High Temperature Crystal Structure of Thorium

High temperature x‐ray diffraction patterns and electrical resistivity measurements show that thorium of 99.8% purity transforms from face‐centered cubic to body‐centered cubic on heating to 1400 ± 25° C. At 1450° C the lattice constant of body‐centered cubic thorium is 4.11 ± 0.01 Å. The extrapolated lattice constant of face‐centered cubic thorium at the same temperature is 5.180 ± 0.005 Å. The lattice constant of the metal used is 5.089 ± 0.001 Å at room temperature. The transformation temperature is rapidly increased as the amount of carbon in the metal is increased. Zirconium has the opposite effect in that small amounts of it are very effective in lowering the temperature at which the transformation begins.