platinum metals review - johnson matthey

UK ISSN 0032-1400

PLATINUM METALS REVIEW

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

V O L . 2 0 A P R I L 1 9 7 6 NO. 2

Contents

Sulphate Emissions from Automobile Exhaust

Palladium Alloys for Electrical Contacts

Coating Methods for Use with the Platinum Metals

Russian Research on the Platinum Group Metals

Hydrogen in Palladium

Carboxylato Complexes of the Platinum Group Metals

Abstracts

New Patents

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44

48

53

54

54

64

69

Communications should be addrmsed to The Editor, Pkrtinum M& R&w

Johnson Matthey & Co Limited, Hatton Garden, London EClN 8EE

Sulphate Emissions from Automobile Exhaust THE INFLUENCE OF A CATALYTIC EMISSION CONTROL SYSTEM

By B. J. Cooper and E. Shutt

and P. O m Group Research Centre, Johnson Matthey & Co Limited

Research and Development Department, Volkswagenwerk AG, Wolfsburg, West Germany

T h e installation of plat inum group metal catalysts on 1975 model year U.S. automobiles f o r control of COiHC emissions has led to concern over the tendency of such catalysts to oxidise SO, to sulphuric acid aerosol. Examin- ation of sulphate emissions f r o m Johnson Matthey and Volkswagen test vehicles suggests that although there i s some tendency to f o r m sulphate, especially under highly oxidising conditions, the levels of sulphate are in general low. Comparison of measured sulphate conversion with thermodynamic equilibrium values shows that only a small fraction of the available exhaust SO, is converted to sulphate, and that the catalyst’s ability to convert is short- lived. Future moves toward a three-way catalyst capable of simultaneously con- verting COIHC and NO, pollutants should eradicate a n y tendency towards sulphuric acid formation in automobile exhaust.

During the early part of 1975 considerable concern was expressed in the United States over the possibility of automobiles equipped with platinum group metal catalytic emission control systems producing large quantities of sulphuric acid aerosol. The fear that airborne

Platinum MetalRev., 1976, 20, (2), 3 8 4 5

sulphate would rise to significant levels and endanger public health, as the catalytic emission controlled automobile population grew, largely contributed to the U. S . Environmental Protection Agency’s decision to delay imposi- tion of stricter carbon monoxide (CO) and hydrocarbon (HC) emission standards in February 1975. Since that time a great deal of information has been accumulated by workers in the field, aimed at (a) establishing a reliable sulphate emission test procedure in view of pending sulphate emission standards, (b) defining the influence of the emission control system on sulphate emissions, and (c) catalyst redesign to minimise sulphate emissions.

This article describes work carried out both at the Johnson Matthey Research Centre and in conjunction with Volkswagenwerk AG in order to assess the level of sulphate emission from cars equipped with Johnson Matthey automobile emission control catalysts.

Sulphate Formation in Automobile Exhaust

Sulphur compounds inherent in all petroleum based fuels are readily oxidised in the combustion chamber of an internal combustion engine to form sulphur dioxide (SO,). It is now recognised that catalyst equipped cars can convert some sulphur dioxide to sulphur trioxide and hence to sulphuric acid. It is, of course, well known

38

that the catalytic oxidation of SO, to SO, followed by hydrolysis is the essential step in the manufacture of sulphuric acid, and that early processes used platinum to catalyse the oxidation reaction. Indeed the fist kinetic study of this reaction was reported by Bodenstein and Fink in 1907 (I).

The oxidation of SO,:

SO2 + 40, % SO, Reaction I

is an exothermic reaction and is controlled by thermodynamic limitations at temperatures above 450°C. Reaction (I) shows that the equilibrium concentration of SO, in the exhaust is proportional to the square root of oxygen concentration, and this fact has important consequences in the selection of an emission control system capable of minimising sulphate emission. Most 1975 model year vehicles have been equipped with a platinum group metal oxidation catalyst and an air pump for control of CO/HC emissions. The delivery of secondary air into the exhaust system prior to the catalyst results in high oxygen partial pressure causing the equilibrium in Reaction (I) to move to the right.

As a result of this, increasing emphasis is

Platinum MetalRev., 1976, 20, (2), 39

being placed on catalytic emission control systems which minimise the amount of excess oxygen either by minimising the amount of secondary air addition, or by deleting the use of an air pump completely. The latter process calls for improved control of the air/fuel mixture entering the combustion chamber to ensure sufficient oxygen available at the catalyst for combustion of residual CO and HC during all driving modes. This approach has been employed by Volkswagen on the VW Beetle for the 1975 model year, using electronic fuel injection (EFI). In this case the engine is tuned lean to provide just sufficient oxygen for CO/HC combustion, but low 0, partial pressures employed limit the equilibrium concentration of SO,.

Advanced catalytic emission control systems incorporating NO, control, take the electronic fuel injection concept a stage further with the development of “closed loop” EFI. This system employs an oxygen sensor in the exhaust system which maintains the air/fuel mixture at the stoichiometric value during all driving modes. Under such conditions it is possible to simultaneously catalyse the conversion of CO, NO, and HC pollutants using a “three way catalyst”

(TWC) according to the following reactions (simplified) :

co + 4 0 % -+ coz CO t NO+ CO, i +Nz

HC+Oz+ COz 4- HpO

Reaction z

Reaction 3

Reaction 4

In this case the oxygen available for conversion of SO, to SO, is theoretically zero. In practice the excess oxygen in the exhaust is maintained at very low concentration, and hence sulphate formation is restricted to very low levels.

The above arguments regarding design of the emission control system are based solely on the effect of oxygen concentration on the thermodynamic equilibrium concentration of SO3 formed over the catalyst, and therefore assume that the catalyst is sufficiently active to promote formation of SO, to the equilibrium values. Under such conditions a platinum group metal exhaust catalyst active enoughto promote Reaction( I) to equilibrium, operating on an air pump equipped car burn- ing fuel containing 0.03 weight per cent sulphur at 20 mpg could produce up to 150 mg/mile sulphate emission. In practice sulphate emissions from catalyst equipped cars rarely reach such high levels for the following reasons. Measured sulphate conversion levels on catalyst equipped cars have shown that the catalyst is usually insufficiently active below about 550°C to promote conversion of SO2 to equilibrium levels, Above this temperature thermodynamic equilibrium limitations reduce the amount of sulphate formed. Figure I demonstrates this effect schematically by comparing the equilibrium and kinetic conversion levels over the typical operating temperature range of a catalyst equipped car. Two equilibrium conversion levels are shown, based on a high exhaust oxygen content (7 per cent) typical of an air pump equipped car, and a low exhaust oxygen content typical of closed loop EFI and TWC operation. Sulphate emissions will be the resultant of the equilibrium curves and the kinetic curve defining the catalytic reaction rate. Thus Figure I clearly demon-


strates that the TWC concept is preferable to the CO/HC catalyst plus air pump concept as a means of controlling sulphate emissions.

A second factor which can also contribute towards lowering sulphate emissions below equilibrium levels is the phenomenon of storage (2, 3, 4). This is generally attributed to the reversible interaction of SO, with the alumina support of the emission control catalyst according to Reaction 5.

M,O, + 3SO, fA12(S0 , ) , Reaction 5

This phenomenon is also capable of creating extremely high sulphate emission levels when stored sulphate is suddenly desorbed during high temperature excursions.

Sulphate Emission Measurement on Test Vehicles

Particulate sulphate, including H $0, aerosol, present in automobile exhaust is generally collected using the dilution tunnel technique. Filtered laboratory air is passed into a flow development tunnel, and the car’s exhaust is admixed countercurrent with the air stream. An axial probe is inserted into the tunnel, and exhaust samples withdrawn isokinetically from the centre of the fully developed turbulent flow region. The samples are filtered, and the filter pads analysed for soluble sulphate.

All tests reported in this article were carried out either using the U S . Federal Test Procedure driving cycle, or operating the car under steady state conditions.

The tests reported cover a range of emission control concepts. Thus Johnson Matthey test vehicles include a Chrysler Avenger, Leyland Marina, and Ford Capri equipped with CO/HC oxidation catalysts and air pumps. Catalysts were installed under floor in these cars, and a typical installation is shown on the Ford Capri in Figure 2. Sul- phate emissions from these vehicles were measured at the Johnson Matthey Labora- tories, and also at Ricardo Engineering, Shoreham-by-Sea. Sulphate emissions were also measured from two Volkswagen Beetles

Fig. 2 Installation of an oxidation catalyst converter for control of CO and hydrocarbon emissions i n the exhaust system of a 2 Eitre Ford Capri. The vehicle is provided with an air p u m p to supply secondary air to the exhaust to ensure excellent combzcstion of CO and HC pollutants over the catalyst

equipped with EFI and an oxidation catalyst. Secondary air was not used on these test vehicles, which were tested in a collaborative Johnson Matthey-Volkswagen programme conducted at Olson Laboratories, California. In addition, sulphate levels have been measured on a VW Beetle equipped with closed-loop fuel injection, oxygen sensor and Johnson Matthey three way catalysts. This test vehicle was kindly loaned to Johnson Matthey by Volkswagen for evaluation of three way catalyst systems. The three way catalyst installation on the V W Beetle is shown in Figure 3.

Concept 1: CO/HC Catalyst Plus Air Pump The effect of secondary air on sulphate

emissions from a catalyst equipped Chrysler Avenger is shown in Table I.

Table I Sulphate Emissions over the FTP on EW2/3C/4 Oxidation Catalyst as a Function of Oxygen Concentration in

the Exhaust Oxygen concentration in the exhaust was varied by changing the engine speed/air pump speed ratio.

Exhaust oxygen per cent Sulphate Max. Min. Average mg/mile

0.4 0.05 0.1 5 negligible

5.25 3.4 4.2 5.5 8.1 4.5 6.1 7.7 10 2.7 7.5 10.7


Fig. 3 Installation of an advanced Three W a y Catalyst converter for control of CO, hydrocarbon, and nitrogen oxide emissions i n the exhaust system of a 1.6 litre Volkswagen Beetle. The vehicle is .fitted with a closed loop electronic fuel injecrtion device provided with an oxygen sensor monitoring the exhaust upstream of the catalyst. I n this way the airlfuel mixture is held at stoichiometric over all driving modes

In this test the car was driven over the Federal Test Procedure, with the air pump operating at differing speeds. The increase in sulphate emissions with increasing exhaust oxygen content is in accord with both thermodynamic prediction, and published kinetic data for SO, formation over platinum catalysts (5).

In another test a Leyland Marina was driven under steady state conditions for 500 miles, and the maximum sulphate emission compared with predicted thermodynamic equilibrium values in terms of conversion of fuel sulphur to sulphuric acid. Tests using fresh catalyst for each steady state condition showed that although a steady increase in the vehicles sulphate emission occurred during early mileage accumulation, due to storage on the fresh catalyst surface, a well-defined maximum sulphate emission could be estab-

lished within 500 miles. Comparison of sulphate emissions with equilibrium levels predicted for each of the steady state conditions (Figure 4) shows that in tests up to 60 mph the maximum sulphate levels were substantially less than the equilibrium values. Maximum sulphate emissions in these tests were around 20 mg/mile, as compared to around 150 mg/mile predicted for equilibrium conversion. These data show that in such steady state tests the rate of catalytic oxidation controls the sulphate level in the exhaust and that the catalytic oxidation process is not sufficiently fast to reach the sulphate levels predicted from thermodynamic data.

The fact that the catalyst’s surface reaction kinetics control the amount of sulphuric acid formed in the exhaust implies that the typical ageing processes experienced by the catalyst during mileage accumulation, such as sinter-


ing and poisoning, should diminish the level of sulphate as the catalyst ages. Sulphate emissions obtained on several Johnson Matthey test vehicles with catalysts of varying mileage accumulation have been com- piled (Figure 5). Data produced on Avenger, Marina, and Capri test vehicles using catalysts aged by different methods give an insight into the sulphate emission profile over a 50,ooo mile test. During early mileage the sulphate levels climb rapidly as the storage capacity of the catalyst becomes saturated. After zoo miles the catalyst


apparently starts to deactivate until after about 10,000 miles the sulphate levels are similar to a non-catalyst equipped car ( I to z mg/ mile). The loss of sulphate activity occurs at no loss to the catalyst’s ability to meet CO and HC emission standards, as shown by the 50,000 mile data generated on the Ford Capri, where the same catalyst met statutory CO and HC standards (Table 11).

A similar sulphate emission profile against mileage has been observed in the Volkswagen Laboratories. Tests ona VW Dasher equipped with an oxidation catalyst and an air pump,

Table II CO/HC and Sulphate Emissions Ob- tained using a Ford Capri equipped with Johnson Matthey Oxidation Catalyst These data were obtained after the car had completed 50,000 road miles.

g/mile g/mile mg/mile I co I HC I I Wi thout catalyst 14.0 1.0 2.1

W i t h 50,000 mile I 2.2 I 0.23 I 1.9 catalyst 1 I I I I

and a VW Beetle equipped with an oxidation catalyst and EFI show (Table 111) a decrease in sulphate emission during the high mileage portion of the durability test.

