Adsorption of anionic polyelectrolyte on an SiC surface and effects on dispersion stability

Silicon carbide(SIC)powder was synthesized from liquid silicon in one step at the presence of a catalyst bar consisting of silica and carbon.The silicon carbide powders were formed by the carbothermal reaction between liquid silicon and gaseous CO,and the average particle size(D_(50))of the as-prepared silicon carbide powder was 0.41μm.The powder was characterized by XRD,SEM,particle size analysis and elemental analysis.The mechanism for the formation of the silicon carbide powder was discussed.

The surface of silicon carbide (SiC) powder was modified by coating with amorphous silica (SiO2) using (C2H5O4)Si (tetraethyl orthosilicate: TEOS) as a precursor by rotary chemical vapor deposition (RCVD). With increasing deposition time from 0.9 to 14.4 ks, the mass content of SiO2 coating increased from 1 to 35 mass%. The SiO2 mass content had a linear relationship with deposition time from 2.7 to 7.2 ks. The effects of O2 gas flow, deposition temperature (Tdep), total pressure (Ptot) and precursor vaporization temperature (Tvap) on the SiO2 yield by RCVD were investigated. At O2 gas flow of 4.2 × 10-7 m3 s-1, Tdep of 948 K, Ptot of 400 Pa and deposition time of 7.2 ks, the maximum SiO2 yield of 1.82 × 10-7 kg/s with SiC powder of 4.5 × 10-3 kg by RCVD was obtained.

Graphite and silicon carbide (SiC) are important materials of fuel elements in High Temperature Reactor-Pebble-bed Modules (HTR-PM) and it is essential to analyze the source term about the radioactive products adsorbed on graphite and SiC surface in HTR-PM. In this article, the adsorption behaviors of activation product Cobalt (Co) on graphite and SiC surface have been studied with the first-principle calculation, including the adsorption energy, charge density difference, density of states, and adsorption ratios. It shows that the adsorption behaviors of Co on graphite and SiC both belong to chemisorption, with an adsorption energy 2.971 eV located at the Hollow site and 6.677 eV located at the hcp-Hollow site, respectively. Combining the charge density difference and density of states, it indicates that the interaction of Co-SiC system is stronger than Co-graphite system. Furthermore, the variation of adsorption ratios of Co on different substrate is obtained by a model of grand canonical ensemble, and it is found that when the temperature is close to 650 K and 1700 K for graphite surface and SiC surface, respectively, the Co adatom on the substrate will desorb dramatically. These results show that SiC layer in fuel element could obstruct the diffusion of Co effectively in normal and accidental operation conditions, but the graphite may become a carrier of Co radioactivity nuclide in the primary circuit of HTR-PM.

Electrical Discharge Machining (EDM) is a complex process due to the involvement of numerous machining indicators. The key input machining indicators affect machining efficiency, tool material, dielectric fluid, and electrical parameters. The conductive silicon carbide and aluminium powder, having a size of 50 microns is used for the improvement of the machining efficiency of EDM. The machining is carried out on AISI D3 material, which is difficult to machine by conventional techniques. The machining performance of EDM is identified by measuring the Surface Roughness (SR). Moreover, research explores the optimization of surface roughness prediction for silicon carbide and aluminium powder using Particle Swarm Optimization (PSO) combined with machine learning algorithms. The performance of the Random Forest (RF), Decision Tree (DT), and Gradient Boosting (GB) is evaluated, trained and tested on respective datasets, with hyperparameters optimized using PSO to minimize prediction errors. For the Aluminium Powder dataset, the Decision Tree model demonstrated superior performance with the lowest Mean Squared Error (MSE) of 0.0603, indicating its ability to accurately capture the dataset’s feature relationships. Conversely, the Gradient Boosting model excelled on the Silicon Carbide dataset, achieving the best MSE of 0.1021, attributed to its robust ensemble learning approach. The significant differences in model performance across the two datasets underscore the importance of dataset-specific optimization and model selection. The findings of the research work highlight the effectiveness of PSO in enhancing model accuracy and emphasize the necessity of modified strategies for different materials in predictive analytics. Moreover, it showed that aluminium powder results are better as compared to silicon carbide powders on Surface roughness analysis.

