Electrochemical and quantum chemical assessment of two organic compounds from pyridine derivatives as corrosion inhibitors for mild steel in HCl solution under stagnant condition and hydrodynamic flow

• Pyridine-2-thiol, P2T, and 2-Pyridyl disulfide, 2PD, are good inhibitors.
• P2T and 2PD reveal 98% efficiency in 200 mg/L concentration at stagnant condition.
• Langmuir isotherm shows both physisorption and chemisorption types for inhibitors.
• Mild steel corrosion rate decreases with rising rotation speed in blank solution.
• Hydrodynamic flow has a destructive effect on inhibitors performance.

In this study, the inhibitive performance of two pyridine derivatives as corrosion inhibitors for mild steel was examined under stagnant condition and hydrodynamic flow in HCl solution at 25 °C. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were employed. To explore the inhibitors adsorption mechanism, Langmuir isotherm and quantum chemical studies were used. The results of electrochemical measurements show that the inhibitor concentration has a positive effect on its efficiency while for hydrodynamic condition, it is vice versa. Corrosion attack morphologies were observed at stagnant and hydrodynamic conditions to verify qualitatively the results obtained by electrochemical methods.