Study On The Effect Of Electromagnetic Field On Structure And Properties Of CaO-SiO₂-M_xN_y Molten Slag By First Principles And Molecular Dynamics Calculation

In the continuous casting process,because of the wide application of electromagnetic stirring technology,the changes in the performance of slags under electromagnetic field conditions begin to gradually attract the attention of professionals.However,due to the limitations of experimental conditions,related research work has been progressed slowly.On the other hand,thanks to the improvement of computer performance,it is possible to study the relationship between the magnetic field and the slags using simulation calculation.To study the mechanism of influence of magnetic field on performance of slags at a micro scale,and to deeply understand the changes of slags caused by the magnetic field,in-depth discussion of the relationship between structure and performance of slags has certain inspiration for design of slags in the mould.Based on this,through the combination of first principles,molecular dynamics and experiment,the mechanism of change of microstructure and macroscopic performance of slags under magnetic field was studied.The first-principle calculation mainly studies the mechanism of Doping different atoms and change of peripheral electronic structure on the structure of silicon oxide.Molecular dynamics is to study the mechanism of change of larger-scale structures affected by magnetic field.Correctness of calculation is proved by experiments.The main conclusions are as follows:(1)In the CaSiO₃ system,the way of bonding between Si-O is sp³ hybridization;the electronic activity of the p orbital on the bridge oxygen is more dynamic than the electronic activity on the same orbit of the non-bridge oxygen,this supplies theoretical foundation of breaking of Si-O bond in slags after adding alkali oxides and alkali earth oxides.(2)In molten slag,the formation mechanism of aluminium-oxygen tetrahedron is that Al atoms form a tetrahedral structure through sp³ hybridization.The electrons on s orbitals of O atoms interact with the electrons on s orbitals of Al atoms;After adding Al₂O₃,the number of electrons in the conduction band of Al atoms has increased,electrons in the conduction band is the base of foundation of aluminium-oxygen tetrahedron.(3)In slag,the destruction of CaSiO₃ by CaF₂ is due to the interaction between Si atoms and F atoms,which destroys the sp³ hybridization of the original silicon-oxygen structure,and the electrons in the s orbital become more localized;The population of Si-F bond is smaller than that of Si-O bond,and its polarity is stronger.When F atoms are nearby Si-O bond,the degree of polymerization will decrease and Si-O bond will break because of electronic interaction.The destruction of CaSiO₃ by Na₂O is due to the formation of silicon-oxygen bonds after Doping Na₂O,the sp³ hybrid orbital will be destroyed;at the same time,the chemical activity of the bridge oxygen increases and it is easier to interact with other atoms interaction,so that the degree of polymerization will decrease.(4)CaO-SiO₂-CaF₂,CaO-SiO₂-Na₂O and CaO-SiO₂-Al₂O₃ system slag have been studied.When the magnetic field strength increases from 0m T to 50m T,the short-range of the system has no obvious change in the structure,and the medium-range structure and long-range structure will become more complicated.The content of complex structures in models will increase,but the degree of increase is related to the composition and content.The viscosity of various slags will also increase.The viscosity of CSF slag changes the most,while the viscosity of CSA slag changes the least.