Molten salt synthesis of continuous tungsten carbide coatings on graphite flakes

Continuous tungsten carbide (WC) coatings were prepared on graphite flakes (G_f) by molten salt synthesis (MSS) technique using NaCl and KCl as reaction medium. The effect of reaction temperature, dwelling times and WO₃/G_f molar ratio on the compositions and morphologies of resultant samples was investigated, and the related formation mechanism for the coatings was also discussed. The results show that continuous WC coatings can be prepared at 1100 °C for 60 min with a WO₃/G_f molar ratio ranging from 1/15 to 1/5. These coatings exhibit homogeneous and crack free features, and their thickness increases with the increase of molar ratio. With the WO₃/G_f molar ratio below or beyond the above range, discontinuous WC coatings or W/W₂C/WC flake-like particles without graphite are obtained, respectively. The varied compositions of the samples obtained with different WO₃/G_f molar ratio can be related to the detailed chemical reaction process between WO₃ and G_f in the molten salts. A “template-growth” mechanism is proposed to explain the formation of WC coatings in the MSS process.     

Molten salt synthesis of in-situ TiC coating on graphite flakes

TiC coating was synthesized on graphite flakes (G_f) by molten salt synthesis (MSS) using metal Ti powder and alkali salts. Three different alkali chloride salts of KCl, NaCl, and NH₄Cl were selected as the molten salt media substrate. Two mass ratios of 1:3 and 1:5 were chosen for Ti: G_f ratio, and the mass ratio of the powder (Ti + G_f) to the salt was 1:1. The synthesis was carried out at a temperature of 1100°? for 4 h. XRD was used to study the effect of alkali chloride salts and the Ti: G_f mass ratio on the synthesized coating. FE-SEM and AFM were accomplished to investigate the carbide formation and microstructure of the samples. Results showed that TiC coating was formed at 1100 °C for 4 h with both mass ratios in all three alkali chloride salts, but KCl was found to be the optimum alkali chloride salt or reaction medium. FE-SEM results displayed the formation of uniform coatings, and results from AFM indicated that the surface roughness increased from 0.72 for G_f to 4.94 nm for TiC coated G_f.     

Molten salt synthesis of a SiC coating on graphite flakes for application in refractory castables

A silicon carbide coating was formed on the surface of graphite flakes by reaction of molten Si with carbon at 1100–1300 °C in a 95%KCl-5%NaF molten salt under Ar atmosphere. The effect of temperature and Si/graphite ratio in the initial mixture on the quality and the amount of SiC were investigated by XRD and SEM/EDS analyses. Also, the water wettability, oxidation resistance and zeta potential of un-coated and coated graphite were examined by TGA analysis and sedimentation test. The results show the amount of coating to increase in the coated flakes with increasing temperature and Si/graphite ratio. The SiC coating improves water wettability of graphite and acts as a protective layer to enhance oxidation resistance. The zeta potential of coated graphite was also increased which indicated a better dispersion in water based systems. These improvements in both the water dispersivity and oxidation resistance of SiC coated graphite would make it as promising candidate raw materials for application in C-containing refractory castables.     

Seamless joining of silicon carbide ceramics through an sacrificial interlayer of Dy3Si2C2

A ternary carbide Dy₃Si₂C₂ coating was fabricated on the surface of SiC through a molten salt technique. Using the Dy₃Si₂C₂ coating as the joining interlayer, seamless joining of SiC ceramic was achieved at temperature as low as 1500 °C. Phase diagram calculation indicates that seamless joining was achieved by the formation of liquid phase at the interface between Dy₃Si₂C₂ and SiC, which was squeezed out under pressure and continuously consumed by the joining interlayer. This work implies the great potential of the family of ternary rare-earth metal carbide Re₃Si₂C₂ (Re = Y, La-Nd) as the sacrificial interlayer for high-quality SiC joining.     

