the influence of electrolysis parameters on the composition

7/29/2019 The Influence of Electrolysis Parameters on the Composition

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.Hydrometallurgy 54 2000 133149

www.elsevier.nlrlocaterhydromet

The influence of electrolysis parameters on thecomposition and morphology of CoNi alloys

L. Burzynska ), E. Rudnik

Department of Physical Chemistry and Electrochemistry, Faculty of Non-Ferrous Metals, Uni

ersity of Miningand Metallurgy, Cracow, Poland

Received 20 September 1999; accepted 20 September 1999

Abstract

The influence of cathodic current density, the concentration of Co2q ions in the electrolyte, .and additional substances saccharin and sodium lauryl sulfate on the composition and morphol-

ogy of CoNi alloys were investigated. Research was carried out in a Watts-type bath in the

presence of boric acid, as a buffer substance. The circulation speed of the electrolyte was 40 dm 3

hy1. Cathodic polarisation curves were determined for parent metals and the CoNi alloy. It was

established that the presence of additives shifts the cathodic potential of alloy deposition towards

more negative values. An increase in the cobalt content in the alloy was observed with decreasing

of the cathodic current density and increasing of the Co 2q ions concentration in the bath. Results

obtained confirmed the anomalous character of deposition of the CoNi alloy. The cathodic

current efficiency is dependent mainly on the current density applied, but the direction of changes

has not been precisely determined, for it depends on the composition of the electrolyte. Using

diffractional X-ray and micro X-ray analyses, it was determined that single-phase deposits with an

fcc lattice for the whole investigated range of current density and electrolyte composition wereobtained. In the presence of additives there were obtained fine-grained, bright alloys which

adhered well to the substrate. q2000 Elsevier Science B.V. All rights reserved.

Keywords: Electrolysis parameters; CoNi alloys; Electrolyte

1. Introduction

Electrolytic nickelcobalt alloys are characterised by high strength even at elevated. w x w x w xtemperatures 13 , hardness 26 , and specific magnetic properties 7,8 . These

)

Corresponding author

0304-386Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. .P I I : S 0 3 0 4 - 3 8 6 X 9 9 0 0 0 6 0 - 2


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( )L. Burzynska, E. RudnikrHydrometallurgy 54 2000 133 149134

features have determined that this material has many applications, among others, in

rocket technology, cosmonautics, sound signal recording, as a material for the electro-

forming of moulds for die-casting and plastics, as an anticorrosive coating, and also forw xdecorative purposes 1,4,6,9,10 .

w xThe cathodic co-deposition of nickel and cobalt is carried out using chloride 11 13 ,

w x w x w xsulfate 11,1416 , chloridesulfate 1719 , and sulfamate 3,5,20 electrolytes, eitherw xwith or without the addition of complexing compounds, e.g., pyrophosphate 21 or

w xcitrates 12 . Applications of simple and complexing bath in the deposition of the CoNi

alloys have been extensively described in the literature. However, the process in the .chloridesulfate solutions Watts-type has been insufficiently studied. The adaptation of

w xthe Watts bath 1719 in the co-deposition of metals results from the comprehensive

research of nickel electrodeposition in this type of the electrolyte, and because of the

similar properties of cobalt and nickel.The composition of the alloy, and therefore some of its properties brightness,

.plasticity, etc. may be regulated by appropriately choosing the bath composition andparameters of electrolysis. The present paper shows the results of laboratory research

centred on the deposition of NiCo alloys using chloridesulfate solutions. The

objective was to determine the way in which the composition of alloys, cathodic current

efficiency and macroscopic properties of deposits are dependent upon the concentration

of cobalt and nickel ions, current density and the presence of additional substances.

