Thermal and chemical approaches for oxygen catalytic recombination evaluation on ceramic materials at high temperature

During the atmospheric entry phase, the physico-chemical phenomena taking place on space shuttle walls can lead to an important excess of heating 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 dʹEssai Solaire dʹOXydation), which associates a solar radiation concentrator and a microwave generator to reach high temperature, low enthalpy flow and low pressure plasma with an air gas flow. The study of atomic oxygen recombination on silicon- or aluminum-based ceramic materials, at high temperature (1000-1800 K) has been done for different pressures (200-2000 Pa) by a thermal and a chemical understanding. The results give a catalycity scale of materials (thermal recombination flux, qr~c, and coefficient of atomic oxygen recombination, 3,). 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 A1203, catalytic effect is obtained with energy fluxes between 90 to 180 kW/m 2. The recombination coefficient 3ʹ confirms the catalycity scale of these ceramic materials. © 1997 Elsevier Science B.V.