Walnut leaf extract as a green corrosion inhibitor for carbon steel in NaCl solution across temperatures from ambient to 70 °C

This study investigates the corrosion inhibition performance of walnut leaf extract (WLE) on carbon steel in a 3.5% NaCl solution using weight loss measurements, electrochemical techniques (PDP and EIS), and surface characterization (SEM-EDXA, and FTIR). Weight loss experiments demonstrated significant corrosion protection, with the highest efficiency of 98.53% observed at 5% inhibitor concentration from weight loss. Electrochemical studies revealed mixed-type inhibition behavior, with a maximum efficiency of 86.39% from EIS, with predominant anodic suppression, as evidenced by Tafel polarization and increased charge transfer resistance ( R ct ) in EIS. The inhibitor exhibited optimal performance at 5% concentration, beyond which inhibition efficiency decreased due to possible molecular aggregation and non-uniform adsorption, reducing the availability of active sites. Temperature studies indicated reduced effectiveness at elevated temperatures, suggesting physisorption as the primary mode of adsorption. Surface analysis confirmed the formation of a protective inhibitor film, preventing chloride-induced corrosion. The findings highlight WLE as an effective, eco-friendly corrosion inhibitor, with concentration and temperature playing critical roles in its performance.