PLATINUM METALS REVIEW · ing of both gold and platinum alloys is shown in Figure I. The most important of the platinum alloys at present used for invest- ment casting was developed

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PLATINUM METALS REVIEW

A quarterly survey of research on the platinum metals and of dmelopments in their application in industry

V O L . 2 2 J U L Y 1 9 7 8 N O . 3

Contents

Platinum Investment Casting Alloys

Catalytic Production of Nitric Acid

Thermocouple Reference Tables

Tantalum Clad Rhodium-Platinum Thermocouples

Storing Hydrogen in the Solid State

Iridium Losses During Oxidation

A Review of Fuel Cell Development

The Electrodeposition of Platinum and Iridium from Fused Salts

Recent Patent Literature on Emission Control

The Platinum Notebooks of William Hyde Wollaston

Abstracts

New Patents

78

88

89

90

91

92

97

98

99

100

107

I I 2

Communications should be addressed to

The Editor, Platinum Metals Review Johnson Matthey & Co Limited, Hatton Garden, London ECI N BEE

Platinum Investment Casting Alloys NEW MATERIALS WITH IMPROVED PROPERTIES AND CASTING CHARACTERISTICS

By G. Ainsley

and A. A. Bourne and R. W. E. Rushforth Johnson Matthey Metals Limited, Birmingham

Group Research Centre, Johnson Matthey and Co Limited

The high melting point of platinum makes stringent demands on the other materials involved when it is investment cast. However, by careful selection of refractories, it has been possible to successfully cast small batches of platinum items for many years. In view of the renewed interest in platinum jewellery it has now become desirable to increase the e@ciency of the process, and a number of new platinum alloys have been developed for this purpose. In some the alloying elements are those traditionally associated with platinum but in others more unusual additions are used to produce alloys with a signi$cantly lower casting temperature.

Investment casting is a development of the very old lost wax method used by the ancient Greeks and Chinese over two thousand years ago. The name, lost wax casting, owes its origin to the fact that an expendable wax pattern was formed of the object to be cast. When this had been surrounded by a heat resistant mould material the pattern was melted out and the wax was “lost”.

Today rhe process is highly sophisticated, enabling thousands of replica castings of one item to be manufactured cheaply, by-passing the need for soldering, sawing, filing or the numerous other operations generally involved when jewellery is fabricated from wrought material. Using the original master pattern a rubber mould is formed and in this the required number of replica wax patterns are produced. If the castings are to be made from a material having a melting point below about 1300OC the replicas are next assembled onto a wax tree. This becomes the pattern for the refractory investment casting mould which is supported by a steel flask. The material to be cast can be melted by induction

or air/fuel gas heating, and to ensure satisfactory filling the molten metal is forced into the previously fired flask, generally by centrifugal means. This technique enables a substantial number of castings to be produced from a single melt and, providing the many stages of the process have been adequately controlled, the castings will possess all the fine detail present on the original master pattern. Equipment suitable for the investment casting of both gold and platinum alloys is shown in Figure I . The most important of the platinum alloys a t present used for investment casting was developed to conform to the United Kingdom Hallmarking Act of 1973; all have melting ranges between 1725 and 1780°C and at these temperatures a modified process is required.

Platinum Casting Process The effect of the very much higher tempera-

tures involved introduces many difficulties into the casting of platinum. The investments used for casting lower melting point materials are generally based on crystobalite/gypsum

Platinum Metals Rev., 1978, 22, (3), 78-87 78

F!g. 1 While some of the casting trials were made with simple equipment most were carried out on the sophisticated machine shown here. The charge is melted by induction heating and then thrown into the mould by a motor driven centrifuge. A radiation pyrometer mounted vertically above the melt gives an accurate measurement of temperature, and a gas probe can be used to introduce a protective atmosphere when this is required

mixes; for platinum a more refractory material is required and compositions based on silica with additions of phosphate based bonding agents are at present used. These more complex high temperature materials require considerably more preparation, including quite prolonged setting and drying periods. Even so the strength of these investments at elevated temperatures is low and it is therefore not practicable to cast a large number of items on one tree, as is possible when casting gold and silver alloys. In general only a few items are cast at one time, on a button rather than a tree, and each has to be well separated from the others to avoid further weakening the investment mould. Typical arrangements of platinum alloy castings on buttons are shown in Figure 2.

This configmation has a deleterious effect on the platinum casting process as it results in a small amount of metal being thrown into

a relatively large and very much cooler mass of investment. The resultant quenching effect on the molten platinum alloy, and the high thermal gradients involved, necessitate a superheat of between 250 and 4oo0C, that is temperatures in excess of 2000°C in the molten metal prior to casting, to ensure filling of each pattern in the mould. Clearly the thermal losses would be less if the temperature differential between the hot flask containing the mould and the molten metal could be reduced, but the inherent properties of the platinum investment restricts the temperature to which the mould can be preheated to about 900°C. However, a more refractory investment material that may be capable of with- standing higher preheat temperatures, and be more durable at the metal/investment interface, is currently under development in the United States of America. If successful this material will alleviate to some extent a number

Platinum Metals Rev., 1978, 22, (3 ) 79

of the problems faced by the platinum investment caster.

Other aspects of the process also have to be changed from those used for gold and silver; for instance oxygen rather than air is required for torch melting opcrations and a highly refractory crucible is necessary, the clay/ graphite type generally used for investment casting being unable to withstand the temperatures involved.

Alloy Development Currently the major platinum alloy used in

Britain in both wrought and cast form for jewellery manufacture is 4.5 per cent copper- platinum. A slightly harder alloy, 4.5 per cent ruthenium-platinum, is used to a lesser extent, mainly in wrought form.

The copper-platinum alloy has basically acceptable mechanical properties for a casting material, being resistant to the deformation which could result from the stresses present in the mould as the metal solidifies and yet being amenable to sutxequent sizing and setting operations. However, our experience in casting this alloy has suggested that it is not completely satisfactory. When in the molten state in air a copper oxide skin forms, and this reduces the fluidity of the alloy

making filling of fine section items difficult and producing a dull grey coloration on the resultant castings. In addition, predominantly with thicker section items, metal-mould reaction occurs causing surface roughness on such castings.

Clearly some further development was required to optimise the process and exploit any increase in the demand for platinum jewellery. This work took two forms covering both the development of an improved high temperature casting alloy and an evaluation of potential lower melting range materials designed to alleviate some of the problems and restrictions associated with the standard process.

1. High Temperature Alloys For this part of the work a range of casting

patterns was selected that would enable an assessment to be made of the most important properties. For example signet rings weighing 40 grams were cast to assess metal-mould reaction, as this was considered to be most likely to occur with a combination of high temperature and large mass of molten metal. In contrast settings for gem stones, weighing as little as 0.5 gram, were cast to determine alloy fluidity. In addition, conventional

Table I Mechanical Properties of Platinum Casting Alloys

Alloy composition weight per cent

4.5 Cu-Pt

4.5 Ru-Pt I lr-3.5 Pd-Pt

4.5 Ir-Pt

10 Ir-Pt

4.5 Pd-Pt

15 Pd-Pt

1 Rh-3.5 Au-Pt

4.5 Co-Pt

1 Ni-3.5 Pd-Pt

2 Ni-2.5 Pd-Pt

Hardness H"

108 114 60 73

113 68 64 90

134 82

104

Ultimate tensile strength MN/m2

318 383 167 205 329 167 187 249 400 21 8 465


0.1% Proof stress MN/m*

190 248 100 139 239 93

103 153 182 139 309

Elongation per cent

20 14 30 22 10 22 22 30 20 20 18

Table II Relative Quality of Castings Produced


4.5 Cu-Pt

4.5 Ru-Pt 1 lr-3.5 Pd-Pt 4.5 Ir-Pt

10 Ir-Pt 4.5 Pd-Pt 15 Pd-Pt

1 Rh-3.5 Au-Pt 4.5 Co-Pt 1 Ni-3.5 Pd-Pr

2 Ni-2.5 Pd-Pr

Engagement rings ('0 g)

Large signet rings (40 9)

Fine patterns settings

(approx. 0.5 g)

P VP

VG G G P

VP P

VG

VG S

VG-Very Good; G-Good; 5-Satisfactory; P-Poor: VP-Very Poor

tensile test pieces were cast and the mechanical properties of each alloy determined. Other properties evaluated were ability to reproduce detail, colour and hardness.

The alloy compositions chosen for evaluation included several of United Kingdom Hallmarking quality in addition to other casting alloys at present used in the United States of America (4.5 per cent ruthenium- platinum and 10.0 iridium-platinum) and in Japan (15.0 per cent palladium-platinum). All are listed in Table I, together with their mechanical properties.

As an oxidation resistant casting alloy would have clear advantages the first investigations were carried out on alloys of platinum with additions of only other platinum group metals. Some of these alloys demonstrated casting characteristics superior to those of 4.5 per cent copper-platinum, as shown in Table 11. In particular, all castings produced in I per cent iridium-3.5 per cent palladium- platinum were free from the effects of metal- mould reaction and had smooth, bright and sound surfaces. The absence of an interfering oxide film was demonstrated by its ability to fill very fine patterns and to reproduce detail.


S P

VG

G VG VG

S

P

VG

VG S

P P

V G VG

S VG

S

P VG

VG S

The quality of castings produced in the two binary iridium-platinum alloys was only marginally inferior. Some very slight surface erosion was observed in the large patterns through metal-mould reaction and in the case of the 10 per cent iridium-platinum alloy, a proportion of the fine scctioned patterns were difficult to fill, both of these effects probably being a function of the higher casting temperature required. Castings in 4.5 per cent palladium-platinum were also superior to those in 4.5 per cent copper-platinum.

All these alloys have limited use, however, in casting application, their poor mechanical properties as shown in Table I resulting in the items being easily distorted during the casting process and subsequent handling.

The surface appearance of the 15 per cent palladium-platinum buttons suggested that considerable gas was absorbed during melting and subsequently evolved during solidifica- tion. Large and medium sectioned patterns were consequently scriously affected by porosity and extensive surface roughness demonstrated metal-mould incompatibility.

Although the mechanical properties of 4.5 per cent ruthenium-platinum were of the

order required for general purpose applications, most of the castings produced suffered from an intolerable degree of surface roughness and fine sectioned patterns were difficult to fill, Surface erosion was most extensive in the signet ring, an example of which is shown in Figure 3. Microprobe examination of the affected region revealed no chemical reaction and therefore the breakdown must have been purely mechanical.

As an extension of the all noble metal approach an alloy composed of I per cent rhodium-3.5 per cent gold-platinum was assessed. Both rhodium and gold have a hardening effect on platinum when present in binary alloys but the poor surface condition of the castings made this alloy unattractive.

Having explored thoroughly alloys containing only noble metals, base metal additions were next considered. Nickel, when added to platinum, imparts a significant increase in hardness and so in an attempt to retain the advantages gained in casting quality by the inclusion of palladium, two alloys, one containing I per cent nickel-3.5 per cent palladium-platinum and the other z per cent nickel-2.5 per cent palladium-platinum were evaluated. The product quality in I per cent nickel-3.5 per cent palladium-platinum was comparable to that of I per cent iridium-3.5 per cent palladium-platinum and there was

Fig. 2 Two typical platinum buttons show the limited number of well-spaced items that can be satisfactorily cast at the elevatpd temperatures involved

no evidence of surface oxidation. The increase of strength and hardness was not, however, sufficient for the application. Con- versely the mechanical properties of z per cent nickel-2.5 per cent palladium-platinum are ideal but the casting quality was no better than 4.5 per cent copper-platinum, and the colour of the castings was characterised by a dull grey appearance resulting from base metal oxidation. I n the large sectioned pattern the surface topography was very irregular due to the metal-mould reaction while porosity was rather more prevalent than in other alloys.

These results suggested that a binary alloy where the addition element hardens platinum to a lesser degree than nickel and which is oxidation resistant, might fulfil our require- ments. It seemed that cobalt could be such an additive, and subsequent trials revealed that castings in 4.5 per cent cobalt-platinum were comparable in quality to both I per cent iridium-3.5 per cent palladium-platinum and I per cent nickel-3.5 per cent palladium- platinum, while the mechanical properties were in the preferred range for an alloy to be used in general purpose applications.

2. Lower Melting Point Alloys As previously stated the platinum alloys at

present used for investment casting have melting ranges between 1725 and 1780"C,


and therefore require a casting temperature of at least 2o5o0C to ensure satisfactory filling of fine sections. Even when the highest quality investment materials are used their properties are only just adequate for casting a few patterns at a time. T o make the casting of platinum a less critical and more economic process, an improved investment material, with better high temperature properties, is therefore required. Alternatively or in addition to this, the development of a platinum alloy requiring a lower casting temperature would extend crucible life and permit more castings per button.

The possibility of developing platinum casting alloys with a significantly reduced melting range has now been explored, the two major objectives being to satisfy the 1973 Hallmarking Act and to obtain the properties required by the manufacturing jeweller.

Initially the effect of additions such as silicon and boron were evaluated. Molten platinum readily reacts with these elements to form low melting point eutectics, and therefore stringent precautions are generally taken to prevent them coming into contact. The eutectic silicon-platinum alloy, at 4.2 per

Fig. 3 The surface erosion, seen on the heavier sectioned ring cust in 4.5 ruthenium- platinum, results from breakdown of the inuestment. Orr the lighter sectioned ring this renrtion is minimal

cent silicon, melts at 830°C and could consequently be airlfuel gas torch melted and cast in standard low temperature investments without undue difficulty; similarly the 2.1 per cent boron-platinum alloy with a melting point of 789°C could also be easily cast. Pre- dictably the hardness of these alloys, 440 H, and 327 H,, respectively, coupled with their extreme brittleness rendered them unsuitable for subsequent fabrication. Figure 4 shows the dark coloured, hard, interdendritic con- stituents that occurred in the microstructure of an as-cast eutectic alloy.

Attempts to modify the structure by ternary and quarternary additions while retaining the reduced melting range, did not reduce the overall hardness of these materials below about 300 H, and the castings were therefore unacceptable.

