Chemical vapour deposition of zirconium carbide and silicon carbide hybrid whiskers

Zirconium carbide and silicon carbide hybrid whiskers were codeposited by chemical vapour deposition using methyl trichlorosilane, zirconium chloride, methane and hydrogen as the precursors. The zirconium carbide and silicon carbide whiskers were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The results indicate that the codeposition process is more effective in the presence of methane than in the absence of methane. The codeposition process and the growth of zirconium carbide in the whiskers can be accelerated at high temperature in the presence of methane. A growth model was proposed based on the deposition model of carbon, zirconium carbide and silicon carbide.     

Synthesis of SiC from rice husk in a plasma reactor

A new route for production of SiC from rice husk is reported by employing thermal plasma technique. The formation of β-SiC is observed in a short time of 5 min. The samples are characterized by XRD and SEM.     

Preparation of aligned silicon carbide whiskers from porous carbon foam by silicon thermal evaporation

Aligned silicon carbide whiskers were prepared from porous carbon foams by thermal evaporation of silicon. High-density silicon carbide whiskers were vertically deposited on the surface of siliconizing carbon foam. The whiskers were straight and hexagon-shaped with diameter of 1-2 μm and length of about 40 μm. They consisted of a single-crystalline zinc blende structure crystal in the [111] growth direction. The pore structure of carbon foam played an important role in determining distribution of the whiskers on the surface of siliconizing carbon foam. When carbon foam with higher porosity and larger pore size was employed, distributions of the whiskers were more ordered and more intensive. The whiskers were grown by the vapor-solid (VS) mechanism.     

混合活化制备稻壳基活性炭研究

以脱硅稻壳灰为原料,采用混合活化法制取活性炭,通过4种单一活化剂物料比的实验,确定了最佳物料比为1∶3;设计了5种混合活化的配比方案,实验结果表明在NaOH&Na2CO3和KOH&K2CO3配比为2.5∶0.5时碘吸附值和亚甲基蓝吸附值分别达到最优,说明辅助活化剂的加入可有效提高稻壳基活性炭的吸附性能。在总物料比和活化剂混合配比确定的条件下,进行了浸渍液质量分数、活化温度、活化时间3个单因素实验,结果显示,浸渍液质量分数为30%、活化温度为500℃、活化时间为40min时活化效果最佳,其中碘吸附值最高可达1528.76mg/g,可知混合活化对制备稻壳基活性炭有显著作用。     

Rapid carbothermal synthesis of nanostructured silicon carbide particles and whiskers from rice husk by microwave heating method

This paper reported a simple and rapid route to large-scale synthesis of nanostructured SiC powders using rice husk as the precursor. Rapid carbothermal reduction reactions were achieved in a 2.45 GHz microwave field in an argon atmosphere. The XRD patterns revealed that complete carbothermal reduction of silica was achieved at 1300 °C for 60 min or at 1500 °C for only 15 min by microwave heating, resulting in β-SiC formation. The FE-SEM images showed that the β-SiC powders were mixtures of particles and whiskers. The β-SiC particles had diameters of 60–130 nm and the β-SiC whiskers, which were several to tens of micrometers in length, had diameters of 110–170 nm. The β-SiC powder synthesized at 1500 °C for 15 min showed the highest BET surface area of 12.2 m²/g. Compared to the conventional heating method, the microwave heating method proved to be an efficient approach for synthesis of SiC in terms of energy and time saving, as well as for fabrication of nanostructured SiC.     

稻壳/高密度聚乙烯复合材料与稻壳炭/高密度聚乙烯复合材料性能对比

采用挤出法制备稻壳/高密度聚乙烯（HDPE）和稻壳炭/HDPE复合材料。利用SEM、XRD对稻壳/HDPE和稻壳炭/HDPE复合材料进行表征,并对其力学性能和抗蠕变性能进行测试对比。结果表明,稻壳和HDPE之间的结合方式与稻壳炭和HDPE之间的结合方式存在根本性的差异,稻壳/HDPE复合材料表现为稻壳被HDPE所包裹,稻壳炭/HDPE复合材料表现为HDPE嵌入稻壳炭的孔隙中;稻壳和稻壳炭的加入都会影响HDPE基复合材料的结晶峰强度,但不会对其微晶结构产生影响;无论是抗弯强度、拉伸强度还是抗蠕变强度,稻壳炭/HDPE复合材料都远远强于稻壳/HDPE复合材料。     

Electrospinning of beta silicon carbide nanofibers

Silicon carbide exhibits many unique properties such as its mechanical robustness, chemical inertness, and thermal stability, which make the material appealing for many applications. Some of these applications include its use as a support for nanocomposites or as a high temperature filter material. The ability to fabricate nanofibers of SiC could enhance its utility in these applications. In the current study, nanofibers of β-SiC have been fabricated through the technique of concentric electrospinning. This method demonstrates the ability to fabricate uniform SiC nanofibers with a diameter ranging from 1 to 2 nm, the smallest to date.     

