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@PHDTHESIS{Li:141077,
      author       = {Li, Xiaoyu},
      title        = {{L}ong {T}erm {S}tability and {P}ermeability of {M}ixed
                      {I}on {C}onducting {M}embranes {U}nder {O}xyfuel
                      {C}onditions},
      volume       = {194},
      school       = {RWTH Aachen},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2013-06279},
      isbn         = {978-3-89336-916-4},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {III, 143 S.},
      year         = {2013},
      note         = {Dissertation, RWTH Aachen, 2013},
      abstract     = {The thermochemical properties, especially the long-term
                      behaviour of mixed electron-ion conducting materials for
                      oxygen separation, were investigated under oxyfuelcondition
                      in this thesis. Amongst those oxygen-permeable materials,
                      perovskite-type oxides demonstrate remarkably high oxygen
                      fluxes. Nevertheless, great effort has been put into the
                      investigation of the long-term sustainable problem occurring
                      in the intermediate temperature (IT) range of 500-800 °C in
                      some perovskite membranes,which is caused by thermodynamic
                      decomposition. This decay of membrane properties during
                      operation becomes a serious obstacle for applications in
                      coal-fired power plants. Besides, a relatively low expansion
                      coefficient of membrane materials is also suggested to avoid
                      compatibility issues. Perovskite-structured
                      BaxSr$_{1-x}$Co$_{y}$Fe$_{1-y}$O$_{3-\delta}$ (BSCF)
                      materials were synthesized by the method of solid state
                      reaction. The sintering behaviour of BSCF powders was
                      studiedprior to the production of the gastight membranes. In
                      view of future application, characteristic membrane
                      properties like melting temperature, oxygen
                      nonstoichiometryand thermal expansion behaviour were
                      measured in synthetic air accordingly. The association
                      between the thermochemical properties and the doping
                      compositions ofBSCF materials as well as temperature effect
                      was investigated. Moreover, the degradation process in BSCF
                      membranes during long-term operation was studied under
                      oxyfuel condition. In the case of oxygen permeation
                      measurements, the variation of oxygen flux through the
                      membranes under the air/He pressure gradient wasrecorded. A
                      slow exponential decay of the permeate flux was observed at
                      800 °C compared to the more stabilized oxygen permeability
                      of membranes at higher temperatures. The reason for the
                      deterioration of membrane permeability is mainly ascribed to
                      the phase decomposition from cubic into hexagonal polymorph.
                      Unexpectedly, an increment of oxygen flux was found in the
                      Ba$_{0.4}$Sr$_{0.6}$Co$_{0.2}$Fe$_{0.8}$O$_{3-\delta}$
                      membrane measured at 850 °C, though kinetic decomposition
                      still occurs in this material. Based on the permeation
                      behaviour of BSCF membranes during cyclic permeation tests,
                      it is confirmed that the cubic-hexagonal phase transition is
                      reversible and membrane performance could be retrieved by
                      the periodical variation of temperatures above 850 °C. The
                      driving force as well as kinetics for the phase transition
                      is discussed in this study according to the long-term
                      annealing measurements. In [...]},
      keywords     = {Dissertation (GND)},
      cin          = {IEK-2},
      cid          = {I:(DE-Juel1)IEK-2-20101013},
      pnm          = {123 - Fuel Cells (POF2-123)},
      pid          = {G:(DE-HGF)POF2-123},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/141077},
}