The Purification Of Metallurgical Grade Silicon By Electron Beam Melting

Metallurgical grade silicon (MG-Si) is obtained from the reduction of silica (SiO 2) in a voltaic arc furnace. The impurities are inherent to the reduction process and they are also dependent on the quality of the initial materials. Among other applications, silicon is used as a substrate for photovoltaic conversion of energy and this conversion is as bigger as greater is the purity of the substrate. Researches are being carried out, in some countries, with the objective of searching for new processes of silicon purification or new materials that can be used as substrates for energy conversion. In this research, the technique of silicon purification in an electron beam furnace was used, where the melting occurs in a high vacuum and the impurities are extracted by evaporation. MG-Si in bulk form without leaching, with an initial purity of 99.88% in mass and ground and leached MG-Si, with an initial purity of 99.92%, were used as starting materials. The final purity obtained, in both materials, was above 99.999% in mass. These results demonstrate that this process is technically viable, while also eliminating the stages of chemical purification used in other techniques. © 2005 Elsevier B.V. All rights reserved.16912125Ikeda, T., Maeda, M., Purification of metallurgical grade silicon for solar grade silicon by electron beam button melting (1992) ISIJ Int., 32 (5), pp. 635-642Ikeda, T., Maeda, M., Refining of silicon for solar cells (1993) First International Conference on Processing Materials for Properties, pp. 441-445. , Honolulu, HI, USASuzuki, K., Kumagai, T., Sano, N., Removal of boron from metallurgical-grade silicon by applying the plasma treatment (1992) ISIJ Int., 32 (5), pp. 630-634Sakagushi, Y., Ishizaki, M., Kawahara, T., Production of high purity silicon by carbothermic reduction of silica using AC-arc furnace with heated shaft (1992) ISIJ Int., 32 (5), pp. 643-649Choudhury, A., Hengsberger, E., Review: Electron beam melting and refining of metals and alloys (1992) ISIJ Int., 32 (5), pp. 673-681Braga, A.F.B., Otubo, J., Mei, P.R., The electron beam melting influence on the metallurgical grade silicon purification for solar-grade silicon (1998) Proceedings of Ninth CIMTEC International Meeting, , Florence, ItalyBraga, A.F.B., Otubo, J., Mei, P.R., The purification of leached metallurgical grade silicon by electron beam melting (1998) The Third Pacific Rim International Conference on Advanced Materials and Processing, Vol. 1, pp. 1057-1062. , Honolulu, HI, USAPires, J.C.S., Upgrade of the purification of silicon through electron beam melting furnace (1999) XV COBEM - Brazilian Congress of Mechanical Engineering, , Águas de Lindóia, São Paulo, Brazil, November 22-26Pires, J.C.S., Obtaining solar grade silicon through electron beam melting (2000) CONEM-2000 - Mechanical Engineering National Congress, , Natal, RN, Brazil, August 7-11Pires, J.C.S., Profile of impurities in sample of polycrystalline silicon purified in electron beam melting furnace (2000) Proceedings of 55th Annual Congress of ABM (Brazilian Association of Metallurgy and Materials), , Rio de Janeiro, RJ, Brazil, July 24-28Braga, A.F.B., (1997) Study of the Potential of Electron Beam Melting Technique to the Metallurgical Grade Silicon Purification, 155p. , Ph.D. Thesis, Mechanical Engineering College, State University of CampinasIkeda, T., Maeda, M., Elimination of boron in molten silicon by reactive rotating plasma arc melting (1996) Mater. Trans., JIM, 37 (5), pp. 983-987Bathey, B.R., Cretella, M.C., Review: Solar-grade silicon (1982) J. Mater. Sci., 7, pp. 3077-309

