PLATINUM METALS REVIEW · Butamer Process The need for a catalyst even more ... -led to the development of the Butamer catalyst. Such a catalyst could take advantage of the marked

PLATINUM METALS REVIEW

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

V O L . 8 J A N U A R Y 1 9 6 4 N O . 1

Contents

Duofunctional Platinum Catalysts in the Petroleum Industry 2

Oxygen Injection Engine for Space Research 8

The Magnetic Properties of Platinum Metals and Alloys

Platinum-lined Furnace for the Fluorination of Uranium Compounds

Determination of Thermal Conductivity I3

Platinum Metals in Electrochemistry I4

A High Temperature Waveguide Termination

9

I2

1.5

Organometallic Compounds of the Platinum Metals 16

Precision Glaze Resistors 22

The Early History of the Thermocouple 23

Abstracts 29

New Patents 37

Communications should be addressed to The Editor, Platinum Metals Review

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

Tin the Petroleum Industry By Vladimir Haensel and Herman S. Bloch Universal Oil Products Company, Des Plaines, Illinois

The transition of petroleum refining from relatively simple thermal operations to more selective and efficient catalytic processes has been one of the major advances of industrial chemistry in modern times. This transition has been made possible by the development of highly selective catalysts designed to meet the exacting requirements of modern petroleum conversion processes. Of such catalysts, those containing platinum as an active component have dominated the petroleum refining art during the past decade.

The ability to “tailor-make” catalysts for specific purposes is well illustrated by the case of four duofunctional catalysts developed for the petroleum refining industry by Universal Oil Products Company and widely used in processes licensed by it throughout the Western hemisphere. These catalysts- Platforming, Penex, Butamer and Hydrar*- all contain platinum as one of the functional agents. The other function is provided by several types and degrees of acidity built into the specially prepared catalyst support in such a way as to provide the necessary balance and co-action between the platinum, the acid function and the support for the specific feedstocks and operating conditions characteristic of the process involved.

Platforming Process Platforming is a method of catalytically

reforming petroleum naphthas to improve their anti-knock properties. Chemically speaking, the naphtha feed contains three types of hydrocarbons (parafiins, naphthenes and aromatics), each of which is capable of *Registered Trade marks of Universal Oil Products Company.

Platinum Metals Rev., 1964, 8, (l), 2-8 2

undergoing a number of reactions under the conditions of high temperature and pressure prevalent in the reactor. The platinum and acid functions in co-action with each other and with the support are balanced with the operating conditions to achieve a proper control of the several possible reactions of each of these hydrocarbon types, so that the course of the reaction is directed toward the production of a maximum yield of desired product with a minimum amount of un- desirable by-products.

Catalytic reforming involves four primary reactions. These are dehydrogenation of naphthenes containing either five- or six- membered rings to aromatics, the de- hydrocyclisation of paraffins to aromatics, the hydrocracking of higher to lower boiling paraffins, and the isomerisation of paraffins to more highly branched structures.

The acid function incorporated in the Platforming catalyst accelerates the isomerisation, cracking and cyclisation of hydrocarbons. The platinum function accelerates hydrogenation and dehydrogenation, such as the conversion of naphthenes into aromatic hydrocarbons, and the dehydrogenation of paraffins to olefins as one of the initiating steps in paraffin cracking and isomerisation.

These two functions are combined in the Platforming catalyst on a rugged, specially prepared alumina support through which the active components are uniformly dispersed so as to provide ready access to the catalyst sites for the enormous hydrocarbon trafiic required for an economical process. In addition to its primary function in the main Platforming reactions, platinum also plays

uofunctional Platinum Catalysts

one other essential role in this process: it maintains a clean, continuously active catalyst surface by hydrogenating intermediate unsaturated by-products which might otherwise condense to high molecular weight carbon- rich deposits that produce catalyst deactivation.

The principal reactions involved in Platforming a naphtha are shown in the representative equations given here. The reactions are carried out at temperatures of about 475 to sso"C, and under hydrogen pressures of approximately 250 to 500 p.s.i. The naphthene-aromatic equilibrium under these conditions lies almost entirely on the aromatic side. Aromatic hydrocarbons

present in the feedstock are little affected for this reason, except for some shortening of the side-chain and rearrangement to a polymethylated structure.

It will be noted from the equations that the platinum function and the acid function must act not only simultaneously, but in some cases consecutively and in close co-operation, if the reactions involved are to be catalysed cleanly. The objective of catalytic reforming is the production of a reforrnate enriched in aromatic hydrocarbons and liquid isoparaffins and with the concomitant production of a minimum of gaseous hydrocarbon by- products. It is therefore apparent that some

Platinum Metals Rev., 1964, 8, (1) 3

Intensive research over a long period of years by 1;TniversaE Oil Products Company has provided the petroleum industry with a number of highly selectiwe platinum catalysts of widely different properties.

Here catalyst performance is being investigated on a pilot plant scale

of the reactions involved (for example hydrocracking to yield gaseous isobutane as shown in equation (4)) must be minimised and the other reactions maximised, if theoretical yields are to be approached. Yet, the apparent paradox must be faced that the same catalyst function required for the desirable reactions likewise induces those which must be minimised. It is clear, therefore, that in the design and manufacture of a catalyst, as well as in the engineering of the process in which the catalyst is employed, there must be a very fine balance among the number of catalyst sites, their location with respect to each other, and the operating conditions employed. As refining needs have changed, it has been possible to vary this balance to maintain a high level of performance.

Penex Process It is characteristic in the Platforming

process just discussed that the isoparaffins formed (for example isobutane and isopentane) are present in higher than equilibrium

concentration in their respective fractions. It is apparent that the Platforming catalyst, under Platforming conditions, does not isomerise the isoparaflins first formed as a result of hydrocracking sufficiently to achieve equilibrium; nor is it desirable to isomerise the light isoparafhs. An increase in effectiveness of the acid function would not only cause such unwanted isomerisation, but the catalyst would be unbalanced for the other reactions necessary for successful Platforming.

For this reason, it was necessary to develop a catalyst for paraffin isomerisation that incorporated a different balance of acid ZI. platinum functions than is present in Platforming catalyst. The resulting Penex catalyst was developed specifically for the hydroisomerisation of pentanes and hexanes to highly branched isomers desirable as components in high octane fuels. Its increased acidity, as compared with that of the Platforming catalyst, permits operation at temperatures of approximately 250 to 375'C- sufficiently lower than the operating range in Platforming to take advantage of the


higher equilibrium concentrations of iso- compounds which are possible at the lower temperatures.

Like Platforming, the Penex process operates in a hydrogen atmosphere to ensure long catalyst life through continuous cleansing via the platinum component, thereby eliminating the need for frequent catalyst regeneration and providing process economy. The Penex process can be employed for isomerisation of pentane alone, or of hexane alone, or for isomerisation of a light naphtha comprising a mixture of the two. So selective is the catalyst and the process which employs it that volumetric yields of isopentane of over 99 per cent have been obtained commercially in the isomerisation of pentane.

The isomerisation of hexane may be conducted either to obtain a higher octane- number hexane product, or selectively to produce individual isomeric products. Thus, z,a-dimethylbutane may be isolated as the

lowest-boiling product and all other isomers recycled to obtain nearly quantitative ultimate yields of this isomer.

Butamer Process The need for a catalyst even more effective

than the Penex catalyst for butane isomerisation-one that would operate at several hundred degrees below the effective temperature for Penex operation-led to the development of the Butamer catalyst. Such a catalyst could take advantage of the marked increase in the isobutane equilibrium yield as a function of temperature as shown in the graph on page 6.

The Butamer catalyst is a platinurn- containing, duofunctional, solid hydroisomerisation catalyst of such enhanced activity and selectivity that it permits isomerisation of butane (or pentanes and hexanes) substantially to equilibrium at temperatures in the range of IOO to z50°C. This catalyst

The Penex process employs a platinum catalyst specijkally designed for the hydroisomerisation of pentanes and hexanes to highly branched isomers for use in high ortane Juels. This

Pmex unit forms part of a refinery in Louisiana


represents a significant extension of platinum capable of uninterrupted use for many catalysis to a lower temperature region of hydrocarbon conversions than hitherto was It will be noted that the mechanism of considered feasible. Like the Platforming isomerisation illustrated in equation ( 5 ) and Penex catalysts, the Butamer catalyst involves dehydrogenation of the paraffin by brings about hydroisomerisation in a con- the platinum function to an olefin as an tinuously self-cleansing manner, so that it is initiating step, followed by conversion of the

months or even years.


A Hydrar process unit at an Oklahoma rejinery. A platinum catalyst is used for the conversion of benzene to high purity cyclohexane, mainly for subsequent oxidation to adipic

acid in the preparation of Nylon-type polyamides

olefin to a carbonium ion by the acid function, isomerisation of the carbonium ion, genera- tion of an iso-olefin from the isomerised ion and, finally, rehydrogenation of the iso-olefin to an isoparaffin. At the lower temperatures of operation, desired because of favourable equilibrium conditions for butane isomerisation, the dehydrogenation step is so slow as to offer a serious obstacle to feasible reaction rates if catalysts of the Penex or Platforming type are used.

As a result of the enhanced acidity of the Butamer catalyst, it is believed that the initial paraffin activating step differs from that of the higher temperature operation employed with Penex or Platforming catalysts. The Butamer initiating reaction is thought to be one of hydride abstraction via the acid function, as shown in equation (6). Once the reaction has been initiated, it is propagated by a chain mechanism under the influence of the exceedingly acidic sites of the Butamer

catalyst as shown in equation (7). The platinum serves to maintain catalyst cleanli- ness and high activity through continuous hydrogenation of polymeric carbonaceous by-products, thus permitting their continuous removal.

Hydrar Process Thus far we have considered three pro-

cesses employing acidic platinum-containing catalysts in which the acidity has been modified to conform with the requirements of each process. In the Hydrar process, a platinum-containing catalyst is used for the convcrsion of benzene to high purity qclo- hexane.

Such cyclohexane is mainly used for oxidation to adipic acid in the preparation of Nylon-type polyamides. So exacting are the purity requirements of cyclohexane for this use that no more than trace amounts of other hydrocarbons may be tolerated.


Since the Hydrar reaction is conducted at a temperature at which from about 2 to 6 per cent of methylcyclopentane might be formed if an isomerisation equilibrium with the cyclohexane product could be established, it was necessary to employ a catalyst that did not induce isomerisation. In addition, to assure virtually quantitative yields of cyclohexane, it was necessary to suppress all cracking to open-chain compounds.

It will be noted from equations (2) and (4) that the acid function of duofunctional catalysts plays a key role in both the isomerisation and cracking of naphthenes. The Hydrar catalyst which was developed for benzene hydrogenation is, therefore, one in which the platinum is disposed on a specially prepared support in which the acidity has been virtually completely suppressed. As a result, benzene is hydrogenated cleanly to cyclohexane of over 99.7 per cent purity in the Hydrar process. If a pure benzene is used as

the feedstock, essentially quantitative yields of cyclohexane are produced during several years of continuous operation without contamination or deactivation of the catalyst.

Summary The Platforming catalyst for reforming

naphthas, the Penex catalyst for hydroisomerisation of pentanes and hexanes, the Butamer catalyst for hydroisomerisation of butane, and the Hydrar catalyst for conversion of benzene to cyclohexane, provide examples of four supported platinum catalysts of widely differing properties obtained by regulating the acidity of thc catalyst composite. Through proper balance of the platinum hydrogenation-dehydrogenation function with the acid function, in co-action with the support, such duofunctional catalysts can provide a high degree of selectivity for hydrocarbon conversion processes operating under widely different conditions.

Oxygen Injection Engine for Space Research PLATINUM ALLOY VALVE SEATS AND FACES

Formidable design problems are encountered in the development of a reciprocating power unit for use in space research programmes. One of the most severe of such problems met with by the Vickers Inc. Division of Sperry Rand Corporation in developing a light- weight hydrogen-oxygen internal combustion engine (shown on the right) concerned the selection of materials for the oxygen injector valve. As this valve, operating at very high speed, handles gaseous oxygen at high temperatures, it must be made of a material that will resist oxidation and also maintain ade- quate strength and impact characteristics.

Tests were carried out on austenitic stainless steel, a nickel-chomium-molybdenum alloy and 10 per cent rhodium-platinum alloy for the poppet valve face, and on stainless steel, 10 per cent rhodium-platinum and the latter alloy flame-plated with alumina for the valve seat. The best combination was found to be a rhodium-platinum poppet face against a flame-plated rhodium-platinum seat. This combination has endured several hours of operation without leakage or deterioration of

the plating surfaces and with good ability to compensate for minor misalignment.


The Magnetic Properties of Platinum Metals and Alloys A SURVEY OF RECENT RESEARCH

By B. K. Coles, D.Phi1. Department of Physics, Imperial College, London

Well-marked magnetic properties are associated always with electrons in incomplete inner electron shells which maintain a comparatively localised and atomic character in the solid state - unlike the delocalised conduction electrons which become a pro- perty of the solid as a whole. There is not, however, an absolutely clear-cut division between localised and non-localised situations. The best example of the well- localised situation is provided by the incomplete f-electron shells of the rare earth metals. In gadolinium the 7f-electrons per atom play no part in bonding and f-electrons on neighbouring atoms in the metal are only “aware of one another” because of indirect coupling through the three conduction electrons per atom which can, as it were, tell one atom of the orientation of the magnetic moment provided by the f-electrons on another atom.

The 3d electron shells of the first transition group metals (especially manganese, iron, cobalt and nickel) are not as well localised as the rare earth f-electrons, and in the pure metals strong direct interactions between d-electrons on neighbouring atoms are certainly present. (We still do not know whether these direct interactions or indirect ones through the conduction electrons are dominant in providing the ferromagnetism of iron, cobalt and nickel.) The d-electrons become somewhat more localised on passing along a transition series (Ti-fNi) but appreciably less localised on going from the first to the second to the third transition

series (Co+Rh+Ir), and strong magnetic interactions are absent in osmium, iridium and platinum because the 5d electrons on neighbouring atoms are behaving more like conduction electrons than like localised ones. Palladium, at the end of the second transition series, is very nearly a magnetically ordered material, and small amounts of iron in solid solution produce a ferromagnetic moment which is not all provided by the iron atoms.

Even stronger effects are produced when small amounts of iron are added to those palladium-rhodium alloys (-5 per cent rhodium) where the work of F. E. Hoare and others at the University of Leeds has shown that the conditions required for ferromagnetism are very nearly satisfied.

A large amount of work has been carried out recently on dilute alloys of transition metals of the 3d series dissolved in palladium or platinum, much of it at the Bell Tele- phone Laboratories. The results have been compared with the magnetic behaviour of solutions of iron in the earlier members of the 4d series, where iron does not always carry a magnetic moment. In niobium where the electronic density of states is high dissolved iron atoms have no moment ; but the high density of states in platinum and palladium does not prevent the appear- ance of a moment on the iron atoms, presumably because of the more localised character of the d-electrons of the solvent.

If manganese, iron or cobalt is dissolved in a non-transition metal (for example gold) the d-electrons have no neighbouring d-elec-

Platinum Metals Rev., 1964, 8, (l), 9-1 1 9

trons to interact with and become more localised -that is, more like the f-electrons or rare earth metals - and there are interesting resemblances between lanthanum- gadolinium* alloys and gold-iron or copper-manganese alloys, since in all three the only magnetic interactions are via the conduction electrons. From this point of view platinum, iridium and rhodium can perhaps be regarded as simple (‘non- magnetic” solvents for iron, but palladium certainly gives a different and more complicated situation. Recent work by the present author has revealed striking effects in the low temperature electrical resistance of dilute solutions of iron in palladium, platinum, rhodium and iridium. These seem to be related to, but much stronger than, the well-known anomalies in electrical resistance shown by the above mentioned gold-iron and copper-manganese alloys.

