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  • Articles  (361,788)
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  • Articles: DFG German National Licenses  (361,788)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (361,788)
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  • Articles  (361,788)
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  • 11
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: Mechanical stress–strain behavior of LaCoO3, La0.8Ca0.2CoO3, and La0.7Ca0.3CoO3 was studied under compression at 25° and 300°C. A hysteresis in the stress–strain relationship due to reorientation of ferroelastic domains (deformation twins) was observed, and a remanent strain is measured after unloading. The cohersive stress, defined as the maximum in effective elastic compliance during first loading, increases with substitution of Ca for La and decreases with increasing temperature. Domain reorientation was confirmed by X-ray diffraction of surfaces parallel and perpendicular to the loading direction. LaCoO3 can be regarded as a soft ferroelastic material while the 30% Ca-substituted material is a hard ferroelastic. The hysteresis of the stress–strain relationship was clearly dependent on both composition and temperature.
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  • 12
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: Ceramic laminates exhibiting a threshold strength have been fabricated by dip-coating thick tape-cast Al2O3 layers into slurries containing mixtures of Al2O3 and either unstabilized zirconia (MZ-ZrO2) or mullite to produce thin compressive layers via both a molar volume change and a differential thermal contraction. Porosity was introduced into the thin compressive layers by adding rice starch to the dip-coating slurries, which decomposed during densification of the laminate. As the volume fraction of porosity is increased, the residual compressive stress (σC), as measured by piezospectroscopy, is reduced and approaches zero at approximately 0.65 volume fraction of porosity. The elastic modulus mismatch (E1/E2) between the thin and thick laminate layers accounted for approximately one-half of the threshold strength for volume fractions of porosity ≤0.30 (E1/E2〈0.4). Above 0.40 volume fraction of porosity, the strength significantly increased as did the scatter in strength values, and it was observed that the highly porous layers completely arrested crack extension; these materials no longer exhibited a threshold strength. For these laminates, failure occurred by the independent, sequential failure of one layer after another, followed by catastrophic failure due to delamination.
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  • 13
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: Single-phase silicon carbide (SiC) nanotubes were successfully synthesized by the reaction of carbon nanotubes with silicon powder at 1200°C for 100 h. X-ray diffraction patterns indicated that most of the carbon from the carbon nanotubes that were reacted with silicon at 1200°C for 100 h was transformed to SiC. Transmission electron microscopy observations revealed that both single-phase SiC nanotubes and C–SiC coaxial nanotubes, which are carbon nanotubes sheathed with a SiC layer, were synthesized after 100 h of reaction. The ratio of single-phase SiC nanotubes to C–SiC nanotubes increased with heat treatment at 600°C in air for 1 h because the remaining carbon was removed.
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  • 14
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: Long crack R-curve of a porous Si3N4 with aligned fibrous grains was investigated, using a chevron-notched beam technique. A crack was constrained to propagate normal to the grain alignment. The crack growth resistance of aligned porous Si3N4 was much larger compared with that of dense Si3N4 ceramics. Microstructure observations showed that pullouts of fibrous grains in aligned porous Si3N4 markedly increased during crack propagation relative to those of dense Si3N4, due to the existence of pores. The efficient grain pullouts in porous Si3N4 increased the bridging stress at the crack wake.
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  • 15
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: Hydroxyapatite (HA) is an interesting ceramic material for orthopedic applications, in particular for implant operations and bone regeneration, owing to its bioactivity and biocompatibility with the surrounding tissues. Even if different shaping processes can be used in order to obtain porous ceramic bodies with optimal final properties, the sponge impregnation method with aqueous HA dispersions is particularly suitable to achieve an appropriate macroporosity to bone regeneration. As for conventional slip or tape casting, the rheological behavior of HA suspensions must be properly fitted to process conditions and controlled through a satisfactory stabilization of the disperse phase, i.e., through an appropriate dispersant dosage and an accurate homogenization of dispersed powder. In the present work, HA powders with different crystallinity degree were used to prepare aqueous dispersions with different contents of solids and dispersant (ammonium polyacrylate). The specific surface area of HA powders is very high, and then special attention must be dedicated to the dispersant selection and the dispersion process since the rheology of HA suspensions is strongly influenced by the structural conditions of the disperse phase. Even small differences in dispersant concentration can lead to dramatic changes in the rheological properties also at relatively low values of solids volume concentration. Above a critical concentration, the viscosity drop associated with the apparently plastic behavior is confined within a very narrow stress range, a neat transition is observed in the linear viscoelastic properties, and the time-dependent effects induced by the shear history become quite important and crucial for the experimental characterization.
