Experimental and theoretical study on corrosion inhibition of pyridinium salts derivatives for API 5L Gr.B steel in acidic media

In this work, we studied the corrosion protection efficiency of three pyridinium salts on steel (API 5L Gr.B) in 0.5 M H2SO4 solution. Gravimetric and electrochemical methods were employed. We conducted investigations at various concentrations of the studied inhibitors and experiment temperature. The morphological of the steel surface was accomplished using scanning electron microscopy. Weight loss shows that an increase in the concentration of inhibitors A and C does not have any notable influence on the inhibition efficiency from 0.5 mM. However, the inhibition efficiency increases significantly with the increase of inhibitor B concentration. The values of (IE%) determined from EIS for these inhibitors follow the order: A ≈ C > B and the most excellent inhibition efficiencies are 97.88%, 86.96%, and 97.65%, respectively at 5 mM and all studied inhibitors are mixed-type inhibitors. In addition, the adsorption of the inhibitor molecules on the steel surface is reliable on the Langmuir adsorption isotherm model and the adsorption mechanism occurs through the combination of three aspects of interactions (physisorption, chemisorptions and retro-donation). IE% values of A, B and C inhibitors determined from EIS increase very slightly with temperature increase; the protective properties are excellent even at 55 °C (98.37% for A, 92.18% for B and 98.78% for C). This investigation is completed by a theoretical calculation of some quantum chemical parameters using the Gaussian09 program. The order of IE determined from experimental measurements is successfully supported by surfaces analysis and the obtained results confirmed an excellent concordance between potentiodynamic polarization, weight loss, EIS and theoretical study.