Silicon Carbide Nanopowders Research Articles

Silicon Carbide Nanopowders: The Parametric Study of Synthesis by Laser Pyrolysis

Silicon carbide (SiC) nanopowders were synthesized by laser pyrolysis using a pilot scale facility to achieve production rates higher than 1.1 kg/h. For a better control of the process, the synthesis parameters have been systematically studied and their influences were determined. The reactants‘ speed has been studied between 128 and 766 cm/s and the power density between 150 and 2050 W/cm². Furthermore, the influence of the injector shape on the homogeneity of the produced nanopowders has been investigated. The powders were characterized by BET and TEM to determine the particle size distribution and their average diameter. This study allowed us to better understand the influence of these key synthesis parameters and produce large quantities of uniform batches of SiC nanopowders, with an average size adjusted between 18 and 100 nm with narrow size distribution.

Integration of UV-LIGA Process with Slip Casting for Fabricating Polycarbosilane-Derived Silicon Carbide MEMS

In this paper, a new technique for fabricating silicon carbide (Si-C) microelectromechanical systems (MEMS) is described. Slip casting to UV-thick photoresist (SU8) micro mold was carried out for the fabrication of three-dimensional Si-C MEMS parts. Ultrahigh molecular weight polycarbosilane (PCS) was used as the precursor. Si-C nano powder was firstly mixed with a PCS solution, and then the slips were cast into SU8 micro mold fabricated on porous tungsten carbide (WC) plate. Firing at 1273 K was conducted for SU8 evaporation and PCS pyrolysis simultaneously. We have succeeded in producing Si-C ceramics micro gears using the "μ slip casting" technique.

Nano-silicon carbide reinforced aluminium produced by high-energy milling and hot consolidation

Abstract High-energy milling was studied for the ex situ strengthening of aluminium with silicon carbide (SiC) nanopowders. Heptane was used as a milling agent for both planetary- and attritor ball milling. Considering the different milling techniques and the differences in the resulting powders, effective dispersion of the nano SiC was achieved. Composite samples compacted by hot pressing showed an increase in hardness (HV 20 = 220) and a decrease in Al crystallite size from 220 to 55 nm with the nano-SiC content increasing from 1 up to 20 vol.%. The ultimate tensile strength was measured for extruded samples which resulted in 205 MPa (17% elongation) for 1 vol.% of nano-SiC and a strength of 420 MPa (4% elongation) for 10 vol.% of nano-SiC reinforcement. The mechanical properties were compared with what was predicted by the Hall–Petch relationship.

RF 열플라즈마를 이용한 TEOS로 부터의 SiC 나노분말 합성

Silicon carbide (SiC) has recently drawn an enormous industrial interest because of its useful mechanical properties such as thermal resistance, abrasion resistance and thermal conductivity at high temperature. RF Thermal plasma (PL-35 Induction Plasma, Tekna CO., Canada) has been utilized for synthesis of high purity SiC powder from cheap inorganic solution (Tetraethyl Orthosilicate, TEOS). It is found that the powders by thermal plasma consist of SiC with free carbon and amorphous silica (SiO₂) and, by thermal treatment and HF treatment, the impurities are driven off resulting high purity SiC nano-powder. The synthesized SiC powder lies below 30 ㎚ and its properties such microstructure, phase composition, specific surface area and free carbon content have been characterized by X-ay diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric (TG) and Brunauer-Emmett- Teller (BET).

Low-level determination of silicon in steels by anodic stripping voltammetry on a hanging mercury drop electrode

The sensitive differential pulse anodic stripping voltammetry (DPASV) proposed originally by Ishiyama et al. (2001) has been revised and improved to allow the accurate measurement of silicon on a hanging mercury drop electrode (HMDE) instead of a glassy carbon electrode. We assessed the rate of formation of the partially reduced β-silicododecamolybdate and found that metallic mercury promotes the reaction in the presence of a large concentration of Fe 3+. The scope of the method has been broadened by carrying out the measurements in the presence of a constant amount of Fe 3+. The limit of detection (LOD) of the method described in the present paper is 100 μg Si g −1 of steel, with a relative precision ranging from 5% to 12%. It can be further enhanced to 700 ng Si g −1 of steel provided the weight of the sample, the dilution factors, the duration of the electrolysis and the ballast of iron are adequately revised. The tolerance to several interfering species has been examined, especially regarding Al 3+, Cr 3+ and Cr VI species. The method was validated using four low-alloy ferritic steels certified by the National Institute of Standards and Technology (NIST). Its application to nickel base alloys as well as to less complicated matrixes is straightforward. It has also been successfully applied to the determination of free silicon into silicon carbide nano-powder.

