Corrosion of C/SiC composite in water vapor and Na₂so ₄ vapor

Corrosion of a 3D woven SiC-C/SiC composite has been investigated between 1000°C and 1500°C in the atmospheres containing Na₂SO ₄ vapor and water vapor through an experimental approach based on weight change, residual flexural strength and morphological change. After the silica film was formed, the corrosion was controlled by the permeation of water vapor through the film. Before the silica film was completed, three main temperature domains were divided according to the corrosion mechanism: below 1200°C, the corrosion was controlled by inward diffusion of water vapor through microcracks in the matrix and the coatings; from 1200 to 1400°C, the rate-controlling step of corrosion was outward diffusion of CO through the defects of coating; above 1400°C, the corrosion was determined by inward diffusion of water vapor through the defects of coating.