Characterization of nanocrystalline porous SiC powder by electrospinning and carbothermal reduction

Silicon carbide (SiC) is a promising material for power electronic devices; however, the fabrication of low-cost and high-quality single-crystal SiC wafers with a smooth surface remains difficult, due to its high mechanical hardness and chemical stability. We report an abrasive-free electrochemical mechanical polishing (AF-ECMP) for a SiC surface using Ce film deposited on a polishing pad. The SiC surface is oxidized by electrolysis between the SiC (anode) and the polishing plate (cathode), the resulting oxide is then removed by interaction with the Ce film. The excess oxide produces a rough surface during continuous electrolysis on the SiC surface. The periodic electrolysis improves the surface quality, and electrolysis conditions such as duty ratio, duty cycle, and applied voltage are optimized. The abrasive ECMP, using CeO2 particles, broadens the initial scratches on SiC, whereas no scratch broadening is observed by the AF-ECMP. Despite a lower material removal rate (MRR) than the abrasive ECMP, the surface roughness was improved by the AF-ECMP with less polishing time. AF-ECMP produces an atomically smooth SiC surface with a roughness of ∼0.5 nm Ra, which is promising for low-cost and environment-friendly finishing process for SiC.

Diffraction of hard synchrotron radiation as well as constant-wavelength and time-of-flight neutron diffraction were used for the structural characterization of a silicon carbide powder having extremely low levels of chemical impurities, high perfection of the crystalline lattice and a grain size of up to 150 μm.The presence of three polytypes was ascertained and the ratios of their mass fractions were determined to be w 15R :w 6H = 0.002,3(8) and w 4H :w 6H = 0.000,6(2).

1. X-ray structural examinations of powders of magnesium oxide and titanium and silicon carbides demonstrated that explosive-shock treatment had markedly decreased the size of coherent scattering regions. The resultant size of coherent scattering regions was of the order of 300 a for all the materials investigated. The powders differed in the extent of broadening of their x-ray interference lines, which was due to the fact that they exhibited different degrees of plastic deformation and hence different magnitudes of microdistortions. There is a close correlation between this finding and the plasticity of the materials investigated. 2. Explosive-shock treatment enables nonporous compacts to be produced from magnesium oxide powder. The treatment substantially improves the compressibility and compactibility of titanium and silicon carbide powders at room temperature. It also produces a marked improvement in the compressibility of silicon carbide in hot pressing. 3. Structural distortions produced in silicon carbide powder by explosive-shock treatment activate its densification during hot pressing only when the pressure is applied in the course of heating at a temperature much lower than that at which the defects are fully annealed out.

An innovative process for preparing silicon carbide (SiC) from acid leaching residue of ferronickel slag through a carbon–thermal reduction process was proposed in this study. The results indicate that the acid leaching residue is an ideal silicon source for SiC preparation according to its high amorphous silica content of 84.20% and fine particle size of d50 = 29.16 μm. Compared with carbon black, activated carbon, and graphite, coke is the more appropriate carbon source for SiC preparation. A micron-size SiC powder with grade of 88.90% and an average particle size (d50) of 44.68 μm can be obtained under the following conditions: the mass ratio of coke to leaching residue as 1.2:1, in an air atmosphere, reducing at 1600 °C for 3 h, following by decarbonizing at 700 °C for 4 h. The XRD, SEM and FTIR analyses show that the prepared powder is 3C-SiC and belongs to the β-SiC crystal type. Based on thermodynamic analysis and micromorphology observation, it can be concluded that with amorphous silica as the silicon source, the carbon–thermal synthesis of SiC powder follows both the solid–solid reaction mechanism and the gas–solid mechanism. The SiC created through solid–solid reaction is primarily nucleated in situ on amorphous SiO2, with a size close to that of the original acid-leaching slag, while the SiC generated according to the gas–solid mechanism mainly nucleates heterogeneously on the surface of carbon particles, resulting in a smaller particle size and mostly adhering to the surface of solid–solid nucleated SiC particles. This study provides a feasible method for the effective utilization of amorphous silica, which is also significant for the efficient consumption of the vast acid leaching residue.

Silicon carbide obtaining with DC arc-discharge plasma: synthesis, product characterization and purification

The wetting of silicon carbide surfaces

Nanocomposites with fine, coarse, and bimodal silicon carbide (SiC) particle‐size distributions were hot pressed and examined by transmission electron microscopy, scanning electron microscopy, and optical microscopy, as well as by four‐point‐bend and indentation tests. The finer SiC nanophase was introduced homogeneously by coating a silicon‐containing polymer onto the alumina (Al 2 O 3 ) powder, followed by a pyrolysis procedure; for the coarser SiC, nanophase conventional powder processing was used. Powder‐ and polymer‐processed nanocomposites both had their maximum strengths at 5 vol% of SiC. High‐strength nanocomposites that contained a higher volume fraction of SiC could be fabricated when the two methods were combined in a hybrid processing route. The SiC phase in the resulting hybrid materials originated from both the polymer and the SiC powder. The mechanical properties of these materials could be correlated with the fabrication route. Processing‐flaw populations and calculated Griffith‐flaw sizes were not only smaller, but they were also significantly different in the nanocomposites, in comparison to those in Al 2 O 3 ceramics; this may explain the strength increase in Al 2 O 3 /SiC nanocomposite materials.

