共查询到20条相似文献,搜索用时 15 毫秒
1.
Yoshikazu Suzuki Héctor A. Calderón Naoki Kondo Tatsuki Ohji 《Journal of the American Ceramic Society》2000,83(6):1346-1350
The in situ formation of magnetoplumbite-type (M-type) hexaferrites within a 3Y-TZP matrix was examined for the La2 O3 –ZnO–Fe2 O3 and BaO–Fe2 O3 systems. The formation of barium hexaferrite (Ba-M) was rapid enough at a temperature of 1300°C for 2 h to result in a uniform dispersion of fine Ba-M particles in a tetragonal zirconia polycrystal (TZP) matrix. However, the formation of lanthanum-substituted hexaferrite (La-M) was rather sluggish, despite the existence of a charge-compensating divalent oxide. The 3Y-TZP/20-wt%-BaFe12 O19 in situ composite possessed good magnetic properties, as well as moderately good mechanical properties. 相似文献
2.
Michiyuki Yoshida Yutaka Shinoda Takashi Akatsu Fumihiro Wakai 《Journal of the American Ceramic Society》2002,85(11):2834-2836
Ultrafine-grained monoclinic ZrO2 polycrystals (MZP) and 3-mol%-Y2 O3 -stabilized tetragonal ZrO2 polycrystals (3Y-TZP) were obtained by hot isostatic pressing (HIP). Both MZP and TZP were "high-purity" materials with impurities less than 0.1 wt%. The deformation behavior was studied at 1373 K, which was lower than the monoclinic ↔ tetragonal transition temperature. The stress exponent of 3Y-TZP with grain size of 63 nm was 3 in the higher stress region, and increased from 3 to 4 with decreasing stress. The deformation of MZP was characterized by a stress exponent of 2.5 over a wide stress range. The strain rate of 3Y-TZP was slower than that of MZP by 1 order of magnitude. It was suggested that either the doped yttrium or the difference in the crystal structure affected the diffusion coefficients of ZrO2 . 相似文献
3.
Junya Kondoh Yoichi Tomii Katsuhiro Kawachi 《Journal of the American Ceramic Society》2003,86(12):2093-2102
Methods of suppressing decreased conductivity in 8 mol% Y2 O3 -stabilized–92 mol% ZrO2 (8YSZ) with aging were investigated. Different amounts of Sc2 O3 were doped into 8YSZ. The electrochemical properties of Sc2 O3 -doped 8YSZ were measured, and the microstructural and local structural changes were characterized. The present results indicate that an appropriate amount of Sc2 O3 doping, 3 or 4 mol%, effectively suppresses decreased conductivity with aging in 8YSZ. 相似文献
4.
Krzysztof Haberko Waldemar Pyda Jan Piekarczyk Miroslaw M. Bucko 《Journal of the American Ceramic Society》1992,75(5):1272-1275
Fully tetragonal and sintered 13 mol% TiO2 ─3 mol% Y2 O3 ─84 mol% ZrO2 was thermally treated at 1300°C for 1 h in argon in the presence of carbon. No phase changes occurred on the as-received surface and in the bulk of the material, but t → m transformation occurred on polished surfaces under reducing conditions, and it resulted in increased fracture toughness, Young's modulus, and modulus of rigidity. Deoxidation of the system occurred and 0.174 wt% of carbon was found in the sample. This seemed to stabilize the tetragonal phase. 相似文献
5.
Composite ceramic materials based on Si3 N4 and ZrO2 stabilized by 3 mol% Y2 O3 have been formed using aluminum isopropoxide as a precursor for the Al2 O3 sintering aid. Densification was carred out by hot-pressing at temperatures in the range 1650° to 1800°C, and the resulting micro-structures were related to mechanical properties as well as to oxidation behavior at 1200°C. Densification at the higher temperatures resulted in a fibrous morphology of the Si3 N4 matrix with consequent high room-temperature toughness and strength. Decomposition of the ZrO2 grains below the oxidized surface during oxidation introduced radial stresses in the subscalar region, and from the oxidation experiments it is suggested that the ZrO2 incorporated some N during densification. 相似文献
6.
A small addition of CuO to 2-mol%-Y2 O3 -stabilized tetragonal zirconia polycrystals significantly enhances superplasticity by forming an amorhous grain-boundary phase containing primarily Cu+ , Y3+ , Zr4+ , and O2− . This phase apparently melts at around 1130°C, but it already provides a fast diffusion path even below the melting temperature. There are abrupt changes in stress exponent, activation energy, and grain size exponent across the melting temperature. Superplasticity is diffusion-controlled below the melting temperature and is interfaced-controlled above that. 相似文献
7.
