Heterocycles as corrosion inhibitors for zinc pigments in aqueous alkaline media

Zinc pigments react in aqueous alkaline media (e.g. water-borne paints) by the evolution of hydrogen. Heterocyclic compounds can inhibit this corrosion reaction. The corrosion inhibiting effect of the heterocycles depends strongly on the base which is used for adjusting the pH value to 10. Ammonia accelerates the corrosion reaction very much; the protection factors for the heterocycles are 5-40%. The examined heterocycles inhibit significantly better if dimethylethanolamine or sodium hydroxide are used as bases; protection factors increase up to 98%. The corrosion inhibiting effect of heterocycles can be explained by reference to Pearson [R.G.Pearson, J. Chem. Ed, 45, 581 (1968)]