Two series of U doped zirconolite-sphene composite materials were prepared by solid state reaction method: CaZr (12m) U m Ti 2 O 7 2(12m) Ca (12x) U x Al 2x Ti (122x) SiO 5 (m57x) and Ca (12n) U 6n Zr (125n) Al 2n Ti (222n) O 7 2(125n) Ca (12y) U y Al 2y Ti (122y) SiO 5 (n55y/6). The effects of U content on the phase structure of the composite materials were mainly investigated. The results show that the optimal synthesis temperature of the composite material is ,1230uC. In comparison with the incorporation of U in the Zr site of zirconolite, U incorporation in the Ca site of zirconolite using Al as charge compensating ions was not very efficient. Hydrothermal stability of the U doped zirconolite-sphene composite material was examined by modified product consistency test method at 90uC in deionised water (pH 7). The normalised U leach rate is fairly constant in a low value below 10 25 g m 22 day 21 after 28 days.
Single phase zirconolite (CaZrTi 2 O 7 ) was synthesised by a novel method using acid corrosion to treat zirconolite-diopside mixture powders (2CaZrTi 2 O 7 -Mg2Si 2 O 6 ). The mixture powders were prepared by solid state reaction method at 1200uC for 2 h. Single phase zirconolite powders were obtained by acid corrosion method with 5% hydrofluoric acid on the zirconolite-diopside Synroc mixture powders and washed with 10% acetic acid.
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