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 electropolymerisation conditions on iron samples must be carefully selected, leading to the choice of phosphoric acid solution. The protection lasts during a period from several hours in pH 0.5 corrosion solution, to several weeks at pH 4.5. A simple electrochemical test characterises the passivation breakdown. Raman and optical spectroscopies allow understanding the mechanisms preceding and accompanying this breakdown: the increase of polarons delocalization does not allow the oxidised PANI form to be regenerated.