Ametryn Leaching in Soils from the Sugarcane Region in Northeastern Brazilian

ABSTRACT Ametryn is one of the most widely used herbicides in the sugarcane culture. Little is known about the interactions between this herbicide and the attributes of soils in the sugarcane region of northeastern Brazil. This knowledge, before recommending herbicide, will minimize the negative effects on the environment, particularly on water resources, and will ensure weed control efficacy. In this work, ametryn leaching potential was estimated through bioassays and chromatography, in five soils from the sugarcane region in northeastern Brazil: Quartzarenic Neosol (Entisol); Red Argisol (Ultisol); Ferrihumiluvic Spodosol (Spodosols); Red-Yellow Acrisol (Oxisol) and Haplic Cambisol (Inceptisols). To achieve this, columns were prepared with samples of the respective soils. On top of these columns ametryn was applied and, 12 hours later, a 60 mm rainfall was simulated. After water draining (72 hours after herbicide application), the columns were longitudinally opened to withdraw samples of each soil, every 5 cm. On some of these samples, ametryn quantification was performed by high-performance liquid chromatography and, on the others, biological assays were performed to confirm the results. Ametryn mobility was influenced by the physical-chemical characteristics of soils, mainly by organic matter content, texture and cation exchange capacity (CEC). However, this cannot be considered for Ferrihumiluvic Spodosol, whose cementing characteristics restrict the infiltration of water and organic compounds. Increased leaching ametryn occurred in Quartzarenic Neosol (Entisol), with higher herbicide concentration in the 5 to 10 cm depth layer, in relation to the 0 to 5 cm surface layer, indicating possible agronomic efficiency loss and higher risk of groundwater contamination

New Processes For The Production Of Solar-grade Polycrystalline Silicon: A Review

The global energy consumption is predicted to grow dramatically every year. Higher energy prices and public awareness for the global warming problem have opened up the market for solar cells. The generation of electricity with solar cells is considered to be one of the key technologies of the new century. The impressive growth is mainly based on solar cells made from polycrystalline silicon. This paper reviews the recent advances in chemical and metallurgical routes for photovoltaic (PV) silicon production. © 2007 Elsevier B.V. All rights reserved.924418424Fally, J., Fabre, E., Chabot, B., (1986) Revue de l'énergie, 37 (385), p. 761Li, J., (1992) Appl. Phys. Lett., 60 (18), p. 2240Schubert, W.K., King, D.L., Hund, T.D., Gee, J.M., (1996) Sol. Energy Mater. Sol. Cells, 41-42, p. 137Koch, E.C., (2007) Propellants, Explosives, Pyrotechnics, 32 (3), p. 1Pires, J.C.S., Otubo, J., Braga, A.F.B., Mei, P.R., (2005) J. Mater. Process. Technol., 169, p. 16Woditscha, P., (2002) Sol. Energy Mater. Sol. Cells, 72, p. 11Williams, E., (2000) Global Production Chains and Sustainability, , United Nation University, Tokyo, Japan 147ppYuge, N., (1994) Sol. Energy Mater. Sol. Cells, 34, p. 24

Thermodynamic and Kinetic Behavior of B and Na Through the Contact of B-Doped Silicon with Na2O-SiO2 Slags

Boron (B) is the most problematic impurity to be removed in the processes applied for the production of solar grade silicon. Boron removal from liquid silicon by sodium-silicate slags is experimentally studied and it is indicated that B can be rapidly removed within short reaction times. The B removal rate is higher at higher temperatures and higher Na2O concentrations in the slag. Based on the experimental results and thermodynamic calculations, it is proposed that B removal from silicon phase takes place through its oxidation at the slag/Si interfacial area by Na2O and that the oxidized B is further gasified from the slag through the formation of sodium metaborate (Na2B2O4) at the slag/gas interfacial area. The overall rate of B removal is mainly controlled by these two chemical reactions. However, it is further proposed that the B removal rate from silicon depends on the mass transport of Na in the system. Sodium is transferred from slag to the molten silicon through the silicothermic reduction of Na2O at the slag/Si interface and it simultaneously evaporates at the Si/gas interfacial area. This causes a Na concentration rise in silicon and its further decline after reaching a maximum. A major part of the Na loss from the slag is due to its carbothermic reduction and formation of Na gas