THORIUM-THORIUM DIOXIDE PHASE EQUILIBRIA

Various Th-ThO2 mixtures were investigated with thermal analysis, X-ray, and microscopic techniques. The following information on phase boundaries is deduced. The oxygen solubility in solid Th is less than the O Th ratio of 0.003. The solid-solid transition of Th saturated with ThO2 occurs at 1370 ± 30 °C. A Th-ThO2 eutectic occurs at 1735 ± 20 °C with the O Th ratio of 0.016 ± 0.005. A monotectic occurs at 2740 ± 100 °C with the Th-rich and the O-rich liquid O Th ratios of 0.40 and 1.5 ± 0.2, respectively. The Th-rich ThO2 solidus varies from the O Th ratio of 1.985 ± 0.01 at the eutectic to 1.87 ± 0.04 at the monotectic and to 1.997 ± 0.01 at the melting point. © 1969.