Oxidation behavior of sol-derived C/Mullite composites in air

Thanks to the reinforcing and toughening of carbon fiber, carbon fiber reinforced mullite (C/Mullite) composites exhibit favorable application potential as thermal structural materials. To further reveal the failure mechanism of the C/Mullite composites in service environment, the oxidation resistance and failure behavior of the composites were systematically investigated in this study. It was found that the oxidation mechanism of the composites inclined to diffusion control at 1300 degrees C similar to 1500 degrees C, the cracks and pores of the composites provided diffusion channels for oxygen to oxidize the composites, the oxidation degree of carbon fibers and interfacial coating after oxidation was responsible for the weight loss and performance degradation of the composites. Additionally, the oxidation resistance of C/Mullite composites can be obviously enhanced by using the SiO2-rich (the Al/Si atomic ratio was 1/2) Al2O3-SiO2 sol to densify at the later stage of fabrication, strength retention and modulus retention of the composites were increased by 28 % and 40% after oxidation at 1500 degrees C in air, respectively.