Corrosion Inhibition of Mild Steel in 0.3 M Hydrochloric Acid Solution Using Urena lobata Leaves Extract

Abstract

The study explored the effectiveness of an ethanolic extract derived from Urena lobata (UL) as a natural inhibitor of corrosion for mild steel when exposed to 0.3 M HCl acid. Various analytical methods including gravimetric analysis, Potentiodynamic Polarization (PDP), Fourier Transform Infrared Spectroscopy (FT-IR), and Scanning Electron Microscopy (SEM) were utilized. The experiments were conducted under different conditions including varying temperatures (303 K, 313 K, and 323 K), inhibitor concentrations (0.2 g/L, 0.4 g/L, and 0.6 g/L), at a fixed acid concentration of 0.3M, and with an immersion time of 4 hours. The findings revealed that the inhibition efficiency (%IE) increased with higher inhibitor concentrations but decreased with rising temperature and immersion time. The highest inhibition efficiency observed was 69.26%, while the lowest was 53.08%. SEM images confirmed the inhibitor's ability to shield the metal surface, while FT-IR spectra identified the functional groups responsible for corrosion inhibition. The enthalpy of activation (∆H) indicated an exothermic process, and the entropy of activation (∆S) pointed to a decrease in disorder, both reflected by negative values. The values of the Free Energy of Adsorption (∆G_ads) indicated the spontaneity and viability of the process, with physical adsorption being proposed as the underlying mechanism. The Freundlich adsorption isotherm was deemed the most applicable model for UL. The activation energy (E_a) increased with higher plant extract concentrations, and first-order kinetics seemed to best describe the inhibition mechanism based on reported R² values, rate constants, and half-life. Potentiodynamic polarization (PDP) result indicates that the inhibition efficiency was quite high showing 84.77 %IE and is a single type inhibitor (anodic). Phytochemical screening analysis indicates that U.L leaves contained alkaloids, tannins, sterols, glycosides, triterpenoid and saponins. Therefore, the leaves extract of UL moderately inhibits mild steel corrosion in hydrochloric acid.