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.