Tracking down corrosion mechanisms
Corrosion is the reaction of a material with its environment. Corrosive processes result in measurable changes in the material and often lead to functional impairment of entire components. Typical corrosion processes are the rusting of iron, the tarnishing of silver or the embrittlement of steel by hydrogen uptake. Analytical methods provide important information about the state of a corrosion process. The data often leads to the implementation of meaningful steps to avoid future corrosion events.
Tracking down a common corrosion mechanism
Glasses that are exposed to moisture for a long time, for example due to weathering, can corrode. Progressive glass corrosion can manifest itself as a white veil or as iridescent films on the glass. Many substances, acting in a moist environment on the glass, are viable candidates for the cause or acceleration of glass corrosion. Examples are pollutants from the air such as sulfur and nitrogen compounds, alkaline substances from concrete washes or residues that have flushed out from sealants.
A ToF-SIMS depth profiling analysis of a glass with a matt veil reveals the typical changes caused by glass corrosion (lower depth profile). In comparison to the undamaged glass (upper depth profile), a loss of Na and K in the near-surface region becomes apparent, which is accompanied by an increased concentration of water molecules. Na ions in the glass are replaced by hydrogen ions. The bonding structure of Si, Na and O is destroyed which leads to microscopic surface roughening. As a result, the visual appearance of the glass surface is changed. Due to the high element sensitivity of the ToF-SIMS depth profiling, the glass corrosion can easily be distinguished from other surface changes, e.g. deposits on the glass.