Oxidation-reduction properties of mixed oxides in lanthanum-uranium-oxygen system.

Abstract

The oxidation-reduction properties and the phase relations of mixed oxides in the system La-U-O were examined by means of thermogravimetry and X-ray diffraction method. The O/M ratios of the mixed oxides LayU1-y O2±x, prepared at 1,650°C in vacuo by the reaction of La2O3 and UO2, were expressed as 2–0.5 y except 0.2≤y≤0.4. The oxides were the single fluorite phase at y0.7. These oxides of 0.2≤y≤0.6 were oxidation-susceptible in air even at room temperature. For the oxides heated or prepared in air at 1,000°C, the O/M ratio vs. y relationship was composed of three line with the turning points, 2.26 at y = 0.27 and 1.92 at y = 0.70. The fluorite phase was observed in the regions of 0.3≤y≤0.45 and 0.7≤y≤0.9, and the rhombohedral phase was in −0.55≤y-0.7. The O/M ratios of the oxides reduced with hydrogen were nearly 2 at y ≤0.2 and decreased with increasing y at y >0.2. The oxide of y =0.5 showed the curious property: The O/M ratio had a minimum when the oxide reduced with hydrogen was oxidized in air.