In more concentrated alloys of the iron group metals neighbouring atom interactions become important, and striking effects can sometimes be produced by transitions from disordered structures to ordered structures. FeAl and Au,Mn provide examples of this, but for metallurgical reasons, such as size factors, most extensive solid solutions where ordering is possible are in alloys with platinum metals. A striking example is the Pt,Fe alloy, which if perfectly ordered (no Fe-Fe nearest neighbours) is antiferromagnetic; but a few extra iron atoms that occupy platinum sites convert much of the neighbouring material to a ferromagnetic state (I).

Iron-Rhodium Alloys A number of papers presented to the

Eighth Conference on Magnetism and Magnetic Materials held recently in Pittsburgh dealt with various aspects of the magnetic properties of the platinum metals and their alloys which can be discussed in relation to the points made above.

*This notation indicates a dilute solid solution of gadolinium in lanthanum.


The striking change with temperature in magnetic properties in iron-rhodium alloys containing equal atomic percentages of each element has been known for some time, and a short review of the data available up to about a year ago was given in this journal in January last year (2). This ordered CsCl type alloy changes from antiferromagnetic to ferromagnetic at -360°K in zero external field, but at -220’K in a field of 120,000

gauss. Now Flippen and Darnel1 of du Pont

(3) have discussed the thermodynamics of this field dependence; while Shirane, Chen and Flinn of Westinghouse, together with Nathans of Brookhaven (4) have published the results of Mossbauer studies of the magnetic field seen by the nucleus of an iron atom and the differences for iron atoms in (‘right” positions and “wrong” positions.

Kouvel and his co-workers at the Schenectady laboratory of General Electric who carried out transformation studies on the iron-rhodium alloy, have now moved on to investigate the possibility of an analogous behaviour being found in its isomorph MnRh (5).

There is a martensitic transformation (with hysteresis) from a high temperature ordered CsCl structure to a low temperature CuAu structure. The high temperature form is paramagnetic (it would probably become antiferromagnetic at low temperatures) and the low temperature form is strongly antiferromagnetic. The change therefore produces a change in density and resistance, but these are not sharp since there seems to be a rather extensive range between the start and end of the martensite transformation. In this connection a survey of the behaviour of the related phases FeRh, MnIr, MnNi and the effects of substitutions into these of other transition metals would probably be of interest.

Platinum Alloys Alloys of platinum with small amounts

of manganese, iron, cobalt and nickel were

described by Bozorth, Davis and Wernick of Bell Laboratories to the International Conference on Magnetism in 1961 and were compared with similar palladium-based alloys (6).

For the platinum alloys effects are much weaker (the highest Curie temperature for a I per cent alloy (Co or Fe) is -17°K as compared with 80°K for Pd-Co I per cent and the size of the magnetic moment produced on platinum atoms is very much less than that produced on palladium atoms. It is clear that even if the d-electrons of iron can be regarded as localised when it is dissolved in platinum (like the f-electrons of gadolinium when dissolved in lanthanum) the strength of the interaction between them (the indirect interaction via the conduction electrons) is very much stronger than in non-transition solvents because the conduction electrons in platinum have a lot of &character themselves.

In another paper to the Pittsburgh Con- ference Pickart and Nathans (7) have reported neutron diffraction studies on manganese-platinum and chromium-platinum alloys. Both have the Cu,Au structure and there seems to be some magnetic moment on the platinum atoms, but in Pt,Cr this is in the opposite direction to the tenfold larger moment on the chromium atoms.

Iron-Palladium and Gadolinium-Palladium Alloys

Iron-palladium alloys with small amounts of iron have also been studied by neutron diffraction by Cable and his colleagues at Oak Ridge (8). The magnetic moment on the iron atoms has been found to be equivalent to 3.0 electron spins (as compared with 2.22 in pure iron). There is a moment of 0.15 units on the palladium atoms in the 3 per cent iron alloy. This has been calculated assuming that all palladium atoms have similar moments. There is other evidence to suggest, however, that for very dilute alloys down to I per cent iron only palladium

atoms next to an iron atom have a moment and that it is -0.5 units.

Gadolinium-palladium alloys with small amounts of gadolinium have been studied extensively by workers at the Bell Labora- tories, using the techniques of electron paramagnetic resonance. The magnetic field for this resonance is significantly different from that for gadolinium in alloys with non-transition metals, so that although the magnetic properties are dominated by the 7 localised 4f-electrons of gadolinium the nearly magnetic character of palladium does modify matters slightly, although less strongly than in palladium-iron. This has now been shown (9) by adding hydrogen to palladium containing gadolinium and thereby filling up with extra electrons the d-electron states of the palladium. The effect is to make the gadolinium behave as it does in non-metallic situations or in solution in simple metals. The same effect is produced, incidentally, by adding silver to palladium containing gadolinium. (With the metals osmium and ruthenium gadolinium forms weakly ferromagnetic inter- metallic compounds GdOs, and GdRu,, but the similarity in properties to GdA1, suggests that the transition metal character of the osmium and ruthenium is less important than that of palladium in the above alloys).

References I G. E. Bacon and J. Crangle, Proc. Ray. SOC.,

2 A. S. Darling, Platinum Metals Rev., 1963, 7,

3 R. B. Flippen and F. J. Darnel1,J. Applied

4 G. Shirane, C. W. Chen, P. A. Flinn and R. Nathans, ibid, p. 1044

5 J. K. Kouvel, C. C. Hartelius and L. M. Osika, ibid. p. 1095

6 R. M. Bozorth, D. D. Davis and J. H. Wernick, J. Phys. SOC. Japan, 1962, 17, Suppl. B.I., 112

7 S . J. Pickart and R. Nathans, J , Applied P b ' S z C S , 196.3, 34, (41, 1203

8 J, W. Cable, E. 0. Wollan and \XI. C. Koehler,

9 D. Shaltiel, ibid, p. 1190

1962,272, 387

29

Physics, 1963,34, (4), 1094

ibid, p. 1189

Platinum Metals Rev., 1964, 8, (1) 1 1

Platinum-lined Furnace for the Fluorination of Uranium Compounds FEATURES OF DESIGN AND CONSTRUCTION

The high temperature stability of platinum and its immunity from attack by hydrogen fluoride gas even at IOOO~C have led to its being specified to form the liner material for a f m a c e recently designed and constructed for use in the fluorination of uranium compounds at the Harwell research establishment of the United Kingdom Atomic Energy Authority. The design, testing, and operation of the furnace are described in report A E R E - R ~ z ~ ~ by D. N. Fletcher and L. J. White of the Scientific Services Department of the Engineering Division at Harwell.

The high level of radio-activity exhibited by uranium compounds, and eventually by the equipment, necessitated that the furnace should be so designed that all operations could be conducted inside a glove box, yet easy access to the furnace chamber and element housings had still to be retained.

The basic design specification called for a furnace capable of producing a chamber temperature of 10oo~C and able to operate at a working pressure of I p.s.i. (gauge). A furnace liner was demanded that would be unaffected by hydrogen fluoride gas at IOOO~C, would protect the charge from contamination by preventing the formation of corrosion products inside the furnace chamber and would itself be unaffected by contact with uranium compounds. The furnace chamber was required to be approximately 8 x 8 x z inches, to accommodate existing platinum trays which were to bear the charges, and there was to be no water cooling of the joint between the lid of the furnace and the chamber in order to avoid any hazard that might arise if water were to come into contact with the charges.

The furnace liner requirements were found to be ideally fulfilled by the use of platinum in the form of 0.010 inch thick sheet, and the furnace chamber, the purge outlet and inlct tubes and the chamber lid are sheathed with the metal.

AS pure platinum surfaces readily weld to each other at high temperatures, a $-inch gap was left between the lid and the sides of the furnace chamber after lining. A water cooled joint ring between the lid and the furnace chamber was not permissible and after many tests a gasket of >&-inch thick white asbestos millboard was used to prevent the platinum surfaces from coming into contact and to provide an effective seal. To avoid the platinum trays from sticking to the chamber lining a separator grid of a rhodium- platinum alloy was placed on the floor of the furnace.

Temperature control is effected by the use of three platinum : rhodium-platinum thermocouples, one sealed into the purge inlet tube and protruding into the furnace chamber, the second fitted into a pocket at the centre of the lid with its hot junction in contact with a flat- headed platinum rivet from the platinum- lining, and the third connected to one of the four silicon carbide heating elements.

In the furnace chamber, on the projecting box section of the lid and in the purge inlet and outlet tubes, the thin platinum liner is supported on Q-inch thick Inconel, which was selected bccause of its good high temperature properties. At the development stage much investigation was carried out to enable precautions to be taken to prevent contamination of the platinum liner by its close contact with Inconel. When platinum is in contact


The furnace chamber and the bor- sprtion lid lined with platinum

at high temperatures with certain base metals, in this case principally chromium, contamination of the platinum can result from the diffusion of these elements into its surface, leading to embrittlement and subsequent failure. To avoid this risk, a barrier was placed in the path of the diffusing elements between the platinum liner and the Inconel support, this taking the form of a thin layer of a proprie- tary aluminium silicate fibre. This material, which can withstand temperatures in the region of IOOO~C, has proved highly successful in protecting the platinum liner and also serves as a soft buffer layer between the metal surfaces.

Once this contamination problem and the difficulty of finding a suitable gasket material were overcome the construction of the furnace

was completed. The furnace construction and assembly were carried out by R. M. Catterson-Smith Limited, the platinum lining being manufactured and fitted to the furnace by Johnson Matthey & Co Limited.

J. A. S.

Determination of Thermal Conductivity PLATINUM AS A REFERENCE STANDARD

The growing demand for materials to operate at high temperatures has brought a need for accurate knowledge of the manner in which they conduct heat. Reliable figures for thermal conductivity are, however, notor- iously difficult to determine, and standard reference materials would be invaluable for checking the reliability of testing equipment and as standards in comparative methods.

Platinum has many advantages as a standard for use at high temperatures, but the values previously determined by various authorities for thermal conductivity up to about IOOO~C have shown significant differences. A careful redetermination at the National Physical

Laboratory over the range oo to 950°C has now been reported by R. W. Powell and R. P. Tye (Brit.J. Appl. Phys., 1963, 14,662), who have for the first time used substantial bars of platinum for the measurements. Two sets of observations were made on bars having diameters of 2 and 4 inch respectively; with both samples the conductivity was found to remain constant within 0.5 per cent of 0.73 w cm-l deg C-l over the whole range. This result is as much as 20 per cent lower than four out of the five previous deter- minations, but yields values of Lorenz function in much closer agreement with the theoretical. J. C. C .


Platinum Metals in Electrochemistry J

PAPERS AT THE MOSCOW CONFERENCE

By T. P. Hoar, s~.D. Department of Metallurgy, University of Cambridge

At the fourteenth meeting of the Inter- national Committee for Electrochemical Thermodynamics and Kinetics (CITCE) in Moscow in August interest in the platinum metals as “inert electrodes” continued to be manifest. Electrochemists have long used platinum as an “inert” basis for hydrogen, oxygen and halogen gas electrodes, as well as for many redox electrodes such as the ferro- cyanide/ferricyanide couple. It proved to be very difficult to set up a reversible oxygen/ hydroxyl-ion electrode on platinum; as long ago as 1933 I summarised the then scanty knowledge of this system, and gave experimental evidence (I) that the platinum acquires an oxide film that renders it a poor catalyst for the 0 ,+zH20+4ee40H- change, as compared with the rather good catalytic action of unoxidised platinum for the hydrogen-electrode reaction, zHf fzeZH,. It may be worth recalling that this evidence was, to say the least, somewhat sceptically received in “pure” electrochemical circles ; to the pure all was pure-certainly the surface of platinum.

Today, with the greatly increased technical interest of “inert” platinum metal electrodes in such fields as fuel cells, chlorine and per- salt production, and cathodic protection, a very intensive study of the behaviour of the platinum metals is being made. I t is now generally agreed (2, 3, 4) that a platinum surface is far from being “inert”, but can be oxidised under several kinds of conditions; only the form of the oxidation is in some cases uncertain.

At the Moscow meeting, much attention was paid to the influence of the surface state of platinum on its effectiveness as a basis for

several technically important reactions. Thus V. S. Bagotzky pointed out that both oxygen reduction at a platinum cathode and organic oxidations at a platinum anode arc inhibited by oxidation of the electrode surface. E. V. Kasatkin and A. A. Rakov showed that persulphate production at a platinum anode in cooled sulphuric acid solution is inhibited by oxidation of the anode; such oxidation is accompanied by an increase of the a.c. resistance and a decrease of the ax. capacitance of the electrode, typical behaviour when very thin oxide films are formed. Also, the current-density changes at the platinum anode when its potential is fairly rapidly varied (the chronopotentiometric technique) depend on its pre-history. Likewise, Gonzalez, Capel-Boute and Decroly reported that the state of the platinum surface is important for sulphur dioxide anodic oxidation. M. W. Breiter, in one of a long series of papers, noted that the anodic oxidation of methanol becomes less easy on a series of platinum metals in the order Pt>Pd>Rh>Ir and that it is much reduced on oxidised surfaces. The anodic oxidation of methanol on oxidised and “bare” platinum was examined in detail by J. E. Oxley, G. K. Johnson and B. T. Buzalski of Leesona Moos Laboratories, New York, who found little or no reaction unless the platinum was “bare”. Finally, S. Toschev and B. Mutaftschiew of the Bulgarian Academy of Science reported that mercury will electrodeposit around the < I I I > poles on platinum single crystals, but not around the <IOO>, unless the initial oxide film is removed cathodically or by drastic pickling: then, nucleation at the ( 100) poles is even faster than at the { I I I ) . Evidently,


the surface of platinum may be vitally affected by oxidation.

Adsorbed anions and neutral molecules, as well as oxide films, markedly influence reaction rates on platinum electrodes by becoming adsorbed thereon. Thus, at Moscow, L. Muller and L. N. Nekrassov pointed out that the overall O,+OH- change (which, as they demonstrated by rotating-disc experiments using the Frumkin “ring”, goes through an intermediate H,O, stage on platinum) is increasingly inhibited by anion adsorption in the order SO,2- < C1- < Br-. Chu Yung- Chao reported that, in anodic persulphate formation, F-, C1-, SCN- and CS(NH,), have little effect on persulphate formation but markedly reduce the concomitant oxygen evolution; NH,+ also inhibits oxygen evolution and seems actually to stimulate persulphate formation. Breiter, in a further paper, gave evidence for increasingly strong adsorption of the halide ions in the order

Cl-<Br-<I- and noted also that this type of adsorption inhibits both the formation and the reduction of the oxidised platinum surface, as well as inhibiting desired reactions on the platinum. Adsorption of I, rather than I,- or I-, in a system containing all three entities, was discussed by R. A. Osteryoung, G. Lauer and F. C. Anson of the North American Aviation Science Centre, California.

With the intense interest in the surface state-especially with regard to oxidation and adsorption-of the platinum metals apparent in so many of the Moscow papers, it may be natural that the inner electronic structure of the metals received less attention than it deserves. However, J. Brenet of the Univer- sity of Strasbourg pointed out that since the primary function of an inert basis for any electrode reaction is to act as an electron donor or acceptor, the distribution of electron energy levels in the inert basis must clearly have pro- found significance.

References I T.P.Hoar .. . . . . . . Proc. Roy. SOC., 1933 A142,628 z T.P.Hoar , . . . . . . . Proc. Eighth Meeting CITCE, Madrid 1956, p. 439.

