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  • 2000-2004  (31)
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Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of Gallium Oxide Hydroxide Crystals in Aqueous Solutions with or without Urea and Their Calcination Behavior (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: Gallium oxide hydroxide (GaOOH·xH2O) single crystals were synthesized in aqueous solutions by using two different precipitation techniques: homogeneous decomposition of urea and forced hydrolysis in pure water. Precipitation of crystals started at exactly the same pH value (i.e., 2.05 at 85°C) in both cases. The morphology of crystals turned out to be quite different (zeppelin-like with urea, rodlike without urea) in each of the above methods. Calcination of these gallium oxide hydroxide crystals in air at temperatures ≥500°C transformed them into Ga2O3. Characterization of the samples was performed by X-ray diffractometry, scanning electron microscopy, thermogravimetry/differential thermal analysis, Fourier transform infrared spectroscopy, and ICP, carbon, and nitrogen analyses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00291.x
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  • 2
    Electronic Resource
    Electronic Resource
    Thermal Stability, Phase Evolution, and Crystallization in Si-B-C-N Ceramics Derived from a Polyborosilazane Precursor (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: Amorphous Si-B-C-N ceramic powder samples obtained by thermolysis of boron-modified polysilazane, {B[C2H4Si(H)NH]3}n, were isothermally annealed at different temperatures (1400–1800°C) and hold times (3, 10, 30, and 100 h). A qualitative and semiquantitative analysis of the crystallization behavior of the materials was performed using X-ray diffraction (XRD). The phase evolution was additionally followed by 11B and 29Si MAS NMR as well as by FT-IR spectroscopy in transmission and diffuse reflection (DRIFTS) modes. Bulk chemical analyses of selected samples were performed to determine changes in the chemistry/phase composition of the materials. It was observed that silicon carbide is the first phase to nucleate around 1400–1500°C, whereas silicon nitride nucleates at and above 1700°C. Crystallization accelerates with increasing annealing temperature and proceeds with increasing annealing time. Furthermore, the surface area of the powders strongly influences the thermal stability of silicon nitride and thus controls overall chemical and phase composition of the materials on thermal treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00357.x
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  • 3
    Electronic Resource
    Electronic Resource
    Crystallization of Polymer-Derived Silicon Carbonitride at 1873 K under Nitrogen Overpressure (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 chemical stability of an amorphous silicon carbonitride ceramic, having the composition 0.57SiC·0.43Si3N4·0.49C is studied as a function of nitrogen overpressure at 1873 K. The ceramic suffers a weight loss at pN2 〈 3.5 bar (1 bar = 100 kPa), does not show a weight change from 3.5 to 11 bar, and gains weight above 11 bar. The structure of the ceramic changes with pressure: it is crystalline from 1 to 6 bar, amorphous at ∼10 bar, and is crystalline above ∼10 bar. The weight-loss transition, at 3.5 bar, is in excellent agreement with the prediction from thermodynamic analysis when the activities of carbon, SiC, and Si3N4 are set equal to those of the crystalline forms; this implies that the material crystallizes before decomposition. The amorphous to crystalline transition that occurs at ∼10 bar, and which is accompanied by weight gain, is likely to have taken place by a different mechanism. A nucleation and growth reaction with the atmospheric nitrogen is proposed as the likely mechanism. The supersaturation required to nucleate α-Si3N4 crystals is calculated to be 30 kJ/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00503.x
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  • 4
    Electronic Resource
    Electronic Resource
    Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the Powder (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), 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 novel dispersant—O-(2-aminopropyl)-O′-(2-methoxyethyl)-polypropylene glycol (AMPG)—was developed to disperse submicrometer-sized Si3N4 powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of 〉0.50) and colloidally stable nonaqueous Si3N4 suspensions can be realized using AMPG.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01261.x
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  • 5
    Electronic Resource
    Electronic Resource
    Metastable Crystal Structure of Strontium- and Magnesium-Substituted LaGaO3 (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), 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 metastable crystal structure of strontium- and magnesium-substituted LaGaO3 (LSGM) was studied at room and intermediate temperatures using powder X-ray diffractometry and Rietveld refinement analysis. With increased strontium and magnesium content, phase transitions were found to occur from orthorhombic (space group Pbnm) to rhombohedral (space group R[Threemacr]c) at the composition La0.825Sr0.175Ga0.825Mg0.175O2.825 and, eventually, to cubic (space group Pm[Threemacr]m) at the composition La0.8Sr0.2Ga0.8Mg0.2O2.8. At 500°C in air and at constant strontium and magnesium content, a phase transformation from orthorhombic (space group Pbnm) to cubic (space group Pm[Threemacr]m) was observed. For the orthorhombic modification, thermal expansion coefficients were determined to be αa,ortho = 10.81 × 10−6 K−1, αb,ortho = 9.77 × 10−6 K−1, and αc,ortho = 9.83 × 10−6 K−1 (25°–400°C), and for the cubic modification to be αcubic= 13.67 × 10−6 K−1 (500°–1000°C).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00656.x
