High performance anticorrosive epoxy paints pigmented with zinc molybdenum phosphate

Abstract

Zinc molybdenum phosphate belongs to the so called second generation phosphate pigments and is claimed to have equal or greater anticorrosive properties than chromates and better than zinc phosphate alone. Little Information is available in the literature about its anticorrosive performance. The aim o f this research was to stucfy the anticorrosive performance o f zinc molybdenum phosphate in solvent borne epoxy paints employing two anticorrosive pigment loadings. The effect o f incorporating zinc oxide as complemetary pigm ent was also studied SAE 1010 Steel ponéis were prim ed and coated with three different paint systems containing the anticorrosive paint and this paint plus a sealer cmd/or a topcoat. The anticorrosive efftciency o f the different paint systems was assessed by accelerated tests (salí spray, humidity and accelerated weathering). Electrochemical measurements were done employing the anticorrosive paints alone. Results showed that the highest anticorrosive effect was obtained employing 30% o f zinc molybdenum phosphate. Polarization measurements showed that the anoche film form ed on Steel blocked the active sites fo r oxygen reduction. The incorporation o f zinc oxide to pigment form ula was detrim ental due to its high water absorption and to the fa ct that it reduced zinc molybdenum phosphate solubility by the common ion effect. Polarization curves o f pigm ents mixtures could be used as a guideline to precüct the anticorrosive coating perform ance in accelerated and electrochemical tests. However, the fin a l decisión on pigm ent selection musí be taken on the basis o f accelerated triáis.