Evaluation of the corrosion performance of zinc-phosphate-painted carbon steel

The effect of pigment concentration (C-p) on the corrosion resistance prope rties of zinc phosphate paints based on epoxy and chlorinated rubber has be en investigated by using accelerated corrosion tests (salt spray, cyclic cl imatic change) of painted carbon steel samples combined with electrochemica l impedance spectroscopy. Results show that all the paints act as a protect ive layer, and the corrosion behaviour of the painted steel samples was fou nd to be dependent on C-p. The physicochemical properties of a zinc phospha te coating are affected by the pigment concentration and the nature of the resin. There is a critical value of C-p above which many such properties ch ange abruptly. Characterization of the corrosion products was performed by scanning electron microscopy coupled to energy-dispersive X-ray spectroscop y. This analysis showed the presence of a mixture of iron and zinc oxide, w hich results from attack of the metallic support and reaction of the pigmen t. (C) 1999 Elsevier Science S.A. All rights reserved.