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  • 1
    Electronic Resource
    Electronic Resource
    Solubility of Si3N4 in Liquid SiO2 (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    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 nitrogen solubility in the SiO2-rich liquid in the metastable binary SiO2-Si3N4 system has been determined by analytical TEM to be 1%–4% of N/(O + N) at 1973–2223 K. Analysis of the near edge structure of the electron energy loss peak indicates that nitrogen is incorporated into the silicate network rather than being present as molecular N2. A regular solution model with a positive enthalpy of mixing for the liquid was used to match the data for the metastable solubility of N in the presence of crystalline Si3N4 and to adjust the computed phase diagram. The solubility of Si3N4 in fused SiO2 is far less than reported in liquid silicates also containing Al, Mg, and/or Y. Apparently, these cations act as modifiers that break anion bridges in the silicate network and, thereby, allow further incorporation of Si3N4 without prohibitive amounts of network cross-linking. Finally, indications emerged regarding the diffuse nature of the Si3N4-SiO2 interface that leads to amorphous regions of higher N content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00033.x
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  • 2
    Electronic Resource
    Electronic Resource
    Variation of Width and Composition of Grain-Boundary Film in a High-Purity Silicon Nitride with Minimal Silica (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    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: Contrary to the widely accepted observation that grain-boundary amorphous films for a given Si3N4 composition have common (equilibrium) widths and compositions, a significant variation for both parameters from film to film was observed in an undoped high-purity Si3N4 prepared using a hot isostatic pressing method. This material previously has been reported to have an equilibrium film width of 0.6 nm, as measured using a high-resolution electron microscopy (HREM) method; this value is significantly different from that which is typical for other high-purity Si3N4 ceramics (1.0 nm). A total of four boundaries were analyzed, using spatially resolved electron energy-loss spectroscopy methods, which can give the chemical width and composition for the film. Widths of these grain-boundary films were substantially different from each other; only the thinnest matches the previous HREM observations. The nitrogen content in the film decreased concurrently as the film thickened. This material had many cavities and complicated configurations at triple pockets, because of the very low total-SiO2 content (0.55 vol%). They created locally different equilibrium conditions for grain-boundary films, in comparison with other fully densified Si3N4, causing such strong variation in both film structure and chemistry. This observation reveals the importance of triple pockets in equilibrium film structures, providing new insight in evaluating the absorption and wetting models. The thinnest film may correspond to the amorphous structure that is required to bind two randomly oriented Si3N4 grains under greater local stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00034.x
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of Dynamic Microstructural Change on Deformation Behavior in Liquid-Phase-Sintered Silicon Carbide with Al2O3–Y2O3–CaO Additions (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    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: Nanocrystalline β-SiC with additions of 7 wt% Al2O3, 2 wt% Y2O3, and 1 wt% CaO was subjected to tensile deformation to study its microstructural behavior under the dynamic process. The liquid-phase-sintered body had a relative density of 〉97% and an average grain size of 170 nm. Tension tests were conducted at initial strain rates ranging from 2 × 10−5 to 5 × 10−4 s−1, in the temperature range 1973–2023 K, in both argon and N2 atmospheres. Although grain-boundary liquids formed by the additions vaporized concurrently with the decomposition of SiC and extensive grain growth, the maximum tensile elongation of 48% was achieved in argon. Annealing experiments under the same conditions revealed that vaporization and grain growth were both dependent on experimental time. Therefore, high strain rates suffered less from the hardening effect when cavitation damage was more severe. Testing in an N2 atmosphere brought about crystallization of the grain-boundary phase and prevented severe vaporization; however, fracture occurred at only 8% elongation. Grain-boundary sliding was still the dominant mechanism for deformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00956.x
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  • 4
    Electronic Resource
    Electronic Resource
    Superplasticity of Silicon Carbide (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    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: Nanocrystalline silicon carbide that was doped with boron and carbon (B,C-SiC) and contained 1 wt% boron additive and 3.5 wt% free carbon was fabricated using hot isostatic pressing under an ultrahigh pressure of 980 MPa and a temperature of 1600°C. The average grain size of the material was 200 nm. The tensile deformation behavior of this material at elevated temperature was investigated. The nanocrystalline B,C-SiC exhibited superplastic elongation of 〉140% at a temperature of 1800°C. High-resolution transmission electron microscopy observation and electron energy-loss spectroscopy analysis revealed that this nanocrystalline SiC did not have a secondary glassy phase at the grain boundary and the grain boundary had a strong covalent nature, which means that an intergranular glassy phase was not necessary to obtain superplasticity of covalent materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02178.x
