Papers by Keyword: Carbothermal Reduction

Abstract: A new preparation of alumina from high iron bauxite, which has not been being made reasonably use of yet, has been studied. Iron in high iron bauxite was removed by carbothermal reduction and aluminum-rich slag could be obtained. Then aluminum was extracted from aluminum-rich slag by ammonium sulfate roasting. After leaching, Al₂(SO₄)₃ was obtained, which can be used for preparation of alumina. The effects of roasting temperature, roasting time, ammonium sulfate/aluminum-rich slag mass ratio were investigated. Optimum roasting conditions from aluminum-rich slag by ammonium sulfate were found as roasting temperature:400°C;roasting time:120min;ammonium sulfate/aluminum-rich slag mass ratio:6. Approximately 98% of aluminum was effectively extracted.

Abstract: In this study, Ca²⁺ stabilized ZrO₂-SiC composite materials were prepared via carbothermal reduction, using natural zircon ore as raw material, CaO as additive, and black carbon as the reducing agent. The effects of synthesis temperature and CaO content on the phase composition of the products were investigated by XRD. The microstructure and micro-area chemical analysis of the products were characterized by SEM and EDS. The results indicate that: (1) Ca²⁺ stabilized ZrO₂-SiC composite materials could be prepared from natural zircon ore with CaO addition between 1500°C and 1600°C for 4 hours by carbothermal reduction process. (2) The synthetic temperature has an important influence on the phase composition of the carbothermal reduction products of zircon. The production of m-ZrO₂ and t-ZrO₂ got obviously enhanced with increasing temperature from 1500°C to 1600°C. (3) At the same synthetic temperature, Ca²⁺ stabilized ZrO₂ got enhanced with increasing adding amount of CaO. The optimized synthesis condition of Ca²⁺ stabilized cubic-ZrO₂/SiC composite materials is sintering at 1600°C for 4 hours with adding 40 mol% CaO as additive.

Abstract: This paper mainly discusses the influences of heating temperatures and CeO₂ additive contents on the phase transformations of zirconia from zircon ore by carbothermal reduction. The phase transformations of zirconia from zircon ore by carbothermal reduction were monitored by X-ray diffraction. The microstructure of the product was characterized by scanning electron microscopy. The results show that without adding CeO₂, the optimized heating temperature of zircon carbothermal reduction was 1600 °C and the main phases of the product were m-ZrO₂, ZrC and β-SiC, t-ZrO₂; After adding CeO₂, the main phase of the products consists of t-ZrO₂, m-ZrO₂, ZrC and β-SiC when the heating temperature is 1600 °C. CeO₂ additive can be introduced into zirconia lattice and can cause it to form cerium stabilized zirconia. Zirconia in the product would be turned into partially stabilized zirconia with cerium addition from 5 wt% to 20 wt%. However, the form of zirconia in the product is not changed greatly with the amount of CeO₂ additive increase.

Abstract: Two kinds of SiC powder having a different impurity contents and particle size were prepared by carbothermal reduction under different conditions from traditional process for controlling the purity of product. SiC single crystal was grown in the RF heating PVT machine at the temperature above 2,100 °C. After crystal growth, boule was cut to wafers in 1mm thickness and fine polished using diamond abrasive slurry. The impurity in the powder and wafer was analyzed using glow discharged mass spectroscopy (GDMS). Major impurities in the SiC wafer were aluminum, boron, iron and titanium which were accorded in the SiC powder and these impurities were decreasing in proportional to those in the powder. However, behavior of each elemental impurity was different from each other during the crystal growth. In case of boron was increased after crystal growth while aluminum decreased. In case of titanium and boron were higher in the wafer than in the powder. It can be explained to other impurity source such as graphite crucible and insulation felt.

Abstract: The reduction of Malaysia Ilmenite (FeTiO₃) with coal by carbothermal reduction under N₂ atmosphere was studied. Characterization of raw materials was done by XRD, XRF, Optical Microscopy (OM) and SEM analysis. Isothermal experiments were carried out using the pellets in a horizontal tube reactor with continuously flowing gas. From the experiments, 0-10 wt. % of FeCl₃ was added in the ilmenite-coal mixtures before reduction. The mixture was reduced at 1100°C for 60, 120 and 180 minutes. The addition of FeCl₃ acted as a catalyst and increased the rate of reduction. The microstructures of the reduced sample were porous with the addition of FeCl₃. Furthermore, defects were observed due to increase release of Cl₂ and CO during reduction. FeCl₃ acted as catalyst in the gasification of coal by the Boudouard reaction. SEM analysis indicates that the microstructure of the particles was coarsened due to the addition of catalyst. Besides that, there was less agglomeration of metallic iron particles at higher addition of FeCl₃. The effect of FeCl₃ on the morphology iron was the nucleation of microscopic iron rich zones in the reduced sample. Keywords: Carbothermal Reduction, Iron Chloride, Malaysian Ilmenite, Nitridation, Titanium Oxycarbonitride.

