共查询到20条相似文献,搜索用时 21 毫秒
1.
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
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3.
An X-ray method to determine the transformation zone size in ceramics containing tetragonal ZrO2 is described. Results obtained on plane fracture surfaces of various composites were correlated to mechanical property data and TEM observations and were found to be in good agreement. This indicates that the method presented is a useful tool for estimating stress-induced transformation zone sizes and for checking the effectiveness of tetragonal particles introduced in a ceramic matrix. 相似文献
4.
Francisco del Monte Willa Larsen John D. Mackenzie 《Journal of the American Ceramic Society》2000,83(3):628-634
Gel-glasses of various compositions in the x ZrO2 . (10 – x )SiO2 system were fabricated by the sol–gel process. Precipitation due to the different reactivities between tetraethyl orthosilicate (TEOS) and zirconium(IV) n -propoxide has been eliminated through the use of 2-methoxyethanol as a chelating agent. Thermal treatment of these gels produced crystalline ZrO2 particles. While monoclinic is the stable crystalline phase of zirconia at low temperatures, the metastable tetragonal phase is usually the first crystalline phase formed on heat treatment. However, stability of the tetragonal phase is low, and it transforms to the monoclinic phase on further heat treatment. In this study, it has been found that the transformation temperature increases as the SiO2 content in the ZrO2 –SiO2 binary oxide increases. The most significant results were from samples containing only 2 mol% SiO2 , where the metastable tetragonal phase formed at low temperatures and remained stable over a broad temperature range. X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to elucidate the structure of these binary oxides as a function of temperature. 相似文献
5.
MICHAEL HOCH 《Journal of the American Ceramic Society》1964,47(12):630-632
The activity of zirconium in the tetragonal ZrO2 phase was measured at 2200° to 2300°K as a function of composition by studying the reaction
From the variation of the zirconium activity with composition, the pairwise interaction energy E11 between vacancies in the oxygen lattice was evaluated at -4.6 ± 1.0 kcal per mole. 相似文献
From the variation of the zirconium activity with composition, the pairwise interaction energy E
6.
Fred F. Lange Burt I. Davis Douglas O. Raleigh 《Journal of the American Ceramic Society》1983,66(3):50-C-
The solid sodium electrolyte β"-Al2 O3 (Li-stabilized) was strengthened with additions of tetragonal ZrO2 (15 vol%). The conductivity of this composite material, measured in an Na/Na cell, was 7.7 Ω· at 300°C. Average values of strength and the critical stress intensity factor were 350 MPa and 4.5 MPa·m1/2 , respectively, for the sintered composite material. 相似文献
7.
Masatomo Yashima Takefumi Mitsuhashi Hiroyuki Takashina Masato Kakihana Takayasu Ikegami Masahiro Yoshimura 《Journal of the American Ceramic Society》1995,78(8):2225-2228
DSC (differential scanning calorimeter) measurements were performed to investigate the tetragonal-monoclinic ( t-m ) transition enthalpy of the compositionally homogeneous ZrO2 - X mol% CeO2 solid solution of X = 0, 4, 8, and 12. The transition enthalpy decreases linearly with an increase of CeO2 content. The m → t transition enthalpy on heating agreed well with the inverse t → m one obtained during cooling. With increasing X , the DSC peak broadens and the transition temperature distribution of each sample increases, while the thermal hysteresis is almost independent of X . 相似文献
8.
Francisco del Monte Willa Larsen John D. Mackenzie 《Journal of the American Ceramic Society》2000,83(6):1506-1512
Metastable tetragonal ZrO2 phase has been observed in ZrO2 –SiO2 binary oxides prepared by the sol–gel method. There are many studies concerning the causes of ZrO2 tetragonal stabilization in binary oxides such as Y3 O2 –ZrO2 , MgO–ZrO2 , or CaO–ZrO2 . In these binary oxides, oxygen vacancies cause changes or defects in the ZrO2 lattice parameters, which are responsible for tetragonal stabilization. Since oxygen vacancies are not expected in ZrO2 –SiO2 binary oxides, tetragonal stabilization should just be due to the difficulty of zirconia particles growing in the silica matrix. Furthermore, changes in the tetragonal ZrO2 crystalline lattice parameters of these binary oxides have recently been reported in a previous paper. The changes of the zirconia crystalline lattice parameters must result from the chemical interactions at the silica–zirconia interface (e.g., formation of Si–O–Zr bonds or Si–O− groups). In this paper, FT-IR and 29 Si NMR spectroscopy have been used to elucidate whether the presence of Si–O–Zr or Si–O− is responsible for tetragonal phase stabilization. Moreover, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy have also been used to study the crystalline characteristics of the samples. 相似文献
9.
