Carbon Thermal Reduction Preparation Of Silicon Carbide Nanowires And Its Properties

Silicon carbide (SiC), as one of the third-generation semiconductor materials, has been attracting extensive interest due to its outstanding properties, such as wide band gap, high melt point, high hardness, high thermal conductivity, high breakdown electric field, high electron velocity, high resistance to radiation, good mechanical property and can be used as a promise material for preparing high power device, high frequency device, low energy consumption device, high temperature device and high radiation device. Compared with bulk SiC material, SiC nanowires have superior optical, electric and mechanical properties. SiC nanowires can be used as reinforced element for metal-, ceramic-and polymer-matrix composites and to prepare luminescence diode, high power transistor and other optical, electric nanodevices. It also has widely potential application in the fields of field emission cathode material, photocatalyst, hydrogen storage material and self-cleaning coating. So, it is very significant to study the preparation and property of SiC nanowires.In this paper, SiC nanowires were prepared via carbothermic reduction of silica under normal atmosphere pressure without catalyst. The composition, morphology and microstructure of the SiC nanowires were characterized by X-ray powder diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) equipped with energy disperse spectrum (EDS), and transmission electron microscopy (TEM). The parameters, thermodynamics of reaction process and the growth mechanism of SiC nanowires were investigated. Finally, the photoluminescence property, field emission property and photocatalytic degradation property of as-synthesized SiC nanowires were also investigated. The main results obtained in this paper are given as below:1. Under normal atmosphere pressure,β-SiC nanowires were synthesized in C/SiO2 mole ratio of 3 and at reaction current 536 A (1400℃) for 20 min by using bamboo carbon as carbon source. Theβ-SiC nanowires have a core-shell structure with crystalline SiC core and amorphous SiO2 shell. The nanowires with diameter of 50-200 nm and length from tens to hundreds of micrometers have a rough surface morphology, and the SiC nanowires grow along<111> direction.2. The effect of the carbon source, mole ratio of C/SiO2, reaction current and reaction time on the morphology of the SiC nanowires synthesized by carbothermic reduction is discussed and the growth mechanism has also been elucidated. The results indicated that under different experiment parameters the synthesized products were allβ-SiC but with different morphology. The platelet-, bamboo-, pagoda-, and bead-like SiC nanostructure are obtained. The reaction current (temperature) has a crucial effect on the morphology of SiC nanowires. When the current (temperature) is low; the supersaturation degree is too low to form stable nucleation, and then lead to reduce the yield of SiC nanowires; when the current (temperature) is high, the SiC nanoparticles are easily formed due to high supersaturation degree, while the formation of SiC nanowires is restrained. The reaction time has little effect on the yield and diameter of SiC nanowires. With the increasing of time, the length and surface of SiC nanowires are gradually become long and smooth, respectively. During the experiment, no metallic catalyst was introduced and no metallic droplets were detected in the nanowires'tips confirmed by FE-SEM and TEM characterization.Thus, the growth of nanowires in our experiment was not following the conventional metal-catalyst VLS mechanism. Based on the experiment results, we proposed the vapor-solid mechanism for the growth of SiC nanowires.3. The photoluminescence, field emission and photocatalytic degradation property of SiC nanowires are investigated. Under 275 nm excitation at room temperature, the SiC nanowires exhibit a strong ultraviolet emission peak at 300 nm. The field emission property of SiC nanowires can be enhanced by annealing treatment and the turn-on field of SiC nanowires before and after annealing at 700℃for 3 h is 9.5 V/μm and 7.5 V/μm, respectively. The field emission is done by quantum-tunneling mechanism; In addition, the as-synthesized silicon carbide nanowires have a high photocatalytic degradation activity (72.20%) to Methylene blue after 6 h degradation.