Papers by Keyword: Carbothermal Reduction

Abstract: Fiber-like SiC had been synthesized using used silica bricks and carbon powder as raw materials by carbothermal reduction. A new kind of beaded SiC also had been found in the specimen. The result showed that well-crystallized β-SiC fibers began to appear at 1550 °C with excessive of 100 wt% content of carbon. While at 1600 °C for 6 h with excessive of 100 wt% content of carbon, the as-synthesized SiC fibers were grown with some beads in the fiber strings. The beaded SiC consisted of strings with diameters of less than 0.5 μm (or even 0.1μm) and periodic beads with diameters of 0.5-1.0 μm. Vapor-solid (VS) mechanism and vapor-liquid-solid (VLS) mechanism were also discussed in the synthesizing process of fiber-like SiC. This kind of fiber-like SiC may used as reinforce materials in ceramic composites, the fracture toughness of brittle ceramics can be effectively improved via the incorporation of strong SiC fibers into the matrix due to crack deflection, bridging and fiber pull-out. Moreover, these toughening mechanisms do not diminish as temperature increases.

Abstract: In this paper, we focus on the phase behaviors of talc minerals by carbothermal reduction (CR) method. The effects of temperature and carbon addition are both discussed in our work. In the experiment, acid-leaching talc was employed as raw material, carbon coke powders were adopted as reducing agent. The XRD results show that: When acid-leaching talc was used as raw material, quartz and few enstatite can be obtained at 1300 °C, with the temperature increasing, the diffraction intensities of enstatite increased. At 1550 °C, enstatite transformed to magnesium silicate and obvious β-SiC can be detected. At 1600 °C, the main phases in the final product are magnesium silicate and β-SiC. The SEM results reveal that the preferred, as-fabricated silicon carbide has morphology of irregular shape. Relatively pure β-SiC can be obtained by using acid-leaching talc mixed together with excess 50% of theoretical quantity of carbon powder sintered at 1550 °C for 4 h.

Abstract: Synthesis of alumina-mullite-silicon carbide composite (Al₂O₃-Al₆Si₂O₁₃-SiCw) was obtained in situ by carbothermal reduction of a mixture of kaolin and two different silica sources. The carbothermal reduction was carried out in a horizontal tube furnace under flow of argon gas. The synthesized products were mixtures of alumina, mullite and silicon carbide in the form of whiskers. The effects of adding two different silica sources of rice husk ash and silica powder to the mixture of kaolin and activated carbon were investigated. XRD and SEM analyses indicate complete reaction of precursors to yield Al₂O₃-Al₆Si₂O₁₃-SiC as product powders, with the SiC having whisker morphology.

Abstract: Using ludwigite as raw material, mass loss of ludwigite on the procedure of carbothermal reduction was studied. The effects of reduction temperature, carbon content, holding time were investigated by orthogonal experiment. Reduction temperature was the most influential factor for affecting the mass loss of ludwigite. The experimental results showed that the mass loss rate of samples increases with rising temperature, of which the maximum is 52.6wt% in the range from 1410°C to 1470°C. Mass loss rate of magnesia in ludwigite went up to 98.0% because it was reduced as gaseous magnesium vapor in the process of carbothermal reduction. The main phase of the reduction product was Fe2B, FeB and SiC. The paper can provide significant references for selective separation of valuable elements form ludwigite.

Abstract: HfC-based precursors with a range of carbon/metal oxide ratios were prepared from polymerization and copolymerization of metal containing monomers during solution-based synthesis. Heat treatments were given to the precursors to produce HfC powders. FTIR was used to record the infra-red spectra of the preceramic powders. HfC powders were assessed using X-ray diffraction and scanning electron microscopy.

Abstract: SiC macroscopic spheres have been synthesized by a microwave heating and carbothermal reduction method with commercial carbon spheres as template and fly ash as silica source. The morphology and structure of SiC hollow spheres were characterized using X-ray diffraction, N2 adsorption isotherms, scanning electron microscope and energy-dispersive. The results show that the SiC hollow spheres have retained the similar size with the original carbon sphere template. The shell of SiC hollow sphere is composed of curving SiC wires, and the shell thickness can be modulated by the ratio between C and SiO2. The formation of curving SiC wires attribute to the VLS mode, the Fe catalyst is indispensable reason of it.

Abstract: Superfined TiC was successfully synthesized from mixtures of acetylene carbon black and TiSO₄ through liquid-phase and subsequent heat treatment at a temperature that was considerably lower than that used in conventional carbonthermal reduction synthesis of TiC. Thermal decomposition of TiSO₄, and carbothermal reduction of the mixtures were investigated by using thermogravimetry-differential thermal analyzer and x-ray diffraction analyzer.

Abstract: A new synthesis technology of titanium carbide with microwave is introduced in this article. Microwave synthesis technology is a fast and relatively low temperature of synthesis method. Nano-titanium carbide powders were synthesized by carbothermal reduction of titanium dioxide and carbon black with the microwave synthesis method at 1100°C-1400°C in argon gas atmosphere. Nano-TiO₂ powder and carbon black were used as raw materials. The TiC powders were characterized with the XRD and TEM. The experimental results show that the synthesis rate is quick, even at relatively low synthesis temperature. The average particle size of the TiC powders synthesized by the microwave synthesis technology under low temperature (<1300°C) is less than 50nm, and the average particle size augments with increasing the microwave synthesis temperature and time.

Abstract: Tabular structure of Al₄SiC₄-Al₈SiC₇ composites was successfully synthesized using a mixture of calcined bauxite, SiC and carbon black by a carbothermal reduction process. The effects of the amount of SiC addition and the heating temperature on synthesis of Al₄SiC₄-Al₈SiC₇ composites by carbothermic reduction were investigated. The results show that SiC amount played an important role in the content of the final products. With the increasing of heating temperature, the Al₄SiC₄ content increased and Al₈SiC₇ content decreased in the products, which indicated the formation and growth of Al₄SiC₄ were promoted.

Abstract: The purpose of this work was to investigated the carbothermic reaction of fluorapatite process by the means of thermodynamics analyses, XRD and element analysis, respectively. Thermodynamic calculations indicated that phosphorus can be prepared by heating the mixture of Ca₅(PO₄)₃F₂ and C at 1173K under the system pressure of 100Pa. CO cannot react with Ca₅(PO₄)₃F₂ in the carbothermic reduction process at 973-1873K and 100Pa. Experimental results demonstrated that phosphorus can be produced by the reaction between Ca₅(PO₄)₃F₂ and C, the main reaction phase is P₂(g), CO(g), CaO and CaF₂, and with increasing temperature, the greater degree of response. The best technology conditions, the molar ratio of Ca₅(PO₄)₃F₂ to C is 1:7.5 at 1723K for 1h when the system pressure was about 100Pa. This study to provide experimental evidence for preparation of phosphorus by carbothermal reaction of fluorapatite in vacuum.