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PLATINUM METALS REVIEW

A quurterly survey of reseurch o n the platinum metuls urrd of dwelopments in their applications in industry

V O L . 2 1 J U L Y 1 9 7 7 NO. 3

Contents

Noble Metal Catalysts on Metal Substrates

The Queen’s Award for Technological Achievement 1977

Intermetallic Compounds of the Platinum Group Metals

Palladium for Electrical Contacts

Catalytic Oxidation of Pollutants from Ink Drying Ovens

Heterogenised Homogeneous Catalysts

Jean Baptiste Boussingault and Platinum

Abstracts

New Patents

74

84

85

89

90

92

97

101

105

Communications should be addressed to The Editor, Platinum Metals Review

Johnson Matthey & Co Limited, Hatton Garden, London ECl N 8EE

Noble Metal Catalysts on Metallic Substrates A NEW GENERATION OF CELLULAR MONOLITHS FOR EMISSION CONTROL

By A. S. Pratt

and J. A. Cairns Group Research Centre, Johnson Matthey and Co Limited

Atomic Energy Research Establishment, Harwell

T h e use of plat inum group metal catalysts supported on ceramic monoliths for control of gaseous emissions f r o m automobiles and chemical plant i s now well established. Research in the Johnson Matthey Laboratories and at AERE Harwell, aimed at meeting the demand for more effective catalysts, has resulted in a new generation of p la t inum catalysts in which the ceramic substrate is replaced by a metal monolith. These metal substrate p la t inum catalysts are found to be more compact and more eficient than conventional ceramic structures. At the same time they overcome the structural limitations of ceramics with greater resistance to thermal shock and mechanical failure. T h e development of the metal substrate catalyst, and its use in hostile high temperature environments such as automobile emission control and catalytic combustion is described.

In recent years attention has been turned towards the effects of man and his technology on the environment, of which a major effect has been the reduction in air quality over the years. Corrective measures are being taken to reduce the emissions to the atmosphere from mobile and stationary sources such as automobiles, power stations and fossil fuel burners. Other controls are in force for chemical plant and major pollutant sources.

Effective emission control is often obtained by the use of noble metal catalysts (I-7), and to date the normal substrate for these catalysts has been a porous ceramic, either in pelleted or cellular monolith form. In general the ceramic monolith has gained greater accept- ance in high-flow velocity operation due to the low pressure drop inherent in its configuration. However, the physical properties of these ceramic substrates are not ideal

since they are relatively fragile and liable to thermal shock fracture.

Platinum catalysts mounted on a metal substrate have been developed to overcome the mechanical and thermal limitations of the ceramic monolith. At the same time metal substrates possess the major advantage of higher surface to volume ratio giving increased reactivity per unit volume, while possessing lower pressure drop per unit length.

The Metal Substrate Concept In order to preserve the advantages in-

herent in the cellular monolith catalyst the metal substrate is designed to give axial flow passages throughout its length (Figure I). This design yields maximum gas/solid contact for catalytic reaction, and maintains low pressure drop over the catalyst bed.

Platinum Metals Rev., 1977, 21, (3), 74-84 74

Fig. 1 The metal units have been developed to overcome the mechanical and thermal shock limitations encountered with ceramic monoliths. Additionally, a metal substrate only 3.5 inches diameter and 3.5 inches long gives similar catalytic performance to a ceramic substrate 4 inches diameter and 6 inches long

Comparable monolithic ceramic and metal catalyst substrates.

Analysis of the parameters of such a structure in relation to catalytic performance reveals that two predominant processes govern the effectiveness of the catalyst. Under low temperature conditions, such as cold start on an automobile, the thermal mass of the catalyst must be kept low in order to assist rapid warni-up of the catalytic surface to its ignition temperature, whence emission control commences. Conversely under high temperature operation the rapid combustion of pollutant species occurs, and the rate limiting process becomes the mass transfer of reactants from the gas phase to the walls of the channel.

During mass transfer limited operation the overall conversion of the monolithic

catalyst is defined by the following equation:

where fR is the residual emission SjV is the geometric surface areajunit

C is the function of the channel geometry A is the percentage open area of the

L is the length of the monolith R is the hydraulic radius of the monolith

channel, and K is a constant incorporating the reactant

gas diffusity, density and feed rate, and the cross sectional area of the reactor.

volume of the monolith

inlet face

From the above equation it can be seen that as the monolith length, open area and

Platinum Metals Rev., 1977, 21, (3) 75

surface volume ratio is increased, and the channel hydraulic radius is decreased, the conversion over the catalyst will increase. Thus we may assess the performance gains of a metal substrate catalyst structure in terms of the advantages of manufacture from thin foil sheet (typically 0.002 inch) in comparison to ceramic structures containing thicker walls (typically 0.010 inch). Fabrication from thin metal sheet allows a much higher cell density (channels/in2) with a resultant increase in surface/volume ratio (S /V), hence increasing effectiveness per unit volume. Metal substrates are currently fabricated up to 600 cells/inz (see Table I) yielding a geometric surface area of 1190 ft2/ft3 which is approximately double that of the ceramic monoliths currently in use. In addition the thin wall thickness allows significant increase in the open area of the monolith inlet face which again increases effectiveness and at the same time reduces the pressure drop per unit length. Channel geometry, and hydraulic radius may be optimised for maximal effect. Thus a metal substrate fabricated from thin sheet should compete effectively with its ceramic counter- part even when using significantly smaller catalyst volumes. Complete analysis of the interrelated parameters of mass transfer and

Ceramic Cell Density celljin'

200 300

thermal mass reveals that a metal substrate 3.5 inch diameter ~ 3 . 5 inch long gives equivalent mass transfer characteristics to a 4 inch diameter x 6 inch long ceramic substrate and possesses lower thermal mass (Figure I). The unit volume effectiveness of the metal substrate proves an attractive feature in automobile pollution control applications where space limitation is often an over-riding criterion (Figure 2).

Improved durability of a catalyst mounted on a metallic substrate may accrue from its inherent resistance to mechanical and thermal failure, provided that the steel is resistant to oxidation and corrosion in high temperature exhaust environments, and the catalytic coating is compatible with the selected steel. The catalyst layer must also be resistant to abrasive attrition in high temperature, high flow, corrosive environments.

Selection of the Steel The operation of a metal substrate cata-

lyst in high temperature oxidative and corrosive environments, typical of automobile exhaust conditions, requires that the alloy selected is resistant to corrosion and that any surface oxide film formed on the alloy is adherent and free from cracks. Oxidation

Metal Cell Density cell/in'

400 500 600

Table I Comparison of Ceramic and Metal Substrate Parameters

Surface t o volume ratio per cm Surface to volume ratio per f t

Open area, per cent

Wall thickness, cm Wal l thickness, inch

Parameter r - ~~

18.9 22.05 32.3 35.8 39.4 576 672 987 1090 1197

70 60 a9 86 83

0.028 0.030 0.005 0.005 0.005 0.01 1 0.012 0.002 0.002 0.002

I Cell area, cm2 1 0.023 0.0143 1 0.015 0.011 0.0097


tests carried out on a series of alloys including (a) ferritic steels, (b) austenitic steels, and (c) non-ferrous alloys based on nickel- chromium, have revealed that the aluminium- containing ferritic steels are particularly attractive in this context.

Examination of the mode of surface oxide growth by scanning electron microscopy reveals the surface topography of some of the alloys considered for this application (Figure 3). The micrograph of an austenitic steel (top, left) shows the unsatisfactory nature of its surface for metal substrate catalyst applications. In this instance the surface oxide film has flaked from the surface and secondary oxidation of the underlying surface has commenced. X-ray analysis of a gold-palladium coated surface oxide film using an energy dispersive analyser (bottom, left) reveals that the surface film is predominantly iron oxide. Obviously attempts to catalyse this material to produce a durable catalyst

unit are likely to lead to loss of the noble metal catalyst as the underlying surface oxide layer spalls from the metal.

Examination of an aluminium-containing ferritic steel reveals a strong contrast to the austenitic steels. This steel shows significant surface oxide growth after high temperature treatment but X-ray analysis shows that the oxide growth is due predominantly to migra- tion of aluminium (bottom, right) from the bulk alloy to the surface to form a protective adherent oxide layer with no evidence of surface cracks (top, right).

The excellent oxidation resistance of aluminium-containing ferritic steels demonstrated in the electron micrography studies was again confirmed by thermogravimetric analysis of thin foil sheet oxidised in air a t temperatures up to IZOO~C. Austenitic steel is shown to have an unacceptably high oxidation rate at 1z0o~C. Surface oxide fracture and reoxidation is evident from the point of


Fig. 3 Electron photomicrographs showing the surface topography of a n austenitic and a ferritic steel after heat-treatment in a n oxidising environment. T h e surface topography i s shown on the two top photomicrographs where the austenitic steel ( 1 . f ) has been severely oxidised, and some ofthe oxide layer has spalled f r o m the steel exposing a new surface to oxidation. O n the other hand, the aluminium-containing ferritic steel (right) is covered by a continuous oxidc layer which shows no signs of spalling or cracking. The energy dispersive analyser shows, in the lower photographs, the spectra obtained f r o m the surfaces of the two materials. T h e oxide on the aluminium-containing ferritic steel (right) i s mainly aluminium which has migrated to the surface to f o r m a protective coating, while on the austenitic steel (left) the oxide i s iron. The gold and palladium indicated are coatings applied f o r analysis purposes only

inflexion in the weight gain curve after 4 hours oxidation, Figure 4(a). In contrast the aluminium-containing ferritic steel, Figure 4(b), shows excellent oxidation resistance up to IZ0OCC.

As a result of these studies, coupled with an assessment of the viability of manufacture of the steel in thin foil form (thickness 0.002

inch), Fecralloy@ steel was selected as the prime contender for a metal catalyst support

matrix. This alloy has been developed by AERE Harwell for automotive exhaust catalyst applications (8).

Fecralloy steels derive from a family of steels containing for example up to 20 per cent chromium, 0.5 to IZ per cent aluminium, 0.1 to 3 per cent yttrium and the balance iron, which on heating in air at typically 800 to IOOOT form an alumina-rich surface layer which endows the steel with excellent


high temperature oxidation resistance. For example, it can be used in various thicknesses at temperatures as high as 1200 to 1300°C in air with none of the surface spalling properties that tend to be associated with austenitic steels and some related commercial ferritic steels. Fecralloy steel sheet 0.5 mm thick has a life of over one year in air at 1200°C but, in common with other steels, maximum usable temperatures are lower in this environment. Nevertheless Fecralloy steel can be exposed to exhaust gases for periods of several hundred hours at temperatures as high as 1050°C. The excellent protective property of the alumina surface layer is thought to be enhanced by the influence of the yttrium.

Fecralloy steel, along with some other aluminium-containing ferritic steels, has the attraction of having an alumina coating which emanates from within the bulk of the material and is essentially self-healing, whereas alumina washcoats applied to conventional steels are prone to spalling on being subjected to repeated thermal cycling or mechanical vibration.

Catalysing the Metal Substrate The conversion of the monolith metal

substrate into an active noble metal catalyst entails deposition of the catalyst layer on the surface of the steel. Initial studies (Figure 5) rapidly revealed that simple deposition of platinum on to an oxidised steel surface was unsatisfactory in that although initial performance was comparable to the ceramic catalyst, the metal supported catalyst rapidly deteriorated during use. Further studies showed that the deactivation process could be prevented by deposition of platinum on to a high surface area gamma alumina (de- signated the catalytic alumina layer), bonded to the surface of the steel. Proprietary techniques have been developed to achieve the firm bonding necessary to overcome spalling of the catalytic alumina layer due to differ- ential thermal expansion of the substrate steel and the alumina layer during cyclic

temperature operation. It is essential for the formation of a satisfactory bond between the substrate and the washcoat that a satisfactory key is provided on the substrate. The oxidation of Fecralloy steel and some other aluminium-containing ferritic steels provides an alumina-rich surface which is adherent and self-healing. The surface oxide also provides an excellent key for washcoat application.

Adhesion tests of the alumina coating, conducted by thermally cycling strips of the steel between 200 and IOOO"C at 15 second intervals for 50 cycles, revealed that coating losses averaged around 2 per cent of the total alumina coating. Measurement of the catalytic


This alumina has the additional advantage that it is fully compatible with existing monolith catalyst production plant (g), allowing the interchange of ceramic and metal substrate catalyst manufacture. Comparative tests of ceramic and metal monolith catalysts, to establish adhesion of the catalytic alumina layer, were carried out by the following procedures: (a) a multiple water wash, (b) a high pressure air jet attrition test and (c) a thermal shock test where the monolith is subjected to 20 temperature cycles between ambient and 650 to 850°C. The results (Table 11) show that excellent adhesion, comparable to the ceramic monolith currently used in automotive emission control applications, is obtained with the metal substrate.

Application of the platinum group metals to the surface of the metal substrate is carried out by proprietary techniques, but again the methods used are fully compatible with existing production plant.

Emission Control Using Catalysts on Metallic Substrates

Catalysts on metallic substrates have been evaluated against two primary emission control applications, namely automobile emission control and catalytic combustion. In the former process the catalyst is installed in the exhaust train to treat the emission from the combustion chamber. An illustration of the environment is shown in Figure 6. The principles of this method have been reviewed previously in this journal (5, 10, 11, 12). In the latter process the catalyst is installed in the combustion chamber and the air/fuel mixture burnt catalytically over the active platinum surface. Hence catalytic combustion possesses the major advantage of lower NO, emission due to lower combustion temperatures preventing fixation of nitrogen. This method of emission control is

alumina surface area after high temperature currently being actively researched (13-16) firing (IIOO'C for 2 hours) showed that it for gas turbine engines, where the continuous retained its high surface area (80 mz/g), combustion process is directly amenable to necessary for high temperature stability of catalytic treatment. the catalyst in emission control applications. Endurance tests made on metal substrate


F‘ . 6 Preliminary evaluation of metal substrate catalysts for automobile emission control appli- catEons were undertaken with units installed in the exhaust system of a single cylinder 4-stroke 50cc engine. On combustion the exhaust gas emitted generates a high temperature close to the catalyst, as is shown i n the photograph where a unit is seen temporarily working in a silica holder

z!

catalysts used for carbon monoxide and hydrogen-oxide emissions from automobile exhaust carbon emission control from automobile (Table 111). exhaust have shown that the catalytic dura- The particular advantages of the metal bility of the metal supported catalyst is substrate are again apparent in the use of equal to or greater than its ceramic counter- catalysts to promote combustion in the gas part. Emission tests conducted over the U.S. Federal emission test procedure have also confmned the original predictions that the metal substrate catalyst is capable of achieving similar emissions to the ceramic catalyst using half the ceramic volume (Figure 5). Fecralloy steel substrate catalysts have been tested over 50,000 miles (Figure 7) and have met Federal statutory limits. Metal substrates are also compatible with “Three Way Cat- alyst” (11) formulations, used for simultaneous control of carbon monoxide, hydro-carbon and nitro-

Platinum Metals Rev., 1977, 21, (3)

Table II Comparison of the Adhesion of the Catalytic Alumina Coating to Metal and Ceramic Substrates by Water Washing, Air Attrition

and Thermal Shock Tests

Alumina Loss per cent I I

Multiple Air Attrition Shock I 650°C 850°C I %ie 1 Water Wash1

Metal 0 0 I Ceramic1 0 I (0.5 I 1.8 3.6

81

SU b- strate

Th er ma1

1.8 2.4

turbine engine. In this context the low pressure drop of the metal substrate catalyst (Figure 8) gives the added advantage that catalytic combustors may be designed with minimal power loss, while at the same time achieving high combustion efficiency (Figure 9). Measurement of NO, emissions from the catalytic combustor operating under conditions typical of a gas turbine engine showed the emission to be less than 25 ppm, which compares with IOO to 500 ppm for the conventional gas phase flame combustor.

Conclusions Research in the Johnson Matthey and

Harwell Laboratories has led to the development of a durable platinum group metal catalyst bonded to an aluminium-containing ferritic steel. Fabrication of the steel substrate into a cellular monolith structure gives a compact and efficient catalyst system free of the thermal and mechanical failure problems associated with similar ceramic structures. Metal substrate catalysts are particularly applicable to high flow, high temperature environments typical of those in automobile emission control and catalytic combustion.


Table 111 Comparison of the Conversion Efficiency of Metal and Ceramic Substrate “Three Way

Catalysts” During a 300 hour Endurance Test

Hydrocarbon Carbon Monoxide Nitrogen Oxide E I I I

Test Hours Test Hours Test Hours

0 100 200 300 0 100 200 300 0 100 200 300

Metal Substrate 6 inches dia. 82 75 80 73 80 84 88 83 98 84 79 80 x 4 inches

Ceramic Su bstrate 6 inches dia. 78 82 70 74 88 87 86 78 67 65 61 63 x 4 inches

Conventional gas phase combustors inject fuel into the combustion chamber in the form of droplets. Combustion occurs on the droplet surface at stoichiometric air/fuel ratio giving rise to high local flame temperatures and leading to the formation of NO,. Attempts to overcome NO, formation by prevapourising the fuel to give a lean homogeneous fuel/air mixture, and hence lower peak combustion temperatures, are fraught with difficulty due to limitation of flame stability under weak fuel/air operation.

Catalytic combustion possesses the major advantage that the combustion process is not subject to the lean flame stability limitation of gas phase combustion. Tests on a Johnson Matthey metal substrate catalyst system have recently been reported by Exxon (16).

Acknowledgements The Harwell research contribution to this work

was made possible by the financial assistance of the Chemicals and Minerals Requirements Board of the Department of Industry.

0 Fecralloy steel is the Registered Trade Mark of the United Kingdom Atomic Energy Authority for a specific range of alloys.

References

I J. B. Hunter, Platinum Metals Rev., 1968, 12, 11 €3. J. Cooper, Platinum Metals Rev., 1975,

2 G. J. K. Acres, Platinum Metals Rev., 1970, 12 B. J. Cooper, E. Shutt and P. her, Platinum Metals Rev., 1976, 10, (z) , 38

3 G. J. K. Acres, Platinum Metals Rev., 1970, I3 w. s. Blazowski and G. E. Bresower, Air Force Aero Propulsion Laboratory, Wright

4 G. J. K. Acres, Platinum Metals Rev., 1971, Patterson Air Force Base, Ohio, Report No.

5 G. J. K. Acres and B. J. Cooper, Platinum I4 J. T. Rosfiord, AIAA Paper No. 76-46, AIAA 14th Aerospace Sciences Meeting, January 26-28, 1976, Washington 6 R. A. Searles, Platinum Metals Rev., 1973,17, 15 D. N. Anderson, NASA Reports TMX- 73410 and TMX-73412. Papers presented to 7 E. J. Sercombe, Platinum Metals Rev., 1975, the Workshop on Catalytic &mbustion

19, (I), 2 sponsored by the U.S. Environmental Pro- 8 J. A. Cairns, J. E. Antill, R. s. Nelson and tection Agency. May 25-26, 1976, Raleigh,

M. L. Noakes. To be published North Carolina 9 G. J. K. Acres, B. J. Cooper and G. L. 16 V. J. Siminski and H. Shaw, Exxon Research

Matlack, Platinum Metals Rev., I973J 171 and Engineering Company “Development of (31, 82 a Hybrid Catalytic Combustor”, zznd Inter-

10 M. Shelef and H. S . Gandhi, Platinum Metals nat. Gas Turbine Conf. Amer. Soc. Mech. Rev., 1974, 18, (I), 2 Eng., March 1977, Philadelphia, Pennsylvania

(0 , 2 19, (41, 141

14, (I), 2

14, (31, 78 AFAPL-TR-74-32 15, (I), 9

Metals Rev., 1972, 16, (31, 74

(21, 57


The Queen’s Award for Technological Achievement 1977

PLATINUM ALLOY CATALYSTS FOR EXHAUST CONTROL

The valuable work of the Johnson Matthey Research Centre in developing platinum alloy catalyst systems for the control of air pollution caused by vehicle exhaust systems has now been recognised by the granting of the Queen’s Award for Technological Achievement 1977. This award, which is given for “a significant advance, leading to increased efficiency, in the application of technology to a production or development process in British industry or the production for sales of goods which incorporate new and ad- vanced technological qualities”, is made only after an outstanding innovation has achieved commercial success. To assist the award assessors in under- standing this innovation two articles on automobile emission control which have previously appeared in this Jour- nal were provided for them.

Having already devised and produced platinum metal catalyst systems for the control of industrial air pollution the Johnson Matthey Research Centre was able to anticipate and re- spond quickly to the world wide concern which arose from a growing realisation of the harmful effects of air pollution caused by motor vehicle exhaust. Two platinum alloy autocatalyst systems were developed for the control of carbon monoxide and hydrocarbons, and for nitrogen oxide emissions, and clearly demonstrated the feasibility of platinum alloy catalysts achieving the very stringent requirements of United States legislation without impairing fuel economy.

This new technology was used to advise car manufacturers in the U.K., U.S.A., mainland Europe and Japan in the use of platinum alloy catalyst systems for emission control. In the U.K. Johnson Matthey worked with Leyland Cars and Rolls-Royce Motors

to develop systems for use on vehicles being exported to the U.S.A.

In addition to the design of autocatalyst systems Johnson Matthey has developed continuous processes for the production of these systems. Johnson Matthey Chemicals Limited in the U.K. and Matthey Bishop Incorporated in the U.S.A. have been in full scale production of the systems for the U.S.A. and European markets since May 1974. Purchasing contracts for the supply of catalyst systems to Ford (U.S.A.), Volkswagen, British Ley- land and Rolls-Royce Motors were concluded in 1g73/74. Those cars fitted with catalyst systems exported from the U.K. to U.S.A. by Leyland Cars and Rolls-Royce, since model year 1975, have all used catalysts manufactured by Johnson Matthey Chemicals Limited.

It is anticipated that platinum alloy autocatalyst technology initially developed for the United States market will, in future, be used on cars sold in Europe and exported to Japan.

Platinum Metals Rev., 1977, 21, (3) 84 84

Intermetallic Compounds of the Platinum Group Metals SELECTED MATERIALS AND THEIR PROPERTIES

By I. R. McGill Group Research Centre, Johnson Matthey & Co Limited

ivany of the platinum group intermetallic compounds possess unique properties which may occur in most interesting combinations. This paper draws attention to a number of these and briejly describes some applications for them. It suggests that further study is required before a full appreciation can be made of their perhaps considerable potential for use in hostiIe environments.

The search for new high temperature materials has gained increasing impetus over the last ten years. Greater demands are being placed on existing materials as the environmental conditions under which they must operate become increasingly severe. In particular the trend towards optimising performance and efficiency in modern gas turbines requires the development of high strength materials with structural stability and corrosion resistance at temperatures in excess of 10oo"C. With few exceptions the desire for higher creep rupture strength linked to better corrosion resistance cannot be economically fulfilled by the use of any single material. Greater emphasis has therefore been placed on the development of protective coating systems which are compatible with new generation high strength materials and offer suitable corrosion protection at operating temperatures. Already the platinum group metals, and in particular the platinum aluminides, have contributed


towards advances in coating technology. The demand for high purity single crystals

of mixed refractory oxides is rapidly increasing. Consequently, the choice of suitable non-reactive container materials becomes more selective. At temperatures around zo00"C iridium and rhodium are obvious choices, although are more often used under an atmosphere of nitrogen to minimise precious metal loss. In terms of thermodynamic stability and resistance to environmental attack, a number of the platinum group intermetallics offer exciting alter- natives to the present range of crucible materials.

From an extensive survey by Paine et a1 (I) in 1960 covering 798 binary metal systems, only 95 were shown to either contain or expected to contain intermetallic compounds with high temperature ranges of stability. Only two systems containing platinum group metals were studied with respect to high temperature oxidation resistance, namely beryllium-platinum and beryllium-palladium. As a result of the unexpected volume expansion of the intermetallics during isother- mal oxidation tests, experimental work on these systems was discontinued. It was unfortunate that other precious metal intermetallics were not considered. The following text gives some insight into the current and potential uses of intermetallics of the precious metals and is based on theoretical prediction supported by a selection of published experimental data.

The extraodinary stability of intermetallic compounds formed by combination of the

platinum group metals with elements from the left of the 3d, 4d and 5d transition series has been satisfactorily explained by the Engel-Brewer approach to metallic bonding. I t would be appropriate, therefore, to sum- marise briefly the basis and implications of the Engel-Brewer correlation before con- sidering a selection of published data on the stability and high temperature properties of a number of platinum group intermetallics.

A Basis For Prediction In general the high melting points of

intermediate phases in binary alloys of the transition elements can be explained on the basis of availability of unpaired s, p and d bonding electrons. Although s andp electrons do contribute to bonding their concentration and ratio have more influence on long range order and crystal symmetry. The d electrons, in transition metal alloys are, however, directly responsible for the degree of metallic bonding and as such their distribution affects bonding capacity. Elements to the left of and including rhenium and technetium in the 4d and 5d transition series make use of all their valence electrons for bonding as their electron con- figurations are not limited by the Pauli exclusion principle. Optimisation of d electron bonding is obtained for elements with the d5 configuration and is clearly reflected by the melting points of Group VI elements, molybdenum and tungsten. The effect of resonance coupling of unpaired d electrons on atomic bond strength is reflected by a lowering of melting point of the elements from ruthenium to palladium and osmium to platinum. Similarly, the general effectiveness of d electron bonding increases from the first to third transition series. The d electrons, therefore, ultimately dictate thermodynamic stability and in this sense are of more concern to the metallurgist as a means of pre- dicting the degree of transition metal interaction and the potential existence of high temperature materials in a number of selected alloy systems.

The genesis of such a prediction must,

therefore, be based on attaining the right combination of transition elements such that d orbital overlap can be maximised. This condition can be fulfilled by the interaction of suitable electron-deficient and electron- rich elements. The position of the platinum group metals in the 4d and 5d transition series is most appropriate as their electron configuration and in particular d orbital structure make them primary source electron donors. The choice of electron acceptor can therefore be made from the transition elements of Groups V to 111.

A simple illustration of the Engel-Brewer concept can be made by comparing the melting or decomposition temperatures of the compounds AIr3, where A is a transition element taken from Group I11 or IV. This is shown in the Table.

Intermetallies and Their Application

Generally high stability compounds of the platinum group metals have received little attention, reference only being made to them as prime examples of the Engel-Brewer approach to metallic bonding. However, their stability and high melting or decomposition temperatures make them attractive materials for use in demanding environments. To limit the scope of transition metal combinations with the platinum group metals, only those elements from Groups IVB and VB will be considered with occasional reference to other combinations worthy of mention.

A general lack of ductility restricts the use of these materials for structural components, although a number of exceptions havc been reported in the literature. In particular a number of isostrvctural phases with narrow ranges of compositional stability in the systems of niobium and tantalum with iridium and rhodium are known to have somewhat higher degrees of ductility than would normally be expected of intermetallic compounds.

The constitution of the tantalum-iridium system was first reported by Ferguson et a1 (2)


An Indication of the High Temperature Stability of Same Platinum Group Intermetallics Resulting from Predictions

Made by the Engel-Brewer Concept

I Transition Series I Group 111 Group IV I Compound Melting Point Compound Melting Point

"C "C

3d Tilr, 2115 Vlr, 21 008

4d Zrlr, - Nblr, 2435

5d Hflr, 2470 Talr, 2450

decomposition temperature

in 1963 from which confirmation was then made on a number of terminal solid solutions and intermediate compounds. The iridium- rich compound u-TaIr, melts congruently at ~450°C. Three other phases y, cc, and a z were also reported all of which are stable up to at least 1860°C. The phase ccl, nominal- ly TaIr, decomposes peritectically at 2120°C and shows a respectable degree of ductility and toughness. The tantalum-rhodium system (3) shows close resemblance to the tantalum-iridium system and similar properties were recorded for a1 (TaRh), although no explanation could be given. The compound TaRh decomposes peritectoidally at 1860°C. Ritter et a1 (4) reported the constitution of the niobium-rhodium system in 1964 and it was used to form the basis for a comparative evaluation of the intermediate phases of the related systems tantalum- iridium and tantalum-rhodium. Although a number of these phases were reported to be hard but ductile, none had stability above 1430°C. The isostructural phase a p in the niobium-iridium system is known to have similar mechanical properties to the a1 phase in the tantalum-rhodium and tantalum- iridium systems.

A measurable degree of ductility and high stability are obviously two criteria which have some relevant importance to high temperature coating technology. However, the

improvement in oxidation resistance of the refractory elements niobium and tantalum at temperatures above IOOO~C by alloying with a variety of suitable elements has proved to be somewhat ineffective. Single phase ac-Nb containing 5 atomic per cent iridium shows only a marginal improvement over pure niobium.

Although further alloying with elements such as tungsten, titanium and nickel might well be foreseen, the interesting combination of strength, ductility and high decomposition temperatures of a number of alloys of niobium and tantalum with the platinum group metals are such as to warrant further attention.

Of the many and varied coating methods developed for high temperature corrosion protection of nickel and cobalt-based alloys, pack aluminising remains one of the most economical and convenient processes. The mode of degradation of aluminide coatings is well understood and has prompted the development of superior coatings containing precious metal diffusion barriers (5-9). There still remains some controversy as to the mechanism by which elements such as platinum and rhodium can effectively increase the durability of conventional aluminide structures. The stability and oxidation resistance of the platinum and rhodium aluminides is, however, an important consideration. Figure I shows a typical platinum-aluminised


structure while the type of component which could benefit from this coating process is shown in Figure 2.

Precious metals are now being considered as beneficial additions to CoCrAlY and NiCrAlY clad coatings. Yttrium, hafnium and the rare earths have been used for some time in these protection systems and are known to create fine dispersions of inert oxides which improve scale adherence by pinning mechanisms. The addition of platinum and/or rhodium to the MCrAlY compositions where M is cobalt, nickel or iron, may well contribute to this mechanism by the formation of discrete

Fig. 2 High temperature applications are one of the more obvious uses for the intermetallic compounds of the platinum group metals

Fig. 1 A typical platinum-alurninised structure is shown in the photomicrograph. The diflusion zone consists basically of a platinum-rich surface layer, an intermediate nickel-rich Zaycr and, at the diffusion ronejsubstrate interface, a layer which has a more characteristic aluminised structure

intermetallic particles at the protective oxide / coating interface. As yet there seems to be no experimental evidence to corroborate this particular theory although work has been conducted on CoCrAlY coatings which shows that the presence of platinum can have a substantial effect upon the adherence of alumina scales (10, 11).

Some of the highest melting point compounds as predicted by the Engel-Brewer theory are those which combine a platinum group metal, in particular platinum or iridium with zirconium and hafnium. Holcombe (12) has suggested that the compound HfPt, may be used for containing reactive oxides. More recent work by Ficalora et a1 (13) on both HfPt, and ZrPt, showed no deterioration when oxidised in air at rooo"C for 5 hours. Fine dispersions of ZrPt, and ZrRh, in rhodium-platinum alloys are thought to


improve significantly high temperature creep strength (14). Obviously there is scope for an improvement in the high temperature mechanical properties of other alloy systems by platinum-group intermetallic dispersion strengthening. In particular it would be interesting to speculate whether small additions of zirconium or hafnium to the ductile phase compositions in the niobium-iridium (rhodium) and tantalum-iridium (rhodium) systems would: (a) improve oxidation resistance by the formation of complex mixed oxide scales of the type Zr(Hf)O,.Nb,O,, having some plasticity and; (b) improve the overall creep properties of the alloys by selective dispersion of intermetallic compounds of the form Zr(Hf),(PGM),. Cer- tainly Barrett and Corey (15) have suggested that fine dispersions of inert platinum group metals in oxides which have very high volume ratios would form a unique basis for a protection system.

Apart from exploiting these intermetallics as high temperature materials, a number of alternative applications can be suggested based on the prediction that low temperature ( < 4 ~ 0 ° C ) properties are comparable with those of the compounds Mo,Ru, and W,Ru, (16, 17). These two compounds produced as thin films have hardness values comparable with sapphire and are virtually inert in the presence of toxic etchants up to temperatures around 550°C. Ficalora et a1 (13) reported similar results, although mainly qualitative, on the chemical inertness of HfPt, in various etchants. Equally attractive is the possible application of the platinum-group intermetallics as bearing and electrical contact materials utilising their high melting point and corrosion and wear resistant properties and as general wear resistant coatings for high quality cutting tools and extrusion or wire drawing dies.

It seems evident from the literature that the high temperature intermetallics of the platinum group metals are still somewhat novel and that their potential has yet to be fully appreciated.

I

2

3

4

5

6 7 8 9 10 11

I2

13

I4 I5

16

I7

Keferences R. M. Paine, A. J. Stonehouse and W. W. Beaver, U.S. Air Force Tech. Rpt. W.A.D.C. TR 59-29, Part I, Jan. 1960 W. H. Ferguson, B. C. Giessen and N. J. Grant, Trans. AIME, 1963, 227, 1401 B. C. Giessen, H. Ibach and N. J. Grant, Ibid, 1964,230, 113 D. L. Ritter, B. C. Giessen and N. J. Grant, Ibid, 1964, 230, 1250 G. Lehnert and H. W. Meinhardt, Electrudcp. Surf. Treatment, 1972i73, I, (I), 71

British Patent 1,350,855; 1974 U S . Patent 3,961,910; 1976 U.S. Patent 3,999,956; 1976 E. J. Felten, Oxid. Met., 1976, 10, (I), 23 L. Aprigliano and G. Wacker, 3rd U.S. /U .K . Conference on Gas Turbine Materials in a Marine Environment, 1976, 2-23 Sept., University of Bath, England C. E. Holcombe, J . Less-Common Metals, 19769 44,331 P. J. Ficalora, V. Srikmishman and L. Pecora, Naval Ordinance Systems Command Con- tract NOOOI7-72-C-4424, 1974 British Patent 1,238,013; 1971 C. A. Barret and J. L. Corey, Nat. Aero- nautics and Space Agency, Note D-283, 1960 L. R. Testardi, W. A. Royer, D. D. Bacon, A. R. Storm and J. H. Wernick, Trans AIME, 1973343 2195 U.S. Patent 3,912,611; 1975

Idem, Ibid, 1973, 1, (3), 189

Palladium for Electrical Contacts The use of electrodeposited palladium

instead of gold on electrical contacts appears economically attractive at the present time. At the Annual Technical Conference of the Institute of Metal Finishing held recently at Windermere, in a session devoted to noble metals, this was one of the topics discussed.

In a paper, “High Speed Plating Solutions for Selective Electroplating”, F. I. Nobel and R. T. Hill of Lea-Ronal dealt with the special plating solutions required to produce the desired results when plating both select- ively and continuously. For palladium plating it has been established that proprietary solutions, at present being successfully used in barrel and rack plating operations to plate electrical contacts, can be modified for use in spot plating machines by increasing the metal content from about 8 to 10 grams per litre to 15 to 25 grams per litre. With the correct conditions 5 microns of sound bright palladium, as good as barrel plating, can be deposited in 15 seconds.


Catalytic Oxidation of Pollutants from Ink Drying Ovens By Thomas H. Snape Matthey Bishop, Inc., Malvern, Pennsylvania

Many industrial processes produce hydrocarbon vapours which, if released to the atmosphere, contribute to the general pollution of the environment. The discharge of such vapours is now, not unnaturally, being subject to legis- lative control in many places as the extent of the damage resulting from such pollution is more fully realised. Platinum catalyst control systems are being increasingly employed to prevent air pollution as the cost bent@ of employing such systems, are becoming more generally known. This paper describes the system one enterprising organisation has successfidy employed to comply with the strict pollution control regulations in Los Angeles, a region where topography and climatic conditions result in particularly difficult pollution problems, while at the same time making substantial savings in fuel.

During the drying stage of web offset printing, ink solvent hydrocarbons are evapor- ated from the work and must be continuously removed from the drying oven. As these solvents consist basically of hydrogen and carbon a most efficient way of getting rid of them consists of burning, so producing harmless carbon dioxide and water. Such a thermal incineration method requires that the fume-laden exhaust from the oven must be heated to a high temperature and held at that temperature for a relatively long time, under turbulent conditions, while the oxidising reaction takes place. In practice a tempera-


ture of approximately 800°C and an exposure time of about 0.5 second is required to reduce the concentration of solvent to an acceptable level before it is discharged to the atmosphere.

A newer more efficient alternative to thermal incineration is catalytic combustion which, because it takes place on the surface of a catalyst bed, operates at a lower temperature and in a much shorter time. These factors reduce the fuel requirement for the catalytic system to approximately half of that required for thermal incineration, and so results in a considerable reduction in operating costs.

A catalytic combusion unit designed and produced by the Catalyst Systems and Equip- ment Division of Matthey Bishop Inc., has recently been installed at Medallion Graphics, Inc., of Los Angeles to control the pollutants from the drying oven of their latest big press. T o comply with the stringent requirements of the local air pollution regulations-Los Angeles Air Pollution Control District Rule 66-it is specified that go per cent of the hydrocarbon vapour entrained in the exhaust of the drying oven must be removed before discharge to the atmosphere takes place, and the new catalytic unit exceeds this requirement by a considerable amount.

The components of the new system, all contained within a refractory-lined combustion chamber, are shown in the figure.

The system’s gas burner is, of course, capable of operating from a cold start up although during normal operation the burner only runs intermittently when it is required to preheat the process exhaust gas and maintain the temperature of approximately 450°C necessary for the required degree of catalytic oxidation. A thermocouple, placed upstream

and adjacent to the catalyst, senses temperature change and actuates a temperature controller which precisely regulates the input of fuel to the burner. The required amount of air is mixed with the fuel in the burner nozzel and the whole arrangement is designed to eliminate the possibility of flash-back.

Once the process gas has been heated to the required temperature it passes through a series of stainless steel baffles arranged to ensure an even flow of gas and even temperature distribution across the catalyst surface.

The Matthey Bishop THT-I catalyst consists of a pure platinum group metal deposited on a monolithic, honeycomb ceramic substrate which has a high surface to volume ratio and causes very little drop in pressure as the gas stream passes through the catalyst bed. The catalyst, surrounded by a dense refractory blanket, to eliminate bypass and provide for thermal expansion, is mounted in a stainless steel basket, readily removable for cleaning or replacement of the catalyst.

The catalyst is heterogeneous in nature, the reaction being completed in the surface pores or active catalytic sites of the catalyst surface. The basic reaction includes diffusion of organics from the untreated gas on to the catalyst surface, adsorption on to the surface, reaction, desorption of the newly-formed materials, and diffusion back into the body of

the gas. At this stage, instead of hydrocarbon pollutants, the gas contains harmless carbon dioxide and water vapour which passes to the atmosphere through a stainless steel stack.

The catalytic oxidation unit, which is fully automatic in operation, is capable of pro- cessing exhaust gas at the rate of2500 SCFM. Its control system includes a fully-proportional temperature indicator and controller, flame failure protection, thermocouple- actuated, high-temperature safety shut-off, IR scanner, purge timer, and other sequencing and protective equipment.

Recent source sampling in compliance with the Los Angeles Total Combustion Analysis method indicates that the conversion efficiency of the new catalytic oxidation unit is better than 95.0 per cent, considerably higher than required by the regulatory body and the new unit is probably the first true catalytic in- cinerator to receive Los Angeles APCD approval. In addition the fuel savings are substantial when the process is compared to more conventional types of fume incineration.

Although the initial Matthey Bishop, Inc., catalytic oxidation units were developed for large-scale printing and metal decorating operations, they have strong potential for pollution control in many other applications.


Heterogenised Homogeneous Catalysts RHODIUM CATALYSTS FOR METHANOL CARBONYLATION

By Michael S. Scnrrell Instituttet for Kemiindustri, Technical University of Denmark, Lyngby, Denmark

Heterogeneous versions of homogeneous catalysts can often he produced and may 1 w e certain advantages in use particularly on a commercial scale. The catalytic chemistr-y of supported rhodium compounds for the carhonylation of methanol is described and the behaviour of heterogeneous and homogeneous operation compared in order to illustrate the relations between the two catulyst types. Particular attention is given to the factors which injuence the activity and the selectivity of the heterogenised f o r m .

Recently a tremendous interest has arisen concerning the behaviour of “heterogenised” forms of catalysts, such as transition metal complexes, which were previously used in homogeneous media (I). The growth of activity in this area reflects the importance which is being attached to the considerable potential offered by the new generation of catalysts. Homogeneous catalysts frequently exhibit very high activity and selectivity but their use on a large scale is often complicated by difficulties associated with their separation from the reaction products and also with problems of corrosion.

These drawbacks can in principle be overcome by binding the catalyst to a solid material, thus using the active compound in a heterogenised form. Suitable support materials which have been used include in- soluble polymers (2, 3,4) and silica (5).

The extent to which the catalytic behaviour of such heterogeneous systems parallels that displayed by the unsupported complex and the possible effects on reaction of the support itself are two obviously important factors which must be considered in the first instance. In addition, we must consider the stability of the bound catalysts and examine their operation with both liquid and vapour

phase reactants. Our knowledge concerning these points is still fragmented, but sufficient work has now been reported to indicate that supported versions can exhibit activities and selectivities comparable with those of their homogeneous counterparts. An excellent illustration is provided by the use of rhodium catalysts in the carbonylation of methanol to acetic acid.

Carbonylation with Homogeneous Catalysts

It is helpful to consider first the behaviour of rhodium catalysts in homogeneous media. The components of the active material com- prise a rhodium compound and a halogen promoter, which is preferably iodine (6, 7). The latter may be supplied as methyl iodide, hydrogen iodide, calcium iodide or iodine itself. Reaction with methanol is normally carried out (6, 7, 8) at 150 to 225OC and at a total pressure of I to IOO atmospheres. Selectivity for the production of acetic acid is typically about 99 per cent.

Traces of dimethyl ether and possibly acetaldehyde are produced, and this is particularly evident if the reaction is conducted using methanol itself as solvent. Acetic acid may not be recovered in all cases


because of esterification to methyl acetate. RhCI,, Rh,O,, RhCI(CO)(PPh,), (Ph= The rate of carbonylation is found (7, 8) phenyl) and Rh(CO),CI,. Suitable solvents

to be directly proportional to the concentra- are low molecular weight hydrocarbons such tions of rhodium and iodine, but is inde- as benzene, or one of the reactants, methanol, pendent of methanol concentration and acetic acid, methyl acetate or water. carbon monoxide pressure. The suggested The catalysts have provided the basis for reaction sequence is depicted below:

CH,OH+HISCH,I +HaO

RhL, + CH,I+CH,Rh(I)L,

CH,Rh(I)L,+ COSCH,Rh(CO)(I)L,

CH,Rh(CO)(I)L,~CH,CO-Rh(I)L, CH:3CO-Rh(I)Lm +H20,C

RhL,+CH,COOH +HI

the development of new technologies for methanol carbonylation (7) and also for the related alkene hydroformylation process (9).

Successful though the homogeneous catalysts have proved, it is clear that heterogeneous analogues, if sufficiently active and selective, could offer considerable advantages in solving both separation and corrosion problems (10).

(i)

(iii)

(iv)

(v!

Step (ii), the oxidative addition of methyl iodide to the rhodium complex is rate determining (7,8), with the remaining steps taking place much more rapidly. Although the initial complex is denoted RhL,, ligands of different types may be present. Roth et a1 (7) have demonstrated that rates of reaction and product distributions are very similar for a variety of rhodium compounds, including


Heterogenised Catalysts Several examples of methanol carbonyla-

tion by solid catalysts comprising in each case one of a range of rhodium compounds bound to a support material have been reported recently. The carriers have included carbon, alumina, poly(styrene-divinylbenzene) and a type X molecular sieve zeolite.

The polymer supported catalyst (11) was prepared by linking chlorocarbonylbis- (triphenylphosphine)rhodium, IuICl(C0)- (PPhJ, to membranes or beads of poly- (styrene-divinylbenzene). The synthesis method (3) is summarised in the Figure. Carbonylation was carried out using vapour phase reactants with the membrane or by suspending the beads in a liquid reactant mixture. Catalytic activity was associated with the presence of a Rh(1) complex. A steady conversion of rhodium from Rh(I) to Rh(II1) during the reaction resulted in a fall in activity of the membrane catalyst. The activity of the catalyst in liquid medium also declined with time but in this case loss of rhodium from the support appeared to be responsible. A reduction in this loss might, it was suggested, be obtained by using a different polymer as support, or by increasing the number of coordinating groups linking the complex and support. Some dimethyl ether was produced in side reactions with these catalysts.

The mechanism suggested by Roth et a1 (7) for homogeneous catalysis and supported by kinetic investigations (8) also affords an explanation of the kinetics observed for the heterogenised catalysts in both liquid and vapour phase operation. The presence of an iodine based promoter is again found to be essential. One difference concerns the evidence that two adjacent rhodium centres are involved in the oxidative addition of methyl iodide for the heterogeneous catalyst rather than one as shown in the reaction sequence for homogeneous reaction.

Carbon has also been found to provide a useful support (12, 13, 14). Here too a close similarity in behaviour of heterogeneous and homogeneous catalysts is observed (14). Rhodium trichloride may be used as a starting material (14) but rhodium nitrate is preferred (12, 13). The nitrate based catalysts are more active than those prepared from such complexes as Rh(acac),, RhCI(CO)(PPh,), and RhCI(PPh3),, where acac is acetylacetonate, by factors of up to 10

for operation at 2ooOC (13). An active material is produced by impregnation of the carbon with a solution of rhodium nitrate followed by decomposition of the latter at temperatures of 300°C and above. An increase in activity is seen on using temperatures in excess of 300°C and this appears to be associated with conversion of the nitrate to oxide. Decomposition in hydrogen rather than nitrogen resulted in a lower rate of reaction and from this evidence it might be inferred that rhodium in the reduced state or as free metal is not required. The situation remains uncertain however, since hydrogen treatment has a favourable effect on the activity of catalysts obtained from rhodium trichloride. Selectivities for carbon supported catalysts of up to 99 per cent have been reported (12).

A number of organometallic complexes of rhodium have been examined for carbonylation activity when supported on y-alumina (IS). The carrier was pre-dried at 650°C and the complexes incorporated by impregnation of the oxide with a benzene solution of the required compound. The resulting solids were active for conversion of methanol (120 to zoo°C, vapour phase reactants, total pressure I atmosphere), but selectivity for acetate formation was in nearly every case rather low (less than 50 per cent) because of ether production, This was true of catalysts based on, for example, RhCI(PPh,),, (codRhCI), and (codRhOCH,), (cod= cycloocta-1,5-diene). On the other hand those derived from RhCI(CO)(PPh,), had about the same overall activity but were much more selective (approaching gg per cent).

As with the work using carbon the exact state of the rhodium complex in an active catalyst remains obscure. Because different starting materials resulted in catalysts having different selectivities there is some reason to suppose that the molecular identity of the complex is retained, at least to some extent.

The rather large amounts of ether produced by most of these catalysts may very well be due to the use of alumina as the support,


I I Comparison of Catalyst Activities for Methanol Carbonylation

Rates of reaction at 250"C, with po=1 atmosphere and molar ratio methano1:rnethyl iodide=lO. All reactants in the vapour phase for heterogenised catalysts.

RhCI(CO)(PPh,),-alumina

R h (N 0,),-carbon

R hCI,-N aX

R h CI ,-NaX

R hCI(CO)(P,),*

RhCI,

Rhodium content of catalyst, in weight

per cent

1.39

3

0.25

1.0

3.6

homogeneous catalysis

*Pp=p-(polystyryl)diphenylphosphine ligand **Molar ratio methano1:methyl iodide typically>l5

particularly since the oxide was dried at high temperature. Such treatment results in high activity for the dehydration of methanol to dimethyl ether (16). The reason for the low activity of the catalyst based on RhCl(C0)- (PPh,), for ether formation is not clear.

The use of a molecular sieve zeolite as a support is of particular interest because of the influence which these materials have had in the design of conventional heterogeneous catalysts.

An active carbonylation catalyst has recently been prepared by the impregnation of a sodium-X zeolite with rhodium trichloride solution (17). As with all the other catalysts the presence of iodine is necessary. Selec- tivity for acetate production approached go per cent, the main side product being dimethyl ether. On decreasing the rhodium content of the catalyst from I weight per cent to 0.05 weight per cent there resulted a steady increase in the rate of reaction per unit weight of rhodium, by a factor of about 20

at 25ooC, but selectivity for acetate formation declined a little. This contrasts with the situation found for rhodium nitrate on carbon where maximum effective use of the rhodium was obtained at a rhodium level of about z weight per cent (13). Catalysts hav-

Rate, expressed as g methyl acetate/g Rh/h

40

25

50

10

%**

3 x103

ing lower or higher rhodium contents than this displayed a smaller rate per unit weight of metal.

Like alumina, zeolites are expected to exhibit a tendency to produce dimethyl ether from the elimination reactions of methanol or methyl iodide (IS), but unlike those based on the former oxide, the zeolite carbonylation catalysts had reasonably high selectivities. Again, the reason may lie in the treatment of the support before use. The zeolite was apparently not subjected to high temperature drying and, in any event, impregnation with the rhodium salt took place in aqueous solution.

These observations naturally lead one to suspect that support pretreatment procedure may have a very great influence on the catalytic behaviour of the heterogenised systems, particularly when the carriers are potentially active materials such as alumina, zeolites and silica.

Relative Activities of Heterogenised Catalysts

A comparison of the activities of various heterogenised catalysts for methanol carbonylation, given in the Table, reveals that the rate per unit weight of rhodium is not


Reference

15

12

17

17

11

8

Catalyst

markedly dependent upon the choice of support or rhodium compound used. Similar conclusions have been drawn before (11, 13). M e have however seen that the selectivity for acetate production is greatly influenced by the nature of the starting materials. Further- more, there appear to be differences in the stability of the supported catalysts. Although studies of the deactivation characteristics of these materials have not been extensive, the loss of activity with use seems to be especially noticeable with the polymer based systems. However, the use of these materials as catalyst supports is still a very recent development and significant improvements may well result from further work.

Insufficient data are available at present to enable the calculation of activities on a rate per unit active site basis (turnover number). This is due to the difficulty, typically associated with heterogeneous catalysts, of know- ing just how many active centres are present in a given quantity of material under working conditions. However, if the heterogeneous forms are compared with the homogeneous catalyst (8) it can be seen in the Table that in order for the turnover numbers for the two catalyst types to be equal, it would be necessary to assume that only about I per cent of the total number of rhodium atoms in the heterogenised material is active. Such a figure does not appear unreasonable.

Until active site concentrations are established for these supported catalysts a more rigorous comparison of activities is not possible. Nevertheless the outstanding similarity between homogeneous and hetero-

References I J. C. Bailar, Jr., Card. Rev.-Sci. Engng., 1974,

2 Z . M. Michalska and D. E. Webster, Platinzim Metals Rev., 1974, 18, (2), 65

3 W. 0. Haag and D. D. Whitehurst, Proc. 5th Int. Congress on Catalysis, Miami Beach 1972, publ. by North Holland Publ. Co., Amsterdam, 1973, I, 465

4 C. U. Pittman, Jr., L. R. Smith and S. E. Jacobson, “Catalysis, Heterogeneous and Homogeneous”, Elsevier, Amsterdam, 1975, P* 393

5 R. D. Hancock, I. V. Howell, R. C. Pitkethly and P. J. Robinson, “Catalysis, Heterogeneous and Homogeneous”, Elsevier, Amsterdam, 19759 P. 361

6 F. E. Paulik and J. F. Roth, Chem. Commun., 1968, (24, 1578

7 J. F. Roth, J. H. Craddock, A. Hershman and F. E. Paulik, Chem. TechnoZ., Oct. 1971, 600

8 J. Hjortkjaer and V. W. Jensen, Id. Engng. Chem., Prod. Res. Dev., 1976,15, (I), 46

9 F. J. Smith, Platinum Metals Rev., 1975, 19,

10 R. G. Schultz, German Offen. I, 939,286; 1970 11 M. S. Jarrell and B. C. Gatcs, J . Catalysis,

12 R. G. Schultz and P. D. Montgomery, J . Catalysis, 1969, 13, (I), 105

13 R. G. Schultz and P. D. Montgomery, Am. Chem. SOC., Div. Petrol. Chem., Preprints, 1972917, BI3

14 K. K. Robinson, A. Hershman, J. H. Craddock and J. F. Roth,J. Catalysis, I972,27, (3), 389

15 A. Krzywicki and G. Pannetier, Bull. Sot. Chim. Fr., 1975, (5-6), 1093

16 H. Knozinger, Adv. Catalysis, 1976,25, 184 17 B. K. Nefedov, N. S. Sergeeva, T. V. Zueva,

E. M. Shutkina and Ya.T. Eidus, Izv. Akad. Nauk S.S.S.R., Ser. Khim., 1976,(3), 582

18 H. Noller and W. Kladnig, Catal. Rev.-Sci. Engng., 1 9 7 6 , ~ ~ 149

19 G. C. Bond, Platinum Metals Rev., 1975,

1% 17

(3), 93

1975% 40, (21,255

19, (41, 126

geneous analogues for methanol carbonylation The paper “Forming Fibres from Basalt Rock”,

issue of this Journal reviewed results of the is very encouraging for we are now one step project on basalt fibres conducted at the Materials

Science and Engineering Department of Washing- nearer in achieving the often mentioned goal ton State University under a grant from the of basing future catalyst design on molecular Pacific Northwest Regional Commission with

which the author was associated. Detailed results

many examples of homogeneous catalysis by mission “Use of Basalt Rock for the Production of Mineral Fiber, Contract No. NR-3001 (1975)”~ complexes Of the by R. V. Subramanian, H. F. Austin, R. A. V. Raff,

likelv that a considerable number of hetero- G. L. Sheldon, R. T. Dailey and D. Wullenwaber.

has been demonstrated. This State of affairs which appeared in the January ‘977, *I> (‘1,

or enzymic (‘9). In view Of the are contained in the final report to the Corn-

it is

Omission of specific -acknowledgements in the paper to these sources of data and finance genised systems be based On the Same

materials. support is regretted.


Acknowledgements

Jean Baptiste Boussingault and Platinum By F. W. J. McCosh Faculty of Education, University of Rhodesia, Salisbury

Although initially trained in mining and metallurgy, at the Ecole des Mines de Saint- Etienne, Jean Baptiste was later to pioneer and devote much of his life to agricultural chemistry. Yet his interest in metallurgy never ceased as when, for personal and family reasons, he left his experimental farm in Alsace in 1867 to initiate a series of investigations on iron and steel at his son-in-law’s factory, that of Jacob Holtzer et Cie at Unieux, near Saint-Etienne. If iron and steel were topics subsidiary to his agricultural pursuits the metal platinum was an obsession, and this is not altogether surprising because the first of his many published papers concerned a

Jean Baptiste Boussingault 1802-1887

Following the formation of the Republic of Colombia f r o m the former Spanish colony of New Granada, a small team of scientists were recruited to investigate the economic potential of the country. Boussingault, a Frenchman who had trained in mining and metallurgy and was later to become a pioneer in agricultural chemistry, was one of this group and was responsible f o r locating the reef which was the source of the alluvial plat inum deposits in the Choco district

silicide of platinum which he had prepared in 1820 (I). Having found significant percentages of silicon in the steels manufactured at a neighbouring foundry, he suggested a theory, since found untenable, that the properties of steel were due, not to the presence of carbon as was generally believed, but to the silicon content.

The Silicide of Platinum Ancillary to the main research on steel was

an attempt to produce a platinum-carbon alloy, or a platinum carbide, analogous to steel, by heating thin leaves of platinum with wood charcoal in a clay crucible. The


occasion was almost catastrophic, as can be gathered from a letter to his father in Paris:

Since my last letter I have seen my cousin, Fouchk-Skguimard, I have set fire to the school and I have melted a metal (platinum) which was believed to be infusible.

.My cousin came to see me the very day my furnace was lit; he spent several moments with me in the laboratory with a local gunsmith and M. Beaunier who had come to see me at work. The heat of the furnace was extraordinary and, according to M. Beaunier, was greater than that found in his steelworks, After three hours firing I drew the fires of the furnace, closed all the dampers of the flue and left. The next day, impatient to know the result of my experiments, I was in the laboratory at five o’clock. I met a teacher who said he had smelt an odour of burning throughout the night. We entered the lecture room and hardly had wc opened the door when flames were seen in the midst of the smoke which filled the room. I at once called the caretaker, gathered together the student miners and in two hours we had mastered the fire, and the insurance company paid for the damage.

The cause of the fire was that the flue had not been constructed for a fusion furnace, and a beam which supported the floor of the first floor, being too near this weak flue, caught fire in the night. Fortunately the door of the lecture room was closed, and more fortunately I had taken the trouble to close the furnace before leaving, otherwise it is certain that the mining school would no longer exist.

As soon as the fire was extinguished I went to look for my crucibles, and had the satisfaction of seeing that my platinum had melted; in another crucible I found that the platinum had combined with carbon and formed a casting similar to an iron casting. Since then, in support of these results I have cemented two pieces of platinum as one cements iron, and thus succeeded in making platinum steel (2). His enthusiasm, however, had bounded

ahead of the facts. First, platinum had been melted as far back as 1758 by Macquer and Baum-5; also, he was to find subsequently that he had prepared, not a platinum-carbon alloy, but a silicide of platinum which was more fusible than the metal. Erroneously he ascribed the formation of a silicide to the presence of silica ash in the wood charcoal.

The Origin of the Silicon After fifty-six years Boussingault returned

to this investigation and we can only surmise that interest in platinum had been rekindled


by the work of the Commission Internationale du Mkre established by the French government in 1869 (3). After a delay, due to the Franco-Prussian War of 1870-71, the first metric bars of iridium-platinum were produced in 1874 under the direction of Henri Tresca, professor of mechanics at the Conservatoire des A r t s et Metiers where Boussingault occupied a chair of agriculture. Whatever the reason for this renewed interest, Boussingault found, by repeating his 1820 experiments in both clay and platinum crucibles, that the silicon in his platinum silicide came not from the siliceous ash in the charcoal but from the silica in the walls of the crucible; but without the intervention of carbon no combination would take place between platinum and silicon (4).

The Platiniferous Region of the Choco

On leaving the Ecole des Mines de Saint- Etienne in 1820, Boussingault managed a lignite mine in Alsace but soon joined a small group of scientists recruited by Alexander von Humboldt in 1822 at the behest of Simon Bolivar who required them to investigate the mineral and agricultural potential of newly liberated Colombia. Boussingault was origin- ally appointed as a professor at the Escuela Nacional de Mineros en Bogota, but like the others in his team he was given assignments which took him to various parts of the country as mine inspector, prospector, assayer and surveyor. Colombia was his home from 1822 to 1832, when he returned to France. In a letter to his mother in 1823 Boussingault

expressed the hope that he would be sent to the platiniferous region of the Choco which is the north-western portion of Colombia with a seaboard on the Pacific Ocean. The presence of platinum in this region was first reported by two Spanish naval officers, Jorge Juan and Antonio de Ulloa who travelled to South America in 1736, although rumours of a mysterious metal, hard and infusible, were known in the sixteenth century and said to be found in Mexican gold mines. Juan and

The .finding of the reef

Alloa accompanied the French scientists Charles Marie Condamine and Pierre Bouger who were sent to Peru to measure a degree of the meridian. South America was then closed to foreign visitors by the Spanish government, and the prcsence of the two Spaniards was to demonstrate that the King of Spain approved of the expedition. Juan and Ulloa provided the first description in Europe of alluvial gold-mining in the Choco, and indeed this was the first literature on platinum which found its way to Europe. They described the difficulties of separating gold from the adhering platinum for which there was little use except as small shot, or for small bags which when filled were used as clock weights, or even for making garden paths. Otherwise it was thrown away and mines whose ores contained excessive amounts of platinum were often compelled to close down (5).

The platiniferous area of the Choco is situated in the river basins of the rio Atrato and the rio San Juan, the Atrato flowing north to the Caribbean Sea and the San Juan flowing south to the Pacific Ocean. Their sources were so close that Boussingault mentions the work of a priest at Novita who, in 1788, encouraged Indians to dig a canal connecting the two rivers and thus providing a link for small craft between the Pacific and Atlantic Oceans. The Choco in Boussingault’s day was a malarial area of almost continuous rainfall, plagued by mosquitoes and known for its impenetrable forests where communication was only

possible by river. The alluvial deposits, owned by Spaniards, were worked by negro slaves whose rations consisted of salted meat, dried bananas and maize biscuits brought from the fertile Cauca valley on the backs of porters, for attempts at crop cultivation and ranching had failed. When Boussingault visited the Choco in 1829 the negro slave population had decreased considerably as a result of an 1816 Act of the Colombian Congress which granted them their freedom, thus anticipating the act of 1833 which abolished slavery in the British Empire.

Boussingault’s Journey in the Choco

Boussingault left Anserma, in the department of Caldas, in February 1829 accompanied by the botanist Goudot and several bearers. The Spaniards appear to have maintained some degree of social life for at the first town, Tamana, they attended a ball at which an uninvited guest was a jaguar. To Novita they travelled down the rio Tamana in hollowed- out tree trunks and from there they journeyed to Tado, the centre of the platiniferous region. There, the priest informed the incredulous Boussingault that platinum could be found locally, mixed with an insignificant amount of gold. He was taken to the priest’s garden where a negress was washing the garden soil in a batea, a wooden dish used for panning, during which the heavier gold and platinum particles sink to the bottom of the batea. The negress was obtaining platinum with only a


The Jinding of the reef which was the source of the C h c o alluvial platinum was Jirst recorded by Boussingault in 1826 (7)

few grains of gold, for the garden had been a which had been entrusted to me; that the

precious gold. Further from the rivers, of a century; concluding where I should have started, by saying that since platinum was infusible by the usual technical processes it would not be possible to cast a statue in this

platinum- and gold-bearing ores were crushed and washed with water, after which the powdered ore underwent sedimentation i n trenches which effected a rough separation of the precious metals, the final separation being accomplished in a batea. Deplatinisa- tion of the gold was then carried out a t Novita by use of mercury which forms a n amalgam with gold but not with platinum, and finally the deplatinised gold was sent to the Mint a t Bogoti (6).

The origin of the alluvial platinum of the Choco had been a subject of speculation since 1785 when it was observed that whereas only fine particles of platinum were to be found i n the plains, larger particles were found nearer the mountains. With a hint from Humboldt, who knew the country as a result of his explorations of 1799-1804, Boussingault discovered the source of the alluvial platinum i n a reef which he studied at Santa Rosa i n the Cauca valley of Antioquia in 1825 where, in the Cordilleras, he found grains of gold and platinum i n the rock syenite (7).

The Bolivar Statue; A Lesson in Diplomacy

T h e discovery of the platinum reef coincided with the zenith of Bolivar’s career in 1825 and this may have been the reason for the Colombian Congress voting for a n equestrian statue of Bolivar i n platinum, but let Boussingault tell the story.

I was at Bogota busy with the map of Colombia when Congress decided to erect in the Plaza Mayor of the capital an equestrian statue of General Bolivar in platinum as a lasting national tribute to the man to whom they owed their liberty. Several days afterwards I received from the Ministers of War and Finance an official letter appointing me to superintend the casting and the erection of an equestrian statue in platinum of the Liberator. The letter was received through the official channels, i.e., through Colonel Lanz. I had to reply to the Minister of Finance. I replied politely that I could not undertake the work

metal. Lanz said to me that all this was correct but

in view of my position my letter lacked common sense because it proved that Congress and the Ministers were ignorant which was inexcusable even if I was right. Write this, he added, I shall dictate the reply which you should make.

