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

Journal Contribution - Journal Article

The nanostructure and phase evolution in low-temperature oxidized (40–250 °C), fine UO2 powders (<200 nm) have been investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The extent of oxidation was also measured via in situ thermogravimetric analysis. The oxidation of fine powders was found to proceed differently as compared to oxidation of coarse-grained UO2. No discrete surface oxide layer was observed and no U3O8 was formed, despite the high degree of oxidation (up to O/U = 2.45). Instead, nanosized (5–15 nm) amorphous nuclei (interpreted as amorphous UO3), unmodulated and modulated U4O9, and a continuous range of U3O7–z phases with varying tetragonal distortion (c/a > 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.
Journal: Inorganic Chemistry
ISSN: 0020-1669
Issue: 8
Volume: 55
Pages: 3915 - 3927
Publication year:2016
BOF-keylabel:yes
IOF-keylabel:yes
BOF-publication weight:3
CSS-citation score:2
Authors from:Government, Higher Education
Accessibility:Closed