Corrosion of rusted steel in aqueous solutions of tannic acid

The use of tannic acid to inhibit metal corrosion has been a controversial issue, particularly in relation to its application to rusted steel prior to painting. In this work, the protective efficiency of aqueous solutions of tannic acid applied on uncontaminated rusted steel is studied. This is done by investigating the changes undergone by the rust layer, the solubility of the tannate films formed, and the resulting inhibition efficiency. This required the use of a variety of experimental techniques including climatic chamber tests, electrochemical measurements, and x-ray photoelectron spectroscopy. The high solubility of the films and the low anti-corrosion efficiency of the treatment question the suitability of tannic acid solutions for protection of rusted steel prior to painting.Peer Reviewe