Surface & Coatings Technology | 2021
Inhibitory effects of hematite nanoparticles on corrosion protection function of TiO2 coating prepared by plasma electrolytic oxidation
Abstract
Abstract Protective oxide coatings were prepared on titanium substrates using the plasma electrolytic oxidation process, and the inhibitory role of hematite nanoparticles (HNPs) in their corrosion performance was evaluated by studying the formation and growth behavior. The results confirmed that the addition of HNPs up to a maximum amount of 3 g.L-1 to the phosphate-based electrolyte softened and stabilized the electrochemical events during titanium oxidation, resulting in an oxide layer with a more uniform microstructure, as well as less porosity and surface roughness. The participation of HNPs in the coating preparation accelerated the growth rate, promoted the anatase-rutile transformation, and reduced the inherent defects. Thus, the thermodynamic stability of the coatings in the corrosive medium improved and the dissolution kinetics of the substrate diminished. Modeling the data obtained from electrochemical impedance spectroscopy revealed that the incorporation of HNPs up to the maximum amount into the coatings increased the corrosion resistance of outer and inner parts of their bilayer microstructure by 5.18 and 9.88 times, respectively. Furthermore, Mott-Schottky analysis demonstrated that the surface reactivity of the coatings with aggressive anions diminished due to the reduction of donor concentration and more negative flat band potential, which proved the inhibiting effects of HNPs.