ACTIVITY COMPOSITION RELATIONS IN PLATINUM CHROMIUM AND PLATINUM VANADIUM ALLOYS AT 1500-DEGREES-C

Activity-composition relations in Pt-Cr and Pt-V alloys at 1500-degrees-c were determined from equilibration of these alloys with Cr2O3 and V2O3, respectively, in CO2-H2 atmospheres of known oxygen partial pressures, followed by quenching to room temperature and microprobe analyses of the quenched alloys. The activities of Cr and V were calculated from known standard free energies of formation of Cr2O3 and V2O3 from the respective elements, and the oxygen pressures were calculated from the C-H-O equilibrium in the gas phase. Both alloy systems show strong negative deviations from Raoultian behavior.