PLATINUM METALS REVIEW
A quurterly survey of reseurch on the platinum metuls urrd of dwelopments in their applications in industry
VOL. 5 JANUARY 1961 NO. 1
Contents
Platinum Alloys in the Production of Viscose Rayon 2
Platinum Reforming Catalysts 9
Cathodic Protection of Water Heaters I2
Rhodium Plating to Specification I3
A History of Platinum 18
The Refractory Noble Metals and Rhenium I9
The Hydrides of Palladium and Palladium Alloys 21
Faraday’s Lecture on Platinum 26
Abstracts 30
New Patents 38
Communications should be addressed to The Editor, Platinum Metals Review Johnson, Mutthey & Co., Limited, Hatton Garden, London, E.C.1 Platinum Alloys in the Production of Viscose Rayon J
THE SELECTION OF MATERIALS FOR SPINNING JETS
By J. w. s. Hearle, MA., Ph.D., and A. Johnson, M.Sc.Tech., Ph.n. Manchester College of Science and Technology
In 1884 Count Hilaire de Chardonnet continuous filament yarn has doubled again. patented a process for making artificial fibres The technical improvements in ordinary by the extrusion of a solution of nitro- textile filament rayon during these forty cellulose derived from mulberry leaves, the years were marginal, but the versatility of natural food of the silkworm. These were viscose rayon was being exploited extensively the first commercially successful man-made in other directions. The production of staple fibres, and the production of rayon by this fibre began in 1930, and by 1940 production method continued until the last nitro-cellulose was greater than that of continuous filament factory was destroyed by fire in Brazil in yarn. Diversification here included the mak- 1949. ing of fibres covering a wide range of lengths Other developments followed rapidly in the and thicknesses, so that they could be spun closing years of the last century. The cupram- on cotton, wool, worsted, flax, jute and monium process, which is still used to a small other spinning machinery. The addition of extent was patented in 1890, and the patents titanium dioxide could be used to dull the for the viscose process followed in 1891.In naturally bright appearance, and the introduc- this process, cellulose-usually obtained from tion of pigments into the spinning solution wood-pulp-is steeped in caustic soda, aged, gave fibres which could be blended into an and reacted with carbon bisulphide to give infinite range of colours. cellulose xanthate which is dissolved in Another important development was the caustic soda. The resulting viscose solution production of Tenasco-a strong industrial is then squirted into an acid bath where it yarn-in 1935. By the end of the war, fibres coagulates as the cellulose is regenerated. of this type had almost completely replaced The filaments so produced are soft and weak, cotton in the big market for tyre-cords. but stretching them increases their strength, The years after the war were devoted to and after washing and drying they are ready increasing the depleted production facilities. for use. However, by 1953, improvements in the The production of viscose rayon was strength of rayon were needed to meet the started in Britain in 1905 by Courtaulds. threat of competition from nylon in tyre- Initially it was an expensive fibre made as a cords. Fortunately earlier academic work had continuous filament yarn which competed provided a basis on which to work. with silk. By 1920 world production was Rayon is unique among man-made fibres 33 million lb per annum, but the price was in that its production is accompanied by a zoo pence per lb: twenty years later produc- chemical reaction-the change from cellulose tion had increased to 1,200 million lb per xanthate to cellulose. By varying the condi- annum and the price had fallen to 33 pence tions under which the reaction proceeds, it is per lb. Since then the world production of possible to vary the fine structure of the
Platinum Metals Rev., 1961, 5, (l), 2-8 2 Many thousands of platinum alloy spinning jets are in use in n modern viscose rayon plant. The illustration shows one unit engaged in spinning continuous $lament in a Courtaulds factory fibres. Ordinarily, rayon has a structure com- carpets, blankets, non-woven fabrics for posed of separate skin and core. In the skin interlinings, surgical swabs, filter fabrics, the texture of the arrangement of the long- ropes, hose-pipes, conveyor belts-the list is chain molecules in crystalline and non- too long to complete. Rayon is now second crystalline regions is finer than in the core, only to cotton in its scale of production and and by increasing the proportion of the skin diversity of applications. structure, stronger fibres can be made. This and other improvements have resulted in a The Heart of the Process rise in the strength of rayon tyre-cords from The heart of the rayon production process 25 lb to 40 lb, and have succeeded in main- is the spinning jet through which the viscose taining the price advantage of rayon over solution is extruded into the coagulating nylon in tyres. solution. Similar developments are taking place, The compositions of these two solutions although more slowly, in textile rayons. All- vary somewhat according to the particular skin fibres should have greater durability, type of viscose rayon being made, but a and their round cross-section changes the reasonably typical viscose would contain appearance and reduces soiling. All-core about 6.5 per cent of alkali in the form of fibres such as the so-called polynosic fibres sodium hydroxide and about 7.5 per cent of have much better dimensional stability, cellulose (present, of course, as the xanthate). especially on wetting. And fibres with an The coagulating solution is essentially dilute asymmetrical skin have a permanently built- sulphuric acid containing about 10 per cent in crimp. Other techniques give a collection by weight of the acid, together with about of fancy yarns. 20 per cent by weight of sodium sulphate Viscose rayon is not really one type of and smaller amounts of zinc sulphate and fibre: it is a great variety of fibres which have glucose, the remainder being water. Thus the a vast range of uses-dress-wear, furnishings, spinneret is subject on the one side to about
Platinum Metals Rev., 1961, 5, (l), 3 A simple demonstration of the formation of a multi-jihment yarn by pumping viscose solution through the holes in a jet immersed in an acid bath (Courtaulds Ltd)
1.5 N sodium hydroxide and on the other to In this case a solution of cellulose in cu- about 1.5 N sulphuric acid. prammonium hydroxide is used, but although These are both severe conditions, which the final coagulation of the filaments requires bring about chemical attack of most metals. an acidic bath they are first spun simply into The use of steels, for example, is immediately water. Thus, the spinneret is not in direct precluded for the manufacture of spinnerets contact with acid, and so may be fabricated for viscose rayon. In this respect, viscose from steel. Another difference between the differs from other manufactured fibres where cuprammonium and viscose processes which steel spinnerets may be used. permits steel to be used for the former con- Thus, for the manufacture of cellulose cerns the diameter of the holes in the spin- acetate filaments, the spinning solution con- neret. In the cuprammonium process this sists simply of the acetate dissolved in either is of the order of 0.8 to 1.00 mm, whereas acetone or methylene chloride, both of which in a viscose spinneret the diameter may be as are without chemical action on steels. The small as 0.03 mm, so that the removal of solution is extruded into warm air, when the metal by corrosion is of greater significance. solvent evaporates, so again there is no corrosive action corresponding to that of the Resistance to Chemical Action acid coagulating bath in viscose rayon To return to the viscose process, we can manufacture. see that spinnerets must be fashioned from A process more akin to viscose spinning is materials that are capable of withstanding the manufacture of cuprammonium rayon. the simultaneous chemical action of 1.5 N
Platinum Metals Rev., 1961, 5, (l), 4 caustic soda and 1.5 N sulphuric acid. So behaves as an electrical cell, most simply far as metals are concerned, this at once regarded as a form of hydrogen ion concen- limits the choice to the noble metals, platinum tration cell. As with all concentration cells, and gold, and some of their alloys, and also the electrode in contact with the more con- tantalum protected by an oxide film. centrated solution will assume a positive Two alloys in particular have been widely charge, so that the spinneret becomes used; 10 per cent rhodium-platinum and polarised, the surface in contact with the 30 per cent platinum-gold. The former, alkaline solution bearing a negative charge because of its higher cost, is normally re- and that on the acid side a positive charge. stricted to use where the conditions are most With steel spinnerets, of course, these exacting and the cheaper one is used where electrochemical effects would in themselves the conditions are less critical. cause corrosion, enhancing the deleterious However, although such alloys will resist effects of direct chemical attack. The noble direct chemical attack by acid and by alkali, metals are not corroded, but nevertheless a and on that account are suitable for spinneret current will flow, resulting in electrolysis of manufacture, other factors also have to be the viscose solution passing through the jet. taken into consideration. One of these, and The most serious result is that the negatively one which mitigates against the use of any charged xanthate ions will be attracted to the metal for spinneret manufacture, is the positive surface of the spinneret, where they occurrence of electrochemical phenomena. will be discharged and decomposed, ulti- In the viscose process, one side of the mately giving rise to a ring of cellulose block- spinneret is in contact with an alkaline ing the jet. Some deposition of sulphur also solution and the other with an acid, and the occurs, but this may arise from the noimal two solutions form a junction inside the bore decomposition of the xanthate in the acid of the spinneret. If the spinneret itself is an solution rather than electrolytically. The acid electrical conductor (i.e. a metal), the system coagulating bath penetrates some distance
The number of holes and their pattern in a jet vary according to the type of rayon to be produced. This type of platinum-gold alloy jet has over 2,000 or$ices and is made and used in the production of staple .fibre by Courtaulds Ltd
Platinum Metals Rev., 1961, 5, (l), 5 Piercing, forming and polishrng the holes in a spinning jet are intricate operations demanding considerable skill and accuracy. Here one of the operators in the Johnson Matthey jet production shop is broaching the holes in small rhodium-platinum alloy jets for spinning tyre-cord. The built- in binorular microscope is a Jeature of the instruments used to pierce and form the jet holes
up the jets, so that coagulation and the pre- also seriously considered. The major diffi- cipitation of insoluble solids actually begins culties are probably connected with piercing in the jet. Thus, although noble metal jets these materials with the necessary precision. are durable and represent a considerable A similar method of approach is to coat the improvement over steel, they are not entirely spinneret with a non-conductor, and silicone without disadvantages. Naturally, a great fluids are now being investigated for this deal of effort has gone into devising ways of purpose. overcoming these defects. There have been Another method of avoiding electrical two methods of approach: first to avoid the effects is to neutralise the charges on the electrochemical effects which are responsible spinneret by passing a current in the opposite for deposition and blockage, and secondly to direction. A more satisfactory method is to prevent deposition while allowing the elec- make the spinneret as a whole carry a large trolysis to continue. charge relative to some other conductor in One obvious method of avoiding electrical contact with the liquid. This is most effects is to fabricate the spinneret from a easily done by using the lead lining of the non-conductor. The material must also coagulating bath as the second electrode withstand thc direct attack of the alkaline -the cathode-and applying a potential of and acidic solutions as well as possessing the the order of I to 1.5 volts. In this way, requisite mechanical properties. Most atten- choking of the jets can be prevented for tion seems to have been paid to the use of periods of up to four weeks. synthetic rubies, and ceramic spinnerets are In practice, however, the most usual
Platinum Metals Rev., 1961, 5, (l), 6 method of avoiding deposition on the spin- a much smaller grain size is 3 pzr cent neret is by the addition of anti-fouling agents ruthenium-platinum. Piercing is simpler and to the viscose solution before spinning. thefinishedspinneret canbe givena high polish. These are dispersing agents which serve to The widely used 30 per cent platinum-gold hold solid particles in solution during the alloy presents little difficulty in working and short interval of time between the entry of will take a high polish. Traditionally the the viscose into the spinneret and the forma- alloy has been rolled to a hardness of approxi- tion of coagulated filaments. mately 180 Vickers before pressing the caps, the holes then being pierced through the hard Mechanical Properties face. However, the addition of a small per- So far, only the chemical and electrical centage of rhodium produces an alloy that requirements of spinnerets have been con- can be worked to a fine-grained structure sidered, and we have seen that these can, in having a hardness of only about 120 Vickers. the main, be met by the use of noble metals. This is accomplished by a carefully controlled Finally, attention must be paid to the mech- cycle of rolling, annealing and solution treat- anical properties required of a satisfactory ment. Caps are produced and pierced from spinneret. For the production of good this relatively soft material and then, by a quality filaments the spinning jets must be suitable heat treatment, brought to a hardness made with great accuracy and possess a high of around 220. This process combines the surface finish and maximum durability. The simplification of piercing associated with the accuracy required in the piercing of the holes soft alloy with the desirable properties of demands a material which is completely the fully hardened form. Increasing the plat- uniform in structure, while the attainment inum content of the alloy to 35 per cent of highly polished surfaces requires as small permits the manufacture of spinnerets with a a grain size as possible. It is these two final hardness of around 280 Vickers, while properties which the metallurgist must seek, for special purposes alloys containing from 40 allied with a convenient method of producing to 50 per cent platinum are also used. the necessary hardness to give durability. The number of holes and their pattern in The blank caps are normally produced from strip by conventional presses, and should at that stage be uniform in thickness and have a high surface polish, particularly on the inside face. According to the metal used, piercing of the jets may be carried out with the metal in the hard or softened form. Piercing is naturally simpler with a soft cap, but can only be done this way if the pierced cap can subsequently be hardened without affecting the size and internal surface finish of the holcs themselves. The 10 per cent rhodium-platinum alloy, while possessing excellent resistance to cor- rosion, unfortunately has a relatively large grain size and this causes difficulties both in drawing and piercing and also in obtaining the necessary high polish. An alternative dloy having the same high corrosion resistance but
Platinum Metals Rev., 1961, 5, (l), 7 Newly formed viscose ruj on thrends being led out of the cougu- luting bath on a textile-type con- tinuous spinning machine in one ?f Coiirtaulds factories
the jet vary according to the type of rayon are accurate to within I 0.0015 mm on all to be produced. Typical figures range from diameters. less than IOO holes per jet for textile rayon, Although it is very likely that many new from 650 to 1,500 for tyre-cords and to as manufactured fibres will make their appear- high as 6,000 for staple manufacture. The ance, and even that existing fibres will be shape of the holes is much the same for all modified in various ways, the development of types of rayon, and it is, indeed, of great radically different spinning arrangements importance if satisfactory filaments are to be seems improbable. Drastic changes in the obtained. The lead-in diameter is always nature of spinnerets are therefore also un- somewhat greater than that of the major part likely, and it seems most probable that the of the orifice, and considerable care is needed main advances will be metallurgical, leading to to ensure completely smooth blending of the alloys having even more desirable properties, lead-in with the straight capillary. The both during manufacture and in use. There maintenance of a sharp junction between the always remains the possibility of using non- capillary and the outlet face is also a critical conducting materials. Artificial gem-stones feature. To achieve this, the outer facc is would be satisfactory if the difficulties of carefully polished after piercing, the holes piercing them could be overcome. Another themselves being filled with glass or some possibility, at present, perhaps more remote, other material that can readily be removed by lies in the use of a synthetic polymer. How- melting, in order to protect the polish of the ever, in spite of these possibilities, it seems jet walls from the abrasive. In jets produced likely that noble metal alloys will remain the by Johnson Matthey, for example, orifice only suitable materials for viscose rayon diameters may be as-small as 0.03 mm and spinnerets for many years to come.
