Anti-oxidation properties of a BN/SiC/Si3N4-ZrO2-SiO2 multilayer coating for carbon/carbon composites

To improve the oxidation behavior of carbon/carbon composites, we developed a multilayer coating system by pack cementation and sol-gel slurry method. The coating consists of a BN-SiC inner dual-layer and a Si3N4-ZrO2-SiO2 outer barrier layer. The coating can effectively protect the C/C composites from oxidizing below 1500 °C. Thermogravimetric analysis shows that the weight loss of the composites is less than 2.40 wt.% after oxidizing at 1400 °C for 220 h. The whole temperature range oxidation resistance can be attributed to the multilayer protection design. The BN-SiC inner dual-layer can cure the cracks by producing borosilicate glass, and the Si3N4-ZrO2-SiO2 outer barrier layer can prevent the formation of cracks and seal the bubbles. The oxidation kinetics of the coated carbon/carbon composites shows that the Arrhenius curve consists of four parts, corresponding to four different oxidation processes and mechanisms in different temperature regions.