Protection of iron against corrosion using a polyaniline layer - III. Spectroscopic analysis of the mechanisms accompanying the breakdown

The protection of iron against corrosion brought by polyaniline (PANI) pote ntiostatically polymerized in phosphoric/metanilic solution is due to the c ombination of the passive layer and the polymer. The passive layer is stren gthened by phosphate incorporation, and sulfonated aniline is inserted in t he chain to yield a copolymer (SPAN). The potentiostatic polarization is pa rtly responsible for the heterogeneity of polymer (block-polymer). Raman an d optical spectroscopies are used to characterize the modifications in the PANI composition preceding and accompanying the passivity breakdown. The br eakdown is associated with the loss of PANI reoxidability, but this step is preceded by slow modifications in the polaron distributions. (C) 2001 The Electrochemical Society.