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1.
Dispersion states of aqueous composite Al2 O3 /ZrO2 colloidal suspensions were studied by measuring particle size distribution as a function of pH. Mutual dispersion was achieved at pH values of 2.0 to 3.5. Consolidated composites formed by colloidal filtration reflected the uniformity of the colloidal state. The mean flexural strength (896 MPa) of the sintered compacts was 1.6 times that of bodies consolidated by isostatic pressing . 相似文献
2.
Byong-Taek Lee In-Cheol Kang Soon-Hee Cho Ho-Yeon Song 《Journal of the American Ceramic Society》2005,88(8):2262-2266
Continuously oriented porous Al2 O3 bodies were fabricated by a multi-pass extrusion process using C powders and ethylene vinyl acetate as an agent for pore forming and as a binder, respectively. The main pore size can be easily controlled by increasing the number of extrusion passes. The edges of the pore frame showed a rough surface having many fine pores about 0.2–1 μm in size. In the continuously porous Al2 O3 bodies having 150 μm pore size, the values of the relative density and bending strength were about 63% and 90 MPa, respectively. These values were higher than those of an Al2 O3 porous body made by a common process. From the in vitro study using human osteoblast-like MG-63 cells, it was confirmed that the cells grew well and adhered to the top surface and inside pores, as well as the outside wall of the continuously porous Al2 O3 body. Without the directionality, the cells showed some spindle-shaped, three-dimensional, and network-type structures. 相似文献
3.
Four nanometer-sized zirconia powders stabilized by 3 mol% Y2 O3 were used for the preparation of dense bulk ceramics. Ceramic green bodies were prepared by cold isostatic pressing at pressures of 300–1000 MPa. The size of the pores in ceramic green bodies and their evolution during sintering were correlated with the characteristics of individual nanopowders and with the sintering behavior of powder compacts. Only homogeneous green bodies with pores of <10 nm could be sintered into dense bodies (>99% t.d.) at a sufficiently low temperature to keep the grain sizes in the range <100 nm. Powders with uniform particles 10 nm in size yielded green bodies of required microstructure. These nanoparticle compacts were sintered without pressure to give bodies (diameter 20 mm, thickness 4 mm) with a relative density higher than 99% and a grain size of about 85 nm (as determined by the linear intercept method). 相似文献
4.
Krenar Shqau Matthew L. Mottern Di Yu Henk Verweij 《Journal of the American Ceramic Society》2006,89(6):1790-1794
Strong and permeable macro-porous α-Al2 O3 membrane supports are made by colloidal filtration of 20 vol% dispersions of α-Al2 O3 with an average particle size of 600 nm. Intact compacts with very good surface quality were obtained at an optimum pH of 9.5 and dosage of 0.2 wt% ammonium aurintricarboxylate (Aluminon), based on dry alumina. The colloidal stability of the aluminon-stabilized slurries is confirmed by ξ potential measurements. Slight sintering of dense-packed α-Al2 O3 compacts was found to result in >67% packing density and a bimodal pore-size distribution as derived from shrinkage behavior and gas adsorption studies. Non-stationary single gas permeation measurements showed improved gas permeability, compared with α-Al2 O3 compacts prepared using powder with a smaller particle size (300 nm). The strength of the disk-shaped alumina compacts within the porosity range of 30%–20% increased from 100 to 300 MPa with a standard deviation of 20 and 50 MPa, respectively. 相似文献
5.
Byong-Taek Lee Dong-Hwi Jang In-Cheol Kang Chi-Woo Lee 《Journal of the American Ceramic Society》2005,88(10):2874-2878
Novel fibrous Al2 O3 –(m-ZrO2 )/t-ZrO2 (m, monoclinic; t, tetragonal) composites having a core/shell structure were fabricated by multi-extrusion, and their microstructures and material properties were investigated depending on the number of extrusions. The composites acquired a homogeneously fine fibrous structure as the number of extrusions increased. The bending strength and fracture toughness increased remarkably as the number of extrusions increased. In the fracture surface of the second passed composite, an Al2 O3 –(m-ZrO2 ) core region appeared, flat type, although some local regions existed with an intergranular fracture. However, the fracture mode of the t-ZrO2 region was of intergranular type having a sharp and rough surface. In the composite made by the fifth passed extrusion, the fracture strength and toughness values were high at about 665 MPa and 9.6 MPa·m1/2 , respectively. The main fracture mode was a typical intergranular mode having a rough fracture surface, and the main multi-toughening was because of mechanisms such as crack bridging, microcracking, and phase transformation. 相似文献
6.
