The protection of iron against corrosion brought by polyaniline ͑PANI͒ potentiostatically polymerized in phosphoric/metanilic solution is due to the combination of the passive layer and the polymer. The passive layer is strengthened by phosphate incorporation, and sulfonated aniline is inserted in the chain to yield a copolymer ͑SPAN͒. The potentiostatic polarization is partly responsible for the heterogeneity of polymer ͑block-polymer͒. Raman and optical spectroscopies are used to characterize the modifications in the PANI composition preceding and accompanying the passivity breakdown. The breakdown is associated with the loss of PANI reoxidability, but this step is preceded by slow modifications in the polaron distributions.
Polyaniline (PANI) has been studied for some years in order to protect mild steels against corrosion in the absence of inorganic conversion layers. During the electropolymerization of PANI film, iron is passivated; the subsequent protection is dependent on the nature of this passive layer, and PANI acts as a stabilizer of this layer. The best conditions for PANI electrodeposition are discussed here, using a simple electrochemical test to characterize the passivity breakdown.
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