Koji Tsukuma 《Journal of the American Ceramic Society》2000,83(12):3219-3221
Composites of β-Ce2 O3 ·11Al2 O3 and tetragonal ZrO2 were fabricated by a reductive atmosphere sintering of mixed powders of CeO2 , ZrO2 (2 mol% Y2 O3 ), and Al2 O3 . The composites had microstructures composed of elongated grains of β-Ce2 O3 ·11Al2 O3 in a Y-TZP matrix. The β-Ce2 O3 ·11Al2 O3 decomposed to α-Al2 O3 and CeO2 by annealing at 1500°C for 1 h in oxygen. The elongated single grain of β-Ce2 O3 ·11Al2 O3 divided into several grains of α-Al2 O3 and ZrO2 doped with Y2 O3 and CeO2 . High-temperature bending strength of the oxygen-annealed α-Al2 O3 composite was comparable to the β-Ce2 O3 ·11Al2 O3 composite before annealing. 相似文献
8.
Nanocrystalline MgAl2 O4 spinel powder was synthesized by pyrolysis of complex compounds of aluminum and magnesium with triethanolamine (TEA). The soluble metal ion–TEA complexes formed the precursor material on complete dehydration of the complexes of aluminum–TEA and magnesium–TEA. Single-phase MgAl2 O4 spinel powder resulted after heat treatment of the precursor material at 675°C. The precursor and the heat-treated powders were characterized by X-ray diffractometry (XRD), differential thermal and thermogravimetric analysis, and transmission electron microscopy (TEM). The average crystallite size as measured from the X-ray line broadening was around 14 nm and the average particle size from TEM studies was around 20 nm. 相似文献
9.
Chang Ming Fang Stephen C. Parker Gijsbertus de With 《Journal of the American Ceramic Society》2000,83(8):2082-2084
Atomistic simulations with atomic potentials including anion polarizibility have been performed for the low-index surfaces of spinel MgAl2 O4 with various terminations. The calculations show that for the most stable surface the surface energy is 2.27 J/m2 for the {100}, about 2.85 J/m2 for the {110}, and 3.07 J/m2 for the {111} orientation. The ratio between the experimental values to the calculated relaxed surface energies is about 1.5. Strong surface relaxation was found for the {110} and {111} orientation but only moderate surface relaxation for the {100} surface. 相似文献
10.
Effect of Ta2 O5 , Nb2 O5 , and HfO2 Alloying on the Transformability of Y2 O3 -Stabilized Tetragonal ZrO2
Dae-Joon Kim 《Journal of the American Ceramic Society》1990,73(1):115-120
The addition of Ta2 O5 , Nb2 O5 , and HfO2 enhanced the transformability of Y2 O3 -stabilized tetragonal ZrO2 polycrystal (Y-TZP), which was indicated by an increase in phase transformation temperatures and fracture toughness of Y-TZP. Comparison of the alloying effects of these oxides on the transformability and crystal structure of Y-TZP suggested that an alloying oxide which increases the c/a axial ratio (tetragonality) of TZP also increases the transformability. Empirical equations to predict the tetragonality are proposed. Calculated tetragonalities showed good agreement with measured values in the systems ZrO2 -Y2 O3 -Ta2 O5 , -Nb2 O5 , and -HfO2 . 相似文献
11.
Chuei-Tang Wang Lang-Sheng Lin Sheng-Jenn Yang 《Journal of the American Ceramic Society》1992,75(8):2240-2243
High-sinterability MgAl2 O4 powder has been produced from alkoxide precursors via a freeze-drying method. Clear alumina sol and magnesium methoxide were used as starting materials in the process. The spinel powders were characterized by various techniques, such as thermal analysis, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The tap density and sinterability of the spinel power are affected by the ball-milling techniques. Highly dense, transparent, polycrystalline MgAl2 O4 has been obtained from these powders by sintering and hot isostatic pressing. Bimodal grain-size microstructure is observed in a HIPed sample. 相似文献
12.
The compression creep behavior of Y2 O3 -stabilized ZrO2 (YSZ) was studied at temperatures to 2000 ° C. The function of Y2 O3 content and grain size was tested in specimens with various impurity concentrations and porosity distributions. For relatively fine-grained specimens, creep rates increased with the 1.5 power of the applied stress at low stresses and with the third power at high stresses. The results for coarse-grained specimens can, in general, be fit by the cube dependence. The 1.5 power can be reduced to a linear dependence by correcting for an apparent threshold stress, which decreases with increasing temperature. Creep activation energies for YSZ are 128 ± 10 kcal/mol, independent of Y2 O3 content, impurity level, grain size, and porosity distribution. In addition, over a broad range of temperatures and stresses the absolute values of the steady-state creep rates are influenced only by grain size and O2 partial pressure. 相似文献
13.
