Nitro- and aminophenols as corrosion inhibitors for aluminium and zinc pigments

Both aluminium and zinc pigments react in aqueous alkaline media (e.g., wat er-borne paints) with the evolution of hydrogen. This corrosion reaction ca n be inhibited by certain nitro- and aminophenols. The corrosion inhibiting effect of 2-amino- and 2-nitrophenol is excellent for aluminium pigment wh ereas 4-nitro- and 4-aminophenol do not inhibit this corrosion reaction. Fo r zinc pigment the corrosion inhibiting effect decreases in the following s eries: 2-nitrophenol > 2-aminophenol > 4-nitrophenol > 4-aminophenol. So, f or aluminium pigment the possibility of chelate formation (2-substituted ph enols) seems to be a basic requirement for corrosion inhibition by phenol d erivatives. For zinc pigment a possible chelating effect of the inhibitor i mproves corrosion inhibition but is not a basic requirement. The best overa ll corrosion inhibitor both for aluminium and zinc pigment is 2-nitrophenol (protection factor 96-99.9%). (C) 1999 Elsevier Science Ltd. All rights re served.