Diffusional aspects of non-stoichiometry a model for UCx

The self-diffusion properties of carbon in are described in terms of an f.c.c. lattice gas model in which the C2 groups attract only when they are nearest neighbours. A modified Monte Carlo method is used to calculate the self diffusion coefficient as a function of x and temperature. The diffusion coefficient shows a maximum at about the composition UC1.2 for the four temperatures studied: 2380, 2500, 2600 and 2650 K. The activation enthalpy for diffusion increases non-uniformly from approximately 54 kcals mole−1 (reference point) at compositions close to UC to about 75 kcals mole−1 for compositions near UC2. The functional form of this variation is in satisfactory agreement with existing experimental data.