Characterization of gas/surface interactions for ceramic matrix composites in high enthalpy, low pressure air flow

Ceramic matrix composites are ideal heat shield materials for reusable spacecrafts re-entering the Earth atmosphere. The interactions between the surface and the surrounding reactive gas determine the total heat flux to the wall and become design drivers for the thermal protection system. This paper presents the characterization of carbon/silicon carbide specimens in an inductively-coupled plasma facility, providing high enthalpy and low pressure conditions, suitable to simulate the hypersonic flight environment. Catalytic recombination coefficients and emissivities at surface temperatures between 1200 and 2000 K are determined. Spectral reflectivity measurements allow to assess the oxidation behavior of the materials, showing the formation of silica at the surface, and its degradation at temperatures above 1800 K. Optical emission spectroscopy measurements in front of the test articles indicate silicon volatilization at high temperatures.