Butterworths, London (1958) 3 Proc. Roy. Soe., 1956 A237,227 4 A. Damjanovic and J. O’M. Bockris . . Private communication, 1963

J. O’M. Bockris and A. M. K. S. Huq . .

The CITCE papers will be published shortly in Electrochimica Acra

A High Temperature Waveguide Termination PLATINUM AS BOTH GUIDE AND HEATING ELEMENT

In measuring the output from various noise sources by means of a radiometer, a standard noise source is required to calibrate the instrument. This generally takes the form of a hot load, i.e. a termination of known temperature connected to the radiometer by a suitably matched waveguide. For most microwave receivers, a load immersed in boiling water can be used.

Because of the high noise level of microwave receivers in the short millimetric band, a relatively high output is also necessary from the standard noise source if accurate calibration of the radiometer and hence the receiver is to be achieved. This makes it necessary to operate the hot load at an extremely high temperature. In a recent paper, Q. V. Davis

of the Royal Radar Establishment, Great Malvern, describes (J . Sci. Instr., 1963, 40, (11), 524) a hot load that has been developed for operation at 1250°C. This load comprises a one inch long, conically tapered rod of pyrophyllite operating at this temperature in a heated circular waveguide.

In the construction of this waveguide assembly platinum sheet 0.005 inch thick is formed around a mandrel to make the round waveguide 0.143 inch in diameter, the ends of the sheet being extended parallel to each other to copper blocks. The platinum is resistance heated by a current of 500 amp passed through the copper blocks. The whole assembly is enclosed in laminated asbestos to reduce heat losses. J. G. W.


Organomet allic Compounds of the Platinum Metals A SURVEY OF THE TYPES OF COMPOUNDS, THEIR STRUCTURES AND REACTIONS

By G. Wilkinson, Ph.D., A.R.C.S. Professor of Inorganic Chemistry, Imperial College, London

Although platinum provided the j r s t known exurnpie of an organorndlic complex of a transition metal, intensive studies of cornpounds of the plutinurn metals with metal to carbon bonds have come mainly during th past decade. The main chsses of srlable organo- complexes such as those having oleJilas, acetylenes, alkyl or cyclopentadienyd groups as 1iganJs are discussed. The study of such stable complexes should assist in the elucidation of the mcch- onism of carious reactions which are catalysed by platiniirn metal salts or

complexes.

Although a platinum ethylene complex, Zeise’s salt, K[C,H,PtCl,], was the first platinum metal-indeed, the first transition metal-organometallic compound to be prepared (I), and although the methyl platinum compounds such as (CH,PtI), were among the first metal alkyls to be prepared, it is generally true to say that only during the past twelve or so years when the organometallic chemistry of the transition elements has been intensively studied have the organo compounds of the platinum metals been examined in detail as part of this general research effort.

The organometallic compounds of the platinum metals are of particular interest since they have provided considerable insight


into the ways in which carbon compounds or radicals can be attached to transition metal atoms-especially regarding the unusual types of chemical bonds not found in the chemistry of non-transition metals and non-metals. However, the chemical utility of these complexes, as chemical compounds, is virtually zero at the present time. Despite this fact, such organometallic species are of considerably more than purely academic interest since their structures and the nature of the bonding in the compounds may throw light on the mechanisms involved in the use of platinum metal catalysts, especially in homogeneous media, and may allow the design of new useful processes. Some of the necessary information may already be at hand and we need only consider that the facts of the hydrolysis of [C,H,PtCl,]- to acetaldehyde and of the reduction of palladous salts by ethylene were known for many years (2) before the development of the Wacker olefin oxidation process. Other reactions which doubtless involve labile organometallic intermediates are the stereospecific polymerisation of butadiene using emulsions containing rhodium salts, polymerisations of acetylenes, olefin isomerisations and hydrogenation and carbon monoxide insertion reactions of olefins using ruthenium, rhodium or platinum species. It is not the purpose of this brief review to discuss such matters but only to consider the isolable organo compounds of the platinum metals.

Some Representative Platinum Metal Organometallic Compounds

C o m p 1 ex

C,H,OPdCl(C,H,N)

Structure type

Colourless oil m.p. -5"

Yellow crystals m.p. 50"

Pale yellow crystals

Yellow crystals m.p. -zqo"(dec.) White crystals

m.p. 215" Orange crystals

map. 150" White crystals

z-cyclopentadien yl alkyl Alkyl

Olefin

Olefin (nor bornadiene)

Acetylene

Acetylene-derived cyclopentadienone

Sandwich

Yellow needles Allylic

I

As part of the main d-block transition elements, the six platinum metals have certain similarities in common with the rest of the group, and many of the classes of compounds discussed below are found also for other metals. For a specific metal, not all types of compound may be known-or indeed be capable of existence. In some cases, explanations of special behaviour may be possible on an ad hoc basis. However, the reasons for stability or criteria for bonding in certain types of complex are not well known and quantitative data such as bond energies and other thermodynamic data, bond dis- tances, etc., are often lacking. Nevertheless there is already an appallingly extensive literature, which is growing rapidly, covering especially preparations of compounds and their reactions and of recent years details of infra-red and high-resolution nuclear magnetic resonance spectra. The latter technique has been of especial importance in the study and characterisation of organometallic compounds. In the following sections we survey, with examples chosen from the platinum metal complexes, all of the major types of organ0 compounds known at present. References are


Comment

Volatile. Stable in air Petroleum soluble Formed by CO insertion into PdC1CHs(PEt3) Water-soluble

Soluble organic solvents. Air-stable. Halogen bridged Stable. Soluble in organic

Extremely chemically inert

Undergoes aromatic substi- tution reactions. Oxidisable

Has mesityl oxide bound as ally1 group with free ketone group

solvents

(z-CjHg) ,Ru+

to recent review articles. The table gives the properties of a few representative compounds.

Alkyls These are compounds of the type usual

among non-transition and non-metallic elements but less common among transition metals, in which aliphatic or aromatic radicals are bound to a metal atom (3). There are two classes: (a) normal alkyls, where the M-CE bond is of the normal 0-bond type, (6) those compounds where the hydrocarbon radical, usually a methyl group, acts as a bridge,

H H H

C \ I /

. . ,~ M,' '.M

and where the bonding must be regarded as of the multicentre type as in the polymeric alkyls of Li, Be or Al; this type of bonding is not found for transition metals.

Although no simple binary alkyls, i.e. M(CR,),, are known for the platinum group of metals, many complex alkyls where other ligands are also bound to the metal atom are well characterised. The criteria for obtaining

Form

alkyls stable enough to isolate under normal conditions and various factors, whose effects are not well understood, are complicated. Some of these factors are (i) the oxidation state of the metal, (ii) the nature of the attached ligands, (iii) the electronegativity of the metal-ligand system-this involves both (i) and (ii), (iv) the electronegativity of the attached -CR, group, (v) steric factors such as large bulky groups around the metal which can inhibit the approach of attacking molecules, so stabilising the M-C bonds. Concerning the ligands, it appears that x-bonding ligands, which, in effect, remove electron density from the metal, tend to stabilise M-CR, bonds ; however, though carbon monoxide is doubtless the best J;-bonding ligand, platinum metal carbonyl alkyls have not been isolated. For compounds of analogous structure, the greater the electronegativity of the -CR, group, generally the more stable the M-C bond and fluorinated derivatives are especially stable. In the absence of any data on M-C bond energies, however, explanations of relative stabilities of complex systems are not necessarily of much significance.

Among the alkyls, there are a few points of special interest. Platinum, especially PtIV, of all the metals appears most readily to form stable Pt-C bonds. This is illustrated by the fact that whereas p-diketones form chelate complexes normally, with PtIV the ligand forms an M-C bond as in (I) and this is so stable that in reactions, e.g., with 2,~'-dipyridyl it is the Pt-0 bond and not the Pt-C bond which breaks, to give (11).

The square planar complexes of Pd", Pt" and Ir', chiefly with phosphine ligands, can undergo two unusual reactions. They can add alkyl halides, halogens or hydrogen halides to give octahedral species of formally oxidation state two higher, e.g.

trans-(Et3P),PtICH3+CH31 =

(Et3P)Zpt12(CH3)2

and they can, like complexes of metal carbonyls such as CH,Mn(CO),, undergo

I ,

I


carbonylation reactions to give acyl deriva- ties, e.g.

(Et3P),PdC1CH3 + CO = (Et3P)2PdC1(COCH3)

Such carbon monoxide insertion reactions are believed to be involved in hydroformy- lation reactions of olefins.

Olefin Complexes Compounds containing > C = C i groups

can generally be bound to transition metals (4a,b,c). In addition to mono-olefins, cyclic conjugated and non-conjugated olefins can be bound and in this class can also be included such unsaturated compounds as quinones or cyclopentadienones although the latter are usually obtained in metal complexes indirectly through the interactions of acetylenes with carbon monoxide containing metal complexes (see below). Olefin complexes were the first and are the most numerous of organ0 compounds of platinum metals. They are commonly obtained by direct interaction of platinum metal salts or complexes with olefins, e.g.

aqueous

so 1 u t i o n KzPtCl,+CzH, -+ K[C2H4PtC13] -+ KC1

Apart from the salts, the complexes are usually air-stable crystalline solids, soluble in organic solvents.

The nature of the binding of an olefin to a metal is fairly well understood. X-ray diffraction on several compounds has shown that the orientation is generally as in (111)

with the olefin group “side-on” to the metal. The C=C bond length is not precisely known but it appears to be longer than the unco-ordinated bond. There is also infra-red cvidence which indicates C-C bond weakening on co-ordination. It is not essential that the metal atom lies on a line perpendicular to the C-C axis-indeed in many cyclic olefin complexes it is not possible for this to be so. Regarding the bonding, it is generally accepted that the bond is rather similar to that in the metal-carbon monoxide bond in metal carbonyls with donation of electron density from the %-electrons of the C=C bond into acceptor orbitals on the metal together with a type of %-bond resulting from “back-donation” of electron density from filled metal orbitals to the empty anti-bonding orbitals on the carbon atoms. Estimates of the contributions of these two components are difficult to make but nuclear magnetic evidence suggests that the amount of “double bond” character in the metal-olefin bond is rather small-insufficient in fact to prevent free rotation of ethylene about the bond axis in simple ethylene complexes.

There has been relatively little work on the reactions of the hydrocarbon when bound to metals. Attack by many reagents leads to oxidation of the metal and dis- ruption of the complex or, where

Platinum Metals Rev., 1964, 8, (1)

relative

stronger donors are used, to displacement of the olefin. Where not all of the olefinic groups in a polyolefin are bound to the metal, the “loose” double bonds may be protonated by acids to give cationic species. These are not usually stable unless it is possible for the hydro-carbon entity to rearrange to give a partially delocalised allylic type system (see below) in which case the resulting cations may be quite stable. For example in cyclo- octatetraene complexes, x-C&RhC8H8, where the olefin is bound in the form shown in (IV), gives an unstable species on pro- tonation since a delocalised system cannot be formed, whereas C,H,Fe(CO), (V) can give such a system.

The inter-relationships of olefin complexes and allylic species are still in the process of development. I t is noteworthy that in some instances the metal appears to be the dominant factor. Thus palladium has given allylic complexes whereas, with the same ligands, platinum forms the olefin complex. Thus with mesityl oxide we have the species (VI) and (VII).

Acetylenic and Acetylene-derived Complexes

Acetylene and acetylenic compounds can interact with platinum metal species in a number of ways depending on the nature of the reacting species and on the reaction conditions. In addition to forming complexes,

V

19

(unstable cation)

(stable cation)

0 A

VI

c H 3 -3 /

/ - o=c n

/ c \ CH, CH,

VII

the acetylenes may be polymerised catalytically. There are two main classes of compound : (4 a, b) (a) those in which the acetylenic group is still recognisable-and sometimes recoverable-as such; (b) those in which the identity of the acetylene has been lost by polymerisation and complexation of the polymer; in presence of carbon monoxide or metal carbonyl compounds, the polymerisation can occur with incorporation of CO to give a cyclopentadienone. Although extensive studies have already been made in this area, mostly on Pd, Pt and Rh, we can quote only a few illustrative examples.

H e x a f l u o r o b u t - 2 - y n e r e a c t s w i t h x-CjH,FUi(CO), to give a cyclopentadienone complex (VIII). Diphenylacetylene reacts with palladium halides to give series of

XI

VIII

compounds some of which may be allylic in nature in addition to other reactions. Thus in alcohol, hexaphenylbenzene is formed together with (IX); this complex with hydrochloric acid gives (X). The formation of hexaphenylbenzene is an example of the polymerisations that can occur; similarly hexafluorobut-2-yne can give CJCF,),, C,(CF,),CO or (C4F&,, the latter being an infusible white powder.

Another class of complex is that which appears to have the acetylene bound by o-bonds as in (XI) which can be made by treating PtCl,(PPh,), with hydrazine in presence of the acetylene. Acetylenes can displace each other in such complexes, the one with most electronegative groups being bound most strongly.

Sandwich Compounds This class of compound, whose name

derives from the structure of (x-C5HJ2Fe, ferrocene, is that in which a completely symmetrically delocalised carboxylic system with six x-electrons is bound to a metal (5 a, b). The most extensive class is that of the 7c-cyclopentadienyls, but arene and cyclohep- tatrienyl complexes are known, although the

Pd C1, OEt

Pd

Ph

Ph Ph Ph Ph

IX X

Ph3P CS6 Hqa (Octaphenylcubane)


\ / C

\ / C

\ /

XI I

/7 T\

H - C - M

C

n R

XI11 (anri)

/ \

latter not for the platinum metals. In some cases, two rings can be bound to the metal but in others one ring with other ligands occupying the remaining co-ordination positions. A x-C,H, ring can crudely be regarded as occupying three co-ordination sites on a metal.

After the recognition of the sandwich structure, the ruthenium analogue was the first other complex of this type to be made; it is one of the few organo complexes of platinum metals which are commercially available. The osmium analogue also exists and cationic species, e.g. (x-C,H,),Rh’, for Ru, Os, Rh and Ir. The ability to form sandwich compounds appears to be related to the stability of a particular oxidation state of the metal and to its ability to give the pseudo-octahedral bonding orbitals necessary to provide overlap with the rings. There are no stable neutral (x-C,H,),M compounds of Rh, Ir, Pd and Pt since these metals have either an unstable I1 state or give normally square planar complexes. Attempts to reduce (x-C,H,),Rh+ lead to a cyclopentadiene olefin complex of Rh‘

NaBH, in tetra-

(T-C5H,),Rh+ +H- :+ --C5H,RhC5H6

hydrofuran

All cyclopentadienyl complexes are made by essentially standard procedure, namely the interaction of a metal halide or complex halide with the sodium salt C,H5-Na in tetrahydrofuran solution. Mono x-cyclopentadienyls result when a complex halide with other suitable ligands are used, e.g. for ally1 palladium chloride

[C,H,PdCl] +zC,H,Na -+zz-C,H,PdC,H,


Arene complexes are of little importance for platinum metals although a few benzene and substituted benzene species of Ru, 0 s and Rh are known; they are not especially stable.

Allylic and Related Complexes These complexes have been noted in

passing above. They are in a sense intermediate between olefin and sandwich compounds in having a partially delocalised “open-ended”, x-electron system bound to a metal (4a,b). The allyls can be written as involving canonical variants of (XII) but nuclear magnetic resonance spectra have shown that a more realistic and correct formulation is (XIII) or (XIV). Two isomers, anti and syra with respect to the hydrogen atom on the “central” carbon atom not only exist theoretically but have been separated in some cases.

