In situ spatiotemporal solute imaging of metal corrosion on the example of magnesium

Visualization and quantification of corrosion processes is essential in materials research. Here we present a new approach for 2D spatiotemporal imaging of metal corrosion dynamics in situ. The approach combines time-integrated Mg²⁺ flux imaging by diffusive gradients in thin films laser ablation inductively coupled plasma mass spectrometry (DGT LA-ICP-MS) and near real-time pH imaging by planar optodes. The parallel assessment of Mg²⁺ flux and pH distributions on a fine-structured, bare Mg alloy (b-WE43) showed intense Mg dissolution with Mg²⁺ flux maxima up to 11.9 ng cm^-2 s^-1 and pH increase >9 during initial corrosion (≤15 min) in aqueous NaNO₃ solution (c = 0.01 mol L^-1). The techniques visualized the lower initial corrosion rate in buffered synthetic body fluid (Hank's balanced salt solution; pH 7.6) compared to unbuffered NaNO₃ (pH 6.0), but precise localization of Mg corrosion remains challenging under these conditions. To further demonstrate the capability of DGT LA-ICP-MS for spatiotemporal metal flux imaging at the microscale, a coated Mg alloy (c-WE43) with lower reactivity was deployed for ≤120 min. The high spatial resolution (∼10 μm × 80 μm) and low limits of detection (≤0.04 ng cm^-2 s^-1, t = 60 min) enabled accurate in situ localization and quantification (U_rel = 20%, k = 2) of distinct Mg²⁺ flux increase, showing micro-confined release of Mg²⁺ from surface coating defects on c-WE43 samples. The presented approach can be extended to other metal species and applied to other materials to better understand corrosion processes and improve material design in technological engineering.