Corrosion inhibition and adsorption behavior of Murraya koenigii extract for corrosion control of aluminum in hydrochloric acid medium

The corrosion behavior of aluminum in the hydrochloric acid medium of pH 3 was studied using Tafel polarization and electrochemical impedance spectroscopy techniques in the presence or the absence of the Murraya koenigii (commonly known as curry) leaves extract at 303 K to 323 K. The concentration of the inhibitor used was in a range of 0.05–0.4 gL⁻¹. The inhibition efficiency was found to increase with increasing the inhibitor concentration and decreasing temperature. Polarization data showed that the curry leaves extract (CLE) acted as anodic type of inhibitor at lower concentrations of the inhibitor and as mixed type at higher concentrations of the inhibitor. The maximal inhibition efficiency of 91.79% was obtained with the CLE at its optimum concentration of 0.4 gL⁻¹. Adsorption of the CLE was found to obey the Langmuir adsorption isotherm and underwent both physisorption and chemisorption process. The kinetic and thermodynamic parameters were calculated and discussed in detail. The results obtained by both methods were in good agreement with each other. The protective film formed on the surface of aluminum by the adsorption of inhibitor molecules present in the CLE in the hydrochloric acid medium of pH 3 was confirmed by the scanning electron microscopy and energy-dispersive X-ray spectroscopy. So, the CLE emerged as a potential, cost-effective and eco-friendly natural inhibitor for the corrosion control of aluminum in the hydrochloric acid medium.