Effects of pH and fluoride on the electrochemical behaviour of titanium and its anodic oxide film in artificial saliva: investigation by atomic force microscopy, energy dispersive spectroscopy, electrochemical impedance spectroscopy and scanning electron microscopy

The growth of the pre-immersion and anodic surface oxide films on titanium was found to be influenced by the pH of the saliva using open-circuit potential (E_ocp), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. It was found that the titanium's E_ocp increased with time as the metal was immersed in saliva with different pH values, from acidic to alkaline. This suggests that the titanium's pre-immersion oxide coating grew in these solutions. Furthermore, the EIS data showed that the oxide film resistances of both anodic and pre-immersion films increased with the saliva's pH, although anodic films did so faster than the pre-immersion films. Even though titanium's pre-immersion coating grows in neutral saliva that contains fluoride ions (F^– ions), the corrosion resistance of the metal diminishes as the concentration of these ions rises because of their aggression. The results of potentiodynamic polarization demonstrated that the rate of corrosion of the titanium surface was reduced by both an increase in pH and a decrease in fluoride ion concentration in saliva. The resistance of titanium's pre-immersion layer increased when the immersion period was raised to 17 days in saliva containing 0.005 M F^– ions at pH 6.34. The titanium surface was examined using scanning electron microscopy (SEM), and it was shown that when the pH of saliva increases, a greater percentage of the faults and notches on the growing pre-immersion oxide layer are repaired and healed. Additionally, the atomic force microscopy (AFM) data demonstrated that the titanium's surface roughness increases with the concentration of F^– ions in saliva due to their corrosive action. Energy dispersive spectroscopy (EDS) revealed that a titanium oxide layer was formed when titanium was submerged in artificial saliva.