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Characterization of the thorium phosphate-hydrogenphosphate hydrate (TPHPH) and study of its transformation into the thorium phosphate-diphosphate ($\beta$-TPD)

Abstract : The preparation of thorium phosphate-diphosphate (Th4(PO4)4P2O7, TPD) was developed through the precipitation of thorium phosphate-hydrogenphosphate hydrate (Th2(PO4)2(HPO4)·H2O, TPHPH) at 150–160 °C in closed PTFE container or in autoclaves. From EPMA analyses and SEM observations, the initial precipitate was single phase and multilayered. The behaviour of TPHPH (orthorhombic system with a = 21.368(2) Å, b = 6.695(1) Å and c = 7.023(1) Å) was followed when heating up to 1250 °C. It was first dehydrated leading to the anhydrous thorium phosphate-hydrogenphosphate (TPHP, orthorhombic system with a = 21.229(2) Å, b = 6.661(1) Å and c = 7.031(1) Å at 220 °C) after heating between 180 and 200 °C. This one turned progressively into the new low-temperature variety of TPD (called α-TPD, orthorhombic system with a = 21.206(2) Å, b = 6.657(1) Å and c = 7.057(1) Å at 300 °C) correlatively to the condensation of hydrogenphosphate groups into diphosphate entities. These three phases (TPHPH, TPHP and α-TPD) exhibit closely related 2D layered structures, therefore different from the 3D structure of the thorium phosphate-diphosphate (high-temperature variety). This latter compound, now called β-TPD, was obtained by heating α-TPD above 950 °C. All the techniques involved in this study (XRD, Raman and IR spectroscopy, 1H and 31P NMR) confirmed the successive chemical reactions proposed.
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Submitted on : Monday, January 16, 2006 - 11:59:00 AM
Last modification on : Wednesday, September 16, 2020 - 4:08:18 PM

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N. Dacheux, Nicolas Clavier, G. Wallez, V. Brandel, J. Emery, et al.. Characterization of the thorium phosphate-hydrogenphosphate hydrate (TPHPH) and study of its transformation into the thorium phosphate-diphosphate ($\beta$-TPD). Materials Research Bulletin, Elsevier, 2005, 40, pp.2225-2242. ⟨10.1016/j.materresbull.2005.06.011⟩. ⟨in2p3-00025401⟩

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