Processing of carbon fiber reinforced silicon oxy-carbide matrix composites through the sol-gel route

Abstract

Restricted applications of carbon-carbon composites due to their susceptibility to oxidation at high temperatures has renewed interest in all aspects relating to fiber reinforced glasses and ceramics. These include choice of reinforcing fibers and matrixes, their processing, fiber/matrix interactions as well as performance under varying conditions. Present studies have been performed to fabricate carbon fiber reinforced Silicon oxy-carbide matrix composites through sol-gel route using tetraethylorthosilicate (TEOS) and 1,4-butanediol as starting precursors. The composites have been fabricated by a polymeric composites route. The structural development specially at the fiber/matrix interface have been studied using SEM. On pyrolysis of the composites at 1000°C, the matrix has been found to be well surrounding the fibers; still, the composites exhibit mixed tensile cum shear mode failure under flexural loading. No oxidation of the fiber surface by oxygen present in silicon oxy-carbide is observed. The composites have been further heat treated to a temperature of around 1450°C. Though consolidation of the matrix is observed to be increased, the fibers are not damaged. XRD analysis of the matrix in the composites exhibit development of SiC. SEM examination of the composites' cross-section does not exhibit any strong reaction between fibers and matrix. Composites heat treated at 1450°C exhibit about 30% improvement in flexural strength over those processed at 1000°C, maintaining the non-catastrophic fracture.

Keywords:

• Sol-gel
• carbon fiber composites
• silicon oxy-carbide
• fiber/matrix bonding
• mechanical properties
• composites fracture