Influence of precursor morphology on the microstructure of silicon carbide nanopowder produced by combustion syntheses

Abstract Silicon carbide nanopowder was synthesized using the combustion-based approach. Combustion synthesis was performed in reduction type SiO 2 –Mg–C system. Silicon oxide powders with different morphologies and average particle size were used as starting powders. It was shown that even micro-size silica allows formation of nano-size silicon carbide powder. However, the specific surface area of synthesized SiC particles increases with the decrease the size of the silicon oxide precursor. The mechanism of silicon carbide formation in the combustion wave is also discussed.

Plasma functionalization of silicon carbide crystalline nanoparticles in a novel low pressure powder reactor

In order to functionalize silicon carbide nanopowders with carboxylic groups, an r.f. (13.56 MHz) low pressure plasma reactor has been developed so that particles can be stirred during the processing to try to coat them on their whole surface. Coatings in an O2/hexamethyldisilazane (HMDSN) mixture have first been optimized on flat substrates; X-ray Photoelectron Spectroscopy (XPS) analysis showed that the O2/HMDSN gas mixture resulted in a coating evolving from a polymer-like structure to a more inorganic SiOx-like structure as the oxygen ratio increased. For a large O2/HMDSN value, carboxylic groups were detected on the sample surface. Silicon carbide nanoparticles have then been plasma processed in such a reactive atmosphere. XPS, Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) and Transmission Electron Microscopy (TEM) analyses evidenced the surface modification of the processed powder and confirmed the grafting of carboxylic groups.

Characterization of silicon-carbide nanopowder by electron microscopy

526 The most important characteristics of nanopow� ders, which determine their basic physicochemical properties and most effective operating conditions, are the particle size and morphology. Electron micros� copy is a direct and clear method of investigating these characteristics [1–4]. At present, electron micro� scopes provide resolution from 1–10 to 0.2 nm. Trans� mission, raster, probe, and other types are employed. Transmission electron microscopes permit the cre� ation of an image in transmitted electron beams in (e)

Investigation of the morphology and particle size of silicon carbide nanopowders using electron microscopy

Using transmission and scanning electron microscopy, the shape and particle size of nanopowders (NP) of silicon carbide and pyrolytic carbon are determined. The results are compared with other methods of analyzing the dimensional characteristics of NPs, and their tendency to aggregation is analyzed. It is established that silicon carbide NPs in the state of delivery are presented by globular aggregates from 0.1 to 1 μm in size which are formed by faced nanoparticles that are preferentially 50–70 nm in size. The latter are characterized by octahedron-, cube-, and intermediate-shaped facing; i.e., the tendency for rounded edges and vertexes and the formation of convex faces is observed. Nanoparticles of pyrolytic graphite form aggregates up to 150–200 nm in size containing globular particles 30–40 nm in size.

Influence of lanthanum on synthesis of SiC nanopowder

Low cost silicon carbide nanopowder, which used nanosized SiO2 and carbon as raw materials, was synthesised by a carbothermal reduction method. Thermogravimetry differential scanning calorimetry (TG-DSC) curves revealed that the SiC synthesis process had two steps for La was added. In the first step, after 0·3 wt-%La was added, the initial temperature for the formation of SiO(g) and CO(g) decreased from 1351·4 to 1250·9°C and the thermal activation energy decreased from 223·6 to 34·7 J g−. In the second step, the initial temperature for the formation of β-SiC decreased from 1526·5 to 1357·8°C and the thermal activation energy decreased from 693·7 to 295·7 J g−. Without La added, the optimum process for the formation of β-SiC was 1550°C for 120 min, meanwhile, the average powder diameter >150 nm. With La added, the optimum process was 1500°C for 120 min and the average powder diameter was ∼100 nm.

