Synthesis and characterization of SiC nano powder with low residual carbon processed by sol–gel method A. Najafi a, ⁎, F. Golestani Fard a, b , H.R. Rezaie a, b , N. Ehsani a a School of Metallurgy and Materials Engineering, Iran University of Science and Technology, 16844, Narmak, Tehran, Iran b Center of Excellence for Advanced Materials, Iran University of Science and Technology, 16845-195, Narmak, Tehran, Iran abstract article info Article history: Received 26 April 2011 Received in revised form 14 November 2011 Accepted 17 December 2011 Available online 24 December 2011 Keywords: Nanostructured materials Sol–gel processes Chemical synthesis Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) Silicon carbide nanopowders and nanowhiskers were synthesized using phenolic resin and silicon alkoxide as precursors through sol–gel process with atomic ratio of C/Si = 1.8 in water–solvent–catalyst–dispersant system. The effects of soaking time on free carbon content and synthesized β-SiC particle morphology were evaluated at 1500 °C. The synthesis process of β-SiC nanopowders was completed at 1500 °C after 1 h while β-SiC nanowhiskers were heterogeneously nucleated and grown from obtained nanopowders after 2–3 h. The detected free carbon content in whiskers was less than 1% after 3 h. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Carbide compounds are generally known as very hard ceramics with outstanding chemical properties on account of strong bonds between carbon atoms and cations such as Si, B, Ti, etc. Among these compounds, silicon carbide is one of the non-oxide ceramics which has various industrial applications in the form of powder, whisker etc. High melting point, high thermal conductivity, high oxidation resistance, high mechanical strength and good chemical properties are some of its most important characteristics [1–3]. Nowadays, nano-sized carbide products are of great importance owing to higher sinterability, lower sintering temperature, pressure or time, high diffusion rates, and high specific surface area. In addi- tion, there is no need for additives as sintering aids in comparison to those associated with coarser particles [4]. Nano-sized silicon carbide powder is used for production of high-temperature ceramic bodies, metal matrix composites (MMCs), ceramic foams, etc. SiC nanowhiskers are extremely useful as composite reinforcement because of their high strength and hardness as well as their high aspect ratio [5]. This material can be used in electrical industries, high temperature ceramic devices and as reinforcement for ceramic composites [6–9]. Silicon carbide is, however, a covalent bond material and is difficult to be sintered without additives [10,11]. The manufacturing of nano-sized powders by milling of Acheson SiC products has never been successful. Nano-sized particles can be obtained by several advanced technologies such as rice hull conver- sion, CVD processes, sol–gel processes and laser gas phase pyrolysis or laser evaporation processes as reported [12]. Fine particle size, uniform spherical shape, high purity and no agglomeration along with low cost are considered as necessary char- acteristics for an ideal powder to be used to produce SiC components. Sol–gel technology has been utilized to prepare ceramic materials using reactive replica techniques because of low cost, no troublesome procedure, high-purity, good chemical homogeneity and relatively low temperatures needed to obtain ultrafine powder [13,14]. There- fore, this method is thought of great interest because it offers relative- ly inexpensive processing of a wide range of materials. On the other hand, sol–gel process has a potential advantage over the other methods not only for achieving homogeneous mixing of the compo- nents on the atomic scale but also for the possibility of forming films or fibers from gels which are of technological significance [15]. The flexibility of sol–gel chemistry, involving Metal alkoxides such as silicon alkoxides as raw materials and the ability to prepare stable inorganic matrices close to room temperature are compatible with a wide variety of dyes. Until now, molecules were dispersed within or grafted onto sol–gel networks [16,17]. Tamon et al. synthesized silica alcogels by the sol–gel polymerization of Tetraethoxysilane (TEOS) using HCl and NH 3 as catalysts and elucidated the influence of the hydrolysis time on the gelation time and the visible light transmission of alcogels [18]. Jinwang Li et al. have developed a two-step sol–gel process to synthesize phenolic resin-SiO 2 hybrid gels with oxalic acid (OA) and hexamethylenetetramine (HMTA) as the catalysts and subsequently, obtained SiC powders by carbothermal reduction of the as-received Powder Technology 219 (2012) 202–210 ⁎ Corresponding author. Tel.: +98 2173912834; fax: +98 2177240291. E-mail address: ab_najafi@iust.ac.ir (A. Najafi). 0032-5910/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2011.12.045 Contents lists available at SciVerse ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec