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 (similar to 10 mu m x 80 mu m) 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.

Automated summary

Visualization and quantification of corrosion processes are crucial for materials research. This paper presents a new approach for 2D spatiotemporal imaging of metal corrosion dynamics. By combining different techniques, the corrosion processes of magnesium alloys were evaluated, and accurate localization and quantification of metal flux were achieved at the microscale.