Reaction Kinetics And Molecular Dynamics Simulation Of Impurities Boron And Phosphorus In Industrial Silicon Out-of-furnace Refining Process

In recent years,with the rapid development of the global economy,energy problems have become increasingly prominent,and photovoltaic power generation has become a hot spot of global concern.As the raw material for the production of solar cells,the demand for polycrystalline silicon is increasing sharply.The existing chemical methods for preparing solar-grade polysilicon have problems such as high cost and high pollution,which cannot meet the rapid development needs of the global photovoltaic industry and the requirements of greatly reducing the cost of solar cells,forcing people to research and develop new solar-grade silicon preparation technologies.The production of solar-grade polysilicon by metallurgical methods has the characteristics of low cost,safety and environmental protection,and has attracted more and more attention at home and abroad.However,compared with the mature chemical methods such as the improved Siemens method,there is still a certain gap in the theoretical development and technical application of the metallurgical method.It is necessary to deeply study the movement and removal behavior of impurities in the silicon melt from the micro level,so as to lay a stable technical foundation for its further promotion and application.In this paper,the kinetics of the removal of B and P from industrial silicon is explored by gas blowing refining.By determining the mass transfer of impurities in the silicon melt during the oxygen blowing refining process,a kinetic model for the removal of non-metallic impurities B and P is established.,And give the kinetic parameters of the removal process of B and P elements.In addition,it is very difficult to accurately describe the industrial silicon refining process through experimental methods.The method of quantum chemistry can explore the microscopic mechanism of the reaction at the level of chemical bonds and molecular structure,so that industrial silicon can achieve the purpose of deep impurity removal.The results of the gas blowing refining experiment show that after 90 minutes of refining at 1550?,the B content can be reduced from 0.0058%to 0.0018%,and the P content can be reduced from 0.0056%to 0.0026%.The content of B and P in industrial silicon decreases with the extension of refining time,and the rate of decrease gradually slows down.By fitting the relationship between the refining time and the concentration of B and P in the refined silicon,the apparent rate constants of the oxidation reaction of B and P are calculated as 5.68 ×10-4s-1 and 2.03×10-4s-1,and the mass transfer coefficients of B and P in the silicon melt are ?B and ?P.These are 1.37×10-5m·s-1 and 4.91×10-6m·s-1 respectively.During the blowing refining process,part of the silicon is oxidized to cause silicon loss,and the loss increases with the extension of the refining time,reaching the maximum value of 10.12%at 90 minutes.The lost silicon can be divided into two parts:the oxidized silicon dioxide that enters the slag phase and the SiO flue gas generated at high temperature.Using ab initio molecular dynamics simulation method to study the reaction mechanism of industrial silicon oxygen blowing refining process,it is found that Si supercell doped with O has a very strong interaction with Ca and Al,which form a Ca-O bond and Al-O bond,respectively.The B-O also has a strong interaction with the increase of temperature,but the interaction between Fe-O bond and P-O bond is weaker.At the same time,it was found that the interaction between impurity atoms and oxygen atoms at 1823K was stronger than 1723K,indicating that raising the temperature during the oxygen blowing refining process helps to remove impurities.The results before and after the kinetic simulation show that although the direct removal effect of O-doped Si supercell on P is very poor,the P-P bond is formed in the later stage,indicating that P will be removed in the form of P2 during the refining process.According to the mean square displacement,the diffusion coefficient of impurity atoms can be obtained.The results show that the diffusion coefficient of metallic impurities Fe,Al,and Ca is greater than that of non-metallic impurities B and P.The diffusion coefficient of the impurity atom at 1823K is generally larger than that at 1723K.The ab initio molecular dynamics simulation method was used to study the reaction mechanism of the industrial silicon slagging and refining process.It was found that after kinetic simulation,B and P produced BO33-and PO43-under the action of the CaO-SiO2 slag system,respectively.The simulation results are consistent with the experimental results are consistent.The diffusion coefficients of BO33-and PO43-at 1823K are DBO33-=1.29 ×10-8 m2s-1,DPO43-=8.05 ×10-9 m2s-1.