunga G A J (2002) Properties of carbon onions produced by anarc discharge in water J Appl Phys 92 2783 ndash 2788

9 Sano(a) N (2004) Low-cost synthesis of single-walled carbonnanohorns using the arc in water method with gas injection J PhysD 37 L17-L20

10 Parkansky N Alterkop B Boxman R L Goldsmith S Barkay ZLereah Y (2005) Pulsed discharge production of nano- andmicroparticles in ethanol and their characterization PowderTechnology 150 36-41

11 Parkansky N Goldsmith S Alterkop B Boxman R L Barkay ZRosenberg Yu Frenkel G (2006) Features of micro and nano-particlesproduced by pulsed arc submerged in ethanol Powder Technology161 215-219

12 P Muthakarn N Sano T Charinpanitkul W TanthapanichakoonT Kanki Characteristics of Carbon Nanoparticles Synthesized by aSubmerged Arc in Alcohols Alkanes and Aromatics Phys Chem Bndash 2006 ndash Vol 110 37 ndash P 18299 -18306

13 D Bera G Johnston H Heinrich S Seal A parametric study on thesynthesis of carbon nanotubes through arc-discharge in water Nanotechn ndash 2006 ndash Vol 17 ndash P 1722-1730

14 Hsin Y L Hwang K C Chen R-R Kay J J (2001) Production and insitu metal filling of carbon nanotubes in water Adv Mater 13 830-833

15 Xu B Guo J Wang X Liu X Ichinose H (2006) Synthesis of carbonnanocapsules containing Fe Ni or Co Carbon 44 2631-2634

16 Lange X Sioda M Huezko A Zhu Y Q Kroto H W Walton D R M(2003) Nanocarbon prodction by arc discharge in water Carbon 411617 ndash 1623

17 Sergienko R Shibata E Akase Z Suwa H Nakamura T Shido (2006) Carbon encapsulated iron carbide nanoparticles synthesized in

181

ethanol by an electric plasma discharge in an ultrasonic cavitationfield Mater Chem Phys 98 34-38

18 Leo G H Jeong S H J W Ri H C (2002) Excelent magnetic propertiesof fullerene encapsulated ferromagnetic nanoclusters J Magn Mater246 404 ndash 411

19 Ang K H Alexandrou I Mathur N D Amaratunga G A J Hag S(2004) The effect of carbon encapsulation on the magnetic propertiesof Ni nanoparticles produced by arc discharge in de-ionized waterNanotechnology 15 520 ndash 524

20 Sano(c) N Nakano J Kanki T (2004) Synthesis of single-walledcarbon nanotubes with nanohorns by arc in liquid nitrogen Carbon42 686-688

21 Bera(c) D Jonston G Heinrich H Seal S (2006) A parametric studyon the synthesis of carbon nanotubes through arc-discharge in waterNanotechnology 171722-1730

22 Yeh M-S Yang Y-S Lee Y-P Yeh Y-H Yeh C-S (1999) Formationand characteristics of Cu colloids from CuO powder by laserirradiation in 2-propanol J PhysChem B 103 6851-6857

23 Aslam M Gopakumar G Shoba T L Mulla I S Vijayamohanan K(2002) Formation of Cu and Cu2O nanoparticles by variation of thesurface ligand preparation structure and insulating-to-metallictransition J Colloid Inter Sci 25579-90

24 Salkar R A Jeevanandam P Kataby G Aruna S T Koltypin YPalchik O Gedanken A (2000) Elongated copper nanoparticlescoated with a zwitterionic surfactant J Phys Chem B 104 893-897

25 Takami A Kurita H Koda S (1999) Laser-induced size reduction ofnoble metal particles J Phys Chem B 1031226-1232

26 Brown JB (1948-1949) The constitution of cupric chloride inaqueous solution Transaction of the Royal Sociaty of New Zeland 7719-23

162

MORPHOLOGICAL STUDY OF DETONATIONSPRAYED COATINGS OF CALCIUM HYDROXYAPATITE

DEPOSITED ON A NANOSTRUCTURED TITANIUMSUBSTRATE

AA Sitnikov VI Yakovlev YuP Sharkeev 1EV Legostaeva 1 AA Popova

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1Institute of Strength Physics and Materials Science SB RASTomsk

Biocompatible coatings are effectively formed by spraying ofcalcium hydroxyapatite Са10(РО4)(ОН)2 powders on a titanium substrateRecently along with the composition macro- and microstructuredevelopment the surface morphology of the coatings has receivedincreasing attention In a number of studies the roughness of thecoatings has been shown to significantly influence the inductionprocesses of cells As a substrate material titanium VT1-0 has beenchosen which has several advantages being highly biocompatiblebioinert practically non-toxic corrosion-resistant and possessing lowthermal conductivity and low coefficient of thermal expansion Themorphology of the gas-detonation sprayed calcium phosphate coatingsdeposited on ultrafine-grained and nanostructured titanium substratesand implant imitations has been studied The substrates and implantimitations were produced in the Institute of Strength Physics andMaterials Science SB RAS Tomsk

It was shown that the detonation sprayed hydroxyapatite powderswith particles ranging from 1 to 20 microm formed coatings non-uniform inthickness and phase composition The roughness of the coatings wasRa=365-472 microm (class 5) When hydroxyapatite particles of 20-100microm in size are sprayed coatings more uniform in thickness and phasecomposition are formed (Fig1) with an average roughness of Ra = 624microm (class 4) Preliminary treatment of the titanium substrate by sandingand chemical etching allows increasing the adhesive strength of thecoating up to 20MPa

163

Fig1 SEM images hydroxyapatite powder (a) detonation sprayedhydroxyapatite coating (b) XRD pattern of the coating (c)

Biological studies have demonstrated biocompatibility andbioactivity of the coatings It was found that the calcium phosphatedetonation sprayed coatings induce growth of tissue cells with 100probability which indicates that the relief of the coatings is optimal forfixation and aging of the cells Comparative studies of calciumphosphate coatings produced by detonation spraying and those producedby micro-arc in an electrolyte containing phosphoric acidhydroxyapatite and calcium carbonate have shown the advantages ofdetonation spraying for providing the required phase composition of thecoating This opens up a possibility of making two-phase coatings(hydroxyapatite and beta-calcium phosphate) ensuring the closest matchin composition to the bone tissue

ва б

100

200 20 30 40 50 60 70 80 90 10

(1

10) (002

) (2

10)

(2

11)

(

300

)

(3

10)

(

222

)

312

)

(3

20)

(

511

)

(

432

)

(5

22)

(

100

)

161

MICROSTRUCTURE STUDIES OF THE COATINGSPRODUCED BY ARC DEPOSITION OF THE

MECHANOACTIVATED SHS-COMPOSITE TIC+XME(R6M5 PR-N70H17S4R4-3) POWDERS

AA Sitnikov VI Yakovlev MA Korchagin1MN Seidurov ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

One of the main challenges in the development of new materialsfor arc deposition using flux-cored wires is to design materials of specialinterest using cost-effective and ecologically friendly technologies Asmaterialstechnologies meeting these requirements we can proposelayered composites produced by self-propagating high-temperaturesynthesis (SHS) in mechanically activated powder mixtures

The samples of SHS-mechanocomposites of TiC+XMe (R6M5PR-N70H17S4R4-3) composition arc-deposited on steel 45 substrateswere selected for investigations Microstructure of the arc-depositedcoatings was studied using a Carl Zeiss AxioObserver A1m OpticalMicroscope For observations cross-sections of the samples wereprepared and etched with a solution containing 20 potassiumferricyanide К3[Fe(CN)6] 20 КОН and 60 H2O Finemicrostructure and composition of the deposited layers were analyzedusing a Carl Zeiss EVO50 Scanning Electron Microscope equipped withan EDS X-ACT laquoOXFORDraquo device

The investigations show that the microstructure of the depositedlayers is uniform with submicron titanium carbide reinforcing phase inthe form of separate inclusions or chains of particles in the matrix

159

WEAR-RESISTANT DETONATION SPRAYED COATINGSBASED ON THE COMPOSITE MECHANICALLY ACTIVATED

SHS-MATERIALS

AA Sitnikov VI Yakovlev MA Korchagin 1DM Skakov AA Popova ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

The application of titanium carbide as a material for thermalspraying is rather difficult mainly due to its high melting temperatureand high hardness

A technology has been developed abroad for the production of thecomposite powders for spraying The production of these compositepowders is a laquoknow-howraquo of MBN Nanomaterialia (Italy)

An approach to the development of TiC-containing coatings canbe based on the technology of mechanocomposites with metallic orintermetallic matrices reinforced with nanosized particles of a ceramicphase [1] The technology of the powder preparation consists of 3 stagesAt the first stage the mixture of initial reactants which in this particularcase are titanium carbon and nichrome is mechanically activated (MA)in a planetary ball mill At the second stage self-propagating hightemperature synthesis (SHS) is conducted resulting in the formation ofTiC particles uniformly distributed in the metallic matrix AdditionalMA of the products of SHS at the third stage along with dispersingtitanium carbide particles creates a principally new state of the matrixwhich experiences grain refinement and shows high internal stresses andhigh concentrations of non-equilibrium defects In addition thesubsequent mechanical activation can be advantageously used forcompositions with higher matrix contents that are not possible to makethrough the SHS special additives can be also introduced into thecomposites at this stage

In order to compose the initial mixtures the following powderswere used titanium PTM lampblack PM-15 and nichrome PR-N70H17S4R4-3 Mechanical activation of the powder mixtures and theSHS-products was carried out in a planetary ball mill AGO-2M

160

Detonation spraying was performed using the laquoKatun-Mraquo set-upIt was found that the chemical composition did not change duringspraying

Wear resistance of the sprayed coatings was evaluated using afriction machine 2168 UMT in the laquoshoe-on-diskraquo mode A coating 02mm thick was deposited on a steel 40 shoe Prior to deposition the shoewas rubbed against the disk until a contact spot was formed over thewhole surface of the shoe After the coating was deposited the workingsurfaces were subjected to abrasive diamond treatment to reduce theirroughness

Tribological tests showed that with increasing metallic matrixcontent from 20 to 60 wt the weight losses under dry friction at 950 Nincreased almost twice Comparative tests of the coatings and thesamples of hardened steel revealed that the wear of the coatings obtainedfrom the mecahnocomposite powders was 8 times lower than that ofsteel 40H

References1 MAKorchagin DVDudina Application of self-propagating high-

temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007 v43 2 p176-187

153

CHEMICAL-THERMAL TREATMENT IN CARBONMANGANESE STEEL

AT INDUCTION-HEATING IN VARIOUS BORATINGCONDITIONS

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

Ural Federal University Ekaterinburg RussiaAltay State Agrarian University Barnaul Russia

Abstract Processes of borating of high-carbon manganese steel65Mn by carbide of boron and amorphous boron in conditions of fluxwith additives of various activators of borating are investigated at high-speed induction-heating It is shown that the nature of the boratingagent the additive of flux activators CaF2 and NH4Cl have influence onstructure and properties which are formed on a surface of boroneutectics

Keywords boron carbide of boron induction heating chemical-thermal processing

Among modern processes of chemical-thermal treatment (CTT)production engineering of saturation of surface layer constructional andalloy steels with boron ndash the borating occupy a special place In boratingit is possible to obtain the extended beds distinguished by high hardnessand strength corrosion-resistance abrasive durability and highreceptivity to wear on a surface of a steel detail [1 2] However themajority of known processes of borating are prolonged and are badlybuilt in into flow diagrams of state of productions

Intensification of CTT processes and in particular borating canbe carried out with application of technology of short-term high-speedheating of steel detail surface with the borating composition put on herrf currents (RFC) up to temperatures of formation of new phases andeutectics (1100-1350 оС) in systems Fe-B Fe-B-C and Fe-Me-B-Cwhere Ме - is an alloy element from group Cr Mn Ni etc [3] Unlikewell investigated processes of borating of alloy steels by mediums anddaubing at temperatures up to 950оС [4] there are open generalquestions of peculiarities of chemical interaction of components in suchsystems phase condition and properties of formed products

154

In the present work chemical-thermal treatment of carbonmanganese 65Mn steel combined with RFC-heating of its surface invarious borating conditions has been investigated

Experimental partAs the basic subject of research 65Mn (GOST 4543-71) alloy

carbon steel was chosen from the group of the same kind manganesechromos chromos-nickel and chromos-manganese steels from group 70U8А 50CrMnА 30CrMnSiА 45Cr 70Mn etc with similar propertiesand composition

Technical carbide of boron B4С in accordance with GOST 5744-85 and reactive amorphous boron of qualification reagent-grade weretaken as borating agents of different nature Known composition for theinduction deposition (F1) consisting of borax glass the boric anhydridecalcium silica and welding flux АN-348А (30 Na2B4O7 20 B2O310 CaSi2 and 40 flux АN-348А) was used as flux Reagent-gradeCaF2 and NH4Cl served as activators

RFC-heating of samples was carried out in a loopback water-cooled copper inductor by diameter of 160 mm connected to RF-lampgenerator VCG 7-600066 The adjustment of a contour and geometryof an inductor provided heating of researched samples to the temperatureof 1300-1350оС during 40-60 sec with the subsequent stabilizationAfter holding at the specified temperature during from 1 up to 2 minsamples were pulled out from an inductor and cooled down loosely

Microstructure of the coverings formed has been investigated andthickness of borated bed has been determined (МIМ-7 Neophot-30)hardness has been measured (PМТ-3 by 50 100 g) phase composition(DRON-2 radiation Co-Kα speed of angular moving of a sample of 1grads min) has been determined

Results and discussionIt is known that classical production engineering of kiln borating

are based on gradual (during 05-6 h) saturation of a surface of a steelproduct by boron from various pastes daubings liquid or a gaseous fluidat temperatures of process from 750 up to 950 оС Thus in the capacityof sources of boron its various compounds (В2О3 В4С ВF3 Na[BF4]etc) are applied capable to decay on active elements at temperatures ofprocess Depending on a phase condition of the borating agent hardness

155

and liquid borating are distinguished and also borating from a gas phase[4] We investigated six variants of mixes for high-speed borating atRFC-heating steel 65Mn Mixes differed in the nature of the boratingagent e borating agent composition presence fluxes componentsactivators and technological additions Compositions of the mixes usedare given in table 1

Table 1

Mixes Boratingagent

Activator Flux

Iа B4C (84) NH4Cl (6) F1 (10)II B4C (84) ndash F1 (16)

IIIа B (90) CaF2 (5) F1 (5)

Mixes I Iа II and IIа used as borating agent contained carbide ofboron mixes III IIIа - amorphous boron in mix Iа activator chloride ofammonium and in mix IIIа - fluoride of calcium has been added allmixes contained melted flux as a fluxing component for inductiondeposition F1

With decrease of density of a borating phase and increase intemperature of process its speed in the interval of temperatures from 800up to 950 оС increases insignificantly therefore for their intensificationcollateral saturation of a surface by several elements at once or thermocycling are applied [5] If the temperature of the process exceeds 1100-1300 оС in an aspect of beginning processes of high-temperaturestructural reorganization in steel speeds of borating sharply increase in2-4 min with the increase in temperature at every 15-20 оС thus theprocess passes from a diffusive zone to a zone of chemical reaction Soat the temperature of 1200-1300 оС according to the data[6] it ispossible to obtain in a few minutes the thickness of the single-phaseboron-bed up to 02-04 mm thus heating of a detail is carried out by thespecial thermo reaction mix

At RFC-heating of the steel 65Mn covered by researched boratingcompositions with chosen parameters of process fig 1 adamantinecoverings are formed on all samples resembling bed covered hard metalX-ray analysis of a material of coverings has shown presence of Fe

156

borides FeB and Fe2B carbon-borides Fe3(C B) and Fe23(C B)6 variousmeta- and orto-borates of iron (Fe3BO3 Fe3BO6 Fe3BO5) traces FeOand FeOFe2O3 Thus at RFC-heating of alloy carbon steels under bedof flux F1 containing from 84 up to 90 of borating agents complexboron-phases are formed on their surfaces hardening a surface of a detailand it is strongly linked with it and oxide films are removed togetherwith slag

To find out the characteristics and structure of received beds andthe conditions of borides in them photomicrography of micro sectionswas taken Typical structures of boron-beds are given in fig 1

a b C

Fig 1

As it is seen from fig1 with the chosen heating environments andthe time of borating the structure and the condition of boundary line ofreceived wear-resistant beds differ but in all cases as against classicalboron two-phase beds on a surface of samples the eutectic with stronglypronounced or with the diffusive boundary line separating it from anoriginal material is formed faster in conditions of heavy abrasive sign-variable and shock wear boron-plate Apparent changes in structure ofparent metal caused by its short-term overheat were not observed

For the mixes containing in the capacity of borating agent equalquantity of carbide of boron similar quantity of fluxes-component anddistinguished only by the presence of activator NH4Cl promoting areinforcement of convertible diffusive and transport reactions especiallyat low temperatures right at the beginning of the process of borating (Т

157

lt300 оС) formation of fine grained structure of eutectic turnings on withhardness not above 700-750 HV thickness of bed of 016 mm and withlegibly discernible interface with parent metal (fig 1а) is observed

For the analogous mix II without this activator the expressedpropagation of dendrites islands and druses of boron-phases withhardness up to 1050-1120 HV thickness of bed of 028 mm and adiffuse interface boron bed with parent metal (fig 1b) is observed Themixes on the basis of amorphous boron (fig 1c) appeared to be the mostreactive thus in mix IIIа containing follow-up 5 of activator CaF2 and5 of fluxes component beyond chosen relationships for 1 minthickness of bed on steel of 65Mn has made 088 mm at its hardness in2200-2300 HV The structure represents the remote eutectichomogenized iron ndash boron formed with such speed that from a melt atits solidification balls of slag had not time to bleed up to the end

Thus amorphous boron which at the presence of flux F1 andactivator CaF2 under the chosen conditions of experiment forms denseclose-grained beds on a surface of alloy steels with depth up to 800microns with hardness up to 2400-2500 HV (fig 2) appeared to be themost efficient borating agent at RFC-heating

Fig 2

It is interesting to note that the structure of the wear-resistantcovering obtained at high-speed 1 min borating steel 65Mn a mix II ismetastable and at borating during 2 min like in picture 1а with hardness2300-2400 HV turns to the fine grained structure and thickness of a

158

covering does not change and the interface with parent metal becomesdiscernible

References1 Methods of raise of longevity of machine components Red VN

Tkacheva M 19712 Belyj AV Karpenko GD Myshkin KN Structure and methods of

formation of wear-resistant surface layers M 19913 Tkachev VN Fishtejn BM Kazintsev NV Aldyrev DA

Induction overlaying welding of hard metals M 19704 Voroshnin LG Lyahovich LS Borating of steel M 19785 Guryev АМ Kozlov EV Ignatenko LN Popova NA Physical of

a basis of thermal-cycle borating Barnaul 2000

138

PHASE STATES OF MECHANOACTIVATED MANGANESEOXIDES

SA Petrova RG Zakharov AYa Fishman LI LeontievInstitute of Metallurgy Ural Division of RAS Ekaterinburg 620016

Russian Federation

An investigation of structural characteristics of the manganeseoxides in order to understand these characteristics affected bymechanochemical treatment conditions has been undertaken Chemicallypure manganese (II III IV) oxides were used as the initial componentsIt is shown that the properties of the mechanoactivated oxides differgreatly from those of initial materials Relationships among structuralcharacteristics of the mechanoactivated oxides and their prehistory wayand conditions of producing have been detected

IntroductionStudy of phase states of mechanoactivated oxides makes it

possible to analyze the patterns of expression of the mechanochemicaleffect in redox processes to determine the mechanism of the effect ofactivation processes on the type and parameters of the structural phasetransitions to establish the role of higher oxides in the redox processesAs one of the consequencies of the intensive mechanical activation is theappearance of nanodisperse states specificity of phase transformationsin nanocrystalline oxides is considered at the same time

It is known now that the decrease in the crystallite size inmechanoactivated systems causes a decrease of structural phasetransition temperatures In metallic alloys reducing of crystallites size isaccompanied by suppression of martensitic transitions [1-2] Completeinhibition occurs when the grain size becomes smaller than that of thecritical nucleus of a new phase It can be regarded as established that theparameters of phase transitions in oxides with relatively lowtemperatures of phase transitions also depend strongly on the grain sizeFor example in barium titanate BaTiO3 transition from cubic to low-symmetry phase is completely suppressed when the grain size is about10 nm [3] Changes in the crystal structure and the effects of reduction(the change of temperature and phase transition heat) in the structuralphase transitions with decreasing grain size also occurred for the oxides

139

Al2O3 Fe2O3 PbTiO3 PbZrO3 La1-xSrxCuO4 YBa2Cu3O7-δBi2CaSr2Cu2O8 [4] and several other oxides [5-6] Besides for the oxidesin nanoscale state the coexistence of two different structuralmodifications [7] was observed The processes of mechanoactivationmay also lead to new types of metastable phase states due to theredistribution of cations between the crystallographically inequivalentsublattices [8]

In the present work the main attention is paid on the analysis ofthe effects associated with the evolution of metastable structures underconditions of temperature increase and oxide interaction with anaggressive environment So far the main contribution to theinvestigation of these issues has made the study of metallic alloys (seefor example [9-10]) The behavior of the activated oxide materials ismuch less studied Study of structural phase transitions in the systemMn-O subjected to mechanochemical activation and structuralcharacteristics of the crystalline phases allows us to test how general arepreviously established patterns for systems with different types ofchemical bonds

The effect of mechanical activation on structural phase transitionsboth of martensate type (from cubic to tetragonal modification Mn3O4)and those accompanied by redox processes (between phases withdifferent degrees of oxidation etc) is investigated The choice of Mn-Ooxides as the object of study is largely connected with the fact that atleast two structural phase transitions observed in the considered crystalswith temperature changes involved the cooperative Jahn-Teller (JT)phase The value of the JT deformation in it is determined by theconcentration of JT ions in octahedral sites that allows to get additionalinformation about the structural changes caused by themechanoactivation of oxide

1 Production and structural properties of themechanoactivated oxides

11 Mechanoactivation of manganese oxidesPure manganese oxides MnO2 Mn2O3 and Mn3O4 annealed at

200deg 900deg and 1250degC respectively were used as the initial materialsFor the mechanical treatment of oxides which was described in

detail in [1112] a planetary mill AGO-2 with water-cooled drums (V =

140

150ml) and a centrifugal factor up to g = 60 [3] was used Download ofballs was 203g the material - from 5g Milling was made dry Theprocessing of powders was carried out after preliminary lining in acontinuous mode or with periodic stops of the mill According toestimates (performed by XPES) contamination by iron was not morethan 02 Previously [14] we found that prolonged continuousmechanical treatment leads to the fact that within the grains matureduring the first seconds along with a further (slow) reduction ofcoherent scattering blocks chemical processes begin leaking Because atthis stage the main purpose was to obtain single-phase samples theduration of continuous grinding was restricted by 30s The temperatureinside the drums during grinding did not exceed 320K which ensuredthe preservation of initial metastable phases During stops of mill thedrums where opened and powder was manually stirred but samplingwas not performed

To be able to conduct magnetic research on the mechanicallyactivated samples and to investigate the effect of intensity ofmechanoactivation (the degree of deformation) on the redox processesand the stability of weakly activated oxides the part of samples wasobtained as a result of mechanical activation in the vario-planetary millPulverizette 4 (Fritsch) in glasses of tungsten carbide Volume of drumwas equal to 250ml loading of crushing balls was 800g and a materialmass was 20 g Milling was made dry the duration was 3 min

12 Attestation of mehanoactivated manganese oxides andmethods of their experimental study

The phase composition of obtained substances the size ofcoherent scattering domains (CSD) and microstresses were determinedby X-ray diffractometer D8 ADVANCE (Bruker) (radiation CuKα Ni-filter position-sensitive detector VANTEC1) High-temperature X-raystudies of the stability of mechanoactivated oxides was carried out usinghigh-temperature chamber HTK1200N (Anton Paar)

The particle size of powders obtained was assessed by dynamiclight scattering using a laser analyzer DelsaNanoC (Beckman Coulter)and an atomic force microscope Solver-Next (NT-MDT) Surface ofoxides was studied by XPES and STEM (Omicron Multiprob)

High-temperature X-ray studies were performed in the range 30-1200degC in air The rate of heating and cooling was 05degCmin Step of

141

the temperature during heating and cooling was 5deg and 10degCrespectively Exposure in the point was 17s (the time of isothermal delayshooting diffractogram was 150s) For the analysis of diffractionpatterns the software package DIFFRACplus [15] was used

13 Results and discussionThe results of the attestation of the initial and mechanoactivated

oxides are presented in Table 1

Table 1 Treatment conditions and characteristics of the manganeseoxides

Cell parameters Initial phasetreating mode

Finalcomposition аAring сAring

Samplename

1 Mn2O3- initial Mn2O3 9412 M232 Mn2O3- AGO 30s Mn2O3 9410 M23A303 Mn2O3- AGO 60s Mn2O3 9410 M23A604 Mn2O3- AGO

10minMn2O3 9410

M23A10

5 Mn2O3- P4 3min Mn2O3 9403 M23P46 Mn2O3-

P4(3min)+USD(70s)Mn2O3 9403

M23P4U

7 Mn3O4-initial Mn3O4 5760 9474 M348 Mn3O4- AGO 30s Mn3O4 5762 9442 М34А309 Mn3O4- AGO 60s Mn3O4 5762 9431 M34A60

5787 950810 Mn3O4- AGO10min

Mn2O3+ Mn3O4

9410M34A10

11 MnO2-initial MnO2 4396 2869 M1212 MnO2- AGO 30s MnO2+Mn2O3(tr) 4397 2872 М12А3013 MnO2- AGO 60s MnO2+Mn2O3(tr) 4397 2872 M12A6014 MnO2- AGO 10min Mn2O3 9408 M12A10

AGO-High-energy planetary mill (60g) P4-Pulverisette 4 (~20g)USD-Ultrasound disintegrator

Since the analysis of the results of mechanoactivation of oxidesMn2O3 showed little difference between the samples activated in theAGO within 30 and 60 seconds further investigation of oxides Mn3O4

and MnO2 was performed on 60-second samples However it is

142

necessary to note that in the case of oxide MnO2 samples after 30 and60-second milling contained different amounts of Mn2O3

According to X-ray phase analysis data chosen mode ofmechanochemical treatment allowed to preserve essentially thecomposition of the initial oxides The exceptions were oxides MnO2which after grinding contained 5 of oxide Mn2O3 and Mn3O4 whichafter grinding for 10 minutes contained a few of Mn2O3

Data on grain size and the coherent scattering domains arepresented in Table 2 It is obvious that even a relatively weakmechanical treatment leads to a decrease in grain size in 2-3 times Inthis case the comparison of grain size and the CSD (comparison of thedynamic light scattering data and X-ray diffraction (XRD) results)shows that the mechanical treatment with a small degree of deformationallows to obtain defect-free grains while increasing of the centrifugalacceleration leads to the appearance and rise of the defects in the grainA tendency to agglomeration of grains with increasing time of intensemechanoactivation should be noted

Table 2 The characteristics of coherent-scattering domains and averagegrain size

Sample nameCoherent-scattering domain

nmGrain size nm

M23 gt200 1026plusmn95M23A30 30 436plusmn168M23A60 23 344plusmn155M23A10 24 939plusmn175M23P4 44 386plusmn50

M23P4U 44 336plusmn22M34 gt200 400plusmn801300plusmn300

M34A60 15 529plusmn340

M34A10 1913 795plusmn104

M12 gt200 428plusmn78M12A60 61 1133plusmn167M12A10 22 565plusmn343

XRD-dataDynamic light-scattering

data

143

Changes in phase composition during heating and cooling ofinitial and mechanically activated manganese oxides are presented inTables 3-4 and Fig 1-2

Comparison of the temperature behavior of the initial unactivatedoxide Mn2O3 and that of grinded for 3 minutes with a force of less than20g shows that mechanoactivation treatment with a small amount ofcentrifugal factor and short times can save not only the phasecomposition but apparently and generally does not alter the propertiesof the powder While increasing the degree of exposure (eg use of millssuch as AGO-2 with acceleration 60g) even at short times leads to achange in system characteristics (the appearance and growth of defectsredox processes) that affect later on behavior of oxide For examplemechanoactivation treatment leads to a shift of phase transitiontemperaures at thermal processing as well as to change of the structuralcharacteristics of the phases formed In particular to different degrees oftetragonal distortion of hausmannite formed during heating Mn2O3 (Fig4)

Table 3 The phase composition of the initial andmechanoactivated manganese oxides at different temperatures

Heating CoolingSample MnO2 Mn2O3 Mn3O4 Spinel Mn3O4 Mn2O3 Phase

1 2 3 4 5 6 7 8- + 920 1140 1120 - appearanceM23

- 955 1170 1010 + - disappear

- + 950 950 1010 - appearanceM23A30

- 995 1105 730 + - disappear

- + 950 950 1040 - appearanceM23A60

- 1000 1120 840 + - disappear

- + - 950 840 840 appearanceM23A10

- 1000 - 290 + 770 disappear

- + 940 1140 1120 - appearanceM23P4

- 980 1165 1080 + - disappear

- + 935 1140 1120 - appearanceM23P4U

- 980 1170 1050 + - disappear

144

1 2 3 4 5 6 7 8

- 685 + 1125 1090 - appearanceM34

- 945 1160 1010 + - disappear

- + appearance370

655

970 1050 -

disappear

900 appearance

M34A60

-

970

1130

880 + -

disappear

- + + 930 880 - appearanceM34A10

- 1005 655 600 + - disappear

+ 550 950 1155 1120 870 appearanceM12

595 1025 1170 1070 + + disappear

+ + 940 985 1110 750 appearanceM12A60

535 985 1165 840 + + disappear

- + 960 960 1000 790 appearanceM12A10

- 1005 1075 630 + + disappear

Table 4 The temperature boundaries of the phases during heating andcooling

Heating CoolingSample Phase

from to from to

1 2 3 4 5 6

Mn2O3 30 955 - -

Mn3O4 920 1170 1120 30

M23

Spinel 1140 1200 1200 1010

Mn2O3 30 995 - -

Mn3O4 950 1105 1010 30

M23A30

Spinel 950 1200 1200 730

Mn2O3 30 1000 - -

Mn3O4 950 1120 1040 30

M23A60

Spinel 950 1200 1200 840

Mn2O3 30 1000 840 770

Mn3O4 - - 840 30

M23A10

Spinel 950 1200 1200 290

145

1 2 3 4 5 6

Mn2O3 30 980 - -

Mn3O4 940 1165 1120 30

M23P4

Spinel 1140 1200 1200 1080

Mn2O3 30 980 - -

Mn3O4 935 1170 1120 30

M23P4U

Spinel 1140 1200 1200 1050

Mn2O3 685 945 - -

Mn3O4 30 1160 1090 30

M34

Spinel 1125 1200 1200 1010

Mn2O3 370 970 - -

Mn3O4 30 655

Mn3O4 900 1130

1050 30

M34A60

Spinel 970 1200 1200 880

Mn2O3 30 1005 - -

Mn3O4 30 655 880 30

M34A10

Spinel 930 1200 1200 600

MnO2 30 595 - -

Mn2O3 550 1025 870 30

Mn3O4 950 1170 1120 30

M12

Spinel 1155 1200 1200 1070

MnO2 30 535 - -

Mn2O3 30 985 750 30

Mn3O4 940 1165 1110 30

M12A60

Spinel 985 1200 1200 840

Mn2O3 30 1005 790 30

Mn3O4 960 1075 1000 30

M12A10

Spinel 960 1200 1200 630

146

a d

be

c fFig 1 The temperature boundaries of the phases during heating and coolingof initial and mechanoactivated Mn2O3 a - original b - M23P4 c -M23P4U d-M23A30 e-M23A60 f-M23A10

147

a

b

cFig 2 The temperature boundaries of the phases during heating and cooling of

initial and mechanoactivated Mn3O4 a-initial b-M34A60 c-M34A10

148

a

b

cFig 3 The temperature boundaries of the phases during heating and cooling ofinitial and mechanically activated MnO2 a - initial b - M12A60 c - M12A10

149

Fig 4 Temperature dependence of the degree of hausmannite tetragonaldistortion for samples with different prehistories

The growth of the crystallite size of mechanoactivated phase withtemperature is shown in Fig 5 Data are shown for the initial phasebelow the temperature of the corresponding phase transition

It is obvious that prolonged treatment in the high-energy millalmost did not give reduction of coherent scattering domains butessentially affected the thermal stability of investigated oxide

150

Fig 5 Temperature dependences of coherent scattering domain size in oxideMn2O3 with varying degrees of mechanoactivation

ConclusionThe main results of investigations are the followingI The conditions of mechanochemical treatment enabling to make

the transfer of Mn-O system to single-phase nanosized state withoutsignificant changes in composition of the initial oxide are found Theexception was oxide MnO2 which after grinding contained a smallamount of oxide Mn2O3

II It is shown that the use of mill of the type AGO-2 with 60gacceleration even at short times of activation treatment of oxides leadswhile maintaining the single-phase of sample to an appreciable changeof lattice parameters growth of stresses and the appearance of defects

III It is found that despite the relaxation character of the evolutionof these metastable structures in the face of rising temperatures there is ashift of phase transition temperatures and changes in structuralcharacteristics of the newly formed phases in comparison with the initialoxides Including marked changes in the parameters of the JT strain (ca

151

- 1) at high-temperature transitions between cubic and tetragonal phasesof oxide Mn3O4

IV It is shown that more prolonged mechanical activation ofoxides MnnOm activates redox processes in these materials theemergence of two-phase states with different degrees of oxidation andeven a complete change of the manganese oxidation degree

V The temperature boundaries of existence of phases duringheating and cooling were determined for the initial andmechanoactivated oxides MnnOm Not only noticeable quantitativedifferences in the position of phase boundaries but also qualitativedifferences in the constructed phase state diagrams were found

This work was supported by RFBR (grant 10-03-96016-p_ural_a) the Program of fundamental research of Presidium ofRussian Academy of Sciences N 27 ldquoFoundations of fundamentalresearch of nanotechnology and nanomaterialsrdquo and the Federal TargetProgram Scientific and scientific-pedagogical staff of innovationRussia (contract 02740 110641)

References1 Glezer AM Blinov EN Pozdnyakov VA Martensitic

transformations in microcrystalline ferro-nickel alloys Izvestiya Aseries of Physical 2002 V66 N9 pp1263-1275

2 Andrievsky PA RAGULYA AV Nanostructured materialsMoscow Academy 2005 192p

3 Polotai AV Ragulya AV Skorohod VV Nanocrystalline BaTiO3

synthesis sintering and size effect Science o Sintering CurrentProblems and New Trends Beograd Kluwer Academic Publishers2003 pp119-125

4 PAyyub VRPalkar SChattopadhyay et al Effect of Crystal SizeReduction on Lattice Symmetry and Cooperative Properties PhysRev B 1995 V51 N9 pp6135-6138

5 Parathasarathi Mondal Dipten Bhattacharya Pranab ChoudhuryDielectric anomaly at orbital order-disorder transition inLaMnO3+ J Phys Condens Matter 2006 V 18 p6869

6 Nandini Das Parathasarathi Mondal Dipten BhattacharyaPartical size dependence of orbital order-disorder transition inLaMnO3 Phys Rev B 2006 V74 p 014410

152

7 VYa Shevchenko OL Khasanov GS Yuriev etc The coexistence ofcubic and tetragonal structures in the nanoparticle of ZrO2Y2O3

oxides Neorg Mater 2001 V37 N9 pp1117-11198 AYa Fishman MA Ivanov SA Petrova et al Specific Features of

Jahn-Teller Structure Phase Transitions in NanocrystallineMaterials Defect and Diffusion Forum 2009Vols 283-286 pp53-58

9 Grigorieva ТF Barinova AP Lyakhov NZ Some features of themechanical alloying in the systems Cu-Bi and Fe-Bi J Metastableand Nanocryst Mater 2003 V15-16 pp475-478

10 Lyakhov N Grigorieva T Barinova A Lomaeva S Yelsukov EUlyanov A Nanosized mechanocomposites and solid solution inimmiscible metal systems J Mater Sci 2004 V39 N 16-17pp5421-5423

11 Zyryanov VV Journal of Structural Chemistry 2004 V45 pp135-143

12 Zyryanov VV Lapina OB Neorg Mater 2001 V37 N3 pp331-337

13 Zyryanov VV Sysoev VF Boldyrev VV Korosteleva TVCertificate of authorship of USSR N 1375328-BI-1988 N 7 p39

14 Fishman AYa Ivanov MA Petrova SA Zakharov RGStructural Phase Transitions in Mechanoactivated ManganeseOxides Defect and Diffusion Forum 2010 Vols 297-301 pp 1306-1311

15 DiffracPlus TOPAS Bruker AXS GmbH OstlicheRheinbruckenstraszlige 50 D-76187 Karlsruhe Germany 2008

118

EFFECT OF HARDENING TEMPERATURE ON THE STRUC-TURAL-MORPHOLOGICAL CHARACTERISTICS OF METAL

CEMENTS BASED ON MECHANOSYNTHESIZED COPPERCOMPOUNDS

NZ Lyakhov1 PA Vityaz2 SA Kovaleva2 TF Grigoreva1VG Lugin3 AP Barinova1 SV Tsybulya4

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS630128 Novosibirsk Kutateladze str 18 grigsolidnscru

2 United Institute of Mechanical Engineering NAS Minsk Belarus3 Belarussian State Technological University Minsk Belarus

4 G K Boreskov Institute of Catalysts SB RAS Novosibirsk Russia

IntroductionMetal cements may be used in many branches of industry due to

good adhesion to the materials of different types (glass ceramics metalsetc) and the metal character of thermal and electric conductivity Theformation of metal cements occurs through the interaction of copper(nickel) alloys with liquid metals and alloys Interactions of a solid metalwith liquid one in particular copper with gallium are known [1 2] tohave diffusion character they are substantially affected by temperatureand the area of contact between the reagents

The use of mechanically synthesized copper compounds allowsone to increase the contact surface between the components and to intro-duce doping elements (Bi In) that improve wettability during gluing andthe strength properties of the alloys to be formed This causes a changeof the kinetics of interaction between a solid metal and a liquid one dueto the acceleration of diffusion processes and due to the formation ofadditional phases

The goal of the present work is investigation of the effect of hard-ening temperature on the structural-morphological characteristics ofmetal cements obtained on the basis of CuBi mechanocomposites andsupersaturated solid solutions Cu(In)

Methods and materialsCopper powder PMS-1 (GOST 4960ndash75) granulated bismuth (TU

6-09-3616ndash82) indium (GOST 10297ndash94) were used in the work Me-chanical activation of the powders was carried out for 15 min in the

119

high-energy ball planetary mill AGO-2 with water cooling in argon at-mosphere (cylinder volume 250 cm3 ball diameter 5 mm loaded wt200 g the weighed portion of the sample under treatment 10 g the fre-quency of rotation of the cylinders around the common axis about 1000rpm) Mechanocomposites having the composition Cu 10 wt Bisolid solutions Cu-12 wt In were obtained [3] Diffusion-hardeningalloys were prepared by mixing the mechanosynthesized copper com-pounds with gallium melt followed by exposure at a temperature of 20C during the whole process of alloy formation To study the effect oftemperature on the structure and morphology of metal cements harden-ing was carried out at 90 С 120 С and 160 С

Surface examination was carried out with the NT-206 atomicforce microscope (Microtestmachines Gomel) using standard commer-cial V-type probes NSC11 (Mikromasch) in the contact mode

The structure of the resulting samples was studied using Mikro200 optical microscope and high-resolution scanning electron micro-scope (SEM) MIRATESCAN with an attachment for micro-X-ray spec-tral analysis (MXSA) The diameter of the electronic probe was 52 nmexcitation region was 100 nm Images were obtained in the mode of re-cording secondary and backward scattered electrons which allowed usto investigate the distribution of chemical elements over the surface andto establish its composition non-homogeneity

The phase composition of powders after mechanical activationand the final products of their interaction with liquid gallium were de-termined with the help of X-ray diffraction techniques X-ray structuralanalysis and semi-quantitative examination of the products were carriedout with the D8 Advance Bruker diffractometer (Germany) by means ofpowder X-ray diffraction in the θ-2θ configuration with a step of 01Phase identification was performed using the diffraction patterns re-corded in CuKα radiation (154051 Aring)

Calorimetric measurements were carried out with Netzsch STA409 PCPG instrument in argon atmosphere in a crucible made ofAl2O3 within the temperature range from room temperature up to 290 Cwith the heating rate of 20 min

120

Results and discussionIt was established in the previous diffraction studies of alloy for-

mation dynamics in CuBi + Ga and Cu(In)+Ga that the formation ofnew phases takes place within a broad time interval During the interac-tion of CuBi mechanocomposite in Bi that is insoluble in copper and ingallium the formation and crystallization of the intermetallic compoundCuGa2 and bismuth take place simultaneously [4]

For the case of Cu(In) solid solution in which the doping elementis soluble in gallium the formation of the phase of solid solution of in-dium has an incubation period of about 210 minutes which is determinedby its concentration in the system with gallium [5]

The interaction processes are described with the following chemi-cal reactions

CuBi + 2 Ga rarr CuGa2 + BiCu(In) + 2 Ga rarr CuGa2 + In(Ga)

1 Effect of the temperature of interaction of CuBimechanocomposites with liquid gallium on the structure andmorphology of the formed metal cementsIt is known that the resulting mechanocomposites are nanosized

copper surrounded by a thin bismuth layer [6] Bismuth is mainly com-posed of the particles less than 5 nm in size

According to the data of AFM topography the size of mechano-composite particles is 150divide250 nm (Fig 1)

Fig 1 Mechanocomposite Cu + 10 wt Bi after activation for 15 mina ndash SEM image b ndash AFM c ndash TEM

121

At first we studied the interaction of CuBi with liquid gallium atroom temperature

The X-ray structural analysis of the resulting cement carried outafter the interaction for 4 and 48 hours showed that the size of the crys-tallites of the intermetallic compound increases from ~ 200 nm to ~ 550nm The size of bismuth crystallites increases up to 100 nm It should benoted that this is accompanied by a decrease in the size of copper crys-tallites down to ~ 10 nm The final phase composition is determined asCuGa2 Bi and unreacted copper (Fig 2)

Fig 2 Diffraction patterns of the product of interaction Cu 10 Bi + Ga

Figure 3 shows the high-resolution SEM images of the micro-structure of the surface of the final interaction product The SEM imageof sample surface after hardening without the mechanical treatment ofthe surface is shown in Fig 3a The image of the surface obtained in thebackward scattered electrons after sample polishing is shown in Fig 3bBecause bismuth is the heaviest element in this system it will be distin-guished by the maximal brightness in the SEM image

The data obtained by means of microscopy show that the structureof the surface of final product is facetted tetragonal crystals СuGa2 withthe size up to 4 μm Bismuth is localized at the faces of crystals and at

122

the boundaries of CuGa2 grains as disperse formations 70-250 nm insize and also forms separate grains with a size up to 10 μm

a bFig 3 Topography of the surface of CuGa2 +Bi alloy after the interaction for48 hours a ndash SEM image of non-polished sample in direct electrons b ndash SEM

image of the polished sample in backward-scattered electrons

The use of AFM allowed us to study the microstructure of facet-ted tetragonal CuGa2 crystals The presence of screw dislocations inthem may be stressed as a result the crystalline layer grows by windingcontinuously on itself so the step takes the shape of a spiral (Fig 4) Thelayer-by-layer growth of crystallographic facets should also be men-tioned The edges of incomplete layers or steps move along the facetwhile they grow The step height that is the thickness of the depositinglayer varies within the range 4 to 200 nm The appearance of highgrowth steps may cause trapping of the melt drops and precipitation ofinsoluble bismuth admixture on the surface of steps of the growing crys-tals which is indeed observed in Fig 4 b Bismuth is adsorbed on facetssteps and along the grain boundaries

It should be stressed that the growth of faceted crystals requiresspecial conditions supersaturation or supercooling of the mother me-dium small number of appearing nuclei We suppose that the localthermal supercooling arises as a consequence of the chemical interactionof copper with gallium melt on the interface between the solid phase andthe liquid one with the formation of chemical compound CuGa2 withcrystallization temperature higher than the temperature of the melt Theconditions of substantial supercooling are created for this compound soits crystallization starts In this process bismuth particles get released

123

into the melt Thee particles are insoluble in liquid gallium and may actas the centres of crystallization and also they may brake down thegrowth of intermetallide particles by getting adsorbed on their surfaceThe latent heat of melting released during crystallization raises the tem-perature of the melt (so gallium remains in the liquid state during reac-tion at 20 C) and decreases the degree of overcooling thus creating theconditions for the growth of larger facetted intermetallide crystals fromthe melt

а b

Fig 4 AFM image of the surface of resulting alloy CuGa2 + Biа - Torsion-image of bismuth on facets and growth steps of CuGa2 (the contrastis formed due to the difference in tribological characteristics of the phases of

intermetallide and bismuth) b ndash layered spiral growth of CuGa2 crystals alongthe screw dislocation (marked with arrows) The upper part shows a scheme ofcrystal growth along the screw dislocation and the shape of the step formed inspiral growth [7]

At room temperature the final product of the interaction of CuBimechanocomposite with liquid gallium is a matrix composed of CuGa2

intermetallide particles 1ndash4 μm in size with bismuth particles distrib-uted in it (from 70 to 250 nm) which form local agglomerations up to 10μm in size

X-ray studies of the alloys obtained at hardening temperature of90 and 120 C showed that an increase in temperature to 120 C does notaffect the phase composition Similarly to the case of room temperature

124

the product is composed of intermetallide CuGa2 (PDF-2 No 25-0275)bismuth (PDF-2 No 44-1246) and residual copper (PDF-2 No 04-0836)(Fig 5)

Fig 5 Diffraction patterns of CuGa2 + Bi samples obtained at temperature 40(a) 90 (b) and 120 (c) C Unmarked peaks relate to CuGa2 intermetallide

With an increase in the interaction temperature the lattice pa-rameters of copper and CuGa2 phases remain almost unchanged Thesize of copper crystallites is about 35 nm Bismuth undergoes tempera-ture-caused changes An increase in the size of bismuth crystallites from100 nm at 20 C to 180 nm at 90 C and to more than 500 nm at 120 C

Alloys obtained by mixing the CuBi mechanocomposite with liq-uid gallium have a composite structure after hardening Their structuremay be described as an intermetallic shell with the unreacted part ofcopper in its centre The СuGa2 intermetallide has a shape of facetedtetragonal crystals up to 4 μm in size With an increase in reaction tem-perature to 90 C the size of het particles of intermetallic compund in-creases to 6-8 μm and remains almost the same at a temperature of 120C In the lateral contrast mode the facets of crystals obtained at 90 and120 C exhibit local accumulations of bismuth as well as substantial de-formation distortions of crystals due to the arising stretching strain inthe crystal in the direction lt001gt (Fig 6) Intermetallide crystal starts to

125

have layered structure The facets of the intermetallide obtained at ele-vated temperatures also exhibit deformation distortions that are likelyconnected with bismuth adsorption on the facets The appearance ofthese lines is due to the development of local fluidity They arise in thecases when the material possesses a distinct yield point even insignifi-cant concentration of strain promotes the appearance and developmentof these figures [8] Change of the straight character of the glide lines islikely to be connected with the effect of boundary volumes intra-grainstructural strain caused by differences in the volumes of the intermetal-lide and bismuth as well as by glide in different systems and with thetransition from one system to the other

а

b

Fig 6 AFM images of CuGa2 + Bi alloys obtained at a temperature of 90 (a)and 120 (b) С

126

Metallographic in-vestigation of the alloysurface after polishing(Fig 7) showed that thenumber of macrodefectssuch as pores and discon-tinuity flaws decreaseswith an increase in crystal-lization temperature Mi-crohardness of the inter-metallide increases fromHV 70 to 125

Investigation of thedistribution of chemicalelements over the sampleby means of SEM involv-ing X-ray spectral analysisrevealed nonuniformity ofthe distribution of insolu-ble bismuth

Bismuth is not ob-served in the regions withthe intermetallic com-pound which may be con-nected with the fine distri-bution of disperse particlesover the boundaries of theintermetallide Local ac-cumulations of bismuth upto 10 μm in size are ob-served mainly in the siteswhere macrodefects (poresgrain boundaries) get ac-cumulated With an in-crease in the temperature ofinteraction up to 120 Сthe number of local bis-muth accumulations de-

а

b

cFig 7 Optical images of the structure of

CuGa2 + Bi alloys obtained at 20 (a) 90 (b)and 120 (c) С

127

creases but their size increases to 20 μm (Fig 8)

а b

Fig 8 SEM images (in backward scattered electrons) of CuGa2 + Bi alloyHardening temperature а ndash 20 С b ndash 120 C

Thermal investigation of the alloys with different hardening tem-perature points showed that the curves of differential scanning calo-rimetry (DSC) exhibit definite differences only during heating the alloyswith hardening temperature 20 C and 90 C The DSC curves of the al-loys with hardening temperature 90 and 120 С are identical Duringheating the alloy with hardening temperature 20 С exhibits the exother-mal heat effect at a temperature of 120-150 С This effect may be con-nected with the occurrence of recrystallization processes in bismuthThis exo-peak is absent during the repeated heating

Thus investigation showed that an increase in the temperature ofthe interaction of CuBi mechanocomposite with liquid gallium leads toan increase in the size of the formed intermetallide as well as to a de-crease in macrodefects in the form of pores discontinuity flaws cracksThe hardness of the intermetallide thus increases

2 Effect of the temperature of interaction of mechanochemi-cally prepared solid solution Cu (In) with liquid gallium onthe structure and morphology of metal cementThe use of mechanochemically prepared powders of Cu-In system

as the solid phase in the reactions with liquid gallium increases the num-

128

ber of interacting systems due to the solubility of indium in gallium Ac-cording to the state diagram of the system GandashIn [9] the solubility of Inin Ga in the solid state is less than 03 at while the solubility of Ga inIn is 31 at At a temperature of 60 С indium may be dissolved in liq-uid gallium up to 48 wt

Mechanochemically synthesized powder in the system Cu + 12wt In was used as the initial solid-phase component The X-ray phaseanalysis of the products of mechanochemical synthesis (Fig 9) showedthat the solid solution of indium in copper in formed during mechanicalactivation of copper powder with 12 wt indium As a result the latticeparameter of copper increases to а = 36659 Ǻ (аref = 36150 Ǻ) The size of copper crystallite is about 30 nm

Fig 9 X-ray diffraction patterns of the powder Cu-12 wt In after mechanicalactivation (for 20 min) in argon

Mechanical activation of the system Cu + 12 wt In leads to theformation of fine particles of the solid solution of indium in copper (150ndash 230 nm) (Fig 10) Recrystallization of the solid solution of copper andthe formation of grains larger than 15 μm are also possible

129

Fig 10 Topography of the ultrafine powder of the solid solution Cu(In)

A decrease in the size of precursor powder is known to providelarger area of contact between the components of the solid phase and theliquid one and therefore shorter diffusion distances during subsequentinteractions with metal melts Because both copper and nickel are solu-ble in liquid gallium one may expect that the rate of dissolution of themechanocomposites of the system Cu-In would be significant

X-ray phase analysis of the final products of the interaction of thesolid solution Cu(In) with gallium at room temperature revealed thepresence of three phases intermetallide CuGa2 indium and unreactedcopper (Fig 11)

Fig 11 Diffraction patterns of the alloys obtained through the interac-tion of Cu 12 wt In + Ga CuGa2 - In - Cu

130

For the initial powder with indium concentration 12 wt theproduct of the interaction exhibits a decrease in the indium unit cell pa-rameter с in the alloy under formation to с = 49306 Ǻ (cref = 49459 Ǻ) The size of copper crystallites is about 7 nm while the size of indiumcrystallites is about 30 nm Slight changes in the unit cell volume of in-dium may be related to the formation of the solid solution of gallium inindium

During the interaction indium gets dissolved in the liquid phaseof gallium gets concentrated and crystallizes at the interfaces betweenthe solid phase and the liquid one The alloys with the 12 indium con-tent are characterized by a large range of the dimensions of tetragonalparticles of the intermetallic compound CuGa2 (from 05 to 8 μm) TheAFM image (Fig 12) exhibits coarse crystals their crystallographicshape is uncharacteristic of the intermetallide CuGa2 Comparing the X-ray data and the results of AFM we may assume that they are a solidsolution of gallium in indium

Fig 12 AFM topography of the surface of CuGa2+ In(Ga) alloy

A decrease in the AFM scanning pitch and simultaneous acquisi-tion of the image of distribution of normal (topography) and lateral (tor-sion) forces allowed us to distinguish the structural features of the phaseof the solid solution of gallium in indium (Fig 13) A specific distin-guishing feature is the presence of strands in the crystals of the solid so-lution of gallium in indium connected with layering of the solid solutioninto the regions with larger and smaller concentration of the componentwhich is well seen in the image of torsion (Fig 13b) The size of separate

131

grains of the solid solution of gallium in indium reaches more than 10μm

Fig 13 AFM topography of the surface of samples of CuGa2+ In(Ga) alloy (а)image of torsion (b)

Fig 14 The SEM image in direct (а) and back-scattered electrons (b) of thealloy CuGa2+ In(Ga) In the upper part the data chart of the quantitative spec-

tral analysis carried out in the indicated points

To investigate the microstructure of the surface of alloys we car-ried out the examination with the scanning electron microscope and ob-tained the images of the surface of resulting alloy for the interaction Cu12 wt In + Ga in direct (Fig 14а) and back-scattered (Fig 14 b) elec-trons The application of imaging in back-scattered electrons allow one

132

to investigate the composite surface non-uniformity with which the in-tensity distribution over the image depends on the atomic number of anelement One can see in Fig 14 b that the contrast in the BSE images isdetermined by the topographic features of the surface and the distribu-tion of intensities is uniform In addition local X-ray spectral analysiscarried out in different points of the alloy surface revealed the presenceof indium in concentrations 01 to 7 This fact allows us to concludethat indium is present on the surface of CuGa2 intermetallic crystals inthe form of thin films

Another characteristic feature of the surface of samples obtainedin the interaction of solid solutions Cu(In) with liquid gallium is thepresence of fine dispersed formations on the surface of crystals andgrains of CuGa2 that are more clearly seen in the AFM images (Fig 13a) and are detected in the SEM images (Fig 15 b) The formation of thestructures of this kind on the surface of the intermetallide may be con-nected with indium crystallization on the surface of the growing crystals

Fig 15 AFM (a) and SEM images (b) of the face of CuGa2 intermetallic ob-tained by the interaction of Cu 20 In + Ga

So on the basis of X-ray spectral data obtained and the results ofAFM and SEM we may assume that indium gets crystallized not only inthe form of large grains of the phase of the solid solution of gallium inindium but also on the faces of the intermetallide thus forming a nano-meter-sized film of indium about 10 nm thick

133

In order to establish the effect of temperature on the structure andmorphology we carried out alloy hardening at temperature of 60 120and 160 C

X-ray structural investigation of the final phase composition (Fig16) of the alloys showed that no changes in the phase composition of themetal cement are observed with an increase in hardening temperature to160 C The parameters of intermetallic compound CuGa2 remain almostunchanged The values of lattice parameters of the indium phase underformation are also insignificantly differing from the reference ones

Fig 16 Diffraction patterns ofCu-In-Gа samples obtained at

different temperatures

Investigation of the microstructure of alloys obtained at 20 Cshowed that indium is well adsorbed on the surface of intermetallidecrystals and crystallizes not only as separate crystals of the solid solutionof gallium in indium but also as the film formations with grained anddendrite structure on the faces of the intermetallide The occurrence ofintercrystal films of indium or the solid solution of indium may be re-sponsible for a decrease in strength characteristics of the alloy and be areason of both the intra-crystal and inter-crystal fractures (Fig 17 b) It

134

is assumed that an increase in hardening temperature causes substantialformation of the film structures of the solid solution of indium

The AFM investigation of the topography of alloys obtained attemperatures 90-160 C showed that the alloys are characterized by alarge size range of the intermetallic compound CuGa2 At the interactiontemperature of 20 C the size of CuGa2 particles was 05 to 8 μm Withan increase in reaction temperature to 90 C the crystal size increases upto 11 μm Crystal concretions are also formed (Fig 17) One can see inFig 17 b that cracks are formed in the grain plastoelastic deformationson the intermetallide face occur which is likely to be due to the differ-ence in interfacial surface tension of the intermetallide and indium film

ab

Fig 17 AFM image of the surface of CuGa2 + In(Ga) alloy obtained at 90 C a- topography b ndash distribution of lateral forces (arrows show cracks deforma-

tion distortions)

At a temperature of 120 and 160 C the contrast of the surface re-lief decreases due to the formation of a continuous film (Fig 18) on thesurface

Investigation of the phase transitions in the alloys was carried outby means of DSC For heating the products of the interaction betweenthe solid solution of indium in copper and liquid gallium at a rate of30Cmin an endothermic effect is observed on the DSC curves of all thealloys at a temperature about 254 C and an exothermic effect at 290 Con cooling the exothermic peak appears at a temperature of 210-220 С

135

а b

Fig 18 AFM topography of the CuGa2 + In(Ga) alloy a ndash 120 C b- 160 C

According to the Cu-Ga state diagram these effects are connectedwith the peritectic transformations of the main phase of intermetallideCuGa2 during heating and cooling The cooling curves exhibit no ther-mal effect due to the phase transition of indium The DSC curve of thealloy obtained at 20 C contains an endothermic peak at about 130 Cwhich gives much smaller heat effect in the second heating cycle Tak-ing into account the fact that the formation of indium films and the solidsolution of indium with the grained and dendrite structures occurs on thesurface of the intermetallide it may be assumed that heating to 130 C isaccompanied by melting of the indium film (taking into account a de-crease in melting temperature for thin films) [10] and the solid solutionIn(Ga) At the temperature of the peritectic transformation 254 C in-dium gets dissolved in the formed liquid Ga(Cu) with subsequent for-mation of the ternary compound Cu-Ga-In during cooling For coolingthe temperature of the peritectic reaction for the obtained compound de-creases to 210-220 C

ConclusionAs a result of the investigation of the structure and morphology of

metal cements prepared on the basis of mechanosynthesized coppercompounds CuBi and Cu(In) the structure and morphology in the reac-tions with liquid gallium are determined by the degree of interaction of

136

the doping component with gallium In the case of the CuBi mechano-composite in which Bi does not interact with gallium an intermetallidewith particle size up to 4 μm and local accumulations of bismuth areformed With an increase in hardening temperature to 120 C intermetal-lide growth to 8 μm occurs

When using the solid solutions Cu(In) in which indium is solublein liquid gallium and the incubation period for the crystallization of thesolid solution In(Ga) the formed particles of intermetallide CuGa2 havea broad size range from 05 to 8 μm With an increase in hardening tem-perature to 160 C the size of intermetallide particles increases to 11 μmredistribution of indium occurs along with an increase in the number ofits film structures that are formed on the faces of the intermetallide andcause a decrease in its strength properties thus providing intra-crystaland inter-crystal fracture A decrease in the melting temperature for in-dium to 130C and a decrease in the heat effect at this temperature in thealloys obtained at the alloy formation temperature of 90 120 and 160 Cmay be connected with an increase of indium film amount

The work is carried out under the Integration Project of SB RASNo 138 and BRFFI Т09СО-014 laquoDevelopment of Fundamental Basisof the Action of Activation on Regulation of the Processes of Interactionof Solid Metals and Their Comopunds with Metal Melts for the Purposeof Obtaining Functional Materials with Required Structure and Proper-tiesraquo

References1 Tikhomirova OI Ruzinov LP Pikunov MV Marchukova ID

Investigation of mutual diffusion in the system gallium ndash copperFiz metallov I metallovedenie 1970 vol 29 issue 4 p 796-802 (inRussian)

2 Glushkova LI Konnikov SG Interaction between components inthe solder paste based on gallium Pressure treatment of metals andwelding Proceedings of the Leningrad Polytechnical Institute1969 No 308 p 205-208 (in Russian)

3 Grigorieva TF Barinova AP Lyakhov NZ Mechanochemicalsynthesis in metal systems Novosibirsk 2008 (in Russian)

4 Ancharov AI Grigorieva TF Barinova AP Lyakhov NZ Investi-gation of the interaction of liquid metals with nanocomposites by

137

means of diffraction of the synchrotron radiation Nuclear Instru-ments amp Methods in Physics Research 2007 v A 575 p 130-133

5 Ancharov AI Grigorieva TF Tsybulya SV Boldyrev VVNeorganicheskie Materialy 2006 V 42 No 9 p 1164-1170 (inRussian)

6 N Lyakhov T Grigorieva A Barinova Nanosized mechanocom-posites and solid solution in immersible metal systems Journal ofmaterials science 39(2004) 5421-5423

7 Chernov AA Crystallization processes Modern CrystallographyMoscow 1980 vol 3 p 5-12 (in Russian)

8 Bernshtein ML Zaymovsky VA Mechanical properties of metalsMoscow Metallurgy 1979

9 State diagrams of binary metal systems Ed by NP Lyakishev1997 vol 2 p 636ndash637 (in Russian)

10 Gromov DG Gavrilov SA Redichev EN Klimovitskaya AVAmmosov R M Factors determining melting temperature of thinfilms of Cu and Ni on inert surfaces Zhurnal Fizicheskoy KhimiiV 80 No 10 2006 p 1856-1862 (in Russian)

104

ZINC IONS REDUCTION ON SOLID METAL ELECTRODES INCHLORIDE MELTS

Alex Lugovskoy 1a Zeev Unger 12b Michael Zinigrad 1cDoron Aurbach 2d

1Material and Chemical Engineering Department Ariel UniversityCenter of Samaria Ariel 40700 Israel

2Department of Chemistry Bar-Ilan University Ramat-Gan 52900Israel

alugovsaarielacil bzevikitoarielacil сzinigradarielacildaurbachmailbiuacil

keywords electrodeposition chloride melts cyclic voltammetry high-temperature electrochemistry

AbstractThe reduction of zinc ions on solid tungsten and platinum

electrodes in chloride melts at the temperatures 700 ndash 750 degC wasstudied by cyclic voltammetry chronoamperometry and energydispersion spectroscopy It was established that no zinc is reduced onplatinum electrodes As for the reduction of zinc ions on tungstenelectrodes the process has a complex character it starts as anirreversible two-electron zinc ion reduction and after the new phase isformed the process of saturation of the electrode surface with lithium orsodium begins As the second process develops the alkaline metalbecomes essentially the only constituent on the electrode surface

GeneralSince zinc is industrially recovered from sulfate solutions rather

than from melts and because its melting temperature (4195 degC) is lowerthan the temperatures of most molten chloride compositions thereduction of zinc ions on solid electrodes in chloride melts has beeninvestigated relatively poorly There are quite a few papers devoted tothe electrolysis of zinc containing chloride melts (1 2) and these coveronly some details of the electrochemistry of this metal However zinc isnot only an engineering metal It can often be a component of moltenchloride systems in which various processes of synthesis or purification

105

are performed Therefore the detailed electrochemical behavior of zinccan be of great importanceThe study of electro-reduction processes of zinc ions on solid tungstenand platinum electrodes in eutectic NaCl ndash KCl and LiCl ndash KCl melts inthe temperature range of 700 ndash 750 degC is presented in this work Thesetemperatures are somewhat higher than the eutectic points of NaCl ndashKCl (646 degC ) and LiCl ndash KCl (628 degC) and the melts are thereforeliquid enough to be used in technologically important processes oflanthanides and actinides separation reduction and rectification On theother hand these temperatures are significantly lower than the boilingpoint of zinc (907 degC) and there is essentially no loss of the metal due toevaporation

ExperimentalThe electrochemical experiments were performed using a three-

electrode cell made of sintered alumina placed in an alumina crucibleunder nitrogen atmosphere Tungsten (9995 1 mm diameter) andplatinum wires (9995 05mm diameter) were used as the workingelectrodes and their surface area was controlled by immersion depth(typically 6ndash12mm) and by measuring their diameter before and aftereach experiment A 1mm tungsten wire served as a pseudo-referenceelectrode and a flat spiral tungsten wire set perpendicular to theworking and reference electrodes close to the bottom of the cell servedas the counter electrode The area of the counter electrode was ~ 20 foldas large as that of the working electrode ZnCl2 LiCl NaCl and KCl(990 +ACS grade Alfa Aesar) were used for the preparation meltswithout further purification

Zinc chloride was mixed with alkaline metals chlorides usingmortar and pestle in a glove-bag in dry nitrogen atmosphere Themixture was then placed into a crucible the electrode cell was mountedand transferred into the furnace (single-zone Carbolite 1600 degC STF tubefurnace) In the furnace the mixture was first dried under vacuum at 40ndash50 degC for an hour After completing the drying dry nitrogen wasbubbled through the electrolyte during its heating up to the temperatureof the experiments (700ndash750 C) for another hour The temperature wascontrolled by a type S thermocouple placed next to the cell andprotected by an alumina capillary thus maintaining a precision of plusmn1 degCin measuring and controlling the temperature Dry nitrogen atmosphere

106

(1 bar) was maintained in the furnace during the measurements and thepost-experimental cooling The electrochemical measurements werecarried out using an Autolab PGStat-12 potentiostat SEM images andelement analysis by EDS were performed with a SEM system fromJEOL Inc Model JSM 7000F

Results and discussion

Deposition of zinc on a tungsten electrodeSome typical voltammograms for the electrochemical reduction ofZn(II) are shown in Fig 1

-02

-01

0

01

02

03

04

-1 -05 0

iA

cm

2

E V vs W

C

A

QaQ

c~ 1

0502005 Vsec

-0680-0650-0600E

p V

(peak C)

164141110Qc Ccm

2

177150113Qa Ccm

2

Fig 1 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0163 mol L) in equimolar NaCl-KCl melt on a W electrode at 700degC Scanrates are 50 mV sec (solid line) 200 mV sec (slashed line) and 500 mV sec(dotted line) Each charge density was calculated as the sum of areas limited bythe baseline and the appropriate current density curves for the forward andbackward semi-cycles

107

As follows from Fig 1 a single cathodic peak C corresponds toone anodic peak A The potential shape and behavior of the cathodicpeak are typical for the metal deposition on a solid electrode (2-4) Nodifference is observed between the reduction of zinc ions in NaCl ndash KCland in LiCl ndash KCl melts Peak A is assigned to the reoxidation of zincBoth peaks are clearly not independent on the scan rate Rather peak Cis shifted to more negative potentials and peak A moves to more positivepotentials as the scan rate increases The dependence of the cathodicpeak potential on the scan rate is shown in Fig 2 Such voltammetricresponse is typical for irreversible processes

055

06

065

07

075

0 01 02 03 04 05 06

-Ep

V

Vs

Fig 2 Dependence of the cathodic peak potential on the scan rate for thereduction of Zn2+ (0163 mol L) at 710degC on a W electrode

The cathodic peak C appears at about -06 V vs tungsten electrodefor the scan rate of 50 mVsec and at -07 V for 500 mVsec Such asignificant shift is a clear indication that the process is irreversible Thecathodic peak not only is shifted as the scan rate grows but it becomes

108

broader so that the difference |Ep ndash Ep2| grows from 01 V for 005 Vsecto 015 V for 05 Vsec Values of n calculated by equation 23 are inthe range of 156 for low scan rates to 104 for high scan rates The mostlogical interpretation of this finding is that the charge-transfer is of two-electrons which is not surprising in the case of Zn2+ ions reduction Thevalue of is then 078 for 005 Vsec and 052 for 05 Vsec This isevident that the rate determining step is the Faradaic process

Zn2+ + 2e- Znwhen the system is close to the steady state Note that at low enoughpotential scanning rates diffusion limitations may be less influencingwhile at higher scan rates the diffusion limitations are more importantRandles-Sevcik dependencies for the zinc (II) ions reductiondemonstrate linearity but their intercepts are apparently non-zero (Fig3)

0

01

02

03

04

05

06

07

0 02 04 06 08 1

i pA

cm

2

12 V12s-12

Fig 3 Randles-Sevcik plots for Zn2+ ions reduction on W in a NaCl-KCl meltat 700 degC different concentration of the ions (peak C in Figure 39) 900x10-5

molmL Zn2+ 163x10-4 molmL Zn2+ 177x10-4 molmL Zn2+

109

It is evident that the process Zn2+ + 2e- Zn is complicated bysomething else Despite the irreversible character of the depositionprocess it is still reasonable to roughly evaluate the diffusion coefficientof Zn2+ according equation 1

ip = 06105 (nF)32(RT)12D12C12 (11)

where ip is the peal current density (A cm2) n is the number ofelectrons F is Faraday constant (96500 C) R is the gas constant (8314Jmol∙K) T is the absolute temperature (K) D is the diffusion coefficient(cm2 sec) C is the bulk concentration of a Red (Ox) species (mol cm3) and is the scan rate (V sec)

Thus calculated diffusion coefficients are shown in Table 1

Table 1 Diffusion coefficients of Zn2+ to a tungsten electrode in NaCl-KCl melt

C105 mol L D 105 cm2 sec900 955n

163 1020n

177 1364n

Given that the value of n for the reduction of Zn2+ cannot exceed 2 and0 le le 1 ( asymp 05 for most cases) reasonable values of n must beclose to 1-2 Therefore the values of the diffusion coefficients fromTable 2 lie in the range of 1-6∙10-4 cm2sec Available literature data forthe diffusion coefficients of most metal ions lie in the range 10-5-10-4

cm2sec Particularly T Stoslashre G M Haarberg and R Tunold found thatthe values of the diffusion coefficients for Zn2+ in KCl-LiCl melts at400degC lie in the range 06 ndash 106∙10-5 cm2sec (2) Delimarski providesthe value of the diffusion coefficient of Zn2+ in NaCl-KCl at 710degCwhich is 23∙10-5 cm2sec (5) The deviation of our results from theliterature data can hint that that the process cannot be treated as simplezinc ion reduction on the surface of tungsten

110

It is worth to mention that the fact that the diffusion coefficientfor zinc ions in the chloride melt lay in the range 10-4 ndash 10-5 cm2sec mayserve as an indirect argument in the discussion about the existence ofcomplex species described by the general formula [ZnxCly]

z+ in chloridemelts While some authors argue in favor of the formation of complexions (6 ndash 10) other studies give evidence for the existence of individualzinc ions as the key reacting species (11 ndash 12) The relatively highvalues of the diffusion coefficients found in our experiments hint that thecharge is transferred by individual ions rather than by more massivecomplex moieties

005

01

015

02

025

03

035

04

02 03 04 05 06 07 08 09 1

700oC

750oC

740oC

720oC

i pA

cm

2

12

V12

s-12

Fig 4 Randles-Sevcik plots for Zn2+ reduction on W in a NaCl-KCl melt fordifferent temperatures [Zn2+] = 900x10-5 molmL

Another intriguing aspect of the zinc ions deposition process ona tungsten electrode can be seen in the temperature dependence of

111

Randles-Sevcik plots (Fig 4) As seen from Fig 4 Randles-Sevcik plotsdo not change (to the accuracy of the experiment) as the temperaturerises from 700degC to 750degC

The lack of dependence of Randles-Sevcik plots on thetemperature is really surprising A plausible explanation to this could bean additional process in the system which occurs simultaneously withthe observed process but does not involve charge-transfer and cannot bedetected electrochemically Such a process could compensate for theexpected increase of the slope of Randles-Sevcik plots as thetemperature grows and thus distort the temperature dependence

The most probable candidates for such competing processes area coupled chemical (not charge-transfer) reaction or a process of phase-formation However cyclic voltammetry alone cannot discriminatebetween these two possibilities

Fig 5 A chronoamperometric plot for the deposition of Zn2+ on a tungstenelectrode Temperature 725degC [Zn2+] = 900x10-5 molmL The potential was

stepped from OCV to -055 V

A further insight on the nature of the deposition process can beprovided by chronoamperometry As seen from Fig 5 the current fallsin the course of the first 11 seconds of the experiment and then risesreaches a peak and gradually declines as expected with time until theend of the experiment (300 seconds)

The initial falling and rising of the current can be attributed tothe nucleation of the deposits fluctuations of current for more advanced

112

reaction times as seen in Fig 5 may indicate to a very active charge-transfer process which cannot be explained by a simple zinc depositionprocess

Even more surprising information is provided by EDS analysisof the working electrode after a 3000 second deposition experiment at ndash055 V (Fig 6 Table 2) The most striking result of the analysis is theunexpectedly high content of sodium on the electrode surface Thisamount of sodium cannot be accounted for melt adhesion or penetrationbecause the percentage of potassium and chlorine is much smaller Infact the working electrode looks as it was made of sodium withmoderate inclusions of tungsten and zinc rather of tungsten

Fig 6 An EDS spectrum of tungsten working electrode after 3000 seconddeposition at ndash 055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Table 2 Element composition of the tungsten working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Element Na K Cl W ZnAt 6084 580 2861 224 191

113

A somewhat similar phenomenon was reported by Thus T StoslashreG M Haarberg and R Tunold for the deposition of Zn2+ on a glassycarbon electrode in KCl-LiCl melts at 400degC (2) They observed aldquosubstantial residual current observed prior to the Zn(II) reductionpeakrdquo This current was attributed by them to lithium intercalation intothe lattice of the glassy carbon electrode

Unfortunately the data about standard reduction potentials ofmany important ions in molten chlorides are lacking The only source inwhich suitable potentials were found is the book of Yu DelimarskildquoElectrochemistry of Ionic Meltsrdquo (5) The values of standard potentialstabulated in this book were calculated on the base a few assumptionsand are far from being strictly thermodynamical However they arehelpful from the practical point of view The potentials relevant for thisdiscussion are summarized in Table 3

Table 3 Standard reduction potentials in molten chlorides (adopted fromref [5])

Half-Element Li+|Li Na+|Na K+|K Zn2+|Zn Fe2+|FeEH2 (700degC) V - 239 - 236 - 250 - 040 - 007

As seen from Table 3 the standard potentials of lithium andsodium are very close to each other Therefore it is not surprising thatthe interference from sodium in the deposition of zinc ions is similar tothat of lithium as reported by T Stoslashre G M Haarberg and R TunoldOf course it is not intercalation that serves as the moving force of theprocess of sodium penetration into the surface layers of zinc deposit onthe tungsten electrode

The large amounts of sodium in the deposits obtained in the studyof the Zn2+ ions reduction on tungsten electrodes cannot be explained asthe formation of a W-Na alloy because such a process is not observedby the cyclic voltammograms of NaCl-KCl on tungsten electrodes in theabsence of zinc ions (3) Therefore it is zinc which triggers thedeposition of sodium Moreover the data obtained bychronoamperometry at E = ndash 055 V vs W (Fig 5) indicate that there aretwo sequential faradaic processes The first of them is relatively weak

114

and is completed after ~ 11 seconds Then the second process starts andits current only grows with time The first process can be related to thereduction of zinc ions and the formation of zinc deposits As theelectrode surface is covered by a layer of zinc the interaction of thislayer with Na+ ions begins Apparently sodium ions are absorbed by theliquid zinc (Tm = 419 degC) and this facilitates their reduction at thepotential so much more positive than the sodium reduction potential inthe absence of zinc ( - 11 V vs W) Both lithium and sodium are liquidat the temperature of the experiment and these two metals form on theelectrode surface a liquid solution with zinc which continues to absorbnew portions of the lithium or sodium ions

The following speculation may account for the phenomenonobserved in our system

1 Zinc ions are discharged on the surface of the tungstenelectrode As the surface concentration of zinc atoms grows nucleationoverpotential starts to dump the overall process This dumping isobserved in the course of the first 11 seconds in Fig 5

2 Zinc (or zinc-tungsten) phase is formed This phase triggers theprocess of sodium-zinc exchange

Zn + Na+ Zn+ + Na or Zn + 2Na+ Zn2+ + 2Na3 The process (2) becomes the main process on the electrode

surface

Deposition of zinc on a platinum electrodeSome typical voltammograms for the electrochemical reduction

of Zn(II) are shown in Fig 7 Again no difference is observed betweenthe processes in NaCl ndash KCl and in LiCl ndash KCl melts and two melts arefurther described on the instance of in NaCl ndash KCl alone

As seen from Fig 7 the voltammogram is completely anomalousas compared to the other studied systems No cathodic peaks areobserved in the range -11V to + 09V ie in the limits of theelectrochemical window The peaks ndash 125V and at +09 V are the sameas for the ldquoblankrdquo melt NaCl-KCl These are the limits of theelectrochemical window

A very poorly pronounced anodic peak A at about ndash 028 V issimilar to the anodic peak A which appears for the zinc deposition on atungsten electrode (Fig 1) However the cathodic branch of thevoltammogram contains a continuous transition to the cathodic limit of

115

the windows rather than a peak It is obvious that zinc deposition ismasked by another process whose nature cannot be studied in theframework of this research

Fig 7 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0176 mol L) in equimolar NaCl-KCl melt on a Pt electrode at 700degC Scanrate is 300 mVsec

Fig 8 An EDS spectrum of a platinum working electrode after 3000 secondcathodic polarization at ndash 07 V vs W at 725degC in equimolar NaCl-

KCl melt containing 176x10-4 molmL of Zn2+ ions

116

An attempt of obtaining a sample of zinc deposit by holding thesystem at ndash 07 V (that is at such a potential which is considerably morepositive than the cathodic limit but more negative than the potential atwhich zinc is deposited on a tungsten electrode) for 3000 seconds wasmade However the analysis (Fig 8) demonstrated that essentially nozinc is found on the surface of the electrode (Table 4) since the value098 At is comparable with the sensitivity of the method The richcontent of potassium (5857 At ) in the surface layers can hint thatpotassium sorption is the process which masks the deposition of zincHowever this information alone is not sufficient for making positiveconclusions

To try to understand the essence of the process other moltenchloride systems containing no potassium could be studied Howeversuch a study is far beyond the framework of the current work

Table 4 Element composition of the platinum working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 176x10-4 molmL

Element Na K Cl Pt ZnAt 555 5857 3426 618 098

ConclusionsThe deposition of zinc on a tungsten electrode starts as an

irreversible two-electron zinc ion reduction Zn2+ + 2e- Zn After anobvious initial nucleation step a new phase is formed This phasecatalytically launches the process of saturating the electrode surface withsodium After the onset of the process of sodium deposition the latterbecomes essentially the only constituent on the electrode surface

The attempts of studying the deposition of zinc ions on a platinumelectrode were unsuccessful because this process is masked by anotherprocess which can result in the saturation of the electrode by potassiumThe exact nature of the latter process demands a separate study

117

References1 Fray D J J Appl Electrochem 3 103 (1973)2 Stoslashre T Haarberg GM Tunold R J Appl Electrochem 30 1351

(2000)3 Lugovskoy A Zinigrad M Aurbach D Israel Journal of

Chemistry 47 (3-4) 409 (2007)4 Lugovskoy A Zinigrad M Aurbach D and Unger Z

Electrochimica Acta 54 (6) 1904 (2009)5 Delimarski Yu K Electrochemistry of Ionic Melts Metallurgiya

Moscow 1978 (in Russian)6 Mackenzie J D and Murphy W K J Chem Phys 33 366 (1960)7 Irish D E and Young T F J Chem Phys 43 1765 (1965)8 Allen DA Howe RA Wood ND Howells WS J Phys

Condens Matter 4 1407 (1992)9 Price D L Saboungi M-L Susman S Volin K J Wright A C J

Phys Condens Matter 3 9835 (1991)10 Bassen A Lemke A Bertagnolli H Phys Chem Chem Phys 2

1445 (2000)11 Biggin S and Enderby J E J Phys C Solid State Phys 14 3129

(1981)12 Badyal Y S and Howe R A J Phys Condens Matter 5 7189

(1993)

89

PREPARATION OF COMPOSITES CuZrO2 AND CuTiO2

BY MA SHS

AI Letsko1 TL Talako1 AF Ilyushchenko1 TF Grigoreva2SV Tsybulya3 IA Vorsina2 NZ Lyakhov2

1 Powder Metallurgy Institute of NAS B Minsk Belarus2 Institute for Solid State Chemistry and Mechanochemistry of SB RAS

18 Kutateladze str Novosibirsk Russia grigsolidnscru3 GK Boreskov Catalysis Institute of SB RAS Novosibirsk Russia

IntroductionMetaloxide composites are quite perspective materials for

application in machine industry instrument engineering and electricalengineering in comparison to pure metals due to their improvedchemical and physical properties (heat resistance strength hardnesserosion resistance) Chemical mixing salt mixture decompositionhydrogen reduction in solutions chemical precipitation from solutionsinternal oxidation are well-known methods of preparing such materialshaving application in industry [1] The above-mentioned technologiesallow attaining metaloxide composites but they are quite expensive andlong-term Based on this a very topical issue is elaboration of newapproaches to production of metal-ceramic materials

In this work we explored possibilities of preparation ofcopperoxide composites (CuZrO2 and CuTiO2) by methods ofmechanochemical synthesis (MS) in planetary mills and of mechanicallyactivated self-propagating high-temperature synthesis (MA SHS)

ExperimentalCopper copper oxide CuO and zirconium M-41 titanium PTOM

were used in this work as raw materials Mechanical activation (MA)was carried out in planetary ball mills with water cooling [2] (the drumvolume ndash 250 cm3 the balls diameter ndash 5 mm the load ndash 200 g sampleweight ndash 10 g the drums rotation speed about the general axis ~ 1000rpm) After MA the activated mixture was compacted (under a load of4ndash6 t) in the mould up of 17 mm diameter and ~25 mm in height (tillstrength sufficient for the sample transfer to the reactor) SHS wascarried out in the argon atmosphere the combustion was initiated withan electrically heated tungsten coil The temperature and burning

90

velocity were evaluated by a thermocouple method (C-A thermocouplesOslash asymp 02 mm) using an outer 2-channel 24-charge analog-to-digitalconverter ADSC24-2T

X-ray diffraction research was conducted with diffractometersXrsquoTRA (Thermo ARL Switzerland) with application of CoK radiation(λ = 1 789 Aring) and URD-63 with application of CuK radiation (λ = 15418 Aring) Evaluation of effective sizes of coherent scattering area wascarried out in compliance with the Scherer formula with the strongestpeaks of phases analysed

The high-resolution scanning electronic microscope (SEM)MIRATESCAN equipped with an INCA 350 accessory for EDXanalysis was used for the structure research The electron probe diameterwas 52 nm excitation area was 100 nm Images in direct electrons andback-scattered electrons were attained and it allowed studying chemicalelements distribution over the surface Brightness distribution in theimage depends on the average atomic element number in eachmicroarea

IR absorption spectra were registered by spectrometer IFS-66The samples were prepared to the exposure by standards methods

Results and discussion

Cu-O-Zr systemMechanochemical reduction of copper oxide with metallic

zirconium was initially investigated in this system This reaction is quitehigh-exothermic (∆H (2 CuO + Zr = 2 Cu + ZrO2) asymp -188 kcalmol) ieit can be implemented under mechanical activation conditions IRspectroscopic investigations have shown that the original copper oxideCu-O band is considerably widened at 505 cm-1 after 20 s of MA ofCuO + Zr mixture of stoichiometric composition This widening (Fig1b) can testify some structural failures After 30 s of activation thefollowing bands are present in the IR-spectrum of the product 505 cm-1

(original oxide CuO) 615 cm-1 (the lowest copper oxide Cu2O) [3] and415 585 735 cm-1 (zirconium oxide (Fig 1c) [4 5] X-ray-phaseanalysis shows the presence of certain amount of Cu2O already after 20 sof activation The 30-second activation product diffractogram showsclear copper (coherent scattering area asymp 80 nm) and zirconium oxide

91

(coherent scattering area asymp 100 nm) reflection and two copper oxidereflections ie mechanochemical reduction of copper oxide takes placeat such activation duration This reaction speed shows that the reactionpresumably takes place in the thermal explosion mode when especiallyhigh heat dissipation speed is needed what is very difficult to performeven in the most effectively cooled highly-energy planetary ball millsAs such a process dimensional scaling seems to be absolutely impossiblein conditions of mechanochemistry an attempt to produce compositeCuZrO2 by the SHS method was made

Fig 1 IR-spectra of mixture CuO + Zr before (a) and after MA for 20 (b) and30 s (c)

At first CuOZr mechanocomposite was used as the SHS-precursor This mechanocomposite formed after 20 s of MA ofstoichiometric composition mixture has a small amount of cuprous oxideCu2O beside original copper oxide and zirconium SHS process proceedsin the heat explosion mode in this system Burning parameters fixingfailed in this case because of the inertia of the equipment applied

92

Not pure metal but solid solutions intermetallic compounds ornano-composites where metal-reducer (zirconium in our case) isdistributed in the inert matrix can be used as a reducing agent todecrease the system reaction capability At the same components ratiochemical energy of the raw mixture would be considerably lower and asa consequence heat release would reduce

In this work mechanocomposite formed during mechanicalactivation of mixture Cu + 20 wt Zr for 20 min with zirconium hadbeen pre-dispersed for 4 minutes (zirconium coherent scattering areasize ~ 20 nm) was used for copper oxide reduction This compositediffractogram shows the widened intensive copper (coherent scatteringarea asymp 20 nm) reflection and very vague zirconium reflection coherentscattering area of which cannot be evaluated (Fig 2) Since copperreflections havenrsquot changed their position we can conclude thatzirconium hasnrsquot become a part of copper crystal lattice ie CuZrmechanocomposite and not solid solution is attained

Fig 2 Diffractograms of Cu + 20 Zr mixture before (a) and after 20 minof MA (b)

93

This is confirmed by the SEM results (Fig 3) The electronmicroscopy data more clearly show zirconium distribution Zr elementalmapping testifies that local zirconium areas are much diffused

Fig 3 SEM-images of sample Cu + 20 Zr after MA for 20 min

94

X-ray research of the product of joint activation of mixture CuO +mechanocomposite Cu + 20 Zr (the mixture composition correspondsto the stoichiometric ratio of copper oxide and zirconium) for 2 and 4minutes show that copper oxides diffraction reflections are retained inall cases although they are substantially widened (Fig 4) Thezirconium oxide reflection is not observed ie mechanochemical copperoxide reduction does not take place in this time gap CuOCuZrmechanomposite formed as a result of joint mechanical activation ofmixture CuO + mechanical composite Cu 20 Zr for 4 min was usedas a precursor for SHS

Fig 4 Diffractogram of sample CuO + CuZr after MA for 4 min

Usage of mechanocomposite CuOCuZr instead of CuOZr one asthe SHS precursor changes a mechanism of interaction between thereactants during the SHS process from the thermal explosion mode (forCuOZr mechanocomposite) to the steady-state combustion with the

95

burning velocity asymp 2 mms temperature rise speed about 730 Cs andburning temperature 1044 C The combustion temperature record (Fig5) shows 2 isothermal plateaus The first one is fixed at temperaturemaximum and most probably points out melting process The secondone is fixed at 580 ndash 590 C and accounts for post-processes in the after-burning zone of combustion wave

Fig 5 Temperature record of the SHS process from mechanical compositeCuOCuZr

X-ray-phase analysis has shown that SHS product consists ofcopper and zirconium oxide with Cu2O traces (Fig 6) Electronicmicroscopy with the EDX analysis confirms composite structureformation (Fig 7 Table 1)

96

Fig 6 Diffractogram of the SHS product from mechanical compositeCuOCuZr

Fig 7 SEM-image of the SHS product from mechanical composite CuOCuZr

97

Table 1 Results of the EDX analysis (from Fig 7)

Number ofspectrum

O Cu Zr

1 382 8744 8742 714 8152 11343 2803 2747 44504 1653 4640 37065 2314 2914 4772

Cu-O-Ti systemChemical reduction of CuO with titanium is also high-exothermic

(∆H (2 CuO + Ti = 2 Cu + TiO2) asymp -151 kcalmol) Mechanicalactivation of equimolar mixture of copper oxide with titanium powderfor 4 minutes did not result in titanium oxide formation Longeractivation is not reasonable since it contaminates the reaction mixturewith balls and drums material That is why the composites formedduring the short-term MA were used as precursors for SHS

After 30 s MA composite structure CuOTi with a small additiveof cuprous oxide reduced from CuO (Fig 8) is formed The SHS processfrom such mechanocomposites proceeds with a very high speed andtemperature (on a levels typical for the thermal explosion mode) andwith the substances scatter

Fig 8 Diffractogram of mixture CuO + Ti after MA for 30 s

98

To decrease combustion temperature and velocitymechanocomposite CuTi containing 20 wt of titanium was used as areducing agent in the next experiment Figure 9 shows the diffractogramof the mechanocomposite formed after 10 min mechanical activation ofthis mixture It shows that metals reflections especially that of titaniumare widened testifying substantial increase of their dispersivityAccording to the X-ray data analysis the titanium coherent scatteringarea size is ~ 10 nm in this composite

Fig 9 Diffractogram of mixture Cu + 20 Ti after 10 min of MA

Mixture of copper oxide and CuTi mechanocomposite (thecomposition corresponds to the stoichiometric ratio of titanium andcopper oxide for its full reduction) was subjected to activation for 4minutes Only a band of valence vibrations of vCu-O copper oxide (Fig10a) is present in the IR-spectrum of the activated mixture like in theoriginal one but its intensity slightly decreases X-ray research alsoindicates that the titanium oxide reflections are absent in the 4-minuteactivation product diffractogram (Fig 11)

99

Fig 10 IR-spectra of sample CuO + CuTi after 4 min of MA (a)and after SHS (b)

Fig 11 Diffractogram of sample CuO + CuTi after 4 min of MA

100

SHS process from CuOCuTi mechanocomposite takes place inthe steady-state combustion mode with burning velocity higher than 20mms and burning temperature ~2000 ordmC A band (~730 cm-1)corresponding to valence vibrations of rutile vTi-O (Fig 10b) [2]appears in the IR-spectrum of the SHS product from CuOCuTimechanicocomposite Diffraction reflections (Fig 12) also correspond toreflections of rutile and copper

Fig12 Diffractogram of the SHS product from CuOCuTi mechanocomposite

Electron-microscopy exposure in back-scattered electronsindicates the partial phase separation of TiO2 and Cu (Fig 13 a) thoughcomposite particles containing TiO2 inclusions with size from 30 nm till1 5 m (Fig 13 c) are also formed The elemental mapping in thetitanium characteristic radiation confirms this fact (Fig 13d)

101

a

b cFig 13 SEM-images of the SHS-product from CuOCuTi mechanocomposite

102

Table 2 The EDX analysis results (from Fig 13 a)

Number ofspectrum

O Ti Cu

1 191 052 9757

2 235 051 9714

3 2230 2094 5676

4 1586 1295 7118

5 180 108 9712

6 336 228 9436

7 4335 4685 980

8 3297 2738 3966

9 4978 4645 377

ConclusionThus our investigations have shown that copper oxide can be

mechanochemically reduced with zirconium resulting in formation ofzirconium oxide and copper but the reaction goes in the thermalexplosion mode

To produce composite CuZrO2 by the method of MASHS usageof mechanocomposite CuZr instead of pure zirconium seems to be morepromising The MASHS product is a copper-based composite withinclusions of ZrO2 and some amount of Cu2O

Mechanical activation of equimolar mixture of copper oxide withtitanium powder for 4 minutes did not result in titanium oxide formationThat is why the composites formed during the short-term MA were usedas precursors for the following SHS

Reduction of CuO with CuTi mechanocomposite can beimplemented by the method of MASHS Partial phase separation of TiO2

and Cu takes place during the synthesis process along with the formationof copper-based composite particles with inclusions of titanium oxidesized from 30 nm up to 15 m

103

References1 PA Vityaz Mechanically alloyed alloys on the basis of aluminum

and copper PA Vityaz FG Lovshenko GF Lovshenko ndashMinsk Belnauka 1998 ndash 351 p

2 YG Avvakumov AP Potkin OI Samarin Authorrsquos certificate ofUSSR 975068 Planetary mill BI 1982 No 43

3 SS Batsanov VPBokarev YVLazareva On CuO interaction withcopper Inorganic Chemistry Journal 1977 V 22 issue 4 P 888ndash 892

4 AI Boldyrev Infrared spectra of minerals M Nedra 19765 BT Kaminsky AS Plygunov GN Prokofyeva Infrared spectra of

oxides of titanium zirconium and hafnium Ukrainian ChemicalJournal 1973 V 35 No 9 P 946 ndash 977

78

THE STANDARD ENTHALPY AND ENTROPY OFFORMATION OF GASEOUS AND LIQUID

POLYCHLORINATED BIPHENYLS POLYCHLORINATEDDIBENZO-n-DIOXINS AND DIBENZOFURANS

TV Kulikova AV Mayorova KYu ShunyaevInstitute of Metallurgy Ural Branch RAS

Yekaterinburg RussiaE-mail kulikogmailcom

AbstractThe study deals with analysis and systematization of the known

and calculation of the unknown thermodynamic characteristics (thestandard enthalpy of formation the standard entropy of formation) ofwidespread hazardous isomers of gaseous and liquid compounds ofpolychlorinated biphenyls (PCBs) polychlorinated dibenzo-n-dioxins(PCDDs) and polychlorinated dibenzofurans (PCDFs) Thecomparison of results obtained in different studies reveals aconsiderable discrepancy between values reported by highlyrespected investigators In this connection laquoindependentraquo results ofthe thermodynamic characteristics have been calculated

IntroductionUnique technological and physicochemical properties of

polychlorinated biphenyls (PCBs) a huge volume of theirproduction considerable volatility and solubility and extremechemical inertness have led to the world-wide spread of PCB-containing equipment and materials resulting in the universalcontamination with these substances The most common method usedin Russia for destruction of PCBs is their incineration with theformation of polychlorinated dibenzo-n-dioxins (PCDDs) anddibenzofurans (PCDFs) which are among the most hazardouschemical substances known to the mankind

As often happens the hazard of PCBs has long beenunderestimated With respect to their severe toxicological effectPCBs are identical to substances that are referred to the high class ofhazard Since these substances are especially toxic they have beenassigned low toxicological standards which necessitate special

79

requirements on the organization of processes assuming formation ofthese substances (the so-called dioxinogenic processes) so thatindustrial emissions meet the norms Instrumental investigations ofthese substances are very expensive and in this connection interestis attracted to calculation methods for simulation of processes by thedata on their thermochemical properties

A quality thermodynamic simulation requires the knowledge ofthermodynamic and thermochemical properties of all reliablycertified compounds of the system under study in the gaseous orcondensed state Therefore the present study deals with the analysisand systematization of the known and calculation of the unknownthermochemical properties (the standard enthalpy and entropy offormation) of most toxic and hazardous isomers of gaseous PCBsPCDDs and PCDFs and liquid PCBs

Calculation of thermochemical propertiesIt is known that there are 209 individual PCB congeners 420

polychlorinated dibenzo-n-dioxins and polychlorinateddibenzofurans which differ by the number and positions of chlorineatoms in a molecule The most widespread PCB compoundscontaining up1 to 10 chlorine atoms were chosen for the study Indeciding on isomers preference was given to ortho-unsubstitutedPCBs because they are most toxic and their effect is similar to theeffect of PCDDs and PCDFs Congeners which do not have chlorineatoms in ortho-positions of molecules (ortho-unsubstituted PCBs)can acquire the planar configuration which is more favorable inenergy terms Such congeners are isostereoisomeric to PCDDs andPCDFs and present the greatest hazard As to the PCDD and PCDFisomers of special hazard to humans and the environment are tri-tetra- penta- and hexa-substituted dioxins and furans containinghalogen atoms in lateral positions 2 3 7 and 8

In this study we analyzed the known and calculated theunknown thermodynamic properties of 17 most widespread andhazardous isomers of PCBs PCDDs and PCDFs in the gaseous stateand 11 compounds of liquid PCBs

80

Gaseous PCBs PCDDs and PCDFsThe literature survey showed that studies dealing with

estimation of the thermochemical properties of gaseous PCB PCDDand PCDF compounds are few Most of them are based oncalculations or are semi-empirical For example Saito and Fuwa [1]calculated thermodynamic functions of all PCBs and some PCDDsand PCDFs on the basis of semi-empirical calculations in terms ofthe PM3 model OV Dorofeeva et al [2-4] used statistical methodsTable 1 presents the literature data on standard enthalpies andentropies of formation of gaseous and liquid PCBs PCDDs andPCDFs The comparison of results obtained in different studiesreveals a considerable discrepancy between values reported by highlyrespected investigators who did very arduous work In particularvalues of the formation enthalpy [1] are 8-70 larger and the entropyis 11-15 smaller than the corresponding values in [2-4] thediscrepancy grows with the number of chlorine atoms in a moleculeSo we thought it reasonable and topical to attempt an independentresult

Bensons method [5] was used to calculate thermodynamiccharacteristics (the standard enthalpy of formation ΔНdeg298 thestandard entropy of formation ΔSdeg298) of the gaseous PCBs PCDDsand PCDFs We shall dwell briefly on this method

Bensons method is the group additivity method involvinganalysis of the molecule structure Atomic or molecular groups areseparated and the nearest neighbors of the atom or the group areconsidered Table 2 gives the number of groups necessary fordetermination of group increments in structural formulas of PCBsPCDFs and PCDDs Values of the thermodynamic characteristics ofgroup increments were determined from available reference andliterature data [5 6] Information about the energy contribution ofeach group (see Table 3) and the number of groups was used tocalculate thermochemical properties of the PCBs PCDDs andPCDFs

81

Table 1 Standard enthalpies (∆Нo298 kJmole) and entropies (∆So

298Jmole K) of formation of gaseous and liquid PCBs PCDDs andPCDFs

Gaseous state Liquid state

Compo-unds Saito Fuwa [1]

the given work

OV Dorofeeva etal

[2-4]

∆Нo298

[7 8 121617]

So298

[781014 16 17]

∆Нo298

the givenwork and

[814]

So298

thegivenworkand[14]

1 2 3 4 5 6 7 8 9

C12H10

(biphenyl)

1986[1]

1797

3454[1]

4104

1820[3]

3908[3]

1819[8]

1814[16]

3927[16]

11711162[8]11710

[14]

257402574[14]

C12H9Cl(3-mono-

chlor-biphenyl)

1705[1]

1500

3851[1]

4413

1561[2]

4323[2]

1548[8]

15088[16]

4214[16]

7629 2840

C12H8Cl2

(44rsquo-dichlor-biphenyl)

1422[1]

1202

3992[1]

4721

1260[2]

4518[2]

1276[8]

12004[16]

4492[16]

3584 3106

C12H7Cl3

(344rsquo-trichlor-biphenyl)

1194[1]

905

4240[1]

5030

1041[2]

4923[2]

1004[8]

892[16]

4780[16]

-452 3372

C12H6Cl4

(33rsquo44rsquo-tetrachlor-biphenyl)

969[1]

608

4444[1]

5338

899[2]

5216[2]

732[8]

5836[16]

5068[16]

-4488 3638

C12H5Cl5

(33rsquo44rsquo5-penta-

chlorbiphenyl

748[1]

310

4620[1]

5647

569[2]

5502[2]

460[8]

2752[16]

5356[16]

-8524 3904

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlor-

biphenyl)

529[1]13

4615[1]

5956

314[2]

5675[2]

190[8]

-332[16]

5644[16]

-12558 4170

C12H3Cl7

(233rsquo44rsquo55rsquo-hepta-

chlor-biphenyl)

400[1]

-284

4842[1]

6264

152[2]

6077[2]

-84[8]

-416[16]

5932[16]

-16596 4436

82

1 2 3 4 5 6 7 8 9

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-

octachlor-biphenyl)

241[1]

-581

4886[1]

6573-90[2]

6342[2]

-356[16]-650[8]

6220[8]

-20632 4702

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-

nanochlor-biphenyl)

873[1]

-878

5048[1]

6881

-153[2]

6607[2]

-628[16]-958[8]

6508[8]

-24668 4968

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlor-biphenyl)

-67[1]

-1176

5034[1]

7190

-247[2]

6757[2]

-901[16]

-1267[8]

6796[8]

-28604 5234

C12H8O2

(dibenzo-n-dioxin)

-402[1]

-448

3764[1]

-592[4]

3965[4]

-592[12]-592[7]

-550[17]

3951[7]

3880[17]

- -

C12H4Cl4O2

(2378-tetrachlor-dibenzo-n-

dioxin)

-1372[1]

-1592

4553[1]

-1640[4]

4781[4]

-1345[7]

-158[17]

5136[7]

4784[17]

4781[10]

4784[9]

- -

С12H3Cl5O2

(12378-pentachlor-dibenzo-n-

dioxin)

-1532[1]

-1900

4931[1]

-1900[4]

54035[4]

-1162[7]

-196[17]

5531[10]

5010[17]

- -

С12H2Cl6O2

(123478-hexachlor-dibenzo-n-

dioxin)

-1691[1]

-2164

4841[1]

-2196[4]

56912[4]

-1224[7]

57559[7]

5236[17]

- -

С12HCl7O2

(1234678-hepta-chlor-

dibenzo-n-dioxin)

-1848[1]

-2472

5005[1]

-2460[4]

59789[4]

-1196[7]

61031[7]

5462[17]

- -

C12H8O(dibenzo-

furan)

1061[1]

518

3787[1]

553[4]

3759[4]

552[17]

3744[17]

- -

C12H4Cl4O(1234-

tetrachlor-dibenzo-furan)

203[1]

-625

4505[1]

-500 [4]49098

[4]-528[17]

4648[14]

- -

83

1 2 3 4 5 6 7 8 9

С12H3Cl5O(12378-pentachlor-

dibenzo-furan)

-123[1]-934

4592[1]

-759[4]

51975[4]

-748[17]

4874[14]

- -

С12H2Cl6O(123478-

hexachlor-dibenzo-furan)

-283[1]

-12424713[1]

-1051[4]

54852[4]

-1043[17]

5100[14]

- -

С12HCl7O(1234678heptachlor-

dibenzo-furan)

-441[1]

-1550

4833[1]

-1315[4]

57729[4]

-1313[17]

5326[14]

- -

Table 2 Number of groups for determination of group increments instructural formulas of PCBs PCDFs and PVDDs

Number of groupsCompound Св-H Св-Cl Св-O Св-Св

Number ofchlorine atoms

in a molecule (n)

PCBs 10 - n n - 2 1 ndash 10

PCDFs 8 - n n 2 2 1 ndash 8

PCDDs 8 - n n 4 - 1 ndash 8

Св is the carbon atom in an aromatic ring

Values presented in Table 1 show the thermodynamiccharacteristics of PCBs PCDDs and PCDFs calculated in this studyand by other investigators

It is seen for example ( Table 1) that the formation enthalpy

(o298H ) of biphenyl (C12H10) equals (kJmole) 1986 [1] 1820 [3]

1819 [7] and 1814 [8] while the formation entropy (o298S ) of

2378-tetrachlordibenzo-n-dioxin (C12H4Cl4O2) is (J(mole K))4553 [1] 4781 [4] 4784 [9] and 4781 [10]

84

Table 3 Values of the thermodynamic characteristics determined bythe method of group increments[58]

(gas) (liquid)Group

o298H

kJmole

o298S

J(moleК)

o298H

kJmole

o298S

J(moleK)

Св-H 1381[8]1382[5]

4831[8]4827[5]

816[8] 2887[8]

Св-Св 2166[8]2077[13]

-3657[8]-3618[5]

1721[8] -

Св-Cl -1703[8]-1591[5]

7708[8]7913[5]

-3220[8] 5547[8]

(Св)2-O -7766[8]-8834[5]

--

- -

orto corrCl-Cl

950[8]921[5]

- 1400[5] -

meta corrCl-Cl

-500[8] - 400[5] -

In this study the values of the standard entropy of formationobtained by using statistical methods (OV Dorofeeva et al [2-4 9])for 17 isomers of PCBs PCDDs and PCDFs are in good agreementwith the values calculated by other investigators [8 10 12 13] andwith the values calculated by us

Liquid PCBsIt should be noted that ample literature data on the

thermochemical properties of liquid ecotoxicants is only available forbiphenyl (C12H10) [8 14] dibenzo-n-dioxin (C12H8O2) [11 15] anddibenzofuran (C12H8O) [5 17] The only study dealing withcalculation of thermodynamic functions for the whole series of liquidPCDD and PCDF homologues was published by VS Iorish et al[11] As to liquid PCB compounds the literature data on theirthermochemical properties are scarce [8 14]

The thermochemical properties namely the standard enthalpyand entropy of formation of liquid PCBs were calculated using thegroup additivity method due to Domalski [8] Values of the groupincrements (Table 3) were adopted from [8] It is seen from Table 3

85

that the energy contribution of the group Св-Св is unavailable for the

entropy calculation However if one uses known values ofo298S for

liquid biphenyl (C12H10) [14] and the data on the contribution of the

Св-H and Св-Cl groups [8] it is possible to calculateo298S for the

whole series of PCBs

o298S (PCB) =

o298S (BP) - (10-n)

o298S (Св-H) + n

o298S (Св-Cl) +

+(morto corr Cl- Cl ) +(pmeta corr Cl- Cl) (1)

where n is the number of chlorine atoms in a PCBs moleculem (p) - spatial amendments number Cl (from two and more) beingin orto - (meta-) position rather each other

The enthalpy of formation (o298H ) for the PCBs series

compounds was calculated by two options using the group additivitymethod due to Domalski [8] and from the equation

o298H (PCB) =

o298H (BP) - (10 - n)

o298H (Св-H) +

+ no298H (Св -Cl) +(morto corr Cl-Cl )+(pmeta corr Cl-Cl) (2)

Table 4 lists values of the standard enthalpy of formation forthe series of liquid PCBs compounds as calculated by the groupadditivity method [8] and the equation (2) It is seen that the values of

o298H which were calculated by the two methods are in good

mutual agreementThe thermochemical properties which were taken as reliable

were added to the TERRA database and were used forthermodynamic simulation of the thermal stability of PCBs PCDDsand PCDFs

86

Table 4 Calculated enthalpy of formation (∆Нo298) for liquid PCBs

compounds∆Нo

298 kJmole

CompoundGroup

incrementsmethod

Eq (5)δ

C12H9Cl(3-monochlorbiphenyl)

7584 76742 12

C12H8Cl2

(44rsquo-dichlorbiphenyl)3530 36382 30

C12H7Cl3

(344rsquo- trichlorbiphenyl)-506 -3978 2138

C12H6Cl4

(33rsquo44rsquo-tetrachlorbiphenyl)-4542 -44338 238

C12H5Cl5

(33rsquo44rsquo5-pentachlorbiphenyl)-8578 -84698 126

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlorbiphenyl)-1261 -125058 083

C12H3Cl7

(233rsquo44rsquo55rsquo-heptachlorbiphenyl)-1665 -165418 065

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-octachlorbiphenyl)-20686 -205778 052

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-nanochlorbiphenyl)-24722 -246138 044

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlorbiphenyl)

-28758 -286498 038

Conclusions1The literature data on the thermochemical properties of 17

most widespread and hazardous isomers of PCBs PCDDs andPCDFs in the gaseous state and 11 compounds of liquid PCBs havebeen analyzed and systematized for the first time

2Methods have been developed for calculating of thethermodynamic characteristics of organic compounds Values of thethermodynamic functions (standard enthalpy and entropy offormation) of liquid PCBs PCDDs and PCDFs have been calculatedfor the first time

87

3The comparison of the calculated values of thethermodynamic functions with the known literature datademonstrated their good mutual correlation

4The obtained data were added to the TERRA database andwere used for thermodynamic simulation of the thermal stability ofPCBs PCDDs and PCDFs

5The obtained data can be used for simulating of the behaviorof complex heterogeneous systems including ecotoxicants over awide interval of temperatures and initial compositions

This study was supported by RFBR (project No 08-03-00362-a)

References1 Nagahiro Saito Akio Fuwa Chemosphere 2000 vol40 p

131-1452 OV Dorofeeva NF Moiseeva VS YungmanLV JPhys

Chem A 2004 vol 108 p 8324-83323 OV Dorofeeva Thermodynamica Acta2001 vol374 p7-114 OV Dorofeeva VS Iorish NF Moiseeva J Chem Eng

Data 1999 vol 44 p 516-5235 SW Benson FR Cruickshank DM Golden GR Haugen

HE OrsquoNeal AS Rodgers R Shaw and R Walsh Chem Rev1969 vol69 p 279 -324

6 HK Eigenmann DM Golden and SW Benson J PhysChem 1973 vol 77 1687-1691

7 Jung Eun Lee and Wonyong Choi J PhysChem A 2003vol 107 p 2693-2699

8 Domalski E S and Hearing E D J of Phys and Chem RefData 1993 vol 22 p 805-1159

9 LV Gurvich OV Dorofeeva VS Iorish Zh Fiz Khimii 1993vol67 No 10 p 2030-2032

10 W-Y Shiu and K-C Ma J Chem Ref Data 2000 vol29No 3 p 387-462

11 VS Iorish OV Dorofeeva NF Moiseeva J Chem Eng Data2001 vol46 p 286-298

12 VA Lukyanova VP Kolesov Zh Fiz Khimii1997 vol 71No 3 p 406-408(in Russian)

88

13 P Reid J Prausnitz T SherwoodLeningrad Khimiya 1982592 p(in Russian)

14 Richard Laurent and Helgeson Harold C Geochimica etCosmochimica Acta 1998 vol 62 No 2324 p 3591 ndash 3636

15 I Barin ldquoThermochemical Data of Pure SubstancesrdquoWeinheim Federal Republic of Germany VCHVerlagsgesellschaft mbH 1997

16 Cambridgesoft database ver 806 December 31 200317 Thompson D Thermochim Acta 1995 vol261 p7-20

76

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OFNANOGRAINED

TiN-TiB2 COMPOSITES

MA Korchagin BB BokhonovInstitute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirsk Russiakorchagsolidnscru

Titanium nitride is known to exhibit high oxidation resistancehigh thermal conductivity and hardness as well as high corrosionresistance in acids Titanium diboride is also very hard possessing highstrength at elevated temperatures and anomalously high electricalconductivity among other ceramic materials

Composite materials based on the mixture of these twocompounds have been widely used in a variety of applications Highperformance parts have been also developed Thus ceramics containing40-50 molTiN shows high oxidation resistance [1] However untilvery recently TiN and TiB2 have been produced separately by twodifferent routes At present new methods are being developed tosynthesize mixtures of these two compounds in a single process One ofthese methods is based on self-propagating high-temperature synthesis(SHS) The use of SHS eliminates the need of having furnace equipmentto synthesize the desired products The possibility of SHS in the systemis due to the high enthalpies of formation of the products serving as aninternal chemical source of energy

In order to simultaneously obtain TiN and TiB2 by SHS the initialreactants can be either the powder mixtures of Ti-BN [3] or Ti-B-BN[4] The products of the reactions consist of highly porous well meltedsintered pieces with the minimum grain size of 1-10 microm [4] Hightemperatures developed in the combustion wave in the traditional SHSdo not allow finer grains of the products to retain

In order to overcome this problem short mechanical activationof the mixtures of reactants is proposed followed by the SHS in anatmosphere of argon or nitrogen

In the previous investigations preliminary mechanical activationhas been shown to significantly reduce the combustion temperatures

77

which to a great extent determine the grain size of the products of SHS[6 7]

Experiments were performed on the stoichiometric mixtures 3Ti +2BN The time of preliminary mechanical activation in a planetary ballmill (AGO-2 type) did not exceed 10 min The influence of the durationof mechanical activation on the combustion rate temperature and phasecomposition of the products was studied

The milled mixtures and the products of SHS were studied usingXRD analysis and Electron Microscopy The experimental conditionshave been found favoring the formation of the two-phase mixtures ofTiN of TiB2 with the grain size ranging from 20 to 50 nm [7]

References1 GV Samsonov Nitridy (Nitrides) Kiev laquoNaukova Dumkaraquo 19692 AG Merzhanov Tverdoplamennoe gorenie (Solid State

Combustion) Chernogolovka ISMAN 2000 224 p3 AEGrygoryan ASRogachev Combustion of titaniumwith

nonmetal nitridesCombustion explosion and shock waves 2001v37 2 p168-172

4 R Tomoshige A Murayma T Matsushita Production of TiB2-TiNcomposites by combustion synthesis and their properties J AmCeram Soc 1997 80[3] 761-764

5 MAKorchagin TFGrigorrsquoeva BBBokhonov MRSharafutdinovAPBarinova NZLyakhov Solid-state combustion in mechanicallyactivated SHS systems Combustion explosion and shock waves2003 v39 1 p43-58

6 MAKorchagin DVDudina Application of self-propagating high-temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007v43 2 p176-187

7 MAKorchagin BBBokhonov Combustion of mechanicallyactivated 3Ti+2BN mixtures Combustion explosion and shockwaves 2010 v 46 2 p170-177

65

SPIN-CROSSOVER IN THE PENTANUCLEAR BYPIRAMIDALCo2Fe3 AND Fe2Fe3 COMPOUNDS

Sophia Klokishner Sergei Ostrovsky Andrei PaliiInstitute of Applied Physics Academy of Sciences of Moldova

Kishinev MoldovaKim Dunbar

Department of Chemistry Texas AampM UniversityCollege Station TX USA

Boris TsukerblatChemistry Department Ben-Gurion University of the Negev

Beer-Sheva Israel

In this article we report a model for a spin-crossover phenomenonin pentanuclear bypiramidal [M(III)(CN)6]2[M(II)(tmphen)2]3 (MM=CoFe FeFe) cluster compounds The spin-crossover phenomenonis considered as a phase transformation accompanied by a change of theground state spin The model takes into account cooperative interactionsin the crystal network local crystal fields and spin-orbit coupling actingwithin the degenerate metal sites Magnetic properties and Moumlssbauerspectra are analyzed and compared to the experimental data

1 IntroductionSpin-crossover compounds have been a subject of many

experimental and theoretical studies [1-6] Till now only a fewexperimental reports on spin crossover in cluster compounds [7-11] havebeen reported Recently FeII ions were introduced into the equatorialmetal sites of discrete cyano-bridged pentanuclear clusters[MIII(CN)6]2[MII(tmphen)2]3 (MM =CoFe(1) FeFe(2) ) [12] with atrigonal bipyramidal (TBP) structure The octahedral nitrogensurrounding of FeII ions facilitates the spin-crossover behavior Theoccurrence of the ls-hs transition in compounds 1 and 2 was proved bythe combination of Moumlssbauer spectroscopy magnetic measurementsand single-crystal X-ray studies For both types of clusters[FeII(tmphen)2]3[M

III(CN)6]2(M=FeCo)7 the T product increases by

~9emumiddotKmol between 150 K and 375 K thus indicating the ls ndashhstransition at the FeII sites The TBP FeII

3CoIII2 cluster due to its electronic

66

structure represents an ideal system for studying the effects ofintracluster short-range and intercluster long-range interactionsfacilitating spin-crossover In the (FeIII)2 (FeII)3 cluster the hs-FeII and ls-FeIII ions are coupled by exchange interaction In spite of the fact that theexchange interaction of the hs-FeII and ls-FeIII ions through the cyanidebridge is sufficiently weak as compared with that in oxide clusters it isinterestingly to understand whether this interaction may affect the spintransformation The effects of orbital degeneracy on the spin-crossovertransformation in the [FeII(tmphen)2]3[FeIII(CN)6]2 crystal will beexamined as well In the present article a microscopic approach to theproblem of spin crossover in crystals containing metal clusters isdeveloped

2 The modelIn the basic structural unit of compounds 1 and 2 two MIII ions

surrounded by six carbon atoms occupy the apical positions and threeFeII ions coordinated by the nitrogen atoms reside in the equatorial plane[12] In a strong crystal field of carbon atoms the ground terms of the

CoIII and FeIII ions are the low-spin orbital singlet )( 621

1 tA ( 0S ) and

the orbital triplet )( 421

3 tT respectively The ground state of a FeII -ion in

the crystal field induced by the nitrogen atoms can be either low-spin

(ls)- term )( 621

1 tA or high spin (hs) ndashterm 2422

5 etT Both magnetic

measurements and Moumlssbauer spectroscopy for water containing crystals[12] demonstrate the presence of some amount of FeII ions in the hsconfiguration even at very low temperatures Further on we consider inthe model two types of FeII ions and denote by x the fraction of FeII -ions which are in the hs ndashstate at all temperatures while theconcentration of those ions which undergo the ls-hs transition is (1-x)The number pi of trigonal bypiramidal clusters in which i (i=0123) ofthree FeII ions are in the hs configuration in the whole temperature range

is estimated as iiii xxCp 33 1 where rllrC r

l

The Hamiltonian of intraion interactions can be written in the form

67

Hg

gllsH

kkB

kkB

kZkk

)(

32)(

211

02

0

H

lsH

(1)

where numbers theIIFehs ions in the k-th bypiramidal cluster the

first term is the spin-orbit (SO) coupling in the cubic )( 2422

5 etT - term of

theIIFehs -ion the second term describes the axial crystal field

splitting the 125 lT term into an orbital singlet ( 0lm ) and an

orbital doublet ( 1lm ) the third term refers to the Zeeman

interaction for hs-FeII ions and contains both the spin and orbitalcontributions B is the Bohr magneton and g0 is the spin Lande factorFinally the fourth term represents the interaction of the ground Kramersdoublets of two ls-FeIII ions in the cluster with the external magnetic

field i is the matrix of the pseudo -spin frac12 of the ls-FeIII ion g1 =173

is the Lande factor Up to room temperature the ls-FeIII can be regardedas an ion with the pseudo-spin frac12 because the ground Kramers doubletand the excited quadruplet arising from the splitting of the 2T2 term by

the spin-orbital interaction are separated by the gap 173023 cm

( 1486 cm [13] for a free ls-FeIII) that is large enough from the

thermal population of the excited quadruplet at room temperatureThe superexchange interaction (several cm-1 [1415]) in the

[FeII(tmphen)2]3[FeIII(CN)6]2 through the cyanide bridges couples the hs-FeII ions in equatorial and ls-FeIII ndashions in axial positions Further on wewill neglect the essentially anisotropic orbitally dependent terms andretain only the isotropic part of the exchange interaction between the hsndashFeII and ls ndashFeIII ions in a cluster The Hamiltonian of exchangeinteraction for the thk cluster looks as follows

kkkex

k

exJH

212 σσs (2)

where 2s is the spin of the hs-FeII ion the summation in (2) takes

into account the hs-FeII ions appearing in the thk cluster due to thespin transition and those which are in the hs-state in the whole

68

temperature range As in [16-18] we suppose that the mechanismresponsible for the ls-hs transition is the interaction of FeII ions with thespontaneous all-round full symmetric lattice strain Applying theprocedure suggested in [16-18] we obtain the Hamiltonian of electron-deformational interaction

2k kkk

kkst

nm

JBH (3)

where 21AB 21AJ

01021

2

ccc

cA n

(n=123) is the number of FeII ions which undergo the ls-hs transition ina complex m is the number of TBP MIII

2MrsquoII3 complexes whose FeII ions

are involved in the spin conversion =1n k=1m 0 is thevolume that falls at a Fe ion and its nearest surrounding and is the unit

cell volume per one iron respectively In the basis of the states 25T and

11A the 1616 matrix k is diagonal and has 15 eigenvalues equal to 1

and one eigenvalue equal to -1 Finally 2)(1 lshs

2)(2 lshs hs and ls are the constants of interaction of the

FeII ion with the full symmetric strain1A in the hs and ls states

respectively The first term in (3) acts as an additional field applied toeach spin-crossover ion and redefines the effective energy gap 0

between the hs and ls states of the FeII in the cubic crystal field Thesecond term in (3) represents an infinite range interaction between theFeII ions which undergo the spin conversion This interaction arises fromthe coupling to the strain The model of the elastic continuum introducedabove satisfactorily describes only the long-wave acoustic vibrations ofthe lattice Therefore the obtained intermolecular interactioncorresponds to the interaction via the field of long-wave acousticphonons

Due to the proximity of the FeII ions in the clusters short-rangeinteractions between these ions inside the cluster are relevant Thelargest is the effect of the exchange arising from the optic phonons [19]

69

The Hamiltonian describing short-range interactions between FeII ionswithin the trigonal bipyramid can be written as

0

kkk

sr JH (4)

The Hamiltonian (4) takes into account the interaction between the FeII

ions participating in the spin transitions the interaction of these ionswith those FeII ions which are in the hs-state in the whole temperaturerange as well as the interaction between the latter It should bementioned that eq (3) as compared with eq(4) only accounts for FeII

ions participating in spin conversion The Hamiltonian for the wholecrystal can be written as

k

kexstsr HHHHH

2

00 (5)

where k

k

exex HH In the molecular field approximation the full

Hamiltonian H can be written as a sum of one-cluster Hamiltonians

)(32)(

)2

(~

211101

2

1

0

0

kkB

kkkB

k

ex

kkZ

kkkkkkk

gIgHIl

IlsJBJH

HlsH

(6)

where in the basis of the states 25T and 1

1A kI1

is a diagonal 1616 -

matrix with 15 eigenvalues equal to 1 and one vanishing eigenvalue is the order parameter In fact the Hamiltonians kH

~describe clusters

with different numbers of spin-crossover FeII ions and k as beforenumbers the clusters in the crystal For calculation of the temperaturedependence of the order parameter the self-consistent procedure wasapplied The calculations of the magnetic properties were based on theHamiltonian given in Eq(6)

3 Results and discussionThe estimation of the parameters J and B was performed

according the procedure suggested in paper [16-18] For characteristicfor compounds 1 and 2 parameters =1026Aring3 0 =8Aring3

c2 (005divide01)c1211

2 10 cmdynec 1046 141

cm 142 1087 cm the

70

parameters J and B take on the values 20divide80 cm-1 and -95 divide -24 cm-1respectively

Fig1 shows the experimental data for compound 1 together withthe calculated T vs T curves The result of the best fit procedure in

the model above developed is presented by curve 1 The best fitparameters are the part of the figure caption One can see that a quitegood agreement with the experimental data is obtained At temperaturesbelow 100 K the T values show that the FeII ions are mainly in the ls ndashstate However some small admixture of hs ions is present In thetemperature range 150-300 K the T product gradually increases thusindicating the ls - hs transition in the FeII ions

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30 35

04

06

08

10

3

2

1

T

cm

3K

mo

l-1

Temperature K

23

1

T

cm

3K

mo

l-1

Temperature K

Fig1 Temperature dependence of the T product for 1 Circles-experimentaldata [12] The solid lines represent a theoretical fit with =-103 cm-1 x=10and (1) hs-ls =640 cm-1 J =35 cm-1 J0=45 cm-1 =180 cm-1 =10 (2) hs-

ls=620 cm-1 = -136 cm-1 J=0 J0=0=06 (3) hs-ls=630 cm-1 =168 cm-1J=0 J0=0 =06

The parameter J of long -range cooperative electron-deformationalinteraction obtained from the best fit procedure falls inside the limits

71

estimated above Relatively small values of the parameters J and J0 ascompared with the gaps hs-ls= 0-2B and are also in agreement withthe observed gradual temperature dependence of T and noticeable

increase of T at temperatures higher than 150K Finally the estimated

from the best fit procedure percentage of FeII ions (x=10) which are inthe hs-state at any temperature is very close to that obtained from theMoumlssbauer spectra [12] For comparison in the same figure (curves 23)the results of fitting of the T curve in neglect of long- and short-

range interactions are shown for the cases of 0 and 0 It isseen that in this approximation the calculated curves 2 and 3 differsignificantly from the experimental one both at low and hightemperatures besides this the obtained value 60 is too small forhs-FeII-ions

For compound 2 the variation of the observed magneticsusceptibility as a function of temperature is presented in Fig2

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

321

T

cm

3K

mo

l-1

Temperature K

Fig2 Temperature dependence of the T product for 2 Circles experimentaldata [12] Curves 1- 3 were calculated with the following parameter values hs-

ls =690 cm-1 J=30 cm-1 J0=40 cm-1 =100 cm-1 =-103 cm-1 =10 x=9and (1) Jex = 3 cm-1 (2) Jex = 0 (3) Jex = -3 cm-1

72

First the magnetic behavior of complex 2 was analyzed withneglect of intracluster Heisenberg exchange interaction between FeII andFeIII ions The result of the best fit procedure is presented by curve 2 inFig2 The best fit parameters are the part of the figure caption One cansee that the values of the key parameters are close to those for complex1 However the obtained energy gap hs-ls between the ls and hsconfigurations for complex 2 is a bit larger than the corresponding gapfor compound 1 while the parameters of short-range and long-rangeinteractions are smaller Namely this difference in the characteristicparameters leads to lower values of T for compound 2 as compared

with compound 1 at temperatures higher than 150K The effect ofexchange interaction on the magnetic behavior is illustrated in Fig2 bycurves 1 and 3 Since typical values of the exchange parameters incyanide bridged complexes are of several cm-1 we calculated the Tproduct with the set of the best fit parameters and Jex = -3 cm-1 and 3cm-1 One can see that at temperatures higher than 50K the smallexchange interaction has no effect on the magnetic properties ofcomplex 2

Moumlssbauer spectra provide direct information about the populationof the hs and ls states and serve a reliable test for the theoreticalbackground of the SCO phenomenon The total Moumlssbauer spectrum(ie the observable spectrum) was obtained by summing up the spectrayielded by different cluster electronic states in the molecular field withdue account for their equilibrium populations for a given (at a certaintemperature) value of the molecular field In calculations theexperimental values for the parameters of the quadrupole splttings andisomeric shifts were taken from [12] The calculated and experimentalspectra are shown in Fig3

Quite good agreement between the experimental data andtheoretical calculations is obtained It should be underlined that themodel takes into account the main effect inducing the temperaturedependence of the Moumlssbauer spectra and this is the temperaturedependence of the cluster energies in the molecular field Namely thiseffect is responsible for the transformations of the Moumlssbauer spectrawith temperature

73

The proposed model gives a good fit to the observed temperaturedependence of the static magnetic susceptibility and the Moumlssbauerspectra The last clearly illustrates the cooperative nature of SCOtransformations in TBP compounds that leads to a crossing of the ls andhs levels due structural phase transition induced by the ordering of thelocal deformations through the field of the acoustic phonons

Fig3 Moumlssbauer spectra for compound 1 calculated at T=42 220 and 300Kwith the set of the best fit parameters (thick solid lines) Contributions from ls -FeII and hs -FeII ions are shown in dash and dot lines respectively The half-width of the individual lines Г=016 cm-1(42 К) Г=018 cm-1(220К)Г=024cm-1(300К)

74

AcknowledgmentsFinancial support of the STCU (project N5062) is highly

appreciated BT and KD gratefully acknowledge financial support ofthe Binational US-Israel Science Foundation (BSF grant no 2006498)BT thanks the Israel Science Foundation for the financial support (ISFgrant no 16809)

References1 Guumltlich P Goodwin H A Spin Crossover in Transition Metal

Compounds Springer-Verlag 20042 Hauser A Light-Induced Spin Crossover and the High-Spin rarrLow-

Spin Relaxation Springer-Verlag 20043 P Guumltlich J Jung Nuovo Cimento D 1996 18 1074 P Guumltlich A Hauser H Spiering Angew Chem Int Ed Engl

1994 33 20245 J Zarembowitch New J Chem 1992 16 2556 A B Gaspar V Ksenofontov M Serdyuk P Guumltlich Coord

Chem Rev 2005 249 26617 JA Real AB Gaspar MC Munoz P Guumltlich V Ksenofontov H

Spiering TopCurrChem2004 2331678 G Vos RAG De Graaff JGHaasnoot AM van der Kraan De

PVaal JReedijk InorgChem 1984 23 29059 EBreuning MRuben JMLehn FRenz YGarcia VKsenofontov

P Guumltlich E Wegelius KRissanen AngewChemIntEd 2000 392504

10 M Nihei MYi MYokota LHan AMaeda HKushida HOkamoto HOshio AngewChem IntEd 2005 446484

11 D-Y Wu O Sato Y Einaga C-Y Duan Angew Chem Int Ed2009 48 1475 ndash1478 2009

12 MShatruk ADragulescu-Andrasi KEChambers SAStoianELBominaar CAchim KRDunbar J Am Chem20071296104

13 AAbragam BBleaney Electron Paramagnetic Resonance ofTransition Ions Clarendon Press Oxford 1970

14 A V Palii SM Ostrovsky S I Klokishner B S Tsukerblat C PBerlinguette K R Dunbar J R Galaacuten-Mascaroacutes JAmChemSoc2004 126 16860

15 HWeihe H Gudel H Comments Inorg Chem 2000 22 75

75

16 SI Klokishner F Varret J Linares ChemPhys 2000 255 31717 SI Klokishner JLinares PhysChemC 2007 111 1064418 SI Klokishner J Linares F Varret Journal of Physics

Condensed Matter 2001 13 59519 JM Baker Rep Prog Phys 1971 341 109

53

NON-CARBON PREPARATION OF SILICON BYMECHANICALLY ACTIVATED THERMAL SYNTHESIS

TF Grigorieva1 TL Talako2 AI Letsko2 V Šepelaacutek3 VG Scholz4MR Sharafutdinov1 IA Vorsina1 AP Barinova1 PA Vitiaz2

NZ Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry Kutateladzestr 18 Novosibirsk 630128 Russia grigsolidnscru

2 Powder Metallurgy Institute Platonov str 41 Minsk 220005 Belarus3 Inst of Nanotechnology KIT Eggenstein-Leopoldshafen 76344 Germany

4 Inst of Chemistry Humboldt Univ Berlin 12489 Germany

IntroductionIn industrial processes the production of Si is based on the

reduction of silicon dioxide by carbon at a temperature of about 1800 C[1] However the coke applied to the reduction can be hardly refinedfrom the most dangerous for silicon impurities like boron phosphorusarsenic and antimony That is why development of non-carbon routes forsilicon production is a topical problem of a silicon industry Reductionof oxides with magnesium and aluminum by the method of self-propagating high-temperature synthesis (SHS) has been used in industryfor a long time [2] As such reactions are highly exothermal they can bealso organized with the use of mechanochemistry for instance reductionof the copper oxide by aluminum Mechanochemical reduction of ironoxide by aluminum aimed at obtaining precursors with differentcompositions for intermetallideoxide SHS composites has been alsoconsidered [3ndash6]

SiO2 + Al reaction is not high exothermic enough to organize theSHS without preliminary heating [7] Mansurov et al [8] reportedcreation of ceramic composites in several stages first the silicon oxidewas mechanochemically treated in an organic compound environmentthen the resultant material was annealed (carbonized) at ~ 850 C andfinally the mixture of the carbonized silicon oxide with aluminum wassubjected to SHS However as-formed product included silicon carbide

The objective of activities described in this paper is to study thepossibility of using mechanochemical treatment for obtainingsiliconaluminum oxide composites by the SHS and thermal synthesis atconsiderably lower temperatures with the following removal of alumina

54

Sample preparation and examination proceduresThe PA-4 aluminum powder and the silicon oxide with a particle

size of ~ 3 nm were used in our experimentsA stoichiometric mixture of the silicon oxide with aluminum was

processed in a high energy planetary ball mill (drum volume 250 cm3ball diameter 5 mm mass of the balls 200 g mass of the sample 10 gand velocity of rotation of the drums around a common axis ~1000 rpm)

The IR spectra were recorded by a Specord IR 75 spectrometerthe samples for this study were pressed with annealed potassiumbromide

The 27Al (I = 52) NMR spectra were recorded on a BrukerAdvance 400 spectrometer corresponding to a 27Al resonance frequencyof 782 MHz MAS experiments were realized with a high speed probeusing 25 mm zirconia rotor The spinning speed was 20 KHz Themagnetic field strength (in frequency unit) was set to 104262 MHz Theexcitation pulse duration was chosen equal to 1 s The recycling delaybetween each acquisition was fixed to 1 s To see weak signals in the Al-O region in mechanically activated samples we applied accumulationsnumbers up to 56000 (ie measurement time of 15 hours)

The dynamics of the SHS process was studied with the use ofdiffraction of synchrotron radiation and an OD-3 single-coordinatedetector The samples for SHS were prepared in the form of pellets 20mm in diameter and 1ndash2 mm thick by pressing at a pressure of 200 atmThe resultant samples were placed onto a ceramic plate so that they werein the center of the goniometer The process was initiated by a nichromespiral The OD-3 detector was triggered to operate in the ldquofast filmingrdquomode simultaneously with the beginning of pellet burning The time ofone ldquoframerdquo was 05 sec and the number of ldquoframesrdquo was 128 Theradiation wavelength was 1527 Aring

For investigation of mechanically activated thermal synthesis thesamples were heated up to 650 C in the reaction chamber XRK 900 inair with a heating rate 10 min The OD-3 detector was also used forstudying the process dynamics though time of one ldquoframerdquo was 1 min

55

Results and discussionFirst we made an attempt of direct mechanochemical reduction of

the silicon oxide by aluminum The study of this process showed that thechemical reaction of SiO2 reduction does not occur within 6 min ofmechanical activation The IR spectrum of the initial mixture containsclear absorption bands with the maximums at 1005 and 480 cmminus1

(valence and deformation oscillations of the SindashO bond of the SiO4

tetrahedra of the siliconndashoxygen skeleton) and two maximums in therange of 900ndash670 cmminus1 due to oscillations of the SindashOndashSi bridges Thephenomena observed in the course of mechanical activation were agradual decrease in intensityand broadening of the characteristic bands of the SindashO bond (Fig 1)

An electron-microscopy study of the SiO2Al composite obtainedafter 1 min of mechanical activation in characteristic radiation revealed a

Fig 2 Microphotograph of themechanocomposite after 1 minactivation in Si characteristic

radiation

Fig 1 IR spectra of the SiO2 + Al mixturebefore mechanical activation (1) and aftermechanical activation during 05 (2) 1 (3)

and 6 (4) min

56

very small grain size and a very uniform distribution of the componentsin the mechanocomposite (Fig 2)

Based on the data of the differential thermal analysis (DTA) evenshort-time activation of this mixture appreciably affects its thermalcharacteristics For the initial mixture the real chemical interactionoccurs at a temperature T gt 1000 C (Tmax = 10836 C) (Fig 3 a) iesubstantially higher than the melting point of aluminum whereas thesituation is different for the mixture subjected to mechanical activationduring 20 sec Two clearly expressed exothermal peaks appear the firstpeak at 6217ndash6486 C (Tmax = 6327 C) and the second peak at 9921ndash10759 C (Tmax = 10292 C) (Fig 3 b) For the mixture activated for 40sec the first peak is at 6045ndash6366 C (Tmax = 612 C) and the secondpeak is extremely broad and smeared in the range of 8161ndash11117 C(Tmax = 10381 C)

These observations can be explained by the fact that a tightcontact is created between some part of the ultrafine non-plastic siliconoxide and plastic aluminum already within 20 sec of mechanicalactivation the silicon oxide is ldquowettedrdquo by aluminum as a result somepart of the silicon oxide starts to interact with aluminum at a temperatureT = 6217C which is lower than the melting point of the latter Asmechanical activation is continued aluminum becomes also dispersed tonanoparticles greater amounts of the components of the mixture areinvolved into the contact and the temperature of the interactionbeginning decreases after 1 minute of activation the interaction beginsat T = 5399 C and ends at T = 6303 C (Fig 3 c)

The curve for this sample obtained by the method of differentialscanning calorimetry (DSC) has only one exothermal peak ie theentire process proceeds at a temperature lower than the melting point ofaluminum Longer activation further decreases the temperature ofreaction beginning (Table 1) but there are no any further significantchanges in the system parameters determined by DSC

The duration of mechanochemical treatment was limited to 6 minfor the following reasons- the IR spectra are so smeared already after 4 min that do not provide

any new information (see Fig 1)- the DTA study does not reveal any significant changes in the thermal

characteristics after 1 min of mechanical activation (see Table 1)

57

- mechanochemical actions should be always minimized to ensure theminimum possible contamination of the products by milling

Fig 3 Results of differential scanning calorimetry (DSC) and thermogravimetry(TG) studies of the SiO2 + Al mixture before (a) and after mechanical activation

during 20 (b) and 60 sec (c)

58

Table 1 Parameters of Exothermal Peaks on DTA Curves of SiO2 + AlSamples after Mechanical Activation

Temperature CDuration of activation

beginning of thereaction

end of the reaction

1 min 5930 6303

2 min 5871 6243

4 min 5867 6291

6 min 5870 6258

27Al MAS NMR spectra of the nanostructured SiO2Almechanocomposites are dominated by a broad resonance associated withthe presence of nanostructured Al matrix (Fig 4) The interestingobservation is that additional resonance lines appear in the spectra ofmechanoactivated samples corresponding to AlO4 AlO5 and AlO6

polyhedra Their content is slightly increasing with increasing millingtime however the relative intensity of AlOx polyhedra compared withthe Al matrix spectral intensity is even after the longest milling periodvery low It can be assumed that these nonequilibrium localcoordinations of aluminium atoms are located on the SiO2-Al interfaces[9] The intensity of the resonance lines belonging to various polyhedrarelative to the total spectral intensity allows us to calculate the volumefraction of interface regions in the nanocomposites Furthermoreassuming a spherical shape of SiO2 nanoparticles the thicknees of theinterface regions was calculated their known volume fraction

Thus the study of mechanically activated SiO2+Al mixturesshows that silicon reduction does not occur during mechanical activationstep except formation of some AlOx species at the interfaces but anexothermal reaction in activated mixtures can proceed at substantiallylower temperatures

In the subsequent step the nanostructured SiO2Almechanocomposites were used as precursors for the preparation ofSiAl2O3 composites via self-propagating high-temperature synthesisOur experience shows that combustion initiation requires sample

59

preheating approximately to 200 C (as compared with 650-860 Сreported in [7])

Fig 4 27 Al MAS NMR spectra of non-activated sample (a) the samplemechanoactivated for 1 (b) and 6 (c) minutes

60

The overall pattern of phase transformations is illustrated in Fig 5a To analyze them however it is more convenient to use the projectiononto the diffraction angle (β)ndashtime plane (Fig 5 b) As the silicon oxideused in these experiments is amorphous to x-ray radiation onlyaluminum peaks are observed

Fig 5 Dynamics of phase transformations in the Al + SiO2 mechanocompositein the SHS mode (a) three-dimensional image (b) projection onto thediffraction anglendashtime plane

61

It is clearly seen thataluminum becomes heatedas the combustion waveapproaches the peaks areshifted toward smallerangles ie greaterdistances between theplanes After that theintensity of these peaksdrastically decreaseswhich is apparently due tomelting No crystallinephases are observed in thetwo frames (~ 1 sec) Inour opinion corundum(Al2O3) peaks appearslightly earlier than siliconpeaks A possible reason isthe lower melting point ofsilicon (1410 C) as compared with corundum (2050 C) An electron-microscopic study of the SHS product of the SiO2 + Al system subjectedto mechanical activation during 1 min in characteristic radiation (Fig 6)shows a fairly uniform distribution and small size of all elements in thesystem including silicon being formed

Previously it was shown that chemical interaction between SiO2

and Al in the mechanocomposites formed during the mechanicalactivation starts at essentially (~ 500 C) lower temperatures as comparedwith the non-activated mixtures

In the final step we used as-formed mechanocomposites asprecursors for the preparation of SiAl2O3 composites via thermalsynthesis The samples after mechanical activation for 6 min wereplaced into cuvette and gently prepressed to get the plane surface Thenthe cuvette with the sample was sited in the furnace The thermocouplewas directly close to the registration area Recording of diffractogramswas started at temperature 230 С Dynamics of phase transformation inAl SiO2 composites during heating from 590 up to 660 C is presentedin Fig7

Fig 6 Microphotograph of the SHS productin Si characteristic radiation

62

As can be seen from the Fig 7 the reaction products (silicon andalumina) start to form at about 590 С It is interesting that corundum isformed during the SHS and thermal synthesis after low activation time

Fig 7 Dynamics of phase transformation in Al SiO2 composites duringheating from 590 up to 660 C

Fig 8 XRD-pattern of the thermal synthesis product from the mechanocompositesactivated for 6 min and heated up to 660 C

63

while -Al2O3 is identified in the product of thermal synthesis afterlonger MA durations (Fig 8)

ConclusionsThus though the silicon oxide is not reduced by aluminum

directly by mechanical activation the use of the mechanocomposite as aprecursor for both SHS and thermal synthesis allows a fine-grainsiliconaluminum oxide composite to be obtained In both caseschemical interaction starts at essentially lower temperatures as comparedwith the non-activated mixtures

AcknowledgementsThis work was supported by the joint project No 5 ldquoNon-carbon

preparation of Si by mechanically activated thermal synthesisrdquo of NASBand SB RAS

References1 Denisov VM Istomin SA Podkopaev OI Serebrjakova LI

Pastuchov EA Beletsky VV Silicon and its alloys EkaterinburgPublishing house of Ural Branch of the Russian Academy ofSciences 2005 467 p (in Russian)

2 AG Merzhanov Forty Years of SHS Happy Life of a ScientificDiscovery (in Russian) Chernogolovka (2007)

3 TF Grigoryeva SA Petrova IA Vorsina et alldquoMechanochemical reduction of a copper oxiderdquo in TheOptimization of the Composition Structure and Properties ofMetals Oxides Composites Nano and Amorphous Materials Proc6th IsraelindashRussian Bi-National Workshop Jerusalem (2007) pp197ndash204

4 TF Grigoryeva TL Talako AA Novakova et al ldquoMA and MASHS production of nanocomposites metaloxides andintermetallicsoxidesrdquo ibid pp 139ndash148

5 NZ Lyakhov PA Vityaz TF Grigorieva et alldquoMechanochemically synthesized SHS precursors for obtainingintermetallideoxide nanocompositesrdquo Dokl Akad Nauk 406 No6 776ndash778 (2005)

64

6 5 T Talaka T Grigorieva P Vitiaz et al ldquoStructure peculiaritiesof nanocomposite powder Fe40AlAl2O3 produced by MA SHSrdquoMater Sci Forum 534ndash536 1421ndash1424 (2007)

7 Maltsev VM Gafiyatulina GP Tavrov AV Spreading of thecombustion wave in SiO2-Al systems Proc SPIE Vol 3172(111997) p 724-727

8 ZA Mansurov RG Abdulkarimova NN Mofa et al ldquoSHS ofcomposite ceramics from mechanochemically treated and thermallycarbonized SiO2 powdersrdquo Int J SHS 16 No 4 213ndash217 (2007)

9 V Sreeja TS Smitha Deepak N Ajithkumar TG and PA JoySize dependent coordination behavior and cation distribution inMgAl2O4 nanoparticles from 27 Al solid state NMR studies J PhysChem C 112 14737-14744 (2008)

37

THE PREPARATION OF MECHANICOMPOSITESTUNGSTEN-METAL AND SINTERING MATERIALS

T Grigoreva1 L Dyachkova2 A Barinova1 S Tsibulya3 N Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS 18Kutateladze str 630004 Novosibirsk Russia grigsolidnscru

2 Institute of Powder Metallurgy NAS B Minsk Belarus3 Boreskov Institute of Catalysis SB RAS Novosibirsk Russia

Tungsten-based materials are used for manufacture of electro-technical items spot welding electrodes spraying cathodes etc

The preparation of the high-melting materials is powerconsumptive as two-stage high-temperature sintering is used tungstenpre-sintering temperature is 1150 ndash 1300 C final tungsten sinteringtemperature is 2900 - 3000 C [1]

Metal additives with a lower melting temperature are introducedinto the high-melting material for sintering temperature reduction andsince the tungsten powder has a bad moldability level more plasticmetals such as copper nickel iron are introduced for the moldabilityimprovement

Tungsten ndash copper mixture has been studied the best so farThe mixture W-Cu sintering process research has shown [2] that

the product density depends on the initial powders dispersion degree andthe mixture composition So at the tungsten particles size 10-15 m themaximum densification is observed at the copper weight ration 50 The blend density sharply decreases with the copper content decrease(less than 35 ndash 40 wt) At the same time mixtures with the coppercontent not higher than 10 are needed Special methods have to beused for the preparation of the tungsten alloys

The active densification (from 44 till 12 ) is known to take placeat 1100 - 1200 C at sintering of mixtures W-20 vol Cu with tungstenparticles size lower than 1 m [3] Even higher densification speed isobserved in a blend attained with copper tungsten reduction whencomponents mixing practically achieves a molecular level [4] ie thesecond element concentration reduction is possible at tungsten particlessize decrease and homogeneous distribution of the both componentsThe original blends mechanical activation process [5ndash7] is very

38

perspective in this trend since grinding and formation of larger contactsurface between the original components take place during mechanicalactivation This process is especially effective at mechanical activationof solid and liquid metals and plastic ndash non-plastic metals pair Thecomposite nucleus (non-plastic component) ndash cover (plastic metal) canbe created in this case The possibility of chemical interaction onbetween tungsten and plastic metal the contact surface duringmechanical activation should be considered here

The work aim is to study structure and morphology of thecomposites formed at mechanochemical activation of the tungsten witha small content (till 10 ) of plastic metals both interacting (nickel iron)with it and not interacting (copper) with it The influence of the structureand morphology of the mechanocomposites on the processes of formingand sintering was studied

Powders of tungsten nickel iron copper were used forpreparation of mechanocomposites Mechanical activation of themixtures was carried out in a high energy planetary ball mill with watercooling in argon atmosphere (drum volume ndash 250 cm3 balls diameter ndash5 mm the load ndash 200 g the sample - 10 g the velocity of rotation of thedrums around a common axis 1000 rpm)

X-ray analysis was carried out with diffractometer D8 AdvanceBruker (Germany) at the CuK radiation Research of the structure andmorphology of the mechanocomposites was carried out with thescanning electronic microscope (SEM) ldquoMira LMHrdquo with the add-ondevice for micro-x-ray analysis The electronic probe comprised 5 2 nmthe actuation area comprised 100 nm The research was carried out inmodes of registration of absorbed (AE) and backscattered (BSE)electrons and also of characteristic radiation of tungsten copper nickeland iron The sintered materials research is carried out with themetallographic microscope MEF-3 (Austria) at zoom times200 and times950

The compressibility was determined via density in compliancewith the ISO 3927-1985 of cylindrical samples with diameter 10 mmheight 12 mm pressed in a steel die-mold at pressure 200 400 600 and800 MPa The pressed samples were sintered in vacuum at temperatureof 1100 ndash 1450 C

Compression strength of mechanically activated blends wasdetermined via the samples of diameter 10 mm height 12 mm

39

transverse strength ndash via prismatic samples with height 5 mm width 10mm length 55 mm The tests were preformed on the testing machineldquoInstronrdquo with the loading speed 2 mmmin

Sintered samples microstructure was studied on metallographicsections etched with solution (10 g K3Fe(CN)6 10 g KOH 100 mlH2O) via metallographic microscope MEF-3 of the company ldquoReihertrdquo(Austria)

Mechanical activation was carried out in two stages for attainingmechanical composites tungsten ndash metal (Cu Ni Fe) The first stagesaw grinding only tungsten for 4 min At the second stage 7 ndash 10 copper (nickel iron) was added and joint mechanical activation wascarried out for 1 ndash 2 min

In compliance with the x-ray data the initial tungsten sample is awell-crystallised powder (Fig 1a) The intensity of the diffraction peaksshows the texture (of the preferred orientation) presence in trend 110The X-ray pattern of the tungsten samples activated during 4 min (Fig1b) has widened peaks The X- ray analysis shows that widening ismostly caused because of micro-defects in the tungsten structure (at thelarge particles sizes retaining) It should be also noted that thedistribution intensity of the peaks shows the texture absence (the equalparticles distribution in powder from the point of view of theircrystallographic orientation)

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

Ia

u

2 Theta degree

110

200

211

220

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

Ia

u

2 Theta degree

a bFig 1 X-Ray patterns for initial W (a) and activated for 4 min (b)

40

During the mechanical activation in a high energy planetary ballmills plastic metals tend to stick to balls and the drums walls even atshort-time activation because of that they were introduced to the blendsinto the already activated for 4 minutes tungsten and the mixture wastreated for 2 minutes more

The different X-Ray patterns were received for the samples withCu Ni Fe additives (Fig 2) The second metal phase is seen to bepresent in a well-crystallised form besides the phase W in all cases thecopper picks relative intensity is however considerably higher than thenickel picks intensity that in turn exceeds the iron reflection intensityFormation of intermetallic compounds in the X-ray-amorphous state oncontact surface WNi WFe can be supposed to be possible forchemically interacting metal pairs (tungsten ndash nickel tungsten ndash iron)X-Ray research data are indirect confirmation of this supposition Thesedata have shown that mechanochemical efforts donrsquot allow to receivehomogeneous distribution of copper in the tungsten matrixMechanocomposites W + 10 Cu is arranged in compliance with theldquosandwichrdquo principle where copper phase of micrometric size is locatedin the tungsten die (Fig 3)

The second metal phase is seen to be present in a well-crystallisedform besides the phase W in all cases the copper picks relative intensityis however considerably higher than the nickel picks intensity that inturn exceeds the iron reflection intensity Formation of intermetalliccompounds in the X-ray-amorphous state on contact surface WNiWFe can be supposed to be possible for chemically interacting metalpairs (tungsten ndash nickel tungsten ndash iron) X-Ray research data areindirect confirmation of this supposition These data have shown thatmechanochemical efforts donrsquot allow to receive homogeneousdistribution of copper in the tungsten matrix Mechanocomposites W +10 Cu is arranged in compliance with the ldquosandwichrdquo principle wherecopper phase of micrometric size is located in the tungsten die (Fig 3)Electron microscopy and X-Ray research of mechanocomposites forinteracting metals (W + 10 Ni) has shown homogenous nickeldistribution

41

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Ia

u

2 Theta degree

Cu

а

40 50 60 70 80 90

0

1000

2000

3000

4000

Ia

u

2 Theta degree

Ni

b

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Iau

2 Theta degree

Fe

c

Fig 2 X-Ray patterns for mechanocomposites W (4 min) + additives Cu(a) Ni (b) Fe (c) (2 min)

The received result allows to suggest that metals distributionhomogeneity depends on the thermodynamical parameters of theirmixture (Нmix(W-Ni) = - 2 kJmol Нmix(W-Cu) = + 10 kJmol [8])and on a possibility of the chemical interaction between them The thinlayers of intermetallic compounds form on the continuously renewingcontact surface in the systems W-Ni and W-Fe for this time period (1-2min) and because of distance these thin layers do not manage to form acrystalline phase that could be fixed in X-Ray way

42

а bFig 3 Micrographs of the mechanocomposites W-Cu (a) W-Ni (b) in

characteristic radiation Cu and Ni

The research of compressibility of various mechanocompositeshas shown that non-interaction metals (W-Cu) couldnrsquot compressed andthe compressibility of the interaction metals (W-Ni W-Fe) depends ofthe contents of additives Research of compressibility of mechanicallyactivated powders of various composition has shown that tungsten ndash10 iron mixture powder has the best compressibility level andtungsten ndash 7 nickel mixture powder has the least compressibility level(Fig 4)

But it should be noted that mechanically activated powderscompressibility level is not high moreover some mechanocompositesdo not have compressibility at specific pressure 200 ndash 300 MPa and thesamples layering is observed at pressure higher than 600 MPa Therelative density of the pressed samples is 50 ndash 78 It indicates at thenecessity of the additional lubricants introduction into the mechanicallyactivated powders for their compressibility increase

43

Fig 4 Tungsten-based mechanocomposites compressibility curve

For the powders compressibility improvement the lubricants areintroduced directly into initial mixture or plated to the press-mouldsurface for decrease of friction between the powder and the press-mouldwall and also between the powder particles The lubricant removaltemperature depends on the lubricant melting or dissociationtemperature The melting and boiling temperature or the lubricantsdissociation temperature generally used in powder metallurgy are givenin table 1 [9]

Stearates especially zink stearates have the leading place Therest lubricants have not got such a wide use since residual remains aftertheir removal [10]

Nowadays nylon-binding-based lubricant has been developedabroad This nylon binder is introduced during the charge mixingprocess and needs warm pressing [11-14] Such a lubricant allowsattaining high (θ is no less than 95 ) density of iron-based materials

The lubricant addition as a rule retains ~1 wt as higher contentleads to the pressing growth if the lubricant is present in the sinteringprocess till the sintering temperature

The lubricant burning-out process is carried out in the protective-reducing atmosphere in separate furnaces or in a sintering furnace (in thearea separated from the sintering area) The lubricant burning-outtemperature is as a rule not high and comprises 600 ndash 800 C

44

Table 1 Temperature of melting and dissociation of solid lubricants

Lubricant Lubricant formulaMeltingpoint С

Boiling ordissociation

point СZink stearate Zn(C18H35O2)2 140 335Calcium stearate Ca(C18H35O2)2 180 350Aluminium stearate Al(C18H35O2)2 120 360Magnesium stearate Mg(C18H35O2)2 132 360Plumbum stearate Pb(C18H35O2)2 116 360Lithium stearate LiC18H35O2 221 320Stearinic acid CH3(CH2)16CООH 694 360Oleinic acid С8Н17СНСН-

(СН2)7СООН13 286

Benzol acid С6Н5СООН 122 249Hexoic acid СН3(СН2)4СООNН2 -4 205Paraffin From С22Н46 till

С27Н56

40-60 320-390

Molybdenum disulfide MoS2 1185 -Tungsten disulfide WS2 1250 -Manganous sulphide MnS 1655 -Graphite С (crystalline) 3500 -Molybdenum trioxide MoO3 795 -

During one-component materials heating till 100 ndash 150 C thechange of the contact character between the particles connected withwater evaporation and elastic stress relief tale place As a result somecontact areas rupture and as a consequence general inter-particlecontact surface decrease are possible

The elastic stress relief is ended the further gases are removedand burning-out of the lubricants and binders introduced to the powdertake place during heating from 150 C till the temperature comprising 40ndash 50 of the metal melting temperature The oxide films reduction andnon-metal contact replacement with a metal one take place at highertemperatures although visible pressings density change does not takeplace

45

This work saw lubricants introduction during mechanicalcomposite formation zink stearate stearinic acid and lauric acid wereused The lubricants were introduced in amount of 0 1 0 2 0 3 0 5wt During mechanical activation metal ndash organic acid the latter ismelted (the melting temperature is lower than 70 C) and thus it wets themetal surface and flows with the formation of a larger contact surface Incase of good wettability and sufficient amount of the low-meltingconstituent all the solid-phase surface becomes contact ie mixturenucleus (metal) ndash cover (organic substance) is formed [15] Thecompressibility level has to be naturally higher in this case andmechanochemical approach allows a substantial reduction of plasticizingagentsrsquo concentration

Research of compressibility of powders with lubricants has shownthat Zink stearate has the least influence in comparison to otherlubricants used (Fig 5)

Fig 5 The compressibility curves of the mechanocomposites W-Fe with thelubricant 1 ndash zink stearate 2 ndash lauric acid

The lubricant content increase leads to the mechanically activatedpowders compressibility improvement (Fig 6) but at the lubricantcontent more than 0 3 the samples destruction takes place at sinteringbecause of intensive gas release Plasticizing agents introduction hasallowed mechanical composites formation also for non-interactingmetals (tungsten ndash copper) (Fig 6 7)

46

Fig 6 The compressibility curve of the mechanically activated blend W-Cuwith stearinic acid 1 ndash 0 1 2 ndash 0 3 3 ndash 0 5

Fig 7 The compressibility curves of the mechanically activated blend W-Cuwith lauric acid 1 ndash 03 2 ndash 05

Lauric and stearinic acids additives allow the pressings densityincrease by 25 ndash 40 (Fig 5 8)

Research of density of sintered samples of mechanocomposite hasshown that the density of the samples from mixtures tungsten ndash ironpressed at 400 and 600 MPa does not practically change after sinteringat 1250 C (Fig 9 line 2 5) and at 1450 C the samples density decreases(Fig 9 line 3 6) Mixtures tungsten ndash nickel are subject to a substantial

8

9

10

11

12

200 400 600

De

nsi

ty g

сm

3

Pressure МPа

1

2

11

115

12

125

13

200 300 400 500 600

10Fe+W

10Ni+W

De

nsi

tyg

cm

3

Compacting pressure MPa

47

shrinkage (Fig 10) and density of the samples of W-Ni pressed at 400MPa is 146 gcm3 after sintering at 1250 C and 147 gcm3 at 1350 CSintering temperature increase till 1450 C leads to samples shrinkinglevel reduction and density does not exceed 117 gcm3

Fig 8 The compressibility curves of blends W + 10 Fe and W-10 Ni withaddition of 1 of stearinic acid

Fig 9 Relation of density of mechanically activated blends W + 10 1 ndash afterpressing at 400 MPa 2 ndash pressing at 400 MPa sintering at 1250 ordmC 3 ndashpressing at 400 MPa sintering ndash at 1450 ordmC 4 ndash after pressing at 600 MPa 5 ndashpressing at 600 MPa sintering at 1250 ordmC 6 ndash pressing at 600 MPa sintering at1450 ordmC

10

11

12

13

14

200 400 600

Pressure МPа

Density

gс

m3

1

2

3

0

2

4

6

8

10

W+Fe

De

nsityg

cm

3

12 3

4 5 6

48

0

3

6

9

12

15

400 МPа 600 МPа

De

nsity g

сm

3

Fig 10 Relation of density of mechanically activated blend W + 10 Ni 1 ndashafter pressing 2 ndash pressing sintering at 1250 C 3 ndash pressing sintering at 1350C 4 ndash pressing sintering at 1450 C

Moulding pressure increase till 600 MPa practically does not

influence the sintered samples density Density reduction of the samples

sintered at 1450 C is apparently explained with dissociation of oxides

and other compounds of tungsten and nickel

Sintering at 1450 ordmC of blends W-Ni leads to meltback and

samples form loss thus sintering should be carried out at temperature

not higher than 1350 ordmC

Tungsten-based mechanocomposite strength research has shown

that strength has a direct relation to their density (Fig 11) The blend

tungsten ndash iron (870 MPa) has the minimal strength

The microstructure analysis has shown that in case of sintering at

temperature 1250 C tungsten ndash nickel have a very fine dispersed

structure (Fig 12) Coagulation of nickel insertions located at the base

grains boundaries in tungsten ndash nickel grains growth take place with

sintering temperature increase

49

0

100

200

300

400

500

600

700

800

900

1000

1100

1 2

Ela

stic

lim

it of

com

pre

ssio

n

МP

а

I - pressure 200 МPа

II - pressure 400 МPа

III - pressure 600 МPа

1 - sintering temperature 1250оС 2 - sintering temperature 1350

оС

I

II

III

Fig 11 Influence of attaining modes of samples from mechanically activatedblend tungsten + 10 nickel on their strength

Substantial grain growth large porosity formation nickel phase

particles growth take place in blends sintered at 1450 C eutectic that is

more visible in the blend tungsten ndash nickel is formed at tungsten grains

boundaries

Conclusions

The conducted research has shown that homogenous copper

distribution is failed to be carried out in tungsten with short-term

mechanical activation method for interacting metals of W-Cu system

These mechanically activated samples can be not compacted (moulded)

50

a b

c dFig 12 Microstructure of mechanically activated blends W-Ni sintered at 1250C (a b) and 1350 C (c d) a c ndash times200 b d ndash times950

Homogenous distribution of nickel and iron in tungsten is ensuredwith short-term mechanical activation in systems from interactingmetals The attained samples are formable mechanically activatedpowders compressibility has however been found to be not high therelative density of the pressed samples is 50 ndash 78 and that points atnecessity of additional lubricants introduction into powders for theircompressibility improvement Lubricants introduction allowed ensuringmoldability of immiscible system tungsten ndash copper and densification ofpressings by 25 ndash 40 - for interacting metals

Density of samples from blends tungsten ndash iron does notpractically change after sintering at 1250ordmC and is decreased at 1450 ordmCBlends tungsten ndash nickel are subject to a substantial shrinkage during

51

sintering Sintering temperature increase till 1450 ordmC also leads to theshrinkage level decrease Strength of sintered blends from mechanicallyactivated tungsten-based powders depends on density and kind of theadditive Grain size dispersivity and type of additive location in theblend structure from mechanically activated powders depend on thesintering temperature

AcknowledgementsThe work was carried out within the framework of Fundamental

Research Programme of Russian Academy of Sciences ldquoElaboration ofchemical substances attaining methods and new materials creationrdquoproject No 1821 ldquoElaboration of tungsten mechanical composites-basedhigh-density alloys creation basicsrdquo

References1 IM Fedorchenko IN Francevich ID Radomyselskiy at al

Powder Metallurgy Materials technologies properties andapplications Kiev Naukova dumka ndash 1985 ndash 624 P

2 VN Eremenko JV Najdich IA Lavrinenko Sintering in thepresence of liquid metal phase Kiev Naukova dumka ndash 1968 ndash 122P

3 VV Panichkina MM Sirotuk VV Skorohod Powder Metallurgyndash 1982 - 6 ndash P27-31

4 VV Skorohod YuM Solonin NI Filippov at al PowderMetallurgy ndash 1983 - 9 ndash P9-13

5 Kim JС Moon IН Nanostruct Mater 1998 Vol 10 No 2 P283-290

6 Moon IH Kim EP Petrow G Powder Metallurgy 1998 Vol41 No 1 P 51-57

7 Kim JC Ryu SS Kim YD Moon IH Scripta Mater 1998 Vol39 No 6 P 669-676

8 FR de Boer R Boom WCM Mattens AR Miedema andAK Niessen Cohesion in metals (Cohesion and structurevol 1) (Elsevier Amsterdam 1988) pp 758

9 Hausner H Handbook of Powder Metallurgy Chemical PublishingCo New York 1973

10 Moyer KH Intern J Powder Met 1971 - 7 Р 33

52

11 US patent В 22 F 100 5368630А Powder Metallic Blend with abinder for densification at the set temperature Journal Inventions ofcountries worldwide 1996 1

12 US patent В 22 F 100 5429792 Metal powder content containing a binder for pressing at elevated temperatures JournalInventions of countries worldwide 1996 7

13 US patent В22F 100 (11) 52980555 (40) 940329 laquoIron-basedpowder mixtures with a binding lubricantraquo 1995

14 US patent В 22 F 100 95372138 (5484469А) laquoMetal powder content and a method of a sintered part manufacture from itraquo 1995

15 TF Grigoryeva AP Barinova NZ Lyahov Mechanochemicalsynthesis of metal systems Novosibirsk Parallel ndash 2008 ndash 311 P

34

THE DETERMINATION OF THE KINETIC FUNCTIONSTRUCTURE FOR THE HIGH-TEMPERATURE SYNTHESIS IN

THE MECHANICALLY ACTIVATED MIXTURE 3Ni-Al

VYu Filimonov1 MA Korchagin2 EV Smirnov1NZ Lyakhov2

1Altai State Technical University Barnaul2Institute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirskvyfilimonovramblerru

The peculiarities of heating-up and phase formation in themechanically activated powder mixture 3Ni + Al reacting in the thermalexplosion mode have been experimentally investigated The self-heatingin the mixtures was studied using a specially designed SHS-reactorusing a technique presented in [1] Tungsten-rhenium thermocouples of100 microm diameter were used to control the temperature and to recordthermograms Preliminary mechanical activation was carried out using aplanetary ball mill of AGO-2 type in an atmosphere of argon under theenergy of 40g (centrifugal acceleration of balls 400 ms2) with varyingtime of the activation process The reactant mixtures were preparedusing the aluminum powder PAndash4 particle size 5 divide 60 microm and thecarbonyl nickel powder PNK-1L5 particle size 1 divide 10 microm

The primary goal of this work was to determine the activationenergy and the structure of the kinetic function during the heat evolutionin the system as a result of the phase formation At the adiabatic stage ofheating a system of equations of the temperature increase and thedynamics of the degree of transformation was considered [2]

0 expdT E

k fdt RT

(1)

f

RT

Ek

dt

d

exp1

(2)

The initial conditions are as follows 00 t 0TT where

T temperature of the reacting mixture degree of transformation

t time 0k 1k exponential factors E activation energy f -

35

kinetic function The search for )(f was performed in the known class

of functions [3]

exp

1nm

f

(3)

At the first step of analysis of the experimental thermograms theeffective activation energy of the phase formation was determined from

the curvature of the experimental plot ln 1dT dt f T Based on the

results of 6 measurements and using the slope of the fitting curvepassing through the point of the minimum curvature the effectiveactivation energy was determined which turned out to be anomalouslylow and equal to E = 95plusmn2 kJmol It was found that the experimental

results are best fitted with a function 1n

f where

09 015n [4] Fig1 shows the results of integration of (11) with the

determined parameters

Fig1 Results of integration of (11) -1 experimental thermogram -2

Since the interaction of the reactants is described by the law ofhomogeneous kinetics we suggest that during thermal explosion in themechanically activated mixture of the composition under study thesynthesis occurs through homogeneous regrouping of atoms of the initialreactants without formation of dense diffusional layers hindering thereaction The latter is possible due to high concentrations of defects andinternal stresses formed as a result of intensive plastic deformation of theinitial reactants during mechanical activation

36

References1 Filimonov VY Evstigneev VV Afanasev AV and Loginova MV

Thermal Explosion Ti + 3Al Mixture Mechanism of PhaseFormation International Journal of Self-Propagating High ndashTemperature Synthesis-2008- vol 17-2рр 101-105

2 Aldushin AP Martemyanova T M Merzhanov A G Propagationof the front of an exothermic reaction in condensed mixtures withthe interaction of the components through a layer of high-meltingproduct Composition Combust Explos Shock Waves19728(2)159

3 M I Shilyaev V Е Borzykh A R Dorokhov and V EOvcharenko Determination of thermokinetic parameters from theinverse problem of an electrothermal explosion Combust ExplosShock Waves 1992 28(3)258

4 MA Korchagin VYu Filimonov EV Smirnov NZ LyakhovThermal explosion of a mechanically activated 3Ni + Al mixture Combustion explosion and shock waves 2010 v 46 1 pp41-46

14

MODERN METHODS OF RHENIUM DETERMINATION

OV Evdokimova NV Pechishcheva KYu ShunyaevInstitute of Metallurgy of UB RAS

101 Amundsen st Ekaterinburg Russiashunuralru

IntroductionRhenium due to its unique properties is the promising metal

widely used in various industries At present day the main areas ofapplication of rhenium is the production of catalysts for the petroleumrefining industry and refractory alloys used for turbines manufacturing[1]

The great demand for this element requires large amounts of itsproduction There is a need extracting rhenium even from industrialwaste water from plants [2] due to the high cost and its low content innatural materials

This situation stimulates the development (or modification) ofmethods of analytical control of various nature materials

The content of rhenium in rhenium-containing materials bothnatural and technogenic and contect of accompanying to rheniumelements vary in a wide range of concentrations from 10-7 to tens ofpercent

Earlier the following methods were used for the determination ofrhenium spectrophotometry gravimetry kinetic electrochemicalextraction-fluorimetric methods X-ray fluorescence analysis [3] Themain disadvantages of mostly methods for determining rhenium are thelow sensitivity the bad reproducibility of results the influence ofaccompanying elements Ag W Mo Pt Cu Fe and etc

In modern analytical practice the following methods for therhenium determination are used inductively coupled plasma atomicemission spectroscopy (AES ICP) inductively coupled plasma - massspectrometry (ICP-MS) [4] electrochemical methods [1] X-rayfluorescence analysis and spectrophotometric methods do not lose theirrelevance [1] they have undergone significant modifications recently

15

Inductively coupled plasma atomic emission spectroscopy(AES ICP) is widely used for the rhenium determination in mineral rawmaterials and products of metallurgy production This method allows todetermine up to 10-4 rhenium The advantage of AES ICP is the highstability and reproducibility of results absence of chemical influences

However analysis of more complex objects such as metallurgicalproducts is a not easy task because the lines of rhenium emission areoverlaped with the lines of accompanying elements in samples So thelines of Mo (221427 nm) W (221431 nm) Fe (227519 nm) whichmay be present in the samples in large quantities are overlaped to themost intense lines of rhenium (221426 nm and 227525 nm) Thisproblem requires the development of new methods of samplepreparation and selection of optimal conditions for determination ofrhenium by atomic emission spectrometres

Also a significant disadvantage of this method is the small rangeof certificated reference materials So there are a limited number ofRussian rhenium standard materials with certified value of the rheniumcontent It is molybdenum and copper-molybdenum ores andconcentrates in which the rhenium content is in the range ofconcentrations from 000047 to 00221

In most cases analysts develop the synthetic mixture to monitorthe rhenium content in the analysis of specific samples of complexcomposition This mixture is similar to composition to the matrix of theanalyzed samples consisting of rhenium ions and other ions with agiven concentration For example the authors [5] to develop a techniquefor rhenium determining together with platinum and palladium in thesamples of spent catalysts by AES-ICP applied a synthetic mixtureprepared on the basis of aluminum oxide and standard solutions of Pt(IV) Pd (II) Re (VII)

One of modern methods and the most sensitive methods for thedetermination of rhenium is inductively coupled plasma - massspectrometry (ICP MS) [4 6 7 8] These days ICP MS withseparation and concentration allows to measure rhenium at lower thanseveral ngg However ICP MS performance in analyses of complexsamples is commonly affected by matrix effects and polyatomicinterference and signal drift High levels of salt solutions content cause

16

plugging of sampling orifice with decrease in analytical signal inaddition many spectral interferences may occur [6]

For the rhenium determination in molybdenite by ICP MS shouldbe use large dilution of sample to reduce the matrix influence and reducethe salts influence However this approach is not feasible in the case ofhigh levels of molybdenum and relatively low levels of rhenium in theanalyzed objects The most effective way to minimize the matrix effectsis separation of rhenium from the matrix Often for this purposeextraction by organic solvents [6] sorption by anion-exchangers [8] areused

Recently X-ray fluorescence analysis becomes more popular Itis rapid and is often used for mass analysis The advantage of thismethod is the possibility of direct determination of rhenium in the solidsamples in water solutions [9 10] in the biological samples (plants) [2]

However the method is not without disadvantages firstly thedetection limit of rhenium by X-ray fluorescence analysis is low and isonly 005-01 secondly there are only few the standard materials witha high rhenium content and thirdly the influence of interfering elementsin the sample related to determination of rhenium

Using the concentration can not only reduce the detection limitbut also in the same time solve and reduce the influence of interferingions For the concentration of rhenium in X-ray fluorescence analysis isoften used sorption of rhenium in the form of perrhenate-ions [9 10]

The authors [11] describes a problem related to the developmentof rhenium-containing standard materials by traditional hightemperature approach for X-ray fluorescence analysis Thus high-temperature studies of MoO3-ReO3 which could be served ascomparison materials for the rhenium determination by X-rayfluorescence analysis showed that 50-90 of rhenium is lost duringcalcination of mixtures it indicates the impossibility to use them fordevelopment of standard materials In the paper [11] the method ofpreparing rhenium glassy reference samples (10 - 50) on the basis ofBi2O3 and B2O3 is described The developed method allows to determinerhenium in the range of 001-10 [11]

17

Electrochemical methods in particular the electrostrippingvoltammetry (ESV) occupy a significant place in the analyticalchemistry of rhenium [12 13] This method allows to determine up to10-6-10-5 of rhenium

To avoid the effects of many electropositive components (Mo WCu Ag Au) which may interfere to the rhenium determination by ESVit has been proposed the sorption concentration of perrhenate ions on thesurface of activated charcoal (BAU) [12 13]

The most widely used techniques determine the 10-2 - 10-5 ofrhenium is spectrophotometric method The advantages of this methodare simplicity low cost equipment and a relatively high sensitivitySpectrophotometric method is based on the formation of coloredcomplex compounds of rhenium with organic and inorganic ligands [1]Photometric methods with thiocyanate ion thiourea are widely spread[14 15 16] Development of spectrophotometric methods for rheniumdetermination is largely due to the searching and using of new reagentsIn [17] for the extraction-photometric determination of perrhenate ionsin the form of ion associates the basic polymethine dyes derivatives of133-trimethyl-3H-indole have been offered but the influence ofoxyanions of tungsten and molybdenum is not excluded [17]

The disadvantage of the spectrophotometric methods is the needfor prior separation of rhenium from a number of interfering elements(Mo W Cu) that it is achieved by concentrating perrhenate-ions bysorption or extraction

Over the past decade main changes in the methods of rheniumdetermination related with the improvement stadium of samplepreparation transfer the sample into an analytical form modification ofknown methods and reagents (eg creation of new facilities developmentof new reagents for measurements) and conditions of analysis

In general in the literature a large number of works are relatedwith the separation of rhenium from the analyzed solutions and theseparation of rhenium (VII) from interfering elements by using newtypes of extractants and new sorbents is given Used extractants andsorbents as well as the optimal conditions for extraction and sorption ofrhenium are presented in Table 1 and 2 respectively

18

Extraction plays a dominant role in the methods of separationand concentration of rhenium

In most cases in the hydrometallurgical processing of rhenium-containing products in the acidic solutions ReO4

- are formed Forperrhenate ions extraction the anion-exchange reagents or extractants ofneutral type are often used The literature contains information on theextraction of rhenium (VII) by various amines and quaternaryammonium compounds [18 19 20] Efficient extractants of rheniumfrom acidic solutions are neutral organophosphorus compounds (tributylphosphate alkylphosphineoxides their derivatives) [21 22] a variety ofsolvent mixtures (tributyl phosphate + trioctylamine [23]) theextractants of neutral type such as ketones and aliphatic alcohols [1624 25]

Alcohols ketones and ethers are more selective having higherspeed separation of organic and aqueous phases as well as higherchemical resistance and lower cost compared with amines andorganophosphorus compounds but inferior to them in the extractioncapacity for rhenium (VII) [16]

Thus for perrhenate ions extraction aliphatic alcohols with 7-10carbon atoms in the aliphatic chain are well proven that can extractmore than 98 of rhenium from sulfuric acid and hydrochloric acidsolutions In the case of alcohol there is no need to use solvents andmodifiers what simplifies their use in extraction processes [16]

The efficiency of rhenium extraction into organic phase by aminesdecrease as follow quaternarygt tertiarygtsecondarygtprimary Amongthem secondary and tertiary amines are widely used as efficientextractants of rhenium from acidic solutions Perrhenate ions areextracted by amines in a wide range of pH For systems of amine - low-polar diluent - H2SO4-ReO4-H2O the formation inverse micelles istypical in the organic phase Acid ions and anionic complexes arelocated inside the aqueous core of the micelle with the metal ioncoordinates the polar functional group of amine [19 20]

It should be noted that the extraction by amines is complicated bythe use of solvents the nature of which depends on the solubility ofamines and their extraction capacity So low-polarity solvent toluene incontrast to the non-polar kerosene enhances the polarity of anionic saltsof amine which increases the reactivity of the extractant to the anion

19

exchange of inorganic acid to extractable anionic rhenium complexes[18]

Tertiary amines are the most effective extractants for rhenium(VII) However in paper [18] it is shown that the secondary amine(diisododecylamine) gives advantage to the tertiary amines on therhenium extraction efficiency from sulfuric acid media It can beexplained by the influence of steric factors and smaller rival extractionof mineral acids by secondary amines [1]

Most papers are related to the rhenium extraction from acidicsolutions but the extraction of rhenium from alkaline medium whichare formed after leaching of ores concentrates also represents a difficultproblem In the paper [23] rhenium extraction from alkaline solutionscontaining also molybdenum by solvent extraction using a mixture oftributylphosphate (TBP) and trioctylamine (N235) is describedMolybdenum which is also extracted by solvents in small amountsinterferes to the extraction of rhenium

Over the last decade most works refer to the development offundamentally new classes of extractants for perrhenate ions [26 2728 29] such as encapsulating ligands (cryptands and podands)macrocycles crown ethers These ligands can interact with ReO4

minus byboth the electrostatic interaction between ReO4

minus and protonated ligandand the hydrogen bond formation compared with simple open-chainligands If the complex between ReO4

minus and ligand has highhydrophobicity ReO4

minus in an aqueous solution may be separatedeffectively by a solvent extraction technique [30]

Crown ethers extract rhenium (VII) in the presence of potassiumor sodium in the form of K(Na)LReO4 (L-crown-ether) into the organicphase (12 - dichloroethane chloroform) [31 32] In the paper [31] theextraction perrhenate-ions by 3m-crown-m-ethers (m = 56) ether and itsmono-benzo-derivatives in 12-dichloroethane are described

Podands are analogues of crown ethers containing terminalphosphoryl ligands in their polyether chains they are used for theextraction of rhenium (VII) The efficiency of extraction by phosphorylpodands depends of the following factors the number of oxygen atomsin the polyether chain molecules the number of donor centers in themolecule of podands hydrophobicity of the reagent molecule the size offorming cycles the nature of substituent at the phosphorus atom Studies

20

have shown that phosphoryl podands with three oxygen atoms in thearomatic polyether chain combined with the phosphoryl group bydimetilen or o-phenylene fragments have high extraction ability forrhenium from sulfuric acid solutions [32]

In the paper [30] authors mark another type of podands such aspodands with nitrogen donor ligand -N N N `N`-tetrakis (2-pyridymethyl) -12-ethylendiamine (TREN) and its hydrophobicanalogs which also allow to extract perrhenate ions from highly acidicenvironments

Perrhenate is characterized by its ability to undergo a change ingeometry specifically from tetrahedral to hexagonal in the presence ofdonor ligands (eg acetonitrile triphenylphosphine) Protonationchanges the electron density present on the oxygen atoms Beer et al[33] suggested that the tripodal ligand L1 would be suitable for thebinding and extraction of perrhenate anion This ligand (Fig 1) basedon the combination of tris(2-aminoethyl)amine and crown ether motifswas found to complex sodium cations and to extract perrhenate anionsfrom aqueous solutions into an organic phase

Atwood and co-workers developed calixarene-type ligand L2(Fig 1) that specifically extracts perrhenate from water solution into anorganic phase The selectivity for extractions decreases as followTcO4

minus ge ReO4minus gt ClO4

minusgtNO3minus gtSO4

2minus gtClminus This selectivity pattern isattributed to a combination of charge size and shape Efficientextraction is observed at high and neutral pH the molar ratio ofligandperrhenate ion = 14 [33]

L1 L2Fig 1 Tripodal ligand L1 and calixarene-type ligand L2 for perrhenateextraction

21

Schiff-base macrocycles are used as a new conjugatedmacrocycles for perrhenate ions Thus a series of amino-azacryptands(L3ndashL16) for encapsulation and extraction of the oxoanions perrhenate(Fig 2) from aqueous solution were proposed by the authors [34]Thecomplexation amino-azacryptands L to ReO4

- is via hydrogen-bondedinteractions

Fig2 Amino-azacryptands (L3ndashL16) for encapsulation and extraction of theoxoanions perrhenate

Thus the main characteristics of the compounds for the effectiveperrhenate ions extraction as follows

Energy coordination of ligand with ReO4- should be higher than

the energy of perrhenate ion hydrationThe interaction between the ligand and perrhenate ions an

electrostatic interaction or the formation of hydrogen bonds Functional ligands to be a suitable size (volume of the cavity

should be more than 736 Aring3) shape electronegativity andhydrophobicity

Ligand should be protonated

22

Table 1 Characteristics of extractants for rhenium extraction

Extractant

Analysis objectComposition of

the initialsolution

Extractonconditions

Interferinginfluences

Aliphatic alcoholswith C 7-10

1-Heptanol 4-Heptanol 1-octanol 1-decanol 4-decanol 2-Heptanol 3-Heptanol

3-octanolback-extractant

NH4OH

Solutions HCland H2SO4

Т=293КTime of phase

contacttex = 5 min

organic phase toaqueous

(OL = 11)4 steps of

extraction 2stripping

Coextractionof mineral

acidsincomplete

re-extractionof Re (VII)

1

OctanolSolutions ofHNO3 and

H2SO4

Т=286-290Кtex = 10 min OL

= 11

Coextractionof HNO3

H2SO4

2

Basic polymethinedyes (derivatives of133-trimethyl-3H-

indole) astrazon violet

Aqueous andaqueous-organic

solution

Т=293КрН=6

tex = 10-30 secextractant mixture

toluene +dichloroethane

(1 1)

do notinterfere

3000-5000fold excess ofS04

2- CO32-

300- HPO42-

MoO42-

WO42-

10-20 S2O32-

Cr2O72- IO3

-metal ions as

sulfates

3

Secondary(diisododecylamine)and tertiary amines

(dioctylamin andtrioctylamine)

Solutions H2SO4

Т=293КA wide range of

pH

tex=5-7 mindiluent - toluene

-

4N-benzoyl-N ndashphenyl-

hydroxylamine

Molybdenitedissolved inHCl HNO3

HCl 05 molltex=15 min

diluent chloroform-

23

Table 1 (continued)

Extractant

Analysisobject

Compositionof the initial

solution

Extractonconditions

Interferinginfluences

5

Phosphoryl podands

back-extractant H2O

СReinitial=2middot105 moll

aqueoussolutions of

salts of alkalimetals

solutions ofmineral acids

Т=286-291КОL=11

tex= 60 mindiluent

nitrobenzene12-

dichloroethanechloroform

toluene

-

6Triotylamine (N235)+

tributyl phosphate(TBP)back-extractant18 NH4OH

Alkalinesolutions

afterleaching

containingMo

СRe 01-165gl

T=293 КрН =90 OL=11

tex=10 мин20

triotylamine+30 tributylphosphate

diluentkerosene

-

7

Podand-type nitrogendonor ligand ndashNNN`N`-tetrakis(2-pyridymethyl)-

12-ethylendiamine (TREN)

Aqueoussolution

NH4ReO4

С =10-4 M

Ionic strength01M

pH=1-65diluent

chloroformОL=11tex=24 h

-

8

3m-crown-m-ethers(m=56) mono-benzo-

derivates12-dichloroethane

СReO4-=

0057-0060М

T=291-295Ktex=2h

-

24

Table 1 (continued)

The range of Re concentrations

RecoveryMethods for determination Ref

Recovery gt99

Determination from back-extractSpectrophotometric method with

thiourea reductant-Sn (II)wavelength of 390 nm

[16 24]

1

gt98 Spectrophotometric method [25]

2The range of Re concentrations

001-550 mcgml

Determination from extractSpectrophotometric method

wavelength of 540 nm[17]

3 -AES-ICP

Spectrophotometric methodwith thiourea

[18 1920]

4Mo W Fe are extracted 97

into the organic phase

Determination from aqua phaseafter extraction

ICP-MS[6]

5 -AES-ICP

Spectrophotometric method[21 22]

6 968Spectrophotometric method with

butyl rhodamine[23]

7 - AES-ICP [30]

8 -AES-ICP

Spectrophotometric method[31]

9 - ICP-MS [32]

25

Table 2 Characteristics of sorbents for rhenium sorption

Sorbent

Analysis objectComposition of the

initial solutionConditions of

sorptionInterferinginfluences

1

Activated carbons(BAU)

Eluenthot soda solution

nitrate media

gold ore raw

static conditionsа)рH =2-3

б) рH =15-25

volume ofsolution 10 mlmass of sorbent

03 g(SL=1333)t=10 min UV

a) electro-positive

components(Mo W Cu

Ag Au)b)1000 fold

excess ofMo W do

not interfere

2

Activated carbons- CN-G CN-PCU developed

from waste woodand grain

processingindustries

sulfuric acidsolutions with CRe= 002 gl pH =2

solid phasesliquid SL==105

t=5-7 days-

3

2 Carbon fibrousmaterials

modified withchitosan

neutral aquasolutions of

rhenium

static conditionsТ=286-289 КSL=11000

-

4

3 Weakly basicanion-exchangersАН-105 Purolite

A 170

mineralizedsulphite solutionsimulating rinsing

water(С Re=001-002

gl Mo Cu Fe As)

static anddynamic

conditionsSL = 1500

t = 150-200 min

-

5

Strongly-basicanion-exchangers

АВ-17(sorbent PAN-АВ-

17)

neutral or slightlyacid

solutions

dynamicconditionst = 20 min

The disks ofpolyacrylonitrilefiber filled resin

1000 foldexcess of

Fe Cu ZnPb Cd do

not interfere

6Lignin anion-

exchangerssolutions NH4ReO4

static conditionsSL=1400

t=15min-2 h-

26

Table 2 (continued)

NotesMethods for

determinationRef

1

а) Sorption capacity of BAU forRe СЕ=14175 mgg AC

Detectionlt 10

б) СЕ=00763 mmolg or 142mgg

The concentrations range of Re050 100 mgL in standard

solutions025 50 mgl in the presence

of Mo and W (11000)

a) Electrostrippingvoltammetry

b) X-ray fluorescenceanalysis

a) [12]b) [9 10]

2 -Spectrophotometric

method [35]

3 СЕ=179-185mggSpectrophotometric

method with ammoniumthiocyanate

[38 39]

4Full dynamic exchange capacity

114 mgg

Spectrophotometricmethod with ammonium

thiocyanatekineticmethod

[36]

