PLATINUM METALS REVIEW · 2016. 1. 28. · ffins or to isomerise straight-chain paraffins to their...

PLATINUM METALS REVIEW

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

V O L . 6 J U L Y 1 9 6 2 N O . 3

Contents

Growth of Platinum Reforming in Western Europe 86

Complex Platinum Compounds and Virus Activity 91

Iridium Electrodes Increase Spark Plug Life 92

Ruthenium Catalyst for Paraffin Wax Synthesis 94

Technique of Field Ion Microscopy 95

A Rhodium-Platinum Thermocouple for High Temperatures 96

Corrosion Resistant Cobalt-Platinum Alloy Magnets 98

Ceramic Thermoelectric Generator 99

The Influence of Alternating Current on the Anodic Rehaviour of Platinum I00

Gold-Platinum Alloys 106

Percival Johnson’s First Publication I12

Abstracts 115

New Patents 123

Communications should be addressed to The Editor, Platinum Metals Review

Johnson, Mutthey & Co., Limited, Hatton Garden, London, E.C.1

Growth of Platinum Reforming in Western Europe MEETING THE DEMAND FOR HIGH-OCTANE FUELS AND AROMATIC HYDROCARBONS

By B. M. Glover, B . s ~ . Industrial Division, Johnson Matthey & Co Limited

In terms of demand for petroleum products Europe differs from America in one vital

whereas American industry has available large supplies of natural gas; the refiner in the U.S.A. can therefore produce high quality fuels partly by catalytic cracking of heavy distillates, but his European counterpart has no such opportunity and must rely to a much greater extent on catalytic reforming processes to produce high quality fuels from straight- run naphthas.

Again, while demand for high-octane gasolines has increased significantly, the growth in demand for aromatic hydrocarbons in Western Europe has been phenomenal. Until fairly recently the coal industry in Europe was able to meet this demand, but this situation has changed materially and it has become an obvious move on the part of oil refiners to install capacity for the separation of benzene and other aromatics from platinum reformates by fractional or extractive distillation.

Today something between 30 and 40 per cent of the organic chemicals produced in Western Europe are derived from petroleum and the proportion is increasing rapidly.

By the beginning of the present year the number of platinum reforming plants in Western Europe had grown to sixty-three, with a capacity of 27.4 million metric tons per year. In fact nearly two-thirds of existing Western European oil refineries have a catalytic reforming unit in operation. These

respect. Consumption of fuel oil is very high,

reforming plants are located in cvery country of Europe with the exception of Luxembourg,

countries active planning is under way for their construction. There are twenty-two in Italy, sixteen in Western Germany, nine in France and eight in the United Kingdom. In the next three years some existing plants are to be extended and at least ten new refineries with platinum reforming units will go on stream; total reforming capacity will then have increased to at least 36 million metric tons per year.

This situation of reliance upon platinum reforming processes has come about in the space of only thirteen years since the intro- duction by Universal Oil Products Co in 1949 of the Platforming process-a catalytic process employing a platinum catalyst. Prior to this date catalytic reforming had certainly been used to a small extent to provide improved automobile and aviation fuels for wartime purposes, but the shortcomings of the catalysts employed and the complexity of their regeneration had ruled out the process in terms of peacetime economics.

The Platforming process, then, marked the beginning of a distinct phase, and although the first installation was not followed by others until more than a year later, the feasibility of this new route to both high-octane fuels and aromatic chemicals had been clearly estab- lished and it was not long before other oil companies and research organisations began to develop broadly similar processes.

Portugal and Yugoslavia, and in the latter two

Platinum Metals Rev., 1962, 6 , (31, 86-9 1 86

Construction of new petroEeum rtfineries in Festern Europe is proceeding at a vigorous pace. In most cases the new plants include a platinum reforming unit producing high-octane fuels and high purity aromatic hydrocarbons. The illustration shows the Universal Oil Products Platforming unit at the

refcnery of Condor Socicta per l’lndustrin PetroEijina e Chemira at Rho, Italy.

There followed rapidly, principally in the United States, a major growth in the utilisa- tion of platinum reforming, with a very considerable usage of platinum in the form of a catalyst dispersed on an alumina support generally in the form of small pellets.

This growth reachcd a peak in terms of new plant construction around the year 1957, after which the building o F new reforming facilities tended to slow down and to run parallel with the growth of general refining capacity.

Platinum reforming processes spread to Europe in the early fifties, but initially progress was much slower than in the United States. Today, however, and for the reasons already outlined, a very different situation exists, and the European scene presents a most active picture of platinum reforming as a means of meeting the rapidly growing demand for both high-octane fuels and petrochemical intermediates.

Catalytic reforming processes are basically continuous high temperature, high pressure

Platinum Metals Rev., 1962, 6 , (31,

processes carried out in an atmosphere of hydrogen. Generally a series of reactors is employed-usually three in number-although with some regenerative types of process an additional or “swing” reactor is installed, to be brought into play during regeneration of the catalyst in any one reactor.

The importance of catalysts to petroleum reforming lies in their highly specific ability to convert the various components present in low-octane petroleum naphthas to branched- chain and aromatic compounds of high-octane numbers. Catalysts for these processes con- sist of platinum on an alumina support, the latter also playing an important role in the various chemical processes taking place and aromatising long-chain saturated paraffins. The percentage of platinum is usually of the order of 0.2 to 0.75, while a small but critical amount of a halogen i s also incorporated in the base to maintain the correct balance between the conversion of paraffins by dehydrocyclisation, hydro-cracking and isomerisation. From

87

One of the three Platforming units at the Gelsenberg Benzin AG rejlnery at Gelsenkirchen, Ves t Germany. In addition to high-octane motor fuel, high purity benzene i s produced by

separation from the reformate in a UOP Udex unit.

time to time improved platinum catalysts have been introduced to provide greater selectivity and longer life, particularly in view of the greater severity of operation imposed on refiners by increasing demands for higher octane ratings.

Platforming, now widely employed in most refineries-it accounts for 50 per cent of installed capacity of all reforming processes throughout the world-is a fixed-bed process operating at temperatures around 550°C and pressures up to 700 lb per square inch. It yields, as do other platinum reforming processes, large quantities of hydrogen which are employed either in other refining operations or for ammonia synthesis, and is able to produce a range of aromatics which may be separated from each other and from un- changed feed stock by fractional or extractive distillation.

Other platinum reforming processes employing an alumina-base catalyst impregnated with platinum and one or more halogens include Ultraforming, a process developed

by the Standard Oil Company of Indiana, which is a regenerative process (that is, the catalyst is frequently regenerated in situ), and Powerforming, developed by Esso Research and Engineering, also a regenerative process using a catalyst developed by the Davison Chemical Company. Houdriforming (Houdry Process Corporation), Sinclair-Baker Reform- ing (Sinclair Oil Company) and Catalytic Reforming (Humble Oil and Refining Com- pany) are again processes yielding high-octane reformates and capable of being operated to produce aromatic chemicals as well as motor and aviation fuels.

Penex-Platforming (U.O.P.), Pentafining (Atlantic Refining) and the Butamer Process (U.O.P.) all employ platinum catalysts either to produce aromatic compounds from paraffins or to isomerise straight-chain paraffins to their branched-chain isomers.

The original distinction between regenerative and non-regenerative operations with platinum catalysts requires some explanatory comment. In the Platforming process the

Platinum Metals Rev., 1962, 6 , (31, 88

catalyst operates over long periods without regeneration, so that for the original relatively mild operations up to about 92-93 clear octane number of product in situ regeneration was not needed or justified. For more severe opcrations, especially with the Middle East naphthas of low naphthene content, occasional regeneration in situ, two to four times per year depending on operating conditions and severity, is employed as being more economi- cal than higher hydrogen circulation and a larger lock-up of platinum catalyst. Other platinum-reforming processes vary in frequency of in situ regeneration, depending on the composition of the catalyst and the operating conditions employed. Since most European operations today demand very high severity-g8 to IOO clear octane number product-and use Middle East naphtha, inter- mittent in situ regeneration is now generally installed, although in some cases swing reactors are employed.

Apart from their use in upgrading gasoline, the major aromatic hydrocarbons produced in the platinum reforming processes-benzene, toluene and the xylenes-are widely used as solvents and as intermediates in the organic

chemical industry. High purity benzene can readily be converted to cyclohexane, or to ethylbenzene for the further production of styrene. Toluene may possibly continue to be produced in excess of demand, but can be converted to benzene by hydrodealkylation j the future of the xylenes, however, could be very large, mainly for the production of terephthalic acid, isophthalic acid and phthalic anhydrine from para-, meta- and ortho- xylene respectively. The production of naph- thalene from reformates by hydrodealkylation of heavy fractions-already in commercial operation in the United States-also presents considerable possibilities. In the light of steadily increasing European demand for plastics, synthetic fibres, synthetic rubbers, detergents, insecticides and lubricant additives the prospects of an enormous growth in the production of aromatic intermediates from petroleum sources are obvious.

In 1953 catalyst manufacturing facilities were set up in the United Kingdom by Universal-Matthey Products, an associated company of Universal Oil Products and Johnson Matthey, to meet the demand from European licensees of the Platforming pro-

Production of platinum-on-aEumina catalyst for European licensees of the Platforming process was begun i n England i n 1953 by Universal-Mntthey Products Ltd. Local demand has been met by the construction of this new plant i n Cologne, operated by Universal-Matthey Products (Deutschland) GmbH.


The Powerforming process, a catalytic reforming operation using a platinum-on-alumina catalyst developed by the Davison Chemical Co, is employed in this section of the Esso Nederland rejnery near Rotterdam. A large new plant is planned on the same site to produce benzene, toluene and xylenes from

the reformates.

ccss. The growth of this process led in 1959 to the construction of additional manufacturing plant in Cologne by a new subsid- iary company, Universal-Matthey Products (Deutschland), to provide a source of supply nearer to continental refineries. Platinum reforming catalysts for other processes have also been made available from Kali-Chemie in West Germany and from the Ketjen organisation in Holland.

One major feature of European development in the use of platinum-reforming processes has been the entry, either alone or jointly with existing chemical producers, of oil companies into the production of organic chemicals as a distinct but allied activity to petroleum refining. For example, British Petroleum and California Chemical have announced plans to build an aromatics plant at the B.P. refinery in Kent, while another aromatics plant is planned by B.P. Benzin und Petroleum at

Dinslaken in West Germany to operate on feed stock from the adjoining B.P. refinery. Esso Nederland is building a major plant on the site of its refinery at Botlek near Rotter- dam for the same purpose, and the new Shell refinery at Godorf is linked by pipe-line to a petrochemical plant jointly owned by Shell and Badische Anilin. New aromatics plants are also to be built near the Mobil Chemica Italiana refinery at Naples and at the Esso refinery at Fawley, near Southampton.

The construction of a number of trans- continental pipelines for the transportation of crude oil has also given impetus to the petrochemical industry in general. Refineries can be, and in fact are being, sited inland in relation to their consuming industries while the prospect of the eventual removal of tariffs in the European Common Market has also led to an increasing number of refinery pro- jects, for instance, along the Franco-German


border. In fact more than half of all new refining capacity at present being planned or built in Europe is located at inland centres. In addition to the refineries in the Ruhr area, served already by two pipelines from Rotter- dam and Wilhelmshaven respectively, five new plants will be constructed near Karlsruhe and Strasbourg close to the main terminals of the new pipeline from Lavera, near Mar- seilles, to be opened in January of next year, while a Swiss refinery at Aigle will receive crude oil by pipeline from Genoa.

Typical of some recent installations are the first major petroleum refinery to be built in Austria-the Oesterreichische Mineralvelver- waltungs A.G. plant at Schwechat near Vienna -with a 250,000 tons per year Platformer; the new B.P. refinery at Dinslaken in the Ruhr with a high severity Platformer of 500,000 tons annual capacity, from which a proportion of the aromatics are passed to Erdoelchemie at Dormagen to be steam- cracked and used as petrochemical raw

materials; the Esso-Rotterdam refinery which includes a Powerformer, and the Shell refinery at Godorf near Cologne with a Plat- former. At the Gelsenberg Benzin refinery at Gelsenkirchen-Horst a third Platforming unit has been put on stream, together with a U.O.P. Udex unit for the separation of high purity benzene from the reformate.

The gencral trend to be discerned in this vigorously growing European industry is towards flexibility of refinery operation-the possibility to produce high-purity aromatics according to market needs while still satisfying the increasing demand for automobile fuels of higher octane ratings. Platinum reforming processes constitute one of the most versatile tools available to the refiner, and by their more severe operation, by the development of improved platinum catalysts and by con- tinual modification and improvement of the processes by the licensors will obviously go on playing a key role in the overall economics of European petroleum refining.

Complex Platinum Compounds and Virus Activity A POSSIBLE MEANS OF ATTACK ON CANCER TUMOURS

Among the many researches being under- taken into the likely causes and possible treatments of cancer, evidence has been accumulating to indicate that viruses may be involved in many types of the disease. Viruses contain proteins, nucleic acids and polypeptide linkages and therefore present obvious possibilities as co-ordinating agents for certain metal ions, with the further possibility that complex inorganic compounds might be used successfully in destroying or reducing their disease-producing activity.

At the meeting of the American Chemical Society held in Washington, D.C., in March a valuable step forward in this direction was reported by Dawn Francis, Dr Stanley Kirchner and Dr J. C. Bergman of the De- partment of Chemistry, Wayne State Uni- versity, Detroit, working in collaboration with Dr Yung-Kang Wei of the National Research Council, Ottawa. Because it would be impossible to introduce a metal ion into a living system with the expectation that

it would by-pass normal proteins and await complexing by co-ordination sites in the virus, these workers proposed to introduce metal ions as co-ordination complexes of intermediate stability; in this way it was hoped that they would be stable enough to escape reaction with normal proteins but not so stable as to resist attack by virus proteins.

Some complex inorganic compounds are known to be carcinostatic, among them 6-mercaptopurine, and the preparations made and tested in this research included this biologically active compound and its complexes with platinum and palladium. In tests with cancer tumours in mice, these latter two compounds proved to be extremely active, showing in fact a much greater activity than that of 6-mercaptopurinc itself. These results certainly lend support to the hypothesis put forward, but further closely controlled tests with 6-mercaptopurine on both complexed and uncomplexed forms are now being conducted.

Platinum Metals Rev., 1962, 6 , (31, 9 1-9 1 91

Iridium Electrodes Increase Spark Plug Life RESISTANCE TO ATTACK BY LEAD COMPOUNDS

By G. w. Shoobert, M.B.E., A.M.1.Mech.E. K.L.G. Sparking Plugs Limited, London

Even in the jet age in which we are now living, the number of aircraft driven by piston engines remains very high, and helicopters and freight aircraft will continue to use these engines for a considerable time.

