Corrosion resistance of BaTiO3 films prepared by plasma electrolytic oxidation

Barium titanate films were directly synthesized on Ti plates by plasma electrolytic oxidation in highly alkaline solutions using Ba(CH3COO)2 and NaOH as the electrolyte. SEM and X-ray diffraction results showed that crater-shaped and large-grained cubic BaTiO3 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 TiO2 films and pure titanium specimens were also investigated for comparison. Open-circuit potential measurements showed that BaTiO3 and TiO2 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 BaTiO3 and TiO2 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 BaTiO3 films suggested that the anodic current may be due to the O2 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 BaTiO3 films could close up the pores in the films and hinder the transportation of OH− ions. Hence the BaTiO3 films possess better corrosion resistance than TiO2 and pure Ti specimens.