Investigating the Influence of Phosphoric Acid Concentration on the Performance of Gallic Acid-Based Rust Converters

Corrosion mitigation remains a critical challenge in industrial applications, with rust converters offering a promising and cost-effective alternative to conventional surface preparation methods. This study systematically investigates the effect of phosphoric acid concentration (۱, ۳, and ۵ wt%) on a Gallic acid-based rust converter applied to ST۱۲ steel coupons carrying adherent rust layers. Electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), and adhesion strength tests were conducted to evaluate corrosion resistance, phase composition, and coating adherence. The inclusion of ۵ wt% phosphoric acid significantly enhanced rust conversion efficiency, forming stable iron phosphate (FePO۴) and ferric gallate complexes with improved durability. This optimized formulation improved corrosion resistance by nearly five orders of magnitude compared to untreated surfaces and showed superior adhesion, characterized by cohesive failure rather than delamination. Overall, these findings highlight the potential of Gallic acid-phosphoric acid systems as highly effective rust converters for industrial use, offering improved barrier properties, enhanced long-term protection, and reduced reactive rust phases.

کلیدواژه ها:

Rust Converter ، Gallic Acid ، Phosphoric Acid ، Corrosion Resistance ، Adhesion Strength