2. Experimental

2.1. Composition of electrolyte

w xUsing data given in literature 17 , we selected the composition of the bath in which

the co-deposition of nickel and cobalt was to take place. The composition of electrolytes

and process parameters are presented in Table 1, points 13. Chloridesulfate solutionsw xwere used. It appears 22 useful to add chloride ions, for these prevent the passivation

of anodes and facilitate their dissolution. Measurements were carried out in the presence

of boric acid, which fulfilled the role of a buffer substance. The alloy deposition wasalso conducted in electrolytes with an addition of saccharin and sodium lauryl sulfate.

Saccharin lowered the internal stresses of cathodic deposits. Sodium lauryl sulfate, as a

surfactant, prevents the incorporation of gaseous hydrogen into the cathodic deposit. The

deposition of the alloy was carried out using a bath in which the concentration of nickel

ions was one order of magnitude higher than that of cobalt ions. This is connected with

the preferential cathodic deposition of cobalt.

The cathodic polarisation curves for the deposition of NiCo alloy were determined

in solutions with compositions given in Table 1, points 1 and 35. The polarisation

curves for the cathodic individual reduction of Co2q

and Ni2q

ions were also deter-mined. The composition of the baths is presented in Table 1, points 6 and 7. These

measurements were carried out in electrolytes with a concentration of cobalt and nickel

ions identical with that existing during the recording of the alloys polarisation curve. In


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( )L. Burzynska, E. RudnikrHydrometallurgy 54 2000 133 149 135

Table 1

Composition of the baths, conditions of CoNi alloys deposition and the determination of cathodic polarisation

curves for the alloy, nickel, and cobalt

No. Composition of electrolyte Concentration Process conditions

y3 y3mol dm g dm

y2 .1 CoSO P7H O 0.089 25 Cathodic current density: 1.02.0 A dm4 23 y1NiCl P6H O 0.841 200 Circulation of electrolyte: 40 dm h2 2

3H BO 0.405 25 Volume of electrolyte: 3 dm3 3Saccharin 0.004 1 Cathode substrate: titanium

Sodium lauryl sulfate 0.0003 0.08 anodes: Ni and Coy2 .2 CoSO P7H O 0.054 0.089 15 25 cathodic current density: 1 A dm4 2

3 y1NiCl P6H O 0.841 200 circulation of electrolyte: 40 dm h2 23H BO 0.405 25 volume of electrolyte: 3 dm3 3

Saccharin 0.004 1 cathode substrate: titanium

Sodium lauryl sulfate 0.0003 0.08 anodes: Ni and Coy2 .3 CoSO P7H O 0.089 25 cathodic current density: 0.42.3 A dm

4 2 3 y1NiCl P6H O 0.841 200 circulation of electrolyte: 40 dm h2 23H BO 0.405 25 volume of electrolyte: 3 dm3 3

cathode substrate: steel

anodes: Ni and Co3 y1 .4 CoSO P7H O 0.089 25 circulation of electrolyte: 40 dm h4 2

NiCl P6H O 0.841 200 volume of electrolyte: 3 dm32 2H BO 0.405 25 cathode substrate: titanium3 3Saccharin 0.004 1 anodes: Ni and Co

3 y1 .5 CoSO P7H O 0.089 25 circulation of electrolyte: 40 dm h4 23NiCl P6H O 0.841 200 volume of electrolyte: 3 dm2 2

H BO 0.405 25 cathode substrate: titanium3 3

Sodium lauryl sulfate 0.0003 0.08 anodes: Ni and Co3 y1 .6 CoSO P7H O 0.089 25 circulation of electrolyte: 7 dm h4 2

3MgCl P6H O 0.841 171 volume of electrolyte: 0.5 dm2 2H BO 0.405 25 cathode substrate: steel3 3

anode: Co3 y1 .7 MgSO P7H O 0.089 22 circulation of electrolyte: 7 dm h4 2

3NiCl P6H O 0.841 200 volume of electrolyte: 0.5 dm2 2H BO 0.405 25 cathode substrate: steel3 3

anode: Ni

order to obtain the same value of the ionic strength of solutions, one of these cations was

replaced with Mg 2q ions.

