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21.
介绍了硬质陶器低温烧成的研究及其结果。研究表明,用优质高岭土与一定粒度的石灰石和硅石按适量配比配料,有助于低温烧制抗弯强度超过60MPa的高强硬质陶器。 相似文献
22.
Microstructural Evolution in Liquid-Phase-Sintered SiC: Part III, Effect of Nitrogen-Gas Sintering Atmosphere 总被引:1,自引:0,他引:1
Angel L. Ortiz Tania Bhatia Nitin P. Padture Giuseppe Pezzotti 《Journal of the American Ceramic Society》2002,85(7):1835-1840
Effects of N2 sintering atmosphere and the starting SiC powder on the microstructural evolution of liquid-phase-sintered (LPS) SiC were studied. It was found that, for the β-SiC starting powder case, there was complete suppression of the β→α phase transformation, which otherwise goes to completion in Ar atmosphere. It was also found that the microstructures were equiaxed and that the coarsening was severely retarded, which was in contrast with the Ar-atmosphere case. Chemical analyses of the specimens sintered in N2 atmosphere revealed the presence of significant amounts of nitrogen, which was believed to reside mostly in the intergranular phase. It was argued that the presence of nitrogen in the LPS SiC helped stabilize the β-SiC phase, thereby preventing the β→α phase transformation and the attendant formation of elongated grains. To investigate the coarsening retardation, internal friction measurements were performed on LPS SiC specimens sintered in either Ar or N2 atmosphere. For specimens sintered in N2 atmosphere, a remarkable shift of the grain-boundary sliding relaxation peak toward higher temperatures and very high activation energy values were observed, possibly due to the incorporation of nitrogen into the structure of the intergranular liquid phase. The highly refractory and viscous nature of the intergranular phase was deemed responsible for retarding the solution–reprecipitation coarsening in these materials. Parallel experiments with specimens sintered using α-SiC starting powders further reinforce these arguments. Thus, processing of LPS SiC in N2 atmosphere open the possibility of tailoring their microstructures for room-temperature mechanical properties and for making high-temperature materials that are highly resistant to coarsening and creep. 相似文献
23.
Zinc vaporization of Mn-Zn ferrites was quantitatively characterized in terms of oxygen partial pressure P O2 , temperature, grain size and sample geometry. The amount of zinc loss was measured as a function of time at various temperatures by a thermogravimetric method. The weight loss due to irreversible zinc vaporization showed a linear behavior with time and increased exponentially with temperature. The observed weight loss due to zinc evaporation at 1100°C was small, whereas a significant weight change was detected at 1200°C. The weight loss was even greater in a reducing atmosphere ( P O2 = 5 × 10−5 ). Below 1300°C, the diffusion of elemental zinc was sufficiently fast to compensate the zinc loss at the interface region, resulting in a linear dependence on time. At temperatures ≥1400°C, the weight change no longer followed the linear dependence and showed a rather parabolic behavior with a concave upward slope. The core shape and the gas flow around ferrite cores were important factors that affected the rate of zinc vaporization, but not the grain size. 相似文献
24.
Ji Yeon Ko Sin-Young Park Duk Yong Yoon Suk-Joong L. Kang 《Journal of the American Ceramic Society》2004,87(12):2262-2267
When TiC–20 wt% Ni powder mixtures are sintered at 1400°C, relatively large TiC grains possibly containing some Ni form with near-equilibrium shapes. When these specimens are heat-treated again at 1400°C in contact with sintered WC–20 wt% Ni pieces, the liquid films between the TiC grains in the contact region migrate against their increasing curvatures, forming (Ti,W)C solid solution behind them. These migrating liquid films reverse their directions on further heat-treatment. As in other alloys, this liquid film migration must be driven by the coherency strain energy produced by W diffusion at the surface of the dissolving TiC grains. Shells of (Ti,W)C solid solution also form around the cores of TiC grains near the contact region, and this process is probably driven by both coherency strain energy and free energy of mixing. At some contact regions, (Ti,W)C precipitates nucleate and grow, probably driven mainly by the free energy of mixing. In powder mixtures, the formation of core-shell grains is expected to be driven by the coherency strain energy, the free energy of mixing, and the capillary effect. 相似文献
25.
