Change search
ReferencesLink to record
Permanent link

Direct link
In-situ impedence spectroscopy study of electrical conductivity and ionic transport in thermally grown oxide scales on a commercial FeCrA1 alloy
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science (closed 20081231).
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science (closed 20081231).ORCID iD: 0000-0002-4431-0671
Kanthal AB, Hallstahammar.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science (closed 20081231).ORCID iD: 0000-0002-9453-1333
2007 (English)In: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 68, no 5-6, 253-269 p.Article in journal (Refereed) Published
Abstract [en]

In-situ impedance-spectroscopy measurements were performed at temperatures between 600 and 1,000 degrees C to investigate ionic transport in oxide scales formed on Kanthal AF alloy. The samples were pre-oxidized at 800, 900 and 1,000 degrees C in air. The impedance spectra of the oxide formed at 1,000 degrees C exhibited essentially one semicircle, whereas samples oxidized at lower temperatures showed an additional semicircle at high frequencies suggesting a more heterogeneous oxide. The ionic-transference number, derived by measuring the voltage across the oxide scale, indicates that the oxide is a predominant electronic conductor. Ionic diffusivity in the oxide scales formed at different pre-oxidizing temperatures was calculated, using the ionic-transference number. The ionic diffusivities obtained in this way are in reasonable agreement with literature data acquired by other methods. The oxide-formation temperature has a significant influence on the conductivity and ionic-transport properties of the oxide scale.

Place, publisher, year, edition, pages
2007. Vol. 68, no 5-6, 253-269 p.
Keyword [en]
alumina scale, FeCrAl alloy, impedance spectroscopy, conductivity, ionic diffusivity, beta-nial alloy, cr-al-alloys, alumina scales, electrochemical method, impedance spectroscopy, oxidation behavior, kanthal af, alpha-alumina, al2o3 scales, dry o-2
National Category
Inorganic Chemistry
URN: urn:nbn:se:kth:diva-17083DOI: 10.1007/s11085-007-9074-xISI: 000250582300004ScopusID: 2-s2.0-35648997906OAI: diva2:335126

QC 20100826

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2013-11-20Bibliographically approved
In thesis
1. Ionic Transport in Metal Oxides Studied in situ by Impedance Spectroscopy and Cyclic Voltammetry
Open this publication in new window or tab >>Ionic Transport in Metal Oxides Studied in situ by Impedance Spectroscopy and Cyclic Voltammetry
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Ionic transport in metal oxides is crucial for the functioning of a broad range of different components, such as heat resistant alloys designed for high temperature applications and oxide electrolytes in solid oxide fuel cells. This thesis presents results from in situ electrochemical studies of properties related to ionic transport in metal oxides that are important for their applications as protective oxides and ionic conductors.

Heat resistant alloys of alumina-former type are known to form an adherent, slowly growing and protective aluminium oxide (Al2O3) scale that protects metals from chemical degradation at high temperature. In situ impedance spectroscopy was used to study highly pure and dense samples of a-alumina in the temperature range 400 – 1000 °C. It was shown that surface conduction on the sample could severely distort the measurement below 700 °C. The magnitude of the distortions appeared to be sensitive to the type of electrodes used. The use of a so-called guard electrode was shown to effectively block the surface conduction in the measurements. By varying the grain size of the sintered alpha-alumina samples, the influence of grain size on the overall conductivity of the a-alumina was studied. It was shown that the activation energy for conductivity increased as the grain size decreased. Molecular dynamics calculations were performed in order to elucidate whether Al- or O ions are dominant in the ionic conductivity of the alpha-alumina. Comparing the calculation and experimental results, the dominating charge carrier was suggested to be oxygen ions.

Moreover, the ionic transport in thermally grown alumina-like oxide scales formed on a FeCrAl alloy was studied in situ by impedance spectroscopy between 600 and 1000 °C. It was shown that the properties of these scales differ largely from those of pure and dense alpha-alumina. Furthermore, the conductivity is mainly electronic, due to the multiphase/multilayer microstructure and substantial incorporation of species from the base metal. However, the diffusivity obtained from the ionic conductivity was in line with diffusion data in literature obtained by other methods such as thermogravimetry. Besides, the initial stage of oxidation of a number of Fe-, Ni- and Co-based alloys at temperatures between 500 and 800 °C was studied in situ by high temperature cyclic voltammetry, in which the oxygen activity was changed over a wide range. From the resulting voltammograms the redox reactions occurring on the alloy surface could be identified. It was concluded that the base metal oxidized readily on these alloys before a protective chromia- or alumina-like scale is formed. The base metal oxide is most likely incorporated into the more protective oxide.

Further, the oxygen ionic conductivity of highly pure and fully dense yttria-stabilized zirconia produced by spark plasma sintering was studied by impedance spectroscopy. The aim was to evaluate intrinsic blocking effects on the ionic conduction associated with the space charge layer in the grain boundary region. It was observed that the ionic conductivity of the spark plasma sintered oxides is equal or slightly higher than what has been achieved by conventional sintering methods. In addition, it was shown that the specific grain boundary conductivity increases with decreasing grain size, which can be explained by a decreasing Schottky barrier height (i.e., decreasing blocking effect). The quantitative results from this work verify the space charge model describing the influence of grain size on the ionic conductivity of yttria-stabilized zirconia through dopant segregation and oxygen vacancy depletion along the grain boundaries.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. x, 61 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2007:3
ionic transport, alumina, zirconia, in situ impedance spectroscopy, molecular dynamics, high temperature cyclic voltammetry, spark plasma sintering, initial oxidation, FeCrAl alloy, grain size, space charge model.
National Category
Inorganic Chemistry
urn:nbn:se:kth:diva-4312 (URN)978-91-7178-587-9 (ISRN)978-91-7178-587-9 (ISBN)
Public defence
2007-03-30, F3, Lindstedtsvägen 26, Stockholm, 14:00
QC 20100825Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2010-08-26Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopusSpringerLink

Search in DiVA

By author/editor
Öijerholm, JohanPan, JinshanLeygraf, Christofer
By organisation
Corrosion Science (closed 20081231)
In the same journal
Oxidation of Metals
Inorganic Chemistry

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 45 hits
ReferencesLink to record
Permanent link

Direct link