The trend in sulphate emission with mileage is not marked with the Dasher and is in all cases close to the vehicles SO,= emission without catalyst. Some increase is shown with the Beetle at around 5,000 miles, but the emissions never reach the 20 mg/mile levels observed in the Johnson Matthey tests using similar catalysts. This may reflect the fact that maximum sulphate levels are found around the 200 mile region of ageing (Figure 5 ) and the VW cars were not tested at this point. However, the fact remains that for the majority of the catalyst's life the sulphate

emissions are extremely low, and only reach appreciable levels during a relatively short period.

Concept 2: COIHC catalyst, EFI, No Air Pump

Tests at Olsen Laboratories in the joint JM/VW programme examined the sulphate emissions of a new and 5,000 mile VW Beetle equipped with electronic fuel injection and a Johnson Matthey catalyst. Each vehicle was preconditioned by driving 200 miles at 50 mph and then the emissions were measured over the Federal Test Procedure (FTP) and at 30, 40, and 55 mph (Table IV).

Highest sulphate emissions were found at the high speed condition, probably reflecting the increasing tendency of the car to run lean (excess oxygen) at higher engine speeds. The 55 mph results reflect clearly the increasing role of sulphate storage at higher catalyst temperatures.

Thus the new car's sulphate emissions progressively increase as sulphate storage diminishes in each subsequent test, whereas the 5,000 mile car shows a decreasing level of sulphate emission as previously stored sulphate is released. In no case did these vehicles reach the 20 mg/mile plus values of sulphate emission found with the air pump equipped cars.

Table 111 Sulphate Emissions from VW Test Vehicles during Mileage Accumulation

(All emissions in g/mile.)

Miles

Zero

5,000

10,000

15,000

22,500

Without catalyst

VW Dasher co HC NO, SO,'

4.41 0.44 1.45 0.003

4.52 0.63 1.38 0.003

6.28 0.59 1.97 0.003

6.96 0.71 1.35 0.003

5.50 0.72 1.59 0.002

23.88 2.40 2.43 0.0015

VW Beetle CO HC NO, SO,'

5.54 0.42 0.67 0.001

7.82 0.43 1.32 0.008

6.10 0.68 1.26 0.006

5.51 0.59 1.15 0.003

6.29 0.62 1.50 0.003

10.68 1.52 1.64 0.002


Table IV Sulphate Emissions from New and 5,000 mile VW Beetles equipped with EFI and

Johnson Mattliey Oxidation Catalyst

Test

Sulphate emission mg/mile

New car 5,000 mile car FTP 30mph 40 rnph 55 mph FTP 30 mph 40 mph 55 mph

1

2 3 4

5

Concept 3: Closed Loop Fuel Injection, 0, Sensor and TWC

As shown previously the low exhaust oxygen levels obtained with the TWC concept inherently produce a low sulphate emitting vehicle. Tests on twenty prototype TWCs, including rhodium promoted catalysts, using the Volkswagen Beetle equipped with closed loop fuel injection confirm the low sulphate emitting characteristics of this advanced emission control concept. These catalysts have shown sulphate emissions as low as o to 6 mgjmile when fresh and o to 0.4 mg/ mile after ageing on a test bed for IOO hours. In most cases the sulphate emissions are negligible, or less than I mg/mile, and only in one instance exceed 5 mg/mile. In the cases where the higher sulphate emissions are recorded, ageing the catalyst again substantially reduces the sulphate emission level.

Conclusions Tests using Johnson Matthey catalyst

equipped vehicles have shown that conversion of sulphur dioxide in the exhaust to harmful sulphuric acid occurs to a much lower extent than would be predicted from thermodynamic equilibrium considerations. Maximum conversion occurs after about 200

miles driving, and thereafter the catalyst’s ability to produce harmful sulphate progres-

0.9 0.3 4.7 6.5 2.2 0.3 4.4 11.6 0.8 0.2 6.7 7.7 2.0 0.4 3.7 10.8

1 .o 0.2 13.1 8.4 0.6 0.2 1.9 6.1

0.7 0.2 13.0 11.0 1.4 0.2 2.0 7.2

6.0 0.1 10.7 18.0 0.8 0.3 4.3 8.5


sively decreases, without a substantial loss in its ability to convert other pollutants (CO/HC/NO,) to harmless substances. This suggests that the contribution of sulphate emissions from catalyst equipped cars to the urban environment could be substantially less than previously estimated.

Examination of sulphate emissions from different emission control concepts shows that limiting the amount of excess oxygen in the exhaust diminishes the tendency toward sulphate formation. Thus the move towards the three way catalyst concept for simultaneous control of CO/HC/NO, in 1978 should virtually totally eradicate any tendency of a catalyst-equipped car to produce sulphuric acid aerosol.

References I M. Bodenstein and C. G. Fink, Z. Phys. Chem.

(Leimid, 1907, 60, (11, 44 z M. Beltzer, R. J. Campion, J. Harlan, and

A. M. Hochhauser, “The Conversion of SO, over Automotive Oxidation Catalysts”, SAE paper 750095, February 24-28, 1975, Detroit, Michigan

3 J . E. Hunter, “Studies of Catalyst Degradation in Automotive Emission Control Systems”, SAE paper 720122, January 1972, Detroit, Michigan

4 R. H. Hammerle and M. Mikkor, “Some Phenomena which Control Sulphuric Acid Emission from Automotive Catalysts”, SAE paper 750097, February 24-28, 1975, Detroit, Michigan

5 0. A. Vyehara and K. M. Watson, Ind. Eng. Chem., 1943, 35, 541

Palladium Allovs for Electrical J

Contacts PAPERS PRESENTED AT THE ANNUAL HOLM SEMINAR

By T. R. Long, Bell Laboratories, Columbus, Ohio

The tarnishing characteristics of the palladium-silver alloys have been a topic of considerable interest for many years. Recent developments in surface analysis techniques have given investigators new tools for studying these alloys and providing solid answers to questions that were more speculative in previous years, and the 1975 Holm Seminar on Electrical Contacts, held in Chicago, provided four papers dealing with palladium and palladium alloys for use as electrical contacts.

Contact Surfaces in Tarnishing Atmospheres

T. R. Long and K. F. Bradford, of Bell Laboratories, Columbus, Ohio, presented a paper on the ‘‘Contact Resistance Behaviour of the 6oPd-4oAg Alloy in Tarnishing Environments”. This report was part of a larger study carried out by the Columbus group studying all aspects of the contact performance of the 6oPd-4oAg alloy corn- pared to pure palladium in telephone applications. As a result of this work, the manufacturing arm of the Bell System, Western Electric, was authorised in April 1974, to convert their general purpose wire spring relay production over to the use of 60Pd- 40Ag where pure palladium had previously been used. This one application had been the major use of palladium by the Bell System.

Samples of the 60Pd-4oAg alloy were prepared as flat coupons and also as factory assembled contacts on test relays. They were

then exposed to tarnishing environments of mixtures of 0.2 p.p.m. H,S, SO, and NO, at 60°C and both 75 and 90 per cent relative humidity for times up to 280 days. In addition, relays which had been made with contacts of these materials in 1943 and put into service in a telephone office in New York City for thirty years were recovered and extensively examined.

Results showed that values of contact resistance tend to be 10 to 30 milliohms higher on the 6oPd-4oAg alloy than on pure palladium, but the changes with exposure are indistinguishable. Film thicknesses are slightly less on the alloy for equivalent exposures and the sulphide film is not a simple silver sulphide but is probably Pd,Ag,S. Statistical analysis of the multitude of test results indicate that no significant changes in contact performance would be expected as a result of the conversion to the alloy.

J. Potinecke, of Standard Electrik Lorenz AG (ITT), Stuttgart, reported on the “Behaviour of Contact Surfaces Consisting of Ag and Pd Alloys in H,S-NO,-SO, Atmospheres”. This is an interim report from a large study of accelerated testing for ten European companics. They, like others, are trying to reproduce the effects of natural environments at an accelerated rate. Uniquely, however, they are separating out the effects of the constituent gases by careful design of the experimental conditions.

Four materials were reported on: Ag,

For pure silver a regression equation was 70Ag-j0Pd, 50Ag-501’d and 85Pd-15Cu.

Platinum MetalRev., 1976, 20, (2), 4 6 4 7 46

generated to predict the contact resistance as a function of constituent gas concentrations and exposure time. The effects of SO, on pure silver were surprising in that a higher concentration of SO, causes a smaller resistance increase with exposure than does a lower concentration. Film thickness measurements also established that 4 p.p.m. SO, exposure led to a much thinner film than a I p.p.m. exposure. H,S and NO, cause contact resistance to increase while SO, reduces the rate of increase.

For the palladium alloys, the regression relations just include the gas effects for an exposure of 144 hours. For the palladium- silver alloys, this analysis shows that H,S reduces the resistance while NO, causes an increase. SO, leads to a resistance increase with 7oAg-3oPd and 85Pd-1gCu while this influence is not significant on the SoAg-SoPd alloy.

These results have not yet been correlated with similar tests on actual component structures where component-specific conditions such as friction, wipe distance and contact pressure will be important, but such investigations are planned.

Metal Transfer C. A. Haque, of Bell Laboratories, Colum-

bus, presented a paper on “Metal Transfer Characteristics in Arcing Pd-Ag 40 wt. per cent versus Au Capped Pd-Ag 40 wt. per cent Metal Alloy Contacts”. By using Auger electron spectroscopy to measure the average composition of the top few hgstroms of the surface he was able to show that the arcing process preferentially transfers silver out of the Pd-Ag alloys on to the cathode and deposits it on to the anode. This produces regions on the anode which are enriched in silver relative to the 14 wt. per cent silver already available in the 22 carat gold cap. The question of tarnish susceptibility of this altered surface composition was naturally posed and tested. No significant detrimental effects were observed on contact resistance performance of relays; it is however, im-

portant to be aware of this segregation process in dealing with alloy contact materials under arcing conditions.

Inlay Materials for Connector Springs

Franklin F. M. Lee, of International Business Machines, Endicott, New York, presented a comprehensive report on “Clad Metal Inlays for Connector Springs”. Several commercially available binary, ternary and even quaternary alloys of gold, silver, palladium, platinum, nickel, copper, cobalt, indium and cadmium, were prepared in inlay form on base metal substrates. They were evaluated in terms of their porosity, wear resistance, formability and resistance stability. Pure gold and palladium in both wrought inlay and electroplated form and some electroplated alloys were also included in the test matrix for comparison purposes. They were evaluated in both strip form and in spring shape. In all, fifteen different inlay materials were studied including five different palladium-silver alloys.

This paper, like Potinecke’s, is the first part of a longer project which will be completed in a few years time. Results in this paper were obtained from accelerated environmental chamber tests, but they plan to report on long term exposures at various field sites in subsequent papers.

The porosity of inlay materials is quite different from that in electroplated materials both in appearance and in cause of formation. Inlay materials tend to be lower in porosity than electroplated materials of the same thickness, but, depending on manufacturing technique, they can range from very good to very poor.

Overall, inlays can perform as well as their electroplated counterparts of the same composition and thickness. The alloy having the composition 6gAu-25Ag-6Pt was found to be the most reliable of those studied. How- ever other good candidates were the alloys 7oPd-3oAg, 75Au-25Ag, and 55Au-39Ag- 3Cd-3111; and palladium.


Coating Methods for Use with the Platinum Metals A REVIEW OF THE AVAILABLE TECHNIQUES

By Christopher Hood Group Research Centre, Johnson Matthey & Co Limited

Th.e economic use of platinum group metal coatings requires that the most appropriate coating method should be used j o r any particular application. This article reviews the techniques available f o r various substrate materials and outlines some of the more important properties obtained with different types of deposit.

There is now a wide variety of methods that can be employed to form coatings of the platinum group metals. The choice of materials and methods to be used can best be made after the manufacturer and the user of the product have considered the required properties and related factors such as the thickness and physical properties of the coating, the properties of suitable substrates, and the cost of alternative processes. This review describes processes which can be used to deposit a coating of a platinum group metal on to a substrate. The properties of the coating and the type of substrate to which the various methods are applicable, and the thickness normally to be obtained, are also discussed. For the purpose of this article the main methods of coating are considered to be as follows:

Vacuum deposition Thermal decomposition and chemical

vapour plating Electroless plating Aqueous electroplating Fused salt electroplating Metallic bonding Metallising

Vacuum Deposition The most versatile method of depositing

very thin coatings is vacuum deposition

Platinum Metal Rev., 1976, 20, (2), 48-52 48

which can be carried out by two techniques : vacuum evaporation and sputtering. These methods are used for the large-scale production of micro-electronic components where platinum provides the required properties of good electrical conductivity and complete freedom from atmospheric corrosion (I , 2).

