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Modeling study of effects of temperature profiling on CVI processing of woven graphite preforms with dimethyldichlorosilane

Published online by Cambridge University Press:  03 March 2011

Merrill K. King
Affiliation:
7711 Random Run Lane, Apt. 204, Falls Church, Virginia 22042
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Abstract

There is currently considerable interest in producing high temperature capability graphitic materials by first weaving graphite fiber tows (yarns) into a “preform” structure, followed by densification via cracking of precursor compounds such as dimethyldichlorosilane within the pores (macro and micro) at high temperature. The model described in this paper addresses this densification process, treating diffusion of gaseous species both within the macropores (spaces between the tows) and the micropores (spaces between individual fibers in the tows) and finite kinetics associated with the cracking of the precursor gas (treated parametrically). The resulting model is used to examine the effects of temperature distributions through cylindrical preforms on ultimate densification distribution. As might be expected (and as observed experimentally), uniform temperature through the preform leads to premature full densification of the pore structure at the periphery of the cylinder (blocking further densification in the interior), leading to severe porosity in the interior regions. Effects of externally imposed nonuniform temperature profiles (possibly via microwave heating) in alleviating this problem are examined, and it is shown that proper profiling can lead to nearly complete uniform densification throughout the preform.

Type
Articles
Copyright
Copyright © Materials Research Society 1994

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References

REFERENCE

1Froment, G. B. and Bischoff, K. B., Chemical Reactor Analysis and Design (John Wiley and Sons, New York, 1979), pp. 163167.Google Scholar