Identification of iron oxide impurities in earliest industrial-scale processed platinum

A detailed investigation of iron oxide inclusions in a 19th century Russian platinum coin is presented. Such coins represent the products of the first industrial-scale purification of platinum metal. The processed metal is far from pure, however, and two types of iron oxide inclusions are identified by electron microprobe and Raman microscopy. The results show that the inclusions mainly consist of magnetite and haematite. The Raman band of magnetite at 668 cm−1 was found to shift to about 680 cm−1 with an increase in the average oxidation state of the iron. It is concluded that the iron oxides are formed during the heating of the platinum metal powder in the manufacturing process.