Nineteenth Century Platinum Coins an EARLY INDUSTRIAL USE of POWDER METALLURGY by Hans-Gert Bachmann and Hermann Renner Degubsa AG, Frankfurt Am Main, West Germanv
Nineteenth Century Platinum Coins AN EARLY INDUSTRIAL USE OF POWDER METALLURGY By Hans-Gert Bachmann and Hermann Renner Degubsa AG, Frankfurt am Main, West Germanv Powder metallurgy is the metallurgist’s platinum sponge which he was able to shape answer to the production of ductile metals of into objects, such as crucibles. This process high melting point by methods differing from remained in use until I 8 10. conventional melting and casting. The history In the meantime Wollaston produced the first of platinum, extensively and vividly recorded malleable platinum by a “wet” method. As early by McDonald and Hunt (I), gives examples of as I 80 I he solved the problem of how to get rid how platinum was worked into objects from of the impurities normally accompanying earliest times onwards. However, the first real naturally occurring placer platinum. By careful melting of platinum was achieved only as late as adjustment of the proportions of hydrochloric I 782, when Lavoisier successfully reached the and nitric acid in aqua regia, and later by using temperature of 1769OC necessary to melt this more dilute mixtures, he separated platinum metal on a very small scale with the aid of an from its associated palladium and rhodium. The oxygen torch (2). Three years earlier, Franz solution, containing only hexachloroplatinate, Karl Achard (1753--1821), whose contributions H2FtCI6, was subsequently treated with sal to metallurgy have only recently been fully ammoniac, resulting in a precipitate of realised (3), made use of the property of ammonium hexachloroplatinate, (NH4)dPtC16]. platinum to form low-melting point alloys with On heating this decomposed to platinum elements such as phosphorus, mercury and sponge, and thus an economical method was arsenic.
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