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.

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