N-Phenylcinnamimide and some of its derivatives as inhibitors for corrosion of lead in HCl solutions

The anodic and cathodic polarization behavior of lead electrode was studied galvanostatically in HCl solutions of various concentrations. Increasing the acid concentration enhances the rate of the anodic dissolution of the metal and the rate of hydrogen evolution reaction, with anodic and cathodic Tafel slopes equal to 30 and 115 ± 5 mV decade−1, respectively. The effect of addition of N-phenylcinnamimide and some of its derivatives, N-(p-nitrophenyl)cinnamimide, N-(p-methylphenyl)cinnamimide, and N-(p-methoxyphenyl)cinnamimide, as inhibitors on the kinetic of the anodic and cathodic reactions of lead in 0.1 M HCl solutions was also studied. These compounds inhibit both the rate of anodic dissolution and the rate of hydrogen evolution reactions without affecting the Tafel slopes. This result indicates that the used compounds were of mixed-type. The inhibition efficiency of these additives increases in the order: N-(p-nitrophenyl)cinnamimide < N-phenylcinnamimide < N-(p-methylphenyl)cinnamimide < N-(p-methoxyphenyl)cinnamimide. The equilibrium constant and the free energy of adsorption process have been calculated and discussed.