CONTINUOUS SYNTHESIS OF SILICON-CARBIDE WHISKERS

A two-step reaction scheme has been employed for the synthesis of SiC whiskers at 1450 degrees C under an argon or hydrogen flow. First, SiO vapour was generated via the carbothermal reduction of silica in a co ntrolled manner. Second, the generated SiO vapour was reacted with car bon-carrying vapours such as CO and CH4, which resulted in the growth of SiC whiskers on a substrate away from the batch. A higher growth ra te was observed in the hydrogen atmosphere due to the formation of CH4 which provides a more favourable reaction route. By the use of thermo dynamic calculations, the preferred reaction routes have been selected for an efficient synthesis of SiC whiskers, and a continuous reactor has been designed. The system consists of a boat-train loaded with the silica-carbon mixture and iron-coated graphite substrate above it in an alumina-tube reactor. By pushing the boat-train into the hot zone a t a fixed speed, SiO vapour is constantly generated. High-quality SiC whiskers have been grown on the substrate with diameters of 1-3 mu m. The yield was about 30% based on the silicon input as SiO2 and silicon output as SiC whiskers. This demonstrates the feasibility of continuo us production of high-quality SiC whiskers which does not require addi tional processes such as purification and classification.