Galvanic coupling of doped poly-aniline and aluminum alloy 2024-T3

The galvanic interaction between electronically conductive polyaniline film s doped with camphor sulfonic acid (PAni-CSA), and aluminum alloy (AA) 2024 -T3 has been investigated for the purpose of assessing PAni-CSA as a corros ion protection coating on AAs. Potentiodynamic polarization and zero resist ance ammeter measurements of galvanic couples between PAni-CSA and AA 2024- T3 in 3.5% NaCl show that the AA dominates the mixed potential response and polarizes the PAni-CSA to approximately the potential of the freely corrod ing alloy (-0.54 V vs. Ag\AgCl). This observation indicates that conductive PAni coatings on XI are rapidly reduced to the nonconductive form on immer sion in an aqueous electrolyte. The results also suggest that any corrosion protection of Al by PAni coatings is due to the barrier properties of the reduced polymer rather than anodic stabilization of passivity as observed w ith ferrous alloys. Mechanisms by which a PAni-CSA coating might provide co rrosion protection of exposed 2024-T3 at defects in the coating are discuss ed. (C) 2000 The Electrochemical Society. S0013-4651(99)11-002-4. All right s reserved.