Viscosity of porous glasses has been derived from the elastic stress analysis, using the viscous analogy. Viscosity as a function of porosity has been estimated for spherical as well as for arbitrary pore geometry. Since the pore geometry changes during sintering, a shape factor that varies with pore geometry has been considered to predict the viscosity–porosity relationship. Viscosity as a function of porosity was measured on cordierite-type glass by isothermal sinter-forging experiments and data showed good agreement with the analysis. Experimental data from literature on viscosity as a function of porosity on two other glasses also show good agreement with the analysis. 相似文献
26.
Nanoindentation Characterization of Submicro- and Nano-Sized Liquid-Phase-Sintered SiC Ceramics 总被引:1,自引:0,他引:1
Stefano Guicciardi Diletta Sciti Cesare Melandri Alida Bellosi 《Journal of the American Ceramic Society》2004,87(11):2101-2107
Submicro- and nano-sized liquid-phase-sintered SiC ceramics were mechanically tested by nanoindentation in the peak load range 5–400 mN. The submicro-sized sample showed a marked indentation size effect which the nano-sized samples did not exhibit. The relevance of indentation depth with respect to the microstructural scale has been outlined. In the investigated grain-size range, the hardness dependence on the grain size could be described by a load-dependent inverse Hall–Petch relation. Young's modulus was less microstructure- and load-dependent. Because of the very fine microstructure, the nano-sized SiC materials gave lower elastic values than the submicro-sized SiC ceramic. 相似文献
27.
介绍了聚四氟乙烯悬浮树脂成型加工有关的物理性能,树脂的成型加工及选用方法.分别叙述了模压成型、自动模压成型和液压成型的原理、过程及设备. 相似文献
28.
Tateoki Iizuka Hideki Kita Hideki Hyuga Takene Hirai Kazuo Osumi 《Journal of the American Ceramic Society》2004,87(3):337-341
A W2 C-nanoparticle-reinforced Si3 N4 -matrix composite was fabricated by sintering porous Si3 N4 that had been infiltrated with a tungsten solution. During the sintering procedure, nanometer-sized W2 C particles grew in situ from the reaction between the tungsten and carbon sources considered to originate mainly from residual binder. The W2 C particles resided in the grain-boundary junctions of the Si3 N4 , had an average diameter of ∼60 nm, and were polyhedral in shape. Because the residual carbon, which normally would obstruct sintering, reacted with the tungsten to form W2 C particles in the composite, the sinterability of the Si3 N4 was improved, and a W2 C–Si3 N4 composite with almost full density was obtained. The flexural strength of the W2 C–Si3 N4 composite was 1212 MPa, ∼34% higher than that of standard sintered Si3 N4 . 相似文献
29.
30.
Zhe-Feng Zhang Zheng Ming Sun Hitoshi Hashimoto Toshihiko Abe 《Journal of the American Ceramic Society》2003,86(3):431-436
Ti/Si/2TiC powders were prepared using a mixture method (M) and a mechanical alloying (MA) method to fabricate Ti3 SiC2 at 1200°–1400°C using a pulse discharge sintering (PDS) technique. The results showed that the Ti3 SiC2 samples with <5 wt% TiC could be rapidly synthesized from the M powders; however, the TiC content was always >18 wt% in the MA samples. Further sintering of the M powder showed that the purity of Ti3 SiC2 could be improved to >97 wt% at 1250°–1300°C, which is ∼200°–300°C lower than that of sintered Ti/Si/C and Ti/SiC/C powders using the hot isostatic pressing (HIPing) technique. The microstructure of Ti3 SiC2 also could be controlled using three types of powders, i.e., fine, coarse, or duplex-grained, within the sintering temperature range. In comparison with Ti/Si/C and Ti/SiC/C mixture powders, it has been suggested that high-purity Ti3 SiC2 could be rapidly synthesized by sintering the Ti/Si/TiC powder mixture at relatively lower temperature using the PDS technique. 相似文献