Nitro- and aminophenols as corrosion inhibitors foraluminium and zinc pigments

Abstract

Both aluminium and zinc pigments react in aqueous alkaline media (e.g.,water-borne paints) with the evolution of hydrogen. This corrosion reaction can be inhibited bycertain nitro- and aminophenols. The corrosion inhibiting effect of 2-amino- and 2-nitrophenol isexcellent for aluminium pigment whereas 4-nitro- and 4-aminophenol do not inhibit thiscorrosion reaction. For zinc pigment the corrosion inhibiting effect decreases in the followingseries: 2-nitrophenol >2-aminophenol >4-nitrophenol >4-aminophenol. So, for aluminiumpigment the possibility of chelate formation (2-substituted phenols) seems to be a basicrequirement for corrosion inhibition by phenol derivatives. For zinc pigment a possible chelatingeffect of the inhibitor improves corrosion inhibition but is not a basic requirement. The bestoverall corrosion inhibitor both for aluminium and zinc pigment is 2-nitrophenol (protectionfactor 96–99.9%).