Effect of tungsten carbide,silicon carbide and graphite particulates on the mechanical and microstructural characteristics of AA 5052 hybrid composites

Reinforced aluminium metal matrix composite materials are being used extensively in diverse fields that include aerospace and automobile. In this investigation, we introduce two distinct and novel types of aluminium hybrid composites and characterize their mechanical properties and microstructure. The first type was fabricated by reinforcing aluminium alloy (AA 5052) with tungsten carbide (WC) and graphite particulates and the second type was fabricated by reinforcing AA 5052 with silicon carbide (SiC) and graphite particulates. The composite material was processed through the melt-stir casting method and characterized by analyzing their densities, micro hardness, Charpy impact strength, tensile strength and peak elongation. Melt-stir casting method was chosen due to its cost effectiveness and productivity. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) studies were conducted to analyze thorough mixing of the reinforcements in the aluminium matrix metal. It was found that addition of tungsten carbide and graphite particulates with AA 5052 resulted in an increase in micro hardness and Charpy impact strength by 10.3% and 34.2% respectively, which are found to be better when compared to that of adding SiC and graphite particulates with AA 5052. Moreover, tensile tests revealed that there was a drop in tensile strength for the Al/SiC/graphite composites, while the peak elongation increases for both composites. On the other hand, while adding WC and graphite particulates the tensile strength of the composite improved by 15.12%. Also, the SEM fractographs taken for Al/SiC/graphite composite samples, subjected to Charpy impact and tensile tests revealed the presence of particle fractures and cracks and confirmed the possibility of plastic deformation. The results showed the Al/WC/graphite composites to be the superior among the two fabricated composites in terms of mechanical properties and therefore have good potential for structural applications.     

利用稻壳合成SiC的研究

稻壳经细粉碎、酸处理、FeCl2·6H2O浸泡、过滤、干燥、高温分解与合成、HF溶液处理,即可得到SiC含量50％～70％的合成碳化硅。     

Synthesis of Ti3SiC2 coatings onto SiC monoliths from molten salts

Coatings with composition close to Ti₃SiC₂ were obtained on SiC substrates from Ti and Si powders with the molten NaCl method. In this work, the growth of coatings by reaction in the salt between monolithic SiC substrates and titanium powder is obtained between 1000 and 1200 °C. At 1000 °C, a coating of 8 µm thickness is formed in 10 h whereas a thin coating of 0.5 µm has been grown in 2 h. A lack in silicon was first found in the coatings prepared at 1100 and 1200 °C. For these temperatures, the addition of silicon powder in the melt had a favorable effect on the final composition, which is found very close to the composition of Ti₃SiC₂. The reaction mechanism implies the formation of TiC_x layers in direct contact with the SiC substrate and the presence of more or less important quantities of Ti₃SiC₂ and Ti₅Si₃C_x in the upper layers.     

Facile synthesis,characterization and antibacterial activity of nanostructured palladium loaded silicon carbide

In this work, noble metal (Palladium) loaded silicon carbide (SiC) nanoparticles have been successfully synthesized using a single step synthetic route and its antibacterial action against gram-negative (E. coli) and gram-positive (S. aureus) bacteria have been investigated. The structural and morphological characterizations of pure SiC and Palladium (Pd) loaded SiC nanoparticles were carried out by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), Energy dispersive x-ray spectroscopy (EDX), Elemental mapping and Transmission electron microscopy (TEM). The characterizations results offer substantial proof that the SiC surface was successfully decorated by Pd. Furthermore the EDS analysis reveals that the product contained Pd as well as W and O, thus reaffirming the production of Pd loaded SiC nanoparticles. The MICs and MBCs values examined by standard agar dilution methods show that MICs and MBCs values of pure SiC were >?16 and >?32?mg/ml, respectively against E. coli and S. aureus, whereas Pd loaded SiC nanoparticles exhibited MIC and MBC value of 4?mg/ml and 8?mg/ml, respectively. The morphological and structural alterations caused by SiC and Pd loaded SiC nanoparticles on E. coli and S. aureus cells were further investigated by SEM analysis. A noteworthy improvement in antibacterial performance was observed, when E. coli and S. aureus cells were exposed to Palladium (Pd) nanoparticles (NPs) loaded silicon carbide (SiC). The results obtained show a significant impact by loading Pd on SiC in the deactivation of microorganisms in vitro.     

