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  • 1
    Electronic Resource
    Electronic Resource
    Effect of silver solubility on microstructure and superconducting properties of YBa2Cu3−xAgxO7−δ superconductors (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2351-2355 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of silver (Ag) solubility on microstructure and superconducting properties of YBa2Cu3−xAgxO7−δ (0≤x≤0.5) superconductors has been evaluated. The solubility limit of Ag for copper sites in YBCO at ambient conditions (room temperature, atmospheric pressure) was evaluated to be x(approximately-equal-to)0.06. Analysis revealed the Ag content (x) of YBCO grains to be lower than the nominal Ag content (xn) used for fabrication, probably due to processing-related problems. Part of the Ag used for fabrication segregates on the YBCO grain boundaries. The segregated Ag particles are believed to pin YBCO grains, resulting in fine-grain microstructures. For low nominal Ag content, xn〈0.2, critical current density (Jc) increased from 98 to 160 A/cm2 as a function of increasing Ag content. These improvements are believed to be due to the increased oxygen content and associated microstructural changes in the YBCO. For higher nominal Ag content, xn(approximately-greater-than)0.2, however, Jc decreased rapidly with the increasing Ag content due to the precipitation of nonsuperconducting phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351088
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of silver and silver oxide additions on the mechanical and superconducting properties of YBa2Cu3O7−δ superconductors (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3154-3159 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of Ag and Ag2 O additions on the mechanical and superconducting properties of YBa2 Cu3 O7−δ superconductors were studied. The addition of 20-vol % Ag resulted in an increase in strength from ≈40 to 75 MPa and a twofold increase in the critical current density (Jc ) of YBa2 Cu3 O7−δ bar specimens. These improvements are believed to be due to the increased density. Furthermore, Ag particles may relax the residual stresses resulting from the expansion anisotropy of individual grains, and may provide increased resistance to crack propagation by pinning the propagating cracks; these effects would also increase the strength. The addition of 30-vol % Ag resulted in an increase in strength to 87 MPa, but it was associated with a decrease in Jc . This decrease in Jc at high Ag content is believed to be due to the presence of oxygen deficient nonsuperconducting tetragonal phase as well as continuous Ag phase. Similar effects were also observed after Ag2 O additions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344152
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  • 3
    Electronic Resource
    Electronic Resource
    rf properties of an oxide-superconductor half-wave resonant line (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 930-932 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cylindrical rods of YBa2Cu3O7−δ from 0.6 to 1.9 mm in diameter and up to 565 mm long have been used as the center conductor of a half-wave resonant coaxial line. The resonant line can be immersed in liquid nitrogen, which provides excellent cooling of the current-carrying superconducting surface, even in the presence of substantial rf losses. Such superconducting resonant lines have been operated at frequencies of a few hundred MHz and at rf surface magnetic fields up to 150 G at 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99277
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  • 4
    Electronic Resource
    Electronic Resource
    Slip casting high-T c superconductors (1989)
    Springer
    Journal of materials science 8 (1989), S. 759-761 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01730129
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  • 5
    Electronic Resource
    Electronic Resource
    Failure mechanisms of ceramic membrane reactors in partial oxidation of methane to synthesis gas (1994)
    Springer
    Catalysis letters 30 (1994), S. 201-212 
    Details
    ISSN: 1572-879X
    Keywords: synthesis gas ; methane ; perovskite ; oxygen permeable membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In the course of generating synthesis gas (H2, CO) from methane, we have observed two types of fractures occurring on the Sr(Co, Fe)Ox-type oxygen membrane reactors. The first type occurred shortly after the reaction started and the second type often occurred days after the reaction. To determine the causes of these fractures, we have examined the starting material and fractured membranes using a combination of X-ray diffraction and thermogravimetric analyses. We found that the first type of fracture was the consequence of an oxygen gradient in the membrane, pointing from the reaction side to the air side. This causes a lattice mismatch inside the membrane, leading to fracture. The second type of fracture, however, was the result of a chemical decomposition. We found that the Sr(Co, Fe)Ox-type membrane had been reduced to SrCO3, and elemental Co and Fe by the synthesis gas generated in the reaction. The decomposition causes enormous expansion leading to a large crack along the axis of tube.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00813686
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  • 6
    Electronic Resource
    Electronic Resource
    Dependence of ceramic fracture properties on porosity (1993)
    Springer
    Journal of materials science 28 (1993), S. 3589-3593 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A connected-grain model developed earlier to study the modulus of elasticity as a power-law of density was extended to study the dependence of the flexural strength of polycrystalline ceramics on porosity. Relations were derived for specific surface fracture energy, fracture toughness and flexural strength as power laws of (1 −p), wherep is porosity. Model validity was confirmed with data on α-alumina, UO2, Si3N4, and the YBa2Cu3O7−δ superconductor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01159841
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  • 7
    Electronic Resource
    Electronic Resource
    Open pore description of mechanical properties of ceramics (1991)
    Springer
    Journal of materials science 26 (1991), S. 3862-3868 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A dependence of Young's modulus of elasticity on open porosity in ceramics is derived from an open-porosity model, which in the literature, is applied to salinity conductivity and fluid permeability in rocks. A random distribution of grain and pore size is assumed. The relation developed,E(p)=E o(1−"p)m, whereE is the modulus of elasticity of the porous ceramic,E o is the theoretical elastic modulus,p is the porosity andm is an exponent dependent on the tortuosity of the structure of the ceramic, adequately describes the dependence of the modulus of elasticity on porosity. The model is applied to the experimental data from several ceramics such as alumina, silicon nitride, silicon carbide, uranium oxide, rare-earth oxides, and YBa2Cu3O7−δ superconductor, and the value ofm is obtained for each case. We have shown thatm has a value of nearly 2 for sintered ceramics, unless sintering aids or hot pressing have been used during fabrication of the ceramic. Such additional procedures approximately double the magnitude ofm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01184983
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