Diffusion in carbides and nitrides
Actinides and transition metal carbides are extensively used as hard materials, "high technology ceramics" for heat engines, advanced fuels for liquid metal cooled fast breeder nuclear reactors, and in thin layers as diffusion barriers or coatings. The available knowledge on diffusion processes and point defect behaviour in these ceramics is reviewed. The diffusion activation enthalpies are all high, and the entropy values are unusually consistent with Zener's theory of volume diffusion. The diffusion mechanisms, however, differ for the different sublattices and may differ for the different parts of the monophase regions. Additional information on point defect formation and migration is available from quenching, radiation damage and recovery studies. Very recent results obtained with Rutherford backscattering and channelling techniques, supported by transmission electron microscopy, are presented and discussed. Important instantaneous defect recovery and defect mobilities at and below room temperature in the metal sublattice have been observed. The metal atoms are, generally, the less mobile species in the carbides and nitrides and are, therefore, rate-controlling for high temperature kinetic processes and matter transport.
Bibliographic Reference: Paper presented: "Diffusion in Materials", NATO Advanced Study Institute, Aussois (FR), March 12-25, 1989
Availability: Available from (1) as Paper EN 34828 ORA
Record Number: 199011017 / Last updated on: 1994-12-01
Original language: en
Available languages: en