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Guo Chen - One of the best experts on this subject based on the ideXlab platform.
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pilot scale study on enhanced Carbothermal Reduction of low grade pyrolusite using microwave heating
Powder Technology, 2020Co-Authors: Jin Chen, Jinhui Peng, Roger Ruan, C Srinivasakannan, Guo ChenAbstract:Abstract Microwave heating through materials' dielectric loss endows energy saving and consumption Reduction and production clean characteristics. Pilot-scale study was initiated to evaluate the enhanced effect of microwave heating on Carbothermal Reduction process of pyrolusite. Results indicated that Carbothermal Reduction process for low-grade pyrolusite was divided into three stages identified by temperatures: 400 °C. Meanwhile, ƞMn value of 95.38% can achieve at 650 °C for 60 min with 15% coal addition, with low Fe2+ content, indicating efficient pyrolusite Reduction by microwave heating. Moreover, MnO2 peaks disappeared and MnO peaks were detected and product surface became loose and porous with numerous cracks and holes, meanwhile grain shape became more regular with a smaller particle size after further microwave treatment. The study highlights that the non-conventional technology by microwave heating to reduce low-grade pyrolusite is very promising and could be considered for full scale applications.
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effect of microwave heating on the microstructures and kinetics of Carbothermal Reduction of pyrolusite ore
Advanced Powder Technology, 2018Co-Authors: Jin Chen, Jinhui Peng, C Srinivasakannan, Guo Chen, Rongsheng RuanAbstract:Abstract This article focuses on the development of phase transformation and morphology of low-grade pyrolusite during Carbothermal Reduction using microwave heating. The XRD, SEM and EDS results show that selective Carbothermal Reduction of MnxOy and FexOy in pyrolusite is easy to realize with microwave heating, which can reduce MnO2 to MnO, and Fe2O3 to Fe3O4, rather than FeO. It was also observed that the phases of Mn2O3, Mn3O4 and MnO appear at 300 °C, 450 °C and 500 °C, respectively. The MnO phase, formed by the accumulation of MnO sphere particle with a diameter of 266.75–420.05 nm, is loose and porous. At a temperature of 750 °C, the Mn2SiO4 layer of about 316 nm in thickness, tightly wrapping SiO2 particle is generated at the interface between MnO and SiO2 embedded with MnO. Above 650 °C, Fe2O3 in pyrolusite can be transformed into a very dense Fe3O4 phase.
Guojun Zhang - One of the best experts on this subject based on the ideXlab platform.
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synthesis of zrb2 nanofibers by Carbothermal Reduction via electrospinning
Chemical Engineering Journal, 2013Co-Authors: Zhuang Kang, Xiao Huang, Guojun ZhangAbstract:Abstract Near-stoichiometric ZrB 2 nanofibers are synthesized via Carbothermal Reduction using electrospinning technique. Polyzirconoxane (PZO), boric acid and polyacrylonitrile (PAN) are used as zirconia, boron and carbon sources, respectively. ZrB 2 is obtained by pyrolyzing the as-spun green fibers at 1500 °C for an hour in argon or vacuum. The obtained ZrB 2 nanofibers are composed of uniformly nano-sized single crystals. The products are rather pure, containing only zirconium, boron and a small amount of oxygen. The atomic percentages of zirconium and boron in the nanofibers formed in vacuum at 1500 °C are 33.4% and 62.8% respectively, which is very close to the stoichiometric ratio of ZrB 2 . The nanofibers are characterized by XRD, SEM, EDS, TEM and TG–DTA.
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zrb2 powders prepared by boro Carbothermal Reduction of zro2 the effects of carbon source and reaction atmosphere
Powder Technology, 2012Co-Authors: Huiyu Qiu, Weiming Guo, Ji Zou, Guojun ZhangAbstract:Abstract ZrB 2 powders with different particle size or different morphologies have been synthesized by boro/Carbothermal Reduction (BCTR) method using ZrO 2 , B 4 C and graphite or carbon black as starting materials in this work. Results revealed that the carbon black with fine particles decreased the synthesis temperature and resulted in a finer ZrB 2 powder compared with graphite in vacuum. However, the synthesis temperature was almost the same for both the carbon black and graphite cases if the reaction took place in argon atmosphere. Furthermore, vacuum atmosphere led to the formation of rod-like ZrB 2 powder, whereas argon atmosphere resulted in quasi-spherical ZrB 2 powder. Thermodynamic calculation was conducted and possible mechanisms were discussed for understanding the above phenomena.
