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  • 1990-1994  (9)
  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1208-1210 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Corrosion of YBa2Cu3O7−x pellets has been studied using magnetic levitation. Pellets compressed at green compaction pressures of 120–200 MPa were exposed to water and air and the levitation heights were measured over a period of more than a month. A model based on diffusion as a rate-controlling step has been proposed. Levitation height normalized with respect to the initial levitation height was used as the modeling parameter. The experiments indicate that the normalized levitation height decreased with time up to a certain level called the saturation leviation, beyond which there is no change in the levitation height. Samples in air degraded faster than samples in water. The initial period of degradation before saturation fits the proposed model well and therefore appears to be diffusion controlled. The saturation levitation shows a dependence on the green compaction pressure. It has been proposed that corrosion (degrading reactions) is due to open porosities which are closed by the reaction products, thus causing a saturation in the levitation height dependent on the porosities.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 3 (1992), S. 181-186 
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Bulk superconducting YBa2Cu3O7−x powder has been synthesized by a solution technique using a mixture of Ba-ethylenediaminetetra-acetic acid (EDTA) and [Y, Cu]-citric acid complexes. A light-blue, molecular-level, homogeneously mixed precursor was prepared, and transferred to powder form through vacuum drying. The vacuum-dried powder was decomposed at 800 °C for 4 h under flowing oxygen, then heat treated at high temperature from 850 to 950 °C for 6–12 h. The results ofT c measurements and X-ray analysis show that the orthorhombic, superconducting phase can be formed at temperatures above 850 °C following low-temperature annealing. A sharp transition (ΔT≃2 K) and high density can be achieved after 930 °C heat treatment. The 930 °C heat treated sample shows aJ c value of 510 A cm−2. It is concluded that this solution technique provides better stoichiometric control and lower reaction temperature than the conventional solid-state sintering process.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 9 (1990), S. 1103-1105 
    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
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  • 4
    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 Debris particles extracted from a small sampling region on the leading edge of the Long Duration Exposure Facility (LDEF) spacecraft have been examined by analytical transmission electron microscopy and the elemental frequency observed by energy-dispersive X-ray spectrometry and compared with upper atmosphere (Earth) particle elemental frequency and the average elemental compositions of interplanetary dust particles. A much broader elemental distribution was observed for the exposed spacecraft surface debris milieu. Numerous metal microfragment analyses, particularly aluminium and stainless steel, were compared with scanning electron microscope observations of impact crater features, and the corresponding elemental spectra on selected LDEF aluminium tray clamps and stainless steel bolts. The compositions and melt features for these impact craters and ejecta have been shown to be consistent with microcrystalline debris fragments in the case of aluminium, and these observations suggest an ever changing debris milieu on exposed surfaces for space craft and space system materials.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 12 (1993), S. 170-172 
    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
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 10 (1991), S. 52-55 
    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
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 28 (1993), S. 2795-2802 
    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 recovered copper shaped-charge jet fragment has been built up by copper electrodeposition for the first time to allow it to be systematically sectioned and polished for detailed observations by optical and electron microscopy. The residual jet fragment microstructure was observed to have a recrystallized grain structure and dislocation substructures similar to those in the undeformed copper shaped charge liner cone. However, the average grain size in the recrystallized jet fragment was 15 μm compared to 45 μm for the liner. More significantly, however, SEM examination near the tips (or ends) of the jet fragment exhibited voids and coalesced void tunnels elongated axially within the fragment geometry, which are believed to have resulted during jet elongation and breakup by diffusion and viscous growth at high strain and strain rate. The observation of additional porosity in the interior of the jet fragment is supported by the lack of any similar observations in the surrounding and supporting (built up) copper electrodeposit.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 25 (1990), S. 2287-2298 
    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 An oblique shock loading arrangement is utilized to dynamically consolidate small diameter solid and hollow cylinders of type 304 stainless steel and tungsten. The experimental arrangement approximates a 2-dimensional consolidation regime when viewed along any plane perpendicular to the cylinder axes. Hot spots and localized melting were observed to occur in regions characterized by interstitial or other void space prior to consolidation due to extrusion of matter into these spaces creating strain heating. The larger the void spaces, the more preponderous the melting. In consolidating hollow cylinders where the internal void area was larger than the interstitial void area, the melt preponderance shifted to the tube centers. By filling void space using solid cylinders of various diameter to approximately a 2-dimensional “particle” size distribution, void space could be minimized and local heating and melting reduced or eliminated. The melt fraction was also observed to increase with increasing peak shock pressure in the range of 12 to 22 GPa.
    Type of Medium: Electronic Resource
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  • 9
    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 preliminary study of materials exposed in space in a low-earth orbit for nearly 6 years (in the NASA Long-Duration Exposure Facility) has revealed a wide range of micrometeorite or microparticle impact craters ranging in size from 1–100 μm diameter, debris particles from adjacent and distant materials systems, reaction products and other growth features on the specimen surfaces, and related phenomena. The exposed-surface features included finegrained and nearly amorphous materials as well as single-crystal particles. A replication-type, lift-off technique was developed to remove reaction products and debris from the specimen surfaces in order to isolate them from the background substrate without creating microchemical or microstructural artefacts or alterations. This resulted in surface features resting on a carbon support film which was virtually invisible to observation by electron microscopy and non-dispersive X-ray analysis. Characterization of these surface features involved observations by optical metallography, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis; including an analytical transmission electron microscope with a STEM attachment. The results illustrate a wide variety of materials phenomena which must be addressed in the evaluation of materials exposure in space, and the formidable materials characterization effort which will be necessary to understand these features.
    Type of Medium: Electronic Resource
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