共查询到20条相似文献,搜索用时 15 毫秒
1.
Köji Yamakata Ken Hirota Osamu Yamaguchi Hideki Kume Suguru Inamura Hiroki Miyamoto 《Journal of the American Ceramic Society》1994,77(8):2207-2208
Alumina/3 mol% yttria-doped zirconia composite powders have been prepared by the hydrazine method. As-prepared powders are AlO(OH) gel solid solutions and the mixtures of this and amorphous ZrO2 below and above 10 mol% ZrO2 , respectively. The formation process leading to α–Al2 O3 – t -ZrO2 composite powders is examined. 相似文献
2.
Koji Ishida Ken Hirota Osamu Yamaguchi Hideki Kume Suguru Inamura Hiroki Miyamoto 《Journal of the American Ceramic Society》1994,77(5):1391-1395
In the system ZrO2 –Al2 O3 , a new method for preparing ZrO2 solid solutions from ZrCl4 and AlCl3 using hydrazine monohydrate is investigated. c -ZrO2 solid solutions containing up to ∼40 mol% Al2 O3 crystallize at low temperatures from amorphous materials. The formation mechanism is discussed from IR spectral data. The values of the lattice parameter α increase linearly from 0.5072 to 0.5105 nm with increasing Al2 O3 content. At higher temperatures, transformation of the solid solutions proceeds as follows: c ( SS ) → t ( ss ) → t ( ss ) +α-Al2 O3 → m +α-Al2 O3 . m -ZrO2 –α-Al2 O3 composite ceramics are fabricated by hot isostatic pressing for 2 h at 1250°C and 196 MPa. Microstructures and mechanical properties are examined, in connection with increasing Al2 O3 content. 相似文献
3.
Sintering Behavior of Nanocrystalline Zirconia Doped with Alumina Prepared by Chemical Vapor Synthesis 总被引:4,自引:0,他引:4
Vladimir V. Srdi Markus Winterer Horst Hahn 《Journal of the American Ceramic Society》2000,83(8):1853-1860
Powders of nanocrystalline zirconia doped with 3–30 mol% alumina have been synthesized using chemical vapor synthesis (CVS). Dense or mesoporous ceramics of small and narrowly distributed grain and pore sizes in the nanometer range are obtained via pressureless vacuum sintering. The microstructural development of the doped samples is strongly dependent on the alumina content. Sintering of zirconia samples with 3 and 5 mol% alumina at temperatures of 1000°C for 1 h results in fully dense, transparent ceramics with grain sizes of 40–45 nm and homogeneous microstructures. 相似文献
4.
Masayuki Ishitsuka Tsugio Sato Tadashi Endo Masahiko Shimada Hideo Ohno Naoki Igawa Takanori Nagasaki 《Journal of the American Ceramic Society》1990,73(8):2523-2525
Thermal-shock fracture behavior of yttria-doped tetragonal zirconia polycrystals (Y-TZP) of various grain sizes was evaluated by the quenching method using water as the quenching solvent. The tetragonal-to-monoclinic phase transformation behavior of Y-TZP around cracks introduced by thermal stress was investigated by using Raman microprobe spectroscopy. The critical quenching temperature difference (Δ T c ) of Y-TZP ceramics increased from 250° to 425°C with increasing grain size of zirconia from 0.4 to 3.0 μm, while the fracture strength decreased from 900 to 680 MPa. The improvement of Δ T c of Y-TZP with increasing grain size of zirconia corresponded with the quantity of tetragonal-to-monoclinic phase transformation around cracks introduced by thermal stress. 相似文献
5.
Prevention of Low-Temperature Surface Transformation by Surface Recrystallization in Yttria-Doped Tetragonal Zirconia 总被引:1,自引:0,他引:1
Philip J. Whalen Franz Reidinger Robert F. Antrim 《Journal of the American Ceramic Society》1989,72(2):319-321
The low-temperature (100° to 400°C) tetragonal to monoclinic transformation in yttria-doped tetragonal zirconia (Y-TZP) can be inhibited by a postsintering grinding and annealing treatment. The surface region so treated contains fine tetragonal grains which have recrystallized from the severely damaged ground surface. The various features of the recrystallized surface that may affect the lowtemperature transformation are analyzed. 相似文献
6.