The first allyls-which are of quite recent recognition-were obtained from the

xv

H H \ /

C CI

XVI

21

interaction of palladous chloride with ally1 alcohol. They can be obtained in a variety of ways. The recognition of allylic binding also led to the reformulation of a number of known complexes, previously held to be olefin complexes. Typical examples are the I : 3-cyclohexadiene palladium complex which is unequivocally now known to be (XV) and the butadiene palladium halide complex now shown to be (XVI). It is now recognised that allylic species may be most important intermediates in a variety of reactions involving olefins and platinum metal salts. I t seems probable, for example, that the polymerisation of butadiene by rhodium salts is of this type and doubtless other olefin reactions will be interpreted in this way in future, although considerably

more experimental work will be required to ascertain the reaction mechanisms in detail.

References I H. Zeise, Pogg. Annalen, 1827, 9, 632 2 See N. V. Sidgwick, The Chemical Elements

and their Compounds, Vol. 11, pp. 1560, 1588. Oxford

3 Far comprehensive reviews see F. A. Cotton, Chem. Rev., 1955, 55, 551; see also for discussion J. Chatt, Proc. Chem. SOL., 1962, 318

4 For reviews see: (a) M. A. Bennett, Chem. Rev., 1962, 62, 11; (b ) R. G. Guy and B. &. Shaw, Advances in Inorganac and Radio- chemistry; 1962, 4, 77; (c) E. 0. Fischer and H. Werner, Angew. Chem. International, 1963, 2,80

5 For reviews see: (a) G. Wilkinson and F. A. Cotton, Progress in Inorganic Chemistry, 1939, I, I; (b) E. 0. Fischer and H . P. Fritz, Advances in Inorganic and Radio- chemistry, 1958, I, 56

P rc~ision Glaze K esis tors PALLADIUM IN NEW SCREEN PRINTING COMPOSITIONS

For use in printed circuits there is a demand for resistors with a wide range of values and good electrical properties and capable of being produced by the simple method of screen printing and firing the resistor film on to a ceramic substrate. In a paper given to the Electronics Division of the American Ceramic Society in October 1962, and now published in the A.C.S. Bulletin (1963, 42, (9), 490), L. C. Hoffman, of the Electrochemicals Department of du Pont, describes the development of resistors of this type in which the elements consist of conducting glazes containing palladium and silver.

The disadvantages are briefly discussed of resistors produced by screen printing carbon- resin dispersions, and of those made by deposition and attenuation of metal films. The failure of early attempts to produce glaze resistors containing particulate oxide and oxide-metal mixtures is attributed mainly to poor resistance-temperature relationships and critical dependence of resistance values on the concentration of powder conductors in the glaze.

These difficulties, and the current noise which is characteristic of conduction between particles, are claimed to have been overcome by using glazes containing finely divided

(0.1 to 0.5~) palladium and silver as conductors. The oxidation-reduction behaviour of palladium heated in air is thought to promote sintering of the palladium and silver particles into chain-like aggregates. These are claimed to give continuous rather than particulate conduction, thereby reducing the dependence of resistance on metal concentration in the glaze, promoting heat dissipation and reducing current noise.

The resistor glazes are made by ball-milling the glassy component or frit to an average particle size of 5p, and mixing this with the metal powders. Screen printing preparations are made by milling two-thirds of the inorganic powder with one-third of organic vehicle and controlling the viscosity of the pastes between 170 and 230 poises. The glazes are fired on ceramic substrates at 760°C.

A range of resistance values can be obtained by varying the ratio of palladium to silver and the concentration of metal powder in the glaze, and by attenuating the current path by selection of the screen printed design. The author gives data on the resistivity, temperature coefficients and current noise of various palladium-silver compositions.

P. E. K.


The Early History of the Thermocouple By L. B. Hunt, M.SC., Ph.D. Johnson Matthey & Co Limited

The name oJ Seebeck is indissolubly associated with the discovery of thermoelectricity and the thermocouple. But how did Seebeck’s researches jit into the general background of contemporary scientijic work, and how did they lead on to the development of the modern thermocouple pyrometer? This article outlines the early history of the couple up to the time when it became accepted as an accurate and reliable means of measu.ring high temperatures.

At this distance from the events, and looking back from our present understanding of the nature and applications of electricity, it is almost impossible to appreciate the excite- ment and enthusiasm that prevailed in the little world of physics around the year 1820. Until Volta announced the discovery of his pile in 1800 physicists had had no means of studying the effects of a steady current. This, and the voltaic cell which rapidly succeeded it, provided for the first time a simple means of maintaining a continuous current, and led to a burst of activity in the study of the chemical effects of electricity.

Oersted and Ampbre As this first wave of enthusiasm was perhaps

dying away, Oersted discovered that a current of electricity flowing in a wire lying parallel with, and close to, a magnetic needle had the power of deflecting the needle. This discovery was announced in 1820, and it immediately set off a new wave of interest all over Europe, this time in the mechanical effects of a current.

Arago, in the same year, produced the first electromagnet, while Ampere, within a week of hearing of Oersted’s experiment, had shown that one electric current had a magnetic influence upon another. No doubt was left that magnetism was essentially an electrical phenomenon.

Among the small band of physicists who were active in this way was Thomas Johann Seebeck. Born at Reval in Estonia on April gth, 1770, the son of a wealthy merchant, he left his native town at the age of 17 and took up the study of medicine in Berlin. His strong inclination for natural science, together with his financial independence, caused him to change his plan, however, and he embarked on a career of private research, first in Bayreuth and later in Jena. Here he worked on optics and on the nature of colour, but in 1810 he left Jena for Nuremberg, and it was here that Oersted spent some time as Seebeck‘s guest. In 1818 he accepted a position with the Berlin Academy of Sciences, and moved to that city.

Seebeck’s Discovery Here it was, of course, that he learned of

Oersted’s discovery, and at once applied himself to the study of electromagnetism; in December of the same year, 1820, he read a paper to the Academy dealing with the magnetic influence of a current. Only a few months later, in August 1821, he announced to the Academy (I) his discovcry that two different metals forming a closed circle, in the absence of moisture, showed magnetic properties when subjected to a difference of temperature at the point of contact. He had experimented with a number of combinations


of metals (finding an antimony-bismuth combination the most effective), and had ascertained the effects of both heating and cooling one of the junctions, He established that the deflection of the magnetic needle arose from the difference in temperature of the metallic junctions, that the effects varied for different metals, and were greater for greater differences of temperature. In his results he reported the movement of the needle in terms of an easterly or a westerly deflection, and he described the phenomenon as ‘ctherm~-magneti~m”, taking objection in later years to the expression “thermoelectricity”.

Second in importance at the time only to Oersted’s experiment, Seebeck’s discovery also spread rapidly among European physicists, and it was repeated in every centre of research.

Faraday and Ohm Among others, Faraday carried out the

experiment, and he records it in his diary as follows:

Octr. 21, 1822 Dr. Seebeck’s Expt. An . Phil. 2V.S. VoE. iv. p . 318

Bar of Antimony and brass wire; the bur being heated at one end the north pole of a needle would go round it as represented in the lower Jigure-the effect on the needle very decided, powerful even and constant.

The dotted lines represent the state of the loire as ascertained from former experiments.


At this time Ohm was working on the propagation of electricity through a conductor and on the concept of resistance, but he was having trouble in his experiments owing to the variations in the current obtained from his batteries. A suggestion was made to him by Poggendorf that he should replace the batteries by a thermo-electric circuit, and this idea Ohm adopted in his classical research in 1826. He used a circuit of bismuth and copper, one junction being immersed in a steam jacket and the other in ice.

The First Measurement of High Temperature

The first recorded suggestion to make use of Seebeck’s discovery as a means of measuring high temperatures came from A. C . Becquerel (2) in a paper read to the Academie Royal des Sciences in Paris on March 13th, 1826. His investigations included observations of the needle deflection obtained with a number of combinations of metal wires when one junction was heated in a spirit lamp, and he deduced that, for certain of these combinations, the intensity of current developed was proportional to the rise in temperature. The most suitable combination, he decided, was a circuit consisting of platinum and palladium wires.

Becquerel further showed that the characteristics were independent of the diameter of the wire, and also that an impure platinum wire would give rise to a current if coupled with a pure platinum wire; he pointed out, in fact, the necessity for cleaning the platinum in nitric acid to avoid spurious effects due to contamination.

The Magnetic Pyrometer In 1836 Professor C. S. M. Pouillet (3), of

Paris, also before the Academie Royal des Sciences, put forward his “magnetic pyrometer” and detailed its construction. This instrument, almost incredible by today’s standards, comprised a platinum wire sealed into the breech of a gun, the wire passing up the barrel but prevented from touching the

sides by a filling of magnesia or asbestos. The breech of the gun was then to be inserted into the hot zone.

In the course of his long and classic researches on heat Henri Regnault (4) made use of Pouillet’s iron-platinum couple, but he found such irregularities that he emphatically condemned the whole idea of the thermo- electric method. Regnault’s unhappy experiences were due partly to his use of iron as one element, and also to his failure to employ a high-resistance galvanometer. Later, in 1862, Edmond Becquerel(5) took up the study of his father’s platinum-palladium thermocouple and used it as an intermediary with an air thermometer in determining the melting points of a number of substances. As a result of his researches he succeeded to some extent in rehabilitating the reputation of the thermocouple, and he derived an expression-much too complex-for the relationship between temperature and electromotive force.

E.m.f. - Temperature Relationship Avenarius (6) also investigated this rela-

tionship, working with the rather curious combinations of steel and nickel-silver, and copper and zinc. He arrived at a parabolic formula of the type:

E =a +bt +cte

but a few years later apparently realised his error and withdrew his arguments.

In the meantime Professor P. G. Tait (7) of Edinburgh University had conducted a series of experiments in an attempt to construct “thermo-electric diagrams”, and concluded that the electromotive force is in general a parabolic function of the absolute temperature, He also reported that a very small amount of impurity, or even of permanent strain, is capable of considerably altering the line of a metal in the diagram.

Professor Tait used “platinum-iridium alloys containing respectively 5 , 10 and 15 per cent of the latter metal. These were prepared for me from pure metals by Messrs. Johnson and Matthey”. This constitutes the


Henry Le Cliatelier The father of the modern thermocouple, Le Chatelier was the $rst to employ a rhodium-platinum alloy against platinum and to recommend calibration in terms of the fired points of melting or boiling

of pure substances

first reference to the use of iridium-platinum alloys in thermocouples.

The Work of Le Chatelier And so to 1885 and Henry Le Chatelier (8),

whose name, together with that of Seebeck, will always be associated with the thermo- electric pyrometer and with the use of a rhodium-platinum alloy. Born in Paris in 1850, Le Chatelier studied chemistry under Sainte-Claire Deville, but in 1870 was called into the army and took part in the siege of Paris. Subsequently he practised as a mining engineer, but in 1877 joined the French School of Mines to teach chemistry, becoming Professor of Industrial Chemistry some nine years later. Many years afterwards Le Chatelier recalled the origins of his work on thermocouples in the following words:

“In 1885, when I attacked the problem of the measurement of high temperatures, it is

25

fair to say there existed nothing definite available on this important question; we possessed only qualitative observations for temperatures above 500°C. Engaged at that time in industrial studies relative to the manufacture of cement, I sought a method which above all would be rapid and simple, and decided on the use of thermo-electric couples, intending to determine the order of magnitude of the sources of error noticed by Regnault. The readings of even a crude galvanometer might be very useful in technical work, provided the limitations of its accuracy were appreciated. I soon recognised that the errors attributed to this method could easily be eliminated by discarding in the construction of the couples certain metals, such as iron, nickel, and palladium, which give rise to singular anomalies. Among the different metals and alloys studied, pure platinum and the alloy of platinum and rhodium which are still used today, gave the most satisfactory results. . . . I recommended also the calibration of the couples, not against the air thermometer directly, as Becquerel had tried to do, but in terms of the fixed points of boiling or fusion of certain pure substances, in such a way that, when these temperatures should be known more exactly, as is the case since my earlier researches, the results could be corrected with certainty.” Le Chatelier devoted considerable time and

effort to the development of the thermocouple pyrometer, and arranged for the instrument to be manufactured by Carpentier, the suc- cessor of the famous Ruhmkorff, at 20 Rue Delambre, Paris. The reputation of these instruments spread rapidly and widely. I n 1890, for instance, the great American metallurgist, Professor H. M. Howe wrote (9):

“Thanks to the labors of M. Le Chatelier, we have at last a pyrorneter capable of measuring easily, accurately and rapidly extremely high temperatures, indeed, those approaching the melting point of platinum. And this is not an apparatus which each must construct for himself; it is for sale ready made. Indeed, it is SO far simplified that it has actually entered into practical use for the control of high temperatures in steel works, glass works and gas works.”

American Investigations Contemporary with Le Chatelier but quite

independently of him, Dr. Carl Barus (10) was engaging himself actively in the measurement of high temperatures. I n 1882 a new physical laboratory had been set up within the

organisation of the United States Geological Survey with the objective of studying the physical constants of rocks. Barus was put in charge of this laboratory, which was located first in New Haven, Connecticut, but moved to Washington two years later. He realised that few important steps in the study of this branch of geology could be made until methods for the accurate measurement of high temperatures and pressures had not only been perfected but rendered easily available, and he therefore undertook a most comprehensive study of temperature measurement; this was published as a memoir of some 300 pages in 1889. Numerous alloys of platinum were investigated as thermocouple elements, most of them having additions of 2, 5 and 10 per cent of other elements, but he came to rest for general use on platinum against 20 per cent iridium-platinum. Barus was aware of the importance of purity and homogeneity in

Sir William Roberts-Austen Chemist to the Royal Mint, Professor of Metallurgy at the Royal School of Mines and Jirst investigator to the Alloys Research Committee of the Institution of Mechanical Engineers, Roberts-Austen was quick to appreciate the usefulness of Le Chatelier’s

thermocouple pyrometer


his thermocouple materials, and he drew upon the resources of the Bishop and Co. Platinum Works at Malvern, Pa., for the preparation of his materials. The couples were then cali- brated at the boiling points of mercury, zinc and certain organic substances.

Roberts-Austen’s Contribution At this time the Institution of Mechanical

Engineers had established its Alloys Research Committee, with the initial objective of studying the effects of alloying elements on the properties of metals, and had appointed W. C. Roberts-Austen, who combined the posts of Chemist to the Royal Mint and Professor of Metallurgy at the Royal School of Mines, as investigator. I n his first report (11) in 1890 to the Institution, Professor (later Sir William) Roberts-Austen said:

“In the present investigation it is necessary to measure much higher temperatures; and fortunately an accurate method is at hand. Early in 1889 I had occasion to employ the pyrometer devised by M. H. Le Chatelier, and was satisfied as to its being extremely trust- worthy and convenient up to temperatures over 10oo”C. or 18oo”Fahr. The instrument in fact enabled me to confirm the fundamental observations of M. Osmond respecting the cri t id points of iron and steel, and to dernon- strate the results in a lecture delivered before the members of the British Association in September 1889.”

Since 1875 Roberts-Austen had interested himself in the problems of liquation or segregation of the constituents of alloys, and had been most painstaking in his measurement of temperatures using the laborious calori- metric methods then available. He therefore welcomed most readily the new type of instrument and proceeded to adapt it for the production of autographic records of the cooling and solidification of molten metals and alloys.

Problems of Homogeneity Some doubt still remained, however, con-

cerning the absolute reliability of the rhodium- platinum alloy, and Roberts-Austen referred to this:


Edward Matthey Investigated the homogeneity of rhodium-platinum alloys and conjirmed the $findings of Le ChateEier and Roberts-Austen as to their suitability for

thermometric use

“It is asserted that even long wires of the platinum-rhodium alloy are homogeneous, and therefore do not give rise to subsidiary currents which would disturb the effect of the main current produccd by hcating the junction; but very careful experiments to determine whether this is the case have yet to be made.”

