| Perovskite-type membranes have been widely studied due to their potential applications in oxygen separation, solid oxide fuel cells, and partial oxidation of methane to syngas, etc. However, the commercialization of this kind of membranes is limited by two factors: one is the lower oxygen permeation flux than that is practically needed, and the other is the poor stability of the membrane materials at high temperature and reducing atmosphere.In current researches, the influence of the composition on the properties of the membrane is highlighted while the influence of the microstructure is neglected, and the influence of the surface modification on the surface exchange of the membranes is highlighted while the influence of doping is neglected. Aiming at these two aspects, the controlling means of the microstructure and its influence on the oxygen permeation performance of the membranes is studied in light of the relationship of preparation technology-microstructure-properties, and the oxygen permeation performance of the membranes doped with different ions is studied in terms of the relationship of doping-structure-properties.1. Influence of powders synthesis method on the properties of Ba0.5Sr0.5Co0.8Fe0.2O3-δ membraneBa0.5Sr0.5Co0.8Fe0.2O3-δ powders are synthesized by solid-state reaction method, modified citrate method and citrate-EDTA complexing method, and the corresponding membranes are sintered under the same conditions.The crystal structure of the powders synthesized by citrate-EDTA method completely transforms to perovskite structure at the lowest temperature, for which the reason is that the existence of the organic components promotes the formation of the perovskite phase.From the scanning electron micrographs, it could be seen that the powders synthesized by solid-state reaction method have distinct grains, while those synthesized by modified citrate method show coralline structure. Grain boundaries also exist for the powders synthesized by the citrate-EDTA method, although the grains merge for certain degree.The shrinkage rates, the relative densities of the microstructures and the oxygen permeation fluxes are in the same orders as solid-state reaction method > modified citrate method > citrate-EDTA method. The grain boundary hinders the transfer of the oxygen ion in the membrane bulk. Therefore, the denser the membrane, the few the grain boundaries, and the higher the oxygen permeation flux. The different powders synthesis method is the reason that leads to the different oxygen permeation flux. A further conclusion is that the activation energy of the membrane for oxygen permeation is the essential character of the material, while is independent of the microstructure of the membrane.2. Influence of sintering conditions on the properties of Bao.5Sro.sCoo.8Feo.2O3-8 membranesBa0.5Sr0.5Co0.8Fe0.2O3-δ powders are synthesized by solid-state reaction methods. The membranes are sintered at different temperatures (1273, 1323, 1373 and 1423 K, the dwell time is 300 min) and are dwelled for different times (5,150,300 and 450 min, the sintering temperature is 1373 K). The crystal structure, the microstructure and the oxygen permeation flux are characterized.The calcined powders consist of BaFeO2.9 phase and Ba0.8Sr0.2Co0.8Fe0.2O3-δ phase. Increasing sintering temperature could promote the solid dissolution of the above two phases, while there is no obvious relationship between the degree of the solid dissolution and the prolongation of the dwell time. It also can be found that the increase of the sintering temperature and the prolongation of the dwell time are beneficial to the formation of the perovskite phase.The relative density increases directly with the sintering temperature for the membrane dwelled for different times, while does not change obviously with the dwell time for the membrane sintered at different temperatures. The membrane sintered at 1423 K for 300 min shows a dense sintering body, which is thought to be caused by the secondary recrystallization. The grain...
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