STUDIES ON THE OXYGEN POTENTIALS OF (UYTH1-Y)O2-SOLUTIONS(X SOLID)

The oxygen potentials of (UyTh1-y)O2+x solid solutions (y varying from 0.54 to 0.9) were measured by using a gas equilibration method, emplo ying H-2 + H2O, CO + CO2 and CO2 + H-2 gas mixtures. The measurements covered an oxygen potential range of -450 to -220 kJ mol(-1) and the O /M ratios varied between 2.000 and 2.035. The attainment of equilibriu m as well as the actual oxygen potentials realised in the gas mixture were determined by using an oxygen probe based on calcia stabilized zi rconia solid electrolyte. The results of the measurements indicate tha t the oxygen potentials of (UyTh1-y)O2+x solid solutions are a functio n of both the uranium valence and the U/(U + Th) ratio. Partial molar enthalpies and entropies of solution of oxygen in the solid solutions were also computed from the temperature dependance of the oxygen poten tials. (C) 1997 Elsevier Science B.V.