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Development of mixed-conducting ceramics for gas separation applications.

Description: Mixed-conducting oxides are used in many applications, including fuel cells, gas separation membranes, sensors, and electrocatalysis. This paper describes mixed-conducting ceramic membranes that are being developed to selectively remove oxygen and hydrogen from gas streams in a nongalvanic mode of operation (i.e., with no electrodes or external power supply). Because of its high combined electronic/ionic conductivity and significant oxygen permeability, the mixed-conducting Sr-Fe-Co oxide (SFC) has been developed for high-purity oxygen separation and/or partial oxidation of methane to synthesis gas, i.e., syngas, a mixture of carbon monoxide and hydrogen. The electronic and ionic conductivities of SFC were found to be comparable in magnitude and are presented as a function of temperature. The oxygen flux through dense SFC tubes during separation of oxygen from air is compared with the oxygen flux during methane conversion. Unlike SFC, in which the ionic and electronic conductivities are nearly equivalent, BaCe{sub 0.80}Y{sub 0.20}O{sub 3} (BCY) exhibits protonic conductivity that is significantly higher than its electronic conductivity. To enhance the electronic conductivity and increase hydrogen permeation, metal powder was combined with the BCY to form a cermet membrane. Nongalvanic permeation of hydrogen through the cermet membrane was demonstrated and characterized as a function of membrane thickness. A sintering aid was developed to avoid interconnected porosity in and improve the mechanical properties of the cermet membrane.
Date: December 2, 1998
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Practical superconductor development for electrical power applications. Annual report for FY 1995

Description: Development of useful high-critical-temperature (high-{Tc}) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds: production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes the technical progress of research and development efforts aimed at producing superconducting components in the (Bi,Pb)-Sr-Ca-Cu, (Tl,Pb,Bi,V)-(Ba,Sr)-Ca-Cu, and Y-Ba-Cu oxide systems. The topics that are discussed are synthesis and heat treatment of high-{Tc} superconductors, formation of monolithic and composite conductors, characterization of structures and superconducting and mechanical properties, and fabrication and testing of prototype components. Collaboration with industry and academia is documented.
Date: October 1, 1995
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Mixed-conducting oxides for gas separation applications.

Description: Mixed-conducting oxides are attracting increased attention because of their potential uses in high-temperature electrochemical applications such as solid-oxide fuel cells, batteries, sensors, and gas-permeable membranes. We are developing mixed-conducting, dense ceramic membranes to selectively transport oxygen and hydrogen. Ceramic membranes made of Sr-Fe-Co oxide (SFC), which exhibits high combined electronic and oxygen ionic conductivities, can be used to selectively transport oxygen during the partial oxidation of methane to synthesis gas (syngas, a mixture of CO and H{sub 2}). Steady-state oxygen permeability of SrFeCo{sub 0.5}O{sub x} has been measured as a function of oxygen-partial-pressure gradient and temperature. At 900 C, oxygen permeability was {approx}2.5 scc{center_dot}cm{sup {minus}2}-min{sup {minus}1} for a 2.9-mm-thick membrane, and this value increases as membrane thickness decreases. We have fabricated tubular SrFeCo{sub 0.5}O{sub x} membranes and operated them at 900 C for >1000 h during conversion of methane into syngas. Yttria-doped BaCeO{sub 3} (BCY) is a good protonic conductor; however, its lack of electronic conductivity can potentially limit its hydrogen permeability. To enhance the electronic conductivity and thus improve hydrogen permeation, a membrane composite material was developed. Nongalvanic permeation of hydrogen through the composite membrane was characterized as a function of thickness.
Date: April 20, 1999
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Recent advances in fabrication of high-T{sub c} superconductors for electric power applications.

