The oxidation of metallic carbides and silicides

The expected oxidation mechanisms of carbides and silicides can be analysed from a thermodynamic viewpoint by a comparison of the relative stabilities 

If we combine the Gibbs energy of formation equations above to derive the equation 

The oxidation rate is decreased by a factor of four in a composite of TiC and Cr. This is because the formation of Ci 203 covers the composite with an oxide which oxidizes slowly because of the low transport number of electrons tlu ough the oxide. 

Clearly the best protection from oxidation by a silicide as a coating on a reactive substrate would be the disilicide, which has the highest silicon content, and could be expected to provide a relatively protective silica coating. 

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