The relation of surface treatment and sub-surface damage on ZERODUR®

Since many years, SCHOTT has continuously published a broad range of statistical data on bending strength of ZERODUR (R). With this data it is possible to do lifetime calculations utilizing on threshold values for the bending strength of ZERODUR (R) under various given surface treatments and environmental conditions. The bending strength of ZERODUR (R) is mainly a function of the sub-surface damage (SSD) residues after final surface processing. Due to the nature of the bending strength of brittle materials, a surface that is free of sub-surface damage will have a significantly higher strength, compared to a surface with remaining SSD. Glass surfaces free of sub-surface damage need to be actively protected or handled with care to avoid any new defects like scratches that subsequently would reduce the strength of the surface. However, there is no data available that answers the questions: "Is every visible scratch automatically reducing the strength of the surface?", "How easy is it to generate scratches on a ZERODUR (R) surface?". This publication discusses various sub-surface damage measurements on ZERODUR (R) surfaces in relation to their surface treatment, including artificially generated scratches on polished and acid etched surfaces.