Abstract
β-silicon carbide (SiC) powders were synthesized by the carbothermal reduction of methyl-modified silica aerogel/carbon mixtures. The correlations between the phase evolution and morphologies of the SiC powders and the C/SiO2 ratio were investigated. At a C/SiO2 ratio of 3, β-SiC formed at 1425 °C and single-phase SiC powders were obtained at 1525 °C. The methyl groups (-CH3) on the silica aerogel surfaces played important roles in the formation of SiC during the carbothermal reduction. SiC could be synthesized from the silica aerogel/carbon mixtures under lower temperature and C/SiO2 ratios than those needed for quartz or hydrophilic silica. The morphology of the SiC powder depended on the C/SiO2 ratio. A low C/SiO2 ratio resulted in β-SiC powder with spherical morphology, while agglomerates consisting of fine SiC particles were obtained at the C/SiO2 ratio of 3. High-purity SiC powder (99.95%) could be obtained with C/SiO2 = 0.5 and 3 at 1525 °C for 5 h.
Highlights
Silicon carbide (SiC) is a typical non-oxide ceramic material that forms covalent bonds in structural units
The absorption peaks near 1100, 800, and 460 cm−1 were assigned to the asymmetry, aerogel has a highly porous structure with mesopores, and its surface was modified by methyl groups symmetry, and bending modes of Si-O-Si, respectively [28,29]
+ 2CO2nanofiber-like (g) methyl groups that are covalently bonded to the silica aerogel serve as a carbon source for the the silicon carbide (SiC) nuclei based on Equation (4), which is similar to the chemical vapor deposition (CVD) of SiC [35,44]
Summary
Silicon carbide (SiC) is a typical non-oxide ceramic material that forms covalent bonds in structural units. Other notable features of SiC are high thermal and electrical conductivities. Based on these excellent mechanical and electronic properties, SiC has been actively studied in various fields with respect to different applications such as for gas turbine components, heat exchangers, high temperature gas filters, power devices, heat dissipation substrates, and catalyst support materials. The SiC ceramics can be fabricated by sintering SiC powders or preceramic polymers [3,4,5] at high temperature because of the covalent nature of the Si-C bond and low self-diffusion coefficient [6]. Single crystals of SiC for power device applications can be grown from SiC powder compacts by physical vapor transport (PVT) or sublimation epitaxial growth (SEG) [7,8]. The defects (stacking faults and dislocations) in SiC single crystals, sinterability, microstructure, and properties of sintered SiC strongly depend on the purity, morphology, size, and distribution of the SiC starting powders [9,10,11,12]
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