Corrosion of a SiC-C/SiC composite in environments with Na₂SO₄ vapor and oxygen

The gaseous salt corrosion of a 3D woven SiC-C/PyC/SiC composite by a mixture of Na₂SO₄ vapor and oxygen has been investigated at temperatures from 1000 to 1500 °C through an experimental approach based on mass and residual flexural strength changes. Below 1200 °C, the corrosion kinetics is controlled by diffusion of oxygen through microcracks in the matrix and the coatings. From 1200 to 1400 °C, the rate-controlling step is permeation of molecular oxygen through the silica film and the SiC coatings. Above 1400 °C, the corrosion kinetics is determined by diffusion of oxygen through pores in the silica film. As a compositional modifier, alkali contamination accelerates the corrosion of composites. Below 1400 °C, the oxygen partial pressure is inversely proportional to strength, but has nearly no effect on weight change. Above 1400 °C, the effect of pressure on weight loss is obvious. However, the pressure has almost no effect on strength. The higher the oxygen partial pressure, the higher the weight loss.