Question

What does oxidation protection do for a carbon/carbon composite?

Answer 1

Carbon composites are utilized at high temperature and in the oxidizing environment. C-C can be easily oxidized under such conditions.So, oxidation protection is done to them so that C-C bond remains intact.
Oxidation protection prevents the diffusion of oxygen into the carbon layers making them useful for aerospace applications.
Carbon fibres are coated with oxidizing protection agents such as calcium magnesium zirconium phosphate.But the coating should be compatible with the carbon substrate.Some oxygen barrier coatings are of nobel metals, borides,carbides,silicides,nitrides etc.