This uncertainty aroused the interest of Edward Matthey, who carried out a lengthy investigation (12) on the liquation of alloys of the platinum metals. On the rhodium- platinum alloys he had the following comment to make:

“Much attention has lately been drawn to an alloy of pure platinum, with 10 per cent of rhodium, which has become important from the excellent service it has rendered in the determination of high temperatures. The alloy of platinum with ID per cent of rhodium is used with pure platinum as a thermocouple, and it is, therefore, interesting to be able to set at rest any doubt which might arise as to this alloy being uniform in composition when melted and drawn into wire.”

27

Matthey prepared a melt of one and a half kilograms of 10 per cent rhodium-platinum, which he cast into a sphere of two inches diameter. The sphere was then sectioned, and samples were taken for analysis from a number of locations between the surface and the centre. The maximum difference between the centre and the outside was found to be 0.6 per cent of platinum and 0.04 per cent of rhodium. He concluded:

“This result proves that the alloy is not subject to liquation, and fully justifies the high opinion that H. Le Chatelier and Roberts- Austen have formed as to its suitability for thermometric measurements.” At much the same time, 1892, Edward

Matthey was concerning himself with the extraction and refining of bismuth and he contributed a series of papers on this subject to the Royal Society. An extract from one of these papers (13)~ dealing with the temperature at which arsenic can be oxidised off from bismuth, reads as follows:

“The work of Roberts-Austen has shown that a thermo-junction is practically the only form of pyrometer that can be used for delicate thermal investigations of rhis kind, but the question arose which particular thermo- junction should be adopted. Was it well to use the platinum-iridium one as advocated by Barus, or the platinum-rhodium one suggested by H. Le Chatelier? My previous work on the

alloys of platinum and rhodium, lately published in the ‘Philosophical Transactions’, settled the question in favour of the rhodium- platinum thermo-junction, for I was satisfied that the alloy of platinum with 10 per cent of rhodium is as homogeneous as any known alloy could well be, and is therefore admirably adapted for use as a thermo-junction, pure platinum being the opposing metal.”

The instrument employed was obtained from Paris and was used in the full scale operation of the oxidation process in the works of Johnson Matthey, being one of the first such pyrometers to be used in industry.

The only earlier record of a Le Chatelier pyrometer being used in this country is that given by Sir Robert Hadfield (rq), who purchased one from Carpentier in April 1890. This gave excellent service in the steel works of Hadfields Ltd. in Sheffield until British- made pyrometers became available just after the turn of the century.

The first mention of thermocouples being available for temperature measurement in this country appears in a Cambridge Instrument Company catalogue of 1898, but the manufacture of them did not begin until 1902, when special stocks of platinum and rhodium-platinum were procured from Johnson Matthey and marketed in suitable porcelain tubes (15).

I

2

3 4 S 6

7 8

9 I 0

I1

I2

I3 14 IS

T. J. Seebeck . . * .

A. C. Becquerel . . _ _ c. s. A M . l’ouillet , . H. V. Regnault . . . . E. Becquerel . . . . Avenarius . . . . . .

P. G. Tait . . . . . . 1-1. Le Chatelier . . . .

13. M. Howe . . . . C. Barus . . . . . .

W. C. Roberts-Austen . .

. .

E. Matthey . . . . B. Matthey . . . . Sir Robert Hadfield , . Anon .. .. ..


References

Abhandlurgen der physikalische Klasse dcr Komglichen Akudemie

Ann. chim. phys., 1827, 31, pp. 371-392 Compt. rend., 1836, 3, pp. 782-790 Relation des Experiences, Paris, 1847, I, p. 246 Compt. rend., 1862, 55, p. 826 Pogg. Ann, 1863, 119, p. 406

Trans. Roy. SOC. Edin., 1872-73, 27, p. 125

Compt. rend., 1886, 102, p. 819 J . de Phys., 1887, 6, p. 23 ling. and Min. J., 189, 50, p. 426 13~11. U.S. Geol. Surwey, 1889, h’o. 54 Phil. Mug., 1892, 34, p. 376 1st Rep. Alloys Hes. Comm., Inst. Mech. Big., 1891 I’hiZ. Trans., 1892, 183, p. 629 I’roc. Roy. Soc., 1893, 52, p. 467 Trans. Fareday SOL., 1917-18, 13, p, 208 Eyineeriqq, 1945, 159,iMay 11th and zgth, pp. 361 and 41

d m Wissenschafrer ZU Berlin, 1822-23, pp. 265-373

1864, 122, p . 193

28

ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES

On the Thermal Expansion Coefficient and the Temperature Coefficient of Young's Modulus of the Alloys of Iron and Platinum H. MASUMOTO and T. KOBAYASHI, J . Japan Inst. Met., 1963, 27, (91, 459-460 53.5 to 57.0'6 Pt alloys with Fe have negative coefficients of thermal expansion with a maximum value of - 23.68 x I O - ~ for 56Oh Pt alloy at o to 40°C. 51 to 69:/, Pt alloys have positive temperature coefficients of Young's modulus with a maximum value of +161.5xro-~ for 5596 Pt alloy in the same temperature range. A vertical dilatometer and a vibrator-controlled oscillator with an electrostatic transducer were used for the respective measurements.

Theory of Hydrogen Adsorption on Platinum T. TOYA, 3. Res. Inst. Catalysis Hokkaido Univ., 1962, 10, (3), 236-260 There are two types of H adsorption on Pt. r-type adsorption increases the work function and electrical resistance of clean Pt while s-type adsorption decreases them. The total effect on Pt is complex as the difference between the two heats of adsorption is only 0.4 kcal/mol whereas for Ni, which behaves similarly, it is ro kcal/mol. The positions and entropies of the two types of adsorption are discussed. The broad, intense infra-red band at 4.8611 in the spectrum of H on Pt is caused by s-type adsorption and the sharp, weak band at 4 . 7 4 ~ by r-type adsorption.

Ultra-pure Hydrogen by Diffusion through Palladium Alloys J. B. HUNTER, Abs. Papers, 145th Meeting, Am. Chem. SOC., 1963, 12s-130 The development of a stable, highly permeable alloy of Pd has led to its industrial application in a variety of diffusion units. H, transfer rate data are presented for wide ranges of pressure and temperature.

Magnetic and Dilatometric Measurements on the Transformation Kinetics of the Iron- Palladium Alloys A. KUSSMAN and K. JESSEN, z. Metallkunde, 1963,

Studies on y-a transformations and yl-yz ordering confirmed the existence of a miscibility gap between 10 and 25 at.% Pd-Fe alloys at high temperatures. The critical temperature curve for yI-y2 ordering showed a maximum at 8oo"C, 65 at. :k Pd. A eutectoid occurred at 46 at. :d Pd,

541 (911 5 0 4 - 5 1 0

605fS'C. The effects of variations in the treatment of the alloys were also studied. Fe-Pd alloys behaved similarly to Ni-Fe alloys after quenching, particularly by showing an Invar effect.

The Iron-Palladium Phase Diagram below 950°C E. RAUB, H. BEESKOW and 0. LOEBICH, Z. Metall- kfmde, 1963, 54, (101, 549-552 The results of room- and high-temperature X-ray analysis of the Fe-Pd system are tabulated. No y/u eutectoid was observed but a miscibility gap extended from 7 to 23 at.X Fe, with a critical temperature of about 900°C. A eutectoid between u-Fe and the yl phase was confirmed at about 62ooC, 43 at.(:; Fe. The two ordering phases y1 and yz were separated by a narrow two-phase region below a eutectoid area. yz has a higher critical temperature than yl. (8zofzo"C and 790 &2Ooc).

On the Structural Form of Copper-Palladium Solid Solutions near the Composition Cu,Pd A. A. PRESNYAKOV, L. I. DAUTOVA and E. A. DZHANBUSINOV, Fiz. Met. Metalloved., 1963, 16, (I) , 61-64 28.8 at.:6 Pd-Cu alloy samples were tempered at 750"C, annealed and studied by X-ray methods. The crystal lattice structure is discussed. At high temperatures a structure was detected which indicated the existence of a new phase but its lattice parameters were not determined.

Properties of Palladium-Rhenium Alloys M. A. TYLKINA and I . A. TSYGANOVA, Zh. hreorg.

Khim., 1963, 8, (IO), 2346-2350. Additions of up to 11.9 wt.76 Re increased the hardness and strength and the specific electrical resistance of Pd but decreased the temperature coefficient of resistance. Re also raised the initial temperature of reaystallisation of Pd; by up to 600°C in the case of 8.74 wt.?,, Re-Pd. Annealing studies on Re-Pd showed that higher temperatures reduced the hardness and strength but improved the elastic properties of the alloys. Electrical properties were unaffected by the annealing treatments.

The Temperature Dependence of the Mag- netic Susceptibility of Some Palladium Alloys w. KOSTER, D. HAGMANN and R. LUECK, Ann.

Temperature-reciprocal paramagnetic susceptibility curves for Pd alloys with up to 4 at.:/, Ru or 10 at. a& Cd, In or Rh between 120 and I 100°K

Phy~dk, 1963, 11, (1-6), 52-58


agreed with the transport aspects of Stoner's theory of paramagnetism. Various explanations of the electron specific heat-susceptibllity dis- crepancy in Pd showed that no one definition of Stoner's parameters OF, q, O1 was possible. An approximation using the reciprocal temperature coefficient of the reciprocal susceptibility ex- plained vacancy variations in the alloys but this quantity was not the same as the Curie constant unless T+OO,. The rigid band model gave a partial interpretation of the results.

Hysteresis in the Palladiuni-Hydrogen Sys- tem N. A. SCHOLTUS and w. K. HALL, J. Chern. Phys., 1963, 391 (412 868-870 When H, dissolves in Pd, the GL phase forms first. The phase nucleates and grows in this causing plastic deformation of the M phase beyond its elastic limit because of the large M+P volume change. Absorption is accompanied by ,!3 phase growth under a phase compression but desorption takes place from the /3 phase of the plastically deformed solid. This is not reversible and hysteresis occurs. Earlier theories are discussed. The absorption loop of the isotherm is calculated from the desorption loop and the yield strength of Pd.

Role of Hydrogen Atoms in Palladium T. TSUCHIDA, J . Phys. Soc. Japan, 1963, 18, (7), 1016-1019 Ag-Pd alloys are similar in electronic structure to Pd but do not have the narrow regions of H, content stability of pure Pd. Measurements of the Hall coefficient and magnetic susceptibility of hydrides of 10 to 30 at.% Ag-Pd alloys were made as functions of Hz content. As Ha was occluded the paramagnetic susceptibility decreased and the Hall coefficicnt decreased considerably in the high H, contcnt p-phase alloys. The H atom was considered to act like a proton in the Pt lattice by transferring a valence electron to the Pd 4d band.

The Phase Diagram Rh-Sb R. N. KUZ'MIN and N. N. ZHURAVLEV, Vestnik Mosk. Univ., Ser. ZII, Fiz. Astron., 1963, 18, (z), 9-14 X-ray and micrographic studies of the Rh-Sb system indicated the existence of a y-phase at about the Rh,Sba composition and a eutectic point between the compositions RhSb and Rh,Sb. The solubility of Sb in Rh reached about 8 wt. 9 ; at 1150OC.

Thermal Analysis of the Rh-Bi System R. I. KUZ'MIN, N. N. ZHURAVLEV and G. s. ZHDANOV, Zh. Neorg. Khim., 1963, 8, (8), 1906-1914 Results of thermal analysis of Bi-rich alloys slightly modified previous constitution diagrams of the Bi-Rh system. The eutectic point was detected at 1.4 at.':/, Rh and 268'C. The transi-

tion temperature between 01- and P-Bi,Rh occurred at 430°C. Peritectic temperatures were 456°C and 775°C.

On the Superconductivity of Ti- and Zr-Rh Alloys c. J. RAUB and c. A. ANDERSEN, Z. Physik, 1963,175, (11, 10.5-114 The connection between superconductivity and valence electron concentration was studied in Ti- and Zr-alloys containing up to IZ at.% Rh. In both the h.c.p. or-phases and b.c.c. 8-phases the transformation temperature increased with valence electron concentration. By extrapolation to 0% Rh it was shown that the transformation temperatures for T i and Zr p-phases lie below those of the a-phases.

The Structure of the Stable Tantalnm- Ruthenium Alloys E. RAUB, H. BEESKOW and w. FRITZSCHE, Z. Metallkunde, 1963, 54, (81, 451-454 The Ru-Ta system is similar to the Ru-V and Ru-Nb systems. X-ray and microscopic analysis of alloys with increasing Ru content showed the occurrence of transitions from the b.c.c. solid solution to an ordered Bz structure, followed by tetragonal distortion, an ordered orthorhombic form and an ordered f.c. tetragonal form at high Ru content.

Melting Points of LaRu,, CeRu, and PrRu, R. D. REISWIG and K. A. GSCHNEIDNER, J. Less-

The observed melting points of the Laves phases were: LaRu, at 1431*3o'C, CeRu, at 1539& 30T, PrRu, at 1681+15OC. Melting was probably incongruent.

Vapour Pressures of Platinum Metals. 111. Iridium and Ruthenium R. c. PAULE and J. L. MARGRAVE, J . Phys. Chem.,

Vapour pressures, heats of sublimation and boiling points were obtained for solid I r and Ru. I r has log P& (solid)=10.1zo-~3,680/T for 2140°K < T < ~ 4 7 7 ° K ~ AH,&= 160.9 32.8 kcall mole and estimated normal b.p. -4850&10o"K. Ru has log P z z (solid)= 11.200-33,600/T for

mole and estimated normal b.p. w435of 100°K.

The Alloys of Ruthenium with Titanium and zirconium E. RAUB and E. ROSCHEL, Z . Metalikunde, 1963, 54,

Microscopic and X-ray methods confirmed the existence of intermediate B2 phases TiRu and ZrRu, which melt congruently at 210~2150°C and show no phase transformations nor decom- positions at lower temperatures, and of the C14

Common Metals, 1963, 5, (51, 432-433

1963967, (9XI896-1897

201 IoK<T<2330"K, AH,;, = 151.5&14 kcd/

(8)~ 455-462


Laves phase ZrRu,, which decomposes eutectoid- ally at 1300t20"C. Ru has low solubility in a-Ti and cc-Zr but more in /%Ti and P-Zr. Ru stabilises P-Ti and can depress the f l f cc transformation below room temperature for 16-20 at. :; Ru. Considerable precipitation hardening occurs in Ti-rich alloys. Study of the P+cc transformation in Zr-Ru alloys is made difficult by the oxidation of Zr, causing the alloys to appear ternary.

A Study of the Adsorption and Decomposi- tion of Hydrocarbons on Clean Iridium Surfaces R. W. ROBERTS, J . PhYS. CheWZ., 1963, 67, (IO), 2035-203 8 CH,, CzHs and C,H, were admitted to Pyrex flasks on the inner surfaces of which Ir films had been prepared under ultra-high vacuum conditions. They were adsorbed on the clean films at 27 and 100°C. CH, did not decompose on Ir but C,H, decomposed to CH, and H, at 27% and to CH, at 100°C. 0, preadsorbed on Ir inhibited C,H, decomposition. CaHl was self-hydrogenated to C,H6 and CHI. The roughness factor of the I r films was about 7.

High Temperature Properties of Refractory Alloys E. J. RAPPERPORT and A. L. GEARY, U.S.A.E.C.

Ten alloy systems of the refractory metals Mo, W, Nb and Ta with additions of Hf, Re, Os, Ru, Rh, Ir and Zr were studied by hot hardness tests up to 1200°C and oxidation resistance tests a t IOOO"C to determine their suitability for use in nuclear reactors. Ru, 0 s and Re additions increased the hardness by up to 7 times at room temperature and up to 17 times compared to the unalloyed refractory metals. These alloys were then tested for tensile strength up to 180orC. 2-10 at.% Ru-W,2-1oat.% Ru-Taand2-1oat.O; Re-Nb showed greater strength worth further study.