Enhanced Magnetization of 3 mol% Yttria-Doped Zirconia/Barium Hexaferrite by Post-Plastic Deformation 总被引:1,自引:0,他引:1
Yoshikazu Suzuki Masanobu Awano Naoki Kondo Tatsuki Ohji 《Journal of the American Ceramic Society》2000,83(5):1113-1116
A 3-mol%-Y2 O3 -doped tetragonal-ZrO2 polycrystal/BaFe12 O19 composite was fabricated by powder metallurgical processes, and its mechanical and magnetic properties were evaluated. Post-plastic deformation (i.e., hot-forging) on the composite improved its magnetic properties—that is, saturation magnetization and coercivity—probably because of the alignment of the hexaferrite platelet particles. Post-plastic deformation may represent a new process to complement conventional slurry-pressing under a magnetic field, for obtaining good magnetic properties in a magnetic-particle-dispersed composite. 相似文献
7.
Shinichi Kikkawa Akio Kijima Ken Hirota † Osamu Yamamoto † 《Journal of the American Ceramic Society》2002,85(3):721-723
Zirconia was prepared by firing the coprecipitate from ZrOCl2 and AlCl3 mixed aqueous solution with ammonia. When fired above 600°C, the products were fine crystalline tetragonal zirconia of crystallite size <10 nm. In previous studies, the tetragonal phase had been assumed to be a (Zr1− x 4+ Al x 3+ )O2− x /2 solid solution, where x ≤ 0.25. However, X-ray diffraction pattern simulation and Al K -edge XANES spectroscopy confirmed the present product to be a mixture of t -ZrO2 fine powder with a small amount of δ-Al2 O3 of very low crystallinity, even below the expected compositional range of x ≤ 0.25 in the (Zr1− x 4+ Al x 3+ )O2− x /2 solid solution. 相似文献
8.
两步烧结法制备纳米氧化钇稳定的四方氧化锆陶瓷 总被引:1,自引:0,他引:1
采用共沉淀法制备纳米氧化钇稳定的四方氧化锆(yttria stabilized tetragonal zirconia,3Y-TZP)粉体。利用X射线衍射、N2吸附–脱附等温线,透射电子显微镜对3Y-TZP粉体的物理性能和化学性能进行表征。研究了纳米3Y-TZP粉体的烧结曲线,分析了3Y-TZP素坯在烧结过程中的致密化行为和显微结构,探讨了两步烧结工艺对3Y-TZP纳米陶瓷微观结构的影响。结果表明:采用共沉淀法,在600℃煅烧2h后,可获得晶粒尺寸为13nm、晶型发育良好、团聚较少的纳米3Y-TZP粉体;采用两步烧结法,将素坯升温至1200℃保温1min后,再降温到1050℃保温35h,可获得相对密度大于98%,晶粒尺寸约为100nm的3Y-TZP陶瓷。两步烧结法通过控制煅烧温度和保温时间,利用晶界扩散及其迁移动力学之间的差异,使晶粒生长受到抑制,样品烧结致密化得以维持,实现在晶粒无显著生长前提下完成致密化。 相似文献
9.
10.
Microstructure and Phase Stability of Yttria-Doped Tetragonal Zirconia Polycrystals Heat Treated in Nitrogen Atmosphere 总被引:2,自引:0,他引:2
Tai-Joo Chung Huesup Song Gyeung-Ho Kim Doh-Yeon Kim 《Journal of the American Ceramic Society》1997,80(10):2607-2612
The low-temperature degradation of zirconia (ZrO2 ) that was doped with 3 mol% yttria (Y2 O3 ) (3Y-TZP) was prevented by the heat treatment of sintered specimens in nitrogen. The heat treatment of sintered specimens resulted in a surface layer that was stabilized by nitrogen ions, whereas the interior was only slightly affected by the heat treatment. X-ray diffractometry and transmission electron microscopy analyses revealed that the stabilized surface layer consisted of cubic grains with tetragonal precipitates. Although the presence of the surface layer decreased the strength of the sintered 3Y-TZP, the strength of nitrified specimens was maintained when low-temperature annealing was applied. 相似文献
11.
Masayuki Imose Akihiro Ohta Yoshihiko Takano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1998,81(4):1050-1052
Mullite/Y-TZP composites in the mullite-rich region, using powders of mullite prepared via the hydrazine method and a commercially available zirconia compound (ZrO2 (2Y)), have been fabricated by sintering for 3 h at 1450°C in air. The grain sizes of mullite and ZrO2 (2Y) are changed with increased ZrO2 (2Y) content; the former decreases from 0.25 µm to 0.13 µm, and the latter increases from 0.21 µm to 0.35 µm. High strength (780 MPa) and fracture toughness (5.4 MPam1/2 ) are obtained in the 50/50 (vol%) mullite/ZrO2 (2Y) composite with 99.6% of theoretical density. 相似文献
12.
