Atomic-Scale Insights into the Initiation and Formation of Corrosion in an Aqueous Environment on Iron-Based Surfaces: A Molecular Dynamics Study

The initiation of electrochemical corrosion on steel surfaces begins with water molecule aggregation, though the atomic-scale mechanisms from adsorption and wetting to corrosive microdroplet formation remain unclear. Using molecular dynamics simulations, this work investigates the formation of corrosive aqueous micro-environments on iron-based surfaces during early condensation. It focuses on the regulatory effects of surface roughness and local hydrophilic sites on condensation nucleation, droplet growth, and wetting. Results show a linear correlation between droplet contact angle and solid–liquid interaction energy, with temperature dependence controlled by the substrate’s intrinsic wettability. For fence-type rough surfaces, we clarify the transition from a critical to a mixed (Cassie–Wenzel) wetting state, confirming that roughness enhances intrinsic wettability. Condensation analysis reveals that stronger solid–liquid interaction promotes water adsorption and induces a shift from dropwise to filmwise condensation, with interphase temperature difference driving heat transfer. On hydrophobic surfaces with local hydrophilic sites, these sites serve as preferential nucleation points. Their size effect can pin the three-phase contact line, leading to droplet growth in a high-contact-angle mode. This study offers an atomic-scale view of how condensation creates the initial aqueous environment required for electrochemical corrosion, providing theoretical insight into phase-change heat transfer and interfacial behaviour on complex surfaces. The findings guide the design of surfaces resistant to condensation-induced corrosion.