Since the early years of the last war, spark plugs in aero engines have been fitted with electrodes in a tungsten-platinum alloy which, although ideal in all other respects, suffers from chemical attack by the lead compounds used in high-octane aviation spirit. The precise mechanism of this attack is not yet fully understood, but the effect

appears to be one of intergranular penetration. This seriously reduces the resistance of the platinum alloy to spark erosion, leading to a rapid increase in gap size and to eventual failure of the plug. Apart from the failure of the plugs themselves, related equipment such as magnetos and ignition harnesses can break down under the additional electrical loading imposed on them by excessively large spark plug gaps, and it has therefore been essential to rate plug life very conservatively and of course to enforce rigid inspection and maintenance at frequent intervals in order to

On the left is a K.L.G. tungsten-platinum plug after 52 hours i n a Bristol Centaurus engine. It already shows the onset of spark erosion from lead attack. The plug on the right is one of the new K.L.G. iridiumplugs removed ufier 925 hours in the same engine. As can be seen. the plug was not rleaned or serviced before the photograph was taken.

Platinum Metals Rev., 1962, 6 , (31, 92-94 92

l’hotomicrographs (X120) of spark plug electrodes after 65 hours running in a single cylinder engine test by Bristol Siddeley Engines Ltd. The tungsten-platinum electrode (left) shows severe lead attack; the iridium electrode (right) is unattacksd.

ensure safe engine performance. During recent years, this problem has emerged as the major outstanding factor affecting aircraft sparking plugs, despite the investigation of a number of alternative platinum alloys. It was then suggested that the problem might be capable of solution if it were possible to use iridium as the electrode material, since this metal is immune from attack by lead. Now iridium, one of the platinum group of metals, is characterised by high hardness and by quite exceptional difficulty in fabrication. Small quantities of iridium strip and wire had been produced in laboratory conditions, but for all practical purposes the metal had been regarded as brittle and non-ductile.

Production of Ductile Iridium Early trials with iridium electrodes showed

some promise, but its brittleness made production and assembly of the electrodes very difficult and it was clear that a ductile form of iridium was essential to the successful adoption of this metal for plug electrodes. Johnson Matthey therefore began an investigation of possible methods of producing iridium in wire form and, early in 1961, were successful in developing a process of working the metal at very high temperatures to yield both round and square wire having a fibrous

structure and good ductility. This material, known as SD Iridium, has now been made available on a quantity basis.

From the earliest days of this development the fullest collaboration was received from Bristol Siddeley Engines Limited, who conducted a number of exhaustive single-cylinder and main engine tests on plugs fitted with SD Iridium electrodes, followed by flight trials in various types of aircraft. In one single- cylinder test a plug life of no less than 1,014 hours was recorded. During this time 22,388 gallons of high octane fuel were used, containing p g lb of tetraethyl lead (468 Ib of lead as metal). At the end of the test the plug was still functioning satisfactorily although the electrodes had been worn to the extent of about 50 per cent.

Flight Trials Flight trials of experimental K.L.G. plugs

using iridium electrodes are still in progress and others are planned, but the remarkable results obtained so far indicate that the new electrode material is well on the way to solving the erosion problem and that there is every likelihood of iridium spark plugs superseding the platinum alloy types, even for service conditions of the less severe kind.

For example, severe spark erosion of the


K.L.G. platinum plugs used in the Alvis Leonides Major engine was experienced in Royal Navy Mark 7 helicopters. This trouble was directly attributable to the particularly arduous conditions imposed by “dunking” operations, wherein the engine is run for long periods at maximum power in the hover. Plug life was seldom better than 80 hours.

With the encouragement and active support of the Ministry of Aviation and the Admiralty a trial set of K.L.G. iridium plugs was installed in one of these helicopters and subjected to the same stringent operating conditions. At 300 hours, electrode erosion was negligible on all plugs, and without servicing of any kind they were re-installed for further running. The trials were extended and continued under operational conditions in the Middle and Far East with results just as satisfactory.

As a result of this, K.L.G. iridium plug Type KA.3 is now officially approved by Alvis Limited for the 14-cylinder Leonides Major engine.

In close collaboration with Bristol Siddeley Engines Limited and Aviation Traders (Engineering) Limited of Southend Airport, K.L.G. are currently running flight trials with a set of iridium plugs in each of five Bristol Freighters operating the Channel Air Bridge. These aircraft were chosen because of their especially strenuous service conditions, involving frequent engine starting, idling, taxiing, maximum power take-offs and climb-outs from congested areas. The plati-

num plugs for these engines had an average servicing life of 250 hours, but cases of unscheduled removal were quite common.

Despite the operating conditions no troubles whatsoever have been experienced with the new plugs and there is a marked increase in serviceability, ranging from over 600 to over 1,000 hours.

The plug has therefore been submitted to the Air Registration Board for standardisation at an initial figure of 600 hours, before servicing, and has been approved for trial extensions to 1,000 hours.

Similar trials of K.L.G. iridium plugs are under way in a number of RAF aircraft types including Avro Shackleton Mark 3 (Rolls- Royce Griffon), Blackburn Beverley (Bristol Centaurus), and Hastings, Varsity and Valetta (all Bristol Hercules). One other civil operator BKS Air Transport Limited, are carrying out trials in Ambassador Aircraft (Bristol Cen- taurus). All exhibit the same remarkably successful results.

It is true to say that the ultimate life of an iridium electrode plug is not yet known under service conditions (as distinct from rig conditions) and substantial further running time will have to be achieved in service before this is known.

The successful results so far obtained with iridium electrodes in aero engine spark plugs indicate that plugs of this type may well find applications in the automobile field before very long.

Ruthenium Catalyst for Paraffin W a x Synthesis LIQUID PHASE HYDROGENATION OF CARBON

The production of high melting point hydrocarbons by reacting carbon monoxide with hydrogen over a suitable catalyst has long been known to be a possible route to paraffin wax and was first of course proposed by Fischer and Tropsch.

In the past few years some work has been carried out on this reaction by H. Kolbel and K. K. Bhattacharyya (Plat. Metals Rev., 1959, 3, 59) and a further paper by these workers, together with W. H. E. Miiller, has recently

MONOXIDE

been published (Angew. Chem., 1962, 74, (z),

It is shown in this paper that straight chain paraffins with melting points up to 130% may be prepared by leading carbon monoxide through a suspension of finely divided ruthenium in water, at pressures of over fifty atmospheres and at temperatures between 150 and 260°C. The mean molecular weight of the product increases with the pressure and falls with increasing temperature.

88).


Technique of Field EXAMINATION OF THE SURFACE

By D. G . Brandon, M.A., Ph.D. Department of Metallurgy, University of Cambridge

Field ion microscopy is a technique for observing individual atoms, and is capable of yielding pictures showing the surface structure of a metal in atomic detail. In the field ion microscope the high electric

field generated at a sharp point is used to overcome the potential barrier at the metal surface. Helium atoms in the neighbourhood of the surface lose electrons to the metal and are accelerated radially away from the point as helium ions. A “pinhole” image of the curved surface at the point is formed on a phosphor screen at a magnification of about one million times.

The resolution is sufficient to enable individual surface atoms to be imaged as bright spots on the screen.

The high electric fields needed to obtain an image produce large stresses which tend to disrupt the crystal lattice. These stresses may even result

A Jield ion micrograph of a 500 A radius platinum tip shoming the regularity of the crystal lattice on an atomic scale

Ion Microscopy STRUCTURE OF PLATINUM

in “field” evaporation of the surface atoms and this effect limits the use of the field ion microscope to the study of refractory metals such as platinum, tungsten and molybdenum, which have high binding energies.

The field ion microscope, which has a resolution of 2 to 3 A, was developed by Professor E. W. Miiller in the United States, and is now being used for the direct observation of lattice defects introduced during irradiation and cold work. I t is perhaps the most direct method of demonstrating the regularity of the crystalline lattice in metals.


A Rhodium-Platinum Thermocouple for High Temperatures NEW CALIBRATION VALUES FOR THE “SIX-THIRTY” COUPLE

For a great many years the thermocouple formed by pure platinum and either a 10 or a 13 per cent rhodium-platinum alloy has been the standard means of measuring temperatures of over IOOO~C, particularly in the steel making industry. As is well known, however, for the determination of temperatures much above 165oOC this combination does not provide an entirely satsifactory solution. The pure platinum limb is naturally very weak mechanically at such temperatures, and needs to be supported carefully to avoid creep failure under quite small loads. In addition, there is the tendency at very high tempera-

tures for rhodium to be lost from the alloy wire by oxidation and volatilisation and then to be picked up by the pure platinum wire, with a consequent reduction in the e.m.f. of the couple.

For special purposes, therefore, there has been an interest in thermocouples consisting of two different rhodium-platinum alloys, and several such combinations have been proposed to provide increased mechanical strength, less sensitivity to contamination by volatilised rhodium and the possibility of being used to measure somewhat higher temperatures. The e.m.f. developed between two

such alloys is, of course, apprcciably less than that between the alloy richest in rhodium and pure platinum, and it is desirable to choose two alloys giving as high an e.rn.f. as possible. On the other hand the melting point of the alloy lower in rhodium content should be as high as possible. Thus thermocouples of 5 per cent rhodium-platinum: 20 per cent rhodium-platinum (“five-twenty”), 6 per cent against 30 per cent rhodium-platinum (“six- thirty”), and 20 per cent against 40 per cent rhodium-platinum (“twenty- forty”) have been developed and have found applications to a moderate extent.

The alloys with 5 or 6


per cent rhodium have a melting point of approximately 1820°C, so that couples employing one of these as the negative limb can be used to measure temperatures up to 18ooOC for a short time. The z0:40 combination, although capable of measuring up to as high as 185oOC for short periods, gives an appreciably lower e.m.f. The relative e.m.f. characteristics of these thermocouples above IOOO~C, and their maximum temperatures of use, are shown in the graph.

Calibration tables have been prepared for these couples, but not unnaturally there has been very much less investigation of these alloys by comparison with the intensive study that has been given over the years to the pure platinum and 10 or 13 per cent alloys by national standardising bodies.

A new series of determinations of the characteristics of the “six-thirty” couple is

Calibration Table for the 6 per cent Rhodium-Platinum :

30 per cent Rhodium-Platinum

Tem- perature

“C.

0 I00 200 300 400 500 600 700 800 900

1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700 1,800

Thermocouple

E.rn.f. in millivolts

lew values

0 0.033 0.177 0.430 0.789 I .247 I .795 2.433 3.159 3.966 4.847 5.795 6.806 7.87 I 8.977 10.1 13 I I .267 12.428 13.583

31d values

0 0.056 0.162 0.4 I9 0.790 I .245 I .796 2.442 3.162 3.964 4.839 5.791 6.81 I 7.890 9.000 10.130 11.260 12.390 13.520

Difference i n

microvolt!

- + 23 -I5 -I I + I - 2

+ I + 9 + 3 - 2 - 8 - 4 + 5 + I9 + 23 + 17 - 7 -38 -63


thus particularly welcome. This has been carried out by Walter Obrowski and Walter Prim of the Degussa Research Laboratories, Hanau, and is published in Archiv fi ir das Eisenhuttenwesen, 1962, 33, (I), 1-3.

The e.m.f. values of the two alloys were measured by the compensating method at the primary fixed points laid down in the Inter- national Temperature Scale, the boiling point of water, the freezing points of silver and gold, and at the secondary fixed points, the melting points of tin, lead, zinc, aluminium, palladium and platinum. For the higher temperatures-the melting points of gold, palladium and platinum-a modified wire melting method was used in which the wire of the calibrating metal was replaced by a disc clamped to and folded over the hot junction. This was found to give an easier and more accurate reading of the melting point. Readings of e.m.f. values were obtained to an accuracy of j0 .1 microvolt, and more than 2,500 determinations were taken in all,

The main values obtained by Obrowski and Prinz are given in the table, together with those formerly accepted, and the differences between the new and the older values. This work helps to establish the “six-thirty” as a standard thermocouple, and alloys are now available that comply with this calibration table within f 3OC at the gold point and within i 4OC at the palladium point.

J. A. S .

Corrosion Resistant Cobalt-Platinum Alloy Magnets METER DESIGNED TO HANDLE

In applications where powerful permanent magnets are called upon to resist prolonged chemical attack Platinax I1 offers many advantages. The composition of Platinax I1 is closely controlled to give an equi-atomic alloy, corresponding to 23.3 per cent cobalt and 76.7 per cent platinum by weight. This high platinum content makes the alloy vir- tually immune to attack by such chemicals as concentrated sulphuric and nitric acids, acetic anhydride, 50 per cent hydrochloric acid, 50 per cent hydrofluoric acid, strong caustic alkali solutions, sodium hypochlorite and calcium hypochlorite. After a special heat treatment which brings about partial ordering of the structure Platinax 11 can be

CORROSIVE LIQUIDS

magnetised to give permanent magnets of outstanding strength.

Because of this unique combination of high magnetic strength, even in magnets of small size, with high chemical resistance, Platinax I1 magnets were chosen for use in a new meter manufactured by Tylors of London Ltd., of Burgess Hill, Sussex, designed specifically to meet the needs of the chemical industry in measuring and controlling accurately the flow of highly corrosive liquids. The meter operates on the rotary piston principle, the body being constructed of perspex and all other internal parts which come in contact with the liquid being manufactured from material having complete resistance to corrosive attack.

Dismantled view o j the meter by Tylors of London Ltd., for handling corrosive liquids such as hydrochloric acid and hypochlorites. Platinax II cobalt-platinum magnets are used in

the drive mechanism.


Component parts of the magnet drive showing the four-pole cobalt-steel claw magnet, the tandurn separating cup and the Platinax I I magnet assembly containing four magnets

backed by pieces of soft iron to increase their effective length.

A four-pole Platinax I1 magnet assembly which is exposed to the corrosive liquid operates in combination with an outer four- pole cobalt steel claw magnet to provide a glandless drive between the piston and the dial mechanism. A tantalum cup separates the two halves of the drive, resulting in a fairly large air gap between the pairs of poles.

This makes essential for the smaller inner magnet the use of a highly powerful non- corrosive magnet material of high coercivity to ensure that the coupling between the piston and the dial mechanism is sufficiently powerful to operate without the occurrence of any slipping.

R. A. M.

Ceramic Thermoelectric Generator PLATINUM AND NICKEL OXIDE JUNCTIONS

A ceramic thermoelectric generator, developed by the Minneapolis-Honeywell Regu- lator Company for the United States Army, is capable of an output of IOO volts at temperatures of around 1300'C.

The unit, illustrated here, consists of a pack of fourteen alumina plates, the continuous series of junctions being formed from platinum-produced by firing on a platinum paste-and a sprayed coating of lithium- doped nickel oxide. The cold junctions are developed by heat losses due to conduction and radiation. The platinum metallising paste is also used to connect the plates together, the pack then being assembled with ceramic nuts and bolts.

The unit is now being tested by the United States Army, utilising waste heat such as exhaust gases from rocket engines and from re-entry nose cone heating.


The Influence on the Anodic

of Alternating Current Behaviour of Platinum

By Dr Romuald Juchniewicz Gdarisk Polytechnic, Poland

In this paper an investigation is described of the e$ect of superimposed a.c. on the corrosion of anodically polarised platinum in sodium chloride solutions, using capacitance and resistance measurements to study the formation and destruction of oxide jilms on the electrode surfaces. Increased corrosion was found when up to 30 per cent a.c. was superimposed on d.c. The importance of reducing the a.c. component in rectijied currents used in cathodic protection and electrolytic processes is shown.