Electrolytes with a pH of 4.4 were applied. This value was achieved through the

addition of sodium hydroxide. The solutions were prepared using analytical grade .reagents supplied by POCh, Poland and twice-distilled water.

The concentration of Co2q and Ni2q ions was determined using the methodw xsuggested by Langford 23 . This consists in a total determination of cobalt and nickel

by means of titration with an EDTA solution in the presence of murexide as theindicator. In a second portion of the solution Co 2q ions are oxidised to Co 3q ions with

the simultaneous creation of an ammonia complex. Ni 2q ions do not undergo such a

reaction and may be determined using EDTA.


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2.2. Electrodes

.Rectangular 5=6 cm plates made from stainless steel or titanium 99.9% were used

as substrates for the cathode. Prior to each measurement, these were cleaned using .

abrasive paper of various gradations in the following order: 280, 400, 600, 800 andsubsequently washed in distilled water and alcohol. The substrates were isolated on one

side for determining the polarisation curves.

Separate rectangular 5=6 cm nickel and cobalt anodes were used. The nickel anodes . .99.9% were rolled plates, while the cobalt anodes 99.0% were cast plates. In order to

remove the oxidised layer from the surface of the electrodes, the anodes were immersed .in a mixture of concentrated acids: HNO , H SO , H PO , and CH COOH 3:1:1:5 at3 2 4 3 4 3

w xa temperature of 858C908C for approximately 1 min 24 . The anodes were isolated on

one side.

The co-deposition of cobalt and nickel was carried out using two nickel anodes and

two cobalt ones. One anode made of the appropriate element was applied for defining

the cathodic polarisation curves of individual metals.

2.3. Measurement circuit

The alloy deposition was conducted in a cuboid vessel made of rigid PVC. The

volume of electrolyte was 3 dm3. The cathodic polarisation curves for parent metals

were determined in a glass vessel containing 0.5 dm3 of the solution.

Within the electrolyser, the electrodes were hung vertically and in parallel withrespect to each other. The anodes were placed symmetrically on both sides of the

centrally located cathode.

The cathode potential was measured with respect to a saturated calomel electrode and

the result thus obtained converted with respect to the normal hydrogen electrode.

Measurements of potential were carried out using a Luggin capillary, placed at the

surface of the electrode in such a way as not to disturb the distribution of the force lines

of the electric field.

The pH of the bath was monitored with a combined electrode connected with a

.pH-meter Radelkis . In order to eliminate the influence of the electric field on thereadings of the apparatus, the electrode was placed in a glass housing that did not,

however, prevent the free flow of electrolyte. The constant pH value of the bath, which

displayed a tendency to alkalify as a result of the cathodic evolution of hydrogen, was

maintained by the periodic addition of a few drops of a mixture of diluted HCl and .H S O 10:1 .2 4

The flow of electrolyte was kept at a constant and stable level using a peristaltic

pump with a circulation speed corresponding to an approximately 13-times exchange of

the volume of the solution within 1 h. The electrolyte was pumped from the direction of

the anodes in the direction of the cathode.In order to precisely determine the charge flowing through the circuit, independent

copper coulometers were used, these being series-connected with the electrodes.

The measurement circuit is given in Fig. 1.


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Fig. 1. Diagram of measurement circuit applied for depositing the CoNi alloy. 1 Cobalt anode; 2

nickel anode; 3 cathode; 4 stabilized power supply; 5 ammeter; 6 copper coulometer; 7

resistor; 8 combined electrode; 9 pH-meter.

2.4. Determination of polarisation cures

The polarisation curves for the deposition of nickel, cobalt and their alloy weredetermined using the galvanostatic method, at a temperature of 21"18C. The cathodic

polarisation curves were registered after a metallic layer had appeared on the substrate.

