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@PHDTHESIS{Huczkowski:58932,
      author       = {Huczkowski, Pawel and Quadakkers, W. J.},
      title        = {{E}ffect of {G}eometry and {C}omposition of {C}r {S}teels
                      on {O}xide {S}cale {P}roperties {R}elevant for
                      {I}nterconnector {A}pplications in {S}olid {O}xide {F}uel
                      {C}ells ({SOFC}s)},
      volume       = {65},
      school       = {RWTH Aachen},
      type         = {Dr. (Univ.)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zenralbibliothek, Verlag},
      reportid     = {PreJuSER-58932},
      isbn         = {978-3-89336-484-8},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Energietechnik / Energy Technology},
      pages        = {159 S.},
      year         = {2007},
      note         = {Record converted from VDB: 12.11.2012; RWTH Aachen, Diss.,
                      2005},
      abstract     = {A number of high-Cr ferritic steels have been investigated
                      as possible construction materials (interconnectors) for
                      Solid Oxide Fuel Cells (SOFCs). The mentioned materials have
                      the advantage of a higher electronic conductivity, lower
                      cost and easier fabrication than so far used lanthanum
                      chromite-based ceramics. A large number of ferritic steels
                      are commercially available in a wide range of compositions,
                      however it seems that none of them can fulfil all
                      requirements for the SOFC interconnector application.
                      Therefore the main emphasis was put to the investigation of
                      the high temperature properties of recently introduced high
                      chromium ferritic steels especially designed for SOFC
                      applications. The scale formation mechanisms were
                      investigated during oxidation times ranging from a few
                      minutes up to 6000 hours. For scale characterization a
                      number of conventional analysis techniques such as optical
                      metallography, scanning electron microscopy and X-ray
                      diffraction were used in combination with two-stage
                      oxidation studies using $^{18}$O-tracer. It was found that
                      the growth rates of the scales were not only governed by the
                      main scale forming alloying elements Cr and Mn, but to a
                      substantial extent by minor additions of Si and Al. At the
                      test temperatures of 800°C and 900°C these latter elements
                      affect the scale formation although they are not directly
                      incorporated in the surface scales. SOFC market requirements
                      lead in many cases to the demand for a reduction of the fuel
                      cell size and/or weight and thus of the interconnector
                      thickness. Therefore, the main emphasis was made to
                      investigate changes in the oxidation behaviour in the case
                      of thin components. It was found that with decreasing sample
                      thickness the lifetime of the mentioned steels decreases due
                      to breakaway phenomena. This effect is caused by faster
                      exhaustion of the chromium reservoir from the bulk alloy in
                      case of thinner components. The observed lifetime limits can
                      be predicted with reasonable accuracy by a theoretical
                      model, using oxide growth rate parameters, initial alloy Cr
                      content and critical Cr content required for protective
                      chromia scale formation. In the calculation of the
                      Cr-reservoir exhaustion it has, however, to be taken into
                      account, that during air exposure the oxidation rates
                      increase with decreasing specimen thickness. The possible
                      explanation of this effect is discussed on the basis of
                      scale formation mechanisms involving microcrack formation in
                      the surface oxide scale and depletion of major and minor
                      alloying additions in the bulk alloy. The electrical
                      conductivity of the interconnect is a crucial property for
                      SOFC application whereby the conductivity of the chromium
                      based oxide scale which forms during high temperature
                      service has to be taken into account in the overall
                      conductivity value. Therefore experimental data concerning
                      the electrical conductivity of the surface oxide scales
                      formed in the temperature range 600-800°C on the
                      investigated ferritic steels have been determined. The data
                      are correlated with oxide scale morphologies and scale
                      formation mechanisms and the results are compared with those
                      obtained for two “pure chromia” forming materials.},
      cin          = {IEF-2},
      ddc          = {620},
      cid          = {I:(DE-Juel1)VDB810},
      pnm          = {Rationelle Energieumwandlung},
      pid          = {G:(DE-Juel1)FUEK402},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/58932},
}