5 -

Determination of Re bythe diffuse reflectance

spectra at 420 nmrhenium thiocyanate

complex in the presenceof tin (II)

[15]

6 СЕ=3427-2328 mgg Traditional polarography [37]

Sorption is one of the methods for separation of rhenium fromvarious solutions

Sorption of rhenium or perrhenate-ions often occurs on solidsorbents from the liquid phase The presence of a large specific surfacearea and a large number of functional groups of the sorbent determinesits high sorption properties with respect to rhenium (VII) Sorbentscontain the same functional groups (amino groups hydroxyl groups

27

phosphorus groups) as extractants for the selective extraction ofrhenium but these groups are fixed on solid carriers or support

Activated carbons (AC) of various brands are used the mostwidely [9 10] The use of activated carbons as sorbents due to the factthat they have a whole set of valuable properties highly polydisperseporous structure a complex but relatively easily controlled surfacechemistry and specific physical properties Activated carbons like manyother carbon materials exhibit high selectivity to perrhenate ions thatexplains the increased interest to this type of sorbents [12]

The characteristic distinction of carbonaceous materials is that thesorption of rhenium is not only due to complexation with surfacefunctional groups (containing oxygen nitrogen sulfur atoms) but alsodue to the interaction with carbon matrix

AC can act as anion-exchanger in acidic media and themechanism can be described by the following scheme

[C2+ OH-] + ReO4-= [C2+ ReO4

-] + OH-On the other hand the AC have significant reduction properties

the reaction of the electrochemical reduction of perrhenate ions in themethods of rhenium determination by voltammetry is based on this it[12]

It has been established [9 10] that ReO4- is sorbed from nitric

acid solutions almost entirely (95-99) by 10 minutes of UV irradiationwhile without irradiation this process takes up to 60 minutes Increasedsorption by UV authors attribute to the fact when UV radiationsolutions of rhenium (VII) salts rhenium (VI) and rhenium (V) areformed which are considerably faster adsorbed on AC

Extensive use of the AС is also associated with their low costActivated carbons - CN-G CN-P CU developed from waste wood andgrain processing industries have a low cost and their capacitance andkinetic characteristics slightly inferior to conventional AC (FAC) [35]

However from acid solutions together with rhenium molybdenumcan also be sorbed by the AC Furthermore perchlorates nitrates andother oxidants can reduce the adsorption capacity of coals by oxidationThe disadvantage of rhenium sorption by activated carbons is as followsa decreasing in their activity after 4-6 cycles of sorption-desorption [1]low mechanical strength [35]

28

Anion-exchange resin is the next width of use which havegreater selectivity and capacity compared with activated carbons Theseanion-exchangers synthesized on the basis of the gel and porouscopolymer of styrene and divinylbenzene From the neutral and acidicsolutions rhenium is adsorbed by low-basicity anion-exchangers with thefunctional groups of primary and tertiary amines In recent studiesconducted on the use of weakly basic macroporous anion-exchangerswith a more developed specific surface area (20-100 m2g) such asPurolite A170 with secondary amino groups [36]

Sorption by strongly-basic anion-exchangers compared to weaklybasic anion-exchangers has several advantages firstly they are almostquantitatively and selectively extract rhenium from solutions andsecondly work in a wide range of pH [15]

The rapid technique for perrhenate ions determination isdeveloped which allows to find their content directly on the site ofsampling for example in lake water using strongly-basic anion-exchangers AB-17 with the sensitivity of the technique is 2-3 orderslower than the best conventional spectrohotometric methods withthiocyanate [15]

Recently the authors of paper [37] synthesized new highlypermeable lignin anion-exchangers on the basis of lignin a naturalpolymer a component of terrestrial plants It is noted that the exchangecapacity of anion-exchangers for rhenium in lignin is much higher (EC =3427-2328 mgg) compared with conventional anion-exchangersHowever the time to reach equilibrium sorption by some anion-exchangers can reach from 2 up to 12 hours

Carbon fibrous materials modified with chitosan haveimproved kinetic (time and rate of sorption) characteristics comparedwith activated carbon and ion-exchange resins [38 39] Carbon fibrousmaterials modified with chitosan contain amino groups includingprotonated The increasing of the number of protonated groupscauses the increasing of sorption capacity of the material withrespect to the negatively-charged perrhenate-ions However thesorption capacity for rhenium (179-185 mgg) still yields to ligninanion in addition investigations were carried out of neutral aquasolutions of rhenium without interfering influences

29

ConclusionIn this review the methods for rhenium determination which over

the last decade have acquired great fame are presented A large numberof works related to improving methods for rhenium determining pointsto the increased interest to this metal The majority of the studies aimedto the selective extraction of rhenium from the analyzed complex objectsand the separating it from interfering elements in the matrix to increasethe sensitivity of the methods Most of the work related to the searchingof various organic reagents selective to rhenium (V VII) ions and usedin extraction and sorption processes In general the development ofrapid selective methods that can determine the content of rhenium in awide range of concentrations in various materials remains an actualproblem nowadays

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

Reference1 AA Palant ID Troshkina AM Chekmarev Metallurgy of

rhenium Science Moscow 2007 298 p2 LV Borisova YuV Demin NG Gatinskaya VV Ermakov

Determnation of rhenium in plant materials Journal of AnalyticalChemistry 2005 V60 1 P 97-103

3 LV Borisova AN Ermakov Analytical chemistry ofrhenium 1974 Science Мoscow 318 p

4 S Uchidaa KTagamia K Tabei Comparison of alkaline fusionand acid digestion methods for the determination of rhenium in rockand soil samples by ICP-MS Analytica Chimica Acta 2005 V535P 317ndash323

5 VI Manshilin EK Vinokurova SA Kapelushniy Determinationof Pt Pd Re mass fraction in dead catalyst samples using ICPatomic emission spectrometry method Methods and objects ofchemical analysis 2009 V41 P 97-100 (in Russian)

6 Jie Li Li-feng Zhong Xiang-lin Tu Xi-rong Liang Ji-feng XuDetermination of rhenium content in molybdenite by ICPndashMS afterseparation of the major matrix by solvent extraction with N-benzoyl-N-phenylhydroxalamine Talanta 2010 V81 P 954ndash958

30

7 T Meisel J Moser N Fellner Wo Wegscheider R SchoenbergSimplified method for the determination of Ru Pd Re Os Ir and Ptin chromitites and other geological materials by isotope dilutionICP-MS and acid digestion Analyst 2001 V126 P 322ndash328

8 K Shinotsuka K Suzuki Simultaneous determination of platinumgroup elements and rhenium in rock samples using isotope dilutioninductively coupled plasma mass spectrometry after cation exchangeseparation followed by solvent extraction Analytica chimica acta2007 V603 P129ndash139

9 NA Kolpakova AS Buinovsky IA Jidkova Determinationof rhenium by X-ray fluorescence analysis Proceedings ofuniversities Physics 2004 12 P147-149 (In Russian)

10 AS Buinovsky NA Kolpakova IA Melnikov Determinationof rhenium in the ore material by X-ray fluorescence analysis News polytechnic university 2007 V311 3 P92-95 (InRussian)

11 DV Drobot AV Belyaev VA Kutvitsky Development of aunified X-ray fluorescence method for the determination ofrhenium in multicomponent oxide compositions News highereducational institutions Non-ferrous metallurgy 1999 4 P23-24 (in Russian)

12 LG Goltz NA Kolpakov Sorption preconcentration anddetermination by voltammetry perrhenate ions in the mineralraw materials Proceedings of the Tomsk PolytechnicUniversity 2006 V 309 6 P77-80 (in Russian)

13 NA Kolpakova LG Gol`ts Determination in mineral rawmaterials by stripping voltammetry Journal of AnalyticalChemistry 2007V62 4 Р418-422

14 Wahi A Kakkar LR Microdeterminaton of rhenium withrhhodamine-B and thiocyanate usng ascorbic acid as the reductant Analytical sciences 1997 august V 13 P657-659

15 LV Borisova SB Gatinskaya SB Savvin VA RyabukhinAdsorbtion-spectrophotometric determination of rhenium fromdiffuse reflectance spectra of its complexes on a PAN-AV-17adsorbent Journal of Analytical Chemistry 2002 V572 P 161-164

31

16 AG Kasikov AM Petrova Extraction of rhenium (VII) byaliphatic alcohols from acid solutions Journal of AppliedSpectroscopy2009 V82 2 P 203-209 (in Russian)

17 ZhA Kormosh YaR Bazel` Extraction of oxyanions with basicpolimethine dyes from aqueous and aqueous-organic solutionsextraction-photometric determination of rhenium (VII) and Tungsten(VI) Journal of Analytical Chemistry 1999 V54 7 P 690-694

18 AA Palant NA Yatsenko VA Petrova Extraction of rhenium

(VII) from sulfuric acid solutions by diisododecylamine

Journal of Inorganic Chemistry 1998 V43 2 P 339-343 (inRussian)

19 NA Yatsenko AA Palant Micelle formation in theextraction of ions W (VI) Mo (VI) Re (VII) from sulfuric acidmedia diisododecylamine dioctylamine and trioctylamine Journal of Inorganic Chemistry 2000 V45 9 P 1595-1599 (in Russian)

20 N Latsenko AA Palant SR Dungan Extraction of tungsten (VI)molybdenum (VI) and rhenium (VII) by diisododecylamine Hydrometallyrgy V 55 Issue 1 Febr 2000 P 1-15

21 AV Antonov AA Ischenko The use of extraction in thedetermination of rhenium in the presence of molybdenumChemistry and chemical technology 2007V50 9113-116 (in Russian)

22 VF Travkin AV Antonov VL Kubasov AA IshchenkoExtraction of rhenium (VII) and molybdenum (VI)hexabutyltriamid phosphoric acid from the acidic environment Journal of Applied Chemistry 2006 V78 6P 920-924 (inRussian)

23 Cao Zhang-fang Zhong Hong Qiu Zhao-hui Solvent extraction ofrhenium from molybdenum in alkaline solution Hydrometallurgy2009 V 97 3-4 P 153-157

24 AG Kasikov AM Petrova Influence the structure of octanolon their extraction ability in acid solutions with respect to

32

rhenium (VII) Journal of Applied Chemistry 2007 V80 4 P689-690 (in Russian)

25 VF Travkin YM Glubokov Extraction of molybdenum andrhenium by aliphatic alcohols Metallurgiya2008 7 P21-25 (in Russian)

26 EA Kataev GV Kolesnikov VN Khrustalev MYu AntipinRecognition of perrhenate and pertechnetate by a neutralmacrocyclic receptor J radioanal Nuclchem 2009 2 V282 P 385-389

27 Bambang Kuswandi Nuriman Willem Verboom David NReinhoudt Tripodal Receptors for Cation and Anion Sensors Sensors 2006V 6 P 978-1017

28 Lagili O Abouderbala Warwick J Belcher Martyn G BoutellePeter J Cragg Jonathan W Steed Cooperative anion binding andelectrochemical sensing by modular podands PNAS April 162002 V 99 8 P 5001ndash5006

29 EA Kataev GV Kolesnikov EK Myshkovskaya Newmacrocyclic ligands based bipyrroles to bind perrhenate andpertechnetate ions radiation safety 2008 4 P16-22(inRussian)

30 Takeshi Ogata Kenji Takeshita Kanako Tsuda Solvent extractionof perrhenate ions with podand-type nitrogen donor ligands Separation and Purification Technology 2009V68 P288ndash290

31 Yoshihiro Kudo Ryo Fujihara Shoichi Katsuta Yasuyuki TakedaSolvent extraction of sodium perrhenate by 3m-crown-m ethers(m=5 6) and their mono-benzo-derivatives into 12-dichloroethane

32 Elucidation of an overall extraction equilibrium based oncomponent equilibria containing an ion-pair formation in water Talanta V 71 2007 656ndash661

33 AN Turanov VK Karandashev VE Baulin Extraction ofrhenium (VII) by phosphorylated podands Russian journal ofinorganic chemistry 2006 V514 P676-682 (in Russian)

34 E A Katayev Yu A Ustynyuk J L Sessler Receptors fortetrahedral oxyanions Coordination Chemistry Reviews 2006V250 P3004ndash3037

33

35 Leroy Cronin Macrocyclic and supramolecular coordinationchemistry Annu Rep Prog Chem Sect A 2004V100 P 323ndash383

36 ID Troshkina ON Ushakova VM Mukhin Sorption ofrhenium from sulfuric acid solutions by activated carbon News of higher educational institutions Non-ferrousmetallurgy 2005 3 P38-41 (in Russian)

37 AA Abdusalomov Sorption of rhenium from sulfuric acidsolutions of molybdenum Sorption and ChromatographicProcesses 2006 Vol6 V 6P 893-894 (In Russian)

38 NN Chopabaeva EE Ergozhin ATasmagambet AI NikitinaSorbtion of perrenate-anons by lignin anion exchangers Chemistry of solid fuel 2009 2 P 43-47 (in Russian)

39 AV Plevaka ID Troshkina LA Zemskova AV Voit Sorption ofrhenium chitosan-fiber materials Journal of InorganicChemistry 2009V54 7 P1229-1232 (in Russian)

40 LA Zemskova AV Voit YuMNikolenko ID Troshkina AVPlevaka Sorption of rhenium on carbon fibrous materials modifiedwith chitozan Journal of nuclear and radiochemical sciences2005 V6 3 P221-222

11

SYNTHESIS AND MICROSTRUCTURE DESIGN OF METALAND CERAMIC MATRIX COMPOSITES USING

MECHANICAL MILLING OF THEREACTANTSCONSTITUENTS

Dina V Dudina Oleg I LomovskyInstitute of Solid State Chemistry and Mechanochemistry

Siberian Branch of Russian Academy of Sciences Kutateladze 18Novosibirsk 630128 Russia

E-mail dina1807gmailcom

Mechanical milling greatly alters the state of a powder mixtureintroducing plastic strain and defects into the components andcreating new interfaces and mutual configurations of nano-sizedgrains This opens up a possibility to design microstructures of thecomposite to be synthesized by modifying the initial state of reactingpowder mixtures In certain mechanically milled reactive systemsone can observe microstructure refinement of the product [1-2] anincrease in the yield of the reaction [3] improved distribution of thephases [3 4] and lower reaction onset and developed temperatures[1-2] The presentation intends to demonstrate several successfulexamples of this approach for synthesizing composites by self-propagating high-temperature synthesis (SHS) shock compressionand electric-current assisted sintering

SHS in the mechanically milled Ti-B-Cu powder mixtures wassuccessfully performed and resulted in a TiB2-Cu composite [1-2]Compared to untreated powders in the mechanically milled mixturestitanium and boron started reacting at a reduced ignition temperaturewhile lower combustion temperatures developed in the combustionwave favored formation of submicron grains of TiB2

The powder particles brought to react with each other by shockcompression of the mixture may not fully transform into the productsif the loading is too short and the temperatures developed during thepressure rise and the post-loading period are not high enough In themechanically milled mixture the yield of the reaction can beincreased as a result of the decreased grain size of the initial reactants

12

and shorter diffusion distances (example Ti-Cu-B system partial andcomplete reaction of Ti and B [3])

When the sintering process ensures temperatures and timesufficient for the completion of the reaction in the mechanicallymilled mixture one can expect more uniform microstructure and finergrains of the products (example Ti-B-C system forming B4C-TiB2

phases during electric-current assisted sintering [4])Ball milling can refine the microstructure of the as-synthesized

composites and can be used to introduce additional quantities of theconstituents in the composite This was applied in order to develophighly conductive Cu-based composites One of the possible reasonsfor low conductivity of in-situ dispersion strengthened copper may bethe incompleteness of the reaction between the initial reactantswhich form solid solutions with the copper matrix In this regard weconducted an in-situ synthesis of TiB2-Cu composites starting fromthe powder mixtures with the limited content of copper ensuring ahigh probability of contact between the particles of titanium andboron and as a result their full conversion into the TiB2 phase Thenanoparticles were formed in a self-propagating mode in the ballmilled Ti-B-Cu powder mixture corresponding to the 57 volTiB2-Cu composition Afterwards in order to adjust the composition thecomposite was ldquodilutedrdquo with the required amount of copper usingsubsequent ball milling [5]

The consolidated nano- and microcomposite materialsdeveloped on the basis of the described systems were tested for theirenhanced mechanical properties (fracture tough composites B4C-TiB2

[4]) electric erosion resistance [6] and electric conductivity [5] Inthis presentation each property is discussed as resulting from thephase and microstructure evolution during the synthesis of thematerial by the selected processing method

AcknowledgementsParts of this work were carried out by DVD at the University

of California Davis USA during her postdoctoral appointment Theauthors greatly appreciate the collaboration with DrKorchagin(ISSCM SB RAS) Dr VIMali and Dr AGAnisimov (Institute of

13

Hydrodynamics SB RAS Novosibirsk Russia) and Prof JSKim(University of Ulsan South Korea)

References1 DVDudina OILomovsky MAKorchagin VIMali Chem

Sust Dev 12 (2004) 319-3252 MAKorchagin DVDudina Comb Expl Shock Waves 43 (2)

(2007)176-1873 DVDudina VIMali AGAnisimov OILomovsky Mater Sci

Eng A 503 (2009) 41-444 DVDudina DMHulbert DJiang CUnuvar SJCytron

AKMukherjee JMaterSci 43 (2008) 3569-35765 JSKim DVDudina JCKim YSKwon JJPark CKRhee J

Nanosci Nanotech 10 (2010) 252-2576 J-SKim Y-SKwon DVDudina OILomovsky MAKorchagin

VIMali JMaterSci 40 ( 2005)3491 - 3495

4

STUDY OF THE EFFECT OF FLUORESCENCE INCREASINGOF N-ARYL-3-AMINOPROPIONIC ACIDS IN THE PRESENCE

OF ZINC AND CADMIUM IONS

EV Dedyukhina1 NV Pechishcheva1 LK Neudachina2KYu Shunyaev1 AA Belozerova1

1 ndash Institute of Metallurgy of UB RAS 101 Amundsen st Ekaterinburgshunuralru

2 ndash Ural State University 51 Lenin av Ekaterinburg Russia

Earlier the effect of increasing of phosphorescence intensity in thefrozen solutions with excess of metal chlorides and sulphates has beenreported Ions оf these metals have filled electronic shells and largevalue of electric field intensity - Li(I) Be(II) Ca(II) Mg(II) Cd(II)Zn(II) Al(III) In(III) and Ga(III) For example this effect was found forbenzene aniline phenol amino acids ndash tyrosine tryptophanephenylalanine [1]

The same effect have been found for fluorescence of onerepresentative of N-aryl-3-aminopropionic acids (AAPA) - NN-di(2-carboxyethyl)-p-anisidine - in the presence of cadmium(II) and zinc(II)ions at Т=77 К [2] Increasing of fluorescence intensity (Ifl) in frozeninorganic matrix is expected for other representatives of AAPA whichnot have electron acceptor groups in structure and demonstrate theconsiderable fluorescence intensity of the protonated form

Fluorescence of some AAPA in frozen inorganic matrixNN-di(2-carboxyethyl)aniline (I) NN-di(2-carboxyethyl)-34-

xylidine (II) NN-di(2-carboxyethyl)-3-methyl-aniline (III) andN-(2-carbamoylethyl)-о-anisidine (IV) are representatives of a class ofAAPA Figure 1 presents structures of the AAPA In the present workthe fluorescence of aqueous solutions of this AAPA with molar excess ofcadmium and zinc sulphates at рH 1-6 and Т=77 К have beeninvestigated

The fluorescence spectra of solutions were measured using aFluorat-02-Panorama spectrofluorometer (Lumex Russia) Fluorescencespectra at T=77 K was excited and recorded using a fiber-optic cablewith a special optical connector

5

It have been established that the Ifl of the protonated form of I-IV(СR=1middot10-4 moldm3) is increased in the presence of cadmium(II) andzinc(II) ions at Т=77 К Figure 2 presents spectra of II We suggest thatcause of this effect is interaction enhancement of reagent with metal inconsequence of isolation from water and micro concentration (waterform ice crystals impurities are displaced in intercrystal area)

CH3

N

O

OHO

OH

1 2 3 4

Fig 1 Structures of AAPA 1 - NN-di(2-carboxyethyl)aniline2 - NN-di(2-carboxyethyl)-34-xylidine 3- NN-di(2-carboxyethyl)-3-

methyl-aniline 4 - N-(2-carbamoylethyl)-о-anisidine

The increasing Ifl of protonated reagent form of I-IV also isobserved at Т=293К but is not as strong as at T=77 K

0

1

2

3

4

5

6

7

240 260 280 300 320 340 360

wavelength nm

Ia

u

1

2

3

Fig 2 Spectra of fluorescence II (СR=1middot10-4 moldm3) in the presence andabsence of Cd(II) и Zn(II) ions (СZn(II)= СCd(II)= 560 mgdm3) рН=60 Т=77 К

λex = 214 nm 1 - II 2 - II+Zn(II) 3 - II+Cd(II)

The fluorescence increasing is observed only when concentrationof metal ions in dozens of times more than concentration of fluorophor

6

This indicate that Ifl increasing is occured due to reagent solvation byions of inorganic salts but not chelation

We have obtained the Ifl of solutions of I-IV as functions of theconcentration of cadmium(II) and zinc(II) ions at Т=77 К pH=6 (table1) The largest increasing of Ifl in the presence of metal ions have beenobserved for IV But the most correlation coefficient R value of linearfunction Ifl=f(CMe) with wider concentrations range has been obtainedfor II

Table 1 The Ifl of I-IV as functions from concentration of metal ions Т=77 КCCd(II)= CZn(II)= 200 mgdm3 СR=10-4 moldm3 рН=6

Metalion

ReagentConcentrationsrange mgdm3 I R+MeIR R Slope

I 11 090 321

II 11 098 494III

25-760

13 092 456Cd(II)

IV 25-245 80 092 2997

I 3 095 82

II 8 098 414

III

30-845

11 096 437Zn(II)

IV 30-560 70 090 1542

In addition we have studied the fluorescence of aniline and naturalamino acids (tyrosine tryptophane phenylalanine) in frozen inorganicmatrix Structures of amino acids are presented on figure 3 thiscompounds are not belong to class of substituted anilines Thiscompounds similarly of investigated AAPA not have electron acceptorgroups in structure tyrosine phenylalanine and AAPA have the samebenzene fluorophore Besides this amino acids are commerciallyavailable reagents

Investigations have been shown that present amino acids alsodisplay the effect of Ifl increasing of protonated reagent form in thepresence of cadmium(II) and zinc(II) ions at Т=77 К But is not asstrong (12ndash5 times) as AAPA Ifl increasing Metal ions at T=298 K havelittle effect on a fluorescent spectra of amino acids

7

1 2 3

Fig 3 Structure of amino acids1 - phenylalanine 2 - tyrosine 3 - tryptophane

Thus we can deduce that the presence of substituted amino groupin benzene ring (especially in combination with others electron donorgroups) allow to observe more effective increasing of Ifl in salt solutionat 77 К Replacement benzene fluorophore to indole one (intryptophane) result to decreasing of observing effect extent

The fluorescence of II in the presence of Mg(II) ions at Т=77 Кwas investigated We tried to find the II0 fluorescence of II functionfrom z2r ratio for two-charged cations where z - ionic charge (+2) r -ionic radius nm [3] Data is presented in table 2

Table 2 Characteristiс of the functions II0 = f(z2r) for II Т=77 К рН=6λexλem= 214286 nm СII =10-4 М

Ion z2r SlopeI I0

CMe= 200 mgdm3

Cd(II) 412 494 107

Zn(II) 541 414 85

Mg(II) 615 352 74

The functions II0=f(z2r) of fluorescence II in frozen inorganicmatrix from are presented in figure 4 they are linear Also linearfunctions of Ifl=f(CMe) slope on z2r ratio have been obtained

N

NH2

OH

O

H2N

OHO

OH

8

y = -016x + 174

R2 = 099

6

7

8

9

10

11

40 45 50 55 60 65

z2r

IIo

Zn

Cd

Mg

Fig 4 Functions II0=f(z2r) of fluorescence II in the presence of metal ions [3]CCd(II)= CZn(II)= CMg(II)= 200 mgdm3 λexλem= 214286 nm Т=77 К

Study of fluorescence of some reagents in glycerolwater andethanolwater mixtures and micellar solutions at Т=298 КWe have studied a fluorescence II and tryptophane in

glycerolwater (11) and ethanolwater (11) mixtures in the presence ofzinc(II) ions at 77 К It was done for proving hypothesis about reducinginteraction fluorophore with water in aqueous media at freezing Wesuggest that interaction between of the solute and solvent molecules arepreserved in nonaqueous solutions

Corresponding spectra of II are presented on figure 3 similarsituation is observed for tryptophane We can see effect of increasing Ifl

is not observed in glycerolwater and ethanolwater mixtures in contrastto aqueous solutions

Isolation reagent from water at room temperature is possible in thepresence of surfactants

Fluorescence II have been study in the presence of surfactants ofdifferent nature in acidic media at Т=298 К The Ifl increasing ofprotonated form II is occured in the presence of Triton Х-100 (non-ionicsurfactant) and sodium dodecylsulphate (anionic surfactant)Fluorescence II is decreased by cetyltrimethylammonium bromide(CTAB cationic surfactant)

Fluorescence of II in the presence of surfactants and excess ofmetal ions have been study at рН=1-6 Zinc and cadmium ions increaseIfl of II at рН 50-65 with CTAB Thus metal ions and CTAB at

9

Т=298 К have same Ifl increasing effect as the effect at Т=77 К withoutsurfactants

0

5

10

15

20

25

240 260 280 300 320 340 360 380

wavelength nm

Ia

u

1

2

3

Рис 5 Fluorescence of II (СII=1middot10-4 moldm3) in ethanolwater (11)mixtures in the presence and absence of Zn(II) pH=60 Т=77 К λex=214 nm

1 - II 2 - II + Zn(II) (44middot10-4 moldm3) 3 - II+ Zn(II) (86middot10-3moldm3)

We have obtained under these conditions the Ifl of II solutions asfunction of the concentration of Cd and Zn ions with variousconcentrations of CTAB (table 3) The plots are linear and have thegreatest slope value at СCTAB=14middot10-3 moldm3 Cadmium ions have agreater influence on the fluorescence of the II than zinc ions

The fluorescence investigations in the presence of CTAB andmetal cations have been carried out on other AAPA (I III and IV)aniline and tyrosine (table 4) It was found that zinc ions increase offluorescence of protonated reagent form of I and III cadmium ions ndashIII

Table 3 Characteristiс of the functions Ifl=f(CMe) of II with addition of CTAB

exem = 218286 Т=298 К

Range of concentrationsCation

С CTABmoll moldm3 mgdm3 tg α

96middot10-4 2middot10-4 ndash 4middot10-3 45-450 18Cd(II)

14middot10-3 2middot10-4 ndash 8middot10-3 45-900 3696middot10-4 4middot10-4 ndash 15middot10-2 25-850 055

Zn(II)14middot10-3 4middot10-4 ndash 11middot10-2 25-850 10

10

Table 4 Fluorescence of reagents in the presence of zinc and cadmium ions(СMe=560 mgdm3) and CTAB (С= 96middot10-4 moldm3) рН=6

Zn(II) Cd(II)

Reagentexem

nm II0 I (R+Zn+CTAB)au

II0I (R+Cd+CTAB)

au

aniline 253278 11 07 10 06I 222300 62 16 08 02II 218286 73 44 85 51III 217288 65 34 33 15IV 218304 10 32 12 12

tyrosine 222302 10 480 11 462

The resulting functions will be used for developing of thefluorescent techniques of zinc and cadmium determination

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

References1 AV Karyakin n-electrons of heteroatoms in hydrogen bonding and

luminescence (in Russian) Nauka Мoscow 1985 135 p2 LK Neudachina EV Dedyukhina OV Evdokimova

NV Pechishcheva EV Osintseva KYu Shunyaev Fluorescenceof NN-di(2-carboxyethyl)-p-anisidine in solution and crystallinestate Journal of Applied Spectroscopy 2010 V 77 2 P 206-212

3 Lurie YuYu Hand-book of analytical chemistry (in Russian)Khimiya Мoscow 1989 447 p

186

CATHODE PROCESSES IN KCl-PbCl2 MELT

YuP Zaikov1 PA Arkhipov1 YuRKhalimullina2 VVAshikhin2

1The Institute of High Temperature Electrochemistry Ural Branch ofRussian Academy of Sciences

S KovalevskayaAcademicheskaya St 2220 620990 Yekaterinburg e-maildirihteuranru

2Open Joint-Stock Company ELECTROMED Scientific ResearchCentre Lenin St 1 624091 Verkhnyaya Pyshma

Technology of crude lead refining is developed in the Institute ofHigh-temperature Electrochemistry The crude lead was obtained fromthe car battery wastes While organizing the refinement in the moltensalts it is important to know deposition mechanisms [1] of lead ions inthe chloride melts containing oxychloride complexes It is necessary tostudy kinetics of electrode processes to understand this mechanism

Many authors studied kinetics of electrode processes of leadelectroreduction from chloride melts [2 ndash 10] Diffusion coefficients ofions in molten salts were measured by using radioactive isotopes [10]and with the help of electrochemical parameters [2 -9]

VPYurkinskyi DV Makarov [2 3] studied the mechanism anddetermined kinetic parameters of Pb(II) ion at electrochemicalreduction process in various individual melts (NaCl KCl и CsCl) aswell as in mixtures with various component content using linearvoltamperometry chronopotentiometry and chronoamperometrymethods Studies of lead ions reduction in lithium sodium potassiumand cesium chlorides showed that cation composition causes significantinfluence on the process Electrochemical reduction is limited by Pb2+

diffusion in LiCl and NaCl melts when in the potassium and cesiumchlorides by chemical reaction of complex ion [PbCln]

2-n dissociationDiffusion coefficient value was found to decrease and lead(II) iondiffusion activation energy to increase in the LiClndashCsCl row

YM Rybuhin EA Ukshe [4] measured lead ions diffusioncoefficients in molten chlorides by chronopotentiometry methodMeasurements were carried out under the argon atmosphere Therectangular polished platinum plate about 1 cm2 square was used as theworking electrode Molten lead placed into the quartz tube connected bycapillary with the bulk melt was the anode and reference electrode

187

NaCl KCl PbCl2 salts of chemically pure grade were used in the workThey were melted under vacuum before the experiment According tothe results of these studies the validity of the Stocks-Einstein equationto ion diffusion in molten salts is limited by the systems where theprocess of complex formation is absent that is why the significantdeviations from the equation take place in KCl ndash NaCl and especially inthe pure KCl

D=KT(6r) (1)where - viscosity r ndash ion radius according to Goldschmidt

Using oscillographic method II Naryshkin and VP Yurkovskyidetermined lead silver and cadmium ions diffusion coefficientsdepending on temperature against the equimolar mixtures NaCl-KCland LiCl-KCl Platinum microelectrode the platinum wire butt with 06mm diameter soldered into a quartz capillary was used 400 mm2

platinum foil was used as anode Chloride-silver electrode was used asthe reference electrode Short circuit during two minutes was used torenovate the electrode surfaces after each observation For obtaining themore reliable results each curve was observed several times and theresults were averaged out Authors showed the direct dependence of thepeak current from the investigated ions concentration This fact confirmsthe conclusion of Hills Ocsley and Terner [11] about the possibility ofthe oscilligraphic voltamperometry for the rapid quantitative analysis inthe molten salts Dependence of the peak potential from the logarithm ofinvestigated ion concentration for cadmium lead and silver was foundIndependence of the peak potential from the concentration logarithm forcadmium and lead chlorides corresponds to the dissolved matterdeposition Linear dependence observed for the silver chloridedemonstrates the absence of solubility in the process of silver depositionThe following valence values were found for silver 116 for lead 24

In the works [7-9] diffusion coefficients of lead zinc andcadmium ions in the LiCl ndash KCl и NaCl ndash KCl melts were determinedRaymond J Heus and James JEgan [7] used polyrophic method to studyprocesses of lead zinc cadmium ions electroreduction in the moltenchlorides Dropping bismuth electrode was a cathode Silver chloridecontaining 2 mass of AgCl in KCl ndash LiCl (eutectics) was a referenceelectrode Authors obtained linear dependencies of the concentration of

188

the investigated chlorides from the diffusion current densities Diffusioncoefficients were calculated with the Ilkovich equation

Richard B Stein [8] investigated the ion reduction reaction ofdivalent lead in the NaCl ndash KCl melt with oscillographic polyrographymethod Platinum microelectrode with 05 mm diameter soldered intothe quartz tube with 189х10-3 cm2 square was a cathode Referenceelectrode was silver chloride and the auxiliary electrode was graphiteAuthor founded out that the lead ion diffusion coefficients obtained bythe experimental data differ from calculated according to the equation ofStocks-Einstein He derived the conclusion that the cation structure ismore complex than just a single ion

HA Laitinen HCGaur [9] investigated lead cobalt and thalliumion reduction in the molten potassium and lithium chlorides withchronopotenciometry method Authors fixed the value of the transitiontime for melts containing the control values of ions under investigationAccording to the experimental data empiric dependences ofconcentrations and transitional time were determined Coefficients ofcadmium cobalt lead and thallium ion diffusion were calculated withSandrsquos equation (208 242 218 38810-5 cm2s correspondingly)

Cathode processes in chloride melts containing lead ions werestudied by chronopotentiometric and stationary galvanostaticpolarization curves methods

Experiments were carried out in the cell made of quartzhermetically closed fluoroplastic cover (2) with the holes for electrodesand thermocouple with accordance to the Fig1

Glassy-carbon was a working electrode (cathode) Glassy-carboncontainer played a role of a counter electrode Melted equimolar mixtureof lead lithium and potassium chlorides was used as the electrolyte forthe reference and working electrodes Electrolytes of the workingelectrode and reference electrode were separated by the diaphragm fromthe Gooch asbestos (7) Measurements were conducted relatively to thelead reference electrode that is a metal lead of C1 grade being in contactwith the melt containing 5 mass of lead chloride

Potassium chloride lithium chloride chemically pure grade andlead chloride of pure for analysis grade were used for electrolytepreparation Glassy-carbon container (4) was placed on the cell bottomon the special fireproof brick support (8)

189

Current lead to liquid-metal reference electrode was realized in aform of molybdenum rod and to glassy-carbon crucible through graphitebar Current leads were protected from the contact with melt by alundumtubes closed with the rubber plugs (1) to keep the cell hermeticallyclosed

Fig 1 Electrolytic cell 1 ndash rubber plugs 2 ndash fluoroplastic cover 3 ndash thermo-couple 4 ndash glassy-carbon container 5 ndash quartz-glass sell 6 ndash workingelectrode 7 ndash diaphragm 8 ndash fireproof brick support 9 ndash current leads toelectrodes 10 ndash electrolyte 11 ndash reference electrode

4

1

2

5

6

8

93

10

11

Vacuum

7

Ar

190

The cell was pumped out and fullfilled with purified argon Laterit was put into the resistance furnace and heated until the giventemperature under the abundant pressure of the inert gas

The setup was equipped with the automatic system of temperaturestabilization Temperature measurement was performed with the help ofchromyl-aluminum thermocouple Content of components in electrolytewere being controlled before and after the experiment with the atomic-absorption method

Stationary polarization measurementsLead ion deposition processes in eutectic melt of lithium and

potassium chlorides were studied at 04 to 30 mol lead chloride intemperature range from 673 to 823 К Polarization curves are given onthe fig 2 and 3 Two characteristic areas are observed on thepolarization curves On the first area little potential deviations from theequilibrium value takes place with cathode current density increasing to008 Acm2

Experimental points on the area with 04 mol lead chlorideconcentration are on straight lines described by equationsE = - 00703lgi - 01203 and E = - 00775lgi - 0091 for 673 and 773 Кcorrespondingly

At temperature 673 К tg is 0070 мВ and at 773 К - 0078 мВAccording to the equation

Ftg

RT23

n (2)

we have n=19 for 673 К and n=20 for 773 КAt lead chloride concentration 30 mol experimental points on

the first area of the polarization curve is described by the equationE= - 00779lgi - 00877

Amount of electrons in the reaction calculated on the equation (2)is equal 2

Reaching current densities 011 012 020 и 032 Асm2 on thefig3 for 673 723 773 823 К temperatures correspondingly Potentialis greatly shifted to the negative area to the values -084 -084 -106and -110 correspondingly

At small values of cathode current density there is one wavecorrespondingly to the fig 4 In some time after current rise potential

191

reaches its stationary value at current density 0045 Асm2 for 35 s forcurrent density 0060 Асm2 for 30 s After current disconnectionpotential comes back to its equilibrium value

Fig 2 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

(04 mol ) melt

192

Fig 3 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

melt at 823 К depending on the lead chloride concentration Concentration oflead chloride in mol per cents 1 - 04 2 - 05 3 ndash 30

193

Fig 4 Engaging curves at 823 К temperature and the different current density

On the engaging curves at current density values corresponding tothe second characteristic area on the polarization curves on the figures 2and 3 two waves on figure 5 are seen Time of reaching stationarypotential tst decreases with the current density increasing (for currentdensity 012 Асm2 tst equals 85 s for current density 017 Асm2 tst -45 s)

Fig 5 Engaging curves at 04 mol lead chloride concentration currentdensity 012 013 017 Асm2 and 823 К

194

Processes taking places on the electrode can be described in thefollowing way On the first characteristic area of the polarization curvelead ion deposition happens

Pb2+ + 2e = Pb0 (3)The limiting current density of lead reduction increases with the

temperature and lead chloride concentration At 30 mol of leadchloride concentration and 823 K limiting current density ilim is 12Acm2

On the second characteristic area of the polarization curvedeposition of the alkaline metal is possible on the reaction

K+ + e = K0 (Pb) (4)Low values of the alkaline metal reduction potentials might be

connected with the process of alloy formation of alkali metal with leadK + 4Pb = KPb4 (5)

Chronopotentiometric measurements at lead deposition from LiClndash KCl (45-55 mol ) ndash PbCl2 melt at 04 mol lead chlorideconcentration were performed at 823 K and current density range from010 to 017 Acm2 There is only one wave on chronopotentiometriccurves under these conditions Values of product i12 depending oncurrent density are given in the table 1 where - transition time

Table 1 Values of product i12 at diverse current density

s i mAcm2 i12 mAcm2s12

095 170 165161 130 165181 120 162

262 102 165

It is seen that the product i12 does not depend on current

density at constant concentration of depolarizator 0OxC In the table 2

potential values Е4 at time equaling the forth of the correspondingvalues of transition time are given

195

Table 2Values of Е4 potential of different current density

i Acm2 s 4 s Е4 V

010 264 0660 -0061

012 181 0453 -0600

013 161 0403 -0061

017 095 0238 -0062

It is seen that the potential Е4 does not depend on the experimentconditions the current density in this case

Equation for the reversible process can be as follows

1ln

nF

RT21

4t

ЕЕ

(6)

for irreversible process

2100

1lnlnnF

RT

t

nF

RT

i

knFCЕ

fhOx (7)

where E ndash electrode potential 4E - measurement potential at frac14

of transition time R ndash gas constant F ndash Faraday number n ndash number

of electrons T ndash temperature - transition time 0OxC - depolarizator

concentration 0fhk - deposition speed constant

On the figure 6 dependencies Е -

1ln

21

t

and Е -

21

1ln

t at 04 mol of lead chloride concentration current

density 01 Acm2 and 823 K are given

196

y = -00835x + 00654

0002

0022

0042

0062

0082

0102

0122

0142

0162

-115 -065 -015 035 085

- E В

1 2

Fig 6 Dependencies 1ndashЕ=f

1ln

21

t

and 2-Е =f

21

1ln

t

From the analysis of given graphic dependencies follows that the

experimental points in coordinates E -

1ln

21

t

are in a straight line

with the confidence interval 095 The can be described by equation

08300650 E

1ln

21

t

(8)

The amount of electrons in the electrode reaction was calculatedfrom the equation

F

RTn

0830 (9)

hence n=2

197

It follows from the experimental conditions on lead ion (II)deposition that the process is reversible ie it is controlled by the speedof divalent lead ions mass transfer from the volume of melt to theelectrode surface

Diffusion coefficient of lead dichloride at 823 K was calculated onSandrsquos equation

20

2

)(

)(2D

oxnFC

i

(10)

Lead ions (II) diffusion coefficient are equal to 23310-

5сm2s It is in good accordance with the data obtained by other authors[5 6]

References1 Yurkinsky V Makarov D Electrochemical reduction of lead ions in

halide melts Russian J Applied Chem 1994 67 p 1283-12862 Yurkinsky V Makarov D The influence of cation composition on

kinetics of lead electrochemical reduction in chloride melts RussianJ Applied Chem 1994 68 p 1474-1477

3 Ryabukhin Yu And Ukshe E The diffusion coefficients of lead inmolten chlorides DAN SSSR 1962 145 p 366-368

4 Naryshkin I Yurkinsky V Oscillographic investigation oftemperature coefficients for some chlorides diffusion in LiCl-KClRussian J Electrochemistry 1968 4 p 871-872

5 Naryshkin I Yurkinsky V Voltammetry in molten salts Russian JElectrochemistry 1968 2 p 856-866

6 Raymond J Heus James J Egan Fused Salt Polarography Using aDropping Bismuth Cathode ndash J of the Electrochemical SocietyOctober 1960 p 824-828

7 Richard B Stein The Diffusion Coefficient of Lead ion in FusedSodium Chloride Eutectic ndash J Electrochem Soc 1959 vol 106 p528

8 Laitinen H A Gaur H C Chronopotentiometry in Fused LithiumChloride-potassium Chloride - Anal Chem Acta 1958 vol 18 p1-13

9 Hills GI Oxley I E Turner D W Silicates Ind 1961 vol 26 p559

184

REPAIR COMPOUND MODIFIED BY NANO PARTICLES OFFERROUS OXIDE

OS Tatarintseva SN Novosyolova TK UglovaInstitute for Problems of Chemical and Energetic Technologies SB RAS

Biysk Altai region Russia labmineralmailru

The results of influence study of nano-dispersed ferrous oxide oncharacteristics of the composite material developed earlier (compound)and intended to repair and recover engineering structures and massifshave been presented in this paper The compound consists ofmulticomponent polymer matrix including epoxy oligomer low-molecular synthetic rubber plasticizer and process additives filler and alow-temperature amine hardener Microcalcite with particle size lessthan 50 μm has been used as filler

The composite has been modified with nano powder of ferrousoxide (II) (manufactured by MACH I Inc USA) consisting of needle-like crystalline particles with average size 4 nm and having specificsurface area 2379 m2g

Experiments have shown that even distribution of nano particlesin epoxy resin is caused with a high-velocity mechanical device underthe additional influence of ultrasonic field

The most important things for low-viscosity repair compositionsapplied to recover the integrity of natural materials are high flowabilitydetermining the ability to fill narrow-opened fractures and stability ofstrength properties for a long time

The positive effect of ultra-dispersed modifier is seen within therange of 030-035 of its percentage in the composition as shown byresults of the study given in the Table At these amounts the maximumvalues of flowability and mechanical characteristics have been providedThe logical increase in samples density indicates the optimality of thepacking developed and reduction in the porosity of a composite materialthat is important while using it in conditions on high humidity

The compound developed is environmentally friendlyincombustible waterproof stable to heat vibration and long mechanicalloads and can be used to perform repair work in construction industrypublic service stone mining and processing industries and architecture

185

Table Percentage influence of ferric oxide nano powder on technicalcharacteristics of the composite material

Value at modifier percentage Characteristics

0 010 020 030 035 040

Dynamic viscosityat T = 20 oC Pamiddots

210 212 225 262 266 288

Flowability cm 48 48 48 52 53 45

Density gm3 141 141 143 145 146 146

Compressive forceMPa

79 78 79 82 86 74

Relative deformation

023 021 021 025 025 020

182

BASALT PLASTICS OF ENHANCED HEAT AND CHEMICALSTABILITIES

OS Tatarintseva NN Ноdakova VV SamoilenkoInstitute for Problems of Chemical and Energetic Technologies

of the SB RAS Biysk Russialabmineralmailru

The experience of the application of metal pipes for chemicalproductions cool and hot water supply systems transportation ofpetroleum products and other aggressive fluids has shown that they aregreatly subjected to corrosion that reduces their lifetimes to severalyears Therefore natural is the observed worldwide tendency ofreplacing steel and cast iron by composite materials of high chemicalstability and durability to which glass-reinforced plastic having acomplex of high service properties should primarily be relatedHowever requirements for composites have presently increasedespecially with regard to their heat and chemical stabilities andresistance to microorganisms ground and waste waters

The paper demonstrates the study results with respect to thedevelopment of a composite material for filament-wound pipe productswhich is superior in its basic parameters to analogous ones in the field ofglass-reinforced plastic application As a reinforced material basaltroving with higher strength characteristics and resistance to aggressiveenvironments as compared to a glass one was chosen the polymermatrix was a heatproof binder TS developed on the basis of nitrogen-containing epoxy resin synthesized Having rheological properties andstrength characteristics similar to those that are widely used in themanufacture of filament-wound glass-reinforced plastic products of thebinders EDI and EChDI the binder TS possesses enhanced heat stabilityand low viscosity at room temperature which permits the reduction ofpower inputs for its processing

The obtained data on advantages of both basalt fiber and thebinder developed have to the full extent been realized in laboratorysamples of the reinforced composite and in basalt plastic pipes producedindustrially (see Table below)

183

Table Temperature dependence of elastic modulus E of basalt plasticpipes

Еmiddot103 MPa at Т degСBinder 20 85 125 155 200

EDI 11701 11263 4363 3528 -EChDI 11277 10951 9944 6217 -

TS 19960 19336 19179 17557 9096

The 9-fold strength reserve of the basalt plastic pipes determinedwhen hydro-tested under extreme conditions (150degC 15 MPa) hasconfirmed the possibility of creating composite polymer materialsoperating under high-temperatures and humidity

164

FABRICATION AND MODIFICATION OF METALLICNANOPOWDERS BY ELECTRICAL DISCHARGE IN LIQUIDS

NV Tarasenko1 AA Nevar1 NA Savastenko2 EI Mosunov3 NZ Lyakhov4 TFGrigoreva4

1 Institute of Physics NAS B Minsk Belarus2 Leibniz-Institute for Plasma Science and Technology Greifswald Germany

3 The Institute of Machine Mechanics and Reliability NAS B Minsk Belarus4Institute of Solid State Chemistry and Mechanochemistry SB RAS

18 Kutateladze Str Novosibirsk 630128 Russia grigsolidnscru

Electrical-discharge technique was developed for preparation ofmetallic and metal-containing nanoparticles as well as for modificationof metal micropowders in liquids The morphology and composition ofthe nanopowders formed under various discharge conditions wereinvestigated by means of transmission electron microscopy and X-raydiffraction analysis The optimal conditions for the production oftitanium carbide and copper nanoparticles embedded in carbon layerswere found

IntroductionA synthesis of metallic and metal-containing nanopowders is of a

great interest due to their potential applications as super hard materials[1] environmentally friendly fuel cells with highly effective catalysts[23] and so on Transition metal carbides have been widely studied aselectrocatalysts because of their electrochemical properties andelectrical conductivities Nanosized carbon particles are suitable supportmaterials for certain types of catalysts Of particular interest for futurecatalytic applications are carbon-based materials with embeded metalnanoparticles [4] As long as carbon nanoparticles are relatively inertsupports many studies have been conducted in order to find which pre-treatment procedures are needed to achieve optimal interaction betweenthe support and metal species [5]

For any application of nanoparticles to be commercially viablelow-cost production methods have to be developed A low-temperatureand non-vacuum synthesis of nanoparticles via discharge in liquid(submerged discharge) provides a versatile choice for economicalpreparation of various nanostructures in a controllable way An arc

165

discharge in liquid nitrogen has firstly been reported as a cost-effectivetechnique for the production of carbon nanotubes in 2000 by Ishigamy etal [6] Since that time many efforts have been devoted to develop thismethod Sano et al proposed to submerge electrodes in water instead ofliquid nitrogen [78] They reported synthesis of carbon onions [78] andsingle-walled carbon nanohorns (SWNHs) [9] In latter case carbonnanoparticles were produced via discharge in water method with thesupport of gas injection Parkansky et al reported nanoparticlessynthesis via a pulsed arc submerged in ethanol Ni W steel andgraphite electrodes were used [1011] The particles composition variedfrom carbon to pure metal including various intermediate combinationsof these materials Bera et al employed an arc-discharge in a palladiumchloride solution to produce carbon nanotubes decorated with in situgenerated Pd nanoparticles [10] Importantly the synthesized materialcontained no chlorine

In this paper methods based on electrical-discharges in liquids forproduction of tungsten and titanium carbide as well as coppernanoparticles embedded in carbon nanostructures is reported Thecapabilities of arc and spark discharges submerged in liquids forsynthesis of nanoparticles as well as electrical-discharge modification ofmetallic powders were studied

Experimental detailsThe experimental reactor (Fig 1) consisted of four main

components a power supply system (pulse generator) the electrodes aglass vessel and a water cooling system outside the beaker A pulseddischarge was generated between two electrodes being immersed in 100ml of liquid (pure (995) ethanol or 0001 M CuCl2 aqueous solution)The appropriate combinations of pairs of metallic (tungsten titanium orcopper) and graphite electrodes were used The choice of ethanol wasmotivated by the fact that organic compounds play a role of a carbonsource to produce nanoparticles in discharge-in-liquid system [7 12]Addition of the copper chloride salt into double distilled water favoredthe activation of discharge process Metal (tungsten titanium or copper)and graphite rods with diameters of 6 mm were employed as electrodesAn optimum distance between the electrodes was kept constant at 03mm to maintain a stable discharge The discharge was initiated byapplying a high-frequency voltage of 35 kV The power supply

166

provided several different types of discharges Both direct current (dc)and alternating current (ac) arc and spark discharges were generatedwith repetition rates of 100 and 50 Hz respectively Current I(t) wasrecorded during the discharge as a function of time by means of anoscilloscope The peak current of the arc discharge was 9 A with a pulseduration of 4 ms The peak current of the pulsed spark discharge was 60A with a pulse duration of 30 μs

The synthesized products were obtained as colloidal solutionsAfter 15 min presedimentation the large particles precipitated at thevessel bottom The top layer contained the small nanoparticles wascarefully poured off into a Petry dish These suspended nanoparticleswere characterized by UV-Visible optical absorption spectroscopytransmission electron microscopy (TEM) and X-ray diffraction analysis(XRD) for their size morphology crystalline structure and composition

The optical absorption spectra of colloids were measured by UVndashVisible spectrophotometer (CARY 500) using 05 cm quartz cuvetteTransmission electron microscopy was performed by LEO 906E (LEOUK Germany) microscope operated at 120 kV A drop of solution putonto the amorphous carbon coated copper grid for TEM measurementsThereafter the liquid was evaporated at the temperature of 80 C Afterthe drying of colloidal solution the deposit obtained on the bottom ofPetri dish was examined by XRD Powder composition and itscrystalline structure were characterized by using X-ray diffraction atCuK (D8-Advance Bruker Germany)

Synthesis of carbide nanopowdersPromising capabilities of the developed technique for synthesis of

tungsten and titanium carbides (WC TiC) as well as carbon-encapsulated copper nanoparticles were demonstrated using theappropriate combinations of pairs of metallic and graphite electrodessubmerged into the appropriate solution Also physical and chemicalprocesses induced by the electrical discharges in liquids were studied tooptimize the process of nanoparticles synthesis

The results of nanoparticles preparation are summarized in theTable1 The synthesis rate varied in range of 2 ndash 40 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofmetal and graphite electrodes The synthesis rate increased withincreasing of discharge current and decreasing of pulse duration The

167

composition and morphology of nanoparticles were also found to dependon discharge parameters It should be noted that there is a possibility toscale-up the process

Table 1 summarized the variation in synthesis rate andcomposition of tungsten nanopowders with the discharge parameters Asa general tendency the synthesis rate was order of magnitude higher forspark discharge than that of arc discharge It may be due to thedifference in current value [13] For both arc and spark discharges itwas found that the synthesis rate is lower when tungsten was acting as acathode This result is consistent with literature data For example Beraet al reported that the consumption of anode is higher than that ofcathode [13]

Table 1 Summary of nanopowder synthesis conditions andresults of nanopowder characterization by XRD

XRD-analysisDischargetype

Electrodes Powdersyield

mgminW2Cvol

WC1-xvol

Cvol

Wvol

1 ac arc W C 02 71 781 147 -2 dc arc W(cathode)C(anode) 01 62 901 37 -3 dc arc W(anode)C(cathode) 02 66 715 219 -4 ac spark W C 25 58 328 614 -5 dc spark W(cathode)C(anode) 12 570 307 89 336 dc spark W(anode)C(cathode) 21 56 325 618 -

As it can be seen from the Table 1 the synthesized nanopowder isa mixture of hexagonal W2C face centered cubic WC1-x and graphite Nopeaks corresponding to WO were observed Nanopowder contained alsosmall amount body centered cubic W when synthesis was performed bydc current spark discharge with tungsten rod acting as cathode Here theparticular behavior of this discharge should be stressed showing ratherhigh ability to synthesize W2C Moreover in contrast to the other sparkdischarges synthesized material contained relatively small amount ofgraphite On the other hand applying tungsten as a cathode materialappears to reduce C content in nanopowder prepared via arc dischargetoo Generally the content of C is higher and content of WC1-x is lowerwhen synthesis was performed by spark discharge

168

Nanoparticles prepared by arc discharge were observed in theiragglomerated form The agglomerated nanoparticles were surrounded bythe grey regions which were probably graphite layers This typical viewwas seen everywhere in TEM images of product synthesized by arc forboth ac and dc current discharges irrespective of electrodes polarityThat fact implies that the morphology of synthesized nanopowders wasgoverned rather by the current pulse duration and value of peak currentthan the polarity of the electrodes Since nanoparticles were observed inthe agglomerated form it was difficult to measure their size correctlyWe suppose that approximately 4 nm nanoparticles are formed duringthe arc discharge in ethanol

Fig1 shows the TEM image of titanium carbide nanopowdersynthesized by spark discharge in ethanol As can be see from the Fig1the nanoparticles were also surrounded by graphite layers Fig 1demonstrates that the nanoparticles synthesized by spark were nearlyspherical with a mean diameter of ~ 7 nm The particle size distributionwas rather narrow (plusmn 2 nm) The XRD pattern of synthesized sample isshown in Fig 1 (right picture) The diffraction peaks at 60deg 418deg605deg 724deg 765deg and 407deg 504deg 590deg 667deg 741deg correspond tothe formation of cubic face-centered titanium carbide TiC and cubicprimitive TiC2 respectively There are some diffraction peaks with 2θvalue of 407deg 504deg 590deg 667deg and 741deg which can be assigned tothe hexagonal C The amount of TiC reached 887 vol The quantitiesof TiC2 and C in samples detected by XRD corresponded to ca 47 vol and ca 67 vol respectively

Fig 1 TEM image (left picture) of titanium carbide nanopowder synthesizedby ac spark discharge and XRD-pattern (right picture) of the sample

169

Synthesis of copper-carbon composite nanostructuresNumerous studies have focused on synthesis of metal-containing

carbon nanocapsules (CNCs) via submerged discharge method[89141516] Because of the carbon sheets surrounding the metal corethe CNCs are protected from the environment and from degradation Thecarbon coatings mean that nanoparticles are biocompatible and stable inmany organic media Thus carbon encapsulated nanoparticles arecandidate for bioengineering application high-density data storagemagnetic toners for use in photocopiers [81718] The metal containingcarbon nanostructures were prepared by using the electrode frommixture of graphite and metal precursor [16 1920] Recently Xu et aldemonstrated a possibility to synthesize Ni- Co- and Fe-containingCNCs by an arc discharge between carbon electrodes in aqueoussolution of NiSO4 CoSO4 and FeSO4 respectively [15] In contrast tothe data reported by Bera et al the synthesized material consisted of Oand S due to SO4

-2 ionic precursors in the solution Since the metal core-forming material was supplied by liquids the production rate of CNCswas limited by the salt concentration [4] This restriction may cause alimit to apply the submerged discharge method to the large-scaleproduction of CNCs

In this paper Cu-based nanoparticles were prepared viasubmerged discharge of bulk copper and graphite electrodes in a copperchloride (CuCl2) aqueous solution Thus material of copper electrode aswell as Cu from solution was supposed to be incorporated into theresulting nanoparticles The effect of discharge parameters and electrodecomposition on the morphology and composition of final products havebeen investigated Additionally synthesized material was modified bylaser irradiation The changes in nanoparticles morphology andcomposition were examined by transmission electron microscopy(TEM) X-ray diffraction (XRD) and UV-Vis spectroscopy

The six types of nanoparticles suspension were prepared underdifferent discharge parameters The synthesis parameters aresummarized in Table 2 As it can be seen the weight change of eachelectrode was generally higher when spark discharge was generatedThe anode consumption rate was higher than that of cathode irrespectiveto a discharge type and electrode material However in contrast to theliterature data [4] there was no cathode gain in weight As a generaltrend the nanopowder synthesis rate was higher for spark discharge than

170

that of arc discharge It may be explained by the difference in currentvalue [21] For both arc and spark discharges it was found that thesynthesis rate was higher when copper was acting as an anode There isa discrepancy between nanopowder synthesis rate and materialconsumption rate The values of discrepancy D listed in the Table 2were calculated as follows

100()

CCu

syn

RR

RD (1)

Here Rsyn is the synthesis rate of nanopowder RCu is theconsumption rate of the copper electrode and RC is the consumptionrate of the graphite electrode The discrepancy D depended ondischarge parameters For ac-discharges the value of discrepancy washigher for spark discharge than that for arc discharge For dc-discharges this trend remained if the polarity of electrodes was takeninto account It is worth to notice here that the discrepancy betweenmaterial consumption rate and nanopowder synthesis rate may be causednot only by separation of sediment fraction but by the reaction of carbonatoms with water resulting in the production of gaseous compounds [9]

Table 2 Summary of nanopowder synthesis parametersType of

dischargepeak currentpulse duration

Electrodes materialRCu and RC

mg min-1RSyn

mg min-1D

Cu 671 ac1) spark60 A 30 micros C 48

59 49

Cu 122 ac arc10 A 4 ms C 26

25 34

Cu (cathode electrode) 473 dc2) spark60 A 30 micros C (anode electrode) 61

21 81

Cu (anode electrode) 664 dc spark60 A 30 micros C (cathode electrode) 46

69 38

Cu (cathode electrode) 115 dc arc10 A 4 ms C (anode electrode) 25

19 47

Cu (anode electrode) 286 dc arc10 A 4 ms C (cathode electrode) 21

33 33

1) Alternating current pulsed discharge2) Direct current pulsed discharge

171

This coincides with the fact that the largest discrepancy (morethan 80) was observed in sample with the largest graphite electrodeconsumption rate (sample 3) For all samples the synthesized powderseparated into three phases one floating in suspension one settling atthe bottom as sediment and one as a layer of film-like material floatingon the liquid surface

The aqueous solutions of CuCl2 were discharge treated for only 20s to acquire yellowish suspensions The transparency of the suspensionsdecreased with the time during the discharge treatment The liquidsturned to dark yellow after treatment by ac-discharge for 10 min Thesuspensions resulting from dc-discharge treatment were conspicuouslydarker when C electrode was acting as an anode The nanoparticlessuspension produced by spark and arc discharges were dark brown anddark grey respectively It might be due to the presence of relatively largeamount of carbon particles in suspension (see Table 3) The dc-dischargetreated solutions were olive-green when Cu was used as the anodeelectrode Yellow or green colour of suspension may indicate theoxidation of copper nanoparticles [22] The presence of Cu2Onanoparticles was further confirmed by XRD analysis No changes incolour were observed after laser irradiation of suspensions

Figure 2 shows the absorption spectra of as prepared (a) and laserirradiated (b) suspended nanopowders synthesized by dischargetreatment of aqueous solution of CuCl2 (2) for 1 min The spectra werecorrected to the contributions of solvents The optical density increasedwith decrease in wavelength Generally the optical density ofsuspensions prepared by spark discharge was higher than that ofsuspension prepared by arc discharge This is consistent with the factthat the nanoparticles production rate was higher when the solution wastreated by spark discharge In the spectral range of 200 ndash 500 nm theoptical density of the samples 1 4 6 was higher than that of samples 23 and 5 This seems to suggest that the main parameter in determiningthe optical properties of suspensions was concentration of Cu-basednanoparticles For the samples number 1 and 4 a weak absorption peakwas observed at very short wavelength According to the literature data[2324] a surface plasmon peak at wavelength of 289 nm may beattributed to the presence of very small separated Cu nanoparticles (lt 4nm in size) Though TEM examination confirmed the presence of smallnanoparticles in sample 1 there were no nanoparticles with diameter less

172

than 4 nm in sample 4 Moreover there were no copper nanoparticles insample 1 as revealed by the XRD (see below) More likely theexistence of weak absorption peak at 280 nm implied formation of liquidbyproducts We did not observe in the absorption spectra surfaceplasmon band around 570 nm Missing of the plasmon band can beexplained by copper oxidation on the particle surface [23] Thissuggestion was further confirmed by XRD analysis (see below) Thesuspensions exhibited the same colours after laser irradiation butabsorption intensity increased for samples 3 1 and to the less extent forsample 5 as illustrated in Figure 2b TEM analysis revealed themorphological similarity of irradiated samples 1 3 and 5 (see below)

Figure 3 depicts the corresponding TEM images for thesuspensions shown in curves 1-6 of Figure 2 Parts (a) and (b) representthe TEM views of the as-prepared and irradiated samples respectivelyThree distinct structures were observed dark small spherical particlesdark particles surrounded by a gray shell and gray flake-like structureshaving diffuse contours The small dark particles with diameter 2-5 nmwere observed in samples 1 2 3 and 5 (marked with black ellipses inFigure 3) Some dark particles notable when using ac spark dischargefor synthesis were bigger than 20 nm indicating coalescence Thenanoparticles synthesized by ac arc discharge (sample 2) were

Fig 2 Absorption spectra for the as-prepared (a) and laser modified (b)suspended nanoparticles produced by ac- (12) and dc- pulsed discharges(3456) The following electrode pairs were used Cu and C for the ac-spark(1) and ac-arc (2) discharges Cu as a cathode electrode and C as an anodeelectrode for the dc-spark (3) and dc-arc (5) Cu as an anode electrode and C asa cathode electrode for the dc-spark (4) and dc-arc (6)

173

surrounded by the arrowed gray regions which were probably carbonshells as shown in Figure 3a

Fig3 TEM images of nanoparticles from as-prepared (a) and irradiated (b)suspensions produced by ac- (12) and dc- pulsed discharges (3456) Thefollowing electrode pairs were used Cu and C for the ac-spark (1) and ac-arc(2) discharges Cu as a cathode electrode and C as an anode electrode for thedc-spark (3) and dc-arc (5) Cu as an anode electrode and C as a cathodeelectrode for the dc-spark (4) and dc-arc (6)

174

As we did not have any direct evidence that the shells consisted ofcarbon these nanostructures will be referred further as core-shellnanoparticles The core-shell nanoparticles were also observed in colloidprepared by dc arc discharge between copper cathode and graphiteanode (sample 5) It can be seen that core-shell nanoparticles rangedfrom 20 to 50 nm in diameter while the cores within the nanoparticlesvaried from 8 to 25 nm The cores were non-spherical They seemed tocompose of small particles clustered together The flake-like structureswith diffuse contours were 50 nm in size They were observed in allsamples Samples 4 and 6 consisted mostly of structures with diffusecontours On the basis of the above observations the ac arc dischargeand dc arc discharge with copper anode electrode seemed to be moresuitable for synthesis of nanoparticles with core-shell structure

It is clear seen that many smaller particles with sizes around 2-7nm were generated after the irradiation of samples 2 4 and 6 Theparticles larger than 10 nm completely disappeared The micrographrevealed that after the irradiation these suspensions consisted ofparticles with circular cross-section whereas before the irradiation theparticle shape was not spherical The nanoparticles were dispersed verywell No small nanoparticles were observed in suspensions 1 3 and 5after the irradiation Though as can be seen by comparing Figure 1(a)3(a) and 5(a) with 1(b) 3(b) and 5(b) the shape of nanoparticleschanged after the irradiation The laser induced morphology change mayoccur through heating of the nanoparticles because of the absorption ofthe laser light [25] According to the mechanism proposed by Takami etal the morphology of irradiated nanoparticles was determined by therelationship between temperature of nanoparticles their melting andboiling point

The laser induced change in shape and size occurred if thetemperature of nanoparticles was at the boiling point If the temperaturewas lower than the melting point no changes took place If thetemperature was between melting point and boiling point only thechange in shape occurred Thus the difference in morphology of theirradiated samples can be attributed to the difference in theircomposition Even being irradiated with the same laser light intensitythe nanoparticles of different composition changed their morphology indifferent ways as they have different melting and boiling points

175

X-ray diffraction data were collected to identify synthesizedsamples The diffraction peaks at 432deg and 503deg correspond to theformation of faced-centered-cubic Cu There are three diffraction peakswith 2θ value of 365deg 423deg and 614deg which can be assigned to theprimitive cubic Cu2O Besides there are two peaks at 240deg and 265degwhich can be assigned to the hexagonal C XRD revealed that dischargetreatment of aqueous solution of CuCl2 led to the formation of Cu2

(OH)3Cl and Cu2OCl2 because of a strong affinity between chlorine andthe metal (peaks with a value of 2θ around 165deg 19deg 31deg 323deg 327deg330deg 387deg 398deg 401deg 503deg 505deg 538deg and 178deg 360degrespectively) For comparison the XRD patterns of initial solution ofCuCl2 are also plotted at the top of Fig 4 Non-treated aqueous solutionof copper chloride was allowed to evaporate and than analyzed by XRDThe diffractogram of this sample showed peaks at about 2θ around162deg 220deg 240deg 267deg 289deg 328deg 340 348deg 352deg 409deg 430deg448deg 453deg 490 and 573deg which are characteristics of CuCl2middot2H2O

XRD data were used to semi-quantitatively determine thepercentage of constituents The semi quantitative analysis of phasecomposition is shown in Table 3 The nanopowder composition wasstrongly dependent on the synthesis parameters It should be noted herethat metallic copper was only formed by dc-discharge treatment whencopper was acting as an anode electrode (samples 4 and 6) Synthesizedmaterial contained copper mostly in form of oxide (Cu2O) copperhydroxychloride (Cu2(OH)3Cl) and copper oxychloride (Cu2OCl2)Difference in Cu2O and C contents among all samples was significantSamples 2 and 5 contained no copper oxide while sample 6 had thelargest percentage of copper oxide (ca 80 vol) On the other handsample 6 contained no carbon The carbon contain in sample 4 exceeded80 vol The quantities of Cu2(OH)3Cl in samples ranged from lessthan 2 vol to ca 30 vol Only three samples contained Cu2OCl2

(samples 12 and 5) The maximal amount of Cu2OCl2 detected by XRDcorresponded to ca 30 vol In spite of high copper electrodeconsumption rate sample 4 contained unexpectedly small quantities ofCu and Cu-containing compound It might be due to the formation ofrelatively large and heavy copper microparticles They precipitated fromcolloid quickly after synthesis Therefore they were not collected andanalyzed by XRD (see experimental section) A correlation was

176

observed between low copper electrode consumption rate and absence ofCu and Cu2O fractions in nanopowder composition for samples 2 and 5

It should be stressed here that the core-shell structures wereobserved for only samples 2 and 5 Taking into account firstly thatsamples 2 5 and 6 were prepared by arc treatment secondly that thesample 6 contained no C and assuming that the shells consisted ofcarbon we can suggest that arc discharge was more suitable forsynthesis of core-shell nanoparticles On the other hand the chemicalcomposition of final product was governed by different competingreactions As they have different equilibrium constants they may form anetwork where the ratios of the products are sensitive to concentrationsof each of the many components Therefore the slight difference ininitial concentration might results in significant difference incomposition and morphology of synthesized material (compare samples5 and 6)

Although the exact mechanism for formation of nanoparticles viadischarge in solution process is not clear the following possibility may

Table 3 Semi-quantitative analysis of synthesized powder by XRD

XRD-analysisType of

dischargeElectrodesmaterial Cu

volCu2Ovol

Cvol

Cu2(OH)3Clvol

Cu2OCl2vol

1 ac1) sparkCuC

- 135 403 165 297

2 ac arcCuC

- - 646 300 54

3 dc2) sparkCu (cathode)C (anode)

- 391 370 239 -

4 dc sparkCu (anode)C (cathode)

78 83 825 14 -

5 dc arcCu (cathode)C (anode)

- - 339 336 325

6 dc arcCu (anode)C (cathode)

74 775 - 151 -

1) Alternating current pulsed discharge2) Direct current pulsed discharge

177

be considered During discharge treatment of the liquid copper andgraphite electrodes were heated melted and vaporized in the region ofthe discharge generated In the vicinity of electrodes the liquid was alsovaporized rapidly due to extremely high temperature Hence the plasmaregion produced by the discharge adjacent to the electrodes wassurrounded by a gas bubble Following Sano et al [8] the gas mixturemay comprise CO and H2 formed as follows

22 HCOOHC (2)

This reaction might cause the discrepancy between electrodeconsumption rate and nanopowder synthesis rate since some of carbonatoms formed gaseous CO Sano et al reported that gas bubbles didnot comprise water vapor since no condensation occurred [8] Howeverwe should consider that water vapour also existed in the discharge zoneas we did not obtain any evidence of its absence

Copper chloride is an anionic compound that dissociates inaqueous solution and may form different ionic species such as Cu2+ Cl-or complex ions such as CuCl2

- CuCl32- CuCl4

2-[26] The reduction ofcopper ions into copper atoms was likely taking place in plasma regionduring discharge treatment of the liquid as shown in Eq 3

02 2 CueCu (3)

As the temperature in the vicinity of the electrodes was estimatedto be around 4000 K [8] the thermal decomposition of complex ions tometallic copper possible took place in discharge zone (Eq (4-6))

20

2 ClCuCuCl (4)

20

3 322 ClCuCuCl (5)

202

4 2ClCuCuCl (6)

The nanoparticles were then formed from the complex gasmixture through different transformation stages namely nucleationgrowth condensation and coalescence Both the evaporated copper fromelectrode and Cu produced by reduction of ions from solutions were

178

supposed to be incorporated into the resulting nanoparticles Becausewater vapor existed in gas bubble the copper nanoparticles were easilyoxidized Reduction of copper oxide by carbon monoxide and hydrogenwas possible the subsequent step (Eq (7) and (8))

OHCuCOOCu 22 2 (7)

222 2 COCuHOCu (8)

According to the XRD measurements (see Table 3) copper oxidewas only partially reduced into copper in sample 4 and 6 The data ofXRD analysis implied also reaction of chlorine with copper andorcopper oxide to form Cu2Cl(OH)3 and Cu2OCl2 These reactions mightinvolve hydrogen produced via reaction (2)

It should be noted that there was no direct evidence to support theabove-mentioned formation sequence and the true mechanism may bemore complicated

ConclusionsFrom the results and discussion presented above the following

conclusions can be madeThe electrical discharge between two electrodes immersed in

ethanol is a suitable method to produce in a controllable waynanoparticles with different contents of metal and carbon By varyingthe current value and its pulse duration morphology of nanoparticlesand their composition can be changed The average diameters of theprepared nanoparticles were in the range of 3-7 nm

Cu-based nanoparticles with different morphologies wereprepared via submerged electrical discharge of bulk copper and graphiteelectrodes in a CuCl2 aqueous solution Synthesized material wassubjected to laser-induced modification It was found that core-shellnanoparticles were formed by treatment of CuCl2 aqueous solution bythe arc pulsed discharge with pulse duration of 4 ms and peak current of10 A

The synthesis rate varied in range of 19 ndash 69 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofcopper and graphite electrodes The synthesis rate was found to behigher when copper was acting as an anode electrode The synthesis rate

179

increased with increasing of discharge current and decreasing of pulseduration The composition and morphology of nanoparticles were alsofound to depend on discharge parameters The copper nanoparticleswere only formed by dc-discharge treatment when copper was acting asan anode electrode The maximum diameter of nanoparticles did notexceed 50 nm while the minimum diameter was around 2 nm Theresults of the experiments imply that plasma treatment with longer pulseduration and lower current leads to the formation of carbon embeddednanoparticles TEM confirms the formation of encapsulatednanoparticles

Irradiation of nanoparticles in aqueous solution by a pulsedNdYAG laser at 532 nm was found to cause the shape change and sizereduction of the particles

AcknowledgementsThe work has been supported by the Integral Program of the

Siberian Branch of RAS under the Grant 138-T-09-CO-014 Authorsare thankful to KV Scrockaya for carrying out the TEM investigations

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2 XG Yang and CY Wang (2005) Nanostructured tungsten carbidecatalysts for polimer electrolyte fuel cells Appl Phys Lett 8624104-1 -224104-3

3 M Rosenbaum F Zhao U Schroder F Scholz (2006) InterfacingElectrocatalysis and Biocatalysis with Tungsten Carbide A High-Performance Noble- Metal-Free Microbial Fuel Cell Angew Chem118 1-4

4 D Bera S C Kuiry M McCutchen S Seal(2004) In situ syntesis ofcarbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method J Appl Phys 96 5152-5157

5 P Serp M Corrias P Kalck Carbon nanotubes and nanofibers incatalysis Applied Catalysis A General ndash 2003 ndash Vol 253 ndash P337-358

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6 Ishigami M Cummings J Zettl A Chen S (2000) A simple method forthe continuous production of carbon nanotubes Chem Phys Lett319 457-459

7 Sano N Wang H Alexandrou I Chhowalla M Amaratunga G A J(2001) Nanotechnology Synthesis of carbon ldquoonionsrdquo in waterNature (London) 414 506-507

8 Sano N Wang H Alexandrou I Chhowalla M Teo K B KAmaratunga G A J (2002) Properties of carbon onions produced by anarc discharge in water J Appl Phys 92 2783 ndash 2788

9 Sano(a) N (2004) Low-cost synthesis of single-walled carbonnanohorns using the arc in water method with gas injection J PhysD 37 L17-L20

10 Parkansky N Alterkop B Boxman R L Goldsmith S Barkay ZLereah Y (2005) Pulsed discharge production of nano- andmicroparticles in ethanol and their characterization PowderTechnology 150 36-41

11 Parkansky N Goldsmith S Alterkop B Boxman R L Barkay ZRosenberg Yu Frenkel G (2006) Features of micro and nano-particlesproduced by pulsed arc submerged in ethanol Powder Technology161 215-219

12 P Muthakarn N Sano T Charinpanitkul W TanthapanichakoonT Kanki Characteristics of Carbon Nanoparticles Synthesized by aSubmerged Arc in Alcohols Alkanes and Aromatics Phys Chem Bndash 2006 ndash Vol 110 37 ndash P 18299 -18306

13 D Bera G Johnston H Heinrich S Seal A parametric study on thesynthesis of carbon nanotubes through arc-discharge in water Nanotechn ndash 2006 ndash Vol 17 ndash P 1722-1730

14 Hsin Y L Hwang K C Chen R-R Kay J J (2001) Production and insitu metal filling of carbon nanotubes in water Adv Mater 13 830-833

15 Xu B Guo J Wang X Liu X Ichinose H (2006) Synthesis of carbonnanocapsules containing Fe Ni or Co Carbon 44 2631-2634

16 Lange X Sioda M Huezko A Zhu Y Q Kroto H W Walton D R M(2003) Nanocarbon prodction by arc discharge in water Carbon 411617 ndash 1623

17 Sergienko R Shibata E Akase Z Suwa H Nakamura T Shido (2006) Carbon encapsulated iron carbide nanoparticles synthesized in

181

ethanol by an electric plasma discharge in an ultrasonic cavitationfield Mater Chem Phys 98 34-38

18 Leo G H Jeong S H J W Ri H C (2002) Excelent magnetic propertiesof fullerene encapsulated ferromagnetic nanoclusters J Magn Mater246 404 ndash 411

19 Ang K H Alexandrou I Mathur N D Amaratunga G A J Hag S(2004) The effect of carbon encapsulation on the magnetic propertiesof Ni nanoparticles produced by arc discharge in de-ionized waterNanotechnology 15 520 ndash 524

20 Sano(c) N Nakano J Kanki T (2004) Synthesis of single-walledcarbon nanotubes with nanohorns by arc in liquid nitrogen Carbon42 686-688

21 Bera(c) D Jonston G Heinrich H Seal S (2006) A parametric studyon the synthesis of carbon nanotubes through arc-discharge in waterNanotechnology 171722-1730

22 Yeh M-S Yang Y-S Lee Y-P Yeh Y-H Yeh C-S (1999) Formationand characteristics of Cu colloids from CuO powder by laserirradiation in 2-propanol J PhysChem B 103 6851-6857

23 Aslam M Gopakumar G Shoba T L Mulla I S Vijayamohanan K(2002) Formation of Cu and Cu2O nanoparticles by variation of thesurface ligand preparation structure and insulating-to-metallictransition J Colloid Inter Sci 25579-90

24 Salkar R A Jeevanandam P Kataby G Aruna S T Koltypin YPalchik O Gedanken A (2000) Elongated copper nanoparticlescoated with a zwitterionic surfactant J Phys Chem B 104 893-897

25 Takami A Kurita H Koda S (1999) Laser-induced size reduction ofnoble metal particles J Phys Chem B 1031226-1232

26 Brown JB (1948-1949) The constitution of cupric chloride inaqueous solution Transaction of the Royal Sociaty of New Zeland 7719-23

162

MORPHOLOGICAL STUDY OF DETONATIONSPRAYED COATINGS OF CALCIUM HYDROXYAPATITE

DEPOSITED ON A NANOSTRUCTURED TITANIUMSUBSTRATE

AA Sitnikov VI Yakovlev YuP Sharkeev 1EV Legostaeva 1 AA Popova

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1Institute of Strength Physics and Materials Science SB RASTomsk

Biocompatible coatings are effectively formed by spraying ofcalcium hydroxyapatite Са10(РО4)(ОН)2 powders on a titanium substrateRecently along with the composition macro- and microstructuredevelopment the surface morphology of the coatings has receivedincreasing attention In a number of studies the roughness of thecoatings has been shown to significantly influence the inductionprocesses of cells As a substrate material titanium VT1-0 has beenchosen which has several advantages being highly biocompatiblebioinert practically non-toxic corrosion-resistant and possessing lowthermal conductivity and low coefficient of thermal expansion Themorphology of the gas-detonation sprayed calcium phosphate coatingsdeposited on ultrafine-grained and nanostructured titanium substratesand implant imitations has been studied The substrates and implantimitations were produced in the Institute of Strength Physics andMaterials Science SB RAS Tomsk

It was shown that the detonation sprayed hydroxyapatite powderswith particles ranging from 1 to 20 microm formed coatings non-uniform inthickness and phase composition The roughness of the coatings wasRa=365-472 microm (class 5) When hydroxyapatite particles of 20-100microm in size are sprayed coatings more uniform in thickness and phasecomposition are formed (Fig1) with an average roughness of Ra = 624microm (class 4) Preliminary treatment of the titanium substrate by sandingand chemical etching allows increasing the adhesive strength of thecoating up to 20MPa

163

Fig1 SEM images hydroxyapatite powder (a) detonation sprayedhydroxyapatite coating (b) XRD pattern of the coating (c)

Biological studies have demonstrated biocompatibility andbioactivity of the coatings It was found that the calcium phosphatedetonation sprayed coatings induce growth of tissue cells with 100probability which indicates that the relief of the coatings is optimal forfixation and aging of the cells Comparative studies of calciumphosphate coatings produced by detonation spraying and those producedby micro-arc in an electrolyte containing phosphoric acidhydroxyapatite and calcium carbonate have shown the advantages ofdetonation spraying for providing the required phase composition of thecoating This opens up a possibility of making two-phase coatings(hydroxyapatite and beta-calcium phosphate) ensuring the closest matchin composition to the bone tissue

ва б

100

200 20 30 40 50 60 70 80 90 10

(1

10) (002

) (2

10)

(2

11)

(

300

)

(3

10)

(

222

)

312

)

(3

20)

(

511

)

(

432

)

(5

22)

(

100

)

161

MICROSTRUCTURE STUDIES OF THE COATINGSPRODUCED BY ARC DEPOSITION OF THE

MECHANOACTIVATED SHS-COMPOSITE TIC+XME(R6M5 PR-N70H17S4R4-3) POWDERS

AA Sitnikov VI Yakovlev MA Korchagin1MN Seidurov ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

One of the main challenges in the development of new materialsfor arc deposition using flux-cored wires is to design materials of specialinterest using cost-effective and ecologically friendly technologies Asmaterialstechnologies meeting these requirements we can proposelayered composites produced by self-propagating high-temperaturesynthesis (SHS) in mechanically activated powder mixtures

The samples of SHS-mechanocomposites of TiC+XMe (R6M5PR-N70H17S4R4-3) composition arc-deposited on steel 45 substrateswere selected for investigations Microstructure of the arc-depositedcoatings was studied using a Carl Zeiss AxioObserver A1m OpticalMicroscope For observations cross-sections of the samples wereprepared and etched with a solution containing 20 potassiumferricyanide К3[Fe(CN)6] 20 КОН and 60 H2O Finemicrostructure and composition of the deposited layers were analyzedusing a Carl Zeiss EVO50 Scanning Electron Microscope equipped withan EDS X-ACT laquoOXFORDraquo device

The investigations show that the microstructure of the depositedlayers is uniform with submicron titanium carbide reinforcing phase inthe form of separate inclusions or chains of particles in the matrix

159

WEAR-RESISTANT DETONATION SPRAYED COATINGSBASED ON THE COMPOSITE MECHANICALLY ACTIVATED

SHS-MATERIALS

AA Sitnikov VI Yakovlev MA Korchagin 1DM Skakov AA Popova ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

The application of titanium carbide as a material for thermalspraying is rather difficult mainly due to its high melting temperatureand high hardness

A technology has been developed abroad for the production of thecomposite powders for spraying The production of these compositepowders is a laquoknow-howraquo of MBN Nanomaterialia (Italy)

An approach to the development of TiC-containing coatings canbe based on the technology of mechanocomposites with metallic orintermetallic matrices reinforced with nanosized particles of a ceramicphase [1] The technology of the powder preparation consists of 3 stagesAt the first stage the mixture of initial reactants which in this particularcase are titanium carbon and nichrome is mechanically activated (MA)in a planetary ball mill At the second stage self-propagating hightemperature synthesis (SHS) is conducted resulting in the formation ofTiC particles uniformly distributed in the metallic matrix AdditionalMA of the products of SHS at the third stage along with dispersingtitanium carbide particles creates a principally new state of the matrixwhich experiences grain refinement and shows high internal stresses andhigh concentrations of non-equilibrium defects In addition thesubsequent mechanical activation can be advantageously used forcompositions with higher matrix contents that are not possible to makethrough the SHS special additives can be also introduced into thecomposites at this stage

In order to compose the initial mixtures the following powderswere used titanium PTM lampblack PM-15 and nichrome PR-N70H17S4R4-3 Mechanical activation of the powder mixtures and theSHS-products was carried out in a planetary ball mill AGO-2M

160

Detonation spraying was performed using the laquoKatun-Mraquo set-upIt was found that the chemical composition did not change duringspraying

Wear resistance of the sprayed coatings was evaluated using afriction machine 2168 UMT in the laquoshoe-on-diskraquo mode A coating 02mm thick was deposited on a steel 40 shoe Prior to deposition the shoewas rubbed against the disk until a contact spot was formed over thewhole surface of the shoe After the coating was deposited the workingsurfaces were subjected to abrasive diamond treatment to reduce theirroughness

Tribological tests showed that with increasing metallic matrixcontent from 20 to 60 wt the weight losses under dry friction at 950 Nincreased almost twice Comparative tests of the coatings and thesamples of hardened steel revealed that the wear of the coatings obtainedfrom the mecahnocomposite powders was 8 times lower than that ofsteel 40H

References1 MAKorchagin DVDudina Application of self-propagating high-

temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007 v43 2 p176-187

153

CHEMICAL-THERMAL TREATMENT IN CARBONMANGANESE STEEL

AT INDUCTION-HEATING IN VARIOUS BORATINGCONDITIONS

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

Ural Federal University Ekaterinburg RussiaAltay State Agrarian University Barnaul Russia

Abstract Processes of borating of high-carbon manganese steel65Mn by carbide of boron and amorphous boron in conditions of fluxwith additives of various activators of borating are investigated at high-speed induction-heating It is shown that the nature of the boratingagent the additive of flux activators CaF2 and NH4Cl have influence onstructure and properties which are formed on a surface of boroneutectics

Keywords boron carbide of boron induction heating chemical-thermal processing

Among modern processes of chemical-thermal treatment (CTT)production engineering of saturation of surface layer constructional andalloy steels with boron ndash the borating occupy a special place In boratingit is possible to obtain the extended beds distinguished by high hardnessand strength corrosion-resistance abrasive durability and highreceptivity to wear on a surface of a steel detail [1 2] However themajority of known processes of borating are prolonged and are badlybuilt in into flow diagrams of state of productions

Intensification of CTT processes and in particular borating canbe carried out with application of technology of short-term high-speedheating of steel detail surface with the borating composition put on herrf currents (RFC) up to temperatures of formation of new phases andeutectics (1100-1350 оС) in systems Fe-B Fe-B-C and Fe-Me-B-Cwhere Ме - is an alloy element from group Cr Mn Ni etc [3] Unlikewell investigated processes of borating of alloy steels by mediums anddaubing at temperatures up to 950оС [4] there are open generalquestions of peculiarities of chemical interaction of components in suchsystems phase condition and properties of formed products

154

In the present work chemical-thermal treatment of carbonmanganese 65Mn steel combined with RFC-heating of its surface invarious borating conditions has been investigated

Experimental partAs the basic subject of research 65Mn (GOST 4543-71) alloy

carbon steel was chosen from the group of the same kind manganesechromos chromos-nickel and chromos-manganese steels from group 70U8А 50CrMnА 30CrMnSiА 45Cr 70Mn etc with similar propertiesand composition

Technical carbide of boron B4С in accordance with GOST 5744-85 and reactive amorphous boron of qualification reagent-grade weretaken as borating agents of different nature Known composition for theinduction deposition (F1) consisting of borax glass the boric anhydridecalcium silica and welding flux АN-348А (30 Na2B4O7 20 B2O310 CaSi2 and 40 flux АN-348А) was used as flux Reagent-gradeCaF2 and NH4Cl served as activators

RFC-heating of samples was carried out in a loopback water-cooled copper inductor by diameter of 160 mm connected to RF-lampgenerator VCG 7-600066 The adjustment of a contour and geometryof an inductor provided heating of researched samples to the temperatureof 1300-1350оС during 40-60 sec with the subsequent stabilizationAfter holding at the specified temperature during from 1 up to 2 minsamples were pulled out from an inductor and cooled down loosely

Microstructure of the coverings formed has been investigated andthickness of borated bed has been determined (МIМ-7 Neophot-30)hardness has been measured (PМТ-3 by 50 100 g) phase composition(DRON-2 radiation Co-Kα speed of angular moving of a sample of 1grads min) has been determined

Results and discussionIt is known that classical production engineering of kiln borating

are based on gradual (during 05-6 h) saturation of a surface of a steelproduct by boron from various pastes daubings liquid or a gaseous fluidat temperatures of process from 750 up to 950 оС Thus in the capacityof sources of boron its various compounds (В2О3 В4С ВF3 Na[BF4]etc) are applied capable to decay on active elements at temperatures ofprocess Depending on a phase condition of the borating agent hardness

155

and liquid borating are distinguished and also borating from a gas phase[4] We investigated six variants of mixes for high-speed borating atRFC-heating steel 65Mn Mixes differed in the nature of the boratingagent e borating agent composition presence fluxes componentsactivators and technological additions Compositions of the mixes usedare given in table 1

Table 1

Mixes Boratingagent

Activator Flux

Iа B4C (84) NH4Cl (6) F1 (10)II B4C (84) ndash F1 (16)

IIIа B (90) CaF2 (5) F1 (5)

Mixes I Iа II and IIа used as borating agent contained carbide ofboron mixes III IIIа - amorphous boron in mix Iа activator chloride ofammonium and in mix IIIа - fluoride of calcium has been added allmixes contained melted flux as a fluxing component for inductiondeposition F1

With decrease of density of a borating phase and increase intemperature of process its speed in the interval of temperatures from 800up to 950 оС increases insignificantly therefore for their intensificationcollateral saturation of a surface by several elements at once or thermocycling are applied [5] If the temperature of the process exceeds 1100-1300 оС in an aspect of beginning processes of high-temperaturestructural reorganization in steel speeds of borating sharply increase in2-4 min with the increase in temperature at every 15-20 оС thus theprocess passes from a diffusive zone to a zone of chemical reaction Soat the temperature of 1200-1300 оС according to the data[6] it ispossible to obtain in a few minutes the thickness of the single-phaseboron-bed up to 02-04 mm thus heating of a detail is carried out by thespecial thermo reaction mix

At RFC-heating of the steel 65Mn covered by researched boratingcompositions with chosen parameters of process fig 1 adamantinecoverings are formed on all samples resembling bed covered hard metalX-ray analysis of a material of coverings has shown presence of Fe

156

borides FeB and Fe2B carbon-borides Fe3(C B) and Fe23(C B)6 variousmeta- and orto-borates of iron (Fe3BO3 Fe3BO6 Fe3BO5) traces FeOand FeOFe2O3 Thus at RFC-heating of alloy carbon steels under bedof flux F1 containing from 84 up to 90 of borating agents complexboron-phases are formed on their surfaces hardening a surface of a detailand it is strongly linked with it and oxide films are removed togetherwith slag

To find out the characteristics and structure of received beds andthe conditions of borides in them photomicrography of micro sectionswas taken Typical structures of boron-beds are given in fig 1

a b C

Fig 1

As it is seen from fig1 with the chosen heating environments andthe time of borating the structure and the condition of boundary line ofreceived wear-resistant beds differ but in all cases as against classicalboron two-phase beds on a surface of samples the eutectic with stronglypronounced or with the diffusive boundary line separating it from anoriginal material is formed faster in conditions of heavy abrasive sign-variable and shock wear boron-plate Apparent changes in structure ofparent metal caused by its short-term overheat were not observed

For the mixes containing in the capacity of borating agent equalquantity of carbide of boron similar quantity of fluxes-component anddistinguished only by the presence of activator NH4Cl promoting areinforcement of convertible diffusive and transport reactions especiallyat low temperatures right at the beginning of the process of borating (Т

157

lt300 оС) formation of fine grained structure of eutectic turnings on withhardness not above 700-750 HV thickness of bed of 016 mm and withlegibly discernible interface with parent metal (fig 1а) is observed

For the analogous mix II without this activator the expressedpropagation of dendrites islands and druses of boron-phases withhardness up to 1050-1120 HV thickness of bed of 028 mm and adiffuse interface boron bed with parent metal (fig 1b) is observed Themixes on the basis of amorphous boron (fig 1c) appeared to be the mostreactive thus in mix IIIа containing follow-up 5 of activator CaF2 and5 of fluxes component beyond chosen relationships for 1 minthickness of bed on steel of 65Mn has made 088 mm at its hardness in2200-2300 HV The structure represents the remote eutectichomogenized iron ndash boron formed with such speed that from a melt atits solidification balls of slag had not time to bleed up to the end

Thus amorphous boron which at the presence of flux F1 andactivator CaF2 under the chosen conditions of experiment forms denseclose-grained beds on a surface of alloy steels with depth up to 800microns with hardness up to 2400-2500 HV (fig 2) appeared to be themost efficient borating agent at RFC-heating

Fig 2

It is interesting to note that the structure of the wear-resistantcovering obtained at high-speed 1 min borating steel 65Mn a mix II ismetastable and at borating during 2 min like in picture 1а with hardness2300-2400 HV turns to the fine grained structure and thickness of a

158

covering does not change and the interface with parent metal becomesdiscernible

References1 Methods of raise of longevity of machine components Red VN

Tkacheva M 19712 Belyj AV Karpenko GD Myshkin KN Structure and methods of

formation of wear-resistant surface layers M 19913 Tkachev VN Fishtejn BM Kazintsev NV Aldyrev DA

Induction overlaying welding of hard metals M 19704 Voroshnin LG Lyahovich LS Borating of steel M 19785 Guryev АМ Kozlov EV Ignatenko LN Popova NA Physical of

a basis of thermal-cycle borating Barnaul 2000

138

PHASE STATES OF MECHANOACTIVATED MANGANESEOXIDES

SA Petrova RG Zakharov AYa Fishman LI LeontievInstitute of Metallurgy Ural Division of RAS Ekaterinburg 620016

Russian Federation

An investigation of structural characteristics of the manganeseoxides in order to understand these characteristics affected bymechanochemical treatment conditions has been undertaken Chemicallypure manganese (II III IV) oxides were used as the initial componentsIt is shown that the properties of the mechanoactivated oxides differgreatly from those of initial materials Relationships among structuralcharacteristics of the mechanoactivated oxides and their prehistory wayand conditions of producing have been detected

IntroductionStudy of phase states of mechanoactivated oxides makes it

possible to analyze the patterns of expression of the mechanochemicaleffect in redox processes to determine the mechanism of the effect ofactivation processes on the type and parameters of the structural phasetransitions to establish the role of higher oxides in the redox processesAs one of the consequencies of the intensive mechanical activation is theappearance of nanodisperse states specificity of phase transformationsin nanocrystalline oxides is considered at the same time

It is known now that the decrease in the crystallite size inmechanoactivated systems causes a decrease of structural phasetransition temperatures In metallic alloys reducing of crystallites size isaccompanied by suppression of martensitic transitions [1-2] Completeinhibition occurs when the grain size becomes smaller than that of thecritical nucleus of a new phase It can be regarded as established that theparameters of phase transitions in oxides with relatively lowtemperatures of phase transitions also depend strongly on the grain sizeFor example in barium titanate BaTiO3 transition from cubic to low-symmetry phase is completely suppressed when the grain size is about10 nm [3] Changes in the crystal structure and the effects of reduction(the change of temperature and phase transition heat) in the structuralphase transitions with decreasing grain size also occurred for the oxides

139

Al2O3 Fe2O3 PbTiO3 PbZrO3 La1-xSrxCuO4 YBa2Cu3O7-δBi2CaSr2Cu2O8 [4] and several other oxides [5-6] Besides for the oxidesin nanoscale state the coexistence of two different structuralmodifications [7] was observed The processes of mechanoactivationmay also lead to new types of metastable phase states due to theredistribution of cations between the crystallographically inequivalentsublattices [8]

In the present work the main attention is paid on the analysis ofthe effects associated with the evolution of metastable structures underconditions of temperature increase and oxide interaction with anaggressive environment So far the main contribution to theinvestigation of these issues has made the study of metallic alloys (seefor example [9-10]) The behavior of the activated oxide materials ismuch less studied Study of structural phase transitions in the systemMn-O subjected to mechanochemical activation and structuralcharacteristics of the crystalline phases allows us to test how general arepreviously established patterns for systems with different types ofchemical bonds

The effect of mechanical activation on structural phase transitionsboth of martensate type (from cubic to tetragonal modification Mn3O4)and those accompanied by redox processes (between phases withdifferent degrees of oxidation etc) is investigated The choice of Mn-Ooxides as the object of study is largely connected with the fact that atleast two structural phase transitions observed in the considered crystalswith temperature changes involved the cooperative Jahn-Teller (JT)phase The value of the JT deformation in it is determined by theconcentration of JT ions in octahedral sites that allows to get additionalinformation about the structural changes caused by themechanoactivation of oxide

1 Production and structural properties of themechanoactivated oxides

11 Mechanoactivation of manganese oxidesPure manganese oxides MnO2 Mn2O3 and Mn3O4 annealed at

200deg 900deg and 1250degC respectively were used as the initial materialsFor the mechanical treatment of oxides which was described in

detail in [1112] a planetary mill AGO-2 with water-cooled drums (V =

140

150ml) and a centrifugal factor up to g = 60 [3] was used Download ofballs was 203g the material - from 5g Milling was made dry Theprocessing of powders was carried out after preliminary lining in acontinuous mode or with periodic stops of the mill According toestimates (performed by XPES) contamination by iron was not morethan 02 Previously [14] we found that prolonged continuousmechanical treatment leads to the fact that within the grains matureduring the first seconds along with a further (slow) reduction ofcoherent scattering blocks chemical processes begin leaking Because atthis stage the main purpose was to obtain single-phase samples theduration of continuous grinding was restricted by 30s The temperatureinside the drums during grinding did not exceed 320K which ensuredthe preservation of initial metastable phases During stops of mill thedrums where opened and powder was manually stirred but samplingwas not performed

To be able to conduct magnetic research on the mechanicallyactivated samples and to investigate the effect of intensity ofmechanoactivation (the degree of deformation) on the redox processesand the stability of weakly activated oxides the part of samples wasobtained as a result of mechanical activation in the vario-planetary millPulverizette 4 (Fritsch) in glasses of tungsten carbide Volume of drumwas equal to 250ml loading of crushing balls was 800g and a materialmass was 20 g Milling was made dry the duration was 3 min

12 Attestation of mehanoactivated manganese oxides andmethods of their experimental study

The phase composition of obtained substances the size ofcoherent scattering domains (CSD) and microstresses were determinedby X-ray diffractometer D8 ADVANCE (Bruker) (radiation CuKα Ni-filter position-sensitive detector VANTEC1) High-temperature X-raystudies of the stability of mechanoactivated oxides was carried out usinghigh-temperature chamber HTK1200N (Anton Paar)

The particle size of powders obtained was assessed by dynamiclight scattering using a laser analyzer DelsaNanoC (Beckman Coulter)and an atomic force microscope Solver-Next (NT-MDT) Surface ofoxides was studied by XPES and STEM (Omicron Multiprob)

High-temperature X-ray studies were performed in the range 30-1200degC in air The rate of heating and cooling was 05degCmin Step of

141

the temperature during heating and cooling was 5deg and 10degCrespectively Exposure in the point was 17s (the time of isothermal delayshooting diffractogram was 150s) For the analysis of diffractionpatterns the software package DIFFRACplus [15] was used

13 Results and discussionThe results of the attestation of the initial and mechanoactivated

oxides are presented in Table 1

Table 1 Treatment conditions and characteristics of the manganeseoxides

Cell parameters Initial phasetreating mode

Finalcomposition аAring сAring

Samplename

1 Mn2O3- initial Mn2O3 9412 M232 Mn2O3- AGO 30s Mn2O3 9410 M23A303 Mn2O3- AGO 60s Mn2O3 9410 M23A604 Mn2O3- AGO

10minMn2O3 9410

M23A10

5 Mn2O3- P4 3min Mn2O3 9403 M23P46 Mn2O3-

P4(3min)+USD(70s)Mn2O3 9403

M23P4U

7 Mn3O4-initial Mn3O4 5760 9474 M348 Mn3O4- AGO 30s Mn3O4 5762 9442 М34А309 Mn3O4- AGO 60s Mn3O4 5762 9431 M34A60

5787 950810 Mn3O4- AGO10min

Mn2O3+ Mn3O4

9410M34A10

11 MnO2-initial MnO2 4396 2869 M1212 MnO2- AGO 30s MnO2+Mn2O3(tr) 4397 2872 М12А3013 MnO2- AGO 60s MnO2+Mn2O3(tr) 4397 2872 M12A6014 MnO2- AGO 10min Mn2O3 9408 M12A10

AGO-High-energy planetary mill (60g) P4-Pulverisette 4 (~20g)USD-Ultrasound disintegrator

Since the analysis of the results of mechanoactivation of oxidesMn2O3 showed little difference between the samples activated in theAGO within 30 and 60 seconds further investigation of oxides Mn3O4

and MnO2 was performed on 60-second samples However it is

142

necessary to note that in the case of oxide MnO2 samples after 30 and60-second milling contained different amounts of Mn2O3

According to X-ray phase analysis data chosen mode ofmechanochemical treatment allowed to preserve essentially thecomposition of the initial oxides The exceptions were oxides MnO2which after grinding contained 5 of oxide Mn2O3 and Mn3O4 whichafter grinding for 10 minutes contained a few of Mn2O3

Data on grain size and the coherent scattering domains arepresented in Table 2 It is obvious that even a relatively weakmechanical treatment leads to a decrease in grain size in 2-3 times Inthis case the comparison of grain size and the CSD (comparison of thedynamic light scattering data and X-ray diffraction (XRD) results)shows that the mechanical treatment with a small degree of deformationallows to obtain defect-free grains while increasing of the centrifugalacceleration leads to the appearance and rise of the defects in the grainA tendency to agglomeration of grains with increasing time of intensemechanoactivation should be noted

Table 2 The characteristics of coherent-scattering domains and averagegrain size

Sample nameCoherent-scattering domain

nmGrain size nm

M23 gt200 1026plusmn95M23A30 30 436plusmn168M23A60 23 344plusmn155M23A10 24 939plusmn175M23P4 44 386plusmn50

M23P4U 44 336plusmn22M34 gt200 400plusmn801300plusmn300

M34A60 15 529plusmn340

M34A10 1913 795plusmn104

M12 gt200 428plusmn78M12A60 61 1133plusmn167M12A10 22 565plusmn343

XRD-dataDynamic light-scattering

data

143

Changes in phase composition during heating and cooling ofinitial and mechanically activated manganese oxides are presented inTables 3-4 and Fig 1-2

Comparison of the temperature behavior of the initial unactivatedoxide Mn2O3 and that of grinded for 3 minutes with a force of less than20g shows that mechanoactivation treatment with a small amount ofcentrifugal factor and short times can save not only the phasecomposition but apparently and generally does not alter the propertiesof the powder While increasing the degree of exposure (eg use of millssuch as AGO-2 with acceleration 60g) even at short times leads to achange in system characteristics (the appearance and growth of defectsredox processes) that affect later on behavior of oxide For examplemechanoactivation treatment leads to a shift of phase transitiontemperaures at thermal processing as well as to change of the structuralcharacteristics of the phases formed In particular to different degrees oftetragonal distortion of hausmannite formed during heating Mn2O3 (Fig4)

Table 3 The phase composition of the initial andmechanoactivated manganese oxides at different temperatures

Heating CoolingSample MnO2 Mn2O3 Mn3O4 Spinel Mn3O4 Mn2O3 Phase

1 2 3 4 5 6 7 8- + 920 1140 1120 - appearanceM23

- 955 1170 1010 + - disappear

- + 950 950 1010 - appearanceM23A30

- 995 1105 730 + - disappear

- + 950 950 1040 - appearanceM23A60

- 1000 1120 840 + - disappear

- + - 950 840 840 appearanceM23A10

- 1000 - 290 + 770 disappear

- + 940 1140 1120 - appearanceM23P4

- 980 1165 1080 + - disappear

- + 935 1140 1120 - appearanceM23P4U

- 980 1170 1050 + - disappear

144

1 2 3 4 5 6 7 8

- 685 + 1125 1090 - appearanceM34

- 945 1160 1010 + - disappear

- + appearance370

655

970 1050 -

disappear

900 appearance

M34A60

-

970

1130

880 + -

disappear

- + + 930 880 - appearanceM34A10

- 1005 655 600 + - disappear

+ 550 950 1155 1120 870 appearanceM12

595 1025 1170 1070 + + disappear

+ + 940 985 1110 750 appearanceM12A60

535 985 1165 840 + + disappear

- + 960 960 1000 790 appearanceM12A10

- 1005 1075 630 + + disappear

Table 4 The temperature boundaries of the phases during heating andcooling

Heating CoolingSample Phase

from to from to

1 2 3 4 5 6

Mn2O3 30 955 - -

Mn3O4 920 1170 1120 30

M23

Spinel 1140 1200 1200 1010

Mn2O3 30 995 - -

Mn3O4 950 1105 1010 30

M23A30

Spinel 950 1200 1200 730

Mn2O3 30 1000 - -

Mn3O4 950 1120 1040 30

M23A60

Spinel 950 1200 1200 840

Mn2O3 30 1000 840 770

Mn3O4 - - 840 30

M23A10

Spinel 950 1200 1200 290

145

1 2 3 4 5 6

Mn2O3 30 980 - -

Mn3O4 940 1165 1120 30

M23P4

Spinel 1140 1200 1200 1080

Mn2O3 30 980 - -

Mn3O4 935 1170 1120 30

M23P4U

Spinel 1140 1200 1200 1050

Mn2O3 685 945 - -

Mn3O4 30 1160 1090 30

M34

Spinel 1125 1200 1200 1010

Mn2O3 370 970 - -

Mn3O4 30 655

Mn3O4 900 1130

1050 30

M34A60

Spinel 970 1200 1200 880

Mn2O3 30 1005 - -

Mn3O4 30 655 880 30

M34A10

Spinel 930 1200 1200 600

MnO2 30 595 - -

Mn2O3 550 1025 870 30

Mn3O4 950 1170 1120 30

M12

Spinel 1155 1200 1200 1070

MnO2 30 535 - -

Mn2O3 30 985 750 30

Mn3O4 940 1165 1110 30

M12A60

Spinel 985 1200 1200 840

Mn2O3 30 1005 790 30

Mn3O4 960 1075 1000 30

M12A10

Spinel 960 1200 1200 630

146

a d

be

c fFig 1 The temperature boundaries of the phases during heating and coolingof initial and mechanoactivated Mn2O3 a - original b - M23P4 c -M23P4U d-M23A30 e-M23A60 f-M23A10

147

a

b

cFig 2 The temperature boundaries of the phases during heating and cooling of

initial and mechanoactivated Mn3O4 a-initial b-M34A60 c-M34A10

148

a

b

cFig 3 The temperature boundaries of the phases during heating and cooling ofinitial and mechanically activated MnO2 a - initial b - M12A60 c - M12A10

149

Fig 4 Temperature dependence of the degree of hausmannite tetragonaldistortion for samples with different prehistories

The growth of the crystallite size of mechanoactivated phase withtemperature is shown in Fig 5 Data are shown for the initial phasebelow the temperature of the corresponding phase transition

It is obvious that prolonged treatment in the high-energy millalmost did not give reduction of coherent scattering domains butessentially affected the thermal stability of investigated oxide

150

Fig 5 Temperature dependences of coherent scattering domain size in oxideMn2O3 with varying degrees of mechanoactivation

ConclusionThe main results of investigations are the followingI The conditions of mechanochemical treatment enabling to make

the transfer of Mn-O system to single-phase nanosized state withoutsignificant changes in composition of the initial oxide are found Theexception was oxide MnO2 which after grinding contained a smallamount of oxide Mn2O3

II It is shown that the use of mill of the type AGO-2 with 60gacceleration even at short times of activation treatment of oxides leadswhile maintaining the single-phase of sample to an appreciable changeof lattice parameters growth of stresses and the appearance of defects

III It is found that despite the relaxation character of the evolutionof these metastable structures in the face of rising temperatures there is ashift of phase transition temperatures and changes in structuralcharacteristics of the newly formed phases in comparison with the initialoxides Including marked changes in the parameters of the JT strain (ca

151

- 1) at high-temperature transitions between cubic and tetragonal phasesof oxide Mn3O4

IV It is shown that more prolonged mechanical activation ofoxides MnnOm activates redox processes in these materials theemergence of two-phase states with different degrees of oxidation andeven a complete change of the manganese oxidation degree

V The temperature boundaries of existence of phases duringheating and cooling were determined for the initial andmechanoactivated oxides MnnOm Not only noticeable quantitativedifferences in the position of phase boundaries but also qualitativedifferences in the constructed phase state diagrams were found

This work was supported by RFBR (grant 10-03-96016-p_ural_a) the Program of fundamental research of Presidium ofRussian Academy of Sciences N 27 ldquoFoundations of fundamentalresearch of nanotechnology and nanomaterialsrdquo and the Federal TargetProgram Scientific and scientific-pedagogical staff of innovationRussia (contract 02740 110641)

References1 Glezer AM Blinov EN Pozdnyakov VA Martensitic

transformations in microcrystalline ferro-nickel alloys Izvestiya Aseries of Physical 2002 V66 N9 pp1263-1275

2 Andrievsky PA RAGULYA AV Nanostructured materialsMoscow Academy 2005 192p

3 Polotai AV Ragulya AV Skorohod VV Nanocrystalline BaTiO3

synthesis sintering and size effect Science o Sintering CurrentProblems and New Trends Beograd Kluwer Academic Publishers2003 pp119-125

4 PAyyub VRPalkar SChattopadhyay et al Effect of Crystal SizeReduction on Lattice Symmetry and Cooperative Properties PhysRev B 1995 V51 N9 pp6135-6138

5 Parathasarathi Mondal Dipten Bhattacharya Pranab ChoudhuryDielectric anomaly at orbital order-disorder transition inLaMnO3+ J Phys Condens Matter 2006 V 18 p6869

6 Nandini Das Parathasarathi Mondal Dipten BhattacharyaPartical size dependence of orbital order-disorder transition inLaMnO3 Phys Rev B 2006 V74 p 014410

152

7 VYa Shevchenko OL Khasanov GS Yuriev etc The coexistence ofcubic and tetragonal structures in the nanoparticle of ZrO2Y2O3

oxides Neorg Mater 2001 V37 N9 pp1117-11198 AYa Fishman MA Ivanov SA Petrova et al Specific Features of

Jahn-Teller Structure Phase Transitions in NanocrystallineMaterials Defect and Diffusion Forum 2009Vols 283-286 pp53-58

9 Grigorieva ТF Barinova AP Lyakhov NZ Some features of themechanical alloying in the systems Cu-Bi and Fe-Bi J Metastableand Nanocryst Mater 2003 V15-16 pp475-478

10 Lyakhov N Grigorieva T Barinova A Lomaeva S Yelsukov EUlyanov A Nanosized mechanocomposites and solid solution inimmiscible metal systems J Mater Sci 2004 V39 N 16-17pp5421-5423

11 Zyryanov VV Journal of Structural Chemistry 2004 V45 pp135-143

12 Zyryanov VV Lapina OB Neorg Mater 2001 V37 N3 pp331-337

13 Zyryanov VV Sysoev VF Boldyrev VV Korosteleva TVCertificate of authorship of USSR N 1375328-BI-1988 N 7 p39

14 Fishman AYa Ivanov MA Petrova SA Zakharov RGStructural Phase Transitions in Mechanoactivated ManganeseOxides Defect and Diffusion Forum 2010 Vols 297-301 pp 1306-1311

15 DiffracPlus TOPAS Bruker AXS GmbH OstlicheRheinbruckenstraszlige 50 D-76187 Karlsruhe Germany 2008

118

EFFECT OF HARDENING TEMPERATURE ON THE STRUC-TURAL-MORPHOLOGICAL CHARACTERISTICS OF METAL

CEMENTS BASED ON MECHANOSYNTHESIZED COPPERCOMPOUNDS

NZ Lyakhov1 PA Vityaz2 SA Kovaleva2 TF Grigoreva1VG Lugin3 AP Barinova1 SV Tsybulya4

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS630128 Novosibirsk Kutateladze str 18 grigsolidnscru

2 United Institute of Mechanical Engineering NAS Minsk Belarus3 Belarussian State Technological University Minsk Belarus

4 G K Boreskov Institute of Catalysts SB RAS Novosibirsk Russia

IntroductionMetal cements may be used in many branches of industry due to

good adhesion to the materials of different types (glass ceramics metalsetc) and the metal character of thermal and electric conductivity Theformation of metal cements occurs through the interaction of copper(nickel) alloys with liquid metals and alloys Interactions of a solid metalwith liquid one in particular copper with gallium are known [1 2] tohave diffusion character they are substantially affected by temperatureand the area of contact between the reagents

The use of mechanically synthesized copper compounds allowsone to increase the contact surface between the components and to intro-duce doping elements (Bi In) that improve wettability during gluing andthe strength properties of the alloys to be formed This causes a changeof the kinetics of interaction between a solid metal and a liquid one dueto the acceleration of diffusion processes and due to the formation ofadditional phases

The goal of the present work is investigation of the effect of hard-ening temperature on the structural-morphological characteristics ofmetal cements obtained on the basis of CuBi mechanocomposites andsupersaturated solid solutions Cu(In)

Methods and materialsCopper powder PMS-1 (GOST 4960ndash75) granulated bismuth (TU

6-09-3616ndash82) indium (GOST 10297ndash94) were used in the work Me-chanical activation of the powders was carried out for 15 min in the

119

high-energy ball planetary mill AGO-2 with water cooling in argon at-mosphere (cylinder volume 250 cm3 ball diameter 5 mm loaded wt200 g the weighed portion of the sample under treatment 10 g the fre-quency of rotation of the cylinders around the common axis about 1000rpm) Mechanocomposites having the composition Cu 10 wt Bisolid solutions Cu-12 wt In were obtained [3] Diffusion-hardeningalloys were prepared by mixing the mechanosynthesized copper com-pounds with gallium melt followed by exposure at a temperature of 20C during the whole process of alloy formation To study the effect oftemperature on the structure and morphology of metal cements harden-ing was carried out at 90 С 120 С and 160 С

Surface examination was carried out with the NT-206 atomicforce microscope (Microtestmachines Gomel) using standard commer-cial V-type probes NSC11 (Mikromasch) in the contact mode

The structure of the resulting samples was studied using Mikro200 optical microscope and high-resolution scanning electron micro-scope (SEM) MIRATESCAN with an attachment for micro-X-ray spec-tral analysis (MXSA) The diameter of the electronic probe was 52 nmexcitation region was 100 nm Images were obtained in the mode of re-cording secondary and backward scattered electrons which allowed usto investigate the distribution of chemical elements over the surface andto establish its composition non-homogeneity

The phase composition of powders after mechanical activationand the final products of their interaction with liquid gallium were de-termined with the help of X-ray diffraction techniques X-ray structuralanalysis and semi-quantitative examination of the products were carriedout with the D8 Advance Bruker diffractometer (Germany) by means ofpowder X-ray diffraction in the θ-2θ configuration with a step of 01Phase identification was performed using the diffraction patterns re-corded in CuKα radiation (154051 Aring)

Calorimetric measurements were carried out with Netzsch STA409 PCPG instrument in argon atmosphere in a crucible made ofAl2O3 within the temperature range from room temperature up to 290 Cwith the heating rate of 20 min

120

Results and discussionIt was established in the previous diffraction studies of alloy for-

mation dynamics in CuBi + Ga and Cu(In)+Ga that the formation ofnew phases takes place within a broad time interval During the interac-tion of CuBi mechanocomposite in Bi that is insoluble in copper and ingallium the formation and crystallization of the intermetallic compoundCuGa2 and bismuth take place simultaneously [4]

For the case of Cu(In) solid solution in which the doping elementis soluble in gallium the formation of the phase of solid solution of in-dium has an incubation period of about 210 minutes which is determinedby its concentration in the system with gallium [5]

The interaction processes are described with the following chemi-cal reactions

CuBi + 2 Ga rarr CuGa2 + BiCu(In) + 2 Ga rarr CuGa2 + In(Ga)

1 Effect of the temperature of interaction of CuBimechanocomposites with liquid gallium on the structure andmorphology of the formed metal cementsIt is known that the resulting mechanocomposites are nanosized

copper surrounded by a thin bismuth layer [6] Bismuth is mainly com-posed of the particles less than 5 nm in size

According to the data of AFM topography the size of mechano-composite particles is 150divide250 nm (Fig 1)

Fig 1 Mechanocomposite Cu + 10 wt Bi after activation for 15 mina ndash SEM image b ndash AFM c ndash TEM

121

At first we studied the interaction of CuBi with liquid gallium atroom temperature

The X-ray structural analysis of the resulting cement carried outafter the interaction for 4 and 48 hours showed that the size of the crys-tallites of the intermetallic compound increases from ~ 200 nm to ~ 550nm The size of bismuth crystallites increases up to 100 nm It should benoted that this is accompanied by a decrease in the size of copper crys-tallites down to ~ 10 nm The final phase composition is determined asCuGa2 Bi and unreacted copper (Fig 2)

Fig 2 Diffraction patterns of the product of interaction Cu 10 Bi + Ga

Figure 3 shows the high-resolution SEM images of the micro-structure of the surface of the final interaction product The SEM imageof sample surface after hardening without the mechanical treatment ofthe surface is shown in Fig 3a The image of the surface obtained in thebackward scattered electrons after sample polishing is shown in Fig 3bBecause bismuth is the heaviest element in this system it will be distin-guished by the maximal brightness in the SEM image

The data obtained by means of microscopy show that the structureof the surface of final product is facetted tetragonal crystals СuGa2 withthe size up to 4 μm Bismuth is localized at the faces of crystals and at

122

the boundaries of CuGa2 grains as disperse formations 70-250 nm insize and also forms separate grains with a size up to 10 μm

a bFig 3 Topography of the surface of CuGa2 +Bi alloy after the interaction for48 hours a ndash SEM image of non-polished sample in direct electrons b ndash SEM

image of the polished sample in backward-scattered electrons

The use of AFM allowed us to study the microstructure of facet-ted tetragonal CuGa2 crystals The presence of screw dislocations inthem may be stressed as a result the crystalline layer grows by windingcontinuously on itself so the step takes the shape of a spiral (Fig 4) Thelayer-by-layer growth of crystallographic facets should also be men-tioned The edges of incomplete layers or steps move along the facetwhile they grow The step height that is the thickness of the depositinglayer varies within the range 4 to 200 nm The appearance of highgrowth steps may cause trapping of the melt drops and precipitation ofinsoluble bismuth admixture on the surface of steps of the growing crys-tals which is indeed observed in Fig 4 b Bismuth is adsorbed on facetssteps and along the grain boundaries

It should be stressed that the growth of faceted crystals requiresspecial conditions supersaturation or supercooling of the mother me-dium small number of appearing nuclei We suppose that the localthermal supercooling arises as a consequence of the chemical interactionof copper with gallium melt on the interface between the solid phase andthe liquid one with the formation of chemical compound CuGa2 withcrystallization temperature higher than the temperature of the melt Theconditions of substantial supercooling are created for this compound soits crystallization starts In this process bismuth particles get released

123

into the melt Thee particles are insoluble in liquid gallium and may actas the centres of crystallization and also they may brake down thegrowth of intermetallide particles by getting adsorbed on their surfaceThe latent heat of melting released during crystallization raises the tem-perature of the melt (so gallium remains in the liquid state during reac-tion at 20 C) and decreases the degree of overcooling thus creating theconditions for the growth of larger facetted intermetallide crystals fromthe melt

а b

Fig 4 AFM image of the surface of resulting alloy CuGa2 + Biа - Torsion-image of bismuth on facets and growth steps of CuGa2 (the contrastis formed due to the difference in tribological characteristics of the phases of

intermetallide and bismuth) b ndash layered spiral growth of CuGa2 crystals alongthe screw dislocation (marked with arrows) The upper part shows a scheme ofcrystal growth along the screw dislocation and the shape of the step formed inspiral growth [7]

At room temperature the final product of the interaction of CuBimechanocomposite with liquid gallium is a matrix composed of CuGa2

intermetallide particles 1ndash4 μm in size with bismuth particles distrib-uted in it (from 70 to 250 nm) which form local agglomerations up to 10μm in size

X-ray studies of the alloys obtained at hardening temperature of90 and 120 C showed that an increase in temperature to 120 C does notaffect the phase composition Similarly to the case of room temperature

124

the product is composed of intermetallide CuGa2 (PDF-2 No 25-0275)bismuth (PDF-2 No 44-1246) and residual copper (PDF-2 No 04-0836)(Fig 5)

Fig 5 Diffraction patterns of CuGa2 + Bi samples obtained at temperature 40(a) 90 (b) and 120 (c) C Unmarked peaks relate to CuGa2 intermetallide

With an increase in the interaction temperature the lattice pa-rameters of copper and CuGa2 phases remain almost unchanged Thesize of copper crystallites is about 35 nm Bismuth undergoes tempera-ture-caused changes An increase in the size of bismuth crystallites from100 nm at 20 C to 180 nm at 90 C and to more than 500 nm at 120 C

Alloys obtained by mixing the CuBi mechanocomposite with liq-uid gallium have a composite structure after hardening Their structuremay be described as an intermetallic shell with the unreacted part ofcopper in its centre The СuGa2 intermetallide has a shape of facetedtetragonal crystals up to 4 μm in size With an increase in reaction tem-perature to 90 C the size of het particles of intermetallic compund in-creases to 6-8 μm and remains almost the same at a temperature of 120C In the lateral contrast mode the facets of crystals obtained at 90 and120 C exhibit local accumulations of bismuth as well as substantial de-formation distortions of crystals due to the arising stretching strain inthe crystal in the direction lt001gt (Fig 6) Intermetallide crystal starts to

125

have layered structure The facets of the intermetallide obtained at ele-vated temperatures also exhibit deformation distortions that are likelyconnected with bismuth adsorption on the facets The appearance ofthese lines is due to the development of local fluidity They arise in thecases when the material possesses a distinct yield point even insignifi-cant concentration of strain promotes the appearance and developmentof these figures [8] Change of the straight character of the glide lines islikely to be connected with the effect of boundary volumes intra-grainstructural strain caused by differences in the volumes of the intermetal-lide and bismuth as well as by glide in different systems and with thetransition from one system to the other

а

b

Fig 6 AFM images of CuGa2 + Bi alloys obtained at a temperature of 90 (a)and 120 (b) С

126

Metallographic in-vestigation of the alloysurface after polishing(Fig 7) showed that thenumber of macrodefectssuch as pores and discon-tinuity flaws decreaseswith an increase in crystal-lization temperature Mi-crohardness of the inter-metallide increases fromHV 70 to 125

Investigation of thedistribution of chemicalelements over the sampleby means of SEM involv-ing X-ray spectral analysisrevealed nonuniformity ofthe distribution of insolu-ble bismuth

Bismuth is not ob-served in the regions withthe intermetallic com-pound which may be con-nected with the fine distri-bution of disperse particlesover the boundaries of theintermetallide Local ac-cumulations of bismuth upto 10 μm in size are ob-served mainly in the siteswhere macrodefects (poresgrain boundaries) get ac-cumulated With an in-crease in the temperature ofinteraction up to 120 Сthe number of local bis-muth accumulations de-

а

b

cFig 7 Optical images of the structure of

CuGa2 + Bi alloys obtained at 20 (a) 90 (b)and 120 (c) С

127

creases but their size increases to 20 μm (Fig 8)

а b

Fig 8 SEM images (in backward scattered electrons) of CuGa2 + Bi alloyHardening temperature а ndash 20 С b ndash 120 C

Thermal investigation of the alloys with different hardening tem-perature points showed that the curves of differential scanning calo-rimetry (DSC) exhibit definite differences only during heating the alloyswith hardening temperature 20 C and 90 C The DSC curves of the al-loys with hardening temperature 90 and 120 С are identical Duringheating the alloy with hardening temperature 20 С exhibits the exother-mal heat effect at a temperature of 120-150 С This effect may be con-nected with the occurrence of recrystallization processes in bismuthThis exo-peak is absent during the repeated heating

Thus investigation showed that an increase in the temperature ofthe interaction of CuBi mechanocomposite with liquid gallium leads toan increase in the size of the formed intermetallide as well as to a de-crease in macrodefects in the form of pores discontinuity flaws cracksThe hardness of the intermetallide thus increases

2 Effect of the temperature of interaction of mechanochemi-cally prepared solid solution Cu (In) with liquid gallium onthe structure and morphology of metal cementThe use of mechanochemically prepared powders of Cu-In system

as the solid phase in the reactions with liquid gallium increases the num-

128

ber of interacting systems due to the solubility of indium in gallium Ac-cording to the state diagram of the system GandashIn [9] the solubility of Inin Ga in the solid state is less than 03 at while the solubility of Ga inIn is 31 at At a temperature of 60 С indium may be dissolved in liq-uid gallium up to 48 wt

Mechanochemically synthesized powder in the system Cu + 12wt In was used as the initial solid-phase component The X-ray phaseanalysis of the products of mechanochemical synthesis (Fig 9) showedthat the solid solution of indium in copper in formed during mechanicalactivation of copper powder with 12 wt indium As a result the latticeparameter of copper increases to а = 36659 Ǻ (аref = 36150 Ǻ) The size of copper crystallite is about 30 nm

Fig 9 X-ray diffraction patterns of the powder Cu-12 wt In after mechanicalactivation (for 20 min) in argon

Mechanical activation of the system Cu + 12 wt In leads to theformation of fine particles of the solid solution of indium in copper (150ndash 230 nm) (Fig 10) Recrystallization of the solid solution of copper andthe formation of grains larger than 15 μm are also possible

129

Fig 10 Topography of the ultrafine powder of the solid solution Cu(In)

A decrease in the size of precursor powder is known to providelarger area of contact between the components of the solid phase and theliquid one and therefore shorter diffusion distances during subsequentinteractions with metal melts Because both copper and nickel are solu-ble in liquid gallium one may expect that the rate of dissolution of themechanocomposites of the system Cu-In would be significant

X-ray phase analysis of the final products of the interaction of thesolid solution Cu(In) with gallium at room temperature revealed thepresence of three phases intermetallide CuGa2 indium and unreactedcopper (Fig 11)

Fig 11 Diffraction patterns of the alloys obtained through the interac-tion of Cu 12 wt In + Ga CuGa2 - In - Cu

130

For the initial powder with indium concentration 12 wt theproduct of the interaction exhibits a decrease in the indium unit cell pa-rameter с in the alloy under formation to с = 49306 Ǻ (cref = 49459 Ǻ) The size of copper crystallites is about 7 nm while the size of indiumcrystallites is about 30 nm Slight changes in the unit cell volume of in-dium may be related to the formation of the solid solution of gallium inindium

During the interaction indium gets dissolved in the liquid phaseof gallium gets concentrated and crystallizes at the interfaces betweenthe solid phase and the liquid one The alloys with the 12 indium con-tent are characterized by a large range of the dimensions of tetragonalparticles of the intermetallic compound CuGa2 (from 05 to 8 μm) TheAFM image (Fig 12) exhibits coarse crystals their crystallographicshape is uncharacteristic of the intermetallide CuGa2 Comparing the X-ray data and the results of AFM we may assume that they are a solidsolution of gallium in indium

Fig 12 AFM topography of the surface of CuGa2+ In(Ga) alloy

A decrease in the AFM scanning pitch and simultaneous acquisi-tion of the image of distribution of normal (topography) and lateral (tor-sion) forces allowed us to distinguish the structural features of the phaseof the solid solution of gallium in indium (Fig 13) A specific distin-guishing feature is the presence of strands in the crystals of the solid so-lution of gallium in indium connected with layering of the solid solutioninto the regions with larger and smaller concentration of the componentwhich is well seen in the image of torsion (Fig 13b) The size of separate

131

grains of the solid solution of gallium in indium reaches more than 10μm

Fig 13 AFM topography of the surface of samples of CuGa2+ In(Ga) alloy (а)image of torsion (b)

Fig 14 The SEM image in direct (а) and back-scattered electrons (b) of thealloy CuGa2+ In(Ga) In the upper part the data chart of the quantitative spec-

tral analysis carried out in the indicated points

To investigate the microstructure of the surface of alloys we car-ried out the examination with the scanning electron microscope and ob-tained the images of the surface of resulting alloy for the interaction Cu12 wt In + Ga in direct (Fig 14а) and back-scattered (Fig 14 b) elec-trons The application of imaging in back-scattered electrons allow one

132

to investigate the composite surface non-uniformity with which the in-tensity distribution over the image depends on the atomic number of anelement One can see in Fig 14 b that the contrast in the BSE images isdetermined by the topographic features of the surface and the distribu-tion of intensities is uniform In addition local X-ray spectral analysiscarried out in different points of the alloy surface revealed the presenceof indium in concentrations 01 to 7 This fact allows us to concludethat indium is present on the surface of CuGa2 intermetallic crystals inthe form of thin films

Another characteristic feature of the surface of samples obtainedin the interaction of solid solutions Cu(In) with liquid gallium is thepresence of fine dispersed formations on the surface of crystals andgrains of CuGa2 that are more clearly seen in the AFM images (Fig 13a) and are detected in the SEM images (Fig 15 b) The formation of thestructures of this kind on the surface of the intermetallide may be con-nected with indium crystallization on the surface of the growing crystals

Fig 15 AFM (a) and SEM images (b) of the face of CuGa2 intermetallic ob-tained by the interaction of Cu 20 In + Ga

So on the basis of X-ray spectral data obtained and the results ofAFM and SEM we may assume that indium gets crystallized not only inthe form of large grains of the phase of the solid solution of gallium inindium but also on the faces of the intermetallide thus forming a nano-meter-sized film of indium about 10 nm thick

133

In order to establish the effect of temperature on the structure andmorphology we carried out alloy hardening at temperature of 60 120and 160 C

X-ray structural investigation of the final phase composition (Fig16) of the alloys showed that no changes in the phase composition of themetal cement are observed with an increase in hardening temperature to160 C The parameters of intermetallic compound CuGa2 remain almostunchanged The values of lattice parameters of the indium phase underformation are also insignificantly differing from the reference ones

Fig 16 Diffraction patterns ofCu-In-Gа samples obtained at

different temperatures

Investigation of the microstructure of alloys obtained at 20 Cshowed that indium is well adsorbed on the surface of intermetallidecrystals and crystallizes not only as separate crystals of the solid solutionof gallium in indium but also as the film formations with grained anddendrite structure on the faces of the intermetallide The occurrence ofintercrystal films of indium or the solid solution of indium may be re-sponsible for a decrease in strength characteristics of the alloy and be areason of both the intra-crystal and inter-crystal fractures (Fig 17 b) It

134

is assumed that an increase in hardening temperature causes substantialformation of the film structures of the solid solution of indium

The AFM investigation of the topography of alloys obtained attemperatures 90-160 C showed that the alloys are characterized by alarge size range of the intermetallic compound CuGa2 At the interactiontemperature of 20 C the size of CuGa2 particles was 05 to 8 μm Withan increase in reaction temperature to 90 C the crystal size increases upto 11 μm Crystal concretions are also formed (Fig 17) One can see inFig 17 b that cracks are formed in the grain plastoelastic deformationson the intermetallide face occur which is likely to be due to the differ-ence in interfacial surface tension of the intermetallide and indium film

ab

Fig 17 AFM image of the surface of CuGa2 + In(Ga) alloy obtained at 90 C a- topography b ndash distribution of lateral forces (arrows show cracks deforma-

tion distortions)

At a temperature of 120 and 160 C the contrast of the surface re-lief decreases due to the formation of a continuous film (Fig 18) on thesurface

Investigation of the phase transitions in the alloys was carried outby means of DSC For heating the products of the interaction betweenthe solid solution of indium in copper and liquid gallium at a rate of30Cmin an endothermic effect is observed on the DSC curves of all thealloys at a temperature about 254 C and an exothermic effect at 290 Con cooling the exothermic peak appears at a temperature of 210-220 С

135

а b

Fig 18 AFM topography of the CuGa2 + In(Ga) alloy a ndash 120 C b- 160 C

According to the Cu-Ga state diagram these effects are connectedwith the peritectic transformations of the main phase of intermetallideCuGa2 during heating and cooling The cooling curves exhibit no ther-mal effect due to the phase transition of indium The DSC curve of thealloy obtained at 20 C contains an endothermic peak at about 130 Cwhich gives much smaller heat effect in the second heating cycle Tak-ing into account the fact that the formation of indium films and the solidsolution of indium with the grained and dendrite structures occurs on thesurface of the intermetallide it may be assumed that heating to 130 C isaccompanied by melting of the indium film (taking into account a de-crease in melting temperature for thin films) [10] and the solid solutionIn(Ga) At the temperature of the peritectic transformation 254 C in-dium gets dissolved in the formed liquid Ga(Cu) with subsequent for-mation of the ternary compound Cu-Ga-In during cooling For coolingthe temperature of the peritectic reaction for the obtained compound de-creases to 210-220 C

ConclusionAs a result of the investigation of the structure and morphology of

metal cements prepared on the basis of mechanosynthesized coppercompounds CuBi and Cu(In) the structure and morphology in the reac-tions with liquid gallium are determined by the degree of interaction of

136

the doping component with gallium In the case of the CuBi mechano-composite in which Bi does not interact with gallium an intermetallidewith particle size up to 4 μm and local accumulations of bismuth areformed With an increase in hardening temperature to 120 C intermetal-lide growth to 8 μm occurs

When using the solid solutions Cu(In) in which indium is solublein liquid gallium and the incubation period for the crystallization of thesolid solution In(Ga) the formed particles of intermetallide CuGa2 havea broad size range from 05 to 8 μm With an increase in hardening tem-perature to 160 C the size of intermetallide particles increases to 11 μmredistribution of indium occurs along with an increase in the number ofits film structures that are formed on the faces of the intermetallide andcause a decrease in its strength properties thus providing intra-crystaland inter-crystal fracture A decrease in the melting temperature for in-dium to 130C and a decrease in the heat effect at this temperature in thealloys obtained at the alloy formation temperature of 90 120 and 160 Cmay be connected with an increase of indium film amount

The work is carried out under the Integration Project of SB RASNo 138 and BRFFI Т09СО-014 laquoDevelopment of Fundamental Basisof the Action of Activation on Regulation of the Processes of Interactionof Solid Metals and Their Comopunds with Metal Melts for the Purposeof Obtaining Functional Materials with Required Structure and Proper-tiesraquo

References1 Tikhomirova OI Ruzinov LP Pikunov MV Marchukova ID

Investigation of mutual diffusion in the system gallium ndash copperFiz metallov I metallovedenie 1970 vol 29 issue 4 p 796-802 (inRussian)

2 Glushkova LI Konnikov SG Interaction between components inthe solder paste based on gallium Pressure treatment of metals andwelding Proceedings of the Leningrad Polytechnical Institute1969 No 308 p 205-208 (in Russian)

3 Grigorieva TF Barinova AP Lyakhov NZ Mechanochemicalsynthesis in metal systems Novosibirsk 2008 (in Russian)

4 Ancharov AI Grigorieva TF Barinova AP Lyakhov NZ Investi-gation of the interaction of liquid metals with nanocomposites by

137

means of diffraction of the synchrotron radiation Nuclear Instru-ments amp Methods in Physics Research 2007 v A 575 p 130-133

5 Ancharov AI Grigorieva TF Tsybulya SV Boldyrev VVNeorganicheskie Materialy 2006 V 42 No 9 p 1164-1170 (inRussian)

6 N Lyakhov T Grigorieva A Barinova Nanosized mechanocom-posites and solid solution in immersible metal systems Journal ofmaterials science 39(2004) 5421-5423

7 Chernov AA Crystallization processes Modern CrystallographyMoscow 1980 vol 3 p 5-12 (in Russian)

8 Bernshtein ML Zaymovsky VA Mechanical properties of metalsMoscow Metallurgy 1979

9 State diagrams of binary metal systems Ed by NP Lyakishev1997 vol 2 p 636ndash637 (in Russian)

10 Gromov DG Gavrilov SA Redichev EN Klimovitskaya AVAmmosov R M Factors determining melting temperature of thinfilms of Cu and Ni on inert surfaces Zhurnal Fizicheskoy KhimiiV 80 No 10 2006 p 1856-1862 (in Russian)

104

ZINC IONS REDUCTION ON SOLID METAL ELECTRODES INCHLORIDE MELTS

Alex Lugovskoy 1a Zeev Unger 12b Michael Zinigrad 1cDoron Aurbach 2d

1Material and Chemical Engineering Department Ariel UniversityCenter of Samaria Ariel 40700 Israel

2Department of Chemistry Bar-Ilan University Ramat-Gan 52900Israel

alugovsaarielacil bzevikitoarielacil сzinigradarielacildaurbachmailbiuacil

keywords electrodeposition chloride melts cyclic voltammetry high-temperature electrochemistry

AbstractThe reduction of zinc ions on solid tungsten and platinum

electrodes in chloride melts at the temperatures 700 ndash 750 degC wasstudied by cyclic voltammetry chronoamperometry and energydispersion spectroscopy It was established that no zinc is reduced onplatinum electrodes As for the reduction of zinc ions on tungstenelectrodes the process has a complex character it starts as anirreversible two-electron zinc ion reduction and after the new phase isformed the process of saturation of the electrode surface with lithium orsodium begins As the second process develops the alkaline metalbecomes essentially the only constituent on the electrode surface

GeneralSince zinc is industrially recovered from sulfate solutions rather

than from melts and because its melting temperature (4195 degC) is lowerthan the temperatures of most molten chloride compositions thereduction of zinc ions on solid electrodes in chloride melts has beeninvestigated relatively poorly There are quite a few papers devoted tothe electrolysis of zinc containing chloride melts (1 2) and these coveronly some details of the electrochemistry of this metal However zinc isnot only an engineering metal It can often be a component of moltenchloride systems in which various processes of synthesis or purification

105

are performed Therefore the detailed electrochemical behavior of zinccan be of great importanceThe study of electro-reduction processes of zinc ions on solid tungstenand platinum electrodes in eutectic NaCl ndash KCl and LiCl ndash KCl melts inthe temperature range of 700 ndash 750 degC is presented in this work Thesetemperatures are somewhat higher than the eutectic points of NaCl ndashKCl (646 degC ) and LiCl ndash KCl (628 degC) and the melts are thereforeliquid enough to be used in technologically important processes oflanthanides and actinides separation reduction and rectification On theother hand these temperatures are significantly lower than the boilingpoint of zinc (907 degC) and there is essentially no loss of the metal due toevaporation

ExperimentalThe electrochemical experiments were performed using a three-

electrode cell made of sintered alumina placed in an alumina crucibleunder nitrogen atmosphere Tungsten (9995 1 mm diameter) andplatinum wires (9995 05mm diameter) were used as the workingelectrodes and their surface area was controlled by immersion depth(typically 6ndash12mm) and by measuring their diameter before and aftereach experiment A 1mm tungsten wire served as a pseudo-referenceelectrode and a flat spiral tungsten wire set perpendicular to theworking and reference electrodes close to the bottom of the cell servedas the counter electrode The area of the counter electrode was ~ 20 foldas large as that of the working electrode ZnCl2 LiCl NaCl and KCl(990 +ACS grade Alfa Aesar) were used for the preparation meltswithout further purification

Zinc chloride was mixed with alkaline metals chlorides usingmortar and pestle in a glove-bag in dry nitrogen atmosphere Themixture was then placed into a crucible the electrode cell was mountedand transferred into the furnace (single-zone Carbolite 1600 degC STF tubefurnace) In the furnace the mixture was first dried under vacuum at 40ndash50 degC for an hour After completing the drying dry nitrogen wasbubbled through the electrolyte during its heating up to the temperatureof the experiments (700ndash750 C) for another hour The temperature wascontrolled by a type S thermocouple placed next to the cell andprotected by an alumina capillary thus maintaining a precision of plusmn1 degCin measuring and controlling the temperature Dry nitrogen atmosphere

106

(1 bar) was maintained in the furnace during the measurements and thepost-experimental cooling The electrochemical measurements werecarried out using an Autolab PGStat-12 potentiostat SEM images andelement analysis by EDS were performed with a SEM system fromJEOL Inc Model JSM 7000F

Results and discussion

Deposition of zinc on a tungsten electrodeSome typical voltammograms for the electrochemical reduction ofZn(II) are shown in Fig 1

-02

-01

0

01

02

03

04

-1 -05 0

iA

cm

2

E V vs W

C

A

QaQ

c~ 1

0502005 Vsec

-0680-0650-0600E

p V

(peak C)

164141110Qc Ccm

2

177150113Qa Ccm

2

Fig 1 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0163 mol L) in equimolar NaCl-KCl melt on a W electrode at 700degC Scanrates are 50 mV sec (solid line) 200 mV sec (slashed line) and 500 mV sec(dotted line) Each charge density was calculated as the sum of areas limited bythe baseline and the appropriate current density curves for the forward andbackward semi-cycles

107

As follows from Fig 1 a single cathodic peak C corresponds toone anodic peak A The potential shape and behavior of the cathodicpeak are typical for the metal deposition on a solid electrode (2-4) Nodifference is observed between the reduction of zinc ions in NaCl ndash KCland in LiCl ndash KCl melts Peak A is assigned to the reoxidation of zincBoth peaks are clearly not independent on the scan rate Rather peak Cis shifted to more negative potentials and peak A moves to more positivepotentials as the scan rate increases The dependence of the cathodicpeak potential on the scan rate is shown in Fig 2 Such voltammetricresponse is typical for irreversible processes

055

06

065

07

075

0 01 02 03 04 05 06

-Ep

V

Vs

Fig 2 Dependence of the cathodic peak potential on the scan rate for thereduction of Zn2+ (0163 mol L) at 710degC on a W electrode

The cathodic peak C appears at about -06 V vs tungsten electrodefor the scan rate of 50 mVsec and at -07 V for 500 mVsec Such asignificant shift is a clear indication that the process is irreversible Thecathodic peak not only is shifted as the scan rate grows but it becomes

108

broader so that the difference |Ep ndash Ep2| grows from 01 V for 005 Vsecto 015 V for 05 Vsec Values of n calculated by equation 23 are inthe range of 156 for low scan rates to 104 for high scan rates The mostlogical interpretation of this finding is that the charge-transfer is of two-electrons which is not surprising in the case of Zn2+ ions reduction Thevalue of is then 078 for 005 Vsec and 052 for 05 Vsec This isevident that the rate determining step is the Faradaic process

Zn2+ + 2e- Znwhen the system is close to the steady state Note that at low enoughpotential scanning rates diffusion limitations may be less influencingwhile at higher scan rates the diffusion limitations are more importantRandles-Sevcik dependencies for the zinc (II) ions reductiondemonstrate linearity but their intercepts are apparently non-zero (Fig3)

0

01

02

03

04

05

06

07

0 02 04 06 08 1

i pA

cm

2

12 V12s-12

Fig 3 Randles-Sevcik plots for Zn2+ ions reduction on W in a NaCl-KCl meltat 700 degC different concentration of the ions (peak C in Figure 39) 900x10-5

molmL Zn2+ 163x10-4 molmL Zn2+ 177x10-4 molmL Zn2+

109

It is evident that the process Zn2+ + 2e- Zn is complicated bysomething else Despite the irreversible character of the depositionprocess it is still reasonable to roughly evaluate the diffusion coefficientof Zn2+ according equation 1

ip = 06105 (nF)32(RT)12D12C12 (11)

where ip is the peal current density (A cm2) n is the number ofelectrons F is Faraday constant (96500 C) R is the gas constant (8314Jmol∙K) T is the absolute temperature (K) D is the diffusion coefficient(cm2 sec) C is the bulk concentration of a Red (Ox) species (mol cm3) and is the scan rate (V sec)

Thus calculated diffusion coefficients are shown in Table 1

Table 1 Diffusion coefficients of Zn2+ to a tungsten electrode in NaCl-KCl melt

C105 mol L D 105 cm2 sec900 955n

163 1020n

177 1364n

Given that the value of n for the reduction of Zn2+ cannot exceed 2 and0 le le 1 ( asymp 05 for most cases) reasonable values of n must beclose to 1-2 Therefore the values of the diffusion coefficients fromTable 2 lie in the range of 1-6∙10-4 cm2sec Available literature data forthe diffusion coefficients of most metal ions lie in the range 10-5-10-4

cm2sec Particularly T Stoslashre G M Haarberg and R Tunold found thatthe values of the diffusion coefficients for Zn2+ in KCl-LiCl melts at400degC lie in the range 06 ndash 106∙10-5 cm2sec (2) Delimarski providesthe value of the diffusion coefficient of Zn2+ in NaCl-KCl at 710degCwhich is 23∙10-5 cm2sec (5) The deviation of our results from theliterature data can hint that that the process cannot be treated as simplezinc ion reduction on the surface of tungsten

110

It is worth to mention that the fact that the diffusion coefficientfor zinc ions in the chloride melt lay in the range 10-4 ndash 10-5 cm2sec mayserve as an indirect argument in the discussion about the existence ofcomplex species described by the general formula [ZnxCly]

z+ in chloridemelts While some authors argue in favor of the formation of complexions (6 ndash 10) other studies give evidence for the existence of individualzinc ions as the key reacting species (11 ndash 12) The relatively highvalues of the diffusion coefficients found in our experiments hint that thecharge is transferred by individual ions rather than by more massivecomplex moieties

005

01

015

02

025

03

035

04

02 03 04 05 06 07 08 09 1

700oC

750oC

740oC

720oC

i pA

cm

2

12

V12

s-12

Fig 4 Randles-Sevcik plots for Zn2+ reduction on W in a NaCl-KCl melt fordifferent temperatures [Zn2+] = 900x10-5 molmL

Another intriguing aspect of the zinc ions deposition process ona tungsten electrode can be seen in the temperature dependence of

111

Randles-Sevcik plots (Fig 4) As seen from Fig 4 Randles-Sevcik plotsdo not change (to the accuracy of the experiment) as the temperaturerises from 700degC to 750degC

The lack of dependence of Randles-Sevcik plots on thetemperature is really surprising A plausible explanation to this could bean additional process in the system which occurs simultaneously withthe observed process but does not involve charge-transfer and cannot bedetected electrochemically Such a process could compensate for theexpected increase of the slope of Randles-Sevcik plots as thetemperature grows and thus distort the temperature dependence

The most probable candidates for such competing processes area coupled chemical (not charge-transfer) reaction or a process of phase-formation However cyclic voltammetry alone cannot discriminatebetween these two possibilities

Fig 5 A chronoamperometric plot for the deposition of Zn2+ on a tungstenelectrode Temperature 725degC [Zn2+] = 900x10-5 molmL The potential was

stepped from OCV to -055 V

A further insight on the nature of the deposition process can beprovided by chronoamperometry As seen from Fig 5 the current fallsin the course of the first 11 seconds of the experiment and then risesreaches a peak and gradually declines as expected with time until theend of the experiment (300 seconds)

The initial falling and rising of the current can be attributed tothe nucleation of the deposits fluctuations of current for more advanced

112

reaction times as seen in Fig 5 may indicate to a very active charge-transfer process which cannot be explained by a simple zinc depositionprocess

Even more surprising information is provided by EDS analysisof the working electrode after a 3000 second deposition experiment at ndash055 V (Fig 6 Table 2) The most striking result of the analysis is theunexpectedly high content of sodium on the electrode surface Thisamount of sodium cannot be accounted for melt adhesion or penetrationbecause the percentage of potassium and chlorine is much smaller Infact the working electrode looks as it was made of sodium withmoderate inclusions of tungsten and zinc rather of tungsten

Fig 6 An EDS spectrum of tungsten working electrode after 3000 seconddeposition at ndash 055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Table 2 Element composition of the tungsten working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Element Na K Cl W ZnAt 6084 580 2861 224 191

113

A somewhat similar phenomenon was reported by Thus T StoslashreG M Haarberg and R Tunold for the deposition of Zn2+ on a glassycarbon electrode in KCl-LiCl melts at 400degC (2) They observed aldquosubstantial residual current observed prior to the Zn(II) reductionpeakrdquo This current was attributed by them to lithium intercalation intothe lattice of the glassy carbon electrode

Unfortunately the data about standard reduction potentials ofmany important ions in molten chlorides are lacking The only source inwhich suitable potentials were found is the book of Yu DelimarskildquoElectrochemistry of Ionic Meltsrdquo (5) The values of standard potentialstabulated in this book were calculated on the base a few assumptionsand are far from being strictly thermodynamical However they arehelpful from the practical point of view The potentials relevant for thisdiscussion are summarized in Table 3

Table 3 Standard reduction potentials in molten chlorides (adopted fromref [5])

Half-Element Li+|Li Na+|Na K+|K Zn2+|Zn Fe2+|FeEH2 (700degC) V - 239 - 236 - 250 - 040 - 007

As seen from Table 3 the standard potentials of lithium andsodium are very close to each other Therefore it is not surprising thatthe interference from sodium in the deposition of zinc ions is similar tothat of lithium as reported by T Stoslashre G M Haarberg and R TunoldOf course it is not intercalation that serves as the moving force of theprocess of sodium penetration into the surface layers of zinc deposit onthe tungsten electrode

The large amounts of sodium in the deposits obtained in the studyof the Zn2+ ions reduction on tungsten electrodes cannot be explained asthe formation of a W-Na alloy because such a process is not observedby the cyclic voltammograms of NaCl-KCl on tungsten electrodes in theabsence of zinc ions (3) Therefore it is zinc which triggers thedeposition of sodium Moreover the data obtained bychronoamperometry at E = ndash 055 V vs W (Fig 5) indicate that there aretwo sequential faradaic processes The first of them is relatively weak

114

and is completed after ~ 11 seconds Then the second process starts andits current only grows with time The first process can be related to thereduction of zinc ions and the formation of zinc deposits As theelectrode surface is covered by a layer of zinc the interaction of thislayer with Na+ ions begins Apparently sodium ions are absorbed by theliquid zinc (Tm = 419 degC) and this facilitates their reduction at thepotential so much more positive than the sodium reduction potential inthe absence of zinc ( - 11 V vs W) Both lithium and sodium are liquidat the temperature of the experiment and these two metals form on theelectrode surface a liquid solution with zinc which continues to absorbnew portions of the lithium or sodium ions

The following speculation may account for the phenomenonobserved in our system

1 Zinc ions are discharged on the surface of the tungstenelectrode As the surface concentration of zinc atoms grows nucleationoverpotential starts to dump the overall process This dumping isobserved in the course of the first 11 seconds in Fig 5

2 Zinc (or zinc-tungsten) phase is formed This phase triggers theprocess of sodium-zinc exchange

Zn + Na+ Zn+ + Na or Zn + 2Na+ Zn2+ + 2Na3 The process (2) becomes the main process on the electrode

surface

Deposition of zinc on a platinum electrodeSome typical voltammograms for the electrochemical reduction

of Zn(II) are shown in Fig 7 Again no difference is observed betweenthe processes in NaCl ndash KCl and in LiCl ndash KCl melts and two melts arefurther described on the instance of in NaCl ndash KCl alone

As seen from Fig 7 the voltammogram is completely anomalousas compared to the other studied systems No cathodic peaks areobserved in the range -11V to + 09V ie in the limits of theelectrochemical window The peaks ndash 125V and at +09 V are the sameas for the ldquoblankrdquo melt NaCl-KCl These are the limits of theelectrochemical window

A very poorly pronounced anodic peak A at about ndash 028 V issimilar to the anodic peak A which appears for the zinc deposition on atungsten electrode (Fig 1) However the cathodic branch of thevoltammogram contains a continuous transition to the cathodic limit of

115

the windows rather than a peak It is obvious that zinc deposition ismasked by another process whose nature cannot be studied in theframework of this research

Fig 7 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0176 mol L) in equimolar NaCl-KCl melt on a Pt electrode at 700degC Scanrate is 300 mVsec

Fig 8 An EDS spectrum of a platinum working electrode after 3000 secondcathodic polarization at ndash 07 V vs W at 725degC in equimolar NaCl-

KCl melt containing 176x10-4 molmL of Zn2+ ions

116

An attempt of obtaining a sample of zinc deposit by holding thesystem at ndash 07 V (that is at such a potential which is considerably morepositive than the cathodic limit but more negative than the potential atwhich zinc is deposited on a tungsten electrode) for 3000 seconds wasmade However the analysis (Fig 8) demonstrated that essentially nozinc is found on the surface of the electrode (Table 4) since the value098 At is comparable with the sensitivity of the method The richcontent of potassium (5857 At ) in the surface layers can hint thatpotassium sorption is the process which masks the deposition of zincHowever this information alone is not sufficient for making positiveconclusions

To try to understand the essence of the process other moltenchloride systems containing no potassium could be studied Howeversuch a study is far beyond the framework of the current work

Table 4 Element composition of the platinum working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 176x10-4 molmL

Element Na K Cl Pt ZnAt 555 5857 3426 618 098

ConclusionsThe deposition of zinc on a tungsten electrode starts as an

irreversible two-electron zinc ion reduction Zn2+ + 2e- Zn After anobvious initial nucleation step a new phase is formed This phasecatalytically launches the process of saturating the electrode surface withsodium After the onset of the process of sodium deposition the latterbecomes essentially the only constituent on the electrode surface

The attempts of studying the deposition of zinc ions on a platinumelectrode were unsuccessful because this process is masked by anotherprocess which can result in the saturation of the electrode by potassiumThe exact nature of the latter process demands a separate study

117

References1 Fray D J J Appl Electrochem 3 103 (1973)2 Stoslashre T Haarberg GM Tunold R J Appl Electrochem 30 1351

(2000)3 Lugovskoy A Zinigrad M Aurbach D Israel Journal of

Chemistry 47 (3-4) 409 (2007)4 Lugovskoy A Zinigrad M Aurbach D and Unger Z

Electrochimica Acta 54 (6) 1904 (2009)5 Delimarski Yu K Electrochemistry of Ionic Melts Metallurgiya

Moscow 1978 (in Russian)6 Mackenzie J D and Murphy W K J Chem Phys 33 366 (1960)7 Irish D E and Young T F J Chem Phys 43 1765 (1965)8 Allen DA Howe RA Wood ND Howells WS J Phys

Condens Matter 4 1407 (1992)9 Price D L Saboungi M-L Susman S Volin K J Wright A C J

Phys Condens Matter 3 9835 (1991)10 Bassen A Lemke A Bertagnolli H Phys Chem Chem Phys 2

1445 (2000)11 Biggin S and Enderby J E J Phys C Solid State Phys 14 3129

(1981)12 Badyal Y S and Howe R A J Phys Condens Matter 5 7189

(1993)

89

PREPARATION OF COMPOSITES CuZrO2 AND CuTiO2

BY MA SHS

AI Letsko1 TL Talako1 AF Ilyushchenko1 TF Grigoreva2SV Tsybulya3 IA Vorsina2 NZ Lyakhov2

1 Powder Metallurgy Institute of NAS B Minsk Belarus2 Institute for Solid State Chemistry and Mechanochemistry of SB RAS

18 Kutateladze str Novosibirsk Russia grigsolidnscru3 GK Boreskov Catalysis Institute of SB RAS Novosibirsk Russia

IntroductionMetaloxide composites are quite perspective materials for

application in machine industry instrument engineering and electricalengineering in comparison to pure metals due to their improvedchemical and physical properties (heat resistance strength hardnesserosion resistance) Chemical mixing salt mixture decompositionhydrogen reduction in solutions chemical precipitation from solutionsinternal oxidation are well-known methods of preparing such materialshaving application in industry [1] The above-mentioned technologiesallow attaining metaloxide composites but they are quite expensive andlong-term Based on this a very topical issue is elaboration of newapproaches to production of metal-ceramic materials

In this work we explored possibilities of preparation ofcopperoxide composites (CuZrO2 and CuTiO2) by methods ofmechanochemical synthesis (MS) in planetary mills and of mechanicallyactivated self-propagating high-temperature synthesis (MA SHS)

ExperimentalCopper copper oxide CuO and zirconium M-41 titanium PTOM

were used in this work as raw materials Mechanical activation (MA)was carried out in planetary ball mills with water cooling [2] (the drumvolume ndash 250 cm3 the balls diameter ndash 5 mm the load ndash 200 g sampleweight ndash 10 g the drums rotation speed about the general axis ~ 1000rpm) After MA the activated mixture was compacted (under a load of4ndash6 t) in the mould up of 17 mm diameter and ~25 mm in height (tillstrength sufficient for the sample transfer to the reactor) SHS wascarried out in the argon atmosphere the combustion was initiated withan electrically heated tungsten coil The temperature and burning

90

velocity were evaluated by a thermocouple method (C-A thermocouplesOslash asymp 02 mm) using an outer 2-channel 24-charge analog-to-digitalconverter ADSC24-2T

X-ray diffraction research was conducted with diffractometersXrsquoTRA (Thermo ARL Switzerland) with application of CoK radiation(λ = 1 789 Aring) and URD-63 with application of CuK radiation (λ = 15418 Aring) Evaluation of effective sizes of coherent scattering area wascarried out in compliance with the Scherer formula with the strongestpeaks of phases analysed

The high-resolution scanning electronic microscope (SEM)MIRATESCAN equipped with an INCA 350 accessory for EDXanalysis was used for the structure research The electron probe diameterwas 52 nm excitation area was 100 nm Images in direct electrons andback-scattered electrons were attained and it allowed studying chemicalelements distribution over the surface Brightness distribution in theimage depends on the average atomic element number in eachmicroarea

IR absorption spectra were registered by spectrometer IFS-66The samples were prepared to the exposure by standards methods

Results and discussion

Cu-O-Zr systemMechanochemical reduction of copper oxide with metallic

zirconium was initially investigated in this system This reaction is quitehigh-exothermic (∆H (2 CuO + Zr = 2 Cu + ZrO2) asymp -188 kcalmol) ieit can be implemented under mechanical activation conditions IRspectroscopic investigations have shown that the original copper oxideCu-O band is considerably widened at 505 cm-1 after 20 s of MA ofCuO + Zr mixture of stoichiometric composition This widening (Fig1b) can testify some structural failures After 30 s of activation thefollowing bands are present in the IR-spectrum of the product 505 cm-1

(original oxide CuO) 615 cm-1 (the lowest copper oxide Cu2O) [3] and415 585 735 cm-1 (zirconium oxide (Fig 1c) [4 5] X-ray-phaseanalysis shows the presence of certain amount of Cu2O already after 20 sof activation The 30-second activation product diffractogram showsclear copper (coherent scattering area asymp 80 nm) and zirconium oxide

91

(coherent scattering area asymp 100 nm) reflection and two copper oxidereflections ie mechanochemical reduction of copper oxide takes placeat such activation duration This reaction speed shows that the reactionpresumably takes place in the thermal explosion mode when especiallyhigh heat dissipation speed is needed what is very difficult to performeven in the most effectively cooled highly-energy planetary ball millsAs such a process dimensional scaling seems to be absolutely impossiblein conditions of mechanochemistry an attempt to produce compositeCuZrO2 by the SHS method was made

Fig 1 IR-spectra of mixture CuO + Zr before (a) and after MA for 20 (b) and30 s (c)

At first CuOZr mechanocomposite was used as the SHS-precursor This mechanocomposite formed after 20 s of MA ofstoichiometric composition mixture has a small amount of cuprous oxideCu2O beside original copper oxide and zirconium SHS process proceedsin the heat explosion mode in this system Burning parameters fixingfailed in this case because of the inertia of the equipment applied

92

Not pure metal but solid solutions intermetallic compounds ornano-composites where metal-reducer (zirconium in our case) isdistributed in the inert matrix can be used as a reducing agent todecrease the system reaction capability At the same components ratiochemical energy of the raw mixture would be considerably lower and asa consequence heat release would reduce

In this work mechanocomposite formed during mechanicalactivation of mixture Cu + 20 wt Zr for 20 min with zirconium hadbeen pre-dispersed for 4 minutes (zirconium coherent scattering areasize ~ 20 nm) was used for copper oxide reduction This compositediffractogram shows the widened intensive copper (coherent scatteringarea asymp 20 nm) reflection and very vague zirconium reflection coherentscattering area of which cannot be evaluated (Fig 2) Since copperreflections havenrsquot changed their position we can conclude thatzirconium hasnrsquot become a part of copper crystal lattice ie CuZrmechanocomposite and not solid solution is attained

Fig 2 Diffractograms of Cu + 20 Zr mixture before (a) and after 20 minof MA (b)

93

This is confirmed by the SEM results (Fig 3) The electronmicroscopy data more clearly show zirconium distribution Zr elementalmapping testifies that local zirconium areas are much diffused

Fig 3 SEM-images of sample Cu + 20 Zr after MA for 20 min

94

X-ray research of the product of joint activation of mixture CuO +mechanocomposite Cu + 20 Zr (the mixture composition correspondsto the stoichiometric ratio of copper oxide and zirconium) for 2 and 4minutes show that copper oxides diffraction reflections are retained inall cases although they are substantially widened (Fig 4) Thezirconium oxide reflection is not observed ie mechanochemical copperoxide reduction does not take place in this time gap CuOCuZrmechanomposite formed as a result of joint mechanical activation ofmixture CuO + mechanical composite Cu 20 Zr for 4 min was usedas a precursor for SHS

Fig 4 Diffractogram of sample CuO + CuZr after MA for 4 min

Usage of mechanocomposite CuOCuZr instead of CuOZr one asthe SHS precursor changes a mechanism of interaction between thereactants during the SHS process from the thermal explosion mode (forCuOZr mechanocomposite) to the steady-state combustion with the

95

burning velocity asymp 2 mms temperature rise speed about 730 Cs andburning temperature 1044 C The combustion temperature record (Fig5) shows 2 isothermal plateaus The first one is fixed at temperaturemaximum and most probably points out melting process The secondone is fixed at 580 ndash 590 C and accounts for post-processes in the after-burning zone of combustion wave

Fig 5 Temperature record of the SHS process from mechanical compositeCuOCuZr

X-ray-phase analysis has shown that SHS product consists ofcopper and zirconium oxide with Cu2O traces (Fig 6) Electronicmicroscopy with the EDX analysis confirms composite structureformation (Fig 7 Table 1)

96

Fig 6 Diffractogram of the SHS product from mechanical compositeCuOCuZr

Fig 7 SEM-image of the SHS product from mechanical composite CuOCuZr

97

Table 1 Results of the EDX analysis (from Fig 7)

Number ofspectrum

O Cu Zr

1 382 8744 8742 714 8152 11343 2803 2747 44504 1653 4640 37065 2314 2914 4772

Cu-O-Ti systemChemical reduction of CuO with titanium is also high-exothermic

(∆H (2 CuO + Ti = 2 Cu + TiO2) asymp -151 kcalmol) Mechanicalactivation of equimolar mixture of copper oxide with titanium powderfor 4 minutes did not result in titanium oxide formation Longeractivation is not reasonable since it contaminates the reaction mixturewith balls and drums material That is why the composites formedduring the short-term MA were used as precursors for SHS

After 30 s MA composite structure CuOTi with a small additiveof cuprous oxide reduced from CuO (Fig 8) is formed The SHS processfrom such mechanocomposites proceeds with a very high speed andtemperature (on a levels typical for the thermal explosion mode) andwith the substances scatter

Fig 8 Diffractogram of mixture CuO + Ti after MA for 30 s

98

To decrease combustion temperature and velocitymechanocomposite CuTi containing 20 wt of titanium was used as areducing agent in the next experiment Figure 9 shows the diffractogramof the mechanocomposite formed after 10 min mechanical activation ofthis mixture It shows that metals reflections especially that of titaniumare widened testifying substantial increase of their dispersivityAccording to the X-ray data analysis the titanium coherent scatteringarea size is ~ 10 nm in this composite

Fig 9 Diffractogram of mixture Cu + 20 Ti after 10 min of MA

Mixture of copper oxide and CuTi mechanocomposite (thecomposition corresponds to the stoichiometric ratio of titanium andcopper oxide for its full reduction) was subjected to activation for 4minutes Only a band of valence vibrations of vCu-O copper oxide (Fig10a) is present in the IR-spectrum of the activated mixture like in theoriginal one but its intensity slightly decreases X-ray research alsoindicates that the titanium oxide reflections are absent in the 4-minuteactivation product diffractogram (Fig 11)

99

Fig 10 IR-spectra of sample CuO + CuTi after 4 min of MA (a)and after SHS (b)

Fig 11 Diffractogram of sample CuO + CuTi after 4 min of MA

100

SHS process from CuOCuTi mechanocomposite takes place inthe steady-state combustion mode with burning velocity higher than 20mms and burning temperature ~2000 ordmC A band (~730 cm-1)corresponding to valence vibrations of rutile vTi-O (Fig 10b) [2]appears in the IR-spectrum of the SHS product from CuOCuTimechanicocomposite Diffraction reflections (Fig 12) also correspond toreflections of rutile and copper

Fig12 Diffractogram of the SHS product from CuOCuTi mechanocomposite

Electron-microscopy exposure in back-scattered electronsindicates the partial phase separation of TiO2 and Cu (Fig 13 a) thoughcomposite particles containing TiO2 inclusions with size from 30 nm till1 5 m (Fig 13 c) are also formed The elemental mapping in thetitanium characteristic radiation confirms this fact (Fig 13d)

101

a

b cFig 13 SEM-images of the SHS-product from CuOCuTi mechanocomposite

102

Table 2 The EDX analysis results (from Fig 13 a)

Number ofspectrum

O Ti Cu

1 191 052 9757

2 235 051 9714

3 2230 2094 5676

4 1586 1295 7118

5 180 108 9712

6 336 228 9436

7 4335 4685 980

8 3297 2738 3966

9 4978 4645 377

ConclusionThus our investigations have shown that copper oxide can be

mechanochemically reduced with zirconium resulting in formation ofzirconium oxide and copper but the reaction goes in the thermalexplosion mode

To produce composite CuZrO2 by the method of MASHS usageof mechanocomposite CuZr instead of pure zirconium seems to be morepromising The MASHS product is a copper-based composite withinclusions of ZrO2 and some amount of Cu2O

Mechanical activation of equimolar mixture of copper oxide withtitanium powder for 4 minutes did not result in titanium oxide formationThat is why the composites formed during the short-term MA were usedas precursors for the following SHS

Reduction of CuO with CuTi mechanocomposite can beimplemented by the method of MASHS Partial phase separation of TiO2

and Cu takes place during the synthesis process along with the formationof copper-based composite particles with inclusions of titanium oxidesized from 30 nm up to 15 m

103

References1 PA Vityaz Mechanically alloyed alloys on the basis of aluminum

and copper PA Vityaz FG Lovshenko GF Lovshenko ndashMinsk Belnauka 1998 ndash 351 p

2 YG Avvakumov AP Potkin OI Samarin Authorrsquos certificate ofUSSR 975068 Planetary mill BI 1982 No 43

3 SS Batsanov VPBokarev YVLazareva On CuO interaction withcopper Inorganic Chemistry Journal 1977 V 22 issue 4 P 888ndash 892

4 AI Boldyrev Infrared spectra of minerals M Nedra 19765 BT Kaminsky AS Plygunov GN Prokofyeva Infrared spectra of

oxides of titanium zirconium and hafnium Ukrainian ChemicalJournal 1973 V 35 No 9 P 946 ndash 977

78

THE STANDARD ENTHALPY AND ENTROPY OFFORMATION OF GASEOUS AND LIQUID

POLYCHLORINATED BIPHENYLS POLYCHLORINATEDDIBENZO-n-DIOXINS AND DIBENZOFURANS

TV Kulikova AV Mayorova KYu ShunyaevInstitute of Metallurgy Ural Branch RAS

Yekaterinburg RussiaE-mail kulikogmailcom

AbstractThe study deals with analysis and systematization of the known

and calculation of the unknown thermodynamic characteristics (thestandard enthalpy of formation the standard entropy of formation) ofwidespread hazardous isomers of gaseous and liquid compounds ofpolychlorinated biphenyls (PCBs) polychlorinated dibenzo-n-dioxins(PCDDs) and polychlorinated dibenzofurans (PCDFs) Thecomparison of results obtained in different studies reveals aconsiderable discrepancy between values reported by highlyrespected investigators In this connection laquoindependentraquo results ofthe thermodynamic characteristics have been calculated

IntroductionUnique technological and physicochemical properties of

polychlorinated biphenyls (PCBs) a huge volume of theirproduction considerable volatility and solubility and extremechemical inertness have led to the world-wide spread of PCB-containing equipment and materials resulting in the universalcontamination with these substances The most common method usedin Russia for destruction of PCBs is their incineration with theformation of polychlorinated dibenzo-n-dioxins (PCDDs) anddibenzofurans (PCDFs) which are among the most hazardouschemical substances known to the mankind

As often happens the hazard of PCBs has long beenunderestimated With respect to their severe toxicological effectPCBs are identical to substances that are referred to the high class ofhazard Since these substances are especially toxic they have beenassigned low toxicological standards which necessitate special

79

requirements on the organization of processes assuming formation ofthese substances (the so-called dioxinogenic processes) so thatindustrial emissions meet the norms Instrumental investigations ofthese substances are very expensive and in this connection interestis attracted to calculation methods for simulation of processes by thedata on their thermochemical properties

A quality thermodynamic simulation requires the knowledge ofthermodynamic and thermochemical properties of all reliablycertified compounds of the system under study in the gaseous orcondensed state Therefore the present study deals with the analysisand systematization of the known and calculation of the unknownthermochemical properties (the standard enthalpy and entropy offormation) of most toxic and hazardous isomers of gaseous PCBsPCDDs and PCDFs and liquid PCBs

Calculation of thermochemical propertiesIt is known that there are 209 individual PCB congeners 420

polychlorinated dibenzo-n-dioxins and polychlorinateddibenzofurans which differ by the number and positions of chlorineatoms in a molecule The most widespread PCB compoundscontaining up1 to 10 chlorine atoms were chosen for the study Indeciding on isomers preference was given to ortho-unsubstitutedPCBs because they are most toxic and their effect is similar to theeffect of PCDDs and PCDFs Congeners which do not have chlorineatoms in ortho-positions of molecules (ortho-unsubstituted PCBs)can acquire the planar configuration which is more favorable inenergy terms Such congeners are isostereoisomeric to PCDDs andPCDFs and present the greatest hazard As to the PCDD and PCDFisomers of special hazard to humans and the environment are tri-tetra- penta- and hexa-substituted dioxins and furans containinghalogen atoms in lateral positions 2 3 7 and 8

In this study we analyzed the known and calculated theunknown thermodynamic properties of 17 most widespread andhazardous isomers of PCBs PCDDs and PCDFs in the gaseous stateand 11 compounds of liquid PCBs

80

Gaseous PCBs PCDDs and PCDFsThe literature survey showed that studies dealing with

estimation of the thermochemical properties of gaseous PCB PCDDand PCDF compounds are few Most of them are based oncalculations or are semi-empirical For example Saito and Fuwa [1]calculated thermodynamic functions of all PCBs and some PCDDsand PCDFs on the basis of semi-empirical calculations in terms ofthe PM3 model OV Dorofeeva et al [2-4] used statistical methodsTable 1 presents the literature data on standard enthalpies andentropies of formation of gaseous and liquid PCBs PCDDs andPCDFs The comparison of results obtained in different studiesreveals a considerable discrepancy between values reported by highlyrespected investigators who did very arduous work In particularvalues of the formation enthalpy [1] are 8-70 larger and the entropyis 11-15 smaller than the corresponding values in [2-4] thediscrepancy grows with the number of chlorine atoms in a moleculeSo we thought it reasonable and topical to attempt an independentresult

Bensons method [5] was used to calculate thermodynamiccharacteristics (the standard enthalpy of formation ΔНdeg298 thestandard entropy of formation ΔSdeg298) of the gaseous PCBs PCDDsand PCDFs We shall dwell briefly on this method

Bensons method is the group additivity method involvinganalysis of the molecule structure Atomic or molecular groups areseparated and the nearest neighbors of the atom or the group areconsidered Table 2 gives the number of groups necessary fordetermination of group increments in structural formulas of PCBsPCDFs and PCDDs Values of the thermodynamic characteristics ofgroup increments were determined from available reference andliterature data [5 6] Information about the energy contribution ofeach group (see Table 3) and the number of groups was used tocalculate thermochemical properties of the PCBs PCDDs andPCDFs

81

Table 1 Standard enthalpies (∆Нo298 kJmole) and entropies (∆So

298Jmole K) of formation of gaseous and liquid PCBs PCDDs andPCDFs

Gaseous state Liquid state

Compo-unds Saito Fuwa [1]

the given work

OV Dorofeeva etal

[2-4]

∆Нo298

[7 8 121617]

So298

[781014 16 17]

∆Нo298

the givenwork and

[814]

So298

thegivenworkand[14]

1 2 3 4 5 6 7 8 9

C12H10

(biphenyl)

1986[1]

1797

3454[1]

4104

1820[3]

3908[3]

1819[8]

1814[16]

3927[16]

11711162[8]11710

[14]

257402574[14]

C12H9Cl(3-mono-

chlor-biphenyl)

1705[1]

1500

3851[1]

4413

1561[2]

4323[2]

1548[8]

15088[16]

4214[16]

7629 2840

C12H8Cl2

(44rsquo-dichlor-biphenyl)

1422[1]

1202

3992[1]

4721

1260[2]

4518[2]

1276[8]

12004[16]

4492[16]

3584 3106

C12H7Cl3

(344rsquo-trichlor-biphenyl)

1194[1]

905

4240[1]

5030

1041[2]

4923[2]

1004[8]

892[16]

4780[16]

-452 3372

C12H6Cl4

(33rsquo44rsquo-tetrachlor-biphenyl)

969[1]

608

4444[1]

5338

899[2]

5216[2]

732[8]

5836[16]

5068[16]

-4488 3638

C12H5Cl5

(33rsquo44rsquo5-penta-

chlorbiphenyl

748[1]

310

4620[1]

5647

569[2]

5502[2]

460[8]

2752[16]

5356[16]

-8524 3904

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlor-

biphenyl)

529[1]13

4615[1]

5956

314[2]

5675[2]

190[8]

-332[16]

5644[16]

-12558 4170

C12H3Cl7

(233rsquo44rsquo55rsquo-hepta-

chlor-biphenyl)

400[1]

-284

4842[1]

6264

152[2]

6077[2]

-84[8]

-416[16]

5932[16]

-16596 4436

82

1 2 3 4 5 6 7 8 9

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-

octachlor-biphenyl)

241[1]

-581

4886[1]

6573-90[2]

6342[2]

-356[16]-650[8]

6220[8]

-20632 4702

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-

nanochlor-biphenyl)

873[1]

-878

5048[1]

6881

-153[2]

6607[2]

-628[16]-958[8]

6508[8]

-24668 4968

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlor-biphenyl)

-67[1]

-1176

5034[1]

7190

-247[2]

6757[2]

-901[16]

-1267[8]

6796[8]

-28604 5234

C12H8O2

(dibenzo-n-dioxin)

-402[1]

-448

3764[1]

-592[4]

3965[4]

-592[12]-592[7]

-550[17]

3951[7]

3880[17]

- -

C12H4Cl4O2

(2378-tetrachlor-dibenzo-n-

dioxin)

-1372[1]

-1592

4553[1]

-1640[4]

4781[4]

-1345[7]

-158[17]

5136[7]

4784[17]

4781[10]

4784[9]

- -

С12H3Cl5O2

(12378-pentachlor-dibenzo-n-

dioxin)

-1532[1]

-1900

4931[1]

-1900[4]

54035[4]

-1162[7]

-196[17]

5531[10]

5010[17]

- -

С12H2Cl6O2

(123478-hexachlor-dibenzo-n-

dioxin)

-1691[1]

-2164

4841[1]

-2196[4]

56912[4]

-1224[7]

57559[7]

5236[17]

- -

С12HCl7O2

(1234678-hepta-chlor-

dibenzo-n-dioxin)

-1848[1]

-2472

5005[1]

-2460[4]

59789[4]

-1196[7]

61031[7]

5462[17]

- -

C12H8O(dibenzo-

furan)

1061[1]

518

3787[1]

553[4]

3759[4]

552[17]

3744[17]

- -

C12H4Cl4O(1234-

tetrachlor-dibenzo-furan)

203[1]

-625

4505[1]

-500 [4]49098

[4]-528[17]

4648[14]

- -

83

1 2 3 4 5 6 7 8 9

С12H3Cl5O(12378-pentachlor-

dibenzo-furan)

-123[1]-934

4592[1]

-759[4]

51975[4]

-748[17]

4874[14]

- -

С12H2Cl6O(123478-

hexachlor-dibenzo-furan)

-283[1]

-12424713[1]

-1051[4]

54852[4]

-1043[17]

5100[14]

- -

С12HCl7O(1234678heptachlor-

dibenzo-furan)

-441[1]

-1550

4833[1]

-1315[4]

57729[4]

-1313[17]

5326[14]

- -

Table 2 Number of groups for determination of group increments instructural formulas of PCBs PCDFs and PVDDs

Number of groupsCompound Св-H Св-Cl Св-O Св-Св

Number ofchlorine atoms

in a molecule (n)

PCBs 10 - n n - 2 1 ndash 10

PCDFs 8 - n n 2 2 1 ndash 8

PCDDs 8 - n n 4 - 1 ndash 8

Св is the carbon atom in an aromatic ring

Values presented in Table 1 show the thermodynamiccharacteristics of PCBs PCDDs and PCDFs calculated in this studyand by other investigators

It is seen for example ( Table 1) that the formation enthalpy

(o298H ) of biphenyl (C12H10) equals (kJmole) 1986 [1] 1820 [3]

1819 [7] and 1814 [8] while the formation entropy (o298S ) of

2378-tetrachlordibenzo-n-dioxin (C12H4Cl4O2) is (J(mole K))4553 [1] 4781 [4] 4784 [9] and 4781 [10]

84

Table 3 Values of the thermodynamic characteristics determined bythe method of group increments[58]

(gas) (liquid)Group

o298H

kJmole

o298S

J(moleК)

o298H

kJmole

o298S

J(moleK)

Св-H 1381[8]1382[5]

4831[8]4827[5]

816[8] 2887[8]

Св-Св 2166[8]2077[13]

-3657[8]-3618[5]

1721[8] -

Св-Cl -1703[8]-1591[5]

7708[8]7913[5]

-3220[8] 5547[8]

(Св)2-O -7766[8]-8834[5]

--

- -

orto corrCl-Cl

950[8]921[5]

- 1400[5] -

meta corrCl-Cl

-500[8] - 400[5] -

In this study the values of the standard entropy of formationobtained by using statistical methods (OV Dorofeeva et al [2-4 9])for 17 isomers of PCBs PCDDs and PCDFs are in good agreementwith the values calculated by other investigators [8 10 12 13] andwith the values calculated by us

Liquid PCBsIt should be noted that ample literature data on the

thermochemical properties of liquid ecotoxicants is only available forbiphenyl (C12H10) [8 14] dibenzo-n-dioxin (C12H8O2) [11 15] anddibenzofuran (C12H8O) [5 17] The only study dealing withcalculation of thermodynamic functions for the whole series of liquidPCDD and PCDF homologues was published by VS Iorish et al[11] As to liquid PCB compounds the literature data on theirthermochemical properties are scarce [8 14]

The thermochemical properties namely the standard enthalpyand entropy of formation of liquid PCBs were calculated using thegroup additivity method due to Domalski [8] Values of the groupincrements (Table 3) were adopted from [8] It is seen from Table 3

85

that the energy contribution of the group Св-Св is unavailable for the

entropy calculation However if one uses known values ofo298S for

liquid biphenyl (C12H10) [14] and the data on the contribution of the

Св-H and Св-Cl groups [8] it is possible to calculateo298S for the

whole series of PCBs

o298S (PCB) =

o298S (BP) - (10-n)

o298S (Св-H) + n

o298S (Св-Cl) +

+(morto corr Cl- Cl ) +(pmeta corr Cl- Cl) (1)

where n is the number of chlorine atoms in a PCBs moleculem (p) - spatial amendments number Cl (from two and more) beingin orto - (meta-) position rather each other

The enthalpy of formation (o298H ) for the PCBs series

compounds was calculated by two options using the group additivitymethod due to Domalski [8] and from the equation

o298H (PCB) =

o298H (BP) - (10 - n)

o298H (Св-H) +

+ no298H (Св -Cl) +(morto corr Cl-Cl )+(pmeta corr Cl-Cl) (2)

Table 4 lists values of the standard enthalpy of formation forthe series of liquid PCBs compounds as calculated by the groupadditivity method [8] and the equation (2) It is seen that the values of

o298H which were calculated by the two methods are in good

mutual agreementThe thermochemical properties which were taken as reliable

were added to the TERRA database and were used forthermodynamic simulation of the thermal stability of PCBs PCDDsand PCDFs

86

Table 4 Calculated enthalpy of formation (∆Нo298) for liquid PCBs

compounds∆Нo

298 kJmole

CompoundGroup

incrementsmethod

Eq (5)δ

C12H9Cl(3-monochlorbiphenyl)

7584 76742 12

C12H8Cl2

(44rsquo-dichlorbiphenyl)3530 36382 30

C12H7Cl3

(344rsquo- trichlorbiphenyl)-506 -3978 2138

C12H6Cl4

(33rsquo44rsquo-tetrachlorbiphenyl)-4542 -44338 238

C12H5Cl5

(33rsquo44rsquo5-pentachlorbiphenyl)-8578 -84698 126

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlorbiphenyl)-1261 -125058 083

C12H3Cl7

(233rsquo44rsquo55rsquo-heptachlorbiphenyl)-1665 -165418 065

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-octachlorbiphenyl)-20686 -205778 052

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-nanochlorbiphenyl)-24722 -246138 044

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlorbiphenyl)

-28758 -286498 038

Conclusions1The literature data on the thermochemical properties of 17

most widespread and hazardous isomers of PCBs PCDDs andPCDFs in the gaseous state and 11 compounds of liquid PCBs havebeen analyzed and systematized for the first time

2Methods have been developed for calculating of thethermodynamic characteristics of organic compounds Values of thethermodynamic functions (standard enthalpy and entropy offormation) of liquid PCBs PCDDs and PCDFs have been calculatedfor the first time

87

3The comparison of the calculated values of thethermodynamic functions with the known literature datademonstrated their good mutual correlation

4The obtained data were added to the TERRA database andwere used for thermodynamic simulation of the thermal stability ofPCBs PCDDs and PCDFs

5The obtained data can be used for simulating of the behaviorof complex heterogeneous systems including ecotoxicants over awide interval of temperatures and initial compositions

This study was supported by RFBR (project No 08-03-00362-a)

References1 Nagahiro Saito Akio Fuwa Chemosphere 2000 vol40 p

131-1452 OV Dorofeeva NF Moiseeva VS YungmanLV JPhys

Chem A 2004 vol 108 p 8324-83323 OV Dorofeeva Thermodynamica Acta2001 vol374 p7-114 OV Dorofeeva VS Iorish NF Moiseeva J Chem Eng

Data 1999 vol 44 p 516-5235 SW Benson FR Cruickshank DM Golden GR Haugen

HE OrsquoNeal AS Rodgers R Shaw and R Walsh Chem Rev1969 vol69 p 279 -324

6 HK Eigenmann DM Golden and SW Benson J PhysChem 1973 vol 77 1687-1691

7 Jung Eun Lee and Wonyong Choi J PhysChem A 2003vol 107 p 2693-2699

8 Domalski E S and Hearing E D J of Phys and Chem RefData 1993 vol 22 p 805-1159

9 LV Gurvich OV Dorofeeva VS Iorish Zh Fiz Khimii 1993vol67 No 10 p 2030-2032

10 W-Y Shiu and K-C Ma J Chem Ref Data 2000 vol29No 3 p 387-462

11 VS Iorish OV Dorofeeva NF Moiseeva J Chem Eng Data2001 vol46 p 286-298

12 VA Lukyanova VP Kolesov Zh Fiz Khimii1997 vol 71No 3 p 406-408(in Russian)

88

13 P Reid J Prausnitz T SherwoodLeningrad Khimiya 1982592 p(in Russian)

14 Richard Laurent and Helgeson Harold C Geochimica etCosmochimica Acta 1998 vol 62 No 2324 p 3591 ndash 3636

15 I Barin ldquoThermochemical Data of Pure SubstancesrdquoWeinheim Federal Republic of Germany VCHVerlagsgesellschaft mbH 1997

16 Cambridgesoft database ver 806 December 31 200317 Thompson D Thermochim Acta 1995 vol261 p7-20

76

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OFNANOGRAINED

TiN-TiB2 COMPOSITES

MA Korchagin BB BokhonovInstitute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirsk Russiakorchagsolidnscru

Titanium nitride is known to exhibit high oxidation resistancehigh thermal conductivity and hardness as well as high corrosionresistance in acids Titanium diboride is also very hard possessing highstrength at elevated temperatures and anomalously high electricalconductivity among other ceramic materials

Composite materials based on the mixture of these twocompounds have been widely used in a variety of applications Highperformance parts have been also developed Thus ceramics containing40-50 molTiN shows high oxidation resistance [1] However untilvery recently TiN and TiB2 have been produced separately by twodifferent routes At present new methods are being developed tosynthesize mixtures of these two compounds in a single process One ofthese methods is based on self-propagating high-temperature synthesis(SHS) The use of SHS eliminates the need of having furnace equipmentto synthesize the desired products The possibility of SHS in the systemis due to the high enthalpies of formation of the products serving as aninternal chemical source of energy

In order to simultaneously obtain TiN and TiB2 by SHS the initialreactants can be either the powder mixtures of Ti-BN [3] or Ti-B-BN[4] The products of the reactions consist of highly porous well meltedsintered pieces with the minimum grain size of 1-10 microm [4] Hightemperatures developed in the combustion wave in the traditional SHSdo not allow finer grains of the products to retain

In order to overcome this problem short mechanical activationof the mixtures of reactants is proposed followed by the SHS in anatmosphere of argon or nitrogen

In the previous investigations preliminary mechanical activationhas been shown to significantly reduce the combustion temperatures

