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 Poissonʹs 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.