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UK ISSN 0032-1400

PLATINUM REVIEW

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

VOL. 36 JANUARY 1992 NO. 1

Contents

Catalysts for Nitrogen Oxides Control under Lean Burn Conditions 2

Rhodium- Resistance Thermometer 11

111-V Semiconductor Vapour Growth 12

Tungsten- Alloys at High Temperatures 13

Reduction of Platinum Corrosion in Molten Glass 14

Platinum Organometallics 26

Osmium- Coatings 33

An Important Work of Reference 34

Efficient Ruthenium Dye-Sensitised Solar Cell 38

Versatility of Compounds 39

Platinum in the Eighteenth Century 40

Abstracts 48

New Patents 60

Communications should be addressed to The Editor, Platinum Metals Review Johnson Matthey Public Limited Company, Hatton Garden, London ECl N 8EE Catalysts for Nitrogen Oxides Control under Lean Burn Conditions THE OPPORTUNITY FOR NEW TECHNOLOGY TO COMPLEMENT PLATINUM GROUP AUTOCATALY STS By T. J. Truex Johnson Matthey Technology Centre R. A. Searles Johnson Matthey Catalytic Systems Division, Royston and D. C. Sun Johnson Matthey Catalytic Systems Division, Wayne

Regulations to control the exhaust emissions from motor vehicles are be- ing adopted by more and more countries around the world, and infuture more stringent regulations will be introduced, particularly in the U.S.A. and Europe. This, together with the need to show good pollution control under real-world driving conditions, has led to the widespread introduc- tion of closed-loop, three-way catalysts based on the use of platinum group metal technology. “he increasing concern about emissions of car- bon dioxide, as well as the three traditional pollutants, offers an oppor- tunity for catalyst technology to control nitrogen oxides from both fuel eficient lean burn petrol engines and from diesel engines, thus com- plementing the use of platinum group metals catalysts to control nitrogen oxides and other emissions. This paper reviews the development of “lean- NOx” technology based on the use of zeolite supported catalysts; it highlights the promise shown and the shortcomings still to be overcome.

Over the last 25 years the motor vehicle has The twin goals of low and efficient fuel use increasingly become a cause for concern on en- and minimum emissions are increasingly being vironmental issues. This initially led to the con- addressed by research in both the motor and trol of , because of the the catalyst industries of the world. potential build-up of this toxic gas in congested city centres, and of hydrocarbons and nitrogen The Lean Burn Engine oxides, both precursors of the photochemical In various prototype forms the lean burn smog and low level ozone prevalent in some engine has been around for nearly 25 years. regions, particularly in the Los Angeles basin. However, successful and widespread usage of Now the motor vehicle is identified as the this engine has been restricted by increasingly contributor of around 15 per cent of carbon strict control on the level of pollutants emitted dioxide emissions. Carbon dioxide is the main under the full range of engine operating condi- “greenhouse” gas contributing to perhaps 50 tions (1). Recent developments have included per cent of the predicted global warming and is the evolution of lean operating two-stroke of course the inevitable product of burning engines (Figure 1). carbon-containing fossil fuels. Lean burn operation involves the burning of

Platinum Metals Rev., 1992, 36, (l), 2-11 2 Fig. 1 Among lean burn engines under development that would benefit from using lean-nitrogen oxides catalysts is the Orbital 2-stroke engine, shown here

fuel with an excess of air, in ratios up to 24 and minimise, but not prevent, hydrocarbon parts of air to one part of fuel. Under these con- emissions. ditions nitrogen oxides and carbon monoxide The main reason that lean burn engines have emissions are at a minimum, but hydrocarbons not so far had widespread acceptance has been can rise at the onset of unstable combustion, as that the power output from an engine falls as can be seen in Figure 2. Engine design to in- the fuelling moves to leaner operation. This crease the swirl of the aidfuel charge can in- means that to meet driver expectations of per- crease the air:fuel ratio at which misfire starts formance and drivability a rich fuel setting is

LEAN 1 ENGINE 1

\\ Hydrocarbons

.. I10.1 1i:l 14:l (4.7.1 16:l ie:i 20 :l 22:l 24:l AIR: FUEL RATIO, by weight Fig. 2 These four curves indicate trends which apply to all petrol engines. Under lean burn operation fuel is burnt with an excess of air at ratios of up to 24 parts of air to 1 part of fuel, and it can be seen that nitrogen oxides and carbon oxides emissions are at a minimum, but that hydrocarbon emissions can rise at the start of unstable combustion. When there is excess fuel, the engine power is high but high levels of hydrocarbons and carbon monox- ide are emitted. Peak combustion temperatures occur just on the lean side of the stoichiometric composition and result in the highest emissions of nitrogen oxides

Platinum Metals Rev., 1992, 36, (1) 3 Table I European Regulations

I 1992 Standards in gramslkm I Pollutants I Type approval I Production

Carbon monoxide 2.72 3.16 Hydrocarbons + nitrogen oxides 0.97 1.13 I Particulates/diesel 0.14 0.18 I On 1/7/92 applies to new models; on 31/12/92 applies to all new registrations provided for acceleration, high speed cruising stoichiometric point at which neither air nor and hill climbing, thus causing nitrogen oxides fuel is in excess at the intake to the engine; for emissions to increase. a typical petrol composition this is at a ratio of 14.7 parts of air to 1 part of petrol. The Diesel Engine Under lean conditions the three-way catalyst The only true lean burn engine in widespread will act as an oxidation catalyst controlling car- use is the diesel engine. The diesel engine stays bon monoxide and hydrocarbon emissions, but in the lean operating region under all engine the conversion of the nitrogen oxides emissions conditions. The petrol engine is throttled on falls to very low levels. the air intake, and ultimate power from a given engine is limited by the amount of air that the Limitations to Lean Operation engine can “breathe”. Conversely the diesel as Legislation Tightens engine is unthrottled and its power output is The introduction of lean bum engines is determined by the amount of fuel that is in- limited by a number of key factors. The Euro- jected into the combustion chamber. The max- pean driving cycle, during which the emissions imum fuel input level is controlled by the onset from motor cars are measured against the of unacceptable levels of smoke or particulate legislated levels, has been changed. The formation. To limit particulate emissions to ac- original City Test Cycle was based on inner city ceptable or legislated levels it is necessary for driving in congested traffic with a top speed of the diesel engine always to operate in the lean 50 k.p.h. (31 m.p.h.) and an average speed of region (2). This means that the diesel engine 18.8 k.p.h. (11.7 m.p.h.). Under these condi- has a significantly lower power output than a tions a typical car might need to use only 15 per petrol engine of the same capacity. cent of its maximum available power, so that lean operation would be possible throughout Three-Way Catalyst Operation the cycle. However, the realisation that a major Conventional three-way catalysts, based on contribution to regional and global pollution is the use of combinations of platinum group made by motor vehicles operating at high metals - platinum, palladium and - can speeds on highways led to the addition of the convert over 90 per cent of the three main Extra Urban Driving Cycle (EUDC), which in- pollutants carbon monoxide, hydrocarbons and cludes speeds up to 120 k.p.h. (75 m.p.h.) and nitrogen oxides (3). They do this by the exhaust needs more power than the City Test Cycle. gas being controlled by an airfuel ratio (or This causes greater nitrogen oxides emissions. lambda) sensor around the so-called The new European Community directive,

Platinum Metals Rev., 1992, 36, (1) 4 Fig. 3 The U.S. Federal Stan- 4 dards include a timetable for the progressive reduction of 2 pollutant emissions in exhaust E 3 gas: E c hydrocarbon reduction 9 from 0.41 glmile in 1991, to VI5 0.125 glmile in 2004 L" carbon monoxide 5 1 reduction from 3.4 glmile in 1991 to 1.7 glmile in 2004

nitrogen oxides reduc- 1991 1994 to 1996 2004 tion from 1.O glmile in 199 1 (40%) llW%) to 0.2 glmile in 2004 YEARS published on 30th August 1991 (4), sets max- emissions by 40 per cent and nitrogen oxides imum pollution levels for all sizes of motor cars emissions by 60 per cent, by 1996 (Figure 3). (Table I) and is based on the combined City and Californian standards call for increasingly lower EUDC cycles. The standards will necessitate and lower emissions, culminating in a require- the use of closed loop, three-way catalysts on all ment for all motor vehicle manufacturers to in- new models sold from 1st July 1992 and on all clude 10 per cent of zero emissions vehicles in new cars registered for sale after 31st December their fleets by 2003 (Figure 4 and Table 11). 1992. The Californian standards are also expected to In the U.S. new, more demanding Federal be adopted by 13 states in north eastern and Californian standards have been set. The U.S.A., which together account for nearly 40 former will reduce the allowed hydrocarbon per cent of U.S. car sales.

100

80

1 c 8 60 LP)

c' 40 LL1

20

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 YEARS

Fig. 4 Californian standards give a timetable for lower emissions and call for motor vehicle manufacturers to include 10 per cent of zero emission vehicles in their fleets by 2003 zero emission vehieles transitional low emission vehicles ultra low emission vehicles 1993 standards a low emission vehicles 0 1991 standards

Platinum Metals Rev., 1992, 36, (1) 5 Table II Californian Standards

Emission limits, gramshile

Year and standard I Hydrocarbons Carbon monoxide Nitrogen oxides

1991 0.39 7.0 0.4 1993 0.25 3.4 0.4 1994 (TLEV) 0.125 3.4 0.4 1997 (LEV) 0.075 3.4 0.2 1997 (ULEV) 0.04 1.7 0.2 1998 (ZEV) 0 0 0

The European Commission will propose the reducing agent has been utilised for the tougher standards for the European Communi- removal of nitric oxide from industrial boilers ty by the end of 1992, for agreement during and gas turbines under conditions of excess ox- 1993 and with implementation expected in ygen (7). Careful stoichiometric control of the 1996. It is anticipated that these will be similar ammonia must be maintained to assure efficient to the new U.S. Federal standards. nitric oxide removal without emission of These increasing restrictions on nitrogen ox- surplus ammonia. For transportation applica- ides emissions and the inclusion of real-world tions this process is not practical because of the driving conditions mitigates against the use of problems associated with the storage of am- lean burn engines, unless the emissions of monia, and controlling ammonia injection nitrogen oxides can be limited in the engine or under transient conditions. An active and controlled externally. durable nitric oxide decomposition catalyst, or a selective reduction catalyst utilising reducing Removal of Nitric Oxide under species present in the engine exhaust stream Lean Operation would be a major breakthrough for the control Nitric oxide is thermodynamically unstable of nitric oxide in transportation applications. relative to nitrogen and oxygen under the full Recent literature reports and work conducted range of exhaust gas stoichiometries and by Johnson Matthey now indicate that progress temperatures encountered in internal combus- is being made towards developing these catalyst tion engines (5). A number of catalysts were technologies employing platinum group metals. studied during the 1970s, including platinum group metals and metal oxides (6) and some New Nitric Oxide Decomposition were found to decompose nitric oxide, but none Catalysts of these had sufficiently high activity to be of -exchangedzeolites have high activity practical importance. In their reduced states, for the catalytic decomposition of nitric oxides these catalysts are rapidly oxidised by nitric ox- according to Iwamoto and co-workers (8). A ide, with release of nitrogen. Oxygen is retained number of zeolite systems were investigated in- on the catalyst surface, however, inhibiting fur- cluding Mordenite, Ferrierite, L-type and ther nitric oxide adsorption and decomposition. ZSM-5, with the Cu-ZSM-5 system showing Reducing agents are required to remove this the highest activities (9, 10). Using gas mix- surface oxygen and regenerate catalyst activity. tures of 0.5-2.1 per cent nitric oxide in helium, Selective catalytic reduction using ammonia as with gas hourly space velocities of 10-80,000

Platinum Metals Rev., 1992, 36, (1) 6 per hour, nitric oxide conversions of 13 to 60 sites of the Cu-ZSM-5 catalyst during steady- per cent were reported. Maximum conversions state reaction is felt to be the key to their high to nitrogen were observed at about 5OO0C, sustained activity. with the degree of decomposition decreasing at Although the above results represent a higher temperatures. This is apparently due to significant advancement in the development of a change in mechanism, as opposed to catalyst catalysts for nitric oxide decomposition, major degradation, as the same conversions were improvements will be required before such observed with decreasing catalyst temperature systems can be used to control nitric oxide after high temperature operation. Water and emissions from combustion sources. Nitric ox- carbon monoxide additions to the gas mixture ide concentrations in exhausts of internal com- did not greatly influence activity. The addition bustion engines are generally <3000 ppm, of oxygen resulted in a decrease in nitric oxide significantly lower than those used in the work decomposition activity, although it is claimed reported above. Tests in our laboratories at that this effect is dependent upon the level of these concentrations with 5 per cent oxygen copper exchange in the zeolite, with high levels present and gas hourly space velocities of of exchange resulting in less oxygen inhibition. 20,000 per hour show little nitric oxide conver- The addition of sulphur dioxide was found to sion. In addition, the almost complete poison- poison catalyst activity completely in the 400 to ing of activity by sulphur dioxide in the 6OOOC temperature range, with restoration of reaction gas mixture would preclude use with activity being achieved after the high present petroleum-derived fuels. temperature desorption of sulphur. Detailed kinetic studies of nitric oxide Selective Catalytic Reduction of decomposition over the Cu-ZSM-5 system have Nitric Oxide by Hydrocarbons been reported by Li and Hall (11, 12). Their Another significant, and potentially more work has shown that the reaction is first order practical, breakthrough has been the reports by in nitric oxide pressure and inhibited by ox- Iwamoto (10, 13, 14), Hamada (15, 16, 17) and ygen. The kinetics can be described in the Held (18) and co-workers demonstrating the Langmuir-Hinshelwood form with the inhibi- selective catalytic reduction of nitric oxide by tion being half-order in oxygen pressure. As hydrocarbons in the presence of excess oxygen. with Iwamoto and co-workers, they observed Hamada and co-workers have studied nitric ox- that the nitrogen formed was significantly less ide reduction over solid acid (19, transition than the equivalent nitric oxide which disap- metal promoted alumina and silica (17), and H- peared. This discrepancy was accounted for by form zeolites (16). Some of their results using nitrogen dioxide which appears in the products C,H, as the selective reducing agent are sum- as a result of homogeneous reaction of product marked in Table 111. Alumina, titania and zir- oxygen with undecomposed nitric oxide conia all showed modest activity for the downstream of the catalyst. The redox capacity selective reduction of nitric oxide with C, H, . of Cu-ZSM-5 was found to be near 0.5 O:Cu, The addition of transition metals to alumina that is le-. In particular, it was shown that ox- resulted in substantially higher activity, with ygen could be desorbed isothermally from the and iron presenting the highest conver- catalyst surface upon reducing the oxygen par- sions. Interestingly, the observation was made tial pressure in the gas stream and that Cu' * that a correlation exists between cobalt was reduced to Cu+I during the desorption of aluminate formation and nitric oxide reduction oxygen. Since it is generally believed that the activity. Of the platinum group metals, rate of removal of strongly adsorbed product platinum exhibited the highest activity. As the oxygen from the surface limits the nitric oxide results presented in Table 111 show, the H-form decomposition on most catalysts, the con- zeolites were the most active catalysts tested by tinuous desorption of oxygen from the active these workers. In all these studies nitric oxide

Platinum Metals Rev., 1992, 36, (1) 7 Table 111 Selective Reduction of Nitric Oxide over Solid Acid (15), Promoted Alumina (17) and Zeolite (16) Catalysts

Nitric oxide conversion to nitrogen, per cent

Catalyst at 3OOOC at 4OOOC at 5OOOC

SiO, < 0.4 < 0.6 < 1.1 403 0.5 13.0 32.0 TiO, 0.8 4.8 8.9 ZrO, - 23.0 20.0 2% Co/AI,O, (blue) 4.2 49.0 29.0 2% Cu/AI,O, (green) 14.0 23.0 11.0 2% Fe/AI,O, (orange) 19.0 35.0 17.0 2% Ni/AI,O, (green) 4.5 31 .O 40.0 2% Mn/AI,O, (brown) 13.0 13.0 7.4 0.5% Pt/AI,O, 9.0 28.0 12.0 0.5% Pd/AI,O, 12.0 5.6 5.4 0.5% Rh/AI,O, 13.0 8.9 8.5 H-ZSM-5 49.0 59.0 38.0 H-Mordenite 58.0 65.0 48.0

~ HY 9.0 19.0 26.0

1000 ppm NO, 329 ppm C,H.. 10% 0, at 3.7 LlHG MHSV Whg mass hourly space velocity1 conversion to nitrogen was observed to go (350°C)cu- nitrogen formation decreases, the hydrocarbon Mordenite (26%) - Cu-L-type (25%)>cu- was completely oxidised to carbon dioxide. It Ferrierite (23%). The effect of space velocity on was also found that the temperature of max- conversion was studied for Cu-ZSM-5, H- imum nitric oxide reduction to nitrogen was ZSM-5, and alumina catalysts. Conversion over dependent upon the hydrocarbon species, with alumina dropped rapidly at gas hourly space maximum conversion occurring at a velocities greater than about 5000 per hour, H- temperature about 100°C lower when C,H, ZSM-5 conversions showed a modest decline in was used as reductant, instead of C,H,. the range of 5-20,000 per hour with a rapid fall A number of ion-exchanged zeolites have at higher space velocities, and conversion over been examined for their selective nitric oxide Cu-ZSM-5 was stable up to 48,000 per hour reduction activity by hydrocarbons (10, 13, 14). with a fall at higher values. These results show Using a gas mixture containing 1000 ppm nitric that transition metal ion-exchanged zeolites can oxide, 250 ppm C,H,, and 2 per cent oxygen have substantially higher activity than the H- at a mass hourly space velocity of 18 form systems, with the copper-exchanged litresihour/gram, the order of activity catalysts showing most promise. (temperature for maximum nitric oxide reduc- Using laboratory gas mixtures more typical of tion to nitrogen) was copper (250°C)

Platinum Metals Rev., 1992, 36, (1) 8 Table IV I Selective Nitric Oxide Reduction over Copper-Mordenite and Copper-ZSM-5 I Nitric oxide conversion to nitrogen, per cent HC Catalyst (ppm as C,) 200OC 3OOOC 4OOOC 5OOOC 6OOOC

Cu-Mordenite C,H, (1001 0 3 2 2 2 C,H, (700) 3 15 13 12 2 C,H, (2500) 4 38 40 33 6 C,H, (5000) 3 58 55 45 8

CU-ZSM-5 C,H, (700) - 12 30 23 12 C,H, (2500) - 16 50 47 20 C,H, (5000) - 12 68 58 40 C,H, (2500) 0 0 15 43 37 CH, (250) 0 0 0 0 7

250 ppm NO. HC ias indicatedl. 5% 0,. 13%CO,, and 10% H,O in N, at 20,000ih gas hourly space velocity evaluation, Held and co-workers (18) have approximately 15,000 per hour, nitrogen oxides reported results on a number of transition metal conversions of 35 to 45 per cent were observed ion-exchanged zeolites. Cu-Mordenite; Cr-, Fe-, at air:fuel ratios of 17.5-19: 1. A correlation Mn-, V-, Cu-, Co-, Ni-, and Ag-Y zeolite; Cu- exists between nitrogen oxides conversion and X zeolite; and Ir-, Pt-, Rh-, Ni-, Co-,and Cu- the hydrocarbonxitrogen oxides ratio in the ZSM-5 were all reported to have some activity exhaust gas mixtllre, with the highest nitrogen for selective reduction of nitric oxide by oxides conversions occurring at the highest hydrocarbons in the presence of excess oxygen. hydrocarb0n:nitrogen oxides ratios. The Cu ion-exchanged systems showed the In our laboratories, monolithic substrates highest activities of those tested. They also have been coated with Cu-Mordenite and Cu- showed that there was an inhibition of activity ZSM-5 catalysts for laboratory flow reactor and when water was added to the reaction gas mix- engine evaluation. Laboratory flow reactor ture. Studies of the two most active catalyst results are summarised in Table IV. It should systems, Cu-ZSM-5 and Cu-Mordenite, with a be noted that under these conditions no sidi- gas mixture containing 1000 ppm nitric oxide, cant nitric oxide conversion was observed in the 400 ppm C,H,, and 1.5 per cent oxygen at absence of hydrocarbons, indicating that direct 35OOC and a gas hourly space velocity of decomposition was not contributing to nitric 13,000 per hour showed that nitric oxide con- oxide conversion. As was found by other versions over Cu-Mordenite dropped from 37 workers, nitric oxide conversion went through to 17 per cent with the inclusion of 10 per cent a maximum as a function of temperature. Car- water vapour. Under the same conditions, the bon monoxide formation was observed during more hydrophobic Cu-ZSM-5 catalyst showed a the onset of nitric oxide conversion. Complete drop in nitric oxide conversion from 50 to 37 conversion of hydrocarbon to carbon dioxide per cent. A conventional autocatalyst was observed at higher temperatures associated monolithic substrate was coated with Cu- with declining nitric oxide conversion. These ZSM-5 for engine evaluation. Under steady- results show that zeolite type, the hydrocar- state conditions at about 4OOOC inlet bon:nitric oxide ratio, and the hydrocarbon temperature and a gas hourly space velocity of species all have a significant effect on nitric

Platinum Metals Rev., 1992, 36, (1) 9 oxide reduction activity. Consistent with other At present there is very little information reports, the Cu-ZSM-5 catalyst gave higher available on catalyst durability but, as ex- conversions than the Cu-Mordenite catalyst. pected¶ there are indications that the zeolite Maximum conversions increased with increas- systems would be limited to temperatures less ing hydrocarbon concentrations (increasing than 600°C to avoid thermal degradation. In- HC:NO ratio). The use of C,H, instead of itial resistance to sulphur dioxide poisoning has C,H, as reductant resulted in an increase in been indicated (14) although longer term temperature for maximum nitric oxide conver- poisoning effects remain to be assessed. sion from - 4OOOC to - 5OOOC. The use of CH, resulted in minimal nitric oxide reduction at Future Work and Requirements temperatures up to 600OC. The dependence on for a Practical Emission Catalyst hydrocarbon species and concentration, A much better understanding of the together with the observation that carbon mechanism(s) involved in the selective nitric monoxide formation occurs simultaneously oxide reduction reaction with hydrocarbons with nitric oxide reduction, implies that must be obtained as a basis for development of hydrocarbon partial oxidation or decomposition improved catalyst systems. These studies, products are involved in the reaction together with engine evaluations, must address mechanism. In separate experiments we have a number of possible limitations of present exposed a Cu-ZSM-5 catalyst first to a technology for vehicle applications. Some of C,H,/O, mixture and subsequently to a these limitations include: NO/O, mixture. Immediately upon switching * Thermal stability of the present Cu-zeolite to the NO/O, mixture, significant nitric oxide systems conversion is observed which decays with time, t Effects of potential poisons, particularly implying that hydrocarbon-containing species sulphur compounds deposited on the catalyst surface are involved in * The relatively narrow range of temperatures the reaction, and are being depleted with time. and low space velocities associated with op- We have also shown that carbon monoxide and timum performance hydrogen are much less effective than * The effects of cyclic engine operation, par- hydrocarbon for selective nitric oxide reduction ticularly the effects of varying emission rates of over these catalyst systems. Iwamoto has hydrocarbons versus nitrogen oxides on catalyst classified reductants into two groups, selective function. (C,H,, C3H,, C,H,, C,H,) and non-selective The importance of these last two effects is (H2,COY CH, and C2H,) based upon similar demonstrated by the work of Held and co- observations (10). His group has also in- workers (18). They tested Cu-ZSM-5 catalysts vestigated the role of oxygen, showing that up on a vehicle under the transient FTP cycle. to about 2 per cent oxygen in the reactant Nitrogen oxides conversions of about 15 per stream strongly activates nitric oxide reduction cent were obtained during cold-start (bag 1) with a slight inhibition observed at higher con- and about 30 per cent during hot-start (bag 3) centrations. Our studies have shown similar ef- tests. The lower conversions were ascribed to fects with the added observation that exposure low catalyst temperatures during cold-start and of a Cu-Mordenite catalyst to nitric oxide and the generally higher space velocities incurred in C H , in the absence of oxygen resulted in a the FTP during the hot-start test. It was also reddish colour change to the catalyst, implying noted that under acceleration conditions where the presence of reduced metallic copper. This significant nitrogen oxides are formed, the occurs even when the reactant gas mixture is nitrogen oxides:hydrocarbon ratio was un- net oxidising and may indicate that the impor- favourable for nitrogen oxides reduction. The tance of oxygen is in maintaining copper in an requirement for high hydrocarb0n:nitrogen ox- active . ides ratios was found to be a major problem in

Platinum Metals Rev., 1992, 36, (1) 10 studies using a diesel engine. Diesel engines of a dual function catalyst system. The first have inherently low hydrocarbon emissions and component would be the selective nitrogen ox- 1 injection of hydrocarbons into the exhaust ides reduction catalyst, followed by a conven- stream was necessary to obtain significant tional platinum group metal catalyst for nitrogen oxides conversion. hydrocarbons and carbon monoxide removal. Finally, a complete automotive emission con- Such concepts are already described in the pa- trol catalyst system must have adequate tent literature. It is obvious that a practical hydrocarbon and carbon monoxide activity in selective nitrogen oxides reduction catalyst for addition to nitrogen oxides removal. The automotive applications is some time away, but catalyst systems described above show deficien- the exciting results obtained in the past several cies in hydrocarbons and, particularly, carbon years and the high level of activity in this area monoxide activity which would require the use are reasons for encouragement.

References 1 R. A. Searles, Platinum Metals Rev., 1988, 32, 9 M. Iwamoto, H. Yahiro and K. Tanda, “Suc- (3~123 cessful Design of Catalysts”, ed. T. hi, 2 B. J. Cooper and S. A. Roth, Platinum Metals Amsterdam, 1988, pp. 219-226 Rev., 1991, 35, (4), 178 10 M. Iwamotoand H. Hamada, Catal. Today, 1991, 3 B. Harrison, B. J. Cooper and A. J. J. Wilkins, 10, 57 Platinum Metals Rev., 1981, 25, (l), 14 11 Y. Li and W. K. Hall, 3. Phys. Chem., 1990,94, 6145 4 Off. 3., 30th August 1991, 34, L242 12 Y. Li and W. K. Hall,3. Catal., 1991, 129, 202 5 B. Harrison, M. Wyatt and K. G. &ugh, 13 S. %to, Y. Yu-u, H. Yahiro, N. WoandM. “”, Vol. 5, R. Sot. Chem., London, Iwamoto, ~ppl.Catal., 1991, 70, ~1 1982, pp. 127-171 14 M. Iwamoto, H. Yahiro, S. Shundo, Y. Yu-u and 6 J. W. Hightower and D. A. VanLeirsburg, in N. &no, Appl. Catal., 1991, 69, L15 ‘‘The Catalytic Chemistry of Ninogen aides”, 15 Y. Kintaichi, H. Hamada, M. Tabata, M. Sasaki ed. R. L. Klimisch and J. G. Larson, 1975, and T. Ito, Catal. Lett., 1990, 6, 239 Plenum Press, New York, p. 63 16 H. Hamada, Y. Kintaichi, M. Sasaki, T. Ito and 7 B. Harrison, A. F. Diwell and M. Wyatt, M. Tabata, Appl. Catal., 1990, 64, L1 Platinum Metals Rev., 1985, 29, (2), 5 17 Op. cir. (Ref. 16), 1991, 75, L1 8 M. Iwamoto, S. Yokoo, K. Sakai and S. Kagawa, 18 W. Held, A. Konig, T. Richter and L. Ruppe, 3. Chem. SOC.,Faraday Trans., 1981, 77, 1629 SAE Paper No. 900496, 1990 Rhodium-Iron Resistance Thermometer For some twenty years the rhodium-iron Fused-Silica Coil Frame”, Cryogenics, 1991, resistance thermometer has been regarded as 31, (lo), 869-873). The use of fused silica one of the most reliable for low temperature enables the sensing element to be annealed at measurement, and in various forms has been temperatures above 600OC. The four lead wires used from millikelvin regions up to room and the protective sheath are made of platinum. temperature. Although it is known that the an- The influence of annealing temperatures bet- nealing treatment is one of the most important ween 700 and 900OC upon the resistance of the factors controlling the thermometric properties thermometer has been investigated, and a of such thermometers, only limited information calibration method proposed for cryogenic use is available about their stability when the of the thermometers. rhodium-iron (mole fraction 0.5 per cent) is in It is concluded that an annealing temperature the form of wire. of 8OOOC is required to remove the strain pro- A resent communication from the National duced in the wire by coiling; thermometers an- Research Laboratory of Metrology, Japan, nealed at or above this temperature have similar reports on the effects of annealing on a new temperature-resistance characteristics and, type of rhodium-iron thermometer, in which after calibrating the deviation from a reference the 50 pm diameter wire is wound bifilarly function at only three calibration points, can be around a cross-shaped frame machined from used with an accuracy better than 0.5 mK over fused silica. (0. Tamura and H. Sakurai, the range 4.2 to 25 K. Self-heating effects were “Rhodium-Iron Resistance Thermometer with found to be of a reasonable magnitude.

