PLATINUM METALS REVIEW...traffic density occurs. As a result, increasingly severe legislation has...

PLATINUM METALS REVIEW

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

VOL. 1 6 J U L Y 1 9 7 2

Contents

Automobile Emission Control Systems

Protection of Gas Turbine Blades

Solubility Relationships in the Ruthenium-Platinum System

The Electrodeposition of Osmium

Vitreous Palladium Alloys

Resistance Ratio and Purification of Platinum

An American Pioneer in Platinum Metal Research

Abstracts

New Patents

N O . 3

74

87

88

90

91

94

101

105

112

Communications should be addressed to The Editor, Platinum Metals Review

Johnson, Matthey & Co Limited, Hatton Garden, London EClP IAE

Automobile Emission Control Systems PLATINUM CATALYSTS FOR EXHAUST PURIFICATION

By G. J. I

Fig. 1 The Johnson Matthey exhaust catalysts consist of promoted p la t inum metals supported o n a ceramic honeycomb. T h e catalyst i s housed in a stainless steel reactor similar in size and shape to a conventional silencer. Both elliptical and cylindrical uni ts of various sires are produced, depending on the space beneath the vehicle to beJitted and on the capacity of the engine o n that vehicle

particulate emission standards. The relative importance of exhaust emission control is reflected in the following figures, which represent the sources of pollution on a car :

Crankcase 20% Carburettor 904 Fuel Tank 6% Exhaust 65%

and further discussion will concentrate on this aspect.

Exhaust emission levels for 1972 model year onwards are measured over a complex driving cycle of 23 minutes duration simulating urban traffic conditions (Fig. 2), the test

being carried out with the vehicle on a roller dynamometer facility. The exhaust is collected from the point when the engine starts to when it stops by constant volume sampling (CVS test). A revised procedure of the CVS test has been introduced for 1975-76 model years incorporating both cold and hot start conditions, a weighted mean of the cold and hot starts being used to calculate the emissions per test in grammes per mile.

U.S. Federal legislation, which is enforced through the Environmental Protection Agency (E.P.A.) also calls for emission control systems

Table I

1975**

Platinum Metals Rev., 1972, 16, (3) 75

Trends in U.S. Federal Legislation Governing Automobile Emissions

co HC NC Particulate Evaporative

**Introduction of revised CVS test *Introduction of CVS test

prjmile prjmile prjmile prjmile g/test

1972*

1973

1976

2

2

2

2

3.4 3.0 0.41

0.41

39

28

3.4

3.4

3.1

3.1

0.4

0.1

0.03

co prjmile

Fig. 2 A Marina test vehicle mounted on a roller dynamometer for the measurement of exhaust emissions over a complex driving cycle simulating urban tra$c conditions. During the 23 minutes of the cycle the exhaust is collected by constant volume sampling (CVS test)

to be effective for 50,000 miles road use on a car. The exact interpretation of 50,ooo mile durability of emission control components is at the present time a matter of debate but the E.P.A. have the option of allowing replace- ment of components, such as catalytic reactors, at any mileage interval.

Methods of Emission Control Control methods for exhaust emissions can

be roughly divided into the two categories of prevention and destruction. Preventive methods have led to the concept of leaner running engines through improved car- buretion, distribution and combustion, all of which aid reduction of CO and HC levels. Incorporation of exhaust gas recycling (E.G.R.), where a small proportion of inert exhaust is by-passed to the inlet manifold to dilute the combustion mixture for NO, control, forms the pattern of emission control system up to model year 1974.

The increasing severity of emission limits in 1975 and 1976 has forced automobile companies to concentrate on post-combustion treatment of exhaust gases by destructive

Platinum Metals Rev., 1972, 16, (3)

methods such as manifold air oxidation (Man Air Ox), thermal reactors, and catalytic reactors, and some combination of preventive and destructive techniques will form the optimum emission control package for these years.

Of the available destructive means, catalytic reactors are the most favoured because of their high efficiency at low operating temperatures, and the relatively few modifications required for their installation. Manifold air oxidation systems, aimed at reacting residual CO and HC in the hot exhaust manifold, suffer due to limited efficiency, and thermal reactors, aimed at reacting pollutants at high temperature, require high thermal efficiency and expensive reactor components. On the other hand, catalytic reactors can be designed to operate at typical exhaust temperatures, with high conversion efficiency, thus negating the need for expensive reactor components, although stainless steel exhaust systems and reactors are required for 50,000 mile durability.

Previous attempts at catalytic purification of exhaust gases have been thwarted by the

76

use of lead (anti-knock) and phosphorus (pre- ignition control) compounds in the fuel, since these compounds can rapidly poison catalysts. However, these compounds have been recog- nised as harmful pollutants, with the result that E.P.A. has called for progressive phasing out of their use by 1975. This involves redesign of engines to cope with lower octane fuels, but advances in petroleum refining using “Platforming” catalysts, recently re- viewed in this journal (5), will vastly contribute to the need for high octane lead-free and phosphorus-free fuel. Thus the way is now clear for catalytic reactors to form a viable part of the emission control concept.

Catalytic Exhaust Purification The aim of catalyst systems is to remove

CO and HC by oxidation to CO, and water, and to remove NO, by either reduction to N, or by decomposition to N2 and 0,. Un- fortunately simple NO, decomposition


catalysts are far too ineffective to be used in a car exhaust reactor, the weight of catalyst required being prohibitive. However, the reduction of NO, by the CO or HC present in the exhaust is a much faster reaction, allowing a viable reactor design.

The oxidation and reduction mechanisms involved have important implications for the type of emission control system to be used. As a result of this and because the 1976 model year imposes a much greater restriction on permitted NO, emission levels, separate systems have had to be developed for 1975 and 1976 models. Up to model year 1975 the required NO, emissions can be achieved by E.G.R., and, therefore, for 1975 the preferred system consists of an oxidation catalyst for control of CO and HC emissions and the E.G.R. engine modification for control of NO,. For the latter, secondary air is supplied to the exhaust for the catalytic oxidation using a small air pump. (Fig. 3.)

The 1976 emissions requiring lower NO, levels cannot be met using E.G.R., as the higher recirculation rate required imposes a severe power loss. Therefore, a second catalyst bed is used for the control of NO, and this operates in a nett reducing atmos- phere. Air from a pump is fed into the exhaust gas stream after the reduction catalyst. This feeds an oxidation catalyst for the control of the CO and HC emissions. Figure 4 shows the dual bed emission control system for 1976. A significant advantage of Johnson Matthey systems to meet 1976 standards for the catalytic control of CO/HC and NO, emissions is their compatibility with the 1975 system, thus reducing engineering costs for modification between 1975 and 1976.

Platinum Catalysts The vast experience obtained in the Catalyst

Research Department at Johnson Matthey, and at our associate company Matthey Bishop

Inc., has shown beyond doubt that the platinum group metals are the most active materials available for control of the type of pollutants produced by the automobile. Previous experience, particularly in organic fume and odour abatement (6, 7), and in nitric acid plant “tail gas” purification requiring NO, removal (8), supports this belief.

It is often mistakenly thought that the high intrinsic cost of platinum prohibits its use in automobile exhaust purification. Recent studies at Johnson Matthey in the U.K. and at Matthey Bishop Inc. in the U.S.A., have demonstrated that, due to its high catalytic activity, and as a result of advanced catalyst design, the contribution of the platinum metal is not a significant proportion of the overall cost of the emission control system and this platinum content is sufficient to maintain adequate activity and durability. Thus platinum availability is not a serious problem, providing the automobile manufacturers give


sufficient notice of their requirements for proper planning to take place to meet those requirements on an acceptable business basis.

Nevertheless, removal of exhaust pollutants by catalytic means using conventional platinum catalysts is not without its problems. The major difficulties arise in three aspects, namely the temperature of reaction, the chemistry of pollutant abatement, and the durability of the catalyst. The complexity of the problem is further enhanced by the fact that exhaust emissions, reaction temperatures and gas velocities vary widely with car- buretted air/fuel ratio and driving mode (idle, acceleration, cruise, and deceleration).

As the 1975 CVS test procedure incor- porates a cold start it is imperative that the catalyst becomes effective as soon as possible into the driving cycle, since with earlier catalysts some 90 per cent of the emissions commence within 75 seconds of the choked cold start. To meet the required limits the catalyst must operate preferably within 20 seconds of the cold start and therefore must possess low ignition temperature characteristics. Also catalysts must not operate above their maximum temperature limits, which can easily occur under full load-full speed conditions with poorly designed catalysts, this problem being enhanced by the exothermicity of the oxidative reactions.

The catalysts must be insensitive to air/fuel ratio, i.e. not affected by the relative concentrations of reacting components, and must operate effectively over a very wide range of space velocities (0-150,000 v/vh). A particular problem prevalent with the

reduction catalyst is the tendency of reduction catalysts to produce ammonia as a result of reduction of NO by either the hydrogen present in the exhaust, or hydrogen produced from a catalytic side reaction. Such ammonia is rapidly reoxidised to nitric oxide in the second stage oxidation reactor and thus reduces the nett conversion efficiency of the system for NO.

As previously stated the catalyst should have a life of at least 25,000 miles, and

preferably 50,000 miles. This means that the catalyst must be resistant to thermal and mechanical shock, to high temperature conditions caused by engine malfunction, to attrition by high gas flow and particulates, and to trace poisons in the system. Current legislation with respect to the latter has proposed that in gasoline, lead shall not exceed 0.05 g1U.S. gallon and phosphorus shall not exceed 0.01 g/U.S. gallon. These represent a massive reduction from conventional levels but could still present problems when using catalysts for the removal of gaseous emissions.

The Advanced Catalyst System Research in Johnson Matthey has con-

centrated on solving the specific problems outlined above with respect to exhaust emission control. Test systems such as those shown in Figures 5, 6 and 7 have been employed in the development of catalysts suitable for meeting the proposed emission levels.

