Growth Of Silicon Carbide Nanowires Research Articles

Pyrolysis of soybean soapstock for hydrocarbon bio-oil over a microwave-responsive catalyst in a series microwave system

A novel Silicon carbide (SiC) foam ceramic based ZSM-5/SiC nanowires microwave-responsive catalyst was developed to upgrade the pyrolysis volatiles in a microwave-assisted series system (both the pyrolysis and catalytic systems were heated by microwave). The growth of SiC nanowires was helpful for the ZSM-5 growth on the SiC foam ceramic. Because the specific surface area of SiC foam ceramic was improved. The dielectric properties of the composite catalyst were improved due to the growth of SiC nanowires. Bio-oil composition analysis showed that area percentage of hydrocarbons and aromatic hydrocarbons could reach 80.89% and 40.48% at catalytic temperature of 450 ℃and 500 ℃, respectively. The microwave-responsive composite catalyst had good aromatization performance in microwave-assisted series system due to high dielectric properties and specific surface area. The composite catalyst performed well after five-cycle regeneration, and the hydrocarbon content could still reach 76.40%, which is 80.89% for the original catalyst.

Features of Synthesizing Ceramic Composites Discretely Reinforced by Carbon Fibers and SiC Nanowires Formed in situ in the Combustion Wave

A new method is proposed for the engineering of SiC-based ceramic-matrix composite materials strengthened by discrete carbon fibers and single-crystal silicon carbide nanowires. Depending on the macrokinetic characteristics of the combustion process, either diffusion layers, particles of silicon carbide, or silicon carbide nanowires with a diameter of 10–50 nm and a length of 15–20 μm can be formed on the surface of carbon fibers. The sequence of chemical transformations and structure formation in the combustion wave of Si–C–C2F4 and Si–C–C2F4–Ta mixtures was studied. Silicon carbide nanowires formed in the combustion wave had high crystallinity and a defect-free TaSi2/SiC interface. The misorientation of the lattices at the interface is about 6%. Nanowires are able to relax the mechanical stresses during growth via the rotation along the growth direction. The optimal combustion temperature for the growth of silicon carbide nanofibers is 1700 K at a ratio of C2F4 : C = 2. The lower temperature threshold for the growth of silicon carbide nanowires is caused by a decrease in the yield of reactive fluorides, while the upper-temperature threshold is caused by a failure of the adsorption blocking mechanism on the surface of the nanofibers and the destabilization of the TaSi2 + Si eutectic droplet. Composites with a SiC–TaSi2 ceramic matrix and a relative density of 98%, a hardness of 19 GPa, a flexural strength of 420 MPa, and fracture toughness of 12.5 MP m1/2 were obtained by hot pressing. An increase in the strength of the carbon fiber-matrix interface has manifested in the suppression of carbon fiber pull-out from the matrix.

Features of synthesizing ceramic composites discretely reinforced by carbon fibers and SiC nanowires formed in situ in the combustion wave

A new method is proposed for the engineering of SiC-based ceramic-matrix composite materials strengthened by discrete carbon fibers and single-crystal silicon carbide nanowires. Depending on the macrokinetic characteristics of the combustion process, either diffusion layers, particles of silicon carbide or silicon csrbide nanowires with a diameter of 10–50 nm and a length of 15–20 μm can be formed on the surface of carbon fibers. The sequence of chemical transformations and structure formation in the combustion wave of Si–C–C 2 F 4 and Si–C–C 2 F 4 –Ta mixtures was studied. Silicon carbide nanowires formed in the combustion wave had high crystallinity and a defect-free TaSi 2 /SiC interface. The misorientation of the lattices at the interface is about 6 %. Nanowires are able to relax the mechanical stresses during growth via the rotation along the growth direction. The optimal combustion temperature for the growth of silicon carbide nanofibers is 1700 K at a ratio of C 2 F 4 : C = 2. The lower temperature threshold for the growth of silicon carbide nanowires is caused by a decrease in the yield of reactive fluorides, while the upper temperature threshold is caused by a failure of the adsorption blocking mechanism on the surface of the nanofibers and the destabilization of the TaSi 2 + Si eutectic droplet. Composites with a SiC–TaSi 2 ceramic matrix and a relative density of 98 %, a hardness of 19 GPa, a flexural strength of 420 MPa, and a fracture toughness of 12.5 MPa·m 1/2 were obtained by hot pressing An increase in the strength of the carbon fiber-matrix interface has manifested in the suppression of carbon fiber pull-out from the matrix.

