A mixed-conduction model for oxide films on Fe, Cr and Fe-Cr alloys in high-temperature aqueous electrolytes: I. Comparison of the electrochemical behaviour at room temperature and at 200 °C

B. Beverskog, Martin Bojinov, Anders Englund, Petri Kinnunen, Timo Laitinen (Corresponding Author), Kari Mäkelä, Timo Saario, Pekka Sirkiä

Research output: Contribution to journalArticleScientificpeer-review

62 Citations (Scopus)

Abstract

The aim of this two-part work is to propose a model for the corrosion mechanism of ferrous alloys in high-temperature aqueous environments.
In the first part of the work, experimental results of the electrochemical behaviour of pure Fe, pure Cr, Fe–12%Cr alloy and Fe–25%Cr alloy during the initial stage of oxide film formation at 200 °C are compared to those obtained at room temperature.
The results have been obtained by using voltammetry, electrochemical impedance spectroscopy (EIS), contact electric resistance (CER) and contact electric impedance (CEI) techniques. An increase of temperature from room temperature up to 200 °C has been found to result in higher currents in the passive region for all the materials.
The CER, EIS and CEI results indicate that the film especially on Fe is considerably thicker at the higher temperature. In addition, the EIS and CEI results give information of an ionic transport process at 200 °C, which has not been observed in the EIS response at room temperature.
The dependence of the electrical and transport properties of the film on potential suggests that the films at 200 °C can also be described by a mixed-conduction model (MCM) introduced recently for room temperature. However, the faster rate of ionic defect transport has to be emphasised at the higher temperature.
The adaptation of the MCM to high-temperature oxide films is discussed in more detail in the second part of this work.
Original languageEnglish
Pages (from-to)1901-1921
JournalCorrosion Science
Volume44
Issue number9
DOIs
Publication statusPublished - 2002
MoE publication typeA1 Journal article-refereed

Keywords

  • iron chromium alloys
  • EIS
  • contact electric resistance
  • passivity
  • high-temperature aqueous corrosion

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