Point defects and self‐diffusion in graphite

  • Thrower P
  • Mayer R
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Abstract

GI aphite is an important industrial niaterial with applications ranging froni nuclear power reactors to the nianufacture of steel and aluniiniuni on a large scale, while on a small scale the wide range of uses encompasses seals and bearings and brushes for electric motors. Graphite is produced by mixing some foini of carbon such as petro- leum coke with a binder such as pitch and heating to high temperatures to “graphitize” the niaterial. In recent years carbon fibers have been graphitized to produce fibers of both high strength and niodulus on an industrial scale. The graphitization process involves the real rangenrent of carbon atoms in a ther- mally activated process with an activation energy similar to that for self-diffusion. Homwrer, the niechanisni by which carbon atoms move in the graphite lattice has never been clearly established. In this paper we shall review the available data concerning diffusion in graphite. This leads to the paradox that, nhile graphite is a highly anisotropic material, diffu- sion is ahiiost isotropic*. Furthermore, iinlilie self-diffusion in metals, diffusion does not occur by a vacancy procrss. We shall then consider the known information about point defects, which is subsequently used to examine possible diffusion processes. These processes are then contrasted with diffusion in other elements. We shall finally briefly consider the process of graphitization.

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Authors

  • P. A. Thrower

  • R. M. Mayer

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