Advances made include such features as low ignition temperature, high thermal stability and shock resistance. For example (Fig. S), the current generation of promoted platinum catalysts show: (a) the ability of oxidation catalysts to convert CO and HC at low exhaust temperatures, and (b) the ability of reduction catalysts to convert NO at low exhaust temperatures while main- taining minimal ammonia formation. The catalytic activity is also insensitive to car- buretted air/fuel ratio providing the catalyst is operated in the appropriate oxidising or reducing exhaust stream. Operation of these catalysts at temperatures of IOOO~C, typical of engine malfunction, for periods of up to 24 hours has shown no serious loss in performance. Similarly, extended tests on static engines have demonstrated the ability of these catalysts to maintain effectiveness even with trace poisons such as lead and phosphorus present in the fuel and lubricating oil. For example. tests using 0.05 g/gallon leaded fuel, and conventional lubricating oil con-


Fig. 5a

Fig. 5 Front ( a ) and rear (a) of simulated exhaust test rig at the Johnson Matthey Research Laboratories. The reactor shown i n (b ) synthesises the components of exhaust gas for preliminary catalyst evaluation tests and for studies of the reaction kinetirs involved in exhaust emission control

Fig. 56


Fig. 6 (above) A single- cylinder laboratory test engine (left) with its exhaust train (centre). Engines of this type are involved in investigations covering the activity of new catalyst systems, the durability of catalysts and the effects of various catalyst poisons o n catalyst life

Fig. 7 A static engine test bed using a two-litre Ford Pinto engine for the evaluation of catalyst performance. The rig i s equipped with a cycle programmer f o r durability tests on the catalyst and i t s reactor system


taining 0.070 wt.:; phosphorus, have shown very little deterioration in catalyst activity.

As a result two types of catalyst are now produced for automobile exhaust emission control. The CO/HC oxidation catalyst is described by the serial number AEC3A and the NO, reduction catalyst by the serial number AEC8A (known in parts of Europe as EC3A and ECSA, respectively). These consist of promoted platinum metals, specifically designed to operate as reductive or oxidative systems and are supported on ceramic honeycomb (Fig. I). The advantage of the honeycomb support in this system is that it offers low pressure drop, and hence low power loss on an engine, together with low attrition loss, and good thermal mechanical shock resistance.

The catalyst is housed in a stainless steel reactor (Fig. I) similar in size and shape to a conventional silencer. As the volume of exhaust to be treated is dependent on engine capacity, two basic sizes have been optimised, containing 55 in3 (900 cm3) of catalyst for cars up to 1.5 1 and 86 in3 (1400 cm3) of catalyst for cars from 1.5 to 2.5 1 capacity.

Higher capacities generally use a catalyst unit to treat the exhaust for each bank of cylinders on a V8 or V6 engine. These units are produced in both elliptical and cylindrical configurations to suit the space on the vehicle.

Although laboratory evaluation of the catalytic reactors forms an invaluable feature of our test programme, it would not be complete without the ultimate test against the US. Federal Regulations. For this reason Johnson Matthey have equipped two test vehicles with 1975 and 1976 catalytic emission control systems respectively.

The 1975 System A Chrysler Avenger 1500 cc vehicle,

equipped with an engine and emission control package to meet 1972 U.S. emission levels has been used as a 1975 test car. This vehicle, which is currently sold in the United States as the Plymouth Cricket, was equipped with a low compression engine possessing induction-hardened valve seats to suit low octane lead-free fuel.

Modifications to this vehicle (Fig. 9a) to meet 1975 emission levels included an E.G.R.


Fig. 9a

Fig. 96

Fig. 9 ( a ) (above) Chrysler Avenger (Plymouth Cricket) engine to meet the 1975 model year U.S. regulations, showing the secondary air p u m p and exhaust gas recirculation in- stallations.

( b ) Beneath this vehicle the CO/HC oxidation catalyst reactor has been installed in the place normally occupied b y u silencer (mufler) . T h e standard silencer i s further along the exhaust train


system recirculating exhaust from the front of the catalyst box to the inlet manifold, and a pump supplying air to the exhaust manifold just above the exhaust valves (Man Air Ox). The E.G.R. system was found suitable for meeting 1975 NO levels when giving about 8 per cent recirculation above 28 m.p.h., and presentcd no serious power loss problems. The Man Air Ox system, primarily designed to supply air to the catalyst, gave a marginal improvement in baseline CO and HC emissions, which helps prevent over-temperature problems in the catalytic reactor during particular driving modes.

The optimum position for the oxidation reactor was found from exhaust temperature surveys to be under the front passenger seat, and proved opportune for available space since the reactor replaced the front silencer of the existing exhaust system (Fig. gb). This position proved adequate for the required rapid reactor warm-up as a result of the low ignition temperature of the catalyst, and enabled the oxidation reaction to commence within 20 to 30 seconds of a cold start.

A second aspect of low ignition temperature proved to be the ability to site the reactor

1975 limits

Avenger

co HC NO, g/mile glmile glmile

3.4 0.41 3.1

0.85 0.1 1 1.65

away from the exhaust manifold. Although the exhaust manifold is an ideal position for extremely rapid warm-up, it presents serious over-temperature problems at full speed, full load conditions. Thus our low ignition catalysts with high temperature stability enable an optimum position to be established for rapid ignition without over-temperature deactivation.

The Avenger emission control system has been optimised to give the typical exhaust emissions shown in Table I1 in comparison to the 1975 limits.

Following this work a durability run was commenced, and to date the vehicle has completed 26,500 miles with exhaust emissions remaining within the specified limits,


Table II

Avenger Test Vehicle Emissions Compared to 1975 Limits

Fig. I l a

Fig. l l b

Fig. I I ( a ) (above) Marina engine to meet the 1976 model year U.S. regulations, showing the secondary air p u m p and other minor modijications. (b) Beneath this vehicle the NO, reduction catalyst reactor is at the top of the picture at the start of the e.&ust train. Below i t can be seen the oxidation catalyst reactor. T h e conventional silencer further along the exhaust train i s not shown in this picture


co HC g/rnile gimile

Zero miles travelled 8.76 0.76

26,500 miles travelled 5.81 1.20

During the test no significant increase was observed in NO and CO emission levels, but HC levels are seen to rise somewhat throughout the test (Fig. 10).

Comparison of untreated exhaust emissions at zero and 26,500 miles (see Table 111) has shown a substantial increase in raw hydro- carbon emissions from the engine that in part accounts for the increase in levels throughout the test. (See Fig. 10).

The attainment of over 25,000 miles within 1975 limits using catalytic reactors represents a major contribution to the emission control concept, and demonstrates the feasibility of emission control within the specified limits for 50,000 miles.

NO, gimile

1.57

2.37

The 1976 System Future development of exhaust emission

catalysts is now concentrating on the dual bed system for 1976 requirements. A Morris Marina 1800 cc vehicle, with a low compression engine suitable for lead-free fuel, has been equipped with a dual-bed catalytic converter (Fig. I I). An air pump installation similar to that used on the Avenger supplies

Marina Test Vehicle Emissions Compared to 1976 Limits

1976 limits

Marina 1.78 0.17 0.25

air to the oxidation catalyst midway between the reduction and oxidation beds. Due to the higher temperatures required for efficient NO reduction (Fig. 8) the first reactor is installed close to the exhaust manifold. This, however, does not create overheating problems, as would be found with an oxidation catalyst in this position, since the heat generated by reaction in this system is minimal. The oxidation catalyst is again installed under the front passenger seat, and, although thermal lag due to the reduction box has been observed during cold starts, the low ignition catalyst has fully coped.

This vehicle is at present completing optimisation trials prior to a 50,000 mile durability run, but has demonstrated that emissions well below the 1976 levels can be achieved using the Johnson Matthey dual-bed catalyst system (See Table IV).

We have demonstrated the technological feasibility of Johnson Matthey catalysts complying with the United States exhaust emission regulations for model year 1975. These catalysts are currently under evaluation by most of the major car companies throughout the world, and further work is in progress to enable car manufacturers to meet the emission regulations by catalytic means.

Further development of these catalyst systems is under way, particularly with respect to the more stringent requirements for model year 1976, and new catalyst formulations offer great promise in those areas where problems remain to be solved.

References I A. J. Haagen-Smit, Ind. Engng. Chem., 1952,

z A. J. Haagen-Smit and M. M. Fox, Ind.

3 L. H. Rogers,?. Chem. Educ., 1958, 35, 310 4 K. L. Chass, P. S. Tow, R. G. Lundie and

N. R. Shaffer, Air Pollution Control Assn. J., 1960,10, 351

5 E. L. Pollitzer, Platinum Metals Rev., 1972, 16, (2), 42-47

6 G. J. K. Acres, Platinum Metals Rev., 1970, 14, (I), 2; Ibid., 1971, 15, (I), 9; Ibid., (4), 132

7 G. J. K. Acres, Ibid., 1970, 14, (3) , 78 8 J. B. Hunter, Ibid., 1968, 12, (I), z

441 1342

Engng. Chem., 1956, 48, 1484


Table Ill Avenger Test Vehicle Emissions

before Exhaust Treatment

co HC NC gjmile gjmile gjmile

Table IV

3.4 0.41 0.41

Protection of Gas Turbine Blades A PLATINUM BARRIER LAYER FOR NICKEL ALLOYS

The nickel-base alloys developed for use as gas turbine blades have to cope with severe conditions of both stress and corrosive environment at temperatures which are continually being pressed higher and higher in the interests of thermal efficiency and specific output of the engines. Whereas increasing high-temperature strength has progressively been achieved by alloy pro- ducers over the last thirty years, it has not always been possible to combine this with adequate corrosion resistance, particularly against the combined attack of sulphur corn- pounds and chlorides, which may arise either from the fuel or in marine environments from the ingested air. Surface coatings have therefore been developed to give added protection against corrosion, and a number of proprietary processes, mainly involving aluminium, silicon or chromium, are in use at the present time.

