Relationship between the Resistivity Profiles Obtained from the Power Law Model and the Physico-Chemical Properties of Passive Films

The constant-phase-element behavior measured for passive films was analysed using the power law model. It allows to obtain the variation of the resistivity through the passive film thickness. To avoid many unknown parameters required for the model, a methodology to analyze the impedance diagrams has been described. It is illustrated with several examples. First, the resistivity profiles were obtained for a Ni-20Cr alloy immersed in solutions with different pH values to validate the proposed methodology. The dielectric properties of the passive films were discussed from the duplex character of these passive layers. It was shown that the shape of the resistivity profile could be attributed to the contribution and the thickness of the inner dense oxide and the outer hydroxide layers, respectively. Then, the second example provided information on the evolution of the behavior of the passive film formed on 316L stainless steel under irradiation.

Automated summary

The power law model was utilized to analyze the constant-phase-element behavior of passive films, allowing the variation of resistivity with passive film thickness to be obtained. A methodology for analyzing impedance diagrams was described to avoid the need for numerous unknown parameters in the model. The dielectric properties of passive films and the duplex character of these layers were discussed, illustrating the contribution of inner dense oxide and outer hydroxide layers to the resistivity profiles. Additionally, information on the evolution of passive film behavior on 316L stainless steel under irradiation was provided as an example.