Numerical Analysis Of SiC Migration In Silicon During Induction Melting Process

With the growth of global population and the rapid development of economy,the demand for energy is increasing year by year.At present,the energy supply mainly depends on fossil energy.It has become an urgent task to explore environmentally friendly renewable resources.Solar energy has become an important new energy because of its unlimited resources,clean environmental protection,safety and reliability.Silicon material is the main basic material of solar cell,and the impurities and inclusions seriously affect the electrical properties of solar cell.Carbon element is a harmful impurity in silicon,which will precipitate during the molding process of silicon ingot,and then form SiC inclusions.The SiC inclusions will greatly increase the fragmentation rate and the preparation cost of solar cells during the process of silicon ingot slicing.In addition,SiC inclusion in solar cells will form parallel resistance,which will have a serious impact on the electrical performance of solar cells.Electromagnetic separation technology is a separation technology with convenient,efficient and environmental friendly for SiC inclusion.However,scholars have little research on the migration mechanism and process parameters of SiC inclusions in induction melting silicon,which leads to unclear migration mechanism of SiC inclusions in induction melting separation and high energy consumption.Based on this background and the law of heat and mass transfer,this paper analyzes the influence of coil frequency and coil current on silicon melt flow and SiC extrusion pressure in the induction melting process and analyzes the migration law of SiC in the induction melting silicon process by using particle tracking model by integrating of the numerical simulation,the theoretical calculation and the experiments.The results show that the influence of induction smelting process parameters on the separation of SiC is different,the flux density,induced current,electromagnetic volume force and the extrusion force of SiC inclusions are increased with the increase of coil current,and the physical quantities are mainly affected by the coil frequency during induction melting process.The force of SiC inclusions in silicon melt during induction melting process comes from two aspects: 1.Drag force caused by silicon melt flow,2.SiC extrusion force.SiC inclusions in different regions are dominated by different forces: SiC inclusions mainly depend on silicon melt flow in the process of migrating from silicon melt to near graphite crucible wall.The SiC inclusions migrating to graphite crucible wall mainly depend on SiC extrusion force.The flow rate of silicon melt is not as high as possible.If the flow rate of silicon melt is too high,the pulling force of silicon melt flow on SiC inclusions will be far greater than the extrusion force of SiC inclusions,and it will not be separated.If the flow rate of silicon melt is too small,the migration rate of SiC inclusions in silicon melt will be too slow,and the separation efficiency will be low.The more number of flow vortices in silicon melt,the better the SiC inclusions be separated.The main reason for this is that free path of SiC inclusions migration is shortened due to the increase of flow vortices,and SiC inclusions are transported to the side wall of graphite crucible and separated to the wall of graphite crucible under the extrusion pressure.It is also found that the separation degree of SiC inclusions increases with the increase of coil frequency,the decrease of coil current and the prolongation of melting time.Therefore,high frequency,low current and long time smelting are helpful to separate SiC inclusions in silicon melt.And the law is verified by experiments.