The transient response of passivated metallic electrode system under potential step is analysed based on a linear model, and a technique for calculating the parameters characterizing the growth and dissolution of passive film is proposed. It is believed that the information which is expected to be got from impedance measurement can be obtained by this technique and that this technique is superior to the impedance measurement as it is much more rapid than the latter, With this technique and other in situ methods such as potentiodynamic polarization, ellipsometric measurement, and potentiostatic cathodic reduction, the effects of alternating voltage modulation and its post-treatment on the properties of passive films on 321, 302 and 316 stainless steels were investigated. Results show that A. V. modulation increases thickness and the resistance against cathodic reductive dissolution of passive film, changes the parameters of impedance of the passivated electrodes and the surface state of passive film which makes post-treatment more effective. And an increase of breakdown potential of passive film can also be achieved to some extent under certain A. V. modulation condition. During the post-treatment, the Mo-containing ion is absorbed on the passive film, which led to the further increase of the stability of passive film.
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