Papers by Keyword: Metallurgical Grade Si

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Authors: Wei Dong, Xu Peng, Da Chuan Jiang, Yi Tan, Qiang Wang, Guo Bin Li
Abstract: In order to investigate Ca evaporation behavior in the electron beam melting process, metallurgical-grade silicon was melted in an electron beam furnace with different experimental conditions. The results showed that the content of impurity Ca was significantly decreased in the early time, while these changed slowly with the extension of the melting. The removal rate of Ca was controlled by the transfer of Ca atoms from the bulk liquid silicon to liquid/gas phase interface within the range of experiment temperature.
Authors: Xiang Yang Mei, Wen Hui Ma, Kui Xian Wei, Yong Nian Dai
Abstract: The main raw material of solar energy is multi-crystalline silicon. Directional solidification technique is one important technological process of metallurgy purification technology for multi-crystalline silicon. It can purify metallurgical grade silicon by removing metal impurities and control crystal growth at the same time. In experiment, metallurgical grade silicon by acid leaching pre-treatment, was purified by our self-assembled directional solidification furnace. The sample was analyzed by electron-prode micro analysis (EPMA). According to the results, the removal efficiency of Fe and Al is 96.3% and 96.7%, respectively. The removing mechanism of metal impurities and the difference between theory value and experiment value were also discussed. The segregation effect in directional solidification is the reason of removing Fe, but analgesic effects of the segregation effect combined with vacuum volatilization are that of removing Al. When the silicon ingot was cooled down, lengthways section of silicon ingot was cut and etched, crystal growth was studied. The results indicate that columnar crystal growth shows diverging tendency from the bottom to the top of silicon ingots, and solidification interface shape is convex. The reasons may be the nucleation of new crystals on crucible sidewall is very serious and the pulling rate is too high.
Authors: Da Chuan Jiang, Wei Dong, Yi Tan, Qiang Wang, Xu Peng, Guo Bin Li
Abstract: The growth in the solar energy technology caused inshortage solar grade Si. As a lowcost, environmental friendly technology, metallurgical method purity silicon is developed significantly. However, as a typical impurity in Si, B is difficult to be removed by directional refining or vacuum melting due to its large segregation coefficient and less evaporation coefficient. In this paper, the big difference of evaporation pressure between Si and B can be applied to separate B from Si, in which, B is remained in molten Si, while most of Si becomes evaporant. Electron beam is applied to scan molten Si and the Si existed in the form of the evaporant is gather on the watercooled crystallizer. The content B in the evaporant is undetectable by ICP-MS.
Authors: Ji Jun Wu, Wen Hui Ma, Bin Yang, Da Chun Liu, Yong Nian Dai
Abstract: The diffusion layer and melt of silicon-boron are respectively obtained after quenched in water at 1300 oC by using metallurgical grade silicon (MG-Si) powder and amorphous boron powder. The phase equilibria for boron in MG-Si have been investigated by using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The back scattered electron (BSE) image of diffusion layer displays the intermediate phase SiB4 in silicon-boron phase band, and the XRD results also indicate that SiB4 exists in silicon-boron diffusion layer at 1300 oC. It is inferred that the intermediate phase SiB4 is formed by the reaction (Si) + SiB6 ↔ SiB4 according to the equilibrium composition of Si/B=4/1 as quantified by Energy Dispersive Spectroscopy.
Authors: Ke Qiang Xie, Zhan Liang Yu, Wen Hui Ma, Yang Zhou, Yong Nian Dai
Abstract: In this paper, removal of iron from metallurgical grade silicon with pressure leaching is carried out. We investigated the factors such as the concentration of hydrochloric, particle size of raw material ground, temperature, pressure and reaction time, which influenced on the removal of iron. The results show that the optimum operating conditions for pressure leaching in hydrochloride are: acid concentration 4 mol/L, diameter for raw material less than 50 μm, leaching temperature 160 0C,leaching pressure 2.0 MPa, leaching time 2.0 h. The content of iron residual in MG-Si powder was reduced to about 200 ppmw. The removal efficiency of iron is up to 90.90 %.
