Thermal decomposition of (UO2)O2(H2O)2·2H2O: Influence on structure, microstructure and hydrofluorination
Résumé
The thermal decomposition of uranyl peroxide tetrahydrate, (UO2)O2(H2O)2·2H2O, was studied by combining high temperature powder X-ray diffraction, scanning electron microscopy, thermal analyses and spectroscopic techniques (Raman, IR and 1H NMR). In situ analyses reveal that intermediates and final uranium oxides obtained upon heating are different from that obtained after cooling at room temperature and that the uranyl precursor used to synthesize (UO2)O2(H2O)2·2H2O, sulfate or nitrate, has a strong influence on the peroxide thermal behavior and morphology. The decomposition of (UO2)O2(H2O)2·2H2O ex sulfate is pseudomorphic and leads to needle-like shaped particles of metastudtite, (UO2)O2(H2O)2, and UO3-x(OH)2x·zH2O, an amorphous phase found in air in the following of (UO2)O2(H2O)2 dehydration. (UO2)O2(H2O)2·2H2O and the compounds resulting from its thermal decomposition are very reactive towards hydrofluorination as long as their needle-like morphology is kept.
Mots clés
Spectroscopic technique
Shaped particles
Powder x ray diffraction
In-situ analysis
High temperature
amorphous phase
X ray diffraction
Needles
Oxidation
Peroxides
Scanning electron microscopy
Thermoanalysis
Thermolysis
Uranium
Uranium alloys
Uranium compounds
Thermal behaviors
Uranium oxides
decomposition