Effect of Sn Addition on the Evolution of Inclusions in Metallurgical Grade Silicon

Inclusions in metallurgical grade silicon (MG-Si) can significantly degrade the quality and performance of silicon materials. Thus, it is essential to implement effective measures to control and minimize their presence. This study investigates the morphology, distribution, and microstructural evolution of inclusions in silicon by introducing varying amounts of Sn. The changes in Fe content at different positions in silicon ingots before and after Sn refining were examined. The study demonstrates that Sn refining can reduce the number of inclusions at the bottom of silicon ingots by up to 71.3 pct. The morphology of inclusions undergoes a transition from fine filaments and sporadic dots to block-like formations, ordered short rods, and dots. There is an upward migration of Fe in the vertical direction, leading to a reduction in Fe content at the bottom from 0.61 to 0.25 pct, representing a significant decrease of 59.03 pct. These findings suggest that the addition of Sn to silicon can effectively remove Fe impurities. Additionally, the incorporation of Sn refining enables a reduction in the formation of the Si₇Al₈Fe₅ phase and enhances the selectivity of the organosilicon monomer synthesis process. Remarkably, the partial substitution of Ti by Al leads to the formation of the FeSi₂Ti(Al) phase. However, Ca tends to concentrate in Sn and remains unaffected by the Sn content. These empirical findings offer experimental evidence for effectively reducing and controlling the quantity and morphology of inclusions in MG-Si, thereby significantly enhancing the quality of MG-Si production.