77

which to a great extent determine the grain size of the products of SHS[6 7]

Experiments were performed on the stoichiometric mixtures 3Ti +2BN The time of preliminary mechanical activation in a planetary ballmill (AGO-2 type) did not exceed 10 min The influence of the durationof mechanical activation on the combustion rate temperature and phasecomposition of the products was studied

The milled mixtures and the products of SHS were studied usingXRD analysis and Electron Microscopy The experimental conditionshave been found favoring the formation of the two-phase mixtures ofTiN of TiB2 with the grain size ranging from 20 to 50 nm [7]

References1 GV Samsonov Nitridy (Nitrides) Kiev laquoNaukova Dumkaraquo 19692 AG Merzhanov Tverdoplamennoe gorenie (Solid State

Combustion) Chernogolovka ISMAN 2000 224 p3 AEGrygoryan ASRogachev Combustion of titaniumwith

nonmetal nitridesCombustion explosion and shock waves 2001v37 2 p168-172

4 R Tomoshige A Murayma T Matsushita Production of TiB2-TiNcomposites by combustion synthesis and their properties J AmCeram Soc 1997 80[3] 761-764

5 MAKorchagin TFGrigorrsquoeva BBBokhonov MRSharafutdinovAPBarinova NZLyakhov Solid-state combustion in mechanicallyactivated SHS systems Combustion explosion and shock waves2003 v39 1 p43-58

6 MAKorchagin DVDudina Application of self-propagating high-temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007v43 2 p176-187

7 MAKorchagin BBBokhonov Combustion of mechanicallyactivated 3Ti+2BN mixtures Combustion explosion and shockwaves 2010 v 46 2 p170-177

65

SPIN-CROSSOVER IN THE PENTANUCLEAR BYPIRAMIDALCo2Fe3 AND Fe2Fe3 COMPOUNDS

Sophia Klokishner Sergei Ostrovsky Andrei PaliiInstitute of Applied Physics Academy of Sciences of Moldova

Kishinev MoldovaKim Dunbar

Department of Chemistry Texas AampM UniversityCollege Station TX USA

Boris TsukerblatChemistry Department Ben-Gurion University of the Negev

Beer-Sheva Israel

In this article we report a model for a spin-crossover phenomenonin pentanuclear bypiramidal [M(III)(CN)6]2[M(II)(tmphen)2]3 (MM=CoFe FeFe) cluster compounds The spin-crossover phenomenonis considered as a phase transformation accompanied by a change of theground state spin The model takes into account cooperative interactionsin the crystal network local crystal fields and spin-orbit coupling actingwithin the degenerate metal sites Magnetic properties and Moumlssbauerspectra are analyzed and compared to the experimental data

1 IntroductionSpin-crossover compounds have been a subject of many

experimental and theoretical studies [1-6] Till now only a fewexperimental reports on spin crossover in cluster compounds [7-11] havebeen reported Recently FeII ions were introduced into the equatorialmetal sites of discrete cyano-bridged pentanuclear clusters[MIII(CN)6]2[MII(tmphen)2]3 (MM =CoFe(1) FeFe(2) ) [12] with atrigonal bipyramidal (TBP) structure The octahedral nitrogensurrounding of FeII ions facilitates the spin-crossover behavior Theoccurrence of the ls-hs transition in compounds 1 and 2 was proved bythe combination of Moumlssbauer spectroscopy magnetic measurementsand single-crystal X-ray studies For both types of clusters[FeII(tmphen)2]3[M

III(CN)6]2(M=FeCo)7 the T product increases by

~9emumiddotKmol between 150 K and 375 K thus indicating the ls ndashhstransition at the FeII sites The TBP FeII

3CoIII2 cluster due to its electronic

66

structure represents an ideal system for studying the effects ofintracluster short-range and intercluster long-range interactionsfacilitating spin-crossover In the (FeIII)2 (FeII)3 cluster the hs-FeII and ls-FeIII ions are coupled by exchange interaction In spite of the fact that theexchange interaction of the hs-FeII and ls-FeIII ions through the cyanidebridge is sufficiently weak as compared with that in oxide clusters it isinterestingly to understand whether this interaction may affect the spintransformation The effects of orbital degeneracy on the spin-crossovertransformation in the [FeII(tmphen)2]3[FeIII(CN)6]2 crystal will beexamined as well In the present article a microscopic approach to theproblem of spin crossover in crystals containing metal clusters isdeveloped

2 The modelIn the basic structural unit of compounds 1 and 2 two MIII ions

surrounded by six carbon atoms occupy the apical positions and threeFeII ions coordinated by the nitrogen atoms reside in the equatorial plane[12] In a strong crystal field of carbon atoms the ground terms of the

CoIII and FeIII ions are the low-spin orbital singlet )( 621

1 tA ( 0S ) and

the orbital triplet )( 421

3 tT respectively The ground state of a FeII -ion in

the crystal field induced by the nitrogen atoms can be either low-spin

(ls)- term )( 621

1 tA or high spin (hs) ndashterm 2422

5 etT Both magnetic

measurements and Moumlssbauer spectroscopy for water containing crystals[12] demonstrate the presence of some amount of FeII ions in the hsconfiguration even at very low temperatures Further on we consider inthe model two types of FeII ions and denote by x the fraction of FeII -ions which are in the hs ndashstate at all temperatures while theconcentration of those ions which undergo the ls-hs transition is (1-x)The number pi of trigonal bypiramidal clusters in which i (i=0123) ofthree FeII ions are in the hs configuration in the whole temperature range

is estimated as iiii xxCp 33 1 where rllrC r

l

The Hamiltonian of intraion interactions can be written in the form

67

Hg

gllsH

kkB

kkB

kZkk

)(

32)(

211

02

0

H

lsH

(1)

where numbers theIIFehs ions in the k-th bypiramidal cluster the

first term is the spin-orbit (SO) coupling in the cubic )( 2422

5 etT - term of

theIIFehs -ion the second term describes the axial crystal field

splitting the 125 lT term into an orbital singlet ( 0lm ) and an

orbital doublet ( 1lm ) the third term refers to the Zeeman

interaction for hs-FeII ions and contains both the spin and orbitalcontributions B is the Bohr magneton and g0 is the spin Lande factorFinally the fourth term represents the interaction of the ground Kramersdoublets of two ls-FeIII ions in the cluster with the external magnetic

field i is the matrix of the pseudo -spin frac12 of the ls-FeIII ion g1 =173

is the Lande factor Up to room temperature the ls-FeIII can be regardedas an ion with the pseudo-spin frac12 because the ground Kramers doubletand the excited quadruplet arising from the splitting of the 2T2 term by

the spin-orbital interaction are separated by the gap 173023 cm

( 1486 cm [13] for a free ls-FeIII) that is large enough from the

thermal population of the excited quadruplet at room temperatureThe superexchange interaction (several cm-1 [1415]) in the

[FeII(tmphen)2]3[FeIII(CN)6]2 through the cyanide bridges couples the hs-FeII ions in equatorial and ls-FeIII ndashions in axial positions Further on wewill neglect the essentially anisotropic orbitally dependent terms andretain only the isotropic part of the exchange interaction between the hsndashFeII and ls ndashFeIII ions in a cluster The Hamiltonian of exchangeinteraction for the thk cluster looks as follows

kkkex

k

exJH

212 σσs (2)

where 2s is the spin of the hs-FeII ion the summation in (2) takes

into account the hs-FeII ions appearing in the thk cluster due to thespin transition and those which are in the hs-state in the whole

68

temperature range As in [16-18] we suppose that the mechanismresponsible for the ls-hs transition is the interaction of FeII ions with thespontaneous all-round full symmetric lattice strain Applying theprocedure suggested in [16-18] we obtain the Hamiltonian of electron-deformational interaction

2k kkk

kkst

nm

JBH (3)

where 21AB 21AJ

01021

2

ccc

cA n

(n=123) is the number of FeII ions which undergo the ls-hs transition ina complex m is the number of TBP MIII

2MrsquoII3 complexes whose FeII ions

are involved in the spin conversion =1n k=1m 0 is thevolume that falls at a Fe ion and its nearest surrounding and is the unit

cell volume per one iron respectively In the basis of the states 25T and

11A the 1616 matrix k is diagonal and has 15 eigenvalues equal to 1

and one eigenvalue equal to -1 Finally 2)(1 lshs

2)(2 lshs hs and ls are the constants of interaction of the

FeII ion with the full symmetric strain1A in the hs and ls states

respectively The first term in (3) acts as an additional field applied toeach spin-crossover ion and redefines the effective energy gap 0

between the hs and ls states of the FeII in the cubic crystal field Thesecond term in (3) represents an infinite range interaction between theFeII ions which undergo the spin conversion This interaction arises fromthe coupling to the strain The model of the elastic continuum introducedabove satisfactorily describes only the long-wave acoustic vibrations ofthe lattice Therefore the obtained intermolecular interactioncorresponds to the interaction via the field of long-wave acousticphonons

Due to the proximity of the FeII ions in the clusters short-rangeinteractions between these ions inside the cluster are relevant Thelargest is the effect of the exchange arising from the optic phonons [19]

69

The Hamiltonian describing short-range interactions between FeII ionswithin the trigonal bipyramid can be written as

0

kkk

sr JH (4)

The Hamiltonian (4) takes into account the interaction between the FeII

ions participating in the spin transitions the interaction of these ionswith those FeII ions which are in the hs-state in the whole temperaturerange as well as the interaction between the latter It should bementioned that eq (3) as compared with eq(4) only accounts for FeII

ions participating in spin conversion The Hamiltonian for the wholecrystal can be written as

k

kexstsr HHHHH

2

00 (5)

where k

k

exex HH In the molecular field approximation the full

Hamiltonian H can be written as a sum of one-cluster Hamiltonians

)(32)(

)2

(~

211101

2

1

0

0

kkB

kkkB

k

ex

kkZ

kkkkkkk

gIgHIl

IlsJBJH

HlsH

(6)

where in the basis of the states 25T and 1

1A kI1

is a diagonal 1616 -

matrix with 15 eigenvalues equal to 1 and one vanishing eigenvalue is the order parameter In fact the Hamiltonians kH

~describe clusters

with different numbers of spin-crossover FeII ions and k as beforenumbers the clusters in the crystal For calculation of the temperaturedependence of the order parameter the self-consistent procedure wasapplied The calculations of the magnetic properties were based on theHamiltonian given in Eq(6)

3 Results and discussionThe estimation of the parameters J and B was performed

according the procedure suggested in paper [16-18] For characteristicfor compounds 1 and 2 parameters =1026Aring3 0 =8Aring3

c2 (005divide01)c1211

2 10 cmdynec 1046 141

cm 142 1087 cm the

70

parameters J and B take on the values 20divide80 cm-1 and -95 divide -24 cm-1respectively

Fig1 shows the experimental data for compound 1 together withthe calculated T vs T curves The result of the best fit procedure in

the model above developed is presented by curve 1 The best fitparameters are the part of the figure caption One can see that a quitegood agreement with the experimental data is obtained At temperaturesbelow 100 K the T values show that the FeII ions are mainly in the ls ndashstate However some small admixture of hs ions is present In thetemperature range 150-300 K the T product gradually increases thusindicating the ls - hs transition in the FeII ions

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30 35

04

06

08

10

3

2

1

T

cm

3K

mo

l-1

Temperature K

23

1

T

cm

3K

mo

l-1

Temperature K

Fig1 Temperature dependence of the T product for 1 Circles-experimentaldata [12] The solid lines represent a theoretical fit with =-103 cm-1 x=10and (1) hs-ls =640 cm-1 J =35 cm-1 J0=45 cm-1 =180 cm-1 =10 (2) hs-

ls=620 cm-1 = -136 cm-1 J=0 J0=0=06 (3) hs-ls=630 cm-1 =168 cm-1J=0 J0=0 =06

The parameter J of long -range cooperative electron-deformationalinteraction obtained from the best fit procedure falls inside the limits

71

estimated above Relatively small values of the parameters J and J0 ascompared with the gaps hs-ls= 0-2B and are also in agreement withthe observed gradual temperature dependence of T and noticeable

increase of T at temperatures higher than 150K Finally the estimated

from the best fit procedure percentage of FeII ions (x=10) which are inthe hs-state at any temperature is very close to that obtained from theMoumlssbauer spectra [12] For comparison in the same figure (curves 23)the results of fitting of the T curve in neglect of long- and short-

range interactions are shown for the cases of 0 and 0 It isseen that in this approximation the calculated curves 2 and 3 differsignificantly from the experimental one both at low and hightemperatures besides this the obtained value 60 is too small forhs-FeII-ions

For compound 2 the variation of the observed magneticsusceptibility as a function of temperature is presented in Fig2

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

321

T

cm

3K

mo

l-1

Temperature K

Fig2 Temperature dependence of the T product for 2 Circles experimentaldata [12] Curves 1- 3 were calculated with the following parameter values hs-

ls =690 cm-1 J=30 cm-1 J0=40 cm-1 =100 cm-1 =-103 cm-1 =10 x=9and (1) Jex = 3 cm-1 (2) Jex = 0 (3) Jex = -3 cm-1

72

First the magnetic behavior of complex 2 was analyzed withneglect of intracluster Heisenberg exchange interaction between FeII andFeIII ions The result of the best fit procedure is presented by curve 2 inFig2 The best fit parameters are the part of the figure caption One cansee that the values of the key parameters are close to those for complex1 However the obtained energy gap hs-ls between the ls and hsconfigurations for complex 2 is a bit larger than the corresponding gapfor compound 1 while the parameters of short-range and long-rangeinteractions are smaller Namely this difference in the characteristicparameters leads to lower values of T for compound 2 as compared

with compound 1 at temperatures higher than 150K The effect ofexchange interaction on the magnetic behavior is illustrated in Fig2 bycurves 1 and 3 Since typical values of the exchange parameters incyanide bridged complexes are of several cm-1 we calculated the Tproduct with the set of the best fit parameters and Jex = -3 cm-1 and 3cm-1 One can see that at temperatures higher than 50K the smallexchange interaction has no effect on the magnetic properties ofcomplex 2

Moumlssbauer spectra provide direct information about the populationof the hs and ls states and serve a reliable test for the theoreticalbackground of the SCO phenomenon The total Moumlssbauer spectrum(ie the observable spectrum) was obtained by summing up the spectrayielded by different cluster electronic states in the molecular field withdue account for their equilibrium populations for a given (at a certaintemperature) value of the molecular field In calculations theexperimental values for the parameters of the quadrupole splttings andisomeric shifts were taken from [12] The calculated and experimentalspectra are shown in Fig3

Quite good agreement between the experimental data andtheoretical calculations is obtained It should be underlined that themodel takes into account the main effect inducing the temperaturedependence of the Moumlssbauer spectra and this is the temperaturedependence of the cluster energies in the molecular field Namely thiseffect is responsible for the transformations of the Moumlssbauer spectrawith temperature

73

The proposed model gives a good fit to the observed temperaturedependence of the static magnetic susceptibility and the Moumlssbauerspectra The last clearly illustrates the cooperative nature of SCOtransformations in TBP compounds that leads to a crossing of the ls andhs levels due structural phase transition induced by the ordering of thelocal deformations through the field of the acoustic phonons

Fig3 Moumlssbauer spectra for compound 1 calculated at T=42 220 and 300Kwith the set of the best fit parameters (thick solid lines) Contributions from ls -FeII and hs -FeII ions are shown in dash and dot lines respectively The half-width of the individual lines Г=016 cm-1(42 К) Г=018 cm-1(220К)Г=024cm-1(300К)

74

AcknowledgmentsFinancial support of the STCU (project N5062) is highly

appreciated BT and KD gratefully acknowledge financial support ofthe Binational US-Israel Science Foundation (BSF grant no 2006498)BT thanks the Israel Science Foundation for the financial support (ISFgrant no 16809)

References1 Guumltlich P Goodwin H A Spin Crossover in Transition Metal

Compounds Springer-Verlag 20042 Hauser A Light-Induced Spin Crossover and the High-Spin rarrLow-

Spin Relaxation Springer-Verlag 20043 P Guumltlich J Jung Nuovo Cimento D 1996 18 1074 P Guumltlich A Hauser H Spiering Angew Chem Int Ed Engl

1994 33 20245 J Zarembowitch New J Chem 1992 16 2556 A B Gaspar V Ksenofontov M Serdyuk P Guumltlich Coord

Chem Rev 2005 249 26617 JA Real AB Gaspar MC Munoz P Guumltlich V Ksenofontov H

Spiering TopCurrChem2004 2331678 G Vos RAG De Graaff JGHaasnoot AM van der Kraan De

PVaal JReedijk InorgChem 1984 23 29059 EBreuning MRuben JMLehn FRenz YGarcia VKsenofontov

P Guumltlich E Wegelius KRissanen AngewChemIntEd 2000 392504

10 M Nihei MYi MYokota LHan AMaeda HKushida HOkamoto HOshio AngewChem IntEd 2005 446484

11 D-Y Wu O Sato Y Einaga C-Y Duan Angew Chem Int Ed2009 48 1475 ndash1478 2009

12 MShatruk ADragulescu-Andrasi KEChambers SAStoianELBominaar CAchim KRDunbar J Am Chem20071296104

13 AAbragam BBleaney Electron Paramagnetic Resonance ofTransition Ions Clarendon Press Oxford 1970

14 A V Palii SM Ostrovsky S I Klokishner B S Tsukerblat C PBerlinguette K R Dunbar J R Galaacuten-Mascaroacutes JAmChemSoc2004 126 16860

15 HWeihe H Gudel H Comments Inorg Chem 2000 22 75

75

16 SI Klokishner F Varret J Linares ChemPhys 2000 255 31717 SI Klokishner JLinares PhysChemC 2007 111 1064418 SI Klokishner J Linares F Varret Journal of Physics

Condensed Matter 2001 13 59519 JM Baker Rep Prog Phys 1971 341 109

53

NON-CARBON PREPARATION OF SILICON BYMECHANICALLY ACTIVATED THERMAL SYNTHESIS

TF Grigorieva1 TL Talako2 AI Letsko2 V Šepelaacutek3 VG Scholz4MR Sharafutdinov1 IA Vorsina1 AP Barinova1 PA Vitiaz2

NZ Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry Kutateladzestr 18 Novosibirsk 630128 Russia grigsolidnscru

2 Powder Metallurgy Institute Platonov str 41 Minsk 220005 Belarus3 Inst of Nanotechnology KIT Eggenstein-Leopoldshafen 76344 Germany

4 Inst of Chemistry Humboldt Univ Berlin 12489 Germany

IntroductionIn industrial processes the production of Si is based on the

reduction of silicon dioxide by carbon at a temperature of about 1800 C[1] However the coke applied to the reduction can be hardly refinedfrom the most dangerous for silicon impurities like boron phosphorusarsenic and antimony That is why development of non-carbon routes forsilicon production is a topical problem of a silicon industry Reductionof oxides with magnesium and aluminum by the method of self-propagating high-temperature synthesis (SHS) has been used in industryfor a long time [2] As such reactions are highly exothermal they can bealso organized with the use of mechanochemistry for instance reductionof the copper oxide by aluminum Mechanochemical reduction of ironoxide by aluminum aimed at obtaining precursors with differentcompositions for intermetallideoxide SHS composites has been alsoconsidered [3ndash6]

SiO2 + Al reaction is not high exothermic enough to organize theSHS without preliminary heating [7] Mansurov et al [8] reportedcreation of ceramic composites in several stages first the silicon oxidewas mechanochemically treated in an organic compound environmentthen the resultant material was annealed (carbonized) at ~ 850 C andfinally the mixture of the carbonized silicon oxide with aluminum wassubjected to SHS However as-formed product included silicon carbide

The objective of activities described in this paper is to study thepossibility of using mechanochemical treatment for obtainingsiliconaluminum oxide composites by the SHS and thermal synthesis atconsiderably lower temperatures with the following removal of alumina

54

Sample preparation and examination proceduresThe PA-4 aluminum powder and the silicon oxide with a particle

size of ~ 3 nm were used in our experimentsA stoichiometric mixture of the silicon oxide with aluminum was

processed in a high energy planetary ball mill (drum volume 250 cm3ball diameter 5 mm mass of the balls 200 g mass of the sample 10 gand velocity of rotation of the drums around a common axis ~1000 rpm)

The IR spectra were recorded by a Specord IR 75 spectrometerthe samples for this study were pressed with annealed potassiumbromide

The 27Al (I = 52) NMR spectra were recorded on a BrukerAdvance 400 spectrometer corresponding to a 27Al resonance frequencyof 782 MHz MAS experiments were realized with a high speed probeusing 25 mm zirconia rotor The spinning speed was 20 KHz Themagnetic field strength (in frequency unit) was set to 104262 MHz Theexcitation pulse duration was chosen equal to 1 s The recycling delaybetween each acquisition was fixed to 1 s To see weak signals in the Al-O region in mechanically activated samples we applied accumulationsnumbers up to 56000 (ie measurement time of 15 hours)

The dynamics of the SHS process was studied with the use ofdiffraction of synchrotron radiation and an OD-3 single-coordinatedetector The samples for SHS were prepared in the form of pellets 20mm in diameter and 1ndash2 mm thick by pressing at a pressure of 200 atmThe resultant samples were placed onto a ceramic plate so that they werein the center of the goniometer The process was initiated by a nichromespiral The OD-3 detector was triggered to operate in the ldquofast filmingrdquomode simultaneously with the beginning of pellet burning The time ofone ldquoframerdquo was 05 sec and the number of ldquoframesrdquo was 128 Theradiation wavelength was 1527 Aring

For investigation of mechanically activated thermal synthesis thesamples were heated up to 650 C in the reaction chamber XRK 900 inair with a heating rate 10 min The OD-3 detector was also used forstudying the process dynamics though time of one ldquoframerdquo was 1 min

55

Results and discussionFirst we made an attempt of direct mechanochemical reduction of

the silicon oxide by aluminum The study of this process showed that thechemical reaction of SiO2 reduction does not occur within 6 min ofmechanical activation The IR spectrum of the initial mixture containsclear absorption bands with the maximums at 1005 and 480 cmminus1

(valence and deformation oscillations of the SindashO bond of the SiO4

tetrahedra of the siliconndashoxygen skeleton) and two maximums in therange of 900ndash670 cmminus1 due to oscillations of the SindashOndashSi bridges Thephenomena observed in the course of mechanical activation were agradual decrease in intensityand broadening of the characteristic bands of the SindashO bond (Fig 1)

An electron-microscopy study of the SiO2Al composite obtainedafter 1 min of mechanical activation in characteristic radiation revealed a

Fig 2 Microphotograph of themechanocomposite after 1 minactivation in Si characteristic

radiation

Fig 1 IR spectra of the SiO2 + Al mixturebefore mechanical activation (1) and aftermechanical activation during 05 (2) 1 (3)

and 6 (4) min

56

very small grain size and a very uniform distribution of the componentsin the mechanocomposite (Fig 2)

Based on the data of the differential thermal analysis (DTA) evenshort-time activation of this mixture appreciably affects its thermalcharacteristics For the initial mixture the real chemical interactionoccurs at a temperature T gt 1000 C (Tmax = 10836 C) (Fig 3 a) iesubstantially higher than the melting point of aluminum whereas thesituation is different for the mixture subjected to mechanical activationduring 20 sec Two clearly expressed exothermal peaks appear the firstpeak at 6217ndash6486 C (Tmax = 6327 C) and the second peak at 9921ndash10759 C (Tmax = 10292 C) (Fig 3 b) For the mixture activated for 40sec the first peak is at 6045ndash6366 C (Tmax = 612 C) and the secondpeak is extremely broad and smeared in the range of 8161ndash11117 C(Tmax = 10381 C)

These observations can be explained by the fact that a tightcontact is created between some part of the ultrafine non-plastic siliconoxide and plastic aluminum already within 20 sec of mechanicalactivation the silicon oxide is ldquowettedrdquo by aluminum as a result somepart of the silicon oxide starts to interact with aluminum at a temperatureT = 6217C which is lower than the melting point of the latter Asmechanical activation is continued aluminum becomes also dispersed tonanoparticles greater amounts of the components of the mixture areinvolved into the contact and the temperature of the interactionbeginning decreases after 1 minute of activation the interaction beginsat T = 5399 C and ends at T = 6303 C (Fig 3 c)

The curve for this sample obtained by the method of differentialscanning calorimetry (DSC) has only one exothermal peak ie theentire process proceeds at a temperature lower than the melting point ofaluminum Longer activation further decreases the temperature ofreaction beginning (Table 1) but there are no any further significantchanges in the system parameters determined by DSC

The duration of mechanochemical treatment was limited to 6 minfor the following reasons- the IR spectra are so smeared already after 4 min that do not provide

any new information (see Fig 1)- the DTA study does not reveal any significant changes in the thermal

characteristics after 1 min of mechanical activation (see Table 1)

57

- mechanochemical actions should be always minimized to ensure theminimum possible contamination of the products by milling

Fig 3 Results of differential scanning calorimetry (DSC) and thermogravimetry(TG) studies of the SiO2 + Al mixture before (a) and after mechanical activation

during 20 (b) and 60 sec (c)

58

Table 1 Parameters of Exothermal Peaks on DTA Curves of SiO2 + AlSamples after Mechanical Activation

Temperature CDuration of activation

beginning of thereaction

end of the reaction

1 min 5930 6303

2 min 5871 6243

4 min 5867 6291

6 min 5870 6258

27Al MAS NMR spectra of the nanostructured SiO2Almechanocomposites are dominated by a broad resonance associated withthe presence of nanostructured Al matrix (Fig 4) The interestingobservation is that additional resonance lines appear in the spectra ofmechanoactivated samples corresponding to AlO4 AlO5 and AlO6

polyhedra Their content is slightly increasing with increasing millingtime however the relative intensity of AlOx polyhedra compared withthe Al matrix spectral intensity is even after the longest milling periodvery low It can be assumed that these nonequilibrium localcoordinations of aluminium atoms are located on the SiO2-Al interfaces[9] The intensity of the resonance lines belonging to various polyhedrarelative to the total spectral intensity allows us to calculate the volumefraction of interface regions in the nanocomposites Furthermoreassuming a spherical shape of SiO2 nanoparticles the thicknees of theinterface regions was calculated their known volume fraction

Thus the study of mechanically activated SiO2+Al mixturesshows that silicon reduction does not occur during mechanical activationstep except formation of some AlOx species at the interfaces but anexothermal reaction in activated mixtures can proceed at substantiallylower temperatures

In the subsequent step the nanostructured SiO2Almechanocomposites were used as precursors for the preparation ofSiAl2O3 composites via self-propagating high-temperature synthesisOur experience shows that combustion initiation requires sample

59

preheating approximately to 200 C (as compared with 650-860 Сreported in [7])

Fig 4 27 Al MAS NMR spectra of non-activated sample (a) the samplemechanoactivated for 1 (b) and 6 (c) minutes

60

The overall pattern of phase transformations is illustrated in Fig 5a To analyze them however it is more convenient to use the projectiononto the diffraction angle (β)ndashtime plane (Fig 5 b) As the silicon oxideused in these experiments is amorphous to x-ray radiation onlyaluminum peaks are observed

Fig 5 Dynamics of phase transformations in the Al + SiO2 mechanocompositein the SHS mode (a) three-dimensional image (b) projection onto thediffraction anglendashtime plane

61

It is clearly seen thataluminum becomes heatedas the combustion waveapproaches the peaks areshifted toward smallerangles ie greaterdistances between theplanes After that theintensity of these peaksdrastically decreaseswhich is apparently due tomelting No crystallinephases are observed in thetwo frames (~ 1 sec) Inour opinion corundum(Al2O3) peaks appearslightly earlier than siliconpeaks A possible reason isthe lower melting point ofsilicon (1410 C) as compared with corundum (2050 C) An electron-microscopic study of the SHS product of the SiO2 + Al system subjectedto mechanical activation during 1 min in characteristic radiation (Fig 6)shows a fairly uniform distribution and small size of all elements in thesystem including silicon being formed

Previously it was shown that chemical interaction between SiO2

and Al in the mechanocomposites formed during the mechanicalactivation starts at essentially (~ 500 C) lower temperatures as comparedwith the non-activated mixtures

In the final step we used as-formed mechanocomposites asprecursors for the preparation of SiAl2O3 composites via thermalsynthesis The samples after mechanical activation for 6 min wereplaced into cuvette and gently prepressed to get the plane surface Thenthe cuvette with the sample was sited in the furnace The thermocouplewas directly close to the registration area Recording of diffractogramswas started at temperature 230 С Dynamics of phase transformation inAl SiO2 composites during heating from 590 up to 660 C is presentedin Fig7

Fig 6 Microphotograph of the SHS productin Si characteristic radiation

62

As can be seen from the Fig 7 the reaction products (silicon andalumina) start to form at about 590 С It is interesting that corundum isformed during the SHS and thermal synthesis after low activation time

Fig 7 Dynamics of phase transformation in Al SiO2 composites duringheating from 590 up to 660 C

Fig 8 XRD-pattern of the thermal synthesis product from the mechanocompositesactivated for 6 min and heated up to 660 C

63

while -Al2O3 is identified in the product of thermal synthesis afterlonger MA durations (Fig 8)

ConclusionsThus though the silicon oxide is not reduced by aluminum

directly by mechanical activation the use of the mechanocomposite as aprecursor for both SHS and thermal synthesis allows a fine-grainsiliconaluminum oxide composite to be obtained In both caseschemical interaction starts at essentially lower temperatures as comparedwith the non-activated mixtures

AcknowledgementsThis work was supported by the joint project No 5 ldquoNon-carbon

preparation of Si by mechanically activated thermal synthesisrdquo of NASBand SB RAS

References1 Denisov VM Istomin SA Podkopaev OI Serebrjakova LI

Pastuchov EA Beletsky VV Silicon and its alloys EkaterinburgPublishing house of Ural Branch of the Russian Academy ofSciences 2005 467 p (in Russian)

2 AG Merzhanov Forty Years of SHS Happy Life of a ScientificDiscovery (in Russian) Chernogolovka (2007)

3 TF Grigoryeva SA Petrova IA Vorsina et alldquoMechanochemical reduction of a copper oxiderdquo in TheOptimization of the Composition Structure and Properties ofMetals Oxides Composites Nano and Amorphous Materials Proc6th IsraelindashRussian Bi-National Workshop Jerusalem (2007) pp197ndash204

4 TF Grigoryeva TL Talako AA Novakova et al ldquoMA and MASHS production of nanocomposites metaloxides andintermetallicsoxidesrdquo ibid pp 139ndash148

5 NZ Lyakhov PA Vityaz TF Grigorieva et alldquoMechanochemically synthesized SHS precursors for obtainingintermetallideoxide nanocompositesrdquo Dokl Akad Nauk 406 No6 776ndash778 (2005)

64

6 5 T Talaka T Grigorieva P Vitiaz et al ldquoStructure peculiaritiesof nanocomposite powder Fe40AlAl2O3 produced by MA SHSrdquoMater Sci Forum 534ndash536 1421ndash1424 (2007)

7 Maltsev VM Gafiyatulina GP Tavrov AV Spreading of thecombustion wave in SiO2-Al systems Proc SPIE Vol 3172(111997) p 724-727

8 ZA Mansurov RG Abdulkarimova NN Mofa et al ldquoSHS ofcomposite ceramics from mechanochemically treated and thermallycarbonized SiO2 powdersrdquo Int J SHS 16 No 4 213ndash217 (2007)

9 V Sreeja TS Smitha Deepak N Ajithkumar TG and PA JoySize dependent coordination behavior and cation distribution inMgAl2O4 nanoparticles from 27 Al solid state NMR studies J PhysChem C 112 14737-14744 (2008)

37

THE PREPARATION OF MECHANICOMPOSITESTUNGSTEN-METAL AND SINTERING MATERIALS

T Grigoreva1 L Dyachkova2 A Barinova1 S Tsibulya3 N Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS 18Kutateladze str 630004 Novosibirsk Russia grigsolidnscru

2 Institute of Powder Metallurgy NAS B Minsk Belarus3 Boreskov Institute of Catalysis SB RAS Novosibirsk Russia

Tungsten-based materials are used for manufacture of electro-technical items spot welding electrodes spraying cathodes etc

The preparation of the high-melting materials is powerconsumptive as two-stage high-temperature sintering is used tungstenpre-sintering temperature is 1150 ndash 1300 C final tungsten sinteringtemperature is 2900 - 3000 C [1]

Metal additives with a lower melting temperature are introducedinto the high-melting material for sintering temperature reduction andsince the tungsten powder has a bad moldability level more plasticmetals such as copper nickel iron are introduced for the moldabilityimprovement

Tungsten ndash copper mixture has been studied the best so farThe mixture W-Cu sintering process research has shown [2] that

the product density depends on the initial powders dispersion degree andthe mixture composition So at the tungsten particles size 10-15 m themaximum densification is observed at the copper weight ration 50 The blend density sharply decreases with the copper content decrease(less than 35 ndash 40 wt) At the same time mixtures with the coppercontent not higher than 10 are needed Special methods have to beused for the preparation of the tungsten alloys

The active densification (from 44 till 12 ) is known to take placeat 1100 - 1200 C at sintering of mixtures W-20 vol Cu with tungstenparticles size lower than 1 m [3] Even higher densification speed isobserved in a blend attained with copper tungsten reduction whencomponents mixing practically achieves a molecular level [4] ie thesecond element concentration reduction is possible at tungsten particlessize decrease and homogeneous distribution of the both componentsThe original blends mechanical activation process [5ndash7] is very

38

perspective in this trend since grinding and formation of larger contactsurface between the original components take place during mechanicalactivation This process is especially effective at mechanical activationof solid and liquid metals and plastic ndash non-plastic metals pair Thecomposite nucleus (non-plastic component) ndash cover (plastic metal) canbe created in this case The possibility of chemical interaction onbetween tungsten and plastic metal the contact surface duringmechanical activation should be considered here

The work aim is to study structure and morphology of thecomposites formed at mechanochemical activation of the tungsten witha small content (till 10 ) of plastic metals both interacting (nickel iron)with it and not interacting (copper) with it The influence of the structureand morphology of the mechanocomposites on the processes of formingand sintering was studied

Powders of tungsten nickel iron copper were used forpreparation of mechanocomposites Mechanical activation of themixtures was carried out in a high energy planetary ball mill with watercooling in argon atmosphere (drum volume ndash 250 cm3 balls diameter ndash5 mm the load ndash 200 g the sample - 10 g the velocity of rotation of thedrums around a common axis 1000 rpm)

X-ray analysis was carried out with diffractometer D8 AdvanceBruker (Germany) at the CuK radiation Research of the structure andmorphology of the mechanocomposites was carried out with thescanning electronic microscope (SEM) ldquoMira LMHrdquo with the add-ondevice for micro-x-ray analysis The electronic probe comprised 5 2 nmthe actuation area comprised 100 nm The research was carried out inmodes of registration of absorbed (AE) and backscattered (BSE)electrons and also of characteristic radiation of tungsten copper nickeland iron The sintered materials research is carried out with themetallographic microscope MEF-3 (Austria) at zoom times200 and times950

The compressibility was determined via density in compliancewith the ISO 3927-1985 of cylindrical samples with diameter 10 mmheight 12 mm pressed in a steel die-mold at pressure 200 400 600 and800 MPa The pressed samples were sintered in vacuum at temperatureof 1100 ndash 1450 C

Compression strength of mechanically activated blends wasdetermined via the samples of diameter 10 mm height 12 mm

39

transverse strength ndash via prismatic samples with height 5 mm width 10mm length 55 mm The tests were preformed on the testing machineldquoInstronrdquo with the loading speed 2 mmmin

Sintered samples microstructure was studied on metallographicsections etched with solution (10 g K3Fe(CN)6 10 g KOH 100 mlH2O) via metallographic microscope MEF-3 of the company ldquoReihertrdquo(Austria)

Mechanical activation was carried out in two stages for attainingmechanical composites tungsten ndash metal (Cu Ni Fe) The first stagesaw grinding only tungsten for 4 min At the second stage 7 ndash 10 copper (nickel iron) was added and joint mechanical activation wascarried out for 1 ndash 2 min

In compliance with the x-ray data the initial tungsten sample is awell-crystallised powder (Fig 1a) The intensity of the diffraction peaksshows the texture (of the preferred orientation) presence in trend 110The X-ray pattern of the tungsten samples activated during 4 min (Fig1b) has widened peaks The X- ray analysis shows that widening ismostly caused because of micro-defects in the tungsten structure (at thelarge particles sizes retaining) It should be also noted that thedistribution intensity of the peaks shows the texture absence (the equalparticles distribution in powder from the point of view of theircrystallographic orientation)

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

Ia

u

2 Theta degree

110

200

211

220

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

Ia

u

2 Theta degree

a bFig 1 X-Ray patterns for initial W (a) and activated for 4 min (b)

40

During the mechanical activation in a high energy planetary ballmills plastic metals tend to stick to balls and the drums walls even atshort-time activation because of that they were introduced to the blendsinto the already activated for 4 minutes tungsten and the mixture wastreated for 2 minutes more

The different X-Ray patterns were received for the samples withCu Ni Fe additives (Fig 2) The second metal phase is seen to bepresent in a well-crystallised form besides the phase W in all cases thecopper picks relative intensity is however considerably higher than thenickel picks intensity that in turn exceeds the iron reflection intensityFormation of intermetallic compounds in the X-ray-amorphous state oncontact surface WNi WFe can be supposed to be possible forchemically interacting metal pairs (tungsten ndash nickel tungsten ndash iron)X-Ray research data are indirect confirmation of this supposition Thesedata have shown that mechanochemical efforts donrsquot allow to receivehomogeneous distribution of copper in the tungsten matrixMechanocomposites W + 10 Cu is arranged in compliance with theldquosandwichrdquo principle where copper phase of micrometric size is locatedin the tungsten die (Fig 3)

The second metal phase is seen to be present in a well-crystallisedform besides the phase W in all cases the copper picks relative intensityis however considerably higher than the nickel picks intensity that inturn exceeds the iron reflection intensity Formation of intermetalliccompounds in the X-ray-amorphous state on contact surface WNiWFe can be supposed to be possible for chemically interacting metalpairs (tungsten ndash nickel tungsten ndash iron) X-Ray research data areindirect confirmation of this supposition These data have shown thatmechanochemical efforts donrsquot allow to receive homogeneousdistribution of copper in the tungsten matrix Mechanocomposites W +10 Cu is arranged in compliance with the ldquosandwichrdquo principle wherecopper phase of micrometric size is located in the tungsten die (Fig 3)Electron microscopy and X-Ray research of mechanocomposites forinteracting metals (W + 10 Ni) has shown homogenous nickeldistribution

41

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Ia

u

2 Theta degree

Cu

а

40 50 60 70 80 90

0

1000

2000

3000

4000

Ia

u

2 Theta degree

Ni

b

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Iau

2 Theta degree

Fe

c

Fig 2 X-Ray patterns for mechanocomposites W (4 min) + additives Cu(a) Ni (b) Fe (c) (2 min)

The received result allows to suggest that metals distributionhomogeneity depends on the thermodynamical parameters of theirmixture (Нmix(W-Ni) = - 2 kJmol Нmix(W-Cu) = + 10 kJmol [8])and on a possibility of the chemical interaction between them The thinlayers of intermetallic compounds form on the continuously renewingcontact surface in the systems W-Ni and W-Fe for this time period (1-2min) and because of distance these thin layers do not manage to form acrystalline phase that could be fixed in X-Ray way

42

а bFig 3 Micrographs of the mechanocomposites W-Cu (a) W-Ni (b) in

characteristic radiation Cu and Ni

The research of compressibility of various mechanocompositeshas shown that non-interaction metals (W-Cu) couldnrsquot compressed andthe compressibility of the interaction metals (W-Ni W-Fe) depends ofthe contents of additives Research of compressibility of mechanicallyactivated powders of various composition has shown that tungsten ndash10 iron mixture powder has the best compressibility level andtungsten ndash 7 nickel mixture powder has the least compressibility level(Fig 4)

But it should be noted that mechanically activated powderscompressibility level is not high moreover some mechanocompositesdo not have compressibility at specific pressure 200 ndash 300 MPa and thesamples layering is observed at pressure higher than 600 MPa Therelative density of the pressed samples is 50 ndash 78 It indicates at thenecessity of the additional lubricants introduction into the mechanicallyactivated powders for their compressibility increase

43

Fig 4 Tungsten-based mechanocomposites compressibility curve

For the powders compressibility improvement the lubricants areintroduced directly into initial mixture or plated to the press-mouldsurface for decrease of friction between the powder and the press-mouldwall and also between the powder particles The lubricant removaltemperature depends on the lubricant melting or dissociationtemperature The melting and boiling temperature or the lubricantsdissociation temperature generally used in powder metallurgy are givenin table 1 [9]

Stearates especially zink stearates have the leading place Therest lubricants have not got such a wide use since residual remains aftertheir removal [10]

Nowadays nylon-binding-based lubricant has been developedabroad This nylon binder is introduced during the charge mixingprocess and needs warm pressing [11-14] Such a lubricant allowsattaining high (θ is no less than 95 ) density of iron-based materials

The lubricant addition as a rule retains ~1 wt as higher contentleads to the pressing growth if the lubricant is present in the sinteringprocess till the sintering temperature

The lubricant burning-out process is carried out in the protective-reducing atmosphere in separate furnaces or in a sintering furnace (in thearea separated from the sintering area) The lubricant burning-outtemperature is as a rule not high and comprises 600 ndash 800 C

44

Table 1 Temperature of melting and dissociation of solid lubricants

Lubricant Lubricant formulaMeltingpoint С

Boiling ordissociation

point СZink stearate Zn(C18H35O2)2 140 335Calcium stearate Ca(C18H35O2)2 180 350Aluminium stearate Al(C18H35O2)2 120 360Magnesium stearate Mg(C18H35O2)2 132 360Plumbum stearate Pb(C18H35O2)2 116 360Lithium stearate LiC18H35O2 221 320Stearinic acid CH3(CH2)16CООH 694 360Oleinic acid С8Н17СНСН-

(СН2)7СООН13 286

Benzol acid С6Н5СООН 122 249Hexoic acid СН3(СН2)4СООNН2 -4 205Paraffin From С22Н46 till

С27Н56

40-60 320-390

Molybdenum disulfide MoS2 1185 -Tungsten disulfide WS2 1250 -Manganous sulphide MnS 1655 -Graphite С (crystalline) 3500 -Molybdenum trioxide MoO3 795 -

During one-component materials heating till 100 ndash 150 C thechange of the contact character between the particles connected withwater evaporation and elastic stress relief tale place As a result somecontact areas rupture and as a consequence general inter-particlecontact surface decrease are possible

The elastic stress relief is ended the further gases are removedand burning-out of the lubricants and binders introduced to the powdertake place during heating from 150 C till the temperature comprising 40ndash 50 of the metal melting temperature The oxide films reduction andnon-metal contact replacement with a metal one take place at highertemperatures although visible pressings density change does not takeplace

45

This work saw lubricants introduction during mechanicalcomposite formation zink stearate stearinic acid and lauric acid wereused The lubricants were introduced in amount of 0 1 0 2 0 3 0 5wt During mechanical activation metal ndash organic acid the latter ismelted (the melting temperature is lower than 70 C) and thus it wets themetal surface and flows with the formation of a larger contact surface Incase of good wettability and sufficient amount of the low-meltingconstituent all the solid-phase surface becomes contact ie mixturenucleus (metal) ndash cover (organic substance) is formed [15] Thecompressibility level has to be naturally higher in this case andmechanochemical approach allows a substantial reduction of plasticizingagentsrsquo concentration

Research of compressibility of powders with lubricants has shownthat Zink stearate has the least influence in comparison to otherlubricants used (Fig 5)

Fig 5 The compressibility curves of the mechanocomposites W-Fe with thelubricant 1 ndash zink stearate 2 ndash lauric acid

The lubricant content increase leads to the mechanically activatedpowders compressibility improvement (Fig 6) but at the lubricantcontent more than 0 3 the samples destruction takes place at sinteringbecause of intensive gas release Plasticizing agents introduction hasallowed mechanical composites formation also for non-interactingmetals (tungsten ndash copper) (Fig 6 7)

46

Fig 6 The compressibility curve of the mechanically activated blend W-Cuwith stearinic acid 1 ndash 0 1 2 ndash 0 3 3 ndash 0 5

Fig 7 The compressibility curves of the mechanically activated blend W-Cuwith lauric acid 1 ndash 03 2 ndash 05

Lauric and stearinic acids additives allow the pressings densityincrease by 25 ndash 40 (Fig 5 8)

Research of density of sintered samples of mechanocomposite hasshown that the density of the samples from mixtures tungsten ndash ironpressed at 400 and 600 MPa does not practically change after sinteringat 1250 C (Fig 9 line 2 5) and at 1450 C the samples density decreases(Fig 9 line 3 6) Mixtures tungsten ndash nickel are subject to a substantial

8

9

10

11

12

200 400 600

De

nsi

ty g

сm

3

Pressure МPа

1

2

11

115

12

125

13

200 300 400 500 600

10Fe+W

10Ni+W

De

nsi

tyg

cm

3

Compacting pressure MPa

47

shrinkage (Fig 10) and density of the samples of W-Ni pressed at 400MPa is 146 gcm3 after sintering at 1250 C and 147 gcm3 at 1350 CSintering temperature increase till 1450 C leads to samples shrinkinglevel reduction and density does not exceed 117 gcm3

Fig 8 The compressibility curves of blends W + 10 Fe and W-10 Ni withaddition of 1 of stearinic acid

Fig 9 Relation of density of mechanically activated blends W + 10 1 ndash afterpressing at 400 MPa 2 ndash pressing at 400 MPa sintering at 1250 ordmC 3 ndashpressing at 400 MPa sintering ndash at 1450 ordmC 4 ndash after pressing at 600 MPa 5 ndashpressing at 600 MPa sintering at 1250 ordmC 6 ndash pressing at 600 MPa sintering at1450 ordmC

10

11

12

13

14

200 400 600

Pressure МPа

Density

gс

m3

1

2

3

0

2

4

6

8

10

W+Fe

De

nsityg

cm

3

12 3

4 5 6

48

0

3

6

9

12

15

400 МPа 600 МPа

De

nsity g

сm

3

Fig 10 Relation of density of mechanically activated blend W + 10 Ni 1 ndashafter pressing 2 ndash pressing sintering at 1250 C 3 ndash pressing sintering at 1350C 4 ndash pressing sintering at 1450 C

Moulding pressure increase till 600 MPa practically does not

influence the sintered samples density Density reduction of the samples

sintered at 1450 C is apparently explained with dissociation of oxides

and other compounds of tungsten and nickel

Sintering at 1450 ordmC of blends W-Ni leads to meltback and

samples form loss thus sintering should be carried out at temperature

not higher than 1350 ordmC

Tungsten-based mechanocomposite strength research has shown

that strength has a direct relation to their density (Fig 11) The blend

tungsten ndash iron (870 MPa) has the minimal strength

The microstructure analysis has shown that in case of sintering at

temperature 1250 C tungsten ndash nickel have a very fine dispersed

structure (Fig 12) Coagulation of nickel insertions located at the base

grains boundaries in tungsten ndash nickel grains growth take place with

sintering temperature increase

49

0

100

200

300

400

500

600

700

800

900

1000

1100

1 2

Ela

stic

lim

it of

com

pre

ssio

n

МP

а

I - pressure 200 МPа

II - pressure 400 МPа

III - pressure 600 МPа

1 - sintering temperature 1250оС 2 - sintering temperature 1350

оС

I

II

III

Fig 11 Influence of attaining modes of samples from mechanically activatedblend tungsten + 10 nickel on their strength

Substantial grain growth large porosity formation nickel phase

particles growth take place in blends sintered at 1450 C eutectic that is

more visible in the blend tungsten ndash nickel is formed at tungsten grains

boundaries

Conclusions

The conducted research has shown that homogenous copper

distribution is failed to be carried out in tungsten with short-term

mechanical activation method for interacting metals of W-Cu system

These mechanically activated samples can be not compacted (moulded)

50

a b

c dFig 12 Microstructure of mechanically activated blends W-Ni sintered at 1250C (a b) and 1350 C (c d) a c ndash times200 b d ndash times950

Homogenous distribution of nickel and iron in tungsten is ensuredwith short-term mechanical activation in systems from interactingmetals The attained samples are formable mechanically activatedpowders compressibility has however been found to be not high therelative density of the pressed samples is 50 ndash 78 and that points atnecessity of additional lubricants introduction into powders for theircompressibility improvement Lubricants introduction allowed ensuringmoldability of immiscible system tungsten ndash copper and densification ofpressings by 25 ndash 40 - for interacting metals

Density of samples from blends tungsten ndash iron does notpractically change after sintering at 1250ordmC and is decreased at 1450 ordmCBlends tungsten ndash nickel are subject to a substantial shrinkage during

51

sintering Sintering temperature increase till 1450 ordmC also leads to theshrinkage level decrease Strength of sintered blends from mechanicallyactivated tungsten-based powders depends on density and kind of theadditive Grain size dispersivity and type of additive location in theblend structure from mechanically activated powders depend on thesintering temperature

AcknowledgementsThe work was carried out within the framework of Fundamental

Research Programme of Russian Academy of Sciences ldquoElaboration ofchemical substances attaining methods and new materials creationrdquoproject No 1821 ldquoElaboration of tungsten mechanical composites-basedhigh-density alloys creation basicsrdquo

References1 IM Fedorchenko IN Francevich ID Radomyselskiy at al

Powder Metallurgy Materials technologies properties andapplications Kiev Naukova dumka ndash 1985 ndash 624 P

2 VN Eremenko JV Najdich IA Lavrinenko Sintering in thepresence of liquid metal phase Kiev Naukova dumka ndash 1968 ndash 122P

3 VV Panichkina MM Sirotuk VV Skorohod Powder Metallurgyndash 1982 - 6 ndash P27-31

4 VV Skorohod YuM Solonin NI Filippov at al PowderMetallurgy ndash 1983 - 9 ndash P9-13

5 Kim JС Moon IН Nanostruct Mater 1998 Vol 10 No 2 P283-290

6 Moon IH Kim EP Petrow G Powder Metallurgy 1998 Vol41 No 1 P 51-57

7 Kim JC Ryu SS Kim YD Moon IH Scripta Mater 1998 Vol39 No 6 P 669-676

8 FR de Boer R Boom WCM Mattens AR Miedema andAK Niessen Cohesion in metals (Cohesion and structurevol 1) (Elsevier Amsterdam 1988) pp 758

9 Hausner H Handbook of Powder Metallurgy Chemical PublishingCo New York 1973

10 Moyer KH Intern J Powder Met 1971 - 7 Р 33

52

11 US patent В 22 F 100 5368630А Powder Metallic Blend with abinder for densification at the set temperature Journal Inventions ofcountries worldwide 1996 1

12 US patent В 22 F 100 5429792 Metal powder content containing a binder for pressing at elevated temperatures JournalInventions of countries worldwide 1996 7

13 US patent В22F 100 (11) 52980555 (40) 940329 laquoIron-basedpowder mixtures with a binding lubricantraquo 1995

14 US patent В 22 F 100 95372138 (5484469А) laquoMetal powder content and a method of a sintered part manufacture from itraquo 1995

15 TF Grigoryeva AP Barinova NZ Lyahov Mechanochemicalsynthesis of metal systems Novosibirsk Parallel ndash 2008 ndash 311 P

34

THE DETERMINATION OF THE KINETIC FUNCTIONSTRUCTURE FOR THE HIGH-TEMPERATURE SYNTHESIS IN

THE MECHANICALLY ACTIVATED MIXTURE 3Ni-Al

VYu Filimonov1 MA Korchagin2 EV Smirnov1NZ Lyakhov2

1Altai State Technical University Barnaul2Institute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirskvyfilimonovramblerru

The peculiarities of heating-up and phase formation in themechanically activated powder mixture 3Ni + Al reacting in the thermalexplosion mode have been experimentally investigated The self-heatingin the mixtures was studied using a specially designed SHS-reactorusing a technique presented in [1] Tungsten-rhenium thermocouples of100 microm diameter were used to control the temperature and to recordthermograms Preliminary mechanical activation was carried out using aplanetary ball mill of AGO-2 type in an atmosphere of argon under theenergy of 40g (centrifugal acceleration of balls 400 ms2) with varyingtime of the activation process The reactant mixtures were preparedusing the aluminum powder PAndash4 particle size 5 divide 60 microm and thecarbonyl nickel powder PNK-1L5 particle size 1 divide 10 microm

The primary goal of this work was to determine the activationenergy and the structure of the kinetic function during the heat evolutionin the system as a result of the phase formation At the adiabatic stage ofheating a system of equations of the temperature increase and thedynamics of the degree of transformation was considered [2]

0 expdT E

k fdt RT

(1)

f

RT

Ek

dt

d

exp1

(2)

The initial conditions are as follows 00 t 0TT where

T temperature of the reacting mixture degree of transformation

t time 0k 1k exponential factors E activation energy f -

35

kinetic function The search for )(f was performed in the known class

of functions [3]

exp

1nm

f

(3)

At the first step of analysis of the experimental thermograms theeffective activation energy of the phase formation was determined from

the curvature of the experimental plot ln 1dT dt f T Based on the

results of 6 measurements and using the slope of the fitting curvepassing through the point of the minimum curvature the effectiveactivation energy was determined which turned out to be anomalouslylow and equal to E = 95plusmn2 kJmol It was found that the experimental

results are best fitted with a function 1n

f where

09 015n [4] Fig1 shows the results of integration of (11) with the

determined parameters

Fig1 Results of integration of (11) -1 experimental thermogram -2

Since the interaction of the reactants is described by the law ofhomogeneous kinetics we suggest that during thermal explosion in themechanically activated mixture of the composition under study thesynthesis occurs through homogeneous regrouping of atoms of the initialreactants without formation of dense diffusional layers hindering thereaction The latter is possible due to high concentrations of defects andinternal stresses formed as a result of intensive plastic deformation of theinitial reactants during mechanical activation

36

References1 Filimonov VY Evstigneev VV Afanasev AV and Loginova MV

Thermal Explosion Ti + 3Al Mixture Mechanism of PhaseFormation International Journal of Self-Propagating High ndashTemperature Synthesis-2008- vol 17-2рр 101-105

2 Aldushin AP Martemyanova T M Merzhanov A G Propagationof the front of an exothermic reaction in condensed mixtures withthe interaction of the components through a layer of high-meltingproduct Composition Combust Explos Shock Waves19728(2)159

3 M I Shilyaev V Е Borzykh A R Dorokhov and V EOvcharenko Determination of thermokinetic parameters from theinverse problem of an electrothermal explosion Combust ExplosShock Waves 1992 28(3)258

4 MA Korchagin VYu Filimonov EV Smirnov NZ LyakhovThermal explosion of a mechanically activated 3Ni + Al mixture Combustion explosion and shock waves 2010 v 46 1 pp41-46

14

MODERN METHODS OF RHENIUM DETERMINATION

OV Evdokimova NV Pechishcheva KYu ShunyaevInstitute of Metallurgy of UB RAS

101 Amundsen st Ekaterinburg Russiashunuralru

IntroductionRhenium due to its unique properties is the promising metal

widely used in various industries At present day the main areas ofapplication of rhenium is the production of catalysts for the petroleumrefining industry and refractory alloys used for turbines manufacturing[1]

The great demand for this element requires large amounts of itsproduction There is a need extracting rhenium even from industrialwaste water from plants [2] due to the high cost and its low content innatural materials

This situation stimulates the development (or modification) ofmethods of analytical control of various nature materials

The content of rhenium in rhenium-containing materials bothnatural and technogenic and contect of accompanying to rheniumelements vary in a wide range of concentrations from 10-7 to tens ofpercent

Earlier the following methods were used for the determination ofrhenium spectrophotometry gravimetry kinetic electrochemicalextraction-fluorimetric methods X-ray fluorescence analysis [3] Themain disadvantages of mostly methods for determining rhenium are thelow sensitivity the bad reproducibility of results the influence ofaccompanying elements Ag W Mo Pt Cu Fe and etc

In modern analytical practice the following methods for therhenium determination are used inductively coupled plasma atomicemission spectroscopy (AES ICP) inductively coupled plasma - massspectrometry (ICP-MS) [4] electrochemical methods [1] X-rayfluorescence analysis and spectrophotometric methods do not lose theirrelevance [1] they have undergone significant modifications recently

15

Inductively coupled plasma atomic emission spectroscopy(AES ICP) is widely used for the rhenium determination in mineral rawmaterials and products of metallurgy production This method allows todetermine up to 10-4 rhenium The advantage of AES ICP is the highstability and reproducibility of results absence of chemical influences

However analysis of more complex objects such as metallurgicalproducts is a not easy task because the lines of rhenium emission areoverlaped with the lines of accompanying elements in samples So thelines of Mo (221427 nm) W (221431 nm) Fe (227519 nm) whichmay be present in the samples in large quantities are overlaped to themost intense lines of rhenium (221426 nm and 227525 nm) Thisproblem requires the development of new methods of samplepreparation and selection of optimal conditions for determination ofrhenium by atomic emission spectrometres

Also a significant disadvantage of this method is the small rangeof certificated reference materials So there are a limited number ofRussian rhenium standard materials with certified value of the rheniumcontent It is molybdenum and copper-molybdenum ores andconcentrates in which the rhenium content is in the range ofconcentrations from 000047 to 00221

In most cases analysts develop the synthetic mixture to monitorthe rhenium content in the analysis of specific samples of complexcomposition This mixture is similar to composition to the matrix of theanalyzed samples consisting of rhenium ions and other ions with agiven concentration For example the authors [5] to develop a techniquefor rhenium determining together with platinum and palladium in thesamples of spent catalysts by AES-ICP applied a synthetic mixtureprepared on the basis of aluminum oxide and standard solutions of Pt(IV) Pd (II) Re (VII)

One of modern methods and the most sensitive methods for thedetermination of rhenium is inductively coupled plasma - massspectrometry (ICP MS) [4 6 7 8] These days ICP MS withseparation and concentration allows to measure rhenium at lower thanseveral ngg However ICP MS performance in analyses of complexsamples is commonly affected by matrix effects and polyatomicinterference and signal drift High levels of salt solutions content cause

16

plugging of sampling orifice with decrease in analytical signal inaddition many spectral interferences may occur [6]

For the rhenium determination in molybdenite by ICP MS shouldbe use large dilution of sample to reduce the matrix influence and reducethe salts influence However this approach is not feasible in the case ofhigh levels of molybdenum and relatively low levels of rhenium in theanalyzed objects The most effective way to minimize the matrix effectsis separation of rhenium from the matrix Often for this purposeextraction by organic solvents [6] sorption by anion-exchangers [8] areused

Recently X-ray fluorescence analysis becomes more popular Itis rapid and is often used for mass analysis The advantage of thismethod is the possibility of direct determination of rhenium in the solidsamples in water solutions [9 10] in the biological samples (plants) [2]

However the method is not without disadvantages firstly thedetection limit of rhenium by X-ray fluorescence analysis is low and isonly 005-01 secondly there are only few the standard materials witha high rhenium content and thirdly the influence of interfering elementsin the sample related to determination of rhenium

Using the concentration can not only reduce the detection limitbut also in the same time solve and reduce the influence of interferingions For the concentration of rhenium in X-ray fluorescence analysis isoften used sorption of rhenium in the form of perrhenate-ions [9 10]

The authors [11] describes a problem related to the developmentof rhenium-containing standard materials by traditional hightemperature approach for X-ray fluorescence analysis Thus high-temperature studies of MoO3-ReO3 which could be served ascomparison materials for the rhenium determination by X-rayfluorescence analysis showed that 50-90 of rhenium is lost duringcalcination of mixtures it indicates the impossibility to use them fordevelopment of standard materials In the paper [11] the method ofpreparing rhenium glassy reference samples (10 - 50) on the basis ofBi2O3 and B2O3 is described The developed method allows to determinerhenium in the range of 001-10 [11]

17

Electrochemical methods in particular the electrostrippingvoltammetry (ESV) occupy a significant place in the analyticalchemistry of rhenium [12 13] This method allows to determine up to10-6-10-5 of rhenium

To avoid the effects of many electropositive components (Mo WCu Ag Au) which may interfere to the rhenium determination by ESVit has been proposed the sorption concentration of perrhenate ions on thesurface of activated charcoal (BAU) [12 13]

The most widely used techniques determine the 10-2 - 10-5 ofrhenium is spectrophotometric method The advantages of this methodare simplicity low cost equipment and a relatively high sensitivitySpectrophotometric method is based on the formation of coloredcomplex compounds of rhenium with organic and inorganic ligands [1]Photometric methods with thiocyanate ion thiourea are widely spread[14 15 16] Development of spectrophotometric methods for rheniumdetermination is largely due to the searching and using of new reagentsIn [17] for the extraction-photometric determination of perrhenate ionsin the form of ion associates the basic polymethine dyes derivatives of133-trimethyl-3H-indole have been offered but the influence ofoxyanions of tungsten and molybdenum is not excluded [17]

The disadvantage of the spectrophotometric methods is the needfor prior separation of rhenium from a number of interfering elements(Mo W Cu) that it is achieved by concentrating perrhenate-ions bysorption or extraction

Over the past decade main changes in the methods of rheniumdetermination related with the improvement stadium of samplepreparation transfer the sample into an analytical form modification ofknown methods and reagents (eg creation of new facilities developmentof new reagents for measurements) and conditions of analysis

In general in the literature a large number of works are relatedwith the separation of rhenium from the analyzed solutions and theseparation of rhenium (VII) from interfering elements by using newtypes of extractants and new sorbents is given Used extractants andsorbents as well as the optimal conditions for extraction and sorption ofrhenium are presented in Table 1 and 2 respectively

18

Extraction plays a dominant role in the methods of separationand concentration of rhenium

In most cases in the hydrometallurgical processing of rhenium-containing products in the acidic solutions ReO4

- are formed Forperrhenate ions extraction the anion-exchange reagents or extractants ofneutral type are often used The literature contains information on theextraction of rhenium (VII) by various amines and quaternaryammonium compounds [18 19 20] Efficient extractants of rheniumfrom acidic solutions are neutral organophosphorus compounds (tributylphosphate alkylphosphineoxides their derivatives) [21 22] a variety ofsolvent mixtures (tributyl phosphate + trioctylamine [23]) theextractants of neutral type such as ketones and aliphatic alcohols [1624 25]

Alcohols ketones and ethers are more selective having higherspeed separation of organic and aqueous phases as well as higherchemical resistance and lower cost compared with amines andorganophosphorus compounds but inferior to them in the extractioncapacity for rhenium (VII) [16]

Thus for perrhenate ions extraction aliphatic alcohols with 7-10carbon atoms in the aliphatic chain are well proven that can extractmore than 98 of rhenium from sulfuric acid and hydrochloric acidsolutions In the case of alcohol there is no need to use solvents andmodifiers what simplifies their use in extraction processes [16]

The efficiency of rhenium extraction into organic phase by aminesdecrease as follow quaternarygt tertiarygtsecondarygtprimary Amongthem secondary and tertiary amines are widely used as efficientextractants of rhenium from acidic solutions Perrhenate ions areextracted by amines in a wide range of pH For systems of amine - low-polar diluent - H2SO4-ReO4-H2O the formation inverse micelles istypical in the organic phase Acid ions and anionic complexes arelocated inside the aqueous core of the micelle with the metal ioncoordinates the polar functional group of amine [19 20]

It should be noted that the extraction by amines is complicated bythe use of solvents the nature of which depends on the solubility ofamines and their extraction capacity So low-polarity solvent toluene incontrast to the non-polar kerosene enhances the polarity of anionic saltsof amine which increases the reactivity of the extractant to the anion

19

exchange of inorganic acid to extractable anionic rhenium complexes[18]

Tertiary amines are the most effective extractants for rhenium(VII) However in paper [18] it is shown that the secondary amine(diisododecylamine) gives advantage to the tertiary amines on therhenium extraction efficiency from sulfuric acid media It can beexplained by the influence of steric factors and smaller rival extractionof mineral acids by secondary amines [1]

Most papers are related to the rhenium extraction from acidicsolutions but the extraction of rhenium from alkaline medium whichare formed after leaching of ores concentrates also represents a difficultproblem In the paper [23] rhenium extraction from alkaline solutionscontaining also molybdenum by solvent extraction using a mixture oftributylphosphate (TBP) and trioctylamine (N235) is describedMolybdenum which is also extracted by solvents in small amountsinterferes to the extraction of rhenium

Over the last decade most works refer to the development offundamentally new classes of extractants for perrhenate ions [26 2728 29] such as encapsulating ligands (cryptands and podands)macrocycles crown ethers These ligands can interact with ReO4

minus byboth the electrostatic interaction between ReO4

minus and protonated ligandand the hydrogen bond formation compared with simple open-chainligands If the complex between ReO4

minus and ligand has highhydrophobicity ReO4

minus in an aqueous solution may be separatedeffectively by a solvent extraction technique [30]

Crown ethers extract rhenium (VII) in the presence of potassiumor sodium in the form of K(Na)LReO4 (L-crown-ether) into the organicphase (12 - dichloroethane chloroform) [31 32] In the paper [31] theextraction perrhenate-ions by 3m-crown-m-ethers (m = 56) ether and itsmono-benzo-derivatives in 12-dichloroethane are described

Podands are analogues of crown ethers containing terminalphosphoryl ligands in their polyether chains they are used for theextraction of rhenium (VII) The efficiency of extraction by phosphorylpodands depends of the following factors the number of oxygen atomsin the polyether chain molecules the number of donor centers in themolecule of podands hydrophobicity of the reagent molecule the size offorming cycles the nature of substituent at the phosphorus atom Studies

20

have shown that phosphoryl podands with three oxygen atoms in thearomatic polyether chain combined with the phosphoryl group bydimetilen or o-phenylene fragments have high extraction ability forrhenium from sulfuric acid solutions [32]

In the paper [30] authors mark another type of podands such aspodands with nitrogen donor ligand -N N N `N`-tetrakis (2-pyridymethyl) -12-ethylendiamine (TREN) and its hydrophobicanalogs which also allow to extract perrhenate ions from highly acidicenvironments

Perrhenate is characterized by its ability to undergo a change ingeometry specifically from tetrahedral to hexagonal in the presence ofdonor ligands (eg acetonitrile triphenylphosphine) Protonationchanges the electron density present on the oxygen atoms Beer et al[33] suggested that the tripodal ligand L1 would be suitable for thebinding and extraction of perrhenate anion This ligand (Fig 1) basedon the combination of tris(2-aminoethyl)amine and crown ether motifswas found to complex sodium cations and to extract perrhenate anionsfrom aqueous solutions into an organic phase

Atwood and co-workers developed calixarene-type ligand L2(Fig 1) that specifically extracts perrhenate from water solution into anorganic phase The selectivity for extractions decreases as followTcO4

minus ge ReO4minus gt ClO4

minusgtNO3minus gtSO4

2minus gtClminus This selectivity pattern isattributed to a combination of charge size and shape Efficientextraction is observed at high and neutral pH the molar ratio ofligandperrhenate ion = 14 [33]

L1 L2Fig 1 Tripodal ligand L1 and calixarene-type ligand L2 for perrhenateextraction

21

Schiff-base macrocycles are used as a new conjugatedmacrocycles for perrhenate ions Thus a series of amino-azacryptands(L3ndashL16) for encapsulation and extraction of the oxoanions perrhenate(Fig 2) from aqueous solution were proposed by the authors [34]Thecomplexation amino-azacryptands L to ReO4

- is via hydrogen-bondedinteractions

Fig2 Amino-azacryptands (L3ndashL16) for encapsulation and extraction of theoxoanions perrhenate

Thus the main characteristics of the compounds for the effectiveperrhenate ions extraction as follows

Energy coordination of ligand with ReO4- should be higher than

the energy of perrhenate ion hydrationThe interaction between the ligand and perrhenate ions an

electrostatic interaction or the formation of hydrogen bonds Functional ligands to be a suitable size (volume of the cavity

should be more than 736 Aring3) shape electronegativity andhydrophobicity

Ligand should be protonated

22

Table 1 Characteristics of extractants for rhenium extraction

Extractant

Analysis objectComposition of

the initialsolution

Extractonconditions

Interferinginfluences

Aliphatic alcoholswith C 7-10

1-Heptanol 4-Heptanol 1-octanol 1-decanol 4-decanol 2-Heptanol 3-Heptanol

3-octanolback-extractant

NH4OH

Solutions HCland H2SO4

Т=293КTime of phase

contacttex = 5 min

organic phase toaqueous

(OL = 11)4 steps of

extraction 2stripping

Coextractionof mineral

acidsincomplete

re-extractionof Re (VII)

1

OctanolSolutions ofHNO3 and

H2SO4

Т=286-290Кtex = 10 min OL

= 11

Coextractionof HNO3

H2SO4

2

Basic polymethinedyes (derivatives of133-trimethyl-3H-

indole) astrazon violet

Aqueous andaqueous-organic

solution

Т=293КрН=6

tex = 10-30 secextractant mixture

toluene +dichloroethane

(1 1)

do notinterfere

3000-5000fold excess ofS04

2- CO32-

300- HPO42-

MoO42-

WO42-

10-20 S2O32-

Cr2O72- IO3

-metal ions as

sulfates

3

Secondary(diisododecylamine)and tertiary amines

(dioctylamin andtrioctylamine)

Solutions H2SO4

Т=293КA wide range of

pH

tex=5-7 mindiluent - toluene

-

4N-benzoyl-N ndashphenyl-

hydroxylamine

Molybdenitedissolved inHCl HNO3

HCl 05 molltex=15 min

diluent chloroform-

23

Table 1 (continued)

Extractant

Analysisobject

Compositionof the initial

solution

Extractonconditions

Interferinginfluences

5

Phosphoryl podands

back-extractant H2O

СReinitial=2middot105 moll

aqueoussolutions of

salts of alkalimetals

solutions ofmineral acids

Т=286-291КОL=11

tex= 60 mindiluent

nitrobenzene12-

dichloroethanechloroform

toluene

-

6Triotylamine (N235)+

tributyl phosphate(TBP)back-extractant18 NH4OH

Alkalinesolutions

afterleaching

containingMo

СRe 01-165gl

T=293 КрН =90 OL=11

tex=10 мин20

triotylamine+30 tributylphosphate

diluentkerosene

-

7

Podand-type nitrogendonor ligand ndashNNN`N`-tetrakis(2-pyridymethyl)-

12-ethylendiamine (TREN)

Aqueoussolution

NH4ReO4

С =10-4 M

Ionic strength01M

pH=1-65diluent

chloroformОL=11tex=24 h

-

8

3m-crown-m-ethers(m=56) mono-benzo-

derivates12-dichloroethane

СReO4-=

0057-0060М

T=291-295Ktex=2h

-

24

Table 1 (continued)

The range of Re concentrations

RecoveryMethods for determination Ref

Recovery gt99

Determination from back-extractSpectrophotometric method with

thiourea reductant-Sn (II)wavelength of 390 nm

[16 24]

1

gt98 Spectrophotometric method [25]

2The range of Re concentrations

001-550 mcgml

Determination from extractSpectrophotometric method

wavelength of 540 nm[17]

3 -AES-ICP

Spectrophotometric methodwith thiourea

[18 1920]

4Mo W Fe are extracted 97

into the organic phase

Determination from aqua phaseafter extraction

ICP-MS[6]

5 -AES-ICP

Spectrophotometric method[21 22]

6 968Spectrophotometric method with

butyl rhodamine[23]

7 - AES-ICP [30]

8 -AES-ICP

Spectrophotometric method[31]

9 - ICP-MS [32]

25

Table 2 Characteristics of sorbents for rhenium sorption

Sorbent

Analysis objectComposition of the

initial solutionConditions of

sorptionInterferinginfluences

1

Activated carbons(BAU)

Eluenthot soda solution

nitrate media

gold ore raw

static conditionsа)рH =2-3

б) рH =15-25

volume ofsolution 10 mlmass of sorbent

03 g(SL=1333)t=10 min UV

a) electro-positive

components(Mo W Cu

Ag Au)b)1000 fold

excess ofMo W do

not interfere

2

Activated carbons- CN-G CN-PCU developed

from waste woodand grain

processingindustries

sulfuric acidsolutions with CRe= 002 gl pH =2

solid phasesliquid SL==105

t=5-7 days-

3

2 Carbon fibrousmaterials

modified withchitosan

neutral aquasolutions of

rhenium

static conditionsТ=286-289 КSL=11000

-

4

3 Weakly basicanion-exchangersАН-105 Purolite

A 170

mineralizedsulphite solutionsimulating rinsing

water(С Re=001-002

gl Mo Cu Fe As)

static anddynamic

conditionsSL = 1500

t = 150-200 min

-

5

Strongly-basicanion-exchangers

АВ-17(sorbent PAN-АВ-

17)

neutral or slightlyacid

solutions

dynamicconditionst = 20 min

The disks ofpolyacrylonitrilefiber filled resin

1000 foldexcess of

Fe Cu ZnPb Cd do

not interfere

6Lignin anion-

exchangerssolutions NH4ReO4

static conditionsSL=1400

t=15min-2 h-

26

Table 2 (continued)

NotesMethods for

determinationRef

1

а) Sorption capacity of BAU forRe СЕ=14175 mgg AC

Detectionlt 10

б) СЕ=00763 mmolg or 142mgg

The concentrations range of Re050 100 mgL in standard

solutions025 50 mgl in the presence

of Mo and W (11000)

a) Electrostrippingvoltammetry

b) X-ray fluorescenceanalysis

a) [12]b) [9 10]

2 -Spectrophotometric

method [35]

3 СЕ=179-185mggSpectrophotometric

method with ammoniumthiocyanate

[38 39]

4Full dynamic exchange capacity

114 mgg

Spectrophotometricmethod with ammonium

thiocyanatekineticmethod

[36]

5 -

Determination of Re bythe diffuse reflectance

spectra at 420 nmrhenium thiocyanate

complex in the presenceof tin (II)

[15]

6 СЕ=3427-2328 mgg Traditional polarography [37]

Sorption is one of the methods for separation of rhenium fromvarious solutions

Sorption of rhenium or perrhenate-ions often occurs on solidsorbents from the liquid phase The presence of a large specific surfacearea and a large number of functional groups of the sorbent determinesits high sorption properties with respect to rhenium (VII) Sorbentscontain the same functional groups (amino groups hydroxyl groups

27

phosphorus groups) as extractants for the selective extraction ofrhenium but these groups are fixed on solid carriers or support

Activated carbons (AC) of various brands are used the mostwidely [9 10] The use of activated carbons as sorbents due to the factthat they have a whole set of valuable properties highly polydisperseporous structure a complex but relatively easily controlled surfacechemistry and specific physical properties Activated carbons like manyother carbon materials exhibit high selectivity to perrhenate ions thatexplains the increased interest to this type of sorbents [12]

The characteristic distinction of carbonaceous materials is that thesorption of rhenium is not only due to complexation with surfacefunctional groups (containing oxygen nitrogen sulfur atoms) but alsodue to the interaction with carbon matrix

AC can act as anion-exchanger in acidic media and themechanism can be described by the following scheme

[C2+ OH-] + ReO4-= [C2+ ReO4

-] + OH-On the other hand the AC have significant reduction properties

the reaction of the electrochemical reduction of perrhenate ions in themethods of rhenium determination by voltammetry is based on this it[12]

It has been established [9 10] that ReO4- is sorbed from nitric

acid solutions almost entirely (95-99) by 10 minutes of UV irradiationwhile without irradiation this process takes up to 60 minutes Increasedsorption by UV authors attribute to the fact when UV radiationsolutions of rhenium (VII) salts rhenium (VI) and rhenium (V) areformed which are considerably faster adsorbed on AC

Extensive use of the AС is also associated with their low costActivated carbons - CN-G CN-P CU developed from waste wood andgrain processing industries have a low cost and their capacitance andkinetic characteristics slightly inferior to conventional AC (FAC) [35]

However from acid solutions together with rhenium molybdenumcan also be sorbed by the AC Furthermore perchlorates nitrates andother oxidants can reduce the adsorption capacity of coals by oxidationThe disadvantage of rhenium sorption by activated carbons is as followsa decreasing in their activity after 4-6 cycles of sorption-desorption [1]low mechanical strength [35]

28

Anion-exchange resin is the next width of use which havegreater selectivity and capacity compared with activated carbons Theseanion-exchangers synthesized on the basis of the gel and porouscopolymer of styrene and divinylbenzene From the neutral and acidicsolutions rhenium is adsorbed by low-basicity anion-exchangers with thefunctional groups of primary and tertiary amines In recent studiesconducted on the use of weakly basic macroporous anion-exchangerswith a more developed specific surface area (20-100 m2g) such asPurolite A170 with secondary amino groups [36]

Sorption by strongly-basic anion-exchangers compared to weaklybasic anion-exchangers has several advantages firstly they are almostquantitatively and selectively extract rhenium from solutions andsecondly work in a wide range of pH [15]

The rapid technique for perrhenate ions determination isdeveloped which allows to find their content directly on the site ofsampling for example in lake water using strongly-basic anion-exchangers AB-17 with the sensitivity of the technique is 2-3 orderslower than the best conventional spectrohotometric methods withthiocyanate [15]

Recently the authors of paper [37] synthesized new highlypermeable lignin anion-exchangers on the basis of lignin a naturalpolymer a component of terrestrial plants It is noted that the exchangecapacity of anion-exchangers for rhenium in lignin is much higher (EC =3427-2328 mgg) compared with conventional anion-exchangersHowever the time to reach equilibrium sorption by some anion-exchangers can reach from 2 up to 12 hours

Carbon fibrous materials modified with chitosan haveimproved kinetic (time and rate of sorption) characteristics comparedwith activated carbon and ion-exchange resins [38 39] Carbon fibrousmaterials modified with chitosan contain amino groups includingprotonated The increasing of the number of protonated groupscauses the increasing of sorption capacity of the material withrespect to the negatively-charged perrhenate-ions However thesorption capacity for rhenium (179-185 mgg) still yields to ligninanion in addition investigations were carried out of neutral aquasolutions of rhenium without interfering influences

29

ConclusionIn this review the methods for rhenium determination which over

the last decade have acquired great fame are presented A large numberof works related to improving methods for rhenium determining pointsto the increased interest to this metal The majority of the studies aimedto the selective extraction of rhenium from the analyzed complex objectsand the separating it from interfering elements in the matrix to increasethe sensitivity of the methods Most of the work related to the searchingof various organic reagents selective to rhenium (V VII) ions and usedin extraction and sorption processes In general the development ofrapid selective methods that can determine the content of rhenium in awide range of concentrations in various materials remains an actualproblem nowadays

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

Reference1 AA Palant ID Troshkina AM Chekmarev Metallurgy of

rhenium Science Moscow 2007 298 p2 LV Borisova YuV Demin NG Gatinskaya VV Ermakov

Determnation of rhenium in plant materials Journal of AnalyticalChemistry 2005 V60 1 P 97-103

3 LV Borisova AN Ermakov Analytical chemistry ofrhenium 1974 Science Мoscow 318 p

4 S Uchidaa KTagamia K Tabei Comparison of alkaline fusionand acid digestion methods for the determination of rhenium in rockand soil samples by ICP-MS Analytica Chimica Acta 2005 V535P 317ndash323

5 VI Manshilin EK Vinokurova SA Kapelushniy Determinationof Pt Pd Re mass fraction in dead catalyst samples using ICPatomic emission spectrometry method Methods and objects ofchemical analysis 2009 V41 P 97-100 (in Russian)

6 Jie Li Li-feng Zhong Xiang-lin Tu Xi-rong Liang Ji-feng XuDetermination of rhenium content in molybdenite by ICPndashMS afterseparation of the major matrix by solvent extraction with N-benzoyl-N-phenylhydroxalamine Talanta 2010 V81 P 954ndash958

30

7 T Meisel J Moser N Fellner Wo Wegscheider R SchoenbergSimplified method for the determination of Ru Pd Re Os Ir and Ptin chromitites and other geological materials by isotope dilutionICP-MS and acid digestion Analyst 2001 V126 P 322ndash328

8 K Shinotsuka K Suzuki Simultaneous determination of platinumgroup elements and rhenium in rock samples using isotope dilutioninductively coupled plasma mass spectrometry after cation exchangeseparation followed by solvent extraction Analytica chimica acta2007 V603 P129ndash139

9 NA Kolpakova AS Buinovsky IA Jidkova Determinationof rhenium by X-ray fluorescence analysis Proceedings ofuniversities Physics 2004 12 P147-149 (In Russian)

10 AS Buinovsky NA Kolpakova IA Melnikov Determinationof rhenium in the ore material by X-ray fluorescence analysis News polytechnic university 2007 V311 3 P92-95 (InRussian)

11 DV Drobot AV Belyaev VA Kutvitsky Development of aunified X-ray fluorescence method for the determination ofrhenium in multicomponent oxide compositions News highereducational institutions Non-ferrous metallurgy 1999 4 P23-24 (in Russian)

12 LG Goltz NA Kolpakov Sorption preconcentration anddetermination by voltammetry perrhenate ions in the mineralraw materials Proceedings of the Tomsk PolytechnicUniversity 2006 V 309 6 P77-80 (in Russian)

13 NA Kolpakova LG Gol`ts Determination in mineral rawmaterials by stripping voltammetry Journal of AnalyticalChemistry 2007V62 4 Р418-422

14 Wahi A Kakkar LR Microdeterminaton of rhenium withrhhodamine-B and thiocyanate usng ascorbic acid as the reductant Analytical sciences 1997 august V 13 P657-659

15 LV Borisova SB Gatinskaya SB Savvin VA RyabukhinAdsorbtion-spectrophotometric determination of rhenium fromdiffuse reflectance spectra of its complexes on a PAN-AV-17adsorbent Journal of Analytical Chemistry 2002 V572 P 161-164

31

16 AG Kasikov AM Petrova Extraction of rhenium (VII) byaliphatic alcohols from acid solutions Journal of AppliedSpectroscopy2009 V82 2 P 203-209 (in Russian)

17 ZhA Kormosh YaR Bazel` Extraction of oxyanions with basicpolimethine dyes from aqueous and aqueous-organic solutionsextraction-photometric determination of rhenium (VII) and Tungsten(VI) Journal of Analytical Chemistry 1999 V54 7 P 690-694

18 AA Palant NA Yatsenko VA Petrova Extraction of rhenium

(VII) from sulfuric acid solutions by diisododecylamine

Journal of Inorganic Chemistry 1998 V43 2 P 339-343 (inRussian)

19 NA Yatsenko AA Palant Micelle formation in theextraction of ions W (VI) Mo (VI) Re (VII) from sulfuric acidmedia diisododecylamine dioctylamine and trioctylamine Journal of Inorganic Chemistry 2000 V45 9 P 1595-1599 (in Russian)

20 N Latsenko AA Palant SR Dungan Extraction of tungsten (VI)molybdenum (VI) and rhenium (VII) by diisododecylamine Hydrometallyrgy V 55 Issue 1 Febr 2000 P 1-15

21 AV Antonov AA Ischenko The use of extraction in thedetermination of rhenium in the presence of molybdenumChemistry and chemical technology 2007V50 9113-116 (in Russian)

22 VF Travkin AV Antonov VL Kubasov AA IshchenkoExtraction of rhenium (VII) and molybdenum (VI)hexabutyltriamid phosphoric acid from the acidic environment Journal of Applied Chemistry 2006 V78 6P 920-924 (inRussian)

23 Cao Zhang-fang Zhong Hong Qiu Zhao-hui Solvent extraction ofrhenium from molybdenum in alkaline solution Hydrometallurgy2009 V 97 3-4 P 153-157

24 AG Kasikov AM Petrova Influence the structure of octanolon their extraction ability in acid solutions with respect to

32

rhenium (VII) Journal of Applied Chemistry 2007 V80 4 P689-690 (in Russian)

25 VF Travkin YM Glubokov Extraction of molybdenum andrhenium by aliphatic alcohols Metallurgiya2008 7 P21-25 (in Russian)

26 EA Kataev GV Kolesnikov VN Khrustalev MYu AntipinRecognition of perrhenate and pertechnetate by a neutralmacrocyclic receptor J radioanal Nuclchem 2009 2 V282 P 385-389

27 Bambang Kuswandi Nuriman Willem Verboom David NReinhoudt Tripodal Receptors for Cation and Anion Sensors Sensors 2006V 6 P 978-1017

28 Lagili O Abouderbala Warwick J Belcher Martyn G BoutellePeter J Cragg Jonathan W Steed Cooperative anion binding andelectrochemical sensing by modular podands PNAS April 162002 V 99 8 P 5001ndash5006

29 EA Kataev GV Kolesnikov EK Myshkovskaya Newmacrocyclic ligands based bipyrroles to bind perrhenate andpertechnetate ions radiation safety 2008 4 P16-22(inRussian)

30 Takeshi Ogata Kenji Takeshita Kanako Tsuda Solvent extractionof perrhenate ions with podand-type nitrogen donor ligands Separation and Purification Technology 2009V68 P288ndash290

31 Yoshihiro Kudo Ryo Fujihara Shoichi Katsuta Yasuyuki TakedaSolvent extraction of sodium perrhenate by 3m-crown-m ethers(m=5 6) and their mono-benzo-derivatives into 12-dichloroethane

32 Elucidation of an overall extraction equilibrium based oncomponent equilibria containing an ion-pair formation in water Talanta V 71 2007 656ndash661

33 AN Turanov VK Karandashev VE Baulin Extraction ofrhenium (VII) by phosphorylated podands Russian journal ofinorganic chemistry 2006 V514 P676-682 (in Russian)

34 E A Katayev Yu A Ustynyuk J L Sessler Receptors fortetrahedral oxyanions Coordination Chemistry Reviews 2006V250 P3004ndash3037

33

35 Leroy Cronin Macrocyclic and supramolecular coordinationchemistry Annu Rep Prog Chem Sect A 2004V100 P 323ndash383

36 ID Troshkina ON Ushakova VM Mukhin Sorption ofrhenium from sulfuric acid solutions by activated carbon News of higher educational institutions Non-ferrousmetallurgy 2005 3 P38-41 (in Russian)

37 AA Abdusalomov Sorption of rhenium from sulfuric acidsolutions of molybdenum Sorption and ChromatographicProcesses 2006 Vol6 V 6P 893-894 (In Russian)

38 NN Chopabaeva EE Ergozhin ATasmagambet AI NikitinaSorbtion of perrenate-anons by lignin anion exchangers Chemistry of solid fuel 2009 2 P 43-47 (in Russian)

39 AV Plevaka ID Troshkina LA Zemskova AV Voit Sorption ofrhenium chitosan-fiber materials Journal of InorganicChemistry 2009V54 7 P1229-1232 (in Russian)

40 LA Zemskova AV Voit YuMNikolenko ID Troshkina AVPlevaka Sorption of rhenium on carbon fibrous materials modifiedwith chitozan Journal of nuclear and radiochemical sciences2005 V6 3 P221-222

11

SYNTHESIS AND MICROSTRUCTURE DESIGN OF METALAND CERAMIC MATRIX COMPOSITES USING

MECHANICAL MILLING OF THEREACTANTSCONSTITUENTS

Dina V Dudina Oleg I LomovskyInstitute of Solid State Chemistry and Mechanochemistry

Siberian Branch of Russian Academy of Sciences Kutateladze 18Novosibirsk 630128 Russia

E-mail dina1807gmailcom

Mechanical milling greatly alters the state of a powder mixtureintroducing plastic strain and defects into the components andcreating new interfaces and mutual configurations of nano-sizedgrains This opens up a possibility to design microstructures of thecomposite to be synthesized by modifying the initial state of reactingpowder mixtures In certain mechanically milled reactive systemsone can observe microstructure refinement of the product [1-2] anincrease in the yield of the reaction [3] improved distribution of thephases [3 4] and lower reaction onset and developed temperatures[1-2] The presentation intends to demonstrate several successfulexamples of this approach for synthesizing composites by self-propagating high-temperature synthesis (SHS) shock compressionand electric-current assisted sintering

SHS in the mechanically milled Ti-B-Cu powder mixtures wassuccessfully performed and resulted in a TiB2-Cu composite [1-2]Compared to untreated powders in the mechanically milled mixturestitanium and boron started reacting at a reduced ignition temperaturewhile lower combustion temperatures developed in the combustionwave favored formation of submicron grains of TiB2

The powder particles brought to react with each other by shockcompression of the mixture may not fully transform into the productsif the loading is too short and the temperatures developed during thepressure rise and the post-loading period are not high enough In themechanically milled mixture the yield of the reaction can beincreased as a result of the decreased grain size of the initial reactants

12

and shorter diffusion distances (example Ti-Cu-B system partial andcomplete reaction of Ti and B [3])

When the sintering process ensures temperatures and timesufficient for the completion of the reaction in the mechanicallymilled mixture one can expect more uniform microstructure and finergrains of the products (example Ti-B-C system forming B4C-TiB2

phases during electric-current assisted sintering [4])Ball milling can refine the microstructure of the as-synthesized

composites and can be used to introduce additional quantities of theconstituents in the composite This was applied in order to develophighly conductive Cu-based composites One of the possible reasonsfor low conductivity of in-situ dispersion strengthened copper may bethe incompleteness of the reaction between the initial reactantswhich form solid solutions with the copper matrix In this regard weconducted an in-situ synthesis of TiB2-Cu composites starting fromthe powder mixtures with the limited content of copper ensuring ahigh probability of contact between the particles of titanium andboron and as a result their full conversion into the TiB2 phase Thenanoparticles were formed in a self-propagating mode in the ballmilled Ti-B-Cu powder mixture corresponding to the 57 volTiB2-Cu composition Afterwards in order to adjust the composition thecomposite was ldquodilutedrdquo with the required amount of copper usingsubsequent ball milling [5]

The consolidated nano- and microcomposite materialsdeveloped on the basis of the described systems were tested for theirenhanced mechanical properties (fracture tough composites B4C-TiB2

[4]) electric erosion resistance [6] and electric conductivity [5] Inthis presentation each property is discussed as resulting from thephase and microstructure evolution during the synthesis of thematerial by the selected processing method

AcknowledgementsParts of this work were carried out by DVD at the University

of California Davis USA during her postdoctoral appointment Theauthors greatly appreciate the collaboration with DrKorchagin(ISSCM SB RAS) Dr VIMali and Dr AGAnisimov (Institute of

13

Hydrodynamics SB RAS Novosibirsk Russia) and Prof JSKim(University of Ulsan South Korea)

References1 DVDudina OILomovsky MAKorchagin VIMali Chem

Sust Dev 12 (2004) 319-3252 MAKorchagin DVDudina Comb Expl Shock Waves 43 (2)

(2007)176-1873 DVDudina VIMali AGAnisimov OILomovsky Mater Sci

Eng A 503 (2009) 41-444 DVDudina DMHulbert DJiang CUnuvar SJCytron

AKMukherjee JMaterSci 43 (2008) 3569-35765 JSKim DVDudina JCKim YSKwon JJPark CKRhee J

Nanosci Nanotech 10 (2010) 252-2576 J-SKim Y-SKwon DVDudina OILomovsky MAKorchagin

VIMali JMaterSci 40 ( 2005)3491 - 3495

4

STUDY OF THE EFFECT OF FLUORESCENCE INCREASINGOF N-ARYL-3-AMINOPROPIONIC ACIDS IN THE PRESENCE

OF ZINC AND CADMIUM IONS

EV Dedyukhina1 NV Pechishcheva1 LK Neudachina2KYu Shunyaev1 AA Belozerova1

1 ndash Institute of Metallurgy of UB RAS 101 Amundsen st Ekaterinburgshunuralru

2 ndash Ural State University 51 Lenin av Ekaterinburg Russia

Earlier the effect of increasing of phosphorescence intensity in thefrozen solutions with excess of metal chlorides and sulphates has beenreported Ions оf these metals have filled electronic shells and largevalue of electric field intensity - Li(I) Be(II) Ca(II) Mg(II) Cd(II)Zn(II) Al(III) In(III) and Ga(III) For example this effect was found forbenzene aniline phenol amino acids ndash tyrosine tryptophanephenylalanine [1]

The same effect have been found for fluorescence of onerepresentative of N-aryl-3-aminopropionic acids (AAPA) - NN-di(2-carboxyethyl)-p-anisidine - in the presence of cadmium(II) and zinc(II)ions at Т=77 К [2] Increasing of fluorescence intensity (Ifl) in frozeninorganic matrix is expected for other representatives of AAPA whichnot have electron acceptor groups in structure and demonstrate theconsiderable fluorescence intensity of the protonated form

Fluorescence of some AAPA in frozen inorganic matrixNN-di(2-carboxyethyl)aniline (I) NN-di(2-carboxyethyl)-34-

xylidine (II) NN-di(2-carboxyethyl)-3-methyl-aniline (III) andN-(2-carbamoylethyl)-о-anisidine (IV) are representatives of a class ofAAPA Figure 1 presents structures of the AAPA In the present workthe fluorescence of aqueous solutions of this AAPA with molar excess ofcadmium and zinc sulphates at рH 1-6 and Т=77 К have beeninvestigated

The fluorescence spectra of solutions were measured using aFluorat-02-Panorama spectrofluorometer (Lumex Russia) Fluorescencespectra at T=77 K was excited and recorded using a fiber-optic cablewith a special optical connector

5

It have been established that the Ifl of the protonated form of I-IV(СR=1middot10-4 moldm3) is increased in the presence of cadmium(II) andzinc(II) ions at Т=77 К Figure 2 presents spectra of II We suggest thatcause of this effect is interaction enhancement of reagent with metal inconsequence of isolation from water and micro concentration (waterform ice crystals impurities are displaced in intercrystal area)

CH3

N

O

OHO

OH

1 2 3 4

Fig 1 Structures of AAPA 1 - NN-di(2-carboxyethyl)aniline2 - NN-di(2-carboxyethyl)-34-xylidine 3- NN-di(2-carboxyethyl)-3-

methyl-aniline 4 - N-(2-carbamoylethyl)-о-anisidine

The increasing Ifl of protonated reagent form of I-IV also isobserved at Т=293К but is not as strong as at T=77 K

0

1

2

3

4

5

6

7

240 260 280 300 320 340 360

wavelength nm

Ia

u

1

2

3

Fig 2 Spectra of fluorescence II (СR=1middot10-4 moldm3) in the presence andabsence of Cd(II) и Zn(II) ions (СZn(II)= СCd(II)= 560 mgdm3) рН=60 Т=77 К

λex = 214 nm 1 - II 2 - II+Zn(II) 3 - II+Cd(II)

The fluorescence increasing is observed only when concentrationof metal ions in dozens of times more than concentration of fluorophor

6

This indicate that Ifl increasing is occured due to reagent solvation byions of inorganic salts but not chelation

We have obtained the Ifl of solutions of I-IV as functions of theconcentration of cadmium(II) and zinc(II) ions at Т=77 К pH=6 (table1) The largest increasing of Ifl in the presence of metal ions have beenobserved for IV But the most correlation coefficient R value of linearfunction Ifl=f(CMe) with wider concentrations range has been obtainedfor II

Table 1 The Ifl of I-IV as functions from concentration of metal ions Т=77 КCCd(II)= CZn(II)= 200 mgdm3 СR=10-4 moldm3 рН=6

Metalion

ReagentConcentrationsrange mgdm3 I R+MeIR R Slope

I 11 090 321

II 11 098 494III

25-760

13 092 456Cd(II)

IV 25-245 80 092 2997

I 3 095 82

II 8 098 414

III

30-845

11 096 437Zn(II)

IV 30-560 70 090 1542

In addition we have studied the fluorescence of aniline and naturalamino acids (tyrosine tryptophane phenylalanine) in frozen inorganicmatrix Structures of amino acids are presented on figure 3 thiscompounds are not belong to class of substituted anilines Thiscompounds similarly of investigated AAPA not have electron acceptorgroups in structure tyrosine phenylalanine and AAPA have the samebenzene fluorophore Besides this amino acids are commerciallyavailable reagents

Investigations have been shown that present amino acids alsodisplay the effect of Ifl increasing of protonated reagent form in thepresence of cadmium(II) and zinc(II) ions at Т=77 К But is not asstrong (12ndash5 times) as AAPA Ifl increasing Metal ions at T=298 K havelittle effect on a fluorescent spectra of amino acids

7

1 2 3

Fig 3 Structure of amino acids1 - phenylalanine 2 - tyrosine 3 - tryptophane

Thus we can deduce that the presence of substituted amino groupin benzene ring (especially in combination with others electron donorgroups) allow to observe more effective increasing of Ifl in salt solutionat 77 К Replacement benzene fluorophore to indole one (intryptophane) result to decreasing of observing effect extent

The fluorescence of II in the presence of Mg(II) ions at Т=77 Кwas investigated We tried to find the II0 fluorescence of II functionfrom z2r ratio for two-charged cations where z - ionic charge (+2) r -ionic radius nm [3] Data is presented in table 2

Table 2 Characteristiс of the functions II0 = f(z2r) for II Т=77 К рН=6λexλem= 214286 nm СII =10-4 М

Ion z2r SlopeI I0

CMe= 200 mgdm3

Cd(II) 412 494 107

Zn(II) 541 414 85

Mg(II) 615 352 74

The functions II0=f(z2r) of fluorescence II in frozen inorganicmatrix from are presented in figure 4 they are linear Also linearfunctions of Ifl=f(CMe) slope on z2r ratio have been obtained

N

NH2

OH

O

H2N

OHO

OH

8

y = -016x + 174

R2 = 099

6

7

8

9

10

11

40 45 50 55 60 65

z2r

IIo

Zn

Cd

Mg

Fig 4 Functions II0=f(z2r) of fluorescence II in the presence of metal ions [3]CCd(II)= CZn(II)= CMg(II)= 200 mgdm3 λexλem= 214286 nm Т=77 К

Study of fluorescence of some reagents in glycerolwater andethanolwater mixtures and micellar solutions at Т=298 КWe have studied a fluorescence II and tryptophane in

glycerolwater (11) and ethanolwater (11) mixtures in the presence ofzinc(II) ions at 77 К It was done for proving hypothesis about reducinginteraction fluorophore with water in aqueous media at freezing Wesuggest that interaction between of the solute and solvent molecules arepreserved in nonaqueous solutions

Corresponding spectra of II are presented on figure 3 similarsituation is observed for tryptophane We can see effect of increasing Ifl

is not observed in glycerolwater and ethanolwater mixtures in contrastto aqueous solutions

Isolation reagent from water at room temperature is possible in thepresence of surfactants

Fluorescence II have been study in the presence of surfactants ofdifferent nature in acidic media at Т=298 К The Ifl increasing ofprotonated form II is occured in the presence of Triton Х-100 (non-ionicsurfactant) and sodium dodecylsulphate (anionic surfactant)Fluorescence II is decreased by cetyltrimethylammonium bromide(CTAB cationic surfactant)

Fluorescence of II in the presence of surfactants and excess ofmetal ions have been study at рН=1-6 Zinc and cadmium ions increaseIfl of II at рН 50-65 with CTAB Thus metal ions and CTAB at

9

Т=298 К have same Ifl increasing effect as the effect at Т=77 К withoutsurfactants

0

5

10

15

20

25

240 260 280 300 320 340 360 380

wavelength nm

Ia

u

1

2

3

Рис 5 Fluorescence of II (СII=1middot10-4 moldm3) in ethanolwater (11)mixtures in the presence and absence of Zn(II) pH=60 Т=77 К λex=214 nm

1 - II 2 - II + Zn(II) (44middot10-4 moldm3) 3 - II+ Zn(II) (86middot10-3moldm3)

We have obtained under these conditions the Ifl of II solutions asfunction of the concentration of Cd and Zn ions with variousconcentrations of CTAB (table 3) The plots are linear and have thegreatest slope value at СCTAB=14middot10-3 moldm3 Cadmium ions have agreater influence on the fluorescence of the II than zinc ions

The fluorescence investigations in the presence of CTAB andmetal cations have been carried out on other AAPA (I III and IV)aniline and tyrosine (table 4) It was found that zinc ions increase offluorescence of protonated reagent form of I and III cadmium ions ndashIII

Table 3 Characteristiс of the functions Ifl=f(CMe) of II with addition of CTAB

exem = 218286 Т=298 К

Range of concentrationsCation

С CTABmoll moldm3 mgdm3 tg α

96middot10-4 2middot10-4 ndash 4middot10-3 45-450 18Cd(II)

14middot10-3 2middot10-4 ndash 8middot10-3 45-900 3696middot10-4 4middot10-4 ndash 15middot10-2 25-850 055

Zn(II)14middot10-3 4middot10-4 ndash 11middot10-2 25-850 10

10

Table 4 Fluorescence of reagents in the presence of zinc and cadmium ions(СMe=560 mgdm3) and CTAB (С= 96middot10-4 moldm3) рН=6

Zn(II) Cd(II)

Reagentexem

nm II0 I (R+Zn+CTAB)au

II0I (R+Cd+CTAB)

au

aniline 253278 11 07 10 06I 222300 62 16 08 02II 218286 73 44 85 51III 217288 65 34 33 15IV 218304 10 32 12 12

tyrosine 222302 10 480 11 462

The resulting functions will be used for developing of thefluorescent techniques of zinc and cadmium determination

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

References1 AV Karyakin n-electrons of heteroatoms in hydrogen bonding and

luminescence (in Russian) Nauka Мoscow 1985 135 p2 LK Neudachina EV Dedyukhina OV Evdokimova

NV Pechishcheva EV Osintseva KYu Shunyaev Fluorescenceof NN-di(2-carboxyethyl)-p-anisidine in solution and crystallinestate Journal of Applied Spectroscopy 2010 V 77 2 P 206-212

3 Lurie YuYu Hand-book of analytical chemistry (in Russian)Khimiya Мoscow 1989 447 p

188

the investigated chlorides from the diffusion current densities Diffusioncoefficients were calculated with the Ilkovich equation

Richard B Stein [8] investigated the ion reduction reaction ofdivalent lead in the NaCl ndash KCl melt with oscillographic polyrographymethod Platinum microelectrode with 05 mm diameter soldered intothe quartz tube with 189х10-3 cm2 square was a cathode Referenceelectrode was silver chloride and the auxiliary electrode was graphiteAuthor founded out that the lead ion diffusion coefficients obtained bythe experimental data differ from calculated according to the equation ofStocks-Einstein He derived the conclusion that the cation structure ismore complex than just a single ion

HA Laitinen HCGaur [9] investigated lead cobalt and thalliumion reduction in the molten potassium and lithium chlorides withchronopotenciometry method Authors fixed the value of the transitiontime for melts containing the control values of ions under investigationAccording to the experimental data empiric dependences ofconcentrations and transitional time were determined Coefficients ofcadmium cobalt lead and thallium ion diffusion were calculated withSandrsquos equation (208 242 218 38810-5 cm2s correspondingly)

Cathode processes in chloride melts containing lead ions werestudied by chronopotentiometric and stationary galvanostaticpolarization curves methods

Experiments were carried out in the cell made of quartzhermetically closed fluoroplastic cover (2) with the holes for electrodesand thermocouple with accordance to the Fig1

Glassy-carbon was a working electrode (cathode) Glassy-carboncontainer played a role of a counter electrode Melted equimolar mixtureof lead lithium and potassium chlorides was used as the electrolyte forthe reference and working electrodes Electrolytes of the workingelectrode and reference electrode were separated by the diaphragm fromthe Gooch asbestos (7) Measurements were conducted relatively to thelead reference electrode that is a metal lead of C1 grade being in contactwith the melt containing 5 mass of lead chloride

Potassium chloride lithium chloride chemically pure grade andlead chloride of pure for analysis grade were used for electrolytepreparation Glassy-carbon container (4) was placed on the cell bottomon the special fireproof brick support (8)

189

Current lead to liquid-metal reference electrode was realized in aform of molybdenum rod and to glassy-carbon crucible through graphitebar Current leads were protected from the contact with melt by alundumtubes closed with the rubber plugs (1) to keep the cell hermeticallyclosed

Fig 1 Electrolytic cell 1 ndash rubber plugs 2 ndash fluoroplastic cover 3 ndash thermo-couple 4 ndash glassy-carbon container 5 ndash quartz-glass sell 6 ndash workingelectrode 7 ndash diaphragm 8 ndash fireproof brick support 9 ndash current leads toelectrodes 10 ndash electrolyte 11 ndash reference electrode

4

1

2

5

6

8

93

10

11

Vacuum

7

Ar

190

The cell was pumped out and fullfilled with purified argon Laterit was put into the resistance furnace and heated until the giventemperature under the abundant pressure of the inert gas

The setup was equipped with the automatic system of temperaturestabilization Temperature measurement was performed with the help ofchromyl-aluminum thermocouple Content of components in electrolytewere being controlled before and after the experiment with the atomic-absorption method

Stationary polarization measurementsLead ion deposition processes in eutectic melt of lithium and

potassium chlorides were studied at 04 to 30 mol lead chloride intemperature range from 673 to 823 К Polarization curves are given onthe fig 2 and 3 Two characteristic areas are observed on thepolarization curves On the first area little potential deviations from theequilibrium value takes place with cathode current density increasing to008 Acm2

Experimental points on the area with 04 mol lead chlorideconcentration are on straight lines described by equationsE = - 00703lgi - 01203 and E = - 00775lgi - 0091 for 673 and 773 Кcorrespondingly

At temperature 673 К tg is 0070 мВ and at 773 К - 0078 мВAccording to the equation

Ftg

RT23

n (2)

we have n=19 for 673 К and n=20 for 773 КAt lead chloride concentration 30 mol experimental points on

the first area of the polarization curve is described by the equationE= - 00779lgi - 00877

Amount of electrons in the reaction calculated on the equation (2)is equal 2

Reaching current densities 011 012 020 и 032 Асm2 on thefig3 for 673 723 773 823 К temperatures correspondingly Potentialis greatly shifted to the negative area to the values -084 -084 -106and -110 correspondingly

At small values of cathode current density there is one wavecorrespondingly to the fig 4 In some time after current rise potential

191

reaches its stationary value at current density 0045 Асm2 for 35 s forcurrent density 0060 Асm2 for 30 s After current disconnectionpotential comes back to its equilibrium value

Fig 2 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

(04 mol ) melt

192

Fig 3 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

melt at 823 К depending on the lead chloride concentration Concentration oflead chloride in mol per cents 1 - 04 2 - 05 3 ndash 30

193

Fig 4 Engaging curves at 823 К temperature and the different current density

On the engaging curves at current density values corresponding tothe second characteristic area on the polarization curves on the figures 2and 3 two waves on figure 5 are seen Time of reaching stationarypotential tst decreases with the current density increasing (for currentdensity 012 Асm2 tst equals 85 s for current density 017 Асm2 tst -45 s)

Fig 5 Engaging curves at 04 mol lead chloride concentration currentdensity 012 013 017 Асm2 and 823 К

194

Processes taking places on the electrode can be described in thefollowing way On the first characteristic area of the polarization curvelead ion deposition happens

Pb2+ + 2e = Pb0 (3)The limiting current density of lead reduction increases with the

temperature and lead chloride concentration At 30 mol of leadchloride concentration and 823 K limiting current density ilim is 12Acm2

On the second characteristic area of the polarization curvedeposition of the alkaline metal is possible on the reaction

K+ + e = K0 (Pb) (4)Low values of the alkaline metal reduction potentials might be

connected with the process of alloy formation of alkali metal with leadK + 4Pb = KPb4 (5)

Chronopotentiometric measurements at lead deposition from LiClndash KCl (45-55 mol ) ndash PbCl2 melt at 04 mol lead chlorideconcentration were performed at 823 K and current density range from010 to 017 Acm2 There is only one wave on chronopotentiometriccurves under these conditions Values of product i12 depending oncurrent density are given in the table 1 where - transition time

Table 1 Values of product i12 at diverse current density

s i mAcm2 i12 mAcm2s12

095 170 165161 130 165181 120 162

262 102 165

It is seen that the product i12 does not depend on current

density at constant concentration of depolarizator 0OxC In the table 2

potential values Е4 at time equaling the forth of the correspondingvalues of transition time are given

195

Table 2Values of Е4 potential of different current density

i Acm2 s 4 s Е4 V

010 264 0660 -0061

012 181 0453 -0600

013 161 0403 -0061

017 095 0238 -0062

It is seen that the potential Е4 does not depend on the experimentconditions the current density in this case

Equation for the reversible process can be as follows

1ln

nF

RT21

4t

ЕЕ

(6)

for irreversible process

2100

1lnlnnF

RT

t

nF

RT

i

knFCЕ

fhOx (7)

where E ndash electrode potential 4E - measurement potential at frac14

of transition time R ndash gas constant F ndash Faraday number n ndash number

of electrons T ndash temperature - transition time 0OxC - depolarizator

concentration 0fhk - deposition speed constant

On the figure 6 dependencies Е -

1ln

21

t

and Е -

21

1ln

t at 04 mol of lead chloride concentration current

density 01 Acm2 and 823 K are given

196

y = -00835x + 00654

0002

0022

0042

0062

0082

0102

0122

0142

0162

-115 -065 -015 035 085

- E В

1 2

Fig 6 Dependencies 1ndashЕ=f

1ln

21

t

and 2-Е =f

21

1ln

t

From the analysis of given graphic dependencies follows that the

experimental points in coordinates E -

1ln

21

t

are in a straight line

with the confidence interval 095 The can be described by equation

08300650 E

1ln

21

t

(8)

The amount of electrons in the electrode reaction was calculatedfrom the equation

F

RTn

0830 (9)

hence n=2

197

It follows from the experimental conditions on lead ion (II)deposition that the process is reversible ie it is controlled by the speedof divalent lead ions mass transfer from the volume of melt to theelectrode surface

Diffusion coefficient of lead dichloride at 823 K was calculated onSandrsquos equation

20

2

)(

)(2D

oxnFC

i

(10)

Lead ions (II) diffusion coefficient are equal to 23310-

5сm2s It is in good accordance with the data obtained by other authors[5 6]

References1 Yurkinsky V Makarov D Electrochemical reduction of lead ions in

halide melts Russian J Applied Chem 1994 67 p 1283-12862 Yurkinsky V Makarov D The influence of cation composition on

kinetics of lead electrochemical reduction in chloride melts RussianJ Applied Chem 1994 68 p 1474-1477

3 Ryabukhin Yu And Ukshe E The diffusion coefficients of lead inmolten chlorides DAN SSSR 1962 145 p 366-368

4 Naryshkin I Yurkinsky V Oscillographic investigation oftemperature coefficients for some chlorides diffusion in LiCl-KClRussian J Electrochemistry 1968 4 p 871-872

5 Naryshkin I Yurkinsky V Voltammetry in molten salts Russian JElectrochemistry 1968 2 p 856-866

6 Raymond J Heus James J Egan Fused Salt Polarography Using aDropping Bismuth Cathode ndash J of the Electrochemical SocietyOctober 1960 p 824-828

7 Richard B Stein The Diffusion Coefficient of Lead ion in FusedSodium Chloride Eutectic ndash J Electrochem Soc 1959 vol 106 p528

8 Laitinen H A Gaur H C Chronopotentiometry in Fused LithiumChloride-potassium Chloride - Anal Chem Acta 1958 vol 18 p1-13

9 Hills GI Oxley I E Turner D W Silicates Ind 1961 vol 26 p559

184

REPAIR COMPOUND MODIFIED BY NANO PARTICLES OFFERROUS OXIDE

OS Tatarintseva SN Novosyolova TK UglovaInstitute for Problems of Chemical and Energetic Technologies SB RAS

Biysk Altai region Russia labmineralmailru

The results of influence study of nano-dispersed ferrous oxide oncharacteristics of the composite material developed earlier (compound)and intended to repair and recover engineering structures and massifshave been presented in this paper The compound consists ofmulticomponent polymer matrix including epoxy oligomer low-molecular synthetic rubber plasticizer and process additives filler and alow-temperature amine hardener Microcalcite with particle size lessthan 50 μm has been used as filler

The composite has been modified with nano powder of ferrousoxide (II) (manufactured by MACH I Inc USA) consisting of needle-like crystalline particles with average size 4 nm and having specificsurface area 2379 m2g

Experiments have shown that even distribution of nano particlesin epoxy resin is caused with a high-velocity mechanical device underthe additional influence of ultrasonic field

The most important things for low-viscosity repair compositionsapplied to recover the integrity of natural materials are high flowabilitydetermining the ability to fill narrow-opened fractures and stability ofstrength properties for a long time

The positive effect of ultra-dispersed modifier is seen within therange of 030-035 of its percentage in the composition as shown byresults of the study given in the Table At these amounts the maximumvalues of flowability and mechanical characteristics have been providedThe logical increase in samples density indicates the optimality of thepacking developed and reduction in the porosity of a composite materialthat is important while using it in conditions on high humidity

The compound developed is environmentally friendlyincombustible waterproof stable to heat vibration and long mechanicalloads and can be used to perform repair work in construction industrypublic service stone mining and processing industries and architecture

185

Table Percentage influence of ferric oxide nano powder on technicalcharacteristics of the composite material

Value at modifier percentage Characteristics

0 010 020 030 035 040

Dynamic viscosityat T = 20 oC Pamiddots

210 212 225 262 266 288

Flowability cm 48 48 48 52 53 45

Density gm3 141 141 143 145 146 146

Compressive forceMPa

79 78 79 82 86 74

Relative deformation

023 021 021 025 025 020

182

BASALT PLASTICS OF ENHANCED HEAT AND CHEMICALSTABILITIES

OS Tatarintseva NN Ноdakova VV SamoilenkoInstitute for Problems of Chemical and Energetic Technologies

of the SB RAS Biysk Russialabmineralmailru

The experience of the application of metal pipes for chemicalproductions cool and hot water supply systems transportation ofpetroleum products and other aggressive fluids has shown that they aregreatly subjected to corrosion that reduces their lifetimes to severalyears Therefore natural is the observed worldwide tendency ofreplacing steel and cast iron by composite materials of high chemicalstability and durability to which glass-reinforced plastic having acomplex of high service properties should primarily be relatedHowever requirements for composites have presently increasedespecially with regard to their heat and chemical stabilities andresistance to microorganisms ground and waste waters

The paper demonstrates the study results with respect to thedevelopment of a composite material for filament-wound pipe productswhich is superior in its basic parameters to analogous ones in the field ofglass-reinforced plastic application As a reinforced material basaltroving with higher strength characteristics and resistance to aggressiveenvironments as compared to a glass one was chosen the polymermatrix was a heatproof binder TS developed on the basis of nitrogen-containing epoxy resin synthesized Having rheological properties andstrength characteristics similar to those that are widely used in themanufacture of filament-wound glass-reinforced plastic products of thebinders EDI and EChDI the binder TS possesses enhanced heat stabilityand low viscosity at room temperature which permits the reduction ofpower inputs for its processing

The obtained data on advantages of both basalt fiber and thebinder developed have to the full extent been realized in laboratorysamples of the reinforced composite and in basalt plastic pipes producedindustrially (see Table below)

183

Table Temperature dependence of elastic modulus E of basalt plasticpipes

Еmiddot103 MPa at Т degСBinder 20 85 125 155 200

EDI 11701 11263 4363 3528 -EChDI 11277 10951 9944 6217 -

TS 19960 19336 19179 17557 9096

The 9-fold strength reserve of the basalt plastic pipes determinedwhen hydro-tested under extreme conditions (150degC 15 MPa) hasconfirmed the possibility of creating composite polymer materialsoperating under high-temperatures and humidity

164

FABRICATION AND MODIFICATION OF METALLICNANOPOWDERS BY ELECTRICAL DISCHARGE IN LIQUIDS

NV Tarasenko1 AA Nevar1 NA Savastenko2 EI Mosunov3 NZ Lyakhov4 TFGrigoreva4

1 Institute of Physics NAS B Minsk Belarus2 Leibniz-Institute for Plasma Science and Technology Greifswald Germany

3 The Institute of Machine Mechanics and Reliability NAS B Minsk Belarus4Institute of Solid State Chemistry and Mechanochemistry SB RAS

18 Kutateladze Str Novosibirsk 630128 Russia grigsolidnscru

Electrical-discharge technique was developed for preparation ofmetallic and metal-containing nanoparticles as well as for modificationof metal micropowders in liquids The morphology and composition ofthe nanopowders formed under various discharge conditions wereinvestigated by means of transmission electron microscopy and X-raydiffraction analysis The optimal conditions for the production oftitanium carbide and copper nanoparticles embedded in carbon layerswere found

IntroductionA synthesis of metallic and metal-containing nanopowders is of a

great interest due to their potential applications as super hard materials[1] environmentally friendly fuel cells with highly effective catalysts[23] and so on Transition metal carbides have been widely studied aselectrocatalysts because of their electrochemical properties andelectrical conductivities Nanosized carbon particles are suitable supportmaterials for certain types of catalysts Of particular interest for futurecatalytic applications are carbon-based materials with embeded metalnanoparticles [4] As long as carbon nanoparticles are relatively inertsupports many studies have been conducted in order to find which pre-treatment procedures are needed to achieve optimal interaction betweenthe support and metal species [5]

For any application of nanoparticles to be commercially viablelow-cost production methods have to be developed A low-temperatureand non-vacuum synthesis of nanoparticles via discharge in liquid(submerged discharge) provides a versatile choice for economicalpreparation of various nanostructures in a controllable way An arc

165

discharge in liquid nitrogen has firstly been reported as a cost-effectivetechnique for the production of carbon nanotubes in 2000 by Ishigamy etal [6] Since that time many efforts have been devoted to develop thismethod Sano et al proposed to submerge electrodes in water instead ofliquid nitrogen [78] They reported synthesis of carbon onions [78] andsingle-walled carbon nanohorns (SWNHs) [9] In latter case carbonnanoparticles were produced via discharge in water method with thesupport of gas injection Parkansky et al reported nanoparticlessynthesis via a pulsed arc submerged in ethanol Ni W steel andgraphite electrodes were used [1011] The particles composition variedfrom carbon to pure metal including various intermediate combinationsof these materials Bera et al employed an arc-discharge in a palladiumchloride solution to produce carbon nanotubes decorated with in situgenerated Pd nanoparticles [10] Importantly the synthesized materialcontained no chlorine

In this paper methods based on electrical-discharges in liquids forproduction of tungsten and titanium carbide as well as coppernanoparticles embedded in carbon nanostructures is reported Thecapabilities of arc and spark discharges submerged in liquids forsynthesis of nanoparticles as well as electrical-discharge modification ofmetallic powders were studied

Experimental detailsThe experimental reactor (Fig 1) consisted of four main

components a power supply system (pulse generator) the electrodes aglass vessel and a water cooling system outside the beaker A pulseddischarge was generated between two electrodes being immersed in 100ml of liquid (pure (995) ethanol or 0001 M CuCl2 aqueous solution)The appropriate combinations of pairs of metallic (tungsten titanium orcopper) and graphite electrodes were used The choice of ethanol wasmotivated by the fact that organic compounds play a role of a carbonsource to produce nanoparticles in discharge-in-liquid system [7 12]Addition of the copper chloride salt into double distilled water favoredthe activation of discharge process Metal (tungsten titanium or copper)and graphite rods with diameters of 6 mm were employed as electrodesAn optimum distance between the electrodes was kept constant at 03mm to maintain a stable discharge The discharge was initiated byapplying a high-frequency voltage of 35 kV The power supply

166

provided several different types of discharges Both direct current (dc)and alternating current (ac) arc and spark discharges were generatedwith repetition rates of 100 and 50 Hz respectively Current I(t) wasrecorded during the discharge as a function of time by means of anoscilloscope The peak current of the arc discharge was 9 A with a pulseduration of 4 ms The peak current of the pulsed spark discharge was 60A with a pulse duration of 30 μs

The synthesized products were obtained as colloidal solutionsAfter 15 min presedimentation the large particles precipitated at thevessel bottom The top layer contained the small nanoparticles wascarefully poured off into a Petry dish These suspended nanoparticleswere characterized by UV-Visible optical absorption spectroscopytransmission electron microscopy (TEM) and X-ray diffraction analysis(XRD) for their size morphology crystalline structure and composition

The optical absorption spectra of colloids were measured by UVndashVisible spectrophotometer (CARY 500) using 05 cm quartz cuvetteTransmission electron microscopy was performed by LEO 906E (LEOUK Germany) microscope operated at 120 kV A drop of solution putonto the amorphous carbon coated copper grid for TEM measurementsThereafter the liquid was evaporated at the temperature of 80 C Afterthe drying of colloidal solution the deposit obtained on the bottom ofPetri dish was examined by XRD Powder composition and itscrystalline structure were characterized by using X-ray diffraction atCuK (D8-Advance Bruker Germany)

Synthesis of carbide nanopowdersPromising capabilities of the developed technique for synthesis of

tungsten and titanium carbides (WC TiC) as well as carbon-encapsulated copper nanoparticles were demonstrated using theappropriate combinations of pairs of metallic and graphite electrodessubmerged into the appropriate solution Also physical and chemicalprocesses induced by the electrical discharges in liquids were studied tooptimize the process of nanoparticles synthesis

The results of nanoparticles preparation are summarized in theTable1 The synthesis rate varied in range of 2 ndash 40 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofmetal and graphite electrodes The synthesis rate increased withincreasing of discharge current and decreasing of pulse duration The

167

composition and morphology of nanoparticles were also found to dependon discharge parameters It should be noted that there is a possibility toscale-up the process

Table 1 summarized the variation in synthesis rate andcomposition of tungsten nanopowders with the discharge parameters Asa general tendency the synthesis rate was order of magnitude higher forspark discharge than that of arc discharge It may be due to thedifference in current value [13] For both arc and spark discharges itwas found that the synthesis rate is lower when tungsten was acting as acathode This result is consistent with literature data For example Beraet al reported that the consumption of anode is higher than that ofcathode [13]

Table 1 Summary of nanopowder synthesis conditions andresults of nanopowder characterization by XRD

XRD-analysisDischargetype

Electrodes Powdersyield

mgminW2Cvol

WC1-xvol

Cvol

Wvol

1 ac arc W C 02 71 781 147 -2 dc arc W(cathode)C(anode) 01 62 901 37 -3 dc arc W(anode)C(cathode) 02 66 715 219 -4 ac spark W C 25 58 328 614 -5 dc spark W(cathode)C(anode) 12 570 307 89 336 dc spark W(anode)C(cathode) 21 56 325 618 -

As it can be seen from the Table 1 the synthesized nanopowder isa mixture of hexagonal W2C face centered cubic WC1-x and graphite Nopeaks corresponding to WO were observed Nanopowder contained alsosmall amount body centered cubic W when synthesis was performed bydc current spark discharge with tungsten rod acting as cathode Here theparticular behavior of this discharge should be stressed showing ratherhigh ability to synthesize W2C Moreover in contrast to the other sparkdischarges synthesized material contained relatively small amount ofgraphite On the other hand applying tungsten as a cathode materialappears to reduce C content in nanopowder prepared via arc dischargetoo Generally the content of C is higher and content of WC1-x is lowerwhen synthesis was performed by spark discharge

168

Nanoparticles prepared by arc discharge were observed in theiragglomerated form The agglomerated nanoparticles were surrounded bythe grey regions which were probably graphite layers This typical viewwas seen everywhere in TEM images of product synthesized by arc forboth ac and dc current discharges irrespective of electrodes polarityThat fact implies that the morphology of synthesized nanopowders wasgoverned rather by the current pulse duration and value of peak currentthan the polarity of the electrodes Since nanoparticles were observed inthe agglomerated form it was difficult to measure their size correctlyWe suppose that approximately 4 nm nanoparticles are formed duringthe arc discharge in ethanol

Fig1 shows the TEM image of titanium carbide nanopowdersynthesized by spark discharge in ethanol As can be see from the Fig1the nanoparticles were also surrounded by graphite layers Fig 1demonstrates that the nanoparticles synthesized by spark were nearlyspherical with a mean diameter of ~ 7 nm The particle size distributionwas rather narrow (plusmn 2 nm) The XRD pattern of synthesized sample isshown in Fig 1 (right picture) The diffraction peaks at 60deg 418deg605deg 724deg 765deg and 407deg 504deg 590deg 667deg 741deg correspond tothe formation of cubic face-centered titanium carbide TiC and cubicprimitive TiC2 respectively There are some diffraction peaks with 2θvalue of 407deg 504deg 590deg 667deg and 741deg which can be assigned tothe hexagonal C The amount of TiC reached 887 vol The quantitiesof TiC2 and C in samples detected by XRD corresponded to ca 47 vol and ca 67 vol respectively

Fig 1 TEM image (left picture) of titanium carbide nanopowder synthesizedby ac spark discharge and XRD-pattern (right picture) of the sample

169

Synthesis of copper-carbon composite nanostructuresNumerous studies have focused on synthesis of metal-containing

carbon nanocapsules (CNCs) via submerged discharge method[89141516] Because of the carbon sheets surrounding the metal corethe CNCs are protected from the environment and from degradation Thecarbon coatings mean that nanoparticles are biocompatible and stable inmany organic media Thus carbon encapsulated nanoparticles arecandidate for bioengineering application high-density data storagemagnetic toners for use in photocopiers [81718] The metal containingcarbon nanostructures were prepared by using the electrode frommixture of graphite and metal precursor [16 1920] Recently Xu et aldemonstrated a possibility to synthesize Ni- Co- and Fe-containingCNCs by an arc discharge between carbon electrodes in aqueoussolution of NiSO4 CoSO4 and FeSO4 respectively [15] In contrast tothe data reported by Bera et al the synthesized material consisted of Oand S due to SO4

-2 ionic precursors in the solution Since the metal core-forming material was supplied by liquids the production rate of CNCswas limited by the salt concentration [4] This restriction may cause alimit to apply the submerged discharge method to the large-scaleproduction of CNCs

In this paper Cu-based nanoparticles were prepared viasubmerged discharge of bulk copper and graphite electrodes in a copperchloride (CuCl2) aqueous solution Thus material of copper electrode aswell as Cu from solution was supposed to be incorporated into theresulting nanoparticles The effect of discharge parameters and electrodecomposition on the morphology and composition of final products havebeen investigated Additionally synthesized material was modified bylaser irradiation The changes in nanoparticles morphology andcomposition were examined by transmission electron microscopy(TEM) X-ray diffraction (XRD) and UV-Vis spectroscopy

The six types of nanoparticles suspension were prepared underdifferent discharge parameters The synthesis parameters aresummarized in Table 2 As it can be seen the weight change of eachelectrode was generally higher when spark discharge was generatedThe anode consumption rate was higher than that of cathode irrespectiveto a discharge type and electrode material However in contrast to theliterature data [4] there was no cathode gain in weight As a generaltrend the nanopowder synthesis rate was higher for spark discharge than

170

that of arc discharge It may be explained by the difference in currentvalue [21] For both arc and spark discharges it was found that thesynthesis rate was higher when copper was acting as an anode There isa discrepancy between nanopowder synthesis rate and materialconsumption rate The values of discrepancy D listed in the Table 2were calculated as follows

100()

CCu

syn

RR

RD (1)

Here Rsyn is the synthesis rate of nanopowder RCu is theconsumption rate of the copper electrode and RC is the consumptionrate of the graphite electrode The discrepancy D depended ondischarge parameters For ac-discharges the value of discrepancy washigher for spark discharge than that for arc discharge For dc-discharges this trend remained if the polarity of electrodes was takeninto account It is worth to notice here that the discrepancy betweenmaterial consumption rate and nanopowder synthesis rate may be causednot only by separation of sediment fraction but by the reaction of carbonatoms with water resulting in the production of gaseous compounds [9]

Table 2 Summary of nanopowder synthesis parametersType of

dischargepeak currentpulse duration

Electrodes materialRCu and RC

mg min-1RSyn

mg min-1D

Cu 671 ac1) spark60 A 30 micros C 48

59 49

Cu 122 ac arc10 A 4 ms C 26

25 34

Cu (cathode electrode) 473 dc2) spark60 A 30 micros C (anode electrode) 61

21 81

Cu (anode electrode) 664 dc spark60 A 30 micros C (cathode electrode) 46

69 38

Cu (cathode electrode) 115 dc arc10 A 4 ms C (anode electrode) 25

19 47

Cu (anode electrode) 286 dc arc10 A 4 ms C (cathode electrode) 21

33 33

1) Alternating current pulsed discharge2) Direct current pulsed discharge

171

This coincides with the fact that the largest discrepancy (morethan 80) was observed in sample with the largest graphite electrodeconsumption rate (sample 3) For all samples the synthesized powderseparated into three phases one floating in suspension one settling atthe bottom as sediment and one as a layer of film-like material floatingon the liquid surface

The aqueous solutions of CuCl2 were discharge treated for only 20s to acquire yellowish suspensions The transparency of the suspensionsdecreased with the time during the discharge treatment The liquidsturned to dark yellow after treatment by ac-discharge for 10 min Thesuspensions resulting from dc-discharge treatment were conspicuouslydarker when C electrode was acting as an anode The nanoparticlessuspension produced by spark and arc discharges were dark brown anddark grey respectively It might be due to the presence of relatively largeamount of carbon particles in suspension (see Table 3) The dc-dischargetreated solutions were olive-green when Cu was used as the anodeelectrode Yellow or green colour of suspension may indicate theoxidation of copper nanoparticles [22] The presence of Cu2Onanoparticles was further confirmed by XRD analysis No changes incolour were observed after laser irradiation of suspensions

Figure 2 shows the absorption spectra of as prepared (a) and laserirradiated (b) suspended nanopowders synthesized by dischargetreatment of aqueous solution of CuCl2 (2) for 1 min The spectra werecorrected to the contributions of solvents The optical density increasedwith decrease in wavelength Generally the optical density ofsuspensions prepared by spark discharge was higher than that ofsuspension prepared by arc discharge This is consistent with the factthat the nanoparticles production rate was higher when the solution wastreated by spark discharge In the spectral range of 200 ndash 500 nm theoptical density of the samples 1 4 6 was higher than that of samples 23 and 5 This seems to suggest that the main parameter in determiningthe optical properties of suspensions was concentration of Cu-basednanoparticles For the samples number 1 and 4 a weak absorption peakwas observed at very short wavelength According to the literature data[2324] a surface plasmon peak at wavelength of 289 nm may beattributed to the presence of very small separated Cu nanoparticles (lt 4nm in size) Though TEM examination confirmed the presence of smallnanoparticles in sample 1 there were no nanoparticles with diameter less

172

than 4 nm in sample 4 Moreover there were no copper nanoparticles insample 1 as revealed by the XRD (see below) More likely theexistence of weak absorption peak at 280 nm implied formation of liquidbyproducts We did not observe in the absorption spectra surfaceplasmon band around 570 nm Missing of the plasmon band can beexplained by copper oxidation on the particle surface [23] Thissuggestion was further confirmed by XRD analysis (see below) Thesuspensions exhibited the same colours after laser irradiation butabsorption intensity increased for samples 3 1 and to the less extent forsample 5 as illustrated in Figure 2b TEM analysis revealed themorphological similarity of irradiated samples 1 3 and 5 (see below)

Figure 3 depicts the corresponding TEM images for thesuspensions shown in curves 1-6 of Figure 2 Parts (a) and (b) representthe TEM views of the as-prepared and irradiated samples respectivelyThree distinct structures were observed dark small spherical particlesdark particles surrounded by a gray shell and gray flake-like structureshaving diffuse contours The small dark particles with diameter 2-5 nmwere observed in samples 1 2 3 and 5 (marked with black ellipses inFigure 3) Some dark particles notable when using ac spark dischargefor synthesis were bigger than 20 nm indicating coalescence Thenanoparticles synthesized by ac arc discharge (sample 2) were

Fig 2 Absorption spectra for the as-prepared (a) and laser modified (b)suspended nanoparticles produced by ac- (12) and dc- pulsed discharges(3456) The following electrode pairs were used Cu and C for the ac-spark(1) and ac-arc (2) discharges Cu as a cathode electrode and C as an anodeelectrode for the dc-spark (3) and dc-arc (5) Cu as an anode electrode and C asa cathode electrode for the dc-spark (4) and dc-arc (6)

173

surrounded by the arrowed gray regions which were probably carbonshells as shown in Figure 3a

Fig3 TEM images of nanoparticles from as-prepared (a) and irradiated (b)suspensions produced by ac- (12) and dc- pulsed discharges (3456) Thefollowing electrode pairs were used Cu and C for the ac-spark (1) and ac-arc(2) discharges Cu as a cathode electrode and C as an anode electrode for thedc-spark (3) and dc-arc (5) Cu as an anode electrode and C as a cathodeelectrode for the dc-spark (4) and dc-arc (6)

174

As we did not have any direct evidence that the shells consisted ofcarbon these nanostructures will be referred further as core-shellnanoparticles The core-shell nanoparticles were also observed in colloidprepared by dc arc discharge between copper cathode and graphiteanode (sample 5) It can be seen that core-shell nanoparticles rangedfrom 20 to 50 nm in diameter while the cores within the nanoparticlesvaried from 8 to 25 nm The cores were non-spherical They seemed tocompose of small particles clustered together The flake-like structureswith diffuse contours were 50 nm in size They were observed in allsamples Samples 4 and 6 consisted mostly of structures with diffusecontours On the basis of the above observations the ac arc dischargeand dc arc discharge with copper anode electrode seemed to be moresuitable for synthesis of nanoparticles with core-shell structure

It is clear seen that many smaller particles with sizes around 2-7nm were generated after the irradiation of samples 2 4 and 6 Theparticles larger than 10 nm completely disappeared The micrographrevealed that after the irradiation these suspensions consisted ofparticles with circular cross-section whereas before the irradiation theparticle shape was not spherical The nanoparticles were dispersed verywell No small nanoparticles were observed in suspensions 1 3 and 5after the irradiation Though as can be seen by comparing Figure 1(a)3(a) and 5(a) with 1(b) 3(b) and 5(b) the shape of nanoparticleschanged after the irradiation The laser induced morphology change mayoccur through heating of the nanoparticles because of the absorption ofthe laser light [25] According to the mechanism proposed by Takami etal the morphology of irradiated nanoparticles was determined by therelationship between temperature of nanoparticles their melting andboiling point

The laser induced change in shape and size occurred if thetemperature of nanoparticles was at the boiling point If the temperaturewas lower than the melting point no changes took place If thetemperature was between melting point and boiling point only thechange in shape occurred Thus the difference in morphology of theirradiated samples can be attributed to the difference in theircomposition Even being irradiated with the same laser light intensitythe nanoparticles of different composition changed their morphology indifferent ways as they have different melting and boiling points

175

X-ray diffraction data were collected to identify synthesizedsamples The diffraction peaks at 432deg and 503deg correspond to theformation of faced-centered-cubic Cu There are three diffraction peakswith 2θ value of 365deg 423deg and 614deg which can be assigned to theprimitive cubic Cu2O Besides there are two peaks at 240deg and 265degwhich can be assigned to the hexagonal C XRD revealed that dischargetreatment of aqueous solution of CuCl2 led to the formation of Cu2

(OH)3Cl and Cu2OCl2 because of a strong affinity between chlorine andthe metal (peaks with a value of 2θ around 165deg 19deg 31deg 323deg 327deg330deg 387deg 398deg 401deg 503deg 505deg 538deg and 178deg 360degrespectively) For comparison the XRD patterns of initial solution ofCuCl2 are also plotted at the top of Fig 4 Non-treated aqueous solutionof copper chloride was allowed to evaporate and than analyzed by XRDThe diffractogram of this sample showed peaks at about 2θ around162deg 220deg 240deg 267deg 289deg 328deg 340 348deg 352deg 409deg 430deg448deg 453deg 490 and 573deg which are characteristics of CuCl2middot2H2O

XRD data were used to semi-quantitatively determine thepercentage of constituents The semi quantitative analysis of phasecomposition is shown in Table 3 The nanopowder composition wasstrongly dependent on the synthesis parameters It should be noted herethat metallic copper was only formed by dc-discharge treatment whencopper was acting as an anode electrode (samples 4 and 6) Synthesizedmaterial contained copper mostly in form of oxide (Cu2O) copperhydroxychloride (Cu2(OH)3Cl) and copper oxychloride (Cu2OCl2)Difference in Cu2O and C contents among all samples was significantSamples 2 and 5 contained no copper oxide while sample 6 had thelargest percentage of copper oxide (ca 80 vol) On the other handsample 6 contained no carbon The carbon contain in sample 4 exceeded80 vol The quantities of Cu2(OH)3Cl in samples ranged from lessthan 2 vol to ca 30 vol Only three samples contained Cu2OCl2

(samples 12 and 5) The maximal amount of Cu2OCl2 detected by XRDcorresponded to ca 30 vol In spite of high copper electrodeconsumption rate sample 4 contained unexpectedly small quantities ofCu and Cu-containing compound It might be due to the formation ofrelatively large and heavy copper microparticles They precipitated fromcolloid quickly after synthesis Therefore they were not collected andanalyzed by XRD (see experimental section) A correlation was

176

observed between low copper electrode consumption rate and absence ofCu and Cu2O fractions in nanopowder composition for samples 2 and 5

It should be stressed here that the core-shell structures wereobserved for only samples 2 and 5 Taking into account firstly thatsamples 2 5 and 6 were prepared by arc treatment secondly that thesample 6 contained no C and assuming that the shells consisted ofcarbon we can suggest that arc discharge was more suitable forsynthesis of core-shell nanoparticles On the other hand the chemicalcomposition of final product was governed by different competingreactions As they have different equilibrium constants they may form anetwork where the ratios of the products are sensitive to concentrationsof each of the many components Therefore the slight difference ininitial concentration might results in significant difference incomposition and morphology of synthesized material (compare samples5 and 6)

Although the exact mechanism for formation of nanoparticles viadischarge in solution process is not clear the following possibility may

Table 3 Semi-quantitative analysis of synthesized powder by XRD

XRD-analysisType of

dischargeElectrodesmaterial Cu

volCu2Ovol

Cvol

Cu2(OH)3Clvol

Cu2OCl2vol

1 ac1) sparkCuC

- 135 403 165 297

2 ac arcCuC

- - 646 300 54

3 dc2) sparkCu (cathode)C (anode)

- 391 370 239 -

4 dc sparkCu (anode)C (cathode)

78 83 825 14 -

5 dc arcCu (cathode)C (anode)

- - 339 336 325

6 dc arcCu (anode)C (cathode)

74 775 - 151 -

1) Alternating current pulsed discharge2) Direct current pulsed discharge

177

be considered During discharge treatment of the liquid copper andgraphite electrodes were heated melted and vaporized in the region ofthe discharge generated In the vicinity of electrodes the liquid was alsovaporized rapidly due to extremely high temperature Hence the plasmaregion produced by the discharge adjacent to the electrodes wassurrounded by a gas bubble Following Sano et al [8] the gas mixturemay comprise CO and H2 formed as follows

22 HCOOHC (2)

This reaction might cause the discrepancy between electrodeconsumption rate and nanopowder synthesis rate since some of carbonatoms formed gaseous CO Sano et al reported that gas bubbles didnot comprise water vapor since no condensation occurred [8] Howeverwe should consider that water vapour also existed in the discharge zoneas we did not obtain any evidence of its absence

Copper chloride is an anionic compound that dissociates inaqueous solution and may form different ionic species such as Cu2+ Cl-or complex ions such as CuCl2

- CuCl32- CuCl4

2-[26] The reduction ofcopper ions into copper atoms was likely taking place in plasma regionduring discharge treatment of the liquid as shown in Eq 3

02 2 CueCu (3)

As the temperature in the vicinity of the electrodes was estimatedto be around 4000 K [8] the thermal decomposition of complex ions tometallic copper possible took place in discharge zone (Eq (4-6))

20

2 ClCuCuCl (4)

20

3 322 ClCuCuCl (5)

202

4 2ClCuCuCl (6)

The nanoparticles were then formed from the complex gasmixture through different transformation stages namely nucleationgrowth condensation and coalescence Both the evaporated copper fromelectrode and Cu produced by reduction of ions from solutions were

178

supposed to be incorporated into the resulting nanoparticles Becausewater vapor existed in gas bubble the copper nanoparticles were easilyoxidized Reduction of copper oxide by carbon monoxide and hydrogenwas possible the subsequent step (Eq (7) and (8))

OHCuCOOCu 22 2 (7)

222 2 COCuHOCu (8)

According to the XRD measurements (see Table 3) copper oxidewas only partially reduced into copper in sample 4 and 6 The data ofXRD analysis implied also reaction of chlorine with copper andorcopper oxide to form Cu2Cl(OH)3 and Cu2OCl2 These reactions mightinvolve hydrogen produced via reaction (2)

It should be noted that there was no direct evidence to support theabove-mentioned formation sequence and the true mechanism may bemore complicated

ConclusionsFrom the results and discussion presented above the following

conclusions can be madeThe electrical discharge between two electrodes immersed in

ethanol is a suitable method to produce in a controllable waynanoparticles with different contents of metal and carbon By varyingthe current value and its pulse duration morphology of nanoparticlesand their composition can be changed The average diameters of theprepared nanoparticles were in the range of 3-7 nm

Cu-based nanoparticles with different morphologies wereprepared via submerged electrical discharge of bulk copper and graphiteelectrodes in a CuCl2 aqueous solution Synthesized material wassubjected to laser-induced modification It was found that core-shellnanoparticles were formed by treatment of CuCl2 aqueous solution bythe arc pulsed discharge with pulse duration of 4 ms and peak current of10 A

The synthesis rate varied in range of 19 ndash 69 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofcopper and graphite electrodes The synthesis rate was found to behigher when copper was acting as an anode electrode The synthesis rate

179

increased with increasing of discharge current and decreasing of pulseduration The composition and morphology of nanoparticles were alsofound to depend on discharge parameters The copper nanoparticleswere only formed by dc-discharge treatment when copper was acting asan anode electrode The maximum diameter of nanoparticles did notexceed 50 nm while the minimum diameter was around 2 nm Theresults of the experiments imply that plasma treatment with longer pulseduration and lower current leads to the formation of carbon embeddednanoparticles TEM confirms the formation of encapsulatednanoparticles

Irradiation of nanoparticles in aqueous solution by a pulsedNdYAG laser at 532 nm was found to cause the shape change and sizereduction of the particles

AcknowledgementsThe work has been supported by the Integral Program of the

Siberian Branch of RAS under the Grant 138-T-09-CO-014 Authorsare thankful to KV Scrockaya for carrying out the TEM investigations

References

1 I Zalite S Ordanyan G Korb (2003) Synthesis of transition metalsnitridecarbonitride nanopowders and application of them formodification of structure of hardmetals Powder Metallurgy Journal46 2143 ndash 147

2 XG Yang and CY Wang (2005) Nanostructured tungsten carbidecatalysts for polimer electrolyte fuel cells Appl Phys Lett 8624104-1 -224104-3

3 M Rosenbaum F Zhao U Schroder F Scholz (2006) InterfacingElectrocatalysis and Biocatalysis with Tungsten Carbide A High-Performance Noble- Metal-Free Microbial Fuel Cell Angew Chem118 1-4

4 D Bera S C Kuiry M McCutchen S Seal(2004) In situ syntesis ofcarbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method J Appl Phys 96 5152-5157

5 P Serp M Corrias P Kalck Carbon nanotubes and nanofibers incatalysis Applied Catalysis A General ndash 2003 ndash Vol 253 ndash P337-358

180

6 Ishigami M Cummings J Zettl A Chen S (2000) A simple method forthe continuous production of carbon nanotubes Chem Phys Lett319 457-459

7 Sano N Wang H Alexandrou I Chhowalla M Amaratunga G A J(2001) Nanotechnology Synthesis of carbon ldquoonionsrdquo in waterNature (London) 414 506-507

8 Sano N Wang H Alexandrou I Chhowalla M Teo K B KAmaratunga G A J (2002) Properties of carbon onions produced by anarc discharge in water J Appl Phys 92 2783 ndash 2788

9 Sano(a) N (2004) Low-cost synthesis of single-walled carbonnanohorns using the arc in water method with gas injection J PhysD 37 L17-L20

10 Parkansky N Alterkop B Boxman R L Goldsmith S Barkay ZLereah Y (2005) Pulsed discharge production of nano- andmicroparticles in ethanol and their characterization PowderTechnology 150 36-41

11 Parkansky N Goldsmith S Alterkop B Boxman R L Barkay ZRosenberg Yu Frenkel G (2006) Features of micro and nano-particlesproduced by pulsed arc submerged in ethanol Powder Technology161 215-219

12 P Muthakarn N Sano T Charinpanitkul W TanthapanichakoonT Kanki Characteristics of Carbon Nanoparticles Synthesized by aSubmerged Arc in Alcohols Alkanes and Aromatics Phys Chem Bndash 2006 ndash Vol 110 37 ndash P 18299 -18306

13 D Bera G Johnston H Heinrich S Seal A parametric study on thesynthesis of carbon nanotubes through arc-discharge in water Nanotechn ndash 2006 ndash Vol 17 ndash P 1722-1730

14 Hsin Y L Hwang K C Chen R-R Kay J J (2001) Production and insitu metal filling of carbon nanotubes in water Adv Mater 13 830-833

15 Xu B Guo J Wang X Liu X Ichinose H (2006) Synthesis of carbonnanocapsules containing Fe Ni or Co Carbon 44 2631-2634

16 Lange X Sioda M Huezko A Zhu Y Q Kroto H W Walton D R M(2003) Nanocarbon prodction by arc discharge in water Carbon 411617 ndash 1623

17 Sergienko R Shibata E Akase Z Suwa H Nakamura T Shido (2006) Carbon encapsulated iron carbide nanoparticles synthesized in

181

ethanol by an electric plasma discharge in an ultrasonic cavitationfield Mater Chem Phys 98 34-38

18 Leo G H Jeong S H J W Ri H C (2002) Excelent magnetic propertiesof fullerene encapsulated ferromagnetic nanoclusters J Magn Mater246 404 ndash 411

19 Ang K H Alexandrou I Mathur N D Amaratunga G A J Hag S(2004) The effect of carbon encapsulation on the magnetic propertiesof Ni nanoparticles produced by arc discharge in de-ionized waterNanotechnology 15 520 ndash 524

20 Sano(c) N Nakano J Kanki T (2004) Synthesis of single-walledcarbon nanotubes with nanohorns by arc in liquid nitrogen Carbon42 686-688

21 Bera(c) D Jonston G Heinrich H Seal S (2006) A parametric studyon the synthesis of carbon nanotubes through arc-discharge in waterNanotechnology 171722-1730

22 Yeh M-S Yang Y-S Lee Y-P Yeh Y-H Yeh C-S (1999) Formationand characteristics of Cu colloids from CuO powder by laserirradiation in 2-propanol J PhysChem B 103 6851-6857

23 Aslam M Gopakumar G Shoba T L Mulla I S Vijayamohanan K(2002) Formation of Cu and Cu2O nanoparticles by variation of thesurface ligand preparation structure and insulating-to-metallictransition J Colloid Inter Sci 25579-90

24 Salkar R A Jeevanandam P Kataby G Aruna S T Koltypin YPalchik O Gedanken A (2000) Elongated copper nanoparticlescoated with a zwitterionic surfactant J Phys Chem B 104 893-897

25 Takami A Kurita H Koda S (1999) Laser-induced size reduction ofnoble metal particles J Phys Chem B 1031226-1232

26 Brown JB (1948-1949) The constitution of cupric chloride inaqueous solution Transaction of the Royal Sociaty of New Zeland 7719-23

162

MORPHOLOGICAL STUDY OF DETONATIONSPRAYED COATINGS OF CALCIUM HYDROXYAPATITE

DEPOSITED ON A NANOSTRUCTURED TITANIUMSUBSTRATE

AA Sitnikov VI Yakovlev YuP Sharkeev 1EV Legostaeva 1 AA Popova

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1Institute of Strength Physics and Materials Science SB RASTomsk

Biocompatible coatings are effectively formed by spraying ofcalcium hydroxyapatite Са10(РО4)(ОН)2 powders on a titanium substrateRecently along with the composition macro- and microstructuredevelopment the surface morphology of the coatings has receivedincreasing attention In a number of studies the roughness of thecoatings has been shown to significantly influence the inductionprocesses of cells As a substrate material titanium VT1-0 has beenchosen which has several advantages being highly biocompatiblebioinert practically non-toxic corrosion-resistant and possessing lowthermal conductivity and low coefficient of thermal expansion Themorphology of the gas-detonation sprayed calcium phosphate coatingsdeposited on ultrafine-grained and nanostructured titanium substratesand implant imitations has been studied The substrates and implantimitations were produced in the Institute of Strength Physics andMaterials Science SB RAS Tomsk

It was shown that the detonation sprayed hydroxyapatite powderswith particles ranging from 1 to 20 microm formed coatings non-uniform inthickness and phase composition The roughness of the coatings wasRa=365-472 microm (class 5) When hydroxyapatite particles of 20-100microm in size are sprayed coatings more uniform in thickness and phasecomposition are formed (Fig1) with an average roughness of Ra = 624microm (class 4) Preliminary treatment of the titanium substrate by sandingand chemical etching allows increasing the adhesive strength of thecoating up to 20MPa

163

Fig1 SEM images hydroxyapatite powder (a) detonation sprayedhydroxyapatite coating (b) XRD pattern of the coating (c)

Biological studies have demonstrated biocompatibility andbioactivity of the coatings It was found that the calcium phosphatedetonation sprayed coatings induce growth of tissue cells with 100probability which indicates that the relief of the coatings is optimal forfixation and aging of the cells Comparative studies of calciumphosphate coatings produced by detonation spraying and those producedby micro-arc in an electrolyte containing phosphoric acidhydroxyapatite and calcium carbonate have shown the advantages ofdetonation spraying for providing the required phase composition of thecoating This opens up a possibility of making two-phase coatings(hydroxyapatite and beta-calcium phosphate) ensuring the closest matchin composition to the bone tissue

ва б

100

200 20 30 40 50 60 70 80 90 10

(1

10) (002

) (2

10)

(2

11)

(

300

)

(3

10)

(

222

)

312

)

(3

20)

(

511

)

(

432

)

(5

22)

(

100

)

161

MICROSTRUCTURE STUDIES OF THE COATINGSPRODUCED BY ARC DEPOSITION OF THE

MECHANOACTIVATED SHS-COMPOSITE TIC+XME(R6M5 PR-N70H17S4R4-3) POWDERS

AA Sitnikov VI Yakovlev MA Korchagin1MN Seidurov ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

One of the main challenges in the development of new materialsfor arc deposition using flux-cored wires is to design materials of specialinterest using cost-effective and ecologically friendly technologies Asmaterialstechnologies meeting these requirements we can proposelayered composites produced by self-propagating high-temperaturesynthesis (SHS) in mechanically activated powder mixtures

The samples of SHS-mechanocomposites of TiC+XMe (R6M5PR-N70H17S4R4-3) composition arc-deposited on steel 45 substrateswere selected for investigations Microstructure of the arc-depositedcoatings was studied using a Carl Zeiss AxioObserver A1m OpticalMicroscope For observations cross-sections of the samples wereprepared and etched with a solution containing 20 potassiumferricyanide К3[Fe(CN)6] 20 КОН and 60 H2O Finemicrostructure and composition of the deposited layers were analyzedusing a Carl Zeiss EVO50 Scanning Electron Microscope equipped withan EDS X-ACT laquoOXFORDraquo device

The investigations show that the microstructure of the depositedlayers is uniform with submicron titanium carbide reinforcing phase inthe form of separate inclusions or chains of particles in the matrix

159

WEAR-RESISTANT DETONATION SPRAYED COATINGSBASED ON THE COMPOSITE MECHANICALLY ACTIVATED

SHS-MATERIALS

AA Sitnikov VI Yakovlev MA Korchagin 1DM Skakov AA Popova ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

The application of titanium carbide as a material for thermalspraying is rather difficult mainly due to its high melting temperatureand high hardness

A technology has been developed abroad for the production of thecomposite powders for spraying The production of these compositepowders is a laquoknow-howraquo of MBN Nanomaterialia (Italy)

An approach to the development of TiC-containing coatings canbe based on the technology of mechanocomposites with metallic orintermetallic matrices reinforced with nanosized particles of a ceramicphase [1] The technology of the powder preparation consists of 3 stagesAt the first stage the mixture of initial reactants which in this particularcase are titanium carbon and nichrome is mechanically activated (MA)in a planetary ball mill At the second stage self-propagating hightemperature synthesis (SHS) is conducted resulting in the formation ofTiC particles uniformly distributed in the metallic matrix AdditionalMA of the products of SHS at the third stage along with dispersingtitanium carbide particles creates a principally new state of the matrixwhich experiences grain refinement and shows high internal stresses andhigh concentrations of non-equilibrium defects In addition thesubsequent mechanical activation can be advantageously used forcompositions with higher matrix contents that are not possible to makethrough the SHS special additives can be also introduced into thecomposites at this stage

In order to compose the initial mixtures the following powderswere used titanium PTM lampblack PM-15 and nichrome PR-N70H17S4R4-3 Mechanical activation of the powder mixtures and theSHS-products was carried out in a planetary ball mill AGO-2M

160

Detonation spraying was performed using the laquoKatun-Mraquo set-upIt was found that the chemical composition did not change duringspraying

Wear resistance of the sprayed coatings was evaluated using afriction machine 2168 UMT in the laquoshoe-on-diskraquo mode A coating 02mm thick was deposited on a steel 40 shoe Prior to deposition the shoewas rubbed against the disk until a contact spot was formed over thewhole surface of the shoe After the coating was deposited the workingsurfaces were subjected to abrasive diamond treatment to reduce theirroughness

Tribological tests showed that with increasing metallic matrixcontent from 20 to 60 wt the weight losses under dry friction at 950 Nincreased almost twice Comparative tests of the coatings and thesamples of hardened steel revealed that the wear of the coatings obtainedfrom the mecahnocomposite powders was 8 times lower than that ofsteel 40H

References1 MAKorchagin DVDudina Application of self-propagating high-

temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007 v43 2 p176-187

153

CHEMICAL-THERMAL TREATMENT IN CARBONMANGANESE STEEL

AT INDUCTION-HEATING IN VARIOUS BORATINGCONDITIONS

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

Ural Federal University Ekaterinburg RussiaAltay State Agrarian University Barnaul Russia

Abstract Processes of borating of high-carbon manganese steel65Mn by carbide of boron and amorphous boron in conditions of fluxwith additives of various activators of borating are investigated at high-speed induction-heating It is shown that the nature of the boratingagent the additive of flux activators CaF2 and NH4Cl have influence onstructure and properties which are formed on a surface of boroneutectics

Keywords boron carbide of boron induction heating chemical-thermal processing

Among modern processes of chemical-thermal treatment (CTT)production engineering of saturation of surface layer constructional andalloy steels with boron ndash the borating occupy a special place In boratingit is possible to obtain the extended beds distinguished by high hardnessand strength corrosion-resistance abrasive durability and highreceptivity to wear on a surface of a steel detail [1 2] However themajority of known processes of borating are prolonged and are badlybuilt in into flow diagrams of state of productions

Intensification of CTT processes and in particular borating canbe carried out with application of technology of short-term high-speedheating of steel detail surface with the borating composition put on herrf currents (RFC) up to temperatures of formation of new phases andeutectics (1100-1350 оС) in systems Fe-B Fe-B-C and Fe-Me-B-Cwhere Ме - is an alloy element from group Cr Mn Ni etc [3] Unlikewell investigated processes of borating of alloy steels by mediums anddaubing at temperatures up to 950оС [4] there are open generalquestions of peculiarities of chemical interaction of components in suchsystems phase condition and properties of formed products

154

In the present work chemical-thermal treatment of carbonmanganese 65Mn steel combined with RFC-heating of its surface invarious borating conditions has been investigated

Experimental partAs the basic subject of research 65Mn (GOST 4543-71) alloy

carbon steel was chosen from the group of the same kind manganesechromos chromos-nickel and chromos-manganese steels from group 70U8А 50CrMnА 30CrMnSiА 45Cr 70Mn etc with similar propertiesand composition

Technical carbide of boron B4С in accordance with GOST 5744-85 and reactive amorphous boron of qualification reagent-grade weretaken as borating agents of different nature Known composition for theinduction deposition (F1) consisting of borax glass the boric anhydridecalcium silica and welding flux АN-348А (30 Na2B4O7 20 B2O310 CaSi2 and 40 flux АN-348А) was used as flux Reagent-gradeCaF2 and NH4Cl served as activators

RFC-heating of samples was carried out in a loopback water-cooled copper inductor by diameter of 160 mm connected to RF-lampgenerator VCG 7-600066 The adjustment of a contour and geometryof an inductor provided heating of researched samples to the temperatureof 1300-1350оС during 40-60 sec with the subsequent stabilizationAfter holding at the specified temperature during from 1 up to 2 minsamples were pulled out from an inductor and cooled down loosely

Microstructure of the coverings formed has been investigated andthickness of borated bed has been determined (МIМ-7 Neophot-30)hardness has been measured (PМТ-3 by 50 100 g) phase composition(DRON-2 radiation Co-Kα speed of angular moving of a sample of 1grads min) has been determined

Results and discussionIt is known that classical production engineering of kiln borating

are based on gradual (during 05-6 h) saturation of a surface of a steelproduct by boron from various pastes daubings liquid or a gaseous fluidat temperatures of process from 750 up to 950 оС Thus in the capacityof sources of boron its various compounds (В2О3 В4С ВF3 Na[BF4]etc) are applied capable to decay on active elements at temperatures ofprocess Depending on a phase condition of the borating agent hardness

155

and liquid borating are distinguished and also borating from a gas phase[4] We investigated six variants of mixes for high-speed borating atRFC-heating steel 65Mn Mixes differed in the nature of the boratingagent e borating agent composition presence fluxes componentsactivators and technological additions Compositions of the mixes usedare given in table 1

Table 1

Mixes Boratingagent

Activator Flux

Iа B4C (84) NH4Cl (6) F1 (10)II B4C (84) ndash F1 (16)

IIIа B (90) CaF2 (5) F1 (5)

Mixes I Iа II and IIа used as borating agent contained carbide ofboron mixes III IIIа - amorphous boron in mix Iа activator chloride ofammonium and in mix IIIа - fluoride of calcium has been added allmixes contained melted flux as a fluxing component for inductiondeposition F1

With decrease of density of a borating phase and increase intemperature of process its speed in the interval of temperatures from 800up to 950 оС increases insignificantly therefore for their intensificationcollateral saturation of a surface by several elements at once or thermocycling are applied [5] If the temperature of the process exceeds 1100-1300 оС in an aspect of beginning processes of high-temperaturestructural reorganization in steel speeds of borating sharply increase in2-4 min with the increase in temperature at every 15-20 оС thus theprocess passes from a diffusive zone to a zone of chemical reaction Soat the temperature of 1200-1300 оС according to the data[6] it ispossible to obtain in a few minutes the thickness of the single-phaseboron-bed up to 02-04 mm thus heating of a detail is carried out by thespecial thermo reaction mix

At RFC-heating of the steel 65Mn covered by researched boratingcompositions with chosen parameters of process fig 1 adamantinecoverings are formed on all samples resembling bed covered hard metalX-ray analysis of a material of coverings has shown presence of Fe

156

borides FeB and Fe2B carbon-borides Fe3(C B) and Fe23(C B)6 variousmeta- and orto-borates of iron (Fe3BO3 Fe3BO6 Fe3BO5) traces FeOand FeOFe2O3 Thus at RFC-heating of alloy carbon steels under bedof flux F1 containing from 84 up to 90 of borating agents complexboron-phases are formed on their surfaces hardening a surface of a detailand it is strongly linked with it and oxide films are removed togetherwith slag

To find out the characteristics and structure of received beds andthe conditions of borides in them photomicrography of micro sectionswas taken Typical structures of boron-beds are given in fig 1

a b C

Fig 1

As it is seen from fig1 with the chosen heating environments andthe time of borating the structure and the condition of boundary line ofreceived wear-resistant beds differ but in all cases as against classicalboron two-phase beds on a surface of samples the eutectic with stronglypronounced or with the diffusive boundary line separating it from anoriginal material is formed faster in conditions of heavy abrasive sign-variable and shock wear boron-plate Apparent changes in structure ofparent metal caused by its short-term overheat were not observed

For the mixes containing in the capacity of borating agent equalquantity of carbide of boron similar quantity of fluxes-component anddistinguished only by the presence of activator NH4Cl promoting areinforcement of convertible diffusive and transport reactions especiallyat low temperatures right at the beginning of the process of borating (Т

157

lt300 оС) formation of fine grained structure of eutectic turnings on withhardness not above 700-750 HV thickness of bed of 016 mm and withlegibly discernible interface with parent metal (fig 1а) is observed

For the analogous mix II without this activator the expressedpropagation of dendrites islands and druses of boron-phases withhardness up to 1050-1120 HV thickness of bed of 028 mm and adiffuse interface boron bed with parent metal (fig 1b) is observed Themixes on the basis of amorphous boron (fig 1c) appeared to be the mostreactive thus in mix IIIа containing follow-up 5 of activator CaF2 and5 of fluxes component beyond chosen relationships for 1 minthickness of bed on steel of 65Mn has made 088 mm at its hardness in2200-2300 HV The structure represents the remote eutectichomogenized iron ndash boron formed with such speed that from a melt atits solidification balls of slag had not time to bleed up to the end

Thus amorphous boron which at the presence of flux F1 andactivator CaF2 under the chosen conditions of experiment forms denseclose-grained beds on a surface of alloy steels with depth up to 800microns with hardness up to 2400-2500 HV (fig 2) appeared to be themost efficient borating agent at RFC-heating

Fig 2

It is interesting to note that the structure of the wear-resistantcovering obtained at high-speed 1 min borating steel 65Mn a mix II ismetastable and at borating during 2 min like in picture 1а with hardness2300-2400 HV turns to the fine grained structure and thickness of a

158

covering does not change and the interface with parent metal becomesdiscernible

References1 Methods of raise of longevity of machine components Red VN

Tkacheva M 19712 Belyj AV Karpenko GD Myshkin KN Structure and methods of

formation of wear-resistant surface layers M 19913 Tkachev VN Fishtejn BM Kazintsev NV Aldyrev DA

Induction overlaying welding of hard metals M 19704 Voroshnin LG Lyahovich LS Borating of steel M 19785 Guryev АМ Kozlov EV Ignatenko LN Popova NA Physical of

a basis of thermal-cycle borating Barnaul 2000

138

PHASE STATES OF MECHANOACTIVATED MANGANESEOXIDES

SA Petrova RG Zakharov AYa Fishman LI LeontievInstitute of Metallurgy Ural Division of RAS Ekaterinburg 620016

Russian Federation

An investigation of structural characteristics of the manganeseoxides in order to understand these characteristics affected bymechanochemical treatment conditions has been undertaken Chemicallypure manganese (II III IV) oxides were used as the initial componentsIt is shown that the properties of the mechanoactivated oxides differgreatly from those of initial materials Relationships among structuralcharacteristics of the mechanoactivated oxides and their prehistory wayand conditions of producing have been detected

IntroductionStudy of phase states of mechanoactivated oxides makes it

possible to analyze the patterns of expression of the mechanochemicaleffect in redox processes to determine the mechanism of the effect ofactivation processes on the type and parameters of the structural phasetransitions to establish the role of higher oxides in the redox processesAs one of the consequencies of the intensive mechanical activation is theappearance of nanodisperse states specificity of phase transformationsin nanocrystalline oxides is considered at the same time

It is known now that the decrease in the crystallite size inmechanoactivated systems causes a decrease of structural phasetransition temperatures In metallic alloys reducing of crystallites size isaccompanied by suppression of martensitic transitions [1-2] Completeinhibition occurs when the grain size becomes smaller than that of thecritical nucleus of a new phase It can be regarded as established that theparameters of phase transitions in oxides with relatively lowtemperatures of phase transitions also depend strongly on the grain sizeFor example in barium titanate BaTiO3 transition from cubic to low-symmetry phase is completely suppressed when the grain size is about10 nm [3] Changes in the crystal structure and the effects of reduction(the change of temperature and phase transition heat) in the structuralphase transitions with decreasing grain size also occurred for the oxides

139

Al2O3 Fe2O3 PbTiO3 PbZrO3 La1-xSrxCuO4 YBa2Cu3O7-δBi2CaSr2Cu2O8 [4] and several other oxides [5-6] Besides for the oxidesin nanoscale state the coexistence of two different structuralmodifications [7] was observed The processes of mechanoactivationmay also lead to new types of metastable phase states due to theredistribution of cations between the crystallographically inequivalentsublattices [8]

In the present work the main attention is paid on the analysis ofthe effects associated with the evolution of metastable structures underconditions of temperature increase and oxide interaction with anaggressive environment So far the main contribution to theinvestigation of these issues has made the study of metallic alloys (seefor example [9-10]) The behavior of the activated oxide materials ismuch less studied Study of structural phase transitions in the systemMn-O subjected to mechanochemical activation and structuralcharacteristics of the crystalline phases allows us to test how general arepreviously established patterns for systems with different types ofchemical bonds

The effect of mechanical activation on structural phase transitionsboth of martensate type (from cubic to tetragonal modification Mn3O4)and those accompanied by redox processes (between phases withdifferent degrees of oxidation etc) is investigated The choice of Mn-Ooxides as the object of study is largely connected with the fact that atleast two structural phase transitions observed in the considered crystalswith temperature changes involved the cooperative Jahn-Teller (JT)phase The value of the JT deformation in it is determined by theconcentration of JT ions in octahedral sites that allows to get additionalinformation about the structural changes caused by themechanoactivation of oxide

1 Production and structural properties of themechanoactivated oxides

11 Mechanoactivation of manganese oxidesPure manganese oxides MnO2 Mn2O3 and Mn3O4 annealed at

200deg 900deg and 1250degC respectively were used as the initial materialsFor the mechanical treatment of oxides which was described in

detail in [1112] a planetary mill AGO-2 with water-cooled drums (V =

140

150ml) and a centrifugal factor up to g = 60 [3] was used Download ofballs was 203g the material - from 5g Milling was made dry Theprocessing of powders was carried out after preliminary lining in acontinuous mode or with periodic stops of the mill According toestimates (performed by XPES) contamination by iron was not morethan 02 Previously [14] we found that prolonged continuousmechanical treatment leads to the fact that within the grains matureduring the first seconds along with a further (slow) reduction ofcoherent scattering blocks chemical processes begin leaking Because atthis stage the main purpose was to obtain single-phase samples theduration of continuous grinding was restricted by 30s The temperatureinside the drums during grinding did not exceed 320K which ensuredthe preservation of initial metastable phases During stops of mill thedrums where opened and powder was manually stirred but samplingwas not performed

To be able to conduct magnetic research on the mechanicallyactivated samples and to investigate the effect of intensity ofmechanoactivation (the degree of deformation) on the redox processesand the stability of weakly activated oxides the part of samples wasobtained as a result of mechanical activation in the vario-planetary millPulverizette 4 (Fritsch) in glasses of tungsten carbide Volume of drumwas equal to 250ml loading of crushing balls was 800g and a materialmass was 20 g Milling was made dry the duration was 3 min

12 Attestation of mehanoactivated manganese oxides andmethods of their experimental study

The phase composition of obtained substances the size ofcoherent scattering domains (CSD) and microstresses were determinedby X-ray diffractometer D8 ADVANCE (Bruker) (radiation CuKα Ni-filter position-sensitive detector VANTEC1) High-temperature X-raystudies of the stability of mechanoactivated oxides was carried out usinghigh-temperature chamber HTK1200N (Anton Paar)

The particle size of powders obtained was assessed by dynamiclight scattering using a laser analyzer DelsaNanoC (Beckman Coulter)and an atomic force microscope Solver-Next (NT-MDT) Surface ofoxides was studied by XPES and STEM (Omicron Multiprob)

High-temperature X-ray studies were performed in the range 30-1200degC in air The rate of heating and cooling was 05degCmin Step of

141

the temperature during heating and cooling was 5deg and 10degCrespectively Exposure in the point was 17s (the time of isothermal delayshooting diffractogram was 150s) For the analysis of diffractionpatterns the software package DIFFRACplus [15] was used

13 Results and discussionThe results of the attestation of the initial and mechanoactivated

oxides are presented in Table 1

Table 1 Treatment conditions and characteristics of the manganeseoxides

Cell parameters Initial phasetreating mode

Finalcomposition аAring сAring

Samplename

1 Mn2O3- initial Mn2O3 9412 M232 Mn2O3- AGO 30s Mn2O3 9410 M23A303 Mn2O3- AGO 60s Mn2O3 9410 M23A604 Mn2O3- AGO

10minMn2O3 9410

M23A10

5 Mn2O3- P4 3min Mn2O3 9403 M23P46 Mn2O3-

P4(3min)+USD(70s)Mn2O3 9403

M23P4U

7 Mn3O4-initial Mn3O4 5760 9474 M348 Mn3O4- AGO 30s Mn3O4 5762 9442 М34А309 Mn3O4- AGO 60s Mn3O4 5762 9431 M34A60

5787 950810 Mn3O4- AGO10min

Mn2O3+ Mn3O4

9410M34A10

11 MnO2-initial MnO2 4396 2869 M1212 MnO2- AGO 30s MnO2+Mn2O3(tr) 4397 2872 М12А3013 MnO2- AGO 60s MnO2+Mn2O3(tr) 4397 2872 M12A6014 MnO2- AGO 10min Mn2O3 9408 M12A10

AGO-High-energy planetary mill (60g) P4-Pulverisette 4 (~20g)USD-Ultrasound disintegrator

Since the analysis of the results of mechanoactivation of oxidesMn2O3 showed little difference between the samples activated in theAGO within 30 and 60 seconds further investigation of oxides Mn3O4

and MnO2 was performed on 60-second samples However it is

142

necessary to note that in the case of oxide MnO2 samples after 30 and60-second milling contained different amounts of Mn2O3

According to X-ray phase analysis data chosen mode ofmechanochemical treatment allowed to preserve essentially thecomposition of the initial oxides The exceptions were oxides MnO2which after grinding contained 5 of oxide Mn2O3 and Mn3O4 whichafter grinding for 10 minutes contained a few of Mn2O3

Data on grain size and the coherent scattering domains arepresented in Table 2 It is obvious that even a relatively weakmechanical treatment leads to a decrease in grain size in 2-3 times Inthis case the comparison of grain size and the CSD (comparison of thedynamic light scattering data and X-ray diffraction (XRD) results)shows that the mechanical treatment with a small degree of deformationallows to obtain defect-free grains while increasing of the centrifugalacceleration leads to the appearance and rise of the defects in the grainA tendency to agglomeration of grains with increasing time of intensemechanoactivation should be noted

Table 2 The characteristics of coherent-scattering domains and averagegrain size

Sample nameCoherent-scattering domain

nmGrain size nm

M23 gt200 1026plusmn95M23A30 30 436plusmn168M23A60 23 344plusmn155M23A10 24 939plusmn175M23P4 44 386plusmn50

M23P4U 44 336plusmn22M34 gt200 400plusmn801300plusmn300

M34A60 15 529plusmn340

M34A10 1913 795plusmn104

M12 gt200 428plusmn78M12A60 61 1133plusmn167M12A10 22 565plusmn343

XRD-dataDynamic light-scattering

data

143

Changes in phase composition during heating and cooling ofinitial and mechanically activated manganese oxides are presented inTables 3-4 and Fig 1-2

Comparison of the temperature behavior of the initial unactivatedoxide Mn2O3 and that of grinded for 3 minutes with a force of less than20g shows that mechanoactivation treatment with a small amount ofcentrifugal factor and short times can save not only the phasecomposition but apparently and generally does not alter the propertiesof the powder While increasing the degree of exposure (eg use of millssuch as AGO-2 with acceleration 60g) even at short times leads to achange in system characteristics (the appearance and growth of defectsredox processes) that affect later on behavior of oxide For examplemechanoactivation treatment leads to a shift of phase transitiontemperaures at thermal processing as well as to change of the structuralcharacteristics of the phases formed In particular to different degrees oftetragonal distortion of hausmannite formed during heating Mn2O3 (Fig4)

Table 3 The phase composition of the initial andmechanoactivated manganese oxides at different temperatures

Heating CoolingSample MnO2 Mn2O3 Mn3O4 Spinel Mn3O4 Mn2O3 Phase

1 2 3 4 5 6 7 8- + 920 1140 1120 - appearanceM23

- 955 1170 1010 + - disappear

- + 950 950 1010 - appearanceM23A30

- 995 1105 730 + - disappear

- + 950 950 1040 - appearanceM23A60

- 1000 1120 840 + - disappear

- + - 950 840 840 appearanceM23A10

- 1000 - 290 + 770 disappear

- + 940 1140 1120 - appearanceM23P4

- 980 1165 1080 + - disappear

- + 935 1140 1120 - appearanceM23P4U

- 980 1170 1050 + - disappear

144

1 2 3 4 5 6 7 8

- 685 + 1125 1090 - appearanceM34

- 945 1160 1010 + - disappear

- + appearance370

655

970 1050 -

disappear

900 appearance

M34A60

-

970

1130

880 + -

disappear

- + + 930 880 - appearanceM34A10

- 1005 655 600 + - disappear

+ 550 950 1155 1120 870 appearanceM12

595 1025 1170 1070 + + disappear

+ + 940 985 1110 750 appearanceM12A60

535 985 1165 840 + + disappear

- + 960 960 1000 790 appearanceM12A10

- 1005 1075 630 + + disappear

Table 4 The temperature boundaries of the phases during heating andcooling

Heating CoolingSample Phase

from to from to

1 2 3 4 5 6

Mn2O3 30 955 - -

Mn3O4 920 1170 1120 30

M23

Spinel 1140 1200 1200 1010

Mn2O3 30 995 - -

Mn3O4 950 1105 1010 30

M23A30

Spinel 950 1200 1200 730

Mn2O3 30 1000 - -

Mn3O4 950 1120 1040 30

M23A60

Spinel 950 1200 1200 840

Mn2O3 30 1000 840 770

Mn3O4 - - 840 30

M23A10

Spinel 950 1200 1200 290

145

1 2 3 4 5 6

Mn2O3 30 980 - -

Mn3O4 940 1165 1120 30

M23P4

Spinel 1140 1200 1200 1080

Mn2O3 30 980 - -

Mn3O4 935 1170 1120 30

M23P4U

Spinel 1140 1200 1200 1050

Mn2O3 685 945 - -

Mn3O4 30 1160 1090 30

M34

Spinel 1125 1200 1200 1010

Mn2O3 370 970 - -

Mn3O4 30 655

Mn3O4 900 1130

1050 30

M34A60

Spinel 970 1200 1200 880

Mn2O3 30 1005 - -

Mn3O4 30 655 880 30

M34A10

Spinel 930 1200 1200 600

MnO2 30 595 - -

Mn2O3 550 1025 870 30

Mn3O4 950 1170 1120 30

M12

Spinel 1155 1200 1200 1070

MnO2 30 535 - -

Mn2O3 30 985 750 30

Mn3O4 940 1165 1110 30

M12A60

Spinel 985 1200 1200 840

Mn2O3 30 1005 790 30

Mn3O4 960 1075 1000 30

M12A10

Spinel 960 1200 1200 630

146

a d

be

c fFig 1 The temperature boundaries of the phases during heating and coolingof initial and mechanoactivated Mn2O3 a - original b - M23P4 c -M23P4U d-M23A30 e-M23A60 f-M23A10

147

a

b

cFig 2 The temperature boundaries of the phases during heating and cooling of

initial and mechanoactivated Mn3O4 a-initial b-M34A60 c-M34A10

148

a

b

cFig 3 The temperature boundaries of the phases during heating and cooling ofinitial and mechanically activated MnO2 a - initial b - M12A60 c - M12A10

149

Fig 4 Temperature dependence of the degree of hausmannite tetragonaldistortion for samples with different prehistories

The growth of the crystallite size of mechanoactivated phase withtemperature is shown in Fig 5 Data are shown for the initial phasebelow the temperature of the corresponding phase transition

It is obvious that prolonged treatment in the high-energy millalmost did not give reduction of coherent scattering domains butessentially affected the thermal stability of investigated oxide

150

Fig 5 Temperature dependences of coherent scattering domain size in oxideMn2O3 with varying degrees of mechanoactivation

ConclusionThe main results of investigations are the followingI The conditions of mechanochemical treatment enabling to make

the transfer of Mn-O system to single-phase nanosized state withoutsignificant changes in composition of the initial oxide are found Theexception was oxide MnO2 which after grinding contained a smallamount of oxide Mn2O3

II It is shown that the use of mill of the type AGO-2 with 60gacceleration even at short times of activation treatment of oxides leadswhile maintaining the single-phase of sample to an appreciable changeof lattice parameters growth of stresses and the appearance of defects

III It is found that despite the relaxation character of the evolutionof these metastable structures in the face of rising temperatures there is ashift of phase transition temperatures and changes in structuralcharacteristics of the newly formed phases in comparison with the initialoxides Including marked changes in the parameters of the JT strain (ca

151

- 1) at high-temperature transitions between cubic and tetragonal phasesof oxide Mn3O4

IV It is shown that more prolonged mechanical activation ofoxides MnnOm activates redox processes in these materials theemergence of two-phase states with different degrees of oxidation andeven a complete change of the manganese oxidation degree

V The temperature boundaries of existence of phases duringheating and cooling were determined for the initial andmechanoactivated oxides MnnOm Not only noticeable quantitativedifferences in the position of phase boundaries but also qualitativedifferences in the constructed phase state diagrams were found

This work was supported by RFBR (grant 10-03-96016-p_ural_a) the Program of fundamental research of Presidium ofRussian Academy of Sciences N 27 ldquoFoundations of fundamentalresearch of nanotechnology and nanomaterialsrdquo and the Federal TargetProgram Scientific and scientific-pedagogical staff of innovationRussia (contract 02740 110641)

References1 Glezer AM Blinov EN Pozdnyakov VA Martensitic

transformations in microcrystalline ferro-nickel alloys Izvestiya Aseries of Physical 2002 V66 N9 pp1263-1275

2 Andrievsky PA RAGULYA AV Nanostructured materialsMoscow Academy 2005 192p

3 Polotai AV Ragulya AV Skorohod VV Nanocrystalline BaTiO3

synthesis sintering and size effect Science o Sintering CurrentProblems and New Trends Beograd Kluwer Academic Publishers2003 pp119-125

4 PAyyub VRPalkar SChattopadhyay et al Effect of Crystal SizeReduction on Lattice Symmetry and Cooperative Properties PhysRev B 1995 V51 N9 pp6135-6138

5 Parathasarathi Mondal Dipten Bhattacharya Pranab ChoudhuryDielectric anomaly at orbital order-disorder transition inLaMnO3+ J Phys Condens Matter 2006 V 18 p6869

6 Nandini Das Parathasarathi Mondal Dipten BhattacharyaPartical size dependence of orbital order-disorder transition inLaMnO3 Phys Rev B 2006 V74 p 014410

152

7 VYa Shevchenko OL Khasanov GS Yuriev etc The coexistence ofcubic and tetragonal structures in the nanoparticle of ZrO2Y2O3

oxides Neorg Mater 2001 V37 N9 pp1117-11198 AYa Fishman MA Ivanov SA Petrova et al Specific Features of

Jahn-Teller Structure Phase Transitions in NanocrystallineMaterials Defect and Diffusion Forum 2009Vols 283-286 pp53-58

9 Grigorieva ТF Barinova AP Lyakhov NZ Some features of themechanical alloying in the systems Cu-Bi and Fe-Bi J Metastableand Nanocryst Mater 2003 V15-16 pp475-478

10 Lyakhov N Grigorieva T Barinova A Lomaeva S Yelsukov EUlyanov A Nanosized mechanocomposites and solid solution inimmiscible metal systems J Mater Sci 2004 V39 N 16-17pp5421-5423

11 Zyryanov VV Journal of Structural Chemistry 2004 V45 pp135-143

12 Zyryanov VV Lapina OB Neorg Mater 2001 V37 N3 pp331-337

13 Zyryanov VV Sysoev VF Boldyrev VV Korosteleva TVCertificate of authorship of USSR N 1375328-BI-1988 N 7 p39

14 Fishman AYa Ivanov MA Petrova SA Zakharov RGStructural Phase Transitions in Mechanoactivated ManganeseOxides Defect and Diffusion Forum 2010 Vols 297-301 pp 1306-1311

15 DiffracPlus TOPAS Bruker AXS GmbH OstlicheRheinbruckenstraszlige 50 D-76187 Karlsruhe Germany 2008

118

EFFECT OF HARDENING TEMPERATURE ON THE STRUC-TURAL-MORPHOLOGICAL CHARACTERISTICS OF METAL

CEMENTS BASED ON MECHANOSYNTHESIZED COPPERCOMPOUNDS

NZ Lyakhov1 PA Vityaz2 SA Kovaleva2 TF Grigoreva1VG Lugin3 AP Barinova1 SV Tsybulya4

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS630128 Novosibirsk Kutateladze str 18 grigsolidnscru

2 United Institute of Mechanical Engineering NAS Minsk Belarus3 Belarussian State Technological University Minsk Belarus

4 G K Boreskov Institute of Catalysts SB RAS Novosibirsk Russia

IntroductionMetal cements may be used in many branches of industry due to

good adhesion to the materials of different types (glass ceramics metalsetc) and the metal character of thermal and electric conductivity Theformation of metal cements occurs through the interaction of copper(nickel) alloys with liquid metals and alloys Interactions of a solid metalwith liquid one in particular copper with gallium are known [1 2] tohave diffusion character they are substantially affected by temperatureand the area of contact between the reagents

The use of mechanically synthesized copper compounds allowsone to increase the contact surface between the components and to intro-duce doping elements (Bi In) that improve wettability during gluing andthe strength properties of the alloys to be formed This causes a changeof the kinetics of interaction between a solid metal and a liquid one dueto the acceleration of diffusion processes and due to the formation ofadditional phases

The goal of the present work is investigation of the effect of hard-ening temperature on the structural-morphological characteristics ofmetal cements obtained on the basis of CuBi mechanocomposites andsupersaturated solid solutions Cu(In)

Methods and materialsCopper powder PMS-1 (GOST 4960ndash75) granulated bismuth (TU

6-09-3616ndash82) indium (GOST 10297ndash94) were used in the work Me-chanical activation of the powders was carried out for 15 min in the

119

high-energy ball planetary mill AGO-2 with water cooling in argon at-mosphere (cylinder volume 250 cm3 ball diameter 5 mm loaded wt200 g the weighed portion of the sample under treatment 10 g the fre-quency of rotation of the cylinders around the common axis about 1000rpm) Mechanocomposites having the composition Cu 10 wt Bisolid solutions Cu-12 wt In were obtained [3] Diffusion-hardeningalloys were prepared by mixing the mechanosynthesized copper com-pounds with gallium melt followed by exposure at a temperature of 20C during the whole process of alloy formation To study the effect oftemperature on the structure and morphology of metal cements harden-ing was carried out at 90 С 120 С and 160 С

Surface examination was carried out with the NT-206 atomicforce microscope (Microtestmachines Gomel) using standard commer-cial V-type probes NSC11 (Mikromasch) in the contact mode

The structure of the resulting samples was studied using Mikro200 optical microscope and high-resolution scanning electron micro-scope (SEM) MIRATESCAN with an attachment for micro-X-ray spec-tral analysis (MXSA) The diameter of the electronic probe was 52 nmexcitation region was 100 nm Images were obtained in the mode of re-cording secondary and backward scattered electrons which allowed usto investigate the distribution of chemical elements over the surface andto establish its composition non-homogeneity

The phase composition of powders after mechanical activationand the final products of their interaction with liquid gallium were de-termined with the help of X-ray diffraction techniques X-ray structuralanalysis and semi-quantitative examination of the products were carriedout with the D8 Advance Bruker diffractometer (Germany) by means ofpowder X-ray diffraction in the θ-2θ configuration with a step of 01Phase identification was performed using the diffraction patterns re-corded in CuKα radiation (154051 Aring)

Calorimetric measurements were carried out with Netzsch STA409 PCPG instrument in argon atmosphere in a crucible made ofAl2O3 within the temperature range from room temperature up to 290 Cwith the heating rate of 20 min

120

Results and discussionIt was established in the previous diffraction studies of alloy for-

mation dynamics in CuBi + Ga and Cu(In)+Ga that the formation ofnew phases takes place within a broad time interval During the interac-tion of CuBi mechanocomposite in Bi that is insoluble in copper and ingallium the formation and crystallization of the intermetallic compoundCuGa2 and bismuth take place simultaneously [4]

For the case of Cu(In) solid solution in which the doping elementis soluble in gallium the formation of the phase of solid solution of in-dium has an incubation period of about 210 minutes which is determinedby its concentration in the system with gallium [5]

The interaction processes are described with the following chemi-cal reactions

CuBi + 2 Ga rarr CuGa2 + BiCu(In) + 2 Ga rarr CuGa2 + In(Ga)