Nature and reactivity of silica available in rice husk and its ashes

Scanning electron microscopy, reactivity and surface area measurements of rice husk and its ashes reveal the gradual formation of amorphous silica during ashing. The reactivity of the silica thus formed is found to be at its maximum for ashing temperatures between 400 and 600°C and hold-time from 6 to 12 h. The reactivity of the ash is found to decrease with increasing temperature (⩾ 600°C) and hold-time. IICT Communication No. 2375.     

Deposition and optical studies of silicon carbide nitride thin films

Thin films of silicon carbide nitride (SiCN) have been prepared by reactive radioactive frequency (r.f.) sputtering using SiC target and nitrogen as the reactant gas. Deposition rates are studied as a function of deposition pressures and argon-nitrogen flow ratios. The optical absorption studies indicated the band edge shifting of the films when the nitrogen ratios are increased during deposition. Fourier transform infrared spectroscopy (FTIR) analysis on the films indicated several stretching modes corresponding to SiC, SiN and CN compositions.     

Crystalline-to-amorphous transition in silicon carbide under neutron irradiation

We have investigated the neutron-induced amorphization in silicon carbide (SiC) film using molecular dynamics (MD) simulations with a modified Tersoff potential. The crystalline-to-amorphous (c-a) transition occurs at about 0.27 dpa along with a structural relaxation, indicating that the amorphization mechanism of neutron-irradiated 3C-SiC is homogeneous. The amorphization level will further be improved during more irradiation, which could be deduced from the increase of C-C bonds and decrease of C-Si bonds after c-a transition. The point defects tend to accumulate in defect-rich areas with C-depleted regions in the core and C-rich regions in the boundary. Such defect-rich areas caused by the displacement spikes results in the local inhomogeneity of C and Si atom distribution in the system, which will enhance the driving force for c-a transition based on thermodynamics. Evidences suggest that the displacement spike plays an important role in amorphization of 3C-SiC.     

碳化硅晶须发展及应用概况

综合论述了ＳｉＣ晶须的高强，高硬，高化学稳定性以及其耐磨耐腐蚀和良好的抗高温氧化性等特点；评述了ＳｉＣ晶须的各种合成方法和国内外发展应用状况。     

Nonlinear thermal characteristics of silicon carbide devices

In the paper, the dynamic nonlinear model of SiC devices is proposed, where the dependencies of the thermal parameters on the temperature are included. The proposed model is applicable and useful in the simulations of electro-thermal transients in the devices working with high power density and in the wide range of temperature.     

Preparation of silicon carbide nanowires via a rapid heating process

Silicon carbide (SiC) nanowires were fabricated in a large quantity by a rapid heating carbothermal reduction of a novel resorcinol-formaldehyde (RF)/SiO₂ hybrid aerogel in this study. SiC nanowires were grown at 1500 °C for 2 h in an argon atmosphere without any catalyst via vapor-solid (V-S) process. The β-SiC nanowires were characterized by field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM) equipped with energy dispersive X-ray (EDX) facility, Fourier transformed infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The analysis results show that the aspect ratio of the SiC nanowires via the rapid heating process is much larger than that of the sample produced via gradual heating process. The SiC nanowires are single crystalline β-SiC phase with diameters of about 20-80 nm and lengths of about several tens of micrometers, growing along the [1 1 1] direction with a fringe spacing of 0.25 nm. The role of the interpenetrating network of RF/SiO₂ hybrid aerogel in the carbothermal reduction was discussed and the possible growth mechanism of the nanowires is analyzed.     