Felipe Gutiérrez-Mora Diego Gómez-García Manuel Jiménez-Melendo Arturo Domínguez-Rodríguez Rachman Chaim 《Journal of the American Ceramic Society》2005,88(6):1529-1535
High temperature mechanical behavior of nanocrystalline 1.7 mol% (3 wt%) yttria tetragonal zirconia polycrystals (nc-YTZP) was characterized by compression creep tests. The hot isostatically pressed nc-YTZP with mean grain size of 120 nm was subjected to grain growth to obtain grain sizes in the range of 120–310 nm. Direct measurements of the creep parameters were performed in the temperature range 1150°–1300°C and stress range 5–400 MPa. The strain rates at 1150°C ranged between 2 × 10−7 and 9 × 10−5 s−1 when increasing the stress from 15 to 400 MPa. Values of the stress exponent, n =2.0±0.3, and the activation energy, Q =630±40 kJ/mol, were obtained for all test conditions. A value of the grain size exponent, p =1.5±0.3, was obtained at 1150°C in the stress range studied. Detailed microstructural observations revealed the absence of glassy phase at the grain boundaries. The creep parameters were compared with those from the literature, and the results were discussed in terms of the model recently developed by the authors, with a reasonable agreement. 相似文献
13.
Tai-Joo Chung † Jong-Sook Lee Doh-Yeon Kim Huesup Song 《Journal of the American Ceramic Society》1999,82(11):3193-3199
Sintered tetragonal-zirconia polycrystals (TZP) were embedded in a zirconium nitride powder bed and heat-treated at various temperatures. Surface layers of the TZP specimens were transformed to a stabilized cubic-zirconia by nitrogen incorporation, and their thickness was observed to increase by a parabolic rate law. The nitrogen diffusivity was evaluated from the temperature dependence of the nitridation rate. The microstructure of the nitrided layer was composed of different zones of equiaxed and columnar grains. The columnar grains were developed along the nitrogen flux lines. The observed microstructural evolution was explained in terms of nucleation and growth kinetics of nitridation. 相似文献
14.
Characterization and Sintering of Reactive Cerium(IV) Oxide Powders Prepared by the Hydrazine Method 总被引:1,自引:0,他引:1
Singo Nakane Toshiaki Tachi Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1997,80(12):3221-3224
Nanocrystalline cerium(IV) oxide (CeO2 ) powders have been prepared by adding hydrazine monohydrate to an aqueous solution of hydrous cerium nitrate (Ce(NO3 )3 ·6H2 O), followed by washing and drying. The lattice parameter of the as-prepared powder is a = 0.5415 nm. The powder characteristics and sinterability of reactive CeO2 have been studied. The surface areas of powders that have been heated at low temperatures are high, and these surface areas do not decrease to 10 m2 /g until the temperature is >1200°C. Crystallite size and particle size are strongly dependent on the heating temperature. Optimum sintered densities are obtained by calcining in the temperature range of 700°–800°C. Ceramics with almost-full density can be fabricated at a temperature as low as 1150°C. 相似文献
15.
Noriyuki Yoshida Yoshihiko Takano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1998,81(8):2213-2215
Picrochromite (MgCr2 O4 ) crystallizes at 480° to 530°C from an amorphous material prepared by the hydrazine method. The MgCr2 O4 powders were characterized for particle size and surface area. Individual particles tend toward a hexagonal morphology above 1000°C. Dense MgCr2 O4 ceramics (99.5% of theoretical) with an average grain size of 2 μm have been fabricated by spark plasma sintering for 5 min at 1400°C and 30 MPa. Their fracture toughness and bending strength are 3.7 MPa·m1/2 and 310 MPa, respectively. 相似文献
16.