Platinum Metals Rev., 1992, 36, (1) 11 111-V Semiconductor Vapour Growth APPLICATION OF PALLADIUM- DIFFUSION MEMBRANES AND THE RESTORATION OF HYDROGEN OUTPUT By J. S. Roberts Department of Electronic and Electrical Engineering, University of Sheffield

The class of semiconductors based on Group established technique for purifying commercial I11 and V elements can be fabricated into effi- grade cylinder hydrogen (2). The hydrogen dif- cient light emitters and lasers for the red and fusion process results in the dissociation of each near infrared spectral regions. Commercially molecule into two protons and two electrons, these devices are used as optical read-write followed by diffusion through the palladium- systems, such as those found in compact disc silver lattice. On reaching the high purity players and data storage systems. An important region the protons and electrons combine to 111-V alloy commonly used in semiconductor reform hydrogen. With appropriate equipment lasers is AliX,Ga~,-,,As,where x = 0 to 0.35. hydrogen of 99.9999 per cent purity or better The aluminium component of the alloy is par- may be obtained, suitable for use as a transport ticularly sensitive to oxygen, which is readily medium for metal alkyl vapour and as a carrier incorporated during vapour phase epitaxial gas during the manufacture of semiconductor growth. Substitutional oxygen within the materials (3). Generally the membrane takes crystal lattice lowers the optical efficiency of the the form of a 1.5 mm internal diameter tube material by creating centres which trap minori- sealed at one end and internally supported. ty carriers, the precursors to light emission. Hydrogen is diffused from the outer to the in- In order to realise large scale uniform single ner surface of the tube using an input pressure crystal layers of AlGaAs the epitaxial growth of 280 psi. A number of these membranes are technique most favoured is Metal Organic brazed into a stainless steel output manifold. Vapour Phase Epitaxy (MOVPE). The precur- Within this department, hydrogen is obtain- sors for this process are usually ed from an “EP-20” diffusion unit, which has trimethylaluminium, trimethylgallium and ar- an output of 20 standard litres per minute at an sine, which are transported to a heated (7OOOC) operating temperature of about 300°C and an GaAs substrate by a carrier gas of ultra pure input pressure of 280 psi. The purity of the hydrogen. Oxygen, inadvertently incorporated hydrogen output is better than can be deter- during crystal growth, can arise from a number mined by simple analytical measurements, of sources including the hydrogen carrier, the necessitating mass spectrography for accurate arsine, alkoxide impurities in the metal-alkyl analysis. Indeed the luminescence efficiency of and leaks, either real or virtual, within the unintentionally doped AlGaAs from a number stainless steel pipework of the reactor. of reactors indicates that the purity of the High purity hydrogen can be generated by a hydrogen exiting from the palladium-silver number of techniques including boil off from membranes is not a controlling factor of the the liquid, gettering using a metalorganic overall material quality. polymer or diffusion through a series of Should the hydrogen supply to the diffusion palladium-silver membranes (1). The latter is unit become depressurised, it can be arranged potentially the most efficient as the unit can be for the input to be automatically switched to made leak tight to all gases except hydrogen. nitrogen. The exchange of nitrogen for The diffusion of hydrogen through 23 per hydrogen promotes reverse diffusion through cent palladium-silver membranes is a well the membrane and the removal of hydrogen

Platinum Metals Rev., 1992, 36, (l), 12-13 12 from the diffuser and associated equipment. In increasing the temperature from 310 to 36OOC addition, cooling the membrane in the absence the full output of the unit was realised. The of hydrogen prevents embrittlement of the operating temperature was then returned to fragile diffusion tubes. 31OOC without any reduction in the pure On a number of occasions, when cylinder hydrogen gas output. hydrogen has been re-introduced to the diffuser after a nitrogen purging process, there has been Conclusion a serious reduction in the rate of hydrogen out- The MOVPE process requires a source of put, apparently due to some form of contamina- oxygen-free carrier gas, this can be readily tion of the membrane. The nitrogen purge was achieved using a palladium-silver membrane undertaken while the unit was at 31OOC using diffusion system. In the event of the external high purity gas, but without an oxygen removal (input) surface of diffuser elements becoming catalyst in the input line. The low hydrogen oxidised a simple etch in hydrofluoric acid is output could therefore result from the forma- able to recover the hydrogen flow. The method tion of an oxide on the surface of the mem- relies on the conversion of the oxide to a brane. One such faulty membrane was removed fluoride, which in the case of the silver fluoride from its housing and etched for 2 minutes in a hydrate is known to have a highwater . hydrofluoric acid solution made from 40 per cent hydrofluoric acid stock diluted by 50. A Acknowledgements simple PVC tube, closed at one end, served as “EP-20” hydrogen diffusion units are supplied by a container for the etchant. The palladium- Hydrogen Engineering Applications Ltd. > Stevenage, Hertfordshire, and incorporate diffusion membranes silver membrane tube was then washed for manufactured byT.M.K.K.,Tokyo,usingpalladium- several minutes in a flow of de-ionised water silver tubes manufactured by Johnson Matthey. and dried at 100°C for about 15 minutes. The hydrofluoric acid treatment was choosen to pro- References mote the formation of silver fluoride, which as 1 G. J. Grasshoff, C. E. Pilkington and C. w. Corti, Platinum Metals Rev., 1983, 27, (4), 157 the hydrate has a high waterWater solubility. The 2 D. A. Stiles and p. H. Wells, platinum Metals reassembled diffuser initially gave only a Rev,, 1972, 16, (41, 124 modest improvement in hydrogen flow but on 3 C.W.C., Platinum Metals Rev., 1981, 25, (l), 12

Tungsten-Iridium Alloys at High Temperatures The benefit of alloying additions of palladium tion, consistent with the mechanism of solid in improving the oxidation resistance of solution strengthening by atoms in substitu- tungsten alloys at elevated temperatures has tional positions causing symmetrical lattice been reported in this journal recently (1). Now, distortion. Examination of the fracture the enhancement of the high temperature behaviour showed that iridium promotes the in- strength of tungsten by alloying with iridium is tergranular failure mode at lower temperatures. the subject of a new study at the Arizona State These results demonstrate that iridium is a University (2). viable alternative to rhenium as a strengthening The investigators report that dilute alloys alloying element in tungsten. Earlier work by containing up to 1 weight per cent iridium in the authors has shown that iridium also im- solid solution display considerably enhanced proves the fabricability of tungsten at ambient yield and tensile strengths at high temperatures, and is better than rhenium. Such temperatures. For a tungsten-0.8 weight per findings should encourage the use of tungsten- cent iridium alloy, a yield strength improve- iridium alloys in industrial applications. ment of 75 per cent is observed at 1727OC. This C.W.C. gain becomes progressively less marked as the References temperature increases towards 2327OC. The in- 1 C.W.C., Platinum Metals Rev., 1991, 35, (3), 133 cremental strength benefit was found to be 2 A. Luo, K. S. Shin and D. L. Jacobson, Scr. linearly dependent on the iridium concentra- Metall. Muter., 1991, 25, (lo), 2411

Platinum Metals Rev., 1992, 36, (1) 13 Reduction of Platinum Corrosion in Molten Glass THE INFLUENCE OF PHOSPHATE GLASS MELTS ON THE MICROSTRUCTURE AND RUPTURE TIME OF PLATINUM METALS By Bernd Fischer Faculty of Technology, Friedrich-Schiller-University,Jena. Germany

In order to ensure the high quality necessary for use in scientific in- struments, most high-technology optical glasses are melted in platinum containers. In general, this has excellent corrosion and ero- sion resistance, as well as low solubility, when in contact with molten glass. Therefore the dangers of discoloration and reduction in optical transmission are low. Glass melts may be contaminated by the uptake of corrosion and erosion products if the glass is melted in ceramic materials. The use of platinum, instead of ceramics,for both containers and stirrers enables glass melts to be stirred more thoroughly and hence become more homogeneous. In this way a better quality and higher yields of glass are obtained. Even totally new glass systems which have superior optical pro- perties, but which would attack ceramics very quickly, can be melted in platinum vessels and produced to extremely high quality. Generally, platinum or its alloys enables optical glass to be produced with high purity, homogeneity and the absence of streaks and bubbles.

The platinum used in the glass industry for platinum during the melting of phosphate glass melting pots, for coating melting vats, for stir- of a selected composition is discussed. Ap- rers and for other auxiliary equipment has to preciable corrosion of platinum can be expected withstand high thermal and mechanical during the preparation of phosphate glass; stresses. For many types of glass the process therefore a study has been made of the cor- conditions are under close control and as a rosive action of the phosphate glass in order to result the platinum apparatus has a very long develop procedures which would enable such service life. On the other hand during the glasses to be melted successfully in platinum manufacture of certain glasses elements such as crucibles. Reports of related work on the pro- phosphorus, lead, silicon and boron, arising duction of lead glass, barium crown glass and from the decomposition of their compounds, glass ceramics will follow. form low melting point eutectin which may cause considerable corrosion of the metal. Experimental Procedure Nowadays there is an increasing tendency to The composition of the phosphate-based melt even such glasses in platinum containers, batch was as follows: 60 per cent Al(PO,),, 15 since the required high quality glass often can- per cent Zn(PO,),, 15 per cent Mg(P0,)2and not be produced by melting in ceramic con- 10 per cent BPO,. Cold drawn 99.9 platinum tainers. Thus, it is necessary to study the basics wire samples 1.5 mm diameter and 70 mm long of such reactions in order that they can be were exposed for various times either to a reduced, or avoided. melting phosphate batch or, in a long time ex- In the first part of this paper the corrosion of posure test, to a melt at 137OOC for up to 500

Platinum Metals Rev., 1992, 36, (l), 14-25 14 Fig. 1 The hot tensile 12 , T 24 ,"I I strength and elongation to .- rupture of platinum is shown Lump melting . 20: (Rernel ting) as a function of the time of 8 u exposure to a melting 0 I phosphate mixture, at a temperature of 137OoC,and to remelting phosphate glass lumps

0 2- -4 4 w Batch melting B 2 4 6810 20 40 60 EXPOSURE TIME, minutes hours. Prior to testing the platinum was anneal- even higher test temperatures and various test ed for 2 hours at 140OOC to recrystallise and atmospheres can be realised. stabilise its microstructure. In the long term tests the samples were only put into the melt Results when it was in the form of a homogeneous The results obtained showed that the hot phosphate glass. In this way it was possible to strength of platinum is reduced drastically as differentiate between the effects of the starting the phosphate batch starts to melt, but it does mixture and the actual melt upon the platinum. not change during long term exposure tests in After exposure - at the same temperature - the the molten glass, even after long times. From hot tensile strength, elongation to rupture, and Figure 1 it can be seen that the melting mixture time to rupture of the samples were determin- reduces the hot tensile strength considerably in ed. The data given below are the average values the first 15 minutes, and that the elongation to from five measurements. The platinum samples rupture is reduced to zero. This reduction in were investigated further by light- and scanning strength, and the embrittlement of the electron-microscopy, electron microprobe, platinum are demonstrated even better by creep secondary ion mass spectrometry (SIMS) and testing. As shown in Figure 2, the time to rup- X-ray diffraction analysis. For the creep tests ture of platinum at constant load, and its rup- specially developed apparatus was used which ture elongation are reduced to zero by the enabled data to be obtained at temperatures up melting phosphate batch after only 2 minutes; to 90 per cent of the melting point of the sam- this means that the samples fail under load ple, in the case of platinum at up to 160OOC (1, without any deformation taking place if they 2). In order to obtain the high testing are cooled and then reheated to the test temperatures, the samples were heated directly temperature. by an electric current. Regulating the power In contrast, during the long term exposure supply ensured a constant temperature despite test in a phosphate glass melt, reductions in the changes in the electrical resistivity of the hot tensile strength and the standing time are samples, resulting from a reduction of their not observed during exposure times of up to cross-sectional area. Due to the temperature 500 hours, Figure 3, provided that the amount gradient along the sample, the holding clamps of melt lost by vaporisation is replaced by the stayed significantly below the testing addition of glass pieces. If the replenishment is temperature. This apparatus has proved its effi- achieved by adding the phosphate mixture, ciency over many years for testing high melting however, the reactions on melting cause an ap- point metals at temperatures up to 2000°C; preciable reduction in the standing time but not

Platinum Metals Rev., 1992, 36, (1) 15 Fig. 2 The time to rupture and the elongation to rupture of platinum at a constant load of 1.7 N and a temperature 0 w' E a3 of 137OoC, as functions of W' the reaction times with a 9 800- Star 11ng cond I t tons -a I- 5(r melting phosphate mixture 3 P and with melting phosphate LJmp melting (Remelting) glass lumps 2 0 05 0 g400-- 0 -4 2 c sc:

2 6 8 10 20 40 60 EXPOSURE TIME, minute5

l2 II6oo 0 500 210- 0 0 2 c I " 3 0 0 400 E $a-\ Lump adding Starting conditions W k! k! (Remelting) 3 300 3

.200g Fig. 3 Hot tensile strength 100 and time to rupture, at a load of 3.9 N, of platinum as a function of the time of reac- 5 10 50 100 5oo tion in a phosphate glass EXPOSURE TIME, hours melting at 137OOC

in the hot tensile strength. The values of and 4(d). At the edge of the samples the early fracture elongation behave accordingly. stages of melting can be seen, Figure 4(e). The Since the results of the long term exposure fracturing suggests the uptake of alien elements tests reveal the changes in the properties of the leading to a reduction in the melting point of platinum better than the hot strengthhpture the sample. Platinum forms low melting point test, in later work only the former were studied. phases and eutectics with many of the elements Scanning electron microscopy investigations that are present in glass and this must be con- of platinum which had been annealed prior to sidered as the main reason for possible failure testing showed that after the exposure test the (3-5). In the platinum-phosphorus system a fracture area displayed transcrystalline defor- eutectic of platinum and R,P2 exists at 3.8 mation, this is evident in Figures 4(a) and qb). weight per cent phosphorus and a temperature During translation on the slip planes a shear lip of only 588OC, see Figure 5. At 6 weight per (Scherlippe) formed in places where the metal cent phosphorus the R,P, phase forms; this finally fractured. The ductile metal showed starts to melt at 59OOC. appreciable reduction in cross-section in the As a result of metallographic and fractured area. microanalytical investigations the following After reaction with the melting phosphate observations can be made about the reduction mixture intercrystalline brittle fracture occurs, in the high temperature mechanical properties exposing crystal grain boundaries, Figures 4(c) of platinum samples caused by the melting

Platinum Metals Rev., 1992, 36, (1) 16 Fig. 4 Fracture surfaces produced by tensile creep testing of platinum samples in both the starting condition and after reaction with a melting phosphate mixture at 137OoC/4 min and showing: (a) starting condition, general view showing transcrystalline deformation fracturing (b) starting condition, shear lip (Scherlippe) on edge of sample (c) intercrystalline brittle fracture following reac- tion with a phosphate batch (a) intercrystalline brittle fracture on the edge of a sample after reaction with the melting phosphate mixture (e)following reaction with the phosphate mixture the start of melting can be seen on the edge of the sample

Platinum Metals Rev., 1992, 36, (1) 17 ______~___~___~~ ~ a series of alien elements and impurities, but it CONCENTRATION OF PHOSPHORUS, weight per cent 0 2 4 6al0 1520 30, is necessary to bear in mind the high sensitivity of the SIMS method. Following reaction with the mixture, 18001600 K"\ phosphorus was the only additional element detected in the products that occurred on cer- tain areas of the surface of the platinum. Figures 8(a) and 8(b) show, respectively, op- tical and X-ray images of such an area. By com- parison with a standard, the phosphorus content was determined to be 5.3 weight per cent. This is in good agreement with the phase 4001 - I . . . . 0 10 20 30 40 50 60 '0 Pt,P, shown in the phase diagram at 6.0 weight CONCENTRATION OF PHOSPHORUS, atomic pl cent per cent phosphorus. Fig. 5 The platinum-phosphorus phase diagram shows a eutectic at 3.8 weight per Additionally, on the surface there are areas cent phosphorus, at 588OC that have been molten. These consist of a eutec- tic of platinum and a Pt-P phase. The photomicrographs Figures 9(a) and 9(b) show a phosphate mixture: if cold deformed platinum solidified platinum eutectic particle at the edge is recrystallised at a moderately high of the sample. This particle would be liquid at temperature a fine grained microstructure the service temperature, due to the melting results, see Figure 6(a). In a high melting point point reduction resulting from the uptake of glass melt a coarse microstructure forms in the phosphorus, and likely to drop into the liquid platinum by collective recrystallisation, Figure glass. In this way glass can be contaminated by 6(b). In this way detrimental alien elements can minute platinum particles. Even in small diffuse rapidly along the grain boundaries into amounts these may be harmful to the optical the platinum. Coarse grains occurred in properties of glass. The uptake of phosphorus platinum which was in the as-annealed starting in eutectically solidified areas of the platinum condition, as well as in samples which were ex- has been confirmed by microprobe analysis, posed to the melting phosphate mixture or to Figure 9(c), and by SIMS, Figure 9(d). No the glass melt. The formation of widened grain other contaminations were detected at a level boundaries, however, is only observed after ex- exceeding that of the initial platinum. In the posure to the phosphate mixture, see Figures hot-stage microscope the start of melting of the 6(b) and 6(c). Pt-P phase was found to be about 58OoC, In samples that had been exposed to the Figure 10, which is in good agreement with the melting mixture, the diffusion of phosphorus figure of 590OC given for Pt,P, in the phase into the grain boundaries of the platinum was diagram. At 63OOC droplets of the melt were always detected. The line scan for phosphorus, clearly observed. Above this temperature some Figure 6(d), the "/PO/+ secondary distribu- evaporation from the sample was seen, an in- tion image, Figure 6(e), and the mass spec- dication of the relatively low thermal stability of trogram, Figure 7, all show the uptake of the Pt-P phase. With further increases in phosphorus at the platinum grain boundaries. temperature the molten areas within the The "/PO/+ ions occurred with Ill'+ in the material also increased. mass spectrometric investigations, since During glass melting, the decomposition of primary oxygen ions were used. In Figure 7 the the Pt-P phase results from its low thermal grain boundary area analysed is shown, stability and explains the presence of together with the 47/PO/+ secondary ion microscopically small particles of fairly pure distribution. The mass spectrogram also reveals platinum within the glass.

Platinum Metals Rev., 1992, 36, (1) 18 Fig. 6 After recrystallisation and reaction with melting phosphate mixtures (137OoC14 min) sectioned platinum wires show: (a) fie grained microstructure following recrystallisation at 6OOOC (b) coarse grained structure following recrystallisation and reaction with the phosphate batch (c) following exposure to the phosphate mixture, scanning electron microscopy reveals an enlarg- ed grained boundary (d) the electron microprobe analysis line trace for phosphorus shows a build up of phosphorus at the grain boundary (e) ‘/PO/+ uecondary ion-distribution photo (primary ions: 01+)again showing enrichment of phosphorus at the grain boundaries following reaction with the phosphate mixture

Platinum Metals Rev., 1992, 36, (1) 19 Fig. 7 The mass spectro- gram of a grain boundary AnalySed grain area near the edge of a boundary area platinum sample following 47~ reaction with a melting SQU phosphate batch (1 37OoC/4 min)

31 P‘

I 16 272831 3940 47 566364 lo3 MASS NUMBER

Finally, the formation of Pt,P, by the reac- forms a liquid phase with phosphorus which tion of platinum with the melting phosphate changes the mechanical properties of the batch was confirmed by X-ray crystallography. platinum. Some areas of the platinum surface consist of a eutectic melt, part of which gets in- Discussion to the glass melt causing platinum inclusions. Changes in the morphology of platinum were Phosphorus can be produced easily by the detected after the reactions involving the reduction of compounds in the phosphate melting phosphate mixture (even though these batch; additionally it is known that such reac- were relatively short term), but not after testing tions are catalysed by platinum. As can be seen in a phosphate glass melt. The results showed from the thermogravimetric curves in Figure 11 that during the heating and melting of a the mass loss during heating in the presence of phosphate batch phosphorus is set free, as the platinum is greater than it is in the absence of element. This diffuses preferentially along the platinum. Furthermore, during the melting of grain boundaries, especially into coarse grained metaphosphates phosphoric acid forms and this platinum, causing hot shortness. Platinum attacks platinum, also Pt, P, may be produced

Fig. 8 Following reaction with a melting phosphate batch (137OoC/4 min) a platinum-phosphorus phase occurs near the edge of the platinum sample (a) optical photomicrograph, (b) the X-ray image using phosphorus K, radiation

Platinum Metals Rev., 1992, 36, (1) 20 Fig. 9 Areas on the surface of a platinum sample after reaction with a melting phosphate mixture (1370OC14 min) (a),(b)the eutectic melt consists of platinum (light coloured) and a platinum-phosphorus phase (grey) (r) scanning electron microprobe Line scan image of the euteetie for phoaphorua (d) "/PO/+ secondary ion-distribution photo of the eutectie (primary ions: O,'), platinum- phosphorus phase (bright) and platinum (dark) by a secondary reaction. Once the phosphate reaction with platinum will occur, providing mixture is molten and phosphate glass formed that no other reducing agents are present. This the remaining phosphorus is tied up and no explains the observation that in the long term

Platinum Metals Rev., 1992, 36, (1) 21 tests at up to 500 hours carried out with boron, silicon and bismuth, which when pre- phosphate glass melts, no uptake of alien sent at even low concentrations cause embrittle- elements was detected even by the highly sen- ment and a reduction in time to rupture sitive SIMS technique, neither was any change strength of platinum because of grain boundary in microstructure observed. cracking (5). Investigations with other batches and glass As long as these elements exist in the glass as melts, which will be discussed in a later article, stable compounds-generally as oxides-they showed results comparable to those with the do no harm. However, as soon as they occur as phosphate glass. Generally one may state that elements their diffusion into platinum takes there are a number of chemical elements, in- place. In this way low melting point phases, cluding phosphorus, lead, arsenic, antimony, eutectics or even peritectics form and influence

Fig. 10 High temperature photomicrographs 01 a platinuui sample after reartion with a melting phosphate batch (1370OC14 inin). The melting of thr platinum-phosphoruu phase begins at about 58OOC. A scanning electron microscope imagr after cooling to room temperature is also shown

Platinum Metals Rev., 1992, 36, (1) 22 Fig. 11 Thermal analysis of the reaction of ‘i ~ a phosphate batch with and without contact OL- 1 with platinum: (a) batch in contact with platinum wire, (b) batch without contact with platinum wire (heating rate about 6OC per 4; 4 min; atmosphere: stationary air; alumina 3: 7 crucible; sample weight 500 mg; sample Za3 loosely poured; substance for comparison, alumina) zi

. . . . , , ] Mx) 700 800 900 loo0 1100 1200 1300 1400 TEMPERATURE, ‘C

the properties of the platinum. Therefore the Figure 11, in the temperature range 850 to conditions under which glasses are melted are 940OC showed an endothermic reaction, with a of decisive importance. If the conditions can be maximum at 92OoC, during which the mixture controlled in such a way that no elements harm- did not change. When operating below these ful to platinum occur then it will be possible to temperatures no sintering reaction was observ- keep the corrosion of platinum low, and to pro- ed. Above 92OOC a very porous low strength cess glass melts in contact with platinum. In body was formed, while at still higher sintering reality many corrosion failures of platinum are temperatures the porosity decreased. not caused by its low resistance to attack by the Based on thermal analysis and other ex- relevant glass but result from neglect of process perimental observations a sintering time of 2 factors. hours, at temperatures of 920, 960, 1000 and If reducing conditions exist, because of the 1050°C, was selected for the pretreatment of composition of the mixture, or the presence of the batch. The sintered material produced in impurities such as carbon, or by improper this way was broken into pieces and used for handling, then “dangerous” elements may be corrosion tests, as was material which had not formed which will then corrode the platinum. been pretreated. In a melting mixture that had not been Reducing Corrosion and Increasing Service Life By making technological changes to the glass c melting process the aggressive nature of the melt can be reduced and the working behaviour of the platinum improved. The investigations on phosphate glass have shown strong corrosion of platinum by the 0 melting batch, but no effect by the melt itself. ii Therefore platinum corrosion can be ap- ‘ 960 950 l& lo!, 4 preciably reduced if the reactions that take SINTERING TEMPERATURE,*C W place during the heating and melting of the Fig. 12 Time to rupture and elongation to rupture data for platinum in the un- mixture are completed before the platinum is sintered condition, and after sintering at brought into contact with the batch. This may the given times, both in the starting condi- be achieved by presintering the batch before tions and after reaction with the melting phosphate batch at 137OOC and constant melting or by using premolten glass lumps. load of 1.7 N batch 0 sintered batch Thermal analysis of the phosphate mixture,

Platinum Metals Rev., 1992, 36, (1) 23 premelted in a ceramic pot then, after it has been cooled and broken into pieces it is finally melted in a platinum container. Figures 1 and 2 show that premelted phosphate glass lumps have no detrimental effects on the high temperature mechanical properties of platinum. Platinum samples subjected to ten- sile testing after contact with molten sintered phosphate glass or with lump melted glass fail- ed in a transcrystalline manner, as did platinum in the as-received condition. The uptake of alien elements and related metallographic struc- tural changes were not seen in platinum which had been in contact with melts prepared from sintered mixtures or glass lumps. Thus by presintering the batches or by using lump remelted material the corrosion of platinum is greatly reduced. Since the glass melt or the raw glass does not affect the platinum a continuous melting process can be set up. In this case the untreated mixture is first melted in ceramic containers, then in the se- cond stage the melt is treated in platinum con- tainers only. In this way glass can be made from mixtures containing elements normally too aggressive to be brought into contact with platinum ware, while glass which is usually processed in platinum ware can now be produced to a higher quality. Thus it is now possible to produce phosphate glass of improved quality using platinum containers.

Fig. 13 The microstructure of DVS-platinuni in Platinum with Improved the as-received condition (a), (b) consist of fine Properties grains in which are embedded small particles of The former Forschungsinstitut fur zirconium dioxide; (e) after reacting with a phosphate glass melt, for 250 hours at 137OOC Nichteisenmetalle in Freiberg, Sachsen the DVS-platinum has retained its fine grained (Freiberger NE-Institute GmbH) developed a structure dispersion hardened platinum known as DVS- platinum (8). This was made from foils produc- pretreated the time to rupture and the elonga- ed by rolling an alloy of platinum containing tion to rupture of platinum during tensile creep 0.3 to 0.5 per cent zirconium, the foils then be- testing was quickly reduced to nearly zero. In ing annealed in an oxygen-containing at- contrast, a melt from a batch which had been mosphere. A number of foils were then welded presintered at 920 to 105OOC had no effect on together by compression at high temperatures, the mechanical properties of the platinum, this and the final “sandwiched” sheet was made by is shown by the data in Figure 12. cold and hot rolling this layered structure. During lump remelting the batch is first DVS-platinum has a fine grained structure

Platinum Merals Rev., 1992, 36, (1) 24 Fig. 14 Time to rupture and elongation to rupture data for DVS-platifium, at a constant load of 20 N, and 5 pure platinum, at a constant load of 4 N. Both have u- diameter 1.5 mm and are 2 held at 1370OC. a3 Az: starting conditions are: a 140OoC/2 hours in air 2 Ge: reaction with a

phosphate mixture at + 1370°/30 minutes Sch: reaction with I-. phosphate glass melt at 1 37OoC/250 hours DVS PLATINUM PURE PLATINUM with small embedded particles of zirconium however, the effect on the properties of DVS- dioxide, Figure 13. This kind of structure pro- platinum is rather small. duces excellent resistance to grain growth at In contrast to pure platinum, for DVS- high temperatures and an appreciable increase platinum no appreciable grain coarsening is in the time to rupture strength. It may be weld- observed. After exposure to the phosphate mix- ed, but as welding is done by adding pure ture and to a phosphate glass melt a small platinum the welds constitute weak points. amount of corrosive attack is seen at a few The corrosion resistance of DVS-platinum places on the rim of the samples, Figure 13(c). has been tested in phosphate glass. For these The uptake of alien elements is never observed. tests a specially prepared and treated phosphate DVS-platinum not only exhibits a better long batch of similar composition to those discussed time to rupture strength but because of its earlier was used. In one series of long term tests stable fine grained microstructure and the approximating to a practical application iron coverage of grains by zirconia it also possesses and powered sugar (for reduction) were added a higher resistance to corrosion. in order to test the DVS-platinum under ex- treme conditions. Iron is known to be an ele- Acknowledgement ment which causes intercrystalline oxidation in The author wishes to thank Professor Dr. Ch. J. platinum, thus reducing its hot strength; the Raub, Forschungsinstitut fur Edelmetalle und Metallchemie, Schwabisch Gmiind, for encouraging liberation by reducing agents of elements harm- discussions and for translating this article into ful to platinum has been considered above. English. The results of these long term tests are shown in Figure 14. It is apparent that DVS-platinum References 1 B. Fischer, H. Topfer and R. Helmich, Silikat- exhibits a much greater time to rupture, and technik, 1984, 35, (]I), 329 reasonable elongation to rupture, even if one 2 B. Fischer, H. Topfer and R. Helmich, East considers that the load on DVS-platinum is 20 German Patent 245,576; 1987 3 G. Reinacher, Glastech. Ber., 1975, 48, (I]), 221 N (2 kg/mm2), five times greater than the 4 N 4 D. Menzel, Prakt. Metallogr., 1976, 13, (3,211 of pure platinum, even without contact with 5 B. Fischer, Diss. B, TH Chemnitz, 1983 glass (Figure 14). For pure platinum the time to 6 Metal Industry, Handbook and Directory; Iliffe & rupture and the elongation to rupture are both Sons Ltd., London, 1960 lowered significantly by the action of the 7 E. Dahl, Acta Chem. Scand., 1967, 21, (9, 1131 melting batches and by the aggressive 8 S. Cirtner, D. Adam and W. Molle, Neue Hiitte, 1979, 24, (3), 103 phosphate glass which contains iron and a 9 D. Adam and S. Gartner, East German Patent reducing agent. Under identical conditions, 120,385; 1976

Platinum Metals Rev., 1992, 36, (1) 25 Platinum Group Organometallics COATINGS FOR ELECTRONICS AND RELATED USES By Professor A. Z. Rubezhov Institute of Organo-Element Compounds. U.S.S.K. Academy of Sciences, Moscow

Platinum group organometallics have recently been the subject of inten- sive investigation designed to establish the basic characteristics of their derontposition, which results in the formation of metallic or nietal- containing coatings. This review has been compiled from a literature search and indicates some of the applications that are, or could be, of commercial significance.

