Papers by Keyword: Carbothermal Reduction

Abstract: Lithium ion batteries with LiFePO₄ cathode have become the focus of research because they are eco-friendly, stable, high average voltage (3.5 V), and high theoretical capacity (170 mAh/g). However, LiFePO₄ has disadvantages such as low electrical conductivity (~10^-9 S/cm) and low lithium ion diffusion coefficient (~10^-14-10^-15 cm²/s) that can inhibit its application as a lithium ion battery cathode material. To increase the electronic conductivity of LiFePO₄, it can be done by adding carbon as a coating material, then doping gadolinium metal ions because it has a radius similar to Fe, and increasing sintering temperature. Optimizing the sintering temperature can control particle growth and research was study the sintering temperature of the electronic conductivity of LiFeGdPO₄/C and obtain the optimum sintering temperature at LiFeGdPO₄/C. The carbothermal reduction method used in synthesis, with a variation of sintering temperature of 800°C, 830°C, 850°C, 870°C, and 900°C using reagents LiH₂PO₄, Fe₂O₃, Gd₂O₃, and carbon black. Furthermore the samples were characterized using XRD, SEM-EDS, and four-point probes. The results of the study were expected to increase the conductivity of LiFePO₄. The results show the effect of sintering temperature can increase the electronic conductivity of LiFeGdPO₄/C. Samples with a sintering temperature 850°C have the highest conductivity among all temperature variations with a value of 1.11 × 10^-5 S cm^-1.

Abstract: The porous ceramic filter material is the most effective filter materials in the integrated gasification combined cycle. The porous silicon nitride due to its higher mechanical strength, as well as good corrosion resistance, is considered as a promising material in the integrated gasification combined cycle, and it were prepared directly though the SiO₂ and α-Si₃N₄ through carbothermal reduction - pressureless sintering in nitrogen. There was a great lot weight loss in this reaction, so it was expected to create the high porosity materials. The rod-like β-Si₃N₄ grains and uniform pores were formed through changing the content of α-Si₃N₄, SiO₂ and C. So high-performance and porosity controlled porous silicon nitride filter material was obtained. With an increasing in the α-Si₃N₄ content, the weight loss, the linear shrinkage, and the porosity decreased, the flexural strength increased accordingly. The porous silicon nitride filter material with addition of 50wt% α-Si₃N₄ showed a higher aspect ratio β-Si₃N₄ grains and better mechanical properties .

Abstract: In this research, the carbothermal reduction of Langkawi ilmenite ore, FeTiO₃ had been conducted by using coke as carbon reductant. All samples were grinded into size of ≤ 63 µm and pelletized using 2.5 g mixture of ilmenite ore with coke based on C/O molar ratio of 1:3 (carbon to reducible oxygen). The carbothermal reduction was conducted in a horizontal tube furnace using 0.1 L/min of argon gas flow at temperature of 1200°C. The ultimate and proximate analysis of carbon reductant was investigated using carbon, hydrogen, oxygen, nitrogen and sulfur (CHONS) analyzer. The phase evolutions and chemical composition analysis was conducted using X-ray diffraction (XRD) and X-ray fluorescence (XRF) for raw ilmenite and reduced ilmenite with coke, respectively. The reduction time was set with 2, 3 and 4 hours to understand the phase evolutions. It was found that Langkawi ilmenite ore contained mainly higher TiO₂ and hematite, Fe₂O₃ where the phases of FeTiO₃ and titanomagnetite, (Fe₂TiO₄-Fe₃O₄) were detected using XRD. The phase of FeTiO₃ evolved into the production of Fe, FeO, TiC, TiO₂ and Fe₃C when increased the reduction time from 2 to 4 hours. The amount of Fe₂O₃ production was decreased from 59.16 to 47.02 wt%, while higher value of TiO₂ was obtained, increasing from 25.2 to 29.1 wt% due to the reduction of TiO₂ to Ti₃O₅ as the reduction time increased. TiC content is also detected when the reduction time increased by reducing TiC_xO_y into TiC.

Abstract: Metallurgical Industry slowly moves towards wider utilization of complex ore minerals. Reduction behavior of complex crystalline structures can hardly be interpreted applying kinetic modeling adopted for pure oxides. The quantitative mathematical analysis of the metal particles forming during solid state reduction of a complex mineral has been suggested. The analysis with 95% reliability showed that during solid phase reduction of dunite at 1300 °C for 60 min about 360 particles with an average size about 0.62 mm formed from the total area S = 20880 mm. Such an approach could be useful for development of sophisticated kinetic models applied for reduction of a low-grade complex ore.

