5 Diffusion in carbides

This chapter presents an extensive set of data for different carbides. Less results have been published for nitrides, limited data are available for hydrides and no quantitative data could be found for borides. All those materials have properties causing unusual difficulties in diffusion measurements and an unusually large scatter (e.g. due to deviation from stoichiometry in an otherwise single phase field of the compound studied). These specific difficulties are summarized as introduction to the four following subchapters, and, if necessary, specific problems are briefly stated for the individual compounds treated within the subchapters (e.g. lack of suitable radioactive tracers for both metal and non-metal atoms in silicon nitride). Due to these specific difficulties, some reported results are unreliable and not recommendable and hence they have not been included in this summary. The chapter presents some helpful information for silicon carbide, followed by monocarbides of the transition metals of groups IV, V and VI, the carbides of the actinides U and Pu (mono-, sesqui-, or dicarbides). It concludes with the available scattered results for other more complex carbides. Properties and phenomena relevant to diffusion processes are pointed out to help the reader to better understand the individual results summarized in the following tables and figures.