Inhibition of corrosion-driven organic coating delamination on zinc by polyaniline

The polyaniline emeraldine salt of para-toluenesulphonic acid (PAni-PTS) is dispersed in polyvinylbutyral (PVB) coatings adherent to a zinc surface. Such dispersions are shown to effectively inhibit corrosion-driven (cathodic) coating delamination when aqueous chloride electrolyte contacts a penetrative coating defect. A scanning Kelvin probe (SKP) is used to determine the influence of PAni-PTS volume fraction (phi(pa)) on both delamination kinetics and the potential of the intact (undelaminated) coated surface (E(intact)). At relative humidities (rh) of ca. 95% no delamination is observed over a 48 h period when phi(pa) greater than or equal to 0.2. However, ennoblement Of Eintact does not persist for longer than 6 h at the same rh. Over a similar period (6 h) a zinc oxide layer develops at the coating-metal interface and attains a thickness proportional to phi(pa). An inhibition mechanism is proposed in which the PAni-PTS induced zinc oxide layer stifles cathodic O(2) reduction and is itself protected from alkaline dissolution through PAni-PTS mediated pH buffering. (C) 2004 Elsevier B.V. All rights reserved.