Green Corrosion Inhibition and Adsorption Characteristics of <i>Rhamnus Alaternus</i> Leaf Extract on API N80 Carbon Steel Under Acid Environment

ABSTRACT In this work, the study of Rhamnus alaternus leaf extract (RALE) as eco‐friendly corrosion inhibitor for N80‐CS in 1 M HCl was studied. This study examined by weight loss (WL), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) techniques. The results showed that increasing the extract concentration improved the inhibition efficiency (% IE), reaching 94.5% at 120 ppm and 298 K. Further increasing the temperature to 338 K at the same concentration resulted the protection decreased (89.2%) as determined by the WL method. The adsorption behavior have analyzed, revealing a predominantly physical interaction, with Gibbs free energy calculations (Δ G °) of –21.4 kJ mol −1 at 25°C. PDP studies, along with thermodynamic calculations, revealed that the extract functions through a mixed‐type adsorption mechanism, involving both the anodic dissolution of iron and the cathodic hydrogen‐evolution process. EIS data demonstrated that the charge‐transfer resistance ( R ct ​) rises while the capacitance of the double layer ( C dl ​) decreases as the extract concentration increases. The presence of an adsorbed film on the N80‐CS surface was confirmed by using scanning electron microscope (SEM), atomic force microscopy (AFM) and fourier transform infrared spectroscopy (FTIR). Values of inhibition efficiency obtained from WL, PDP, and EIS are in good agreement.