Silicon Carbide Precursor Research Articles

Study on process and parameter optimization of selective laser sintering of SiC composite powder

This study aims to utilize silicon carbide (SiC) powder and phenol-formaldehyde resin (PF) as the primary raw materials to prepare phenol-formaldehyde coated silicon carbide composite (PCSC) using a thermal coating method. Then, single-factor experiment and orthogonal experiment were used to optimize the process parameters of selective laser sintering (SLS). Finally, SiC precursors were formed using optimized process parameters with excellent density and dimensional accuracies. The results show that the best combination of process parameters is: laser power of 25W, scanning speed of 1.7m/s, scanning spacing of 0.12mm and layer thickness of 0.16mm.

Fabrication of dense SiSiC ceramics by a hybrid additive manufacturing process

AbstractIn this work, we report the fabrication of Silicon infiltrated Silicon Carbide (SiSiC) components by a hybrid additive manufacturing process. Selective laser sintering of polyamide powders was used to 3D print a polymeric preform with controlled relative density, which allows manufacturing geometrically complex parts with small features. Preceramic polymer infiltration with a silicon carbide precursor followed by pyrolysis (PIP) was used to convert the preform into an amorphous SiC ceramic, and five PIP cycles were performed to increase the relative density of the part. The final densification was achieved via liquid silicon infiltration (LSI) at 1500°C, obtaining a SiSiC ceramic component without change of size and shape distortion. The crystallization of the previously generated SiC phase, with associated volume change, allowed to fully infiltrate the part leading to an almost fully dense material consisting of β‐SiC and Si in the volume fraction of 45% and 55% respectively. The advantage of this approach is the possibility of manufacturing SiSiC ceramics directly from the preceramic precursor, without the need of adding ceramic powder to the infiltrating solution. This can be seen as an alternative AM approach to Binder jetting and direct ink writing for the production of templates to be further processed by silicon infiltration.

Direct ink writing of ZrB2-SiC chopped fiber ceramic composites

Ultra-high temperature ceramics (UHTCs) are of interest for thermally- and/or mechanically- extreme environments because of their high melting temperatures (> 3000 °C) and ablation resistance. More widespread use is limited by low fracture toughness and inability to be processed into complex-shaped components. Here, we report the production of fiber-reinforced UHTC matrix composites (UHTCMCs) formed via the additive manufacturing technique of direct ink writing (DIW). Slurry 'inks' were developed containing up to 47.5 vol% of the UHTC zirconium diboride (ZrB 2 ), up to 10 vol% chopped silicon carbide fiber (SiC f ), and a silicon carbide (SiC) precursor polymer. Lattice structures and flexural specimens were printed and pyrolyzed to form UHTCMCs with aligned (relative to the print direction) SiC f in the ZrB 2 – SiC matrix. Flexural strength of fiber-containing parts is presented, and fiber alignment due to deposition is analyzed with X-ray computed tomography. Defects that occurred during the DIW process, and their probable causes and mitigation strategies are also discussed.

Effects of Hydrogen Passivation on Fullerene-Derived Si30C30 Clusters

Silicon carbide (SiC) is technologically a significant material. A recent report on the abundance of C60 fullerenes in interstellar space, along with the presence of the SiC precursors, sparked interest in potentially similar SiC nanostructures. The C60 fullerene was found experimentally and is an exceptionally stable form of carbon. As Si and C have similar valence electron properties, it has been long envisioned that Si and SiC could also form similar fullerene type structures. In this paper, Si30C30 fullerene-derived clusters were studied from the first principle starting from an ideal Si60 fullerene templet with various arrangements of silicon and carbon atoms, and then relax them without any symmetry constraint. Hydrogen passivation was considered as well to model the effect of ligands that may be available during the chemical synthesis processes. We have found that after passivation, the relative stability of different configurations of Si30C30 clusters changed compared to the unpassivated structures, while some structures collapsed. We have also noticed several Si-Si and Si-C double bonds in the unpassivated structures. Upon relaxation, some Si atoms lost their hydrogen, while carbon atoms capture those hydrogen atoms. Finally, we tested the endohedral doping of a transition metal, tungsten atom, to stabilize and magnetize Si30C30. With hydrogen passivation, the magnetic moment on W atom was enhanced. Overall, the effects of passivation on these fullerene structures are not very straightforward.

