Local scaling of CaCO3 on carbon steel surface with different corrosion types

CaCO3 scaling on metal is closely related to its electrochemical corrosion. However, little attention has been paid to the influences of interfacial corrosion on scaling behavior. In this work, the local deposition behavior of CaCO3 on carbon steel with different corrosion types was investigated. Results reveal that the interfacial distribution of anodically released Fe2+ plays important roles in CaCO3 polymorph. For general corrosion, anodically released Fe2+ easily diffuses to all micro cathodic regions and suppresses pH increase by preferentially consuming cathodically produced OH– and interfacial O2, and its incomplete hydrolysis. This lowers CaCO3 nucleation driving force and favors aragonite deposition. In contrast, localized corrosion results in an uneven distribution of Fe2+ at carbon steel/water interface. Aragonite tends to deposit in the micro cathodic regions where Fe2+ ions easily arrive from the adjacent anodic sites, while this effect diminishes in the cathodic regions where fewer Fe2+ ions arrive.