THERMODYNAMICS OF ALLOYS. STUDIES OF PALLADIUM-COPPER-SILVER AND PALLADIUM-INDIUM ALLOYS

Reversible galvanic cells employing zirconia-caloia solid electrolytes were used to investigate the thermodynamic properties of the face- centered cubic solid solutions of the ternary system palladium-copper-silver. Measurements were made between 870 and 1250 K over a wide range of compositions and the data used to calculate activities of copper and integral free energies of formation of the entire range of ternary alloys at 1000K. Tin solution calorimetry was used to measure the heats of formation of solid palladium-indium alloys. Values for the palladium-rich f.c.c. solid solution and for the intermediate phases Pd3In, Pd2In, Pd5In3, PdIn, Pd2In3 and PdIn3 were obtained. The system is extremely exothermic in character. This is considered to be due to electron transfer to the subvalency transition metal electron levels which contributes a large heteropolar component to the bonding in the intermediate phases. The phase PdIn has been investigated in detail; the occurrence of defect structures is indicated. New measurements of the heats of solution of palladium and indium in liquid tin were obtained.