Research On The Influence Of Electromagnetic Strengthening On The Segregation Of Impurities In Industrial Silicon

Metallurgical grade silicon?MG-Si?plays a vital role in the polysilicon,organic silicon and silicon alloy industries due to its rich,non-toxic and mature processing technology.The microstructure and distribution of its precipitates not only directly determine the subsequent leaching efficiency,but play a decisive role in the efficiency and quality of downstream organic silicon monomer synthesis.Additionally,the microstructure of inclusions also has a certain effect on the purification process of Siemens and silane methods.Therefore,it is particularly important to study the microstructure and distribution of inclusions in silicon.This paper systematically investigated the effect of enhanced removal of impurities by electromagnetic strengthening combined with wet leaching and microstructure of precipitates,and discusses the microstructure of inclusions under resistance remelting and induction remelting evolution process.?1?The inclusions in the source silicon are mainly distributed in blocks,strips or islands,and their distribution is scattered and randomly distributed with small regularity among each other,mainly including Fe Si₂,Si₈Al₆Fe₄Ca,Si₃Al₃Fe₂,Si₇Al₈Fe₅,Fe Si₂Ti,Si-Fe-Al-Ti-V,Si-Fe-Al-Ni-Zr,Si-Al-Ni-Cu phase.?2?Slow solidification will lead to an increase in the size of impurity phases in silicon.The impurity phases mainly include Si₇Al₈Fe₅,Fe Si₂,Si-Fe-Al-Ti-V,and Si-Fe-Al-Ni-Zr.After electromagnetic strengthening,almost all inclusions in silicon include Fe Si₂,Si₈Al₆Fe₄Ca and Si-Fe-Al-Ti-V phases,but only a small amount of Si-Fe-Al-Ni-Zr and Fe Si₂,Ti Si₂,VSi₂mixed phase appear in the center of the melt;and quantitative analysis showed that the enrichment effects of elements Fe,Al,Ca,Ti,V,Ni,Mn,and Zr were 1.19,1.26,2.35,1.17,2.06,2.39,3.59,and 1.24 times compared to the source silicon,respectively.To investigate the effect of phase control on its impurity removal rate,4 mol/L HCl+2 mol/L HF leaching results showed that the impurity content of source silicon,resistance remelting,and electromagnetic strengthening silicon was reduced to 171.8,158.1 and 99 ppmw.?3?The transformation process of the impurity phase in silicon subjected resistance remelted shows that the Al element in the Fe Si₂?Al?phase is confirmed to exist in the form of dissolved Al.The Si-Fe-Al phase gradually increased with the solidification process,and finally evolved into Si₇Al₈Fe₅and Si₆Fe₄Al₉phases.The Si₈Al₆Fe₄Ca phase is relatively stable during the solidification process,and its form has hardly changed.The V element of the Fe Si₂Ti?V?phase gradually separates with the solidification process and eventually evolves into a mixed phase of VSi₂and Ti Si₂.All in all,the impurity phases in metallurgical grade silicon tend to be more stable with the solidification process.?4?The transformation process of the impurity phase in the silicon by resistance remelted shows that the Fe Si₂and Si₈Al₆Fe₄Ca phase in the inclusions do not change with the solidification process.The content of Al in Si-Fe-Al-Ti-V gradually decreases,and the content of Ti and V gradually increases.Finally,two impurity phases are formed:a bright white Fe Si₂Ti phase and a dark black Ti Si₂;VSi₂mixed phase.