Corrosion resistance of BaTiO 3 films prepared by plasma electrolytic oxidation

Abstract

Barium titanate films were directly synthesized on Ti plates by plasma electrolytic oxidation in highly alkaline solutions using Ba(CH 3COO) 2 and NaOH as the electrolyte. SEM and X-ray diffraction results showed that crater-shaped and large-grained cubic BaTiO 3 films near 10 μm thick were formed at an anodic voltage of 90 V for 55 °C. The corrosion behavior of the films was studied by means of open-circuit potential measurements and potentiodynamic polarization in the 0.1 M NaOH corrosive environment. Anodized TiO 2 films and pure titanium specimens were also investigated for comparison. Open-circuit potential measurements showed that BaTiO 3 and TiO 2 films exhibited quite stable corrosion potential of approximately 0.02 V (vs. Ag/AgCl). This corrosion potential is very close to the open-circuit potential of the cathode and therefore the electrochemical reaction is anodically controlled. The shift of open-circuit potential of BaTiO 3 and TiO 2 films toward positive values represents the increased anodic polarization resistance and reduced corrosion current, which is consistent with the mixed potential theory. From potentiodynamic polarization results, the high polarization resistance of BaTiO 3 films suggested that the anodic current may be due to the O 2 evolution on the exposed Ti surface by transporting OH − ion through open pores of the oxide to react on the titanium surface. The obtained thick oxide layers of BaTiO 3 films could close up the pores in the films and hinder the transportation of OH − ions. Hence the BaTiO 3 films possess better corrosion resistance than TiO 2 and pure Ti specimens.