Conduction mechanism in oxide films on ferrous alloys studied by impedance spectroscopy in symmetrical and asymmetrical configurations

Betova, Iva; Bojinov, Martin; Kinnunen, Petri; Mäkelä, Kari; Saario, Timo

doi:10.1016/j.jelechem.2003.08.030

Cited by 25 publications

(31 citation statements)

References 57 publications

(135 reference statements)

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“…3,4,14,46 In the following, the relationship between the defect structure, ionic and electronic conduction is treated on the basis of the MCM for oxide films. 18,19 According to this model, the growth of the barrier layer proceeds into the steel by ingress of oxygen transported via oxygen vacancies ͑reaction sequence k 2 -k 4 coupled via the oxygen vacancy transport flux, Fig. 9͒.…”

Section: Discussionmentioning

confidence: 99%

“…Qualitatively similar spectra have been measured at the other temperatures and also in earlier work. 19,28 It is worth mentioning that no significant hysteresis between measurements performed from negative to positive potentials and vice versa has been found as long as the system has been allowed to reach a constant current density at each potential.…”

Section: B252mentioning

confidence: 99%

“…To a first approximation, the high-frequency time constant in the spectra can be ascribed to a relaxation in a space-charge layer or an interfacial charge-transfer process, whereas the low-frequency part has been best described as a Warburg-type transport impedance in a finitelength layer. 18,19,21 Impedance spectra in the alloy/oxide/inert metal (symmetrical) configuration.- Figure 4 shows the impedance spectra measured at 150°C in the alloy/oxide/inert metal configuration after an oxidation procedure similar to that for the spectra presented in Fig. 2.…”

Section: B252mentioning

confidence: 99%

“…18,19,21 For a detailed explanation of all the symbols used in the paper, the reader is referred to the List of Symbols. It follows from Eq.…”

Section: B256mentioning

confidence: 99%

“…3,9,18 It has been demonstrated that the compact layer in the oxide film formed on material surfaces in high-temperature water contains a significantly larger number of ionic defects than roomtemperature passive films. 3,18,19 The presence of ionic defects offers routes for ionic species to be transported through the film, making the dissolution of the metal through the film possible. It can be generally stated that the more defects the film contains and the higher their mobility, the more susceptible the underlying alloy is to corrosion.…”

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confidence: 99%

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A Mixed-Conduction Model for the Oxidation of Stainless Steel in a High-Temperature Electrolyte

Bojinov

Kinnunen

Lundgren³

et al. 2005

J. Electrochem. Soc.

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The oxide films formed on AISI 316L͑NG͒ in the temperature range 150-300°C have been characterized by impedance spectroscopy and ex situ analysis using Auger electron spectroscopy. Relatively thick films containing a high concentration of mobile defects form on stainless steel in a high-temperature borate electrolyte, but their impedance response is most probably controlled by the properties of a thin barrier sublayer. The ability of the mixed conduction model for passive films to reproduce the experimental impedance data in both alloy/oxide/electrolyte and alloy/oxide/inert metal configurations has been tested. A procedure for the calculation of the kinetic constants of the interfacial reactions of point defect generation/consumption, as well as those characterizing the transport rates of ionic/electronic defects in the oxide, has been developed. The effect of temperature on the kinetic and transport parameters has been assessed, and the relevance of these parameters for the corrosion behavior of stainless steel in a high-temperature electrolyte is discussed. The results show that the nature of the barrier layer does not change drastically with temperature, although the growth mechanism of the oxide film is different at 150-300°C than at room temperature.The materials used in contact with the coolant in nuclear power plants rely almost exclusively on a passivating oxide film to ensure durability and structural integrity. A slow and well-controlled growth of the passive film is necessary in order to limit the impact of the coolant on these materials and to minimize the concentration of impurities that may reach the nuclear fuel surfaces and thus become radioactive.The development of knowledge of the oxide film composition and behavior, as well as the knowledge of the local coolant chemistries, has converged considerably during the last few years. 1,2 It is hence known that the oxide films formed on stainless steels and nickel-based alloys in high-temperature water have basically the same main structure and that the important compounds ensuring the protective character of the oxide film ͑nickel ferrite and nickel and iron chromites͒ are essentially the same for all the nickel-based materials and stainless steels. [3][4][5][6][7][8][9][10][11][12][13][14][15] In addition to the increased understanding of growth and restructuring of oxide films, recent development of radiolysis codes allows the modeling of the chemistry resulting from the radiolysis in virtually any location where the coolant is in contact with any material in light water reactors. The modeling provides the concentration of all radiolysis products, including radicals, and also calculates the local electrochemical corrosion potential in each location, hence providing the basis for determining or establishing thermodynamic, kinetic, and electrokinetic phenomena. 16 We hence have the qualitative understanding of most of the important processes during film growth and restructuring, with their background and implications. 17,18 What we still lack today i...

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