The impurities in silicon ingots during directional solidification (DS) were effectively controlled by Thermoelectric Magnetic Convection (TEMC). In details, the application of a 1 T static magnetic field (SMF) significantly improved the removal efficiency of metallic impurities (Fe, Cu, Mg, and Al), with the proportion of high-purity regions in silicon ingots increased from 70.1% to 80.7%. The SMF generated intense TEMC at the solid-liquid interface, driving upward displacement of metal impurities within the silicon melt. This convection led to a reduction in the diffusion layer thickness and effective segregation coefficient. The changes in the microstructure under the SMF were characterized using Electron Backscatter Diffraction (EBSD). The results revealed that under a 1 T SMF, the average grain size increased by 10.4%, and the proportion of Σ3 grain boundaries rose from 54.55% to 74.3%. The simulation of TEMC further elucidated both the magnitude and direction of induced convective flow at the solid-liquid interface. The results demonstrated a pronounced counterclockwise vortex formation, which critically influenced impurity redistribution. These findings provide valuable insights for optimizing parameters to improve silicon purification techniques, thereby facilitating the production of high-quality polysilicon for photovoltaic applications.
Gao et al. (Sun,) studied this question.