Preparation and anti-oxidation performance of AlO-containing TaSi-MoSi-borosilicate glass coating on porous SiCO ceramic composites for thermal protection.

In order to improve the thermal oxidation resistance of carbon fiber-reinforced porous silicon oxycarbide (SiCO) ceramic composites, an AlO-containing TaSi-MoSi-borosilicate glass coating was formed on the surface of the composites brushing and sintering. The anti-oxidation property of the coated composites at 1873 K was investigated. Microstructures and chemical compositions of the sample before and after anti-oxidation test were determined using XRD, SEM and EDS. After heating in air at 1873 K for 20 min, the AlO-containing TaSi-MoSi-borosilicate glass coating effectively protects the SiCO ceramic composites and the coated sample kept its appearance well without obvious defects on the surface. The cross-sectional SEM images show that the coating is covered by a film of oxidation products with a thickness of about 40 μm, which is dense and crack free. Inside the A-TMG coating, irregular-shaped silicides are surrounded by continuous borosilicate glass and no penetrating holes or visible cracks are found. AlO increases the viscosity of the borosilicate glass, which improves oxidation resistance of the coated sample by enhancing gas-penetration resistance of the glass. In contrast, the sample without AlO in the coating slurry is severely oxidized and exhibits lots of open pores on the surface after oxidation test.