Platinum Metals Rev., 1961, 5, (l), 8 Platinum Reforming Catalysts
PRODUCTION OF HIGH-OCTANE FUELS AND OF AROMATIC CHEMICALS
To meet the steadily increasing compression ratios characteristic of modern automobile As part of a two-day symposium in engine design the petroleum industry is faced Liverpool organised by the Society of with the problem of producing high-octane Chemical Industry on “The Manufac- fuels at the lowest possible cost. To achieve ture and Use of some Catalysts in the this end, catalytic reforming processes are Petroleum and Petrochemical Indus- employed, followed by the addition of tetra- tries”, Mr. H. Connor of Johnson, ethyl lead to the reformates and the blending Matthey & Co., Limited presented a of refinery products of high-octane number paper on “Platinum Reforming Cata- such as a range of aromatic alkylates. The lysts”. Dealing both with the use of same processes that are employed for up- platinum reforming processes to yield grading low-octane napthas may also be used high-octane fuels to meet the require- as a valuable source of aromatics for the ments of modern internal combustion chemical industry. engines and with the growing production Newer developments in these processes by this route of aromalics as raw have been almost entirely towards increased materials or intermediates for the operating severity. These include feedstock chemical industry, the author outlined pre-treatment with process hydrogen to re- the principles of platinum reforming move sulphur and trace elements which poison and described the major processes that catalysts, the developihent of new catalysts have been developed. A summary of his especially with higher platinum contents and paper is given here. the use of lower space velocities. Alkylation processes are expected to contribute to a greater extent to the production of higher employ platinum group metal catalysts; these grade fuels, and isomerisation processes will latter account for less than 10per cent of the probably rise in importance. The growth of installed reforming capacity of the world. the petrochemical industry will be responsible Platforming, the first platinum reforming for some of the expansion of platinum re- process developed, accounts for over 50 per forming processes. cent of installed capacity. As requirements for The following processes are available for up- increased operating severity increase, how- grading petroleum stocks: ever, the newer regenerative processes are (I) Catalytic reforming beginning to rise considerably in importance. (2) Reformate splitting (3) Alkylation Platinum Reforming (4) Isomerisation The primary purpose of catalytic reforming (5) Extraction of pure aromatics is the conversion of low-octane number hydro- (6) Blending of products obtained in (I) to carbon fuel to high-octane fuel. Several (5) above. reactions contribute to this increase in octane Eleven catalytic reforming processes have number, but the most important in platinum been developed, of which Only four do not reforming are as follow^^
Platinum Metals Rev., 1961, 5, (l), 9-12 9 (I) The formation of aromatic hydro- reactions. Since high hydrogen pressures are carbons from paraffins and cyclic com- employed, any olefins that are fomcd are pounds saturated immediately and the reaction is (2) The formation of branched-chain paraf- generally termed “hydrocracking”. fins from straight-chain paraffins. The individual chemical reactions occurring Platinum Reforming Processes in platinum reforming and the mechanisms by Various oil companies have developed a which platinum catalysts bring them about number of commercial reforming processes include the following. employing platinum catalysts. The most im- portant of these are described below. Hydrogenation of Olefins The straightforward reduction of the double Platforming bond (or bonds) present in paraffinic olefins The Universal Oil Products Company is rapidly achieved by platinum catalysts. The introduced in 1949 the first platinum reform- reaction requires low operating seventy and ing process, termed Platforming. Today, the resultant saturated straight- or branched- although several other processes exist, Plat- chain paraffins are then available for other forming still accounts for the greater part of reactions, e.g. isomerisation, cyclisation, etc. platinum reforming operations. It employs a catalyst consisting of platinum on alumina Dehydrocyclisation with a small but critical percentage of halogen The formation of aromatics from paraffins added to maintain correct balance between ocws by the linking of carbon atoms with the conversion of paraffins by dehydrocyclisation, elimination of hydrogen. hydrocracking and isomerisation. Platforming raises the research octane Isomerisation of Paras numbers of feed napthas from 30 to 50 to Branched-chain paraffins have considerably over 90 with 85 to 95 per cent yields. This higher octane numbers than their correspond- is a fixed bed, non-regenerative process, ing n-isomers and the isomerisation of the operating at 850 to 950°F and at 200 to 700 latter is an important function of platinum psig. Catalyst life may exceed 200 bbl. per reforming. In most instances, however, lb catalyst, although lower values are usual. paraffins present in feedstock are already present as mixtures of isomers, hence the Ultraforming isomerisation activity of a catalyst is import- Ultraforming was developed in 1954 by the ant chiefly for the isomerisation of cyclopen- Standard Oil Company (Indiana) and is a tane derivatives. fixed-bed cyclic regenerative process. It employs a 0.6 per cent platinum on alumina Isomerisation of Napthenes catalyst and operates at low pressures, 200 to Naphthenes, in particular cyclopentane 300 psig. Usually five reactors with a derivatives, constitute a high proportion of “swing” reactor are employed, enabling feed naphthas. The isomerisation of these regular regeneration in situ to be carried out. compounds to C, structures and the aromatis- The relatively high rate of decrease in catalyst ation of the latter are the most important activity necessitates frequent regeneration- reactions contributing to an increase in octane up to 30 to 40 regenerations are possible with number of a feedstock. a total catalyst life of 150 to 240 bbl.!lb.
Hydrocracking Powerforming Under the conditions of platinum reform- Powerforming was developed by the Esso ing, cracking competes with dehydrogenation Research & Engineering Company utilising
Platinum Metals Rev., 1961, 5, (l), 10 a catalyst manufactured by the Davison of n-butane to iso-butane over a platinum- Chemical Company. It is a fixed-bed re- containing catalyst. Over 40 per cent of the generative system producing a reformate of feed (n-butane) is converted to iso-butane in octane number IOO and over. Operating a single pass. pressure is 300 to 600 psig with catalyst temperatures 900 to IOOOOF using a platinum- Production of Aromatics alumina-halogen catalyst. The conversion of paraffins is more complete at low pressures Aromatics for the chemical industry had and high temperatures, which are conditions been produced during the first half of this also favourable to the formation of aromatics. century primarily from coal. The tremendous increase in size of the chemical industry during Houdriforming the past twenty years, however, has coincided Houdriforming was introduced by the with a similarly rapid growth of the petroleum Houdry Process Corporation, Philadelphia, in industry. The platinum reforming processes 1950 and is a fixed-bed reforming process described in the foregoing paragraphs are employing a platinum-alumina catalyst. It able to produce a large range of aromatics operates with a catalyst temperature of 875 which may be separated from each other to 950°F and an operating pressure of 250 to and from unchanged feed by fractional or 600 psig. A desulphurised feed is generally extractive distillation. used and high conversion efficiencies are Today the total world production of aro- obtained yielding a reformate of research matics from petroleum somewhat exceeds octane number exceeding 90. production from coal. In the United States 35 per cent of benzene Penex-Platforming is produced from petroleum, 78 per cent of The Penex process was introduced by toluene, 90 per cent of xylenes and per Universal Oil Products as a means of isomeris- 12 cent of phenol. The bulk of petrochemical ing the unchanged n-pentane and n-hexane aromatics is obtained from virgin naphtha obtained from platformates. Pentane and or catalytically reformed naphthas-very little hexane are separated from the latter and from catalytically cracked napthas. passed once through a bed consisting of a There are several aromatic chemicals whose dual-function platinum-alumina (“ 1-3”) cata- large-scale production by platinum reforming lyst. By isomerisation the octane number is not so well developed as that of others. of an n-pentane feed may be raised from 62 For example, very little use is made at present to 93, that of n-hexane from 25 to 100. Complete isomerisation is not possible, but of compounds such as monocarboxylic aro- the high activity of the catalyst allows con- matic acids, aromatic alcohols and aromatic version at lower temperatures which favour aldehydes compared with the large-scale utilisation of other substitcted aromatic mate- the equilibrium. rials, e.g. chlorobenzene, phenol, styrene. The Iso-Kel Process In addition, no important use has been found This process, developed by M. W. Kellogg so far for the C, or C,, aromatics from re- Company, is also specifically for the isomeris- formates other than for cumene production ation of n-pentanes and n-hexanes. It em- for phenol and acetone manufacture via ploys a precious metal, non-platinum catalyst cumene hydroperoxide. as of 1116th inch extrudates and operates Several processes have been developed at 700 to 850°F~IOO to 750 psig pressure. which combine platinum reforming with ex- The Butamer Process traction or extractive distillation to produce The Butamer process was developed by aromatics. One such proccss, Rexforming Universal Oil Products for the isomerisation (Universal Oil Products), employs an aqueous
Platinum Metals Rev., 1961, 5, (l), 11 glycol solution to solvent-extract aromatics specific surface, density and pore- and light high-octane paraffins. characteristics (c) The nature and concentration of halogen Manufacture of Platinum or other additive which serves to modify Reforming Catalysts the acidity of the support Each platinum atom in a petroleum re- (d) The manner in which the support is forming catalyst is required to perform a prepared and by which it is impreg- tremendous catalytic feat. In addition, al- nated with platinum and halogen though constituting less than I per cent of the (e) The particle size, shape and bulk catalyst, the platinum must maintain this density of the finished catalyst. active and selective performance over the The platinum concentration is a critical entire time it is in a reforming unit. It is not factor in determining catalyst costs, and con- uncommon to have a catalyst life of two years centrations from 0.3 to 1.3 per cent are usual. or more, so that on average each platinum Increasing the platinum concentration raises atom has catalysed the conversion of more the aromatics production by raising somewhat than twenty million hydrocarbon molecules. the dehydrogenation activity (not in direct The platinum cannot perform in this way if proportion). it is inaccessible, or poisoned, or in too large The paper concludes with a survey of the crystallites, or in a position which makes it extensive patent literature relating to platinum ineffective against coke formation. reforming catalysts and their manufacture and The following factors influence the activity some notes on the methods of recovering of a platinum reforming catalyst, and their platinum from spent catalysts-a subject vital accurate control has been the subject of much to the economics of platinum reforming. The study and very numerous patent applications: full paper (published in Chemistry and (a) Platinum concentration and distribution Industry, 1960, 1454 - 1472) includes 280 (b) Phase-type of alumina support, its references to the literature.
Cathodic Protection of Water Heaters USE OF PLATINUM-PROTECTED TITANIUM ANODES The short life, due to corrosion, of gal- low current densities required, non-sacrificial vanised iron domestic water tanks has led anodes of bare titanium or titanium wound to the development of glass-lined water with platinum-clad tantalum ribbon have heaters in the United States. Less serious proved both effective and economic. One tank corrosion caused by small holes in the anode described consists of a 30-inch glass linings may be controlled by the use of titanium wire, 0.051 inch in diameter, around a cathodic protection system requiring a small which is wrapped a 0.002 by 0.008 by 36- impressed current. The design of such a inch platinum-clad tantalum ribbon. Field system is discussed in a recent paper by trials are being conducted using platinum- H. C. Fischer of the Thermo-Craft Corpora- plated titanium wire anodes which have tion, New York (Corrosion, 1960, 16, (g), proved satisfactory in preliminary tests. 9-17). Cathodic protection has been found effec- It has been found that the bare area of a tive for glass-lined domestic water tanks single-coated, glass-lined tank may be pro- heated either electrically or by gas. Power tected adequately by a current of 5 milli- for the impressed current system for gas amperes even in waters of high resistance. water heaters is supplied by a thermo- The presence in the system of copper ions electric generator. In this case, in order to derived from copper plumbing gives rise to keep the anode voltage as low as possible, local cell corrosion which renders magnesium only platinum-plated titaniumor the platinum- and zinc anodes unsuitable. However, at the tantalum-titanium anodes may be used.
Platinum Metals Rev., 1961, 5, (1),12-12 12 Rhodium Plating to Specification
By li. K. Benham, F.R.I.C. .John~on,Matthey & Co., Limited
The Ministry of Aviation has recently issued Process Specijcation DTD 931, covering the rhodium plating of silver, copper, steel and aluminium components primarily for electrical and electronic applica- tions. This article reviews the specijication and outlines recommended procedures for the successful preparation of rhodium electrodeposits.
The electrodeposition of rhodium is of rhodium, coupled with its excellent resist- conducted on normal plating lines and, at ance to abrasion, provided just the right least for the thinner deposits, there are no combination of properties required in certain special difficulties. It is some twenty-five types of sliding or rubbing contacts in years since the process was first carried out on electronic equipment, and a demand arose a commercial scale. Originally it was chiefly for thicker deposits than had formerly been used on jewellery to provide a white non- needed. The Second World War, with its tarnishing surface of high reflectivity; for this rapid development of radio communication purpose deposits of only 0.000005 to o.oo0010 and radar, led to an enormous increase in the inch were adequate, and fortunately were amount of rhodium used for this type of relatively free from porosity. In addition the application and to the appearance on many great hardness of electrodeposited rhodium engineering drawings and individual specifica- gave an excellent resistance to wear. tions of a note calling for such-and-such a Within a few years it was found that the thickness of electrodeposit. complete freedom from tarnish characteristic In using a high-cost metal such as rhodium
A group of typical electrical and electronic components with rhodium plated contact surfaces
Platinum Metals Rev., 1961, 5, (l), 13-18 13 Masking of surfaces not required to be plated is carried out with a chlorinated rubber paint a good deal of discrimination naturally needs surface was required without wear-resisting to be used in deciding on the appropriate qualities, the thickness of rhodium was thickness of deposit to meet any particular specified as a minimum of O.OOOOI inch. This set of design requirements, and in the earlier specification made no reference, however, to days of its employment there was sometimes the methods or procedures to be adopted in a tendency for users to settle upon one producing rhodium electrodeposits. arbitrary thickness to meet a variety of con- The recent issue by the Ministry of Avia- ditions. Much more information is nowadays tion of Process Specification DTD 931, available on the thickness of rhodium “Rhodium Plating” fills this gap and pro- suitable for a particular application, and it is vides both users and electroplaters with a well understood that thicknesses may range comprehensive guide to the factors involved from a minimum of, say, O.OOOOI inch for the in the successful use of rhodium. protection of a silver surface from tarnish up to something over 0.001 inch where heavy Basis Metals and Undercoats mechanical wear is to be met with. Most of the metals and alloys commonly This variation in optimum thickness was used may readily be rhodium plated directly, recognised to some extent in the Ministry of although for reasons of skin conductivity, Supply Inter-Service Specification RCS/IOOO exposure to high temperatures or other special (now replaced by Defence Specification requirements it is more usual to deposit first DEF-~OOO),“General Requirements for an undercoating of silver or less frequently of Service Telecommunication Equipment”, nickel. which called for a rhodium thickness of The exceptions to this include steel and 0.00015 inch over a silver undercoating, but aluminium, which are readily attacked by the added that special requirements might be strongly acid plating bath unless a dense non- demanded where unusually heavy wear was porous undercoating of silver or nickel is first to be encountered. Where an untarnishable applied. Masking materials such as lacquers
Platinum Metals Rev., 1961, 5, (l), 14 or chlorinated rubber paints are not sufficiently The choice of undercoat for rhodium is protective when the rhodium plating time is often dictated by the application. Thus, as more than a few minutes. For the deposition already mentioned, silver is specified when of say 0.00025 inch of rhodium this may be the plated component is to be used in a high- of the order of I to I* hours, and much damage frequency circuit. Here, particularly at very could result in this time unless the steel or high frequencies, the “skin effect” is pro- aluminium were completely protected. ‘The nounced, the current being concentrated more specification therefore calls for a deposit of in the outer skin of the conductor as the silver, copper or nickel not less than 0.001 frequency increases. In certain very high inch in thickness for steel or 0.0015 inch for frequency circuits the thickness of rhodium aluminium after polishing. may therefore have to be restricted because Tin-lead solders also present a problem in of its inferior conductivity compared with that that unless they are completely covered with of silver (35 per cent IACS against 106 per a non-porous undercoat before immersion in cent). The choice of rhodium thickness then the rhodium bath a dense black stain is becomes a compromise between the con- produced on the solder and over an appreci- flicting requirements of long life and con- able area around the joint. A similar require- ductivity. ment of a minimum deposit of silver, copper Silver is also the preferred undercoat to or nickel is therefore specified on all areas of minimise the possibility of cracking in thick soft solder. rhodium deposits. Where the application As soldered joints are frequently located on involves conditions of exposure to high temp- the inside corners of assemblies to be rhodium eratures, however, such as in reflectors of plated, it is essential that allowance be made various kinds, a nickel undercoat is to be for the fact that less silver will deposit in ‘such preferred. areas by comparison with the average thickness over the whole component. It would appear to be the tin content of the solder that gives rise to the problem, and where possible the use of a tin- silver-lead solder containing no more than 5 per cent tin is to be preferred. The writer has found that only 0.0001 inch of silver is adequate before rhodium plating over joints made with this alloy, while they may even be plated directly with no more than a very slight yellow- ing of the rhodium over the sol- dered area. A straight 5 per cent silver-lead solder is completely satisfactory for direct rhodium plating but is rather more difficult to use.