This survey is devoted to some aspects of the regarded as separate techniques. These types of use of organometallic platinum group com- organometallic compounds can decompose to a pounds for the preparation of materials suitable metal, or to an oxide under the influence of for industrial applications, mainly in electronics heat, electric discharge, electron beam, and (1,2). The detailed chemistry of organometallic laser radiation, and these techniques are platinum group compounds is not included, as employed for vapour phase decomposition. a number of monographs on this subject are Decomposition of organometallic compounds available (3, 4, 5). In some instances, however, in solution is frequently performed thermally, information about co-ordination complexes of photochemically, electrochemically or via platinum group metals will be included. The chemical reduction and hydrolysis. Each possible practical use of organometallic method will now be considered separately, and platinum group compounds for the deposition a list of the compounds and metals used in each of coatings and films by various decomposition will be given. techniques was suggested in early works on The requirements for vapour phase thermal synthesis, see for example (6). To date, decomposition are as follows (1, 2): however, organic derivatives of platinoids have (a) the compound should be transformed into found little commercial use despite fairly exten- the vapour phase without decomposition sive data, especially in the patent literature. (b) the compound should be highly volatile The reasons for this include the high cost of the (c) organic products resulting from the decom- compounds, the lack of suitable coating equip- position of the organometallic compounds ment, and, in some cases, the lack of routine should be gaseous, and should not contaminate production processes for the synthesis of the the coating required complexes. (d) the organometallic compounds should be A brief outline of general coating and film non-toxic and ideally should be stable to air and deposition techniques based on organometallic moisture. platinum group compounds is first given. The first two of these are the determining fac- To date, there are two main decomposition tors. In order to characterise the volatility of methods for the production of coatings, namely organometallic compounds, the vapour vapour phase decomposition and decomposi- pressure-temperature equation should be ap- tion in solutions. The decompositions of plied. However, for organometallic platinum organometallic compounds in the solid state group compounds, this is known only for and as components of various viscous composi- ruthenocene (7), CpPtMe, (8) and MeC,- tions, such as pastes and polymers, can be H,PtMe, (8). For a number of compounds

Platinum Metals Rev., 1992, 36, (11, 26-33 26 sublimation point (sub1m.p.) and boiling point individual ruthenium tris-p-diketonates are (b.p.) data are available, but in most cases there mentioned in the literature. The latter com- are no known quantitative values for the pounds are patented for use in the formation of volatility of the organometallic platinum group ruthenium films on various substrates via the compounds. deposition of (acac) ,Ru or (F, acac) ,Ru Most of the data on the decomposition of vapour onto a suitable support, heated to the organometallic platinum group compounds is decomposition point of the compound (16-18). concerned with their thermal decomposition. Ruthenocene, (C,H,),Ru, is the most pro- (The formation of iridium oxide films via mising compound for the formation of vapour deposition in an oxygen discharge (9) is ruthenium films. First, it is a commercially not considered in this review.) Information on available product, and it is suitably volatile each metal is considered separately. (sub1m.p. 100°C/lO-l mm), air-stable, non- toxic and may be prepared in a highly pure Ruthenium state. Attention was first drawn to the possibili- Complexes potentially suitable for the deposi- ty of preparing high purity ruthenium via tion of ruthenium films are ruthenium car- ruthenocene decomposition in 1964 (19). A bonyls, ruthenium carbonyl halides, ruthenium pure ruthenium film was generated at 595OC in cyclopentadienyls, ruthenium acetyl- a hydrogen atmosphere; iron (- 0.01 per cent) acetonates, and some of their organic and and palladium ( - 0.005 per cent) were present co-ordination derivatives. Pentacarbonyl as admixtures, and silicon and boron as trace ruthenium, Ru(CO),, with a vapour pressure elements. Patented applications for of 50 mm Hg at 18OC (lo), starts to decompose ruthenocene include: the preparation of layer at -18OC to form Ru,(CO),, and at a resistors (20), additives to liquid crystals (21) temperature of 22OOC decomposition to the and for plating multilayer electrodes with ox- metal occurs. The thermal decomposition of ides and metals (22). The plasma-induced trinuclear Ru,(CO),, to the metal has been vapour phase decomposition of ruthenocene studied by infrared spectroscopy and ther- enables thin metallic films to be produced at a mogravimetric analysis (1 1). A bright metallic sufficiently high rate (23, 24). film is formed on decomposition of Ru(CO),Cl, or of RuCOBr at 2OO0C, in the absence of air (10, 12). Annealing Ru(CO),Br According to data in the literature (lo), on (b.p. 118OC, sub1m.p. 140OC) or Ru(CO),I decomposition, osmium carbonyl halides are (b.p. 114OC, sub1m.p. 120OC) in a stream of capable of forming bright osmium fdms. Thin oxygen and phosgene leads to the formation films of osmium metal were prepared via the of ruthenium films (10). decomposition of OsO, complexes with However, the thermal decomposition of terpenes in a hydrogen stream at 3OOOC (25, ruthenium carbonyls and ruthenium carbonyl 26). It should be noted that osmium tetroxide chlorides, like analogous platinum metals exhibits high volatility, but its high toxicity, derivatives, is accompanied by severe corrosion equal to that of hydrogen cyanide, precludes its of the equipment and the support materials, use for fdm preparation. The application of a also, the majority of these ruthenium com- solid complex of OsO, with dioxane has been pounds are moisture- and oxygen-sensitive. patented. It is less volatile than osmium tetrox- Thermodynamic functions have been determin- ide and also less toxic (27). Among other ed for ruthenium and osmium carbonyls, osmium derivatives, it should be noted that M(C0) 5, in the gaseous state (13). cyclooctatetraene(tricarbony1)osmium has been Some volatile ruthenium compounds, namely patented for the deposition of coatings from the mixed dienecarbonyls (14) and diene-P- gas phase (14), while osmocene, bis(cyc1openta- diketonate ruthenium complexes (15) and dienyl)osmium, has been recommended as an

Platinum Metals Rev., 1992, 36, (1) 27 additive to liquid crystals (21) and also for the to that of carbon (6). The known volatile preparation of high purity osmium (28). The iridium compounds include carbonyl hydrides thermal decomposition of Os, (CO) to and chlorides, which are readily decomposed metallic osmium has been reported in the and sublimed to form bright metallic films (lo), literature (1 1). tris(r-ally1)-iridium (29), r-cyclopentadiene-r- cyclopentadienyliridium (29) and iridium 0- Rhodium diketonates (31-33). The decomposition of The ability of rhodium carbonyls and tris(acety1acetonato)iridium in a stream of rhodium carbonyl halides to form bright hydrogen at 11 5 to 132OC, with deposition onto rhodium films on decomposition has been a support heated to between 400 and 75OoC, known for some time (10). For example, yields an iridium film. The use of [Rh(CO),l, on heating without solvent, and tris(acety1acetonato)iridium for the preparation

Rh, (CO) ,? on heating in air, deposit a rhodium of fuel elements, has been claimed (31). Other film (1 1). A dimeric carbonylrhodium chloride volatile organometallic iridium compounds, [Rh(CO)? C11 ? melts at 123OC, readily sublimes namely r-cyclooctadiene-r-cyclopentadienyl- above 100°C, and decomposes at around 300°C iridium (34) and *-cyclooctadieneiridium in a stream of carbon dioxide to deposit a bright acetylacetonate (34) should be mentioned. A metallic film. In the presence of oxygen or four nuclear carbonyl, Ir, (CO) is readily COCl,, [Rh(CO) C11 “flares up” and “burns sublimed in a stream of carbon monoxide under out”, thus depositing bright rhodium films atmospheric pressure (29). (10). Among other volatile rhodium compounds, Palladium tris(ally1)rhodium and liquid r-allyl-a- Palladium is one of the less expensive allyl(cyclopentadienyl)rhodium (29) as well as platinum group metals, and the chemistry of its rhodium complexes with 0-diketones should be organometallic compounds is well developed mentioned. For example, the reduction of (4, 5). In decreasing order of volatility, the tris(trifluoroacety1acetonato)rhodium with volatile compounds are: r-allyl-r-cyclopenta- hydrogen in the vapour phase has been propos- dienylpalladium r-C, H ,Pd-r-C ,H, (sub1m.p. ed for the preparation of thin rhodium films 3O-4O0C/1-2 mm) (35), bis(r-ally1)palladium (30). At a vaporisation temperature of 13OoC, a (a-C, H,),Pd (sub1m.p. 35-4OoC/10- mm) reduction temperature of 25OOC and a (36), and bis(trifluoroethy1dithiocarbonato) hydrogen flow-rate of 16 ml/min, thick uniform palladium compound (CF CH OCS 2) Pd films with good adhesion and good electrocon- (sub1m.p. 130-150°C/10-1-10-2 mm) (5). ductivity were deposited. X-ray phase analysis The volatile co-ordination compounds of the revealed no admixtures in the films. The use of metal with sulphur- and nitrogen-containing acetylacetonates of rhodium and other metals ligands have been the subject of a review (37) for the production of fuel elements has been and reported elsewhere (38-42). patented (31), and data on the vapour pressures r-Allyl-r-cyclopentadienylpalladium (43-49, and heats of sublimation of rhodium and bis-x-allylpalladium chloride (44, 46), and iridium tris(trifluoroacetonate) complexes have bis(acety1acetonato)palladium (47, 48) have been published (32). been used for the preparation of films. The characteristics of the thermal decomposition of Iridium bis-a-allylpalladium chloride in the solid state Iridium occupies a special place among the (49-52) and the thermal stability of a series of because of its hardness, high r-allylpalladium complexes (53) have been resistance to oxidation and ability to form car- studied by differential thermal analysis and bides. The temperature dependence of the coef- thermogravimetric analysis. The thermal ficient of thermal expansion for iridium is close decomposition of bis(hexafluoroacetonato)

Platinum Metals Rev., 1992, 36, (1) 28 palladium follows a radical mechanism (54), preliminary decomposition taking place on the bis-?r-allylpalladium chloride decomposes to way to the support. Reduction of the car- precipitate metallic palladium which catalyses a bonylchloride vapours with hydrogen prevents further decay of the complex. The initial the formation of coarse grained films, and pro- decomposition temperature is 137OC, and motes the formation of smooth, uniform palladium is precipitated at 160-225OC. On platinum films. precipitation of the palladium, secondary reac- The preparation of thin platinum films via tions of the allylchloride moieties occur, the thermal decomposition of bis resulting in the contamination of the metallic (acety1acetonato)platinum has been described palladium by carbon. The catalytic activity of (57, 58). The (acac),Pt compound vaporises the metal, which precipitates on decomposition at 180°C/10-4 mm, and the deposition of of (C,H,PdX)2, is considered elsewhere (55). lO-lOOA thick films onto a silicon support At 130-135°C/10-2 mm and at a pumping rate heated to 500-6OO0C is carried out at a vapour of not less than 1-1.5 pmls, a palladium film pressure of 20-200 mm. Hydrogen is not was deposited onto a support heated at 200 to suitable as a carrier gas, because it results in the 35OOC. The maximum film thickness was 8 pm, formation of a black non-volatile compound. and no chlorine was present. The resulting The films are contaminated by carbon. films exhibited good adhesion to ceramics, The thermal decomposition of tri- fluoroplast-4, sodium chloride and potassium methyl(acetylacetonato)platinum at 165OC was chloride crystals. investigated in a flow type system, with pump- Bis(acety1acetonato)palladium is vaporised at ing of the decomposition products at 150°C/10-4 mm and is decomposed to the 250-30O0C (59-61). Platinum was deposited as metal at 35O-40O0C. The addition of an ox- a bright metallic film, and acetylacetone and idiser, such as carbon dioxide, suppresses the methane were identified in the decomposition codeposition of carbon. Good results were ob- products. tained for a palladium film deposited from The other most suitable platinum derivatives C, H, PdC, H, . The compound vapours for film formation via deposition from the entered the reactor either at 40-5OoC/1 mm or vapour phase, are tetrakis(trifluoro- at 70-8OoC/760 mm; and rapid film formation ph0sphine)platinum Pt(PF,), (b.p. 7OOC) (62), occurred on a suitable support heated to 300OC. bis-?r-allylplatinum (C, H5)2pt (sublm.p. The thickness of the palladium film depended 40°C/10-2 mm (63), ?r-allyl-?r-cyclopenta- on the time that the support was located in the dienylplatinum C, H, PtC, H, (sub1m.p. C,H,PdC,H, vapour stream. The films 40°C/10-2 mm) (63), trimethyl-?r-cyclopenta- obtained exhibited good adhesion. dienylplatinum Me,Pt-r-C,H, (sublm.p. 100°C/10-2 mm) (8, 65) and its monomethyl Platinum derivative (8). The production of platinum- Historically, chlorocarbonyl complexes were gallium films has been reported (66). the first platinum compounds to be employed for film formation. Precipitation of platinum Decomposition in Solution occurs during thermal decomposition of Having reviewed the literature on the ap- platinum carbonylchloride compounds at plication of organometallic platinum group 100-120°C/0.01-0.02 mm, the temperature of compounds for the preparation of coatings and the metallised support being 600OC. Thus thin films via vapour phase deposition, the decom- uniform films were produced on platinum, position of organometallic compounds in solu- molybdenum and wires (56). The use of tions is now considered. In this case the carbon dioxide as a carrier gas prevents the majority of the data is concerned with thermal decomposition of the compound in the decompositions which is due to the fact that evaporator and reduces the possibility of electrochemical and chemical deposition of

Platinum Metals Rev., 1992, 36, (1) 29 Organometallic Platinum Group Compounds for Film Deposition

I ~ Organometallic compound Support Temperature Reference

Synthetic fibres 67 67 6767

(DieneIPdCI,(DieneIPdCI, Polymer I 50-150°C50-1 5OoC I 6868

Os0,terpene Glass 3OOOC3OOOC 69 H, streamstream (DieneIPdCI,(DieneIPdCI, 70

LML' Electrodes 7171 (M(M =Pd, Pt, Rh, Ir,Ir, Ru, 0s; L,L'=cyclic hydrocarbon ligands)ligands)

Pd,DBA,Pd, DBA, Plastics 72 (DBA(DBA = dibenzylideneacetone) 72 I I I Rh,(CO),CI,Rh,(COl,CI, Glass" 73

IC,H,PtCI,lH Zeolites,Zeolites, metal metal 74 oxides 1 74 CODPtCI, 74 1 I " I 74 CpRh(CO),H Divinylbenzene, 75 polystyrene I 75 For data on application of the compounds: C,H.M(XlC,H.IM=Rh lr. X=SR SeR TeR AsR PR 1. (LMXI lL=cyclic r-enyl; M=Pd, Pt; X=halogenl; [QM(COI €]+A- IM=Ru. 0s;Q=C.H.. C.H.; €Liefin; ALAIX;. PF., BPh:: haiogenide);'M(Csl.(PR,IX (M=Ru, Rh, yd, F't; R=Ph; X=CI, Brl~L,Rh(COICL see Refs. 76-80 Preliminary treatment with CI,SICH,I,CN

metals from solutions are being seldom used. held there until it becomes coated, and the film Films of metals and metal oxides may be pro- is then annealed into the sample. duced on a variety of supports from (iii) A stream of the solution is directed under organometallic compounds and their mixtures pressure onto the sample being plated, which is via thermal decomposition. The method is heated to the specified temperature. technologically facile, and as a rule the follow- Organometallic platinum group compounds ing procedures are carried out (1): for use with this technology require the follow- (i) The solution is applied to a sample, the sol- ing (1): vent is evaporated, the organometallic com- (a) high solubility of the organometallic com- pound is decomposed at ambient temperature pound in organic solvents and the film formed is then annealed into the (b) the organometallic compounds should not sample at elevated temperatures. undergo sublimation, even at elevated (ii) The heated sample is placed in the solution, temperatures

Platinum Merals Rev., 1992, 36, (1) 30 (c) the organic solvent and organic decomposi- ruthenium and platinum by thermolysis of tion products should be completely vaporised at Ru,(OOCPh),(PhCOOH), and (DMSO),PtCl,, the decomposition temperature of the respectively, has been reported (88, 89)). organometallic compounds. Osmium films were also produced on glass by In view of these requirements, the literature heating osmium tetroxide complexes with is now considered. It should be noted that the terpenes (90, 91). Ruthenium films were majority of organometallic platinum group prepared by the pyrolysis of Ru,(CO),, (92), compounds exhibit hlgher solubility than in- and platinum films by the decomposition of organic compounds. The first requirement, Me,PtC,H, (66, 92). Ruthenium plated elec- therefore, is easy to meet. Any organometallic trodes were made by annealing pastes contain- platinum group compound is potentially ing tris(acety1acetonato)ruthenium and suitable for the formation of films from solu- trichlorosilane (93), and thick palladium and tion, via thermal decomposition. The determin- platinum films were produced by thermolysis ing factor is the availability of the compound of the corresponding resinates (94, 95). and its possible commercial production. Infor- Another application of organometallic mation on the use of organometallic platinum platinum group compounds in electronics group compounds for film deposition via ther- relates to the production of multilayer circuits mal decomposition is given in the Table. This for computers. Usually circuit boards or shows that a wide range of compounds, cover- substrates prepared from a polymeric material, ing practically all types of platinum group such as polyamides or polyphenolfor- organometallic compounds, have been maldehyde, are subjected to chemical and elec- patented. These compounds can be readily trochemical metallisation, frequently with prepared under both laboratory and industrial copper or nickel. The metallic films thus form- conditions. ed become metallic patterns and the prepared The literature contains no data on the circuits are layered and perforated. It is photochemical and electrochemical decomposi- desirable that the holes are metallised. In order tion of organometallic platinum group com- to produce well metallised circuits, chemical pound solutions. metallisation catalysts are employed, these be- There is however information on the ing incorporated into the polymer. The com- chemical deposition of platinum metals from position is then heated to the decomposition solutions of the corresponding organometallic temperature of the organometallic compound to compounds. The deposition is carried out in form the metal. Copper and nickel are the presence of a suitable reducing agent, fre- deposited on the materials thus formed. quently hydrogen. Thus platinum films can be Palladium compounds are mainly used for these deposited on aluminium oxide and other non- applications and there are a number of patents conducting supports by the reaction of relating to complexes with phosphines (96), hydrogen with solutions of the diene platinum with phosphites (97, 98), tris(diben- complexes (8 1-84). zy1ideneacetone)dipaUadium and olefinic and Therefore, by this method, platinum metals acetylacetonate derivatives of palladium alloyed with silver and (85) or nickel (86) (98-103). For the metallising of polymers, see may be deposited from mixed a-complex solu- also (104-108). tions. One-electron reagents of the sodium naphthalenide type have been patented as Summary reducing agents (87). It is apparent, therefore, that organic Coatings may be prepared by thermal decom- platinum metals compounds have some specific position of organometallic compounds which applications in electronics, but to date these are generally applied to the support as a paste, have been limited due to difficulties in produc- or in a pure form. (The preparation of metallic ing the compounds on an industrial scale.

Platinum Metals Rev., 1992, 36, (1) 31 Refersences 1 G. A. Razuvaev, B. G. Gribov, G. A. Domrachev 29 V. S. Khandkarova, in “Cobalt, Nickel, and B. A. Solomatin, “Metalloorganicheske“Metalloorganicheskie Platinum Metals”, Nauka, Moscow, 1978, 360 Soedineniya v Electronike”, Nauka, Moscow, 30 R. L Hemmert, L. B. Spendlove and R. E. 1972 Severs, 3. Electrochem. Soc., 1965, 112, 1123 2 “Osazhdenie Plenok ii Pokrytii Razlozheniem 31 K. V. Kordesch, U.S. Patent 3,364,074; 1968 Metalloorganicheskich Soedinenii”, Nauka, Moscow, 1981 32 I. K. Irmmenov, Yu. V. Chumachenko, V. T. Isakova-and S. V. Zamekov, Zh. Fiz. .Khim., 3 S. E. Livingstone, “The Chemistry of 1979, 53, 1612 Ruthenium, Rhodium, Palladium, Osmium, Iridium and Platinum”, Pergamon Press, Ox- 33 V. E. Ivanov, E. P. Nechiporenko, V. M. ford, 1973 Krivoruchko and V. S. Sagalovich, “Kristallizat- siya Tugoplavkikh Metallov Gazovoi Fazy”, 4 “Cobalt, Nickel, Platinum Metals”, Nauka, iz 1974 Moscow, 1978 Atomizdat, Moscow, 5 P. M. Maitlis, “The Organic Chemistry of 34 E. 0. Fischer and U. Zahn, Chem. Ber., 1959,92, Palladium”, Acad. Press, New York, 1971 1624 6 E. 0. Fisher and H. Werner, German Appl. 35 B. L. Show and N. S. Sheppard, Chem. Ind., 1,132,423; 1%2 1961, 517 7 J. F. Cordes and S. Schreiner, Z. Anorg. Allg. 36 J. K. Beconsall, B. E. Job and S. O’Brien, J. SOC. 1967, 423 Chem., 1959,.. 290, 87 Chem. A, 8 Z.2. Hue, M. F. Strouse, D. K. Shuh, C. B. 37 L. A. Kosareva and S. V. Larionov, Izv. Akad. Knobler, H. D. Kaesz, R. F. Hicks and R. S. Nauk SSSR, Ser. Khim., 1975, 1211 Williams, J. Am. Chem. SOC.,1989, 111, 8779 38 S. V. Larionov, Zh. Neorg. Khim., 1979,24, 1446 9 G. Beni, 2. M. Schiavone, J. L. Shay, W. C. 39 S. V. LarionovandL. A. Kosareva,op. cit. (Ref. Dautremont-Smith and B. S. Schneider, Nature, 38), 1986, 31, 2334 1979, 282, 231 40 S. V. Larionov, L. A. Patrina, S. N. Dolgoruk, 10 N. A. Belozerskii, “Karbonoly Metallov”, E. G. Bormslavskii. I. Kovachik and V. B. Metallurgia, Moscow, 1958 Durasov, I;?. Akad Nauk SSSR, Ser. Khim., 11 R. Psaro, A. Fusi, R. Ugo, J. M. Basset, A. K. 1988, 1137 Smith and F. Hugues, J. Mol. Catal., 1980, 7, 41 V. I. Ovchazenko, L. A. Patrina, E. G. Boguslav- (4), 511 skii, V. N. Ikirskii, V. B. Durasov and S. V. 12 E. H. Reerink, U.S. Parent 1,818,909; 1931 Larionov, Zh. Neorg. Khim., 1987, 32, 1129 13 R. G. Behrens, J. Less-Common Met., 1977, 56, 42 T. Honjo and K. Nukui, Bull. Chem. SOC.Jpn., 55 1986, 59, 2645 14 K. G. Ihrman and T. H. Coffield, U.S. Patent 43 A. 2. Rubezhov, “Reaktsionnaya Sposobnost T- 3,077,489; 1963 Allilnych i Monotsiklopentadienilnych Soedinenii 15 C. Potvin, Thesis Doct. Sci. Phys., Univ. Pierre Nikelya, Palladiya i Platiny”, Dissert., Moscow, et Marie Curie, 1975, 197 INEOS U.S. Academy of Sciences, 1967 16 International Nickel, Dutch Appl. 76/5,022; 1976 44 J. E. Gczum, D. M. Pollina, J. A. Jensen and G. 17 J. N. Crosby and R. S. Hanley, U.S. Patent S. Girolami, J. Am. Chem. SOC.,1988, 110, 2688 4,250,210; 1981 45 E. Feurer and H. Suhr, Thin Solid Films, 1988, 18 International Nickel, Gennan Appl. 2,622,181; 157, 81 1976 46 G. A. Domrachev, G. B. Kazarinov and K. K. 19 D. E. Trent, B. Paris and H. H. Krause, Inorg. Fukin, in ‘‘Khimiya Elemento-Organicheskikh Chem., 1964, 3, 1057 Soedinenii”, Gorkii Gos. Univ., 1977, 96 20 Siemens, German Appl. 2,300,481; 1974 47 ”Osazhdenie iz Gazovoi Fazy”, Atomizdat, 21 Hughes Aircraft Corp., British Patent 1,559,593; Moscow, 1970 1980 48 A. J. Bird, British Patent 1,578,123; 1980 22 J. Muller and D. Lohrberg, U.S. Patent 49 A. Christ and R. Hiittel, Angew. Chem., 1963,75, 3,788,968; 1974 92 1 23 0. Gorochov and H. Ezzaquia, World Appl. 50 G. B. Kazarinov, 0. N. Valegzhaninova, G. A. 8615,824; 1987 Domrachev and G. A. Razuvaev, in “Metody 24 Nippon Engelhard K.K., Japanese Appl. Polucheniya i Analiza Vetshestv Osoboi Chisto- 621207,868; 1988 ty”, Nauka, Moscow, 1970 25 Engelhard and Chemicals Corp., British 51 G. A. Domrachev, K. G. Shalnova and S. N. Patent 1,277,360;... 1972 Titova, Zh. Obshch. Khim., 1975, 45, 319 26 R. C. Langley, U.S. Patent 3,573,970; 1970 52 G. B. Kazarinov and G. A. Domrachev, op. cit., 27 P. D. Klimstra, U.S. Patent 3,424,768; 1969 (Ref. 51), 1969, 39, 2155 28 Union Carbide Corp., British Patent 1,114,908; 53 L. M. Zaitsev, A. P. Belov, M. N. Vargaptik and 1968 I. I. Moiseev, Zh. Neorg. Khim., 1967, 12, 396

Platinum Metals Rev., 1992, 36, (1) 32 54 V. A. Nedolinnyi, P. P. Semyannikov, V. M. 87 D. B. Smith, British Appl. 1,456,844; 1977 Grankin, I. K. Igumenov and A. P. Bykov, Zzv. 88 M. Spohn, J. Strahl and W. Hiller, Z. Natur- Akad. Nauk SSSR, Ser. Khim., 1986, 45 forsh.B, 1986, 41, 541 55 T. A. Sladkova, G. A. Domrachev and K. G. 89 P. Khodadad and R. Ceolin, 3. Them. Anal., Shalnova, Dokl. Akad. Nauk SSSR, 1972, 203, 1985, 30, 1141 848 90 Engelhard Corp., Germun Appl. 2,018,104; 1970 56 E. N. Reirink, Z. Amrg. Allg. Chem., 1928, 174, 91 Engelhard Carp., Dutch. Appl. 7015,496; 1970 45 92 Shoei Chemical Industries Co. Ltd., British 57 E. C. Marboe, U.S. Patent 2,430,520; 1947 Patent 1,520,513; 1978 58 M. J. Rand, 3. Electrochem. SOC.,1973, 120, 686 93 BASF AG., British Parent 1,303,865; 1973 59 G. G. Petukhov, N. M. Uvazova and V. B. 94 Alps. Electric K. K., Japanese Appl. 6146,977; Polikazpov, “Trudy PO Khirnii i Tekhnologii”, 1987 Gorky, 1973, N 2, 119 95 P. H. Nguyen, European Appl. 266,877; 1989 60 Inst. Chem. at Gorkovsky State Univ., Russian 96 IBM Corp., German Appl. 2,555,257; 1976 Parent 441,359; 1974; Bull. Zzobr., 1974, N 32 97 C. R. Brummett. R. N. Shaak and D. M. 61 N. M. Uvarova, V. B. Polikarpov, 0. N. Andrews, U.S. Patent 3,937,857; 1976 Druzhkov and T. K. Postnikova, in ‘‘0- 98 G. Wunsch, P. Deigner, R. Falk, K. Mahler, Diketonaty Metallov”, Nauka, Moscow, 1978, 14 W. Loeser, F. Domas, P. Felleisen and W. 62 T. Kruck, Angezu. Chem., Int. Ed. Engl., 1967,6, Steck, U.S. Patent 4,128,672; 1978 53 99 Bayer AG., German Appl. 3,025,307; 1982 63 G. Wilke, B. Bogdanovic, P. Hardt et al., op. cit. 100 Bayer AG., German Appl. 3,117,247; 1982 (Ref. 62), 1966, 5, 151 101 H. Ebneth, H. Giesecke and G. D. Wolf, 64 B. E. Mann and B. L. Shaw, 3. Chem. SOC.A, European Appl. 66,073; 1982 1971, 3536 102 G. D. Wolf, K. Sirinyan, U. Von Gizyckiand R. 65 A. P. Fritz and K. E. Schwarzhaus, 3. Merten, European Appl. 259,754; 1988 Organomet. Chem., 1966, 5, 181 103 Nitto Boseki K. K., Japanese Appl. 611186,250; 66 X.-J. Chen, H. D. Kaesz, Y. K. Kim, H.-J. 1988 Miiller, R. S. Williams and Z. Xue, Appl. Phys. 104 T. Kohama, Japanese Appl. 621284,082; 1988 Lett., 1989, 55, 2760; H. D. Kaesz, R. S. 105 Y. Matsumura, I. Nozue and T. Ukachi, U.S. Williams, R. F. Hicks, J. I. Zink, X.-J. Chen, Parent 4,349,664; 1982 H.- J. Miiller, Z. Xue, D. Xu, D. K. Shuh and Y. 106 Y. Matsumura, I. Nozue and T. Ukachi, K. Kim, Nm3. Chem., 1990, 14, 527 European Appl. 22,271; 1981 67 Shoei Chemical Industries, German Appl. 107 I. Nozue, Y. Yumoto and Y. Matsumura, 2,532,254; 1976 European Appl. 59,646; 1982 68 AMP Inc., German Appl. 2,532,792; 1976 108 Nisshin Spinning K. K., Japanese Appl. 69 Engelhard Minerals and Chemicals Corp., British 631274,778; 1989 Patent 1,277,360; 1972 70 BASF AG., French Patent 1,435,663; 1966 Osmium-Ruthenium Coatings 71 Union Carbide Corp., British Patent 1,114,908; 1968 To accommodate new uses, the cathodes in 72 BASF, Gennan Appl. 2,451,217; 1976 travelling wave tubes need to operate at higher 73 J. Pelz, East German Patent 104,966; 1974 frequencies and output powers; thus they have 74 W. 0. Haag and D. D. Whitehurst, U.S.Patent to function at higher temperatures and current 3,622,367; 1971 densities. The life of coated tungsten cathodes 75 U.S. Department of Energy, German Appl. is limited by tungsten diffusion; to prevent this 3,018,976; 1980 the cathodes operate at 950OC~(brightness 76 G. Wilkinson, U.S.Patent 3,088,961; 1963 temperature). 77 E. 0. Fischer and H. Werner, U.S. Patent Therefore the degradation of a porous 3,159,658; 1964 tungsten cathode impregnated with barium 78 E. 0. Fischer and K. Fichtel, U.S. Patent calcium aluminate and coated with an osmium- 3,268,565; 1966 ruthenium film has been studied (N. fita, 79 G. Wilkinson, U.S. Patent 3,452,068; 1969 ZEEE Trans. Electron Devices, 1991, 38, (ll), 80 G. Wilkinson, U.S. Patent 3,459,780; 1969 2554). During tests tungsten diffused into the 81 Mobil Oil Corp., British Patent 1,180,891; 1970 surface, converting it to osmium-ruthenium- 82 W. 0. Haag and D. D. Whitehurst, U.S Patent tungsten. The activation energy for the 3,635,761; 1972 tungsten diffusion coefficient was 8.4 eV, giv- 83 Mobi OiCorp., French Parent 1,568,527; 1969 ing a stable for the coating of over 84 Mobil Oil Corp., Dutch Appl. 68/7,769; 1968 100,000 hours at a cathode temperature of 85 Mobil Oil Corp., British Appl. 1,299,413; 1972 105OoCe,and the coating could be operated at 86 B. Blanc, Comptes Rend., 1975, 281, 603 a current density of 30 A/cm2.

