Phase relations in the Ru-Ir-O2 system in air

Abstract

The equilibrium phase relations were determined in an air environment for the system Ru-Ir-O2. In air Ru oxidizes at moderate temperatures, to form RuO2, which in turn dissociates at 1405 ?C. Similarly Ir oxidizes to form IrO2 and dissociates at 1020 ?C. The dissociation of RuO2 and IrO2 are reversible processes. A ternary equilibrium phase diagram was constructed indicating selected oxygen reaction lines and isotherms. A binary representation of the Ru-lr-O2 system in air is given. Up to 1020 ?C, RuO2 reacts with IrO2 to form a complete solid solution series having the rutile-type structure. At 1345 ?C three solid phases, rutiless, Russ, and Irss, exist in equilibrium for compositions between approximately 2 and 45 mole percent IrO2. Above 1405 ?C dissociation is complete for all compositions and the phase relations are represented by the Ru-Ir system. At 1500 ?C solid solution of Ru and Ir occurs with the addition of up to 45 mole percent Ir and up to 44 mole percent Ru, respectively.