Rhodium plating a batrh of electrical contart springs
Platinum Metals Rev., 1961, 5, (l), IS Preparation for Plating paint should never be immediately adjacent The degreasing and alkaline cleaning to the essential contact area, but should be procedures given in the DTD specification brought to within about one-sixteenth inch follow the normally accepted practice for of this area. Rhodium deposits adjacent to these operations, but with rhodium plating stopping-off materials are sometimes found very great care must be exercised to ensure to be defective and this small margin is thorough cleaning, or poor adhesion of the helpful in reducing the possibility of failure deposit may result. When thick deposits of on this score. When using chlorinated rubber rhodium are to be applied an additional paint, stoving for two or three hours at etching step may well be incorporated, such 160°F effectively removes solvents in the as the anodic etch in cyanide for silver and paint film and also reduces the possibility of the immersion in a ferric chloride-hydro- failure. When parts are stopped-off it is also chloric acid solution for nickel described in advisable to use a cold cleaner to prevent the an appendix to the specification. Activation paint or lacquer from “frilling” at the edges. of nickel by cathodic treatment in sulphuric acid (say 10 per cent by volume) at 20 to 25 Plating Procedure amperes per square foot for half a minute is The concentration of rhodium in the also beneficial. Work so treated should be plating bath, its temperature, and the current transferred without rinsing with as little delay density at which it is operated may be varied as possible into the rhodium solution. It is over quite a wide range. For the production the writer’s experience, however, that ad- of thick deposits, a high metal content and a hesion on nickel is inferior to that to be low current density are to be preferred, obtained on silver even when these etching especially when pinholes in the deposit must treatments have been used. be avoided. This particular defect is also For stopping-off materials, either chlorin- minimised by regular tapping of the work bar ated rubber paints or special cellulose lacquers to dislodge hydrogen bubbles adhering to the are to be recommended, but wax is not surface. Alternatively, it is possible to fit a satisfactory. The edge of the stopping-off cam, operated by a fractional H.P. motor, to
Recommendations for Rhodium Thickness and Electrolyte Composition
Minimum Thickness Recommended on Agreed Recommended Minimum Significant Rhodium Sulphuric Class General Type of Surfaces Content, Acid Content, No. Application (inch) gmllitre millitre
Rh 15 Tarnish protection . . . . 0.0000 I5 12 20 Rh 25 Reflectors ...... 0.000025 I Rh 100 Light mechanical loading and infrequent use .. .. 0.000 I 20 R h 200 Medium mechanical loading.. 0.0002 Rh 400 Heavy mechanical loading . . 0.0004
Rh 800 Very heavy loading conditions 50 in special applications only 0.0008
Platinum Metals Rev., 1961, 5, (1) 16 lift the work bar say one inch and then drop failure to meet specification. The simplest it back on to the top of the vat at intervals of means of control is to weigh a piece of copper about 20 or 30 seconds. foil before and after plating for a known time Thin deposits may be obtained from a more at a given current density, and a further dilute solution, thus economising in the appendix gives the simple formula to be amount of metal tied up, and higher current applied. densities are satisfactory. The specification recognises these variables, and to some extent Thickness Recommendations correlates recommended electrolyte com- The thickness of rhodium deposit called positions with thickness of metal to be for by the user should naturally bear a relation deposited. The table on page 16 combines the to the application or service duty involved. suggested rhodium and sulphuric acid con- Too often the phrase “rhodium flash” has centrations appropriate to the thicknesses of been employed to cover requirements ranging deposit set out in the specification. from the thinnest plate for tarnish prevention The electrolyte is recommended to be to a heavy deposit needed to withstand heavy operated between 30 and 50°C, with a cathode mechanical wear. The specification adopts current density of 10 to 20 amp.,/sq.ft., six classes of deposit to give guidance to although in special cases a reduction to engineers and designers in selecting an 5 amp./sq.ft. is preferable. appropriate thickness. These recommenda- Rhodium plating is an insoluble anode tions, reproduced in the table, will undoubt- process, the anodes normally being of edly be of value to users and potential users of platinum or rhodium-platinum, and the metal electrodeposited rhodium. deposited from solution must therefore be Naturally the thicker deposits are normally replaced by the addition of rhodium sulphate restricted to the areas where they are actually concentrate. The specification calls for this required, but in many cases it is usual to apply replenishment to be made before the rhodium a thin tarnish-preventive deposit over the content of the bath has fallen by TO per cent remainder of the part. of its nominal value. Attention to this is most It should also be said that the heavier important, as if proper replenishment is not deposits, from say 0.00025 inch upwards, carried out the cathode efficiency of the bath require considerable care and experience to will fall and less rhodium will be deposited, produce sound plates free from fine hair other things being equal. The best practice cracks. Rhodium as deposited is normally in is to add the necessary quantity of concentrate a state of considerable mechanical stress. immediately after the completion of each Where excessive cracking is due to organic batch of work. Periodic chemical analyses of contamination, either from stopping-off paints the solution should be made to ensure that or other sources, treatment of the solution the correct rate of replenishment has been with activated charcoal is usually effective. achieved, and reliable methods for the determination of rhodium are given in an Inspection Requirements appendix to the specification. The inspection clauses of the specification It is also of utmost importance to carry out cover freedom from surface defects, reflect- regular checks to determine the rate of ivity, adhesion, hardness and thickness of the deposition, or in other words to control the deposit. thickness being deposited in a particular set The question of surface appearance is of operating conditions. Failure to observe usually a matter of opinion, and it is often this requirement can lead either to the deposi- found advisable for the plater to discuss tion of more rhodium than is necessary and so requirements with the user and to agree on an to needless COY, or of course to less-and acceptance test. The present specification
Platinum Metals Rev., 1961, 5, (l), 17 allows the presence of fine hair cracks, par- electrodeposits. The specification accepts this ticularly in deposits thicker than 0.0001 inch. difficulty for deposits less than 0.0004 inch A bend test is laid down for the assess- in thickness, but for thicker deposits states ment of adhesion, but the specification that the hardness, as determined by a suitable draws attention to the fact that the rhodium micro-hardness tester, may be checked at the deposit may well crack on bending and that a discretion of the inspector. distinction must be made between such Owing to the chemical stability of rhodium cracking and actual exfoliation. the only means of measuring the thickness of a The hardness of electrodeposited rhodium deposit is by a destructive method. Mounting is extremely high-of the order of 800 to 900 and sectioning, followed by measurement with Vickers-but it is naturally extremely difficult an eyepiece graticule or direct measurement to determine hardness values on very thin of a photomicrograph, is the specified method.
A HistorvJ of Platinum LATINUM, by comparison with metals Psuch as copper, silver and gold, has a rela- tively short history, but there is none the less a fascinating story to unfold in tracing the be- ginnings of an understanding of its character and in outlining its commercial exploitation. It was not until the Spanish conquest of South America that rumours were heard of a new metal that could not readily be melted, the first pub- lished reference occurring in 1557 in the writings of the Italian scholar and poet Julius Caesar Scaliger. Only in the middle of the eighteenth century were specimens of this metal received in Europe and subjected to proper scientific examin- ation, first by the Englishman Brownrigg and Two illustrations from Donald then in quick succession by chemists in France, 1WcDonald’s“AHistoryofPlatznum”. Above, Julius Caesur Scaliger. the Germany, Spain and Sweden. Italian scholar whose writings In- Much effort was then directed towards the cluded the fcrst reference to platinum, refining, melting and working of platinum, published in 1557. Below, the PTPSS culminating in the well-known work of Wollaston, used by W’ollaston to compress plat- early in the nineteenth century, in producing inum powder into cakes before forging malleable platinum by the technique nowadays known as powder metallurgy. From then on the pace quickened and the commercial development of platinum, its sister metals and its alloys really began; the discovery of catalysis by Dobereiner, the introduction of the melting of glass in platinum vessels by Faraday, the design and manufacture of enormous platinum boilers for the concentration of sul- phuric acid by Johnson and Matthey are but a few of the outstanding features along the way. In A History of Platinum, published bv Johnson, Matthey & Co., Limited (35s or $5.50j, Donald McDonald has, by diligent research into both published literature and private archives, succeeded in putting together a clear and readable account of these developments that has never before been given as a continuous story.
Platinum Metals Rev., 1961, 5, (l), 18-18 18 The Refractory Noble Metals J and Rhenium
ALLOYING POSSIBILITIES WITH MOLYBDENUM AND TUNGSTEN
The four scarcer platinum group metals- tion of the noble metals is remarkably con- rhodium, ruthenium, iridium and osmium- sistent. A volatile oxide forms at temperatures have higher melting points than platinum and above the oxide decomposition temperature, palladium, they are more resistant to acid and metal loss is due to oxide volatilisation attack (in massive form they are virtually and metal vaporisation”. Nearly all other insoluble in aqua regia) and mechanically metals form stable oxides. they are stronger and much less ductile. In More than half of the review is concerned the past, they have thus often been referred with the alloying behaviour of the refractory to as the “insoluble” platinum metals. How- noble metals with each other and with other ever, in a recent paper presented by R. I. elements. Arising from this extensive review, Jaffee, D. J. Maykuth and R. W. Douglass the authors particularly note the very remark- at the Refractory Metal Conference of the able, and indeed spectacular, effect of addi- American Institute of Metals in Detroit in tions of rhenium on the working properties May 1960, attention is drawn to the relation- of molybdenum and tungsten. This was first ship between these metals and the neigh- noted by Geach and Hughes, working in the bouring transition metal, rhenium. “It is laboratories of Associated Electrical Indus- apparent,” write the authors, “in considering tries, who found that molybdenum when rhenium and the (above four) platinum-group alloyed with 50 per cent by weight of rhenium metals we are really talking about one could be cold-rolled to sheet direct from the family”; and they propose that the family cast condition and that tungsten alloyed with should be termed the “refractory noble 30 per cent by weight of rhenium could be metals” . rolled at slightly elevated temperatures. The The authors present an excellent compre- amounts of rhenium that need to be added hensive review of the literature dealing with are, it will be seen, very large, and the the mechanical, physical and chemical proper- authors have accordingly been responsible ties of this group of metals, emphasising for initiating at Battelle Memorial Institute, always the transition found in properties under the sponsorship of the Office of Naval between members of the group. Research, an investigation into the possibility that similar effects might be produced by Resistance to Oxidation adding smaller amounts of the refractory One feature of the group that frequently platinum-group metals. needs to be considered concerns oxidation resistance. Although the group is rightly Improving Ductility placed among the noble metals, the oxidation The effects of rhenium additions in im- resistance ranges from that of rhodium, one proving the ductility of molybdenum and of the most oxidation-resistant of all metals, tungsten are ascribed to three factors. First, to that of rhenium, which is among the most the rhenium is said to form with oxygen a readily oxidised. The authors point out, complex molybdenum-rhenium oxide which however, that “despite this vast difference in does not, like MOO,, give rise to a eutectic oxidation hehaviour, the mechanism of oxida- that wets the grain boundaries but tends to
Platinum Metals Rev., 1961, 5, (l), 19-20 19 be redistributed within the alloy grains. cast molybdenum. Small additions, of Secondly, the rhenium promotes twinning at the order of 0.1 atomic per cent of room temperature and lowers the ductile-to- ruthenium, reduced the hardness from brittle transition temperature, thus improving 170 to 140 V.H.N., this being ascribed low-temperature ductility. Finally, it is to a reduction in the oxygen solubility. suggested that rhenium additions reduce the Similar additions of iridium, rhodium, solubility of oxygen in molybdenum. This osmium (and platinum) reduced the is said to be in accord with the theoretical hardness to 145-150 V.H.N. There predictions of D. A. Robins, who considers are indications that about I per cent that the solubility of interstitial elements in of osmium reduces thc hardness of Group VIA metals may be lowered by cast chromium. Larger additions of all additions of higher group metals because of the platinum metals increase the hard- the tendency to maintain six bonding elec- ness of cast molybdenum, tungsten trons. The addition of rhenium with seven and chromium; no data are available electrons reduces the solubility of oxygen on the effect of small additions to because the oxygen atoms tend to ionise and tungsten and chromium. contribute electrons to the alloy. It is The work is by no means comprehensive thought that the soluble oxygen atoms tend or complete. An attempt to get a quick to lock dislocations, reducing low-temperature solution to the problem of finding a malleable slip and influencing the yield point; so that, complex molybdenum alloy was made by by reducing the oxygen content, the ductility adding tantalum or niobium to redistribute is improved generally. the oxygen, together with small amounts of The influences of additions of the platinum osmium, ruthenium, iridium or platinum to group refractory metals to molybdenum, promote twinning and to reduce interstitial tungsten and chromium on these three factors solubility, and small amounts of other de- have been examined in a very general way. oxidising elements (for luck) to supplement, The results may be summarised as follows: it was hoped, all these effects. (I) None of the platinum group elements The most successful molybdenum alloys appeared to have any significant effect contained the following additions, in atomic in redistributing molybdenum oxide at percentages: the grain boundaries (osmium additions (a) (b) (4 (4 may have a very slight effect); and of Ru 1.0 Ru 1.0 0s 1.0 0s 1.0 Si 0.1 Co 0.05 Ta 1.0 Ta 1.0 other elements, those only which pro- Si 0.1 Co 0.05 duced a real change in the oxide All these could be rolled directly to strip, morphology were niobium and tanta- but when recrystallised they were brittle on lum, added in amounts of 5 to 10atomic bending, indicating no marked improvement per cent. in the ductile-to-brittle transformation. (2)Room temperature twinning in molyb- It is considered by the authors that the denum, tungsten and chromium appears most significant effect of these small additions to be promoted by 5 to 7.5 atomic per of platinum metals is the reduced solubility cent of ruthenium or osmium and, to for oxygen (and presumably of other inter- a lesser extent, by about the same stitial impurity elements) through increase in amounts of the other platinum metals. the valence electron concentration. It may The effect, for some unexplained reason, well be that further studies will prove that is more pronounced in cast than in successful methods of producing industrially annealed samples. important alloys with the help of the refrac- (3) The most interesting effect of noble tory noble metals can be developed. metal additions was on the hardness of J. C. C.
Platinum Metals Rev., 1961, 5, (l), 20 The HvdridesJ of Palladium and Palladium Alloys
By F. A. Lewis, n.D. Chemistry Department, The Queen’s University of Belfast
In the second part of this article, concluded from the October issue of ‘Platinum Metals Review’, a short account is given of changes in the ph.ysical properties of palladium following absorption of hydrogen. The behaviour of certain palladium alloys is compared with that of palladium and alternative methods of approach towards an under- standing of the constitution of the hydrides are briefly outlined.
