Characterization of Zr(IV)-Phosphonate Thin films which inhibit O ₂ reduction on AA2024-T3

Zr(IV)-alkyl-phosphonate and Zr(IV)-aryl-phosphonate thin films of varying compositions were investigated for corrosion inhibition capabilities on AA2024-T3. A strong correlation between the alkyl chain length and the ability of these self-assembled systems to inhibit the O ₂ reduction reaction at the alloy surface was found. In particular, modification using Zr(IV)-octadecyl-phosphonate initially inhibits O ₂ reduction currents by more than 2 orders of magnitude in 0.1 M Na ₂ SO ₄ at a potential of -0.80 V vs a saturated calomel electrode and by greater than 95% after 5500 s under similar conditions. Scanning electrochemical microscopy reveals uniform inhibition of cathodic processes. Auger electron spectroscopy confirms the presence of Zr and P in the thin film. Infrared reflection-absorption spectroscopy indicates that the alkyl chains are in a liquidlike environment. Long-term testing of the Zr(IV)-octadecyl-phosphonate system in a sulfate-containing solution yields low levels of surface activation, as evidenced by small amounts of trenching adjacent to intermetallic particles and little change in near-surface Cu content.