THERMAL AND CHEMICAL APPROACHES FOR OXYGEN CATALYTIC RECOMBINATION EVALUATION ON CERAMIC MATERIALS AT HIGH-TEMPERATURE

During the atmospheric entry phase, the physico-chemical phenomena tak ing place on space shuttle walls can lead to an important excess of he ating and damage of the protective materials. The aim of this work is the study of the catalytic recombination of atomic oxygen under plasma conditions chosen to simulate the atmospheric reentry. To do that, we have developed an experimental set-up MESOX (Moyen d'Essai Solaire d' OXydation), which associates a solar radiation concentrator and a micr owave generator to reach high temperature, low enthalpy flow and low p ressure plasma with an air gas flow. The study of atomic oxygen recomb ination on silicon-or aluminum-based ceramic materials, at high temper ature (1000-1800 K) has been done for different pressures (200-2000 Pa ) by a thermal and a chemical understanding. The results give a cataly city scale of materials (thermal recombination flux, q(rec), and coeff icient of atomic oxygen recombination, gamma). The catalycity activity is weak for the sintered SiC target with atomic oxygen recombination flux reaching 35 kW/m(2) however, for a target of sintered Al2O3, cata lytic effect is obtained with energy fluxes between 90 to 180 kW/m(2). The recombination coefficient gamma confirms the catalycity scale of these ceramic materials. (C) 1997 Elsevier Science B.V.