Adsorption and corrosion inhibitive properties of Azadirachta indica in acid solutions

Purpose - To assess the protective effect and adsorption behaviour of Azadirachta indica extract in controlling mild steel corrosion in 1 M H2SO4 and 2 M HCl. Design/methodology/approach - The inhibitive effect of the plant extract was monitored using the gas-volumetric technique. The inhibition mechanism was inferred by curve fitting of the experimental data to known adsorption isotherms and the trend of inhibition efficiency with temperature. Findings - Azadirachta indica extract effectively inhibited steel corrosion in the acid media studied by virtue of adsorption. The inhibitor adsorption characteristics were approximated by Langmuir isotherm. The extract functioned as a mixed inhibitor, depending on its concentration. The prime effect at lower concentration was mitigation of the cathodic reaction by physical adsorption of protonated species in the extract and at higher concentration the anodic reaction was inhibited by chemisorption of molecular species. Originality/value - This paper provides novel information on the effectiveness of Azadirachta indica extract as a green corrosion inhibitor for steel in highly acidic environments as well as possible mechanisms of the inhibitive action.