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In the reaction: $$\ce{SiC + 2H2O <=> SiO2 + CH4}$$ The oxidation state of Si is +4 in both SiC and SiO2, while the oxidation state of carbon is -4 in both SiC and CH4 (confirmed by this).
Here (page 69, middle) it says that silicon carbide is oxidized in humid air.
So actual oxidation states of C and Si do not change, but this is considered a redox reaction? What a I missing?
Silicon carbide is very inert chemically, so this is more of a terminology discussion than discussion of a chemical mechanism. There are two ways of describing the reaction:
1) water oxygenates the silicon and hydrogenates the carbon. Or
2) water oxidizes the silicon and reduces the carbon.
The question predisposes an answer like #2, but maybe #1 is more descriptive. Or, perhaps better:
3) water oxidizes the silicon and hydrogenates the carbon. Or
4) water reacts with SiC to give xyz (CH4, CO2, CO, SiO2). Avoid "redox" entirely.
You can't compare this high temperature reaction with redox reactions at room temperature where voltage is applied to electrodes in solutions.
