In situ pH responsive fluorescent probing of localized iron corrosion

•Fluorescence imaging based corrosion detection method was developed.•Time and spatial resolutions of 125 ms and <1 μm respectively were achieved.•Incipient corrosion pits on iron surfaces in salt solutions were observed.•Corrosion pits preferentially forms along surface features such as scratches.

A fast and versatile method has been demonstrated to detect the early stage of iron corrosion in situ, with minimum external perturbation, by using a pH sensitive fluorescence dye. The decreasing fluorescence intensity inside corrosion pits induced by hydrogen ions produced during iron corrosion is used as a signal indicator. Identification of corrosion pits (with resolution of <1 μm) and quantification of corrosion rate based on local hydrogen concentration were achieved. The developed technique has been applied to show that surface roughness, under a constant current condition, influences the corrosion of iron. Corrosion occurs preferentially adjacent to local topographic features.