Dopant effects in polyaniline inhibition of corrosion-driven organic coating cathodic delamination on iron

Coatings comprising various volume fractions of particulate polyaniline dispersed in a polyvinylbutyral binder are applied to iron substrates. A scanning Kelvin probe is used to measure substrate potentials in humid air and follow corrosion-driven coating delamination (cathodic disbondment) when 5% w/v (0.86 M) aqueous NaCl contacts a coating defect. Emeraldine base has no effect on substrate potential or delamination kinetics. Emeraldine salts (ES) doped using p-toluenesulfonic (HpTS), camphorsulfonic (HCS), phosphoric (H3PO4), and phenylphosphonic (H2PP) acids increase substrate potentials by up to 0.36 V and inhibit delamination with efficiency order of HpTS < HCS < H3PO4 << H2PP. Dopant salts added to the corrosive electrolyte do not inhibit delamination. It is proposed that inhibition arises primarily from cathodic O-2 reduction becoming relocated from the ennobled substrate onto the ES coating. However, Fe-3(PO4)(2) and FePP salt films formed at the ES-substrate interface also contribute by hindering interfacial electron transfer. (c) 2006 The Electrochemical Society.