Open-celled silicon carbide foams with high porosity from boron-modified polycarbosilanes

Open-Celled silicon carbide (SiC) foams were prepared from a mixture of a boron-modified polycarbosilane as a preceramic polymer and poly(methymetacrylate) (PMMA) microbeads as sacrificial agents. The process consists in the cross-linking of the liquid allylhydridopolycarbosilane (AHPCS, SiC precursor) with borane dimethylsulfide (BDMS, boron source) to form a solid boron-modified polycarbosilane with an adjusted cross-linking degree. The latter is mixed with PMMA microbeads (25 μm) in a 20:80 ratio and the mixture is warm-pressed at 120 °C forming consolidated green bodies to be pyrolyzed at 1000 °C under argon and to deliver open-celled SiC foams with an interconnected porosity of 73.4 vol%. These foams combine a low density with a compressive strength of 3.49 ± 0.56 MPa and a thermal and mechanical stability under argon up to 1300 °C. Ageing and microfiltration tests in the conditions of a primary loop of coolant in a Pressurized Water Reactor (PWR) showed that foams display a relatively high stability while retaining particles of 5 μm in diameter making these materials as appropriate candidates to work in separation techniques under harsh environments.

Liquid polycarbosilane as a potential chemical liquid vapour deposition precursor for SiC

Abstract A low-viscous liquid polycarbosilane (LPCS) is being proposed as a silicon carbide (SiC) precursor for chemical liquid vapour deposition (CLVD) process. The LPCS was characterized by Gel permeation chromatography (GPC), Fourier transformation infrared (FT-IR) spectroscopy, Nuclear magnetic resonance (NMR) spectroscopy, GC-MS and Thermogravimetric analysis (TGA). Spectroscopic investigations together with Gas chromatography Mass spectrum (GC-MS) indicated that the synthesized LPCS is a mixture of cyclic/linear silanes and carbosilanes. TGA showed the complete evaporation of the LPCS below 250 °C, a suitable property for application as a CLVD precursor. Ceramic conversion of LPCS at different temperatures (900 °C, 1100 °C and 1300 °C) under argon, indicated the formation of nano-sized crystallites of β-SiC at 1300 °C.

Microstructural studies of core/rim structure of polycarbosilane-derived SiC consolidated by spark plasma sintering

Abstract Recently, attempts have been made to use silicon carbide (SiC) ceramics as a fuel compact in nuclear reactors. However, the use of sintering additives in the conventional sintering of SiC leads to a coarse microstructure with high porosity and large grains due to the low sinterability and the large amount of grain boundaries or a second phase, deteriorating the mechanical properties, and hence limiting widespread industrial applications. In this study, polycarbosilane (PCS) and spark plasma sintering (SPS) as the SiC precursor and sintering method, respectively, were applied to overcome the low sinterability and the use of sintering additives. As the raw material, amorphous PCS was prepared by pyrolysis at 1000 °C. To decrease the particle size, pyrolyzed PCS powder was subjected to ball milling by using high-energy ball milling. The ball-milled amorphous PCS powder was sintered by SPS. Sintering was carried out at different temperatures (i.e., 1700, 1800, and 1900 °C) and pressures (i.e., 40 and 80 MPa). After SPS, the core/rim structure of the sintered pellet was formed on account of the oxygen originating from the native oxide layer and free carbon in the PCS powder as the raw materials. In the core/rim structure comprising the core, as well as the intermediate and rim regions, the microstructure and chemistry of each region exhibited marginal difference with respect to the free carbon and oxygen. The phase fraction of α-SiC increased from the rim region to core region due to the discrepancy of actual loaded pressure on account of friction with the wall surface. The existing carbon was verified to be graphitized carbon. Owing to the short reaction time, graphitization did not completely proceed, and deficient graphitization led to graphitized carbon as not graphite. The introduced oxygen changed to amorphous SiO2, which was applied to the sintering-additive-like liquid-phase sintering.

