Influence of phase separation microstructure on the mechanical properties of transparent modifier-free glasses

In this work, we use heat treatment to vary the size of nanoscale droplets in a phase-separated B2O3-SiO2-Al2O3-P2O5 glass without traditional modifiers and explore the effect of phase separation on the mechanical properties. The melt-quenched version of this glass already exhibits phase separation with a droplet phase rich in B2O3. The glass transition temperature (Tg) of the droplet phase is lower than that of silica-rich glass matrix. Upon heat treatment at a temperature below the Tg of the droplet phase, the size of droplets decreases but the fraction of the droplet phase increases. Consequently, the crack initiation resistance more than doubles. Upon heat treatment at the Tg of the matrix phase, the fracture toughness increases from 0.61 to 0.73 MPa·m0.5, which is primarily due to the aggregation of individual droplets. Upon the different heat treatments, the phase-separated glasses retain their optical transparency, while the hardness increases slightly.