| Perovskite-type mixed-conducting oxides have received considerable attention as possible candidate materials for application in oxygen separation membrane, solid oxide fuel cells and catalytic membrane reactors. For practical applications, these materials were required to have high oxygen permeability as well as sustainable structural stability to withstand harsh conditions. But the present mixed-conducting oxides which showed high oxygen permeability were often faced with poor structural and thermochemical stability in reducing atmosphere. Therefore, it is important to develop new materials and optimize known materials for oxygen separation and catalytic membrane reactors.The present study was based on the previous work and aimed at investigating, optimizing and exploiting new mixed-conducting perovksite-type membrane materials for oxygen permeation with the aid of XRD, SEM-EDX, TG-DSC and O2-TPD analysis. Firstly, the structure, oxygen transport and stability of 9 wt % ZrO2-promoted SrCo_{0.4}Fe_{0.6}O_{3-δ} (SCFZ) were systematically studied. The results showed that a change from cubic phase to an oxygen vacancy ordered phase occurred for SrCo_{0.4}Fe_{0.6}O_{3-δ} (SCF) in the low oxygen partial pressure atmosphere, while no phase transition was found for SCFZ. Although the oxygen permeation flux decreased a little with the addition of ZrO2, the long-term stability was greatly improved. Meanwhile, the oxygen stoichiometry and chemical diffusion coefficient of SCFZ was investigated by TG. A simple transport equation correlating oxygen flux to the oxygen diffusion coefficient was deduced. The diffusion coefficients derived from the transport equation and the weight relaxation experiment was in agreement within a factor of 2. Secondly, the reasons for the improvement of structural stability of SCF with the addition of ZrO2 were revealed after we carefully investigated the effect of ZrO2 particle sizes on the structure, oxygen permeation and stability of SCF, which provided new ideas for choosing the membrane materials. The results showed that the dissolution of Zr cation into the B sites of SCF phase occurred after calcinations,resulting in a lattice expansion of SCF. The amount of Zr dissolved varied with different ZrO2 particle size and therefore influenced the properties of the materials. The oxygen permeability decreased, while the structural stability increased with the increasing amount of Zr cation dissolution. Our study indicated that a certain amount of Zr cation dissolution was necessary to maintain the structural stability of SCF in the low oxygen partial pressure atmosphere and ZrO2 added with 1(m by directly mixing the oxides was the effective way to attain Zr cation dissolution in SCF. Simultaneously, the influence of sintering temperature on the structure of the materials was investigated. The reaction mechanism between SCF and ZrO2 was proposed: the solid solution of Zr into SCF lattice occurred as well as the solid state reaction to form SrZrO3 phase after calcination, and with the further increase of the temperature, the SrZrO3 phase was resorbed into the perovskite phase till the limit of solid solubility of Zr was reached.Thirdly, the amount of ZrO2 addition was optimized in an attempt to search for a suitable composition exhibiting high oxygen flux as well as structural stability in the low oxygen partial pressure atmosphere. It was found that the amount of Zr cation dissolution in SCF phase increased directly with the amount of ZrO2 addition and sintering temperatures. The limit of solid solubility of ZrO2 in the SCF at 1473 K was estimated to be about 7 wt %. As indicated by XRD and TG-DSC analysis that the phase stability decreased with increasing amount of added ZrO2, and the samples with the addition of ZrO2 ( 3 wt % could stabilize their structure in the low oxygen partial pressure atmosphere. From the dependence of stability and oxygen permeability, the optimum ZrO2 addition to greatly improve the structural stability without deleteriously affecting the oxygen permeab...
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