Corrosion Inhibition of Aluminum Alloy 2024-T3 by Praseodymium Chloride

The mechanism of inhibition of AA2024-T3 (EMS A92024) by praseodymium chloride (PrCl) at varying pH was investigated using electrochemical, microscopic, and spectroscopic techniques. Polarization curves in naturally aerated solutions showed that praseodymium (Pr) provides cathodic inhibition in near-neutral pH solution. Corrosion inhibition of AA2024-T3 by Pr involves the formation of an insoluble film composed of praseodymium carbonate hydroxide (PrCO3 center dot OH) over the intermetallic particles in response to an increase in the pH at the metal/electrolyte interface. As the cathodes on the surface become blocked by a thick oxide, new sites are activated, resulting in the formation of a thick film across the whole surface. The hydroxycarbonate protective layer formed in aerated solution was essential for the protection of the alloy, indicating that carbon dioxide (CO2) played an important role in the inhibition mechanism by Pr. In low and high pH solutions, Pr provided poor inhibition. In the latter case, Pr formed a thick oxide film over the intermetallic particles as a result of oxygen reduction, but was unable to stop uniform dissolution of the AI-oxide film.