Role of pores in the carbothermal reduction of carbon-silica nanocomposites into silicon carbide nanostructures

Abstract

Silicon carbide nanostructures were synthesized by carbothermal reduction of carbon-silica (C-SiO2) nanocomposites. C-SiO2 nanocomposites with C/SiO2 molar ratios of 1.90-4.21 were used in this study. Thermogravimetric analysis, nitrogen sorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared spectroscopy were used to characterize C-SiO2 nanocomposites and SiC products. Highly crystalline SiC nanoparticles and nanofibers (CS-3.28 and CS-4.21) were obtained from mesoporous C-SiO2 nanocomposites with the carbon content greater than a C/SiO2 stoichiometric ratio of 3 (e.g., C/SiO2 = 3.28 and 4.21 by mole), and they had a BET surface area of 83.0-76.7 m(2)/g after unreacted silica and carbon were removed. In contrast, SiC was not formed in the mesoporous C-SiO2 nanocomposites with a lower carbon content (e.g., C/SiO2 = 1.91 and 2.51 by mole). However, when such mesoporous nanocomposites were infiltrated with a small amount of carbon, SiC nanoparticles and nanofibers with high crystallinity were produced. The major phase formed from the mesoporous C-SiO2 nanocomposite with C/SiO2 = 2.51 was nanofibers, and only less than 15% nanoparticles was observed in this sample. The carbothermal reduction of dense C-SiO2 nanocomposites resulted in mesoporous SiC with low crystallinity under the heating conditions used. As a result, the pores play a vital role in the carbothermal reduction of C-SiO2 nanocomposites. SiC with controlled nanostructures can be synthesized by simply varying the porosity, C/SiO2 ratio, and structure of the precursor