Thermal decomposition of (UO2)O2(H2O)2•2H2O: Influence on structure, microstructure and hydrofluorination

The thermal decomposition of uranyl peroxide tetrahydrate, (UO2)O-2(H2O)(2)center dot 2H(2)O, was studied by combining high temperature powder X-ray diffraction, scanning electron microscopy, thermal analyses and spectroscopic techniques (Raman, IR and H-1 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)O-2(H2O)(2)center dot 2H(2)O, sulfate or nitrate, has a strong influence on the peroxide thermal behavior and morphology. The decomposition of (UO2)O-2(H2O)(2)center dot 2H(2)O ex sulfate is pseudomorphic and leads to needle-like shaped particles of metastudtite, (UO2)O-2(H2O)(2), and UO3-x(OH)(2x)center dot 2H(2)O, an amorphous phase found in air in the following of (UO2)O-2(H2O)(2) dehydration. (UO2)O-2(H2O)(2)center dot 2H(2)O and the compounds resulting from its thermal decomposition are very reactive towards hydrofluorination as long as their needle-like morphology is kept. (C) 2016 Elsevier B.V. All rights reserved.