Research On Composition, Structure And Properties Of High Strength Float Glass Of Na₂O-CaO-Al₂O₃-SiO₂System

With the development of modern high-rise building, automobile, informationand optoelectronic industry, the high-performance flat glass are applied widely.However, as the chemical stability, mechanical and thermal property of traditionalsoda-lime-silicate flat glasses is not good enough, this greatly limits its application forthe window, windscreen and substrate glass. Therefore, the research and developmentof a new float glass with higher physicochemical property is essential for thecommercial flat glass. Al2O3can improve many physicochemical properties oftraditional soda-lime-silicate flat glass, such as thermal stability, chemical durabilityand mechanical properties. But there is some problems in the melting and formingprocess of this glass with high aluminum content, such as high melting temperature,larger viscosity, glass refining for a longer time, many cords and striae. The key ofdeveloping a new float glass with high aluminum content is to solve these aboveprocess problems, so the research of glass melt properties is very important.Based on the composition of traditional soda-lime-silicate flat glass, the aim ofthis work is to enhance the physicochemical properties of glassy products byincreasing the Al2O3/SiO2ratio and B2O3/Na2O ratio. The structure, viscosity,workability, thermal expansion, bending strength, chemical durability andweatherabiliy of glass were investigated by FT-IR, Raman spectroscopy, rotatingcrucible viscometer, horizontal dual-rod dilatometer, ICP-AES, optiacal andelectronic microscopy. Besides, the mechanism of ion-exchange chemical reinforcingthis system glass was investigated by EPMA and stress analyzer. The results showthat:When SiO2was substituted by Al2O3, increasing Al/Si ratio,[AlO4] tetrahedronforming into the glass network caused to variation of structure species Qn, decreasingof NBO and increasing glass network connectivity; the viscosity of glass increasingcaused all characteristic temperature increased; as the influence degree ofcomposition on glass viscosity increasing gradually with cooling, workability andkinetic fragility index were shortened and increased respectively; thermal expansioncoefficient of glass decreased slightly; bending strength, density, chemical durabilityand weatherability of glass got a certain amount of improvement. When Na2O was substituted by B2O3, increasing B/Na ratio,[BO3] triangle and[BO4] tetrahedron forming into the glass network caused to increasing of BO numberand glass network polymerization; transition temperature (Tg) and thermal expansiontemperature (Td) both increased, but all other characteristic temperatures above Tddecreased firstly and then increased, resulting in workability and kinetic fragilityindex got a minimum and maximum respectively around R=(Na2O-Al2O3)/B2O3=1;thermal expansion coefficient of glass decreased sharply; chemical durability andweatherability of glass were enhanced effectively.This work used the ion-exchange chemical reinforce process to enhance themechanical property of glass. The influencing factors of ion-exchange come from theion concentration gradient and the glass structure compactness. The influencingfactors on glass surface stress after ion-exchange mainly originate from two aspects:the “stuffing” effect and the stress relaxation. The strengthening comes from the buildup of a residual compressive stress state, up to a certain depth on the glass surfaceexceeded the depth of microcrack and the mechanical strength increase with theresidual compressive stress increasing.