Description: The U.S. Department of Energy (DOE) supports an applied superconductivity program entitled ''Superconductivity Program for Electric Power Systems.'' Activities within this program contribute to development of the high-temperature superconductor (HTS) technology needed for industry to proceed with the commercial development of electric power applications such as motors, generators, transformers, transmission cables, and current limiters. Research is conducted in three categories: wire development, systems technology development, and Superconductivity Partnership Initiative (SPI). Wire development activities are devoted to improving the critical current density (J{sub c}) of short-length HTS wires, whereas systems technology development focuses on fabrication of long-length wires, coils, and on magnets. The SPI activities are aimed at development of prototype products. Significant progress has been made in the development of (HTSs) for various applications: some applications have already made significant strides in the marketplace, while others are still in the developmental stages. For successful electric power applications, it is very important that the HTS be fabricated into long-length conductors that exhibit desired superconducting and mechanical properties. Several parameters of the PIT technique must be carefully controlled to obtain the desired properties. Long lengths of Bi-2223 tapes with respectable superconducting properties have been fabricated by a carefully designed thermomechanical treatment process. A 1-MVA capacity fault current limiter, a 286-hp motor, and 630-kVA transformers, and a 50-m-long conductor, all using HTSs, have already been demonstrated. While the use of HTS devices in the electric utility area has clear advantages, impediments to successful commercialization remain. Issues such as AC losses, conductor cost, and reliable superconducting joints must be addressed. The cost of HTS conductors are still quite high, and significant R and D effort must be focused on this issue. The general acceptance of HTS power equipment will ultimately be based on system performance, reliability and maintenance, efficiency, and installed cost relative to ...
Date: March 25, 1998
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Advances in fabrication of Ag-clad Bi-2223 superconductors.

Description: Powder-in-tube (PIT) processing was used to fabricate multifilamentary Ag-clad Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconductors for various electric power applications. Enhancements in the transport current properties of long lengths of multifilament tapes were achieved by increasing the packing density of the precursor powder, improving the mechanical deformation, and adjusting the cooling rate. The dependence of the critical current density on magnetic field and temperature for the optimally processed tapes was measured. J{sub c} was greater than 10{sup 4} (A/cm{sup 2}) at 20 K for magnetic field up to 3 T and parallel to the c-axis which is of interest for use in refrigerator coded magnets. An attempt was made to combine the good alignment of Bi-2223 grains in Ag-sheathed superconducting tapes to obtain high J{sub c} values at high temperature and low field, and good intrinsic pinning of YBa{sub 2}Cu{sub 3}O{sub 7{minus}d} (Y-123) thin film to maintain high J{sub c} values in high fields. A new composite multifilament tape was fabricated such that the central part contained Bi-2223 filaments, with the primary function of conducting the transport current. The central Bi-2223 filaments were surrounded by Y-123 thin film to shield the applied magnetic field and protect the Bi-2223 filaments. The J{sub c} values of the composite tape were better than those of an uncoated tape. In the case of 77 K applications, an I{sub c} of about 60 A was obtained in a 150 m long tape and zero applied magnetic field. In-situ strain characteristics of the mono- and multifilament tapes were conducted.
Date: September 4, 1998
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Fabrication and characterization of Ag-clad Bi-2223 tapes.

Description: The powder-in-tube (PIT) technique was used to fabricate multifilament (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes. Transport current properties of these tapes were enhanced by increasing the packing density of the precursor powder and improving the mechanical deformation condition. A critical current (I{sub c}) of > 35 A in long lengths (> 200 m) tapes has been achieved. In measuring the dependence of critical current density on magnetic field and temperature for the optimally processed tapes, we found a J{sub c} of > 10{sup 4} A/cm{sup 2} at 20 K in magnetic fields up to 3 T and parallel to the c-axis, which is of interest for use in refrigerator-cooled magnets. I{sub c} declined exponentially when an external field was applied perpendicular to the tape surface at 77 K. Mechanical stability was tested for tapes sheathed with pure Ag and Ag-Mg alloy. Tapes made with pure Ag sheathing can withstand a tensile stress of {approx}20 MPa with no detrimental effect on I{sub c} values. Mechanical performance was improved by using Ag-Mg alloy sheathing: values of transport critical current began to decrease at the tensile stress of {approx} 100 MPa. Transport current measurements on tapes wound on a mandrel of 3.81 cm (1.5 in.) diameter at 30{degree} to the longitudinal axis, showed a reduction of {approx} 10% in I{sub c} values for pure Ag-sheathed tapes and 5% reduction in I{sub c} values for Ag-Mg sheathed tapes, compared with the I{sub c} values of as-coiled tapes.
Date: April 20, 1999
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Enhancement of critical currents in (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes.

Description: The performance of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes in magnetic fields at 77 K is critical for winding this material into high-field magnets. We have recently enhanced the transport current (I{sub c}) of multifilament Ag-clad Bi-2223 tapes in a self-field at 77 K by increasing the packing density of the precursor powder improving the mechanical deformation, optimizing the conductor design, and adjusting the cooling rate. I{sub c} values of >40 A were obtained repeatedly. However, a transport current of 42 A in a self-field declined to 4 A in a 0.2 T magnetic field applied parallel to the c-axis at 77 K. A new composite tape was then fabricated in which a YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (Y-123) film was deposited on the top of the Ag-sheathed Bi-2223 tape to shield the applied magnetic field and protect the central Bi-2223 filaments. Magnetization measurements showed that the critical current densities of the Y-123-coated, Ag-sheathed Bi-2223 tapes were higher than those of an uncoated tape. These preliminary results may provide the basis for further improving the processing of long-length Bi-2223 tapes for high-field applications.
Date: November 11, 1998
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Practical superconductor development for electrical power applications, annual report for FY 1994

Description: Development of useful high-critical-temperature superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes technical progress of research and development efforts aimed at producing superconducting components in the Y-Ba-Cu, (Bi,Pb)-Sr-Ca-Cu, (Tl,Pb,Bt)-(Ba,Sr)-Ca-Cu. and Hg-Ba-Ca-Cu-0 oxide systems. Topics discussed are synthesis and heat treatment of high-Tc superconductors, formation of monolithic and composite conductors. characterization of structures and superconducting and mechanical properties, and fabrication and testing of prototype components. Collaborations with industry and academia are documented.
Date: October 1, 1994
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Fabrication of Yb-123 Tapes

Description: While Bi-2223 tapes have been the workhorses of the superconductor industry, their poor performance in applied magnetic fields restrict their use to below 30 K. Melt-processing of Ag-clad Yb-123 PIT tapes offers a simple and scalable technique for fabricating long-length HTS conductors capable of being used at 77 K. Under reduced oxygen partial pressure, the peritectic temperature of Yb-123 is below the melting point of Ag, and this facilitates the adaptation of melt-texturing methods for fabricating these tapes. The effect of melt-processing temperature on current density was also explored; a temperature of 965 C yielded optimal critical current values. The critical current density achieved at 4.2 K was 20,000 A/cm{sup 2}, corresponding to a critical current of 52 A. Based on the above results, an optimal processing zone for melt-processing of Ag-clad Yb-123 tapes was determined. These results hold promise for melt-processing of Ag-clad Yb-123 tapes as an alternative to Bi-2223 PIT technology.
Date: November 15, 2000
Creator: Athur, S.; Balachandran, U. & Salama, K.
Partner: UNT Libraries Government Documents Department

Development of ceramic membranes for conversion of methane into syngas.

Description: The abundantly available natural gas (mostly methane) discovered in remote areas has stimulated considerable research on upgrading this gas to high-value-added clean-burning fuels such as dimethyl ether and alcohols and to pollution-fighting fuel additives. Of the two routes to convert methane to valuable products, direct and indirect, the indirect route involving partial oxidation of methane to syngas (a mixture of CO and H{sub 2}) is preferred. Syngas is used as feedstock to produce a variety of petrochemicals and transportation fuels. A mixed-conducting dense ceramic membrane was developed from Sr-Fe-Co oxide. Extruded and sintered tubes of SrFeCoO{sub 0.5}O{sub x} have been evaluated in a reactor operating at {approx}850 C for conversion of methane into syngas in the presence of a reforming catalyst. Some of the reactor tubes have been run for more than 1000 h, and methane conversion efficiencies of {approx}98% and CO selectivities of >96% were observed.
Date: September 23, 1999
Creator: Balachandran, U. & Ma, B.
Partner: UNT Libraries Government Documents Department

Electronic/ionic conductivity and oxygen diffusion coefficient of Sr-Fe-Co-O system

Description: Oxides in the system Sr-Fe-Co-O exhibit both electronic and ionic conductivities. Recently, Sr-Fe-Co-O system attracted great attention because of the potential to be used for oxygen permeable membranes that can operate without the electrodes or external electrical circuitry. Electronic and ionic conductivities at various temperatures have been measured on two compositions in Sr-Fe-Co-O system named SFC-1 and SFC-2. The electronic transference number is much greater than the ionic transference number in SFC-1 sample, while the electronic and ionic transference numbers are very close in SFC-2 sample. At 800{degrees}C, the electronic conductivity and ionic conductivity are {approx}76 S{center_dot}cm-1 and =4 S-cm-1, respectively, for SFC-1. While, for SFC-2, the electronic and ionic conductivities are =10 S-cm-1 and {approx}7 S-cm-1, respectively. By a local fitting to {sigma}{center_dot}T = A exp(-E{sub {alpha}}/{kappa}{Tau}), we found that the oxide ion activation energies are 0.92 eV and 0.37 eV respectively for SFC-1 and SFC-2 samples. Oxygen diffusion coefficient of SFC-2 is {approx}{times}10{sup {minus}7} cm{sup 2}/sec at 900C.
Date: March 1, 1995
Creator: Ma, B.; Park, J.H.; Balachandran, U. & Segre, C.U.
Partner: UNT Libraries Government Documents Department

Dense ceramic membranes for methane conversion

Description: This report focuses on a mechanism for oxygen transport through mixed- oxide conductors as used in dense ceramic membrane reactors for the partial oxidation of methane to syngas (CO and H{sub 2}). The in-situ separation of O{sub 2} from air by the membrane reactor saves the costly cryogenic separation step that is required in conventional syngas production. The mixed oxide of choice is SrCo{sub 0.5}FeO{sub x}, which exhibits high oxygen permeability and has been shown in previous studies to possess high stability in both oxidizing and reducing conditions; in addition, it can be readily formed into reactor configurations such as tubes. An understanding of the electrical properties and the defect dynamics in this material is essential and will help us to find the optimal operating conditions for the conversion reactor. In this paper, we discuss the conductivities of the SrFeCo{sub 0.5}O{sub x} system that are dependent on temperature and partial pressure of oxygen. Based on the experimental results, a defect model is proposed to explain the electrical properties of this system. The oxygen permeability of SrFeCo{sub 0.5}O{sub x} is estimated by using conductivity data and is compared with that obtained from methane conversion reaction.
Date: May 1, 1996
Creator: Balachandran, U.; Mieville, R.L.; Ma, B. & Udovich, C.A.
Partner: UNT Libraries Government Documents Department

Ceramic membranes for partial oxygenation of hydrocarbon fuels to high-value-added products

Description: This report describes the design of a membrane reactor for converting methane into value added products. The design includes an outer tube of perovskite which contacts air, an inner tube of zirconium oxide which contacts methane, and a bonding layer of a mixture of zirconium oxide and perovskite.
Date: December 31, 1994
Creator: Balachandran, U.; Dusek, J.T.; Kleefisch, M.S. & Kobylinski, T.P.
Partner: UNT Libraries Government Documents Department

Development of a ceramic membrane for upgrading methane to high-value-added clean fuels

Description: The upgrading of natural gas (which consists mostly of methane) to high-value-added clean-burning fuels such as dimethyl ether, alcohols, and pollution-fighting fuel additives is driven by the abundance of natural gas discovered in remote areas. Recently, extensive efforts have focused on both direct and indirect conversion of methane to these value-added products. The direct-conversion route is the most difficult approach because the products are more reactive than the starting reactant, methane. Indirect routes require the partial oxidation of methane to synthesis gas (syngas, CO + H{sub 2}) in a first stage. The syngas is then converted to upgraded products in a second stage. The most significant cost associated with partial oxidation of methane to syngas is that of the oxygen plant. In this paper, we offer a technology that is based on dense ceramic membranes and that uses air as the oxidant for methane-conversion reaction; thus eliminating tile need for the costly oxygen plant. Certain ceramic materials exhibit both electronic and oxide-ionic conductivities. These mixed-conductor materials transport not only oxygen ions (functioning as selective oxygen separators), but also electrons. No external electrodes are required and such a system will operate without an externally applied potential. Oxygen is transported across the ceramic material in the form of oxygen anions, not oxygen molecules.
Date: December 1, 1996
Creator: Balachandran, U.; Dusek, J.T. & Picciolo, J.J.
Partner: UNT Libraries Government Documents Department

