This research introduces a novel ultrasonic technique for in situ, 3D monitoring of corrosion substrate morphologies. The technique boasts customizable lateral resolution, ultra-high axial resolution (100 nm), and validated measurement accuracy. Experiments on carbon steel in alkaline environments revealed that iron dissolution initially accelerates, then slows, due to corrosion product deposition (Fe3O4) consuming electrons. The corrosion product layer eventually collapses, halting Fe3O4 formation.