The use of platinum and platinised titanium as anodic materials is rapidly growing, both in cathodic protection applications and in the field of industrial electrolysis. In view of its considerable theoretical interest and practical importance, the corrosion with superimposed a.c. of these materials in salt water at high current densities has been investigated.

In a paper presented by the author at the First International Congress on Metallic Corrosion, London, 1961 (I), the effect of a x . on the corrosion behaviour of anodically polarised platinum and platinised titanium in static sodium chloride solutions was discussed. Further experimental work using both static and flowing electrolytes is now reported.

With solutions containing chlorine ions, anodes dissolve as PtCl,--, this corrosion being quantitative for low current densities. It is known that attack by d.c. is enhanced by increasing temperature, by high concentration of chlorine ions, by high acidity, and when a.c. is superimposed.

Bombara and Gherardi (2) have observed with only d.c. that platinum-coated titanium electrodes have a limited period of usefulness which depends to some extent on the adhesion of the platinum and thus on the type of plating process used. Llopis and Sancho (3)

found a close relationship between the corrosion of platinum and superimposed a.c. in hydrochloric acid solutions. For d.c. high enough to passivate the electrode, corrosion is nil, until a “critical” value of the superimposed a.c. is reached. Juchniewicz ( I ) has observed a large increase in corrosion of platinum when about 14 per cent a.c. is superimposed on 600 mA/cm2 d.c. The surface is covered with a yellow film and there is an associated increase in capacitance.

One group of workers (4, 5, 6) considers that corrosion is due to the depolarising effect of a.c., while another group (7, 8) concludes that the decreasing capacitance of the double layer is largely responsible for corrosion.

The circuit described in the earlier work (I) was used. Conventional methods of controlling the magnitude of alternating and direct current and of varying the proportion of a.c. were employed. Anode material was Thermopure platinum wire (supplied by Johnson, Matthey & Co., Limited). Solutions of 3 per cent and 10 per cent A.R. sodium chloride were used as static electrolytes, while the flowing electrolyte was 3 per cent domestic table salt solution. The corrosion cell was designed around a 500 ml Pyrex beaker. In static conditions, 350 ml of electrolyte were used and with flowing electrolyte the volume


was 200 ml. The ambient temperature during these experiments was 20T & 1'.

A d.c. of up to 1200 mA/cm2 was applied and up to 30 per cent ax. at a frequency of 500 cis was superimposed. The amount of corrosion over periods up to 1200 hours was determined by measurement of weight loss of the electrodes.

The a.c. bridge built by Cole (9) with an output of 5 mV was used for impedance measurements. Variable resistance and capacitance boxes in the measuring circuit

Id.c.rnA/cm2

Per cent a.c. 0 .. . . 4.5 . , . 6.5 . . .

30 . . . .

Time 1,400 hours 13 . . . .

were placed in series. The method used by Lorking (10) was applied to the present work, in which the cell used for measurements on platinum was set up in a 250 ml beaker. Three electrodes were used: the electrode under test, a length of platinum wire with surface area of 0.1 cm2 exposed to the solution; a counter electrode of platinised platinum having an apparent surface area of 3200 cm2, and a plain platinum electrode for applying the polarising current. A study was made of the concentration of hypochlorous acid

65 I30 260 520

0.043 I 0.0728 0.1321 0. I700 0.101 0. I384 - 0.4785 - 0. I654 0.05 I 2.030 I - 3.412 - 4.9250

0.426 I .635 14.613 34.53 I


Table I

Influence of Superimposed ax. at 50 cis on d.c. Polarisation in Static 3 per cent Sodium Chloride Solution

Platinum wire 0.020 inch diameter. Weight loss measured in mg/cm2. Time 500 hours

Id.c.mA:cme I50 300

Per cent a.c. 5 . 5 . . . . 0.1401 0.425 I

formed during polarisation in these conditions. The principal results obtained are set out

in the tables and in Figs. I and 2. It can be seen from Table I that at con-

stant d.c. density an increase in superimposed a.c. causes increased anodic dissolution. Furthermore, although the data shown in Tables I1 and IV are not strictly comparable, it is apparent that polarisation with flowing electrolyte produces significantly less corrosion than in the experiments with static solutions. The difference is probably related to the effect of hypochlorite formed under static conditions and to changes in pH.

During electrolysis hypochlorite is formed by anodic oxidation, and Table V shows that under a particular set of conditions its concentration becomes substantially constant after 150 hours. The pH change from 5.2 to 8.6 was complete in two hours.

Table VI shows the influence of increasing a.c. density alone on the corrosion of platinum. It is noticeable that there is a sharp increase in weight loss at a current density of around 30 mA:cmZ.

Table VII shows series capacitance and resistance measurements for unpolarised platinum in 3 and 10 per cent sodium chloride solutions. These results indicate the probable

600 1,200

3.1751 7.223 I

presence of an intact oxide film on the platinum surface.

With a.c. polarisation alone, it was found that both corrosion and capacitance increased significantly as illustrated by the results in Table VI and Fig. I. The plot of electrode potential shows two discontinuities with increasing a.c. Fig. I also shows that an increase of polarising time from fifteen minutes to two hours resulted in a great increase in capacitance with only a small change in resistance.

Fig. 2 shows that a large increase in capacitance was found after polarisation with a.c. alone, the final capacitance remaining stable for many hours. With d.c. and superimposed a.c. after twenty-four hours polarisation there was only a small increase which fell rapidly after switching off the polarising current. These results indicate that a.c. has some influence on film formation, probably through the formation of a surface layer of insoluble salt, since a yellow film was often observed on the electrode.

Titanium covered with a 3 p- platinum layer and titanium plated with platinum in a bath of chloroplatinic acid were used in the experiments. In the latter case, microscopic examination showed that the platinised layer was I ,U thick.

Id.c.rnA/cm2

Per cent a.c. 0 . . . . 4.5 . . . .

10 .. .. 14 .. ..

Table Ill

Conditions the same as for Table I , but with I

75

0.05 I 0.0598 0.0664 0.0723


I50

0.0643 0.072 I 0.1 184 0.1498

102

l e r cent sodium chloride

300

0. I49 0. I948 0.290 I 0.400 I

600

0. I69 0.2284 0.3481 0.9964

Table Ii

100 I I

In both cases, when platinised titanium was polarised at a d.c. density of 70 mA/cm2 without a.c., no corrosion was observed after 2,000-5,000 hours. Superimposed a.c., as with pure platinum, caused corrosion. The degree of corrosion depends on the thickness of the platinum and applied current density during the test, but a certain amount of corrosion always occurs,

I t was noted during the experiments that the thickness of the platinum layer fell to 0.1 p to 0.2 p. Below these values the electrode fails after a limited period of time. Platinised titanium wire with a 3 p layer of platinum was more resistant, and over long periods of time with superimposed a.c. up to I per cent, no corrosion was observed. More detailed research on the corrosion of platinised titanium is at present under way.

Results of this investigation indicate that up to 30 per cent superimposed a.c. causes an increase in the anodic dissolution of platinum and platinised titanium both in static and flowing electrolytes. With increase of electrolyte concentration a decrease in corrosion was observed. It was also confirmed that d.c. alone causes corrosion of platinum (11).

Juchniewicz (I) found that if an a s . is

superimposed on a d.c. anodically polarising a platinum electrode in sodium chloride solution, the overpotential decreases, the depolarising effect being greater as the a.c. density increases. Anodic polarisation of platinised titanium pro-passivates the titanium in the pores of the platinised layer, thus main- taining the stability of the electrodes for long periods with d.c. alone. Previous work (12, 13 and 3) had indicated that the surface of the platinum is covered by an oxide layer later identified as a PtO:PtO, film (14).

Capacitance and resistance measurements with an a x . bridge may be used to follow

Influence of 3 per eent Sodium Chloride Flowing at a rate of 1.25 litres/hour

Time 350 hours

Per cent a.c. 0.1710 0.365 I 0.3812

14 0.933 I

Platirium Metals Rev., 1962, 6 9 (31, 103

625

Table V

Increase in Sodium Hypochlorite Concentration determined during Experiments in Static 3 per cent

Sodium Chloride Solution Direct current density 520 mA/cmz with

4.5 per cent a.c.

Time in hours

6 24 48 62 I00 I50 200 350

Per cent sodium hypochlorite

0.04 0.10 0.3 I 0.40 0.50 0.58 0.58 0.57

changes in thickness of films formed on the electrode surface. Lorking (10) in a series of experiments on aluminium has shown that for a surface covered with an intact oxide film, the capacitance is low, while the resistance at low frequencies is high. Other workers (IS) have pointed out that the variation of capacitance with frequency is low while that of resistance is high.

Table VI Influence of Alternating Current Density alone on Corrosion in 10 per cent Sodium Chloride (pH 8.5) containing 0.5 per cent

Sodium Hypochlorite Time 150 hours

3.0 6.0 8.0

10.6 14.0 15.8 27.2 30.4 42.4 60.8

0.098 0.123 0.140 0. I80 0. I98 0.28 I 0.693 0.900 3.7 6.5


Walkiden (16) has correctly drawn attention to the fact that the amplitude and frequency of the ripple depends on the circuit used. For small currents, the supply is upally obtained from a single-phase transformer and a full-wave bridge rectifier and the main ripple component of the output has an RMS value of 47 per cent of the mean d.c. voltage and a frequency of IOO cis. For larger installations a three-phase full-wave bridge rectifier is usually employed, and the main ripple component of the output has an RMS value of 4 per cent of the mean d.c. voltage and a frequency of 300 c/s. In both cases there will be smaller percentages of the corresponding harmonic frequencies. It would be useful to carry out further experiments using rectified a.c. of these two types, with and without smoothing, as the ds. source.

At 60 cis the capacitance of the unpolarised platinum electrode was found to be 31-32 p Fl cmz and this value was practically the same for 3 per cent and 10 per cent sodium chloride solutions while the resistance was about 1000 ohm,’cm2.

It has been observed previously (I) that small proportions of a.c. superimposed for short times do not cause any decrease in capacitance and therefore corrosion is probably negligible. The high oxidation state of the platinum electrode opposes the effect of small ripple of a.c.

In 10 per cent sodium chloride solution the change in capacitance with superimposed a.c. was more marked than in 3 per cent solution. This might be explained by the increase in chloride ion concentration or a decrease in concentration of dissolved oxygen.

The formation of a yellow film on the electrode surface was always accompanied by a large increase in capacitance. Film formation was dependent upon the ratio of a.c. to d.c. and upon the time of polarisation. The longest polarisation times with large superimposed a.c., or with a.c. alone, caused a rapid rise in capacitance, which, after switching off the polarising current, required up to two

104

Wt. loss mg,icm2

Table Vll Series Capacitance and Resistance

Measurements of Unpolarised Platinum Electrodes in Sodium Chloride Solutions

Frequency c; 5

3 per cent NaCl 60

600 2,000

10 per cent: NaCl 60

600 2,000

Resistance ohm/cm*

I ,200 245 I68

750 90 68

Capacitance pFjcm2

31.6 25.0 21.4

32.0 26.5 25.0

weeks to drop to its original value. Platinised titanium gave lower values of capacitance and resistance than platinum, and when corrosion started a decrease of capacitance was observed. These studies on the corrosion of platinum in sodium chloride solutions have shown that:

I. With up to 30 per cent superimposed a s . the corrosion increases with increase in a.c.

2. Corrosion is dependent upon the concentration of electrolyte, increasing temperature, hypochlorite formation, pH of electrolyte, “critical” value of the superimposed a.c., and the circuit used for superimposition of ax.

3. From capacitance and resistance measurements, the platinum surface is covered by an intact film which is destroyed by a s .

4. With a.c. alone, or with a high superimposed a.c., there is a similar influence on capacitance causing a large increase when polarisation is cut off. The behaviour of platinised titanium differs from that of platinum in these conditions.

5. After the longest time of polarisation, a long period without polarisation was required for the capacitance to regain its original value. This is probably related to the re-establishment of an oxide film.

Platinum Metals Rev., 1962, 6 Y (31, 105

6. The superimposition of a.c. on d.c. has a depolarising effect increasing with magnitude of a.c. However, this effect is not so significant as the changes in capacitance which occur. I t would appear that depassivation of platinum electrodes during the negative semi-cycle is not the main cause of corrosion.

A practical consequence of these results is the importance of incorporating sufficient inductance in cathodic protection installations involving platinum and platinised titanium to reduce the a.c. component in rectified currents to a harmless level.

References I R. Juchniewicz, First International Congress

on Metallic Corrosion, London, April 1961. Preprints 436-439

2 G. Bombara and D. Gherardi, La Metallurgia ltaliana, 1959, 51, (10), 462

3 J. Llopis and A. Sancho, J . Electrochem. SOC., 1961, 108, (8), 720-726

4 A. Rius, J. Llopis and F. Colom, CITCE, 1954, 6, 306 (Butterworths, London)

J. Llopis and F. Colom, Ann. Real. Sac. Esp. Fis. Y Quim., 1955, 51 By (6), 379-394

5 R. Bentley and T. R. Prentice, J . Appl. Ckem.,

6 M. Margules, Wied. Ann. Pkys., 1898, 65, 629; 1899,66, 540; R. Ruer, Z. Electrochem., 1903, 9, 235; J. C. Ghosh, J. Anzer. Ckem. SOC., 1915, 37,733-752; A. Hickling, Trans. Farday Sot., 1945, 41, (6), 333-339

7 B. V. Ershler, Comptes rend. (Doklady) Acad. Sci. U.R.S.S., 1942, 37, 226-229; Acta Pkysicochim. U.R.S.S., 1944, 19, 139-147; Disc. Faraday Soc., 1947, I, 269-277

8 J. N. Sarmousakis and M. J. Prager,J. Electro-

9 M. Cole, Ph.D. Thesis, 1954, Cambridge

I957,7, 619-626

them. Soc., 1957, 104, 454-459

University 10 K. F. Lorking. In the press 1959 11 U. R. Evans, Metals and Metallic Compounds,

Vol. 11, 1923, 238 (Arnold, London) 12 G. Grube and B. Dulk, Z. Electrochem., 1918,

24,237 12 S Altmann and R. H. Busch, Trans. Faraday -_I

sot., 1949, 459 (8), 720-724 S. E. S. El Wakkad and S. H. Emara, J . Ckenz.

Soc., 1952, Part 1, 461-466 14 F. C. Anson and J. L. Lingane, J . Amer.

15 D. C. Grahame,?. Amer. Ckem. Soc., 1942, 639 (5)j 1207-1215; 1942,64,(7)> 1548-1552; L. Young, Trans. Faraday SOC., 1954,jO, (z), 153-171; J. N. WanklynandD. R. Silvester, J . Elecirochem. SOC., 1958, 10 j, 647-654

16 6. W. Walkiden, First International Congress on Metallic Corrosion, London, April 1961. Discussion

C k m . Soc., 1957,79, (18),4901-4904

(PH 5.5)

Gold-Platinum Alloys

75- 25

70- 30

60 - 40

J

I00 220

208 258

300 310

A CRITICAL REVIEW OF THEIR CONSTITUTION AND PROPERTIES

By A. s. Darling, Ph.D., A.M.1.Mech.E.