1 Effect of the temperature of interaction of CuBimechanocomposites with liquid gallium on the structure andmorphology of the formed metal cementsIt is known that the resulting mechanocomposites are nanosized

copper surrounded by a thin bismuth layer [6] Bismuth is mainly com-posed of the particles less than 5 nm in size

According to the data of AFM topography the size of mechano-composite particles is 150divide250 nm (Fig 1)

Fig 1 Mechanocomposite Cu + 10 wt Bi after activation for 15 mina ndash SEM image b ndash AFM c ndash TEM

121

At first we studied the interaction of CuBi with liquid gallium atroom temperature

The X-ray structural analysis of the resulting cement carried outafter the interaction for 4 and 48 hours showed that the size of the crys-tallites of the intermetallic compound increases from ~ 200 nm to ~ 550nm The size of bismuth crystallites increases up to 100 nm It should benoted that this is accompanied by a decrease in the size of copper crys-tallites down to ~ 10 nm The final phase composition is determined asCuGa2 Bi and unreacted copper (Fig 2)

Fig 2 Diffraction patterns of the product of interaction Cu 10 Bi + Ga

Figure 3 shows the high-resolution SEM images of the micro-structure of the surface of the final interaction product The SEM imageof sample surface after hardening without the mechanical treatment ofthe surface is shown in Fig 3a The image of the surface obtained in thebackward scattered electrons after sample polishing is shown in Fig 3bBecause bismuth is the heaviest element in this system it will be distin-guished by the maximal brightness in the SEM image

The data obtained by means of microscopy show that the structureof the surface of final product is facetted tetragonal crystals СuGa2 withthe size up to 4 μm Bismuth is localized at the faces of crystals and at

122

the boundaries of CuGa2 grains as disperse formations 70-250 nm insize and also forms separate grains with a size up to 10 μm

a bFig 3 Topography of the surface of CuGa2 +Bi alloy after the interaction for48 hours a ndash SEM image of non-polished sample in direct electrons b ndash SEM

image of the polished sample in backward-scattered electrons

The use of AFM allowed us to study the microstructure of facet-ted tetragonal CuGa2 crystals The presence of screw dislocations inthem may be stressed as a result the crystalline layer grows by windingcontinuously on itself so the step takes the shape of a spiral (Fig 4) Thelayer-by-layer growth of crystallographic facets should also be men-tioned The edges of incomplete layers or steps move along the facetwhile they grow The step height that is the thickness of the depositinglayer varies within the range 4 to 200 nm The appearance of highgrowth steps may cause trapping of the melt drops and precipitation ofinsoluble bismuth admixture on the surface of steps of the growing crys-tals which is indeed observed in Fig 4 b Bismuth is adsorbed on facetssteps and along the grain boundaries

It should be stressed that the growth of faceted crystals requiresspecial conditions supersaturation or supercooling of the mother me-dium small number of appearing nuclei We suppose that the localthermal supercooling arises as a consequence of the chemical interactionof copper with gallium melt on the interface between the solid phase andthe liquid one with the formation of chemical compound CuGa2 withcrystallization temperature higher than the temperature of the melt Theconditions of substantial supercooling are created for this compound soits crystallization starts In this process bismuth particles get released

123

into the melt Thee particles are insoluble in liquid gallium and may actas the centres of crystallization and also they may brake down thegrowth of intermetallide particles by getting adsorbed on their surfaceThe latent heat of melting released during crystallization raises the tem-perature of the melt (so gallium remains in the liquid state during reac-tion at 20 C) and decreases the degree of overcooling thus creating theconditions for the growth of larger facetted intermetallide crystals fromthe melt

а b

Fig 4 AFM image of the surface of resulting alloy CuGa2 + Biа - Torsion-image of bismuth on facets and growth steps of CuGa2 (the contrastis formed due to the difference in tribological characteristics of the phases of

intermetallide and bismuth) b ndash layered spiral growth of CuGa2 crystals alongthe screw dislocation (marked with arrows) The upper part shows a scheme ofcrystal growth along the screw dislocation and the shape of the step formed inspiral growth [7]

At room temperature the final product of the interaction of CuBimechanocomposite with liquid gallium is a matrix composed of CuGa2

intermetallide particles 1ndash4 μm in size with bismuth particles distrib-uted in it (from 70 to 250 nm) which form local agglomerations up to 10μm in size

X-ray studies of the alloys obtained at hardening temperature of90 and 120 C showed that an increase in temperature to 120 C does notaffect the phase composition Similarly to the case of room temperature

124

the product is composed of intermetallide CuGa2 (PDF-2 No 25-0275)bismuth (PDF-2 No 44-1246) and residual copper (PDF-2 No 04-0836)(Fig 5)

Fig 5 Diffraction patterns of CuGa2 + Bi samples obtained at temperature 40(a) 90 (b) and 120 (c) C Unmarked peaks relate to CuGa2 intermetallide

With an increase in the interaction temperature the lattice pa-rameters of copper and CuGa2 phases remain almost unchanged Thesize of copper crystallites is about 35 nm Bismuth undergoes tempera-ture-caused changes An increase in the size of bismuth crystallites from100 nm at 20 C to 180 nm at 90 C and to more than 500 nm at 120 C

Alloys obtained by mixing the CuBi mechanocomposite with liq-uid gallium have a composite structure after hardening Their structuremay be described as an intermetallic shell with the unreacted part ofcopper in its centre The СuGa2 intermetallide has a shape of facetedtetragonal crystals up to 4 μm in size With an increase in reaction tem-perature to 90 C the size of het particles of intermetallic compund in-creases to 6-8 μm and remains almost the same at a temperature of 120C In the lateral contrast mode the facets of crystals obtained at 90 and120 C exhibit local accumulations of bismuth as well as substantial de-formation distortions of crystals due to the arising stretching strain inthe crystal in the direction lt001gt (Fig 6) Intermetallide crystal starts to

125

have layered structure The facets of the intermetallide obtained at ele-vated temperatures also exhibit deformation distortions that are likelyconnected with bismuth adsorption on the facets The appearance ofthese lines is due to the development of local fluidity They arise in thecases when the material possesses a distinct yield point even insignifi-cant concentration of strain promotes the appearance and developmentof these figures [8] Change of the straight character of the glide lines islikely to be connected with the effect of boundary volumes intra-grainstructural strain caused by differences in the volumes of the intermetal-lide and bismuth as well as by glide in different systems and with thetransition from one system to the other

а

b

Fig 6 AFM images of CuGa2 + Bi alloys obtained at a temperature of 90 (a)and 120 (b) С

126

Metallographic in-vestigation of the alloysurface after polishing(Fig 7) showed that thenumber of macrodefectssuch as pores and discon-tinuity flaws decreaseswith an increase in crystal-lization temperature Mi-crohardness of the inter-metallide increases fromHV 70 to 125

Investigation of thedistribution of chemicalelements over the sampleby means of SEM involv-ing X-ray spectral analysisrevealed nonuniformity ofthe distribution of insolu-ble bismuth

Bismuth is not ob-served in the regions withthe intermetallic com-pound which may be con-nected with the fine distri-bution of disperse particlesover the boundaries of theintermetallide Local ac-cumulations of bismuth upto 10 μm in size are ob-served mainly in the siteswhere macrodefects (poresgrain boundaries) get ac-cumulated With an in-crease in the temperature ofinteraction up to 120 Сthe number of local bis-muth accumulations de-

а

b

cFig 7 Optical images of the structure of

CuGa2 + Bi alloys obtained at 20 (a) 90 (b)and 120 (c) С

127

creases but their size increases to 20 μm (Fig 8)

а b

Fig 8 SEM images (in backward scattered electrons) of CuGa2 + Bi alloyHardening temperature а ndash 20 С b ndash 120 C

Thermal investigation of the alloys with different hardening tem-perature points showed that the curves of differential scanning calo-rimetry (DSC) exhibit definite differences only during heating the alloyswith hardening temperature 20 C and 90 C The DSC curves of the al-loys with hardening temperature 90 and 120 С are identical Duringheating the alloy with hardening temperature 20 С exhibits the exother-mal heat effect at a temperature of 120-150 С This effect may be con-nected with the occurrence of recrystallization processes in bismuthThis exo-peak is absent during the repeated heating

Thus investigation showed that an increase in the temperature ofthe interaction of CuBi mechanocomposite with liquid gallium leads toan increase in the size of the formed intermetallide as well as to a de-crease in macrodefects in the form of pores discontinuity flaws cracksThe hardness of the intermetallide thus increases

2 Effect of the temperature of interaction of mechanochemi-cally prepared solid solution Cu (In) with liquid gallium onthe structure and morphology of metal cementThe use of mechanochemically prepared powders of Cu-In system

as the solid phase in the reactions with liquid gallium increases the num-

128

ber of interacting systems due to the solubility of indium in gallium Ac-cording to the state diagram of the system GandashIn [9] the solubility of Inin Ga in the solid state is less than 03 at while the solubility of Ga inIn is 31 at At a temperature of 60 С indium may be dissolved in liq-uid gallium up to 48 wt

Mechanochemically synthesized powder in the system Cu + 12wt In was used as the initial solid-phase component The X-ray phaseanalysis of the products of mechanochemical synthesis (Fig 9) showedthat the solid solution of indium in copper in formed during mechanicalactivation of copper powder with 12 wt indium As a result the latticeparameter of copper increases to а = 36659 Ǻ (аref = 36150 Ǻ) The size of copper crystallite is about 30 nm

Fig 9 X-ray diffraction patterns of the powder Cu-12 wt In after mechanicalactivation (for 20 min) in argon

Mechanical activation of the system Cu + 12 wt In leads to theformation of fine particles of the solid solution of indium in copper (150ndash 230 nm) (Fig 10) Recrystallization of the solid solution of copper andthe formation of grains larger than 15 μm are also possible

129

Fig 10 Topography of the ultrafine powder of the solid solution Cu(In)

A decrease in the size of precursor powder is known to providelarger area of contact between the components of the solid phase and theliquid one and therefore shorter diffusion distances during subsequentinteractions with metal melts Because both copper and nickel are solu-ble in liquid gallium one may expect that the rate of dissolution of themechanocomposites of the system Cu-In would be significant

X-ray phase analysis of the final products of the interaction of thesolid solution Cu(In) with gallium at room temperature revealed thepresence of three phases intermetallide CuGa2 indium and unreactedcopper (Fig 11)

Fig 11 Diffraction patterns of the alloys obtained through the interac-tion of Cu 12 wt In + Ga CuGa2 - In - Cu

130

For the initial powder with indium concentration 12 wt theproduct of the interaction exhibits a decrease in the indium unit cell pa-rameter с in the alloy under formation to с = 49306 Ǻ (cref = 49459 Ǻ) The size of copper crystallites is about 7 nm while the size of indiumcrystallites is about 30 nm Slight changes in the unit cell volume of in-dium may be related to the formation of the solid solution of gallium inindium

During the interaction indium gets dissolved in the liquid phaseof gallium gets concentrated and crystallizes at the interfaces betweenthe solid phase and the liquid one The alloys with the 12 indium con-tent are characterized by a large range of the dimensions of tetragonalparticles of the intermetallic compound CuGa2 (from 05 to 8 μm) TheAFM image (Fig 12) exhibits coarse crystals their crystallographicshape is uncharacteristic of the intermetallide CuGa2 Comparing the X-ray data and the results of AFM we may assume that they are a solidsolution of gallium in indium

Fig 12 AFM topography of the surface of CuGa2+ In(Ga) alloy

A decrease in the AFM scanning pitch and simultaneous acquisi-tion of the image of distribution of normal (topography) and lateral (tor-sion) forces allowed us to distinguish the structural features of the phaseof the solid solution of gallium in indium (Fig 13) A specific distin-guishing feature is the presence of strands in the crystals of the solid so-lution of gallium in indium connected with layering of the solid solutioninto the regions with larger and smaller concentration of the componentwhich is well seen in the image of torsion (Fig 13b) The size of separate

131

grains of the solid solution of gallium in indium reaches more than 10μm

Fig 13 AFM topography of the surface of samples of CuGa2+ In(Ga) alloy (а)image of torsion (b)

Fig 14 The SEM image in direct (а) and back-scattered electrons (b) of thealloy CuGa2+ In(Ga) In the upper part the data chart of the quantitative spec-

tral analysis carried out in the indicated points

To investigate the microstructure of the surface of alloys we car-ried out the examination with the scanning electron microscope and ob-tained the images of the surface of resulting alloy for the interaction Cu12 wt In + Ga in direct (Fig 14а) and back-scattered (Fig 14 b) elec-trons The application of imaging in back-scattered electrons allow one

132

to investigate the composite surface non-uniformity with which the in-tensity distribution over the image depends on the atomic number of anelement One can see in Fig 14 b that the contrast in the BSE images isdetermined by the topographic features of the surface and the distribu-tion of intensities is uniform In addition local X-ray spectral analysiscarried out in different points of the alloy surface revealed the presenceof indium in concentrations 01 to 7 This fact allows us to concludethat indium is present on the surface of CuGa2 intermetallic crystals inthe form of thin films

Another characteristic feature of the surface of samples obtainedin the interaction of solid solutions Cu(In) with liquid gallium is thepresence of fine dispersed formations on the surface of crystals andgrains of CuGa2 that are more clearly seen in the AFM images (Fig 13a) and are detected in the SEM images (Fig 15 b) The formation of thestructures of this kind on the surface of the intermetallide may be con-nected with indium crystallization on the surface of the growing crystals

Fig 15 AFM (a) and SEM images (b) of the face of CuGa2 intermetallic ob-tained by the interaction of Cu 20 In + Ga

So on the basis of X-ray spectral data obtained and the results ofAFM and SEM we may assume that indium gets crystallized not only inthe form of large grains of the phase of the solid solution of gallium inindium but also on the faces of the intermetallide thus forming a nano-meter-sized film of indium about 10 nm thick

133

In order to establish the effect of temperature on the structure andmorphology we carried out alloy hardening at temperature of 60 120and 160 C

X-ray structural investigation of the final phase composition (Fig16) of the alloys showed that no changes in the phase composition of themetal cement are observed with an increase in hardening temperature to160 C The parameters of intermetallic compound CuGa2 remain almostunchanged The values of lattice parameters of the indium phase underformation are also insignificantly differing from the reference ones

Fig 16 Diffraction patterns ofCu-In-Gа samples obtained at

different temperatures

Investigation of the microstructure of alloys obtained at 20 Cshowed that indium is well adsorbed on the surface of intermetallidecrystals and crystallizes not only as separate crystals of the solid solutionof gallium in indium but also as the film formations with grained anddendrite structure on the faces of the intermetallide The occurrence ofintercrystal films of indium or the solid solution of indium may be re-sponsible for a decrease in strength characteristics of the alloy and be areason of both the intra-crystal and inter-crystal fractures (Fig 17 b) It

134

is assumed that an increase in hardening temperature causes substantialformation of the film structures of the solid solution of indium

The AFM investigation of the topography of alloys obtained attemperatures 90-160 C showed that the alloys are characterized by alarge size range of the intermetallic compound CuGa2 At the interactiontemperature of 20 C the size of CuGa2 particles was 05 to 8 μm Withan increase in reaction temperature to 90 C the crystal size increases upto 11 μm Crystal concretions are also formed (Fig 17) One can see inFig 17 b that cracks are formed in the grain plastoelastic deformationson the intermetallide face occur which is likely to be due to the differ-ence in interfacial surface tension of the intermetallide and indium film

ab

Fig 17 AFM image of the surface of CuGa2 + In(Ga) alloy obtained at 90 C a- topography b ndash distribution of lateral forces (arrows show cracks deforma-

tion distortions)

At a temperature of 120 and 160 C the contrast of the surface re-lief decreases due to the formation of a continuous film (Fig 18) on thesurface

Investigation of the phase transitions in the alloys was carried outby means of DSC For heating the products of the interaction betweenthe solid solution of indium in copper and liquid gallium at a rate of30Cmin an endothermic effect is observed on the DSC curves of all thealloys at a temperature about 254 C and an exothermic effect at 290 Con cooling the exothermic peak appears at a temperature of 210-220 С

135

а b

Fig 18 AFM topography of the CuGa2 + In(Ga) alloy a ndash 120 C b- 160 C

According to the Cu-Ga state diagram these effects are connectedwith the peritectic transformations of the main phase of intermetallideCuGa2 during heating and cooling The cooling curves exhibit no ther-mal effect due to the phase transition of indium The DSC curve of thealloy obtained at 20 C contains an endothermic peak at about 130 Cwhich gives much smaller heat effect in the second heating cycle Tak-ing into account the fact that the formation of indium films and the solidsolution of indium with the grained and dendrite structures occurs on thesurface of the intermetallide it may be assumed that heating to 130 C isaccompanied by melting of the indium film (taking into account a de-crease in melting temperature for thin films) [10] and the solid solutionIn(Ga) At the temperature of the peritectic transformation 254 C in-dium gets dissolved in the formed liquid Ga(Cu) with subsequent for-mation of the ternary compound Cu-Ga-In during cooling For coolingthe temperature of the peritectic reaction for the obtained compound de-creases to 210-220 C

ConclusionAs a result of the investigation of the structure and morphology of

metal cements prepared on the basis of mechanosynthesized coppercompounds CuBi and Cu(In) the structure and morphology in the reac-tions with liquid gallium are determined by the degree of interaction of

136

the doping component with gallium In the case of the CuBi mechano-composite in which Bi does not interact with gallium an intermetallidewith particle size up to 4 μm and local accumulations of bismuth areformed With an increase in hardening temperature to 120 C intermetal-lide growth to 8 μm occurs

When using the solid solutions Cu(In) in which indium is solublein liquid gallium and the incubation period for the crystallization of thesolid solution In(Ga) the formed particles of intermetallide CuGa2 havea broad size range from 05 to 8 μm With an increase in hardening tem-perature to 160 C the size of intermetallide particles increases to 11 μmredistribution of indium occurs along with an increase in the number ofits film structures that are formed on the faces of the intermetallide andcause a decrease in its strength properties thus providing intra-crystaland inter-crystal fracture A decrease in the melting temperature for in-dium to 130C and a decrease in the heat effect at this temperature in thealloys obtained at the alloy formation temperature of 90 120 and 160 Cmay be connected with an increase of indium film amount

The work is carried out under the Integration Project of SB RASNo 138 and BRFFI Т09СО-014 laquoDevelopment of Fundamental Basisof the Action of Activation on Regulation of the Processes of Interactionof Solid Metals and Their Comopunds with Metal Melts for the Purposeof Obtaining Functional Materials with Required Structure and Proper-tiesraquo

References1 Tikhomirova OI Ruzinov LP Pikunov MV Marchukova ID

Investigation of mutual diffusion in the system gallium ndash copperFiz metallov I metallovedenie 1970 vol 29 issue 4 p 796-802 (inRussian)

2 Glushkova LI Konnikov SG Interaction between components inthe solder paste based on gallium Pressure treatment of metals andwelding Proceedings of the Leningrad Polytechnical Institute1969 No 308 p 205-208 (in Russian)

3 Grigorieva TF Barinova AP Lyakhov NZ Mechanochemicalsynthesis in metal systems Novosibirsk 2008 (in Russian)

4 Ancharov AI Grigorieva TF Barinova AP Lyakhov NZ Investi-gation of the interaction of liquid metals with nanocomposites by

137

means of diffraction of the synchrotron radiation Nuclear Instru-ments amp Methods in Physics Research 2007 v A 575 p 130-133

5 Ancharov AI Grigorieva TF Tsybulya SV Boldyrev VVNeorganicheskie Materialy 2006 V 42 No 9 p 1164-1170 (inRussian)

6 N Lyakhov T Grigorieva A Barinova Nanosized mechanocom-posites and solid solution in immersible metal systems Journal ofmaterials science 39(2004) 5421-5423

7 Chernov AA Crystallization processes Modern CrystallographyMoscow 1980 vol 3 p 5-12 (in Russian)

8 Bernshtein ML Zaymovsky VA Mechanical properties of metalsMoscow Metallurgy 1979

9 State diagrams of binary metal systems Ed by NP Lyakishev1997 vol 2 p 636ndash637 (in Russian)

10 Gromov DG Gavrilov SA Redichev EN Klimovitskaya AVAmmosov R M Factors determining melting temperature of thinfilms of Cu and Ni on inert surfaces Zhurnal Fizicheskoy KhimiiV 80 No 10 2006 p 1856-1862 (in Russian)

104

ZINC IONS REDUCTION ON SOLID METAL ELECTRODES INCHLORIDE MELTS

Alex Lugovskoy 1a Zeev Unger 12b Michael Zinigrad 1cDoron Aurbach 2d

1Material and Chemical Engineering Department Ariel UniversityCenter of Samaria Ariel 40700 Israel

2Department of Chemistry Bar-Ilan University Ramat-Gan 52900Israel

alugovsaarielacil bzevikitoarielacil сzinigradarielacildaurbachmailbiuacil

keywords electrodeposition chloride melts cyclic voltammetry high-temperature electrochemistry

AbstractThe reduction of zinc ions on solid tungsten and platinum

electrodes in chloride melts at the temperatures 700 ndash 750 degC wasstudied by cyclic voltammetry chronoamperometry and energydispersion spectroscopy It was established that no zinc is reduced onplatinum electrodes As for the reduction of zinc ions on tungstenelectrodes the process has a complex character it starts as anirreversible two-electron zinc ion reduction and after the new phase isformed the process of saturation of the electrode surface with lithium orsodium begins As the second process develops the alkaline metalbecomes essentially the only constituent on the electrode surface

GeneralSince zinc is industrially recovered from sulfate solutions rather

than from melts and because its melting temperature (4195 degC) is lowerthan the temperatures of most molten chloride compositions thereduction of zinc ions on solid electrodes in chloride melts has beeninvestigated relatively poorly There are quite a few papers devoted tothe electrolysis of zinc containing chloride melts (1 2) and these coveronly some details of the electrochemistry of this metal However zinc isnot only an engineering metal It can often be a component of moltenchloride systems in which various processes of synthesis or purification

105

are performed Therefore the detailed electrochemical behavior of zinccan be of great importanceThe study of electro-reduction processes of zinc ions on solid tungstenand platinum electrodes in eutectic NaCl ndash KCl and LiCl ndash KCl melts inthe temperature range of 700 ndash 750 degC is presented in this work Thesetemperatures are somewhat higher than the eutectic points of NaCl ndashKCl (646 degC ) and LiCl ndash KCl (628 degC) and the melts are thereforeliquid enough to be used in technologically important processes oflanthanides and actinides separation reduction and rectification On theother hand these temperatures are significantly lower than the boilingpoint of zinc (907 degC) and there is essentially no loss of the metal due toevaporation

ExperimentalThe electrochemical experiments were performed using a three-

electrode cell made of sintered alumina placed in an alumina crucibleunder nitrogen atmosphere Tungsten (9995 1 mm diameter) andplatinum wires (9995 05mm diameter) were used as the workingelectrodes and their surface area was controlled by immersion depth(typically 6ndash12mm) and by measuring their diameter before and aftereach experiment A 1mm tungsten wire served as a pseudo-referenceelectrode and a flat spiral tungsten wire set perpendicular to theworking and reference electrodes close to the bottom of the cell servedas the counter electrode The area of the counter electrode was ~ 20 foldas large as that of the working electrode ZnCl2 LiCl NaCl and KCl(990 +ACS grade Alfa Aesar) were used for the preparation meltswithout further purification

Zinc chloride was mixed with alkaline metals chlorides usingmortar and pestle in a glove-bag in dry nitrogen atmosphere Themixture was then placed into a crucible the electrode cell was mountedand transferred into the furnace (single-zone Carbolite 1600 degC STF tubefurnace) In the furnace the mixture was first dried under vacuum at 40ndash50 degC for an hour After completing the drying dry nitrogen wasbubbled through the electrolyte during its heating up to the temperatureof the experiments (700ndash750 C) for another hour The temperature wascontrolled by a type S thermocouple placed next to the cell andprotected by an alumina capillary thus maintaining a precision of plusmn1 degCin measuring and controlling the temperature Dry nitrogen atmosphere

106

(1 bar) was maintained in the furnace during the measurements and thepost-experimental cooling The electrochemical measurements werecarried out using an Autolab PGStat-12 potentiostat SEM images andelement analysis by EDS were performed with a SEM system fromJEOL Inc Model JSM 7000F

Results and discussion

Deposition of zinc on a tungsten electrodeSome typical voltammograms for the electrochemical reduction ofZn(II) are shown in Fig 1

-02

-01

0

01

02

03

04

-1 -05 0

iA

cm

2

E V vs W

C

A

QaQ

c~ 1

0502005 Vsec

-0680-0650-0600E

p V

(peak C)

164141110Qc Ccm

2

177150113Qa Ccm

2

Fig 1 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0163 mol L) in equimolar NaCl-KCl melt on a W electrode at 700degC Scanrates are 50 mV sec (solid line) 200 mV sec (slashed line) and 500 mV sec(dotted line) Each charge density was calculated as the sum of areas limited bythe baseline and the appropriate current density curves for the forward andbackward semi-cycles

107

As follows from Fig 1 a single cathodic peak C corresponds toone anodic peak A The potential shape and behavior of the cathodicpeak are typical for the metal deposition on a solid electrode (2-4) Nodifference is observed between the reduction of zinc ions in NaCl ndash KCland in LiCl ndash KCl melts Peak A is assigned to the reoxidation of zincBoth peaks are clearly not independent on the scan rate Rather peak Cis shifted to more negative potentials and peak A moves to more positivepotentials as the scan rate increases The dependence of the cathodicpeak potential on the scan rate is shown in Fig 2 Such voltammetricresponse is typical for irreversible processes

055

06

065

07

075

0 01 02 03 04 05 06

-Ep

V

Vs

Fig 2 Dependence of the cathodic peak potential on the scan rate for thereduction of Zn2+ (0163 mol L) at 710degC on a W electrode

The cathodic peak C appears at about -06 V vs tungsten electrodefor the scan rate of 50 mVsec and at -07 V for 500 mVsec Such asignificant shift is a clear indication that the process is irreversible Thecathodic peak not only is shifted as the scan rate grows but it becomes

108

broader so that the difference |Ep ndash Ep2| grows from 01 V for 005 Vsecto 015 V for 05 Vsec Values of n calculated by equation 23 are inthe range of 156 for low scan rates to 104 for high scan rates The mostlogical interpretation of this finding is that the charge-transfer is of two-electrons which is not surprising in the case of Zn2+ ions reduction Thevalue of is then 078 for 005 Vsec and 052 for 05 Vsec This isevident that the rate determining step is the Faradaic process

Zn2+ + 2e- Znwhen the system is close to the steady state Note that at low enoughpotential scanning rates diffusion limitations may be less influencingwhile at higher scan rates the diffusion limitations are more importantRandles-Sevcik dependencies for the zinc (II) ions reductiondemonstrate linearity but their intercepts are apparently non-zero (Fig3)

0

01

02

03

04

05

06

07

0 02 04 06 08 1

i pA

cm

2

12 V12s-12

Fig 3 Randles-Sevcik plots for Zn2+ ions reduction on W in a NaCl-KCl meltat 700 degC different concentration of the ions (peak C in Figure 39) 900x10-5

molmL Zn2+ 163x10-4 molmL Zn2+ 177x10-4 molmL Zn2+

109

It is evident that the process Zn2+ + 2e- Zn is complicated bysomething else Despite the irreversible character of the depositionprocess it is still reasonable to roughly evaluate the diffusion coefficientof Zn2+ according equation 1

ip = 06105 (nF)32(RT)12D12C12 (11)

where ip is the peal current density (A cm2) n is the number ofelectrons F is Faraday constant (96500 C) R is the gas constant (8314Jmol∙K) T is the absolute temperature (K) D is the diffusion coefficient(cm2 sec) C is the bulk concentration of a Red (Ox) species (mol cm3) and is the scan rate (V sec)

Thus calculated diffusion coefficients are shown in Table 1

Table 1 Diffusion coefficients of Zn2+ to a tungsten electrode in NaCl-KCl melt

C105 mol L D 105 cm2 sec900 955n

163 1020n

177 1364n

Given that the value of n for the reduction of Zn2+ cannot exceed 2 and0 le le 1 ( asymp 05 for most cases) reasonable values of n must beclose to 1-2 Therefore the values of the diffusion coefficients fromTable 2 lie in the range of 1-6∙10-4 cm2sec Available literature data forthe diffusion coefficients of most metal ions lie in the range 10-5-10-4

cm2sec Particularly T Stoslashre G M Haarberg and R Tunold found thatthe values of the diffusion coefficients for Zn2+ in KCl-LiCl melts at400degC lie in the range 06 ndash 106∙10-5 cm2sec (2) Delimarski providesthe value of the diffusion coefficient of Zn2+ in NaCl-KCl at 710degCwhich is 23∙10-5 cm2sec (5) The deviation of our results from theliterature data can hint that that the process cannot be treated as simplezinc ion reduction on the surface of tungsten

110

It is worth to mention that the fact that the diffusion coefficientfor zinc ions in the chloride melt lay in the range 10-4 ndash 10-5 cm2sec mayserve as an indirect argument in the discussion about the existence ofcomplex species described by the general formula [ZnxCly]

z+ in chloridemelts While some authors argue in favor of the formation of complexions (6 ndash 10) other studies give evidence for the existence of individualzinc ions as the key reacting species (11 ndash 12) The relatively highvalues of the diffusion coefficients found in our experiments hint that thecharge is transferred by individual ions rather than by more massivecomplex moieties

005

01

015

02

025

03

035

04

02 03 04 05 06 07 08 09 1

700oC

750oC

740oC

720oC

i pA

cm

2

12

V12

s-12

Fig 4 Randles-Sevcik plots for Zn2+ reduction on W in a NaCl-KCl melt fordifferent temperatures [Zn2+] = 900x10-5 molmL

Another intriguing aspect of the zinc ions deposition process ona tungsten electrode can be seen in the temperature dependence of

111

Randles-Sevcik plots (Fig 4) As seen from Fig 4 Randles-Sevcik plotsdo not change (to the accuracy of the experiment) as the temperaturerises from 700degC to 750degC

The lack of dependence of Randles-Sevcik plots on thetemperature is really surprising A plausible explanation to this could bean additional process in the system which occurs simultaneously withthe observed process but does not involve charge-transfer and cannot bedetected electrochemically Such a process could compensate for theexpected increase of the slope of Randles-Sevcik plots as thetemperature grows and thus distort the temperature dependence

The most probable candidates for such competing processes area coupled chemical (not charge-transfer) reaction or a process of phase-formation However cyclic voltammetry alone cannot discriminatebetween these two possibilities

Fig 5 A chronoamperometric plot for the deposition of Zn2+ on a tungstenelectrode Temperature 725degC [Zn2+] = 900x10-5 molmL The potential was

stepped from OCV to -055 V

A further insight on the nature of the deposition process can beprovided by chronoamperometry As seen from Fig 5 the current fallsin the course of the first 11 seconds of the experiment and then risesreaches a peak and gradually declines as expected with time until theend of the experiment (300 seconds)

The initial falling and rising of the current can be attributed tothe nucleation of the deposits fluctuations of current for more advanced

112

reaction times as seen in Fig 5 may indicate to a very active charge-transfer process which cannot be explained by a simple zinc depositionprocess

Even more surprising information is provided by EDS analysisof the working electrode after a 3000 second deposition experiment at ndash055 V (Fig 6 Table 2) The most striking result of the analysis is theunexpectedly high content of sodium on the electrode surface Thisamount of sodium cannot be accounted for melt adhesion or penetrationbecause the percentage of potassium and chlorine is much smaller Infact the working electrode looks as it was made of sodium withmoderate inclusions of tungsten and zinc rather of tungsten

Fig 6 An EDS spectrum of tungsten working electrode after 3000 seconddeposition at ndash 055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Table 2 Element composition of the tungsten working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Element Na K Cl W ZnAt 6084 580 2861 224 191

113

A somewhat similar phenomenon was reported by Thus T StoslashreG M Haarberg and R Tunold for the deposition of Zn2+ on a glassycarbon electrode in KCl-LiCl melts at 400degC (2) They observed aldquosubstantial residual current observed prior to the Zn(II) reductionpeakrdquo This current was attributed by them to lithium intercalation intothe lattice of the glassy carbon electrode

Unfortunately the data about standard reduction potentials ofmany important ions in molten chlorides are lacking The only source inwhich suitable potentials were found is the book of Yu DelimarskildquoElectrochemistry of Ionic Meltsrdquo (5) The values of standard potentialstabulated in this book were calculated on the base a few assumptionsand are far from being strictly thermodynamical However they arehelpful from the practical point of view The potentials relevant for thisdiscussion are summarized in Table 3

Table 3 Standard reduction potentials in molten chlorides (adopted fromref [5])

Half-Element Li+|Li Na+|Na K+|K Zn2+|Zn Fe2+|FeEH2 (700degC) V - 239 - 236 - 250 - 040 - 007

As seen from Table 3 the standard potentials of lithium andsodium are very close to each other Therefore it is not surprising thatthe interference from sodium in the deposition of zinc ions is similar tothat of lithium as reported by T Stoslashre G M Haarberg and R TunoldOf course it is not intercalation that serves as the moving force of theprocess of sodium penetration into the surface layers of zinc deposit onthe tungsten electrode

The large amounts of sodium in the deposits obtained in the studyof the Zn2+ ions reduction on tungsten electrodes cannot be explained asthe formation of a W-Na alloy because such a process is not observedby the cyclic voltammograms of NaCl-KCl on tungsten electrodes in theabsence of zinc ions (3) Therefore it is zinc which triggers thedeposition of sodium Moreover the data obtained bychronoamperometry at E = ndash 055 V vs W (Fig 5) indicate that there aretwo sequential faradaic processes The first of them is relatively weak

114

and is completed after ~ 11 seconds Then the second process starts andits current only grows with time The first process can be related to thereduction of zinc ions and the formation of zinc deposits As theelectrode surface is covered by a layer of zinc the interaction of thislayer with Na+ ions begins Apparently sodium ions are absorbed by theliquid zinc (Tm = 419 degC) and this facilitates their reduction at thepotential so much more positive than the sodium reduction potential inthe absence of zinc ( - 11 V vs W) Both lithium and sodium are liquidat the temperature of the experiment and these two metals form on theelectrode surface a liquid solution with zinc which continues to absorbnew portions of the lithium or sodium ions

The following speculation may account for the phenomenonobserved in our system

1 Zinc ions are discharged on the surface of the tungstenelectrode As the surface concentration of zinc atoms grows nucleationoverpotential starts to dump the overall process This dumping isobserved in the course of the first 11 seconds in Fig 5

2 Zinc (or zinc-tungsten) phase is formed This phase triggers theprocess of sodium-zinc exchange

Zn + Na+ Zn+ + Na or Zn + 2Na+ Zn2+ + 2Na3 The process (2) becomes the main process on the electrode

surface

Deposition of zinc on a platinum electrodeSome typical voltammograms for the electrochemical reduction

of Zn(II) are shown in Fig 7 Again no difference is observed betweenthe processes in NaCl ndash KCl and in LiCl ndash KCl melts and two melts arefurther described on the instance of in NaCl ndash KCl alone

As seen from Fig 7 the voltammogram is completely anomalousas compared to the other studied systems No cathodic peaks areobserved in the range -11V to + 09V ie in the limits of theelectrochemical window The peaks ndash 125V and at +09 V are the sameas for the ldquoblankrdquo melt NaCl-KCl These are the limits of theelectrochemical window

A very poorly pronounced anodic peak A at about ndash 028 V issimilar to the anodic peak A which appears for the zinc deposition on atungsten electrode (Fig 1) However the cathodic branch of thevoltammogram contains a continuous transition to the cathodic limit of

115

the windows rather than a peak It is obvious that zinc deposition ismasked by another process whose nature cannot be studied in theframework of this research

Fig 7 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0176 mol L) in equimolar NaCl-KCl melt on a Pt electrode at 700degC Scanrate is 300 mVsec

Fig 8 An EDS spectrum of a platinum working electrode after 3000 secondcathodic polarization at ndash 07 V vs W at 725degC in equimolar NaCl-

KCl melt containing 176x10-4 molmL of Zn2+ ions

116

An attempt of obtaining a sample of zinc deposit by holding thesystem at ndash 07 V (that is at such a potential which is considerably morepositive than the cathodic limit but more negative than the potential atwhich zinc is deposited on a tungsten electrode) for 3000 seconds wasmade However the analysis (Fig 8) demonstrated that essentially nozinc is found on the surface of the electrode (Table 4) since the value098 At is comparable with the sensitivity of the method The richcontent of potassium (5857 At ) in the surface layers can hint thatpotassium sorption is the process which masks the deposition of zincHowever this information alone is not sufficient for making positiveconclusions

To try to understand the essence of the process other moltenchloride systems containing no potassium could be studied Howeversuch a study is far beyond the framework of the current work

Table 4 Element composition of the platinum working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 176x10-4 molmL

Element Na K Cl Pt ZnAt 555 5857 3426 618 098

ConclusionsThe deposition of zinc on a tungsten electrode starts as an

irreversible two-electron zinc ion reduction Zn2+ + 2e- Zn After anobvious initial nucleation step a new phase is formed This phasecatalytically launches the process of saturating the electrode surface withsodium After the onset of the process of sodium deposition the latterbecomes essentially the only constituent on the electrode surface

The attempts of studying the deposition of zinc ions on a platinumelectrode were unsuccessful because this process is masked by anotherprocess which can result in the saturation of the electrode by potassiumThe exact nature of the latter process demands a separate study

117

References1 Fray D J J Appl Electrochem 3 103 (1973)2 Stoslashre T Haarberg GM Tunold R J Appl Electrochem 30 1351

(2000)3 Lugovskoy A Zinigrad M Aurbach D Israel Journal of

Chemistry 47 (3-4) 409 (2007)4 Lugovskoy A Zinigrad M Aurbach D and Unger Z

Electrochimica Acta 54 (6) 1904 (2009)5 Delimarski Yu K Electrochemistry of Ionic Melts Metallurgiya

Moscow 1978 (in Russian)6 Mackenzie J D and Murphy W K J Chem Phys 33 366 (1960)7 Irish D E and Young T F J Chem Phys 43 1765 (1965)8 Allen DA Howe RA Wood ND Howells WS J Phys

Condens Matter 4 1407 (1992)9 Price D L Saboungi M-L Susman S Volin K J Wright A C J

Phys Condens Matter 3 9835 (1991)10 Bassen A Lemke A Bertagnolli H Phys Chem Chem Phys 2

1445 (2000)11 Biggin S and Enderby J E J Phys C Solid State Phys 14 3129

(1981)12 Badyal Y S and Howe R A J Phys Condens Matter 5 7189

(1993)

89

PREPARATION OF COMPOSITES CuZrO2 AND CuTiO2

BY MA SHS

AI Letsko1 TL Talako1 AF Ilyushchenko1 TF Grigoreva2SV Tsybulya3 IA Vorsina2 NZ Lyakhov2

1 Powder Metallurgy Institute of NAS B Minsk Belarus2 Institute for Solid State Chemistry and Mechanochemistry of SB RAS

18 Kutateladze str Novosibirsk Russia grigsolidnscru3 GK Boreskov Catalysis Institute of SB RAS Novosibirsk Russia

IntroductionMetaloxide composites are quite perspective materials for

application in machine industry instrument engineering and electricalengineering in comparison to pure metals due to their improvedchemical and physical properties (heat resistance strength hardnesserosion resistance) Chemical mixing salt mixture decompositionhydrogen reduction in solutions chemical precipitation from solutionsinternal oxidation are well-known methods of preparing such materialshaving application in industry [1] The above-mentioned technologiesallow attaining metaloxide composites but they are quite expensive andlong-term Based on this a very topical issue is elaboration of newapproaches to production of metal-ceramic materials

In this work we explored possibilities of preparation ofcopperoxide composites (CuZrO2 and CuTiO2) by methods ofmechanochemical synthesis (MS) in planetary mills and of mechanicallyactivated self-propagating high-temperature synthesis (MA SHS)

ExperimentalCopper copper oxide CuO and zirconium M-41 titanium PTOM

were used in this work as raw materials Mechanical activation (MA)was carried out in planetary ball mills with water cooling [2] (the drumvolume ndash 250 cm3 the balls diameter ndash 5 mm the load ndash 200 g sampleweight ndash 10 g the drums rotation speed about the general axis ~ 1000rpm) After MA the activated mixture was compacted (under a load of4ndash6 t) in the mould up of 17 mm diameter and ~25 mm in height (tillstrength sufficient for the sample transfer to the reactor) SHS wascarried out in the argon atmosphere the combustion was initiated withan electrically heated tungsten coil The temperature and burning

90

velocity were evaluated by a thermocouple method (C-A thermocouplesOslash asymp 02 mm) using an outer 2-channel 24-charge analog-to-digitalconverter ADSC24-2T

X-ray diffraction research was conducted with diffractometersXrsquoTRA (Thermo ARL Switzerland) with application of CoK radiation(λ = 1 789 Aring) and URD-63 with application of CuK radiation (λ = 15418 Aring) Evaluation of effective sizes of coherent scattering area wascarried out in compliance with the Scherer formula with the strongestpeaks of phases analysed

The high-resolution scanning electronic microscope (SEM)MIRATESCAN equipped with an INCA 350 accessory for EDXanalysis was used for the structure research The electron probe diameterwas 52 nm excitation area was 100 nm Images in direct electrons andback-scattered electrons were attained and it allowed studying chemicalelements distribution over the surface Brightness distribution in theimage depends on the average atomic element number in eachmicroarea

IR absorption spectra were registered by spectrometer IFS-66The samples were prepared to the exposure by standards methods

Results and discussion

Cu-O-Zr systemMechanochemical reduction of copper oxide with metallic

zirconium was initially investigated in this system This reaction is quitehigh-exothermic (∆H (2 CuO + Zr = 2 Cu + ZrO2) asymp -188 kcalmol) ieit can be implemented under mechanical activation conditions IRspectroscopic investigations have shown that the original copper oxideCu-O band is considerably widened at 505 cm-1 after 20 s of MA ofCuO + Zr mixture of stoichiometric composition This widening (Fig1b) can testify some structural failures After 30 s of activation thefollowing bands are present in the IR-spectrum of the product 505 cm-1

(original oxide CuO) 615 cm-1 (the lowest copper oxide Cu2O) [3] and415 585 735 cm-1 (zirconium oxide (Fig 1c) [4 5] X-ray-phaseanalysis shows the presence of certain amount of Cu2O already after 20 sof activation The 30-second activation product diffractogram showsclear copper (coherent scattering area asymp 80 nm) and zirconium oxide

91

(coherent scattering area asymp 100 nm) reflection and two copper oxidereflections ie mechanochemical reduction of copper oxide takes placeat such activation duration This reaction speed shows that the reactionpresumably takes place in the thermal explosion mode when especiallyhigh heat dissipation speed is needed what is very difficult to performeven in the most effectively cooled highly-energy planetary ball millsAs such a process dimensional scaling seems to be absolutely impossiblein conditions of mechanochemistry an attempt to produce compositeCuZrO2 by the SHS method was made

Fig 1 IR-spectra of mixture CuO + Zr before (a) and after MA for 20 (b) and30 s (c)

At first CuOZr mechanocomposite was used as the SHS-precursor This mechanocomposite formed after 20 s of MA ofstoichiometric composition mixture has a small amount of cuprous oxideCu2O beside original copper oxide and zirconium SHS process proceedsin the heat explosion mode in this system Burning parameters fixingfailed in this case because of the inertia of the equipment applied

92

Not pure metal but solid solutions intermetallic compounds ornano-composites where metal-reducer (zirconium in our case) isdistributed in the inert matrix can be used as a reducing agent todecrease the system reaction capability At the same components ratiochemical energy of the raw mixture would be considerably lower and asa consequence heat release would reduce

In this work mechanocomposite formed during mechanicalactivation of mixture Cu + 20 wt Zr for 20 min with zirconium hadbeen pre-dispersed for 4 minutes (zirconium coherent scattering areasize ~ 20 nm) was used for copper oxide reduction This compositediffractogram shows the widened intensive copper (coherent scatteringarea asymp 20 nm) reflection and very vague zirconium reflection coherentscattering area of which cannot be evaluated (Fig 2) Since copperreflections havenrsquot changed their position we can conclude thatzirconium hasnrsquot become a part of copper crystal lattice ie CuZrmechanocomposite and not solid solution is attained

Fig 2 Diffractograms of Cu + 20 Zr mixture before (a) and after 20 minof MA (b)

93

This is confirmed by the SEM results (Fig 3) The electronmicroscopy data more clearly show zirconium distribution Zr elementalmapping testifies that local zirconium areas are much diffused

Fig 3 SEM-images of sample Cu + 20 Zr after MA for 20 min

94

X-ray research of the product of joint activation of mixture CuO +mechanocomposite Cu + 20 Zr (the mixture composition correspondsto the stoichiometric ratio of copper oxide and zirconium) for 2 and 4minutes show that copper oxides diffraction reflections are retained inall cases although they are substantially widened (Fig 4) Thezirconium oxide reflection is not observed ie mechanochemical copperoxide reduction does not take place in this time gap CuOCuZrmechanomposite formed as a result of joint mechanical activation ofmixture CuO + mechanical composite Cu 20 Zr for 4 min was usedas a precursor for SHS

Fig 4 Diffractogram of sample CuO + CuZr after MA for 4 min

Usage of mechanocomposite CuOCuZr instead of CuOZr one asthe SHS precursor changes a mechanism of interaction between thereactants during the SHS process from the thermal explosion mode (forCuOZr mechanocomposite) to the steady-state combustion with the

95

burning velocity asymp 2 mms temperature rise speed about 730 Cs andburning temperature 1044 C The combustion temperature record (Fig5) shows 2 isothermal plateaus The first one is fixed at temperaturemaximum and most probably points out melting process The secondone is fixed at 580 ndash 590 C and accounts for post-processes in the after-burning zone of combustion wave

Fig 5 Temperature record of the SHS process from mechanical compositeCuOCuZr

X-ray-phase analysis has shown that SHS product consists ofcopper and zirconium oxide with Cu2O traces (Fig 6) Electronicmicroscopy with the EDX analysis confirms composite structureformation (Fig 7 Table 1)

96

Fig 6 Diffractogram of the SHS product from mechanical compositeCuOCuZr

Fig 7 SEM-image of the SHS product from mechanical composite CuOCuZr

97

Table 1 Results of the EDX analysis (from Fig 7)

Number ofspectrum

O Cu Zr

1 382 8744 8742 714 8152 11343 2803 2747 44504 1653 4640 37065 2314 2914 4772

Cu-O-Ti systemChemical reduction of CuO with titanium is also high-exothermic

(∆H (2 CuO + Ti = 2 Cu + TiO2) asymp -151 kcalmol) Mechanicalactivation of equimolar mixture of copper oxide with titanium powderfor 4 minutes did not result in titanium oxide formation Longeractivation is not reasonable since it contaminates the reaction mixturewith balls and drums material That is why the composites formedduring the short-term MA were used as precursors for SHS

After 30 s MA composite structure CuOTi with a small additiveof cuprous oxide reduced from CuO (Fig 8) is formed The SHS processfrom such mechanocomposites proceeds with a very high speed andtemperature (on a levels typical for the thermal explosion mode) andwith the substances scatter

Fig 8 Diffractogram of mixture CuO + Ti after MA for 30 s

98

To decrease combustion temperature and velocitymechanocomposite CuTi containing 20 wt of titanium was used as areducing agent in the next experiment Figure 9 shows the diffractogramof the mechanocomposite formed after 10 min mechanical activation ofthis mixture It shows that metals reflections especially that of titaniumare widened testifying substantial increase of their dispersivityAccording to the X-ray data analysis the titanium coherent scatteringarea size is ~ 10 nm in this composite

Fig 9 Diffractogram of mixture Cu + 20 Ti after 10 min of MA

Mixture of copper oxide and CuTi mechanocomposite (thecomposition corresponds to the stoichiometric ratio of titanium andcopper oxide for its full reduction) was subjected to activation for 4minutes Only a band of valence vibrations of vCu-O copper oxide (Fig10a) is present in the IR-spectrum of the activated mixture like in theoriginal one but its intensity slightly decreases X-ray research alsoindicates that the titanium oxide reflections are absent in the 4-minuteactivation product diffractogram (Fig 11)

99

Fig 10 IR-spectra of sample CuO + CuTi after 4 min of MA (a)and after SHS (b)

Fig 11 Diffractogram of sample CuO + CuTi after 4 min of MA

100

SHS process from CuOCuTi mechanocomposite takes place inthe steady-state combustion mode with burning velocity higher than 20mms and burning temperature ~2000 ordmC A band (~730 cm-1)corresponding to valence vibrations of rutile vTi-O (Fig 10b) [2]appears in the IR-spectrum of the SHS product from CuOCuTimechanicocomposite Diffraction reflections (Fig 12) also correspond toreflections of rutile and copper

Fig12 Diffractogram of the SHS product from CuOCuTi mechanocomposite

Electron-microscopy exposure in back-scattered electronsindicates the partial phase separation of TiO2 and Cu (Fig 13 a) thoughcomposite particles containing TiO2 inclusions with size from 30 nm till1 5 m (Fig 13 c) are also formed The elemental mapping in thetitanium characteristic radiation confirms this fact (Fig 13d)

101

a

b cFig 13 SEM-images of the SHS-product from CuOCuTi mechanocomposite

102

Table 2 The EDX analysis results (from Fig 13 a)

Number ofspectrum

O Ti Cu

1 191 052 9757

2 235 051 9714

3 2230 2094 5676

4 1586 1295 7118

5 180 108 9712

6 336 228 9436

7 4335 4685 980

8 3297 2738 3966

9 4978 4645 377

ConclusionThus our investigations have shown that copper oxide can be

mechanochemically reduced with zirconium resulting in formation ofzirconium oxide and copper but the reaction goes in the thermalexplosion mode

To produce composite CuZrO2 by the method of MASHS usageof mechanocomposite CuZr instead of pure zirconium seems to be morepromising The MASHS product is a copper-based composite withinclusions of ZrO2 and some amount of Cu2O

Mechanical activation of equimolar mixture of copper oxide withtitanium powder for 4 minutes did not result in titanium oxide formationThat is why the composites formed during the short-term MA were usedas precursors for the following SHS

Reduction of CuO with CuTi mechanocomposite can beimplemented by the method of MASHS Partial phase separation of TiO2

and Cu takes place during the synthesis process along with the formationof copper-based composite particles with inclusions of titanium oxidesized from 30 nm up to 15 m

103

References1 PA Vityaz Mechanically alloyed alloys on the basis of aluminum

and copper PA Vityaz FG Lovshenko GF Lovshenko ndashMinsk Belnauka 1998 ndash 351 p

2 YG Avvakumov AP Potkin OI Samarin Authorrsquos certificate ofUSSR 975068 Planetary mill BI 1982 No 43

3 SS Batsanov VPBokarev YVLazareva On CuO interaction withcopper Inorganic Chemistry Journal 1977 V 22 issue 4 P 888ndash 892

4 AI Boldyrev Infrared spectra of minerals M Nedra 19765 BT Kaminsky AS Plygunov GN Prokofyeva Infrared spectra of

oxides of titanium zirconium and hafnium Ukrainian ChemicalJournal 1973 V 35 No 9 P 946 ndash 977

78

THE STANDARD ENTHALPY AND ENTROPY OFFORMATION OF GASEOUS AND LIQUID

POLYCHLORINATED BIPHENYLS POLYCHLORINATEDDIBENZO-n-DIOXINS AND DIBENZOFURANS

TV Kulikova AV Mayorova KYu ShunyaevInstitute of Metallurgy Ural Branch RAS

Yekaterinburg RussiaE-mail kulikogmailcom

AbstractThe study deals with analysis and systematization of the known

and calculation of the unknown thermodynamic characteristics (thestandard enthalpy of formation the standard entropy of formation) ofwidespread hazardous isomers of gaseous and liquid compounds ofpolychlorinated biphenyls (PCBs) polychlorinated dibenzo-n-dioxins(PCDDs) and polychlorinated dibenzofurans (PCDFs) Thecomparison of results obtained in different studies reveals aconsiderable discrepancy between values reported by highlyrespected investigators In this connection laquoindependentraquo results ofthe thermodynamic characteristics have been calculated

IntroductionUnique technological and physicochemical properties of

polychlorinated biphenyls (PCBs) a huge volume of theirproduction considerable volatility and solubility and extremechemical inertness have led to the world-wide spread of PCB-containing equipment and materials resulting in the universalcontamination with these substances The most common method usedin Russia for destruction of PCBs is their incineration with theformation of polychlorinated dibenzo-n-dioxins (PCDDs) anddibenzofurans (PCDFs) which are among the most hazardouschemical substances known to the mankind

As often happens the hazard of PCBs has long beenunderestimated With respect to their severe toxicological effectPCBs are identical to substances that are referred to the high class ofhazard Since these substances are especially toxic they have beenassigned low toxicological standards which necessitate special

79

requirements on the organization of processes assuming formation ofthese substances (the so-called dioxinogenic processes) so thatindustrial emissions meet the norms Instrumental investigations ofthese substances are very expensive and in this connection interestis attracted to calculation methods for simulation of processes by thedata on their thermochemical properties

A quality thermodynamic simulation requires the knowledge ofthermodynamic and thermochemical properties of all reliablycertified compounds of the system under study in the gaseous orcondensed state Therefore the present study deals with the analysisand systematization of the known and calculation of the unknownthermochemical properties (the standard enthalpy and entropy offormation) of most toxic and hazardous isomers of gaseous PCBsPCDDs and PCDFs and liquid PCBs

Calculation of thermochemical propertiesIt is known that there are 209 individual PCB congeners 420

polychlorinated dibenzo-n-dioxins and polychlorinateddibenzofurans which differ by the number and positions of chlorineatoms in a molecule The most widespread PCB compoundscontaining up1 to 10 chlorine atoms were chosen for the study Indeciding on isomers preference was given to ortho-unsubstitutedPCBs because they are most toxic and their effect is similar to theeffect of PCDDs and PCDFs Congeners which do not have chlorineatoms in ortho-positions of molecules (ortho-unsubstituted PCBs)can acquire the planar configuration which is more favorable inenergy terms Such congeners are isostereoisomeric to PCDDs andPCDFs and present the greatest hazard As to the PCDD and PCDFisomers of special hazard to humans and the environment are tri-tetra- penta- and hexa-substituted dioxins and furans containinghalogen atoms in lateral positions 2 3 7 and 8

In this study we analyzed the known and calculated theunknown thermodynamic properties of 17 most widespread andhazardous isomers of PCBs PCDDs and PCDFs in the gaseous stateand 11 compounds of liquid PCBs

80

Gaseous PCBs PCDDs and PCDFsThe literature survey showed that studies dealing with

estimation of the thermochemical properties of gaseous PCB PCDDand PCDF compounds are few Most of them are based oncalculations or are semi-empirical For example Saito and Fuwa [1]calculated thermodynamic functions of all PCBs and some PCDDsand PCDFs on the basis of semi-empirical calculations in terms ofthe PM3 model OV Dorofeeva et al [2-4] used statistical methodsTable 1 presents the literature data on standard enthalpies andentropies of formation of gaseous and liquid PCBs PCDDs andPCDFs The comparison of results obtained in different studiesreveals a considerable discrepancy between values reported by highlyrespected investigators who did very arduous work In particularvalues of the formation enthalpy [1] are 8-70 larger and the entropyis 11-15 smaller than the corresponding values in [2-4] thediscrepancy grows with the number of chlorine atoms in a moleculeSo we thought it reasonable and topical to attempt an independentresult

Bensons method [5] was used to calculate thermodynamiccharacteristics (the standard enthalpy of formation ΔНdeg298 thestandard entropy of formation ΔSdeg298) of the gaseous PCBs PCDDsand PCDFs We shall dwell briefly on this method

Bensons method is the group additivity method involvinganalysis of the molecule structure Atomic or molecular groups areseparated and the nearest neighbors of the atom or the group areconsidered Table 2 gives the number of groups necessary fordetermination of group increments in structural formulas of PCBsPCDFs and PCDDs Values of the thermodynamic characteristics ofgroup increments were determined from available reference andliterature data [5 6] Information about the energy contribution ofeach group (see Table 3) and the number of groups was used tocalculate thermochemical properties of the PCBs PCDDs andPCDFs

81

Table 1 Standard enthalpies (∆Нo298 kJmole) and entropies (∆So

298Jmole K) of formation of gaseous and liquid PCBs PCDDs andPCDFs

Gaseous state Liquid state

Compo-unds Saito Fuwa [1]

the given work

OV Dorofeeva etal

[2-4]

∆Нo298

[7 8 121617]

So298

[781014 16 17]

∆Нo298

the givenwork and

[814]

So298

thegivenworkand[14]

1 2 3 4 5 6 7 8 9

C12H10

(biphenyl)

1986[1]

1797

3454[1]

4104

1820[3]

3908[3]

1819[8]

1814[16]

3927[16]

11711162[8]11710

[14]

257402574[14]

C12H9Cl(3-mono-

chlor-biphenyl)

1705[1]

1500

3851[1]

4413

1561[2]

4323[2]

1548[8]

15088[16]

4214[16]

7629 2840

C12H8Cl2

(44rsquo-dichlor-biphenyl)

1422[1]

1202

3992[1]

4721

1260[2]

4518[2]

1276[8]

12004[16]

4492[16]

3584 3106

C12H7Cl3

(344rsquo-trichlor-biphenyl)

1194[1]

905

4240[1]

5030

1041[2]

4923[2]

1004[8]

892[16]

4780[16]

-452 3372

C12H6Cl4

(33rsquo44rsquo-tetrachlor-biphenyl)

969[1]

608

4444[1]

5338

899[2]

5216[2]

732[8]

5836[16]

5068[16]

-4488 3638

C12H5Cl5

(33rsquo44rsquo5-penta-

chlorbiphenyl

748[1]

310

4620[1]

5647

569[2]

5502[2]

460[8]

2752[16]

5356[16]

-8524 3904

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlor-

biphenyl)

529[1]13

4615[1]

5956

314[2]

5675[2]

190[8]

-332[16]

5644[16]

-12558 4170

C12H3Cl7

(233rsquo44rsquo55rsquo-hepta-

chlor-biphenyl)

400[1]

-284

4842[1]

6264

152[2]

6077[2]

-84[8]

-416[16]

5932[16]

-16596 4436

82

1 2 3 4 5 6 7 8 9

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-

octachlor-biphenyl)

241[1]

-581

4886[1]

6573-90[2]

6342[2]

-356[16]-650[8]

6220[8]

-20632 4702

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-

nanochlor-biphenyl)

873[1]

-878

5048[1]

6881

-153[2]

6607[2]

-628[16]-958[8]

6508[8]

-24668 4968

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlor-biphenyl)

-67[1]

-1176

5034[1]

7190

-247[2]

6757[2]

-901[16]

-1267[8]

6796[8]

-28604 5234

C12H8O2

(dibenzo-n-dioxin)

-402[1]

-448

3764[1]

-592[4]

3965[4]

-592[12]-592[7]

-550[17]

3951[7]

3880[17]

- -

C12H4Cl4O2

(2378-tetrachlor-dibenzo-n-

dioxin)

-1372[1]

-1592

4553[1]

-1640[4]

4781[4]

-1345[7]

-158[17]

5136[7]

4784[17]

4781[10]

4784[9]

- -

С12H3Cl5O2

(12378-pentachlor-dibenzo-n-

dioxin)

-1532[1]

-1900

4931[1]

-1900[4]

54035[4]

-1162[7]

-196[17]

5531[10]

5010[17]

- -

С12H2Cl6O2

(123478-hexachlor-dibenzo-n-

dioxin)

-1691[1]

-2164

4841[1]

-2196[4]

56912[4]

-1224[7]

57559[7]

5236[17]

- -

С12HCl7O2

(1234678-hepta-chlor-

dibenzo-n-dioxin)

-1848[1]

-2472

5005[1]

-2460[4]

59789[4]

-1196[7]

61031[7]

5462[17]

- -

C12H8O(dibenzo-

furan)

1061[1]

518

3787[1]

553[4]

3759[4]

552[17]

3744[17]

- -

C12H4Cl4O(1234-

tetrachlor-dibenzo-furan)

203[1]

-625

4505[1]

-500 [4]49098

[4]-528[17]

4648[14]

- -

83

1 2 3 4 5 6 7 8 9

С12H3Cl5O(12378-pentachlor-

dibenzo-furan)

-123[1]-934

4592[1]

-759[4]

51975[4]

-748[17]

4874[14]

- -

С12H2Cl6O(123478-

hexachlor-dibenzo-furan)

-283[1]

-12424713[1]

-1051[4]

54852[4]

-1043[17]

5100[14]

- -

С12HCl7O(1234678heptachlor-

dibenzo-furan)

-441[1]

-1550

4833[1]

-1315[4]

57729[4]

-1313[17]

5326[14]

- -

Table 2 Number of groups for determination of group increments instructural formulas of PCBs PCDFs and PVDDs

Number of groupsCompound Св-H Св-Cl Св-O Св-Св

Number ofchlorine atoms

in a molecule (n)

PCBs 10 - n n - 2 1 ndash 10

PCDFs 8 - n n 2 2 1 ndash 8

PCDDs 8 - n n 4 - 1 ndash 8

Св is the carbon atom in an aromatic ring

Values presented in Table 1 show the thermodynamiccharacteristics of PCBs PCDDs and PCDFs calculated in this studyand by other investigators

It is seen for example ( Table 1) that the formation enthalpy

(o298H ) of biphenyl (C12H10) equals (kJmole) 1986 [1] 1820 [3]

1819 [7] and 1814 [8] while the formation entropy (o298S ) of

2378-tetrachlordibenzo-n-dioxin (C12H4Cl4O2) is (J(mole K))4553 [1] 4781 [4] 4784 [9] and 4781 [10]

84

Table 3 Values of the thermodynamic characteristics determined bythe method of group increments[58]

(gas) (liquid)Group

o298H

kJmole

o298S

J(moleК)

o298H

kJmole

o298S

J(moleK)

Св-H 1381[8]1382[5]

4831[8]4827[5]

816[8] 2887[8]

Св-Св 2166[8]2077[13]

-3657[8]-3618[5]

1721[8] -

Св-Cl -1703[8]-1591[5]

7708[8]7913[5]

-3220[8] 5547[8]

(Св)2-O -7766[8]-8834[5]

--

- -

orto corrCl-Cl

950[8]921[5]

- 1400[5] -

meta corrCl-Cl

-500[8] - 400[5] -

In this study the values of the standard entropy of formationobtained by using statistical methods (OV Dorofeeva et al [2-4 9])for 17 isomers of PCBs PCDDs and PCDFs are in good agreementwith the values calculated by other investigators [8 10 12 13] andwith the values calculated by us

Liquid PCBsIt should be noted that ample literature data on the

thermochemical properties of liquid ecotoxicants is only available forbiphenyl (C12H10) [8 14] dibenzo-n-dioxin (C12H8O2) [11 15] anddibenzofuran (C12H8O) [5 17] The only study dealing withcalculation of thermodynamic functions for the whole series of liquidPCDD and PCDF homologues was published by VS Iorish et al[11] As to liquid PCB compounds the literature data on theirthermochemical properties are scarce [8 14]

The thermochemical properties namely the standard enthalpyand entropy of formation of liquid PCBs were calculated using thegroup additivity method due to Domalski [8] Values of the groupincrements (Table 3) were adopted from [8] It is seen from Table 3

85

that the energy contribution of the group Св-Св is unavailable for the

entropy calculation However if one uses known values ofo298S for

liquid biphenyl (C12H10) [14] and the data on the contribution of the

Св-H and Св-Cl groups [8] it is possible to calculateo298S for the

whole series of PCBs

o298S (PCB) =

o298S (BP) - (10-n)

o298S (Св-H) + n

o298S (Св-Cl) +

+(morto corr Cl- Cl ) +(pmeta corr Cl- Cl) (1)

where n is the number of chlorine atoms in a PCBs moleculem (p) - spatial amendments number Cl (from two and more) beingin orto - (meta-) position rather each other

The enthalpy of formation (o298H ) for the PCBs series

compounds was calculated by two options using the group additivitymethod due to Domalski [8] and from the equation

o298H (PCB) =

o298H (BP) - (10 - n)

o298H (Св-H) +

+ no298H (Св -Cl) +(morto corr Cl-Cl )+(pmeta corr Cl-Cl) (2)

Table 4 lists values of the standard enthalpy of formation forthe series of liquid PCBs compounds as calculated by the groupadditivity method [8] and the equation (2) It is seen that the values of

o298H which were calculated by the two methods are in good

mutual agreementThe thermochemical properties which were taken as reliable

were added to the TERRA database and were used forthermodynamic simulation of the thermal stability of PCBs PCDDsand PCDFs

86

Table 4 Calculated enthalpy of formation (∆Нo298) for liquid PCBs

compounds∆Нo

298 kJmole

CompoundGroup

incrementsmethod

Eq (5)δ

C12H9Cl(3-monochlorbiphenyl)

7584 76742 12

C12H8Cl2

(44rsquo-dichlorbiphenyl)3530 36382 30

C12H7Cl3

(344rsquo- trichlorbiphenyl)-506 -3978 2138

C12H6Cl4

(33rsquo44rsquo-tetrachlorbiphenyl)-4542 -44338 238

C12H5Cl5

(33rsquo44rsquo5-pentachlorbiphenyl)-8578 -84698 126

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlorbiphenyl)-1261 -125058 083

C12H3Cl7

(233rsquo44rsquo55rsquo-heptachlorbiphenyl)-1665 -165418 065

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-octachlorbiphenyl)-20686 -205778 052

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-nanochlorbiphenyl)-24722 -246138 044

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlorbiphenyl)

-28758 -286498 038

Conclusions1The literature data on the thermochemical properties of 17

most widespread and hazardous isomers of PCBs PCDDs andPCDFs in the gaseous state and 11 compounds of liquid PCBs havebeen analyzed and systematized for the first time

2Methods have been developed for calculating of thethermodynamic characteristics of organic compounds Values of thethermodynamic functions (standard enthalpy and entropy offormation) of liquid PCBs PCDDs and PCDFs have been calculatedfor the first time

87

3The comparison of the calculated values of thethermodynamic functions with the known literature datademonstrated their good mutual correlation

4The obtained data were added to the TERRA database andwere used for thermodynamic simulation of the thermal stability ofPCBs PCDDs and PCDFs

5The obtained data can be used for simulating of the behaviorof complex heterogeneous systems including ecotoxicants over awide interval of temperatures and initial compositions

This study was supported by RFBR (project No 08-03-00362-a)

References1 Nagahiro Saito Akio Fuwa Chemosphere 2000 vol40 p

131-1452 OV Dorofeeva NF Moiseeva VS YungmanLV JPhys

Chem A 2004 vol 108 p 8324-83323 OV Dorofeeva Thermodynamica Acta2001 vol374 p7-114 OV Dorofeeva VS Iorish NF Moiseeva J Chem Eng

Data 1999 vol 44 p 516-5235 SW Benson FR Cruickshank DM Golden GR Haugen

HE OrsquoNeal AS Rodgers R Shaw and R Walsh Chem Rev1969 vol69 p 279 -324

6 HK Eigenmann DM Golden and SW Benson J PhysChem 1973 vol 77 1687-1691

7 Jung Eun Lee and Wonyong Choi J PhysChem A 2003vol 107 p 2693-2699

8 Domalski E S and Hearing E D J of Phys and Chem RefData 1993 vol 22 p 805-1159

9 LV Gurvich OV Dorofeeva VS Iorish Zh Fiz Khimii 1993vol67 No 10 p 2030-2032

10 W-Y Shiu and K-C Ma J Chem Ref Data 2000 vol29No 3 p 387-462

11 VS Iorish OV Dorofeeva NF Moiseeva J Chem Eng Data2001 vol46 p 286-298

12 VA Lukyanova VP Kolesov Zh Fiz Khimii1997 vol 71No 3 p 406-408(in Russian)

88

13 P Reid J Prausnitz T SherwoodLeningrad Khimiya 1982592 p(in Russian)

14 Richard Laurent and Helgeson Harold C Geochimica etCosmochimica Acta 1998 vol 62 No 2324 p 3591 ndash 3636

15 I Barin ldquoThermochemical Data of Pure SubstancesrdquoWeinheim Federal Republic of Germany VCHVerlagsgesellschaft mbH 1997

16 Cambridgesoft database ver 806 December 31 200317 Thompson D Thermochim Acta 1995 vol261 p7-20

76

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OFNANOGRAINED

TiN-TiB2 COMPOSITES

MA Korchagin BB BokhonovInstitute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirsk Russiakorchagsolidnscru

Titanium nitride is known to exhibit high oxidation resistancehigh thermal conductivity and hardness as well as high corrosionresistance in acids Titanium diboride is also very hard possessing highstrength at elevated temperatures and anomalously high electricalconductivity among other ceramic materials

Composite materials based on the mixture of these twocompounds have been widely used in a variety of applications Highperformance parts have been also developed Thus ceramics containing40-50 molTiN shows high oxidation resistance [1] However untilvery recently TiN and TiB2 have been produced separately by twodifferent routes At present new methods are being developed tosynthesize mixtures of these two compounds in a single process One ofthese methods is based on self-propagating high-temperature synthesis(SHS) The use of SHS eliminates the need of having furnace equipmentto synthesize the desired products The possibility of SHS in the systemis due to the high enthalpies of formation of the products serving as aninternal chemical source of energy

In order to simultaneously obtain TiN and TiB2 by SHS the initialreactants can be either the powder mixtures of Ti-BN [3] or Ti-B-BN[4] The products of the reactions consist of highly porous well meltedsintered pieces with the minimum grain size of 1-10 microm [4] Hightemperatures developed in the combustion wave in the traditional SHSdo not allow finer grains of the products to retain

In order to overcome this problem short mechanical activationof the mixtures of reactants is proposed followed by the SHS in anatmosphere of argon or nitrogen

In the previous investigations preliminary mechanical activationhas been shown to significantly reduce the combustion temperatures

77

which to a great extent determine the grain size of the products of SHS[6 7]

Experiments were performed on the stoichiometric mixtures 3Ti +2BN The time of preliminary mechanical activation in a planetary ballmill (AGO-2 type) did not exceed 10 min The influence of the durationof mechanical activation on the combustion rate temperature and phasecomposition of the products was studied

The milled mixtures and the products of SHS were studied usingXRD analysis and Electron Microscopy The experimental conditionshave been found favoring the formation of the two-phase mixtures ofTiN of TiB2 with the grain size ranging from 20 to 50 nm [7]

References1 GV Samsonov Nitridy (Nitrides) Kiev laquoNaukova Dumkaraquo 19692 AG Merzhanov Tverdoplamennoe gorenie (Solid State

Combustion) Chernogolovka ISMAN 2000 224 p3 AEGrygoryan ASRogachev Combustion of titaniumwith

nonmetal nitridesCombustion explosion and shock waves 2001v37 2 p168-172

4 R Tomoshige A Murayma T Matsushita Production of TiB2-TiNcomposites by combustion synthesis and their properties J AmCeram Soc 1997 80[3] 761-764

5 MAKorchagin TFGrigorrsquoeva BBBokhonov MRSharafutdinovAPBarinova NZLyakhov Solid-state combustion in mechanicallyactivated SHS systems Combustion explosion and shock waves2003 v39 1 p43-58

6 MAKorchagin DVDudina Application of self-propagating high-temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007v43 2 p176-187

7 MAKorchagin BBBokhonov Combustion of mechanicallyactivated 3Ti+2BN mixtures Combustion explosion and shockwaves 2010 v 46 2 p170-177

65

SPIN-CROSSOVER IN THE PENTANUCLEAR BYPIRAMIDALCo2Fe3 AND Fe2Fe3 COMPOUNDS

Sophia Klokishner Sergei Ostrovsky Andrei PaliiInstitute of Applied Physics Academy of Sciences of Moldova

Kishinev MoldovaKim Dunbar

Department of Chemistry Texas AampM UniversityCollege Station TX USA

Boris TsukerblatChemistry Department Ben-Gurion University of the Negev

Beer-Sheva Israel

In this article we report a model for a spin-crossover phenomenonin pentanuclear bypiramidal [M(III)(CN)6]2[M(II)(tmphen)2]3 (MM=CoFe FeFe) cluster compounds The spin-crossover phenomenonis considered as a phase transformation accompanied by a change of theground state spin The model takes into account cooperative interactionsin the crystal network local crystal fields and spin-orbit coupling actingwithin the degenerate metal sites Magnetic properties and Moumlssbauerspectra are analyzed and compared to the experimental data

1 IntroductionSpin-crossover compounds have been a subject of many

experimental and theoretical studies [1-6] Till now only a fewexperimental reports on spin crossover in cluster compounds [7-11] havebeen reported Recently FeII ions were introduced into the equatorialmetal sites of discrete cyano-bridged pentanuclear clusters[MIII(CN)6]2[MII(tmphen)2]3 (MM =CoFe(1) FeFe(2) ) [12] with atrigonal bipyramidal (TBP) structure The octahedral nitrogensurrounding of FeII ions facilitates the spin-crossover behavior Theoccurrence of the ls-hs transition in compounds 1 and 2 was proved bythe combination of Moumlssbauer spectroscopy magnetic measurementsand single-crystal X-ray studies For both types of clusters[FeII(tmphen)2]3[M

III(CN)6]2(M=FeCo)7 the T product increases by

~9emumiddotKmol between 150 K and 375 K thus indicating the ls ndashhstransition at the FeII sites The TBP FeII

3CoIII2 cluster due to its electronic

66

structure represents an ideal system for studying the effects ofintracluster short-range and intercluster long-range interactionsfacilitating spin-crossover In the (FeIII)2 (FeII)3 cluster the hs-FeII and ls-FeIII ions are coupled by exchange interaction In spite of the fact that theexchange interaction of the hs-FeII and ls-FeIII ions through the cyanidebridge is sufficiently weak as compared with that in oxide clusters it isinterestingly to understand whether this interaction may affect the spintransformation The effects of orbital degeneracy on the spin-crossovertransformation in the [FeII(tmphen)2]3[FeIII(CN)6]2 crystal will beexamined as well In the present article a microscopic approach to theproblem of spin crossover in crystals containing metal clusters isdeveloped

2 The modelIn the basic structural unit of compounds 1 and 2 two MIII ions

surrounded by six carbon atoms occupy the apical positions and threeFeII ions coordinated by the nitrogen atoms reside in the equatorial plane[12] In a strong crystal field of carbon atoms the ground terms of the

CoIII and FeIII ions are the low-spin orbital singlet )( 621

1 tA ( 0S ) and

the orbital triplet )( 421

3 tT respectively The ground state of a FeII -ion in

the crystal field induced by the nitrogen atoms can be either low-spin

(ls)- term )( 621

1 tA or high spin (hs) ndashterm 2422

5 etT Both magnetic

measurements and Moumlssbauer spectroscopy for water containing crystals[12] demonstrate the presence of some amount of FeII ions in the hsconfiguration even at very low temperatures Further on we consider inthe model two types of FeII ions and denote by x the fraction of FeII -ions which are in the hs ndashstate at all temperatures while theconcentration of those ions which undergo the ls-hs transition is (1-x)The number pi of trigonal bypiramidal clusters in which i (i=0123) ofthree FeII ions are in the hs configuration in the whole temperature range

is estimated as iiii xxCp 33 1 where rllrC r

l

The Hamiltonian of intraion interactions can be written in the form

67

Hg

gllsH

kkB

kkB

kZkk

)(

32)(

211

02

0

H

lsH

(1)

where numbers theIIFehs ions in the k-th bypiramidal cluster the

first term is the spin-orbit (SO) coupling in the cubic )( 2422

5 etT - term of

theIIFehs -ion the second term describes the axial crystal field

splitting the 125 lT term into an orbital singlet ( 0lm ) and an

orbital doublet ( 1lm ) the third term refers to the Zeeman

interaction for hs-FeII ions and contains both the spin and orbitalcontributions B is the Bohr magneton and g0 is the spin Lande factorFinally the fourth term represents the interaction of the ground Kramersdoublets of two ls-FeIII ions in the cluster with the external magnetic

field i is the matrix of the pseudo -spin frac12 of the ls-FeIII ion g1 =173

is the Lande factor Up to room temperature the ls-FeIII can be regardedas an ion with the pseudo-spin frac12 because the ground Kramers doubletand the excited quadruplet arising from the splitting of the 2T2 term by

the spin-orbital interaction are separated by the gap 173023 cm

( 1486 cm [13] for a free ls-FeIII) that is large enough from the

thermal population of the excited quadruplet at room temperatureThe superexchange interaction (several cm-1 [1415]) in the

[FeII(tmphen)2]3[FeIII(CN)6]2 through the cyanide bridges couples the hs-FeII ions in equatorial and ls-FeIII ndashions in axial positions Further on wewill neglect the essentially anisotropic orbitally dependent terms andretain only the isotropic part of the exchange interaction between the hsndashFeII and ls ndashFeIII ions in a cluster The Hamiltonian of exchangeinteraction for the thk cluster looks as follows

kkkex

k

exJH

212 σσs (2)

where 2s is the spin of the hs-FeII ion the summation in (2) takes

into account the hs-FeII ions appearing in the thk cluster due to thespin transition and those which are in the hs-state in the whole

68

temperature range As in [16-18] we suppose that the mechanismresponsible for the ls-hs transition is the interaction of FeII ions with thespontaneous all-round full symmetric lattice strain Applying theprocedure suggested in [16-18] we obtain the Hamiltonian of electron-deformational interaction

2k kkk

kkst

nm

JBH (3)

where 21AB 21AJ

01021

2

ccc

cA n

(n=123) is the number of FeII ions which undergo the ls-hs transition ina complex m is the number of TBP MIII

2MrsquoII3 complexes whose FeII ions

are involved in the spin conversion =1n k=1m 0 is thevolume that falls at a Fe ion and its nearest surrounding and is the unit

cell volume per one iron respectively In the basis of the states 25T and

11A the 1616 matrix k is diagonal and has 15 eigenvalues equal to 1

and one eigenvalue equal to -1 Finally 2)(1 lshs

2)(2 lshs hs and ls are the constants of interaction of the

FeII ion with the full symmetric strain1A in the hs and ls states

respectively The first term in (3) acts as an additional field applied toeach spin-crossover ion and redefines the effective energy gap 0

between the hs and ls states of the FeII in the cubic crystal field Thesecond term in (3) represents an infinite range interaction between theFeII ions which undergo the spin conversion This interaction arises fromthe coupling to the strain The model of the elastic continuum introducedabove satisfactorily describes only the long-wave acoustic vibrations ofthe lattice Therefore the obtained intermolecular interactioncorresponds to the interaction via the field of long-wave acousticphonons

Due to the proximity of the FeII ions in the clusters short-rangeinteractions between these ions inside the cluster are relevant Thelargest is the effect of the exchange arising from the optic phonons [19]

69

The Hamiltonian describing short-range interactions between FeII ionswithin the trigonal bipyramid can be written as

0

kkk

sr JH (4)

The Hamiltonian (4) takes into account the interaction between the FeII

ions participating in the spin transitions the interaction of these ionswith those FeII ions which are in the hs-state in the whole temperaturerange as well as the interaction between the latter It should bementioned that eq (3) as compared with eq(4) only accounts for FeII

ions participating in spin conversion The Hamiltonian for the wholecrystal can be written as

k

kexstsr HHHHH

2

00 (5)

where k

k

exex HH In the molecular field approximation the full

Hamiltonian H can be written as a sum of one-cluster Hamiltonians

)(32)(

)2

(~

211101

2

1

0

0

kkB

kkkB

k

ex

kkZ

kkkkkkk

gIgHIl

IlsJBJH

HlsH

(6)

where in the basis of the states 25T and 1

1A kI1

is a diagonal 1616 -

matrix with 15 eigenvalues equal to 1 and one vanishing eigenvalue is the order parameter In fact the Hamiltonians kH

~describe clusters

with different numbers of spin-crossover FeII ions and k as beforenumbers the clusters in the crystal For calculation of the temperaturedependence of the order parameter the self-consistent procedure wasapplied The calculations of the magnetic properties were based on theHamiltonian given in Eq(6)

3 Results and discussionThe estimation of the parameters J and B was performed

according the procedure suggested in paper [16-18] For characteristicfor compounds 1 and 2 parameters =1026Aring3 0 =8Aring3

c2 (005divide01)c1211

2 10 cmdynec 1046 141

cm 142 1087 cm the

70

parameters J and B take on the values 20divide80 cm-1 and -95 divide -24 cm-1respectively

Fig1 shows the experimental data for compound 1 together withthe calculated T vs T curves The result of the best fit procedure in

the model above developed is presented by curve 1 The best fitparameters are the part of the figure caption One can see that a quitegood agreement with the experimental data is obtained At temperaturesbelow 100 K the T values show that the FeII ions are mainly in the ls ndashstate However some small admixture of hs ions is present In thetemperature range 150-300 K the T product gradually increases thusindicating the ls - hs transition in the FeII ions

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30 35

04

06

08

10

3

2

1

T

cm

3K

mo

l-1

Temperature K

23

1

T

cm

3K

mo

l-1

Temperature K

Fig1 Temperature dependence of the T product for 1 Circles-experimentaldata [12] The solid lines represent a theoretical fit with =-103 cm-1 x=10and (1) hs-ls =640 cm-1 J =35 cm-1 J0=45 cm-1 =180 cm-1 =10 (2) hs-

ls=620 cm-1 = -136 cm-1 J=0 J0=0=06 (3) hs-ls=630 cm-1 =168 cm-1J=0 J0=0 =06

The parameter J of long -range cooperative electron-deformationalinteraction obtained from the best fit procedure falls inside the limits

71

estimated above Relatively small values of the parameters J and J0 ascompared with the gaps hs-ls= 0-2B and are also in agreement withthe observed gradual temperature dependence of T and noticeable

increase of T at temperatures higher than 150K Finally the estimated

from the best fit procedure percentage of FeII ions (x=10) which are inthe hs-state at any temperature is very close to that obtained from theMoumlssbauer spectra [12] For comparison in the same figure (curves 23)the results of fitting of the T curve in neglect of long- and short-

range interactions are shown for the cases of 0 and 0 It isseen that in this approximation the calculated curves 2 and 3 differsignificantly from the experimental one both at low and hightemperatures besides this the obtained value 60 is too small forhs-FeII-ions

For compound 2 the variation of the observed magneticsusceptibility as a function of temperature is presented in Fig2

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

321

T

cm

3K

mo

l-1

Temperature K

Fig2 Temperature dependence of the T product for 2 Circles experimentaldata [12] Curves 1- 3 were calculated with the following parameter values hs-

ls =690 cm-1 J=30 cm-1 J0=40 cm-1 =100 cm-1 =-103 cm-1 =10 x=9and (1) Jex = 3 cm-1 (2) Jex = 0 (3) Jex = -3 cm-1

72

First the magnetic behavior of complex 2 was analyzed withneglect of intracluster Heisenberg exchange interaction between FeII andFeIII ions The result of the best fit procedure is presented by curve 2 inFig2 The best fit parameters are the part of the figure caption One cansee that the values of the key parameters are close to those for complex1 However the obtained energy gap hs-ls between the ls and hsconfigurations for complex 2 is a bit larger than the corresponding gapfor compound 1 while the parameters of short-range and long-rangeinteractions are smaller Namely this difference in the characteristicparameters leads to lower values of T for compound 2 as compared

with compound 1 at temperatures higher than 150K The effect ofexchange interaction on the magnetic behavior is illustrated in Fig2 bycurves 1 and 3 Since typical values of the exchange parameters incyanide bridged complexes are of several cm-1 we calculated the Tproduct with the set of the best fit parameters and Jex = -3 cm-1 and 3cm-1 One can see that at temperatures higher than 50K the smallexchange interaction has no effect on the magnetic properties ofcomplex 2

Moumlssbauer spectra provide direct information about the populationof the hs and ls states and serve a reliable test for the theoreticalbackground of the SCO phenomenon The total Moumlssbauer spectrum(ie the observable spectrum) was obtained by summing up the spectrayielded by different cluster electronic states in the molecular field withdue account for their equilibrium populations for a given (at a certaintemperature) value of the molecular field In calculations theexperimental values for the parameters of the quadrupole splttings andisomeric shifts were taken from [12] The calculated and experimentalspectra are shown in Fig3

Quite good agreement between the experimental data andtheoretical calculations is obtained It should be underlined that themodel takes into account the main effect inducing the temperaturedependence of the Moumlssbauer spectra and this is the temperaturedependence of the cluster energies in the molecular field Namely thiseffect is responsible for the transformations of the Moumlssbauer spectrawith temperature

73

The proposed model gives a good fit to the observed temperaturedependence of the static magnetic susceptibility and the Moumlssbauerspectra The last clearly illustrates the cooperative nature of SCOtransformations in TBP compounds that leads to a crossing of the ls andhs levels due structural phase transition induced by the ordering of thelocal deformations through the field of the acoustic phonons

Fig3 Moumlssbauer spectra for compound 1 calculated at T=42 220 and 300Kwith the set of the best fit parameters (thick solid lines) Contributions from ls -FeII and hs -FeII ions are shown in dash and dot lines respectively The half-width of the individual lines Г=016 cm-1(42 К) Г=018 cm-1(220К)Г=024cm-1(300К)

74

AcknowledgmentsFinancial support of the STCU (project N5062) is highly

appreciated BT and KD gratefully acknowledge financial support ofthe Binational US-Israel Science Foundation (BSF grant no 2006498)BT thanks the Israel Science Foundation for the financial support (ISFgrant no 16809)

References1 Guumltlich P Goodwin H A Spin Crossover in Transition Metal

Compounds Springer-Verlag 20042 Hauser A Light-Induced Spin Crossover and the High-Spin rarrLow-

Spin Relaxation Springer-Verlag 20043 P Guumltlich J Jung Nuovo Cimento D 1996 18 1074 P Guumltlich A Hauser H Spiering Angew Chem Int Ed Engl

1994 33 20245 J Zarembowitch New J Chem 1992 16 2556 A B Gaspar V Ksenofontov M Serdyuk P Guumltlich Coord

Chem Rev 2005 249 26617 JA Real AB Gaspar MC Munoz P Guumltlich V Ksenofontov H

Spiering TopCurrChem2004 2331678 G Vos RAG De Graaff JGHaasnoot AM van der Kraan De

PVaal JReedijk InorgChem 1984 23 29059 EBreuning MRuben JMLehn FRenz YGarcia VKsenofontov

P Guumltlich E Wegelius KRissanen AngewChemIntEd 2000 392504

10 M Nihei MYi MYokota LHan AMaeda HKushida HOkamoto HOshio AngewChem IntEd 2005 446484

11 D-Y Wu O Sato Y Einaga C-Y Duan Angew Chem Int Ed2009 48 1475 ndash1478 2009

12 MShatruk ADragulescu-Andrasi KEChambers SAStoianELBominaar CAchim KRDunbar J Am Chem20071296104

13 AAbragam BBleaney Electron Paramagnetic Resonance ofTransition Ions Clarendon Press Oxford 1970

14 A V Palii SM Ostrovsky S I Klokishner B S Tsukerblat C PBerlinguette K R Dunbar J R Galaacuten-Mascaroacutes JAmChemSoc2004 126 16860

15 HWeihe H Gudel H Comments Inorg Chem 2000 22 75

75

16 SI Klokishner F Varret J Linares ChemPhys 2000 255 31717 SI Klokishner JLinares PhysChemC 2007 111 1064418 SI Klokishner J Linares F Varret Journal of Physics

Condensed Matter 2001 13 59519 JM Baker Rep Prog Phys 1971 341 109

53

NON-CARBON PREPARATION OF SILICON BYMECHANICALLY ACTIVATED THERMAL SYNTHESIS

TF Grigorieva1 TL Talako2 AI Letsko2 V Šepelaacutek3 VG Scholz4MR Sharafutdinov1 IA Vorsina1 AP Barinova1 PA Vitiaz2

NZ Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry Kutateladzestr 18 Novosibirsk 630128 Russia grigsolidnscru

2 Powder Metallurgy Institute Platonov str 41 Minsk 220005 Belarus3 Inst of Nanotechnology KIT Eggenstein-Leopoldshafen 76344 Germany

4 Inst of Chemistry Humboldt Univ Berlin 12489 Germany

IntroductionIn industrial processes the production of Si is based on the

reduction of silicon dioxide by carbon at a temperature of about 1800 C[1] However the coke applied to the reduction can be hardly refinedfrom the most dangerous for silicon impurities like boron phosphorusarsenic and antimony That is why development of non-carbon routes forsilicon production is a topical problem of a silicon industry Reductionof oxides with magnesium and aluminum by the method of self-propagating high-temperature synthesis (SHS) has been used in industryfor a long time [2] As such reactions are highly exothermal they can bealso organized with the use of mechanochemistry for instance reductionof the copper oxide by aluminum Mechanochemical reduction of ironoxide by aluminum aimed at obtaining precursors with differentcompositions for intermetallideoxide SHS composites has been alsoconsidered [3ndash6]

SiO2 + Al reaction is not high exothermic enough to organize theSHS without preliminary heating [7] Mansurov et al [8] reportedcreation of ceramic composites in several stages first the silicon oxidewas mechanochemically treated in an organic compound environmentthen the resultant material was annealed (carbonized) at ~ 850 C andfinally the mixture of the carbonized silicon oxide with aluminum wassubjected to SHS However as-formed product included silicon carbide

The objective of activities described in this paper is to study thepossibility of using mechanochemical treatment for obtainingsiliconaluminum oxide composites by the SHS and thermal synthesis atconsiderably lower temperatures with the following removal of alumina

54

Sample preparation and examination proceduresThe PA-4 aluminum powder and the silicon oxide with a particle

size of ~ 3 nm were used in our experimentsA stoichiometric mixture of the silicon oxide with aluminum was

processed in a high energy planetary ball mill (drum volume 250 cm3ball diameter 5 mm mass of the balls 200 g mass of the sample 10 gand velocity of rotation of the drums around a common axis ~1000 rpm)

The IR spectra were recorded by a Specord IR 75 spectrometerthe samples for this study were pressed with annealed potassiumbromide

The 27Al (I = 52) NMR spectra were recorded on a BrukerAdvance 400 spectrometer corresponding to a 27Al resonance frequencyof 782 MHz MAS experiments were realized with a high speed probeusing 25 mm zirconia rotor The spinning speed was 20 KHz Themagnetic field strength (in frequency unit) was set to 104262 MHz Theexcitation pulse duration was chosen equal to 1 s The recycling delaybetween each acquisition was fixed to 1 s To see weak signals in the Al-O region in mechanically activated samples we applied accumulationsnumbers up to 56000 (ie measurement time of 15 hours)

The dynamics of the SHS process was studied with the use ofdiffraction of synchrotron radiation and an OD-3 single-coordinatedetector The samples for SHS were prepared in the form of pellets 20mm in diameter and 1ndash2 mm thick by pressing at a pressure of 200 atmThe resultant samples were placed onto a ceramic plate so that they werein the center of the goniometer The process was initiated by a nichromespiral The OD-3 detector was triggered to operate in the ldquofast filmingrdquomode simultaneously with the beginning of pellet burning The time ofone ldquoframerdquo was 05 sec and the number of ldquoframesrdquo was 128 Theradiation wavelength was 1527 Aring

For investigation of mechanically activated thermal synthesis thesamples were heated up to 650 C in the reaction chamber XRK 900 inair with a heating rate 10 min The OD-3 detector was also used forstudying the process dynamics though time of one ldquoframerdquo was 1 min

55

Results and discussionFirst we made an attempt of direct mechanochemical reduction of

the silicon oxide by aluminum The study of this process showed that thechemical reaction of SiO2 reduction does not occur within 6 min ofmechanical activation The IR spectrum of the initial mixture containsclear absorption bands with the maximums at 1005 and 480 cmminus1

(valence and deformation oscillations of the SindashO bond of the SiO4

tetrahedra of the siliconndashoxygen skeleton) and two maximums in therange of 900ndash670 cmminus1 due to oscillations of the SindashOndashSi bridges Thephenomena observed in the course of mechanical activation were agradual decrease in intensityand broadening of the characteristic bands of the SindashO bond (Fig 1)

An electron-microscopy study of the SiO2Al composite obtainedafter 1 min of mechanical activation in characteristic radiation revealed a

Fig 2 Microphotograph of themechanocomposite after 1 minactivation in Si characteristic

radiation

Fig 1 IR spectra of the SiO2 + Al mixturebefore mechanical activation (1) and aftermechanical activation during 05 (2) 1 (3)

and 6 (4) min

56

very small grain size and a very uniform distribution of the componentsin the mechanocomposite (Fig 2)

Based on the data of the differential thermal analysis (DTA) evenshort-time activation of this mixture appreciably affects its thermalcharacteristics For the initial mixture the real chemical interactionoccurs at a temperature T gt 1000 C (Tmax = 10836 C) (Fig 3 a) iesubstantially higher than the melting point of aluminum whereas thesituation is different for the mixture subjected to mechanical activationduring 20 sec Two clearly expressed exothermal peaks appear the firstpeak at 6217ndash6486 C (Tmax = 6327 C) and the second peak at 9921ndash10759 C (Tmax = 10292 C) (Fig 3 b) For the mixture activated for 40sec the first peak is at 6045ndash6366 C (Tmax = 612 C) and the secondpeak is extremely broad and smeared in the range of 8161ndash11117 C(Tmax = 10381 C)

These observations can be explained by the fact that a tightcontact is created between some part of the ultrafine non-plastic siliconoxide and plastic aluminum already within 20 sec of mechanicalactivation the silicon oxide is ldquowettedrdquo by aluminum as a result somepart of the silicon oxide starts to interact with aluminum at a temperatureT = 6217C which is lower than the melting point of the latter Asmechanical activation is continued aluminum becomes also dispersed tonanoparticles greater amounts of the components of the mixture areinvolved into the contact and the temperature of the interactionbeginning decreases after 1 minute of activation the interaction beginsat T = 5399 C and ends at T = 6303 C (Fig 3 c)

The curve for this sample obtained by the method of differentialscanning calorimetry (DSC) has only one exothermal peak ie theentire process proceeds at a temperature lower than the melting point ofaluminum Longer activation further decreases the temperature ofreaction beginning (Table 1) but there are no any further significantchanges in the system parameters determined by DSC

The duration of mechanochemical treatment was limited to 6 minfor the following reasons- the IR spectra are so smeared already after 4 min that do not provide

any new information (see Fig 1)- the DTA study does not reveal any significant changes in the thermal

characteristics after 1 min of mechanical activation (see Table 1)

57

- mechanochemical actions should be always minimized to ensure theminimum possible contamination of the products by milling

Fig 3 Results of differential scanning calorimetry (DSC) and thermogravimetry(TG) studies of the SiO2 + Al mixture before (a) and after mechanical activation

during 20 (b) and 60 sec (c)

58

Table 1 Parameters of Exothermal Peaks on DTA Curves of SiO2 + AlSamples after Mechanical Activation

Temperature CDuration of activation

beginning of thereaction

end of the reaction

1 min 5930 6303

2 min 5871 6243

4 min 5867 6291

6 min 5870 6258

27Al MAS NMR spectra of the nanostructured SiO2Almechanocomposites are dominated by a broad resonance associated withthe presence of nanostructured Al matrix (Fig 4) The interestingobservation is that additional resonance lines appear in the spectra ofmechanoactivated samples corresponding to AlO4 AlO5 and AlO6

polyhedra Their content is slightly increasing with increasing millingtime however the relative intensity of AlOx polyhedra compared withthe Al matrix spectral intensity is even after the longest milling periodvery low It can be assumed that these nonequilibrium localcoordinations of aluminium atoms are located on the SiO2-Al interfaces[9] The intensity of the resonance lines belonging to various polyhedrarelative to the total spectral intensity allows us to calculate the volumefraction of interface regions in the nanocomposites Furthermoreassuming a spherical shape of SiO2 nanoparticles the thicknees of theinterface regions was calculated their known volume fraction

Thus the study of mechanically activated SiO2+Al mixturesshows that silicon reduction does not occur during mechanical activationstep except formation of some AlOx species at the interfaces but anexothermal reaction in activated mixtures can proceed at substantiallylower temperatures

In the subsequent step the nanostructured SiO2Almechanocomposites were used as precursors for the preparation ofSiAl2O3 composites via self-propagating high-temperature synthesisOur experience shows that combustion initiation requires sample

59

preheating approximately to 200 C (as compared with 650-860 Сreported in [7])

Fig 4 27 Al MAS NMR spectra of non-activated sample (a) the samplemechanoactivated for 1 (b) and 6 (c) minutes

60

The overall pattern of phase transformations is illustrated in Fig 5a To analyze them however it is more convenient to use the projectiononto the diffraction angle (β)ndashtime plane (Fig 5 b) As the silicon oxideused in these experiments is amorphous to x-ray radiation onlyaluminum peaks are observed

Fig 5 Dynamics of phase transformations in the Al + SiO2 mechanocompositein the SHS mode (a) three-dimensional image (b) projection onto thediffraction anglendashtime plane

61

It is clearly seen thataluminum becomes heatedas the combustion waveapproaches the peaks areshifted toward smallerangles ie greaterdistances between theplanes After that theintensity of these peaksdrastically decreaseswhich is apparently due tomelting No crystallinephases are observed in thetwo frames (~ 1 sec) Inour opinion corundum(Al2O3) peaks appearslightly earlier than siliconpeaks A possible reason isthe lower melting point ofsilicon (1410 C) as compared with corundum (2050 C) An electron-microscopic study of the SHS product of the SiO2 + Al system subjectedto mechanical activation during 1 min in characteristic radiation (Fig 6)shows a fairly uniform distribution and small size of all elements in thesystem including silicon being formed

Previously it was shown that chemical interaction between SiO2

and Al in the mechanocomposites formed during the mechanicalactivation starts at essentially (~ 500 C) lower temperatures as comparedwith the non-activated mixtures

In the final step we used as-formed mechanocomposites asprecursors for the preparation of SiAl2O3 composites via thermalsynthesis The samples after mechanical activation for 6 min wereplaced into cuvette and gently prepressed to get the plane surface Thenthe cuvette with the sample was sited in the furnace The thermocouplewas directly close to the registration area Recording of diffractogramswas started at temperature 230 С Dynamics of phase transformation inAl SiO2 composites during heating from 590 up to 660 C is presentedin Fig7

Fig 6 Microphotograph of the SHS productin Si characteristic radiation

62

As can be seen from the Fig 7 the reaction products (silicon andalumina) start to form at about 590 С It is interesting that corundum isformed during the SHS and thermal synthesis after low activation time

Fig 7 Dynamics of phase transformation in Al SiO2 composites duringheating from 590 up to 660 C

Fig 8 XRD-pattern of the thermal synthesis product from the mechanocompositesactivated for 6 min and heated up to 660 C

63

while -Al2O3 is identified in the product of thermal synthesis afterlonger MA durations (Fig 8)

ConclusionsThus though the silicon oxide is not reduced by aluminum

directly by mechanical activation the use of the mechanocomposite as aprecursor for both SHS and thermal synthesis allows a fine-grainsiliconaluminum oxide composite to be obtained In both caseschemical interaction starts at essentially lower temperatures as comparedwith the non-activated mixtures

AcknowledgementsThis work was supported by the joint project No 5 ldquoNon-carbon

preparation of Si by mechanically activated thermal synthesisrdquo of NASBand SB RAS

References1 Denisov VM Istomin SA Podkopaev OI Serebrjakova LI

Pastuchov EA Beletsky VV Silicon and its alloys EkaterinburgPublishing house of Ural Branch of the Russian Academy ofSciences 2005 467 p (in Russian)

2 AG Merzhanov Forty Years of SHS Happy Life of a ScientificDiscovery (in Russian) Chernogolovka (2007)

3 TF Grigoryeva SA Petrova IA Vorsina et alldquoMechanochemical reduction of a copper oxiderdquo in TheOptimization of the Composition Structure and Properties ofMetals Oxides Composites Nano and Amorphous Materials Proc6th IsraelindashRussian Bi-National Workshop Jerusalem (2007) pp197ndash204

4 TF Grigoryeva TL Talako AA Novakova et al ldquoMA and MASHS production of nanocomposites metaloxides andintermetallicsoxidesrdquo ibid pp 139ndash148

5 NZ Lyakhov PA Vityaz TF Grigorieva et alldquoMechanochemically synthesized SHS precursors for obtainingintermetallideoxide nanocompositesrdquo Dokl Akad Nauk 406 No6 776ndash778 (2005)

64

6 5 T Talaka T Grigorieva P Vitiaz et al ldquoStructure peculiaritiesof nanocomposite powder Fe40AlAl2O3 produced by MA SHSrdquoMater Sci Forum 534ndash536 1421ndash1424 (2007)

7 Maltsev VM Gafiyatulina GP Tavrov AV Spreading of thecombustion wave in SiO2-Al systems Proc SPIE Vol 3172(111997) p 724-727

8 ZA Mansurov RG Abdulkarimova NN Mofa et al ldquoSHS ofcomposite ceramics from mechanochemically treated and thermallycarbonized SiO2 powdersrdquo Int J SHS 16 No 4 213ndash217 (2007)

9 V Sreeja TS Smitha Deepak N Ajithkumar TG and PA JoySize dependent coordination behavior and cation distribution inMgAl2O4 nanoparticles from 27 Al solid state NMR studies J PhysChem C 112 14737-14744 (2008)

37

THE PREPARATION OF MECHANICOMPOSITESTUNGSTEN-METAL AND SINTERING MATERIALS

T Grigoreva1 L Dyachkova2 A Barinova1 S Tsibulya3 N Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS 18Kutateladze str 630004 Novosibirsk Russia grigsolidnscru

2 Institute of Powder Metallurgy NAS B Minsk Belarus3 Boreskov Institute of Catalysis SB RAS Novosibirsk Russia

Tungsten-based materials are used for manufacture of electro-technical items spot welding electrodes spraying cathodes etc

The preparation of the high-melting materials is powerconsumptive as two-stage high-temperature sintering is used tungstenpre-sintering temperature is 1150 ndash 1300 C final tungsten sinteringtemperature is 2900 - 3000 C [1]

Metal additives with a lower melting temperature are introducedinto the high-melting material for sintering temperature reduction andsince the tungsten powder has a bad moldability level more plasticmetals such as copper nickel iron are introduced for the moldabilityimprovement

Tungsten ndash copper mixture has been studied the best so farThe mixture W-Cu sintering process research has shown [2] that

the product density depends on the initial powders dispersion degree andthe mixture composition So at the tungsten particles size 10-15 m themaximum densification is observed at the copper weight ration 50 The blend density sharply decreases with the copper content decrease(less than 35 ndash 40 wt) At the same time mixtures with the coppercontent not higher than 10 are needed Special methods have to beused for the preparation of the tungsten alloys

The active densification (from 44 till 12 ) is known to take placeat 1100 - 1200 C at sintering of mixtures W-20 vol Cu with tungstenparticles size lower than 1 m [3] Even higher densification speed isobserved in a blend attained with copper tungsten reduction whencomponents mixing practically achieves a molecular level [4] ie thesecond element concentration reduction is possible at tungsten particlessize decrease and homogeneous distribution of the both componentsThe original blends mechanical activation process [5ndash7] is very

38

perspective in this trend since grinding and formation of larger contactsurface between the original components take place during mechanicalactivation This process is especially effective at mechanical activationof solid and liquid metals and plastic ndash non-plastic metals pair Thecomposite nucleus (non-plastic component) ndash cover (plastic metal) canbe created in this case The possibility of chemical interaction onbetween tungsten and plastic metal the contact surface duringmechanical activation should be considered here

The work aim is to study structure and morphology of thecomposites formed at mechanochemical activation of the tungsten witha small content (till 10 ) of plastic metals both interacting (nickel iron)with it and not interacting (copper) with it The influence of the structureand morphology of the mechanocomposites on the processes of formingand sintering was studied

Powders of tungsten nickel iron copper were used forpreparation of mechanocomposites Mechanical activation of themixtures was carried out in a high energy planetary ball mill with watercooling in argon atmosphere (drum volume ndash 250 cm3 balls diameter ndash5 mm the load ndash 200 g the sample - 10 g the velocity of rotation of thedrums around a common axis 1000 rpm)

X-ray analysis was carried out with diffractometer D8 AdvanceBruker (Germany) at the CuK radiation Research of the structure andmorphology of the mechanocomposites was carried out with thescanning electronic microscope (SEM) ldquoMira LMHrdquo with the add-ondevice for micro-x-ray analysis The electronic probe comprised 5 2 nmthe actuation area comprised 100 nm The research was carried out inmodes of registration of absorbed (AE) and backscattered (BSE)electrons and also of characteristic radiation of tungsten copper nickeland iron The sintered materials research is carried out with themetallographic microscope MEF-3 (Austria) at zoom times200 and times950

The compressibility was determined via density in compliancewith the ISO 3927-1985 of cylindrical samples with diameter 10 mmheight 12 mm pressed in a steel die-mold at pressure 200 400 600 and800 MPa The pressed samples were sintered in vacuum at temperatureof 1100 ndash 1450 C

Compression strength of mechanically activated blends wasdetermined via the samples of diameter 10 mm height 12 mm

39

transverse strength ndash via prismatic samples with height 5 mm width 10mm length 55 mm The tests were preformed on the testing machineldquoInstronrdquo with the loading speed 2 mmmin

Sintered samples microstructure was studied on metallographicsections etched with solution (10 g K3Fe(CN)6 10 g KOH 100 mlH2O) via metallographic microscope MEF-3 of the company ldquoReihertrdquo(Austria)

Mechanical activation was carried out in two stages for attainingmechanical composites tungsten ndash metal (Cu Ni Fe) The first stagesaw grinding only tungsten for 4 min At the second stage 7 ndash 10 copper (nickel iron) was added and joint mechanical activation wascarried out for 1 ndash 2 min

In compliance with the x-ray data the initial tungsten sample is awell-crystallised powder (Fig 1a) The intensity of the diffraction peaksshows the texture (of the preferred orientation) presence in trend 110The X-ray pattern of the tungsten samples activated during 4 min (Fig1b) has widened peaks The X- ray analysis shows that widening ismostly caused because of micro-defects in the tungsten structure (at thelarge particles sizes retaining) It should be also noted that thedistribution intensity of the peaks shows the texture absence (the equalparticles distribution in powder from the point of view of theircrystallographic orientation)

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

Ia

u

2 Theta degree

110

200

211

220

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

Ia

u

2 Theta degree

a bFig 1 X-Ray patterns for initial W (a) and activated for 4 min (b)

40

During the mechanical activation in a high energy planetary ballmills plastic metals tend to stick to balls and the drums walls even atshort-time activation because of that they were introduced to the blendsinto the already activated for 4 minutes tungsten and the mixture wastreated for 2 minutes more

The different X-Ray patterns were received for the samples withCu Ni Fe additives (Fig 2) The second metal phase is seen to bepresent in a well-crystallised form besides the phase W in all cases thecopper picks relative intensity is however considerably higher than thenickel picks intensity that in turn exceeds the iron reflection intensityFormation of intermetallic compounds in the X-ray-amorphous state oncontact surface WNi WFe can be supposed to be possible forchemically interacting metal pairs (tungsten ndash nickel tungsten ndash iron)X-Ray research data are indirect confirmation of this supposition Thesedata have shown that mechanochemical efforts donrsquot allow to receivehomogeneous distribution of copper in the tungsten matrixMechanocomposites W + 10 Cu is arranged in compliance with theldquosandwichrdquo principle where copper phase of micrometric size is locatedin the tungsten die (Fig 3)

The second metal phase is seen to be present in a well-crystallisedform besides the phase W in all cases the copper picks relative intensityis however considerably higher than the nickel picks intensity that inturn exceeds the iron reflection intensity Formation of intermetalliccompounds in the X-ray-amorphous state on contact surface WNiWFe can be supposed to be possible for chemically interacting metalpairs (tungsten ndash nickel tungsten ndash iron) X-Ray research data areindirect confirmation of this supposition These data have shown thatmechanochemical efforts donrsquot allow to receive homogeneousdistribution of copper in the tungsten matrix Mechanocomposites W +10 Cu is arranged in compliance with the ldquosandwichrdquo principle wherecopper phase of micrometric size is located in the tungsten die (Fig 3)Electron microscopy and X-Ray research of mechanocomposites forinteracting metals (W + 10 Ni) has shown homogenous nickeldistribution

41

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Ia

u

2 Theta degree

Cu

а

40 50 60 70 80 90

0

1000

2000

3000

4000

Ia

u

2 Theta degree

Ni

b

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Iau

2 Theta degree

Fe

c

Fig 2 X-Ray patterns for mechanocomposites W (4 min) + additives Cu(a) Ni (b) Fe (c) (2 min)

The received result allows to suggest that metals distributionhomogeneity depends on the thermodynamical parameters of theirmixture (Нmix(W-Ni) = - 2 kJmol Нmix(W-Cu) = + 10 kJmol [8])and on a possibility of the chemical interaction between them The thinlayers of intermetallic compounds form on the continuously renewingcontact surface in the systems W-Ni and W-Fe for this time period (1-2min) and because of distance these thin layers do not manage to form acrystalline phase that could be fixed in X-Ray way

42

а bFig 3 Micrographs of the mechanocomposites W-Cu (a) W-Ni (b) in

characteristic radiation Cu and Ni

The research of compressibility of various mechanocompositeshas shown that non-interaction metals (W-Cu) couldnrsquot compressed andthe compressibility of the interaction metals (W-Ni W-Fe) depends ofthe contents of additives Research of compressibility of mechanicallyactivated powders of various composition has shown that tungsten ndash10 iron mixture powder has the best compressibility level andtungsten ndash 7 nickel mixture powder has the least compressibility level(Fig 4)

But it should be noted that mechanically activated powderscompressibility level is not high moreover some mechanocompositesdo not have compressibility at specific pressure 200 ndash 300 MPa and thesamples layering is observed at pressure higher than 600 MPa Therelative density of the pressed samples is 50 ndash 78 It indicates at thenecessity of the additional lubricants introduction into the mechanicallyactivated powders for their compressibility increase

43

Fig 4 Tungsten-based mechanocomposites compressibility curve

For the powders compressibility improvement the lubricants areintroduced directly into initial mixture or plated to the press-mouldsurface for decrease of friction between the powder and the press-mouldwall and also between the powder particles The lubricant removaltemperature depends on the lubricant melting or dissociationtemperature The melting and boiling temperature or the lubricantsdissociation temperature generally used in powder metallurgy are givenin table 1 [9]

Stearates especially zink stearates have the leading place Therest lubricants have not got such a wide use since residual remains aftertheir removal [10]

Nowadays nylon-binding-based lubricant has been developedabroad This nylon binder is introduced during the charge mixingprocess and needs warm pressing [11-14] Such a lubricant allowsattaining high (θ is no less than 95 ) density of iron-based materials

The lubricant addition as a rule retains ~1 wt as higher contentleads to the pressing growth if the lubricant is present in the sinteringprocess till the sintering temperature

The lubricant burning-out process is carried out in the protective-reducing atmosphere in separate furnaces or in a sintering furnace (in thearea separated from the sintering area) The lubricant burning-outtemperature is as a rule not high and comprises 600 ndash 800 C

44

Table 1 Temperature of melting and dissociation of solid lubricants

Lubricant Lubricant formulaMeltingpoint С

Boiling ordissociation

point СZink stearate Zn(C18H35O2)2 140 335Calcium stearate Ca(C18H35O2)2 180 350Aluminium stearate Al(C18H35O2)2 120 360Magnesium stearate Mg(C18H35O2)2 132 360Plumbum stearate Pb(C18H35O2)2 116 360Lithium stearate LiC18H35O2 221 320Stearinic acid CH3(CH2)16CООH 694 360Oleinic acid С8Н17СНСН-

(СН2)7СООН13 286

Benzol acid С6Н5СООН 122 249Hexoic acid СН3(СН2)4СООNН2 -4 205Paraffin From С22Н46 till

С27Н56

40-60 320-390

Molybdenum disulfide MoS2 1185 -Tungsten disulfide WS2 1250 -Manganous sulphide MnS 1655 -Graphite С (crystalline) 3500 -Molybdenum trioxide MoO3 795 -

During one-component materials heating till 100 ndash 150 C thechange of the contact character between the particles connected withwater evaporation and elastic stress relief tale place As a result somecontact areas rupture and as a consequence general inter-particlecontact surface decrease are possible

The elastic stress relief is ended the further gases are removedand burning-out of the lubricants and binders introduced to the powdertake place during heating from 150 C till the temperature comprising 40ndash 50 of the metal melting temperature The oxide films reduction andnon-metal contact replacement with a metal one take place at highertemperatures although visible pressings density change does not takeplace

45

This work saw lubricants introduction during mechanicalcomposite formation zink stearate stearinic acid and lauric acid wereused The lubricants were introduced in amount of 0 1 0 2 0 3 0 5wt During mechanical activation metal ndash organic acid the latter ismelted (the melting temperature is lower than 70 C) and thus it wets themetal surface and flows with the formation of a larger contact surface Incase of good wettability and sufficient amount of the low-meltingconstituent all the solid-phase surface becomes contact ie mixturenucleus (metal) ndash cover (organic substance) is formed [15] Thecompressibility level has to be naturally higher in this case andmechanochemical approach allows a substantial reduction of plasticizingagentsrsquo concentration

Research of compressibility of powders with lubricants has shownthat Zink stearate has the least influence in comparison to otherlubricants used (Fig 5)

Fig 5 The compressibility curves of the mechanocomposites W-Fe with thelubricant 1 ndash zink stearate 2 ndash lauric acid

The lubricant content increase leads to the mechanically activatedpowders compressibility improvement (Fig 6) but at the lubricantcontent more than 0 3 the samples destruction takes place at sinteringbecause of intensive gas release Plasticizing agents introduction hasallowed mechanical composites formation also for non-interactingmetals (tungsten ndash copper) (Fig 6 7)

46

Fig 6 The compressibility curve of the mechanically activated blend W-Cuwith stearinic acid 1 ndash 0 1 2 ndash 0 3 3 ndash 0 5

Fig 7 The compressibility curves of the mechanically activated blend W-Cuwith lauric acid 1 ndash 03 2 ndash 05

Lauric and stearinic acids additives allow the pressings densityincrease by 25 ndash 40 (Fig 5 8)

Research of density of sintered samples of mechanocomposite hasshown that the density of the samples from mixtures tungsten ndash ironpressed at 400 and 600 MPa does not practically change after sinteringat 1250 C (Fig 9 line 2 5) and at 1450 C the samples density decreases(Fig 9 line 3 6) Mixtures tungsten ndash nickel are subject to a substantial

8

9

10

11

12

200 400 600

De

nsi

ty g

сm

3

Pressure МPа

1

2

11

115

12

125

13

200 300 400 500 600

10Fe+W

10Ni+W

De

nsi

tyg

cm

3

Compacting pressure MPa

47

shrinkage (Fig 10) and density of the samples of W-Ni pressed at 400MPa is 146 gcm3 after sintering at 1250 C and 147 gcm3 at 1350 CSintering temperature increase till 1450 C leads to samples shrinkinglevel reduction and density does not exceed 117 gcm3

Fig 8 The compressibility curves of blends W + 10 Fe and W-10 Ni withaddition of 1 of stearinic acid

Fig 9 Relation of density of mechanically activated blends W + 10 1 ndash afterpressing at 400 MPa 2 ndash pressing at 400 MPa sintering at 1250 ordmC 3 ndashpressing at 400 MPa sintering ndash at 1450 ordmC 4 ndash after pressing at 600 MPa 5 ndashpressing at 600 MPa sintering at 1250 ordmC 6 ndash pressing at 600 MPa sintering at1450 ordmC

10

11

12

13

14

200 400 600

Pressure МPа

Density

gс

m3

1

2

3

0

2

4

6

8

10

W+Fe

De

nsityg

cm

3

12 3

4 5 6

48

0

3

6

9

12

15

400 МPа 600 МPа

De

nsity g

сm

3

Fig 10 Relation of density of mechanically activated blend W + 10 Ni 1 ndashafter pressing 2 ndash pressing sintering at 1250 C 3 ndash pressing sintering at 1350C 4 ndash pressing sintering at 1450 C

Moulding pressure increase till 600 MPa practically does not

influence the sintered samples density Density reduction of the samples

sintered at 1450 C is apparently explained with dissociation of oxides

and other compounds of tungsten and nickel

Sintering at 1450 ordmC of blends W-Ni leads to meltback and

samples form loss thus sintering should be carried out at temperature

not higher than 1350 ordmC

Tungsten-based mechanocomposite strength research has shown

that strength has a direct relation to their density (Fig 11) The blend

tungsten ndash iron (870 MPa) has the minimal strength

The microstructure analysis has shown that in case of sintering at

temperature 1250 C tungsten ndash nickel have a very fine dispersed

structure (Fig 12) Coagulation of nickel insertions located at the base

grains boundaries in tungsten ndash nickel grains growth take place with

sintering temperature increase

49

0

100

200

300

400

500

600

700

800

900

1000

1100

1 2

Ela

stic

lim

it of

com

pre

ssio

n

МP

а

I - pressure 200 МPа

II - pressure 400 МPа

III - pressure 600 МPа

1 - sintering temperature 1250оС 2 - sintering temperature 1350

оС

I

II

III

Fig 11 Influence of attaining modes of samples from mechanically activatedblend tungsten + 10 nickel on their strength

Substantial grain growth large porosity formation nickel phase

particles growth take place in blends sintered at 1450 C eutectic that is

more visible in the blend tungsten ndash nickel is formed at tungsten grains

boundaries

Conclusions

The conducted research has shown that homogenous copper

distribution is failed to be carried out in tungsten with short-term

mechanical activation method for interacting metals of W-Cu system

These mechanically activated samples can be not compacted (moulded)

50

a b

c dFig 12 Microstructure of mechanically activated blends W-Ni sintered at 1250C (a b) and 1350 C (c d) a c ndash times200 b d ndash times950

Homogenous distribution of nickel and iron in tungsten is ensuredwith short-term mechanical activation in systems from interactingmetals The attained samples are formable mechanically activatedpowders compressibility has however been found to be not high therelative density of the pressed samples is 50 ndash 78 and that points atnecessity of additional lubricants introduction into powders for theircompressibility improvement Lubricants introduction allowed ensuringmoldability of immiscible system tungsten ndash copper and densification ofpressings by 25 ndash 40 - for interacting metals

Density of samples from blends tungsten ndash iron does notpractically change after sintering at 1250ordmC and is decreased at 1450 ordmCBlends tungsten ndash nickel are subject to a substantial shrinkage during

51

sintering Sintering temperature increase till 1450 ordmC also leads to theshrinkage level decrease Strength of sintered blends from mechanicallyactivated tungsten-based powders depends on density and kind of theadditive Grain size dispersivity and type of additive location in theblend structure from mechanically activated powders depend on thesintering temperature

AcknowledgementsThe work was carried out within the framework of Fundamental

Research Programme of Russian Academy of Sciences ldquoElaboration ofchemical substances attaining methods and new materials creationrdquoproject No 1821 ldquoElaboration of tungsten mechanical composites-basedhigh-density alloys creation basicsrdquo

References1 IM Fedorchenko IN Francevich ID Radomyselskiy at al

Powder Metallurgy Materials technologies properties andapplications Kiev Naukova dumka ndash 1985 ndash 624 P

2 VN Eremenko JV Najdich IA Lavrinenko Sintering in thepresence of liquid metal phase Kiev Naukova dumka ndash 1968 ndash 122P

3 VV Panichkina MM Sirotuk VV Skorohod Powder Metallurgyndash 1982 - 6 ndash P27-31

4 VV Skorohod YuM Solonin NI Filippov at al PowderMetallurgy ndash 1983 - 9 ndash P9-13

5 Kim JС Moon IН Nanostruct Mater 1998 Vol 10 No 2 P283-290

6 Moon IH Kim EP Petrow G Powder Metallurgy 1998 Vol41 No 1 P 51-57

7 Kim JC Ryu SS Kim YD Moon IH Scripta Mater 1998 Vol39 No 6 P 669-676

8 FR de Boer R Boom WCM Mattens AR Miedema andAK Niessen Cohesion in metals (Cohesion and structurevol 1) (Elsevier Amsterdam 1988) pp 758

9 Hausner H Handbook of Powder Metallurgy Chemical PublishingCo New York 1973

10 Moyer KH Intern J Powder Met 1971 - 7 Р 33

52

11 US patent В 22 F 100 5368630А Powder Metallic Blend with abinder for densification at the set temperature Journal Inventions ofcountries worldwide 1996 1

12 US patent В 22 F 100 5429792 Metal powder content containing a binder for pressing at elevated temperatures JournalInventions of countries worldwide 1996 7

13 US patent В22F 100 (11) 52980555 (40) 940329 laquoIron-basedpowder mixtures with a binding lubricantraquo 1995

14 US patent В 22 F 100 95372138 (5484469А) laquoMetal powder content and a method of a sintered part manufacture from itraquo 1995

15 TF Grigoryeva AP Barinova NZ Lyahov Mechanochemicalsynthesis of metal systems Novosibirsk Parallel ndash 2008 ndash 311 P

34

THE DETERMINATION OF THE KINETIC FUNCTIONSTRUCTURE FOR THE HIGH-TEMPERATURE SYNTHESIS IN

THE MECHANICALLY ACTIVATED MIXTURE 3Ni-Al

VYu Filimonov1 MA Korchagin2 EV Smirnov1NZ Lyakhov2

1Altai State Technical University Barnaul2Institute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirskvyfilimonovramblerru

The peculiarities of heating-up and phase formation in themechanically activated powder mixture 3Ni + Al reacting in the thermalexplosion mode have been experimentally investigated The self-heatingin the mixtures was studied using a specially designed SHS-reactorusing a technique presented in [1] Tungsten-rhenium thermocouples of100 microm diameter were used to control the temperature and to recordthermograms Preliminary mechanical activation was carried out using aplanetary ball mill of AGO-2 type in an atmosphere of argon under theenergy of 40g (centrifugal acceleration of balls 400 ms2) with varyingtime of the activation process The reactant mixtures were preparedusing the aluminum powder PAndash4 particle size 5 divide 60 microm and thecarbonyl nickel powder PNK-1L5 particle size 1 divide 10 microm

The primary goal of this work was to determine the activationenergy and the structure of the kinetic function during the heat evolutionin the system as a result of the phase formation At the adiabatic stage ofheating a system of equations of the temperature increase and thedynamics of the degree of transformation was considered [2]

0 expdT E

k fdt RT

(1)

f

RT

Ek

dt

d

exp1

(2)

The initial conditions are as follows 00 t 0TT where

T temperature of the reacting mixture degree of transformation

t time 0k 1k exponential factors E activation energy f -

35

kinetic function The search for )(f was performed in the known class

of functions [3]

exp

1nm

f

(3)

At the first step of analysis of the experimental thermograms theeffective activation energy of the phase formation was determined from

the curvature of the experimental plot ln 1dT dt f T Based on the

results of 6 measurements and using the slope of the fitting curvepassing through the point of the minimum curvature the effectiveactivation energy was determined which turned out to be anomalouslylow and equal to E = 95plusmn2 kJmol It was found that the experimental

results are best fitted with a function 1n

f where

09 015n [4] Fig1 shows the results of integration of (11) with the

determined parameters

Fig1 Results of integration of (11) -1 experimental thermogram -2

Since the interaction of the reactants is described by the law ofhomogeneous kinetics we suggest that during thermal explosion in themechanically activated mixture of the composition under study thesynthesis occurs through homogeneous regrouping of atoms of the initialreactants without formation of dense diffusional layers hindering thereaction The latter is possible due to high concentrations of defects andinternal stresses formed as a result of intensive plastic deformation of theinitial reactants during mechanical activation

36

References1 Filimonov VY Evstigneev VV Afanasev AV and Loginova MV

Thermal Explosion Ti + 3Al Mixture Mechanism of PhaseFormation International Journal of Self-Propagating High ndashTemperature Synthesis-2008- vol 17-2рр 101-105

2 Aldushin AP Martemyanova T M Merzhanov A G Propagationof the front of an exothermic reaction in condensed mixtures withthe interaction of the components through a layer of high-meltingproduct Composition Combust Explos Shock Waves19728(2)159

3 M I Shilyaev V Е Borzykh A R Dorokhov and V EOvcharenko Determination of thermokinetic parameters from theinverse problem of an electrothermal explosion Combust ExplosShock Waves 1992 28(3)258

4 MA Korchagin VYu Filimonov EV Smirnov NZ LyakhovThermal explosion of a mechanically activated 3Ni + Al mixture Combustion explosion and shock waves 2010 v 46 1 pp41-46

14

MODERN METHODS OF RHENIUM DETERMINATION

OV Evdokimova NV Pechishcheva KYu ShunyaevInstitute of Metallurgy of UB RAS

101 Amundsen st Ekaterinburg Russiashunuralru

IntroductionRhenium due to its unique properties is the promising metal

widely used in various industries At present day the main areas ofapplication of rhenium is the production of catalysts for the petroleumrefining industry and refractory alloys used for turbines manufacturing[1]

The great demand for this element requires large amounts of itsproduction There is a need extracting rhenium even from industrialwaste water from plants [2] due to the high cost and its low content innatural materials

This situation stimulates the development (or modification) ofmethods of analytical control of various nature materials

The content of rhenium in rhenium-containing materials bothnatural and technogenic and contect of accompanying to rheniumelements vary in a wide range of concentrations from 10-7 to tens ofpercent

Earlier the following methods were used for the determination ofrhenium spectrophotometry gravimetry kinetic electrochemicalextraction-fluorimetric methods X-ray fluorescence analysis [3] Themain disadvantages of mostly methods for determining rhenium are thelow sensitivity the bad reproducibility of results the influence ofaccompanying elements Ag W Mo Pt Cu Fe and etc

In modern analytical practice the following methods for therhenium determination are used inductively coupled plasma atomicemission spectroscopy (AES ICP) inductively coupled plasma - massspectrometry (ICP-MS) [4] electrochemical methods [1] X-rayfluorescence analysis and spectrophotometric methods do not lose theirrelevance [1] they have undergone significant modifications recently

15

Inductively coupled plasma atomic emission spectroscopy(AES ICP) is widely used for the rhenium determination in mineral rawmaterials and products of metallurgy production This method allows todetermine up to 10-4 rhenium The advantage of AES ICP is the highstability and reproducibility of results absence of chemical influences

However analysis of more complex objects such as metallurgicalproducts is a not easy task because the lines of rhenium emission areoverlaped with the lines of accompanying elements in samples So thelines of Mo (221427 nm) W (221431 nm) Fe (227519 nm) whichmay be present in the samples in large quantities are overlaped to themost intense lines of rhenium (221426 nm and 227525 nm) Thisproblem requires the development of new methods of samplepreparation and selection of optimal conditions for determination ofrhenium by atomic emission spectrometres

Also a significant disadvantage of this method is the small rangeof certificated reference materials So there are a limited number ofRussian rhenium standard materials with certified value of the rheniumcontent It is molybdenum and copper-molybdenum ores andconcentrates in which the rhenium content is in the range ofconcentrations from 000047 to 00221

In most cases analysts develop the synthetic mixture to monitorthe rhenium content in the analysis of specific samples of complexcomposition This mixture is similar to composition to the matrix of theanalyzed samples consisting of rhenium ions and other ions with agiven concentration For example the authors [5] to develop a techniquefor rhenium determining together with platinum and palladium in thesamples of spent catalysts by AES-ICP applied a synthetic mixtureprepared on the basis of aluminum oxide and standard solutions of Pt(IV) Pd (II) Re (VII)

One of modern methods and the most sensitive methods for thedetermination of rhenium is inductively coupled plasma - massspectrometry (ICP MS) [4 6 7 8] These days ICP MS withseparation and concentration allows to measure rhenium at lower thanseveral ngg However ICP MS performance in analyses of complexsamples is commonly affected by matrix effects and polyatomicinterference and signal drift High levels of salt solutions content cause

16

plugging of sampling orifice with decrease in analytical signal inaddition many spectral interferences may occur [6]

For the rhenium determination in molybdenite by ICP MS shouldbe use large dilution of sample to reduce the matrix influence and reducethe salts influence However this approach is not feasible in the case ofhigh levels of molybdenum and relatively low levels of rhenium in theanalyzed objects The most effective way to minimize the matrix effectsis separation of rhenium from the matrix Often for this purposeextraction by organic solvents [6] sorption by anion-exchangers [8] areused

Recently X-ray fluorescence analysis becomes more popular Itis rapid and is often used for mass analysis The advantage of thismethod is the possibility of direct determination of rhenium in the solidsamples in water solutions [9 10] in the biological samples (plants) [2]

However the method is not without disadvantages firstly thedetection limit of rhenium by X-ray fluorescence analysis is low and isonly 005-01 secondly there are only few the standard materials witha high rhenium content and thirdly the influence of interfering elementsin the sample related to determination of rhenium

Using the concentration can not only reduce the detection limitbut also in the same time solve and reduce the influence of interferingions For the concentration of rhenium in X-ray fluorescence analysis isoften used sorption of rhenium in the form of perrhenate-ions [9 10]

The authors [11] describes a problem related to the developmentof rhenium-containing standard materials by traditional hightemperature approach for X-ray fluorescence analysis Thus high-temperature studies of MoO3-ReO3 which could be served ascomparison materials for the rhenium determination by X-rayfluorescence analysis showed that 50-90 of rhenium is lost duringcalcination of mixtures it indicates the impossibility to use them fordevelopment of standard materials In the paper [11] the method ofpreparing rhenium glassy reference samples (10 - 50) on the basis ofBi2O3 and B2O3 is described The developed method allows to determinerhenium in the range of 001-10 [11]

17

Electrochemical methods in particular the electrostrippingvoltammetry (ESV) occupy a significant place in the analyticalchemistry of rhenium [12 13] This method allows to determine up to10-6-10-5 of rhenium

To avoid the effects of many electropositive components (Mo WCu Ag Au) which may interfere to the rhenium determination by ESVit has been proposed the sorption concentration of perrhenate ions on thesurface of activated charcoal (BAU) [12 13]

The most widely used techniques determine the 10-2 - 10-5 ofrhenium is spectrophotometric method The advantages of this methodare simplicity low cost equipment and a relatively high sensitivitySpectrophotometric method is based on the formation of coloredcomplex compounds of rhenium with organic and inorganic ligands [1]Photometric methods with thiocyanate ion thiourea are widely spread[14 15 16] Development of spectrophotometric methods for rheniumdetermination is largely due to the searching and using of new reagentsIn [17] for the extraction-photometric determination of perrhenate ionsin the form of ion associates the basic polymethine dyes derivatives of133-trimethyl-3H-indole have been offered but the influence ofoxyanions of tungsten and molybdenum is not excluded [17]

The disadvantage of the spectrophotometric methods is the needfor prior separation of rhenium from a number of interfering elements(Mo W Cu) that it is achieved by concentrating perrhenate-ions bysorption or extraction

Over the past decade main changes in the methods of rheniumdetermination related with the improvement stadium of samplepreparation transfer the sample into an analytical form modification ofknown methods and reagents (eg creation of new facilities developmentof new reagents for measurements) and conditions of analysis

In general in the literature a large number of works are relatedwith the separation of rhenium from the analyzed solutions and theseparation of rhenium (VII) from interfering elements by using newtypes of extractants and new sorbents is given Used extractants andsorbents as well as the optimal conditions for extraction and sorption ofrhenium are presented in Table 1 and 2 respectively

18

Extraction plays a dominant role in the methods of separationand concentration of rhenium

In most cases in the hydrometallurgical processing of rhenium-containing products in the acidic solutions ReO4

- are formed Forperrhenate ions extraction the anion-exchange reagents or extractants ofneutral type are often used The literature contains information on theextraction of rhenium (VII) by various amines and quaternaryammonium compounds [18 19 20] Efficient extractants of rheniumfrom acidic solutions are neutral organophosphorus compounds (tributylphosphate alkylphosphineoxides their derivatives) [21 22] a variety ofsolvent mixtures (tributyl phosphate + trioctylamine [23]) theextractants of neutral type such as ketones and aliphatic alcohols [1624 25]

Alcohols ketones and ethers are more selective having higherspeed separation of organic and aqueous phases as well as higherchemical resistance and lower cost compared with amines andorganophosphorus compounds but inferior to them in the extractioncapacity for rhenium (VII) [16]

Thus for perrhenate ions extraction aliphatic alcohols with 7-10carbon atoms in the aliphatic chain are well proven that can extractmore than 98 of rhenium from sulfuric acid and hydrochloric acidsolutions In the case of alcohol there is no need to use solvents andmodifiers what simplifies their use in extraction processes [16]

The efficiency of rhenium extraction into organic phase by aminesdecrease as follow quaternarygt tertiarygtsecondarygtprimary Amongthem secondary and tertiary amines are widely used as efficientextractants of rhenium from acidic solutions Perrhenate ions areextracted by amines in a wide range of pH For systems of amine - low-polar diluent - H2SO4-ReO4-H2O the formation inverse micelles istypical in the organic phase Acid ions and anionic complexes arelocated inside the aqueous core of the micelle with the metal ioncoordinates the polar functional group of amine [19 20]

It should be noted that the extraction by amines is complicated bythe use of solvents the nature of which depends on the solubility ofamines and their extraction capacity So low-polarity solvent toluene incontrast to the non-polar kerosene enhances the polarity of anionic saltsof amine which increases the reactivity of the extractant to the anion

19

exchange of inorganic acid to extractable anionic rhenium complexes[18]

Tertiary amines are the most effective extractants for rhenium(VII) However in paper [18] it is shown that the secondary amine(diisododecylamine) gives advantage to the tertiary amines on therhenium extraction efficiency from sulfuric acid media It can beexplained by the influence of steric factors and smaller rival extractionof mineral acids by secondary amines [1]

Most papers are related to the rhenium extraction from acidicsolutions but the extraction of rhenium from alkaline medium whichare formed after leaching of ores concentrates also represents a difficultproblem In the paper [23] rhenium extraction from alkaline solutionscontaining also molybdenum by solvent extraction using a mixture oftributylphosphate (TBP) and trioctylamine (N235) is describedMolybdenum which is also extracted by solvents in small amountsinterferes to the extraction of rhenium

Over the last decade most works refer to the development offundamentally new classes of extractants for perrhenate ions [26 2728 29] such as encapsulating ligands (cryptands and podands)macrocycles crown ethers These ligands can interact with ReO4

minus byboth the electrostatic interaction between ReO4

minus and protonated ligandand the hydrogen bond formation compared with simple open-chainligands If the complex between ReO4

minus and ligand has highhydrophobicity ReO4

minus in an aqueous solution may be separatedeffectively by a solvent extraction technique [30]

Crown ethers extract rhenium (VII) in the presence of potassiumor sodium in the form of K(Na)LReO4 (L-crown-ether) into the organicphase (12 - dichloroethane chloroform) [31 32] In the paper [31] theextraction perrhenate-ions by 3m-crown-m-ethers (m = 56) ether and itsmono-benzo-derivatives in 12-dichloroethane are described

Podands are analogues of crown ethers containing terminalphosphoryl ligands in their polyether chains they are used for theextraction of rhenium (VII) The efficiency of extraction by phosphorylpodands depends of the following factors the number of oxygen atomsin the polyether chain molecules the number of donor centers in themolecule of podands hydrophobicity of the reagent molecule the size offorming cycles the nature of substituent at the phosphorus atom Studies

20

have shown that phosphoryl podands with three oxygen atoms in thearomatic polyether chain combined with the phosphoryl group bydimetilen or o-phenylene fragments have high extraction ability forrhenium from sulfuric acid solutions [32]

In the paper [30] authors mark another type of podands such aspodands with nitrogen donor ligand -N N N `N`-tetrakis (2-pyridymethyl) -12-ethylendiamine (TREN) and its hydrophobicanalogs which also allow to extract perrhenate ions from highly acidicenvironments

Perrhenate is characterized by its ability to undergo a change ingeometry specifically from tetrahedral to hexagonal in the presence ofdonor ligands (eg acetonitrile triphenylphosphine) Protonationchanges the electron density present on the oxygen atoms Beer et al[33] suggested that the tripodal ligand L1 would be suitable for thebinding and extraction of perrhenate anion This ligand (Fig 1) basedon the combination of tris(2-aminoethyl)amine and crown ether motifswas found to complex sodium cations and to extract perrhenate anionsfrom aqueous solutions into an organic phase

Atwood and co-workers developed calixarene-type ligand L2(Fig 1) that specifically extracts perrhenate from water solution into anorganic phase The selectivity for extractions decreases as followTcO4

minus ge ReO4minus gt ClO4

minusgtNO3minus gtSO4

2minus gtClminus This selectivity pattern isattributed to a combination of charge size and shape Efficientextraction is observed at high and neutral pH the molar ratio ofligandperrhenate ion = 14 [33]

L1 L2Fig 1 Tripodal ligand L1 and calixarene-type ligand L2 for perrhenateextraction

21

Schiff-base macrocycles are used as a new conjugatedmacrocycles for perrhenate ions Thus a series of amino-azacryptands(L3ndashL16) for encapsulation and extraction of the oxoanions perrhenate(Fig 2) from aqueous solution were proposed by the authors [34]Thecomplexation amino-azacryptands L to ReO4

- is via hydrogen-bondedinteractions

Fig2 Amino-azacryptands (L3ndashL16) for encapsulation and extraction of theoxoanions perrhenate

Thus the main characteristics of the compounds for the effectiveperrhenate ions extraction as follows

Energy coordination of ligand with ReO4- should be higher than

the energy of perrhenate ion hydrationThe interaction between the ligand and perrhenate ions an

electrostatic interaction or the formation of hydrogen bonds Functional ligands to be a suitable size (volume of the cavity

should be more than 736 Aring3) shape electronegativity andhydrophobicity

Ligand should be protonated

22

Table 1 Characteristics of extractants for rhenium extraction

Extractant

Analysis objectComposition of

the initialsolution

Extractonconditions

Interferinginfluences

Aliphatic alcoholswith C 7-10

1-Heptanol 4-Heptanol 1-octanol 1-decanol 4-decanol 2-Heptanol 3-Heptanol

3-octanolback-extractant

NH4OH

Solutions HCland H2SO4

Т=293КTime of phase

contacttex = 5 min

organic phase toaqueous

(OL = 11)4 steps of

extraction 2stripping

Coextractionof mineral

acidsincomplete

re-extractionof Re (VII)

1

OctanolSolutions ofHNO3 and

H2SO4

Т=286-290Кtex = 10 min OL

= 11

Coextractionof HNO3

H2SO4

2

Basic polymethinedyes (derivatives of133-trimethyl-3H-

indole) astrazon violet

Aqueous andaqueous-organic

solution

Т=293КрН=6

tex = 10-30 secextractant mixture

toluene +dichloroethane

(1 1)

do notinterfere

3000-5000fold excess ofS04

2- CO32-

300- HPO42-

MoO42-

WO42-

10-20 S2O32-

Cr2O72- IO3

-metal ions as

sulfates

3

Secondary(diisododecylamine)and tertiary amines

(dioctylamin andtrioctylamine)

Solutions H2SO4

Т=293КA wide range of

pH

tex=5-7 mindiluent - toluene

-

4N-benzoyl-N ndashphenyl-

hydroxylamine

Molybdenitedissolved inHCl HNO3

HCl 05 molltex=15 min

diluent chloroform-

23

Table 1 (continued)

Extractant

Analysisobject

Compositionof the initial

solution

Extractonconditions

Interferinginfluences

5

Phosphoryl podands

back-extractant H2O

СReinitial=2middot105 moll

aqueoussolutions of

salts of alkalimetals

solutions ofmineral acids

Т=286-291КОL=11

tex= 60 mindiluent

nitrobenzene12-

dichloroethanechloroform

toluene

-

6Triotylamine (N235)+

tributyl phosphate(TBP)back-extractant18 NH4OH

Alkalinesolutions

afterleaching

containingMo

СRe 01-165gl

T=293 КрН =90 OL=11

tex=10 мин20

triotylamine+30 tributylphosphate

diluentkerosene

-

7

Podand-type nitrogendonor ligand ndashNNN`N`-tetrakis(2-pyridymethyl)-

12-ethylendiamine (TREN)

Aqueoussolution

NH4ReO4

С =10-4 M

Ionic strength01M

pH=1-65diluent

chloroformОL=11tex=24 h

-

8

3m-crown-m-ethers(m=56) mono-benzo-

derivates12-dichloroethane

СReO4-=

0057-0060М

T=291-295Ktex=2h

-

24

Table 1 (continued)

The range of Re concentrations

RecoveryMethods for determination Ref

Recovery gt99

Determination from back-extractSpectrophotometric method with

thiourea reductant-Sn (II)wavelength of 390 nm

[16 24]

1

gt98 Spectrophotometric method [25]

2The range of Re concentrations

001-550 mcgml

Determination from extractSpectrophotometric method

wavelength of 540 nm[17]

3 -AES-ICP

Spectrophotometric methodwith thiourea

[18 1920]

4Mo W Fe are extracted 97

into the organic phase

Determination from aqua phaseafter extraction

ICP-MS[6]

5 -AES-ICP

Spectrophotometric method[21 22]

6 968Spectrophotometric method with

butyl rhodamine[23]

7 - AES-ICP [30]

8 -AES-ICP

Spectrophotometric method[31]

9 - ICP-MS [32]

25

Table 2 Characteristics of sorbents for rhenium sorption

Sorbent

Analysis objectComposition of the

initial solutionConditions of

sorptionInterferinginfluences

1

Activated carbons(BAU)

Eluenthot soda solution

nitrate media

gold ore raw

static conditionsа)рH =2-3

б) рH =15-25

volume ofsolution 10 mlmass of sorbent

03 g(SL=1333)t=10 min UV

a) electro-positive

components(Mo W Cu

Ag Au)b)1000 fold

excess ofMo W do

not interfere

2

Activated carbons- CN-G CN-PCU developed

from waste woodand grain

processingindustries

sulfuric acidsolutions with CRe= 002 gl pH =2

solid phasesliquid SL==105

t=5-7 days-

3

2 Carbon fibrousmaterials

modified withchitosan

neutral aquasolutions of

rhenium

static conditionsТ=286-289 КSL=11000

-

4

3 Weakly basicanion-exchangersАН-105 Purolite

A 170

mineralizedsulphite solutionsimulating rinsing

water(С Re=001-002

gl Mo Cu Fe As)

static anddynamic

conditionsSL = 1500

t = 150-200 min

-

5

Strongly-basicanion-exchangers

АВ-17(sorbent PAN-АВ-

17)

neutral or slightlyacid

solutions

dynamicconditionst = 20 min

The disks ofpolyacrylonitrilefiber filled resin

1000 foldexcess of

Fe Cu ZnPb Cd do

not interfere

6Lignin anion-

exchangerssolutions NH4ReO4

static conditionsSL=1400

t=15min-2 h-

26

Table 2 (continued)

NotesMethods for

determinationRef

1

а) Sorption capacity of BAU forRe СЕ=14175 mgg AC

Detectionlt 10

б) СЕ=00763 mmolg or 142mgg

The concentrations range of Re050 100 mgL in standard

solutions025 50 mgl in the presence

of Mo and W (11000)

a) Electrostrippingvoltammetry

b) X-ray fluorescenceanalysis

a) [12]b) [9 10]

2 -Spectrophotometric

method [35]

3 СЕ=179-185mggSpectrophotometric

method with ammoniumthiocyanate

[38 39]

4Full dynamic exchange capacity

114 mgg

Spectrophotometricmethod with ammonium

thiocyanatekineticmethod

[36]

5 -

Determination of Re bythe diffuse reflectance

spectra at 420 nmrhenium thiocyanate

complex in the presenceof tin (II)

[15]

6 СЕ=3427-2328 mgg Traditional polarography [37]

Sorption is one of the methods for separation of rhenium fromvarious solutions

Sorption of rhenium or perrhenate-ions often occurs on solidsorbents from the liquid phase The presence of a large specific surfacearea and a large number of functional groups of the sorbent determinesits high sorption properties with respect to rhenium (VII) Sorbentscontain the same functional groups (amino groups hydroxyl groups

27

phosphorus groups) as extractants for the selective extraction ofrhenium but these groups are fixed on solid carriers or support

Activated carbons (AC) of various brands are used the mostwidely [9 10] The use of activated carbons as sorbents due to the factthat they have a whole set of valuable properties highly polydisperseporous structure a complex but relatively easily controlled surfacechemistry and specific physical properties Activated carbons like manyother carbon materials exhibit high selectivity to perrhenate ions thatexplains the increased interest to this type of sorbents [12]

The characteristic distinction of carbonaceous materials is that thesorption of rhenium is not only due to complexation with surfacefunctional groups (containing oxygen nitrogen sulfur atoms) but alsodue to the interaction with carbon matrix

AC can act as anion-exchanger in acidic media and themechanism can be described by the following scheme

[C2+ OH-] + ReO4-= [C2+ ReO4

-] + OH-On the other hand the AC have significant reduction properties

the reaction of the electrochemical reduction of perrhenate ions in themethods of rhenium determination by voltammetry is based on this it[12]

It has been established [9 10] that ReO4- is sorbed from nitric

acid solutions almost entirely (95-99) by 10 minutes of UV irradiationwhile without irradiation this process takes up to 60 minutes Increasedsorption by UV authors attribute to the fact when UV radiationsolutions of rhenium (VII) salts rhenium (VI) and rhenium (V) areformed which are considerably faster adsorbed on AC

Extensive use of the AС is also associated with their low costActivated carbons - CN-G CN-P CU developed from waste wood andgrain processing industries have a low cost and their capacitance andkinetic characteristics slightly inferior to conventional AC (FAC) [35]

However from acid solutions together with rhenium molybdenumcan also be sorbed by the AC Furthermore perchlorates nitrates andother oxidants can reduce the adsorption capacity of coals by oxidationThe disadvantage of rhenium sorption by activated carbons is as followsa decreasing in their activity after 4-6 cycles of sorption-desorption [1]low mechanical strength [35]

28

Anion-exchange resin is the next width of use which havegreater selectivity and capacity compared with activated carbons Theseanion-exchangers synthesized on the basis of the gel and porouscopolymer of styrene and divinylbenzene From the neutral and acidicsolutions rhenium is adsorbed by low-basicity anion-exchangers with thefunctional groups of primary and tertiary amines In recent studiesconducted on the use of weakly basic macroporous anion-exchangerswith a more developed specific surface area (20-100 m2g) such asPurolite A170 with secondary amino groups [36]

Sorption by strongly-basic anion-exchangers compared to weaklybasic anion-exchangers has several advantages firstly they are almostquantitatively and selectively extract rhenium from solutions andsecondly work in a wide range of pH [15]

The rapid technique for perrhenate ions determination isdeveloped which allows to find their content directly on the site ofsampling for example in lake water using strongly-basic anion-exchangers AB-17 with the sensitivity of the technique is 2-3 orderslower than the best conventional spectrohotometric methods withthiocyanate [15]

Recently the authors of paper [37] synthesized new highlypermeable lignin anion-exchangers on the basis of lignin a naturalpolymer a component of terrestrial plants It is noted that the exchangecapacity of anion-exchangers for rhenium in lignin is much higher (EC =3427-2328 mgg) compared with conventional anion-exchangersHowever the time to reach equilibrium sorption by some anion-exchangers can reach from 2 up to 12 hours

Carbon fibrous materials modified with chitosan haveimproved kinetic (time and rate of sorption) characteristics comparedwith activated carbon and ion-exchange resins [38 39] Carbon fibrousmaterials modified with chitosan contain amino groups includingprotonated The increasing of the number of protonated groupscauses the increasing of sorption capacity of the material withrespect to the negatively-charged perrhenate-ions However thesorption capacity for rhenium (179-185 mgg) still yields to ligninanion in addition investigations were carried out of neutral aquasolutions of rhenium without interfering influences

29

ConclusionIn this review the methods for rhenium determination which over

the last decade have acquired great fame are presented A large numberof works related to improving methods for rhenium determining pointsto the increased interest to this metal The majority of the studies aimedto the selective extraction of rhenium from the analyzed complex objectsand the separating it from interfering elements in the matrix to increasethe sensitivity of the methods Most of the work related to the searchingof various organic reagents selective to rhenium (V VII) ions and usedin extraction and sorption processes In general the development ofrapid selective methods that can determine the content of rhenium in awide range of concentrations in various materials remains an actualproblem nowadays

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

Reference1 AA Palant ID Troshkina AM Chekmarev Metallurgy of

rhenium Science Moscow 2007 298 p2 LV Borisova YuV Demin NG Gatinskaya VV Ermakov

Determnation of rhenium in plant materials Journal of AnalyticalChemistry 2005 V60 1 P 97-103

3 LV Borisova AN Ermakov Analytical chemistry ofrhenium 1974 Science Мoscow 318 p

4 S Uchidaa KTagamia K Tabei Comparison of alkaline fusionand acid digestion methods for the determination of rhenium in rockand soil samples by ICP-MS Analytica Chimica Acta 2005 V535P 317ndash323

5 VI Manshilin EK Vinokurova SA Kapelushniy Determinationof Pt Pd Re mass fraction in dead catalyst samples using ICPatomic emission spectrometry method Methods and objects ofchemical analysis 2009 V41 P 97-100 (in Russian)

6 Jie Li Li-feng Zhong Xiang-lin Tu Xi-rong Liang Ji-feng XuDetermination of rhenium content in molybdenite by ICPndashMS afterseparation of the major matrix by solvent extraction with N-benzoyl-N-phenylhydroxalamine Talanta 2010 V81 P 954ndash958

30

7 T Meisel J Moser N Fellner Wo Wegscheider R SchoenbergSimplified method for the determination of Ru Pd Re Os Ir and Ptin chromitites and other geological materials by isotope dilutionICP-MS and acid digestion Analyst 2001 V126 P 322ndash328

8 K Shinotsuka K Suzuki Simultaneous determination of platinumgroup elements and rhenium in rock samples using isotope dilutioninductively coupled plasma mass spectrometry after cation exchangeseparation followed by solvent extraction Analytica chimica acta2007 V603 P129ndash139

9 NA Kolpakova AS Buinovsky IA Jidkova Determinationof rhenium by X-ray fluorescence analysis Proceedings ofuniversities Physics 2004 12 P147-149 (In Russian)

10 AS Buinovsky NA Kolpakova IA Melnikov Determinationof rhenium in the ore material by X-ray fluorescence analysis News polytechnic university 2007 V311 3 P92-95 (InRussian)

11 DV Drobot AV Belyaev VA Kutvitsky Development of aunified X-ray fluorescence method for the determination ofrhenium in multicomponent oxide compositions News highereducational institutions Non-ferrous metallurgy 1999 4 P23-24 (in Russian)

12 LG Goltz NA Kolpakov Sorption preconcentration anddetermination by voltammetry perrhenate ions in the mineralraw materials Proceedings of the Tomsk PolytechnicUniversity 2006 V 309 6 P77-80 (in Russian)

13 NA Kolpakova LG Gol`ts Determination in mineral rawmaterials by stripping voltammetry Journal of AnalyticalChemistry 2007V62 4 Р418-422

14 Wahi A Kakkar LR Microdeterminaton of rhenium withrhhodamine-B and thiocyanate usng ascorbic acid as the reductant Analytical sciences 1997 august V 13 P657-659

15 LV Borisova SB Gatinskaya SB Savvin VA RyabukhinAdsorbtion-spectrophotometric determination of rhenium fromdiffuse reflectance spectra of its complexes on a PAN-AV-17adsorbent Journal of Analytical Chemistry 2002 V572 P 161-164

31

16 AG Kasikov AM Petrova Extraction of rhenium (VII) byaliphatic alcohols from acid solutions Journal of AppliedSpectroscopy2009 V82 2 P 203-209 (in Russian)

17 ZhA Kormosh YaR Bazel` Extraction of oxyanions with basicpolimethine dyes from aqueous and aqueous-organic solutionsextraction-photometric determination of rhenium (VII) and Tungsten(VI) Journal of Analytical Chemistry 1999 V54 7 P 690-694

18 AA Palant NA Yatsenko VA Petrova Extraction of rhenium

(VII) from sulfuric acid solutions by diisododecylamine

Journal of Inorganic Chemistry 1998 V43 2 P 339-343 (inRussian)

19 NA Yatsenko AA Palant Micelle formation in theextraction of ions W (VI) Mo (VI) Re (VII) from sulfuric acidmedia diisododecylamine dioctylamine and trioctylamine Journal of Inorganic Chemistry 2000 V45 9 P 1595-1599 (in Russian)

20 N Latsenko AA Palant SR Dungan Extraction of tungsten (VI)molybdenum (VI) and rhenium (VII) by diisododecylamine Hydrometallyrgy V 55 Issue 1 Febr 2000 P 1-15

21 AV Antonov AA Ischenko The use of extraction in thedetermination of rhenium in the presence of molybdenumChemistry and chemical technology 2007V50 9113-116 (in Russian)

22 VF Travkin AV Antonov VL Kubasov AA IshchenkoExtraction of rhenium (VII) and molybdenum (VI)hexabutyltriamid phosphoric acid from the acidic environment Journal of Applied Chemistry 2006 V78 6P 920-924 (inRussian)

23 Cao Zhang-fang Zhong Hong Qiu Zhao-hui Solvent extraction ofrhenium from molybdenum in alkaline solution Hydrometallurgy2009 V 97 3-4 P 153-157

24 AG Kasikov AM Petrova Influence the structure of octanolon their extraction ability in acid solutions with respect to

32

rhenium (VII) Journal of Applied Chemistry 2007 V80 4 P689-690 (in Russian)

25 VF Travkin YM Glubokov Extraction of molybdenum andrhenium by aliphatic alcohols Metallurgiya2008 7 P21-25 (in Russian)

26 EA Kataev GV Kolesnikov VN Khrustalev MYu AntipinRecognition of perrhenate and pertechnetate by a neutralmacrocyclic receptor J radioanal Nuclchem 2009 2 V282 P 385-389

27 Bambang Kuswandi Nuriman Willem Verboom David NReinhoudt Tripodal Receptors for Cation and Anion Sensors Sensors 2006V 6 P 978-1017

28 Lagili O Abouderbala Warwick J Belcher Martyn G BoutellePeter J Cragg Jonathan W Steed Cooperative anion binding andelectrochemical sensing by modular podands PNAS April 162002 V 99 8 P 5001ndash5006

29 EA Kataev GV Kolesnikov EK Myshkovskaya Newmacrocyclic ligands based bipyrroles to bind perrhenate andpertechnetate ions radiation safety 2008 4 P16-22(inRussian)

30 Takeshi Ogata Kenji Takeshita Kanako Tsuda Solvent extractionof perrhenate ions with podand-type nitrogen donor ligands Separation and Purification Technology 2009V68 P288ndash290

31 Yoshihiro Kudo Ryo Fujihara Shoichi Katsuta Yasuyuki TakedaSolvent extraction of sodium perrhenate by 3m-crown-m ethers(m=5 6) and their mono-benzo-derivatives into 12-dichloroethane

32 Elucidation of an overall extraction equilibrium based oncomponent equilibria containing an ion-pair formation in water Talanta V 71 2007 656ndash661

33 AN Turanov VK Karandashev VE Baulin Extraction ofrhenium (VII) by phosphorylated podands Russian journal ofinorganic chemistry 2006 V514 P676-682 (in Russian)

34 E A Katayev Yu A Ustynyuk J L Sessler Receptors fortetrahedral oxyanions Coordination Chemistry Reviews 2006V250 P3004ndash3037

33

35 Leroy Cronin Macrocyclic and supramolecular coordinationchemistry Annu Rep Prog Chem Sect A 2004V100 P 323ndash383

36 ID Troshkina ON Ushakova VM Mukhin Sorption ofrhenium from sulfuric acid solutions by activated carbon News of higher educational institutions Non-ferrousmetallurgy 2005 3 P38-41 (in Russian)

37 AA Abdusalomov Sorption of rhenium from sulfuric acidsolutions of molybdenum Sorption and ChromatographicProcesses 2006 Vol6 V 6P 893-894 (In Russian)

38 NN Chopabaeva EE Ergozhin ATasmagambet AI NikitinaSorbtion of perrenate-anons by lignin anion exchangers Chemistry of solid fuel 2009 2 P 43-47 (in Russian)

39 AV Plevaka ID Troshkina LA Zemskova AV Voit Sorption ofrhenium chitosan-fiber materials Journal of InorganicChemistry 2009V54 7 P1229-1232 (in Russian)

40 LA Zemskova AV Voit YuMNikolenko ID Troshkina AVPlevaka Sorption of rhenium on carbon fibrous materials modifiedwith chitozan Journal of nuclear and radiochemical sciences2005 V6 3 P221-222

11

SYNTHESIS AND MICROSTRUCTURE DESIGN OF METALAND CERAMIC MATRIX COMPOSITES USING

MECHANICAL MILLING OF THEREACTANTSCONSTITUENTS

Dina V Dudina Oleg I LomovskyInstitute of Solid State Chemistry and Mechanochemistry

Siberian Branch of Russian Academy of Sciences Kutateladze 18Novosibirsk 630128 Russia

E-mail dina1807gmailcom

Mechanical milling greatly alters the state of a powder mixtureintroducing plastic strain and defects into the components andcreating new interfaces and mutual configurations of nano-sizedgrains This opens up a possibility to design microstructures of thecomposite to be synthesized by modifying the initial state of reactingpowder mixtures In certain mechanically milled reactive systemsone can observe microstructure refinement of the product [1-2] anincrease in the yield of the reaction [3] improved distribution of thephases [3 4] and lower reaction onset and developed temperatures[1-2] The presentation intends to demonstrate several successfulexamples of this approach for synthesizing composites by self-propagating high-temperature synthesis (SHS) shock compressionand electric-current assisted sintering

SHS in the mechanically milled Ti-B-Cu powder mixtures wassuccessfully performed and resulted in a TiB2-Cu composite [1-2]Compared to untreated powders in the mechanically milled mixturestitanium and boron started reacting at a reduced ignition temperaturewhile lower combustion temperatures developed in the combustionwave favored formation of submicron grains of TiB2

The powder particles brought to react with each other by shockcompression of the mixture may not fully transform into the productsif the loading is too short and the temperatures developed during thepressure rise and the post-loading period are not high enough In themechanically milled mixture the yield of the reaction can beincreased as a result of the decreased grain size of the initial reactants

12

and shorter diffusion distances (example Ti-Cu-B system partial andcomplete reaction of Ti and B [3])

When the sintering process ensures temperatures and timesufficient for the completion of the reaction in the mechanicallymilled mixture one can expect more uniform microstructure and finergrains of the products (example Ti-B-C system forming B4C-TiB2

phases during electric-current assisted sintering [4])Ball milling can refine the microstructure of the as-synthesized

composites and can be used to introduce additional quantities of theconstituents in the composite This was applied in order to develophighly conductive Cu-based composites One of the possible reasonsfor low conductivity of in-situ dispersion strengthened copper may bethe incompleteness of the reaction between the initial reactantswhich form solid solutions with the copper matrix In this regard weconducted an in-situ synthesis of TiB2-Cu composites starting fromthe powder mixtures with the limited content of copper ensuring ahigh probability of contact between the particles of titanium andboron and as a result their full conversion into the TiB2 phase Thenanoparticles were formed in a self-propagating mode in the ballmilled Ti-B-Cu powder mixture corresponding to the 57 volTiB2-Cu composition Afterwards in order to adjust the composition thecomposite was ldquodilutedrdquo with the required amount of copper usingsubsequent ball milling [5]

The consolidated nano- and microcomposite materialsdeveloped on the basis of the described systems were tested for theirenhanced mechanical properties (fracture tough composites B4C-TiB2

[4]) electric erosion resistance [6] and electric conductivity [5] Inthis presentation each property is discussed as resulting from thephase and microstructure evolution during the synthesis of thematerial by the selected processing method

AcknowledgementsParts of this work were carried out by DVD at the University

of California Davis USA during her postdoctoral appointment Theauthors greatly appreciate the collaboration with DrKorchagin(ISSCM SB RAS) Dr VIMali and Dr AGAnisimov (Institute of

13

Hydrodynamics SB RAS Novosibirsk Russia) and Prof JSKim(University of Ulsan South Korea)

References1 DVDudina OILomovsky MAKorchagin VIMali Chem

Sust Dev 12 (2004) 319-3252 MAKorchagin DVDudina Comb Expl Shock Waves 43 (2)

(2007)176-1873 DVDudina VIMali AGAnisimov OILomovsky Mater Sci

Eng A 503 (2009) 41-444 DVDudina DMHulbert DJiang CUnuvar SJCytron

AKMukherjee JMaterSci 43 (2008) 3569-35765 JSKim DVDudina JCKim YSKwon JJPark CKRhee J

Nanosci Nanotech 10 (2010) 252-2576 J-SKim Y-SKwon DVDudina OILomovsky MAKorchagin

VIMali JMaterSci 40 ( 2005)3491 - 3495

4

STUDY OF THE EFFECT OF FLUORESCENCE INCREASINGOF N-ARYL-3-AMINOPROPIONIC ACIDS IN THE PRESENCE

OF ZINC AND CADMIUM IONS

EV Dedyukhina1 NV Pechishcheva1 LK Neudachina2KYu Shunyaev1 AA Belozerova1

1 ndash Institute of Metallurgy of UB RAS 101 Amundsen st Ekaterinburgshunuralru

2 ndash Ural State University 51 Lenin av Ekaterinburg Russia

Earlier the effect of increasing of phosphorescence intensity in thefrozen solutions with excess of metal chlorides and sulphates has beenreported Ions оf these metals have filled electronic shells and largevalue of electric field intensity - Li(I) Be(II) Ca(II) Mg(II) Cd(II)Zn(II) Al(III) In(III) and Ga(III) For example this effect was found forbenzene aniline phenol amino acids ndash tyrosine tryptophanephenylalanine [1]

The same effect have been found for fluorescence of onerepresentative of N-aryl-3-aminopropionic acids (AAPA) - NN-di(2-carboxyethyl)-p-anisidine - in the presence of cadmium(II) and zinc(II)ions at Т=77 К [2] Increasing of fluorescence intensity (Ifl) in frozeninorganic matrix is expected for other representatives of AAPA whichnot have electron acceptor groups in structure and demonstrate theconsiderable fluorescence intensity of the protonated form

Fluorescence of some AAPA in frozen inorganic matrixNN-di(2-carboxyethyl)aniline (I) NN-di(2-carboxyethyl)-34-

xylidine (II) NN-di(2-carboxyethyl)-3-methyl-aniline (III) andN-(2-carbamoylethyl)-о-anisidine (IV) are representatives of a class ofAAPA Figure 1 presents structures of the AAPA In the present workthe fluorescence of aqueous solutions of this AAPA with molar excess ofcadmium and zinc sulphates at рH 1-6 and Т=77 К have beeninvestigated

The fluorescence spectra of solutions were measured using aFluorat-02-Panorama spectrofluorometer (Lumex Russia) Fluorescencespectra at T=77 K was excited and recorded using a fiber-optic cablewith a special optical connector

5

It have been established that the Ifl of the protonated form of I-IV(СR=1middot10-4 moldm3) is increased in the presence of cadmium(II) andzinc(II) ions at Т=77 К Figure 2 presents spectra of II We suggest thatcause of this effect is interaction enhancement of reagent with metal inconsequence of isolation from water and micro concentration (waterform ice crystals impurities are displaced in intercrystal area)

CH3

N

O

OHO

OH

1 2 3 4

Fig 1 Structures of AAPA 1 - NN-di(2-carboxyethyl)aniline2 - NN-di(2-carboxyethyl)-34-xylidine 3- NN-di(2-carboxyethyl)-3-

methyl-aniline 4 - N-(2-carbamoylethyl)-о-anisidine

The increasing Ifl of protonated reagent form of I-IV also isobserved at Т=293К but is not as strong as at T=77 K

0

1

2

3

4

5

6

7

240 260 280 300 320 340 360

wavelength nm

Ia

u

1

2

3

Fig 2 Spectra of fluorescence II (СR=1middot10-4 moldm3) in the presence andabsence of Cd(II) и Zn(II) ions (СZn(II)= СCd(II)= 560 mgdm3) рН=60 Т=77 К

λex = 214 nm 1 - II 2 - II+Zn(II) 3 - II+Cd(II)

The fluorescence increasing is observed only when concentrationof metal ions in dozens of times more than concentration of fluorophor

6

This indicate that Ifl increasing is occured due to reagent solvation byions of inorganic salts but not chelation

We have obtained the Ifl of solutions of I-IV as functions of theconcentration of cadmium(II) and zinc(II) ions at Т=77 К pH=6 (table1) The largest increasing of Ifl in the presence of metal ions have beenobserved for IV But the most correlation coefficient R value of linearfunction Ifl=f(CMe) with wider concentrations range has been obtainedfor II

Table 1 The Ifl of I-IV as functions from concentration of metal ions Т=77 КCCd(II)= CZn(II)= 200 mgdm3 СR=10-4 moldm3 рН=6

Metalion

ReagentConcentrationsrange mgdm3 I R+MeIR R Slope

I 11 090 321

II 11 098 494III

25-760

13 092 456Cd(II)

IV 25-245 80 092 2997

I 3 095 82

II 8 098 414

III

30-845

11 096 437Zn(II)

IV 30-560 70 090 1542

In addition we have studied the fluorescence of aniline and naturalamino acids (tyrosine tryptophane phenylalanine) in frozen inorganicmatrix Structures of amino acids are presented on figure 3 thiscompounds are not belong to class of substituted anilines Thiscompounds similarly of investigated AAPA not have electron acceptorgroups in structure tyrosine phenylalanine and AAPA have the samebenzene fluorophore Besides this amino acids are commerciallyavailable reagents

Investigations have been shown that present amino acids alsodisplay the effect of Ifl increasing of protonated reagent form in thepresence of cadmium(II) and zinc(II) ions at Т=77 К But is not asstrong (12ndash5 times) as AAPA Ifl increasing Metal ions at T=298 K havelittle effect on a fluorescent spectra of amino acids

7

1 2 3

Fig 3 Structure of amino acids1 - phenylalanine 2 - tyrosine 3 - tryptophane

Thus we can deduce that the presence of substituted amino groupin benzene ring (especially in combination with others electron donorgroups) allow to observe more effective increasing of Ifl in salt solutionat 77 К Replacement benzene fluorophore to indole one (intryptophane) result to decreasing of observing effect extent

The fluorescence of II in the presence of Mg(II) ions at Т=77 Кwas investigated We tried to find the II0 fluorescence of II functionfrom z2r ratio for two-charged cations where z - ionic charge (+2) r -ionic radius nm [3] Data is presented in table 2

Table 2 Characteristiс of the functions II0 = f(z2r) for II Т=77 К рН=6λexλem= 214286 nm СII =10-4 М

Ion z2r SlopeI I0

CMe= 200 mgdm3

Cd(II) 412 494 107

Zn(II) 541 414 85

Mg(II) 615 352 74

The functions II0=f(z2r) of fluorescence II in frozen inorganicmatrix from are presented in figure 4 they are linear Also linearfunctions of Ifl=f(CMe) slope on z2r ratio have been obtained

N

NH2

OH

O

H2N

OHO

OH

8

y = -016x + 174

R2 = 099

6

7

8

9

10

11

40 45 50 55 60 65

z2r

IIo

Zn

Cd

Mg

Fig 4 Functions II0=f(z2r) of fluorescence II in the presence of metal ions [3]CCd(II)= CZn(II)= CMg(II)= 200 mgdm3 λexλem= 214286 nm Т=77 К

Study of fluorescence of some reagents in glycerolwater andethanolwater mixtures and micellar solutions at Т=298 КWe have studied a fluorescence II and tryptophane in

glycerolwater (11) and ethanolwater (11) mixtures in the presence ofzinc(II) ions at 77 К It was done for proving hypothesis about reducinginteraction fluorophore with water in aqueous media at freezing Wesuggest that interaction between of the solute and solvent molecules arepreserved in nonaqueous solutions

Corresponding spectra of II are presented on figure 3 similarsituation is observed for tryptophane We can see effect of increasing Ifl

is not observed in glycerolwater and ethanolwater mixtures in contrastto aqueous solutions

Isolation reagent from water at room temperature is possible in thepresence of surfactants

Fluorescence II have been study in the presence of surfactants ofdifferent nature in acidic media at Т=298 К The Ifl increasing ofprotonated form II is occured in the presence of Triton Х-100 (non-ionicsurfactant) and sodium dodecylsulphate (anionic surfactant)Fluorescence II is decreased by cetyltrimethylammonium bromide(CTAB cationic surfactant)

Fluorescence of II in the presence of surfactants and excess ofmetal ions have been study at рН=1-6 Zinc and cadmium ions increaseIfl of II at рН 50-65 with CTAB Thus metal ions and CTAB at

9

Т=298 К have same Ifl increasing effect as the effect at Т=77 К withoutsurfactants

0

5

10

15

20

25

240 260 280 300 320 340 360 380

wavelength nm

Ia

u

1

2

3

Рис 5 Fluorescence of II (СII=1middot10-4 moldm3) in ethanolwater (11)mixtures in the presence and absence of Zn(II) pH=60 Т=77 К λex=214 nm

1 - II 2 - II + Zn(II) (44middot10-4 moldm3) 3 - II+ Zn(II) (86middot10-3moldm3)

We have obtained under these conditions the Ifl of II solutions asfunction of the concentration of Cd and Zn ions with variousconcentrations of CTAB (table 3) The plots are linear and have thegreatest slope value at СCTAB=14middot10-3 moldm3 Cadmium ions have agreater influence on the fluorescence of the II than zinc ions

The fluorescence investigations in the presence of CTAB andmetal cations have been carried out on other AAPA (I III and IV)aniline and tyrosine (table 4) It was found that zinc ions increase offluorescence of protonated reagent form of I and III cadmium ions ndashIII

Table 3 Characteristiс of the functions Ifl=f(CMe) of II with addition of CTAB

exem = 218286 Т=298 К

Range of concentrationsCation

С CTABmoll moldm3 mgdm3 tg α

96middot10-4 2middot10-4 ndash 4middot10-3 45-450 18Cd(II)

14middot10-3 2middot10-4 ndash 8middot10-3 45-900 3696middot10-4 4middot10-4 ndash 15middot10-2 25-850 055

Zn(II)14middot10-3 4middot10-4 ndash 11middot10-2 25-850 10

10

Table 4 Fluorescence of reagents in the presence of zinc and cadmium ions(СMe=560 mgdm3) and CTAB (С= 96middot10-4 moldm3) рН=6

Zn(II) Cd(II)

Reagentexem

nm II0 I (R+Zn+CTAB)au

II0I (R+Cd+CTAB)

au

aniline 253278 11 07 10 06I 222300 62 16 08 02II 218286 73 44 85 51III 217288 65 34 33 15IV 218304 10 32 12 12

tyrosine 222302 10 480 11 462

The resulting functions will be used for developing of thefluorescent techniques of zinc and cadmium determination

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

References1 AV Karyakin n-electrons of heteroatoms in hydrogen bonding and

luminescence (in Russian) Nauka Мoscow 1985 135 p2 LK Neudachina EV Dedyukhina OV Evdokimova

NV Pechishcheva EV Osintseva KYu Shunyaev Fluorescenceof NN-di(2-carboxyethyl)-p-anisidine in solution and crystallinestate Journal of Applied Spectroscopy 2010 V 77 2 P 206-212

3 Lurie YuYu Hand-book of analytical chemistry (in Russian)Khimiya Мoscow 1989 447 p

190

The cell was pumped out and fullfilled with purified argon Laterit was put into the resistance furnace and heated until the giventemperature under the abundant pressure of the inert gas

The setup was equipped with the automatic system of temperaturestabilization Temperature measurement was performed with the help ofchromyl-aluminum thermocouple Content of components in electrolytewere being controlled before and after the experiment with the atomic-absorption method

Stationary polarization measurementsLead ion deposition processes in eutectic melt of lithium and

potassium chlorides were studied at 04 to 30 mol lead chloride intemperature range from 673 to 823 К Polarization curves are given onthe fig 2 and 3 Two characteristic areas are observed on thepolarization curves On the first area little potential deviations from theequilibrium value takes place with cathode current density increasing to008 Acm2

Experimental points on the area with 04 mol lead chlorideconcentration are on straight lines described by equationsE = - 00703lgi - 01203 and E = - 00775lgi - 0091 for 673 and 773 Кcorrespondingly

At temperature 673 К tg is 0070 мВ and at 773 К - 0078 мВAccording to the equation

Ftg

RT23

n (2)

we have n=19 for 673 К and n=20 for 773 КAt lead chloride concentration 30 mol experimental points on

the first area of the polarization curve is described by the equationE= - 00779lgi - 00877

Amount of electrons in the reaction calculated on the equation (2)is equal 2

Reaching current densities 011 012 020 и 032 Асm2 on thefig3 for 673 723 773 823 К temperatures correspondingly Potentialis greatly shifted to the negative area to the values -084 -084 -106and -110 correspondingly

At small values of cathode current density there is one wavecorrespondingly to the fig 4 In some time after current rise potential

191

reaches its stationary value at current density 0045 Асm2 for 35 s forcurrent density 0060 Асm2 for 30 s After current disconnectionpotential comes back to its equilibrium value

Fig 2 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

(04 mol ) melt

192

Fig 3 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

melt at 823 К depending on the lead chloride concentration Concentration oflead chloride in mol per cents 1 - 04 2 - 05 3 ndash 30

193

Fig 4 Engaging curves at 823 К temperature and the different current density

On the engaging curves at current density values corresponding tothe second characteristic area on the polarization curves on the figures 2and 3 two waves on figure 5 are seen Time of reaching stationarypotential tst decreases with the current density increasing (for currentdensity 012 Асm2 tst equals 85 s for current density 017 Асm2 tst -45 s)

Fig 5 Engaging curves at 04 mol lead chloride concentration currentdensity 012 013 017 Асm2 and 823 К

194

Processes taking places on the electrode can be described in thefollowing way On the first characteristic area of the polarization curvelead ion deposition happens

Pb2+ + 2e = Pb0 (3)The limiting current density of lead reduction increases with the

temperature and lead chloride concentration At 30 mol of leadchloride concentration and 823 K limiting current density ilim is 12Acm2

On the second characteristic area of the polarization curvedeposition of the alkaline metal is possible on the reaction

K+ + e = K0 (Pb) (4)Low values of the alkaline metal reduction potentials might be

connected with the process of alloy formation of alkali metal with leadK + 4Pb = KPb4 (5)

Chronopotentiometric measurements at lead deposition from LiClndash KCl (45-55 mol ) ndash PbCl2 melt at 04 mol lead chlorideconcentration were performed at 823 K and current density range from010 to 017 Acm2 There is only one wave on chronopotentiometriccurves under these conditions Values of product i12 depending oncurrent density are given in the table 1 where - transition time

Table 1 Values of product i12 at diverse current density

s i mAcm2 i12 mAcm2s12

095 170 165161 130 165181 120 162

262 102 165

It is seen that the product i12 does not depend on current

density at constant concentration of depolarizator 0OxC In the table 2

potential values Е4 at time equaling the forth of the correspondingvalues of transition time are given

195

Table 2Values of Е4 potential of different current density

i Acm2 s 4 s Е4 V

010 264 0660 -0061

012 181 0453 -0600

013 161 0403 -0061

017 095 0238 -0062

It is seen that the potential Е4 does not depend on the experimentconditions the current density in this case

Equation for the reversible process can be as follows

1ln

nF

RT21

4t

ЕЕ

(6)

for irreversible process

2100

1lnlnnF

RT

t

nF

RT

i

knFCЕ

fhOx (7)

where E ndash electrode potential 4E - measurement potential at frac14

of transition time R ndash gas constant F ndash Faraday number n ndash number

of electrons T ndash temperature - transition time 0OxC - depolarizator

concentration 0fhk - deposition speed constant

On the figure 6 dependencies Е -

1ln

21

t

and Е -

21

1ln

t at 04 mol of lead chloride concentration current

density 01 Acm2 and 823 K are given

196

y = -00835x + 00654

0002

0022

0042

0062

0082

0102

0122

0142

0162

-115 -065 -015 035 085

- E В

1 2

Fig 6 Dependencies 1ndashЕ=f

1ln

21

t

and 2-Е =f

21

1ln

t

From the analysis of given graphic dependencies follows that the

experimental points in coordinates E -

1ln

21

t

are in a straight line

with the confidence interval 095 The can be described by equation

08300650 E

1ln

21

t

(8)

The amount of electrons in the electrode reaction was calculatedfrom the equation

F

RTn

0830 (9)

hence n=2

197

It follows from the experimental conditions on lead ion (II)deposition that the process is reversible ie it is controlled by the speedof divalent lead ions mass transfer from the volume of melt to theelectrode surface

Diffusion coefficient of lead dichloride at 823 K was calculated onSandrsquos equation

20

2

)(

)(2D

oxnFC

i

(10)

Lead ions (II) diffusion coefficient are equal to 23310-

5сm2s It is in good accordance with the data obtained by other authors[5 6]

References1 Yurkinsky V Makarov D Electrochemical reduction of lead ions in

halide melts Russian J Applied Chem 1994 67 p 1283-12862 Yurkinsky V Makarov D The influence of cation composition on

kinetics of lead electrochemical reduction in chloride melts RussianJ Applied Chem 1994 68 p 1474-1477

3 Ryabukhin Yu And Ukshe E The diffusion coefficients of lead inmolten chlorides DAN SSSR 1962 145 p 366-368

4 Naryshkin I Yurkinsky V Oscillographic investigation oftemperature coefficients for some chlorides diffusion in LiCl-KClRussian J Electrochemistry 1968 4 p 871-872

5 Naryshkin I Yurkinsky V Voltammetry in molten salts Russian JElectrochemistry 1968 2 p 856-866

6 Raymond J Heus James J Egan Fused Salt Polarography Using aDropping Bismuth Cathode ndash J of the Electrochemical SocietyOctober 1960 p 824-828

7 Richard B Stein The Diffusion Coefficient of Lead ion in FusedSodium Chloride Eutectic ndash J Electrochem Soc 1959 vol 106 p528

8 Laitinen H A Gaur H C Chronopotentiometry in Fused LithiumChloride-potassium Chloride - Anal Chem Acta 1958 vol 18 p1-13

9 Hills GI Oxley I E Turner D W Silicates Ind 1961 vol 26 p559

184

REPAIR COMPOUND MODIFIED BY NANO PARTICLES OFFERROUS OXIDE

OS Tatarintseva SN Novosyolova TK UglovaInstitute for Problems of Chemical and Energetic Technologies SB RAS

Biysk Altai region Russia labmineralmailru

The results of influence study of nano-dispersed ferrous oxide oncharacteristics of the composite material developed earlier (compound)and intended to repair and recover engineering structures and massifshave been presented in this paper The compound consists ofmulticomponent polymer matrix including epoxy oligomer low-molecular synthetic rubber plasticizer and process additives filler and alow-temperature amine hardener Microcalcite with particle size lessthan 50 μm has been used as filler

The composite has been modified with nano powder of ferrousoxide (II) (manufactured by MACH I Inc USA) consisting of needle-like crystalline particles with average size 4 nm and having specificsurface area 2379 m2g

Experiments have shown that even distribution of nano particlesin epoxy resin is caused with a high-velocity mechanical device underthe additional influence of ultrasonic field

The most important things for low-viscosity repair compositionsapplied to recover the integrity of natural materials are high flowabilitydetermining the ability to fill narrow-opened fractures and stability ofstrength properties for a long time

The positive effect of ultra-dispersed modifier is seen within therange of 030-035 of its percentage in the composition as shown byresults of the study given in the Table At these amounts the maximumvalues of flowability and mechanical characteristics have been providedThe logical increase in samples density indicates the optimality of thepacking developed and reduction in the porosity of a composite materialthat is important while using it in conditions on high humidity

The compound developed is environmentally friendlyincombustible waterproof stable to heat vibration and long mechanicalloads and can be used to perform repair work in construction industrypublic service stone mining and processing industries and architecture

185

Table Percentage influence of ferric oxide nano powder on technicalcharacteristics of the composite material

Value at modifier percentage Characteristics

0 010 020 030 035 040

Dynamic viscosityat T = 20 oC Pamiddots

210 212 225 262 266 288

Flowability cm 48 48 48 52 53 45

Density gm3 141 141 143 145 146 146

Compressive forceMPa

79 78 79 82 86 74

Relative deformation

023 021 021 025 025 020

182

BASALT PLASTICS OF ENHANCED HEAT AND CHEMICALSTABILITIES

OS Tatarintseva NN Ноdakova VV SamoilenkoInstitute for Problems of Chemical and Energetic Technologies

of the SB RAS Biysk Russialabmineralmailru

The experience of the application of metal pipes for chemicalproductions cool and hot water supply systems transportation ofpetroleum products and other aggressive fluids has shown that they aregreatly subjected to corrosion that reduces their lifetimes to severalyears Therefore natural is the observed worldwide tendency ofreplacing steel and cast iron by composite materials of high chemicalstability and durability to which glass-reinforced plastic having acomplex of high service properties should primarily be relatedHowever requirements for composites have presently increasedespecially with regard to their heat and chemical stabilities andresistance to microorganisms ground and waste waters

The paper demonstrates the study results with respect to thedevelopment of a composite material for filament-wound pipe productswhich is superior in its basic parameters to analogous ones in the field ofglass-reinforced plastic application As a reinforced material basaltroving with higher strength characteristics and resistance to aggressiveenvironments as compared to a glass one was chosen the polymermatrix was a heatproof binder TS developed on the basis of nitrogen-containing epoxy resin synthesized Having rheological properties andstrength characteristics similar to those that are widely used in themanufacture of filament-wound glass-reinforced plastic products of thebinders EDI and EChDI the binder TS possesses enhanced heat stabilityand low viscosity at room temperature which permits the reduction ofpower inputs for its processing

The obtained data on advantages of both basalt fiber and thebinder developed have to the full extent been realized in laboratorysamples of the reinforced composite and in basalt plastic pipes producedindustrially (see Table below)

183

Table Temperature dependence of elastic modulus E of basalt plasticpipes

Еmiddot103 MPa at Т degСBinder 20 85 125 155 200

EDI 11701 11263 4363 3528 -EChDI 11277 10951 9944 6217 -

TS 19960 19336 19179 17557 9096

The 9-fold strength reserve of the basalt plastic pipes determinedwhen hydro-tested under extreme conditions (150degC 15 MPa) hasconfirmed the possibility of creating composite polymer materialsoperating under high-temperatures and humidity

164

FABRICATION AND MODIFICATION OF METALLICNANOPOWDERS BY ELECTRICAL DISCHARGE IN LIQUIDS

NV Tarasenko1 AA Nevar1 NA Savastenko2 EI Mosunov3 NZ Lyakhov4 TFGrigoreva4

1 Institute of Physics NAS B Minsk Belarus2 Leibniz-Institute for Plasma Science and Technology Greifswald Germany

3 The Institute of Machine Mechanics and Reliability NAS B Minsk Belarus4Institute of Solid State Chemistry and Mechanochemistry SB RAS

18 Kutateladze Str Novosibirsk 630128 Russia grigsolidnscru

Electrical-discharge technique was developed for preparation ofmetallic and metal-containing nanoparticles as well as for modificationof metal micropowders in liquids The morphology and composition ofthe nanopowders formed under various discharge conditions wereinvestigated by means of transmission electron microscopy and X-raydiffraction analysis The optimal conditions for the production oftitanium carbide and copper nanoparticles embedded in carbon layerswere found

IntroductionA synthesis of metallic and metal-containing nanopowders is of a

great interest due to their potential applications as super hard materials[1] environmentally friendly fuel cells with highly effective catalysts[23] and so on Transition metal carbides have been widely studied aselectrocatalysts because of their electrochemical properties andelectrical conductivities Nanosized carbon particles are suitable supportmaterials for certain types of catalysts Of particular interest for futurecatalytic applications are carbon-based materials with embeded metalnanoparticles [4] As long as carbon nanoparticles are relatively inertsupports many studies have been conducted in order to find which pre-treatment procedures are needed to achieve optimal interaction betweenthe support and metal species [5]

For any application of nanoparticles to be commercially viablelow-cost production methods have to be developed A low-temperatureand non-vacuum synthesis of nanoparticles via discharge in liquid(submerged discharge) provides a versatile choice for economicalpreparation of various nanostructures in a controllable way An arc

