Dense ceramic tubes of the multi phase mixed ionic/electronic conductor SrFeCo0.5Oy (SFC2) have been synthesized by solid-state reaction, Stability of the component phases of SFC2 was studied by insitu neutron diffraction in the temperature range of 900-1200 degreesC in air and Ar environments. In air between 900 and 1050 degreesC, the material is stable, with Sr-2(Fe,Co)(3)O-y (236) being the major phase. Above 1050 degreesC, 236 undergoes decomposition into perovskite and rocksalt phases, and at 1200 degreesC, only a small fraction of the 236 phase is stable. In Ar, the 236 phase is completely stable at 900 degreesC but is completely decomposed by 1100 degreesC, whereupon only the perovskite and rocksalt phases remain. Rietveld analysis indicates that the 236 and perovskite phases become more Fe-rich as decomposition occurs, while the perovskite phase lattice parameter and oxygen content vary readily as temperature and gas environment are changed. (C) 2002 Published by Elsevier Science Ltd.

Dense ceramic tubes of the multi-phase mixed ionic/electronic conductor SrFeCo0.5Oy have been synthesized by solid-state reaction, and the stability of its component phases studied using in-situ neutron diffraction over the oxygen partial pressure (pO2) range 10−0.68 to 10−15.0atm at 900°C. This being the likely conditions to which membranes are exposed in operational methane conversion reactors. This material is stable between air and log pO2 = −2.3, with Sr2(Fe,Co)3Oy (236) being the majority phase. When the oxygen partial pressure is lowered, 236 starts decomposing into perovskite and rocksalt phases. The small fraction of remaining 236 rapidly undergoes decomposition at log pO2 = −12.2, leaving only SrFeO2.5 and CoO. Rietveld analysis indicates that the oxygen content of the perovskite phase does not drop below O = 2.5 when log pO2 = −15.0, while there is an indication that CoO is reduced to cobalt metal. This decomposition at low partial pressures may be reversed when the gas is switched back to air, i.e., SrFeO2.5 + CoO re-form Sr2(Fe,Co)3Oy, to an extent that is seemingly dependent on sample and thermal history.