Sealing of porous titanium oxides produced by plasma electrolytic oxidation

Plasma electrolytic oxidation is a powerful technique allowing the formation of ceramic coatings with a high degree of functionalization. Plasma–chemical interactions, resulting from the application of a high voltage in a conductive electrolyte, like 0.5 M NaOH, favor the development of a porous surface, which deserves to be sealed to obtain proper corrosion resistance. In the present work, the effect of temperature employed during sealing in calcium acetate is investigated, finding 85°C as an optimum temperature to allow pores closure. Furthermore, a comparison with sealing performed in hot water is presented, which demonstrated similar sealing efficiency. Scanning electron microscope and electrochemical impedance spectroscopy are the tools selected to investigate sealing effects. Impedance spectra are fitted according to feasible electrochemical equivalent circuits finding two-time constants when applied to sealed samples indicative of the presence of barrier and porous layer, respectively.