Preparation and structure of a MoSi_(2)/SiC high temperature anti-oxidative gradient coating for carbon/carbon composites

An appropriately structured gradient coating on the surface of C/C composites,consisting of,from inner to outer,a SiC transiting layer,a SiC compacting layer,a MoSi_(2)/SiC double phase layer and a MoSi_(2)-containing outer layer,was prepared by a two-stage coating method.As the holding time at high temperature stage is increased,the MoSi_(2) outer layer becomes more continuous.The adhesion between the coating and the composites is mainly caused by a metallurgical bond and a mechanical bond.The surface of the coating is sealed by Si(OC_(2)H_5)_4,and SiO_2 gel fills the cracks in the coating and covers it.Oxidation of the specimen with an unsealed coating causes mass loss,while the specimen with the sealed coating shows a mass gain in air at(1 500 ℃.)