Session: RIP: Predictive Modeling and Characterization of Corrosion Processes in Complex Environments (In Honor of Professor Digby Macdonald) (Part I of IV)
Developing A Mechanistic Model to Study Iron Anodic Dissolution in 0.5 M NaCl, with/without CO2 (RIP2026-00007)
Indian Institute of Technology-Madras, Chennai 600036, India, Institute for Corrosion and Multiphase Technology (ICMT), Ohio University, Ohio University, Ohio University
Mild steel corrosion in aqueous CO2 solutions is critically important in the oil and gas industry. The anodic dissolution of iron in strong acidic solution proceeds via multistep pathways involving adsorbed intermediates, typically described by the catalytic and consecutive mechanisms. Polarization measurements show that chloride ions suppress anodic current density, and electrochemical impedance spectroscopy (EIS) reveals an intermediate relaxation process associated with chloride participation. The effect of chloride is more pronounced in CO2-saturated solutions, suggesting that dissolved CO2 stabilizes chloride-containing intermediates and alters anodic kinetics. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) further confirms the formation of chloride-containing intermediates during polarization. To mechanistically describe these observations, a comprehensive model was developed that integrates both catalytic and consecutive dissolution mechanisms with an additional reaction pathway involving chloride ions. The model was optimized using potentiodynamic polarization (PDP) and EIS data obtained in 0.5 M NaCl solutions with and without CO2, demonstrating excellent agreement with experimental results. Extracted kinetic parameters provide quantitative insights into the effects of CO2 and chloride ions on iron dissolution. Furthermore, the steady-state surface coverages of reaction intermediates, derived from the optimized parameters across the studied potential range, provide deeper insight into the surface processes governing iron dissolution.