Design and installation of DC plasma reactor for SiC nanoparticle production

In order to get the high quality SiC nanopowders, a DC plasma reactor system with adjustable torch has been developed. SiC nanopowders were synthesized using this system and the synthesized primary particles have nearly spherical structures, mostly β-SiC phase with a particle size of 10–30 nm. Larger aggregate particles have been produced in our system probably due to longer particle growth times and faster collisions. The synthesized particles collected from the reactor wall and cyclone bottom have some free silicon and free carbon. To produce high quality silicon carbide nanopowders, it is highly necessary to improve the experimental conditions such as lower system pressures, shorter residence time, and higher quenching rates during powder synthesis.

Investigation of the corrosion resistance of nanopowders of refractory borides and carbides in electrolytic solutions

Solubility of nanopowders of vanadium, titanium, chromium, and zirconium borides and carbides and of silicon carbide has been studied in standard electrolytes used for nickel plating. As the objects of the investigation, nanopowders with the contents of the main phase of 92.6–95.3% and an average particle size of 35–62 nm have been used. Their corrosion resistance was estimated depending on the electrolyte acidity, temperature, and duration of the interaction. It has been established that within each group of compounds the nanopowders are close in terms of their corrosion resistance in the electrolytic solutions and are characterized by an unlimited induction period in alkaline media, except for the silicon-carbide nanopowder, which is stable in solutions of any acidity.

The influence of diluent gas composition and temperature on SiC nanopowder formation by CVD

Crystalline cubic silicon carbide (3C-SiC) nanopowders were synthesized using hexamethyldisilane (HMDS) in a resistance heated chemical vapour deposition (CVD) reactor. The effects of different diluent gases on the synthesis of the SiC powder were also studied. The deposited powder was characterized using high-resolution X-ray diffraction (HRXRD) analysis, transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and BET surface area measurements. The crystallite size was estimated to be in the range of nanometer (10–20 nm) from XRD data and the particle size (∼10–30 nm) was obtained by TEM, HRTEM and BET. The growth condition was optimized in terms of crystallinity, chemical composition and deposition rate by varying different parameters such as the diluent gas (H2/Ar ratio) and temperature.

Influence of Network Structure on Abnormally High Viscosity of Mixed Slurries of Silicon Carbide Nanopowder and Polycarbosilane

Silicon carbide powder, polycarbosilane (PCS) and xylene mixed slurries were prepared for viscosity measurement and microstructure observation. Absolute slurry viscosity and shear rate dependence of viscosity were investigated at various SiC concentrations and particle sizes. Temperature dependence of viscosity was also investigated. As the primary particle size in powders decreases, viscosity increases relatively at a low SiC concentration. Microstructure observation on diluted slurries revealed the existence of secondary particles composed with primary nanoparticles and network formation by physically or chemically contacted secondary particles. Some of the microstructure changes with shearing was consistent with a strong shear thinning phenomenon of slurry viscosity.

Synthesis of SiC Nano-Powders by Solid-Vapor Reaction

Silicon carbide (SiC) nano-powders are successfully synthesized by a reaction between carbon nano-powders (carbon black) and SiO gas at 1300°C for 9 hrs in dynamic argon atmosphere (flow rate; 400 cm3 min-1), using the solid-vapor reaction method. The particle size of synthesized SiC nano-powders is below 40 nm and the shape is uniform. Unexpectedly, SiC nano-fibers are also coexisted in the SiC nano-powders. The quantitative and qualitative properties of the SiC nanopowders and nano-fibers are analyzed by scanning electron microscopy (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). Carbon residuals removed by heating over 700°C in air are estimated by thermogravimetry analysis (TGA). It is found that the SiC nanopowders are easily produced by direct synthesis via the solid-vapor reaction method. The morphological characteristics of the resulting SiC nano-powders are dependent upon the morphology of carbon black used as precursor.

Structural Study of SiC Nanoparticles Grown by Inductively Coupled Plasma and Laser Pyrolysis for Nanostructured Ceramics Elaboration

AbstractRefractory carbide nanostructured ceramics as SiC constitute interesting materials for high temperature applications and particularly for fourth generation nuclear plants. To elaborate such nanomaterials, weighable amounts of SiC nanopowders have to be synthesized first with an accurate control of the grain size and stoichiometry. The inductively coupled plasma and the laser pyrolysis techniques, respectively developed at EMPA Thun and CEA Saclay, allow meeting these requirements. Both techniques are able to produce dozens of grams per hour of silicon carbide nanopowders. The particle size can be adjusted down to around 20 nm for the plasma synthesis and even down to 5-10 nm for the laser pyrolysis. The stoichiometry Si/C can be tuned by the addition of methane into the plasma and acetylene for the laser process.

