Investigation of oxidation protected C/C heat shield material in different plasma wind tunnels

Fiber ceramic materials for the heat protection of re-entry bodies and space probes have been developed during the last decade in several countries. C/C and C/SiC materials are the most promising candidates for very high heat loads, but they have to be protected against oxidation for most applications. Most of these protection layers basically consist of silicon carbide and/or silica, which show a different oxidation behaviour depending on the partial pressures of oxygen and atomic nitrogen and on the surface temperature. This phenomenon has not been investigated systematically under re-entry conditions so far. For the investigation and qualification of these materials, plasma wind tunnels which can be operated continuously are in use world-wide. Within a co-operative research program between the NASDA (National Aeronautics and Space Development Agency) and the IRS (Institut fur Raumfahrt-systeme of the University of Stuttgart) a covered CIC material was investigated systematically over a wide range of stagnation pressures (50-3500 Pa) and surface temperatures (1300-1700 degrees C) within the magnetoplasmadynamic wind tunnel at IRS. In the NASDA plasma wind tunnel tests have been performed at higher pressures, but at 3500 Pa both the IRS and NASDA facilities have been used in order to compare the results. The candidate material was fabricated by MHI (Mitsubishi Heavy Industries). It was coated first with about 75 mu m of conversion SiC and then with a CVD-SiC layer of 180 mu m nominal thickness. Finally this layer is covered by a 2-3 mu m layer of SiO2/B2O3 The weight loss and the reduction of the protection layer system had been determined and cuts of each material have been investigated after the test series at MHI. In this paper the test facilities and test conditions are described and the material test results are presented and discussed. (C) 1996 International Astronautical Federation. Published by Elsevier Science Ltd. All rights reserved.