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reaction processes and characterization of zrb2 powder prepared by boro Carbothermal Reduction of zro2 in vacuum
Journal of the American Ceramic Society, 2009Co-Authors: Weiming Guo, Guojun ZhangAbstract:The present work was concentrated mainly on the reaction processes of boro/Carbothermal Reduction (BCTR) of ZrO2 with B4C and carbon in vacuum, and characterization of morphology and sinterability of the obtained ZrB2 powder. Combining the thermodynamic calculations, X-ray diffraction results, and the trend of furnace pressure with temperature during synthesis, a detailed explanation of the reaction processes of BCTR was developed. Most of the ZrB2 particles obtained at 1650°C presented a nearly spherical morphology, whereas those synthesized at 1750°C showed a nearly columnar morphology with an increased size. Compared with the powder synthesized at 1750°C as well as the commercially additive-free powder used in the reported work, the ZrB2 powder synthesized at 1650°C showed a better sinterability due to its smaller particle size and lower oxygen content.
Oleg Ostrovski - One of the best experts on this subject based on the ideXlab platform.
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Carbothermal Reduction and nitridation of ilmenite concentrates
Isij International, 2012Co-Authors: Sheikh Abdul Rezan, Guangqing Zhang, Oleg OstrovskiAbstract:Carbothermal Reduction and nitridation of ilmenite concentrates of different grades and synthetic rutile were studied in isothermal experiments in hydrogen – nitrogen gas atmosphere and pure nitrogen in a tube reactor. Concentrations of CO and CO2 in the off gas were measured online using infrared gas analyser. The reaction products were analysed by X-ray diffraction. Iron oxides in ilmenite concentrates were reduced to metallic iron, and titanium oxides were converted to titanium oxycarbonitride. Reduction of ilmenite concentrates and synthetic rutile in hydrogen containing gas was significantly faster than in pure nitrogen. The rate of conversion of titania to titanium oxycarbonitride in the 50 vol% H2-50 vol% N2 gas mixture decreased with increasing grade of ilmenite concentrate. In nitrogen, Reduction of synthetic rutile was faster than Reduction of ilmenite concentrates.
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Carbothermal Reduction and nitridation of titanium dioxide in a h2 n2 gas mixture
Journal of the American Ceramic Society, 2011Co-Authors: Sheikh Abdul Rezan, Guangqing Zhang, Oleg OstrovskiAbstract:This article examines Carbothermal Reduction/nitridation of rutile in a H2–N2 gas mixture in the temperature-programmed and isothermal experiments in a fixed-bed reactor. The aim of this investigation was to establish the Reduction/nitridation sequence, the reaction degree, and the rate of synthesis of titanium oxycarbonitride under different experimental conditions. The off-gas composition was monitored using an infrared sensor (CO, CO2, and CH4) and a dew point analyzer (H2O). Extents of Reduction and nitridation were determined from the off-gas composition and LECO analysis. Phase composition of reduced samples was analyzed using powder X-ray diffraction (XRD). Rate and extent of conversion of titanium oxides to titanium oxycarbonitride increased with increasing temperature. The conversion of titania into titanium oxycarbonitride at 1150°C was completed in 180 min; the conversion time decreased to 30 min at 1300°C. Increasing temperature resulted in formation of titanium oxycarbonitride with higher TiC content. Porosity had a minor effect on the Reduction/nitridation of titania with the tendency to increase the Reduction rate with increasing porosity. Reduction/nitridation of titania at 1150°C followed the sequence: TiO2→Ti5O9→Ti4O7→Ti3O5→TiOxCyNz.
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phase development in Carbothermal Reduction of ilmenite concentrates and synthetic rutile
Isij International, 2010Co-Authors: Mohammad A Dewan, Guangqing Zhang, Oleg OstrovskiAbstract:The phase development in the course of Carbothermal Reduction of ilmentie concentrates and synthetic rutile was studied in temperature programmed Reduction (350–1600°C) and isothermal Reduction at 1100°C in hydrogen and 1300°C in argon and helium. Ilmenites and synthetic rutile were reduced in a tube reactor with continuously flowing gas. The rate and extent of Reduction were monitored by online off-gas analysis. Samples reduced to different extent were subjected to XRD and SEM/BSE analyses. Pseudorutile and ilmenite were the main phases in ilmenite concentrates; rutile was the main phase in synthetic rutile. The phase changes in the course of Reduction followed the same sequence in both hydrogen and inert gases. Pseudorutile was converted to ilmenite and titania; iron oxides in ilmenite were quickly reduced to metallic iron. Titania was reduced to titanium suboxides and further to titanium oxycarbide. Reduction of ilmenites and synthetic rutile in hydrogen was much faster than in inert atmosphere. The rate of conversion of titanium oxides to oxycarbide was affected by iron content in the ilmenites. The Reduction of lower grade ilmenite with high iron content was faster in hydrogen; but slower in an inert gas. The latter was attributed to the higher porosity of highly weathered ilmenite and synthetic rutile.
