Production Of Silicon Carbide Research Articles

Synthesis of silicon carbide in a nitrogen plasma torch: rotational temperature determination and material analysis

Experiments on silicon carbide synthesis were performed using a dc nitrogen plasma torch. Measurements of rotational temperature of nitrogen molecules by emission spectroscopy were performed, based on the band (0, 1) of the first negative system of nitrogen for the R branch. Three different plasma torch powers were studied in order to optimize the production of silicon carbide with our experimental set-up. The synthesized products were characterized by x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy.

Synthesis of amorphous silicon carbide nanoparticles in a low temperature low pressureplasma reactor

Commercial scale production of silicon carbide (SiC) nanoparticles smaller than 10 nmremains a significant challenge. In this paper, a microwave plasma reactor and appropriatereaction conditions have been developed for the synthesis of amorphous SiC nanoparticles.This continuous gas phase process is amenable to large scale production use and utilizes thedecomposition of tetramethylsilane (TMS) for both the silicon and the carbon source. Theinfluence of synthesis parameters on the product characteristics was investigated.The as-prepared SiC particles with sizes between 4 and 6 nm were obtained fromthe TMS precursor in a plasma operated at low temperature and low precursorpartial pressure (0.001–0.02 Torr) using argon as the carrier gas (3 Torr). Thecarbon:silicon ratio was tuned by the addition of hydrogen and characterized by x-rayphotoelectron spectroscopy. The reaction mechanism of SiC nanoparticle formation in themicrowave plasma was investigated by mass spectroscopy of the gaseous products.

Modeling and Development of a Microwave Heated Pilot Plant for the Production of SiC-Based Ceramic Matrix Composites

This paper outlines the development of a microwave heated apparatus for the production of silicon carbide (SiC) based ceramic matrix composites via chemical vapor infiltration. An innovative pilot scale reactor was designed and built. A coupled thermal and electromagnetic model was developed in order to predict the temperature profile inside the reactor. The results obtained from the model demonstrated that the electric field inside the sample was constant. This fact is particularly important in order to prevent the thermal instabilities (run-aways) that are typical in the case of microwave heating. Therefore the heating was uniform with the aid of a mode stirrer that achieved a better distribution of the microwave power and then improved the process efficiency. The infiltration cycles were carried out on SiC fiber preforms and resulted in an excellent average weight increase with respect to the initial sample. By using microwave heating, the treatment times were considerably reduced with respect to the conventional process times reported in the literature. The microstructure of the SiC composites were observed by scanning the electron microscopy in order to evaluate the quality and the degree of densification which was achieved within the fiber tows. The SiC deposition inside of the sample was sufficiently homogeneous and compact, even if a certain degree of inter-tow porosity was still evident.

Synthesis of Silicon Carbide Platelets by Double-Heating Technique

A new method for producing silicon carbide platelets with low cost and high yield was introduced. The silicon carbide platelets were synthesized by double-heating technique with carbon black and SiO2 powder as raw materials without using any catalysts. The starting mixtures were heated at a temperature in the range of 1800-2000°C for the duration of about 2-4h to produce substantially completely unagglomerated silicon carbide platelets with the thickness of 5-15μm and the average diameter of 50-150μm. Compared to the conventional heating, double-heating technique has different heating mechanism and has advantages of less investment for equipment, easy to manufacture and convenient to operate. Furthermore, it is very suitable for realizing the scaled production because of the lower synthesizing temperature, shorter reaction time and greater output.

Effect of temperature on the formation of β-silicon carbide by hot isostatic pressing the pyrolyzed phenol resin–silicon composite

The aim of the present study is to investigate the effect of temperature on the formation of β-SiC below the melting point of silicon; and to develop a new technique that might be implied to convert the used polymeric materials to produce silicon carbide and to minimize the environmental problems caused by the gases formed during combustion of used polymeric products. In the first step, preforms were produced by pyrolysing phenolic resin and silicon powders at 850 °C, then HIPed at 1300–1400 °C, in second step. XRD peaks of β-SiC were observed at 1300 °C; and then these peaks were heightened with increasing the temperature. SEM photographs showed the formation of whisker and crystals of β-SiC in pores and matrix of the composite HIPed at 1400 °C. The increase in apparent density and Vickers micro-hardness of the composites; and the results of EDS and XPS analyses suggested that the formation of β-SiC was enhanced at higher temperatures.

