Silicon Carbide Nanopowders Research Articles

Synthesis of Silicon Carbide in Hypervelocity Plasma Jet

Results of plasmodynamic synthesis of silicon carbide nanopowders are given in the article. Studies of the synthesis product by X-ray diffractometry and transmission electron microscopy indicated that the product consists mainly of cubic silicon carbide and also includes cubic silicon, ultradispersed graphite and carbon onion-like structures. It was shown that a phase composition change in the synthesis product is possible by changing the ratio of precursor mixture.

Production of silicon carbide powder and its based composition powders in azide SHS-process

Combustion of «silicon – sodium azide – ammonium hexafluorosilicate – carbon – aluminum» powder mixture in the nitrogen atmosphere has been investigated. The conditions of self-propagating high-temperature synthesis (SHS) of silicon carbide nanopowder composition with silicon nitride whiskers and flux have been determines. The composition can be used as a modifier of casting aluminum alloys and reinforcing phase in age-hardened aluminomatrix composites.

Preparation of silicon-carbide nanopowder and compositions based on it using SHS azide technology

Combustion of the “silicon-sodium azide-ammonium hexafluorosilicate-carbon-aluminum” powder mixture in the nitrogen medium is investigated. Conditions of the self-propagating high-temperature synthesis (SHS) of the composition of the silicon carbide nanopowder with whisker silicon nitride crystals and flux, which can be used as a modifier of cast aluminum alloys and a reinforcing phase in dispersion-hardened alumomatrix composites, are determined.

Structural Evolution of Silicon Carbide Nanopowders during the Sintering Process

Processes of sintering of silicon carbide nanopowder were investigated. Values of density (ρ=3.17 g/cm3) and strength (σ=450 MPa) were obtained. Within the theory of dispersed systems, the temperature evolution of the materials structure was considered. The relationship between sintering temperature, characteristics of crystal structure and physical properties, in particular, density, and strength of aforementioned ceramics was established. It was concluded that it is necessary to suppress the anomalous diffusion at temperatures above 2080°C.

Effect of nanosilicon carbide on the carbonisation process of coal tar pitch

The study describes the effect of silicon carbide (SiC) nanopowder on the process of coal tar pitch thermal decomposition during heat treatment to a temperature of 2000°C. The influence of nanosized SiC powder on the pyrolysis mechanism of carbonisation product yield, as well as structural and microstructural parameters of carbon obtained via carbonisation and further heating up to 2000°C was studied. The results show that the incorporation of a suitable amount of ceramic nanopowder into the liquid coal tar pitch results in a decrease in the crystallite sizes of carbon residue, while further heating up to 2000°C gives rise to two carbon phases, differing in crystallinity and interplanar distance between graphene layers. The SiC addition enhances the formation of well-ordered graphite domains in comparison with those present within a pure carbon matrix.

Microwave Synthesis of Silicon Carbide Nano Powders with Silicon and Carbon

Nanosized silicon carbide powders were synthesized from a mixture of silicon and carbon by microwave heating methods. The Result Indicates SiC can be formed at lower temperatures by using the Si-C reaction at 1200°C for 30min. XRD patterns shows that SiC peaks appeared as the only crystalline phase. SEM photo shows the particle size was 100～200 nanometer. At the same time, Effects of chemical reaction of silicon and carbon was researched by mechanical activated microwave synthesis.

Self-Propagating High-Temperature Synthesis of Silicon Carbide and Silicon Nitride Nanopowders Composition using Sodium Azide and Halides

