The relatively large number of adjustable parameters often precludes the unambiguous interpretation of electrochemical impedance spectra in terms of a unique kinetic model. In the present paper, the possibilities offered by a combination between in situ electrochemical impedance spectroscopic data and ex situ surface analytical information to improve the credibility of the estimates of the kinetic and transport parameters are discussed. Two electrode systems in which passive oxide films are formed—stainless steel in simulated pressurised water reactor coolant and tungsten in sulphate–fluoride solutions—are used as representative examples to demonstrate the different approaches taken to analyse the experimental data in terms of the Mixed-Conduction Model. Ways to extract information on the rate-limiting steps of the process of passive film formation, growth and restructuring by quantitative comparison of the model equations to electrochemical impedance and X-ray photoelectron spectroscopic data are described and the significance of the obtained parameters for the kinetics of the overall process of metal and alloy dissolution in the passive state is discussed.
- Kinetic model
- Electrochemical impedance spectroscopy
- X-ray photoelectron spectroscopy
- Passive film