Oxidation behavior and kinetics of SiC/alumina–borosilicate coating for carbon–carbon composites

A SiC/alumina–borosilicate double-layer coating was prepared by a two-step slurry technique for the protection of carbon–carbon composites from oxidation. SEM, XRD and EDX analysis showed that the inner layer coating obtained from the first step consisted of β-SiC, Si and SiO2. The outer layer consisted of B4C, Al, amorphous SiO2 and quartz. The oxidation behavior and kinetics of the SiC/alumina–borosilicate coating were investigated. It was found that the as-prepared coating could effectively protect carbon–carbon composites from oxidation at 1300 °C for 100 h. The isothermally oxidation kinetics could be described by Microflaws Model and Diffusion Model. During short-time oxidation, the overall oxidation kinetics was determined by the transport processes through microflaws, which resulted in a linear growth law. While during oxidation of longer time, the weight loss rate was controlled by the diffusion processes in the coating with growing oxide layer, which led to a parabolic growth law.