Operando Surface Optical Reflectance Microscopy Study of Corrosion Film Growth on a Ni-Cr-Mo Alloy During Anodic Polarization

The solid-liquid interface, where corrosion reactions occur, is notoriously difficult to study in operando conditions. Few experimental techniques can provide surface sensitivity and spatial and temporal resolution and are compatible with liquid environments. 2-Dimensional surface optical reflectance (2D-SOR) is an emerging optical technique providing microscopic information with high temporal resolution. It complements methods such as ambient pressure X-ray photoelectron spectroscopy or inductively coupled plasma-mass spectrometry, which provides valuable chemical information from the surface and the dissolving species but lacks spatial resolution. Here, we show how 2D-SOR can be used to measure the formation and growth of corrosion products in operando through oscillations in the reflected signal caused by constructive and destructive interference of the light in the film of growing corrosion products. The total thickness of the corrosion product film obtained with 2D-SOR agrees well with that measured using scanning electron microscopy ex situ. 2D-SOR has proved to be an excellent and valuable tool for monitoring the corrosion process with spatial resolution in operating conditions.