Behavior of titanium alloys in neutral solutions by EIS and potentiostaticmethods

Passivity of Ti and Ti-15Mo, Ti-15Mo-5Al alloys in concentrated chlorides s olutions and sea water was investigated by electrochemical impedance spectr oscopy (EIS) and potentiostatic techniques. The anodic polarization curves do not present the active-passive transition range, Ti and its alloys being passive even from the beginning of the anodic polarization because of the primary pre-existing oxide film. The curves are similar and are characteriz ed by the passive current density; this does not change with the temperatur e and alloy composition. The molybdenum increases the stability of the pass ive film enlarging considerably the passive range of the alloys; this fact can be explained by the formation of the insoluble molybdenum chlorides. El ectrochemical impedance spectroscopy (EIS) measurements have been performed on titanium alloys in order to characterize the passive films on these all oys. The impedance spectra were obtained at different potential values of 0.2 V; +0.8 V and E-corr Nyquist and Bode diagrams were recorded at these p otentials. These diagrams are the same for Ti and its alloys; so, the equiv alent circuit is the same for Ti and its alloys. This equivalent circuit co ntains two time constants: one time constant represents the passive film an d double layer, the second is for the,diffusion processes.