These layers were obtained carrying on the cathodic process for 1 h at a current density

of 0.4 A dmy2 . After that the flow of the electric current was cut off and the potential

value read for i s 0. Next, curves were determined at increasing and decreasing currentKdensities until reproducible values were found. Polarisation curves were registered under

.a fixed set conditions the electrolyte composition, speed of circulation, temperature .

Measurements were carried out in stationary conditions, i.e., the established potential

value was read at a set current density. Partial cathodic polarisation curves for nickel andcobalt were determined on the basis of the composition of alloys.

2.5. Cathodic alloy deposition

The deposition of CoNi alloys was conducted over a period of 10 to 20 h under

galvanostatic conditions, at a temperature of 21"18C. The influence of current density

on the composition of the cathodic deposit was examined in electrolytes having

compositions presented in Table 1, points 1 and 3, while the dependence of the

composition of the alloy on the concentration of metal ions was determined in solutionshaving concentrations given in Table 1, point 2.

The cathodic current efficiencies were calculated on the basis of the mass of deposit

and coulometric data. Various current densities were used for nickel and cobalt anodes


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for each measurement. Nickel anodes were dissolved by passing 75% of total electric

current through them; the remainder dissolved the cobalt anodes.Phase identification of deposits was performed using an X-ray diffractometer DRON

.3 and filtered radiation CuKa . Deposited alloys underwent X-ray microanalysis, while

cobalt and nickel were analysed quantitatively at points on the surface 900 nm distant

from each other. This enabled graphs of changes in concentration for both elementsalong selected lines to be plotted. An analysis of the surface distribution of alloy

constituents was also carried out. Due to the possibility of CoKb and NiKa spectral

lines overlapping, CoKa and NiKb radiation was used for measurements. Measure-

ments were carried out with a Philips XL 30 electron scanning microscope with an EDS

analyser ISIS model. In order to investigate the microstructure of deposits, a scanning

analysis and measurements using the Atomic Force Microscopy method were executed,

the latter applying a Nanoscope E apparatus.

In the course of electrolysis, changes in the composition of the electrolyte were

examined. Samples of the solution were taken at hourly intervals. Cathodic deposits .were dissolved in HNO 1:1 , and their composition subsequently determined applying3

the Atomic Absorption Spectrometry method Perkin Elmer Atomic Absorption Spec-.trometer 3110 . Alloys were estimated visually and layers obtained were documented

photographically. The brightness of coatings was measured using a Corning-EEL

glossmeter. A mirror was adopted as a model surface with 100% brightness.

3. Results and discussion

3.1. Polarisation cures

Fig. 2 shows the cathodic polarisation curves for the individual deposition of cobaltand nickel, their sum and partial polarisation curves for both metals calculated on the

Fig. 2. Cathodic polarisation curves of cobalt, nickel, their sum and partial curves of cobalt and nickel.


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.basis of the composition of alloys . It was observed that the deposition of the parent

metals requires considerable overvoltage. This means that at very low current densities y2 .to 0.5 A dm , the flat course of the polarisation curves is observed. However, this

w xphenomenon is characteristic for elements of the iron group 25 .

The occurrence of polarisation is connected with the inhibition of one of the

intermediate stages of the electrode process. The dependence of the cathode potential oncurrent density in the case of activation polarisation is given by Tafels equation:

E yE sh s a q b log i 1 .i 0 K K

where E is potential of the polarised electrode, E equilibrium potential of thei 0electrode, h cathodic overvoltage, i cathodic current density, a and b are constants.K K

Fig. 3 is a plot illustrating the dependence of the pure metal deposition potential upon

the logarithm of the cathodic current density. It is worth noting that the potential of both

electrodes determined at i s 0 changed with time from the moment the flow of theKelectric current was cut off. For nickel, the stabilized value does not correspond to the

potential calculated using Nernsts equation. According to data given in literaturew x26,27 , difficulties with attaining a state of equilibrium are connected with the passive

state of the surfaces of nickel and cobalt electrodes. This hypothesis appears credible,

since the electrolyte contains dissolved oxygen, which may react with both nickel and

cobalt, thereby creating oxidised layers. One cannot, however, exclude the steadying of

Fig. 3. Dependence of the nickel and cobalt cathode potential on the logarithm of the cathodic current density.


