Corrosion Behaviour of the Anodic Oxide Film on Commercially Pure Titanium in NaCl Environment

Abstract

Anodic oxide growths on commercially pure titanium in 1 M sulphuric and phosphoric acids have been investigated in the present study. Ruptures and blisters of the oxide layers were found as result of a huge pressure of oxygen bubbles developed within the film. The ruptures were more pronounced when higher anodic voltages are reached for both acid anodizations. The oxygen evolution was probably inhibited more significantly for phosphoric acid anodization compared to sulphuric acid anodization. The anodic oxides also showed more ruptures after anodized titanium specimens were immersed for 60 days in naturally aerated 3.5% NaCl electrolyte in higher anodic voltage compared to the immediately ‘just’ immersed conditions in the NaCl electrolyte. The corrosion behaviours of the anodic oxides were studied in the 3.5% NaCl by potentiodynamic polarization and electrochemical impedance spectroscopy. Increased corrosion resistance of the anodic oxides on titanium in NaCl were observed with increase in anodic voltages. The anodic oxide produced in the phosphoric acid showed a higher corrosion resistance than that of the sulphuric acid at each anodizing condition; indicates that the corrosion protection by anodizing for titanium in phosphoric acid should probably be considered in priority compared with sulphuric acid.