| As a very important inorganic membrane, perovskite-type dense oxygen permeable membranes have great potential applications in high temperature gas separation and membrane catalytic reaction research. Specically, perovskite-type dense oxygen permeable membranes are promising in producing pure oxygen, cathode for SOFC (solid oxide fuel cell) and chemical reactor. For practical application, these materials were required to have high oxygen permeability as well as sustainable structural stability to withstand harsh conditions. However, the present perovskite-type mixed-conducting oxides either showed high oxygen permeability but with poor structural and thermochemical stability in reducing atmosphere or showed high stability but poor oxygen permeation ability, and ideal materials are very few, therefore, it is a critical problem to develop novel materials both with high oxygen permeability and high structure stability, and this is also my thesis's purpose.Based on the previous work, the present study was to exploited new mixed-conducting perovksite-type membrane materials for oxygen permeation with the aids of XRD, SEM-EDX, TG-DSC, O2-TPD and H2-TPR analysis.It was found that it was difficult to synthesize the pure phase BaCo0.4Fe0.4Zr0.2O3-δsince the Zr4+ ion is relatively large for the occupation of the B-site of the perovskite structure, therefore Zn which exhibits constant state was chosen to substitute Zr in BaCo0.4Fe0.4Zr0.2O3-δperovskite, From the XRD analysis, it is proved that the doping of B site of the perovskite structure with a divalent metal like zinc leads to the elimination of nonstoichiometric oxygen variations and lattice expansion of oxygen,from the O2-TPD it can be seen that BaCo0.4Fe0.4Zn0.2O3-δperovskite keep very good structure stability under high temperature and low oxygen partial pressure. Oxygen permeation test was investigated by the gas chromatography, an oxygen permeation flux of 0.9 ml/min.cm2 (6.72×10-7 mol/cm2.s) was found at 950 ?C with a membrane thickness of 0.56 mm. It was also found out that the oxygen permeation was controlled by the bulk diffusion under the experimental conditions. The membrane was steadily operated for more than 100 h in the oxygen permeation test. The XRD analysis after long term test proved that membrane still kept perovskite structure without been destroyed.The effects of Ta ion doping on the structure,high temperature oxygen desorption(O2-TPD), high temperature hydrogen reduction and oxygen transporting properties of SrCo(1-y)TayO3-δ(y=0.0, 0.01, 0.05, 0.1, 0.2, 0.3)were investigated. The perovskite phase structure of the as prepared SrCo(1-y)TayO3-δwas shown to change in the sequence of the hexagonal– cubic– cubic + browmnillerite as Ta ion content y increased. It was found that SrCo0.9Ta0.1O3-δpossessed the most optimized perovskite phase structure. The SrCo0.9Ta0.1O3-δmembrane was investigated by SEM-EDX analysis, it was found that membrane was dense and the compositions both on the surface and the cross agreed with SrCo0.9Ta0.1O3-δstoichiometry. Oxygen permeation test was performed within the temperature range of 700 - 950 oC, and the oxygen permeation flux of 2.07 ml/min·cm2 (1.63×10-6 mol/cm2.s)was obtained at 950°C with a thickness of 0.65 mm. It was found that the oxygen permeation of SrCo0.9Ta0.1O3-δmembrane disk were controlled by the bulk diffusion under the research conditions. The oxygen permeation fluxes varied within a very narrow range, i.e., from 1.70 to 1.96 ml/min·cm2 in the entire 520 h long-term operation. The XRD analysis of the spent membrane showed that the perovskite structure had been well preserved after the long-term permeation test both in the air feed gas side and He sweep gas side which indicated that SrCo0.9Ta0.1O3-δceramic membrane was a promising material used in high-temperature oxygen separation. |
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