I thanked the Minister for wishing to entrust me with so important a work, adding that I would spare no effort to assure its success. Before signing I again told Colonel Lanz that success was impossible since the fusion of platinum was impracticable. It doesn’t matter, he replied, you have promised to make every effort. Besides, you know that you will never have enough metal. It will be forgotten and you have offended nobody. It happened as Lanz had said; the Minister was delighted and thanked me for the enthusiasm which I had shown, then it was forgotten, Altogether I received two kilograms of platinum which was used tc construct several pieces of apparatus in the laboratory (8).

I f Boussingault’s adventures engender a nostalgia for the world as it was, no doubt today’s pioneers are equally resourceful in their search for uranium ores, and those of tomorrow may even revel i n the location of platinum on another planet.

References I J. B. Boussingault, “Note sur la combinaison du silicium avec le platine, et sur sa presence dans I’acier’’, Ann. Cham. Phys., 1821, 16, 5-15

2 ‘‘Memoires de J. B. Boussingault”, ( 5 vols), publ. Chamerot et Renouard, Paris, 1892- 1903, VOl. I, 224-226

3 B. Swindells, “Centenary of the Convention of the Metre”, Platinum iWetals Rev., 1975, 19, ( 3 ) Y 110-113

4 J. B. Boussingault, “Sur la siliciuration du platine et de quelques autres mttaux”, Compt. Rend., 1876, 82, 591-596

j (a) D. MacDonald, “A History of Platinum”, Johnson Matthey, London, 1960,14-19 (b) Op. c i t . (Ref. 2), Vol. 5, 7

6 (a) J. B. Boussingault, “Sur un gisement du platine signal6 dans un filon de la province d‘Antioquia”, Compt. Rend., 18 56, 42, 917-922 (b) Op. cir. (Ref. 2), Vol. 4, 218-261, passim

7 J. B. Boussingault, “Sur le gisement du platine”, Ann. Chim. Phys., 1826,32, 204-212

8 Op. cit. (Ref, 2), Vol. 2, 54-56.


washing place where platinum had been removed from what was then the more

necessary quantity of platinum was so great (I stated the weight) that ail the mines in Columbia could not uroduce it in the course

ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES The Kinetics of Platinum Dissolving in Molten Copper. (The Rotary Disc Method) T. E. ,mummy E. L. LUBININ, A. I. TIMOPEEV and A. L. SHUNIN, Izv. Vysshikh Ucheb. Zaved., Tsvet- naya Metallurgiya, 1977, (I), 151-153 The dissolution of Pt in molten Cu was studied using the rotary disc method at II~0-1300°c. The results show that the rate of Pt dissolution is 0.0054.13 g/cm2ss. The dissolution of Pt in Cu was found to take place by diffusion. The diffusion coescients are derived.

The Influence of Static Stresses on Ordering of the CuPt Type Alloys A. K. RANYUKA, Fiz. M e t d Metdloved., 1977, 43, (3), 493-497 The influence of uniform static stresses, caused by external loading, on the temperature of the order-disorder phase transition in an alloy of the CuPt type is discussed.

Ageing Characteristics of Aluminium Wire Bonds on Thick Film Platinum-Silver Metalliiation s. KHADPE, I9~sulationlCircuits, 1977, 23, (2), 23-24 The ageing characteristics of A1 wire bonds on Pt-Ag metallisation was determined using a bond strength vs. ageing time at 1 5 0 T plot. The results show that the bond strength does not decrease significantly with ageing at 150°C. After roooh of ageing more than 80% of the initial bond strength was retained. The Pt-Ag conductor materials can be used as substitutes for Au and Pd-Ag materials.

An Investigation of High Temperature Thermodynamic Properties in the Pt-Zr and Pt-Hf Systems P. J. MESCHTER and w. L. WORRELL, Met. Trans.,

The thermodynamic properties of 2-25 at. 7 ; Zr-Pt and 33-25 at. % Hf-Pt alloys were studied at 11oo-14ooK using a galvanic cell technique with a Tho,-based electrolyte. The results show that the activities of Zr and Hf exhibit large negative deviations from Raoult's Law. The standard free energies of formation, Gf", for the intermetallic compounds ZrPt,, ZrPt, and HfPt, at 1300K were found -92.680, -91.740 and -97.350 cal/mole, respectively. Possible applications in fuel cells and thermocouple systems are discussed.

1977, 8 4 (3), 503-509

The Superconducting Properties of PdH, I

D. S. McLACHLAN and T. B. DOYLE,J. Low Temp. PAYS., 1977, 26, (3141, 589-601 The superconducting parameters of PdH, (x = H jPd =0.9801-0.9957) foils were determined using measurements of the magnetisation curves and resistive transitions in magnetic fields at 2-10.4K. The results show that PdH is a type I superconductor with a Tc of 10.2-10.4K, HC(o)c9ooG and X-0.6 at absolute zero. PdH, becomes a type I1 superconductor for x<o.ggg, due to the increasing resistivity of the material.

The 50K Transition in Palladium Hydrogen Alloys: 11. Specific Heat and Thermal Relaxation J. K . JACOBS and P. D. MANCHESTER,J. Phys. F: Metal Phys., 1977, 7, (I), 23-33 Studies of the specific heat anomaly at 5oK in Pd-H p-phase samples show that the magnitude of the anomaly depends on the rate of temperature change used in the specific heat measurements-the slower the rate, the larger the anomaly. The data of the spontaneous heat released by the Pd-H sample after sudden cooling to temperatures in the ~ o K region showed a thermal relaxation in Pd-H with fast and slow relaxation times and a common activation energy of (1.98fo.03) x ro3Jg/atom of H.

Influence of Deformation on the Low- temperature Specific Heat of a Dilute a-Phase PI-H Alloy

VANDERVOORT, J . Phys. F: Metal Phys., 1977, 7 ,

Low temperature specific heats were measured at 1.5-4.2K in cc-phase Pd-H sample of H/Pd ratio 0.005 in two different conditions: after deformation at room temperature, and after deformation at liquid N temperature and a short ageing at room temperature. The value of the electronic specific heat coefficient in the latter case was found to be close to that of pure Pd, suggesting the formation of p hydride.

Solution of Hydrogen in Palladium/Copper Alloys D. FISHER, D. M. CHISDES and T. B. PLANAGAN, J . Solid State Chem., 1977, 20, (2), 149-158 Studies of the solution of H, in Pd-Cu f.c.c. substitutional alloys at low H, content show that the relative partial molar enthalpies of absorption at infinite dilution are less exothermic for the alloys than for Pd. I t was found that interstitial

U. MIZUTANI, T. B. MASSALSKI, J. BEVK and R. R.

( 3 1 3 L63-L68


H, increases the relative electrical resistance to a lesser extent with increase of Xcu, but the absolute increase of resistance is nearly invariant with XcU.

Direct Observation of Pd/MgO and Pd/SiO, Reactions in the Transmission Electron Microscope A. F. MOODIE and c . E. WARBLE, Phil. Mag., 1977, 35, ( I ) , 201-211

Studies of the surface reaction between Pd and MgO and Pd and quartz at temperatures below the melting point of the metal were carried out using a transmission electron microscope. It is shown that for Pd/MgO the reacting phase has liquid-like characteristics, while the ceramic remains strain-free both during and after the reaction. In the case of Pd/SiO,, the reaction is similar with the exception that small amorphous regions develop randomly over the surface which later move, disperse and sometimes coalesce into droplets. A bond between the metal and the ceramic was found to exist.

Nickel-Palladium-Germanium Alloys w. WOPERSNOW and K. SCHUBERT, J . Less-Common Metals, 1977, 52, (I), 1-12

Crystal structure studies of the Ni-Pd-Ge alloys show that Ni may be substituted for Pd up to the composition Ni2,Pd4eGes3 in the Pd,Ge phase. A phase with the composition NiPdGe having the PbFCl type of structure is formed below 600°C. A phase of composition Ni,Pd,Ge, having an Fe,P type of structure forms below ~00°C.

The Niobium-Gallium-Iridium System. I. Phase Equilibria at 1000°C and Supercon- ductivity in the Niobium-rich Part of the System M . DRYS, J. Less-Common Metals, 1977, 52, (I), 81-85 X-ray diffraction and electron microprobe techniques were used to study the phase equilibria at IOOO"C in the Nb-rich section of the Nb-Ga-Ir system. The results show that complete solid solubility exists between Nb,Ir and Nb,Ga while the o-phase and Nb,Ga, form limited solid solutions. The superconducting transition temperatures were also determined.

Some Properties of Alloys of the Ti-Ru System N. G . BORISKINA and I. I. KORNILOV, 12-0. Akad. Nauk S.S.S.R., Metally, 1977, (I), 193-197 Studies of the changes of hardness, specific resistance and thermoelectromotive force of Ru-Ti alloys in the as cast state and also after quenching from 1100 and 860°C and annealing at 600 and 400°C were carried out. The results show that the changes take place as a result of phase composition changes of the alloys. The alloys with the 8-phase structure, having high e.m.f. values can be practically used for instrument making.

X-ray and Microspectroscopic Studies of the RuO,-TiO,-Cl System

Zh. Neorg. Khim., 1977, 22, (I), 201-205 X-ray and microspectroscopic studies of the quasi-binary RuO,-TiO,-Cl system were made using Ru-Ti oxide layers containing 25, 50 and 75 "t: o/n RuOa deposited from Ru and T i chloride solutions on quartz or Ti substrates. The results showed the formation of solid solution with the rutile type structure. When the C1 concentration was -0.1 at.%, the solid solution decomposed into two rutile phases at > 8oo"C : RuO , and TiO, phases accompanied by the increase in the crys- tallisation of these phases.

YU. E. ROGINSKAYA, V. I. BYSTROV and D. M. SHUB,

CHEMICAL COMPOUNDS The Enneacarbonyls of Ruthenium and Osmium J. R. MOSS and W. A. G. GRAHAM, J. Chem. Soc., Dalton TTans., 1977, (I), 95-99 Studies of the U.V. irradiation of n-heptane solutions of the pentacarbonyls of Ku and 0 s at -40°C were carried out. It is shown that in the case of [Os(CO),] the newly isolated carbonyl compound [Os,(CO),], decomposes slowly in solution. The new compound [Ru,(CO),] which is a product of the low temperature irradiation of [Ru(CO),] is extremely unstable in both the solid state and in solution at room temperature.

Preparation and Characterisation of Members of a Homologous Series of Dihydrido- carbonyl Compounds of Osmium J. R. MOSS and W. A. G. GRAHAM, Inorg. Chem.,

The preparation of carbonyl hydrides H,[Os (C0),ln (n=I, 2 or 3) by the high pressure carbonylation of 0 s tetroxide in the presence of H, is described. A compound H,Os,(CO),, is also formed in this reaction. The preparation of dihydrides, H,Os,(CO), and H,Os,(CO),,, is also described and their structures are discussed.

'977, I 6 Y ('1, 75-79

ELECTROCHEMISTRY The Oxidation of Carbon Monoxide at Platinum and Gold Metallised Membrane Electrodes

Electrochim. Acta, 1977, 22, (s), 525-530 Studies of the oxidation of CO at Pt and Au membrane electrodes show similar electrochemical characteristics to those of massive electrodes. The short time response at Pt is determined by the oxidation of a surface mono- layer of CO by a reactant pair mechanism occur- ring at the edges of growing islands of an oxidised P t species. The construction of an analytical device is discussed.

T. K. GIBBS, C. MCCALLUM and D. PLETCHER,


Activated Metal Anodes in Electrochemical Procesl3es J.-w. KUHN VON BURGSDORFF, Chem. Ing. Tech., 1977, 49, (413 294-298 Various activated metal anodes used in electrochemical processes are reviewed. The three stages of this development include the Ta-Pt anode for persulphate production, the platinised Ti anode and the “dimensionally stable anode” (DSA) consisting of a valve metal and a semi- conduction mixed oxide coating. The advantages of the DSA are shown in their application to the caustic chlorine electrolysis.

Preparation of Ruthenium Dioxide Elec- trodes and Their Anodic Polarisation Characteristics in Acidic Solutions C. IWAKW, K. HIMO and H. TAhlURA, Electrochim.

Studies of the anodic polarisation behaviour of anhydrous RuOe eIectrodes prepared by heating hydrous RuO, at different temperatures in acidic solutions showed that excellent anode material was obtained by heating hydrous RuOa in air at “450°C. This electrode was quite stable and had strong resistance against the anodic dissolution together with very low overvoltage for the 0, evolution. Generally, the electrode composed of poorly crystalline RuOl showed the good anodic polarisation characteristics.

The Reason for the Loss of Activity of Titanium Anodes Coated with a Layer of RuO, and TiO, T. LOUCKA, J. Appl. Electrochem., 1977, 7 , (3), 211-214 The loss of activity of two types of activated Ti anodes with a layer of RuO, only and with a layer of RuO, and TiOt prepared by applying ethanol solution of RuCI, or RuCl, fTiC1, respectively was studied in o.gN H,SO, using the galvano- static method. On the basis of the experimental data it is suggested that the ATA activity results from the formation of a non-conductive oxide film at the Ti-active layer interface.

