TiO2 Microparticles Incorporation in Coatings Produced by Plasma Electrolytic Oxidation (PEO) on Titanium

Abstract

This research describes the influence of two types of particles, namely rutile and anatase microparticles (average d < 5 µm), on the morphology, structure, and anticorrosive properties of PEO coatings on titanium produced in an alkaline solution based on NaOH and sodium metasilicates. The paper reports the experimental results relating to the study of the influence of the electrical regime and working frequency of the anodizing treatment on the interaction between the particles, the substrate, and the oxide to determine the optimal conditions that favour the incorporation of the particles and the production of a thick oxide. PEO coatings are characterized by using a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) analysis, and X-ray diffraction (XRD) testing. The electrochemical behaviour is evaluated by free corrosion potential monitoring and electrochemical impedance spectroscopy analysis (EIS) performed in a sulphuric acid solution. The particles are successfully incorporated into the coating under any electrical condition and at any frequency. However, only treatments carried out at 1000 Hz allow the production of coatings that combine a large thickness (up to 50 µm) and improved anticorrosion behaviour. In contrast, oxide layers produced at 20 Hz and in DC show a quite damaged structure, affecting their anticorrosion behaviour and resulting in lower corrosion potential and impedance values.