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mixed potentials as a result of the course of the corrosive process under hydrogen

depolarisation. Nevertheless, the rate of this process is negligible, this due to the low .concentration of hydrogen ions in the electrolyte pHs 4.4 .

The cobalt electrode potential determined empirically at i s 0 equalled the equilib-Krium potential. It appears that this fact is connected with the composition of the

electrolyte within which the polarisation curve was registered. This contained 1.7 moldmy3 of chloride ions. The effectiveness of action of chloride ions depends not only on

their concentration in the solution, but also on the ratio of metal ions concentrations tow xthose of chloride ions. From the data presented in literature 28 , it is known that these

anions adsorb on the surface of the electrode and thereby block the secondary reactions.

Data given in Fig. 3 indicate that at the current densities from 0.33 to 0.98 A dmy2

for cobalt and from 0.14 to 1.44 A dmy2 for nickel, the potential of the cathode is a

linear function of the logarithm of the cathodic current density. It seems that the process

ran under activation control during the investigated conditions. It was observed that an

increase in the current density was accompanied by a deviation from this linearity,which in fact may be indicative of the growing participation of concentration polarisa-

w xtion 29 .

During the co-deposition of the metals, there was observed a certain decreasing of the2q .rate of the cathodic reduction of Ni ions in relation to that of pure element Fig. 2 .

This caused the shifting of the partial curve for nickel towards more negative potentials.

At the same time, it was observed that at the current densities higher than 0.5 A dmy2 ,

the cathodic reduction of Co2q ions rate is increased. This means that the deposition of

alloy alters the course of polarisation curves for both constituents.

The sum of polarisation curves determined empirically for the parent metals makes it .possible to draw the predicted polarisation curve for the alloy Fig. 2 . Their course

indicates that at the current density higher than 0.7 A dmy2 , the nickel fraction is

significantly higher than the cobalt one. This fact determines the rate with which the

content of metal ions in the bath is to be replenished so as to maintain their

concentration at a constant level and thereby obtain a cathodic deposit with a uniform

composition throughout its volume, independently of the duration of electrolysis. As a

result, the dissolution of nickel anodes was carried out at current densities that were

three times greater. The choice of another anodic current density would have led to a

rapid change in the composition of the electrolyte.Fig. 4 shows cathodic polarisation curves of the CoNi alloys registered in the baths

with different compositions. The presence of saccharin and sodium lauryl sulfate in the

solution causes a considerable shift of the alloy polarisation curve towards more

negative potentials in comparison with the curve determined in the electrolyte without

additives. The highest inhibition of the cobalt and nickel co-deposition is observed in the

case of saccharin. It appears that it is connected with strong adsorption of its molecules

on the cathode surface. However, the influence of sodium lauryl sulfate on the process

rate is significantly weaker. The addition of a small amount of the surfactant to the bath

containing saccharin lowers the disadvantageous influence of the latter the polarisa-tion curve lies between curves determined in the solutions with one of the additives.

The determination of the experimental alloy polarisation curve and of the partialcurves for its constituents enables one to precisely define the cathodic current density at


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. . . .Fig. 4. Cathodic polarisation curves of CoNi alloy bath composition Table 1 : a point 3, b point 5, c .point 1, d point 4.

.fixed bath composition, temperature, circulation at which it is possible to obtain a

material having a desired composition.

3.2. Composition of CoNi alloys

The influence of current density and the composition of electrolyte on the composi-

tion of deposit were studied.