ACtU, 1977, 22, (41, 335-340

LABORATORY APPARATUS AND TECHNIQUE The Coulometric Determination of the Amount of Adsorbed Hydrogen as a Method of Measuring the Surface Area of Platinum Powder8 T. c. FRANKLIN and Y . MYAKOSHI, swfuce Tech- nol., 1977, 5, (21, 119-134 The catalytic activity of Pt was measured using the coulometrically determined amount of HI that adsorbs on Pt black. This technique was used to measure the surface area of Pt black powders as catalysts for formaldehyde oxidation

Platinum Metals Rev., 1977, 21, (3)

and acetone hydrogenation. It is shown that the oxidation of formaldehyde takes place on sites associated with the strongly bonded hydrogen, while the hydrogenation of acetone occurs mainly on sites associated with the weakly bonded hydrogen.

HETEROGENEOUS CATALYSIS The Relation of Actual Specific Activity of Platinum on Alumina Catalysts with Their Stabiity in Cyclohexane Dehydrogenation N. M. ZAIDMAN, w. A. SAVOSTIN and N. G. KOZHBVNIKOVA, Khim. Tekhnol. Topliv Masel, 1977, (21, 30-34 Studies of cyclohexane dehydrogenation over Pt/Al,O, catalysts show that the deposition of C on these catalysts depends on the actual specific activity of these catalysts. The rate of coke deposition increases sharply with a decrease of the actual specific activity.

Activity and Selectivity of Bimetallic Cata- lysts in n-Hexane Aromatisation

Neftekhimiya, 1977, 17, (11, 69-75 The influence of Gay Cd, Ge, Sb, Sn and Pb additions on the activity and selectivity of Pt/Al,O, catalysts was studied in n-hexane aromatisation. The results show that the catalyst containing o.t~-o.gwt.% Pt and having Pt:Pb= I-2:1 gives the highest activity and selectivity for this reaction.

Hydrogenation of Styrene on a Pt/BasO, Catalyst under Hydrogen Pressure D. v. SOKOL’SKII and A. UALJKHANOVA, Zh. Fiz. m i m . , 1977, 51, (21,492-494 The hydrogenation of styrene was carried out on a 5 at.% Pt/BaSO, catalyst in H,O and in 96% ethanol at 10-50°C and at Ha pressure 2- 100 atm. It is shown that the reaction rate in ethanol increases with increasing H, pressure. The apparent activation energies remain practically constant at 8.37.9 kcal/mole. The reaction was found to be of zero order in the substrate at 20 and 80 am. The reaction product, ethyl benzene, has no poisonous effect on the catalyst.

The Role of Ultraviolet Radiation in Pro- moting the Palladium-Catdyd Oxidation of Carbon Monoxide

W. N. USOV, L. G. ZUBANOVA and N. I. KWSHINOVA,

B.-H. CHEN, J. S. CLOSE and J. M. WHITE,J. C U t U b -

SGJ 1977~4% (31,253-258 Studies of the photoenhancement of the oxidation of CO over Pd were carried out at low and high pressures, and 300-443K. A marked photoenhancement of the rate occurred at a total pressure of 20 Torr while at below IO-’ Torr no increase was observed. The temperature dependence of the photdec t is discussed.

103

Hydrogenation of Acetylene in Excess Ethylene on an Alumina Supported Pal- ladium Catalyst in a Static System W. T. MCGOWN, C. KEIMBALL, D. A. WHAN and M. S. SCURRELL,~. Chon. Sac., Faraday Trans. I ,

Studies of the kinetics of the hydrogenation of acetylene in ethylene mixture on a Pd/Al,O,

catalyst in a static system showed that the produced ethane comes predominantly from the ethylene. It is suggested that two types of site exist on the surface: type X which hydrogenates both acetylene and ethylene and on which acetylene is adsorbed -2200 times stronger than ethylene at zg3K and type Y which is easily poisoned by CO and can hydrogenate ethylene even in the presence of acetylene.

A Mossbauer Study of Automotive Emission Control Catalysts c. A. CLAUSEN and M. L. GOOD, 7. Cata[ssis, 1977,

The state of Ru in a series of barium oxide stabilised Ru automotive emission control catalysts was studied. The results show that the chemical form of the Ru in these catalysts is a mixture of RuO, and BaRuO,. It was found that a loss in Ru stabilisation occurs during repeated oxidation-reduction cycling. I t is suggested that this is due to the separation of Ru metal from the stabilising barium oxide phase.

Kinetics of Ternary Nitric Oxide Reduction on Ruthenium R. SCHLEPPY and Y. T. SHAH, Ind. Engng. Chem., Product Res. Dev., I977,16, (I), 47-51 Studies of the reduction of NO and N 2 0 over a fibre glass supported Ru catalyst in a ternary mixture, NO-CO-H,, were carried out. Feed concentration of the NO and N,O were from 0.2 to 1.7 mole%, while those of the CO and H, were from 1.0-5.0 mole%. N,O was found to be a significant intermediate of NO reduction at low conversions.

1977, 73, (413 632447

46, (I), 58-64

HOMOGENEOUS CATALYSIS Transfer Hydrogenation and Transfer Hydro- genolysis. 13. Hydrogen Transfer from Cyclic Amines to Aromatic Nitro Compounds Catalysed by Noble Metal Salts H. IMAI, T. NISHIGUCHI and K. FUKUZUMI, 3. Org.

Studies of the homogeneous transfer hydrogenation of nitrobenzenes to anilines, using indoline as a H donor, showed that RuCl,*H20 and RhCI,-3H,O had high and PdBr, and PdC1, moderate catalytic activity. A mechanism is proposed in which the initial formation of Rh(1) species, the coordination of nitrobenzene to Rh(1) species and the hydrogen transfer from indoline to nitrobenzene are involved.

Chem.9 1977142, (3)~ 43I-434

Reductive Coupling of Benzhydrols by Homogeneous Ruthenium Catalysts I. PRI-BAR, 0. BUCHMAN and J. BLUM, Tetrahedron Letters, 1977, (17)~ 1443-1446 A new RuCl,(PPh,), cataIysed H transfer reaction in which secondary carbinols undergo reductive coupling is reported. A number of Pt metal compounds were studied for the various transfor- mation of benzhydrol at 200°C but only RuCI,(PPh,), was found to be an effective catalyst for the reductive coupling. PdCI,(PPh,), and PtCI,(PPh3), promote only ether formation while RhCl(PPh3), gives a molar ratio of I :Z of dibenzhydryl ether and I ,I,t,z-tetraphenylethane.

Complexes of the Platinum Metals. 7. Homogeneous Ruthenium and Osmium Catalysts for the Dehydrogenation of Primary and Secondary Alcohols A. DOBSON and S. D. ROBINSON, h r g . Chem., 1977, 16, (I), 137-142 Studies of the dehydrogenation of primary and secondary alcohols to aldehydes and ketones show that Ru and 0 s complexes [M(OCORF),- (CO)(PPh,),] (RF=CF,, C2F5 or CBFB) are useful catalysts for this process. Catalyst efficiency was found to decrease in the following order Ru>Os and CF,-C,F,> C,F, for a given alcohol under standard conditions.

FUEL CELLS State and Action of the Tin Atoms in Platinum-Tin Catalysts for Methanol Fuel Cells M. M. P. JANSSEN and J. MOOLHUYSEN,J. Catalysis,

Studies of the behaviour and the kinetics of Pt-Sn electrodes in pure acid and during methanol oxidation were carried out using cyclic voltammetry. It is shown that the zero-valent Sn atoms influence the adsorption properties of the Pt atoms, The increase in methanol oxidation rate on Pt-Sn electrodes is explained in terms of a “ligand” effect.

I977J 46J (31, 289296

CATHODIC PROTECTION Platinum Consumption in Cathodic Pro- tection Anodes R. BABOIAN, Mater. Pmformance, 1977, 16, (3), 20-22

Studies of the effects of current density and electrolyte composition on the corrosion of Pt-clad Nb base anodes were carried out in fresh and in salt water. It is shown that corrosion rates are roughly proportional to current density and are greater in fresh than in salt water. This is due to different anodic species in the two environments. The corrosion occurs as a result of oxide film formation on the Pt surface.

Platinum Metals Rev., 1977, 21, ( 3 ) 104

Increase of Passivity and Corrosion Resis- tance of Titanium by Alloying Its Surface with Palladium N. D. TOMASHOV, G. P. CHERNOVA and T. A. FEDOSEEVA, Zashchita Metal., 1977, 13, (2), 164-169 Studies of the electrochemical behaviour and corrosion resistance of T i modified by Pd electrodeposits (I, 5 and 10 pm thick) show its high passivity and corrosion resistance in 20-

so;/, H,SO, and s-zo:; HCl at 100°C. The unmodified T i in these conditions becomes fully corroded. It is shown that a Ti surface with electrodeposited Pd has a higher corrosion resistance in both acids than Ti+o.z?;Pd alloy.

GLASS TECHNOLOGY Effect of Some Manufacturing Conditions on the Optical Loss of Compound Glass Fibers s. SHIBATA and s. TAKAHASHI, J. Non-Cryst. Solids, I977,23, ( I ) , I I 1-122 The production of low-loss optical glass fibres in Pt crucibles was studied and the effects of the Pt contamination and gas flow on the optical loss of compound silicate glass fibres were investigated. It is shown that when the concentration of Pt dissolved into the glass from the Pt crucible is >50 ppm, the optical loss is ~ ~ o o o dB/km.

N E W PATENTS METALS AND ALLOYS Electroconductive, Corrosion Resistant Silicon Alloys P.P.G. INDUSTRIES INC. British Patent 1,466,455 A Si alloy has an electroconductivity greater than Ioo/ikm and consists of 0.2-224 of a dopant selected from N, P, B and Al, 1-<5o% of a transition metal such as Ru, Rh, Os, Ir, Pt, Pd, Ag or Au, balance Si. The alloy has a structure in the form of a predominant, discontinuous, Si rich phase, continuous rivulets of a transition metal silicide rich phase surrounding the Si rich phase, and discrete nodules of a phase rich in the dopant material.

Re-orientation of Grain Stabilised Platinum

U.S. Patent 4,002,503 The mechanical properties of a previously hard- ened Pt-Rh alloy which includes dispersed phase Zr oxide as a strengthening element are improved by cold working the composition at a temperature below that at which recrystallisation occurs and

JOHNSON MATTHEY & CO. LTD.

ELECTRICAL AND ELECTRONIC ENGINEERING Study of Al/Pd,Si Contacts on Si H. GRINOLDS and G. Y. KOBINSON,J. Vacuum sci.

Studies of the interaction of an A1 interconnect layer with Pd,Si contacts on an n-type Si substrate show that the contact barrier energy 0 B n decreased initially from -0.71 to 0.65 eV. This decrease was shown to be due to the decomposition of the Pd,Si layer. It is suggested that Al may enter the n-type Si as a compensating im- purity during prolonged heat treatments.

Technol., 1977, 14, (11, 75-78

MEDICAL USES The Crystal and Molecular Structure of cis-Dichlorobis(cyc1ohexylamine)platinum (11) J. IBALL and s. N. SCRIMGEOUR, Acta Cryst. B, 1977Y33, (4), 1194-1 196 Crystallographic studies of the anti-tumour agent, cis-dichlorobis(cyclohexylamine)Pt(II) show it to be orthorhombic with a=26.12, b=6.660, c -8.981& Z=4, space group Pbcn. The Pt atom is surrounded by two N and two C1 atoms in a cis square-planar arrangement. The shortest Pt-Pt distance is 4.498.

then annealing. The recrystallisation which occurs during annealing results in an elongated grain structure highly oriented in the direction of working.

High Temperature-stable Metal Powder JOHNSON MATTHEY & CO. LTD.

German Offen. 2,630,062 A metal powder which does not agglomerate or sinter at or around the melting point of the metal consists of a refractory substrate such as A1,0,, SiOz or Si carbide coated with a Pt group metal, Au or Ag.

CHEMICAL COMPOUND§ Osmium Tetroxide Complexes JOHNSON MATTHEY & CO. LTD.

German Offen. 2,630,823 Complexes may be formed from OsO, and compounds with a heterocyclic ring having one or two N atoms, such as phthalazine, and used for the fixing and/or dyeing of cells. The treated cells may then be examined by electron microscopy.


ELECTROCHEMISTRY Bipolar Cell SOLVAY ET CIE. S.A. British Patent 1,469,832 A bipolar diaphragm-type multicompartment cell consisting of a stack of bipolar elements has the anode structure of the elements of the cell formed of T i with a coating including one or more Pt group metals or oxides.

Platinum-Iridium Catalytic Anode GENERAL ELECTRIC co. U.S. Patent 3,992,271 A catalytic anode, for use in a gas generation apparatus, used for concentrating O 2 or generat- ing O 2 and H, by electrolysis, employs a Pt-Ir alloy, with an Ir content of 5-5oOi:, as a catalyst.

