Micromechanical properties of (Na,Zn)-sulfophosphate glasses

Elastic constants, hardness and crack initiation resistance of sulfur-bearing sodium-zinc-phosphate glasses were determined by ultrasonic echography and Vickers indentation experiments. Incorporation of up to 35 mol% of sulfur into the glass structure resulted in a decrease in molar volume of 23% and an increase of Poisson's ratio up to a value of ~ 0.32. Resistance against permanent deformation and cracking decreased with compaction of the glass structure, i.e. a more brittle character of softer sulfophosphate glasses was observed when tested under normal atmosphere. Under flowing N2 gas only a weak compositional dependence of the crack-to-indent size ratio was evident, which indicates that surface reactions dominate micromechanical crack initiation in sulfophosphate glasses.

► Compactness of the sodium-zinc-sulfophosphate glass structure is leading to a high Poisson's ratio of up to ≈ 0.32. ► Increasingly ionic bonded sulfophosphate glasses are exhibiting a more brittle response to sharp contact loading in normal atmosphere. ► Micromechanical crack initiation in sulfophosphate glasses is governed by surface reactions.