RESUMO

The heating of a spacecraft during the reentry phase, leads to the oxidation of the surface causing a loss of catalycity properties of the material. The aim of this work is the study of the ageing of the materials (SiC) and the change of its catalycity [1]. The heating due to the transfer of the kinetic energy from the plasma is created in the nozzle of the spacecraft. Oxygen atoms created from this plasma recombine on the surface leading to an additional increase of the temperature from 373 K to 773 K depending on the catalycity of the thermal protection material and its partial degradation. The heat transfer on materials depends on the recombination coefficient (γ) [2] of the oxygen atoms and the accommodation coefficient (β) [3]. The diffusion of oxygen in the bulk increases the porosity, while new surface layer of oxides such as SiO₂ are formed and replaced the SiC surface of the matrix. This oxide which is formed by the recombination of atomic oxygen on the surface leads to a change of the γ coefficient. The propagation of the defects in the lattice, with formation of microcracks, metallic oxides, and the diffusion of impurities modifies the composition of the surface and the material properties. Our interest was focused on the study of the pollution-regeneration of silicon carbide. However it is possible to retrieve the original catalycity properties of SiC by applying a thin layer of silica. Moreover the association of chromium with silica layer can notably improve these properties.