Molecular sieve SiC-based membrane for hydrogen separation produced by radiation curing of preceramic polymers

Polycarbosilane and its blend with polyvinylsilane of 20 wt% were used as precursor polymers to produce silicon carbide (SiC)-based membranes for gas separation. Preceramic polymers were spin coated onto porous γ-alumina substrate and crosslinked with oxygen by irradiation method. It was found that the blend undergoes higher oxidation than pure PCS due to plasticizing effect of PVS and faster oxidation of PVS itself. Subsequent pyrolysis at 1123 K converted the polymer film into inorganic material. Hydrogen and nitrogen gas permeation experiments revealed temperature activated gas transport process with temperature dependent H 2 permeance of 10 −10 to 10 −8 mol s −1 m −2 Pa −1 order. Excellent H 2/N 2 perm-selectivity was achieved of nearly 150 and over 250 at 523 K for PCS and PCS/PVS blend derived membranes, respectively. The permeation was governed by a molecular sieving mechanism.

SiC Platelets Synthesized by Powder-Heating Technique

A new method for producing silicon carbide platelets with low cost and high yield was introduced. The silicon carbide platelets were synthesized by powder-heating techniques with carbon black and SiO2 powder as raw materials and CoCl2 as catalyst. The starting mixtures were heated at a temperature in the range of 1800-2000°C for the duration of about 2-4h to produce substantially completely unagglomerated silicon carbide platelets with a thickness of 5-20μm and the average diameter of 50-200μm. Compared to the conventional heating, the powder-heating technique is advantageous of less investment on equipment, easy to manufacture and convenient to operate. Furthermore, it is very suitable for realizing the scaled production because of the lower synthesizing temperature, shorter reaction time and greater output.

Effect of process parameters on the production of nanocrystalline silicon carbide from water glass

Nanocrystalline silicon carbide was synthesized from the precursor prepared by spray drying slurry of water glass and carbon black. The effect of process parameters, such as reaction temperature, reaction time and carbon content, on phase evolution, crystallite size and specific surface of the resulting samples were characterized by XRD, SEM and BET. The results show the powder produced in this process has a very fine crystallite size and high specific area and the reaction can be completed at 1550 °C for 2 h when the C/Si ratio is 5 or larger. In addition, the powder is of high purity, because sodium oxide in the precursor can be eliminated by the escape of sodium at high temperature. It is a simple and cost-efficient method to synthesize nanocrystalline silicon carbide using cheap and abundant water glass as silicon source.

New processing methods to produce silicon carbide and beryllium oxide inert matrix and enhanced thermal conductivity oxide fuels

For inert matrix fuels, SiC and BeO represent two possible matrix phase compounds that exhibit very high thermal conductivity, high melting points, low neutron absorption, and reasonably high radiation stability. BeO is chemically compatible with UO2, PuO2 and Zircaloy to very high temperatures, but SiC reacts with all three at somewhat lower temperatures. We have developed the Polymer Impregnation and Pyrolysis or PIP method, making use of a commercial SiC polymeric precursor, to consolidate both particulate fuels like ‘TRISO’ microsphere fuels, and to impregnate UO2 fuels with pure stoichiometric SiC to improve their thermal conductivity. This method was employed to fabricate Enhanced Conductivity Oxide fuels, or ECO fuels with 5–10vol.% of the high conductivity phase, and with 50vol.% for TRISO dispersion fuels. For ECO fuels, a new ‘slug/bisque’ method of fabricating the UO2 fuel granules was necessary to produce sintered fuel with open pore structures, allowing almost complete impregnation of the continuous SiC phase. The advantages of the PIP process are that it is a non-damaging consolidation process for particulates (TRU, UC or TRISO microspheres), forms a continuous, pure β-SiC phase at temperatures as low as 1573K, and allows the maximum in fissile atom density. However, several PIP impregnation cycles and high crystallization temperatures are necessary to obtain high thermal conductivity SiC. For producing IMF fuels using the PIP process, the fissile PuC and/or TRU actinides can be added in small concentrations along with SiC ‘filler particles’ and consolidated with the SiC precursor for either open or closed fuel cycles. For BeO, a second approach was developed for ECO fuels that involves a ‘co-sintering’ route to produce high density fuels with a continuous BeO phase of 5–10vol.%. Special granulation and mixing techniques were developed, but only one normal sintering cycle is required. For BeO matrix IMF fuels, PuO2 granules and TRU actinides or YSZ granules containing actinides could be simply dry-mixed with BeO powder and co-sintered to produce a dispersed fuel form. Alternatively, the BeO could be granulated, and the PuO2 and/or TRU oxides would fill the interstices forming a continuous minor phase that could be recycled in closed fuel cycles. Some advantages and disadvantages of these matrices are discussed.

