Study On The Effect Of Oxide Doping On The Structure And Properties Of Alkali-free Aluminoborosilicate Glass System Based On Molecular Dynamics Simulation

Alkali-free aluminoborosilicate glass is widely used as electronic glass fiber?E-glass fiber?and thin film transistor liquid crystal display?TFT-LCD?glass substrate because of its excellent dielectric properties,low thermal expansion coefficient,good chemical corrosion resistance and high strain point.However,at present,there are some shortcomings in the industrial production of alkali-free aluminoborosilicate glass and glass fiber,such as high melting temperature,high melt viscosity,difficult molding and low qualified rate of products,which seriously affect the development of informatization in our country.Therefore,it is of great significance to explore the relationship between composition,structure and properties of alkali-free aluminoborosilicate glass,so as to prepare glass/glass fiber materials with excellent properties.In view of the above problems,this paper discusses the effects of different oxide doping on the structure and properties of alkali-free aluminum borosilicate glass from two aspects of experiment and molecular dynamics simulation.Compared with the traditional experimental techniques,molecular dynamics simulation can better characterize the changes of glass structure on the atomic scale.The reliability of the results of molecular dynamics simulation is verified by comparing the glass properties obtained by molecular dynamics simulation with those measured by experiments?including the density,the glass transition temperature?Tg?,the thermal expansion coefficient,the viscosity and the mechanical properties of the glass,etc.?.The microstructure characteristics of the glass?including the radial distribution function of the ions in the glass,the bond length and bond angle distribution between the ions,the coordination number of the network formers and network modifiers,the bridge oxygen content in the glass,the distribution of Qn and the degree of network polymerization of the glass,etc.?are provided by molecular dynamics simulation results.This paper is divided into three parts,and the effects of Al/Si ratio,B/Si ratio and Ca/Mg ratio on the structure and properties of alkali-free aluminum borosilicate glass are discussed respectively.The results show that:?1?On the premise of keeping a certain content of alkaline earth metals in the glass,changing the Al/Si ratio in the glass results in the change of the structure and properties of the glass.When?RO-Al₂O₃?/B₂O₃?1,the bridge oxygen content in the glass increases from 76.5%to 82.54%with the increase of Al/Si ratio from 0 to 1/3,and the network polymerization degree of the glass increases,resulting in the increase of the Tg of the glass from 665?to 718?,the viscosity of the glass increases,the Young's modulus of the glass increases from 84GPa to89GPa,and the thermal expansion coefficient of the glass decreases from 36.2×10^-7/K to 33.1×10^-7/K.With the increase of Al/Si ratio,?RO-Al₂O₃?/B₂O₃<1 in the glass,the content of[AlO₅]and[AlO₆]in the glass increased,the content of[BO₄]tetrahedron decreased,the content of[BO₃]triangle increased,the bridge oxygen content in the glass decreased from 82.54%to65.12%,the degree of network polymerization of the glass decreased,the glass structure depolymerized,the viscosity of the glass decreased,the Tg decreased from 718?to 672?,and the Young's modulus of the glass decreased from 89GPa to 79GPa.The coefficient of thermal expansion of glass increases from 33.1×10^-7/K to 42.7×10^-7/K.?2?On the premise of keeping a certain content of alkaline earth metals in the glass,changing the B/Si ratio in the glass will lead to changes in the structure and properties of the glass.With the increase of B/Si ratio from 0 to 0.15,the content of[AlO₄]tetrahedron in glass remained about 92.85%,and the content of[BO₄]tetrahedron increased from 0 to 89.05%.At this time,the bridge oxygen content in the glass reached the maximum value of 80.12%,the degree of polymerization of the glass network increased,the viscosity of the glass increased,and the Young's modulus of the glass increased from 80.8GPa to 82GPa.With the increase of B/Si ratio?0.15-0.8?,the content of[AlO₄]tetrahedron in the glass decreased from 92.85%to83.63%,and the content of[BO₄]tetrahedron decreased from 89.05%to 45.72%.At this time,the bridge oxygen content in the glass decreased from 80.72%to 70.78%,the glass structure depolymerized,the viscosity of the glass decreased sharply,and the Young's modulus of the glass decreased from 82GPa to 72.65GPa.?3?On the premise of keeping a certain content of alkaline earth metals in the glass,changing the Ca/Mg ratio in the glass will lead to changes in the structure and properties of the glass.The simulation results show that even in the case of?RO-Al₂O₃?/B₂O₃>1,the Al³⁺and B³⁺in the glass are not all in a four-coordination state,in which the content of[AlO₄]and[BO₄]tetrahedron are about 90%and 70%respectively.With the continuous decrease of the Ca/Mg ratio,the bridge oxygen content in the glass,the degree of polymerization of the glass network decreased at first and then increased,and had a minimum value at Ca/Mg=1,at which time the bridge oxygen content in the glass was 80.62%.The properties related to the transport properties of glass,that is,the viscosity of glass shows an obvious nonlinear behavior with the decrease of Ca/Mg ratio,and it has a minimum at Ca/Mg=1.This phenomenon in the glass indicates that there is an obvious mixed alkaline earth effect in the glass.The Young's modulus of glass increases from 83.87GPa to 95.65GPa with the decrease of Ca/Mg ratio,that is,the mechanical properties of glass are enhanced with the decrease of Ca/Mg ratio.