The relevant phase diagrams were examined for an element that, on alloying, could substantially reduce the melting point of platinum without exceeding the 5 per cent addition limit. Gallium appeared to do this, although not to the same extent as silicon and boron, and it offered the possibility of forming alloys having mechanical properties within


Fig. 4 The microstructure of a 4.2 per cent silicon-platinum ring cast at about 1000°C shows the very hard eutectir compound which made this experimental alloy unsuitable for most jewellery investment casting applications

Alloy composition As-cast hardness weight per cent H"

the range that might be acceptable to manu- therefore evaluated, the melting range and facturing jewellers. The relevant part of the as-cast hardness values being given in Table phase diagram is shown in Figure 5. A series 111. Increasing the gallium content resulted of exploratory binary alloys covering the in lower melting temperatures, but also range 2 to 5 per cent gallium-platinum were increased the hardness values to such an

Solidus temperature "C

__ Alloy corn posi t ion

weight per cent

2 Ga-Pt 3 Ga-Pt

3.5 Ga-Pt

5 Ga-Pt

1 Au-4 Ga-Pt

2 Au-3 Ga-Pt

2.5 Au-2.5 Ga-Pt 3 Au-2 Ga-Pt 2.5 Pd-2.5 Ga-Pt

1 Ag-4 Ga-Pt 2.5 Ag-2.5 Ga-Pt 3 Ag-2 Ga-Pt

Table Ill Properties of Some Gallium-Platinum Alloys

360 1500 183 1560 171 1560 134 1580 1 54 1580 290 1490 145 1525 130 1560

As-cast hardness H"

1 30-1 42

1 53-1 60 292-304 354-360

Solidus temperature "C

1650 1550 1525 1440

Liquidus temperature "C

1730 1640 1620 1580

Properties of Some Ternary Alloys Based on the Gallium-Platinum System


Liquidus temperature "C

> 1600 > 1600

1 620 > 1600 > 1600 > 1600

1590 > 1600

Table IV

qualities of the solid solution gold-gallium- platinum alloys. Larger scale trials using cent gold-2 per cent gallium-platinum, the production equipment determined the mini- structure of which is shown in Figure 6, mum casting temperature required to fill a could be successfully cast at a lower tempera- standard production flask consisting of a ture than alloys containing 2.5 or 3 per cent button of six dress rings. In these the 3 per gallium despite having the higher melting

Fig. 6 The single phase microstructure of 3 per cent gold-2 per cent gallium-plazinum shows some coring and fine interdendritic porosity. This alloy is also a suitable replacement for the 4.5 per cent copper-platinum alloy at present used for investment casting and has a signijicantly lower casting temperature


platinum-

extent that alloys containing 3.5 per cent or more gallium were unusable.

Some further optimisation of the casting and mechanical properties was required and a series of ternary alloys based on the gallium- platinum system was evaluated; several combinations appeared to show a reasonable melting range while retaining good ductility, the relevant figures being given in Table IV. Small scale centrifugal casting trials using a fine claw setting dress ring pattern provided a critical test of fluidity and general casting characteristics, and revealed the good casting


_ _ - 4.5 Cu-Pt 3 Ga-Pt

2.5 Au-2.5 Ga-Pt

3 Au-2 Ga-Pt

Table VI Variation of Oxygen Content in Castings with Melting

Atmosphere

-

Casting t e m p e i z r x n g of a 6 dress 1 r ing casting button in a i r 'C

~ --+- 2050 Complete

1960 ' Incomplete

1990 Complete

1960 Complete


2.5 Au-2.5 Ga-Pt

3 Au-2 Ga-Pt

3 Au-2 Ga-Pt

3 Ga-Pt

3 Ga-Pt

2.5 Au-2.5 Ga-Pt 10% hydrogen:nitrogen

A i r

10% hydrogen/nitrogen

___ - - - ~

Atmosphere during Oxygen content of melting

A i r

10% hydrogenjnitrogen

I Air I 14

18

8

range. The results are given in Table V, together with comparable data for 4.5 per cent copper-platinum. This suggested that the gallium-containing alloys were susceptible to the absorption of oxygen, with a consequent reduction in fluidity. Further trials, in which the melt was protected by a reducing atmosphere, showed a significant improvement in the fluidity of these alloys thus enabling the

casting temperature required to fill the six- ring button to be reduced to about I ~ o o " ~ . Gas analysis of the castings produced showed a significant decrease in the oxygen content when a reducing atmosphere of 10 per cent hydrogen/nitrogen had been used to protect the melt; the results are given in Table VI.

As an alternative approach the effects of adding a deoxidant to the alloy at the make-up stage or to the melt prior to casting, were evaluated. A small addition of yttrium in- corporated in the alloy was found to be very effective in increasing alloy fluidity without

promoting metal-mould reaction, and any casting scrap could be re-cast providing 25 per cent virgin alloy, containing the deoxidiser, was added to each charge. While a small gain in alloy fluidity could be obtained when a deoxidant such as calcium boride was added to the melt prior to casting, the associated metal-mould interaction was considerable and made the castings unacceptable.

Table VII The Optimised Casting Temperatures Required to Ensure Complete Filling of Fine

Section Castings


4.5 Cu-Pt

3 Au-2 Ga-Pt

3 Au-2 Ga-Pt+O.l yttrium

3 Au-2 Ga-Pt

Atmosphere during melting

A i r

A i r

A i r

10% hyd rogen/nitrogen

Minimum casting temperature "C

2050 1960 1930

-1 900


Table IV

Table IV Results of Casting Trials on Existing and New Alloys

Table Vlll Comparison of Some Mechanical Properties of Existing and New Alloys in the


4.5 Cu-Pt

4.5 Co-Pt 3 Ga-Pt

2.5 Au-2.5 Ga-Pt

3 Au-2 Ga-Pt

Density g k m J

20.0 20.1 19.8 20.0 20.3

As-Cast State

Hardness H"

108 134 153 171 134

To summarise, 3 per cent gold-z per cent gallium-platinum can offer an advantage in casting temperature of between 90 and 15o"C, depending on casting conditions, over the existing casting alloy, see Table VII.

Practical Evaluations A comparison of the mechanical properties

of the 4.5 per cent copper-platinum alloy, the 4.5 per cent cobalt-platinum and these lower temperature casting materials, which are given in Table VIII, suggests that the 4.5 per cent cobalt-platinum and the 3 per cent gold- 2 per cent gallium alloys are similar to the 4.5 per cent copper-platinum in most aspects. They should therefore be amenable to the finishing techniques that the manufacturing jeweller normally applies to cast items. This has now been confirmed by the results of extensive trials completed by an independent jeweller who examined the stone-setting, ring sizing, soldering and polishing characteristics of 4.5 per cent copper-platinum, 4.5 per cent ruthenium-platinum, 4.5 per cent cobalt- platinum and the three gallium-platinum based alloys.

His report firmly recommends the cobalt- platinum alloy which was found to be superior to both 4.5 per cent copper- and 4.5 per cent ruthenium-platinum, while the 3 per cent gold-2 per cent gallium-platinum was considered to be a fully acceptable replace-


Ultimate tensile

strength MN/mZ

31 8 400 262 285 346

0.1% Proof stress

MN/m2

190 1 a2 139 182 162

Elongation per cent

17.0 18.5

ment for the 4.5 p x cent copper-platinum. There are no practical reasons against the use of either of the other two gallium-bearing alloys where a harder alloy is required, although the casting advantage of these is clearly less.

Conclusions The work reviewed in this paper has

shown that the high temperature alloy 4.5 per cent cobalt-platinum is superior in all aspects to the existing 4.5 per cent copper- platinum alloy for investment casting. The versatility of this alloy for casting the whole range of patterns from fine filigree to heavy section items has been clearly demonstrated. This together with its amenability to all the usual fabricating and finishing operations applied to such castings gives the jeweller the opportunity to improve both the quality of his product and the efficiency of his manufacturing process.

A significant decrease in casting temperature has been achieved with the 3 per cent gold-2 per cent gallium-platinum alloy, although it has not been possible to produce a platinum alloy that can be cast at temperatures comparable with those used for gold alloys. The advantage of this lower casting temperature is likely to assume even greater importance if the anticipated improvement in investment durability is achieved.

Catalvtic Production of Nitric Acid J

ESSENTIAL STEP IN ARTIFICIAL FERTILISER MANUFACTURE

Our current standard of living is highly dependent on the use of artificial fertilisers in agriculture, and these in turn are equally dependent on the use of catalysts in their manufacture. Recognition of these facts was the basis of a recent symposium, organised by the Fertiliser Society of London, in which the full day meeting was devoted to the catalytic aspects of fertiliser production.

Among the papers presented on this occa- sion was an invited contribution from J. A. Busby, A. G. Knapton and A. E. R. Budd of Johnson Matthey dealing with the catalytic processes involved in nitric acid manufacture. (Proceedings No. 169, read 20th April 1978.) Although base metal catalysts are employed to a minor extent, nearly the whole of the nitric acid production in the world is carried out by the oxidation of ammonia over a catalyst consisting of a pack of rhodium-platinum alloy gauzes, and the opportunity was taken to review some of the principles and practice in the use of such catalysts, together with the recent techniques for NO, fume abatement using Honeycat catalytic systems.

Process Chemistry After a brief historic introduction, the paper

considers in some detail the more important basic chemistry of the nitric acid process. The oxidation of ammonia with air to nitric oxide over rhodium-platinum gauze is one of the most efficient catalytic reactions known, giving yields of 95 per cent or more when operated at temperatures between 700 and 950°C. However, in spite of the widespread use of the process, the precise nature of the transient species taking part in thc reaction at the gauze surface is still a matter of con- tention, as are the detailed mechanisms of rhodium and platinum losses from the gauze, or whether these volatilised elements partici- pate catalytically when in the vapour phase.


A large section of the paper deals with the various interrelated factors that contribute to the efficiency of conversion of ammonia to nitric oxide, many of which have been the subject of an extensive research programme on an experimental nitric acid plant in Johnson Matthey for a number of years. Such factors as gauze composition, make-up of the gauze pack and optimisation of number of gauzes are discussed, and the basis of current practice in the industry is outlined.

It is concluded that the best available system would appear to consist of a plant in which the reactants are well filtered, but in which the inevitable contamination of the leading gauzes is catered for by additional layers in the pack. Any concomitant extra metal loss may be reduced to a low level by the use of a catchment gauze system based on a gold-palladium alloy.

Pollution Control Greater awareness of environmental effects

has led to a demand for the control of emissions, in particular the coloured nitrous plumes, from nitric acid plants. The platinum group metals again feature promin- ently and are used almost exclusively as the catalyst in emission treatment on account of their high intrinsic activity, durability and resistance to poisoning. The Honeycat system, in which the catalyst is supported on a ceramic honeycomb, is now a well established technology and can effectively and economically reduce emissions to a low level.

The presentation of the paper, by Dr. J. A. Busby, was accompanied by a film showing the direct electron microscope observation of the movement of metal on the rhodium-platinum wire surface during ammonia oxidation, leading ultimately to the marked surface restruc- turing associated with used nitric acid gauzes.

A. G . K.

Thermocouple Reference Tables AN INTERNATIONAL STANDARD ACCEPTED

By P. I. Roberts Johnson Matthey Metals Limited, London

The accurate measurement of high temperatures made possible by the use of rhodium- platinum thermocouples depends upon the use of reference tables which are themselves not only accurate and reliable but are accepted throughout the world of science and technology. For many years differences were to be found between the tables issued respectively by British and American standardising bodies, but a move to eliminate this confusion and to provide internationally agreed tables was made jointly by Johnson Matthey and Engelhard Industries in 1965 in an approach to the British Standards Institution and the National Physical Laboratory. This led to a collaborative investigation by the National Bureau of Standards in Washington, the National Research Council of Canada and the N.P.L. and to the re-calibration of couples supplied by seven leading manufacturers. An account of this work was published in this journal in 1972 (I).

The resulting reference tables, based upon the 1968 revision of the International Prac- tical Temperature Scale ( IPTS-I~~S), were adopted and published in 1973 by the British Standards Institution as B.S. 4937 and in identical form by the National Bureau of Standards as Monograph 125, these replacing the older sets of tables (B.S. 1826 of 1962 and N.B.S. Circular 561 of 1955) which showed substantial differences, more particularly between N.B.S. 561 and the new tables (2).

The next move was to secure wider international agreement and so to promote the interchangeability of thermocouples and to eliminate a common source of error and confusion, but there has been some reluctance on the part of many of the major industrialised nations to amend their own standards until

such international agreement could be achieved. This was a matter for the Inter- national Electrotechnical Commission (IEC) based in Geneva and in 1974 a committee was formed for this purpose. Now an IEC Standard-384-1 “Thermocouples, Part I Reference Tables” has been issued. These tables are in agreement with both B.S. 4937 and N.B.S. 125, and the letter designation employed in those standards is confirmed:

Type S: 10 per cent Rhodium-Platinum : Platinum

Type R : 13 per cent Rhodium-Platinum : Platinum

Type B: 30 per cent Rhodium-Platinum : 6 per cent Rhodium-Platinum

The remainder of the standards cover the base metal combinations iron : copper-nickel, copper: copper-nickel, nickel-chromium : copper-nickel and nickel-chromium : nickel- aluminium.

The following countries represented on the IEC committee voted in favour of publication of this new international standard :

Australia Holland Sweden Austria Hungary Switzerland Belgium Israel Turkey Bulgaria Japan United Kingdom Czechoslovakia Poland United States

Republic of Of America France Germany South Africa Yugoslavia

This step forward towards international unification is of great importance, and it is to be hoped that all national bodies will now amend their standards-particularly those based upon the old N.B.S. 561-to fall into line with IEC 584-1. The general adoption of these tables will be of great value in eliminating a common sourcle of error and of confusion between workers in different


countries. A further advantage is that the seven thermocouple combinations, and these new values show a much smoother pro- should eventually be issued as Part I1 of the gression, providing an increased accuracy of 584-1 standard. interpolation. References

Further work is being carried out by an I T. J. Quinn and T. R. D. Chandler, I’htirlun? Metals Rev., 1972, 16, (I), 2-9 p. H. wells, platinrrm Metals K ~ ~ . , 1973, I,, (3), 96-97

IEC Technifai Committee ( 6 9 3 ) on a set of internationally acceptable tolerances for all

Tantalum Clad Rhodium-Platinum Thermocouples LARGE DECALIBRATIONS INDUCED BY UNFAVOURABLE COMBINATION OF MATERIALS

The robustness and resistance to mechanical and thermal damage displayed by metal sheathed thermocouples have prompted their use in many arduous industrial environments, where the conventional, alumina insulated, alumina sheathed devices display limited durability. Great care must be taken, however, in the design and construction of metal sheathed thermocouple probes in order to minimise thermoelectric instability. In particular, the materials of construction must be chemically compatible at the temperature of operation, and a recent paper by T. G. Kollie, W. H. Christie and R. L. Anderson ( J . Less Common Metals, 1978, 57, (I), 9-27) illustrates very clearly how an incorrect choice of materials can lead to substantial reaction- induced decalibrations.

During experiments conducted at the Oak Ridge National Laboratory, platinum: 10 per cent rhodium-platinum and 6 per cent rhodium-platinum: 30 per cent rhodium- platinum thermocouples alumina insulated and encased within a pure tantalum sheath, were heated at temperatures up to 1gjc”C in an atmosphere of pure helium. After only a few hours at temperature, decalibrations equivalent to -152“C, and - 11°C respectively were observed in the two assemblies. Subsequent metallographic examination and microprobe analyses showed that severe reactions had occurred at the interface between the alumina insulation material and the thermocouple wires, resulting in the presence of up to 27 atomic per cent aluminium in the thermocouple limbs.