In the second part of this article, concluded from the April issue of ‘Platinum Metals Review’, the author deals with the mechanical and physical properties of the gold-platinum alloys, their melting and working technology, resistance to oxidation and corrosion, and jinally with their applications in industry.

In spite of their corrosion resistance and high mechanical properties certain inherent characteristics of the gold-rich alloys diminish their industrial significance. Because the shape of the diagram tends to induce slight composition variations, the response to age- hardening of alloys containing approximately 70 per cent by weight of gold is somewhat erratic. Homogenisation and solution treatments cause considerable grain growth, and the ductility of some of the age-hardened alloys is rather lower than desirable. In an endeavour to minimise such defects, third element additions have been made to gold- platinum alloys for many years.

Iron was once commonly used for this purpose. Although 0.2 per cent by weight of iron ensures an effective age-hardening response from material containing up to 94 per cent of gold (41) it does not inhibit grain growth and has little effect upon the ductility

of age-hardened material. Similar objections apply to rhenium and magnesium (45, 46), both of which expedite the hardening process. Rhodium and ruthenium are the best general purpose additions (40, 42, 43). Rhodium is the element now generally added to the alloys used for the manufacture of spinning jets. Provided that a suitable quantity is added considerable advantages accrue.

The basic effect is to broaden the miscibility gap (40)~ and it is also claimed that 0.5 per cent of rhodium is sufficient to displace the two-phase region up to the solidus, thus turning the system into one of the peritectic type (39). Some fairly recent metallography by Schmid (36) tends to support this hypothesis. Table I1 illustrates the effect of rhodium additions of 0.5 per cent upon the mechanical properties of three heat-treated gold-platinum alloys (40). The rhodium endows the 75 per cent gold alloy with

Table II

Effect of Rhodium Additions upon the Mechanical Properties of Three Heat Treated Gold-Platinum Alloys (Ref. 40)

Vickers Hardness I Au-Pt I NoRh W i t h Rh U.T.S. Tons/sq. in.

No Rh W i t h Rh

27.3 52.7

44.3 62.2

79.5 76.0

Elongation per cent No Rh With Rh

16 21

13 18

10 14

Platinum Metals Rev., 1962, 6 9 (31, 106-1 11 106

3'0 I I

0 1 I , I0 I00 1000 10000

TIME IN HOURS BEFORE RUPTURE

Fig. 12 Efect of gold additions upon the time to fraciure of platinum at 900°C

considerable response to heat treatment. Rhodium contents greater than I per cent are less effective than smaller additions, the optimum quantity for the 75 per cent gold alloy, which does not normally age-harden, being about 0.5 per cent (42).

Because rhodium broadens the miscibility gap it facilitates the manufacture of harden- able spinning jets from the cheaper and more workable alloys. In some instances, however, operating conditions justify the employment of alloys containing approximately equal quantities of gold and platinum (39, 43). Such spinning jets are usually perforated in the soft condition, quenched, and finally aged. Rhodium additions reduce considerably the quenched hardness of alloys containing 35 to 80 per cent of platinum. Claims of improved ductility after ageing within this composition range are not fully substanti- ated when the platinum content exceeds 45 per cent (36).

Mechanical Properties at High Temperatures

Gold additions improve the creep resistance of platinum at moderately high temperatures. Fig. 12, which summarises the results of some time-to-rupture tests made at 900°C (37), shows that 5 per cent of gold increases the tensile strength of


platinum for a given life by a factor of three. The presence of gold increases a tendency towards intercrystalline separa t ion u n d e r s t r e s s ; rhodium-platinum alloys, being less prone to this defect, are more generally suitable for high temperature service. Gold- platinum alloys are, however, more resistant to wetting by molten glass. This characteristic can be profitably utilised in some high temperature applications.

Electrical Properties Alloys quenched from the single-phase

region have well defined resistivities, as shown by the outer curve of Fig. 13, which indicates that 50 per cent of gold raises the resistivity to a rather flat maximum of approximately 44 microhm-cm. The electrical properties of alloys quenched from the duplex region depend upon the temperature of heat treatment and the extent to which equilibrium has been attained. Fig. 13, based upon the data of Johansson and Linde (IO), indicates the resistivity at room temperature of alloys which, after slow cooling over a period of 72 hours from IOOO'C, were quenched after 156 hours at 500°C or 39 hours at 800°C. Since the structure is a mechanical mixture of two solid solutions the resistivities of all

SINGLE PHASE ALLOYS

2 0 4 0 6 0 80 I1 WEIGHT PER CENT GOLD

Fig. 13 Electrical resistivity of single phase and duplex gold- platinum alloys

107

composition duplex alloys in an vary approx- with ' O O b j * l Aaforence

imately linear manner. The 5 Oo5 !!!

time taken to approach a 0 constant resistance value ::

within regions of retarded pre- $ O0' cipitation can be very lengthy. 5 2 This characteristic is well illus- f Oo2

trated by the results of z: Johansson and Hagsten (29). 5 Ool

Fig. 14, largely based upon 3" the results of Geibel (44), I

Johansson and Linde (IO), and

16 A 4 4

u." 004

depends upon composition, and u 0:

t

2 0 40 6 0 8 0 WEIGHT PER CENT GOLD

0

Wictorin (13), illustrates the Fig. 14 kfean instantaneous temperature coegcients of gold- platinum alloys quenched from the single phase regiou mean instantaneous tempera-

ture coefficients, over the temperature ranges indicated, of alloys quenched from the single phase region. Most of these alloys are in a metastable condition and the values indicated apply only as long as the single phase structure is retained.

Careful studies of the resistance variations of specimens brought into some semblance of equilibrium within the duplex region have been made by Wictorin (13) Grube, Schneider and Esch (16), and Johansson and Hagsten (29). The compositions of the two phases change rapidly at temperatures above 7oo0C, and the apparent temperature coefficients, which increase at a rate largely determined by the slope of the limiting solubility curve, are many times higher than those of the single phase alloys.

25 5 0 7 5 100

Fig. 15 Thermal e m . $ with respect to pure gold or gold-platinum alloys (10)

ATOMIC PER CENT GOLD

Information on the instantaneous temperature coefficient at room temperature of alloys quenched from the duplex region has not been published, but it is reasonable to expect, as in the case of resistivity, a linear dependence upon composition between the limiting values of the terminal solid solutions. All the alloys have a negative thermal e.m.f. with respect to pure gold. Fig. 15, from Johansson and Linde (IO), illustrates that the maximum e.m.f., of 19.5 microvolts per "C at 18"c, is generated by the 65 per cent gold alloy.

Physical Properties The density composition curve shown on

Fig. 16 displays a slight positive deviation from linearity in accordance with the corresponding negative deflexion on the lattice

I 25 5 0 75 I ' WEIGHT PER CENT GOLD

3

Fig, 16 Density curve of quenched gold-platinum alloys (37 )


parameter curve for quenched single phase 4.0 2 5 Q

alloys (37). Fig. 17 provides the essential 2 0 -

bility data for alloys at 18°C. Although gold '.?

additions initially decrease the thermal I-w J conductivity of platinum, thc curve rapidly - m

- 10 k

W thermal conductivity and magnetic suscepti- x

"O - - 2 0 * r r

W U u)

3 Lo

levels out and rcmains almost constant at a 2~ value of about 0.25 watts/cm./dcgrec over the composition range 25 to 70 per cent of gold (10). The conductivity then rises rapidly to that of purc gold. It is now known y

-0 2 i- W z u 2

. -10 that the intermediate alloys on this curve SINGLE PHASE ALLOYS

could not all have been quenched from the single phase region and it is probable that the true thermal conductivity of single phased alloys containing 40 to 50 per cent of gold is lower than the values indicated.

Small quantities of gold rapidly reduce the paramagnetic properties of platinum, but after 10 per cent has been added the change becomes more gradual. (10). The susceptibility of quenched single phase alloys varies continuously with composition, and becomes zero for a gold content of 74 per cent. The susceptibility of alloys quenched from lower temperatures varies with gold content in a linear manner over the duplex region.

Melting and Working Practice The alloys are generally induction melted

in air in zircon crucibles, ingots being cast into moulds of graphite or water-cooled copper (45). However satisfactory the casting operation, the characteristics of the system ensure a tendency towards inverse segregation and industrial working procedures, although varying considerably in detail, are all designed to promote efficient homogenisation. The coarsc dendritic structure is preferably broken down by hot forging or rolling, after which long soaking periods are required to eliminate small areas of platinum-rich metal.

The whole range of alloys can be cold worked after quenching from temperatures not higher than IOOO'C. The most ductile material is achieved by annealing at IOOO~C, after which the temperature can be slowly dropped before water-quenching from 850°C.

2 0 4 0 60 80 I00 ATOMIC PER CENT GOLD

Fig, 17 Thermal conductivity and magnetic susceptibility data at 18°C for quenched gold-

platinum alloys (10)

Although the difficulty of working increases with platinum content up to 80 per cent, even this alloy can be easily worked after a reduction in thickness of 50 per cent. As the final properties of the resultant rod and sheet reflect the entire thermal and mechanical history of the material, casting and working procedures require very careful control.

Interesting dimensional changes result during the heat treatment of gold-platinum alloys which have been insufficiently homo- genised. This behaviour was first reported by Holzmann (47). Drawn 70/30 gold-platinum rods were found to shorten by as much as 9 per cent when heated for I hour at I 100°C. The effect became less pronounced as the specimen diameter decreased. Specimens produced from ingots which had been very slowly solidified contracted less than those from chill-cast ingots and extremely slow rates of heating tended to diminish the extent of dimensional change. The shrinkage is attributable to the more or less rapid elimina- tion of strong concentration gradients during heat treatment.

Resistance to Oxidation and Corrosion

Gold volatilises at a negligible rate in oxygen, platinum evaporates readily. The evaporation curves of gold-platinum alloys as


obtained by Raub and Plate (48) illustrate the basic characteristics of this system in a striking manner. Fig. 18 shows that small additions of gold to platinum initially decrease the evaporation rate fairly rapidly. Over the duplex region, however, the evaporation rate remains fairly constant, suggesting that the composition of vapour in equilibrium with the two phases is independent of their relative volumes. Only when the platinum-rich phase has

0 - h N 10 HOURS 1 0 0 0 ° C

20 HOURS 1 0 0 0 D C N 6 -_ E 10 HOURS I 100°C u \

I

0

0.

c) 2 0 HOURS I I OO°C

/ I

2 0 4 0 6 0 a 0 100 ATOMIC PER CENT GOLD

Fig. 18 Effect of romposition upon the rate of volatilisation of gold-platinum alloys heated in a current of oxygen (48)

disappeared does the gold reduce sensibly the rate of volatilisation. Duplex alloys which have been soaked at about 1200°C for several days in air frequently show thin surface layers of a gold-rich alloy when microscopically examined (37). This behaviour is probably a consequence of preferential evaporation from the platinum-rich phase in which platinum diffuses very slowly (33).

The alloys, very resistant to corrosion by most acids are dissolved fairly rapidly by aqua regia. Cyanide solutions dissolve the gold- rich alloys rather more slowly. The complete resistance of the gold-rich alloys to simul- taneous attack by sodium sulphate, sulphuric acid, and caustic soda is demonstrated by their prolonged employment in the viscose rayon industry.

Klochko and Nikitina (49) reported on the anodic behaviour of the system in 1955. Experiments in which a IN solution of chlorauric acid was used as an electrolyte showed that alloys annealed by cooling from ~ooo"C in air over a period of 12 days were very much more negative with respect to gold than quenched alloys. Plateaus on both sets of e.m.f. curves agreed with the width of the duplex region corresponding to the metal- lurgical condition of the spccimcns. Anodic solubility tests carried out in a 5N solution of HC1 showed that the gold-rich phase was always the first to go into solution. With all duplex alloys the dissolved part of the anode


had the composition of the limiting gold-rich solid solution. Quenched and slowly cooled alloys both dissolved at roughly the same rate, which remained fairly constant at about 0.2

to 0.3 gm, cmZ/amp-hour across the entire duplex region. The solubility of the platinum- rich solid solution compared to that of the duplex alloys was very low indeed.

Applications Gold-platinum alloys are now primarily

used as spinning jets in the viscose rayon industry (50) where they withstand corrosive conditions for long periods. Due to the abrasive action of the alkaline viscose solutions which may contain titanium dioxide (40) mechanical conditions are also severe. Heat treatable alloys are preferred, as the perfora- tion process can be performed on soft solution treated material which is subsequently aged to develop its full mechanical properties. A high hardness also facilitates the maintenance of the polished surface so desirable on the outlet faces of these spinning jets. Alloys containing 50 to 85 per cent of gold are employed. While the 70 '30 gold-platinum alloy is very widely used special conditions frequently justify the use of alloys containing 40 to 50 per cent of platinum, which have a longer working life (39, 43, 46). The benefi- cial effects of small additions of rhodium to spinning jet alloys have already been discussed.

Platinum hardens gold considerably, and laboratory utensils containing 5 and 10 per cent of platinum are frequently used for operations which do not require a more expensive or refractory alloy. Crucibles of the 10 per cent platinum alloy are, for example, very suitable for the ashing of flour and other phosphorus-containing organic materials (51). Although equal to pure platinum in its resistance to hydrofluoric and other acids, fused alkalis and sodium carbonate, the ten per cent platinum alloy is inferior with respect to aqueous or fused cyanides and fused nitrate mixtures, I t can, like platinum, be readily fused with soft glass (58).

Platinum-rich alloys are also used in the laboratory. Platinum crucibles alloyed with a few per cent of gold have a higher strength than pure platinum at I O O O " ~ , a finer grain structure, better shape stability and lower weight losses when used for a variety of analytical operations (53). Platinum-gold alloys are more readily soft soldered than pure platinum or iridium-platinum. This was once considered a factor of some importance although in these days of refined laboratory techniques the use of soft solder on platinum alloys cannot be recommended.

Films of gold-platinum alloys are applied to non-conducting substrates for a variety of purposes. Deposits are achieved by sputtering or by using a metallising paint. Sputtered films ranging in thickness from 75-2000 a can be applied to soft glass, borosilicate glass, alumina, silica and other refractories. The temperature coefficient of sputtered films is not greatly affected by thickness, being about 0.0004 per "C over the range 25 to 600°C (54).

Thicker deposits, achieved by firing on metallising preparations are being increasingly used for the production of stable, non- oxidisable resistors suitable for high temperature operations. Films having electrical resistivities of 20 to 50 ohms per square have temperature coefficients of about 0.0003 per "C. Thicker films have very much higher, and thinner films very much lower temperature coefficients (55).

Photographic methods of achieving meandering resistance paths have been developed, and these portions of the resistance over which sliding contact occurs can be suitably reinforced. The wear on such paths is very low, resistance changes being of the order of 0.6 per cent after 300,000 operations under a 4 g/load. Resistance noise values from 70' to 550°K are within the range 0.013 to 0.003 uVliV. Abrasion techniques can produce patterns having resistances of 5 million ohms within a 2 inch diameter circle (56). Elements of even higher resistance are achieved by winding alloy coated glass fibres around cylindrical formers (57).

