Anti-corrosion protection of carbon steel by expired Anaprilin in acidic media

Environmentally friendly corrosion inhibitors, also known as "green" inhibitors, have been used for the past decade in corrosion inhibition experiments. Scientific research is actively conducted on the use of expired medicines as "green" corrosion inhibitors of metals and alloys. In this work, the inhibitory effect of the expired drug Anaprilin against corrosion of carbon steel St3 in 1.0 N solutions of hydrochloric and sulfuric acids was studied. The concentration of the drug varied within 20-80 mg/L. The research was carried out using the methods of gravimetry, potentiodynamic polarization, impedance spectroscopy, and electrochemical diffusion techniques. Gravimetric corrosion tests conducted at room temperature and 80degree celsius showed the protective effectiveness of the drug, reaching 90% in sulfuric acid solution at the highest concentration under study. The analysis of polarization curves in the media studied showed that Anaprilin slows down the anodic process. A decrease in the double layer capacitance upon the introduction of the inhibitor into the media under study indicates the adsorption of its molecules on the metal surface. The impedance spectroscopy data made it possible to determine the adsorption isotherms and calculate the free adsorption energy of Anaprilin.