Thermodynamic properties of liquid silver-gallium alloys determined from e.m.f. and calorimetric measurements

The thermodynamic properties of the liquid Ag-Ga alloys were determined using e.m.f. and calorimetric methods. In the e.m.f. method, solid oxide galvanic cells were used with zirconia electrolyte. The cells of the type W, AgxGa(1-x), Ga2O3//ZrO2 + (Y2O3)//FeO, Fe, W were used in the temperature range from 1098 K to 1273 K. and in the range of mole fraction from x(Ga) = 0.1 to x(Ga) = 1.0. At first, the Gibbs free energy of formation of pure solid gallium oxide, Ga2O3, from pure elements was derived. Using values of the measured e.m.f. for the cell with x(Ga) = 1.0, the following temperature dependence was obtained: Delta fG(m)degrees,Ga2O3 (+/- 4 kj . mol(-1) J) = -1061.7235 + 0.2899T/K. Next, the activity of the gallium was derived as a function of the alloy composition from the values of the measured e.m.f. Activities of silver were calculated using the Gibbs-Duhem equation. The drop calorimetric measurements were carried out at two temperatures, viz. 923 K and 1123 K, using a Setaram MHTC calorimeter. Integral enthalpies of mixing of liquid binary alloys were determined at those temperatures. Finally, thermodynamic properties of the liquid alloys were described with the Redlich-Kister equation using ThermoCalc software. (C) 2010 Elsevier Ltd. All rights reserved.