Repmt N . M . I . - I ~ ~ ~ , 67 pp.

Oxidation of the Platinum-Group MetaIs c. A. KRIER and R. I. JAFFEE, J . Less-Common

Samples of the six Pt-group metals were heated in a slowly moving stream of dry air at IOOO- 14oo0C and all showed linear weight loss rates in the range 1200-1400@C by the formation of volatile oxides. Rh gained weight at ro0o"C by the formation of an oxide film and Pd initially absorbed 0,. At 14oo0C in a slow air stream at I atm. the rates of weight loss were 6 . 8 ~ 1 0 - ~ mg/cm2/hr for Rh, 9.6 x I O - ~ for Pt, 3.1 for Ir, 1.2 x 102 for Ru and 1.2 x 10-3 for 0 s . The rates depended on the gas flow rate, the partial pressure of Oe and the total gas pressure. The kinetics of the reactions also depended on the temperature. The mechanism of reaction of the 0, at the surface is discussed and specimens are illustrated.

Metals, 19633 5 3 ( 5 ) ~ 411-431

Superconductivity of Some New Pt-Metal Compounds c. J. RAUB, w. H. ZACHARIASEN, T. H. GEBALLE and B. T. MATTHIAS, J . Phys. Chem. Solids., 1963, 24,

Tests on compounds of the Pt metals with P, As, Sb, Bi and S revealed several previously unknown superconductors in the systems Rh-As, Pd-P and Pd-As. Transition temperatures and crystallo- graphic data are listed for all known superconductors of the Pt metals with elements of groups IVA, VA, and VIA.

The Problem of Producing Superconducting Materials

Gmnoe Delo, 1963, (9, 3-12 Among a large number of superconducting substances reviewed there are more than thirty compounds of the Pt metals, for which the transition temperatures and Curie points are tabulated. Their formation, properties and uses are discussed. (24 references.)

(9)i 1093-1 100

E. M. SAVITSKII and V. V. BARON, Metallurgiyu i

CHEMICAL COMPOUNDS

Structure and Reactivity of the Oxyanions of Transition Metals A. CARRINGTON and M. C. R. SYMONS, Chem. Rev., 19633 63, (9,443-460 Known oxyanions of the Pt metals are RuO,, RuO,, RuOZ- and OsO, and Rho% is also believed to exist. The electronic structure and reactions of these tetrahedral oxyanions, together with those of V, Nb, Ta, Cr, Mo, W, Mn, Ti, Re and Fe are critically discussed. (115 references,)

Unusual Oxidation States of the Noble Elements

The structure and properties of the fluorides, oxides and oxyfluorides of the Pt metals are discusscd. Particular note is made of OsOF, and PtO,F,. Work on the [PtF,]- ion led to the discovery of the noble gas fluoride compounds, the bonding of which is also reviewed. (38 references.)

Aroniaticity of Five-Membered Rings Con- taining Platinum (11) P. HAAKE and P. A. CRONIN, Imrg . Chem., 1963, 2,

Conducmmetric studies on the kinetics of displacement of chloride by dithiooxamide in methanol indicated that a strong trans effect resulting from aromaticity in the Pt- cc-diimine chelate ring caused the Pt(bipy)Cl, complex to react marly one hundred times faster than the cis-?t(py),Cl, or Pt(en)Cl, complexes.

N. BARTLETT, Chem. in CUnadU, 1963,I5, (8),33-40

(4)J 879-880


Aromatic Complexes of Metals. LXXV. C yclopentadienyl-palladium-~kos yl E. 0. FISCHER and A. vOGLER, 2. Naturf., 1963,186, (9)Y 771-772 C,H,PdNO was prepared by the reaction of PdNOCl with NaC,H, in pentane with air excluded and its absorption spectrum was studied.

Complexes between Palladium (II) and Pyridine-2-aldoxime c. F. LIU and C. H. LIU, Znorg. Chem., 1963, 2, (419706-707 The tetrachloropalladate (11), chloride and nitrate of monohydrogen bis-(pyridine-2-a1doxime)-palladium (11) ion were prepared and compared to similar Pt(I1) and Cu(I1) compounds. The inner complex between pyridine-2-aldoxime and Pd(I1) was also prepared. In contrast to the Pt(I1) inner complex only the tram isomer of Pd(I1) was obtained.

Preparation and Properties of Anhydrous Rhodium (11) Acetate and Some Adducts Thereof S. A. JOHNSON, H. R. HUNT and H. M. NEUMANN, Inorg. Chem., 1963, 2, ( 5 ) , 960-962 Rh(I1) acetate was prepared by the reaction of Rh(OH),. H,O with glacial acetic acid. Stable adducts with 2 ligands to each dimer were formed with H,O, tetrahydrofuran, acetonitrile, dimethyl sulphoxide, dimethyl sulphide, trimethylamine, NH,, NO2 and ethylenediamine. The properties and spectra of Rh(I1) acetate and these adducts are discussed.

Ruthenium Tetrafluoride J. H. HOLLOWAY and R. D. PEACOCK,J. Chem. SOL,

RuF, was formed by the reaction of I, with RuF, dissolved in IF,. RuF, was highly reactive and reacts violently with H,O to form RuO,. The magnetic moments of RuFI were measured in the range 90 to 300°K. X-ray diffraction analysis suggested that it has a simple structure.

Anhydrous Ruthenium Chlorides J. M. FLETCHER, W. E. GARDNER, E. W. HOOFER, K. R. HYDE, F. H. MOORE and J. L. WOODHEAD, Nature, 1963,199, (4898), 1089-1090 The preparation and magnetic properties of r-RuCl,, 6-RuCI, and Ru,OCl, are described. a-RuC1, formed by heating Ru and C1, in siliceous vessels at 600°C contains some Ru,OCI, which is diamagnetic and reduces the susceptibility. a-RuC1, has now been made by heating fi-RuCI, above the &transition temperature of 450°C. F-RuCl, is formed by reacting Ru in CO and C1, at 360-39ooC, with some u-RuC1, formation. Ru,OCI, occurs as a volatile oxide chloride in the mixture of aquochloro complexes known as commercial RuCl,. u-RuCI, is antiferromagnetic and /?-RuCI, has low magnetic susceptibility.

1963, !July), 3892-3893

ELECTROCHEMISTRY

Relation between the Activation Energy of Some Electrochemical and Catalytic Pro- cesses and the Properties of Metals v. v. DEMCHENKO, Zh. Fiz. Khim., 1963, 37, (8),

Electrochemical and catalytic processes such as hydrogenation, isotope exchange and H a formation at the electrode, where metal-H, bonding occurs as an intermediate step, are reviewed. Activation energy is proportional to the increase in surface tension of the cathode or catalyst surface. Graphs illustrate this effect for Pt, Pd, Rh, Ir, 0 s and a number of base metals. (16 references).

On the Thermodynamics of Platinum Oxide Electrodes B. NOVAK and T. MARKOVIC, Monat. Chenz., 1963,

The energy of formation of each oxide, hydroxide and oxide hydrate of Pt in aqueous solution was determined. Data are fully tabulated and extensively discussed.

Electrochemical Oxygen- and Hydrogen- Chemisorption on Smooth and Rough Plati- num H. DIETZ and H. GOHR, Z. phys. Chem., Leapzig,

The chemisorbed H, or 0, films which can be formed on Pt electrodes are produced continuously only if the electrodes are continually cleaned. Film formation then becomes a steady process whereas if the films are allowed to build up the potential of the circuit alters and the current is reduced.

1718-1725

94, (31, 607-420

1963, 223, (I12), 113-131

The Mechanism of Electrochemical Oxida- tion of Carbon Monoxide and Methanol on Platinum. I. Carbon Monoxide Adsorption and Desorption and SimuItaneous Oxidation of the Platinum Surface at Constant Poten- tial s. GILMAN, J. Phys. Chem., 1963, 67, (9), 1898- 190.5 The oxidation of the surface of a Pt electrode covered with adsorbed CO in a saturated solution in I NHClO, of a IOO?;, or I”: CO gas mixture is rate-controlled by the removal of adsorbed CO, as shown by current-time traces after raising the electrode potential from 0.4 to >0.8V.

11. Interpretation of the CO and “Oxygen” Adsorption Data Obtained at Constant Potential S. GILMAN, Abs. Papers, 145th Meeting, Am. Chem.

The oxidation of both the adsorbed CO and the SOC., 1963, 22B-49

Platinum Metals Rev., 1964, 8, ( 1 ) 32

Pt surface are interpreted by a reactant-pair mechanism which assumes that the actual reactants are adjacent CO and H,O adsorption molecules.

Mechanism of Anodic Oxidation of Organic Compounds on Platinum v. s. BAGOTZKY, Abs. Papers, 145th Meeting, Am. Chem SOC., 1963, 2rK-58 The adsorption of reacting species on the Pt surface affects the rate of oxidation. Adsorption of 0% on the surface reduces the reaction rate exponentially.

The Normal Oxygen Potential on Bright Platinum J. P. HOARE,?. Electrochem. SOL., 1963, 110, (9), 10 I 9-102 I

Experiments showed that when a Pt surface was completely covered by a chemisorbed monolayer of 0, the surface was passivated with respect to its reaction with oxygen. The layer was produced by passivating Pt beads in HNO,. A rest potential of 1225310 mV was observed for up to 24 hours or more.

Electrochemical Corrosion of Iridium in Hydrochloric Acid Solutions J. LLOPIS and L. JORGE, J . Electrochem. soc., 1963, 11% (9X 947-951 Electrolysis of I r in HCI showed that in all respects I r is more corrosion resistant than k. Ir was attacked more strongly as the HCl concentration and temperature increased. An a.c. superimposed on the d.c. increased the effect, especially at low frequencies, but the corrosion was negligible until a threshold value of ia.c.Sid.c. was reached. Dissolution and passivation mechanisms were studied.

LABORATORY APPARATUS AND TECHNIQUE Purity of Hydrogen Permeating through Pd, Pil-25?/, Ag, and Ni J. R. YOUNG, Rev. Scient. Instrum., 1963, 34, (8),

A technique for determining the purity o f diffused H, is described. Impurities in H, permeating through Pd or 25:< Ag-Pd alloy tubes were a few parts in 10~". The lowest impurity content from Ni was found to be I part in ro6. CO was the main impurity in all cases.

Specimen Heating with Temperature Measurement from -1150°C to 2200°C inside the EM6 Electron Microscope J. A. HEADLEY and J. MCGEAGH, J. Scient. Instrim.,

Equipment is described to enable the temperature range -150 to zzoo"C to be studied. The high

891-892

1963, 40, (I0)i 484-486


and medium temperature heating stages incor- porate solid Pt in the grid holders and caps because of its high melting point, low electrical resistance and resistance to oxidation. The Pt carries the current to heat the grid in the high temperature stage. Pt wire forms a resistance furnace in the other case.

The Durability of Pt-Rh Alloys in Analytical Apparatus G. REINACHER, Werkszoffe u. Korrosion, 1963, 14, (7), 574-579 Five typical analytical laboratory operations tested Rh-Pt alloys to show that they can well be used in corrosive conditions up to IOOOT. A tarnish developed during annealing in air and during soda-potash fusions but weight constancy was of the same order as ordinary apparatus Pt. Resistance to acids was as good as with Pt. Weight losses during potassium bisulphate fusions increased with temperature but, by lining with Pt, the crucibles combined resistance to attack with resistance to deformation. zo?/o Rh-Pt has been used for ferrophosphorus and ferrosilicon extrac- tions and roo4 Rh-Pt for HF and H,S04 evapora- tions and various fusions. The dark Rh oxide tarnish could be avoided by Pt linings. Lined and unlined 1o,20 and 30 wt.;;:) Rh-Pt alloy apparatus is therefore profitable for many high temperature analyses.

BRAZING New Era Brazing Turns to Filler Metals with Palladium A. s. CROSS and J. B. ADAMEC, Welding J., 1963, 42, (8), 645-649 Pd-containing brazing alloys are ductile with good wetting and flowing properties and do not erode the base metals with which they are used. Sixteen alloys are described of which five Ag-Pd and Ag-Cu-Pd alloys cover the melting range 1490°C to 2250T which is so important for electronic equipment. The alloys possess considerable strength at high temperature. They also fill gaps satisfactorily and reduce stress cracking. Their low vapour pressure makes them suitable for vacuum applications. (13 references).

Ceramic-to-Metal Seals for High Tempera- ture Operation E. L. BRUNDIGE and G. s. HANKS, U.S.A.E.C. Report L A M S 2 ~ 1 7 , 1963, 36 pp. A nuclear fuel element design required Nb components to be separated by Al,O,-Y,O,, a ceramic capable of withstanding Cs vapour at 1500°C. Bonding the ceramic to Nb was by metallking with W and then brazing with Pd applied by plating the W surface or as Pd foil before joining and sealing. Seals for use to rooo°C can be made from Co-Pd braze alloy added to the joint as foil or by plating with alternate layers of Co and Pd.

CATALYSIS

Active Centres of Platinum Adsorption Catalyst in the Oxidation of Ammonia v. I. SHEKHOBALOVA and N. I. KOBOZEV, Zh. Fiz. Khim., 1963, 37, (9), 2131-2132 Analysis of the reaction products of oxidation of NH, over Pt/SiO, showed that the Pt exists in monoatomic form on the catalyst support. Theoretical relations were established such that for SiO, with 300 m*/g and temperatures of 300 and 35o"C, the apparent activation energy could be calculated as 10,700 cal/mol.

The Relation of the Catalytic Properties of Platinised Silica Gel to the Conditions of its Preparation M. D. ADAMENKOVA and 0. M. POLTORAK, vat. Mosk. Univ., Ser. II, Khim., 1963, (5), 12-16 The catalytic activity of Pt/SiO, prepared by the adsorption of ammines of Pt on SiO, depends on the SiO, grain size, the drying temperature and the conditions of ammine reduction by H,. S O , should be homogeneous but too much grind- ing reduces the activity. Pt ammine adsorption is uniform after 3 days but not after 5 minutes. Drying at 100°C gives higher activity than drying at 60°C. 300°C is the optimum reduction temperature for the Pt ammines. Tests on three series of differently prepared samples showed that the level of activity for 0.5 to 3.15:6 Pt contents is higher than for 3.5 to 7% Pt.

The Hydrogenation of Diene Hydrocarbons over a Platinum Catalyst in Liquid Phase L. KH. FREIDLIN and E. F. LITVIN, Izv. Akad. Nauk S.S.S.R., Ser. Khim., 1963, (7), 1307-1312 Saturated hydrocarbons were formed by the hydrogenation of dienes over Pt black catalyst at conversions of up to 70 to 80%, mainly by two H, molecules becoming attached to each diene molecule without desorption of intermediate products from the catalyst surface. Tests with isoprene, tram-piperylene and 2, 3-dimethyl- butadiene-I, 3 and binary mixtures of a-olefins with isoprene showed that, at high degrees of diene conversion, some saturated hydrocarbon was derived from the a-olefins, simultaneous hydrogenation having taken place. There was high diene selectivity with alkaline solution but poor selectivity with acid solutions.

Kinetics of Dehydration of Cyclohexa- diene-1, 3 on Platinum Films over a Wide Range of Temperature

SAVEL'EVA, Kinetika i Kataliz, 1963,4, (5) , 746752 The activation energy of the dehydrogenation of cyclohexadiene-I, 3 on thin Pt films was shown to increase sharply at higher temperatures in the 20c-500"C range. Treatment of the Pt films at

V. D. YAGODOVSKII, V. M. GRYAZNOV and E. A.

7moC further increased the activation energy for tests in the ~oG-~oo'C range, An interpretation of the results relates the condition of the active part of the Pt surface to the thermodynamic equilibrium of the system.