They are applied by spraying, evaporation or electrodeposition on to the prepared alloy surface and are thermally diffused to key to the basic alloy. While such coatings are effective in controlling corrosion they have a limited life, since at the operating temperature continued diffusion of the protective elements into the underlying alloy takes place; an effective diffusion barrier has therefore been sought.

Giinter Lehnert and Helmut Meinhardt of Deutsche Edelstahlwerke (D.E.W. Tech. Ber., 1971, 11, (4, 236) claim that an electrolytically deposited layer of platinum less than 10 pm thick is effective; it is followed by a pack-aluminising treatment during which the aluminium and platinum interdiffuse. The details of the process are not given, but the properties of the coating when applied to the alloy ATS 290-G are outlined, particularly

aluminide coating. Oxidation tests in burnt natural gas at 1100-C showed that the duplex coating had a life (measured by the extent of the plateau in the weight change curve) exceeding four times that of the simple coating, and metallographic examination showed that the corrosion proceeded uniformly, whereas deep penetrating attack took place with the simple coating. Cyclic corrosion tests in burnt kerosene with additions of sulphur and sodium chloride and a peak temperature of 1120°C showed an improvement of 230 per cent for the duplex coating.

I t is also claimed that by virtue of the high throwing-power of the platinum electrolyte used an effective coating can be applied on the inside of cooling passages in air-cooled blades, even when these involve 10 mm deep holes only 0.4 m in diameter. A 15 pm coating of LDC-2, involving only z to 3 [Am thickness of platinum is claimed to give a better performance than a 60 pm coating of the simple aluminide type. An LDC-2 coating degraded by interdiffusion with the base metal can be removed and renewed.

The new coating shows promise of providing a dear advance on the current protective coatings, although it must be noted that all the tests described relate to its application to ATSz9o-G, an alloy containing only IZ per cent chromium. Considerable improvement in the inherent corrosion resistance of nickel-base superalloys has been obtained in recent years by increase of the chromium content from the more normal figure of about 20 per cent to 25 per cent or more, without loss of high-temperature creep resistance, and it is perhaps uncertain whether any protective coating will then be necessary. It is nevertheless helpful to engine builders to know that alternative solutions to their

in comparison with those of a conventional problems are available. W. B.

Platinum Metals Rev., 1972, 16, (3), 87-87 87

Solubility Relationships in the Ruthenium-Platinum System By Joan M. Hutchinson Johnson Matthey & Co Limited Research Laboratories

Ruthenium hardens platinum very effectively and the dilute solid solutions thus obtained are strong, ductile, and remarkably resistant to corrosion. In view of their wide application in electrical technology and in the manufacture of jewellery it is surprising that little has hitherto been published on the true nature of these valuable noble metal alloys. Until very recently the widths of the primary solid solutions at each end of the diagram were very uncertain. Whereas early Russian workers had suggested that platinum would dissolve at least 70 atomic per cent (I) and probably 79 atomic per cent (2) of ruthenium,

more recent investigations at the Battelle Memorial Institute (3) indicated that the solid solubility of ruthenium in platinum was only about 32 atomic per cent.

Practical experience within the Johnson Matthey Research Laboratories supported the view that the solubility of ruthenium in platinum was very high indeed. Although difficulty was experienced in working alloys containing more than about 30 atomic per cent of ruthenium this was invariably found to be associated with internal and grain boundary oxidation effects, which occurred whenever these alloys were heated in air to


temperatures much in excess of 900°C. No evidence of a ruthenium-rich phase was found even in alloys containing 40 and 50 atomic per cent of ruthenium, and it has now been established that platinum at 1000°C will dissolve approximately 62 atomic per cent of ruthenium. This solubility increases to 70 atomic per cent at 19oo0C.

The boundaries of the two-phase region separating the cubic platinum and hexagonal ruthenium solid solutions are shown in Fig. I . The solidus and liquidus lines in this diagram are purely tentative, but in view of the complete absence of intermediate phases in these alloys it seems evident that the system is, as indicated, of the simple peritectic type.

The experimental points defining the limits of the solubility of platinum in ruthenium were obtained without difficulty by micro-probe analysis, and showed little inconsistency. The solubility of platinum in ruthenium increases with temperature very slowly indeed and little precipitation from these solutions occurred on quenching. The solubility of ruthenium in platinum, however,

increases fairly rapidly with increasing temperature, and it was found that the high temperature structure of the saturated platinum solutions could not be fully retained by quenching. Considerable precipitation occurred, and this influenced the composition of the retained phases and reflected itself in the high hardness of the quenched duplex alloys. In the hardness curve shown in Fig. 2 a gently ascending line typical of normal solution hardening is followed by a well-defined hardness peak associated with precipitation across the whole duplex region.

Metallography provided supporting evidence for the phase boundaries shown in Fig. I. Thus, the microstructure of the quenched 70 atomic per cent ruthenium alloy shown in Fig. 3 displays a volumetric distribution of the two phases commensurate with the position of this alloy within the two- phase area. The So atomic per cent alloy shown in Fig. 4 contains only a small proportion of the platinum-rich phase, thus confirming that the alloy is just within the duplex boundary at IOOOT.


Fig. 3 ?'he microstructure of quenched 70 at.% ruthenium-platinum allo-y displays a volumetric distrihution of the two phases commPnsurate mith the position of this alloy zcithin the two-phase area

Acknowledgements are due to Mr J. H. F. Notton for the micro-probe analysis.

I N. V. Ageev and V. G. Kuznetsov, Zzv. Akud. h'uuk S.S.S.R. (Khzm.) , 1937, 753-755

The Electrodeposition of Of all the platinum group of metals osmium

has the highest melting point and hardness, and it is chemically very resistant although oxidised in air above 400'C. These properties make it potentially useful in the form of an electrodeposited coating where the atmos- phere is not oxidising, as for example in reed relays, and in the last few years efforts have been made to develop a suitable electrolyte for this purpose.

A number of workers have reported un- satisfactory results with hexachloroosmate solutions, while other electrolytes that have been tried include molten cyanides, which gave granular deposits and were unstable, and alkaline electrolytes prepared from Os04 and sulphuric acid. The latter showed some promise, but now further and more successful results with hexachloroosmate baths have been reported by J. M. Notley of International Nickel in a paper presented to the annual conference of the Institute of Metal Finishing held in May 1972. (Trans. Inst. Metal Finish., 1972, 50, (2), 58).

The advancement described in the paper is the stabilisation of the electrolyte by addition of (i) potassium chloride to suppress hydrolysis of the hexachloroosmate to osmium

Fig. 4 The microstructure of 80 at.')" ruthenium- platinum. This alloy contains only a small proportion of the platinum-rich phuse, thus co@rming that it is just within the duplex boundary at ZOOU'C

2 V. A. Nemilov and A. A. Rudnitskii, Izv . Akad. Nuuk S.S.S.R. (Khim.), 1937, 33-40

3 R. I. Jaffee et al., AIME Metallurgical SOC. Conferences, Vol. 11, Refractory Metals and Alloys, 383-463 (especially ~IS-~ZO), Intcrscience Publishers Inc., New York, 1961

Osmium dioxide, and (ii) buffer the pH at

of potassium bisulphate -1.5. Any dioxide that

to is

precipitated is redissolved by chlorine generated at the anode. If the bath is being operated at too low a current density to produce chlorine then a short burst at high current density is usually sufficient to redissolve the dioxide.

The osmium is deposited at I to 4 A/dm2 at 70'C with a current efficiency of 20 to 30 per cent, and plating rates up to 4 pm/h. The deposits are bright and although cracked at thicknesses greater than 1.5 pm may be obtained up to 10 pm thick.

Very careful control of the electrolyte at pH 1.0 to 1.5 is necessary to prevent precipitation of OsO, on to the cathode.

Details are given of the synthesis of the plating salt, K,OsCl,, and of the preparation and analysis of the bath. The kinetics of the decomposition of the electrolyte were investigated and the results were used to adjust the composition to obtain a stable system. The effects of current density and temperature on plating rate and efficiency were determined for a bath using ammonium hexachloroosmate and a sulphamic acid/ ammonium sulphamate buffer. c. w. B.


Vitreous Palladium Alloys LOW-TEMPERATURE MEASUREMENT IN A NUCLEAR ENVIRONMENT

The philosophy of conventional resistance thermometry places considerable emphasis on the ability of metallic sensing elements to be used and retained in a state which approaches crystalline perfection. The high- purity wires are carefully supported to avoid strain and are also carefully annealed to eliminate lattice defects. Only in this way can the relationship between temperature and electrical resistance be uniquely defined, and platinum is still primarily responsible for embodying this relationship in concrete form. Departures from this policy of perfection have hitherto been fairly marginal and have involved, for example, very slight alloying with other noble metals to strengthen the platinum wire for industrial applications, or perhaps the use of iron-rhodium alloys for low-temperature applications (I) where pure platinum behaves in an anomalous manner.

An alternative approach to the problems of resistance thermometry is obviously required in those situations where ionising radiations are encountered and where heavy neutron fluxes inflict permanent and progressive damage on conventional metallic sensing elements. A viewpoint diametrically opposed to conventional ideas suggests that the best resistance element for low-temperature measurement in a high neutron flux would already contain so many lattice defects that radiation damage could be ignored and any irreversible strains which occurred would have only a marginal defect upon measuring accuracy.

Vitreous Alloys for Resistance Thermometry

Liquid metals have a completely random structure which is not seriously affected by radiation damage. If this random or amorphous structure could be frozen into a solid


state it would form, therefore, a resistance element containing the maximum possible number of lattice defects and would, therefore, be relatively immune to radiation damage. The implications of this approach have been recently explored by C. R. Tallman (2) of the Los Alamos Laboratory of the University of California during the development of the nuclear rocket engines needed for the Nerva and Rover programmes. Severe problems were encountered in the measurement of cryogenic temperatures in these engines. In addition to damage caused by neutron bombardment, internal gamma heating caused errors which sometimes approached several tens of degrees, and it became necessary, therefore, to consider amorphous alloy resistance elements which were less severely affected than crystalline wires by neutrons and gamma fluxes.

