Study of the Inhibitive Property of Azadirachta indica (Neem Tree) Gum on Mild Steel Corrosion in Various Acidic Media

Abstract

Aims: The aim of this work is to investigate the inhibitive properties of Azadirachta indica (neem) gum on mild steel corrosion in different acidic media using gravimetric method. Place and Duration of Study: Chemistry Laboratory, Department of Chemistry, Kano University of Science and Technology, Wudil, between January 2018 and March 2018. Methodology: Gravimetric method was used to analyse the effectiveness of Azadirachta Indica (AZI) gum as a mild steel corrosion inhibitor in 1.0M nitric acid (HNO3), sulphuric acid (H2SO4) and hydrochloric acid (HCl) solutions at 298K and 313K. Weight loss was obtained at different concentrations of the inhibitor; 0.50, 1.00, 1.50, 2.00 and 2.50% w/v. From the weight measurements, the degree of surface coverage and inhibitor efficiency were computed. The activation energy was calculated using the Arrhenius equation, and Gibbs free energy and heat of adsorption were determined to study the spontaneity and enthalpy of the corrosion process. Adsorption isotherms; Langmuir, Temkin and Fraudlish were employed in order to have insight into the possible mechanism of adsorption involved. Results: Gravimetric measurements of pure solvents used at several concentrations (0.5, 1, 1.5 and 2 M) showed that weight loss increases with temperature and concentration of the acids. When different concentrations of inhibitor were introduced into the solvents, a similar trend was observed. Inhibitor efficiency increases with temperature and with concentration of the inhibitor. H2SO4 was found to have the highest inhibition efficiency of 89.93% and 95.82% at 298K and 313K respectively in 2.5%w/v concentration of the inhibitor. Its strong hydrogen bonding and high surface tension may be a contributing factor. Corrosion rate was calculated and HNO3 was found to be more corrosive than HCl and H2SO4 both in the presence and absence of the inhibitor at 298K and 313K. Conclusion: From the study, Azadiracta indica gum was found to retard corrosion of mild steel. HNO3 acid was more aggressive and has the highest corrosion rate. Therefore corrosion retardation in this medium was least effective. This might be attributed to the strong oxidising ability of HNO3 than HCl and H2SO4. The rate of corrosion was more retarded in H2SO4. Free energy of the process was negative all through the inhibitor concentrations indicating that the action of the inhibitor on the metal surface was spontaneous. Data of the corrosion process also fitted well in to Langmuir isotherm suggesting that the mechanism of corrosion could be predominantly physisorption.