UO₂ oxidation at low temperature

The oxidation of UO_2,10 and of UO_2,40 oxide has been studied, mostly in air and at 120 degrees. In the initial stages, the oxygen fixation followed by weighting is partly in an undetectable form. the crystallographic parameters of the starting material remaining unchanged at the oxidative titration. When the quantity of fixed oxygen increases, an α quadratic phase appears with substantially constant parameters (a = 5.436, c/a = 0.991) and whose titre is a little higher than UO_{2, 32}. This oxide is distinct from the γ quadratic phase previously described. Contrary to previous indications, the composition of the latter, UO_{2 , 40} is fixed for temperatures lower than 400 deg. Its parameters are a = 5,364, c/a = 1,031. The α cubic phase, previously reported, is metastable with respect to UO₂ + U₄O₉; this oxide constitutes, above 700 deg., the limit of a homogeneity range which extends towards the lower titers, reaching UO_{2 , 21} at 1000 deg. The author discusses his results and those published earlier. Reprint of a paper published in 'Bulletin de la Societe Chimique de France', no. 1712, 1. quarter 1953.