A new SiC precursor with high ceramic yield: Synthesis and characterization of CHxMeSiH2‐containing poly(methylsilane‐carbosilane)

ABSTRACTA new poly(methylsilane‐carbosilane) (PMSCS) for silicon carbide precursor was prepared using Wurtz‐type copolymerization of methyldichlorosilane (MeHSiCl2), chloromethyldichloromethylsilane (ClCH2MeSiCl2), and (dichloromethyl)methylsilane (Cl2CHMeSiH2), with (chloromethyl)methylsilane (ClCH2MeSiH2) or trimethylchlorosilane (Me3SiCl) as terminated reagent. The ceramic yield of PMSCS was markedly increased by introduction of Cl2CHMeSiH2 comonomer and capped with ClCH2MeSiH2. The H2MeSiCH2‐capped PMSCS with CHMeSiH2 structure unit in main chain produced SiC ceramic with 1.21 of C/Si atomic ratio in a ceramic yield of 78 wt % upon pyrolyzed at 1000 °C. The excellent pyrolytic properties, combining with its economical preparation, good storage stability in air, and favorable processabilty, make the CHxMeSiH2‐containing PMSCS a new cost‐effective SiC ceramic precursor. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47618.

Evaluation of poly(methylsilane‐carbosilane) synthesized from methyl‐dichlorosilane and chloromethyldichloromethylsilane as a precursor for SiC

ABSTRACTA new poly(methylsilane‐carbosilane) (PMSCS) for silicon carbide precursor was synthesized by Wurtz‐type copolycondensation of methyldichlorosilane (MeHSiCl2) with chloromethyldichloromethylsilane (ClCH2MeSiCl2) and terminated with vinylmagnesium chloride (ViMgCl). The use of insufficient sodium made the reaction more economic and safe. By changing the ratios of two monomers and the end‐block agent, the properties of the obtained PMSCS and the C/Si ratio of its derived ceramic could be tuned. Upon pyrolysis at 1000 °C under argon, silicon carbide with nearly stoichiometric C/Si ratio and low oxygen content was obtained in 64% of ceramic yield. PMSCS showed high potential as an economical SiC ceramic precursor for the fabrication of SiC matrix, coating, and adhesives. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46610.

Fabrication of silicon carbide coating on mullite fiber-reinforced mullite matrix composite via dip-coating

Silicon carbide (SiC) coating was fabricated on mullite fiber using polycarbosilane as SiC precursor. The concentration of the precursor solution and the dip-coating cycle were considered variables to determine optimum amounts. Results showed that the SiC coating prepared with 0.01mol/L SiC precursor for one impregnation cycle was uniform and thin. It had a thickness of 62.2nm, which completely covered the mullite fiber. This SiC coating inhibited the reaction between the fibers and the matrix. It also weakened interface bonding, thereby resulting in a toughened fracture behavior of the composite with SiC coating.

Synthesis of Silicon Carbide-Derived Carbon as an Electrode of a Microbial Fuel Cell and an Adsorbent of Aqueous Cr(VI)

Micron-sized nonporous silicon carbide (SiC) powder of the spent heating elements of a graphite furnace were used as the common precursor of two different forms of carbide-derived carbon (CDC) synthesized by chlorination at different temperatures: (1) graphitic and (2) amorphous Si-CDCs. Whereas the former material having high electroconductivity was used as an efficient electrode of a microbial fuel cell (MFC), the latter material having high specific surface area was used as an efficient adsorbent for aqueous hexavalent chromium (Cr(VI)). The MFCs generated a significantly high maximum power density of ∼1570 ± 30 mW/m2 and open circuit potential of ∼460 ± 5 mV. The adsorbents exhibited a significantly large adsorption capacity of ∼95 ± 5 mg/g. This study has developed for the first time two types of Si-CDCs having different physicochemical characteristics, from the common SiC precursor via the facile route of different temperature conditions, for bioelectricity generation and environmental remediation a...

Soft templated mesoporous SiC from polycarbosilane grafted onto triblock copolymers

Mesoporous silicon carbide (SiC) presenting very large specific surface area was elaborated following an original soft-templating approach based on polymeric precursors. The polystyrene units of a poly(styrene-block-butadiene-block-styrene) triblock copolymer are used as a templating agent, while a polycarbosilane preceramic polymer is employed as SiC precursor. Thanks to the self-organization of polycarbosilane around PS blocks in liquid medium, and to the subsequent elimination of the copolymer during the polycarbosilane conversion into SiC, a mesoporous SiC can be formed. High specific surface areas of more than 400m2g−1 are measured on the final SiC, opening the doors to the viable production of SiC of controlled porosity.