It is well known (I) that platinum will react with most refractory oxides under conditions which maintain a low oxygen potential in the

surrounding environment, the driving force being the extremely high affinity of platinum for the metal released upon decomposition of the oxide. In the devices described in the Oak Ridge paper, the tantalum sheath itself would be expected to act as a continuous “getter” for oxygen and thus allow the platinum-alumina reaction to proceed un- hindered.

A Successful Combination If the same thermocouples were sheathed

with a material exhibiting little or no affinity for oxygen, then the oxide-platinum reaction becomes self stifling, in that the slightest tendency towards reaction raises the oxygen partial pressure in the surrounding environment to the equilibrium value. A practical embodiment of this argument is the 5 per cent rhodium-plarinum sheathed 6 per cent rhodium-platinum : 30 per cent rhodium-platinum thermocouple, which, when provided with an inert gas internal atmosphere, decalibrates by only --5“C, after 500 hours at a temperature of 1450°C (2). This combination of sheath and thermocouple resulted from a detailed consideration of material compatibility, high temperature strength and mechanical durability; and in recent years it has proved to be an accurate means of sensing temperatures in many industrial processes.

G . L. S.

References

A. S. Darling, G. L. Selrnan and R. W. E. Rushforth, Platinum Meiuls Rev., 1970, 14,

G. L. Selrnan and R. W. E. Rushforth, l’luiinurn Metals Rev., 1971, 15, (3), 82-89

(21, 54-60


Storing Hydrogen in the Solid State INTERMETALLICS CONTAIN PLATINUM GROUP METALS

Recent activity in the field of energy research indicates that hydrogen may par- ticipate to an ever increasing extent in future energy utilisation. For instance, hydrogen could be piped for domestic consumption, either being converted by fuel cells into electricity for lighting, or used directly as a heating and cooking fuel.

Many of these applications for hydrogen will require it to be stored in a more con- venient manner than at present. Solid state hydrogen storage, that is, storing hydrogen in a metal alloy that will absorb and desorb hydrogen to a high level, has attracted much attention in the literature in recent times.

Two new papers (1,2) have been published by workers at the Bell Laboratories, Murray Hill, New Jersey, which shed light on possible degradation mechanisms for storage compounds. The investigations were based on experiments on the properties of EuPd and EuRh,. I t was found that EuPd changed structure during hydrogen absorption although the europium remained divalent. EuRh, was found to be particularly interesting because although the initial absorption of hydrogen by the compound indicated a higher reversible capacity than LaNi,, this reversibility declined during cycling until the material became a stable hydride.

Although deterioration in the hydrogen capacity of other compounds has been observed, it has generally been associated with the presence of water or oxygen, which lead to the production of hydroxides or oxides. This EuRh, degradation mechanism appears to be intrinsic to the hydrogen absorption process.

Using Mossbauer spectroscopy the authors were able to characterise the europium environment of the compound before and after cycling. They considered the initial hydriding spectra showed evidence that the europium in hydrided EuRh, was in mole-

cular complexes or clusters similar to those found for europium in EuH,. Further cycling produced a spectra that contained a significant component of unhydrided material. The formation of a rhodium rich phase and a relatively stable EuH, phase was postulated to fit the experimental observations. Initial absorption is said to occur via the formation of a metastable ternary hydride:

zEuRh, + SH, -* 2EuRhZHs (a) the reaction being less exothermic than:

EuRh, + H, + EuH, + ZRh (b) It is postulated that reaction (a) occurs initially, with phase separation of the type shown in (b) virtually impossible due to negligible diffusion taking place at the temperature of absorption. After several absorption cycles, however, the lattice is severely strained by the volume changes involved, which enhances diffusion. This is accompanied by the comminution of the sample into a very fine powder, of which not all the particles are in good thermal contact with each other. As reaction (a) is exothermic, local heating can occur, leading to the possibility of diffusion and the formation of EuH,.

The authors were able to restore the original hydrogen absorption properties by vacuum annealing at 350°C for 5 hours, evidently allowing the rhodium to diffuse into regions of high europium concentration.

Although the degradation effects described above rely on the rapid dissociation of EuRh,, the authors suggest that the phenomenon may also exist in the LaNi, family of intermetallic compounds. The regeneration processes should be equally applicable in other cases where similar mechanisms are operable.

P. R. E. References

I R. L. Cohen, K. W. West and K. H. J. Buschow,

z K. H. J. Buschow, R, L. Cohenand K. W. West, Sold State Commun., 1978, 25, (9, 293

3- APPl- ph~3.3 1977,48, (121, 5289


Iridium Losses During Oxidation REACTIONS AT HIGH TEMPERATURES IN LOW-PRESSURE OXYGEN ATMOSPHERES

By Hermann Jehn, Reinhart Volker and Muhamed I. Ismail Max-Planck-Institut fur Metallforschung, Institut fur Werkstoffwissenschaften, Stuttgart, West Germany

Iridium reacts with oxygen at high temperatures forming volatile oxides, the evaporation of which considerably increases the iridium losses i n oxygen- containing atmospheres, when compared with high-vacuum conditions. This paper describes investigations carried out to determine the metal losses

from polycrystalline iridium discs, by means of a magnetic suspension balance, at low pressures and high temperatures. The results are presented and discussed, and a strong temperature and pressure dependence is noted.

At high temperatures the platinum metals and alloys are increasingly used as thermocouple pairings and as a crucible material for liquid glasses and oxides, that is for the growth of single crystals. In both fields iridium metal and iridium alloys have considerable advantages due to their high melting points and good physical and mechanical properties. They also show good chemical stability even in oxidising atmospheres. At low temperatures thin protective oxide films are formed' but at temperatures above about I I O O " ~ the oxides decompose and the metal surfaces remain bare. However, volatile oxides are formed and increase the metal losses when compared with the evaporation of the pure metal in high vacuum. In that temperature range the oxidation rates in air of the various platinum metals show differences up to about six orders of magnitude (1,2). Platinum and rhodium have the lowest metal losses, followed by iridium and ruthenium, while osmium has the highest losses. The high-temperature oxidation of iridium metal has only rarely been studied (2 to 7). In a recently published paper by Wimber et al, systematic investigations extended over a wider pressure and temperature range, 10- to 1.3 x105 pascals of oxygen and 1675 to

226ooC, have now been reported (7). In the present study the metal losses of

polycrystalline iridium in an oxygen atmosphere have been determined gravimetrically at high temperatures of 1500 to ZIOO'C and low pressures of 0.1 to IOO pascals of oxygen.

Experimental The experiments were performed under a

flow of 99.99 volume per cent oxygen in a high vacuum apparatus, shown schematically in Figure I . The pressures were adjusted by a needle valve and were measured by an ionisation gauge, and the temperature of the inductively heated specimen was measured by an optical micropyrometer.

The weight change of the iridium discs was determined by a suspension balance having an accuracy of I ~ N . The oxidation anneals were interrupted for weighing because the electromagnetic forces did not allow continuous weighing during the induction heating. The oxidation periods were chosen in a manner which gave reliable readings of the weight changes.

Polycrystalline iridium discs 10 mm diameter and I mm thick were employed as specimens, and before the experiments they were cleaned and then recrystallised and


degassed by a v a c u m heat treatment at 18oo0C for 15 minutes. When the same sample was used for different runs it was vacuum annealed, at 18oo0C for 10 minutes, before each series, to give defined starting conditions. An analysis of the impurities found in the samples is given in the Table.

Results The weight change of the iridium speci-

mens as a function of oxidation time is shown in Figure 2. I t can be seen that the linear weight loss strongly increases with increase- ing pressure, at a constant temperature of 2000°C; and with increasing temperature, at a pressure of I pascal. From these curves the volatilisation rates and recession rates, respectively, of iridium have been calculated. In Figure 3 these rates are plotted versus r/temperature. Each line in Figure 2 is represented by one point in Figure 3. The curves show a continuous increase with rising temperature and at lower pressures approach the straight line plot of the evaporation of the pure metal in vacuum. The temperature dependence of the oxidation

Impurities in the Iridium Disc Specimens

Element

Platinum

Rhodium

Palladium

Ruthenium

Iron

Nickel

Copper

Magnesium

Boron

Silver

Gold

Chrome

Weight, ppm

Platinum Metals Rev., 1978, 22, (3 )

520

280

220

25

60

20

20

10

10

6

5

<5

93

process lies in the range of 125 kJ/mol. Figure 3 shows that a marked increase of the iridium losses exists when it is annealed in oxygen atmospheres, which extends up- wards to several orders of magnitudes, especially in the lower temperature range. In the upper temperature range the increase of the iridium losses by the oxygen atmosphere is less pronounced.

Figure 4 shows the iridium weight loss plotted against the oxygen pressure. The pressure dependence follows the relation v a poa3 between I and IOO pascals and at temperatures between 1500 and 20oo0C. At lower pressures and at temperatures greater than 2000°C the recession rate becomes pressure independent, because here the pure iridium metal evaporation predominates. Between 1500 and 1900°C and at lower pressures the rate is proportional to the

pressure. In Figure 4 the pure metal evapora- direct conclusion can be drawn on the tion rate at 1900 and 2000°C is plotted mechanism of the reaction between oxygen additionally at the ordinate. and iridium. The weight change gives the

iridium losses due to the pure iridium metal Discussion evaporation together with the iridium com-

From the gravimetrical determination of ponent of the volatilising iridium oxides. The oxygen component is not determined because in the steady state between the oxygen sorption from the gas phase and the evaporation of the volatile oxides this part is con- tinuously compensated.

By mass spectrometric investigations (9) the oxides IrO,(g) and IrO,(g) have been detected by the Knudsen cell technique and partial pressures in the range of 10 pascals within the cell. The oxide evaporation from a free iridium surface in the non-equilibrium kinetically controlled process has not been investigated up to now as it has been done in similarly reacting systems, for example molybdenum ( IO), tungsten (I I) and rhenium (12). In analogy to the rhenium system the reactions between oxygen and iridium at high temperatures and low pressures resulting in the steady states between oxygen sorption and oxide evaporation can be described by a kinetic model based on the following assumptions (12). The chemisorbed

the iridium losses in the present work no


oxygen atoms can desorb as 0 atoms, as 0, photographically measuring the reduction molecules, and as oxide molecules (predo- of the wire diameter during the oxidation minantly IrO, and Ir03). All reactions take anneal. Both studies cover pressure range place in the adsorption layer and the oxygen atoms are mobile on the surface at the experimental temperatures. The total iridium loss vIr can be described by the relation:

Where kIIO2, kIrOs and k,, are temperature dependent rate constants of the volatilisation of I r02 , IrO, and Ir, respectively, and 0, is the oxygen coverage ( 5 , 12, 13). The oxygen is balanced by the absorption and desorption reactions, equalising their rates :

In the lowpressure range under consideration the kinetics of all processes are surface- controlled and neither true equilibrium states between gas phase and adsorption layer are established nor mass transfer in the gas phase or through a gaseous boundary layer near the surface have to be regarded, as in the case of high-pressure oxidation (7, 8).

The results of the present gravimetric investigation are compared in Figure 5 with those of Wimber et: a1 (71, obtained by



from about 0.1 pascal up to annospheric pressure, and temperatures from 1500 to 2260OC. In the overlapping pressure and temperature range the agreement i s good. Again it is evident that at low pressures the weight losses become pressure independent at high temperatures, when rhe weight losses are predominantly caused by the pure iridium metal evaporation, for exampIe at 2260,2110 and 2000'C with oxygen pressures less than 2, less then 0.2 and less than o a r pascals, respectively. Further oxjdatjon studies at very low

pressures, in the range 1.3 x 10-6 to 1.3 x IO-' pascals, are reported by Olivei (9, where the fraction of incident molecules pumped by an iridium surface is determined as a function of pressure and temperature. Assuming an

average composition of the volatile oxides of Ir02.5 the weight loss can be estimated from these values but the results obtained seem to be too high by about two orders of magnitude.

The theoretical treatment of the oxidation process at higher pressures is rather difficult (6 to 8) since in addition to the chemical surface reactions, eventually occurring equilibrium reactions, the mass transfer in the gas phase and natural or forced convection have to be taken into consideration. Specifically, the influence of the convection fluxes cannot be definitely determined due to geometrical parameters like shape and size of the sample and of the receiver. A theoretical treatment of iridium oxidation based on the diffusion of the evaporating species through the gaseous boundary layer is given by Wimber et a1 (6, 7). The strong influence of the sample dimen- sions is shown, for example, by Fryburg (8) studying the oxidation of platinum wires 0.29 to 2.2 mm diameter. Further difficulties may arise in an inert gas/oxygen mixture like air, where the inert gas pressure reduces the evaporation rate (14,15).

Finally, in Figures 6 and 7 the results of oxidation studies in air are compiled. Figure 6 shows the weight loss of iridium during oxidation at reduced pressures, 10 to 6 . 7 ~ 104 pascals, reported by Wimber et a1 (7). Compared with oxygen the iridium losses lie half an order to one order of magnitude lower. Figure 7 gives the iridium losses during the oxidation in the range of atmospheric pressure. A relatively fair agreement is obtained over the large temperature range (800 to 2260OC) taking into consideration the difficulties of measuring the very low weight losses at low temperatures, and the factors influencing the oxidation rate, which were mentioned above. In particular at temperatures below 2o0o3C the iridium losses are enlarged by several orders of magnitude when compared with pure evaporation in vacuum.

Muhamed I . lsmail has been on leave of absence from the University oJ Alexandriu, Faculty of Engineering, Alexandria, Egypt.

References I E. Raub, “Platinmetalle” (Platinum Metals) ;

in “Gase und Kohlenstoff in Metallen” (Gases and Carbon in Metals), E. Fromm and E. Gebhardt eds., Springer-Verlag, Berlin,

2 C. A. Krier and R. I. Jaffee, 3. Less-Common Metals, 1963~5, WJ411

3 J. C. Chaston, Platinum Metals Rev., 1965, 9, ( Z ) , 5 1

4 W. L. Phillips, Jr., Trans. A.S .M. , 1964, 57,

5 A. Olivei, J . Less-Common Metals, 1972, 29,

6 R. T. Wimber and H. G. Kraus, Met. Trans.,

7 R. T. Wimber, S. W. Hills, N. K. Wall and C . R. Tempero, Met. Tram., 1977, SA, (I), 193

8 G. C. Fryburg, Trans. Metall. SOC. A.I.M.E.3

9 J. H. Norman, H. G. Staley and W. E. Bell, 7. Chem. Phys., 1965,42, (3), 1123

10 ‘W. C. Steele, cited in J. C . Batty and R. E. StickneyJ. Chem. Phys., 1969, 51, (IO), 4475

11 P. 0. Schissel and 0. C. Trulson, 3. Chem.

IZ B. Weber and A. Cassuto, Surface Sci., 1973,

17 H. Jehn and E. Fromm, Z. Metallkunde, 1973,

1976, P- 636

( I h 3 3

( I ) , I I

1974.51 (71, I565

1965> 233, (II), 1986

Ph~s.7 1965,43, (2), 737

36, (I),81 . ..

