Ion-exchange pigments in primer paints for anticorrosive protection of steel in atmospheric service: Anion-exchange pigments

Abstract

In the field of anticorrosive primer paints there is growing interest to find environmentally friendly anticorrosive pigments to replace Cr(VI) pigments which are highly toxic both to the environment and to human health, with known carcinogenic effects. This has become a major challenge of the last decades for all the sectors involved in metallic protection. One of the alternatives of great scientific interest is the use of ion exchange pigments, which are mostly naturally abundant, easily synthesised, relatively cheap, and above all environmentally friendly. Studies of these pigments have not been conclusive about their anticorrosive efficiency and controversy surrounds their functional mechanisms, exchange capacity and anticorrosive performance.This paper focuses on the anticorrosive protection afforded by one anion-exchange pigment: hydrotalcite/vanadate (HT/V). Alkyd primer coatings formulated with non-toxic HT/V pigment have been applied on carbon steel specimens, and the effect of the pigment on the protective properties of the coatings has been evaluated by means of natural and accelerated corrosion tests (humidity, salt spray and Kesternich, 0.2L SO2). A traditional zinc chromate (ZC) pigment has also been used for comparative purposes. The exchange and inhibitor capacity of the HT/V has also been evaluated.The inhibiting power of the HT/V pigment in solution is seen to be less than that of the traditional ZC pigment, showing also a low exchange capacity and solubility. On the other hand, the behaviour of the HT/V pigmented primers applied on carbon steel is suitable in moderate environments and deficient in aggressive environments, in both natural atmospheres and accelerated tests, and is much poorer than that of the zinc chromate.