In-situ resistance mapping of surface corrosion of iron using contact-mode carbon fibre as potentiometric tip

Scanning Probe Microscopy (SPM) has recently gained significant attention from both scientists and engineers for its unique capability to investigate localized corrosion phenomena. This paper introduces a novel application of SPM that offers a unique in-situ means to quantitatively evaluate the resistance of a spontaneously formed oxide layer on the conductive surface of an uncoated iron sample. This approach involved rastering a thin carbon fibre on the iron sample immersed on a corrosive medium while maintaining direct contact between the tip of the carbon fibre and the studied surface. Depending on the resistance between the tip and the sample, the measured voltage proportionally varied between 0 and the potential of the potentiometric circuit formed by the iron sample, the electrolyte and the carbon fibre. Through the application of the voltage divider formula, the measured potential map was transformed into a resistance map. This process allowed us to render a visual representation of the resistance distribution across the surface of the iron sample, providing some insights into the properties of the oxide layer.