Thermodynamic properties of solid Pt-Mn, Pt-Cr, and Pt-Mn-Cr alloys at 1500 degrees C

Equations for the activity coefficients of manganese and chromium in platinum at 1500 degrees C were determined from activity-composition relations in the Pt-Mn, Pt-Cr, and Pt-Mn-Cr systems. This was done by equilibrating platinum wire with, respectively, MnO, Cr2O3, and an equimolar mixture of Cr2O3 and (Mn, Cr)(3)O-4, under oxygen partial pressures that ranged from 10(-6.5) to 10(-10.0) atm. It was found that equations for the activity coefficients can be represented by Darken's quadratic formalism. The experimental data confirmed that the Pt-Mn, Pt-Cr, and Pt-Mn-Cr alloys studied show strong negative deviations from ideality, as is expected from the respective phase diagrams.