<p>Regularities of self-propagating high-temperature synthesis (SHS) or combustion synthesis (CS) by using “silicon – sodium azide – ammonium hexafluorosilicate – carbon – aluminum” powder mixture in the nitrogen atmosphere were investigated. The thermodynamic analysis of the combustion synthesis was performed. Experimental investigation of the combustion process: the measurement of linear rates of the combustion front propagation and the maximum combustion temperatures was conducted in a laboratory reactor with working volume 4.5 liters. The influence of the components ratio in the initial mixture on the combustion temperature, combustion rate and composition of reaction product was studied. The phase composition of the product synthesized was determined with an X-ray diffractometer. It was disclosed that the SHS product consists of the composition (mixture) of silicon carbide nanopowder with silicon nitride whiskers and a final halide. Investigation of surface topography and morphology of the product particles was carried out with a scanning electron microscope. Optimal mixture for the synthesis of nanoscale composition based on silicon carbide was determined: “14Si+6NaN<sub>3</sub>+(NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub>+15C+Al”. In this case, the SHS product consists of four phases: silicon carbide (β-SiC) – 48.57 wt.%, α-silicon nitride (<em>α</em>-Si<sub>3</sub>N<sub>4</sub>) – 27.04 wt.%, β-silicon nitride (β-Si<sub>3</sub>N<sub>4</sub>) – 5.83 wt.%, and sodium hexafluoroaluminate (Na<sub>3</sub>AlF<sub>6</sub>) – 18.56 wt.%. The average particle size of the composition was in the range of 70–130 nm. It was shown that the composition of the silicon carbide with silicon nitride and the final halide Na<sub>3</sub>AlF<sub>6</sub> playing a role a flux can be used as a modifier of castable aluminum alloys and as a reinforcing phase of aluminomatrix composites.</p>

Corrosion Resistance of Nanopowders of Borides and Carbides of the Metals of Groups IV–VIB in Nickel-Plating Electrolytes

We study the solubility of the nanopowders of borides and carbides of metals of groups IV–VIB and a nanopowder of silicon carbide in standard nickel-plating electrolytes. As objects of investigation, we use nanopowders containing 91.8–97.6% of the main phase with average particle sizes of 32–78 nm. Their corrosion resistances are evaluated as functions of the acidity of electrolyte, temperature, and duration of interaction. It is discovered that the corrosion resistances of boride and carbide nanopowders in solutions of electrolytes are similar within each group of compounds and characterized by an unbounded period of holding in alkaline media. A silicon carbide nanopowder, which is stable in solutions of any pH value, proves to be an exception.

Determination of fracture toughness using the area of micro-crack tracks left in brittle materials by Vickers indentation test

In this article, a new method has been presented for the estimation of fracture toughness in brittle materials, which enjoys improved accuracy and reduced costs associated with fracture toughness testing procedure compared to similar previous methods, because a vast range of specimens with irregular cracks can be accommodated for testing. Micron-sized alumina powders containing 0.05 wt% magnesium oxide (MgO) nanoparticles were mixed and also together with 2.5 vol%, 5 vol%, 7.5 vol%, 10 vol%, and 15 vol% of silicon carbide (SiC) nanopowders separately. By making and testing various types of ceramics with different mechanical properties, and considering the irregular cracks around the indented area caused by Vickers diamond indenter, a semi-empirical fracture toughness equation has been obtained.

Self-propagating high-temperature synthesis of silicon carbide nanopowders

Ceramic materials based on silicon carbide SiChave unique properties, such as thermostability andrefractoriness, chemical stability, and high hardnessand thermal conductivity. Due to these properties, SiChas a wide range of applications, including abrasivesand cutting materials, structural ceramics and crystalsfor microelectronics, catalysts, and coatings [1].The traditional method of manufacturing SiC is theprocess invented by E. Atcheson in the 19th century.The process is based on the reduction of silica SiO

Direct Combustion Synthesis of Silicon Carbide Nanopowder from the Elements

Direct synthesis of silicon carbide (SiC) nanopowders (size 50–200 nm, BET ~20 m2/g) in Si–C system is conducted in an inert atmosphere (argon) using a self‐propagating high‐temperature synthesis (SHS) approach. A preliminary short‐term (e.g., minutes) high‐energy ball milling (HEBM) of the initial mixture, which involves pure Si and C powders, is used to enhance system reactivity. Two conditions of HEBM with different force fields (17G and 90G) are applied and the results are compared. The influence of HEBM's conditions on the microstructure of mechanically treated mixtures and combustion products is also investigated and discussed. Obtained results suggest that by changing the intensity of mechanical treatment one may prepare a completely amorphous reactive mixture containing carbon and silicon, or gradually change the ratio of (Si/C)–SiC phases and finally produce pure silicon carbide powder during the milling process. The influence of HEBM on the combustibility of the Si/C mixture possesses a critical character: the self‐sustained reaction becomes feasible only after a critical time of ball milling (i.e., 10 min for 90G; 30 min for 17G). Comparison of the microstructures for as‐milled and as‐synthesized powders reveals that for all investigated conditions the morphologies of the as‐milled reactive Si/C media are essentially the same as that for SiC combustion products. The mechanism for direct synthesis of SiC by combustion reaction is also proposed.

