Synthesis of SiC microtube with villus-like morphology and SiC fiber
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Baig-Gyu Choi and Chang-Yong Jo High Temperature Materials Group, Korea Institute of Machinery and Materials, Changwon, Kyungnam 641-010, Republic of Korea
Ungyu Paik Department of Ceramic Engineering, Hanyang University, Seoul 133-791, Republic of Korea (Received 1 October 2004; accepted 28 October 2004)
Silicon carbide (SiC) microtubes were synthesized and characterized via a vapor–solid (VS) reaction of carbon fiber (Csolid) and SiO(gas). The synthesis mechanisms were investigated. The precursor led complete conversion of [SiO(gas) + C(solid)] into [SiC(solid) + CO(gas)] through overall reaction under inert gas flow at and above 1350 °C. Carbon fibers with small surface area (0.7–2.0 m2 g−1) were gradually converted to SiC microtubes with large specific surface area (45–63 m2 g−1). Inner surface of SiC microtubes indicated a villus-like morphology, which consisted of submicron-sized SiC villi. The outer surface of the SiC microtubes was smooth. Inner surface morphology of SiC microtubes was dependent upon synthesizing temperature. Thickness of villus-like layer in SiC microtubes increased with increasing synthesizing temperature, showing 0.25 and 0.5 at 1350 and 1400 °C, respectively. Both VS and gas–liquid–solid (VLS) growth mechanisms were investigated in synthesis of SiC fiber as a reaction byproduct, and the reaction was governed by both growth mechanisms.
I. INTRODUCTION
Silicon carbide (SiC) has been applied to various industries due to its attractive properties: high hardness and strength, low thermal expansion coefficient, good heat transfer characteristics, and good oxidation resistance due to the formation of protective silica (SiO2) layer. These properties allow SiC to fully meet the conditions required to be a catalyst support. In spite of the above advantages, there is still a challenging technical problem in preparing porous SiC materials of large surface area, with limitations of conventional methods. Alternative processes to increase surface area of ceramic materials have been developed.1–4 Several methods related to overcome the major drawback of SiC, very small surface area, have been reported.5–8 In particular, there have been many attempts to increase the specific surface area of SiC as a catalyst support.11,12 Recently, preparation of SiC material with the desired morphology using a
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0049 J. Mater. Res., Vol. 20, No. 2, Feb 2005
shape memory synthesis (SMS) technique has been developed.9–14 Keller et al. developed SiC as a catalyst support of smooth inner and outer surface morphology with medium surface area (70 m2 g−1).11,12 They show the limited thickness in SiC microtube due to diffraction distance or diffusion barrier and relatively smooth surface. Therefore, to increase thickness and to form the desired morphology, i.e., villus-like (or radial) grain morphology, a development of new type morphology with large surface area is still needed for the efficient catalyst support. Preparation
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