Stereoisomeric 3/3,17/3-Dihydroxyandrostan- 16-ylacetic Acids

G. R. STONE and E. v. SCHUBER, J. org. Chem.,

The conditions of hydrogenation of 38, 178- diacetoxy-5-androsten-16-ylidenacetic acid over PtO, were adjusted to improve the yield of 38, 17~-diacetoxy-5-androsten-16/3-ylacetic acid and the stercochemistry of the four possible tetra- hydro products was derived.

The Hydrogenation of the Stereoisomers of Piperylene on Metallic Catalysts L. KH. FREIDLIN and E. F. LITYIN, Neftekhimiya,

The hydrogenation of the cis and trans isomers of piperylene (I, 3-pentadiene) in methanol using Pt and Pd blacks and Raney Ni as catalysts yields all the three possible pentenes in amounts which differ substantially from one system to another. Very little pentane is formed in the early stages of the reaction over Pd and Ni, but pentane constitutes about 35% of the initial products formed over Pt. No isomerisation between the piperylene isomers was detected.

Selectivity and Stereospecificity in the Hy- drogentdtion of Acetylene Hydrocarbons on Metal Catalysts L. m. FRIEDLIN and YU. w. KAUP, Doklady Akad. Nauk S.S.S.R., 1963, 152, (6), 1383-1386 Tests on pentyne-2 and pentyne-r, using Raney Ni, Raney Co, Pd black, Pt black, and Rh black catalysts established that the order of selectivity in the first stage of hydrogenation is P d > R > Rh>Ni>Co and that the order of stereospecificity is Pd> Ni=Co>Pt>Rh. Isomerisation of the products was also studied.

Hydrogenation of 2-Methyl-5-acetylfurans in Liquid Phase N. I. SHUIKIN, I. F. BEL'SKII, G. K . VASILEVSKAYA and Y. M. sHOSTAKOVSKII, Izv. Akad. Nauk S.S.S.R., Ser. Khim., 1963, (8), 1475-1478 When 2-methyl-5-acetylfuran was hydrogenated over P t /C and PdjC in liquid phase at 100°C with IOO atm. initial pressure of H,, the furan ring was not reduced but hydrogenolysis occurred at the C - 0 bond adjacent to the CO group. Heptane- dione-2, 6 was produced which was further converted by cyclisation to cyclohexanone and cyclohexanol (20-300;,) and by reduction to heptanediol-a, 6, which was partly cyclised to 2, 6-dimethyltetrahydropyrane (about 50-6ooi;). Over Pd/Al,Os at 180°C the CO group was

P. KURATH, W. COLE, J. TADANIER, M. FREIFELDER,

1963~28, (9), 2189-2194

19631 3j (319 326-329

Platinum Metals Rev., 1964, 8, ( 1 ) 34

reduced to CH2 followed by hydrogenation of the furan ring to produce 2-methyl-5-ethyltetra- hydrofuran (about 607,).

The Oxidation of Olefines by Palladium Chloride Catalyst J. SMIDT, Bull. Assoc. Franc. Tech. PCtrole, 1963,

The oxidation of olefines to carbonyl compounds with the same number of C atoms by 0, in aqueous solutions of PdCle and CuC1, is described and reaction mechanisms are discussed. Higher olefines and other unsaturated compounds are attacked by O 2 at points within the molecule depending on the groups attached to the double- bond C atoms and on the Pd ligands. Ketones and aldehydes are formed from a-olefines in fixed proportions. The transesterification of vinyl esters is the most important non-oxidation reaction of unsaturated compound in which Pd salts act as catalysts.

Kinetic Study on the Oxidation of Propylene in the Presence of Palladium Chloride T. DOZONO and T. SHIBA, Bull. Japan Petroleum Inst., 1963,5, (March), 8-12 The rate of the catalytic oxidation of propylene to form carbonyl compounds by Smidt’s process, using acidic PdCl,;CuCl, solution, was shown to

(160), 467-487

[PdClJ pprop, where [PdCl,] and be r=k

TC1-1 are the total concentrations of PdCl, and [Cl-] 2.21 [H+]

kl’ ion respectively, where [Hf] is the initial H+ ion concentration and where pprop is the partial pressure of propylene; k is a constant.

Oxidation of Alcohols by Palladium Salts in Aqueous Solution A. v. NIKIFOROVA, I. I. MOISEEV and YA. K. SYRKIN, Zh. Obshch. Khim., 1963,33, (lo), 32393242 Aliphatic alcohols were oxidised to aldehydes and aliphatic-aromatic alcohols to ketones by PdCl, in aqueous solution. The reactions were slower than for the corresponding olefines. Alcohols tested were ethyl-, isopropyl, N-butyl, N-arnyl- and benzoyl-alcohol.

Isomerisation of Hexenes in Liqnid Phase Hydrogenation Conditions in the Presence of Palladium Black I. V. GOSTUNSKAYA, A. I . LEONOVA, N. B. DOBROSERDOVA and B. A. KAZANSKII, Nefte- khimiya, 1963, 3, (4,498-502 Double bond transfer from position f to position 2, but no further along the C chain, was observed during partial hydrogenations of hexene-I, 2-methylpentene-I, 3-methylpentene-I, 4- methylpentene-1 and 2, 3-dimethylbutene- f in the presence of Pd black at atm. pressure and 20°C in C2H,0H medium. Compounds with two H atoms in the ally1 positions were isomerised more readily than those with only one. Where

the numbers of H atoms were equal, isomerisation occurred more readily with the compound more difficult to hydrogenate.

Isomerisation of Hexenes in the Presence of Palladium on Charcoal

BAKHMET’EVA and I. V. GOSTUNSKAYA, Neftek- himiya, 1963,3, (41,503-5c6 The transfer of double bonds in hexenes was studied at 80°C in the presence of Pd/C and a stream of H2. The relation bctween the initial hexenes and the rates of transfer was obtained and this agreed with the associative mechanism for the reaction.

Inhibitors in the Palladium-Catalysed Hy- drogenation of Aryl Nitro Groups

2434-2435 Potential inhibitors of the hydrogenation of p-nitrotoluene to p-toluidine over 5”/D Pd/C were added to the reaction mixture at the rate of 5 mole‘)” with respect to p-nitrotoluene, i.e. more than trace amounts. Sodium nitrate, acetate, sulphate, carbonate, phosphate, hydroxide, fluoride, bromide and chloride and ferrous chloride, n-octyl chloride, chlorobenzenc, bromobenzene, aniline, piperidine, sodium methoxide, phenol and p-nitrophenol caused no inhibition. Various amounts of poisoning were caused by potassium nitrite and sodium nitrate, sulphite, iodide, cyanide, sulphide and bisulphite and also by nickel (11), ferric, cobalt (11), chromium (111), copper (11), silver, aluminium, zinc and lead nitrates, ferric chloride, copper chloride and by certain nitroso compounds. Phenyl disulphide caused inhibition at very low concentrations.

Comparison of the Rates of Catalytic Reduction and Electroreduction of Some Organic Substances on Rhodium. 111

VOVCHENKO, Vest. Mosk. Univ., Ser. 11, Khim., 1963, (41, 55-58 The catalytic reduction rate on Rh was several times as great as its electroreduction rate for crotonaldehyde, acetone and amylaldehyde. Both rates decreased in the same order of substances. The rates decreased with changes in the electrolyte in the order H2S04, HCl, KOH and HBr. Br- ions particularly poisoned the reductions. Rh has lower reduction rates than Pt but higher than Ru.

Study of Ruthenium Catalyst. I. Hydrogen- ation of Organic Compounds by Ruthenium Catalyst Y. TAGAKI, sci. Papers Inst. Phys. Chem. Res. (Japan), 1963,57, (2), 105-109 Ru and RuIC catalysts were prepared and used in liquid phase hydrogenations at ordinary and

B. A. KAZANSKII, N. B. DOBROSERDOVA, G. S.

H. GREENFIELD, J . OTg. Chem., f963. 28, (9),

T. M . GRISHINA, L. P. KHOMCIIENKO and G . D.

Platinum Metals Rev., 1964, 8, (1) 3s

high pressures. Carbonyl groups were more easily hydrogenated at ordinary pressure over Ru than over Pd. HzO and alkaline solvents were more effective than alcohol for these reactions. The hydrogenation of double bonds was difficult. Nitro groups could be hydrogenated but nitriles could not. At high pressure the rate of hydrogenation of ally1 alcohol was rapid. Citronella1 was used for studies on the hydrogenation of unsaturated aldehydes and the selectivity of such processes.

The Production of Polyhydroxy Alcohols from Wood-Polysaccharides v. I. SCHARKOW, Chem. -Ing. -Tech., 1963, 35, (7), 494-497 Optimum conditions for the simultaneous hydrolysis and hydrogenation of polysaccharides in the presence of RuiBaSO, or of RujC are 0.794 H,PO, solution, 16c-165T, 60-80 atm. pressure of H, and a reaction time of 50-60 min. Other processes developed in the U.S.S.R. are based on the hydrolysis of the polysaccharides to monosaccharides which are subsequently hydrogenated, on hydrogenolysis of monosaccharides and on the pyrolysis of cellulose.

An Investigation of Catalysts Produced by Reactions between Sodium Borohydride and Salts of Heavy Metals A. M. TABER, B. D. POLKOVNIKOV, N. N. MAL'TSEVA, V. I. MIKHEEVA and A. A. BALANDIN, Doklady Akad. Nauk S.S.S.R., 1963, 152,(1), 119-121 0.25 g samples of PdCl,, RhC1, and H,PtCl, were reacted with I g samples of NaBH, and the products were analysed chemically, thermally and by spectrography. The infra-red spectra of Pd-B alloys and of borided Pd catalyst were very similar. H, in the catalysts acted similarly to adsorbed H,.

Charging Curves of the B o d e Catalysts of Pt-Group Metals A. M. TABER, A. A. BALANDIN, D. v. SOKOL'SKII and B. D. POLKOVNIKOV, Doklady Akad. Nauk S.S.S.R.,

Results were plotted for Pt, Pd and Rh boride catalysts in 0.1 N solutions of NaOH, HzSO, and HC1 and for the anodic polarisation of phenyl- acetylene and diphenylacetylene. Charging was most rapid for the NaOH electrolyte and the acetylenes were most readily polarised over Pt. Isotherms for the solution of H, in the catalysts were also determined.

Hydrogenolysis and Reciprocal Transitions of cis- and trans-1, 2-Dimethylcyclopen- tanes in the Presence of Rhodium, Osmium, Iridium and Palladium Catalysts

and B. A. KAZANSKII, Doklady Akad. Nauk S.S.S.R., 1963, 152, (4), 865-868 Studies at 150 to 280°C over Rh/C, Os/C, IrIC

1963,152, (z), 379-381

0. V. BRAGIN, A. L. LIBERIMAN, G. K. GURIANOVA

and PdjC showed the relative amounts of isomerisation and hydrogenolysis of cis- and trans-I, 2-dimethylcyclopentane. The amount of hydrogenolysis and the proportion of cis- to trans- isomer increase with temperature. PdjC and RhjC appeared to be most active in these respects. The reaction mechanism is discussed and the effects are compared with PtjC catalyst action.

FUEL CELLS A High Performance Saturated Hydrocarbon Fuel Cell W. T. GRUBB and L. W. NIEDRACH, J . Electrochem. Soc., 1963,110, (IO), 10861087 Propane has been oxidised rapidly in a new propane-oxygen fuel cell operating at only 150°C with a new porous eleLTrode structure to preserve the catalytic properties of the Pt incorporatedin it. The electrolyte was HJ'O,. A voltage-current density curve when 14.6 M H,PO, was used showed no limiting current in the range examined thanks to the thin structure of the electrodes.

A Direct Hydrocarbon/Air Fuel Cell H. G. OSWIN, A. J . HARTNER and F. MALASPINA,

Nature, 1963,200, (49031,256257 The combustion of propane in a fuel cell using Pt black electrodes and H,P04 electrolyte at temperatures up to 220'C produced currents of 100-zoo mA/cms at 20-350/0 thermal efficiency. The process appeared to consist of catalytic cracking followed by combustion and again demonstrated the feasibility of direct hydrocarbon/air fuel cells.

The Development of a High-efficiency Hydrogen-diffusing Palladium-Alloy Anode for Use in Fuel Cells H. G. OSWIN, s. M. CHODOSH and N. I. PALMER, Abs. Papers, 145th Meeting, Am. Chem. SOC., 1963, 14K-39 Thin Pd alloy membranes for use as H,-diffusing anodes were studied electrochemically and the effect of various operating parameters on anode polarisation were determined. Variables discussed include temperature, electrolyte composition, gas pressure and composition, membrane thickness and surface preparation.

Thin Fuel Cell Electrodes R. G. HALDEMAN, w. P. COLMAN, s. H. LANGER and w. A. BARBER, Abs. Papers, 145th Meeting, Am. Chem. SOC., 1963, I5K-42 Thin electrodes consisting of Pt and Pt-C supported on screens were found to be capable of very high performance. The Pt used was from I to 9 mg/cma. Electrodes were tested in acidic and basic media and were studied for initial polarisation, length of service, effect of temperature and operation in air.


ANODIC PROTECTION

Anodic Protection of Carbon Steel in Sul- phuric Acid w. P. BANKS and J. D. SUDBURY, Corrosion, 1963,

Pt cathodes were used in tests on 102.0-type mild steel samples. The tests showed that the effectiveness of anodic protection and the current density for maintaining protection depended on acid concentration and temperature. H,S04 varied from 45 to I O ~ " ! ~ concentration and temperature from 80 to 535°F. Graphs illustrate the large increase in current density required with higher temperatures.

19, (91, 300t-307t

N E W P A T E N T S Production of Semi-Conductor Devices THE INTERNATIONAL NICKEL CO. (MOND) LTD. British Patent 930,091 An electrically conducting joint is made between a wire and a metal layer adherent to a semi- conductor material with the use of a paste-like dispersion of a metal powder in a liquid vehicle consisting of a thermally decomposable compound. Pt metal and a decomposable Pt compound is used.

Catalytic Decomposition of Hydrazine ENGELHARD INDUSTRIES INC. British Patent 930,499 Hydrazine is contacted with a catalyst composed of one or more of Rh, Ir, Ru and Pd, with, if desired, Pt.

Preparation of 20-Alkylamine Steroid Deri- vatives SMITH KLINE & FRENCH LABORATORIES. British Patent, 930,676 A Pt oxide hydrogenation catalyst is used in the preparation of the above substances.

Isomerisation of Olefinic Hydrocarbons BRITISH PETROLEUM CO. LTD. British Patent

The isomerisation of an olefine is carried out using as catalyst a compound of the olefine with a halide of a Pt group metal.

Preparation of Cyanoalkyl Chlorosilanes GENERAL ELECTRIC GO. British Patent 932,380 Relates to a method of forming alpha-cyanoethyl methyl dichlorosilane which comprises reacting methyl dichlorosilane with acrylonitrile in the presence of a catalyst composition comprising palladous chloride, a trialkylamine and a poly- amine.

931,922

Platinum Metals Rev., 1964, 8, (l), 3 7 4 0 37

ELECTRICAL ENGINEERING

Effect of Organic Vapours on Contact Materials in Communication Engineering J. TLAMSA and J. NUSZBERGER, Nachrichtentechnik,

Ag and Pd contacts were tested for the effects of organic vapours arising from the atmosphere around them or from wire sheathing materials. The vapours can cause sparking, deposits, erosion and changes of resistance. Results are tabulated and cover most of the more common organic materials likely to be present. The activities of contacts in various surroundings are also listed.

