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  • 1
    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: γ-Al2O3 nanoparticles with an average size of 5 nm were synthesized by the hydrolysis of aluminum triisopropoxide under the influence of power ultrasound (100 W/cm2) and in the presence of formic or oxalic acids as peptizers, followed by calcination. The structural and morphological properties of the as-prepared precursor hydroxides and calcined nanocrystalline powders were characterized by XRD, SEM, TEM, TGA, IR, and BET. The ultrasound-driven cavitation process has been shown to affect the agglomeration of the precursor nanoparticles by condensation of interparticle hydroxyls. The oxalate anions were strongly adsorbed on the surface of the precursor nanoparticles and thus retarded the ultrasound-driven condensation of interparticle hydroxyls. Formic acid showed a lesser degree of adsorption on the surface of the precursor particles. The ultrasound-driven agglomeration of the primary particles as well as the role of organic modifiers on the microstructural properties of the precursor and the target alumina phases have been discussed.
    Type of Medium: Electronic Resource
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  • 2
    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: High temperature mechanical behavior of nanocrystalline 1.7 mol% (3 wt%) yttria tetragonal zirconia polycrystals (nc-YTZP) was characterized by compression creep tests. The hot isostatically pressed nc-YTZP with mean grain size of 120 nm was subjected to grain growth to obtain grain sizes in the range of 120–310 nm. Direct measurements of the creep parameters were performed in the temperature range 1150°–1300°C and stress range 5–400 MPa. The strain rates at 1150°C ranged between 2 × 10−7 and 9 × 10−5 s−1 when increasing the stress from 15 to 400 MPa. Values of the stress exponent, n=2.0±0.3, and the activation energy, Q=630±40 kJ/mol, were obtained for all test conditions. A value of the grain size exponent, p=1.5±0.3, was obtained at 1150°C in the stress range studied. Detailed microstructural observations revealed the absence of glassy phase at the grain boundaries. The creep parameters were compared with those from the literature, and the results were discussed in terms of the model recently developed by the authors, with a reasonable agreement.
    Type of Medium: Electronic Resource
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