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  • 1
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    Stabilization of Tungsten-Uranium Dioxide Composites Under Thermal Cycling Conditions (1966)
    In:  CASI
    Details
    Publication Date: 2019-06-26
    Description: Uranium losses during thermal cycling of tungsten - uranium dioxide composites to 2500 C in flowing purified hydrogen for specimens initially containing 35 volume percent uranium dioxide were reduced by the use of thorium dioxide, calcium oxide, or yttrium oxide as additives in solid solution with the uranium dioxide. The effectiveness of the additives decreased in the order yttrium oxide, calcium oxide, and thorium dioxide. Stabilization of uranium dioxide by calcium oxide or yttrium oxide can be explained in part on the basis of the introduction of oxygen vacancies into the fluorite lattice and the associated lowered partial molar free energy of oxygen. The difference in the effectiveness of calcium oxide and yttrium oxide is discussed, and a possible explanation of the observed behavior is proposed. Of the concentrations of yttrium oxide tested (i.e., 2. 5, 5, and 10 mole percent), 10 mole percent of yttrium oxide was the most effective in pre venting loss of uranium from composities.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA-TM-X-1295 , E-3238
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Thermal History Of PMRs Via Pyrolysis-Gas Chromatography (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Pyrolysis-gas chromatography (PY-GC) useful as analytical technique to determine extents of cure or postcure of PMR-15 polyimides and to lesser extent, cumulative thermal histories of PMR-15 polyimides exposed to high temperatures. Also applicable for same purposes to other PMR polyimides and to composite materials containing PMR polyimides. Valuable in reducing costs and promoting safety in aircraft industry by helping to identify improperly cured or postcured PMR-15 composite engine and airframe components and helping to identify composite parts nearing ends of their useful lives.
    Keywords: PHYSICAL SCIENCES
    Type: LEW-15725 , NASA Tech Briefs (ISSN 0145-319X); 18; 11; P. 66
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Cyclopentadiene evolution during pyrolysis-gas chromatography of PMR polyimides (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The effect of formulated molecular weight (FMW), extent of cure, and cumulative aging on the amount of cyclopentadiene (CPD) evolved from Polymerization of Monomeric Reactants (PMR) polyimides were investigated by pyrolysis-gas chromotography (PY-GC). The PMR polyimides are additional crosslinked resins formed from an aromatic diamine, a diester of an aromatic tetracarboxylic acid and a monoester of 5-norbornene-2, 3-dicarboxylic acid. The PY-GC results were related to the degree of crosslinking and to the thermo-oxidative stability (weight loss) of PMR polyimides. Thus, PY-GC has shown to be a valid technique for the characterization of PMR polyimide resins and composites via correlation of the CPD evolved versus the thermal history of the PMR sample.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TM-105629 , E-6971 , NAS 1.15:105629 , AVSCOM-TR-91-C-023 , International Conference on Polyimides; Oct 30, 1991 - Nov 01, 1991; Ellenville, NY; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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