共查询到20条相似文献,搜索用时 10 毫秒
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Philippe Boch Thierry Chartier Muriel Huttepain 《Journal of the American Ceramic Society》1986,69(8):191-C
Fracture toughness of ZrO2 -toughened alumina could he increased by macroscopic interfaces, such as those existing in laminated composites. In this work, tape casting was used to produce A/A or A/B laminates, where A and B can be Al2 O3 , Al2 O3 /5 vol% ZrO2 , and Al2 O3 /l0 vol% ZrO2 . An increase of toughness is observed, even in the Al2 O3 /Al2 O3 laminates. 相似文献
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Janet Rankin 《Journal of the American Ceramic Society》1999,82(6):1560-1564
In situ TEM heating experiments at temperatures between 820° and 860°C provide significant insights into the atomistics of neck formation during the sintering of nanoscale faceted, single-crystal particles of ZrO2 . High-resolution TEM was used to observe the crystallography and the relative orientation in a variety of original particle-pairs and the relative orientation of their evolving necks. Previous studies have determined that unconstrained particles can rotate during neck growth. When there is a significant amount of misalignment, the particles are not able to align completely. In these instances, the neck that forms is epitaxial with one of the particles. Additionally, in particle-pairs with significant misalignment, the neck stops growing when it forms a crystallographic facet which is continuous with the preexisting facet of the template particle. When the two particles have close to the same orientation, the particles rotate into complete alignment and the neck that forms is consequently epitaxial with both particles. When the neck-particle system is in complete registry, the growing neck is rounded: there is an aperiodic arrangement of steps, even on the atomic resolution scale. The experimental results are discussed in terms of the random starting state of the two particles, the equilibrium crystal shape of the particle-neck system, and the operative kinetic mechanisms. 相似文献
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Crystals of SrY2 O4 (space group Pnam ) were examined by high-temperature powder X-ray diffractometry to determine the changes in unit-cell dimensions with temperature. The individual cell dimensions linearly increased with increasing temperature up to 1473 K. The expansion coefficients (K−1 ) were 1.263(8) × 10−5 along the a- axis, 7.46(6) × 10−6 along the b- axis, and 9.93(10) × 10−6 along the c- axis. The coefficient of mean linear expansion was 1.001(8) × 10−5 K−1 . 相似文献
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Dae-Joon Kim Paul F. Becher Camden R. Hubbard 《Journal of the American Ceramic Society》1993,76(11):2904-2908
Tetragonal ZrO2 ( t -ZrO2 ) solid solutions were prepared with addit ons of 2 mol% Y2 O3 plus up to 0.45 mol% Nb2 O5 . The thermal expansion coefficients in both the a- and c -axis lattice directions increased with Nb2 O5 alloying and the thermal expansion in the c -axis direction was greater than that in the a -axis direction over the entire composition range. This anisotropic thermal expansion behavior was related to the 4-fold coordination of Nb5+ with oxygen ions in t -ZrO2 solid solutions in the system ZrO2 –Y2 O3 –Nb2 O5 . The fracture toughness continuously increased with Nb2 O5 alloying and suggested that the c/a axial ratio is a more significant factor than the internal stress that arises from the thermal expansion anisotropy, in the determination of the transformability of t -ZrO2 in this system. 相似文献
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W. R. MANNING O. HUNTER JR. F. W. CALDERWOOD D. W. STACY† 《Journal of the American Ceramic Society》1972,55(7):342-347
The high-temperature thermal expansion of monoclinic Nb2 O5 was studied with X-ray and dilatometric techniques. The X-ray axial thermal expansion was anisotropic; the mean coefficients in the a, b , and c directions, respectively, were 5.3, 0, and 5.9×10−6 °C-1 from room temperature to 1000°C. It is proposed that this anisotropy causes microcrack formation in sintered polycrystalline samples. The bulk linear thermal expansion of both sintered and hot-pressed samples was determined with a dilatometer from room temperature to 1200°C. A hysteresis effect between heating and cooling data observed for sintered samples was attributed to the occurrence and recombination of internal microcracks. 相似文献