Platinum Metals Rev., 1992, 36, (1) 33 An Important Work of Reference Chemistry of the Platinum Group Metals: Recent Developments EDITED BY F. R. HARTLEY, Elsevier Science Publishers, Amsterdam, 1991, 642 pages, ISBN 0-444-88 189- 1, U.S.$274.50, Dfl.480 The declared aim of this very readable and in the electronics and electrochemical areas, welcome volume is to cover recent and the market for rhodium is strongly led by developments in the chemistry of the platinum its requirement in autocatalysts. group metals. The variety of treatments and styles used depends partly on the subject matter Catalytic Activity of each chapter, partly on when the area of The general introduction to catalysis by the technology was last reviewed and partly on the platinum group metals, written by G. C. Bond particular interests and expertise of each in- of Brunel University, U. K., puts the subject in- dividual author. The result is a collection of to good historical perspective and draws most chapters in a variety of styles, but each is useful of its exemplification from the heterogeneous and interesting, in its own way. field, although the common factors present in The opening chapter is by Professor F. R. homogeneous, heterogeneous and enzymic Hartley of the Cranfield Institute of catalysis are indicated. The analytical techni- Technology, Bedford, U. K., and considers the ques available for structure determinations of occurrence, extraction, properties and uses of chemisorbed layers are described, and there are the platinum group metals. The dominant pro- sections on catalyst poisons, metallic catalysts ducers of the platinum group metals are South and supported metal catalysts. The various Africa, the U.S.S.R. and, to a lesser extent, types of useful reactor configurations are con- . The route for conversion of the South sidered, as are the kinetics and reactor model- African into final concentrate is indicated, ling aspects. Important industrial applications as are the classical separation and more recently of the platinum group metals catalysts include developed solvent extraction methods for ammonia oxidation, power station and dividing the concentrate into the six individual automobile emission control, petroleum refor- metals. The physical and chemical properties of ming, and catalytic hydrogenation in fine the six metals are described. Therefore the chemicals manufacture. principal applications of the platinum group metals depend on either their nobility or their Benefits of Catalytic Combustion catalytic properties. The chapter on catalytic combustion by D. At first sight nobility and catalytic activity L. Trimm of the University of New South might seem unlikely properties to be exhibited Wales, , describes an extension of by the same element, but their nobility depends pollution control technology, using the heat on the large number of d-electrons produced, preferably with the minimum pro- which are available for tight cohesive bonding. duction of unwanted pollutants. The design re- These same valence shell d-electrons provide quirements for catalytic heaters are discussed, orbitals having characteristics which match with indications that the combustion efficiency those of a range of simple substrates such as depends on the material used to support the hydrogen, carbon monoxide and unsaturated platinum or platinum/palladium catalyst, on hydrocarbons, and thus promote their reactivi- fuel flow rate, the type of fuel used and oxygen ty. The predominant uses of platinum are in diffusion from the ambient atmosphere. autocatalysts and , while palladium Therefore the use of catalytic combustion in gas finds application principally in the electrical turbines can reduce the temperature of gas and dental areas, uses of ruthenium are mainly phase free radical reactions to below 165OoC,

Platinum Metals Rev., 1992, 36, (l), 34-38 34 thus reducing nitrogen oxide emissions by an palladium-catalysed route to vinyl acetate, the order of magnitude. Wacker process for the palladium-catalysed production of acetaldehyde from ethene, Synthesis Gas Chemistry supported palladium catalysts for the The chapter on the use of platinum group hydrogenation of unsaturated hydrocarbons, metals catalysis in the synthesis of chemicals and platinum catalysed hydrosilylation reac- from syngas by G. R. Steinmetz and Z. R. tions. Fischer-Tropsch reactions for the syn- Zoeller of Eastman Chemical Company, Ten- thesis of higher hydrocarbons and other nessee, U. S.A. , indicates that the dramatic rise chemicals from methane and syngas, based on in crude oil prices in the early 1970s gave a cor- ruthenium catalyst systems, are described by responding surge in the quest for alternative Steinmetz and Zoeller and by Parkins. The carbon sources. This need followed the signifi- Texaco molten salt process for the conversion cant developments in organometallic chemistry of syngas to alcohols/esters in and the result was an explosive growth in the tetrabutylphosphonium iodide (m.p. 96OC) in use of organometallic catalysts (particularly the presence of ruthenium carbonyl is also homogeneous systems) for the generation of described, together with a number of other chemicals from synthesis gas. The platinum reactions with industrial potential. group metals have played an integral part in these developments and several processes have Catalysis in Molten Salts either been commercialised or are under con- The chapter by J. F. Knifton of Texaco sideration; these include the Monsanto process Chemical Company, Austin, Texas, U.S.A., on for the rhodium-catalysed carbonylation of platinum group catalysis in molten salts is a methanol to acetic acid, and the Tennessee valuable review of the wide range of chemical Eastman and Halcon SD rhodium-catalysed reactions now studied in this type of medium, carbonylation of methyl acetate in the presence which should be considered in parallel with of hydrogen and dimethyl ether to yield acetic homogeneous and heterogeneous catalysis in anhydride. Rhodium based catalyst systems are the methodology of both laboratory and com- also used in the Johnson Mattheymnion Car- mercial scale operations. In addition to the bide/Davy McKee hydroformylation process alcohol synthesis mentioned above, this techni- for the conversion of olefins (for example pro- que has been used for the direct synthesis of pylene) to aldehydes. One common feature of ethylene glycol (ruthenium-rhodium catalyst or these three rhodium-based processes is that ruthenium alone), or ethene and propene most or all of the oxygen component is retain- (ruthenium-cobalt) from syngas. ed. Current economics dictate that a new pro- cess must possess both high selectivities and a C-H Bond Activation high overall yield. The review of C-H bond activation by J. R. There is some overlap of the content of the Chipperfield of the University of Hull, U.K., syngas chapter with that written by A. W. covers this important area of work as far as the Parkins of King’s College, London, on recent recent developments in homogeneous catalysis developments in platinum group metal catalysts are concerned. The homogeneous systems are in the chemical industry, but both dealt with in the context of the heterogeneous heterogeneous and homogeneous processes are industrial processes concerned with dehydro- considered here, and the growing inter- genation, cracking and partial oxidation. dependence of these two areas of catalysis is recognised. This chapter deals with both major Oxidation Chemistry and minor processes of interest to industry, The comprehensive chapter on oxidation by including the rhodium-catalysed reactions E. S. Gore of Johnson Matthey, New Jersey, indicated above, the vapour phase U.S.A., gives an historical introduction,

Platinum Metals Rev., 1992, 36, (1) 35 indicating that the first example of catalysis by tions by E. N. Balk0 of the Engelhard Corpora- a metal was reported by Sir Humphry Davy in tion, New Jersey, U.S.A., the area considered 1817 who described the oxidation of inflam- is platinum group metals coated anodes in mable gases over platinum. The declared pur- which the requirements for industrial anodes pose of this chapter is to review the present are listed and then the anodic characteristics of state of platinum group metals catalysed platinum, iridium and ruthenium and their ox- homogeneous oxidations with the emphasis on ides are considered in some detail. At least 80 reactions of synthetic and industrial potential per cent of the chlorine production in the and on recent developments since 1980. Even western world is now manufactured on so, the chapter has four hundred references and ruthenised titanium. This review is primarily covers a wide spectrum of organic chemical concerned with several of the most widely used transformations, including the reactions of platinum group metals coatings in their com- aliphatic and aromatic hydrocarbons, alcohols, mon industrial applications, that is oxygen and ethers, sulphides and amines. Although chlorine discharge. platinum is well established for use in commer- An authoritative chapter on the role of cial heterogeneous catalytic processes, it was platinum group metals in the photodecomposi- not until 1962 that the use of a platinum group tion of water, written by A. Mills of the Univer- metal (palladium) in an industrial homogeneous sity College of Swansea, U. K., includes both catalytic process was first reported, this being homogeneous and heterogeneous systems and in the Wacker process for the conversion of indicates the relevance of this approach to the ethene into acetaldehyde. conversion of solar energy into chemical energy. Electro- and Photochemistry At the present state of knowledge, the A chapter indicating the importance of heterogeneous systems are considered to be platinum group carbonyls in developing the more durable. Homogeneous catalysts for potential of catalytic processing is written by J. either hydrogen or oxygen evolution will re- A. Davies and C. T. Eagle of the University of quire substantial further development before Toledo, Ohio and Williams College, they are likely to offer a serious alternative to Massachusetts, U. S.A., respectively. The prin- their heterogeneous counterparts, such as col- cipal sections in this chapter are on photo- and loidal platinum or powdered hydrated electrochemistry and reduction reactions. The ruthenium(IV)oxide, respectively. use of light to generate thermally active catalysts has led to the catalytic synthesis of Homogeneous Catalysis functionalised compounds from arenes and by Palladium and Platinum Systems alkanes under exceptionally mild conditions. The contribution by G. K. Anderson of the Through an understanding of fundamental University of Missouri, U.S.A., is on the electrode processes, it may prove possible to organometallic and homogeneous catalytic design solution phase systems or modified elec- chemistry of palladium and platinum and is trodes capable of exerting a significant elec- very substantial with over four hundred trocatalytic effect on the reduction of carbon references, in spite of its focus being on work dioxide, an alternative to hydrocarbons as a ma- carried out only in the past ten years. Both the jor initial source of carbon. Platinum group car- organometallic aspects of the topic and the use bonyls have begun to show promise as catalysts of these species in catalytic reactions are for a number of novel reduction reactions described. which have potential for future developments, Soluble palladium catalyst systems have been including the reduction of nitrogen oxides by widely applied in organic chemical synthesis carbon monoxide. using, for example, carbonylation reactions; In the chapter on electrochemical applica- both platinum and palladium systems have

Platinum Metals Rev., 1992, 36, (1) 36 featured in catalytic hydrogenation, hydrofor- platinum complexes exhibit anti-cancer activi- mylation and hydrosilylation reactions. ty. Intensive research to explain the chemistry and biochemistry of platinum complexes which Iridium and Rhodium Systems behave as cytotoxic agents and to produce effec- Another very substantial review, with over tive and less toxic anti-cancer drugs has led to five hundred references, has been contributed huge projects based on the chemistry of by F. H. Jardine of the North East London platinum complexes with many biologically ac- Polytechnic, U.K. The organometallic and tive ligands, including amino acids and pep- homogeneous catalytic chemistries of rhodium tides. Amino acid complexes of the platinum and iridium are described, including group metals are also of interest as catalysts hydrogenation and dehydrogenation reactions, and, as such, have been the subject of several hydroformylation, hydrosilylation and car- recent studies; this may become a rewarding bonylation and decarbonylation. In general, on- field for research, although it is made difficult ly recent work is covered but a special feature by the kinetic inertness of many of the com- is made of rhodium(I1)carboxylate catalysed plexes formed and the complicated aquo- cyclisations involving alpha-diazo esters or chemistry of the metal ions themselves. ketones, a topic which has been overlooked in A review of cancer chemotherapy involving previous reviews. platinum and other platinum group complexes The chapter by W. Levason of the University has been written by C. A. McAuliffe, H. L. of Southampton, U.K., on the chemistry of the Sharma and N. D. Tinker of the University of platinum metals in high oxidation states brings Manchester Institute of Science and up to date a topic frequently reviewed in the Technology, U.K. The parent of this class of past. The text is in a highly summarised form platinum drugs is “cisplatin” and this is widely and is a very useful reference work for in- used for the successful treatment of ovarian and organic chemists working in this area. For testicular cancers and, to a lesser extent, head halides, oxides and the related anions, there is and neck tumours. A very significant research sufficient resemblance between the chemistries effort on the synthesis and evaluation of can- of the six elements to allow the topics to be didate platinum compounds for new drug for- treated together. For the co-ordination mulations has now led to the introduction of the chemistries with neutral ligands, however, the second generation drug “carboplatin” which differences currently seem large enough for produces less severe side effects in patients. them to be treated separately. There are 443 references in this chapter and it also includes an Electronic Applications addendum covering the 1989 literature, The final chapter in this wide ranging book is whereas the main text covers principally the written by P. D. Gurney and R. J. Seymour of years 1981 to 1988. Johnson Matthey Technology Centre, Reading, U.K., and indicates the many uses for the Activity with Biologically platinum group metals in electronics. Platinum Important Molecules finds most of its applications in the thin film Amino acid and peptide complexes are area but palladium and ruthenium are predomi- reviewed by H. Kozlowski and L. D. Pettit of nant in the formulation of thick film conductor the University of Wroclaw, Poland and the and resistor systems. In fact, 51 per cent of the University of Leeds, U. K. , respectively. In- demands for palladium and ruthenium in the terest in the interaction of platinum metals with western world are in the electrical/electronics biologically important molecules was area. A wide variety of platinum group metal stimulated some twenty years ago with the compounds have been used to deposit thin discovery by Barnett Rosenberg and colleagues metal films via chemical vapour decomposition at Michigan State University, that certain techniques, while physical vapour deposition

Platinum Metals Rev., 1992, 36, (1) 37 involves the production of a metal film via conductors where the columnar structures sputtering or evaporation at low pressure. result in the compound having highly Platinum silicide, made by the sputtering of a anisotropic properties. thin platinum film onto a silicon surface, Overall, this book reviews progress in the finds application in bipolar integrated circuits development of knowledge on the chemistry of and in Complementary Metal Oxide Semicon- the platinum group metals in the areas where ductor (CMOS) structures. Amongst other there have been significant technological ad- topics discussed in this chapter are platinum vances during the last ten years. There are good group metal alloys for liquid metal ion sources links throughout between scientific investiga- (LMIS) and the use of platinum group metals tion and its commercial application, although in magnetic data storage media, thin-film one very important application area, that is magneto resistive sensors, magneto-optic automotive emission control catalysts, only media, and gas sensors. Ruthenium oxide finds receives brief comments, and there is no discus- wide application in thick film resistors, and sion of the platinum fuel cell catalyst systems palladium-silver systems are the basis of the which are currently receiving significant atten- most widely used thick film conductors as well tion in both research and commercial develop- as being valuable components in multilayer ment. The book provides a useful and ceramic capacitors. stimulating reference work, particularly as it The use of platinum group metals is helping covers many different fields of scientific in the development of the new high research in the same volume and it should temperature superconducting systems; they are therefore appeal to a wide range of research being used in the formation of barrier layers for workers, particularly those interested in thin films of these materials. Platinum group developing new areas of platinum metals metals complexes have also been incorporated research or commercial applications in a into semiconductors, and into one-dimensional synergistic manner. D.T.T. Efficient Ruthenium Dye-Sensitised Solar Cell To-date, a large scale use of photovoltaic the ideal spectral characteristics of the dye lead devices for electricity generation has not to a high proportion of the incident solar energy developed because the available technology is flux being harvested in a cell employing this prohibitively expensive. However, a recent system in the photoanode; the counter elec- letter from the Swiss Federal Institute of trode consisting of conducting glass coated with Technology describes a photovoltaic cell system a few monolayers of platinum. The very fast for which a commercially realistic energy con- electron injection observed with dyes such as version efficiency is claimed (B. O'Regan and this tri-ruthenium complex, combined with M. Griitzel, Nature, 1991, 353, (6346), 737). their high chemical stability, makes these Colourless, optically transparent films of compounds look attractive for practical titanium dioxide, displaying the fundamental development. absorption edge of anatase (band gap 3.2 eV) Exceptionally high efficiencies for the con- are deposited on conducting glass sheet. These version of incident photons to electrical current 10 pm films, which consist of particles with an are claimed, with the device harvesting 46 per average size of 15 nm and a particle surface cent of the incident solar energy flux. The roughness factor of 780, gave linear photo- overall light to electric energy conversion yield current response up to full sunlight. is 7.1 to 7.9 per cent in a simulated solar light The subsequent deposition of a monolayer of and 12 per cent in diffuse daylight. With cur- the trimeric ruthenium complex dye rent densities greater than 12 mA/cm2 and with RuL2(p(CN)Ru(CN)Lr2), (where L is at least five million turnovers being achieved 2,2'bipyridine-4,4'dicarboxylic acid and L' is without decomposition, practical applications 2,2'-bipyridine) onto the titania results in a may be feasible. The technology described thus deep brownish red coloration of the film. The seems to represent a significant advance in high surface area of the semiconductor film and photovoltaic cell technology. D.T.T.

Platinum Metals Rev., 1992, 36, (1) 38 Versatility of Palladium Compounds Carbonylation: Direct Synthesis of Carbonyl Compounds BY H. M. COLQUHOUN, D. J. THOMPSON AND M. V. TWIGG, Plenum Press, New York, 1991, 296 pages, ISBN 0-306-43747-3, U.S.$65 The authors have used their experience of in- rhodium catalyst systems which have become dustrial catalysis to provide an authoritative the dominant technology for the carbonylation and practical account of carbonylation. of methanol to acetic acid. This catalyst is less The volume deals with the carbonylation of useful for the carbonylation of higher alcohols organic compounds, principally mediated by where strong acids find some application. transition metal catalysts but also including Other sources of carboxylic acids are alkynes, relevant reactions which use stoichiometric diazonium ions (using palladium catalysts) and reagents. The major parts of the book are aldehydes. organised according to the chemical nature of The preparation of esters via similar the product. In addition, there are useful sec- substrates is described, and in addition the tions which deal with mechanistic and practical hydroesterification of alkenes with carbon aspects of carbonylation. monoxide and ethanol using bimetallic catalysts The use of carbon monoxide is proving in- containing platinum or palladium with tin creasingly useful in organic synthesis and the halide as co-catalyst is discussed, as is the car- chapter on practical aspects of carbonylation is bonylation of organometallic reagents such as a valuable guide to chemists not experienced in Grignard, organothallium, organoboron and handling these materials. It includes valuable organosilicon reagents with palladium or cobalt details on the properties of carbon monoxide catalysts. and metal carbonyls, it describes the handling The Tennessee Eastman rhodium process for of these materials and also deals with the equip- the production of acetic anhydride is described ment and procedures required to carry out reac- along with other routes to acid anhydrides. tions and isolate the products. The major There are further sections on the synthesis of sections of the book on organic syntheses are amides, acyl halides, lactones, lactames and organised in a clear and concise way. They con- related heterocycles. tain practical details of selected compounds and A chapter is devoted to decarbonylation point out limitations of particular methodology. where aromatic aldehydes can be useful starting The chapter on aldehydes describes their syn- materials. Palladium-on-carbon catalysts have thesis from halocarbons using either soluble been employed at high temperatures and also palladium catalysts or stoichiometric iron homogeneous rhodium systems under less ex- reagents. Hydroformylation of alkenes is also treme conditions. discussed with an emphasis on the commercial The final chapter deals with the preparation rhodium catalysts and to a lesser extent cobalt. and recovery of precious metals catalysts. This The section on ketones describes their syn- includes sufficient detail to enable a qualified thesis from halocarbons (using iron reagents or chemist to prepare relevant catalysts of interest. palladium catalysts) and from dienes (using This volume demonstrates that palladium palladium, rhodium or cobalt catalysts). compounds serve as versatile catalysts in organic The synthesis of carboxylic acids from alkyl synthesis involving carbon bond-forming reac- and benzyl halides with palladium- tions. The authors have provided a good balance triphenylphosphine or anionic nickel carbonyl between established reactions and emerging catalysts and from vinyllic halides using chemistry. It should serve as a useful text for syn- palladium or cobalt catalysts is described. thetic chemists working in a research and There is discussion of the Monsanto based development environment. M.J.H.R.

Platinum Metals Rev., 1992, 36, (l), 39 39 Platinum in the Eighteenth Century A FURTHER SPANISH CONTRIBUTION To AN UNDERSTANDING OF ITS DISCOVERY AND EARLY METALLURGY By A. Galhn and R. Moreno Department of Chemistry, Informatic Faculty and E.T.S.I. de Montes, Polytechnic University of Madrid, Spain

It is generally accepted that the first description of “platina” to appear in Europe was by a young Spanish naval officer, Antonio de Ulloa, whose famous work “Relacibn del Viaje a la America Meridional” was publish- ed in 1748. Important though this was, of even greater significance was the fact that the primary metallurgy of platinum must have been established much earlier, enabling it to be extracted, purified and manufactured. These processes appear to have been kept secret from other European countries, and until recently their details had not been deduced. Now manuscripts discovered in the Colombian Archives enable known methods of purification to be linked to the description of the primitive manufacturing process.

The date ofthe discovery of platinum has often earlier by Luis Ulloa, when attributing the been debated, but current opinion favours the discovery of platinum to Sgnchez. claim of Antonio de Ulloa (1) over that of The Sanchez manuscript has been studied by Charles Wood (see (2) where W. Watson refers Espinosa Baquero and also by Luis Fermin to a letter in which C. Wood communicated to Capitan (6) but their interpretations of the him in 1741 the existence of platina). Earlier separation procedure differ from that of the this century, however, in a little known present authors. publication, a Peruvian historian named Luis Ulloa ascribed the discovery to Jose Sanchez, a Background to the Early Spanish assayer who had worked at the Casa de Metallurgy of Platinum la Moneda de Santa F6 de Bogota (3). Unfor- Historically the significance of the various tunately Luis Ulloa did not support this at- claims concerning the discovery of platinum, tribution with any bibliographical evidence. arising from the writings of Ulloa, Wood and From his biographical details, however, there is even Sanchez, have been complicated by the no doubt that he was extremely knowledgeable fact that they considered only the , about the archives of Colombia, Ecuador and “platina”, which may have been adulterated Peru, and therefore it would not be surprising with other metals, and which received no kind if he knew of the existence of documents con- of scientific purification. cerning platinum that pre-dated the arrival in Of even greater importance is the fact that of Antonio de Ulloa. fabricated platinum articles existed in the first In a work published in 1985 (4) Espinosa Ba- third of the Eighteenth Century, necessitating a quero, a Spanish-American author, reproduced refining or purification process and, in the a manuscript by Jose Sanchez de la Torre y Ar- absence of the means to melt it, a hot-pressing mas (5). This included a balance sheet, dated or sintering process that enabled the platinum 1726, for a separation of gold and platinum, to be worked subsequently (7). and is very likely the manuscript referred to The possibilities of platinum fabrication were

Platinum Metals Rev., 1992, 36, (I), 40-47 40 acknowledged by experts in other European swords, boxes and buckles, not any piece is to be countries, dating it before the voyage of found today, either for the no appreciation that Antonio de Ulloa to South America. In a letter this invention got from its residents, or for the re- quests from foreigners who wanted to verify the from William Watson to Georg Mattias Bose, fact of the fusion they doubted about, they have dated 15th January 1751, (included in the entirely vanished”. review by M. Morin (8)), the following This is not a technical report, but it gives the reference is made to “platina’ ’: opinions of Mutis upon the advantages of “It is not possible to forge, but it has already been platinum for industrial applications. It includes found in America the way of moulding hilts of a report of melting tests carried out in the Casa swords”. de la Moneda de Santa Fe to make two medals On the other hand, in 1750 Watson had already embellished with the head and shoulders of the noted in the Philosophical Transactions: King.* Although no details of the refining or “But the Spaniards have a way of melting it down, melting procedures are given, Mutis says: either alone, or by means of some Flux; and cast “The fusions that on this occasion have been it into Sword-hilts, Buckles, Snuff-boxes, and practiced in order to form those samples, have other Utensils.” (2) been very easy and yet without all that difficul- ty . . . with the result that, being the fusion of Charles Wood adds (see (8) pp.31-32) that they this metal very easy . . . may achieve the fusion by adding another The portrait of the royal person in medal number metal, or non-metal. He supports this assertion 1 is the sample of the pure platina . . .” by referring to cupellation experiments carried Thus, it seems unquestionable that pure out in Jamaica by M. Brownrigg, where a platinum could be “melted”, although this weight loss occurred during the process due to may actually mean “hot-forged”, but the result impurities. However, cupellation was not a for medal number 1 was not excellent. The guarantee of pure platinum, as it would not be craftsman who carried out the “melting” was possible to eliminate all the lead from the Francisco de Benito, the engraver at the Casa cupellation residue because of the solidification de la Moneda de Santa Fe. According to Man- of the lead-platinum alloy prill before the jarres (lo), the Junta de Comercio asked for in- cupellation was properly finished. None the formation about the method used by Benito, less, objects made from pure platinum may the engraver from la Ceca, who had been have existed, and if they did then they could awarded a prize for discovering the procedure have been taken from Cartagena de Indias to which he had been recommended to keep Jamaica where Wood could have obtained secret. This he apparently did, because there is them. no record of it in the Archivo General de Indias. In his survey of the literature on platinum, The medals resulted from a revival of interest Morin writes-although possibly without first in platinum by the Junta de Comercio, who hand knowledge: knew of the Santa Fe directive concerning “The Spaniards have found the secret of its fu- platinum. According to Manjarres, this direc- sion, since they have fused hilts of swords, boxes, tive required that the platinum which was tobacco-boxes, etc.. .. ” (8) separated from gold in the Casas de la Moneda These comments were all corroborated in a was to be thrown into the rivers, as it was im- much later, 1774, report on platinum by Jose possible to melt, but more especially to avoid its Celestino Mutis, Director of the Real Expedi- fraudulent use as an adulterant. The Viceroy cidn Botinica al Nuevo Rein0 de Granada, the manuscript being in the Real Jardin Botinico *In Reference 10, Manjarres indicates that de Madrid (9). Referring to earlier times, Mutis the American publisher Jose Toribio Medina possessed a platinum medal from Santa Fe notes that: which carried a bust of King Carlos 111, and “Although in this city, small pieces of platina wonders if this medal was one sent by the were fused years ago, forming hilts for ceremonial Viceroy.

Platinum Metals Rev., 1992, 36, (1) 41 encouraged experimentation with the platinum, they consisted of primary unrefined gold and in 1774 he reported that although it had not which naturally contained platinum or were been known how to melt platinum, this had gold adulterated with platinum. now been achieved as a result of the ex- By virtue of the first refining procedure periments carried out; as proof of this he sent adopted, we are of the opinion that the bars the medals carrying the portrait of the King, as were new unrefined material. Initially the gold related by Mutis. was melted several times to give what Sanchez With hindsight it seems curious that a regarded as “clean” 18 carat gold, free of melting process was not known in Santa FC, platinum, together with a gold residue which although one had been available earlier. It is, contained the platinum. There was, additional- perhaps, also surprising how quickly it was re- ly, a melting loss of 58 castellanos. Clearly the discovered when experimentation started. gold and platinum cannot have been perfectly Again, it is interesting to consider that before alloyed, since if they had been they would have the arrival of Ulloa platinum had been been inseparable by simple melting. It must be fabricated in a primitive way, but over a period concluded that the platinum was present as par- of only thirty years this ability had been lost, ticles in the body of the gold, resulting from in- perhaps due to lack of interest. complete initial fusion before the bars were Thus, as a working hypothesis we will cast. When the gold was re-melted, the insolu- assume that Francisco de Benito re-discovered ble platinum could be separated with a strainer. the process that had been used in la Ceca in the This procedure saved Sanchez from having to first part of the century, making use of informa- refine the whole of the 5958 castellanos by the tion contained in a manuscript stored in the next procedure, known as inquartation. Casa de la Moneda de Santa FC which he was A flow-sheet of the whole process is shown in probably able to access when commencing his the Scheme. In the manuscript Sanchez claims study of the fusion of platinum. that he obtained 3000 castellanos of clean gold, free from platinum, although admittedly only The Bogoti Manuscript 18 carat. This is unlikely to be strictly true The manuscript of Jose Sgnchez de la Torre since some platinum would probably have y Armas contains a mass balance and a cost dissolved during the melting processes, analysis for refining a batch of gold which con- although possibly only trace amounts. This tained platinum (5). The report is unclear does not seem to have been noticed by him, and because it mixes the language of the time, it would not have changed in a perceptible way which was probably associated with commercial the colour or the melting point of the gold, or aspects of the process, with mention of the its mechanical properties. Also, at low concen- balances. The author makes no attempt to trations it would have been difficult to detect by describe the technical aspects of the process us- fire assay. ed; this has to be deduced from the comments It is considered that both the separation by that he makes about the difficulties of the pro- melting and the formation of an 18 carat alloy cess as he tries to justify the high costs involv- are evidence that the bars had originated from ed. Important technical conclusions about costs the incorrect melting of natural gold, contain- and weights of materials can be deduced from ing some platinum. If the gold had been inten- the report, as will now be demonstrated. tionally adulterated, the separation would be impossible if alloying had occurred, and the The Separation Procedure gold alloy would probably have been of a higher The manuscript refers to six bars of gold mix- quality, for example, a 22 carat coinage alloy. ed with platinum and having a total weight of Also in an adulterated alloy the platinum would 5958 castellanos. The origin of the bars is not presumably have been well alloyed in order to given and, therefore, it is not known whether make it more difficult to detect.

