Efficacy of Fleurya aestuans on Mild Steel Protection in Acidic Systems: Combined Gravimetry, Gasometry, and Electrochemical Evaluations

The anticorrosion studies of Fleurya aestuans extract on mild steel in acidic media was carried out in 2 M HCl and 1 M H₂SO₄ using gasometric, gravimetric, and electrochemical techniques at room temperature and at elevated temperatures (303 and 323 K). In all test settings, the inhibitory effectiveness changed in direct proportion to the extract concentration and in inverse proportion to the exposure duration and temperature. The anticorrosion potential of the extract is attributed to the adsorption of its phytoconstituents on the metal surface, blocking the active corrosion sites on mild steel. The adsorption mechanism conformed to the Langmuir, Freundlich, and Temkin adsorption isotherm models with the best fits recorded for the Langmuir model (R² of 0.9777 and 0.9850 in HCl and H₂SO₄, respectively). The calculated thermodynamic parameters, namely Gibbs free energy (∆G^o_ads), activation energy (E_a), and heat of adsorption (Q_ads) all favored a spontaneous and exothermic physical adsorption reaction mechanism of the extract. Potentiodynamic polarization experiments revealed that the extract displayed mixed-type corrosion suppression ability and electrochemical impedance spectroscopy (EIS) evaluations showed increasing charge transfer resistance with increasing extract concentration. Moreover, scanning electron microscopy examinations disclosed the presence of a protective covering on the surface of mild steel coupons in the acid solutions containing F. aestuans extract. The outcomes of the several tests show strong correlations with one another.