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Carbothermal Reduction of a primary ilmenite concentrate in different gas atmospheres
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2010Co-Authors: Mohammad A Dewan, Guangqing Zhang, Oleg OstrovskiAbstract:The Carbothermal Reduction of a primary ilmenite concentrate was studied in hydrogen, argon, and helium. Ilmenite and graphite were uniformly mixed and pressed into pellets. Reduction was studied in isothermal and temperature-programmed Reduction experiments in a tube reactor with continuously flowing gas. CO, CO2, and CH4 contents in the off-gas were measured online using infrared sensors. The phase composition of reduced samples was characterized by X-ray diffraction (XRD). Oxygen and carbon contents in reduced samples were determined by LECO analyzers (LECO Corporation, St. Joseph, MI). The main phases in the ilmenite concentrate were ilmenite and pseudorutile. The reaction started with the Reduction of pseudorutile to ilmenite and titania, followed by the Reduction of ilmenite to metallic iron and titania. Titania was reduced to Ti3O5 and even more to Ti2O3, which was converted to titanium oxycarbide. Reduction was faster in hydrogen than in helium and argon, which was attributed to involvement of hydrogen in the Reduction reactions. The formation of titanium oxycarbide in hydrogen started at 1000 °C and was completed in 300 minutes at 1200 °C, and 30 minutes at 1500 °C. The formation of titanium oxycarbide in argon and helium started at 1200 °C and was not completed after 300 minutes at 1300 °C.
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Carbothermal Reduction of titania in different gas atmospheres
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2009Co-Authors: Mohammad A Dewan, Guangqing Zhang, Oleg OstrovskiAbstract:The synthesis of titanium oxycarbide by Carbothermal Reduction of titania was studied in hydrogen, argon, and helium in isothermal and temperature programmed Reduction experiments in a tube reactor with continuously flowing gas. In the temperature range of 1000 °C to 1500 °C, the Reduction rate increased with increasing temperature. Formation of titanium oxycarbide started at 1200 °C in all three gases. The Reduction was the fastest in hydrogen. Formation of titanium oxycarbide in hydrogen was close to completion in 120 minutes at 1300 °C, 60 minutes at 1400 °C, and less than 30 minutes at 1500 °C. The Reduction in argon and helium had similar rates and reached 90 to 95 pct after a 300-minute Reduction at 1400 °C to 1500 °C. Faster Carbothermal Reduction of titania in hydrogen than in argon and helium was attributed to involvement of hydrogen in the reaction. Hydrogen reduced titania to titanium suboxides and reacted with carbon, forming methane, which reduced titanium suboxides to titanium oxycarbide. Titanium oxycarbide synthesized in hydrogen for 180 minutes at 1300 °C contained 13 mol pct TiO. At 1500 °C, oxygen concentration decreased to a degree corresponding to 1.4 mol pct TiO. In the titanium oxycarbide produced by a 300-minute Reduction at 1600 °C, the TiO content was 0.6 mol pct.
Shaowei Zhang - One of the best experts on this subject based on the ideXlab platform.
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preparation and characterization of zrb2 sic composite powders from zircon via microwave assisted boro Carbothermal Reduction
Ceramics International, 2015Co-Authors: Xiangong Deng, Haijun Zhang, Junkai Wang, Wanguo Zhao, Feng Liang, Zhong Huang, Shaowei ZhangAbstract:Abstract ZrB 2 –SiC composite powders were successfully synthesized via microwave-assisted boro/Carbothermal Reduction technique using zircon (ZrSiO 4 ), activated carbon (C) and boron oxide (B 2 O 3 ) as raw materials. They were characterized by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). Thermodynamic analysis on the synthesis process was carried out, and the effects of SiC bedding powder, reaction temperature, soaking time and n(B 2 O 3 ):n(ZrSiO 4 ) molar ratio on the formation of ZrB 2 –SiC composite powders were examined. The results showed that phase pure ZrB 2 –SiC composite powders were successfully synthesized at 1573 K which was 200 K lower than that required by using the conventional boro/Carbothermal Reduction method. In the final composite powders, fibrous SiC phases with 0.1–0.5 μm in diameter and 1.4–4.2 μm in length were homogeneously distributed among spherical ZrB 2 particles with the average size of 0.1–1 μm.
