Activity measurements of liquid Ag-Bi alloys by an EMF method using a zirconia electrolyte

The emf measurements of the following galvanic cells have been carried out to determine the standard free energy of formation of Bi₂O₃(s) and the thermodynamic quantities of liquid Ag-Bi alloys: -Pt/Ni(s), NiO(s) |ZrO₂(+ CaO) |Ag-Bi(1), Bi₂O₃(s)/Ir/Pt⊕ (for N_Bi = 0.20 approximately 0.90 at 886 to 1068 K), -Pt/Ni(s), NiO(s) |ZrO₂(+ CaO) |Bi(1), Bi₂O₃(s)/Ir/Pt⊕ (at 888 to 1065 K). The standard free energy of formation of Bi₂O₃(s) are determined as follows: ΔG°_Bi(2)O(3)(s)/J·mol^-1 = -582520 + 293.94T ± 530 between 888 and 997 K ΔG°_Bi(2)O(3)(s)/J·mol^-1 = -549700 + 261.06T ± 460 between 997 and 1065 K. The concentration dependence of activities of bismuth shows a positive moderate deviation from the Raoult's law. Activities of silver show both positive and negative deviations from Raoult's law. Our data for bismuth do not agree with the result by Gregorczyk but roughly do well with that by Aldred et al. and Predel et al. The order of magnitude of both activities and heats of mixing of IB metals (Cu, Ag and Au)-bismuth binary alloys in the intermediate composition range is approximately the same as that in the Periodic Table (i.e., Cu, Ag and Au). The activities and the heats of mixing of the Au-Bi alloys show small negative deviations and smaller exothermic values, respectively, over the whole concentration range. Such a affinity of Au-Bi alloys may be ascribed to the larger differences in the electronegativities in the gold alloys. In addition, the results of both activities and heats of mixing measurements in the liquid binary alloys composed of IB metals and bismuth and those composed of IB metals and other typical normal metals (i.e., Zn, Cd, Al, Ga, In, Sn and Sb etc.,) have been compared and discussed in connection with the electronic structure of the elements and with the alloy theory by Engel concerning the phase stability of solid solution between IB metals and typical normal metals.