Degradation of CVD-SiC coated C/SiC composites exposed to the monopropellant combustion products based on Hydroxylammonium nitrate (HAN)

• C/SiC composites were tested under hot fire by a Hydroxylammonium nitrate monopropellant.
• Ablation mechanism of C/SiC composites by the combustion products was investigated.
• Silica layer derived from C/SiC passive-oxidation by the combustion products.
• High-concentration steam corroded some of the silica layer to volatile Si(OH)4.
• Corrosion of C/SiC by steam was limited at the relatively moderate temperature of about 1273 K.

C/SiC composites with CVD-SiC coating were tested under hot fire in a HAN-propellant thruster. The degradation of the composite was determined from weight change and characterization of the surface variations. According to the responses to the corrosive combustion gases, two different ablation modes of C/SiC were discussed. Attributed to the relatively moderate temperature, the water vapor invasion to the silica film via passive-oxidation on the composite was limited, which produced an even, glassy, and honeycombed morphology on surface and about 1% weight gain.