- 64>15!>353 ILL E. Fromm and H. Tehn, Z. Metallkunde, 1976, - . - _ . .

67J (’)> 75 15 E. Fromm and H. Jehn, Freprints of the 9th

Plansee-Seminar, Reutte, Austria, 1977; High Temp.-High Pressures, in press

A Review of Fuel Cell Development As the industrial countries of the world

continue to search for satisfactory alternatives to their present sources of energy a timely review of twenty-five years of fuel cell development has been published (J . Electrochem.

Well supported by a bibliography listing 33 major titles on fuel cells and related subjects, and with 187 references from international literature, the review by K. V. Kordesch-formerly with the Union Carbide Corporation, and now at the Technical Uni- versity of Graz, Austria-covers a third cycle of interest in fuel cells, which is considered to start after the second world war. During this period numerous systems have of course been investigated and in many of them the properties of the platinum group metals have been utilised with advantage.

In the future, if the technology of fuel cells is better supported by basic scientific studies of the principles involved, further improvements in efficiency could result.

1978J 125J (3)> 77c-91c).

Platinum Metals Rev., 1978, 22, ( 3 ) 97

The Electrodeposition of Platinum and Iridium from Fused Salts AN ELECTROANALYTICAL STUDY OF THE REACTIONS

The electrodeposition of platinum from fused salt electrolytes has been successfully developed in the past few years and is being used increasingly, particularly because the deposits show better ductility and a freedom from porosity compared with those from aqueous solutions. A recent paper by the present writer ( I ) gave an account of the process developed in the Johnson Matthey Research Centre and described a number of its applications.

A further study of the process by William B. Harding of the Bendix Corporation, Kansas City, (z), carries our knowledge of electrodeposition from fused salts a little deeper as it is the first work on these systems in which electroanalytical methods have been applied to elucidate the chemical reactions involved. The work used specially purified melts, generally kept under glove box conditions to control closely melt oxidation.

Initial experiments with lithium chloride- potassium chloride eutectic melts at 450°C gave deposits which were always dendritic and non-adherent. Platinum and iridium could be added to this melt either as the salts K,PtCl, and KJrCl, or by electrolytic dissolution of a metal anode. The deposit from melts with both metals added was always pure platinum. Voltammetry showed that iridium was about IoomV less noble than platinum and would not be expected 10

co-deposit . Greater success was obtained with experi-

ments in the cyanide system. Three melt compositions were chosen, pure sodium cyanide, equal weights of sodium and potassium cyanides and equal weights of sodium cyanide and potassium cyanate. These enabled operation between 450 and 600°C.

Platinum was introduced into these melts using soluble anodes or by adding Pt(CN), or Na,Pt(CN),. The electroplating performance was unaffected by the melt used, cathode efficiencies from 60 to 80 per cent being obtained throughout, with anode efficiencies ranging from IOO to 275 per cent according to the melt oxidation rate. At low temperatures the sublimation of the cyanide was reduced and so was the decomposition of the platinum salt in the melt. The platinum content of an unused melt fell from I

per cent to 0.5 per cent over ten days, and then more slowly. This is taken as evidence for the reaction:

analogous to the thermal decomposition of PtCl,. I t was therefore recommended to use rhe cyanide-cyanate melt for a practical process because of its greater stability.

Iridium was also added to the melts electrolytically or as K31r(CN)6. Cathode efficiency fell rapidly to zero in melts containing cyanate or in cyanide melts after exposure to air. However, an efficiency of 15 per cent could be obtained by raising the melt temperature to 650°C and the current density to 4omAicm2. In pure cyanide melts containing 0.2 per cent iridium anode efficiencies of 100

per cent were reported and cathode efficiencies of 70 per cent, which fell after a period of use to 20 per cent. Higher current den- sities equated to lower cathode efficiencies and this appeared to be partly due to the formation of a passive layer of polymeiised cyanogen on the anode. The fall of the cathode efficicncy with time was believed to be due to the presence of an Ir(1V) complex formed by oxidation of Ir(II1) a t the anode. I t was proposed that future work should

ZPt(CN), Pt -L Pt(CN),


include the use of porous diaphragms to separate the anode and cathode in an attempt to eliminate these side reactions.

For alloy deposition, melts containing mixtures of the metals were prepared by the methods described. Although platinum is again more noble the metals will now co- deposit. Deposit composition was not constant in its thickness nor did it bear any relation to the melt composition except at high current density (zomA/cm2) when deposition was diffusion limited. Alloy deposition was not seen as a practical process unless the side reactions outlined for the individual metals could be controlled.

The deposits were described as being sound and coherent and with mechanical properties comparable to the wrought metal, but no

details of the deposit thicknesses obtained are given except in the case of platinum. Platinum formed columnar deposits with a visibly crystalline surface at 75 microns. Nodular deposits formed at greater thickness.

The carefully controlled experimental conditions used by the author of this work were previously recommended by him in his review paper (3) and the results obtained have done much to resolve apparent differences in the results of previous workers.

J. H. F. N.

References I J. H. F. Notton, Platinum Metals Rev., 1977,

2 W. B. Harding, Plating Surface Finish., 1978,

3 W. B. Harding, ibid., 1977, 64, (9), 48-55

21, (4), 122-128

653 ( 2 ) J 30-35

Recent Patent Literature on Emission Control Automotive Pollution Control Catalysts and Devices BY MARSHALL SITTIG,

Noyes Data Corporation, Park Ridge, New Jersey, 1977, 323 pages, $39

With catalyst systems now firmly established as the means for controlling exhaust emissions from motor vehicles sold in America, it is opportune for the technology associated with this major new development to be summarised and made available to future researchers in this and related fields.

In their series of Pollution Technology Reviews, the Noyes Data Corporation have followed their previous practice in publishing a book based upon a digest of United States patents in this instance granted in the years I970 to mid 1977. This period is particularly relevant as it spans the interval in which the major developments in catalyst and related technology were made leading to full commercial exploitation which started in 1974.

In an introductory chapter, the background to the problem of exhaust emissions from motor vehicles is described together with the legislation which has largely determined the systems which have been employed by the car industry for the control of exhaust emissions. These and other possible technical solutions are compared to complete a good summary of the subject.

The following seven chapters are concerned entirely with catalysts and the means for incorporating them into the exhaust system

of a motor vehicle. A chapter on methods for making catalyst supports in the form of pellets, ceramic and metal monoliths is followed by chapters on carbon monoxide/ hydrocarbon oxidation catalysts, NO, reduction catalysts and the advanced “Three Way” systems. Both base and noble metal catalysts that have been evaluated are in many cases described in detail. The review is completed with chapters on the overall con- verter systems and their components and control devices.

While, there is no detailed subject index, the combined contents and subject index are adequate to enable information on a particular aspect of the subject to be found without reading the complete book.

The book is likely to be of interest to those already working in this field as a source of reference information. T o others involved in catalyst research but not familiar with this particular application the book will provide an insight into new developments in support technology, the use of promoters to achieve specific activity goals and not least, the means for achieving high temperature stability and durability in conditions previously considered beyond the reach of catalyst technology.

G . J. K. A.


The Platinum Notebooks of William Hyde Wollaston By Melvyn C. Usselman Department of Chemistry, University of Western Ontario, London, Canada

Examination of the laboratory notebooks of W. H . Wollaston makes possible a complete reconstruction of his platinum researches, and valuable insights into the jinancial details of his platinum business, originally in partnership with Smithson Tennant, may be obtained. The leading role played by Wollaston in both the research and marketing aspects of the business is conjirmed. Although the use of platinum for laboratory ware and vessels for the concentration of sulphuric acid were important applications, the gunmakers provided the greatest market for malleable platinum over the years 1808 to 1820. The business ground to a halt in 1820 when Wollaston could no longer procure supplies of crude platinum.

In November of 1801 William Hyde Wollaston wrote from his newly purchased house at 14 Buckingham Street (now Green- well Street), London to his close friend at Bury St. Edmunds, Henry Hasted:

I do not publish for the gratification of idle curiosity but to friends I make no mystery of my intentions. I am partial to Chemistry; I have here room for a laboratory, and though many have spent fortunes in such amusements more have made fortunes by the same processes differently conducted. Is it impossible to mix rhe utile duk-if it be I have erred egregiously and may be ruined, but I have no fears at present. When I quitted the terra firma of Physic this was my sheet anchor, though not my only hope. I thought it possible that some- thing more eligible might offer, (therefore kept my own counsel till it was decided), nothing has appeared equally so, and I now hope that I am fixed for life. If I make L40 it is as good as most curacies and I may be content except- ing that there need then be no obstacle to my making 10 times as much ( I ) .

Wollaston’s decision to quit the practice of medicine at 35 years of age and devote his time to chemistry marked the beginning of a glittering scientific career, one that would place him in the forefront of English scientists. and bring him financial returns many times greater than his most optimistic estimates. Over the course of the first three decades of the nineteenth century, Wollaston published nearly 60 papers, each characterised by care-

ful, yet often highly imaginative, reasoning and rigorous attention to experimental detail. He made fundamental discoveries in physiology, optics, crystallography, clectro- chemistry, astronomy and botany, but his fame derives principally from his contributions to chemistry and metallurgy. Of his chemical researches, those on the platinum metals are of greatest general interest, for his isolation and characterisation of palladium and rhodium remain a highlight of early nineteenth-century analytical chemistiy, and the production of pure, malleable platinum represents a mile- stone in the history of powder metallurgy (2).

Despite the scientific achievements which placed Wollaston with Humphry Davy, Thomas Young, and John Dalton as the major figures of English science in the early nineteenth century, he has been little studied by historians of science. A significant factor contributing to this neglect was the disappearance of Wollaston’s laboratory notebooks and personal records shortly after his death in 1828. We now know that they passed on to his close friend Henry Warburton, who intended to publish a full biography, but was prevented from completing the task by an increasingly active political career. Late in the


William Hyde Wollaston 1766-1828

During a brilliant scientijk career, which followed an early retirement from medicine, Wollaston made fundamental discoveries in many diferent branches of science, although it is for his contribution to chemistry and metallurgy that he is principally remembered. During the course of his work he discovered palladium and rhodium, and put the production of malleable platinum on to a scientijic basis thus encouraging i ts use as an industrial material

nineteenth century, the Wollaston papers could no longer be traced. By immense good fortune, a collection of notebooks and documents was discovered in the Department of Mineralogy and Petrology of the University of Cambridge in 1949, and they were identified as the valuable Wollaston papers. The collection, now in the Cambridge University Library, was examined by L. F. Gilbert and a brief but fascinating description of the material was published (3). The collection includes twenty laboratory notebooks in Wollaston’s hand, eight of them devoted entirely to the purchase, purification, production and sale of platinum. One pertains to the metal palladium, and three contain miscellaneous experiments on a wide range of subjects, including early research on crude platinum. Although the notebooks contain no coherent, continuous record of his investigations, the wealth of detailed information contained in them will allow a reconstruction of Wollaston’s entire research programme from its inception about ISOO to his death in 1828, especially with respect to his efforts at rendering platinum malleable. In this paper I will present a brief summary of the contents of the platinum notebooks, together with

some of the most interesting information which they have yielded.

Included in the Cambridge collection is a notebook in Warburton’s hand containing references to the Wollaston notebooks under alphabetical headings. By careful study of the entries it is possible to correlate the notebooks in Warburton’s possession with those now in the collection-there appear to be none missing. In fact, there are two notebooks currently in the collection which were not referred to by Warburton. One of them, a short entry notebook containing both personal and scientific details, is not mentioned in Gilbert’s I952 paper, so it appears as if the collection is at least as complete as it was in Warburton’s time, and perhaps even somewhat expanded.

Platinum Purchases Full records were maintained in the note-

books on the acquisition and sale of platinum. Crude platinum was purchased at irregular


intervals from 1800 to 1819 from various suppliers. Over this period, 47,000 troy Ounces were purchased at a total cost of L ~ , I z ~ , at an average price of 3s. per ounce. The prices ranged from a low of 2s. 2d. for 684 Ounces in 1818 to a high of 4s. per ounce for 800 ounces in 1801. The prices paid by Wollaston include interest charges at 5 per cent of the purchase price, paid to the supplier from the time the order was placed until delivery. In one instance Wollaston did not receive the ordered platinum until 670 days after the order was placed, and delays of 200 days were the norm. This suggests that platinum was not immediately available in London, but was imported, likely from Jamaica, to which platinum smuggled out of Colombia-the major source at the time- found its way. Thus the average price of crude platinum given by Gilbert as 2s. rod. represents the average ordered price, a price slightly lower than the final cost to Wollaston given here (4).

Of the total amount purchased over the years at least 36 per cent was purchased from John Johnson, whose son, Percival Norton, was the founder of Johnson Matthey and Co Limited. I n a few instances (1806, 1807), Johnson is actually identified as the supplier, while in others (1x18)~ payments to him by draft on Wollaston’s bank account agree in date and amount with records of platinum purchases. It is quite possible that Johnson supplied much more than 36 per cent, for only 18 per cent of the total purchased can be definitely traced to other suppliers.

There has been some debate over the reason why purchases of platinum ceased in 1819, but it was certainly not due to lack of demand, which remained strong. Evidence in the notebooks suggests that Wollaston could no longer purchase crude platinum at a price he felt reasonable. There are notes which reveal that he sought to purchase crude platinum in the early 1820s in Jamaica and Colombia. The request for platinum in Jamaica was made on Wollaston’s behalf by a Mr. Hibbert to Messrs. Taylor and Simpson of Kingston,

who replied by letter on June 12, 1820. Upon enquiring amongst the Spaniards we

find that this article [platinum] has never been brought to this Island, but in very small Quantities and from the Information we have yet received, we have not been able to ascertain that the Quantity can be materially increased by offering an adequate encouragement for its import ( 5 )

Presumably, the amounts brought to the island acknowledged by the Spaniards represented the legal imports, for there is much evidence that Jamaica was the source of a great deal of smuggled platinum in the early nineteenth century. On a piece of paper in one of the notebooks, Wollaston wrote:

By a letter from Mr. Henderson English Consul General at Bogota in his enumeration of articles prohibited to be exported is Platina under penalty of loss of metal and also a fine of 50 dollars per pound (6).

I n a different notebook, Wollaston dates the prohibition as November, 1824.

