Recombination coefficient of atomic oxygen on ceramic materials under earth re-entry conditions by optical emission spectroscopy

Abstract

Abstract To develop heat shields for space vehicles, materials must be characterized in simulation conditions close to those in space environments. The most important conditions for simulating the Earth re-entry phase of space vehicles (high temperatures, low pressure air plasma,…) are achieved through the MESOX set-up associating a solar radiation concentrator and a microwave plasma generator. After determining the thermal recombination flux transferred to the material (thermal approach, accommodation), we developed a chemical approach for evaluating the recombination coefficient of atomic oxygen γO by Optical Emission Spectroscopy. We also measured the gas temperature above the material, close to the surface where recombination occurs, using the rotational temperature of nitrogen. The recombination coefficients of atomic oxygen were determined in function of the temperatures of two types of silica materials. Finally, the activation energy of the atomic oxygen recombination reaction was obtained for each material. Results showed that the microstructure of the topmost layer has an important effect and that the recombination coefficient of β-cristobalite is four times higher than that of quartz.