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Uranium trioxide and the UO3 hydrates

1964; Pergamon Press; Volume: 26; Issue: 11 Linguagem: Inglês

10.1016/0022-1902(64)80007-5

1878-1225

V.J. Wheeler, R.M. Dell, Elizabeth Wait,

Radioactive contamination and transfer

The preparations and characterization of five crystalline polymorphs of UO3 (α, β, γ, δ, ζ) as well as of amorphous UO3 and UO2·9 are described. A detailed X-ray study has been made of phases formed during the thermal decomposition of amorphous and β-UO3. Amorphous UO3 loses oxygen to form UO2·94 at 450°C; this may exhibit either the hexagonal structure of α-UO3 or the orthorhombic structure of UO2·9, depending upon the decomposition conditions. Further decomposition leads to U3O8 in air and UO2·6 in vacuum. β-UO3 decomposes directly to U3U8 or UO2·6. The UO3H2O system has been investigated and an attempt made to rationalise the hydrate phases described previously. Each of the above UO3 phases has been hydrated under a range of conditions, and five different hydrates have been identified crystallographically: UO3.2H2O, three forms of UO3.H2O, and UO3.0·5H2O. The decomposition of each has been studied and the UO3 products identified. The application of further experimental techniques (D.T.A., infra-red absorption) has revealed a still wider range of hydrates. In particular, a second dihydrate (β-UO3.2H2O), prepared from γ-UO3, has an X-ray pattern indistinguishable from that of α-UO3.2H2O but decomposes at a lower temperature and shows a distinct infra-red spectrum.