Specimens of hydrided palladium for ever, although scattered measurements have which equilibrium with gaseous hydrogen is been reported on a variety of properties such inhibited can remain either in vaciio or in air as elastic constants, hardness, Hall coefficient for long periods without appreciable loss of and thermoelectric power (2, 29, 36, 37), the absorbed hydrogen (8): very many of the data available for most properties are generally physical measurements on palladium hydrides not detailed over a wide range of hydrogen have been carried out under such conditions contents. (2).However, particularly in the presence of More complete studies have been made of oxygen, the loss of hydrogen may be subject changes in paramagnetism (12) which is to erratic behaviour and once begun can found to decrease almost linearly with hydro- sometimes proceed very rapidly indeed (8). gen content up to HjPd - 0.6, and particular Although it is usual that, on completion of attention has been paid to changes of electrical physical measurements, an analysis of the resistance. final hydrogen content is obtained either by The salient features of the changes of using strong oxidising solutions (8, 9, 33) or relative electrical resistance, R/R, (R, is the by degassing in vacuo (10,34, 36), this alone initial, hydrogen-free, resistance) with hydro- will give no absolute indication of the content gen Content (H/Pd, atomic ratio) at about at the time of measurement. 25°C are shown in Fig. 5. R/Ro increases It is thus important in these circumstances almost linearly with H/Pd until H/Pd - 0.55 that convenient, reliable and non-destructive with a definite change of slope at the termi- physical measurements be developed to pro- nation of cr-phase(10, 12). Beyond HjPd- vide a continuous measurement of hydrogen 0.55 there is enhanced disagreement between content at all times. the results available (10): R/R, is believed to decrease (12,14, IS) when the content exceeds Physical Properties of Palladium H/Pd - 0.7. H ydrides Although a somewhat larger variation has When compared to other solid systems the recently been suggested (39, the R/R,-H/Pd detailed measurement of physical properties relationships appear to be almost independent as a function of hydrogen content is in prin- of temperature (34, up to HjPd - 0.5, ciple especially convenient due to the ability within the range o to 100°C. of palladium to absorb large quantities of For reasons discussed in the first pat of hydrogen without macro-disruption. How- this article, electrolysis has often been em-
Platinum Metals Rev., 1961, 5, (l), 21-25 21 ployed to introduce hydrogen 1.8 for resistance studies, and it #- - 5 c . is unfortunate that sources of I 9-10 Pt - Pd / error (31) in the measurement 1-6 of hydrogen content have not 0 LK been fully appreciated in many \ 1.4 of the earlier and most de- U tailed studies of the R/R,- I2 H/Pd relationships. Errors in RjR,, can also 1.0 result from proton transfer effects (38, 39) during the L application of the bridge I 1 1 I 01 02 03 04 05 06 07 08 (measuring) current in the H/M. (ATOMIC RATIO) relatively strong (I-2N) acid Fig. 5 Relationships between relative electrical resistance and solutions which have generally hydrogen content been used as electrolyte and possible effects of absorbed oxygen (12, 40), perature for the lower contents of alloying which may be introduced during pre-anneal- metal (2). Properties such as electrical resist- ing and activation of palladium must also be ance are altered by a similar order of magni- considered. Particularly since doubts that the tude to those of palladium although with removal of hydrogen is not always reflected minor differences. For example, with increas- by a change in R/Ro now appear to be largely ing platinum content (Fig. 5) R/R,increases unfounded ( IO), resistance changes fulfil, in more steeply (34) with hydrogen content than principle, several of the necessary require- for pure palladium, and increases less steeply ments of a continuous analytical measure in the case of silver-palladium alloys (12, 41, of absorbed hydrogen. 42). As is shown in Fig. 5 the resistance may actually decrease slightly with increasing Palladium Alloy -Hydrogen hydrogen content over the region of a- and Systems p-phase coexistence for certain silver alloys Little work has so far been reported on (42), cf. Fig. 7. alloys of palladium with a metal such as titan- Aside from somewhat more complex ium or vanadium that is also capable of behaviour found with the silver-palladium, absorbing large quantities of hydrogen. and almost certainly with gold-palladium The information available has been largely alloys, which are further discussed below, the restricted to the behaviour of alloys with general effect of a feebly absorbing metal is metals which, by themselves, absorb very to reduce the equilibrium amount of hydrogen little hydrogen such as the other metals of absorbed by the alloy to below the amount Group VIII or silver or gold. (Although such absorbed by pure palladium, when compari- alloys may form ordered lattices in certain son is made at almost any temperature and composition ranges after prolonged annealing pressure. (40), the samples which have so far been used Apart from some early study by Sieverts have almost certainly been in the form of (43) of the Pt-Pd-H, Ag-Pd-H, and Au-Pd-H supercooled solid solutions). systems (at temperatures of 138°C and above The hydrides formed by these alloys again and at pressures up to one atmosphere), vir- show no tendency for macro-disruption. tually no P-C-T data have been obtained for Regions of coexistence of a- and p-phase palladium alloy-hydrogen systems by direct hydrides are still found at close to room tem- equilibration with molecular hydrogen in the
Platinum Metals Rev., 1961, 5, (l), 22 the chemical potential for the I 6% Pt - Pd / I /I absorption of hydrogen, and 600 by the use of the Clapeyron equation it has also been 400 shown to reflect a decrease in the heat of absorption (4). F 200 In addition the P-C-T data I \5 indicates (Fig. 6) that the critical temperature and pres- ul a sure for cc and @-phase co- u)2 existence is also steadily re- 2 600 a duced with increase of the platinum content of the Pt-Pd 400 ooc alloys (34, 44). The behaviour of the Ag- 200 ) :roc 12"/o Pt-Pd 15.590 Pt - Pd Pd-H system is, however, somewhat more complex. For , 0.2 04 0.6 0.2 0.4 0.6 example, with increase in silver H/MC (ATOMIC RATIO) content, at about 25"C, the Fig. 6 Isotherms for a series of Pt-Pd- H systems ratio of hydrogen atoms to the total number of metal gas phase. For the bulk of the experimental atoms (H,'Me) in the P-phase hydrides (over work which has been carried out the hydrogen the region of cr and P-phase coexistence) has been introduced into the alloys by becomes progressively less than for pure electrolysis : since, until recently, electrode palladium (H/Pd-o.r7). Nevertheless, again potentials were not generally measured in over the corresponding ranges of 01 and P- conjunction it is not surprising that there has phase coexistence, the equilibrium vapour been disagreement between the results pressure steadily diminishes with increase in obtained (12).There has been particular con- silver content up to about 30 per cent troversy with regard to the behaviour of the (42, 45) (Fig. 7). Ag-Pd-H system (12). As a result, although with increasing silver Certain of the difficulties appear to have content at about 25°C the amount of hydro- been resolved by some further P-C-T data gen, absorbed under a pressure of one atmo- which has more recently been derived from sphere, decreases continuously from the electrode potential measurements. Although amount absorbed by pure palladium, more the electrochemical data have so far been hydrogen is retained by the alloys with up to obtained only over a rather narrow tern- 30 per cent silver when the pressure is reduced perature range around 25T, it has been to about 16mm. (Roughly the minimum sufficient to indicate that the family of iso- vapour pressure for existence of the P-phase therms for each alloy that absorbs hydrogen hydride of palladium at 25°C (42, 45).) It have a similar general appearance to those of now seems clear that a consolidation of these the Pd/H system (34, 44). data will give a complete thermodynamic For the Pt-Pd-H system at 25 'C it has been justification for the experimental findings of found that increase of platinum content is Sieverts (43), that at higher temperatures paralleled by a steady increase in the eqaili- (2 138°C) the amount of hydrogen absorbed brium hydrogen vapour pressure over regions by alloys with up to 30 per cent silver exceeds where cr and P-phase hydrides coexist (Fig. the amount absorbed by pure palladium, 6). This reflects a corresponding decrease in when compared at a pressure of one atmo-
Platinum Metals Rev., 1961, 5, (l), 23 sphere. In view, for example, of the complex Ag-Pd-H be- 3 40% Aq-Pd Ill / 760mm haviour, it is important not to Q overgeneralise when discus- I2 E sing these alloy-hydrogen sys- E u PALLAD I U M tems. However, it seems that mrn the minimum atomic percent- I0“1. A9 - Pd ca 3 8 rnrn age of feebly absorbing metal which has to be added to W ca 0.3 rnrn palladium so that the resultant 0 2 -1 alloy does not absorb hydrogen 2sDc with the evolution of heat (exothermic absorption) 0.1 0.2 03 0.4 0.5 06 0.7 0.8 appears to be roughly cor- H/Me (ATOMIC RATIO) related with oxidation number. Fig. 7 Isotherms for Ag-Pd-H systems at 25°C For example, exothermic ab- sorption appears to be unlikely for alloys with >35 atomic per cent platinum system in terms of the electron band theory (44) (the most common oxidation states of of solids. For example, if the electrons lost Pt are f2 and -t4). The minimum per- by the hydrogen atoms were accepted into centage of nickel or rhodium (for which +2 vacancies which exist in the ‘48 band of oxidation states are common) that has to palladium, a plausible explanation could also be added to produce a non-exothermally be given of the seemingly linear decrease of absorbing alloy is somewhat higher than 35 the paramagnetic susceptibility of palladium per cent (46, 47) and about 70 per cent of up to HjPd N 0.55 (~~48).As an extension of either gold (with oxidation states of +I and this picture it has been suggested that for +3) or silver (with a common +I oxidation HjPd > 0.55 the electrons donated by hydro- state) have to be added to palladium to gen could be incorporated into the ‘5s’ band achieve the same purpose (12~44).It has been of palladium (49). suggested (44) that alloys which do not form As further support for this ‘free proton’ p-phase hydrides within experimentally theory, a good matching of the experimental convenient pressure ranges at room tem- P-C-T data, including the region near to the perature, but which can still exothermally critical temperature for CL and P-phase co- absorb appreciable amounts of hydrogen in existence, was obtained by a statistical a-phase, may prove to have advantages thermodynamic analysis (49) which considered over palladium for application as diffusion the interaction energy between the protons as membranes. a function of their concentration. On the other hand, Coehn’s interpretations Constitution of the Hydrides of his experimental results have not gone It appeared from the results of experiments unchallenged (39), and it may be claimed that by Coehn and co-workers (12,41) that, under similar changes of magnetic properties would an electrical potential gradient, hydrogen was result from other more usual forms of chemical transferred from the positive to the negative union (37). It has also been pointed out that pole of a specimen of palladium hydride. It the ‘free proton’ theory has not allowed for was, therefore, concluded that the hydrogen any alteration of the electron bands of palla- was present in the solid in the form of protons. dium which should result from the inter- These results could be conveniently incor- atomic expansion when $-phase hydride is porated into a simple picture of the Pd/H formed (50).
Platinum Metals Rev., 1961, 5, (l), 24 Since a system of resonating hydrogen resistance of palladium to disruption by bridge bonds has been suggested to account hydrogen. It does appear, however, that the for certain features of uranium hydrides, this similarities of features such as the P-C-T data has helped to encourage a proposal (3) that and electrical properties to those of the the chemical binding in the Pd/H system may remainder of the transition metal hydrides he of a more covalent type at temperatures may be at least as important a consideration. below 0°C. Although the covalent model is It is thus of interest to note that interatomic advanced (3) as being complementary to the distances in several transition metal hydrides free proton model at higher temperatures a are compatible with the hydrogen being A type specific heat anomaly observed at present as negative ions (53, 54, 55). around 70°K has been suggested (3) to indi- cate local ordering to covalently bonded References molecular units with a formula PdH,. It is of 36 F. A. Lewis, G. E. Roberts and A. R. interest to note that marked electrical resist- Ubbelohde, Proc. Roy. SOC., 1953, 2mA, 279 ance changes have also recently been reported 37 A. I. Schindler, R. J. Smith and E. W. (37) over the same temperature range as the Kammer, Tenth Int. Congress on Refrig- specific heat anomaly. eration: Copenhagen, r959 An approach more diametrically opposed 38 A. W. Carson, T. B. Flanagan and F. A. Lewis, Naturwiss., 1959, 46,374, and Trans. to the free proton theory is to consider the Faraday SOC.,1960,56, 1311, 1324 p-phase hydrides as ionic structures in which 39 C. A. Rnorr and E. Schwartz, Z. Elektrochem., the hydrogen is present as negative ions. 1933, 39,281; iKd., 1934,40, 37 Some attention to this approach seems 40 E. Raub, J. Less Common Metals, 1959, I, 3 warranted if for no other reason than to 41 A. Coehn and H. Jurgens, Z. Physik, 1931, 71, I79 examine any possible correlation between the 42 F. A. Lewis and W. H. Schurter, Naturwiss, hydrides of palladium and its alloys and other 19% 47, I77 broad groups of solids. 43 A. Sieverts, E. Jurisch and A. Metz, Z. anorg. Pressure-concentration isotherms of many Chem., 1915, 92, 329 chemical systems, including a number which 44 A. W. Carson, T. B. Flanagan and F. A. Lewis, Nature, 19.59, 183, 39, 510, and comprise a transition metal and a more Trans. Faraday SOC.,1960, 56, 1332 electronegative element such as oxygen and 45 Z. L. Vert and I. P. Tverdovskii, Zhur. Fiz. suluhur,-~ show similarities with the Pd/H iso- Khim., 1954, 28, 317 therms (sI). The solid phases of these 46 I. P. Tverdovskii and A. I. Stetsenko, Doklady Akad. Nauk S.S.S.R., 1952, 84, 997 systems are likewise found to show marked 47 I. P. Tverdovskii and Z. L. Vert, Doklady divergence from stoichiometry and to exhibit Akad. Nauk S.S.S.R., 1953, 88, 305 considerable electronic conductance. Although 48 N. F. Matt and H. Jones, Theory of the detailed explanations are often complex, such Properties of Metals and Alloys: Oxford University Press, 1936, p. 316 behaviour is generally dealt with in terms of 49 J. R. Lacher, Proc. Roy. SOC.,1937, 16rA, 525 lattice vacancies or interstitial species in a 50 A. R. Ubbelohde, Proc. Roy. SOC., 1937, reference stoichiometric crystal (51). There 159A, 295; cf. also A. Harashima, T. Tanaka appears to be an increasing amount of evidence and K. Sakaoku,?. Phys. SOC.Japan, 1948, 3,208 that the hydrides of other transition and rare 51 See, for example, A. L. G. Rees, Chemistry earth metals can be included in this general of the Defect Solid State, Methuen: group (52). London, 1954 The PdiH system has generally been some- 52 E. J. Goon,?. Phys. Chem., 1959, 63, 2018 what set apart, even from the other ‘exo- 53 G. G. Libowitz and T. R. P. Gibb, 3. Phys. Chem., 1956, 60, 510 thermic’ transition metal hydrides. This seems 54 T. R. P. Gibb, in course of publication due both to the apparent success of the 55 G. G. Libowitz, J. Nuclear Materials, 1960, ‘proton gas’ model and to the superior 2, 1
Platinum Metals Rev., 1961, 5, (l), 25 Faraday’s Lecture on Platinum
THE CENTENARY OF A CLASSIC
In the course of his long researches Michael Faraday more than once turned his attention to platinum and its properties, and on February 22nd 1861-when in his 71st year-he delicered his famous ‘Lecture on Platinum’ to the members of the Royal Institution. An abridged version of this address is reprinted here for the historical interest it inill undoubtedly haw for the metallurgist of today and for the picture it conveys of a great but modest scientist
When I was tempted to propose this subject indicate the great weight of the substance, for your attention this evening, it was founded which is, indeed, nearly at the head of all upon a promise, and a full intent of perform- substances in that respect. This substance has ing that promise, on the part of my friend been given to us hitherto mainly through the Deville, of Paris, to come here to show before philosophy of Dr. Wollaston, whom many of you a phenomenon in metallurgic chemistry us know, and it is obtained in great purity not common. In that I have been disappointed. and beauty, It is a very remarkable metal in His intention was to have fused here some many points, besides its known special uses. thirty or forty pounds of platinum, and so to Now, with regard to this substance, let me have made manifest, through my mouth and tell you briefly how we get it. The process my statement, the principles of a new process used to be this. The ore was taken, and in metallurgy in relation to this beautiful, digested in nitro-muriatic acid of a certain magnificent, and valuable metal; but circum- strength, and partly converted into a solution, stances over which neither he nor I, nor others with the leaving behind of certain bodies. concerned, have sufficient control, have pre- The platinum being dissolved with care in vented the fulfilment of that intention, and acids, to the solution the muriate of ammonia the period at which I learned the fact was so was added, as I am about to add it here. A recent, that I could hardly leave my place yellow precipitate was then thrown down, as here to be filled by another, or permit you, you perceive is the case now; and this, care- who in your kindness have come to hear what fully washed and cleansed, gave us that body might be said, to remain unreceived in the [pointing to a specimen of the chloride of best manner possible to me under the ur- platinum and ammonium], the other elements, cumstances. I therefore propose to state as or nearly all, being ejected. This substance well as I can what the principles are on which being heated, gave us what we call platinum M. Deville proceeds by means of drawings, sponge, or platinum in the metallic state, so and some subordinate or inferior experiments. finely divided as to form a kind of heavy mass The metal platinum, of which you see or sponge, which, at the time that Dr. some very fine specimens on the table, has Wollaston first sent it forth, was not fusible been known to us about a hundred years. It for the market or in the manufacturers’ work- has been wrought in a beautiful way in this shops, inasmuch as the temperature required country, in France, and elsewhere, and sup- was so high, and there were no furnaces that plied to the consumer in ingots of this kind, could bring the mass into a globule, and or in plates, such as we have here, or in cause the parts to adhere together. These masses, that by their very fall upon the table divided grains of spongy platinum having been
