Substructure and some processing properties of explosive-shock-treated powders of refractory materials

Aluminum nitrate (Al(NO3)3) and sodium polystyrene sulfonate (PSS) were used to improve the dispersion of fine silicon carbide (SiC) powders. Effects of modification parameters on the viscosity of modified SiC slurry were studied by orthogonal experiments. Modified SiC slurry with the solid loading of 50 vol% reached the lowest viscosity of 34 MPa s. The adsorption processes of PSS on the as‐received and Al(NO3)3 premodified SiC surface were investigated. The results indicated that the adsorption between PSS and premodified SiC surfaces was a high affinity type and was mainly controlled by active sites on an SiC surface. The Langmuir model and the pseudo‐second‐order model could better fit the adsorption isotherm and kinetics data, respectively. The contact angle decreased from 32.8 to 15.2° and the wettability was improved by modification. The isoelectric point of modified SiC powder shifted to the acidic region and the maximum zeta potential was obtained at pH 11. Sedimentation results also showed that a stable dispersed suspension of modified SiC was achieved at pH 11. Density–pressure curves demonstrated that the flowability and formability of SiC powder were improved by modification. The dispersion effect of PSS on SiC and Al2O3 composite powder was verified by viscosity and sedimentation results.

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.

Purpose. The article is aimed to evaluate the influence of structural parameters of low-carbon steel on arcing process. Methodology. The values of the micro- and substructure characteristics of the electrode wire metal were changed by varying the parameters of heat treatment and cold deformation by drawing. The degree of plastic deformation was obtained by drawing blanks from different initial diameter to final dimension of 1 mm. The thermal treatment was carried out in electric chamber furnace of the SNOL-1,6.2,5.1/11-IZ type. The temperature was measured by chromel-alumel thermocouple and the electromotive force was determined using the DC potentiometer. In order to obtain the substructure of different dispersion degree the steel (after quenching from temperatures and tempering at 650°C for 1 hour) was subjected to cold drawing to reduction 17 – 80%. To form structure with different ferrite grain size the steel after drawing was annealed at 680°C for 1 hour. The microstructure was examined under a light and electron transmission microscope UEMV-100K at the accelerating voltage 100 kV. The grain and subgrain sizes were evaluated using the methodologies of quantitative metallography. A welding converter of the PSG-500 type was used to study the arc welding process of direct and reverse polarities. Findings. The experimentally detected value of the welding current, which depends on the degree of deformation during wire drawing, under conditions of stable arc burning of direct polarity is about an order of magnitude lower than the calculated value. Similar difference was found for the arc of reverse polarity: the experimental value of the welding current is 5...6 times less than the calculated value. Dependence analysis shows that, regardless of the polarity of the welding arc, a good enough agreement between the calculated and experimental values of the welding current is limited to deformations of 60%. For deformation degrees of more than 60%, the differences are explained by qualitative changes in the dislocation cell structure. Originality. In the conditions of stable arcing of different polarity for the electrode of low-carbon steel, an extreme dependence of welding current on the degree of cold plastic deformation was observed. Practical value. Influence of ferrite grain size of electrode wire on the value of welding current is much greater than that from substructure presence.

Bond behaviors of magnesium and potassium phosphate cement (MKPC) matrix with glass fiber bundle (GFB) were investigated through measuring pullout forces of GFB. Test results showed that, the self-made inorganic adhesive could permeate into glass fibrils well and rectified damage weakness possessed by fiber, pullout force of GFB which was dipped self-made inorganic adhesive added in some magnesium oxide (MgO) powders was greatly improved due to chemical reaction between MgO powders and phosphate in MKPC matrix. Fluidity of MKPC paste mixed proper water glass would be improved, and compressive strength of MKPC paste added in some fly ash would be reinforced, amorphous hydrates would increase in both of the concretion, the microstructure would be more compact and the pullout force of GFB was greatly improved as well. Minimum embedded length of GFB existed achieved its maximum pullout force which could guarantee the tension strength of GFB

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

The purpose of the research is to investigate the destruction processes in coating materials during friction. These researches have been conducted on composite electrolytic coatings with titanium carbide and silicon carbide powders used as fillers. The assessment of surface layer destruction has been performed using the methods of theoretical and experimental research results analysis as part of an energy model based on wear particles formation in surface areas of a friction pair. Besides, the dependence of wear particle size on the mechanical properties of material has been determined. The analysis shows that material is destructed faster for carrying particles of larger sizes during friction. This means that materials with a higher hardness have a smaller size of carrying particle and materials with higher strength have a bigger size of carrying particles

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).

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.

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.

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.

This paper describes a novel process, carbide micro-reaction-sintering, to reaction-sinter three-dimensional silicon carbide microstructures using micromachined silicon molds. This process consists of micromachining of silicon molds, filling the molds with material powders (/spl alpha/-silicon carbide, graphite and phenol resin), bonding of the molds with adhesive, reaction-sintering by hot isostatic pressing (HIP) and release of a reaction-sintered workpiece from the mold by wet etching. Using this process, we have successfully fabricated silicon carbide microrotors with a diameter of 5 and 10 mm for a micromachined gas turbine. The shape of the silicon molds could be well transferred to the reaction-sintered samples within 3% shrinkage of the size. We used scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis to evaluate the reaction-sintered samples. They revealed the generation of /spl beta/-silicon carbide by the reaction between silicon and graphite in reaction-sintering process. They also revealed the presence of residual free silicon in the reaction-sintered samples due to low concentration of graphite in the material powders. We measured mechanical properties such as bending strength and Vickers hardness. The reaction-sintered samples had approximately 70% bending strength and 70-80% Vickers hardness compared with those of a commercially-available reaction-sintered silicon carbide.

Characterization and catalytic activity of silicon carbide powder as catalyst support in exhaust catalysts

Fabrication and characterization of a carbon fibre reinforced carbon–silicon carbide–titanium silicon carbide hybrid matrix composite