Passive, non-destructive chemical imaging using diffusive gradients in thin films (DGT) in combination with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has become an important tool to visualize and quantify chemical processes occurring at reactive interfaces in situ. While the increasing application of DGT LA-ICP-MS in environmental science substantially improved our knowledge of e.g. biogeochemical cycles in nature, its recent application in materials science opened the door to study metal corrosion processes at unprecedented spatiotemporal resolution.

In this study, we develop and apply DGT LA-ICP-MS for in situ tracking of pitting corrosion, a highly localised form of corrosion that initiates the formation of cavities in the metal, which is difficult to detect due to the small size of early pits. The 7075 aluminium (Al) alloy (AA7075), containing Zn (w = 5.6-6.1 %), Mg (w = 2.1-2.5 %), and Cu (w = 1.2-1.6 %), is used as sample material that is being widely applied in aircraft structural parts where susceptibility to pitting corrosion is critical because pits can act as starters for fatigue cracks. Advanced polyacrylamide-based DGT binding gels with a highly homogeneous distribution of Chelex (iminodiacetate) only, or both Chelex and Metsorb (TiO2) binding phases are evaluated and applied for the simultaneous and quantitative sampling of corrosion products of Al, Mg, Zn, and Cu. The novel approach is combined with optical microscopy to obtain detailed information on surface structural changes during AA7075 corrosion.

Preliminary results of this study show that the application of DGT LA-ICP-MS using Chelex gels enables accurate in situ visualization of corrosion reactions on AA7075 exposed to NaCl solution (w = 1.5 %) at pH 4.5 and room temperature with different exposure times. Precise localisation of pitting corrosion remains, however, challenging due to the creation of occluded spaces with stagnant solution flow by the current DGT gel deployment setup, inducing less localised crevice corrosion. First results of the development of a novel experimental DGT setup allowing for non-invasive mapping of pitting events will be presented.