Montmorilonitas como pigmentos anticorrosivos

Abstract

The role of montmorillonites (MMTs) as pigments in anticorrosive coatings is investigated in this work. Pigmented novolac epoxy coatings with approximately 60% wt. micaceous iron oxide, and 1 or 5% wt. of different MMTs were evaluated. The experimental methodology involved titrations of filtrates and suspensions of the clays, gravimetric tests, such as water absorption and water vapor permeability through the polymer film, long term corrosion tests, observing aging kinetics of coatings with electrochemical impedance analysis. The literature emphasizes that the MMTs improves barrier properties of them, however, active corrosion inhibition and pH control were observed for filtrates and suspensions of the clays. In the coatings, it was observed that the MMTs were able to control the permeation of the corrosive H+ through the paint film, depending on clay affinity by water. It was verified that with 5% of any MMT, there was undercoating corrosion inhibition. Organophilization treatments may have side effects, such as organophilized MMT with hydrogenated tallow methyl dihydroxyethylammonium, which improved barrier properties but impaired adherence. The results revealed that MMT are not inert pigments. Instead, they can act as intelligent pigments, with properties complementary to those of barrier, which are activated as the coating is dumped with the electrolyte.