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  • 1
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Room-temperature tensile properties were measured for two thin C–SiC composites fabricated from single sheets of carbon fiber fabric with nominally the same weave architecture, but different fiber packing densities. The SiC matrixes were formed by infiltration and pyrolysis of a polymer precursor (allylhydridopolycarbosilane). The tensile properties are related to microstructural characteristics, observed damage mechanisms, and measurements of local strain concentrations by speckle interferometry. Differences are observed between the responses of these thin-sheet composites and conventional CVI-matrix composites of larger thickness. Debonding between transverse and longitudinal fiber tows allows significant strains due to straightening of initial wavy fiber tows and leads to local stress concentrations. The strength and elastic modulus are affected by the waviness of the longitudinal tows.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Thin C/SiC composites were fabricated by infiltrating a woven carbon fiber fabric with a slurry of SiC powder and polymer precursor for SiC, followed by heat treatment for pyrolysis. The effects of heat treatment parameters on the crystallization of the polymer-derived SiC, the composite microstructure, and the transverse thermal properties were assessed. Whereas composites heat-treated at 1000°C were crack-free and nearly fully dense, composites that were subjected to further multiple reinfiltration and heat treatment cycles at 1600°C developed porosity and cracking. However, the transverse thermal conductivity was increased significantly by the higher-temperature heat treatment, to values higher than that of a composite with a chemical-vapor-infiltration SiC matrix and the same fiber reinforcement.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The distribution of yttrium and lanthanum dopants has been mapped in yttrium- and lanthanum-doped polycrystalline aluminas using imaging secondary-ion mass spectrometry (imaging-SIMS). Both dopants segregate to grain boundaries and pore surfaces. On average, yttrium occupies 7.1%–9.0% of the available grain-boundary cation sites, whereas lanthanum occupies only 2.0%–5.2%. In 1000-ppm-yttrium-doped alumina, an abundance of yttrium aluminum garnet precipitates also is observed. Implications of these observations to the creep behavior of alumina are discussed. The similarity in the segregation behavior of yttrium and lanthanum highlights the potential of lanthanum-doped alumina for improved creep properties.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A nonvacuum reel-to-reel dip-coating system has been used to continuously fabricate epitaxial Gd2O3 buffer layers on mechanically strengthened, biaxially textured Ni–(3 at.% W–1.7 at.% Fe), defined as Ni-alloy, metal tapes. Because of its significance as a seed layer, optimum processing conditions (postannealing speed and temperature) of Gd2O3 buffer layers have been studied. Highly textured films were obtained under reducing (96% Ar + 4% H2) atmosphere at temperatures between 1100° and 1150°C; postannealing speed did not significantly affect the crystalline quality of the Gd2O3. Scanning electron microscopy revealed a continuous, dense, and crack-free surface morphology for these dip-coated buffers. The Gd2O3 layer thickness led to pronounced differences in the growth characteristics of the subsequent YSZ and CeO2 layers deposited by rf-magnetron sputtering. Epitaxial YBCO films grown by pulsed laser deposition on the short prototype CeO2/YSZ/Gd2O3/Ni–(3 at.% W–1.7 at.% Fe) conductors yielded self-field critical current densities (Jc) as high as 1.2 × 106 A/cm2 at 77 K. Pure Ni tapes were used to assess the viability of dip-coated buffers for long length coated conductor fabrication. The YBCO films, grown on 80 cm long and 1 cm wide CeO2/YSZ/Gd2O3 buffered Ni tapes by the industrially scalable ex situ BaF2 precursor process, exhibited end-to-end self-field Jc values of 6.25 × 105 A/cm2 at 77 K. These results demonstrate the reproducible epitaxy of solution-derived seed layers on pure Ni and Ni-alloy tapes as well as underscore the viability of solution approaches for the production of long length YBCO-based coated conductors.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A low-cost, nonvacuum, solution precursor route has been developed to produce epitaxial oxide buffer layers of Eu2O3 or La2Zr2O7 on biaxially textured Ni (100) tapes. A reel-to-reel continuous dip-coating unit consisting of a constant-tension tape transport system attached to a controlled atmosphere furnace was fabricated. Nickel tapes were pulled through a 2-methoxyethanol solution of europium methoxyethoxide/acetate or lanthanum zirconium methoxyethoxide. The double-sided dip-coated tapes were then annealed in a preheated furnace at 1000°–1100°C with a high flow rate of Ar/H2 (4%) gas. The dip-coated buffers were dense, continuous, crack-free, and epitaxial with a single cube texture. A critical current (Jc) of 〉1 MA/cm2 at 77 K and self-field was obtained for YBa2Cu3O7-δ (YBCO) films with a layer sequence of YBCO (ex situ BaF2 process)/CeO2 (sputtered)/YSZ (sputtered)/Eu2O3 (dip-coated)/nickel. We have produced 1–2 m lengths of epitaxial buffer layers on textured nickel substrates using a nonvacuum process for the first time.