Carbon carbon composite material will occur oxidation in the circumstance of temperature above 450 C°,the rate of oxidation will increase rapidly with the temperature raising.some researches show that the strength of the carbon carbon composite material will reduce 10% with the oxidation loss 1%.the oxidation can not only cause the material loss,but also have the security risks on the material itself. So it’s important to do some protection of the C/C composite material.
The method of antioxidant treatment mainly divided into two categories.one is matrix modification to be antioxidant, and another one is surface coating to be antioxidant.the matrix modification way is to treat the CFC material during the preparation process,by using the CVI, impregnation or chemical reaction synthesis etc to add into the matrix or form antioxidation particles,such as Si,SiO2,B,B4C,MoSi etc.
However,it will make the CFC material can not be continuous with carbon,so it will change the thermophysical and strength properties(if too much antioxidation particles). During the friction process of the carbon carbon composite material,the antioxidation particles will wear and tear(because of the hard phase),so it will have a big influence on the carbon carbon composite material during the friction processing.the CFC material will start to oxidation when 370 C°,after mixing the antioxidation particles,the starting temperature of the oxidation can be increase to 600 C°.
The surface coating method need to confirm the oxygen barrier agent. The agent need to isolate the composite material and the oxygen circumstance. In addition,the agent must have low volatility,because it can avoid excess loss during the high velocity air.The coating must also have a good adhesiveness with the carbon matrix,and can prevent carbon from leaking out.
Si3N4,SiC,are some good oxygen barrier agent,they have a high temperature resistance,meanwhile,the SiO2 (forming of the surface)can be oxidation resistance.