165

discharge in liquid nitrogen has firstly been reported as a cost-effectivetechnique for the production of carbon nanotubes in 2000 by Ishigamy etal [6] Since that time many efforts have been devoted to develop thismethod Sano et al proposed to submerge electrodes in water instead ofliquid nitrogen [78] They reported synthesis of carbon onions [78] andsingle-walled carbon nanohorns (SWNHs) [9] In latter case carbonnanoparticles were produced via discharge in water method with thesupport of gas injection Parkansky et al reported nanoparticlessynthesis via a pulsed arc submerged in ethanol Ni W steel andgraphite electrodes were used [1011] The particles composition variedfrom carbon to pure metal including various intermediate combinationsof these materials Bera et al employed an arc-discharge in a palladiumchloride solution to produce carbon nanotubes decorated with in situgenerated Pd nanoparticles [10] Importantly the synthesized materialcontained no chlorine

In this paper methods based on electrical-discharges in liquids forproduction of tungsten and titanium carbide as well as coppernanoparticles embedded in carbon nanostructures is reported Thecapabilities of arc and spark discharges submerged in liquids forsynthesis of nanoparticles as well as electrical-discharge modification ofmetallic powders were studied

Experimental detailsThe experimental reactor (Fig 1) consisted of four main

components a power supply system (pulse generator) the electrodes aglass vessel and a water cooling system outside the beaker A pulseddischarge was generated between two electrodes being immersed in 100ml of liquid (pure (995) ethanol or 0001 M CuCl2 aqueous solution)The appropriate combinations of pairs of metallic (tungsten titanium orcopper) and graphite electrodes were used The choice of ethanol wasmotivated by the fact that organic compounds play a role of a carbonsource to produce nanoparticles in discharge-in-liquid system [7 12]Addition of the copper chloride salt into double distilled water favoredthe activation of discharge process Metal (tungsten titanium or copper)and graphite rods with diameters of 6 mm were employed as electrodesAn optimum distance between the electrodes was kept constant at 03mm to maintain a stable discharge The discharge was initiated byapplying a high-frequency voltage of 35 kV The power supply

166

provided several different types of discharges Both direct current (dc)and alternating current (ac) arc and spark discharges were generatedwith repetition rates of 100 and 50 Hz respectively Current I(t) wasrecorded during the discharge as a function of time by means of anoscilloscope The peak current of the arc discharge was 9 A with a pulseduration of 4 ms The peak current of the pulsed spark discharge was 60A with a pulse duration of 30 μs

The synthesized products were obtained as colloidal solutionsAfter 15 min presedimentation the large particles precipitated at thevessel bottom The top layer contained the small nanoparticles wascarefully poured off into a Petry dish These suspended nanoparticleswere characterized by UV-Visible optical absorption spectroscopytransmission electron microscopy (TEM) and X-ray diffraction analysis(XRD) for their size morphology crystalline structure and composition

The optical absorption spectra of colloids were measured by UVndashVisible spectrophotometer (CARY 500) using 05 cm quartz cuvetteTransmission electron microscopy was performed by LEO 906E (LEOUK Germany) microscope operated at 120 kV A drop of solution putonto the amorphous carbon coated copper grid for TEM measurementsThereafter the liquid was evaporated at the temperature of 80 C Afterthe drying of colloidal solution the deposit obtained on the bottom ofPetri dish was examined by XRD Powder composition and itscrystalline structure were characterized by using X-ray diffraction atCuK (D8-Advance Bruker Germany)

Synthesis of carbide nanopowdersPromising capabilities of the developed technique for synthesis of

tungsten and titanium carbides (WC TiC) as well as carbon-encapsulated copper nanoparticles were demonstrated using theappropriate combinations of pairs of metallic and graphite electrodessubmerged into the appropriate solution Also physical and chemicalprocesses induced by the electrical discharges in liquids were studied tooptimize the process of nanoparticles synthesis

The results of nanoparticles preparation are summarized in theTable1 The synthesis rate varied in range of 2 ndash 40 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofmetal and graphite electrodes The synthesis rate increased withincreasing of discharge current and decreasing of pulse duration The

167

composition and morphology of nanoparticles were also found to dependon discharge parameters It should be noted that there is a possibility toscale-up the process

Table 1 summarized the variation in synthesis rate andcomposition of tungsten nanopowders with the discharge parameters Asa general tendency the synthesis rate was order of magnitude higher forspark discharge than that of arc discharge It may be due to thedifference in current value [13] For both arc and spark discharges itwas found that the synthesis rate is lower when tungsten was acting as acathode This result is consistent with literature data For example Beraet al reported that the consumption of anode is higher than that ofcathode [13]

Table 1 Summary of nanopowder synthesis conditions andresults of nanopowder characterization by XRD

XRD-analysisDischargetype

Electrodes Powdersyield

mgminW2Cvol

WC1-xvol

Cvol

Wvol

1 ac arc W C 02 71 781 147 -2 dc arc W(cathode)C(anode) 01 62 901 37 -3 dc arc W(anode)C(cathode) 02 66 715 219 -4 ac spark W C 25 58 328 614 -5 dc spark W(cathode)C(anode) 12 570 307 89 336 dc spark W(anode)C(cathode) 21 56 325 618 -

As it can be seen from the Table 1 the synthesized nanopowder isa mixture of hexagonal W2C face centered cubic WC1-x and graphite Nopeaks corresponding to WO were observed Nanopowder contained alsosmall amount body centered cubic W when synthesis was performed bydc current spark discharge with tungsten rod acting as cathode Here theparticular behavior of this discharge should be stressed showing ratherhigh ability to synthesize W2C Moreover in contrast to the other sparkdischarges synthesized material contained relatively small amount ofgraphite On the other hand applying tungsten as a cathode materialappears to reduce C content in nanopowder prepared via arc dischargetoo Generally the content of C is higher and content of WC1-x is lowerwhen synthesis was performed by spark discharge

168

Nanoparticles prepared by arc discharge were observed in theiragglomerated form The agglomerated nanoparticles were surrounded bythe grey regions which were probably graphite layers This typical viewwas seen everywhere in TEM images of product synthesized by arc forboth ac and dc current discharges irrespective of electrodes polarityThat fact implies that the morphology of synthesized nanopowders wasgoverned rather by the current pulse duration and value of peak currentthan the polarity of the electrodes Since nanoparticles were observed inthe agglomerated form it was difficult to measure their size correctlyWe suppose that approximately 4 nm nanoparticles are formed duringthe arc discharge in ethanol

Fig1 shows the TEM image of titanium carbide nanopowdersynthesized by spark discharge in ethanol As can be see from the Fig1the nanoparticles were also surrounded by graphite layers Fig 1demonstrates that the nanoparticles synthesized by spark were nearlyspherical with a mean diameter of ~ 7 nm The particle size distributionwas rather narrow (plusmn 2 nm) The XRD pattern of synthesized sample isshown in Fig 1 (right picture) The diffraction peaks at 60deg 418deg605deg 724deg 765deg and 407deg 504deg 590deg 667deg 741deg correspond tothe formation of cubic face-centered titanium carbide TiC and cubicprimitive TiC2 respectively There are some diffraction peaks with 2θvalue of 407deg 504deg 590deg 667deg and 741deg which can be assigned tothe hexagonal C The amount of TiC reached 887 vol The quantitiesof TiC2 and C in samples detected by XRD corresponded to ca 47 vol and ca 67 vol respectively

Fig 1 TEM image (left picture) of titanium carbide nanopowder synthesizedby ac spark discharge and XRD-pattern (right picture) of the sample

169

Synthesis of copper-carbon composite nanostructuresNumerous studies have focused on synthesis of metal-containing

carbon nanocapsules (CNCs) via submerged discharge method[89141516] Because of the carbon sheets surrounding the metal corethe CNCs are protected from the environment and from degradation Thecarbon coatings mean that nanoparticles are biocompatible and stable inmany organic media Thus carbon encapsulated nanoparticles arecandidate for bioengineering application high-density data storagemagnetic toners for use in photocopiers [81718] The metal containingcarbon nanostructures were prepared by using the electrode frommixture of graphite and metal precursor [16 1920] Recently Xu et aldemonstrated a possibility to synthesize Ni- Co- and Fe-containingCNCs by an arc discharge between carbon electrodes in aqueoussolution of NiSO4 CoSO4 and FeSO4 respectively [15] In contrast tothe data reported by Bera et al the synthesized material consisted of Oand S due to SO4

-2 ionic precursors in the solution Since the metal core-forming material was supplied by liquids the production rate of CNCswas limited by the salt concentration [4] This restriction may cause alimit to apply the submerged discharge method to the large-scaleproduction of CNCs

In this paper Cu-based nanoparticles were prepared viasubmerged discharge of bulk copper and graphite electrodes in a copperchloride (CuCl2) aqueous solution Thus material of copper electrode aswell as Cu from solution was supposed to be incorporated into theresulting nanoparticles The effect of discharge parameters and electrodecomposition on the morphology and composition of final products havebeen investigated Additionally synthesized material was modified bylaser irradiation The changes in nanoparticles morphology andcomposition were examined by transmission electron microscopy(TEM) X-ray diffraction (XRD) and UV-Vis spectroscopy

The six types of nanoparticles suspension were prepared underdifferent discharge parameters The synthesis parameters aresummarized in Table 2 As it can be seen the weight change of eachelectrode was generally higher when spark discharge was generatedThe anode consumption rate was higher than that of cathode irrespectiveto a discharge type and electrode material However in contrast to theliterature data [4] there was no cathode gain in weight As a generaltrend the nanopowder synthesis rate was higher for spark discharge than

170

that of arc discharge It may be explained by the difference in currentvalue [21] For both arc and spark discharges it was found that thesynthesis rate was higher when copper was acting as an anode There isa discrepancy between nanopowder synthesis rate and materialconsumption rate The values of discrepancy D listed in the Table 2were calculated as follows

100()

CCu

syn

RR

RD (1)

Here Rsyn is the synthesis rate of nanopowder RCu is theconsumption rate of the copper electrode and RC is the consumptionrate of the graphite electrode The discrepancy D depended ondischarge parameters For ac-discharges the value of discrepancy washigher for spark discharge than that for arc discharge For dc-discharges this trend remained if the polarity of electrodes was takeninto account It is worth to notice here that the discrepancy betweenmaterial consumption rate and nanopowder synthesis rate may be causednot only by separation of sediment fraction but by the reaction of carbonatoms with water resulting in the production of gaseous compounds [9]

Table 2 Summary of nanopowder synthesis parametersType of

dischargepeak currentpulse duration

Electrodes materialRCu and RC

mg min-1RSyn

mg min-1D

Cu 671 ac1) spark60 A 30 micros C 48

59 49

Cu 122 ac arc10 A 4 ms C 26

25 34

Cu (cathode electrode) 473 dc2) spark60 A 30 micros C (anode electrode) 61

21 81

Cu (anode electrode) 664 dc spark60 A 30 micros C (cathode electrode) 46

69 38

Cu (cathode electrode) 115 dc arc10 A 4 ms C (anode electrode) 25

19 47

Cu (anode electrode) 286 dc arc10 A 4 ms C (cathode electrode) 21

33 33

1) Alternating current pulsed discharge2) Direct current pulsed discharge

171

This coincides with the fact that the largest discrepancy (morethan 80) was observed in sample with the largest graphite electrodeconsumption rate (sample 3) For all samples the synthesized powderseparated into three phases one floating in suspension one settling atthe bottom as sediment and one as a layer of film-like material floatingon the liquid surface

The aqueous solutions of CuCl2 were discharge treated for only 20s to acquire yellowish suspensions The transparency of the suspensionsdecreased with the time during the discharge treatment The liquidsturned to dark yellow after treatment by ac-discharge for 10 min Thesuspensions resulting from dc-discharge treatment were conspicuouslydarker when C electrode was acting as an anode The nanoparticlessuspension produced by spark and arc discharges were dark brown anddark grey respectively It might be due to the presence of relatively largeamount of carbon particles in suspension (see Table 3) The dc-dischargetreated solutions were olive-green when Cu was used as the anodeelectrode Yellow or green colour of suspension may indicate theoxidation of copper nanoparticles [22] The presence of Cu2Onanoparticles was further confirmed by XRD analysis No changes incolour were observed after laser irradiation of suspensions

Figure 2 shows the absorption spectra of as prepared (a) and laserirradiated (b) suspended nanopowders synthesized by dischargetreatment of aqueous solution of CuCl2 (2) for 1 min The spectra werecorrected to the contributions of solvents The optical density increasedwith decrease in wavelength Generally the optical density ofsuspensions prepared by spark discharge was higher than that ofsuspension prepared by arc discharge This is consistent with the factthat the nanoparticles production rate was higher when the solution wastreated by spark discharge In the spectral range of 200 ndash 500 nm theoptical density of the samples 1 4 6 was higher than that of samples 23 and 5 This seems to suggest that the main parameter in determiningthe optical properties of suspensions was concentration of Cu-basednanoparticles For the samples number 1 and 4 a weak absorption peakwas observed at very short wavelength According to the literature data[2324] a surface plasmon peak at wavelength of 289 nm may beattributed to the presence of very small separated Cu nanoparticles (lt 4nm in size) Though TEM examination confirmed the presence of smallnanoparticles in sample 1 there were no nanoparticles with diameter less

172

than 4 nm in sample 4 Moreover there were no copper nanoparticles insample 1 as revealed by the XRD (see below) More likely theexistence of weak absorption peak at 280 nm implied formation of liquidbyproducts We did not observe in the absorption spectra surfaceplasmon band around 570 nm Missing of the plasmon band can beexplained by copper oxidation on the particle surface [23] Thissuggestion was further confirmed by XRD analysis (see below) Thesuspensions exhibited the same colours after laser irradiation butabsorption intensity increased for samples 3 1 and to the less extent forsample 5 as illustrated in Figure 2b TEM analysis revealed themorphological similarity of irradiated samples 1 3 and 5 (see below)

Figure 3 depicts the corresponding TEM images for thesuspensions shown in curves 1-6 of Figure 2 Parts (a) and (b) representthe TEM views of the as-prepared and irradiated samples respectivelyThree distinct structures were observed dark small spherical particlesdark particles surrounded by a gray shell and gray flake-like structureshaving diffuse contours The small dark particles with diameter 2-5 nmwere observed in samples 1 2 3 and 5 (marked with black ellipses inFigure 3) Some dark particles notable when using ac spark dischargefor synthesis were bigger than 20 nm indicating coalescence Thenanoparticles synthesized by ac arc discharge (sample 2) were

Fig 2 Absorption spectra for the as-prepared (a) and laser modified (b)suspended nanoparticles produced by ac- (12) and dc- pulsed discharges(3456) The following electrode pairs were used Cu and C for the ac-spark(1) and ac-arc (2) discharges Cu as a cathode electrode and C as an anodeelectrode for the dc-spark (3) and dc-arc (5) Cu as an anode electrode and C asa cathode electrode for the dc-spark (4) and dc-arc (6)

173

surrounded by the arrowed gray regions which were probably carbonshells as shown in Figure 3a

Fig3 TEM images of nanoparticles from as-prepared (a) and irradiated (b)suspensions produced by ac- (12) and dc- pulsed discharges (3456) Thefollowing electrode pairs were used Cu and C for the ac-spark (1) and ac-arc(2) discharges Cu as a cathode electrode and C as an anode electrode for thedc-spark (3) and dc-arc (5) Cu as an anode electrode and C as a cathodeelectrode for the dc-spark (4) and dc-arc (6)

174

As we did not have any direct evidence that the shells consisted ofcarbon these nanostructures will be referred further as core-shellnanoparticles The core-shell nanoparticles were also observed in colloidprepared by dc arc discharge between copper cathode and graphiteanode (sample 5) It can be seen that core-shell nanoparticles rangedfrom 20 to 50 nm in diameter while the cores within the nanoparticlesvaried from 8 to 25 nm The cores were non-spherical They seemed tocompose of small particles clustered together The flake-like structureswith diffuse contours were 50 nm in size They were observed in allsamples Samples 4 and 6 consisted mostly of structures with diffusecontours On the basis of the above observations the ac arc dischargeand dc arc discharge with copper anode electrode seemed to be moresuitable for synthesis of nanoparticles with core-shell structure

It is clear seen that many smaller particles with sizes around 2-7nm were generated after the irradiation of samples 2 4 and 6 Theparticles larger than 10 nm completely disappeared The micrographrevealed that after the irradiation these suspensions consisted ofparticles with circular cross-section whereas before the irradiation theparticle shape was not spherical The nanoparticles were dispersed verywell No small nanoparticles were observed in suspensions 1 3 and 5after the irradiation Though as can be seen by comparing Figure 1(a)3(a) and 5(a) with 1(b) 3(b) and 5(b) the shape of nanoparticleschanged after the irradiation The laser induced morphology change mayoccur through heating of the nanoparticles because of the absorption ofthe laser light [25] According to the mechanism proposed by Takami etal the morphology of irradiated nanoparticles was determined by therelationship between temperature of nanoparticles their melting andboiling point

The laser induced change in shape and size occurred if thetemperature of nanoparticles was at the boiling point If the temperaturewas lower than the melting point no changes took place If thetemperature was between melting point and boiling point only thechange in shape occurred Thus the difference in morphology of theirradiated samples can be attributed to the difference in theircomposition Even being irradiated with the same laser light intensitythe nanoparticles of different composition changed their morphology indifferent ways as they have different melting and boiling points

175

X-ray diffraction data were collected to identify synthesizedsamples The diffraction peaks at 432deg and 503deg correspond to theformation of faced-centered-cubic Cu There are three diffraction peakswith 2θ value of 365deg 423deg and 614deg which can be assigned to theprimitive cubic Cu2O Besides there are two peaks at 240deg and 265degwhich can be assigned to the hexagonal C XRD revealed that dischargetreatment of aqueous solution of CuCl2 led to the formation of Cu2

(OH)3Cl and Cu2OCl2 because of a strong affinity between chlorine andthe metal (peaks with a value of 2θ around 165deg 19deg 31deg 323deg 327deg330deg 387deg 398deg 401deg 503deg 505deg 538deg and 178deg 360degrespectively) For comparison the XRD patterns of initial solution ofCuCl2 are also plotted at the top of Fig 4 Non-treated aqueous solutionof copper chloride was allowed to evaporate and than analyzed by XRDThe diffractogram of this sample showed peaks at about 2θ around162deg 220deg 240deg 267deg 289deg 328deg 340 348deg 352deg 409deg 430deg448deg 453deg 490 and 573deg which are characteristics of CuCl2middot2H2O

XRD data were used to semi-quantitatively determine thepercentage of constituents The semi quantitative analysis of phasecomposition is shown in Table 3 The nanopowder composition wasstrongly dependent on the synthesis parameters It should be noted herethat metallic copper was only formed by dc-discharge treatment whencopper was acting as an anode electrode (samples 4 and 6) Synthesizedmaterial contained copper mostly in form of oxide (Cu2O) copperhydroxychloride (Cu2(OH)3Cl) and copper oxychloride (Cu2OCl2)Difference in Cu2O and C contents among all samples was significantSamples 2 and 5 contained no copper oxide while sample 6 had thelargest percentage of copper oxide (ca 80 vol) On the other handsample 6 contained no carbon The carbon contain in sample 4 exceeded80 vol The quantities of Cu2(OH)3Cl in samples ranged from lessthan 2 vol to ca 30 vol Only three samples contained Cu2OCl2

(samples 12 and 5) The maximal amount of Cu2OCl2 detected by XRDcorresponded to ca 30 vol In spite of high copper electrodeconsumption rate sample 4 contained unexpectedly small quantities ofCu and Cu-containing compound It might be due to the formation ofrelatively large and heavy copper microparticles They precipitated fromcolloid quickly after synthesis Therefore they were not collected andanalyzed by XRD (see experimental section) A correlation was

176

observed between low copper electrode consumption rate and absence ofCu and Cu2O fractions in nanopowder composition for samples 2 and 5

It should be stressed here that the core-shell structures wereobserved for only samples 2 and 5 Taking into account firstly thatsamples 2 5 and 6 were prepared by arc treatment secondly that thesample 6 contained no C and assuming that the shells consisted ofcarbon we can suggest that arc discharge was more suitable forsynthesis of core-shell nanoparticles On the other hand the chemicalcomposition of final product was governed by different competingreactions As they have different equilibrium constants they may form anetwork where the ratios of the products are sensitive to concentrationsof each of the many components Therefore the slight difference ininitial concentration might results in significant difference incomposition and morphology of synthesized material (compare samples5 and 6)

Although the exact mechanism for formation of nanoparticles viadischarge in solution process is not clear the following possibility may

Table 3 Semi-quantitative analysis of synthesized powder by XRD

XRD-analysisType of

dischargeElectrodesmaterial Cu

volCu2Ovol

Cvol

Cu2(OH)3Clvol

Cu2OCl2vol

1 ac1) sparkCuC

- 135 403 165 297

2 ac arcCuC

- - 646 300 54

3 dc2) sparkCu (cathode)C (anode)

- 391 370 239 -

4 dc sparkCu (anode)C (cathode)

78 83 825 14 -

5 dc arcCu (cathode)C (anode)

- - 339 336 325

6 dc arcCu (anode)C (cathode)

74 775 - 151 -

1) Alternating current pulsed discharge2) Direct current pulsed discharge

177

be considered During discharge treatment of the liquid copper andgraphite electrodes were heated melted and vaporized in the region ofthe discharge generated In the vicinity of electrodes the liquid was alsovaporized rapidly due to extremely high temperature Hence the plasmaregion produced by the discharge adjacent to the electrodes wassurrounded by a gas bubble Following Sano et al [8] the gas mixturemay comprise CO and H2 formed as follows

22 HCOOHC (2)

This reaction might cause the discrepancy between electrodeconsumption rate and nanopowder synthesis rate since some of carbonatoms formed gaseous CO Sano et al reported that gas bubbles didnot comprise water vapor since no condensation occurred [8] Howeverwe should consider that water vapour also existed in the discharge zoneas we did not obtain any evidence of its absence

Copper chloride is an anionic compound that dissociates inaqueous solution and may form different ionic species such as Cu2+ Cl-or complex ions such as CuCl2

- CuCl32- CuCl4

2-[26] The reduction ofcopper ions into copper atoms was likely taking place in plasma regionduring discharge treatment of the liquid as shown in Eq 3

02 2 CueCu (3)

As the temperature in the vicinity of the electrodes was estimatedto be around 4000 K [8] the thermal decomposition of complex ions tometallic copper possible took place in discharge zone (Eq (4-6))

20

2 ClCuCuCl (4)

20

3 322 ClCuCuCl (5)

202

4 2ClCuCuCl (6)

The nanoparticles were then formed from the complex gasmixture through different transformation stages namely nucleationgrowth condensation and coalescence Both the evaporated copper fromelectrode and Cu produced by reduction of ions from solutions were

178

supposed to be incorporated into the resulting nanoparticles Becausewater vapor existed in gas bubble the copper nanoparticles were easilyoxidized Reduction of copper oxide by carbon monoxide and hydrogenwas possible the subsequent step (Eq (7) and (8))

OHCuCOOCu 22 2 (7)

222 2 COCuHOCu (8)

According to the XRD measurements (see Table 3) copper oxidewas only partially reduced into copper in sample 4 and 6 The data ofXRD analysis implied also reaction of chlorine with copper andorcopper oxide to form Cu2Cl(OH)3 and Cu2OCl2 These reactions mightinvolve hydrogen produced via reaction (2)

It should be noted that there was no direct evidence to support theabove-mentioned formation sequence and the true mechanism may bemore complicated

ConclusionsFrom the results and discussion presented above the following

conclusions can be madeThe electrical discharge between two electrodes immersed in

ethanol is a suitable method to produce in a controllable waynanoparticles with different contents of metal and carbon By varyingthe current value and its pulse duration morphology of nanoparticlesand their composition can be changed The average diameters of theprepared nanoparticles were in the range of 3-7 nm

Cu-based nanoparticles with different morphologies wereprepared via submerged electrical discharge of bulk copper and graphiteelectrodes in a CuCl2 aqueous solution Synthesized material wassubjected to laser-induced modification It was found that core-shellnanoparticles were formed by treatment of CuCl2 aqueous solution bythe arc pulsed discharge with pulse duration of 4 ms and peak current of10 A

The synthesis rate varied in range of 19 ndash 69 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofcopper and graphite electrodes The synthesis rate was found to behigher when copper was acting as an anode electrode The synthesis rate

179

increased with increasing of discharge current and decreasing of pulseduration The composition and morphology of nanoparticles were alsofound to depend on discharge parameters The copper nanoparticleswere only formed by dc-discharge treatment when copper was acting asan anode electrode The maximum diameter of nanoparticles did notexceed 50 nm while the minimum diameter was around 2 nm Theresults of the experiments imply that plasma treatment with longer pulseduration and lower current leads to the formation of carbon embeddednanoparticles TEM confirms the formation of encapsulatednanoparticles

Irradiation of nanoparticles in aqueous solution by a pulsedNdYAG laser at 532 nm was found to cause the shape change and sizereduction of the particles

AcknowledgementsThe work has been supported by the Integral Program of the

Siberian Branch of RAS under the Grant 138-T-09-CO-014 Authorsare thankful to KV Scrockaya for carrying out the TEM investigations

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2 XG Yang and CY Wang (2005) Nanostructured tungsten carbidecatalysts for polimer electrolyte fuel cells Appl Phys Lett 8624104-1 -224104-3

3 M Rosenbaum F Zhao U Schroder F Scholz (2006) InterfacingElectrocatalysis and Biocatalysis with Tungsten Carbide A High-Performance Noble- Metal-Free Microbial Fuel Cell Angew Chem118 1-4

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7 Sano N Wang H Alexandrou I Chhowalla M Amaratunga G A J(2001) Nanotechnology Synthesis of carbon ldquoonionsrdquo in waterNature (London) 414 506-507

8 Sano N Wang H Alexandrou I Chhowalla M Teo K B KAmaratunga G A J (2002) Properties of carbon onions produced by anarc discharge in water J Appl Phys 92 2783 ndash 2788

9 Sano(a) N (2004) Low-cost synthesis of single-walled carbonnanohorns using the arc in water method with gas injection J PhysD 37 L17-L20

10 Parkansky N Alterkop B Boxman R L Goldsmith S Barkay ZLereah Y (2005) Pulsed discharge production of nano- andmicroparticles in ethanol and their characterization PowderTechnology 150 36-41

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12 P Muthakarn N Sano T Charinpanitkul W TanthapanichakoonT Kanki Characteristics of Carbon Nanoparticles Synthesized by aSubmerged Arc in Alcohols Alkanes and Aromatics Phys Chem Bndash 2006 ndash Vol 110 37 ndash P 18299 -18306

13 D Bera G Johnston H Heinrich S Seal A parametric study on thesynthesis of carbon nanotubes through arc-discharge in water Nanotechn ndash 2006 ndash Vol 17 ndash P 1722-1730

14 Hsin Y L Hwang K C Chen R-R Kay J J (2001) Production and insitu metal filling of carbon nanotubes in water Adv Mater 13 830-833

15 Xu B Guo J Wang X Liu X Ichinose H (2006) Synthesis of carbonnanocapsules containing Fe Ni or Co Carbon 44 2631-2634

16 Lange X Sioda M Huezko A Zhu Y Q Kroto H W Walton D R M(2003) Nanocarbon prodction by arc discharge in water Carbon 411617 ndash 1623

17 Sergienko R Shibata E Akase Z Suwa H Nakamura T Shido (2006) Carbon encapsulated iron carbide nanoparticles synthesized in

181

ethanol by an electric plasma discharge in an ultrasonic cavitationfield Mater Chem Phys 98 34-38

18 Leo G H Jeong S H J W Ri H C (2002) Excelent magnetic propertiesof fullerene encapsulated ferromagnetic nanoclusters J Magn Mater246 404 ndash 411

19 Ang K H Alexandrou I Mathur N D Amaratunga G A J Hag S(2004) The effect of carbon encapsulation on the magnetic propertiesof Ni nanoparticles produced by arc discharge in de-ionized waterNanotechnology 15 520 ndash 524

20 Sano(c) N Nakano J Kanki T (2004) Synthesis of single-walledcarbon nanotubes with nanohorns by arc in liquid nitrogen Carbon42 686-688

21 Bera(c) D Jonston G Heinrich H Seal S (2006) A parametric studyon the synthesis of carbon nanotubes through arc-discharge in waterNanotechnology 171722-1730

22 Yeh M-S Yang Y-S Lee Y-P Yeh Y-H Yeh C-S (1999) Formationand characteristics of Cu colloids from CuO powder by laserirradiation in 2-propanol J PhysChem B 103 6851-6857

23 Aslam M Gopakumar G Shoba T L Mulla I S Vijayamohanan K(2002) Formation of Cu and Cu2O nanoparticles by variation of thesurface ligand preparation structure and insulating-to-metallictransition J Colloid Inter Sci 25579-90

24 Salkar R A Jeevanandam P Kataby G Aruna S T Koltypin YPalchik O Gedanken A (2000) Elongated copper nanoparticlescoated with a zwitterionic surfactant J Phys Chem B 104 893-897

25 Takami A Kurita H Koda S (1999) Laser-induced size reduction ofnoble metal particles J Phys Chem B 1031226-1232

26 Brown JB (1948-1949) The constitution of cupric chloride inaqueous solution Transaction of the Royal Sociaty of New Zeland 7719-23

162

MORPHOLOGICAL STUDY OF DETONATIONSPRAYED COATINGS OF CALCIUM HYDROXYAPATITE

DEPOSITED ON A NANOSTRUCTURED TITANIUMSUBSTRATE

AA Sitnikov VI Yakovlev YuP Sharkeev 1EV Legostaeva 1 AA Popova

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1Institute of Strength Physics and Materials Science SB RASTomsk

Biocompatible coatings are effectively formed by spraying ofcalcium hydroxyapatite Са10(РО4)(ОН)2 powders on a titanium substrateRecently along with the composition macro- and microstructuredevelopment the surface morphology of the coatings has receivedincreasing attention In a number of studies the roughness of thecoatings has been shown to significantly influence the inductionprocesses of cells As a substrate material titanium VT1-0 has beenchosen which has several advantages being highly biocompatiblebioinert practically non-toxic corrosion-resistant and possessing lowthermal conductivity and low coefficient of thermal expansion Themorphology of the gas-detonation sprayed calcium phosphate coatingsdeposited on ultrafine-grained and nanostructured titanium substratesand implant imitations has been studied The substrates and implantimitations were produced in the Institute of Strength Physics andMaterials Science SB RAS Tomsk

It was shown that the detonation sprayed hydroxyapatite powderswith particles ranging from 1 to 20 microm formed coatings non-uniform inthickness and phase composition The roughness of the coatings wasRa=365-472 microm (class 5) When hydroxyapatite particles of 20-100microm in size are sprayed coatings more uniform in thickness and phasecomposition are formed (Fig1) with an average roughness of Ra = 624microm (class 4) Preliminary treatment of the titanium substrate by sandingand chemical etching allows increasing the adhesive strength of thecoating up to 20MPa

163

Fig1 SEM images hydroxyapatite powder (a) detonation sprayedhydroxyapatite coating (b) XRD pattern of the coating (c)

Biological studies have demonstrated biocompatibility andbioactivity of the coatings It was found that the calcium phosphatedetonation sprayed coatings induce growth of tissue cells with 100probability which indicates that the relief of the coatings is optimal forfixation and aging of the cells Comparative studies of calciumphosphate coatings produced by detonation spraying and those producedby micro-arc in an electrolyte containing phosphoric acidhydroxyapatite and calcium carbonate have shown the advantages ofdetonation spraying for providing the required phase composition of thecoating This opens up a possibility of making two-phase coatings(hydroxyapatite and beta-calcium phosphate) ensuring the closest matchin composition to the bone tissue

ва б

100

200 20 30 40 50 60 70 80 90 10

(1

10) (002

) (2

10)

(2

11)

(

300

)

(3

10)

(

222

)

312

)

(3

20)

(

511

)

(

432

)

(5

22)

(

100

)

161

MICROSTRUCTURE STUDIES OF THE COATINGSPRODUCED BY ARC DEPOSITION OF THE

MECHANOACTIVATED SHS-COMPOSITE TIC+XME(R6M5 PR-N70H17S4R4-3) POWDERS

AA Sitnikov VI Yakovlev MA Korchagin1MN Seidurov ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

One of the main challenges in the development of new materialsfor arc deposition using flux-cored wires is to design materials of specialinterest using cost-effective and ecologically friendly technologies Asmaterialstechnologies meeting these requirements we can proposelayered composites produced by self-propagating high-temperaturesynthesis (SHS) in mechanically activated powder mixtures

The samples of SHS-mechanocomposites of TiC+XMe (R6M5PR-N70H17S4R4-3) composition arc-deposited on steel 45 substrateswere selected for investigations Microstructure of the arc-depositedcoatings was studied using a Carl Zeiss AxioObserver A1m OpticalMicroscope For observations cross-sections of the samples wereprepared and etched with a solution containing 20 potassiumferricyanide К3[Fe(CN)6] 20 КОН and 60 H2O Finemicrostructure and composition of the deposited layers were analyzedusing a Carl Zeiss EVO50 Scanning Electron Microscope equipped withan EDS X-ACT laquoOXFORDraquo device

The investigations show that the microstructure of the depositedlayers is uniform with submicron titanium carbide reinforcing phase inthe form of separate inclusions or chains of particles in the matrix

159

WEAR-RESISTANT DETONATION SPRAYED COATINGSBASED ON THE COMPOSITE MECHANICALLY ACTIVATED

SHS-MATERIALS

AA Sitnikov VI Yakovlev MA Korchagin 1DM Skakov AA Popova ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

The application of titanium carbide as a material for thermalspraying is rather difficult mainly due to its high melting temperatureand high hardness

A technology has been developed abroad for the production of thecomposite powders for spraying The production of these compositepowders is a laquoknow-howraquo of MBN Nanomaterialia (Italy)

An approach to the development of TiC-containing coatings canbe based on the technology of mechanocomposites with metallic orintermetallic matrices reinforced with nanosized particles of a ceramicphase [1] The technology of the powder preparation consists of 3 stagesAt the first stage the mixture of initial reactants which in this particularcase are titanium carbon and nichrome is mechanically activated (MA)in a planetary ball mill At the second stage self-propagating hightemperature synthesis (SHS) is conducted resulting in the formation ofTiC particles uniformly distributed in the metallic matrix AdditionalMA of the products of SHS at the third stage along with dispersingtitanium carbide particles creates a principally new state of the matrixwhich experiences grain refinement and shows high internal stresses andhigh concentrations of non-equilibrium defects In addition thesubsequent mechanical activation can be advantageously used forcompositions with higher matrix contents that are not possible to makethrough the SHS special additives can be also introduced into thecomposites at this stage

In order to compose the initial mixtures the following powderswere used titanium PTM lampblack PM-15 and nichrome PR-N70H17S4R4-3 Mechanical activation of the powder mixtures and theSHS-products was carried out in a planetary ball mill AGO-2M

160

Detonation spraying was performed using the laquoKatun-Mraquo set-upIt was found that the chemical composition did not change duringspraying

Wear resistance of the sprayed coatings was evaluated using afriction machine 2168 UMT in the laquoshoe-on-diskraquo mode A coating 02mm thick was deposited on a steel 40 shoe Prior to deposition the shoewas rubbed against the disk until a contact spot was formed over thewhole surface of the shoe After the coating was deposited the workingsurfaces were subjected to abrasive diamond treatment to reduce theirroughness

Tribological tests showed that with increasing metallic matrixcontent from 20 to 60 wt the weight losses under dry friction at 950 Nincreased almost twice Comparative tests of the coatings and thesamples of hardened steel revealed that the wear of the coatings obtainedfrom the mecahnocomposite powders was 8 times lower than that ofsteel 40H

References1 MAKorchagin DVDudina Application of self-propagating high-

temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007 v43 2 p176-187

153

CHEMICAL-THERMAL TREATMENT IN CARBONMANGANESE STEEL

AT INDUCTION-HEATING IN VARIOUS BORATINGCONDITIONS

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

Ural Federal University Ekaterinburg RussiaAltay State Agrarian University Barnaul Russia

Abstract Processes of borating of high-carbon manganese steel65Mn by carbide of boron and amorphous boron in conditions of fluxwith additives of various activators of borating are investigated at high-speed induction-heating It is shown that the nature of the boratingagent the additive of flux activators CaF2 and NH4Cl have influence onstructure and properties which are formed on a surface of boroneutectics

Keywords boron carbide of boron induction heating chemical-thermal processing

Among modern processes of chemical-thermal treatment (CTT)production engineering of saturation of surface layer constructional andalloy steels with boron ndash the borating occupy a special place In boratingit is possible to obtain the extended beds distinguished by high hardnessand strength corrosion-resistance abrasive durability and highreceptivity to wear on a surface of a steel detail [1 2] However themajority of known processes of borating are prolonged and are badlybuilt in into flow diagrams of state of productions

Intensification of CTT processes and in particular borating canbe carried out with application of technology of short-term high-speedheating of steel detail surface with the borating composition put on herrf currents (RFC) up to temperatures of formation of new phases andeutectics (1100-1350 оС) in systems Fe-B Fe-B-C and Fe-Me-B-Cwhere Ме - is an alloy element from group Cr Mn Ni etc [3] Unlikewell investigated processes of borating of alloy steels by mediums anddaubing at temperatures up to 950оС [4] there are open generalquestions of peculiarities of chemical interaction of components in suchsystems phase condition and properties of formed products

154

In the present work chemical-thermal treatment of carbonmanganese 65Mn steel combined with RFC-heating of its surface invarious borating conditions has been investigated

Experimental partAs the basic subject of research 65Mn (GOST 4543-71) alloy

carbon steel was chosen from the group of the same kind manganesechromos chromos-nickel and chromos-manganese steels from group 70U8А 50CrMnА 30CrMnSiА 45Cr 70Mn etc with similar propertiesand composition

Technical carbide of boron B4С in accordance with GOST 5744-85 and reactive amorphous boron of qualification reagent-grade weretaken as borating agents of different nature Known composition for theinduction deposition (F1) consisting of borax glass the boric anhydridecalcium silica and welding flux АN-348А (30 Na2B4O7 20 B2O310 CaSi2 and 40 flux АN-348А) was used as flux Reagent-gradeCaF2 and NH4Cl served as activators

RFC-heating of samples was carried out in a loopback water-cooled copper inductor by diameter of 160 mm connected to RF-lampgenerator VCG 7-600066 The adjustment of a contour and geometryof an inductor provided heating of researched samples to the temperatureof 1300-1350оС during 40-60 sec with the subsequent stabilizationAfter holding at the specified temperature during from 1 up to 2 minsamples were pulled out from an inductor and cooled down loosely

Microstructure of the coverings formed has been investigated andthickness of borated bed has been determined (МIМ-7 Neophot-30)hardness has been measured (PМТ-3 by 50 100 g) phase composition(DRON-2 radiation Co-Kα speed of angular moving of a sample of 1grads min) has been determined

Results and discussionIt is known that classical production engineering of kiln borating

are based on gradual (during 05-6 h) saturation of a surface of a steelproduct by boron from various pastes daubings liquid or a gaseous fluidat temperatures of process from 750 up to 950 оС Thus in the capacityof sources of boron its various compounds (В2О3 В4С ВF3 Na[BF4]etc) are applied capable to decay on active elements at temperatures ofprocess Depending on a phase condition of the borating agent hardness

155

and liquid borating are distinguished and also borating from a gas phase[4] We investigated six variants of mixes for high-speed borating atRFC-heating steel 65Mn Mixes differed in the nature of the boratingagent e borating agent composition presence fluxes componentsactivators and technological additions Compositions of the mixes usedare given in table 1

Table 1

Mixes Boratingagent

Activator Flux

Iа B4C (84) NH4Cl (6) F1 (10)II B4C (84) ndash F1 (16)

IIIа B (90) CaF2 (5) F1 (5)

Mixes I Iа II and IIа used as borating agent contained carbide ofboron mixes III IIIа - amorphous boron in mix Iа activator chloride ofammonium and in mix IIIа - fluoride of calcium has been added allmixes contained melted flux as a fluxing component for inductiondeposition F1

With decrease of density of a borating phase and increase intemperature of process its speed in the interval of temperatures from 800up to 950 оС increases insignificantly therefore for their intensificationcollateral saturation of a surface by several elements at once or thermocycling are applied [5] If the temperature of the process exceeds 1100-1300 оС in an aspect of beginning processes of high-temperaturestructural reorganization in steel speeds of borating sharply increase in2-4 min with the increase in temperature at every 15-20 оС thus theprocess passes from a diffusive zone to a zone of chemical reaction Soat the temperature of 1200-1300 оС according to the data[6] it ispossible to obtain in a few minutes the thickness of the single-phaseboron-bed up to 02-04 mm thus heating of a detail is carried out by thespecial thermo reaction mix

At RFC-heating of the steel 65Mn covered by researched boratingcompositions with chosen parameters of process fig 1 adamantinecoverings are formed on all samples resembling bed covered hard metalX-ray analysis of a material of coverings has shown presence of Fe

156

borides FeB and Fe2B carbon-borides Fe3(C B) and Fe23(C B)6 variousmeta- and orto-borates of iron (Fe3BO3 Fe3BO6 Fe3BO5) traces FeOand FeOFe2O3 Thus at RFC-heating of alloy carbon steels under bedof flux F1 containing from 84 up to 90 of borating agents complexboron-phases are formed on their surfaces hardening a surface of a detailand it is strongly linked with it and oxide films are removed togetherwith slag

To find out the characteristics and structure of received beds andthe conditions of borides in them photomicrography of micro sectionswas taken Typical structures of boron-beds are given in fig 1

a b C

Fig 1

As it is seen from fig1 with the chosen heating environments andthe time of borating the structure and the condition of boundary line ofreceived wear-resistant beds differ but in all cases as against classicalboron two-phase beds on a surface of samples the eutectic with stronglypronounced or with the diffusive boundary line separating it from anoriginal material is formed faster in conditions of heavy abrasive sign-variable and shock wear boron-plate Apparent changes in structure ofparent metal caused by its short-term overheat were not observed

For the mixes containing in the capacity of borating agent equalquantity of carbide of boron similar quantity of fluxes-component anddistinguished only by the presence of activator NH4Cl promoting areinforcement of convertible diffusive and transport reactions especiallyat low temperatures right at the beginning of the process of borating (Т

157

lt300 оС) formation of fine grained structure of eutectic turnings on withhardness not above 700-750 HV thickness of bed of 016 mm and withlegibly discernible interface with parent metal (fig 1а) is observed

For the analogous mix II without this activator the expressedpropagation of dendrites islands and druses of boron-phases withhardness up to 1050-1120 HV thickness of bed of 028 mm and adiffuse interface boron bed with parent metal (fig 1b) is observed Themixes on the basis of amorphous boron (fig 1c) appeared to be the mostreactive thus in mix IIIа containing follow-up 5 of activator CaF2 and5 of fluxes component beyond chosen relationships for 1 minthickness of bed on steel of 65Mn has made 088 mm at its hardness in2200-2300 HV The structure represents the remote eutectichomogenized iron ndash boron formed with such speed that from a melt atits solidification balls of slag had not time to bleed up to the end

Thus amorphous boron which at the presence of flux F1 andactivator CaF2 under the chosen conditions of experiment forms denseclose-grained beds on a surface of alloy steels with depth up to 800microns with hardness up to 2400-2500 HV (fig 2) appeared to be themost efficient borating agent at RFC-heating

Fig 2

It is interesting to note that the structure of the wear-resistantcovering obtained at high-speed 1 min borating steel 65Mn a mix II ismetastable and at borating during 2 min like in picture 1а with hardness2300-2400 HV turns to the fine grained structure and thickness of a

158

covering does not change and the interface with parent metal becomesdiscernible

References1 Methods of raise of longevity of machine components Red VN

Tkacheva M 19712 Belyj AV Karpenko GD Myshkin KN Structure and methods of

formation of wear-resistant surface layers M 19913 Tkachev VN Fishtejn BM Kazintsev NV Aldyrev DA

Induction overlaying welding of hard metals M 19704 Voroshnin LG Lyahovich LS Borating of steel M 19785 Guryev АМ Kozlov EV Ignatenko LN Popova NA Physical of

a basis of thermal-cycle borating Barnaul 2000

138

PHASE STATES OF MECHANOACTIVATED MANGANESEOXIDES

SA Petrova RG Zakharov AYa Fishman LI LeontievInstitute of Metallurgy Ural Division of RAS Ekaterinburg 620016

Russian Federation

An investigation of structural characteristics of the manganeseoxides in order to understand these characteristics affected bymechanochemical treatment conditions has been undertaken Chemicallypure manganese (II III IV) oxides were used as the initial componentsIt is shown that the properties of the mechanoactivated oxides differgreatly from those of initial materials Relationships among structuralcharacteristics of the mechanoactivated oxides and their prehistory wayand conditions of producing have been detected

IntroductionStudy of phase states of mechanoactivated oxides makes it

possible to analyze the patterns of expression of the mechanochemicaleffect in redox processes to determine the mechanism of the effect ofactivation processes on the type and parameters of the structural phasetransitions to establish the role of higher oxides in the redox processesAs one of the consequencies of the intensive mechanical activation is theappearance of nanodisperse states specificity of phase transformationsin nanocrystalline oxides is considered at the same time

It is known now that the decrease in the crystallite size inmechanoactivated systems causes a decrease of structural phasetransition temperatures In metallic alloys reducing of crystallites size isaccompanied by suppression of martensitic transitions [1-2] Completeinhibition occurs when the grain size becomes smaller than that of thecritical nucleus of a new phase It can be regarded as established that theparameters of phase transitions in oxides with relatively lowtemperatures of phase transitions also depend strongly on the grain sizeFor example in barium titanate BaTiO3 transition from cubic to low-symmetry phase is completely suppressed when the grain size is about10 nm [3] Changes in the crystal structure and the effects of reduction(the change of temperature and phase transition heat) in the structuralphase transitions with decreasing grain size also occurred for the oxides

139

Al2O3 Fe2O3 PbTiO3 PbZrO3 La1-xSrxCuO4 YBa2Cu3O7-δBi2CaSr2Cu2O8 [4] and several other oxides [5-6] Besides for the oxidesin nanoscale state the coexistence of two different structuralmodifications [7] was observed The processes of mechanoactivationmay also lead to new types of metastable phase states due to theredistribution of cations between the crystallographically inequivalentsublattices [8]

In the present work the main attention is paid on the analysis ofthe effects associated with the evolution of metastable structures underconditions of temperature increase and oxide interaction with anaggressive environment So far the main contribution to theinvestigation of these issues has made the study of metallic alloys (seefor example [9-10]) The behavior of the activated oxide materials ismuch less studied Study of structural phase transitions in the systemMn-O subjected to mechanochemical activation and structuralcharacteristics of the crystalline phases allows us to test how general arepreviously established patterns for systems with different types ofchemical bonds

The effect of mechanical activation on structural phase transitionsboth of martensate type (from cubic to tetragonal modification Mn3O4)and those accompanied by redox processes (between phases withdifferent degrees of oxidation etc) is investigated The choice of Mn-Ooxides as the object of study is largely connected with the fact that atleast two structural phase transitions observed in the considered crystalswith temperature changes involved the cooperative Jahn-Teller (JT)phase The value of the JT deformation in it is determined by theconcentration of JT ions in octahedral sites that allows to get additionalinformation about the structural changes caused by themechanoactivation of oxide

1 Production and structural properties of themechanoactivated oxides

11 Mechanoactivation of manganese oxidesPure manganese oxides MnO2 Mn2O3 and Mn3O4 annealed at

200deg 900deg and 1250degC respectively were used as the initial materialsFor the mechanical treatment of oxides which was described in

detail in [1112] a planetary mill AGO-2 with water-cooled drums (V =

140

150ml) and a centrifugal factor up to g = 60 [3] was used Download ofballs was 203g the material - from 5g Milling was made dry Theprocessing of powders was carried out after preliminary lining in acontinuous mode or with periodic stops of the mill According toestimates (performed by XPES) contamination by iron was not morethan 02 Previously [14] we found that prolonged continuousmechanical treatment leads to the fact that within the grains matureduring the first seconds along with a further (slow) reduction ofcoherent scattering blocks chemical processes begin leaking Because atthis stage the main purpose was to obtain single-phase samples theduration of continuous grinding was restricted by 30s The temperatureinside the drums during grinding did not exceed 320K which ensuredthe preservation of initial metastable phases During stops of mill thedrums where opened and powder was manually stirred but samplingwas not performed

To be able to conduct magnetic research on the mechanicallyactivated samples and to investigate the effect of intensity ofmechanoactivation (the degree of deformation) on the redox processesand the stability of weakly activated oxides the part of samples wasobtained as a result of mechanical activation in the vario-planetary millPulverizette 4 (Fritsch) in glasses of tungsten carbide Volume of drumwas equal to 250ml loading of crushing balls was 800g and a materialmass was 20 g Milling was made dry the duration was 3 min

12 Attestation of mehanoactivated manganese oxides andmethods of their experimental study

The phase composition of obtained substances the size ofcoherent scattering domains (CSD) and microstresses were determinedby X-ray diffractometer D8 ADVANCE (Bruker) (radiation CuKα Ni-filter position-sensitive detector VANTEC1) High-temperature X-raystudies of the stability of mechanoactivated oxides was carried out usinghigh-temperature chamber HTK1200N (Anton Paar)

The particle size of powders obtained was assessed by dynamiclight scattering using a laser analyzer DelsaNanoC (Beckman Coulter)and an atomic force microscope Solver-Next (NT-MDT) Surface ofoxides was studied by XPES and STEM (Omicron Multiprob)

High-temperature X-ray studies were performed in the range 30-1200degC in air The rate of heating and cooling was 05degCmin Step of

141

the temperature during heating and cooling was 5deg and 10degCrespectively Exposure in the point was 17s (the time of isothermal delayshooting diffractogram was 150s) For the analysis of diffractionpatterns the software package DIFFRACplus [15] was used

13 Results and discussionThe results of the attestation of the initial and mechanoactivated

oxides are presented in Table 1

Table 1 Treatment conditions and characteristics of the manganeseoxides

Cell parameters Initial phasetreating mode

Finalcomposition аAring сAring

Samplename

1 Mn2O3- initial Mn2O3 9412 M232 Mn2O3- AGO 30s Mn2O3 9410 M23A303 Mn2O3- AGO 60s Mn2O3 9410 M23A604 Mn2O3- AGO

10minMn2O3 9410

M23A10

5 Mn2O3- P4 3min Mn2O3 9403 M23P46 Mn2O3-

P4(3min)+USD(70s)Mn2O3 9403

M23P4U

7 Mn3O4-initial Mn3O4 5760 9474 M348 Mn3O4- AGO 30s Mn3O4 5762 9442 М34А309 Mn3O4- AGO 60s Mn3O4 5762 9431 M34A60

5787 950810 Mn3O4- AGO10min

Mn2O3+ Mn3O4

9410M34A10

11 MnO2-initial MnO2 4396 2869 M1212 MnO2- AGO 30s MnO2+Mn2O3(tr) 4397 2872 М12А3013 MnO2- AGO 60s MnO2+Mn2O3(tr) 4397 2872 M12A6014 MnO2- AGO 10min Mn2O3 9408 M12A10

AGO-High-energy planetary mill (60g) P4-Pulverisette 4 (~20g)USD-Ultrasound disintegrator

Since the analysis of the results of mechanoactivation of oxidesMn2O3 showed little difference between the samples activated in theAGO within 30 and 60 seconds further investigation of oxides Mn3O4

and MnO2 was performed on 60-second samples However it is

142

necessary to note that in the case of oxide MnO2 samples after 30 and60-second milling contained different amounts of Mn2O3

According to X-ray phase analysis data chosen mode ofmechanochemical treatment allowed to preserve essentially thecomposition of the initial oxides The exceptions were oxides MnO2which after grinding contained 5 of oxide Mn2O3 and Mn3O4 whichafter grinding for 10 minutes contained a few of Mn2O3

Data on grain size and the coherent scattering domains arepresented in Table 2 It is obvious that even a relatively weakmechanical treatment leads to a decrease in grain size in 2-3 times Inthis case the comparison of grain size and the CSD (comparison of thedynamic light scattering data and X-ray diffraction (XRD) results)shows that the mechanical treatment with a small degree of deformationallows to obtain defect-free grains while increasing of the centrifugalacceleration leads to the appearance and rise of the defects in the grainA tendency to agglomeration of grains with increasing time of intensemechanoactivation should be noted

Table 2 The characteristics of coherent-scattering domains and averagegrain size

Sample nameCoherent-scattering domain

nmGrain size nm

M23 gt200 1026plusmn95M23A30 30 436plusmn168M23A60 23 344plusmn155M23A10 24 939plusmn175M23P4 44 386plusmn50

M23P4U 44 336plusmn22M34 gt200 400plusmn801300plusmn300

M34A60 15 529plusmn340

M34A10 1913 795plusmn104

M12 gt200 428plusmn78M12A60 61 1133plusmn167M12A10 22 565plusmn343

XRD-dataDynamic light-scattering

data

143

Changes in phase composition during heating and cooling ofinitial and mechanically activated manganese oxides are presented inTables 3-4 and Fig 1-2

Comparison of the temperature behavior of the initial unactivatedoxide Mn2O3 and that of grinded for 3 minutes with a force of less than20g shows that mechanoactivation treatment with a small amount ofcentrifugal factor and short times can save not only the phasecomposition but apparently and generally does not alter the propertiesof the powder While increasing the degree of exposure (eg use of millssuch as AGO-2 with acceleration 60g) even at short times leads to achange in system characteristics (the appearance and growth of defectsredox processes) that affect later on behavior of oxide For examplemechanoactivation treatment leads to a shift of phase transitiontemperaures at thermal processing as well as to change of the structuralcharacteristics of the phases formed In particular to different degrees oftetragonal distortion of hausmannite formed during heating Mn2O3 (Fig4)

Table 3 The phase composition of the initial andmechanoactivated manganese oxides at different temperatures

Heating CoolingSample MnO2 Mn2O3 Mn3O4 Spinel Mn3O4 Mn2O3 Phase

1 2 3 4 5 6 7 8- + 920 1140 1120 - appearanceM23

- 955 1170 1010 + - disappear

- + 950 950 1010 - appearanceM23A30

- 995 1105 730 + - disappear

- + 950 950 1040 - appearanceM23A60

- 1000 1120 840 + - disappear

- + - 950 840 840 appearanceM23A10

- 1000 - 290 + 770 disappear

- + 940 1140 1120 - appearanceM23P4

- 980 1165 1080 + - disappear

- + 935 1140 1120 - appearanceM23P4U

- 980 1170 1050 + - disappear

144

1 2 3 4 5 6 7 8

- 685 + 1125 1090 - appearanceM34

- 945 1160 1010 + - disappear

- + appearance370

655

970 1050 -

disappear

900 appearance

M34A60

-

970

1130

880 + -

disappear

- + + 930 880 - appearanceM34A10

- 1005 655 600 + - disappear

+ 550 950 1155 1120 870 appearanceM12

595 1025 1170 1070 + + disappear

+ + 940 985 1110 750 appearanceM12A60

535 985 1165 840 + + disappear

- + 960 960 1000 790 appearanceM12A10

- 1005 1075 630 + + disappear

Table 4 The temperature boundaries of the phases during heating andcooling

Heating CoolingSample Phase

from to from to

1 2 3 4 5 6

Mn2O3 30 955 - -

Mn3O4 920 1170 1120 30

M23

Spinel 1140 1200 1200 1010

Mn2O3 30 995 - -

Mn3O4 950 1105 1010 30

M23A30

Spinel 950 1200 1200 730

Mn2O3 30 1000 - -

Mn3O4 950 1120 1040 30

M23A60

Spinel 950 1200 1200 840

Mn2O3 30 1000 840 770

Mn3O4 - - 840 30

M23A10

Spinel 950 1200 1200 290

145

1 2 3 4 5 6

Mn2O3 30 980 - -

Mn3O4 940 1165 1120 30

M23P4

Spinel 1140 1200 1200 1080

Mn2O3 30 980 - -

Mn3O4 935 1170 1120 30

M23P4U

Spinel 1140 1200 1200 1050

Mn2O3 685 945 - -

Mn3O4 30 1160 1090 30

M34

Spinel 1125 1200 1200 1010

Mn2O3 370 970 - -

Mn3O4 30 655

Mn3O4 900 1130

1050 30

M34A60

Spinel 970 1200 1200 880

Mn2O3 30 1005 - -

Mn3O4 30 655 880 30

M34A10

Spinel 930 1200 1200 600

MnO2 30 595 - -

Mn2O3 550 1025 870 30

Mn3O4 950 1170 1120 30

M12

Spinel 1155 1200 1200 1070

MnO2 30 535 - -

Mn2O3 30 985 750 30

Mn3O4 940 1165 1110 30

M12A60

Spinel 985 1200 1200 840

Mn2O3 30 1005 790 30

Mn3O4 960 1075 1000 30

M12A10

Spinel 960 1200 1200 630

146

a d

be

c fFig 1 The temperature boundaries of the phases during heating and coolingof initial and mechanoactivated Mn2O3 a - original b - M23P4 c -M23P4U d-M23A30 e-M23A60 f-M23A10

147

a

b

cFig 2 The temperature boundaries of the phases during heating and cooling of

initial and mechanoactivated Mn3O4 a-initial b-M34A60 c-M34A10

148

a

b

cFig 3 The temperature boundaries of the phases during heating and cooling ofinitial and mechanically activated MnO2 a - initial b - M12A60 c - M12A10

149

Fig 4 Temperature dependence of the degree of hausmannite tetragonaldistortion for samples with different prehistories

The growth of the crystallite size of mechanoactivated phase withtemperature is shown in Fig 5 Data are shown for the initial phasebelow the temperature of the corresponding phase transition

It is obvious that prolonged treatment in the high-energy millalmost did not give reduction of coherent scattering domains butessentially affected the thermal stability of investigated oxide

150

Fig 5 Temperature dependences of coherent scattering domain size in oxideMn2O3 with varying degrees of mechanoactivation

ConclusionThe main results of investigations are the followingI The conditions of mechanochemical treatment enabling to make

the transfer of Mn-O system to single-phase nanosized state withoutsignificant changes in composition of the initial oxide are found Theexception was oxide MnO2 which after grinding contained a smallamount of oxide Mn2O3

II It is shown that the use of mill of the type AGO-2 with 60gacceleration even at short times of activation treatment of oxides leadswhile maintaining the single-phase of sample to an appreciable changeof lattice parameters growth of stresses and the appearance of defects

III It is found that despite the relaxation character of the evolutionof these metastable structures in the face of rising temperatures there is ashift of phase transition temperatures and changes in structuralcharacteristics of the newly formed phases in comparison with the initialoxides Including marked changes in the parameters of the JT strain (ca

151

- 1) at high-temperature transitions between cubic and tetragonal phasesof oxide Mn3O4

IV It is shown that more prolonged mechanical activation ofoxides MnnOm activates redox processes in these materials theemergence of two-phase states with different degrees of oxidation andeven a complete change of the manganese oxidation degree

V The temperature boundaries of existence of phases duringheating and cooling were determined for the initial andmechanoactivated oxides MnnOm Not only noticeable quantitativedifferences in the position of phase boundaries but also qualitativedifferences in the constructed phase state diagrams were found

This work was supported by RFBR (grant 10-03-96016-p_ural_a) the Program of fundamental research of Presidium ofRussian Academy of Sciences N 27 ldquoFoundations of fundamentalresearch of nanotechnology and nanomaterialsrdquo and the Federal TargetProgram Scientific and scientific-pedagogical staff of innovationRussia (contract 02740 110641)

References1 Glezer AM Blinov EN Pozdnyakov VA Martensitic

transformations in microcrystalline ferro-nickel alloys Izvestiya Aseries of Physical 2002 V66 N9 pp1263-1275

2 Andrievsky PA RAGULYA AV Nanostructured materialsMoscow Academy 2005 192p

3 Polotai AV Ragulya AV Skorohod VV Nanocrystalline BaTiO3

synthesis sintering and size effect Science o Sintering CurrentProblems and New Trends Beograd Kluwer Academic Publishers2003 pp119-125

4 PAyyub VRPalkar SChattopadhyay et al Effect of Crystal SizeReduction on Lattice Symmetry and Cooperative Properties PhysRev B 1995 V51 N9 pp6135-6138

5 Parathasarathi Mondal Dipten Bhattacharya Pranab ChoudhuryDielectric anomaly at orbital order-disorder transition inLaMnO3+ J Phys Condens Matter 2006 V 18 p6869

6 Nandini Das Parathasarathi Mondal Dipten BhattacharyaPartical size dependence of orbital order-disorder transition inLaMnO3 Phys Rev B 2006 V74 p 014410

152

7 VYa Shevchenko OL Khasanov GS Yuriev etc The coexistence ofcubic and tetragonal structures in the nanoparticle of ZrO2Y2O3

oxides Neorg Mater 2001 V37 N9 pp1117-11198 AYa Fishman MA Ivanov SA Petrova et al Specific Features of

Jahn-Teller Structure Phase Transitions in NanocrystallineMaterials Defect and Diffusion Forum 2009Vols 283-286 pp53-58

9 Grigorieva ТF Barinova AP Lyakhov NZ Some features of themechanical alloying in the systems Cu-Bi and Fe-Bi J Metastableand Nanocryst Mater 2003 V15-16 pp475-478

10 Lyakhov N Grigorieva T Barinova A Lomaeva S Yelsukov EUlyanov A Nanosized mechanocomposites and solid solution inimmiscible metal systems J Mater Sci 2004 V39 N 16-17pp5421-5423

11 Zyryanov VV Journal of Structural Chemistry 2004 V45 pp135-143

12 Zyryanov VV Lapina OB Neorg Mater 2001 V37 N3 pp331-337

13 Zyryanov VV Sysoev VF Boldyrev VV Korosteleva TVCertificate of authorship of USSR N 1375328-BI-1988 N 7 p39

14 Fishman AYa Ivanov MA Petrova SA Zakharov RGStructural Phase Transitions in Mechanoactivated ManganeseOxides Defect and Diffusion Forum 2010 Vols 297-301 pp 1306-1311

15 DiffracPlus TOPAS Bruker AXS GmbH OstlicheRheinbruckenstraszlige 50 D-76187 Karlsruhe Germany 2008

118

EFFECT OF HARDENING TEMPERATURE ON THE STRUC-TURAL-MORPHOLOGICAL CHARACTERISTICS OF METAL

CEMENTS BASED ON MECHANOSYNTHESIZED COPPERCOMPOUNDS

NZ Lyakhov1 PA Vityaz2 SA Kovaleva2 TF Grigoreva1VG Lugin3 AP Barinova1 SV Tsybulya4

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS630128 Novosibirsk Kutateladze str 18 grigsolidnscru

2 United Institute of Mechanical Engineering NAS Minsk Belarus3 Belarussian State Technological University Minsk Belarus

4 G K Boreskov Institute of Catalysts SB RAS Novosibirsk Russia

IntroductionMetal cements may be used in many branches of industry due to

good adhesion to the materials of different types (glass ceramics metalsetc) and the metal character of thermal and electric conductivity Theformation of metal cements occurs through the interaction of copper(nickel) alloys with liquid metals and alloys Interactions of a solid metalwith liquid one in particular copper with gallium are known [1 2] tohave diffusion character they are substantially affected by temperatureand the area of contact between the reagents

The use of mechanically synthesized copper compounds allowsone to increase the contact surface between the components and to intro-duce doping elements (Bi In) that improve wettability during gluing andthe strength properties of the alloys to be formed This causes a changeof the kinetics of interaction between a solid metal and a liquid one dueto the acceleration of diffusion processes and due to the formation ofadditional phases

The goal of the present work is investigation of the effect of hard-ening temperature on the structural-morphological characteristics ofmetal cements obtained on the basis of CuBi mechanocomposites andsupersaturated solid solutions Cu(In)

Methods and materialsCopper powder PMS-1 (GOST 4960ndash75) granulated bismuth (TU

6-09-3616ndash82) indium (GOST 10297ndash94) were used in the work Me-chanical activation of the powders was carried out for 15 min in the

119

high-energy ball planetary mill AGO-2 with water cooling in argon at-mosphere (cylinder volume 250 cm3 ball diameter 5 mm loaded wt200 g the weighed portion of the sample under treatment 10 g the fre-quency of rotation of the cylinders around the common axis about 1000rpm) Mechanocomposites having the composition Cu 10 wt Bisolid solutions Cu-12 wt In were obtained [3] Diffusion-hardeningalloys were prepared by mixing the mechanosynthesized copper com-pounds with gallium melt followed by exposure at a temperature of 20C during the whole process of alloy formation To study the effect oftemperature on the structure and morphology of metal cements harden-ing was carried out at 90 С 120 С and 160 С

Surface examination was carried out with the NT-206 atomicforce microscope (Microtestmachines Gomel) using standard commer-cial V-type probes NSC11 (Mikromasch) in the contact mode

The structure of the resulting samples was studied using Mikro200 optical microscope and high-resolution scanning electron micro-scope (SEM) MIRATESCAN with an attachment for micro-X-ray spec-tral analysis (MXSA) The diameter of the electronic probe was 52 nmexcitation region was 100 nm Images were obtained in the mode of re-cording secondary and backward scattered electrons which allowed usto investigate the distribution of chemical elements over the surface andto establish its composition non-homogeneity

The phase composition of powders after mechanical activationand the final products of their interaction with liquid gallium were de-termined with the help of X-ray diffraction techniques X-ray structuralanalysis and semi-quantitative examination of the products were carriedout with the D8 Advance Bruker diffractometer (Germany) by means ofpowder X-ray diffraction in the θ-2θ configuration with a step of 01Phase identification was performed using the diffraction patterns re-corded in CuKα radiation (154051 Aring)

Calorimetric measurements were carried out with Netzsch STA409 PCPG instrument in argon atmosphere in a crucible made ofAl2O3 within the temperature range from room temperature up to 290 Cwith the heating rate of 20 min

120

Results and discussionIt was established in the previous diffraction studies of alloy for-

mation dynamics in CuBi + Ga and Cu(In)+Ga that the formation ofnew phases takes place within a broad time interval During the interac-tion of CuBi mechanocomposite in Bi that is insoluble in copper and ingallium the formation and crystallization of the intermetallic compoundCuGa2 and bismuth take place simultaneously [4]

For the case of Cu(In) solid solution in which the doping elementis soluble in gallium the formation of the phase of solid solution of in-dium has an incubation period of about 210 minutes which is determinedby its concentration in the system with gallium [5]

The interaction processes are described with the following chemi-cal reactions

CuBi + 2 Ga rarr CuGa2 + BiCu(In) + 2 Ga rarr CuGa2 + In(Ga)

1 Effect of the temperature of interaction of CuBimechanocomposites with liquid gallium on the structure andmorphology of the formed metal cementsIt is known that the resulting mechanocomposites are nanosized

copper surrounded by a thin bismuth layer [6] Bismuth is mainly com-posed of the particles less than 5 nm in size

According to the data of AFM topography the size of mechano-composite particles is 150divide250 nm (Fig 1)

Fig 1 Mechanocomposite Cu + 10 wt Bi after activation for 15 mina ndash SEM image b ndash AFM c ndash TEM

121

At first we studied the interaction of CuBi with liquid gallium atroom temperature

The X-ray structural analysis of the resulting cement carried outafter the interaction for 4 and 48 hours showed that the size of the crys-tallites of the intermetallic compound increases from ~ 200 nm to ~ 550nm The size of bismuth crystallites increases up to 100 nm It should benoted that this is accompanied by a decrease in the size of copper crys-tallites down to ~ 10 nm The final phase composition is determined asCuGa2 Bi and unreacted copper (Fig 2)

Fig 2 Diffraction patterns of the product of interaction Cu 10 Bi + Ga

Figure 3 shows the high-resolution SEM images of the micro-structure of the surface of the final interaction product The SEM imageof sample surface after hardening without the mechanical treatment ofthe surface is shown in Fig 3a The image of the surface obtained in thebackward scattered electrons after sample polishing is shown in Fig 3bBecause bismuth is the heaviest element in this system it will be distin-guished by the maximal brightness in the SEM image

The data obtained by means of microscopy show that the structureof the surface of final product is facetted tetragonal crystals СuGa2 withthe size up to 4 μm Bismuth is localized at the faces of crystals and at

122

the boundaries of CuGa2 grains as disperse formations 70-250 nm insize and also forms separate grains with a size up to 10 μm

a bFig 3 Topography of the surface of CuGa2 +Bi alloy after the interaction for48 hours a ndash SEM image of non-polished sample in direct electrons b ndash SEM

image of the polished sample in backward-scattered electrons

The use of AFM allowed us to study the microstructure of facet-ted tetragonal CuGa2 crystals The presence of screw dislocations inthem may be stressed as a result the crystalline layer grows by windingcontinuously on itself so the step takes the shape of a spiral (Fig 4) Thelayer-by-layer growth of crystallographic facets should also be men-tioned The edges of incomplete layers or steps move along the facetwhile they grow The step height that is the thickness of the depositinglayer varies within the range 4 to 200 nm The appearance of highgrowth steps may cause trapping of the melt drops and precipitation ofinsoluble bismuth admixture on the surface of steps of the growing crys-tals which is indeed observed in Fig 4 b Bismuth is adsorbed on facetssteps and along the grain boundaries

It should be stressed that the growth of faceted crystals requiresspecial conditions supersaturation or supercooling of the mother me-dium small number of appearing nuclei We suppose that the localthermal supercooling arises as a consequence of the chemical interactionof copper with gallium melt on the interface between the solid phase andthe liquid one with the formation of chemical compound CuGa2 withcrystallization temperature higher than the temperature of the melt Theconditions of substantial supercooling are created for this compound soits crystallization starts In this process bismuth particles get released

123

into the melt Thee particles are insoluble in liquid gallium and may actas the centres of crystallization and also they may brake down thegrowth of intermetallide particles by getting adsorbed on their surfaceThe latent heat of melting released during crystallization raises the tem-perature of the melt (so gallium remains in the liquid state during reac-tion at 20 C) and decreases the degree of overcooling thus creating theconditions for the growth of larger facetted intermetallide crystals fromthe melt

а b

Fig 4 AFM image of the surface of resulting alloy CuGa2 + Biа - Torsion-image of bismuth on facets and growth steps of CuGa2 (the contrastis formed due to the difference in tribological characteristics of the phases of

intermetallide and bismuth) b ndash layered spiral growth of CuGa2 crystals alongthe screw dislocation (marked with arrows) The upper part shows a scheme ofcrystal growth along the screw dislocation and the shape of the step formed inspiral growth [7]

At room temperature the final product of the interaction of CuBimechanocomposite with liquid gallium is a matrix composed of CuGa2

intermetallide particles 1ndash4 μm in size with bismuth particles distrib-uted in it (from 70 to 250 nm) which form local agglomerations up to 10μm in size

X-ray studies of the alloys obtained at hardening temperature of90 and 120 C showed that an increase in temperature to 120 C does notaffect the phase composition Similarly to the case of room temperature

124

the product is composed of intermetallide CuGa2 (PDF-2 No 25-0275)bismuth (PDF-2 No 44-1246) and residual copper (PDF-2 No 04-0836)(Fig 5)

Fig 5 Diffraction patterns of CuGa2 + Bi samples obtained at temperature 40(a) 90 (b) and 120 (c) C Unmarked peaks relate to CuGa2 intermetallide

With an increase in the interaction temperature the lattice pa-rameters of copper and CuGa2 phases remain almost unchanged Thesize of copper crystallites is about 35 nm Bismuth undergoes tempera-ture-caused changes An increase in the size of bismuth crystallites from100 nm at 20 C to 180 nm at 90 C and to more than 500 nm at 120 C

Alloys obtained by mixing the CuBi mechanocomposite with liq-uid gallium have a composite structure after hardening Their structuremay be described as an intermetallic shell with the unreacted part ofcopper in its centre The СuGa2 intermetallide has a shape of facetedtetragonal crystals up to 4 μm in size With an increase in reaction tem-perature to 90 C the size of het particles of intermetallic compund in-creases to 6-8 μm and remains almost the same at a temperature of 120C In the lateral contrast mode the facets of crystals obtained at 90 and120 C exhibit local accumulations of bismuth as well as substantial de-formation distortions of crystals due to the arising stretching strain inthe crystal in the direction lt001gt (Fig 6) Intermetallide crystal starts to

125

have layered structure The facets of the intermetallide obtained at ele-vated temperatures also exhibit deformation distortions that are likelyconnected with bismuth adsorption on the facets The appearance ofthese lines is due to the development of local fluidity They arise in thecases when the material possesses a distinct yield point even insignifi-cant concentration of strain promotes the appearance and developmentof these figures [8] Change of the straight character of the glide lines islikely to be connected with the effect of boundary volumes intra-grainstructural strain caused by differences in the volumes of the intermetal-lide and bismuth as well as by glide in different systems and with thetransition from one system to the other

а

b

Fig 6 AFM images of CuGa2 + Bi alloys obtained at a temperature of 90 (a)and 120 (b) С

126

Metallographic in-vestigation of the alloysurface after polishing(Fig 7) showed that thenumber of macrodefectssuch as pores and discon-tinuity flaws decreaseswith an increase in crystal-lization temperature Mi-crohardness of the inter-metallide increases fromHV 70 to 125

Investigation of thedistribution of chemicalelements over the sampleby means of SEM involv-ing X-ray spectral analysisrevealed nonuniformity ofthe distribution of insolu-ble bismuth

Bismuth is not ob-served in the regions withthe intermetallic com-pound which may be con-nected with the fine distri-bution of disperse particlesover the boundaries of theintermetallide Local ac-cumulations of bismuth upto 10 μm in size are ob-served mainly in the siteswhere macrodefects (poresgrain boundaries) get ac-cumulated With an in-crease in the temperature ofinteraction up to 120 Сthe number of local bis-muth accumulations de-

а

b

cFig 7 Optical images of the structure of

CuGa2 + Bi alloys obtained at 20 (a) 90 (b)and 120 (c) С

127

creases but their size increases to 20 μm (Fig 8)

а b

Fig 8 SEM images (in backward scattered electrons) of CuGa2 + Bi alloyHardening temperature а ndash 20 С b ndash 120 C

Thermal investigation of the alloys with different hardening tem-perature points showed that the curves of differential scanning calo-rimetry (DSC) exhibit definite differences only during heating the alloyswith hardening temperature 20 C and 90 C The DSC curves of the al-loys with hardening temperature 90 and 120 С are identical Duringheating the alloy with hardening temperature 20 С exhibits the exother-mal heat effect at a temperature of 120-150 С This effect may be con-nected with the occurrence of recrystallization processes in bismuthThis exo-peak is absent during the repeated heating

Thus investigation showed that an increase in the temperature ofthe interaction of CuBi mechanocomposite with liquid gallium leads toan increase in the size of the formed intermetallide as well as to a de-crease in macrodefects in the form of pores discontinuity flaws cracksThe hardness of the intermetallide thus increases

2 Effect of the temperature of interaction of mechanochemi-cally prepared solid solution Cu (In) with liquid gallium onthe structure and morphology of metal cementThe use of mechanochemically prepared powders of Cu-In system

as the solid phase in the reactions with liquid gallium increases the num-

128

ber of interacting systems due to the solubility of indium in gallium Ac-cording to the state diagram of the system GandashIn [9] the solubility of Inin Ga in the solid state is less than 03 at while the solubility of Ga inIn is 31 at At a temperature of 60 С indium may be dissolved in liq-uid gallium up to 48 wt

Mechanochemically synthesized powder in the system Cu + 12wt In was used as the initial solid-phase component The X-ray phaseanalysis of the products of mechanochemical synthesis (Fig 9) showedthat the solid solution of indium in copper in formed during mechanicalactivation of copper powder with 12 wt indium As a result the latticeparameter of copper increases to а = 36659 Ǻ (аref = 36150 Ǻ) The size of copper crystallite is about 30 nm

Fig 9 X-ray diffraction patterns of the powder Cu-12 wt In after mechanicalactivation (for 20 min) in argon

Mechanical activation of the system Cu + 12 wt In leads to theformation of fine particles of the solid solution of indium in copper (150ndash 230 nm) (Fig 10) Recrystallization of the solid solution of copper andthe formation of grains larger than 15 μm are also possible

129

Fig 10 Topography of the ultrafine powder of the solid solution Cu(In)

A decrease in the size of precursor powder is known to providelarger area of contact between the components of the solid phase and theliquid one and therefore shorter diffusion distances during subsequentinteractions with metal melts Because both copper and nickel are solu-ble in liquid gallium one may expect that the rate of dissolution of themechanocomposites of the system Cu-In would be significant

X-ray phase analysis of the final products of the interaction of thesolid solution Cu(In) with gallium at room temperature revealed thepresence of three phases intermetallide CuGa2 indium and unreactedcopper (Fig 11)

Fig 11 Diffraction patterns of the alloys obtained through the interac-tion of Cu 12 wt In + Ga CuGa2 - In - Cu

130

For the initial powder with indium concentration 12 wt theproduct of the interaction exhibits a decrease in the indium unit cell pa-rameter с in the alloy under formation to с = 49306 Ǻ (cref = 49459 Ǻ) The size of copper crystallites is about 7 nm while the size of indiumcrystallites is about 30 nm Slight changes in the unit cell volume of in-dium may be related to the formation of the solid solution of gallium inindium

During the interaction indium gets dissolved in the liquid phaseof gallium gets concentrated and crystallizes at the interfaces betweenthe solid phase and the liquid one The alloys with the 12 indium con-tent are characterized by a large range of the dimensions of tetragonalparticles of the intermetallic compound CuGa2 (from 05 to 8 μm) TheAFM image (Fig 12) exhibits coarse crystals their crystallographicshape is uncharacteristic of the intermetallide CuGa2 Comparing the X-ray data and the results of AFM we may assume that they are a solidsolution of gallium in indium

Fig 12 AFM topography of the surface of CuGa2+ In(Ga) alloy

A decrease in the AFM scanning pitch and simultaneous acquisi-tion of the image of distribution of normal (topography) and lateral (tor-sion) forces allowed us to distinguish the structural features of the phaseof the solid solution of gallium in indium (Fig 13) A specific distin-guishing feature is the presence of strands in the crystals of the solid so-lution of gallium in indium connected with layering of the solid solutioninto the regions with larger and smaller concentration of the componentwhich is well seen in the image of torsion (Fig 13b) The size of separate

131

grains of the solid solution of gallium in indium reaches more than 10μm

Fig 13 AFM topography of the surface of samples of CuGa2+ In(Ga) alloy (а)image of torsion (b)

Fig 14 The SEM image in direct (а) and back-scattered electrons (b) of thealloy CuGa2+ In(Ga) In the upper part the data chart of the quantitative spec-

tral analysis carried out in the indicated points

To investigate the microstructure of the surface of alloys we car-ried out the examination with the scanning electron microscope and ob-tained the images of the surface of resulting alloy for the interaction Cu12 wt In + Ga in direct (Fig 14а) and back-scattered (Fig 14 b) elec-trons The application of imaging in back-scattered electrons allow one

132

to investigate the composite surface non-uniformity with which the in-tensity distribution over the image depends on the atomic number of anelement One can see in Fig 14 b that the contrast in the BSE images isdetermined by the topographic features of the surface and the distribu-tion of intensities is uniform In addition local X-ray spectral analysiscarried out in different points of the alloy surface revealed the presenceof indium in concentrations 01 to 7 This fact allows us to concludethat indium is present on the surface of CuGa2 intermetallic crystals inthe form of thin films

Another characteristic feature of the surface of samples obtainedin the interaction of solid solutions Cu(In) with liquid gallium is thepresence of fine dispersed formations on the surface of crystals andgrains of CuGa2 that are more clearly seen in the AFM images (Fig 13a) and are detected in the SEM images (Fig 15 b) The formation of thestructures of this kind on the surface of the intermetallide may be con-nected with indium crystallization on the surface of the growing crystals

Fig 15 AFM (a) and SEM images (b) of the face of CuGa2 intermetallic ob-tained by the interaction of Cu 20 In + Ga

So on the basis of X-ray spectral data obtained and the results ofAFM and SEM we may assume that indium gets crystallized not only inthe form of large grains of the phase of the solid solution of gallium inindium but also on the faces of the intermetallide thus forming a nano-meter-sized film of indium about 10 nm thick

133

In order to establish the effect of temperature on the structure andmorphology we carried out alloy hardening at temperature of 60 120and 160 C

X-ray structural investigation of the final phase composition (Fig16) of the alloys showed that no changes in the phase composition of themetal cement are observed with an increase in hardening temperature to160 C The parameters of intermetallic compound CuGa2 remain almostunchanged The values of lattice parameters of the indium phase underformation are also insignificantly differing from the reference ones

Fig 16 Diffraction patterns ofCu-In-Gа samples obtained at

different temperatures

Investigation of the microstructure of alloys obtained at 20 Cshowed that indium is well adsorbed on the surface of intermetallidecrystals and crystallizes not only as separate crystals of the solid solutionof gallium in indium but also as the film formations with grained anddendrite structure on the faces of the intermetallide The occurrence ofintercrystal films of indium or the solid solution of indium may be re-sponsible for a decrease in strength characteristics of the alloy and be areason of both the intra-crystal and inter-crystal fractures (Fig 17 b) It

134

is assumed that an increase in hardening temperature causes substantialformation of the film structures of the solid solution of indium

The AFM investigation of the topography of alloys obtained attemperatures 90-160 C showed that the alloys are characterized by alarge size range of the intermetallic compound CuGa2 At the interactiontemperature of 20 C the size of CuGa2 particles was 05 to 8 μm Withan increase in reaction temperature to 90 C the crystal size increases upto 11 μm Crystal concretions are also formed (Fig 17) One can see inFig 17 b that cracks are formed in the grain plastoelastic deformationson the intermetallide face occur which is likely to be due to the differ-ence in interfacial surface tension of the intermetallide and indium film

ab

Fig 17 AFM image of the surface of CuGa2 + In(Ga) alloy obtained at 90 C a- topography b ndash distribution of lateral forces (arrows show cracks deforma-

tion distortions)

At a temperature of 120 and 160 C the contrast of the surface re-lief decreases due to the formation of a continuous film (Fig 18) on thesurface

Investigation of the phase transitions in the alloys was carried outby means of DSC For heating the products of the interaction betweenthe solid solution of indium in copper and liquid gallium at a rate of30Cmin an endothermic effect is observed on the DSC curves of all thealloys at a temperature about 254 C and an exothermic effect at 290 Con cooling the exothermic peak appears at a temperature of 210-220 С

135

а b

Fig 18 AFM topography of the CuGa2 + In(Ga) alloy a ndash 120 C b- 160 C

According to the Cu-Ga state diagram these effects are connectedwith the peritectic transformations of the main phase of intermetallideCuGa2 during heating and cooling The cooling curves exhibit no ther-mal effect due to the phase transition of indium The DSC curve of thealloy obtained at 20 C contains an endothermic peak at about 130 Cwhich gives much smaller heat effect in the second heating cycle Tak-ing into account the fact that the formation of indium films and the solidsolution of indium with the grained and dendrite structures occurs on thesurface of the intermetallide it may be assumed that heating to 130 C isaccompanied by melting of the indium film (taking into account a de-crease in melting temperature for thin films) [10] and the solid solutionIn(Ga) At the temperature of the peritectic transformation 254 C in-dium gets dissolved in the formed liquid Ga(Cu) with subsequent for-mation of the ternary compound Cu-Ga-In during cooling For coolingthe temperature of the peritectic reaction for the obtained compound de-creases to 210-220 C

ConclusionAs a result of the investigation of the structure and morphology of

metal cements prepared on the basis of mechanosynthesized coppercompounds CuBi and Cu(In) the structure and morphology in the reac-tions with liquid gallium are determined by the degree of interaction of

136

the doping component with gallium In the case of the CuBi mechano-composite in which Bi does not interact with gallium an intermetallidewith particle size up to 4 μm and local accumulations of bismuth areformed With an increase in hardening temperature to 120 C intermetal-lide growth to 8 μm occurs

When using the solid solutions Cu(In) in which indium is solublein liquid gallium and the incubation period for the crystallization of thesolid solution In(Ga) the formed particles of intermetallide CuGa2 havea broad size range from 05 to 8 μm With an increase in hardening tem-perature to 160 C the size of intermetallide particles increases to 11 μmredistribution of indium occurs along with an increase in the number ofits film structures that are formed on the faces of the intermetallide andcause a decrease in its strength properties thus providing intra-crystaland inter-crystal fracture A decrease in the melting temperature for in-dium to 130C and a decrease in the heat effect at this temperature in thealloys obtained at the alloy formation temperature of 90 120 and 160 Cmay be connected with an increase of indium film amount

The work is carried out under the Integration Project of SB RASNo 138 and BRFFI Т09СО-014 laquoDevelopment of Fundamental Basisof the Action of Activation on Regulation of the Processes of Interactionof Solid Metals and Their Comopunds with Metal Melts for the Purposeof Obtaining Functional Materials with Required Structure and Proper-tiesraquo

References1 Tikhomirova OI Ruzinov LP Pikunov MV Marchukova ID

Investigation of mutual diffusion in the system gallium ndash copperFiz metallov I metallovedenie 1970 vol 29 issue 4 p 796-802 (inRussian)

2 Glushkova LI Konnikov SG Interaction between components inthe solder paste based on gallium Pressure treatment of metals andwelding Proceedings of the Leningrad Polytechnical Institute1969 No 308 p 205-208 (in Russian)

3 Grigorieva TF Barinova AP Lyakhov NZ Mechanochemicalsynthesis in metal systems Novosibirsk 2008 (in Russian)

4 Ancharov AI Grigorieva TF Barinova AP Lyakhov NZ Investi-gation of the interaction of liquid metals with nanocomposites by

137

means of diffraction of the synchrotron radiation Nuclear Instru-ments amp Methods in Physics Research 2007 v A 575 p 130-133

5 Ancharov AI Grigorieva TF Tsybulya SV Boldyrev VVNeorganicheskie Materialy 2006 V 42 No 9 p 1164-1170 (inRussian)

6 N Lyakhov T Grigorieva A Barinova Nanosized mechanocom-posites and solid solution in immersible metal systems Journal ofmaterials science 39(2004) 5421-5423

7 Chernov AA Crystallization processes Modern CrystallographyMoscow 1980 vol 3 p 5-12 (in Russian)

8 Bernshtein ML Zaymovsky VA Mechanical properties of metalsMoscow Metallurgy 1979

9 State diagrams of binary metal systems Ed by NP Lyakishev1997 vol 2 p 636ndash637 (in Russian)

10 Gromov DG Gavrilov SA Redichev EN Klimovitskaya AVAmmosov R M Factors determining melting temperature of thinfilms of Cu and Ni on inert surfaces Zhurnal Fizicheskoy KhimiiV 80 No 10 2006 p 1856-1862 (in Russian)

104

ZINC IONS REDUCTION ON SOLID METAL ELECTRODES INCHLORIDE MELTS

Alex Lugovskoy 1a Zeev Unger 12b Michael Zinigrad 1cDoron Aurbach 2d

1Material and Chemical Engineering Department Ariel UniversityCenter of Samaria Ariel 40700 Israel

2Department of Chemistry Bar-Ilan University Ramat-Gan 52900Israel

alugovsaarielacil bzevikitoarielacil сzinigradarielacildaurbachmailbiuacil

keywords electrodeposition chloride melts cyclic voltammetry high-temperature electrochemistry

AbstractThe reduction of zinc ions on solid tungsten and platinum

electrodes in chloride melts at the temperatures 700 ndash 750 degC wasstudied by cyclic voltammetry chronoamperometry and energydispersion spectroscopy It was established that no zinc is reduced onplatinum electrodes As for the reduction of zinc ions on tungstenelectrodes the process has a complex character it starts as anirreversible two-electron zinc ion reduction and after the new phase isformed the process of saturation of the electrode surface with lithium orsodium begins As the second process develops the alkaline metalbecomes essentially the only constituent on the electrode surface

GeneralSince zinc is industrially recovered from sulfate solutions rather

than from melts and because its melting temperature (4195 degC) is lowerthan the temperatures of most molten chloride compositions thereduction of zinc ions on solid electrodes in chloride melts has beeninvestigated relatively poorly There are quite a few papers devoted tothe electrolysis of zinc containing chloride melts (1 2) and these coveronly some details of the electrochemistry of this metal However zinc isnot only an engineering metal It can often be a component of moltenchloride systems in which various processes of synthesis or purification

105

are performed Therefore the detailed electrochemical behavior of zinccan be of great importanceThe study of electro-reduction processes of zinc ions on solid tungstenand platinum electrodes in eutectic NaCl ndash KCl and LiCl ndash KCl melts inthe temperature range of 700 ndash 750 degC is presented in this work Thesetemperatures are somewhat higher than the eutectic points of NaCl ndashKCl (646 degC ) and LiCl ndash KCl (628 degC) and the melts are thereforeliquid enough to be used in technologically important processes oflanthanides and actinides separation reduction and rectification On theother hand these temperatures are significantly lower than the boilingpoint of zinc (907 degC) and there is essentially no loss of the metal due toevaporation

ExperimentalThe electrochemical experiments were performed using a three-

electrode cell made of sintered alumina placed in an alumina crucibleunder nitrogen atmosphere Tungsten (9995 1 mm diameter) andplatinum wires (9995 05mm diameter) were used as the workingelectrodes and their surface area was controlled by immersion depth(typically 6ndash12mm) and by measuring their diameter before and aftereach experiment A 1mm tungsten wire served as a pseudo-referenceelectrode and a flat spiral tungsten wire set perpendicular to theworking and reference electrodes close to the bottom of the cell servedas the counter electrode The area of the counter electrode was ~ 20 foldas large as that of the working electrode ZnCl2 LiCl NaCl and KCl(990 +ACS grade Alfa Aesar) were used for the preparation meltswithout further purification

Zinc chloride was mixed with alkaline metals chlorides usingmortar and pestle in a glove-bag in dry nitrogen atmosphere Themixture was then placed into a crucible the electrode cell was mountedand transferred into the furnace (single-zone Carbolite 1600 degC STF tubefurnace) In the furnace the mixture was first dried under vacuum at 40ndash50 degC for an hour After completing the drying dry nitrogen wasbubbled through the electrolyte during its heating up to the temperatureof the experiments (700ndash750 C) for another hour The temperature wascontrolled by a type S thermocouple placed next to the cell andprotected by an alumina capillary thus maintaining a precision of plusmn1 degCin measuring and controlling the temperature Dry nitrogen atmosphere

106

(1 bar) was maintained in the furnace during the measurements and thepost-experimental cooling The electrochemical measurements werecarried out using an Autolab PGStat-12 potentiostat SEM images andelement analysis by EDS were performed with a SEM system fromJEOL Inc Model JSM 7000F

Results and discussion

Deposition of zinc on a tungsten electrodeSome typical voltammograms for the electrochemical reduction ofZn(II) are shown in Fig 1

-02

-01

0

01

02

03

04

-1 -05 0

iA

cm

2

E V vs W

C

A

QaQ

c~ 1

0502005 Vsec

-0680-0650-0600E

p V

(peak C)

164141110Qc Ccm

2

177150113Qa Ccm

2

Fig 1 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0163 mol L) in equimolar NaCl-KCl melt on a W electrode at 700degC Scanrates are 50 mV sec (solid line) 200 mV sec (slashed line) and 500 mV sec(dotted line) Each charge density was calculated as the sum of areas limited bythe baseline and the appropriate current density curves for the forward andbackward semi-cycles

107

As follows from Fig 1 a single cathodic peak C corresponds toone anodic peak A The potential shape and behavior of the cathodicpeak are typical for the metal deposition on a solid electrode (2-4) Nodifference is observed between the reduction of zinc ions in NaCl ndash KCland in LiCl ndash KCl melts Peak A is assigned to the reoxidation of zincBoth peaks are clearly not independent on the scan rate Rather peak Cis shifted to more negative potentials and peak A moves to more positivepotentials as the scan rate increases The dependence of the cathodicpeak potential on the scan rate is shown in Fig 2 Such voltammetricresponse is typical for irreversible processes

055

06

065

07

075

0 01 02 03 04 05 06

-Ep

V

Vs

Fig 2 Dependence of the cathodic peak potential on the scan rate for thereduction of Zn2+ (0163 mol L) at 710degC on a W electrode

The cathodic peak C appears at about -06 V vs tungsten electrodefor the scan rate of 50 mVsec and at -07 V for 500 mVsec Such asignificant shift is a clear indication that the process is irreversible Thecathodic peak not only is shifted as the scan rate grows but it becomes

108

broader so that the difference |Ep ndash Ep2| grows from 01 V for 005 Vsecto 015 V for 05 Vsec Values of n calculated by equation 23 are inthe range of 156 for low scan rates to 104 for high scan rates The mostlogical interpretation of this finding is that the charge-transfer is of two-electrons which is not surprising in the case of Zn2+ ions reduction Thevalue of is then 078 for 005 Vsec and 052 for 05 Vsec This isevident that the rate determining step is the Faradaic process

Zn2+ + 2e- Znwhen the system is close to the steady state Note that at low enoughpotential scanning rates diffusion limitations may be less influencingwhile at higher scan rates the diffusion limitations are more importantRandles-Sevcik dependencies for the zinc (II) ions reductiondemonstrate linearity but their intercepts are apparently non-zero (Fig3)

0

01

02

03

04

05

06

07

0 02 04 06 08 1

i pA

cm

2

12 V12s-12

Fig 3 Randles-Sevcik plots for Zn2+ ions reduction on W in a NaCl-KCl meltat 700 degC different concentration of the ions (peak C in Figure 39) 900x10-5

molmL Zn2+ 163x10-4 molmL Zn2+ 177x10-4 molmL Zn2+

109

It is evident that the process Zn2+ + 2e- Zn is complicated bysomething else Despite the irreversible character of the depositionprocess it is still reasonable to roughly evaluate the diffusion coefficientof Zn2+ according equation 1

ip = 06105 (nF)32(RT)12D12C12 (11)

where ip is the peal current density (A cm2) n is the number ofelectrons F is Faraday constant (96500 C) R is the gas constant (8314Jmol∙K) T is the absolute temperature (K) D is the diffusion coefficient(cm2 sec) C is the bulk concentration of a Red (Ox) species (mol cm3) and is the scan rate (V sec)

Thus calculated diffusion coefficients are shown in Table 1

Table 1 Diffusion coefficients of Zn2+ to a tungsten electrode in NaCl-KCl melt

C105 mol L D 105 cm2 sec900 955n

163 1020n

177 1364n

Given that the value of n for the reduction of Zn2+ cannot exceed 2 and0 le le 1 ( asymp 05 for most cases) reasonable values of n must beclose to 1-2 Therefore the values of the diffusion coefficients fromTable 2 lie in the range of 1-6∙10-4 cm2sec Available literature data forthe diffusion coefficients of most metal ions lie in the range 10-5-10-4

cm2sec Particularly T Stoslashre G M Haarberg and R Tunold found thatthe values of the diffusion coefficients for Zn2+ in KCl-LiCl melts at400degC lie in the range 06 ndash 106∙10-5 cm2sec (2) Delimarski providesthe value of the diffusion coefficient of Zn2+ in NaCl-KCl at 710degCwhich is 23∙10-5 cm2sec (5) The deviation of our results from theliterature data can hint that that the process cannot be treated as simplezinc ion reduction on the surface of tungsten

110

It is worth to mention that the fact that the diffusion coefficientfor zinc ions in the chloride melt lay in the range 10-4 ndash 10-5 cm2sec mayserve as an indirect argument in the discussion about the existence ofcomplex species described by the general formula [ZnxCly]

z+ in chloridemelts While some authors argue in favor of the formation of complexions (6 ndash 10) other studies give evidence for the existence of individualzinc ions as the key reacting species (11 ndash 12) The relatively highvalues of the diffusion coefficients found in our experiments hint that thecharge is transferred by individual ions rather than by more massivecomplex moieties

005

01

015

02

025

03

035

04

02 03 04 05 06 07 08 09 1

700oC

750oC

740oC

720oC

i pA

cm

2

12

V12

s-12

Fig 4 Randles-Sevcik plots for Zn2+ reduction on W in a NaCl-KCl melt fordifferent temperatures [Zn2+] = 900x10-5 molmL

Another intriguing aspect of the zinc ions deposition process ona tungsten electrode can be seen in the temperature dependence of

111

Randles-Sevcik plots (Fig 4) As seen from Fig 4 Randles-Sevcik plotsdo not change (to the accuracy of the experiment) as the temperaturerises from 700degC to 750degC

The lack of dependence of Randles-Sevcik plots on thetemperature is really surprising A plausible explanation to this could bean additional process in the system which occurs simultaneously withthe observed process but does not involve charge-transfer and cannot bedetected electrochemically Such a process could compensate for theexpected increase of the slope of Randles-Sevcik plots as thetemperature grows and thus distort the temperature dependence

The most probable candidates for such competing processes area coupled chemical (not charge-transfer) reaction or a process of phase-formation However cyclic voltammetry alone cannot discriminatebetween these two possibilities

Fig 5 A chronoamperometric plot for the deposition of Zn2+ on a tungstenelectrode Temperature 725degC [Zn2+] = 900x10-5 molmL The potential was

stepped from OCV to -055 V

A further insight on the nature of the deposition process can beprovided by chronoamperometry As seen from Fig 5 the current fallsin the course of the first 11 seconds of the experiment and then risesreaches a peak and gradually declines as expected with time until theend of the experiment (300 seconds)

The initial falling and rising of the current can be attributed tothe nucleation of the deposits fluctuations of current for more advanced

112

reaction times as seen in Fig 5 may indicate to a very active charge-transfer process which cannot be explained by a simple zinc depositionprocess

Even more surprising information is provided by EDS analysisof the working electrode after a 3000 second deposition experiment at ndash055 V (Fig 6 Table 2) The most striking result of the analysis is theunexpectedly high content of sodium on the electrode surface Thisamount of sodium cannot be accounted for melt adhesion or penetrationbecause the percentage of potassium and chlorine is much smaller Infact the working electrode looks as it was made of sodium withmoderate inclusions of tungsten and zinc rather of tungsten

Fig 6 An EDS spectrum of tungsten working electrode after 3000 seconddeposition at ndash 055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Table 2 Element composition of the tungsten working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Element Na K Cl W ZnAt 6084 580 2861 224 191

113

A somewhat similar phenomenon was reported by Thus T StoslashreG M Haarberg and R Tunold for the deposition of Zn2+ on a glassycarbon electrode in KCl-LiCl melts at 400degC (2) They observed aldquosubstantial residual current observed prior to the Zn(II) reductionpeakrdquo This current was attributed by them to lithium intercalation intothe lattice of the glassy carbon electrode

Unfortunately the data about standard reduction potentials ofmany important ions in molten chlorides are lacking The only source inwhich suitable potentials were found is the book of Yu DelimarskildquoElectrochemistry of Ionic Meltsrdquo (5) The values of standard potentialstabulated in this book were calculated on the base a few assumptionsand are far from being strictly thermodynamical However they arehelpful from the practical point of view The potentials relevant for thisdiscussion are summarized in Table 3

Table 3 Standard reduction potentials in molten chlorides (adopted fromref [5])

Half-Element Li+|Li Na+|Na K+|K Zn2+|Zn Fe2+|FeEH2 (700degC) V - 239 - 236 - 250 - 040 - 007

As seen from Table 3 the standard potentials of lithium andsodium are very close to each other Therefore it is not surprising thatthe interference from sodium in the deposition of zinc ions is similar tothat of lithium as reported by T Stoslashre G M Haarberg and R TunoldOf course it is not intercalation that serves as the moving force of theprocess of sodium penetration into the surface layers of zinc deposit onthe tungsten electrode

The large amounts of sodium in the deposits obtained in the studyof the Zn2+ ions reduction on tungsten electrodes cannot be explained asthe formation of a W-Na alloy because such a process is not observedby the cyclic voltammograms of NaCl-KCl on tungsten electrodes in theabsence of zinc ions (3) Therefore it is zinc which triggers thedeposition of sodium Moreover the data obtained bychronoamperometry at E = ndash 055 V vs W (Fig 5) indicate that there aretwo sequential faradaic processes The first of them is relatively weak

114

and is completed after ~ 11 seconds Then the second process starts andits current only grows with time The first process can be related to thereduction of zinc ions and the formation of zinc deposits As theelectrode surface is covered by a layer of zinc the interaction of thislayer with Na+ ions begins Apparently sodium ions are absorbed by theliquid zinc (Tm = 419 degC) and this facilitates their reduction at thepotential so much more positive than the sodium reduction potential inthe absence of zinc ( - 11 V vs W) Both lithium and sodium are liquidat the temperature of the experiment and these two metals form on theelectrode surface a liquid solution with zinc which continues to absorbnew portions of the lithium or sodium ions

The following speculation may account for the phenomenonobserved in our system

1 Zinc ions are discharged on the surface of the tungstenelectrode As the surface concentration of zinc atoms grows nucleationoverpotential starts to dump the overall process This dumping isobserved in the course of the first 11 seconds in Fig 5

2 Zinc (or zinc-tungsten) phase is formed This phase triggers theprocess of sodium-zinc exchange

Zn + Na+ Zn+ + Na or Zn + 2Na+ Zn2+ + 2Na3 The process (2) becomes the main process on the electrode

surface

Deposition of zinc on a platinum electrodeSome typical voltammograms for the electrochemical reduction

of Zn(II) are shown in Fig 7 Again no difference is observed betweenthe processes in NaCl ndash KCl and in LiCl ndash KCl melts and two melts arefurther described on the instance of in NaCl ndash KCl alone

As seen from Fig 7 the voltammogram is completely anomalousas compared to the other studied systems No cathodic peaks areobserved in the range -11V to + 09V ie in the limits of theelectrochemical window The peaks ndash 125V and at +09 V are the sameas for the ldquoblankrdquo melt NaCl-KCl These are the limits of theelectrochemical window

A very poorly pronounced anodic peak A at about ndash 028 V issimilar to the anodic peak A which appears for the zinc deposition on atungsten electrode (Fig 1) However the cathodic branch of thevoltammogram contains a continuous transition to the cathodic limit of

115

the windows rather than a peak It is obvious that zinc deposition ismasked by another process whose nature cannot be studied in theframework of this research

Fig 7 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0176 mol L) in equimolar NaCl-KCl melt on a Pt electrode at 700degC Scanrate is 300 mVsec

Fig 8 An EDS spectrum of a platinum working electrode after 3000 secondcathodic polarization at ndash 07 V vs W at 725degC in equimolar NaCl-

KCl melt containing 176x10-4 molmL of Zn2+ ions

116

An attempt of obtaining a sample of zinc deposit by holding thesystem at ndash 07 V (that is at such a potential which is considerably morepositive than the cathodic limit but more negative than the potential atwhich zinc is deposited on a tungsten electrode) for 3000 seconds wasmade However the analysis (Fig 8) demonstrated that essentially nozinc is found on the surface of the electrode (Table 4) since the value098 At is comparable with the sensitivity of the method The richcontent of potassium (5857 At ) in the surface layers can hint thatpotassium sorption is the process which masks the deposition of zincHowever this information alone is not sufficient for making positiveconclusions

To try to understand the essence of the process other moltenchloride systems containing no potassium could be studied Howeversuch a study is far beyond the framework of the current work

Table 4 Element composition of the platinum working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 176x10-4 molmL

Element Na K Cl Pt ZnAt 555 5857 3426 618 098

ConclusionsThe deposition of zinc on a tungsten electrode starts as an

irreversible two-electron zinc ion reduction Zn2+ + 2e- Zn After anobvious initial nucleation step a new phase is formed This phasecatalytically launches the process of saturating the electrode surface withsodium After the onset of the process of sodium deposition the latterbecomes essentially the only constituent on the electrode surface

The attempts of studying the deposition of zinc ions on a platinumelectrode were unsuccessful because this process is masked by anotherprocess which can result in the saturation of the electrode by potassiumThe exact nature of the latter process demands a separate study

117

References1 Fray D J J Appl Electrochem 3 103 (1973)2 Stoslashre T Haarberg GM Tunold R J Appl Electrochem 30 1351

(2000)3 Lugovskoy A Zinigrad M Aurbach D Israel Journal of

Chemistry 47 (3-4) 409 (2007)4 Lugovskoy A Zinigrad M Aurbach D and Unger Z

Electrochimica Acta 54 (6) 1904 (2009)5 Delimarski Yu K Electrochemistry of Ionic Melts Metallurgiya

Moscow 1978 (in Russian)6 Mackenzie J D and Murphy W K J Chem Phys 33 366 (1960)7 Irish D E and Young T F J Chem Phys 43 1765 (1965)8 Allen DA Howe RA Wood ND Howells WS J Phys

Condens Matter 4 1407 (1992)9 Price D L Saboungi M-L Susman S Volin K J Wright A C J

Phys Condens Matter 3 9835 (1991)10 Bassen A Lemke A Bertagnolli H Phys Chem Chem Phys 2

1445 (2000)11 Biggin S and Enderby J E J Phys C Solid State Phys 14 3129

(1981)12 Badyal Y S and Howe R A J Phys Condens Matter 5 7189

(1993)

89

PREPARATION OF COMPOSITES CuZrO2 AND CuTiO2

BY MA SHS

AI Letsko1 TL Talako1 AF Ilyushchenko1 TF Grigoreva2SV Tsybulya3 IA Vorsina2 NZ Lyakhov2

1 Powder Metallurgy Institute of NAS B Minsk Belarus2 Institute for Solid State Chemistry and Mechanochemistry of SB RAS

18 Kutateladze str Novosibirsk Russia grigsolidnscru3 GK Boreskov Catalysis Institute of SB RAS Novosibirsk Russia

IntroductionMetaloxide composites are quite perspective materials for

application in machine industry instrument engineering and electricalengineering in comparison to pure metals due to their improvedchemical and physical properties (heat resistance strength hardnesserosion resistance) Chemical mixing salt mixture decompositionhydrogen reduction in solutions chemical precipitation from solutionsinternal oxidation are well-known methods of preparing such materialshaving application in industry [1] The above-mentioned technologiesallow attaining metaloxide composites but they are quite expensive andlong-term Based on this a very topical issue is elaboration of newapproaches to production of metal-ceramic materials

In this work we explored possibilities of preparation ofcopperoxide composites (CuZrO2 and CuTiO2) by methods ofmechanochemical synthesis (MS) in planetary mills and of mechanicallyactivated self-propagating high-temperature synthesis (MA SHS)

ExperimentalCopper copper oxide CuO and zirconium M-41 titanium PTOM

were used in this work as raw materials Mechanical activation (MA)was carried out in planetary ball mills with water cooling [2] (the drumvolume ndash 250 cm3 the balls diameter ndash 5 mm the load ndash 200 g sampleweight ndash 10 g the drums rotation speed about the general axis ~ 1000rpm) After MA the activated mixture was compacted (under a load of4ndash6 t) in the mould up of 17 mm diameter and ~25 mm in height (tillstrength sufficient for the sample transfer to the reactor) SHS wascarried out in the argon atmosphere the combustion was initiated withan electrically heated tungsten coil The temperature and burning

90

velocity were evaluated by a thermocouple method (C-A thermocouplesOslash asymp 02 mm) using an outer 2-channel 24-charge analog-to-digitalconverter ADSC24-2T

X-ray diffraction research was conducted with diffractometersXrsquoTRA (Thermo ARL Switzerland) with application of CoK radiation(λ = 1 789 Aring) and URD-63 with application of CuK radiation (λ = 15418 Aring) Evaluation of effective sizes of coherent scattering area wascarried out in compliance with the Scherer formula with the strongestpeaks of phases analysed

The high-resolution scanning electronic microscope (SEM)MIRATESCAN equipped with an INCA 350 accessory for EDXanalysis was used for the structure research The electron probe diameterwas 52 nm excitation area was 100 nm Images in direct electrons andback-scattered electrons were attained and it allowed studying chemicalelements distribution over the surface Brightness distribution in theimage depends on the average atomic element number in eachmicroarea

IR absorption spectra were registered by spectrometer IFS-66The samples were prepared to the exposure by standards methods

Results and discussion

Cu-O-Zr systemMechanochemical reduction of copper oxide with metallic

zirconium was initially investigated in this system This reaction is quitehigh-exothermic (∆H (2 CuO + Zr = 2 Cu + ZrO2) asymp -188 kcalmol) ieit can be implemented under mechanical activation conditions IRspectroscopic investigations have shown that the original copper oxideCu-O band is considerably widened at 505 cm-1 after 20 s of MA ofCuO + Zr mixture of stoichiometric composition This widening (Fig1b) can testify some structural failures After 30 s of activation thefollowing bands are present in the IR-spectrum of the product 505 cm-1

(original oxide CuO) 615 cm-1 (the lowest copper oxide Cu2O) [3] and415 585 735 cm-1 (zirconium oxide (Fig 1c) [4 5] X-ray-phaseanalysis shows the presence of certain amount of Cu2O already after 20 sof activation The 30-second activation product diffractogram showsclear copper (coherent scattering area asymp 80 nm) and zirconium oxide

91

(coherent scattering area asymp 100 nm) reflection and two copper oxidereflections ie mechanochemical reduction of copper oxide takes placeat such activation duration This reaction speed shows that the reactionpresumably takes place in the thermal explosion mode when especiallyhigh heat dissipation speed is needed what is very difficult to performeven in the most effectively cooled highly-energy planetary ball millsAs such a process dimensional scaling seems to be absolutely impossiblein conditions of mechanochemistry an attempt to produce compositeCuZrO2 by the SHS method was made

Fig 1 IR-spectra of mixture CuO + Zr before (a) and after MA for 20 (b) and30 s (c)

At first CuOZr mechanocomposite was used as the SHS-precursor This mechanocomposite formed after 20 s of MA ofstoichiometric composition mixture has a small amount of cuprous oxideCu2O beside original copper oxide and zirconium SHS process proceedsin the heat explosion mode in this system Burning parameters fixingfailed in this case because of the inertia of the equipment applied

92

Not pure metal but solid solutions intermetallic compounds ornano-composites where metal-reducer (zirconium in our case) isdistributed in the inert matrix can be used as a reducing agent todecrease the system reaction capability At the same components ratiochemical energy of the raw mixture would be considerably lower and asa consequence heat release would reduce

In this work mechanocomposite formed during mechanicalactivation of mixture Cu + 20 wt Zr for 20 min with zirconium hadbeen pre-dispersed for 4 minutes (zirconium coherent scattering areasize ~ 20 nm) was used for copper oxide reduction This compositediffractogram shows the widened intensive copper (coherent scatteringarea asymp 20 nm) reflection and very vague zirconium reflection coherentscattering area of which cannot be evaluated (Fig 2) Since copperreflections havenrsquot changed their position we can conclude thatzirconium hasnrsquot become a part of copper crystal lattice ie CuZrmechanocomposite and not solid solution is attained

Fig 2 Diffractograms of Cu + 20 Zr mixture before (a) and after 20 minof MA (b)

93

This is confirmed by the SEM results (Fig 3) The electronmicroscopy data more clearly show zirconium distribution Zr elementalmapping testifies that local zirconium areas are much diffused

Fig 3 SEM-images of sample Cu + 20 Zr after MA for 20 min

94

X-ray research of the product of joint activation of mixture CuO +mechanocomposite Cu + 20 Zr (the mixture composition correspondsto the stoichiometric ratio of copper oxide and zirconium) for 2 and 4minutes show that copper oxides diffraction reflections are retained inall cases although they are substantially widened (Fig 4) Thezirconium oxide reflection is not observed ie mechanochemical copperoxide reduction does not take place in this time gap CuOCuZrmechanomposite formed as a result of joint mechanical activation ofmixture CuO + mechanical composite Cu 20 Zr for 4 min was usedas a precursor for SHS

Fig 4 Diffractogram of sample CuO + CuZr after MA for 4 min

Usage of mechanocomposite CuOCuZr instead of CuOZr one asthe SHS precursor changes a mechanism of interaction between thereactants during the SHS process from the thermal explosion mode (forCuOZr mechanocomposite) to the steady-state combustion with the

95

burning velocity asymp 2 mms temperature rise speed about 730 Cs andburning temperature 1044 C The combustion temperature record (Fig5) shows 2 isothermal plateaus The first one is fixed at temperaturemaximum and most probably points out melting process The secondone is fixed at 580 ndash 590 C and accounts for post-processes in the after-burning zone of combustion wave

Fig 5 Temperature record of the SHS process from mechanical compositeCuOCuZr

X-ray-phase analysis has shown that SHS product consists ofcopper and zirconium oxide with Cu2O traces (Fig 6) Electronicmicroscopy with the EDX analysis confirms composite structureformation (Fig 7 Table 1)

96

Fig 6 Diffractogram of the SHS product from mechanical compositeCuOCuZr

Fig 7 SEM-image of the SHS product from mechanical composite CuOCuZr

97

Table 1 Results of the EDX analysis (from Fig 7)

Number ofspectrum

O Cu Zr

1 382 8744 8742 714 8152 11343 2803 2747 44504 1653 4640 37065 2314 2914 4772

Cu-O-Ti systemChemical reduction of CuO with titanium is also high-exothermic

(∆H (2 CuO + Ti = 2 Cu + TiO2) asymp -151 kcalmol) Mechanicalactivation of equimolar mixture of copper oxide with titanium powderfor 4 minutes did not result in titanium oxide formation Longeractivation is not reasonable since it contaminates the reaction mixturewith balls and drums material That is why the composites formedduring the short-term MA were used as precursors for SHS

After 30 s MA composite structure CuOTi with a small additiveof cuprous oxide reduced from CuO (Fig 8) is formed The SHS processfrom such mechanocomposites proceeds with a very high speed andtemperature (on a levels typical for the thermal explosion mode) andwith the substances scatter

Fig 8 Diffractogram of mixture CuO + Ti after MA for 30 s

98

To decrease combustion temperature and velocitymechanocomposite CuTi containing 20 wt of titanium was used as areducing agent in the next experiment Figure 9 shows the diffractogramof the mechanocomposite formed after 10 min mechanical activation ofthis mixture It shows that metals reflections especially that of titaniumare widened testifying substantial increase of their dispersivityAccording to the X-ray data analysis the titanium coherent scatteringarea size is ~ 10 nm in this composite

Fig 9 Diffractogram of mixture Cu + 20 Ti after 10 min of MA

Mixture of copper oxide and CuTi mechanocomposite (thecomposition corresponds to the stoichiometric ratio of titanium andcopper oxide for its full reduction) was subjected to activation for 4minutes Only a band of valence vibrations of vCu-O copper oxide (Fig10a) is present in the IR-spectrum of the activated mixture like in theoriginal one but its intensity slightly decreases X-ray research alsoindicates that the titanium oxide reflections are absent in the 4-minuteactivation product diffractogram (Fig 11)

99

Fig 10 IR-spectra of sample CuO + CuTi after 4 min of MA (a)and after SHS (b)

Fig 11 Diffractogram of sample CuO + CuTi after 4 min of MA

100

SHS process from CuOCuTi mechanocomposite takes place inthe steady-state combustion mode with burning velocity higher than 20mms and burning temperature ~2000 ordmC A band (~730 cm-1)corresponding to valence vibrations of rutile vTi-O (Fig 10b) [2]appears in the IR-spectrum of the SHS product from CuOCuTimechanicocomposite Diffraction reflections (Fig 12) also correspond toreflections of rutile and copper

Fig12 Diffractogram of the SHS product from CuOCuTi mechanocomposite

Electron-microscopy exposure in back-scattered electronsindicates the partial phase separation of TiO2 and Cu (Fig 13 a) thoughcomposite particles containing TiO2 inclusions with size from 30 nm till1 5 m (Fig 13 c) are also formed The elemental mapping in thetitanium characteristic radiation confirms this fact (Fig 13d)

101

a

b cFig 13 SEM-images of the SHS-product from CuOCuTi mechanocomposite

102

Table 2 The EDX analysis results (from Fig 13 a)

Number ofspectrum

O Ti Cu

1 191 052 9757

2 235 051 9714

3 2230 2094 5676

4 1586 1295 7118

5 180 108 9712

6 336 228 9436

7 4335 4685 980

8 3297 2738 3966

9 4978 4645 377

ConclusionThus our investigations have shown that copper oxide can be

mechanochemically reduced with zirconium resulting in formation ofzirconium oxide and copper but the reaction goes in the thermalexplosion mode

To produce composite CuZrO2 by the method of MASHS usageof mechanocomposite CuZr instead of pure zirconium seems to be morepromising The MASHS product is a copper-based composite withinclusions of ZrO2 and some amount of Cu2O

Mechanical activation of equimolar mixture of copper oxide withtitanium powder for 4 minutes did not result in titanium oxide formationThat is why the composites formed during the short-term MA were usedas precursors for the following SHS

Reduction of CuO with CuTi mechanocomposite can beimplemented by the method of MASHS Partial phase separation of TiO2

and Cu takes place during the synthesis process along with the formationof copper-based composite particles with inclusions of titanium oxidesized from 30 nm up to 15 m

103

References1 PA Vityaz Mechanically alloyed alloys on the basis of aluminum

and copper PA Vityaz FG Lovshenko GF Lovshenko ndashMinsk Belnauka 1998 ndash 351 p

2 YG Avvakumov AP Potkin OI Samarin Authorrsquos certificate ofUSSR 975068 Planetary mill BI 1982 No 43

3 SS Batsanov VPBokarev YVLazareva On CuO interaction withcopper Inorganic Chemistry Journal 1977 V 22 issue 4 P 888ndash 892

4 AI Boldyrev Infrared spectra of minerals M Nedra 19765 BT Kaminsky AS Plygunov GN Prokofyeva Infrared spectra of

oxides of titanium zirconium and hafnium Ukrainian ChemicalJournal 1973 V 35 No 9 P 946 ndash 977

78

THE STANDARD ENTHALPY AND ENTROPY OFFORMATION OF GASEOUS AND LIQUID

POLYCHLORINATED BIPHENYLS POLYCHLORINATEDDIBENZO-n-DIOXINS AND DIBENZOFURANS

TV Kulikova AV Mayorova KYu ShunyaevInstitute of Metallurgy Ural Branch RAS

Yekaterinburg RussiaE-mail kulikogmailcom

AbstractThe study deals with analysis and systematization of the known

and calculation of the unknown thermodynamic characteristics (thestandard enthalpy of formation the standard entropy of formation) ofwidespread hazardous isomers of gaseous and liquid compounds ofpolychlorinated biphenyls (PCBs) polychlorinated dibenzo-n-dioxins(PCDDs) and polychlorinated dibenzofurans (PCDFs) Thecomparison of results obtained in different studies reveals aconsiderable discrepancy between values reported by highlyrespected investigators In this connection laquoindependentraquo results ofthe thermodynamic characteristics have been calculated

IntroductionUnique technological and physicochemical properties of

polychlorinated biphenyls (PCBs) a huge volume of theirproduction considerable volatility and solubility and extremechemical inertness have led to the world-wide spread of PCB-containing equipment and materials resulting in the universalcontamination with these substances The most common method usedin Russia for destruction of PCBs is their incineration with theformation of polychlorinated dibenzo-n-dioxins (PCDDs) anddibenzofurans (PCDFs) which are among the most hazardouschemical substances known to the mankind

As often happens the hazard of PCBs has long beenunderestimated With respect to their severe toxicological effectPCBs are identical to substances that are referred to the high class ofhazard Since these substances are especially toxic they have beenassigned low toxicological standards which necessitate special

79

requirements on the organization of processes assuming formation ofthese substances (the so-called dioxinogenic processes) so thatindustrial emissions meet the norms Instrumental investigations ofthese substances are very expensive and in this connection interestis attracted to calculation methods for simulation of processes by thedata on their thermochemical properties

A quality thermodynamic simulation requires the knowledge ofthermodynamic and thermochemical properties of all reliablycertified compounds of the system under study in the gaseous orcondensed state Therefore the present study deals with the analysisand systematization of the known and calculation of the unknownthermochemical properties (the standard enthalpy and entropy offormation) of most toxic and hazardous isomers of gaseous PCBsPCDDs and PCDFs and liquid PCBs

Calculation of thermochemical propertiesIt is known that there are 209 individual PCB congeners 420

polychlorinated dibenzo-n-dioxins and polychlorinateddibenzofurans which differ by the number and positions of chlorineatoms in a molecule The most widespread PCB compoundscontaining up1 to 10 chlorine atoms were chosen for the study Indeciding on isomers preference was given to ortho-unsubstitutedPCBs because they are most toxic and their effect is similar to theeffect of PCDDs and PCDFs Congeners which do not have chlorineatoms in ortho-positions of molecules (ortho-unsubstituted PCBs)can acquire the planar configuration which is more favorable inenergy terms Such congeners are isostereoisomeric to PCDDs andPCDFs and present the greatest hazard As to the PCDD and PCDFisomers of special hazard to humans and the environment are tri-tetra- penta- and hexa-substituted dioxins and furans containinghalogen atoms in lateral positions 2 3 7 and 8

In this study we analyzed the known and calculated theunknown thermodynamic properties of 17 most widespread andhazardous isomers of PCBs PCDDs and PCDFs in the gaseous stateand 11 compounds of liquid PCBs

80

Gaseous PCBs PCDDs and PCDFsThe literature survey showed that studies dealing with

estimation of the thermochemical properties of gaseous PCB PCDDand PCDF compounds are few Most of them are based oncalculations or are semi-empirical For example Saito and Fuwa [1]calculated thermodynamic functions of all PCBs and some PCDDsand PCDFs on the basis of semi-empirical calculations in terms ofthe PM3 model OV Dorofeeva et al [2-4] used statistical methodsTable 1 presents the literature data on standard enthalpies andentropies of formation of gaseous and liquid PCBs PCDDs andPCDFs The comparison of results obtained in different studiesreveals a considerable discrepancy between values reported by highlyrespected investigators who did very arduous work In particularvalues of the formation enthalpy [1] are 8-70 larger and the entropyis 11-15 smaller than the corresponding values in [2-4] thediscrepancy grows with the number of chlorine atoms in a moleculeSo we thought it reasonable and topical to attempt an independentresult

Bensons method [5] was used to calculate thermodynamiccharacteristics (the standard enthalpy of formation ΔНdeg298 thestandard entropy of formation ΔSdeg298) of the gaseous PCBs PCDDsand PCDFs We shall dwell briefly on this method

Bensons method is the group additivity method involvinganalysis of the molecule structure Atomic or molecular groups areseparated and the nearest neighbors of the atom or the group areconsidered Table 2 gives the number of groups necessary fordetermination of group increments in structural formulas of PCBsPCDFs and PCDDs Values of the thermodynamic characteristics ofgroup increments were determined from available reference andliterature data [5 6] Information about the energy contribution ofeach group (see Table 3) and the number of groups was used tocalculate thermochemical properties of the PCBs PCDDs andPCDFs

81

Table 1 Standard enthalpies (∆Нo298 kJmole) and entropies (∆So

298Jmole K) of formation of gaseous and liquid PCBs PCDDs andPCDFs

Gaseous state Liquid state

Compo-unds Saito Fuwa [1]

the given work

OV Dorofeeva etal

[2-4]

∆Нo298

[7 8 121617]

So298

[781014 16 17]

∆Нo298

the givenwork and

[814]

So298

thegivenworkand[14]

1 2 3 4 5 6 7 8 9

C12H10

(biphenyl)

1986[1]

1797

3454[1]

4104

1820[3]

3908[3]

1819[8]

1814[16]

3927[16]

11711162[8]11710

[14]

257402574[14]

C12H9Cl(3-mono-

chlor-biphenyl)

1705[1]

1500

3851[1]

4413

1561[2]

4323[2]

1548[8]

15088[16]

4214[16]

7629 2840

C12H8Cl2

(44rsquo-dichlor-biphenyl)

1422[1]

1202

3992[1]

4721

1260[2]

4518[2]

1276[8]

12004[16]

4492[16]

3584 3106

C12H7Cl3

(344rsquo-trichlor-biphenyl)

1194[1]

905

4240[1]

5030

1041[2]

4923[2]

1004[8]

892[16]

4780[16]

-452 3372

C12H6Cl4

(33rsquo44rsquo-tetrachlor-biphenyl)

969[1]

608

4444[1]

5338

899[2]

5216[2]

732[8]

5836[16]

5068[16]

-4488 3638

C12H5Cl5

(33rsquo44rsquo5-penta-

chlorbiphenyl

748[1]

310

4620[1]

5647

569[2]

5502[2]

460[8]

2752[16]

5356[16]

-8524 3904

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlor-

biphenyl)

529[1]13

4615[1]

5956

314[2]

5675[2]

190[8]

-332[16]

5644[16]

-12558 4170

C12H3Cl7

(233rsquo44rsquo55rsquo-hepta-

chlor-biphenyl)

400[1]

-284

4842[1]

6264

152[2]

6077[2]

-84[8]

-416[16]

5932[16]

-16596 4436

82

1 2 3 4 5 6 7 8 9

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-

octachlor-biphenyl)

241[1]

-581

4886[1]

6573-90[2]

6342[2]

-356[16]-650[8]

6220[8]

-20632 4702

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-

nanochlor-biphenyl)

873[1]

-878

5048[1]

6881

-153[2]

6607[2]

-628[16]-958[8]

6508[8]

-24668 4968

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlor-biphenyl)

-67[1]

-1176

5034[1]

7190

-247[2]

6757[2]

-901[16]

-1267[8]

6796[8]

-28604 5234

C12H8O2

(dibenzo-n-dioxin)

-402[1]

-448

3764[1]

-592[4]

3965[4]

-592[12]-592[7]

-550[17]

3951[7]

3880[17]

- -

C12H4Cl4O2

(2378-tetrachlor-dibenzo-n-

dioxin)

-1372[1]

-1592

4553[1]

-1640[4]

4781[4]

-1345[7]

-158[17]

5136[7]

4784[17]

4781[10]

4784[9]

- -

С12H3Cl5O2

(12378-pentachlor-dibenzo-n-

dioxin)

-1532[1]

-1900

4931[1]

-1900[4]

54035[4]

-1162[7]

-196[17]

5531[10]

5010[17]

- -

С12H2Cl6O2

(123478-hexachlor-dibenzo-n-

dioxin)

-1691[1]

-2164

4841[1]

-2196[4]

56912[4]

-1224[7]

57559[7]

5236[17]

- -

С12HCl7O2

(1234678-hepta-chlor-

dibenzo-n-dioxin)

-1848[1]

-2472

5005[1]

-2460[4]

59789[4]

-1196[7]

61031[7]

5462[17]

- -

C12H8O(dibenzo-

furan)

1061[1]

518

3787[1]

553[4]

3759[4]

552[17]

3744[17]

- -

C12H4Cl4O(1234-

tetrachlor-dibenzo-furan)

203[1]

-625

4505[1]

-500 [4]49098

[4]-528[17]

4648[14]

- -

83

1 2 3 4 5 6 7 8 9

С12H3Cl5O(12378-pentachlor-

dibenzo-furan)

-123[1]-934

4592[1]

-759[4]

51975[4]

-748[17]

4874[14]

- -

С12H2Cl6O(123478-

hexachlor-dibenzo-furan)

-283[1]

-12424713[1]

-1051[4]

54852[4]

-1043[17]

5100[14]

- -

С12HCl7O(1234678heptachlor-

dibenzo-furan)

-441[1]

-1550

4833[1]

-1315[4]

57729[4]

-1313[17]

5326[14]

- -

Table 2 Number of groups for determination of group increments instructural formulas of PCBs PCDFs and PVDDs

Number of groupsCompound Св-H Св-Cl Св-O Св-Св

Number ofchlorine atoms

in a molecule (n)

PCBs 10 - n n - 2 1 ndash 10

PCDFs 8 - n n 2 2 1 ndash 8

PCDDs 8 - n n 4 - 1 ndash 8

Св is the carbon atom in an aromatic ring

Values presented in Table 1 show the thermodynamiccharacteristics of PCBs PCDDs and PCDFs calculated in this studyand by other investigators

It is seen for example ( Table 1) that the formation enthalpy

(o298H ) of biphenyl (C12H10) equals (kJmole) 1986 [1] 1820 [3]

1819 [7] and 1814 [8] while the formation entropy (o298S ) of

2378-tetrachlordibenzo-n-dioxin (C12H4Cl4O2) is (J(mole K))4553 [1] 4781 [4] 4784 [9] and 4781 [10]

84

Table 3 Values of the thermodynamic characteristics determined bythe method of group increments[58]

(gas) (liquid)Group

o298H

kJmole

o298S

J(moleК)

o298H

kJmole

o298S

J(moleK)

Св-H 1381[8]1382[5]

4831[8]4827[5]

816[8] 2887[8]

Св-Св 2166[8]2077[13]

-3657[8]-3618[5]

1721[8] -

Св-Cl -1703[8]-1591[5]

7708[8]7913[5]

-3220[8] 5547[8]

(Св)2-O -7766[8]-8834[5]

--

- -

orto corrCl-Cl

950[8]921[5]

- 1400[5] -

meta corrCl-Cl

-500[8] - 400[5] -

In this study the values of the standard entropy of formationobtained by using statistical methods (OV Dorofeeva et al [2-4 9])for 17 isomers of PCBs PCDDs and PCDFs are in good agreementwith the values calculated by other investigators [8 10 12 13] andwith the values calculated by us

Liquid PCBsIt should be noted that ample literature data on the

thermochemical properties of liquid ecotoxicants is only available forbiphenyl (C12H10) [8 14] dibenzo-n-dioxin (C12H8O2) [11 15] anddibenzofuran (C12H8O) [5 17] The only study dealing withcalculation of thermodynamic functions for the whole series of liquidPCDD and PCDF homologues was published by VS Iorish et al[11] As to liquid PCB compounds the literature data on theirthermochemical properties are scarce [8 14]

The thermochemical properties namely the standard enthalpyand entropy of formation of liquid PCBs were calculated using thegroup additivity method due to Domalski [8] Values of the groupincrements (Table 3) were adopted from [8] It is seen from Table 3

85

that the energy contribution of the group Св-Св is unavailable for the

entropy calculation However if one uses known values ofo298S for

liquid biphenyl (C12H10) [14] and the data on the contribution of the

Св-H and Св-Cl groups [8] it is possible to calculateo298S for the

whole series of PCBs

o298S (PCB) =

o298S (BP) - (10-n)

o298S (Св-H) + n

o298S (Св-Cl) +

+(morto corr Cl- Cl ) +(pmeta corr Cl- Cl) (1)

where n is the number of chlorine atoms in a PCBs moleculem (p) - spatial amendments number Cl (from two and more) beingin orto - (meta-) position rather each other

The enthalpy of formation (o298H ) for the PCBs series

compounds was calculated by two options using the group additivitymethod due to Domalski [8] and from the equation

o298H (PCB) =

o298H (BP) - (10 - n)

o298H (Св-H) +

+ no298H (Св -Cl) +(morto corr Cl-Cl )+(pmeta corr Cl-Cl) (2)

Table 4 lists values of the standard enthalpy of formation forthe series of liquid PCBs compounds as calculated by the groupadditivity method [8] and the equation (2) It is seen that the values of

o298H which were calculated by the two methods are in good

mutual agreementThe thermochemical properties which were taken as reliable

were added to the TERRA database and were used forthermodynamic simulation of the thermal stability of PCBs PCDDsand PCDFs

86

Table 4 Calculated enthalpy of formation (∆Нo298) for liquid PCBs

compounds∆Нo

298 kJmole

CompoundGroup

incrementsmethod

Eq (5)δ

C12H9Cl(3-monochlorbiphenyl)

7584 76742 12

C12H8Cl2

(44rsquo-dichlorbiphenyl)3530 36382 30

C12H7Cl3

(344rsquo- trichlorbiphenyl)-506 -3978 2138

C12H6Cl4

(33rsquo44rsquo-tetrachlorbiphenyl)-4542 -44338 238

C12H5Cl5

(33rsquo44rsquo5-pentachlorbiphenyl)-8578 -84698 126

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlorbiphenyl)-1261 -125058 083

C12H3Cl7

(233rsquo44rsquo55rsquo-heptachlorbiphenyl)-1665 -165418 065

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-octachlorbiphenyl)-20686 -205778 052

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-nanochlorbiphenyl)-24722 -246138 044

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlorbiphenyl)

-28758 -286498 038

Conclusions1The literature data on the thermochemical properties of 17

most widespread and hazardous isomers of PCBs PCDDs andPCDFs in the gaseous state and 11 compounds of liquid PCBs havebeen analyzed and systematized for the first time

2Methods have been developed for calculating of thethermodynamic characteristics of organic compounds Values of thethermodynamic functions (standard enthalpy and entropy offormation) of liquid PCBs PCDDs and PCDFs have been calculatedfor the first time

87

3The comparison of the calculated values of thethermodynamic functions with the known literature datademonstrated their good mutual correlation

4The obtained data were added to the TERRA database andwere used for thermodynamic simulation of the thermal stability ofPCBs PCDDs and PCDFs

5The obtained data can be used for simulating of the behaviorof complex heterogeneous systems including ecotoxicants over awide interval of temperatures and initial compositions

This study was supported by RFBR (project No 08-03-00362-a)

References1 Nagahiro Saito Akio Fuwa Chemosphere 2000 vol40 p

131-1452 OV Dorofeeva NF Moiseeva VS YungmanLV JPhys

Chem A 2004 vol 108 p 8324-83323 OV Dorofeeva Thermodynamica Acta2001 vol374 p7-114 OV Dorofeeva VS Iorish NF Moiseeva J Chem Eng

Data 1999 vol 44 p 516-5235 SW Benson FR Cruickshank DM Golden GR Haugen

HE OrsquoNeal AS Rodgers R Shaw and R Walsh Chem Rev1969 vol69 p 279 -324

6 HK Eigenmann DM Golden and SW Benson J PhysChem 1973 vol 77 1687-1691

7 Jung Eun Lee and Wonyong Choi J PhysChem A 2003vol 107 p 2693-2699

8 Domalski E S and Hearing E D J of Phys and Chem RefData 1993 vol 22 p 805-1159

9 LV Gurvich OV Dorofeeva VS Iorish Zh Fiz Khimii 1993vol67 No 10 p 2030-2032

10 W-Y Shiu and K-C Ma J Chem Ref Data 2000 vol29No 3 p 387-462

11 VS Iorish OV Dorofeeva NF Moiseeva J Chem Eng Data2001 vol46 p 286-298

12 VA Lukyanova VP Kolesov Zh Fiz Khimii1997 vol 71No 3 p 406-408(in Russian)

88

13 P Reid J Prausnitz T SherwoodLeningrad Khimiya 1982592 p(in Russian)

14 Richard Laurent and Helgeson Harold C Geochimica etCosmochimica Acta 1998 vol 62 No 2324 p 3591 ndash 3636

15 I Barin ldquoThermochemical Data of Pure SubstancesrdquoWeinheim Federal Republic of Germany VCHVerlagsgesellschaft mbH 1997

16 Cambridgesoft database ver 806 December 31 200317 Thompson D Thermochim Acta 1995 vol261 p7-20

76

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OFNANOGRAINED

TiN-TiB2 COMPOSITES

MA Korchagin BB BokhonovInstitute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirsk Russiakorchagsolidnscru

Titanium nitride is known to exhibit high oxidation resistancehigh thermal conductivity and hardness as well as high corrosionresistance in acids Titanium diboride is also very hard possessing highstrength at elevated temperatures and anomalously high electricalconductivity among other ceramic materials

Composite materials based on the mixture of these twocompounds have been widely used in a variety of applications Highperformance parts have been also developed Thus ceramics containing40-50 molTiN shows high oxidation resistance [1] However untilvery recently TiN and TiB2 have been produced separately by twodifferent routes At present new methods are being developed tosynthesize mixtures of these two compounds in a single process One ofthese methods is based on self-propagating high-temperature synthesis(SHS) The use of SHS eliminates the need of having furnace equipmentto synthesize the desired products The possibility of SHS in the systemis due to the high enthalpies of formation of the products serving as aninternal chemical source of energy

In order to simultaneously obtain TiN and TiB2 by SHS the initialreactants can be either the powder mixtures of Ti-BN [3] or Ti-B-BN[4] The products of the reactions consist of highly porous well meltedsintered pieces with the minimum grain size of 1-10 microm [4] Hightemperatures developed in the combustion wave in the traditional SHSdo not allow finer grains of the products to retain

In order to overcome this problem short mechanical activationof the mixtures of reactants is proposed followed by the SHS in anatmosphere of argon or nitrogen

In the previous investigations preliminary mechanical activationhas been shown to significantly reduce the combustion temperatures

77

which to a great extent determine the grain size of the products of SHS[6 7]

Experiments were performed on the stoichiometric mixtures 3Ti +2BN The time of preliminary mechanical activation in a planetary ballmill (AGO-2 type) did not exceed 10 min The influence of the durationof mechanical activation on the combustion rate temperature and phasecomposition of the products was studied

The milled mixtures and the products of SHS were studied usingXRD analysis and Electron Microscopy The experimental conditionshave been found favoring the formation of the two-phase mixtures ofTiN of TiB2 with the grain size ranging from 20 to 50 nm [7]

References1 GV Samsonov Nitridy (Nitrides) Kiev laquoNaukova Dumkaraquo 19692 AG Merzhanov Tverdoplamennoe gorenie (Solid State

Combustion) Chernogolovka ISMAN 2000 224 p3 AEGrygoryan ASRogachev Combustion of titaniumwith

nonmetal nitridesCombustion explosion and shock waves 2001v37 2 p168-172

4 R Tomoshige A Murayma T Matsushita Production of TiB2-TiNcomposites by combustion synthesis and their properties J AmCeram Soc 1997 80[3] 761-764

5 MAKorchagin TFGrigorrsquoeva BBBokhonov MRSharafutdinovAPBarinova NZLyakhov Solid-state combustion in mechanicallyactivated SHS systems Combustion explosion and shock waves2003 v39 1 p43-58

6 MAKorchagin DVDudina Application of self-propagating high-temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007v43 2 p176-187

7 MAKorchagin BBBokhonov Combustion of mechanicallyactivated 3Ti+2BN mixtures Combustion explosion and shockwaves 2010 v 46 2 p170-177

65

SPIN-CROSSOVER IN THE PENTANUCLEAR BYPIRAMIDALCo2Fe3 AND Fe2Fe3 COMPOUNDS

Sophia Klokishner Sergei Ostrovsky Andrei PaliiInstitute of Applied Physics Academy of Sciences of Moldova

Kishinev MoldovaKim Dunbar

Department of Chemistry Texas AampM UniversityCollege Station TX USA

Boris TsukerblatChemistry Department Ben-Gurion University of the Negev

Beer-Sheva Israel

In this article we report a model for a spin-crossover phenomenonin pentanuclear bypiramidal [M(III)(CN)6]2[M(II)(tmphen)2]3 (MM=CoFe FeFe) cluster compounds The spin-crossover phenomenonis considered as a phase transformation accompanied by a change of theground state spin The model takes into account cooperative interactionsin the crystal network local crystal fields and spin-orbit coupling actingwithin the degenerate metal sites Magnetic properties and Moumlssbauerspectra are analyzed and compared to the experimental data

1 IntroductionSpin-crossover compounds have been a subject of many

experimental and theoretical studies [1-6] Till now only a fewexperimental reports on spin crossover in cluster compounds [7-11] havebeen reported Recently FeII ions were introduced into the equatorialmetal sites of discrete cyano-bridged pentanuclear clusters[MIII(CN)6]2[MII(tmphen)2]3 (MM =CoFe(1) FeFe(2) ) [12] with atrigonal bipyramidal (TBP) structure The octahedral nitrogensurrounding of FeII ions facilitates the spin-crossover behavior Theoccurrence of the ls-hs transition in compounds 1 and 2 was proved bythe combination of Moumlssbauer spectroscopy magnetic measurementsand single-crystal X-ray studies For both types of clusters[FeII(tmphen)2]3[M

III(CN)6]2(M=FeCo)7 the T product increases by

~9emumiddotKmol between 150 K and 375 K thus indicating the ls ndashhstransition at the FeII sites The TBP FeII

3CoIII2 cluster due to its electronic

66

structure represents an ideal system for studying the effects ofintracluster short-range and intercluster long-range interactionsfacilitating spin-crossover In the (FeIII)2 (FeII)3 cluster the hs-FeII and ls-FeIII ions are coupled by exchange interaction In spite of the fact that theexchange interaction of the hs-FeII and ls-FeIII ions through the cyanidebridge is sufficiently weak as compared with that in oxide clusters it isinterestingly to understand whether this interaction may affect the spintransformation The effects of orbital degeneracy on the spin-crossovertransformation in the [FeII(tmphen)2]3[FeIII(CN)6]2 crystal will beexamined as well In the present article a microscopic approach to theproblem of spin crossover in crystals containing metal clusters isdeveloped

2 The modelIn the basic structural unit of compounds 1 and 2 two MIII ions

surrounded by six carbon atoms occupy the apical positions and threeFeII ions coordinated by the nitrogen atoms reside in the equatorial plane[12] In a strong crystal field of carbon atoms the ground terms of the

CoIII and FeIII ions are the low-spin orbital singlet )( 621

1 tA ( 0S ) and

the orbital triplet )( 421

3 tT respectively The ground state of a FeII -ion in

the crystal field induced by the nitrogen atoms can be either low-spin

(ls)- term )( 621

1 tA or high spin (hs) ndashterm 2422

5 etT Both magnetic

measurements and Moumlssbauer spectroscopy for water containing crystals[12] demonstrate the presence of some amount of FeII ions in the hsconfiguration even at very low temperatures Further on we consider inthe model two types of FeII ions and denote by x the fraction of FeII -ions which are in the hs ndashstate at all temperatures while theconcentration of those ions which undergo the ls-hs transition is (1-x)The number pi of trigonal bypiramidal clusters in which i (i=0123) ofthree FeII ions are in the hs configuration in the whole temperature range

is estimated as iiii xxCp 33 1 where rllrC r

l

The Hamiltonian of intraion interactions can be written in the form

67

Hg

gllsH

kkB

kkB

kZkk

)(

32)(

211

02

0

H

lsH

(1)

where numbers theIIFehs ions in the k-th bypiramidal cluster the

first term is the spin-orbit (SO) coupling in the cubic )( 2422

5 etT - term of

theIIFehs -ion the second term describes the axial crystal field

splitting the 125 lT term into an orbital singlet ( 0lm ) and an

orbital doublet ( 1lm ) the third term refers to the Zeeman

interaction for hs-FeII ions and contains both the spin and orbitalcontributions B is the Bohr magneton and g0 is the spin Lande factorFinally the fourth term represents the interaction of the ground Kramersdoublets of two ls-FeIII ions in the cluster with the external magnetic

field i is the matrix of the pseudo -spin frac12 of the ls-FeIII ion g1 =173

is the Lande factor Up to room temperature the ls-FeIII can be regardedas an ion with the pseudo-spin frac12 because the ground Kramers doubletand the excited quadruplet arising from the splitting of the 2T2 term by

the spin-orbital interaction are separated by the gap 173023 cm

( 1486 cm [13] for a free ls-FeIII) that is large enough from the

thermal population of the excited quadruplet at room temperatureThe superexchange interaction (several cm-1 [1415]) in the

[FeII(tmphen)2]3[FeIII(CN)6]2 through the cyanide bridges couples the hs-FeII ions in equatorial and ls-FeIII ndashions in axial positions Further on wewill neglect the essentially anisotropic orbitally dependent terms andretain only the isotropic part of the exchange interaction between the hsndashFeII and ls ndashFeIII ions in a cluster The Hamiltonian of exchangeinteraction for the thk cluster looks as follows

kkkex

k

exJH

212 σσs (2)

where 2s is the spin of the hs-FeII ion the summation in (2) takes

into account the hs-FeII ions appearing in the thk cluster due to thespin transition and those which are in the hs-state in the whole

68

temperature range As in [16-18] we suppose that the mechanismresponsible for the ls-hs transition is the interaction of FeII ions with thespontaneous all-round full symmetric lattice strain Applying theprocedure suggested in [16-18] we obtain the Hamiltonian of electron-deformational interaction

2k kkk

kkst

nm

JBH (3)

where 21AB 21AJ

01021

2

ccc

cA n

(n=123) is the number of FeII ions which undergo the ls-hs transition ina complex m is the number of TBP MIII

2MrsquoII3 complexes whose FeII ions

are involved in the spin conversion =1n k=1m 0 is thevolume that falls at a Fe ion and its nearest surrounding and is the unit

cell volume per one iron respectively In the basis of the states 25T and

11A the 1616 matrix k is diagonal and has 15 eigenvalues equal to 1

and one eigenvalue equal to -1 Finally 2)(1 lshs

2)(2 lshs hs and ls are the constants of interaction of the

FeII ion with the full symmetric strain1A in the hs and ls states

respectively The first term in (3) acts as an additional field applied toeach spin-crossover ion and redefines the effective energy gap 0

between the hs and ls states of the FeII in the cubic crystal field Thesecond term in (3) represents an infinite range interaction between theFeII ions which undergo the spin conversion This interaction arises fromthe coupling to the strain The model of the elastic continuum introducedabove satisfactorily describes only the long-wave acoustic vibrations ofthe lattice Therefore the obtained intermolecular interactioncorresponds to the interaction via the field of long-wave acousticphonons

Due to the proximity of the FeII ions in the clusters short-rangeinteractions between these ions inside the cluster are relevant Thelargest is the effect of the exchange arising from the optic phonons [19]

69

The Hamiltonian describing short-range interactions between FeII ionswithin the trigonal bipyramid can be written as

0

kkk

sr JH (4)

The Hamiltonian (4) takes into account the interaction between the FeII

ions participating in the spin transitions the interaction of these ionswith those FeII ions which are in the hs-state in the whole temperaturerange as well as the interaction between the latter It should bementioned that eq (3) as compared with eq(4) only accounts for FeII

ions participating in spin conversion The Hamiltonian for the wholecrystal can be written as

k

kexstsr HHHHH

2

00 (5)

where k

k

exex HH In the molecular field approximation the full

Hamiltonian H can be written as a sum of one-cluster Hamiltonians

)(32)(

)2

(~

211101

2

1

0

0

kkB

kkkB

k

ex

kkZ

kkkkkkk

gIgHIl

IlsJBJH

HlsH

(6)

where in the basis of the states 25T and 1

1A kI1

is a diagonal 1616 -

matrix with 15 eigenvalues equal to 1 and one vanishing eigenvalue is the order parameter In fact the Hamiltonians kH

~describe clusters

with different numbers of spin-crossover FeII ions and k as beforenumbers the clusters in the crystal For calculation of the temperaturedependence of the order parameter the self-consistent procedure wasapplied The calculations of the magnetic properties were based on theHamiltonian given in Eq(6)

3 Results and discussionThe estimation of the parameters J and B was performed

according the procedure suggested in paper [16-18] For characteristicfor compounds 1 and 2 parameters =1026Aring3 0 =8Aring3

c2 (005divide01)c1211

2 10 cmdynec 1046 141

cm 142 1087 cm the

70

parameters J and B take on the values 20divide80 cm-1 and -95 divide -24 cm-1respectively

Fig1 shows the experimental data for compound 1 together withthe calculated T vs T curves The result of the best fit procedure in

the model above developed is presented by curve 1 The best fitparameters are the part of the figure caption One can see that a quitegood agreement with the experimental data is obtained At temperaturesbelow 100 K the T values show that the FeII ions are mainly in the ls ndashstate However some small admixture of hs ions is present In thetemperature range 150-300 K the T product gradually increases thusindicating the ls - hs transition in the FeII ions

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30 35

04

06

08

10

3

2

1

T

cm

3K

mo

l-1

Temperature K

23

1

T

cm

3K

mo

l-1

Temperature K

Fig1 Temperature dependence of the T product for 1 Circles-experimentaldata [12] The solid lines represent a theoretical fit with =-103 cm-1 x=10and (1) hs-ls =640 cm-1 J =35 cm-1 J0=45 cm-1 =180 cm-1 =10 (2) hs-

ls=620 cm-1 = -136 cm-1 J=0 J0=0=06 (3) hs-ls=630 cm-1 =168 cm-1J=0 J0=0 =06

The parameter J of long -range cooperative electron-deformationalinteraction obtained from the best fit procedure falls inside the limits

71

estimated above Relatively small values of the parameters J and J0 ascompared with the gaps hs-ls= 0-2B and are also in agreement withthe observed gradual temperature dependence of T and noticeable

increase of T at temperatures higher than 150K Finally the estimated

from the best fit procedure percentage of FeII ions (x=10) which are inthe hs-state at any temperature is very close to that obtained from theMoumlssbauer spectra [12] For comparison in the same figure (curves 23)the results of fitting of the T curve in neglect of long- and short-

range interactions are shown for the cases of 0 and 0 It isseen that in this approximation the calculated curves 2 and 3 differsignificantly from the experimental one both at low and hightemperatures besides this the obtained value 60 is too small forhs-FeII-ions

For compound 2 the variation of the observed magneticsusceptibility as a function of temperature is presented in Fig2

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

321

T

cm

3K

mo

l-1

Temperature K

Fig2 Temperature dependence of the T product for 2 Circles experimentaldata [12] Curves 1- 3 were calculated with the following parameter values hs-

ls =690 cm-1 J=30 cm-1 J0=40 cm-1 =100 cm-1 =-103 cm-1 =10 x=9and (1) Jex = 3 cm-1 (2) Jex = 0 (3) Jex = -3 cm-1

72

First the magnetic behavior of complex 2 was analyzed withneglect of intracluster Heisenberg exchange interaction between FeII andFeIII ions The result of the best fit procedure is presented by curve 2 inFig2 The best fit parameters are the part of the figure caption One cansee that the values of the key parameters are close to those for complex1 However the obtained energy gap hs-ls between the ls and hsconfigurations for complex 2 is a bit larger than the corresponding gapfor compound 1 while the parameters of short-range and long-rangeinteractions are smaller Namely this difference in the characteristicparameters leads to lower values of T for compound 2 as compared

with compound 1 at temperatures higher than 150K The effect ofexchange interaction on the magnetic behavior is illustrated in Fig2 bycurves 1 and 3 Since typical values of the exchange parameters incyanide bridged complexes are of several cm-1 we calculated the Tproduct with the set of the best fit parameters and Jex = -3 cm-1 and 3cm-1 One can see that at temperatures higher than 50K the smallexchange interaction has no effect on the magnetic properties ofcomplex 2

Moumlssbauer spectra provide direct information about the populationof the hs and ls states and serve a reliable test for the theoreticalbackground of the SCO phenomenon The total Moumlssbauer spectrum(ie the observable spectrum) was obtained by summing up the spectrayielded by different cluster electronic states in the molecular field withdue account for their equilibrium populations for a given (at a certaintemperature) value of the molecular field In calculations theexperimental values for the parameters of the quadrupole splttings andisomeric shifts were taken from [12] The calculated and experimentalspectra are shown in Fig3

Quite good agreement between the experimental data andtheoretical calculations is obtained It should be underlined that themodel takes into account the main effect inducing the temperaturedependence of the Moumlssbauer spectra and this is the temperaturedependence of the cluster energies in the molecular field Namely thiseffect is responsible for the transformations of the Moumlssbauer spectrawith temperature

73

The proposed model gives a good fit to the observed temperaturedependence of the static magnetic susceptibility and the Moumlssbauerspectra The last clearly illustrates the cooperative nature of SCOtransformations in TBP compounds that leads to a crossing of the ls andhs levels due structural phase transition induced by the ordering of thelocal deformations through the field of the acoustic phonons

Fig3 Moumlssbauer spectra for compound 1 calculated at T=42 220 and 300Kwith the set of the best fit parameters (thick solid lines) Contributions from ls -FeII and hs -FeII ions are shown in dash and dot lines respectively The half-width of the individual lines Г=016 cm-1(42 К) Г=018 cm-1(220К)Г=024cm-1(300К)

74

AcknowledgmentsFinancial support of the STCU (project N5062) is highly

appreciated BT and KD gratefully acknowledge financial support ofthe Binational US-Israel Science Foundation (BSF grant no 2006498)BT thanks the Israel Science Foundation for the financial support (ISFgrant no 16809)

References1 Guumltlich P Goodwin H A Spin Crossover in Transition Metal

Compounds Springer-Verlag 20042 Hauser A Light-Induced Spin Crossover and the High-Spin rarrLow-

Spin Relaxation Springer-Verlag 20043 P Guumltlich J Jung Nuovo Cimento D 1996 18 1074 P Guumltlich A Hauser H Spiering Angew Chem Int Ed Engl

1994 33 20245 J Zarembowitch New J Chem 1992 16 2556 A B Gaspar V Ksenofontov M Serdyuk P Guumltlich Coord

Chem Rev 2005 249 26617 JA Real AB Gaspar MC Munoz P Guumltlich V Ksenofontov H

Spiering TopCurrChem2004 2331678 G Vos RAG De Graaff JGHaasnoot AM van der Kraan De

PVaal JReedijk InorgChem 1984 23 29059 EBreuning MRuben JMLehn FRenz YGarcia VKsenofontov

P Guumltlich E Wegelius KRissanen AngewChemIntEd 2000 392504

10 M Nihei MYi MYokota LHan AMaeda HKushida HOkamoto HOshio AngewChem IntEd 2005 446484

11 D-Y Wu O Sato Y Einaga C-Y Duan Angew Chem Int Ed2009 48 1475 ndash1478 2009

12 MShatruk ADragulescu-Andrasi KEChambers SAStoianELBominaar CAchim KRDunbar J Am Chem20071296104

13 AAbragam BBleaney Electron Paramagnetic Resonance ofTransition Ions Clarendon Press Oxford 1970

14 A V Palii SM Ostrovsky S I Klokishner B S Tsukerblat C PBerlinguette K R Dunbar J R Galaacuten-Mascaroacutes JAmChemSoc2004 126 16860

15 HWeihe H Gudel H Comments Inorg Chem 2000 22 75

75

16 SI Klokishner F Varret J Linares ChemPhys 2000 255 31717 SI Klokishner JLinares PhysChemC 2007 111 1064418 SI Klokishner J Linares F Varret Journal of Physics

Condensed Matter 2001 13 59519 JM Baker Rep Prog Phys 1971 341 109

53

NON-CARBON PREPARATION OF SILICON BYMECHANICALLY ACTIVATED THERMAL SYNTHESIS

TF Grigorieva1 TL Talako2 AI Letsko2 V Šepelaacutek3 VG Scholz4MR Sharafutdinov1 IA Vorsina1 AP Barinova1 PA Vitiaz2

NZ Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry Kutateladzestr 18 Novosibirsk 630128 Russia grigsolidnscru

2 Powder Metallurgy Institute Platonov str 41 Minsk 220005 Belarus3 Inst of Nanotechnology KIT Eggenstein-Leopoldshafen 76344 Germany

4 Inst of Chemistry Humboldt Univ Berlin 12489 Germany

IntroductionIn industrial processes the production of Si is based on the

reduction of silicon dioxide by carbon at a temperature of about 1800 C[1] However the coke applied to the reduction can be hardly refinedfrom the most dangerous for silicon impurities like boron phosphorusarsenic and antimony That is why development of non-carbon routes forsilicon production is a topical problem of a silicon industry Reductionof oxides with magnesium and aluminum by the method of self-propagating high-temperature synthesis (SHS) has been used in industryfor a long time [2] As such reactions are highly exothermal they can bealso organized with the use of mechanochemistry for instance reductionof the copper oxide by aluminum Mechanochemical reduction of ironoxide by aluminum aimed at obtaining precursors with differentcompositions for intermetallideoxide SHS composites has been alsoconsidered [3ndash6]

SiO2 + Al reaction is not high exothermic enough to organize theSHS without preliminary heating [7] Mansurov et al [8] reportedcreation of ceramic composites in several stages first the silicon oxidewas mechanochemically treated in an organic compound environmentthen the resultant material was annealed (carbonized) at ~ 850 C andfinally the mixture of the carbonized silicon oxide with aluminum wassubjected to SHS However as-formed product included silicon carbide

The objective of activities described in this paper is to study thepossibility of using mechanochemical treatment for obtainingsiliconaluminum oxide composites by the SHS and thermal synthesis atconsiderably lower temperatures with the following removal of alumina

54

Sample preparation and examination proceduresThe PA-4 aluminum powder and the silicon oxide with a particle

size of ~ 3 nm were used in our experimentsA stoichiometric mixture of the silicon oxide with aluminum was

processed in a high energy planetary ball mill (drum volume 250 cm3ball diameter 5 mm mass of the balls 200 g mass of the sample 10 gand velocity of rotation of the drums around a common axis ~1000 rpm)

The IR spectra were recorded by a Specord IR 75 spectrometerthe samples for this study were pressed with annealed potassiumbromide

The 27Al (I = 52) NMR spectra were recorded on a BrukerAdvance 400 spectrometer corresponding to a 27Al resonance frequencyof 782 MHz MAS experiments were realized with a high speed probeusing 25 mm zirconia rotor The spinning speed was 20 KHz Themagnetic field strength (in frequency unit) was set to 104262 MHz Theexcitation pulse duration was chosen equal to 1 s The recycling delaybetween each acquisition was fixed to 1 s To see weak signals in the Al-O region in mechanically activated samples we applied accumulationsnumbers up to 56000 (ie measurement time of 15 hours)

The dynamics of the SHS process was studied with the use ofdiffraction of synchrotron radiation and an OD-3 single-coordinatedetector The samples for SHS were prepared in the form of pellets 20mm in diameter and 1ndash2 mm thick by pressing at a pressure of 200 atmThe resultant samples were placed onto a ceramic plate so that they werein the center of the goniometer The process was initiated by a nichromespiral The OD-3 detector was triggered to operate in the ldquofast filmingrdquomode simultaneously with the beginning of pellet burning The time ofone ldquoframerdquo was 05 sec and the number of ldquoframesrdquo was 128 Theradiation wavelength was 1527 Aring

For investigation of mechanically activated thermal synthesis thesamples were heated up to 650 C in the reaction chamber XRK 900 inair with a heating rate 10 min The OD-3 detector was also used forstudying the process dynamics though time of one ldquoframerdquo was 1 min

55

Results and discussionFirst we made an attempt of direct mechanochemical reduction of

the silicon oxide by aluminum The study of this process showed that thechemical reaction of SiO2 reduction does not occur within 6 min ofmechanical activation The IR spectrum of the initial mixture containsclear absorption bands with the maximums at 1005 and 480 cmminus1

(valence and deformation oscillations of the SindashO bond of the SiO4

tetrahedra of the siliconndashoxygen skeleton) and two maximums in therange of 900ndash670 cmminus1 due to oscillations of the SindashOndashSi bridges Thephenomena observed in the course of mechanical activation were agradual decrease in intensityand broadening of the characteristic bands of the SindashO bond (Fig 1)

An electron-microscopy study of the SiO2Al composite obtainedafter 1 min of mechanical activation in characteristic radiation revealed a

Fig 2 Microphotograph of themechanocomposite after 1 minactivation in Si characteristic

radiation

Fig 1 IR spectra of the SiO2 + Al mixturebefore mechanical activation (1) and aftermechanical activation during 05 (2) 1 (3)

and 6 (4) min

56

very small grain size and a very uniform distribution of the componentsin the mechanocomposite (Fig 2)

Based on the data of the differential thermal analysis (DTA) evenshort-time activation of this mixture appreciably affects its thermalcharacteristics For the initial mixture the real chemical interactionoccurs at a temperature T gt 1000 C (Tmax = 10836 C) (Fig 3 a) iesubstantially higher than the melting point of aluminum whereas thesituation is different for the mixture subjected to mechanical activationduring 20 sec Two clearly expressed exothermal peaks appear the firstpeak at 6217ndash6486 C (Tmax = 6327 C) and the second peak at 9921ndash10759 C (Tmax = 10292 C) (Fig 3 b) For the mixture activated for 40sec the first peak is at 6045ndash6366 C (Tmax = 612 C) and the secondpeak is extremely broad and smeared in the range of 8161ndash11117 C(Tmax = 10381 C)

These observations can be explained by the fact that a tightcontact is created between some part of the ultrafine non-plastic siliconoxide and plastic aluminum already within 20 sec of mechanicalactivation the silicon oxide is ldquowettedrdquo by aluminum as a result somepart of the silicon oxide starts to interact with aluminum at a temperatureT = 6217C which is lower than the melting point of the latter Asmechanical activation is continued aluminum becomes also dispersed tonanoparticles greater amounts of the components of the mixture areinvolved into the contact and the temperature of the interactionbeginning decreases after 1 minute of activation the interaction beginsat T = 5399 C and ends at T = 6303 C (Fig 3 c)

The curve for this sample obtained by the method of differentialscanning calorimetry (DSC) has only one exothermal peak ie theentire process proceeds at a temperature lower than the melting point ofaluminum Longer activation further decreases the temperature ofreaction beginning (Table 1) but there are no any further significantchanges in the system parameters determined by DSC

The duration of mechanochemical treatment was limited to 6 minfor the following reasons- the IR spectra are so smeared already after 4 min that do not provide

any new information (see Fig 1)- the DTA study does not reveal any significant changes in the thermal

characteristics after 1 min of mechanical activation (see Table 1)

57

- mechanochemical actions should be always minimized to ensure theminimum possible contamination of the products by milling

Fig 3 Results of differential scanning calorimetry (DSC) and thermogravimetry(TG) studies of the SiO2 + Al mixture before (a) and after mechanical activation

during 20 (b) and 60 sec (c)

58

Table 1 Parameters of Exothermal Peaks on DTA Curves of SiO2 + AlSamples after Mechanical Activation

Temperature CDuration of activation

beginning of thereaction

end of the reaction

1 min 5930 6303

2 min 5871 6243

4 min 5867 6291

6 min 5870 6258

27Al MAS NMR spectra of the nanostructured SiO2Almechanocomposites are dominated by a broad resonance associated withthe presence of nanostructured Al matrix (Fig 4) The interestingobservation is that additional resonance lines appear in the spectra ofmechanoactivated samples corresponding to AlO4 AlO5 and AlO6

polyhedra Their content is slightly increasing with increasing millingtime however the relative intensity of AlOx polyhedra compared withthe Al matrix spectral intensity is even after the longest milling periodvery low It can be assumed that these nonequilibrium localcoordinations of aluminium atoms are located on the SiO2-Al interfaces[9] The intensity of the resonance lines belonging to various polyhedrarelative to the total spectral intensity allows us to calculate the volumefraction of interface regions in the nanocomposites Furthermoreassuming a spherical shape of SiO2 nanoparticles the thicknees of theinterface regions was calculated their known volume fraction

Thus the study of mechanically activated SiO2+Al mixturesshows that silicon reduction does not occur during mechanical activationstep except formation of some AlOx species at the interfaces but anexothermal reaction in activated mixtures can proceed at substantiallylower temperatures

In the subsequent step the nanostructured SiO2Almechanocomposites were used as precursors for the preparation ofSiAl2O3 composites via self-propagating high-temperature synthesisOur experience shows that combustion initiation requires sample

59

preheating approximately to 200 C (as compared with 650-860 Сreported in [7])

Fig 4 27 Al MAS NMR spectra of non-activated sample (a) the samplemechanoactivated for 1 (b) and 6 (c) minutes

60

The overall pattern of phase transformations is illustrated in Fig 5a To analyze them however it is more convenient to use the projectiononto the diffraction angle (β)ndashtime plane (Fig 5 b) As the silicon oxideused in these experiments is amorphous to x-ray radiation onlyaluminum peaks are observed

Fig 5 Dynamics of phase transformations in the Al + SiO2 mechanocompositein the SHS mode (a) three-dimensional image (b) projection onto thediffraction anglendashtime plane

61

It is clearly seen thataluminum becomes heatedas the combustion waveapproaches the peaks areshifted toward smallerangles ie greaterdistances between theplanes After that theintensity of these peaksdrastically decreaseswhich is apparently due tomelting No crystallinephases are observed in thetwo frames (~ 1 sec) Inour opinion corundum(Al2O3) peaks appearslightly earlier than siliconpeaks A possible reason isthe lower melting point ofsilicon (1410 C) as compared with corundum (2050 C) An electron-microscopic study of the SHS product of the SiO2 + Al system subjectedto mechanical activation during 1 min in characteristic radiation (Fig 6)shows a fairly uniform distribution and small size of all elements in thesystem including silicon being formed

Previously it was shown that chemical interaction between SiO2

and Al in the mechanocomposites formed during the mechanicalactivation starts at essentially (~ 500 C) lower temperatures as comparedwith the non-activated mixtures

In the final step we used as-formed mechanocomposites asprecursors for the preparation of SiAl2O3 composites via thermalsynthesis The samples after mechanical activation for 6 min wereplaced into cuvette and gently prepressed to get the plane surface Thenthe cuvette with the sample was sited in the furnace The thermocouplewas directly close to the registration area Recording of diffractogramswas started at temperature 230 С Dynamics of phase transformation inAl SiO2 composites during heating from 590 up to 660 C is presentedin Fig7

Fig 6 Microphotograph of the SHS productin Si characteristic radiation

62

As can be seen from the Fig 7 the reaction products (silicon andalumina) start to form at about 590 С It is interesting that corundum isformed during the SHS and thermal synthesis after low activation time

Fig 7 Dynamics of phase transformation in Al SiO2 composites duringheating from 590 up to 660 C

Fig 8 XRD-pattern of the thermal synthesis product from the mechanocompositesactivated for 6 min and heated up to 660 C

63

while -Al2O3 is identified in the product of thermal synthesis afterlonger MA durations (Fig 8)

ConclusionsThus though the silicon oxide is not reduced by aluminum

directly by mechanical activation the use of the mechanocomposite as aprecursor for both SHS and thermal synthesis allows a fine-grainsiliconaluminum oxide composite to be obtained In both caseschemical interaction starts at essentially lower temperatures as comparedwith the non-activated mixtures

AcknowledgementsThis work was supported by the joint project No 5 ldquoNon-carbon

preparation of Si by mechanically activated thermal synthesisrdquo of NASBand SB RAS

References1 Denisov VM Istomin SA Podkopaev OI Serebrjakova LI

Pastuchov EA Beletsky VV Silicon and its alloys EkaterinburgPublishing house of Ural Branch of the Russian Academy ofSciences 2005 467 p (in Russian)

2 AG Merzhanov Forty Years of SHS Happy Life of a ScientificDiscovery (in Russian) Chernogolovka (2007)

3 TF Grigoryeva SA Petrova IA Vorsina et alldquoMechanochemical reduction of a copper oxiderdquo in TheOptimization of the Composition Structure and Properties ofMetals Oxides Composites Nano and Amorphous Materials Proc6th IsraelindashRussian Bi-National Workshop Jerusalem (2007) pp197ndash204

4 TF Grigoryeva TL Talako AA Novakova et al ldquoMA and MASHS production of nanocomposites metaloxides andintermetallicsoxidesrdquo ibid pp 139ndash148

5 NZ Lyakhov PA Vityaz TF Grigorieva et alldquoMechanochemically synthesized SHS precursors for obtainingintermetallideoxide nanocompositesrdquo Dokl Akad Nauk 406 No6 776ndash778 (2005)

64

6 5 T Talaka T Grigorieva P Vitiaz et al ldquoStructure peculiaritiesof nanocomposite powder Fe40AlAl2O3 produced by MA SHSrdquoMater Sci Forum 534ndash536 1421ndash1424 (2007)

7 Maltsev VM Gafiyatulina GP Tavrov AV Spreading of thecombustion wave in SiO2-Al systems Proc SPIE Vol 3172(111997) p 724-727

8 ZA Mansurov RG Abdulkarimova NN Mofa et al ldquoSHS ofcomposite ceramics from mechanochemically treated and thermallycarbonized SiO2 powdersrdquo Int J SHS 16 No 4 213ndash217 (2007)

9 V Sreeja TS Smitha Deepak N Ajithkumar TG and PA JoySize dependent coordination behavior and cation distribution inMgAl2O4 nanoparticles from 27 Al solid state NMR studies J PhysChem C 112 14737-14744 (2008)

37

THE PREPARATION OF MECHANICOMPOSITESTUNGSTEN-METAL AND SINTERING MATERIALS

T Grigoreva1 L Dyachkova2 A Barinova1 S Tsibulya3 N Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS 18Kutateladze str 630004 Novosibirsk Russia grigsolidnscru

2 Institute of Powder Metallurgy NAS B Minsk Belarus3 Boreskov Institute of Catalysis SB RAS Novosibirsk Russia

Tungsten-based materials are used for manufacture of electro-technical items spot welding electrodes spraying cathodes etc

The preparation of the high-melting materials is powerconsumptive as two-stage high-temperature sintering is used tungstenpre-sintering temperature is 1150 ndash 1300 C final tungsten sinteringtemperature is 2900 - 3000 C [1]

Metal additives with a lower melting temperature are introducedinto the high-melting material for sintering temperature reduction andsince the tungsten powder has a bad moldability level more plasticmetals such as copper nickel iron are introduced for the moldabilityimprovement

Tungsten ndash copper mixture has been studied the best so farThe mixture W-Cu sintering process research has shown [2] that

the product density depends on the initial powders dispersion degree andthe mixture composition So at the tungsten particles size 10-15 m themaximum densification is observed at the copper weight ration 50 The blend density sharply decreases with the copper content decrease(less than 35 ndash 40 wt) At the same time mixtures with the coppercontent not higher than 10 are needed Special methods have to beused for the preparation of the tungsten alloys

The active densification (from 44 till 12 ) is known to take placeat 1100 - 1200 C at sintering of mixtures W-20 vol Cu with tungstenparticles size lower than 1 m [3] Even higher densification speed isobserved in a blend attained with copper tungsten reduction whencomponents mixing practically achieves a molecular level [4] ie thesecond element concentration reduction is possible at tungsten particlessize decrease and homogeneous distribution of the both componentsThe original blends mechanical activation process [5ndash7] is very

38

perspective in this trend since grinding and formation of larger contactsurface between the original components take place during mechanicalactivation This process is especially effective at mechanical activationof solid and liquid metals and plastic ndash non-plastic metals pair Thecomposite nucleus (non-plastic component) ndash cover (plastic metal) canbe created in this case The possibility of chemical interaction onbetween tungsten and plastic metal the contact surface duringmechanical activation should be considered here

The work aim is to study structure and morphology of thecomposites formed at mechanochemical activation of the tungsten witha small content (till 10 ) of plastic metals both interacting (nickel iron)with it and not interacting (copper) with it The influence of the structureand morphology of the mechanocomposites on the processes of formingand sintering was studied

Powders of tungsten nickel iron copper were used forpreparation of mechanocomposites Mechanical activation of themixtures was carried out in a high energy planetary ball mill with watercooling in argon atmosphere (drum volume ndash 250 cm3 balls diameter ndash5 mm the load ndash 200 g the sample - 10 g the velocity of rotation of thedrums around a common axis 1000 rpm)

X-ray analysis was carried out with diffractometer D8 AdvanceBruker (Germany) at the CuK radiation Research of the structure andmorphology of the mechanocomposites was carried out with thescanning electronic microscope (SEM) ldquoMira LMHrdquo with the add-ondevice for micro-x-ray analysis The electronic probe comprised 5 2 nmthe actuation area comprised 100 nm The research was carried out inmodes of registration of absorbed (AE) and backscattered (BSE)electrons and also of characteristic radiation of tungsten copper nickeland iron The sintered materials research is carried out with themetallographic microscope MEF-3 (Austria) at zoom times200 and times950

The compressibility was determined via density in compliancewith the ISO 3927-1985 of cylindrical samples with diameter 10 mmheight 12 mm pressed in a steel die-mold at pressure 200 400 600 and800 MPa The pressed samples were sintered in vacuum at temperatureof 1100 ndash 1450 C

Compression strength of mechanically activated blends wasdetermined via the samples of diameter 10 mm height 12 mm

39

transverse strength ndash via prismatic samples with height 5 mm width 10mm length 55 mm The tests were preformed on the testing machineldquoInstronrdquo with the loading speed 2 mmmin

Sintered samples microstructure was studied on metallographicsections etched with solution (10 g K3Fe(CN)6 10 g KOH 100 mlH2O) via metallographic microscope MEF-3 of the company ldquoReihertrdquo(Austria)

Mechanical activation was carried out in two stages for attainingmechanical composites tungsten ndash metal (Cu Ni Fe) The first stagesaw grinding only tungsten for 4 min At the second stage 7 ndash 10 copper (nickel iron) was added and joint mechanical activation wascarried out for 1 ndash 2 min

In compliance with the x-ray data the initial tungsten sample is awell-crystallised powder (Fig 1a) The intensity of the diffraction peaksshows the texture (of the preferred orientation) presence in trend 110The X-ray pattern of the tungsten samples activated during 4 min (Fig1b) has widened peaks The X- ray analysis shows that widening ismostly caused because of micro-defects in the tungsten structure (at thelarge particles sizes retaining) It should be also noted that thedistribution intensity of the peaks shows the texture absence (the equalparticles distribution in powder from the point of view of theircrystallographic orientation)

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

Ia

u

2 Theta degree

110

200

211

220

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

Ia

u

2 Theta degree

a bFig 1 X-Ray patterns for initial W (a) and activated for 4 min (b)

40

During the mechanical activation in a high energy planetary ballmills plastic metals tend to stick to balls and the drums walls even atshort-time activation because of that they were introduced to the blendsinto the already activated for 4 minutes tungsten and the mixture wastreated for 2 minutes more

The different X-Ray patterns were received for the samples withCu Ni Fe additives (Fig 2) The second metal phase is seen to bepresent in a well-crystallised form besides the phase W in all cases thecopper picks relative intensity is however considerably higher than thenickel picks intensity that in turn exceeds the iron reflection intensityFormation of intermetallic compounds in the X-ray-amorphous state oncontact surface WNi WFe can be supposed to be possible forchemically interacting metal pairs (tungsten ndash nickel tungsten ndash iron)X-Ray research data are indirect confirmation of this supposition Thesedata have shown that mechanochemical efforts donrsquot allow to receivehomogeneous distribution of copper in the tungsten matrixMechanocomposites W + 10 Cu is arranged in compliance with theldquosandwichrdquo principle where copper phase of micrometric size is locatedin the tungsten die (Fig 3)

The second metal phase is seen to be present in a well-crystallisedform besides the phase W in all cases the copper picks relative intensityis however considerably higher than the nickel picks intensity that inturn exceeds the iron reflection intensity Formation of intermetalliccompounds in the X-ray-amorphous state on contact surface WNiWFe can be supposed to be possible for chemically interacting metalpairs (tungsten ndash nickel tungsten ndash iron) X-Ray research data areindirect confirmation of this supposition These data have shown thatmechanochemical efforts donrsquot allow to receive homogeneousdistribution of copper in the tungsten matrix Mechanocomposites W +10 Cu is arranged in compliance with the ldquosandwichrdquo principle wherecopper phase of micrometric size is located in the tungsten die (Fig 3)Electron microscopy and X-Ray research of mechanocomposites forinteracting metals (W + 10 Ni) has shown homogenous nickeldistribution

41

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Ia

u

2 Theta degree

Cu

а

40 50 60 70 80 90

0

1000

2000

3000

4000

Ia

u

2 Theta degree

Ni

b

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Iau

2 Theta degree

Fe

c

Fig 2 X-Ray patterns for mechanocomposites W (4 min) + additives Cu(a) Ni (b) Fe (c) (2 min)

The received result allows to suggest that metals distributionhomogeneity depends on the thermodynamical parameters of theirmixture (Нmix(W-Ni) = - 2 kJmol Нmix(W-Cu) = + 10 kJmol [8])and on a possibility of the chemical interaction between them The thinlayers of intermetallic compounds form on the continuously renewingcontact surface in the systems W-Ni and W-Fe for this time period (1-2min) and because of distance these thin layers do not manage to form acrystalline phase that could be fixed in X-Ray way

42

а bFig 3 Micrographs of the mechanocomposites W-Cu (a) W-Ni (b) in

characteristic radiation Cu and Ni

The research of compressibility of various mechanocompositeshas shown that non-interaction metals (W-Cu) couldnrsquot compressed andthe compressibility of the interaction metals (W-Ni W-Fe) depends ofthe contents of additives Research of compressibility of mechanicallyactivated powders of various composition has shown that tungsten ndash10 iron mixture powder has the best compressibility level andtungsten ndash 7 nickel mixture powder has the least compressibility level(Fig 4)

But it should be noted that mechanically activated powderscompressibility level is not high moreover some mechanocompositesdo not have compressibility at specific pressure 200 ndash 300 MPa and thesamples layering is observed at pressure higher than 600 MPa Therelative density of the pressed samples is 50 ndash 78 It indicates at thenecessity of the additional lubricants introduction into the mechanicallyactivated powders for their compressibility increase

43

Fig 4 Tungsten-based mechanocomposites compressibility curve

For the powders compressibility improvement the lubricants areintroduced directly into initial mixture or plated to the press-mouldsurface for decrease of friction between the powder and the press-mouldwall and also between the powder particles The lubricant removaltemperature depends on the lubricant melting or dissociationtemperature The melting and boiling temperature or the lubricantsdissociation temperature generally used in powder metallurgy are givenin table 1 [9]

Stearates especially zink stearates have the leading place Therest lubricants have not got such a wide use since residual remains aftertheir removal [10]

Nowadays nylon-binding-based lubricant has been developedabroad This nylon binder is introduced during the charge mixingprocess and needs warm pressing [11-14] Such a lubricant allowsattaining high (θ is no less than 95 ) density of iron-based materials

The lubricant addition as a rule retains ~1 wt as higher contentleads to the pressing growth if the lubricant is present in the sinteringprocess till the sintering temperature

The lubricant burning-out process is carried out in the protective-reducing atmosphere in separate furnaces or in a sintering furnace (in thearea separated from the sintering area) The lubricant burning-outtemperature is as a rule not high and comprises 600 ndash 800 C

44

Table 1 Temperature of melting and dissociation of solid lubricants

Lubricant Lubricant formulaMeltingpoint С

Boiling ordissociation

point СZink stearate Zn(C18H35O2)2 140 335Calcium stearate Ca(C18H35O2)2 180 350Aluminium stearate Al(C18H35O2)2 120 360Magnesium stearate Mg(C18H35O2)2 132 360Plumbum stearate Pb(C18H35O2)2 116 360Lithium stearate LiC18H35O2 221 320Stearinic acid CH3(CH2)16CООH 694 360Oleinic acid С8Н17СНСН-

(СН2)7СООН13 286

Benzol acid С6Н5СООН 122 249Hexoic acid СН3(СН2)4СООNН2 -4 205Paraffin From С22Н46 till

С27Н56

40-60 320-390

Molybdenum disulfide MoS2 1185 -Tungsten disulfide WS2 1250 -Manganous sulphide MnS 1655 -Graphite С (crystalline) 3500 -Molybdenum trioxide MoO3 795 -

During one-component materials heating till 100 ndash 150 C thechange of the contact character between the particles connected withwater evaporation and elastic stress relief tale place As a result somecontact areas rupture and as a consequence general inter-particlecontact surface decrease are possible

The elastic stress relief is ended the further gases are removedand burning-out of the lubricants and binders introduced to the powdertake place during heating from 150 C till the temperature comprising 40ndash 50 of the metal melting temperature The oxide films reduction andnon-metal contact replacement with a metal one take place at highertemperatures although visible pressings density change does not takeplace

45

This work saw lubricants introduction during mechanicalcomposite formation zink stearate stearinic acid and lauric acid wereused The lubricants were introduced in amount of 0 1 0 2 0 3 0 5wt During mechanical activation metal ndash organic acid the latter ismelted (the melting temperature is lower than 70 C) and thus it wets themetal surface and flows with the formation of a larger contact surface Incase of good wettability and sufficient amount of the low-meltingconstituent all the solid-phase surface becomes contact ie mixturenucleus (metal) ndash cover (organic substance) is formed [15] Thecompressibility level has to be naturally higher in this case andmechanochemical approach allows a substantial reduction of plasticizingagentsrsquo concentration

Research of compressibility of powders with lubricants has shownthat Zink stearate has the least influence in comparison to otherlubricants used (Fig 5)

Fig 5 The compressibility curves of the mechanocomposites W-Fe with thelubricant 1 ndash zink stearate 2 ndash lauric acid

The lubricant content increase leads to the mechanically activatedpowders compressibility improvement (Fig 6) but at the lubricantcontent more than 0 3 the samples destruction takes place at sinteringbecause of intensive gas release Plasticizing agents introduction hasallowed mechanical composites formation also for non-interactingmetals (tungsten ndash copper) (Fig 6 7)

46

Fig 6 The compressibility curve of the mechanically activated blend W-Cuwith stearinic acid 1 ndash 0 1 2 ndash 0 3 3 ndash 0 5

Fig 7 The compressibility curves of the mechanically activated blend W-Cuwith lauric acid 1 ndash 03 2 ndash 05

Lauric and stearinic acids additives allow the pressings densityincrease by 25 ndash 40 (Fig 5 8)

Research of density of sintered samples of mechanocomposite hasshown that the density of the samples from mixtures tungsten ndash ironpressed at 400 and 600 MPa does not practically change after sinteringat 1250 C (Fig 9 line 2 5) and at 1450 C the samples density decreases(Fig 9 line 3 6) Mixtures tungsten ndash nickel are subject to a substantial

8

9

10

11

12

200 400 600

De

nsi

ty g

сm

3

Pressure МPа

1

2

11

115

12

125

13

200 300 400 500 600

10Fe+W

10Ni+W

De

nsi

tyg

cm

3

Compacting pressure MPa

47

shrinkage (Fig 10) and density of the samples of W-Ni pressed at 400MPa is 146 gcm3 after sintering at 1250 C and 147 gcm3 at 1350 CSintering temperature increase till 1450 C leads to samples shrinkinglevel reduction and density does not exceed 117 gcm3

Fig 8 The compressibility curves of blends W + 10 Fe and W-10 Ni withaddition of 1 of stearinic acid

Fig 9 Relation of density of mechanically activated blends W + 10 1 ndash afterpressing at 400 MPa 2 ndash pressing at 400 MPa sintering at 1250 ordmC 3 ndashpressing at 400 MPa sintering ndash at 1450 ordmC 4 ndash after pressing at 600 MPa 5 ndashpressing at 600 MPa sintering at 1250 ordmC 6 ndash pressing at 600 MPa sintering at1450 ordmC

10

11

12

13

14

200 400 600

Pressure МPа

Density

gс

m3

1

2

3

0

2

4

6

8

10

W+Fe

De

nsityg

cm

3

12 3

4 5 6

48

0

3

6

9

12

15

400 МPа 600 МPа

De

nsity g

сm

3

Fig 10 Relation of density of mechanically activated blend W + 10 Ni 1 ndashafter pressing 2 ndash pressing sintering at 1250 C 3 ndash pressing sintering at 1350C 4 ndash pressing sintering at 1450 C

Moulding pressure increase till 600 MPa practically does not

influence the sintered samples density Density reduction of the samples

sintered at 1450 C is apparently explained with dissociation of oxides

and other compounds of tungsten and nickel

Sintering at 1450 ordmC of blends W-Ni leads to meltback and

samples form loss thus sintering should be carried out at temperature

not higher than 1350 ordmC

Tungsten-based mechanocomposite strength research has shown

that strength has a direct relation to their density (Fig 11) The blend

tungsten ndash iron (870 MPa) has the minimal strength

The microstructure analysis has shown that in case of sintering at

temperature 1250 C tungsten ndash nickel have a very fine dispersed

structure (Fig 12) Coagulation of nickel insertions located at the base

grains boundaries in tungsten ndash nickel grains growth take place with

sintering temperature increase

49

0

100

200

300

400

500

600

700

800

900

1000

1100

1 2

Ela

stic

lim

it of

com

pre

ssio

n

МP

а

I - pressure 200 МPа

II - pressure 400 МPа

III - pressure 600 МPа

1 - sintering temperature 1250оС 2 - sintering temperature 1350

оС

I

II

III

Fig 11 Influence of attaining modes of samples from mechanically activatedblend tungsten + 10 nickel on their strength

Substantial grain growth large porosity formation nickel phase

particles growth take place in blends sintered at 1450 C eutectic that is

more visible in the blend tungsten ndash nickel is formed at tungsten grains

boundaries

Conclusions

The conducted research has shown that homogenous copper

distribution is failed to be carried out in tungsten with short-term

mechanical activation method for interacting metals of W-Cu system

These mechanically activated samples can be not compacted (moulded)

50

a b

c dFig 12 Microstructure of mechanically activated blends W-Ni sintered at 1250C (a b) and 1350 C (c d) a c ndash times200 b d ndash times950

Homogenous distribution of nickel and iron in tungsten is ensuredwith short-term mechanical activation in systems from interactingmetals The attained samples are formable mechanically activatedpowders compressibility has however been found to be not high therelative density of the pressed samples is 50 ndash 78 and that points atnecessity of additional lubricants introduction into powders for theircompressibility improvement Lubricants introduction allowed ensuringmoldability of immiscible system tungsten ndash copper and densification ofpressings by 25 ndash 40 - for interacting metals