3.2.1. Cathodic current density

The dependence of the alloy composition on the cathodic current density is presented

in Fig. 5. The plot shows that an increase in this parameter is accompanied by a

reduction in the cobalt content in the cathodic deposit. Simultaneously, at the set current

density, the content of this metal in the alloy is dependent upon the composition of theelectrolyte. The same metal ions concentration was maintained, and therefore the change

in the composition of alloys is connected with the presence of additional components.

The addition of saccharin and sodium lauryl sulfate brought about a reduction of the

cobalt content in relation to the composition of coatings obtained in baths without

additives. It follows therefore that these substances facilitate the deposition of pure

nickel and hinder that of cobalt. It is known, however, that during the cathodic

deposition of pure nickel in the presence of saccharin, the cathodic overvoltage increasesw x30 . The presence of sodium lauryl sulfate in the bath not only compensates for the

unfavourable influence of saccharin, but in addition reduces the alloy depositionovervoltage. What is more, the considerable current efficiency of the cathodic process in

the presence of additives in the electrolyte appears to indicate that the hydrogen

evolution overvoltage increases, too.


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Fig. 5. Influence of cathodic current density on the composition of CoNi alloys bath composition Table . . .1: a point 3, b point 1 .

The observed direction of changes in the composition of the alloy under the influence

of alterations of current density is in good agreement with results obtained by otherw xresearchers 5,15,17 using solutions of simple salts.

3.2.2. Concentration of Co 2 q in electrolyte

The dependence of the composition of CoNi alloys on the concentration of Co 2q

ions in the electrolyte at a fixed concentration of Ni 2q ions is presented in Fig. 6. The

course of the curve indicates that an increase in the content of Co 2q ions in the solution

is accompanied by an increase in the fraction of this metal in the deposit. A characteris-

2q Fig. 6. Influence of Co ions content in electrolyte on the composition of the CoNi alloy bath.composition: Table 1, point 2 .


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.tic feature is that the Cor Co q Ni ratio in the alloy is considerably higher than in the

bath, for example, 7% wt. of cobalt in the electrolyte corresponds to a 30% wt. content

of this metal in the cathodic deposit. This fact is confirmed by the anomalous character

of CoNi alloy deposition, where the less noble constituent is deposited preferentiallyw x31 . Data given in literature indicate that this phenomenon occurs only in baths that

w xcontain simple cobalt and nickel salts 12 , whereas in electrolytes with an addition of .complexing substances there is observed the deposition of alloys with Cor Co q Ni

ratio equal or substantially lower than in the solution.

3.3. Cathodic current efficiency

Fig. 7 shows the dependence of cathodic current efficiency on the current density.

This is clearly connected with the composition of the electrolyte. In baths containing

simple nickel or cobalt salts without surfactants, complexing or other similar additives, itwas observed that a change in current density from 0.4 to 2.3 A dm y2 was accompanied

by an increase in current efficiency from 94.5% to 99.0%. In solutions with saccharin

and sodium lauryl sulfate, there were observed no changes in the efficiency of the

cathodic process in connection with an increase in current density; this equalledw x99.7"0.1%. From the data given in literature 18 , it is known that in baths having

similar compositions within the range of high current densities from 16 to 64 A dm y2

w xthe cathodic current efficiency equals 80%90%, whereas sulfamate solutions 3 with

an addition of sodium lauryl sulfate yielded current efficiencies of 97%100% within

y2 the range of the current densities from 2 to 5 A dm the alloys contained 30%75%.of nickel .

Research carried out indicates that an increase in the concentration of Co2q ions in

the electrolyte causes an increase in the cathodic current efficiency of approximatelyw x1%. Similar results were obtained by Abd El-Rehim et al. 17 in chloridesulfate baths

which did not contain any additional substances.

.Fig. 7. Dependence of cathodic current efficiency upon current density bath composition Table 1: a point . .3, b point 1 .


