Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Ionic Transport in Metal Oxides Studied in situ by Impedance Spectroscopy and Cyclic Voltammetry
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
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.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:3
Keyword [en]
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
Identifiers
URN: urn:nbn:se:kth:diva-4312ISRN: 978-91-7178-587-9ISBN: 978-91-7178-587-9 (print)OAI: oai:DiVA.org:kth-4312DiVA: diva2:11750
Public defence
2007-03-30, F3, Lindstedtsvägen 26, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100825Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2010-08-26Bibliographically approved
List of papers
1. In-situ measurements by impedance spectroscopy of highly resistive alpha-alumina
Open this publication in new window or tab >>In-situ measurements by impedance spectroscopy of highly resistive alpha-alumina
2006 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 48, no 1, 243-257 p.Article in journal (Refereed) Published
Abstract [en]

In-situ impedance spectroscopy has been used for characterisation of oxides at elevated temperatures. However, for highly resistive oxides, the influence of electrode contact and leakage currents due to gas phase and surface conduction needs to be taken into account. In this study, IS measurements of pure and dense alpha-alumina (alpha-Al2O3) samples were performed in the temperature range 400-1000 degrees C with different types of electrode contact, in air and in nitrogen. The results show that above 700 degrees C the influence is negligible, whereas at lower temperatures the surface leakage current was substantial, and a so-called guard electrode recommendable.

Keyword
aluminium oxide; impedance spectroscopy; ionic conductivity; high temperature corrosion; HIGH-TEMPERATURE OXIDATION; SINGLE-CRYSTAL ALUMINA; ELECTRICAL CONDUCTIVITY; SELF-DIFFUSION; OXIDE-FILMS; POLARIZATION; ALPHA-AL2O3; STEEL
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-6899 (URN)10.1016/j.corsci.2004.11.027 (DOI)000234618800017 ()2-s2.0-28044446986 (Scopus ID)
Note
QC 20100825Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2017-12-14Bibliographically approved
2. Influence of Grain Size on Ionic Conductivity of Pure and Dense alpha-Al2O3 in the Temperature Range 400-1000 degrees C
Open this publication in new window or tab >>Influence of Grain Size on Ionic Conductivity of Pure and Dense alpha-Al2O3 in the Temperature Range 400-1000 degrees C
2004 (English)In: High Temperature Corrosion And Protection Of Materials 6, Prt 1 And 2, Proceedings, 2004, Vol. 461-464, no II, 865-872 p.Conference paper, Published paper (Refereed)
Abstract [en]

Ionic transport in alpha-Al2O3 at high temperatures is important for oxidation/corrosion resistance of Al2O3-forming heat resistant alloys. Whereas most of previous studies were performed at temperatures above 1000degreesC, this work concerns the temperature range 400 to 1000degreesC. Electrical proper-ties of polycrystalline and single crystal alpha-Al2O3 were measured in air by using impedance spectroscopy in order to study the ionic transport in Al2O3. The influence of grain size was investigated by measurements on a series of highly pure and dense samples with well-defined grain size ranging from 0.5 to 15 mum, produced by the spark plasma sintering technique. The results show that the grain size has a certain influence on the conductivity in the temperature range between 650 and 1000degreesC, where the activation energy for conductivity decrease from 2.4 to 1.6 eV with increasing grain size. At lower temperatures the activation energy is about 1.0 eV and independent of the grain size, indicating a different conduction mechanism.

Series
Materials Science Forum, ISSN 0255-5476 ; 461-464
Keyword
Alumina; Electrical conductivity; Grain size; Impedance spectroscopy; Charge transport; Impedance spectroscopy; Ionic transport; Low conductivity; Activation energy; Corrosion resistance; Diffusion; Electric conductivity; Grain size and shape; Ionic conduction; Leakage currents; Oxidation; Single crystals; Sintering; Superalloys; Thermal effects; Transport properties; alumina
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-6900 (URN)000223339700103 ()2-s2.0-8744239371 (Scopus ID)0-87849-945-8 (ISBN)
Conference
6th International Symposium on High Temperature Corrosion and Protection of Materials Les Embiez, FRANCE, MAY 16-21, 2004
Note

QC 20141208

Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2014-12-08Bibliographically approved
3. Self-diffusion activation energies in alpha-Al2O3 below 1000 degrees C: measurements and molecular dynamics calculation
Open this publication in new window or tab >>Self-diffusion activation energies in alpha-Al2O3 below 1000 degrees C: measurements and molecular dynamics calculation
Show others...
2004 (English)In: Philosophical Magazine Letters, ISSN 0950-0839, E-ISSN 1362-3036, Vol. 84, no 12, 781-789 p.Article in journal (Refereed) Published
Abstract [en]

