THERMODYNAMIC MODELING OF EQUILIBRIUM SUBSOLIDUS PHASE-RELATIONS IN THE AG-PD-O2 SYSTEM

From literature values of the thermodynamic activity of Pd in Ag/Pd solid solutions and the Gibbs free energy of formation of PdO as a function of temperature, subsolidus equilibrium phase relations in the Pd-Ag-O2 system have been calculated and compared to results from high-temperature XRD analyses. The developed model takes into account the nonideal activity of Pd in Ag/Pd solid solutions and confirms that increasing the Ag/Pd ratio or decreasing the oxygen activity decreases the temperature at which PdO reduces. It also accurately predicts that the temperature range over which the PdO reduces is broad for Ag-rich compositions, and narrow for Pd-rich compositions.