Corrosion mitigation of mild steel in 1 M HCl acid using an expired drug: An experimental approach.

[Display omitted] • The effectiveness of Phenobarbitone (5-Ethyl-5-phenyl-1,3-diazinane-2,4,6-trione), for mitigating the deterioration of mild steel (MS) in 1 M HCl by using an expired drug. • Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) studies were performed to measure the -efficiency and to explain the adsorption isotherm. • To analyze thermodynamic and kinetic parameters at higher temperatures. • Surface morphology studies were conducted using scanning electron microscopy (SEM), electron-dispersive X-ray (EDAX), atomic force microscopy (AFM) techniques and contact angle measurements (CA). The research undertaken highlights the effectiveness of pharmaceutical drug Phenobarbitone (5-Ethyl-5-phenyl-1,3-diazinane-2,4,6-trione) (PB) as inhibitor to mitigate corrosion of mild steel (MS) in 1 M HCl. Corrosion studies were done by electrochemical techniques including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in the absence and presence of the Phenobarbitone (PB) drug. Kinetic parameters were calculated by studying the corrosion rate at different temperatures. Results were fitted into suitable adsorption isotherm and from the adsorption data thermodynamic parameters were computed and discussed in detail. Surface morphology studies were conducted using scanning electron microscopy (SEM), electron-dispersive X-ray (EDAX), and atomic force microscopy (AFM) techniques. The nature of the protective layer formed over the metal was studied by measuring the contact angle (CA), which demonstrated the formation of the adsorbed inhibitor layer. Inhibition efficiency increased with increase in concentration of inhibitor and with increase in temperature. For the addition of 0.04 gL-1, the maximum corrosion inhibition efficiency of 78.3 % was achieved at 313 K. Inhibitor acted as a mixed inhibitor with more control over the anodic reaction. Increase in efficiency with increase in temperature suggested the possibility of chemical adsorption. Inhibitor obeyed Langmuir adsorption isotherm, supporting chemical adsorption. Surface morphology clearly demonstrated the formation of barrier film on the surface of metal which prevented further dissolution of metal thereby decreasing the corrosion rate. [ABSTRACT FROM AUTHOR]