SINOPSIS

The heating of the space vehicle during the re-entry phase and the oxidation of the material surface leads to the loss of protective properties. The atmospheric re-entry conditions are recreated with a non equilibrium low pressure RF plasma and the relative oxygen atom concentration is measured by Actinometric Optical Spectroscopy. Silicon carbide targets polluted with metallic species show different degrees of reactivity than SiC alone [1].
In this work a systematic study of SiC oxidation at high temperature (1100K) has been performed in order to determine kinetic and the oxidation mechanisms. Also the role of chromium oxide as a diffusion barrier into the bulk is examined [2]. In order to determine the oxidation mechanisms the isotopic oxygen O₂¹⁸ has been used, in targets with different deposition layers at different times ranging from 10 to 30 min and the formation of CO, CO₂ and SiO, during the ablation has been followed by mass spectrometry analysis. Surface oxidation and Oxygen diffusion in the material bulk was measured by Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) [3], secondary ion mass spectroscopy (SIMS).
Besides the recombination of oxygen atoms, the ablation of the material and the diffusion of oxygen coming from the gas phase in the bulk of this material have been pointed out.
The results show that at 1300K the kinetic of oxidation is faster than at 1000K. In this range of temperatures chromium oxide remains stable and limits the diffusion of oxygen.