NAMS 2002 Workshop - ICOM 2008

Inorganic Membranes III – 3
Friday July 18, 10:45 AM-11:15 AM, O’ahu/Waialua
Electronic Conduction and Oxygen Permeation Through Mixed-Conducting
SrCoFeO(x) Membranes
J. Kniep (Speaker), Arizona State University, Tempe, Arizona, USA
J. Lin, Arizona State University, Tempe, Arizona, USA - Jerry.Lin@asu.edu
The total conductivity and oxygen permeation properties of dense SrCoFeO(x)
membranes synthesized from the solid state method were studied in the
temperature range of 700 to 900 degrees C. SrCoFeO(x) powder has been
shown to have favorable oxygen adsorption and desorption rates as well as a
large oxygen sorption capacity above 800 degrees C. X ray diffraction analysis
verifies that the SrCoFeO(x) samples consist of an intergrowth Sr(4)Fe(6x)Co(x)O(13
+ or - delta), perovskite SrFe(1-x)Co(x)O(3-delta), and spinel Co(3x)Fe(x)O(4)
phase. SrCoFeO(x) exhibits n- type and p-type conduction at low
and high oxygen partial pressures, respectively, and has a total conductivity of
16.5 S/cm at 900 degrees C in air. SrCoFeO(x) membranes were structurally
stable during oxygen permeation experiments with one side exposed to air and
the other side exposed to either an inert gas or carbon monoxide. The oxygen
permeation fluxes with a carbon monoxide sweep gas were approximately two
orders of magnitude higher than the fluxes measured with an inert sweep gas.
The highest measured oxygen flux through a 0.80 mm thick SrCoFeO(x)
membrane with a carbon monoxide sweep was 4.8 ml/cm 2. min at 900 degrees C.
The oxygen flux through SrCoFeO(x) membranes was higher than the oxygen
flux through SrFeCo(0.5)O(x) membranes of the same thickness under the same
experimental conditions.
Asymmetical SrCoFeO(x) membranes consisting of a dense thin layer and a
porous support layer of the same material were made using a cold pressing
technique. Finely ground powder was used for the dense layer while larger
particle sized powder was used for the porous support. The thickness of the
dense layer was controlled by using varying amounts of the finely ground
powder, with the thinnest dense layer being approximately 150 micrometers.
When helium was used as the sweep gas, the critical thickness was determined
to be approximately 600 micrometers. When carbon monoxide was used as the
sweep gas, the oxygen flux continued to increase as the dense layer decreased
down to 150 micrometers due to the more favorable surface kinetics on the
sweep side.