Importance of the catalycity during an atmospheric re-entry phase of aerospace vehicles

During the atmospheric re-entry phase of aerospace vehicles, the physico-chemical phenomena taking place on the hot parts (nose cap and wing leading edges) can lead to an important excess of heating and a damage of the protective materials. One aim of the researches undertaken at the PROMES-CNRS laboratory is the study of the catalytic recombination of atomic oxygen under conditions nearby Earth or Mars atmospheric re-entry. Four parameters allow to fully describe the catalycity phenomena: the recombination coefficient gamma, the accommodation coefficient beta, the catalycity rate k(w) linked to the apparent recombination coefficient gamma' (equal to gamma.beta) and the recombination thermal flux transferred to the material. Experimental determination of these four parameters, simulation and modeling are presented according to a multi-scale approach: for the experimental part, microscopic scale for the recombination coefficient, mesoscopic scale for both the thermal flux of recombination and accommodation coefficient, and for the theoretical part, atomic scale for molecular dynamic simulation and macroscopic scale for kinetic modeling. Examples of results are given for silica and alumina ceramics in the temperature range 800-2300 K.