Polyaniline films for protection against corrosion

Polyaniline (PANI) is able to protect mild steels against corrosion, owing to the stabilisation of the iron oxide passive layer. The electropolymerisa tion conditions on iron samples must be carefully selected, leading to the choice of phosphoric acid solution. The protection lasts during a period fr om several hours in pH 0.5 corrosion solution, to several weeks at pH 4.5. A simple electrochemical test characterises the passivation breakdown. Rama n and optical spectroscopies allow understanding the mechanisms preceding a nd accompanying this breakdown: the increase of polarons delocalization doe s not allow the oxidised PANI form to be regenerated.