1963, 1 3 ~ (7), 272-277

Isomerisation of Olefines BRITISH PETROLEUM GO. LTD. British Patent 932,748 The isomerisation of a branched chain olefine is carried out using as catalyst a complex of the olefine with a halide of a platinum group metal.

Electrolytic Apparatus D. J. EVANS (RESEARCH) LTD. British Patent 932,945 Provides an improved closed electrolytic cell for the production of chlorine by the electrolysis of brine. Electrodes consist of thin sheets of T i coated with Pt.

Reforming Catalyst THE STANDARD OIL CO. British Patent 934,080 A hydroforming catalyst comprises Pt/Al,O, in which at least 40% by wt. of the Pt is maintained in an HF-soluble form.

Selective Hydrogenation

Process for the selective hydrogenation of acetylene/diolefine components of a liquid hydrocarbon mixture comprises trickling the hydrocarbon mixture over a Pt or Pd hydrogenation catalyst carried on a macroporous support.

Ignition Device ROLLS-ROYCE LTD. British Patent 934,499 Ignition device for combustion eqpipment comprises a mass of refractory material and a foramin- ate catalytic element of Pt, or Rh, or a Pt alloy of less than 0.030 in. thick.

Fuel Cells LEESONA CORP. British Patent 935,430 Provides a fuel cell constructed for high temperature operation in which at least one electrode is composed of a mixture of zinc oxide and

FARBENFABRIKEN BAYER A.G. British Patent 934,429

metallic Ag, the gas interface of the electrode bcing coated with A1 silicate or alumina activated with an activating metal, e.g. Pd, Pt or Rh.

Removal of Methane ENGELHARD INDUSTRIES INC. British Patent 935,951 Process for removing methane or oxygen from a gaseous mixture comprises adding oxygen or methane respectively to the gaseous mixture to form a stoichiometric excess, and passing the resultant mixture over a Pt group metal catalyst to effect combustion.

Metal-Loaded Molecular Sieves UNION CARBIDE CORP. British Patent 937,748, 937,749, 937,750 All relate to metal-loaded molecular sieves suitahle for use as catalysts, scavengers, getters and the like, the sieves being loaded with one or more of the Pt group metals.

Hydrogenation Cyclisation Catalyst

Patent 3,09~,423 Succinonitrile is catalytically hydrogenated and cyclised simultaneously to 2-pyrrolidone by heating in an aqueous medium at 20-2o0°C in the presence of a Ru or Pt oxide catalyst.

Fuel Cell Electrode AIR PRODUCTS & CHEMICALS INC. U.S. Patent 3,0973974 The electrode is produced by forming a suspension of active C powder impregnated with Pt or Pd and depositing the suspension in the porcs of an electrode matrix made from Ni, Ag, Fe, etc.

MINNESOTA MINING & MANUFACTURING CO. GT.s.

Platinum Composite Hydrocracking Catalyst

A high boiling petroleum hydrocarbon or hydrocarbon mixture is cracked in the presence of hydrogen using a physical particle-form mixture of (I) a Mo oxide combined with an acidic component of two or more oxides of Groups IIA, IIIB, IVA and VIB and (2) an inert support containing 0.05-10 wt."& of a Pt metal.

Catalytic Removal of Oxygen from Mixtures Containing Nitric Oxide ENGELHARD INDUSTRIES INC. U.S. Patent 3,098,712 A Pt or Rh catalyst, e.g. supported on alumina, may be used to strip oxygen from mixturcs containing oxygen and nitric oxide, and optionally other gases, when hydrogen is added to the mixture before passing over the catalyst. This keeps down the catalyst operating temperature.

Fuel Cell Electrode

A platinised carbon electrode specifically for use with acid electrolytes is produced by firing a

SOCONY MOBIL OIL CO. U.S. Patent 3,098,030

U S . SECRETARY OF ARMY. U.S. Patent 3,098,772

known carbon electrode in an atmosphere of carbon dioxide at 800"C, wet proofing the fired electrode in the usual way and then impregnating it with chloroplatinic acid containing 90 mgiml Pt so that the electrode contains 2 mg Pt per sq. m. of electrode.

Thin Film Noble Metal Thermocouple ENGELHARD INDUSTRIES INC. U S . Patent 3,099,575 New thermocouples consist of thin films of electrically dissimilar noble metals bonded to a refractory support and connected together, one of these films comprising at least one of Pt, Pd, Rh and Ir, and the other film of at least two of Pd, Rh and Ir, the films being produced by applying the finely divided metals in an organic liquid carrier vehicle. In an example, one film consists of Pt metal and the other of 90X Pt and I O " ~ Rh.

Hydrocracking Catalyst PHILLIPS PETROLEUM GO. U.S. Patent 3,099,618 High sulphur petroleum oils are cracked at lower temperatures with less coke formation by using a Pt-activated Co-molybdate catalyst containing 1-3 wt.O/D Pt, 1-10 wt.9; Co and 1-20 wt.9, Mo on a suitable support.

Anode Assembly for Cathodic Protection CHEMIONICS ENGINEERING LABORATORIES INC. u. s. Patent 3,101,311 In providing cathodic protection with an im- pressed current, the anode is an assembly consisting of a Pt disc of foil thickness in a suitable holder, the foil having a grid-like pattern on its surface to facilitate the release of gaseous electrolysis products.

Catalytic Production of Hydrocyanic Acid IMPERIAL CHEMICAL INDUSTRIES LTD. U S . Patent 3,102,001 The reaction of the NH,, a hydrocarbon and oxygen over a Pt metal or alloy is improved by adding 1-500 mg/m3 of S and controlling the oxygen content to give maximum conversion of the NHs. In No. 3,102,269 the catalyst is specifically claimed and consists of a Pt metal or alloy in massive form, such as one or more layers of metal gauze. At least 50°(, Pt must be present, as in an alloy of 90°{, Pt and ID":, Rh.

Brine Purification Cathode IMPERIAL CHEMICAL INDUSTRIES LTD. U S . Patent 3,102,085 Brine containing free and available chlorine is purified by passing it through an electrolytic diaphragm cell having a cathode not attacked by Cl,, e.g. a Pt-coated Ti electrode.

Platinum Cathode for Titanium Protection IMPERIAL CHEMICAL INDUSTRIES LTD. U. S. Patent 3,102,086 When T i and its alloys are exposed to corrosion by


strong acids, they are protected by immersing in the acid a Pt/C electrode and impressing a current on the system.

Sulphur-resistant Hydrogenation Catalyst THE STANDARD OIL co. US. Putent 3,102,864 Catalysts suitable for a variety of feedstocks where the fatty substance, olefine, etc., contains S consist of an alumina support impregnated with 0.05-1y0 of Pt and 0.05-6';" of thiocyanate ion and optionally also a small amount of halogen.

Catalytic Hydrogenation of Nitrosamine E. I. DU PONT DE NEMOURS & co. U.S. Patent

Unsymmetrical disubstituted hydrazines are produced by the catalytic hydrogenation of the corresponding nitrosamine using a Pt metal catalyst, as hitherto, but now hydrogenation, e.g. with Pd/C, is carried out in a solution of ionic strength of at least 0.6 to improve the yields.

Complexed Platinum Metal Hydrogenation Catalyst SHELL OIL CO. U.S. Patent 3,102,899 The Pt metals are amongst the transition metals which may be complexed with trihydrocarbon phosphites, arsenites and stibenites to provide new hydrogenation catalyst, etc.

Fuel Cell Reduction System IONICS INC. U.S. Patent 3,103,473 Fuel cell producing the electrochemical reduction of organic and inorganic compounds has a 'permanent' electrode for the fuel and this contains a Pt metal as catalyst. In No. 3,103,474 the same invention is applied to the recovery of metals, e.g. Cu, Fe, Zn, Cr, Ni, Mn, Co, or Cd, by the reduction of solutions of their compounds.

Reduction Catalyst for Organometallic Com- pounds ETHYL CORP. U.S. Patent 3,103,525 Zerovalent aryl cyclopentadienyl compounds of the iron subgroup (Mn, Tc, Rh, Fe, Ru, 0s) are produced by the reduction of the corresponding halide by hydrogen over Pt, Pd, etc.

Palladium and/or Platinum Reformation Catalyst THE STANDARD OIL CO. Dutch Patent 234,680 A new Pt and/or Pd supported catalyst containing 0.1-10 wt.o/b Ge is produced by impregnating the support with one or more Pt or Pd compounds and at least one Ge compound and reducing the product.

Catalyst for Hydrogen Cyanide Production IMPERIAL CHEMICAL INDUSTRIES LTD. French Patent 80,273. Addition to 1,248,895. The reaction of NH,, a hydrocarbon(s) such as

3,102,887

methane and oxygen is catalysed on a high temperature plate made of an alloy of 90 '7; Pt and approximately 10% Rh.

Fritted Platinum Surface Coatings INTERNATIONAL NICKEL CO. (MOND) LTD. French Patent 1,320,963 Pt-coated metal and refractory surfaces, particularly for use in contact with molten glass and enamels, are produced by applying a dispersion of flake Pt metal in a liquid medium, capable of being volatilised or destroyed, and then heating the coated surface to remove the dispersion medium and sintering or fritting the resulting layer of Pt metal flakes. Typically Pt coatings can be produced on alumina in this way.

Catalyst for the Reduction of Mononitro Aromatic Compounds GENERAL ANILINE AND FILM CORP. French Patent

Mononitro ethers are reduced to the corresponding amines with hydrogen in the liquid phase using a noble metal catalyst having a surface of at least about 150 sq. m/g at a temperature of 25-125"C with the reaction water held in dispersion. Suitable catalysts are PdfC or Pt/Al,O,.

Activation of Platinum Metal- Alumina Catalysts TEXACO DEVELOPMENT CORPORATION. French Patent 1,322,457 The activity of catalysts containing a Pt metaI used for hydrocarbon isomerisation is increased by contacting them with an activating chloride (e.g. a chloroalkane or an organic chloro acid) having a C1 : C atom ratio of a t least z : I at a temperature between 149 and 345°C. Typical activating compounds are CCI,, CH,CI and trichloroacetic acid chloride.

Oxidation of a Palladium or Platinum Group Metal

N.V. French Putent 1,325,696 Metallic Pd, Pt, Rh, Ru, 0 s or Ir or a lower valency compound thereof is oxidised in a non- aqueous medium by a gas containing oxygen in the presence of one or more carboxylic acids, one or more other acids and one or more metal oxidation promoters. The carboxylic acid preferably provides the oxidation medium. This process is particularly intended for reoxidising Pd compounds produced when the higher Pd compounds are reduced in producing alkenyl esters of carboxylic acids.

Duplex Chemical Plating

1,3213689

SHELL INTERNATIONAL RESEARCH MAATSCHAPPIJ

ENGELHARD INDUSTRIES INC. Ererzclz Patent 1,326,441 New economic form of the noble metal-plated deposit required for printed circuit manufacture


consists of a layer of Pt, Rh, Pd or Ru covered with a thin layer of Au, instead of the wholly Au layer previously employed. Normal chemical plating methods are used.

Fusion Production of Platinum COMPTOIR LYON-ALEIMAND, LOUYOT & CIE. French Patent 1,326,597 Pt, Rh and similar metals are produced by first pyrolysing a compound to yield a sponge or foam, as hitherto, which is then degassed by heating to a temperature just below its melting point, com- pressed, melted in a vacuum and cast to give articles such as spinnerets which come into contact with molten glass.

Gold-Palladium Brazing Alloy AEROJET-GENERAL CORP. French Patent 1,326,619 Brazing alloys which require less critical conditions consist of 1-96% Au, 1-720/" Pd and 2-61?; of Ni, Co and/or Cry e.g. 45-35O4 Au, 30-200/~ Pd, 40-30% Ni and 0-100/4 Cr.

Electroless Metallising of Powdered Metal Oxides and/or Sulphides SHERRITT GORDON MINES LTD. German Patent 1,1439372 In the electroless metallising of difficult-to-melt powdered metal oxides, and/or sulphides, by dispersion of the previously activated powder in a metallic salt solution under reducing conditions, the powder is treated in an ammoniacal metal salt solution of Os, Rh, Ru, Pt or Pd with reducing gases under a partial pressure of over 4 atm at a temperature above 90°C. See also No. 1,143,373 for similar treatment of powdered carbides, borides, silicides or nitrides.

Electrodeposition of Thick Stress Free Platinum Coating SEL-REX CORP. German Patent 1,144,074 A plating bath for depositing thick stress-free Pt coatings comprises an aqueous solution of platino- diamino-nitrite, in amount corresponding to a Pt content of at least 6 g /I in sulphamic acid.

Process for Production of Highly Active Metal Catalysts from Laminar Silicates VEB FARBENFABRIKEN WOLFEN. German Patent 1,1441696 Barium phyllosilicate, BaSi,O, or sodium phyllosilicate Na,Si,O, is treated with a salt solution of catalytically active metals at normal pressure or in an autoclave and the metal laminar silicate so formed is, after separation, reduced. The treating solution may be a solution of bivalent salts of e.g. Pd or Pt.

Reforming Catalyst THE STANDARD OIL CO. German Patent 1,151,082 A new reforming catalyst consists of Ge and Pt and/or Pd deposited on a support. Preferably the

Pt and/or Pd represents 5 to 95Y0 of the mixture with Ge. The mixture is said to be a solid solution and is 0.1 to 10 wt.:& of the total weight of the catalyst and support together.

Catalyst for Methane Production ENGELHARD INDUSTRIES LTD. German Patent 1,151,247 Catalyst giving low ignition temperatures (e.g. of the order of 271-40o"C) for mixtures lean in CHI and 0, consists of Rh, or Rh and another Pt metal, on a support, preferably activated alumina.

Gold-platinum Alloy for Tensioning Strips

An alloy consisting of I--soo/,, preferably 1-3074, of one or more Pt metals, particularly Pt and Rh and/or 1-50u/i,, preferably 5-400/;, of one or more of the metals Fe, Co and Ni, remainder at least zoy$ Au, is used as material for making tensioning strips in measuring instruments with rotating measuring parts.

Catalyst for Benzyl Chloride Amination

N.V. German Patent 1,152,098 ~,6-Dichlorobenzonitrile is produced from 2,6- dicblorobenzyl chloride or 2,6-dichlorobenzal chloride by reaction at I50-50Ooc with a mixture of ammonia and oxygen in the presence of a Pt metal catalyst on a C support, e.g. palladised animal charcoal.

Platinum Metal Alloy for Tensioning Strips W. C. HERAEUS G.m.b.H. German Patent 1,152,826 An alloy for making tensioning strips for precision instruments consists of r-50'Z/oY preferably 5-40;,, of one or more of Fey Co, Ni, W, Mo, Cu or Ag with the remainder Pt, Pd andlor Rh with a minimum of 15% Fe group metal in the case of binary alloys. Optionally part of the three Pt metals may be replaced by other Pt metals, particularly Ir.

Catalytic Olefine Oxidation FARBWERKE HOECHST A.G. German Patent 1,153,008 Aldehydes and/or ketones are produced from olefines by oxidation in the presence of a solution containing a Pt metal salt in a new process in which the amount of oxygen allowed to come into contact with the catalyst is strictly limited.

Separation of Palladium from Other Plati- num Metals CANADIAN COPPER REFINERS LTD. German Patent

A solution of Pt metals in HCI, HNO, or H,SO, is treated with SO, to give an SO2 content of 0.3-4 gll and then a soluble iodide is added in stoichiometric amount to precipitate Pd quan- titatively by itself as PdI,.

W. C. HERAEUS G.m.b.H. German Patent 1,151,944

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