Response surface modeling of H2S conversion by catalytic oxidation reaction over catalysts based on SiC nanoparticles using Box − Behnken experimental design

Catalysts of sodium silicate and cadmium oxide supported on silicon carbide nanopowders were synthesized and used in catalytic oxidation of H2S to elemental sulfur. The effect of temperature (from 150 to 250°C); gas hour space velocity (from 2000 to 4000h−1) and sodium:cadmium weight ratio (from 1 to 5), on the conversion of H2S were studied by a Box–Behnken experimental design method. A quadratic regression equation was developed to describe relationship between the operating conditions and the response. The significance of main factors and their quadratic interactions on the conversion of H2S in catalytic oxidation were examined by means of the analysis of variance (ANOVA). The results showed that temperature had the most significant effect on H2S conversion compared with other two variables. F value of 29.46, coefficient of determination (R2) of 0.9779, adjusted-R2 of 0.9447, absolute average deviation (AAD) of 0.29% and, coefficient of variation (CV) of 0.59%, implied the satisfactory adjustment of the quadratic model. The results indicated that up to 100% H2S conversion was obtained at the optimum conditions.

RF 유도 열플라즈마를 이용한 유기 용매로 부터의 탄화규소 나노 분말 합성

Silicon carbide (SiC) has recently drawn an enormous amount of industrial interest due to its useful mechanical properties, such as its thermal resistance, abrasion resistance and thermal conductivity at high temperatures. In this study, RF thermal plasma (PL-35 Induction Plasma, Tekna CO., Canada) was utilized for the synthesis of high-purity SiC powder from an organic precursor (hexamethyldisilazane, vinyltrimethoxysilane). It was found that the SiC powders obtained by the RF thermal plasma treatment included free carbon and amorphous silica (SiO₂). The SiC powders were further purified by a thermal treatment and a HF treatment, resulting in high-purity SiC nano-powder. The particle diameter of the synthesized SiC powder was less than 30 nm. Detailed properties of the microstructure, phase composition, and free carbon content were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), a thermogravimetric (TG) analysis, according to the and Brunauer-Emmett-Teller (BET) specific surface area from N2 isotherms at 77 K.

Dispersion behaviour of laser-synthesized silicon carbide nanopowders in ethanol for electrophoretic infiltration

Abstract SiC nanopowders of 30 nm in diameter were successfully synthesized by laser-pyrolysis with high production rate (1.7 kg/h) and high quantity (>2 kg). The as-synthesized nanopowders were heat-treated in order to slightly oxidize the surface. It was shown that the heat-treatment does not modify structural properties or morphology but modifies the surface chemistry. Ethanolic suspensions with polyethylenimine (PEI) as dispersant were prepared from the heat-treated powders. The suspensions properties were characterized in terms of rheology, zeta potential and size distribution before and after operational pH adjustment with hydrochloric acid (HCl 1 M) or acetic acid (CH 3 COOH). High concentrated suspensions (28 wt%) with low viscosity were obtained after pH adjustment with CH 3 COOH. Electrophoretic infiltrations of carbon preforms carried out with these suspensions lead to a high quality infiltration of the inter-tows area as well as of the intra-tows area, some tows being completely filled with the nanopowders.

Fabrication and characterization of nano-particles-enhanced epoxy

Epoxy has been widely used as adhesives in retrofitting structures with carbon fiber reinforced polymer (CFRP). In this study, different weight fractions of multi-walled carbon nanotubes (MWCNTs) and Silicon Carbide nanopowder (SiC) will be dispersed into epoxy to produce toughened adhesives that can effectively improve the CFRP/structure bonding performance. The preliminary experimental results indicate that adding 2wt.% MWCNTs into Araldite-420 will increase its ultimate strength by 17% and its elastic modulus by 14%. On the other hand, Araldite-420’s elastic modulus will increase by nearly 50% when 1.0wt.% of SiC powder is added. Ultrasonic mixing may increase the elastic modulus of Sikadur-30 but reduce its strength and ductility regardless of the amount of nanoparticles dispersed. No significant effect of nano-particle infusion on the glass transition temperature of the epoxies was found. The mechanism of nanoparticles infusion effects on the mechanical properties of the epoxies is also examined using SEM.

