Development and characterization of thin-film perovskite membranes with oxygen permeability.
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Development and characterization of thin-film perovskite membranes with oxygen permeability. R. Muydinov, M.Popova, A.Kaul D.Stiens1, G.Wahl1 Department of Chemistry, Moscow State University, 119992, Russia 1 Institute of Surface Technology, TU Braunschweig, D-38108, Germany ABSTRACT Two conceptions of oxygen selective membrane’s development, ceramic and thin film ones were considered using perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) with mixed oxygen ionic and electronic conductivity. The films of BSCF (2-3mkm thick) were deposited by a MOCVD technique on the porous substrates (YSZ, Al2O3). Gas tightness, selective oxygen flux at 750950oC and stability of the asymmetric film membranes in working conditions were investigated in comparison with ceramic ones. Sufficiently gas tight films can be directly obtained only on the substrates with submicron pores and at Tdep < 600°C. New alternative approach of large-pore substrates modification for obtaining gas-tight oxygen selectively permeable membranes was developed. To avoid the chemical interaction between BSCF and YSZ or Al2O3 the intermediate layer of BaO was pre-deposited. Resulting permeation through asymmetric membranes was thought to be dependent on oxygen exchange surface reaction and gas permeability of the porous supports. INTRODUCTION Selective oxygen permeability is known for solids with mixed O2-– and electronic conductivity when the material is exposed to oxygen potential gradient. Such materials can be used for oxygen separation and in membrane catalysis. Recently a new perspective mixed conductor – Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) was proposed as the material revealing high selective oxygen permeability [1] and oxygen exchange activity [2] in conjunction with phase stability under working conditions [3]. In spite of high oxygen permeability of BSCF for practical applications even higher oxygen fluxes are desirable. According to the Wagner’s equation [4] the membrane thickness decrease leads to increase of permeation flux if it is limited by diffusion in solid. Therefore the conception of thin oxygen selective films on the porous supports (so called asymmetric membranes) could be perspective, especially if the material is exploited at high temperatures (∼800-900°C) when the kinetics of surface reactions is not a limiting factor of an overall process of oxygen transport. Thus BSCF was chosen in our study as the material for development of asymmetric membranes. The goal of present work was to realize the asymmetric membrane approach and to understand the material science problems accompanying it; the ceramic membranes were also regarded for the comparison. EXPERIMENTAL DETAILS Ceramics of BSCF were prepared as follows: BSCF powder was obtained using the chemical homogenization method consisting in burning of ash free filters impregnated with the mixture of metal nitrates solutions. The rests were annealed at 800°C, 2h, in oxygen. According to X-rays
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