Unveiling the inhibition mechanism of oleic acid polyethylene glycol ester phosphate for Mg and Mg alloy

Abstract

Compared to single-function inhibitors, the novel multifunctional corrosion inhibitor developed in this study—oleic acid polyethylene glycol ester phosphate (OPP400)—achieves synergistic corrosion inhibition through molecular engineering that integrates multiple active functional segments. Its corrosion inhibition behavior and mechanism on Mg and Mg alloy in 3.5 wt% NaCl solutions were systematically investigated. The corrosion inhibition performance of OPP400 was evaluated using a combination of EIS, PDP, SEM, AFM, and contact angle measurements. The results demonstrate that at the optimal concentration of 100 mg L⁻¹, OPP400 achieves corrosion inhibition efficiencies of 89.07% for pure Mg and 79.55% for Mg alloy. The PDP curves reveal OPP400 to be a mixed-type corrosion inhibitor. EIS reveals a marked increase in charge transfer resistance and a marked decrease in double-layer capacitance, which indicates the formation of a dense adsorbed film on the metal surface. Mott–Schottky analysis further corroborates that OPP400 selectively blocks Cl⁻ ions by reducing the carrier density in the oxide film and enhancing the energy barrier of the passivation film. Surface analysis reveals that OPP400 significantly reduces the surface roughness of the substrate and enhances its hydrophobicity, thereby increasing the water contact angle from 37° to more than 66°. The inhibition mechanism is attributed to the synergistic effects of chemical adsorption, hydrophobic layer formation, and ionic barrier action, which collectively block the penetration of corrosive species (e.g., Cl⁻ and H₃O⁺). This study offers critical theoretical basis and practical guidance for the molecular design of corrosion inhibitors targeting Mg and Mg alloy.