Plasma electrolytic oxidation in the presence of multiwall carbon nanotubes on aluminum substrate: Morphological and corrosion studies

Plasma electrolytic oxidation processes were performed on aluminum substrates in a solution composed of KOH, Na4P2O7 and NaAlO2 compounds at constant applied potential, i.e. 520 V DC, with and without incorporating multiwall carbon nanotubes (MWCNTs). The morphology and chemical composition of PEO coatings was studied using SEM and XRD techniques. The SEM characterizations revealed that MWCNTs were incorporated into the PEO coating with the detrimental effect on the coating compactness, particularly in the inner barrier layer. In addition, the characteristic peaks corresponding to the gamma-Al2O3 phase get more intensified by loading MWCNTs. The corrosion protection performance of the PEO coatings was also studied by the Electrochemical Impedance Spectroscopy (EIS) and Scanning Kelvin Probe (SKP) techniques. The results revealed that protective properties of the PEO coating are deteriorated with incorporating MWCNTs by reducing the compactness of the inner and outer layer of the PEO coating. The obtained results also demonstrated that both types of PEO coatings exhibit a similar mechanism of protection by barrier effects.