THERMODYNAMIC INVESTIGATION OF ANTIMONY + OXYGEN AND BISMUTH + OXYGEN USING SOLID-STATE ELECTROCHEMICAL TECHNIQUES

Thermodynamic properties of Sb + O and Bi + O were investigated over the temperature range of 1073 to 1223 K using solid-state electrochemical techniques. The major techniques employed were potentiometric measurements to measure the cell e.m.f. and the oxygen potential, and coulometric titration to control composition. An yttria-stabilized zirconia (7 moles per cent of Y2O3) cylindrical tube was used as the electrolyte. The standard Gibbs energies of formation of the oxides Sb2O3 and Bi2O3 were measured over this temperature interval and the standard enthalpies and entropies of formation were calculated. A least-squares analysis of the results led to the following analytical representations for the standard Gibbs energies of formation ΔGfo: ΔGof(Sb2O3)/kcalth mol-1 = (-109.1 + 0.020T/K) ± 0.4; 1073 K ≤ T ≤ 1223 K. ΔGof(Bi2O3)/kcalth mol-1 = (-99.3 + 0.031T/K) ± 0.4; 1073 K ≤ T ≤ 1223 K. Coulometric-potentiometric titrations were used to measure the oxygen activity as a function of oxygen composition and the maximum solubility of oxygen. Least-squares analysis of the results produced the following expression for the maximum mole-fraction solubility s(O) of oxygen in the respective liquid metals: s(O in Sb) = 0.0367 exp {-(12.60 ± 0.68) kcalth K-1 mol- /RT}; s(O in Bi) = 0.2981 exp {-(16.39 ± 0.66) kcalth K-1 mol- /RT}. These experimental results are compared with previous literature values. © 1979.