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3.4. X-ray diffraction analysis

The phase composition of alloys was studied applying X-ray diffraction analysis. It

follows therefrom that peaks solely related to a solid solution with the face-centred cubic

structure are present. This is in agreement with the phase diagram for the CoNi system

w xwithin the researched range of alloy compositions 32 . There are no peaks related topure metallic phases. This would suggest that single-phase cathodic deposits have been

obtained.

There exists no possibility of precisely determining the parameter of the lattice

and therefrom the composition of the alloy on the basis of diffraction patterns

obtained. It is a well-known fact that solid CoNi solutions of decidedly differentw xcompositions have very similar lattice parameters 33 .

3.5. X-ray microanalysis

Fig. 8 shows the results of X-ray microanalysis along lines for two samples obtained

in electrolyte having the same composition, but at different current densities. At the

current density of 2 A dmy2 , the concentration of both nickel and cobalt in the sample

had a constant value, while in the case of the sample obtained at a current density of 1 A

dmy2 , a change in the content of these elements in an area near the edge of the cathode

was observed. This may have been caused by local changes in current density.

The distribution of both metals on an 8P10 4=10P10 4 nm surface area in the form

of a map was determined. An even distribution of nickel and cobalt over the whole

surface was observed. Sections with a higher concentration of one element were notobserved.

.Fig. 8. Distribution of nickel and cobalt along a line on the surface of alloys. The inset v shows the place of . . y2 .cutting out the samples from the cathode bath composition Table 1, point 1 : a i s1 A dm , bK

i s 2 A dmy2 .K


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3.6. Scanning analysis

The alloys underwent scanning electron microscope analysis. Fig. 9 shows the

example microphotographs. These would suggest that the microstructure of deposits is

dependent mainly on the composition of the bath. The current density within the.researched range is a less significant factor.

Spherical growths are clearly visible on the surfaces of alloys obtained in baths that

did not contain additional substances. The presence of saccharin brought about a strong

levelling of the surface. This is especially visible in Fig. 10, which shows the results of

analysis using the AFM method. A similar morphology was observed in nickel depositsw xobtained from Watts-type baths with the addition of saccharin 34 . It would appear,

therefore, that the change in the microstructure of alloys is the result of a specific

adsorption of particles of this compound on the surface of the cathode, which leads to

the deposition of metal in the hollows and thereby to the levelling of surface.Moreover, scanning analysis shows that irrespective of the place at which theinvestigations were carried out in areas taken about 1 mm from the edge and in the

. .middle of the cathode , the composition local analysis and morphology of alloys are

identical.

. y2Fig. 9. Micrographs of surface of CoNi alloys bath composition Table 1: a point 3; i s0.5 A dm ,K . y2 .b point 1, i s1 A dm .K


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Table 2

Results of measurements of brightness of CoNi alloys

No. Additional substance Quantity of light reflected, %

1 Without additives 0

2 Saccharin 59

3 Saccharinqsodium lauryl sulfate 34

have presented the results of measurements of the brightness of alloys obtained in baths

with the same concentration of metal ions without additional substances and in their

presence. The results thus obtained indicate that the presence of sodium lauryl sulfate

does, however, reduce the brightness of the surface. The appearance of surfaces of alloys

obtained is given in Fig. 11.

3.8. Changes in the composition of electrolyte

During the 1020 h deposition of CoNi alloys there were observed no changes in

the concentration of cobalt and nickel ions in the electrolyte within the scope of

sensitivity of the method applied. This was facilitated by the considerable volume of the

solution, the application of great speeds of the solution flow, and also by the appropriate

. . y2 .Fig. 11. Appearance of surfaces of alloys basic bath composition: Table 1, point 3 a i s0.4 A dm ; bK y3 . y2 . y3 .with an addition of saccharin 1 g dm , i s0.5 A dm ; c with an addition of saccharin 1 g dm andK

y3 . y2sodium lauryl sulfate 0.08 g dm , i s1 A dm .K


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the influence of electrolysis parameters on the composition

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