Platinum Metals Rev., 1961, 5, (1),26-29 26 well washed and sunk in water for the purpose bring before you is of another kind, and it is of excluding air, and pressed together, and in the hope that we shall be able before long heated, and hammered, and pressed again, to have such a thing as the manufacture of until they come into a pretty close, dense, platinum of this kind that I am encouraged compact mass, did so cohere, that when the to come before you, and tell you how far mass was put into the furnace of charcoal, Deville has gone in the matter, and to give and raised to a high temperature, the particles, you illustrations of the principles on which at first, infinitely divided-for they were he proceeds. chemically divided-adhered the one to the Deville’s process depends upon three other, each to all the rest, until they made points-upon intense heat, blowpipe action, that kind of substance which you see here, and the volatility of certain metals. We know which will bear rolling and expansion of every that there are plenty of metals that are volatile, kind. No other process than that has hitherto but this, I think, is the first time that it has been adopted for the purpose of obtaining this been proposed to use the volatility of certain substance from the particles by solution, pre- metals, such as gold and palladium, for the cipitation, ignition, and welding. purpose of driving them off and leaving some- This is the process adopted by Messrs. thing else behind. He counts largely upon the Johnson and Matthey, to whose great kind- volatility of metals which we have not been ness I am indebted for these ingots and for in the habit of considering volatile, but which the valuable assistance I have received in the we have rather looked upon as fixed. illustrations. Let me now tell you briefly what Deville The treatment, however, that I have to proposes to do. First of all, he takes this ore
Faraday deliuering a lecture at the Royal Institution. The illustration, from a painting by Blaikley in the possession of the Royal Institution, shows him giving the jirst of a series of lectures on ‘Metals’ in 1855. In the centre of the front row is the Prince Consort with his sons the Prinre of Wales (afterwards King Edward YYl)and Prinrs Alfred on either side
Platinum Metals Rev., 1961, 5, (l), 27 with its impurities and mixes it (as he finds it (which he calls weak platinum), and he then essential and best) with its own weight of places it in the kind of vessel that you see sulphuret of lead-lead combined with sul- before you. The combustible metal-that is, phur. Both the lead and the sulphur are the lead-and the part that will oxidise, are wanted; for the iron thar is there present, as thoroughly oxidised; the litharge flows out in you see by the table, is one of the most annoy- a fused state into a vessel placed to receive it, ing substances in the treatment that you can and the platinum remains behind. imagine, because it is not volatile; and while the iron remains adhering to the platinum, the platinum will not flow readily. It cannot be sent away by a high temperature-sent into the atmosphere so as to leave the plati- num behind. Well, then, a hundred parts of ore and a hundred parts of sulphuret of lead, with about fifty parts of metallic lead, being all mingled together in a crucible, the sulphur of the sulphuret takes the iron, the copper, Removing the Eitharge in a fused state from the and some of the other metals and impurities, surface of the molten platinum and combines with them to form a slag; and as it goes on boiling and oxidising, it carries Here is the process which Deville adopts off the iron, and so a great cleansing takes for the purpose of casting off the lead after he place. has got out the platinum from the ore. Now you ought to know that these metals, (Having made use of your friend, you get rid such as platinum, iridium, and palladium, of him as quickly as you can.) He gets his have a strong affinity for such metals as lead heat by applying the combination of oxygen and tin, and upon this a great deal depends. and hydrogen, or of carburetted fuel, for the Very much depends upon the platinum throw- purpose of producing a fire. Having obtained ing out its impurities of iron and so forth by heat like this, the next consideration is, what being taken up with the lead present in it. vessel is he to employ which could retain the When he (Deville) has melted these sub- platinum when so heated, or bear the effects stances and stirred them up well, and so of the flame? Such vessels are happily well obtained a complete mixture, he throws in supplied at Paris, and arc formed of a sub- air upon the surface to burn off all the sulphur stance which surrounds Paris; it is a kind of from the remaining sulphuret of lead; and at chalk (called, I believe, by geologists calcaire last he gets an ingot of lead together with gross&), and it has the property of enduring platinum-much lead comparatively, and an extreme degree of heat. little platinum. I am now going to get the highest heat that He gets that in the crucible with a lot of we can obtain. First, I show you the com- scorias and other things, which he treats bustion of hydrogen by itself. If I put a afterwards. It is that platiniferous lead which piece of lime obtained from this chalk into we have to deal with in our future process. the gas, you see we get a pretty hot flame Now let me tell you what he does with it. which would burn one’s fmgers a good deal. His first object is to get rid of the lead. He But now let me subject a piece of it to the has thrown out all the iron, and a number of joint action of oxygen and hydrogen. I do other things, and he has got this kind of com- this for the purpose of showing you the value pound. He may get it as high as 78 per cent. of lime as a material for the furnaces and of platinum, and 22 of lead; or 5, or 10,or 15 chambers that are to contain the substances of platinum, and 95, or 90, or 85 of lead to be operated on, and that are consequently
Platinum Metals Rev., 1961, 5, (l), 28 to sustain the action of this extreme heat. is raised to a heat that no eye can bear. There I have two or three rough drawings here is no light and shadow, no chiaroscuro there; representing the kind of furnace which Deville all is the same intensity of glow: you look in employs. It is made of a piece of lime below and you cannot see where the metal or the and a piece of lime above. You see how lime is; it is all as one. We have, therefore, a beautifully lime sustains heat without altering platform with a handle, which turns upon an in shape; and you may have thought how axis, that coincides with the gutter that is beautifully it prevents the dissipation of the formed for the pouring of the metal; and heat by its very bad conducting powers. when all is known to be ready, by means of While the front part of the lime which you dark glasses, the workmen take off the top saw here was so highly ignited, I could at any piece and lift up the handle, and the mould moment touch the back of it without feeling being then placed in a proper position, he knows that the issue of the metal will be exactly in the line of the axis. I have said that Deville depends upon intense heat for carrying off vapour and pro- poses to throw out in this way all those extraneous things except two, namely iridium and rhodium. It so happens that iridium and rhodium do make the metal more capable of resisting the attacks of acids than platinum itself. Alloys are compounded up to 25 per cent of rhodium and iridium by which the chemical inaction of the platinum is increased and also its malleability and other physical The lime-blork furnare designed by Deville properties. I have now finished this imperfect account. any annoyance from the heat. So, by having It is but an apology for not having brought a chamber of lime of this sort, he is able to the process itself before you. I have done the get a vessel to containthese metals with scarcely best I could under the circumstances, and I any loss of heat. He puts the blow-pipes through know your kindness well, for if I were not these apertures and sends down these gases aware that I might trust to it, I would not upon the metals, which are gradually appear here so often as I have done. The melted. He then puts in more metal through gradual loss of memory and of my other facul- a hole at the top. The results of the com- ties is making itself painfully evident tQ me, bustion issue out of the aperture which you and requires, every time I appear before you, see represented. If there be strips of platinum the continued remembrance of your kindness he pushes them through the mouth out of to enable me to get through my task. If I which the heated current is coming, and there should happen to go on too long, or should they get red-hot and white-hot before they fail in doing what you might desire, remember get into the bath of platinum. So he is able to it is yourselves who are chargeable by wishing fuse a large body of platinum in this very me to remain. I have desired to retire, as I manner. think every man ought to do before his facul- When the platinum is melted he takes off ties become impaired; but I must confess that the top and pours out from the bottom piece, the affection I have for this place, and for like a crucible, and makes his cast. This is the those who frequent this place, is such that I furnace by which he fuses his forty pounds or hardly know when the proper time has fifty pounds of platinum at once. The metal arrived.
Platinum Metals Rev., 1961, 5, (l), 29 ABSTRACTS of current literature on the platinum metals and their alloys
PROPERTIES type structure and Ir,Te, has a defect (CZ)type structure with approximately one-quarter of the Tensile Properties of the Platinum Group cation sites vacant. The structures are discussed Metals in relation to the arrangement of the electronic F. c. HOLDEN, R. w. DOUGLASS and R. I. JAFFEE, energy levels of the metal atoms. Paper presented at the Third Pacific Area Na- tional Meeting, A.S.T.M., San Francisco, Oct. Absorption of Hydrogen by Palladium/ 1959. A.S.T.M. Special Technical Publication No. Platinum Alloys. Part 3. Some Thermo- 272. Tests were carried out in the temperature range dynamic Factors A. w. CARSON, T. B. FLANAGAN and F. A. LEWIS, -196" to IOOO"Con Ru, Rh, Pd, Ir and Pt, all in the annealed condition. With the exception of Trans. Faraduy SOL., 1960, 56, (9), 1332-1339 Pd, material representing different grades of Electrode potential measurements were made on purity or methods of fabrication were used for a series of Pt-Pd alloys over a temperature range each metal. Ru was prepared by powder metal- 0"-59"C and free energies of solution of hydrogen lurgy techniques; Rh, Pd, Ir and Pt were obtained and hydride vapour pressures were derived as a as rod or wire; electron-beam melted Rh and Ir function of the hydrogen content. Entropies and also were tested. Ru showed rather low ductility partial molar heats of formation of P-phase at 750"~IOOOO and IZOO"~and a tensile strength hydrides were derived for alloys containg 2.79, of 31,400 psi at 1000°C. Throughout the range 5.73 and 8.80 at.:: Pt. It is suggested that hydro- -196" to IOOO'C,Rh showed good ductility, and gen absorption in alloys with greater than 35 at.:; at IOOO~C,a tensile strength of about 12,500 psi. hydrogen is unlikely to be exothermic. Results Pd, over the whole temperature range, showed indicate that, with increasing Pt content, the low strength and high ductility. Tensile strengths critical temperature and pressure for x-p phase of Ir decreased with increasing temperature to coexistence decreases. about 45,000 psi at rooo"C; ductility was good at higher temperatures, but low up to SOOT.Pt Low Temperature Dependence of the Elec- resembled Pd with high ductility and low tensile trical Resistivity and Thermoelectric Power strength. Twinning was observed in all five of Palladium and Palladium-Nickel Alloys metals. Strengths plotted a. homologous tem- Containing Absorbed Hydrogen perature indicate that Rh, Ir and Ru are stronger A. I. SCHINDLER, R. J. SMITH and E. w. KAMMER, than Pd and Pt. U.S. Naval Research Laboratory Report 5481, 196% Jun. 3,6 PP. Iron-Ruthenium Alloys Measurements of electrical resistivity and thermo- E. RAUB and W. PLATE, Z. Metallkunde, 1960, 51, electric power were made on wires of Pd, IoO,, (81,477-481 Ni-Pd and 1774 Ni-Pd containing various A series of Fe-Ru alloys were investigated in the amounts of absorbed hydrogen. At T=50°K, temperature range 400"-1300"c by X-ray and a resistivity maximum and, relative to pure Pd, dilatometer methods, and microscopy. Earlier a thermoelectric power minimum were found for reports on the stabilisatjon of y-Fe by Ru were samples with H/Pd>o.58. These samples also confirmed. The y-cx and y-c transformations showed a resistivity minimum at approximately and their influence on the thermal expansion 9o'K. The absolute thermoelectric power for curves were studied for various alloys up to Pd-H decreases rapidly as a function of composi- 30 at. 94, Ru. The crystal structure of the alloys tion in the region HjPd 0.6 at temperatures after heat treatment at various temperatures is 85"K, while above 95°K a maximum is shown given in some detail. at H/Pd-o.6. The System Iridium-Tellurium On the Contamination of Platinum with E. P. HOCKINGS and J. G. WHITE, 7. Phys. Chem., Fission Products and the Decontamination 1960, 64, (8), 1042-1045 of Contaminated Platinum with Acids Specimens, obtained by heating Ir powder and T. YANAGIIIARA, H. KIMURA and M. CHIBA, J. Jap. Te in vacuo, were examined by X-ray powder Inst. Metals, 1960, 24, (7), 413-417 (English diffraction methods. Two compounds, IrTe, summary) and IrsTes, were observed and their crystal Pt plates were soaked in a solution of fission structures were determined. IrTe, has the (C6) products and maximum contamination was
Platinum Metals Rev., 1961, 5, (l), 30-38 30 reached in about 3 hours. It was shown by Kinetics of Hydrogen and Oxygen Adsorp- autoradiography, electron microscopy and optical tion and Their Reaction on Platinum microscopy that the contamination is affected P. K. MIGAL' and v. A. TSIPLYAKOVA, Zhur. Fiz. by the surface condition of the Pt. The plates Khim., 1960, 34, (6), 1153-1160 (English sum- were decontaminated with tap water, HC1, mary) HNO,, H,SO,, H,PO,, HF and fused salts. Of The adsorption of hydrogen and oxygen and their those investigated hot HC1 and fused KHSO, were interaction in the presence of As, Hg and of (CN)' the most effective decontaminating agents. The ions were investigated. The adsorption rate for degree of contamination of Pt with fission hydrogen on non-poisoned Pt was found to be of products is very low. zero order. The effect of the poisons on the hydrogen adsorption rate diminishes in intensity Mass-Spectrometric Study of the Osmium- in the order (CN)'>Hg>As. It is suggested Oxygen System that the reaction between adsorbed hydrogen and R. T. GRIMLEY, R. P. BURNS and M. G. INGHRAM, molecular oxygen takes place according to the J. Chem. Phys., 1960, 33, (I), 308-309 "impact" mechanism with redistribution of The main ionic species produced from a Knudsen hydrogen on the surface. A similar mechanism cell in the temperature range I 1oo-175o"K were without surface redistribution of oxygen is OsO,+ and OsO,'. The ratio OsO,+:OsO,+ suggested for the reaction between adsorbed is a function of the oxygen pressure and the tem- oxygen and molecular hydrogen. The effect of perature and confirms the presence of OsO, As, Hg, and (CN)' ions on the reaction rates and OsO, molecules in the vapour phase. Above was studied. 1700°K, evidence supports the existence of a stable OsO, molecule. Modern Industrial Uses of the Platinum Metals Equilibrium Measurements in the Iridium- w. BETTERIDGE and D. w. RHYS, Metal Industry, Oxygen System. Gaseous Iridium Trioxide 1960, 97, (9, 10 and 11), 163-166, 183-185 and H. SCHAFER and H. J. HEITLAND, z.Anorg. Allgem. 203-205 Chem., 1960, 304, (5/6), 249-265 The physical and chemical properties of the Pt Measurements made by the carrier gas method metals upon which many of their applications have shown that Ir and IrO, heated in currents depend are given. Major uses of the metals in of oxygen or oxygen-nitrogen are volatilised with the metallurgical, chemical, petroleum, electrical, the formation of gaseous Ir03, which is stable up glass, synthetic fibre and atomic energy industries to 1700°C. This confirms previous hot wire are reviewed. experiments. The interpretation of published hot wire experiments with Pt and Rh indicates The Thermal and Magnetic Properties of the existence of Pt,O, and Rh,O,. Thermo- Some Transition Element Alloys dynamic data for IrO&) and IrO&) have been D. w. BUDWORTH, F. E. HOARE and J. PRESTON, obtained. Proc. Roy. SOC.,Series A, 1960, 257, (1289), 250-262 Equilibrium Measurements in the Platinum- Magnetic measurements were made on 40 Oxygen System. Gaseous Platinum Dioxide different Pd-Rh, Pt-Ir and Pt-Au alloys. The H. SCHAFER and A. TEBEEN, Z. Anorg. Allgem. Chem. specific heats of Pd-Rh and Pt-Au alloys and the 1960, 304, (5/6), 317-321 pure metals Rh, Pt and Au were measured in the Pt was volatilised as the dioxide by heating in an range 1.8 to 4.2"K and the electronic heats and oxygen atmosphere. The equilibrium Pt+ O,= Debye temperatures were computed. Tables of PtO&) was measured in the range I 107"-1208'C results are given. Similarities between alloys of and the following data were obtained: AH,,,== Pd and Ag or Rh with alloys of Pt and Au or Ir 41.30 kcal; AS2,,-3.o1 cl; S(PtO,(,), 298)= are noted. 62.0 cl. Magnetic Properties of the Pd and Pt Group Changes in Resistance on the Chemisorption Transition Metal Complexes of Gases on Thin Metal Films H. KAMIMURA, s. KOIDE, H. SEKIYAMA and s. w. M. H. SACHTLER and G. J. H. DORGELO, 2. Phys. SUGANO, 3. Phys. soc. Japan, 1960, 15, (7), Chem. (Frankfurt), 1960, 25, (I/?,), 69-74 1264-1272 The Pt-H system was investigated. It was found Magnetic susceptibilities and g-values are calcu- that, as with other metals, chemisorption of lated by means of the intermediate coupling hydrogen effects a sharp initial increase in the scheme. The effect of the dy orbitals is neglected electrical resistance of the films. Absorption of because of the cubic symmetry of the crystalline hydrogen in the metal lattice often causes a field. The effect of the Coulomb repulsion is decrease in resistance. A temperature as low as regarded as comparable to that of the spin-orbit -21oOC is necessary for suppressing the absorp- interaction. The results are compared with tion of hydrogen in Pt. experimental data.
