Graphite-Base Refractory Composites for Aerospace Applications
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Graphite is one of the most widely used high-temperature materials because of its combination of refractoriness, thermal shock resistance, and machinability. Present-day applications, nevertheless, call for improvements of graphite with respect to oxidation resistance, strength, and hardness. Improvements of metals with respect to these properties have been accomplished by alloying; and, in a similar manner, the purpose of this study has been to enhance the properties of graphite by the use of additives. The manufacturing process employed was hot-pressing with final temperatures ranging from 1800–3200°C depending on the additives used, and pressures up to 10,000 lb/in were applied in some cases. The starting ingredients were powdery blends of graphite, pitch, and selected refractory materials not exceeding 30 vol. %. The most effective additives were zirconium, silicon, niobium, thorium, and some of the rare earth metals. The relative evaluation of the resulting composites was primarily based on oxidation studies. The latter were conducted in various apparatuses comprising resistance heating, arc image techniques, induction heating coupled with levitation and arc plasma exposure. The composites form an oxidation-resistant coating of the oxides of the additives which enables the material to withstand temperatures to 4000°F in an oxidizing atmosphere. Some of the composites have been applied as thrust chamber liners for liquid-fueled, attitude-control motors with success. The theoretical flame temperature of the fuels ranges from 4000–5300°F.
KeywordsOxidation Resistance Induction Coil Thermal Shock Resistance Aerospace Application Mold Insert
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