Fabrication and characterization of fully ceramic microencapsulated fuels

The current generation of fully ceramic microencapsulated fuels, consisting of Tristructural Isotropic fuel particles embedded in a silicon carbide matrix, is fabricated by hot pressing. Matrix powder feedstock is comprised of alumina–yttria additives thoroughly mixed with silicon carbide nanopowder using polyethyleneimine as a dispersing agent. Fuel compacts are fabricated by hot pressing the powder–fuel particle mixture at a temperature of 1800–1900°C using compaction pressures of 10–20MPa. Detailed microstructural characterization of the final fuel compacts shows that oxide additives are limited in extent and are distributed uniformly at silicon carbide grain boundaries, at triple joints between silicon carbide grains, and at the fuel particle–matrix interface.

Rapid carbothermic synthesis of silicon carbide nano powders by using microwave heating

Abstract This paper reports an improved procedure for synthesis of silicon carbide nanopowders from silica by carbothermic reduction under fast microwave-induced heating. The powders have been prepared by direct solid-state reaction in a 2.45 GHz microwave field in nitrogen atmosphere after 40 h milling. For the first time, the formation of silicon carbide (β-SiC) as a major phase can be achieved at 1200 °C in 5 min of microwave exposure, resulting in nano sized particles ranging from 10 to 40 nm under optimized synthesis condition. The Rietveld quantitative phase-composition analysis confirmed that the major SiC polytype is cubic SiC (β-SiC) with 98.5(4) weight fraction and the remained is minor hexagonal SiC polytypic (α-SiC) phases. Therefore this method is the most efficient one for SiC powder synthesis in terms of energy and time saving as well as preparation of SiC nano powders.

STUDY OF MECHANICAL PROPERTIES AND FRACTURE MODE OF ALUMINA-SILICON CARBIDE NANOCOMPOSITES

In this study Al 2 O 3- SiC nanocomposites have been fabricated by mixing of alumina and silicon carbide nano powders, followed by hot pressing at 1700°C. The mechanical properties and fracture mode of Al 2 O 3- SiC nanocomposites containing different volume fractions (5, 10 and 15%) of nano scale SiC particles were investigated and compared with those of alumina. Al 2 O 3- SiC powders were prepared by planetary milling in isopropanol. Fracture mode of specimens was investigated by means of scanning electron microscopy. Nanocomposites were tougher than alumina when they were hot pressed at the same temperature, and the values of nanocomposite's flexural strength and hardness were higher than those of alumina. Flexural strength, hardness and fracture toughness of the nanocomposites increase by increasing the volume percent of SiC up to 10% and then decrease slightly. The Scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to transgranular for nanocomposites. Finally X-ray diffraction analysis couldn't detect any chemical reactions between Al 2 O 3 and SiC particles.

Synthesis and characterization of SiC nano powder with low residual carbon processed by sol–gel method

Silicon carbide nanopowders and nanowhiskers were synthesized using phenolic resin and silicon alkoxide as precursors through sol–gel process with atomic ratio of C/Si=1.8 in water–solvent–catalyst–dispersant system. The effects of soaking time on free carbon content and synthesized β-SiC particle morphology were evaluated at 1500°C. The synthesis process of β-SiC nanopowders was completed at 1500°C after 1h while β-SiC nanowhiskers were heterogeneously nucleated and grown from obtained nanopowders after 2–3h. The detected free carbon content in whiskers was less than 1% after 3h.

Synthesis of SiC nano-powder from organic precursors using RF inductively coupled thermal plasma

Silicon carbide (SiC) has recently drawn an enormous amount of industrial interest owing to useful mechanical properties such as its thermal resistance, abrasion resistance and thermal conductivity at high temperatures. RF inductively thermal plasma (PL-35 Induction Plasma, Tekna Co., Canada) has been utilized for synthesis of fine SiC nano-powder from organic precursors (tetraethylorthosilicate, hexamethyldisilazane and vinyltrimethoxy silane). It was found that powders exposed to thermal plasma consist of SiC with free carbon and amorphous silica (SiO2), after a thermal treatment and a HF treatment, the impurities are driven off, resulting in fine SiC nano-powder. The synthesized SiC nano-powder lies between 30 and 100nm, and the characteristics of its microstructure, phase composition and specific surface are determined by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and thermogravimetric (TG) and Brunauer–Emmett–Teller (BET) analyses.