Evaluation of Aqueous Extract of Mandevilla fragrans Leaves as Environmental-Friendly Corrosion Inhibitor for Mild Steel in Acid Medium

The Mandevilla fragrans leaves extract was evaluated as an environmental-friendly corrosion inhibitor for mild steel in 1 mol L−1 HCl. The inhibitive properties of the extract were tested by gravimetric measurements, polarization curves, linear polarization resistance, and electrochemical impedance spectrometry. The performed experiments showed a good correlation with each other and, using a concentration of 0.800 g L−1, an average anti-corrosion efficiency of 94.1% was reached. The mechanism of inhibition is based on the adsorption of molecules present in the extract on the steel surface generating a layer that protects the surface-to-corrosion process. The surface analysis of the material in the inhibitor presence in aggressive medium using atomic force microscopy sustains the surface protection by the inhibitor adsorption. The study of the adsorption isotherms showed that the Langmuir model is the most adequate one.