Amorphous Noble Metal Alloys The possibility of retaining, by extremely

rapid solidification, the amorphous structure of liquid metals was first demonstrated in 1960 by Duwez et al. (3) The gold-silicon amorphous foils then produced were quite unstable at room temperature and some decomposition occurred even during X-ray examination. It was soon established, however, that those alloys most likely to respond to the rapid quenching treatment were those forming low melting point eutectics, and in particular those in which the packing density in the liquid state was higher than in the crystalline form so that expansion occurred on solidification. Typical examples of such alloys occurred in the gold-silicon, gold-germanium and gold-tin systems (4, 5).

Low melting point eutectics are also formed in the binary alloys of platinum and silicon, in platinum alloyed with germanium or anti-

mony, and in the alloys of rhodium with germanium (6 ) . From all these platinum metal systems amorphous material can be retained by the extremely rapid solidification of compositions close to the eutectic. Among these binary alloys the palladium-silicon eutectic composition is noteworthy because of the stability of the vitreous phases obtained by solidification at cooling rates of the order of I G ~ deg C per second and above.

Although the palladium-silicon diagram is now known to be more complicated than was hitherto supposed (7), all the alloys containing 10 to 30 atomic per cent of silicon have a strong tendency to undercool (8). Amorphous phases can be successfully retained by rapidly quenching palladium alloys containing from 15 to 23 atomic per cent of silicon.

The resistance temperature curve of the Pd,,Si,, amorphous alloy is contrasted with that of the crystalline material in Fig. I. When slowly heated a strong exothermic reaction occurs at about 400°C and the amorphous metal reverts to the crystalline state. The heat evolved, about 1000 cals/mole, compares with the latent heat of solidification of this alloy. Although PdsoSiBo retains its amorphous state for at least 15,000 hours at 250°C, its use as a resistance thermometer

material is not very feasible because of the very low temperature coefficient of resistance.

Palladium - Silicon -Chr omium Alloys

The new resistance thermometer developed at the Los Alamos Scientific Laboratory uses an amorphous Pd,,Si,,Cr, alloy which has a high negative temperature coefficient of resistance even at very low temperatures. As shown by the curve on Fig. 2, the resistance ratio of the alloy decreases from 1.028 at t o K to 1.016 at 120 K, and temperatures in the range 1.2 to 20 K can be readily monitored.

The remarkable effect of chromium on the electrical characteristics of these amorphous palladium-silicon alloys has been interpreted by Tallman in terms of the Kondo effect, which in crystalline materials manifests itself as a small low-temperature resistivity perturbation caused by the presence of very small concentrations of magnetic impurities in a non-magnetic matrix. This anomaly appears to be magnified considerably in an amorphous matrix, which discourages strong magnetic coupling between the chromium atoms, and allows them, by virtue of their individual magnetic moments, to scatter the conduction electrons very effectively. As


The whole subject of amorphous metal alloys is now of considerable theoretical and practical interest and it is becoming very apparent that quenched noble metal eutectic alloys provide the bridge between the crystalline and vitreous state which has so long been required. Since the pioneer experiments of Duwez in 1960 more than zoo technical papers have been published on this rapidly expanding subject and a recent bibliographical review (9) deserves very close attention.

The true nature of the amorphous state was considered in considerable detail during the Autumn Meetings of the Metallurgical Society of A.I.M.E. and of the A.S.M. held in October 1971, and two recent papers by Polk (10) and Turnbull (I I) propose structural models for these metallic glasses that help to explain their visco-elastic behaviour. This can be simulated realistically by a geometrical structure based on random hard sphere packing. The large polyhedral voids inherent in such a structure (12) are conveniently occupied by metalloid atoms, thus explaining why approximately 20 atomic per cent of silicon or germanium, when added to palladium or rhodium, successfully stabilises the glassy condition. A. S. D.

the temperature falls, these individual magnetic moments become less randomised, thus causing more scattering and accounting, therefore, for the strong negative temperature coefficient of the amorphous alloy.

Applications The amorphous palladium-silicon-

chromium alloy can be cold rolled into foil and cut into resistance elements by conventional press-tool techniques. The preparation of thin foil resistance thermometers which can be bonded on to substrates of very low thermal capacity is, therefore, fairly straightforward. Such elements, it is reported, have a high electrical stability even after prolonged cycling between I and 600 K.

Although unsuitable for resistance thermometers, the amorphous binary palladium- silicon alloy might possibly be used for making radiation-tolerant strain gauges or balance resistances in circuits subjected to intense radiation. In such applications its low-temperature coefficient of resistance would be of considerable value.

References I B. R. Coles, Pkys. Lett., 1964, 8, (41, 243-246 2 C. R. Tallman, Ann. I .S.A. Conf. Proc., 1970,

3 W. Klement, R. H. Willens and Pol Duwez, Nature, 1960, 187, 869

4 T. R. Anantharaman, H. L. Luo and W. Klement, Trans. Metall. SOC. A.I.M.E.,

2.5, (21,619

Ig65J 233, 2014 5 B. C. Giessen, Z. Metallkunde, 1968, 59, 805 6 Pol Duwez, Tians. Metall. SOC. A.I.M.E.,

7 E. Roschel and C. J. Raub, Z. Metallkunde,

8 P. Lebeau and P. Jolibois, Compt. Rend.,

9 T. R. Anantharaman and C. Suryanarayana,

10 D. E. Polk, Acta. Metall., 1972, 20, (4), 485-

11 D. E. Polk and D. Turnbull, Acta Metall.,

12 J. D. Bernal, Proc. R . Soc., 1964, A280, 299

1967,60,607

'97I, 62J (I1), 840

1908, 146, 1028

J . Mater. Sci., 1971, 6, 1111

491

1972, 20, (41, 493-498


Resistance Ratio and Purification of Platinum By J. S. Shah and D. M. Brookbanks H. 11. Wills Phyrics Laboratory, University of Bristol

Accurate correlation between the purity and the properties of platinum is essential both to quantifi the properties of the metal with a view to its practical applications and to establish the behaviour of platinum as a rep- resentative metal f o r various physical and chemical measurements, The authors of this paper describe the systematic purijcation o j a platinum bar b.y vacuum-melting and zone- rejning. The j n a l residual resistance ratio obtained was very high. The purity of the platinum, as indicated by optical and mass spectrography, then compared toell with the best values previously reportd.

The importance of reducing the impurity content in platinum metal hardly needs to be emphasised, as the demand is growing for high purity platinum for industrial usage, such as thin film deposition in micro-solid state electronic circuits and thermometry. Indeed, it appears from a recent detailed account of the impurity concentrations by Chaston (I) that we have made considerable progress since the days of Chabaneau, Achard, Janety and Wollaston (2, 3). It should, however, be pointed out that the purity of the presently available bulk platinum is inadequate to perform some experiments in electron physics of the metal. This paper is essentially a part of the progress report of a systematic investigation of ways and means of obtaining ultra-pure platinum,

Platinum Metals Rev., 1972, 16, (3), 94-100

One of the most direct methods of deter- mining the purity of a relatively pure metal (particularly for the assessment of the suitability of the metal for experiments to determine electronic properties) is the measurement of the ratio of the resistance (or resistivity) of the metal at room temperature to that at liquid helium temperature, 1.e. :

(1) P300K

P4 2K s1.2 - -

This ratio increases with the purity of the metal. The precise relationship between the impurity content and the resistance ratio can be shown to stem from the well known Matthiessen’s rule which states that the observed resistivity p ( T ) of a metal at any temperature T consists of a temperature independent part p0, known as the residual resistivity, and a temperature dependent part p,(T), i.e.:

F(T)-F~ : P,(T) (2)

It is known that Matthiessen’s rule is not strictly obeyed in platinum. The argument pertaining to the residual resistivity however is valid. The residual resistivity arises because of the scattering of electrons by impurities and other lattice defects. It can be shown that commonly observed values of the residual resistivity of platinum are unlikely to be limited by dislocation-type defects. The contribution to the residual resistance by point defects other than impurities can be eliminating by annealing. p,(T), however, rapidly approaches zero at low temperatures and one can reasonably assume that at 4.2 K,

F(4.2 K) <

Thus it can be seen that S4.2 in well annealed samples would directly vary with the impurity content of the specimen.

The resistance ratio of a 6 m h diameter cylindrical bar of “Thermopure”* grade platinum is typically in the range 80-100. This particularly low value can be attributed to a high density of point defects arising from the cold work in the forged bar. The value of S4.2 can be raised fourfold, by a simple vacuum annealing, treatment at a relatively low temperature (-973 K). For instance, Flynn and O’Hagan (4) have reported a value S4.2 -393 in a platinum bar of diameter 20 mm, after the annealing treatment.

For “Fermi surface” determination of the metal a much higher resistance ratio is required. For instance, the de Haas-van Alphen (dHvA) effect, in which one en- deavours to detect variations in the dia- magnetic susceptibility with the variations in the applied magnetic field at low temperatures, is dependent upon the impurity content. The effect arises duc to the variations in free electron energy in the course of electron orbits as Landau energy levels cross Fermi energy. (In the space of this article it is impossible to define fully the various terms used here. A detailed description of the various phenomena may be found in Ziman (5)). To observe the effect it is necessary to fulfil certain conditions so that electrons have a reasonable chance of completing an orbit in the magnetic field without being scattered. The above conditions can be specified by the inequality

U C T > I (4)

where 7 is the scattering time in an orbit, and oc is a characteristic cyclotron frequency of electrons describing orbits and is defined by eH

m*c w c = ~ ( 5 )

where e is the electronic charge, c is the velocity of electromagnetic radiation, H is the applied magnetic field, and m* is the *Registered trade mark.

