Gray powder of somewhat lighter color and lower density than the parent metal powder. In contrast to the Ti and Zr hydrides, the Th hydrides with high hydrogen content are labile and ignite spontaneously in the air.
Hydrogen dissolves in the Th metal lattice until the composition of ThH3 is reached. Thorium starts to absorb H2 at 400°C; the maximum H2 concentration corresponds to a hydride composition of ThH3.24. The metal is weighed into a boat of sintered clay (or, better, of stainless steel, provided traces of Fe in the product are not detrimental) and placed in a quartz tube connected to the system with a ground joint. The apparatus consists of a glass burette with 0.1-ml. Divisions are provided with a levelling tube and Hg reservoir and are connected to an electrolytic H2 generator; this apparatus is attached to a high-vacuum system. The quartz tube volume is measured, and the metal is degassed by heating to 550°C. Hydrides with the desired H2 content are obtained by varying the absorption temperature and the quantity of hydrogen introduced.
