Corrosion Inhibition of Carbon Steel in 1M HCl by Glaucium flavum Alkaloids: Experimental Evaluation, Theoretical Insights, and Surface Characterization

Abstract

The corrosion inhibition of carbon steel (CS) in a 1 M HCl solution using the alkaloid extract from Glaucium flavum (AEGF) was investigated through a comprehensive and rigorous approach, including weight-loss measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results demonstrate that the inhibition efficiency of AEGF increases with concentration, reaching a maximum value of 81% at 200 ppm, but decreases at elevated temperatures. Potentiodynamic polarization studies reveal that AEGF acts as a mixed-type inhibitor, affecting both anodic and cathodic reactions. The adsorption behavior of the extract follows the Langmuir adsorption isotherm model. Thermodynamic parameters, including the apparent activation energy, enthalpy, and entropy of the dissolution process, were also evaluated, confirming that the inhibition mechanism is predominantly physisorption. The results obtained from different methodologies were consistent and mutually corroborative. In addition, surface analysis by scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) showed that samples treated with the extract exhibited a smoother surface compared with untreated samples. This smoother surface morphology indicates reduced corrosion due to the decreased exposure of the metal surface to the corrosive medium, which was further confirmed by profilometry analysis. A theoretical study based on conceptual density functional theory (DFT) was also conducted to predict the reactive sites of the molecules. These predictions were based on the analysis of both local and global chemical reactivity indices.