SABURO HORI MASAHIRO YOSHIMURA SHIGEYUKI SMIYA 《Journal of the American Ceramic Society》1986,69(3):169-172
The fracture toughness of fine-grained undoped ZrO2 -toughened Al2 O3 (ZTA) was essentially unchanged by postsintering hot isostatic pressing and increased monotonically with ZrO2 additions up to 25 wt%. The strength of ZTA with 5 to 15 wt% tetragonal ZrO2 , which depended monotonically on the amount of ZrO2 present before hot isostatic pressing, was increased by pressing but became almost constant between 5 and 15 wt% ZrO2 addition. The strength appeared to be controlled by pores before pressing and by surface flaws after pressing; the size of flaws after pressing increased with ZrO2 content. The strength of ZTA containing mostly monoclinic ZrO2 (20 to 25 wt%) remained almost constant despite the noticeable density increase upon hot isostatic pressing because the strength was controlled by preexisting microcracks whose extent did not change on postsintering pressing. These strength-toughness relations in sintered and isostatically hot-pressed ZTA are explained on the basis of R -curve behavior. The importance of the contribution of microcracks to the toughness of ZTA is emphasized. 相似文献
7.
Electroconductive Al2 O3 –NbN ceramic composites were prepared by hot pressing. Dense sintered bodies of ball-milled Al2 O3 –NbN composite powders were obtained at 1550°C and 30 MPa for 1 h under a nitrogen atmosphere. The bending strength and fracture toughness of the composites were enhanced by incorporating niobium nitride (NbN) particles into the Al2 O3 matrix. The electrical resistivity of the composites decreased with increasing amount of NbN phase. For a 25 vol% NbN–Al2 O3 composite, the values of bending strength, fracture toughness, Vickers hardness, and electrical resistivity were 444.2 MPa, 4.59 MPa·m1/2 , 16.62 GPa, and 1.72 × 10−2 Ω·cm, respectively, making the composite suitable for electrical discharge machining. 相似文献
8.
Mathias Herrmann Hans-Joachim Kleebe Jan Raethel Kerstin Sempf Stefan Lauterbach Mathis M. Müller Iakovos Sigalas 《Journal of the American Ceramic Society》2009,92(10):2368-2372
B6 O is a possible candidate of superhard materials with a hardness of 45 GPa measured on single crystals. Up to now, densification of these materials was only possible at high pressure. However, recently it was found that Al2 O3 can be utilized as an effective sintering additive, similar to the addition of Y2 O3 /Al2 O3 that was used in this work. The densification behavior of the material as a function of applied pressure, its microstructure evolution, and the resulting mechanical properties were investigated. A strong dependence of the densification with increasing pressure was found. The material revealed characteristic triple junctions filled with amorphous residue composed of B2 O3 , Al2 O3 , and Y2 O3 , while no amorphous grain-boundary films were observed along internal interfaces. Mechanical testing revealed on average a hardness of 33 GPa, a fracture toughness of 4 MPa·m1/2 , and a strength value of 520 MPa. 相似文献
9.
Je-Won Choi Young-Min Kong Hyoun-Ee Kim In-Seop Lee 《Journal of the American Ceramic Society》1998,81(7):1743-1748
The effects of Ni3 Al and Al2 O3 additions on the mechanical properties of hydroxyapatite (HAp) were investigated. The addition of Ni3 Al particles increased the strength as well as the fracture toughness of HAp. However, the improvements in the properties were limited because of the formation of microcracks around the metal particles. The microcracks were formed because of the large difference in the coefficients of thermal expansion between HAp and Ni3 Al, and because of the relatively large size of Ni3 Al particles (∼20 µm). The addition of submicrometer Al2 O3 powder was also effective in increasing the mechanical properties. The flexural strength and the fracture toughness were increased from about 100 MPa and 0.7 MPam1/2 , respectively, to 200 MPa and 1.5 MPam1/2 by the addition of 20 vol% Al2 O3 . When Ni3 Al and Al2 O3 were added together, the fracture toughness was further increased to 2.3 MPam1/2 . This increase in the fracture toughness was attributed to the synergistic effect of matrix strengthening and crack interactions with the metal particles. 相似文献
10.