Abstract: Statistical design analysis (factorial design) was utilized to verify the significance and the interaction between the studied factors include temperature, reduction time and catalyst amount. Carbothermal reduction of iron ore sample was carried out at temperature between 1000°C to 1200°C. The effects of operating parameters studied were extent of reduction (X), carbon consumed (C_consumed ) and nitridation (X_N). Temperature was the most influential parameter that showed strong interaction with the operating parameters, meanwhile, reduction time and catalyst have showed the contrary results and had a very low percentage of contribution. The results of the experimental design showed that the extent of reduction reached up to 93% at 1200°C using 10 wt. % catalysts after 180 minutes reduction. The use of 0-10 wt % catalyst at 1200°C for 180 min reduction significantly affect the X but did not for C_consumed and X_N.Keywords: Carbothermal Reduction, Factorial Design, Malaysian Ilmenite, Nitridation.

Abstract: nfluencing factors of target products such as X phase, β-SiAlON phase and O-SiAlON phase of Inner Mongolia coal gangue carbothermal reduction and nitridation were researched by calculating the loss rate on ignition of specimens, and by means of XRD and SEM. During the carbothermal reduction and nitridation reaction of coal gangue, the loss rate on ignition of specimens rises with carbon reducer increasing, and keeping time has a little influence on the loss rate on ignition of specimens. If β-SiAlON is target phase, the yield from corundum is much higher than that from special grade bauxite. Corundum or bauxite is used as starting material, the yield of X phase is low and the highest yield is only 12.88%. For the carbothermal reduction and nitridation reaction of coal gangue, the appropriate addition of reducer carbon is 10%-16%, and temperature influence is larger. The reaction temperature over 1420°C and keeping time of 6h are beneficial to the formation of X phase, β-SiAlON and O-SiAlON.

Abstract: LiFePO₄/C was successfully synthesized by one-step solid-state reaction using Fe₂O₃, LiH₂PO₄ and sucrose as raw materials. The effect of synthesis temperature and sintering atmosphere on the electrochemical performance were investigated. LiFePO₄/C materials were characterized by differential scanning calorimetry and thermogravimetry, X-ray diffraction, scanning electron microscopy and XPS. The results show that the synthesis temperature between 750 °C and 800 °C were appropriate and the reductive ambience can enhance the electrochemical performance effectively especially at high rates. The precursor calcined at 750°C for 5h in a N₂+5%H₂ atmosphere exhibited the highest discharge capacity of 155 mAh/g at 0.1C and 141 mAh/g at 1C and showed the best cycle performance.

Abstract: Pure submicron-sized ZrC powder was successfully synthesized in KCl by using ZrO2, Mg and carbon black as the starting raw materials. KCl showed strong accelerating effect on the molten salt synthesis. As a result, the reaction temperature was reduced to as low as 800oC, which is much lower than the temperatures used by most of the other synthesis techniques reported so far. It is believed that both ZrO2 and carbon black had acted as the “templates” in the synthesis process. High quality ZrC powders prepared with the present technique could be used for making important ZrC based composites for various applications.

Abstract: Porous TiN ceramics with high porosity and uniform pore structure was prepared following the carbothermal reduction reaction between TiO₂ and carbon. Influences of sintering additives and particle size of TiO₂ on the microstructure and mechanical properties of porous TiN ceramics were investigated. Microstructure and mechanical properties of porous TiN ceramics were studied by XRD, SEM and three-point bending measurement. XRD analysis proved that the TiN phase has completely formed after reaction. In addition, SEM analysis showed that the resultant porous TiN ceramics were composed of fine grains with uniform pore structure. The addition of La₂O₃ not only accelerated the densification of porous TiN ceramics, but also decreased the porosity and increased the flexural strength. With a decrease in TiO₂ particle size, the linear shrinkage increased and the porosity decreased accordingly.