Thermodynamic investigation of antimony + oxygen and bismuth + oxygen using solidstate electrochemical techniques

Abstract

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 Y 2O 3) cylindrical tube was used as the electrolyte. The standard Gibbs energies of formation of the oxides Sb 2O 3 and Bi 2O 3 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 ΔG f o: ΔG o f(Sb 2O 3)/kcal th mol −1 = (−109.1 + 0.020T/K) ± 0.4; 1073 K ⩽ T ⩽ 1223 K. ΔG o f(Bi 2O 3)/kcal th 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) kcal th K −1 mol − /RT}; s(O in Bi) = 0.2981 exp {−(16.39 ± 0.66) kcal th K −1 mol − /RT}. These experimental results are compared with previous literature values.