References

40 E. Grafried, K. Portzmann, K. Ruthardt and H. Speidel, Heraeus Festchrift, 1951

41 W. Goedecke, Siebert Festchrift, 1931, 100-107

42 D.R.P., 691,061, W. C . Heraeus 43 D.B.P. 873,145, Degussa 44 W. Geibel, 2. anorg. Chem., 1911,70,240-254 45 B.I.O.S. Trip No. 3370, Technical Research

46 F.I.A.T. Final Report No. 47 47 H. Holzmann, Z. Merallkunde, 1938, 30, 160 48 E. Raub and W. Plate, Z. Metallkunde, 1957,

48, (101, 529-539 49 M. A. Klochko and V. K. Nikitina, Zzvest.

Sekt. Platiny. Akad Nauk, S.S.S.R., 1955, 29, 197-206

50 J. W. S . Hearle and A. Johnson, Platinum Metals Rev., 1961, 5, 2

51 G. Reinacher, Z. Metallkunde, 1956, 47, 607 52 G. Reinacher, Z. Metallkunde, 1957, 48,

53 G. Reinacher, Werksroffe u. Korrosion, 1959,

Netherlands Military Mission to A.C.C.

162-178

10, (9), 564-572. Also B.P. 825,079, Degussa

Physic., 1959, 30, (31, 313-322 54 R. B. Belser and W. H. Hicklin, J . Appl.

55 G. V. Planer, Inst. Radio Eng. Trans., Component Parts, 1959, CP-6, (2), 105-108

56 G. V. Planer, Paper given at the International Symposium on Component Design, Mal- vem, Sept. 1957, (Extended Summary in J . Brit. Inst. Radio Eng., 1958, 18, (3), 177)

57 R. H. Burkett, Znsr. Radio Eng. Trans., Component Parts, 1959, CP-6, (2), 109-113

58 K. W. Frohlich, Angew Chem., I948,2% B. 72


Percival Johnson’s First Publication By Donald McDonald

It is perhaps natural that this periodical, published as it is by Johnson, Matthey & Co., Limited, should occasionally look back to the early days of that company for the beginnings of the activity of which it is a modern example. In this respect the present year is a significant one, since precisely one hundred and fifty years ago its founder, Percival Norton Johnson, made his first public contribution to the knowledge of platinum by sending a short article to the Philosophical Magazine ( I ) .

The main part of this communication dealt with the fact that small quantities of platinum, when mixed with gold and such excess of silver as enabled the alloy to be parted in nitric acid, dissolved with the silver and left the gold completely freed from it. This happening was unexpected, since platinum by itself is quite insoluble in that acid, but it had been known for some time to take place.

The early workers in platinum in the later years of the previous century were very much concerned about the possible use of platinum as an adulterant for gold, with which it could be alloyed without appreciable effects on the latter’s specific gravity. Indeed this was one of the main reasons why the King of Spain prohibited the export of native platinum from New Granada. But the danger was soon shown not to exist. A platinum content of only 5 per cent already affects the colour of gold, and further additions soon whiten it completely and seriously affect its physical properties. Also it was noticed that smaller quantities of platinum in gold-less than 5 per cent-completely disappeared from it during the ordinary assaying process of cupelling with silver and parting in nitric acid. Soon it was found that it had simply dissolved with the silver and remained in solution with it, leaving the gold yielding a true assay figure for the original mixture.

Percival Norton Johnson Founder of the Jirm of Johnson Mutthey, Johnson published his jirst paper on platinum just u hundred and $By years ago. The portrait is from the oil painting by G. J . Robertson, dated 1829, now in the boardroom of Johnson, Matthey & Co.,

Limited

The first precise recording of this behaviour seems to have been that made by M. Tillet of the Paris Mint in 1779 (2). He experi- mented with 12 to 24 grains of fine gold, 2 to 4 grains of ductile platinum and fine silver about three times the weight of the gold, and found that all the platinum dissolved with the silver in nitric acid. He further reported that if the platinum was added to h e silver only the solution in nitric acid was incomplete.

A more complete investigation was made in 1798 by Robert Bingley, King’s Assay Master at the Royal Mint, London, but he did not publish his findings. Nevertheless they are known, since in 1800 he wrote a lctter

Platinum Metals Rev., 1962, 6 , (31, 112-1 14 112

describing them in detail to Charles Hatchett, a well-known chemist of the time still remembered as the dis- coverer of niobium. This letter has been preserved in the archives of the Royal Society (3), and in it Bingley describes how he alloyed platinum with gold in the proportions of 1/48, 1/24, 1/12 and 1/10 and repeatedly assayed the products by variants of the usual assay process. His findings were that with 1,/48 “the whole of the platina will be destroyed in the common process of assaying when the operation is properly carried out”, but that with 1/24 special care is necessary with the quality of the acid; with the 1/12 and 1/10 alloys further special measures have to be taken. He remarks that the alloy should be cupelled with at least three times its weight of silver and eight times its weight of lead, and that the last stages of the operation should be carried out at a higher temperature to ensure the removal of all the lead, traces of which interfere with the complete solution of the platinum on parting.

In 1812 Percival Johnson (he had not yet begun to use the second name of Norton) was a young apprentice of the Worshipful Company of Gold- smiths working with his father, John Johnson, at his home at 7 Maiden Lane (now part of Gresham Street) in the City of London. The business con- sisted of the assaying of gold and silver, the analysis of ores and minerals and the buying and selling of materials containing the precious metals, including native platinum. Percival was born on September 29th, 1792, and apprenticed on January 7th, 1807. In July 1812, when his paper was published, he was therefore aged 19 and was still an apprentice. The paper itself fills only a little more than one of the small pages in which the

Platinum Metals Rev., 1962, 6 9 (31,

1. ~ x p e i m c n i s uphicft PTOPL? Pkiina, w k a fwnlrined with By .&. Goid m d SiLvef, i~ k s o 6 d h in Nitric Ad-

PENCXVAL J O ~ N W N ,

To MF-. Tilloclr, SIR$ r h z r ~ r , the practike o f a profession where much depends nix deprivitrg gold of its alloys, having heard it suggested that plaiina might he used aq at? a d v a n t a p u s one, under the idea of $s bring but slightfy deeted by, the nitric acid, 1 Jeteintinpd un a closer irispertion of its action on that metal than had hitherto been described- The insertion of the ftrliowing remarks on my experiments wilt obliqr ine.

I 6nci;ahhough ptatina when in a pure stste I s nor acted upon by the nitric acid, that when atloycd with gold and silver it is perrrctky sofuhle, and with silver alone psrtiallg

From 1 to $ 3 per cent. OF ptatiiia to the eold was entirely dism~vrd, feavin the gold a good colaur a d perfectly pi&, having preuiou& nitxed the gold with three times its weight of silver for qwrtation.

T\wity per cent. lost &ths( leaving the cornet flaked a n d black ingide; 30 per cent, lost j ibs with the sanie 3 p penrances.

The huttons have Stn indented crystalline and red sppesr- ante afiw eitiwliatinn, nme so in prnportion to the quantity of platitis, and in the t w o lattrc propvrtions 3re rounded at the edge!.

Bv niixing douhfe the quantity o f silver the gnld was f r d of uptrards of 90 per cent. of ptatina, and more a=-

5Q-

cording lo the quantity of siivcr empioued ; md y& tbc yld seeins €0 be a necessary cotnportent for the perfect so- u t m ; for b~ mixing the following proportions of setuPr

and ftbfina, the results uwe’lhur : Platiira and silver equal to i pe; ccnt, of the former left

in dilute rctd a Iight p v d e r p m l v subsiding. 3 per cent. ave the acid a stma coltrur, half the platina emploved

&ring dissolved. 10 per cent, ti wry bright straw colour, having d;ssi&erd the $ante proportml,

15 per cent. B bright light brown, having dissolved *ha of the pJatina. 95 per c&t. a deep hrourn, dissolving @3 of the plaiina. The tao tatter pmpattinns required concentrskd acid

after the action of rhe dilute. &%ideu Lac, We& Xreet,

It may also he aorthv the notice of wur rraderc, that w4 Bod palladttim to be such a senera1 aftbe of Brazrt grttd as often to alter the coleirr thereof. We have paritcuiariy ob- xrved zt in rhe Brazil MJO, msnt of which wvtm rejeered at first sight, suspecting thcni in he eotmterleits. We tuund it I( ohert ttnrt since in a B r w 1 bar to the atneunt of nrariy +& per vent. dfte6ng the coJour thereof to neqrty that of

PEECIVAL Joawsox, Jo’y I, 1812. Awyer of Me&.

tbt metal pal&&unr. 3. ARB p. J.

The paper published by Johnson in the Philosophical Magazine in July 1812, his Frst contribution, at the

age of 19, to the metallurgy ofplatinum

113

T H E

Philosophical Magazine then appeared and is addressed to Mr. Tilloch, the Editor. Its title is : “Experiments which prove Platina, when combined with Gold and Silver, to be soluble in Nitric Acid. By Mr. Percival Johnson.” It is subscribed Maiden Lane, Wood Street, July Ist, 1812.

After a short introductory paragraph he states: “I find, although platina when in a pure state is not acted upon by the nitric acid, that when alloyed with gold and silver it is perfectly soluble, and with silver alone partially so. From I to 15 per cent. of platina to the gold was entirely dissolved-having previously mixed the gold with three times its weight of silver for quartation. Twenty per cent. lost 7,’1zths . . . 30 per cent. lost 4’9th”’ He then describes the appearance of the cupelled buttons and continues: “By mixing double the quantity of silver the gold was freed of upwards of 20 per cent. of platina, and more according to the quantity of silver employed; and yet the gold seems to be a necessary component for the perfect solution; for by mixing the following proportions of silver and pdatina, the results were thus: Platina and Silver equal to I per cent. of the former left in dilute acid a light powder partly subsiding. 5 per cent. gave the acid a straw colour, half the platina employed being dissolved. 10 per cent. a very bright straw colour, having dissolved the same proportion. 15 per cent. a bright light brown, having dissolved 4,7ths of the platina. 25 per cent. a deep brown, dissolving z,/3rds of the platina. The two latter proportions required concentrated acid after the action of the dilute.”

So it appears that this young man set about his experiments in a completely logical manner and expressed his results in a plain and simple style, with a nice economy in

commas. His meaning is perfectly clear and he uses no unnecessary words and no far- fetched ones.

In short, it is a model statement of the results of a scientific enquiry.

The question now arises as to how much he knew of the previous work on the subject. Whether he was aware of Tillet’s paper is a question no one can answer, but undoubtedly he was acquainted with Bingley. The latter had been King’s Assay Master at the Mint since 1798 and must have had intimate business connections with the Johnsons, and there is plenty of evidence later of close personal friendship between him and Percival. It seems safe to assume that Bingley knew of Johnson’s proposal to publish and probably encouraged it. That neither the help nor the precedence are acknowledged is not at all unusual for those times, and the fact remains that this was the first publication of the observations in English.

But the statements about the solubility of platinum in nitric acid under these circum- stances was not the only communication in this paper. There is also, as will be seen, a short appendix concerning the presence of palladium in Brazilian gold. This addendum is initialled “J. and P. J.”, showing that both father and son were responsible for it. Their observation had important results some twenty years later, when Brazilian gold had become a drug in the market owing to the difficulty of removing the palladium, and the tellurium which accompanied it, from the native bullion. At that time Percival Johnson proved to be the only refiner in Europe who could successfully undertake this work, and in the course of the next twenty years he refined more than a quarter of a million ounces of the product of the Imperial Brazilian Mining Association.

References

I P. N. Johnson . . . . .. . . Phil. Mag., 1812, 40, 3-4 2 M. Tillet . . . . . . . . . . Mim. Aced. Sci. Paris, 1779, pp. 373-377, 385-437,

3 Robert Bingley . . . . . . . . Letter to Charles Hatchett in the Manuscript Collec- 545-549

tion of the Royal Society


ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES The Constitution Diagram of the Ruthenium- Rhenium System E. M. SAVITSKII, M. A. TYLKINA and v . P. POLYAKOVA, Zhw. I\ieorg.Khim., 1962, 7, (2), 439-441 Alloys of the system at intervals of 10 wt.:, were prepared and examined by thermal analysis, microstructural and X-ray analysis, and hardness measurements. An uninterrupted series of solid solutions with melting points between those of Ru (2250%) and Re (3170°C) was found. The maximum hardness in the cast and annealed states occurs in alloys with 60-70 wt.:, Ru. Lat- tice parameters increase with increasing Re content.

A Study of the Ruthenium-Rhenium System E. RUDY, B. KIEFFER and H. EROHLICH, Z. Metall-

Sintered and arc-melted specimens were used in the investigation. Melting point determinations and X-ray, electrical conductivity, hardness and ductility measurements were made on a series of alloys. A continuous series of solid solutions was found. The hardness curve shows a maximum at about 40% Re. The cold-deformability of Re is decreased by Ru additions.

Research on the Alloys of Noble Metals with the More Electropositive Elements. V. Micrographic and X-Ray Examination of Some Magnesium-Iridium Alloys R. FERRO, G. RAMBALDI and R. CAPELLI, J. Less- Common Merals, 1962, 4, (I), 16-23 Alloys in the range 0-75 wt. "/, Ir were studied by chemical analysis, specific gravity determination, micrographic and X-ray examination. Thermal analysis of alloys with up to 16 wt.:; I r was carried out. Results obtained indicate the exis- tence of a eutectic point (3.2 at.O/, Ir and 615'C). The solid solution c-phase, corresponding to Mg&, and the &-phase, corresponding to Mg,Ir, were identified. A third phase (Mg,Ir ?) was detected. Crystal structure data for the c- and %phases are given.

Revision of the Phase Diagram for the Bi-Rh System R. N. KUZ'MIN and N. N. ZHURAVLEV, Soviet Phys. Cryst., 1961, 6, (2), 209-210 (Transl. of Kristallo- grafilva, 1961, 6, (21, 269-2711 Thermal analysis showed that for the alloy containing 19.80 wt.% Rh the transition from

kunde, 1962,53, (2),90-92

$-Bi,Rh to cr-Bi,Rh occurs at 420'C. Needle- shaped crystals of P-Bi,Rh were obtained by a casting method.

Crystal Structures of ThRh,, ThRn and ThIr J. R. THOMSON, Nature, 1962, 194, (May 5), 465 ThRh, (65 at."/, Rh) was found to have a hexa- gonal crystal structure of the NiJn (B 8,) type. ThRu and T h l r have orthorhombic crystal structures. Lattice parameters are given.

The Oxidation of a Work-Hardened and Recrystallised Tungsten-Platinum Alloy R. F. VoITovIcH, MetaZloved. Term. Obrab. Met.,

It was found that in the temperature range 500"- g00"C a small addition of Pt to W sharply decreases the oxidation resistance of W. The oxidation resistance of a 1 . 5 ~ ~ ~ Pt-W alloy is reduced by work-hardening, particularly at temperatures above 650°C.

