A study by electrochemical impedance spectroscopy and surface analysis of corrosion product layers formed during CO2 corrosion of low alloy steel

• Published in: Corrosion science Vol. 172; p. 108666
• Main Authors: De Motte, Rehan, Basilico, Edoardo, Mingant, Rémy, Kittel, Jean, Ropital, Francois, Combrade, Pierre, Necib, Sophia, Deydier, Valérie, Crusset, Didier, Marcelin, Sabrina
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.08.2020; Elsevier BV; Elsevier
• Subjects: Carbon dioxide; Carbon steel; Chemical Sciences; CO2 corrosion; Corrosion; Corrosion prevention; Corrosion products; Diffusion barriers; Diffusion layers; Electrochemical impedance spectroscopy; Electrochemical impedance spectroscopy analysis; High temperature; Iron carbonate; Iron oxides; Low alloy steels; Magnetite; Material chemistry; Open circuit voltage; Porosity; Pseudo-Passivation; Surface analysis (chemical); A; Rct; Pseudo-Passivation; Zd; Cdl; VRMS; LPR; Rd; Re; Rsolution; Magnetite; Qdl; EDX; MF; ε0; EEC; GIXRD; d; pCO2; Di; Cfilm; Iron carbonate; i; l; Wd; EIS; Sa; CO2 corrosion; STEM; Qfilm; α; δf; t; ε; Electrochemical impedance spectroscopy analysis; CPE; LF; SEM; Carbon steel; Rpore; OCP; Ki; HF; ξ; pseudo-passivation; magnetite; iron carbonate; electrochemical impedance spectroscopy analysis; carbon steel
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2020.108666

•Evolution of the corrosion product layer was studied with EIS.•Initially the surface behaves as a plain corroding electrode gradually blocked by scales.•OCP rise characteristic of “pseudo-passivation” is concomitant with diffusion limitation.•High frequency time constant associated with the corrosion product film. In the following research, electrochemical and surface analysis techniques are used to define the main contributing factor to the protectiveness offered by a scale formed at high temperature and pH under CO2 saturated conditions. At 80 °C and pH 6.6, trace amounts of a magnetite (Fe3O4) phase was identified at certain locations beneath a more dominant iron carbonate (FeCO3) film. Furthermore, over time, the evolution of the corrosion product layer towards a very low porosity results in a “diffusion barrier” that is indicated by a positive shift in the open circuit potential and is considered key to corrosion protection.