Y.J. Wu

Preparation of high-quality ß-SiC nanowhiskers by using carbon fibres as carbon source

Recently, many novel one-dimensional nanomaterials have been prepared and investigated in detail. Since s-SiC nanowhiskers are of extremely high hardness, high thermal and chemical stability and possess a wide band gap, they are viewed as promising material in applications from electronic devices to novel composite materials [1–6]. s-SiC nanowhiskers have been synthesized by various techniques, such as carbon nanotubes confined reaction (CNCR), hot filament chemical vapor deposition (HFCVD), carbothermal reduction, and floating catalyst method [7–10]. In the process of preparing s-SiC nanowhiskers, the selection of the carbon source is a key factor. Presently, the carbon sources used usually include carbon nanotubes, carbon powders, activated carbon, and C6H6. CNCR needs expensive carbon nanotubes as carbon source [7], which is unfavorable to large-scale production. HFCVD [8] and the floating catalyst method [10] use carbon powders and C6H6 as carbon source, respectively. Both of these two methods need to employ catalysts, which are difficult to be removed from the final products. Activated carbon used in the carbothermal reduction method easily makes the SiC nanowhisker connect to chains [9]. At present, suitable carbon sources are still under investigation for effectively preparing SiC nanowhiskers. In the present paper we chose cheap carbon fibers with diameters in micrometer scale as the carbon source to react with the mixture of SiO2 and Si powders to prepare high-quality s-SiC nanowhiskers. The microstructure of the product is analyzed and a possible formation mechanism is proposed. The schematic diagram of the SiC nanowhisker preparation apparatus is depicted in Fig. 1. This highfrequency induction heating system is mainly composed of a quartz tube, a high-purity graphite cylinder, and copper induction coil. The high-purity graphite cylinder is placed in the middle of the quartz tube wrapped by the induction coil. Micrometer-scale carbon fibers were packed tightly in the upside of the graphite cylinder and the mixture of SiO2 and Si powders with molar ratio of 1:1 was placed at the bottom of the graphite cylinder. After pumping down the quartz tube to a pressure of 5.3 Pa, argon gas was flowed through the quartz tube at 100 sccm for keeping