Metallurgical Grade Silicon Refining Research, In Addition To Boron

With the decreasing of fossil energy, more and more people pay attention to new energy materials. High purity silicon, as a main material of solar cells, its preparation has become a main bottlenecks to develop a clean, eco-friendly, low-cost preparation technology of solar grade silicon.In this paper, firstly, the form and distribution of boron in the silicon and the binding mode of Si-B in silicon ingots were analyzed. Secondly, the activity formulas of six main slags were established. According to the activity, optical basicity, surface tension and melting point of SiO2, SiO2-CaO, SiO2-CaO-MgO, SiO2-CaO-MgO-CaF2, the better ratios of slag systems were fixed. Four systems as the slag were chosen to refine with metallurgical grade silicon in the induction furnace, moreover, different effects of boron removal were dicussed in the different slag ratios and different holding time. Thirdly, binary compounds of vary ratios were refined with metallurgical grade silicon. The following conclusions can be drawn:(1) the experiment of reaction between silicon and boron prove that the distribution of boron in silicon is lamination.(2) The ratios of 100% SiO2,64% SiO2-36% CaO,45% SiO2-45% CaO-10% MgO,35 % CaO-40% SiO2-10% MgO-15% CaF2 could have a good effect to remove boron in theory.(3) The experiments prove that the content of boron in silicon after refining can meet the requirement of solar grade silicon. With the slag increases, the content of boron in sample will be less.(4) Binary compounds PbS, CuCl2, FeCl3, CrCl3 can get the aim of removing boron, with the increase content of binary compounds, the content of boron in sample will be less.