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Daniel R. Mumm David B. Marshall Alair Griffin Curtis W Griffin Colleen S. Turner 《Journal of the American Ceramic Society》1996,79(5):1416-1418
The hardness of zirconia-alumina laminar composites has been measured over contact size scales ranging from much smaller to much larger than the layer thicknesses. The results correlate with a weighted average of the hardnesses of the two layer constituents based on the volume of the plastic zone; and they deviate significantly from a similar average based on the contact area. 相似文献
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Monika Agarwal Mark R. de Guire Arthur H. Heuer 《Journal of the American Ceramic Society》1997,80(12):2967-2981
Undoped or Y2 O3 -doped ZrO2 thin films were deposited on self-assembled monolayers (SAMs) with either sulfonate or methyl terminal functionalities on single-crystal silicon substrates. The undoped films were formed by enhanced hydrolysis of zirconium sulfate (Zr(SO4 )·4H4 O) solutions in the presence of HCl at 70°C. Typically, these films were a mixture of two phases: nanocrystalline tetragonal- ( t -) ZrO2 and an amorphous basic zirconium sulfate. However, films with little or no amorphous material could be produced. The mechanism of film formation and the growth kinetics have been explained through a coagulation model involving homogeneous nucleation, particle adhesion, and aggregation onto the substrate. Annealing of these films at 500°C led to complete crystallization to t -ZrO2 . Amorphous Y2 O3 -containing ZrO2 films were prepared from a precursor solution containing zirconium sulfate, yttrium sulfate (Y2 (SO4 )3 8·H2 O), and urea (NH2 CONH2 ) at pH 2.2–3.0 at 80°C. These films also were fully crystalline after annealing at 500°C. 相似文献
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Koji Tsukuma Kuniyoshi Ueda Kenichi Matsushita Masahiko Shimada 《Journal of the American Ceramic Society》1985,68(2):56-C-
The temperature dependence of bending strength, fracture toughness, and Young's modulus of composite materials fabricated in the ZrO2 (Y2 O3 )-Al2 O3 system were examined. The addition of A1203 enhanced the high-temperature strength. Isostatically hot-pressed, 60 wt% ZrO2 (2 mol% Y2 O3 )/40 wt% Al2 O3 exhibited an extremely high strength, 1000 MPa, at 1000°C. 相似文献
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Zirconia-rich subsolidus phase relationships in the ZrO2 –Sc2 O3 and ZrO2 –In2 O3 systems were investigated. Phase inconsistencies in the ZrO2 –Sc2 O3 system resulted from a diffusionless cubic-to-tetragonal ( t' ) phase transformation not being recognized in the past. Through three different measuring techniques, along with microstructural observations, the solubility limits of the tetragonal and cubic phases were determined. 相似文献
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HARRO BESTGEN RACHMAN CHAIM ARTHUR H. HEUER 《Journal of the American Ceramic Society》1988,71(10):826-831
Tetragonal zirconia ( t -ZrO2 ) grains in an annealed ZrO2 8 wt% Y2 O3 alloy transformed to orthorhombic ( o ) or monoclinic ( m ) symmetry by stresses induced by localized electron beam heating in the transmission electron microscope. Different transformation mechanisms were observed, depending on foil thickness and orientation of individual grains. In thicker grains (≥150 nm), the transformation proceeded by a burst-like growth of m laths, and this is believed to approximate bulk behavior. In thinner grains near the edge of the foil, usually those with a [100], orientation perpendicular to the thin-foil surface, "continuous" growth of an o or m phase with an antiphase-boundary-containing microstructure was observed. The o phase is believed to be a high-pressure poly-morph of ZrO2 , which forms (paradoxically) as a thin-foil artifact because it is less dense than t -ZrO2 , but more dense than m -ZrO2 . In some very thin grains, the t → m transformation was thermoelastic. Furthermore, a mottled structure often occurred just before the t → m or t → o transformation, which is attributed to surface transformation. Aside from the lath formation, the observed transformation modes are a result of the reduced constraints in thin foils. 相似文献
