Electrical Resistivity and Phase Boundaries for Thorium-Carbon Alloys

摘要

Electrical resistivity measurements have been made on a series of thorium-carbon alloys. The electrical resistivities of thorium monocarbide, ThC, and thoriumdicarbide, ThC2, at room temperature were found to be 115 = 15 and 15 = 2 microhm-cm respectively. The dicarbide undergoes two allotropic transformations, one at 1440 and one at 1490C. These transformation temperatures were observed on carburized thorium wires which had a thin layer of pyrolytic graphite on the surface. The trend of the transformation temperatures with decreasing carbon content, and hence the phase boundaries, was not definitely established. A reproducible resistivity discontinuity with temperature was observed at 1220 = 20C for alloys in the composition range between ThC and ThC2. The size of the discontinuity appeared to be a maximum at the composition of Th2C3 suggesting the possible existence of this compound at temperatures above 1200C and its decomposition into ThC and ThC2 on cooling below 1200C. The phase boundaries suggested by the resistivity data have been outlined in a tentative phase diagram. (Author)