Research On Structural And Properties Of Aluminosilicate Melts By Molecular Dynamics Simulation

The structure and properties of aluminosilicate melt have been the most important subject in the fields of metallurgy,ceramics,glass and geology.In the field of metallurgy,CaO-SiO₂-Al₂O₃ ternary system melt is a very important basic slag system.The main components of blast furnace slag,smelting slag,refining slag and mold flux can be attributed to the CaO-SiO₂-Al₂O₃ system.As an important component,the amphoteric oxide Al₂O₃ is generally considered to be acidic in the alkaline environment and alkaline in the acidic environment.However,the influence of component changes on the amphoteric behavior of Al₂O₃ is rarely reported.In addition,CaF₂ is a kind of common flux which plays an important role in the regulation of slag properties,but the understanding of F on the mechanism of action of aluminosilicate melt structure is not consistent.Therefore,it is very important to study the effect of Al₂O₃in CaO-SiO₂-Al₂O₃system on the microstructure and properties of the aluminosilicate melt.Firstly,the influence of the change of the melt composition of CaO-SiO₂-Al₂O₃ternary system on the microstructure and macroscopic property was studied by molecular dynamics simulation.The average bond length,coordination number,oxygen type distribution and structure unit distribution,as well as the dynamic mechanical properties such as mean square displacement and self diffusion coefficient were analyzed to explore the mechanism of Al₂O₃ on the melt structure.Then,CaO-Al₂O₃-CaF₂ and CaO-Al₂O₃-CaF₂ systems were used to study the effect of F on the microstructure of the melt.At the same time,the relative contents of various structural units in typical melts and changing rules were studied by spectroscopy analysis,and verified with the results of molecular dynamics simulation.The results of the structure analysis show that,[SiO₄]^4-and[AlO₄]^5-tetrahedron are the main structural units in the melts,and[SiO₄]^4-tetrahedron can exist stably.Ca²⁺tends to be closer to Al,preferentially plays the role of compensating the excess negative charge of[AlO₄]^5-tetrahedron.With the increase of Al₂O₃ content,the degree of polymerization of the system increases,the disorder of Al-O structure increases.There is not enough Ca²⁺in high Al₂O₃ systems to provide charge compensation,the the triclusters oxygen and high coordinated Alincrease significantly to achieve the effect of balancing the system charge.With the increase of the basicity of the systems,the complex network structure is depolymerized and the[AlO₄]^5-tetrahedron tends to be regularized.When the system lacks O^2-ions to form a[AlO₄]^5-tetrahedron structure,part of Al₂O₃ is alkaline,providing O^2-and equilibrium charge.Spectroscopy analysis showed that the free form[AlO₆]faujasite structural body significantly enhanced peaks in the high-Al₂O₃ slag.Based on the analysis of the relationship between the structure and the properties of the CaO-SiO₂-Al₂O₃ system melt,the order of the self diffusion coefficient of the atoms in the melt is D_Ca>D_Al>D_O>D_Si.The[SiO₄]^4-and[AlO₄]^5-tetrahedron structures in the systems are the basic units of particle diffusion.The self-diffusion coefficient of Aland O atoms were affected by the triclusters oxygen and high coordination Al.When the basicity CaO/SiO₂=1,the melt viscosity with increasing concentration of Al₂O₃ increases,reaches a maximum when the Al₂O₃=26 mol%.With the further increase of Al₂O₃,the number of Caatoms is relatively insufficient,the triclusters oxygen and Al^V increase significantly,the structure tends to be unstable,the D_Al and D_O increase,and the viscosity decreases.It is considered that the amphotic change of Al₂O₃ depends on the composition of melts.When the basic cations are sufficient,Al₂O₃ is acidic and forms a network structure;when the basic cations are insufficient,some Al₂O₃ is alkaline and providing O atoms and equilibrium charge.The molecular dynamics simulation results of CaO-Al₂O₃-CaF₂ and CaO-Al₂O₃-CaF₂ systems show that,F behaves differently on silicate and aluminate melt structures.In silicate melts,F does not participate in the formation of network structure,and acts as a diluent in the network gap in the form of Ca-F ion cluster.In aluminate melt,F has double effects on the melt structure.On the one hand,F and Caform Ca-F ion cluster as diluent.On the other hand,F and[AlO₄]^5-react to displace O,forming[AlO₃F]^4-tetrahedral,and the released O atom are absorbed by other[AlO₄]^5-structure to form unstable high-coordination Al.The electrically neutral[AlO₃F]^4-and Ca²⁺balance the charge of the Al-O structure makes the Al-O-Alstructure stable.