Vacuum evaporation is carried out at a pressure of I O - ~ Torr or below. The metal from which the coating is to be formed is heated to a sufficiently high temperature to cause it to volatilise at the extremely low pressure of the chamber, the substrate being arranged to condense this vaporised metal. Excellent films can be formed by this method although there are a number of difficulties, the main one encountered with the platinum group metals being the high temperatures required for evaporation. The most effective heating method is by an electron beam using a water-cooled copper crucible to contain the platinum group metal and as only the central part of the exposed surface of this metal is heated, contamination is avoided, The high temperatures involved may, however, cause additional problems because, as both radiant heat and the evaporated atoms are propagated rectilinearly from the source, it is not possible to shield the substrate from the radiant heat during deposition. The resulting temperature

rise could not only damage a sensitive substrate such as plastic, but may also change the structure and properties of the deposited film. In addition, the pressure in the vacuum chamber must be sufficiently low for the mean free path of the evaporated atoms to exceed the source to substrate distance, otherwise the metal will tend to nucleate before reaching the substrate and produce a soot-like deposit instead of a continuous film of metal.

Many substrates have substantial amounts of adsorbed gas on their surfaces, and this can take a long time to remove by pumping, water being particularly troublesome in this respect. Poor adhesion is often a problem with evaporated films of the platinum group metals especially on oxide surfaces such as ceramic and glass. This results from their low chemical reactivity so can generally be overcome by coating the substrate with a more reactive metal such as chromium before the platinum metal is deposited. Adhesion to plastic substrates, however, is usually very good.

Many of the problems associated with thermal evaporation can be avoided by sputtering techniques. Instead of vaporising the coating material by thermal energy, the surface of the target-the source of the platinum group metal-is bombarded with positive ions from a low pressure plasma of an inert gas, usually argon. The ions are accelerated towards this target by a potential of several kilovolts and as they collide with it their kinetic energy is transferred to the platinum group atoms so giving them sufficient energy to leave the surface and travel to the substrate. These sputtered platinum metal atoms have much greater kinetic energy than thermally volatilised atoms and can undergo collisions en route to the substrate without nucleation occurring. This means that higher pressures in the 1 0 - 3 to I O - ~ Torr range can be used, thus easing the pumping requirements. As the sputtered atoms arrive at the substrate with much higher energies than evaporated atoms the adhesion between this coating and

the substrate is improved because gas adsorbed on the substrate surface is displaced and the sputtered atoms embed themselves in the surface layers. Although ion bombard- ment does raise the temperature of the target the radiant heat emission is small compared with that from a thermal source, and in most commercial plants is completely suppressed by cooling the target. One disadvantage of sputtering in comparison with thermal evaporation is that the deposition rate is much lower, unless powerful radio frequency plasma is employed.

With both types of vacuum deposition, a vast range of materials can be coated, almost the only condition being that the substrate can be safely subjected to vacuum conditions. Unless the substrate being coated is very small in relation to the source, it is necessary to move it around during deposition in order to obtain an even coating. The size of the substrate being coated is obviously limited by the capacity of the vacuum chamber, and the shape by the rectilinear form of the emission from the source; it is not possible to coat surfaces which cannot be placed approximately perpendicular to the line of emission.

The thickness of deposit which can usefully be formed is limited by the amount of strain which can be accommodated in the coating. This strain may be caused by structural imperfections at the atomic level or by incorporated impurities, and leads to crazing, cracking and peeling of the coating. Although the strain can be reduced to some extent by heating the substrate during deposition, so annealing the deposit, the process is best suited to the production of thin coatings in the range from a few atomic layers up to I

micrometre.

Thermal Decomposition and Chemical Vapour Plating

Thin coatings of platinum and of gold- palladium alloys can be applied to heat resistant substrates by the thermal decomposition of organometallic compounds of


these metals to which resins and solvents have been added to give the required properties for application by such methods as brushing, spraying or screen printing. After drying, the substrate is fired in air in the temperature range 500 to 900°C to decompose the organometallic compound and to oxidise all carbon- aceous residue, leaving the required metal film. Obviously, this process can only be carried out with a metal which does not oxidise at the required temperature.

An alternative method of utilising thermal decomposition is known as chemical vapour plating (3). The substrate is heated in an atmosphere containing the vapour of a metal compound which decomposes to the metal at the temperature of the substrate. The process is usually carried out under reduced pressure in order to obtain the necessary volatility without decomposing the metal- bearing compound prematurely. Further- more, the process can be, and normally is, conducted in an inert atmosphere, so coatings of materials sensitive to oxidation at elevated temperature, such as palladium, can be applied by this method. The coating is deposited over the entire surface of the substrate, application to selected areas can therefore be achieved only by masking or by subsequent etching of unwanted areas. This ability to coat the entire surface of the substrate extends to the interior of fine pores and crevices so the method is well suited to the impregnation of porous materials, For this purpose, the process can be modified with advantage. The material to be treated is first impregnated with a solution of the volatile organometallic compound, dried, and then heated to volatilise the compound and decompose it throughout the pore structure. A remarkably even distribution of metal is obtained throughout the porous substrate by this technique (4).

Electroless Plating Thermal decomposition methods cannot be

used with heat sensitive substrates such as plastics, but coatings can be formed on such materials, as well as on many others, by

chemical reduction methods, often called electroless plating. The substrate is usually first treated chemically or mechanically to roughen the surface, thus providing a mechanical key which improves the adhesion of the coating, before being treated with palladium chloride followed by stannous chloride. The resulting layer of colloidal palladium then acts as a catalyst for the formation of the coating proper, which is formed by immersion in a bath containing a salt of the coating metal together with a reducing agent such as sodium hypophosphite. This method can be used to produce coatings of base metals such as copper or nickel which can subsequently be electroplated with one of the platinum group metals.

Because of the position of the platinum group metals at the bottom of the electrochemical series, coatings can often be obtained on the base metals simply by immersing the substrate in an aqueous solution of a platinum group metal salt. The quality of coating obtained is not usually good, but the method is a simple way of producing composite metal powders containing small proportions of platinum group metals.

Aqueous Electroplating Aqueous electroplating is a well-established

and widely practised method of applying many metals to metallic substrates, and good results can be obtained with most of the platinum metals (5, 6). The nature and thickness of the deposits obtainable with the various members of the group vary considerably. Platinum deposited from baths containing dinitro sulphato platinous acid is highly stressed and the resulting hard, bright plate cracks at thicknesses greater than 4 micrometres. If thicker deposits are required, intermediate stress relieving anneals must be carried out when thicknesses up to 40 micrometres may be obtained. The thickness obtainable with ruthenium is limited to 4 micrometres.

Rhodium, however, can be plated from acidic rhodium sulphate solution in thick-


nesses up to 40 micrometres without cracking problems, but heavy deposits are dull in appearance. Palladium is the most amenable of the platinum group metals to electroplating and bright, heavy deposits are obtained from electrolytes based on tetrammino palladous nitrite.

Fused Salt Electroplating In addition to electrodeposition from

aqueous solution, electroplating of platinum from a fused salt electrolyte is also an established process (7). The advantage of this process is that stress-free and ductile deposits up to 200 micrometres thick can be readily produced, but the process is limited to substrates which can withstand the high temperature of the fused salt. Titanium, tantalum, niobium, molybdenum, tungsten and even graphite have been coated by this technique. Other members of the platinum group metals have also been successfully plated by this method.

Metallic Bonding When substantial coatings of platinum

group metals are required on metallic substrates recourse has to be made to metallurgical bonding techniques to produce the required composite. The process of joining two pieces of metal by diffusion bonding is carried out by bringing them into close contact under pressure and raising the temperature until the rate of interdiffusion is appreciable.

The simplest application of this technique is hot pressing, when the composite is bonded by heating while under a hydraulic press. This process can only be used for bonding flat plates, although these can subsequently be rolled into sheet and fabricated by normal workshop practice. However, not all metal combinations can be bonded in this way. In some cases the base metal substrate may form a very thin tenacious film of oxide on its surface which prevents the formation of the diffusion bond, or oxygen may cause embrittlement in the vicinity of the bond which


results in failure of the bond when rolling operations are carried out or when the composite is subjected to other stresses. Similar embrittlement and subsequent failure may also be caused by the formation of brittle inter-metallic compounds at the substrate- coating interface.

Successful bonding even in the presence of oxide films can sometimes be achieved by hot rolling, instead of hot pressing, if the metallurgical properties of the materials permit this. The metals to be joined are heated to a suitable temperature and then reduced in thickness by 20 to 50 per cent in a single pass through a rolling mill. The gross deformation produced by this treatment breaks up the oxide film and enables bonding to take place. Similar results can be obtained by hot swaging a tube of a platinum group metals on to a rod of substrate material. Unfortunately, failures resulting from embrittlement may still occur.

The problems of surface oxide scale and brittle intermetallic compound formation, both of which may impede diffusion bonding, can be circumvented by the use of an explosion bonding technique. Flat plates of the two materials are laid together with a small gap between them and a charge of low detonation velocity explosive on top. The detonator is fixed to one edge so that the explosion progresses across the sheet. The first effect of the explosion is to peel off a layer from the upper sheet which then scours across the face of the substrate. The clean surfaces so produced are then bonded by the pressure of the explosion. As the oxide scale is actually blown out of the interface, no oxygen embrittlement can occur, and the heating effects are too low in temperature and too short in duration to allow intermetallic compounds to form by diffusion.

Metallising Where the purpose of a coating is to provide

an electrically conducive area, resistant to atmospheric corrosion, on a glass or ceramic substrate, metallising pastes can be used.

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The possibility-and indeed the need- for the creation of new alloys based on the platinum metals result from both technologi- cal developments in the using industries and scientific progress in the methods of physical metallurgy. An outline of the extent to which this field is being cultivated in the U.S.S.R., with some background information on the general approach to the problems involved, is given in a paper from two well-known Russian workers, Professor E. M. Savitskii, Head of the A. A. Baikov Metallurgical Institute in Moscow, and his colleague, Mad- ame V. P. Polyakova. This is published in a special double number of Journalof Less- Common Metals (1975,43, 169-177) dedicated to Professor Ernst Raub on the occasion of his 70th birthday.

Professor Raub’s very long career at the Forschungsinstitut fur Edelmetalle in Schwabisch Gmund has, of course, been characterised by a great deal of research into the structure and the equilibrium diagrams of the platinum metals and their alloys, and his work is well appreciated in Russia, where physico-chemical research in this area was initiated under N. S. Kurnakov at the beginning of the present century and is continuing at the A. A. Baikov Metallurgical Institute of the Academy of Sciences.

Emphasising that the unique properties of the platinum metals make them available for wide technical applications in conditions where no other metallic or non-metallic materials can operate safely, Savitskii and Polyakova describe some of their work in their purification and in the production of single crystals for a closer study of their structure and properties. In the cases of rhodium and ruthenium, for example, they have shown that significant amounts of impurities, both metallic (Mg, Pb, Fe, Cu and Au) and non-

metallic (Si, C, 0, H and S) interact both with the basic metal and with themselves during melting, thereby of course influencing the mechanical properties and physical characteristics. By using arc and electron beam melting, and by zone refining in a high vacuum, purification of these metals has been achieved.

The fusible elements such as magnesium, aluminium, lead and silicon are well known to reduce significantly the life and operating temperature range of the platinum metals, these elements forming low melting point eutectics with the basis metal so that a thin layer is formed around the grain boundaries and failure can result.

A study of a polycrystalline sample of rhodium by scanning electron microscopy showed, for example, that glass-like oxide inclusions containing silicon and aluminium as well as other base metals could give rise to brittle fracture. This and other researches on the platinum metals have shown that the initial high purity of the basic metal is of primary importance.

Over the past twenty years or so a large proportion of the equilibrium diagrams of the platinum metals with other elements has been established. In the authors’ laboratory recent work has been concerned with the interaction of palladium and ruthenium with tungsten, rhenium, vanadium, hafnium and the rare earth metals and this study is still continuing. In particular the work with the rare earth metals is helpful in assessing the desirability of their use for improving the structure and properties of the refractory platinum metals iridium, rhodium and ruthenium which Professor Savitskii and Dr Polyakova foresee as the main components of some new and effective metallic materials for use in modern technology. L. B. H.

Platinum MetalRev., 1976, 20, (2), 53-53 53

Hydrogen in Palladium AN INTERNATIONAL CONFERENCE IN BIRMINGHAM

An International Conference on hydrogen in metals was held at the University of Birmingham on January 5th and 6th under the auspices of the Faraday Division of the Chemical Society. Over forty papers were presented, many of them dealing with palladium and its alloys. These latter papers are reviewed briejly in this note.

The interaction of the smallest interstitial atom, hydrogen, with the metallic lattice continues to attract considerable interest from the scientific community, as was amply evidenced at the international meeting held recently in Birmingham. As may be expected, many of the papers featured the classical palladium-hydrogen system and related alloys. The rare earth metals and the Group VA elements vanadium, niobium and tantalum also commanded a good deal of attention.

