W0048

In-situ Neutron Diffraction Studies of SrFeCo0.5Ox Ceramic Membrane under pO2 Gradients. Yaping Li, Evan R. Maxey and James W. Richardson Jr., Intense Pulsed Neutron Source, Argonne National Laboratory Argonne, IL 60439.

Understanding the performance of multi-phase SrFeCo0.5Ox (SFC2) membranes operating at elevated temperature and pO2 gradients relies on accurate determination of both structural and phase stability of the ceramic membranes. An air-sintered dense ceramic membrane with composition SFC2 was prepared by solid-state reactions. In-situ time-of-flight neutron diffraction data were collected on the membrane with a wall thickness of ~1 mm that was exposed on one side to air with pO2’ of ~10-0.9 atm, and to pO2” of reducing atmosphere on the other side under isothermal condition (~900ºC), and neutron diffraction data were analyzed through Rietveld refinements. Phase evolution of SFC2 was investigated through changing the pO2” in the range of ~10-0.9 – 10-17.5 atm. At least a total of six phases were identified in the diffraction patterns with various pO2 gradients, including intergrowth 236, perovskite, brownmillerite, rocksalt, and metallic phases (_ and _). Our results revealed that the phase composition of SFC2 is dependent upon the pO2” on the reducing side, and that the phase evolution of the SFC2 membrane under pO2 gradients is much more complex than previously thought; based on static studies with pO2 down to 10-15 atm. The 236 can remain in the SFC2 at pO2” of ~10-15 atm, and was completely decomposed to perovskite and rocksalt at pO2” of 10-17 atm, demonstrating that the stability field of 236 was extended to lower pO2 region by oxygen transported from the oxidizing side. Perovskite was stable in entire pO2 gradients, and a small amount of oxygen vacancy ordered brownmillerite was found at strongly reducing atmosphere. Metallic phases of _ and _-(Co,Fe) were observed at pO2” of ~10-15 atm from the reduction of rocksalt. The structures of 236 and rocksalt can be reestablished when pO2” went back to 10-15 atm. It is expected that this complex assemblage of multiple phases in SFC2 at pO2 gradient has significant impact on the mixed conducting behavior of SFC2 membranes.