In non-oxide ceramics such as SiC, SiC itself stays stable up to 1,700 deg. C, but the carbon or boron nitride accumulating in the boundary layer shows oxidation degradation. This means that fibers consisting mainly of SiO2 and glass layers adhering strongly to the matrix are formed in the fiber/matrix boundary face by a reaction with oxygen. As a result, we cannot attain the characteristics necessary for the boundary layer. Because of the oxidization degradation problem on the boundary and the widening operating-temperature range of heat-resistant metals realized by advances in cooling technologies, actual applications are still few for SiC-based, fiber-reinforced ceramics, which are inferior to carbon in heat-resistant performance. In fact, applications are limited to static parts on some military jet engines. The lifespan of approximately 1,000 hours currently achieved by SiC-based composite materials is not sufficient for commercial aircraft engines, but is acceptable for space-application engines.
Under the circumstances, and despite having no actual applications in the world to date, JAXA is developing a large fiber-reinforced ceramic combustion chamber (Fig. 4), using the latest design and manufacturing technology. The weakest point with fiber-reinforced ceramics as a new material is that there is no record of an actual application. We plan to expand applications of fiber-reinforced ceramics by building a high-performance rocket engine using this unprecedented light, high-thermal-resistant, composite material. We are currently encountering various research problems. However, we will continue going forward, even though the ride may be bumpy.