The spall strength of silicon carbide and boron carbide ceramics processed by spark plasma sintering

The spall strength of silicon carbide (SiC) and boron carbide (B₄C) ceramics processed by Spark Plasma Sintering (SPS) has been studied as a function of the loading stress. In the course of the planar impact experiments, the velocity of either the sample free surface or of the sample–window interface was continuously monitored by a Velocity Interferometer System for Any Reflector (VISAR). With the increase of impact stress the spall strength of both ceramics, increases initially and then declines monotonously until it vanishes almost completely, as the impact stress approaches the respective Hugoniot Elasic Limit (HEL). The mechanisms that may account for that behavior and, in particular, the role of the compressive wing cracks in the onset of the spall strength decline are discussed.     

Preparation of silicon carbide whiskers from silicon nitride

Silicon carbide whiskers have been prepared by sintering silicon nitride powder in a graphite reactor at 1800°C under a nitrogen atmosphere. The whiskers differ in morphology: tubular needles, hollow faceted fibers with a square cross section, and solid fibers with a triangular cross section. The average diameter of the needles is 0.5?5 μm, and that of the faceted fibers is up to 20 μm. The fibers range in length up to several millimeters. Such silicon carbide whiskers can be used as reinforcing agents for structural ceramics based on nonoxide materials.     

Preparation of silicon carbide using bamboo charcoal as carbon source

Silicon carbide (SiC) was prepared by carbothermal reduction with amorphous silica sol as silicon source and bamboo charcoal powder as carbon source. The compositions and microstructure of prepared SiC were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). XRD of prepared SiC showed that the major phase of prepared SiC was hexagonal 6H-SiC with the existence of some 4H-SiC. SEM showed that SiC particle was granular, rod-like and of tower-shape, and it inherited the shape of bamboo charcoal. EDS showed that prepared SiC was pure without being doped by the mineral elements from bamboo charcoal.     

Thermal conductivity and mechanical properties of high density polyethylene composites filled with silicon carbide whiskers modified by cross-linked poly (vinyl alcohol)

A thin layer of poly (vinyl alcohol) (PVA) was coated on the surface of silicon carbide whiskers (SCWs) and crosslinked by glutaraldehyde, and then these modified whiskers (mSCWs) were incorporated into high density polyethylene (HDPE) to prepare HDPE/mSCW composites with a high thermal conductivity. The thermal conductivity, mechanical properties, heat resistance, thermal stability and morphology of HDPE/mSCW and HDPE/SCW composites were characterized and compared. The results reveal that the thermal conductivity of both HDPE/SCW and HDPE/mSCW composites increases with the increase of filler loading, and reaches a maximum of 1.48 and 1.69?W/(m?K) at 40?wt% filler loading, which is 251.2% and 300.75% higher than that of HDPE, respectively. Significantly, HDPE/mSCW composites have a higher thermal conductivity than their HDPE/SCW counterparts with the same filler loading. In addition, the heat resistance, Young’s modulus and yield strength of both HDPE/SCW and HDPE/mSCW composites are also improved compared with that of HDPE. mSCW can be homogenously dispersed in the HDPE matrix, which contributes to the formation of thermally conductive networks by the inter-connection of mSCWs.     

High-purity nano silica powder from rice husk using a simple chemical method

A highly pure, small particle-sized and high surface area nano silica powder was prepared from rice husk using alkali extraction, followed by an acid precipitation method. The composition, phase, morphology, size and surface area of the as-synthesised nano silica powder was investigated by energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, particle size analyser and BET surface area analyser. High-purity nano silica powder was obtained by sodium hydroxide (NaOH) purification treatment (0.5, 1, 1.5, 2 and 2.5?N). The high purity of silica (～99.9%) was obtained at 2.5?N NaOH treatment. The pure nano silica powder that is obtained shows an average particle size of ～25?nm with a high-specific surface area (SSA) of 274?m²?g^?1, with an average pore diameter of 1.46?nm.     

Direct determination of carbothermal reduction temperature for preparing silicon carbide from the vacuum furnace thermobarogram

In this study, we combined the traditional vacuum furnace with a sur-high accuracy vacuum gauge for measuring the change of gas pressure in the furnace as a function of temperature. The modified vacuum furnace was used for preparing silicon carbide (SiC), and the recorded data named thermobarogram were applied to detect the reaction temperature for synthesis of SiC, which, in particular, changes as catalysts are used. The results showed that the carbothermal reduction temperature for synthesizing SiC, under dynamic vacuum condition, would decrease to 850 °C when the mole ratio of Fe/Si=0.06 was employed in the SiC precursor.