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  • Other Sources  (3)
  • 1985-1989  (3)
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  • 1
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    Unknown
    Properties of Pb(1-x)Bi(x)/Ba2YCu3O(x) composites - Reaction of Ba2YCu3O(x) with Pb and Bi (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper describes experiments conducted with a purpose of fabricating superconducting composites from Pb, Bi, and Ba2YCu3O(x), together the results of SEM examinations and energy dispersive spectroscopy performed on products. Results showed a limited utility of Pb and Pb(1-x)Bi(x) as matrices for ceramic superconductors. It was found that cold pressing followed by sintering at 200 C resulted in a composite which excluded flux below 90 K but did not show zero electrical resistance until the metal superconducting transition. Processing at 400 or 950 C resulted in oxygen depleted perovskite and/or metal oxides; these materials displayed greatly degraded superconducting properties. Finally, processing at 800 C resulted in high Tc only for composites containing more than 90 wt pct ceramic.
    Keywords: SOLID-STATE PHYSICS
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Fuel-rich catalytic combustion: A soot-free technique for in situ hydrogen-like enrichment (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An experimental program on the catalytic oxidation of iso-octane demonstrated the feasibility of the two-stage combustion system for reducing particulate emissions. With a fuel-rich (phi = 4.8 to 7.8) catalytic combustion preburner as the first stage the combustion process was soot free at reactor outlet temperatures of 1200 K or less. Although soot was not measured directly, its absence was indicated. Reaction products collected at two positions downstream of the catalyst bed were analyzed on a gas chromatograph. Comparison of these products indicated that pyrolysis of the larger molecules continued along the drift tube and that benzene formation was a gas-phase reaction. The effective hydrogen-carbon ratio calculated from the reaction products increased by 20 to 68 percent over the range of equivalence ratios tested. The catalytic partial oxidation process also yielded a large number of smaller-containing molecules. The fraction of fuel carbon in compounds having two or fewer carbon atoms ranged from 30 percent at 1100 K to 80 percent at 1200 K.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA-TP-2498 , E-2604 , NAS 1.60:2498
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    A theoretical analysis of the extinction limits of a methane-air opposed-jet diffusion flame (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A theoretical analysis is described for a methane-air diffusion flame stabilized in the forward stagnation region of a porous metal cylinder in a forced convective flow. The analysis includes effects of radiative heat loss from the porous metal surface and finite rate kinetics but neglects the effects of gravity. The theoretically predicted extinction limits compare well with experimentally observed extinction limits from the literature. After the predicted limits compared well with the experimental limits, a parametric study of the effect of fuel surface emissivity and Lewis number was conducted with the numerical model. It was found that the computed blowoff limit is independent of radiative heat loss for high fuel blowing velocities but is a strong function of Lewis number. At low fuel blowing velocities, the extinction limit varies with both radiative heat loss and Lewis number. It is discovered, however, that even if thermal losses from the fuel surface are absent, the flame can extinguish at the fuel surface independently of Lewis number due to excessive reaction zone thinning.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Combustion and Flame (ISSN 0010-2180); 70; 161-170
    Format: text
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    NASA TECHNICAL REPORTS
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