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Pulsed-power volume-heating chemical vapor infiltration

Published online by Cambridge University Press:  31 January 2011

José I. Morell ,
Demetre J. Economou  and
Neal R. Amundson
José I. Morell
Affiliation:
Department of Chemical Engineering, University of Houston, Houston, Texas 77204-4792
Demetre J. Economou*
Affiliation:
Department of Chemical Engineering, University of Houston, Houston, Texas 77204-4792
Neal R. Amundson
Affiliation:
Department of Chemical Engineering, University of Houston, Houston, Texas 77204-4792
*
a)Author to whom correspondence should be addressed.
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Abstract

The dynamic behavior of a novel chemical vapor infiltration (CVI) technique called pulsed-power volume-heating CVI is investigated using a diffusion-reaction model. In this technique, a volume-heating source (e.g., RF or microwave) is used to heat the preform. The source power is modulated in time (e.g., square-wave modulation) with a specific period and duty cycle. During the low-power part of the cycle, the temperature of the composite drops, reducing the reaction rate and thus allowing the precursor gas to diffuse into the composite, essentially “refilling” the composite. This alleviates reactant concentration gradients within the composite minimizing density nonuniformities. The high-power part of the cycle is used to achieve rapid reaction rates, thereby minimizing processing time. CVI of a carbon fiber preform with carbon resulting from methane decomposition is taken as an example to illustrate the technique. The results reveal the dependence of density uniformity and processing time on relevant variables such as pulse period, duty cycle, power density level, and methane mole fraction. It is shown that pulsed-power volume-heating CVI can provide a window of operating conditions leading to rapid and complete densification.

Type
Articles
Information
Journal of Materials Research , Volume 7 , Issue 9 , September 1992 , pp. 2447 - 2457
Copyright
Copyright © Materials Research Society 1992

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