Glass Corrosion

Glasses often corrode when they are exposed for prolonged times to moisture e.g. due to weather. Additionally, many compounds can affect the corrosion under such humid conditions either as its cause or as an accelerator.These amaging compounds can originate from the ambient air like Sulfur- and Nitrogen-containing compounds. Other examples are alkalis, that are leached out from concrete, or residues, that are sweated out from kits. Corrosion can be often recognised by a haze or by iridescent opalescent layers on the glass.
A valuable method for the chemical characterisation of corroded glasses is Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The ToF-SIMS depth profile on a glass with a matt haze shows the typical changes caused by glass corrosion (lower depth profile). When compared to a non-damaged glass (upper depth profile) it is clear that there is a loss of Na and K in the region close to the surface that is accompanied by an increased water concentration. Na ions in the glass are replaced by hydrogen ions. The structure of the glass built by Si, Na and O is disturbed which causes microscopically thin roughening of the surface. This leads to a change in the optical appearance of the glass. Because of its high sensitivity, ToF-SIMS is able to discriminate between glass corrosion and other changes to the surface, such as surface depositions on top of the glass.