Platinum Metals Rev., 1972, 16, (3)

effective (cyclotron) mass of the electrons. The value of 7 is directly dependent upon

the impurity scattering; it is necessary to have high purity. The dHvA effect may be observed in platinum with relative ease (6, 7, 8, 9) if S4.2 -3000. For the observa- tion of another phenomenon known as Azbe1’- Kaner cyclotron resonance (AKCR) (10) one requires even higher resistance ratio. In this experiment one applies a magnetic field precisely parallel t u the surface of the metal specimen together with an imposed radio frequency (r.f.) alternating field. Under these conditiond electrons travel in helical orbits. If the frequency (mimp) of the r.f. field is such that

mimp n coC (6)

where n is an integer and fiiC is the cyclotron frequency defined by (5), then electrons are able to absorb energy from the r.f. field and one observes anomalies in the surface impedance in the direction of the field. The strength of the signal in the above- mentioned resonance phenomenon is dependent upon the magnitude of airnp~. In the case of platinum, to observe the AKCR phenomenon arising due to electrons with heavier effective masses, a resistance ratio of the order of 5000 is required. Further- more, it is also necessary to have a perfectly flat specimen area of a relatively larger (-6 mm) diameter to observe the effect at an easily attainable frequency of the imposed r.f. field.

High resistance ratios can be obtained in specimens of small diameter ( < I mm). For instance, Jackson (11) and Huebener (12) were able to achieve resistance ratios >7mo in wires of diameter 0.6 mm and 0.25 mm respectively, by a series of annealing treatment in air (temperature range 1673 to 773 K) followed by quenching and/or etching. The purification effect of air annealing in small diameter wires is also described by Misek (13) and by Polk and Kunz (14). Ketterson and Windmiller (9) have reported resistance ratios between 2000 and 3000 in float-zone

95

grown crystals of diameter -0.92 mm after a similar treatment. To date, the resistance ratio achieved in larger diameter rods (-several mm) are much smaller than the above-quoted values.

The detailed mechanism of the purification by annealing in air has not been investigated. It may, however, be suggested from the descriptions of the treatments that in the course of annealing, oxygen ‘combines’ with impurity atoms in platinum to render them ineffective or less effective as electron scattering centres. The reaction may take place either (i) because oxygen diffuses into the metal or (ii) because the impurity atoms diffuse out at the surface. The product of the reaction is either driven away because of high volatility, or because the end products of oxygen impurity combination are incapable of diffusing back into the metal, or because the presence of the above products does not contribute to the scattering as substantially as that due to original impurity atoms. In any case, following the approximate diffusion equation,

where Xz is the mean square distance covered by diffusing atoms in time t, and D is the diffusion coefficient of the diffusing species, it is easy to see that the length of the time required to complete the combination of oxygen with impurities in a large diameter platinum bar may be prohibitively long.

It was, therefore, decided to adopt a new approach based on combined zone refining and chemical treatments and to investigate correlation of impurity removal for each treatment with the aid of emission spectrographic and mass spectrometric analyses.

A nominally 99.999 per cent pure platinum rod (6 mm diam ~ 2 0 0 mm long) fabricated from a “high alpha” platinum with resistance alpha value ratio (i.e. P3731

Fig. 1 Resistance ratio.$ for plat inum were measured by a n eddy current decay method i n avhirh the resistance i s measured by observing the time decay of the potential generated by a n induced current due to the magnetic Jux penetration in a metal speri- men. The voltage funct ion approaches a simple exponential form and some typical voltage-time traces are shown here (time along the horizontal axis)

would set up large localised magnetic moments. It is therefore evident that the resistance ratio in the main is limited by the major impurities Fe, C and Pd. It is clear that particularly in the case of Pd the discrepancy between emission and mass spectrometric analysis is the largest. It is, however, not unusual in platinum to have Pd content -20 p.p.m. atomic.

The resistance ratios in the entire work were measured by the eddy current decay method originated by Bean, De Blois and Nesbitt (15). Briefly, in this method the

resistance is measured by observing the time decay of the potential generated by an induced current due to the magnetic flux penetration in a metal specimen. The voltage function V(t) can be shown to approach a simple exponential of the form

v(t) A P(T) CXP (t/: (T)) (8) where A is a constant for a given geometry, p(T) is the resistivity of a sample at a temperature (T) and -(T) is a time constant of the decay function. Some typical traces of the above function are shown in Fig. I.


Table I I Emission Spectrographic Analyses of Platinum Before and After

Melting and Zone Refining

Element

Pd

Rh

Al

c u

Fe

Mg

Si

Ag

In Vacu u m-heated

Pt

10

4

10

3

14

8

7

2

In In Vacuum-melted

Pt

8

2

N D

3

4

Table I l l Mass Spectrometric Analysis of the

Specimen Z.R.1.

Element

Pd Rh Au Al Bi c u Fe Pb

Si

Ti W C r N i 0 C

Mg

Ag

Concentration p.p.m. atomic

< 0.04 0.3 0.2 1

.:: 0.1 i.' 0.05

3

Further the l50 is separated from 13N, 99.999 per cent pure platinum are iron, ”C and l60 by an isotopic exchange of l50. The accuracy of the oxygen deter- (2) Palladium concentrations can be sub- mination by the above method is around stantially reduced b y melting and zone- *I p.p.m. (wt./wt.). refining.

In view of the above results and the argu- (3) Iron content can be reduced by zone- ment that the diffusivity of oxygen in liquid melting. platinum should be considerably higher it is (4) The electron scattering due to iron apparent that the oxygen had diffused through can be reduced by oxygenation. the bulk of the platinum during oxygenation. ( 5 ) Carbon content cannot be reduced by Accepting the above argument, the fact that zone-refining. the resistance ratio of the polycrystalline (6) S4.2 may be significantly improved by platinum improved considerably more than hydrogenation. (It is premature to that of the zone-refined section can only be discuss in detail the effect of hydrogen explained by assuming that oxygen-iron treatment here as it is hoped to present interaction is responsible for the improve- more conclusive evidence pertaining ment in the polycrystalline material. The to the individual purities in the near iron content in the polycrystalline material future.) is much higher than that in the molten section. Financial support from the S.R.C. during the It must also be accepted that carbon, which is earlier part of this work is gratefully acknowledged. probably in solution, cannot be driven away

References by oxidation reaction.

I J. C. Chaston, Platinum Metals Rev., 1971, A possible method of reducing the effect

of carbon is hydrogen reduction. Two further 2 D. McDonald, ‘A History of Platinum’, zone passes were carried out in the residual Metals Rev., r968, hydrogen pressure 1.33 x I O - - ~ Pa. The 12,142 resistance ratio measurements are given in 4 D. R- Flynn and M. E. O’Hagan, J . Res. Fig. 2. Thus after all the treatment listed J. M. Ziman, ‘Physics of Metals I,, above the resistance ratio achieved was 1969, C.U.P. S4.,-~600. I t is of interest to record that M- D. Staflau and A. R. De Vrooman~ phYs. Lett., 1965, 19, 81 by combining further treatment, to be 7 J. B. Ketterson, M. G. Priestley and J. J. described in a future article elsewhere, with Vuillman, p h ~ s . Lett., 1966, 2% 452

the chemical treatment described here, it ’* Ketterson~ phys. has been Possible to achieve s4.2-3200. 9 J. B. Ketterson and L. R. Windmiller, Phys. For the moment, however, it may suffice Rev. B, ‘97OJ 2~

10 M. Ya. Azbel’ and E. A. Kaner, Sov. Phys. to say that both emission spectrographic J.n.T.P., Iy57, 5, 533 and mass spectrometric analyses compare 11 J. J. Jackson, Proc. Internat. Symp. ‘Reinsto/J favourably with the purity obtained else- in Wissenschafz und Technip, Dresden, 1965

12 R. P. Huebener, Phys. Rev., 1964,146,490 where. For that Of N’B’S. Std’ 13 K. Misek, Czech. J . Phys., 1967, 17B, 647 681 (s4.2=2.110 measured on 0.51 mm 14 J. Polk and L. Kunz, Czech.?. Phys., 1971, diameter wire) (18) and other zone-refined

15 C. P. Bean, R. W. De Blois and L. B. Nesbitt, platinum (19).

16 F. S. Norton,?. Appl. Phys., 1958,29, IIZZ Conclusions 17 G. L. Selman, P. J. Ellison and A. S. Darling,

Platinum Metals Rev., 1970, 14, 14 18 Private communication: U.S. Department of

Commerce, Nat. Bur. Stds., 1970. See also Platinum Metals Rev., 1968, 12, 45

19 G. T. Murray, Platinum Metals Rev., 1970,

carbon and palladium.

122

1960, London D. McDonald,

Nut. Bur. Stds., 1967, 71C, 255

z l B ~ 269

J . APPl. P~Ys . , 1959,369 1976

The main conclusions Of the foregoing

( I ) The major impurities limiting resist- study can be summed up as follows:

ance ratio in commercially available 14, 42

Metals Rev., 1972, 16, (3) 1 00

instance.

Platinum

8 L. R. Windmiller and J. B. Ketterson, Phys. Rev. Lett., 1968, 20, 324

2

3

and J. B. Ketterson, Phys.

6

5 Ed.,

An American Pioneer in Platinum Metal Research THE LIFE AND WORK OF WOLCOTT GIBBS

By Professor Gcorgc B. Kaiifhian California State University at Frrsno, U.S.A.

This year marks the 150th anniversary of the birth of the man whom Ferenc Szabadvhry has called “the first great personality in American chemistry” (I). According to Donald McDonald, Gibbs’ work on the platinum metals “led to a considerable increase in the knowledge of the chemical properties of the salts of these metals but not to a satisfactory method for their separation on either an analytical or a commercial scale. His work was important and useful, and no record of the history of platinum should omit to mention it” (2). Strangely enough, Raleigh Gilchrist, in a review (3) that has been described as “the most effective condensation of acceptable wet methods of

Wolcott Gibhs 1822-1908

Born one hundred and jifty years ago, Gibbs received a training in medicine bat turned to chemistry and undertook a very varied programme of work, including some of the earliest research in the United States on the platinum metals. He has been called “the j i r s t great personality in

Ameriran chemistry”

[platinum metal] separations on a macro scale published before 1943” (4), does not mention Gibbs among his 813 references. Nevertheless, Gibbs’ method of separating rhodium by use of sodium sulphide ( 5 ) has more recently received attention (6). This brief review of Gibbs’ research on the platinum metals is given with the hope that perhaps some of his now neglected procedures may yet be employed in newer methods of separation and determination.

