Basic Research On Phosphorus Migration Process And Suspension Behavior In Metallurgical Grade Silicon And Ferrosilicon Under Electromagnetic Suspensio

Electromagnetic levitation(EML)metallurgy is developed with the demand for special pure,highly active aerospace materials.Phosphorus is an impurity element that needs to be removed in the process of metallurgical grade silicon(MG-Si)purification,and it is also a sensitive element for the powdering of ferrosilicon(Si-Fe).This research takes advantage of EML technology to explore the migration and transformation of phosphorus in MG-Si and SiFe under EML,component transfer and distribution,droplet levitation,and solidification structure regulation,on the basis of considering the difficulties existing in the current metallurgical volatilization for dephosphorization.These basic change laws could provide a certain theoretical reference for the study of impurity removal and new material preparation technology under EML conditions.In this study,a combination of theoretical analysis,numerical simulation and experimental verification was adopted,and MG-Si and Si-Fe alloys were taken as the research objects.Droplet oscillation and deformation behavior,internal transfer of molten droplets and regulation behavior of solidification structure.The main conclusions are as follows:(1)Study on dephosphorization mechanism of MG-Si and Si-Fe alloy under EML shows that: The activity self-interaction coefficient of phosphorus in the binary system: ε_P~P=0.9369 + 2342.9? and the activity interaction coefficient between Fe and P in the ternary system:?ε_P~Fe= 0.5095 + 548.69.In the process of dephosphorization from MG-Si and SiFe under EML,the volatile form contains monoatomic phosphorus(P)and diatomic phosphorus(P2).For MG-Si,monoatomic phosphorus(P)dominates with phosphorus content less than 0.0196 wt.%;monoatomic phosphorus(P)and diatomic phosphorus(P2)coexist with phosphorus content greater than 0.0196 wt.%.When H2 is added into atmosphere,the evaporation of phosphorus is promoted,and the gas phase components include monoatomic phosphorus(P),diatomic phosphorus(P2)and phosphine compound(PH3).(2)Study on the limitation of phosphorus migration in MG-Si and Si-Fe alloy under EML shows that: At the temperature of 1450~1750 K,the limiting step is the evaporation of phosphorus on the droplet surface;with the increase of system temperature,it is controlled by surface evaporation and liquid boundary layer mass transfer.When the system temperature rises above 2000 K,the limiting step is transformed into mass transfer control in liquid boundary layer.By analyzing the thermodynamic and kinetic characteristics of phosphorus,a kinetic mass transfer model for dephosphorization in EML refining of metallurgical silicon materials under finite vacuum is constructed.Meanwhile,the evaporation coefficient is modified:(3)Study on the levitation behavior of silicon droplet under EML shows that: Through the “electromagnetic force-oscillation” numerical model of silicon droplet,what found is that the equilibrium position of silicon droplet with different diameters is 2.5 mm below the geometric center at the same levitation parameters.Through the numerical simulation for tracking the influence of initial position and static magnetic field on the oscillation trajectory of the levitated droplet,it is found that the axial static magnetic field with intensity of 1 T can produce obvious damping effect on the oscillating droplet and promote it to achieve stable levitation quickly.(4)Study on the internal transfer behavior of silicon droplet under EML shows that: Through the “electromagnetic-fluid-deformation” coupling numerical model,it is found that there is an obvious “expansion and compression” cycle in the shape of silicon droplet during levitation,with a period of 45 ms.Moreover,the deformation rate increases significantly under the Marangoni effect.Through the “electromagnetic-thermal-fluid” coupling numerical model,it is found that there are two annular vortices with different sizes and opposite directions in the silicon droplet,the maximum flow rate can reach 0.275 m/s.Under the application of 1T axial static magnetic field,the droplet circulation is significantly suppressed,and the internal heat transfer mode is changed from convective heat transfer to heat conduction.(5)Experimental study on the phosphorus removal of MG-Si and Si-Fe alloy under EML shows that: When EML is used for dephosphorization from MG-Si and Si-Fe alloy in 2023 K for 55 minutes within 50%Ar+50%H2 atmosphere,the maximum dephosphorization ratio of 69.95% and 91.62% can be achieved respectively.Since the phosphorus content in MG-Si and Si-Fe alloy is relatively less,it is mainly removed in the form of monoatomic phosphorus.Using hydrogen as a cooling medium to solidify MG-Si and Si-Fe droplets EML,it is found that the precipitation morphology of trace elements in the droplets can be greatly refined.