Platinum Metals Rev., 1992, 36, (1) 42 GOLD CONTAINING PLATINUM (platinum forming nodules)

Fusions and refusions

18 CARATJ’ LOSS GOLD CONTAINING GOLD PLATINUM

Inquartation, silver is added in the ratio of 4: 1IAg:Au + Pt

Taken aside or separation with nitric acid

(with mercury remainders)

Calcination Calcination

i v

Platinum Metals Rev., 1992, 36, (1) 43 The second part of the procedure for refining base metals having been dissolved in the nitric the gold is based on inquartation, which is a acid. Sanchez does not specifically indicate how well known process for refining gold although he achieves the further separation of the two little used in practice. It is based on the solubili- noble metals, but the key information is con- ty in nitric acid of silver and the base metals tained in the detail of the costs: commonly present in the alloy. The gold to be “Por el cost0 que hay y que se tuvo . . . plata refined is melted with three to four times its consumida, peones, azogado del or0 que sale para weight of silver; when this alloy is treated with separar la platina calcinada . . .” [“By the cost that there is and was . . . consumed nitric acid everything dissolves except the gold silver, labourers, treatment with mercury of the which remains as a powder at the bottom of the leaving gold in order to separate the calcined container, and can be easily separated by decan- platina . . .”I ting the solution. This method is unlikely to There seems to be little doubt that he separated have been used for normal gold refining the platinum and gold by amalgamation with because of the high cost of nitric acid, as will be mercury, which would rapidly dissolve the fine shown later in the analysis of costs. Other gold powder leaving behind the platinum which methods such as “real foundation” and “fus- does not alloy with mercury. This residue ing precipitation” (12) might have been prefer- would then be calcined to yield practically pure red, the use of inquartation being limited to platinum. assaying. But it will be shown next that inquar- Espinosa Baquero, in his interpretation of the tation was the only process available to Sanchez process, suggested that was used which could have been used to separate rather than nitric acid (4), basing it on a remark platinum and gold. by Sanchez “that it dissolves the gold and the Sanchez carried out the inquartation correct- platinum”. Sanchez does not mention aqua ly, using a 4:l ratio of silver to the 2900 regia, however, and the large mass of silver bas- castellanos of platinum-containing gold, in ed alloy would be unlikely to dissolve in the order to transform the gold-base metal alloy in- reagent owing to the formation of insoluble to a silver-base metal alloy soluble in nitric acid. silver chloride; this would prevent or make dif- The problem he faced, as he acknowledged, ficult the dissolution of the rest of the alloy. was in achieving an homogeneous alloy since Capitan proposes that the platinum is all the platinum did not alloy readily with silver at dissolved by the nitric acid (6), this assumption the temperature of his furnaces. He notes: possibly being based upon the work of Mathieu “. . . happening to make a new alloy in some Tillet (1714-1791). This work was not publish- granules, when the platina flocculates and does ed until 1779, however, so the information not have itself enough silver, for the water to would not have been available to Sanchez in cause its effect”. 1726; even if they had been contemporaries It was necessary for the alloy to be they were unlikely to have meet in Santa Fe. homogeneous, so that when the silver dissolves Furthermore, the solubility of platinum in it leaves behind a finely divided residue of gold nitric acid is quite limited and repeated cupella- and platinum and not platinum nodules. Ac- tions and partings in nitric acid would be re- tually, under these conditions platinum has quired to effect a separation. some solubility in nitric acid, particularly in Having obtained a solution of platinum in strong acid (but this would not necessarily have nitric acid, Capitan next proposes that Sanchez been available in this case), something which separated the silver from the platinum by does not happen with gold. However, we do not cementation with brass, but this process was think that this solubility is likely to have been not widely known at that time. noticed by Sanchez. The procedure that we deduce from the Thus, after the inquartation a mixture of gold manuscript is in keeping with the information and platinum powders is left; the silver and known at that time; in addition to the fact that

Platinum Metals Rev., 1992, 36, (1) 44 it was mentioned in the Sanchez manuscript, improvement in the mechanical properties the amalgamation process was well known at compared to those of native platinum, which that time, being used on alluvial gold grains was not malleable and could not be worked. to separate them from admixed platinum Since the process described was the only one particles. then available for the production of pure We have deduced from the manuscript that platinum, we propose that it may well have Sanchez was neither a scientist nor an in- been the one used for the platinum that was vestigator. He is far more likely to have been an fabricated into the buckles, boxes and other assayer applying the established procedures of articles which circulated in the neighbourhood his craft. It is probable that these assay pro- of Santa FC de Bogota. cedures had been known in the Ceca de Santa It also seems likely to have been the process FC for some years and were passed from one used many years later by the engraver Fran- assayer to another, as was the case with other cisco de Benito to mint the medals that carried craftsmen's knowledge at that time. For the the King's bust. moment, however, this is the oldest written Finally, it is surprising that the gold document on the subject from which any separated by the nitric acid and amalgamation technical conclusions can be drawn. stages should have the unusual fineness of 21 In the light of present knowledge, we con- carat. Gold refined by this procedure would sider that the platinum obtained by Sanchez normally be expected to be almost pure. would have been practically pure, although it is certain that his objective would have been the The Analysis of Costs separation of platinum from the gold, rather The study of the refining costs presented by than the refining of the platinum. Sanchez Sanchez is very interesting because of the pic- states that he produced calcined platinum and ture it presents of the problems, both technical platinum grains, in which state the platinum and economic, that were caused by the could be readily hot-forged. This suggests an adulteration of gold with platinum.

Table I Yields and Costs of the First Refining

~

Gold obtained = 2250 castellanos of fine gold (3000 Cs 18 carat gold) Value of this gold = 6474.4 patacones Cost of the loss in gold = 105.14 patacones (58 Cs of original alloy") Fusion cost = 323.66 patacones"

Total cost = 428.8 patacones We suppose the original alloy to be of an average fineness of 630 O/OO in gold. ** He does not compute the fusion expenditures, but indicates it is the middle per cent, we understand that it is the melted metal, that is, of 3000 Cs of 18 carat gold.

Units of Weight for the Gold Monetary Units 1 marco = 50 castellanos = 8 onzas 1 doblon = 2 Cs gold (8385Gr fine gold) 1 castellano = 8 tomines = 96 granos 1 doblon = 4patacones 1 onza = 6 castellanos + 2 tomines 1 patacon = 1 onza silver (28,608 Gr silver) 1 onza = 8ochavas 1 patacon = 8 reales 1 ochava = 6 tomines + 3 granos 1 real = 34 meravedies 1 marco = 228.86 gramos (sistema metric0 decimal)

Platinum Metals Rev., 1992, 36, (1) 45 I Table II Yields and Costs of the Second Refining

Gold obtained = 1504 castellanos of fine gold (1719 Cs 18 carat gold) Value of this gold = 4329 patacones Platina obtained = 325 Cs (We do not know its value but it might be worthless) Cost of the nitric acid = (261 pounds) = 2349 patacones Cost of manual labour and consumable = 145 patacones Physical loss in weight = 569 Cs = 1031 .3 patacones”

Total cost = 3525 patacones As we shall see in the balance of weights, he does not recognise this sum as a loss but he imputes it to platinum (in order not to recognise such physical waste); we evaluate this loss as referred to original alloy (it is an estimation) and therefore it is equivalent to 358 Cs of fine gold

The costs of the first refining operation, the These data provide ample justification for the repeated fusions stage, are shown in Table I. It attitude of the Spanish Administration in at- can be seen that the cost of this part of the pro- tempting to prevent, at all costs, the adultera- cedure is equivalent to 6.6 per cent of the value tion of gold with platinum. It did not signify, of the gold recovered. as has often been inferred, any lack of interest The costs for the second part of the opera- in the proper scientific investigation and ex- tion, that is the recovery of the gold from the ploitation of this new metal. 2900 castellanos of platinum-containing residue The act of throwing the platinum into the by the inquartation process, are given in Table rivers can easily be justified. The cost to the 11. These costs amount to 81.4 per cent of the Spanish Crown of the introduction of just 5.4 value of the gold recovered! per cent of platinum into the gold alloy would The difference between the costs of the two be the value of 2515 castellanos of gold com- refining stages is considerable; those for the pared to 3750 castellanos of separation costs, first stage appear reasonable, while those for and all for a fraudulent gain to the miner of just the second are clearly prohibitive. The most 325 castellanos. Under these circumstances, significant charge is for nitric acid, which when the fraud was successfully achieved it amounts to 54 per cent of the value of the gold. would have been better to “turn a blind eye”, When averaged over the whole yield, the total in the knowledge that the normal cupellation refining cost amounts to 36 per cent of the value assay methods would be unlikely to detect low of the gold recovered. levels of adulteration. As we have noted previously, it was very for- Where the platinum addition was high, the tunate for Sanchez that the platinum was not same result could be achieved by diluting its already alloyed perfectly with the gold. If this concentration by adding more pure gold. had been the case the extrapolated costs for Nevertheless, the policy of dumping the treating the whole mass of alloy by inquartation platinum was reasonable in the sense of would have risen to 7240 patacones, based on ‘‘avoiding temptation”, particularly since costs of 4826 patacones for nitric acid, 298 platinum had no recognised value or uses in patacones for manual labour and 2116 those days. patacones for process losses (735 castellanos of The balance of weights shown is somewhat fine gold), so increasing the refining costs to 67 confusing in that it is not a balance of physical per cent of value of the refined gold. weights. It is an accounting balance in terms of

Platinum Metals Rev., 1992, 36, (1) 46 the weights of 18 carat gold, this being the by 25 per cent to refer the presumed content of fineness of the first gold product obtained. This the loss to 18 carat, which is a nonsense. He may have led Sanchez to make certain mistakes, calculated a content of 64,366 granos (670 or possibly even to make intentional falsifica- castellanos) as the waste and described it as tions so that the true gold losses were difficult “what is identifyed as platina”. From the 894 to detect. castellanos he calculated the loss as 15 per cent The first stage is clear, from the 5958 of the original mass of 5958 castellanos, and castellanos to be refined he obtained 3000 refers to it all as platinum. This is unlikely, castellanos of 18 carat gold (which he called the since it assumes no loss of gold, which is im- “first benefit”) and another 2900 castellanos of probable considering the complexity of the gold containing platinum, giving a loss of 58 operations. castellanos. He inquarts the 2900 castellanos On the other hand, he physically delivered with silver in the proportion 1:4, so obtaining only 325 castellanos of platinum and not 894, 290 Marcos (14,500 castellanos) of granulated the difference being a real loss. The platinum in silver-rich alloy, which he subjects to the the original material would thus have been separation process, and this is where the ac- much less than 15 per cent. counting problems begin. It is apparent that Sgnchez de la Torre had Sanchez claims to have obtained 144,434 been able to achieve a balance of accountable granos of gold; by implication pure gold, since material, which would not have been possible he said that it made 2006 castellanos of 18 carat for the true physical items. Attributing all the gold alloy. These are not physical weights, loss to the “valueless” platinum enabled him to however, since what he actually obtained was avoid admitting the gold losses, which would 1719 castellanos of 21 carat gold alloy. These have been a serious matter and one for which he weights are all definitely self-consistent. From would have been held responsible. Saying that now on, in balancing the accounts he began to there were “894 castellanos recognised as make mistakes. He used the calculated weight platina” did not, however, stop him saying in of 2006 castellanos to derive a figure of 894 the last paragraph of the report “I deliver 325 castellanos for the loss, whereas he should have castellanos of calcined platina”. The difference used the weight he actually had, namely the is unimportant, since it would have been much 1719 castellanos of 21 carat alloy. He then more serious to acknowledge equivalent losses reduced the presumed value content of the loss of gold.

References 1 Antonio de Ulloa and Jorge Juan, “Relacion 7 J. C. Chaston, “The Powder Metallurgy of Hist6rica del Viaje a la America Meridional”, 4 Platinum”, Platinum Metals Rev., 1980, 24, (2), vols., Madrid, A. Marin, 1748 70-79 2 W. Watson, “Several Papers concerning a new 8 M. Morin, “La Platine, L’or blanc ou le huitieme Semi-Metal, called Platina; communicated to the Metal”, Paris, 1758 (Avec approbation & Permis- Royal Society”, Philos. Trans., 1750, 584-596 sion du Roy) 3 Luis Ulloa Cisneros, “Historia Universal”, 9 Jose Celestino Mutis, Informe sobre la Platina, Publications of the Instituto Mach de Libreria y June 15th 1774, Real Jardin Bothico de Madrid Ediciones, Barcelona, S.L., 1932, 6 vols. 10 Ramon de Manjarres, “D. Jorge Juan y D. 4 Armando Espinosa Baquero, “Nuevos datos Antonio de Ulloa, La Medicion del Arc0 sobre el descubrimiento del platino y su Terrestre, La Historia del Platino (conclusion)”, metalurgia en la Nueva Granada en el siglo Revista de Archivos Bibliorecas y Museos, Tercera XVIII”, Quipu, 1985, 2, (l), 7-21 Eva, January 1913, Madrid, 58-91 5 Jose Sinchez de la Torre y Armas, Manuscript: 11 Expediente del Platino, Audiencia de Santa Fe, Archivo Nacional de Colombia, Wasde Tolima, Legajo 835, Doc.3, Archivo General de Indias V01.5, folios 330-331 Seville 6 L. F. Capitin, “Separating Platinum from Gold 12 A. Galin and R. Moreno, “La Separaci6n del Or0 During the Early Eighteenth Century: The de la Plata. Un problema de la Metalurgia en la Methods Used in Spanish South America”, America Colonial”, ZnvestigacGn y Ciencia, 1992 Platinum Metals Rev., 1989, 33, (2), 73-80 (in press)

Platinurn Metals Rev., 1992, 36, (1) 47 ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES Hydrogen Adsorption on Cobalt/ Pt( 1 10)(1x 2) Surfaces STM Investigation of the Adsorption and M. ALNOT and J. FIJSY, Appl. Surf. Sci., 1991, 52, Temperature Dependent Reactions of (1/2), 77-84 Ethylene on Pt( 111) A thin Co overlayer on a Pt(llO)(lx2) surface T. A. LAND. T. MICHELY. R. J. BEHM, J. C. HEMMINGER substantially modifies the adsorption energy of H, . A and G. COMSA, Appl. Phys. A, 1991, A53, (S), new state appears with an adsorption energy near 9 4 14-417 kcal/mol, which is lower than that usually observed The adsorption and reactions of C,H, adsorbed in on bulk Pt and bulk Co. At above one monolayer UHV on Pt(ll1) were studied as a function of desorption conditions appear similar to those observ- temperature by STM. The STM images at 160K ed on bulk Co. show an ordered structure of adsorbed C, H,, which on annealing to 300K produces ethylidyne (C-CH,) Observation of Inverse U-Shaped Profiles irreversibly. The ethylidyne on Pt(ll1) is not visible after Platinum Diffusion in Silicon to STM at room temperature, but cooling allows the H. ZIMMERMANN and H. RYSSEL, Appl. Phys. Lett., ethylidyne ordered structure to be observed. Anneal- 1991, 59, (lo), 1209-1211 ing at >430K causes further dehydrogenation, leav- Studies of inverse U-shaped profiles of Pt in Si ob- ing only C on the surface. Further annealing at tained after diffusion at 7OOOC were performed by XOOK produces graphite islands, having seveTal deep level transient spectroscopy to determine the in- superstructures with lattice parameters of up to 22A. itial concentration of vacancies. The Pt profiles were called ‘inverse U-shaped profiles’ because in the The Role of Defects in the Specific bulk, a higher concentration of Pt was found than at Adsorption of Anions on Pt(ll1) the surface. Pt diffusion was found to offer, for the P. N. ROSS, 3. Chim. Phys. Phys. Chem. Biol., 1991, first time the possibility to check and improve process 88, (7-8), 1353-1380 simulation models which are based on point defects. The specific adsorption of anions from HC1 and Microstructural and Magnetic Character- H,SO, acids was studied on Pt(ll1) surfaces with two types of induced defects: a step-terrace structure ization of Rapidly Solidified and Annealed and a random up-anddown stepped surface. All step Pt-Co-B Alloys defects lowered the work function of the surface in N. QIU, J. A. TEUBERT, R. A. OVERFELT and J. E. WITTIG. direct proportion to the step density, indicating a 3. Appl. Phys., 1991, 70, (lo), 6137-6139 local dipole at the step with its positive end outward The intrinsic coercivity (Hit) of Pt-Co alloys from the surface. The local work function at the step significantly increased on the addition of B and by and thus the local potential of zero charge (pzc) is rapid solidification processing. After rapid solidifica- lower at the step than at atomically flat terraces. The tion by double anvil splat quenching with subsequent difference in pzc controls the coupling of H adsorp- annealing at 65OOC for 30 min, Pt42C045Bllshowed tion and anion desorption. On atomically flat (111) an HI, as high as 14 kOe. The magnetic hardening terraces having the most positive pzc of all Pt sur- mechanism is a combination of inhibited magnetic faces, the processes are completely decoupled in domain nucleation and difficult reverse domain dilute acids, with desorption of anions from terraces at growth caused by the interaction of the magnetically potentialsmoreanodicthanfor Hadsorption. (44Refs.) anisotropic Co borides with the LlUPt-CO matrix. Scanning Tunneling Microscopy of Pt/Co Thermodynamics of the Uranium- Multilayers on Pt Buffer Layers Platinum Metals Systems s. L. TANG, P. F. CARCIA, D. COULMAN and A. I. MCGHIE, H. KLEYKAMP, pure Appl. Chem., 1991, 63, (lo), Appl. Phys. Lett., 1991, 59, (22), 2898-2900 1401- 1408 Systematic STM studies of the surface structure of The thermodynamics of the systems: U-Pt, U-I’d, U- Pt/& multilayers sputter-deposited on various Pt Rh, U-Ir, U-0s and U-Ru are critically assessed. The buffer layer thicknesses showed that it evolved isothermal sections of the ternary U-Rh-F, U-Ru-F, toward nanometer-scale crystallites with distinct, U-0s-F and U-Ir-F systems were found, and the mostly six-sided polygonal grain boundaries with in- Gibbs energies of formation of URu,, U,Ru,, creasing Pt buffer layer thickness. It is concluded that URu,C,.,, U,RuC,, URh,, UOs,, UIr, and UIr, improved (111) texture and the appearance of distinct were determined between 900 and 1200 K. Ther- grain boundaries contributed to the higher magnetic modynamic results of the intermetallic phases and the coercivity of the multilayer on a Pt buffer layer. platinum rich solid solution regions are discussed.

Platinum Metals Rev., 1992, 36, (l), 48-59 48 The Effect of Hydriding on the Physical Hydrogen-Induced Ordering in Structure of Palladium and on the Palladium-Rich Pd-Mn Alloys Release of Contained Tritium K. BABA. Y. NIKI, Y. SAKAMOTO and T. B. FLANAGAN, 3. E. STORMS and C. TALCOTT-STORMS, Fusion Technol., Less-Common Met., 1991, 172-174, 246-253 1991, 20, (2), 246-257 Hydrogen-induced formation of an L1, ordered The behaviour of T released from a contaminated Pd structure from an a-L1 ,,(Ag,Mg-type) structure cathode was compared with the pattern found in cells was observed in the presence of H, at a pressure of which were claimed to produce T by . 5.0 MPa at 726K in the a-phase of rapidly quenched Void space is produced in Pd when subjected to H ab- alloys of Pd-Mn alloys containing 12.5-31.0 at.% sorption and desorption cycles. This void space can Mn. In Pd-29.0 at.% Mn and Pd-31.0 at.% Mn produce channels through which H can be lost from alloys the /3, -L1 ,-s (M=2) structure transforms the cathode, thus reducing the H concentration. This under the effect of H, into the /3,-L1,, (M=4) effect is influenced by impurities, the electrode structure, where the domain size increases from M =2 shape, charging rate, the H concentration achieved to M=4. and the length of time of maximum concentration. Thermodynamic Stability of Palladium Formation of Decagonal Quasicrystal in Alloys: Part I: The Palladium-Niobium the Al-Pd-Mn System and Its Structure System M. 1. STICKNEY, M. S. CHANDRASEKHARAIAH, K. A. D. HIRACA, W. SUN, F. J. LINCOLN, M. KANEKO and Y. GINGER~CHand J. A. SPEED, Metall. Trans. A, 1991, MATSUO, 3pn. 3. Appl. Phys., 1991, 30, (9A), 2028-2034 ZZA, (9), 1937-1943 Studies of formation of a decagonal quasicrystal in The Pd activities of 12Pd-Nb alloys, with composi- Al,,Pd,,_,Mn, alloys (x=8-20) showed that the tions from 60Pd40Nb to 97Pd3Nb, were determined decagonal quasicrystal was formed as a coexisting experimentally with a twin-chamber Knudsen cell phase with an icosahedral phase in the composition mass spectrometer at 1450-1750 K. The results range of x = 10-15, and as a single phase at a composi- showed a strong interaction in the solid state between tion of x about 20. It is proposed that the structure the Pd and the Nb atoms. of Al-Pd-Mn decagonal quasicrystal may be inter- preted as a tiling formed by atom cluster linkages. Effect of Soluted Hydrogen on the Mechanical Properties of Palladium- Effect of Ordering Processes on Elec- Rhodium Alloys trical and Magnetic Properties of N. I. TIMOFEEV and F. N. BERSENEVA, Fiz. Met. Metallov., 1991, (7), 147-152 Pd2Cu,-xAlloy (0.40 \< x \< 0.48) Studies of structural changes and physico-mechanical A. A. SENCHENKO, I. I. PIRATINSKAYA, L. P. ZELENN and properties of Pd-Rh alloys containing up to 25 at.% Yu. A. VERESHCHAGIN, Fiz. Met. Metdoved., 1991, Rh were performed during H implantation in the (8), 106-111 alloy. The results showed that the mechanism of pro- Studies of transformation of crystal structure, elec- perty changes in the Pd-Rh-H system can be trical resistance and magnetic susceptibility of characterised both for Pd alloys containing Pd,Cu, --x alloys with x =0.40-0.48 were performed monovalent noble metals, and for these alloys con- under homogeneous conditions near to the taining transition elements. Depending on the con- stoichiometric region at 300-1200K. The results centration of the soluted H and on the phase showed that ordering was accompanied by compres- compositions in the Pd-Rh alloys, the observed ef- sion of the crystal lattice, and by sharp changes in fects were either a simultaneous rise in their stability electrical resistivity and diamagnetic susceptibility. and ductility, or their sudden embrittlement. The results were evaluated on the basis of density state in ordered and disordered alloys. Mechanical Alloying of the Pd-Si System in Controlled Conditions of Energy Constitutional Studies of Molybdenum- Transfer Palladium Alloys Using Ultra-Rapidly F. PADELLA, E. PARADISO, N. BURGIO, M. MAGINI, S. Solidified Samples MARTELLI, w. GUO and A. IASONNA, 3. Less-Common R. CURLER and 1. N. PRATT, 3. Less-Common Met., Met., 1991, 175, (l), 79-90 1991, 175, (l),71-78 The composition Pd,Si,, was milled, starting from Studies of phase relationships in the Mo-Pd system at pure elemental powders, in different milling condi- 880-1 100°C were performed using ultra-rapidly tions, and the mechanical alloying process was follow- solidified samples. The finely divided microstruc- ed by X-ray and differential scanning calorimetry tures produced by this technique were found to measurements. For high levels of energy transfer the achieve equilibrium on annealing more rapidly than system evolves towards the formation of the in- conventionally prepared materials. The solubility termetallic Pd, Si. At lower levels of energy transfer, limits of the Pd-rich and Mo-rich terminal solid solu- formation of a stable intermetallic phase was hindered tions were established. and the product was a fully amorphous phase.

Platinum Metals Rev., 1992, 36, (1) 49 Thermal Stability and Phase Studies of CHEMICAL COMPOUNDS Crystalline Zr ,Pd Hydrides J. S. CANTRELL and R. C. BOWMAN, 3. Less-Common Ligand-Stabilized Bimetallic Colloids Met., 1991, 172-174, 29-35 Identified by HRTEM and EDX Studies of the crystalline metal hydrides Zr,PdH, for x<2.0 showed that they underwent an endother- G. SCHMID, A. LEHNERT, J:O. MALM and J.-0.BOVIN, mic reaction above 8WK, and decomposed to ZrH, Angew. Chem., Int. Ed. Engl., 1991,30, (7), 874-876 and ZrPd on further heating. When the crystalline The synthesis of ligand-stabilised bimetallic colloids hydride has x>3.0, it undergoes abrupt endothermic and the identification of their shell structures is transitions around 550K @OK) which leads to the described. Au colloids of diameter 18 nm were formation of lower H content ternary hydrides. covered by Pt or Pd shells, when aqueous solutions of Upon further heating above 800K, the ternary the colloids is added to a solution of H,PtCI, or hydrides go through more endothermic reactions H ,PdCI, and H ,NOHCI, stabilising the particles forming a mixture of phases that includes ZrPd, formed with p-H,NC,H, S0,Na. Uniform ZrH, and ZrO,. heterogeneous AuPt agglomerates of a Au core sur- rounded by Pt crystals of - 5 nm, with two kinds of intergranular structures are found. For AuPd a Investigations of Rh-Based Multilayers homogeneous system of Pd and Au solid solutions is for Soft X-Ray Applications by High- formed. The sequence of metals can also be reversed, Resolution Electron Microscopy so that 15 nm Pd colloids can be prepared and coated z. G. LI, D. J. SMITH, s.-c.Y. TSEN, P. BOHER and PH. with Au. HOUDY, 3. Appl. Phys., 1991, 70, (6), 2905-2910 A series of Rh-based multilayer structures was Metallic Properties in the Series developed for soft X-ray applications by using K 2 Pd(II)H, 9 Na ,Pd(0)H2 and ‘trilayer’ structures and low density B,C spacing Li, Pd(0)H2 Correlated with the Stabiliza- material. The microstructure of the multilayers was tion of a Formally Zero-Valent Palladium- studied and compared with those of W- and Ni-based multilayers. Rh crystals with f.c.c. structure but with Hydrogen Complex different preferred orientations were identified in Rh- K. KADIR, M. KRITIKOS, D. NO~USand A. F. ANDRESEN, based layers. High reflectivity and selectivity for X- 3. Less-Common Met., 1991, 172-174, 36-41 ray mirrors was obtained in the case of WiRh/C New hydrides, Li,PdH, and K,I’dH,, were com- multilayers due to significant improvement in their pared with Na,PdH,. The Li,PdH, and Na,PdH, microstructure, especially the interface roughness. were found to be metals and their structures were characterised by linear, formally zero-valent PdH, Magnetic Properties of U(Ru,,Rh,) Si, complexes in an alkali atom framework. The Pd-H bond lengths was 1.68 A. In K,PdH,, with the Single Crystals (0 < x < 1) Na,PtH,-type structure, the larger and more elec- Y. MIYAKO, S. KAWARAZAKI, H. AMITSUKA, C. C. tropositive K atom allows a four-co-ordinated ds PAULSEN and K. HASSELBACH, 3. Appl. Phys., 1991, square planar I’d com lex to be formed. The Pd-H 70, (lo), 5791-5793 bond length was 1.63f. The electrons were localised The temperature dependence of the non-linear and K, PdH, was a yellow-green non-conducting susceptibility of URu,Si, was studied in order to powder. determine the properties of the phase transition at 17.5 K. Various magnetic phases of U(Rul,Rh,)Si, N-Bonded TCNQ in Stacked Dimeric were studied as a function of x by means of specific Systems. Synthesis and Crystal Structure heat, susceptibility, and neutron scattering methods. Two successive phase transition occurred when of [Ru(PPh,),(TCNQ)I, (TCNQ= 7,7,8, x=0.3. 8-tetracyanoquinodimethane) L. BALLESTER, M. C. BARRAL, A. GUTIl?RREZ, R. JIMkNEZ- Electrical Conductivity of BaRuO APAF’JCIO, J. M. MARTfNEZ-MUYO, M. F. PERPINAN, M. A. MONGE and C. RUfZ-VALERO, y. Chem. soc., Chem. Ceramics Commun., 1991, (19), 1396-1397 B. SZYMANIK and A. EDGAR, Solid State Commun., The reaction of RuCI,(CO),(PPh,), with AgBF, in 1991, 79, (4), 355-357 tetrahydrofuran (thf) resulted in the formation of BaRuO, and Bal,&RuO, ceramics contain a mix- IRu(C0) ,(PPh, ) ,(tho l(BF, ), which when further ture of 4H and 9R polytypes whose volume fraction reacted with PPh, in CH,Cl, and LiTCNQ in depends on quenching temperature and the concen- MeOH yielded purple crystals of tration of K dopant. Both polytypes have a room tRu(PPh,),(TCNQ)I (1). The crystal structure of temperature resistivity of - 10 mQcm, but with op- this compound showed ‘a tetrahedral environment of posite signs for the temperature coefficient. The the Ru atom with the TCNQ molecule co-ordinated negative temperature coefficient for the 9R polytype via N. All the TCNQ units act as bridges bonding is ascribed to localisation effects arising from the two Ru atoms via opposite nitrile groups which gives existence of two distinct crystallographic Ru sites. rise to dimers [Ru(PPh,),(TCNQ)I,.

