ACTIVITY OF ZINC IN MOLTEN GOLD AND GOLD-COPPER ALLOY

The activities of Zn in dilute solution with molten Au and Au-Cu alloy have been measured by the use of an isopiestic method at 1423 K, and the first and second order interaction parameters between Zn and Cu in molten Au have been determined. Additions of Cu to Au-Zn binary alloy increase the activity of Zn. The activities of Zn in the Au-Cu-Zn ternary molten alloys are well expressed by Wagner's relation taken into account the second order terms, in the composition range N(Zn) + N(Cu) less-than-or-equal-to 0.10. It has been demonstrated that the quadratic formalism proposed by Darken is valid for this system in the composition range, N(Cu) less-than-or-equal-to 0.08 and N(Zn) < 0.07. Activity coefficient of Zn at infinite dilution of Zn in Au-Cu binary solvent varies with N(Au)/N(Cu) smoothly, and seems to be qualitatively in accordance with the prediction from the equation formulated by Richardson.