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  • 11
    Electronic Resource
    Electronic Resource
    Hot-Pressed Silicon Nitride with Lu2O3 Additives: Oxidation and Its Effect on Strength (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 oxidation behavior and effect of oxidation on room-temperature flexural strength were investigated for hot-pressed Si3N4 ceramics, with 3.33 and 12.51 wt% Lu2O3 additives, exposed to air at 1400° and 1500°C for up to 200 h. Parabolic oxidation behavior was observed for both compositions. The oxidation products consisted of Lu2Si2O7 and SiO2. The Lu2Si2O7 grew out of the surface silicate in preferred orientations. The morphology of oxidized surfaces was dependent on the amount of additive; Lu2Si2O7 grains in the 3.33 wt% composition appeared partially in a needlelike type, compared with a more equiaxed type exhibited in the 12.51 wt% case. The high resistance to oxidation shown for both compositions was attributed to the extensive amounts of crystalline, refractory secondary phases formed during the sintering process. Moreover, after 200 h of oxidation at 1400° and 1500°C, the strength retention displayed by the two compositions was 93%–95% and 85%–87%, respectively. The strength decrease was associated with the formation of new defects at the interface between the oxide layer and the Si3N4 bulk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03579.x
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  • 12
    Electronic Resource
    Electronic Resource
    High-Temperature Strength of Liquid-Phase-Sintered SiC with AlN and Re2O3 (RE = Y, Yb) (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: Using AlN and RE2O3 (RE = Y, Yb) as sintering additives, two different SiC ceramics with high strength at 1500°C were fabricated by hot-pressing and subsequent annealing under pressure. The ceramics had a self-reinforced microstructure consisting of elongated α-SiC grains and a grain-boundary glassy phase. High-temperature strength up to 1600°C was measured and compared with that of the SiC ceramics fabricated with AlN and Er2O3. SiC ceramics with AlN and Y2O3 showed the best strength (∼630 MPa) at 1500°C, while SiC ceramics with AlN and Er2O3 the best strength (∼550 MPa) at 1600°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00211.x
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  • 13
    Electronic Resource
    Electronic Resource
    Heat-Resistant Silicon Carbide with Aluminum Nitride and Erbium Oxide (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: Fully dense SiC ceramics with high strength at high temperature were obtained by hot-pressing and subsequent annealing under pressure, with AlN and Er2O3 as sintering additives. The ceramics had a self-reinforced microstructure consisting of elongated SiC grains and a grain-boundary glassy phase. The strength of these ceramics was ∼550 MPa at 1600°C, and the fracture toughness was ∼6 MPa·m1/2 at room temperature. The beneficial effect of the new additive composition on high-temperature strength might be attributable to the introduction of aluminum from the liquid composition into the SiC lattice, resulting in a refractive grain-boundary glassy phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00958.x
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  • 14
    Electronic Resource
    Electronic Resource
    Synthesis and Sintering of Cerium(II) Monosulfide (2004)
    Oxford, UK : Blackwell Publishing Ltd
    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: Cerium monosulfide (CeS) powder was synthesized by the reduction of Ce2S3 powder with metallic Ce, which was obtained from ceria (CeO2) powder using carbon disulfide (CS2) gas. To obtain the maximum amount of CeS from a mixture of Ce2S3 and Ce, an excess amount of metallic Ce, a stoichiometric composition, was necessary in the synthesis at 1273 K for 10.8 ks. The preliminary sintering experiments also were performed using a synthetic CeS powder containing a small amount of Ce, Ce2O2S, and β-Ce2S3 as impurities. It was found that the oxygen content in the sintered compact decreases gradually as the sintering temperature increases, because of the removal of the impurities due to the evaporation of the volatile CeO. Single-phase CeS was formed by sintering at 2173 K. To evaluate the activation energy for densification of single-phase CeS, a CeS powder was prepared by milling an initial sintered compact and was used as an ingredient for hot-press experiments. Densification data during hot-press sintering were analyzed using a kinetic equation, showing that boundary diffusion is a rate-limiting process. The results suggest that this boundary diffusion model can explain well the densification data, with an apparent activation energy of 479 kJ·mol-1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb19939.x
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  • 15
    Electronic Resource
    Electronic Resource
    Nonequiaxial Grain Growth and Polytype Transformation of Sintered α-Silicon Carbide and β-Silicon Carbide (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: α(6H)- and β(3C)-SiC powders were sintered with the addition of AlB2 and carbon. α-SiC powder could be densified to ∼98% of the theoretical density over a wide range of temperatures from 1900° to 2150°C and with the additives of 0.67–2.7 mass% of AlB2 and 2.0 mass% of carbon. Sintering of the β-SiC powder required a temperature of 〉2000°C for densification with these additives. Grains in the α-SiC specimens grew gradually from spherical-shaped to plate-shaped grains at 2000°C; the 6H polytype transformed mainly to 4H. On the other hand, grains in the β-SiC largely grew at 〉2000°C; the 3C polytype transformed to 4H, 6H, and 15R. The stacking faults introduced in grains were denser in β-SiC than in α-SiC. The rapid grain growth in the β-SiC specimen was attributed to polytype transformation from the unstable 3C polytype at the sintering temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03638.x
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  • 16
    Electronic Resource
    Electronic Resource
