Low-Temperature Oxidation of Fine UO2 Powders: A Process of Nanosized Domain Development

The nanostructure and phase evolution in low-temperature oxidized (40–250 °C), fine UO2 powders ( 1) were observed. Oxidation involves formation of higher uranium oxides in nanodomains near the grain surface which, initially, have a disordered defect structure (“disordered U4O9”). As oxidation progresses, domain growth increases and the long-period modulated structure of U4O9 develops (“ordered U4O9”). A similar mechanism is understood to happen also in U3O7–z .