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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Sintering Additive Composition on the Processing and Thermal Conductivity of Sintered Reaction-Bonded Si3N4 (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: Two compositions of the Y2O3–MgO (YM) and Yb2O3–MgO (YbM) systems were chosen to study the effect of the sintering additive composition on the processing and thermal conductivity of sintered reaction-bonded silicon nitride (SRBSN). The nitridation, postdensification, microstructural evolution, and thermal conductivity of SRBSN were found to depend strongly on the sintering additive composition. The RBSN materials with YbM exhibited a poor sinterability, whereas those with YM exhibited an excellent sinterability. However, the SRBSN materials with YbM showed a higher thermal conductivity than those with YM. This was associated primarily with the isolated distribution and lower amount of secondary phase and the higher percentage of large grains in the former materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07747.x
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  • 2
    Electronic Resource
    Electronic Resource
    Tribological Properties of Silicon Carbide and Silicon Carbide–Graphite Composite Ceramics in Sliding Contact (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 monolithic SiC ceramic and two SiC–C composite ceramics containing 10 and 20 vol% graphite were fully densified with Al4C3 and B4C as additives. The tribological properties of these materials were evaluated by sliding against sintered silicon carbide under dry conditions using two tribometers, block-on-ring and pin-on-disk, where wear occurred under low and high contact stresses, respectively. For all three materials, under low stress, worn surfaces were smooth and wear processes were dominated by tribochemical reaction; under high stress, worn surfaces were rough and wear processes were dominated by fracture and three-body abrasion. A lubricating effect of the graphite particles in the SiC–C composites was observed in all sliding tests. However, while the addition of graphite could concurrently result in a reduction in friction and an increase in wear resistance in the block-on-ring tests, the addition of graphite led to sharply enhanced wear rates despite the lowered coefficients of friction in the pin-on-disk tests. The cause for that difference was attributed to the effect of both the hardness of the materials and the contact stresses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03407.x
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  • 3
    Electronic Resource
    Electronic Resource
    Reaction-Formed Porous Yb4Si2N2O7 Materials with Uniform Open-Cell Network Structure (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: A novel porous Yb4Si2O7N2 material with uniform open-cell network structure was fabricated from the reaction between Si3N4, Yb2O3, and SiO2. The formation of Yb4Si2O7N2 during heating was studied using X-ray diffractometry. The porous structure was characterized using scanning electron microscopy and mercury porosimeter. It is shown that the formation of Yb4Si2O7N2 phase starts at ∼1150°C and completes at 1350°C for 4 h, accompanied by the development of open-cell network structure. The necks between Yb4Si2O7N2 particles become much thicker with increasing temperature because of the coarsening of Yb4Si2O7N2 particles, thus leading to a uniform three-dimensional network structure. Furthermore, the pore size can be well controlled by adjusting reacting temperature and altering atmosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00310.x
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  • 4
    Electronic Resource
    Electronic Resource
    Fracture-Mode Change in Alumina-Silicon Carbide Composites Doped with Rare-Earth Impurities (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: Al2O3-5 vol% SiC particle composites doped with 800 ppm rare-earth impurities (Y3+, Nd3+, and La3+) were fabricated by hot-pressing at a temperature of 1550°C. Doping of rare-earth impurities in Al2O3-SiC composites led to a fracture- mode change from transgranular in dopant-free composites to intergranular in rare-earth-doped composites. The fracture mode change obviously increased the crack deflection so that the fracture toughness of rare-earth-doped composites was higher than that of the composites without dopants, especially for the Nd3+- and La3+-doped composites. It was found that the fracture-mode change originated from a weak grain-boundary bonding caused by co-segregation of the rare-earth dopants and Si4+ ions dissolved from the SiC particle surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03556.x
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  • 5
    Electronic Resource
    Electronic Resource
    Very Rapid Densification of Nanometer Silicon Carbide Powder by Pulse Electric Current Sintering (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: Rapid densification of a nanometer SiC powder doped with 2.04 wt% Al4C3 and 0.4 wt% B4C was conducted by using a nonconventional sintering technique called pulse electric current sintering (PECS). In all experiments, the sintering temperature and applied pressure were kept to be 1600oC and 47 MPa, respectively, while heating rates varied between 100oC/min and 400oC/min and the holding time was either 2 or 5 min. All of the specimens which were PECS-sintered under various conditions reached near-theoretical density. The microstructures of the rapidly densified SiC ceramics consisted of large elongated grains, and the grain size increased with the increase of heating rate. Polytype transformation of SiC occurred during the PECS process, where faster heating favored the formation of 6H polytype while slower heating favored 4H polytype.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01249.x
