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Xue H.-Y.,Kunming University of Science and Technology | Xue H.-Y.,State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province | Xue H.-Y.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | Lv G.-Q.,Kunming University of Science and Technology | And 14 more authors.
Materials Science Forum | Year: 2015

Solar grade silicon and modified Al-Si alloys are widely used in the world. These two favored materials are expected to obtain by the electromagnetic directional solidification of hypereutectic Al-Si melts. The segregation of hypereutectic Al-Si alloy is feasible with respect to the process of either pull-up or drop-down in electromagnetic directional solidification. To explore the segregation efficiency, experiments have been conducted in a high-frequency induction furnace with different pulling conditions of hypereutectic Al-Si melts. The results show that the segregation efficiency of dropping-down is higher than that of pulling-up; the slower dropping-down rate lead to higher segregation efficiency in the electromagnetic directional solidification; increasing the temperature gradient may promote the separation efficiency. A separation mechanism model responsible for the formation of the distribution of primary silicon in the cross-sections is also proposed. Wish to provide theoretical basis for the more efficiency of the segregation of hypereutectic Al-Si melts. © (2015) Trans Tech Publications, Switzerland.


Zhu W.,Kunming University of Science and Technology | Zhu W.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | Li X.,Kunming University of Science and Technology | Wu D.,Kunming University of Science and Technology | And 9 more authors.
Microporous and Mesoporous Materials | Year: 2016

Spherical mesoporous silica material (SMSM) was hydrothermally synthesized using cetyltrimethylammonium bromide (CTAB) as the template agent and silica fume as the silica source. High-quality SMSMs were successfully prepared by pseudomorphic transformation. The structure and morphology of the SMSMs are investigated by X-ray diffraction, N2 sorption/desorption, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses. The effects of synthetic parameters, such as crystallization time, crystallization temperature, n(NaOH)/n(SiO2) molar ratio, and n(CTAB)/n(SiO2) molar ratio, are quantitatively investigated. The optimal synthetic conditions for high-quality SMSMs are a crystallization time of 48 h, crystallization temperature of 363 K, n(NaOH)/n(SiO2) molar ratio of 0.2-0.3, and n(CTAB)/n(SiO2) molar ratio of 0.15. The qualities of Si-OH are tested by NaOH titration and IR. The results of the both methods confirm that the amount of Si-OH in SMSM is higher than silica fume. Furthermore, SMSMs are employed as effective adsorbents for removing Pb2+ from the static, competitive and column experiments. The capacity for Pb2+ removal demonstrates great improvement. © 2015 Elsevier Inc. All rights reserved.


Li X.,Kunming University of Science and Technology | Han C.,Kunming University of Science and Technology | Zhu W.,Kunming University of Science and Technology | Ma W.,Kunming University of Science and Technology | And 8 more authors.
Journal of Chemistry | Year: 2014

Amino-functionalized mesoporous silica MCM-41 materials have been prepared to develop efficient adsorbents of Cr(VI) in wastewater, using silica fume as silica source. Functionalization with amino groups has been carried out by using grafting method. The materials have been characterized by means of X-ray diffraction (XRD), nitrogen (N adsorption-desorption, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Adsorption potential of the material for Cr(VI) removal from aqueous solution was investigated by varying experimental conditions such as pH, initial metal concentration, and contact time. The equilibrium data were analyzed using the Langmuir and Freundlich isotherm by linear regression analysis, and the results show that the adsorption equilibrium data obeyed the Langmuir model. In addition, the kinetics analysis revealed that the overall adsorption process was successfully fitted with the pseudo-second-order kinetic model. © 2014 Xitong Li et al.


Luo T.,Kunming University of Science and Technology | Luo T.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | Lv G.,Kunming University of Science and Technology | Lv G.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | And 8 more authors.
Journal of Crystal Growth | Year: 2013

A transient global simulation was carried out to investigate the effect of pulling-down rate on the temperature distribution, melt convection and melt/crystal (m-c) interface in vacuum directional solidification purification process for SoG-Si in metallurgical route. Simulation results show that pulling-down rate has little effect on flow behavior of melt. The isotherms change in the bottom area of silicon for 10 μm/s pulling-down rate is larger than that of 5 μm/s, and it may lead to higher thermal tress in this part of the silicon ingot. The m-c interface is less convex to the crystal and its variation is smaller for 10 μm/s, it further contributes to desirable crystal growth. We found that silicon ingots produced by vacuum directional solidification purification with pulling-down rate of 10 μm/s can meet the crystal morphology requirement of solar grade silicon (SoG-Si). So we proposed a new route for metallurgical production of solar wafers which combining with removal of impurities and ingot casting process into a process. Preparation of multi-crystalline silicon (mc-Si) by the directional solidification process will have large-size columnar grain growth and produce the solar wafers with appropriate technological parameters for directional solidification process. © 2013 Elsevier B.V.


Wu J.-J.,Kunming University of Science and Technology | Wu J.-J.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | Ma W.-H.,Kunming University of Science and Technology | Ma W.-H.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | And 6 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2013

Gas blowing is a valid method to remove the impurities from metallurgical grade silicon (MG-Si) melt. The thermodynamic behavior of impurities Fe, Al, Ca, Ti, Cu, C, B and P in MG-Si was studied in the process of O2 blowing. The removal efficiencies of impurities in MG-Si were investigated using O2 blowing in ladle. It is found that the removal efficiencies are higher than 90% for Ca and Al and nearly 50% for B and Ti. The morphology of inclusions was analyzed and the phases Al3Ni, NiSi2 and Al3Ni were confirmed in MG-Si by X-ray diffraction. It was found that SiB4 exists in Si-B binary system. The chemical composition of inclusions in MG-Si before and after refining was analyzed by SEM-EDS. It is found that the amount of white inclusion reduces for the removal of most Al and Ca in the forms of molten slag inclusion and the contents of Fe, Ni and Mn in inclusion increase for their inertia in silicon melt with O2 blowing. © 2013 The Nonferrous Metals Society of China.


