Unlocking the Potential of Cinnamaldehyde: A Comprehensive Study on Its Dual Role as an Effective Inhibitor Against Corrosion and Microbial Corrosion of Mild Steel in Saline Environments

In this investigation, the application of cinnamaldehyde (CIN) on carbon steel under aggressive saline conditions (3.5% w/w NaCl solution) at ambient temperature and pressure led to a substantial reduction in both microbial and electrochemical corrosion. CIN exhibited notable corrosion-inhibitory properties, with increased effectiveness at lower concentrations. While it demonstrated the highest efficiency in mitigating corrosion, its impact on microbial corrosion, specifically planktonic and sessile bacteria, showed a more moderate effect. The study underscores CIN's ability to effectively reduce carbon steel corrosion in a 3.5% w/w NaCl medium. Carbon steel specimens exposed to the NaCl medium, with and without inhibitors, underwent various tests, including assessments of open circuit potential, potentiodynamic polarization reactions, electrochemical impedance spectroscopy, and post-experiment surface characterization, supported by quantum chemical calculations. The optimal concentration for CIN was identified as 50 ppm, achieving an impressive inhibition capacity of 89.68%. The inhibition mechanism primarily involved the adsorption of CIN onto the metal surface. The findings indicated a strong affinity between CIN and the metal surface, favoring physical adsorption over chemical adsorption, correlating with a modest increase in inhibition efficiency. Notably, the open circuit potential shifted towards a positive potential, and polarization calculations indicated a reduction in both cathodic and anodic current densities, indicating the inhibitory effect. The measured inhibition efficiency, evaluated through potentiodynamic polarization and impedance spectroscopy, aligned with existing literature. Scanning electron microscopy provided visual evidence of an adsorbed protective layer of the inhibitor on the metal surface. Quantum chemical parameters were computed, supporting the conclusion that the inhibition of carbon steel by CIN, along with thiourea and sodium lauryl sulfate, operates through a chemical adsorption process.