Study On Cracking Behavior Of Silicate Glass

Silicate glass has been widely used because of its high transparency and chemical resistance.However,the brittleness and low strength of glass limit its application,so it is of great significance to study the cracking behavior of glass and how to improve the cracking resistance of glass.In thisthesis,silicate glass as the research object,through the glass component design,a small amount of P₂O₅ instead of SiO₂,heat treatment system and SiO₂ content on the structure and mechanical properties of silicate glass.The research results are as follows:（1）In silicate glass composition,a small amount of SiO₂ was replaced by the P₂O₅,glass in the process of cooling liquid will spontaneously occur the phenomenon of phase separation,and the process will have a small amount of crystal precipitation,however,since the crystallization degree is not high,this is because the rich silicon phase matrix,as a result of crystal is difficult to further grow up high viscosity,So you can still maintain a high degree of transparency.The structure characterization of the glass shows that the polymerization degree of the silicon-rich phase in the glass is higher,which increases the average network stiffness,but reduces the atomic packing density.That is,the network structure of the phosphosilicate glass is more open and rigid than that of the glass without P₂O₅.Therefore,although the elastic modulus and Vickers hardness are slightly decreased,the cracking resistance is greatly improved.Controlled phase separation at the nanometer scale can improve the crack resistance of oxide glass without seriously affecting the transparency of the glass.（2）The liquid-liquid phase separation and crystallization behavior of phosphosilicate glasses were investigated by heat treatment at 650℃and 750℃.It is found that Na₃PO₄ crystals tend to form in phosphate-rich droplets,and this process is independent of heat treatment temperature and time.Meanwhile,phosphate-rich droplets belong to the flexible region,so the diffusion rate of ions is higher.When the glass is heat treated at 650℃,the lower scale phase separation in the glass does not affect the high transparency of the sample.When the temperature is raised to 750℃,the size of the second phase grows further,which will obviously affect the transparency of the glass.On the other hand,we also study the subcritical crack propagation behavior of heat-treated glass after cracking.In the process of heat treatment,with the evolution of droplet,the increase of compressive stress in matrix is the main reason for the improvement of crack propagation ability.（3）The hardness and cracking resistance of glass were studied by Vickers indentation test,the changes of glass structure were investigated by infrared and Raman spectroscopy,and the influence of SiO₂ content and load on mechanical properties of glass and the changes of deformation and fracture mechanism were analyzed.In indentation experiments,there are two different processes of glass resistance to deformation:plastic（or shear flow）and densification.Plastic flow is a volume-conserved displacement of the material,while densification causes the material to compress into a tighter structure,which creates hemispherical regions of increased density beneath the indentation.The results show that:With the increase of SiO₂ content,the atomic packing coefficient of glass decreases,while the molar volume increases,the elastic modulus of glass decreases,and the hardness of glass decreases from 7.22 GPa to 6.83 GPa（the load is 100 gf）.However,the fracture toughness of glass increases,and the cracking resistance becomes stronger.The CR value increases from 190 gf to 330 gf.With the increase of SiO₂ content,the indentation opposite edge recovery rate increases after annealing,indicating that the proportion of densification in the indentation process increases,which reduces the residual stress and improves the crack resistance of glass.