Density of samples from blends tungsten ndash iron does notpractically change after sintering at 1250ordmC and is decreased at 1450 ordmCBlends tungsten ndash nickel are subject to a substantial shrinkage during

51

sintering Sintering temperature increase till 1450 ordmC also leads to theshrinkage level decrease Strength of sintered blends from mechanicallyactivated tungsten-based powders depends on density and kind of theadditive Grain size dispersivity and type of additive location in theblend structure from mechanically activated powders depend on thesintering temperature

AcknowledgementsThe work was carried out within the framework of Fundamental

Research Programme of Russian Academy of Sciences ldquoElaboration ofchemical substances attaining methods and new materials creationrdquoproject No 1821 ldquoElaboration of tungsten mechanical composites-basedhigh-density alloys creation basicsrdquo

References1 IM Fedorchenko IN Francevich ID Radomyselskiy at al

Powder Metallurgy Materials technologies properties andapplications Kiev Naukova dumka ndash 1985 ndash 624 P

2 VN Eremenko JV Najdich IA Lavrinenko Sintering in thepresence of liquid metal phase Kiev Naukova dumka ndash 1968 ndash 122P

3 VV Panichkina MM Sirotuk VV Skorohod Powder Metallurgyndash 1982 - 6 ndash P27-31

4 VV Skorohod YuM Solonin NI Filippov at al PowderMetallurgy ndash 1983 - 9 ndash P9-13

5 Kim JС Moon IН Nanostruct Mater 1998 Vol 10 No 2 P283-290

6 Moon IH Kim EP Petrow G Powder Metallurgy 1998 Vol41 No 1 P 51-57

7 Kim JC Ryu SS Kim YD Moon IH Scripta Mater 1998 Vol39 No 6 P 669-676

8 FR de Boer R Boom WCM Mattens AR Miedema andAK Niessen Cohesion in metals (Cohesion and structurevol 1) (Elsevier Amsterdam 1988) pp 758

9 Hausner H Handbook of Powder Metallurgy Chemical PublishingCo New York 1973

10 Moyer KH Intern J Powder Met 1971 - 7 Р 33

52

11 US patent В 22 F 100 5368630А Powder Metallic Blend with abinder for densification at the set temperature Journal Inventions ofcountries worldwide 1996 1

12 US patent В 22 F 100 5429792 Metal powder content containing a binder for pressing at elevated temperatures JournalInventions of countries worldwide 1996 7

13 US patent В22F 100 (11) 52980555 (40) 940329 laquoIron-basedpowder mixtures with a binding lubricantraquo 1995

14 US patent В 22 F 100 95372138 (5484469А) laquoMetal powder content and a method of a sintered part manufacture from itraquo 1995

15 TF Grigoryeva AP Barinova NZ Lyahov Mechanochemicalsynthesis of metal systems Novosibirsk Parallel ndash 2008 ndash 311 P

34

THE DETERMINATION OF THE KINETIC FUNCTIONSTRUCTURE FOR THE HIGH-TEMPERATURE SYNTHESIS IN

THE MECHANICALLY ACTIVATED MIXTURE 3Ni-Al

VYu Filimonov1 MA Korchagin2 EV Smirnov1NZ Lyakhov2

1Altai State Technical University Barnaul2Institute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirskvyfilimonovramblerru

The peculiarities of heating-up and phase formation in themechanically activated powder mixture 3Ni + Al reacting in the thermalexplosion mode have been experimentally investigated The self-heatingin the mixtures was studied using a specially designed SHS-reactorusing a technique presented in [1] Tungsten-rhenium thermocouples of100 microm diameter were used to control the temperature and to recordthermograms Preliminary mechanical activation was carried out using aplanetary ball mill of AGO-2 type in an atmosphere of argon under theenergy of 40g (centrifugal acceleration of balls 400 ms2) with varyingtime of the activation process The reactant mixtures were preparedusing the aluminum powder PAndash4 particle size 5 divide 60 microm and thecarbonyl nickel powder PNK-1L5 particle size 1 divide 10 microm

The primary goal of this work was to determine the activationenergy and the structure of the kinetic function during the heat evolutionin the system as a result of the phase formation At the adiabatic stage ofheating a system of equations of the temperature increase and thedynamics of the degree of transformation was considered [2]

0 expdT E

k fdt RT

(1)

f

RT

Ek

dt

d

exp1

(2)

The initial conditions are as follows 00 t 0TT where

T temperature of the reacting mixture degree of transformation

t time 0k 1k exponential factors E activation energy f -

35

kinetic function The search for )(f was performed in the known class

of functions [3]

exp

1nm

f

(3)

At the first step of analysis of the experimental thermograms theeffective activation energy of the phase formation was determined from

the curvature of the experimental plot ln 1dT dt f T Based on the

results of 6 measurements and using the slope of the fitting curvepassing through the point of the minimum curvature the effectiveactivation energy was determined which turned out to be anomalouslylow and equal to E = 95plusmn2 kJmol It was found that the experimental

results are best fitted with a function 1n

f where

09 015n [4] Fig1 shows the results of integration of (11) with the

determined parameters

Fig1 Results of integration of (11) -1 experimental thermogram -2

Since the interaction of the reactants is described by the law ofhomogeneous kinetics we suggest that during thermal explosion in themechanically activated mixture of the composition under study thesynthesis occurs through homogeneous regrouping of atoms of the initialreactants without formation of dense diffusional layers hindering thereaction The latter is possible due to high concentrations of defects andinternal stresses formed as a result of intensive plastic deformation of theinitial reactants during mechanical activation

36

References1 Filimonov VY Evstigneev VV Afanasev AV and Loginova MV

Thermal Explosion Ti + 3Al Mixture Mechanism of PhaseFormation International Journal of Self-Propagating High ndashTemperature Synthesis-2008- vol 17-2рр 101-105

2 Aldushin AP Martemyanova T M Merzhanov A G Propagationof the front of an exothermic reaction in condensed mixtures withthe interaction of the components through a layer of high-meltingproduct Composition Combust Explos Shock Waves19728(2)159

3 M I Shilyaev V Е Borzykh A R Dorokhov and V EOvcharenko Determination of thermokinetic parameters from theinverse problem of an electrothermal explosion Combust ExplosShock Waves 1992 28(3)258

4 MA Korchagin VYu Filimonov EV Smirnov NZ LyakhovThermal explosion of a mechanically activated 3Ni + Al mixture Combustion explosion and shock waves 2010 v 46 1 pp41-46

14

MODERN METHODS OF RHENIUM DETERMINATION

OV Evdokimova NV Pechishcheva KYu ShunyaevInstitute of Metallurgy of UB RAS

101 Amundsen st Ekaterinburg Russiashunuralru

IntroductionRhenium due to its unique properties is the promising metal

widely used in various industries At present day the main areas ofapplication of rhenium is the production of catalysts for the petroleumrefining industry and refractory alloys used for turbines manufacturing[1]

The great demand for this element requires large amounts of itsproduction There is a need extracting rhenium even from industrialwaste water from plants [2] due to the high cost and its low content innatural materials

This situation stimulates the development (or modification) ofmethods of analytical control of various nature materials

The content of rhenium in rhenium-containing materials bothnatural and technogenic and contect of accompanying to rheniumelements vary in a wide range of concentrations from 10-7 to tens ofpercent

Earlier the following methods were used for the determination ofrhenium spectrophotometry gravimetry kinetic electrochemicalextraction-fluorimetric methods X-ray fluorescence analysis [3] Themain disadvantages of mostly methods for determining rhenium are thelow sensitivity the bad reproducibility of results the influence ofaccompanying elements Ag W Mo Pt Cu Fe and etc

In modern analytical practice the following methods for therhenium determination are used inductively coupled plasma atomicemission spectroscopy (AES ICP) inductively coupled plasma - massspectrometry (ICP-MS) [4] electrochemical methods [1] X-rayfluorescence analysis and spectrophotometric methods do not lose theirrelevance [1] they have undergone significant modifications recently

15

Inductively coupled plasma atomic emission spectroscopy(AES ICP) is widely used for the rhenium determination in mineral rawmaterials and products of metallurgy production This method allows todetermine up to 10-4 rhenium The advantage of AES ICP is the highstability and reproducibility of results absence of chemical influences

However analysis of more complex objects such as metallurgicalproducts is a not easy task because the lines of rhenium emission areoverlaped with the lines of accompanying elements in samples So thelines of Mo (221427 nm) W (221431 nm) Fe (227519 nm) whichmay be present in the samples in large quantities are overlaped to themost intense lines of rhenium (221426 nm and 227525 nm) Thisproblem requires the development of new methods of samplepreparation and selection of optimal conditions for determination ofrhenium by atomic emission spectrometres

Also a significant disadvantage of this method is the small rangeof certificated reference materials So there are a limited number ofRussian rhenium standard materials with certified value of the rheniumcontent It is molybdenum and copper-molybdenum ores andconcentrates in which the rhenium content is in the range ofconcentrations from 000047 to 00221

In most cases analysts develop the synthetic mixture to monitorthe rhenium content in the analysis of specific samples of complexcomposition This mixture is similar to composition to the matrix of theanalyzed samples consisting of rhenium ions and other ions with agiven concentration For example the authors [5] to develop a techniquefor rhenium determining together with platinum and palladium in thesamples of spent catalysts by AES-ICP applied a synthetic mixtureprepared on the basis of aluminum oxide and standard solutions of Pt(IV) Pd (II) Re (VII)

One of modern methods and the most sensitive methods for thedetermination of rhenium is inductively coupled plasma - massspectrometry (ICP MS) [4 6 7 8] These days ICP MS withseparation and concentration allows to measure rhenium at lower thanseveral ngg However ICP MS performance in analyses of complexsamples is commonly affected by matrix effects and polyatomicinterference and signal drift High levels of salt solutions content cause

16

plugging of sampling orifice with decrease in analytical signal inaddition many spectral interferences may occur [6]

For the rhenium determination in molybdenite by ICP MS shouldbe use large dilution of sample to reduce the matrix influence and reducethe salts influence However this approach is not feasible in the case ofhigh levels of molybdenum and relatively low levels of rhenium in theanalyzed objects The most effective way to minimize the matrix effectsis separation of rhenium from the matrix Often for this purposeextraction by organic solvents [6] sorption by anion-exchangers [8] areused

Recently X-ray fluorescence analysis becomes more popular Itis rapid and is often used for mass analysis The advantage of thismethod is the possibility of direct determination of rhenium in the solidsamples in water solutions [9 10] in the biological samples (plants) [2]

However the method is not without disadvantages firstly thedetection limit of rhenium by X-ray fluorescence analysis is low and isonly 005-01 secondly there are only few the standard materials witha high rhenium content and thirdly the influence of interfering elementsin the sample related to determination of rhenium

Using the concentration can not only reduce the detection limitbut also in the same time solve and reduce the influence of interferingions For the concentration of rhenium in X-ray fluorescence analysis isoften used sorption of rhenium in the form of perrhenate-ions [9 10]

The authors [11] describes a problem related to the developmentof rhenium-containing standard materials by traditional hightemperature approach for X-ray fluorescence analysis Thus high-temperature studies of MoO3-ReO3 which could be served ascomparison materials for the rhenium determination by X-rayfluorescence analysis showed that 50-90 of rhenium is lost duringcalcination of mixtures it indicates the impossibility to use them fordevelopment of standard materials In the paper [11] the method ofpreparing rhenium glassy reference samples (10 - 50) on the basis ofBi2O3 and B2O3 is described The developed method allows to determinerhenium in the range of 001-10 [11]

17

Electrochemical methods in particular the electrostrippingvoltammetry (ESV) occupy a significant place in the analyticalchemistry of rhenium [12 13] This method allows to determine up to10-6-10-5 of rhenium

To avoid the effects of many electropositive components (Mo WCu Ag Au) which may interfere to the rhenium determination by ESVit has been proposed the sorption concentration of perrhenate ions on thesurface of activated charcoal (BAU) [12 13]

The most widely used techniques determine the 10-2 - 10-5 ofrhenium is spectrophotometric method The advantages of this methodare simplicity low cost equipment and a relatively high sensitivitySpectrophotometric method is based on the formation of coloredcomplex compounds of rhenium with organic and inorganic ligands [1]Photometric methods with thiocyanate ion thiourea are widely spread[14 15 16] Development of spectrophotometric methods for rheniumdetermination is largely due to the searching and using of new reagentsIn [17] for the extraction-photometric determination of perrhenate ionsin the form of ion associates the basic polymethine dyes derivatives of133-trimethyl-3H-indole have been offered but the influence ofoxyanions of tungsten and molybdenum is not excluded [17]

The disadvantage of the spectrophotometric methods is the needfor prior separation of rhenium from a number of interfering elements(Mo W Cu) that it is achieved by concentrating perrhenate-ions bysorption or extraction

Over the past decade main changes in the methods of rheniumdetermination related with the improvement stadium of samplepreparation transfer the sample into an analytical form modification ofknown methods and reagents (eg creation of new facilities developmentof new reagents for measurements) and conditions of analysis

In general in the literature a large number of works are relatedwith the separation of rhenium from the analyzed solutions and theseparation of rhenium (VII) from interfering elements by using newtypes of extractants and new sorbents is given Used extractants andsorbents as well as the optimal conditions for extraction and sorption ofrhenium are presented in Table 1 and 2 respectively

18

Extraction plays a dominant role in the methods of separationand concentration of rhenium

In most cases in the hydrometallurgical processing of rhenium-containing products in the acidic solutions ReO4

- are formed Forperrhenate ions extraction the anion-exchange reagents or extractants ofneutral type are often used The literature contains information on theextraction of rhenium (VII) by various amines and quaternaryammonium compounds [18 19 20] Efficient extractants of rheniumfrom acidic solutions are neutral organophosphorus compounds (tributylphosphate alkylphosphineoxides their derivatives) [21 22] a variety ofsolvent mixtures (tributyl phosphate + trioctylamine [23]) theextractants of neutral type such as ketones and aliphatic alcohols [1624 25]

Alcohols ketones and ethers are more selective having higherspeed separation of organic and aqueous phases as well as higherchemical resistance and lower cost compared with amines andorganophosphorus compounds but inferior to them in the extractioncapacity for rhenium (VII) [16]

Thus for perrhenate ions extraction aliphatic alcohols with 7-10carbon atoms in the aliphatic chain are well proven that can extractmore than 98 of rhenium from sulfuric acid and hydrochloric acidsolutions In the case of alcohol there is no need to use solvents andmodifiers what simplifies their use in extraction processes [16]

The efficiency of rhenium extraction into organic phase by aminesdecrease as follow quaternarygt tertiarygtsecondarygtprimary Amongthem secondary and tertiary amines are widely used as efficientextractants of rhenium from acidic solutions Perrhenate ions areextracted by amines in a wide range of pH For systems of amine - low-polar diluent - H2SO4-ReO4-H2O the formation inverse micelles istypical in the organic phase Acid ions and anionic complexes arelocated inside the aqueous core of the micelle with the metal ioncoordinates the polar functional group of amine [19 20]

It should be noted that the extraction by amines is complicated bythe use of solvents the nature of which depends on the solubility ofamines and their extraction capacity So low-polarity solvent toluene incontrast to the non-polar kerosene enhances the polarity of anionic saltsof amine which increases the reactivity of the extractant to the anion

19

exchange of inorganic acid to extractable anionic rhenium complexes[18]

Tertiary amines are the most effective extractants for rhenium(VII) However in paper [18] it is shown that the secondary amine(diisododecylamine) gives advantage to the tertiary amines on therhenium extraction efficiency from sulfuric acid media It can beexplained by the influence of steric factors and smaller rival extractionof mineral acids by secondary amines [1]

Most papers are related to the rhenium extraction from acidicsolutions but the extraction of rhenium from alkaline medium whichare formed after leaching of ores concentrates also represents a difficultproblem In the paper [23] rhenium extraction from alkaline solutionscontaining also molybdenum by solvent extraction using a mixture oftributylphosphate (TBP) and trioctylamine (N235) is describedMolybdenum which is also extracted by solvents in small amountsinterferes to the extraction of rhenium

Over the last decade most works refer to the development offundamentally new classes of extractants for perrhenate ions [26 2728 29] such as encapsulating ligands (cryptands and podands)macrocycles crown ethers These ligands can interact with ReO4

minus byboth the electrostatic interaction between ReO4

minus and protonated ligandand the hydrogen bond formation compared with simple open-chainligands If the complex between ReO4

minus and ligand has highhydrophobicity ReO4

minus in an aqueous solution may be separatedeffectively by a solvent extraction technique [30]

Crown ethers extract rhenium (VII) in the presence of potassiumor sodium in the form of K(Na)LReO4 (L-crown-ether) into the organicphase (12 - dichloroethane chloroform) [31 32] In the paper [31] theextraction perrhenate-ions by 3m-crown-m-ethers (m = 56) ether and itsmono-benzo-derivatives in 12-dichloroethane are described

Podands are analogues of crown ethers containing terminalphosphoryl ligands in their polyether chains they are used for theextraction of rhenium (VII) The efficiency of extraction by phosphorylpodands depends of the following factors the number of oxygen atomsin the polyether chain molecules the number of donor centers in themolecule of podands hydrophobicity of the reagent molecule the size offorming cycles the nature of substituent at the phosphorus atom Studies

20

have shown that phosphoryl podands with three oxygen atoms in thearomatic polyether chain combined with the phosphoryl group bydimetilen or o-phenylene fragments have high extraction ability forrhenium from sulfuric acid solutions [32]

In the paper [30] authors mark another type of podands such aspodands with nitrogen donor ligand -N N N `N`-tetrakis (2-pyridymethyl) -12-ethylendiamine (TREN) and its hydrophobicanalogs which also allow to extract perrhenate ions from highly acidicenvironments

Perrhenate is characterized by its ability to undergo a change ingeometry specifically from tetrahedral to hexagonal in the presence ofdonor ligands (eg acetonitrile triphenylphosphine) Protonationchanges the electron density present on the oxygen atoms Beer et al[33] suggested that the tripodal ligand L1 would be suitable for thebinding and extraction of perrhenate anion This ligand (Fig 1) basedon the combination of tris(2-aminoethyl)amine and crown ether motifswas found to complex sodium cations and to extract perrhenate anionsfrom aqueous solutions into an organic phase

Atwood and co-workers developed calixarene-type ligand L2(Fig 1) that specifically extracts perrhenate from water solution into anorganic phase The selectivity for extractions decreases as followTcO4

minus ge ReO4minus gt ClO4

minusgtNO3minus gtSO4

2minus gtClminus This selectivity pattern isattributed to a combination of charge size and shape Efficientextraction is observed at high and neutral pH the molar ratio ofligandperrhenate ion = 14 [33]

L1 L2Fig 1 Tripodal ligand L1 and calixarene-type ligand L2 for perrhenateextraction

21

Schiff-base macrocycles are used as a new conjugatedmacrocycles for perrhenate ions Thus a series of amino-azacryptands(L3ndashL16) for encapsulation and extraction of the oxoanions perrhenate(Fig 2) from aqueous solution were proposed by the authors [34]Thecomplexation amino-azacryptands L to ReO4

- is via hydrogen-bondedinteractions

Fig2 Amino-azacryptands (L3ndashL16) for encapsulation and extraction of theoxoanions perrhenate

Thus the main characteristics of the compounds for the effectiveperrhenate ions extraction as follows

Energy coordination of ligand with ReO4- should be higher than

the energy of perrhenate ion hydrationThe interaction between the ligand and perrhenate ions an

electrostatic interaction or the formation of hydrogen bonds Functional ligands to be a suitable size (volume of the cavity

should be more than 736 Aring3) shape electronegativity andhydrophobicity

Ligand should be protonated

22

Table 1 Characteristics of extractants for rhenium extraction

Extractant

Analysis objectComposition of

the initialsolution

Extractonconditions

Interferinginfluences

Aliphatic alcoholswith C 7-10

1-Heptanol 4-Heptanol 1-octanol 1-decanol 4-decanol 2-Heptanol 3-Heptanol

3-octanolback-extractant

NH4OH

Solutions HCland H2SO4

Т=293КTime of phase

contacttex = 5 min

organic phase toaqueous

(OL = 11)4 steps of

extraction 2stripping

Coextractionof mineral

acidsincomplete

re-extractionof Re (VII)

1

OctanolSolutions ofHNO3 and

H2SO4

Т=286-290Кtex = 10 min OL

= 11

Coextractionof HNO3

H2SO4

2

Basic polymethinedyes (derivatives of133-trimethyl-3H-

indole) astrazon violet

Aqueous andaqueous-organic

solution

Т=293КрН=6

tex = 10-30 secextractant mixture

toluene +dichloroethane

(1 1)

do notinterfere

3000-5000fold excess ofS04

2- CO32-

300- HPO42-

MoO42-

WO42-

10-20 S2O32-

Cr2O72- IO3

-metal ions as

sulfates

3

Secondary(diisododecylamine)and tertiary amines

(dioctylamin andtrioctylamine)

Solutions H2SO4

Т=293КA wide range of

pH

tex=5-7 mindiluent - toluene

-

4N-benzoyl-N ndashphenyl-

hydroxylamine

Molybdenitedissolved inHCl HNO3

HCl 05 molltex=15 min

diluent chloroform-

23

Table 1 (continued)

Extractant

Analysisobject

Compositionof the initial

solution

Extractonconditions

Interferinginfluences

5

Phosphoryl podands

back-extractant H2O

СReinitial=2middot105 moll

aqueoussolutions of

salts of alkalimetals

solutions ofmineral acids

Т=286-291КОL=11

tex= 60 mindiluent

nitrobenzene12-

dichloroethanechloroform

toluene

-

6Triotylamine (N235)+

tributyl phosphate(TBP)back-extractant18 NH4OH

Alkalinesolutions

afterleaching

containingMo

СRe 01-165gl

T=293 КрН =90 OL=11

tex=10 мин20

triotylamine+30 tributylphosphate

diluentkerosene

-

7

Podand-type nitrogendonor ligand ndashNNN`N`-tetrakis(2-pyridymethyl)-

12-ethylendiamine (TREN)

Aqueoussolution

NH4ReO4

С =10-4 M

Ionic strength01M

pH=1-65diluent

chloroformОL=11tex=24 h

-

8

3m-crown-m-ethers(m=56) mono-benzo-

derivates12-dichloroethane

СReO4-=

0057-0060М

T=291-295Ktex=2h

-

24

Table 1 (continued)

The range of Re concentrations

RecoveryMethods for determination Ref

Recovery gt99

Determination from back-extractSpectrophotometric method with

thiourea reductant-Sn (II)wavelength of 390 nm

[16 24]

1

gt98 Spectrophotometric method [25]

2The range of Re concentrations

001-550 mcgml

Determination from extractSpectrophotometric method

wavelength of 540 nm[17]

3 -AES-ICP

Spectrophotometric methodwith thiourea

[18 1920]

4Mo W Fe are extracted 97

into the organic phase

Determination from aqua phaseafter extraction

ICP-MS[6]

5 -AES-ICP

Spectrophotometric method[21 22]

6 968Spectrophotometric method with

butyl rhodamine[23]

7 - AES-ICP [30]

8 -AES-ICP

Spectrophotometric method[31]

9 - ICP-MS [32]

25

Table 2 Characteristics of sorbents for rhenium sorption

Sorbent

Analysis objectComposition of the

initial solutionConditions of

sorptionInterferinginfluences

1

Activated carbons(BAU)

Eluenthot soda solution

nitrate media

gold ore raw

static conditionsа)рH =2-3

б) рH =15-25

volume ofsolution 10 mlmass of sorbent

03 g(SL=1333)t=10 min UV

a) electro-positive

components(Mo W Cu

Ag Au)b)1000 fold

excess ofMo W do

not interfere

2

Activated carbons- CN-G CN-PCU developed

from waste woodand grain

processingindustries

sulfuric acidsolutions with CRe= 002 gl pH =2

solid phasesliquid SL==105

t=5-7 days-

3

2 Carbon fibrousmaterials

modified withchitosan

neutral aquasolutions of

rhenium

static conditionsТ=286-289 КSL=11000

-

4

3 Weakly basicanion-exchangersАН-105 Purolite

A 170

mineralizedsulphite solutionsimulating rinsing

water(С Re=001-002

gl Mo Cu Fe As)

static anddynamic

conditionsSL = 1500

t = 150-200 min

-

5

Strongly-basicanion-exchangers

АВ-17(sorbent PAN-АВ-

17)

neutral or slightlyacid

solutions

dynamicconditionst = 20 min

The disks ofpolyacrylonitrilefiber filled resin

1000 foldexcess of

Fe Cu ZnPb Cd do

not interfere

6Lignin anion-

exchangerssolutions NH4ReO4

static conditionsSL=1400

t=15min-2 h-

26

Table 2 (continued)

NotesMethods for

determinationRef

1

а) Sorption capacity of BAU forRe СЕ=14175 mgg AC

Detectionlt 10

б) СЕ=00763 mmolg or 142mgg

The concentrations range of Re050 100 mgL in standard

solutions025 50 mgl in the presence

of Mo and W (11000)

a) Electrostrippingvoltammetry

b) X-ray fluorescenceanalysis

a) [12]b) [9 10]

2 -Spectrophotometric

method [35]

3 СЕ=179-185mggSpectrophotometric

method with ammoniumthiocyanate

[38 39]

4Full dynamic exchange capacity

114 mgg

Spectrophotometricmethod with ammonium

thiocyanatekineticmethod

[36]

5 -

Determination of Re bythe diffuse reflectance

spectra at 420 nmrhenium thiocyanate

complex in the presenceof tin (II)

[15]

6 СЕ=3427-2328 mgg Traditional polarography [37]

Sorption is one of the methods for separation of rhenium fromvarious solutions

Sorption of rhenium or perrhenate-ions often occurs on solidsorbents from the liquid phase The presence of a large specific surfacearea and a large number of functional groups of the sorbent determinesits high sorption properties with respect to rhenium (VII) Sorbentscontain the same functional groups (amino groups hydroxyl groups

27

phosphorus groups) as extractants for the selective extraction ofrhenium but these groups are fixed on solid carriers or support

Activated carbons (AC) of various brands are used the mostwidely [9 10] The use of activated carbons as sorbents due to the factthat they have a whole set of valuable properties highly polydisperseporous structure a complex but relatively easily controlled surfacechemistry and specific physical properties Activated carbons like manyother carbon materials exhibit high selectivity to perrhenate ions thatexplains the increased interest to this type of sorbents [12]

The characteristic distinction of carbonaceous materials is that thesorption of rhenium is not only due to complexation with surfacefunctional groups (containing oxygen nitrogen sulfur atoms) but alsodue to the interaction with carbon matrix

AC can act as anion-exchanger in acidic media and themechanism can be described by the following scheme

[C2+ OH-] + ReO4-= [C2+ ReO4

-] + OH-On the other hand the AC have significant reduction properties

the reaction of the electrochemical reduction of perrhenate ions in themethods of rhenium determination by voltammetry is based on this it[12]

It has been established [9 10] that ReO4- is sorbed from nitric

acid solutions almost entirely (95-99) by 10 minutes of UV irradiationwhile without irradiation this process takes up to 60 minutes Increasedsorption by UV authors attribute to the fact when UV radiationsolutions of rhenium (VII) salts rhenium (VI) and rhenium (V) areformed which are considerably faster adsorbed on AC

Extensive use of the AС is also associated with their low costActivated carbons - CN-G CN-P CU developed from waste wood andgrain processing industries have a low cost and their capacitance andkinetic characteristics slightly inferior to conventional AC (FAC) [35]

However from acid solutions together with rhenium molybdenumcan also be sorbed by the AC Furthermore perchlorates nitrates andother oxidants can reduce the adsorption capacity of coals by oxidationThe disadvantage of rhenium sorption by activated carbons is as followsa decreasing in their activity after 4-6 cycles of sorption-desorption [1]low mechanical strength [35]

28

Anion-exchange resin is the next width of use which havegreater selectivity and capacity compared with activated carbons Theseanion-exchangers synthesized on the basis of the gel and porouscopolymer of styrene and divinylbenzene From the neutral and acidicsolutions rhenium is adsorbed by low-basicity anion-exchangers with thefunctional groups of primary and tertiary amines In recent studiesconducted on the use of weakly basic macroporous anion-exchangerswith a more developed specific surface area (20-100 m2g) such asPurolite A170 with secondary amino groups [36]

Sorption by strongly-basic anion-exchangers compared to weaklybasic anion-exchangers has several advantages firstly they are almostquantitatively and selectively extract rhenium from solutions andsecondly work in a wide range of pH [15]

The rapid technique for perrhenate ions determination isdeveloped which allows to find their content directly on the site ofsampling for example in lake water using strongly-basic anion-exchangers AB-17 with the sensitivity of the technique is 2-3 orderslower than the best conventional spectrohotometric methods withthiocyanate [15]

Recently the authors of paper [37] synthesized new highlypermeable lignin anion-exchangers on the basis of lignin a naturalpolymer a component of terrestrial plants It is noted that the exchangecapacity of anion-exchangers for rhenium in lignin is much higher (EC =3427-2328 mgg) compared with conventional anion-exchangersHowever the time to reach equilibrium sorption by some anion-exchangers can reach from 2 up to 12 hours

Carbon fibrous materials modified with chitosan haveimproved kinetic (time and rate of sorption) characteristics comparedwith activated carbon and ion-exchange resins [38 39] Carbon fibrousmaterials modified with chitosan contain amino groups includingprotonated The increasing of the number of protonated groupscauses the increasing of sorption capacity of the material withrespect to the negatively-charged perrhenate-ions However thesorption capacity for rhenium (179-185 mgg) still yields to ligninanion in addition investigations were carried out of neutral aquasolutions of rhenium without interfering influences

29

ConclusionIn this review the methods for rhenium determination which over

the last decade have acquired great fame are presented A large numberof works related to improving methods for rhenium determining pointsto the increased interest to this metal The majority of the studies aimedto the selective extraction of rhenium from the analyzed complex objectsand the separating it from interfering elements in the matrix to increasethe sensitivity of the methods Most of the work related to the searchingof various organic reagents selective to rhenium (V VII) ions and usedin extraction and sorption processes In general the development ofrapid selective methods that can determine the content of rhenium in awide range of concentrations in various materials remains an actualproblem nowadays

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

Reference1 AA Palant ID Troshkina AM Chekmarev Metallurgy of

rhenium Science Moscow 2007 298 p2 LV Borisova YuV Demin NG Gatinskaya VV Ermakov

Determnation of rhenium in plant materials Journal of AnalyticalChemistry 2005 V60 1 P 97-103

3 LV Borisova AN Ermakov Analytical chemistry ofrhenium 1974 Science Мoscow 318 p

4 S Uchidaa KTagamia K Tabei Comparison of alkaline fusionand acid digestion methods for the determination of rhenium in rockand soil samples by ICP-MS Analytica Chimica Acta 2005 V535P 317ndash323

5 VI Manshilin EK Vinokurova SA Kapelushniy Determinationof Pt Pd Re mass fraction in dead catalyst samples using ICPatomic emission spectrometry method Methods and objects ofchemical analysis 2009 V41 P 97-100 (in Russian)

6 Jie Li Li-feng Zhong Xiang-lin Tu Xi-rong Liang Ji-feng XuDetermination of rhenium content in molybdenite by ICPndashMS afterseparation of the major matrix by solvent extraction with N-benzoyl-N-phenylhydroxalamine Talanta 2010 V81 P 954ndash958

30

7 T Meisel J Moser N Fellner Wo Wegscheider R SchoenbergSimplified method for the determination of Ru Pd Re Os Ir and Ptin chromitites and other geological materials by isotope dilutionICP-MS and acid digestion Analyst 2001 V126 P 322ndash328

8 K Shinotsuka K Suzuki Simultaneous determination of platinumgroup elements and rhenium in rock samples using isotope dilutioninductively coupled plasma mass spectrometry after cation exchangeseparation followed by solvent extraction Analytica chimica acta2007 V603 P129ndash139

9 NA Kolpakova AS Buinovsky IA Jidkova Determinationof rhenium by X-ray fluorescence analysis Proceedings ofuniversities Physics 2004 12 P147-149 (In Russian)

10 AS Buinovsky NA Kolpakova IA Melnikov Determinationof rhenium in the ore material by X-ray fluorescence analysis News polytechnic university 2007 V311 3 P92-95 (InRussian)

11 DV Drobot AV Belyaev VA Kutvitsky Development of aunified X-ray fluorescence method for the determination ofrhenium in multicomponent oxide compositions News highereducational institutions Non-ferrous metallurgy 1999 4 P23-24 (in Russian)

12 LG Goltz NA Kolpakov Sorption preconcentration anddetermination by voltammetry perrhenate ions in the mineralraw materials Proceedings of the Tomsk PolytechnicUniversity 2006 V 309 6 P77-80 (in Russian)

13 NA Kolpakova LG Gol`ts Determination in mineral rawmaterials by stripping voltammetry Journal of AnalyticalChemistry 2007V62 4 Р418-422

14 Wahi A Kakkar LR Microdeterminaton of rhenium withrhhodamine-B and thiocyanate usng ascorbic acid as the reductant Analytical sciences 1997 august V 13 P657-659

15 LV Borisova SB Gatinskaya SB Savvin VA RyabukhinAdsorbtion-spectrophotometric determination of rhenium fromdiffuse reflectance spectra of its complexes on a PAN-AV-17adsorbent Journal of Analytical Chemistry 2002 V572 P 161-164

31

16 AG Kasikov AM Petrova Extraction of rhenium (VII) byaliphatic alcohols from acid solutions Journal of AppliedSpectroscopy2009 V82 2 P 203-209 (in Russian)

17 ZhA Kormosh YaR Bazel` Extraction of oxyanions with basicpolimethine dyes from aqueous and aqueous-organic solutionsextraction-photometric determination of rhenium (VII) and Tungsten(VI) Journal of Analytical Chemistry 1999 V54 7 P 690-694

18 AA Palant NA Yatsenko VA Petrova Extraction of rhenium

(VII) from sulfuric acid solutions by diisododecylamine

Journal of Inorganic Chemistry 1998 V43 2 P 339-343 (inRussian)

19 NA Yatsenko AA Palant Micelle formation in theextraction of ions W (VI) Mo (VI) Re (VII) from sulfuric acidmedia diisododecylamine dioctylamine and trioctylamine Journal of Inorganic Chemistry 2000 V45 9 P 1595-1599 (in Russian)

20 N Latsenko AA Palant SR Dungan Extraction of tungsten (VI)molybdenum (VI) and rhenium (VII) by diisododecylamine Hydrometallyrgy V 55 Issue 1 Febr 2000 P 1-15

21 AV Antonov AA Ischenko The use of extraction in thedetermination of rhenium in the presence of molybdenumChemistry and chemical technology 2007V50 9113-116 (in Russian)

22 VF Travkin AV Antonov VL Kubasov AA IshchenkoExtraction of rhenium (VII) and molybdenum (VI)hexabutyltriamid phosphoric acid from the acidic environment Journal of Applied Chemistry 2006 V78 6P 920-924 (inRussian)

23 Cao Zhang-fang Zhong Hong Qiu Zhao-hui Solvent extraction ofrhenium from molybdenum in alkaline solution Hydrometallurgy2009 V 97 3-4 P 153-157

24 AG Kasikov AM Petrova Influence the structure of octanolon their extraction ability in acid solutions with respect to

32

rhenium (VII) Journal of Applied Chemistry 2007 V80 4 P689-690 (in Russian)

25 VF Travkin YM Glubokov Extraction of molybdenum andrhenium by aliphatic alcohols Metallurgiya2008 7 P21-25 (in Russian)

26 EA Kataev GV Kolesnikov VN Khrustalev MYu AntipinRecognition of perrhenate and pertechnetate by a neutralmacrocyclic receptor J radioanal Nuclchem 2009 2 V282 P 385-389

27 Bambang Kuswandi Nuriman Willem Verboom David NReinhoudt Tripodal Receptors for Cation and Anion Sensors Sensors 2006V 6 P 978-1017

28 Lagili O Abouderbala Warwick J Belcher Martyn G BoutellePeter J Cragg Jonathan W Steed Cooperative anion binding andelectrochemical sensing by modular podands PNAS April 162002 V 99 8 P 5001ndash5006

29 EA Kataev GV Kolesnikov EK Myshkovskaya Newmacrocyclic ligands based bipyrroles to bind perrhenate andpertechnetate ions radiation safety 2008 4 P16-22(inRussian)

30 Takeshi Ogata Kenji Takeshita Kanako Tsuda Solvent extractionof perrhenate ions with podand-type nitrogen donor ligands Separation and Purification Technology 2009V68 P288ndash290

31 Yoshihiro Kudo Ryo Fujihara Shoichi Katsuta Yasuyuki TakedaSolvent extraction of sodium perrhenate by 3m-crown-m ethers(m=5 6) and their mono-benzo-derivatives into 12-dichloroethane

32 Elucidation of an overall extraction equilibrium based oncomponent equilibria containing an ion-pair formation in water Talanta V 71 2007 656ndash661

33 AN Turanov VK Karandashev VE Baulin Extraction ofrhenium (VII) by phosphorylated podands Russian journal ofinorganic chemistry 2006 V514 P676-682 (in Russian)

34 E A Katayev Yu A Ustynyuk J L Sessler Receptors fortetrahedral oxyanions Coordination Chemistry Reviews 2006V250 P3004ndash3037

33

35 Leroy Cronin Macrocyclic and supramolecular coordinationchemistry Annu Rep Prog Chem Sect A 2004V100 P 323ndash383

36 ID Troshkina ON Ushakova VM Mukhin Sorption ofrhenium from sulfuric acid solutions by activated carbon News of higher educational institutions Non-ferrousmetallurgy 2005 3 P38-41 (in Russian)

37 AA Abdusalomov Sorption of rhenium from sulfuric acidsolutions of molybdenum Sorption and ChromatographicProcesses 2006 Vol6 V 6P 893-894 (In Russian)

38 NN Chopabaeva EE Ergozhin ATasmagambet AI NikitinaSorbtion of perrenate-anons by lignin anion exchangers Chemistry of solid fuel 2009 2 P 43-47 (in Russian)

39 AV Plevaka ID Troshkina LA Zemskova AV Voit Sorption ofrhenium chitosan-fiber materials Journal of InorganicChemistry 2009V54 7 P1229-1232 (in Russian)

40 LA Zemskova AV Voit YuMNikolenko ID Troshkina AVPlevaka Sorption of rhenium on carbon fibrous materials modifiedwith chitozan Journal of nuclear and radiochemical sciences2005 V6 3 P221-222

11

SYNTHESIS AND MICROSTRUCTURE DESIGN OF METALAND CERAMIC MATRIX COMPOSITES USING

MECHANICAL MILLING OF THEREACTANTSCONSTITUENTS

Dina V Dudina Oleg I LomovskyInstitute of Solid State Chemistry and Mechanochemistry

Siberian Branch of Russian Academy of Sciences Kutateladze 18Novosibirsk 630128 Russia

E-mail dina1807gmailcom

Mechanical milling greatly alters the state of a powder mixtureintroducing plastic strain and defects into the components andcreating new interfaces and mutual configurations of nano-sizedgrains This opens up a possibility to design microstructures of thecomposite to be synthesized by modifying the initial state of reactingpowder mixtures In certain mechanically milled reactive systemsone can observe microstructure refinement of the product [1-2] anincrease in the yield of the reaction [3] improved distribution of thephases [3 4] and lower reaction onset and developed temperatures[1-2] The presentation intends to demonstrate several successfulexamples of this approach for synthesizing composites by self-propagating high-temperature synthesis (SHS) shock compressionand electric-current assisted sintering

SHS in the mechanically milled Ti-B-Cu powder mixtures wassuccessfully performed and resulted in a TiB2-Cu composite [1-2]Compared to untreated powders in the mechanically milled mixturestitanium and boron started reacting at a reduced ignition temperaturewhile lower combustion temperatures developed in the combustionwave favored formation of submicron grains of TiB2

The powder particles brought to react with each other by shockcompression of the mixture may not fully transform into the productsif the loading is too short and the temperatures developed during thepressure rise and the post-loading period are not high enough In themechanically milled mixture the yield of the reaction can beincreased as a result of the decreased grain size of the initial reactants

12

and shorter diffusion distances (example Ti-Cu-B system partial andcomplete reaction of Ti and B [3])

When the sintering process ensures temperatures and timesufficient for the completion of the reaction in the mechanicallymilled mixture one can expect more uniform microstructure and finergrains of the products (example Ti-B-C system forming B4C-TiB2

phases during electric-current assisted sintering [4])Ball milling can refine the microstructure of the as-synthesized

composites and can be used to introduce additional quantities of theconstituents in the composite This was applied in order to develophighly conductive Cu-based composites One of the possible reasonsfor low conductivity of in-situ dispersion strengthened copper may bethe incompleteness of the reaction between the initial reactantswhich form solid solutions with the copper matrix In this regard weconducted an in-situ synthesis of TiB2-Cu composites starting fromthe powder mixtures with the limited content of copper ensuring ahigh probability of contact between the particles of titanium andboron and as a result their full conversion into the TiB2 phase Thenanoparticles were formed in a self-propagating mode in the ballmilled Ti-B-Cu powder mixture corresponding to the 57 volTiB2-Cu composition Afterwards in order to adjust the composition thecomposite was ldquodilutedrdquo with the required amount of copper usingsubsequent ball milling [5]

The consolidated nano- and microcomposite materialsdeveloped on the basis of the described systems were tested for theirenhanced mechanical properties (fracture tough composites B4C-TiB2

[4]) electric erosion resistance [6] and electric conductivity [5] Inthis presentation each property is discussed as resulting from thephase and microstructure evolution during the synthesis of thematerial by the selected processing method

AcknowledgementsParts of this work were carried out by DVD at the University

of California Davis USA during her postdoctoral appointment Theauthors greatly appreciate the collaboration with DrKorchagin(ISSCM SB RAS) Dr VIMali and Dr AGAnisimov (Institute of

13

Hydrodynamics SB RAS Novosibirsk Russia) and Prof JSKim(University of Ulsan South Korea)

References1 DVDudina OILomovsky MAKorchagin VIMali Chem

Sust Dev 12 (2004) 319-3252 MAKorchagin DVDudina Comb Expl Shock Waves 43 (2)

(2007)176-1873 DVDudina VIMali AGAnisimov OILomovsky Mater Sci

Eng A 503 (2009) 41-444 DVDudina DMHulbert DJiang CUnuvar SJCytron

AKMukherjee JMaterSci 43 (2008) 3569-35765 JSKim DVDudina JCKim YSKwon JJPark CKRhee J

Nanosci Nanotech 10 (2010) 252-2576 J-SKim Y-SKwon DVDudina OILomovsky MAKorchagin

VIMali JMaterSci 40 ( 2005)3491 - 3495

4

STUDY OF THE EFFECT OF FLUORESCENCE INCREASINGOF N-ARYL-3-AMINOPROPIONIC ACIDS IN THE PRESENCE

OF ZINC AND CADMIUM IONS

EV Dedyukhina1 NV Pechishcheva1 LK Neudachina2KYu Shunyaev1 AA Belozerova1

1 ndash Institute of Metallurgy of UB RAS 101 Amundsen st Ekaterinburgshunuralru

2 ndash Ural State University 51 Lenin av Ekaterinburg Russia

Earlier the effect of increasing of phosphorescence intensity in thefrozen solutions with excess of metal chlorides and sulphates has beenreported Ions оf these metals have filled electronic shells and largevalue of electric field intensity - Li(I) Be(II) Ca(II) Mg(II) Cd(II)Zn(II) Al(III) In(III) and Ga(III) For example this effect was found forbenzene aniline phenol amino acids ndash tyrosine tryptophanephenylalanine [1]

The same effect have been found for fluorescence of onerepresentative of N-aryl-3-aminopropionic acids (AAPA) - NN-di(2-carboxyethyl)-p-anisidine - in the presence of cadmium(II) and zinc(II)ions at Т=77 К [2] Increasing of fluorescence intensity (Ifl) in frozeninorganic matrix is expected for other representatives of AAPA whichnot have electron acceptor groups in structure and demonstrate theconsiderable fluorescence intensity of the protonated form

Fluorescence of some AAPA in frozen inorganic matrixNN-di(2-carboxyethyl)aniline (I) NN-di(2-carboxyethyl)-34-

xylidine (II) NN-di(2-carboxyethyl)-3-methyl-aniline (III) andN-(2-carbamoylethyl)-о-anisidine (IV) are representatives of a class ofAAPA Figure 1 presents structures of the AAPA In the present workthe fluorescence of aqueous solutions of this AAPA with molar excess ofcadmium and zinc sulphates at рH 1-6 and Т=77 К have beeninvestigated

The fluorescence spectra of solutions were measured using aFluorat-02-Panorama spectrofluorometer (Lumex Russia) Fluorescencespectra at T=77 K was excited and recorded using a fiber-optic cablewith a special optical connector

5

It have been established that the Ifl of the protonated form of I-IV(СR=1middot10-4 moldm3) is increased in the presence of cadmium(II) andzinc(II) ions at Т=77 К Figure 2 presents spectra of II We suggest thatcause of this effect is interaction enhancement of reagent with metal inconsequence of isolation from water and micro concentration (waterform ice crystals impurities are displaced in intercrystal area)

CH3

N

O

OHO

OH

1 2 3 4

Fig 1 Structures of AAPA 1 - NN-di(2-carboxyethyl)aniline2 - NN-di(2-carboxyethyl)-34-xylidine 3- NN-di(2-carboxyethyl)-3-

methyl-aniline 4 - N-(2-carbamoylethyl)-о-anisidine

The increasing Ifl of protonated reagent form of I-IV also isobserved at Т=293К but is not as strong as at T=77 K

0

1

2

3

4

5

6

7

240 260 280 300 320 340 360

wavelength nm

Ia

u

1

2

3

Fig 2 Spectra of fluorescence II (СR=1middot10-4 moldm3) in the presence andabsence of Cd(II) и Zn(II) ions (СZn(II)= СCd(II)= 560 mgdm3) рН=60 Т=77 К

λex = 214 nm 1 - II 2 - II+Zn(II) 3 - II+Cd(II)

The fluorescence increasing is observed only when concentrationof metal ions in dozens of times more than concentration of fluorophor

6

This indicate that Ifl increasing is occured due to reagent solvation byions of inorganic salts but not chelation

We have obtained the Ifl of solutions of I-IV as functions of theconcentration of cadmium(II) and zinc(II) ions at Т=77 К pH=6 (table1) The largest increasing of Ifl in the presence of metal ions have beenobserved for IV But the most correlation coefficient R value of linearfunction Ifl=f(CMe) with wider concentrations range has been obtainedfor II

Table 1 The Ifl of I-IV as functions from concentration of metal ions Т=77 КCCd(II)= CZn(II)= 200 mgdm3 СR=10-4 moldm3 рН=6

Metalion

ReagentConcentrationsrange mgdm3 I R+MeIR R Slope

I 11 090 321

II 11 098 494III

25-760

13 092 456Cd(II)

IV 25-245 80 092 2997

I 3 095 82

II 8 098 414

III

30-845

11 096 437Zn(II)

IV 30-560 70 090 1542

In addition we have studied the fluorescence of aniline and naturalamino acids (tyrosine tryptophane phenylalanine) in frozen inorganicmatrix Structures of amino acids are presented on figure 3 thiscompounds are not belong to class of substituted anilines Thiscompounds similarly of investigated AAPA not have electron acceptorgroups in structure tyrosine phenylalanine and AAPA have the samebenzene fluorophore Besides this amino acids are commerciallyavailable reagents

Investigations have been shown that present amino acids alsodisplay the effect of Ifl increasing of protonated reagent form in thepresence of cadmium(II) and zinc(II) ions at Т=77 К But is not asstrong (12ndash5 times) as AAPA Ifl increasing Metal ions at T=298 K havelittle effect on a fluorescent spectra of amino acids

7

1 2 3

Fig 3 Structure of amino acids1 - phenylalanine 2 - tyrosine 3 - tryptophane

Thus we can deduce that the presence of substituted amino groupin benzene ring (especially in combination with others electron donorgroups) allow to observe more effective increasing of Ifl in salt solutionat 77 К Replacement benzene fluorophore to indole one (intryptophane) result to decreasing of observing effect extent

The fluorescence of II in the presence of Mg(II) ions at Т=77 Кwas investigated We tried to find the II0 fluorescence of II functionfrom z2r ratio for two-charged cations where z - ionic charge (+2) r -ionic radius nm [3] Data is presented in table 2

Table 2 Characteristiс of the functions II0 = f(z2r) for II Т=77 К рН=6λexλem= 214286 nm СII =10-4 М

Ion z2r SlopeI I0

CMe= 200 mgdm3

Cd(II) 412 494 107

Zn(II) 541 414 85

Mg(II) 615 352 74

The functions II0=f(z2r) of fluorescence II in frozen inorganicmatrix from are presented in figure 4 they are linear Also linearfunctions of Ifl=f(CMe) slope on z2r ratio have been obtained

N

NH2

OH

O

H2N

OHO

OH

8

y = -016x + 174

R2 = 099

6

7

8

9

10

11

40 45 50 55 60 65

z2r

IIo

Zn

Cd

Mg

Fig 4 Functions II0=f(z2r) of fluorescence II in the presence of metal ions [3]CCd(II)= CZn(II)= CMg(II)= 200 mgdm3 λexλem= 214286 nm Т=77 К

Study of fluorescence of some reagents in glycerolwater andethanolwater mixtures and micellar solutions at Т=298 КWe have studied a fluorescence II and tryptophane in

glycerolwater (11) and ethanolwater (11) mixtures in the presence ofzinc(II) ions at 77 К It was done for proving hypothesis about reducinginteraction fluorophore with water in aqueous media at freezing Wesuggest that interaction between of the solute and solvent molecules arepreserved in nonaqueous solutions

Corresponding spectra of II are presented on figure 3 similarsituation is observed for tryptophane We can see effect of increasing Ifl

is not observed in glycerolwater and ethanolwater mixtures in contrastto aqueous solutions

Isolation reagent from water at room temperature is possible in thepresence of surfactants

Fluorescence II have been study in the presence of surfactants ofdifferent nature in acidic media at Т=298 К The Ifl increasing ofprotonated form II is occured in the presence of Triton Х-100 (non-ionicsurfactant) and sodium dodecylsulphate (anionic surfactant)Fluorescence II is decreased by cetyltrimethylammonium bromide(CTAB cationic surfactant)

Fluorescence of II in the presence of surfactants and excess ofmetal ions have been study at рН=1-6 Zinc and cadmium ions increaseIfl of II at рН 50-65 with CTAB Thus metal ions and CTAB at

9

Т=298 К have same Ifl increasing effect as the effect at Т=77 К withoutsurfactants

0

5

10

15

20

25

240 260 280 300 320 340 360 380

wavelength nm

Ia

u

1

2

3

Рис 5 Fluorescence of II (СII=1middot10-4 moldm3) in ethanolwater (11)mixtures in the presence and absence of Zn(II) pH=60 Т=77 К λex=214 nm

1 - II 2 - II + Zn(II) (44middot10-4 moldm3) 3 - II+ Zn(II) (86middot10-3moldm3)

We have obtained under these conditions the Ifl of II solutions asfunction of the concentration of Cd and Zn ions with variousconcentrations of CTAB (table 3) The plots are linear and have thegreatest slope value at СCTAB=14middot10-3 moldm3 Cadmium ions have agreater influence on the fluorescence of the II than zinc ions

The fluorescence investigations in the presence of CTAB andmetal cations have been carried out on other AAPA (I III and IV)aniline and tyrosine (table 4) It was found that zinc ions increase offluorescence of protonated reagent form of I and III cadmium ions ndashIII

Table 3 Characteristiс of the functions Ifl=f(CMe) of II with addition of CTAB

exem = 218286 Т=298 К

Range of concentrationsCation

С CTABmoll moldm3 mgdm3 tg α

96middot10-4 2middot10-4 ndash 4middot10-3 45-450 18Cd(II)

14middot10-3 2middot10-4 ndash 8middot10-3 45-900 3696middot10-4 4middot10-4 ndash 15middot10-2 25-850 055

Zn(II)14middot10-3 4middot10-4 ndash 11middot10-2 25-850 10

10

Table 4 Fluorescence of reagents in the presence of zinc and cadmium ions(СMe=560 mgdm3) and CTAB (С= 96middot10-4 moldm3) рН=6

Zn(II) Cd(II)

Reagentexem

nm II0 I (R+Zn+CTAB)au

II0I (R+Cd+CTAB)

au

aniline 253278 11 07 10 06I 222300 62 16 08 02II 218286 73 44 85 51III 217288 65 34 33 15IV 218304 10 32 12 12

tyrosine 222302 10 480 11 462

The resulting functions will be used for developing of thefluorescent techniques of zinc and cadmium determination

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

References1 AV Karyakin n-electrons of heteroatoms in hydrogen bonding and

luminescence (in Russian) Nauka Мoscow 1985 135 p2 LK Neudachina EV Dedyukhina OV Evdokimova

NV Pechishcheva EV Osintseva KYu Shunyaev Fluorescenceof NN-di(2-carboxyethyl)-p-anisidine in solution and crystallinestate Journal of Applied Spectroscopy 2010 V 77 2 P 206-212

3 Lurie YuYu Hand-book of analytical chemistry (in Russian)Khimiya Мoscow 1989 447 p

192

Fig 3 Polarization curves of lead ions (II) deposition in LiCl ndash KCl ndash PbCl2

melt at 823 К depending on the lead chloride concentration Concentration oflead chloride in mol per cents 1 - 04 2 - 05 3 ndash 30

193

Fig 4 Engaging curves at 823 К temperature and the different current density

On the engaging curves at current density values corresponding tothe second characteristic area on the polarization curves on the figures 2and 3 two waves on figure 5 are seen Time of reaching stationarypotential tst decreases with the current density increasing (for currentdensity 012 Асm2 tst equals 85 s for current density 017 Асm2 tst -45 s)

Fig 5 Engaging curves at 04 mol lead chloride concentration currentdensity 012 013 017 Асm2 and 823 К

194

Processes taking places on the electrode can be described in thefollowing way On the first characteristic area of the polarization curvelead ion deposition happens

Pb2+ + 2e = Pb0 (3)The limiting current density of lead reduction increases with the

temperature and lead chloride concentration At 30 mol of leadchloride concentration and 823 K limiting current density ilim is 12Acm2

On the second characteristic area of the polarization curvedeposition of the alkaline metal is possible on the reaction

K+ + e = K0 (Pb) (4)Low values of the alkaline metal reduction potentials might be

connected with the process of alloy formation of alkali metal with leadK + 4Pb = KPb4 (5)

Chronopotentiometric measurements at lead deposition from LiClndash KCl (45-55 mol ) ndash PbCl2 melt at 04 mol lead chlorideconcentration were performed at 823 K and current density range from010 to 017 Acm2 There is only one wave on chronopotentiometriccurves under these conditions Values of product i12 depending oncurrent density are given in the table 1 where - transition time

Table 1 Values of product i12 at diverse current density

s i mAcm2 i12 mAcm2s12

095 170 165161 130 165181 120 162

262 102 165

It is seen that the product i12 does not depend on current

density at constant concentration of depolarizator 0OxC In the table 2

potential values Е4 at time equaling the forth of the correspondingvalues of transition time are given

195

Table 2Values of Е4 potential of different current density

i Acm2 s 4 s Е4 V

010 264 0660 -0061

012 181 0453 -0600

013 161 0403 -0061

017 095 0238 -0062

It is seen that the potential Е4 does not depend on the experimentconditions the current density in this case

Equation for the reversible process can be as follows

1ln

nF

RT21

4t

ЕЕ

(6)

for irreversible process

2100

1lnlnnF

RT

t

nF

RT

i

knFCЕ

fhOx (7)

where E ndash electrode potential 4E - measurement potential at frac14

of transition time R ndash gas constant F ndash Faraday number n ndash number

of electrons T ndash temperature - transition time 0OxC - depolarizator

concentration 0fhk - deposition speed constant

On the figure 6 dependencies Е -

1ln

21

t

and Е -

21

1ln

t at 04 mol of lead chloride concentration current

density 01 Acm2 and 823 K are given

196

y = -00835x + 00654

0002

0022

0042

0062

0082

0102

0122

0142

0162

-115 -065 -015 035 085

- E В

1 2

Fig 6 Dependencies 1ndashЕ=f

1ln

21

t

and 2-Е =f

21

1ln

t

From the analysis of given graphic dependencies follows that the

experimental points in coordinates E -

1ln

21

t

are in a straight line

with the confidence interval 095 The can be described by equation

08300650 E

1ln

21

t

(8)

The amount of electrons in the electrode reaction was calculatedfrom the equation

F

RTn

0830 (9)

hence n=2

197

It follows from the experimental conditions on lead ion (II)deposition that the process is reversible ie it is controlled by the speedof divalent lead ions mass transfer from the volume of melt to theelectrode surface

Diffusion coefficient of lead dichloride at 823 K was calculated onSandrsquos equation

20

2

)(

)(2D

oxnFC

i

(10)

Lead ions (II) diffusion coefficient are equal to 23310-

5сm2s It is in good accordance with the data obtained by other authors[5 6]

References1 Yurkinsky V Makarov D Electrochemical reduction of lead ions in

halide melts Russian J Applied Chem 1994 67 p 1283-12862 Yurkinsky V Makarov D The influence of cation composition on

kinetics of lead electrochemical reduction in chloride melts RussianJ Applied Chem 1994 68 p 1474-1477

3 Ryabukhin Yu And Ukshe E The diffusion coefficients of lead inmolten chlorides DAN SSSR 1962 145 p 366-368

4 Naryshkin I Yurkinsky V Oscillographic investigation oftemperature coefficients for some chlorides diffusion in LiCl-KClRussian J Electrochemistry 1968 4 p 871-872

5 Naryshkin I Yurkinsky V Voltammetry in molten salts Russian JElectrochemistry 1968 2 p 856-866

6 Raymond J Heus James J Egan Fused Salt Polarography Using aDropping Bismuth Cathode ndash J of the Electrochemical SocietyOctober 1960 p 824-828

7 Richard B Stein The Diffusion Coefficient of Lead ion in FusedSodium Chloride Eutectic ndash J Electrochem Soc 1959 vol 106 p528

8 Laitinen H A Gaur H C Chronopotentiometry in Fused LithiumChloride-potassium Chloride - Anal Chem Acta 1958 vol 18 p1-13

9 Hills GI Oxley I E Turner D W Silicates Ind 1961 vol 26 p559

184

REPAIR COMPOUND MODIFIED BY NANO PARTICLES OFFERROUS OXIDE

OS Tatarintseva SN Novosyolova TK UglovaInstitute for Problems of Chemical and Energetic Technologies SB RAS

Biysk Altai region Russia labmineralmailru

The results of influence study of nano-dispersed ferrous oxide oncharacteristics of the composite material developed earlier (compound)and intended to repair and recover engineering structures and massifshave been presented in this paper The compound consists ofmulticomponent polymer matrix including epoxy oligomer low-molecular synthetic rubber plasticizer and process additives filler and alow-temperature amine hardener Microcalcite with particle size lessthan 50 μm has been used as filler

The composite has been modified with nano powder of ferrousoxide (II) (manufactured by MACH I Inc USA) consisting of needle-like crystalline particles with average size 4 nm and having specificsurface area 2379 m2g

Experiments have shown that even distribution of nano particlesin epoxy resin is caused with a high-velocity mechanical device underthe additional influence of ultrasonic field

The most important things for low-viscosity repair compositionsapplied to recover the integrity of natural materials are high flowabilitydetermining the ability to fill narrow-opened fractures and stability ofstrength properties for a long time

The positive effect of ultra-dispersed modifier is seen within therange of 030-035 of its percentage in the composition as shown byresults of the study given in the Table At these amounts the maximumvalues of flowability and mechanical characteristics have been providedThe logical increase in samples density indicates the optimality of thepacking developed and reduction in the porosity of a composite materialthat is important while using it in conditions on high humidity

The compound developed is environmentally friendlyincombustible waterproof stable to heat vibration and long mechanicalloads and can be used to perform repair work in construction industrypublic service stone mining and processing industries and architecture

185

Table Percentage influence of ferric oxide nano powder on technicalcharacteristics of the composite material

Value at modifier percentage Characteristics

0 010 020 030 035 040

Dynamic viscosityat T = 20 oC Pamiddots

210 212 225 262 266 288

Flowability cm 48 48 48 52 53 45

Density gm3 141 141 143 145 146 146

Compressive forceMPa

79 78 79 82 86 74

Relative deformation

023 021 021 025 025 020

182

BASALT PLASTICS OF ENHANCED HEAT AND CHEMICALSTABILITIES

OS Tatarintseva NN Ноdakova VV SamoilenkoInstitute for Problems of Chemical and Energetic Technologies

of the SB RAS Biysk Russialabmineralmailru

The experience of the application of metal pipes for chemicalproductions cool and hot water supply systems transportation ofpetroleum products and other aggressive fluids has shown that they aregreatly subjected to corrosion that reduces their lifetimes to severalyears Therefore natural is the observed worldwide tendency ofreplacing steel and cast iron by composite materials of high chemicalstability and durability to which glass-reinforced plastic having acomplex of high service properties should primarily be relatedHowever requirements for composites have presently increasedespecially with regard to their heat and chemical stabilities andresistance to microorganisms ground and waste waters

The paper demonstrates the study results with respect to thedevelopment of a composite material for filament-wound pipe productswhich is superior in its basic parameters to analogous ones in the field ofglass-reinforced plastic application As a reinforced material basaltroving with higher strength characteristics and resistance to aggressiveenvironments as compared to a glass one was chosen the polymermatrix was a heatproof binder TS developed on the basis of nitrogen-containing epoxy resin synthesized Having rheological properties andstrength characteristics similar to those that are widely used in themanufacture of filament-wound glass-reinforced plastic products of thebinders EDI and EChDI the binder TS possesses enhanced heat stabilityand low viscosity at room temperature which permits the reduction ofpower inputs for its processing

The obtained data on advantages of both basalt fiber and thebinder developed have to the full extent been realized in laboratorysamples of the reinforced composite and in basalt plastic pipes producedindustrially (see Table below)

183

Table Temperature dependence of elastic modulus E of basalt plasticpipes

Еmiddot103 MPa at Т degСBinder 20 85 125 155 200

EDI 11701 11263 4363 3528 -EChDI 11277 10951 9944 6217 -

TS 19960 19336 19179 17557 9096

The 9-fold strength reserve of the basalt plastic pipes determinedwhen hydro-tested under extreme conditions (150degC 15 MPa) hasconfirmed the possibility of creating composite polymer materialsoperating under high-temperatures and humidity

164

FABRICATION AND MODIFICATION OF METALLICNANOPOWDERS BY ELECTRICAL DISCHARGE IN LIQUIDS

NV Tarasenko1 AA Nevar1 NA Savastenko2 EI Mosunov3 NZ Lyakhov4 TFGrigoreva4

1 Institute of Physics NAS B Minsk Belarus2 Leibniz-Institute for Plasma Science and Technology Greifswald Germany

3 The Institute of Machine Mechanics and Reliability NAS B Minsk Belarus4Institute of Solid State Chemistry and Mechanochemistry SB RAS

18 Kutateladze Str Novosibirsk 630128 Russia grigsolidnscru

Electrical-discharge technique was developed for preparation ofmetallic and metal-containing nanoparticles as well as for modificationof metal micropowders in liquids The morphology and composition ofthe nanopowders formed under various discharge conditions wereinvestigated by means of transmission electron microscopy and X-raydiffraction analysis The optimal conditions for the production oftitanium carbide and copper nanoparticles embedded in carbon layerswere found

IntroductionA synthesis of metallic and metal-containing nanopowders is of a

great interest due to their potential applications as super hard materials[1] environmentally friendly fuel cells with highly effective catalysts[23] and so on Transition metal carbides have been widely studied aselectrocatalysts because of their electrochemical properties andelectrical conductivities Nanosized carbon particles are suitable supportmaterials for certain types of catalysts Of particular interest for futurecatalytic applications are carbon-based materials with embeded metalnanoparticles [4] As long as carbon nanoparticles are relatively inertsupports many studies have been conducted in order to find which pre-treatment procedures are needed to achieve optimal interaction betweenthe support and metal species [5]

For any application of nanoparticles to be commercially viablelow-cost production methods have to be developed A low-temperatureand non-vacuum synthesis of nanoparticles via discharge in liquid(submerged discharge) provides a versatile choice for economicalpreparation of various nanostructures in a controllable way An arc

165

discharge in liquid nitrogen has firstly been reported as a cost-effectivetechnique for the production of carbon nanotubes in 2000 by Ishigamy etal [6] Since that time many efforts have been devoted to develop thismethod Sano et al proposed to submerge electrodes in water instead ofliquid nitrogen [78] They reported synthesis of carbon onions [78] andsingle-walled carbon nanohorns (SWNHs) [9] In latter case carbonnanoparticles were produced via discharge in water method with thesupport of gas injection Parkansky et al reported nanoparticlessynthesis via a pulsed arc submerged in ethanol Ni W steel andgraphite electrodes were used [1011] The particles composition variedfrom carbon to pure metal including various intermediate combinationsof these materials Bera et al employed an arc-discharge in a palladiumchloride solution to produce carbon nanotubes decorated with in situgenerated Pd nanoparticles [10] Importantly the synthesized materialcontained no chlorine

In this paper methods based on electrical-discharges in liquids forproduction of tungsten and titanium carbide as well as coppernanoparticles embedded in carbon nanostructures is reported Thecapabilities of arc and spark discharges submerged in liquids forsynthesis of nanoparticles as well as electrical-discharge modification ofmetallic powders were studied

Experimental detailsThe experimental reactor (Fig 1) consisted of four main

components a power supply system (pulse generator) the electrodes aglass vessel and a water cooling system outside the beaker A pulseddischarge was generated between two electrodes being immersed in 100ml of liquid (pure (995) ethanol or 0001 M CuCl2 aqueous solution)The appropriate combinations of pairs of metallic (tungsten titanium orcopper) and graphite electrodes were used The choice of ethanol wasmotivated by the fact that organic compounds play a role of a carbonsource to produce nanoparticles in discharge-in-liquid system [7 12]Addition of the copper chloride salt into double distilled water favoredthe activation of discharge process Metal (tungsten titanium or copper)and graphite rods with diameters of 6 mm were employed as electrodesAn optimum distance between the electrodes was kept constant at 03mm to maintain a stable discharge The discharge was initiated byapplying a high-frequency voltage of 35 kV The power supply

166

provided several different types of discharges Both direct current (dc)and alternating current (ac) arc and spark discharges were generatedwith repetition rates of 100 and 50 Hz respectively Current I(t) wasrecorded during the discharge as a function of time by means of anoscilloscope The peak current of the arc discharge was 9 A with a pulseduration of 4 ms The peak current of the pulsed spark discharge was 60A with a pulse duration of 30 μs

The synthesized products were obtained as colloidal solutionsAfter 15 min presedimentation the large particles precipitated at thevessel bottom The top layer contained the small nanoparticles wascarefully poured off into a Petry dish These suspended nanoparticleswere characterized by UV-Visible optical absorption spectroscopytransmission electron microscopy (TEM) and X-ray diffraction analysis(XRD) for their size morphology crystalline structure and composition

The optical absorption spectra of colloids were measured by UVndashVisible spectrophotometer (CARY 500) using 05 cm quartz cuvetteTransmission electron microscopy was performed by LEO 906E (LEOUK Germany) microscope operated at 120 kV A drop of solution putonto the amorphous carbon coated copper grid for TEM measurementsThereafter the liquid was evaporated at the temperature of 80 C Afterthe drying of colloidal solution the deposit obtained on the bottom ofPetri dish was examined by XRD Powder composition and itscrystalline structure were characterized by using X-ray diffraction atCuK (D8-Advance Bruker Germany)

Synthesis of carbide nanopowdersPromising capabilities of the developed technique for synthesis of

tungsten and titanium carbides (WC TiC) as well as carbon-encapsulated copper nanoparticles were demonstrated using theappropriate combinations of pairs of metallic and graphite electrodessubmerged into the appropriate solution Also physical and chemicalprocesses induced by the electrical discharges in liquids were studied tooptimize the process of nanoparticles synthesis

The results of nanoparticles preparation are summarized in theTable1 The synthesis rate varied in range of 2 ndash 40 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofmetal and graphite electrodes The synthesis rate increased withincreasing of discharge current and decreasing of pulse duration The

167

composition and morphology of nanoparticles were also found to dependon discharge parameters It should be noted that there is a possibility toscale-up the process

Table 1 summarized the variation in synthesis rate andcomposition of tungsten nanopowders with the discharge parameters Asa general tendency the synthesis rate was order of magnitude higher forspark discharge than that of arc discharge It may be due to thedifference in current value [13] For both arc and spark discharges itwas found that the synthesis rate is lower when tungsten was acting as acathode This result is consistent with literature data For example Beraet al reported that the consumption of anode is higher than that ofcathode [13]

Table 1 Summary of nanopowder synthesis conditions andresults of nanopowder characterization by XRD

XRD-analysisDischargetype

Electrodes Powdersyield

mgminW2Cvol

WC1-xvol

Cvol

Wvol

1 ac arc W C 02 71 781 147 -2 dc arc W(cathode)C(anode) 01 62 901 37 -3 dc arc W(anode)C(cathode) 02 66 715 219 -4 ac spark W C 25 58 328 614 -5 dc spark W(cathode)C(anode) 12 570 307 89 336 dc spark W(anode)C(cathode) 21 56 325 618 -

As it can be seen from the Table 1 the synthesized nanopowder isa mixture of hexagonal W2C face centered cubic WC1-x and graphite Nopeaks corresponding to WO were observed Nanopowder contained alsosmall amount body centered cubic W when synthesis was performed bydc current spark discharge with tungsten rod acting as cathode Here theparticular behavior of this discharge should be stressed showing ratherhigh ability to synthesize W2C Moreover in contrast to the other sparkdischarges synthesized material contained relatively small amount ofgraphite On the other hand applying tungsten as a cathode materialappears to reduce C content in nanopowder prepared via arc dischargetoo Generally the content of C is higher and content of WC1-x is lowerwhen synthesis was performed by spark discharge

168

Nanoparticles prepared by arc discharge were observed in theiragglomerated form The agglomerated nanoparticles were surrounded bythe grey regions which were probably graphite layers This typical viewwas seen everywhere in TEM images of product synthesized by arc forboth ac and dc current discharges irrespective of electrodes polarityThat fact implies that the morphology of synthesized nanopowders wasgoverned rather by the current pulse duration and value of peak currentthan the polarity of the electrodes Since nanoparticles were observed inthe agglomerated form it was difficult to measure their size correctlyWe suppose that approximately 4 nm nanoparticles are formed duringthe arc discharge in ethanol

Fig1 shows the TEM image of titanium carbide nanopowdersynthesized by spark discharge in ethanol As can be see from the Fig1the nanoparticles were also surrounded by graphite layers Fig 1demonstrates that the nanoparticles synthesized by spark were nearlyspherical with a mean diameter of ~ 7 nm The particle size distributionwas rather narrow (plusmn 2 nm) The XRD pattern of synthesized sample isshown in Fig 1 (right picture) The diffraction peaks at 60deg 418deg605deg 724deg 765deg and 407deg 504deg 590deg 667deg 741deg correspond tothe formation of cubic face-centered titanium carbide TiC and cubicprimitive TiC2 respectively There are some diffraction peaks with 2θvalue of 407deg 504deg 590deg 667deg and 741deg which can be assigned tothe hexagonal C The amount of TiC reached 887 vol The quantitiesof TiC2 and C in samples detected by XRD corresponded to ca 47 vol and ca 67 vol respectively

Fig 1 TEM image (left picture) of titanium carbide nanopowder synthesizedby ac spark discharge and XRD-pattern (right picture) of the sample

169

Synthesis of copper-carbon composite nanostructuresNumerous studies have focused on synthesis of metal-containing

carbon nanocapsules (CNCs) via submerged discharge method[89141516] Because of the carbon sheets surrounding the metal corethe CNCs are protected from the environment and from degradation Thecarbon coatings mean that nanoparticles are biocompatible and stable inmany organic media Thus carbon encapsulated nanoparticles arecandidate for bioengineering application high-density data storagemagnetic toners for use in photocopiers [81718] The metal containingcarbon nanostructures were prepared by using the electrode frommixture of graphite and metal precursor [16 1920] Recently Xu et aldemonstrated a possibility to synthesize Ni- Co- and Fe-containingCNCs by an arc discharge between carbon electrodes in aqueoussolution of NiSO4 CoSO4 and FeSO4 respectively [15] In contrast tothe data reported by Bera et al the synthesized material consisted of Oand S due to SO4

-2 ionic precursors in the solution Since the metal core-forming material was supplied by liquids the production rate of CNCswas limited by the salt concentration [4] This restriction may cause alimit to apply the submerged discharge method to the large-scaleproduction of CNCs

In this paper Cu-based nanoparticles were prepared viasubmerged discharge of bulk copper and graphite electrodes in a copperchloride (CuCl2) aqueous solution Thus material of copper electrode aswell as Cu from solution was supposed to be incorporated into theresulting nanoparticles The effect of discharge parameters and electrodecomposition on the morphology and composition of final products havebeen investigated Additionally synthesized material was modified bylaser irradiation The changes in nanoparticles morphology andcomposition were examined by transmission electron microscopy(TEM) X-ray diffraction (XRD) and UV-Vis spectroscopy

The six types of nanoparticles suspension were prepared underdifferent discharge parameters The synthesis parameters aresummarized in Table 2 As it can be seen the weight change of eachelectrode was generally higher when spark discharge was generatedThe anode consumption rate was higher than that of cathode irrespectiveto a discharge type and electrode material However in contrast to theliterature data [4] there was no cathode gain in weight As a generaltrend the nanopowder synthesis rate was higher for spark discharge than

170

that of arc discharge It may be explained by the difference in currentvalue [21] For both arc and spark discharges it was found that thesynthesis rate was higher when copper was acting as an anode There isa discrepancy between nanopowder synthesis rate and materialconsumption rate The values of discrepancy D listed in the Table 2were calculated as follows

100()

CCu

syn

RR

RD (1)

Here Rsyn is the synthesis rate of nanopowder RCu is theconsumption rate of the copper electrode and RC is the consumptionrate of the graphite electrode The discrepancy D depended ondischarge parameters For ac-discharges the value of discrepancy washigher for spark discharge than that for arc discharge For dc-discharges this trend remained if the polarity of electrodes was takeninto account It is worth to notice here that the discrepancy betweenmaterial consumption rate and nanopowder synthesis rate may be causednot only by separation of sediment fraction but by the reaction of carbonatoms with water resulting in the production of gaseous compounds [9]

Table 2 Summary of nanopowder synthesis parametersType of

dischargepeak currentpulse duration

Electrodes materialRCu and RC

mg min-1RSyn

mg min-1D

Cu 671 ac1) spark60 A 30 micros C 48

59 49

Cu 122 ac arc10 A 4 ms C 26

25 34

Cu (cathode electrode) 473 dc2) spark60 A 30 micros C (anode electrode) 61

21 81

Cu (anode electrode) 664 dc spark60 A 30 micros C (cathode electrode) 46

69 38

Cu (cathode electrode) 115 dc arc10 A 4 ms C (anode electrode) 25

19 47

Cu (anode electrode) 286 dc arc10 A 4 ms C (cathode electrode) 21

33 33

1) Alternating current pulsed discharge2) Direct current pulsed discharge

171

This coincides with the fact that the largest discrepancy (morethan 80) was observed in sample with the largest graphite electrodeconsumption rate (sample 3) For all samples the synthesized powderseparated into three phases one floating in suspension one settling atthe bottom as sediment and one as a layer of film-like material floatingon the liquid surface

The aqueous solutions of CuCl2 were discharge treated for only 20s to acquire yellowish suspensions The transparency of the suspensionsdecreased with the time during the discharge treatment The liquidsturned to dark yellow after treatment by ac-discharge for 10 min Thesuspensions resulting from dc-discharge treatment were conspicuouslydarker when C electrode was acting as an anode The nanoparticlessuspension produced by spark and arc discharges were dark brown anddark grey respectively It might be due to the presence of relatively largeamount of carbon particles in suspension (see Table 3) The dc-dischargetreated solutions were olive-green when Cu was used as the anodeelectrode Yellow or green colour of suspension may indicate theoxidation of copper nanoparticles [22] The presence of Cu2Onanoparticles was further confirmed by XRD analysis No changes incolour were observed after laser irradiation of suspensions

Figure 2 shows the absorption spectra of as prepared (a) and laserirradiated (b) suspended nanopowders synthesized by dischargetreatment of aqueous solution of CuCl2 (2) for 1 min The spectra werecorrected to the contributions of solvents The optical density increasedwith decrease in wavelength Generally the optical density ofsuspensions prepared by spark discharge was higher than that ofsuspension prepared by arc discharge This is consistent with the factthat the nanoparticles production rate was higher when the solution wastreated by spark discharge In the spectral range of 200 ndash 500 nm theoptical density of the samples 1 4 6 was higher than that of samples 23 and 5 This seems to suggest that the main parameter in determiningthe optical properties of suspensions was concentration of Cu-basednanoparticles For the samples number 1 and 4 a weak absorption peakwas observed at very short wavelength According to the literature data[2324] a surface plasmon peak at wavelength of 289 nm may beattributed to the presence of very small separated Cu nanoparticles (lt 4nm in size) Though TEM examination confirmed the presence of smallnanoparticles in sample 1 there were no nanoparticles with diameter less

172

than 4 nm in sample 4 Moreover there were no copper nanoparticles insample 1 as revealed by the XRD (see below) More likely theexistence of weak absorption peak at 280 nm implied formation of liquidbyproducts We did not observe in the absorption spectra surfaceplasmon band around 570 nm Missing of the plasmon band can beexplained by copper oxidation on the particle surface [23] Thissuggestion was further confirmed by XRD analysis (see below) Thesuspensions exhibited the same colours after laser irradiation butabsorption intensity increased for samples 3 1 and to the less extent forsample 5 as illustrated in Figure 2b TEM analysis revealed themorphological similarity of irradiated samples 1 3 and 5 (see below)

Figure 3 depicts the corresponding TEM images for thesuspensions shown in curves 1-6 of Figure 2 Parts (a) and (b) representthe TEM views of the as-prepared and irradiated samples respectivelyThree distinct structures were observed dark small spherical particlesdark particles surrounded by a gray shell and gray flake-like structureshaving diffuse contours The small dark particles with diameter 2-5 nmwere observed in samples 1 2 3 and 5 (marked with black ellipses inFigure 3) Some dark particles notable when using ac spark dischargefor synthesis were bigger than 20 nm indicating coalescence Thenanoparticles synthesized by ac arc discharge (sample 2) were

Fig 2 Absorption spectra for the as-prepared (a) and laser modified (b)suspended nanoparticles produced by ac- (12) and dc- pulsed discharges(3456) The following electrode pairs were used Cu and C for the ac-spark(1) and ac-arc (2) discharges Cu as a cathode electrode and C as an anodeelectrode for the dc-spark (3) and dc-arc (5) Cu as an anode electrode and C asa cathode electrode for the dc-spark (4) and dc-arc (6)

173

surrounded by the arrowed gray regions which were probably carbonshells as shown in Figure 3a

Fig3 TEM images of nanoparticles from as-prepared (a) and irradiated (b)suspensions produced by ac- (12) and dc- pulsed discharges (3456) Thefollowing electrode pairs were used Cu and C for the ac-spark (1) and ac-arc(2) discharges Cu as a cathode electrode and C as an anode electrode for thedc-spark (3) and dc-arc (5) Cu as an anode electrode and C as a cathodeelectrode for the dc-spark (4) and dc-arc (6)

174

As we did not have any direct evidence that the shells consisted ofcarbon these nanostructures will be referred further as core-shellnanoparticles The core-shell nanoparticles were also observed in colloidprepared by dc arc discharge between copper cathode and graphiteanode (sample 5) It can be seen that core-shell nanoparticles rangedfrom 20 to 50 nm in diameter while the cores within the nanoparticlesvaried from 8 to 25 nm The cores were non-spherical They seemed tocompose of small particles clustered together The flake-like structureswith diffuse contours were 50 nm in size They were observed in allsamples Samples 4 and 6 consisted mostly of structures with diffusecontours On the basis of the above observations the ac arc dischargeand dc arc discharge with copper anode electrode seemed to be moresuitable for synthesis of nanoparticles with core-shell structure

It is clear seen that many smaller particles with sizes around 2-7nm were generated after the irradiation of samples 2 4 and 6 Theparticles larger than 10 nm completely disappeared The micrographrevealed that after the irradiation these suspensions consisted ofparticles with circular cross-section whereas before the irradiation theparticle shape was not spherical The nanoparticles were dispersed verywell No small nanoparticles were observed in suspensions 1 3 and 5after the irradiation Though as can be seen by comparing Figure 1(a)3(a) and 5(a) with 1(b) 3(b) and 5(b) the shape of nanoparticleschanged after the irradiation The laser induced morphology change mayoccur through heating of the nanoparticles because of the absorption ofthe laser light [25] According to the mechanism proposed by Takami etal the morphology of irradiated nanoparticles was determined by therelationship between temperature of nanoparticles their melting andboiling point

The laser induced change in shape and size occurred if thetemperature of nanoparticles was at the boiling point If the temperaturewas lower than the melting point no changes took place If thetemperature was between melting point and boiling point only thechange in shape occurred Thus the difference in morphology of theirradiated samples can be attributed to the difference in theircomposition Even being irradiated with the same laser light intensitythe nanoparticles of different composition changed their morphology indifferent ways as they have different melting and boiling points

175

X-ray diffraction data were collected to identify synthesizedsamples The diffraction peaks at 432deg and 503deg correspond to theformation of faced-centered-cubic Cu There are three diffraction peakswith 2θ value of 365deg 423deg and 614deg which can be assigned to theprimitive cubic Cu2O Besides there are two peaks at 240deg and 265degwhich can be assigned to the hexagonal C XRD revealed that dischargetreatment of aqueous solution of CuCl2 led to the formation of Cu2

(OH)3Cl and Cu2OCl2 because of a strong affinity between chlorine andthe metal (peaks with a value of 2θ around 165deg 19deg 31deg 323deg 327deg330deg 387deg 398deg 401deg 503deg 505deg 538deg and 178deg 360degrespectively) For comparison the XRD patterns of initial solution ofCuCl2 are also plotted at the top of Fig 4 Non-treated aqueous solutionof copper chloride was allowed to evaporate and than analyzed by XRDThe diffractogram of this sample showed peaks at about 2θ around162deg 220deg 240deg 267deg 289deg 328deg 340 348deg 352deg 409deg 430deg448deg 453deg 490 and 573deg which are characteristics of CuCl2middot2H2O

XRD data were used to semi-quantitatively determine thepercentage of constituents The semi quantitative analysis of phasecomposition is shown in Table 3 The nanopowder composition wasstrongly dependent on the synthesis parameters It should be noted herethat metallic copper was only formed by dc-discharge treatment whencopper was acting as an anode electrode (samples 4 and 6) Synthesizedmaterial contained copper mostly in form of oxide (Cu2O) copperhydroxychloride (Cu2(OH)3Cl) and copper oxychloride (Cu2OCl2)Difference in Cu2O and C contents among all samples was significantSamples 2 and 5 contained no copper oxide while sample 6 had thelargest percentage of copper oxide (ca 80 vol) On the other handsample 6 contained no carbon The carbon contain in sample 4 exceeded80 vol The quantities of Cu2(OH)3Cl in samples ranged from lessthan 2 vol to ca 30 vol Only three samples contained Cu2OCl2

(samples 12 and 5) The maximal amount of Cu2OCl2 detected by XRDcorresponded to ca 30 vol In spite of high copper electrodeconsumption rate sample 4 contained unexpectedly small quantities ofCu and Cu-containing compound It might be due to the formation ofrelatively large and heavy copper microparticles They precipitated fromcolloid quickly after synthesis Therefore they were not collected andanalyzed by XRD (see experimental section) A correlation was

176

observed between low copper electrode consumption rate and absence ofCu and Cu2O fractions in nanopowder composition for samples 2 and 5

It should be stressed here that the core-shell structures wereobserved for only samples 2 and 5 Taking into account firstly thatsamples 2 5 and 6 were prepared by arc treatment secondly that thesample 6 contained no C and assuming that the shells consisted ofcarbon we can suggest that arc discharge was more suitable forsynthesis of core-shell nanoparticles On the other hand the chemicalcomposition of final product was governed by different competingreactions As they have different equilibrium constants they may form anetwork where the ratios of the products are sensitive to concentrationsof each of the many components Therefore the slight difference ininitial concentration might results in significant difference incomposition and morphology of synthesized material (compare samples5 and 6)

Although the exact mechanism for formation of nanoparticles viadischarge in solution process is not clear the following possibility may

Table 3 Semi-quantitative analysis of synthesized powder by XRD

XRD-analysisType of

dischargeElectrodesmaterial Cu

volCu2Ovol

Cvol

Cu2(OH)3Clvol

Cu2OCl2vol

1 ac1) sparkCuC

- 135 403 165 297

2 ac arcCuC

- - 646 300 54

3 dc2) sparkCu (cathode)C (anode)

- 391 370 239 -

4 dc sparkCu (anode)C (cathode)

78 83 825 14 -

5 dc arcCu (cathode)C (anode)

- - 339 336 325

6 dc arcCu (anode)C (cathode)

74 775 - 151 -

1) Alternating current pulsed discharge2) Direct current pulsed discharge

177

be considered During discharge treatment of the liquid copper andgraphite electrodes were heated melted and vaporized in the region ofthe discharge generated In the vicinity of electrodes the liquid was alsovaporized rapidly due to extremely high temperature Hence the plasmaregion produced by the discharge adjacent to the electrodes wassurrounded by a gas bubble Following Sano et al [8] the gas mixturemay comprise CO and H2 formed as follows

22 HCOOHC (2)

This reaction might cause the discrepancy between electrodeconsumption rate and nanopowder synthesis rate since some of carbonatoms formed gaseous CO Sano et al reported that gas bubbles didnot comprise water vapor since no condensation occurred [8] Howeverwe should consider that water vapour also existed in the discharge zoneas we did not obtain any evidence of its absence

Copper chloride is an anionic compound that dissociates inaqueous solution and may form different ionic species such as Cu2+ Cl-or complex ions such as CuCl2

- CuCl32- CuCl4

2-[26] The reduction ofcopper ions into copper atoms was likely taking place in plasma regionduring discharge treatment of the liquid as shown in Eq 3

02 2 CueCu (3)

As the temperature in the vicinity of the electrodes was estimatedto be around 4000 K [8] the thermal decomposition of complex ions tometallic copper possible took place in discharge zone (Eq (4-6))

20

2 ClCuCuCl (4)

20

3 322 ClCuCuCl (5)

202

4 2ClCuCuCl (6)

The nanoparticles were then formed from the complex gasmixture through different transformation stages namely nucleationgrowth condensation and coalescence Both the evaporated copper fromelectrode and Cu produced by reduction of ions from solutions were

178

supposed to be incorporated into the resulting nanoparticles Becausewater vapor existed in gas bubble the copper nanoparticles were easilyoxidized Reduction of copper oxide by carbon monoxide and hydrogenwas possible the subsequent step (Eq (7) and (8))

OHCuCOOCu 22 2 (7)

222 2 COCuHOCu (8)

According to the XRD measurements (see Table 3) copper oxidewas only partially reduced into copper in sample 4 and 6 The data ofXRD analysis implied also reaction of chlorine with copper andorcopper oxide to form Cu2Cl(OH)3 and Cu2OCl2 These reactions mightinvolve hydrogen produced via reaction (2)

It should be noted that there was no direct evidence to support theabove-mentioned formation sequence and the true mechanism may bemore complicated

ConclusionsFrom the results and discussion presented above the following

conclusions can be madeThe electrical discharge between two electrodes immersed in

ethanol is a suitable method to produce in a controllable waynanoparticles with different contents of metal and carbon By varyingthe current value and its pulse duration morphology of nanoparticlesand their composition can be changed The average diameters of theprepared nanoparticles were in the range of 3-7 nm

Cu-based nanoparticles with different morphologies wereprepared via submerged electrical discharge of bulk copper and graphiteelectrodes in a CuCl2 aqueous solution Synthesized material wassubjected to laser-induced modification It was found that core-shellnanoparticles were formed by treatment of CuCl2 aqueous solution bythe arc pulsed discharge with pulse duration of 4 ms and peak current of10 A

The synthesis rate varied in range of 19 ndash 69 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofcopper and graphite electrodes The synthesis rate was found to behigher when copper was acting as an anode electrode The synthesis rate

179

increased with increasing of discharge current and decreasing of pulseduration The composition and morphology of nanoparticles were alsofound to depend on discharge parameters The copper nanoparticleswere only formed by dc-discharge treatment when copper was acting asan anode electrode The maximum diameter of nanoparticles did notexceed 50 nm while the minimum diameter was around 2 nm Theresults of the experiments imply that plasma treatment with longer pulseduration and lower current leads to the formation of carbon embeddednanoparticles TEM confirms the formation of encapsulatednanoparticles

Irradiation of nanoparticles in aqueous solution by a pulsedNdYAG laser at 532 nm was found to cause the shape change and sizereduction of the particles

AcknowledgementsThe work has been supported by the Integral Program of the

Siberian Branch of RAS under the Grant 138-T-09-CO-014 Authorsare thankful to KV Scrockaya for carrying out the TEM investigations

References

1 I Zalite S Ordanyan G Korb (2003) Synthesis of transition metalsnitridecarbonitride nanopowders and application of them formodification of structure of hardmetals Powder Metallurgy Journal46 2143 ndash 147

2 XG Yang and CY Wang (2005) Nanostructured tungsten carbidecatalysts for polimer electrolyte fuel cells Appl Phys Lett 8624104-1 -224104-3

3 M Rosenbaum F Zhao U Schroder F Scholz (2006) InterfacingElectrocatalysis and Biocatalysis with Tungsten Carbide A High-Performance Noble- Metal-Free Microbial Fuel Cell Angew Chem118 1-4

4 D Bera S C Kuiry M McCutchen S Seal(2004) In situ syntesis ofcarbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method J Appl Phys 96 5152-5157

5 P Serp M Corrias P Kalck Carbon nanotubes and nanofibers incatalysis Applied Catalysis A General ndash 2003 ndash Vol 253 ndash P337-358

180

6 Ishigami M Cummings J Zettl A Chen S (2000) A simple method forthe continuous production of carbon nanotubes Chem Phys Lett319 457-459

7 Sano N Wang H Alexandrou I Chhowalla M Amaratunga G A J(2001) Nanotechnology Synthesis of carbon ldquoonionsrdquo in waterNature (London) 414 506-507

8 Sano N Wang H Alexandrou I Chhowalla M Teo K B KAmaratunga G A J (2002) Properties of carbon onions produced by anarc discharge in water J Appl Phys 92 2783 ndash 2788

9 Sano(a) N (2004) Low-cost synthesis of single-walled carbonnanohorns using the arc in water method with gas injection J PhysD 37 L17-L20

10 Parkansky N Alterkop B Boxman R L Goldsmith S Barkay ZLereah Y (2005) Pulsed discharge production of nano- andmicroparticles in ethanol and their characterization PowderTechnology 150 36-41

11 Parkansky N Goldsmith S Alterkop B Boxman R L Barkay ZRosenberg Yu Frenkel G (2006) Features of micro and nano-particlesproduced by pulsed arc submerged in ethanol Powder Technology161 215-219

12 P Muthakarn N Sano T Charinpanitkul W TanthapanichakoonT Kanki Characteristics of Carbon Nanoparticles Synthesized by aSubmerged Arc in Alcohols Alkanes and Aromatics Phys Chem Bndash 2006 ndash Vol 110 37 ndash P 18299 -18306

13 D Bera G Johnston H Heinrich S Seal A parametric study on thesynthesis of carbon nanotubes through arc-discharge in water Nanotechn ndash 2006 ndash Vol 17 ndash P 1722-1730

14 Hsin Y L Hwang K C Chen R-R Kay J J (2001) Production and insitu metal filling of carbon nanotubes in water Adv Mater 13 830-833

15 Xu B Guo J Wang X Liu X Ichinose H (2006) Synthesis of carbonnanocapsules containing Fe Ni or Co Carbon 44 2631-2634

16 Lange X Sioda M Huezko A Zhu Y Q Kroto H W Walton D R M(2003) Nanocarbon prodction by arc discharge in water Carbon 411617 ndash 1623

17 Sergienko R Shibata E Akase Z Suwa H Nakamura T Shido (2006) Carbon encapsulated iron carbide nanoparticles synthesized in

181

ethanol by an electric plasma discharge in an ultrasonic cavitationfield Mater Chem Phys 98 34-38

18 Leo G H Jeong S H J W Ri H C (2002) Excelent magnetic propertiesof fullerene encapsulated ferromagnetic nanoclusters J Magn Mater246 404 ndash 411

19 Ang K H Alexandrou I Mathur N D Amaratunga G A J Hag S(2004) The effect of carbon encapsulation on the magnetic propertiesof Ni nanoparticles produced by arc discharge in de-ionized waterNanotechnology 15 520 ndash 524

20 Sano(c) N Nakano J Kanki T (2004) Synthesis of single-walledcarbon nanotubes with nanohorns by arc in liquid nitrogen Carbon42 686-688

21 Bera(c) D Jonston G Heinrich H Seal S (2006) A parametric studyon the synthesis of carbon nanotubes through arc-discharge in waterNanotechnology 171722-1730

22 Yeh M-S Yang Y-S Lee Y-P Yeh Y-H Yeh C-S (1999) Formationand characteristics of Cu colloids from CuO powder by laserirradiation in 2-propanol J PhysChem B 103 6851-6857

23 Aslam M Gopakumar G Shoba T L Mulla I S Vijayamohanan K(2002) Formation of Cu and Cu2O nanoparticles by variation of thesurface ligand preparation structure and insulating-to-metallictransition J Colloid Inter Sci 25579-90

24 Salkar R A Jeevanandam P Kataby G Aruna S T Koltypin YPalchik O Gedanken A (2000) Elongated copper nanoparticlescoated with a zwitterionic surfactant J Phys Chem B 104 893-897

25 Takami A Kurita H Koda S (1999) Laser-induced size reduction ofnoble metal particles J Phys Chem B 1031226-1232

26 Brown JB (1948-1949) The constitution of cupric chloride inaqueous solution Transaction of the Royal Sociaty of New Zeland 7719-23

162

MORPHOLOGICAL STUDY OF DETONATIONSPRAYED COATINGS OF CALCIUM HYDROXYAPATITE

DEPOSITED ON A NANOSTRUCTURED TITANIUMSUBSTRATE

AA Sitnikov VI Yakovlev YuP Sharkeev 1EV Legostaeva 1 AA Popova

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1Institute of Strength Physics and Materials Science SB RASTomsk

Biocompatible coatings are effectively formed by spraying ofcalcium hydroxyapatite Са10(РО4)(ОН)2 powders on a titanium substrateRecently along with the composition macro- and microstructuredevelopment the surface morphology of the coatings has receivedincreasing attention In a number of studies the roughness of thecoatings has been shown to significantly influence the inductionprocesses of cells As a substrate material titanium VT1-0 has beenchosen which has several advantages being highly biocompatiblebioinert practically non-toxic corrosion-resistant and possessing lowthermal conductivity and low coefficient of thermal expansion Themorphology of the gas-detonation sprayed calcium phosphate coatingsdeposited on ultrafine-grained and nanostructured titanium substratesand implant imitations has been studied The substrates and implantimitations were produced in the Institute of Strength Physics andMaterials Science SB RAS Tomsk

It was shown that the detonation sprayed hydroxyapatite powderswith particles ranging from 1 to 20 microm formed coatings non-uniform inthickness and phase composition The roughness of the coatings wasRa=365-472 microm (class 5) When hydroxyapatite particles of 20-100microm in size are sprayed coatings more uniform in thickness and phasecomposition are formed (Fig1) with an average roughness of Ra = 624microm (class 4) Preliminary treatment of the titanium substrate by sandingand chemical etching allows increasing the adhesive strength of thecoating up to 20MPa

163

Fig1 SEM images hydroxyapatite powder (a) detonation sprayedhydroxyapatite coating (b) XRD pattern of the coating (c)

Biological studies have demonstrated biocompatibility andbioactivity of the coatings It was found that the calcium phosphatedetonation sprayed coatings induce growth of tissue cells with 100probability which indicates that the relief of the coatings is optimal forfixation and aging of the cells Comparative studies of calciumphosphate coatings produced by detonation spraying and those producedby micro-arc in an electrolyte containing phosphoric acidhydroxyapatite and calcium carbonate have shown the advantages ofdetonation spraying for providing the required phase composition of thecoating This opens up a possibility of making two-phase coatings(hydroxyapatite and beta-calcium phosphate) ensuring the closest matchin composition to the bone tissue

ва б

100

200 20 30 40 50 60 70 80 90 10

(1

10) (002

) (2

10)

(2

11)

(

300

)

(3

10)

(

222

)

312

)

(3

20)

(

511

)

(

432

)

(5

22)

(

100

)

161

MICROSTRUCTURE STUDIES OF THE COATINGSPRODUCED BY ARC DEPOSITION OF THE

MECHANOACTIVATED SHS-COMPOSITE TIC+XME(R6M5 PR-N70H17S4R4-3) POWDERS

AA Sitnikov VI Yakovlev MA Korchagin1MN Seidurov ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

One of the main challenges in the development of new materialsfor arc deposition using flux-cored wires is to design materials of specialinterest using cost-effective and ecologically friendly technologies Asmaterialstechnologies meeting these requirements we can proposelayered composites produced by self-propagating high-temperaturesynthesis (SHS) in mechanically activated powder mixtures

The samples of SHS-mechanocomposites of TiC+XMe (R6M5PR-N70H17S4R4-3) composition arc-deposited on steel 45 substrateswere selected for investigations Microstructure of the arc-depositedcoatings was studied using a Carl Zeiss AxioObserver A1m OpticalMicroscope For observations cross-sections of the samples wereprepared and etched with a solution containing 20 potassiumferricyanide К3[Fe(CN)6] 20 КОН and 60 H2O Finemicrostructure and composition of the deposited layers were analyzedusing a Carl Zeiss EVO50 Scanning Electron Microscope equipped withan EDS X-ACT laquoOXFORDraquo device

The investigations show that the microstructure of the depositedlayers is uniform with submicron titanium carbide reinforcing phase inthe form of separate inclusions or chains of particles in the matrix

159

WEAR-RESISTANT DETONATION SPRAYED COATINGSBASED ON THE COMPOSITE MECHANICALLY ACTIVATED

SHS-MATERIALS

AA Sitnikov VI Yakovlev MA Korchagin 1DM Skakov AA Popova ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

The application of titanium carbide as a material for thermalspraying is rather difficult mainly due to its high melting temperatureand high hardness

A technology has been developed abroad for the production of thecomposite powders for spraying The production of these compositepowders is a laquoknow-howraquo of MBN Nanomaterialia (Italy)

An approach to the development of TiC-containing coatings canbe based on the technology of mechanocomposites with metallic orintermetallic matrices reinforced with nanosized particles of a ceramicphase [1] The technology of the powder preparation consists of 3 stagesAt the first stage the mixture of initial reactants which in this particularcase are titanium carbon and nichrome is mechanically activated (MA)in a planetary ball mill At the second stage self-propagating hightemperature synthesis (SHS) is conducted resulting in the formation ofTiC particles uniformly distributed in the metallic matrix AdditionalMA of the products of SHS at the third stage along with dispersingtitanium carbide particles creates a principally new state of the matrixwhich experiences grain refinement and shows high internal stresses andhigh concentrations of non-equilibrium defects In addition thesubsequent mechanical activation can be advantageously used forcompositions with higher matrix contents that are not possible to makethrough the SHS special additives can be also introduced into thecomposites at this stage

In order to compose the initial mixtures the following powderswere used titanium PTM lampblack PM-15 and nichrome PR-N70H17S4R4-3 Mechanical activation of the powder mixtures and theSHS-products was carried out in a planetary ball mill AGO-2M

160

Detonation spraying was performed using the laquoKatun-Mraquo set-upIt was found that the chemical composition did not change duringspraying

Wear resistance of the sprayed coatings was evaluated using afriction machine 2168 UMT in the laquoshoe-on-diskraquo mode A coating 02mm thick was deposited on a steel 40 shoe Prior to deposition the shoewas rubbed against the disk until a contact spot was formed over thewhole surface of the shoe After the coating was deposited the workingsurfaces were subjected to abrasive diamond treatment to reduce theirroughness

Tribological tests showed that with increasing metallic matrixcontent from 20 to 60 wt the weight losses under dry friction at 950 Nincreased almost twice Comparative tests of the coatings and thesamples of hardened steel revealed that the wear of the coatings obtainedfrom the mecahnocomposite powders was 8 times lower than that ofsteel 40H

References1 MAKorchagin DVDudina Application of self-propagating high-

temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007 v43 2 p176-187

153

CHEMICAL-THERMAL TREATMENT IN CARBONMANGANESE STEEL

AT INDUCTION-HEATING IN VARIOUS BORATINGCONDITIONS

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

Ural Federal University Ekaterinburg RussiaAltay State Agrarian University Barnaul Russia

Abstract Processes of borating of high-carbon manganese steel65Mn by carbide of boron and amorphous boron in conditions of fluxwith additives of various activators of borating are investigated at high-speed induction-heating It is shown that the nature of the boratingagent the additive of flux activators CaF2 and NH4Cl have influence onstructure and properties which are formed on a surface of boroneutectics

Keywords boron carbide of boron induction heating chemical-thermal processing

Among modern processes of chemical-thermal treatment (CTT)production engineering of saturation of surface layer constructional andalloy steels with boron ndash the borating occupy a special place In boratingit is possible to obtain the extended beds distinguished by high hardnessand strength corrosion-resistance abrasive durability and highreceptivity to wear on a surface of a steel detail [1 2] However themajority of known processes of borating are prolonged and are badlybuilt in into flow diagrams of state of productions

Intensification of CTT processes and in particular borating canbe carried out with application of technology of short-term high-speedheating of steel detail surface with the borating composition put on herrf currents (RFC) up to temperatures of formation of new phases andeutectics (1100-1350 оС) in systems Fe-B Fe-B-C and Fe-Me-B-Cwhere Ме - is an alloy element from group Cr Mn Ni etc [3] Unlikewell investigated processes of borating of alloy steels by mediums anddaubing at temperatures up to 950оС [4] there are open generalquestions of peculiarities of chemical interaction of components in suchsystems phase condition and properties of formed products

154

In the present work chemical-thermal treatment of carbonmanganese 65Mn steel combined with RFC-heating of its surface invarious borating conditions has been investigated

Experimental partAs the basic subject of research 65Mn (GOST 4543-71) alloy

carbon steel was chosen from the group of the same kind manganesechromos chromos-nickel and chromos-manganese steels from group 70U8А 50CrMnА 30CrMnSiА 45Cr 70Mn etc with similar propertiesand composition

Technical carbide of boron B4С in accordance with GOST 5744-85 and reactive amorphous boron of qualification reagent-grade weretaken as borating agents of different nature Known composition for theinduction deposition (F1) consisting of borax glass the boric anhydridecalcium silica and welding flux АN-348А (30 Na2B4O7 20 B2O310 CaSi2 and 40 flux АN-348А) was used as flux Reagent-gradeCaF2 and NH4Cl served as activators

RFC-heating of samples was carried out in a loopback water-cooled copper inductor by diameter of 160 mm connected to RF-lampgenerator VCG 7-600066 The adjustment of a contour and geometryof an inductor provided heating of researched samples to the temperatureof 1300-1350оС during 40-60 sec with the subsequent stabilizationAfter holding at the specified temperature during from 1 up to 2 minsamples were pulled out from an inductor and cooled down loosely

Microstructure of the coverings formed has been investigated andthickness of borated bed has been determined (МIМ-7 Neophot-30)hardness has been measured (PМТ-3 by 50 100 g) phase composition(DRON-2 radiation Co-Kα speed of angular moving of a sample of 1grads min) has been determined

Results and discussionIt is known that classical production engineering of kiln borating

are based on gradual (during 05-6 h) saturation of a surface of a steelproduct by boron from various pastes daubings liquid or a gaseous fluidat temperatures of process from 750 up to 950 оС Thus in the capacityof sources of boron its various compounds (В2О3 В4С ВF3 Na[BF4]etc) are applied capable to decay on active elements at temperatures ofprocess Depending on a phase condition of the borating agent hardness

155

and liquid borating are distinguished and also borating from a gas phase[4] We investigated six variants of mixes for high-speed borating atRFC-heating steel 65Mn Mixes differed in the nature of the boratingagent e borating agent composition presence fluxes componentsactivators and technological additions Compositions of the mixes usedare given in table 1

Table 1

Mixes Boratingagent

Activator Flux

Iа B4C (84) NH4Cl (6) F1 (10)II B4C (84) ndash F1 (16)

IIIа B (90) CaF2 (5) F1 (5)

Mixes I Iа II and IIа used as borating agent contained carbide ofboron mixes III IIIа - amorphous boron in mix Iа activator chloride ofammonium and in mix IIIа - fluoride of calcium has been added allmixes contained melted flux as a fluxing component for inductiondeposition F1

With decrease of density of a borating phase and increase intemperature of process its speed in the interval of temperatures from 800up to 950 оС increases insignificantly therefore for their intensificationcollateral saturation of a surface by several elements at once or thermocycling are applied [5] If the temperature of the process exceeds 1100-1300 оС in an aspect of beginning processes of high-temperaturestructural reorganization in steel speeds of borating sharply increase in2-4 min with the increase in temperature at every 15-20 оС thus theprocess passes from a diffusive zone to a zone of chemical reaction Soat the temperature of 1200-1300 оС according to the data[6] it ispossible to obtain in a few minutes the thickness of the single-phaseboron-bed up to 02-04 mm thus heating of a detail is carried out by thespecial thermo reaction mix

At RFC-heating of the steel 65Mn covered by researched boratingcompositions with chosen parameters of process fig 1 adamantinecoverings are formed on all samples resembling bed covered hard metalX-ray analysis of a material of coverings has shown presence of Fe

156

borides FeB and Fe2B carbon-borides Fe3(C B) and Fe23(C B)6 variousmeta- and orto-borates of iron (Fe3BO3 Fe3BO6 Fe3BO5) traces FeOand FeOFe2O3 Thus at RFC-heating of alloy carbon steels under bedof flux F1 containing from 84 up to 90 of borating agents complexboron-phases are formed on their surfaces hardening a surface of a detailand it is strongly linked with it and oxide films are removed togetherwith slag

To find out the characteristics and structure of received beds andthe conditions of borides in them photomicrography of micro sectionswas taken Typical structures of boron-beds are given in fig 1

a b C

Fig 1

As it is seen from fig1 with the chosen heating environments andthe time of borating the structure and the condition of boundary line ofreceived wear-resistant beds differ but in all cases as against classicalboron two-phase beds on a surface of samples the eutectic with stronglypronounced or with the diffusive boundary line separating it from anoriginal material is formed faster in conditions of heavy abrasive sign-variable and shock wear boron-plate Apparent changes in structure ofparent metal caused by its short-term overheat were not observed

For the mixes containing in the capacity of borating agent equalquantity of carbide of boron similar quantity of fluxes-component anddistinguished only by the presence of activator NH4Cl promoting areinforcement of convertible diffusive and transport reactions especiallyat low temperatures right at the beginning of the process of borating (Т

157

lt300 оС) formation of fine grained structure of eutectic turnings on withhardness not above 700-750 HV thickness of bed of 016 mm and withlegibly discernible interface with parent metal (fig 1а) is observed

For the analogous mix II without this activator the expressedpropagation of dendrites islands and druses of boron-phases withhardness up to 1050-1120 HV thickness of bed of 028 mm and adiffuse interface boron bed with parent metal (fig 1b) is observed Themixes on the basis of amorphous boron (fig 1c) appeared to be the mostreactive thus in mix IIIа containing follow-up 5 of activator CaF2 and5 of fluxes component beyond chosen relationships for 1 minthickness of bed on steel of 65Mn has made 088 mm at its hardness in2200-2300 HV The structure represents the remote eutectichomogenized iron ndash boron formed with such speed that from a melt atits solidification balls of slag had not time to bleed up to the end

Thus amorphous boron which at the presence of flux F1 andactivator CaF2 under the chosen conditions of experiment forms denseclose-grained beds on a surface of alloy steels with depth up to 800microns with hardness up to 2400-2500 HV (fig 2) appeared to be themost efficient borating agent at RFC-heating

Fig 2

It is interesting to note that the structure of the wear-resistantcovering obtained at high-speed 1 min borating steel 65Mn a mix II ismetastable and at borating during 2 min like in picture 1а with hardness2300-2400 HV turns to the fine grained structure and thickness of a

158

covering does not change and the interface with parent metal becomesdiscernible

References1 Methods of raise of longevity of machine components Red VN

Tkacheva M 19712 Belyj AV Karpenko GD Myshkin KN Structure and methods of

formation of wear-resistant surface layers M 19913 Tkachev VN Fishtejn BM Kazintsev NV Aldyrev DA

Induction overlaying welding of hard metals M 19704 Voroshnin LG Lyahovich LS Borating of steel M 19785 Guryev АМ Kozlov EV Ignatenko LN Popova NA Physical of

a basis of thermal-cycle borating Barnaul 2000

138

PHASE STATES OF MECHANOACTIVATED MANGANESEOXIDES

SA Petrova RG Zakharov AYa Fishman LI LeontievInstitute of Metallurgy Ural Division of RAS Ekaterinburg 620016

Russian Federation

An investigation of structural characteristics of the manganeseoxides in order to understand these characteristics affected bymechanochemical treatment conditions has been undertaken Chemicallypure manganese (II III IV) oxides were used as the initial componentsIt is shown that the properties of the mechanoactivated oxides differgreatly from those of initial materials Relationships among structuralcharacteristics of the mechanoactivated oxides and their prehistory wayand conditions of producing have been detected

IntroductionStudy of phase states of mechanoactivated oxides makes it

possible to analyze the patterns of expression of the mechanochemicaleffect in redox processes to determine the mechanism of the effect ofactivation processes on the type and parameters of the structural phasetransitions to establish the role of higher oxides in the redox processesAs one of the consequencies of the intensive mechanical activation is theappearance of nanodisperse states specificity of phase transformationsin nanocrystalline oxides is considered at the same time

It is known now that the decrease in the crystallite size inmechanoactivated systems causes a decrease of structural phasetransition temperatures In metallic alloys reducing of crystallites size isaccompanied by suppression of martensitic transitions [1-2] Completeinhibition occurs when the grain size becomes smaller than that of thecritical nucleus of a new phase It can be regarded as established that theparameters of phase transitions in oxides with relatively lowtemperatures of phase transitions also depend strongly on the grain sizeFor example in barium titanate BaTiO3 transition from cubic to low-symmetry phase is completely suppressed when the grain size is about10 nm [3] Changes in the crystal structure and the effects of reduction(the change of temperature and phase transition heat) in the structuralphase transitions with decreasing grain size also occurred for the oxides

139

Al2O3 Fe2O3 PbTiO3 PbZrO3 La1-xSrxCuO4 YBa2Cu3O7-δBi2CaSr2Cu2O8 [4] and several other oxides [5-6] Besides for the oxidesin nanoscale state the coexistence of two different structuralmodifications [7] was observed The processes of mechanoactivationmay also lead to new types of metastable phase states due to theredistribution of cations between the crystallographically inequivalentsublattices [8]

In the present work the main attention is paid on the analysis ofthe effects associated with the evolution of metastable structures underconditions of temperature increase and oxide interaction with anaggressive environment So far the main contribution to theinvestigation of these issues has made the study of metallic alloys (seefor example [9-10]) The behavior of the activated oxide materials ismuch less studied Study of structural phase transitions in the systemMn-O subjected to mechanochemical activation and structuralcharacteristics of the crystalline phases allows us to test how general arepreviously established patterns for systems with different types ofchemical bonds

The effect of mechanical activation on structural phase transitionsboth of martensate type (from cubic to tetragonal modification Mn3O4)and those accompanied by redox processes (between phases withdifferent degrees of oxidation etc) is investigated The choice of Mn-Ooxides as the object of study is largely connected with the fact that atleast two structural phase transitions observed in the considered crystalswith temperature changes involved the cooperative Jahn-Teller (JT)phase The value of the JT deformation in it is determined by theconcentration of JT ions in octahedral sites that allows to get additionalinformation about the structural changes caused by themechanoactivation of oxide

1 Production and structural properties of themechanoactivated oxides

11 Mechanoactivation of manganese oxidesPure manganese oxides MnO2 Mn2O3 and Mn3O4 annealed at

200deg 900deg and 1250degC respectively were used as the initial materialsFor the mechanical treatment of oxides which was described in

detail in [1112] a planetary mill AGO-2 with water-cooled drums (V =

140

150ml) and a centrifugal factor up to g = 60 [3] was used Download ofballs was 203g the material - from 5g Milling was made dry Theprocessing of powders was carried out after preliminary lining in acontinuous mode or with periodic stops of the mill According toestimates (performed by XPES) contamination by iron was not morethan 02 Previously [14] we found that prolonged continuousmechanical treatment leads to the fact that within the grains matureduring the first seconds along with a further (slow) reduction ofcoherent scattering blocks chemical processes begin leaking Because atthis stage the main purpose was to obtain single-phase samples theduration of continuous grinding was restricted by 30s The temperatureinside the drums during grinding did not exceed 320K which ensuredthe preservation of initial metastable phases During stops of mill thedrums where opened and powder was manually stirred but samplingwas not performed

To be able to conduct magnetic research on the mechanicallyactivated samples and to investigate the effect of intensity ofmechanoactivation (the degree of deformation) on the redox processesand the stability of weakly activated oxides the part of samples wasobtained as a result of mechanical activation in the vario-planetary millPulverizette 4 (Fritsch) in glasses of tungsten carbide Volume of drumwas equal to 250ml loading of crushing balls was 800g and a materialmass was 20 g Milling was made dry the duration was 3 min

12 Attestation of mehanoactivated manganese oxides andmethods of their experimental study

The phase composition of obtained substances the size ofcoherent scattering domains (CSD) and microstresses were determinedby X-ray diffractometer D8 ADVANCE (Bruker) (radiation CuKα Ni-filter position-sensitive detector VANTEC1) High-temperature X-raystudies of the stability of mechanoactivated oxides was carried out usinghigh-temperature chamber HTK1200N (Anton Paar)

The particle size of powders obtained was assessed by dynamiclight scattering using a laser analyzer DelsaNanoC (Beckman Coulter)and an atomic force microscope Solver-Next (NT-MDT) Surface ofoxides was studied by XPES and STEM (Omicron Multiprob)

High-temperature X-ray studies were performed in the range 30-1200degC in air The rate of heating and cooling was 05degCmin Step of

141

the temperature during heating and cooling was 5deg and 10degCrespectively Exposure in the point was 17s (the time of isothermal delayshooting diffractogram was 150s) For the analysis of diffractionpatterns the software package DIFFRACplus [15] was used

13 Results and discussionThe results of the attestation of the initial and mechanoactivated

oxides are presented in Table 1

Table 1 Treatment conditions and characteristics of the manganeseoxides

Cell parameters Initial phasetreating mode

Finalcomposition аAring сAring

Samplename

1 Mn2O3- initial Mn2O3 9412 M232 Mn2O3- AGO 30s Mn2O3 9410 M23A303 Mn2O3- AGO 60s Mn2O3 9410 M23A604 Mn2O3- AGO

10minMn2O3 9410

M23A10

5 Mn2O3- P4 3min Mn2O3 9403 M23P46 Mn2O3-

P4(3min)+USD(70s)Mn2O3 9403

M23P4U

7 Mn3O4-initial Mn3O4 5760 9474 M348 Mn3O4- AGO 30s Mn3O4 5762 9442 М34А309 Mn3O4- AGO 60s Mn3O4 5762 9431 M34A60

5787 950810 Mn3O4- AGO10min

Mn2O3+ Mn3O4

9410M34A10

11 MnO2-initial MnO2 4396 2869 M1212 MnO2- AGO 30s MnO2+Mn2O3(tr) 4397 2872 М12А3013 MnO2- AGO 60s MnO2+Mn2O3(tr) 4397 2872 M12A6014 MnO2- AGO 10min Mn2O3 9408 M12A10

AGO-High-energy planetary mill (60g) P4-Pulverisette 4 (~20g)USD-Ultrasound disintegrator

Since the analysis of the results of mechanoactivation of oxidesMn2O3 showed little difference between the samples activated in theAGO within 30 and 60 seconds further investigation of oxides Mn3O4

and MnO2 was performed on 60-second samples However it is

142

necessary to note that in the case of oxide MnO2 samples after 30 and60-second milling contained different amounts of Mn2O3

According to X-ray phase analysis data chosen mode ofmechanochemical treatment allowed to preserve essentially thecomposition of the initial oxides The exceptions were oxides MnO2which after grinding contained 5 of oxide Mn2O3 and Mn3O4 whichafter grinding for 10 minutes contained a few of Mn2O3

Data on grain size and the coherent scattering domains arepresented in Table 2 It is obvious that even a relatively weakmechanical treatment leads to a decrease in grain size in 2-3 times Inthis case the comparison of grain size and the CSD (comparison of thedynamic light scattering data and X-ray diffraction (XRD) results)shows that the mechanical treatment with a small degree of deformationallows to obtain defect-free grains while increasing of the centrifugalacceleration leads to the appearance and rise of the defects in the grainA tendency to agglomeration of grains with increasing time of intensemechanoactivation should be noted

Table 2 The characteristics of coherent-scattering domains and averagegrain size

Sample nameCoherent-scattering domain

nmGrain size nm

M23 gt200 1026plusmn95M23A30 30 436plusmn168M23A60 23 344plusmn155M23A10 24 939plusmn175M23P4 44 386plusmn50

M23P4U 44 336plusmn22M34 gt200 400plusmn801300plusmn300

M34A60 15 529plusmn340

M34A10 1913 795plusmn104

M12 gt200 428plusmn78M12A60 61 1133plusmn167M12A10 22 565plusmn343

XRD-dataDynamic light-scattering

data

143

Changes in phase composition during heating and cooling ofinitial and mechanically activated manganese oxides are presented inTables 3-4 and Fig 1-2

Comparison of the temperature behavior of the initial unactivatedoxide Mn2O3 and that of grinded for 3 minutes with a force of less than20g shows that mechanoactivation treatment with a small amount ofcentrifugal factor and short times can save not only the phasecomposition but apparently and generally does not alter the propertiesof the powder While increasing the degree of exposure (eg use of millssuch as AGO-2 with acceleration 60g) even at short times leads to achange in system characteristics (the appearance and growth of defectsredox processes) that affect later on behavior of oxide For examplemechanoactivation treatment leads to a shift of phase transitiontemperaures at thermal processing as well as to change of the structuralcharacteristics of the phases formed In particular to different degrees oftetragonal distortion of hausmannite formed during heating Mn2O3 (Fig4)

Table 3 The phase composition of the initial andmechanoactivated manganese oxides at different temperatures

Heating CoolingSample MnO2 Mn2O3 Mn3O4 Spinel Mn3O4 Mn2O3 Phase

1 2 3 4 5 6 7 8- + 920 1140 1120 - appearanceM23

- 955 1170 1010 + - disappear

- + 950 950 1010 - appearanceM23A30

- 995 1105 730 + - disappear

- + 950 950 1040 - appearanceM23A60

- 1000 1120 840 + - disappear

- + - 950 840 840 appearanceM23A10

- 1000 - 290 + 770 disappear

- + 940 1140 1120 - appearanceM23P4

- 980 1165 1080 + - disappear

- + 935 1140 1120 - appearanceM23P4U

- 980 1170 1050 + - disappear

144

1 2 3 4 5 6 7 8

- 685 + 1125 1090 - appearanceM34

- 945 1160 1010 + - disappear

- + appearance370

655

970 1050 -

disappear

900 appearance

M34A60

-

970

1130

880 + -

disappear

- + + 930 880 - appearanceM34A10

- 1005 655 600 + - disappear

+ 550 950 1155 1120 870 appearanceM12

595 1025 1170 1070 + + disappear

+ + 940 985 1110 750 appearanceM12A60

535 985 1165 840 + + disappear

- + 960 960 1000 790 appearanceM12A10

- 1005 1075 630 + + disappear

Table 4 The temperature boundaries of the phases during heating andcooling

Heating CoolingSample Phase

from to from to

1 2 3 4 5 6

Mn2O3 30 955 - -

Mn3O4 920 1170 1120 30

M23

Spinel 1140 1200 1200 1010

Mn2O3 30 995 - -

Mn3O4 950 1105 1010 30

M23A30

Spinel 950 1200 1200 730

Mn2O3 30 1000 - -

Mn3O4 950 1120 1040 30

M23A60

Spinel 950 1200 1200 840

Mn2O3 30 1000 840 770

Mn3O4 - - 840 30

M23A10

Spinel 950 1200 1200 290

145

1 2 3 4 5 6

Mn2O3 30 980 - -

Mn3O4 940 1165 1120 30

M23P4

Spinel 1140 1200 1200 1080

Mn2O3 30 980 - -

Mn3O4 935 1170 1120 30

M23P4U

Spinel 1140 1200 1200 1050

Mn2O3 685 945 - -

Mn3O4 30 1160 1090 30

M34

Spinel 1125 1200 1200 1010

Mn2O3 370 970 - -

Mn3O4 30 655

Mn3O4 900 1130

1050 30

M34A60

Spinel 970 1200 1200 880

Mn2O3 30 1005 - -

Mn3O4 30 655 880 30

M34A10

Spinel 930 1200 1200 600

MnO2 30 595 - -

Mn2O3 550 1025 870 30

Mn3O4 950 1170 1120 30

M12

Spinel 1155 1200 1200 1070

MnO2 30 535 - -

Mn2O3 30 985 750 30

Mn3O4 940 1165 1110 30

M12A60

Spinel 985 1200 1200 840

Mn2O3 30 1005 790 30

Mn3O4 960 1075 1000 30

M12A10

Spinel 960 1200 1200 630

146

a d

be

c fFig 1 The temperature boundaries of the phases during heating and coolingof initial and mechanoactivated Mn2O3 a - original b - M23P4 c -M23P4U d-M23A30 e-M23A60 f-M23A10

147

a

b

cFig 2 The temperature boundaries of the phases during heating and cooling of

initial and mechanoactivated Mn3O4 a-initial b-M34A60 c-M34A10

148

a

b

cFig 3 The temperature boundaries of the phases during heating and cooling ofinitial and mechanically activated MnO2 a - initial b - M12A60 c - M12A10

149

Fig 4 Temperature dependence of the degree of hausmannite tetragonaldistortion for samples with different prehistories

The growth of the crystallite size of mechanoactivated phase withtemperature is shown in Fig 5 Data are shown for the initial phasebelow the temperature of the corresponding phase transition

It is obvious that prolonged treatment in the high-energy millalmost did not give reduction of coherent scattering domains butessentially affected the thermal stability of investigated oxide

150

Fig 5 Temperature dependences of coherent scattering domain size in oxideMn2O3 with varying degrees of mechanoactivation

ConclusionThe main results of investigations are the followingI The conditions of mechanochemical treatment enabling to make

the transfer of Mn-O system to single-phase nanosized state withoutsignificant changes in composition of the initial oxide are found Theexception was oxide MnO2 which after grinding contained a smallamount of oxide Mn2O3

II It is shown that the use of mill of the type AGO-2 with 60gacceleration even at short times of activation treatment of oxides leadswhile maintaining the single-phase of sample to an appreciable changeof lattice parameters growth of stresses and the appearance of defects

III It is found that despite the relaxation character of the evolutionof these metastable structures in the face of rising temperatures there is ashift of phase transition temperatures and changes in structuralcharacteristics of the newly formed phases in comparison with the initialoxides Including marked changes in the parameters of the JT strain (ca

151

- 1) at high-temperature transitions between cubic and tetragonal phasesof oxide Mn3O4

IV It is shown that more prolonged mechanical activation ofoxides MnnOm activates redox processes in these materials theemergence of two-phase states with different degrees of oxidation andeven a complete change of the manganese oxidation degree

V The temperature boundaries of existence of phases duringheating and cooling were determined for the initial andmechanoactivated oxides MnnOm Not only noticeable quantitativedifferences in the position of phase boundaries but also qualitativedifferences in the constructed phase state diagrams were found

This work was supported by RFBR (grant 10-03-96016-p_ural_a) the Program of fundamental research of Presidium ofRussian Academy of Sciences N 27 ldquoFoundations of fundamentalresearch of nanotechnology and nanomaterialsrdquo and the Federal TargetProgram Scientific and scientific-pedagogical staff of innovationRussia (contract 02740 110641)

References1 Glezer AM Blinov EN Pozdnyakov VA Martensitic

transformations in microcrystalline ferro-nickel alloys Izvestiya Aseries of Physical 2002 V66 N9 pp1263-1275

2 Andrievsky PA RAGULYA AV Nanostructured materialsMoscow Academy 2005 192p

3 Polotai AV Ragulya AV Skorohod VV Nanocrystalline BaTiO3

synthesis sintering and size effect Science o Sintering CurrentProblems and New Trends Beograd Kluwer Academic Publishers2003 pp119-125

4 PAyyub VRPalkar SChattopadhyay et al Effect of Crystal SizeReduction on Lattice Symmetry and Cooperative Properties PhysRev B 1995 V51 N9 pp6135-6138

5 Parathasarathi Mondal Dipten Bhattacharya Pranab ChoudhuryDielectric anomaly at orbital order-disorder transition inLaMnO3+ J Phys Condens Matter 2006 V 18 p6869

6 Nandini Das Parathasarathi Mondal Dipten BhattacharyaPartical size dependence of orbital order-disorder transition inLaMnO3 Phys Rev B 2006 V74 p 014410

152

7 VYa Shevchenko OL Khasanov GS Yuriev etc The coexistence ofcubic and tetragonal structures in the nanoparticle of ZrO2Y2O3

oxides Neorg Mater 2001 V37 N9 pp1117-11198 AYa Fishman MA Ivanov SA Petrova et al Specific Features of

Jahn-Teller Structure Phase Transitions in NanocrystallineMaterials Defect and Diffusion Forum 2009Vols 283-286 pp53-58

9 Grigorieva ТF Barinova AP Lyakhov NZ Some features of themechanical alloying in the systems Cu-Bi and Fe-Bi J Metastableand Nanocryst Mater 2003 V15-16 pp475-478

10 Lyakhov N Grigorieva T Barinova A Lomaeva S Yelsukov EUlyanov A Nanosized mechanocomposites and solid solution inimmiscible metal systems J Mater Sci 2004 V39 N 16-17pp5421-5423

11 Zyryanov VV Journal of Structural Chemistry 2004 V45 pp135-143

12 Zyryanov VV Lapina OB Neorg Mater 2001 V37 N3 pp331-337

13 Zyryanov VV Sysoev VF Boldyrev VV Korosteleva TVCertificate of authorship of USSR N 1375328-BI-1988 N 7 p39

14 Fishman AYa Ivanov MA Petrova SA Zakharov RGStructural Phase Transitions in Mechanoactivated ManganeseOxides Defect and Diffusion Forum 2010 Vols 297-301 pp 1306-1311

15 DiffracPlus TOPAS Bruker AXS GmbH OstlicheRheinbruckenstraszlige 50 D-76187 Karlsruhe Germany 2008

118

EFFECT OF HARDENING TEMPERATURE ON THE STRUC-TURAL-MORPHOLOGICAL CHARACTERISTICS OF METAL

CEMENTS BASED ON MECHANOSYNTHESIZED COPPERCOMPOUNDS

NZ Lyakhov1 PA Vityaz2 SA Kovaleva2 TF Grigoreva1VG Lugin3 AP Barinova1 SV Tsybulya4

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS630128 Novosibirsk Kutateladze str 18 grigsolidnscru

2 United Institute of Mechanical Engineering NAS Minsk Belarus3 Belarussian State Technological University Minsk Belarus

4 G K Boreskov Institute of Catalysts SB RAS Novosibirsk Russia

IntroductionMetal cements may be used in many branches of industry due to

good adhesion to the materials of different types (glass ceramics metalsetc) and the metal character of thermal and electric conductivity Theformation of metal cements occurs through the interaction of copper(nickel) alloys with liquid metals and alloys Interactions of a solid metalwith liquid one in particular copper with gallium are known [1 2] tohave diffusion character they are substantially affected by temperatureand the area of contact between the reagents

The use of mechanically synthesized copper compounds allowsone to increase the contact surface between the components and to intro-duce doping elements (Bi In) that improve wettability during gluing andthe strength properties of the alloys to be formed This causes a changeof the kinetics of interaction between a solid metal and a liquid one dueto the acceleration of diffusion processes and due to the formation ofadditional phases

The goal of the present work is investigation of the effect of hard-ening temperature on the structural-morphological characteristics ofmetal cements obtained on the basis of CuBi mechanocomposites andsupersaturated solid solutions Cu(In)

Methods and materialsCopper powder PMS-1 (GOST 4960ndash75) granulated bismuth (TU

6-09-3616ndash82) indium (GOST 10297ndash94) were used in the work Me-chanical activation of the powders was carried out for 15 min in the

119

high-energy ball planetary mill AGO-2 with water cooling in argon at-mosphere (cylinder volume 250 cm3 ball diameter 5 mm loaded wt200 g the weighed portion of the sample under treatment 10 g the fre-quency of rotation of the cylinders around the common axis about 1000rpm) Mechanocomposites having the composition Cu 10 wt Bisolid solutions Cu-12 wt In were obtained [3] Diffusion-hardeningalloys were prepared by mixing the mechanosynthesized copper com-pounds with gallium melt followed by exposure at a temperature of 20C during the whole process of alloy formation To study the effect oftemperature on the structure and morphology of metal cements harden-ing was carried out at 90 С 120 С and 160 С

Surface examination was carried out with the NT-206 atomicforce microscope (Microtestmachines Gomel) using standard commer-cial V-type probes NSC11 (Mikromasch) in the contact mode

The structure of the resulting samples was studied using Mikro200 optical microscope and high-resolution scanning electron micro-scope (SEM) MIRATESCAN with an attachment for micro-X-ray spec-tral analysis (MXSA) The diameter of the electronic probe was 52 nmexcitation region was 100 nm Images were obtained in the mode of re-cording secondary and backward scattered electrons which allowed usto investigate the distribution of chemical elements over the surface andto establish its composition non-homogeneity

The phase composition of powders after mechanical activationand the final products of their interaction with liquid gallium were de-termined with the help of X-ray diffraction techniques X-ray structuralanalysis and semi-quantitative examination of the products were carriedout with the D8 Advance Bruker diffractometer (Germany) by means ofpowder X-ray diffraction in the θ-2θ configuration with a step of 01Phase identification was performed using the diffraction patterns re-corded in CuKα radiation (154051 Aring)

Calorimetric measurements were carried out with Netzsch STA409 PCPG instrument in argon atmosphere in a crucible made ofAl2O3 within the temperature range from room temperature up to 290 Cwith the heating rate of 20 min

120

Results and discussionIt was established in the previous diffraction studies of alloy for-

mation dynamics in CuBi + Ga and Cu(In)+Ga that the formation ofnew phases takes place within a broad time interval During the interac-tion of CuBi mechanocomposite in Bi that is insoluble in copper and ingallium the formation and crystallization of the intermetallic compoundCuGa2 and bismuth take place simultaneously [4]

For the case of Cu(In) solid solution in which the doping elementis soluble in gallium the formation of the phase of solid solution of in-dium has an incubation period of about 210 minutes which is determinedby its concentration in the system with gallium [5]

The interaction processes are described with the following chemi-cal reactions

CuBi + 2 Ga rarr CuGa2 + BiCu(In) + 2 Ga rarr CuGa2 + In(Ga)

1 Effect of the temperature of interaction of CuBimechanocomposites with liquid gallium on the structure andmorphology of the formed metal cementsIt is known that the resulting mechanocomposites are nanosized

copper surrounded by a thin bismuth layer [6] Bismuth is mainly com-posed of the particles less than 5 nm in size

According to the data of AFM topography the size of mechano-composite particles is 150divide250 nm (Fig 1)

Fig 1 Mechanocomposite Cu + 10 wt Bi after activation for 15 mina ndash SEM image b ndash AFM c ndash TEM

121

At first we studied the interaction of CuBi with liquid gallium atroom temperature

The X-ray structural analysis of the resulting cement carried outafter the interaction for 4 and 48 hours showed that the size of the crys-tallites of the intermetallic compound increases from ~ 200 nm to ~ 550nm The size of bismuth crystallites increases up to 100 nm It should benoted that this is accompanied by a decrease in the size of copper crys-tallites down to ~ 10 nm The final phase composition is determined asCuGa2 Bi and unreacted copper (Fig 2)

Fig 2 Diffraction patterns of the product of interaction Cu 10 Bi + Ga

Figure 3 shows the high-resolution SEM images of the micro-structure of the surface of the final interaction product The SEM imageof sample surface after hardening without the mechanical treatment ofthe surface is shown in Fig 3a The image of the surface obtained in thebackward scattered electrons after sample polishing is shown in Fig 3bBecause bismuth is the heaviest element in this system it will be distin-guished by the maximal brightness in the SEM image

The data obtained by means of microscopy show that the structureof the surface of final product is facetted tetragonal crystals СuGa2 withthe size up to 4 μm Bismuth is localized at the faces of crystals and at

122

the boundaries of CuGa2 grains as disperse formations 70-250 nm insize and also forms separate grains with a size up to 10 μm

a bFig 3 Topography of the surface of CuGa2 +Bi alloy after the interaction for48 hours a ndash SEM image of non-polished sample in direct electrons b ndash SEM

image of the polished sample in backward-scattered electrons

The use of AFM allowed us to study the microstructure of facet-ted tetragonal CuGa2 crystals The presence of screw dislocations inthem may be stressed as a result the crystalline layer grows by windingcontinuously on itself so the step takes the shape of a spiral (Fig 4) Thelayer-by-layer growth of crystallographic facets should also be men-tioned The edges of incomplete layers or steps move along the facetwhile they grow The step height that is the thickness of the depositinglayer varies within the range 4 to 200 nm The appearance of highgrowth steps may cause trapping of the melt drops and precipitation ofinsoluble bismuth admixture on the surface of steps of the growing crys-tals which is indeed observed in Fig 4 b Bismuth is adsorbed on facetssteps and along the grain boundaries

It should be stressed that the growth of faceted crystals requiresspecial conditions supersaturation or supercooling of the mother me-dium small number of appearing nuclei We suppose that the localthermal supercooling arises as a consequence of the chemical interactionof copper with gallium melt on the interface between the solid phase andthe liquid one with the formation of chemical compound CuGa2 withcrystallization temperature higher than the temperature of the melt Theconditions of substantial supercooling are created for this compound soits crystallization starts In this process bismuth particles get released

123

into the melt Thee particles are insoluble in liquid gallium and may actas the centres of crystallization and also they may brake down thegrowth of intermetallide particles by getting adsorbed on their surfaceThe latent heat of melting released during crystallization raises the tem-perature of the melt (so gallium remains in the liquid state during reac-tion at 20 C) and decreases the degree of overcooling thus creating theconditions for the growth of larger facetted intermetallide crystals fromthe melt

а b

Fig 4 AFM image of the surface of resulting alloy CuGa2 + Biа - Torsion-image of bismuth on facets and growth steps of CuGa2 (the contrastis formed due to the difference in tribological characteristics of the phases of

intermetallide and bismuth) b ndash layered spiral growth of CuGa2 crystals alongthe screw dislocation (marked with arrows) The upper part shows a scheme ofcrystal growth along the screw dislocation and the shape of the step formed inspiral growth [7]

At room temperature the final product of the interaction of CuBimechanocomposite with liquid gallium is a matrix composed of CuGa2

intermetallide particles 1ndash4 μm in size with bismuth particles distrib-uted in it (from 70 to 250 nm) which form local agglomerations up to 10μm in size

X-ray studies of the alloys obtained at hardening temperature of90 and 120 C showed that an increase in temperature to 120 C does notaffect the phase composition Similarly to the case of room temperature

124

the product is composed of intermetallide CuGa2 (PDF-2 No 25-0275)bismuth (PDF-2 No 44-1246) and residual copper (PDF-2 No 04-0836)(Fig 5)

Fig 5 Diffraction patterns of CuGa2 + Bi samples obtained at temperature 40(a) 90 (b) and 120 (c) C Unmarked peaks relate to CuGa2 intermetallide

With an increase in the interaction temperature the lattice pa-rameters of copper and CuGa2 phases remain almost unchanged Thesize of copper crystallites is about 35 nm Bismuth undergoes tempera-ture-caused changes An increase in the size of bismuth crystallites from100 nm at 20 C to 180 nm at 90 C and to more than 500 nm at 120 C

Alloys obtained by mixing the CuBi mechanocomposite with liq-uid gallium have a composite structure after hardening Their structuremay be described as an intermetallic shell with the unreacted part ofcopper in its centre The СuGa2 intermetallide has a shape of facetedtetragonal crystals up to 4 μm in size With an increase in reaction tem-perature to 90 C the size of het particles of intermetallic compund in-creases to 6-8 μm and remains almost the same at a temperature of 120C In the lateral contrast mode the facets of crystals obtained at 90 and120 C exhibit local accumulations of bismuth as well as substantial de-formation distortions of crystals due to the arising stretching strain inthe crystal in the direction lt001gt (Fig 6) Intermetallide crystal starts to

125

have layered structure The facets of the intermetallide obtained at ele-vated temperatures also exhibit deformation distortions that are likelyconnected with bismuth adsorption on the facets The appearance ofthese lines is due to the development of local fluidity They arise in thecases when the material possesses a distinct yield point even insignifi-cant concentration of strain promotes the appearance and developmentof these figures [8] Change of the straight character of the glide lines islikely to be connected with the effect of boundary volumes intra-grainstructural strain caused by differences in the volumes of the intermetal-lide and bismuth as well as by glide in different systems and with thetransition from one system to the other

а

b

Fig 6 AFM images of CuGa2 + Bi alloys obtained at a temperature of 90 (a)and 120 (b) С

126

Metallographic in-vestigation of the alloysurface after polishing(Fig 7) showed that thenumber of macrodefectssuch as pores and discon-tinuity flaws decreaseswith an increase in crystal-lization temperature Mi-crohardness of the inter-metallide increases fromHV 70 to 125

Investigation of thedistribution of chemicalelements over the sampleby means of SEM involv-ing X-ray spectral analysisrevealed nonuniformity ofthe distribution of insolu-ble bismuth

Bismuth is not ob-served in the regions withthe intermetallic com-pound which may be con-nected with the fine distri-bution of disperse particlesover the boundaries of theintermetallide Local ac-cumulations of bismuth upto 10 μm in size are ob-served mainly in the siteswhere macrodefects (poresgrain boundaries) get ac-cumulated With an in-crease in the temperature ofinteraction up to 120 Сthe number of local bis-muth accumulations de-

а

b

cFig 7 Optical images of the structure of

CuGa2 + Bi alloys obtained at 20 (a) 90 (b)and 120 (c) С

127

creases but their size increases to 20 μm (Fig 8)

а b

Fig 8 SEM images (in backward scattered electrons) of CuGa2 + Bi alloyHardening temperature а ndash 20 С b ndash 120 C

Thermal investigation of the alloys with different hardening tem-perature points showed that the curves of differential scanning calo-rimetry (DSC) exhibit definite differences only during heating the alloyswith hardening temperature 20 C and 90 C The DSC curves of the al-loys with hardening temperature 90 and 120 С are identical Duringheating the alloy with hardening temperature 20 С exhibits the exother-mal heat effect at a temperature of 120-150 С This effect may be con-nected with the occurrence of recrystallization processes in bismuthThis exo-peak is absent during the repeated heating

Thus investigation showed that an increase in the temperature ofthe interaction of CuBi mechanocomposite with liquid gallium leads toan increase in the size of the formed intermetallide as well as to a de-crease in macrodefects in the form of pores discontinuity flaws cracksThe hardness of the intermetallide thus increases

2 Effect of the temperature of interaction of mechanochemi-cally prepared solid solution Cu (In) with liquid gallium onthe structure and morphology of metal cementThe use of mechanochemically prepared powders of Cu-In system

as the solid phase in the reactions with liquid gallium increases the num-

128

ber of interacting systems due to the solubility of indium in gallium Ac-cording to the state diagram of the system GandashIn [9] the solubility of Inin Ga in the solid state is less than 03 at while the solubility of Ga inIn is 31 at At a temperature of 60 С indium may be dissolved in liq-uid gallium up to 48 wt

Mechanochemically synthesized powder in the system Cu + 12wt In was used as the initial solid-phase component The X-ray phaseanalysis of the products of mechanochemical synthesis (Fig 9) showedthat the solid solution of indium in copper in formed during mechanicalactivation of copper powder with 12 wt indium As a result the latticeparameter of copper increases to а = 36659 Ǻ (аref = 36150 Ǻ) The size of copper crystallite is about 30 nm

Fig 9 X-ray diffraction patterns of the powder Cu-12 wt In after mechanicalactivation (for 20 min) in argon

Mechanical activation of the system Cu + 12 wt In leads to theformation of fine particles of the solid solution of indium in copper (150ndash 230 nm) (Fig 10) Recrystallization of the solid solution of copper andthe formation of grains larger than 15 μm are also possible

129

Fig 10 Topography of the ultrafine powder of the solid solution Cu(In)

A decrease in the size of precursor powder is known to providelarger area of contact between the components of the solid phase and theliquid one and therefore shorter diffusion distances during subsequentinteractions with metal melts Because both copper and nickel are solu-ble in liquid gallium one may expect that the rate of dissolution of themechanocomposites of the system Cu-In would be significant

X-ray phase analysis of the final products of the interaction of thesolid solution Cu(In) with gallium at room temperature revealed thepresence of three phases intermetallide CuGa2 indium and unreactedcopper (Fig 11)

Fig 11 Diffraction patterns of the alloys obtained through the interac-tion of Cu 12 wt In + Ga CuGa2 - In - Cu

130

For the initial powder with indium concentration 12 wt theproduct of the interaction exhibits a decrease in the indium unit cell pa-rameter с in the alloy under formation to с = 49306 Ǻ (cref = 49459 Ǻ) The size of copper crystallites is about 7 nm while the size of indiumcrystallites is about 30 nm Slight changes in the unit cell volume of in-dium may be related to the formation of the solid solution of gallium inindium

During the interaction indium gets dissolved in the liquid phaseof gallium gets concentrated and crystallizes at the interfaces betweenthe solid phase and the liquid one The alloys with the 12 indium con-tent are characterized by a large range of the dimensions of tetragonalparticles of the intermetallic compound CuGa2 (from 05 to 8 μm) TheAFM image (Fig 12) exhibits coarse crystals their crystallographicshape is uncharacteristic of the intermetallide CuGa2 Comparing the X-ray data and the results of AFM we may assume that they are a solidsolution of gallium in indium

Fig 12 AFM topography of the surface of CuGa2+ In(Ga) alloy

A decrease in the AFM scanning pitch and simultaneous acquisi-tion of the image of distribution of normal (topography) and lateral (tor-sion) forces allowed us to distinguish the structural features of the phaseof the solid solution of gallium in indium (Fig 13) A specific distin-guishing feature is the presence of strands in the crystals of the solid so-lution of gallium in indium connected with layering of the solid solutioninto the regions with larger and smaller concentration of the componentwhich is well seen in the image of torsion (Fig 13b) The size of separate

131

grains of the solid solution of gallium in indium reaches more than 10μm

Fig 13 AFM topography of the surface of samples of CuGa2+ In(Ga) alloy (а)image of torsion (b)

Fig 14 The SEM image in direct (а) and back-scattered electrons (b) of thealloy CuGa2+ In(Ga) In the upper part the data chart of the quantitative spec-

tral analysis carried out in the indicated points

To investigate the microstructure of the surface of alloys we car-ried out the examination with the scanning electron microscope and ob-tained the images of the surface of resulting alloy for the interaction Cu12 wt In + Ga in direct (Fig 14а) and back-scattered (Fig 14 b) elec-trons The application of imaging in back-scattered electrons allow one

132

to investigate the composite surface non-uniformity with which the in-tensity distribution over the image depends on the atomic number of anelement One can see in Fig 14 b that the contrast in the BSE images isdetermined by the topographic features of the surface and the distribu-tion of intensities is uniform In addition local X-ray spectral analysiscarried out in different points of the alloy surface revealed the presenceof indium in concentrations 01 to 7 This fact allows us to concludethat indium is present on the surface of CuGa2 intermetallic crystals inthe form of thin films

Another characteristic feature of the surface of samples obtainedin the interaction of solid solutions Cu(In) with liquid gallium is thepresence of fine dispersed formations on the surface of crystals andgrains of CuGa2 that are more clearly seen in the AFM images (Fig 13a) and are detected in the SEM images (Fig 15 b) The formation of thestructures of this kind on the surface of the intermetallide may be con-nected with indium crystallization on the surface of the growing crystals

Fig 15 AFM (a) and SEM images (b) of the face of CuGa2 intermetallic ob-tained by the interaction of Cu 20 In + Ga

So on the basis of X-ray spectral data obtained and the results ofAFM and SEM we may assume that indium gets crystallized not only inthe form of large grains of the phase of the solid solution of gallium inindium but also on the faces of the intermetallide thus forming a nano-meter-sized film of indium about 10 nm thick

133

In order to establish the effect of temperature on the structure andmorphology we carried out alloy hardening at temperature of 60 120and 160 C

X-ray structural investigation of the final phase composition (Fig16) of the alloys showed that no changes in the phase composition of themetal cement are observed with an increase in hardening temperature to160 C The parameters of intermetallic compound CuGa2 remain almostunchanged The values of lattice parameters of the indium phase underformation are also insignificantly differing from the reference ones

Fig 16 Diffraction patterns ofCu-In-Gа samples obtained at

different temperatures

Investigation of the microstructure of alloys obtained at 20 Cshowed that indium is well adsorbed on the surface of intermetallidecrystals and crystallizes not only as separate crystals of the solid solutionof gallium in indium but also as the film formations with grained anddendrite structure on the faces of the intermetallide The occurrence ofintercrystal films of indium or the solid solution of indium may be re-sponsible for a decrease in strength characteristics of the alloy and be areason of both the intra-crystal and inter-crystal fractures (Fig 17 b) It

134

is assumed that an increase in hardening temperature causes substantialformation of the film structures of the solid solution of indium

The AFM investigation of the topography of alloys obtained attemperatures 90-160 C showed that the alloys are characterized by alarge size range of the intermetallic compound CuGa2 At the interactiontemperature of 20 C the size of CuGa2 particles was 05 to 8 μm Withan increase in reaction temperature to 90 C the crystal size increases upto 11 μm Crystal concretions are also formed (Fig 17) One can see inFig 17 b that cracks are formed in the grain plastoelastic deformationson the intermetallide face occur which is likely to be due to the differ-ence in interfacial surface tension of the intermetallide and indium film

ab

Fig 17 AFM image of the surface of CuGa2 + In(Ga) alloy obtained at 90 C a- topography b ndash distribution of lateral forces (arrows show cracks deforma-

tion distortions)

At a temperature of 120 and 160 C the contrast of the surface re-lief decreases due to the formation of a continuous film (Fig 18) on thesurface

Investigation of the phase transitions in the alloys was carried outby means of DSC For heating the products of the interaction betweenthe solid solution of indium in copper and liquid gallium at a rate of30Cmin an endothermic effect is observed on the DSC curves of all thealloys at a temperature about 254 C and an exothermic effect at 290 Con cooling the exothermic peak appears at a temperature of 210-220 С

135

а b

Fig 18 AFM topography of the CuGa2 + In(Ga) alloy a ndash 120 C b- 160 C

According to the Cu-Ga state diagram these effects are connectedwith the peritectic transformations of the main phase of intermetallideCuGa2 during heating and cooling The cooling curves exhibit no ther-mal effect due to the phase transition of indium The DSC curve of thealloy obtained at 20 C contains an endothermic peak at about 130 Cwhich gives much smaller heat effect in the second heating cycle Tak-ing into account the fact that the formation of indium films and the solidsolution of indium with the grained and dendrite structures occurs on thesurface of the intermetallide it may be assumed that heating to 130 C isaccompanied by melting of the indium film (taking into account a de-crease in melting temperature for thin films) [10] and the solid solutionIn(Ga) At the temperature of the peritectic transformation 254 C in-dium gets dissolved in the formed liquid Ga(Cu) with subsequent for-mation of the ternary compound Cu-Ga-In during cooling For coolingthe temperature of the peritectic reaction for the obtained compound de-creases to 210-220 C

ConclusionAs a result of the investigation of the structure and morphology of

metal cements prepared on the basis of mechanosynthesized coppercompounds CuBi and Cu(In) the structure and morphology in the reac-tions with liquid gallium are determined by the degree of interaction of

136

the doping component with gallium In the case of the CuBi mechano-composite in which Bi does not interact with gallium an intermetallidewith particle size up to 4 μm and local accumulations of bismuth areformed With an increase in hardening temperature to 120 C intermetal-lide growth to 8 μm occurs

When using the solid solutions Cu(In) in which indium is solublein liquid gallium and the incubation period for the crystallization of thesolid solution In(Ga) the formed particles of intermetallide CuGa2 havea broad size range from 05 to 8 μm With an increase in hardening tem-perature to 160 C the size of intermetallide particles increases to 11 μmredistribution of indium occurs along with an increase in the number ofits film structures that are formed on the faces of the intermetallide andcause a decrease in its strength properties thus providing intra-crystaland inter-crystal fracture A decrease in the melting temperature for in-dium to 130C and a decrease in the heat effect at this temperature in thealloys obtained at the alloy formation temperature of 90 120 and 160 Cmay be connected with an increase of indium film amount

The work is carried out under the Integration Project of SB RASNo 138 and BRFFI Т09СО-014 laquoDevelopment of Fundamental Basisof the Action of Activation on Regulation of the Processes of Interactionof Solid Metals and Their Comopunds with Metal Melts for the Purposeof Obtaining Functional Materials with Required Structure and Proper-tiesraquo

References1 Tikhomirova OI Ruzinov LP Pikunov MV Marchukova ID

Investigation of mutual diffusion in the system gallium ndash copperFiz metallov I metallovedenie 1970 vol 29 issue 4 p 796-802 (inRussian)

2 Glushkova LI Konnikov SG Interaction between components inthe solder paste based on gallium Pressure treatment of metals andwelding Proceedings of the Leningrad Polytechnical Institute1969 No 308 p 205-208 (in Russian)

3 Grigorieva TF Barinova AP Lyakhov NZ Mechanochemicalsynthesis in metal systems Novosibirsk 2008 (in Russian)

4 Ancharov AI Grigorieva TF Barinova AP Lyakhov NZ Investi-gation of the interaction of liquid metals with nanocomposites by

137

means of diffraction of the synchrotron radiation Nuclear Instru-ments amp Methods in Physics Research 2007 v A 575 p 130-133

5 Ancharov AI Grigorieva TF Tsybulya SV Boldyrev VVNeorganicheskie Materialy 2006 V 42 No 9 p 1164-1170 (inRussian)

6 N Lyakhov T Grigorieva A Barinova Nanosized mechanocom-posites and solid solution in immersible metal systems Journal ofmaterials science 39(2004) 5421-5423

7 Chernov AA Crystallization processes Modern CrystallographyMoscow 1980 vol 3 p 5-12 (in Russian)

8 Bernshtein ML Zaymovsky VA Mechanical properties of metalsMoscow Metallurgy 1979

9 State diagrams of binary metal systems Ed by NP Lyakishev1997 vol 2 p 636ndash637 (in Russian)

10 Gromov DG Gavrilov SA Redichev EN Klimovitskaya AVAmmosov R M Factors determining melting temperature of thinfilms of Cu and Ni on inert surfaces Zhurnal Fizicheskoy KhimiiV 80 No 10 2006 p 1856-1862 (in Russian)

104

ZINC IONS REDUCTION ON SOLID METAL ELECTRODES INCHLORIDE MELTS

Alex Lugovskoy 1a Zeev Unger 12b Michael Zinigrad 1cDoron Aurbach 2d

1Material and Chemical Engineering Department Ariel UniversityCenter of Samaria Ariel 40700 Israel

2Department of Chemistry Bar-Ilan University Ramat-Gan 52900Israel

alugovsaarielacil bzevikitoarielacil сzinigradarielacildaurbachmailbiuacil

keywords electrodeposition chloride melts cyclic voltammetry high-temperature electrochemistry

AbstractThe reduction of zinc ions on solid tungsten and platinum

electrodes in chloride melts at the temperatures 700 ndash 750 degC wasstudied by cyclic voltammetry chronoamperometry and energydispersion spectroscopy It was established that no zinc is reduced onplatinum electrodes As for the reduction of zinc ions on tungstenelectrodes the process has a complex character it starts as anirreversible two-electron zinc ion reduction and after the new phase isformed the process of saturation of the electrode surface with lithium orsodium begins As the second process develops the alkaline metalbecomes essentially the only constituent on the electrode surface

GeneralSince zinc is industrially recovered from sulfate solutions rather

than from melts and because its melting temperature (4195 degC) is lowerthan the temperatures of most molten chloride compositions thereduction of zinc ions on solid electrodes in chloride melts has beeninvestigated relatively poorly There are quite a few papers devoted tothe electrolysis of zinc containing chloride melts (1 2) and these coveronly some details of the electrochemistry of this metal However zinc isnot only an engineering metal It can often be a component of moltenchloride systems in which various processes of synthesis or purification

105

are performed Therefore the detailed electrochemical behavior of zinccan be of great importanceThe study of electro-reduction processes of zinc ions on solid tungstenand platinum electrodes in eutectic NaCl ndash KCl and LiCl ndash KCl melts inthe temperature range of 700 ndash 750 degC is presented in this work Thesetemperatures are somewhat higher than the eutectic points of NaCl ndashKCl (646 degC ) and LiCl ndash KCl (628 degC) and the melts are thereforeliquid enough to be used in technologically important processes oflanthanides and actinides separation reduction and rectification On theother hand these temperatures are significantly lower than the boilingpoint of zinc (907 degC) and there is essentially no loss of the metal due toevaporation

ExperimentalThe electrochemical experiments were performed using a three-

electrode cell made of sintered alumina placed in an alumina crucibleunder nitrogen atmosphere Tungsten (9995 1 mm diameter) andplatinum wires (9995 05mm diameter) were used as the workingelectrodes and their surface area was controlled by immersion depth(typically 6ndash12mm) and by measuring their diameter before and aftereach experiment A 1mm tungsten wire served as a pseudo-referenceelectrode and a flat spiral tungsten wire set perpendicular to theworking and reference electrodes close to the bottom of the cell servedas the counter electrode The area of the counter electrode was ~ 20 foldas large as that of the working electrode ZnCl2 LiCl NaCl and KCl(990 +ACS grade Alfa Aesar) were used for the preparation meltswithout further purification

Zinc chloride was mixed with alkaline metals chlorides usingmortar and pestle in a glove-bag in dry nitrogen atmosphere Themixture was then placed into a crucible the electrode cell was mountedand transferred into the furnace (single-zone Carbolite 1600 degC STF tubefurnace) In the furnace the mixture was first dried under vacuum at 40ndash50 degC for an hour After completing the drying dry nitrogen wasbubbled through the electrolyte during its heating up to the temperatureof the experiments (700ndash750 C) for another hour The temperature wascontrolled by a type S thermocouple placed next to the cell andprotected by an alumina capillary thus maintaining a precision of plusmn1 degCin measuring and controlling the temperature Dry nitrogen atmosphere

106

(1 bar) was maintained in the furnace during the measurements and thepost-experimental cooling The electrochemical measurements werecarried out using an Autolab PGStat-12 potentiostat SEM images andelement analysis by EDS were performed with a SEM system fromJEOL Inc Model JSM 7000F

Results and discussion

Deposition of zinc on a tungsten electrodeSome typical voltammograms for the electrochemical reduction ofZn(II) are shown in Fig 1

-02

-01

0

01

02

03

04

-1 -05 0

iA

cm

2

E V vs W

C

A

QaQ

c~ 1

0502005 Vsec

-0680-0650-0600E

p V

(peak C)

164141110Qc Ccm

2

177150113Qa Ccm

2

Fig 1 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0163 mol L) in equimolar NaCl-KCl melt on a W electrode at 700degC Scanrates are 50 mV sec (solid line) 200 mV sec (slashed line) and 500 mV sec(dotted line) Each charge density was calculated as the sum of areas limited bythe baseline and the appropriate current density curves for the forward andbackward semi-cycles

107

As follows from Fig 1 a single cathodic peak C corresponds toone anodic peak A The potential shape and behavior of the cathodicpeak are typical for the metal deposition on a solid electrode (2-4) Nodifference is observed between the reduction of zinc ions in NaCl ndash KCland in LiCl ndash KCl melts Peak A is assigned to the reoxidation of zincBoth peaks are clearly not independent on the scan rate Rather peak Cis shifted to more negative potentials and peak A moves to more positivepotentials as the scan rate increases The dependence of the cathodicpeak potential on the scan rate is shown in Fig 2 Such voltammetricresponse is typical for irreversible processes

055

06

065

07

075

0 01 02 03 04 05 06

-Ep

V

Vs

Fig 2 Dependence of the cathodic peak potential on the scan rate for thereduction of Zn2+ (0163 mol L) at 710degC on a W electrode

The cathodic peak C appears at about -06 V vs tungsten electrodefor the scan rate of 50 mVsec and at -07 V for 500 mVsec Such asignificant shift is a clear indication that the process is irreversible Thecathodic peak not only is shifted as the scan rate grows but it becomes

108

broader so that the difference |Ep ndash Ep2| grows from 01 V for 005 Vsecto 015 V for 05 Vsec Values of n calculated by equation 23 are inthe range of 156 for low scan rates to 104 for high scan rates The mostlogical interpretation of this finding is that the charge-transfer is of two-electrons which is not surprising in the case of Zn2+ ions reduction Thevalue of is then 078 for 005 Vsec and 052 for 05 Vsec This isevident that the rate determining step is the Faradaic process

Zn2+ + 2e- Znwhen the system is close to the steady state Note that at low enoughpotential scanning rates diffusion limitations may be less influencingwhile at higher scan rates the diffusion limitations are more importantRandles-Sevcik dependencies for the zinc (II) ions reductiondemonstrate linearity but their intercepts are apparently non-zero (Fig3)

0

01

02

03

04

05

06

07

0 02 04 06 08 1

i pA

cm

2

12 V12s-12

Fig 3 Randles-Sevcik plots for Zn2+ ions reduction on W in a NaCl-KCl meltat 700 degC different concentration of the ions (peak C in Figure 39) 900x10-5

molmL Zn2+ 163x10-4 molmL Zn2+ 177x10-4 molmL Zn2+

109

It is evident that the process Zn2+ + 2e- Zn is complicated bysomething else Despite the irreversible character of the depositionprocess it is still reasonable to roughly evaluate the diffusion coefficientof Zn2+ according equation 1

ip = 06105 (nF)32(RT)12D12C12 (11)

where ip is the peal current density (A cm2) n is the number ofelectrons F is Faraday constant (96500 C) R is the gas constant (8314Jmol∙K) T is the absolute temperature (K) D is the diffusion coefficient(cm2 sec) C is the bulk concentration of a Red (Ox) species (mol cm3) and is the scan rate (V sec)

Thus calculated diffusion coefficients are shown in Table 1

Table 1 Diffusion coefficients of Zn2+ to a tungsten electrode in NaCl-KCl melt

C105 mol L D 105 cm2 sec900 955n

163 1020n

177 1364n

Given that the value of n for the reduction of Zn2+ cannot exceed 2 and0 le le 1 ( asymp 05 for most cases) reasonable values of n must beclose to 1-2 Therefore the values of the diffusion coefficients fromTable 2 lie in the range of 1-6∙10-4 cm2sec Available literature data forthe diffusion coefficients of most metal ions lie in the range 10-5-10-4

cm2sec Particularly T Stoslashre G M Haarberg and R Tunold found thatthe values of the diffusion coefficients for Zn2+ in KCl-LiCl melts at400degC lie in the range 06 ndash 106∙10-5 cm2sec (2) Delimarski providesthe value of the diffusion coefficient of Zn2+ in NaCl-KCl at 710degCwhich is 23∙10-5 cm2sec (5) The deviation of our results from theliterature data can hint that that the process cannot be treated as simplezinc ion reduction on the surface of tungsten

110

It is worth to mention that the fact that the diffusion coefficientfor zinc ions in the chloride melt lay in the range 10-4 ndash 10-5 cm2sec mayserve as an indirect argument in the discussion about the existence ofcomplex species described by the general formula [ZnxCly]

z+ in chloridemelts While some authors argue in favor of the formation of complexions (6 ndash 10) other studies give evidence for the existence of individualzinc ions as the key reacting species (11 ndash 12) The relatively highvalues of the diffusion coefficients found in our experiments hint that thecharge is transferred by individual ions rather than by more massivecomplex moieties

005

01

015

02

025

03

035

04

02 03 04 05 06 07 08 09 1

700oC

750oC

740oC

720oC

i pA

cm

2

12

V12

s-12

Fig 4 Randles-Sevcik plots for Zn2+ reduction on W in a NaCl-KCl melt fordifferent temperatures [Zn2+] = 900x10-5 molmL

Another intriguing aspect of the zinc ions deposition process ona tungsten electrode can be seen in the temperature dependence of

111

Randles-Sevcik plots (Fig 4) As seen from Fig 4 Randles-Sevcik plotsdo not change (to the accuracy of the experiment) as the temperaturerises from 700degC to 750degC

The lack of dependence of Randles-Sevcik plots on thetemperature is really surprising A plausible explanation to this could bean additional process in the system which occurs simultaneously withthe observed process but does not involve charge-transfer and cannot bedetected electrochemically Such a process could compensate for theexpected increase of the slope of Randles-Sevcik plots as thetemperature grows and thus distort the temperature dependence

The most probable candidates for such competing processes area coupled chemical (not charge-transfer) reaction or a process of phase-formation However cyclic voltammetry alone cannot discriminatebetween these two possibilities

Fig 5 A chronoamperometric plot for the deposition of Zn2+ on a tungstenelectrode Temperature 725degC [Zn2+] = 900x10-5 molmL The potential was

stepped from OCV to -055 V

A further insight on the nature of the deposition process can beprovided by chronoamperometry As seen from Fig 5 the current fallsin the course of the first 11 seconds of the experiment and then risesreaches a peak and gradually declines as expected with time until theend of the experiment (300 seconds)

The initial falling and rising of the current can be attributed tothe nucleation of the deposits fluctuations of current for more advanced

112

reaction times as seen in Fig 5 may indicate to a very active charge-transfer process which cannot be explained by a simple zinc depositionprocess

Even more surprising information is provided by EDS analysisof the working electrode after a 3000 second deposition experiment at ndash055 V (Fig 6 Table 2) The most striking result of the analysis is theunexpectedly high content of sodium on the electrode surface Thisamount of sodium cannot be accounted for melt adhesion or penetrationbecause the percentage of potassium and chlorine is much smaller Infact the working electrode looks as it was made of sodium withmoderate inclusions of tungsten and zinc rather of tungsten

Fig 6 An EDS spectrum of tungsten working electrode after 3000 seconddeposition at ndash 055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Table 2 Element composition of the tungsten working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Element Na K Cl W ZnAt 6084 580 2861 224 191

113

A somewhat similar phenomenon was reported by Thus T StoslashreG M Haarberg and R Tunold for the deposition of Zn2+ on a glassycarbon electrode in KCl-LiCl melts at 400degC (2) They observed aldquosubstantial residual current observed prior to the Zn(II) reductionpeakrdquo This current was attributed by them to lithium intercalation intothe lattice of the glassy carbon electrode

Unfortunately the data about standard reduction potentials ofmany important ions in molten chlorides are lacking The only source inwhich suitable potentials were found is the book of Yu DelimarskildquoElectrochemistry of Ionic Meltsrdquo (5) The values of standard potentialstabulated in this book were calculated on the base a few assumptionsand are far from being strictly thermodynamical However they arehelpful from the practical point of view The potentials relevant for thisdiscussion are summarized in Table 3

Table 3 Standard reduction potentials in molten chlorides (adopted fromref [5])

Half-Element Li+|Li Na+|Na K+|K Zn2+|Zn Fe2+|FeEH2 (700degC) V - 239 - 236 - 250 - 040 - 007

As seen from Table 3 the standard potentials of lithium andsodium are very close to each other Therefore it is not surprising thatthe interference from sodium in the deposition of zinc ions is similar tothat of lithium as reported by T Stoslashre G M Haarberg and R TunoldOf course it is not intercalation that serves as the moving force of theprocess of sodium penetration into the surface layers of zinc deposit onthe tungsten electrode

The large amounts of sodium in the deposits obtained in the studyof the Zn2+ ions reduction on tungsten electrodes cannot be explained asthe formation of a W-Na alloy because such a process is not observedby the cyclic voltammograms of NaCl-KCl on tungsten electrodes in theabsence of zinc ions (3) Therefore it is zinc which triggers thedeposition of sodium Moreover the data obtained bychronoamperometry at E = ndash 055 V vs W (Fig 5) indicate that there aretwo sequential faradaic processes The first of them is relatively weak

114

and is completed after ~ 11 seconds Then the second process starts andits current only grows with time The first process can be related to thereduction of zinc ions and the formation of zinc deposits As theelectrode surface is covered by a layer of zinc the interaction of thislayer with Na+ ions begins Apparently sodium ions are absorbed by theliquid zinc (Tm = 419 degC) and this facilitates their reduction at thepotential so much more positive than the sodium reduction potential inthe absence of zinc ( - 11 V vs W) Both lithium and sodium are liquidat the temperature of the experiment and these two metals form on theelectrode surface a liquid solution with zinc which continues to absorbnew portions of the lithium or sodium ions

The following speculation may account for the phenomenonobserved in our system

1 Zinc ions are discharged on the surface of the tungstenelectrode As the surface concentration of zinc atoms grows nucleationoverpotential starts to dump the overall process This dumping isobserved in the course of the first 11 seconds in Fig 5

2 Zinc (or zinc-tungsten) phase is formed This phase triggers theprocess of sodium-zinc exchange

Zn + Na+ Zn+ + Na or Zn + 2Na+ Zn2+ + 2Na3 The process (2) becomes the main process on the electrode

surface

Deposition of zinc on a platinum electrodeSome typical voltammograms for the electrochemical reduction

of Zn(II) are shown in Fig 7 Again no difference is observed betweenthe processes in NaCl ndash KCl and in LiCl ndash KCl melts and two melts arefurther described on the instance of in NaCl ndash KCl alone

As seen from Fig 7 the voltammogram is completely anomalousas compared to the other studied systems No cathodic peaks areobserved in the range -11V to + 09V ie in the limits of theelectrochemical window The peaks ndash 125V and at +09 V are the sameas for the ldquoblankrdquo melt NaCl-KCl These are the limits of theelectrochemical window

A very poorly pronounced anodic peak A at about ndash 028 V issimilar to the anodic peak A which appears for the zinc deposition on atungsten electrode (Fig 1) However the cathodic branch of thevoltammogram contains a continuous transition to the cathodic limit of

115

the windows rather than a peak It is obvious that zinc deposition ismasked by another process whose nature cannot be studied in theframework of this research

Fig 7 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0176 mol L) in equimolar NaCl-KCl melt on a Pt electrode at 700degC Scanrate is 300 mVsec

Fig 8 An EDS spectrum of a platinum working electrode after 3000 secondcathodic polarization at ndash 07 V vs W at 725degC in equimolar NaCl-

KCl melt containing 176x10-4 molmL of Zn2+ ions

116

An attempt of obtaining a sample of zinc deposit by holding thesystem at ndash 07 V (that is at such a potential which is considerably morepositive than the cathodic limit but more negative than the potential atwhich zinc is deposited on a tungsten electrode) for 3000 seconds wasmade However the analysis (Fig 8) demonstrated that essentially nozinc is found on the surface of the electrode (Table 4) since the value098 At is comparable with the sensitivity of the method The richcontent of potassium (5857 At ) in the surface layers can hint thatpotassium sorption is the process which masks the deposition of zincHowever this information alone is not sufficient for making positiveconclusions

To try to understand the essence of the process other moltenchloride systems containing no potassium could be studied Howeversuch a study is far beyond the framework of the current work

Table 4 Element composition of the platinum working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 176x10-4 molmL

Element Na K Cl Pt ZnAt 555 5857 3426 618 098

ConclusionsThe deposition of zinc on a tungsten electrode starts as an

irreversible two-electron zinc ion reduction Zn2+ + 2e- Zn After anobvious initial nucleation step a new phase is formed This phasecatalytically launches the process of saturating the electrode surface withsodium After the onset of the process of sodium deposition the latterbecomes essentially the only constituent on the electrode surface

The attempts of studying the deposition of zinc ions on a platinumelectrode were unsuccessful because this process is masked by anotherprocess which can result in the saturation of the electrode by potassiumThe exact nature of the latter process demands a separate study

117

References1 Fray D J J Appl Electrochem 3 103 (1973)2 Stoslashre T Haarberg GM Tunold R J Appl Electrochem 30 1351

(2000)3 Lugovskoy A Zinigrad M Aurbach D Israel Journal of

Chemistry 47 (3-4) 409 (2007)4 Lugovskoy A Zinigrad M Aurbach D and Unger Z

Electrochimica Acta 54 (6) 1904 (2009)5 Delimarski Yu K Electrochemistry of Ionic Melts Metallurgiya

Moscow 1978 (in Russian)6 Mackenzie J D and Murphy W K J Chem Phys 33 366 (1960)7 Irish D E and Young T F J Chem Phys 43 1765 (1965)8 Allen DA Howe RA Wood ND Howells WS J Phys

Condens Matter 4 1407 (1992)9 Price D L Saboungi M-L Susman S Volin K J Wright A C J

Phys Condens Matter 3 9835 (1991)10 Bassen A Lemke A Bertagnolli H Phys Chem Chem Phys 2

1445 (2000)11 Biggin S and Enderby J E J Phys C Solid State Phys 14 3129

(1981)12 Badyal Y S and Howe R A J Phys Condens Matter 5 7189

(1993)

89

PREPARATION OF COMPOSITES CuZrO2 AND CuTiO2

BY MA SHS

AI Letsko1 TL Talako1 AF Ilyushchenko1 TF Grigoreva2SV Tsybulya3 IA Vorsina2 NZ Lyakhov2

1 Powder Metallurgy Institute of NAS B Minsk Belarus2 Institute for Solid State Chemistry and Mechanochemistry of SB RAS

18 Kutateladze str Novosibirsk Russia grigsolidnscru3 GK Boreskov Catalysis Institute of SB RAS Novosibirsk Russia

IntroductionMetaloxide composites are quite perspective materials for

application in machine industry instrument engineering and electricalengineering in comparison to pure metals due to their improvedchemical and physical properties (heat resistance strength hardnesserosion resistance) Chemical mixing salt mixture decompositionhydrogen reduction in solutions chemical precipitation from solutionsinternal oxidation are well-known methods of preparing such materialshaving application in industry [1] The above-mentioned technologiesallow attaining metaloxide composites but they are quite expensive andlong-term Based on this a very topical issue is elaboration of newapproaches to production of metal-ceramic materials

In this work we explored possibilities of preparation ofcopperoxide composites (CuZrO2 and CuTiO2) by methods ofmechanochemical synthesis (MS) in planetary mills and of mechanicallyactivated self-propagating high-temperature synthesis (MA SHS)

ExperimentalCopper copper oxide CuO and zirconium M-41 titanium PTOM

were used in this work as raw materials Mechanical activation (MA)was carried out in planetary ball mills with water cooling [2] (the drumvolume ndash 250 cm3 the balls diameter ndash 5 mm the load ndash 200 g sampleweight ndash 10 g the drums rotation speed about the general axis ~ 1000rpm) After MA the activated mixture was compacted (under a load of4ndash6 t) in the mould up of 17 mm diameter and ~25 mm in height (tillstrength sufficient for the sample transfer to the reactor) SHS wascarried out in the argon atmosphere the combustion was initiated withan electrically heated tungsten coil The temperature and burning

90

velocity were evaluated by a thermocouple method (C-A thermocouplesOslash asymp 02 mm) using an outer 2-channel 24-charge analog-to-digitalconverter ADSC24-2T

X-ray diffraction research was conducted with diffractometersXrsquoTRA (Thermo ARL Switzerland) with application of CoK radiation(λ = 1 789 Aring) and URD-63 with application of CuK radiation (λ = 15418 Aring) Evaluation of effective sizes of coherent scattering area wascarried out in compliance with the Scherer formula with the strongestpeaks of phases analysed

The high-resolution scanning electronic microscope (SEM)MIRATESCAN equipped with an INCA 350 accessory for EDXanalysis was used for the structure research The electron probe diameterwas 52 nm excitation area was 100 nm Images in direct electrons andback-scattered electrons were attained and it allowed studying chemicalelements distribution over the surface Brightness distribution in theimage depends on the average atomic element number in eachmicroarea

IR absorption spectra were registered by spectrometer IFS-66The samples were prepared to the exposure by standards methods

Results and discussion

Cu-O-Zr systemMechanochemical reduction of copper oxide with metallic

zirconium was initially investigated in this system This reaction is quitehigh-exothermic (∆H (2 CuO + Zr = 2 Cu + ZrO2) asymp -188 kcalmol) ieit can be implemented under mechanical activation conditions IRspectroscopic investigations have shown that the original copper oxideCu-O band is considerably widened at 505 cm-1 after 20 s of MA ofCuO + Zr mixture of stoichiometric composition This widening (Fig1b) can testify some structural failures After 30 s of activation thefollowing bands are present in the IR-spectrum of the product 505 cm-1

(original oxide CuO) 615 cm-1 (the lowest copper oxide Cu2O) [3] and415 585 735 cm-1 (zirconium oxide (Fig 1c) [4 5] X-ray-phaseanalysis shows the presence of certain amount of Cu2O already after 20 sof activation The 30-second activation product diffractogram showsclear copper (coherent scattering area asymp 80 nm) and zirconium oxide

91

(coherent scattering area asymp 100 nm) reflection and two copper oxidereflections ie mechanochemical reduction of copper oxide takes placeat such activation duration This reaction speed shows that the reactionpresumably takes place in the thermal explosion mode when especiallyhigh heat dissipation speed is needed what is very difficult to performeven in the most effectively cooled highly-energy planetary ball millsAs such a process dimensional scaling seems to be absolutely impossiblein conditions of mechanochemistry an attempt to produce compositeCuZrO2 by the SHS method was made

Fig 1 IR-spectra of mixture CuO + Zr before (a) and after MA for 20 (b) and30 s (c)

At first CuOZr mechanocomposite was used as the SHS-precursor This mechanocomposite formed after 20 s of MA ofstoichiometric composition mixture has a small amount of cuprous oxideCu2O beside original copper oxide and zirconium SHS process proceedsin the heat explosion mode in this system Burning parameters fixingfailed in this case because of the inertia of the equipment applied

92

Not pure metal but solid solutions intermetallic compounds ornano-composites where metal-reducer (zirconium in our case) isdistributed in the inert matrix can be used as a reducing agent todecrease the system reaction capability At the same components ratiochemical energy of the raw mixture would be considerably lower and asa consequence heat release would reduce

In this work mechanocomposite formed during mechanicalactivation of mixture Cu + 20 wt Zr for 20 min with zirconium hadbeen pre-dispersed for 4 minutes (zirconium coherent scattering areasize ~ 20 nm) was used for copper oxide reduction This compositediffractogram shows the widened intensive copper (coherent scatteringarea asymp 20 nm) reflection and very vague zirconium reflection coherentscattering area of which cannot be evaluated (Fig 2) Since copperreflections havenrsquot changed their position we can conclude thatzirconium hasnrsquot become a part of copper crystal lattice ie CuZrmechanocomposite and not solid solution is attained

Fig 2 Diffractograms of Cu + 20 Zr mixture before (a) and after 20 minof MA (b)

93

This is confirmed by the SEM results (Fig 3) The electronmicroscopy data more clearly show zirconium distribution Zr elementalmapping testifies that local zirconium areas are much diffused

Fig 3 SEM-images of sample Cu + 20 Zr after MA for 20 min

94

X-ray research of the product of joint activation of mixture CuO +mechanocomposite Cu + 20 Zr (the mixture composition correspondsto the stoichiometric ratio of copper oxide and zirconium) for 2 and 4minutes show that copper oxides diffraction reflections are retained inall cases although they are substantially widened (Fig 4) Thezirconium oxide reflection is not observed ie mechanochemical copperoxide reduction does not take place in this time gap CuOCuZrmechanomposite formed as a result of joint mechanical activation ofmixture CuO + mechanical composite Cu 20 Zr for 4 min was usedas a precursor for SHS

Fig 4 Diffractogram of sample CuO + CuZr after MA for 4 min

Usage of mechanocomposite CuOCuZr instead of CuOZr one asthe SHS precursor changes a mechanism of interaction between thereactants during the SHS process from the thermal explosion mode (forCuOZr mechanocomposite) to the steady-state combustion with the

95

burning velocity asymp 2 mms temperature rise speed about 730 Cs andburning temperature 1044 C The combustion temperature record (Fig5) shows 2 isothermal plateaus The first one is fixed at temperaturemaximum and most probably points out melting process The secondone is fixed at 580 ndash 590 C and accounts for post-processes in the after-burning zone of combustion wave

Fig 5 Temperature record of the SHS process from mechanical compositeCuOCuZr

X-ray-phase analysis has shown that SHS product consists ofcopper and zirconium oxide with Cu2O traces (Fig 6) Electronicmicroscopy with the EDX analysis confirms composite structureformation (Fig 7 Table 1)

96

Fig 6 Diffractogram of the SHS product from mechanical compositeCuOCuZr

Fig 7 SEM-image of the SHS product from mechanical composite CuOCuZr

97

Table 1 Results of the EDX analysis (from Fig 7)

Number ofspectrum

O Cu Zr

1 382 8744 8742 714 8152 11343 2803 2747 44504 1653 4640 37065 2314 2914 4772

Cu-O-Ti systemChemical reduction of CuO with titanium is also high-exothermic

(∆H (2 CuO + Ti = 2 Cu + TiO2) asymp -151 kcalmol) Mechanicalactivation of equimolar mixture of copper oxide with titanium powderfor 4 minutes did not result in titanium oxide formation Longeractivation is not reasonable since it contaminates the reaction mixturewith balls and drums material That is why the composites formedduring the short-term MA were used as precursors for SHS

After 30 s MA composite structure CuOTi with a small additiveof cuprous oxide reduced from CuO (Fig 8) is formed The SHS processfrom such mechanocomposites proceeds with a very high speed andtemperature (on a levels typical for the thermal explosion mode) andwith the substances scatter

Fig 8 Diffractogram of mixture CuO + Ti after MA for 30 s

98

To decrease combustion temperature and velocitymechanocomposite CuTi containing 20 wt of titanium was used as areducing agent in the next experiment Figure 9 shows the diffractogramof the mechanocomposite formed after 10 min mechanical activation ofthis mixture It shows that metals reflections especially that of titaniumare widened testifying substantial increase of their dispersivityAccording to the X-ray data analysis the titanium coherent scatteringarea size is ~ 10 nm in this composite

Fig 9 Diffractogram of mixture Cu + 20 Ti after 10 min of MA

Mixture of copper oxide and CuTi mechanocomposite (thecomposition corresponds to the stoichiometric ratio of titanium andcopper oxide for its full reduction) was subjected to activation for 4minutes Only a band of valence vibrations of vCu-O copper oxide (Fig10a) is present in the IR-spectrum of the activated mixture like in theoriginal one but its intensity slightly decreases X-ray research alsoindicates that the titanium oxide reflections are absent in the 4-minuteactivation product diffractogram (Fig 11)

99

Fig 10 IR-spectra of sample CuO + CuTi after 4 min of MA (a)and after SHS (b)

Fig 11 Diffractogram of sample CuO + CuTi after 4 min of MA

100

SHS process from CuOCuTi mechanocomposite takes place inthe steady-state combustion mode with burning velocity higher than 20mms and burning temperature ~2000 ordmC A band (~730 cm-1)corresponding to valence vibrations of rutile vTi-O (Fig 10b) [2]appears in the IR-spectrum of the SHS product from CuOCuTimechanicocomposite Diffraction reflections (Fig 12) also correspond toreflections of rutile and copper

Fig12 Diffractogram of the SHS product from CuOCuTi mechanocomposite

Electron-microscopy exposure in back-scattered electronsindicates the partial phase separation of TiO2 and Cu (Fig 13 a) thoughcomposite particles containing TiO2 inclusions with size from 30 nm till1 5 m (Fig 13 c) are also formed The elemental mapping in thetitanium characteristic radiation confirms this fact (Fig 13d)

101

a

b cFig 13 SEM-images of the SHS-product from CuOCuTi mechanocomposite

102

Table 2 The EDX analysis results (from Fig 13 a)

Number ofspectrum

O Ti Cu

1 191 052 9757

2 235 051 9714

3 2230 2094 5676

4 1586 1295 7118

5 180 108 9712

6 336 228 9436

7 4335 4685 980

8 3297 2738 3966

9 4978 4645 377

ConclusionThus our investigations have shown that copper oxide can be

mechanochemically reduced with zirconium resulting in formation ofzirconium oxide and copper but the reaction goes in the thermalexplosion mode

To produce composite CuZrO2 by the method of MASHS usageof mechanocomposite CuZr instead of pure zirconium seems to be morepromising The MASHS product is a copper-based composite withinclusions of ZrO2 and some amount of Cu2O

Mechanical activation of equimolar mixture of copper oxide withtitanium powder for 4 minutes did not result in titanium oxide formationThat is why the composites formed during the short-term MA were usedas precursors for the following SHS

Reduction of CuO with CuTi mechanocomposite can beimplemented by the method of MASHS Partial phase separation of TiO2

and Cu takes place during the synthesis process along with the formationof copper-based composite particles with inclusions of titanium oxidesized from 30 nm up to 15 m

103

References1 PA Vityaz Mechanically alloyed alloys on the basis of aluminum

and copper PA Vityaz FG Lovshenko GF Lovshenko ndashMinsk Belnauka 1998 ndash 351 p

2 YG Avvakumov AP Potkin OI Samarin Authorrsquos certificate ofUSSR 975068 Planetary mill BI 1982 No 43

3 SS Batsanov VPBokarev YVLazareva On CuO interaction withcopper Inorganic Chemistry Journal 1977 V 22 issue 4 P 888ndash 892

4 AI Boldyrev Infrared spectra of minerals M Nedra 19765 BT Kaminsky AS Plygunov GN Prokofyeva Infrared spectra of

oxides of titanium zirconium and hafnium Ukrainian ChemicalJournal 1973 V 35 No 9 P 946 ndash 977

78

THE STANDARD ENTHALPY AND ENTROPY OFFORMATION OF GASEOUS AND LIQUID

POLYCHLORINATED BIPHENYLS POLYCHLORINATEDDIBENZO-n-DIOXINS AND DIBENZOFURANS

TV Kulikova AV Mayorova KYu ShunyaevInstitute of Metallurgy Ural Branch RAS

Yekaterinburg RussiaE-mail kulikogmailcom

AbstractThe study deals with analysis and systematization of the known

and calculation of the unknown thermodynamic characteristics (thestandard enthalpy of formation the standard entropy of formation) ofwidespread hazardous isomers of gaseous and liquid compounds ofpolychlorinated biphenyls (PCBs) polychlorinated dibenzo-n-dioxins(PCDDs) and polychlorinated dibenzofurans (PCDFs) Thecomparison of results obtained in different studies reveals aconsiderable discrepancy between values reported by highlyrespected investigators In this connection laquoindependentraquo results ofthe thermodynamic characteristics have been calculated

IntroductionUnique technological and physicochemical properties of

polychlorinated biphenyls (PCBs) a huge volume of theirproduction considerable volatility and solubility and extremechemical inertness have led to the world-wide spread of PCB-containing equipment and materials resulting in the universalcontamination with these substances The most common method usedin Russia for destruction of PCBs is their incineration with theformation of polychlorinated dibenzo-n-dioxins (PCDDs) anddibenzofurans (PCDFs) which are among the most hazardouschemical substances known to the mankind

As often happens the hazard of PCBs has long beenunderestimated With respect to their severe toxicological effectPCBs are identical to substances that are referred to the high class ofhazard Since these substances are especially toxic they have beenassigned low toxicological standards which necessitate special

