Platinum Metals Review - Volume 22, Issue 3, 1978

The high melting point of platinum makes stringent demands on the other materials involved when it is investment cast. However, by careful selection of refractories, it has been possible to successfully cast small batches of platinum items for many years. In view of the renewed interest in platinum jewellery it has now become desirable to increase the efficiency of the process, and a number of new platinum alloys have been developed for this purpose. In some the alloying elements are those traditionally associated with platinum but in others more unusual additions are used to produce alloys with a significantly lower casting temperature.

Iridium reacts with oxygen at high temperatures forming volatile oxides, the evaporation of which considerably increases the iridium losses in oxygen-containing atmospheres, when compared with high-vacuum conditions. This paperdescribes investigations carried out to determine the metal losses from polycrystalline iridium discs, by means of a magnetic suspension balance, at low pressures and high temperatures. The results are presented and discussed, and a strong temperature and pressure dependence is noted.

Examination of the laboratory notebooks of W. H. Wollaston makes possible a complete reconstruction of his platinum researches, and valuable insights into the financial details of his platinum business, originally in partnership with Smithson Tennant, may be obtained. The leading role played by Wollaston in both the research and marketing aspects of the business is confirmed. Although the use of platinum for laboratory ware and vessels for the concentration of sulphuric acid were important applications, the gunmakers provided the greatest market for malleable platinum over the years 1808 to 1820. The business ground to a halt in 1820 when Wollaston could no longer procure supplies of crude platinum.