Abstract: Al₂O₃-SiC composite powders are prepared by carbothermal reduction method using coal gangue as raw material and carbonaceous materials (such as coke, anthracite, and carbon black) as reducing agents. The optimum conditions are as follows: when the addition of coke or anthracite is 50%, the temperature is at 1600 °C for 5 h, and adding 50% carbon black’s best temperature is at 1600 °C for 4 h. Based on the formula of stemming used in an iron and steel factory, Al₂O₃-SiC-C series blast furnace stemming refractory was prepared by adding Al₂O₃-SiC composite powder. The results show that the addition of Al₂O₃-SiC composite powders has a positive influence on the apparent porosity, volume density, and bending strength of the refractory. The effect of the amount of Al₂O₃-SiC composite powder on the slag corrosion resistance of the blast furnace stemming refractory was also studied by the static crucible method.

Abstract: ZrCO ceramic microspheres were fabricated by sol-gel combined with carbothermic reduction. The effect of carbon on the physicochemical characteristics of the microspheres was investigated. The results indicated that with the increase of carbon content in the broth, the interior structure of the sintered microspheres would become loose, which led to the lowering of the density and the decreasing of crush strength of the ZrCO microspheres. Crack-free ZrCO ceramic microspheres with the high mass fraction of ZrC could be successfully obtained with C/Zr = 3 in the broth sintered at 1550°C for 4h in argon containing 5%CO.

Abstract: In the present study, we report on the synthesis and carbothermal reduction of ultra-fine zirconium diboride powders by using inorganic-organic hybrid precursors of Zirconium (IV) nitrate pentahydrate, boric acid and citric acid as sources of zirconia, boron oxide and carbon, resoectively. The effect of molar ratio of reactants and reaction temperatures on the as-synthesized precursors were investigated. The thermodynamic change in the ZrO₂-B₂O₃-C system was mainly studied by thermogravimetric and differential scanning calorimetry. The phase compositions and crystalline state of the products after heat treatment was determined by X-ray diffraction and the crystallite size and morphology of the synthesized powders were characterized by scanning electron microscopy. It was found that the as-synthesized precursor with B/Zr molar ratio of 3.5 can transform into zirconium diboride and zirconium carbide by heating in an argon atmosphere with temperatures as low as 1400°C and the synthesized powders exhibited near-spherical morphology with a samll average crystallite size of about 200nm and dispersed relatively uniformly. Moreover, with the reaction temperature increased, the purity of the zirconium diboride powders are higher. The mixture was finally transformed into pure zirconium diboride at 1600°C. However, the grain sizes increased significantly and tended to be aggregated with the reaction temperature increased to 1600°C. The synthesized ZrB₂ powders showed a porous structure and the grain sizes on the exterior is larger than the interior because of the higher heat treatment temperature. The finally single ultra-fine ZrB₂ grain sizes were distributed from 190nm to 690nm in two-dimensions and have a larger specific surface area of 88.14m²/g.

Abstract: TiO₂, B₂O₃, H₃BO₃, B₄C and carbon black were used as the raw materials to prepare TiB₂ powders by carbothermal reduction method. The influence of different content of carbon black (13.6~14.8 wt%) on products was discussed. The effects of different boron sources and holding time (10~50 min) on the microstructure of TiB₂ powders were also investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to study the phase composition and structural evolution of the powder. The final results showed that hexagonal TiB₂ crystal grain could be successfully synthesized without impurities when heated at 1700°C for 30 min in Ar atmosphere with the addition of 14.1 wt% carbon black. Submicrometric TiB₂ powders range from 0.5 to 1.0 μm could be obtained when B₄C was used as the boron source. The increase in holding time contributed to the grain growth and completion of chemical reactions, but could also result in oversintering.

Abstract: In this paper, TiC powders have been prepared under vacuum condition using titanium dioxide powders and charcoal powders as raw materials. The impacts of temperature and holding time on TiC were studied. The results show as follows: the products will absorb lots of heat and transform into titanium oxide with lower valence with the increasing of holding time at the same temperature and at last be converted into titanium carbide. At a higher temperature, the time of the product transforms into single-phase titanium carbide is shorter.

Abstract: TiC powders have been prepared with titanium dioxide and charcoal powders as raw materials by vacuum carbothermal reduction technique. Meanwhile the as-prepared TiC powders were characterized by acid corrosion resistance test and oxidizability test. The results show as follows: the acid corrosion resistance of titanium carbide powders prepared at the optimum experiment conditions is better than that of industrial powders. It hardly dissolves in HCl, H₂SO₄, HNO₃, HF, HClO₄ and aqua regia, and slightly dissolves in mixed solution HF+HNO₃. The TiC powders are gradually oxidized at 352°C~917°C at air atmosphere and the product may be titanium dioxide and titanium oxides with lower valence. When the temperature rises to 546°C, a large quantity of titanium carbide powders are oxidized. And when the temperature rises to 688°C, besides the titanium carbide powders are oxidized to release heat, the free carbon is also oxidized and transformed into CO₂ gas to escape.