79

requirements on the organization of processes assuming formation ofthese substances (the so-called dioxinogenic processes) so thatindustrial emissions meet the norms Instrumental investigations ofthese substances are very expensive and in this connection interestis attracted to calculation methods for simulation of processes by thedata on their thermochemical properties

A quality thermodynamic simulation requires the knowledge ofthermodynamic and thermochemical properties of all reliablycertified compounds of the system under study in the gaseous orcondensed state Therefore the present study deals with the analysisand systematization of the known and calculation of the unknownthermochemical properties (the standard enthalpy and entropy offormation) of most toxic and hazardous isomers of gaseous PCBsPCDDs and PCDFs and liquid PCBs

Calculation of thermochemical propertiesIt is known that there are 209 individual PCB congeners 420

polychlorinated dibenzo-n-dioxins and polychlorinateddibenzofurans which differ by the number and positions of chlorineatoms in a molecule The most widespread PCB compoundscontaining up1 to 10 chlorine atoms were chosen for the study Indeciding on isomers preference was given to ortho-unsubstitutedPCBs because they are most toxic and their effect is similar to theeffect of PCDDs and PCDFs Congeners which do not have chlorineatoms in ortho-positions of molecules (ortho-unsubstituted PCBs)can acquire the planar configuration which is more favorable inenergy terms Such congeners are isostereoisomeric to PCDDs andPCDFs and present the greatest hazard As to the PCDD and PCDFisomers of special hazard to humans and the environment are tri-tetra- penta- and hexa-substituted dioxins and furans containinghalogen atoms in lateral positions 2 3 7 and 8

In this study we analyzed the known and calculated theunknown thermodynamic properties of 17 most widespread andhazardous isomers of PCBs PCDDs and PCDFs in the gaseous stateand 11 compounds of liquid PCBs

80

Gaseous PCBs PCDDs and PCDFsThe literature survey showed that studies dealing with

estimation of the thermochemical properties of gaseous PCB PCDDand PCDF compounds are few Most of them are based oncalculations or are semi-empirical For example Saito and Fuwa [1]calculated thermodynamic functions of all PCBs and some PCDDsand PCDFs on the basis of semi-empirical calculations in terms ofthe PM3 model OV Dorofeeva et al [2-4] used statistical methodsTable 1 presents the literature data on standard enthalpies andentropies of formation of gaseous and liquid PCBs PCDDs andPCDFs The comparison of results obtained in different studiesreveals a considerable discrepancy between values reported by highlyrespected investigators who did very arduous work In particularvalues of the formation enthalpy [1] are 8-70 larger and the entropyis 11-15 smaller than the corresponding values in [2-4] thediscrepancy grows with the number of chlorine atoms in a moleculeSo we thought it reasonable and topical to attempt an independentresult

Bensons method [5] was used to calculate thermodynamiccharacteristics (the standard enthalpy of formation ΔНdeg298 thestandard entropy of formation ΔSdeg298) of the gaseous PCBs PCDDsand PCDFs We shall dwell briefly on this method

Bensons method is the group additivity method involvinganalysis of the molecule structure Atomic or molecular groups areseparated and the nearest neighbors of the atom or the group areconsidered Table 2 gives the number of groups necessary fordetermination of group increments in structural formulas of PCBsPCDFs and PCDDs Values of the thermodynamic characteristics ofgroup increments were determined from available reference andliterature data [5 6] Information about the energy contribution ofeach group (see Table 3) and the number of groups was used tocalculate thermochemical properties of the PCBs PCDDs andPCDFs

81

Table 1 Standard enthalpies (∆Нo298 kJmole) and entropies (∆So

298Jmole K) of formation of gaseous and liquid PCBs PCDDs andPCDFs

Gaseous state Liquid state

Compo-unds Saito Fuwa [1]

the given work

OV Dorofeeva etal

[2-4]

∆Нo298

[7 8 121617]

So298

[781014 16 17]

∆Нo298

the givenwork and

[814]

So298

thegivenworkand[14]

1 2 3 4 5 6 7 8 9

C12H10

(biphenyl)

1986[1]

1797

3454[1]

4104

1820[3]

3908[3]

1819[8]

1814[16]

3927[16]

11711162[8]11710

[14]

257402574[14]

C12H9Cl(3-mono-

chlor-biphenyl)

1705[1]

1500

3851[1]

4413

1561[2]

4323[2]

1548[8]

15088[16]

4214[16]

7629 2840

C12H8Cl2

(44rsquo-dichlor-biphenyl)

1422[1]

1202

3992[1]

4721

1260[2]

4518[2]

1276[8]

12004[16]

4492[16]

3584 3106

C12H7Cl3

(344rsquo-trichlor-biphenyl)

1194[1]

905

4240[1]

5030

1041[2]

4923[2]

1004[8]

892[16]

4780[16]

-452 3372

C12H6Cl4

(33rsquo44rsquo-tetrachlor-biphenyl)

969[1]

608

4444[1]

5338

899[2]

5216[2]

732[8]

5836[16]

5068[16]

-4488 3638

C12H5Cl5

(33rsquo44rsquo5-penta-

chlorbiphenyl

748[1]

310

4620[1]

5647

569[2]

5502[2]

460[8]

2752[16]

5356[16]

-8524 3904

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlor-

biphenyl)

529[1]13

4615[1]

5956

314[2]

5675[2]

190[8]

-332[16]

5644[16]

-12558 4170

C12H3Cl7

(233rsquo44rsquo55rsquo-hepta-

chlor-biphenyl)

400[1]

-284

4842[1]

6264

152[2]

6077[2]

-84[8]

-416[16]

5932[16]

-16596 4436

82

1 2 3 4 5 6 7 8 9

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-

octachlor-biphenyl)

241[1]

-581

4886[1]

6573-90[2]

6342[2]

-356[16]-650[8]

6220[8]

-20632 4702

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-

nanochlor-biphenyl)

873[1]

-878

5048[1]

6881

-153[2]

6607[2]

-628[16]-958[8]

6508[8]

-24668 4968

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlor-biphenyl)

-67[1]

-1176

5034[1]

7190

-247[2]

6757[2]

-901[16]

-1267[8]

6796[8]

-28604 5234

C12H8O2

(dibenzo-n-dioxin)

-402[1]

-448

3764[1]

-592[4]

3965[4]

-592[12]-592[7]

-550[17]

3951[7]

3880[17]

- -

C12H4Cl4O2

(2378-tetrachlor-dibenzo-n-

dioxin)

-1372[1]

-1592

4553[1]

-1640[4]

4781[4]

-1345[7]

-158[17]

5136[7]

4784[17]

4781[10]

4784[9]

- -

С12H3Cl5O2

(12378-pentachlor-dibenzo-n-

dioxin)

-1532[1]

-1900

4931[1]

-1900[4]

54035[4]

-1162[7]

-196[17]

5531[10]

5010[17]

- -

С12H2Cl6O2

(123478-hexachlor-dibenzo-n-

dioxin)

-1691[1]

-2164

4841[1]

-2196[4]

56912[4]

-1224[7]

57559[7]

5236[17]

- -

С12HCl7O2

(1234678-hepta-chlor-

dibenzo-n-dioxin)

-1848[1]

-2472

5005[1]

-2460[4]

59789[4]

-1196[7]

61031[7]

5462[17]

- -

C12H8O(dibenzo-

furan)

1061[1]

518

3787[1]

553[4]

3759[4]

552[17]

3744[17]

- -

C12H4Cl4O(1234-

tetrachlor-dibenzo-furan)

203[1]

-625

4505[1]

-500 [4]49098

[4]-528[17]

4648[14]

- -

83

1 2 3 4 5 6 7 8 9

С12H3Cl5O(12378-pentachlor-

dibenzo-furan)

-123[1]-934

4592[1]

-759[4]

51975[4]

-748[17]

4874[14]

- -

С12H2Cl6O(123478-

hexachlor-dibenzo-furan)

-283[1]

-12424713[1]

-1051[4]

54852[4]

-1043[17]

5100[14]

- -

С12HCl7O(1234678heptachlor-

dibenzo-furan)

-441[1]

-1550

4833[1]

-1315[4]

57729[4]

-1313[17]

5326[14]

- -

Table 2 Number of groups for determination of group increments instructural formulas of PCBs PCDFs and PVDDs

Number of groupsCompound Св-H Св-Cl Св-O Св-Св

Number ofchlorine atoms

in a molecule (n)

PCBs 10 - n n - 2 1 ndash 10

PCDFs 8 - n n 2 2 1 ndash 8

PCDDs 8 - n n 4 - 1 ndash 8

Св is the carbon atom in an aromatic ring

Values presented in Table 1 show the thermodynamiccharacteristics of PCBs PCDDs and PCDFs calculated in this studyand by other investigators

It is seen for example ( Table 1) that the formation enthalpy

(o298H ) of biphenyl (C12H10) equals (kJmole) 1986 [1] 1820 [3]

1819 [7] and 1814 [8] while the formation entropy (o298S ) of

2378-tetrachlordibenzo-n-dioxin (C12H4Cl4O2) is (J(mole K))4553 [1] 4781 [4] 4784 [9] and 4781 [10]

84

Table 3 Values of the thermodynamic characteristics determined bythe method of group increments[58]

(gas) (liquid)Group

o298H

kJmole

o298S

J(moleК)

o298H

kJmole

o298S

J(moleK)

Св-H 1381[8]1382[5]

4831[8]4827[5]

816[8] 2887[8]

Св-Св 2166[8]2077[13]

-3657[8]-3618[5]

1721[8] -

Св-Cl -1703[8]-1591[5]

7708[8]7913[5]

-3220[8] 5547[8]

(Св)2-O -7766[8]-8834[5]

--

- -

orto corrCl-Cl

950[8]921[5]

- 1400[5] -

meta corrCl-Cl

-500[8] - 400[5] -

In this study the values of the standard entropy of formationobtained by using statistical methods (OV Dorofeeva et al [2-4 9])for 17 isomers of PCBs PCDDs and PCDFs are in good agreementwith the values calculated by other investigators [8 10 12 13] andwith the values calculated by us

Liquid PCBsIt should be noted that ample literature data on the

thermochemical properties of liquid ecotoxicants is only available forbiphenyl (C12H10) [8 14] dibenzo-n-dioxin (C12H8O2) [11 15] anddibenzofuran (C12H8O) [5 17] The only study dealing withcalculation of thermodynamic functions for the whole series of liquidPCDD and PCDF homologues was published by VS Iorish et al[11] As to liquid PCB compounds the literature data on theirthermochemical properties are scarce [8 14]

The thermochemical properties namely the standard enthalpyand entropy of formation of liquid PCBs were calculated using thegroup additivity method due to Domalski [8] Values of the groupincrements (Table 3) were adopted from [8] It is seen from Table 3

85

that the energy contribution of the group Св-Св is unavailable for the

entropy calculation However if one uses known values ofo298S for

liquid biphenyl (C12H10) [14] and the data on the contribution of the

Св-H and Св-Cl groups [8] it is possible to calculateo298S for the

whole series of PCBs

o298S (PCB) =

o298S (BP) - (10-n)

o298S (Св-H) + n

o298S (Св-Cl) +

+(morto corr Cl- Cl ) +(pmeta corr Cl- Cl) (1)

where n is the number of chlorine atoms in a PCBs moleculem (p) - spatial amendments number Cl (from two and more) beingin orto - (meta-) position rather each other

The enthalpy of formation (o298H ) for the PCBs series

compounds was calculated by two options using the group additivitymethod due to Domalski [8] and from the equation

o298H (PCB) =

o298H (BP) - (10 - n)

o298H (Св-H) +

+ no298H (Св -Cl) +(morto corr Cl-Cl )+(pmeta corr Cl-Cl) (2)

Table 4 lists values of the standard enthalpy of formation forthe series of liquid PCBs compounds as calculated by the groupadditivity method [8] and the equation (2) It is seen that the values of

o298H which were calculated by the two methods are in good

mutual agreementThe thermochemical properties which were taken as reliable

were added to the TERRA database and were used forthermodynamic simulation of the thermal stability of PCBs PCDDsand PCDFs

86

Table 4 Calculated enthalpy of formation (∆Нo298) for liquid PCBs

compounds∆Нo

298 kJmole

CompoundGroup

incrementsmethod

Eq (5)δ

C12H9Cl(3-monochlorbiphenyl)

7584 76742 12

C12H8Cl2

(44rsquo-dichlorbiphenyl)3530 36382 30

C12H7Cl3

(344rsquo- trichlorbiphenyl)-506 -3978 2138

C12H6Cl4

(33rsquo44rsquo-tetrachlorbiphenyl)-4542 -44338 238

C12H5Cl5

(33rsquo44rsquo5-pentachlorbiphenyl)-8578 -84698 126

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlorbiphenyl)-1261 -125058 083

C12H3Cl7

(233rsquo44rsquo55rsquo-heptachlorbiphenyl)-1665 -165418 065

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-octachlorbiphenyl)-20686 -205778 052

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-nanochlorbiphenyl)-24722 -246138 044

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlorbiphenyl)

-28758 -286498 038

Conclusions1The literature data on the thermochemical properties of 17

most widespread and hazardous isomers of PCBs PCDDs andPCDFs in the gaseous state and 11 compounds of liquid PCBs havebeen analyzed and systematized for the first time

2Methods have been developed for calculating of thethermodynamic characteristics of organic compounds Values of thethermodynamic functions (standard enthalpy and entropy offormation) of liquid PCBs PCDDs and PCDFs have been calculatedfor the first time

87

3The comparison of the calculated values of thethermodynamic functions with the known literature datademonstrated their good mutual correlation

4The obtained data were added to the TERRA database andwere used for thermodynamic simulation of the thermal stability ofPCBs PCDDs and PCDFs

5The obtained data can be used for simulating of the behaviorof complex heterogeneous systems including ecotoxicants over awide interval of temperatures and initial compositions

This study was supported by RFBR (project No 08-03-00362-a)

References1 Nagahiro Saito Akio Fuwa Chemosphere 2000 vol40 p

131-1452 OV Dorofeeva NF Moiseeva VS YungmanLV JPhys

Chem A 2004 vol 108 p 8324-83323 OV Dorofeeva Thermodynamica Acta2001 vol374 p7-114 OV Dorofeeva VS Iorish NF Moiseeva J Chem Eng

Data 1999 vol 44 p 516-5235 SW Benson FR Cruickshank DM Golden GR Haugen

HE OrsquoNeal AS Rodgers R Shaw and R Walsh Chem Rev1969 vol69 p 279 -324

6 HK Eigenmann DM Golden and SW Benson J PhysChem 1973 vol 77 1687-1691

7 Jung Eun Lee and Wonyong Choi J PhysChem A 2003vol 107 p 2693-2699

8 Domalski E S and Hearing E D J of Phys and Chem RefData 1993 vol 22 p 805-1159

9 LV Gurvich OV Dorofeeva VS Iorish Zh Fiz Khimii 1993vol67 No 10 p 2030-2032

10 W-Y Shiu and K-C Ma J Chem Ref Data 2000 vol29No 3 p 387-462

11 VS Iorish OV Dorofeeva NF Moiseeva J Chem Eng Data2001 vol46 p 286-298

12 VA Lukyanova VP Kolesov Zh Fiz Khimii1997 vol 71No 3 p 406-408(in Russian)

88

13 P Reid J Prausnitz T SherwoodLeningrad Khimiya 1982592 p(in Russian)

14 Richard Laurent and Helgeson Harold C Geochimica etCosmochimica Acta 1998 vol 62 No 2324 p 3591 ndash 3636

15 I Barin ldquoThermochemical Data of Pure SubstancesrdquoWeinheim Federal Republic of Germany VCHVerlagsgesellschaft mbH 1997

16 Cambridgesoft database ver 806 December 31 200317 Thompson D Thermochim Acta 1995 vol261 p7-20

76

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OFNANOGRAINED

TiN-TiB2 COMPOSITES

MA Korchagin BB BokhonovInstitute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirsk Russiakorchagsolidnscru

Titanium nitride is known to exhibit high oxidation resistancehigh thermal conductivity and hardness as well as high corrosionresistance in acids Titanium diboride is also very hard possessing highstrength at elevated temperatures and anomalously high electricalconductivity among other ceramic materials

Composite materials based on the mixture of these twocompounds have been widely used in a variety of applications Highperformance parts have been also developed Thus ceramics containing40-50 molTiN shows high oxidation resistance [1] However untilvery recently TiN and TiB2 have been produced separately by twodifferent routes At present new methods are being developed tosynthesize mixtures of these two compounds in a single process One ofthese methods is based on self-propagating high-temperature synthesis(SHS) The use of SHS eliminates the need of having furnace equipmentto synthesize the desired products The possibility of SHS in the systemis due to the high enthalpies of formation of the products serving as aninternal chemical source of energy

In order to simultaneously obtain TiN and TiB2 by SHS the initialreactants can be either the powder mixtures of Ti-BN [3] or Ti-B-BN[4] The products of the reactions consist of highly porous well meltedsintered pieces with the minimum grain size of 1-10 microm [4] Hightemperatures developed in the combustion wave in the traditional SHSdo not allow finer grains of the products to retain

In order to overcome this problem short mechanical activationof the mixtures of reactants is proposed followed by the SHS in anatmosphere of argon or nitrogen

In the previous investigations preliminary mechanical activationhas been shown to significantly reduce the combustion temperatures

77

which to a great extent determine the grain size of the products of SHS[6 7]

Experiments were performed on the stoichiometric mixtures 3Ti +2BN The time of preliminary mechanical activation in a planetary ballmill (AGO-2 type) did not exceed 10 min The influence of the durationof mechanical activation on the combustion rate temperature and phasecomposition of the products was studied

The milled mixtures and the products of SHS were studied usingXRD analysis and Electron Microscopy The experimental conditionshave been found favoring the formation of the two-phase mixtures ofTiN of TiB2 with the grain size ranging from 20 to 50 nm [7]

References1 GV Samsonov Nitridy (Nitrides) Kiev laquoNaukova Dumkaraquo 19692 AG Merzhanov Tverdoplamennoe gorenie (Solid State

Combustion) Chernogolovka ISMAN 2000 224 p3 AEGrygoryan ASRogachev Combustion of titaniumwith

nonmetal nitridesCombustion explosion and shock waves 2001v37 2 p168-172

4 R Tomoshige A Murayma T Matsushita Production of TiB2-TiNcomposites by combustion synthesis and their properties J AmCeram Soc 1997 80[3] 761-764

5 MAKorchagin TFGrigorrsquoeva BBBokhonov MRSharafutdinovAPBarinova NZLyakhov Solid-state combustion in mechanicallyactivated SHS systems Combustion explosion and shock waves2003 v39 1 p43-58

6 MAKorchagin DVDudina Application of self-propagating high-temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007v43 2 p176-187

7 MAKorchagin BBBokhonov Combustion of mechanicallyactivated 3Ti+2BN mixtures Combustion explosion and shockwaves 2010 v 46 2 p170-177

65

SPIN-CROSSOVER IN THE PENTANUCLEAR BYPIRAMIDALCo2Fe3 AND Fe2Fe3 COMPOUNDS

Sophia Klokishner Sergei Ostrovsky Andrei PaliiInstitute of Applied Physics Academy of Sciences of Moldova

Kishinev MoldovaKim Dunbar

Department of Chemistry Texas AampM UniversityCollege Station TX USA

Boris TsukerblatChemistry Department Ben-Gurion University of the Negev

Beer-Sheva Israel

In this article we report a model for a spin-crossover phenomenonin pentanuclear bypiramidal [M(III)(CN)6]2[M(II)(tmphen)2]3 (MM=CoFe FeFe) cluster compounds The spin-crossover phenomenonis considered as a phase transformation accompanied by a change of theground state spin The model takes into account cooperative interactionsin the crystal network local crystal fields and spin-orbit coupling actingwithin the degenerate metal sites Magnetic properties and Moumlssbauerspectra are analyzed and compared to the experimental data

1 IntroductionSpin-crossover compounds have been a subject of many

experimental and theoretical studies [1-6] Till now only a fewexperimental reports on spin crossover in cluster compounds [7-11] havebeen reported Recently FeII ions were introduced into the equatorialmetal sites of discrete cyano-bridged pentanuclear clusters[MIII(CN)6]2[MII(tmphen)2]3 (MM =CoFe(1) FeFe(2) ) [12] with atrigonal bipyramidal (TBP) structure The octahedral nitrogensurrounding of FeII ions facilitates the spin-crossover behavior Theoccurrence of the ls-hs transition in compounds 1 and 2 was proved bythe combination of Moumlssbauer spectroscopy magnetic measurementsand single-crystal X-ray studies For both types of clusters[FeII(tmphen)2]3[M

III(CN)6]2(M=FeCo)7 the T product increases by

~9emumiddotKmol between 150 K and 375 K thus indicating the ls ndashhstransition at the FeII sites The TBP FeII

3CoIII2 cluster due to its electronic

66

structure represents an ideal system for studying the effects ofintracluster short-range and intercluster long-range interactionsfacilitating spin-crossover In the (FeIII)2 (FeII)3 cluster the hs-FeII and ls-FeIII ions are coupled by exchange interaction In spite of the fact that theexchange interaction of the hs-FeII and ls-FeIII ions through the cyanidebridge is sufficiently weak as compared with that in oxide clusters it isinterestingly to understand whether this interaction may affect the spintransformation The effects of orbital degeneracy on the spin-crossovertransformation in the [FeII(tmphen)2]3[FeIII(CN)6]2 crystal will beexamined as well In the present article a microscopic approach to theproblem of spin crossover in crystals containing metal clusters isdeveloped

2 The modelIn the basic structural unit of compounds 1 and 2 two MIII ions

surrounded by six carbon atoms occupy the apical positions and threeFeII ions coordinated by the nitrogen atoms reside in the equatorial plane[12] In a strong crystal field of carbon atoms the ground terms of the

CoIII and FeIII ions are the low-spin orbital singlet )( 621

1 tA ( 0S ) and

the orbital triplet )( 421

3 tT respectively The ground state of a FeII -ion in

the crystal field induced by the nitrogen atoms can be either low-spin

(ls)- term )( 621

1 tA or high spin (hs) ndashterm 2422

5 etT Both magnetic

measurements and Moumlssbauer spectroscopy for water containing crystals[12] demonstrate the presence of some amount of FeII ions in the hsconfiguration even at very low temperatures Further on we consider inthe model two types of FeII ions and denote by x the fraction of FeII -ions which are in the hs ndashstate at all temperatures while theconcentration of those ions which undergo the ls-hs transition is (1-x)The number pi of trigonal bypiramidal clusters in which i (i=0123) ofthree FeII ions are in the hs configuration in the whole temperature range

is estimated as iiii xxCp 33 1 where rllrC r

l

The Hamiltonian of intraion interactions can be written in the form

67

Hg

gllsH

kkB

kkB

kZkk

)(

32)(

211

02

0

H

lsH

(1)

where numbers theIIFehs ions in the k-th bypiramidal cluster the

first term is the spin-orbit (SO) coupling in the cubic )( 2422

5 etT - term of

theIIFehs -ion the second term describes the axial crystal field

splitting the 125 lT term into an orbital singlet ( 0lm ) and an

orbital doublet ( 1lm ) the third term refers to the Zeeman

interaction for hs-FeII ions and contains both the spin and orbitalcontributions B is the Bohr magneton and g0 is the spin Lande factorFinally the fourth term represents the interaction of the ground Kramersdoublets of two ls-FeIII ions in the cluster with the external magnetic

field i is the matrix of the pseudo -spin frac12 of the ls-FeIII ion g1 =173

is the Lande factor Up to room temperature the ls-FeIII can be regardedas an ion with the pseudo-spin frac12 because the ground Kramers doubletand the excited quadruplet arising from the splitting of the 2T2 term by

the spin-orbital interaction are separated by the gap 173023 cm

( 1486 cm [13] for a free ls-FeIII) that is large enough from the

thermal population of the excited quadruplet at room temperatureThe superexchange interaction (several cm-1 [1415]) in the

[FeII(tmphen)2]3[FeIII(CN)6]2 through the cyanide bridges couples the hs-FeII ions in equatorial and ls-FeIII ndashions in axial positions Further on wewill neglect the essentially anisotropic orbitally dependent terms andretain only the isotropic part of the exchange interaction between the hsndashFeII and ls ndashFeIII ions in a cluster The Hamiltonian of exchangeinteraction for the thk cluster looks as follows

kkkex

k

exJH

212 σσs (2)

where 2s is the spin of the hs-FeII ion the summation in (2) takes

into account the hs-FeII ions appearing in the thk cluster due to thespin transition and those which are in the hs-state in the whole

68

temperature range As in [16-18] we suppose that the mechanismresponsible for the ls-hs transition is the interaction of FeII ions with thespontaneous all-round full symmetric lattice strain Applying theprocedure suggested in [16-18] we obtain the Hamiltonian of electron-deformational interaction

2k kkk

kkst

nm

JBH (3)

where 21AB 21AJ

01021

2

ccc

cA n

(n=123) is the number of FeII ions which undergo the ls-hs transition ina complex m is the number of TBP MIII

2MrsquoII3 complexes whose FeII ions

are involved in the spin conversion =1n k=1m 0 is thevolume that falls at a Fe ion and its nearest surrounding and is the unit

cell volume per one iron respectively In the basis of the states 25T and

11A the 1616 matrix k is diagonal and has 15 eigenvalues equal to 1

and one eigenvalue equal to -1 Finally 2)(1 lshs

2)(2 lshs hs and ls are the constants of interaction of the

FeII ion with the full symmetric strain1A in the hs and ls states

respectively The first term in (3) acts as an additional field applied toeach spin-crossover ion and redefines the effective energy gap 0

between the hs and ls states of the FeII in the cubic crystal field Thesecond term in (3) represents an infinite range interaction between theFeII ions which undergo the spin conversion This interaction arises fromthe coupling to the strain The model of the elastic continuum introducedabove satisfactorily describes only the long-wave acoustic vibrations ofthe lattice Therefore the obtained intermolecular interactioncorresponds to the interaction via the field of long-wave acousticphonons

Due to the proximity of the FeII ions in the clusters short-rangeinteractions between these ions inside the cluster are relevant Thelargest is the effect of the exchange arising from the optic phonons [19]

69

The Hamiltonian describing short-range interactions between FeII ionswithin the trigonal bipyramid can be written as

0

kkk

sr JH (4)

The Hamiltonian (4) takes into account the interaction between the FeII

ions participating in the spin transitions the interaction of these ionswith those FeII ions which are in the hs-state in the whole temperaturerange as well as the interaction between the latter It should bementioned that eq (3) as compared with eq(4) only accounts for FeII

ions participating in spin conversion The Hamiltonian for the wholecrystal can be written as

k

kexstsr HHHHH

2

00 (5)

where k

k

exex HH In the molecular field approximation the full

Hamiltonian H can be written as a sum of one-cluster Hamiltonians

)(32)(

)2

(~

211101

2

1

0

0

kkB

kkkB

k

ex

kkZ

kkkkkkk

gIgHIl

IlsJBJH

HlsH

(6)

where in the basis of the states 25T and 1

1A kI1

is a diagonal 1616 -

matrix with 15 eigenvalues equal to 1 and one vanishing eigenvalue is the order parameter In fact the Hamiltonians kH

~describe clusters

with different numbers of spin-crossover FeII ions and k as beforenumbers the clusters in the crystal For calculation of the temperaturedependence of the order parameter the self-consistent procedure wasapplied The calculations of the magnetic properties were based on theHamiltonian given in Eq(6)

3 Results and discussionThe estimation of the parameters J and B was performed

according the procedure suggested in paper [16-18] For characteristicfor compounds 1 and 2 parameters =1026Aring3 0 =8Aring3

c2 (005divide01)c1211

2 10 cmdynec 1046 141

cm 142 1087 cm the

70

parameters J and B take on the values 20divide80 cm-1 and -95 divide -24 cm-1respectively

Fig1 shows the experimental data for compound 1 together withthe calculated T vs T curves The result of the best fit procedure in

the model above developed is presented by curve 1 The best fitparameters are the part of the figure caption One can see that a quitegood agreement with the experimental data is obtained At temperaturesbelow 100 K the T values show that the FeII ions are mainly in the ls ndashstate However some small admixture of hs ions is present In thetemperature range 150-300 K the T product gradually increases thusindicating the ls - hs transition in the FeII ions

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30 35

04

06

08

10

3

2

1

T

cm

3K

mo

l-1

Temperature K

23

1

T

cm

3K

mo

l-1

Temperature K

Fig1 Temperature dependence of the T product for 1 Circles-experimentaldata [12] The solid lines represent a theoretical fit with =-103 cm-1 x=10and (1) hs-ls =640 cm-1 J =35 cm-1 J0=45 cm-1 =180 cm-1 =10 (2) hs-

ls=620 cm-1 = -136 cm-1 J=0 J0=0=06 (3) hs-ls=630 cm-1 =168 cm-1J=0 J0=0 =06

The parameter J of long -range cooperative electron-deformationalinteraction obtained from the best fit procedure falls inside the limits

71

estimated above Relatively small values of the parameters J and J0 ascompared with the gaps hs-ls= 0-2B and are also in agreement withthe observed gradual temperature dependence of T and noticeable

increase of T at temperatures higher than 150K Finally the estimated

from the best fit procedure percentage of FeII ions (x=10) which are inthe hs-state at any temperature is very close to that obtained from theMoumlssbauer spectra [12] For comparison in the same figure (curves 23)the results of fitting of the T curve in neglect of long- and short-

range interactions are shown for the cases of 0 and 0 It isseen that in this approximation the calculated curves 2 and 3 differsignificantly from the experimental one both at low and hightemperatures besides this the obtained value 60 is too small forhs-FeII-ions

For compound 2 the variation of the observed magneticsusceptibility as a function of temperature is presented in Fig2

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

321

T

cm

3K

mo

l-1

Temperature K

Fig2 Temperature dependence of the T product for 2 Circles experimentaldata [12] Curves 1- 3 were calculated with the following parameter values hs-

ls =690 cm-1 J=30 cm-1 J0=40 cm-1 =100 cm-1 =-103 cm-1 =10 x=9and (1) Jex = 3 cm-1 (2) Jex = 0 (3) Jex = -3 cm-1

72

First the magnetic behavior of complex 2 was analyzed withneglect of intracluster Heisenberg exchange interaction between FeII andFeIII ions The result of the best fit procedure is presented by curve 2 inFig2 The best fit parameters are the part of the figure caption One cansee that the values of the key parameters are close to those for complex1 However the obtained energy gap hs-ls between the ls and hsconfigurations for complex 2 is a bit larger than the corresponding gapfor compound 1 while the parameters of short-range and long-rangeinteractions are smaller Namely this difference in the characteristicparameters leads to lower values of T for compound 2 as compared

with compound 1 at temperatures higher than 150K The effect ofexchange interaction on the magnetic behavior is illustrated in Fig2 bycurves 1 and 3 Since typical values of the exchange parameters incyanide bridged complexes are of several cm-1 we calculated the Tproduct with the set of the best fit parameters and Jex = -3 cm-1 and 3cm-1 One can see that at temperatures higher than 50K the smallexchange interaction has no effect on the magnetic properties ofcomplex 2

Moumlssbauer spectra provide direct information about the populationof the hs and ls states and serve a reliable test for the theoreticalbackground of the SCO phenomenon The total Moumlssbauer spectrum(ie the observable spectrum) was obtained by summing up the spectrayielded by different cluster electronic states in the molecular field withdue account for their equilibrium populations for a given (at a certaintemperature) value of the molecular field In calculations theexperimental values for the parameters of the quadrupole splttings andisomeric shifts were taken from [12] The calculated and experimentalspectra are shown in Fig3

Quite good agreement between the experimental data andtheoretical calculations is obtained It should be underlined that themodel takes into account the main effect inducing the temperaturedependence of the Moumlssbauer spectra and this is the temperaturedependence of the cluster energies in the molecular field Namely thiseffect is responsible for the transformations of the Moumlssbauer spectrawith temperature

73

The proposed model gives a good fit to the observed temperaturedependence of the static magnetic susceptibility and the Moumlssbauerspectra The last clearly illustrates the cooperative nature of SCOtransformations in TBP compounds that leads to a crossing of the ls andhs levels due structural phase transition induced by the ordering of thelocal deformations through the field of the acoustic phonons

Fig3 Moumlssbauer spectra for compound 1 calculated at T=42 220 and 300Kwith the set of the best fit parameters (thick solid lines) Contributions from ls -FeII and hs -FeII ions are shown in dash and dot lines respectively The half-width of the individual lines Г=016 cm-1(42 К) Г=018 cm-1(220К)Г=024cm-1(300К)

74

AcknowledgmentsFinancial support of the STCU (project N5062) is highly

appreciated BT and KD gratefully acknowledge financial support ofthe Binational US-Israel Science Foundation (BSF grant no 2006498)BT thanks the Israel Science Foundation for the financial support (ISFgrant no 16809)

References1 Guumltlich P Goodwin H A Spin Crossover in Transition Metal

Compounds Springer-Verlag 20042 Hauser A Light-Induced Spin Crossover and the High-Spin rarrLow-

Spin Relaxation Springer-Verlag 20043 P Guumltlich J Jung Nuovo Cimento D 1996 18 1074 P Guumltlich A Hauser H Spiering Angew Chem Int Ed Engl

1994 33 20245 J Zarembowitch New J Chem 1992 16 2556 A B Gaspar V Ksenofontov M Serdyuk P Guumltlich Coord

Chem Rev 2005 249 26617 JA Real AB Gaspar MC Munoz P Guumltlich V Ksenofontov H

Spiering TopCurrChem2004 2331678 G Vos RAG De Graaff JGHaasnoot AM van der Kraan De

PVaal JReedijk InorgChem 1984 23 29059 EBreuning MRuben JMLehn FRenz YGarcia VKsenofontov

P Guumltlich E Wegelius KRissanen AngewChemIntEd 2000 392504

10 M Nihei MYi MYokota LHan AMaeda HKushida HOkamoto HOshio AngewChem IntEd 2005 446484

11 D-Y Wu O Sato Y Einaga C-Y Duan Angew Chem Int Ed2009 48 1475 ndash1478 2009

12 MShatruk ADragulescu-Andrasi KEChambers SAStoianELBominaar CAchim KRDunbar J Am Chem20071296104

13 AAbragam BBleaney Electron Paramagnetic Resonance ofTransition Ions Clarendon Press Oxford 1970

14 A V Palii SM Ostrovsky S I Klokishner B S Tsukerblat C PBerlinguette K R Dunbar J R Galaacuten-Mascaroacutes JAmChemSoc2004 126 16860

15 HWeihe H Gudel H Comments Inorg Chem 2000 22 75

75

16 SI Klokishner F Varret J Linares ChemPhys 2000 255 31717 SI Klokishner JLinares PhysChemC 2007 111 1064418 SI Klokishner J Linares F Varret Journal of Physics

Condensed Matter 2001 13 59519 JM Baker Rep Prog Phys 1971 341 109

53

NON-CARBON PREPARATION OF SILICON BYMECHANICALLY ACTIVATED THERMAL SYNTHESIS

TF Grigorieva1 TL Talako2 AI Letsko2 V Šepelaacutek3 VG Scholz4MR Sharafutdinov1 IA Vorsina1 AP Barinova1 PA Vitiaz2

NZ Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry Kutateladzestr 18 Novosibirsk 630128 Russia grigsolidnscru

2 Powder Metallurgy Institute Platonov str 41 Minsk 220005 Belarus3 Inst of Nanotechnology KIT Eggenstein-Leopoldshafen 76344 Germany

4 Inst of Chemistry Humboldt Univ Berlin 12489 Germany

IntroductionIn industrial processes the production of Si is based on the

reduction of silicon dioxide by carbon at a temperature of about 1800 C[1] However the coke applied to the reduction can be hardly refinedfrom the most dangerous for silicon impurities like boron phosphorusarsenic and antimony That is why development of non-carbon routes forsilicon production is a topical problem of a silicon industry Reductionof oxides with magnesium and aluminum by the method of self-propagating high-temperature synthesis (SHS) has been used in industryfor a long time [2] As such reactions are highly exothermal they can bealso organized with the use of mechanochemistry for instance reductionof the copper oxide by aluminum Mechanochemical reduction of ironoxide by aluminum aimed at obtaining precursors with differentcompositions for intermetallideoxide SHS composites has been alsoconsidered [3ndash6]

SiO2 + Al reaction is not high exothermic enough to organize theSHS without preliminary heating [7] Mansurov et al [8] reportedcreation of ceramic composites in several stages first the silicon oxidewas mechanochemically treated in an organic compound environmentthen the resultant material was annealed (carbonized) at ~ 850 C andfinally the mixture of the carbonized silicon oxide with aluminum wassubjected to SHS However as-formed product included silicon carbide

The objective of activities described in this paper is to study thepossibility of using mechanochemical treatment for obtainingsiliconaluminum oxide composites by the SHS and thermal synthesis atconsiderably lower temperatures with the following removal of alumina

54

Sample preparation and examination proceduresThe PA-4 aluminum powder and the silicon oxide with a particle

size of ~ 3 nm were used in our experimentsA stoichiometric mixture of the silicon oxide with aluminum was

processed in a high energy planetary ball mill (drum volume 250 cm3ball diameter 5 mm mass of the balls 200 g mass of the sample 10 gand velocity of rotation of the drums around a common axis ~1000 rpm)

The IR spectra were recorded by a Specord IR 75 spectrometerthe samples for this study were pressed with annealed potassiumbromide

The 27Al (I = 52) NMR spectra were recorded on a BrukerAdvance 400 spectrometer corresponding to a 27Al resonance frequencyof 782 MHz MAS experiments were realized with a high speed probeusing 25 mm zirconia rotor The spinning speed was 20 KHz Themagnetic field strength (in frequency unit) was set to 104262 MHz Theexcitation pulse duration was chosen equal to 1 s The recycling delaybetween each acquisition was fixed to 1 s To see weak signals in the Al-O region in mechanically activated samples we applied accumulationsnumbers up to 56000 (ie measurement time of 15 hours)

The dynamics of the SHS process was studied with the use ofdiffraction of synchrotron radiation and an OD-3 single-coordinatedetector The samples for SHS were prepared in the form of pellets 20mm in diameter and 1ndash2 mm thick by pressing at a pressure of 200 atmThe resultant samples were placed onto a ceramic plate so that they werein the center of the goniometer The process was initiated by a nichromespiral The OD-3 detector was triggered to operate in the ldquofast filmingrdquomode simultaneously with the beginning of pellet burning The time ofone ldquoframerdquo was 05 sec and the number of ldquoframesrdquo was 128 Theradiation wavelength was 1527 Aring

For investigation of mechanically activated thermal synthesis thesamples were heated up to 650 C in the reaction chamber XRK 900 inair with a heating rate 10 min The OD-3 detector was also used forstudying the process dynamics though time of one ldquoframerdquo was 1 min

55

Results and discussionFirst we made an attempt of direct mechanochemical reduction of

the silicon oxide by aluminum The study of this process showed that thechemical reaction of SiO2 reduction does not occur within 6 min ofmechanical activation The IR spectrum of the initial mixture containsclear absorption bands with the maximums at 1005 and 480 cmminus1

(valence and deformation oscillations of the SindashO bond of the SiO4

tetrahedra of the siliconndashoxygen skeleton) and two maximums in therange of 900ndash670 cmminus1 due to oscillations of the SindashOndashSi bridges Thephenomena observed in the course of mechanical activation were agradual decrease in intensityand broadening of the characteristic bands of the SindashO bond (Fig 1)

An electron-microscopy study of the SiO2Al composite obtainedafter 1 min of mechanical activation in characteristic radiation revealed a

Fig 2 Microphotograph of themechanocomposite after 1 minactivation in Si characteristic

radiation

Fig 1 IR spectra of the SiO2 + Al mixturebefore mechanical activation (1) and aftermechanical activation during 05 (2) 1 (3)

and 6 (4) min

56

very small grain size and a very uniform distribution of the componentsin the mechanocomposite (Fig 2)

Based on the data of the differential thermal analysis (DTA) evenshort-time activation of this mixture appreciably affects its thermalcharacteristics For the initial mixture the real chemical interactionoccurs at a temperature T gt 1000 C (Tmax = 10836 C) (Fig 3 a) iesubstantially higher than the melting point of aluminum whereas thesituation is different for the mixture subjected to mechanical activationduring 20 sec Two clearly expressed exothermal peaks appear the firstpeak at 6217ndash6486 C (Tmax = 6327 C) and the second peak at 9921ndash10759 C (Tmax = 10292 C) (Fig 3 b) For the mixture activated for 40sec the first peak is at 6045ndash6366 C (Tmax = 612 C) and the secondpeak is extremely broad and smeared in the range of 8161ndash11117 C(Tmax = 10381 C)

These observations can be explained by the fact that a tightcontact is created between some part of the ultrafine non-plastic siliconoxide and plastic aluminum already within 20 sec of mechanicalactivation the silicon oxide is ldquowettedrdquo by aluminum as a result somepart of the silicon oxide starts to interact with aluminum at a temperatureT = 6217C which is lower than the melting point of the latter Asmechanical activation is continued aluminum becomes also dispersed tonanoparticles greater amounts of the components of the mixture areinvolved into the contact and the temperature of the interactionbeginning decreases after 1 minute of activation the interaction beginsat T = 5399 C and ends at T = 6303 C (Fig 3 c)

The curve for this sample obtained by the method of differentialscanning calorimetry (DSC) has only one exothermal peak ie theentire process proceeds at a temperature lower than the melting point ofaluminum Longer activation further decreases the temperature ofreaction beginning (Table 1) but there are no any further significantchanges in the system parameters determined by DSC

The duration of mechanochemical treatment was limited to 6 minfor the following reasons- the IR spectra are so smeared already after 4 min that do not provide

any new information (see Fig 1)- the DTA study does not reveal any significant changes in the thermal

characteristics after 1 min of mechanical activation (see Table 1)

57

- mechanochemical actions should be always minimized to ensure theminimum possible contamination of the products by milling

Fig 3 Results of differential scanning calorimetry (DSC) and thermogravimetry(TG) studies of the SiO2 + Al mixture before (a) and after mechanical activation

during 20 (b) and 60 sec (c)

58

Table 1 Parameters of Exothermal Peaks on DTA Curves of SiO2 + AlSamples after Mechanical Activation

Temperature CDuration of activation

beginning of thereaction

end of the reaction

1 min 5930 6303

2 min 5871 6243

4 min 5867 6291

6 min 5870 6258

27Al MAS NMR spectra of the nanostructured SiO2Almechanocomposites are dominated by a broad resonance associated withthe presence of nanostructured Al matrix (Fig 4) The interestingobservation is that additional resonance lines appear in the spectra ofmechanoactivated samples corresponding to AlO4 AlO5 and AlO6

polyhedra Their content is slightly increasing with increasing millingtime however the relative intensity of AlOx polyhedra compared withthe Al matrix spectral intensity is even after the longest milling periodvery low It can be assumed that these nonequilibrium localcoordinations of aluminium atoms are located on the SiO2-Al interfaces[9] The intensity of the resonance lines belonging to various polyhedrarelative to the total spectral intensity allows us to calculate the volumefraction of interface regions in the nanocomposites Furthermoreassuming a spherical shape of SiO2 nanoparticles the thicknees of theinterface regions was calculated their known volume fraction

Thus the study of mechanically activated SiO2+Al mixturesshows that silicon reduction does not occur during mechanical activationstep except formation of some AlOx species at the interfaces but anexothermal reaction in activated mixtures can proceed at substantiallylower temperatures

In the subsequent step the nanostructured SiO2Almechanocomposites were used as precursors for the preparation ofSiAl2O3 composites via self-propagating high-temperature synthesisOur experience shows that combustion initiation requires sample

59

preheating approximately to 200 C (as compared with 650-860 Сreported in [7])

Fig 4 27 Al MAS NMR spectra of non-activated sample (a) the samplemechanoactivated for 1 (b) and 6 (c) minutes

60

The overall pattern of phase transformations is illustrated in Fig 5a To analyze them however it is more convenient to use the projectiononto the diffraction angle (β)ndashtime plane (Fig 5 b) As the silicon oxideused in these experiments is amorphous to x-ray radiation onlyaluminum peaks are observed

Fig 5 Dynamics of phase transformations in the Al + SiO2 mechanocompositein the SHS mode (a) three-dimensional image (b) projection onto thediffraction anglendashtime plane

61

It is clearly seen thataluminum becomes heatedas the combustion waveapproaches the peaks areshifted toward smallerangles ie greaterdistances between theplanes After that theintensity of these peaksdrastically decreaseswhich is apparently due tomelting No crystallinephases are observed in thetwo frames (~ 1 sec) Inour opinion corundum(Al2O3) peaks appearslightly earlier than siliconpeaks A possible reason isthe lower melting point ofsilicon (1410 C) as compared with corundum (2050 C) An electron-microscopic study of the SHS product of the SiO2 + Al system subjectedto mechanical activation during 1 min in characteristic radiation (Fig 6)shows a fairly uniform distribution and small size of all elements in thesystem including silicon being formed

Previously it was shown that chemical interaction between SiO2

and Al in the mechanocomposites formed during the mechanicalactivation starts at essentially (~ 500 C) lower temperatures as comparedwith the non-activated mixtures

In the final step we used as-formed mechanocomposites asprecursors for the preparation of SiAl2O3 composites via thermalsynthesis The samples after mechanical activation for 6 min wereplaced into cuvette and gently prepressed to get the plane surface Thenthe cuvette with the sample was sited in the furnace The thermocouplewas directly close to the registration area Recording of diffractogramswas started at temperature 230 С Dynamics of phase transformation inAl SiO2 composites during heating from 590 up to 660 C is presentedin Fig7

Fig 6 Microphotograph of the SHS productin Si characteristic radiation

62

As can be seen from the Fig 7 the reaction products (silicon andalumina) start to form at about 590 С It is interesting that corundum isformed during the SHS and thermal synthesis after low activation time

Fig 7 Dynamics of phase transformation in Al SiO2 composites duringheating from 590 up to 660 C

Fig 8 XRD-pattern of the thermal synthesis product from the mechanocompositesactivated for 6 min and heated up to 660 C

63

while -Al2O3 is identified in the product of thermal synthesis afterlonger MA durations (Fig 8)

ConclusionsThus though the silicon oxide is not reduced by aluminum

directly by mechanical activation the use of the mechanocomposite as aprecursor for both SHS and thermal synthesis allows a fine-grainsiliconaluminum oxide composite to be obtained In both caseschemical interaction starts at essentially lower temperatures as comparedwith the non-activated mixtures

AcknowledgementsThis work was supported by the joint project No 5 ldquoNon-carbon

preparation of Si by mechanically activated thermal synthesisrdquo of NASBand SB RAS

References1 Denisov VM Istomin SA Podkopaev OI Serebrjakova LI

Pastuchov EA Beletsky VV Silicon and its alloys EkaterinburgPublishing house of Ural Branch of the Russian Academy ofSciences 2005 467 p (in Russian)

2 AG Merzhanov Forty Years of SHS Happy Life of a ScientificDiscovery (in Russian) Chernogolovka (2007)

3 TF Grigoryeva SA Petrova IA Vorsina et alldquoMechanochemical reduction of a copper oxiderdquo in TheOptimization of the Composition Structure and Properties ofMetals Oxides Composites Nano and Amorphous Materials Proc6th IsraelindashRussian Bi-National Workshop Jerusalem (2007) pp197ndash204

4 TF Grigoryeva TL Talako AA Novakova et al ldquoMA and MASHS production of nanocomposites metaloxides andintermetallicsoxidesrdquo ibid pp 139ndash148

5 NZ Lyakhov PA Vityaz TF Grigorieva et alldquoMechanochemically synthesized SHS precursors for obtainingintermetallideoxide nanocompositesrdquo Dokl Akad Nauk 406 No6 776ndash778 (2005)

64

6 5 T Talaka T Grigorieva P Vitiaz et al ldquoStructure peculiaritiesof nanocomposite powder Fe40AlAl2O3 produced by MA SHSrdquoMater Sci Forum 534ndash536 1421ndash1424 (2007)

7 Maltsev VM Gafiyatulina GP Tavrov AV Spreading of thecombustion wave in SiO2-Al systems Proc SPIE Vol 3172(111997) p 724-727

8 ZA Mansurov RG Abdulkarimova NN Mofa et al ldquoSHS ofcomposite ceramics from mechanochemically treated and thermallycarbonized SiO2 powdersrdquo Int J SHS 16 No 4 213ndash217 (2007)

9 V Sreeja TS Smitha Deepak N Ajithkumar TG and PA JoySize dependent coordination behavior and cation distribution inMgAl2O4 nanoparticles from 27 Al solid state NMR studies J PhysChem C 112 14737-14744 (2008)

37

THE PREPARATION OF MECHANICOMPOSITESTUNGSTEN-METAL AND SINTERING MATERIALS

T Grigoreva1 L Dyachkova2 A Barinova1 S Tsibulya3 N Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS 18Kutateladze str 630004 Novosibirsk Russia grigsolidnscru

2 Institute of Powder Metallurgy NAS B Minsk Belarus3 Boreskov Institute of Catalysis SB RAS Novosibirsk Russia

Tungsten-based materials are used for manufacture of electro-technical items spot welding electrodes spraying cathodes etc

The preparation of the high-melting materials is powerconsumptive as two-stage high-temperature sintering is used tungstenpre-sintering temperature is 1150 ndash 1300 C final tungsten sinteringtemperature is 2900 - 3000 C [1]

Metal additives with a lower melting temperature are introducedinto the high-melting material for sintering temperature reduction andsince the tungsten powder has a bad moldability level more plasticmetals such as copper nickel iron are introduced for the moldabilityimprovement

Tungsten ndash copper mixture has been studied the best so farThe mixture W-Cu sintering process research has shown [2] that

the product density depends on the initial powders dispersion degree andthe mixture composition So at the tungsten particles size 10-15 m themaximum densification is observed at the copper weight ration 50 The blend density sharply decreases with the copper content decrease(less than 35 ndash 40 wt) At the same time mixtures with the coppercontent not higher than 10 are needed Special methods have to beused for the preparation of the tungsten alloys

The active densification (from 44 till 12 ) is known to take placeat 1100 - 1200 C at sintering of mixtures W-20 vol Cu with tungstenparticles size lower than 1 m [3] Even higher densification speed isobserved in a blend attained with copper tungsten reduction whencomponents mixing practically achieves a molecular level [4] ie thesecond element concentration reduction is possible at tungsten particlessize decrease and homogeneous distribution of the both componentsThe original blends mechanical activation process [5ndash7] is very

38

perspective in this trend since grinding and formation of larger contactsurface between the original components take place during mechanicalactivation This process is especially effective at mechanical activationof solid and liquid metals and plastic ndash non-plastic metals pair Thecomposite nucleus (non-plastic component) ndash cover (plastic metal) canbe created in this case The possibility of chemical interaction onbetween tungsten and plastic metal the contact surface duringmechanical activation should be considered here

The work aim is to study structure and morphology of thecomposites formed at mechanochemical activation of the tungsten witha small content (till 10 ) of plastic metals both interacting (nickel iron)with it and not interacting (copper) with it The influence of the structureand morphology of the mechanocomposites on the processes of formingand sintering was studied

Powders of tungsten nickel iron copper were used forpreparation of mechanocomposites Mechanical activation of themixtures was carried out in a high energy planetary ball mill with watercooling in argon atmosphere (drum volume ndash 250 cm3 balls diameter ndash5 mm the load ndash 200 g the sample - 10 g the velocity of rotation of thedrums around a common axis 1000 rpm)

X-ray analysis was carried out with diffractometer D8 AdvanceBruker (Germany) at the CuK radiation Research of the structure andmorphology of the mechanocomposites was carried out with thescanning electronic microscope (SEM) ldquoMira LMHrdquo with the add-ondevice for micro-x-ray analysis The electronic probe comprised 5 2 nmthe actuation area comprised 100 nm The research was carried out inmodes of registration of absorbed (AE) and backscattered (BSE)electrons and also of characteristic radiation of tungsten copper nickeland iron The sintered materials research is carried out with themetallographic microscope MEF-3 (Austria) at zoom times200 and times950

The compressibility was determined via density in compliancewith the ISO 3927-1985 of cylindrical samples with diameter 10 mmheight 12 mm pressed in a steel die-mold at pressure 200 400 600 and800 MPa The pressed samples were sintered in vacuum at temperatureof 1100 ndash 1450 C

Compression strength of mechanically activated blends wasdetermined via the samples of diameter 10 mm height 12 mm

39

transverse strength ndash via prismatic samples with height 5 mm width 10mm length 55 mm The tests were preformed on the testing machineldquoInstronrdquo with the loading speed 2 mmmin

Sintered samples microstructure was studied on metallographicsections etched with solution (10 g K3Fe(CN)6 10 g KOH 100 mlH2O) via metallographic microscope MEF-3 of the company ldquoReihertrdquo(Austria)

Mechanical activation was carried out in two stages for attainingmechanical composites tungsten ndash metal (Cu Ni Fe) The first stagesaw grinding only tungsten for 4 min At the second stage 7 ndash 10 copper (nickel iron) was added and joint mechanical activation wascarried out for 1 ndash 2 min

In compliance with the x-ray data the initial tungsten sample is awell-crystallised powder (Fig 1a) The intensity of the diffraction peaksshows the texture (of the preferred orientation) presence in trend 110The X-ray pattern of the tungsten samples activated during 4 min (Fig1b) has widened peaks The X- ray analysis shows that widening ismostly caused because of micro-defects in the tungsten structure (at thelarge particles sizes retaining) It should be also noted that thedistribution intensity of the peaks shows the texture absence (the equalparticles distribution in powder from the point of view of theircrystallographic orientation)

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

Ia

u

2 Theta degree

110

200

211

220

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

Ia

u

2 Theta degree

a bFig 1 X-Ray patterns for initial W (a) and activated for 4 min (b)

40

During the mechanical activation in a high energy planetary ballmills plastic metals tend to stick to balls and the drums walls even atshort-time activation because of that they were introduced to the blendsinto the already activated for 4 minutes tungsten and the mixture wastreated for 2 minutes more

The different X-Ray patterns were received for the samples withCu Ni Fe additives (Fig 2) The second metal phase is seen to bepresent in a well-crystallised form besides the phase W in all cases thecopper picks relative intensity is however considerably higher than thenickel picks intensity that in turn exceeds the iron reflection intensityFormation of intermetallic compounds in the X-ray-amorphous state oncontact surface WNi WFe can be supposed to be possible forchemically interacting metal pairs (tungsten ndash nickel tungsten ndash iron)X-Ray research data are indirect confirmation of this supposition Thesedata have shown that mechanochemical efforts donrsquot allow to receivehomogeneous distribution of copper in the tungsten matrixMechanocomposites W + 10 Cu is arranged in compliance with theldquosandwichrdquo principle where copper phase of micrometric size is locatedin the tungsten die (Fig 3)

The second metal phase is seen to be present in a well-crystallisedform besides the phase W in all cases the copper picks relative intensityis however considerably higher than the nickel picks intensity that inturn exceeds the iron reflection intensity Formation of intermetalliccompounds in the X-ray-amorphous state on contact surface WNiWFe can be supposed to be possible for chemically interacting metalpairs (tungsten ndash nickel tungsten ndash iron) X-Ray research data areindirect confirmation of this supposition These data have shown thatmechanochemical efforts donrsquot allow to receive homogeneousdistribution of copper in the tungsten matrix Mechanocomposites W +10 Cu is arranged in compliance with the ldquosandwichrdquo principle wherecopper phase of micrometric size is located in the tungsten die (Fig 3)Electron microscopy and X-Ray research of mechanocomposites forinteracting metals (W + 10 Ni) has shown homogenous nickeldistribution

41

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Ia

u

2 Theta degree

Cu

а

40 50 60 70 80 90

0

1000

2000

3000

4000

Ia

u

2 Theta degree

Ni

b

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Iau

2 Theta degree

Fe

c

Fig 2 X-Ray patterns for mechanocomposites W (4 min) + additives Cu(a) Ni (b) Fe (c) (2 min)

The received result allows to suggest that metals distributionhomogeneity depends on the thermodynamical parameters of theirmixture (Нmix(W-Ni) = - 2 kJmol Нmix(W-Cu) = + 10 kJmol [8])and on a possibility of the chemical interaction between them The thinlayers of intermetallic compounds form on the continuously renewingcontact surface in the systems W-Ni and W-Fe for this time period (1-2min) and because of distance these thin layers do not manage to form acrystalline phase that could be fixed in X-Ray way

42

а bFig 3 Micrographs of the mechanocomposites W-Cu (a) W-Ni (b) in

characteristic radiation Cu and Ni

The research of compressibility of various mechanocompositeshas shown that non-interaction metals (W-Cu) couldnrsquot compressed andthe compressibility of the interaction metals (W-Ni W-Fe) depends ofthe contents of additives Research of compressibility of mechanicallyactivated powders of various composition has shown that tungsten ndash10 iron mixture powder has the best compressibility level andtungsten ndash 7 nickel mixture powder has the least compressibility level(Fig 4)

But it should be noted that mechanically activated powderscompressibility level is not high moreover some mechanocompositesdo not have compressibility at specific pressure 200 ndash 300 MPa and thesamples layering is observed at pressure higher than 600 MPa Therelative density of the pressed samples is 50 ndash 78 It indicates at thenecessity of the additional lubricants introduction into the mechanicallyactivated powders for their compressibility increase

43

Fig 4 Tungsten-based mechanocomposites compressibility curve

For the powders compressibility improvement the lubricants areintroduced directly into initial mixture or plated to the press-mouldsurface for decrease of friction between the powder and the press-mouldwall and also between the powder particles The lubricant removaltemperature depends on the lubricant melting or dissociationtemperature The melting and boiling temperature or the lubricantsdissociation temperature generally used in powder metallurgy are givenin table 1 [9]

Stearates especially zink stearates have the leading place Therest lubricants have not got such a wide use since residual remains aftertheir removal [10]

Nowadays nylon-binding-based lubricant has been developedabroad This nylon binder is introduced during the charge mixingprocess and needs warm pressing [11-14] Such a lubricant allowsattaining high (θ is no less than 95 ) density of iron-based materials

The lubricant addition as a rule retains ~1 wt as higher contentleads to the pressing growth if the lubricant is present in the sinteringprocess till the sintering temperature

The lubricant burning-out process is carried out in the protective-reducing atmosphere in separate furnaces or in a sintering furnace (in thearea separated from the sintering area) The lubricant burning-outtemperature is as a rule not high and comprises 600 ndash 800 C

44

Table 1 Temperature of melting and dissociation of solid lubricants

Lubricant Lubricant formulaMeltingpoint С

Boiling ordissociation

point СZink stearate Zn(C18H35O2)2 140 335Calcium stearate Ca(C18H35O2)2 180 350Aluminium stearate Al(C18H35O2)2 120 360Magnesium stearate Mg(C18H35O2)2 132 360Plumbum stearate Pb(C18H35O2)2 116 360Lithium stearate LiC18H35O2 221 320Stearinic acid CH3(CH2)16CООH 694 360Oleinic acid С8Н17СНСН-

(СН2)7СООН13 286

Benzol acid С6Н5СООН 122 249Hexoic acid СН3(СН2)4СООNН2 -4 205Paraffin From С22Н46 till

С27Н56

40-60 320-390

Molybdenum disulfide MoS2 1185 -Tungsten disulfide WS2 1250 -Manganous sulphide MnS 1655 -Graphite С (crystalline) 3500 -Molybdenum trioxide MoO3 795 -

During one-component materials heating till 100 ndash 150 C thechange of the contact character between the particles connected withwater evaporation and elastic stress relief tale place As a result somecontact areas rupture and as a consequence general inter-particlecontact surface decrease are possible

The elastic stress relief is ended the further gases are removedand burning-out of the lubricants and binders introduced to the powdertake place during heating from 150 C till the temperature comprising 40ndash 50 of the metal melting temperature The oxide films reduction andnon-metal contact replacement with a metal one take place at highertemperatures although visible pressings density change does not takeplace

45

This work saw lubricants introduction during mechanicalcomposite formation zink stearate stearinic acid and lauric acid wereused The lubricants were introduced in amount of 0 1 0 2 0 3 0 5wt During mechanical activation metal ndash organic acid the latter ismelted (the melting temperature is lower than 70 C) and thus it wets themetal surface and flows with the formation of a larger contact surface Incase of good wettability and sufficient amount of the low-meltingconstituent all the solid-phase surface becomes contact ie mixturenucleus (metal) ndash cover (organic substance) is formed [15] Thecompressibility level has to be naturally higher in this case andmechanochemical approach allows a substantial reduction of plasticizingagentsrsquo concentration

Research of compressibility of powders with lubricants has shownthat Zink stearate has the least influence in comparison to otherlubricants used (Fig 5)

Fig 5 The compressibility curves of the mechanocomposites W-Fe with thelubricant 1 ndash zink stearate 2 ndash lauric acid

The lubricant content increase leads to the mechanically activatedpowders compressibility improvement (Fig 6) but at the lubricantcontent more than 0 3 the samples destruction takes place at sinteringbecause of intensive gas release Plasticizing agents introduction hasallowed mechanical composites formation also for non-interactingmetals (tungsten ndash copper) (Fig 6 7)

46

Fig 6 The compressibility curve of the mechanically activated blend W-Cuwith stearinic acid 1 ndash 0 1 2 ndash 0 3 3 ndash 0 5

Fig 7 The compressibility curves of the mechanically activated blend W-Cuwith lauric acid 1 ndash 03 2 ndash 05

Lauric and stearinic acids additives allow the pressings densityincrease by 25 ndash 40 (Fig 5 8)

Research of density of sintered samples of mechanocomposite hasshown that the density of the samples from mixtures tungsten ndash ironpressed at 400 and 600 MPa does not practically change after sinteringat 1250 C (Fig 9 line 2 5) and at 1450 C the samples density decreases(Fig 9 line 3 6) Mixtures tungsten ndash nickel are subject to a substantial

8

9

10

11

12

200 400 600

De

nsi

ty g

сm

3

Pressure МPа

1

2

11

115

12

125

13

200 300 400 500 600

10Fe+W

10Ni+W

De

nsi

tyg

cm

3

Compacting pressure MPa

47

shrinkage (Fig 10) and density of the samples of W-Ni pressed at 400MPa is 146 gcm3 after sintering at 1250 C and 147 gcm3 at 1350 CSintering temperature increase till 1450 C leads to samples shrinkinglevel reduction and density does not exceed 117 gcm3

Fig 8 The compressibility curves of blends W + 10 Fe and W-10 Ni withaddition of 1 of stearinic acid

Fig 9 Relation of density of mechanically activated blends W + 10 1 ndash afterpressing at 400 MPa 2 ndash pressing at 400 MPa sintering at 1250 ordmC 3 ndashpressing at 400 MPa sintering ndash at 1450 ordmC 4 ndash after pressing at 600 MPa 5 ndashpressing at 600 MPa sintering at 1250 ordmC 6 ndash pressing at 600 MPa sintering at1450 ordmC

10

11

12

13

14

200 400 600

Pressure МPа

Density

gс

m3

1

2

3

0

2

4

6

8

10

W+Fe

De

nsityg

cm

3

12 3

4 5 6

48

0

3

6

9

12

15

400 МPа 600 МPа

De

nsity g

сm

3

Fig 10 Relation of density of mechanically activated blend W + 10 Ni 1 ndashafter pressing 2 ndash pressing sintering at 1250 C 3 ndash pressing sintering at 1350C 4 ndash pressing sintering at 1450 C

Moulding pressure increase till 600 MPa practically does not

influence the sintered samples density Density reduction of the samples

sintered at 1450 C is apparently explained with dissociation of oxides

and other compounds of tungsten and nickel

Sintering at 1450 ordmC of blends W-Ni leads to meltback and

samples form loss thus sintering should be carried out at temperature

not higher than 1350 ordmC

Tungsten-based mechanocomposite strength research has shown

that strength has a direct relation to their density (Fig 11) The blend

tungsten ndash iron (870 MPa) has the minimal strength

The microstructure analysis has shown that in case of sintering at

temperature 1250 C tungsten ndash nickel have a very fine dispersed

structure (Fig 12) Coagulation of nickel insertions located at the base

grains boundaries in tungsten ndash nickel grains growth take place with

sintering temperature increase

49

0

100

200

300

400

500

600

700

800

900

1000

1100

1 2

Ela

stic

lim

it of

com

pre

ssio

n

МP

а

I - pressure 200 МPа

II - pressure 400 МPа

III - pressure 600 МPа

1 - sintering temperature 1250оС 2 - sintering temperature 1350

оС

I

II

III

Fig 11 Influence of attaining modes of samples from mechanically activatedblend tungsten + 10 nickel on their strength

Substantial grain growth large porosity formation nickel phase

particles growth take place in blends sintered at 1450 C eutectic that is

more visible in the blend tungsten ndash nickel is formed at tungsten grains

boundaries

Conclusions

The conducted research has shown that homogenous copper

distribution is failed to be carried out in tungsten with short-term

mechanical activation method for interacting metals of W-Cu system

These mechanically activated samples can be not compacted (moulded)

50

a b

c dFig 12 Microstructure of mechanically activated blends W-Ni sintered at 1250C (a b) and 1350 C (c d) a c ndash times200 b d ndash times950

Homogenous distribution of nickel and iron in tungsten is ensuredwith short-term mechanical activation in systems from interactingmetals The attained samples are formable mechanically activatedpowders compressibility has however been found to be not high therelative density of the pressed samples is 50 ndash 78 and that points atnecessity of additional lubricants introduction into powders for theircompressibility improvement Lubricants introduction allowed ensuringmoldability of immiscible system tungsten ndash copper and densification ofpressings by 25 ndash 40 - for interacting metals

Density of samples from blends tungsten ndash iron does notpractically change after sintering at 1250ordmC and is decreased at 1450 ordmCBlends tungsten ndash nickel are subject to a substantial shrinkage during

51

sintering Sintering temperature increase till 1450 ordmC also leads to theshrinkage level decrease Strength of sintered blends from mechanicallyactivated tungsten-based powders depends on density and kind of theadditive Grain size dispersivity and type of additive location in theblend structure from mechanically activated powders depend on thesintering temperature

AcknowledgementsThe work was carried out within the framework of Fundamental

Research Programme of Russian Academy of Sciences ldquoElaboration ofchemical substances attaining methods and new materials creationrdquoproject No 1821 ldquoElaboration of tungsten mechanical composites-basedhigh-density alloys creation basicsrdquo

References1 IM Fedorchenko IN Francevich ID Radomyselskiy at al

Powder Metallurgy Materials technologies properties andapplications Kiev Naukova dumka ndash 1985 ndash 624 P

2 VN Eremenko JV Najdich IA Lavrinenko Sintering in thepresence of liquid metal phase Kiev Naukova dumka ndash 1968 ndash 122P

3 VV Panichkina MM Sirotuk VV Skorohod Powder Metallurgyndash 1982 - 6 ndash P27-31

4 VV Skorohod YuM Solonin NI Filippov at al PowderMetallurgy ndash 1983 - 9 ndash P9-13

5 Kim JС Moon IН Nanostruct Mater 1998 Vol 10 No 2 P283-290

6 Moon IH Kim EP Petrow G Powder Metallurgy 1998 Vol41 No 1 P 51-57

7 Kim JC Ryu SS Kim YD Moon IH Scripta Mater 1998 Vol39 No 6 P 669-676

8 FR de Boer R Boom WCM Mattens AR Miedema andAK Niessen Cohesion in metals (Cohesion and structurevol 1) (Elsevier Amsterdam 1988) pp 758

9 Hausner H Handbook of Powder Metallurgy Chemical PublishingCo New York 1973

10 Moyer KH Intern J Powder Met 1971 - 7 Р 33

52

11 US patent В 22 F 100 5368630А Powder Metallic Blend with abinder for densification at the set temperature Journal Inventions ofcountries worldwide 1996 1

12 US patent В 22 F 100 5429792 Metal powder content containing a binder for pressing at elevated temperatures JournalInventions of countries worldwide 1996 7

13 US patent В22F 100 (11) 52980555 (40) 940329 laquoIron-basedpowder mixtures with a binding lubricantraquo 1995

14 US patent В 22 F 100 95372138 (5484469А) laquoMetal powder content and a method of a sintered part manufacture from itraquo 1995

15 TF Grigoryeva AP Barinova NZ Lyahov Mechanochemicalsynthesis of metal systems Novosibirsk Parallel ndash 2008 ndash 311 P

34

THE DETERMINATION OF THE KINETIC FUNCTIONSTRUCTURE FOR THE HIGH-TEMPERATURE SYNTHESIS IN

THE MECHANICALLY ACTIVATED MIXTURE 3Ni-Al

VYu Filimonov1 MA Korchagin2 EV Smirnov1NZ Lyakhov2

1Altai State Technical University Barnaul2Institute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirskvyfilimonovramblerru

The peculiarities of heating-up and phase formation in themechanically activated powder mixture 3Ni + Al reacting in the thermalexplosion mode have been experimentally investigated The self-heatingin the mixtures was studied using a specially designed SHS-reactorusing a technique presented in [1] Tungsten-rhenium thermocouples of100 microm diameter were used to control the temperature and to recordthermograms Preliminary mechanical activation was carried out using aplanetary ball mill of AGO-2 type in an atmosphere of argon under theenergy of 40g (centrifugal acceleration of balls 400 ms2) with varyingtime of the activation process The reactant mixtures were preparedusing the aluminum powder PAndash4 particle size 5 divide 60 microm and thecarbonyl nickel powder PNK-1L5 particle size 1 divide 10 microm

The primary goal of this work was to determine the activationenergy and the structure of the kinetic function during the heat evolutionin the system as a result of the phase formation At the adiabatic stage ofheating a system of equations of the temperature increase and thedynamics of the degree of transformation was considered [2]

0 expdT E

k fdt RT

(1)

f

RT

Ek

dt

d

exp1

(2)

The initial conditions are as follows 00 t 0TT where

T temperature of the reacting mixture degree of transformation

t time 0k 1k exponential factors E activation energy f -

35

kinetic function The search for )(f was performed in the known class

of functions [3]

exp

1nm

f

(3)

At the first step of analysis of the experimental thermograms theeffective activation energy of the phase formation was determined from

the curvature of the experimental plot ln 1dT dt f T Based on the

results of 6 measurements and using the slope of the fitting curvepassing through the point of the minimum curvature the effectiveactivation energy was determined which turned out to be anomalouslylow and equal to E = 95plusmn2 kJmol It was found that the experimental

results are best fitted with a function 1n

f where

09 015n [4] Fig1 shows the results of integration of (11) with the

determined parameters

Fig1 Results of integration of (11) -1 experimental thermogram -2

Since the interaction of the reactants is described by the law ofhomogeneous kinetics we suggest that during thermal explosion in themechanically activated mixture of the composition under study thesynthesis occurs through homogeneous regrouping of atoms of the initialreactants without formation of dense diffusional layers hindering thereaction The latter is possible due to high concentrations of defects andinternal stresses formed as a result of intensive plastic deformation of theinitial reactants during mechanical activation

36

References1 Filimonov VY Evstigneev VV Afanasev AV and Loginova MV

Thermal Explosion Ti + 3Al Mixture Mechanism of PhaseFormation International Journal of Self-Propagating High ndashTemperature Synthesis-2008- vol 17-2рр 101-105

2 Aldushin AP Martemyanova T M Merzhanov A G Propagationof the front of an exothermic reaction in condensed mixtures withthe interaction of the components through a layer of high-meltingproduct Composition Combust Explos Shock Waves19728(2)159

3 M I Shilyaev V Е Borzykh A R Dorokhov and V EOvcharenko Determination of thermokinetic parameters from theinverse problem of an electrothermal explosion Combust ExplosShock Waves 1992 28(3)258

4 MA Korchagin VYu Filimonov EV Smirnov NZ LyakhovThermal explosion of a mechanically activated 3Ni + Al mixture Combustion explosion and shock waves 2010 v 46 1 pp41-46

14

MODERN METHODS OF RHENIUM DETERMINATION

OV Evdokimova NV Pechishcheva KYu ShunyaevInstitute of Metallurgy of UB RAS

101 Amundsen st Ekaterinburg Russiashunuralru

IntroductionRhenium due to its unique properties is the promising metal

widely used in various industries At present day the main areas ofapplication of rhenium is the production of catalysts for the petroleumrefining industry and refractory alloys used for turbines manufacturing[1]

The great demand for this element requires large amounts of itsproduction There is a need extracting rhenium even from industrialwaste water from plants [2] due to the high cost and its low content innatural materials

This situation stimulates the development (or modification) ofmethods of analytical control of various nature materials

The content of rhenium in rhenium-containing materials bothnatural and technogenic and contect of accompanying to rheniumelements vary in a wide range of concentrations from 10-7 to tens ofpercent

Earlier the following methods were used for the determination ofrhenium spectrophotometry gravimetry kinetic electrochemicalextraction-fluorimetric methods X-ray fluorescence analysis [3] Themain disadvantages of mostly methods for determining rhenium are thelow sensitivity the bad reproducibility of results the influence ofaccompanying elements Ag W Mo Pt Cu Fe and etc

In modern analytical practice the following methods for therhenium determination are used inductively coupled plasma atomicemission spectroscopy (AES ICP) inductively coupled plasma - massspectrometry (ICP-MS) [4] electrochemical methods [1] X-rayfluorescence analysis and spectrophotometric methods do not lose theirrelevance [1] they have undergone significant modifications recently

15

Inductively coupled plasma atomic emission spectroscopy(AES ICP) is widely used for the rhenium determination in mineral rawmaterials and products of metallurgy production This method allows todetermine up to 10-4 rhenium The advantage of AES ICP is the highstability and reproducibility of results absence of chemical influences

However analysis of more complex objects such as metallurgicalproducts is a not easy task because the lines of rhenium emission areoverlaped with the lines of accompanying elements in samples So thelines of Mo (221427 nm) W (221431 nm) Fe (227519 nm) whichmay be present in the samples in large quantities are overlaped to themost intense lines of rhenium (221426 nm and 227525 nm) Thisproblem requires the development of new methods of samplepreparation and selection of optimal conditions for determination ofrhenium by atomic emission spectrometres

Also a significant disadvantage of this method is the small rangeof certificated reference materials So there are a limited number ofRussian rhenium standard materials with certified value of the rheniumcontent It is molybdenum and copper-molybdenum ores andconcentrates in which the rhenium content is in the range ofconcentrations from 000047 to 00221

In most cases analysts develop the synthetic mixture to monitorthe rhenium content in the analysis of specific samples of complexcomposition This mixture is similar to composition to the matrix of theanalyzed samples consisting of rhenium ions and other ions with agiven concentration For example the authors [5] to develop a techniquefor rhenium determining together with platinum and palladium in thesamples of spent catalysts by AES-ICP applied a synthetic mixtureprepared on the basis of aluminum oxide and standard solutions of Pt(IV) Pd (II) Re (VII)

One of modern methods and the most sensitive methods for thedetermination of rhenium is inductively coupled plasma - massspectrometry (ICP MS) [4 6 7 8] These days ICP MS withseparation and concentration allows to measure rhenium at lower thanseveral ngg However ICP MS performance in analyses of complexsamples is commonly affected by matrix effects and polyatomicinterference and signal drift High levels of salt solutions content cause

16

plugging of sampling orifice with decrease in analytical signal inaddition many spectral interferences may occur [6]

For the rhenium determination in molybdenite by ICP MS shouldbe use large dilution of sample to reduce the matrix influence and reducethe salts influence However this approach is not feasible in the case ofhigh levels of molybdenum and relatively low levels of rhenium in theanalyzed objects The most effective way to minimize the matrix effectsis separation of rhenium from the matrix Often for this purposeextraction by organic solvents [6] sorption by anion-exchangers [8] areused

Recently X-ray fluorescence analysis becomes more popular Itis rapid and is often used for mass analysis The advantage of thismethod is the possibility of direct determination of rhenium in the solidsamples in water solutions [9 10] in the biological samples (plants) [2]

However the method is not without disadvantages firstly thedetection limit of rhenium by X-ray fluorescence analysis is low and isonly 005-01 secondly there are only few the standard materials witha high rhenium content and thirdly the influence of interfering elementsin the sample related to determination of rhenium

Using the concentration can not only reduce the detection limitbut also in the same time solve and reduce the influence of interferingions For the concentration of rhenium in X-ray fluorescence analysis isoften used sorption of rhenium in the form of perrhenate-ions [9 10]

The authors [11] describes a problem related to the developmentof rhenium-containing standard materials by traditional hightemperature approach for X-ray fluorescence analysis Thus high-temperature studies of MoO3-ReO3 which could be served ascomparison materials for the rhenium determination by X-rayfluorescence analysis showed that 50-90 of rhenium is lost duringcalcination of mixtures it indicates the impossibility to use them fordevelopment of standard materials In the paper [11] the method ofpreparing rhenium glassy reference samples (10 - 50) on the basis ofBi2O3 and B2O3 is described The developed method allows to determinerhenium in the range of 001-10 [11]

17

Electrochemical methods in particular the electrostrippingvoltammetry (ESV) occupy a significant place in the analyticalchemistry of rhenium [12 13] This method allows to determine up to10-6-10-5 of rhenium

To avoid the effects of many electropositive components (Mo WCu Ag Au) which may interfere to the rhenium determination by ESVit has been proposed the sorption concentration of perrhenate ions on thesurface of activated charcoal (BAU) [12 13]

The most widely used techniques determine the 10-2 - 10-5 ofrhenium is spectrophotometric method The advantages of this methodare simplicity low cost equipment and a relatively high sensitivitySpectrophotometric method is based on the formation of coloredcomplex compounds of rhenium with organic and inorganic ligands [1]Photometric methods with thiocyanate ion thiourea are widely spread[14 15 16] Development of spectrophotometric methods for rheniumdetermination is largely due to the searching and using of new reagentsIn [17] for the extraction-photometric determination of perrhenate ionsin the form of ion associates the basic polymethine dyes derivatives of133-trimethyl-3H-indole have been offered but the influence ofoxyanions of tungsten and molybdenum is not excluded [17]

The disadvantage of the spectrophotometric methods is the needfor prior separation of rhenium from a number of interfering elements(Mo W Cu) that it is achieved by concentrating perrhenate-ions bysorption or extraction

Over the past decade main changes in the methods of rheniumdetermination related with the improvement stadium of samplepreparation transfer the sample into an analytical form modification ofknown methods and reagents (eg creation of new facilities developmentof new reagents for measurements) and conditions of analysis

In general in the literature a large number of works are relatedwith the separation of rhenium from the analyzed solutions and theseparation of rhenium (VII) from interfering elements by using newtypes of extractants and new sorbents is given Used extractants andsorbents as well as the optimal conditions for extraction and sorption ofrhenium are presented in Table 1 and 2 respectively

18

Extraction plays a dominant role in the methods of separationand concentration of rhenium

In most cases in the hydrometallurgical processing of rhenium-containing products in the acidic solutions ReO4

- are formed Forperrhenate ions extraction the anion-exchange reagents or extractants ofneutral type are often used The literature contains information on theextraction of rhenium (VII) by various amines and quaternaryammonium compounds [18 19 20] Efficient extractants of rheniumfrom acidic solutions are neutral organophosphorus compounds (tributylphosphate alkylphosphineoxides their derivatives) [21 22] a variety ofsolvent mixtures (tributyl phosphate + trioctylamine [23]) theextractants of neutral type such as ketones and aliphatic alcohols [1624 25]

Alcohols ketones and ethers are more selective having higherspeed separation of organic and aqueous phases as well as higherchemical resistance and lower cost compared with amines andorganophosphorus compounds but inferior to them in the extractioncapacity for rhenium (VII) [16]

Thus for perrhenate ions extraction aliphatic alcohols with 7-10carbon atoms in the aliphatic chain are well proven that can extractmore than 98 of rhenium from sulfuric acid and hydrochloric acidsolutions In the case of alcohol there is no need to use solvents andmodifiers what simplifies their use in extraction processes [16]

The efficiency of rhenium extraction into organic phase by aminesdecrease as follow quaternarygt tertiarygtsecondarygtprimary Amongthem secondary and tertiary amines are widely used as efficientextractants of rhenium from acidic solutions Perrhenate ions areextracted by amines in a wide range of pH For systems of amine - low-polar diluent - H2SO4-ReO4-H2O the formation inverse micelles istypical in the organic phase Acid ions and anionic complexes arelocated inside the aqueous core of the micelle with the metal ioncoordinates the polar functional group of amine [19 20]

It should be noted that the extraction by amines is complicated bythe use of solvents the nature of which depends on the solubility ofamines and their extraction capacity So low-polarity solvent toluene incontrast to the non-polar kerosene enhances the polarity of anionic saltsof amine which increases the reactivity of the extractant to the anion

19

exchange of inorganic acid to extractable anionic rhenium complexes[18]

Tertiary amines are the most effective extractants for rhenium(VII) However in paper [18] it is shown that the secondary amine(diisododecylamine) gives advantage to the tertiary amines on therhenium extraction efficiency from sulfuric acid media It can beexplained by the influence of steric factors and smaller rival extractionof mineral acids by secondary amines [1]

Most papers are related to the rhenium extraction from acidicsolutions but the extraction of rhenium from alkaline medium whichare formed after leaching of ores concentrates also represents a difficultproblem In the paper [23] rhenium extraction from alkaline solutionscontaining also molybdenum by solvent extraction using a mixture oftributylphosphate (TBP) and trioctylamine (N235) is describedMolybdenum which is also extracted by solvents in small amountsinterferes to the extraction of rhenium

Over the last decade most works refer to the development offundamentally new classes of extractants for perrhenate ions [26 2728 29] such as encapsulating ligands (cryptands and podands)macrocycles crown ethers These ligands can interact with ReO4

minus byboth the electrostatic interaction between ReO4

minus and protonated ligandand the hydrogen bond formation compared with simple open-chainligands If the complex between ReO4

minus and ligand has highhydrophobicity ReO4

minus in an aqueous solution may be separatedeffectively by a solvent extraction technique [30]

Crown ethers extract rhenium (VII) in the presence of potassiumor sodium in the form of K(Na)LReO4 (L-crown-ether) into the organicphase (12 - dichloroethane chloroform) [31 32] In the paper [31] theextraction perrhenate-ions by 3m-crown-m-ethers (m = 56) ether and itsmono-benzo-derivatives in 12-dichloroethane are described

Podands are analogues of crown ethers containing terminalphosphoryl ligands in their polyether chains they are used for theextraction of rhenium (VII) The efficiency of extraction by phosphorylpodands depends of the following factors the number of oxygen atomsin the polyether chain molecules the number of donor centers in themolecule of podands hydrophobicity of the reagent molecule the size offorming cycles the nature of substituent at the phosphorus atom Studies

20

have shown that phosphoryl podands with three oxygen atoms in thearomatic polyether chain combined with the phosphoryl group bydimetilen or o-phenylene fragments have high extraction ability forrhenium from sulfuric acid solutions [32]

In the paper [30] authors mark another type of podands such aspodands with nitrogen donor ligand -N N N `N`-tetrakis (2-pyridymethyl) -12-ethylendiamine (TREN) and its hydrophobicanalogs which also allow to extract perrhenate ions from highly acidicenvironments

Perrhenate is characterized by its ability to undergo a change ingeometry specifically from tetrahedral to hexagonal in the presence ofdonor ligands (eg acetonitrile triphenylphosphine) Protonationchanges the electron density present on the oxygen atoms Beer et al[33] suggested that the tripodal ligand L1 would be suitable for thebinding and extraction of perrhenate anion This ligand (Fig 1) basedon the combination of tris(2-aminoethyl)amine and crown ether motifswas found to complex sodium cations and to extract perrhenate anionsfrom aqueous solutions into an organic phase

Atwood and co-workers developed calixarene-type ligand L2(Fig 1) that specifically extracts perrhenate from water solution into anorganic phase The selectivity for extractions decreases as followTcO4

minus ge ReO4minus gt ClO4

minusgtNO3minus gtSO4

2minus gtClminus This selectivity pattern isattributed to a combination of charge size and shape Efficientextraction is observed at high and neutral pH the molar ratio ofligandperrhenate ion = 14 [33]

L1 L2Fig 1 Tripodal ligand L1 and calixarene-type ligand L2 for perrhenateextraction

21

Schiff-base macrocycles are used as a new conjugatedmacrocycles for perrhenate ions Thus a series of amino-azacryptands(L3ndashL16) for encapsulation and extraction of the oxoanions perrhenate(Fig 2) from aqueous solution were proposed by the authors [34]Thecomplexation amino-azacryptands L to ReO4

- is via hydrogen-bondedinteractions

Fig2 Amino-azacryptands (L3ndashL16) for encapsulation and extraction of theoxoanions perrhenate

Thus the main characteristics of the compounds for the effectiveperrhenate ions extraction as follows

Energy coordination of ligand with ReO4- should be higher than

the energy of perrhenate ion hydrationThe interaction between the ligand and perrhenate ions an

electrostatic interaction or the formation of hydrogen bonds Functional ligands to be a suitable size (volume of the cavity

should be more than 736 Aring3) shape electronegativity andhydrophobicity

Ligand should be protonated

22

Table 1 Characteristics of extractants for rhenium extraction

Extractant

Analysis objectComposition of

the initialsolution

Extractonconditions

Interferinginfluences

Aliphatic alcoholswith C 7-10

1-Heptanol 4-Heptanol 1-octanol 1-decanol 4-decanol 2-Heptanol 3-Heptanol

3-octanolback-extractant

NH4OH

Solutions HCland H2SO4

Т=293КTime of phase

contacttex = 5 min

organic phase toaqueous

(OL = 11)4 steps of

extraction 2stripping

Coextractionof mineral

acidsincomplete

re-extractionof Re (VII)

1

OctanolSolutions ofHNO3 and

H2SO4

Т=286-290Кtex = 10 min OL

= 11

Coextractionof HNO3

H2SO4

2

Basic polymethinedyes (derivatives of133-trimethyl-3H-

indole) astrazon violet

Aqueous andaqueous-organic

solution

Т=293КрН=6

tex = 10-30 secextractant mixture

toluene +dichloroethane

(1 1)

do notinterfere

3000-5000fold excess ofS04

2- CO32-

300- HPO42-

MoO42-

WO42-

10-20 S2O32-

Cr2O72- IO3

-metal ions as

sulfates

3

Secondary(diisododecylamine)and tertiary amines

(dioctylamin andtrioctylamine)

Solutions H2SO4

Т=293КA wide range of

pH

tex=5-7 mindiluent - toluene

-

4N-benzoyl-N ndashphenyl-

hydroxylamine

Molybdenitedissolved inHCl HNO3

HCl 05 molltex=15 min

diluent chloroform-

23

Table 1 (continued)

Extractant

Analysisobject

Compositionof the initial

solution

Extractonconditions

Interferinginfluences

5

Phosphoryl podands

back-extractant H2O

СReinitial=2middot105 moll

aqueoussolutions of

salts of alkalimetals

solutions ofmineral acids

Т=286-291КОL=11

tex= 60 mindiluent

nitrobenzene12-

dichloroethanechloroform

toluene

-

6Triotylamine (N235)+

tributyl phosphate(TBP)back-extractant18 NH4OH

Alkalinesolutions

afterleaching

containingMo

СRe 01-165gl

T=293 КрН =90 OL=11

tex=10 мин20

triotylamine+30 tributylphosphate

diluentkerosene

-

7

Podand-type nitrogendonor ligand ndashNNN`N`-tetrakis(2-pyridymethyl)-

12-ethylendiamine (TREN)

Aqueoussolution

NH4ReO4

С =10-4 M

Ionic strength01M

pH=1-65diluent

chloroformОL=11tex=24 h

-

8

3m-crown-m-ethers(m=56) mono-benzo-

derivates12-dichloroethane

СReO4-=

0057-0060М

T=291-295Ktex=2h

-

24

Table 1 (continued)

The range of Re concentrations

RecoveryMethods for determination Ref

Recovery gt99

Determination from back-extractSpectrophotometric method with

thiourea reductant-Sn (II)wavelength of 390 nm

[16 24]

1

gt98 Spectrophotometric method [25]

2The range of Re concentrations

001-550 mcgml

Determination from extractSpectrophotometric method

wavelength of 540 nm[17]

3 -AES-ICP

Spectrophotometric methodwith thiourea

[18 1920]

4Mo W Fe are extracted 97

into the organic phase

Determination from aqua phaseafter extraction

ICP-MS[6]

5 -AES-ICP

Spectrophotometric method[21 22]

6 968Spectrophotometric method with

butyl rhodamine[23]

7 - AES-ICP [30]

8 -AES-ICP

Spectrophotometric method[31]

9 - ICP-MS [32]

25

Table 2 Characteristics of sorbents for rhenium sorption

Sorbent

Analysis objectComposition of the

initial solutionConditions of

sorptionInterferinginfluences

1

Activated carbons(BAU)

Eluenthot soda solution

nitrate media

gold ore raw

static conditionsа)рH =2-3

б) рH =15-25

volume ofsolution 10 mlmass of sorbent

03 g(SL=1333)t=10 min UV

a) electro-positive

components(Mo W Cu

Ag Au)b)1000 fold

excess ofMo W do

not interfere

2

Activated carbons- CN-G CN-PCU developed

from waste woodand grain

processingindustries

sulfuric acidsolutions with CRe= 002 gl pH =2

solid phasesliquid SL==105

t=5-7 days-

3

2 Carbon fibrousmaterials

modified withchitosan

neutral aquasolutions of

rhenium

static conditionsТ=286-289 КSL=11000

-

4

3 Weakly basicanion-exchangersАН-105 Purolite

A 170

mineralizedsulphite solutionsimulating rinsing

water(С Re=001-002

gl Mo Cu Fe As)

static anddynamic

conditionsSL = 1500

t = 150-200 min

-

5

Strongly-basicanion-exchangers

АВ-17(sorbent PAN-АВ-

17)

neutral or slightlyacid

solutions

dynamicconditionst = 20 min

The disks ofpolyacrylonitrilefiber filled resin

1000 foldexcess of

Fe Cu ZnPb Cd do

not interfere

6Lignin anion-

exchangerssolutions NH4ReO4

static conditionsSL=1400

t=15min-2 h-

26

Table 2 (continued)

NotesMethods for

determinationRef

1

а) Sorption capacity of BAU forRe СЕ=14175 mgg AC

Detectionlt 10

б) СЕ=00763 mmolg or 142mgg

The concentrations range of Re050 100 mgL in standard

solutions025 50 mgl in the presence

of Mo and W (11000)

a) Electrostrippingvoltammetry

b) X-ray fluorescenceanalysis

a) [12]b) [9 10]

2 -Spectrophotometric

method [35]

3 СЕ=179-185mggSpectrophotometric

method with ammoniumthiocyanate

[38 39]

4Full dynamic exchange capacity

114 mgg

Spectrophotometricmethod with ammonium

thiocyanatekineticmethod

[36]

5 -

Determination of Re bythe diffuse reflectance

spectra at 420 nmrhenium thiocyanate

complex in the presenceof tin (II)

[15]

6 СЕ=3427-2328 mgg Traditional polarography [37]

Sorption is one of the methods for separation of rhenium fromvarious solutions

Sorption of rhenium or perrhenate-ions often occurs on solidsorbents from the liquid phase The presence of a large specific surfacearea and a large number of functional groups of the sorbent determinesits high sorption properties with respect to rhenium (VII) Sorbentscontain the same functional groups (amino groups hydroxyl groups

27

phosphorus groups) as extractants for the selective extraction ofrhenium but these groups are fixed on solid carriers or support

Activated carbons (AC) of various brands are used the mostwidely [9 10] The use of activated carbons as sorbents due to the factthat they have a whole set of valuable properties highly polydisperseporous structure a complex but relatively easily controlled surfacechemistry and specific physical properties Activated carbons like manyother carbon materials exhibit high selectivity to perrhenate ions thatexplains the increased interest to this type of sorbents [12]

The characteristic distinction of carbonaceous materials is that thesorption of rhenium is not only due to complexation with surfacefunctional groups (containing oxygen nitrogen sulfur atoms) but alsodue to the interaction with carbon matrix

AC can act as anion-exchanger in acidic media and themechanism can be described by the following scheme

[C2+ OH-] + ReO4-= [C2+ ReO4

-] + OH-On the other hand the AC have significant reduction properties

the reaction of the electrochemical reduction of perrhenate ions in themethods of rhenium determination by voltammetry is based on this it[12]

It has been established [9 10] that ReO4- is sorbed from nitric

acid solutions almost entirely (95-99) by 10 minutes of UV irradiationwhile without irradiation this process takes up to 60 minutes Increasedsorption by UV authors attribute to the fact when UV radiationsolutions of rhenium (VII) salts rhenium (VI) and rhenium (V) areformed which are considerably faster adsorbed on AC

Extensive use of the AС is also associated with their low costActivated carbons - CN-G CN-P CU developed from waste wood andgrain processing industries have a low cost and their capacitance andkinetic characteristics slightly inferior to conventional AC (FAC) [35]

However from acid solutions together with rhenium molybdenumcan also be sorbed by the AC Furthermore perchlorates nitrates andother oxidants can reduce the adsorption capacity of coals by oxidationThe disadvantage of rhenium sorption by activated carbons is as followsa decreasing in their activity after 4-6 cycles of sorption-desorption [1]low mechanical strength [35]

28

Anion-exchange resin is the next width of use which havegreater selectivity and capacity compared with activated carbons Theseanion-exchangers synthesized on the basis of the gel and porouscopolymer of styrene and divinylbenzene From the neutral and acidicsolutions rhenium is adsorbed by low-basicity anion-exchangers with thefunctional groups of primary and tertiary amines In recent studiesconducted on the use of weakly basic macroporous anion-exchangerswith a more developed specific surface area (20-100 m2g) such asPurolite A170 with secondary amino groups [36]

Sorption by strongly-basic anion-exchangers compared to weaklybasic anion-exchangers has several advantages firstly they are almostquantitatively and selectively extract rhenium from solutions andsecondly work in a wide range of pH [15]

The rapid technique for perrhenate ions determination isdeveloped which allows to find their content directly on the site ofsampling for example in lake water using strongly-basic anion-exchangers AB-17 with the sensitivity of the technique is 2-3 orderslower than the best conventional spectrohotometric methods withthiocyanate [15]

Recently the authors of paper [37] synthesized new highlypermeable lignin anion-exchangers on the basis of lignin a naturalpolymer a component of terrestrial plants It is noted that the exchangecapacity of anion-exchangers for rhenium in lignin is much higher (EC =3427-2328 mgg) compared with conventional anion-exchangersHowever the time to reach equilibrium sorption by some anion-exchangers can reach from 2 up to 12 hours

Carbon fibrous materials modified with chitosan haveimproved kinetic (time and rate of sorption) characteristics comparedwith activated carbon and ion-exchange resins [38 39] Carbon fibrousmaterials modified with chitosan contain amino groups includingprotonated The increasing of the number of protonated groupscauses the increasing of sorption capacity of the material withrespect to the negatively-charged perrhenate-ions However thesorption capacity for rhenium (179-185 mgg) still yields to ligninanion in addition investigations were carried out of neutral aquasolutions of rhenium without interfering influences

29

ConclusionIn this review the methods for rhenium determination which over

the last decade have acquired great fame are presented A large numberof works related to improving methods for rhenium determining pointsto the increased interest to this metal The majority of the studies aimedto the selective extraction of rhenium from the analyzed complex objectsand the separating it from interfering elements in the matrix to increasethe sensitivity of the methods Most of the work related to the searchingof various organic reagents selective to rhenium (V VII) ions and usedin extraction and sorption processes In general the development ofrapid selective methods that can determine the content of rhenium in awide range of concentrations in various materials remains an actualproblem nowadays

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

Reference1 AA Palant ID Troshkina AM Chekmarev Metallurgy of

rhenium Science Moscow 2007 298 p2 LV Borisova YuV Demin NG Gatinskaya VV Ermakov

Determnation of rhenium in plant materials Journal of AnalyticalChemistry 2005 V60 1 P 97-103

3 LV Borisova AN Ermakov Analytical chemistry ofrhenium 1974 Science Мoscow 318 p

4 S Uchidaa KTagamia K Tabei Comparison of alkaline fusionand acid digestion methods for the determination of rhenium in rockand soil samples by ICP-MS Analytica Chimica Acta 2005 V535P 317ndash323

5 VI Manshilin EK Vinokurova SA Kapelushniy Determinationof Pt Pd Re mass fraction in dead catalyst samples using ICPatomic emission spectrometry method Methods and objects ofchemical analysis 2009 V41 P 97-100 (in Russian)

6 Jie Li Li-feng Zhong Xiang-lin Tu Xi-rong Liang Ji-feng XuDetermination of rhenium content in molybdenite by ICPndashMS afterseparation of the major matrix by solvent extraction with N-benzoyl-N-phenylhydroxalamine Talanta 2010 V81 P 954ndash958

30

7 T Meisel J Moser N Fellner Wo Wegscheider R SchoenbergSimplified method for the determination of Ru Pd Re Os Ir and Ptin chromitites and other geological materials by isotope dilutionICP-MS and acid digestion Analyst 2001 V126 P 322ndash328

8 K Shinotsuka K Suzuki Simultaneous determination of platinumgroup elements and rhenium in rock samples using isotope dilutioninductively coupled plasma mass spectrometry after cation exchangeseparation followed by solvent extraction Analytica chimica acta2007 V603 P129ndash139

9 NA Kolpakova AS Buinovsky IA Jidkova Determinationof rhenium by X-ray fluorescence analysis Proceedings ofuniversities Physics 2004 12 P147-149 (In Russian)

10 AS Buinovsky NA Kolpakova IA Melnikov Determinationof rhenium in the ore material by X-ray fluorescence analysis News polytechnic university 2007 V311 3 P92-95 (InRussian)

11 DV Drobot AV Belyaev VA Kutvitsky Development of aunified X-ray fluorescence method for the determination ofrhenium in multicomponent oxide compositions News highereducational institutions Non-ferrous metallurgy 1999 4 P23-24 (in Russian)

12 LG Goltz NA Kolpakov Sorption preconcentration anddetermination by voltammetry perrhenate ions in the mineralraw materials Proceedings of the Tomsk PolytechnicUniversity 2006 V 309 6 P77-80 (in Russian)

13 NA Kolpakova LG Gol`ts Determination in mineral rawmaterials by stripping voltammetry Journal of AnalyticalChemistry 2007V62 4 Р418-422

14 Wahi A Kakkar LR Microdeterminaton of rhenium withrhhodamine-B and thiocyanate usng ascorbic acid as the reductant Analytical sciences 1997 august V 13 P657-659

15 LV Borisova SB Gatinskaya SB Savvin VA RyabukhinAdsorbtion-spectrophotometric determination of rhenium fromdiffuse reflectance spectra of its complexes on a PAN-AV-17adsorbent Journal of Analytical Chemistry 2002 V572 P 161-164

31

16 AG Kasikov AM Petrova Extraction of rhenium (VII) byaliphatic alcohols from acid solutions Journal of AppliedSpectroscopy2009 V82 2 P 203-209 (in Russian)

17 ZhA Kormosh YaR Bazel` Extraction of oxyanions with basicpolimethine dyes from aqueous and aqueous-organic solutionsextraction-photometric determination of rhenium (VII) and Tungsten(VI) Journal of Analytical Chemistry 1999 V54 7 P 690-694

18 AA Palant NA Yatsenko VA Petrova Extraction of rhenium

(VII) from sulfuric acid solutions by diisododecylamine

Journal of Inorganic Chemistry 1998 V43 2 P 339-343 (inRussian)

19 NA Yatsenko AA Palant Micelle formation in theextraction of ions W (VI) Mo (VI) Re (VII) from sulfuric acidmedia diisododecylamine dioctylamine and trioctylamine Journal of Inorganic Chemistry 2000 V45 9 P 1595-1599 (in Russian)

20 N Latsenko AA Palant SR Dungan Extraction of tungsten (VI)molybdenum (VI) and rhenium (VII) by diisododecylamine Hydrometallyrgy V 55 Issue 1 Febr 2000 P 1-15

21 AV Antonov AA Ischenko The use of extraction in thedetermination of rhenium in the presence of molybdenumChemistry and chemical technology 2007V50 9113-116 (in Russian)

22 VF Travkin AV Antonov VL Kubasov AA IshchenkoExtraction of rhenium (VII) and molybdenum (VI)hexabutyltriamid phosphoric acid from the acidic environment Journal of Applied Chemistry 2006 V78 6P 920-924 (inRussian)

23 Cao Zhang-fang Zhong Hong Qiu Zhao-hui Solvent extraction ofrhenium from molybdenum in alkaline solution Hydrometallurgy2009 V 97 3-4 P 153-157

24 AG Kasikov AM Petrova Influence the structure of octanolon their extraction ability in acid solutions with respect to

32

rhenium (VII) Journal of Applied Chemistry 2007 V80 4 P689-690 (in Russian)

25 VF Travkin YM Glubokov Extraction of molybdenum andrhenium by aliphatic alcohols Metallurgiya2008 7 P21-25 (in Russian)

26 EA Kataev GV Kolesnikov VN Khrustalev MYu AntipinRecognition of perrhenate and pertechnetate by a neutralmacrocyclic receptor J radioanal Nuclchem 2009 2 V282 P 385-389

27 Bambang Kuswandi Nuriman Willem Verboom David NReinhoudt Tripodal Receptors for Cation and Anion Sensors Sensors 2006V 6 P 978-1017

28 Lagili O Abouderbala Warwick J Belcher Martyn G BoutellePeter J Cragg Jonathan W Steed Cooperative anion binding andelectrochemical sensing by modular podands PNAS April 162002 V 99 8 P 5001ndash5006

29 EA Kataev GV Kolesnikov EK Myshkovskaya Newmacrocyclic ligands based bipyrroles to bind perrhenate andpertechnetate ions radiation safety 2008 4 P16-22(inRussian)

30 Takeshi Ogata Kenji Takeshita Kanako Tsuda Solvent extractionof perrhenate ions with podand-type nitrogen donor ligands Separation and Purification Technology 2009V68 P288ndash290

31 Yoshihiro Kudo Ryo Fujihara Shoichi Katsuta Yasuyuki TakedaSolvent extraction of sodium perrhenate by 3m-crown-m ethers(m=5 6) and their mono-benzo-derivatives into 12-dichloroethane

32 Elucidation of an overall extraction equilibrium based oncomponent equilibria containing an ion-pair formation in water Talanta V 71 2007 656ndash661

33 AN Turanov VK Karandashev VE Baulin Extraction ofrhenium (VII) by phosphorylated podands Russian journal ofinorganic chemistry 2006 V514 P676-682 (in Russian)

34 E A Katayev Yu A Ustynyuk J L Sessler Receptors fortetrahedral oxyanions Coordination Chemistry Reviews 2006V250 P3004ndash3037

33

35 Leroy Cronin Macrocyclic and supramolecular coordinationchemistry Annu Rep Prog Chem Sect A 2004V100 P 323ndash383

36 ID Troshkina ON Ushakova VM Mukhin Sorption ofrhenium from sulfuric acid solutions by activated carbon News of higher educational institutions Non-ferrousmetallurgy 2005 3 P38-41 (in Russian)

37 AA Abdusalomov Sorption of rhenium from sulfuric acidsolutions of molybdenum Sorption and ChromatographicProcesses 2006 Vol6 V 6P 893-894 (In Russian)

38 NN Chopabaeva EE Ergozhin ATasmagambet AI NikitinaSorbtion of perrenate-anons by lignin anion exchangers Chemistry of solid fuel 2009 2 P 43-47 (in Russian)

39 AV Plevaka ID Troshkina LA Zemskova AV Voit Sorption ofrhenium chitosan-fiber materials Journal of InorganicChemistry 2009V54 7 P1229-1232 (in Russian)

40 LA Zemskova AV Voit YuMNikolenko ID Troshkina AVPlevaka Sorption of rhenium on carbon fibrous materials modifiedwith chitozan Journal of nuclear and radiochemical sciences2005 V6 3 P221-222

11

SYNTHESIS AND MICROSTRUCTURE DESIGN OF METALAND CERAMIC MATRIX COMPOSITES USING

MECHANICAL MILLING OF THEREACTANTSCONSTITUENTS

Dina V Dudina Oleg I LomovskyInstitute of Solid State Chemistry and Mechanochemistry

Siberian Branch of Russian Academy of Sciences Kutateladze 18Novosibirsk 630128 Russia

E-mail dina1807gmailcom

Mechanical milling greatly alters the state of a powder mixtureintroducing plastic strain and defects into the components andcreating new interfaces and mutual configurations of nano-sizedgrains This opens up a possibility to design microstructures of thecomposite to be synthesized by modifying the initial state of reactingpowder mixtures In certain mechanically milled reactive systemsone can observe microstructure refinement of the product [1-2] anincrease in the yield of the reaction [3] improved distribution of thephases [3 4] and lower reaction onset and developed temperatures[1-2] The presentation intends to demonstrate several successfulexamples of this approach for synthesizing composites by self-propagating high-temperature synthesis (SHS) shock compressionand electric-current assisted sintering

SHS in the mechanically milled Ti-B-Cu powder mixtures wassuccessfully performed and resulted in a TiB2-Cu composite [1-2]Compared to untreated powders in the mechanically milled mixturestitanium and boron started reacting at a reduced ignition temperaturewhile lower combustion temperatures developed in the combustionwave favored formation of submicron grains of TiB2

The powder particles brought to react with each other by shockcompression of the mixture may not fully transform into the productsif the loading is too short and the temperatures developed during thepressure rise and the post-loading period are not high enough In themechanically milled mixture the yield of the reaction can beincreased as a result of the decreased grain size of the initial reactants

12

and shorter diffusion distances (example Ti-Cu-B system partial andcomplete reaction of Ti and B [3])

When the sintering process ensures temperatures and timesufficient for the completion of the reaction in the mechanicallymilled mixture one can expect more uniform microstructure and finergrains of the products (example Ti-B-C system forming B4C-TiB2

phases during electric-current assisted sintering [4])Ball milling can refine the microstructure of the as-synthesized

composites and can be used to introduce additional quantities of theconstituents in the composite This was applied in order to develophighly conductive Cu-based composites One of the possible reasonsfor low conductivity of in-situ dispersion strengthened copper may bethe incompleteness of the reaction between the initial reactantswhich form solid solutions with the copper matrix In this regard weconducted an in-situ synthesis of TiB2-Cu composites starting fromthe powder mixtures with the limited content of copper ensuring ahigh probability of contact between the particles of titanium andboron and as a result their full conversion into the TiB2 phase Thenanoparticles were formed in a self-propagating mode in the ballmilled Ti-B-Cu powder mixture corresponding to the 57 volTiB2-Cu composition Afterwards in order to adjust the composition thecomposite was ldquodilutedrdquo with the required amount of copper usingsubsequent ball milling [5]

The consolidated nano- and microcomposite materialsdeveloped on the basis of the described systems were tested for theirenhanced mechanical properties (fracture tough composites B4C-TiB2

[4]) electric erosion resistance [6] and electric conductivity [5] Inthis presentation each property is discussed as resulting from thephase and microstructure evolution during the synthesis of thematerial by the selected processing method

AcknowledgementsParts of this work were carried out by DVD at the University

of California Davis USA during her postdoctoral appointment Theauthors greatly appreciate the collaboration with DrKorchagin(ISSCM SB RAS) Dr VIMali and Dr AGAnisimov (Institute of

13

Hydrodynamics SB RAS Novosibirsk Russia) and Prof JSKim(University of Ulsan South Korea)

References1 DVDudina OILomovsky MAKorchagin VIMali Chem

Sust Dev 12 (2004) 319-3252 MAKorchagin DVDudina Comb Expl Shock Waves 43 (2)

(2007)176-1873 DVDudina VIMali AGAnisimov OILomovsky Mater Sci

Eng A 503 (2009) 41-444 DVDudina DMHulbert DJiang CUnuvar SJCytron

AKMukherjee JMaterSci 43 (2008) 3569-35765 JSKim DVDudina JCKim YSKwon JJPark CKRhee J

Nanosci Nanotech 10 (2010) 252-2576 J-SKim Y-SKwon DVDudina OILomovsky MAKorchagin

VIMali JMaterSci 40 ( 2005)3491 - 3495

4

STUDY OF THE EFFECT OF FLUORESCENCE INCREASINGOF N-ARYL-3-AMINOPROPIONIC ACIDS IN THE PRESENCE

OF ZINC AND CADMIUM IONS

EV Dedyukhina1 NV Pechishcheva1 LK Neudachina2KYu Shunyaev1 AA Belozerova1

1 ndash Institute of Metallurgy of UB RAS 101 Amundsen st Ekaterinburgshunuralru

2 ndash Ural State University 51 Lenin av Ekaterinburg Russia

Earlier the effect of increasing of phosphorescence intensity in thefrozen solutions with excess of metal chlorides and sulphates has beenreported Ions оf these metals have filled electronic shells and largevalue of electric field intensity - Li(I) Be(II) Ca(II) Mg(II) Cd(II)Zn(II) Al(III) In(III) and Ga(III) For example this effect was found forbenzene aniline phenol amino acids ndash tyrosine tryptophanephenylalanine [1]

The same effect have been found for fluorescence of onerepresentative of N-aryl-3-aminopropionic acids (AAPA) - NN-di(2-carboxyethyl)-p-anisidine - in the presence of cadmium(II) and zinc(II)ions at Т=77 К [2] Increasing of fluorescence intensity (Ifl) in frozeninorganic matrix is expected for other representatives of AAPA whichnot have electron acceptor groups in structure and demonstrate theconsiderable fluorescence intensity of the protonated form

Fluorescence of some AAPA in frozen inorganic matrixNN-di(2-carboxyethyl)aniline (I) NN-di(2-carboxyethyl)-34-

xylidine (II) NN-di(2-carboxyethyl)-3-methyl-aniline (III) andN-(2-carbamoylethyl)-о-anisidine (IV) are representatives of a class ofAAPA Figure 1 presents structures of the AAPA In the present workthe fluorescence of aqueous solutions of this AAPA with molar excess ofcadmium and zinc sulphates at рH 1-6 and Т=77 К have beeninvestigated

The fluorescence spectra of solutions were measured using aFluorat-02-Panorama spectrofluorometer (Lumex Russia) Fluorescencespectra at T=77 K was excited and recorded using a fiber-optic cablewith a special optical connector

5

It have been established that the Ifl of the protonated form of I-IV(СR=1middot10-4 moldm3) is increased in the presence of cadmium(II) andzinc(II) ions at Т=77 К Figure 2 presents spectra of II We suggest thatcause of this effect is interaction enhancement of reagent with metal inconsequence of isolation from water and micro concentration (waterform ice crystals impurities are displaced in intercrystal area)

CH3

N

O

OHO

OH

1 2 3 4

Fig 1 Structures of AAPA 1 - NN-di(2-carboxyethyl)aniline2 - NN-di(2-carboxyethyl)-34-xylidine 3- NN-di(2-carboxyethyl)-3-

methyl-aniline 4 - N-(2-carbamoylethyl)-о-anisidine

The increasing Ifl of protonated reagent form of I-IV also isobserved at Т=293К but is not as strong as at T=77 K

0

1

2

3

4

5

6

7

240 260 280 300 320 340 360

wavelength nm

Ia

u

1

2

3

Fig 2 Spectra of fluorescence II (СR=1middot10-4 moldm3) in the presence andabsence of Cd(II) и Zn(II) ions (СZn(II)= СCd(II)= 560 mgdm3) рН=60 Т=77 К

λex = 214 nm 1 - II 2 - II+Zn(II) 3 - II+Cd(II)

The fluorescence increasing is observed only when concentrationof metal ions in dozens of times more than concentration of fluorophor

6

This indicate that Ifl increasing is occured due to reagent solvation byions of inorganic salts but not chelation

We have obtained the Ifl of solutions of I-IV as functions of theconcentration of cadmium(II) and zinc(II) ions at Т=77 К pH=6 (table1) The largest increasing of Ifl in the presence of metal ions have beenobserved for IV But the most correlation coefficient R value of linearfunction Ifl=f(CMe) with wider concentrations range has been obtainedfor II

Table 1 The Ifl of I-IV as functions from concentration of metal ions Т=77 КCCd(II)= CZn(II)= 200 mgdm3 СR=10-4 moldm3 рН=6

Metalion

ReagentConcentrationsrange mgdm3 I R+MeIR R Slope

I 11 090 321

II 11 098 494III

25-760

13 092 456Cd(II)

IV 25-245 80 092 2997

I 3 095 82

II 8 098 414

III

30-845

11 096 437Zn(II)

IV 30-560 70 090 1542

In addition we have studied the fluorescence of aniline and naturalamino acids (tyrosine tryptophane phenylalanine) in frozen inorganicmatrix Structures of amino acids are presented on figure 3 thiscompounds are not belong to class of substituted anilines Thiscompounds similarly of investigated AAPA not have electron acceptorgroups in structure tyrosine phenylalanine and AAPA have the samebenzene fluorophore Besides this amino acids are commerciallyavailable reagents

Investigations have been shown that present amino acids alsodisplay the effect of Ifl increasing of protonated reagent form in thepresence of cadmium(II) and zinc(II) ions at Т=77 К But is not asstrong (12ndash5 times) as AAPA Ifl increasing Metal ions at T=298 K havelittle effect on a fluorescent spectra of amino acids

7

1 2 3

Fig 3 Structure of amino acids1 - phenylalanine 2 - tyrosine 3 - tryptophane

Thus we can deduce that the presence of substituted amino groupin benzene ring (especially in combination with others electron donorgroups) allow to observe more effective increasing of Ifl in salt solutionat 77 К Replacement benzene fluorophore to indole one (intryptophane) result to decreasing of observing effect extent

The fluorescence of II in the presence of Mg(II) ions at Т=77 Кwas investigated We tried to find the II0 fluorescence of II functionfrom z2r ratio for two-charged cations where z - ionic charge (+2) r -ionic radius nm [3] Data is presented in table 2

Table 2 Characteristiс of the functions II0 = f(z2r) for II Т=77 К рН=6λexλem= 214286 nm СII =10-4 М

Ion z2r SlopeI I0

CMe= 200 mgdm3

Cd(II) 412 494 107

Zn(II) 541 414 85

Mg(II) 615 352 74

The functions II0=f(z2r) of fluorescence II in frozen inorganicmatrix from are presented in figure 4 they are linear Also linearfunctions of Ifl=f(CMe) slope on z2r ratio have been obtained

N

NH2

OH

O

H2N

OHO

OH

8

y = -016x + 174

R2 = 099

6

7

8

9

10

11

40 45 50 55 60 65

z2r

IIo

Zn

Cd

Mg

Fig 4 Functions II0=f(z2r) of fluorescence II in the presence of metal ions [3]CCd(II)= CZn(II)= CMg(II)= 200 mgdm3 λexλem= 214286 nm Т=77 К

Study of fluorescence of some reagents in glycerolwater andethanolwater mixtures and micellar solutions at Т=298 КWe have studied a fluorescence II and tryptophane in

glycerolwater (11) and ethanolwater (11) mixtures in the presence ofzinc(II) ions at 77 К It was done for proving hypothesis about reducinginteraction fluorophore with water in aqueous media at freezing Wesuggest that interaction between of the solute and solvent molecules arepreserved in nonaqueous solutions

Corresponding spectra of II are presented on figure 3 similarsituation is observed for tryptophane We can see effect of increasing Ifl

is not observed in glycerolwater and ethanolwater mixtures in contrastto aqueous solutions

Isolation reagent from water at room temperature is possible in thepresence of surfactants

Fluorescence II have been study in the presence of surfactants ofdifferent nature in acidic media at Т=298 К The Ifl increasing ofprotonated form II is occured in the presence of Triton Х-100 (non-ionicsurfactant) and sodium dodecylsulphate (anionic surfactant)Fluorescence II is decreased by cetyltrimethylammonium bromide(CTAB cationic surfactant)

Fluorescence of II in the presence of surfactants and excess ofmetal ions have been study at рН=1-6 Zinc and cadmium ions increaseIfl of II at рН 50-65 with CTAB Thus metal ions and CTAB at

9

Т=298 К have same Ifl increasing effect as the effect at Т=77 К withoutsurfactants

0

5

10

15

20

25

240 260 280 300 320 340 360 380

wavelength nm

Ia

u

1

2

3

Рис 5 Fluorescence of II (СII=1middot10-4 moldm3) in ethanolwater (11)mixtures in the presence and absence of Zn(II) pH=60 Т=77 К λex=214 nm

1 - II 2 - II + Zn(II) (44middot10-4 moldm3) 3 - II+ Zn(II) (86middot10-3moldm3)

We have obtained under these conditions the Ifl of II solutions asfunction of the concentration of Cd and Zn ions with variousconcentrations of CTAB (table 3) The plots are linear and have thegreatest slope value at СCTAB=14middot10-3 moldm3 Cadmium ions have agreater influence on the fluorescence of the II than zinc ions

The fluorescence investigations in the presence of CTAB andmetal cations have been carried out on other AAPA (I III and IV)aniline and tyrosine (table 4) It was found that zinc ions increase offluorescence of protonated reagent form of I and III cadmium ions ndashIII

Table 3 Characteristiс of the functions Ifl=f(CMe) of II with addition of CTAB

exem = 218286 Т=298 К

Range of concentrationsCation

С CTABmoll moldm3 mgdm3 tg α

96middot10-4 2middot10-4 ndash 4middot10-3 45-450 18Cd(II)

14middot10-3 2middot10-4 ndash 8middot10-3 45-900 3696middot10-4 4middot10-4 ndash 15middot10-2 25-850 055

Zn(II)14middot10-3 4middot10-4 ndash 11middot10-2 25-850 10

10

Table 4 Fluorescence of reagents in the presence of zinc and cadmium ions(СMe=560 mgdm3) and CTAB (С= 96middot10-4 moldm3) рН=6

Zn(II) Cd(II)

Reagentexem

nm II0 I (R+Zn+CTAB)au

II0I (R+Cd+CTAB)

au

aniline 253278 11 07 10 06I 222300 62 16 08 02II 218286 73 44 85 51III 217288 65 34 33 15IV 218304 10 32 12 12

tyrosine 222302 10 480 11 462

The resulting functions will be used for developing of thefluorescent techniques of zinc and cadmium determination

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

References1 AV Karyakin n-electrons of heteroatoms in hydrogen bonding and

luminescence (in Russian) Nauka Мoscow 1985 135 p2 LK Neudachina EV Dedyukhina OV Evdokimova

NV Pechishcheva EV Osintseva KYu Shunyaev Fluorescenceof NN-di(2-carboxyethyl)-p-anisidine in solution and crystallinestate Journal of Applied Spectroscopy 2010 V 77 2 P 206-212

3 Lurie YuYu Hand-book of analytical chemistry (in Russian)Khimiya Мoscow 1989 447 p

194

Processes taking places on the electrode can be described in thefollowing way On the first characteristic area of the polarization curvelead ion deposition happens

Pb2+ + 2e = Pb0 (3)The limiting current density of lead reduction increases with the

temperature and lead chloride concentration At 30 mol of leadchloride concentration and 823 K limiting current density ilim is 12Acm2

On the second characteristic area of the polarization curvedeposition of the alkaline metal is possible on the reaction

K+ + e = K0 (Pb) (4)Low values of the alkaline metal reduction potentials might be

connected with the process of alloy formation of alkali metal with leadK + 4Pb = KPb4 (5)

Chronopotentiometric measurements at lead deposition from LiClndash KCl (45-55 mol ) ndash PbCl2 melt at 04 mol lead chlorideconcentration were performed at 823 K and current density range from010 to 017 Acm2 There is only one wave on chronopotentiometriccurves under these conditions Values of product i12 depending oncurrent density are given in the table 1 where - transition time

Table 1 Values of product i12 at diverse current density

s i mAcm2 i12 mAcm2s12

095 170 165161 130 165181 120 162

262 102 165

It is seen that the product i12 does not depend on current

density at constant concentration of depolarizator 0OxC In the table 2

potential values Е4 at time equaling the forth of the correspondingvalues of transition time are given

195

Table 2Values of Е4 potential of different current density

i Acm2 s 4 s Е4 V

010 264 0660 -0061

012 181 0453 -0600

013 161 0403 -0061

017 095 0238 -0062

It is seen that the potential Е4 does not depend on the experimentconditions the current density in this case

Equation for the reversible process can be as follows

1ln

nF

RT21

4t

ЕЕ

(6)

for irreversible process

2100

1lnlnnF

RT

t

nF

RT

i

knFCЕ

fhOx (7)

where E ndash electrode potential 4E - measurement potential at frac14

of transition time R ndash gas constant F ndash Faraday number n ndash number

of electrons T ndash temperature - transition time 0OxC - depolarizator

concentration 0fhk - deposition speed constant

On the figure 6 dependencies Е -

1ln

21

t

and Е -

21

1ln

t at 04 mol of lead chloride concentration current

density 01 Acm2 and 823 K are given

196

y = -00835x + 00654

0002

0022

0042

0062

0082

0102

0122

0142

0162

-115 -065 -015 035 085

- E В

1 2

Fig 6 Dependencies 1ndashЕ=f

1ln

21

t

and 2-Е =f

21

1ln

t

From the analysis of given graphic dependencies follows that the

experimental points in coordinates E -

1ln

21

t

are in a straight line

with the confidence interval 095 The can be described by equation

08300650 E

1ln

21

t

(8)

The amount of electrons in the electrode reaction was calculatedfrom the equation

F

RTn

0830 (9)

hence n=2

197

It follows from the experimental conditions on lead ion (II)deposition that the process is reversible ie it is controlled by the speedof divalent lead ions mass transfer from the volume of melt to theelectrode surface

Diffusion coefficient of lead dichloride at 823 K was calculated onSandrsquos equation

20

2

)(

)(2D

oxnFC

i

(10)

Lead ions (II) diffusion coefficient are equal to 23310-

5сm2s It is in good accordance with the data obtained by other authors[5 6]

References1 Yurkinsky V Makarov D Electrochemical reduction of lead ions in

halide melts Russian J Applied Chem 1994 67 p 1283-12862 Yurkinsky V Makarov D The influence of cation composition on

kinetics of lead electrochemical reduction in chloride melts RussianJ Applied Chem 1994 68 p 1474-1477

3 Ryabukhin Yu And Ukshe E The diffusion coefficients of lead inmolten chlorides DAN SSSR 1962 145 p 366-368

4 Naryshkin I Yurkinsky V Oscillographic investigation oftemperature coefficients for some chlorides diffusion in LiCl-KClRussian J Electrochemistry 1968 4 p 871-872

5 Naryshkin I Yurkinsky V Voltammetry in molten salts Russian JElectrochemistry 1968 2 p 856-866

6 Raymond J Heus James J Egan Fused Salt Polarography Using aDropping Bismuth Cathode ndash J of the Electrochemical SocietyOctober 1960 p 824-828

7 Richard B Stein The Diffusion Coefficient of Lead ion in FusedSodium Chloride Eutectic ndash J Electrochem Soc 1959 vol 106 p528

8 Laitinen H A Gaur H C Chronopotentiometry in Fused LithiumChloride-potassium Chloride - Anal Chem Acta 1958 vol 18 p1-13

9 Hills GI Oxley I E Turner D W Silicates Ind 1961 vol 26 p559

184

REPAIR COMPOUND MODIFIED BY NANO PARTICLES OFFERROUS OXIDE

OS Tatarintseva SN Novosyolova TK UglovaInstitute for Problems of Chemical and Energetic Technologies SB RAS

Biysk Altai region Russia labmineralmailru

The results of influence study of nano-dispersed ferrous oxide oncharacteristics of the composite material developed earlier (compound)and intended to repair and recover engineering structures and massifshave been presented in this paper The compound consists ofmulticomponent polymer matrix including epoxy oligomer low-molecular synthetic rubber plasticizer and process additives filler and alow-temperature amine hardener Microcalcite with particle size lessthan 50 μm has been used as filler

The composite has been modified with nano powder of ferrousoxide (II) (manufactured by MACH I Inc USA) consisting of needle-like crystalline particles with average size 4 nm and having specificsurface area 2379 m2g

Experiments have shown that even distribution of nano particlesin epoxy resin is caused with a high-velocity mechanical device underthe additional influence of ultrasonic field

The most important things for low-viscosity repair compositionsapplied to recover the integrity of natural materials are high flowabilitydetermining the ability to fill narrow-opened fractures and stability ofstrength properties for a long time

The positive effect of ultra-dispersed modifier is seen within therange of 030-035 of its percentage in the composition as shown byresults of the study given in the Table At these amounts the maximumvalues of flowability and mechanical characteristics have been providedThe logical increase in samples density indicates the optimality of thepacking developed and reduction in the porosity of a composite materialthat is important while using it in conditions on high humidity

The compound developed is environmentally friendlyincombustible waterproof stable to heat vibration and long mechanicalloads and can be used to perform repair work in construction industrypublic service stone mining and processing industries and architecture

185

Table Percentage influence of ferric oxide nano powder on technicalcharacteristics of the composite material

Value at modifier percentage Characteristics

0 010 020 030 035 040

Dynamic viscosityat T = 20 oC Pamiddots

210 212 225 262 266 288

Flowability cm 48 48 48 52 53 45

Density gm3 141 141 143 145 146 146

Compressive forceMPa

79 78 79 82 86 74

Relative deformation

023 021 021 025 025 020

182

BASALT PLASTICS OF ENHANCED HEAT AND CHEMICALSTABILITIES

OS Tatarintseva NN Ноdakova VV SamoilenkoInstitute for Problems of Chemical and Energetic Technologies

of the SB RAS Biysk Russialabmineralmailru

The experience of the application of metal pipes for chemicalproductions cool and hot water supply systems transportation ofpetroleum products and other aggressive fluids has shown that they aregreatly subjected to corrosion that reduces their lifetimes to severalyears Therefore natural is the observed worldwide tendency ofreplacing steel and cast iron by composite materials of high chemicalstability and durability to which glass-reinforced plastic having acomplex of high service properties should primarily be relatedHowever requirements for composites have presently increasedespecially with regard to their heat and chemical stabilities andresistance to microorganisms ground and waste waters

The paper demonstrates the study results with respect to thedevelopment of a composite material for filament-wound pipe productswhich is superior in its basic parameters to analogous ones in the field ofglass-reinforced plastic application As a reinforced material basaltroving with higher strength characteristics and resistance to aggressiveenvironments as compared to a glass one was chosen the polymermatrix was a heatproof binder TS developed on the basis of nitrogen-containing epoxy resin synthesized Having rheological properties andstrength characteristics similar to those that are widely used in themanufacture of filament-wound glass-reinforced plastic products of thebinders EDI and EChDI the binder TS possesses enhanced heat stabilityand low viscosity at room temperature which permits the reduction ofpower inputs for its processing

The obtained data on advantages of both basalt fiber and thebinder developed have to the full extent been realized in laboratorysamples of the reinforced composite and in basalt plastic pipes producedindustrially (see Table below)

183

Table Temperature dependence of elastic modulus E of basalt plasticpipes

Еmiddot103 MPa at Т degСBinder 20 85 125 155 200

EDI 11701 11263 4363 3528 -EChDI 11277 10951 9944 6217 -

TS 19960 19336 19179 17557 9096

The 9-fold strength reserve of the basalt plastic pipes determinedwhen hydro-tested under extreme conditions (150degC 15 MPa) hasconfirmed the possibility of creating composite polymer materialsoperating under high-temperatures and humidity

164

FABRICATION AND MODIFICATION OF METALLICNANOPOWDERS BY ELECTRICAL DISCHARGE IN LIQUIDS

NV Tarasenko1 AA Nevar1 NA Savastenko2 EI Mosunov3 NZ Lyakhov4 TFGrigoreva4

1 Institute of Physics NAS B Minsk Belarus2 Leibniz-Institute for Plasma Science and Technology Greifswald Germany

3 The Institute of Machine Mechanics and Reliability NAS B Minsk Belarus4Institute of Solid State Chemistry and Mechanochemistry SB RAS

18 Kutateladze Str Novosibirsk 630128 Russia grigsolidnscru

Electrical-discharge technique was developed for preparation ofmetallic and metal-containing nanoparticles as well as for modificationof metal micropowders in liquids The morphology and composition ofthe nanopowders formed under various discharge conditions wereinvestigated by means of transmission electron microscopy and X-raydiffraction analysis The optimal conditions for the production oftitanium carbide and copper nanoparticles embedded in carbon layerswere found

IntroductionA synthesis of metallic and metal-containing nanopowders is of a

great interest due to their potential applications as super hard materials[1] environmentally friendly fuel cells with highly effective catalysts[23] and so on Transition metal carbides have been widely studied aselectrocatalysts because of their electrochemical properties andelectrical conductivities Nanosized carbon particles are suitable supportmaterials for certain types of catalysts Of particular interest for futurecatalytic applications are carbon-based materials with embeded metalnanoparticles [4] As long as carbon nanoparticles are relatively inertsupports many studies have been conducted in order to find which pre-treatment procedures are needed to achieve optimal interaction betweenthe support and metal species [5]

For any application of nanoparticles to be commercially viablelow-cost production methods have to be developed A low-temperatureand non-vacuum synthesis of nanoparticles via discharge in liquid(submerged discharge) provides a versatile choice for economicalpreparation of various nanostructures in a controllable way An arc

165

discharge in liquid nitrogen has firstly been reported as a cost-effectivetechnique for the production of carbon nanotubes in 2000 by Ishigamy etal [6] Since that time many efforts have been devoted to develop thismethod Sano et al proposed to submerge electrodes in water instead ofliquid nitrogen [78] They reported synthesis of carbon onions [78] andsingle-walled carbon nanohorns (SWNHs) [9] In latter case carbonnanoparticles were produced via discharge in water method with thesupport of gas injection Parkansky et al reported nanoparticlessynthesis via a pulsed arc submerged in ethanol Ni W steel andgraphite electrodes were used [1011] The particles composition variedfrom carbon to pure metal including various intermediate combinationsof these materials Bera et al employed an arc-discharge in a palladiumchloride solution to produce carbon nanotubes decorated with in situgenerated Pd nanoparticles [10] Importantly the synthesized materialcontained no chlorine

In this paper methods based on electrical-discharges in liquids forproduction of tungsten and titanium carbide as well as coppernanoparticles embedded in carbon nanostructures is reported Thecapabilities of arc and spark discharges submerged in liquids forsynthesis of nanoparticles as well as electrical-discharge modification ofmetallic powders were studied

Experimental detailsThe experimental reactor (Fig 1) consisted of four main

components a power supply system (pulse generator) the electrodes aglass vessel and a water cooling system outside the beaker A pulseddischarge was generated between two electrodes being immersed in 100ml of liquid (pure (995) ethanol or 0001 M CuCl2 aqueous solution)The appropriate combinations of pairs of metallic (tungsten titanium orcopper) and graphite electrodes were used The choice of ethanol wasmotivated by the fact that organic compounds play a role of a carbonsource to produce nanoparticles in discharge-in-liquid system [7 12]Addition of the copper chloride salt into double distilled water favoredthe activation of discharge process Metal (tungsten titanium or copper)and graphite rods with diameters of 6 mm were employed as electrodesAn optimum distance between the electrodes was kept constant at 03mm to maintain a stable discharge The discharge was initiated byapplying a high-frequency voltage of 35 kV The power supply

166

provided several different types of discharges Both direct current (dc)and alternating current (ac) arc and spark discharges were generatedwith repetition rates of 100 and 50 Hz respectively Current I(t) wasrecorded during the discharge as a function of time by means of anoscilloscope The peak current of the arc discharge was 9 A with a pulseduration of 4 ms The peak current of the pulsed spark discharge was 60A with a pulse duration of 30 μs

The synthesized products were obtained as colloidal solutionsAfter 15 min presedimentation the large particles precipitated at thevessel bottom The top layer contained the small nanoparticles wascarefully poured off into a Petry dish These suspended nanoparticleswere characterized by UV-Visible optical absorption spectroscopytransmission electron microscopy (TEM) and X-ray diffraction analysis(XRD) for their size morphology crystalline structure and composition

The optical absorption spectra of colloids were measured by UVndashVisible spectrophotometer (CARY 500) using 05 cm quartz cuvetteTransmission electron microscopy was performed by LEO 906E (LEOUK Germany) microscope operated at 120 kV A drop of solution putonto the amorphous carbon coated copper grid for TEM measurementsThereafter the liquid was evaporated at the temperature of 80 C Afterthe drying of colloidal solution the deposit obtained on the bottom ofPetri dish was examined by XRD Powder composition and itscrystalline structure were characterized by using X-ray diffraction atCuK (D8-Advance Bruker Germany)

Synthesis of carbide nanopowdersPromising capabilities of the developed technique for synthesis of

tungsten and titanium carbides (WC TiC) as well as carbon-encapsulated copper nanoparticles were demonstrated using theappropriate combinations of pairs of metallic and graphite electrodessubmerged into the appropriate solution Also physical and chemicalprocesses induced by the electrical discharges in liquids were studied tooptimize the process of nanoparticles synthesis

The results of nanoparticles preparation are summarized in theTable1 The synthesis rate varied in range of 2 ndash 40 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofmetal and graphite electrodes The synthesis rate increased withincreasing of discharge current and decreasing of pulse duration The

167

composition and morphology of nanoparticles were also found to dependon discharge parameters It should be noted that there is a possibility toscale-up the process

Table 1 summarized the variation in synthesis rate andcomposition of tungsten nanopowders with the discharge parameters Asa general tendency the synthesis rate was order of magnitude higher forspark discharge than that of arc discharge It may be due to thedifference in current value [13] For both arc and spark discharges itwas found that the synthesis rate is lower when tungsten was acting as acathode This result is consistent with literature data For example Beraet al reported that the consumption of anode is higher than that ofcathode [13]

Table 1 Summary of nanopowder synthesis conditions andresults of nanopowder characterization by XRD

XRD-analysisDischargetype

Electrodes Powdersyield

mgminW2Cvol

WC1-xvol

Cvol

Wvol

1 ac arc W C 02 71 781 147 -2 dc arc W(cathode)C(anode) 01 62 901 37 -3 dc arc W(anode)C(cathode) 02 66 715 219 -4 ac spark W C 25 58 328 614 -5 dc spark W(cathode)C(anode) 12 570 307 89 336 dc spark W(anode)C(cathode) 21 56 325 618 -

As it can be seen from the Table 1 the synthesized nanopowder isa mixture of hexagonal W2C face centered cubic WC1-x and graphite Nopeaks corresponding to WO were observed Nanopowder contained alsosmall amount body centered cubic W when synthesis was performed bydc current spark discharge with tungsten rod acting as cathode Here theparticular behavior of this discharge should be stressed showing ratherhigh ability to synthesize W2C Moreover in contrast to the other sparkdischarges synthesized material contained relatively small amount ofgraphite On the other hand applying tungsten as a cathode materialappears to reduce C content in nanopowder prepared via arc dischargetoo Generally the content of C is higher and content of WC1-x is lowerwhen synthesis was performed by spark discharge

168

Nanoparticles prepared by arc discharge were observed in theiragglomerated form The agglomerated nanoparticles were surrounded bythe grey regions which were probably graphite layers This typical viewwas seen everywhere in TEM images of product synthesized by arc forboth ac and dc current discharges irrespective of electrodes polarityThat fact implies that the morphology of synthesized nanopowders wasgoverned rather by the current pulse duration and value of peak currentthan the polarity of the electrodes Since nanoparticles were observed inthe agglomerated form it was difficult to measure their size correctlyWe suppose that approximately 4 nm nanoparticles are formed duringthe arc discharge in ethanol

Fig1 shows the TEM image of titanium carbide nanopowdersynthesized by spark discharge in ethanol As can be see from the Fig1the nanoparticles were also surrounded by graphite layers Fig 1demonstrates that the nanoparticles synthesized by spark were nearlyspherical with a mean diameter of ~ 7 nm The particle size distributionwas rather narrow (plusmn 2 nm) The XRD pattern of synthesized sample isshown in Fig 1 (right picture) The diffraction peaks at 60deg 418deg605deg 724deg 765deg and 407deg 504deg 590deg 667deg 741deg correspond tothe formation of cubic face-centered titanium carbide TiC and cubicprimitive TiC2 respectively There are some diffraction peaks with 2θvalue of 407deg 504deg 590deg 667deg and 741deg which can be assigned tothe hexagonal C The amount of TiC reached 887 vol The quantitiesof TiC2 and C in samples detected by XRD corresponded to ca 47 vol and ca 67 vol respectively

Fig 1 TEM image (left picture) of titanium carbide nanopowder synthesizedby ac spark discharge and XRD-pattern (right picture) of the sample

169

Synthesis of copper-carbon composite nanostructuresNumerous studies have focused on synthesis of metal-containing

carbon nanocapsules (CNCs) via submerged discharge method[89141516] Because of the carbon sheets surrounding the metal corethe CNCs are protected from the environment and from degradation Thecarbon coatings mean that nanoparticles are biocompatible and stable inmany organic media Thus carbon encapsulated nanoparticles arecandidate for bioengineering application high-density data storagemagnetic toners for use in photocopiers [81718] The metal containingcarbon nanostructures were prepared by using the electrode frommixture of graphite and metal precursor [16 1920] Recently Xu et aldemonstrated a possibility to synthesize Ni- Co- and Fe-containingCNCs by an arc discharge between carbon electrodes in aqueoussolution of NiSO4 CoSO4 and FeSO4 respectively [15] In contrast tothe data reported by Bera et al the synthesized material consisted of Oand S due to SO4

-2 ionic precursors in the solution Since the metal core-forming material was supplied by liquids the production rate of CNCswas limited by the salt concentration [4] This restriction may cause alimit to apply the submerged discharge method to the large-scaleproduction of CNCs

In this paper Cu-based nanoparticles were prepared viasubmerged discharge of bulk copper and graphite electrodes in a copperchloride (CuCl2) aqueous solution Thus material of copper electrode aswell as Cu from solution was supposed to be incorporated into theresulting nanoparticles The effect of discharge parameters and electrodecomposition on the morphology and composition of final products havebeen investigated Additionally synthesized material was modified bylaser irradiation The changes in nanoparticles morphology andcomposition were examined by transmission electron microscopy(TEM) X-ray diffraction (XRD) and UV-Vis spectroscopy

The six types of nanoparticles suspension were prepared underdifferent discharge parameters The synthesis parameters aresummarized in Table 2 As it can be seen the weight change of eachelectrode was generally higher when spark discharge was generatedThe anode consumption rate was higher than that of cathode irrespectiveto a discharge type and electrode material However in contrast to theliterature data [4] there was no cathode gain in weight As a generaltrend the nanopowder synthesis rate was higher for spark discharge than

170

that of arc discharge It may be explained by the difference in currentvalue [21] For both arc and spark discharges it was found that thesynthesis rate was higher when copper was acting as an anode There isa discrepancy between nanopowder synthesis rate and materialconsumption rate The values of discrepancy D listed in the Table 2were calculated as follows

100()

CCu

syn

RR

RD (1)

Here Rsyn is the synthesis rate of nanopowder RCu is theconsumption rate of the copper electrode and RC is the consumptionrate of the graphite electrode The discrepancy D depended ondischarge parameters For ac-discharges the value of discrepancy washigher for spark discharge than that for arc discharge For dc-discharges this trend remained if the polarity of electrodes was takeninto account It is worth to notice here that the discrepancy betweenmaterial consumption rate and nanopowder synthesis rate may be causednot only by separation of sediment fraction but by the reaction of carbonatoms with water resulting in the production of gaseous compounds [9]

Table 2 Summary of nanopowder synthesis parametersType of

dischargepeak currentpulse duration

Electrodes materialRCu and RC

mg min-1RSyn

mg min-1D

Cu 671 ac1) spark60 A 30 micros C 48

59 49

Cu 122 ac arc10 A 4 ms C 26

25 34

Cu (cathode electrode) 473 dc2) spark60 A 30 micros C (anode electrode) 61

21 81

Cu (anode electrode) 664 dc spark60 A 30 micros C (cathode electrode) 46

69 38

Cu (cathode electrode) 115 dc arc10 A 4 ms C (anode electrode) 25

19 47

Cu (anode electrode) 286 dc arc10 A 4 ms C (cathode electrode) 21

33 33

1) Alternating current pulsed discharge2) Direct current pulsed discharge

171

This coincides with the fact that the largest discrepancy (morethan 80) was observed in sample with the largest graphite electrodeconsumption rate (sample 3) For all samples the synthesized powderseparated into three phases one floating in suspension one settling atthe bottom as sediment and one as a layer of film-like material floatingon the liquid surface

The aqueous solutions of CuCl2 were discharge treated for only 20s to acquire yellowish suspensions The transparency of the suspensionsdecreased with the time during the discharge treatment The liquidsturned to dark yellow after treatment by ac-discharge for 10 min Thesuspensions resulting from dc-discharge treatment were conspicuouslydarker when C electrode was acting as an anode The nanoparticlessuspension produced by spark and arc discharges were dark brown anddark grey respectively It might be due to the presence of relatively largeamount of carbon particles in suspension (see Table 3) The dc-dischargetreated solutions were olive-green when Cu was used as the anodeelectrode Yellow or green colour of suspension may indicate theoxidation of copper nanoparticles [22] The presence of Cu2Onanoparticles was further confirmed by XRD analysis No changes incolour were observed after laser irradiation of suspensions

Figure 2 shows the absorption spectra of as prepared (a) and laserirradiated (b) suspended nanopowders synthesized by dischargetreatment of aqueous solution of CuCl2 (2) for 1 min The spectra werecorrected to the contributions of solvents The optical density increasedwith decrease in wavelength Generally the optical density ofsuspensions prepared by spark discharge was higher than that ofsuspension prepared by arc discharge This is consistent with the factthat the nanoparticles production rate was higher when the solution wastreated by spark discharge In the spectral range of 200 ndash 500 nm theoptical density of the samples 1 4 6 was higher than that of samples 23 and 5 This seems to suggest that the main parameter in determiningthe optical properties of suspensions was concentration of Cu-basednanoparticles For the samples number 1 and 4 a weak absorption peakwas observed at very short wavelength According to the literature data[2324] a surface plasmon peak at wavelength of 289 nm may beattributed to the presence of very small separated Cu nanoparticles (lt 4nm in size) Though TEM examination confirmed the presence of smallnanoparticles in sample 1 there were no nanoparticles with diameter less

172

than 4 nm in sample 4 Moreover there were no copper nanoparticles insample 1 as revealed by the XRD (see below) More likely theexistence of weak absorption peak at 280 nm implied formation of liquidbyproducts We did not observe in the absorption spectra surfaceplasmon band around 570 nm Missing of the plasmon band can beexplained by copper oxidation on the particle surface [23] Thissuggestion was further confirmed by XRD analysis (see below) Thesuspensions exhibited the same colours after laser irradiation butabsorption intensity increased for samples 3 1 and to the less extent forsample 5 as illustrated in Figure 2b TEM analysis revealed themorphological similarity of irradiated samples 1 3 and 5 (see below)

Figure 3 depicts the corresponding TEM images for thesuspensions shown in curves 1-6 of Figure 2 Parts (a) and (b) representthe TEM views of the as-prepared and irradiated samples respectivelyThree distinct structures were observed dark small spherical particlesdark particles surrounded by a gray shell and gray flake-like structureshaving diffuse contours The small dark particles with diameter 2-5 nmwere observed in samples 1 2 3 and 5 (marked with black ellipses inFigure 3) Some dark particles notable when using ac spark dischargefor synthesis were bigger than 20 nm indicating coalescence Thenanoparticles synthesized by ac arc discharge (sample 2) were

Fig 2 Absorption spectra for the as-prepared (a) and laser modified (b)suspended nanoparticles produced by ac- (12) and dc- pulsed discharges(3456) The following electrode pairs were used Cu and C for the ac-spark(1) and ac-arc (2) discharges Cu as a cathode electrode and C as an anodeelectrode for the dc-spark (3) and dc-arc (5) Cu as an anode electrode and C asa cathode electrode for the dc-spark (4) and dc-arc (6)

173

surrounded by the arrowed gray regions which were probably carbonshells as shown in Figure 3a

Fig3 TEM images of nanoparticles from as-prepared (a) and irradiated (b)suspensions produced by ac- (12) and dc- pulsed discharges (3456) Thefollowing electrode pairs were used Cu and C for the ac-spark (1) and ac-arc(2) discharges Cu as a cathode electrode and C as an anode electrode for thedc-spark (3) and dc-arc (5) Cu as an anode electrode and C as a cathodeelectrode for the dc-spark (4) and dc-arc (6)

174

As we did not have any direct evidence that the shells consisted ofcarbon these nanostructures will be referred further as core-shellnanoparticles The core-shell nanoparticles were also observed in colloidprepared by dc arc discharge between copper cathode and graphiteanode (sample 5) It can be seen that core-shell nanoparticles rangedfrom 20 to 50 nm in diameter while the cores within the nanoparticlesvaried from 8 to 25 nm The cores were non-spherical They seemed tocompose of small particles clustered together The flake-like structureswith diffuse contours were 50 nm in size They were observed in allsamples Samples 4 and 6 consisted mostly of structures with diffusecontours On the basis of the above observations the ac arc dischargeand dc arc discharge with copper anode electrode seemed to be moresuitable for synthesis of nanoparticles with core-shell structure

It is clear seen that many smaller particles with sizes around 2-7nm were generated after the irradiation of samples 2 4 and 6 Theparticles larger than 10 nm completely disappeared The micrographrevealed that after the irradiation these suspensions consisted ofparticles with circular cross-section whereas before the irradiation theparticle shape was not spherical The nanoparticles were dispersed verywell No small nanoparticles were observed in suspensions 1 3 and 5after the irradiation Though as can be seen by comparing Figure 1(a)3(a) and 5(a) with 1(b) 3(b) and 5(b) the shape of nanoparticleschanged after the irradiation The laser induced morphology change mayoccur through heating of the nanoparticles because of the absorption ofthe laser light [25] According to the mechanism proposed by Takami etal the morphology of irradiated nanoparticles was determined by therelationship between temperature of nanoparticles their melting andboiling point

The laser induced change in shape and size occurred if thetemperature of nanoparticles was at the boiling point If the temperaturewas lower than the melting point no changes took place If thetemperature was between melting point and boiling point only thechange in shape occurred Thus the difference in morphology of theirradiated samples can be attributed to the difference in theircomposition Even being irradiated with the same laser light intensitythe nanoparticles of different composition changed their morphology indifferent ways as they have different melting and boiling points

175

X-ray diffraction data were collected to identify synthesizedsamples The diffraction peaks at 432deg and 503deg correspond to theformation of faced-centered-cubic Cu There are three diffraction peakswith 2θ value of 365deg 423deg and 614deg which can be assigned to theprimitive cubic Cu2O Besides there are two peaks at 240deg and 265degwhich can be assigned to the hexagonal C XRD revealed that dischargetreatment of aqueous solution of CuCl2 led to the formation of Cu2

(OH)3Cl and Cu2OCl2 because of a strong affinity between chlorine andthe metal (peaks with a value of 2θ around 165deg 19deg 31deg 323deg 327deg330deg 387deg 398deg 401deg 503deg 505deg 538deg and 178deg 360degrespectively) For comparison the XRD patterns of initial solution ofCuCl2 are also plotted at the top of Fig 4 Non-treated aqueous solutionof copper chloride was allowed to evaporate and than analyzed by XRDThe diffractogram of this sample showed peaks at about 2θ around162deg 220deg 240deg 267deg 289deg 328deg 340 348deg 352deg 409deg 430deg448deg 453deg 490 and 573deg which are characteristics of CuCl2middot2H2O

XRD data were used to semi-quantitatively determine thepercentage of constituents The semi quantitative analysis of phasecomposition is shown in Table 3 The nanopowder composition wasstrongly dependent on the synthesis parameters It should be noted herethat metallic copper was only formed by dc-discharge treatment whencopper was acting as an anode electrode (samples 4 and 6) Synthesizedmaterial contained copper mostly in form of oxide (Cu2O) copperhydroxychloride (Cu2(OH)3Cl) and copper oxychloride (Cu2OCl2)Difference in Cu2O and C contents among all samples was significantSamples 2 and 5 contained no copper oxide while sample 6 had thelargest percentage of copper oxide (ca 80 vol) On the other handsample 6 contained no carbon The carbon contain in sample 4 exceeded80 vol The quantities of Cu2(OH)3Cl in samples ranged from lessthan 2 vol to ca 30 vol Only three samples contained Cu2OCl2

(samples 12 and 5) The maximal amount of Cu2OCl2 detected by XRDcorresponded to ca 30 vol In spite of high copper electrodeconsumption rate sample 4 contained unexpectedly small quantities ofCu and Cu-containing compound It might be due to the formation ofrelatively large and heavy copper microparticles They precipitated fromcolloid quickly after synthesis Therefore they were not collected andanalyzed by XRD (see experimental section) A correlation was

176

observed between low copper electrode consumption rate and absence ofCu and Cu2O fractions in nanopowder composition for samples 2 and 5

It should be stressed here that the core-shell structures wereobserved for only samples 2 and 5 Taking into account firstly thatsamples 2 5 and 6 were prepared by arc treatment secondly that thesample 6 contained no C and assuming that the shells consisted ofcarbon we can suggest that arc discharge was more suitable forsynthesis of core-shell nanoparticles On the other hand the chemicalcomposition of final product was governed by different competingreactions As they have different equilibrium constants they may form anetwork where the ratios of the products are sensitive to concentrationsof each of the many components Therefore the slight difference ininitial concentration might results in significant difference incomposition and morphology of synthesized material (compare samples5 and 6)

Although the exact mechanism for formation of nanoparticles viadischarge in solution process is not clear the following possibility may

Table 3 Semi-quantitative analysis of synthesized powder by XRD

XRD-analysisType of

dischargeElectrodesmaterial Cu

volCu2Ovol

Cvol

Cu2(OH)3Clvol

Cu2OCl2vol

1 ac1) sparkCuC

- 135 403 165 297

2 ac arcCuC

- - 646 300 54

3 dc2) sparkCu (cathode)C (anode)

- 391 370 239 -

4 dc sparkCu (anode)C (cathode)

78 83 825 14 -

5 dc arcCu (cathode)C (anode)

- - 339 336 325

6 dc arcCu (anode)C (cathode)

74 775 - 151 -

1) Alternating current pulsed discharge2) Direct current pulsed discharge

177

be considered During discharge treatment of the liquid copper andgraphite electrodes were heated melted and vaporized in the region ofthe discharge generated In the vicinity of electrodes the liquid was alsovaporized rapidly due to extremely high temperature Hence the plasmaregion produced by the discharge adjacent to the electrodes wassurrounded by a gas bubble Following Sano et al [8] the gas mixturemay comprise CO and H2 formed as follows

22 HCOOHC (2)

This reaction might cause the discrepancy between electrodeconsumption rate and nanopowder synthesis rate since some of carbonatoms formed gaseous CO Sano et al reported that gas bubbles didnot comprise water vapor since no condensation occurred [8] Howeverwe should consider that water vapour also existed in the discharge zoneas we did not obtain any evidence of its absence

Copper chloride is an anionic compound that dissociates inaqueous solution and may form different ionic species such as Cu2+ Cl-or complex ions such as CuCl2

- CuCl32- CuCl4

2-[26] The reduction ofcopper ions into copper atoms was likely taking place in plasma regionduring discharge treatment of the liquid as shown in Eq 3

02 2 CueCu (3)

As the temperature in the vicinity of the electrodes was estimatedto be around 4000 K [8] the thermal decomposition of complex ions tometallic copper possible took place in discharge zone (Eq (4-6))

20

2 ClCuCuCl (4)

20

3 322 ClCuCuCl (5)

202

4 2ClCuCuCl (6)

The nanoparticles were then formed from the complex gasmixture through different transformation stages namely nucleationgrowth condensation and coalescence Both the evaporated copper fromelectrode and Cu produced by reduction of ions from solutions were

178

supposed to be incorporated into the resulting nanoparticles Becausewater vapor existed in gas bubble the copper nanoparticles were easilyoxidized Reduction of copper oxide by carbon monoxide and hydrogenwas possible the subsequent step (Eq (7) and (8))

OHCuCOOCu 22 2 (7)

222 2 COCuHOCu (8)

According to the XRD measurements (see Table 3) copper oxidewas only partially reduced into copper in sample 4 and 6 The data ofXRD analysis implied also reaction of chlorine with copper andorcopper oxide to form Cu2Cl(OH)3 and Cu2OCl2 These reactions mightinvolve hydrogen produced via reaction (2)

It should be noted that there was no direct evidence to support theabove-mentioned formation sequence and the true mechanism may bemore complicated

ConclusionsFrom the results and discussion presented above the following

conclusions can be madeThe electrical discharge between two electrodes immersed in

ethanol is a suitable method to produce in a controllable waynanoparticles with different contents of metal and carbon By varyingthe current value and its pulse duration morphology of nanoparticlesand their composition can be changed The average diameters of theprepared nanoparticles were in the range of 3-7 nm

Cu-based nanoparticles with different morphologies wereprepared via submerged electrical discharge of bulk copper and graphiteelectrodes in a CuCl2 aqueous solution Synthesized material wassubjected to laser-induced modification It was found that core-shellnanoparticles were formed by treatment of CuCl2 aqueous solution bythe arc pulsed discharge with pulse duration of 4 ms and peak current of10 A

The synthesis rate varied in range of 19 ndash 69 mg min-1 dependingon peak current and pulse duration of discharge as well as polarity ofcopper and graphite electrodes The synthesis rate was found to behigher when copper was acting as an anode electrode The synthesis rate

179

increased with increasing of discharge current and decreasing of pulseduration The composition and morphology of nanoparticles were alsofound to depend on discharge parameters The copper nanoparticleswere only formed by dc-discharge treatment when copper was acting asan anode electrode The maximum diameter of nanoparticles did notexceed 50 nm while the minimum diameter was around 2 nm Theresults of the experiments imply that plasma treatment with longer pulseduration and lower current leads to the formation of carbon embeddednanoparticles TEM confirms the formation of encapsulatednanoparticles

Irradiation of nanoparticles in aqueous solution by a pulsedNdYAG laser at 532 nm was found to cause the shape change and sizereduction of the particles

AcknowledgementsThe work has been supported by the Integral Program of the

Siberian Branch of RAS under the Grant 138-T-09-CO-014 Authorsare thankful to KV Scrockaya for carrying out the TEM investigations

References

1 I Zalite S Ordanyan G Korb (2003) Synthesis of transition metalsnitridecarbonitride nanopowders and application of them formodification of structure of hardmetals Powder Metallurgy Journal46 2143 ndash 147

2 XG Yang and CY Wang (2005) Nanostructured tungsten carbidecatalysts for polimer electrolyte fuel cells Appl Phys Lett 8624104-1 -224104-3

3 M Rosenbaum F Zhao U Schroder F Scholz (2006) InterfacingElectrocatalysis and Biocatalysis with Tungsten Carbide A High-Performance Noble- Metal-Free Microbial Fuel Cell Angew Chem118 1-4

4 D Bera S C Kuiry M McCutchen S Seal(2004) In situ syntesis ofcarbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method J Appl Phys 96 5152-5157

5 P Serp M Corrias P Kalck Carbon nanotubes and nanofibers incatalysis Applied Catalysis A General ndash 2003 ndash Vol 253 ndash P337-358

180

6 Ishigami M Cummings J Zettl A Chen S (2000) A simple method forthe continuous production of carbon nanotubes Chem Phys Lett319 457-459

7 Sano N Wang H Alexandrou I Chhowalla M Amaratunga G A J(2001) Nanotechnology Synthesis of carbon ldquoonionsrdquo in waterNature (London) 414 506-507

8 Sano N Wang H Alexandrou I Chhowalla M Teo K B KAmaratunga G A J (2002) Properties of carbon onions produced by anarc discharge in water J Appl Phys 92 2783 ndash 2788

9 Sano(a) N (2004) Low-cost synthesis of single-walled carbonnanohorns using the arc in water method with gas injection J PhysD 37 L17-L20

10 Parkansky N Alterkop B Boxman R L Goldsmith S Barkay ZLereah Y (2005) Pulsed discharge production of nano- andmicroparticles in ethanol and their characterization PowderTechnology 150 36-41

11 Parkansky N Goldsmith S Alterkop B Boxman R L Barkay ZRosenberg Yu Frenkel G (2006) Features of micro and nano-particlesproduced by pulsed arc submerged in ethanol Powder Technology161 215-219

12 P Muthakarn N Sano T Charinpanitkul W TanthapanichakoonT Kanki Characteristics of Carbon Nanoparticles Synthesized by aSubmerged Arc in Alcohols Alkanes and Aromatics Phys Chem Bndash 2006 ndash Vol 110 37 ndash P 18299 -18306

13 D Bera G Johnston H Heinrich S Seal A parametric study on thesynthesis of carbon nanotubes through arc-discharge in water Nanotechn ndash 2006 ndash Vol 17 ndash P 1722-1730

14 Hsin Y L Hwang K C Chen R-R Kay J J (2001) Production and insitu metal filling of carbon nanotubes in water Adv Mater 13 830-833

15 Xu B Guo J Wang X Liu X Ichinose H (2006) Synthesis of carbonnanocapsules containing Fe Ni or Co Carbon 44 2631-2634

16 Lange X Sioda M Huezko A Zhu Y Q Kroto H W Walton D R M(2003) Nanocarbon prodction by arc discharge in water Carbon 411617 ndash 1623

17 Sergienko R Shibata E Akase Z Suwa H Nakamura T Shido (2006) Carbon encapsulated iron carbide nanoparticles synthesized in

181

ethanol by an electric plasma discharge in an ultrasonic cavitationfield Mater Chem Phys 98 34-38

18 Leo G H Jeong S H J W Ri H C (2002) Excelent magnetic propertiesof fullerene encapsulated ferromagnetic nanoclusters J Magn Mater246 404 ndash 411

19 Ang K H Alexandrou I Mathur N D Amaratunga G A J Hag S(2004) The effect of carbon encapsulation on the magnetic propertiesof Ni nanoparticles produced by arc discharge in de-ionized waterNanotechnology 15 520 ndash 524

20 Sano(c) N Nakano J Kanki T (2004) Synthesis of single-walledcarbon nanotubes with nanohorns by arc in liquid nitrogen Carbon42 686-688

21 Bera(c) D Jonston G Heinrich H Seal S (2006) A parametric studyon the synthesis of carbon nanotubes through arc-discharge in waterNanotechnology 171722-1730

22 Yeh M-S Yang Y-S Lee Y-P Yeh Y-H Yeh C-S (1999) Formationand characteristics of Cu colloids from CuO powder by laserirradiation in 2-propanol J PhysChem B 103 6851-6857

23 Aslam M Gopakumar G Shoba T L Mulla I S Vijayamohanan K(2002) Formation of Cu and Cu2O nanoparticles by variation of thesurface ligand preparation structure and insulating-to-metallictransition J Colloid Inter Sci 25579-90

24 Salkar R A Jeevanandam P Kataby G Aruna S T Koltypin YPalchik O Gedanken A (2000) Elongated copper nanoparticlescoated with a zwitterionic surfactant J Phys Chem B 104 893-897

25 Takami A Kurita H Koda S (1999) Laser-induced size reduction ofnoble metal particles J Phys Chem B 1031226-1232

26 Brown JB (1948-1949) The constitution of cupric chloride inaqueous solution Transaction of the Royal Sociaty of New Zeland 7719-23

162

MORPHOLOGICAL STUDY OF DETONATIONSPRAYED COATINGS OF CALCIUM HYDROXYAPATITE

DEPOSITED ON A NANOSTRUCTURED TITANIUMSUBSTRATE

AA Sitnikov VI Yakovlev YuP Sharkeev 1EV Legostaeva 1 AA Popova

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1Institute of Strength Physics and Materials Science SB RASTomsk

Biocompatible coatings are effectively formed by spraying ofcalcium hydroxyapatite Са10(РО4)(ОН)2 powders on a titanium substrateRecently along with the composition macro- and microstructuredevelopment the surface morphology of the coatings has receivedincreasing attention In a number of studies the roughness of thecoatings has been shown to significantly influence the inductionprocesses of cells As a substrate material titanium VT1-0 has beenchosen which has several advantages being highly biocompatiblebioinert practically non-toxic corrosion-resistant and possessing lowthermal conductivity and low coefficient of thermal expansion Themorphology of the gas-detonation sprayed calcium phosphate coatingsdeposited on ultrafine-grained and nanostructured titanium substratesand implant imitations has been studied The substrates and implantimitations were produced in the Institute of Strength Physics andMaterials Science SB RAS Tomsk

It was shown that the detonation sprayed hydroxyapatite powderswith particles ranging from 1 to 20 microm formed coatings non-uniform inthickness and phase composition The roughness of the coatings wasRa=365-472 microm (class 5) When hydroxyapatite particles of 20-100microm in size are sprayed coatings more uniform in thickness and phasecomposition are formed (Fig1) with an average roughness of Ra = 624microm (class 4) Preliminary treatment of the titanium substrate by sandingand chemical etching allows increasing the adhesive strength of thecoating up to 20MPa

163

Fig1 SEM images hydroxyapatite powder (a) detonation sprayedhydroxyapatite coating (b) XRD pattern of the coating (c)

Biological studies have demonstrated biocompatibility andbioactivity of the coatings It was found that the calcium phosphatedetonation sprayed coatings induce growth of tissue cells with 100probability which indicates that the relief of the coatings is optimal forfixation and aging of the cells Comparative studies of calciumphosphate coatings produced by detonation spraying and those producedby micro-arc in an electrolyte containing phosphoric acidhydroxyapatite and calcium carbonate have shown the advantages ofdetonation spraying for providing the required phase composition of thecoating This opens up a possibility of making two-phase coatings(hydroxyapatite and beta-calcium phosphate) ensuring the closest matchin composition to the bone tissue

ва б

100

200 20 30 40 50 60 70 80 90 10

(1

10) (002

) (2

10)

(2

11)

(

300

)

(3

10)

(

222

)

312

)

(3

20)

(

511

)

(

432

)

(5

22)

(

100

)

161

MICROSTRUCTURE STUDIES OF THE COATINGSPRODUCED BY ARC DEPOSITION OF THE

MECHANOACTIVATED SHS-COMPOSITE TIC+XME(R6M5 PR-N70H17S4R4-3) POWDERS

AA Sitnikov VI Yakovlev MA Korchagin1MN Seidurov ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

One of the main challenges in the development of new materialsfor arc deposition using flux-cored wires is to design materials of specialinterest using cost-effective and ecologically friendly technologies Asmaterialstechnologies meeting these requirements we can proposelayered composites produced by self-propagating high-temperaturesynthesis (SHS) in mechanically activated powder mixtures

The samples of SHS-mechanocomposites of TiC+XMe (R6M5PR-N70H17S4R4-3) composition arc-deposited on steel 45 substrateswere selected for investigations Microstructure of the arc-depositedcoatings was studied using a Carl Zeiss AxioObserver A1m OpticalMicroscope For observations cross-sections of the samples wereprepared and etched with a solution containing 20 potassiumferricyanide К3[Fe(CN)6] 20 КОН and 60 H2O Finemicrostructure and composition of the deposited layers were analyzedusing a Carl Zeiss EVO50 Scanning Electron Microscope equipped withan EDS X-ACT laquoOXFORDraquo device

The investigations show that the microstructure of the depositedlayers is uniform with submicron titanium carbide reinforcing phase inthe form of separate inclusions or chains of particles in the matrix

159

WEAR-RESISTANT DETONATION SPRAYED COATINGSBASED ON THE COMPOSITE MECHANICALLY ACTIVATED

SHS-MATERIALS

AA Sitnikov VI Yakovlev MA Korchagin 1DM Skakov AA Popova ME Tatarkin

IIPolzunov Altai State Technical University Barnaulanicptramblerru

1 Institute of Solid State Chemistry and Mechanochemistry SB RASNovosibirsk

The application of titanium carbide as a material for thermalspraying is rather difficult mainly due to its high melting temperatureand high hardness

A technology has been developed abroad for the production of thecomposite powders for spraying The production of these compositepowders is a laquoknow-howraquo of MBN Nanomaterialia (Italy)

An approach to the development of TiC-containing coatings canbe based on the technology of mechanocomposites with metallic orintermetallic matrices reinforced with nanosized particles of a ceramicphase [1] The technology of the powder preparation consists of 3 stagesAt the first stage the mixture of initial reactants which in this particularcase are titanium carbon and nichrome is mechanically activated (MA)in a planetary ball mill At the second stage self-propagating hightemperature synthesis (SHS) is conducted resulting in the formation ofTiC particles uniformly distributed in the metallic matrix AdditionalMA of the products of SHS at the third stage along with dispersingtitanium carbide particles creates a principally new state of the matrixwhich experiences grain refinement and shows high internal stresses andhigh concentrations of non-equilibrium defects In addition thesubsequent mechanical activation can be advantageously used forcompositions with higher matrix contents that are not possible to makethrough the SHS special additives can be also introduced into thecomposites at this stage

In order to compose the initial mixtures the following powderswere used titanium PTM lampblack PM-15 and nichrome PR-N70H17S4R4-3 Mechanical activation of the powder mixtures and theSHS-products was carried out in a planetary ball mill AGO-2M

160

Detonation spraying was performed using the laquoKatun-Mraquo set-upIt was found that the chemical composition did not change duringspraying

Wear resistance of the sprayed coatings was evaluated using afriction machine 2168 UMT in the laquoshoe-on-diskraquo mode A coating 02mm thick was deposited on a steel 40 shoe Prior to deposition the shoewas rubbed against the disk until a contact spot was formed over thewhole surface of the shoe After the coating was deposited the workingsurfaces were subjected to abrasive diamond treatment to reduce theirroughness

Tribological tests showed that with increasing metallic matrixcontent from 20 to 60 wt the weight losses under dry friction at 950 Nincreased almost twice Comparative tests of the coatings and thesamples of hardened steel revealed that the wear of the coatings obtainedfrom the mecahnocomposite powders was 8 times lower than that ofsteel 40H

References1 MAKorchagin DVDudina Application of self-propagating high-

temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007 v43 2 p176-187

153

CHEMICAL-THERMAL TREATMENT IN CARBONMANGANESE STEEL

AT INDUCTION-HEATING IN VARIOUS BORATINGCONDITIONS

SM Shanchurov VV Ivanajskij AV Ishkov NT KrivochurovNM Mishustin

Ural Federal University Ekaterinburg RussiaAltay State Agrarian University Barnaul Russia

Abstract Processes of borating of high-carbon manganese steel65Mn by carbide of boron and amorphous boron in conditions of fluxwith additives of various activators of borating are investigated at high-speed induction-heating It is shown that the nature of the boratingagent the additive of flux activators CaF2 and NH4Cl have influence onstructure and properties which are formed on a surface of boroneutectics

Keywords boron carbide of boron induction heating chemical-thermal processing

Among modern processes of chemical-thermal treatment (CTT)production engineering of saturation of surface layer constructional andalloy steels with boron ndash the borating occupy a special place In boratingit is possible to obtain the extended beds distinguished by high hardnessand strength corrosion-resistance abrasive durability and highreceptivity to wear on a surface of a steel detail [1 2] However themajority of known processes of borating are prolonged and are badlybuilt in into flow diagrams of state of productions

Intensification of CTT processes and in particular borating canbe carried out with application of technology of short-term high-speedheating of steel detail surface with the borating composition put on herrf currents (RFC) up to temperatures of formation of new phases andeutectics (1100-1350 оС) in systems Fe-B Fe-B-C and Fe-Me-B-Cwhere Ме - is an alloy element from group Cr Mn Ni etc [3] Unlikewell investigated processes of borating of alloy steels by mediums anddaubing at temperatures up to 950оС [4] there are open generalquestions of peculiarities of chemical interaction of components in suchsystems phase condition and properties of formed products

154

In the present work chemical-thermal treatment of carbonmanganese 65Mn steel combined with RFC-heating of its surface invarious borating conditions has been investigated

Experimental partAs the basic subject of research 65Mn (GOST 4543-71) alloy

carbon steel was chosen from the group of the same kind manganesechromos chromos-nickel and chromos-manganese steels from group 70U8А 50CrMnА 30CrMnSiА 45Cr 70Mn etc with similar propertiesand composition

Technical carbide of boron B4С in accordance with GOST 5744-85 and reactive amorphous boron of qualification reagent-grade weretaken as borating agents of different nature Known composition for theinduction deposition (F1) consisting of borax glass the boric anhydridecalcium silica and welding flux АN-348А (30 Na2B4O7 20 B2O310 CaSi2 and 40 flux АN-348А) was used as flux Reagent-gradeCaF2 and NH4Cl served as activators

RFC-heating of samples was carried out in a loopback water-cooled copper inductor by diameter of 160 mm connected to RF-lampgenerator VCG 7-600066 The adjustment of a contour and geometryof an inductor provided heating of researched samples to the temperatureof 1300-1350оС during 40-60 sec with the subsequent stabilizationAfter holding at the specified temperature during from 1 up to 2 minsamples were pulled out from an inductor and cooled down loosely

Microstructure of the coverings formed has been investigated andthickness of borated bed has been determined (МIМ-7 Neophot-30)hardness has been measured (PМТ-3 by 50 100 g) phase composition(DRON-2 radiation Co-Kα speed of angular moving of a sample of 1grads min) has been determined

Results and discussionIt is known that classical production engineering of kiln borating

are based on gradual (during 05-6 h) saturation of a surface of a steelproduct by boron from various pastes daubings liquid or a gaseous fluidat temperatures of process from 750 up to 950 оС Thus in the capacityof sources of boron its various compounds (В2О3 В4С ВF3 Na[BF4]etc) are applied capable to decay on active elements at temperatures ofprocess Depending on a phase condition of the borating agent hardness

155

and liquid borating are distinguished and also borating from a gas phase[4] We investigated six variants of mixes for high-speed borating atRFC-heating steel 65Mn Mixes differed in the nature of the boratingagent e borating agent composition presence fluxes componentsactivators and technological additions Compositions of the mixes usedare given in table 1

Table 1

Mixes Boratingagent

Activator Flux

Iа B4C (84) NH4Cl (6) F1 (10)II B4C (84) ndash F1 (16)

IIIа B (90) CaF2 (5) F1 (5)

Mixes I Iа II and IIа used as borating agent contained carbide ofboron mixes III IIIа - amorphous boron in mix Iа activator chloride ofammonium and in mix IIIа - fluoride of calcium has been added allmixes contained melted flux as a fluxing component for inductiondeposition F1

With decrease of density of a borating phase and increase intemperature of process its speed in the interval of temperatures from 800up to 950 оС increases insignificantly therefore for their intensificationcollateral saturation of a surface by several elements at once or thermocycling are applied [5] If the temperature of the process exceeds 1100-1300 оС in an aspect of beginning processes of high-temperaturestructural reorganization in steel speeds of borating sharply increase in2-4 min with the increase in temperature at every 15-20 оС thus theprocess passes from a diffusive zone to a zone of chemical reaction Soat the temperature of 1200-1300 оС according to the data[6] it ispossible to obtain in a few minutes the thickness of the single-phaseboron-bed up to 02-04 mm thus heating of a detail is carried out by thespecial thermo reaction mix

At RFC-heating of the steel 65Mn covered by researched boratingcompositions with chosen parameters of process fig 1 adamantinecoverings are formed on all samples resembling bed covered hard metalX-ray analysis of a material of coverings has shown presence of Fe

156

borides FeB and Fe2B carbon-borides Fe3(C B) and Fe23(C B)6 variousmeta- and orto-borates of iron (Fe3BO3 Fe3BO6 Fe3BO5) traces FeOand FeOFe2O3 Thus at RFC-heating of alloy carbon steels under bedof flux F1 containing from 84 up to 90 of borating agents complexboron-phases are formed on their surfaces hardening a surface of a detailand it is strongly linked with it and oxide films are removed togetherwith slag

To find out the characteristics and structure of received beds andthe conditions of borides in them photomicrography of micro sectionswas taken Typical structures of boron-beds are given in fig 1

a b C

Fig 1

As it is seen from fig1 with the chosen heating environments andthe time of borating the structure and the condition of boundary line ofreceived wear-resistant beds differ but in all cases as against classicalboron two-phase beds on a surface of samples the eutectic with stronglypronounced or with the diffusive boundary line separating it from anoriginal material is formed faster in conditions of heavy abrasive sign-variable and shock wear boron-plate Apparent changes in structure ofparent metal caused by its short-term overheat were not observed

For the mixes containing in the capacity of borating agent equalquantity of carbide of boron similar quantity of fluxes-component anddistinguished only by the presence of activator NH4Cl promoting areinforcement of convertible diffusive and transport reactions especiallyat low temperatures right at the beginning of the process of borating (Т

157

lt300 оС) formation of fine grained structure of eutectic turnings on withhardness not above 700-750 HV thickness of bed of 016 mm and withlegibly discernible interface with parent metal (fig 1а) is observed

For the analogous mix II without this activator the expressedpropagation of dendrites islands and druses of boron-phases withhardness up to 1050-1120 HV thickness of bed of 028 mm and adiffuse interface boron bed with parent metal (fig 1b) is observed Themixes on the basis of amorphous boron (fig 1c) appeared to be the mostreactive thus in mix IIIа containing follow-up 5 of activator CaF2 and5 of fluxes component beyond chosen relationships for 1 minthickness of bed on steel of 65Mn has made 088 mm at its hardness in2200-2300 HV The structure represents the remote eutectichomogenized iron ndash boron formed with such speed that from a melt atits solidification balls of slag had not time to bleed up to the end

Thus amorphous boron which at the presence of flux F1 andactivator CaF2 under the chosen conditions of experiment forms denseclose-grained beds on a surface of alloy steels with depth up to 800microns with hardness up to 2400-2500 HV (fig 2) appeared to be themost efficient borating agent at RFC-heating

Fig 2

It is interesting to note that the structure of the wear-resistantcovering obtained at high-speed 1 min borating steel 65Mn a mix II ismetastable and at borating during 2 min like in picture 1а with hardness2300-2400 HV turns to the fine grained structure and thickness of a

158

covering does not change and the interface with parent metal becomesdiscernible

References1 Methods of raise of longevity of machine components Red VN

Tkacheva M 19712 Belyj AV Karpenko GD Myshkin KN Structure and methods of

formation of wear-resistant surface layers M 19913 Tkachev VN Fishtejn BM Kazintsev NV Aldyrev DA

Induction overlaying welding of hard metals M 19704 Voroshnin LG Lyahovich LS Borating of steel M 19785 Guryev АМ Kozlov EV Ignatenko LN Popova NA Physical of

a basis of thermal-cycle borating Barnaul 2000

138

PHASE STATES OF MECHANOACTIVATED MANGANESEOXIDES

SA Petrova RG Zakharov AYa Fishman LI LeontievInstitute of Metallurgy Ural Division of RAS Ekaterinburg 620016

Russian Federation

An investigation of structural characteristics of the manganeseoxides in order to understand these characteristics affected bymechanochemical treatment conditions has been undertaken Chemicallypure manganese (II III IV) oxides were used as the initial componentsIt is shown that the properties of the mechanoactivated oxides differgreatly from those of initial materials Relationships among structuralcharacteristics of the mechanoactivated oxides and their prehistory wayand conditions of producing have been detected

IntroductionStudy of phase states of mechanoactivated oxides makes it

possible to analyze the patterns of expression of the mechanochemicaleffect in redox processes to determine the mechanism of the effect ofactivation processes on the type and parameters of the structural phasetransitions to establish the role of higher oxides in the redox processesAs one of the consequencies of the intensive mechanical activation is theappearance of nanodisperse states specificity of phase transformationsin nanocrystalline oxides is considered at the same time

It is known now that the decrease in the crystallite size inmechanoactivated systems causes a decrease of structural phasetransition temperatures In metallic alloys reducing of crystallites size isaccompanied by suppression of martensitic transitions [1-2] Completeinhibition occurs when the grain size becomes smaller than that of thecritical nucleus of a new phase It can be regarded as established that theparameters of phase transitions in oxides with relatively lowtemperatures of phase transitions also depend strongly on the grain sizeFor example in barium titanate BaTiO3 transition from cubic to low-symmetry phase is completely suppressed when the grain size is about10 nm [3] Changes in the crystal structure and the effects of reduction(the change of temperature and phase transition heat) in the structuralphase transitions with decreasing grain size also occurred for the oxides

139

Al2O3 Fe2O3 PbTiO3 PbZrO3 La1-xSrxCuO4 YBa2Cu3O7-δBi2CaSr2Cu2O8 [4] and several other oxides [5-6] Besides for the oxidesin nanoscale state the coexistence of two different structuralmodifications [7] was observed The processes of mechanoactivationmay also lead to new types of metastable phase states due to theredistribution of cations between the crystallographically inequivalentsublattices [8]

In the present work the main attention is paid on the analysis ofthe effects associated with the evolution of metastable structures underconditions of temperature increase and oxide interaction with anaggressive environment So far the main contribution to theinvestigation of these issues has made the study of metallic alloys (seefor example [9-10]) The behavior of the activated oxide materials ismuch less studied Study of structural phase transitions in the systemMn-O subjected to mechanochemical activation and structuralcharacteristics of the crystalline phases allows us to test how general arepreviously established patterns for systems with different types ofchemical bonds

The effect of mechanical activation on structural phase transitionsboth of martensate type (from cubic to tetragonal modification Mn3O4)and those accompanied by redox processes (between phases withdifferent degrees of oxidation etc) is investigated The choice of Mn-Ooxides as the object of study is largely connected with the fact that atleast two structural phase transitions observed in the considered crystalswith temperature changes involved the cooperative Jahn-Teller (JT)phase The value of the JT deformation in it is determined by theconcentration of JT ions in octahedral sites that allows to get additionalinformation about the structural changes caused by themechanoactivation of oxide

1 Production and structural properties of themechanoactivated oxides

11 Mechanoactivation of manganese oxidesPure manganese oxides MnO2 Mn2O3 and Mn3O4 annealed at

200deg 900deg and 1250degC respectively were used as the initial materialsFor the mechanical treatment of oxides which was described in

detail in [1112] a planetary mill AGO-2 with water-cooled drums (V =

140

150ml) and a centrifugal factor up to g = 60 [3] was used Download ofballs was 203g the material - from 5g Milling was made dry Theprocessing of powders was carried out after preliminary lining in acontinuous mode or with periodic stops of the mill According toestimates (performed by XPES) contamination by iron was not morethan 02 Previously [14] we found that prolonged continuousmechanical treatment leads to the fact that within the grains matureduring the first seconds along with a further (slow) reduction ofcoherent scattering blocks chemical processes begin leaking Because atthis stage the main purpose was to obtain single-phase samples theduration of continuous grinding was restricted by 30s The temperatureinside the drums during grinding did not exceed 320K which ensuredthe preservation of initial metastable phases During stops of mill thedrums where opened and powder was manually stirred but samplingwas not performed

To be able to conduct magnetic research on the mechanicallyactivated samples and to investigate the effect of intensity ofmechanoactivation (the degree of deformation) on the redox processesand the stability of weakly activated oxides the part of samples wasobtained as a result of mechanical activation in the vario-planetary millPulverizette 4 (Fritsch) in glasses of tungsten carbide Volume of drumwas equal to 250ml loading of crushing balls was 800g and a materialmass was 20 g Milling was made dry the duration was 3 min

12 Attestation of mehanoactivated manganese oxides andmethods of their experimental study

The phase composition of obtained substances the size ofcoherent scattering domains (CSD) and microstresses were determinedby X-ray diffractometer D8 ADVANCE (Bruker) (radiation CuKα Ni-filter position-sensitive detector VANTEC1) High-temperature X-raystudies of the stability of mechanoactivated oxides was carried out usinghigh-temperature chamber HTK1200N (Anton Paar)

The particle size of powders obtained was assessed by dynamiclight scattering using a laser analyzer DelsaNanoC (Beckman Coulter)and an atomic force microscope Solver-Next (NT-MDT) Surface ofoxides was studied by XPES and STEM (Omicron Multiprob)

High-temperature X-ray studies were performed in the range 30-1200degC in air The rate of heating and cooling was 05degCmin Step of

141

the temperature during heating and cooling was 5deg and 10degCrespectively Exposure in the point was 17s (the time of isothermal delayshooting diffractogram was 150s) For the analysis of diffractionpatterns the software package DIFFRACplus [15] was used

13 Results and discussionThe results of the attestation of the initial and mechanoactivated

oxides are presented in Table 1

Table 1 Treatment conditions and characteristics of the manganeseoxides

Cell parameters Initial phasetreating mode

Finalcomposition аAring сAring

Samplename

1 Mn2O3- initial Mn2O3 9412 M232 Mn2O3- AGO 30s Mn2O3 9410 M23A303 Mn2O3- AGO 60s Mn2O3 9410 M23A604 Mn2O3- AGO

10minMn2O3 9410

M23A10

5 Mn2O3- P4 3min Mn2O3 9403 M23P46 Mn2O3-

P4(3min)+USD(70s)Mn2O3 9403

M23P4U

7 Mn3O4-initial Mn3O4 5760 9474 M348 Mn3O4- AGO 30s Mn3O4 5762 9442 М34А309 Mn3O4- AGO 60s Mn3O4 5762 9431 M34A60

5787 950810 Mn3O4- AGO10min

Mn2O3+ Mn3O4

9410M34A10

11 MnO2-initial MnO2 4396 2869 M1212 MnO2- AGO 30s MnO2+Mn2O3(tr) 4397 2872 М12А3013 MnO2- AGO 60s MnO2+Mn2O3(tr) 4397 2872 M12A6014 MnO2- AGO 10min Mn2O3 9408 M12A10

AGO-High-energy planetary mill (60g) P4-Pulverisette 4 (~20g)USD-Ultrasound disintegrator

Since the analysis of the results of mechanoactivation of oxidesMn2O3 showed little difference between the samples activated in theAGO within 30 and 60 seconds further investigation of oxides Mn3O4

and MnO2 was performed on 60-second samples However it is

142

necessary to note that in the case of oxide MnO2 samples after 30 and60-second milling contained different amounts of Mn2O3

According to X-ray phase analysis data chosen mode ofmechanochemical treatment allowed to preserve essentially thecomposition of the initial oxides The exceptions were oxides MnO2which after grinding contained 5 of oxide Mn2O3 and Mn3O4 whichafter grinding for 10 minutes contained a few of Mn2O3

Data on grain size and the coherent scattering domains arepresented in Table 2 It is obvious that even a relatively weakmechanical treatment leads to a decrease in grain size in 2-3 times Inthis case the comparison of grain size and the CSD (comparison of thedynamic light scattering data and X-ray diffraction (XRD) results)shows that the mechanical treatment with a small degree of deformationallows to obtain defect-free grains while increasing of the centrifugalacceleration leads to the appearance and rise of the defects in the grainA tendency to agglomeration of grains with increasing time of intensemechanoactivation should be noted

Table 2 The characteristics of coherent-scattering domains and averagegrain size

Sample nameCoherent-scattering domain

nmGrain size nm

M23 gt200 1026plusmn95M23A30 30 436plusmn168M23A60 23 344plusmn155M23A10 24 939plusmn175M23P4 44 386plusmn50

M23P4U 44 336plusmn22M34 gt200 400plusmn801300plusmn300

M34A60 15 529plusmn340

M34A10 1913 795plusmn104

M12 gt200 428plusmn78M12A60 61 1133plusmn167M12A10 22 565plusmn343

XRD-dataDynamic light-scattering

data

143

Changes in phase composition during heating and cooling ofinitial and mechanically activated manganese oxides are presented inTables 3-4 and Fig 1-2

Comparison of the temperature behavior of the initial unactivatedoxide Mn2O3 and that of grinded for 3 minutes with a force of less than20g shows that mechanoactivation treatment with a small amount ofcentrifugal factor and short times can save not only the phasecomposition but apparently and generally does not alter the propertiesof the powder While increasing the degree of exposure (eg use of millssuch as AGO-2 with acceleration 60g) even at short times leads to achange in system characteristics (the appearance and growth of defectsredox processes) that affect later on behavior of oxide For examplemechanoactivation treatment leads to a shift of phase transitiontemperaures at thermal processing as well as to change of the structuralcharacteristics of the phases formed In particular to different degrees oftetragonal distortion of hausmannite formed during heating Mn2O3 (Fig4)

Table 3 The phase composition of the initial andmechanoactivated manganese oxides at different temperatures

