Redistribution of iron during directional solidification ofmetallurgical-grade silicon at low growth rate
(1.Fujian Key Laboratory of Advanced Materials, College of Materials, Xiamen University, Xiamen 361005, China;
2.School of Materials Science and Engineering, Dalian University of Technology, Dalian 116023, China;
3. Qingdao Longsun Silicon Technology Company Ltd., Qingdao 266200, China)
2.School of Materials Science and Engineering, Dalian University of Technology, Dalian 116023, China;
3. Qingdao Longsun Silicon Technology Company Ltd., Qingdao 266200, China)
Abstract: 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.
Key words: directional solidification; metallurgical-grade silicon; redistribution; iron; grain boundary