TAKAKI MASAKI 《Journal of the American Ceramic Society》1986,69(7):519-522
Yttria-partially-stabilized zirconia (Y-PSZ) materials containing 2.5, 3.0, and 5.0 mol% of Y2 O3 prepared by hot pressing were subjected to ageing in air for >10 h at temperatures in the range of 800°C and 1200°C. The sintered materials were measured to determine the mechanical properties and microstructures and analyzed for trace elements. A sharp reduction in bending strength was observed after the ageing, the cause for which was suggested to be the formation of cavities produced by the oxidation of carbon. 相似文献
14.
Chang Ming Fang Gijsbertus de With Stephen C. Parker 《Journal of the American Ceramic Society》2001,84(7):1553-1558
Atomistic simulation techniques have been used to model the dissociative adsorption of water onto the low-index {100}, {110}, and {111} surfaces of spinel MgAl2 O4 . The Born model of solids and the shell model for oxygen polarization have been used. The resulting structures and chemical bonding on the clean and hydrated surfaces are described. The calculations show that the dissociative adsorption of water on the low-index surfaces is generally energetically favorable. For the {110} and {111} orientations, the surfaces cleaved between oxygen layers show high absorption and stability. The calculations also show that, for the {111} orientation, the surfaces may absorb chemically water molecules up to ∼90% coverage and have the highest stability. It is suggested that, during fracture, only partial hydration occurs, leading to cleavage preferentially along the {100} orientation. 相似文献
15.
The cubic ( c -ZrO2 ) and tetragonal zirconia ( t -ZrO2 ) phase stability regions in the system ZrO2 –Y2 O3 –Ta2 O5 were delineated. The c -ZrO2 solid solutions are formed with the fluorite structure. The t -ZrO2 solid solutions having a c/a axial ratio (tetragonality) smaller than 1.0203 display high fracture toughness (5 to 14 MPa · m1/2 ), and their instability/transformability to monoclinic zirconia ( m -ZrO2 ) increases with increasing tetragonality. On the other hand, the t -ZrO2 solid solutions stabilized at room temperature with tetragonality greater than 1.0203 have low toughness values (2 to 5 MPa · m1/2 ), and their transformability is not related to the tetragonality. 相似文献
16.
Lattice parameter and density data were compiled for Y2 O3 -Stabilized ZrO2 , both from the literature and from experimental measurements. The data are described very well over a wide range of composition by the model of Aleksandrov et al. , which assumes Y substitution for Zr in the unit cell with compensating anion vacancies. Effects are noted in two-phase cubic-tetragonal materials which indicate significant lattice strains in the two-phase materials. 相似文献
17.
Yuxiang Ma Erich H. Kisi Shane J. Kennedy 《Journal of the American Ceramic Society》2001,84(2):399-405
In situ neutron diffraction patterns were recorded from a 3Y-TZP sample during a complete loading–unloading cycle at compressive loads up to 2.3 GPa. The macroscopic stress–strain diagram shows elastic behavior to 1.7 GPa followed by volume conserving plastic strains of ∼1.6 × 10− 3 . There were no signs of t → m transformation in the neutron diffraction patterns, and intensity changes in the pattern show that the plasticity is due to ferroelastic switching of tetragonal zirconia crystals. Quantification of the degree of switching gives good agreement with the macroscopic strains. The ferroelastic switching is completely reversed by a process akin to creep relaxation on unloading. Lattice parameters, elastic constants, and structural changes as a function of load are also discussed. 相似文献
18.
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
19.
A. DOMINGUEZ-RODRIGUEZ K. P. D. LAGERLöF A. H. HEUER 《Journal of the American Ceramic Society》1986,69(3):281-284
Fully stabilized cubic ZrO2 single crystals containing various Y2 O3 concentrations were deformed at 1400°C in air. The orientation chosen favored (001)(110) slip, which was confirmed by slip-trace analysis and transmission electron microscopy; (111)(110) slip could also be activated. The yield and flow stresses increased with increasing Y2 O3 concentration, and stress-strain curves were dominated by a region of zero work hardening from very small strains for all compositions. 相似文献
20.
H. SCHUBERT 《Journal of the American Ceramic Society》1986,69(3):270-271
The transformability of the grains in tetragonal zirconia polycrystals is determined by thermal stresses (eigenstresses) which develop because of anisotropic expansion behavior of the tetragonal grains on cooling. Anisotropic thermal expansion coefficients based on lattice parameter determinations at room temperature and 600° and 800°C are presented for tetragonal zirconia containing 2 and 3 mol% Y2 O3 . The sources of errors in these data are discussed. 相似文献