Structures and Compositions of the Silicides of Ruthenium, Osmium, Rhodium and Iridium L. N . FINNIE, J . Less-Common Metals, 1962, 4, (11, 24-34 The X-ray powder method was used to study the silicides of Ru, Os, Rh, and Ir stable at r340", I35OC, 1170' and 1j4o"C, respectively. The structure types and cell constants of previously reported RuSi (FeSi-type) and IrSi, (Na,As- type) and for the new phases OsSi (CsC1-type) and OsSi, were determined. OsSi, OsSi, and RhSi are stabilised by A1 or oxygen. The phases RUS~~.~&, , .~ , OsSil.8ho.3, O S S ~ ~ . ~ + ~ . ~ , RhSio.,+o.l, lrSi~.5~,,.l , and IrSi2.,,*o., were also found,

Structures and Properties of Uraninm- Fissium Alloys s. T. ZEGLER and M. v. NEVITT, U.S.A.E.C. Report

Synthetic U-Fs (Fs-Zr, Nb, Mo, Ru, Rh and Pd) alloys similar to those intended for the first core loading of the Experimental Breeder Reactor I1 were studied. Phase relations were shown to be similar to those in the U-Mo-Ru ternary system.

The Solid Solution of Mercury in Palladium K. TERADA, Acta Cryst., 1961, 14, (12), I299 The lattice parameter of Pd in solid solutions containing up to 13.8 at."',, Hg was determined. A body-centred tetragonal PdHg phase was obtained at concentrations above 13.8 at.?; Hg.

1961, (7),47-48

ANL-6116, Jd. 1961, 50 pp.

PZatinumMetaZsRev., 1962, 6 (31, 115-123 115

The Palladium-Hydrogen System J. G. ASTON and P. MITACEK, Abstracts of Papers, 10 M, Div. of Inorganic Chem., 141st Meeting, A.C.S., Washington,D.C.,Mar. 1962 Heat capacity measurements were made on hydrogen absorbed in block Pd with 8,4,2 and approximately I Pd atom/mole H2, respectively. In the temperature range I j " to I jo"K, the heat capacity per atom of hydrogen is independent of the composition. Either only a molecule such as PdHa exists in this region or only one of the two phases contains hydrogen and is of constant composition. Hysteresis occurs. Measurements of the energy of activation associated with diffusion showed two distinct processes with energies of activation of 4600 and 2900 cal, respectively. X-ray data on Pd-H and data on resistivity and rates of diffusion were reviewed.

The Solubility of Oxygen in Transition Metal Alloys R. T. BRYANT, J. Less-Common Metals, 1962, 4, (I), 62-68 The solid solubility of oxygen in Nb, and alloys of Nb with Mo, Re, Ru, Zr and Ti was determined. The solubility in Nb is reduced by additions of Mo, Re, Ru, and Zr, but is increased by alloying with Ti.

Hall Effect in Palladium-Silver and Pal- ladium-Copper Alloys K. K. RAO, M. E. NICHOLSON and J. M. SIVERTSON, Bdl. Amer. Phys. Sac., Series II , 1962, 7, (2), 116 (Abstract of paper presented at the Amer. Phys. SOC. Southwestern Meeting, Austin, Texas, Feb. 1962) Hall coefficients were determined at 309°K. The Hall constants for alloys having C in solid solution were found to have lower numerical values than those for the alloys with no C. Results indicate that, for Pd-Ag and Pd-Cu up to about 60% noble metal, part of the Hall coefficients may be associated with the paramagnetism of the alloys.

Temperature Dependence of the Thermo- electric Power of the Pd-Ni Alloy System A. I. SCHINDLER and E. W. KAMMER, Bull. Amer. Phys. SOC., Series II , 1962, 7, ( 9 , 230 (Abstract of paper presented at the Amer. Phys. SOC. March Meeting, Baltimore, Mar. 1962) The thermoelectric power (T.E.P.) of the alloy system was measured relative to pure Pd in the range 77" to 273°K. Measurements were also made at 4" and 20°K for several selected alloys. The isothermal variation of the relative T.E.P. as a function of composition shows a minimum around 50 at.yb Pd. With increase of temperature the position of the minimum shifts to lower compositions. A distinct break in the T.E.P. appears to be related to the ferromagnetic- paramagnetic transition boundary. Only 10 at. Ni-Pd and 17.2 at.:/, Ni-Pd have Curie temperatures within 77" to 273°K.


Superconductivity and Ferromagnetism of Chromium Alloys and Compounds B. T. MATTHIAS, T. H. GEBALLE, E. CORENZWIT and G. W. HULL, Bull. Amer. Phys. SOC., Series II , 1962, 7, (3), 176 (Abstract of paper presented at the Amer. Phys. SOC. March Meeting, Baltimore, Mar. 1962) It was found that Cr-Rh and Cr-Ir alloys become superconducting below 1°K. Cr-Ru alloys also become superconducting near I "K. The transition temperature for j"/> Cr-Ru is less than that of pure Ru.

Thermoelectricity at Low Temperatures. IX. The Transition Metals as Solute and Solvent

TEMPLETON, &'roc. Ray. soc., series A, 1962, 266, (13q), 161-184 Experiments were carried out on alloys of Au with Cr, Mn, Fe, Co, and Ni and alloys of Pt and Pd, separately, with Fey Mn, Cu, and Sn in the temperature range o.r"K to a few degrees K. Data are presented of the thermoelectric behaviour of these alloys and theories are proposed to account for the anomalous behaviour observed.

Interface Impedance and the Apparent Electrical Resistance of Palladium Hydrides in Aqueous Solutions J. c. BARTON and F. A. LEWIS, Trans. Faraday Sac.,

Measurements of electrical resistance of hydrided Pd wires by a.c. methods in strongly acid solutions show even greater errors than d.c. measurements. It is possible to compensate for these errors by simulating the equivalent components of the electrolyte and interface impedance in the bridge balancing arm. The reduced resistance values obtained by a.c. measurements are related to the magnitude of co-conduction of the bridge current through the electrolyte.

The Rhodium-Chlorine System at High Temperature w. E. BELL, M. TAGAMI and u. MERTEN, J. Phys. Chem., 1962~66, (3), 490-494 The system was studied over the temperature range 700" to 15oo~C and over the chlorine pressure range 0.01 to 1.0 atm. Under these conditions solid RhCl, is the only stable condensed chloride. The dissociation pressure of RhCl,(s) reaches I atm at 970°C. RhCI, and RhC1, are the important gaseous species. Vapour pressure data for RhC1, and RhC1, are shown in a table.

Sorption and Magnetic Susceptibility Studies on Palladium-Nitric Oxide Systems R. w. ZUEHLKE, Diss. Abs., 1961, 22, 1432 The sorption of NO on finely divided Pd and Pd/SiOz gel was studied in the temperature range 195" to 308°K. On Pd, NO is first adsorbed by chemisorption which is followed by additional

D. K. C. MACDONALD, W. B. PEARSON and I. M.

1962, 58, (469), 103-109

physical adsorption and then by dimerisation of the physically adsorbed layer to N,O,. The magnetic susceptibility steadily decreases as adsorption progresses. The sorption of NO on Pd/SiO, gel at room temperatures seems to proceed as a pseudo-chemisorption. The nature of the Pd layer is discussed.

Thermodynamic Properties of Palladium- Iron Alloys in the Temperature Range 1200-1460°C E. AUKRUST and A. MUAN, Acta Met., 1962, 10,

(51, 555-560 Oxidation experiments were carried out on Pd-Fe alloy samples suspended in a thermal balance. The oxygen potential of the system was increased in small increments by adjusting the ratio of the CO, /CO mixture surrounding the alloy. Weight increase of the sample indicated the start of oxidation of Fe in the alloys. The activity of Fe in the alloys was calculated.

Surface Self-Diffusion and Surface Energy Measurements on Platinum by the Multiple Scratch Method J. M. BLAKELY and H. MYKURA, Acta Met., 1962,

Interference microscopy was used to observe the decay of sets of parallel scratches on Pt crystal surfaces during vacuum annealing at temperatures between 890' and 1310'C. Surface self-diffusion constants were evaluated from smoothing rates and surface energy was estimated.

The Corrosion Resistance and Mechanical Properties of Titanium-Molybdenum Alloys Containing Noble Metals M. STERN and c. R. BISHOP, A.S.M. Trans. Quarterly,

Mo-Ti alloys with o to 35y0 Mo and with or without about 0.2~: Pd were prepared both by consumable arc melting and induction melting in graphite. The corrosion resistance of these alloys in both oxidising and reducing media was evaluated in laboratory and field tests. Mechanical properties were also tested. Additions d' 30 to 4076 Mo to T i increase its corrosion resistance in reducing media, but decrease its resistance in oxidising conditions. Additions of about 0 . 2 ~ ; Pd to Mo-Ti alloys do not increase their corrosion resistance to oxidising media, but increase the resistance of alloys with 5 to 15"" Mo in reducing environments. An alloy containing 15 to 2on0 Mo and 0.2% Pd has the most satisfactory combination of corrosion resistance and mechanical properties.

The Behaviour of Ruthenium Trichloride in Aqueous Solutions F. PANTANI, J. Less-Common Metals, 1962, 4, (2), 116-123 The formation of hydroxy-camplexes in aqueous

10, (513 565-572

1961, 54, (319286-298

solutions and mixtures of chlorohydroxy- and chloro-complexes in the presence of alkali chloride and HCI were shown by argentometric and alkalimetric titrations. A reduction to Ru(II), a further reduction, and the catalytic discharge of H+ were recorded polarographically. The presence of Ru in the -4 valency state is indicated.

Ring substitution Reactions of Metal- Cyclopentadienyls and Metal- Arenes M. D. RAUSCH, Abstracts of Papers, 25 M, Div. of Inorganic Chem., 141s Meeting, A.C.S., Wash- ington, D.C., Mar. 1962 Ring substitution reactions of ferrocene and other x-cyclopentadienyl derivatives of V, Cr, Mn, Ru, and 0 s have been shown. Similar reactions of several x-arene Cr compounds have also been observed. Oxidation, reduction, dehydration, addition, and rearrangement reactions of sub- stituted metal-cyclopentadienyls are described.

Substitution and Exchange Reactions in Rhodium (I) and Iridium (I) Carbonyl Com- plexes A. WOJCICKI, Abstracts of Papers, 32 M, Div. of Inorganic Chem., 141st Meeting, A.C.S., Washington, D.C., Mar. 1962 It was found that Rh(CO),(am)Cl and Ir(C0) (am)Cl (am =p-anisidine and p-toluidine) rapidly exchange with radiochloride ion at -35°C in C,H,OH and that their reaction with C,H,N to displace the co-ordinated C1 is extremely rapid at -80°C. CO exchange with Rh,(CO),Cl,, R h ( C O ) , ( a m ) C l , R h ( P P h , ) , ( C O ) C l , Rh(PPhz),(CO)NCS, and Ir(CO),(am)Cl was also studied, Results indicate that carbonyls of Rh(1) and Ir(1) react at comparable rates.

Contact Potentials of Homologous Fatty Amines Adsorbed on Platinum w. A. ZISMAN and K. w. BEWIG, Abstracts of Papers, 20-1, Div. of Colloid and Surface Chemistry, 141s Meeting, A.C.S., Washington, D.C., Mar. 1962 Monomolecular films of a homologous series of pure, primary fatty amines from C, to C,, were adsorbed on pure polished Pt. The change in the contact p.d. between the Pt electrode and a reference electrode of Teflon-coated Au as a result of the adsorption of each monolayer was measured at 20°C and 50°, R.H. The effects of homology, molecular packing, orientation, and solvent inclusion were studied.

Effect of Progressive Fluorination o f a Fatty Acid on the Wettability of Its Adsorbed Monolayer E. G. SHAFRIN and w. A. ZISMAN, Abstracts of Papers, 20-1, Div. of Colloid and Surface Chemistry, 141s Meeting, A.C.S., Washington, D.C., Mar. 1962 Films of a series of heptadecanoic acids with


perfluoroalkyl substitutions in 17-position of 9-ethyl, 9-propyl, 9-pentyl, and 9-heptyl groups were prepared by adsorption from the melt on Cr. Films of the 9-heptyl compound were also prepared on Pt, Ni, quartz, and soda-lime glass. Wettability tests showed that the metal substrates were less wettable than the siliceous surfaces. Differences in rhe wettability of terminally fluorinated aliphatic acids and analogous fully fluorinated acids were examined.

ELECTROCHEMISTRY The Nature of Hydrogen Adsorption on Electrodes of the Platinum Metals M. BREITER, Electrochim. Acta, 1962~7, (Jan. ;Feb.), 25-38 Adsorption studies were carried out in 2.3M H 2 S 0 4 for Pt, Ir and Rh, and in various other solutions for Pt. With Pt and I r electrodes, hydrogen is strongly bound at relatively positive potentials and weakly bound at relatively negative potentials. The strongly bound hydrogen is adsorbed as H atoms and it is suggested that the weakly bound hydrogen is similarly adsorbed. The influence of anions on the adsorption of hydrogen by Pt is discussed.

A Study of the Electrochemical Properties of Powders W. TOMASSI, Electrochim. Acta, 1962, 7, (Jan./ Feb.), 91-99 Powder electrodes consisting of activated C or Pt black were found to have a potential lower than that of a Pt wire electrode in the same (C12/Ckaq) system. A cell which gave electrical work and could be charged and discharged, with the properties of an accumulator, was constructed. The powder electrodes may also be used in electrolytic gas evolution processes with a profitable lowering of the electrolysis potential. Gases evolved are adsorbed on the powder of the electrode. Results obtained in the electrolysis of 0.5 N HC1, 0.5 N H,SO,, 25:" KOH, 25", NaOH, and 5 N NaCl solutions are given.

An Investigation of Anion Adsorption with the Aid of Marked Ions K. SCHWtlBE, Electrochim. Acta, 1962, 6, (I-4), 223-235 Adsorption on Pt, Ni, and Fe sheets and films was measured by means of 3GCl-, **Brr, 3GC10,-, 35S0,2-, H 3 W and W N - . A method was developed for the measurement of adsorption when the metal was in contact with the solution. It is thought that exchange between oxygen on the metal and the anion occurs. It was shown by autoradio- graphy that adsorption occurs preferentially at the grain boundaries and increases with decreasing grain size. Results obtained in the investigation show that passivation may be considered as a competition between metal dissolution, coverage by a passivating oxide film, and exchange between the oxygen and anions.

Consideration of the Mechanism of the Electrode Process of the Chlorine Electrode on Carbon and Platinum Powders. Part I w. TOMASSI, Przemysl, 1962, 41, (z), 62-64 (English summary) Results are given of experiments using a Pt/C electrode in an aqueous solution containing chlorine and C1- ions. The phenomena observed during electrolysis are explained by a thermodynamic model. The reaction zAg(s) -2HClaq+ zAgCl(s) FH, is used to illustrate the possibility of an easy spontaneous reversion of the course of some reactions.