Simulation and experimental study of CVD process for low temperature nanocrystalline silicon carbide coating

There is a huge requirement for development of a coating technique in nuclear industry, which is environmentally safe, economical and applicable to large scale components. In this view, simulation of gas-phase behavior in specially designed CVD reactor was carried out using computational tool, COMSOL. There were two important zones in CVD reactor first one is precursor vaporization zone and second one is coating zone. Optimized parameters for coating were derived from the simulation of gas phase dynamics in both zone of CVD reactor. The overall effect of fluid velocity, heat flow and concentration profile showed that Re=54 is the optimum reaction condition for uniform coating in CVD system. In CVD coating experiments a synthesized halogen free, non-toxic and non-corrosive silicon carbide precursor was used. Uniform coating of SiC was obtained on zircaloy substrate at 900°C using as synthesized organosilicon precursor. The X-ray diffraction and scanning electron microscopy analysis show that dense nano crystalline SiC film was deposited on zircaloy substrate.

In situ incorporation of silicon into a CVD diamond layer deposited under atmospheric conditions

Chemical vapour deposited (CVD) diamond coatings were obtained by a laser-based plasma CVD process without a chamber at atmospheric pressure. The aim of this study is to influence the conductivity by incorporating silicon content into a diamond layer. The modification of the diamond coatings was carried out by the supply of a solid silicon carbide precursor into the plasma flame during the CVD process. In this way, the CVD process was combined with a physical vapour deposition process to incorporate in situ impurities into the diamond layer. The crystal structure of the diamond films was verified by Raman spectroscopy and secondary electron microscopy. To analyse the distribution of the incorporated silicon, focused ion beam profiles were produced and recorded by scanning electron microscopy. Hereby it is shown that the silicon is incorporated underneath, on top, and in between the polycrystalline diamond coating. Using backscattered electron microscopy, it was detected that the silicon content in the centre of the process position is lower than at the edges. No silicon signal could be detected inside the diamond crystals by wavelength-dispersive X-ray spectroscopy. The luminescence spectra showed a sharp peak at 738nm, which proves the existence of silicon-vacancy centres.A sheet resistance of 2.43MΩ±1.98MΩ was measured by a 4-point probe van der Pauw resistivity measurement on a single diamond crystal in the centre of the coating. Feasibility studies of electrical discharge machining of the diamond layers proved that the modification of conductivity was successful.

Effects of Ceramic Precursor Ratio on Antioxidation Properties of Pitch-based Carbon Materials Doped with Si-Zr-B

The Si-Zr-B doped coal-tar pitch was synthesized by co-pyrolysis of xylene soluble pitch, silicon carbide precursor, zirconium boride precursor, and zirconium carbide precursor. The pitch-based carbon materials doped with Si-Zr-B were prepared through co-carbonization, cold moulding and followed by high temperature heat treatment from the obtained Si-Zr-B doped coal-tar pitch. The phase composition and microstructure of the carbon materials were characterized by XRD, SEM and EDS. The oxidation behavior of specimens was tested at 1500°C in static air. The results show that weight loss of the doped carbon materials is increased firstly and then decreased with the decrease of content of silicon carbide precursor in Si-Zr-B doped coal-tar pitch. The doped carbon materials obtained from Si-Zr-B doped coal-tar pitch, with a mass ratio of the polycarbosilane, zirconium carbide precursor and zirconium boride precursor at 1:2:1, shows an excellent oxidant resistance. After oxidation in air at 1500°C for 4 h, its weight loss and oxidation depth is 27.5wt% and 0.7 mm, respectively. A dense SiO2-ZrO2-B2O3 glassy oxide layer which formed during oxidation in air can effectively reduce the rate of oxygen diffusion and thus improve the oxidation resistance of the carbon materials derived from the doped coal-tar pitch. 1312 无 机 材 料 学 报 第 31卷

Template Synthesis of 3D High-Temperature Silicon-Oxycarbide and Silicon-Carbide Ceramic Photonic Crystals from Interference Lithographically Patterned Organosilicates