The first paper of the conference dealing with palladium was presented by Professor T. B. Flanagan of the University of Vermont. In the work described, an unambiguous demonstration has been made of the effect of dislocations on the solubility of hydrogen in the low content a-Pd phase. Solubility enhancements up to 23 per cent were observed in palladium heavily cold worked by milling. A good correlation between this solubility increase and dislocation density was obtained. Almost identical enhancement was found for deuterium, in spite of the solubility of this isotope in &-palladium being significantly lower.

Internal Friction Measurements Internal friction measurement is a searching

technique for the determination of interstitial behaviour, and Dr F. A. Lewis of Queen’s University, Belfast, presented one of several papers on this topic. His study involved a novel resonance vibration method using disc samples of palladium-silver alloys. From the discontinuities in the plots of vibration frequencies against temperature it was pos-

Platinum MetalRev., 1976, 20, (2), 54-55

sible to construct the phase diagram of the Pd/Ag/H system showing the hydride transformation boundaries. The upper temperature limit of the two-phase region is reduced from 300°C for pure palladium to near room temperature for the 23 per cent silver alloy or to -120°C for the 40 per cent silver- palladium alloy.

The “50K transition” in PdH was also the subject of internal friction studies by Dr G. J. Zimmermann of Munich University, and by Professor F. D. Manchester of Toronto. In spite of extensive new data being available from specific heat, neutron diffraction, n.m.r. and other physical measurements, doubt still remains on the precise nature of the structural changes involved in the transformation.

Dr M. Mahnig and Dr G. Sicking, both of the Institute of Physical Chemistry, Munster, presented papers dealing with the electronic structures of palladium-hydrogen and other alloys. One of the few techniques available for obtaining quantitative information on the local densities of states is Appearance Poten- tional Spectroscopy. New data from this and other sources show good agreement with the model proposed.

A study of the absorption of hydrogen and deuterium by palladium sponge over the range 80 to 140°C was reported by Professor D. H. Everett of Bristol University. Detailed thermodynamic analysis of the data obtained has given new information on the enthalpies and entropies of absorption over the whole composition range.

54

The only paper of the conference dealing specifically with mechanical properties was from the University of Birmingham, presented by Dr M. L. H. Wise. Alloy solid solution softening in body-centred cubic metals is now a commonplace phenomenon but the hydrogen softening reported by the Birmingham investigators is unusual. Micro- hardness measurements on a series of palladium-rare earth alloys (Pd-Y, Pd-Gd, Pd-Eu and Pd-Ce) showed that, apart from pure palladium and a few dilute alloys, pronounced softening occurred in these materials when charged with hydrogen by electrolysis. The hardness of a particular binary alloy was correlated with the product of the lattice expansion, determined by X-ray methods, and the electron concentration. The softening on hydrogenation can be explained by a reduction in the shear modulus and the atomic mismatch factor resulting from the filling of the 4d states. A consequence of this finding is that fabrication of palladium alloys may be facilitated if the material is in the hydrogenated state.

Significant progress in extending the range of hydrogen contents in P-phase palladium was described by Dr J. P. Burger of the Universite D'Orsay. By a low temperature electrolytic technique, PdH, was obtained with 3t values near to unity. Studies of these high hydrogen content samples by electrical resistivity and magnetic susceptibility measurements suggests that the X = I region is simpler than at x=o.7; the hydrogen atoms only occupy interstitial sites and the 50K transition is absent.

Dr H. Zuchner of the Institute of Physical Chemistry, Munster, discussed several var- iants of electrolytic methods for the study of metal-hydrogen systems. The poor interphase transfer at the electrolyte/metal boundary for most metals has now been overcome by coating with a thin evaporated palladium layer after an ultra-high vacuum cleaning operation. The versatility of the electrochemical method resides in the possibility of varying the boundary conditions, for

example by constant current, pulse methods, etc. Diffusion constants, permeabilities and solubility data may all be derived from the measurements.

Transport Brocessess Experiments on the mobility of interstitial

atoms in metals by various transport processes constitute a powerful method for studying thermodynamic properties of such systems. Three such transport processes were analysed in detail by Dr H. Wipf of Munich University, the Gorsky effect (stress- induced transport), electrotransport and thermotransport. The magnitude and behaviour with time of the concentration changes were shown to depend on the applied forces, the diffusion coefficient and chemical potential of the hydrogen atoms. A comparison was made between these transport processes and microscopic techniques for determining hydrogen mobility, and Mossbauer spectroscopy was discussed as a new method of studying hydrogen diffusion.

Contributions to the conference of direct industrial significance were few and far between. An exception was the description by Dr S. C. Lawrence, of Lawrence Elec- tronics Co, Seattle, of a new hydrogen detection gauge. This is based on a slightly modified thermionic valve (6V6) fitted with a hydrogen permeable membrane. The membrane may be either a 0.016 in thick 1020 (0.2 XC) steel window or a silver-palladium tube attached to the metal envelope of the valve. Hydrogen permeating through these membranes may be measured from the ionisa- tion current between the electrodes. Many measurements of practical importance are possible with the gauge including control of hydrogen embrittlement during plating, internal corrosion in oil-wells, chemical or nuclear reactors, and sorbed hydrogen during pickling or other similar processes.

The papers presented at Birmingham will be published in full in a special issue of the Journal of the Less-Common Metals.

A. G. K.


Carboxylato Complexes of the Platinum Group Metals A REVIEW OF RECENT DEVELOPMENTS

By Alan Dobson and Stephen D. Robinson Department of Chemistry, King’s College, London

The recent rapid growth of interest in the carboxylato complexes of the platinum group metals has led to many signijcant advances. This article describes some of the more important chemical, structural and catalytic properties displayed by this class of compound.

Oxygen donors are generally regarded as class ‘a’ ligands and, except in certain high oxidation-state oxy species, do not feature particularly extensively in the coordination chemistry of the platinum group metals. However, a small number of oxygen donor ligands have gained considerable importance in platinum metal chemistry, and carboxylate anions are the most common and versatile of these. Platinum metal carboxylato complexes are of relatively recent origin (I), most of our present knowledge having been gained within the past decade. Progress has been helped by X-ray diffraction techniques and magnetic studies, and has been encouraged by the promise of novel structural features and important catalytic applications. Surprisingly transition-metal carboxylates have rarely been reviewed (2, 3), and platinum-metal carboxylates in particular have not previously been surveyed. The carboxylate anions (general form RC0,-) are versatile ligands capable of existing as counter anions or coordinating to the metal in unidentate, chelate or bridging modes. Their geometry is particularly suited to the last of these func- tions, and has permitted the isolation of bi- and trinuclear complexes often containing platinum metals in unusual oxidation states (i.e. Ru’, Os’, Rh”, and Pd’). The versatility of carboxylate ligands is greatly enhanced by

the extensive variety of available groups, R; these include hydrogen, simple alkyl or aryl radicals, their perfluoro analogues and numerous more complex entities. The last- mentioned group includes polybasic carboxylic acids (particularly oxalic) , amino acids and sequestering agents (i-e., EDTA). This review concentrates on those complexes containing simple carboxylate anions RCO (R=H, alkyl, aryl, perfluoro alkyl, etc.).

Syntheses General methods employed in the synthesis

of platinum metal carboxylato complexes, based on the use of carboxylic acids and their alkali metal, silver or thallium salts have been surveyed in two recent papers (4, 5) . More novel preparative procedures include in- sertion of carbon dioxide into metal-hydrogen (6) or metal-carbon bonds (7), reaction of vinyl or alkyl carboxylates with metal hydrides (8) and oxidative-addition of acid anhydrides, (RCO,),O, with iridium(1) and platinum(0) complexes (9). Details of syntheses appropriate for individual complexes, including the many polynuclear species, can be obtained from the references given in later sections of this review. The carboxylato complexes are usually crystalline, air-stable species and frequently display good solubility in common organic solvents.

Platinum MetalRev., 1976, 20, (2), 56-63 56

Structure The versatility of carboxylate ligands is

amply demonstrated by the variety of structures observed for their platinum metal complexes. Salts containing (RC0,-) or H-bonded (RCO,HO,CR-) counter anions are frequently found, particularly when R is a perfluoro alkyl or similar electron withdrawing group (10, 11, 12). Simple mono- nuclear complexes containing carboxylate anions bound in unidentate fashion, as in [Rh(OCOMe)(PPh,),] (13) and [Rh(OCOPh) (PPh,),] (7), or as chelate ligands in, for example, [RuH(OCOMe)(PPh,),] (14), frequently feature long metal-oxygen linkages. These are particularly pronounced when located trans to good a-donor ligands, and further demonstrate the rather weak ligand character of carboxylate anions. The common occurrence of polynuclear carboxylato complexes reflects the good bridging geometry of carboxylate anions. Di-, tri- and oc- casional tetranuclear platinum-metal clusters with metal-mctal interactions ranging from zero to formal triple bonds have been characterised by magnetic, spectroscopic and, in particular, X-ray diffraction studies (15). Some important structural types are illustrated in Figures I to 6. Binuclear carboxylato-bridged structures, Fig. I, have been established by X-ray diffraction studies for [Pd,(OCOMe),(n3-CC,H,),] (16) and [Pd,(OCOMe), (2-methylallyl-3-norbornyl) ,] (17). Relatively short Pd-Pd distances in these structures (2.94 and 2.96 8 respectively) have led to speculation concerning possible metal-metal interactions, but may simply reflect the steric constraints of the bridging ligands (16, 17). Similar 'folded' structures have been proposed for a range of binuclear complexes including the species [M,(OCOR), X,(EMe,Ph),] (M=Pd, Pt; X=Cl, Br, I; E=P, As) (18L [M,(OCOR),(alkenyl- OCOR),] (M=Pd, Pt) (19, zo), [Pd, (OCOR),L,] (L =PPh,, AsPh,, Me,CO)

(OCOR),(C0),1 (23) and [RhdOCOR), (CO),(PPh,),] (24). The diamagnetic

(21), IRh2(OCOR)z(Cd312)21 (221, [Kh,

ruthenium( I) species [Ru ,(OCOMe) ,( CO)4 (py),] (25) and the related osmium(1) complex [Os,(OCOMe),(CO),] (26) have been shown to possess binuclear, metal-metal bonded, acetate-bridged structures of the type shown as Fig. 2 . Metal-metal distances are 2.678 (Ru-Ru) and 2.731 8 (0s-0s) respectively. Similar structures have been postulated for other ruthenium(1) and osmium(1) complexes of stoichiometry [M,(OCOR),(CO!,(L),] (L=CO, py, amine, MeCN, PR,, AsR,) (27, 28, 29, 30) and probably exist in the binuclear palladium(1) complex [Pd,(OCOMe),(C6Hs)(o.5 MeCOOH)] (31). Quadruple-bridged binuclear structures, Fig. 3, with metal-metal interactions ranging from weak antiferromagnetic spin-spin coupling to strong multiple bonds, occur frequently in transition metal chemistry and have aroused much interest (15). Established examples involving platinum group metals include the rhodium(I1) species [Rhz(OCOH),(HzO)I (321, [Rhz(OCOMe)p (H2O)zI (33, 34) and [ R ~ , ( O C O M ~ ) ~ ( P P ~ ~ ) Z ] (35), and the ruthenium cation [Ru, (OCOPrn)4]+ in [Ru,(OCOPr"),Cl] (36). The revised rhodium-rhodium bond length (2.3855 instead of 2.45 8) for [Rh,(OCOMe)* (H,O),1 is the shortest known, and indicates the presence of a full triple bond, thus confirming the most recent theoretical pre- dictions (34). A very short ruthenium- ruthenium bond length (z.2X1 8) and a two-fold crystallographic axis are reported for the [Ru,(OCOPr"),]+ ion; the latter is indicative of equivalent metal ions and, by implication, a non-integral oxidation state (f2.5) for the ruthenium (36). This conclusion is supported by magnetic data (see below). Species previously formulated as [Ru,(OCOR),] and [Ru,(OCOR),L,] have now been recognised as oxygen-centred trinuclear species [Ru,O(OCOR),(H,O),(OH)] and [Ru,O(OCOR),L,] respectively (L =py, PPh,, etc.) (37). However, one-electron electrolytic reduction of [Ru,(OCOR),CI] is reported to yield authentic [Ru,(OCOR),] (R=Me, Pr") in a non-crystalline form


Platinum Metal Rev., 1976, 20, (2), 58

(38, 39). The oxygen-centred, trinuclear ‘basic’ carboxylate structure, commody found in transition-metal chemistry, has recently been established for a range of ruthenium (37, 40), rhodium (42) and iridium (42) complexes. An X-ray diffraction study has confirmed an oxygen-centred trinuclear structure, of the type shown in Fig. 4, for [Ru,O (OCOMe),(PPh3),] (37, 43). In the absence of any direct metal-metal interactions (Ru-Ru distances about 3.3 A), the diamagnetism of the complex and the non-integral oxidation state (+2#) for ruthenium are rationalised in terms of a qualitative MO treatment of the Ru,OP, x-electron system (43). Redox and substitution reactions (see below) lead to other products containing the [M,O(OCOR),] moiety. Further evidence for the delocalisa- tion of electrons over the Ru,O cluster is supplied by ESCA data for the species

The trinuclear structure, Fig. 5, devoid of metal-mttal bonding, has been established for [Pd,(OCOMe),(o.gH,O)] (45) and a ligated version of this structure possibly exists in the trinuclear ruthenium complexes

A similar trinuclear structure has been reported for tris(pacetat0-p-acetoximato palladium)o.5-benzene (46). The “platinum(I1) acetate” obtained by reducing platinum(1V) in acetic acid/nitric acid contains a variety of nitrogenous complexes including the species [Pt,(OCOMe),(NO),] for which the tetranuclear structure shown in Fig. 6, with bridging acetate and nitrosyl ligands, has been established (47). An alternative synthesis (48) leads to authentic platinum(I1) acetate but the structure of this product has not been determined.