Although Wollaston could not obtain platinum, his competitors in the platinum vessel business, the French, had ample supplies, for about 1819, Jean Brkant, assayer of the Paris mint, was given permission by the Spanish Government to process the nearly 30,000 ounces of crude platinum held by Spain since late in the eighteenth century (7). With such a large amount of crude platinum at their disposal, the French quickly began producing platinum vessels, thus ending Wollaston’s monopoly in the market. An entry in one of the notebooks reads:

Feb., 1819. I understand from Mr. Tennant that [platinum] retorts have been made in Paris of about 30 gallon capacity and weighing about 900 ounces at 15 shillings per ounce (8).

Thus it appears that the lack of crude platinum in England in the early 1820s was the determining factor in the cessation of Wollaston’s platinum business, and French manufacturers gradually moved to meet the demand for malleable platinum.

Partnership with Smithson Tennant The account books present in the collection

reveal that Wollaston formed a partnership with Tennant in 1800, a collaboration un- announced and unsuspected at the time. The


two originally agreed to share the cost of all platinum, chemicals and apparatus, and to divide the income evenly. The account books from 1800 to 1815 (the year of Tennant’s death) confirm that Wollaston was by far the most active of the two. Up to February 22, 1815, the gross expenditures by the two men had totalled E8,334, of which Wollaston had contributed L ~ , o ~ o . The leading role played by the younger Wollaston is even more dramatically illustrated if the amount spent on the purchase of crude platinum is excluded. Over the 15 year period of the partnership, a total of E3,998 was paid out for chemicals and apparatus. Of this, only E74, or z per cent, was contributed by Tennant. The in- equity of this situation was partially rectified early in 1809, when the two men came to a new agreement which stipulated that Wollaston was to

Fig. 1 An entry in one of Wollaston’s account books detailing income for the$rst half of 1807. The entry for January 27 indicates that, of El00 brought in, Cary retained 6110 as commission, 6125 went to Tennant, and 6165 to Wollaston. Wollaston’s larger share is proportional to his greater expenditures. Entries on March 4 , May 4 and July 4 represent payment by Philip Sandmann f o r the platinum boiler purchased early in 1806. The totals rejlect accumulated income from January 1, 1800

receive some payment for platinum sold before division of the profit. From the account books there is evidence that from April I, 1809 onwards Wollaston received 10 per cent of the profits before division. Al- though the notebooks provide much evidence for the diminishing role played by Tennant, there is little doubt that he rendered much assistance in the early years of the partnership, and it is quite possible that Wollaston might not have chosen to pursue chemistry as a career without the initial financial and intel- lectual support of Tennant. Many more details of the chemical partnership of these two men could be cited, but a thorough treatment is beyond the scope of this paper.

Platinum Sales From the crude platinum processed over

the years, a little over 38,000 ounces of purified, malleable metal were sold at an average price of nearly 16s. per ounce, for a total income of approximately E30,ooo. Of this amount roughly half was accumulated

during Tennant’s lifetime and was shared by the two men, and the remaining half was Wollaston’s alone. Thus Wollaston’s profit from the platinum business can be estimated as close to E14,000, and Tennant’s as E3,000, after expenditures have been deducted from income. Wollaston obviously became a wealthy man through his platinum business. The ultimate success of the endeavour, however, was not foreshadowed in the early years of the partnership, for only in 1805 did yearly revenue begin to exceed expenditure, and it was not until 1809 that the entrepreneurs began to show an overall profit from the platinum operation.

Information concerning the commercial market for platinum is also available in the notebooks. Nearly all the platinum was sold in ingot form by William Cary, a respected London instrument maker, who received 10 per cent of the selling price as commission. Cary’s selling price was generally 17s. per ounce, which yielded Wollaston nearly 15s. per ounce after the vendor’s deduction, see


Fig. 2 A nearly complete record of the Troy weights of platinum sold personally by Wollaston from 1805 to 1818. The larger weights were used for the construction of boilers, and the smaller for varioris accessories, such as siphons, etc. The amounts sold to Johnson i n 1810 were for the construction of a boiler for Pepper, one of the few boilers not fabricated by Wollaston or Kepp

Figure I. One of the notebooks records the weights of platinum delivered to Cary, and from the nature of the entries it is possible to determine the use to which the platinum was put (9). Of the nearly 30,000 ounces sold by Cary, 19,000 ounces are denoted as of “touch- hole” quality. As mentioned by Gilbert, the use of platinum for the touch-holes or orna- mentation of guns began in England about I 805-Wollaston’s first sale of “touch-hole’’ platinum was made in 1806-and it is obvious that gunmakers were by far the largest con- sumers of malleable platinum (10). In addition to the amount specifically noted as

touch-hole” ingots, nearly 9,000 ounces are referred to simply as “bars”, or “ingots”. Of this total, 8,000 ounces were sold during the years 1819 to 1821 when no ingots were specifically referred to as of “touch-hole”

“

quality, and consequently were in all likeli- hood also sold to gunmakers, since there is no evidence that the gunmaking market suddenly disappeared in 1819. If this assumption is correct, then 27,000 ounces, or 70 per cent of the total weight of platinum sold, was consumed by the gunmaking industry. In retrospect, this figure should not be too surprising, for even at 17s. per ounce malleable platinum was only one-fifth the cost of gold, which continued to be employed in the finest firearms for touch-holes and dccoration. The remaining 3,000 ounces sold by Cary were put to use for crucibles, balance pans, evaporating dishes, wire and other miscellaneous items.

In addition to the amounts sold by Cary, Wollaston disposed of 8,000 ounces himself, all but 625 ounces of which were used in the

Platinum Metals Rev., 1978, 22, (3 ) 1 04

manufacture of boilers for the concentration of sulphuric acid, see Figure 2. Over the years 1805 to 1818, sixteen boilers were fashioned and sold. They ranged in weight from 320 to 470 ounces, and sold for A300 to A4oo. The selling price was based on the weight of platinum employed, usually at 15s. per ounce, and the costs of construction were added on. For all but the first few, Wollaston had the boilers made to his specifications by local metal- workers, principally John Kepp of Chandos Street, who fabricated the last ten boilers.

An interesting entry in a notebook devoted primarily to boiler construction attests to the value of the platinum boilers to the nianufac- turers of sulphuric acid (11). The entry, dated February, 1816, states that at Charles Tennant’s acid works in Glasgow:

They boil off 3 times per day [oil of vitriol] and turn out 50 bottles of 150 Ib per week. They reckon to save the prime cost [of a A300 boiler] in 2 years, oil of vitriol being now at 3as. to 39s. per lb.

Tennant’s production of nearly four tGns of of per week was no doubt made possible by his use

which had been purchased from Wollaston, and one from Sandmann,

Fig. 3 A record of some of vollaston’s earliest attempts at consolidation (incorrectly labelled ‘casts’) of his partially purified plat inum in 1801. The unsuitability of the product is evident from the frequent mechanical fai lure of the ingots during forging

of five platinum boilers, four of

who had used it for ten years after purchasing it from Wollaston in 1805.

Demand for boilers remained strong in the early 1820s. The notebook lists seven orders for boilers which remained unfilled, due, as noted earlier, to Wollaston’s inability to obtain the 4,000 ounces of crude platinum required.

The Production Process The chemical analysis of the crude platinum

by Wollaston and Smithson Tennant which was carried out in the years 1801 to 1803 and

Platinum Metals Rev., 1978, 22, (3 )

resulted in the isolation and characterisation of the metals osmium, iridium, rhodium and palladium is now widely recognised as a brilliant example of early nineteenth-century analytical chemistry. There is sufficient data in the notebooks to reconstruct Wollaston’s meticulous, and often frustrating, analysis of the aqua regia-soluble fraction of the crude platinum, but the details must wait for a future paper. I t is perhaps sufficient to say that he was plagued initially by the same problems as his predecessors. After the

105

oil of vitriol

platinum was precipitated from solution as ammonium chloroplatinate, (NH,),PtCl,, and ignited to obtain a somewhat purified spongy metal, the platinum was consolidated under pressure, and forged. The earliest ingots produced frequently cracked on hammering or blistered badly on heating, see Figure 3. Wollaston at first attributed the source of such difficulties to impurities, and refined his purification technique to minimise the inclusion of base metals and the newly discovered platinum metals in the spongy precipitate. Even with improvements in the chemistry of the process, an inconsistent product was frequently obtained. As a consequence, Wollaston directed his attention more to the metallurgical aspects of the process, and improved it to a point where a consistently malleable product was the rule. Only by about 1808 could Wollaston con- fidently market platinum with the mechanical properties required by the purchasers, and the business then began to prosper rapidly.

In general, the crude metal purchased by Wollaston contained roughly 75 per cent platinum, 16 per cent iron, 3 per cent copper, 3 per cent sand, 2 per cent osmium and iridium, and I per cent rhodium and palladium. The processing began and continued over the years in 16 to 30 ounce batches, and Wollaston early calculated the average cost of processing as 2s. per ounce. This, coupled with the 3s. per ounce paid out for platinum,

made Wollaston’s expenses 5s. per ounce. Consequently, at a selling price of 15s. per ounce, Wollaston turned a considerable profit, but not an unreasonable one when all the hours required for the purification and forging are considered.

Some Remaining Questions The notebooks discussed here provide a

wealth of information on the technical aspects of Wollaston’s platinum researches, information which is of great interest to the student of chemistry and metallurgy. However, there is a paucity of information on the broader aspects of Wollaston’s endeavour. Why did Wollaston and Tennant guard so carefully the secret of their partnership ? Why were the details of the platinum process only published in 1828, eight years after Wollaston had brought the business to a halt ? Did Wollas- ton’s success stimulate the pursuit of chemistry in the early nineteenth century, or did his retention of information hinder the development of the English platinum industry?

These and other questions intrigue historians of science and I am optimistic that answers will soon be forthcoming. Acknowledgements

This research was made possible by a grant from the Canada Council.

The photographs are reproduced through the courtesy of the Syndics of Cambridge University Library, and I am much indebted to Mr. A. E. B. Owen of that library for his continued kind assistance.

References

I Letter from W. H. Wollaston to H. Hasted, November 16, 1801. Copies of the Wollaston: Hasted letters are in University College Library, London; the originals, once in possession of Wollaston’s descendants, can no longer be found

2 (a) A history of platinum, and Wollaston’s place in it, has been admirably and capably compiled; see Donald McDonald, “A History of Platinum”, Johnson Matthey, London, I 960 (b) A brief assessment of Wollaston’s platinum researches has also been published by the same author: D. McDonald, “William Hyde Wollaston; the Production of Malleable Platinum”, Platinum Metals Rev., 1966, 10, (3), 101-106

3 L. F. Gilbert, “W. H. Wollaston MSS at Cambridge”, Notes and Records Roy. SOL. Lond., 1952, 9, 311-332

4 Ibid., 318 5 Wollaston MSS, Cambridge University

6 Wollaston MSS, note enclosed in notebook F 7 Op. cit. (Ref. 2(a)), 136 8 Wollaston MSS, notehook H, 57. The

Tennant referred to is Charles Tennant, a Glasgow acid manufacturer who purchased four platinum boilers from Wollaston

Library, letter enclosed in notebook F

9 Wollaston MSS, notebook I 10 Op. cit. (Ref. 3), 319 I I Wollaston MSS, notebook H, 4


ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES The Combined Reduction of Oxides by Carbon in the Presence of Metals of the Platinum Group. Parts 1 and 2 D. OTT and c. J. RAuB, Metall, 1978,32, (I), 35-41 ; (2),140-144 The reduction of Cr, Si, Al, Mg and Zr oxides by C in the presence of Pt metals, and the effects of Pt, Pd, Ru and Rh on the reduction of Cr,O, and SiO, by C in vacuum are discussed. From 600- IOOO"C Pd and Pt strongly enhance reduction by the formation of solid solutions and/or Cr and Si carbides, but Ru and Rh have little influence. The influence of Pt, Pd, Rh and Ru on the reduction of A1,0,, ZrO, and MgO by C in a vacuum is also discussed.

Competitive Hydrogenation of Benzene and Toluene Dehydrogenation of the Corre- sponding Naphthenes over Platinum Wire J. F. AKYURTLU and w. E. STEWART, J. Catalysis, 1978) 511 (I), 101-107 The relative rates for benzene and toluene hydrogenation on a Pt wire catalyst were examined at 600-672K and 4.4-24.9 atm. The catalyst activity declined during processing but was restored by H, treatment. Kinetic and equilibrium constants and the common stoichiometric number for the reactions are given. The ratio of the rates during a catalytic deactivation implies that the two reactions use the same number and kinds of sites in their controlling steps.

Structure of the Rare-Earth-Platinum Com- pounds R7Pt,, R,Pt, R,Pt and RPt J. LE ROY, J. -M. MOREAU and D. PACCARD, Acra CVst. B, 1978,34, (I), 9-13 Rare-earth-platinum compound structures are identified. R,Pt, compounds (R =La, Ce, Pr, Nd, Sm, Gd) crystallise with ThjFe3 type structure. PrPt and NdPt have a high temperature modifi- cation corresponding to the CrB type. R,Pt and R,Pt, crystallise with the N,Si and Mn,Si, structures, with R = Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y for both structures.

The Ordered Phase Fields of the Iron- Nickel-Platinum Equilibrium Diagram

J . M u m . Sci., 1978~13, (3), 499-504 The approximate limits of the ordered phases in the Fe-Ni-Pt system at 600°C were examined. Continuous solid solutions form between FePt and NiPt, and between Fe,Pt and Ni,Pt, at temperatures below the relevant cxitical temperatures,

G. T. STEVENS, M. HATHERLY and J. S. BOWLES,

but not between FeNi, and Ni,Pt. Two tetragonal phases were found in alloys containing 60 at."4 Pt. Since high magnetic hardness of ordered Co-Pt alloys is due to small ordered particles, the ability to produce similar structures in Fe-Ni-Pt alloys can be used to test this, and may lead to the discovery of alloys with similar properties.

A Low-Temperature X-ray Diffraction Study of Pd and Some Pd-H Alloys H. w. KING and F. D. MANCHESTER, J . Phys. F: Metal Phys., 1978,8, (I), 15-26 Measurements of the lattice parameter of Pd from room temperature down to 4K showed it to be a smooth function of temperature over this range. Studies of the X-ray diffraction patterns of some P-phase Pd-H alloys, and a mixed ( a + p) phase alloy, and of their dependence on cooling through the 5oK region showed no visible effect on the state of the Pd lattice.

Hydrogen Sorption by Palladium-Gold Wires

Faraday Trans. I , 1978~74, ( 2 ) ) 223-236 Hydrogen sorption was studied on Pd-Au wires prepared in ultra high vacuum, at a Hz pressure of 6.25pPa and wire temperatures of 100, 150, 200 and 304K. The initial sticking coefficient for Pd at IOOK was 0.16, falling to 0.006 at a fractional monolayer coverage 0 =0.8. The activation energies decreased sharply with coverage to a value of -2ok Jimol. H, sorption increased slightly from Pd to goPd-roAu, decreasing sharply towards zero at 4oPd-6oAu.