Production of Silicon Carbide Pieces by Immersion of Silicon Preforms in Carbonaceous Powders

In this work a novel method for production of silicon carbide (SiC) pieces, which involves the heating of silicon (Si) preforms immersed in graphite powder is presented. Such preforms were obtained via low‐pressure injection molding (LPIM), although any other conformation route can be used. The process can be carried out at modest temperatures and gradients in standard furnaces used for processing other ceramics. These features make this process a simpler and cheaper alternative, when compared with other methods of SiC fabrication. The variables affecting the process have been identified, and an optimum‐heating ramp has been established. Under these conditions, the obtained SiC products show no remnant‐free Si, and their mechanical behavior allows their use in several less‐demanding SiC applications, for which expensive high‐performance SiC products are unaffordable. In the proposed chain of reactions, CO(g) is responsible for the carburization of the pieces. All phases present are identified, and their distribution is explained by means of competitive reactions. In our opinion, this novel method can be extended to an industrial scale because it is simple and involves cheap raw materials.

Silicon Carbide from Sludged Silicon Powder

Abstract Sawing silicon ingot with abrasive slurry generates sludge that includes abrasive powders, cutting oil, and silicon powders. The abrasive powders and cutting oil are being separated and reused. Mixing the remained sludged silicon powders with carbon powders and subsequent heattreatment are conducted to produce silicon carbide. Thermodynamic calculation is performed to find an optimum formation condition for the silicon carbide. Silicon carbide whiskers are mainly formed at 1400°C in a closed system, instead of silicon carbide powders. Impurity related mechanism is attributed to the formation of the silicon carbide whiskers, as metal impurities are contained in the sludged silicon powders.

Airborne Fibres in the Norwegian Silicon Carbide Industry

Morphology of silicon carbide (SiC) fibres from the Norwegian SiC industry has been studied by scanning electron microscopy (SEM). The fibres are an unwanted side-product in SiC production. They represent a probable cause of the observed increased occurrence of lung diseases among SiC workers. The main aim of this work is to give a detailed description of the morphological variation of the fibres. Furthermore, it is important to study the occurrence of various morphological types with respect to job types and process parameters. SiC fibres accounted for >90% of all fibres observed. Eight categories of SiC fibres are described based on their morphology. The most frequent fibre category had a smooth surface and accounted for more than half of the observed SiC fibres. The diameter distributions of the eight fibre types were significantly different except for two of the categories. More than 99% of the SiC fibres observed were <3 microm in diameter, satisfying one WHO criterion for health relevant fibres. The aspect ratio and diameter of health-relevant fibres generally followed a lognormal distribution for different fibre categories, whereas fibre length did not. The proportions of SiC fibres (all categories) did not differ significantly between the plants. The proportions differed between plants for two SiC fibre categories including the most dominant type. For two SiC fibre categories and the SiC cleavage fragments differences were observed between job groups. Two other fibre categories were correlated with type of SiC produced (i.e. black or green SiC) and sawdust added to the raw material mix.