Part 11. Mechanism of the Electrode Process Ibid., (3), 126-128 The mechanism of the electrode process of the chlorine on C and Pt powder is discussed. The parts played by three zones of the surface of the disintegrated phase is described.

The Phenomenon of the Decrease of Poten- tial of Powder Electrodes in the C1,-Cl--H,O System and Its Possible Interpretation H. JANKOWSKA, w . TOMASSI, and D. KOCOT- BONCZAKOWA, Electrochim. Acta, 1962, 6, (I-4), 237-243 A study of powder electrodes in the CI,-Cl-- H,O system showed that the C and Pt powder electrodes have a smaller potential than a Pt wire dipping into the same system. This effect was not found with a SiO, gel electrode. An adsorption element consisting of a Pt wire electrode and a C powder electrode in contact with the C1,-Cl--H,O system was developed. An interpretation of the observed phenomena is given.

Reduction Mechanism of Chemisorbed Oxy- gen on Platinum Electrodes by Molecular Hydrogen

( 5 1 3 425-47 M. W. BREITER, J. Electrochem. SOC. , 1962, 109,

Experimental work was carried out to distinguish between chemical and electrochemical reduction of chemisorbed hydrogen on a smooth Pt wire electrode in IN HCIO, at 3orC. Reduction by molecular hydrogen at open circuit occurs at a much lower rate than the electrochemical reduction. The anodic current of hydrogen oxidation equals the cathodic electrochemical reduction current on the oxygen layer.

ELECTRODEPOSITION Deposition of Several Platinum Metals from Molten Cyanide Electrolytes R. N . RHODA, Plating, 1962, 49, (I), 69-71 A method is described for depositing hydrogen- free Pt, Ir, and Ru from molten NaCN or 53 wt. "/, NaCN-KCN electrolytes. The Pt metal to be deposited is dissolved in the electrolyte by passing ax. between electrodes of this metal suspended


in the molten salt. The maximum thickness of sound deposits is 0.01 in. for Pt, 0.003 in. for Ir, and 0.0025 in. for Ru. Current densities are 0.3 to 3.0 amp/dm2 for Pt, 1.4 to 5.1 amp/dm2 for Ir, and 0.5 to 1.8 arnp/dm* for Ru, with cathode current efficiencies of 65 to 98% for Pt2+, 9 to 20% for Ir3+ and I I to 45 74, for Ru3+.

Palladium Plating J. J. MILES, A.T.E.Journa& 1962, 18, (I), 63-65 The electrodeposition of Pd from a bath based on sulphamate complexes of the metal and electroless deposition of Pd from a bath based on sulphamic acid solutions of Pd sulphamate complexes are discussed briefly. Properties of Pd electrodeposits and applications of both types of deposit in electrical engineering are described.

Noble Metal Electroplating for Electrical Engineering A. KLEINLE and 0. LOEBICH, Galvanotechnik, 1962, 539 (21, 62-74 The properties and applications of electrodeposited Ag, Au, Pt, Pd, and Rh are discussed in detail. Among the many applications described are electrical contacts, printed circuits, semiconductors, electron tubes, high-frequency circuits, and platinised Ti anodes. Plating techniques, including those for electroless plating of Ru, Rh, Pd, and Pt, are also discussed. (10 references)

The Properties and Applications of Noble Metal Coatings in Engineering H. w. DETTNER, Galvanotechnik, 1962, 53, ( z ) , 87-92 In this review the mechanical and corrosion properties of Ag, Au, Pt, Pd, and Rh coatings are described. Details are given of the electrical properties of Ag, Au, Pt, Rh, Pd, Os, and Ir. Applications of Ag and Au coatings in the electrical industry and of materials coated with the Pt metals are mentioned. (23 references)

CATALYSIS Catalytic and Electron Spin Resonance Investigations of Supported Platinum Catalysts c. NICOLAU and K.-H. SCHNABEL, Nature, 1962, 193, (iMar. 3), 871-872 Pt/A1,0,, Pt/C/Al,O,, Pt/SiO,, and Pt/C/SiO, catalysts were evaluated for activity in the C,-dehydrocyclisation of iso-C,HIa and the production of I, I, 3-trimethylcyclopentane. Electron spin resonance spectra of these catalyst systems were investigated. The activity of the catalysts containing C is higher than that of those without C . It is suggested that a relationship exists between the free electrons recorded by means of the electron spin resonance method and the activity of the catalyst systems.

Chemisorption Studies on Supported Platinum H. L. GRUBER,~ . Phys. Chem., 1962, 66, ( I ) , 48-64 The adsorption of hydrogen, oxygen and CO on q-A1,O8 and on 1.1% Pt/q-Al,O, reforming catalysts was investigated. Hydrogen adsorption was used to determine the Pt surface area of the catalysts, which were prepared by impregnation. Heat treatment of the catalysts at 500°C results in a decrease of Pt dispersion. The amounts of hydrogen and oxygen adsorbed by the catalysts in different steps of oxidation-reduction cycles were measured. A mechanism for the oxidation- reduction cycle is proposed. Studies of CO adsorption showed that it depends on the degree of Pt dispersion and the naturc of the support and that the Pt is present as a discontinuous monolayer or as small crystallites.

Catalysis of Fuel Cell Electrode Reactions R. B. RozELLE, Dks. Abs., 1961, 22, (6), 1842 The catalytic activity of Group VIII and Ib metals in fuel cell anode reactions was investigated. Group VIII noble metal catalysts produce theoretical or near theoretical potentials for the hydrogen electrode in aqueous NaOH electrolyte. Group Ib metal catalysts produce much lower potentials for this electrode. Similar results are obtained with CO, C,H,, C,H,, and C,Ha electrodes.

Platinum (11) Catalysed Reaction of Silicon Hydrides with Olefins as an Example of Co- ordination Catalysis A. J. CHALK and J. F. HARROD, Abstracts of Papers, zgM, Div. of Inorganic Chem., 141st Meeting, A.C.S., Washington, D.C., Mar. 1962 The activation of chemical bonds by certain metal ions and the effects of the retention of the resulting species in the co-ordination sphere of the metal ion are discussed. The reactions of silicon hydrides with olefins are compared with other co-ordination catalyses. It was found that Pt(I1) olefin complexes are simple homogeneous catalysts for the addition of ESi-H to olefins and it is proposed that a Pt(I1) olefin hydride complex is a reaction intermediate. When the olefin is replaced by a similar but less reactive x acceptor ligand, a hydride may be isolated.

The Stability of Hydrocracking Catalysts

WADLINGER and w. P. HAWTHORNE, Abstracts of Papers, 64, Div. of Petroleum Chem., 141st Meeting, A.C.S., Washington, D.C., Mar. 1962 Pt and Co-MOO, catalysts were compared for stability in cycles of gas oil hydrocracking and oxidative regeneration at conditions causing declining activity and product value. Acid sites appear to be rate-controlling with Pt catalysts, while with Co-MOO, catalysts hydrogenation- dehydrogenation activity appears to be rate-

C. G. MYERS, W. E. GARWOOD, B. W. ROPE, R. L.


controlling. The reduction in the surface area of the catalysts during operation was studied.

Some Recent Advances in Hydrocracking

6Q, Div. of Petroleum Chem., 141s Meeting, A.C.S., Washington, D.C., Mar. 1962 The performance of a new unspecified noble metal-containing hydrocracking catalyst is described. This catalyst is more resistant to the deactivating effects of naturally occurring feed N compounds than catalysts previously used for hydrocracking. It is shown that the catalyst may be used at 1500 p.s.i. when feed N content is as high as 1000-2000 p.p.m.

Mechanisms of Homogeneous Catalytic Hydrogenation and Related Processes J. HALPERN, Abstracts of Papers, IOQ, Div. of Petroleum Chem., 141st Meeting, A.C.S., Washington, D.C., Mar. 1962 Recent studies on the mechanisms of homogeneous catalytic hydrogenation are described. The function of a Ru(I1) chloride catalyst in the hydrogenation of some olefinic compounds is discussed. Other related reactions which involve (i) activation of the C=C bond through x- complexing and (ii) addition across the C=C bond by rearrangement of the x-bonded complex to an u-bonded one, are considered.

A. VOORHIES and W. M. SMITH, Abstracts Of papers,

Selective Catalytic Hydrogenation of Acety- lenes

R. A. RAPHAEL and R. G. WILLIS, Tetrahedron, 1961, 16, (I-4), 16-24 A royo PdlC catalyst was used in the study of the stepwise catalytic hydrogenation of undeca-I, 7-diyne. Protection of the ethynyl group during hydrogenation was achieved by conversion into the corresponding I-bromoacetylene. The partial catalytic reduction of several acetylenic hydrocarbons using Pd/CaCO,, Pd/BaSO, and Pd/C catalysts was found to produce substantial amounts of trans-ethylenes. Stereomutation of cis- to trans-ethylenes occurred. The extent of the stereomutation depends on the quantity of catalyst used and on its origin.

N. A. DOBSON, G. EGLINTON, M. KRISHNAMURTI,

Effects of Temperature and Catalyst Varia- tion upon the Stereochemistry of Hydro- genation of Disubstituted Benzenes R. D. SCHUETZ and L. R. CASWELL,~. Org. Chem.,

The hydrogenation of the three xylenes was carried out on Adams' (PtO,) and Raney Ni catalysts. With PtO, catalyst the yields of trans- dimethylcyclohexanes obtained from the xylenes were in the order para>meta>ortho, while with Raney Ni they were in the order meta>mtho> para. Hydrogenation of diethyl phthalate on PtO, failed to give a trans product, but on

19623 279 (21, 486-489

Raney Ni significant amounts were obtained. For all xylenes, increase of temperature resulted in increased yield of tram isomers, but increased pressure had little effect. The amount of catalytic isomerisation of cis isomers was insufficient to account for the amounts of trans products of hydrogenation, and it is concluded that the trans products are formed during hydrogenation.

The Erdolwerke Frisia Refinery at Emden J. H. SCHEWE, Erdol u.Kohle, 1962, 15, (I), 11-14 The layout and operation of this refinery are described. Principal units are the 30,000 b/d crude oil distillation plant, the naphtha desul- phuriser, the 4000 bid catalytic reformer, and the LPG recovery plant.

Activation of Metal Hydrogenation Catalysts by Irradiation D. G R A H A M , ~ . Phys. Chem., 1962, 66, (3), 510-511 The activity of 30% NiIFilter-Cel, SYL Pd/C and I "4 Pt iC catalysts was measured after high-energy irradiation. Both the Ni and Pd catalysts showed increased activity after 2 meV p- and X-irradiation although the activity decreased again with time. The Pt catalyst was not affected by radiation at the 2 meV level, but its activity increased after 3 meV irradiation. It appears that active centres are both created and destroyed by irradiation. The energy required for forming new active centres and the stability of these centres vary directly with the temperature required for atomic diffusion in the catalyst metal surface. This temperature is a function of the metal's melting point.

Mechanism of Oxidation, Hydrogenation and Electrochemical Combustion on Solid Cata- lysts. VII. Problems of Chemisorption. Mechanisms of the Origin of the Hydrogen and Oxygen Electrode Potentials on Platin- ised Platinum 0. K. DAVTYAN and E. G. MISYUK, Zhur. Fiz Khim., 1962, 36, (4), 673-680 (English summary) Changes in potential arising from the electrochemical deposition of oxygen or hydrogen on the surface of platinised Pt electrodes, or from their removal, are explained by assuming migration of chemisorbed atoms. Atoms from active centres migrate to the less active or inactive centres in the case of deposition of gas, and vice versa in the case of removal of gas. The migrational processes tend towards dynamic equilibrium with time. I t was shown that active centres for hydrogen and oxygen on Pt are energetically inhomogeneous.

Olefin Oxidation with Palladium Chloride Catalysts

SEDLMEIER and A. SABEL, Angew. Chem., 1962, 74, (31, 93-128 The mechanism of the oxidation process, with

J. SMIDT, W. HAFNER, R. JIRA, R. SIEBER, J.


particular reference to the oxidation of C,H, to CH,CHO is discussed in detail. A commercial process for the manufacture of CH,CHO employing a PdC1,-CuC1, catalyst solution is described.

Enrichment of Heavy Water by High- Pressure Exchange Between Hydrogen and an Aqueous Catalyst Suspension. Part 11. Construction and Operation of a Pilot-Scale Experimental Plant S. WALTER, E. NITSCHICE, C. BODE, E. W. BECKER, R. P. HUBENER, R. W. KESSLER and U. SCHINDEWOLF, Chem.-2ng.-Techn., 1962, 34, (I), 7-10 The principles of operating this dual-temperature exchange process using an aqueous suspension of o . I " /~ Pt/C as catalyst are discussed. The construction and operation of the pilot-plant are described. Results of an 86-day experiment show the technical feasibility of the process and justify earlier estimates of its economics.

Part 111. Influence of Specific Exchange Efficiency by Additives E. w. BECKER, R. w. KESSLER and R. r. H ~ E N E R , Chem.-Ing.-Techn., 1962, 34, (2), 105-108 The effect of additions to the liquid phase of various acid, neutral and basic inorganic materials and of surface-active organic materials was studied. Additions of nitrogen, CH,, H,S and CO were also made to the gas phase. The results obtained are discussed with reference to the deleterious effects which may be produced by impurities present in the process materials.

The Effect of Oxygen on the Catalytic Activity of Platinum Films in Hydrogen Isotope Exchange G. K. BORESKOV and A. A. V A S l ~ ~ V 1 C H ~ K i n e t i k a i Kataliz, 1961, 2, (5), 679-683 The poisoning effect of oxygen on the adsorption of hydrogen by Pt films, on the exchange of adsorbed tritiumwithmolecular hydrogen, and onthe exchange in molecular hydrogen was studied. With increased adsorption of oxygen, hydrogen absorp- tion decreases. The presence of small amounts of oxygen has no marked effect on the adsorptive and catalytic properties of the films. The adsorption of hydrogen and velocity of isotope exchange on sites not occupied by oxygen are not affected by the presence of considerable quantities of oxygen.

The Poisoning of Platinum/Alumina Cata- lysts Containing Different Amounts of Metal, Investigated by Means of Thi0~hene-S~~ KH. M. MINACHEV, D. A. KONDRAT'EV and P. I. SLYUNYAEV,KinetikaiKatuliz, 1961,2, (5), 690-693 The distribution of S on catalysts containing 0.05 to I O . ~ " , Pt as a result of the passage over them of a mixture of 98,: cyclohexane and 2 O / ,

thiophene was investigated. The experimental temperature and hydrogen pressure were 450°C

and 20 atm, respectively. The regeneration of the poisoned catalyst by the passage of pure cyclohexane was also investigated.

Different Catalytic Activities of Platinum and Palladium in Cydohexene and Cyclo- hexadiene Conversions V. M. GRYAZNOV, v. D. YAGODOVSKII, E. A. SAVEL'EVA and V. I. SHIMULIS, Kinetika i Kataliz, 1962,3, (I), 99-102 Films of Pt and Pd prepared in the same way differed greatly in their catalytic properties. In the conversion of cyclohexene and cyclohexa- diene- 1,3 dehydrogenation predominated when the Pt catalyst was used, and redistribution of hydrogen occurred when the I'd catalyst was used. The difference in catalyst activity is attributed to the ability of Pd to absorb much greater quantities of hydrogen than does Pt.

