A study regarding the passive films on titanium alloys in sulphuric acid solutions

The passive layers on Ti and two ternary (Ti-15Mo-5Al, Ti-10Mo-10Al) alloys in sulphuric acid solutions (5%, 30%, 40% H2SO4) were investigated by potentiostatic and electrochemical impedance spectroscopy (EIS) techniques. The anodic curves for ternary alloys exhibit active passive behaviour with two current peaks for the critical passivation current densities (i(cr1), i(cr2)) which correspond to the same anodic critical passivation potentials (E-cr1, E-cr2) So, the passivation model is the same for titanium and ternary alloys and consists of the formation of an oxide with inferior valency (Ti2O3) at the first critical potential and a compact and protecting TiO2 oxide at the second potential. The impedance spectra (at the corrosion potential) show ii capacitive behaviour for the charge transfer reactions. So, was proposed an equivalent circuit with one time constant.