Processing and properties of Ag-clad BSCCO superconductors

Description: Long lengths of mono- and multifilament Ag-clad BSCCO (Bi-Sr-Ca-Cu-O) conductors with critical current densities of >10{sup 4} A/cm{sup 2} at 77 K were fabricated by the powder-in-tube method. {Tc} magnets were assembled by stacking pancake coils fabricated from long tapes and then tested vs applied magnetic field at various temperatures. A magnet that contained {approx}2400 m of {Tc} conductor generated a field of 3.2 T at 4.2 K. In-situ tensile and bending properties of the Ag-clad conductors were studied. Multilayer Ag/superconductor composites were fabricated by chemical etching. Preliminary results with multilayer tapes show that continuous Ag reinforcement of the BSCCO core improves strain tolerance of the tapes so they can carry 90% of their initial I{sub c} at 1% bend strain desite a higher superconductor/Ag ratio than that of unreinforced tapes.
Date: March 1, 1996
Creator: Jammy, R.; Iyer, A.N.; Chudzik, M.; Balachandran, U. & Haldar, P.
Partner: UNT Libraries Government Documents Department

Explosive consolidation of (Bi,Pb)-Sr-Ca-Cu-O superconductor powders during powder-in-tube processing

Description: Superconducting (2212) Bi-Sr-Ca-Cu-O (BSCCO) and BSCCO-Ag composites were explosively consolidated in silver tubing and then drawn and rolled into tapes. The silver-sheathed tapes were then subjected to repeated cycles of pressing and heat treatment, which resulted in enhanced texturing and grain growth and a subsequent increase in critical current density (J{sub c}). The effect of silver flake additions to the superconducting powder further increased texturing and J{sub c}, with optimal properties occurring in powders with 10 vol.% silver flake. Density measurements on the superconductor tapes showed that near-theoretical densities had been achieved at the end of the thermomechanical treatment (TMT). Scanning electron microscopy indicated that grain alignment increased after TMT, with an apparent reduction in grain size after the fourth treatment. X-ray diffraction studies showed that grain orientation and conversion of 2212 to Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10{minus}x} are improved when explosive consolidation is introduced before the drawing step in the powder-in-tube process.
Date: August 1995
Creator: Thomas, H.; Inal, O.T. & Balachandran, U.
Partner: UNT Libraries Government Documents Department

Design of a high-current downlink using Bi-based superconductors

Description: Recent processing developments in Bi{sub 1.8}Pb{sub 0.4}Sr{sub 2}Ca{sub 2}Cu{sub 3}0{sub x} (BSCCO-2223) bars have produced bulk BSCCO-2223 bars with properties advantageous for power applications. Cold isostatically pressed (CIP) and sinter-forged BSCCO-2223 both have low AC loss, which make them desirable for use in power devices. Thermal conductivity of the CIP bars is lower than that of the previously used sinter-forged samples by a factor of 2. CIP bars with cross-sectional areas of =0.75 cm{sup 2} and carrying 250 A RMS transport current have AC loss values of 30 pJ/cycle-cm at 50 Hz and 77 K. A pair of prototype downlinks were designed and built with sinter forged bars to deliver a continuous AC current of 1500 A over a temperature gradient of 77 to 4.2 K while delivering about -200 MW of heat to the liquid-helium-cooled end. This paper will discuss the design considerations and modeling of downlinks, which supply high AC currents over the 77 to 4.2 K temperature gradient with low thermal losses.
Date: August 1996
Creator: Fisher, B. L.; Lanagan, M. T.; Balachandran, U.; Honjo, S. & Hara, T.
Partner: UNT Libraries Government Documents Department