The Effect of Stellar Evolution on SiC Dust Grain Sizes

Stars on the asymptotic giant branch (AGB) produce dust in their circumstellar shells. The nature of the dust-forming environment is influenced by the evolution of the stars, in terms of both chemistry and density, leading to an evolution in the nature of the dust that is produced. Carbon-rich AGB stars are known to produce silicon carbide (SiC). Furthermore, observations of the ~11um SiC feature show that the spectral features change in a sequence that correlates with stellar evolution. We present new infrared spectra of amorphous SiC and show that the ~9um feature seen in both emission and absorption, and correlated with trends in the ~11um feature, may be due to either amorphous SiC or to nano-crystalline diamond with a high proportion of Si substituting for C. Furthermore, we identify SiC absorption in three ISO spectra of extreme carbon stars, in addition to the four presented by Speck et al. (1997). An accurate description of the sequence in the IR spectra of carbon stars requires accounting for both SiC emission and absorption features. This level of detail is needed to infer the role of dust in evolution of carbon stars. Previous attempts to find a sequence in the infrared spectra of carbon stars considered SiC emission features, while neglecting SiC absorption features, leading to an interpretation of the sequence inadequately describes the role of dust. We show that the evolutionary sequence in carbon star spectra is consistent with a grain size evolution, such that dust grains get progressively smaller as the star evolves. The evolution of the grain sizes provides a natural explanation for the shift of the ~11um SiC feature in emission and in absorption. Further evidence for this scenario is seen in both post-AGB star spectra and in meteoritic studies of presolar grains.

Morphology and structure of airborne β-SiC fibres produced during the industrial production of non-fibrous silicon carbide

Clusters of airborne SiC fibres from the SiC industry have been studied by scanning and transmission electron microscopy (SEM, TEM). These fibres are produced as an unwanted side product during the industrial manufacturing of non-fibrous silicon carbide. It was found that the complex morphology seen for clusters of SiC fibres can be explained on the basis of the crystal structure of the fibres. By use of electron diffraction (ED) and high resolution electron microscopy (HREM) it was found that the SiC fibres can be described as needles based on face centred cubic structure (space group F\(\overline{4}\)3m and a = 0.4385 nm). The needles are covered by a thin amorphous layer of carbon. The needles contain a high degree of stacking faults and twinned areas. No long-range order of a hexagonal structure as a result of stacking faults was found.

Complex Thermal Chemistry of Vinyltrimethylsilane on Si(100)-2×1

The surface chemistry of vinyltrimethylsilane (VTMS) on Si(100)-2x1 has been investigated using multiple internal reflection-Fourier transform infrared spectroscopy, Auger electron spectroscopy, and thermal desorption mass spectrometry. Molecular adsorption of VTMS at submonolayer coverages is dominating at cryogenic temperatures (100 K). Upon adsorption at room temperature, chemical reaction involving rehybridization of the double bond in VTMS occurs. Further annealing induces several reactions: molecular desorption from a monolayer by 400 K, formation and desorption of propylene by 500 K, decomposition leading to the release of silicon-containing products around 800 K, and, finally, surface decomposition leading to the production of silicon carbide and the release of hydrogen as H(2) at 800 K. This chemistry is markedly different from the previously reported behavior of VTMS on Si(111)-7x7 surfaces resulting in 100% conversion to silicon carbide. Thus, some information about the surface intermediates of the VTMS reaction with silicon surfaces can be deduced.

Assessment of Exposure to Quartz, Cristobalite and Silicon Carbide Fibres (Whiskers) in a Silicon Carbide Plant

The main objective of the present paper is to report on the concentration of silicon carbide (SiC) fibres, crystalline silica and respirable dust in a Canadian SiC production plant and to compare the results with earlier investigations. The second objective is to tentatively explain the differences in concentration of the fibrogenic substances between different countries. The assessment of SiC fibres, dusts, respirable quartz and cristobalite was performed according to standard procedures. The highest 8 h time-weighted average concentrations of fibres were found among the crusher and backhoe attendants and the carboselectors with an arithmetic mean of 0.63 fibres ml(-1) for the former group and 0.51 fibres ml(-1) for the latter group. The results of respirable SiC fibres in the Canadian plant were lower than in the Norwegian and Italian industries. Most of the 8 h time-weighted average concentrations for quartz were less than or around the limit of detection of 0.01 mg m(-3). The maximum 8 h time-weighted average concentration for quartz was found among the carboselectors (0.157 mg m(-3)), followed by the labourers (0.032 mg m(-3)). Similarly, most of the 8 h time-weighted average cristobalite measurements were less than the limit of detection of 0.01 mg m(-3) except for the carboselectors where it was found to be 0.044 mg m(-3). The assessment of the Italian occupational settings exposure demonstrated elevated quartz concentrations, while cristobalite was absent. The authors have concluded that the investigations that were performed in the last two decades in this field by researchers from different countries seem to support that SiC fibres (whiskers) constitute a major airborne health hazard.