Gibbs’ Life Wolcott Gibbs-he dropped his first name

Oliver early in his career-was born in New York City on February 21st, 1822, of a


distinguished family (7). He graduated from Columbia College at the age of 19. After graduation he served in Philadelphia as assistant to Robert Hare, inventor of the oxyhydrogen blowpipe. In 1845, at the age of 23, he received the degree of Doctor of iMedicinc with a dissertation on a natural system of classification of the chemical elements. He never practiced medicine but in later life studied the physiological effects of chemical compounds upon animals.

Since at that time advanced scientific education was not readily available in the United States, Gibbs next spent several years studying in Europe. In 1849 he was appointed Professor of Chemistry at the newly established Free Academy, which later became the City College of New York and is now the City University of New York. He remained therc for fourteen years during which time he produced in collaboration with Frederick Augustus Genth his first really notable research, a memoir entitled “Researches on the Ammonia-Cobalt Bases” (1856)~ that has become famous in the annals of co-ordination chemistry. In 1863, largely as a result of his recent research on the platinum metals, he was called to Harvard University as Rumford Professor in the “Application of Science to the Useful Arts”, a position which he retained until his retire- ment in 1887. He continued to work in his private laboratory in his home at Newport, Rhode Island for several years. He died on December gth, 1908, at the age of almost eighty-seven.

More than any other one man, Gibbs introduced into the United States the German system of research as a means of chemical instruction, a practice which is now taken for granted. Known primarily as an experimentalist rather than a theorist, Gibbs’ work was extremely varied. In analytical chemistry, he is best known as the discoverer of electrogravimetry. He also invented several pieces of chemical apparatus. His later years were devoted to a vast, extremely complicated and almost unexplored field,

the chemistry of heteropoly compounds, which he called the complex inorganic acids. He was editor of the American Journal of Science and one of the founders of the U.S. National Academy of Sciences. His face is sculptured in relief on the wall of the Capitol in Washington, D.C.

Gibbs’ Researches Gibbs’ work on the platinum metals can

be divided into two parts-(I) osmium complexes (1858-1881), and (2) separation procedures (1860-1864).

Dioxotetraammineosmium(V1) Salts Gibbs and Genth peripherally dealt with

the platinum metals in their classic memoir of 1856 (8). On the theoretical side, they proposed “a new theory of the platinum bases” (platinum-ammines), while experi- mentally they prepared the hexachloro- platinates(1V) of their four cobalt-ammines. Yet their first publication devoted specifically to the platinum metals was a one-page “Preliminary notice of a new base containing Osmium and the elements of Ammonia”, published in March of 1858 (9). In this, their last joint publication, they pointed out that their “investigation of the ammonia- cobalt bases . . . led us to direct our attention to the production of similar compounds with other metals”.

Gibbs and Genth reinvestigated the yellow crystalline salt first discovered in 1844 by Edmond Fremy and called by him “osmia- mide” (10). This compound, formulated by Fremy in pre-Karlsruhe terms as NH,CI i OsO,.NH, (actually zNH,Cl.OsO,~(NH,),) was prepared by adding ammonium chloride to a solution of potassium osmate: K,[OsO,]

2H,O. Gibbs and Genth found that the compound, “of much interest from a theoretical point of view”, was the salt of a cation (in their older terminology, base) which Gibbs later called “osmyl-ditetramin” to distinguish it from the as yet undiscovered “osmio- ditetramin” (OS-~NH,, i.e., [OS(NH,),]~~,

-+ 4NHdCI 4 [OSO,(NHJ,]C~, ’- ZKCl +-


which, incidentally, has still not been discovered). They prepared the hexachloroplatinate(1V) of this cation as well as a well- defined crystalline sulphate, nitrate, and ox- alate. The full report including analysis was not published until more than twenty-three years later in 1881 (11) by Gibbs alone, who stated that:

“My researches on the metals of the platinum group were interrupted many years since by the want of a laboratory in which the separation and collection of osrnic hyperoxide, OsO,, could be effected without serious danger to the air- passages and to the eyes. . . . The experimental part of the work here published was finished long since. I have delayed its publication in the hope of rendering it more complete, and especially of generalising the results in various ways. . , .”

Gibbs found that the chloride decomposed on heating according to the equation: [OsOz(NH,).JCl,-t 0 s + ZNH,Cl+ zHZO f N ~ J thus furnishing “perhaps the most simple and convenient method of obtaining pure metallic osmium”. He also observed that a solution of the chloride produced a violet colour with potassium ferrocyanide. He described this reaction as “very delicate” and claimed that it “affords the best method yet discovered for the detection of minute quantities of osmic hyperoxide [OsO,] in the wet way”. Gibbs gave specific directions for this test, which he claimed made it “possible to recognise quantities of osmium too small to be detected by the characteristic odour of the hyperoxide”. He concluded his report by mentioning the possibility that, inasmuch as ruthenium forms RuO, analogous to OsO,, ruthenium might form a similar series of compounds [Ru02(NH,),]X,. Such compounds have still not been discovered.

Analytical Separations Inasmuch as Gibbs was primarily an

analytical chemist, it is not surprising that his research on the platinum metals was directed largely toward analytical applications. In a published letter of March 3oth, 1860, to one of the editors of the American Journal of Science (12), Gibbs, in addition to giving a preliminary report of his work on

osmium discussed above, declared: “I am confident that I shall be able to effect a perfect separation of all the metals of the platinum group”.

In 1850, the existence of alluvial native platinum in California was reported. It was found in the gold placers at the western foot of the Sierra Nevada (13) and was normally much richer in osmiridium than are the better known larger deposits. In 1861, Gibbs published the first of his series of three articles entitled “Researches on the Platinum Metals”, which firmly established his reputation as one of the foremost chemists in America. In his first article (14), he differentiated and contrasted the Siberian variety of osmiridium from the Californian variety. Although the amount of osmiridium obtained at the time did not exceed a few ounces for every million dollars’ worth of gold, Gibbs predicted “large quantities of the ore will be obtained whenever important practical applications of the metals contained in it shall create a demand”.

Gibbs then addressed himself to what had “always been considered as among the most difficult problems with which the chemist [had] to deal”, viz., the separation of the different platinum metals from each other. Gibbs felt that “much remained to be done, especially as the Californian ore differs from the Siberian in the greater relative proportion of Ruthenium which it contains”. In the course of his investigations, “at great expense of time and labour”, Gibbs was “able to test upon considerable quantities of material, nearly all the methods of working the ores of osmium, etc., which have hitherto been employed”. He gave critical evaluations, with modifications and improvements for the Californian ore, for the methods of Fremy (IS), Persoz (16)~ Weiss and Dobereiner (17), Wohler (IS), Fritzsche and Struve (IS), and especially Claus (20).

Claus’ method of treating Siberian osmiridium consisted of fusing it with a mixture of potassium hydroxide and potassium nitrate, powdering the cooled melt, and


dissolving the resulting soluble potassium osmate (K,OsO,) and potassium ruthenate (K,RuO,) in cold water. Gibbs found that with the Californian ore even after three or four successive fusions a large quantity of black matter insoluble in aqua regia still remained. He therefore suggested : (I) fusion of the ore with sodium carbonate prior to the fusion with the potassium hydroxide-potassium nitrate mixture, which greatly facilitated the subsequent action of the oxidising mixture; and (2) boiling the oxidised fused mass with water containing alcohol, which reduced the potassium osmate to potassium osmite (probably K20.30s0,), thus avoiding escape of toxic osmium(VII1) oxide, and decomposed the potassium ruthenate to a mixture of insoluble ruthenium oxides, which remained with the oxides of the other platinum metals.

In his second paper (21), Gibhs declared “the problem of the complete separation of the metals of the platinum group worthy of a new investigation”, and he proposed a method based on the results of his research on the reactions of potassium nitrite and sodium nitrite with all six platinum metals, which seems to be the first systematic study of the platinum metal nitro complexes.

In his third article (22), Gihhs presented a second general method of separating the four platinum metals (Pt, Ir, Rh, and Ru), which involved hexaamminccobalt(II1) chloride, the “luteocobalt chloride” first discovered by Genth in 1847 (23), reported by him in an obscure German-language journal published in Philadelphia (24), and described in great detail in Gihhs and Genth’s mono- graph of 1856 (8). The process was based upon the fact that the hexachlororhodate(II1) and hexachloroiridate(II1) of the hexa- amminecobalt( 111) ion are almost completely insoluble in boiling water and in boiling dilute hydrochloric acid, whereas the corresponding hexachloroplatinate(1V) and hexa- chlororuthenate(1V) are easily soluble.

Some of the substances formed in Gibbs’ separation schemes are still not too well

investigated, and a new study employing modern methods would be a fitting tribute to Gibbs and might simultaneously yield some interesting data.

The author wishes to thank the John Simon Guggenheim Memorial Foundation for a Guggenheim Fellowship, and the California State University at Fresno for a sabbatical leave.

References I F. SzabadvAry, “History of Analytical Chem-

istry” (Pergamon Press, Oxford, London, New York, 1966), 312-314

2 D. McDonald, “A History of Platinum: From the Earliest Times to the Eighteen- Eighties” (Johnson Matthey & Co. Ltd, London, 1960)

3 R. Gilchrist, Chem. Rev., 1943, 32, 277-372 4 F. E. Beamish, TaZanta, 1y60,5, 1-35 5 W. Gibbs, Chem. News, 1863,7, 61 ,73 ,97 6 N. K. Pshenitsyn, I. A. Federov, and P. V.

