Sintering studies of carbon fibre-reinforced fused silica for high-temperature applications

Due to its negligible thermal expansion coefficient (nearly zero) and low weight (specific gravity 2.1), fused silica can potentially be used in high-temperature applications involving thermal shock and in aerospace applications where weight savings is an important consideration. However, fused silica is limited by its intrinsic brittleness and thus, fibres can be added to increase its toughness. Carbon fibres have high-temperature capabilities, high strength, and matching thermal expansion coefficient with fused silica. However, inorganic additives tend to devitrify fused silica at elevated temperatures (during sintering) into its crystalline counterparts, thereby destroying its thermal shock resistance. We investigated the effects of adding different forms of carbon fibres on the mechanical properties and devitrification of fused silica. The devitrification temperature was greater than the temperature required for full sintering. Compressive strength and modulus of the fused silica increased significantly, and the toughness was substantially improved.