CORROSION INHIBITION OF ZINC PIGMENTS IN AQUEOUS ALKALINE MEDIA BY POLYMERS

Zinc pigments react in aqueous alkaline paint media with the evolution of hydrogen. Poly(meth)acrylic acids inhibit this corrosion reaction. With addition of these polymers the hydrogen volumes evolved are high er at pH 8 (below the isoelectric point (IEP) of zinc oxide) compared to pH 10 (above the IEP). It is assumed that this fact is caused by an increased adsorption of the poly(meth)acrylic acid polyanions at pH 8 (below the IEP) which is followed by a chemical reaction of the adsor bed carboxylates with zinc that produces hydrogen. Ordinarily, styrene -maleic acid copolymers inhibit the corrosion of zinc pigment better c ompared to poly(meth)acrylic acids. The hydrogen volumes evolved with addition of styrene-maleic acid copolymers are higher at pH 8 compared to pH 10 again. The two low-molecular styrene-maleic acid copolymers (molecular mass 1600 and 1700) are the best corrosion inhibiting polym ers examined in this study. (C) 1997 Elsevier Science S.A.