Synthesis And Characterization Of Silicon Carbide Nanomaterials

On the basis of comprehensive and thorough investigation of literature concerning the synthesis and application developments of silicon carbide (SiC) nanomaterials, in this dissertation, solid state high-temperature pyrolysis of transition metal organic compounds and reduction route was used to synthesize SiC nanomaterials. 3C-SiC nanowires was prepared starting from SiO₂, C₂H₅OH, and Mg was used as reductant through solvothermal route at 200℃. As polyvinylpyrrolidine (PVP) was added into the above reactant system, the final products obtained at 180℃were mixed 3C and 2H- SiC. Tetraethyl orthosilicate (TEOS) was used as silicon source and hydrolized under alkaline conditions. SiO₂ spheres were prepared by hydrolysis of TEOS. The as-produced SiO₂ spheres was used as reactant, and C₂H₅OH was used as carbon source, Mg as reductant in an autoclave at 200℃for 10 h, 3C-SiC was finally obtained. The thermal stabilities and optical properties were reported here. The main contents can be summarized as follows:1.β-SiC nanomaterials were successfully produced by the reduction of H₂SiO₃ and by the high-temperature pyrolysis of transition metal organic compounds (ferrocene) with metallic Mg powder at 550℃in an autoclave. X-ray diffraction patterns of the sample can be indexed as the cubic SiC with the lattice constant a = 4.351(?) which is close to that of the reported value (JCPDS card no. 29-1129, a = 4.359(?)). Transmission electron microscopy images show that the product mainly composed of belt-like nanostructures and irregular nanoparticles. The nanobelts with width ranging from 20-50 nm and lengths up to hundreds of nanometers. The HRTEM image of a part of SiC nanocrystals reveals that the inter-planar spacing of the two adjacent frings is about 0.25 nm, which is consistent with the reported value (JCPDS card, no. 29-1129) to the (111) lattice planes of the crystalline SiC. The regular arranged lattice fringes can be clearly seen from HRTEM images, indicating the well crystalline of the as-prepared samples. TGA curve reveals that the sample has thermal stability below 700℃, and room-temperature photoluminescence (PL) spectrum of the sample show a strong emission peak centered at 400 nm. 2. 3C-SiC nanowires were prepared starting from SiO₂, C₂H₅OH, and Mg as reductant through a solvothermal route at 200℃. X-ray diffraction patterns of the sample can be indexed as the cubic cell of SiC with the lattice constant a = 4.357(?), in good agreement with a = 4.359(?) (JCPDS card no. 29-1129). Transmission electron microscopy images show that the product mainly composed of nanowires with diameters of 10-30 nm and lengths up to tens of micrometers; The High-resolution transmission electron microscopy image of a part of SiC nanowires reveals that the inter-planar spacing of the two adjacent frings is about 0.25 nm, which is consistent with the reported value (JCPDS card, No. 29-1129) to the (111) lattice planes of the crystalline SiC. In addition, the [111] direction is parallel to the axis of the nanowire, indicating that the nanowire grows along the [111] direction. Thermal gravimetric analysis curves reveal that the nanowires have thermal stability below 800℃, and room-temperature photoluminescence spectrum of the 3C-SiC sample show a strong emission peak centered at 403 nm. As polyvinylpyrrolidine was added into the above reactant system, the final products obtained at 180℃or 200℃all were mixed 3C and 2H-SiC flakes. The calculated lattice constants of a = 3.079(?) and c = 5.037(?) agree well with those of the 2H-SiC (JCPDS card no. 29-1126), while 3C-SiC with the calculated lattice constant a = 4.357(?) is close to the reported value ofβ-SiC (JCPDS card no. 29-1129). TEM image of the sample with mixed phases, displaying that the products are mainly composed of hexagonal flakes and irregular shaped nano-flakes. The corresponding HRTEM images reveal that the irregular flake was 3C-SiC and the hexagonal flake was 2H-SiC.3. SiO₂ spheres were prepared at first by hydrolysis of tetraethyl orthosilicate (TEOS) under alkaline conditions. These as-prepared SiO₂ spheres was used as silicon source, while C₂H₅OH was used as carbon source, Mg was used as reductant at 200℃for 10 h, nanoscale SiC powder was obtained. X-ray diffraction patterns of the sample can be indexed as the cubic cell of SiC with the lattice constant a = 4.357(?), in good agreement with a = 4.359(?) (JCPDS card no. 29-1129). Transmission electron microscopy images show that the product mainly composed of nanoparticles and hollow nanospheres (with diameters ranging from 600-1000 nm). The High-resolution transmission electron microscopy image of a part of the SiC nanospheres reveals that the inter-planar spacing of the two adjacent frings is about 0.25 nm, which is consistent with the reported value (JCPDS card, no. 29-1129) to the (111) lattice planes of the crystalline SiC. The regular arranged lattice fringes can be clearly seen from the HRTEM images, indicating the well crystalline of the as-prepared samples.