Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Patent
1994-06-29
1998-03-10
Speer, Timothy
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
428426, 428428, 428432, 428699, 428701, 428702, 427421, 427422, 427427, 427429, B32B 1700
Patent
active
057259550
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to anti-oxidation protection for products made of composite material containing carbon.
So-called "thermostructural" composite materials are used for making parts that are required to exhibit good mechanical behavior when hot, in particular in the fields of braking, aviation and space. Such materials are constituted by refractory fiber reinforcement, e.g. made of carbon or of a ceramic, that is densified by a matrix, e.g. likewise carbon or a ceramic.
For applications that require the parts to spend time at high temperature in an oxidizing medium, ceramic matrix composites may be preferred to carbon matrix composites because of the poor resistance of carbon to oxidation.
Nevertheless, anti-oxidation protection remains necessary for ceramic matrix composites if they contain any carbon. This applies to composites of the carbon ceramic type in which the fiber reinforcement is made of carbon, e.g. C--SiC (carbon-silicon carbide) composites. This also applies to composites of the ceramic-ceramic type, e.g. SiC--SiC (silicon carbide-silicon carbide) including an interphase layer of carbon between the fibers and the matrix, as described in document FR-A-2 567 874.
A large amount of work has been done on anti-oxidation protection for thermostructural composites.
A known solution consists in forming a coating on the part made of composite material, which coating withstands wear and oxidation, and is generally a coating of silicon carbide (SIC) implemented by chemical vapor deposition.
Nevertheless, it is impossible in practice to make such an external coating without defects occurring, either at the moment of manufacture (pinhole defects) or else while the product is in use (cracking). The composite material is then not completely isolated from the ambient oxidizing medium.
To remedy such defects, proposals have been made to use an additional coating made of a material such as a silicate, borate, or borosilicate type glass which seals holes and cracks in the SiC coating by taking on a semi-solid state above a certain temperature.
Another known solution consists in providing internal type protection by vapor deposition of boron within the residual pores of the composite material, as described in U.S. Pat. No. 4 582 751. The fiber reinforcement of the composite material is initially porous to some extent and its pores are only incompletely blocked by the matrix material. Accessible pores therefore remain not only on the surface, but also within the bulk of the material, thus making it possible to form internal protection.
Internal type anti-oxidation protection for C--C (carbon-carbon) composite friction material is also described in document JP-A-63/023 036. Internal protection is obtained by impregnation with an aqueous solution of aluminum phosphate and by heating to 700.degree. C. in a non-oxidizing atmosphere.
The use of aluminum phosphate for forming a coating that provides protection against oxidation is well known. Thus, document GB-A-812 740 already discloses a method of protecting graphite against oxidation by carbon dioxide, in particular for graphite used as a moderator in a nuclear reaction that is cooled by carbon dioxide, with protection being provided by a coating composition in the form of a refractory cement containing graphite powder and a binder derived from a solution of aluminum phosphate with additions of kaolin, silicon, alumina, and/or other refractory oxides.
Finally, in order to further improve protection against oxidation, document FR-A-2 640 619 proposes providing internal protection by impregnating the residual pores of the composite material by means of a liquid solution of an alkaline silicate. Impregnation is followed by a drying stage and then by a heat treatment stage which has a lining effect to form an internal protective coating on the surfaces of the open pores in the composite material, which coating constitutes a non-oxidizing refractory residue and is self-sealing. The composite material comprising the internal protection may be provided with a r
REFERENCES:
patent: 4487804 (1984-12-01), Reven
patent: 4530853 (1985-07-01), Lewallen
patent: 4582751 (1986-04-01), Vasilos
patent: 4726995 (1988-02-01), Chiu
patent: 5102698 (1992-04-01), Cavalier
Chemical Abstracts, vol. 108, No. 22, May 1988, Columbus Ohio, US, p. 311, Abstract No. 191634r, JP,A, 6323036 (Showa Denko K.K.), Jan. 30, 1988.
"Oxidation Protective Coating for Polycrystalline Carbon", Ceramic Engineering and Science Proceedings, vol. 10, No. 9-10, Oct. 1989, U.S. G. Palavit et al, p. 1425.
Bernard Xavier
Cavalier jean-Claude
Tawil Henri
Societe Europeenne de Propulsion
Speer Timothy
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