Zinc hypophosphite as suitable inhibitive agent for anticorrosive paints

G. BLUSTEIN, M. C. DEYÁ, R. ROMAGNOLI, B. DEL AMO.

Rio de Janeiro, Brasil

Congreso; XXIV CONBRASCORR. Congresso Brasileiro de Corrosão; 2004

The objetive of this paper was to evaluate the effect of incorporating a little amount of zinc hypophosphite to anticorrosive paints formulated with zinc phosphate. The anticorrosive performance of a commercial product containing both substances and zinc oxide was evaluated. Previously the exact composition of this commercial pigment was established by current analytical techniques and FTIR. The inhibitive properties of each one of the pigments and of a mixture of them were studied in aqueous suspensions by means of suitable electrochemical measurements, employing a steel electrode. The morphology and composition of the protective layer formed on steel immersed in a suspension of the each pigment and in a mixture of them were studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA).             Anticorrosive paints were formulated using solvent (alkyd and epoxy/polyamide) and water-borne (epoxy/poliamidoamin) resins. The anticorrosive pigment was the commercial blend composed by zinc hypophosphite, zinc phosphate and zinc oxide. The active pigment content was 30% by volume with respect to the total pigment concentration. The PVC/CPVC (pigment volume concentration/critical pigment volume concentration) ration used was 0.8 for the solvent borne paints. A PVC of 17.1% was used in the case of the water-borne paint, in order to enhance its barrier properties.             Painted panels were evaluated by accelerated (salt spray cabinet and humidity chamber) and electrochemical (corrosion potential, ionic resistance and polarization resistance) tests.             The results show that the addition of zinc hypophosphite to zinc phosphate enhance the performance of the alkyd paint in a very striking way. The epoxy paints have a better behaviour when zinc hypophosphite is used, while the behaviour of the water-borne paints is not affected by the incorporation of zinc hypophosphite to the pigment formula. Perhaps, the most outstanding feature is that the employment of zinc hypophosphite allowed to reduce the zinc phosphate content with concomitant money saving.