Platinum Metals Rev., 1961, 5, (l), 31 Vapour Pressures of Platinum Metals. I. Miscibility Curves and Critical Point of the Palladium and Platinum Gold-Platinum System L. H. DREGER and J. I. MARGRAVE, 3. Phys. Chem., A. M~~NSTERand K. SAGEL, Z, Phys. Chem. (Frank- 1960, 64, (91, 1323-1324 furt), 196% 23, (5/6), 415-425 Vaporisation studies were carried out by the Miscibility curves and the critical point of the Langmuir free evaporation technique. Results system were determined by measurement of obtained for Pt are: log Pmso1id=1o.362- electrical conductivity. The critical temperature, 29,1oo/T; AH",,,: 135.2 fo.8 kcal/mole; esti- tk, is given as 1agz*1.5"C and the critical atomic mated boiling point%4100i 100°K. For Pd: fraction of Pt, Xk, is 0.40fo.007. The results of log P,,solid=9.075-19,425/T; AH0298=9~.~a study of the shape of the miscibility curves were fo.8 kcal/mole; estimated boiling point w 3200% compared with the Fuchs theory of lattice models. 100°K. Nitrides of Iron with Nickel, Palladium, and Investigation of Adsorption on Platinised Platinum Carbon by Change of the Gaseous Atmosphere H. H. STADELMAIER and A. c. FRAKER, Trans. Met. A. N. MOSEVICH, B. P. NIKOL'SKII, v. I. PARAMONOVA SOC.A.Z.M.E., 1960, 218, (3), 571-572 and E. L. MORDBERG, Zhur. Phys. Khim., 1960, 34, Nitrides were prepared as powders and their (9), 1900-1906 (English summary) crystal structure was derermined with a powder The adsorption of Cs and Br ions from aqueous camera. A perovskite structure is assumed for solutions in hydrogen and air atmospheres was Fe,PdN with Pd and the interstitial nitrogen investigated. Adsorption and desorption studies fully ordered. were carried out both in the presence and absence of a buffer and of foreign ions. The adsorption New High-Coercivity Alloys in the Binary of Cs and Br ions was shown to have an electro- Systems Fe-Pt, Fe-Pd and Ni-Pd static character and to conform to the basic laws z. I. ALIZADE, Bull. Acad. Sci. U.S.S.R., Phys. of ion exchange. Series, 1959, 23, (3), 399-400 (Izvest. Akad. Nauk S.S.S.R., Ser.fiz., 1959, 23, (3), 416-417) Increasing the Stability of the Passive State The magnetostriction of alloys with a wide range in Titanium of Pt and Pd concentrations was investigated. N. D. TOMASHOV, G. P. TSHCHERNOVA and R. M. Results obtained for the three systems of the ALTOWSKI, 2. Phys. chem. (Leipzig), 1960, 214, relationship between saturation magnetostriction (5/6), 312-323 and alloy composition are shown graphically. The behaviour of Ti and its alloys with 1% and Fe-Pt and Fe-Pd alloys have a positive maximum 2% of Pt and Pd on cathodic and anodic polarisa- saturation magnetostriction. The Ni-Pd system, tion in H,SO, and HCl solutions was studied by however, comprises a number of alloys with a potentiostatic methods. It was shown that the high negative magnetostriction. complete passivation of Ti is made more difficult by increasing the temperature and concentration Elastic Constants of Palladium from 4.2 to of the acid solution. The alloys of Ti with Pt and 500°K Pd have a substantially higher corrosion stability J. A. RAYNE, Phys. Rev. Letters, 1960, 4, (8), than Ti. Ti may be protected anodically in 437-438 H,SO, and HC1 of all concentrations and may be Extrapolation to absolute zero of the data passivated by cathodic depolarisers such as ions obtained on a single crystal gives the following of Pt", Cu2+and Fe3f in the corrosive medium. results: c,,=(~.~~I&o.oz~)x rola dyne cm-', cI2= Some Aspects of the Structural Chemistry (1.761 k0.027) x roI2 dyne cm-', cd4=(o.712& of Platinum 0.003) x 10'~dyne an-'. E. G. cox, J. Roy. Znst. Chem., 1960, 84, (Aug.), 283-284 Research on the Alloys of Noble Metals The historical development of the study of the with the More Electropositive Elements. 111. stereochemistry of Pt co-ordination compounds Micrographic and X-Ray Examination of is outlined. The structure of derivatives of Some Magnesium-Platinum Alloys Pt(CH,),I is discussed. R. FERRO and G. RAMBALDI, J. Less-Common Metals, 1960, 2, (s), 383-391 The Melting Point of Osmium Alloys in the range 0-30 at.% Pt were prepared A. G. KNAPTON, J. SAVILL and R. SIDDALL, J. Less- and examined by chemical analysis, specific Common Metals, 1960, 2, (9, 357-359 gravity determination, micrographic and X-ray The melting point was redetermined as 3045i examination. The eutectic composition and tem- 30% by direct measurement of the black-body perature were estimated to be about 7.5-7.6 at.% radiation from a hole near the centre of an Pt and 575"C, respectively. Intermediary <- electrically heated bar. and &phases were detected. The &phase,
Platinum Metals Rev., 1961, 5, (l), 32 corresponding to Mg,Pt, is face-centred cubic measurements of anodic or cathodic limiting and the &phase, corresponding to MgsPt, is current densities. DH, was measured in o.5N hexagonal Na,As type. H,SO,, 5N H$O, and o.rM Na,SO, in the temperature range -10' to 60°C from the anodic limiting current density of hydrogen molecules. ELECTROCHEMISTRY DH+was obtained in weakly acid O.IM Na,SO, at 20°C from the cathodic limiting current Proton Transfer between PdiH and Pd/Pt/H density of H- ions and DOH- was obtained in Electrodes weakly alkaline 0.1 M Na,SO, from the anodic Part 1. Equilibrium Hydrogen Electrodes OH- ion limiting current density. A. w. CARSON, T. B. FLANAGAN and F. A. LEWIS, Trans. Furaduy SOC.,1960, 56, (9), 1311-1323 The Electrolytic Formation and Dissolution The investigation was carried out in IN HC1 of Oxide Films on Platinum without evolution of hydrogen using continuous H. A. LAITINEN and C. G. ENKE,~.Electrochem. soc., and separated wire electrodes of Pd and Pt-Pd 1960, 107, (911 773-731 alloys containing 2.79, 5.73, 8.80 and 12.03 at.o; An electrolytic cell consisting of a Pt foil indi- Pt. It was found that polarisation of proton cator electrode, a Pt gauze counter electrode and transfer is relatcd to imposed changes of the HC10, electrolytes of varying strengths was used hydrogen content of the electrodes. The activa- in conjunction with a calomel reference electrode. tion energy for proton transfer was determined as The formation of surface PtO was believed to be 4.9 kcal/mole. The effect of proton transfer in an irreversible reaction due to a mechanism solution upon electrical resistance measurements which involves a hydroxyl radical intermediate. was studied. It was concluded that the steady-state cvolution Part 2. Incomplete Polarisation of Proton occurs on a surface which has at least one atom Transfer of oxygen per surface Pt atom. A first order Ibid., 1324-1328 reduction of the surface oxide was shown experi- mentally. The surface oxide is reduced at Studies on specimens as above showed that when potentials several hundred mV cathodic to the the hydrogen content of the electrodes corres- oxide formation potential and the rate of dissolu- ponds to the coexistence of dc- and $phases, tion increases with increasing cathodic electrode reversible concentration polarisation of proton potential. transfer may be incomplete. Effects of the incomplete polarisation on the measurement of Catalytic Activity and Electronic Structure electrical resistance in acidic solutions were observed for the series of Pt-Pd alloys and of Rhodium-Palladium-Hydrogen Cathodes reasons for errors are discussed. in Acid Solution J. P. HOARE, J. Electrochem. SOC., 1960, 107, A Study of the Adsorption Phenomena of (IO), 820-825 Rhodium, Iridium, Pallarlium and Gold Hydrogen overvoltage measurements were made with the Potentiostatic Triangle Method on Rh-Pd cathode beads containing I, 2, 5, 10, F. G. WILL and c. A. KNORR, Z. Elektrochem., 1960. 15, 20, 50 and 90 at.o/, Rh hydrogen stirred in 64, (2))270-275 2N H,SO, at 25°C. u- and $-phases, similar to The adsorption of hydrogen and oxygen on the those existing in the Pd-H system, were investi- precious metals was studied. It was found that gated. The mechanisms of the reactions on the the maximum hydrogen coverage of the roughened various cathodes are discussed. The catalytic surface was 6z00 for Rh, 45q4 for Ir, and 3076 activity of the cathode surface for the hydrogen for Au. The surface coverage is dependent on reaction was determined at low current densities. the potential velocity and preliminary treatment, It is suggested that vacancies in the d-band of For each metal oxygen evolution and layer- the cathodes make possible the strong chemical formation commences at a different value of bonds between the absorbed hydrogen and the potent@. With the exception of Ir, in the range surface and that there is a direct relationship investigated oxygen layer-formation increases up between the heat of absorption of hydrogen and to 2.2V. Some characteristic measurements for the catalytic activity. The density of states at each precious metal studied are given in a table. the Fermi level determines rhe strength of the bonds. The Determination of Diffusion Coefficients DH,, DH+ and DOH- with a Platinum Disc Electrochemical Phenomenon at the Glass- Electrode Refractory Material Interface M. BREITER and K. HOFFMANN, z. Elektrochem., L. LEGER, M. BOFFE and E. PLUMAT, Glass Technol., 1960, 64, (41, 462-467 1960, 1, (4), 174-179 The apparatus with the Pt disc electrode is Measurements of the e.m.f. developed at the described. The diffusion coefficients were deter- glass-refractory contact served to record con- mined by means of the Lewitsch formula from tinuously alkali penetration of the refractory and
Platinum Metals Rev., 1961, 5, (l), 33 to study the kinetics of the refractory attack by this polarisation is diminished in thc presence of the molten glass. Solid-solid, solid-liquid, and Cu in the electrolyte due to the simultaneous liquid-liquid systems were investigated and in discharge of the Cu cations with the Pt metals. each case, Pt connecting plates or wires were used. The influence of the atmosphere was studied by introducing different atmospheres LABORATORY APPARATUS around two Pt wire electrodes dipping in molten AND TECHNIQUE glass. Both static and dynamic tests were carried out and the experimental procedures are Compact Palladium Diffusion Leak for described in detail. Hydrogen L. A. NOBLE, W. H. SAIN and R. K. WAITS, Rev, SCi. Hydrogen Evolution on Platinum Elec- Instr., 1960, 31, (7), 789-790 trodes. The Heats of Activation for the A Pd thimble (2 in. diameter, 0.005 in. wall Component Reactions thickncss) is brazed to an inner Heliarc ring R. PARSONS, Trans, Faraduy Sac., 1960, 56, (9), which is brazed to a stacked ceramic arrangement. 1340-1350 The heater, a spiral of thoriated W wire, is located Measurements were made at various tempcratures concentrically within the Pd thimble. An outer in o.5M HCI of steady-state current-voltage Heliarc weld ring brazed to the inlet tubulation curves in the range 4 x 10-’ to 10 Acm-2 using a forms the outlet assembly. The heater requires Pt sphere electrode. The heat of activation at a maximum of about 5.5 amp at gV and the Pd the reversible potential was found from the temperature is about 270’C at 2oW with I atm polarisation curves to be 5.2 kcal. The impedance inlet and 5-10 mm Hg outlet pressures. of the electrode was measured as a function of frequency and temperature. It is estimated that Infrared Absorption Spectra of Alkali Metal the exchange cu+rent of the discharge reaction is Nitrates and Nitrites Above and Below the more than IOO times that of the overall reaction, Melting Point but the heat of activation is approximately the J. GREENBERG and L. J. HALLGREN, J. Chem. Phys., same. 1960, 331 (3), 900-902 Spectra of fused LiNO,, NaNO,, KNO,, RbNO,, Investigation of Surface Changes of a CsNO,, NaNO, and KNO, were obtained by Platinum Electrode supporting the salts in the interstices of a 32 mesh H. GRUBITSCH and K. HECKEL, Werkstoffe u. Pt screen. Spectra below the melting points were Korrosion, 1960, I I, (5), 271-273 obtained by allowing the salt to solidify on the The surface changes of a polished electrode, screen. The screen was heated by the passage of an used as a cathode in the galvanic cell electric current and temperatures were measured -Cd 1 O.IN NaCllI O.IN NaC1, air I Pt I-, were by a Pt : IO:, Rh-Pt thermocouple. investigated by electron microscopy. The circuit was alternately completed and broken every Platinum-to-Pyrex Tubular Housekeeper 15 mins. Observed changes in the surface of the Seals Pt electrode apparently correspond to a recon- B. B. GRAVES, Rev. sci. Instr., 1960, 31, (3), 349- struction of the surface and to a lessening of its 350 activity. This decrease in surface activity explains A modification of the Housekeeper technique for the slow current decrease with ventilating ele- sealing Pt to Pyrex entails reduction of the ments, the cathodes of which are immersed in an included angle of the feather edge of the Pt from electrolyte with constant oxygen content. 9” to between I’ and 14”. Methods of producing the edges and of testing the seals are described. ELECTRODEPOSITION CATALYSIS Peculiarities of Cathodic Reduction of Platinum Metals from Complex Electrolytes Hydrogenation of Unsaturated Compounds A. I. LEVIN and B. A. FANKRATOV, J. Appl. Chem. in the Presence of Colloidal Palladium. XI. U.S.S.R., 1959, 32, (8), 1825-1831 (Transl. of Hydrogenation of Vinylacetylene Zhur. Priklud. Khim., 1959, 32, (8), 1787-1793) KH. v. BAL’YAN and N. A. BOROVIKOVA, J. Gen. Shifts of potential in absence of current in various Chem.U.S.S.R., 1959,29, (8),2516-2519 (Transl. electrolytes containing Pt metals were investi- of Zhur. ObshcheiKhim., 1959,29, (8), 2553-2556) gated. The potentials depend on the salt content The hydrogenation was carried out with ratios of and concentration of the electrolyte and shift in vinylacetylene to hydrogen of I : I, I : 0.75, the negative direction with increasing dilution. and I : 0.5 (in moles) and the effect of various Electrode polarisation accompanying simul- additives on the composition of the hydrogenation taneous discharge of Pt metals from complex products was studied. It was found that without mother liquors was studied. It was found that additives and at any ratio of thc reactants, buty-