Isothermal Section of a Phase Diagram of the System Ag-Pd-Dy at 600°C A. G. SLAVEV, v. K. PORTNOI, M. v. RAEVSKAYA and E. M. SOKOLOVSKAYA, Vest. Moskov. univ., Ser. Khim., 1977,18, (6), 695-698 The characteristics of phase equilibrium in the system Ag-Pd-Dy were studied at 600°C by microanalysis, by hardness and microhardness and by X-ray spectroscopy. The formation of a new ternary phase was observed. The growth of the Pd content was found to increase alloy hardness.

The Energy Loss Spectra and Auger Spectra of Palladium Hydride and Palladium Glasses L. Y. L. SHEN, H. S. CHBN, R. C. DYNES and J. P. GAR NO,^. Phys. Chem. Solids, 1978~39, (I), 33-38 The Auger and energy loss spectra of Pd hydrides and Pd glasses, Pd-Ni-P and Pd-Cu-Si, were measured. The energy loss spectra of these amorphous and crystalline state alloys are similar and the surface compositions of Pd glasses are in good agreement with their bulk compositions.

D. D. ELEY and E. J. PEARSON, J . Chem. SOC.,


Strong Metal-Support Interactions. Group 8 Noble Metals Supported on TiO, s. J. TAUSTEX, s . c. FUNG and R. L. GAR TEN,^. Am. Chem. SOC., 1978, 100, ( I ) , 170-175 The reduction of noble metals on TiO, at 200°C produces well dispersed metals which exhibit the capacity to sorb both H, and CO. Reduction of the same materials at soo"C, however, decreases H, and CO sorption to near zero. Loss of this sorption capacity is not due to metal agglomera- tion. The effect for well dispersed metals is evidence for a chemical interaction between the noble metal and its support. This interaction is examined in terms of metal-metal bonding between noble metal and Ti cations.

Adsorption of Nitrogen on Iridium J. -M. DEROCHETTE, Phys. Status Solidi A, 1978, 45, (I), 163-169 Adsorption of N, on perfect and stepped planes of Ir, carried out by a high sensitive probe hole technique at 77K, was studied. Positively charged N, is found on the (111), (100) and (311) faces, while a negative N, film is found on all the other surfaces examined. For the (110) plane the two films occur, first positive, then negative, and this is attributable to the face surface structure.

Adsorption and Desorption of Ammonia, Hydrogen, and Nitrogen on a Ruthenium (0001) Surface and Electron Beam Induced Effects R. L. DANIELSON, Washington State University Ph.D. Thesis, 1977 The adsorption and desorption of NH,, H, and N, on a RU(OOOI) surface were investigated by AES, LEED and thermal flash desorption. NH, adsorbs at IOOK into two weakly bonded molecular states, but not at room temperature. At 4ooK it adsorbs with activation energy of o.52eV and forms a (2x2) LEED pattern. Evidence that dissociation of NH, and diffusion of N atoms into the bulk also occurs is presented. H, adsorbs at IOOK and desorbs with 2nd order kinetics between 350-450K. N, does not adsorb on RU(OOOI). Maximum N, coverage was <2 "b of a monolayer.

CHEMICAL COMPOUNDS Reactions of Acetylene with Noble-Metal Carbonyl Halides. 11. Insertions into the Chloro-Platinum Bond F. CANZIANI, L. GARLASCHELLI and M. c. MALATESTA, J . Organometal. Chem., 1978,146, (2), 179-196 The reaction of dichlorodicarbonylplatinum with ROOCC=CCOOR(R =CH,, C,H,) in benzene and toluene gives carbo;lyl chloro( 1,2-trans-dicar- boalkoxy-2-chloroetheny1)Pt compounds by insertion of the active acetylene molecule into the Pt-Cl bond. These chelated stable square-planar vinyl derivatives react with neutral donor ligands to give simple o-alkenyl derivatives.

A Novel Rutheuium Bronze: KRu,08 M. WILHELM and R. HOPPE, Z . Anorg. Aligem. Chem., 1978,438, (1),90-96 Crystal structure studies of a new compound KRu,O, prepared as black rod-shaped crystals showed it to crystallise tetragonal in the space group C:b-~4:m, with a=9.88 and c=3.12& c/a=o.316and Z=2.

ELECTROCHEMISTRY The Electrocatalytic Reduction of Nitrogen Compounds. Part 11: The Influence of the Electrode Material on the Electrochemical Reduction of Nitrite J. F. VAN DER PLAS and E. BARENDRECIIT, Rec. Trav. Chin?., 1978~97, (3), 65-69 The electrochemical reduction of nitrite was studied at Pt, Ir, Rh, Nb, Pb and Ta electrodes in 7.5M H,SO, solutions. The results showed that the thin oxide films on the Pt, Ir and Rh did not interfere with the reduction process. However, a thick oxide layer, as on Nb and Ta, positively shifted the reducing potential by several hundreds of mV. It is concluded that poisoning of the active surface area of the electrodes by Oe changes the reduction mechanism of nitrite.

The Platinum/Platinum Oxide/Carbonate/ Carbon Dioxide Electrode at 350°C in Fused Potassium and Sodium Nitrates A. G. KEENAN and T. R. WILLIAMSON, 3. Phys. Chem.,

A preoxidised Pt electrode responds reversibly to the electroactive species CO, and COi- in pure Na and K nitrate melts at 350°C. The electrode reaction was Pt + CO:-= PtO + CO, + 2e-. Standard potentials for this system with respect to a AglAg nitrate reference electrode in the pure solvents are given. For work involving the solute COi-, the system may be exposed to the ambient atmosphere which provides the necessary equilibrium concentration of CO1.

Study of Platinum Electrodes by Means of Electrochemistry and Low-Energy Electron Diffraction. Part 11. Comparison of the Electrochemical Activity of Pt(100) and Pt(ll1) Surfaces A. T. HUBBARD, R. M. ISHIKAWA and J. KATEKARU, J . Electroanal. Chern. Interfacial Electrochem., 1978~86, (2), 271-288 LEED patterns were obtained for Pt(Ioo), Pt(rr1) and polycrystalline electrodes before and after exposure to aqueous IM H,S04 and linear potential scan voltammograms were recorded. The maximum amount of chemisorbed H, correspon- ded to one H atom per surface Pt atom. The Pt (100) [IXI], Pt(r I I) and the polycrystalline electrode surfaces appeared to withstand prolonged voltammetric characteristics at -0.2 to 1.2 V vs. a calomel reference electrode.

1978382, (I)> 46-49


Investigation of the Surface of Platinum Paste Electrodes N. H. TURNER, J . Electroanal. Chem. Interfacial Electrochem., 1978,87, (I), 67-72 AES and X P S studies of electrodes made from a Pt paste on stabilised zirconia showed the presence of C, O,, Ag, S and chlorine in addition to Pt. The results showed the existence of Pt oxides together with metallic Pt.

The Effect of Electrolyte Concentration on the Catalytic Activity of Platinum for Electrochemical Oxygen Reduction in Phos- phoric Acid H. R. KUNZ and G. A. GRUVER, Electrochim. Acta, I978,23, (3), 219-222 Catalytic activity of Pt supported on C for the electrochemical reduction of 0, in HJ'O, was studied as a function of temperature (up to 191°C) and electrolyte concentration. The exchange current decreased with an increase in electrolyte concentration from 88-105 wt.Yo. The activation energy was --zzkcal~mole and independent of electrolyte concentration from 85 to 105 wt.O:.

Use of the Coulometrically Measured Amount of Adsorbed Hydrogen to Determine the Active Surface Area of Platinum for the Electro-Oxidation of Iron(I1) T. C. FRANKLIN and R. GRAVES, Surface Technol., I978,6, (9,347-359 The kinetics of the electron transfer between Fe(I1) and bright Pt electrodes was studied in 2N H2S04 and in H,SO, containing azide, bromide, chloride, oxalate, thiocyanate and tetrafluorobor- ate ions. Chloride, bromide and azide ions func- tioned only as blocking agents for the electron transfer reaction. The oxolate increased the measure current by forming an Fe(II1) complex which increased the desorption rate of the oxalate from the electrode, thus cleaning the electrode surface.

ELECTRODEPOSITION AND SURFACE COATINGS The Behaviour of Electroplated Noble Metal Coatings in Different Atmospheres u. MAYER, Metalloberfliiche, 1978,32, (I), 3-7 Electroplated deposits of Ru, Rh and Pd and of 99.89; Au, Au alloys (7596 Au, Cu, Cd and 6705 Au, Cu) with and without a covering of o.5Fm hard gold (sandwiches) were exposed to several natural and artificial atmospheres. The corrosion resistance of the sandwiches is nearly comparable to the resistance of high purity hard Au deposits. The corrosion behaviour of electrodeposited Ru, Rh and Pd depends on the test atmosphere. Pd is highly stable in artificial atmospheres. No single laboratory atmosphere can predict the long term tarnishing of noble metal electrodeposits.

HETEROGENEOUS CATALYSIS Effects of Platinum and Palladium Impreg- nation on the Performance and Durability of Automobile Exhaust Oxidising Catalysts J. C. SUMMERS and L. L. HEGEDUS, J . Cata&sis, 1978,

The performance and durability of noble metal: A1,0, oxidation catalysts are influenced by the relative location of the metals along the radius of the pore catalyst pellets. Five Pt and Pd containing catalysts were prepared by varying the metal distribution along the radius of the catalyst pellets. The catalysts were either poisoned or sintered. Improvements in steady-state and light- off performance occurred when the catalyst had an outer shell of Pt and an inner shell of Pd.

Activity of Platinum-Palladium Catalysts in the Dehydrogenation of Cyclohexane

and I. P. STREMOK, Neftekhimiya, 1978, 18, (2), 178-181 X-ray and spectroscopic studies of the catalytic activity of supported Pt-Pd catalysts prepared by the impregnation of y-Al,O, supports by aqueous solutions of H,PtCl, or PdCl, (containing 0.6 wt.% metal in total) were carried out during dehydrogenation of cyclohexane in a flow reactor at 250'C. The rate of dehydrogenation over catalysts containing s;50 wt.O/b Pd-Pt alloys was found to be the same as over 0.6 wt.o/, Pt:AI,O, catalysts. The results showed the formation of Pt and Pd solid compounds on the surfaces of the catalysts.

Catalytic Dehydrogenation of Reducing Sugars in Alkaline Solution at Ambient Conditions. Transfer Hydrogenation of Fruc- tose G. DE WIT, J. J. DE VLIEGER, A. C. KOCK VAN DALEN, A. P. G. KIEBOOM and H. VAN BEKKUM, Tetrahedron Lett., 1978, (IS), 1327-1330 In an alkaline medium under ambient conditions in the presence of transition metals, aldoses can be converted to their sugar acids with high selectivity and with production of H,. Glucose gave excellent results when either sod Pt.'C or 5" ; RhjC was used as the catalyst.

Effects of Mn Deposits from RlMT on Auto- motive Catalysts in the Absence and Pre- sence of Other Fuel Additives K. OTTO and R. J. sULAK, Environ. Sci. Technol., 1978,12, (2), 181-184 The chemical effects of deposits from methyl- cyclopentadienyl manganese tricarbonyl(MMT) on three-way catalysts containing Pt and Rh were investigated. Automotive exhaust emissions were simulated by burning isooctane and M M T and /or other fuel additives were introduced. Two formu- lations on monolithic supports did not show any

51, (2), 185-192

N. S. KOZLOV, L. YA. MOSTOVAYA, M. V. ZARETSKII


chemical poisoning beyond that caused by the same fuels without MMT. M M T had no effect on H,SO, formation over these catalysts.

Hydrogenation of Acetylene in Excess Ethyl- ene on an Alumina-Supported Palladium Catalyst at Atmospheric Pressure in a Spin- ning Basket Reactor w. T. MCGOWN, C. KEMBALL and D. A. WHAN, J . Catalysis, 1978, 51, (2), 173-184 The hydrogenation of acetylene in the presence of ethylene and CO was investigated in a spinning basket reactor on a supported Pd catalyst. The rate of acetylene disappearance was controlled by pore diffusion at low acetylene concentrations. In the non-diffusion controlled region the reaction of acetylene was first order in H,, and the rate of ethane formation was independent of both ethylene and acetylene pressures.

Catalytic Cigarette Filter for Carbon Mon- oxide Reduction D. R. ROWE and w. G. LLOYD, J. Air Polluz. Contr.

The efficiency of a Pd(II)/Cu(II) catalyst as a cigarette filter to reduce CO levels in cigarette smoke was studied. This works by effectively oxidising CO to CO, via Pd(I1) chloride which is reduced by CO to Pd(O), then being reoxidised to Pd(I1). The catalyst was supported on 14/28 mesh Al,Oa. The catalyst removed over 900); of the CO present in the cigarette smoke, and such a catalytic filter could reduce CO lung exposure by from 15 to 20 ppm. CO removal is improved by increased catalyst and longer exposure times.

Dehydrogenation of Isopropyl Alcohol on Membrane Catalysts from Binary Alloys of Palladium with Ruthenium or Nickel N. N. MIKHALENKO, E. v. KHRAPOVA and v. M. GRYAZNOV, Neftekhiwziya, 1978,18, (2), 189-192 The effect of composition of membrane catalysts made from binary alloys of Pd with Ru or Ni, and their preliminary treatment, on their catalytic activity was studied in a flow reactor during the dehydrogenation of isopropyl alcohol. The mem- branes were made of Pd foils, containing 5.5 wt. :d Ni or either 6.8, or 10 wt.04 Ru, on which a Ru layer I pm thick was electrochemically deposited. Pd and 10 wt.ybRu-Pd alloy catalysts were found to be the most active.

Palladium Catalysed Amine Exchange Reac- tion of Tertiary Amines. Insertion of Palla- dium(0) into Carbon-Hydrogen Bonds

Chem. SOC., 1978,100, (I), 348-350 A novel Pd catalysed exchange reaction of tertiary amines possibly involving an initial insertion of Pd into a C-H bond adjacent to the N,, is described. This leads tg a highly active intermediate iminium ion complex.

Ass., I978,28> (3)3 253-255

S.-I . MURAHASHI, T. HIRANO and T. YANO, 3. Am.

Selective Hydrogenation of Heptyne-1 and Its Mixture with Hexene-1 on Pd/BaSO, D. v. SOKOL'SKII, v. A. SHOSHENKOVA and N. P. TRUKHACHEVA, Zh. Priklad. Khim., 1978, 51, (2), 409-412 Hydrogenation of acetylene-heptyne-homologues and their mixture with ethylene-hydrocarbons- hexene was carried out over 504 mole PdiBaSO, catalyst and 5"/, PdOlBaSO, in 960.6 mole ethanol,

.and the selectivity of the reaction after addition of CdSO, into the system was measured. The presence of CdSO, increases the selectivity ofthe hydrogenation of heptyne-r to heptene-I and the adsorption of Cd cations depresses the migration of double bonds on Pd/BaSO, catalysts. It is concluded that the addition of the optimal amount of CdSO, allows a strong selective release of hexene-r ( 9 0 ~ ~ ) from heptyne-1 (1004).

