Morphology-Controlled Synthesis of Nanostructured Silicon Carbide
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Morphology-Controlled Synthesis of Nanostructured Silicon Carbide Xiang-Yun Guo*, Guo-Qiang Jin and Ya-Juan Hao State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China Email: [email protected] ABSTRACT Phenolic resin and tetraethoxysilane were used to prepare a binary carbonaceous silicon xerogel, the precursor of silicon carbide (SiC). By employing different additives in the sol-gel process, a series of xerogel precursors with differently chemical composition were obtained. Heating these xerogels to 1250 , nanostructured β-SiC with various morphologies including nanowires, nanofibers, nanoparticles and mesoporous SiC were produced via carbothermal reduction. The preparation method of the xerogels was presented and the influences of different additives on the sol-gel process and the SiC formation were discussed in this paper. INTRODUCTION Silicon carbide (SiC) is a kind of covalent material with a tetrahedral structural unit similar to diamond, and therefore has excellent mechanical property and chemical stability. As a result the SiC materials have been applied to many fields such as high temperature, high power, high frequency and other harsh environments as advanced structural and functional materials [1]. Generally the physical and chemical properties of materials are strongly dependent on their morphology. For the SiC materials, nanoparticles, nanowires, whiskers and mesoporous SiC possess different properties and therefore have various applications, respectively. For example, SiC whiskers have high mechanical intensity, and they are usually employed as reinforcing materials in metallic and ceramic composites [2]. SiC nanowires have good elasticity and unique field emission properties, and have potential applications in the development of nanodevices [3]. Porous SiC is an important optical material because it possesses much more intense visible luminescence than crystalline SiC at room temperature [4-5]. Additionally, porous SiC materials also have potential applications in heterogeneous catalysis and separation due to their excellent thermal stability and chemical inertness. As a result, the morphology-controlled synthesis of nanostructured SiC becomes very active in the field. The preparation of nanostructured SiC materials has been achieved through several routes including chemical or physical vapor depositions [6], pyrolysis of polycarbosilane [7], shape memory synthesis [8] and carbothermal reduction of gel-derived precursors [9]. In this paper, we describe an improved sol-gel route to prepare nanostructured β-SiC materials. The present route can produce whiskers, nanowires, nanoparticles and mesoporous SiC via employing different additives in the sol-gel process.
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EXPERIMENTAL DETAILS In the present route, phenolic resin (condensation polymer from formaldehyde and phenol, softening point 80-90 ) and tetraethoxysilane (TEOS) were employed for preparation of a binary carbonaceous silicon sol. In the sol, phenolic resin and TEO
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