Coumarin Derivatives as Corrosion Inhibitors for Zinc in HCl Solutions

(a) 4-hydroxy - coumarin

The inhibiting effect of some coumarin derivatives toward the corrosion of Zinc in 0.1M HCl solution was studied using weight loss and galvanostatic polarization techniques. Addition of KI to acidic 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 rising the temperature, so that the adsorption of these compounds is physically adsorbed on the zinc surface. Temkin’s adsorption isotherm fits the experimental data for the studied compounds. Some thermodynamic parameters for the adsorption and activation process were computed. The values of Tafel slopes indicate that these compounds act as a mixed type inhibitors but cathode is more polarized when an external current was applied. The inhibitors are explained in terms of adsorption on the zinc surface. The order of inhibition efficiency are interpreted on the basis of the molecular structure, the subsistent groups and their charge densities of the coumarin derivatives. Continue reading…