Platinum Metals Rev., 1992, 36, (1) 50 ELECTROCHEMISTRY Platinum Electrocatalysts Applied to Car- bon Fibres Electrochemistry at Platinum Single A. A. VEDENYAPIN. A. W. KRYLOVA. A. C. GAZARYAN, T. Crystal Surfaces in Acidic Media: 1. KUZNETSOVA. 0.A. MALYKH, G. 1. EMEL'YANOVA, A. L. Hydrogen and Oxygen Adsorption LAPIDUS and s. v. WSHIN, Elektrokhimiya, 1991, 27, (7), 848-853 J. CLAVILIER, A. RODES. K. EL ACHI and M. A. ZAMAKHCHARI, J. Chim. Phys. Phys.-Chim. Biol., Studies were performed of Pt/C fibre catalysts 1991, 88, (7-8), 1291-1337 prepared by impregnation of C fibres by H,PtCI, solution or by electrochemical deposition of on C A review of the adsorption properties of H, and 0, Pt fibres from the analogue solution at 0.2 V. The at the Ptlacid solution interface, and their results showed that Pt/C fibre catalysts prepared by dependence on the crystalline surface structure of the electrochemical deposition have greater dispersion electrode is presented. Unusual adsorption states Pt than those obtained by impregnation. It is suggested are seen on (111) and (100) oriented electrodes, which that two types of polarisation processes with different appear to be controlled by two-dimensional long range order. Studies on the Pt(hkl)/solution system rates occur on the catalyst surfaces. are- examined; these include the electrochemical behaviour of stepped surfaces, surface reconstruction Oxidation of Sulfur Dioxide in Sulfur- in solution, size of the ordered domains and the Modified Platinum-Graphite Packed Bed characterisation of point defects and ordered defects. Electrodes (75 Refs.) S. E. LYKE and S. H. IANGER,._ 7. Electrochem. ~OC., 1991, 138, (6), 1682-1687 In situ Infrared Studies of Glucose Oxida- The oxidation of dissolved SO, at Pt supported in tion on Platinum in an Alkaline Medium porous graphite sheet electrodes was studied at 1. T. BAE, E. YEAGER, X. XING and C. C. LIU, J. Elec- 450-750 mV (RHE) using various Pt loadings and troanal. Chem. Interfacial Electrochem., 1991, 309, (1 SO, concentrations. Controlled reductive pretreat- and 2), 131-145 ment of the electrodes in the presence of SO, was The oxidation of a-(+)-glucose on a Pt electrode in found to produce catalytic effects which resulted in 0.1 M NaOH was investigated by in situ FTIR- enhanced steady-state oxidation currents due to for- absorption spectroscopy in the range -0.76 to +0.46 mation of a S-modified Pt surface. In hybrid cells V vs. Hg/HgO, OH . The surface adsorbates involv- with fuel cell type 0, gas diffusion cathodes ed linear CO and bridged CO. The linear CO per- operating in the electrogenerative mode, the sisted on Pt in the entire potential range, with gradual pretreated Pt-graphite anodes were used to oxidise shifts to higher frequencies, of - 70 /cmN, while the 3-500 mM SO, in 3M H,SO,. bridged CO disappeared as the electrode potential reached -0.05 V. The oxidation products were car- Irreversible Adsorption of Chlorophyll on boxylic acid and CO,. A potential excursion up to an Amalgamated Platinum Electrode in +0.46 V caused a pH swing of >8 in the spectroelec- Aprotic Solvents trochemical thin layer, due to glucose oxidation. L. F.F. LAFI,LAFI. L. A. KHANOVA andand M. R. TARASEVICH,TARASEVICH. Elektrokhimiya, 1991, 27, 961-%8 Structural Effects in Electroca~lysis. Elekfrokhimiya, 19919 27, (8), Ethylene Glycol Oxidation on Platinum Studies of adsorptionadsoWion of chlorophyll on an Single-Crystal Surfaces amalgamated Pt electrode inin various aproticaprotic solventssolvents were performed under controlledcontrolled potentials. The ad-ad- N. M. MARKOVIC, M. L. AVRAMOV-IVIC,AVRAMoVJVIC, N. S.'. MARINKOVICMA"KoV1C sorptionsorption of chlorophyll was stablestable and itit couldcould onlyonly and R. R. ADZIC, 3.J. Electroanal. Chem. Interfacial desorb&sorb with thethe surfacesurface heldheid under a significant significant Elecrrochem.,Electrochem., 1991, 312, (1 and 2), 115-130 negative potential. The adsorptionadsorption was affected by The oxidation of ethylene glycol (EG) was studied on thethe amountamount of adsorption substancesubstance andand on itsits con- Pt single crystal surfaces in 0.1 M NaOH. Strong centration inin solution,solution, andand alsoalso by thethe adsorption con- structural dependence of the reaction kinetics occur- ditions. red for all 12 orientations investigated. The onset of the reaction occurs in the sequence Investigations of the O2 Reduction Reac- Pt(llO)>Pt(lOO)-Pt(ll1).Pt(llO)>Pt(lOO)-Pt(lll). The peaks of the voltam- metry curves for the low-index planes decrease in the tion at the PlatinumlNafion Interface order (lll)>(llO)>(lOO). Either the (111) or the Using a Solid-state Electrochemical Cell (100) oriented steps cause a decrease in the activity of A. PARTHASARATHY, c. R. MARTTN and s. SRIMVASAN, the (111) plane. Surfaces near the (100) plane have 3. Electrochem. SOC.,1991, 138, (4), 916-921 higher activity than Pt( 11 1). The (11 1) oriented steps The processes occurring at the PtiNafion interface in in the Pt(ll0) plane increased the activity, while the the absence of a contacting electrolyte phase was in- (100) oriented steps decreased it. PtOH layer forma- vestigated in an electrochemical cell to determine tion and onset of EG oxidation occurred together, such conditions in a SPE fuel cell. From cyclic showing the reaction involves interaction of the ad- voltammetric measurements the purity of the Nafion sorbed and dehydrogenated EG with R(OH),,.J,.P~(OH),,.J,. and the roughness factor of the electrode were found.

Platinum Metals Rev., 1992, 36, (1) 51 Characteristics of a Rechargeable Cell Photocatalytic Hydrogen Production with Constructed by Coupling Na,,,WO and Semiconductor Particulate Systems: An Na,,Pd,O, Effort to Enhance the Efficiency Y. MURANUSHI, T. MIURA and T. KISHI, Solid State M. ASHOKKUMAR and P. MARUTHAMUTHU, Inl. 3. Ionics, 1991, 46, (1,2), 63-66 Hydrogen Energy, 1991, 16, (9), 591-595 The electrochemical behaviour of NaPd,O, and H, production in visible light (437 nm) with the Na,WO, was investigated in 0.5 M H,SO, at 25OC. following semiconductor particulate systems, A Na depleted surface layer can be formed on the Ag(I)/WO,, Fe(III)/WO, and Cr(III)/WO, and mix- electrode surface of NaPd,O, by anodic pre- ed semiconductors, W0,-PtICdS and W0,-CdS was polarisation, and this surface layer absorbs or desorbs studied in the presence of an electron relay, H' reversibly at - 1.0 V vs. SHE. A new type of methylviologen, MV? +. Pt loaded CdS powders rechargeable cell with a long cyclability can thus be mixed with WO, powders (W0,-Pt/CdS) showed a constructed by coupling Na,_,WO, and Na,,Pd ,0, notable enhancement in the photocatalytic activity as in an acidic solution. compared to that of W0,-CdS. The sample sintered at 8OOOC had higher efficiency than that sintered at Adsorption of Nitroethane on Rh-Ru 300OC. Catalytic Systems T. M. GRISHINA, Vesm. Mosk. Univ., Ser. Khim., Photodissociation of Phosgene on 1991, 32, (4), 392-395 Pd(ll1) at 193 nm The adsorption of nitroethane was studied on skeletal c. n. FLOES, x.-Y.zm and J. M. WHITE, 3. Phys. Rh-Ru catalysts containing 5, 10, 20, 50, 60, 90 and Chem., 1991, 95, (23), 9431-9436 95 at.% Ru which had preliminary pretreatment The UV photodissociation of phosgene (C1,CO) on under various conditions. At 40-60°C, a decrease of Pd( 11 1) was studied by isothermal mass spectroscopy stationary potential was observed with nitroethane during irradiation and by TPD and XPS following ir- adsorption. It was explained by an increase in radiation. Phosgene absorbs reversibly on Pd(ll1) at temperature in H SO,, resulting in the formation of 110K and photodissociates when irradiated with 6.4 active electrochemical phases, which affect the poten- eV photons, thus resulting in the evolution of CO and tial. A maximum rise of potential of 10 mV was found retention of C1 adatoms. The initial photodissociation on Rh in ethylamine. cross-section is (5.320.8) x lo-'* cm'.

Photocatalysis of the Homogeneous PHOTOCONVERSION Water-Gas Shift Reaction under Ambient Photoinduced Dissociation and Desorp- Conditions by Cationic Iridium(II1) Com- tion of N20on a Pt(ll1) Surface plexes n. ZIESSEL, Angm. Chem., Inr. Ed. Engl., 1991, 30, J. KISS, D. LENNON, S. K. JOand J. M. WHITE, 3. Phys. Chem., 1991, 95, (21), 8054-8059 (7), 844-847 The first highly efficient light-assisted water gas shift N 0 adsorbed on a Pt( 11 1) surface was irradiated by , reaction to take place under the extremely mild con- UV light, and the photochemistry was studied by XPS, UPS and TPD. Upon radiation at 50K, adsorb- ditions of room temperature, ambient pressure, ed N?0 undergoes dissociation and desorption. neutral pH and visible light is reported. It is catalysed Photon energies >4.35 eV are required. The cross by Ir"' pentamethylcyclopentadienyl complexes con- taining novel 4,4'-bipyridine ligands, substituted by section is in the range 10- i9-10-'u cm?. This is the first UV photon-driven chemistry in this system. electron-withdrawing groups which enhance the catalytic activity. Photon-Driven Chemistry in Coadsorbed N,O and CO on Pt(ll1) Formation of Paramagnetic Complex from Bischelate of Palladium (11) with J. KISS and J. M. WHITE, 3. Phys. Chem., 1991, 95, (20), 7852-7857 Dehydrogenated N-(3-Hydroximinol-2- Methylbutyl-2) Hydroxylaminooxime and The UV photon-driven chemistry of coadsorbed N?0 and CO on Pt( 11 1) at 47 K was investigated by XPS, o-Phenanthroline UPS and TPD. Results depend on the order of ad- L. A. KOSAREVA, E. G. BOGUSLAVSKII and S. V. sorption. When one monolayer of N20is dosed first LANOKOV, Izv. Akad. Nauk SSSR, Ser. Khim., and CO is coadsorbed the UV irradiation causes CO, 1991, (9), 1959-1961 production, much being desorbed during the irradia- Paramagnetic Pd complexes were formed during in- tion, but when one monolayer of CO is dosed first the teraction in pure ethanol of o-phenanthroline and photon-driven production of CO, is not detectable. diamagnetic bischelate of Pd(I1) containing ligand Whatever the order of adsorption there is photon- anions of N-(3-hydroximinol-2-methylbutyl-2) driven desorption of N,O, but the cross-section is hydroxylaminooxime. The paramagnetic Pd com- higher for N,O bound to R than it is for N20 plexes contained co-ordinated anion-radical separated from Pt by CO layer. dehydrogenated 1,2-hydroxylaminooxime.

Platinum Metals Rev., 1992, 36, (1) 52 Chemiluminescence of Tryptophan with Temperature Effect on Photolytic Electrogenerated Tris(2,2'-Bipyridine) Deposition of Platinum Ohmic Contacts Ruthenium(lI1) and Schottky Diodes K. UCHIKURA and M. KIRISAWA, Chem. Lett. Jpn., C. GARRIDO and H. VAN DEN BERGH, Appl. Phys. A, 1991, (8), 1373-1376 1991, A53, (3), 265-272 A system for producing electrogenerated The deposition of Pt from Pt bihexafluoroacetyl- chemiluminescence based on the reaction of elec- acetonate by an Ar laser inducing laser chemical

trogenerated Ru(bpy) ' + (1) with tryptophan (2) is vapour deposition was investigated. The process can described. The orange luminescence is generated by be photolytic or pyrolytic, depending on the laser the reaction of (1) with (2) in acidic solution. The power. Photolytic deposition takes place in the ad- lowest detection limit was 0.1 pmol for (2), and this sorbed phase or in the gaseous phase, depending on system should therefore be useful for selective and the temperature induced by radiation absorption. sensitive detection of tryptophan and related com- The effect of the substrate base temperature and the pounds. precursor product vapour pressure confirms photolytic deposition from the adsorbed phase for Electron-Transfer Quenching of a low powers and from the vapour phase onwards for Photoexcited Ruthenium Complex by high powers. The deposits obtained have a typical Stearyl Viologen in Barium Stearate 96% Pt composition and good device characteristics Langmuir-Blodgett Films are obtained by this method in Schottky diodes. T. MIYASHITA, Y. HASEGAWA and M. MATSUDA, 3. Phys. Chem., 1991, 95, (23), 9403-9405 APPARATUS AND TECHNIQUE Photoinduced electron transfer of the Ru complex tris(4,7-diphenyl-l,lO-phenanthroline)Ru, that is Microstructure and Superconducting (Ru(dpphen),'+) to stearyl viologen (SV?') in Ba Properties of Bi-Sr-Ca-Cu-0 System stearate LB assembly systems was studied by a Prepared by a Melt Process steady-state quenching method. Even when the K. EGAWA, T. UMEMURA, S.-I.KINOUCH1, M. WAKATA and monolayer of the Ru complex was in direct contact s. UTSUNOMIYA, 3pn. 3. Appl. Phys., 1991, 30, (7A), with the layer of SV?+ quencher at the hydrophilic L1160-L1162 interface, the quenching of the Ru complex had low Bi,Sr,Ca, +~XC~2+IOY,where x=O, 0.2, 1.0, was efficiency, indicating that Ru(dpphen), l' is located at a more hydrophobic region. In an assembly where prepared from powders and calcined several times at both Ru(dpphen),?+ and SV?' exist within the 84OOC for 30 h. It was melted in a Pt crucible at same monolayer, the quenching efficiency depended >lOOO°C and splat-quenched onto Cu. The strongly on the two-dimensional density of SV' +. microstructure and superconducting properties were The results showed that electron-transfer rate examined. The magnetic field dependence of the in- decreases exponentially with distance and agrees with tragrain critical current density was improved by the conclusion that electron-transfer quenching pro- enriching the Ca and Cu contents. Two precipitates ceeds via an electron-tunnelling mechanism. were found: (Ca,Sr),CuO., and the much smaller (lpm) Sr-Pt-0 compounds. The latter may be more A Novel Photosynthetic Mimic Reaction effective in enhancing the pinning force. Catalysed by K[Ru(H-EDTA)ClI .2H,O; All-Solid-state Glucose Sensor Using Reduction of Carbon Dioxide to Formate Proton-Conductive Thick Film and Formaldehyde in the Presence of an N. MATAYOSHI, N. MIURA and N. YAMAZOE, 3Pn. 7. Aqueous Suspension of Pt-CdS-RuO, Appl. Phys., 1991, 30, (9A), L1594-L1597 M. M. TAQUI KHAN, N. NAGESWARA RAO and D. CHAT- A solid state glucose sensor using a proton-conductor TERJEE, 3. Photochem. Photobiol. A: Chem., 1991, thick film was tested as a miniaturised enzyme sen- 60, (3), 311-318 sor. A planar electrochemical cell, of sputtered An efficient photocatalytic reduction of CO, to Au(reference electrode)/antimonic acid thick HCOOH and HCHO is reported, using the title Ru fdm(proton conductor)/sputtered Pt-glucose oxidase compound, and Pt-CdS-RuO, as photon absorber at (sensing electrode) was fabricated on a porous Al ? 0 505 nm. The system produces 0.22 M of HCOOH substrate. In phosphate buffer solution the e.m.f. of and 0.10 M of HCHO in 6 h of photolysis at rates of the sensor vaned logarithmically, with change in 3.05 x lo-' 1Wh and 2.0~10-I M/h, respectively. glucose concentration in the range 5x lo-' to The rates of formation exhibit a first-order 4x lo-' M, following a Nernst equation. The 90% dependence on the catalyst and dissolved CO, con- response time was - 1 minute. The glucose sensitivi- centrations. The reaction shows D isotope effects ty was fairly stable for 10 days, and the Nernst slope (kH/kD) of 1.5 and 2.0 for the formation of HCOOH -54 mV/decade was very close to that of the response and HCHO, respectively. The rate of formate decom- to H, O,, indicating that the glucose sensing signal position was slower by 2 orders of magnitude than the was generated by responding to the H,O, produced formate formation rate, even at high formate by the enzymatic reaction of glucose. Extensions of concentrations. this type of sensor to other enzymes is possible.

Platinum Metals Rev., 1992, 36, (1) 53 Bulk Single Crystal Growth of Bi,,TiO,, Selective Conversion of Decane into by the Czochralski Method Branched Isomers. A Comparison of Y. OKANO, H. WADA. T. FUKUDA~~~s. MIYAZAWA, Jpn. PlatinumlZSM-22, Platinum/ZSM-5 and J. Appl. Phys., 1991, 30, (7B), L1307-LI309 PlatinumlUSY Zeolite Catalysts A Pt wire was used as an initial seed crystal and J. A. MARTENS, R. PARTON, L. UYlTERHOEVEN. P. A. crystals were grown from melts of differing JACOBS and G. F. FROMENT, Appl. Catal., 1991, 76, TiO, :Bi,O ratios to produce the title photorefrac- (I), 95-1 16 tive crystal. Crystals were grown in a 15 kW r.f. Detailed product distribution from the bifunctional heating Czochralski furnace with a Pt crucible of 50 conversion of decane over Pt/ZSM-22, Pt/ZSM-5 and mm diameter. Crystals of diameter up to 2 cm and 3 Pt/USY catalysts were compared. Pt/ZSM-22 pro- cm long were grown from a Bi,O, rich melt, with an duced high yields of feed isomers under mild reaction upper limit of 11 mol% TiO,. conditions. It is suggested that isomerisation of decane on ZSM-22 is a zeolite pore-mouth catalysis. Detection of Nitrite Using Electrodes Type C hydrocracking of methylnonanes does not oc- Modified with an Electrodeposited cur on PtlZSM-22, due to the limited access of these Ruthenium-Containing Polymer molecules in the zeolite pores. J. N. BARISCI~~~G.G. WALLACE, Anal. Lett., 1991, 24, (1 l), 2059-2073 Influence of Iridium, Rhenium and Lan- The electrochemical detection of nitrite in flowing thanum on Propane Aromatization over solutions using a polymer modified electrode with Platinum/ZSM-5 Catalysts electocatalytic properties is described. The modifier R. MAGGIORE. S. SCIRE, S. GALVAGNO, C. CRISAF'ULLI and used was an electrodeposited film of the G. TOSCANO, Appl. Catal. A: General, 1991, 79, (I),

[R~(bpy)~(vpy),l+ complex where bpy is 2,2'- 29-40 bypyridyl and vpy is 4-vinylpyridine. The modified A study of the effect of operating conditions on the electrode enhances the response to nitrite and avoids conversion of propane to aromatics over surface fouling. The electrodeposited fdms thus pro- Pt- Me/ZSM-5 catalysts (Me=Ir, Re, La) showed that duced exhibit high mechanical stability. the catalytic behaviour of Pt-Me/ZSM-5 depended on the nature of the added elements. Pt-Ir/ZSM-5 was HETEROGENEOUS CATALYSIS the most selective catalyst, with a yield of 61.2%. Combinations of Platinum and Palladium Effects of Hydroxylation of a Silica Sur- on Alumina Supports as Oxidation face on the Metal Dispersion in Sup- Catalysts ported Platinum Catalysts M. SKOGLUNDH, L. 0. LOWENDAHL and J:E. OT- M. AM, s.-L.GUO and Y. NISHIYAMA, Appl. Catal., TERSTED, Appl. catal., 1991, 77, (I), 9-20 1991, 77, (I), 141-148 The effects of the total Pd+Pt content, the mol% The effect of the surface hydroxyl groups of porous ratio of Pd+Pt, the hydrothermal treatment of the SiO , on the degree of Pt dispersion was studied using catalyst wash-coat, and the 0, concentration on the SiO, supports with the same surface area but with an light-off temperature were studied for the complete increasing number of these functional groups. The oxidation of xylene isomers, propene, and CO. The suppons were prepared by immersing a calcined light-off temperatures had a minimum at a Pd:Pt mol 50, in H,O at 70°C and Pt was deposited on it by % ratio of 80:20, and decreased with increasing total wet impregnation with aqueous solutions of Pt metals concentration, increasing 0, concentration tetraamine dichloride (PTD) and chloroplatinic acid. and hydrothermal treatment of the Al ,O , wash-coat . Catalysts with PTD reduced at 4OOOC showed that maximum Pt dispersion occurred on supports with Effect of Gamma Irradiation on Textural moderately hydroxylated surfaces. and Dehydrogenation Properties of Pt/AI 0 System Catalytic Palladium-Based Membrane A. M. YOUSSEF and N. A. YOUSSEF, Radial. Phys. Reactors: A Review Chem., 1991, 38, (3), 307-311 J. SHU, B. P. A. GRANDJEAN, A. VAN NESTE and S. Pt/Al,O, catalysts with 0.2-2 mol% Pt were KALIAGUINE, Can. J. Chem. Eng., 1991, 69, (5), prepared and irradiated with y-radiation to a dose of 1036-1060 50 Mrad. Textural properties were found from the A review of literature on catalytic membrane reactors low temperature N, adsorption. The catalytic using H permeable Pd and I'd-Ag alloys is presented. dehydrogenation of cyclohexane was determined for Factors involved in H purification, design parameters irradiated and non irradiated catalysts. y-Irradiation of the membranes and reactors, hydrogenation and caused textural changes of the metal/metal oxide dehydrogenation reactions and H diffusion are system depending on the metal content, and discussed. Thin Pd coatings on porous inorganic and increased the dispersion of the metal on the polymeric supports are expected to increase the im- surface. plementation of this technology.

Platinum Metals Rev., 1992, 36, (1) 54 Maximum Conversion of Dehydrogena- Conversion of Primary Amines to N,N’- tion in Palladium Membrane Reactors Disubstituted Ureas Using Mont- N. ITOH, J. Chem. Eng. Jpn., 1991, 25, (3,664-666 morillonitebipyridinepalladium(I1)Ace ta- A comparison of the maximum conversions for te and Di-Tert Butyl Peroxide cyclohexane dehydrogenation in Pd membrane reac- B. M. CHOUDARY, K. KOTESWARA RAO, S. D. PIROZHKOV tors using cocurrent and countercurrent flow models and A. L. LAPIDUS, Synth. Commun., 1991, 21, with the maximum conversion, determined ther- (18&19), 1923-1927 modynamically, in a conventional catalytic reactor, is A simple convenient method for the synthesis of presented. In the countercurrent reactor there was no N,N’-disubstituted ureas from primary amines is limit to the rise in the conversion, and 100% conver- reported, using a Pd(I1) complex anchored on an in- sion is attainable. The maximum conversion of the expensive clay support, and with a cocatalyst of cocurrent reactor was the same as that determined cupric chloride as reoxidant. The conditions are room thermodynamically. temperature and atmospheric pressure.

Adsorption Properties of Ni-Pd Catalysts Polymer-Bound Palladium Acetate as a Supported on the N203 Catalyst for the Reduction of Nitro and A. A. VEDENYAPIN, S. V. WSHIN. L. T. KONDRAT’EV and Azo Groups A. L. LAPIDUS, Izv. Akad. Nauk SSSR, Ser. Khim., R. MANI, v. MAHADEVAN and M. SRINIVASAN, React. 1991, (8), 1746-1750 Polym., 1991, 14, (3), 263-268 Studies of the surface compositions of Ni-Pd/Al,O, Pd(0Ac) , anchored to a copolymer containing catalysts were performed by adsorption methods and pyridyl and carboxyl groups was used as a catalyst for by X-ray spectroscopy. The results showed that the hydrogenation of azo and nitro groups under 1 bimetallic catalysts differ from monometallic Pd- and atm H, pressure and 3OOC. The selective hydrogena- Ni-catalysts by dispersion of metallic phases, depen- tion of azobenzene to hydrazobenzene was highly ding on a method of preparation and on the presence selective on using the polymer-bound Pd catalyst, of K’ promoter. Catalysts prepared by the immer- and is reported for the first time. The catalyst is quite sion method had more strongly Pd enriched surfaces, stable and has been well used for more than a year. as compared to those prepared by precipitation. Reactions of Formic Acid and For- Design of the Catalyst for Partial Oxida- maldehyde on Rh(l11) and Rh(ll1)- tion of Ethylene by Applying an Elec- (2 x 2)0 Surfaces trochemical Device C. HOUTMANandM. A. BARTEAU, surf. SCl., 1991,248, K OTSUKAand A. KOBAYASHI, Chem. Lett. Jpn., 1991, (1/2), 57-76 (7)/(8), 1197-1200 The adsorption and decomposition of HCOOH and An electrochemical device composed of a H,PO, HCHO on the Rh(ll1) surface was studied by membrane on which were attached Pt and Pd blacks, HEELS. HCOOH adsorbed on the surface via the Ru, Rh, 0s and Ir, MiH,PO,/M’, where M=anode lone pair electrons on the hydroxyl 0, and H bonding metal and M’ =cathode metal, was demonstrated as a among the molecules in the adlayer is indicated. At - probe of the catalysts for the partial oxidation of 140K a formate intermediate was formed, which C,H, . From the results a catalyst, Pd-Ru-graphite- decomposed to CO,, CO, H, and H,O via two chan- H,PO,, has been designed for the selective synthesis nels. Adding 1/4 monolayer of 0 atoms to the of CH,CHO from C,H, - a Wacker oxidation. The Rh( 11 1) surface shifted the formate decomposition formation rate of CH,CHO was 3.18 pmollmin. temperature to 330K. Below 130K on a clean Rh( 11 1) surface HCHO dehydrogenated completely to ad- Oxidative Leaching of Cu Atoms from sorbed CO and H atoms. Exposing an 0 predoped PdCu Particles in Zeolite Y surface to HCHO resulted in formation of adsorbed paraformaldehyde, CO, formate and q ’ -HCHO. z. ZHANG, L. xu and w. M. H. SACHTLER, J. Catal., 1991, 131, (2), 502-512 Infrared Spectroscopy of High Pressure: Nay-supported PdCu samples of various Cu:Pd ratios were prepared by ion exchange with Interaction of H, and D2 with Rh/AI,03 J. P. WEY, W. C. NEELY S. D. WORLEY,

Pd(NH,), and Cu(NH),), + precursors. Reduc- and 3. Phys. tion of Cu was enhanced by Pd. Reduction with H, Chem., 1991, 95, (22), 8881-8886 resulted in bimetallic PdCu particles and protons of A novel high pressure-IR-cell reactor was used to high Bronsted acidity. Complete oxidation of the Cu study the interaction of ultrapure, high-pressure H, component occurred at 5OOOC and the Cu ions leach- and D, with Rh/Al,O, films. The H, may dissociate ed from PdCu particles migrated to small zeolite on the Rh sites to produce a weakly bound Rh-H sur- cages. After complete leaching of Cu, the face species, with the remaining H spilling over to the monometallic Pd particles were discerned from the support where it reacts with surface hydroxyl groups original particles in PdCu/NaY and PdCu,/NaY by to produce H,O. The new Rh-H species was easily their propensity to form TPD-detectable hydrides. removed by reduction under H, pressure.

Platinum Metals Rev., 1992, 36, (1) 55 Effects of Polymer Support on the Alcohol Synthesis from Syngas on Substrate Selectivity of Covalently Im- Supported Ir-Based Composite Catalyst mobilized Ultrafine Rhodium Particles as A. KURUSU. M. INOUE and T. INUI, Shokubai, 1991, 33, a Catalyst for Olefin Hydrogenation (2), 129-136 M. OHTAKI. M. KOMIYAMA, H. HIRAI and N. TOSHIMA, Alcohol synthesis from syngas over supported Ir- Macromolecules, 1991, 24, (20), 5567-5572 based composite catalysts was examined. Ir catalysts Immobilised ultrafine Rh particles were prepared promoted with Mo, V and Cr had the highest activity from a protective polymer, and deposited onto a for alcohol formation. The predominant formation of cross-linked polymer support, by forming the amide MeOH and 2-methylalcohols on the Ir-Cr catalyst bond between the primary amino group contained in strongly suggests that CO insertion occurs. Alcohols the support and the methyl acrylate residue in the produced on Ir/Cr303seem to be formed in the same protective polymer of the Rh. The catalytic activity of way as for the Ir-Cr composite catalyst. Ir/MoO, had the Rh was investigated by olefin hydrogenations. the highest CO conversion, but CH, was the main Activity strongly depended on the substrates used. product. The Rh preferentially hydrogenated hydrophilic substrates. Substrates containing a carboxyl group A Mild, Osmium Tetraoxide-Catalyzed were hydrogenated by the immobilised catalyst more Method for the Oxidation of to easily than by the dispersed catalyst. The difference Sulfones in hydrogenation rates can .be correlated with the s. w. KALDOR and M. HAMMOND. Tetrahedron Lett., solubility parameter of the substrate. Electrostatic in- 1991, 32, (38), 5043-5046 teraction between substrates and the polymer support OsO, was examined for the chemoselective oxidation leads to increased reaction rates. of sulphides to sulphones, in the presence of the co- oxidant N-methylmorpholine-N-oxide.One mole per New Rhodium Complexes Anchored on cent of the catalyst was sufficient at room Modified USY Zeolites. A Remarkable temperature to oxidise a variety of sulphides to the Effect of the Support on the Enantio- corresponding sulphones in nearly quantitative selectivity of Catalytic Hydrogenation of yields. The oxidation is tolerant of the presence of a Prochiral Alkenes number of other functional groups. A. CORMA, M. IGLESIAS. c. DEL PINO and F. SANCHEZ, 3. Chem. SOC.,Chem. Cornmun., 1991, (18), 1253-1255 HOMOGENEOUS CATALYSIS Studies of Rh-complexes with N-based chiral ligands which were anchored on a modified USY-zeolite con- a-Stacking and the Platinum-Catalyzed taining profuse supermicropores showed a Asymmetric Hydroformylation Reaction: remarkable increase of enantioselectivity (>%YO) in A Molecular Modeling Study the hydrogenation of N-acyldehydmphenylalanine L. A. CASTONGUAY, A. K. RAP& and C. J. CASEWIT, 3. derivatives. The zeolite supported-Rh catalysts were Am. Chem. SOC.,1991, 113, (19), 7177-7183 re-used several times with no loss of activity or Rh content. The increase obtained in the enantioselec- The importance of steric factors in determining the tivity indicated that this type of catalyst is a truly regioselectivity of a class of Pt(I1) hydroformylation heterogeneous counterpart of the homogeneous catalysts (L,Pt(C0)X) was theoretically studied by catalysts for the hydrogenation of prochiral alkenes. using an augmented Dreiding force field. The differential stabilisation of the initially formed Pt alkyl complexes resulting from styrene insertion into Catalytic and Physical-Chemical Proper- a Pt-H bond formed either the primary phenethyl ties of Indium Modified Iridium-Alumina product or the secondary a-methyl styryl Catalysts for Dehydrogenation of Highest intermediate. Normal Paraffins A. V. ZAITSEV, A. P. TWPAEV. V. YU. ROROVKOV, 0 D. A Homogeneous Platinum Catalyst in the STERLIGOV. G. V. ISAGULYANTS and V. B. KAZANSKII, Stationary BF,.H20 Phase for the Izv. Akad. Nauk SSSR, Ser. Khim., 1991, (lo), Hydrogenation of Arenes 2222-2227 1. T. HORVATH, Angew. Chem., Int. Ed. Engl., 1991, Spectroscopic studies of monometallic and In 30, (8), 1009-1011 modified Ir/Al, 0, catalysts during dehydrogenation A stationary liquid-phase catalyst comprising of high n-paraffins showed that Ir-In/Al,O catalysts PtCl (CH ,CN) in BF ,.HI 0 on clay or silica sup- had higher activity and increased selectivity towards ports was prepared and used for the hydrogenation of the highest olefins. In modified the Ir surface, form- various aromatic hydrocarbons under mild condi- ing mixed clusters. At the same time, a decrease was tions. The catalyst was tested for continuous perfor- observed in the number of surface Ir atoms capable mance in a tubular trickle-bed reactor. Products are of adsorbing H, at 300K, but the number of centres separable by simple filtration, and the hydrogenation of high temperature H?dissociation which adsorbed proceeds selectively, in a 1: 1: 1: 1 mixture of benzene, H, on the support noticeably increased. toluene, o-xylene and 1,2,4-trimethylbenzene.

