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  • 1
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 603-605 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thick films of YBa2Cu3O7−x have been deposited on highly polished alumina, magnesia spinel, nickel aluminum titanate (Ni-Al-Ti), and barium tetratitanate (Ba-Ti) substrates by the screen printing technique. They were baked at 1000 °C for 15 min, oxygen annealed at a lower temperature, and characterized by electrical resistivity measurements, x-ray diffraction, and optical and scanning electron microscopy. Properties of the films were found to be highly sensitive to the choice of the substrate material. The film on Ba-Ti turned green after firing, due to a reaction with the substrate and were insulating. A film on Ni-Al-Ti had a Tc (onset) ∼95 K and lost 90% of its resistance by ∼75 K. However, even at 4 K it was not fully superconducting, possibly due to a reaction between the film and the substrate and interdiffusion of the reaction products. The film on alumina had Tc (onset) ∼96 K, Tc (zero) ∼66 K, and ΔTc (10–90%) ∼10 K. Our best film was obtained on spinel and had Tc (onset) ∼94 K, zero resistance at 81 K, and a transition width (10–90%) of ∼7 K.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 323-325 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The stability of YBa2Cu3O7−x in water and 100% humidity has been investigated at three temperatures using pH measurements, x-ray diffraction, and scanning electron microscopy. The oxide-ceramic superconductor is highly unstable and reacts rapidly with water and also degrades in moisture. Dissolution of the oxide perovskite in water is highly incongruent. The corrosion products are found to be BaCO3, CuO, O2, etc. Barium hydroxide is first formed which further reacts with atmospheric CO2 to form needle-shaped crystals of BaCO3. For any practical applications, devices made from these materials would have to be protected with an impermeable coating to prevent deterioration from atmosphere.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 838-840 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effect of fluoride doping on the superconducting transition temperature, Tc, of YBa2Cu3O6.5+δ has been investigated. Samples of nominal composition YBa2Cu3FxO6.5+δ−0.5x were synthesized where x was varied by two orders of magnitude from 0.0165 to 1.65. Tc systematically increased with x, reached a maximum of 93.4 K (midpoint) for x=0.066 and then dropped for higher concentrations. The sharpest transition, ΔTc(10–90%)=0.7±0.1 K, coincided with a maximum in Tc. From powder x-ray diffraction measurements, samples with x≤0.066 were found to be single phase perovskite whereas those with x≥0.165 also contained BaF2, CuO, and an unknown phase. Although we find no evidence for the very high Tc's reported by S. R. Ovshinsky, R. T. Young, D. D. Allred, G. DeMaggio, and G. A. Van der Leeden [Phys. Rev. Lett. 58, 2579 (1987)], our results do indicate that the effect of fluorine is qualitatively different from that produced by other dopants.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1572-1574 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A melt of composition Bi1.5Pb0.5Sr2Ca2Cu3Ox was fast quenched to form a glass. This was subsequently air annealed and the influence of annealing time and temperature on the formation of various crystalline phases was investigated. X-ray powder diffraction indicated that none of the resulting samples were single phase. However, for an annealing temperature of 840 °C, the volume fraction of the high Tc phase (isostructural with Bi2 Sr2 Ca2 Cu3O10 ) increased with annealing time. A specimen annealed at this temperature for 243 h followed by slow cooling showed a sharp transition [ΔTc (10–90%) ∼2 K] and Tc (R=0)=107.2 K. To our knowledge, this is the highest Tc yet reported for any superconductor prepared via the glass route.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 87 (2004), S. 0 
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: Both interlaminar and in-plane shear strengths of a unidirectional Hi-Nicalon™-fiber-reinforced barium strontium aluminosilicate (SiCf/BSAS) composite were determined at 1100°C in air as a function of test rate using double-notch shear test specimens. The composite exhibited a significant effect of test rate on shear strength, regardless of orientation. The shear strength degraded by about 50% as the test rate decreased from 3.3 × 10−1 to 3.3 × 10−5 mm/s. The rate dependency of shear strength was similar to that observed for ultimate tensile strength at 1100°C for the two-dimensional (2-D) SiCf/BSAS composite, in which tensile strength decreased by about 60% when the test rate varied from 5 to 0.005 MPa/s. A phenomenological, power-law slow crack growth model is proposed and formulated to account for the rate dependency of shear strength of the composite. The proposed model has been validated with additional results of both constant stress-rate and constant stress testing in shear at 1100°C using a 2-D Nicalon-fiber-reinforced crossply magnesium aluminosilicate (SiCf/MAS-5) ceramic matrix composite.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: Band shifts in Raman spectra were used to assess, on a microscopic scale, the residual strain existing in Hi-Nicalon silicon carbide fibers reinforcing celsian-matrix composites. Uncoated as well as p-BN/SiC-coated and p-B(Si)N/SiC-coated Hi-Nicalon fibers were used as the reinforcements. We unambiguously conclude that the fibers were in a state of compressive residual stress. Quantitative determination of the residual stress was made possible by taking into account the heating induced by laser probing and by using a reference line, of fixed wavenumber. We found fiber compressive residual stress values between 110 and 960 MPa, depending on the fiber/matrix coating in the composite. A stress relaxation-like phenomenon was observed at the surface of p-BN/SiC-coated Hi-Nicalon fibers whereas the uncoated or p-B(Si)N/SiC-coated Hi-Nicalon fibers did not show any stress relaxation in the celsian-matrix composites.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: Current state-of-the-art environmental barrier coatings (EBCs) for Si-based ceramics consist of three layers: a silicon bond coat, an intermediate mullite (3Al2O3·2SiO2) or mullite + BSAS ((1−x)BaO·xSrO·Al2O3·2SiO2, 0 ≤x≤ 1) layer, and a BSAS top coat. Areas of concern for long-term durability are environmental durability, chemical compatibility, volatility, phase stability, and thermal conductivity. Variants of this family of EBC were applied onto monolithic SiC and melt-infiltrated SiC/SiC composites. Reaction between BSAS and silica results in a low-melting (∼1300°C) glass, which can cause the spallation of the EBC. At temperatures greater than ∼1400°C BSAS suffers significant recession via volatilization in water-vapor-containing atmospheres. Both reactions can be EBC life-limiting factors. BSAS undergoes a very sluggish phase transformation (hexagonal celsian to monoclinic celsian), the implications of which are not fully understood at this point. Initial rapid increase in thermal conductivity at temperatures as low as 1300°C indicates the sintering of EBC.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: Hi-Nicalon-fiber-reinforced celsian-matrix composites were characterized by Raman spectroscopy and imaging, using several laser wavelengths. Composite 1 was reinforced by as-received fibers while coatings of p-BN and SiC protected the fibers in composite 2. The matrix contained traces of the hexagonal phase of celsian, which was concentrated in the neighborhood of fibers in composite 1. Some free silicon was evident in the coating of composite 2 which might have involved a {BN + SiC → BNC + Si}“reaction” at the p-BN/SiC interface. Careful analysis of C–C peaks revealed no abnormal degradation of the fiber core in the composites.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 5-6 (Jan. 1985), p. 211-218 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 5-6 (Jan. 1985), p. 291-297 
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
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