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Corrosion Inhibition of Zinc in Sodium Hydroxide Solutions using Coumarin Derivatives

M. Abdallah , O.A.Hazazi, B.A.ALJahdaly, A. S. Fouda , W. El-Nagar

The corrosion behaviour of Zinc in 2M sodium hydroxide solution and its inhibition by some coumarin derivatives was studied using weight loss and galvanostatic polarization techniques. Addition of Ba2+ ion to alkaline medium containing the coumarin derivatives increases the inhibition efficiency of the system. The obtained results showed that the inhibition efficiency of these compounds increased by increasing their concentrations and decreased by raising the temperature, so that the adsorption of these compounds is physically adsorbed on the zinc surface. The adsorption of the inhibitors on the zinc surface in alkaline solution was found to obey Temkin adsorption isotherm. The activation energy and some activated thermodynamic parameters for the corrosion process were calculated and discussed. The polarization technique indicates that these compounds act as a mixed type inhibitors but cathode is more polarized when an external current was applied. The results were explained on the basis of the molecular structure and the substituent groups and their charge densities.