Corrosion Inhibition of Aluminum Alloy 2024-T3 by Sodium Molybdate

The mechanism of corrosion inhibition of AA2024-T3 by sodium molybdate was investigated using various electrochemical, microscopic and spectroscopic techniques. Polarization curves in naturally-aerated solution showed that molybdate provided mixed inhibition in near-neutral pH solution and at a threshold concentration of 0.1 M. The largest effect was a 250 mV increase in the breakdown potential associated with pitting and a 350 mV decrease in the open-circuit potential (OCP). In addition, electrochemical impedance indicated that the corrosion inhibition mechanism is oxygen-dependent owing to the protection afforded by Mo(VI) species. It is proposed that the corrosion inhibition of AA2024-T3 by molybdate may occur following a two-step process whereby molybdate is rapidly reduced to MoO·(OH)2 over the intermetallic particles and is subsequently oxidized to intermediate molybdenum oxides (e.g. Mo4O11) in the presence of oxygen.