Expired Actifed Drug as Corrosion Inhibitor for Low-Carbon Steel in Phosphoric Acid: Experimental and Theoretical Investigation

Corrosion remains a significant challenge for industrial infrastructure and equipment made from low-carbon steel, especially in acidic environments. Inhibitors have proven effective in mitigating corrosion, and expired pharmaceuticals offer an innovative class of potential solutions. This study explores using expired Actifed (ACD) as a sustained corrosion inhibitor for low-carbon steel in a 0.5 M H₃PO₄ solution. Both experimental and theoretical approaches were employed to assess the inhibitor's efficiency. Experimental techniques included PotentioDynamic Polarization (PDP), Scanning Electron Microscopy (SEM), Fourier Transform InfraRed (FT-IR) spectroscopy, and microbiological tests. Theoretical evaluations utilized quantum chemical calculations to investigate how ACD interacts with the steel surface. The findings indicated that ACD significantly decreases the corrosion rate, resulting in an inhibition efficiency of 73.5% under the conditions (concentration of 60 mL/L and a temperature of 303 K). It was observed that ACD forms protective layers on the steel, providing mixed protection for both anodic and cathodic sites. The outcomes from FT-IR, SEM, and theoretical studies corroborate the electrochemical findings, confirming the effectiveness of Actifed as an inhibitor under the selected conditions.