Platinum Metals Rev., 1992, 36, (1) 56 Platinum(I1) Catalysed Selective Remote Efficient Palladium Catalysts for the Oxidation of Unactivated C-H Bonds in Copolymerization of Carbon Monoxide Aliphatic Carboxylic Acids with Olefins to Produce Perfectly Alter- L.-c. KAO and A. SEN, 3. Chem. Soc., Chem. Commun., nating Polyketones 1991, (18), 1242-1243 E. DRENT, 1. A. M. VAN BROEKHOVEN and M. J. DOYLE, The use of the 'chelate effect' in achieving the selec- 3. Organomet. Chem., 1991, 417, (1-2), 235-251 tive oxidation (hydroxylation) of C-H bonds of Highly efficient homogeneous Pd catalyst systems aliphatic chains by Pt" in aqueous medium under were developed to produce perfectly alternating mild conditions is reported. By adding a co-oxidant copolymers of CO with C,H,. CO, C,H, and pro- that is capable of reoxidising Pt" to F'"' it is possible pene mixtures are converted into the corresponding to make the system catalytic in Pt". In the presence alternating CO/olefin terpolymers where C, units of Pt(IV),Pt(I1) ion was found to catalyse the hydrox- randomly replace C,H, units in the chain. The ylation of unactivated C-H bonds of aliphatic carbox- catalyst systems are formed by combining an ylic acids in water. equimolar quantity of a suitable bidentate phosphine ligand with a Pd(I1) species in which the counter Isomerisation and Carbonylation of anions are very weakly co-ordinating. For Esters Catalysed by Platinum Phosphide diphenylphosphinoalkanes: Ph,P(CH,),PPh,, the Complexes in the Presence of Lewis most efficient system to produce high molecular weight polyketones has m = 3. High rates with conver- Acids sions of >lob molecules of CO and C,H, per Pd cen- N. w. KOZITSYNA and I. I. MOISEEV, Akad. Nauk tre are obtained. SSSR, Kinet. Katal., 1991, 32, (4), 985-989 Polynuclear Pt phosphide complexes IPPh, Ptl, Palladium-Catalyzed Intramolecular Ad- (n =8-10) in RCOOR solution, containing acid types dition of Amines to Acetylenes. Synthesis BF,, SbFI, CF,COOH or C,H,OCF(CF,)- CF,OC,F,SO,H, catalysed the isomerisation of of Cyclic Imines methylformate in acetic acid, and carbonylation of Y. FUKUDA, s. MATSUBARA and K. UTIMOTO, 3. Org. methylacetate in acetic anhydride at 20-25OC and in Chem., 1991, 56, (20), 5812-5816 Ar or CO, respectively. Intramolecular aminopalladation of alkynylamines gave intermediary alkenyl I'd compounds that Palladium-Catalyzed Insertion of Iso- hydrolysed and isomerised to thermodynamically cyanides into the Silicon-Silicon Linkages stable cyclic imines. Treating 3-alkynylamines with of Oligosilanes PdCl ,(MeCN) , gave exclusively 1-pyrrolines in good yields; 5-alkynylamines afforded 2,3,4,5-tetrahydro- Y. ITO, M. SUGINOME, T. MATSUURA and M. MURAKAMI, pyridines selectively. Treating 4-alkynylamines with 3. Am. Chem. SOC.,1991, 113, (6), 8899-8908 Pd(I1) gave mixtures of both 5- and 6-membered Oligosilanes were reacted with isocyanides when pro- cyclic imines. moted by a Pd catalyst. Heating oligosilanes with ex- cess 2,6-disubstituted aryl isocyanide in the presence Palladium Catalyzed Carboxylation of of Pd(I1) acetate led to the complete insertion of iso- cyanide into all Si-Si linkages, giving oligo(sily1imine) Cyclohexane with Carbon Monoxide derivatives. The oligo(sily1imine)s were isolated and K. NAKARA,J. WATANABE, K. TAKAKI and Y. FUIIWARA, characterised in the complete insertion reaction with Chem. Lett. Jpn., 1991, (8), 1437-1438 oligosilanes up to a hexasilane. New skeletal rear- Very high turnover numbers have been obtained for rangement of oligosilanes took place in a Pd-catalysed the carboxylation of cyclohexane with CO to form reaction of substituted aryl isocyanide with tetra- and cyclohexanecarboxylic acid using Pd(0Ac) ,. The hexasilanes, yielding 3,3-bis(silyl)-1 -aza-2,4-disila- product yield was 8.8% based on the starting alkane cyclobutane derivatives. and the turnover number was 205.

Synthesis and Catalytic Activity of Pd(I1) Synthesis of a,fi-Disubstituted Aldehydes Complexes with Bi- and Tridentate from Metallated 1-Aza-l,3-Butadienes Salicylaldimines Containing S terically and Palladium Phosphine Complexes Hindered Phenols U. M. DZHEMILEV, A. G. IBRAGIMOV, D. L. MINSKER, R. R. A. A. FUAEV. V. T. KASUMOV and A. A. MEDZHIDOV, MUSLUKHOV and G. A. TOLSTIKOV, Izv. Akad. Nauk Akad. Nauk SSSR, Kinet. Katal., 1991, 32, (3), SSSR, Ser. Khim., 1991, (lo), 2339-2348 594-599 a,/l-Disubstituted aldehydes were prepared from The synthesis of binuclear Pd chelates with tridentate metallated I-aza-1,3-butadienes in the presence of salicylaldimines is reported. The catalytic activity of Pd(acac), +2Ph,P catalysts by reactions of N-, 0- the Pd complexes was studied during the hydrogena- and S-containing ally1 electrophiles with Mg tion of nitrobenzene in a homogeneous medium. The azaenolate and organic halogenides. The reaction per- dependence of the activity on solvents and cir- formed with the Pd phoshine catalyst was highly cumferential ligand substitutes is discussed. regio- and stereoselective.

Platinum Metals Rev., 1992, 36, (1) 57 Kinetics of the Water Gas Shift Reaction ELECTRICAL AND ELECTRONIC Catalyzed by Rhodium(II1) Chloride in ENGINEERING Aqueous Picoline Studied by Use of a Continuous-Flow Stirred Reactor Magnetoresistance of Co/Pd and Co/Pt B. s. L. NETO, K. H. FORD, A. J. PARDEY, R. c. RINKER~~~Multilayer Films for Magneto-Optical P. c. FORD, Inorg. Chzm., 1991, 30, (20), 3837-3842 Data Storage Applications Homogeneous water gas shift catalysis by R. A. HAJJAR, T.-H. wu and M. MANSURIPUR, J. Appl. Rh(III)CI, .3H20 in aqueous picoline solution in a Phys., 1991, 70, (lo), 6041-6043 continuous-flow stirred reactor is described. The Galvanomagnetic, magnetic and magneto-optical pro- catalysis rates were non-linear in total IRhl over the perties of multilayered Comd and Co/Pt films with range 3-20 mM, which was interpreted by the system varied content were studied. Corn films, an in- having dinuclear and mononuclear species pre- Co In Rh crease of content resulted in a decrease of the s-d sent, with the mononuclear cycles being more reac- Co slope approaching the value for a pure films. The tive. The rates have a non-linear dependence on Co PCo magnetic and electronic properties of these films were over range 0.3-1.8 atm, although this was indepen- correlated with the magnetoresistance measurements dent of [Rhl. There may be reversible addition of CO performed with fields applied parallel and perpen- to the catalytically active species prior to rate-limiting dicular to the plane of the samples. in the mono- and dinuclear catalytic cycles. Through-Wafer Optical Communication CORROSION PROTECTION Using Monolithic JnGaAs-on-Si LED’S and Monolithic PtSi-Si Schottky-Barrier Cathodic Protection System Detectors R. S. ROHELLA, B. C. SWAIN and J, S. MURTY, Anti- G. W. TURNER, C. K. CHEN, B.-Y. TSAUR and A. M. WAX- Corros. Methods Mater., 1991, 38, (6), 4-7 MAN, IEEE Photonics Technol. Lett., 1991, 3, (@, Steel corrosion in sea water and methods of overcom- 761-763 ing it are discussed, with particular reference to the Through wafer optical communication has been design and implementation of a cathodic protection shown for the first time using two vertically stacked system for steel piles. An impressed current cathodic Si wafers, the upper one with InGaAs-InAlAs double- protection system was chosen, and typical current re- heterostructure LEDs grown by MBE on its top sur- quirements for various steel structures are given. The face and the lower one with PtSi-Si Schottky barrier design characteristics and application for different detectors fabricated on its bottom surface. IR radia- types of anodes are given. Pt clad Nb anodes were tion emitted by the LEDs in a band peaking at l. 12 selected as having the highest current carrying capaci- pm just beyond the Si absorption edge is transmitted ty, lowest anode consumption and longest life. The Pt through the upper Si wafer, focused with a lens of metal available on the anodes is expected to last focal length 25 mm, transmitted through the lower Si longer than the designed life of the cathodic protec- wafer and detected by the Pt-Si detectors. In a single tion system, assuming that only 90% of the Pt can be LED-detector pair the detector S:N ratio was lO:l, used. The anodes have current output of 25-35 A. for a LED drive current of 1 mA at room temperature. Effect of Paint Damage and Under-Way Conditions upon Ship ICCP Current Annealing Studies on Pdln-GaAs Schot- Demands tky Diodes D. J. TIGHE-FORD and P. KHAMBHAITA, Corros. Prev. H. SHARDA, K. PRASAD, L. FARAONE and A. c. NASSI- Control, 1991, 38, (4), 85-89 BIAN, Semicond. sci. Technol., 1991, 6, (8), The dimension and conductivity scaling modelling 765-770 technique was used to assess three impressed current Pdh-GaAs Schottky diodes were fabricated using cathodic protection systems on ships’ hulls. Up to six either spin-on or evaporated Pd sources. Barrier Pt foil anodes, each mounted on a polymethyl heights and electrical characteristics were measured. methacrylate shield placed directly on the plate were The ideality factor for both diodes was close to 1. tested. The current output of these systems in static Ageing at temperatures up to 2OOOC for 1000 h pro- and simulated under-way conditions with an intact duced little or no change in diode parameters; but an- paint coating and with damage along the hull were ex- nealing at 2SOOC for up to 1000 h produced a gradual amined. Potential profiles with anodes in different degradation of diode parameters. This degradation places are presented. The best protection overall was significantly faster during a 4OOOC anneal, and is came from the two-zone system: with one poten- attributed to the atomic intermixing and/or diffusion tiostat, midship reference electrodes (RE), two for- at the Pd-GaAs interface. Pd spin-on devices had a ward and two after anodes, plus second potentiostat, much longer operating life compared to the stern RE, and two stern anodes. Modelling predicts evaporated ones. The spin-on technique is the performance and current output of impressed economical, simple and easy to implement in any ex- current cathodic protection systems. isting GaAs device technology.

Platinum Metals Rev., 1992, 36, (1) 58 Palladium as a Lead Finish for Surface MEDICAL USES Mount Integrated Circuit Packages D. c. ABBOTT, R M. BROOK, N. MCLELLAND and J. s. Design and in Vitro Studies of a Needle- WILEY, IEEE Trans. Componenu, Hybrids Manuf. Type Glucose Sensor for Subcutaneous Technol., 1991, 14, (3), 567-572 Monitoring The use of a thin preplated Pd Pb finish as an alter- D. S. BINDRA, Y. ZHANG, G. S. WILSON, R. STERNBERG, D. native to SnPb solder is discussed for surface mount R. THBVENOT, D. MOA~and G. REACH, Anal. Chem., IC packages. Tests performed on the Pd included 1991, 63, (17), 1692-1696 wetting, solder joint metallurgy, wire bonding, in- A new miniaturised glucose oxidase based needle- teraction with molding compounds and elec- type glucose microsensor has been developed for sub- trochemical characteristics. Reliability and cutaneous glucose monitoring. The sensor has a 10 performance tests were also run, including operating cm long Teflon coated Pt-Ir wire of 0.25 mm 0.d. life, temperaturehumidity, thermal cyclekhock, Pb with a 1 mm long bare part acting as a sensing cavity. finish performance and mechanical tests. Pd plated The reference electrode was Ag/AgCl, and the whole leadframes were successful on small outline packages sensor was coated with 5% polyurethane solution in (8-28 pin) and fine pitch packages. 98% THF-2% DMF.

AC Complex Impedance Investigation for The Effect of Some Platinum Compounds RuO -Glass Composites on the Activity of the CTP Synthetase of B. K. KOO, K. s. NO and H. G. KIM, IEEE Trans. Com- Ehrlich Ascites Tumor Cells: In Vitro and ponents, Hybrids, Manuf. Technol., 1991, 14, (3), In Vivo Studies 580-584 R. L. GANEVA, N. C. SPASSOVSKA and D. D. GENCHEV, 3. The AC complex impedance spectra of Ru0,-glass Inorg. Bwchem., 1991, 43, (4), 717-722 composites were investigated from 1 kHz-13 ME, The effect of cis-diamminedichloroPt(I1): (cis-DDP), as functions of RuO, content and heat treatment con- trans-DDP, spermine Pt(I1) and K,RCI, on the ac- ditions. Since the amount of Ru ion in the PbO- tivity of CTP synthetase in the cytosol of Ehrlich B,O1-Si0,-AI,O3-Zn0 system increases with in- ascites tumour cells was studied. For in vitro study creasing reaction temperature and time, the elec- the pt compounds were added to the incubation mix- tronic properties of the matrix are changed. Samples ture for the enzyme assay. A concentration dependent reacted at low temperature and for short times show- inhibition of CTP synthetase was found, which was ed vertical lines in complex impedance spectra plots, strongest for the trans-DDP. Ascites cells from mice which indicated that the samples consisted of lone pretreated in vivo with Pt compounds showed that in- capacitor circuits. As temperature and time increas- hibition is strongest for cis-DDP and K, PtQ, . ed, the spectra consisted of semicircle arcs represen- ting RC combination circuits. Samples with more Synthesis and Characterization of Highly RuO ,showed a change from a vertical line to semicir- Lipophilic Antitumor Platinum(I1) Com- cle arcs at a lower reaction temperature. A sample with 5 vol.% RuO, and reacted at 1000°C had an plexes equivalent circuit model which was only resistive. A. R. KHOKHAR, Q. xu and s. AL-BAKER, 3. Coord. Chem., 1991, 24, (l), 77-82 The preparation and characterisation of a series of TEMPERATURE highly lipophilic Pt(I1) complexes of .type MEASUREMENT [Pt(OCOR),(A)I or [Pt(OCOR),(A'),I are described, where R=a highly branched or long chain alkyl A GoldlPlatinum Thermocouple group of 4-13 C atoms, A=lR,ZR-diamino- Reference Table cyclohexane, cis-l,2-diamir1ocyclohexane, 1,l-bis (aminomethy1)cyclohexane or ethylenediamine and M.GOTOH, K. D. HILL and E. G. MuRDOCK, Rev. sci. In- A' = neopentylamine or cyclopentylamine. strum., 1991, 62, (ll), 2778-2791 The thermoelectric voltage of the Au/Pt thermocou- Myoglobin Oxygen Binding Curves ple was measured over the range 0-%2OC, by com- Determined by Phosphorescence Quen- parison with calibrated Pt resistance thermometers. ching of Palladium Porphyrin From 0 to 50OOC the measurements were taken in a stirred liquid bath, while from 660 to 964OC they J. J. KELLY, K. A. KELLY, S. A. HARTLEY and C. H. were performed in a pressure controlled Na-fded BARLOW, Appl. Specmsc., 1991, 45, (7), 1177-1182 heat pipe furnace that provided an isothermal inter- A completely optical method has been developed for comparison environment. Measurements were made evaluating myoglobin-0, saturation. Using this solu- at the freezing points of In, Sn, Zn, Sb and Ag, at the tion 0, concentrations were computed for function- melting point of Ga and at the liquidus point of the ing heart muscle by measuring the phosphorescence Ag-Cu eutectic. A reference function was obtained decay of a soluble Pd porphyrin, 5,10,15,20-teuakis that gives e.m.f. as a function of temperature to (4-sulphanatophenyl)-porphyrinPd(II), according to within k10 mK from 0 to 962OC. the Stern-Volmer quenching relationship.

Platinum Metals Rev., 1992, 36, (1) 59 NEW PATENTS METALS AND ALLOYS CHEMICAL COMPOUNDS Platinum-Aluminium-Copper Alloys for Preparation of Stable Platinum Jewellery Compounds for Use in Platinum Pastes MINTEK European Appl. 42 1,73 1A TANAKA KIKINZOKU KOGYO The colour of intermetallic Pt-Al compounds is Japanese Appls. 3/99,087-89 modified from yellow through orange to Cu red by Pt camphene mercaptate, Pt limonene mercaptate or the addition of Cu. The alloys consist of 50-81 wt.% Pt terpineol sulphide are useful materials for Pt pastes Pt, 5-30 wt.% Al and 1-47.5 wt.% Cu, and may be used to prepare Pt catalysts, electronic parts, formed by addition of Cu to the compound PtAl, or corrosion-proofing layers or liquefied Pt film by melting individual components together in an in- materials; and have good storage stability and are ert atmosphere. The addition of Cu gives a range of easily prepared. Preparation comprises reacting aesthetically pleasing colours, and the alloys are used platinic acid salts with camphene mercaptan, in the jewellery trade. limonene mercaptan or terpineol sulphide respective- ly, extracting with chloroform, washing, evaporating, Palladium Based Alloys for Metal and in the final step crystallising the products to give Powders light yellow crystals. LEACH & GARNER U.S. Patent 5,000,779 Metal powder alloys consist of at least one of Pd, Au ELECTROCHEMISTRY and Ag; Cu; and 0.20-0.80 wt.% of at least one from B, P, Si and Li; with preparation in- New Electrode for Oxygen Generation cluding atomisation and rapid solidification. A Process preferred metal powder contains 40 wt.% Pd, 30 wt.% Ag, 30 wt.% CU,0.5 wt.% B and 0.5 wt.% P, TDK CORP. British Appl. 2,239,260A and has particle size 400 pm and grain size <10 pm. A new electrode for 0, generation has a metal The alloys have increased hardness, the supersolidus substrate such as Ti coated with alternate layers of temperature is reduced, and the metal powders have composite oxides containing (a) 40-79.9 mol% Ir ox- optimum particle and grain size for supersolidus ide and 60-20.1 mol% Ta oxide, and (b) 80-99.9 sintering. mol% Ir oxide and 20-0.1 mol% Ta oxide. The elec- trode has good adhesion, long life at low cell voltage High Brightness White Gold Alloy and current densities up to 100 A/dm?, and low 0, NIPPON KIKINZOKU KO. Japanese Appl. 3/87,323 overvoltage and enhanced durability when used for An alloy having high brightness contains 75 wt.% O? generation by electrolysis of aqueous solutions. Au, 8-12 wt.% Pd, 7-5 wt.% Ag, 54wt.% Ni and 5-4 wt.O/o Cu and/or Co in total. The alloy is an 18 Electrolytic Cell with Hollow Anodes carat Au (white Au), has high brightness similar to Containing Platinum Pt, and has good physical, mechanical and chemical PEROXID-CHEMIE c.m.b.H. European Appl. 428,171A properties. An electrolytic cell has alternating cathodes and anodes which are shaped hollow bodies, with the ef- Platinum Alloy Material for Colouring fective anode surface consisting of R valve Pt Ornaments Black overlayer made by hot isostatic press! L_ IPt foil onto AGENCY OF IND. SCI. TECH. Japanese A@!. 3/100,159 a metal substrate. The cell blocks are useful elec- A Pt alloy material consists of 3-20 wt.% Pt and 3-20 trochemical reactors for production of peroxo and wt.% of at least one of Cu, Fe, Co and Ti. The pro- perhalogenate compounds, have a long working life cess includes heat treatment in a low oxidation at- and high current density, and can be used together, mosphere and cooling the material to room with low energy consumption. temperature with air, water or oil, and the material is used for black colouring of ornaments to give a lustre. Production of High Purity Ammonium Paratungstate Silver-Palladium Alloy Powder GTE PRODUCTS CORP. U.S. Patent 5,021,133 Preparation A cemented tungsten carbide-Pt anode is used in the KOJUNDO KAGAKU KENK. Japanese Appl. 3/126,805 electrolysis of an electrolyte consisting of ammonium A Ag-Pd alloy for use in thick film pastes is prepared hydroxide and an ammonium salt, where electro- by dissolving a Ag-Pd alloy in HNO, , and then ad- dissolution decomposes the cemented tungsten car- ding a reducing agent to obtain a precipitate of the bide to form a solution of ammonium tungstate from Ag-Pd alloy. The process is suitable for mass produc- which ammonium paratungstate is crystallised. A tion, giving an alloy powder of uniform quality which product of high purity is obtained without firing the is capable of providing good electric and soldering starting material to tungstic oxide and without diges- properties when used as pastes. tion in sodium hydroxide.

Platinum Merals Rev., 1992, 36, (l), 60-68 60 Electrochemical Oxygen Separator with Radionuclide Source Preparation Iridium Anode V.M. RADCHENKO Russian Patent 1,266,366 JAPAN STORAGE BATTERY Japanese Appl. 3194,086 An increased power radionuclide source has a ra- An electrochemical separator has an integrated elec- dionuclide oxide layer on a Pt wire, and is prepared trochemical cell consisting of a cathode for elec- by electromechanicallycoating a 0.3 mm Pt wire with trolytic reduction of 0, , an ion-exchange membrane the hydroxide of Cm-244 at 1200 pglcm’ of surface. used as a solid electrolyte, and an Ir anode used for The composition is then calcined at 80OOC in air to generating 0,. The cell is used to separate 0, from obtain a Cm oxide layer of 0.5 mm thickness. Forma- a gas mixture by supplying the mixed gas to the tion of the radionuclide source is thus simplified. cathode, and collecting the 0, from the anode. By us- ing an Ir anode the cell operates under low voltage and at increased efficiency. APPARATUS AND TECHNIQUE Determination of Nitrous Oxide and Electrolysis Electrodes with Porous Oxygen in Gas Mixtures Platinum Protective Coating GTE LABS INC. European Appl. 432,649A PERMELEC ELECTRODE LTD. Japanese Appl. 3/126,884 A sensor used in medical anaesthesia for determina- Electrodes are manufactured by electrodeposition of tion of N,O and 0, concentrations in a N,O, 0, and a PbO, coating layer on a metal or alloy base, follow- N, mixture has Pt electrodes separated by a solid ed by forming a porous Pt protective layer by elec- electrolyte wall, preferably of yttria stabilised ZrO,. trodeposition or electroless plating. The electrode A negative voltage is applied to the electrodes which consists of multiple layers of PbO, and multiple are first exposed to a gas containing a known amount porous Pt layers. An insoluble electrode is obtained. of O,, and then to the gas mixture for determination. Comparison of the current plateaux obtained gives ELECTRODEPOSITION AND the N,O and 0, concentrations. SURFACE COATINGS Platinum Resistance Thermometer for Use in a Gas Detector Metal Surface Substitution Using MICROSYSTEM DESIGN World Appl. 9115,998A Palladium Plating Solution A gas detector to monitor the concentration of a com- ORIENT TOKE1 KK. Japanese Appl. 3194,072 ponent of a gas mixture, for example 0, or CI diox- A process to effect metal surface substitution has as ide, has a catalyst coated Pt resistance thermometer the first stage an etching process in a mixed solution which effects an exothermic decomposition of the of NaOH, KOH, KCN and NaCN at 5-35OC, and as component and generates a signal indicating its con- second stage electroless plating using a 0.1-1.0 gfl centration. A cheap, accurate and reliable sensor with solution of PdCI,, Pd(NO,),, PdSO,, Pd(COOH), no moving parts is obtained which is specific to the or its salt, at pH 10-12, and at 5-35OC. The process gas to be detected, and can detect a wide range of con- is useful for plating onto thin metal foil or film of centrations. electronic devices, and for forming Al foil patterns. Platinum Cup for Pyrolysis of Pulp Membrane Coating for Spinning Nozzle Samples TANAKA KlKlNZOKU KOGYO P. SHAKKOTTAI U.S. Patent 5,002,894 Japanese Appl. 31104,909 A Pt cup is used for pyrolysis of samples of paper A mixture consisting of chloroplatinic acid and Pt making materials for measurement of the lignin con- metal chlorides such as PdCl ,, IrCl and RuCI, in an tent by mass spectrometry. The Pt cup is welded to organic solvent is used to coat the spinning face of a a ribbon of poor heat conducting metal such as spinning nozzle which consists of an alloy of Pt and stainless steel, and is electrically puked for a short Au, Ta and stainless steel. The coating is then dried time for pyrolysis of the samples at 530-570OC. The and sintered to form a thin membrane having a micro method is used for quality control of pulp manufac- structure of Pt and Pt group metal oxides which is tured in a paper making mill. very stable and has good anti-corrosion properties. Ruthenium Concentration Sensor for Palladium Deposition Bath Containing Atomic Fuel Reprocessing Plant Ethylenediamine HITACHI K.K. Japanese Appl. 3148,748 OFF. NAT. AEROSPATIALE French Appl. 2,652,823 A Ru concentration sensor for detecting RuO, con- A basic aqueous bath for chemical deposition of Pd centration uses oscillators where an organic mem- contains Pd chloride, hydrazine as reducing agent, brane is provided on the surface of an electrode. Ru ethylenediamine as the Pd ion complexing agent and concentration is measured by the difference in fre- a stabiliser. The complexing agent is present in suffi- quency change between oscillators in sample and cient amount to complex all of the Pd ions and the C1 reference environments. The sensor enables RuO, ions near the plating surface, and the bath has an concentration to be detected on the spot with high autocatalytic action. sensitivity, and is useful in atomic fuel reprocessing.