Li X.,Kunming University of Science and Technology | Wu D.,Kunming University of Science and Technology | Wang J.,Kunming University of Science and Technology | Zhu W.,Kunming University of Science and Technology | And 6 more authors.
Microporous and Mesoporous Materials | Year: 2016

Large-sized spherical mesoporous silica (LMS > 3 mm) has been synthesized through a pseudomorphic transformation method. For this, cetyltrimethylammonium bromide (CTAB) was selected as a templating agent and commercial silica spheres were used as the parent silica material. The effects of synthesis parameters, such as NaOH:SiO2 molar ratio, reaction time, and ethanol:H2O volume ratio, have been quantitatively investigated. The structure and morphology of the spheres have been investigated by N2 sorption-desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. The pore structure of LMS obtained from a molar ratio of 140H2O:0.1NaOH:0.27CTAB after 48 h was examined with the addition of ethanol, and the optimal volume ratio of ethanol:H2O was identified as 0.252. Under the optimum conditions, high-quality mesoporous silica spheres were synthesized with a high specific surface area (about 1078.19 m2/g) after post-hydrothermal treatment. The ordered pore structure was maintained over four cycles in recyclability experiments on the reaction solution. The large-sized particles showed improved capacity for Pb2+ removal, suggesting that they might be applied as a basic material for heavy metal adsorption in treating industrial or natural waste water. © 2016 Elsevier Inc. All rights reserved.


Wu J.,Kunming University of Science and Technology | Wu J.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | Ma W.,Kunming University of Science and Technology | Ma W.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | And 6 more authors.
Journal of Non-Crystalline Solids | Year: 2012

The distribution of boron between CaO-SiO 2 slag phase and silicon phase was examined in order to establish the effects of slag composition and basicity on boron removal from metallurgical grade silicon (MG-Si). Though the addition of Li 2O to CaO-SiO 2 slag showed a little obvious advantage to boron removal, the boron concentration in MG-Si can be reduced from 18 ppmw to 1.3 ppmw with the ratio of CaO-Li 2O-SiO 2 slag to MG-Si for 4:1 (mass). The reactive mechanism between boron in MG-Si and CaO-Li 2O-SiO 2 slag is described using an ionization theory of molten slag and an electrochemical model was established, which depicted the oxidation and transfer of boron between silicon and slag phases. The experiment of slag refining for rich-B Si-B alloy showed that the generated (BO 3) 3- combines into Li 2O· 2B 2O 3 with slag instead of CaO·B 2O 3 on account of the more negative standard Gibbs free energy of formation for Li 2O·2B 2O 3 than that of CaO·B 2O 3. © 2012 Elsevier B.V.


Yang X.-W.,Kunming University of Science and Technology | Yang X.-W.,State Key Laboratory Complex Nonferrous Metal Resour Cleaning Utilization Yunnan Province | Ma W.-H.,Kunming University of Science and Technology | Ma W.-H.,State Key Laboratory Complex Nonferrous Metal Resour Cleaning Utilization Yunnan Province | And 8 more authors.
Guocheng Gongcheng Xuebao/The Chinese Journal of Process Engineering | Year: 2016

Bio-char reductant was prepared with walnut shells, and characterized to analyze the relationship between chemical components, functional group distribution and resistivity. The results showed that resistivity of bio-char declined from 6288.7 to 1515.9 μΩ·m with increasing of pyrolysis temperature from 400℃ to 1450℃. Fixed carbon content increased and volatile matter content declined with increasing of pyrolysis temperature. Carbonyl and aliphatic functional groups in the char were gradually decomposed, the interlamellar spacing of d002 on the lattice plane decreased gradually, its crystallinity, aromatization and carbon structure ordering degree increased with increasing of pyrolysis temperature. In the pyrolysis temperature range of 500~700℃, high-performance bio-char reductant with high yield (≥24%), high resistivity (≥5800 μΩ·m), high fixed carbon content (≥80%) and low ash content (≤4%) was obtained. The char had developed pores, and could be used as the reductant for industrial silicon production. © 2016, Science Press. All right reserved.


Ma W.,Kunming University of Science and Technology | Ma W.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | Yang X.,Kunming University of Science and Technology | Yang X.,Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities | And 2 more authors.
TMS Annual Meeting | Year: 2015

Cast multicrystalline silicon ingots are widely used in photovoltaic manufacturing. A key issue to achieve high solar cell efficiencies is to attain an optimized temperature field during directional solidification (DS) process. This paper reports numerical investigation of multicrystalline silicon (mc-Si) ingot production using two major types of DS furnace. Specific examination is made on thermal distribution, interface shape and stress field. Evaluation is performed for the applicability of thermal system design to reduce thermal stress, improve crystal quality and enhance energy efficiency. The effects of procedure parameters and geometric configuration on temperature distribution are discussed as well to provide the viable solutions for systems optimization. Copyright © 2015 by The Minerals, Metals & Materials Society. All rights reserved.

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