Tara Tannins as a Green Sustainable Corrosion Inhibitor for Aluminum

Tara tannin is studied as an inhibitor of aluminum corrosion, immersed in an aerated and near-neutral NaCl solution and in a wash-primer formulation. Electrochemical tests prove that tara tannins provide good corrosion resistance for aluminum, and scanning electron microscopy coupled to energy dispersive x-ray spectroscopy shows a low formation of corrosion products, absence of Cl and presence of C. These results indicate that tannins act as a mixed-type inhibitor without changing the mechanism of oxygen or aluminum reactions, and that tannin is adsorbed on aluminum surfaces forming a compact hydrophobic barrier that blocks anodic and cathodic areas. A tara tannin primer was formulated and applied on aluminum. Its anticorrosive properties were studied by electrochemical techniques and humidity chamber testing, in which it exhibited an acceptable performance compared with a zinc tetroxychromate primer. Taking into account their less harmful environmental impact, tara tannins are proposed as an alternative to chromates in the formulation of wash-primers.