Co-precipitation or co-reduction of two or more platinum metals from mixed solutions of their salts has been widely practised in the past but there are few records of any study of the structure of the resulting powders.

In a letter to Nature (1964, 203, 857)Eugene L. Holt, of Esso Research & Engineering Co, reports on the examination of some platinum-gold, platinum-iridium and palladium-gold powders made by reducing mixed 0.5M chloride solutions with 1.85M sodium borohydride solution at50°C. The powders precipitated from platinum-gold solutions had compositions corresponding closely to those of the solutions from which they were formed and X-ray analyses indicated them to have the structure of a uniform solid solution of the two metals. Solid solution powders containing 40, 60 and 80 per cent of gold were made in this manner.

Powders precipitated from platinum-iridium solutions, however, contained appreciably less iridium than the solutions from which they were precipitated and the powders from solutions containing 80 per cent of iridium, for example, showed two sets of X-ray patterns indicating the presence of a platinum-rich alloy and an iridium-rich alloy.