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preparation and characterization of ultrafine zrb2 sic composite powders by a combined sol gel and microwave boro Carbothermal Reduction method
Ceramics International, 2015Co-Authors: Yingnan Cao, Haijun Zhang, Shaowei ZhangAbstract:Abstract A combined sol–gel and microwave boro/Carbothermal Reduction technique was investigated and used to synthesize ultrafine ZrB2–SiC composite powders from raw starting materials of zirconium oxychloride, boric acid, tetraethoxysilane and glucose. The effects of reaction temperature, molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) on the synthesis of ultrafine ZrB2–SiC composite powders were studied. The results showed that the optimum molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) for the preparation of phase pure ultrafine ZrB2–SiC composite powders were 2.5 and 8.0, respectively, and the firing temperature required was 1300 °C. This temperature was 200 °C lower than that require by using the conventional boro/Carbothermal Reduction method. Microstructures and phase morphologies of as-prepared ultrafine ZrB2–SiC composite powders were examined by field emission-scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM), showing that SiC grains were formed evenly among the ZrB2 grains, and the grain sizes of ZrB2 in the samples prepared at 1300 °C for 3 h were about 1–2 μm. The average crystalline sizes of these two phases in the as-prepared samples were calculated by using the Scherrer equation as about 58 and 27 nm, respectively.
Haijun Zhang - One of the best experts on this subject based on the ideXlab platform.
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preparation and characterization of zrb2 sic composite powders from zircon via microwave assisted boro Carbothermal Reduction
Ceramics International, 2015Co-Authors: Xiangong Deng, Haijun Zhang, Junkai Wang, Wanguo Zhao, Feng Liang, Zhong Huang, Shaowei ZhangAbstract:Abstract ZrB 2 –SiC composite powders were successfully synthesized via microwave-assisted boro/Carbothermal Reduction technique using zircon (ZrSiO 4 ), activated carbon (C) and boron oxide (B 2 O 3 ) as raw materials. They were characterized by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). Thermodynamic analysis on the synthesis process was carried out, and the effects of SiC bedding powder, reaction temperature, soaking time and n(B 2 O 3 ):n(ZrSiO 4 ) molar ratio on the formation of ZrB 2 –SiC composite powders were examined. The results showed that phase pure ZrB 2 –SiC composite powders were successfully synthesized at 1573 K which was 200 K lower than that required by using the conventional boro/Carbothermal Reduction method. In the final composite powders, fibrous SiC phases with 0.1–0.5 μm in diameter and 1.4–4.2 μm in length were homogeneously distributed among spherical ZrB 2 particles with the average size of 0.1–1 μm.
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preparation and characterization of ultrafine zrb2 sic composite powders by a combined sol gel and microwave boro Carbothermal Reduction method
Ceramics International, 2015Co-Authors: Yingnan Cao, Haijun Zhang, Shaowei ZhangAbstract:Abstract A combined sol–gel and microwave boro/Carbothermal Reduction technique was investigated and used to synthesize ultrafine ZrB2–SiC composite powders from raw starting materials of zirconium oxychloride, boric acid, tetraethoxysilane and glucose. The effects of reaction temperature, molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) on the synthesis of ultrafine ZrB2–SiC composite powders were studied. The results showed that the optimum molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) for the preparation of phase pure ultrafine ZrB2–SiC composite powders were 2.5 and 8.0, respectively, and the firing temperature required was 1300 °C. This temperature was 200 °C lower than that require by using the conventional boro/Carbothermal Reduction method. Microstructures and phase morphologies of as-prepared ultrafine ZrB2–SiC composite powders were examined by field emission-scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM), showing that SiC grains were formed evenly among the ZrB2 grains, and the grain sizes of ZrB2 in the samples prepared at 1300 °C for 3 h were about 1–2 μm. The average crystalline sizes of these two phases in the as-prepared samples were calculated by using the Scherrer equation as about 58 and 27 nm, respectively.
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preparation of titanium carbide powders by sol gel and microwave Carbothermal Reduction methods at low temperature
Journal of Sol-Gel Science and Technology, 2008Co-Authors: Haijun Zhang, Quanli JiaAbstract:Titanium carbide ultrafine powders were prepared from tetrabutyl titanate and sucrose by sol–gel and microwave Carbothermal Reduction. The influences of reaction temperature and molar ratio of Ti to C on the synthesis of titanium carbide were studied. The results show that excess amount of carbon plays a positive effect on the Carbothermal Reduction of TiO2 at low temperature. The inceptive Carbothermal Reduction temperature of TiO2 and formation of titanium oxycarbide was below 900 °C, and pure TiC can be prepared at 1,200 °C, which was considerably lower compared to that by conventional Carbothermal Reduction using a mixture of TiO2 and carbon powders as raw materials. The morphology and particle size of synthesized TiC powder were examined by field emission-scanning electron microscopy (FE-SEM) and the quantities of the phases of the powders were analyzed by Rietveld refinement method, the particle sizes of the TiC powders synthesized at 1,300 °C distribute over 0.1–0.5 μm.