Reaction between Uranium Mononitride and Graphite Powders

The carbothermic reaction of UN with graphite in the form of loose powder mixture has been studied in vacuo with the aid of a high-temperature thermobalance in the temperature range of 1,270~1,675°C. The gravimetric measurements were conducted continuously to determine the effect of varying reaction temperature and differences in sample particle size.

The kinetics of the reaction was found to follow the diffusion—controlled kinetic equation for mixed powder, and activation energies of 76.1, 55.1 and 72.7kcal/mol were obtained for samples of (1)—400 mesh UN and—400 mesh natural graphite mixture, (2)—150 +270 mesh UN and—150 +270 mesh natural graphite mixture, and (3)—150 +270 mesh UN and—150 +270 mesh artificial graphite mixture, respectively. X-ray diffraction studies revealed the reaction products of the coarse sample to be composed of two different kinds of UC_xN_1-x solid solutions, one having a x value of 0~0.2, and the other 0.8~0.9. From the above observations, the diffusion of C and/or N atoms through the outer carbon rich UC_xN_1-x layer may be considered to be the rate determining step.