Conversion of Carbon Fibers to SiC

The objectives of this program are to study the partial or complete conversion of small diameter, high strength carbon fiber multifilament tows to SiC and to understand the relationship of the conversion mechanisms to the morphology and properties of the resultant fibers. The project will utilize chemical vapor conversion processes in combination with a novel electromagnetic spreading technique for the precursor carbon yarns developed by MSNW, Inc. which should facilitate the uniform surface conversion of each filament of the precursor multifilament tow. The ultimate objective of the conversion process is the production of low cost, small diameter "psuedo-SiC" fibers for use in high temperature ceramic matrix composites. Commercial carbon fibers in multifilament yarns will be converted to SiC at elevated temperatures in an atmosphere of SiCl4, HC1, and H2. The kinetics of the conversion process will be studied as a function of temperature and the addition of boron to the system to modify the diffusional conversion mechanism. The morphologies, microstructures, and tensile properties of the resulting fibers will be determined. Anticipated Benefits: Potential applications for such fibers are reinforcements for high temperature composites for use in advanced defense and aerospace systems. Commercial applications include heat exchangers, vehicular and industrial turbine engines, and fusion energy conversion devices.