Electrochemical investigation of polyaniline blends on galvanized steel

This work reports a systematic investigation of PAni blends deposited on galvanized steel using different electrochemical approaches, namely anodic polarization and cyclic accelerated electrochemical techniques, in 3.5 wt.% NaCl. PAni blends consisted of dispersed emeraldine base (EB 0.1, 0.5 and 1%) in an alkyd epoxy resin. Similar coating system but containing a silicate based inhibitor was studied in parallel for reference purposes. Pseudo-doping of EB due to interactions with Zn2+ determines the superior inhibition of galvanized steel anodic dissolution and the higher resistance to cathodic disbonding of PAni blends, also in the presence of large defects. Such interactions promote development of passive and/or barrier-like states. Possible processes involve formation of a leucosalt layer due to the enhanced electroativity of EB with complexation, compaction of the leucosalt with cathodic polarization, and formation of irreversible pernigraniline-metal (hydr)oxide structures with anodic polarization. The interconnectivity of EB particles within the organic matrix plays a decisive role on the efficiency of these processes.