Simanovskii, Izve~t . Sektora Platiny i Drug. Blagorod. Metal., Imt. Obshch. Neorg. Khim., Akad. Nauk S.S.S.R., 1948,22,22-27

7 C. S. Pierce, The Evening Post, New York, Dec. 10, 1908; T. W. Richards, Ber., 1909, 42, 5037-5054, Science, 1909, 29, 101-103; F. W. Clarke,3. Chem. SOC., 1909, 95, 1299- 1312; Biog. Mem., Nat. Acad. Sci., 1910, 7, 1-22; C. L. Jackson, Am. J . Sci., 1909,28, 253-259; C. E. Munroe, Science, 1911, 34, 8 6 ~ - 8 6 8

8

9

I 0

I 1 I2

I3 I4 15 16 17

18 19

20

21 22

23

24

W.’ Gibbs and F. A. Genth, “Researches on the Ammonia-Cobalt Bases” (Smithsonian Contributions to Knowledge, Washington, D.C., 1856) W. Gibbs and I;. A. Genth, Am. J . Sci.,

E. Fremy, Ann. Chim., 1844, [3], 12, 521 W. Gibbs, Am. Chem.J., 1881,3,233-241 W. Gibbs, Am.3. Sci., 1860, [21, 29, 427-429 Anon., Berg-u Hattenm. Z., 1850, 9, 609-613 W. Gibbs, Am.3. Sci., 1861, [2], 31, 63-71 E. Frerny, Compt. rend., 1854, 38, 1008-1012 J. F. Persoz, Ann. Chim., 1835, 55,210 C. S. Weiss and J. W. Dobereiner, Ann. Pharm., 1835,14,15 I?. Wohler,Pogg. Ann., 1839,31,161 C. 3. Fritzsche and H. W. Struve, J. Prakt. Chem., 1846,37,483 C. Claus, “Beitrage zur Chemie der Platin- metalle” (Festschrift Universitat Kasan, Dor- pat, 1854) W. Gibbs, Am.J. Sci., 1862, [2], 34,341-356 W. Gibbs, Am. J . Sci., 1864, [2], 37, 57-61 G. B. Kauffman, Proc. X l l l th Int. Congr. Hist. Sci., Moscow, ~ 9 7 r , in press;J. Chem. Educ., in press F. A. Genth, Nordamerikanischer Monats- bericht f u r Natur- und Heilkunde, 1851, 2, 8-12

18583 [21, 25, 248


ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES Infrared Spectra of Carbon Monoxide Ad- sorbed on Alloys of the Platinum Metals. I. Investigation of Infrared Spectra of Carbon Monoxide Adsorbed on Ir-Pd Alloys of Various Compositions N. P. SOKOLOVA, 2%. Fiz. Khim., 1972,46, (I), 17- 171 Studies of the infrared spectra of CO adsorbed on 10, 50 and 90:h Ir-Pd at 30-400"c showed that introduction of I O ~ { ~ Ir into Pd increased its stability and heat desorption.

Diffusivity and Solubility of Oxygen in Platinum and Pt-Ni Alloys

1972, 3, (1) 65-72 L. R. VELHO and R. W. BARTLETT, Metall. Trans.,

The diffusivity and solubility of 0, in Pt were calculated from measurements of the permeation of 0, through heated thin walled tubes. The solubility is proportional to pt2. The diffusivity and solubility are expressed as a function of temperature in terms of exponential equations.

Transition from Ferromagnetknl to Para- magnetism in Ni-Pt Alloys M. J. BESNUS and A. HERR, Phys. Lett. A, 1972, 39, (2), 83-84 Magnetisation measurements on 5-75 at.(:,& Pt-Ni show that a transition from ferromagnetism to paramagnetism occurs at -59 at.?: Pt. Results indicate that these alloys may be classified as weak itinerant homogeneous ferromagnets.

Atomic Ordering and Magnetic Hardening in Pt-Pd-Pc Alloys s. SHIMIZU and E. HASHIMOTO, J . Japan Inst. Metals, 1972, 36, (11, 53-57 Atomic ordering and magnetic hardening in Pt-Pd-Fe in the composition range 0-60 at.(,!,& Pd, 0-50 at.94 Pd and 40-65 at.:/, Fe were studied. Optimum magnetic properties are obtained in 5 at.% Pd-Fe.

Fabrication of Two-phase Alloys in the Ruthenium-Gold-Palladium System R. SAVAGE and V. A. TRACEY, Mod. Develop. Powder Metall., 1971, 5, 273-286 A Ru-Au-Pd alloy was produced by infiltrating a Ru skeleton with a Pd-Au alloy or, alternatively, by liquid phase sintering of a compact of the elemental powders ; both methods were carried out at 1520-155o~C. The fabrication of the alloy into wire or strip using hot and cold working treatments is described.

Effects of Hydrogen Absorption in Palladium and Palladium-24Ob Silver Foils B. DUGGAN, J. P. G. FARR, J. B. KUSHNER and M. WISE, Nature Phys. Sci., 1972,236, (66, Apr. 3), 73-74 Thin foils of annealed Pd and 2400 Ag-Pd were hydrogenated electrolytically and studied by electron microscopy. Dislocations were produced, forming tangles which caused the foils to become opaque as hydrogenation progressed. Needle-like features were found, but no rifts. Ag-Pd foils resembled Pd, but there were fewer needles and the dislocation tangles accumulated less readily. The observations support explanations of X-ray line broadening on the formation of one phase from another in terms of lattice distortion.

Occurrence of Superconductivity in Simple Cubic (Aul,Pd,)Te2 Alloys W. Y. K. CHEN and C. C. TSUEI, Phys. Rev. B, 1972, 51 (3), 901-903 The superconducting transition temperatures (T,) and lattice parameters of metastable simple cubic (Au,-,Pd,)Te, alloys, where o < x G0.6, were measured as a function of x. As x increases, T, goes through a minimum of 1.6K near ~'0.05, and then increases steadily to a maximum of 4.5K at x -0.45 ; the lattice parameter shows a slight linear decrease as x increases. The trans- verse magnetoresistance for x=0.2 saturates at -2kG and has an unusually large value.

Influence of the Magnetostatic Interaction of Phases on the Magnetic Properties of Powders of the Fe, ,Pa,,, Alloy v. s. BOIDENKO, YA. s. SHUR, G . s. KANDAUROVA and L. M. MhGAT, Fiz. Metal. Metalloved., 1972, 33, (I), 54-58 The magnetic properties of powders were studied for Fe,,.,Pdo., alloy containing y1 and c1 phases, for the highly anistropic yI phase produced by corrosion of the c( phase, and for a mechanical mixture of y, with powdered Fe carbonyl similar to powdered Fe,.,Pd,.,. Comparison of results indicates the effect of magnetostatic interaction of the phases on the magnetic properties of the Fe,.,Pd,., powdered alloy.

Kinetic and Magnetic Properties of AUoys of the System Palladium-Iron. I. Temperature Dependence of Electrical Resistance

VOLKENSHTEIN, Fiz. Metal. Metallwed., 1972, 33, (31, 527-534 During studies of the temperature dependence of the electrical resistance of 0.5, 1.0, 1.5, 2.0, 3.0,

L. I . ABRAMOVA, G. V. FEDOROV and N. V.


8.0,20,25,50,60,75,93,98,99, 99.5 at.% Fe-Pd and of pure Pd at 1.8-3ooK the magnetic part of the effect was isolated for alloys with up to 8 at.?" Fe. The concentration dependence of the residual electrical resistance was determined for hardened and annealed alloys.

Magnetic Properties of Finely Dispersed Nondeformed Powders of Alloys of the Fe-Pd System

G. S. KANDAUROVA and L. M. MAGAT, Fiz. Metal.

Studies of the magnetic properties and phase state of IO-IO-- '~ Fe-Pd alloy powders with highly anisotropic -(,-phase led to a mechanism for magnetic reversal in these powders.

On the Compound PdAl and Its Alloys with Copper

Y. A. S. SHUR, N. G. ILYUSHCHENKO, V. S. BOIDENKO,

Metalloved., 1972,33, (31, 552-557

L. A. FANTELEIMONOV, D. N. GUBIEVA, N. R. SEREBRYANAYA, V. V. ZUBENKO, B. A. POZHARSKII and z. M. ZHIKHAREVA, Vest. Moskov. Univ., Ser.

PdAl was found to undergo polymorphous transformations at 560°C and 700°C. The phase diagram of the system PdAl-Cu is given.

Anomalous Viscoelastic Behaviours of Metallic Glasses of Pd-Si Based Alloys H. S. CHEN and M. GOLDSTEIN, J. Appl. Phys., 197% 43, (41, 1642-1648 The viscoelastic properties of Pd-Si based alloy glasses near the glass transition temperature was studied. Results are compared with those for other types of liquid. The temperature and stress dependence of the viscoelastic behaviour of these metallic glasses closely resembles that of a low molecular weight polymer glass.

Electronic Specific Heat of Ce,La,,Pd, Ternary Alloys R. D. HUTCHENS, v. u. s. RAO, J. E. GREEDAN and R. S. CRAIG, J . Phys. soc. Japan, 1972, 32, (2), 451-454 The heat capacity of the cubic CexLa,_,Pd, alloys was measured at 1.5-1oK. The alloys consist of single phases except in the region 0.3 4 x Go.5. The specific heats for x-1.0 and x-0.8 comply with Cp=yT-/3T3 with a high value for y; the heat capacities for the remaining compositions show marked deviations from this equation, and exhibit well-defined minima in the C,iT vs. T2 curves in some cases. Results are discussed in terms of a model for the electronic structure of these alloys.

Note on the Resistance Anomaly in Rh with Dilute Magnetic Impurities H . NAGASAWA, Solid State Comrnun., 1972, 10, (I), 33-36 The anomaly of the temperature dependence of

11, Khim., 1972, 27, (1),70-74

the resistivity of Rh with dilute magnetic impurities is discussed on the basis of the simple Friedel's sum rule and the difference of the d electron number between the impurity and Rh.

