| The chemical stability and oxygen permeability of ceramic oxygen separatingmembrane for oxyfuel combustion in CO2atmosphere were studied. The basic material isSrFeO3-, the two systems of SrFe1-xNbxO3-(x=0-0.30) and SrFe1-xSbxO3-(x=0-0.30)based on SrFeO3-were synthesized by solid state reaction with the elements Nb and Sb asdopants. X-ray diffraction (XRD), field emission scanning electron microscopy (FeSEM),thermal gravimetric-differential thermal analysis (TG-DTA), X-ray energy dispersivespectroscopy (EDS) techniques were utilized to characterize the chemical stability, whilethe oxygen permeabilities were analyzed by gas chromatography.The research background, the permeation principle of oxygen mixed conductingmembrane and the research progress were discussed in Chapter1. This part focused onthe problem of poor chemical stability of mixed conductor membrane for oxyfuelcombustion and gave some suggestions about improving chemical stability. Chapter2proposed the strategies for exploring the CO2-tolarent membrane materials andintroduced the relevant characterization methods.The chemical stability in CO2atmosphere and oxygen permeation of SrFe1-xNbxO3-(x=0-0.30) were studied in Chapter3. The single cubic perovskite structure was revealedfor as-prepared SrFe1-xNbxO3-(x=0-0.30). The weight of SrFeO3-in CO2increasedobviously in the temperature range of720-900°C, which was associated withdecomposition of the perovskite into SrCO3and SrFe12O19. The carbonation reactionbecame less pronounced with Nb doping concentration up to x=0.2, and accordingly, theoxygen permeation flux at800°C decreased rapidly in the presence of CO2. For the x=0.3sample, no CO2absorption or carbonation reaction was observed, and the oxygen fluxremained almost unchanged in CO2at800°C. The improvement of the CO2resistance withNb doping may result from increase of the metal-oxygen bonding in the perovskite.In Chapter4, the chemical stability in CO2atmosphere and oxygen permeation ofSrFe1-xSbxO3-(x=0-0.30) were invesgated and compared with SrFe1-xNbxO3-. Thestructure transformed from a single phase cubic perovskite phase to double perovskite for the samples x0.30. Under the same conditions, the similar CO2adsorption and chemicalstability were discovered for SrFe1-xSbxO3-and SrFe1-xNbxO3-. However, when CO2assweep gas, the oxygen permeation flux of Sb doped SrFeO3-at800°C did not reduce butincrease. More experiments are to be conducted to verify this finding.The research results and deficiencies of this work are elaborated in Chapter5, andworks to be further conducted are also suggested. |
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