High‐Temperature X‐Ray Diffraction Investigation of the Uranium‐Carbon System

The system UC‐UC 2 was investigated at temperatures to 2200°C. utilizing high‐temperature X‐ray diffraction techniques. UC 2 , which has the CaC 2 structure, was shown to transform to the CaF 2 structure at 1820°C. Mean coefficients of expansion of UC, U 2 C 3 , and UC 2 were determined. The decomposition of U 2 C 3 to cubic UC 2 and to UC saturated metastably with carbon was observed. Solubilities of UC in UC 2 and UC 2 in UC were determined near 1800°C. by a method based on lattice‐parameter measurements. The formation of, and existence conditions for, U 2 C 3 were confirmed. It was observed that UC 2 tends to decompose toward UC at the extreme temperatures, probably by loss of carbon to CO.