The C diffusivity was determined, as a function of the stoichiometry, at temperatures of between 1200 and 1750C. Electron probe micro-analyses of couples between the pure metal and C, or between metal-plus-carbide and C-plus-carbide, were performed. Marker experiments indicated that C was essentially the only mobile species. Also, the partial molar volume of C was almost zero and the intrinsic diffusion coefficient of C was therefore equal to the interdiffusion coefficient. It was found that the C diffusivity was a function of the C concentration, and that the coefficient increased with decreasing C content. It was noted that the C diffusivities in the 2 carbides, as a function of the homologous temperature, were almost the same. The data could be described by the expression:

ZrC1-x:     D (cm2/s) = (0.0083 exp[9.2x])exp[-36600/T]

F.J.J.Van Loo, W.Wakelkamp, G.F.Bastin, R.Metselaar: Solid State Ionics, 1989, 32-33, 824-32