Hydrogenation of Acetylene over Supported Metal Catalysts. Part 2. Ll4CC] Trace Study of Deactivation Phenomena A. S. AL-AMMAR and G. WEBB, J. Chem. SOL., Faraday Trans. I , 1978,74, (3), 657-664 Deactivation of supported Pd/SiO,, Rh/SiO,, Ir/ SiO, and Pd/Al,O, catalysts was studied during C,H, hydrogenation using [14C] trace. The results are interpreted in terms of the hydrogenation reaction occurring by a H transfer mechanism between a dissociatively adsorbed C,H, species and associatively adsorbed acetylene.

Hydrogenation of Unsaturated Compounds on Rhodium Skeletal Catalysts from Rh-Mg Alloys

OSPANOVA, Dokl. Akad. Nauk S.S.S.R., 1978,239, (I), 120-122

The hydrogenation of unsaturated compounds, isoprene, phenylacetylene and hexene-I, were carried out over skeletal Rh catalysts (prepared by the leaching of 5-60 wt. :/; Rh-Mg alloys in a 20% solution of CH,COOH at 96'C for rh) in the presence of 96nd ethanole at 20°C. Catalysts containing 5-26 wt.oi, Rh were found to be most active, and the specific activity of the catalysts sharply decreased when increasing Rh content resulted in the appearance of the Rh,Mg, phase.

Particle size Effect in the Carbon Monoxide Chemisorption on Supported Rhodium N. KAUFHERR, M. PRIMET, M. DUPAUX and C. NACCACHE, Compt. Rend., sir. c, 1978, 286, (4, 131-133 Spectroscopic studies of CO adsorption on Rh catalysts supported by zeolite and A1,0, showed that particle sizes below IOA (Rh dispersed on zeolite) were suitable for the formation of gem dicarbonyl species detected in i. r. spectra around 2100 and zo4o/cm. The chemisorption led to linear and muhicentred species for particles > zoA (Rh /A1 no,).

T. K. KABIEN, D. V. SOKOL'SKII and G. SH.


Hydroformylation, Hydrogenation, and Iso- merization of Olefins over Polymer-Immobi- lized Rhodium Complexes H. ARAI, J . Catalysis, 1978,51, (2), 135-142 In order to make a catalyst with the selectivity and activity of a homogeneous catalyst but with the advantages of a heterogeneous catalyst, Rh complex (RhCl(CO),) was co-ordinatively bonded to the phosphine group on polystyrene-coated silica gel. Its activity was tested for hydroformylation, hydrogenation and isomerisation of olefins in the vapour phase. The dependence of rates and product yields on the partial pressure of H,, CO and olefins was examined and compared with those of homogeneous catalysis. The reaction rate dependence for olefins on partial pressure was in the order olefin > H,> CO. Hydroformylation, hydrogenation and isomerisation are all inhibited by CO.

A Fischer-Tropsch Study of Supported Ruthenium Catalysts D. L. KING,^. Catalysis, 1978,51, (3), 386-397 The effect of catalyst support on activity and selectivity of CO hydrogenation by Ru is discussed. The specific activity and selectivity depend on the support and the metal loading. Activity increases with metal particle size either by increasing metal loading or having a support which poorly disperses the metal. Product saturation increases with increasing CO conversion. Hydro- carbon chain length depends on temperature, pressure and support. Branched-chain hydrocarbons are produced on acid supports, Si0,- A1,0, or zeolites, and isomerisation of straight- chain products. The support may alter the catalytic behaviour of Ru through electronic and dispersional effects.

HOMOGENEOUS CATALYSIS Study of Hydrogenation of Ole fins Catalysed by Polymer-Bound Pallallium(I1) Complexes M. TERASAWA, K. KANEDA, T. IMANAKA and S. TERANISIII, J . Cc?tab.ris, 1978,5I, (3), 406-421 A polymer-bound Pd(I1) chloride complex catalyst was prepared by the reaction of PdCl, with a phosphinated polystyrene. Under mild conditions it catalyses the hydrogenation of alkenes and alkynes, particularly selective hydrogenation of conjugated dienes to monoenes. Catalytic activity decreases in the order: conjugated dienes > non- conjugated dienes>terminal olefins >internal olefins. 0,-containing solvents promote catalytic activity. Hydrogenation rates, dependent on substrate concentration, catalyst concentration, pressure and temperature, have been worked out. The reactivities of the polymer Pd complex catalysts and of an analogous catalyst system PdC12(PI'h,)2SnCI, reflect the electronic state and co-ordination number of the complexes.

Transfer Hydrogenation and Transfer Hydro- genolysis : XII. Selective Hydrogenation of Fatty Acid Methyl Esters by Various Hydro- gen Donors T. TAGAWA, T. NISHIGUCHI and K. FUKUZUMI, J . A m . OiZChem. SOL., 1978,55,(3), 332-336 The selective hydrogenation of methyl linoleate was studied using various organic compounds as hydrogen sources in the presence of homogeneous Pd, Ru, Rh and metallic Pd catalysts. Complete selectivity to monoenes and little formation of isolated trans double bonds occurred by the hydrogen transfer from L-ascorbic acid at 4706 conversion of the starting material to hydrogenation products. Hydrogenation by trans-1,2-cyclo- hexanediol catalysed by RuH,(PPh,), showed high selectivity to cis-monoenes. In the reaction catalysed by RuH,(PPh,), the presence of these hydroxy compounds increased the isomerisation of methyl elaidate to cis-monoenes.

Rhodium Catalysed Cyclopropenation of Acetylenes N. PETINIOT, A. J. ANCIAUX, A. F. NOELS, A. J. HUBERT and PH. TEYSSI~, Tetrahedron Lett., 1978, (1413 1239-1242 Rhodium carboxylates are reported to be very effective for the cyclopropenation of acetylenes. The catalyst influence on the competitive insertion- cyclopropenation reactions for acetylenic alcohols, that is control of the relative reactivities of a triple bond against an alcohol group in intra- molecular competitions, is examined.

Homogeneous Catalytic Hydrogenation of Aldehydes by RuC1,(C0)2(PPh,), by Chlorine up to Turnover Figure 95,000 W. STROHMEIER and L. WEIGELT, J. Organometal. Chew., 1978,145, (21,189-194 Linear and branched aliphatic and aromatic aldehydes are homogeneously hydrogenated with the catalyst RuCl,(CO),(PPh,), at 16~-200~C and H, pressure of 15 atm. Mean catalytic activities up to 243 and turnover numbers up to 95,000 were observed. With branched aliphatic aldehydes no side reactions were found and selectivity for alcohol formation was up to 99".

CHEMICAL TECHNOLOGY Determination of Precious Metals at PPB Levels in Rocks by a Combined Wet Chemical and Flameless Atomic Absorption Method B. J. FRYER and R. KERRICH, At. Absorp. Newsl.,

An easier method to determine the presence, at ppb levels, of Pt, Pd, Au and Ag in igneous rocks than previously involves using an aqua regia extraction followed by HI? treatment to eliminate silica. Quantitative precipitation of precious metals is achieved by reduction of T e chloride to T e

1978,17, (I) , 4-6


metal by stannous chloride. A double T e precipitation is performed on samples. This method can handle Wantities of rocks UP to 30g in mass, and can therefore be used on rocks containing very little precious metals.

The Semiconductivity and Stability of Palla- dium Oxide E. my, M. R. KAMAL, R. B. MILES and B. s. H. ROYCE, 3, M ~ ~ ~ ~ . sci., 1978~13, Q), 812-816 The use of Pd oxide in photoelectrolytic cells was

Interfacial Noble-Metal Corrosion in Metal to Ceramic Reaction Welding H. J. DE BRUIN, Nature, 1978,272, (5655), 712-713 Welding refractory ceramic oxides to transition metals to form Pd/MgO and Pd/AlaOs couples involves two different bond types when annealed in air. Below 800°C a visible intermediate oxide layer forms, the thickness of which increases with time, and the bond strength depends on the corrosion of the metal and strength of the oxide layer. Above 800°C there is a sharp metal-ceramic interfacial discontinuity and the bond strengths reach their maximum after a few hours and do not deteriorate with time. These different bond types suggest a new corrosion phenomenon.

ELECTRICAL AND ELECTRONIC ENGINEERING Investigation of the Ti-Pt Diffusion Barrier for Gold Beam Leads on Aluminium

SHENG and M. H. READ, J. Electrochem. SOL., 1978, 125, (I), 156-162 Ti -Pt diffusion barriers were inserted between A1 and Au beam leaded sealed structures (used in integrated circuit multichip assemblies) to stop interactions. The Al-Ti-Pt-Au structures were then aged and examined by electron microscopy, X-ray diffraction and sheet resistance measurements. Metallurgical interactions occurred at hillocks in Al, forming black spots which eventually covered the surface. This was inhibited by annealing A1 before barrier metallisation and using at least zoooA each of T i and Pt in the barrier. Thicker T i covers the A1 hillocks and prevents Al-Pt interactions, and thicker Pt prevents Ti-Au interactions.

S. P. MURARKA, H. J. LEVINSTEIN, I. BLECH, T. T.

NEW PATENTS ELECTROCHEMISTRY

investigated in an attempt to use it to convert sunlight to electricity. Pd oxide is a semiconductor with an estimated bond gap at 8zonm. The extrapolated bond gaps of Pd oxide films, prepared by oxidation of sputtered Pd films were examined by optical absorption spectroscopy and photoconductivity measurements. Band gaps occur at z.13$0.03 and 2.67=ko.o3eV, respectively. Photoconductivity occurs for energies smaller than the extrapolated band gap. The thermal stability of the films was reduced from 580K in a vacuum down to 350K by H,.

TEMPERATURE MEASUREMENT Temperature Detectors Engng. Muter. Design, 1978~22, (4,284 A ceramic bodied Pt resistance thermometer covering the temperature range -22oOC to +8oo0C has been developed, with a close physical toler- ance (&o.o13mm) for interchangeability. Ther- mal shocks do not alter its stability.

MEDICAL USES Stainless Tubing Provides High-Reliability Connector E. J. STEFANIDES, Design News, 1978, 34J (I), 82-83 A high-reliability connector for the leads of a cardiac pacing system is used for a lithium battery powered pulse generator. It provides a low-resistance electrical connection with high mechanical strength, One end of each conductor is attached to the flat-tipped platinum-iridium electrodes. The terminals and the electrodes are encased in moulded silicone rubber jackets.

Electrodes SOLAR10 LTD. U.S. Patent 4,054,496 In the electrolysis of heavy water the electrodes may be of Ru, Rh, Pd, Os, Ir or Pt, or coatings of these metals on substrates of Ti, N b or Ta.

Electrode T.D.K. ELECTRONICS CO. LTD.

British Patent 1,508,091 C1, is produced free from O 2 by the electrolysis of brine in the presence of an anode which is a conductive substrate (Ti, Ta or Zr) coated with a mixture of Pd oxide (5-40 mol. :lo), Ru oxide (2-10 mol.o/), and Sn oxide (50-93 mol.O/b), of which up to 40 mol.?!, may be substituted by TiO,.

Palladium Electrode SEMICONDUCTOR SENSORS INC.

U.S. Patent 4,058,368 A device for the detection of hydrogen has a metal electrode made of Pd, Ni and/or Pt.

Hutinurn MetuZsRev., 1978, 22, (3), 112-116 112

Mater

Noble Metal Catalyst for Oxygen Electrode W. A. ARMSTRONG U.S. Patent 4,066,823 A gas permeable hydrophobic electrode consists of a current collecting grid formed of Pt, Au or Ag; a catalyst chosen from Ag, Pt or Pd and a hydrophobic semipermeable membrane.

ELECTRODEPOSITION AND SURFACE COATINGS Electroless Plating A.M.P. INC. British Patent 1,499,163 The electroless deposition of Au on to a plastic surface is catalysed by the thermal decomposition products of a Pt or preferably I'd organo complex.

Vacuum Deposition of Ruthenium INCO EUROPE LTD. British Patent 1,499,549 Ru is deposited on to a hot substrate, such as a cutting tool, from a complex RuL,, where L is a p-dicarbonyl compound.

Electroforming Meshes or Screens E.M.I. LTD. British Patent 1,499,876 A mesh of Cu is obtained by electrodeposition into a grooved pattern scribed on a nonconductive substrate, the grooves being rendered conductive by a sputtered layer of Pd.

Metal Foil Production IMPERIAL METAL INDUSTRIES (KYNOCH) LTD.

British Patent 1,504,360 Metal foils are obtained by electrodeposition on to a rotating anode of a platinum group metal from a consumable cathode of Cu or Au.

Electroless Plating SHIPLEY CO. INC. British Patent 1,507,730 Nonconductive substrates are sensitised for electroless plating by immersion in a solution of Pd chloride and stannous chloride. The plating solutions of base metal, Pd or Au are stabilised by S.

Gold- Coloured Films

Transparent substrates, such as glass, are provided with multiple coatings of Cu, Ni and Cu oxide in combination to give them a gold-coloured appearance and selective reflectance and transmittance properties for radiation over an extended spectral range. The layer nearest the substrate contains Pd.

P.P.G. INDUSTRIES INC. U.S. Patent 4,065,626

Palladium Activator for Electroless Deposi- tion Processes INTERNATIONAL BUSINESS MACHINES CORP.

U.S. Patent 4,066,809 In a three-step seeding process for preparing substrate surfaces for electroless deposition, a Pd chloride activator is used together with a Pd chloride/stannous chloride/HCl seeder bath.

LABORATORY APPARATUS AND TECHNIQUES


CO, Sensor U.K. SECRETARY OF STATE FOR SOCIAL SERVICES

British Patent 1,503,908 A CO, sensor, particularly suitable for monitoring the partial pressure of CO, in a blood stream, has a sensing electrode of Pd-H or Ir-H, and a Ag reference electrode.

Platinum Catalyst for Detecting Combustible Gases BAILEY METER CO. U.S. Patent 4,063,898 A detector for monitoring combustible gases in an airstream uses a Pt tube as catalyst, formed around one of two thermocouple functions.

JOINING Platinum for Use as Braze Metal R. D. MITCHELL U.S. Patent 4,063,909 An abrasive compact of diamond andlor cubic boron nitride abrasive particles, bonded into a hard conglomerate, has a metal brazing layer of Pt bonded to at least one of its surfaces.

