The electrochemical behavior of anodic alumina films implanted with Ni ions

The motivation of this study is to investigate the possibility of improving corrosion resistance of anodic films on aluminum by Ni ions implantation. The implantation of Ni ions was carried out using a MEVVA source at an energy of 40 keV and a dose of 5.0 × 1017 ions cm−2. Electrochemical impedance spectroscopy (EIS) was used to study the influence of the ions implantation on electrochemical behavior of anodic films in basic NaCl solution. The results show that Ni ions implantation strengthens the self-sealing process of the anodic film in solutions. The resistance of the porous layer (Rp) increases and the capacitance of the porous layer (Cp) decreases after implantation of Ni ions. For the anodic layer without implantation of Ni ions, as the immersion time increases, changes of Cp and Rp are slower. A more rapid change is observed for the anodic films implanted with Ni ions. XPS results reveal that Ni is present on the anodic film surface as metallic Ni and nickel oxide (NiO). AFM results show that the implantation of Ni ions made the surface structure and morphology of anodic films more uniform and less rough. The semi conductive property of anodic films in basic NaCl solution with and without Ni ions implantation was studied by Mott–Schottky analysis. For anodic films implanted with Ni ions, the profile is characteristic of p-type semiconductors from −1.0 V to −0.5 V. By expanding the M–S plots at high potentials to more positive potential than −0.5 V, the anodic film shows n-type characteristic. Possible reasons for the observed changes in surface properties are discussed.