Computational and experimental studies on the efficiency of Rosmarinus officinalis polyphenols as green corrosion inhibitors for XC48 steel in acidic medium

The performances of the extract obtained from Rosmarinus officinalis (RO) on the corrosion inhibition of XC48 steel is examined by mass loss method, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), potentiodynamic polarization (PDP), Fourier transform infrared (FTIR) spectroscopy and liquid chromatography–mass spectrometry (LC–MS). Investigations are performed in hydrochloric acid solution at 1 M concentration at different temperatures. Results show that the RO extract behaves as an inhibitor of mixed-type; in particular, the inhibition efficiency is augmented at greater concentration of the inhibitor and decreases with the rise of the temperature from 303 K to 333 K. The values of activation and free energy of inhibition reaction support the hypothesis of a mechanism of physisorption that is adequately described by the Langmuir equilibrium model. The retrieved outcomes are confirmed by SEM observations, which reveal that the adsorbed inhibitor molecules completely hinder the HCl attacks at the steel grain boundaries. Finally, quantum chemical calculations show that among the most abundant component detected in the RO extract, carnosic acid has a greater inhibitor potential with respect to carnosol.