Investigation of the Effect of Willow Tree Gall Extract as a Green Corrosion Inhibitor for St37 Steel in 1 M Hydrochloric Acid Environment

<p style="text-align: left;"><strong>Introduction:</strong> With the advancement of industries and the widespread use of St37 steel, its protection against corrosion, especially in acidic environments such as HCl, has gained significant importance. Traditional inhibitors like chromates have been restricted due to their environmental impacts, leading to the substitution of green inhibitors such as plant extracts. These extracts reduce corrosion by forming a protective film on the metal surface. In this study, the inhibitory effect of willow tree gall extract on the corrosion of St37 steel in 1 molar HCl solution was investigated. <p style="text-align: left;"><strong>Methods:</strong> The gall extract was collected, dried, ground, and extracted using ethanol. Different concentrations of the extract were added to the corrosive medium, and electrochemical tests including Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) were conducted. The weight loss of the samples was also examined at various intervals. FTIR analysis was used to identify the bonds present in the extract. Additionally, the surfaces of the samples immersed in the solution were studied using Scanning Electron Microscopy (SEM). Results demonstrated that the gall extract, by forming a protective film, effectively reduced the corrosion rate and protected the steel. <p style="text-align: left;"><strong>Findings:</strong> FTIR analysis identified functional groups (-OH, C-H, N-H, aromatic, and aliphatic compounds) in the willow gall extract that contribute to corrosion inhibition. EIS results showed stronger protective films and increased charge transfer resistance with higher extract concentrations, reducing corrosion rates. Polarization tests demonstrated a 95.8% inhibition efficiency at 1200 ppm. Weight loss tests confirmed reduced corrosion rates, and adsorption studies indicated Langmuir isotherm behavior. SEM images validated the formation of a protective film shielding the steel surface from aggressive ions.