Electrical Resistivity of Giant Moment Systems: Ni-Rh R. w. HOUGHTON, M. r. SARACHIK and J. s. KOWEL, Solid State Conimun., 1972, 10, (4), 369-371 Electrical resistivity measurements at 2-70oK on Ni-Rh alloys, which have giant magnetic polarisa- tion clouds, reveal a magnetic scattering behaviour differing considerably from that of giant moment Ni-Cu alloys.

Energetics, Morphology, Crystallography, and Theory of Displacive Transformations in Xear-equiatomic Niobium-Ruthenium Alloys B. KISHORE, U.S.A.E.C. Rept. coo-I IP8-807, 1971, (Jun.1, 168 PP The displacive phase transformations in Nb-Ru alloys were studied using magnetic susceptibility, electrical resistivity, optical metallography and X- ray diffraction. Alloys containing 41-45 at.% Ru undergo a CsCl (p) to f.c.t. (p') transformation on cooling to room temperature; alloys containing >46 at.", Ru exhibit a two step CsCl (8) to f. c. 0. (p") transformation. A model for the transformation process is developed.

Investigation of the Ternary System Zirconium-Niobium-Ruthenium

RAEVSKAYA, I. G. SOKOLOVA and A. N. ESIPOVA, Vest. Moskov. Univ., Ser. I I , Khim., 1972, 27,

The Zr-Nb-Ru system was studied and isothermal sections at 1600T and 1050°C are presented.

Thermal E.M.F. and Ettinghausen-Nernst Coefficients of Rhenium and of the Platinum Group Metals v. F. NEMCHENKO, s. N. L'VOV, P. J. MAL'KO and v. N. DELIEV, Fiz. Metal. Metalloved., 1972, 33, (3), 540-545 The Ettinghausen-Nernst coefficient was determined during studies on the temperature dependence of the thermal e.m.f. of Re, Os, Ir and Pt at 100-r3oo K.

Experimental Determination of the Lattice Parameters of the Platinum Metals in the Temperature Range from -190 to 1709°C R. H. SCHRODER, N. SCHMITZ-PRANGHE and R. KOHLHAAS, 2. Metallkunde, 1972, 63, (I), 12-16 The lattice parameters of the Pt metals were measured at -189 to 1709°C. Supposed phase transformations of Rh and Ru above IOOOT were not found. The measurements were evalu- ated in terms of an equation of srate due to Bradburn and Firth to determine the exponent of

A. L. TATARKINA, E. M . SOKOLOVSKAYA, M. V.

(11, 64-69


an exponential potential. This evaluation gave equivalent results for Rh, Pd, Ir and Pt that were used successfully to calculate the melting points.

CHEMICAL COMPOUNDS Crystal Structure of Platinum Tetrachloride M. F. PILBROW,J. Chem. soc., Chem. Commun.,

PtCl, was studied by X-ray powder techniques. It is isostructural with a-PtI, and PtBr,; the unit cell is orthorhombic, witha=11.37, b=13.65 and c=5.95 A.

Two Forms of cis-Dibromodiammine- platinum

0. N. EVSTAF'EVA, Zh. Neorg. Khim., 1972, 17, (2), 556-557 The infra-red spectra and heat capacities of the yellow and red forms of cis-[Pt(NH,),Br,] were studied with a view to explaining why the two modifications exist.

The Crystal Structure of K,PtCl, and K,PdCl, with Estimates of the Factors Affecting Accuracy

1972, (512 27C-271

V. A. PALKIN, N. N. KUZ'MINA, V. E. GORBUNOV and

R. H. B. MAIS, P. G . OWSTON and A. M. WOOD, CrYJt., 1972, B28, (21, 393-399

The structures of K,PtCl, and K,PdCl, were determined with improved accuracy and new values for the interatomic distances are presented. Details of the various corrections applied to these measurements are given.

Electrical Conduction Studies on the Par- tially Oxidised Metal-atom Chain Compounds K,Pt(CN),Clo.,,.2.6H,0 and K2Pt(CN),Br,,,. 2.3 H,O P. S. GOMM and A. E. UNDERHILL, J. Chem. Soc.,

The a.c. and d.c. conductivities for single crystals of K,Pt(CN),C10.,,,~.6H,0 and K,Pt(CN), Br0.3,,. 2.3H20 were measured. For d.c. fields of

Oxidation of Ammonia-Oxygen Mixtures on Platinum in a Hardening Heterothermal Reactor M. G. WLOMB and P. M. STADNIK, Kinet. Katal., I971J (71, 50-54 The oxidation of NH, by 0% on a IO./; Rh-Pt catalyst without preliminary heating and at variable flow rates was studicd. The degree of oxidation increased with increased 0,:NH8 ratio. In the oxidation of NH,-air mixtures, the con- densate obtained contained IXo-zoog/l HNO,; with NH,-0, mixtures the HNO, content was 85c--87Og!1. The relation between degree of oxidation and NH, flow rate was studied.

Effect of Preparation on the Apparent Surface Composition of PI-Rh Alloy Films Used for CO Oxidation

24, (113 48-56 Pd-Rh alloy films were shown by X-ray diffraction to consist of two phases in the range 30-goX Rh. Rates of CO oxidation were increased by addition of Rh. The rate of CO oxidation increased linearly with apparent surface content of Rh. This was used to estimate the surface composition of Pd-Rh alloy films prepared in other ways.

On the Effect of Metal Particle Size on the Isomerisation of n-Hexme over Supported Platinum Catalysts F. M. DAUTZENBERG and J. c. PLATTEEUW, J . Catalysis, 1972,24, (z), 364-365 The isomerisation of n-hexane over Pt/AI,O, containing 1,5 and 10 wt.7; Pt was studied. The initial relative formation of 2- and 3-methyl- pentane is independent of Pt loading from 0.5 to 10 wt.% Pt and hence of metal particle size.

Study of the Mechanism of Aromatisation of n-Hexane on Platinum/Alumina Catalyst L. I. ZABOTIN and M. E. LEVINTER, Neftekhimiya,

Aromatisation activity of Pt/A120, drops during poisoning by NH, due to reduced acidity and suppression of isomerisation of n- to iso-hexane and of dehydroisomerisation of methylcyclo- penane to C6H,. Aromatisation of la-hexane occurs mainly via the formation of the intermediate methylcylcopentane on the active centres.

Dehydrocyclisation of Paraffins. Influence of Chlorine on Cyclisation Pathway over Pt- A1,0, Catalysts B. H. DAVIS, J . Catalysis, 1971, 23, (3), 355-357 The aromatic isomer distribution for the dehydrocyclisation of 3-methylheptane over Pt 'A1,0, with and without C1 was studied. The presence of C1 does not alter the selectivity or the reaction pathway but provides an easier methyl migration pathway. C1 added as NH,Cl

R. L. MOSS and H. R. GIBBENS,J. CUta&5iS, 1972,

1972, 12, (I), 9-13

did not have as much effect as C1 added as H2PtC16 in the catalyst preparation; the latter is probably of a specific type.

Aromatic Distribution from Paraffins and Naphthalenes Containing a Quaternary Carbon B. H. D A V I S , ~ . Catalysis, 1971, 23, (3), 340-354 The aromatic product distribution from the dehydrocyclisation of paraffins containing a quaternary C atom and a 6-C chain were compared to those obtained from conversion of the naphthenes corresponding to 6-C ring formation from the paraffis. Pt and CrzOs on "non-acidic" Also, were compared. Geminal dimethyl naphthenes gave similar results over Cr,O, and over a low isomerisation Pt iAl,02 catalyst. Demethylation at the quaternary C was the main reaction pathway. Over Pt dehydrocyclisation occurs by direct 6-C ring formation. The aromatic distribution is very sensitive to the method of preparation of

Kinetics of Olefin Hydrogenation over a Platinum Catalyst with More than One Set of Active Sites s. K O L B O E , ~ . Catalysis, 1972,24, (I), 40-47 The hydrogenation of C,H, and iso-C4H, over Pt:Al,O, is explained using a dissociative model with two types of active catalyst site. The mean deviation between calculated and observed reaction rates is less than 3y0.

Platinum-catalysed Hydrazine Reductions of PIutonium(1V) and Uranium(V1) J. L. SWANSON, U.S.A.E.C. Rept. BNWL-1584, 1971, 25 PP The use of Pt/A1,0, for the reduction of U(V1) to U(IV) and of Pu(1V) from irradiated reactor fuels was studied. The reaction took place in a solution of NzHd in HNO, without added H2. The effects of reaction temperature, and of the concentration of U(VI), N,H, and HNO, were studied, together with catalyst stability and poisoning.

Catalytic Selective Removal of Nitrogen Oxides from Exhaust Gases A. P. ZASORIN, v. I. ATROSHCHENKO and 0. N. KULISH, Khim. Tekhnol. :Kiev), 1971, (5 ) , 8-9 Pd,'A120, with NH, was 96"a effective in reducing to N a the 0.15 v01.4, NO contained in the exhaust gases. Only small amounts of NH,NO, and NH,NO, were formed. At an 0 content of 3.0 vol.% a maximum NO conversion of -55% was obtained at -260°C.

Determination of the Platinum Surface in Platinised Silicia from the Isotherms of Chemisorption of Hydrogen v. s. BORONIN, v. s. NIKULINA and 0. M. POLTORAK, Zh. Fiz. Khim., I972,46, (2), 463-466 The Pt surface area in Pt/SiO, was measured by

Pt ,A1,0,.


comparing H, chemisorption isotherms of the Pt/SiO, catalyst with that of a Pt sponge of known surface area. Results agreed with data from electron microscopy.

Kinetics of Hydrogen Chemisorption and the Dispersion of Platinum Crystals v. s. BORONIN, v. s. NIKULINA and 0. M. POLTORAK, Vest. Moskov. Univ., Ser. 11, Khim., 1972, 27,

The chemisorption of H, on Pt/SiO, was studied at various degrees of Pt dispersion; at low temperatures the behaviour is in agreement

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