An Object-Oriented Modeling Approach in Materials Processing: Case Study of the Acheson and Carburizing Processes

Numerical results can be conveyed effectively to any one using an object-oriented framework. Therefore, it becomes essential to couple the object-oriented approach with numerical analysis. A simple object-oriented methodology for creating a graphical user interface (GUI) as a framework is presented. This work tries to fill a gap between scientific computer code written in a noninteractive way and interactive programming in materials processing. The GUI interface framework has been created in such a way that at any point of time one need not create a new GUI framework. The user only needs to create the process object and attach it to the framework. Two examples have been presented involving interactive finite volume-based gas carburizing and interactive finite difference-based Acheson process (used for the production of silicon carbide).

Experimental investigation into the selective laser sintering of silicon carbide polyamide composites

This paper presents an experimental investigation into the production of particulate silicon carbide (SiC) polyamide matrix composites via the selective laser sintering (SLS) process. FEPA standard F240 SiC grit was blended with Duraform polyamide to produce a powder blend composition of 50 wt% SiC for direct SLS processing. A full factorial experimental approach was applied to examine the effects and interactions of key fabrication parameters, with regard to the tensile strength and porosity of the composite SLS processed parts. Output from the factorial analyses is presented and discussed and a comparison between the responses obtained for tensile properties and morphology of the SLS processed parts was also investigated. The optimum energy density for producing parts with maximum strength and minimum porosity was determined experimentally. A further study into the effects of powder blend composition and energy density with regard to tensile strength of composite specimens is also presented. This investigation revealed that the optimum energy density for producing parts of maximum strength was independent of the initial powder blend composition.

Characterization of High Temperature Oxidation Properties of Silicon Carbide Nanofibers

Carbon nanofibers were reacted with SiO vapor generated from a mixture of Si and SiO2 to produce silicon carbide nanofibers at 1350oC for 2 h under vacuum. The obtained SiC nanofibers with a diameter ranging 100~200 nm had the specific surface area as high as 124 m2/g. The SiC nanofibers were not oxidation resistant, showing nearly complete oxidation at 1000 oC after about 60 h in air, though the oxidation product was amorphous silica which was generally considered to be oxidation resistant. The poor oxidation resistance was attributed to the inherent nanoporous nature of the fibers resulted from the gas-solid reaction.

Fullerene freejets-based synthesis of silicon carbide: heteroepitaxial growth on Si(111) at low temperatures

The growth of silicon carbide (SiC), a large band-gap semiconductor, on Si is very promising for applications to sensors, electronics and optoelectronics. However, difficulties in controlling the growth of the material and the interface have inhibited the production of SiC based devices. We have developed a new technique (Supersonic Molecular Beam Epitaxy, SuMBE) for the heteroepitaxial growth of SiC on Si by means of supersonic molecular beams of fullerene (C 60). The carbide synthesis can be induced by the kinetic activation of the process due to the kinetic energy released in C 60–Si collision. This has made possible a reduction of the growth substrate temperature and an improvement of electronic and structural properties of the SiC film. We present a study of the processes governing the growth of very thin SiC film by C 60 supersonic beam. Two films were grown in Ultra High Vacuum (UHV) on Si(111)-7×7, at substrate temperature of 800 °C, using the same fullerene beam but selecting C 60 particles having different characteristics. Surface electronic and structural characterizations were done both in situ and ex situ. The results show that strongly different growth processes can be achieved by controlling the precursor kinetic energy.