Effect of specific electrochemical settings and anion types on titanium oxide layer properties after anodization in near-neutral electrolytes for dental applications

The effect of anodically formed oxide layer on titanium using different anion namely phosphate, acetate, sulfate, iodide, and thiocyanate containing electrolytes on the corrosion resistance and electrochemical behavior in artificial saliva (AS) was investigated at physiological temperature 37°C, using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. We also evaluated the impact of anodization parameters specifically applied voltage and current density on these oxide films. The galvanostatic growth of anodic oxide films on titanium can be accompanied by the incorporation of species from the electrolyte into the oxide, affecting the properties of the final oxide. OCP was shifted to less negative values for all anodized Ti compared to polished Ti. The thickness of the oxide layer was dependent on the oxidation potential. Titanium anodized with phosphate and acetate reflected robust and stable oxide layer showing consistent performance. Higher corrosion current density was measured for oxide prepared with sulfate and thiocyanate electrolytes, especially for oxide layer prepared up to 10 V_SCE. When TiO₂ is prepared up to 10 V_SCE, no distinct porous layer resistance (R_p) appears and the barrier layer resistance (R_b) dominates, indicating a compact oxide. TiO₂ shows both R_p and R_b, indicating a dual-layer structure with a porous outer layer and a dense barrier layer beneath when prepared up to 90 V_SCE, both R_p and R_b are present, showing a dual‐layer structure with a porous top layer and a dense barrier beneath. Regardless of the anion, all electrolytes produced strong barrier layers with R_b values exceeding those of the polished reference. After 14 days’ incubation in AS, all anodized titanium samples exhibited significantly higher OCP and corrosion potentials than polished titanium, indicating greater electrochemical stability across formation voltages and current densities. A voltage of 10 V_SCE already generated compact and protective barrier layers, with slightly better stability at higher current density (25 mA/cm²). In contrast, 90 V_SCE produced thicker two-layer oxides, but these did not consistently outperform the compact films formed at 10 V_SCE.