Anodic behaviour of titanium in acidic chloride containing media (HCl - NaCl). Influence of the constituents of the medium—III. Analysis of the electrochemical impedance. General dissolution — passivation mechanism
Résumé
Analysing the electrochemical impedance diagrams plotted in a large frequency range (10−3 Hz104 Hz) enables to complete and support the dissolution—passivation scheme of titanium elaborated from steady state measurements.
The analysis of the Rt. I product (charge transfer resistance by stationary current) reveals the presence of two active dissolution paths in tervalen titanium, one of which depends on the presence of the hydride (TiH2). Moreover it confirms the participation of the tetravalent oxide TiO2 in the establishment of the stable passivity. A complete reaction model specifying the chemical nature of all the intermediates and final products is proposed.