Role of catalyst in controlling the growth and morphology of one-dimensional SiC nanostructures

To control the morphologies of one-dimensional (1D) nanostructures, especially during the catalyst-assisted growth of semiconductor nanostructures, is the key to unlock their potential applications. In this work, we demonstrate that, the morphology of the 1D silicon carbide (SiC) nanostructures can be controlled by manipulating the composition of the catalyst in the microwave plasma chemical vapor deposition process. It is revealed that iron silicide presents as the main catalyst to initiate the growth of 1D SiC nanostructure. High-resolution transmission electron microscopic analysis shows that, the stoichiometry of the iron silicide governs the final morphology of 1D SiC nanowire. For the growth of SiC nanowires, the catalyst is Fe5Si3, while it is Fe3Si for SiC nanoneedles. A special orientation match between the iron silicide catalyst and the SiC nanowire is observed for the first time during the growth of SiC nanostructures. The mechanism for the different morphology of the SiC nanostructures is believed to be the different etching resistivity of the catalyst particles under H2 plasma etching. Based on the above mechanism, a continuous change in the morphology of the SiC nanostructures has been achieved by controlling the supply of Si during growth.

Extended vapor-liquid-solid growth of silicon carbide nanowires.

We developed an alloy catalytic method to explain extended vapor-liquid-solid (VLS) growth of silicon carbide nanowires (SiC NWs) by a simple thermal evaporation of silicon and activated carbon mixture using lanthanum nickel (LaNi5) alloy as catalyst in a chemical vapor deposition process. The LaNi5 alloy binary phase diagram and the phase relationships in the La-Ni-Si ternary system were play a key role to determine the growth parameters in this VLS mechanism. Different reaction temperatures (1300, 1350 and 1400 degrees C) were applied to prove the established growth process by experimentally. Scanning electron microscopy and transmission electron microscopy studies show that the crystalline quality of the SiC NWs increases with the temperature at which they have been synthesized. La-Ni alloyed catalyst particles observed on the top of the SiC NWs confirms that the growth process follows this extended VLS mechanism. The X-ray diffraction and confocal Raman spectroscopy analyses demonstrate that the crystalline structure of the SiC NWs was zinc blende 3C-SiC. Optical property of the SiC NWs was investigated by photoluminescence technique at room temperature. Such a new alloy catalytic method may be extended to synthesis other one-dimensional nanostructures.

Growth of SiC NWs by vapor phase technique using Fe as catalyst

In this paper we report on the growth of silicon carbide nanowires deposited on silicon substrate with vapor phase technique at atmospheric pressure, using propane and silane as precursors and hydrogen as carrier gas.A thin layer of iron deposited on the silicon surface was used as catalyst.The morphology, crystal structure and details such as the growth direction of the as-prepared SiC NWs were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM).The SiC NWs have a diameter ranging from 30 to 100nm and length of tens of micrometers.XRD and High resolution TEM confirm the cubic structure of the nanowires and evidence a growth habit along the 〈111〉 direction.

Molten-salt-mediated synthesis of SiC nanowires for microwave absorption applications

Silicon carbide (SiC) nanowires were synthesized by a reaction of multiwall carbon nanotubes (MWCNTs) and silicon vapor from molten salt medium at 1250 °C. The phase, morphology, and microstructure of the nanowires were systemically characterized by X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission electron microscopy. The results revealed that the nanowires were of single-crystalline β-SiC phase with the growth direction along [111] and had diameters of 20–80 nm and lengths up to several tens of micrometers. The molten salt introduced facilitated the evaporation of Si (vapor) onto MWCNTs (solid) and the growth of SiC nanowires followed the vapor–solid process. The investigation of microwave absorbability indicated that a minimum reflection loss of −17.4 dB at 11.2 GHz could be achieved with 30 wt% SiC nanowires as the filler in the silicone matrix. The attenuation of microwave could be attributed to the dielectric loss and a possible absorption mechanism was also discussed.