To date, tetranuclear platinum metal complexes, analogous to the cobalt species [Co,O(OCOR),], have not been reported. Structural studies on carboxylato complexes including oxalate, amino acid and EDTA derivatives of the platinum group metals are comprehensively listed in an annual publication (49).

[R~~O(OCOM~),(PY),I”+ (n=O-2) (44).

[Ru,(OCOR),L31 (L =H,O,MeOH,py), (40).

Spectroscopic and Magnetic Studies Infra-red spectral data, in particular the

parameters v(OCo),,,, v(OCO),, and [v(ocO),,, -V(OCO),~~], have been extensively employed in the assignment of carboxylate ligand bonding modes. Bidentate carboxylate ligands have values of v(OCO),,,, and V ( O C O ) , ~ ~ rather similar to those found for the corresponding free carboxylate anions, whereas unidentate carboxylate ligands have v(OCO),,, at substantially higher frequencies and thus display larger values of [v(OCO),,, -v(OCO),,,] (21, 50, 51). However, in several instances the situation is complicated by the occurrence of hydrogen-bonding between the non- coordinated oxygen atom of a unidentate carboxylate ligand and a solvate molecule leading to a reduction of v(OCO),,, (50). Moreover, the infra-red frequencies v(OCO),,, and V ( O C O ) , ~ ~ are highly sensitive to the structure of the carboxylate group, the nature of the accompanying ligands and the identity of the central metal ion. In consequence considerable caution must be exercised in any attempt to deduce carboxylate bonding modes on the basis of infra-red data alone. Far infra-red and Raman data have been reported for the rhodium(I1) complexes [Rh,(OCOR),] and [Rh,(OCOR),L,] (R=Me, Et; L=H,O, MeOH,Me,SO,PPh,); Raman active vibra- tions in the range 288 fo 351 cm-l are attributed to rhodium-rhodium triple-bond stretching, infra-red bands at about 320 to 440 cm-l are assigned to v ( R h - 0 ) (52).

Very little work has been reported on the n.m.r. spectra of carboxylate ligands. How- ever, variable-temperature n.m.r. has been used to demonstrate the rapid exchange of uni- and bi-dentate carboxylate ligands in the complexes [ M(OC0R) %( CO)(PPh3) (M=Ru, 0 s ; R-Me, CFJ (4, 51, and to study the dynamic stereo-chemistry of the dimeric palladium(I1) and platinum(I1) species [Pd 2(OCOR),(ns-allyl),] and [M ,(OCOR) ,X ,(PMe,Ph) 2] (X = halide or OCOR) (18, 53).


Electronic spectra have been recorded and interpreted for the binuclear species [Rh,

(38) and [Ru,(OCOMe),Cl] (36, 38), and the trinuclear products [M,O(OCOR),L,]X (M=Rh, Ir, Ru) (40, 41, 42).

Use of ESCA data in the study of the trinuclear systems has been noted above. Detailed magnetic susceptibility and e.p.r. spectra measurements for [Ru,(OCOBu"),Cl] indicate a quartet ground state and support the symmetrical structure deduced from crystallographic data (39). Magnetic data have also been reported for the trinuclear species [M,O(OCOMe),L,] [XI (40, 42).

Reactivity Interesting and important results have been

achieved in this highly promising area; however, studies are fragmented and much remains to be done. Known reactions encompass ligand substitution, ligand frag- mentation and redox processes. The excellent leaving characteristics of carboxylate anions in general and perfluorocarboxylate anions in particular are reflected in a range of substitution and/or reductive elimination reactions. Thus [RuH(OCOMe)(PPh,),], [Ru,O(OCOMe),(H,O),][OCOMe] and [Rh,(OCOMe),], the last in the presence of

(0COR)LI (541, [RhdOCOMe),(H,O),l+

acid, react with carbon monoxide under mild conditions to yield [Ru(CO),(PPh,),] ( 5 9 ,

respectively. The complexes [Rh,(OCOMe),], [Ru,O(OCOMe) 6(H20)3] [OCOMe] and [Ru,(OCOMe),Cl] react with stron, 0 non- coordinating acids (such as HBF,) in hydroxylic media to afford air-sensitive solutions containing cationic species of high catalytic activity (41, 57, 58). The green solution formed in the rhodium system is now thought to contain the aquated cations [Rh,(OCOMe),]+ and [Rh,(OCOMe),]2+ rather than the species [Rh,aq14+ (38). Reaction of [RuH(OCOMe)(PPh,),] with fluoroboric acid in hot methanol affords the novel x-arene complex [RuH(n6 -C,H,PPh,) (PPh,),][BF,] (59). The unusual versatility of carboxylato complexes in synthesis is dramatically illustrated by formation of the metal-metal bonded, acetlyene-bridged, palladium(1) complex [(n5 -C,Fh,)Pd(PhC= CFh)Pd(n5 -CC,Ph5)] (Pd-Pd 2.639 a) from [Pd,(OCOMe),] and diphenylacetylene in methanol (60). The species [M,O(OCOMe), (L)J [XI (M=Ru, Rh, Ir; L=H,O, MeOH) frequently undergo substitution of the ligands L, with retention of the trinuclear cluster (40, 41, 42, 61). The trinuclear ruthenium complexes [Ru,O(OCOR),L,] are unique in

[RudcO)~zI (56) and [Rh~(co)i ,] (56)

Scheme 1

oc L \ / / \

Ir

L c1

CF,CICOO-

- c1- +

oc L \ /

Ir

L' \OCOCF,CI

CF,COO-

+ Ir -+

oc I L CF2C1C00- \ I ,/ -coz --

L' I 'Cl OCOCF,CI

(refluxing diglyme, L =PPhJ


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(84), [Ru(OCOMe),(PPh,),] or [Rh(OCOMe) (PPh,),l ( W , and [RuWOCOR)(PPh,),l (55) respectively. Other hydrogenation catalysts include the complexes [Rh, (OCOMe),] (86,) and [Rh(OCOR)(PPh,),] (87), and the species obtained on treating ruthenium or rhodium carboxylates with strong non-coordinating acids (57, 58, 85). Inter- or intra-molecular hydrogen-transfer from alcohols to olefins and acetylenes are catalysed by [Ru,O(OCOMe),][OCOMe] (88) and [RuH(OCOCF,)(CO)(PPh,),] (89) respectively. Dehydrogenation of alcohols to aldehydes or ketones is catalysed by [Ru (OCOCF,),(CO)(PPh,),] (90). Other interest-

ing catalytic reactions include the carbonylation of amines in the presence of the ruthenium(1) species [Ru(OCOMe)(CO), (amine)] (29, 30) and the hydroformylation of olefins i n the presence of the rhodium(1) complexes trans-[Rh(OCOR)(CO)(PR,f,] (24). Very little has been reported on the catalytic activity of platinum, iridium and osmium carboxylates. However, decarbonyl- ation of aldehydes by [IrH,(OCOMe)(PPh,),] and related species has been described (66).

Acknowledgement One of the authors (S.D.R.) wishes to thank the

University of British Columbia for a temporary appointment during tenure of which this article was written.

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ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES The Ordering Mechanism in CuPt as Studied by Electrical Resistance Measure- ments and Electron Microscopy E. TORFS, J. VAN LANDUYT, L. STALS and s. AMELINCKX, Phys. Status Solidi A, Appl . Res., 1975, 31, (2)> 633-645 Resistivity measurements and electron microscopic studies of the ordering mechanism in Cur t showed a complex ordering mode consisting of homogeneous and heterogeneous processes at <475%; the dispersed ordered domains stopped growing at 475-620°C. Transformation twins observed near the critical temperature for ordering are related to stress relief in the larger domains.

Diffusion of Platinum in the Fe-Pt System J. KUEBRA and B. MILLION, Phys. Status Solidi A, Appl . Res., 1975, 31, (I), 275-282 The diffusion of Pt in 15 to 60°,Pt-Fe alloys was studied at 78c-1420'C by the residual activity method using the isotope Pt-193 m; Pt homo- diffusion coefficients D were obtained. The results are discussed on the basis of the Fe-Pt equilibrium diagram. The increasc of activation enthalpy 8 ( A H ) which is due to the FePt ordered structure is 6.8 kcal/mol.

Effect of Oxygen on the Thermionic Emission of Impurity Ions from a Platinum Surface L. P. REKOVA, V. V. MOZGIN, L. N. ZVYAGINTSEVA, v. N. BONDARENKO and YA. M. FOGEL, Sov. Phys., Tech. Phys., 1975, 20, (3), 382-386 The influence of 0, on the emission of thermionic ions and secondary and gas ions of particles of volume impurities from the surface of heated Pt was studied. Results at 1573K show a specific influence of 0, on the diffuse flux of impurity particlcs from the interior of the Pt to its surface through dislocations.

Surface Composition of Pd-Au and Pd-Ag Catalysts by Auger Electron Spectroscopy B. J. WOOD and H. WISE, Surface sci., 1975, 52, (I), I 5 1-1 60 Studies of the metal surface composition of Pd-Au and Pd-Ag alloys in microspheres (Sovrn in diameter) and in Al,O,-supported crystallite (<Ioo!~ in diameter) forms made by Auger electron spectroscopy showed the agreement of the observed Pd-Au ratios at the surface with those of the bulk in both forms. However, in the case of supported Pd-Ag, the surface exhibited

- Ag-enrichment relative to the bulk. The results

are explained with the help of the regular solution monolayer model and the binding energies between the dissimilar metal atoms are calculated.

Magnetic Properties and Electrical Resisti- vity of (Nil-,Pdx)3Al M. SATO, J . Phys. Soc. Japan, 1975,39, (I), 98-102 The magnetic properties and electrical resistivity of (Ni,-,PdX),Al were measured, the value of x being varied up to 0.20 through the ferromagnetic critical concentration of xc 1.0.095. The magnetic susceptibility of these alloys is explained approximately by the simple uniform enhancement model. Experimental results are in good agreement with theory.

Low Field Magnetic Susceptibility of Amor- phous CoxPdao-,Si,o and Fe,Pd~~-,Si,, -41107s A. ZENTKO, P. DUHAJ, L. POTOCKY, T. TIMA and J. BhNsKq , Phys. Status Solidi A, Appl . Res., 1975,

Temperature dependence of the magnetic susceptibility x(T) of CoxPdso-xSiz,, and FexPdso-xSi,o alloys was measured in a low magnetic field (c2Oe) by the induction method using the a.c. mutual inductance bridge. A sharp peak in the observed course of x(T) which appeared in Co alloys with x 5 Ioat."/,Co and in all Fe alloys was due to the loss of the short-range order of the amorphous basal Co- or Fe-Pd-Si alloys. At higher concentrations (x> roat. "/oCo) the long- range random ferromagnetic ordering appeared also in the basal matrix and the maximum in the case of x(T) disappeared.

31, (11, K41-K42

Studies of Hydride Formation and Super- conductivity in Hydrides of Th-Pd Com-

H. OSTERREICHER, J. CLINTON and H. BITTNER, J. Solid State Chem., 1976, 16, (1-2), 209-210

X-ray studies were made of hydride formation and superconductivity of intermetallic compounds of the Th-Pd binary system produced during the reaction of H, with Th-Pd phases (ThPd,, ThPd,, Th,Pd,, ThPd and Th,Pd) at up to 20ooC and 100 atm. The results showed that only Th,Pd,, ThPd and Th,Pd absorb a noticeable amount of H forming Th,Pd,H,, ThPdH, and Th,PdH,. Superconductivity was measured and no transitions were observed down to 1.8K. From the results presented the conclusion is made that higher Hz concentrations in these intermetallic compounds are beneficial for superconductivity.

pounds


Upper Critical Fields of Noncrystalline Zr77Rh23 Alloy and Intermetallic Zr,Rh Compound K. TOGANO and K. TACHIKAWA, PhyS. Lett. A, 1975, 54, (3)1 205-206 The temperature dependence of the upper critical field for the noncrystalline Zr,,Rh,, alloy obtained by liquid quenching was measured and is discussed in terms of existing theory. The same measurement was also carried out for the intermetallic Zr,Rh compound.