Platinum Metals Rev., 1992, 36, (1) 61 Durable Gas Sensor Element Gas Sensor with Long Term Stability at KURABE K. K. Japanese Appl. 3159,450 Low Temperatures A gas sensor element consists of an insulating base FUJI ELECTRIC MFG. K.K. Japanese Appl. 3/90,848 plate such as AI,O, or SiO,, a pair of comb shaped A gas sensor consists of a base plate made of an in- Pt or Au electrodes, a SnO, or ZnO, gas sensor, a Pt sulator material, a gas sensitive layer containing andlor Pd catalyst layer up to 5 nm thick, and a 0.1-1 wt.% (total) of Pt and Pd in the proportion heater. The gas sensor is kept at 15OOC and is used 1-3, and an n-type oxide semiconductor coating layer for reducing gases such as CO and H,. The sensor carrying 2-10 wt.% ofa noble metal, for example Sn has a simple structure, high sensitivity, good oxide carrying 3 wt.% Pt. The catalytic activity of the durability and is stable over a long period of time. gas sensitive layer is stable over a long period, even at low temperatures. Enzyme Electrode with Conductive Platinum Base Body Gas Sensor for Detecting Oxygen and KANZAKl PAPER MFG. K.K. Japanese Appl. 3159,453 Ozone An enzyme electrode consists of a conductive base OAK SEISAKUSHO K.K. Japanese Appl. 3195,452 body of Au or C, having its surrounding part Pt, A gas sensor consists of a semiconductor base plate covered with a hydrophobic insulator such as polyethylene, and the section covered with an im- such as a p-type silicon wafer, an insulating layer, a La fluoride laye: having La:F atomic ratio 1:2-1:3, mobilised enzyme film such as glucose oxidase and a 100-500 A laminated electrode having pro- through a permselective membrane. The electrode Pt perties intermediate between those of and Pt can be assembled simply, and has good durability. Pt black. The gas sensor is useful for detecting 0, and Heat Resistant Humidity Sensing 0, at normal temperatures, and functions by absorb- Element ing the gas on the electrode and detecting the change in properties. SHINETSU CHEM. IND. K.K. Japanese Appl. 3172,253 A humidity sensing element consists of an insulating Platinum-Rhodium Melt Crucible with base plate, a pair of Ag-Pd, Ru oxide or Au electrodes on the base plate, and a polysiloxane film. The sensor Longer Operational Life can be used at

Platinum Metals Rev., 1992, 36, (1) 62 HETEROGENEOUS CATALYSIS Iridium Catalyst for Preparation of Chlorofluoroethanes Production of Amines for Polyurethane ATOCHEM. European Appl. 435,705A Foam Chlorofluoroethanes are prepared by hydrogenation BAYER A.G. European Appl. 424,764A of a perhalogenoethane at 50-300°C and 1-20 bar us- Bis- and tris(3-dimethylaminopropy1)amine com- ing a catalyst consisting of 0.1-10 wt.% Ir on a sup- pounds are produced by hydrogenation of port of Al,O,, AIF, or active charcoal. Use of the Ir 3-dimethylaminopropionitrile using a catalyst con- catalyst improves selectivity so that only one Cl atom sisting of 0.1-10 wt.% Pd on an Al,O, or sup- is eliminated from the starting material. port. Selectivity to the bis product is increased by using an Al,O, support, and to the tris product by Platinum Catalyst for Isomerisation of using a spinel, preferably LiAl spinel. The products Alkanes are obtained with high yield and are useful for UOP U.S. Patents 5,004,859 and 5,017,541 polyurethane foam production. Isomerisable hydrocarbons are isomerised by contact Platinum or Palladium Catalyst for with a bed of catalyst particles consisting of an M,O, support, 1-15 wt.% of a Friedel-Crafts metal halide, Preparation of N-Alkylaminophenols preferably Al chloride, and 0.01-2 wt.% of a surface- SUMITOMO CHEM IND. K.K. European Appl. 427,572A layer Pt group metal component, preferably Pt. N-alkylaminophenols are prepared by reductive Isomerisation is at 40-250°C and 1-100 atm alkylation of an aminophenol with an aldehyde or pressure, and an organic promoter such as CCI ,is op- ketone, in an organic solvent, and in the presence of tionally present in the feed or catalyst. The method H, and a catalyst consisting of Pt or Pd with at least is used for isomerisation of 4-7C alkanes, giving in- one metal from Groups IB, IIB, IVB, VB and VIB on creased octane numbers for a 5-6C naphtha stream. an activated C support. Side reactions are suppressed, and the catalyst can be used repeatedly with a high New Noble Metal Catalytic Composites yield of desired products, which are used as with Long Life intermediates for various dyes. UOP U.S. Patent 5,013,703 Rhodium Catalyst System for New catalytic composites of silicalite impregnated with at least 8 wt.% of Pt, Pd, Rh, Ir, Os, Ru, Au Preparation of Perfumery Intermediate and/or Re have > 60% dispersion of the noble metal FIRMENICH S.A. European Appl. 427,965A resulting from base pretreatment and double im- 4-Tertiary-butyl-cyclohexanolcan be prepared main- pregnation stages in the preparation. The composites ly in its isomeric cis form by hydrogenation of have hydrophobic molecular sieve properties, long 4-tertiary-butyl-phenol or 4-tertiary-butyl-cyclo- life, and are not combustible or pyrophoric. The Pt hexanone in the presence of Rh supported on Al ,0 ,, composite can be dispersed in a PTFE matrix and us- charcoal or others, in combination with HBF, or a ed to catalyse isotopic exchange between H, and substituted BF , compound. The catalyst system can H ,0 vapour. be recycled, has long service life, and gives high selectivity. Molybdenum Promoted Catalyst for Production of Lower Alcohols Platinum-Zeolite Exhaust Purification TEXACO INC. U.S. Patent 5 ,O 13,764 Catalyst Lower aliphatic alcohols are prepared from the reac- TOYOTA JIDOSHA K.K. European Appl. 427,970A tion of CO and H , in the presence of a catalyst com- A catalyst for purification of exhaust gases from inter- position consisting of 0.5-6.0 wt.% Pd, 2.0-15.0 nal combustion engines consists of a zeolite layer or wt.% of one or more of Cs, K, Na and/or Rb, and a support (metal or zeolite) loaded with at least 1.3 1.0-10 wt.% Mo as a promoter, on a support which parts wt. Pt, or at least 0.8 parts wt. Pd, or at least is especially Al,O,, The catalyst is devoid of Cu and 0.7 parts wt. Rh. The catalysts have better high Th, and is useful for production of alcohol mixtures temperature durability and conversion of NOx. containing a substantial amount of 2-7C alcohols, used for example as fuel extenders or gasoline Three-Way Catalyst with Enhanced High substitutes. Temperature Activity FORD MOTOR CO. LTD. Platinum Wire Catalyst for Use in a European Appls. 430,435A and 430,437A Carbon Dioxide Laser A three-way catalyst for vehicle emission control con- HUGHES AIRCRAFT CO. U.S. Patent 5,020,069 sists of a carrier such as cordierite coated with an A catalyst for use in a laser consists of a Pt wire coated Al,O, support, optionally having 2-30 wt.% La,O, with a layer of Pt black and is preferably carried on discontinuously deposited on it, then 0.05-5 wt.% of an insulating support. The wire is heated by passing deposited Pd and up to 8 wt.% of a discontinuous a current through it, and is used in a CO, laser for re- TiO, phase adjacent to or deposited on the Pd com- converting CO and 0, lasing by-products to form ponent. The catalyst reduces light-off temperatures CO, at 150-300OC. The low temperature catalyst has by 20-100OC. It may also include F’t. prolonged activity.

Platinum Metals Rev., 1992, 36, (1) 63 New Poison Resistant Three-Way Catalyst Palladium Catalyst for Preparation of with Silica and Alumina Layers Bisnaphthalic Acid TOYOTA JIDOSHA K.K. Japanese Appl. 3168,448 NIPIWN STEEL CHEM. K.K. Japanese Appl. 3177,844 A new catalyst for removal of hydrocarbons, CO and Bisnaphthalic acid, its alkyl derivatives or salts are NOx from car exhaust consists of a support, a SiO, prepared by dimerisation of 4-halonaphthalic acids or layer loaded with Pd, and an Al,O, layer loaded with their alkyl derivatives at 9O-12O0C in the presence of Pt andlor Rh. The new catalyst is resistant to poison- a PdlC catalyst, in an aqueous alkaline medium con- ing, and operates over a long time without degrada- taining bases, formic acid and lower alcohols. The tion. In an example the catalyst consisted of a products are prepared in 60-84% yield, and are used monolithic support, a SiO, layer impregnated with for polyimide resins or pigments. 0.5 gfl Pd, and an AI,O, layer containing La and Ce, impregnated with 0.5 gfl Pt and 0.1 gA Rh. Preparation of Malonic Acid Esters in High Yield Differentially Charged Impregnation of Exhaust Purification Catalysts NIPPON KOKAN KK. Japanese Appl. 3177,847 Malonic acid esters are prepared from reaction of TOY0 KOGYO K.K Japanese Appl. 3172,948 dibromomethane, an alcohol and CO in the liquid An exhaust gas purification catalyst consists of a sup- phase, in the presence of a catalyst consisting of Pd, port with an A,O, coating layer supporting metals Rh and/or Co or a compound supported on a C carrier such as Pt and Rh. Preparation is characterised by of activated charcoal, C black or graphite. Malonic differentiating the charged states of the noble metal acid esters can be prepared in high yield, and are ions and the Al,O, layer during impregnation, useful for pharmaceutical intermediates. equalising those of the second noble metal ions and the Al, 0, layer. Thermal deterioration of the catalyst Exhaust Gas Purification Catalysts with can be prevented. Ultrafine Platinum and Rhodium Exhaust Purification Catalysts for TODA KOGYO K. K. Japanese Appl. 3186,240 Alcohol Fuelled Engines Catalysts for exhaust gas purification are prepared by NIPPON SHOKUBAI KAGAKU coating the surface of a ceramic catalyst support, Japanese Appls. 3172,949-50 preferably a honeycomb support, with a mixture of Pt Catalysts for purifying exhaust gas from internal com- and Rh organosols in an organic solvent, and then bustion engines using alcohol as a fuel consist of a vaporising the solvent. The method provides 3-dimensional structure coated with a catalyst com- ultrafine Pt and Rh particles uniformly dispersed on position containing: (a) 0.5-4.0 g of R,Pd or Rh and the support, without heating in H, and then air. The 1.0-20 g of Ag on stable Ce oxide (50-200 g) contain- catalysts are used for removal of CO, hydrocarbons ing at least Mg, Ba, Ca, Sr or Y; or (b) 0.5-1.5 gfl and N0x contained in exhaust gases. Pd and 5-10 gA Ag on AI,O , (80-150 gfl) containing at least one oxide of Ti, Si and Zr. The catalysts Selective Low Temperature Removal of decompose CO, CH, OH and HCHO in the exhaust Carbon Monoxide from Hydrogen gas at low temperature, and catalyst (a) shows im- ASAHI CHEMICAL IND. KK. Japanese Appl. 3193,602 proved heat stability of the Ce oxide. CO is selectively removed from H, gas by contacting with a supported Ru catalyst at 100-200OC. In an ex- Palladium Catalyst for Preparation of ample the catalyst consisted of 1 wt.% Ru on y- Intermediates for Amino Acids AI,O,, and after treatment in N,/H, was used to DAICEL CHEM. IND.Im. K.K. Japanese Appl. 3174,346 purify H, gas containing 60 ppm CO. As CO can be 2-0x0-4-phenylbutanoic acid derivatives are removed at low temperature, inexpensive heating prepared by reduction of 2-0~0-4-phenyl-3-butenoic media can be used. acid derivatives in solution, at pH 6-10.5, in the presence of a Pd catalyst. Reaction can take place in Waste Gas Purification Catalysts with a solution or a slurry, with water as the most ap- Improved Heat Resistance propriate solvent. The products can be formed selec- TOYOTA JIDOSHA K.K. tively in excellent yield, and are useful intermediates. Japanese Appls. 3194,830 and 3198,644 with Different Inflow Waste gas purification catalysts are produced by im- mersing an inorganic support in (a) a solution con- and Outflow Catalysts taining Pt andlor Rh, Ir andlor Ru, and citric acid, NIPPON sn0KuB.u KAGAKU Japanese Appl. 3177,625 or (b) an aqueous Pd solution, drying, then immers- A catalytic converter contains exhaust gas purifica- ing in a solution containing Rh, Ir andlor Ru salts and tion catalysts in a converter unit, with the catalyst on citric acid; then drying, calcining and reducing. the exhaust gas inflow side containing Pd and Rh, Citric acid promotes inter-diffusion of the Pt group and that on the outflow side containing Pt, Rh and metals, and prevents grain growth and evaporation of optionally Pd. The volumetric ratio of inflow to Ir or Ru. The catalysts are used to remove hydrocar- outflow catalysts is 1:8 to 3: 1. The catalyst converter bons, CO and NOx from car exhaust, and have im- has improved hydrocarbon purification. proved activity, heat resistance and durability.

Platinum Metals Rev., 1992, 36, (1) 64 Platinum-Zinc Oxide Whisker Catalyst Lanthanum-Aluminium-Platinum Waste for High Temperature Oxidation Gas Purification Catalyst MATSUSHITA ELEC. IND. K.K. BABCOCK-HITACHI K.K. Japanese Appl. 3/131,342 Japanese Appl. 3/101,835 A catalyst for purifying waste combustion gas con- An oxidation catalyst for gas or liquid phase reactions tains a double oxide of formula LaAl,,&O, where x consists of a tetrapod shaped whisker of ZnO op- is 0.01-1, and B is Pt or Pd. In an example a tionally coated with porous SiO, or Al,O, and sup- honeycomb body was coated with a mixture of the porting 0.5-1.0% Pt on its surface. The whisker of double oxide and Al,O,. The precious metals are ZnO has a core with needle crystals projecting in 4 highly dispersed over the catalyst which is resistant to directions from the core centre. The catalyst has high temperatures (>8OO0C) even in an oxidising at- superior properties, giving high speed reaction, and is mosphere, and is used to purify waste gas. used for high temperature oxidation, for example cleaning waste gas from combustion devices. Palladium Catalyst for Vinyl Acetate Preparation Ruthenium Catalysts for Ammonia Production HOECHST A.G. Germon Appl. 3,940,125 A catalyst for gas phase preparation of vinyl acetate SHIN NENSHO SYST. KE. JUpa?teSe Appl. 3/106,445 from ethylene, acetic acid and 0, consists of Pd Catalysts for NH, production are obtained by sup- and/or its compounds, optionally Au and/or its com- porting a c1-free Ru compound - such as a carbonyl pounds, alkali compounds, and optionally Cd com- complex or nitrate - on a reduction resistant oxide, pounds as activators, on a SiO, or SiO,/Al,O, evacuating and/or reducing in a H, stream to obtain carrier having specifiid surface characteristics, and a metallic Ru catalyst, and supporting a Sm, La or Ce using a binder such as a Mg carboxylate for the car- compound on the catalyst. The catalysts have high ac- rier particles. The selectivity and space/time yield of tivities for the synthesis of NH, from N, and H,, the catalyst are raised, and side reactions are reduced. particularly when the support is AI,O,; and have water and heat resistance. New Platinum-Tin Reforming Catalysts Exhaust Purification Catalyst with High INST. MEXICANO DEL. P. German Appl. 4,006,884 Activity New catalysts are prepared by a two-stage impregna- tion process in which an inorganic oxide support is NIPPON SHOKUBAl KAGAKU Japanese Appl. 3/114,539 first impregnated with a solution of a Sn salt, a A catalyst with high activity for purification of ex- compound and an organic acid, and then haust gases consists of a tungstate; F’t, Pd or Rh as the with a solution of a Pt compound and a halogen com- metal and/or oxide; and Ba or La molybdates sup- pound; finally activating in a reducing atmosphere. ported on a moulded inorganic pellet or a gas filtering refractory three-dimensional material, and is Three-Stage Removal of Oxygen and preferably treated at 700-10OO0C in air. In an exam- Hydrogen from Inert Gas ple, a catalyst containing Pt, Rh, BaWO,, BaMoO, , Al,O, and a cogealite support was prepared. ELECTROTHERM. EQUIP. R. Russian Patent 1,604,440 0,and H , are removed from inert gases by first pass- High Temperature Combustion Catalyst ing over a catalyst of 48-51% Ni and 26-28% Cr at UBE INDUSTRIES K.K. Japanese Appl. 3/118,835 180-250OC to remove 0,, then over a catalyst of A new high temperature combustion catalyst for com- 0.45-0.55% Pd/AI,O, where H, reacts with residual plete burning of a fuel gas and 0, containing gas to 0, to produce H ,0, and fmally over the Ni catalyst give only CO,, H,O and heat energy consists of Pt where residual H, reacts with NiO to produce H,O group elements and high purity magnesia single and regenerate Ni. Lower 0, and H, contents in the crystal fine powder 0.01-0.2 Fm in diameter. The inert gases are obtained using this method. catalyst has higher heat resistance and is not sintered even at 125OoC, and is used for body warmers, kerosene stoves or boilers, or for car exhaust purifica- HOMOGENEOUS CATALYSIS tion or deodorising apparatus. Rhodium Catalyst for Preparation of Platinum-Carbon Catalyst with Ultrafme Difunctional Monomers Particles DU PONT DE NEMOURS co. European Appl. 428,979A FUJI ELECTRIC MFG. K.K Japanese Appl. 31127,458 3-Pentenoic acid and carboxylic acid anhydride A Pt catalyst is prepared by depositing Pt on C by im- derivatives are prepared by carbonylation of allylic mersing a C powder support in a mixed solution con- butenols and allylic butenol esters. The allylic com- taining H, PtCl,, a colloid coagulation protector and pound is reacted with CO at 10-250°C in the a reducing agent with an aldehyde group. The C presence of 0.005-0.50 wt.% of a Rh catalyst and a powder support has had hydmphilic treatment and HBr or HI promoter, with a pmmoter:Rh molar ratio can be, for example, acetylene black. Ultra pure of 1:l. The products are useful as difunctional water is used as the solvent and for washing, giving monomers and intermediates in the synthesis of a catalyst with ultra fine Pt particles dispersed on C. adipic acid, and can be prepared selectively.

Platinum Metals Rev., 1992, 36, (1) 65 Palladium Catalyst for Preparation of Rhodium Hydrocarbonylation Catalyst Adipic Acid Precursors for Ethylidene Diacetate Production RHONE-POULENC CHIM. WACKER CHEMIE G.m.b.H. German Appl. 3,934,860 European Appls. 433,189A and 433,191A Ethylidene diacetate is prepared by reaction of A Pd catalyst, especially Pd chloride, and metal methyl acetate with CO and H, at 180-220°C and halides are used in the preparation of (a) 50-250 bar absolute, using a catalyst consisting of 1,6-hexenedioic acid &om the reaction of CO with a 0.05-0.50 rnol % of a Rh compound, 0.04-0.50 mol butenediol, or (b) hex-3-ene dioic diesters from the YO of a Pd or Ru compound, an ether-phosphane reaction of diacryloxy-substituted butene, an alcohol ligand to give a 1: 1-2 Rh:ligand rnol ratio, and 3-15 and CO. The reactions take place in a basic, aprotic, rnol % of an alkali(ne earth) iodide. High conversions polar solvent, at 50-150°C, at 10-250 bar pressure, with high selectivity to the product can be obtained. and with 0.001-1 molA Pd. Both products are precursors for adipic acid, and can be produced with Preparation of Symmetrical high selectivity using a metal halide. Diarylacetylene Compounds BAYER A.G. German Appl. 3,936,297 Rhodium Catalyst System for Production Symmetrical diarylacetylenes are prepared by reac- of Moist-Grain Preservatives tion of an aryl halide with acetylene in the presence CHEVRON RESEARCH CO. U.S. Patent 5,008,451 of a Pd catalyst and a base. The acetylene is fed into Carboxylic acid anhydrides are produced by reacting the liquid reaction mixture using an intensive a carboxylic ester and CO at 50-300°C and an initial gasifier, and the aryl halide is a stable, cheap, easily pressure of 1-100 atm, under anhydrous conditions, prepared bromide. The products are obtained from in the liquid phase, and in the presence of a catalyst one reaction stage, with high yield and selectivity, at system consisting of a Rh compound, an iodide pro- high spaceltime yields, and are used as intermediates moter, and a proton donor. The process can be used for diary1 olefins. to produce methylene and oxymethylene bis-esters. Rhodium Catalyst System for Production Platinum Catalyst for Deblocking N- of Aldehydes Formyl Protected Compounds HOECHST A.G. German Appl. 3,942,954 W.R. GRACE & COCONN. U.S. Patent 5,017,690 Aldehydes are produced by reacting olefinically un- The formyl groups are removed from the N atom of saturated compounds with CO and H, in a an N-formyl aspartame compound by heating at homogeneous phase at 20-150OC and 0.1-20 Mpa in 70-75OC using a catalyst consisting of 5% Pt on C or the presence of a catalyst system containing Rh and Pt chloride, with P present at 0.1-5 wt.% of the an ammonium salt of a sulphonated phosphite aspartame compound, and in the presence of a pro- triester. The catalyst system is especially useful in moting amount of aniline or methylene dianiline. The hydroformylation of 4-20C olefins with non-terminal method is used to deblock N-formyl protected amino unsaturation. Use of the organic P compound acids, peptides and polypeptides, and minimises for- prevents side reactions and the catalyst retains its mation of the diketopiperazine by-product. activity for very long periods. Ruthenium Catalyst for Lactone FUEL CELLS Preparation MITSUBISHI KASEI CORP. Platinum-Iridium-Iron Catalyst for Japanese Appls. 3174,377 and 3183,974 Phosphoric Acid Fuel Cell Cathode Lactones are prepared by liquid phase hydrogenation INT. FUEL CELLS CORP. U.S. Patent 5,013,618 of dicarboxylic acids, dicarboxylic anhydrides andlor A catalyst for 0, reduction in a phosphoric acid fuel dicarboxylic acid esters at Ru 5O-25O0C, under cell consists of a ternary noble metal alloy of Pt, Ir 0.1-100 kglcmz H,, and in the presence of a catalyst. and one of Ti, Mn, Ni, CQ, V, Cr or Fe, preferably The yield and selectivity to lactones can be improved Cr or Fe. The catalyst is used on the cathode of a markedly if the concentration of diols in the reaction phosphoric acid fuel cell, and has high activity and zone is controlled below 5 wt.%, or catalyst deteriora- stability, showing 50% less surface area loss in use tion can be prevented if the concentration of dicar- than a conventional PtCrCo catalyst. boxylic anhydrides is kept below 3 wt.%. Platinum-Iron Alloy Catalyst for Ruthenium Catalyst for Selective Phosphoric Acid Fuel Cell Electrode Production of Cycloolefms FUJI ELECTRIC MFG. K.K. Japanese Appl. 3168,452 ASAHl CHEMICAL IND. K.K. Japanese Appl. 31115,233 A Pt alloy catalyst is produced by depositing a Pt Cycloolefins are produced by partial hydrogenation of alloy on a C support, then depositing Fe, and heating monocyclic aromatic hydrocarbons in the presence of in a controlled manner to 900-1000°C for 5-30 a Ru catalyst, and by dispersing at least one dissolved seconds to form a Pt-Fe alloy. The Pt alloy catalyst Zn oxide or hydroxide into the reaction system, with has smaller crystallite size, and is used for a water or alcohol as solvent. Cycloolefms are produced phosphoric acid fuel cell electrode, giving a higher with a high invert ratio and high selectivity. cell performance at a current >200 mAlcm’ .

Platinum Metals Rev., 1992, 36, (1) 66 ELECTRICAL AND ELECTRONIC Palladium-Silver Conductor Paste ENGINEERING NIPPON CHEMICON K.K. Japanese Appl. 3149,106 A conductor paste consists of 5-30 parts wt. Pd Magneto-Optical Recording Element powder, 70-95 parts wt. Ag powder, and 0.5-10 Containing Palladium parts wt. glass frit to which 0.1-10 parts wt. metal EASTMAN KODAK CO. European Appl. 428,454A iodide was added. The paste is used for forming con- A magneto-optic recording element has a substrate ductor patterns and electrodes on Al nitride compacts. and a recording layer containing a Tb, Fe and Co alloy with added Zr and Pd. The recording layer has Longer Life Soft Magnetic Thin Film improved corrosion and oxidation resistance without MATSUSHITA ELEC. IND. K.K. Japanese Appl. 3154,705 affecting the magneto-optic recording properties. A soft magnetic thin fdm has a laminated structure consisting of 2-100 nm Fe thin fdms and 1-50 nm Multilayer Platinum-Cobalt Films for fdms of at least one kind of metal or at least 2 kinds Magneto-Optical Recording of alloy of Pt, Rh, Ir, Ru, Au, Ag, Re or Ta. The soft DU FQNT DE NEMOURS CO. world Appl. 91/8,578A magnetic thin film can be used at least as part of the Multilayer fdms no more than 75 nm thick consist of core of a magnetic head, which has longer life and is alternating layers of Pt and Co deposited by a sputter- suitable for high density writehead information. ing process using Kr or Xe or a mixture as the sputter gas. All of the Co layers are a maximum of 1.2 nm Vertically Magnetic Recording Medium thick, and all of the Pt layers are a maximum of 2.4 SONY COW. Japanese Appl. 3/58,3 16 nm thick, with a Pt:Co layer thickness ratio of 1-5. A magnetic recording medium consists of a non- The deposited films are used in magneto-optical magnetic substrate with a Co-Pt-B-0 magnetic layer recording, and have a higher coercivity than fdms composed of SO-lOOhi diameter acicular crystals sputtered in Ar. having a face centred cubic lattice. The magnetic High Coercivity Thin Film Magnetic crystal form, size and orientation are controlled to Recording Medium give greatly enhanced coercivity in the vertical direc- tion. In an example a magnetic recording medium HMT TECHN. COW. U.S. Patent 5,004,652 had a polyamide fdm substrate with a Pt underlayer A thin fdm magnetic recording medium has ,a and a Co-Pt-B-0 magnetic layer. substrate, a sputtered Cr underlayer 300-3000 A thick, and a sputtered magnetic layer 200-1000 A Plasma Deposited Magnetic Recording thick consisting of an alloy of 8-20 at.% Pt, 70-80 Medium at.% Co, 10-20 at.% Cr and 2-10 at.% Ta. The MATSUSHITA ELEC. IND. K.K. Japanese Appl. 3178,114 magnetic recording medium has high coercivity, resolution, amplitude and loop squareness values, A magnetic recording medium has a substrate with a low bit shift, is used for high recording density 7-type Fe oxide magnetic layer including one of Pd, and Ti, or where the read/write memory devices in computers. Rh, Os, Ru, Co, CU, V Nb, magnetic layer is deposited in a plasma state Silver-Palladium Alloy Sheath for High generated by electron cyclotron resonance (ECR). Temperature Superconductor The magnetic properties and recording fidelity of the medium are improved by utilising the activity of the WESTINGHOUSE ELEC. U.S. Patent 5,017,553 COW. ECR plasma. A metallic sheath for a superconductingcore is a layer of Ag-Pd alloy having 10-50 wt.% Pd and containing Manufacture of a Superconductor Wire 5-45 wt.% of interdispersed particles of W, Mo or Ni with a Platinum Core or mixtures of these of 0.05-75 pm diameter; and may have an inner or outer wall of Ag. A supercon- NICHIDEN ANERUBA K.K. Japanese Appl. 3179,766 ductor having a high strength, thermally matched, A superconductor wire consisting of a superficial ox- high-temperature sheath is provided, which is useful ide superconductor film formed on a continuous fine for fine wires or magnet windings. wire of Pt or ceramic is manufactured by shifting the fine wire continuously, while sputtering the thin Ruthenium-Containing Screen Printing superconductor fdm onto it, and then heating in an Ink for Forming Resistors 0, atmosphere to effect crystal growth of the fdrn. MATSUSHITA ELEC. IND. K.K. Japanese Appl. 3140,402 Magnetic Alloy Memory with Thermal A screen printing ink consists of a Ru compound op- Hysteresis of Magnetisation tionally mixed with another metal compound, car- TOSHIBA K.K. Gennan Appl. 4,030,476 boxylic acids of terpenoids or their esters as viscosity A magnetic alloy has as the main phase an isomolar increasing agent, and an additive consisting of an compound phase of formula Pt(Fel,Mn.JSn, in aliphatic carboxylic acid. The ink is used to form a which x=O-1 exclusive. The magnetic alloy exhibits resistor for a thermosensitive printer head, electrode significant thermal hysteresis of magnetisation, and and resistors. A good quality thin resistor film can be allows production of magnetic memories of simple prepared by screen printing and calcination. structure and operation for recording systems.

Platinum Metals Rev., 1992, 36, (1) 67 Thermoseneitive Circuit Breakers for Low Toxicity Platinum Anti-Tumour Automatic Fire Alarms Agents M. A. AKIMOV Russian Patent 1,238,610 TSUMURA & CO. World Appl. 9119,042A A thermosensitive circuit breaker has an insulating New oxalate-diaminocyclooctane Pt(I1) complexes substrate with sprung contact plates, and a Pt, Pd or and stereoisomers are prepared from dinitrato Mo dispersing plate on these plates. The dispersion (diaminocyclooctane) Pt(I1) and oxalic acid. The material acts as a catalyst for oxidising processes on complexes are anti-tumour agents with low toxicity, its surface. The circuit breaker has reduced inertia, used at a dosage of 5-600 mglday. and is used in electrical engineering, for example in automatic fire signalling. Zirconium-Palladium-Ruthenium Alloy for Dental or Medical Use TEMPERATURE AMER. DENTAL ASSOC. H. U.S. Patent 5,019,337 An alloy composition for dental or medical use con- MEASUREMENT sists of 35-60 wt.% Zr, 1-60 wt.% Pd and 1-60 Thermocouple-Type Temperature wt.% Ru, while another composition has Pt, Rh, Ir, Sensor Os, Ru, Al, Si or Co as the second element. The alloy has a cubic CsCl or B, type structure which can ASAHI GLASS K.K. World Appl. 9117,643A undergo stress-induced transformations at body The Pt-Rh thermocouple of a thermoelectric temperature. The alloy is used for casting crowns, temperature sensor has an insulating tube inserted in bridges, dental or medical implants or prosthetic a metal-boride ceramic protective tube to prevent devices, and has enhanced ductility, adequate deterioration of the thermocouple by reducing gas at strength, and biocompatibility. high temperatures. The tip of the insulating tube is covered with a cap made of a Pt group metal. The Platinum Complex for Tumour Inhibition thermocouple has extended life, and is used to or Radio-Sensitisation measure the temperature of hot metal and molten BRIT. COLUMBIA CANCE. U.S. Patent 5,026,694 steel continuously, for extended periods of time. A composition for tumour inhibition or radio- Melt-Adhered Platinum-Rhodium sensitisation consists of a square planar Pt(I1) com- Thermocouples for High Temperature plex of formula PtX,(NR,H)L and an excipient; where n is 1 or 2, X is an anion, R is H or alkyl or Measurements NRR is piperidino or morpholino, and L is a radio- KOBE STEEL K.K Japanese Appl. 3166,48 1 sensitising ligand. The complex is used at 0.1-5 Pt-Rh thermocouples are melt-adhered on the surface mgkg and can bind DNA, sensitise hypoxic cells to of a Ti(alloy) material test piece by incorporating a radiation and is directly toxic to tumours. thin Ta plate between the thermocouple and test specimen. Temperature measurements of Ti(a1loy) Laser Beam Reflectors Containing materials can then be made at 130OOC or above which Ruthenium is requisite for recognising thermal properties of these TOSHIBA K.K. Japanese Appl. 31104,839 materials for use in the space and aero industries. A laser beam reflector is prepared by laser beam ir- radiating a sintering of 5-60 wt.% Ru, 0.5-3 wt.% MEDICAL USES Zr andlor Ti, 0.001-0.1 wt.% C and balance Mo in vacuum or under an inert gas atmosphere, to densify New Platinum Anti-Tumour Compounds the mixture. The method provides reflectors free BRISTOL-MYERS SQUIB. European Appl. 423,7076 from surface degradation due to oxidation or corro- sion, for use in laser knives or other surgery devices, New Pt(1V) complexes containing axial hydroxy or and used in place of conventional Cu reflectors. mono- or dicarboxylate groups are used as anti- tumour compounds, and have lower kidney and bone New Platinum Complexes with Anti- marrow toxicity than known Pt-containing anti- Tumour or Anti-Microbial Activity tumour compounds. Certain of the complexes are water soluble, while others are lipo-soluble and can S. HANESSIAN Canadian Patent 1,282,058 therefore be used in liposomes, in oil-water emul- New Pt complexes are derived from vicinal diamines sions, injected as oil solutions, or used topically. substituted by carboxy, hydroxy or alkoxy groups, for example diamino sugars, and are useful as anti- Low Toxicity Platinum Anti-Tumour microbial or anti-tumour agents. Compared with Complexes known Pt complexes they have better water solubili- TORAY IND. INC. World Appl. 9119,041A ty, more rapid excretion, improved transport in the body, improved biocompatibility, and a more selec- New y-butyrolactone Pt complexes have a cis, trans-], tive interaction with DNA receptors. or trans-d 1,2diaminocyclohexane ring, and have high anti-tumour activity and low toxicity. In an ex- ample, one of the complexes was used to treat L1210 The New Patents abstracts have been prepared from leukaemia in mice. material published by Derwent Publications Limited.

Platinum Metals Rev., 1992, 36, (1) 68