    Phase Relationships in the Si3N4–SiO2–Lu2O3 System (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: Phase relationships in the Si3N4–SiO2–Lu2O3 system were investigated at 1850°C in 1 MPa N2. Only J-phase, Lu4Si2O7N2 (monoclinic, space group P21/c, a= 0.74235(8) nm, b= 1.02649(10) nm, c= 1.06595(12) nm, and β= 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si3N4–SiO2–Lu2O3 system. The Si3N4/Lu2O3 ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu–J-phase, β-Si3N4, and a new phase of Lu3Si5ON9, having orthorhombic symmetry, space group Pbcm (No. 57), with a= 0.49361(5) nm, b= 1.60622(16) nm, and c= 1.05143(11) nm. The new phase is best represented in the new Si3N4–LuN–Lu2O3 system. The phase diagram suggests that Lu4Si2O7N2 is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00545.x
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  • 17
    Electronic Resource
    Electronic Resource
    Synthesis and Sintering of Cerium(III) Sulfide Powders (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), 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: Cerium(III) sulfide (Ce2S3) powder was synthesized via the sulfurization of ceria (CeO2) powder using carbon disulfide gas. Single-phase α-Ce2S3 could be formed via sulfurization at 973 K for 28.8 ks. The preparation of α-Ce2S3 became feasible at low temperature, in comparison to sulfurization using hydrogen sulfide gas. According to the fact that the formation of α-Ce2S3 was accelerated by the addition of carbon black to the CeO2 powder, carbothermic reduction was considered to become a dominant reaction, as the temperature increased. To obtain the activation energy for the densification of β-Ce2S3 powder, which was prepared by vacuum heating α-Ce2S3, the data of densification by hot pressing was analyzed by a kinetic equation that was proposed by other researchers. As a result, the sintering behavior could be best explained by a grain-boundary-diffusion mechanism that had an apparent activation energy of 382 kJ/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02306.x
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  • 18
    Electronic Resource
    Electronic Resource
    Grain Boundary Film Thicknesses in Superplastically Deformed Silicon Nitride (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), 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 thickness of intergranular films in polycrystalline β-Si3N4 ceramics, both before and after superplastic deformation, has been systematically investigated using high-resolution transmission electron microscopy. In characterizing the film thickness, care was taken to correlate the grain boundary orientation with the direction of the compressive stress applied during the hot-pressing and the superplastic deformation. The film thickness shows a dependence on the intersection angle between the grain boundary and the applied force direction, typically ranging from around a characteristic value for most of the boundaries to zero for a boundary which has an overall short length and is perpendicular to the applied force direction. The film thicknesses in the deformed material, as compared with those before deformation, are marked by a wider distribution and an increased fraction of boundaries free of films, unequivocally demonstrating that during the superplastic deformation the liquid phase is redistributed within short ranges, a process governed by the local stress level as well as kinetic factors. Possible consequences of the liquid-phase redistribution on the deformation behavior are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02967.x
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  • 19
    Electronic Resource
    Electronic Resource
    Superplastic Behavior of Fine-Grained β-Silicon Nitride Material under Compression (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: The deformation behavior of a hot-pressed, fine-grained β-Si3N4 ceramic was investigated in the temperature range 1450°—1650°C, under compression, and the results for strain rate and temperature dependence of the flow stress are presented here. The present results show that the material is capable of high rates of deformation (∼10−4—10−3 s−1) within a wide range of deformation temperatures and under a pressure of 5—100 MPa; no strain hardening occurs in the material, even at slow deformation rates, because of its stable microstructure; Newtonian flow occurs, with a stress exponent of approximately unity; and the material has activation energy values for flow in the range 344—410 kJ·mol−1. Grain-boundary sliding and grain rotation, accommodated by viscous flow, might be the mechanisms of superplasticity for the present material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01283.x
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  • 20
    Electronic Resource
    Electronic Resource
    Synthesis and Characterization of Nano-Hetero-Structured Dy Doped CeO2 Solid Electrolytes Using a Combination of Spark Plasma Sintering and Conventional Sintering (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: Doped ceria (CeO2) compounds are fluorite-type oxides that show oxide ionic conductivity higher than yttria-stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for “low” (500°–650°C) temperature operation of solid oxide fuel cells (SOFCs). To improve the conductivity in dysprosium (Dy) doped CeO2, nano-size round shape particles were prepared using a coprecipitation method. The dense sintered bodies with small grain sizes (〈300 nm) were fabricated using a combined process of spark plasma sintering (SPS) and conventional sintering (CS). Dy-doped CeO2 sintered body with large grains (1.1 μm) had large micro-domains. The conductivity in the sintered body was low (−3.2 S/cm at 500°C). On the other hand, the conductivity in the specimens obtained by the combined process was considerably improved. The micro-domain size in the grain was minimized using the present process. It is concluded that the enhancement of conductivity in dense specimens produced by the combined process (SPS+CS) is attributable to the microstructural changes within the grains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00260.x
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