Characterization of Surface-Treated NiTi Alloy by Various Electrochemical Techniques in Phosphate-Buffered Saline

Sol–gel titania thin film coating was prepared on NiTi surfaces, modified with acidified ferric chloride solution. Nanogrids formed on chemical treatment were uniformly covered with titania coating. Cyclic voltammetry studies in phosphate-buffered saline solution revealed that sol–gel titania-coated surface displayed electrochemical properties which were similar to those observed for pure titanium. During polarization, the passive layer formed on modified NiTi was stable for potentials greater than 0.9 V. The overall resistance measured by electrochemical impedance spectroscopy for sol–gel titania surface was in the order of 10⁵ Ω, which was approximately two orders higher than bare NiTi surface. The current noise analyzed using electrochemical noise measurements was minimum after sol–gel coating, which emphasizes the better protection power of the surface from the attack of corrosive species. Dynamic impedance studies carried out on bare and titania-coated NiTi also supports the results obtained from cyclic polarization