Research and Development on Advanced Graphite Materials. Volume Xxxiv. Oxidationresistant Coatings for Graphite

摘要

The refractory materials that could be used for hightemperature, oxidation-resistant coatings for graphite are reviewed. A study of these materials shows which are thermodynamically stable when applied directly to graphite and those which are thermodynamically stable when an intermediate coating is applied between an oxidationresistant outer coating and the graphite. Calculations are made showing that, with properly selected intermediate reaction barriers, many very refractory oxides, such as thoria, can be used as coatings at temperatures up to their melting points. The application of TiB2, B6Si, MgO.ZrO2, CaZrO3 and SrZrO3 coatings by arc-plasma spraying is described and the results of oxidation studies to determine the protection afforded graphite by these coatings are presented. Coating of TiC-TiN and SiC-Si applied to graphite by vapor deposition using the source-target method are discussed. Techniques of applying SiC coatings by pack-diffusion methods are reported and the oxidation protection afforded by the coatings is compared with that of the SiC produced by the source-target method. (Author)