Hermetic ceramic composite structures

Details Hermetic ceramic composite structures Hermetic ceramic composite structures

1996-09-11

1997-10-28

Derrington, James

Plastic and nonmetallic article shaping or treating: processes

Carbonizing to form article

264 297, 264 62, 264 81, C04B 3580

Patent

active

056815115

ABSTRACT:
Methods for making hermetic silicon carbide matrix composite structures by CVI. A fibrous preform is created by winding strands of yarn of refractory fiber material helically about a graphite mandrel. Impregnation of the preform is carried out in a subatmospheric pressure zone at a pressure of about 700 Pa or less by maintaining a relatively slow flow of a mixture of helium and an alkyl chlorosilane through a coating zone heated to a temperature of between about 1100.degree. to 1200.degree. C. at a rate between about 2 and about 10 times the diffusion rate of the gaseous atmosphere in the fibrous preform. Coating is continued until silicon carbide impregnates the interstices of the fibrous preform and preferably deposits an outer layer of dense pore-free silicon carbide thereupon. The resultant structures are hermetic and provide leak-free containment of gases such as helium at temperatures of as high as 1,000.degree. C. and a pressure differential as high as about 20 MPa.

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Caputo et al., "Fiber-Reinforced Ceramic Tubular Composites", (ORNL/TM-10466), pp. 1-47, Nov. 1988.
Chin et al., "The Structure of Chemical Vapor Deposited Silicon Carbide", Thin Solid Films, vol. 40, pp. 57-72, (1977).
Gulden, T.D., "Deposition and Microstrucutre of Vapor-Deposited Silicon Carbide", J. Am. Cer. Soc., vol. 51, No. 8, pp. 424-427, Aug. 1968.

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