Isao Yamashita Koji Tsukuma Takafumi Kusunose 《Journal of the American Ceramic Society》2009,92(9):2136-2138
A translucent alumina composite containing 1 vol% LaAl11 O18 , prepared by the hot isostatic pressing (HIP) method, displays both high translucency and high fracture toughness. Its total forward transmission at 600 nm is 75% (thickness 1 mm), and its bending strength and fracture toughness are estimated to be 574±15 MPa and 5.9±0.46 MPa·m0.5 , respectively. Its high translucency is due to the similarity of refractive index between the additive phase (LaAl11 O18 ) and the matrix (alumina). 相似文献
11.
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
12.
α - Al2 O3 nanopowders with mean particle sizes of 10, 15, 48, and 80 nm synthesized by the doped α-Al2 O3 seed polyacrylamide gel method were used to sinter bulk Al2 O3 nanoceramics. The relative density of the Al2 O3 nanoceramics increases with increasing compaction pressure on the green compacts and decreasing mean particle size of the starting α-Al2 O3 nanopowders. The densification and fast grain growth of the Al2 O3 nanoceramics occur in different temperature ranges. The Al2 O3 nanoceramics with an average grain size of 70 nm and a relative density of 95% were obtained by a two-step sintering method. The densification and the suppression of the grain growth are achieved by exploiting the difference in kinetics between grain-boundary diffusion and grain-boundary migration. The densification was realized by the slower grain-boundary diffusion without promoting grain growth in second-step sintering. 相似文献
13.
Masaki Yasuoka Kiyoshi Hirao Manuel E. Brito Shuzo Kanzaki 《Journal of the American Ceramic Society》1995,78(7):1853-1856
Control of microstructure in the Al2 O3 /LaAl11 O18 system was performed. Elongated alumina grains were formed by doping with small addition of silica, and 20 vol% lanthana- luminate was formed in situ by the reaction of LaAlO3 - A12 O3 in an alumina matrix. Strengths of over 600 MPa and a high fracture toughness (6 MPa.m1/2 ) were achieved in the material with both elongated A12 O3 grains and LaAl11 O18 platelets. Generally antagonistic properties such as strength and fracture toughness have been made compatible in the same ceramic system. 相似文献
14.
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
15.
The fracture strengths of sintered Al2 O3 containing 20 and 40 vol% ZrO2 (12 mol% CeO2 )—zirconia-toughened alumina (ZTA)—composites along with the fracture resistance can be increased (e.g., to ∼900 MPa and >12 Mpa·m1/2 , respectively), by increasing the mean grain size of the t -ZrO2 (and the Al2 O3 ) from ∼0.5 μm to ∼3 μm. At these lower t -ZrO2 contents, the fracture strength-fracture resistance curves show a continuous rise as opposed to the strength maxima observed in polycrystalline t -ZrO2 (12 mol% CeO2 ), CeTZP, and ZrO2 (12 mol% CeO2 ) ceramics containing ≤20 vol% Al2 O3 . The toughened composites also exhibit excellent damage resistance with fracture strengths of 500 MPa retained with surfaces containing ∼150- N Vickers indentations which produce cracks of ∼160-μm radius. Greater damage resistance correlates with an increase in the apparent R -curve response of these composites. 相似文献
16.
Jing-Fong Tsai Uong Chon N. Ramachandran Dinesh K. Shetty 《Journal of the American Ceramic Society》1992,75(5):1229-1238
Microstructure, phase stability, and mechanical properties of CeO2 -partially-stabilized zirconia (12 mol% Ce-TZP) containing 10 wt% Al2 O3 and 1.5 wt% MnO were studied in relation to the base Ce-TZP and the Ce-TZP/Al2 O3 composite without MnO. The MnO reacted with both CeO2 and Al2 O3 to form a new phase of approximate composition CeMnAl11 O19 . The reacted phase had a magnetoplumbite structure and formed elongated, needlelike crystals. The MnO-doped Ce-TZP/Al2 O3 composites sintered at an optimum temperature of 1550°C exhibited high strength (650 MPa in four-point bending) and rising crack-growth-resistance behavior, with fracture toughness increasing from 7.6 to 10.3 MPa.In12 in compact tension tests. These improved mechanical properties were associated with relatively high tetragonal-to-monoclinic transformation temperature ( M s =−42°C) at small grain size (2.5 μm), significant transformation plasticity in mechanical tests (bending, uniaxial tension, and uniaxial compression) and transformation zones at crack tips in compact tension specimens. The transformation yield stress, zone size, and fracture toughness were sensitive to the sintering temperature varied in the range 1500° to 1600°C. Analysis of the transformation zones using Raman microprobe spectroscopy and calculation of zone shielding for the observed zones indicated that a large fraction of the fracture toughness (∼70%) was derived from transformation toughening. 相似文献
17.
