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@PHDTHESIS{Ramasamy:827514,
author = {Ramasamy, Madhumidha},
title = {{D}ual {P}hase {O}xygen {T}ransport {M}embrane for
{E}fficient {O}xyfuel {C}ombustion},
volume = {351},
school = {Universität Bochum},
type = {Dr.},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
reportid = {FZJ-2017-01634},
isbn = {978-3-95806-196-5},
series = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
Umwelt / Energy $\&$ Environment},
pages = {VIII, 136 S.},
year = {2016},
note = {Universität Bochum, Diss., 2016},
abstract = {Oxygen transport membranes (OTMs) are attracting great
interest for the separation of oxygenfrom air in an energy
efficient way. A variety of solid oxide ceramic materials
that possess mixed ionic and electronic conductivity (MIEC)
are being investigated for efficient oxygen separation (Betz
'10, Skinner '03). Unfortunately these materials do not
exhibit high degradation stability under harsh ambient
conditions such as flue gas containing C$_{2}$, SO$_{x}$,
H$_{2}$O and dust, pressure gradients and high temperatures
that are typical in fossil fuel power plants. For this
reason, dual phase composite membranes are developed to
combine the best characteristics of different compounds to
achieve high oxygen permeability and sufficient chemical and
mechanical stability at elevated temperatures. In this
thesis, the dual phase membrane
Ce$_{0.8}$Gd$_{0.2}$O$_{2-\delta}$ - FeCo$_{2}$O$_{4}$
(CGO-FCO) was developed after systematic investigation of
various combinations of ionic and electronic conductors. The
phase distribution of the composite was investigated in
detail using electron microscopes and this analysis revealed
the phase interaction leading to grain boundary rock salt
phase and formation of perovskite secondary phase. A
systematic study explored the onset of phase interactions to
form perovskite phase and the role of this unintended phase
as pure electronic conductor was identified. Additionally
optimization of conventional sintering process to eliminate
spinel phase decomposition into rock salt was identified. An
elaborate study on the absolute minimum electronic conductor
requirement for efficient percolation network was carried
out and its influence on oxygen flux value was measured.
Oxygen permeation measurements in the temperature range of
600 °C - 1000°C under partial pressure gradient provided
by air and argonas feed and sweep gases are used to identify
limiting transport processes. The dual phase membranes are
much more prone to surface exchange limitations because of
the limited length of the active triple phase boundaries. A
porous catalytic layer made of a single phase MIEC material,
i.e. LSCF, showed evidence of these limitations even when
using 1 mm thick samples. The dual phase composites were
also subjected to thermo-chemical stability in flue gas
conditions and mechanical stability under high pressure
applications. Microstructure variation based on different
powder synthesis routes of the composite impacting oxygen
permeation has been investigated. On the other hand,
microstructure variation via alternate densification/
sintering techniques such as hot pressing and SPS/FAST were
also explored. The finalized dual phase composition was
developed into thin film supported membrane layers. An
oxygen flux of 1.08 ml cm$^{-2}$ min$^{-1}$ was achieved on
an asymmetric membrane at 1015 °C successfully. However,
impregnation of catalysts into the porous support can
significantly improve the oxygen flux at lower temperatures,
overcoming the surface limitations at the interface between
the support and dense membrane.},
cin = {IEK-1},
cid = {I:(DE-Juel1)IEK-1-20101013},
pnm = {113 - Methods and Concepts for Material Development
(POF3-113) / HITEC - Helmholtz Interdisciplinary Doctoral
Training in Energy and Climate Research (HITEC)
(HITEC-20170406)},
pid = {G:(DE-HGF)POF3-113 / G:(DE-Juel1)HITEC-20170406},
typ = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
url = {https://juser.fz-juelich.de/record/827514},
}