Hydrothermal Growth and Thermal Property Characterization of ThO₂ Single Crystals

Abstract

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.

Anisotropic thermal conductivity in uranium dioxide

“…This effect is illustrated in Fig. 2c, which compares the UO 2 thermal conductivity to recent measurements on ThO 2 single crystals 14 . ThO 2 is isostructural with UO 2 although it is diamagnetic 15 and thus there is no phonon-spin scattering.…”

Revisiting the Hydrothermal growth of YAG

“…Given our recent progress in the hydrothermal growth in several challenging refractory oxide systems [27][28][29] we feel it is worthwhile to build upon these preliminary experiments in garnet growth with a fresh perspective and revisit this field of crystal growth that has been dormant for nearly 40 years. When considering some of today's new ideas of epitaxial growth (where slower growth may actually afford a degree of in situ thickness control) including complex single crystal architectures and targeted materials compositions, the hydrothermal method may offer some unique advantages.…”

The Crystal Structures of CsTh6F25 and NaTh3F13

“…Since it was determined that thorium oxide can be grown as large high-quality single crystals using fluoride mineralizers [2], we have successfully grown a number of alkali thorium fluorides under hydrothermal conditions [3,4], doing so due to their potential as a fuel source for both fusion and fission reactors.…”