Noble Metal Electrodes for a Combustible Sensor WESTINGHOUSE ELECTRIC CORP.

U.S. Patent 4,005,001 An apparatus for determining the presence of predetermined combustible constituents such as methane, H, and CO, in an excess 0, gas mixture is a solid electrolyte electrochemical cell which has one electrode made from Pt, Pd or Rh and the other from Ag or Au.

LABORATORY APPARATUS AND TECHNIQUE Particle Detection W. L. FITE ET AL British Putent 1,465,751 A particle of dust or a macromolecule of 1000 AMU or greater is induced to strike a heated surface of Pt, Ir, Re or Rh, to cause the release of electrons or ions as a detached burst, and a detector is located so as to sense the electrical charge of the burst. This induces in the detector an electrical pulse, the magnitude of which is related to the particle size.

Ceramic Gas Sensor FORD MOTOR c0. LTD. British Patent 1,467,735 The partial pressure of 0, in an ICE exhaust gas, is sensed by a device which has a porous, sintered ceramic body of particles of a 99.5% pure transition metal oxide, a pair of Pt electrodes and electrical means connected to the electrodes for responding to the inter-electrode resistance. They include a Pt-Rh alloy resistance wire and a Au-Pd-Pt and Au-Pd combination thermocouple.

Ignition Device JOHNSON MATTHEY & CO. LTD.

German Offen. 2,630,749 An ignition device generates sparks between two electrodes projecting from or mounted on insu- lating or semiconducting surfaces. The active surfaces consist predominantly of Co or Ni alloyed

or composited with one or more metals from the group consisting of Ru, Rh, Pd, Ir, Pt, Au or Ag.

JOnUING Brazing Alloys Containing Noble Metals

A brazing spelter composition for joining high melting carbides, ceramics, etc., to each other or to high melting alloys consists of 2-30% CU, Au and/or Ag, 2-21% Al, B, Sc, Y, lanthanides, C, Si, Ge, Ti, Zr, V, Nb, Ta, P, Cr, Mo, W, Mn, Tc, Re, Os, Co, Ni, Rh, Ir and/or Pt, and the balance Hf.

V. P. KOSTERUK ET AL V.S. Patent 3,998,632

Platinum Metals Rev., 1977, 21, ( 3 ) 106

HETEROGENEOUS CATALYSIS Amorphous Platinum Metal Particles BRITISH PETROLEUM CO. LTD.

British Patent 1,470,034 A new form of Pt consists of amorphous Pt metal particles which do not produce the X-ray diffraction pattern characteristic of crystalline Pt. The particles are produced by depositing Pt on a support, oxidising it at a temperature of at least 300°C and then reducing it at a similar temperature in H,.

Hydrazine Decomposition Catalyst KALI-CHEMIE A.G. British Patent 1,470,260 A catalyst for the spontaneous decomposition of hydrazine and its derivatives, especially for space propulsion systems, is obtained by impregnating active A1,0, with an Ir compound and optionally an 0 s compound at least four times. After each impregnation the damp product is dried at 100-300°C in an inert atmosphere before finally the compound is reduced to metal at a temperature of 18c-300~C in H,.

Helium Cooled Nuclear Reactors U.K. ATOMIC ENERGY AUTHORITY

British Patent 1,470,795 The reactor has further (recycling) circuitry in addition to a closed loop main coolant circuit, which includes a Pt catalyst for oxidising the H, content of the coolant gas.

Storage Battery Catalysts ROBERT BOSCH G.m.b.H. British Patent 1,471,307 A recombination catalyst for gases generated in a secondary cell consists of bodies of Pd or C, or the like, sheathed in PTFE so that they are able to float in the battery electrolyte.

Platinum Metal Conversion Catalysts EXXON RESEARCH & ENGINEERING GO.

U.S. Patent 3,993,598 The preparation of two novel catalysts for the catalytic hydro-conversion of hydrocarbon mat-

erial contained in heavy crudes and residuals is described. The method consists of dispersing a compound of a Group VIB and/or Group VIII, such as Pt, Pd, Ir, Os, Ru, Rh, etc., and an A1 halide salt in an aqueous or alcoholic medium, maintaining the temperature at 3c-1oo"F, adding olefin oxide and maintaining the p H at 5-8, raising the temperature so as to form a cogel, ageing the cogel, separating, washing, drying and calcining the cogel and impregnating the resulting catalyst with a Group IVA metal oxide.

Catalyst Support Assembly

A catalyst support structure, for use with woven gauzes of Pt metal or Pt/Rh alloy, in catalytic convertors, consists of a number of woven screens stacked together, the screens being composed of an alloy of 4-6"/0 Al, 2c-30% Ni, o.z~-I.oSJ, Cr and the balance Fe.

MATTHEY BISHOP INC. U.S. Patent 3,993,600

Platinum Group Exhaust Gas Purification E. I. DU FONT DE NEMOURS & GO.

U.S. Patent 4,001,143 The catalyst is prepared by impregnating Also, with a solution which contains at least one Pt group metal which will be present in a concentration of 0.001-5.07; on the support, at least one lanthanide in an atomic amount of 1-1000 times that of the Pt group metal and at least one Group IA or IIA metal compound in an atomic amount of 0.25-4 times that of the Pt group metal, drying and heating at least 80o"C for I h.

Platinum Group Catalyst for a Battery JAPAN STORAGE BATTERY CO. LTD.

U.S. Patent 4,002,496 A catalyst produced by impregnating a Pt group metal, such as Pd, into granules obtained by sintering and forming active A1,03, is used in a battery which contains an aqueous electrolyte.

Noble Metal Catalyst for Cleaning Air Which Contains Carbon Monoxide KANEBO LTD. US. Patent 4,003,979 Polluted air containing CO is cleaned by passing it through an adsorbent filter and through a noble metal catalyst layer. The catalyst preferably consists of I'd on active C with 2c-50% H,O.

Purification of Exhaust Gases INSTI'MJT FRANCAIS DU PETROLE

French Appl. 2,298,688 The exhaust gas, together with air, is passed over a catalyst bed, the air being introduced in variable quantities during the passage of the gas over the catalyst bed. The amount of air introduced depends on the quantity of the exhaust gas produced by the engine. The catalyst consists of the oxide(s) of Pt, Rh, Cu, Ag, Zn, V, Cr, Mo, W and Mn on a refractory support.

HOMOGENEOUS CATALYSIS Colloidal Platinum Catalyst

U.S. Patent 3,992,331 An improved catalyst, for various uses, especially under high temperature conditions, is prepared by applying a compound of formula H3Pt(S0,), OH to a substrate, thermally decomposing the acid in air and then reducing it to form metallic Pt particles having an average particle size in the range 15-258.

Ruthenium, Iridium and Rhodium Hydro- genation Catalyst

PROTOTECH CO.

FIRESTONE TYRE & RUBBER CO. U.S. Patent 3,993,855

Selective hydrogenation of unsaturated hydrocarbon polymers is catalysed by the complexes

RuHCl(PPh,), and IrH,(PPh,),. RhCI(PPh,),, RhCICO(PPh3),, RhHCO(PPh,),,

Asymmetric Hydrogenation Catalyst

Asymmetric hydrogenation, especially of ace- tamidophenyl propane enantiomorphs, is catalysed by a Rh, Ru or I r optically active bisphosphine complex, such as a Rh fluoroborate complex of a di(anisylpheny1phosphino)ethane.

Hydroformylation Catalyst

MONSANTO GO. Dutch ApplS. 76.09339-40

JOHNSON MATTHEY & GO. LTD. Russian Patent 503,503

The hydroformylation of olefins e.g., propylene to alcohols and aldehydes is catalysed by a neutral Rh complex, specifically hydrocarbonyl tris- (triphenylphosphine)Rh, RhH(CO)(PPh3),, in the presence of an excess of triphenylphosphine.

FUEL CELLS Flow-Through Type Fuel Cells KANEBO LTD. British Patent 1,467,147 The cell consists of a cathode, an anode and an electrochemical separator. At least one of the electrodes consists of a layer of a woven or knitted fabric formed from organic high polymer fibres of 1-30 pm diameter, each fibre having a 0.1-10 pm thick metal layer on its surface and an electro- catalyst on the metal layer. The metal is Ti, Cr, Rh, Pd, Ru, Pt, Ag, Au etc., and the electro- catalyst is Pt, Pd, Rh, Ir, Ni, Cu and Ag.

CHEMICAL TECHNOLOGY Recovery of Small Particles of Precious Metals E. 0. ANDERS U.S. Patent 3,998,629 Small particles of Pt or Au are recovered from a slurry by feeding the slurry on to a layer of Hg


which is flowing down along a conical, down- wardly converging inner wall of a housing. The housing is rotated about the vertical axis of the wall at a speed which reduces particles to settle out or amalgamate with the Hg. The particles are subsequently separated out and recovered.

Regeneration of Platinum Group Hydro- genation Catalysts E. I. DU PONT DE NEMOURS & CO.

U.S. Patent 3,998,936 A Pt group hydrogenation catalyst, used in the manufacture of peroxide from an alkylanthra- quinone, is regenerated by contacting it, in the presence of the working solution and in the ab- sence of H,, with either an 0, containing gas or H&,.

Palladium Additive for Metallisation Acti- vation Bath LANGBEIN-PFANHAUSER WERKE A.G.

U S . Patent 4,001,470 An activation bath for use in the chemical coating of synthetic resin bodies with Ni or Cu contains 0.1-20 g gelatin or gum arabic, 1-5 g tartaric or citric acid, 1-5 g H,SO, or HCl, 0.1-5.0 g Pd sulphate, 1-20 g maleic or 1-6 g fumaric acid and H,O to a volume of I 1.

Palladium Treatment of Electroconductive Non-Woven Fabrics HOECHST A.G. U.S. Patent 4,002,779 The fabrics are manufactured by cleaning a non- woven polar fabric with a polar organic solvent, sensitising the fibre surfaces of the fabric with an aqueous HCl solution of stannous chloride, rinsing with H,O, activating the surface of the fibres with an aqueous HCI solution of PdCl,.

Pressed Metal Powder Coins METALLWERK PLANSEC A.G.

German Offen. 2,633,323 The counterfeiting of coins is made more difficult by pressing coins from a powder mixture which is not homogeneous and/or which contains “tracers” such as Mo, Ta or T h oxide. Pt alloys can be used to produce homogeneous coins containing such a tracer.

GLASS TECHNOLOGY Glass Fibre Spinneret Mounting PILKINGTON BROTHERS LTD.

British Patent 1,471,306 Glass is supplied from a forehearth through a duct and an apertured cover plate before reaching a bushing. This arrangement keeps the duct hot and reduces spun fibre breakage. The cover plate and duct are preferably made of the same material as the bushing, a Pt-Rh alloy.

ELECTRICAL AND ELECTRONIC ENGINEERING Manufacturing Microwave Devices GENERAL ELECTRIC CO. LTD.

British Patent 1,464~51 I A microwave device has a component of ferrite material in which are embedded Pt group metal conductors produced by laying the conductors in grooves in the ferrite body and plasma- spraying ferrite onto the conductors.

Compression Bond Assembly for a Planar Semiconductor Device WESTINGHOUSE ELECTRIC CORP.

British Parent 1,465,328 Thermal and electrical contact is obtained between a first mounting electrode contact and a first semiconductor region using a planar electri- cally and thermally conductive preform of Pt and/or Ir or their alloys.

Schottky Barrier Field Effect Transistor U.S. SECRETARY OF THE AIR FORCE

U.S. Patent 3,999,281 In the manufacture of the transistor Pt is deposited only at the bottom of the groove of a single high resolution mask. This obviates the need for an additional photo-masking step or the necessity of subsequent removal of Pt from other surfaces of the wafer.

Silver Electrical Conductor Compositions E. I. DU PONT DE NEMOURS & CO.

U.S. Patent 4,001,146 Compositions for making electrical conductor patterns on a non-conductive substrate consist of a metal powder and 1-5% glass-free inorganic binder. The binder is made up of Bi oxide and Cu and/or Pb oxides, and optionally MnB, andlor MnO,. The metal powder is either Ag or a mixture of Ag with Pt, Pd, Au or an alloy of Cu with one or more of Pt, Pd, Au and Ag.

TEMPERATURE MEASUREMENT

Platinum Metals Rev., 1977, 21, (3) I ox

Paint-On Thermocouple U.S. SECRETARY OF THE NAVY

U.S. Patent 4,004,948 A paint-on thermocouple is made of thin films of a finely divided mixture of Pt, Ag and Au and the alloy constant is painted on to the surface to be tested.

Resistance for a Resistance Thermometer W. C. HERAEUS G.m.b.H. German Offen. 2,527,739 A resistance for temperature measuring purposes consists of 0.1-10pm of Pt deposited on an oxidic support, such as Al,03.

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