OXIDATION PROTECTION OF HIGH TEMPERATURE CARBON-CARBON COMPOSITES

CURRENT APPLICATIONS FOR RE-ENTRY VEHICLES AND HIGH TEMPERATURE AIR BREATHING PROPULSION SYSTEMS, AND DESIGNS FOR ADVANCED AIRCRAFT AND SPACECRAFT SUCH AS THE NATIONAL AEROSPACE PLANE HAVE SIMULATED INTEREST IN A CLASS OF MATERIALS WHICH CAN OPERATE IN AN OXYGEN ATMOSPHERE AT TEMPERATURES RANGING BETWEEN 500 C AND 2200 C. CARBONCARBON COMPOSITES ARE ATTRACTIVE FOR THIS TEMPERATURE RANGE FROM THE DUE TO COMPATIBILITY BETWEEN REINFORCEMENT AND MATRIX, MATERIAL DENSITY, MELTING TEMPERATURE, MECHANICAL PROPERTIES, RESISTANCE TO THERMAL SHOCK, COST, AND AVAILABILITY. THE ONE MAJOR DEFECT IS OXIDATION OF CARBON, LEADING TO EROSION OF THE STRUCTURE, AND RAPID LOSS OF STRENGTH. THE PROPOSED EFFORT WOULD DEVELOP A CARBON-CARBON COMPOSITE WHICH UTILIZES A HIGHLY EXIDATION-RESISTANT DOPED CARBON FIBER WHICH IS SUBSEQUENTLY COATED WITH A THIN SIC LAYER, AND INCORPORATED INTO A CARBON-CARBON COMPOSITE, THE MATRIX OF WHICH IS SIMILARLY TREATED WITH ADDITION OF BORON, AND FINALLY EXTERNALLY COATED WITH A SIC LAYER. THIS APPROACH OFFERS THE POTENTIAL FOR A HIGH STRENGTH, STABLE COMPOSITE FOR TEMPERATURES UP TO AT LEAST 1750 C.