Raiford E. Hann Paul R. Suitch Joseph L. Pentecost 《Journal of the American Ceramic Society》1985,68(10):285-C
The crystal structures of ZrO2 and HfO2 (P21 /c) were refined in detail from X-ray powder diffraction data. The precision obtained for the atom positions for both compounds is comparable to that of previous single-crystal work. 相似文献
10.
Fine single-domain and polydomain particles of tetragonal ZrO2 were prepared by hydrothermal and heat treatment of ZrO2 · n H2 O. The particles were characterized by X-ray diffraction, electron microscopy, NMR, mass spectrometry, and ir spectroscopy. The main impurity in the samples was 1 to 2 wt% OH− ions, most of which were concentrated on the particle surfaces or at domain boundaries; some were also distributed in the lattice. Fine single-domain tetragonal particles were strain-free, but polydomain particles had large strains. The single-domain tetragonal particles were transformed much more easily than the polydomain particles by mechanical treatment. The stablization of metastable tetragonal ZrO2 cannot be explained adequately by the surface-energy theory. An explanation based on the concept of a martensitic transformation may be more reasonable. 相似文献
11.
Eiji Tani Masahiro Yoshimura Shigeyuki Somiya 《Journal of the American Ceramic Society》1981,64(12):181-C
Ultrafine powder of single-phase manoclinic ZrO2 was prepared by hydrothermal treatments of amorphous hydrated zirconia with 8 wt% KF solution under 100 MPa at 200° to 500°C for 24 h. The process yielded well-crystallized particles 16 nm and 22 nm in size at 200° and 500°C, respectively . 相似文献
12.
Koichiro Fukuda Iwao Maki Suketoshi Ito 《Journal of the American Ceramic Society》1997,80(6):1595-1598
Crystals of β-Ca2 SiO4 (space group P 121 / n 1) were examined by high-temperature powder X-ray diffractometry to determine the change in unit-cell dimensions with temperature up to 645°C. The temperature dependence of the principal expansion coefficients (αi ) found from the matrix algebra analysis was as follows: α1 = 20.492 × 10−6 + 16.490 × 10−9 ( T - 25)°C−1 , α2 = 7.494 × 10−6 + 5.168 × 10−9 ( T - 25)°C−1 , α3 =−0.842 × 10−6 − 1.497 × 10−9 ( T - 25)°C−1 . The expansion coefficient α1 , nearly along [302] was approximately 3 times α2 along the b -axis. Very small contraction (α3 ) occurred nearly along [ 01]. The volume changes upon martensitic transformations of β↔αL ' were very small, and the strain accommodation would be almost complete. This is consistent with the thermoelasticity. 相似文献
13.
Tetragonal ( t ) ZrO2 precipitates in Mg-, Ca-, and Y-partially-stabilized ZrO2 (Mg-PSZ, Ca-PSZ, Y-PSZ) have different habit planes and different morphologies. These differences arise because of differences in lattice parameters of precipitate and cubic ( c ) ZrO2 matrix in the three systems. The approximate {001} habit plane and oblate spheroid precipitate morphology observed in Mg-PSZ are explained in terms of anisotropic elasticity using the theory of Khachaturyan. The aspect ratio of ∼5 of these particles is used to calculate a c/t interfacial energy of ∼0.15 J·m–2 . The aligned equiaxed precipitates observed in Ca-PSZ and the twinned colonies observed in Y-PSZ can also be explained using this theory and arise from interactions between strain fields during coarsening; the aligned particles in Ca-PSZ may actually represent an intermediate state before the formation of colonies in this system. 相似文献
14.
A. H. HEUER N. CLAUSSEN W.M. KRIVEN M. RUHLE 《Journal of the American Ceramic Society》1982,65(12):642-650
The stability of tetragonal ZrO2 particles in ceramic matrices was considered, with particular reference to Al2 O3 -ZrO2 composites and to partially stabilized ZrO2 . In both systems, particles above a "critical" size transform martensitically to monoclinic symmetry on cooling to room temperature. The critical factors that could affect the size dependence of the transformation temperature—surface and strain energy effects, the chemical free energy driving force, and the difficulty of nucleating the martensitic transformation—were considered. Nucleation arguments are probably the most important. 相似文献
15.
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
16.
Analytical electron microscopy of ZrO2 particles in a zirconia-toughened alumina was performed. Significant solute heterogeneities in these particles were found but did not seem to affect the particle size dependence of Ms . 相似文献
17.
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
18.
R. Morena P. E. Lockwood L. Evans C. W. Fairhurst 《Journal of the American Ceramic Society》1986,69(4):75-C-
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance. 相似文献
19.
G. L. KULCINSKI 《Journal of the American Ceramic Society》1968,51(10):582-583
Tetragonal ZrO2 can be formed directly from the mono-clinic form at 25° C by applying pressures greater than 37 kbars. The transition is reversible, and the tetragonal phase cannot be retained in a metastable condition at ambient conditions. 相似文献
20.
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