Liquid-Phase Catalytic Oxidation of Organic Compounds on Noble Metals. 111. Oxidation of Ethylene Glycol to Glyoxal I. I. IOFFE, N. v. KLIMOVA and A. G. MAKEEV, Kinetika i Kataliz, 1962, 3, (I), 107-1 10 Up to 15"h conversion of ethylene glycol to glyoxal was obtained with the use of supported Pt or Pt-Pd catalysts in the liquid-phase. In addition glycolic acid, glycolaldehyde, HCOOH, and CH,O were formed. The solubility of various catalyst supports in the reaction conditions was investigated. C and A1,0, are the most stable supports in the given process.

Isomerisation of n-Pentane on Platinum/ Alumina Catalysts J. MAR~CHAL, R. CAHEN and H. DEBUS, Rev. Inst. FranF. PPtroZe, 1961, 16, (11), 1299-1306 The investigation was carried out in a fixed-bed flow system. A study of the influence of pressure, hydrogen-to-hydrocarbon ratio, C,H and hydrogen flow showed that the reaction is first order with respect to the n-C6H,8 mole fraction. Pressure has no influence in the range 5 to 50 kg/cm2. The influence on the catalyst activity of the presence of a chloride in the feed and of the addition of A1 fluorides to the catalyst was studied. Increasing Pt content of the catalyst up to about 0.5"h Pt raises its activity.

Reduction of Aromatic Nitro-Compounds by Sodium Borohydride Catalysed by Pal- ladised Charcoal T. NEILSON, H. c. s. WOOD and A. G. wYLIE, 3. Chem. Soc., 1962, (Jan.), 371-372 Very pure amines have been obtained from a number of nitro-compounds by this reduction method. A roo: Pd;C catalyst was used and the reductions were carried out at room temperature in alkaline solution or in aqueous CH,OH. The rate of reduction was shown to be roughly proportional to the amount of catalyst used.


Steroids and Related Natural Products IX. Selective Osmium Tetroxide Oxidation of Olefins G . R. PETTIT and B. GREEN, 3. org. Chem., 1961, 26, (II), 4673-4675 A glycol is obtained from 2-apoallobetulin by treatment of the olefin with OsO, in C,H,N solution followed by H,S. 3 - isopropyl - A - norlanost - 3(5)-ene treated with OsO,/C,H,N and sodium bisulphite yields a diketone, while a glycol is obtained by treatment of the olefin with OsO,/C,H, and H,S.

Patterns of Behaviour in Catalysis by Metals

WINTERBOTTOM~J. Catalysis, 1962, I, (I), 74-84 Relative advantages of supported metals, metal powders and evaporated metal films as hydrogenation catalysts are discussed. A literature survey shows that certain properties of metal catalysts are characteristic of the metal and not of its physical form. Two such features of Group VIII metals are (i) the degree of selectivity shown in the hydrogenation of multiply unsaturated hydrocarbons and (ii) the degree of olefin isomerisation and exchange during hydrogenation. Results are reported of new work using a-Al,O,- supported Ru, Rd, Pd, Os, I r and Pt catalysts in the hydrogenation of unsaturated hydrocarbons. Ru, Rh, and Pd give substantial isomerisation and exchange, in contrast to the behaviour of Os, Ir, and Pt. These differences in behaviour are used to explain the selectivity sequence of the metals in the hydrogenation of acetylenes and diolehs which has been reported previously and confirmed in this work.

G . C. BOND, G . WEBB, P. B. WELLS and J. M.

The Determination of the Free-Metal Surface Area of Palladium Catalysts J . J. F. SCHOLTEN and A. VAN MONTFOORT, J. Catalysis, 1962, I, (I), 85-95 Two methods described for determining the free- metal surface area of supported Pd catalysts are based on the chemisorption of CO at room temperature. Catalysts examined were Pd black, Pd sponge, Pd/a-Al,O,, PdIC and Pd/kieselguhr. In some cases results are compared with those obtained by other techniques and good agreement is shown. The dispersion of Pd on the supports is discussed.

The Catalytic Dehydrogenation of Dihydro- furans N. I. SHUIKIN, I. F. BEL'SKII and R. A. KARAKHANOV, Izvest. Akad. Nauk S.S.S.R., Otdel. Khim. Nauk, 1962, (I), 138-142 The dehydrogenation of a-methyl-4, 5-dihydro- furan on RulC, RhIC, Os/C and IrlC catalysts was investigated at zoo' and 300°C. The first reaction in these conditions is dehydrogenation to or-methylfuran. Hydrogen which is separated either hydrogenates the original dihydromethyl-

furan to tetrahydromethylfuran or promotes the hydrogenolysis of cc-methylfuran to methylpropyl ketone. The latter compound may also be formed by the isomerisation of tetrahydromethylfuran.

CATHODIC PROTECTION Platinum in Anodes. Cathodic Protection Applications. Part 1 G. w. WALKIDEN, Corrosion Technul., 1962, 9,

The design and performance of various types of supported Pt anodes are discussed. Among the anodes described are a ring of Pt-Pd foil supported by a reinforced plastic holder, a Pt-clad Ag trailing anode, and platinised T i or T a anodes. The advantages of the use of Pt-Pd alloys and platinised T i or Ta over other anode materials are stressed. (17 references)

(11, 14-16

Part 2 Ibid., 1962, 9, (21, 38-40, 44 The applications of platinised T i anodes in the cathodic protection of small ships, boats and a jetty are described. A coating of Pt O.OOOI in. thick obtained electrolytically is usually employed. The loss of Pt due to corrosion of the anodes in chloride-containing solutions, and the effects of the geometry of the anode and a.c. ripple on corrosion of the anode are discussed. Pt/Pb bielectrodes in which Pt micro-electrodes are inserted in Pb anodes and their use in sea water or 0.1 M to 1.3 M NaCl solutions are described. (22 references)

Cathodic Protection-Something Old-Some thing New G. G. PAGE, Corrosion Technol., 1962, 9, (4), 89-93, I I2

The development of cathodic protection methods is described. Facts necessary for the assessment of a corrosion problem and the possible applica- tion are outlined. Future trends in cathodic protection are discussed.

ELECTRICAL ENGINEERING Surface Films on Precious Metal Contacts H. C. ANGUS, Brit. 3. Appl. Pkys., 1962, 13, (2), 58-63 Surfaces of Pt, Pd, Rh, Ir, and Ru were examined and compared with a Au reference surface. The Pt metals were in the wrought, electrodeposited, melted or sintered forms. Variation of contact resistance with loading (I mg to 5000 mg) was studied and the results are interpreted in terms of film behaviour. Reproducible contact resistances may be obtained at loads of < I g corresponding to film thicknesses of the order of 5 8. Abrasion


causes surface deterioration at light loads. Frac- tured sintered compacts have the most stable surfaces, but cold-formed and electrodeposited surfaces deteriorate only slowly if abrasion is minimised.

Properties and Behaviour of Precious Metal Electrodeposits for Electrical Contacts H. c. ANGUS, Trans. Inst. Metal Finishing, 1962,

Au, Rh, and Pd contact coatings electrodeposited from conventional electrolytes have been examined. The importance in the performance of the contacts of the thickness, hardness, and electrical resistivity of the deposits is discussed. Results of exposure tests under various conditions show that porosity of the coating has a significant effect on the behaviour of the contacts. Effects of mechanical wear during service are also discussed. Suitable deposit thicknesses are suggested for each metal.

39, (I), 20-28

ELECTRONICS AND TELECOMMUNICATIONS The Solion K. JOACHIM, Elektronik, 1962, 11, (I), 7-11 The electrochemical principles underlying the operation of the solion are discussed. This electrochemical control cell consists basically of Pt electrodes in a KI/12 solution. Devices which incorporate the solion include electrochemical diodes, flow- and pressure meters, inte- grators, multipliers, and electrokinetic pressure generators. The simplicity of construction of the

NEW PATENTS Semiconductors WESTINGHOUSE ELECTRIC CORP. British Patent 888,829 A junction is formed in a silicon carbide single crystal by applying to a crystal of one conductivity type an alloy comprising palladium andior rhodium and a doping impurity for converting a region of the crystal into a different conductivity type so that a junction between the region and the remainder of the crystal is produced. The alloy consists of 78.5-99.5OL platinum, palladium and/ or rhodium, and I C - O . ~ ~ ~ lead, tin and/or bis- muth.

solion and low current requirements are em- phasised.

TEMPERATURE MEASUREMENT Progress in Platinum Resistance Ther- mometry c. R. BARBER and J. A. HALL, Brit. 7. Appl. Phys.,

The history of the development of Pt resistance thermometry is discussed. Various thermometers designed for the measurement of temperatures in the ranges -183' to 630T and 630" to 1063"C, and below -183°C are described. Improvements in accuracy have been achieved by refinements in and new methods of measurement and by better reproducibility of fixed calibration points. Methods of measurement based on the potentiometer, the Wheatstone bridge and the Kelvin double bridge are outlined. The role of the Pt resistance thermometer in the International Practical Scale of Temperature is discussed and the extension of its use for measurements up to 1063°C and down to 20°K is predicted. (34 references)

An Improved Resistance Thermometer Bridge ANON., Nat. Birr. Stds. Tech. News Bull., 1962,

A modified Mueller bridge for use with a Pt resistance thermometer is described. The addition of a lower resistance decade has increased maximum measurement definition to I p ohm. The range of the instrument is o to 422 ohms.

1962, 13, ( 4 ) ~ 147-154

46, (2), 8-10

Catalysts THE DISTILLERS CO. LTD. British Patent 888,999 A catalyst for selective hydrogenation of an acetylenically unsaturated compound to the corresponding ethylenically unsaturated compound is made by contacting a platinum group metal, supported on a carrier, with a solution of a lead compound in an organic solvent. Palladium on calcium carbonate, or on charcoal, or on barium sulphate may be used.

Electrode Structures IMPERIAL CHEMICAL INDUSTRIES LTD. British Patent 889,147 An electrode structure consists of an anodically polarisable metal (titanium, titanium-base alloy, niobium, tantalum or alloy of titanium with niobium andlor tantalum), to the surface of which is secured a platinum group metal in reticulate

Electrochemical Detectors UNION CARBIDE CORP. British Patent 888,915 A detecting electrode comprising a strip of platinum having a number of bosses on both sides is used in an electrochemical detector device.


wrought form, e.g. wire mesh, perforated foil, expanded metal, etc.

Pyrimidines IMPERIAL CHEMICAL INDUSTRIES LTD. British Patent

2 :6-dihydroxy-pyrimidines are produced by oxidation of a 4-hydrazino-2 :6-dihydroxy-pyrimidine of given general formula in air or oxygen and in the presence of a platinum oxide catalyst.

Preparation of Cyclohexanone STAMICARBON N.V. British Patent 890,095 Cyclohexaaone is prepared by passing gaseous phenol and hydrogen over a platinum group metal catalyst, preferably palladium, at below 250°C.

Method of Oxygen Determination THE BRITISH OXYGEN Co. LTD. British Patent 890,923 Apparatus for determining the concentration of oxygen in solution in an electrolyte includes a silver tube as an anode in which is mounted coaxially a platinum wire forming a cathode, the space between the wire and the wall of the tube being filled with electrically insulating material.

Method of Making Filters ENGELHARD INDUSTRIES INC. British Patent 891,181 A filter is made by feeding a platinum metal rod into a gas flame in an open-ended combustion conduit, melting the end of the rod and expelling molten metal in the form of globules from the end of the rod by means of a high velocity gas, the globules passing into a coolant and the resultant shot being packed into a frame and fritted.

Coated Particles VARCO INC. British Patent 891,494 Particles of thermo-plastic material are prepared for chemical nickel coating by first depositing a thin discontinuous coating of metallic copper on the particles and then activating the copper by immersion in a solution containing palladium to cause replacement of some of the copper by metallic palladium.

Electrodes IMPERIAL CHEMICAL INDUSTRIES LTD. British Patent

Electrodes for electrolytic purposes are made by compacting powdered titanium, or an alloy thereof with soh zirconium or 2 . ~ ~ 4 nickel, to form a sheet and then scattering on one or both surfaces of the sheet powdered platinum or a mixture of platinum and an oxide of lead, the coated sheet being then rolled.

Electrically Heatable Filaments NATIONAL RESEARCH DEVELOPMENT CORP. British Patent 892,530 An electrically heatable filament of the helical

890,076

891,720

coil type used for detection of combustible gases in air is embedded in a layer or layers of an oxide or other refractory forming a coating or pellet, on which is a layer of palladium or a mixture of platinum and palladium to form a catalyst. The filament is preferably formed of a wire of a platinum group metal or alloy.

Preparation of Dibenz (b,f,) azepines smm KLINE & FRENCH LABORATORIES U.S. Patent

10, 11, -dihydro-5H-dibenz (b,f,) azepines of given formula are formed by dehydrating with phosphorus of given formula to form a 5H-dibenz- (b,f,) azepine and hydrogenating the latter in the presence of a platinum or palladium catalyst.

Film Resistor RESISTANCE PRODUCTS co. U.S. Patent 3,018,198 A film-type resistor is made by applying to an insulating base by vacuum evaporation at at least 2000°C a film composed of 10-75% by wt. copper and balance platinum, to a thickness of 50-1500 A and then heat-treating the film in an oxidising atmosphere at from 150°C for I h to 350°C for I min.

Preparation of 1-acetyl-2, 2, 3-trimethylcyclobutane

I-acetyl-2, 2, 3-trimethylcyclobutane is made by hcating z,z-dimethyl-3-acet yl-cyclobutylacetalde- hyde in the presence of palladium at from 100' to 300"C, the reaction mixture being continuously withdrawn.

Platinum Catalyst SOCONY MOBIL OIL CO. U.S. Patent 3,025,247 A catalyst is made by contacting an inorganic refractory oxide support with an aqueous solution of a water-soluble compound of a platinum metal in a concentration corresponding to 0.01-5 wt.O/, of the metal on the finished catalyst basis, contacting the resulting aqueous slurry with a solid metallic element, higher in the electromotive series than the platinum metal, in amount sufficient to reduce ions of the platinum metal to the metallic state and to deposit and fix the latter on the support.

Platinum-alumina Catalyst SOCONY MOBIL OIL co. US. Patent 3,025,248 A platinum-alumina catalyst is made by irnpreg- nating a hydrous alumina having a phase composition, on a total solids basis, of 5-507~ by wt. of alpha alumina monohydrate and 50-950/~ by wt. of alumina trihydrate (mainly beta form), with a solution of a platinum compound of concentration to give 0.01-5 wt. yo platinum, drying the composite, mixing it with an aqueous acid solution, drying and calcining at elevated temperature.

3,016,373

THE GIVAUDAN GORP. U.S. Patent 3,019,263

Platinum Metals Rev., 1962, 6 (31, 124

PLATINUM METALS REVIEW · 2016. 1. 28. · ffins or to isomerise straight-chain paraffins to their...

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