Study On The Oxidation Kinetics Of Silicon And Impurity Elements During The Refining Process Outside The Furnace

Secondary refining can effectively remove the main impurities from metallurgical grade silicon.The agitation of the silicon melt during the blowing process enhances the kinetic conditions of impurity removal,but at the same time,the oxidizing gas is bound to cause oxidation loss of silicon in the molten pool.In this paper,the silicon loss is measured by oxygen blowing refining and slag treatment refining process,established the kinetic rate equation of main element oxidation in the refining process,and the scheme of reducing silicon loss is discussed,which has guiding significance for industrial silicon production.Oxygen is blown into metallurgical grade silicon for refining different times.The oxidation of the element includes direct oxidation and indirect oxidation.The oxidized SiO₂ is used as an oxidant to deoxidize the element[M]from the molten pool to the slag-silicon interface,on the other hand,according to the law of distribution,enters the silicon melt in the form of dissolved oxygen atoms[O],oxidizing the elements therein.After refining,the cooling rate is faster,the impurity components are unbalanced and crystallized,and the impurity components are grown by Si compound as a skeleton,the slag and silicon is well separated.The silicon loss rate increases with increasing refining time,reaching a maximum of 5.24%at 90min,and the rate of silicon loss is slowing.It is calculated that the rate of elemental oxidation in the molten pool is mainly limited by the diffusion of[M]in the silicon liquid and（MO）in the slag.The mass transfer coefficient of Al in the silicon melt is calculated,_Al=1.26×10^-5 m?s^-1.The slag of CaO∶SiO₂=1∶1 is added to metallurgical grade silicon for 1∶1 of the mass ratio of slag and silicon.After refining,wollastonite Ca₃（Si₃O₉）with isolated three-ring structure is found in the slag.The metal element forms pre-eutectic compound having a regular shape with Si.Refining cause loss of silicon,but the change is not significant over time,and the average loss rate is 3.33%.As the refining time increases,the mass fraction of Al decreases from 0.21%to 0.037%;the mass fraction of B decreases from0.0018%to 0.00061%.Limited by the diffusion of[Al]in the silicon melt and（Al₂O₃）in the slag,the mass transfer coefficient of Al in the silicon melt is calculated,_Al=2.53×10^-5 m?s^-1.The silicon-aluminum alloy pre-melted in the induction furnace,from the outer layer of the first solidified crystal to the inside of the post-crystallization,the concentration of Al is gradually increased,and the formed dendrites are made of Si having a high melting point and Al is distributed between the branches.After oxidation,the content of Al decreased from 10%to 1.95%,and the mass transfer coefficient of Al in silicon melt is calculated,_Al=4.67×10^-6 m?s^-1.With the help of Ab Initio Molecular Dynamics Simulation（AIMD）at the temperature of 1823K,the diffusion coefficient of Al in Si-Al-O system is calculated,_Al=6.40×10^-88)²?^-1.