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 degrees 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 beta-TAnPD, An2O(PO4)2, and/or alpha-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.

Some thorium phosphates have been synthesised: caesium-thorium phosphate, barium-thorium phosphate, thorium fluoride phosphate, thorium sulphate phosphate, and thorium silicate phosphate, starting from aqueous solutions. Their chemical composition was established by Electron Probe Microanalysis (EPMA) and/or by Particle Induced X-ray Emission (PIXE). The X-rays diffraction patterns and/or the infrared spectra are given for these series of thorium phosphate.

Compounds of type Th2-xMx(PO4)2(HPO4)·H2O with M: U, Np, Pu and 0.08 ≤ x ≤ 2.0 are prepared hydrothermally from nitric solutions containing the corresponding actinide cations and conc. H3PO4, as well as N2H4 and H2NOH to keep U and Np in the tetravalent state (Parr bomb, 130°C, several weeks) followed by annealing at 1100°C. This hydrothermal route is also applied to the synthesis of a phosphate incorporating simultaneously tetravalent uranium, neptunium and plutonium. The products are characterized by powder XRD and UV/VIS and IR spectroscopy. - (DACHEUX*, N.; GRANDJEAN, S.; ROUSSELLE, J.; CLAVIER, N.; Inorg. Chem. 46 (2007) 24, 10390-10399; Inst. Phys. Nucl., Univ. Paris Sud, F-91406 Orsay, Fr.; Eng.) -Schramke 09-028