Synthesis of silicon carbide nanorods from mixture of polymer and sol–gel silica

Abstract

Silicon carbide possesses many unique properties like superior strength, corrosion and oxidation resistance at elevated temperature [1]. Silicon carbide in the fibrous form is employed for the development of ceramicmatrix and metalmatrix composites (CMCs and MMCs) [2, 3]. Recently there is growing interest in the synthesis of nanofibres, which could be used for the development of nanocomposites, solid-state lubricants, catalysts and components of magnetic devices [4]. Nano silicon carbides are synthesized as nanorods, nanowires, nanotubes and nanofibres [5–8]. Silicon carbide nanomaterials which can be used as reinforcing material are generally prepared by chemical vapor deposition (CVD) [9], arc-discharge [10], polymer blend technique [11] and by reaction between carbon nanotubes and silicon monoxide [12]. The authors had also employed and reported polymer blend technique for the development of pitch based carbon fibres [13, 14]. It was seen by the authors during their efforts to develop carbon fibres from pitches modified with polymers that polyphenylene oxide–polystyrene (PPO–PS) blend does not give fibres on spinning and gives rod like materials [13]. Based on the results of the above studies, attempts have been made in the present investigation to synthesize SiC nanorods by blending sol–gel derived silica with PPO–PS polymer. Commercially available PPO–PS was used as carbon source and methyltriethoxysilane [(MTEOS) Lancaster, 98%] and tetraethoxysilane [(TEOS) E’Merck, 98%] are used as silica source. PPO–PS was carbonized at 1000 C in inert atmosphere to determine carbon residue. PPO–PS was dissolved in dichloromethane and was mixed with MTEOS sol, which was prepared by hydrolyzing a mixture of MTEOS, water and dichloromethane. The mixture was stirred well for about 2 h. The sol-containing polymer was then allowed to gel at room temperature and dried at 60 C to obtain polymer incorporated with sol–gel derived silica, which is the silicon carbide nanorods precursor. The same experiment was repeated with TEOS sol. The SiC precursor prepared as above was carbonized at 1000 C and analyzed for carbon and silica contents. The carbonized product was further heated at 1400 C under argon atmosphere to get a mixture of SiC, carbon and silica. The pyrolysed products (Heat treatment temperature = 1400 C) were oxidised in air at 800 C to remove the free carbon. The carbonized, pyrolysed and oxidized products of PPO–PS + MTEOS and PPO– PS + TEOS were characterized by scanning electron microscopy (SEM, LEO-440). The oxidized sample derived from PPO–PS + MTEOS derived silica was also characterized by transmission electron microscopy (TEM, Jeol JEM 2000 CX). The FTIR spectra of the precursor (PPO–PS + MTEOS derived SiO2) and the pyrolysed sample (heat treatment temperature = 1400 C) were recorded by KBr pellet method using Perkin Elmer FTIR 2000. X-ray diffraction V. Raman (&) G. Bhatia P. R. Sengupta Carbon Technology Unit, Division of Engineering Materials, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012, India e-mail: vasantha@mail.nplindia.ernet.in