Perovskite proton-conducting ceramic membrane

General Properties of Perovskite-structured Proton-conducting Ceramic Membranes 51... 

General Properties of Perovskite-strucUired Proton-conducting Ceramic Membranes 57... 

An ideal membrane must have high electronic and protonic conductivities it should be fairly thin (1-10 pm), and chemically stable for prolonged periods of time under the presence of various gases such as CO2, H2O and H2S etc. The low electronic conductivity limits the H2 flux of the protonceramic membranes. Under pure H2 atmosphere at 900 "C, the protonic conductivities of SCYb and BCNd are about 0.7 x 10 2 and 2.2 x 10 2 S cm , respectively. These values are sh tly lower than the oxygen ionic conductivity of yttria stabilized zirconia (YSZ) or lanthanum strontium cobaltite (LSC) perovskite-type ceramics in air at the same temperature, so that there is room for further improvement in protonic conductivity. 

In Chapter 10, the use of membranes for different applications are described. One of the possible membranes for hydrogen cleaning is an asymmetric membrane comprised of the dense end of a proton conduction perovskite such as BaCe0 95 Yb0 05O3 5 and a porous end to bring mechanical stability to the membrane. In this case, it is possible to take from the slurry, obtained by the acetate procedure, several drops to be released over a porous ceramic membrane, located in the spinning bar of a spin-coating machine. Thereafter, the assembly powder, thin film porous membrane is heated from room temperature up to 1573 K at a rate of 2K/min, kept at this temperature for 12 h, and then cooled at the same rate in order to get the perovskite end film over the porous membrane [50],... 

Hydrogen-permselective silica membranes [8,10] can be, as well, synthesized by a particular application of solgel techniques [142,143], Additionally, hydrogen permselective asymmetric membranes composed of a dense ceramic of a proton-conducting perovskite over a porous support have been developed [40], However, some difficulties with respect to their stability is possible in certain reactive environments [121],... 

One category of dense proton conducting membranes that has received considerable attention in the preceding decade is proton conducting perovskite type oxide ceramics [4-6]. The stoichiometric chemical composition of perovskites is represented as ABO3, where A is a divalent ion (A +) such as calcium, magnesium, barium or strontium and B is a tetravalent ion (B +) such as cerium or zirconium. Although simple perovskites such as barium cerate (BaCeOs) and strontium cerate... 

A series of perovskite compositions were synthesized using oxides and carbonates of the cations by conventional ceramic process. The synthesized powders were characterized using powder x-ray diffraction technique to ensure phase purity. Conductivity measurements were made in H2-H2O atmosphere to determine proton conductity. As the perovskite compositions are inherently mixed conducting, the transference numbers for proton and electron conduction were also determined by varying the partial pressures of hydrogen and steam across the membrane. 

Composite membranes also employ dense cermets fabricated by sintering together mixed powders of metal and ceramic [10-12], Examples include powders of Pd and its alloys sintered with powders of perovskites [11,12], niobium sintered together with AI2O3 [12], and nickel sintered with proton-conducting perovskites. Layers of dense cermets, 25-100 xm thick, are supported by porous ceramic tubes. Cermets employing chemically reactive metals, Nb, Ta, U, V, Zr, and their alloys, are typically coated with Pd and alloys thereof [11,12],... 

Although a variety of protonceramic materials has been found in the past decade, only very limited studies have dealt with experimental measurements of H2 flux, and little effort has been made to model the experimentally measured data in these studies. H2 permeation flux data on more perovskite-based membranes are needed so that the mathematical models can be verified with experimental data. Such models, when rigorous and accurate, can provide essential guidance in the design and understanding of the mixed conducting materials. Fundamental study should be conducted to understand the stractural,... 

Abstract Dense ceramic membrane reactors are made from composite oxides, usually having perovskite or fluorite structure with appreciable mixed ionic (oxygen ion and/or proton) and electronic conductivity. They combine the oxygen or hydrogen separation process with the catalytic reactions into a single step at elevated temperatures (>700°C), leading to significantly improved yields, simplified production processes and reduced capital costs. This chapter mainly describes the principles of various types of dense ceramic membrane reactors, and the fabrication of the membranes and membrane reactors. 

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