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Inorganic Chemistry 46 (2007) 10390-10399
Hydrothermal Method of Preparation of Actinide(IV) Phosphate Hydrogenphosphate Hydrates and Study of Their Conversion into Actinide(IV) Phosphate Diphosphate Solid Solutions
N. Dacheux1, S. Grandjean, J. Rousselle, N. Clavier

Several compositions of Th2-x/2AnIVx/2(PO4)2(HPO4)·H2O (An = U, Np, Pu) were prepared through hydrothermal precipitation from a mixture of nitric solutions containing cations and concentrated phosphoric acid. All the samples were fully characterized by X-ray diffraction, UV-vis, and infrared spectroscopies to check for the existence of thorium-actinide(IV) phosphate hydrogenphosphate hydrates solid solutions. Such compounds were obtained as single phases, up to x = 4 for uranium, x = 2 for neptunium, and x < 4 for plutonium, the cations being fully maintained in the tetravalent oxidation state. In a second step, the samples obtained after heating crystallized precursors at high temperature (1100 C) were characterized. Single-phase thorium-actinide(IV) phosphate-diphosphate solid solutions were obtained up to x = 0.8 for Np(IV) and x = 1.6 for Pu(IV). For higher substitution rates, polyphase systems composed by -TAnPD, An2O(PO4)2, and/or -AnP2O7 were formed. Finally, this hydrothermal route of preparation was applied successfully to the synthesis of an original phosphate-based compound incorporating simultaneously tetravalent uranium, neptunium and plutonium.
1 :  IPNO - Institut de Physique Nucléaire d'Orsay