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Synthesis and characterization of low-temperature precursors of thorium–uranium (IV) phosphate–diphosphate solid solutions

Abstract : Several compositions of new precursor of thorium–uranium (IV) phosphate–diphosphate solid solutions (Th4−xUx(PO4)4P2O7, called β-TUPD) were synthesized in closed PTFE containers either in autoclave (160 °C) or on sand bath (90–160 °C). All the samples appeared to be single phase. From XRD data and TEM observations, the diffraction lines matched well with that of pure thorium phosphate–hydrogenphosphate hydrate (TPHPH), Th2(PO4)2(HPO4) · H2O, which confirmed the preparation of a complete solid solution between pure thorium and uranium (IV) compounds. TGA/DTA experiments showed that samples of thorium–uranium (IV) phosphate–hydrogenphosphate hydrate (TUPHPH) prepared at 150–160 °C were monohydrated leading to the proposed formula Th2−x/2Ux/2(PO4)2(HPO4) · H2O. The variation of the XRD diagrams versus the heating temperature showed that TUPHPH remained crystallized and single phase from room temperature to 200 °C. After heating between 200 °C and 800 °C, the presence of diphosphate groups in the solid was evidenced. In this range of temperature, the solid was transformed into the low-temperature monoclinic form of thorium–uranium (IV) phosphate–diphosphate (α-TUPD). This latter compound finally turned into well-crystallized, homogeneous and single-phase β-TUPD (orthorhombic form) above 930–950 °C for x values lower than 2.80. For higher x values, a mixture of β-TUPD, α-Th1−zUzP2O7 and U2−wThwO(PO4)2 was obtained. By this new chemical route of preparation of β-TUPD solid solutions, the homogeneity of the samples is significantly improved, especially considering the distribution of thorium and uranium.
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Submitted on : Monday, January 3, 2005 - 12:26:41 PM
Last modification on : Friday, July 16, 2021 - 3:35:04 AM

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Nicolas Clavier, N. Dacheux, P. Martinez, V. Brandel, Renaud Podor, et al.. Synthesis and characterization of low-temperature precursors of thorium–uranium (IV) phosphate–diphosphate solid solutions. Journal of Nuclear Materials, Elsevier, 2004, 335, pp.397-409. ⟨10.1016/j.jnucmat.2004.07.048⟩. ⟨in2p3-00023435⟩

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