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@PHDTHESIS{Grnwald:848365,
      author       = {Grünwald, Nikolas},
      title        = {{S}elbstheilende plasmagespritzte
                      {M}n$_{1,0}${C}o$_{1,9}${F}e$_{0,1}${O}$_{4}$-{S}chutzschichten
                      in {F}estoxidbrennstoffzellen},
      volume       = {422},
      school       = {Universität Bochum},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-03606},
      isbn         = {978-3-95806-327-3},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {x, 140 S.},
      year         = {2018},
      note         = {Universität Bochum, Diss., 2018},
      abstract     = {Applying dense chromium protective layers between
                      interconnector and cathode can efficientlydiminish chromium
                      related degradation of solid oxide fuel cells (SOFCs).
                      Especiallyatmospherically plasma sprayed (APS)
                      Mn$_{1.0}$Co$_{1.9}$Fe$_{0.1}$O$_{4}$ (MCF) coatings
                      demonstrated their effectiveness concerning Cr retention
                      within stacks tested in Jülich. Nevertheless, strong
                      microstructural and phase changes of these coatings during
                      operation were reported in literature, but not fully
                      understood yet. This thesis was part of a collaborative
                      project called “SOFC-Degradation” (grant no.03SF0494A),
                      which was focused on different degradation phenomena
                      emerging during SOFC operation. The goal of the present work
                      was to investigate the basic mechanisms leading to the
                      observed changes of APS-MCF coatings during operation. The
                      results should enable long-term prediction and facilitate
                      accelerated test-procedures. Additionally, wet powder
                      spraying (WPS) was investigated as a cost efficient
                      alternate coating technique. APS-MCF coatings were heat
                      treated in air in combination with common steel substrates
                      and cathode contact layers to simulate SOFC operation
                      conditions. During the APS-process MCF is reduced and
                      deposited in a rock salt configuration
                      ((Mn,Co,Fe)$_{1}$O$_{1}$), which is metastable at room
                      temperature. By annealing these coatings in air, the
                      material transforms to the low temperature (T < 1100 °C)
                      stable spinel phase ((Mn,Co,Fe)$_{3}$O$_{4}$). This phase
                      transformation is connected to an oxygen uptake and is
                      accompanied by a volume expansion of the material. Inside
                      the crack-network that can be found in as-sprayed coatings,
                      this volume expansion leads to a densification and
                      crack-healing. Subsequently, the phase transformation, which
                      is also anoxidation process, is dominated by solid state
                      diffusion of cations as soon as the cracks areclosed.
                      Thereby cobalt is enriched at the layer’s surface as its
                      diffusion coefficient is higher than that of manganese or
                      iron within the layer formed. The outward diffusion of
                      cations generates a counterflow of vacancies into the bulk,
                      where they accumulate to form small pores. A
                      two-phase-system composed of a cobalt-rich rock salt phase
                      and a manganese- and iron-rich spinel phase can be observed
                      in the coating’s bulk. Extending the annealing time
                      results in a decrease of rock salt phase and an increase of
                      spinel phase. When the transformation to the spinel phase is
                      completed, solid state diffusion strives for a homogeneous
                      distribution of elements on the long term. An increase of
                      the annealing temperature accelerates the observed
                      phenomena. [...]},
      cin          = {IEK-1},
      cid          = {I:(DE-Juel1)IEK-1-20101013},
      pnm          = {113 - Methods and Concepts for Material Development
                      (POF3-113)},
      pid          = {G:(DE-HGF)POF3-113},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/848365},
}