Date of Award
Master of Science
Department of Engineering Physics
Timothy Zens, PhD.
Hydrothermal synthesis of ThO2 and UxTh1-xO2, and UOx at temperatures between 670°C and 700°C has been demonstrated. Synthesis at these temperatures is 50-80°C below prior crystal growths and represents a new lower bound of successful growth. Hydrothermal synthesis represents a cost effective, environmentally friendly way of growing bulk actinide materials of optical quality. These refractory oxide single crystals offer potential applications in thorium nuclear fuel technology, wide-band-gap uranium-based direct-conversion solid state neutron detectors, and understanding how actinide fuels age with time. ThO2 single crystals of dimensions 6.49mm x 4.89mm x 3.89 mm and weighing 0.633g have been synthesized at growth rates near 0.125mm/wk. Single crystal UxTh1-xO2 crystals with mole fractions up to x approx. equal 0.30 have also been grown. The largest alloyed crystal with mole fraction x approx. equal 0.23 has dimensions of 2.97mm x 3.23mm x 3mm and saw growth rates likely near 0.2mm/wk. Mineralizer molarity, temperature gradient, and synthesis temperature were gradually optimized to produce a faceted, cubic crystal approximately 3mm a side. X-ray diffraction of single crystal ThO2 determined the unit cell to be of the calcium fluorite structure with a lattice parameter of 5.596(4) Angstrom. Lattice parameters for UxTh1-xO2 varied linearly with thorium concentration suggesting homogenous uranium incorporation into the lattice.
DTIC Accession Number
Castilow, Jacob G., "Crystal Growth and Characterization of ThO2 and UxTh1-xO2" (2013). Theses and Dissertations. 922.