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Mixtures of ultrafine monoclinic zirconia and aluminum hydroxide were prepared by adding NH4 OH to hydrolyzed zirconia sols containing varied amounts of aluminum sulfate. The mixtures were heat-treated at 500° to 1300°C. The relative stability of monoclinic and tetragonal ZrO2 in these ultrafine particles was studied by X-ray diffractometry. Growth of ZrO2 crystallites at elevated temperatures was strongly inhibited by Al2 O3 derived from aluminum hydroxide. The monoclinic-to-tetragonal phase transformation temperature was lowered to ∼500°C in the mixture containing 10 vol% Al2 O3 , and the tetragonal phase was retained on cooling to room temperature. This behavior may be explained on the basis of Garvie's hypothesis that the surface free energy of tetragonal ZrO2 is lower than that of the monoclinic form. With increasing A12 O3 content, however, the transformation temperature gradually increased, although the growth of ZrO2 particles was inhibited; this was found to be affected by water vapor formed from aluminum hydroxide on heating. The presence of atmospheric water vapor elevates the transformation temperature for ultrafine ZrO2 . The reverse tetragonal-to-monoclinic transformation is promoted by water vapor at lower temperatures. Accordingly, it was concluded that the monoclinic phase in fine ZrO2 particles was stabilized by the presence of water vapor, which probably decreases the surface energy. 相似文献
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PAUL F. BECKER 《Journal of the American Ceramic Society》1981,64(1):37-39
The initial strength of (σi ) and thermal shock resistances (Δ Tc and σr /σi ), as determined by quench tests, of Al2 O3 -ZrO2 composites are increased by increasing amounts of tetragonal ZrO2 second phase for contents of up to ∼15 vol%. For composites with ≤9 vol% ZrO2 the increases in σr and Δ Tc reflect the increase in γIC with addition of ZrO2 However, for ZrO2 contents >9 vol%, the thermal shock resistances (Δ Tc and σr /σi ) and σi are also affected by machining-induced microcracking in the surface of the samples. For ZrO2 contents >14 vol%, bulk microcracking can become extensive and result in a degradation of σi and Δ Tc . 相似文献
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《Journal of the American Ceramic Society》1975,58(9-10):460-460
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Kenji Kanamori Tohru Kineri Ryohei Fukuda Keishi Nishio Masashi Hashimoto Hideo Mae 《Journal of the American Ceramic Society》2009,92(1):32-35
Dense ZrW2 O8 was prepared by spark plasma sintering (SPS), using amorphous ZrW2 O8 nanopowder as a raw material, at 873 K for 10 min. We investigated the effects of SPS conditions, such as sintering temperature, heating rate, and the discharge power that is expressed as the product of pulsed direct current and voltage, on the densification process of ZrW2 O8 . The relative density and microstructure of ZrW2 O8 prepared by SPS were compared with those of ZrW2 O8 prepared by hot pressing (HP). The relative density of ZrW2 O8 prepared by HP at 873 K for 1 h was 63.1%. On the contrary, the relative density of ZrW2 O8 prepared by SPS at 873 K for 10 min at a heating rate of 50 K/min was 98.6%. These results show that the discharge pressure that is proportional to discharge power enhances the densification and grain growth of ZrW2 O8 in the SPS process. 相似文献
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Koji Tsukuma Kuniyoshi Ueda Masahiko Shimada 《Journal of the American Ceramic Society》1985,68(1):4-C-5
Composites of Al2 O3 and Y2 O3 partially-stabilized ZrO2 were isostatically hot-pressed using submicrometer powders as the starting material. The addition of Al2 O3 resulted in a large increase in bending strength. The average bending strength for a composite containing 20 wt% Al2 O3 was 2400 MPa, and its fracture toughness was 17 MN·w−3/2 相似文献