Reactions of Oxygen with the Platinum Metals

In the second part of this survey of the oxidation of the platinum metals attention is given to the formation of solid oxide films on the more reactive metals ruthenium, rhodium, iridium and osmium. The films formed in air on these metals are thick enough to give tarnish colours at temperatures of 400 to 500°C, and they may be in equilibrium with an appreciable partial pressure of gaseous oxides at temperatures below that at which they decompose. Diagrams showing the solid (oxide and metal) phases and the vapour pressures of the gaseous oxide phases in equilibrium with one atmosphere of oxygen at temperatures up to about 1800°C are given for four of the platinum metals. A third part of this paper will deal with the oxidation of palladium.