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The existing knowledge of diffusion processes, of point defect behaviour and of radiation damage in carbides and nitrides is discussed. Most data relate to transition metal carbides and for actinide carbides and nitrides, and some data exist for SiC. Very little information is available for other carbides and, in particular, for many interesting nitrides. The diffusion activation enthalpies are generally high, and the entropy values are generally consistent with Zener's theory of volume diffusion. However, the mechanisms of diffusion usually differ for the metal and the non-metal sublattice. They may even change with composition for different parts of the often very wide region of existence of the monocarbides. Recent work on the actinide compounds UC and UN, including self-diffusion and quenching studies as well as work on radiation damage produced by ion or electron bombardment with subsequent damage recovery followed by measurements of electrical resistivity or with the aid of the Rutherford backscattering-channelling technique, has provided further insight into defect formation, and into instantaneous and thermally activated recovery. Supporting electron microscopy helped to define better the defect behaviour. Though in the carbides and nitrides considered, the metal atoms are generally the less mobile species - and are therefore rate-controlling for high-temperature kinetic processes and matter transport - important metal atom mobility at and below room temperature has recently been seen in UN. Finally, some high-temperature diffusion-related processes (e.g. sintering, creep, grain growth, etc.) are also considered.

Additional information

Authors: MATZKE H-J, JRC Karlsruhe (DE)
Bibliographic Reference: Paper presented: NATO Advanced Research Workshop, "The Physics and Chemistry of Carbides, Nitrides and Borides", Manchester (GB), Sept. 18-22, 1990
Availability: Available from (1) as Paper EN 35085 ORA Also published in The Physics and Chemistry of Carbides; Nitrides and Bromides, pp. 357-383
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