Quantum Chemical and Electrochemical Evaluation of Isoperthiocyanic Acid Derivatives as Novel Corrosion Inhibitors of Mild Steel in 2 M Hydrochloric Acid

The present paper deals with the analysis of corrosion inhibition effects of four isoperthiocyanic acid (IPA) derivatives, namely, N-(3-thioxo-3H-1,2,4-dithiazol-5-yl) thiophene-2-carboxamide, 4-(3-thioxo-3H-1,2,4-dithiazol-5-yl) benzene-1,4-dicarboxamide, N-[(3-thioxo-3H-1 2,4-dithiazol-5-yl) cyclohexane carboxamide, and N-(3-thioxo-3H-1,2,4-dithiazol-5-yl) acetamide on the anti-corrosion behaviour of mild steel in 2 M solution of HCl by quantum chemical and electrochemical methods. Electrochemical impedance spectroscopy, the Tafel polarization, and weight loss methods were employed to obtain experimental data. The computational studies as well as the experimental results showed that TRIPA exhibits the maximum inhibition efficiency of 95.12% due to the presence of heteroatoms and aromaticity of the compound. That IPA inhibitor retarded the adsorption through physisorption and concurred with the Langmuir adsorption isotherm model. Temperature studies were carried out to assess the effectiveness of the IPA derivatives on mild steel within the range of 303 to 343 K. The thermodynamic parameters clearly indicate that the inhibition process is spontaneous, and the studied inhibitors predominantly act as mixed type inhibitors with anodic dominance. Scanning electron microscopy revealed the retention of the mild steel polished surface corrosion in the presence of an inhibitor. Thus, four novel IPA derivatives at a very low concentration were found to be potent inhibitors.