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@PHDTHESIS{Stanislowski:51107,
      author       = {Stanislowski, Michael},
      title        = {{V}erdampfung von {W}erkstoffen beim {B}etrieb von
                      {H}ochtemperatur-{B}rennstoffzellen ({SOFC})},
      volume       = {54},
      school       = {RWTH Aachen},
      type         = {Dr. (FH)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-51107},
      isbn         = {3-89336-438-2},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Energietechnik / Energy Technology},
      pages        = {IV, 154 S.},
      year         = {2006},
      note         = {Record converted from VDB: 12.11.2012; RWTH Aachen, Diss.,
                      2005},
      abstract     = {Due to their high efficiencies and versatility planar solid
                      oxide fuel cells (SOFCs) offer a lot of advantages compared
                      to other fuel cell systems and combustion engines. One of
                      the main problems concerning the development of state of the
                      art planar SOFCs are the occurrence of ageing effects in
                      long term application. To a great deal these effects are
                      caused by the release of volatile Cr-species from metallic
                      interconnects which leads to an inhibition of the
                      electrochemical processes at the cathode resulting in a
                      rapid degradation of the cell performance. A goal in further
                      development of SOFC-systems is the reduction of the
                      operation temperature of the cell from currently 800°C to
                      700°C and below. For this purpose alternative electrolyte
                      materials with higher oxygen ion conductivities have to be
                      developed. Doped lanthanum gallates have been identified as
                      promising materials. However for these materials a depletion
                      of Ga by vaporization has been observed under anodic
                      conditions which may lead to a destruction of their
                      electrolyte properties. The aim of this work is the study of
                      the vaporization processes leading to the mentioned
                      degradation effects. For this purpose an experimental setup
                      according to the transpiration method has been developed.
                      Concerning the vaporization of chromium the Cr release rates
                      of the main ferritic interconnect alloys, namely Crofer 22
                      APU, ZMG 232, E-Brite, IT-10, IT-11, IT-14 and Ducrolloy as
                      well as a variety of Ni- and Co-base superalloys and
                      stainless steels with different contents of Al, Si, Ti, Mn,
                      W, Ni and Co were measured at 800°C in air and compared to
                      each other. The alloys that form an upper layer of
                      Cr-Mn-spinel on top of the grown chromia scale showed a
                      reduction of the Cr release by 61-75 $\%$ compared to pure
                      chromia scales whereas alloys with an outer
                      Co$-{3}$O$_{4}$(s) scale had a by more than 90 \% reduced Cr
                      release. For the former alloys a significant vaporization of
                      Mn under anodic conditions could be detected. On the base of
                      empirical data it could be extrapolated that in order to
                      achieve the long term requirements for SOFC-systems
                      additional coatings are necessary. Tests with sputtered
                      perovskite and metal coatings showed that the Cr release
                      could be reduced by up to three orders of magnitude by
                      coatings of Co, Ni or Cu. Additionally the Cr vaporization
                      rates of alumina forming and alitized alloys was
                      investigated. Due to the high electrical resistance of
                      alumina these materials are not suitable for interconnect
                      but for other components like heat exchanges, pipes, pumps
                      etc. After short oxidation times these materials showed Cr
                      release rates that are by more than 3 orders of magnitude
                      lower than those of chromia forming materials. Concerning
                      the vaporization of doped lanthanum gallates the
                      vaporization rates of the elements Ga, Mg, Sr and La were
                      measured as function time, temperature, gas flow rate and
                      stoichiometry for compositions of the type
                      La$_{(1-x)}$Sr$_{x}$Mg$_{y}$(Fe$_{z}$)Ga$_{(1-y-z)}$O$_{3-\delta}$(s)
                      with x=0,1-0,3, y=0,12-0,32 and z=0-0,08. As a consequence
                      of the depletion of Ga the formation of the impurity phases
                      LaSrGaO$_{4}$(s) and LaSrGa$_{3}$O$_{7}$(s) was observed.
                      Kinetic parameters were obtained by fitting the results to a
                      vaporization model with imposed solid state diffusion. In
                      order to elucidate the quality of thermodynamic calculations
                      equilibrium measurements were performed with pure
                      Cr$_{2}$O$_{3}$(s) and Ga$_{2}$O$_{3}$(s) in air or
                      Ar/H$_{2}$ respectively as function of temperature and
                      humidity. For the vaporization of Ga$_{2}$O$_{3}$(s) it
                      could be shown that GaOH(g) is the most abundant Ga species
                      in the gas phase. The determined partial pressures for
                      CrO$_{2}$(OH)$_{2}$(g) and CrO$_{3}$(g) or GaOH(g)
                      respectively and the derived enthalpies and entropies of
                      reaction for CrO$_{2}$(OH)$_{2}$(g) and GaOH(g) showed
                      significant differences compared to the thermodynamical data
                      in the literature.},
      cin          = {IWV-2},
      ddc          = {620},
      cid          = {I:(DE-Juel1)VDB2},
      pnm          = {Rationelle Energieumwandlung},
      pid          = {G:(DE-Juel1)FUEK402},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/51107},
}