Platinum Metals Rev., 1961, 5, (l), 34 lenes and butane were formed together with a Derivation of an Equation for the Kinetics predominant amount of butadiene. Butylene of Hydrogenation of Benzene by Hydrogen formation falls with a decrease in the amount of hydrogen used. Pb(C,H,O,), and Cu(C2H302), in the Presence of Palladium Catalysts Slow the hydrogenation reaction, decrease the I. M. KOLESNIKOV, Zhur. Fiz. I<&n., 1960, 34, butylene content, and increase thc yield of (7), 1528-1533 (English summary) butadiene. The derived equation was applied to experimental results previously obtained using catalysts con- XII. Hydrogenation of Alkylacetylenes and taining 1.4, 1.03, 0.49 and 0.18% Pd. It was Phenylacetylene shown that the adsorption of CbHson the catalyst is considerablc. “Fatiguability” of the catalyst KH. v. BAL’YAN and N. A. BOROVIKOVA, J. Gen. varies inverscly with the Pd content. The Ckem. U.S.S.R., 1959, 29, (81, 2520-2523 concept of the uniformity of the catalytic surface (Transl. of Zhzrr. Obshchei Khim., 1959, 29, (8), of Pd is shown to be applicable to this reaction. 2557-2559) Some monoalkylacetylenes and phenylacetylene Progress in the Study of Heterogeneous were hydrogenated with colloidal Pd in a Catalysis CH,COOH solution. It was found that hydro- C. KEMBALL, PrOC. Chem. SOL., 1960, (Aug.), genation proceeds selectively at the triple bond 264-274 to form the corresponding olefins and styrene. The course of catalytic reactions has been After the addition of the first two atoms of followed by using the mass spectrometer to hydrogen, the hydrogenation rate increases analyse reaction products. Types of reactions sharply and then decreases again. studied were (i) exchange reactions with deu- terium, (ii) reactions involving deuteration, and Hydrogenation and Dehydrogenation (iii) reactions with hydrogen. Metal catalysts J. T. BRADBURY, W. M. KEELY, F. J. O’HARA and used in the various reactions included films of R. F. VANCE, Ind. Eng. Chem., 1960, 52, (9), Ni, Mo, W, Pd, Pt, and Rh and some supported 803-806 and wire types. In order to explain the experi- In this review of recent literature on hydrogena- mental results it was necessary to consider the tion and dehydrogenation processes, the many types of adsorbed species present on the catalysts uses of Pt metal and other catalysts are outlined. and the manner in which the relative stabilities Fundamental studies as well as many industrial or reactivities of the species affect the mechanism processes are reviewed. (I I I references.) of heterogeneous catalysis. Examples of each type of reaction arc discussed. (28 references.) Purifying Hydrogen by Selective Oxidation of Carbon Monoxide Hydrogenation of Methyl Oleate in Solvents M. L. morn, A. w. GREEN, G. corn and H. c. E. n. COUSINS and R. O. FEUGE, J. Amer. Oil Chem. ANDERSEN, Ind. Eng. Chem., 1960, gz, (IO), SOC.,1960, 37, (91, 435-438 841-844 Hydrogenation was carried out to an iodine value Laboratory and pilot plant work in which CO in of about 50 at 30°C and under atmospheric NH, synthesis gas was oxidised catalytically to pressure with the methyl oleate alone or dissolved CO, with air or oxygen is described. The in C,H,OH, C‘H,,, CH,COOH or n-butyl selective oxidation process was studied in relation ethyl ether. Of the total double bonds produced to hydrogen and CO content of the gas stream, with a 100,; PdjC catalyst, with or without a oxygen/CO ratio, catalyst composition, space solvent, 76.6-79.1:/, were trans bonds. With velocity and temperature. Effective catalysts for Raney Ni and solvents, trans bonds obtained the reaction in the temperature range 250-320°F were in the range 20.7-34.8%. When Raney Ni are supported Pt, Rh, Rh-Pt and Ru. The without a solvent and the Pd catalyst were used, temperature is held within the selective range by positional isomers were formed extensively. steam dilution. In C0,-free gas streams, ao4,CO Raney Ni with solvcnts gave products with a may be reduced to 10 p.p.m. Proposed single- large proportion of double bonds in the 9-position. and two-stage oxidation units are illustrated. Hydrogenation of Fatty Oils with Palladium A New Catalyst System for the Polymerisa- Catalysts. V. Products of the Tall Oil tion of Acetylenic Compounds Industry L. B. LUTTNGER, Chem. & Ind., 1960, (36), 1135 M. ZAJCEW, J. Amer. Oil Chem. SOC.,1960, 37, The system consists of a freshly prepared mixture (IO), 473-475 of an hydridic reducing agent (e.g. an alkali Tall oil distillate was reduced to an iodine borohydride, LiAlH, or B,H,) with a salt or number of 22 using a 5”; Pd/C catalyst with a complex of a Group VIII metal (e.g. Co, Ni, pressure of 2600 psi at 200’C. The resulting Ru, Os, Pt or Pd). This system is effective under tall oil fatty acids were reduced using a Pd/C wide variations in composition and conditions. catalyst and the linoleic acid, cis-oleic acid,
Platinum Metals Rev., 1961, 5, (l), 35 saturated acid and trans-isomers produced were on Rh/C, the furan ring undergoes hydrogenation determined. Pt, Ir, Rh and Ru were also ex- into tetrahydrofuran (40 yo) and hydrogenolysis amined for activity, selectivity and tendency to at the 1-5 C-0 bond with the formation of the form trans-isomers and were found to be less corresponding ketone (607,). On Rh/C at suitable catalysts. 300°C there is only hydrogenolysis of the furan ring. Development of Gas-Recombination Cata- lysts. Palladium Catalyst Development Reaction of Polyhalornethanes with Enol- J. P. MCBRIDE and L. E. MORSE, U.S.A.E.C. ethers of A4-3-Ketosteroids. A Kew Path- Homogeneous Reactor Programme Quarterly Pro- way to 6a-Methylsteroids gress Report, Apr. 30, 1960, ORNL-2947, 87-90 s. LIISBERG, w. 0. GODTFREDSEN and s. VANGEDAL, The sol method of preparing the Pd/ThO, Tetrahedron, 1960, 9, (3/4), 149-155 catalyst is described. The effects of catalyst Reaction of enol ethers of A4-3-ketosteroids with concentration and pretreatment with oxygen or CBr, affords via 6-tribromomethylsteroids the hydrogen and of Tho, slurry concentration on corresponding 6-dibromomethylene-A4-3-keto- catalytic activity in the hydrogen-oxygen reac- steroids. Upon catalytic hydrogenolysis over tion were studied. Specific activity of the sol- Pd/SrCO, these are smoothly transformed into prepared catalyst appears to be independent of 6-methyl-AL-3-ketosteroids. Other polyhalo- the type and concentration of the slurry solids. rnethanes react in a similar way with enol ethers Pretreatment of the slurry catalyst system with of A l-3-ketosteroids. hydrogen or maintaining an excess hydrogen overpressure results in a greatly increased specific The Heterogeneous Catalysis by Metals of activity. Electron-Transfer Reactions in Solution M. SPIRO, 3. Chem. SOC.,1960 (Sep.), 3678-3679 Kinetics of the Reaction between Hydrogen The catalytic action of Pt, Ru, Ir, Pd, and Au and Oxygen on Platinum in the reaction zF~(CN),~-+~I-+ZF~(CN)~~-+ E. N. KIIAR'KOVSKAYA, G. K. BORESKOV and M. G. I,- was observed. Pt and Hg were also exposed SLIN'KO, Proc. Acad. Sci. U.S.S.R., Phys. Chem. to the reactions 2Fe3' t3I-+zFe2+--j I,- and Section, 1959, 127, (I-6), 563-566 (Transl. of S,O,Z-+ 31-+2s0,2-~I,-. Results may be Doklady Akad. Nauk S.S.S.R., 1959, 127, (I), explained on the hypothesis that iodide ions and 145-148) oxidant ions are adsorbed on the metal surface and A stationary flow method was used to mcasure that electrons may be transferred between them the catalytic activity of a Pt wire working in the through the metal. temperature range 20 to 180°C and at pressures from 50 to 750 mm with various initial reaction The Mechanism of the Reactions between mixtures. The gases were circulated at 4m-1100 Palladium Salts and Olefins in Hydroxyl- l/hr. It was found that with a large excess of hydrogen in the gas mixture the reaction was Bearing Solvents first order with respect to oxygen. With a large I. I. MOISEYEV, M. N. VARGAFTIK and YA. K. SYRKIN, excess of oxygen and with high Pt activity the Doklady Akad. Nauk S.S.S.R., 1960, 133, (2), reaction is first order with respect to hydrogen, 377-380 but with low Pt activity the order with respect Four types of reaction studied were: (i) inter- to hydrogen is reduced to 0.1-0.2. The relation- action between the (PdCl,.C,H,), complex and ship between reaction rate and the concentration non-aqueous solvents; (ii) interaction between of oxygen and hydrogen was studied. Results PdC1, and C,H, in glacial CH,COOH containing are discussed in terms of the various forms of CH,COONa; (iii) oxidation of C,H, by n- chernisorption which occur. benzoquinone in glacial CH,COOH in the presence of PdC1,; (iv) oxidation of C,H, by n-benzoquinone in alcohol solution in the pres- Hydrogenation of Furan Compounds on ence of PdCls. It is suggested that the decomposi- Platinum and Rhodium Catalysts tion of the x-complex in hydroxyl-bearing N. I. SHUIKIN and I. F. BEL'SKII, J. Gen. Chem. solvents entails intermediate formation of vinyl U.S.S.R., 1959, 29, (4), 1063-1065 (Transl. of compounds. Methods of preparation of complex Zhur. Obschchei Khim., 1959, 29, (4), 1093-1095) vinyl esters and of acetals are indicated. The furans were hydrogenated on Pt/C and RhjC in the vapour phase at various temperatures. It was found that with a-alkenyl furans at 150"C, Evolution of Atomic Oxygen from Platinum reduction of the olefin bond in the side chain Surface Treated Previously with Nitrous gives the corresponding a-alkyl furans in 90-95?,, Oxide yield, On PtjC at 150°C the furan ring reacts K. MITANI and Y. HARANG, null. Chem. Soc.Japan, slowly with hydrogen, undergoing hydrogenolysis 1960, 33, (8), 1147 at the double bonds (z0-25?/,) and hydrogen- Atomic oxygen was evolved in vacuo on heating olysis at the 1-5 C-0 bond (75-So"&). At zm"C to 1400'C a Pt surface previously treated at
Platinum Metals Rev., 1961, 5, (l), 36 I 100°C with N,O at pressures of 10-50 mm Hg. The Correlation between the Activity of a A dark brown film of PtO, deposited on the wall Platforming Catalyst and Certain Physical of the reaction vessel. It is believed that PtO, Properties formed on the Pt surface is the source of the I. V. NICOLESCU, A. POPESCU, C. FOREDA, A. PAPIA atomic oxygen. and I. BALLY, J. Chim. Phys., 1960, 57, (51, 409-415 The Treatment of Nitric Acid Plant Tail Gas An active and thermally deactivated I', I"/ W. FLETCHER, Brit. Chem. Eng., 1960, 5, (II), A1,0, catalyst was studied by X-ray and elec- 789-790 trical methods. It was found that the active The tail gas, which usually contains 0.3-0.50/, support material is q-Al,O, and not ;.-A1,0,. NO,, 2-474 excess oxygen and nitrogen, may be The decrease in catalyst activity results from a catalytically reduced by hydrogen, CH, or other decrease in the degree of dispersion of the Pt as fuel gases. Four types of catalyst at present in well as from deformation of the crystal lattice of use are: (i) Pt metals deposited on A1,0, spheres the Pt. In the temperature range 429°-5000c, or pellets; (ii) Pt metals on ceramic pellets; the specific electrical conductivity of the active (iii) supported Ni-Cu; (iv) Pt metals deposited catalyst in air and in hydrogen is greater than on crimped Ni-Cr ribbon. The designs of the that of the deactivated catalyst. The energy of reactors is discussed and operating conditions activation of the electrical conductivity increases are described in detail. on deactivation of the catalyst. The existence of a correlation between physical properties of the Thermal and Catalytic Decomposition of catalyst and its activity in the Platforming process Hydrocarbons are indicated. A. J. DE ROSSET and c. v. BERGER, Ind. Eng. Chem., 1960, 52, (81, 711-716 An Investigation of Thiophene Poisoning Recent literature concerning the processes of Effect on a Platinum Catalyst under Re- thermal decomposition, catalytic cracking, cata- forming Conditions. 3. Effeet of Tempera- lytic reforming and dehydrogenation in petroleum ture and Hydrogen Pressure refining is reviewed. Both industrial methods KH. M. MINACHEV, D. A. KONDRAT'EV and 0. K. and research work are outlined. (100references.) SHCHUKINA, Izvest. Akad. Nauk S.S.S.R., Otdel. Khim. Nauk, 1960, (7), 1263-1266 Heterogeneous Catalysis in the Petroleum The deactivation of a 19; Pt/AI,O, catalyst in Jildllstry the dehydrogenation of C,H,, containing 2.65% H. PICHLER, Trans. Instn. Chem. Engrs., 1960, 38, thiophene was studied at a constant hydrogen (41, 225-233 pressure of 20 atm with pressures of 10-40 atm The history of the development of the processes and temperatures of 450" and 475°C. It was of hydrogenation, oxidation, cracking, dehydro- found that the degree of hydrogenation increases genation, isomerisation, reforming and polymer- with increase of tcmperature and diminishes isation is given briefly in this review. Funda- with increasing pressures. The specific surface mental properties of catalytic reactions are dis- area of the deactivated catalysts diminishes with cussed. Reaction mechanisms and properties of increased temperature, but in practice is not the Pt metal and base metal catalysts for CO- changed with alteration of pressure. hydrogenation, catalytic cracking, reforming and Ziegler reactions are examined. (20 references.) A Study of the Effect of the Specific Surface Area of Platinised Alumina-Silica on the Kinetics of n-Pentane Isomerisation over Degree of n-Nonane Conversion. 2. Change Pt/Al,O, Catalyst in the Catalytic Activity of Platinised J. H. SINFELT, H. HURWITZ and J. C. ROHRER, Alumina-Silica in the Course of the Carrier J. Phys. Chem., 1960,64, (7), 892-894 Treatment by Water Vapour The investigation was carried out at 372°C in a KH. M. MINACHEV, N. I. SHUIKIN and M. A. MARKOV, flow reactor in the presence of added hydrogen. Izvest. Akad. Nauk S.S.S.R., Otdel, Khim. Nauk, Pressures varied from 7.7 to 27.7 atm and the 1960, (8), 1466-1470 hydrogenln-pentane ratio varied from 1.4 to 18. The investigation was carried out using 0.5~~ The isomerisation rate was found to be inde- Pt iAl,O,\SiO, catalysts with varying specific pendent of the total pressure at a fixed n-pcntane: surface area at temperatures of 360-450°C and a hydrogen mole ratio and to be correlated with the hydrogen pressure of 10 atm in a fluid system. n-pentane/hydrogen mole ratio. A mechanism It was found that the degree of hydrocracking by which isomerisation proceeds via an olefin is reduced with decreasing specific surface area intermediate, n-pentene, which migrates to acidic of the catalyst. A yield of 5400 i-C,H,, was sites to isomerise, is supported by these results. obtained at 380'C and at 450°C with catalysts The isomerisation of the intermediate olefin is having specific surface areas of 320 mz'g and the rate-controlling step. 60 m2;g, respectively.
