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−SiO 2 ) nanocomposites. C−SiO 2 nanocomposites with C/SiO 2 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−SiO 2 nanocomposites and SiC products. Highly crystalline SiC nanoparticles and nanofibers (CS-3.28 and CS-4.21) were obtained from mesoporous C−SiO 2 nanocomposites with the carbon content greater than a C/SiO 2 stoichiometric ratio of 3 (e.g., C/SiO 2 = 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−SiO 2 nanocomposites with a lower carbon content (e.g., C/SiO 2 = 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−SiO 2 nanocomposite with C/SiO 2 = 2.51 was nanofibers, and only less than 15% nanoparticles was observed in this sample. The carbothermal reduction of dense C−SiO 2 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−SiO 2 nanocomposites. SiC with controlled nanostructures can be synthesized by simply varying the porosity, C/SiO 2 ratio, and structure of the precursors.