Thermoelectric Power of Ir(Fe) J. s. TOUGER and M. P. SARACHIK, Solid State Commun., 1g75,17, (II), 1389-1391 Thermoelectric power is measured in 0.5-1.0:;, Fe-Ir and in pure I r at 4.2-3mK. Peaks similar to those found in Pd-Ni and Rh-Fe occurred in Fe-Ir at the spin fluctuation temperature Tsr= 28K, independent of solute concentration. These three alloy systems are compared and their similarities and differences are discussed.

Electrical Resistivity and Magnetic Ordering in C.P.H. Ruthenium-Iron Solid Solutions B. V. B. SARKISSIAN and B. R. COLES,J. Less-Common Metals, 1975, 43, 83-88 Electrical resistivity, susceptibility and magneti- sation measurements at low temperatures on Ru-Fe solid solutions with up to 70o/b Fe, show that some type of magnetic ordering occurs at 50f2% Fe. It is suggested that the ordering is of variable antiferromagnetic character.

The Physico-chemical Investigation of the Re-Ru-Ti and Re-Ru-V Systems V. K. YURTAEVA, M. V. RAEVSKAYA, I. G. SOKOLOVA, 0. I. CHECHERNIKOVA and E. M. SOKOLOVSKAYA, Vest. Moskov. Univ. Ser. 11, Khim., 1975,16, (5), 572-575 The phase diagrams of the Re-Ru-Ti and Re-Ru-V systems were constructed at 1ooo"C and the ternary intermediate phase -c and --y, were found. The magnetic susceptibility of these alloys was studied as a function of temperature.

CHEMICAL COMPOUNDS Preparation of Silylplatinum Complexes by Interaction of Organosilicon Hydridcs and Carbonatobis(phosphine)platinum(II) Com- plexes C. EABORN, T. N. METHAM and A. PIDCOcK,J. Chem. Soc., Dalton Trans., 1975, (21), 2212-2214 Bis(sily1) complexes [Pt(SiR,),L,] (R3=MePha; L=PMe,Ph, PEt,Ph, PMePh, and PPhs) or Ft(SiHR,),L,] (R,=Ph, or MePh) were produced by reacting Fr(COs)L,] with SiHR, in benzene. H n.m.r. spectroscopic studies showed that all the products had cis configurations.

Magnetic Susceptibility of the One-dimensional Conductor (H,O),,[Pt(C,O,),],H,O D. HEITKAMP, H. s. &E, H. J. KELLER and H. H. R U P F , ~ . Solid State Chem., I975,15, (3), 292-296 The magnetic susceptibility of the (H,0)l.6 lJ't(CzO,)JnHZO, a mixed valency planar compound with columnar structure and one- dimensional metallic conduction properties, was measured at 1.5-300 K. The observed para- magnetism is described by a linear I / T dependence with a break in the slope at a characteristic temperature. The Curie constants as well as the point of discontinuity are found to depend on the crystal H20 content. The results are discussed in terms of different theoretical concepts.


Novel Rhodium(1)-Porphyrin Complexes and Organorhodium(II1)-Porphyrin Com- plexes. IV. H. OGOSHI, J. SETSUNE, T. OMURA and z. YOSHIDA, J. Am. Chem. Soc., 1975, 97, (22), 6461-6466 The preparation of two new Rh(1) porphyrins, porphyrin[Rh(CO),] and N-alkyl-porphyrin [Rh(CO),Cl], as a result of the reaction of [Rh(CO),Cl], with octaethylporphyrin and N- alkyloctaethylporphyrin is described. An oxygen- sensitive Rh(1) porphyrin was also obtained from chlororhodium(II1) porphyrin by using NaBH,.

Chloro- 1,2- bis ( diphenylphosphino ) ethane- carbonylrhodium(I) : an Exceptional Com- plex within a Series A. R. SANGER, J. Chem. soc., Chem. Commun., 197.5, (21),893-894 Spectroscopic studies of the series of complexes [{RhCI(CO)(Ph~P[CH&PPh~)}~] (n = I to 4) showed that all the square-planar complexes were dimeric (m==2) with a trans configuration about Rh. The complex with n=2 is monomeric with cis configuration.

Iridium and Rhodium Dihydride-hydroborate Complexes of the Type [MH,(BH,)L,] H. D. EMPSALL, E. MENTZER and B. L. SHAW, J. Chem. SOL, Chem. Commun., 197.5, (21), 861- 8 62 Studies of [IrH,(BH,)L,] (L =bulky tertiary phosphine) complexes showed them to be the first metal-hydroborates in which the BH, ligand was not fluxional; an analogous Rh complex showed some fluxionality. H, resonances for the bridging hydrogens (IrH,B) and the terminal hydrogens (BH,) were observed.

Information on KIrO, R. HOPPE and K. u r n s , J. Less-Common Metals, I975,43> 129-142 The preparation of KIrO, from mixtures of KOz+Ir (K:Ir=1.8:1) is described. KIrO, crystallises in a cubic structure of space group Pn3-Ti with a=9.48A and Z=r2.

The Interaction of 1,2,3-Bemotriazole with Rutheniumw) A. I. BESEV, L. N, LOMAKINA, M. N. MIKHEEVA and T. I. IGNAT'EVA, Vest. Moskov. Univ. Ser. 11,

The interaction of Ru(1V) with I ,2,3-benzotriazole was studied as a function of ionic state of metal in the initial solution, acidity of the solution and the presence of reducers. The crimson compound formed during the reaction of RuC1, at p H 0-2.9 turned gradually into the green compound with the ratio Ru:R = I : I . In the presence of redoxon the yellow compound formed at p H 0.5-2.3.

Tetracarbonyl(phosphine)ruthenium Com- plexes: Synthesis and Kinetics of Carhonyl Substitution B. F. G. JOHNSON, J. LEWIS and M. v. TWIGG, J , Chem. SOC., Dalton Trans., 1975, (IS), 1876- I879 The preparation of the complexes [Ru(CO),L] and tram-[Ru(CO),L,] (L=PPh3, PMePh, or PBui) during photolysis of [Ru,(CO),,] in the presence of an excess of ligand is described. These complexes can be also obtained by high pressure carbonylation of trans-[Ru(CO),IPPh,),]. Solid [Ru(CO),PPh,] forms [Ru,(CO),(PPh,),] on heating and reacts with excess of ligand to form trans- [Ru(CO),L,] while in solution.

Transition-metal Nitrosyl Compounds. Part XI. The Preparation and the Study of Fluxional Behaviour of Some Cationic Acetylene Complexes of Osmium

Dalton Trans., 1975, (20)~ 1990-1992 A number of cationic acetylene 0 s complexes of the type [Os(CO)NO(A)L,] [PF,] [L=PPh,, A=C,H,, C,HPh, C,Ph,, or C,(CO,Me),; L=P(C,H,,),, A =C,H,] were prepared, and characterised by their 'H n.m.r. spectra. For the complex where A =C,H, the variable-temperature studies are consistent with acetylene rotation about the metal-acetylene bond with AGT~= 1 1 . 5 f o . 2 kcal/mol [L=PPh,] and 14.450.5 kcal/mol [L =P(C6HII),].

Khim.9 1975, 16, (51, 581-585

J. A. SEGAL and B. F. G. JOHNSON, J . Chem. SOC. ,

ELECTROCHEMISTRY Hydrogen Production under Sunlight with an Electrochemical Photocell A. FUJISHIMA, K. KOHAYAKAWA and K. HONDA, J . Electrochem SOC., 1975, 122, (II), 1487-1489 An electrochemical photocell for H, production consists of five Pt cathode and TiO, anode units in which four anode plates are connected in parallel. The cell containing I.OM NaOH and o.5M H,SO, electrolyte solutions, works under irradiation with sunlight. The sunlight intensity of 110,000 lux produces 6.6 litres of Hz/mz of TiO,. The energy conversion efficiency of the photocell is estimated to be more than 0.4%.

The Behaviour of Ir(IV) in Perchlorate Solutions A. T. PILIPENKO, N, F. FALENDYSH and E. P. PARKHOMENKO, Zh. Neorg. Khim., 1975, 20, ( I I),

3044-3047 Studies of the state of Ir(IV) in HCIO, solutions show that the following processes take place: the reduction of Ir(1V) to Ir(TII), hydrolysis and hydrolytic polymerisation. The extent of these reactions depends on the acidity of the medium and the age of the solution, I t is found that in 0.1 N HCIO, all Ir(1V) i s fully reduced to Ir(II1) in the course of one month, and that molecules having a polymerisation factor > 2 are also present in this solution.

ELECTRODEPOSITION AND SURFACE COATINGS On the Electrolytic Activity of Electro- deposited Palladium on Pyrolytic Graphite I. MORCOS, 3. Electrochem. Soc., 1975, 122, (11),

1492-1493 The electrocatalytic activity toward oxygen reduction of both bulk Pd electrodes and electrodes prepared by the electrodeposition of a Pd layer on pyrolytic graphite substrates was studied by slow scanning voltammetry in acid and alkaline media. Current-potential curves obtained as a function of the disc rotation speed show that the electrodeposited Pd has a higher electrolytic activity than the bulk Pd and that the difference in the activity increases with the increase in rotation speed. The results are interpreted in terms of different intrinsic electrocatalytic properties of the electrodeposited Pd.

Electrodeposition of Palladium-Manganese Alloy s. I. VINOGRADOV, v. c. YANIN and v. I. SEKACHEVA, Zashchita Metal., 1975, 11, (6) , 751-752 Studies were made of Pd-Mn alloys deposited on Pt or C electrodes from an electrolyte containing ethylendiamino Pd and Mn sulphate at a current density of 1-7 A/dm2, 3-7 pH and at 20-5oOC. The 8 to Io%Mn-Pd alloy, deposited from an electrolyte containing 15-20 g/1 Pd, 5-20 g/1 Mn, at 4 - 4 . 5 pH, 20-4ooC and 1.5-4 A/dm2, has a microhardness of 240 kg/mm2 and wear resistance to stress on contact of 200 g/mmz which is five times higher than that of a pure Pd.

A Rutherford Scattering Study of Catalyst Systems for Electroless Cu Plating 11. SnCl, Sensitisation and PdCl, Activation R. L. MEEK,J. Electrochem. soc., 1975, 122, (11), 1478-1 48 I Preparation of graphite substrates, for electroless Cu plating, by sensitisation in SnC1, solutions and activation in a PdCl, solution was compared to a method using mixed Pd-Sn colloidal solutions.


The results obtained by a high energy ion back- scattering technique show that in the first method the Pd/Sn ratio is considerably less; more Pd and Sn are lost into the electroless plating solution and longer times (2210~ sec) are required to initiate the electroless plating reaction than in the case of the mixed Pd-Sn colloidal catalyst systems.

LABORATORY APPARATUS AND TECHNIQUE Measurement of Heat Conductivity of Metals in an Environment of Compressed Gas. The Palladium/Hydrogen System up to 24 kbar at 25°C. A. W. SZAFRANSKI and B. BARANOWSKI, J . Phys. E: Sci. Instrum., 1975, 8, (IO), 823-825 A comparative method of measurement of heat conductivity of metals in an environment of a compressed gas is given. Two samples, one of an unknown heat conductivity and the second as a reference, are placed inside the cylindrical Cu shield with attached Cu-Pt thermocouples. The temperature difference between two samples can be measured with accuracy of -0.o15K. The method was applied to the Pd/H, PdiHe and manganin/H systems up to zqkbar at 25°C.

A Hydrogen-sensitive Pd-gate M.O.S. Transistor

SVENSSON, J. Appl. Phys., 1975, 46, (g), 3876-81 A thin palladium film is used as the gate metal of a M.O.S. transistor which can be employed as a sensitive detector for hydrogen in air, nitrogen or argon. At a device temperature of 150°C the sensitivity in air is 10 p.p.m. hydrogen.

Intermetallic Compounds of Yttrium and Hafnium with Platinum c . E. HOLCOMBE,J. Less-Common Metals, 1976,44, 331-335 The platinum-hafnium intermetallic compounds HfPt, and HfPt,, prepared by powder metallurgical techniques, have high melting points and great stability. Studies made suggest that such materials could be suitable containers for reactive oxides undergoing high temperature investigations.

K. I. LUNDSTROM, M. S. SHIVARAMAN and C. M.

HETEROGENEOUS CATALYSIS Cb-Hydrocarbon Transformations under Poisoning of Alumina-Platinum Catalyst by Thiophene and Pyridine

Neftekhimiya, 1975, 15, (6), 842-847 The influence of thiophene and pyridine poisoning on the activity of Pt/AI,O, catalyst was studied in the reactions of aromatisation and C,-dehydrogenation of n-hexane, and other hydrocarbons, at 407-480°C by a pulsed chroma-

YU. N. USOV, L. G. ZUBANOVA and N. I. KUVSHINOVA,

tographic method. The results show a fast decrease in activity depending on the temperature and the amount of the poisonous agent.

Hydrogen Cyanide Production During Re- duction of Nitric Oxide over Platinum Catalysts

and R. J. KERL, Science, 1975, 190, ( e I O ) , 149-151 Studies of the catalytic reduction of N O with CO and H, over Pt supported on cordierite and Pt sponge catalysts were made using a bench-scale flow reactor at 400-800°C. Up to 80 p.p.m. of HCN is formed over Pt at 600-800°C in the presence of H,O vapour. In the absence of HZO vapour the HCN concentration rises to 700 p.p.m. No significant differences were found between a Pt sponge and Pt supported on cordierite. The results are discussed in relation to the catalytic treatment of automotive exhaust.

R. J. H. VOORHOEVE, C. K. N . PATEL, L. E. TRIMBLE

The Catalytic Effect of Platinum in the Oxidation of Monocrystalline S icon E. S. VORONTSOV and v. M. STRUKOV, Kinet. Kataliz,

The oxidation rates of monocrystalline Si in the presence and absence of Pt black were studied in air at 500-1200~C by the interference observation method. The results show that the reaction rate increases by a factor of 2400 at 1200°C in the presence of Pt black. High oxidation rates can also be obtained at as low a temperature as 500°C at which the reaction would not proceed without the catalyst. Extensive coking and recrystallisa- tion of the Pt black, taking place at temperatures > I IOOT, cause a decrease in its catalytic activity.

Ammonia Oxidation on Metals N. I. IL’MENKO, G. I. GOLODETS and I. M. AVILOVA, Kinet. Kataliz, 1975, 16, (6), 1455-1460 Studies of NH, oxidation on various metals show that the specific catalytic activity at 300°C decreases in the following order: Pt>Pd> Cu> Ag> Ni> Au> Fe> W> Ti. As the 0, binding energy increases, the catalytic activity and selectivity with respect to N,O decrease. The starting temperature of N, formation is lower than the temperature of NaO formation.

Stability of Metal Catalysts in the Liquid- phase Hydrogenation of Organic Unsaturated Sulphur Compounds. I. Hydrogenation of Divalent Sulphur in the Presence of Palladium A. V. MASHKINA, Kinet. Kataliz, 1975, 16, (4), 925-930 The influence of thioethers and thiophenes on the activity of 4.7:/a Pd/Al,O, catalyst was studied in the hydrogenation of z,5-dihydrothiophene sulphone. It is shown that all thioethers and thiophenes have a poisonous effect on the catalyst. The quick deactivation of the catalyst is proposed to be due to the formation of a bond between

I975J 1 6 J (4)> Io75-I077


S and Pd. This finding is in disagreement with the literature views about the high stability of Pd catalysts in the hydrogenation of divalent unsaturated S compounds.

Hydrogenation of Dimethylethynylcarbinol on Ruthenium-Palladium Catalysts Sup- ported on Titanium Oxide

DZHARDAMALIEVA, Zh. Fiz. Khim., 1975, 49, (II),

The hydrogenation of dimethylethynylcarbinol over I:; Ru-Pd/TiO, catalysts at 20-40°C in H20, O.IN KOH, O . I N H2S04 and 96% C,H,OH was studied. The change in the RujPd ratio is found to influence the rate of H, absorption. The selectivity of hydrogenation is found to be 80-g0%. The activation energies are 2.5- 10.5 kcal/mol and depend on the Ru content.

Hydrogenation of Hexene-1 on Supported Osmium-Palladium Catalysts

DIL’MAGAMBETOV, Zh. Fiz. Khim., 1975, 49, (8),

Liquid-phase hydrogenation of hexene-1 on I “’0 Os-Pd/AI20, catalysts in C2H50H, at 20, 30 and 40°C was found to be accompanied by a dis- placement of the double bond and cis- and trans-isomerisation. The catalytic activity of the contacts decreases monotonically with an increase of 0 s content of the catalyst.

D. V. SOKOL’SKII, T. M. DUKHOVNAYA and K. K.

2852-2856

D. V. SOKOL’SKII, K. K. DZHARDAMALIEVA and S. N.

2132-2134

HOMOGENEOUS CATALYSIS Interaction of Acyl Chlorides and Triethyl- silane Catalysed by cis-Dichlorobis (tri- phenylphosphine)platinum(II) and Related Complexes s. P. DENT, c. EABORN and A. PIDCOCK,J. Chem. SOC., Dalton Trans., 1975, (23), 2646-2648 The reaction of the acyl halides and triethylsilane catalysed by cis-[PtCl,(PPh,),] at 120’C produced aldehydes XCGH,CHO (X=H, p-Me, o-MeO, p-MeO, p-C1, p-Br, and p-NO2) in 50-849; yield. When p-methoxybenzoyl chloride was used the triethyl-p-methoxybenzyloxysilane was also formed. The conversion of this chloride into aldehyde is also catalysed by ci~-[PdCl,(PPh,)~], [RuCI,(FPh,),] and trans-[IrC1(CO)(PPh3),] and benzyloxysilane is formed.

On the Rate of Interaction of Diiodine-bis (diethylsulphide) platinum (TI) with Ammonia V. A. VALYAEVA, Zh. Neorg.Khim., 1975, 20, (IO), 2724-2727 The reaction rate coefficients of isomers of [PtI,.2Et2S] with NHO in C2HBOH and benzene were studied. An increased trans effect of diethylsulphide in complex Pt(I1) compounds was observed. A possible mechanism of the reaction of [PtI,.2Et,S] isomers with NH, is suggested.

Isomerisation of Phenylcyclopropanes by a Homogeneous Rhodium Catalyst P.-w. CHUM and J. A. ROTH, J . Catalysis, 1975, 39, (21,198-204 The isomerisation of isomeric phenylcyclopropanes in chloroform over a ~h(CO),CI] , catalyst yielded conjugated phenyl alkenes. The rate of reaction and isomer distribution was mainly influenced by conformational, conjugative and steric interactions of the substituted cyclopropanes.

GLASS TECHNOLOGY Contribution on the Corrosion of Pt/Rh 90110 Alloy in Glass Melts under the Influence of an Electric Current G. REINACHER, Glastech. Ber., 1975, 48, (XI), 221- 226 The corrosion of 90% Pt/Rh alloy crucible used for melting glass at IZOO~C was studied. The crucible formed one electrode, and a centrally immersed strip of the same metal the other. Severe corrosion of the electrodes occurred when a voltage of 1.5V was applied to the central electrode. Spectral analysis, metallographic and hot-stage microscope methods were used to examine the corroded electrodes. A method of preventing the corrosion by earthing the electrodes and the melt with Pt wire or strip is suggested.

Oxidation State and Optical Absorption of Rhodium in Borate and Silicate Glasses A. PAUL and J. M. PARKER, phys. Chem. Glasses,

The optical and redox characteristics of Rh(II1) in sodium and potassium borate glasses, soda-lime- silica glasses and a series of (17.1-x) Na,O, zxNaC1, 82.9 B,O, glasses was studied by absorption spectrometry and X-ray and chemical analysis. All the absorption bands are consistent with the low spin d6 configuration for Rh(III), the ion being in octahedral co-ordination. The solubility of Rh in the borate glass increases with the increase of alkali and chloride contents. Silicate glasses melted in Pt-Rh crucibles are also found to have a substantial Rh(II1) content.

1975, 16, (511 103-107

DENTAL AND MEDICAL USES “Braille” Reading by a Blind Volunteer by Visual Cortex Stimulation W. H. DOBELLE, M. G. MLADEJOVSKY, J. R. EVANS,T. S. ROBERTSandJ. P. G I R V I N , i ~ a t w e , 1976,259,111-1 I2 An array of 64 platinum electrodes insulated with Teflon are utilised in a chronic implant which has been used for preliminary experiments in information transfer by cortial stimulation. In the reported case a blind volunteer was able to read “braille” transmitted by cortical phosphenes at 30 letters per minute, much quicker than he was able to read tactile braille.


NEW PATENTS

CHEMICAL COMPOUNDS Activation Method for Electroless Plating

Rhodium and Ruthenium Compositions

U.S . Patent 3,904,404 A composition of the formula Z,TX, where Z is Rh or Ru, T is Fe, Co, Ni, V, Cr or Cu and X is Al, Ga, In, TI, Ge, Sn or Sb, is a useful ferromagnetic material suitable for inductive magnetic recording devices. A typical composition is Rh,FeSn.

Preparing Electrochemically Active Thallium Palladate C. CONRADTY French Appl. 2,249,038 Thallium palladate (TlPd,O,) is obtained in a pure crystalline form, cardinal red in colour as a cube with an atom at the centre of each face, for use as an electrochemically active coating for metal anodes.

INTERNATIONAL BUSINESS MACHINES CORP.

ELECTROCHEMISTRY Corrosion Resistant and Dimensionally Stable Electrode for Electrochemical Processes HOECHST A.G. British Patent 1,415,684 The electrode consists of at least one electrically conductive oxido compound of Ru and/or Ir with a metal selected from Ga, In, Cu, Zn, Co and T1.

Electrolytic Production of Hypochlorite Compositions

British Patent 1,417,949 Hypochlorite is produced by electrolysing an aqueous alkali metal chloride solution. The anode consists of a conductive base carrying a coating formed of 30-90y0 SnO,, 1.0-1074 Sb,O,, 1.0-50% of at least one Pt group metal oxide, and 0.5-30% of a valve metal oxide, e.g. Ta ,OL.

DIAMOND SHAMROCK CORP.

ELECTRODEPOSITION AND SURFACE COATINGS Composite Structure IMPERIAL METAL INDUSTRIES (KYNOCK) LTD. British Patent 1,412,836 A composite structure consists of a precious metal, particularly Pt, Ir, Rh, Pd, Os, Ru and Au (alloys), bonded to a substrate of a film- forming metal, and is made by assembling a sheet of precious metal foil between a substrate of a film-forming metal having a higher electrical conductivity core and a protection, and a lubri- cation material.

- BELL & HOWELL CO. U.S. Patent 3,900,320 A plastic or ceramic is coated with a 20-3000 A film of a mixture of a Pd salt in a binder. A dry film of this thickness is produced from a solution of 0.05 parts PdC1, and 0.25 parts vinyl chloride copolymer in IOO parts MEK. The coated surface is heated to pyrolyse the binder and the residual metal to catalyse subsequent chemical plating.

Chemical Metal Plating

U S . Patent 3,900,614 SnCI,/PdCl, sensitising solution is applied to a surface which has the required pattern delineated in reducing agent. Only these patterned areas acquire the required chemical plating nuclei.

WESTERN ELECTRIC CO. INC.

LABORATORY APPARATUS AND TECHNIQUE Catalytic Fluid Heater

U.S. Patent 3,910,255 The heater has a housing in which is contained a Cu tube formed into a series of concentric helical coils, and a number of perforated A1 plates that are supported by the coils in various symmetric locations along the vertical axis of the Cu tube. The undersides of the plates are coated with a catalyst, e.g. of the Pt metal group, for com- busting H,, reformed natural gas or low CO- content manufactured gas. The fluid to be heated flows through the Cu tube.

Oxygen Detector Having a Platinum Elec- trode on a Zirconia Electrolyte

U.S. Patent 3,914,169 An 0% detection device consists of a first electrode layer, an intermediate ZrO, layer and a second electrode layer consisting of 7697.6% Pt and 1.2-12% Al,08 and/or a lanthanide oxide.

INSTITUTE OF GAS TECHNOLOGY

E. I. DU PONT DE NEMOURS & CO.

HETEROGENEOUS CATALYSIS Treatment of Platinum Group Metal Re- forming Catalysts

British Patent 1,412,277 The activity of fresh reforming catalysts containing Pt group metal is improved by treatment at 400-55o"C with a gas containing O.~-ZO% free 0,, 5-500 p.p.m. Ci, HCI, C1-containing compound, and 50-20,000 p.p.m. H,O, then stopping the injection of C1, but continuing the operation

THE BRITISH PETROLEUM GO. LTD.


at the same 0, and H,O concentrations and the same or reduced temperature and then rcducing the catalyst at 350-550”C.

Petroleum Additives

British Patent 1,414,622 Supported catalysts for I.C.E. exhaust systems are activated or re-activated by supplying a suspension or solution in a hydrocarbon solvent of one or more metals or mixtures or alloys containing one or more metals or compounds selected from Ru, Rh, Pd, Ir, Pt, Ag and Au into the engine exhaust gas stream at a point upstream of the catalyst support, or (b) supplying to the engine a fuel and/or lubricant to which such a suspension or solution has been added.

Ruthenium Promoter JOHNSON, MATTHEY & CO. LTD. British Patent 1,415,155 A process for reducing NO, or oxidising CO and/or hydrocarbons uses a catalyst comprising a support of an inert material, preferably wash- coated and finally impregnated or coated with a metallic mixture or alloy which contains 5-7~7;~ preferably ~-Io”/, Ru; 5-30%, preferably 5-20?:, base metal chosen from Al, Mg, Cr, Mo, M, Mn, Fey Co, Ni, Ti, V, Cu, Ag, Zn, Cd, Hg, In, T1, Bi, Sn, Pb, Sb, the lanthanides and the actinides, and the balance Pt in an amount { 596.