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  • 6
    Electronic Resource
    Electronic Resource
    La1+xSr1–xGa3O7–δ Melilite-Type Ceramics - Preparation, Composition, and Structure (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), 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: Ceramic samples of the melilite-type La1+xSr1–xGa3O7–δ (x=−0.15 to 0.60) compound were prepared by conventional ceramic processing. Sintering characteristics and microstructural evolution were studied. A phase diagram study was performed to establish the solid solubility limits as a function of the La:Sr ratio. Structural investigations of the Dalton composition as well as strontium- and lanthanum-rich samples entailed X-ray, neutron, and electron diffraction techniques at ambient and elevated temperatures. The homogeneity region was remarkably broad (x=−0.15 to 0.60) with no changes in space group observed. A small shrinkage of the unit cell was found with increased lanthanum content. Phase transitions at ambient and intermediate temperatures did not occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00662.x
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  • 7
    Electronic Resource
    Electronic Resource
    Thermodynamic Assessment of the Gallium-Oxygen System (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), 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 experimental information relevant to the Ga-O binary system has been critically assessed. A self-consistent set of Gibbs energy functions describing the phases in this system and a phase diagram are presented for the first time. The adjustable parameters of the models are obtained by a least-squares fit to the experimental data. The liquid phase is described by Hillert's partially ionic liquid model. The gallium oxides (α-, β-, γ-, and δ-Ga2O3) are modeled as stoichiometric phases. The gas phase is treated as an ideal solution of the species Ga, Ga2, Ga2O, GaO, O, O2, and O3. The calculated phase diagram and thermodynamic properties agree very well with most of the experimental measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00683.x
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of Precursor-Derived Silicon-Carbon-Nitrogen Ceramics after Creep Testing (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: Precursor-derived Si-C-N ceramics after creep testing in air were characterized using X-ray diffractometry (XRD) and transmission electron microscopy (TEM). XRD analysis showed that the crept Si-C-N ceramics were covered by an α-cristobalite layer. TEM observations revealed that the precipitated nanocrystallites in the crept Si-C-N ceramics were β-SiC. Between α-cristobalite and crept Si-C-N ceramic, there was an intermediate zone in which Si2N2O nanocrystallites were distributed homogeneously. Moreover, Si2N2O nanocrystallites were often found covering the surface of nanosized gas channels in the crept Si-C-N ceramics, where no α-cristobalite phase was detected. Based on these observations, a two-step oxidation mechanism of Si-C-N ceramics during creep testing in air was proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03521.x
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  • 9
    Electronic Resource
    Electronic Resource
    Electrical Conduction Behavior of La1+xSr1−xGa3O7–δ Melilite-Type Ceramics (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), 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: Ceramics of the melilite-type compound La1+xSr1−xGa3O7−δ were prepared by conventional ceramic processing. Samples prepared represented the entire homogeneity region of the phase (i.e., x=−0.15 to 0.60). Electrochemical characterization under variable temperature and atmospheric conditions in the vicinity of air entailed four-point direct-current conductivity measurements and electromotive force measurements. La1+xSr1−xGa3O7−δ samples exhibited a p-type behavior with generally increased conductivity with increased substitution of lanthanum for strontium, which reached a saturation value of ∼10−1 S·cm−1 at 950°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01795.x
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  • 10
    Electronic Resource
    Electronic Resource
    Microstructural Changes in Liquid-Phase-Sintered Silicon Carbide during Creep in an Oxidizing Environment (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: The knowledge of the microstructural evolution during exposure to high temperatures is important to understanding the mechanisms responsible for the creep resistance of silicon carbide (SiC) ceramics. This includes not only the phase transformation of the SiC grains, but also the phase transformations of the oxynitride grain-boundary phases. For this study, a series of SiC specimens were prepared with varying molar ratios of AlN-Y2O3 additives. Increased creep resistance was observed in specimens with an additive system containing a 2:3 molar ratio or 60 mol% Y2O3. A continuous oxide layer of Y2Si2O7 formed at the surface during elevated temperature testing in air. No blistering or cracking was observed in this oxide coating. Further increase of the creep resistance was achieved by a post-sintering nitrogen anneal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03328.x
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