Oxidation behaviour of SiC ceramic coating for C/C composites prepared by pressure-less reactive sintering in wet oxygen: Experiment and first-principle simulation

Abstract

SiC ceramic coating, for prevention of C/C composites against oxidation, was prepared by pressure-less reactive sintering to investigate the oxidation behaviour in an oxidising environment containing water vapour at 1773 K. The experimental results demonstrated that the oxidation behaviour of porous SiC ceramics could be divided into two stages, following the parabolic model, which was attributed to the variation in the contact area involved in the oxidation reactions. During the entire oxidation process, water vapour could accelerate the oxidation of the SiC ceramics, according to the weight change. By first-principle calculations, the accelerated oxidation rate of the SiC ceramics was attributed to weakened Si–O and Al–O bonds in the formed glassy scale, which were caused by hydroxide radicals from the water. Atomic thermal motions at high temperature could lead to the breakage of the network structure, promoting the diffusion and solution of oxidising gases. When the as-prepared SiC ceramics were applied as anti-oxidative coatings for the C/C composites, the SiC ceramic coating and C/C matrix could be sealed and protected faster per unit time, because water vapour was beneficial to the formation of a glassy layer. The weight loss of the C/C matrix could be attributed to unsealed microcracks inside the SiC coating in the initial stage.