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Platinum Metals Rev., 1965, 9, (2), 56

Galvanic Couples with Platinum Metals

Surface Poisoning By Intermetallic Compounds

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There is a fascination in observing how a skilled experimenter learns to exploit little known phenomena. For instance, the seasoned analytical chemist knows instinctively that if a sample of tin is slow to dissolve in acid the reaction can be made to proceed simply by placing a clean platinum wire through the liquid into contact with the tin. Some years ago, Buck and Leidheiser (Nature, 1958, 181, 1681) observed that some platinum metals were more effective than others in catalysing reactions of this type, the relative effect of each platinum metal depending on the particular base metal with which it was coupled.

They now report (Nature, 1964, 204, 177) some further observations on platinum metal and base metal couples, both in direct contact and (connected externally) separated by a porous diaphragm. The results indicate that the behaviour of the platinum metals is influenced by films of intermetallic compounds which form on the surface. When used to catalyse the dissolution of tin, for instance, platinum and iridium are not seriously poisoned, but palladium rapidly loses its catalytic powers, and X-ray diffraction analyses show the formation on its surface of PdSn4 and also of an unidentified compound.

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