Influence of anions on the inhibition of corrosion of zinc in acidic solutions by n-heterocyclics

The influence of anions such as chloride and sulphate on the corrosion of zinc in 1 N HCl and 1 N H2SO4 by N-heterocyclics such as imidazole (1m), 2-methyl imidazole (M 1m) and benzimidazole (B 1m) has been studied using weight loss and gasometric measurements potentiodynamic polarization studies, a.c.impedance measurements and UV reflectance studies. Imidazoles are found to be more inhibitive in 1 N HCl than in 1 N H2SO4. The inhibition of corrosion of zinc by these compounds is found to be under mixed control, but predominantly under cathodic control. Trends in the increase of charge transfer resistence (Rt) and decrease in double layer capacitance (Cdl) values also indicate the absorption of these compounds on the metal surface. UV spectral studies were also carried out to establish the actual mechanism of inhibition of corrosion. The absorption of these compounds from both the acids on the surface of zinc obeys Temkin's absorption isotherm