Authors: Yu Liu, Dong Liang Lu, Yu Yan Hu, Tao Lin, Yan Hui Sun, Hong Yu Chen, Qian Shu Li
Abstract: A low-cost process for removing boron from metallurgical grade silicon was developed by Si-Al alloying, and the separation procedure of silicon grains from Si-Al melt by solidification was investigated in this paper. The microstructure and purity of silicon were characterized and detected by metallographic analysis, energy dispersive X-ray spectrometers analysis and inductive coupled plasma atomic emission spectroscopy analysis. The results showed that the content of boron in the purified silicon decreased from 128.00 ppmw to 27.62 ppmw. In addition, the process of purification with Si-Al alloying combined with the treatment of hydrofluoric acid could remove boron to a low content of 13.81 ppmw, the removal rate of which is 89.21 %. The results indicated that the removal of boron from metallurgical grade silicon by Si-Al alloying is an efficient and prospective method.
Authors: Yu Yan Hu, Dong Liang Lu, Tao Lin, Yu Liu, Bo Wang, Chang Juan Guo, Yan Hui Sun, Hong Yu Chen, Qian Shu Li
Abstract: Refining of solar grade silicon by metallurgical method is the research hotspot of polycrystalline field. Slagging method is benefit to the removal of the impurities especially to boron exsisted in the raw silicon. In this study, the influence of the density, the viscosity and liquidus temperature of the slag components on the refining process were discussed, and then the slag system SiO2-Na2CO3 was choosed as the slagging agents. And then the impact factors on the removal efficiency of boron such as the composition of SiO2 and Na2CO3, the ratio of slag to silicon and the refining time were investigated by the orthogonal experiment. The results showed that the optimum parameters of the oxidation refining for removing boron were as follows: the main composition of the oxidant is “SiO2 : Na2CO3 = 60% : 40%”; the slag/silicon ratio is 0.5; time for refining is 60min at 1550 . The results indicated that the removal efficiency of boron was 88.28%, and the content of boron in MG-Si can be reduced to 7ppmw under the best refining process¬.
Authors: Yong Chao Gao, Bai Tong Zhao
Abstract: As solar energy is inexhaustible, solar cells have become one of the options to the future energy. The raw material silicon as one of the Earth's most abundant resources elements, have the advantage of non-toxic, no pollution, no radiation, high photoelectric conversion efficiency, stability and reliability of optical performance become the main raw material for production of solar cells. Because of its supply is limited, We used relatively inexpensive metallurgical grade silicon as a starting material to produce solar grade silicon for solar cells is considered relatively inexpensive method. Therefore, the removal of impurities from metal silicon witch reduce solar cell carrier lifetime and thus reducing its power generation efficiency is a significant issue. To this end, according to impurities in molten silicon and solid silicon demonstrated various characteristics and existence forms, in this paper we used acid leaching, directional solidification, electron and magnetic field, vacuum melting, blow reactive gases and so on to fabricate solar grade silicon from metal silicon in theory to analyze and optimize process.
Authors: Rui Xun Zou, Da Chuan Jiang, Wei Dong, Zheng Gu, Yi Tan
Abstract: The electron beam injection (EBI) process involves offering electrons around silicon powder, whose surface was oxidized, and subsequently the powder is washed by HF acid so as to remove the SiO2 film. The new electron beam injection process, in which micro electric filed formed between Si and SiO2 film will accelerate impurities diffusion from Si to SiO2 film, was developed and applied to eliminate the transition-metal impurities of MG-Si. It is proved to be effective to remove transition-metal impurities from metallurgical grade silicon (MG-Si). By applying the electron beam injection method, the removal rate of 10% to 59% was achieved during the refining process. The efficiency of impurity removal originates from two aspects: the impurity concentration gradient on both sides of Si/SiO2 interface; the micro electric field formed from Si to SiO2 film. A further increase in the removal rate can be realized by controlling the processing parameters.
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