(131d) Dual-Phase Ceramic Membrane for Oxygen Separation

The design of dual-phase ceramic membranes is discussed in detail from the point of view of solid state chemistry. Dual-phase membranes with high performance have been designed by considering the permeability, stability and compatibility of the dual-phase system. It is deduced that dual-phase membranes made of Fe-based perovskite oxides (such as Sm_0.6Sr_0.4FeO₃, mixed conductors) and Ce-based fluorite oxides (such as Ce_0.85Sm_0.15O_1.925, ionic conductors) have both good permeability and stability. A dual-phase membrane made of an ionic conductor and pure electronic conductor was studied for comparison purposes, with a nominal composition of 75 wt.%Ce_0.85Sm_0.15O_1.925-25 wt.%Sm_0.6Sr_0.4CrO₃. Experimental investigation of selected membranes is reported with attention to processing, microstructures, conductivity and oxygen permeation properties. Microstructure effects of dual-phase membranes on oxygen exchange reactions and bulk oxide ionic transport were investigated by AC impedance spectroscopy, high resolution transmission electron microscopy and oxygen permeation. Oxygen permeation experiments revealed when the Fe-based mixed conducting perovskite is used in dual-phase membranes, higher oxygen permeation fluxes were achieved than that of the Cr-based pure electronic conducting perovskite was used in the dual-phase membrane. The phenomenon can be well explained by the mutual blocking of electronic and ionic transport by pure electronic conductors and ionic conductors, and the enrichments of Cr-based impurities between the ionic conducting grains. Membranes with various weight ratios of the two phases were synthesized to find the optimal composition. 75 wt.%Ce_0.85Sm_0.15O_1.925-25 wt.%Sm_0.6Sr_0.4FeO₃ was found to be the best membrane from the point of view of both oxygen permeability and stability. The idea of designing dual-phase membranes was verified by the comparison.