Development of mixed-conducting oxides for gas separation

Description: Mixed-conducting oxides have been used in many applications, including fuel cells, gas separation membranes, sensors, and electrocatalysis. The authors are developing a mixed-conducting, dense ceramic membrane for selectively transporting oxygen and hydrogen. Ceramic membranes made of Sr-Fe-Co oxide, which has high combined electronic and oxygen ionic conductions, can be used to selectively transport oxygen during the partial oxidation of methane to synthesis gas (syngas, CO + H{sub 2}). The authors have measured the steady-state oxygen permeability of SrFeCo{sub 0.5}O{sub x} as a function of oxygen-partial-pressure gradient and temperature. At 900{degrees}C, oxygen permeability was {approx}2.5 scc{center_dot}cm{sup {minus}2}{center_dot}min{sup {minus}1} for a 2.9-mm-thick membrane and this value increases as membrane thickness decreases. The authors have fabricated tubular SrFeCo{sub 0.5}O{sub x} membranes and operated them at 900{degrees}C for >1000 h during conversion of methane into syngas. The hydrogen ion (proton) transport properties of yttria-doped BaCeO{sub 3} were investigated by impedance spectroscopy and open-cell voltage measurements. High proton conductivity and a high protonic transference number make yttria-doped BaCeO{sub 3} a potential membrane for hydrogen separation.
Date: August 1, 1997
Creator: Balachandran, U.; Ma, B. & Maiya, P.S.
Partner: UNT Libraries Government Documents Department

Development of ceramic superconductors for electric power applications

Description: The U.S. Department of Energy supports an applied superconductivity program entitled {open_quotes}Superconductivity Program for Electric Power Systems.{close_quotes} Activities under this program are designed to help develop the high-temperature superconductor (HTS) technology that is needed for industry to proceed with the commercial development of electric power applications. Research is conducted in three categories: wire development, systems technology development, and Superconductivity Partnership Initiative (SPI). Wire development activities are devoted to improving the critical current density (J{sub c}) of short-length HTS wire, whereas activities in systems technology development focus on fabrication of long-length wires, coils, and magnets. Finally, SPI activities focus on the development of prototypes that consist of a generator coil, a fault current limiter, a transmission cable, and a motor. A current overview and recent progress in the development of HTSs are outlined in this paper. 48 refs., 6 figs.
Date: March 1, 1997
Creator: Balachandran, U.
Partner: UNT Libraries Government Documents Department

Rapid formation of phase-clean 110 K (Bi-2223) powders derived via freeze-drying process

Description: This invention relates to an improved process of preparing Bi-Sr-Ca-Cu-O (BSCCO) powders, and more particularly, to a process for preparing BSCCO powders that utilize freeze-drying. The process generally includes splat freezing a nitrate solution of Bi, Pb, Sr, Ca, and Cu to form flakes of the solution; grinding the flakes to form a powder; freeze-drying the frozen powder; heating the powder to form dry green precursor powders; denitrating the powders; and heating the powders to form phase-clean Bi-2223 powders.
Date: December 31, 1994
Creator: Balachandran, U.; Krishnaraj, P.; Eror, N.G. & Lelovic, M.
Partner: UNT Libraries Government Documents Department

Development of proton-conducting membranes for separating hydrogen from gas mixtures

Description: Thin and dense ceramic membranes fabricated from mixed protonic/electronic conductors can provide a simple, efficient means of separating hydrogen from gas streams and offer an alternative to existing methods of hydrogen recovery. Because mixed electronic/protonic conductors internally transport not only hydrogen (and thus provide the means to separate hydrogen from other gaseous components) but also electrons, hydrogen separation could be achieved in a non-Galvanic mode of operation (i.e., without the need for external electrodes, circuitry, and/or power supply). To be suitable as a hydrogen-permeable membrane, a material must exhibit sufficiently high electronic and protonic conductivities, and these conductivities must be approximately equal to one another to maximize hydrogen permeation through the material. In addition, the material must have sufficient mechanical integrity to withstand normal operating stresses and must be chemically stable under a wide range of gas atmospheres. This talk summarizes results obtained in Argonne`s effort to develop material for use as a hydrogen separation membrane. The transport properties of BaCe{sub 0.95}Y{sub 0.05}O{sub 3{minus}{alpha}} (5%-BCY) and SrCe{sub 0.95}Y{sub 0.05}O{sub 3{minus}{alpha}} (5%-SCY) were characterized by impedance spectroscopy, gas permeation, and open-cell voltage measurements. In this presentation, the authors describe the materials selection, synthesis, characterization, and performance evaluation of mixed-conducting dense ceramic membranes for hydrogen separation applications.
Date: September 1, 1997
Creator: Balachandran, U.; Guan, J.; Dorris, S.E. & Liu, M.
Partner: UNT Libraries Government Documents Department