Results from impedance spectroscopy measurements at temperatures between 400 and 1000° C, for single crystal and highly pure and dense polycrystalline α-Al2O3 samples with well-defined grain size, are compared with that from molecular dynamics calculation. Between 650 and 1000° C, the measured activation energy for conductivity is 1.5 eV for the single crystal, and increases from 1.6 to 2.4 eV as the grain size decreases from 15 to 0.5 μ m. The molecular dynamics calculation leads to the conclusion that the self-diffusion activation energy is about 1.5 eV for O and 1.0 eV for Al in single crystal α-Al2O3. The much higher mobility of O ions makes the O ions responsible for the conductivity of the single crystal oxide. It seems that the grain boundary leads to an increase in the activation energy. However, the quantitative influence of grain boundary still needs to be explained. Between 400 and 650° C, the measured activation energy is about 1.0 eV and independent of the grain size.

Keyword
Activation energy; Crystal growth from melt; Diffusion; Electric conductivity; Grain boundaries; Grain size and shape; Molecular dynamics; Polycrystalline materials; Single crystals; Spectroscopic analysis; Thermal effects; Impedance spectroscopy; Molecular dynamics calculation; Self-diffusion activation energy; Single crystal oxides; Alumina
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-6901 (URN)10.1080/09500830500071051 (DOI)000228882900004 ()2-s2.0-19944413992 (Scopus ID)
Note
QC 20100826Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2017-12-14Bibliographically approved
4. In-situ impedence spectroscopy study of electrical conductivity and ionic transport in thermally grown oxide scales on a commercial FeCrA1 alloy
Open this publication in new window or tab >>In-situ impedence spectroscopy study of electrical conductivity and ionic transport in thermally grown oxide scales on a commercial FeCrA1 alloy
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.

Keyword
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
Identifiers
urn:nbn:se:kth:diva-17083 (URN)10.1007/s11085-007-9074-x (DOI)000250582300004 ()2-s2.0-35648997906 (Scopus ID)
Note

QC 20100826

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
5. Study of Initial Oxidation of Engineering Alloys by High Temperature Cyclic Voltammetry
Open this publication in new window or tab >>Study of Initial Oxidation of Engineering Alloys by High Temperature Cyclic Voltammetry
2007 (English)In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 10, no 6, 47-50 p.Article in journal (Refereed) Published
Abstract [en]

The initial oxidation of Fe-, Co-, and Ni-based engineering alloys was studied in situ by high-temperature cyclic voltammetry. Measurements were performed at constant temperatures between 500 and 800 degrees C in an electrochemical cell utilizing oxygen ion-conducting yttria-stabilized zirconia as electrolyte and a reference electrode whose potential is determined by the oxygen activity in the ambient gas. The recorded voltammograms show clear current peaks that are associated with the oxidation of the base metal in the investigated alloys. For the Fe- based alloy, multiple peaks are observed, showing oxidation of Fe into different valence oxides. The results indicate that the base metal oxide is formed in the initial oxidation process of these engineering alloys, which may influence long-term high-temperature oxidation resistance of the alloys.

Keyword
Cyclic voltammetry; Electrochemistry; Measurement theory; Oxidation; Thermal effects; Zirconia; Ambient gas; Engineering alloys; Yttria-stabilized zirconia; Iron alloys
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-6903 (URN)10.1149/1.2717361 (DOI)000245472500005 ()2-s2.0-34047268324 (Scopus ID)
Note
QC 20100826. Uppdaterad från Accepted från Published 20100826.Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2017-12-14Bibliographically approved
6. Cyclic Voltammetry Study of the Early Stage of High Temperature Oxidation of Fe-, Co- and Ni-based alloys
Open this publication in new window or tab >>Cyclic Voltammetry Study of the Early Stage of High Temperature Oxidation of Fe-, Co- and Ni-based alloys
(English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111Article in journal (Other academic) Submitted
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-6904 (URN)
Note
QS 20120328Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2017-12-14Bibliographically approved
7. Microstructure and electrical conductivity of yttria stabilized zirconia ceramics sintered by spark plasma sintering: Part I. 3Y-TZP
Open this publication in new window or tab >>Microstructure and electrical conductivity of yttria stabilized zirconia ceramics sintered by spark plasma sintering: Part I. 3Y-TZP
(English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689Article in journal (Other academic) Submitted
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-6905 (URN)
Note
QS 20120328Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2017-12-14Bibliographically approved

Open Access in DiVA

fulltext(2841 kB)3087 downloads
File information
File name FULLTEXT01.pdfFile size 2841 kBChecksum MD5
148629a85c94cbd349db8cd19687bfa5697f905b7e08d01137032b607e5f12f30c976422
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Öijerholm, Johan
By organisation
Chemistry
Inorganic Chemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 3087 downloads
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

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1086 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf