Analysis of the formation of Ta2O5 passive films in acid media through mechanistic modeling

Electrochemical impedance spectroscopy (EIS) analyses are carried out to evaluate the passive features of tantalum oxide films (Ta2O5) formed at different potentiostatic conditions (0.5, 1.0, 1.5 and 2.0 V vs SSE). A supporting electrolyte of 0.1 M H2SO4 (pH 1) has been used to emulate acidic corrosive conditions for the growth of films with an n-type electronic character. A modification of the point defect model (PDM) accounting for the formation of molecular hydrogen (blistering damage) is used to fit the experimental EIS diagrams, and obtain the kinetic parameters that best describe the semiconductive behavior of the passive films. After this analysis, diffusivities in the order of 5.37 ± 1.6 x 10-17 and 1.98 ± 1.4 x 10-20 cm2 s-1 were obtained for the oxygen (DVO··) and hydroxyl vacancies (DVOH·), respectively. These findings show the capabilities of the EIS and the physicochemical modeling to account for the formation of valve-metal oxide films on a different range of conditions.