Silicon Nitride Rapid Decomposition for Ceramic Nanopowder Manufacturing

Rapid decomposition of silicon nitride at high temperatures has been successfully used to manufacture ceramic nanopowders in the Si-C-N and Si-O-N systems. For powder processing, the solid combustion called self-propagating high-temperature synthesis (SHS) was realized and investigated. The well-mixed powdered reactants were placed in porous container; then, the reaction was locally ignited and combustion was propagated in a self-sustaining regime, achieving temperatures of over 2000°C. In all these experiments, combustion propagated with the formation of the transient Si3N4 phase resulted in either SiC or Si2ON2 nanosized grains. To elucidate the role of the decomposition of silicon nitride in the formation of nanosized products, thermodynamic data, temperature profiles, morphology (SEM, TEM), dispersion (BET) and phase composition (XRD) of the products were evaluated. It was found that, in both Si-C-N and Si-O-N systems, silicon nitride forms transiently at early stages of combustion because of thermodynamic and kinetic considerations. Finally, it was demonstrated that the technology of silicon carbide and silicon oxynitride nanopowders achieved by the decomposition of Si3N4 is very efficient compared to other conventional techniques. The powders obtained are well sinterable and, after further processing, can be used in a wide range of applications, such as refractory materials, ceramic armor, elements of chemical equipment, etc.

Anomalous behavior of the second and third harmonics generated by femtosecond Cr:forsterite laser pulses in SiC–polymer nanocomposite materials as functions of the SiC nanopowder content

AbstractFemtosecond pulses of 1.25 µm Cr:forsterite laser radiation were used to study second‐ and third‐harmonic generation in silicon carbide nanopowders embedded in a poly(methyl methacrylate) (PMMA) film. Harmonic generation processes extend the analytical and sensing abilities of light‐scattering techniques, including Raman spectroscopy, offering a convenient and efficient approach to the analysis of nanocomposite materials where nanoparticles tend to agglomerate, masking informative features in Raman spectra. The second‐ and third‐harmonic yields are shown to display an anomalous, counterintuitive behavior as functions of the SiC nanopowder content in a polymer film. Whereas harmonic generation in polymer films with a high content of SiC nanocrystals is quenched by the absorption of agglomerating nanoparticles, the influence of absorption is less detrimental in nanocomposite films with a lower SiC content, leading to the growth of the second‐ and third‐harmonic yields. Nanocomposite films with a lower SiC content are also characterized by a higher breakdown threshold, allowing pump pulses with higher fluences to be applied for more efficient harmonic generation. Copyright © 2003 John Wiley & Sons, Ltd.

Diffuse optical harmonic generation in SiC nanopowder films: hunting scattered photons

Second- and third-harmonic generation in polymer films doped with silicon carbide nanopowders is experimentally studied in the regime of weak scattering, with the size of nanoparticles a, the elastic scattering length l, the radiation wavelength λ, and the film thickness L meeting the relations a≪λ≪l∼L. The strong wavelength dependence of diffuse second- and third-harmonic generation observed under these conditions indicates a significant role of scattering effects in nonlinear optical interactions in nanopowder materials, which allows diffuse harmonic generation to be controlled by varying the ratio of the characteristic size of the nanoparticles to the wavelength of the pump radiation. The contribution of scattering-delayed pump photons to diffuse third-harmonic generation in a SiC nanopowder film is visualized by measuring the third-harmonic intensity as a function of the delay time between two pump pulses.

Effects of thermal and laser annealing on silicon carbide nanopowder produced in radio frequency glow discharge

Hydrogenated SiC nanoparticles of high purity have been produced in radio frequency (RF) glow discharges from silane and methane gas mixtures. These nanoparticles show high surface reactivity and can undergo spontaneous oxidation when exposed to the atmosphere. In order to analyze the chemical stability of SiC particles, we present a study of the structural, chemical and compositional modifications induced by thermal annealing at different temperatures (400, 600 and 800 °C). The post-treated powder was analyzed by RAMAN, FTIR and XPS spectroscopy. The effects of the thermal annealing of SiC powder include: change of colour from yellow to dark brown; hydrogen desorption; and an increase in CC and SiC bonds in detriment to SiSi bonds. In addition, annealing with a KrF excimer laser induced the presence of Si and SiC nanocrystallites.