氮化硅结合碳化硅耐火材料的氧化

氮化硅结合碳化硅耐火材料高温氧化后，其抗折强度有所提高，但经扫描电镜观察，材料断面结构已发生了明显的变化。该材料长时间在氧化气氛中使用，可靠性将下降。     

Synthesis and characterization of submicron silicon carbide powders with silicon and phenolic resin

A novel three-step process is used to fabricate submicron silicon carbide powders in this paper. The commercially available silicon powders and phenolic resin are used as raw materials. In the first step, precursor powders are produced by coating each silicon powder with phenolic resin shell. Then, precursor powders are converted into carbonized powders by decomposing the phenolic resin shell. The submicron silicon carbide powders are formed in the reaction of silicon with carbon during the third step of thermal treatment. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric (TG) analyses are employed to characterize the microstructure, phase composition and free carbon content. It is found that the sintered powders consist of β-SiC with less than 0.2 wt.% of free carbon. The particle size of the obtained silicon carbide powders varies from 0.1 to 0.4 μm and the mean particle size is 0.2 μm. The silicon carbide formation mechanism of this method is based on the liquid-solid reaction between liquid silicon and carbon derived from phenolic resin. The heat generated during the reaction leads to great thermal stress in silicon carbide shell, which plays an important role in its fragmenting into submicron powders.     

Effect of reactivity of silicon and magnesium on the preparation of SiCMgAl2O4 composites for immobilizing graphite

SiCMgAl₂O₄ ceramic has a novel application for immobilizing radioactive graphite. The interface reaction between silicon and magnesium offers a significant challenge in the synthesis of SiCMgAl₂O₄ composites. In this paper, the effects of silicon source, magnesium source, sintering temperature and holding time on the interface reactivity were investigated by characterizing the phase compositions, microstructures, and hardness. The results show that the reactivity of silicon and magnesium varies with silicon sources and magnesium sources which also have a great effect on the microstructure of SiCMgAl₂O₄ composites. Either excessive sintering temperature or excessive holding time makes SiCMgAl₂O₄ composites decomposed into different phases, leading to a decreased hardness value. It is found that silicon as silicon source can contribute to the formation of SiC nanowires, which is in line with VS growth mechanism of SiC. The interface reactivity of element Si and Mg, which is positively correlated with high temperature and long holding time, has a negative effect on the phase compositions and performance of SiCMgAl₂O₄ ceramic by pressureless sintering.     

氮化硅结合碳化硅树料的抗渣侵蚀性

借助光学显微镜、扫描电子显微镜和Ｘ射线衍射分析等手段，研究了矿渣侵蚀后的氮化硅结合碳化硅材料的显微结构和物相组成．探讨了氮化硅结合碳化硅材料的损坏机理。     

A perspective on non-stoichiometry in silicon carbide

The non-stoichiometric ceramics are amazing materials with potential to offer applications that are unachievable by using otherwise ideal stoichiometric counterparts. These materials have contributed in wide areas including superconductivity, optical, magnetic, electronic, structural, mechanical and transport applications. The deviation form stoichiometry in a large number of compounds, though usually avoided, has numerous benefits; by increasing ionic conductivity, offering band structure modifications, causing paramagnetic to ferromagnetic transitions, reducing magnetoresistance, increasing mechanical strength, enhancing electrochemical efficiency etc. Keeping in mind the promising contributions of silicon carbide among family of ceramic materials, this review highlights the implications of non-stoichiometry and its properties. The non-stoichiometry produced unintentionally or purposefully is strongly influenced by synthesis conditions and varies for silicon carbide grown in amorphous, crystalline, polycrystalline polytypes in the form of bulk, surfaces and low dimensional structures. The prospects of tuning the properties of silicon carbide on the basis of fabrication of silicon rich and carbon rich by monitoring silicon to carbon ratio are discussed in detail.     

High temperature corrosion resistance of electrically conductive nitrogen doped silicon carbide ceramics in molten fluorides

Electrically conductive nitrogen-doped SiC ceramics were exposed to molten FLiNaK at 700 °C for 100, 200, and 500 h, and at 1000 °C for 100 h in Ar atmosphere. The SEM-EDX investigations of corroded samples showed that the main corrosion attack proceeds through the intergranular phase, where the fluoride melt interacts with the oxide phases and partly dissolves also the SiC grains. It was proved that N-doped SiC has good corrosion resistance against molten FLiNaK. After corrosion at 700 °C for 100, 200, and 500 h the corroded layer thicknesses were 85, 90, and 120 µm, respectively.     