Catalyst for Reducing Nitro-compounds BAYER A.G. British Patent 1,416,612 A supported catalyst for the reduction of nitro- compounds consists of O.I-IO~~ Pd metal and 0.1-5y; V (metal or compound) supported on an A1,0, at least 20y0 of which has been converted into Li-A1 spinel.

JOHNSON, MATTHEY & CO. LTD.

1-20y0 Rh/Pt Catalysts

Britisla Patent 1,417,544 A catalyst of particular use in the catalytic vapour- phase oxidation of C-containing compounds, e.g. CO and the lower hydrocarbons, but also of use for the reduction of NO, and the steam reforming of naphtha to produce methane, consists of a support of inert material, an intermediate layer of a refractory oxide, at least 5% of which is constituted by one or more oxides selected from Sc, Y and lanthanide oxides, and finally a layer of a mixture or alloy of Pt and Rh, the Rh being present in less than 20% of the total metal content of the mixture or alloy.


1-20y0 Rh/Pt Catalysts - Oxidation Process JOHNSON, MATTHEY & CO. LTD. British Patent 1,417,545 A process for the purification of a gas containing a C compound and 0, comprises contacting the gas at an elevated temperature with an oxidation

catalyst comprising an inert support carrying a layer of a mixture or alloy of Pt and Rh, the Rh constituting less than 20 wt. % of the total metal content of the mixture or alloy.

1-20% Rh/Pt Catalysts - Reduction Process

British Patent 1,417,546 A process for the purification of a gas containing an oxide of nitrogen comprises contacting the gas at an elevated temperaturc and together with a reducing fuel with a catalyst comprising an inert support carrying a layer of a mixture or alloy of Pt and Rh, the Rh constituting less than 20 wt. ”/, of the total metal content of the mixture or alloy.

Regeneration of Damaged Zeolite-supported Metal Catalysts

U.S. Patent 3,899,441 Pd or Pt oxide catalysts finely divided on a zeolite support are regenerated by hydrating and ammon- iating to produce, e.g. Pt(NH2),(0H), or Pt(NH8),(0H), which being stronger bases than NH,OH will tend to combine with the original acid sites on the support. The catalyst is then dried and calcined in a dry, oxygen-containing gas stream at a controlled temperature between 500 and 1200°F.

Ruthenium-Zinc Oxide Catalyst for Steam Reforming BRITISH GAS CORP. U.S. Patent 3,904,544 A catalyst composition for steam reforming hydrocarbons to produce gases containing a major proportion of methane, consists of I-ZO% Ru, 30-500:~ Zn oxide and 65-35?; of an A1,0, carrier, the catalyst being prepared by co-precipi- tation from a solution of water soluble salts of Ru, Zn and Al.

Catalytic Ignition System

U.S. Patent 3,909,187 A supported Pt or Pd catalyst is used in a pilot ignition system for gas appliances which utilises a short-circuited, air-starved electrochemical cell or battery with an inert electrode and a metal electrode which will produce a small flow of pure H2 gas which is ignited on the catalyst.

Refractory Metal Oxide Coated Ceramic Honeycombs as Catalyst Support

US. Patent 3,909,452 A catalyst for the oxidation of organic compounds which would otherwise cause atmospheric contamination consists of an inert rigid porous refractory ceramic honeycomb coated with a first adherent catalytically active refractory metal oxide coating containing at least 50% A1,03 in which one or more of the oxides TiO,, ZrO,, HfO, and


UNION OIL CO. OP CALIFORNIA

INSTITUTE OF GAS TECHNOLOGY



T h o z constitute at least 50% of the refractory metal oxide and having a second coating of an alloy containing 1 3 0 % Rh, 0.01-25% base metal selected from Cr, Fe, Co, Ni, Cu, Ag, Zn, In, Sn and Nd and balance Pt.

Layered Rhodium and Nickel Catalyst for NO, Reduction MONSANTO ca. U.S. Patent 3,914,376 I.C.E. exhaust gases are treated to remove N0,in reducing conditions with a catalyst consisting of Ni fixed on an inert support and having Also3 deposited over the Ni and Rh dispersed on the A1,0,.

Rh/Pt - Stainless Steel Catalyst

U.S. Patent 3,915,898 In an arrangement for reacting at least two gases by passing them through a pack of catalytic gauzes, the pack consists of a first group of gauzes made of an alloy consisting essentially of Pt and Rh and a second group of gauzes disposed on the downstream side of the first group of gauzes for supporting the first group, the second group of gauzes being made of an alloy consisting essentially of Pt, Ni and Cr. The system is typically used in the oxidation of NH, gas to oxides of N and HzO during the manufacture of HNO,, and the second group of gauzes are made from an alloy containing 16% Pt, 6796 Ni, balance Cr.

Paraffin Hydroisomerisation Process W. R. GRACE & CO. U.S. Patent 3,917,739 A process for hydroisomerisation of 4-7C paraffins, at 400-650°F, 300-500 p.s.i.g. and H2 to hydrocarbon mole ratio of 3-10 : I uses a catalyst consisting of 0.1-1.5% Pt and/or Pd and 0.13% CeO,, the Pt or Pd hornogenously dispersed as crystallites in the 5-30 A size range, the metal being dispersed into H, form mordenite by contacting the base with a mixed solution of Pt or Pd nitrate and Ce nitrate followed by controlled calcination and reduction with H, at a temperature of 500-900°F.

Preparing Catalysts for Hydrocarbon Hydro- treatment COMPAGNIE FRANCAISE DE RAFFINAGE French Appl. 2,252,394 Hydrocarbon treatment catalyst consists of a refractory mineral oxide support which has acid sites and includes a halogenic element and the free or combined metals (a) O.OZ-Z% at least one Pt group metal, (b) o.oz-z% at least one of Zr, Ti and W, (c) optionally o .o~- I~ / , Sn.

Metallic Substrate Catalysts

French Appl. 2,257,336 A catalyst consists of a drawn metal support constituted by an Fe alloy which is heat and



oxidation resistant and which contains at least one of: 3-40% Cr, 1-10?; Al, traces -5% Coy traces -720/, Ni and traces -0.5% C, a first layer on the drawn metal support, consisting of an adherent coating containing 0,, e.g. as an oxide such as Al,O,, SO,, Ti, Zr, etc., oxides, and a second catalytic layer including a metal chosen from Ru, Rh, Pd, Pt, Ag, Au and Ir, an alloy containing at least one of three metals, and alloys containing at least 10% of one of these metals and a base metal. The catalysts are useful in, e.g. oxidation of NH, in the manufacture of €€NO,, oxidation of organic compounds, e.g. methane, and reduction of NO, in I.C.E. exhausts.

HOMOGENEOUS CATALYSIS Improving the Dispersibility of Small Metallic Magnetic Particles in Organic Resin Binders

British Patent 1,416,127 0.1 % PdCl, is used in a solution in which particles of Co-I? are prepared by reacting a solution of a hypophosphite anion reducing agent and Co cations which are reducible to Co metal, the process including the step of reacting the Co-P particles with a H,SO,-containing solution to improve the dispersion characteristics of the particles in an organic resin.

Carbalkoxylation and Carboalkoxylation of Olefins

US. Patent 3,906,015 The carbalkoxylation or carboalkoxylation of olefins is catalysed by LzMXY, where M is Pt or Pd, X and Y are halogen or pseudohalogen and L is a phosphine, phosphite or thiophosphite, e.g. dichlorobis (methyl diphenyl phosphinite) Pd(I1) used in the conversion of hexene to methyl- n-hexanoate.

INTERNATIONAL BUSINESS MACHINES CORP.


0x0-reaction for Trietbanolmetbane and Methylpentanediol CHEVRON RESEARCH co. U.S. Patent 3,912,785 Triethanolmethane and 3-methyl-I, 5-pentanediol are produced by contacting a mixture of 3-methy- lene-I ,g-pentanediol and 3-methyl-z-pentene-I , 5-diol with a rhodium carbonyl complex catalyst in homogeneous liquid phase with the mixture and in the presence of CO at a partial pressure of 25-5,ooo p.s.i.g. and Hz at a partial pressure of 50-10,000 p.s.i.g. and at a temperature of 75-250"C for a time sufficient to react at least 90% of the olefinic double bonds.

Hydroformylation of Unsaturated Organic Compounds UNION CARBIDE CORP. U.S. Patent 3,917,661 A hydroformylation catalyst to produce aldehydes is a complex of Rh, CO and a phosphine or


phosphite ligand. A claimed catalyst is used in the combination 84g (1.0 mole) hex-I-ene, Isog acetophenone, 25g tri-n-butylphosphine and 2.0g tris(tripheny1phosphine) R h carbonyl hydride, which upon charging with CO+H2 synthesis gas and heating to 80"C, gave a product with 85% unreacted hex-I-ene and 15% aldehydes.

CHEMICAL TECHNOLOGY Recovery of Platinum Group Metals MATTHEY RUSTENBURG REFINERS (PROPRIETARY) LTD. French Appl. 2,254,648 Pt, Rh and I r salts in aqueous solutions are separated and purified by (a) adjusting the p H of the solution, (b) contacting the acid solution with an oxidising agent to oxidise all the I r present to Ir(IV), (c) contacting the oxidised solution with an organic compound including Nz chosen from the group formed by secondary or tertiary amines, and quaternary ammonium compounds, and (d) withdrawing from the oxidised solution an organic phase including practically all the Pt and Ir present associated with the organic compound used in (c). The Ir is subsequently separated from the organic phase containing Pt by, (e) contacting the organic phase with an aqueous solution of a reducing agent.

Platinum Group Metals Separation using H2SO4 MATTHEY RUSTENBURG REFINERS (PROPRIETARY) LTD. German Offen. 2,512,559 A process for refining and separation of Pt group metals from mixtures also containing Ag and base metals comprises contacting a solid, particulate mixture, preferably a powder, of the metals or metal compounds with concentrated H,SO, at a temperature sufficient to convert the base metals and Ag to H,O-soluble sulphates and dissolving out these sulphates into dilute H,SO, or HaO to leave a residue rich in precious metals.

GLASS TECHNOLOGY Transparent Glass or Plastic with a Reflecting Metal Layer W. C. HERAEUS, G.m.b.H. British Patent 1,419,036

the solution is denitrated because of the volatility of Ru at high temperature.

ELECTRICAL AND ELECTRONIC ENGINEERING Met allising Compositions

British Patent 1,419,549 A metallising composition, especially useful for printing metals on to substrates prior to firing to make electrical, e.g. microcircuit elements consists of finely divided metal particles, e.g. Pd and/or Au and/or Ag and/or Pt, dispersed in a long-chain saturated polymer of castor oil.

Low Temperature Coefficient of Resistivity Cermet Resistors GLOBE-UXION INC. U. S. Patent 3,899,449 A cermet resistor composition having a low temperature coefficient of resistivity for firing on a substrate composed of high temperature, electrically nonconductive material consists of a conductive phase of I .OO-IO.OO~~ V oxide and 1.00-30.00% RuO, and 50.00-98.000/, of an interdispersed glass phase. The glass phase is composed of 35.00-45.000/, Pb oxide, 15.00- 25.00% B203 and 30.00-40.000/~ SiO,.


TEMPERATURE MEASUREMENT Thick Film Resistance Thermometer

British Patent 1,415,644 A temperature sensitive element for use as part of a resistance thermometer consists of a substrate of electrically non-conducting material, e.g. a wafer of A1,0,, carrying an electrically conducting tortile path consisting of fused vitreous material loaded with electrically conducting particles made from a metal chosen from the group Au, Ag and the Pt group metals.


Heat MEDICAL USES

Transparent glass or plastics has an intermediate layer of a volatilisable metal compound deposited on one side of it, and on the compound is deposited a heat reflecting Ag alloy layer which consists of 80-95% Ag, and 9 2 0 % of one or more of Pd, Ni, Cd, and Si. The alloy layer has a transmission of light in the visible spectrum of 3 5 4 0 % .

Formation of Phosphate Glass GELSENBERG A.G. British Patent 1,421,219 During formation of a phosphate glass from a solution or slurry of radioactive waste materials,


Pharmaceutical Platinum Compositions

U.S. Patent 3,904,663 A complex active against tumours in mice is a Pt(I1) complex of an optionally substituted o-phenylenediamine, e.g. a PtClZ-4,g-dimethyl- o-phenylenediamine complex.

Dental Gold Alloy

German Offen. 2,424,575 An alloy which adheres to porcelain contains 80-90% Au, 5-15% Pt, 0.1-274 In, G-2% Sn, 0.05-o.5% I r and 0.5-3% Rh.

RUSTENBURG PLATINUM MINES LTD.

DEUTSCHE GOLD- & SILBER-SCHEIDEANSTALT

platinum metals review - johnson matthey

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