Influence of oxygen on the microstructural growth of SiC nanowires

We examined the influence of oxygen (O2) on the growth of silicon carbide nanowires (SiC NWs) by chemical vapor deposition (CVD), because vacuum environments are susceptible to O2 leakage inflow. We investigated the effect of increasing the O2 flow rate on the microstructural changes of SiC NWs and then evaluated the effect at various growth temperatures. The O2 content was highly related to the density of NWs, which continued to increase actively at higher temperatures. High-resolution transmission electron microscopy (HR-TEM) revealed that NWs change from a single-crystalline phase to a polycrystalline phase and then to a SiC/SiO2 core–shell structure.

Ultrafast self-catalytic growth of silicon carbide nanowires

Abstract

Improvement of porous silicon carbide filters by growth of silicon carbide nanowires using a modified carbothermal reduction process

Porous ceramics which contain nanowires are promising candidates for catalyst support applications. Here we report a cost-efficient carbothermal reduction process to produce a porous SiC filter with SiC nanowires in the honeycomb structure. For this, the mixture of SiO 2 and carbon black was applied as a source of SiO gas. In addition, the SiC filter was coated with diluted phenolic resin to induce additional carbothermal reduction in the filter. β-SiC nanowires were successfully obtained at and above 1400 °C. Surface area of the porous SiC filter increased from 18.72 to 54.51 m 2 /g by the in situ formation of the nanowires.

Growth of Silicon Carbide Nanowires by a Microwave Heating-Assisted Physical Vapor Transport Process Using Group VIII Metal Catalysts

SiC nanowires are grown by a novel catalyst-assisted sublimation-sandwich method. This involves microwave heating-assisted physical vapor transport from a “source” 4H-SiC wafer to a closely positioned “substrate” 4H-SiC wafer. The “substrate wafer” is coated with a group VIII (Fe, Ni, Pd, Pt) metal catalyst film about 5 nm thick. The nanowire growth is performed in a nitrogen atmosphere, in the temperature range of 1650-1750 °C for 40 s durations. The nanowires grow by the vapor-liquid-solid (VLS) mechanism facilitated by metal catalyst islands that form on the substrate wafer surface at the growth temperatures used in this work. The nanowires are 10-30 Im long. Electron backscatter diffraction (EBSD) and selected area electron diffraction analyses confirm the nanowires to crystallize with a cubic 3C structure of 3C-SiC. EBSD from the nanowire caps are indexed as Fe2Si, Ni3Si, Pd2Si, and PtSi phases for the nanowires grown using Fe, Ni, Pd, and Pt as the metal catalysts, respectively. The nanowires are found to grow along the 〈112〉 directions, as opposed to the commonly observed 〈111〉 directions. The micro-Raman spectra from single nanowires indicate regions with varying compressive strain in the nanowires and also show modes not arising from the Brillouin zone center, which may indicate the presence of defects in the nanowire.

MOCVD Growth of SiC Nanowires Aiming at the Control of their Shape

We report the growth of silicon carbide (SiC) nanowires on silicon substrates by metal organic chemical vapor deposition (MOCVD) using dimethylvinyllsilane [CH2CHSi(CH3)Cl2] as a source gas and metal catalysts of Ni and Fe. Various growth conditions such as the growth temperature and the pressure of the source gas are examined to achieve high yield growth of SiC nanowires and to control their shape. No SiC nanowires were formed when using Fe. In contrast, by using Ni catalyst, numerous SiC nanowires of about 30 nm thick can be grown at the pressure of the source gas of 30 Pa at 800 °C. Their microstructure is revealed by scanning electron microscopy (SEM) and transmission electron microscope (TEM).