Phase stability investigations of the palladium-cadmium system: part i. thermodynamic studies

The vapor pressure of cadmium in palladium-cadmium alloys was determined between 830 and 1350 K and between 33 and 65 at. pct Cd by two different isopiestic methods. An analysis of the resulting partial molar quantities of Cd in the β₁-phase in terms of Chang's theoretical model for the Ll₀-structure yielded a disorder parameter α= 7 × 10^-4 and a second-nearest neighbor parameter η = 0.75 at 1073 K. Available literature data for the thermodynamic activities of Cd in the α-phase (solid solution of Cd in Pd) were evaluated using a subregular solution model. By combining these values with the present experimental data, all relevant partial and integral thermodynamic properties for the α- and β₁-phase could be derived. At the stoichiometric composition of the β₁-phase, values of ΔG = -38.0 kJ(g-atom)^-1 and ΔH = -53.7 kJ(g-atom)^-1, referred to Pd(s) and Cd(l), were obtained for a temperature of 1073 K. Y. MAA, formerly Graduate Student, Materials Department, University of Wisconsin-Milwaukee Y. A. CHANG, formerly Professor of Materials Engineering and Associate Dean for Research, Graduate School, University of Wisconsin-Milwaukee W. SCHUSTER, formerly a Postdoctoral Research Associate, Materials Department, University of Wisconsin-Milwaukee.