Influence of raw powder size, reaction temperature, and soaking time on synthesis of SiC/SiO2 coaxial nanowires via thermal evaporation

Abstract

High-yield SiC/SiO2 core-shell nanowires were synthesized without adding metal catalysts from outside through a simple thermal evaporation of silicon powders during decomposition of methane gas. The influence of three parameters, size of Si raw powder (50 nm and 5 μ m), reaction temperature (1573, 1623 and 1673 K), and soaking time (1, 3 and 6 h), was investigated.The typical synthesized nanowires from different conditions possess the diameter of no thicker than 100 nm with several tens micrometers in length. It was addressed that the condition using the smaller size Si powder, which contained the highest amount of oxygen, at higher temperature lead to more complete reaction to obtain a large quantity of nanowires. The synthesized nanowires at higher reaction temperature and longer soaking time possessed larger core than those nanowires prepared at lower reaction temperature and shorter soaking time. Oxidation of larger size Si powder improved yield of nanowires. Based on these results, it was suggested that the typical nanowires should be grown via the oxide-assisted growth mechanism.

Exhaust gas analysis and formation mechanism of SiC nanowires synthesized by thermal evaporation method

“…3, and five diffraction peaks could be identified as (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) reflections of ␤-SiC without any other impurities. From the transmission electron microscope (TEM) observation, and Fourier-transform infrared spectroscopy (FT-IR) characterizations in our previous work [22], it was confirmed that the SiCNWs produced by this process were core-shell type nanowires those had a single crystal ␤-SiC core and low-crystalline SiO 2 shell.…”

“…Silicon powder (average particle size 5 m, 99.99% purity, Kojundo Chemical Laboratory Co., Ltd., Japan) was pre-oxidized in air at 800 • C for 1 h to increase the oxygen content in the raw powder as mentioned in the previous research [22]. Oxidized silicon powder was placed in a mullite boat which was covered with an alumina fiber net (3025-T Standard Woven Fabric, Nitivy Co., Ltd., Japan), and was carefully put in the center of a mullite tube furnace as schematically shown in Fig.…”

“…These methods require special equipments and complicated procedures that make the production cost very high, and also need some metal catalysts, which reduce the purity and then degrade the crucial properties of SiCNWs. Thermal evaporation method for the synthesis of SiCNWs was developed by Khongwong et al [21,22]. Silicon powder and methane gas (CH 4 ) were used in this method as sources of Si and C, respectively, while without using any metal catalyst.…”

Cubic SiC Nanowires: Growth, Characterization and Applications

“…Alternatively, a CVD method can be employed making use of Fe as catalyst and methane as precursor (Zang et al, 2002). A high yield core/shell SiC/SiO 2 NW production method without the use of catalyst was developed starting from raw powders of Si via an oxide assisted thermal evaporation process (Khongwong et al, 2009). Core-shell SiC NW have also been synthesized from carbon monoxide using Ni catalyst by carbothermal reduction method (Attolini et al, 2008).…”

Synthesis of several millimeters long SiC–SiO2 nanowires by a catalyst-free technique

“…Four fundamental growth mechanisms were proposed to explain the growth model of nanowires, including VS, VLS, solid-liquid-solid (SLS) and oxide assisted growth (OAG), in which VS and VLS mechanisms were most commonly involved [33][34][35]. On the basis of experimental results, a catalyst-free VS growth mechanism was proposed to disclose the growth model of several millimeters long SiC-SiO 2 nanowires.…”