Assessment of Corrosion Product Formation (Iron Oxides and Oxyhydroxides) on Carbon Steel in Saline Media Containing Protic Ionic Liquids by Advanced Structural and Microstructural Characterization.

Résumé

This study investigates protic ionic liquids (PILs) as corrosion inhibitors for carbon steel in a saline environment, focusing on their influence on the formation and stability of corrosion products during exposure. By examining corrosion product evolution under inhibited conditions, this work provides a mechanistic perspective beyond conventional inhibition efficiency, evaluating whether the resulting corrosion layers can act as a protective barrier during prolonged exposure. X-ray diffraction, Mossbauer, and Raman spectroscopy techniques were applied to characterize the surface and corrosion product. Moreover, optical and scanning electron microscopy techniques (SEM-ED and FIB-SEM) were selected to identify the oxides/oxyhydroxides externally. At the same time, X-ray spectrometers with energy dispersion were used to analyze the elemental composition, mainly O, Fe, N, Cl, and Na. Fundamentally, this preliminary investigation seeks to identify corrosion products (iron oxides/oxyhydroxides), including lepidocrocite, magnetite, and goethite, elucidate their formation mechanisms, and contribute a novel perspective to the corrosion inhibitor literature. In particular, the study focuses on the interaction between carbon steel and Protic Ionic Liquids (PILs), exploring their potential influence on the formation and evolution of distinct oxide phases on the material's surface. As a key distinguishing feature, the addition of the corrosion inhibitors PILs (2-HEAF) and (2-HDEAF) revealed the presence of a dense and compact goethite, a phase that can aid in blocking chloride penetration, potentially extending the longevity of carbon steel in saline environments. This observation supports the efficacy of these inhibitors, as previously demonstrated in electrochemical and weight-loss experiments, suggesting their potential for long-term corrosion protection.