Coating processes – Coating by vapor – gas – or smoke
Patent
1995-06-19
1997-08-26
King, Roy V.
Coating processes
Coating by vapor, gas, or smoke
427249, 4272554, 427427, C23C 1600, C04B 4187
Patent
active
056608802
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of production of carbon materials and articles and is intended for oxidation protection of parts operating in an oxidizing environment at high temperatures. Such materials and articles can be useful in metallurgy (furnace lining, heaters for electric sets, etc.), aircraft and other industries where such protection of structural elements and articles is required.
DESCRIPTION OF PRIOR ART
Widely known in the art are processes for applying protective antioxidative coatings onto carbon articles, which are mainly directed at forming a surface layer of refractory inorganic substances, in particular refractory metal carbides and borides.
Also known in the art is a process for applying a protective antioxidative silicon carbide coating onto carbon-carbon articles, according to which an article is first placed into silicon filling [Carry D. M., Cunningham J. A. Frahm J. R., Space Shuttle Orbiter leading edge structural subsystem thermal performance. AIAA Paper No. 82-0004]. And here silicon carbide is formed in the article material surface layer as a result of silicon diffusion and temperature exposure. Then the article is repeatedly impregnated (up to 6 times) in a tetraoxymethyl silicate solution, with intermediate drying after each impregnation cycle to ensure gas impermeability.
The thus obtained coating is useful for operating in a high-speed stream of dissociated air at 1600.degree. to 1650.degree. C.
This process makes it possible to obtain a coating whose composition is limited to certain components and is characterized by a high labour input in view of the necessity in repeated impregnations of the article at a relatively low upper limit of the coating operating temperatures.
Further known in the art is a process for obtaining a protective coating on a carbon material via depositing silicon and hafnium carbides, as well as hafnium silicide, from a gaseous mixture of silicon and hafnium chlorides, methane, and hydrogen [CVD multilayer protective coating. Proceedings of the 35th International SAMPE Symposium-35, No. 2, p. 1348-1355, 1990]. The reaction mixture is fed onto a preheated surface to be protected, and the interaction of the mixture components results in depositing silicon carbide, hafnium carbide, and hafnium silicide on the article surface.
This process makes it possible to obtain a heat-resistant multicomponent coating operable in the temperature range of up to 1800.degree. C., yet requires special equipment, and is ecologically unsafe.
Still further known in the art is a process for obtaining boride-oxide protective coatings on carbon-based materials by impregnation thereof with a mixture of phenol or furyl resins and refractory metals (vanadium, chromium, niobium, molybdenum, tungsten), as well as boron-containing components (amorphous boron, boron carbide, boron nitride), drying, heat-treating in a neutral medium [FR, A, 2,128,809].
The thus obtained coating has a low thermal resistance (up to 1000.degree. C.) in view of the structure porosity.
Still further known in the art is a process for obtaining a protective hafnium diboride and silicon carbide coating using a low-pressure plasma, according to which the powdery coating components are fed by a plasma Jet onto the surface to be protected [Process for applying HfB.sub.2 +20SiC coating from low-pressure plasma. Catalogue of United Technologies Corp., 1988]. This process makes it possible to obtain a multicomponent coating operable at temperatures of up to 2000.degree. C. in an oxidizing gas atmosphere.
However when applying the coating onto large size articles, special equipment is required with a controlled atmosphere and a working space more than twice as large as the size of the articles to be coated. Moreover, it is practically impossible to uniformly apply coatings onto articles of intricate configurations having deep cavities and narrow grooves.
Still further known in the art is a CVR-Si process for obtaining protective coatings which comprises reaction bonding of the substrate material ca
REFERENCES:
patent: 3770487 (1973-11-01), Gibson et al.
patent: 5368940 (1994-11-01), Takei et al.
Demin Alexander Victorovich
Kostikov Valery Ivanovich
Kravetkii Gennady Alexandrovich
Kuznetzov Andrey Vasiljevich
Rodionova Valeriya Veniaminovna
Aerospatiale - Societe Nationale Industrielle
King Roy V.
Nii, Grafit Research Institute
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