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  • 6
    Electronic Resource
    Electronic Resource
    Low-Temperature Pressureless Sintering of alpha-SiC with Al4C3-B4C-C Additions (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: Various combinations of Al4C3, B4C, and carbon were used as sintering aids for pressureless sintering of alpha-SiC (94% 6H+ 6% 15R) powders. Densification behavior, polytypic transformation, microstructural development, and mechanical properties were studied. Appropriate amounts of Al4C3-B4C-C additions could facilitate alpha-SiC powders being pressureless sintered to high densities (〉95% TD) at temperatures greaterthan equal to1850°C. Even using an alpha-SiC as a starting powder, many elongated grains developed in the microstructures during sintering at low temperature that might contribute to toughening. Anisotropic grain growth was found to be associated with the faulted structures and the 6H→ 4H phase transformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02026.x
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of Intergranular Phase Chemistry on the Microstructure and Mechanical Properties of Silicon Carbide Ceramics Densified with Rare-Earth Oxide and Alumina 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: Based on the processing strategy of improving the mechanical properties of liquid-phase-sintered materials by modifying the secondary phase chemistry, four rare-earth oxides (RE2O3, RE = La, Nd, Y, and Yb), in combination with alumina, were used as sintering aids for a submicrometer-size β-SiC powder. Doped with 5 vol% RE2O3+ Al2O3 additives, all specimens were hot-pressed to near full-densities at 1800°C, and they exhibited similar microstructures and grain size distributions. The SiC grains in all specimens revealed a core-rim structure after being plasma-etched, indicating that they were densified via the same solution-reprecipitation mechanism. It was found that a decrease in the cationic radius of the rare-earth oxides was accompanied by an increase in Young’s modulus, hardness, and flexural strength of the SiC ceramics, whereas the fracture toughness was improved by incorporating rare-earth oxides of larger cationic radius. The changes in the mechanical properties were attributed to the difference in the chemistry of the intergranular phases in the four ceramics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00891.x
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of Silica and Aluminum Contents on Sintering of and Grain Growth in 6H-SiC Powders (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: To clarify the influence of impurities on the sintering of SiC powder, three 6H-SiC powder samples—with different levels of SiO2 and aluminum impurities—were sintered with additions of boron and carbon. The densification, grain growth, and transformation of 6H-SiC during sintering were studied qualitatively. The powder that contained the most SiO2 required the greatest amount of boron additive for complete densification. SiO2 apparently reacted with the boron additive and was consumed during sintering. The powder with the greater aluminum impurity level exhibited partial transformation of 6H-SiC to 4H-SiC, and the sintered SiC from this powder had elongated grains. The partial transformation in the SiC crystal accelerated non-equiaxial grain growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01177.x
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  • 9
    Electronic Resource
    Electronic Resource
    Altered gene expression in plants with constitutive expression of a mitochondrial small heat shock protein suggests the involvement of retrograde regulation in the heat stress response (2005)
    Oxford, UK; Malden, USA : Munksgaard International Publishers
    Physiologia plantarum 123 (2005), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Heat stress can negatively affect crop productivity. One way in which plants attempt to alleviate the effects of heat stress is to induce the expression of genes encoding heat shock proteins (HSPs), including small HSPs (sHSPs). We produced transgenic lines of Arabidopsis thaliana expressing a transgene encoding a maize mitochondrial sHSP, ZmHSP22. The transgene, under the control of the cauliflower mosaic virus 35S promoter, is constitutively highly expressed in these lines. As demonstrated by confocal immunofluorescence microscopy and analyses of isolated mitochondria, ZmHSP22 is directed to the mitochondria of Arabidopsis and is processed into the mature form. These transgenic lines demonstrated altered expression of nuclear genes encoding the endogenous mitochondrial sHSP, AtHSP23.6, chloroplast localized AtHSP25.3, class I cytosolic AtHSP17.4, cytosolic AtHSP70-1 and chloroplast localized AtHSP70-6, but not cytosolic AtHSP70-15, following exposure to heat stress. This suggests that the expression of HSPs can be affected by heat-induced mitochondrial retrograde regulation. Three-week-old plants from the transgenic Arabidopsis lines expressing ZmHSP22 have increased thermotolerance, as measured by the maintenance of higher leaf mass following successive days with short periods of heat stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.2005.00473.x
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  • 10
    Electronic Resource
    Electronic Resource
    The spatial correlation function of cD Abell clusters
    Amsterdam : Elsevier
    Chinese Astronomy and Astrophysics 12 (1988), S. 279-282 
    Details
    ISSN: 0275-1062
    Keywords: Cosmology ; clustering ; galaxies ; galaxy clusters
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0275-1062(88)90031-8
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