Corrosion of a SiC-C/PyC/SiC composite by sodium sulfate vapor at high temperatures

The gaseous salt corrosion of a 3D woven SiC-C/PyC/SiC composite in an atmosphere containing Na₂SO₄ vapor has been investigated between 1000 °C and 1400 °C by an experimental approach based on mass and residual flexural strength changes. Two main temperature domains exist for the 3D woven SiC-C/PyC/SiC composite. Below 1200 °C, the corrosion kinetics is controlled by the competition of consumption of C fibers by SO₃ and gas phase diffusion through a network of microcracks in the SiC matrix and coating. Above 1200 °C, the corrosion kinetics is controlled by SO₃ diffusion through the product film formed on the SiC coating. A more serious corrosion caused by a higher concentration of Na₂SO₄ was discovered in the present work. The thickness of the corrosion product film increases linearly with the temperature of the samples. Active corrosion may occur in the investigation atmosphere.