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of Powder Coating on Stabilizer Distribution in CeO2-Stabilized ZrO2 Ceramics (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    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 phase and microstructure relationship of 12 mol% CeO2-stabilized ZrO2 ceramics prepared from coated powder was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersed X-ray spectroscopy (EDS). As compared with the sample prepared with co-precipitated method, which exhibited a similar grain size distribution, the EDS analysis revealed that the powder coating induced a wide distribution of CeO2 solubility, which decreases monotonically with the increase of grain size. This variation of stabilizer content from grain to grain rendered many large grains in the monoclinic phase. Stronger cerium segregation to grain boundaries was observed between large grains, which often form thin amorphous films there. The inhomogeneous CeO2 distribution keeps more tetragonal ZrO2 grains close to the phase boundary to facilitate the transforming toughness. Addition of an Al2O3 precursor in coated powders effectively raises the overall CeO2 stabilizer content in the grains and preserves more transformable tetragonal phase in the microstructure, which further enhanced the fracture toughness. The dependence of CeO2 solubility on grain size may be explained in a simple coating-controlled diffusion and growth process that deserves further investigation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00342.x
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  • 6
    Electronic Resource
    Electronic Resource
    Evidence of Bilevel Solubility in the Bimodal Microstructure of TiO2-Doped Alumina (2003)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    Details
    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 phenomenon of bilevel solubility was observed in a TiO2-doped (2.0 wt%) alumina with bimodal microstructure sintered in N2. Surface contributions to dopant signals in individual grains were identified and removed, using a spatially resolved energy dispersive spectroscopy analysis. Two levels of solubility, 1.005 ± 0.166 and 0.504 ± 0.082 mol% of TiO2 in Al2O3, were obtained for anisotropic and equiaxed grains, respectively. No grain size dependence of solubility was found, but segregation of SiO2 to boundaries with the anisotropic grains was observed. This phenomenon was explained by the incorporation of Ti3+ into the Al2O3 lattice during the abnormal grain growth caused by SiO2 liquid under a reducing atmosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03587.x
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamic Evolution of Grain-Boundary Films in Liquid-Phase-Sintered Ultrafine Silicon Carbide Material (2003)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    Details
    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: Spatially resolved electron energy-loss spectroscopy (EELS) analysis revealed a dynamic evolution of grain-boundary (GB) films in a liquid phase (Al2O3–Y2O3–CaO) sintered β-SiC, which had been deformed both in tension and in compression. An effective chemical width was measured from the oxygen segregation to GBs. Significant increase of Al content in GB films was correlated to devitrification of amorphous pockets to form YAG during both deformations. This brought Y into and expelled Al from the pockets. The extra Al was pushed into GBs to form alumina-based films. Al-Y interdiffusion between GB films and pockets is related to deformation time, indicating a constant and limited interdiffusion rate. This evolution of GB films demonstrated that the dynamic process equilibrated these intergranular regions and phases. GB sliding and interdiffusion among intergranular regions were common mechanisms for both deformation modes. Fracture was mainly caused by YAG formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03550.x
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  • 8
    Electronic Resource
    Electronic Resource
    Densification of Precursor-Derived Si-C-N Ceramics by High-Pressure Hot Isostatic Pressing (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    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: Densification behavior of precursor-derived Si-C-N ceramics by hot isostatic pressing (HIP) has been investigated to obtain dense ceramics derived from polymer precursor. An as-pyrolyzed ceramic monolith, which had a porosity of about 17%, could be deformed up to a strain of 8% in preliminary uniaxial compression tests. The flow stress of the material was much higher than 200 MPa at 1600°C; thus high stress was necessary for densification by HIP. The density of the monolith increased from 1.9 to 2.4 g/cm3 by HIP at 1600°C and 980 MPa. Although the number of pores decreased, large pores were formed in the hot isostatically pressed monolith. On the other hand, denser ceramics, in which pores were not observed by optical microscopy, were obtained by hot isostatically pressing the pyrolyzed powder compact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00339.x
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  • 9
    Electronic Resource
    Electronic Resource
    Detection of Boron Segregation to Grain Boundaries in Silicon Carbide by Spatially Resolved Electron Energy-Loss Spectroscopy (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    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: Boron segregation to grain boundaries in SiC was directly observed for the first time by using spatially resolved electron energy-loss spectroscopy methods. The hot-pressed, fully dense material was doped with 0.3 wt% of boron and was free of other additives, except for 2 wt% of free carbon. The detection of boron was achieved in the difference spectra at all the grain boundaries that were examined. Its interfacial excess was in the range of 15–29 atoms/nm2, or approximately one monolayer. Concurrently, silicon depletion occurred at these boundaries, although to a lesser extent (−13.5 atoms/nm2 on average), which indicated that boron mainly replaces silicon and bonds with carbon at the grain boundary. These findings validate the dual role of boron at the grain boundary for promoting densification via improved grain-boundary diffusivity while maintaining a covalent grain boundary without an oxide phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.1999.tb20089.x
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  • 10
    Electronic Resource
    Electronic Resource
    Molten Salt Synthesis of Acicular Ba2NaNb5O15 Seed Crystals (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    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: Well-developed acicular Ba2NaNb5O15 (BNN) seed crystals have been successfully prepared by the reaction between BaCO3, Nb2O5 and molten NaCl salt. The effects of the calcination temperature, time, and weight ratio of the oxide mixture to salt on the morphology of BNN particles were investigated. Uniform acicular seeds with high aspect ratio could be achieved at 1200°C for 4 h with the salt-to-oxide mixture of 2:1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00058.x
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