Effect of different oxide additives on the properties of a SiC coating on carbon/carbon composites

Double-layer SiC-based coatings on carbon/carbon composites were prepared by a wrapping cementation method with different oxides(MgO,Al2O3 or B2O3) as additives to the inner layer.The phase morphologies and antioxidation properties of the SiC coated carbon/carbon composites were investigated by SEM,EDS and XRD.Results show that the SiC coating with B2O3 as an additive to the inner layer is more compact than those with MgO or Al2O3 as the additive.Different phases exist in the three different inner layer SiC coatings.The double-layer SiC coating modified by B2O3 is dense and uniform with few flaws and holes,and can protect carbon/carbon composites from oxidation at 1500℃ for 200h in air.