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GAN C.-H.,Xiamen University | FANG M.,Dalian University of Technology | FANG M.,Qingdao Longsun Silicon Technology Co. | ZHANG L.,Xiamen University | And 9 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2016

Redistribution of iron during directional solidification of metallurgical-grade silicon (MG-Si) was conducted at low growth rate. Concentrations of iron were examined by ICP-MS and figured in solid and liquid phases, at grain boundary and in growth direction. Concentrations are significantly different between solid and liquid phases. The thickness of the solute boundary layer is about 4 mm verified by mass balance law, and the effective distribution coefficient is 2.98×10−4. Iron element easily segregates at grain boundary at low growth rate. In growth direction, concentrations are almost constant until 86% ingot height, and they do not meet the Scheil equation completely, which is caused by the low growth rate. The effect of convection on the redistribution of iron was discussed in detail. Especially, the “dead zone” of convection plays an important role in the iron redistribution. © 2016 The Nonferrous Metals Society of China


Gan C.H.,Xiamen University | Gan C.H.,Qingdao Longsun Silicon Technology Co. | Zeng X.,Xiamen University | Fang M.,Dalian University of Technology | And 11 more authors.
Journal of Crystal Growth | Year: 2015

Abstract Directional solidification is often used to remove metallic impurity in the photovoltaic industry for the low equilibrium distribution coefficient between solid and melt. However, in our present experiments, compared with other impurities, the removal of calcium is variable at the low height of ingot, which is caused by the existence of insoluble CaO particle. CaO exists as insoluble particle in the feedstock. During directional solidification stage, CaO motions with the melt convection, and it is likely to envelop in solid. Consequently, the content of calcium is relatively high if many CaO particles are just contained, which is verified by the analysis of SEM-EDS. In a word, the removal efficiency depends upon the chemical state of calcium. The reason why CaO exists is studied, and the envelopment of the particle is mainly discussed by means of thermodynamics, especially on gravitational force, repulsive force, and drag force. © 2015 Elsevier B.V.


Wen S.,Dalian University of Technology | Wen S.,Key Laboratory for Solar Energy Photovoltaic System of Liaoning Province | Jiang D.,Dalian University of Technology | Jiang D.,Key Laboratory for Solar Energy Photovoltaic System of Liaoning Province | And 8 more authors.
Vacuum | Year: 2016

A theoretical model for investigating the crystal growth rate and the solidified height during silicon purification by directional solidification is proposed. The growth rate is not constant usually and it has profound effects on the distribution of metal impurity in production process. The crystal growth rate and the solidified height, based on thermal equilibrium on the melt-crystal interface, were discussed. The relationship between the surface temperature of silicon melt (T1) and temperature of graphite heater (TC′1) was found. The result shows that the value of T1 has an approximate linear relationship with the TC′1. The theoretical model can be used to design or predict the crystal growth rate by controlling the TC1 according to the different request. Then, the distribution of metal impurity during silicon purification by directional solidification can be calculated according to the crystal growth rate. Thus, the theoretical model can be used to design the growth rate and predict the distribution of impurity to the silicon purification process by directional solidification. The experiments proved that the calculation agreed well with the existing experimental results. © 2015 Elsevier Ltd. All rights reserved.

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