Evaluation of electrical breakdown of anodic films on titanium in phosphate-base solutions

Titanium is a highly reactive metal, so that whenever it is exposed to air or other environments containing available oxygen, a thin layer of oxide is formed on the surface. This layer increases the corrosion resistance of titanium. The formation of the oxide film can be electrochemically performed by anodizing. In this research, anodizing of titanium was performed in phosphate-base solutions such as H3PO4, NaH2PO4·2H2O and Na2HPO4 at 9.75 mA/cm2 and 35 °C under galvanostatic conditions. The potential-time curves in the above mentioned solutions show that the anodic films formed on Ti are compact and their thickness depends on the solution type and concentration. The SEM and XRD studies show that these layers are amorphous. In this article, the effect of electrolyte concentration, composition and resistivity on breakdown voltage has been discussed in terms of Ikonopisov electron avalanch breakdown model. This model shows that the major factor contributing to the decrease in breakdown voltage with increasing electrolyte concentration is the increasing primary electronic current.