Catalycity of silica surfaces at high temperature: Comparison between Experimental Recombination Coefficients and Molecular Dynamics Simulation.

A joint experimental and theoretical investigation on the molecular oxygen formation after atom recombination on silica surfaces has been performed that can be relevant for the thermal protection system of shuttles reentering in terrestrial atmosphere. The experimental method we have developed for the measurement of the atomic oxygen recombination coefficient ?? at high temperature (900 - 2000 K) using a direct method on surfaces of silica (?-cristobalite and quartz) and alumina (sintered and native oxide on AlN substrate) is presented. Then the experimental results are compared with semiclassical Molecular Dynamics calculations performed on the same catalytic system aiming at determining, at a molecular level, the basic features of the surface catalytic activity. A substantial quantitative agreement between the experimental and the theoretical recombination coefficient on ?-cristobalite has been found in the surface temperature range explored in the experiments.