Influence of different aggressive media on the protective behaviour of zinc rich paints

The aim of the present work is to determine the influence that different at mospheric agents have in steel protection by zinc rich paints based on inor ganic silicate binder. The presence of pollutants in the atmosphere has bee n simulated by periodical deposition of sulphate and/or chloride solutions on the surface of the samples. With the aim of determining the validity of immersion tests, usually used in these types studies, the samples were kept in a controlled atmosphere at 20 degrees C and 60 % RH. These exposition c onditions could represent a relative dry atmosphere allowing the zinc corro sion. Electrochemical imps dance spectroscopy was employed to follow the ti me evolution of the studied paints. The corresponding impedance spectra wer e modelled using an electrical equivalent circuit approach. This methodolog y allows establishing that pollutants as well as weathering conditions defi ne the protecting mechanism of these zinc rich paints. The results show a f ast evolution towards a barrier-type protecting mechanism.