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Structural Behavior of Oxygen Permeable SrFe 0.2 Co 0.8 O x Ceramic Membranes with and Without p O 2 Gradients
Author(s) -
Li Yaping,
Maxey Evan R.,
Richardson James W.
Publication year - 2005
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2005.00171.x
Subject(s) - perovskite (structure) , oxygen , membrane , partial pressure , ceramic membrane , analytical chemistry (journal) , permeation , ceramic , phase (matter) , chemistry , neutron diffraction , rietveld refinement , materials science , mineralogy , crystallography , crystal structure , chromatography , metallurgy , biochemistry , organic chemistry
The oxygen partial pressure ( p O 2 )‐dependent structural behaviors of two dense tubular ceramic membranes in composition SrFe 0.2 Co 0.8 O x with cubic perovskite structure have been investigated by high‐temperature neutron powder diffraction: one in “static” mode and one in simulated‐operation mode in which one side of the membrane was exposed to air and the other side to reducing gases with variable p O 2 levels. Rietveld analysis on data collected for the membrane without p O 2 gradients showed that the perovskite is stable in p O 2 down to ∼10 −12 atm, and at ∼10 −14 atm it starts to decompose into a three‐phase mixture containing layered intergrowth Ruddlesden–Popper phases Sr n +1 (Fe,Co) n O x with n =2 and 3, along with CoO with rocksalt structure. Similar phase evolution was observed when insufficient air flowed on the air side of the membrane exposed to a p O 2 gradient. The data support a nonlinear model of oxygen content in perovskite across the membrane thickness, corresponding to a p O 2 profile that is shallow inside and steep near the reducing side surface. Gas compositions measured with mass spectrometry indicated that oxygen is permeated from the air side to the reducing side of the membrane. The oxygen permeation fluxes at 900°C were estimated to be 0.4–0.9 sccm/cm 2 for the ∼1 mm thick membrane containing perovskite, depending upon p O 2 gradient.