Shingo Hirano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1996,79(1):171-176
In the ZrO2 -Cr2 O3 system, metastable t -ZrO2 solid solutions containing up to 11 mol% Cr2 O3 crystallize at low temperatures from amorphous materials prepared by the hydrazine method. The lattice parameter c decreases linearly from 0.5149 to 0.5077 nm with increased Cr2 O3 content, whereas the lattice parameter a is a constant value ( a = 0.5077 nm) regardless of the starting composition. At higher temperatures, transformation (decomposition) of the solid solutions proceeds in the following way: t (ss)→ t (ss) + m + Cr2 O3 → m + Cr2 O3 . Above 11 mol% Cr2 O3 addition, c-ZrO2 phases are formed in the presence of Cr2 O3 . The t -ZrO2 solid solution powders have been characterized for particle size, shape, and surface area. They consist of very fine particles (15–30 nm) showing thin platelike morphology. Dense ZrO2 (3Y)-Cr2 O3 composite ceramics (∼99.7% of theoretical) with an average grain size of 0.3 μm have been fabricated by hot isostatic pressing for 2 h at 1400°C and 196 MPa. Their fracture toughness increases with increased Cr2 O3 content. The highest K Ic value of 9.5 MPa·;m1/2 is achieved in the composite ceramics containing 10 mol% Cr2 O3 . 相似文献
18.
Masanori Hirano Shinzi Watanabe Etsuro Kato Yasunobu Mizutani Masayuki Kawai Yasuhisa Nakamura 《Journal of the American Ceramic Society》1999,82(10):2861-2864
The microstructure, crystal phase, electrical conductivity, and mechanical strength of less than 7-mol%-Sc2 O3 -doped zirconia ceramics fabricated by comparatively low-temperature sintering at 1200–1300°C for 1 h were investigated. Zirconia ceramics having a uniform microstructure (grain size < 0.5 μm) stabilized with 6 mol% Sc2 O3 showed high electrical conductivity (0.15 S/cm at 1000°C) and high fracture strength (660 MPa). With the increase of Sc2 O3 content from 3.5 to 7 mol%, the grain size, fracture strength, and electrical conductivity at 1000°C changed from 0.2 to 0.5 μm, 970 to 440 MPa, and 0.07 to >0.2 S/cm, respectively. Sc2 O3 -doped zirconia polycrystals with high fracture strength and high electrical conductivity are promising candidates for the electrolyte material of solid oxide fuel cells. 相似文献
19.
TAKAKI MASAKI 《Journal of the American Ceramic Society》1986,69(8):638-640
Tetragonal zirconia polycrystals were produced from high-purity powders containing 1.5 to 5.0 mol% Y2 O3 by cold isostatic pressing and sintering, hot-pressing, and hot isostatic pressing. The mechanical properties and microstructures of these resulting materials were examined, with emphasis on the relation between strength and fracture toughness. 相似文献
20.
Strength and fracture toughness results are presented for ZrO2 single crystals stabilized with Y2 O3 . The crystals (2 cm in diameter by 5 cm long) were prepared by skull melting. The partially stabilized compositions with 4 to 6 wt% Y2 O3 showed a dramatic improvement in mechanical properties over the fully stabilized samples containing 20 wt% Y2 O3 , i.e. a strength exceeding 1000 MPa and a fracture toughness of 8 Mpa,.m 1/2 were achieved compared to 200 MPa and 2 Mpa.m1/2 , respectively, for fully stabilized ZrO2 single crystals. 相似文献