Molecular Dynamics Simulation Of The Microstructure And Properties Of The CaO-SiO 2 -Al 2 O 3 -Na 2 O System

CaO-SiO₂-Al₂O₃-Na₂ O quaternary system is a very important basic slag system in the field of metallurgy.It is commonly used in steel refining slag and continuous casting mold powder,as a refining slag and continuous casting mold powder,it is an important part of the process of high temperature metallurgy refining.Its structure on the extraction of valuable elements,separation and protection of molten steel has an very important impact,Therefore,it is necessary to research the micro structure effect by Alkalinity,Na₂ O and Al₂O₃ content.In this paper,the binary system SiO₂-Al₂O₃ and the ternary system CaO-SiO₂-Al₂O₃,Na₂O-SiO₂-Al₂O₃ were simulated by molecular dynamics simulation method using Materials Studio 8.0 software.Then,the molecular dynamics simulation of CaO-SiO₂-Al₂O₃-Na₂ O quaternary system was carried out on the basis of binary and ternary simulation.Through the analysis of the oxygen distribution,tetrahedral micro structure and network structure degree.The influence of Na₂ O,Al₂O₃ and alkalinity on the structure and properties of the system was investigated,and the relationship between viscosity and micro structure information was discussed.The main conclusions are as follows:1.Under the atmospheric pressure,the Si in the binary molten system of SiO₂-Al₂O₃ is a stable structure of Si-O tetrahedron,and the average bond length of Si-O is between 1.61 and1.62?.The state of Si is same to the pure SiO₂ melt.Al in the SiO₂-Al₂O₃ binary melt system mainly exists as a lattice-forming element,that is,the Al-O tetrahedral structure is mainly formed,but its stability is not as good as Si-O tetrahedron,and with the increase of Al₂O₃ content,average bond length of Al-O has an increasing tendency.At the same time there will find five coordination of aluminum,even,it is possible to find six-coordinated aluminum.The aluminum avoidance principle is not present in all silicate systems,but only in the system that there has enough Si to separate the Al-O tetrahedrons so that the Al-O tetrahedra will not be connected to each other in the case of existence.2.When the fixed Al/Si ratio,CaO and Na₂ O were added into SiO₂-Al₂O₃ system,it was found that the increase of Ca?Na?/Al and the decrease of Al/Si ratio were all beneficial to improve the stability of [AlO4] tetrahedral structure.?1?In the CaO-SiO₂-Al₂O₃ and Na₂O-SiO₂-Al₂O₃ systems,when the Ca/Al is equal to 1/2 and Na/Al is equal to 1/1,the Bridge oxygen content and the Qn content of the tetrahedral micro structure reaching the maximum value,indicating that the degree of polymerization of the network structure has reached the maximum.?2?Ca²⁺and Na⁺in the system are compensated for Al3+ instead of Si4+ when Ca/Al is less than 1/2 and less than 1/1of Na/Al,and Al3+ is converted into network formation as part of the network.And increase the degree of polymerization of the system;when Ca²⁺ and Na⁺ are excessive,they are used as network modifier to depolymerize the architecture.3.In CaO-SiO₂-Al₂O₃-Na₂ O system,it is found that Na is superior to Ca to modify and charge the system,and the charge compensation ability of Na⁺ ions is greater than that of Ca²⁺with the increase of Na₂ O content,Si-O-Si will take precedence over Si-O-Al which is destroyed by Na to form Si-O-Na.With the increase of Na₂ O content and alkalinity,the oxygen content and viscosity of the Bridge oxygen are reduced.The relationship between NBO/T and viscosity in CaO-SiO₂-Al₂O₃-Na₂ O system at 1873 K was established by linear fitting.And it is found that CaO-SiO₂-Al₂O₃-Na₂ O system with high Al₂O₃ concentration tends to form a more complex network structure.