Thermodynamic properties of the O–U system. II – Critical assessment of the stability and composition range of the oxides UO2+x, U4O9−y and U3O8−z

The published data concerned with the determination of the composition ranges of uranium oxides, UO2+x, U4O9−y and U3O8−z, which have been determined using thermogravimetric, X-ray diffraction and electrochemical techniques are critically assessed. U4O9 and U3O8 have quite small domains of composition and the assessment of such data has carefully considered the uncertainties in the experimental determinations. In addition, the thermodynamic properties of U4O9 and U3O8, enthalpies of formation and transformation, entropies, and thermal capacities are analyzed and selected to build a primary data base for compounds.