HETEROGENEOUS CATALYSIS Silicones UNION CARBIDE CORP. British Patent 1,500,924 Silicones prepared by the Pt-catalysed addition of aliphatically unsaturated epoxy compounds to hydrosiloxanes are used in emulsions for treatment of paper and textile fabrics.

Purification of I.C.E. Exhaust Gas NISSAN MOTOR co. LTD. British Patent 1,501,054 The air:fuel supply ratio to an I.C.E. provided with catalytic exhaust-gas purification means is monitored by an oxygen-sensor device using an electrolytic element coated with microporous layers of Pt.

Oxygenated Hydrocarbons Synthesis UNION CARBIDE CORP. British Patents 1,501,891-2 Ethanol, acetaldehyde and acetic acid are obtained by reaction of CO with H, in the presence of Rh, optionally in the presence of Fe, as catalyst.

I.C.E. Exhaust Gas Catalyst Support U.O.P. INC. British Patent 1,502,882 A tension- and deformation-resistant ceramic catalyst support comprises a honeycomb formed by fusing and sintering together specially formed curved wall sheets, each set of walls being at about 120' with respect to adjacent walls. The support is coated with catalyst, of Groups I, V, VI or VIII, especially Pt, Pd, Cu, Ag, V, Cr, Fe, Co or Ni.

Battery Recombination Catalyst ROBERT BOSCH G.m.b.H. British Patent 1,503,736 A secondary battery includes a catalyst for recombination of H, and 0,. The catalyst consists of a carrier such as A1,0, or A1 silicate coated on its upper surface with a thin layer of Pd or Pt and then with a water-repellent material, such as porous PTFE.

Aminoacids CHINOIM GYOKYSZERES VEGHESZETI TERMEKEK GYARART British Patent 1,504,541 In the preparation of aminoacids from their derivatives, protective groups may be removed by hydrogenolysis in the presence of PdIC.

Mo and W Bronzes for NO, Decomposition JOHNSON MATTHEY 82 CO. LTD.

British Patent 1,507,976 Catalysts for the purification of air comprise a ceramic or metallic support carrying a bronze of general formula AXBOY, where A is a metal of Groups IA, IIA or the lanthanide group, Pb, T1, Cu, Ni, H, NH4 or Ag; B is Ti, V, Nb, IMO, Ta, W, Re or Pt, x is C-z and y is 2-3.

O l e h Oxidation Catalysts UNION OIL CO. OF CALIFORNIA

U.S. Patent 4,057,575 Olefins are converted to esters or ethers by reaction with a carboxylic acid or alcohol and oxygen in the presence of a Si0,-supported catalyst which is a Group VIII noble metal, preferably Pt or Pd, and a non-noble metal redox agent.

Catalyst Containing a Platinum Group or Noble Metal INSTITUT FRANCAIS DU PETROLE

US. Patent 4,058,450 A catalyst for use in a process for preparing aromatic hydrocarbons from gasolines, free from olefin or diene consists of an alumina support, one or more halogens and at least two metals or their compounds chosen from the platinum group metals, such as Pt, Ir and Rh, and optionally an additional metal which may be Ag or Au.

Group VIII Metal Hydrogenation Catalyst SHELL OIL co. U.S. Patent 4,059,644 Group VIII metals such as Pt, Pd and Rh are used as hydrogenating catalysts in the second step of a 2-step process for preparing high density fuels from (meth)cyclopentadiene dimers.

Palladium Hydrogenation Catalyst E. r. DU PONT DE NEMOURS & co.

U.S. Patent 4,061,598 A catalyst of high activity and long life for use in the manufacture of H,O, is obtained by impreg- nating Al,O, with Pd under conditions such that the pore surfaces are rendered alkaline and the rate of metal diffusion is controlled.

Silicone-Curing Catalyst GENERAL ELECTRIC CO. U.S. Patent 4,061,609 The curing of a vinyl-containing polysiloxane rubber is catalysed by not less than 0.1 ppm Pt.

Palladium Catalyst for Alcoholysis Reaction SUN VENTURES INC. U.S. Patent 4,064,180 The ionic alcoholysis of Binor-S, a 14C heptacy- clic saturated hydrocarbon, in the presence of a primary alcohol, hydrogen and Pd:C or Pd/Al,O, as catalyst yields new alkyl ethers of Binor-S for use as a high energy fuel.

Platinum or Palladium Coated Ribbon Catalyst E. C. BETZ U.S. Patent 4,065,268 A catalyst bed, for use in converting hydrocarbon waste gas streams consists of catalytically active crimped metal ribbon, of at least two different crimp configurations. The ribbon may be coated with Pt and/or Pd as catalyst.

Palladium Hydrogenation Catalyst TEXACO INC. U.S. Patent 4,066,699 Nitrated hydrocarbons, such as nitroparaffins, are reduced to mines using a PdiC catalyst characterised by low ash and/or halide contents.

Noble Metal Catalyst for Coal Liquefaction Catalyst BATTELLE MEMORIAL INSTITUTE

U.S. Patent 4,067,795 Particles of solid hydrocarbonaceous material are electroplated with a metal catalyst, including Pt, Ag or Au, suspended in a hydrocarbon oil and subjected to hydrogenolysis to liquify them. The oil product is separated from the charkatalyst metal residue.

Platinum Group Metal Catalyst for Produc- tion of Hydrogen Rich Gas CONTINENTAL OIL co. U.S. Patent 4,067,958 A hydrogen-rich gas is produced from a fuel gas containing CO and N, and/or methane by a two-stage process, the second stage of which uses a platinum group metal catalyst.

Platinum Group Catalyst for Hydrocarbon Conversion U.O.P. INC. U.S. Patents 4,069,135-7 A multiple stage catalytic hydrocarbon conversion system uses gravity flowing catalyst particles which consist of a platinurn group metal on A1,03. Suit- able metals are Pt, Ir, Rh and Pd. There are variations in the amount of catalyst used in each zone.

Platinum Group Metal Catalyst ATLANTIC RICHFIELD co. U.S. Patent 4,069,388 Oxalate esters are prepared by the oxidative carbonylation of an alkoxycycloalkene with CO,

Platinum Metals Rev., 1978, 22, (3 ) I14

an alcohol and oxygen in the presence of an amine base and a metal salt, such as Pd, Pt or Rh, as catalyst.

Three-Way Control of an Exhaust Stream GENERAL MOTORS CORP. U.S. Patent 4,071,600 The procedure involves contacting the exhaust gas with a Rh catalyst and contacting the gas with a Pt or Pd catalyst, without adding 0, to the exhaust gas.

Platinum Group Metal Catalyst for Tereph- thalic Acid Purification JOHNSON MATTHEY & CO. LTD.

French APPl. 2,342,955 Terephthalic acid is purified by hydrogenation of the aldehyde impurities using a catalyst containing two metals chosen from Pt, Pd, Rh, Ru, 0 s and Ir. Other transition metals may also be present.

Rh/SiO, for NO, Removal JOHNSON MATTHEY & CO. LTD.

French Appl. 2,344,323 A process for removal of NO, andlor oxidation of hydrocarbons and CO uses as catalyst one or more of the platinum group metals, Au and Ag supported on or associated with SO,, A1,0, or mixtures thereof.

Hydrogenation Catalyst JOHNSON MATTHEY & CO. LTD.

German Offen. 2,722,771 The hydrogenation of animal and vegetable oils is catalysed by a product obtained by deposition on a porous particulate carrier of I'd bisacetylacetonate, and heating to deposit metallic Pd on the particle surfaces and in the larger pores only. The deposition is carried out in the vapour phase and the carrier may be maintained at a temperature above the decomposition temperature of the Pd compound.

Hydrogenation Catalysts UNIROYAL INC. German Offen. 2,736,228 p-Aminarylamines are obtained by hydrogenation or reductive alkylation of corresponding nitroso- arylamines in the presence of a platinum group metal sulphide, preferably 594 on C.

Supported Palladium Catalyst JOHNSON MATTHEY & CO. LTD.

Dutch Appl. 77.05481 A supported Pd catalyst is prepared by the vapour deposition of a compound of Pd on to the surface of a solid porous particulate support in such a way that metallic Pd is deposited upon the outer surfaces of the particles and within the pore mouths only of those pores having a diameter greater than so& The preferred support is pow- dered charcoal and the catalyst is useful for the hydrogenation of trienoic unsaturated fatty acids to the dienoic forms.

HOMOGENEOUS CATALYSIS Ruthenium and Osmium Metallocenes as Dopants for Liquid Crystals HUGHES AIRCRAFT co. U.S. Patent 4,066,569 Metallocenes, including those of Ru and Os, when mixed with conjugated cyanoorganic compounds, such as 7, 7', 8,8'-tetracyanoquinodimethane, act as dopants for liquid crystals.

FUEL CELLS Fuel Cell Electrodes SHELL INTERNATIONAL RESEARCH MIJ B.V.

British Patent 1,501,102 A catalytic Group VIII metal Pd, Rh, Ir, Os, Ru, Ni or preferably Pd is covered with a layer of H, and then with a discontinuous layer of a cocatalyst metal which may be Ag, Au, platinum group metal, lanthanide metal or oxides thereof.

Fuel Cell UNITED TECXINOLOGIES CORP.

British Patent 1,504,676 In a fuel cell which has electrodes of Pt black on PTFE, a porous electrolyte-retaining matrix comprises 95-98q4, of S i c particles having a size of < ropm and 2-5:(, of binder.

Platinum Catalyst for Fuel Cell Electrode UNITED TECHNOLOGIES CORP.

U.S. Parent 4,058,482 A fuel cell electrode has a mixture of polymer co- agglomerates, PTFE and Pt /C catalyst.

CHEMICAL TECHNOLOGY Photographic Emulsions KODAK LTD. British Patent 1,500,278 Cationic complexes of Ru can be used at considerably lower concentrations than the Co and Cr complexes to improve the sensitivity and contrast of Ag halide photographic emulsions.

Fine-Gauge Wire Production SUMITOMO ELECTRIC INDUSTRIES LTD.

British Patent 1,500,751 A hydrostatic extrusion process is used for producing wires of Pt or Au of diameter i 250pm.

Hydrogen Filter RESOURCE SYSTEMS INC. U.S. Patent 4,056,373 A hydrogen-purification filter is a helical tubular coil of a Pd alloy.

Ferromagnetic Powders FUJI PHOTO FILM CO. LTD. U.S. Patent 4,063,000 The properties of Fe, Ni and/or Co ferromagnetic metal powders may be improved by 0.5-5~; of Rh, Pd, Ag, Au or lanthanide metal.

Platinum Metals Rev., 1978, 22, (3) 115

Hydrogen Storage JOHNSON MATTHEY & CO. LTD.

French Appl. 2,337,303 Apparatus for H, storage comprises a membrane constructed of Pd or toy0 Ag-Pd in gas-tight connection with a heat-exchange chamber containing an intermetallic compound capable of reversibly absorbing H,, for example LaNi, for ambicnt temperature operation or Mg,Ni for operation at 250°C.

GLASS TECHNOLOGY Platinum Metal/Porcelain Articles NATIONAL RESEARCH DEVELOPMENT CORP.

U.S. Patent 4,064,31 I Porcelain is fired on to a metal substrate, specifically a platinum group metal. The substrate already has an adherent layer of a metal oxide on its surface of Sn or In which is wetted by the fused porcelain.

Noble Metal-Containing Cermets JOHNSON MATTHEY & CO. LTD.

French Appl. 2,336,358 The cermets consist of a ceramic particle phase and a metallic phase of Ru, Rh, Pd, Os, Ir, Pt, Au, Ag or their alloys, the greater part of the surface of the ceramic particles being treated with an additive which will form a solid solution with materials of the first and second phases.

Glass Fibres SIEMENS A.G. German Offen. 2,629,658 Glass fibres in which the core and periphery are of different composition are obtained by drawing from a double crucible of Pt, Ir or a Pt-Rh alloy.

ELECTRICAL AND ELECTRONIC ENGINEERING Anode PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES LTD. British Patent 1,498,654 A layered rotary anode for an X-ray tube has an electron target area of W alloyed with Os, Ir, Pt, Ru, Rh or Pd.

Display Devices NIPPON TOKI K.K. British Patent 1,499,524 Fluorescent display devices arc produced using conductive pastes which contain a vehicle, binders, and finely divided Pt, Pd, Rh, Au or Ag.

Self-Defogging Glass ASAHI GLASS co. LTD. British Patent 1,504~654 A glass plate for a vehicle window is provided with electrodes of Ru oxide, a sensitive membrane of a metal orthophosphate covering the gap between the electrodes, and a screen-printed heating element of Pd, Pt or Ag.

Platinum Metals Rev., 1978, 22, ( 3 ) 116

Resistance Heater CORNING GLASS WORKS U.S. Patent 4,057,707 An electrical cooking or heating unit is a glass- ceramic plate heated by a strip of electrical- resistance alloy containing preferably about 5 "" Au, optionally 1-40/; Rh, remainder Pt.

Palladium and Platinum Catalytic Anodes R.C.A. CORP. U.S. Patent 4,060,660 Pt or Pd catalytic anodes can be used in a glow discharge chamber for applying a d.c. glow discharge to a heated glassy substrate in the presence of a volatile hydrocarbon.

TEMPERATURE MEASUREMENT Resistance Thermometer W.C. HERAEUS G.m.b.H. British Patent 1,501,959 Thermal stresses in convemional Pt /ceramic resistance thermometers are reduced by depositing a layer having an intermediate thermal coefficient of expansion on to the substrate before depositing the Pt resistance layer. The intermediate layer is at least one of TiO,, ferric oxide and lanthanide metal(s) oxide.

Precious Metal Chips for Temperature Sensor HITACHI LTD. U.S. Parent 4,058,787 A thermistor for sensing high temperatures contains precious metal chips which are used to form a contact between the shaft and the sheath of the electrode. The chips are of Pt, Rh, Pd and/or their alloys.

MEDICAL USES Acyl Cyanoguanidmes MERCK & CO. INC. British Patent 1,502,740 Procedures for production of the title compounds, useful in treatment of rheumatoid arthritis, may include catalytic hydrogenation of a nitro-compound to the corresponding amine in the presence of Pd or Pt.

Tooth Crowning Process 0. W. ROGERS British Patent 1,502,813 The base of an impression of a tooth cavity is electrolytically coated with Pt, Pd, Rh, Au or an alloy thereof, the impression material is removed, and a porcelain inlay is built up on the metal base.

Antidandruff Agents F. HOFFMANN-LA ROCHE & CO. A.G.

British Patent 1,504,350 Antidandruff agents comprise aryl-long-chain- polyene amides, and may be obtained by partial hydrogenation of corresponding acetylenic compounds in the presence of a Pd catalyst.

Documents

PLATINUM METALS REVIEW · ing of both gold and platinum alloys is shown in Figure I. The most important of the platinum alloys at present used for invest- ment casting was developed