Platinum Metals Rev., 1961, 5, (l), 37 ELECTRICAL ENGINEERING GLASS TECHNOLOGY An Investigation of the Effect of Materials The Increasing Use of Platinum in the Glass Used for the Construction of Telephone Industry Exchanges on Contact Materials Containing KASWANT, Sprechsaal, 1960, 93, (IS), 473-477 Silver and Palladium Economic aspects of the world supply and con- H. LIPKE and W. CLEMENT, Xachrichtentech. Z. sumption of the Pt metals are reviewed. The (hr*T.Z.),1960, 133 (9),431-435 principal physical properties of these metals are Contact materials investigated at constant tem- given in graphical and tabular form. Examples perature and humidity levels were Ag, Pd, given of the applications of Rh-Pt alloys include 50y0 Pd-Ag and 30:~Pd-Ag. Resistance changes feeders, crucibles for melting optical glass and with time were the basis for conclusions on the bushings for glass fibre manufacture. Mention effects of the various materials on the contacts. is made of the use of a Re-Pt alloy for silicate Organic substances such as oil of turpentine and melts. linseed oil mainly affect Pd-containing contacts. TEMPERATURE CHEMICAL TECHNOLOGY MEASUREMENT The Use of Precious Metals in Plant Con- Techniques in Calorimetry. I. A Noble- struction Metal Thermocouple for Differential Use M. WITTUM, Metall, 1960, 14, (9), 897-901 E. D. WEST, Rev. Sci. Instr., 1960, 31, (S), Uses of Ag, Au, Pt and their alloys in the con- 896-897 struction of chemical plant are described. The A 40"" Pd-Au: 1o0/, Rh-Pt thermocouple for suitability of these metals for this purpose is use in an adiabatic calorimeter up to 600°C is shown by a study of their corrosion resistance described. The e.m.f. of the thermocouple and mechanical and physical properties. together with dEjdT values are shown on a graph.
NEW PATENTS
Thermocouples electrical make-and-break members have, at the ELECTROFLO METERS GO. LTD. et al. British Patent point of contact, a flame-sprayed coating of 845,031 platinum or of an alloy of platinum with another A thermocouple consists of an insulating sheath Of the Same group. formed as a solid elongated block of high-refrac- - L tory ceramic, the hot junction being embedded Hydroforming Process in the block close to one end and the thermo- THE BRITISH PETROLEUM GO. LTD. British Patent couple wires emerging from the other end. A metal cladding is provided around the block 847,728 leaving the hot junction end exposed. The The first stage of a two-stage platinum reforming thermocouple wires are of platinum-rhodium process for treating petroleum hydrocarbons 20% alloy and platinum-rhodium 4096 alloy. boiling within the gasoline and naphtha ranges is carried out at at least 450°C with a catalyst of Purification of Ethylene platinum on a normally acidic support rendered non-acidic by the addition of sodium; the second ENGELHARD INDUSTRIES INC. British Patent stage is carried out at a similar temperature using 846,077 a catalyst of platinum on an acidic support. Carbon monoxide is removed from a mixture Support preferably consists of alumina. thereof with ethylene and oxygen by passing the mixture over a rhodium-containing catalyst at 25-15oOC. The catalyst is preferably rhodium Dehydrogenation of Alicyclic Alcohols on activated alumina. Another platinum group ENGELHARD INDUSTRIES INC. British Patent metal, e.g. platinum, may also be included. 849,135 An alicyclic alcohol is dehydrogenated to an Electrical Contacts alicyclic ketone by passing the alcohol at a NORTON GRINDING WHEEL co. LTD. British Patent pressure from subatmospheric to atmospheric 847,200 over a catalyst consisting of ruthenium supported For the purpose of inhibiting the detrimental on carbon preferably at a temperature of 50- effects of disruption at the points of contact, 700°C.
Platinum Metals Rev., 1961, 5, (l), 3840 38 Nitrocy clododecanes Purification of Waste Gases STUDIENGESELLSCHAFT KOHLE m.b.H. British ENGELHARD INDUSTRIES INC. British Patent Patent 849,237 849,842 A palladium-barium sulphate catalyst is used in Waste gases containing oxides of nitrogen are a process for making the oxime of cyclodode- purified by contacting the gases, mixed with a canone by mild selective reduction of aci-nitro- gaseous hydrocarbon fuel, with a rhodium- or cyclododecane. palladium-containing catalyst at at least 690°F. The catalyst may consist of palladium, palladium Electrical Resistance Element and rhodium, or palladium and/or rhodium BECKMAN INSTRUMENTS INC. British Patent mixed with another platinum group metal. An 849,305 alumina support is used. A resistance element consists of a high tempera- ture resistant base on which is fired a layer of Photographic Screens resistance material composed of a minor amount GRATICIJLES LTD. British Patent 850,047 of one or more noble metals and a major amount A graticule or half-tone or gravure screen is of non-absorptive, electrically non-conductive made by forming a photographic image thereof binder material of glass of lower melting point of a platinum group metal in a collodion emulsion than the metal, the metal being finely divided and on a glass support, treating it with an aqueous dispersed throughout a continuous phase of solution of a soluble salt of tin, bismuth or lead solidified glass. The metal, which may be platin- and burning off the collodion. um, rhodium or palladium, constitutes 1-16% by weight of the resistance material. Hydrogen Gauges WESTINGHOUSE ELECTRIC COW. British Patent Chlorination of Hydrocarbons 850,064 BADISCHE ANILIN & SODA PABRIK A.G. British A hydrogen gauge includes a first conductor, the Patent 849,434 electrical resistance of which changes in response Chlorination of a hydrocarbon or a partly hydro- to changes in environmental hydrogen concentra- genated derivative thereof is effected by allowing tion, a second conductor exposed to the same chlorine to act on it in the gas phase at a tempera- environment, the resistance of which is not ture at or above its boiling point up to about affected thereby, but having the same tempera- 400°C in the presence of a catalyst containing a ture coefficient of resistance as the first con- halide of platinum, palladium, iridium or rhodium. ductor, both conductors being insulated from one another and means for measuring the elec- Magnet Alloys trical resistance of each conductor or the differ- JOHNSON, MATTHEY & co., LTD. British Patent ential resistance between them. The first con- 849,505 ductor is formed of palladium and the second of A cobalt-platinum alloy (17-27% cobalt) is heat- platinum. treated to produce permanent magnet properties at a temperature to produce disordering within Electrical Contacts the alloy, followed by quenching to an ordering METALS AND CONTROLS cow. British Patent temperature of 5oo-750°C, the alloy being main- 850,185 tained at this temperature for i-5 hours and One contact of a co-operating contact pair is finally quenched in water or allowed to cool in air. composed of an alloy of 60-80Y0 by wt. of palladium, 0.5-1.8% of nickel, cobalt or copper Electric Furnace Heater Elements or mixtures thereof and remainder silver. The JOHNSON, MATTHEY & CO., LTD. British Patent other contact consists of an alloy of 50-80% by 849,507 wt. of gold and balance silver. The combination An electric furnace heater element is made by is stated to have an average life of three times flame-spraying on to a platinum group metal or those at present used in voltage regulators. alloy wire or strip a thin layer of alumina of 2-50 thousandths of an inch. A platinum-rhodium Purification of Gas Mixtures (10-40%) alloy is used. IMPERIAL CHEMICAL INDUSTRIES LTD. British Patent 850,760 Spinning Nozzles The amount of methyl-acetylene in propylene- W. C. HERAEUS G.m.b.H. British Patent 849,840 rich gas is decreased by passing the gas, together A spinning nozzle is made of an alloy of palla- with hydrogen, over a catalyst comprising dium and I-30% ruthenium, up to 15y0 of the 0.01% to 0.1% of palladium on gamma alumina. palladium being replaceable by another platinum The catalyst is made by precipitating aluminium group metal. Ex: (I) 90% Pd, 10% Ru; (2) 90% hydroxide from aluminium nitrate by addition of Pd, 5% Ru and 5% Ir; (3) 85% Pd, 5% Ru and aqueous ammonia, separating, drying, calcining 10% Ir; (4) 85% Pd, 10% Ru and 5% Rh. and pelleting to give pellets of gamma alumina Heat-treatment is stated to increase the hardness. and then impregnating them with an aqueous
Platinum Metals Rev., 1961, 5, (l), 39 solution of an appropriate palladium salt, followed amount to give the required amount of platinum, by heating in hydrogen. See also No. 850,761 drying and calcining. Impregnation is effected covering the production of propylene free from in the presence of an aqueous solution of 'J. methyl acetylene. halogen-containing aliphatic carboxylic acid having 2-5 carbon atoms in the molecule and an Alloy for Spinning Nozzles ionisation constant greater than IO-~ at 25°C in DEUTSCHE GOLD-UND-SILBER-SCHEIDEANSTALT a molar ratio to alumina of o.mr-o.05. German Patent 1,075,838 A spinning nozzle is formed of an alloy com- Catalysts posed of more than 32%, up to 93%, platinum, STANDARD OIL co. U.S. Patent 2,950,243 0.05-294, preferably 0.25-1 96, rhenium and re- A hydroforming process is carried out with a mainder gold. platinum-alumina catalyst prepared by forming a m:ixture by commingling an alumina hydrosol Palladium Alloy for Spinning Nozzles with a solution consisting of water, ammonium W. C. HERAEUS G.m.b.H. German Patent 1,077,434 hydroxide, or a water-soluble amine or a quater- The palladium- and iridium-containing alloy for nary ammonium hydroxide, and a water-miscible making spinning nozzles for the production of oxygen-containing organic solvent (an alkyY artificial fibres, according to German patent No. alcohol, acetone, an alkyl glycol or an alkyl 1,010,742, is modified so as to contain from 7:/; ether). Sufficient alkaline substance is used to to less than 15% iridium, j-30:/~, preferably adjuirt the pH of the mixture to 8.5-12; the 10-2 j %, rhodium and remainder palladium. solvmt comprising 10-50Y; by vol. of thc mix- ture. The mixture is held at 50-250"F for over Alloy for Electrical Contacts I hour, whereby the alumina present is con- verted to a filterable slurry of solid hydrous W. C. HERAEUS G.m.b.H. German Patent 1,077,435 alumina from which the alumina is separated A rhodium-nickel alloy containing 10-25 :L, and dried to a volatile content of 15-500& wet preferably 12-21 24, nickel, remainder rhodium, basis. The dried alumina is then impregnated is used for making electrical contacts, particularly with an aqueous chloroplatinic acid solution to a telephone selector contacts, platinum level of o.o5-10& by wt., based on dry A1,0,, dried and calcined. Hydrocracking Catalyst PHILLIPS PETROLEUM CO. U.S. Patent 2,946,739 Platinum Catalyst Wafra 400°F plus crude is hydrocracked at ESSO RESEARCH & ENGINEERING GO. US. Patent 750-85ooF, a pressure of 500-3000 psig and 2,95'W59 a liquid hourly space velocity of 0.1-1, using In the manufacture of an alumina supported 500-5000 cu. ft of hydrogen per barrel of oil platinum catalyst activated by heat-treatmentJ with a catalyst containing 0.1-1 wt.Yn of rhodium, the impregnated alumina is heatcd at at least 1-5 wt.:a of cobalt, 3-10 wt.u& of molybdenum, 900°F for a suitable time to form platinum metal on an alumina support. crystallite particles from the impregnating solu- tion, the heat-treatment being controlled to keep Selective Hydrogenation and Catalyst the particles from growing to a crystallite size therefor of ovI:r SOB,as shown by an X-ray test. CHEMETRON CORP. U.S. Patent 2,946,829 A catalyst for the seleaive hydrogenation of Conversion of Petroleum highly unsaturated hydrocarbons in a concen- UNION CARBIDE CORP. U.S. Patent 2,953,509 trated olefin stream is composed of o.or-o.09 wt.% of palladium metal on an alumina support, The viscosity and boiling range of petroleum are the catalyst having a pore volume of surface reduced by gamma irradiating the petroleum with pores of a threshold diameter not over 8008, about IOO million rantgens from a cobalt 60 bomb in the range of 0.6-0.4 cc/g and the palladium in the presence of a catalyst of platinum oxide being mainly concentrated in the external portions or palladium chloride. of the carrier. Preparing Beta-Phenyl-Ethylchlorosilanes CatdlySt UNION CARBIDE CORP. U.S. Patent 2,954,390 STANDARD OIL 60. U.S. Patent 2,948,672 Beta-phenyl-ethylchlorosilanes are produced by A hydrocarbon conversion process is carried out forming a mixture of styrene, a chlorosilane con- using a platinum-alumina hydroforming catalyst taining at least one hydrogen atom bonded to of improved activity containing 0.05-1 04 by wt. silicon, tetrahydrofuran in amount from 0.5 to of platinum, based on dry A1,0,, uniformly dis- 10 times the weight of styrene, and a catalyst tributed in it. The catalyst is prepared by consisting of chloroplatinic acid, platinum or impregnating solid hydrous alumina containing platinum on an inert carbon-free carrier, and 1-300; by wt. of combined water, dry basis, heating the mixture to cause addition of the with a solution of a platinum compound in chlorosilane to the styrene.
Platinum Metals Rev., 1961, 5, (l), 40