Single crystals of ThO 2 exceeding 8 mm in length have been produced by hydrothermal synthesis in aqueous cesium fluoride solutions at 750 °C. Solubility studies have confirmed ThO 2 is congruently saturating in aqueous cesium fluoride with positive solubility with respect to temperature and increasing mineralizer concentration. Bulk transport growth of ThO 2 was performed to determine the viability of large-scale production of ThO 2 single crystals for possible nuclear fuel applications. The thermal conductivity and thermal expansion properties of single crystal ThO 2 were measured and are reported here for the first time. The single crystal sample, in regard to nuclear fuel applications, showed improved thermal performance compared with previously reported polycrystalline values.

No abstract

Two new cesium thorium fluorides and three new rubidium thorium fluorides have been synthesized hydrothermally and structurally characterized. The structures of two polymorphs of CsTh(3)F(13) are described in space group P6/mmm with a = 8.2608(14) and c = 8.6519(17) and space group Pmc2(1) with a = 8.1830(16), b = 7.5780(15), and c = 8.6244(17). The analogous orthorhombic compound RbTh(3)F(13), with a = 8.1805(16), b = 7.4378(15), and c = 8.6594(17) in space group Pmc2(1), is also reported. Two other rubidium thorium fluorides are also described: RbTh(2)F(9) crystallizes in the space group Pnma where a = 8.9101(18), b = 11.829(2), and c = 7.4048(15), and Rb(7)Th(6)F(31) crystallizes in the space group R3 where a = 15.609(2) and c = 10.823(2). Comparison of these materials was made on the basis of their structures and synthesis conditions. The formation of these species in hydrothermal fluids appears to be dependent upon the concentration of the alkali fluoride mineralizer solution and, thus, the ratio of alkali ions to thorium in the system.

No abstract

No abstract