3D Modelling of steel corrosion in alkaline chloride solutions: Thermodynamic-kinetic analysis of HFeO2-speciation

Corrosion of steel in alkaline media, with the presence of chloride, causes a very complex electrochemical behaviour. This phenomenon is governed by the speciation of iron during corrosion evolution, the formation of passive film, the formation of salt film, and chloride-induced breakdown. This study develops a thermodynamic–kinetic three-dimensional geometric model for the ferrite ion HFeO2−, a key species in alkaline conditions, and evaluates its influence on steel corrosion at pH 8, 10, and 12 in chloride‐containing solutions. The model integrates equilibrium speciation through hydrolysis and oxidation equilibria, Pourbaix diagram data for Fe-H2O systems, the dynamic concentrations of ionic species, and their kinetics into and out of a corroding pit. The results show that at pH 8, HFeO2− concentration is negligible, and steel remains prone to active dissolution intensified by the presence of chloride. Partial stabilization of HFeO2− occurs at pH 10, enhancing passivity, even though chloride ions significantly reduce film stability. At pH 12, HFeO2− is thermodynamically stable, supporting the development of a strong passive layer. These findings are aligned with published pitting models in alkaline environments and highlight the central role of HFeO2− in mediating steel durability under alkaline-chloride conditions.