Date of Award
Doctor of Philosophy
Carbon-carbon (C/C, carbon fiber reinforced carbon matrix) composites are widely used in the aerospace industry because of the material's high temperature capability and structural properties. C/C maintains its mechanical and friction properties during extreme conditions so it is used extensively for high energy brakes, clutches, nosecones and leading edges of aircraft/spacecraft. Manufacturing C/C is expensive, requires high temperatures (approx. 1000°C) and typically requires rough vacuum environments (5-225 Torr). There are 5 general types of chemical vapor infiltration (CVI) systems and each type has a standard configuration in terms of a vacuum plumbing circuit. Standard CVI systems have a total carbon deposition efficiency of 5-30% using a reaction zone filled with carbon fiber preforms. Total processing time varies from 50 to 2000 hours depending on the type of system and its temperature, pressure and residence time. Unused hydrocarbon reaction exhaust (effluent) gases are either burned off or used to power something externally adding more CO2 and CO to the environment. A reduction of processing time and waste is needed to reduce the cost of production and the emissions of greenhouse gases. A new method can be added to 4 of the general types of CVI that decreases the residence time by re-circulating a controlled amount of the effluent gases through a separate in-situ isobaric semi-closed loop circuit which also allows for more carbon to be deposited per liter of virgin precursor gas in the reaction zone. An electric potential is also applied to compare the effect on carbon deposition to standard techniques. Re-circulating a portion of effluent gases through the reaction zone decreases the residence time with minimal effect on the desired matrix microstructure. Decreasing the residence time and re-circulating a portion of effluent gases increases the deposition rate and total carbon deposition efficiency. This re-circulating loop can be added to any CVI system to enhance the process, lower production costs and reduce greenhouse emissions.
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