Electrochemical and thermodynamic investigation of the corrosion behavior of mild steel in 1 M hydrochloric acid solution containing organic compounds

Background: Inhibition effect of 1-((4-chlorophenyl)(2-hydroxynaphtalen-1-yl)(phenyl)methyl)urea (CPHU) and 1-((2-hidroxynaphtalen-1-yl)(4-methoxyphenyl)methyl)urea (HNMU) in 1 M HCl solution on mild steel was investigated using weight loss and potentiostatic polarization techniques. Results: It is found that the studied compounds exhibit a good performance as inhibitors for mild steel corrosion in acid solutions. The inhibition efficiency increased with decreasing temperature and increasing concentration of the inhibitors. Potentiostatic polarization measurements indicate that these compounds act as mixed-type inhibitors. The values of activation energy and the thermodynamic parameters, such as adsorption equilibrium constant, adsorption free energy, adsorption heat, and adsorption entropy values, were calculated and discussed. The scanning electron microscopy analysis indicated the existence of an adsorbed film on the steel surface in the presence of the inhibitors. The results obtained from infrared spectra confirmed adsorption of the inhibitor on the metal surface after immersion in acidic solution containing CPHU. Conclusions: The adsorption of the inhibitors on the surface obeys the Langmuir adsorption isotherm. The percentage of inhibition efficiency values obtained from polarization measurements show good agreement with those obtained from weigh loss experiments. The overall results revealed that the investigated compounds are efficient inhibitors of corrosion in mild steel in 1 M hydrochloric acid solution, and CPHU showed better performance.