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The compatibility of Al2O3 and LaPO4 at temperatures up to 1600°C is examined. Provided the ratio of La to P was close to 1:1, no reactions were observed after 200 h at 1600°C. Moreover, the Al2O3/LaPO4 interface remained sufficiently weakly bonded to cause deflection of cracks, as reported previously. In the presence of excess P or La, reactions occurred as expected, forming AlPO4 in the case of excess P, and LaAlO3 and LaAl11O18 in the case of excess La.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Room-temperature debonding and sliding of fibers coated with La-monazite is assessed using a composite with a polycrystalline alumina matrix and fibers of several different single crystal (mullite and sapphire) and directionally solidified eutectic (Al2O3/Y3Al5O12 and Al2O3/Y-ZrO2) compositions. These fibers provide a range of residual stresses and interfacial roughnesses. Sliding occurred over a debond crack at the fiber-coating interface when the sliding displacement and surface roughness were relatively small. At large sliding displacements with relatively rough interfaces, the monazite coatings were deformed extensively by fracture, dislocations, and occasional twinning, whereas the fibers were undamaged. Dense, fine-grained areas (10 nm grain size) resembling recrystallized microstructures were also observed in the most heavily deformed regions of the coatings. Frictional heating during sliding is assessed. Potential mechanisms for forming such microstructures at low temperature are discussed, and a parallel is drawn with the known resistance of monazite to radiation damage. The ability of La-monazite to undergo both debonding and plastic deformation relatively easily at low temperatures may enable its use as a composite interface.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The use of transient glass-phase processing to lower the glass-melting temperature and subsequent heat-treatment temperature of stoichiometric SrAl2Si2O8 to produce the stable monoclinic form has been described. Two nonstoichiometric, low-melting, alumina-deficient, strontium aluminosilicate compositions were melted, quenched, and milled into glass powders. B2O3 was dissolved into one of the glass compositions to control the crystallization behavior. The glass powders were then wet-mixed with enough alpha-Al2O3 powder so that the overall composition was that of stoichiometric SrAl2Si2O8 (B2O3 neglected). The four compositions were dry-pressed into pellets and sintered in three processes. Glass-alumina pellets with dissolved B2O3 were densified via viscous-phase sintering at 1100°C, followed by complete dissolution of the alumina and crystallization to ~100% monoclinic SrAl2Si2O8. Pellets without dissolved B2O3 required considerably higher temperatures to form ~100% monoclinic SrAl2Si2O8 in a modified process.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Three composites that were 96% alumina were mixed and uniaxially dry-pressed into bars and pellets; all had monoclinic SrAl2Si2O8 as an intergranular phase. The diffraction patterns, microstructure, density, dielectric properties, strength, and toughness were measured. The first composition, which contained crystalline SrCO3, Al2O3, and SiO2, in a 1:1:2 molar ratio, as the 4% component, densified but was generally inferior to the second and third compositions, which contained strontium aluminosilicate (SrAlxSiyOz, SAS) glass as the 4% component, in terms of mechanical properties, defects, and monoclinic SrAl2Si2O8 transformation. The second composition, which lacked B2O3, was very tough and was comparable to commercial alumina, in terms of the dielectric constant. The third, which contained 0.068% of B2O3 that was dissolved in the SAS glass as a sintering aid, had high strength and toughness and no macroscopically visible defects. Mullite formed, in addition to monoclinic SrAl2Si2O8 in all three composites. Alumina–monoclinic SrAl2Si2O8 composites of the third composition had room-temperature properties that were comparable to commercial aluminas that contained 96% alumina and also had potential for mechanical and refractory applications.
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  • 10
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two-phase composites consisting of LaPO4 or CePO4 and alumina, mullite, or zirconia were found to be machinable; i.e., they can be cut and drilled using conventional tungsten carbide metal-working tools. Single-phase LaPO4 was also machinable. Measurements of drilling rates, grinding rates, and normal forces are used to compare the ease of machining in these materials and in a conventional machinable glass-ceramic material, and to provide preliminary information on the relation between microstructure and machining properties. In Hertzian contact experiments these materials showed extensive nonlinear behavior associated with a damage zone beneath the contact site, similar to other machinable ceramics. Mechanisms of material removal are discussed.
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