Antioxidative protective coatings for carbon materials

A widespread use of carbon-carbon and carbon-ceramic materials (CCM) in the aerospace industry, metallurgy (crucibles for melting metals) and electrical engineering is limited because of the need for protecting CCM parts against oxidation at service temperatures above 500 to 700{degrees}C. At temperatures up to 1300-1400{degrees}C, the problem can be solved by volume siliconizing CCM parts, impregnating C-C substrates with organosilicon compounds or gas-phase depositing (CVD process) silicon-containing compounds (SiC or Si{sub 3}N{sub 4}). For CCM parts to be used at temperatures above 1500{degrees}C in oxidative environments (space structures; aircraft gas-turbine engine components in contact with a hot gas; crucibles for melting metals), the following techniques are being devised to apply protective coatings, as evident from a patent literature analysis: (1) Application of SiC coatings onto the surface of graphite or C-C parts by the CVD or CVR methods; such coatings can be quite efficient for parts operating short time at temperatures up to 2000{degrees}C, for example in rocket engines; (2) SiC coatings applied onto the surface of large-sized or intricately-shaped parts frequently experience cracking; this necessitates the application of multilayered or multicomponent coatings (by subsequent impregnation with various silicate compositions, covering with glass or glass-like compositions to {open_quotes}heal{close_quotes} cracks; applyingmore » surface oxide or silicate coatings); (3) Application on the surface of CCM parts of refractory, self-healing-in use coatings containing refractory borides and silicides; to this end the CVD method and plasma spraying in controlled atmospheres are employed. Given below are results of the investigations conducted at NIIGRA-FIT in the above-mentioned directions with the use of the slip-casting technology.« less