As a new post-implantation activation annealing of Silicon Carbide (SiC), we propose the Si-vapor ambient anneal using Tantalum Carbide / metal Tantalum composite materials (TaC/Ta). In this technique, semi-closed TaC/Ta container which can supply Si-vapor ambient is used, and Si vapor compensates thermal desorption Si atoms from the SiC surface above 1500°C and can maintain the original surface morphology by controlling a process temperature and Ar back pressure. Therefore the Si-vapor ambient anneal is able to simplify the process of conventional activation anneal methods using refractory cap-layers for protecting SiC surface from thermal damage of Si-atom desorption. Experiments were performed under Ar 1.3kPa at 1600/1700°C for 5min optimized conditions in a 6inch TaC/Ta container, and the Al+ ion-implanted 4H-SiC properties after annealing were characterized by atomic force microscopy (AFM), Rutherford Back-scattering Spectrometry (RBS) channeling method, and four-point probe method. According to evaluation, there was no roughening of SiC surface from AFM topographic images and recovery of crystallinity at the ion-implanted layer was equivalent to by the conventional cap-layer method from RBS channeling measurement. The sheet resistance of 12kΩ/ at 1700°C equal to the typical Al+ ion implanted p-type SiC is confirmed by four-point probe method.

ABSTRACTThe present study investigates the processing of heat-treated silicon carbide (SiC) particle-reinforced 6061 aluminum alloy (AA) composites. As-received SiC powders were heat treated at 1300ºC, 1400ºC, and 1500ºC in nitrogen atmosphere for 2 h, and the 6061 AA–SiC composites were developed by spark plasma sintering at 560ºC and 60 MPa for 5 min in argon atmosphere. The amorphous silicon nitride is found to form in SiC particles as a result of heating at 1400ºC. The microstructure of the composites exhibited uniform distribution of SiC or SiC/Si3N4 particles in 6061 AA matrix. Further, the heat-treated SiC-reinforced 6061AA composites exhibited improved mechanical properties. A typical combination of UTS of 240 MPa and elongation of 21% is obtained for the 6061 AA composites prepared using SiC powders heated at 1400ºC.

A hydrogen selective membrane as a membrane reactor (MR) can significantly improve the power generation efficiency with a reduced capital and operating cost for the waster-gas-shift reaction. Existing hydrogen selective ceramic membranes are not suitable for the proposed MR due to their poor hydrothermal stability. In this project we have focused on the development of innovative silicon carbide (SiC) based hydrogen selective membranes, which can potentially overcome this technical barrier. SiC macro-porous membranes have been successfully fabricated via extrusion of commercially available SiC powder. Also, an SiC hydrogen selective thin film was prepared via our CVD/I technique. This composite membrane demonstrated excellent hydrogen selectivity at high temperature ({approx}600 C). More importantly, this membrane also exhibited a much improved hydrothermal stability at 600 C with 50% steam (atmospheric pressure) for nearly 100 hours. In parallel, we have explored an alternative approach to develop a H{sub 2} selective SiC membrane via pyrolysis of selected pre-ceramic polymers and sol-gel techniques. Building upon the positive progress made in the membrane development study, we conducted an optimization study to develop an H{sub 2} selective SiC membrane with sufficient hydrothermal stability suitable for the WGS environment. In addition, mathematical simulation has been performed to compare the performance of the membrane reactor (MR) vs conventional packed bed reactor for WGS reaction. Our result demonstrates that >99.999% conversion can be accomplished via WGS-MR using the hydrogen selective membrane developed by us. Further, water/CO ratio can be reduced, and >97% hydrogen recovery and <200 ppm CO can be accomplished according to the mathematical simulation. Thus, we believe that the operating economics of WGS can be improved significantly based upon the proposed MR concept. In parallel, gas separations and hydrothermal and long-term-storage stability of the hydrogen selected membrane have been experimentally demonstrated using a pilot-scale tubular membrane under a simulated WGS environment.