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  • 16
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: Pristine, Si-doped, and Si/Nd-codoped yttrium aluminum garnet (YAG) nanoparticles were synthesized by pyrolysis of complex compounds of aluminum and yttrium with triethanolamine. It was found that the coexistence of Si4+ and Nd3+ increased the solubility of both ions and promoted the formation of YAG phase. Single-phase, nanocrystalline Si/Nd:YAG powders were obtained at calcination temperatures as low as 920°C. The optical behavior of the Si/Nd:YAG nanopowders was similar to that of single-crystal Nd:YAG.
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  • 17
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: Alumina bilayers of different relative thicknesses and densities were produced with a strong interface using a modified gel-casting technique. Tolerance to surface damage is examined using biaxial flexure of disks damaged with a single Vickers indentation at various loads. The greatest surface flaw tolerance is seen in bilayers consisting of a thin porous layer on the tensile surface coupled to a thick dense layer. Here, the modulus mismatch causes redistribution of the applied stress, and fracture initiates at the internal porous-dense interface rather than at the surface from the introduced indentation flaw.
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  • 18
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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: An extensive X-ray study of CeO2–Nd2O3 solid solutions was performed, and the densities of solid solutions containing various concentrations of NdO1.5 were measured using several techniques. Solid solutions containing 0–80 mol% NdO1.5 were synthesized by coprecipitation from Ce(NO3)3 and Nd(NO3)3 aqueous solutions, and the coprecipitated samples were sintered at 1400°C. A fluorite structure was observed for CeO2–NdO1.5 solid solutions with 0–40 mol% NdO1.5, which changed to a rare earth C-type structure at 45–75 mol% NdO1.5. The change in the lattice parameters of CeO2–NdO1.5 solid solutions, when plotted with respect to the NdO1.5 concentration, showed that the lattice parameters followed Vegard's law in both the fluorite and rare earth C-type regions. The maximum solubility limit for NdO1.5 in CeO2 solid solution was approximately 75 mol%. The relationship between the density and the Nd concentration indicated that the defect structure followed the anion vacancy model over the entire range (0–70 mol% NdO1.5) of solid solution.
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  • 19
    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: Yttrium silicates are promising materials for improved oxidation and erosion protection for carbon fiber-reinforced composites. A two-layer coating system of low-pressure plasma-sprayed yttrium silicate on chemical vapor deposition-SiC-precoated C/C–SiC was tested under atmospheric re-entry conditions simulated within a plasma wind tunnel test facility. The thermal expansion behavior of Y2SiO5 and Y2Si2O7 was investigated. The chemical compatibility with and without increasing oxygen partial pressure at the interface of the two-layer system was calculated by the CALPHAD method. The calculations were compared with experimental results. Furthermore, a thermodynamic explanation is presented to understand and predict the observed coating failure mechanism, identified as blister formation.
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  • 20
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), 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 early stage of phase separation in aluminoborosilicate glass for liquid crystal display substrates was investigated using a scanning electron microscope (SEM) and small-angle X-ray scattering measurement device (SAXS). The phase-separated particles were detected with SAXS in samples in which no particle was observed with SEM. The particle diameter in an as-formed sample was 2 nm. The relationship between the diameter and heat-treatment time indicates that the phase separation proceeds by a diffusion-controlled process. Based on the results of Fourier-transform infrared spectroscopy, fast compositional change may occur in the early stage of phase separation.
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