Thermodynamic properties of Thsub(0.80)Usub(0.20)Osub(2+x) solid solution

Oxygen-potential (Δanti Gsub(O2)) measurements employing a thermogravimetric method have been performed for Thsub(0.80)Usub(0.20)Osub(2+x). A complete set of data is presented at 1273-1473 K in the ranges 2.000 < or approx. O/M < or approx. 2.024 and -95 < or approx. Δanti Gsub(O2) < or approx. -32 kcal/mol. Partial molar entropies and enthalpies of solution of oxygen in the mixed oxide were derived from the temperature variation of Δanti Gsub(O2). Vapor pressures over Thsub(0.80)Usub(0.20)Osub(2+x) at 2000 at 2300 K were calculated from our experimental Δanti Gsub(O2) data and the known free energies of formation for gaseous and condensed oxides. It is predicted that with an increase in O/M ratio the vapor pressure of UO3(g) increases rapidly while maintaining an extremely lower pressure of ThO2(g). (orig.)