Heating CoolingSample MnO2 Mn2O3 Mn3O4 Spinel Mn3O4 Mn2O3 Phase

1 2 3 4 5 6 7 8- + 920 1140 1120 - appearanceM23

- 955 1170 1010 + - disappear

- + 950 950 1010 - appearanceM23A30

- 995 1105 730 + - disappear

- + 950 950 1040 - appearanceM23A60

- 1000 1120 840 + - disappear

- + - 950 840 840 appearanceM23A10

- 1000 - 290 + 770 disappear

- + 940 1140 1120 - appearanceM23P4

- 980 1165 1080 + - disappear

- + 935 1140 1120 - appearanceM23P4U

- 980 1170 1050 + - disappear

144

1 2 3 4 5 6 7 8

- 685 + 1125 1090 - appearanceM34

- 945 1160 1010 + - disappear

- + appearance370

655

970 1050 -

disappear

900 appearance

M34A60

-

970

1130

880 + -

disappear

- + + 930 880 - appearanceM34A10

- 1005 655 600 + - disappear

+ 550 950 1155 1120 870 appearanceM12

595 1025 1170 1070 + + disappear

+ + 940 985 1110 750 appearanceM12A60

535 985 1165 840 + + disappear

- + 960 960 1000 790 appearanceM12A10

- 1005 1075 630 + + disappear

Table 4 The temperature boundaries of the phases during heating andcooling

Heating CoolingSample Phase

from to from to

1 2 3 4 5 6

Mn2O3 30 955 - -

Mn3O4 920 1170 1120 30

M23

Spinel 1140 1200 1200 1010

Mn2O3 30 995 - -

Mn3O4 950 1105 1010 30

M23A30

Spinel 950 1200 1200 730

Mn2O3 30 1000 - -

Mn3O4 950 1120 1040 30

M23A60

Spinel 950 1200 1200 840

Mn2O3 30 1000 840 770

Mn3O4 - - 840 30

M23A10

Spinel 950 1200 1200 290

145

1 2 3 4 5 6

Mn2O3 30 980 - -

Mn3O4 940 1165 1120 30

M23P4

Spinel 1140 1200 1200 1080

Mn2O3 30 980 - -

Mn3O4 935 1170 1120 30

M23P4U

Spinel 1140 1200 1200 1050

Mn2O3 685 945 - -

Mn3O4 30 1160 1090 30

M34

Spinel 1125 1200 1200 1010

Mn2O3 370 970 - -

Mn3O4 30 655

Mn3O4 900 1130

1050 30

M34A60

Spinel 970 1200 1200 880

Mn2O3 30 1005 - -

Mn3O4 30 655 880 30

M34A10

Spinel 930 1200 1200 600

MnO2 30 595 - -

Mn2O3 550 1025 870 30

Mn3O4 950 1170 1120 30

M12

Spinel 1155 1200 1200 1070

MnO2 30 535 - -

Mn2O3 30 985 750 30

Mn3O4 940 1165 1110 30

M12A60

Spinel 985 1200 1200 840

Mn2O3 30 1005 790 30

Mn3O4 960 1075 1000 30

M12A10

Spinel 960 1200 1200 630

146

a d

be

c fFig 1 The temperature boundaries of the phases during heating and coolingof initial and mechanoactivated Mn2O3 a - original b - M23P4 c -M23P4U d-M23A30 e-M23A60 f-M23A10

147

a

b

cFig 2 The temperature boundaries of the phases during heating and cooling of

initial and mechanoactivated Mn3O4 a-initial b-M34A60 c-M34A10

148

a

b

cFig 3 The temperature boundaries of the phases during heating and cooling ofinitial and mechanically activated MnO2 a - initial b - M12A60 c - M12A10

149

Fig 4 Temperature dependence of the degree of hausmannite tetragonaldistortion for samples with different prehistories

The growth of the crystallite size of mechanoactivated phase withtemperature is shown in Fig 5 Data are shown for the initial phasebelow the temperature of the corresponding phase transition

It is obvious that prolonged treatment in the high-energy millalmost did not give reduction of coherent scattering domains butessentially affected the thermal stability of investigated oxide

150

Fig 5 Temperature dependences of coherent scattering domain size in oxideMn2O3 with varying degrees of mechanoactivation

ConclusionThe main results of investigations are the followingI The conditions of mechanochemical treatment enabling to make

the transfer of Mn-O system to single-phase nanosized state withoutsignificant changes in composition of the initial oxide are found Theexception was oxide MnO2 which after grinding contained a smallamount of oxide Mn2O3

II It is shown that the use of mill of the type AGO-2 with 60gacceleration even at short times of activation treatment of oxides leadswhile maintaining the single-phase of sample to an appreciable changeof lattice parameters growth of stresses and the appearance of defects

III It is found that despite the relaxation character of the evolutionof these metastable structures in the face of rising temperatures there is ashift of phase transition temperatures and changes in structuralcharacteristics of the newly formed phases in comparison with the initialoxides Including marked changes in the parameters of the JT strain (ca

151

- 1) at high-temperature transitions between cubic and tetragonal phasesof oxide Mn3O4

IV It is shown that more prolonged mechanical activation ofoxides MnnOm activates redox processes in these materials theemergence of two-phase states with different degrees of oxidation andeven a complete change of the manganese oxidation degree

V The temperature boundaries of existence of phases duringheating and cooling were determined for the initial andmechanoactivated oxides MnnOm Not only noticeable quantitativedifferences in the position of phase boundaries but also qualitativedifferences in the constructed phase state diagrams were found

This work was supported by RFBR (grant 10-03-96016-p_ural_a) the Program of fundamental research of Presidium ofRussian Academy of Sciences N 27 ldquoFoundations of fundamentalresearch of nanotechnology and nanomaterialsrdquo and the Federal TargetProgram Scientific and scientific-pedagogical staff of innovationRussia (contract 02740 110641)

References1 Glezer AM Blinov EN Pozdnyakov VA Martensitic

transformations in microcrystalline ferro-nickel alloys Izvestiya Aseries of Physical 2002 V66 N9 pp1263-1275

2 Andrievsky PA RAGULYA AV Nanostructured materialsMoscow Academy 2005 192p

3 Polotai AV Ragulya AV Skorohod VV Nanocrystalline BaTiO3

synthesis sintering and size effect Science o Sintering CurrentProblems and New Trends Beograd Kluwer Academic Publishers2003 pp119-125

4 PAyyub VRPalkar SChattopadhyay et al Effect of Crystal SizeReduction on Lattice Symmetry and Cooperative Properties PhysRev B 1995 V51 N9 pp6135-6138

5 Parathasarathi Mondal Dipten Bhattacharya Pranab ChoudhuryDielectric anomaly at orbital order-disorder transition inLaMnO3+ J Phys Condens Matter 2006 V 18 p6869

6 Nandini Das Parathasarathi Mondal Dipten BhattacharyaPartical size dependence of orbital order-disorder transition inLaMnO3 Phys Rev B 2006 V74 p 014410

152

7 VYa Shevchenko OL Khasanov GS Yuriev etc The coexistence ofcubic and tetragonal structures in the nanoparticle of ZrO2Y2O3

oxides Neorg Mater 2001 V37 N9 pp1117-11198 AYa Fishman MA Ivanov SA Petrova et al Specific Features of

Jahn-Teller Structure Phase Transitions in NanocrystallineMaterials Defect and Diffusion Forum 2009Vols 283-286 pp53-58

9 Grigorieva ТF Barinova AP Lyakhov NZ Some features of themechanical alloying in the systems Cu-Bi and Fe-Bi J Metastableand Nanocryst Mater 2003 V15-16 pp475-478

10 Lyakhov N Grigorieva T Barinova A Lomaeva S Yelsukov EUlyanov A Nanosized mechanocomposites and solid solution inimmiscible metal systems J Mater Sci 2004 V39 N 16-17pp5421-5423

11 Zyryanov VV Journal of Structural Chemistry 2004 V45 pp135-143

12 Zyryanov VV Lapina OB Neorg Mater 2001 V37 N3 pp331-337

13 Zyryanov VV Sysoev VF Boldyrev VV Korosteleva TVCertificate of authorship of USSR N 1375328-BI-1988 N 7 p39

14 Fishman AYa Ivanov MA Petrova SA Zakharov RGStructural Phase Transitions in Mechanoactivated ManganeseOxides Defect and Diffusion Forum 2010 Vols 297-301 pp 1306-1311

15 DiffracPlus TOPAS Bruker AXS GmbH OstlicheRheinbruckenstraszlige 50 D-76187 Karlsruhe Germany 2008

118

EFFECT OF HARDENING TEMPERATURE ON THE STRUC-TURAL-MORPHOLOGICAL CHARACTERISTICS OF METAL

CEMENTS BASED ON MECHANOSYNTHESIZED COPPERCOMPOUNDS

NZ Lyakhov1 PA Vityaz2 SA Kovaleva2 TF Grigoreva1VG Lugin3 AP Barinova1 SV Tsybulya4

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS630128 Novosibirsk Kutateladze str 18 grigsolidnscru

2 United Institute of Mechanical Engineering NAS Minsk Belarus3 Belarussian State Technological University Minsk Belarus

4 G K Boreskov Institute of Catalysts SB RAS Novosibirsk Russia

IntroductionMetal cements may be used in many branches of industry due to

good adhesion to the materials of different types (glass ceramics metalsetc) and the metal character of thermal and electric conductivity Theformation of metal cements occurs through the interaction of copper(nickel) alloys with liquid metals and alloys Interactions of a solid metalwith liquid one in particular copper with gallium are known [1 2] tohave diffusion character they are substantially affected by temperatureand the area of contact between the reagents

The use of mechanically synthesized copper compounds allowsone to increase the contact surface between the components and to intro-duce doping elements (Bi In) that improve wettability during gluing andthe strength properties of the alloys to be formed This causes a changeof the kinetics of interaction between a solid metal and a liquid one dueto the acceleration of diffusion processes and due to the formation ofadditional phases

The goal of the present work is investigation of the effect of hard-ening temperature on the structural-morphological characteristics ofmetal cements obtained on the basis of CuBi mechanocomposites andsupersaturated solid solutions Cu(In)

Methods and materialsCopper powder PMS-1 (GOST 4960ndash75) granulated bismuth (TU

6-09-3616ndash82) indium (GOST 10297ndash94) were used in the work Me-chanical activation of the powders was carried out for 15 min in the

119

high-energy ball planetary mill AGO-2 with water cooling in argon at-mosphere (cylinder volume 250 cm3 ball diameter 5 mm loaded wt200 g the weighed portion of the sample under treatment 10 g the fre-quency of rotation of the cylinders around the common axis about 1000rpm) Mechanocomposites having the composition Cu 10 wt Bisolid solutions Cu-12 wt In were obtained [3] Diffusion-hardeningalloys were prepared by mixing the mechanosynthesized copper com-pounds with gallium melt followed by exposure at a temperature of 20C during the whole process of alloy formation To study the effect oftemperature on the structure and morphology of metal cements harden-ing was carried out at 90 С 120 С and 160 С

Surface examination was carried out with the NT-206 atomicforce microscope (Microtestmachines Gomel) using standard commer-cial V-type probes NSC11 (Mikromasch) in the contact mode

The structure of the resulting samples was studied using Mikro200 optical microscope and high-resolution scanning electron micro-scope (SEM) MIRATESCAN with an attachment for micro-X-ray spec-tral analysis (MXSA) The diameter of the electronic probe was 52 nmexcitation region was 100 nm Images were obtained in the mode of re-cording secondary and backward scattered electrons which allowed usto investigate the distribution of chemical elements over the surface andto establish its composition non-homogeneity

The phase composition of powders after mechanical activationand the final products of their interaction with liquid gallium were de-termined with the help of X-ray diffraction techniques X-ray structuralanalysis and semi-quantitative examination of the products were carriedout with the D8 Advance Bruker diffractometer (Germany) by means ofpowder X-ray diffraction in the θ-2θ configuration with a step of 01Phase identification was performed using the diffraction patterns re-corded in CuKα radiation (154051 Aring)

Calorimetric measurements were carried out with Netzsch STA409 PCPG instrument in argon atmosphere in a crucible made ofAl2O3 within the temperature range from room temperature up to 290 Cwith the heating rate of 20 min

120

Results and discussionIt was established in the previous diffraction studies of alloy for-

mation dynamics in CuBi + Ga and Cu(In)+Ga that the formation ofnew phases takes place within a broad time interval During the interac-tion of CuBi mechanocomposite in Bi that is insoluble in copper and ingallium the formation and crystallization of the intermetallic compoundCuGa2 and bismuth take place simultaneously [4]

For the case of Cu(In) solid solution in which the doping elementis soluble in gallium the formation of the phase of solid solution of in-dium has an incubation period of about 210 minutes which is determinedby its concentration in the system with gallium [5]

The interaction processes are described with the following chemi-cal reactions

CuBi + 2 Ga rarr CuGa2 + BiCu(In) + 2 Ga rarr CuGa2 + In(Ga)

1 Effect of the temperature of interaction of CuBimechanocomposites with liquid gallium on the structure andmorphology of the formed metal cementsIt is known that the resulting mechanocomposites are nanosized

copper surrounded by a thin bismuth layer [6] Bismuth is mainly com-posed of the particles less than 5 nm in size

According to the data of AFM topography the size of mechano-composite particles is 150divide250 nm (Fig 1)

Fig 1 Mechanocomposite Cu + 10 wt Bi after activation for 15 mina ndash SEM image b ndash AFM c ndash TEM

121

At first we studied the interaction of CuBi with liquid gallium atroom temperature

The X-ray structural analysis of the resulting cement carried outafter the interaction for 4 and 48 hours showed that the size of the crys-tallites of the intermetallic compound increases from ~ 200 nm to ~ 550nm The size of bismuth crystallites increases up to 100 nm It should benoted that this is accompanied by a decrease in the size of copper crys-tallites down to ~ 10 nm The final phase composition is determined asCuGa2 Bi and unreacted copper (Fig 2)

Fig 2 Diffraction patterns of the product of interaction Cu 10 Bi + Ga

Figure 3 shows the high-resolution SEM images of the micro-structure of the surface of the final interaction product The SEM imageof sample surface after hardening without the mechanical treatment ofthe surface is shown in Fig 3a The image of the surface obtained in thebackward scattered electrons after sample polishing is shown in Fig 3bBecause bismuth is the heaviest element in this system it will be distin-guished by the maximal brightness in the SEM image

The data obtained by means of microscopy show that the structureof the surface of final product is facetted tetragonal crystals СuGa2 withthe size up to 4 μm Bismuth is localized at the faces of crystals and at

122

the boundaries of CuGa2 grains as disperse formations 70-250 nm insize and also forms separate grains with a size up to 10 μm

a bFig 3 Topography of the surface of CuGa2 +Bi alloy after the interaction for48 hours a ndash SEM image of non-polished sample in direct electrons b ndash SEM

image of the polished sample in backward-scattered electrons

The use of AFM allowed us to study the microstructure of facet-ted tetragonal CuGa2 crystals The presence of screw dislocations inthem may be stressed as a result the crystalline layer grows by windingcontinuously on itself so the step takes the shape of a spiral (Fig 4) Thelayer-by-layer growth of crystallographic facets should also be men-tioned The edges of incomplete layers or steps move along the facetwhile they grow The step height that is the thickness of the depositinglayer varies within the range 4 to 200 nm The appearance of highgrowth steps may cause trapping of the melt drops and precipitation ofinsoluble bismuth admixture on the surface of steps of the growing crys-tals which is indeed observed in Fig 4 b Bismuth is adsorbed on facetssteps and along the grain boundaries

It should be stressed that the growth of faceted crystals requiresspecial conditions supersaturation or supercooling of the mother me-dium small number of appearing nuclei We suppose that the localthermal supercooling arises as a consequence of the chemical interactionof copper with gallium melt on the interface between the solid phase andthe liquid one with the formation of chemical compound CuGa2 withcrystallization temperature higher than the temperature of the melt Theconditions of substantial supercooling are created for this compound soits crystallization starts In this process bismuth particles get released

123

into the melt Thee particles are insoluble in liquid gallium and may actas the centres of crystallization and also they may brake down thegrowth of intermetallide particles by getting adsorbed on their surfaceThe latent heat of melting released during crystallization raises the tem-perature of the melt (so gallium remains in the liquid state during reac-tion at 20 C) and decreases the degree of overcooling thus creating theconditions for the growth of larger facetted intermetallide crystals fromthe melt

а b

Fig 4 AFM image of the surface of resulting alloy CuGa2 + Biа - Torsion-image of bismuth on facets and growth steps of CuGa2 (the contrastis formed due to the difference in tribological characteristics of the phases of

intermetallide and bismuth) b ndash layered spiral growth of CuGa2 crystals alongthe screw dislocation (marked with arrows) The upper part shows a scheme ofcrystal growth along the screw dislocation and the shape of the step formed inspiral growth [7]

At room temperature the final product of the interaction of CuBimechanocomposite with liquid gallium is a matrix composed of CuGa2

intermetallide particles 1ndash4 μm in size with bismuth particles distrib-uted in it (from 70 to 250 nm) which form local agglomerations up to 10μm in size

X-ray studies of the alloys obtained at hardening temperature of90 and 120 C showed that an increase in temperature to 120 C does notaffect the phase composition Similarly to the case of room temperature

124

the product is composed of intermetallide CuGa2 (PDF-2 No 25-0275)bismuth (PDF-2 No 44-1246) and residual copper (PDF-2 No 04-0836)(Fig 5)

Fig 5 Diffraction patterns of CuGa2 + Bi samples obtained at temperature 40(a) 90 (b) and 120 (c) C Unmarked peaks relate to CuGa2 intermetallide

With an increase in the interaction temperature the lattice pa-rameters of copper and CuGa2 phases remain almost unchanged Thesize of copper crystallites is about 35 nm Bismuth undergoes tempera-ture-caused changes An increase in the size of bismuth crystallites from100 nm at 20 C to 180 nm at 90 C and to more than 500 nm at 120 C

Alloys obtained by mixing the CuBi mechanocomposite with liq-uid gallium have a composite structure after hardening Their structuremay be described as an intermetallic shell with the unreacted part ofcopper in its centre The СuGa2 intermetallide has a shape of facetedtetragonal crystals up to 4 μm in size With an increase in reaction tem-perature to 90 C the size of het particles of intermetallic compund in-creases to 6-8 μm and remains almost the same at a temperature of 120C In the lateral contrast mode the facets of crystals obtained at 90 and120 C exhibit local accumulations of bismuth as well as substantial de-formation distortions of crystals due to the arising stretching strain inthe crystal in the direction lt001gt (Fig 6) Intermetallide crystal starts to

125

have layered structure The facets of the intermetallide obtained at ele-vated temperatures also exhibit deformation distortions that are likelyconnected with bismuth adsorption on the facets The appearance ofthese lines is due to the development of local fluidity They arise in thecases when the material possesses a distinct yield point even insignifi-cant concentration of strain promotes the appearance and developmentof these figures [8] Change of the straight character of the glide lines islikely to be connected with the effect of boundary volumes intra-grainstructural strain caused by differences in the volumes of the intermetal-lide and bismuth as well as by glide in different systems and with thetransition from one system to the other

а

b

Fig 6 AFM images of CuGa2 + Bi alloys obtained at a temperature of 90 (a)and 120 (b) С

126

Metallographic in-vestigation of the alloysurface after polishing(Fig 7) showed that thenumber of macrodefectssuch as pores and discon-tinuity flaws decreaseswith an increase in crystal-lization temperature Mi-crohardness of the inter-metallide increases fromHV 70 to 125

Investigation of thedistribution of chemicalelements over the sampleby means of SEM involv-ing X-ray spectral analysisrevealed nonuniformity ofthe distribution of insolu-ble bismuth

Bismuth is not ob-served in the regions withthe intermetallic com-pound which may be con-nected with the fine distri-bution of disperse particlesover the boundaries of theintermetallide Local ac-cumulations of bismuth upto 10 μm in size are ob-served mainly in the siteswhere macrodefects (poresgrain boundaries) get ac-cumulated With an in-crease in the temperature ofinteraction up to 120 Сthe number of local bis-muth accumulations de-

а

b

cFig 7 Optical images of the structure of

CuGa2 + Bi alloys obtained at 20 (a) 90 (b)and 120 (c) С

127

creases but their size increases to 20 μm (Fig 8)

а b

Fig 8 SEM images (in backward scattered electrons) of CuGa2 + Bi alloyHardening temperature а ndash 20 С b ndash 120 C

Thermal investigation of the alloys with different hardening tem-perature points showed that the curves of differential scanning calo-rimetry (DSC) exhibit definite differences only during heating the alloyswith hardening temperature 20 C and 90 C The DSC curves of the al-loys with hardening temperature 90 and 120 С are identical Duringheating the alloy with hardening temperature 20 С exhibits the exother-mal heat effect at a temperature of 120-150 С This effect may be con-nected with the occurrence of recrystallization processes in bismuthThis exo-peak is absent during the repeated heating

Thus investigation showed that an increase in the temperature ofthe interaction of CuBi mechanocomposite with liquid gallium leads toan increase in the size of the formed intermetallide as well as to a de-crease in macrodefects in the form of pores discontinuity flaws cracksThe hardness of the intermetallide thus increases

2 Effect of the temperature of interaction of mechanochemi-cally prepared solid solution Cu (In) with liquid gallium onthe structure and morphology of metal cementThe use of mechanochemically prepared powders of Cu-In system

as the solid phase in the reactions with liquid gallium increases the num-

128

ber of interacting systems due to the solubility of indium in gallium Ac-cording to the state diagram of the system GandashIn [9] the solubility of Inin Ga in the solid state is less than 03 at while the solubility of Ga inIn is 31 at At a temperature of 60 С indium may be dissolved in liq-uid gallium up to 48 wt

Mechanochemically synthesized powder in the system Cu + 12wt In was used as the initial solid-phase component The X-ray phaseanalysis of the products of mechanochemical synthesis (Fig 9) showedthat the solid solution of indium in copper in formed during mechanicalactivation of copper powder with 12 wt indium As a result the latticeparameter of copper increases to а = 36659 Ǻ (аref = 36150 Ǻ) The size of copper crystallite is about 30 nm

Fig 9 X-ray diffraction patterns of the powder Cu-12 wt In after mechanicalactivation (for 20 min) in argon

Mechanical activation of the system Cu + 12 wt In leads to theformation of fine particles of the solid solution of indium in copper (150ndash 230 nm) (Fig 10) Recrystallization of the solid solution of copper andthe formation of grains larger than 15 μm are also possible

129

Fig 10 Topography of the ultrafine powder of the solid solution Cu(In)

A decrease in the size of precursor powder is known to providelarger area of contact between the components of the solid phase and theliquid one and therefore shorter diffusion distances during subsequentinteractions with metal melts Because both copper and nickel are solu-ble in liquid gallium one may expect that the rate of dissolution of themechanocomposites of the system Cu-In would be significant

X-ray phase analysis of the final products of the interaction of thesolid solution Cu(In) with gallium at room temperature revealed thepresence of three phases intermetallide CuGa2 indium and unreactedcopper (Fig 11)

Fig 11 Diffraction patterns of the alloys obtained through the interac-tion of Cu 12 wt In + Ga CuGa2 - In - Cu

130

For the initial powder with indium concentration 12 wt theproduct of the interaction exhibits a decrease in the indium unit cell pa-rameter с in the alloy under formation to с = 49306 Ǻ (cref = 49459 Ǻ) The size of copper crystallites is about 7 nm while the size of indiumcrystallites is about 30 nm Slight changes in the unit cell volume of in-dium may be related to the formation of the solid solution of gallium inindium

During the interaction indium gets dissolved in the liquid phaseof gallium gets concentrated and crystallizes at the interfaces betweenthe solid phase and the liquid one The alloys with the 12 indium con-tent are characterized by a large range of the dimensions of tetragonalparticles of the intermetallic compound CuGa2 (from 05 to 8 μm) TheAFM image (Fig 12) exhibits coarse crystals their crystallographicshape is uncharacteristic of the intermetallide CuGa2 Comparing the X-ray data and the results of AFM we may assume that they are a solidsolution of gallium in indium

Fig 12 AFM topography of the surface of CuGa2+ In(Ga) alloy

A decrease in the AFM scanning pitch and simultaneous acquisi-tion of the image of distribution of normal (topography) and lateral (tor-sion) forces allowed us to distinguish the structural features of the phaseof the solid solution of gallium in indium (Fig 13) A specific distin-guishing feature is the presence of strands in the crystals of the solid so-lution of gallium in indium connected with layering of the solid solutioninto the regions with larger and smaller concentration of the componentwhich is well seen in the image of torsion (Fig 13b) The size of separate

131

grains of the solid solution of gallium in indium reaches more than 10μm

Fig 13 AFM topography of the surface of samples of CuGa2+ In(Ga) alloy (а)image of torsion (b)

Fig 14 The SEM image in direct (а) and back-scattered electrons (b) of thealloy CuGa2+ In(Ga) In the upper part the data chart of the quantitative spec-

tral analysis carried out in the indicated points

To investigate the microstructure of the surface of alloys we car-ried out the examination with the scanning electron microscope and ob-tained the images of the surface of resulting alloy for the interaction Cu12 wt In + Ga in direct (Fig 14а) and back-scattered (Fig 14 b) elec-trons The application of imaging in back-scattered electrons allow one

132

to investigate the composite surface non-uniformity with which the in-tensity distribution over the image depends on the atomic number of anelement One can see in Fig 14 b that the contrast in the BSE images isdetermined by the topographic features of the surface and the distribu-tion of intensities is uniform In addition local X-ray spectral analysiscarried out in different points of the alloy surface revealed the presenceof indium in concentrations 01 to 7 This fact allows us to concludethat indium is present on the surface of CuGa2 intermetallic crystals inthe form of thin films

Another characteristic feature of the surface of samples obtainedin the interaction of solid solutions Cu(In) with liquid gallium is thepresence of fine dispersed formations on the surface of crystals andgrains of CuGa2 that are more clearly seen in the AFM images (Fig 13a) and are detected in the SEM images (Fig 15 b) The formation of thestructures of this kind on the surface of the intermetallide may be con-nected with indium crystallization on the surface of the growing crystals

Fig 15 AFM (a) and SEM images (b) of the face of CuGa2 intermetallic ob-tained by the interaction of Cu 20 In + Ga

So on the basis of X-ray spectral data obtained and the results ofAFM and SEM we may assume that indium gets crystallized not only inthe form of large grains of the phase of the solid solution of gallium inindium but also on the faces of the intermetallide thus forming a nano-meter-sized film of indium about 10 nm thick

133

In order to establish the effect of temperature on the structure andmorphology we carried out alloy hardening at temperature of 60 120and 160 C

X-ray structural investigation of the final phase composition (Fig16) of the alloys showed that no changes in the phase composition of themetal cement are observed with an increase in hardening temperature to160 C The parameters of intermetallic compound CuGa2 remain almostunchanged The values of lattice parameters of the indium phase underformation are also insignificantly differing from the reference ones

Fig 16 Diffraction patterns ofCu-In-Gа samples obtained at

different temperatures

Investigation of the microstructure of alloys obtained at 20 Cshowed that indium is well adsorbed on the surface of intermetallidecrystals and crystallizes not only as separate crystals of the solid solutionof gallium in indium but also as the film formations with grained anddendrite structure on the faces of the intermetallide The occurrence ofintercrystal films of indium or the solid solution of indium may be re-sponsible for a decrease in strength characteristics of the alloy and be areason of both the intra-crystal and inter-crystal fractures (Fig 17 b) It

134

is assumed that an increase in hardening temperature causes substantialformation of the film structures of the solid solution of indium

The AFM investigation of the topography of alloys obtained attemperatures 90-160 C showed that the alloys are characterized by alarge size range of the intermetallic compound CuGa2 At the interactiontemperature of 20 C the size of CuGa2 particles was 05 to 8 μm Withan increase in reaction temperature to 90 C the crystal size increases upto 11 μm Crystal concretions are also formed (Fig 17) One can see inFig 17 b that cracks are formed in the grain plastoelastic deformationson the intermetallide face occur which is likely to be due to the differ-ence in interfacial surface tension of the intermetallide and indium film

ab

Fig 17 AFM image of the surface of CuGa2 + In(Ga) alloy obtained at 90 C a- topography b ndash distribution of lateral forces (arrows show cracks deforma-

tion distortions)

At a temperature of 120 and 160 C the contrast of the surface re-lief decreases due to the formation of a continuous film (Fig 18) on thesurface

Investigation of the phase transitions in the alloys was carried outby means of DSC For heating the products of the interaction betweenthe solid solution of indium in copper and liquid gallium at a rate of30Cmin an endothermic effect is observed on the DSC curves of all thealloys at a temperature about 254 C and an exothermic effect at 290 Con cooling the exothermic peak appears at a temperature of 210-220 С

135

а b

Fig 18 AFM topography of the CuGa2 + In(Ga) alloy a ndash 120 C b- 160 C

According to the Cu-Ga state diagram these effects are connectedwith the peritectic transformations of the main phase of intermetallideCuGa2 during heating and cooling The cooling curves exhibit no ther-mal effect due to the phase transition of indium The DSC curve of thealloy obtained at 20 C contains an endothermic peak at about 130 Cwhich gives much smaller heat effect in the second heating cycle Tak-ing into account the fact that the formation of indium films and the solidsolution of indium with the grained and dendrite structures occurs on thesurface of the intermetallide it may be assumed that heating to 130 C isaccompanied by melting of the indium film (taking into account a de-crease in melting temperature for thin films) [10] and the solid solutionIn(Ga) At the temperature of the peritectic transformation 254 C in-dium gets dissolved in the formed liquid Ga(Cu) with subsequent for-mation of the ternary compound Cu-Ga-In during cooling For coolingthe temperature of the peritectic reaction for the obtained compound de-creases to 210-220 C

ConclusionAs a result of the investigation of the structure and morphology of

metal cements prepared on the basis of mechanosynthesized coppercompounds CuBi and Cu(In) the structure and morphology in the reac-tions with liquid gallium are determined by the degree of interaction of

136

the doping component with gallium In the case of the CuBi mechano-composite in which Bi does not interact with gallium an intermetallidewith particle size up to 4 μm and local accumulations of bismuth areformed With an increase in hardening temperature to 120 C intermetal-lide growth to 8 μm occurs

When using the solid solutions Cu(In) in which indium is solublein liquid gallium and the incubation period for the crystallization of thesolid solution In(Ga) the formed particles of intermetallide CuGa2 havea broad size range from 05 to 8 μm With an increase in hardening tem-perature to 160 C the size of intermetallide particles increases to 11 μmredistribution of indium occurs along with an increase in the number ofits film structures that are formed on the faces of the intermetallide andcause a decrease in its strength properties thus providing intra-crystaland inter-crystal fracture A decrease in the melting temperature for in-dium to 130C and a decrease in the heat effect at this temperature in thealloys obtained at the alloy formation temperature of 90 120 and 160 Cmay be connected with an increase of indium film amount

The work is carried out under the Integration Project of SB RASNo 138 and BRFFI Т09СО-014 laquoDevelopment of Fundamental Basisof the Action of Activation on Regulation of the Processes of Interactionof Solid Metals and Their Comopunds with Metal Melts for the Purposeof Obtaining Functional Materials with Required Structure and Proper-tiesraquo

References1 Tikhomirova OI Ruzinov LP Pikunov MV Marchukova ID

Investigation of mutual diffusion in the system gallium ndash copperFiz metallov I metallovedenie 1970 vol 29 issue 4 p 796-802 (inRussian)

2 Glushkova LI Konnikov SG Interaction between components inthe solder paste based on gallium Pressure treatment of metals andwelding Proceedings of the Leningrad Polytechnical Institute1969 No 308 p 205-208 (in Russian)

3 Grigorieva TF Barinova AP Lyakhov NZ Mechanochemicalsynthesis in metal systems Novosibirsk 2008 (in Russian)

4 Ancharov AI Grigorieva TF Barinova AP Lyakhov NZ Investi-gation of the interaction of liquid metals with nanocomposites by

137

means of diffraction of the synchrotron radiation Nuclear Instru-ments amp Methods in Physics Research 2007 v A 575 p 130-133

5 Ancharov AI Grigorieva TF Tsybulya SV Boldyrev VVNeorganicheskie Materialy 2006 V 42 No 9 p 1164-1170 (inRussian)

6 N Lyakhov T Grigorieva A Barinova Nanosized mechanocom-posites and solid solution in immersible metal systems Journal ofmaterials science 39(2004) 5421-5423

7 Chernov AA Crystallization processes Modern CrystallographyMoscow 1980 vol 3 p 5-12 (in Russian)

8 Bernshtein ML Zaymovsky VA Mechanical properties of metalsMoscow Metallurgy 1979

9 State diagrams of binary metal systems Ed by NP Lyakishev1997 vol 2 p 636ndash637 (in Russian)

10 Gromov DG Gavrilov SA Redichev EN Klimovitskaya AVAmmosov R M Factors determining melting temperature of thinfilms of Cu and Ni on inert surfaces Zhurnal Fizicheskoy KhimiiV 80 No 10 2006 p 1856-1862 (in Russian)

104

ZINC IONS REDUCTION ON SOLID METAL ELECTRODES INCHLORIDE MELTS

Alex Lugovskoy 1a Zeev Unger 12b Michael Zinigrad 1cDoron Aurbach 2d

1Material and Chemical Engineering Department Ariel UniversityCenter of Samaria Ariel 40700 Israel

2Department of Chemistry Bar-Ilan University Ramat-Gan 52900Israel

alugovsaarielacil bzevikitoarielacil сzinigradarielacildaurbachmailbiuacil

keywords electrodeposition chloride melts cyclic voltammetry high-temperature electrochemistry

AbstractThe reduction of zinc ions on solid tungsten and platinum

electrodes in chloride melts at the temperatures 700 ndash 750 degC wasstudied by cyclic voltammetry chronoamperometry and energydispersion spectroscopy It was established that no zinc is reduced onplatinum electrodes As for the reduction of zinc ions on tungstenelectrodes the process has a complex character it starts as anirreversible two-electron zinc ion reduction and after the new phase isformed the process of saturation of the electrode surface with lithium orsodium begins As the second process develops the alkaline metalbecomes essentially the only constituent on the electrode surface

GeneralSince zinc is industrially recovered from sulfate solutions rather

than from melts and because its melting temperature (4195 degC) is lowerthan the temperatures of most molten chloride compositions thereduction of zinc ions on solid electrodes in chloride melts has beeninvestigated relatively poorly There are quite a few papers devoted tothe electrolysis of zinc containing chloride melts (1 2) and these coveronly some details of the electrochemistry of this metal However zinc isnot only an engineering metal It can often be a component of moltenchloride systems in which various processes of synthesis or purification

105

are performed Therefore the detailed electrochemical behavior of zinccan be of great importanceThe study of electro-reduction processes of zinc ions on solid tungstenand platinum electrodes in eutectic NaCl ndash KCl and LiCl ndash KCl melts inthe temperature range of 700 ndash 750 degC is presented in this work Thesetemperatures are somewhat higher than the eutectic points of NaCl ndashKCl (646 degC ) and LiCl ndash KCl (628 degC) and the melts are thereforeliquid enough to be used in technologically important processes oflanthanides and actinides separation reduction and rectification On theother hand these temperatures are significantly lower than the boilingpoint of zinc (907 degC) and there is essentially no loss of the metal due toevaporation

ExperimentalThe electrochemical experiments were performed using a three-

electrode cell made of sintered alumina placed in an alumina crucibleunder nitrogen atmosphere Tungsten (9995 1 mm diameter) andplatinum wires (9995 05mm diameter) were used as the workingelectrodes and their surface area was controlled by immersion depth(typically 6ndash12mm) and by measuring their diameter before and aftereach experiment A 1mm tungsten wire served as a pseudo-referenceelectrode and a flat spiral tungsten wire set perpendicular to theworking and reference electrodes close to the bottom of the cell servedas the counter electrode The area of the counter electrode was ~ 20 foldas large as that of the working electrode ZnCl2 LiCl NaCl and KCl(990 +ACS grade Alfa Aesar) were used for the preparation meltswithout further purification

Zinc chloride was mixed with alkaline metals chlorides usingmortar and pestle in a glove-bag in dry nitrogen atmosphere Themixture was then placed into a crucible the electrode cell was mountedand transferred into the furnace (single-zone Carbolite 1600 degC STF tubefurnace) In the furnace the mixture was first dried under vacuum at 40ndash50 degC for an hour After completing the drying dry nitrogen wasbubbled through the electrolyte during its heating up to the temperatureof the experiments (700ndash750 C) for another hour The temperature wascontrolled by a type S thermocouple placed next to the cell andprotected by an alumina capillary thus maintaining a precision of plusmn1 degCin measuring and controlling the temperature Dry nitrogen atmosphere

106

(1 bar) was maintained in the furnace during the measurements and thepost-experimental cooling The electrochemical measurements werecarried out using an Autolab PGStat-12 potentiostat SEM images andelement analysis by EDS were performed with a SEM system fromJEOL Inc Model JSM 7000F

Results and discussion

Deposition of zinc on a tungsten electrodeSome typical voltammograms for the electrochemical reduction ofZn(II) are shown in Fig 1

-02

-01

0

01

02

03

04

-1 -05 0

iA

cm

2

E V vs W

C

A

QaQ

c~ 1

0502005 Vsec

-0680-0650-0600E

p V

(peak C)

164141110Qc Ccm

2

177150113Qa Ccm

2

Fig 1 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0163 mol L) in equimolar NaCl-KCl melt on a W electrode at 700degC Scanrates are 50 mV sec (solid line) 200 mV sec (slashed line) and 500 mV sec(dotted line) Each charge density was calculated as the sum of areas limited bythe baseline and the appropriate current density curves for the forward andbackward semi-cycles

107

As follows from Fig 1 a single cathodic peak C corresponds toone anodic peak A The potential shape and behavior of the cathodicpeak are typical for the metal deposition on a solid electrode (2-4) Nodifference is observed between the reduction of zinc ions in NaCl ndash KCland in LiCl ndash KCl melts Peak A is assigned to the reoxidation of zincBoth peaks are clearly not independent on the scan rate Rather peak Cis shifted to more negative potentials and peak A moves to more positivepotentials as the scan rate increases The dependence of the cathodicpeak potential on the scan rate is shown in Fig 2 Such voltammetricresponse is typical for irreversible processes

055

06

065

07

075

0 01 02 03 04 05 06

-Ep

V

Vs

Fig 2 Dependence of the cathodic peak potential on the scan rate for thereduction of Zn2+ (0163 mol L) at 710degC on a W electrode

The cathodic peak C appears at about -06 V vs tungsten electrodefor the scan rate of 50 mVsec and at -07 V for 500 mVsec Such asignificant shift is a clear indication that the process is irreversible Thecathodic peak not only is shifted as the scan rate grows but it becomes

108

broader so that the difference |Ep ndash Ep2| grows from 01 V for 005 Vsecto 015 V for 05 Vsec Values of n calculated by equation 23 are inthe range of 156 for low scan rates to 104 for high scan rates The mostlogical interpretation of this finding is that the charge-transfer is of two-electrons which is not surprising in the case of Zn2+ ions reduction Thevalue of is then 078 for 005 Vsec and 052 for 05 Vsec This isevident that the rate determining step is the Faradaic process

Zn2+ + 2e- Znwhen the system is close to the steady state Note that at low enoughpotential scanning rates diffusion limitations may be less influencingwhile at higher scan rates the diffusion limitations are more importantRandles-Sevcik dependencies for the zinc (II) ions reductiondemonstrate linearity but their intercepts are apparently non-zero (Fig3)

0

01

02

03

04

05

06

07

0 02 04 06 08 1

i pA

cm

2

12 V12s-12

Fig 3 Randles-Sevcik plots for Zn2+ ions reduction on W in a NaCl-KCl meltat 700 degC different concentration of the ions (peak C in Figure 39) 900x10-5

molmL Zn2+ 163x10-4 molmL Zn2+ 177x10-4 molmL Zn2+

109

It is evident that the process Zn2+ + 2e- Zn is complicated bysomething else Despite the irreversible character of the depositionprocess it is still reasonable to roughly evaluate the diffusion coefficientof Zn2+ according equation 1

ip = 06105 (nF)32(RT)12D12C12 (11)

where ip is the peal current density (A cm2) n is the number ofelectrons F is Faraday constant (96500 C) R is the gas constant (8314Jmol∙K) T is the absolute temperature (K) D is the diffusion coefficient(cm2 sec) C is the bulk concentration of a Red (Ox) species (mol cm3) and is the scan rate (V sec)

Thus calculated diffusion coefficients are shown in Table 1

Table 1 Diffusion coefficients of Zn2+ to a tungsten electrode in NaCl-KCl melt

C105 mol L D 105 cm2 sec900 955n

163 1020n

177 1364n

Given that the value of n for the reduction of Zn2+ cannot exceed 2 and0 le le 1 ( asymp 05 for most cases) reasonable values of n must beclose to 1-2 Therefore the values of the diffusion coefficients fromTable 2 lie in the range of 1-6∙10-4 cm2sec Available literature data forthe diffusion coefficients of most metal ions lie in the range 10-5-10-4

cm2sec Particularly T Stoslashre G M Haarberg and R Tunold found thatthe values of the diffusion coefficients for Zn2+ in KCl-LiCl melts at400degC lie in the range 06 ndash 106∙10-5 cm2sec (2) Delimarski providesthe value of the diffusion coefficient of Zn2+ in NaCl-KCl at 710degCwhich is 23∙10-5 cm2sec (5) The deviation of our results from theliterature data can hint that that the process cannot be treated as simplezinc ion reduction on the surface of tungsten

110

It is worth to mention that the fact that the diffusion coefficientfor zinc ions in the chloride melt lay in the range 10-4 ndash 10-5 cm2sec mayserve as an indirect argument in the discussion about the existence ofcomplex species described by the general formula [ZnxCly]

z+ in chloridemelts While some authors argue in favor of the formation of complexions (6 ndash 10) other studies give evidence for the existence of individualzinc ions as the key reacting species (11 ndash 12) The relatively highvalues of the diffusion coefficients found in our experiments hint that thecharge is transferred by individual ions rather than by more massivecomplex moieties

005

01

015

02

025

03

035

04

02 03 04 05 06 07 08 09 1

700oC

750oC

740oC

720oC

i pA

cm

2

12

V12

s-12

Fig 4 Randles-Sevcik plots for Zn2+ reduction on W in a NaCl-KCl melt fordifferent temperatures [Zn2+] = 900x10-5 molmL

Another intriguing aspect of the zinc ions deposition process ona tungsten electrode can be seen in the temperature dependence of

111

Randles-Sevcik plots (Fig 4) As seen from Fig 4 Randles-Sevcik plotsdo not change (to the accuracy of the experiment) as the temperaturerises from 700degC to 750degC

The lack of dependence of Randles-Sevcik plots on thetemperature is really surprising A plausible explanation to this could bean additional process in the system which occurs simultaneously withthe observed process but does not involve charge-transfer and cannot bedetected electrochemically Such a process could compensate for theexpected increase of the slope of Randles-Sevcik plots as thetemperature grows and thus distort the temperature dependence

The most probable candidates for such competing processes area coupled chemical (not charge-transfer) reaction or a process of phase-formation However cyclic voltammetry alone cannot discriminatebetween these two possibilities

Fig 5 A chronoamperometric plot for the deposition of Zn2+ on a tungstenelectrode Temperature 725degC [Zn2+] = 900x10-5 molmL The potential was

stepped from OCV to -055 V

A further insight on the nature of the deposition process can beprovided by chronoamperometry As seen from Fig 5 the current fallsin the course of the first 11 seconds of the experiment and then risesreaches a peak and gradually declines as expected with time until theend of the experiment (300 seconds)

The initial falling and rising of the current can be attributed tothe nucleation of the deposits fluctuations of current for more advanced

112

reaction times as seen in Fig 5 may indicate to a very active charge-transfer process which cannot be explained by a simple zinc depositionprocess

Even more surprising information is provided by EDS analysisof the working electrode after a 3000 second deposition experiment at ndash055 V (Fig 6 Table 2) The most striking result of the analysis is theunexpectedly high content of sodium on the electrode surface Thisamount of sodium cannot be accounted for melt adhesion or penetrationbecause the percentage of potassium and chlorine is much smaller Infact the working electrode looks as it was made of sodium withmoderate inclusions of tungsten and zinc rather of tungsten

Fig 6 An EDS spectrum of tungsten working electrode after 3000 seconddeposition at ndash 055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Table 2 Element composition of the tungsten working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 138x10-4 molmL

Element Na K Cl W ZnAt 6084 580 2861 224 191

113

A somewhat similar phenomenon was reported by Thus T StoslashreG M Haarberg and R Tunold for the deposition of Zn2+ on a glassycarbon electrode in KCl-LiCl melts at 400degC (2) They observed aldquosubstantial residual current observed prior to the Zn(II) reductionpeakrdquo This current was attributed by them to lithium intercalation intothe lattice of the glassy carbon electrode

Unfortunately the data about standard reduction potentials ofmany important ions in molten chlorides are lacking The only source inwhich suitable potentials were found is the book of Yu DelimarskildquoElectrochemistry of Ionic Meltsrdquo (5) The values of standard potentialstabulated in this book were calculated on the base a few assumptionsand are far from being strictly thermodynamical However they arehelpful from the practical point of view The potentials relevant for thisdiscussion are summarized in Table 3

Table 3 Standard reduction potentials in molten chlorides (adopted fromref [5])

Half-Element Li+|Li Na+|Na K+|K Zn2+|Zn Fe2+|FeEH2 (700degC) V - 239 - 236 - 250 - 040 - 007

As seen from Table 3 the standard potentials of lithium andsodium are very close to each other Therefore it is not surprising thatthe interference from sodium in the deposition of zinc ions is similar tothat of lithium as reported by T Stoslashre G M Haarberg and R TunoldOf course it is not intercalation that serves as the moving force of theprocess of sodium penetration into the surface layers of zinc deposit onthe tungsten electrode

The large amounts of sodium in the deposits obtained in the studyof the Zn2+ ions reduction on tungsten electrodes cannot be explained asthe formation of a W-Na alloy because such a process is not observedby the cyclic voltammograms of NaCl-KCl on tungsten electrodes in theabsence of zinc ions (3) Therefore it is zinc which triggers thedeposition of sodium Moreover the data obtained bychronoamperometry at E = ndash 055 V vs W (Fig 5) indicate that there aretwo sequential faradaic processes The first of them is relatively weak

114

and is completed after ~ 11 seconds Then the second process starts andits current only grows with time The first process can be related to thereduction of zinc ions and the formation of zinc deposits As theelectrode surface is covered by a layer of zinc the interaction of thislayer with Na+ ions begins Apparently sodium ions are absorbed by theliquid zinc (Tm = 419 degC) and this facilitates their reduction at thepotential so much more positive than the sodium reduction potential inthe absence of zinc ( - 11 V vs W) Both lithium and sodium are liquidat the temperature of the experiment and these two metals form on theelectrode surface a liquid solution with zinc which continues to absorbnew portions of the lithium or sodium ions

The following speculation may account for the phenomenonobserved in our system

1 Zinc ions are discharged on the surface of the tungstenelectrode As the surface concentration of zinc atoms grows nucleationoverpotential starts to dump the overall process This dumping isobserved in the course of the first 11 seconds in Fig 5

2 Zinc (or zinc-tungsten) phase is formed This phase triggers theprocess of sodium-zinc exchange

Zn + Na+ Zn+ + Na or Zn + 2Na+ Zn2+ + 2Na3 The process (2) becomes the main process on the electrode

surface

Deposition of zinc on a platinum electrodeSome typical voltammograms for the electrochemical reduction

of Zn(II) are shown in Fig 7 Again no difference is observed betweenthe processes in NaCl ndash KCl and in LiCl ndash KCl melts and two melts arefurther described on the instance of in NaCl ndash KCl alone

As seen from Fig 7 the voltammogram is completely anomalousas compared to the other studied systems No cathodic peaks areobserved in the range -11V to + 09V ie in the limits of theelectrochemical window The peaks ndash 125V and at +09 V are the sameas for the ldquoblankrdquo melt NaCl-KCl These are the limits of theelectrochemical window

A very poorly pronounced anodic peak A at about ndash 028 V issimilar to the anodic peak A which appears for the zinc deposition on atungsten electrode (Fig 1) However the cathodic branch of thevoltammogram contains a continuous transition to the cathodic limit of

115

the windows rather than a peak It is obvious that zinc deposition ismasked by another process whose nature cannot be studied in theframework of this research

Fig 7 Cyclic voltammograms related to the electrochemistry of Zn2+ ions(0176 mol L) in equimolar NaCl-KCl melt on a Pt electrode at 700degC Scanrate is 300 mVsec

Fig 8 An EDS spectrum of a platinum working electrode after 3000 secondcathodic polarization at ndash 07 V vs W at 725degC in equimolar NaCl-

KCl melt containing 176x10-4 molmL of Zn2+ ions

116

An attempt of obtaining a sample of zinc deposit by holding thesystem at ndash 07 V (that is at such a potential which is considerably morepositive than the cathodic limit but more negative than the potential atwhich zinc is deposited on a tungsten electrode) for 3000 seconds wasmade However the analysis (Fig 8) demonstrated that essentially nozinc is found on the surface of the electrode (Table 4) since the value098 At is comparable with the sensitivity of the method The richcontent of potassium (5857 At ) in the surface layers can hint thatpotassium sorption is the process which masks the deposition of zincHowever this information alone is not sufficient for making positiveconclusions

To try to understand the essence of the process other moltenchloride systems containing no potassium could be studied Howeversuch a study is far beyond the framework of the current work

Table 4 Element composition of the platinum working electrode surfacecalculated from the EDS spectrum after 3000 second deposition at ndash055 V Temperature 725degC [Zn2+] = 176x10-4 molmL

Element Na K Cl Pt ZnAt 555 5857 3426 618 098

ConclusionsThe deposition of zinc on a tungsten electrode starts as an

irreversible two-electron zinc ion reduction Zn2+ + 2e- Zn After anobvious initial nucleation step a new phase is formed This phasecatalytically launches the process of saturating the electrode surface withsodium After the onset of the process of sodium deposition the latterbecomes essentially the only constituent on the electrode surface

The attempts of studying the deposition of zinc ions on a platinumelectrode were unsuccessful because this process is masked by anotherprocess which can result in the saturation of the electrode by potassiumThe exact nature of the latter process demands a separate study

117

References1 Fray D J J Appl Electrochem 3 103 (1973)2 Stoslashre T Haarberg GM Tunold R J Appl Electrochem 30 1351

(2000)3 Lugovskoy A Zinigrad M Aurbach D Israel Journal of

Chemistry 47 (3-4) 409 (2007)4 Lugovskoy A Zinigrad M Aurbach D and Unger Z

Electrochimica Acta 54 (6) 1904 (2009)5 Delimarski Yu K Electrochemistry of Ionic Melts Metallurgiya

Moscow 1978 (in Russian)6 Mackenzie J D and Murphy W K J Chem Phys 33 366 (1960)7 Irish D E and Young T F J Chem Phys 43 1765 (1965)8 Allen DA Howe RA Wood ND Howells WS J Phys

Condens Matter 4 1407 (1992)9 Price D L Saboungi M-L Susman S Volin K J Wright A C J

Phys Condens Matter 3 9835 (1991)10 Bassen A Lemke A Bertagnolli H Phys Chem Chem Phys 2

1445 (2000)11 Biggin S and Enderby J E J Phys C Solid State Phys 14 3129

(1981)12 Badyal Y S and Howe R A J Phys Condens Matter 5 7189

(1993)

89

PREPARATION OF COMPOSITES CuZrO2 AND CuTiO2

BY MA SHS

AI Letsko1 TL Talako1 AF Ilyushchenko1 TF Grigoreva2SV Tsybulya3 IA Vorsina2 NZ Lyakhov2

1 Powder Metallurgy Institute of NAS B Minsk Belarus2 Institute for Solid State Chemistry and Mechanochemistry of SB RAS

18 Kutateladze str Novosibirsk Russia grigsolidnscru3 GK Boreskov Catalysis Institute of SB RAS Novosibirsk Russia

IntroductionMetaloxide composites are quite perspective materials for

application in machine industry instrument engineering and electricalengineering in comparison to pure metals due to their improvedchemical and physical properties (heat resistance strength hardnesserosion resistance) Chemical mixing salt mixture decompositionhydrogen reduction in solutions chemical precipitation from solutionsinternal oxidation are well-known methods of preparing such materialshaving application in industry [1] The above-mentioned technologiesallow attaining metaloxide composites but they are quite expensive andlong-term Based on this a very topical issue is elaboration of newapproaches to production of metal-ceramic materials

In this work we explored possibilities of preparation ofcopperoxide composites (CuZrO2 and CuTiO2) by methods ofmechanochemical synthesis (MS) in planetary mills and of mechanicallyactivated self-propagating high-temperature synthesis (MA SHS)

ExperimentalCopper copper oxide CuO and zirconium M-41 titanium PTOM

were used in this work as raw materials Mechanical activation (MA)was carried out in planetary ball mills with water cooling [2] (the drumvolume ndash 250 cm3 the balls diameter ndash 5 mm the load ndash 200 g sampleweight ndash 10 g the drums rotation speed about the general axis ~ 1000rpm) After MA the activated mixture was compacted (under a load of4ndash6 t) in the mould up of 17 mm diameter and ~25 mm in height (tillstrength sufficient for the sample transfer to the reactor) SHS wascarried out in the argon atmosphere the combustion was initiated withan electrically heated tungsten coil The temperature and burning

90

velocity were evaluated by a thermocouple method (C-A thermocouplesOslash asymp 02 mm) using an outer 2-channel 24-charge analog-to-digitalconverter ADSC24-2T

X-ray diffraction research was conducted with diffractometersXrsquoTRA (Thermo ARL Switzerland) with application of CoK radiation(λ = 1 789 Aring) and URD-63 with application of CuK radiation (λ = 15418 Aring) Evaluation of effective sizes of coherent scattering area wascarried out in compliance with the Scherer formula with the strongestpeaks of phases analysed

The high-resolution scanning electronic microscope (SEM)MIRATESCAN equipped with an INCA 350 accessory for EDXanalysis was used for the structure research The electron probe diameterwas 52 nm excitation area was 100 nm Images in direct electrons andback-scattered electrons were attained and it allowed studying chemicalelements distribution over the surface Brightness distribution in theimage depends on the average atomic element number in eachmicroarea

IR absorption spectra were registered by spectrometer IFS-66The samples were prepared to the exposure by standards methods

Results and discussion

Cu-O-Zr systemMechanochemical reduction of copper oxide with metallic

zirconium was initially investigated in this system This reaction is quitehigh-exothermic (∆H (2 CuO + Zr = 2 Cu + ZrO2) asymp -188 kcalmol) ieit can be implemented under mechanical activation conditions IRspectroscopic investigations have shown that the original copper oxideCu-O band is considerably widened at 505 cm-1 after 20 s of MA ofCuO + Zr mixture of stoichiometric composition This widening (Fig1b) can testify some structural failures After 30 s of activation thefollowing bands are present in the IR-spectrum of the product 505 cm-1

(original oxide CuO) 615 cm-1 (the lowest copper oxide Cu2O) [3] and415 585 735 cm-1 (zirconium oxide (Fig 1c) [4 5] X-ray-phaseanalysis shows the presence of certain amount of Cu2O already after 20 sof activation The 30-second activation product diffractogram showsclear copper (coherent scattering area asymp 80 nm) and zirconium oxide

91

(coherent scattering area asymp 100 nm) reflection and two copper oxidereflections ie mechanochemical reduction of copper oxide takes placeat such activation duration This reaction speed shows that the reactionpresumably takes place in the thermal explosion mode when especiallyhigh heat dissipation speed is needed what is very difficult to performeven in the most effectively cooled highly-energy planetary ball millsAs such a process dimensional scaling seems to be absolutely impossiblein conditions of mechanochemistry an attempt to produce compositeCuZrO2 by the SHS method was made

Fig 1 IR-spectra of mixture CuO + Zr before (a) and after MA for 20 (b) and30 s (c)

At first CuOZr mechanocomposite was used as the SHS-precursor This mechanocomposite formed after 20 s of MA ofstoichiometric composition mixture has a small amount of cuprous oxideCu2O beside original copper oxide and zirconium SHS process proceedsin the heat explosion mode in this system Burning parameters fixingfailed in this case because of the inertia of the equipment applied

92

Not pure metal but solid solutions intermetallic compounds ornano-composites where metal-reducer (zirconium in our case) isdistributed in the inert matrix can be used as a reducing agent todecrease the system reaction capability At the same components ratiochemical energy of the raw mixture would be considerably lower and asa consequence heat release would reduce

In this work mechanocomposite formed during mechanicalactivation of mixture Cu + 20 wt Zr for 20 min with zirconium hadbeen pre-dispersed for 4 minutes (zirconium coherent scattering areasize ~ 20 nm) was used for copper oxide reduction This compositediffractogram shows the widened intensive copper (coherent scatteringarea asymp 20 nm) reflection and very vague zirconium reflection coherentscattering area of which cannot be evaluated (Fig 2) Since copperreflections havenrsquot changed their position we can conclude thatzirconium hasnrsquot become a part of copper crystal lattice ie CuZrmechanocomposite and not solid solution is attained

Fig 2 Diffractograms of Cu + 20 Zr mixture before (a) and after 20 minof MA (b)

93

This is confirmed by the SEM results (Fig 3) The electronmicroscopy data more clearly show zirconium distribution Zr elementalmapping testifies that local zirconium areas are much diffused

Fig 3 SEM-images of sample Cu + 20 Zr after MA for 20 min

94

X-ray research of the product of joint activation of mixture CuO +mechanocomposite Cu + 20 Zr (the mixture composition correspondsto the stoichiometric ratio of copper oxide and zirconium) for 2 and 4minutes show that copper oxides diffraction reflections are retained inall cases although they are substantially widened (Fig 4) Thezirconium oxide reflection is not observed ie mechanochemical copperoxide reduction does not take place in this time gap CuOCuZrmechanomposite formed as a result of joint mechanical activation ofmixture CuO + mechanical composite Cu 20 Zr for 4 min was usedas a precursor for SHS

Fig 4 Diffractogram of sample CuO + CuZr after MA for 4 min

Usage of mechanocomposite CuOCuZr instead of CuOZr one asthe SHS precursor changes a mechanism of interaction between thereactants during the SHS process from the thermal explosion mode (forCuOZr mechanocomposite) to the steady-state combustion with the

95

burning velocity asymp 2 mms temperature rise speed about 730 Cs andburning temperature 1044 C The combustion temperature record (Fig5) shows 2 isothermal plateaus The first one is fixed at temperaturemaximum and most probably points out melting process The secondone is fixed at 580 ndash 590 C and accounts for post-processes in the after-burning zone of combustion wave

Fig 5 Temperature record of the SHS process from mechanical compositeCuOCuZr

X-ray-phase analysis has shown that SHS product consists ofcopper and zirconium oxide with Cu2O traces (Fig 6) Electronicmicroscopy with the EDX analysis confirms composite structureformation (Fig 7 Table 1)

96

Fig 6 Diffractogram of the SHS product from mechanical compositeCuOCuZr

Fig 7 SEM-image of the SHS product from mechanical composite CuOCuZr

97

Table 1 Results of the EDX analysis (from Fig 7)

Number ofspectrum

O Cu Zr

1 382 8744 8742 714 8152 11343 2803 2747 44504 1653 4640 37065 2314 2914 4772

Cu-O-Ti systemChemical reduction of CuO with titanium is also high-exothermic

(∆H (2 CuO + Ti = 2 Cu + TiO2) asymp -151 kcalmol) Mechanicalactivation of equimolar mixture of copper oxide with titanium powderfor 4 minutes did not result in titanium oxide formation Longeractivation is not reasonable since it contaminates the reaction mixturewith balls and drums material That is why the composites formedduring the short-term MA were used as precursors for SHS

After 30 s MA composite structure CuOTi with a small additiveof cuprous oxide reduced from CuO (Fig 8) is formed The SHS processfrom such mechanocomposites proceeds with a very high speed andtemperature (on a levels typical for the thermal explosion mode) andwith the substances scatter

Fig 8 Diffractogram of mixture CuO + Ti after MA for 30 s

98

To decrease combustion temperature and velocitymechanocomposite CuTi containing 20 wt of titanium was used as areducing agent in the next experiment Figure 9 shows the diffractogramof the mechanocomposite formed after 10 min mechanical activation ofthis mixture It shows that metals reflections especially that of titaniumare widened testifying substantial increase of their dispersivityAccording to the X-ray data analysis the titanium coherent scatteringarea size is ~ 10 nm in this composite

Fig 9 Diffractogram of mixture Cu + 20 Ti after 10 min of MA

Mixture of copper oxide and CuTi mechanocomposite (thecomposition corresponds to the stoichiometric ratio of titanium andcopper oxide for its full reduction) was subjected to activation for 4minutes Only a band of valence vibrations of vCu-O copper oxide (Fig10a) is present in the IR-spectrum of the activated mixture like in theoriginal one but its intensity slightly decreases X-ray research alsoindicates that the titanium oxide reflections are absent in the 4-minuteactivation product diffractogram (Fig 11)

99

Fig 10 IR-spectra of sample CuO + CuTi after 4 min of MA (a)and after SHS (b)

Fig 11 Diffractogram of sample CuO + CuTi after 4 min of MA

100

SHS process from CuOCuTi mechanocomposite takes place inthe steady-state combustion mode with burning velocity higher than 20mms and burning temperature ~2000 ordmC A band (~730 cm-1)corresponding to valence vibrations of rutile vTi-O (Fig 10b) [2]appears in the IR-spectrum of the SHS product from CuOCuTimechanicocomposite Diffraction reflections (Fig 12) also correspond toreflections of rutile and copper

Fig12 Diffractogram of the SHS product from CuOCuTi mechanocomposite

Electron-microscopy exposure in back-scattered electronsindicates the partial phase separation of TiO2 and Cu (Fig 13 a) thoughcomposite particles containing TiO2 inclusions with size from 30 nm till1 5 m (Fig 13 c) are also formed The elemental mapping in thetitanium characteristic radiation confirms this fact (Fig 13d)

101

a

b cFig 13 SEM-images of the SHS-product from CuOCuTi mechanocomposite

102

Table 2 The EDX analysis results (from Fig 13 a)

Number ofspectrum

O Ti Cu

1 191 052 9757

2 235 051 9714

3 2230 2094 5676

4 1586 1295 7118

5 180 108 9712

6 336 228 9436

7 4335 4685 980

8 3297 2738 3966

9 4978 4645 377

ConclusionThus our investigations have shown that copper oxide can be

mechanochemically reduced with zirconium resulting in formation ofzirconium oxide and copper but the reaction goes in the thermalexplosion mode

To produce composite CuZrO2 by the method of MASHS usageof mechanocomposite CuZr instead of pure zirconium seems to be morepromising The MASHS product is a copper-based composite withinclusions of ZrO2 and some amount of Cu2O

Mechanical activation of equimolar mixture of copper oxide withtitanium powder for 4 minutes did not result in titanium oxide formationThat is why the composites formed during the short-term MA were usedas precursors for the following SHS

Reduction of CuO with CuTi mechanocomposite can beimplemented by the method of MASHS Partial phase separation of TiO2

and Cu takes place during the synthesis process along with the formationof copper-based composite particles with inclusions of titanium oxidesized from 30 nm up to 15 m

103

References1 PA Vityaz Mechanically alloyed alloys on the basis of aluminum

and copper PA Vityaz FG Lovshenko GF Lovshenko ndashMinsk Belnauka 1998 ndash 351 p

2 YG Avvakumov AP Potkin OI Samarin Authorrsquos certificate ofUSSR 975068 Planetary mill BI 1982 No 43

3 SS Batsanov VPBokarev YVLazareva On CuO interaction withcopper Inorganic Chemistry Journal 1977 V 22 issue 4 P 888ndash 892

4 AI Boldyrev Infrared spectra of minerals M Nedra 19765 BT Kaminsky AS Plygunov GN Prokofyeva Infrared spectra of

oxides of titanium zirconium and hafnium Ukrainian ChemicalJournal 1973 V 35 No 9 P 946 ndash 977

78

THE STANDARD ENTHALPY AND ENTROPY OFFORMATION OF GASEOUS AND LIQUID

POLYCHLORINATED BIPHENYLS POLYCHLORINATEDDIBENZO-n-DIOXINS AND DIBENZOFURANS

TV Kulikova AV Mayorova KYu ShunyaevInstitute of Metallurgy Ural Branch RAS

Yekaterinburg RussiaE-mail kulikogmailcom

AbstractThe study deals with analysis and systematization of the known

and calculation of the unknown thermodynamic characteristics (thestandard enthalpy of formation the standard entropy of formation) ofwidespread hazardous isomers of gaseous and liquid compounds ofpolychlorinated biphenyls (PCBs) polychlorinated dibenzo-n-dioxins(PCDDs) and polychlorinated dibenzofurans (PCDFs) Thecomparison of results obtained in different studies reveals aconsiderable discrepancy between values reported by highlyrespected investigators In this connection laquoindependentraquo results ofthe thermodynamic characteristics have been calculated

IntroductionUnique technological and physicochemical properties of

polychlorinated biphenyls (PCBs) a huge volume of theirproduction considerable volatility and solubility and extremechemical inertness have led to the world-wide spread of PCB-containing equipment and materials resulting in the universalcontamination with these substances The most common method usedin Russia for destruction of PCBs is their incineration with theformation of polychlorinated dibenzo-n-dioxins (PCDDs) anddibenzofurans (PCDFs) which are among the most hazardouschemical substances known to the mankind

As often happens the hazard of PCBs has long beenunderestimated With respect to their severe toxicological effectPCBs are identical to substances that are referred to the high class ofhazard Since these substances are especially toxic they have beenassigned low toxicological standards which necessitate special

79

requirements on the organization of processes assuming formation ofthese substances (the so-called dioxinogenic processes) so thatindustrial emissions meet the norms Instrumental investigations ofthese substances are very expensive and in this connection interestis attracted to calculation methods for simulation of processes by thedata on their thermochemical properties

A quality thermodynamic simulation requires the knowledge ofthermodynamic and thermochemical properties of all reliablycertified compounds of the system under study in the gaseous orcondensed state Therefore the present study deals with the analysisand systematization of the known and calculation of the unknownthermochemical properties (the standard enthalpy and entropy offormation) of most toxic and hazardous isomers of gaseous PCBsPCDDs and PCDFs and liquid PCBs

Calculation of thermochemical propertiesIt is known that there are 209 individual PCB congeners 420

polychlorinated dibenzo-n-dioxins and polychlorinateddibenzofurans which differ by the number and positions of chlorineatoms in a molecule The most widespread PCB compoundscontaining up1 to 10 chlorine atoms were chosen for the study Indeciding on isomers preference was given to ortho-unsubstitutedPCBs because they are most toxic and their effect is similar to theeffect of PCDDs and PCDFs Congeners which do not have chlorineatoms in ortho-positions of molecules (ortho-unsubstituted PCBs)can acquire the planar configuration which is more favorable inenergy terms Such congeners are isostereoisomeric to PCDDs andPCDFs and present the greatest hazard As to the PCDD and PCDFisomers of special hazard to humans and the environment are tri-tetra- penta- and hexa-substituted dioxins and furans containinghalogen atoms in lateral positions 2 3 7 and 8

In this study we analyzed the known and calculated theunknown thermodynamic properties of 17 most widespread andhazardous isomers of PCBs PCDDs and PCDFs in the gaseous stateand 11 compounds of liquid PCBs

80

Gaseous PCBs PCDDs and PCDFsThe literature survey showed that studies dealing with

estimation of the thermochemical properties of gaseous PCB PCDDand PCDF compounds are few Most of them are based oncalculations or are semi-empirical For example Saito and Fuwa [1]calculated thermodynamic functions of all PCBs and some PCDDsand PCDFs on the basis of semi-empirical calculations in terms ofthe PM3 model OV Dorofeeva et al [2-4] used statistical methodsTable 1 presents the literature data on standard enthalpies andentropies of formation of gaseous and liquid PCBs PCDDs andPCDFs The comparison of results obtained in different studiesreveals a considerable discrepancy between values reported by highlyrespected investigators who did very arduous work In particularvalues of the formation enthalpy [1] are 8-70 larger and the entropyis 11-15 smaller than the corresponding values in [2-4] thediscrepancy grows with the number of chlorine atoms in a moleculeSo we thought it reasonable and topical to attempt an independentresult

Bensons method [5] was used to calculate thermodynamiccharacteristics (the standard enthalpy of formation ΔНdeg298 thestandard entropy of formation ΔSdeg298) of the gaseous PCBs PCDDsand PCDFs We shall dwell briefly on this method

Bensons method is the group additivity method involvinganalysis of the molecule structure Atomic or molecular groups areseparated and the nearest neighbors of the atom or the group areconsidered Table 2 gives the number of groups necessary fordetermination of group increments in structural formulas of PCBsPCDFs and PCDDs Values of the thermodynamic characteristics ofgroup increments were determined from available reference andliterature data [5 6] Information about the energy contribution ofeach group (see Table 3) and the number of groups was used tocalculate thermochemical properties of the PCBs PCDDs andPCDFs

81

Table 1 Standard enthalpies (∆Нo298 kJmole) and entropies (∆So

298Jmole K) of formation of gaseous and liquid PCBs PCDDs andPCDFs

Gaseous state Liquid state

Compo-unds Saito Fuwa [1]

the given work

OV Dorofeeva etal

[2-4]

∆Нo298

[7 8 121617]

So298

[781014 16 17]

∆Нo298

the givenwork and

[814]

So298

thegivenworkand[14]

1 2 3 4 5 6 7 8 9

C12H10

(biphenyl)

1986[1]

1797

3454[1]

4104

1820[3]

3908[3]

1819[8]

1814[16]

3927[16]

11711162[8]11710

[14]

257402574[14]

C12H9Cl(3-mono-

chlor-biphenyl)

1705[1]

1500

3851[1]

4413

1561[2]

4323[2]

1548[8]

15088[16]

4214[16]

7629 2840

C12H8Cl2

(44rsquo-dichlor-biphenyl)

1422[1]

1202

3992[1]

4721

1260[2]

4518[2]

1276[8]

12004[16]

4492[16]

3584 3106

C12H7Cl3

(344rsquo-trichlor-biphenyl)

1194[1]

905

4240[1]

5030

1041[2]

4923[2]

1004[8]

892[16]

4780[16]

-452 3372

C12H6Cl4

(33rsquo44rsquo-tetrachlor-biphenyl)

969[1]

608

4444[1]

5338

899[2]

5216[2]

732[8]

5836[16]

5068[16]

-4488 3638

C12H5Cl5

(33rsquo44rsquo5-penta-

chlorbiphenyl

748[1]

310

4620[1]

5647

569[2]

5502[2]

460[8]

2752[16]

5356[16]

-8524 3904

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlor-

biphenyl)

529[1]13

4615[1]

5956

314[2]

5675[2]

190[8]

-332[16]

5644[16]

-12558 4170

C12H3Cl7

(233rsquo44rsquo55rsquo-hepta-

chlor-biphenyl)

400[1]

-284

4842[1]

6264

152[2]

6077[2]

-84[8]

-416[16]

5932[16]

-16596 4436

82

1 2 3 4 5 6 7 8 9

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-

octachlor-biphenyl)

241[1]

-581

4886[1]

6573-90[2]

6342[2]

-356[16]-650[8]

6220[8]

-20632 4702

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-

nanochlor-biphenyl)

873[1]

-878

5048[1]

6881

-153[2]

6607[2]

-628[16]-958[8]

6508[8]

-24668 4968

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlor-biphenyl)

-67[1]

-1176

5034[1]

7190

-247[2]

6757[2]

-901[16]

-1267[8]

6796[8]

-28604 5234

C12H8O2

(dibenzo-n-dioxin)

-402[1]

-448

3764[1]

-592[4]

3965[4]

-592[12]-592[7]

-550[17]

3951[7]

3880[17]

- -

C12H4Cl4O2

(2378-tetrachlor-dibenzo-n-

dioxin)

-1372[1]

-1592

4553[1]

-1640[4]

4781[4]

-1345[7]

-158[17]

5136[7]

4784[17]

4781[10]

4784[9]

- -

С12H3Cl5O2

(12378-pentachlor-dibenzo-n-

dioxin)

-1532[1]

-1900

4931[1]

-1900[4]

54035[4]

-1162[7]

-196[17]

5531[10]

5010[17]

- -

С12H2Cl6O2

(123478-hexachlor-dibenzo-n-

dioxin)

-1691[1]

-2164

4841[1]

-2196[4]

56912[4]

-1224[7]

57559[7]

5236[17]

- -

С12HCl7O2

(1234678-hepta-chlor-

dibenzo-n-dioxin)

-1848[1]

-2472

5005[1]

-2460[4]

59789[4]

-1196[7]

61031[7]

5462[17]

- -

C12H8O(dibenzo-

furan)

1061[1]

518

3787[1]

553[4]

3759[4]

552[17]

3744[17]

- -

C12H4Cl4O(1234-

tetrachlor-dibenzo-furan)

203[1]

-625

4505[1]

-500 [4]49098

[4]-528[17]

4648[14]

- -

83

1 2 3 4 5 6 7 8 9

С12H3Cl5O(12378-pentachlor-

dibenzo-furan)

-123[1]-934

4592[1]

-759[4]

51975[4]

-748[17]

4874[14]

- -

С12H2Cl6O(123478-

hexachlor-dibenzo-furan)

-283[1]

-12424713[1]

-1051[4]

54852[4]

-1043[17]

5100[14]

- -

С12HCl7O(1234678heptachlor-

dibenzo-furan)

-441[1]

-1550

4833[1]

-1315[4]

57729[4]

-1313[17]

5326[14]

- -

Table 2 Number of groups for determination of group increments instructural formulas of PCBs PCDFs and PVDDs

Number of groupsCompound Св-H Св-Cl Св-O Св-Св

Number ofchlorine atoms

in a molecule (n)

PCBs 10 - n n - 2 1 ndash 10

PCDFs 8 - n n 2 2 1 ndash 8

PCDDs 8 - n n 4 - 1 ndash 8

Св is the carbon atom in an aromatic ring

Values presented in Table 1 show the thermodynamiccharacteristics of PCBs PCDDs and PCDFs calculated in this studyand by other investigators

It is seen for example ( Table 1) that the formation enthalpy

(o298H ) of biphenyl (C12H10) equals (kJmole) 1986 [1] 1820 [3]

1819 [7] and 1814 [8] while the formation entropy (o298S ) of

2378-tetrachlordibenzo-n-dioxin (C12H4Cl4O2) is (J(mole K))4553 [1] 4781 [4] 4784 [9] and 4781 [10]

84

Table 3 Values of the thermodynamic characteristics determined bythe method of group increments[58]

(gas) (liquid)Group

o298H

kJmole

o298S

J(moleК)

o298H

kJmole

o298S

J(moleK)

Св-H 1381[8]1382[5]

4831[8]4827[5]

816[8] 2887[8]

Св-Св 2166[8]2077[13]

-3657[8]-3618[5]

1721[8] -

Св-Cl -1703[8]-1591[5]

7708[8]7913[5]

-3220[8] 5547[8]

(Св)2-O -7766[8]-8834[5]

--

- -

orto corrCl-Cl

950[8]921[5]

- 1400[5] -

meta corrCl-Cl

-500[8] - 400[5] -

In this study the values of the standard entropy of formationobtained by using statistical methods (OV Dorofeeva et al [2-4 9])for 17 isomers of PCBs PCDDs and PCDFs are in good agreementwith the values calculated by other investigators [8 10 12 13] andwith the values calculated by us

Liquid PCBsIt should be noted that ample literature data on the

thermochemical properties of liquid ecotoxicants is only available forbiphenyl (C12H10) [8 14] dibenzo-n-dioxin (C12H8O2) [11 15] anddibenzofuran (C12H8O) [5 17] The only study dealing withcalculation of thermodynamic functions for the whole series of liquidPCDD and PCDF homologues was published by VS Iorish et al[11] As to liquid PCB compounds the literature data on theirthermochemical properties are scarce [8 14]

The thermochemical properties namely the standard enthalpyand entropy of formation of liquid PCBs were calculated using thegroup additivity method due to Domalski [8] Values of the groupincrements (Table 3) were adopted from [8] It is seen from Table 3

85

that the energy contribution of the group Св-Св is unavailable for the

entropy calculation However if one uses known values ofo298S for

liquid biphenyl (C12H10) [14] and the data on the contribution of the

Св-H and Св-Cl groups [8] it is possible to calculateo298S for the

whole series of PCBs

o298S (PCB) =

o298S (BP) - (10-n)

o298S (Св-H) + n

o298S (Св-Cl) +

+(morto corr Cl- Cl ) +(pmeta corr Cl- Cl) (1)

where n is the number of chlorine atoms in a PCBs moleculem (p) - spatial amendments number Cl (from two and more) beingin orto - (meta-) position rather each other

The enthalpy of formation (o298H ) for the PCBs series

compounds was calculated by two options using the group additivitymethod due to Domalski [8] and from the equation

o298H (PCB) =

o298H (BP) - (10 - n)

o298H (Св-H) +

+ no298H (Св -Cl) +(morto corr Cl-Cl )+(pmeta corr Cl-Cl) (2)

Table 4 lists values of the standard enthalpy of formation forthe series of liquid PCBs compounds as calculated by the groupadditivity method [8] and the equation (2) It is seen that the values of

o298H which were calculated by the two methods are in good

mutual agreementThe thermochemical properties which were taken as reliable

were added to the TERRA database and were used forthermodynamic simulation of the thermal stability of PCBs PCDDsand PCDFs

86

Table 4 Calculated enthalpy of formation (∆Нo298) for liquid PCBs

compounds∆Нo

298 kJmole

CompoundGroup

incrementsmethod

Eq (5)δ

C12H9Cl(3-monochlorbiphenyl)

7584 76742 12

C12H8Cl2

(44rsquo-dichlorbiphenyl)3530 36382 30

C12H7Cl3

(344rsquo- trichlorbiphenyl)-506 -3978 2138

C12H6Cl4

(33rsquo44rsquo-tetrachlorbiphenyl)-4542 -44338 238

C12H5Cl5

(33rsquo44rsquo5-pentachlorbiphenyl)-8578 -84698 126

C12H4Cl6

(33rsquo44rsquo55rsquo-hexachlorbiphenyl)-1261 -125058 083

C12H3Cl7

(233rsquo44rsquo55rsquo-heptachlorbiphenyl)-1665 -165418 065

C12H2Cl8

(22rsquo33rsquo44rsquo55rsquo-octachlorbiphenyl)-20686 -205778 052

C12HCl9

(22rsquo33rsquo44rsquo55rsquo6-nanochlorbiphenyl)-24722 -246138 044

C12Cl10

(22rsquo33rsquo44rsquo55rsquo66rsquo-decachlorbiphenyl)

-28758 -286498 038

Conclusions1The literature data on the thermochemical properties of 17

most widespread and hazardous isomers of PCBs PCDDs andPCDFs in the gaseous state and 11 compounds of liquid PCBs havebeen analyzed and systematized for the first time

2Methods have been developed for calculating of thethermodynamic characteristics of organic compounds Values of thethermodynamic functions (standard enthalpy and entropy offormation) of liquid PCBs PCDDs and PCDFs have been calculatedfor the first time

87

3The comparison of the calculated values of thethermodynamic functions with the known literature datademonstrated their good mutual correlation

4The obtained data were added to the TERRA database andwere used for thermodynamic simulation of the thermal stability ofPCBs PCDDs and PCDFs

5The obtained data can be used for simulating of the behaviorof complex heterogeneous systems including ecotoxicants over awide interval of temperatures and initial compositions

This study was supported by RFBR (project No 08-03-00362-a)

References1 Nagahiro Saito Akio Fuwa Chemosphere 2000 vol40 p

131-1452 OV Dorofeeva NF Moiseeva VS YungmanLV JPhys

Chem A 2004 vol 108 p 8324-83323 OV Dorofeeva Thermodynamica Acta2001 vol374 p7-114 OV Dorofeeva VS Iorish NF Moiseeva J Chem Eng

Data 1999 vol 44 p 516-5235 SW Benson FR Cruickshank DM Golden GR Haugen

HE OrsquoNeal AS Rodgers R Shaw and R Walsh Chem Rev1969 vol69 p 279 -324

6 HK Eigenmann DM Golden and SW Benson J PhysChem 1973 vol 77 1687-1691

7 Jung Eun Lee and Wonyong Choi J PhysChem A 2003vol 107 p 2693-2699

8 Domalski E S and Hearing E D J of Phys and Chem RefData 1993 vol 22 p 805-1159

9 LV Gurvich OV Dorofeeva VS Iorish Zh Fiz Khimii 1993vol67 No 10 p 2030-2032

10 W-Y Shiu and K-C Ma J Chem Ref Data 2000 vol29No 3 p 387-462

11 VS Iorish OV Dorofeeva NF Moiseeva J Chem Eng Data2001 vol46 p 286-298

12 VA Lukyanova VP Kolesov Zh Fiz Khimii1997 vol 71No 3 p 406-408(in Russian)

88

13 P Reid J Prausnitz T SherwoodLeningrad Khimiya 1982592 p(in Russian)

14 Richard Laurent and Helgeson Harold C Geochimica etCosmochimica Acta 1998 vol 62 No 2324 p 3591 ndash 3636

15 I Barin ldquoThermochemical Data of Pure SubstancesrdquoWeinheim Federal Republic of Germany VCHVerlagsgesellschaft mbH 1997

16 Cambridgesoft database ver 806 December 31 200317 Thompson D Thermochim Acta 1995 vol261 p7-20

76

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OFNANOGRAINED

TiN-TiB2 COMPOSITES

MA Korchagin BB BokhonovInstitute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirsk Russiakorchagsolidnscru

Titanium nitride is known to exhibit high oxidation resistancehigh thermal conductivity and hardness as well as high corrosionresistance in acids Titanium diboride is also very hard possessing highstrength at elevated temperatures and anomalously high electricalconductivity among other ceramic materials

Composite materials based on the mixture of these twocompounds have been widely used in a variety of applications Highperformance parts have been also developed Thus ceramics containing40-50 molTiN shows high oxidation resistance [1] However untilvery recently TiN and TiB2 have been produced separately by twodifferent routes At present new methods are being developed tosynthesize mixtures of these two compounds in a single process One ofthese methods is based on self-propagating high-temperature synthesis(SHS) The use of SHS eliminates the need of having furnace equipmentto synthesize the desired products The possibility of SHS in the systemis due to the high enthalpies of formation of the products serving as aninternal chemical source of energy

In order to simultaneously obtain TiN and TiB2 by SHS the initialreactants can be either the powder mixtures of Ti-BN [3] or Ti-B-BN[4] The products of the reactions consist of highly porous well meltedsintered pieces with the minimum grain size of 1-10 microm [4] Hightemperatures developed in the combustion wave in the traditional SHSdo not allow finer grains of the products to retain

In order to overcome this problem short mechanical activationof the mixtures of reactants is proposed followed by the SHS in anatmosphere of argon or nitrogen

In the previous investigations preliminary mechanical activationhas been shown to significantly reduce the combustion temperatures

77

which to a great extent determine the grain size of the products of SHS[6 7]

Experiments were performed on the stoichiometric mixtures 3Ti +2BN The time of preliminary mechanical activation in a planetary ballmill (AGO-2 type) did not exceed 10 min The influence of the durationof mechanical activation on the combustion rate temperature and phasecomposition of the products was studied

The milled mixtures and the products of SHS were studied usingXRD analysis and Electron Microscopy The experimental conditionshave been found favoring the formation of the two-phase mixtures ofTiN of TiB2 with the grain size ranging from 20 to 50 nm [7]

References1 GV Samsonov Nitridy (Nitrides) Kiev laquoNaukova Dumkaraquo 19692 AG Merzhanov Tverdoplamennoe gorenie (Solid State

Combustion) Chernogolovka ISMAN 2000 224 p3 AEGrygoryan ASRogachev Combustion of titaniumwith

nonmetal nitridesCombustion explosion and shock waves 2001v37 2 p168-172

4 R Tomoshige A Murayma T Matsushita Production of TiB2-TiNcomposites by combustion synthesis and their properties J AmCeram Soc 1997 80[3] 761-764

5 MAKorchagin TFGrigorrsquoeva BBBokhonov MRSharafutdinovAPBarinova NZLyakhov Solid-state combustion in mechanicallyactivated SHS systems Combustion explosion and shock waves2003 v39 1 p43-58

6 MAKorchagin DVDudina Application of self-propagating high-temperature synthesis and mechanical activation for obtainingnanocompositesCombustion explosion and shock waves 2007v43 2 p176-187

7 MAKorchagin BBBokhonov Combustion of mechanicallyactivated 3Ti+2BN mixtures Combustion explosion and shockwaves 2010 v 46 2 p170-177

65

SPIN-CROSSOVER IN THE PENTANUCLEAR BYPIRAMIDALCo2Fe3 AND Fe2Fe3 COMPOUNDS

Sophia Klokishner Sergei Ostrovsky Andrei PaliiInstitute of Applied Physics Academy of Sciences of Moldova

Kishinev MoldovaKim Dunbar

Department of Chemistry Texas AampM UniversityCollege Station TX USA

Boris TsukerblatChemistry Department Ben-Gurion University of the Negev

Beer-Sheva Israel

In this article we report a model for a spin-crossover phenomenonin pentanuclear bypiramidal [M(III)(CN)6]2[M(II)(tmphen)2]3 (MM=CoFe FeFe) cluster compounds The spin-crossover phenomenonis considered as a phase transformation accompanied by a change of theground state spin The model takes into account cooperative interactionsin the crystal network local crystal fields and spin-orbit coupling actingwithin the degenerate metal sites Magnetic properties and Moumlssbauerspectra are analyzed and compared to the experimental data

1 IntroductionSpin-crossover compounds have been a subject of many

experimental and theoretical studies [1-6] Till now only a fewexperimental reports on spin crossover in cluster compounds [7-11] havebeen reported Recently FeII ions were introduced into the equatorialmetal sites of discrete cyano-bridged pentanuclear clusters[MIII(CN)6]2[MII(tmphen)2]3 (MM =CoFe(1) FeFe(2) ) [12] with atrigonal bipyramidal (TBP) structure The octahedral nitrogensurrounding of FeII ions facilitates the spin-crossover behavior Theoccurrence of the ls-hs transition in compounds 1 and 2 was proved bythe combination of Moumlssbauer spectroscopy magnetic measurementsand single-crystal X-ray studies For both types of clusters[FeII(tmphen)2]3[M

III(CN)6]2(M=FeCo)7 the T product increases by

~9emumiddotKmol between 150 K and 375 K thus indicating the ls ndashhstransition at the FeII sites The TBP FeII

3CoIII2 cluster due to its electronic

66

structure represents an ideal system for studying the effects ofintracluster short-range and intercluster long-range interactionsfacilitating spin-crossover In the (FeIII)2 (FeII)3 cluster the hs-FeII and ls-FeIII ions are coupled by exchange interaction In spite of the fact that theexchange interaction of the hs-FeII and ls-FeIII ions through the cyanidebridge is sufficiently weak as compared with that in oxide clusters it isinterestingly to understand whether this interaction may affect the spintransformation The effects of orbital degeneracy on the spin-crossovertransformation in the [FeII(tmphen)2]3[FeIII(CN)6]2 crystal will beexamined as well In the present article a microscopic approach to theproblem of spin crossover in crystals containing metal clusters isdeveloped

2 The modelIn the basic structural unit of compounds 1 and 2 two MIII ions

surrounded by six carbon atoms occupy the apical positions and threeFeII ions coordinated by the nitrogen atoms reside in the equatorial plane[12] In a strong crystal field of carbon atoms the ground terms of the

CoIII and FeIII ions are the low-spin orbital singlet )( 621

1 tA ( 0S ) and

the orbital triplet )( 421

3 tT respectively The ground state of a FeII -ion in

the crystal field induced by the nitrogen atoms can be either low-spin

(ls)- term )( 621

1 tA or high spin (hs) ndashterm 2422

5 etT Both magnetic

measurements and Moumlssbauer spectroscopy for water containing crystals[12] demonstrate the presence of some amount of FeII ions in the hsconfiguration even at very low temperatures Further on we consider inthe model two types of FeII ions and denote by x the fraction of FeII -ions which are in the hs ndashstate at all temperatures while theconcentration of those ions which undergo the ls-hs transition is (1-x)The number pi of trigonal bypiramidal clusters in which i (i=0123) ofthree FeII ions are in the hs configuration in the whole temperature range

is estimated as iiii xxCp 33 1 where rllrC r

l

The Hamiltonian of intraion interactions can be written in the form

67

Hg

gllsH

kkB

kkB

kZkk

)(

32)(

211

02

0

H

lsH

(1)

where numbers theIIFehs ions in the k-th bypiramidal cluster the

first term is the spin-orbit (SO) coupling in the cubic )( 2422

5 etT - term of

theIIFehs -ion the second term describes the axial crystal field

splitting the 125 lT term into an orbital singlet ( 0lm ) and an

orbital doublet ( 1lm ) the third term refers to the Zeeman

interaction for hs-FeII ions and contains both the spin and orbitalcontributions B is the Bohr magneton and g0 is the spin Lande factorFinally the fourth term represents the interaction of the ground Kramersdoublets of two ls-FeIII ions in the cluster with the external magnetic

field i is the matrix of the pseudo -spin frac12 of the ls-FeIII ion g1 =173

is the Lande factor Up to room temperature the ls-FeIII can be regardedas an ion with the pseudo-spin frac12 because the ground Kramers doubletand the excited quadruplet arising from the splitting of the 2T2 term by

the spin-orbital interaction are separated by the gap 173023 cm

( 1486 cm [13] for a free ls-FeIII) that is large enough from the

thermal population of the excited quadruplet at room temperatureThe superexchange interaction (several cm-1 [1415]) in the

[FeII(tmphen)2]3[FeIII(CN)6]2 through the cyanide bridges couples the hs-FeII ions in equatorial and ls-FeIII ndashions in axial positions Further on wewill neglect the essentially anisotropic orbitally dependent terms andretain only the isotropic part of the exchange interaction between the hsndashFeII and ls ndashFeIII ions in a cluster The Hamiltonian of exchangeinteraction for the thk cluster looks as follows

kkkex

k

exJH

212 σσs (2)

where 2s is the spin of the hs-FeII ion the summation in (2) takes

into account the hs-FeII ions appearing in the thk cluster due to thespin transition and those which are in the hs-state in the whole

68

temperature range As in [16-18] we suppose that the mechanismresponsible for the ls-hs transition is the interaction of FeII ions with thespontaneous all-round full symmetric lattice strain Applying theprocedure suggested in [16-18] we obtain the Hamiltonian of electron-deformational interaction

2k kkk

kkst

nm

JBH (3)

where 21AB 21AJ

01021

2

ccc

cA n

(n=123) is the number of FeII ions which undergo the ls-hs transition ina complex m is the number of TBP MIII

2MrsquoII3 complexes whose FeII ions

are involved in the spin conversion =1n k=1m 0 is thevolume that falls at a Fe ion and its nearest surrounding and is the unit

cell volume per one iron respectively In the basis of the states 25T and

11A the 1616 matrix k is diagonal and has 15 eigenvalues equal to 1

and one eigenvalue equal to -1 Finally 2)(1 lshs

2)(2 lshs hs and ls are the constants of interaction of the

FeII ion with the full symmetric strain1A in the hs and ls states

respectively The first term in (3) acts as an additional field applied toeach spin-crossover ion and redefines the effective energy gap 0

between the hs and ls states of the FeII in the cubic crystal field Thesecond term in (3) represents an infinite range interaction between theFeII ions which undergo the spin conversion This interaction arises fromthe coupling to the strain The model of the elastic continuum introducedabove satisfactorily describes only the long-wave acoustic vibrations ofthe lattice Therefore the obtained intermolecular interactioncorresponds to the interaction via the field of long-wave acousticphonons

Due to the proximity of the FeII ions in the clusters short-rangeinteractions between these ions inside the cluster are relevant Thelargest is the effect of the exchange arising from the optic phonons [19]

69

The Hamiltonian describing short-range interactions between FeII ionswithin the trigonal bipyramid can be written as

0

kkk

sr JH (4)

The Hamiltonian (4) takes into account the interaction between the FeII

ions participating in the spin transitions the interaction of these ionswith those FeII ions which are in the hs-state in the whole temperaturerange as well as the interaction between the latter It should bementioned that eq (3) as compared with eq(4) only accounts for FeII

ions participating in spin conversion The Hamiltonian for the wholecrystal can be written as

k

kexstsr HHHHH

2

00 (5)

where k

k

exex HH In the molecular field approximation the full

Hamiltonian H can be written as a sum of one-cluster Hamiltonians

)(32)(

)2

(~

211101

2

1

0

0

kkB

kkkB

k

ex

kkZ

kkkkkkk

gIgHIl

IlsJBJH

HlsH

(6)

where in the basis of the states 25T and 1

1A kI1

is a diagonal 1616 -

matrix with 15 eigenvalues equal to 1 and one vanishing eigenvalue is the order parameter In fact the Hamiltonians kH

~describe clusters

with different numbers of spin-crossover FeII ions and k as beforenumbers the clusters in the crystal For calculation of the temperaturedependence of the order parameter the self-consistent procedure wasapplied The calculations of the magnetic properties were based on theHamiltonian given in Eq(6)

3 Results and discussionThe estimation of the parameters J and B was performed

according the procedure suggested in paper [16-18] For characteristicfor compounds 1 and 2 parameters =1026Aring3 0 =8Aring3

c2 (005divide01)c1211

2 10 cmdynec 1046 141

cm 142 1087 cm the

70

parameters J and B take on the values 20divide80 cm-1 and -95 divide -24 cm-1respectively

Fig1 shows the experimental data for compound 1 together withthe calculated T vs T curves The result of the best fit procedure in

the model above developed is presented by curve 1 The best fitparameters are the part of the figure caption One can see that a quitegood agreement with the experimental data is obtained At temperaturesbelow 100 K the T values show that the FeII ions are mainly in the ls ndashstate However some small admixture of hs ions is present In thetemperature range 150-300 K the T product gradually increases thusindicating the ls - hs transition in the FeII ions

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30 35

04

06

08

10

3

2

1

T

cm

3K

mo

l-1

Temperature K

23

1

T

cm

3K

mo

l-1

Temperature K

Fig1 Temperature dependence of the T product for 1 Circles-experimentaldata [12] The solid lines represent a theoretical fit with =-103 cm-1 x=10and (1) hs-ls =640 cm-1 J =35 cm-1 J0=45 cm-1 =180 cm-1 =10 (2) hs-

ls=620 cm-1 = -136 cm-1 J=0 J0=0=06 (3) hs-ls=630 cm-1 =168 cm-1J=0 J0=0 =06

The parameter J of long -range cooperative electron-deformationalinteraction obtained from the best fit procedure falls inside the limits

71

estimated above Relatively small values of the parameters J and J0 ascompared with the gaps hs-ls= 0-2B and are also in agreement withthe observed gradual temperature dependence of T and noticeable

increase of T at temperatures higher than 150K Finally the estimated

from the best fit procedure percentage of FeII ions (x=10) which are inthe hs-state at any temperature is very close to that obtained from theMoumlssbauer spectra [12] For comparison in the same figure (curves 23)the results of fitting of the T curve in neglect of long- and short-

range interactions are shown for the cases of 0 and 0 It isseen that in this approximation the calculated curves 2 and 3 differsignificantly from the experimental one both at low and hightemperatures besides this the obtained value 60 is too small forhs-FeII-ions

For compound 2 the variation of the observed magneticsusceptibility as a function of temperature is presented in Fig2

0 50 100 150 200 250 300

0

1

2

3

4

5

6

7

321

T

cm

3K

mo

l-1

Temperature K

Fig2 Temperature dependence of the T product for 2 Circles experimentaldata [12] Curves 1- 3 were calculated with the following parameter values hs-

ls =690 cm-1 J=30 cm-1 J0=40 cm-1 =100 cm-1 =-103 cm-1 =10 x=9and (1) Jex = 3 cm-1 (2) Jex = 0 (3) Jex = -3 cm-1

72

First the magnetic behavior of complex 2 was analyzed withneglect of intracluster Heisenberg exchange interaction between FeII andFeIII ions The result of the best fit procedure is presented by curve 2 inFig2 The best fit parameters are the part of the figure caption One cansee that the values of the key parameters are close to those for complex1 However the obtained energy gap hs-ls between the ls and hsconfigurations for complex 2 is a bit larger than the corresponding gapfor compound 1 while the parameters of short-range and long-rangeinteractions are smaller Namely this difference in the characteristicparameters leads to lower values of T for compound 2 as compared

with compound 1 at temperatures higher than 150K The effect ofexchange interaction on the magnetic behavior is illustrated in Fig2 bycurves 1 and 3 Since typical values of the exchange parameters incyanide bridged complexes are of several cm-1 we calculated the Tproduct with the set of the best fit parameters and Jex = -3 cm-1 and 3cm-1 One can see that at temperatures higher than 50K the smallexchange interaction has no effect on the magnetic properties ofcomplex 2

Moumlssbauer spectra provide direct information about the populationof the hs and ls states and serve a reliable test for the theoreticalbackground of the SCO phenomenon The total Moumlssbauer spectrum(ie the observable spectrum) was obtained by summing up the spectrayielded by different cluster electronic states in the molecular field withdue account for their equilibrium populations for a given (at a certaintemperature) value of the molecular field In calculations theexperimental values for the parameters of the quadrupole splttings andisomeric shifts were taken from [12] The calculated and experimentalspectra are shown in Fig3

Quite good agreement between the experimental data andtheoretical calculations is obtained It should be underlined that themodel takes into account the main effect inducing the temperaturedependence of the Moumlssbauer spectra and this is the temperaturedependence of the cluster energies in the molecular field Namely thiseffect is responsible for the transformations of the Moumlssbauer spectrawith temperature

73

The proposed model gives a good fit to the observed temperaturedependence of the static magnetic susceptibility and the Moumlssbauerspectra The last clearly illustrates the cooperative nature of SCOtransformations in TBP compounds that leads to a crossing of the ls andhs levels due structural phase transition induced by the ordering of thelocal deformations through the field of the acoustic phonons

Fig3 Moumlssbauer spectra for compound 1 calculated at T=42 220 and 300Kwith the set of the best fit parameters (thick solid lines) Contributions from ls -FeII and hs -FeII ions are shown in dash and dot lines respectively The half-width of the individual lines Г=016 cm-1(42 К) Г=018 cm-1(220К)Г=024cm-1(300К)

74

AcknowledgmentsFinancial support of the STCU (project N5062) is highly

appreciated BT and KD gratefully acknowledge financial support ofthe Binational US-Israel Science Foundation (BSF grant no 2006498)BT thanks the Israel Science Foundation for the financial support (ISFgrant no 16809)

References1 Guumltlich P Goodwin H A Spin Crossover in Transition Metal

Compounds Springer-Verlag 20042 Hauser A Light-Induced Spin Crossover and the High-Spin rarrLow-

Spin Relaxation Springer-Verlag 20043 P Guumltlich J Jung Nuovo Cimento D 1996 18 1074 P Guumltlich A Hauser H Spiering Angew Chem Int Ed Engl

1994 33 20245 J Zarembowitch New J Chem 1992 16 2556 A B Gaspar V Ksenofontov M Serdyuk P Guumltlich Coord

Chem Rev 2005 249 26617 JA Real AB Gaspar MC Munoz P Guumltlich V Ksenofontov H

Spiering TopCurrChem2004 2331678 G Vos RAG De Graaff JGHaasnoot AM van der Kraan De

PVaal JReedijk InorgChem 1984 23 29059 EBreuning MRuben JMLehn FRenz YGarcia VKsenofontov

P Guumltlich E Wegelius KRissanen AngewChemIntEd 2000 392504

10 M Nihei MYi MYokota LHan AMaeda HKushida HOkamoto HOshio AngewChem IntEd 2005 446484

11 D-Y Wu O Sato Y Einaga C-Y Duan Angew Chem Int Ed2009 48 1475 ndash1478 2009

12 MShatruk ADragulescu-Andrasi KEChambers SAStoianELBominaar CAchim KRDunbar J Am Chem20071296104

13 AAbragam BBleaney Electron Paramagnetic Resonance ofTransition Ions Clarendon Press Oxford 1970

14 A V Palii SM Ostrovsky S I Klokishner B S Tsukerblat C PBerlinguette K R Dunbar J R Galaacuten-Mascaroacutes JAmChemSoc2004 126 16860

15 HWeihe H Gudel H Comments Inorg Chem 2000 22 75

75

16 SI Klokishner F Varret J Linares ChemPhys 2000 255 31717 SI Klokishner JLinares PhysChemC 2007 111 1064418 SI Klokishner J Linares F Varret Journal of Physics

Condensed Matter 2001 13 59519 JM Baker Rep Prog Phys 1971 341 109

53

NON-CARBON PREPARATION OF SILICON BYMECHANICALLY ACTIVATED THERMAL SYNTHESIS

TF Grigorieva1 TL Talako2 AI Letsko2 V Šepelaacutek3 VG Scholz4MR Sharafutdinov1 IA Vorsina1 AP Barinova1 PA Vitiaz2

NZ Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry Kutateladzestr 18 Novosibirsk 630128 Russia grigsolidnscru

2 Powder Metallurgy Institute Platonov str 41 Minsk 220005 Belarus3 Inst of Nanotechnology KIT Eggenstein-Leopoldshafen 76344 Germany

4 Inst of Chemistry Humboldt Univ Berlin 12489 Germany

IntroductionIn industrial processes the production of Si is based on the

reduction of silicon dioxide by carbon at a temperature of about 1800 C[1] However the coke applied to the reduction can be hardly refinedfrom the most dangerous for silicon impurities like boron phosphorusarsenic and antimony That is why development of non-carbon routes forsilicon production is a topical problem of a silicon industry Reductionof oxides with magnesium and aluminum by the method of self-propagating high-temperature synthesis (SHS) has been used in industryfor a long time [2] As such reactions are highly exothermal they can bealso organized with the use of mechanochemistry for instance reductionof the copper oxide by aluminum Mechanochemical reduction of ironoxide by aluminum aimed at obtaining precursors with differentcompositions for intermetallideoxide SHS composites has been alsoconsidered [3ndash6]

SiO2 + Al reaction is not high exothermic enough to organize theSHS without preliminary heating [7] Mansurov et al [8] reportedcreation of ceramic composites in several stages first the silicon oxidewas mechanochemically treated in an organic compound environmentthen the resultant material was annealed (carbonized) at ~ 850 C andfinally the mixture of the carbonized silicon oxide with aluminum wassubjected to SHS However as-formed product included silicon carbide

The objective of activities described in this paper is to study thepossibility of using mechanochemical treatment for obtainingsiliconaluminum oxide composites by the SHS and thermal synthesis atconsiderably lower temperatures with the following removal of alumina

54

Sample preparation and examination proceduresThe PA-4 aluminum powder and the silicon oxide with a particle

size of ~ 3 nm were used in our experimentsA stoichiometric mixture of the silicon oxide with aluminum was

processed in a high energy planetary ball mill (drum volume 250 cm3ball diameter 5 mm mass of the balls 200 g mass of the sample 10 gand velocity of rotation of the drums around a common axis ~1000 rpm)

The IR spectra were recorded by a Specord IR 75 spectrometerthe samples for this study were pressed with annealed potassiumbromide

The 27Al (I = 52) NMR spectra were recorded on a BrukerAdvance 400 spectrometer corresponding to a 27Al resonance frequencyof 782 MHz MAS experiments were realized with a high speed probeusing 25 mm zirconia rotor The spinning speed was 20 KHz Themagnetic field strength (in frequency unit) was set to 104262 MHz Theexcitation pulse duration was chosen equal to 1 s The recycling delaybetween each acquisition was fixed to 1 s To see weak signals in the Al-O region in mechanically activated samples we applied accumulationsnumbers up to 56000 (ie measurement time of 15 hours)

The dynamics of the SHS process was studied with the use ofdiffraction of synchrotron radiation and an OD-3 single-coordinatedetector The samples for SHS were prepared in the form of pellets 20mm in diameter and 1ndash2 mm thick by pressing at a pressure of 200 atmThe resultant samples were placed onto a ceramic plate so that they werein the center of the goniometer The process was initiated by a nichromespiral The OD-3 detector was triggered to operate in the ldquofast filmingrdquomode simultaneously with the beginning of pellet burning The time ofone ldquoframerdquo was 05 sec and the number of ldquoframesrdquo was 128 Theradiation wavelength was 1527 Aring

For investigation of mechanically activated thermal synthesis thesamples were heated up to 650 C in the reaction chamber XRK 900 inair with a heating rate 10 min The OD-3 detector was also used forstudying the process dynamics though time of one ldquoframerdquo was 1 min

55

Results and discussionFirst we made an attempt of direct mechanochemical reduction of

the silicon oxide by aluminum The study of this process showed that thechemical reaction of SiO2 reduction does not occur within 6 min ofmechanical activation The IR spectrum of the initial mixture containsclear absorption bands with the maximums at 1005 and 480 cmminus1

(valence and deformation oscillations of the SindashO bond of the SiO4

tetrahedra of the siliconndashoxygen skeleton) and two maximums in therange of 900ndash670 cmminus1 due to oscillations of the SindashOndashSi bridges Thephenomena observed in the course of mechanical activation were agradual decrease in intensityand broadening of the characteristic bands of the SindashO bond (Fig 1)

An electron-microscopy study of the SiO2Al composite obtainedafter 1 min of mechanical activation in characteristic radiation revealed a

Fig 2 Microphotograph of themechanocomposite after 1 minactivation in Si characteristic

radiation

Fig 1 IR spectra of the SiO2 + Al mixturebefore mechanical activation (1) and aftermechanical activation during 05 (2) 1 (3)

and 6 (4) min

56

very small grain size and a very uniform distribution of the componentsin the mechanocomposite (Fig 2)

Based on the data of the differential thermal analysis (DTA) evenshort-time activation of this mixture appreciably affects its thermalcharacteristics For the initial mixture the real chemical interactionoccurs at a temperature T gt 1000 C (Tmax = 10836 C) (Fig 3 a) iesubstantially higher than the melting point of aluminum whereas thesituation is different for the mixture subjected to mechanical activationduring 20 sec Two clearly expressed exothermal peaks appear the firstpeak at 6217ndash6486 C (Tmax = 6327 C) and the second peak at 9921ndash10759 C (Tmax = 10292 C) (Fig 3 b) For the mixture activated for 40sec the first peak is at 6045ndash6366 C (Tmax = 612 C) and the secondpeak is extremely broad and smeared in the range of 8161ndash11117 C(Tmax = 10381 C)

These observations can be explained by the fact that a tightcontact is created between some part of the ultrafine non-plastic siliconoxide and plastic aluminum already within 20 sec of mechanicalactivation the silicon oxide is ldquowettedrdquo by aluminum as a result somepart of the silicon oxide starts to interact with aluminum at a temperatureT = 6217C which is lower than the melting point of the latter Asmechanical activation is continued aluminum becomes also dispersed tonanoparticles greater amounts of the components of the mixture areinvolved into the contact and the temperature of the interactionbeginning decreases after 1 minute of activation the interaction beginsat T = 5399 C and ends at T = 6303 C (Fig 3 c)

The curve for this sample obtained by the method of differentialscanning calorimetry (DSC) has only one exothermal peak ie theentire process proceeds at a temperature lower than the melting point ofaluminum Longer activation further decreases the temperature ofreaction beginning (Table 1) but there are no any further significantchanges in the system parameters determined by DSC

The duration of mechanochemical treatment was limited to 6 minfor the following reasons- the IR spectra are so smeared already after 4 min that do not provide

any new information (see Fig 1)- the DTA study does not reveal any significant changes in the thermal

characteristics after 1 min of mechanical activation (see Table 1)

57

- mechanochemical actions should be always minimized to ensure theminimum possible contamination of the products by milling

Fig 3 Results of differential scanning calorimetry (DSC) and thermogravimetry(TG) studies of the SiO2 + Al mixture before (a) and after mechanical activation

during 20 (b) and 60 sec (c)

58

Table 1 Parameters of Exothermal Peaks on DTA Curves of SiO2 + AlSamples after Mechanical Activation

Temperature CDuration of activation

beginning of thereaction

end of the reaction

1 min 5930 6303

2 min 5871 6243

4 min 5867 6291

6 min 5870 6258

27Al MAS NMR spectra of the nanostructured SiO2Almechanocomposites are dominated by a broad resonance associated withthe presence of nanostructured Al matrix (Fig 4) The interestingobservation is that additional resonance lines appear in the spectra ofmechanoactivated samples corresponding to AlO4 AlO5 and AlO6

polyhedra Their content is slightly increasing with increasing millingtime however the relative intensity of AlOx polyhedra compared withthe Al matrix spectral intensity is even after the longest milling periodvery low It can be assumed that these nonequilibrium localcoordinations of aluminium atoms are located on the SiO2-Al interfaces[9] The intensity of the resonance lines belonging to various polyhedrarelative to the total spectral intensity allows us to calculate the volumefraction of interface regions in the nanocomposites Furthermoreassuming a spherical shape of SiO2 nanoparticles the thicknees of theinterface regions was calculated their known volume fraction

Thus the study of mechanically activated SiO2+Al mixturesshows that silicon reduction does not occur during mechanical activationstep except formation of some AlOx species at the interfaces but anexothermal reaction in activated mixtures can proceed at substantiallylower temperatures

In the subsequent step the nanostructured SiO2Almechanocomposites were used as precursors for the preparation ofSiAl2O3 composites via self-propagating high-temperature synthesisOur experience shows that combustion initiation requires sample

59

preheating approximately to 200 C (as compared with 650-860 Сreported in [7])

Fig 4 27 Al MAS NMR spectra of non-activated sample (a) the samplemechanoactivated for 1 (b) and 6 (c) minutes

60

The overall pattern of phase transformations is illustrated in Fig 5a To analyze them however it is more convenient to use the projectiononto the diffraction angle (β)ndashtime plane (Fig 5 b) As the silicon oxideused in these experiments is amorphous to x-ray radiation onlyaluminum peaks are observed

Fig 5 Dynamics of phase transformations in the Al + SiO2 mechanocompositein the SHS mode (a) three-dimensional image (b) projection onto thediffraction anglendashtime plane

61

It is clearly seen thataluminum becomes heatedas the combustion waveapproaches the peaks areshifted toward smallerangles ie greaterdistances between theplanes After that theintensity of these peaksdrastically decreaseswhich is apparently due tomelting No crystallinephases are observed in thetwo frames (~ 1 sec) Inour opinion corundum(Al2O3) peaks appearslightly earlier than siliconpeaks A possible reason isthe lower melting point ofsilicon (1410 C) as compared with corundum (2050 C) An electron-microscopic study of the SHS product of the SiO2 + Al system subjectedto mechanical activation during 1 min in characteristic radiation (Fig 6)shows a fairly uniform distribution and small size of all elements in thesystem including silicon being formed

Previously it was shown that chemical interaction between SiO2

and Al in the mechanocomposites formed during the mechanicalactivation starts at essentially (~ 500 C) lower temperatures as comparedwith the non-activated mixtures

In the final step we used as-formed mechanocomposites asprecursors for the preparation of SiAl2O3 composites via thermalsynthesis The samples after mechanical activation for 6 min wereplaced into cuvette and gently prepressed to get the plane surface Thenthe cuvette with the sample was sited in the furnace The thermocouplewas directly close to the registration area Recording of diffractogramswas started at temperature 230 С Dynamics of phase transformation inAl SiO2 composites during heating from 590 up to 660 C is presentedin Fig7

Fig 6 Microphotograph of the SHS productin Si characteristic radiation

62

As can be seen from the Fig 7 the reaction products (silicon andalumina) start to form at about 590 С It is interesting that corundum isformed during the SHS and thermal synthesis after low activation time

Fig 7 Dynamics of phase transformation in Al SiO2 composites duringheating from 590 up to 660 C

Fig 8 XRD-pattern of the thermal synthesis product from the mechanocompositesactivated for 6 min and heated up to 660 C

63

while -Al2O3 is identified in the product of thermal synthesis afterlonger MA durations (Fig 8)

ConclusionsThus though the silicon oxide is not reduced by aluminum

directly by mechanical activation the use of the mechanocomposite as aprecursor for both SHS and thermal synthesis allows a fine-grainsiliconaluminum oxide composite to be obtained In both caseschemical interaction starts at essentially lower temperatures as comparedwith the non-activated mixtures

AcknowledgementsThis work was supported by the joint project No 5 ldquoNon-carbon

preparation of Si by mechanically activated thermal synthesisrdquo of NASBand SB RAS

References1 Denisov VM Istomin SA Podkopaev OI Serebrjakova LI

Pastuchov EA Beletsky VV Silicon and its alloys EkaterinburgPublishing house of Ural Branch of the Russian Academy ofSciences 2005 467 p (in Russian)

2 AG Merzhanov Forty Years of SHS Happy Life of a ScientificDiscovery (in Russian) Chernogolovka (2007)

3 TF Grigoryeva SA Petrova IA Vorsina et alldquoMechanochemical reduction of a copper oxiderdquo in TheOptimization of the Composition Structure and Properties ofMetals Oxides Composites Nano and Amorphous Materials Proc6th IsraelindashRussian Bi-National Workshop Jerusalem (2007) pp197ndash204

4 TF Grigoryeva TL Talako AA Novakova et al ldquoMA and MASHS production of nanocomposites metaloxides andintermetallicsoxidesrdquo ibid pp 139ndash148

5 NZ Lyakhov PA Vityaz TF Grigorieva et alldquoMechanochemically synthesized SHS precursors for obtainingintermetallideoxide nanocompositesrdquo Dokl Akad Nauk 406 No6 776ndash778 (2005)

64

6 5 T Talaka T Grigorieva P Vitiaz et al ldquoStructure peculiaritiesof nanocomposite powder Fe40AlAl2O3 produced by MA SHSrdquoMater Sci Forum 534ndash536 1421ndash1424 (2007)

7 Maltsev VM Gafiyatulina GP Tavrov AV Spreading of thecombustion wave in SiO2-Al systems Proc SPIE Vol 3172(111997) p 724-727

8 ZA Mansurov RG Abdulkarimova NN Mofa et al ldquoSHS ofcomposite ceramics from mechanochemically treated and thermallycarbonized SiO2 powdersrdquo Int J SHS 16 No 4 213ndash217 (2007)

9 V Sreeja TS Smitha Deepak N Ajithkumar TG and PA JoySize dependent coordination behavior and cation distribution inMgAl2O4 nanoparticles from 27 Al solid state NMR studies J PhysChem C 112 14737-14744 (2008)

37

THE PREPARATION OF MECHANICOMPOSITESTUNGSTEN-METAL AND SINTERING MATERIALS

T Grigoreva1 L Dyachkova2 A Barinova1 S Tsibulya3 N Lyakhov1

1 Institute of Solid State Chemistry and Mechanochemistry SB RAS 18Kutateladze str 630004 Novosibirsk Russia grigsolidnscru

2 Institute of Powder Metallurgy NAS B Minsk Belarus3 Boreskov Institute of Catalysis SB RAS Novosibirsk Russia

Tungsten-based materials are used for manufacture of electro-technical items spot welding electrodes spraying cathodes etc

The preparation of the high-melting materials is powerconsumptive as two-stage high-temperature sintering is used tungstenpre-sintering temperature is 1150 ndash 1300 C final tungsten sinteringtemperature is 2900 - 3000 C [1]

Metal additives with a lower melting temperature are introducedinto the high-melting material for sintering temperature reduction andsince the tungsten powder has a bad moldability level more plasticmetals such as copper nickel iron are introduced for the moldabilityimprovement

Tungsten ndash copper mixture has been studied the best so farThe mixture W-Cu sintering process research has shown [2] that

the product density depends on the initial powders dispersion degree andthe mixture composition So at the tungsten particles size 10-15 m themaximum densification is observed at the copper weight ration 50 The blend density sharply decreases with the copper content decrease(less than 35 ndash 40 wt) At the same time mixtures with the coppercontent not higher than 10 are needed Special methods have to beused for the preparation of the tungsten alloys

The active densification (from 44 till 12 ) is known to take placeat 1100 - 1200 C at sintering of mixtures W-20 vol Cu with tungstenparticles size lower than 1 m [3] Even higher densification speed isobserved in a blend attained with copper tungsten reduction whencomponents mixing practically achieves a molecular level [4] ie thesecond element concentration reduction is possible at tungsten particlessize decrease and homogeneous distribution of the both componentsThe original blends mechanical activation process [5ndash7] is very

38

perspective in this trend since grinding and formation of larger contactsurface between the original components take place during mechanicalactivation This process is especially effective at mechanical activationof solid and liquid metals and plastic ndash non-plastic metals pair Thecomposite nucleus (non-plastic component) ndash cover (plastic metal) canbe created in this case The possibility of chemical interaction onbetween tungsten and plastic metal the contact surface duringmechanical activation should be considered here

The work aim is to study structure and morphology of thecomposites formed at mechanochemical activation of the tungsten witha small content (till 10 ) of plastic metals both interacting (nickel iron)with it and not interacting (copper) with it The influence of the structureand morphology of the mechanocomposites on the processes of formingand sintering was studied

Powders of tungsten nickel iron copper were used forpreparation of mechanocomposites Mechanical activation of themixtures was carried out in a high energy planetary ball mill with watercooling in argon atmosphere (drum volume ndash 250 cm3 balls diameter ndash5 mm the load ndash 200 g the sample - 10 g the velocity of rotation of thedrums around a common axis 1000 rpm)

X-ray analysis was carried out with diffractometer D8 AdvanceBruker (Germany) at the CuK radiation Research of the structure andmorphology of the mechanocomposites was carried out with thescanning electronic microscope (SEM) ldquoMira LMHrdquo with the add-ondevice for micro-x-ray analysis The electronic probe comprised 5 2 nmthe actuation area comprised 100 nm The research was carried out inmodes of registration of absorbed (AE) and backscattered (BSE)electrons and also of characteristic radiation of tungsten copper nickeland iron The sintered materials research is carried out with themetallographic microscope MEF-3 (Austria) at zoom times200 and times950

The compressibility was determined via density in compliancewith the ISO 3927-1985 of cylindrical samples with diameter 10 mmheight 12 mm pressed in a steel die-mold at pressure 200 400 600 and800 MPa The pressed samples were sintered in vacuum at temperatureof 1100 ndash 1450 C

Compression strength of mechanically activated blends wasdetermined via the samples of diameter 10 mm height 12 mm

39

transverse strength ndash via prismatic samples with height 5 mm width 10mm length 55 mm The tests were preformed on the testing machineldquoInstronrdquo with the loading speed 2 mmmin

Sintered samples microstructure was studied on metallographicsections etched with solution (10 g K3Fe(CN)6 10 g KOH 100 mlH2O) via metallographic microscope MEF-3 of the company ldquoReihertrdquo(Austria)

Mechanical activation was carried out in two stages for attainingmechanical composites tungsten ndash metal (Cu Ni Fe) The first stagesaw grinding only tungsten for 4 min At the second stage 7 ndash 10 copper (nickel iron) was added and joint mechanical activation wascarried out for 1 ndash 2 min

In compliance with the x-ray data the initial tungsten sample is awell-crystallised powder (Fig 1a) The intensity of the diffraction peaksshows the texture (of the preferred orientation) presence in trend 110The X-ray pattern of the tungsten samples activated during 4 min (Fig1b) has widened peaks The X- ray analysis shows that widening ismostly caused because of micro-defects in the tungsten structure (at thelarge particles sizes retaining) It should be also noted that thedistribution intensity of the peaks shows the texture absence (the equalparticles distribution in powder from the point of view of theircrystallographic orientation)

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

Ia

u

2 Theta degree

110

200

211

220

30 40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

Ia

u

2 Theta degree

a bFig 1 X-Ray patterns for initial W (a) and activated for 4 min (b)

40

During the mechanical activation in a high energy planetary ballmills plastic metals tend to stick to balls and the drums walls even atshort-time activation because of that they were introduced to the blendsinto the already activated for 4 minutes tungsten and the mixture wastreated for 2 minutes more

The different X-Ray patterns were received for the samples withCu Ni Fe additives (Fig 2) The second metal phase is seen to bepresent in a well-crystallised form besides the phase W in all cases thecopper picks relative intensity is however considerably higher than thenickel picks intensity that in turn exceeds the iron reflection intensityFormation of intermetallic compounds in the X-ray-amorphous state oncontact surface WNi WFe can be supposed to be possible forchemically interacting metal pairs (tungsten ndash nickel tungsten ndash iron)X-Ray research data are indirect confirmation of this supposition Thesedata have shown that mechanochemical efforts donrsquot allow to receivehomogeneous distribution of copper in the tungsten matrixMechanocomposites W + 10 Cu is arranged in compliance with theldquosandwichrdquo principle where copper phase of micrometric size is locatedin the tungsten die (Fig 3)

The second metal phase is seen to be present in a well-crystallisedform besides the phase W in all cases the copper picks relative intensityis however considerably higher than the nickel picks intensity that inturn exceeds the iron reflection intensity Formation of intermetalliccompounds in the X-ray-amorphous state on contact surface WNiWFe can be supposed to be possible for chemically interacting metalpairs (tungsten ndash nickel tungsten ndash iron) X-Ray research data areindirect confirmation of this supposition These data have shown thatmechanochemical efforts donrsquot allow to receive homogeneousdistribution of copper in the tungsten matrix Mechanocomposites W +10 Cu is arranged in compliance with the ldquosandwichrdquo principle wherecopper phase of micrometric size is located in the tungsten die (Fig 3)Electron microscopy and X-Ray research of mechanocomposites forinteracting metals (W + 10 Ni) has shown homogenous nickeldistribution

41

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Ia

u

2 Theta degree

Cu

а

40 50 60 70 80 90

0

1000

2000

3000

4000

Ia

u

2 Theta degree

Ni

b

40 50 60 70 80 90

0

500

1000

1500

2000

2500

3000

3500

4000

Iau

2 Theta degree

Fe

c

Fig 2 X-Ray patterns for mechanocomposites W (4 min) + additives Cu(a) Ni (b) Fe (c) (2 min)

The received result allows to suggest that metals distributionhomogeneity depends on the thermodynamical parameters of theirmixture (Нmix(W-Ni) = - 2 kJmol Нmix(W-Cu) = + 10 kJmol [8])and on a possibility of the chemical interaction between them The thinlayers of intermetallic compounds form on the continuously renewingcontact surface in the systems W-Ni and W-Fe for this time period (1-2min) and because of distance these thin layers do not manage to form acrystalline phase that could be fixed in X-Ray way

42

а bFig 3 Micrographs of the mechanocomposites W-Cu (a) W-Ni (b) in

characteristic radiation Cu and Ni

The research of compressibility of various mechanocompositeshas shown that non-interaction metals (W-Cu) couldnrsquot compressed andthe compressibility of the interaction metals (W-Ni W-Fe) depends ofthe contents of additives Research of compressibility of mechanicallyactivated powders of various composition has shown that tungsten ndash10 iron mixture powder has the best compressibility level andtungsten ndash 7 nickel mixture powder has the least compressibility level(Fig 4)

But it should be noted that mechanically activated powderscompressibility level is not high moreover some mechanocompositesdo not have compressibility at specific pressure 200 ndash 300 MPa and thesamples layering is observed at pressure higher than 600 MPa Therelative density of the pressed samples is 50 ndash 78 It indicates at thenecessity of the additional lubricants introduction into the mechanicallyactivated powders for their compressibility increase

43

Fig 4 Tungsten-based mechanocomposites compressibility curve

For the powders compressibility improvement the lubricants areintroduced directly into initial mixture or plated to the press-mouldsurface for decrease of friction between the powder and the press-mouldwall and also between the powder particles The lubricant removaltemperature depends on the lubricant melting or dissociationtemperature The melting and boiling temperature or the lubricantsdissociation temperature generally used in powder metallurgy are givenin table 1 [9]

Stearates especially zink stearates have the leading place Therest lubricants have not got such a wide use since residual remains aftertheir removal [10]

Nowadays nylon-binding-based lubricant has been developedabroad This nylon binder is introduced during the charge mixingprocess and needs warm pressing [11-14] Such a lubricant allowsattaining high (θ is no less than 95 ) density of iron-based materials

The lubricant addition as a rule retains ~1 wt as higher contentleads to the pressing growth if the lubricant is present in the sinteringprocess till the sintering temperature

The lubricant burning-out process is carried out in the protective-reducing atmosphere in separate furnaces or in a sintering furnace (in thearea separated from the sintering area) The lubricant burning-outtemperature is as a rule not high and comprises 600 ndash 800 C

44

Table 1 Temperature of melting and dissociation of solid lubricants

Lubricant Lubricant formulaMeltingpoint С

Boiling ordissociation

point СZink stearate Zn(C18H35O2)2 140 335Calcium stearate Ca(C18H35O2)2 180 350Aluminium stearate Al(C18H35O2)2 120 360Magnesium stearate Mg(C18H35O2)2 132 360Plumbum stearate Pb(C18H35O2)2 116 360Lithium stearate LiC18H35O2 221 320Stearinic acid CH3(CH2)16CООH 694 360Oleinic acid С8Н17СНСН-

(СН2)7СООН13 286

Benzol acid С6Н5СООН 122 249Hexoic acid СН3(СН2)4СООNН2 -4 205Paraffin From С22Н46 till

С27Н56

40-60 320-390

Molybdenum disulfide MoS2 1185 -Tungsten disulfide WS2 1250 -Manganous sulphide MnS 1655 -Graphite С (crystalline) 3500 -Molybdenum trioxide MoO3 795 -

During one-component materials heating till 100 ndash 150 C thechange of the contact character between the particles connected withwater evaporation and elastic stress relief tale place As a result somecontact areas rupture and as a consequence general inter-particlecontact surface decrease are possible

The elastic stress relief is ended the further gases are removedand burning-out of the lubricants and binders introduced to the powdertake place during heating from 150 C till the temperature comprising 40ndash 50 of the metal melting temperature The oxide films reduction andnon-metal contact replacement with a metal one take place at highertemperatures although visible pressings density change does not takeplace

45

This work saw lubricants introduction during mechanicalcomposite formation zink stearate stearinic acid and lauric acid wereused The lubricants were introduced in amount of 0 1 0 2 0 3 0 5wt During mechanical activation metal ndash organic acid the latter ismelted (the melting temperature is lower than 70 C) and thus it wets themetal surface and flows with the formation of a larger contact surface Incase of good wettability and sufficient amount of the low-meltingconstituent all the solid-phase surface becomes contact ie mixturenucleus (metal) ndash cover (organic substance) is formed [15] Thecompressibility level has to be naturally higher in this case andmechanochemical approach allows a substantial reduction of plasticizingagentsrsquo concentration

Research of compressibility of powders with lubricants has shownthat Zink stearate has the least influence in comparison to otherlubricants used (Fig 5)

Fig 5 The compressibility curves of the mechanocomposites W-Fe with thelubricant 1 ndash zink stearate 2 ndash lauric acid

The lubricant content increase leads to the mechanically activatedpowders compressibility improvement (Fig 6) but at the lubricantcontent more than 0 3 the samples destruction takes place at sinteringbecause of intensive gas release Plasticizing agents introduction hasallowed mechanical composites formation also for non-interactingmetals (tungsten ndash copper) (Fig 6 7)

46

Fig 6 The compressibility curve of the mechanically activated blend W-Cuwith stearinic acid 1 ndash 0 1 2 ndash 0 3 3 ndash 0 5

Fig 7 The compressibility curves of the mechanically activated blend W-Cuwith lauric acid 1 ndash 03 2 ndash 05

Lauric and stearinic acids additives allow the pressings densityincrease by 25 ndash 40 (Fig 5 8)

Research of density of sintered samples of mechanocomposite hasshown that the density of the samples from mixtures tungsten ndash ironpressed at 400 and 600 MPa does not practically change after sinteringat 1250 C (Fig 9 line 2 5) and at 1450 C the samples density decreases(Fig 9 line 3 6) Mixtures tungsten ndash nickel are subject to a substantial

8

9

10

11

12

200 400 600

De

nsi

ty g

сm

3

Pressure МPа

1

2

11

115

12

125

13

200 300 400 500 600

10Fe+W

10Ni+W

De

nsi

tyg

cm

3

Compacting pressure MPa

47

shrinkage (Fig 10) and density of the samples of W-Ni pressed at 400MPa is 146 gcm3 after sintering at 1250 C and 147 gcm3 at 1350 CSintering temperature increase till 1450 C leads to samples shrinkinglevel reduction and density does not exceed 117 gcm3

Fig 8 The compressibility curves of blends W + 10 Fe and W-10 Ni withaddition of 1 of stearinic acid

Fig 9 Relation of density of mechanically activated blends W + 10 1 ndash afterpressing at 400 MPa 2 ndash pressing at 400 MPa sintering at 1250 ordmC 3 ndashpressing at 400 MPa sintering ndash at 1450 ordmC 4 ndash after pressing at 600 MPa 5 ndashpressing at 600 MPa sintering at 1250 ordmC 6 ndash pressing at 600 MPa sintering at1450 ordmC

10

11

12

13

14

200 400 600

Pressure МPа

Density

gс

m3

1

2

3

0

2

4

6

8

10

W+Fe

De

nsityg

cm

3

12 3

4 5 6

48

0

3

6

9

12

15

400 МPа 600 МPа

De

nsity g

сm

3

Fig 10 Relation of density of mechanically activated blend W + 10 Ni 1 ndashafter pressing 2 ndash pressing sintering at 1250 C 3 ndash pressing sintering at 1350C 4 ndash pressing sintering at 1450 C

Moulding pressure increase till 600 MPa practically does not

influence the sintered samples density Density reduction of the samples

sintered at 1450 C is apparently explained with dissociation of oxides

and other compounds of tungsten and nickel

Sintering at 1450 ordmC of blends W-Ni leads to meltback and

samples form loss thus sintering should be carried out at temperature

not higher than 1350 ordmC

Tungsten-based mechanocomposite strength research has shown

that strength has a direct relation to their density (Fig 11) The blend

tungsten ndash iron (870 MPa) has the minimal strength

The microstructure analysis has shown that in case of sintering at

temperature 1250 C tungsten ndash nickel have a very fine dispersed

structure (Fig 12) Coagulation of nickel insertions located at the base

grains boundaries in tungsten ndash nickel grains growth take place with

sintering temperature increase

49

0

100

200

300

400

500

600

700

800

900

1000

1100

1 2

Ela

stic

lim

it of

com

pre

ssio

n

МP

а

I - pressure 200 МPа

II - pressure 400 МPа

III - pressure 600 МPа

1 - sintering temperature 1250оС 2 - sintering temperature 1350

оС

I

II

III

Fig 11 Influence of attaining modes of samples from mechanically activatedblend tungsten + 10 nickel on their strength

Substantial grain growth large porosity formation nickel phase

particles growth take place in blends sintered at 1450 C eutectic that is

more visible in the blend tungsten ndash nickel is formed at tungsten grains

boundaries

Conclusions

The conducted research has shown that homogenous copper

distribution is failed to be carried out in tungsten with short-term

mechanical activation method for interacting metals of W-Cu system

These mechanically activated samples can be not compacted (moulded)

50

a b

c dFig 12 Microstructure of mechanically activated blends W-Ni sintered at 1250C (a b) and 1350 C (c d) a c ndash times200 b d ndash times950

Homogenous distribution of nickel and iron in tungsten is ensuredwith short-term mechanical activation in systems from interactingmetals The attained samples are formable mechanically activatedpowders compressibility has however been found to be not high therelative density of the pressed samples is 50 ndash 78 and that points atnecessity of additional lubricants introduction into powders for theircompressibility improvement Lubricants introduction allowed ensuringmoldability of immiscible system tungsten ndash copper and densification ofpressings by 25 ndash 40 - for interacting metals

Density of samples from blends tungsten ndash iron does notpractically change after sintering at 1250ordmC and is decreased at 1450 ordmCBlends tungsten ndash nickel are subject to a substantial shrinkage during

51

sintering Sintering temperature increase till 1450 ordmC also leads to theshrinkage level decrease Strength of sintered blends from mechanicallyactivated tungsten-based powders depends on density and kind of theadditive Grain size dispersivity and type of additive location in theblend structure from mechanically activated powders depend on thesintering temperature

AcknowledgementsThe work was carried out within the framework of Fundamental

Research Programme of Russian Academy of Sciences ldquoElaboration ofchemical substances attaining methods and new materials creationrdquoproject No 1821 ldquoElaboration of tungsten mechanical composites-basedhigh-density alloys creation basicsrdquo

References1 IM Fedorchenko IN Francevich ID Radomyselskiy at al

Powder Metallurgy Materials technologies properties andapplications Kiev Naukova dumka ndash 1985 ndash 624 P

2 VN Eremenko JV Najdich IA Lavrinenko Sintering in thepresence of liquid metal phase Kiev Naukova dumka ndash 1968 ndash 122P

3 VV Panichkina MM Sirotuk VV Skorohod Powder Metallurgyndash 1982 - 6 ndash P27-31

4 VV Skorohod YuM Solonin NI Filippov at al PowderMetallurgy ndash 1983 - 9 ndash P9-13

5 Kim JС Moon IН Nanostruct Mater 1998 Vol 10 No 2 P283-290

6 Moon IH Kim EP Petrow G Powder Metallurgy 1998 Vol41 No 1 P 51-57

7 Kim JC Ryu SS Kim YD Moon IH Scripta Mater 1998 Vol39 No 6 P 669-676

8 FR de Boer R Boom WCM Mattens AR Miedema andAK Niessen Cohesion in metals (Cohesion and structurevol 1) (Elsevier Amsterdam 1988) pp 758

9 Hausner H Handbook of Powder Metallurgy Chemical PublishingCo New York 1973

10 Moyer KH Intern J Powder Met 1971 - 7 Р 33

52

11 US patent В 22 F 100 5368630А Powder Metallic Blend with abinder for densification at the set temperature Journal Inventions ofcountries worldwide 1996 1

12 US patent В 22 F 100 5429792 Metal powder content containing a binder for pressing at elevated temperatures JournalInventions of countries worldwide 1996 7

13 US patent В22F 100 (11) 52980555 (40) 940329 laquoIron-basedpowder mixtures with a binding lubricantraquo 1995

14 US patent В 22 F 100 95372138 (5484469А) laquoMetal powder content and a method of a sintered part manufacture from itraquo 1995

15 TF Grigoryeva AP Barinova NZ Lyahov Mechanochemicalsynthesis of metal systems Novosibirsk Parallel ndash 2008 ndash 311 P

34

THE DETERMINATION OF THE KINETIC FUNCTIONSTRUCTURE FOR THE HIGH-TEMPERATURE SYNTHESIS IN

THE MECHANICALLY ACTIVATED MIXTURE 3Ni-Al

VYu Filimonov1 MA Korchagin2 EV Smirnov1NZ Lyakhov2

1Altai State Technical University Barnaul2Institute of Solid State Chemistry and Mechanochemistry SB RAS

Novosibirskvyfilimonovramblerru

The peculiarities of heating-up and phase formation in themechanically activated powder mixture 3Ni + Al reacting in the thermalexplosion mode have been experimentally investigated The self-heatingin the mixtures was studied using a specially designed SHS-reactorusing a technique presented in [1] Tungsten-rhenium thermocouples of100 microm diameter were used to control the temperature and to recordthermograms Preliminary mechanical activation was carried out using aplanetary ball mill of AGO-2 type in an atmosphere of argon under theenergy of 40g (centrifugal acceleration of balls 400 ms2) with varyingtime of the activation process The reactant mixtures were preparedusing the aluminum powder PAndash4 particle size 5 divide 60 microm and thecarbonyl nickel powder PNK-1L5 particle size 1 divide 10 microm

The primary goal of this work was to determine the activationenergy and the structure of the kinetic function during the heat evolutionin the system as a result of the phase formation At the adiabatic stage ofheating a system of equations of the temperature increase and thedynamics of the degree of transformation was considered [2]

0 expdT E

k fdt RT

(1)

f

RT

Ek

dt

d

exp1

(2)

The initial conditions are as follows 00 t 0TT where

T temperature of the reacting mixture degree of transformation

t time 0k 1k exponential factors E activation energy f -

35

kinetic function The search for )(f was performed in the known class

of functions [3]

exp

1nm

f

(3)

At the first step of analysis of the experimental thermograms theeffective activation energy of the phase formation was determined from

the curvature of the experimental plot ln 1dT dt f T Based on the

results of 6 measurements and using the slope of the fitting curvepassing through the point of the minimum curvature the effectiveactivation energy was determined which turned out to be anomalouslylow and equal to E = 95plusmn2 kJmol It was found that the experimental

results are best fitted with a function 1n

f where

09 015n [4] Fig1 shows the results of integration of (11) with the

determined parameters

Fig1 Results of integration of (11) -1 experimental thermogram -2

Since the interaction of the reactants is described by the law ofhomogeneous kinetics we suggest that during thermal explosion in themechanically activated mixture of the composition under study thesynthesis occurs through homogeneous regrouping of atoms of the initialreactants without formation of dense diffusional layers hindering thereaction The latter is possible due to high concentrations of defects andinternal stresses formed as a result of intensive plastic deformation of theinitial reactants during mechanical activation

36

References1 Filimonov VY Evstigneev VV Afanasev AV and Loginova MV

Thermal Explosion Ti + 3Al Mixture Mechanism of PhaseFormation International Journal of Self-Propagating High ndashTemperature Synthesis-2008- vol 17-2рр 101-105

2 Aldushin AP Martemyanova T M Merzhanov A G Propagationof the front of an exothermic reaction in condensed mixtures withthe interaction of the components through a layer of high-meltingproduct Composition Combust Explos Shock Waves19728(2)159

3 M I Shilyaev V Е Borzykh A R Dorokhov and V EOvcharenko Determination of thermokinetic parameters from theinverse problem of an electrothermal explosion Combust ExplosShock Waves 1992 28(3)258

4 MA Korchagin VYu Filimonov EV Smirnov NZ LyakhovThermal explosion of a mechanically activated 3Ni + Al mixture Combustion explosion and shock waves 2010 v 46 1 pp41-46

14

MODERN METHODS OF RHENIUM DETERMINATION

OV Evdokimova NV Pechishcheva KYu ShunyaevInstitute of Metallurgy of UB RAS

101 Amundsen st Ekaterinburg Russiashunuralru

IntroductionRhenium due to its unique properties is the promising metal

widely used in various industries At present day the main areas ofapplication of rhenium is the production of catalysts for the petroleumrefining industry and refractory alloys used for turbines manufacturing[1]

The great demand for this element requires large amounts of itsproduction There is a need extracting rhenium even from industrialwaste water from plants [2] due to the high cost and its low content innatural materials

This situation stimulates the development (or modification) ofmethods of analytical control of various nature materials

The content of rhenium in rhenium-containing materials bothnatural and technogenic and contect of accompanying to rheniumelements vary in a wide range of concentrations from 10-7 to tens ofpercent

Earlier the following methods were used for the determination ofrhenium spectrophotometry gravimetry kinetic electrochemicalextraction-fluorimetric methods X-ray fluorescence analysis [3] Themain disadvantages of mostly methods for determining rhenium are thelow sensitivity the bad reproducibility of results the influence ofaccompanying elements Ag W Mo Pt Cu Fe and etc

In modern analytical practice the following methods for therhenium determination are used inductively coupled plasma atomicemission spectroscopy (AES ICP) inductively coupled plasma - massspectrometry (ICP-MS) [4] electrochemical methods [1] X-rayfluorescence analysis and spectrophotometric methods do not lose theirrelevance [1] they have undergone significant modifications recently

15

Inductively coupled plasma atomic emission spectroscopy(AES ICP) is widely used for the rhenium determination in mineral rawmaterials and products of metallurgy production This method allows todetermine up to 10-4 rhenium The advantage of AES ICP is the highstability and reproducibility of results absence of chemical influences

However analysis of more complex objects such as metallurgicalproducts is a not easy task because the lines of rhenium emission areoverlaped with the lines of accompanying elements in samples So thelines of Mo (221427 nm) W (221431 nm) Fe (227519 nm) whichmay be present in the samples in large quantities are overlaped to themost intense lines of rhenium (221426 nm and 227525 nm) Thisproblem requires the development of new methods of samplepreparation and selection of optimal conditions for determination ofrhenium by atomic emission spectrometres

Also a significant disadvantage of this method is the small rangeof certificated reference materials So there are a limited number ofRussian rhenium standard materials with certified value of the rheniumcontent It is molybdenum and copper-molybdenum ores andconcentrates in which the rhenium content is in the range ofconcentrations from 000047 to 00221

In most cases analysts develop the synthetic mixture to monitorthe rhenium content in the analysis of specific samples of complexcomposition This mixture is similar to composition to the matrix of theanalyzed samples consisting of rhenium ions and other ions with agiven concentration For example the authors [5] to develop a techniquefor rhenium determining together with platinum and palladium in thesamples of spent catalysts by AES-ICP applied a synthetic mixtureprepared on the basis of aluminum oxide and standard solutions of Pt(IV) Pd (II) Re (VII)

One of modern methods and the most sensitive methods for thedetermination of rhenium is inductively coupled plasma - massspectrometry (ICP MS) [4 6 7 8] These days ICP MS withseparation and concentration allows to measure rhenium at lower thanseveral ngg However ICP MS performance in analyses of complexsamples is commonly affected by matrix effects and polyatomicinterference and signal drift High levels of salt solutions content cause

16

plugging of sampling orifice with decrease in analytical signal inaddition many spectral interferences may occur [6]

For the rhenium determination in molybdenite by ICP MS shouldbe use large dilution of sample to reduce the matrix influence and reducethe salts influence However this approach is not feasible in the case ofhigh levels of molybdenum and relatively low levels of rhenium in theanalyzed objects The most effective way to minimize the matrix effectsis separation of rhenium from the matrix Often for this purposeextraction by organic solvents [6] sorption by anion-exchangers [8] areused

Recently X-ray fluorescence analysis becomes more popular Itis rapid and is often used for mass analysis The advantage of thismethod is the possibility of direct determination of rhenium in the solidsamples in water solutions [9 10] in the biological samples (plants) [2]

However the method is not without disadvantages firstly thedetection limit of rhenium by X-ray fluorescence analysis is low and isonly 005-01 secondly there are only few the standard materials witha high rhenium content and thirdly the influence of interfering elementsin the sample related to determination of rhenium

Using the concentration can not only reduce the detection limitbut also in the same time solve and reduce the influence of interferingions For the concentration of rhenium in X-ray fluorescence analysis isoften used sorption of rhenium in the form of perrhenate-ions [9 10]

The authors [11] describes a problem related to the developmentof rhenium-containing standard materials by traditional hightemperature approach for X-ray fluorescence analysis Thus high-temperature studies of MoO3-ReO3 which could be served ascomparison materials for the rhenium determination by X-rayfluorescence analysis showed that 50-90 of rhenium is lost duringcalcination of mixtures it indicates the impossibility to use them fordevelopment of standard materials In the paper [11] the method ofpreparing rhenium glassy reference samples (10 - 50) on the basis ofBi2O3 and B2O3 is described The developed method allows to determinerhenium in the range of 001-10 [11]

17

Electrochemical methods in particular the electrostrippingvoltammetry (ESV) occupy a significant place in the analyticalchemistry of rhenium [12 13] This method allows to determine up to10-6-10-5 of rhenium

To avoid the effects of many electropositive components (Mo WCu Ag Au) which may interfere to the rhenium determination by ESVit has been proposed the sorption concentration of perrhenate ions on thesurface of activated charcoal (BAU) [12 13]

The most widely used techniques determine the 10-2 - 10-5 ofrhenium is spectrophotometric method The advantages of this methodare simplicity low cost equipment and a relatively high sensitivitySpectrophotometric method is based on the formation of coloredcomplex compounds of rhenium with organic and inorganic ligands [1]Photometric methods with thiocyanate ion thiourea are widely spread[14 15 16] Development of spectrophotometric methods for rheniumdetermination is largely due to the searching and using of new reagentsIn [17] for the extraction-photometric determination of perrhenate ionsin the form of ion associates the basic polymethine dyes derivatives of133-trimethyl-3H-indole have been offered but the influence ofoxyanions of tungsten and molybdenum is not excluded [17]

The disadvantage of the spectrophotometric methods is the needfor prior separation of rhenium from a number of interfering elements(Mo W Cu) that it is achieved by concentrating perrhenate-ions bysorption or extraction

Over the past decade main changes in the methods of rheniumdetermination related with the improvement stadium of samplepreparation transfer the sample into an analytical form modification ofknown methods and reagents (eg creation of new facilities developmentof new reagents for measurements) and conditions of analysis

In general in the literature a large number of works are relatedwith the separation of rhenium from the analyzed solutions and theseparation of rhenium (VII) from interfering elements by using newtypes of extractants and new sorbents is given Used extractants andsorbents as well as the optimal conditions for extraction and sorption ofrhenium are presented in Table 1 and 2 respectively

18

Extraction plays a dominant role in the methods of separationand concentration of rhenium

In most cases in the hydrometallurgical processing of rhenium-containing products in the acidic solutions ReO4

- are formed Forperrhenate ions extraction the anion-exchange reagents or extractants ofneutral type are often used The literature contains information on theextraction of rhenium (VII) by various amines and quaternaryammonium compounds [18 19 20] Efficient extractants of rheniumfrom acidic solutions are neutral organophosphorus compounds (tributylphosphate alkylphosphineoxides their derivatives) [21 22] a variety ofsolvent mixtures (tributyl phosphate + trioctylamine [23]) theextractants of neutral type such as ketones and aliphatic alcohols [1624 25]

Alcohols ketones and ethers are more selective having higherspeed separation of organic and aqueous phases as well as higherchemical resistance and lower cost compared with amines andorganophosphorus compounds but inferior to them in the extractioncapacity for rhenium (VII) [16]

Thus for perrhenate ions extraction aliphatic alcohols with 7-10carbon atoms in the aliphatic chain are well proven that can extractmore than 98 of rhenium from sulfuric acid and hydrochloric acidsolutions In the case of alcohol there is no need to use solvents andmodifiers what simplifies their use in extraction processes [16]

The efficiency of rhenium extraction into organic phase by aminesdecrease as follow quaternarygt tertiarygtsecondarygtprimary Amongthem secondary and tertiary amines are widely used as efficientextractants of rhenium from acidic solutions Perrhenate ions areextracted by amines in a wide range of pH For systems of amine - low-polar diluent - H2SO4-ReO4-H2O the formation inverse micelles istypical in the organic phase Acid ions and anionic complexes arelocated inside the aqueous core of the micelle with the metal ioncoordinates the polar functional group of amine [19 20]

It should be noted that the extraction by amines is complicated bythe use of solvents the nature of which depends on the solubility ofamines and their extraction capacity So low-polarity solvent toluene incontrast to the non-polar kerosene enhances the polarity of anionic saltsof amine which increases the reactivity of the extractant to the anion

19

exchange of inorganic acid to extractable anionic rhenium complexes[18]

Tertiary amines are the most effective extractants for rhenium(VII) However in paper [18] it is shown that the secondary amine(diisododecylamine) gives advantage to the tertiary amines on therhenium extraction efficiency from sulfuric acid media It can beexplained by the influence of steric factors and smaller rival extractionof mineral acids by secondary amines [1]

Most papers are related to the rhenium extraction from acidicsolutions but the extraction of rhenium from alkaline medium whichare formed after leaching of ores concentrates also represents a difficultproblem In the paper [23] rhenium extraction from alkaline solutionscontaining also molybdenum by solvent extraction using a mixture oftributylphosphate (TBP) and trioctylamine (N235) is describedMolybdenum which is also extracted by solvents in small amountsinterferes to the extraction of rhenium

Over the last decade most works refer to the development offundamentally new classes of extractants for perrhenate ions [26 2728 29] such as encapsulating ligands (cryptands and podands)macrocycles crown ethers These ligands can interact with ReO4

minus byboth the electrostatic interaction between ReO4

minus and protonated ligandand the hydrogen bond formation compared with simple open-chainligands If the complex between ReO4

minus and ligand has highhydrophobicity ReO4

minus in an aqueous solution may be separatedeffectively by a solvent extraction technique [30]

Crown ethers extract rhenium (VII) in the presence of potassiumor sodium in the form of K(Na)LReO4 (L-crown-ether) into the organicphase (12 - dichloroethane chloroform) [31 32] In the paper [31] theextraction perrhenate-ions by 3m-crown-m-ethers (m = 56) ether and itsmono-benzo-derivatives in 12-dichloroethane are described

Podands are analogues of crown ethers containing terminalphosphoryl ligands in their polyether chains they are used for theextraction of rhenium (VII) The efficiency of extraction by phosphorylpodands depends of the following factors the number of oxygen atomsin the polyether chain molecules the number of donor centers in themolecule of podands hydrophobicity of the reagent molecule the size offorming cycles the nature of substituent at the phosphorus atom Studies

20

have shown that phosphoryl podands with three oxygen atoms in thearomatic polyether chain combined with the phosphoryl group bydimetilen or o-phenylene fragments have high extraction ability forrhenium from sulfuric acid solutions [32]

In the paper [30] authors mark another type of podands such aspodands with nitrogen donor ligand -N N N `N`-tetrakis (2-pyridymethyl) -12-ethylendiamine (TREN) and its hydrophobicanalogs which also allow to extract perrhenate ions from highly acidicenvironments

Perrhenate is characterized by its ability to undergo a change ingeometry specifically from tetrahedral to hexagonal in the presence ofdonor ligands (eg acetonitrile triphenylphosphine) Protonationchanges the electron density present on the oxygen atoms Beer et al[33] suggested that the tripodal ligand L1 would be suitable for thebinding and extraction of perrhenate anion This ligand (Fig 1) basedon the combination of tris(2-aminoethyl)amine and crown ether motifswas found to complex sodium cations and to extract perrhenate anionsfrom aqueous solutions into an organic phase

Atwood and co-workers developed calixarene-type ligand L2(Fig 1) that specifically extracts perrhenate from water solution into anorganic phase The selectivity for extractions decreases as followTcO4

minus ge ReO4minus gt ClO4

minusgtNO3minus gtSO4

2minus gtClminus This selectivity pattern isattributed to a combination of charge size and shape Efficientextraction is observed at high and neutral pH the molar ratio ofligandperrhenate ion = 14 [33]

L1 L2Fig 1 Tripodal ligand L1 and calixarene-type ligand L2 for perrhenateextraction

21

Schiff-base macrocycles are used as a new conjugatedmacrocycles for perrhenate ions Thus a series of amino-azacryptands(L3ndashL16) for encapsulation and extraction of the oxoanions perrhenate(Fig 2) from aqueous solution were proposed by the authors [34]Thecomplexation amino-azacryptands L to ReO4

- is via hydrogen-bondedinteractions

Fig2 Amino-azacryptands (L3ndashL16) for encapsulation and extraction of theoxoanions perrhenate

Thus the main characteristics of the compounds for the effectiveperrhenate ions extraction as follows

Energy coordination of ligand with ReO4- should be higher than

the energy of perrhenate ion hydrationThe interaction between the ligand and perrhenate ions an

electrostatic interaction or the formation of hydrogen bonds Functional ligands to be a suitable size (volume of the cavity

should be more than 736 Aring3) shape electronegativity andhydrophobicity

Ligand should be protonated

22

Table 1 Characteristics of extractants for rhenium extraction

Extractant

Analysis objectComposition of

the initialsolution

Extractonconditions

Interferinginfluences

Aliphatic alcoholswith C 7-10

1-Heptanol 4-Heptanol 1-octanol 1-decanol 4-decanol 2-Heptanol 3-Heptanol

3-octanolback-extractant

NH4OH

Solutions HCland H2SO4

Т=293КTime of phase

contacttex = 5 min

organic phase toaqueous

(OL = 11)4 steps of

extraction 2stripping

Coextractionof mineral

acidsincomplete

re-extractionof Re (VII)

1

OctanolSolutions ofHNO3 and

H2SO4

Т=286-290Кtex = 10 min OL

= 11

Coextractionof HNO3

H2SO4

2

Basic polymethinedyes (derivatives of133-trimethyl-3H-

indole) astrazon violet

Aqueous andaqueous-organic

solution

Т=293КрН=6

tex = 10-30 secextractant mixture

toluene +dichloroethane

(1 1)

do notinterfere

3000-5000fold excess ofS04

2- CO32-

300- HPO42-

MoO42-

WO42-

10-20 S2O32-

Cr2O72- IO3

-metal ions as

sulfates

3

Secondary(diisododecylamine)and tertiary amines

(dioctylamin andtrioctylamine)

Solutions H2SO4

Т=293КA wide range of

pH

tex=5-7 mindiluent - toluene

-

4N-benzoyl-N ndashphenyl-

hydroxylamine

Molybdenitedissolved inHCl HNO3

HCl 05 molltex=15 min

diluent chloroform-

23

Table 1 (continued)

Extractant

Analysisobject

Compositionof the initial

solution

Extractonconditions

Interferinginfluences

5

Phosphoryl podands

back-extractant H2O

СReinitial=2middot105 moll

aqueoussolutions of

salts of alkalimetals

solutions ofmineral acids

Т=286-291КОL=11

tex= 60 mindiluent

nitrobenzene12-

dichloroethanechloroform

toluene

-

6Triotylamine (N235)+

tributyl phosphate(TBP)back-extractant18 NH4OH

Alkalinesolutions

afterleaching

containingMo

СRe 01-165gl

T=293 КрН =90 OL=11

tex=10 мин20

triotylamine+30 tributylphosphate

diluentkerosene

-

7

Podand-type nitrogendonor ligand ndashNNN`N`-tetrakis(2-pyridymethyl)-

12-ethylendiamine (TREN)

Aqueoussolution

NH4ReO4

С =10-4 M

Ionic strength01M

pH=1-65diluent

chloroformОL=11tex=24 h

-

8

3m-crown-m-ethers(m=56) mono-benzo-

derivates12-dichloroethane

СReO4-=

0057-0060М

T=291-295Ktex=2h

-

24

Table 1 (continued)

The range of Re concentrations

RecoveryMethods for determination Ref

Recovery gt99

Determination from back-extractSpectrophotometric method with

thiourea reductant-Sn (II)wavelength of 390 nm

[16 24]

1

gt98 Spectrophotometric method [25]

2The range of Re concentrations

001-550 mcgml

Determination from extractSpectrophotometric method

wavelength of 540 nm[17]

3 -AES-ICP

Spectrophotometric methodwith thiourea

[18 1920]

4Mo W Fe are extracted 97

into the organic phase

Determination from aqua phaseafter extraction

ICP-MS[6]

5 -AES-ICP

Spectrophotometric method[21 22]

6 968Spectrophotometric method with

butyl rhodamine[23]

7 - AES-ICP [30]

8 -AES-ICP

Spectrophotometric method[31]

9 - ICP-MS [32]

25

Table 2 Characteristics of sorbents for rhenium sorption

Sorbent

Analysis objectComposition of the

initial solutionConditions of

sorptionInterferinginfluences

1

Activated carbons(BAU)

Eluenthot soda solution

nitrate media

gold ore raw

static conditionsа)рH =2-3

б) рH =15-25

volume ofsolution 10 mlmass of sorbent

03 g(SL=1333)t=10 min UV

a) electro-positive

components(Mo W Cu

Ag Au)b)1000 fold

excess ofMo W do

not interfere

2

Activated carbons- CN-G CN-PCU developed

from waste woodand grain

processingindustries

sulfuric acidsolutions with CRe= 002 gl pH =2

solid phasesliquid SL==105

t=5-7 days-

3

2 Carbon fibrousmaterials

modified withchitosan

neutral aquasolutions of

rhenium

static conditionsТ=286-289 КSL=11000

-

4

3 Weakly basicanion-exchangersАН-105 Purolite

A 170

mineralizedsulphite solutionsimulating rinsing

water(С Re=001-002

gl Mo Cu Fe As)

static anddynamic

conditionsSL = 1500

t = 150-200 min

-

5

Strongly-basicanion-exchangers

АВ-17(sorbent PAN-АВ-

17)

neutral or slightlyacid

solutions

dynamicconditionst = 20 min

The disks ofpolyacrylonitrilefiber filled resin

1000 foldexcess of

Fe Cu ZnPb Cd do

not interfere

6Lignin anion-

exchangerssolutions NH4ReO4

static conditionsSL=1400

t=15min-2 h-

26

Table 2 (continued)

NotesMethods for

determinationRef

1

а) Sorption capacity of BAU forRe СЕ=14175 mgg AC

Detectionlt 10

б) СЕ=00763 mmolg or 142mgg

The concentrations range of Re050 100 mgL in standard

solutions025 50 mgl in the presence

of Mo and W (11000)

a) Electrostrippingvoltammetry

b) X-ray fluorescenceanalysis

a) [12]b) [9 10]

2 -Spectrophotometric

method [35]

3 СЕ=179-185mggSpectrophotometric

method with ammoniumthiocyanate

[38 39]

4Full dynamic exchange capacity

114 mgg

Spectrophotometricmethod with ammonium

thiocyanatekineticmethod

[36]

5 -

Determination of Re bythe diffuse reflectance

spectra at 420 nmrhenium thiocyanate

complex in the presenceof tin (II)

[15]

6 СЕ=3427-2328 mgg Traditional polarography [37]

Sorption is one of the methods for separation of rhenium fromvarious solutions

Sorption of rhenium or perrhenate-ions often occurs on solidsorbents from the liquid phase The presence of a large specific surfacearea and a large number of functional groups of the sorbent determinesits high sorption properties with respect to rhenium (VII) Sorbentscontain the same functional groups (amino groups hydroxyl groups

27

phosphorus groups) as extractants for the selective extraction ofrhenium but these groups are fixed on solid carriers or support

Activated carbons (AC) of various brands are used the mostwidely [9 10] The use of activated carbons as sorbents due to the factthat they have a whole set of valuable properties highly polydisperseporous structure a complex but relatively easily controlled surfacechemistry and specific physical properties Activated carbons like manyother carbon materials exhibit high selectivity to perrhenate ions thatexplains the increased interest to this type of sorbents [12]

The characteristic distinction of carbonaceous materials is that thesorption of rhenium is not only due to complexation with surfacefunctional groups (containing oxygen nitrogen sulfur atoms) but alsodue to the interaction with carbon matrix

AC can act as anion-exchanger in acidic media and themechanism can be described by the following scheme

[C2+ OH-] + ReO4-= [C2+ ReO4

-] + OH-On the other hand the AC have significant reduction properties

the reaction of the electrochemical reduction of perrhenate ions in themethods of rhenium determination by voltammetry is based on this it[12]

It has been established [9 10] that ReO4- is sorbed from nitric

acid solutions almost entirely (95-99) by 10 minutes of UV irradiationwhile without irradiation this process takes up to 60 minutes Increasedsorption by UV authors attribute to the fact when UV radiationsolutions of rhenium (VII) salts rhenium (VI) and rhenium (V) areformed which are considerably faster adsorbed on AC

Extensive use of the AС is also associated with their low costActivated carbons - CN-G CN-P CU developed from waste wood andgrain processing industries have a low cost and their capacitance andkinetic characteristics slightly inferior to conventional AC (FAC) [35]

However from acid solutions together with rhenium molybdenumcan also be sorbed by the AC Furthermore perchlorates nitrates andother oxidants can reduce the adsorption capacity of coals by oxidationThe disadvantage of rhenium sorption by activated carbons is as followsa decreasing in their activity after 4-6 cycles of sorption-desorption [1]low mechanical strength [35]

28

Anion-exchange resin is the next width of use which havegreater selectivity and capacity compared with activated carbons Theseanion-exchangers synthesized on the basis of the gel and porouscopolymer of styrene and divinylbenzene From the neutral and acidicsolutions rhenium is adsorbed by low-basicity anion-exchangers with thefunctional groups of primary and tertiary amines In recent studiesconducted on the use of weakly basic macroporous anion-exchangerswith a more developed specific surface area (20-100 m2g) such asPurolite A170 with secondary amino groups [36]

Sorption by strongly-basic anion-exchangers compared to weaklybasic anion-exchangers has several advantages firstly they are almostquantitatively and selectively extract rhenium from solutions andsecondly work in a wide range of pH [15]

The rapid technique for perrhenate ions determination isdeveloped which allows to find their content directly on the site ofsampling for example in lake water using strongly-basic anion-exchangers AB-17 with the sensitivity of the technique is 2-3 orderslower than the best conventional spectrohotometric methods withthiocyanate [15]

Recently the authors of paper [37] synthesized new highlypermeable lignin anion-exchangers on the basis of lignin a naturalpolymer a component of terrestrial plants It is noted that the exchangecapacity of anion-exchangers for rhenium in lignin is much higher (EC =3427-2328 mgg) compared with conventional anion-exchangersHowever the time to reach equilibrium sorption by some anion-exchangers can reach from 2 up to 12 hours

Carbon fibrous materials modified with chitosan haveimproved kinetic (time and rate of sorption) characteristics comparedwith activated carbon and ion-exchange resins [38 39] Carbon fibrousmaterials modified with chitosan contain amino groups includingprotonated The increasing of the number of protonated groupscauses the increasing of sorption capacity of the material withrespect to the negatively-charged perrhenate-ions However thesorption capacity for rhenium (179-185 mgg) still yields to ligninanion in addition investigations were carried out of neutral aquasolutions of rhenium without interfering influences

29

ConclusionIn this review the methods for rhenium determination which over

the last decade have acquired great fame are presented A large numberof works related to improving methods for rhenium determining pointsto the increased interest to this metal The majority of the studies aimedto the selective extraction of rhenium from the analyzed complex objectsand the separating it from interfering elements in the matrix to increasethe sensitivity of the methods Most of the work related to the searchingof various organic reagents selective to rhenium (V VII) ions and usedin extraction and sorption processes In general the development ofrapid selective methods that can determine the content of rhenium in awide range of concentrations in various materials remains an actualproblem nowadays

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

Reference1 AA Palant ID Troshkina AM Chekmarev Metallurgy of

rhenium Science Moscow 2007 298 p2 LV Borisova YuV Demin NG Gatinskaya VV Ermakov

Determnation of rhenium in plant materials Journal of AnalyticalChemistry 2005 V60 1 P 97-103

3 LV Borisova AN Ermakov Analytical chemistry ofrhenium 1974 Science Мoscow 318 p

4 S Uchidaa KTagamia K Tabei Comparison of alkaline fusionand acid digestion methods for the determination of rhenium in rockand soil samples by ICP-MS Analytica Chimica Acta 2005 V535P 317ndash323

5 VI Manshilin EK Vinokurova SA Kapelushniy Determinationof Pt Pd Re mass fraction in dead catalyst samples using ICPatomic emission spectrometry method Methods and objects ofchemical analysis 2009 V41 P 97-100 (in Russian)

6 Jie Li Li-feng Zhong Xiang-lin Tu Xi-rong Liang Ji-feng XuDetermination of rhenium content in molybdenite by ICPndashMS afterseparation of the major matrix by solvent extraction with N-benzoyl-N-phenylhydroxalamine Talanta 2010 V81 P 954ndash958

30

7 T Meisel J Moser N Fellner Wo Wegscheider R SchoenbergSimplified method for the determination of Ru Pd Re Os Ir and Ptin chromitites and other geological materials by isotope dilutionICP-MS and acid digestion Analyst 2001 V126 P 322ndash328

8 K Shinotsuka K Suzuki Simultaneous determination of platinumgroup elements and rhenium in rock samples using isotope dilutioninductively coupled plasma mass spectrometry after cation exchangeseparation followed by solvent extraction Analytica chimica acta2007 V603 P129ndash139

9 NA Kolpakova AS Buinovsky IA Jidkova Determinationof rhenium by X-ray fluorescence analysis Proceedings ofuniversities Physics 2004 12 P147-149 (In Russian)

10 AS Buinovsky NA Kolpakova IA Melnikov Determinationof rhenium in the ore material by X-ray fluorescence analysis News polytechnic university 2007 V311 3 P92-95 (InRussian)

11 DV Drobot AV Belyaev VA Kutvitsky Development of aunified X-ray fluorescence method for the determination ofrhenium in multicomponent oxide compositions News highereducational institutions Non-ferrous metallurgy 1999 4 P23-24 (in Russian)

12 LG Goltz NA Kolpakov Sorption preconcentration anddetermination by voltammetry perrhenate ions in the mineralraw materials Proceedings of the Tomsk PolytechnicUniversity 2006 V 309 6 P77-80 (in Russian)

13 NA Kolpakova LG Gol`ts Determination in mineral rawmaterials by stripping voltammetry Journal of AnalyticalChemistry 2007V62 4 Р418-422

14 Wahi A Kakkar LR Microdeterminaton of rhenium withrhhodamine-B and thiocyanate usng ascorbic acid as the reductant Analytical sciences 1997 august V 13 P657-659

15 LV Borisova SB Gatinskaya SB Savvin VA RyabukhinAdsorbtion-spectrophotometric determination of rhenium fromdiffuse reflectance spectra of its complexes on a PAN-AV-17adsorbent Journal of Analytical Chemistry 2002 V572 P 161-164

31

16 AG Kasikov AM Petrova Extraction of rhenium (VII) byaliphatic alcohols from acid solutions Journal of AppliedSpectroscopy2009 V82 2 P 203-209 (in Russian)

17 ZhA Kormosh YaR Bazel` Extraction of oxyanions with basicpolimethine dyes from aqueous and aqueous-organic solutionsextraction-photometric determination of rhenium (VII) and Tungsten(VI) Journal of Analytical Chemistry 1999 V54 7 P 690-694

18 AA Palant NA Yatsenko VA Petrova Extraction of rhenium

(VII) from sulfuric acid solutions by diisododecylamine

Journal of Inorganic Chemistry 1998 V43 2 P 339-343 (inRussian)

19 NA Yatsenko AA Palant Micelle formation in theextraction of ions W (VI) Mo (VI) Re (VII) from sulfuric acidmedia diisododecylamine dioctylamine and trioctylamine Journal of Inorganic Chemistry 2000 V45 9 P 1595-1599 (in Russian)

20 N Latsenko AA Palant SR Dungan Extraction of tungsten (VI)molybdenum (VI) and rhenium (VII) by diisododecylamine Hydrometallyrgy V 55 Issue 1 Febr 2000 P 1-15

21 AV Antonov AA Ischenko The use of extraction in thedetermination of rhenium in the presence of molybdenumChemistry and chemical technology 2007V50 9113-116 (in Russian)

22 VF Travkin AV Antonov VL Kubasov AA IshchenkoExtraction of rhenium (VII) and molybdenum (VI)hexabutyltriamid phosphoric acid from the acidic environment Journal of Applied Chemistry 2006 V78 6P 920-924 (inRussian)

23 Cao Zhang-fang Zhong Hong Qiu Zhao-hui Solvent extraction ofrhenium from molybdenum in alkaline solution Hydrometallurgy2009 V 97 3-4 P 153-157

24 AG Kasikov AM Petrova Influence the structure of octanolon their extraction ability in acid solutions with respect to

32

rhenium (VII) Journal of Applied Chemistry 2007 V80 4 P689-690 (in Russian)

25 VF Travkin YM Glubokov Extraction of molybdenum andrhenium by aliphatic alcohols Metallurgiya2008 7 P21-25 (in Russian)

26 EA Kataev GV Kolesnikov VN Khrustalev MYu AntipinRecognition of perrhenate and pertechnetate by a neutralmacrocyclic receptor J radioanal Nuclchem 2009 2 V282 P 385-389

27 Bambang Kuswandi Nuriman Willem Verboom David NReinhoudt Tripodal Receptors for Cation and Anion Sensors Sensors 2006V 6 P 978-1017

28 Lagili O Abouderbala Warwick J Belcher Martyn G BoutellePeter J Cragg Jonathan W Steed Cooperative anion binding andelectrochemical sensing by modular podands PNAS April 162002 V 99 8 P 5001ndash5006

29 EA Kataev GV Kolesnikov EK Myshkovskaya Newmacrocyclic ligands based bipyrroles to bind perrhenate andpertechnetate ions radiation safety 2008 4 P16-22(inRussian)

30 Takeshi Ogata Kenji Takeshita Kanako Tsuda Solvent extractionof perrhenate ions with podand-type nitrogen donor ligands Separation and Purification Technology 2009V68 P288ndash290

31 Yoshihiro Kudo Ryo Fujihara Shoichi Katsuta Yasuyuki TakedaSolvent extraction of sodium perrhenate by 3m-crown-m ethers(m=5 6) and their mono-benzo-derivatives into 12-dichloroethane

32 Elucidation of an overall extraction equilibrium based oncomponent equilibria containing an ion-pair formation in water Talanta V 71 2007 656ndash661

33 AN Turanov VK Karandashev VE Baulin Extraction ofrhenium (VII) by phosphorylated podands Russian journal ofinorganic chemistry 2006 V514 P676-682 (in Russian)

34 E A Katayev Yu A Ustynyuk J L Sessler Receptors fortetrahedral oxyanions Coordination Chemistry Reviews 2006V250 P3004ndash3037

33

35 Leroy Cronin Macrocyclic and supramolecular coordinationchemistry Annu Rep Prog Chem Sect A 2004V100 P 323ndash383

36 ID Troshkina ON Ushakova VM Mukhin Sorption ofrhenium from sulfuric acid solutions by activated carbon News of higher educational institutions Non-ferrousmetallurgy 2005 3 P38-41 (in Russian)

37 AA Abdusalomov Sorption of rhenium from sulfuric acidsolutions of molybdenum Sorption and ChromatographicProcesses 2006 Vol6 V 6P 893-894 (In Russian)

38 NN Chopabaeva EE Ergozhin ATasmagambet AI NikitinaSorbtion of perrenate-anons by lignin anion exchangers Chemistry of solid fuel 2009 2 P 43-47 (in Russian)

39 AV Plevaka ID Troshkina LA Zemskova AV Voit Sorption ofrhenium chitosan-fiber materials Journal of InorganicChemistry 2009V54 7 P1229-1232 (in Russian)

40 LA Zemskova AV Voit YuMNikolenko ID Troshkina AVPlevaka Sorption of rhenium on carbon fibrous materials modifiedwith chitozan Journal of nuclear and radiochemical sciences2005 V6 3 P221-222

11

SYNTHESIS AND MICROSTRUCTURE DESIGN OF METALAND CERAMIC MATRIX COMPOSITES USING

MECHANICAL MILLING OF THEREACTANTSCONSTITUENTS

Dina V Dudina Oleg I LomovskyInstitute of Solid State Chemistry and Mechanochemistry

Siberian Branch of Russian Academy of Sciences Kutateladze 18Novosibirsk 630128 Russia

E-mail dina1807gmailcom

Mechanical milling greatly alters the state of a powder mixtureintroducing plastic strain and defects into the components andcreating new interfaces and mutual configurations of nano-sizedgrains This opens up a possibility to design microstructures of thecomposite to be synthesized by modifying the initial state of reactingpowder mixtures In certain mechanically milled reactive systemsone can observe microstructure refinement of the product [1-2] anincrease in the yield of the reaction [3] improved distribution of thephases [3 4] and lower reaction onset and developed temperatures[1-2] The presentation intends to demonstrate several successfulexamples of this approach for synthesizing composites by self-propagating high-temperature synthesis (SHS) shock compressionand electric-current assisted sintering

SHS in the mechanically milled Ti-B-Cu powder mixtures wassuccessfully performed and resulted in a TiB2-Cu composite [1-2]Compared to untreated powders in the mechanically milled mixturestitanium and boron started reacting at a reduced ignition temperaturewhile lower combustion temperatures developed in the combustionwave favored formation of submicron grains of TiB2

The powder particles brought to react with each other by shockcompression of the mixture may not fully transform into the productsif the loading is too short and the temperatures developed during thepressure rise and the post-loading period are not high enough In themechanically milled mixture the yield of the reaction can beincreased as a result of the decreased grain size of the initial reactants

12

and shorter diffusion distances (example Ti-Cu-B system partial andcomplete reaction of Ti and B [3])

When the sintering process ensures temperatures and timesufficient for the completion of the reaction in the mechanicallymilled mixture one can expect more uniform microstructure and finergrains of the products (example Ti-B-C system forming B4C-TiB2

phases during electric-current assisted sintering [4])Ball milling can refine the microstructure of the as-synthesized

composites and can be used to introduce additional quantities of theconstituents in the composite This was applied in order to develophighly conductive Cu-based composites One of the possible reasonsfor low conductivity of in-situ dispersion strengthened copper may bethe incompleteness of the reaction between the initial reactantswhich form solid solutions with the copper matrix In this regard weconducted an in-situ synthesis of TiB2-Cu composites starting fromthe powder mixtures with the limited content of copper ensuring ahigh probability of contact between the particles of titanium andboron and as a result their full conversion into the TiB2 phase Thenanoparticles were formed in a self-propagating mode in the ballmilled Ti-B-Cu powder mixture corresponding to the 57 volTiB2-Cu composition Afterwards in order to adjust the composition thecomposite was ldquodilutedrdquo with the required amount of copper usingsubsequent ball milling [5]

The consolidated nano- and microcomposite materialsdeveloped on the basis of the described systems were tested for theirenhanced mechanical properties (fracture tough composites B4C-TiB2

[4]) electric erosion resistance [6] and electric conductivity [5] Inthis presentation each property is discussed as resulting from thephase and microstructure evolution during the synthesis of thematerial by the selected processing method

AcknowledgementsParts of this work were carried out by DVD at the University

of California Davis USA during her postdoctoral appointment Theauthors greatly appreciate the collaboration with DrKorchagin(ISSCM SB RAS) Dr VIMali and Dr AGAnisimov (Institute of

13

Hydrodynamics SB RAS Novosibirsk Russia) and Prof JSKim(University of Ulsan South Korea)

References1 DVDudina OILomovsky MAKorchagin VIMali Chem

Sust Dev 12 (2004) 319-3252 MAKorchagin DVDudina Comb Expl Shock Waves 43 (2)

(2007)176-1873 DVDudina VIMali AGAnisimov OILomovsky Mater Sci

Eng A 503 (2009) 41-444 DVDudina DMHulbert DJiang CUnuvar SJCytron

AKMukherjee JMaterSci 43 (2008) 3569-35765 JSKim DVDudina JCKim YSKwon JJPark CKRhee J

Nanosci Nanotech 10 (2010) 252-2576 J-SKim Y-SKwon DVDudina OILomovsky MAKorchagin

VIMali JMaterSci 40 ( 2005)3491 - 3495

4

STUDY OF THE EFFECT OF FLUORESCENCE INCREASINGOF N-ARYL-3-AMINOPROPIONIC ACIDS IN THE PRESENCE

OF ZINC AND CADMIUM IONS

EV Dedyukhina1 NV Pechishcheva1 LK Neudachina2KYu Shunyaev1 AA Belozerova1

1 ndash Institute of Metallurgy of UB RAS 101 Amundsen st Ekaterinburgshunuralru

2 ndash Ural State University 51 Lenin av Ekaterinburg Russia

Earlier the effect of increasing of phosphorescence intensity in thefrozen solutions with excess of metal chlorides and sulphates has beenreported Ions оf these metals have filled electronic shells and largevalue of electric field intensity - Li(I) Be(II) Ca(II) Mg(II) Cd(II)Zn(II) Al(III) In(III) and Ga(III) For example this effect was found forbenzene aniline phenol amino acids ndash tyrosine tryptophanephenylalanine [1]

The same effect have been found for fluorescence of onerepresentative of N-aryl-3-aminopropionic acids (AAPA) - NN-di(2-carboxyethyl)-p-anisidine - in the presence of cadmium(II) and zinc(II)ions at Т=77 К [2] Increasing of fluorescence intensity (Ifl) in frozeninorganic matrix is expected for other representatives of AAPA whichnot have electron acceptor groups in structure and demonstrate theconsiderable fluorescence intensity of the protonated form

Fluorescence of some AAPA in frozen inorganic matrixNN-di(2-carboxyethyl)aniline (I) NN-di(2-carboxyethyl)-34-

xylidine (II) NN-di(2-carboxyethyl)-3-methyl-aniline (III) andN-(2-carbamoylethyl)-о-anisidine (IV) are representatives of a class ofAAPA Figure 1 presents structures of the AAPA In the present workthe fluorescence of aqueous solutions of this AAPA with molar excess ofcadmium and zinc sulphates at рH 1-6 and Т=77 К have beeninvestigated

The fluorescence spectra of solutions were measured using aFluorat-02-Panorama spectrofluorometer (Lumex Russia) Fluorescencespectra at T=77 K was excited and recorded using a fiber-optic cablewith a special optical connector

5

It have been established that the Ifl of the protonated form of I-IV(СR=1middot10-4 moldm3) is increased in the presence of cadmium(II) andzinc(II) ions at Т=77 К Figure 2 presents spectra of II We suggest thatcause of this effect is interaction enhancement of reagent with metal inconsequence of isolation from water and micro concentration (waterform ice crystals impurities are displaced in intercrystal area)

CH3

N

O

OHO

OH

1 2 3 4

Fig 1 Structures of AAPA 1 - NN-di(2-carboxyethyl)aniline2 - NN-di(2-carboxyethyl)-34-xylidine 3- NN-di(2-carboxyethyl)-3-

methyl-aniline 4 - N-(2-carbamoylethyl)-о-anisidine

The increasing Ifl of protonated reagent form of I-IV also isobserved at Т=293К but is not as strong as at T=77 K

0

1

2

3

4

5

6

7

240 260 280 300 320 340 360

wavelength nm

Ia

u

1

2

3

Fig 2 Spectra of fluorescence II (СR=1middot10-4 moldm3) in the presence andabsence of Cd(II) и Zn(II) ions (СZn(II)= СCd(II)= 560 mgdm3) рН=60 Т=77 К

λex = 214 nm 1 - II 2 - II+Zn(II) 3 - II+Cd(II)

The fluorescence increasing is observed only when concentrationof metal ions in dozens of times more than concentration of fluorophor

6

This indicate that Ifl increasing is occured due to reagent solvation byions of inorganic salts but not chelation

We have obtained the Ifl of solutions of I-IV as functions of theconcentration of cadmium(II) and zinc(II) ions at Т=77 К pH=6 (table1) The largest increasing of Ifl in the presence of metal ions have beenobserved for IV But the most correlation coefficient R value of linearfunction Ifl=f(CMe) with wider concentrations range has been obtainedfor II

Table 1 The Ifl of I-IV as functions from concentration of metal ions Т=77 КCCd(II)= CZn(II)= 200 mgdm3 СR=10-4 moldm3 рН=6

Metalion

ReagentConcentrationsrange mgdm3 I R+MeIR R Slope

I 11 090 321

II 11 098 494III

25-760

13 092 456Cd(II)

IV 25-245 80 092 2997

I 3 095 82

II 8 098 414

III

30-845

11 096 437Zn(II)

IV 30-560 70 090 1542

In addition we have studied the fluorescence of aniline and naturalamino acids (tyrosine tryptophane phenylalanine) in frozen inorganicmatrix Structures of amino acids are presented on figure 3 thiscompounds are not belong to class of substituted anilines Thiscompounds similarly of investigated AAPA not have electron acceptorgroups in structure tyrosine phenylalanine and AAPA have the samebenzene fluorophore Besides this amino acids are commerciallyavailable reagents

Investigations have been shown that present amino acids alsodisplay the effect of Ifl increasing of protonated reagent form in thepresence of cadmium(II) and zinc(II) ions at Т=77 К But is not asstrong (12ndash5 times) as AAPA Ifl increasing Metal ions at T=298 K havelittle effect on a fluorescent spectra of amino acids

7

1 2 3

Fig 3 Structure of amino acids1 - phenylalanine 2 - tyrosine 3 - tryptophane

Thus we can deduce that the presence of substituted amino groupin benzene ring (especially in combination with others electron donorgroups) allow to observe more effective increasing of Ifl in salt solutionat 77 К Replacement benzene fluorophore to indole one (intryptophane) result to decreasing of observing effect extent

The fluorescence of II in the presence of Mg(II) ions at Т=77 Кwas investigated We tried to find the II0 fluorescence of II functionfrom z2r ratio for two-charged cations where z - ionic charge (+2) r -ionic radius nm [3] Data is presented in table 2

Table 2 Characteristiс of the functions II0 = f(z2r) for II Т=77 К рН=6λexλem= 214286 nm СII =10-4 М

Ion z2r SlopeI I0

CMe= 200 mgdm3

Cd(II) 412 494 107

Zn(II) 541 414 85

Mg(II) 615 352 74

The functions II0=f(z2r) of fluorescence II in frozen inorganicmatrix from are presented in figure 4 they are linear Also linearfunctions of Ifl=f(CMe) slope on z2r ratio have been obtained

N

NH2

OH

O

H2N

OHO

OH

8

y = -016x + 174

R2 = 099

6

7

8

9

10

11

40 45 50 55 60 65

z2r

IIo

Zn

Cd

Mg

Fig 4 Functions II0=f(z2r) of fluorescence II in the presence of metal ions [3]CCd(II)= CZn(II)= CMg(II)= 200 mgdm3 λexλem= 214286 nm Т=77 К

Study of fluorescence of some reagents in glycerolwater andethanolwater mixtures and micellar solutions at Т=298 КWe have studied a fluorescence II and tryptophane in

glycerolwater (11) and ethanolwater (11) mixtures in the presence ofzinc(II) ions at 77 К It was done for proving hypothesis about reducinginteraction fluorophore with water in aqueous media at freezing Wesuggest that interaction between of the solute and solvent molecules arepreserved in nonaqueous solutions

Corresponding spectra of II are presented on figure 3 similarsituation is observed for tryptophane We can see effect of increasing Ifl

is not observed in glycerolwater and ethanolwater mixtures in contrastto aqueous solutions

Isolation reagent from water at room temperature is possible in thepresence of surfactants

Fluorescence II have been study in the presence of surfactants ofdifferent nature in acidic media at Т=298 К The Ifl increasing ofprotonated form II is occured in the presence of Triton Х-100 (non-ionicsurfactant) and sodium dodecylsulphate (anionic surfactant)Fluorescence II is decreased by cetyltrimethylammonium bromide(CTAB cationic surfactant)

Fluorescence of II in the presence of surfactants and excess ofmetal ions have been study at рН=1-6 Zinc and cadmium ions increaseIfl of II at рН 50-65 with CTAB Thus metal ions and CTAB at

9

Т=298 К have same Ifl increasing effect as the effect at Т=77 К withoutsurfactants

0

5

10

15

20

25

240 260 280 300 320 340 360 380

wavelength nm

Ia

u

1

2

3

Рис 5 Fluorescence of II (СII=1middot10-4 moldm3) in ethanolwater (11)mixtures in the presence and absence of Zn(II) pH=60 Т=77 К λex=214 nm

1 - II 2 - II + Zn(II) (44middot10-4 moldm3) 3 - II+ Zn(II) (86middot10-3moldm3)

We have obtained under these conditions the Ifl of II solutions asfunction of the concentration of Cd and Zn ions with variousconcentrations of CTAB (table 3) The plots are linear and have thegreatest slope value at СCTAB=14middot10-3 moldm3 Cadmium ions have agreater influence on the fluorescence of the II than zinc ions

The fluorescence investigations in the presence of CTAB andmetal cations have been carried out on other AAPA (I III and IV)aniline and tyrosine (table 4) It was found that zinc ions increase offluorescence of protonated reagent form of I and III cadmium ions ndashIII

Table 3 Characteristiс of the functions Ifl=f(CMe) of II with addition of CTAB

exem = 218286 Т=298 К

Range of concentrationsCation

С CTABmoll moldm3 mgdm3 tg α

96middot10-4 2middot10-4 ndash 4middot10-3 45-450 18Cd(II)

14middot10-3 2middot10-4 ndash 8middot10-3 45-900 3696middot10-4 4middot10-4 ndash 15middot10-2 25-850 055

Zn(II)14middot10-3 4middot10-4 ndash 11middot10-2 25-850 10

10

Table 4 Fluorescence of reagents in the presence of zinc and cadmium ions(СMe=560 mgdm3) and CTAB (С= 96middot10-4 moldm3) рН=6

Zn(II) Cd(II)

Reagentexem

nm II0 I (R+Zn+CTAB)au

II0I (R+Cd+CTAB)

au

aniline 253278 11 07 10 06I 222300 62 16 08 02II 218286 73 44 85 51III 217288 65 34 33 15IV 218304 10 32 12 12

tyrosine 222302 10 480 11 462

The resulting functions will be used for developing of thefluorescent techniques of zinc and cadmium determination

The work is supported by grants of Presidium of UB RAS(program 09-P-3-1022)

References1 AV Karyakin n-electrons of heteroatoms in hydrogen bonding and

luminescence (in Russian) Nauka Мoscow 1985 135 p2 LK Neudachina EV Dedyukhina OV Evdokimova

NV Pechishcheva EV Osintseva KYu Shunyaev Fluorescenceof NN-di(2-carboxyethyl)-p-anisidine in solution and crystallinestate Journal of Applied Spectroscopy 2010 V 77 2 P 206-212

3 Lurie YuYu Hand-book of analytical chemistry (in Russian)Khimiya Мoscow 1989 447 p