The thermodynamic properties of silver-gold alloys

Abstract

Correlating functions have been developed for the purpose of evaluating thermodynamic data on binary alloy systems, and these functions have been applied to the extensive published data on the Ag-Au system. Several discrepancies in the data became evident, and calorimetric investigations using a liquid tin solution calorimeter were made on solid Ag-Au alloys to resolve these inconsistencies. The heat of formation measurements were found to fit the sub-regular solution model suggested by Hardy but with negative deviations from ideality. On this basis the properties of the solid alloys were defined, and these properties combined with the liquidus of the phase diagram aided in the choice of the best representation of the liquid alloy properties. The solidus calculated from the selected data lies much closer to the liquidus than is generally indicated in phase diagrams. Strain energy is a minor factor in solid Ag-Au alloys, and it is suggested that the apparent variation in the exchange interaction energy of nearest neighbor atoms with composition results from changes in the distribution of quantum states for the cohesive electrons.