High-Temperature Thermodynamic Properties of Oxygen-Deficient Urania

Abstract

Measurements of oxygen partial pressures over oxygen-deficient urania compositions, including the difficult region very close to stoichiometry, have been made in the temperature range 2080–°2705°K. The transpiration method was used with flowing H2–H2O mixtures in order to fix the oxygen potential of the carrier gases. The shape of the isotherms are qualitatively in accord with expectations based on defect theory. At the lower temperatures (2080°–2390°K), the isotherms exhibit a sharp increase in oxygen partial pressure near the stoichiometric composition. At the higher temperatures (2495°–2705°K), large deviations from the stoichiometric composition are accompanied by relatively small changes in oxygen partial pressures. Relative partial molar free energies, entropies, and enthalpies of solution were calculated and discussed in relation to defect theory.