Polypyrrole films on Al alloys: The role of structural changes on protection performance

Polypyrrole (PPy) films were electrochemically synthesized on AA6082, AA5083 and AA2024 Al alloys by a two-step galvanostatic procedure: (1) activation in nitric acid and (2) deposition in oxalic acid. PPy films were characterized by elemental analysis, cyclic voltammetry, SEM/EDX, RAIR, solid-state 13C NMR, and EPR. The corrosion behaviour of PPy-coated alloys was evaluated in near neutral NaCl solution by single-cycle anodic polarization and open circuit potential monitoring. Film adhesion and polymer structure are principally determined by the nature of the Al substrate. Good quality films are obtained on the most reactive AA5083 and AA2024, while highly degraded, partially saturated polymer is electrogenerated on AA6082. The performance of PPy films was observed to depend strongly on the electrochemical test used for corrosion protection evaluation. Accordingly, the rate at which structural changes are driven within the polymeric matrix is of paramount importance to understand the corrosion inhibition properties of conducting polymers.