METAL-CHELATES OF CITRIC-ACID AS CORROSION-INHIBITORS FOR ZINC PIGMENT

Zinc pigments react in aqueous alkaline media (e.g. water-borne paints ) by the evolution of hydrogen which can be measured gasvolumetrically . The addition of both pure citric acid or pure metal salts stimulated the corrosion reaction of zinc pigment in aqueous alkaline media. The addition of soluble zinc(II) and aluminium(III) chelates of citric ac id reduced the hydrogen evolution of zinc pigment dispersions compared to pure citric acid; but the level of hydrogen evolved was still very high. In contrast, soluble cerium(III) chelates of citric acid were p owerful corrosion inhibitors for zinc pigments in aqueous alkaline med ia. The pronounced corrosion inhibiting effect of the cerium(III) chel ates could be attributed to cerium and not to the charge of the chelat es. (C) 1997 Elsevier Science Ltd.