A mixed-conduction model for oxide films on Fe, Cr and Fe-Cr alloys in high-temperature aqueous electrolytes

II. Adaptation and justification of the model

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

Research output: Contribution to journalArticleScientificpeer-review

63 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 this second part, the modifications to the mixed-conduction model (MCM) are discussed on the basis of experimental data presented in the first part for Fe, Cr and two Fe–Cr alloys (12 and 25 wt% Cr) in an aqueous solution at 200 °C. Application of the MCM to fit and predict experimental behaviour both at room temperature and at 200 °C is demonstrated.
The major difference between the behaviour of films at room temperature and at 200 °C is that the mobility of ionic defects is much higher at the higher temperature. Estimates show that the ratio of the electronic and ionic diffusion coefficients (De/Di) is of the order of 105 at room temperature and ≈30 at 200 °C for pure Fe.
Such a large difference explains the higher growth rate and thickness of films formed on Fe at the higher temperature. It is also in agreement with the higher defect content and lower field strengths in high-temperature films.
The application of the MCM to Fe–Cr alloys indicates that the diffusion coefficient of major ionic current carriers is smaller for the alloys than for pure Fe. Alloying with Cr thus lowers the ionic mobility in the passive film on a ferrous alloy also at 200 °C.

Original languageEnglish
Pages (from-to)1923-1940
JournalCorrosion Science
Volume44
Issue number9
DOIs
Publication statusPublished - 2002
MoE publication typeA1 Journal article-refereed

Fingerprint

Electrolytes
Oxide films
Iron alloys
Temperature
Defects
Alloying
Corrosion

Keywords

  • iron chromium alloys
  • EIS
  • passivity
  • passive films
  • ion and electron transport

Cite this

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title = "A mixed-conduction model for oxide films on Fe, Cr and Fe-Cr alloys in high-temperature aqueous electrolytes: II. Adaptation and justification of the model",
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 this second part, the modifications to the mixed-conduction model (MCM) are discussed on the basis of experimental data presented in the first part for Fe, Cr and two Fe–Cr alloys (12 and 25 wt{\%} Cr) in an aqueous solution at 200 °C. Application of the MCM to fit and predict experimental behaviour both at room temperature and at 200 °C is demonstrated. The major difference between the behaviour of films at room temperature and at 200 °C is that the mobility of ionic defects is much higher at the higher temperature. Estimates show that the ratio of the electronic and ionic diffusion coefficients (De/Di) is of the order of 105 at room temperature and ≈30 at 200 °C for pure Fe. Such a large difference explains the higher growth rate and thickness of films formed on Fe at the higher temperature. It is also in agreement with the higher defect content and lower field strengths in high-temperature films. The application of the MCM to Fe–Cr alloys indicates that the diffusion coefficient of major ionic current carriers is smaller for the alloys than for pure Fe. Alloying with Cr thus lowers the ionic mobility in the passive film on a ferrous alloy also at 200 °C.",
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A mixed-conduction model for oxide films on Fe, Cr and Fe-Cr alloys in high-temperature aqueous electrolytes : II. Adaptation and justification of the model. / Beverskog, B.; Bojinov, Martin; Kinnunen, Petri; Laitinen, Timo (Corresponding Author); Mäkelä, Kari; Saario, Timo.

In: Corrosion Science, Vol. 44, No. 9, 2002, p. 1923-1940.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - A mixed-conduction model for oxide films on Fe, Cr and Fe-Cr alloys in high-temperature aqueous electrolytes

T2 - II. Adaptation and justification of the model

AU - Beverskog, B.

AU - Bojinov, Martin

AU - Kinnunen, Petri

AU - Laitinen, Timo

AU - Mäkelä, Kari

AU - Saario, Timo

PY - 2002

Y1 - 2002

N2 - 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 this second part, the modifications to the mixed-conduction model (MCM) are discussed on the basis of experimental data presented in the first part for Fe, Cr and two Fe–Cr alloys (12 and 25 wt% Cr) in an aqueous solution at 200 °C. Application of the MCM to fit and predict experimental behaviour both at room temperature and at 200 °C is demonstrated. The major difference between the behaviour of films at room temperature and at 200 °C is that the mobility of ionic defects is much higher at the higher temperature. Estimates show that the ratio of the electronic and ionic diffusion coefficients (De/Di) is of the order of 105 at room temperature and ≈30 at 200 °C for pure Fe. Such a large difference explains the higher growth rate and thickness of films formed on Fe at the higher temperature. It is also in agreement with the higher defect content and lower field strengths in high-temperature films. The application of the MCM to Fe–Cr alloys indicates that the diffusion coefficient of major ionic current carriers is smaller for the alloys than for pure Fe. Alloying with Cr thus lowers the ionic mobility in the passive film on a ferrous alloy also at 200 °C.

AB - 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 this second part, the modifications to the mixed-conduction model (MCM) are discussed on the basis of experimental data presented in the first part for Fe, Cr and two Fe–Cr alloys (12 and 25 wt% Cr) in an aqueous solution at 200 °C. Application of the MCM to fit and predict experimental behaviour both at room temperature and at 200 °C is demonstrated. The major difference between the behaviour of films at room temperature and at 200 °C is that the mobility of ionic defects is much higher at the higher temperature. Estimates show that the ratio of the electronic and ionic diffusion coefficients (De/Di) is of the order of 105 at room temperature and ≈30 at 200 °C for pure Fe. Such a large difference explains the higher growth rate and thickness of films formed on Fe at the higher temperature. It is also in agreement with the higher defect content and lower field strengths in high-temperature films. The application of the MCM to Fe–Cr alloys indicates that the diffusion coefficient of major ionic current carriers is smaller for the alloys than for pure Fe. Alloying with Cr thus lowers the ionic mobility in the passive film on a ferrous alloy also at 200 °C.

KW - iron chromium alloys

KW - EIS

KW - passivity

KW - passive films

KW - ion and electron transport

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JO - Corrosion Science

JF - Corrosion Science

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