Inorganic dual-phase membranes for oxygen separation: Synthesis and properties

Dense inorganic membranes made of oxygen ionic conducting solid oxides offer great potential for gas separation and membrane reactor applications at elevated temperatures. This dissertation focuses on preparation and characterization of inorganic ceramic-metal dual-phase composite membranes, with improved electronic conductivity by inserting a metal phase into the fast oxygen ionic conductors.; This dissertation first presents synthesis and properties of Bi 1.5Y0.3Sm0.2O3 (BYS)/Ag dual-phase membranes in the bulk form. The conventional preparation method was used to prepare dual-phase composites. The percolative and non-percolative BYS/Ag dual-phase membranes were prepared by mixing BYS and Ag powders. Oxygen permeation and electrical conductivity through these BYS/Ag dual-phase membranes were studied in the temperature range of 650∼850°C. Percolative BYS/Ag 40% and non-percolative BYS/Ag 30% membranes exhibit respectively about 50 fold and 10 fold increases in oxygen permeation flux compared to the BYS membrane.; The major part is and properties of this dissertation is focused on synthesis and properties of thin dual-phase membranes. Preparing thin dual-phase membranes supported on porous ceramic substrates is highly desirable as these thin dual-phase membranes offer not only a higher oxygen permeation flux but also a substantial saving in the use of expensive membrane materials. Thin dense yttria stabilized zirconia (YSZ)/Pd composite (dual-phase) membranes have been fabricated on porous YSZ membranes by a new approach that combines the reservoir method and chemical vapor deposition (CVD) technique. Thin porous YSZ layers were coated on porous alumina supports by dip-coating YSZ colloidal solutions prepared by the suspension and sol-gel methods.; The energy-dispersive spectrometry (EDS) dot mapping across the thin YSZ/Pd composite (dual-phase) membranes showed that palladium was concentrated inside the YSZ layer, leaving some Pd traces in the alpha-alumina support. It also showed a fairly uniform distribution of palladium in the YSZ top-layer, indicating the effectiveness of loading Pd uniformly on the top-layer by the reservoir method.; The oxygen permeation fluxes through these composite (dual-phase) membranes, measured in-situ in the CVD reactor, are in the range of 2 x 10 -9 to 5 x 10-8 mol/cm2-s. These oxygen permeation values are about one order of magnitude higher than those of pure YSZ membranes prepared under similar conditions. The apparent activation energies for oxygen permeation in the temperature range of 900--1050°C are 193 kJ/mol for thin YSZ/Pd composite (dual-phase) membranes and 124 kJ/mol for the pure YSZ membranes. These results are explained in terms of relative importance of various mass transfer steps for oxygen permeation and microstructure of the YSZ/Pd composite membranes prepared by this technique. (Abstract shortened by UMI.)...