Influence of mechanical activation on combustion synthesis of fine silicon carbide (SiC) powder

The influence of mechanical activation of powder mixtures of Si and C, via high energy attrition milling (up to 12 h), on combustion synthesis of SiC was experimentally investigated. β-SiC fine powder was successfully fabricated in 1.0 MPa N₂ atmosphere without other additional treatments, such as preheating, electric action, or chemical activation. Relatively weak peaks of α-SiC, α-Si₃N₄ and Si₂ON₂ were also found in the final products. The experimental results and their theoretical treatment showed that mechanical activation via high energy ball-milling provides to the initial Si/C powder mixture extra energy, which is needed to increase the reactivity of powder mixture and to make possible the ignition and the sustaining of combustion reaction to form SiC.     

Synthesis and characterisation of a submicrometre silicon carbide powder

A beta-silicon carbide powder with a surface area of 30m²g^?l and a mean particle size of < 1μm was produced from the thermal conversion of silicon resin in an atmosphere of hydrogen. The amount of product increased with increasing iron content (0–2.1 wt%) and firing temperature (1200–1500°C). Chemical analysis, X-ray diffraction and i.r. absorption spectrometry were used to follow the conversion reaction.     

氮化硅结合碳化硅耐火材料在钢水中的腐蚀行为

运用扫描电镜（ＳＥＭ）技术，研究了氮化硅结合碳化硅耐火材料在钢水中的腐蚀行为。结果表明，金属与氮化硅结合碳化硅材料之间的界面清晰，基体内部无任何金属渗入，但氧化的材料表面有氧化物粘附。     

氮化物结合碳化硅耐火材料的研究现状

分别概述了以氮化硅、赛隆和氧氮化硅作为结合相 的SiC材料的结构特点、理化性能、生产工艺和应用情况,详细 介绍了国内这3种材料的研究现状,并对今后氮化物结合SiC 材料的研究内容提出了自己的观点。     

Green preparation of vanadium carbide through one-step molten salt electrolysis

Vanadium carbide (VC) as excellent ceramic and functional material is usually prepared by carbothermal reduction of V₂O₅ which must be extracted from a typical V slag by complex processes. Pollutants, such as ammonia-nitrogen wastewater, NH₃ and CO₂ are inevitably discharged. A novel and green method for VC preparation was proposed by one-step co-electrolysis of soluble NaVO₃ and CO₂ in molten salt. It was found that VC with high purity was easily obtained by reducing electrolysis temperature and CO₂ flow rate to 600 °C and 10 mL min⁻¹ at 3.0 V. Besides VC with particles and layered stacking structure in products, a small amount of carbon and oxygen elements existed. The atomic percentage contents of C, V, and O elements in VC were about 50.0%, 44.5% and 3.8%, respectively. During electrolysis, CO₃²⁻ and VO₃⁻ was reduced at about −0.55 V (vs. Ag/AgCl) and −1.38 V (vs. Ag/AgCl), respectively. CO₃²⁻ ions were more easily reduced than VO₃⁻, and was firstly reduced to CO₂²⁻ and then converted to C. Then, VC was prepared by two routes from CO₂ and NaVO₃. One route is that VO₃⁻ ions are firstly electroreduced to VO₂⁻ ions and then are further electroreduced to VC with C. Another route is that VO₃⁻ ions are electroreduced to V which in-situ reacted with C to VC. Both VO₃⁻ and CO₃²⁻ ions are electroreduced by two-step process. In final, VC is in-situ deposited on cathode. It provides a novel and green way to prepare VC and also achieves the high value-added utilization of vanadium slag and CO₂.     

氧氮化硅结合碳化硅制品的生产与使用

以工业用黑色碳化硅砂、硅粉为主要原料，研制出了导热性能优良、抗热震性好、耐高温、耐侵蚀及耐磨损，且生产工艺较简单、成本较低的氧氮化硅结合的碳化硅制品．该产品已广泛应用于冶金炉、化工设备及发电用锅炉的内衬，并取得了较满意的效果。