Investigation of metal-solution interface during iron carbonate formation in aqueous CO2 environment using quartz crystal microbalance

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The present study uses a quartz crystal microbalance (QCM) to investigate the formation of iron carbonate ( FeC O 3 ) in C O 2 -saturated brines. While frequency changes ( Δ f ) measured using QCM have been traditionally used to quantify FeC O 3 precipitation kinetics, the associated changes in motional resistance ( R ) are often overlooked. Here, both frequency change and motional resistance change are analyzed simultaneously to gain deeper insight into interfacial changes during the substrate corrosion and subsequent layer formation, including intermediate steps such as ion accumulation, surface dissolution, and precipitation. Experiments were conducted using quartz crystal resonators (QCR) coated with either inert gold or actively corroding iron, across varying conditions. Increase in motional resistance was observed during FeC O 3 layer formation on both substrates, with noticeable differences in the early-stage behavior. Transient features in Δ R appeared only in select cases and are attributed to surface-specific processes like active corrosion and local ion buildup near the QCR surface. These findings offer new perspectives on interpreting QCM data in corrosion environments and motivate the analysis of motional resistance response in future work, as it provides a useful window into the interplay between corrosion and corrosion product layer formation. • Validated the application of the Sauerbrey’s equation for FeC O 3 formation. • Illustrated the use of motional resistance response from QCM to distinctly resolve FeC O 3 formation dynamics for iron substrate versus gold substrate. • Proposed schematics for the evolution of near surface solution due to corrosion and FeC O 3 formation.

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