SOL-GEL SYNTHESIS AND CHARACTERIZATION OF MESOPOROUS CERIA MEMBRANES
CeO2, has numerous applications in industry including catalysts, electrolytes and in superconductors. One of the major area in which CeO2 research is lacking is in mesoporous inorganic membranes. The use of inorganic instead of organic membranes is advantageous if one is dealing with high temperatures, aggressive mixtures (chemical, mechanical, microbiological), high pressures (no compaction of inorganic membranes) or separation circumstances which make frequent cleaning of the membrane necessary. In addition to the ultrafiltration and gas separations, ceria is also most attractive as support for ultrathin dense ceramic or metallic membranes because of its thermal expansion coefficient, which match more closely with that of some dense membrane materials. Few researchers tried to prepare supported ceria membranes by the sol gel method. However they were unsuccessful to coat ceria layer directly on the support. So they coated ceria on top of alpha-alumina layer making a multilayer system. The ceria coating obtained had a very low surface area and consisted of some pinholes and cracks. Membranes with a narrow pore size distribution, in which especially large pores should be absent, are necessary to obtain a high degree of separation of mixtures. The present work is an attempt to prepare crack free and pinhole free supported and unsupported mesoporous ceria membranes by the sol gel method. A systematic study on microstructure and chemical evolution of ceria sols was done and the best available sol, which can give required ceria film thickness, was used for membrane preparation. Factors such as solid concentration, surface area and the organic impurities in the sols were considered. Ceria sol derived from cerium (IV) nitrate precursor having solid concentration of 172 g/L of CeO2 and whose particles showed a surface area of 101 m2/g was selected for fabrication of porous ceria membranes. Ceria was coated on chemically treated alpha-alumina support by dip-coating method. The pore structure and permeability properties of the supported membrane were studied by helium permeation experiments. SEM image shows ceria top-layer of thickness 28micron with an average pore diameter of 6.42 nm obtained by single dip coating of the ceria sol on the alumina support. XRD data reveal the fluorite type structure of ceria membranes. The permeability of ceria membrane is however low inspite of its high porosity, because of the thick top-layer obtained by the single dip-coating of ceria sol. The ionic conductivity of the ceria membranes is 0.06 - 8.5 S/cm in the temperature range of 600 - 900oC. These properties were compared with those of yttria-stabilized-zirconia (YSZ) membranes reported in the literature.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:ceria sol gel inorganic membranes cerium nitrate ceo2
Date of Publication:01/01/2003