Green Corrosion Inhibition of Mild Steel in 0.5 M HCl Using Tecoma stans Leaf Extract: Experimental and Thermodynamic Study

Abstract

Corrosion of mild steel in acidic environments remains a critical challenge in industrial applications, particularly in oil and gas operations. In this study, the inhibitory performance of Tecoma stans leaf extract as an eco-friendly corrosion inhibitor for mild steel in 0.5 M HCl solution was investigated using the weight loss method. The effects of inhibitor concentration and extraction medium (aqueous and alcoholic) were evaluated. The results revealed that inhibition efficiency increases with increasing extract concentration, with the alcoholic extract showing superior performance, achieving a maximum efficiency of 84.98%. Adsorption studies indicated that the inhibitor molecules adsorb onto the metal surface, The calculated standard free energy of adsorption (ΔG°ads = −10.5 kJ/mol) suggests that the inhibition process is spontaneous and predominantly governed by physisorption with possible chemisorption contributions. The high inhibition efficiency is attributed to the presence of phytochemical constituents containing heteroatoms and π-electrons, which facilitate adsorption and formation of a protective film. These findings confirm that Tecoma stans extract is a promising, low-cost, and environmentally friendly corrosion inhibitor for mild steel in acidic media