Evidence of a Passive Layer Formation from a Conductive Polymer Coating on Aluminum Alloys

Evidence for the formation of a passive layer between a conductive polymer coating and aluminum alloy surfaces is reported Experimental results from electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) on aluminum alloys coated with a novel double strand conductive polymer coating based on polyaniline reveal the evidence for the formation of passive layer. The key results are: (1) Modeling of EIS data is best fit with a three RC circuit, indicating a third interface between the polymer coating and the alloys's surface; (2) EIS testing in acidic salt solutions shows the conductive polymer coating performs differently and better than a typical anodized or chromate conversion coating indicating a possibly different interface layer than a typical aluminum oxide and (3) SEM studies of the aluminum surface, after the polymer film is removed, indicates that this interfacial layer has a dense and smooth s'oxide types' surface morphology. The experimental results are consistent with a mechanism in which the conducting polymer serves as a surface conversion agent that oxidizes the aluminum metal surface to form a passive layer.