The fabrication of 3D diamond-like silicon-oxycarbide and silicon-carbide high-temperature ceramic photonic crystals has been achieved by a strategy involving (1) the use of four-beam interference lithography (IL) to construct a patterned silsesquioxane (POSS) template and (2) infiltration of the polymeric allylhydridopolycarbosilane (AHPCS) silicon-carbide precursor into the patterned POSS template followed by high temperature ceramic conversion and HF etching. Energy-dispersive X-ray mapping analysis and Fourier transform infrared (FT-IR) studies suggested that the 3D ceramic photonic crystals formed at 1100 °C were SiC-like silicon oxycarbide. Additional thermal treatment at 1300 °C in vacuo resulted in the carbothermic reduction of the 3D silicon-oxycarbide to form 3D β-SiC with less than 10% shrinkage in the (111) plane and [111] direction, respectively. The reflectivities of the inverse 3D ceramic photonic crystals obtained at different stages were characterized by FT-IR in the [111] direction. Both the inverse 3D silicon-oxycarbide and silicon-carbide crystals showed bandgaps at 1.84 μm. These experimental values matched well with the calculated bandgaps, further supporting the robustness of such fabricated 3D ceramic photonic crystals.

High-Rate Electrochemical Capacitors Based on Ordered Mesoporous Silicon Carbide-Derived Carbon

Microporous carbons, produced by selective etching of metal carbides in a chlorine-containing environment, offer narrow distribution of micropores and one of the highest specific capacitances reported when used in electrical double layer capacitors (EDLC) with organic electrolytes. Previously, the small micropores in these carbons served as an impediment to ion transport and limited the power storage characteristics of EDLC. Here we demonstrate, for the first time, how the preparation and application of templated carbide-derived carbon (CDC) can overcome the present limitations and show the route for dramatic performance enhancement. The ordered mesoporous channels in the produced CDC serve as ion-highways and allow for very fast ionic transport into the bulk of the CDC particles. The enhanced transport led to 85% capacitance retention at current densities up to approximately 20 A/g. The ordered mesopores in silicon carbide precursor also allow the produced CDC to exhibit a specific surface area up to 2430 m(2)/g and a specific capacitance up to 170 F/g when tested in 1 M tetraethylammonium tetrafluoroborate solution in acetonitrile, nearly doubling the previously reported values.

Oxidation behavior of green coke-based carbon–ceramic composites incorporating micro- and nano-silicon carbide

The oxidation resistance of the carbon–ceramic composites developed using green coke-based carbon and carbon black as carbon source, boron carbide, and micro- and nano-silicon carbide was carried out in the temperature range of 800 to 1,200 °C. Silicon carbide particulate as such and silicon carbide obtained by the reaction of green coke and silicon provided micro silicon carbide while silicon and carbon black and sol–gel silica and carbon black used as silicon carbide precursors led to the formation of nano-silicon carbide. The oxidation resistance of these composites at 800 to 1,200 °C for 10 h showed that the size of the silicon carbide influenced the oxidation resistance. The weight gain due to protective coating formed on oxidation was higher in composites containing nano-silicon carbide as compared to the composites containing micro silicon carbide.

Synthesis and characterization of high surface area silicon carbide by dynamic vacuum carbothermal reduction

Silicon carbide (SiC) precursor was obtained by sol–gel used tetraethoxysilane as silicon source and saccharose as carbon source, and then the precursor was used to prepare SiC by carbothermal reduction under dynamic vacuum condition. The samples were characterized by X-ray diffraction, scanning electron microscope, and low-temperature nitrogen adsorption–desorption measurement. The results showed that the carbothermal temperature for synthesizing SiC needed to be at 1,100 °C under dynamic vacuum. At this temperature, the obtained sample is composed of agglomerated regular grains with size ranging from 20 to 40 nm and has a high surface area of 167 m2/g and the main pore size center at 5.3 nm.

Alumina/silicon carbide composites fabricated via in situ synthesis of nano-sized SiC particles

Alumina/silicon carbide composites have been fabricated by a new technique involving the in situ synthesis of nano-sized SiC particles. A mixture of alumina powder and silicon carbide precursors was prepared in an aqueous suspension. Green bodies were formed by cold isostatic pressing of granules obtained by freeze granulation, and pressureless sintered at 1750 °C for 4 h in an argon atmosphere. Mullite (10–20 vol%) formed in addition to SiC during sintering. The SiC particles were located predominantly to the interior of the mullite and alumina matrix grains.