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  • 1995-1999  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), 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 results for the corrosion of alumina single crystals at 1700-2000°C in argon, argon/water vapor, air, and air/water vapor for 10 h are reported. There were no obvious weight and volume changes after corrosion. White spots were observed on the surfaces of the specimens after corrosion tests. The initial temperature for the appearance of these white spots was 1800°C for argon and air, 1900°C for argon/water vapor, and 2000°C for air/water vapor. These white spots were likely formed by internal impurities, which diffused outward to the surface and coalesced at high temperatures. There was no evidence of corrosion damage inside the specimens. The flexural strength of the specimens was clearly enhanced after the corrosion tests and showed no evident relation to the corrosion conditions. This increase in strength after corrosion was likely due to the healing of surface machining flaws. The surface flaw healing temperature for alumina crystals was higher than 1400°C.
    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 82 (1999), 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: A high-temperature multilayer composite (MLC) with hot hard layers and superplastic layers was proposed in this communication. The hard layer can provide the MLC high-temperature strength; the superplastic layer can deform plastically at high temperatures, disperse the applied stress, and stop the crack from advancing. Such an MLC was prepared via tape casting in the Al2O3/MoSi2+Mo2B5 system in the present work; in this system, Al2O3 was the hard layer and MoSi2+Mo2B5 was the superplastic layer. The microstructures and the stress-displacement behaviors of the MLCs were investigated. Finally, the design rules for the high-temperature MLCs were discussed briefly.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1436-2813
    Keywords: color Doppler flow imaging ; deep venous thrombosis ; venography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To evaluate the ability of color Doppler flow imaging (CDFI) to detect deep venous thrombosis (DVT), which is difficult to diagnose clinically, 67 limbs of 60 patients who presented with clinical signs strongly indicative of DVT during the period between June 1988 and June 1992, were examined. The iliac, common femoral, and superficial femoral veins were assessed with the patient in the supine position, and the popliteal vein was examined with the patient prone. Gentle but firm compression with the transducer probe was used to test for the presence of DVT. Ascending contrast venograms were also obtained within 24 h after the ultrasound procedure, with venography being used as the standard for comparison with CDFI. DVT was identified in 63 limbs by contrast venography and in 62 limbs by CDFI. The sensitivity and specificity of CDFI were 98.4% and 100%, respectively, while the positive and negative predictive values were 100% and 80%, respectively. The thromboses were classified into three patterns: the filling type, the local type, and mural thrombus, detected in 63%, 27%, and 10%, of the limbs respectively, with the filling type being the most common in this series. The results of our study illustrated that CDFI is highly sensitive and specific for detecting symptomatic DVT and that it should be gradually substituted for venography in such patients.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 34 (1999), S. 997-1001 
    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 Phase composition change and mechanical properties at room temperature of MoSi2 materials with the addition of aluminum were investigated. An explanation was given to the appearance of Mo5Si3 when hot pressing MoSi2 raw powder containing oxygen. The mechanical properties including Vickers hardness, bending strength and fracture toughness were improved with the addition of aluminum up to the limit content needed for absorbing the oxygen in MoSi2 raw powder. More aluminum addition than the limit content (in this study it is 5 wt %) will result in the formation of Mo(Si ,Al)2 and Si. The in situ formed Al2O3 could act as a crack pinning element. However, because the thermal expansion coefficients of Al2O3 and MoSi2 are near and there is a strong bonding between them, the toughening effect by such in situ formed small Al2O3 particles (less than 2 μm) is limited.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 34 (1999), S. 593-597 
    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 Mo(Si,Al)2 alloy was prepared by reactive hot pressing at low temperatures for a short time under 20MPa in a vacuum using MoSi2, Mo and Al as starting powders. At 1160 °C, 5 min of soaking time was enough to obtain a high density alloy. At 1060 °C, however, 10min was needed. The formation of Mo(Si,Al)2 was accompanied by the melting of aluminum and controlled by the dissolution of molybdenum into the aluminum melt. It was proposed that the oxygen present in MoSi2 raw powder would react with aluminum and form Al2O3 in an amorphous or poor crystallization state. The mechanical properties of the alloy were a little stronger than those of monolithic MoSi2 alloy. The formed Al2O3 particles acted as crack-pinning elements, but a large toughening effect could not be obtained by this crack-pinning because of the strong interface bonding and the similar thermal expansion coefficients of Mo(Si,Al)2 and Al2O3.
    Type of Medium: Electronic Resource
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