Hiroki Kondo Tohru Sekino Norihito Tanaka Tadachika Nakayama Takafumi Kusunose Koichi Niihara 《Journal of the American Ceramic Society》2005,88(6):1468-1473
Dense ceramic/metal nanocomposite has been fabricated by internal reduction method, which includes a two-step process: sintering of ceramic–metal oxide solid solution and subsequent heat treatment in a reducing atmosphere to precipitate metal nanoparticles. This novel technique has been applied to yttria-stabilized tetragonal zirconia (Y-TZP) and nickel oxide (NiO) system to fabricate Y-TZP/Ni nanocomposite. Dense Y-TZP and 0.3 mol% NiO solid solution ceramic was successively prepared by the pressureless sintering, and Y-TZP/Ni was fabricated by the internal reduction treatment. The obtained Y-TZP/Ni nanocomposite possessed characteristic intragranular nanostructure with nano-sized metallic Ni particles of around 20 nm. Fracture toughness of both the solid solution and nanocomposite was remarkably improved because of the solid solution of NiO into Y-TZP and resultant destabilization of the tetragonal phase, and the Y-TZP/Ni nanocomposite was still destabilized by the remaining nickel solution after the reduction. The nanocomposite exhibited ferromagnetism, while the Y-TZP–NiO solid solution had diamagnetic nature. Comparison of saturation magnetization values revealed that 39.5 at.% of introduced nickel was reduced to metallic nanoparticle, proving the existence of residual NiO solute in zirconia that contributed to higher toughness value than the monolithic Y-TZP. It is concluded that the introduced internal reduction method is a suitable process to achieve multifunctional ZrO2 /Ni nanocomposite with high toughness and coexistent magnetic characteristic. 相似文献
17.
Microstructure and Fracture Toughness of Yttria-Daped Tetragonal Zirconia Polycrystal/Mullite Composites Prepared by an in Situ Method 总被引:1,自引:0,他引:1
Kiyoshi Okada Nozomu tsuka Richard J. Brook A. J. Moulson 《Journal of the American Ceramic Society》1989,72(12):2369-2372
Yttria-daped tetragonal zirconia polycrystal (Y-TZP)/ mullite composites were prepared by three methods: in situ whisker growth (IS), physical mixing (PM) of zirconia powder and mullite whiskers, and reaction sintering (RS). Microstructures and fracture toughness values were compared. All the composites with 15 vol% of mullite could be densified to more than 95% relative density by firing at 1500° to 1500°C for 10 h. The fracture toughness of the composites as measured by the indentation method showed a clear enhancement compared with that of pure Y-TZP; the ranking was Y-TZP ≦ RS composite < PM composite < IS composite. Enhancement of the fracture toughness in composites was found to relte strongly to the aspect ratio of mullite particles. 相似文献
18.
Vladimir V. Srdi Markus Winterer Horst Hahn 《Journal of the American Ceramic Society》2000,83(4):729-736
Powder synthesis and ceramic processing methods have to be improved to take full advantages of new, improved properties of nanocrystalline ceramics. Sintered nanocrystalline ceramics of pure, undoped zirconia are formed from nanocrystalline powder of optimized quality obtained by the chemical vapor synthesis (CVS) method. The as-synthesized CVS ZrO2 powder is nonagglomerated with a crystallite size of about 5 nm, narrow size distribution, and high crystallinity. On uniaxial compaction a transparent green body of ultrafine, uniform microstructure and narrow pore size distribution corresponding to the grain size distribution is formed, which is sintered under vacuum at 950°C into a transparent, fully dense ZrO2 ceramic with a grain size of 60 nm. 相似文献
19.
由氨基乙酸/硝酸盐闷烧方法制备了含8%Y2O3的纳米晶钇稳定氧化锆粉末,用火花等离子体烧结(SPS)、热压(HP)和传统烧结法(CS)研究了其致密性。SPS技术比其余烧结方法优异,能在较低温度和较短烧结时间获取具有均匀形态的致密化材料(≥96%)。经SiX5、热压和传统烧结方法制备的材料,其晶粒尺寸分别是0.21、0.37和12μm。材料的总电导率与晶粒尺寸并无明确关系,但SPS烧结材料的活化能比其余两种致密化方法的稍高。由Vickers压痕法测得的硬度与晶粒尺寸无关,而断裂韧性(由压痕法测得)随晶粒尺寸增大而轻微下降。 相似文献
20.
Sarit B. Bhaduri Amitavo Chakraborty R. Mohan Rao 《Journal of the American Ceramic Society》1988,71(9):410-C
Most zirconia-based toughened ceramics need specialized processes to achieve their desired properties. In this paper, we report the fabrication of toughened ceria-stabilized tetragonal zirconia polycrystal by conventional processing, i.e., ball milling and cold-pressing followed by sintering. We believe that ball milling works here because a somewhat coarser particle size is actually beneficial in this case. Although the samples were not fully dense (they need not be), a composition of ZrO2 -12 mol% CeO2 yielded a fracture toughness value of 14.1 MPa·m1/2 . This is comparable to values reported for materials processed by specialized techniques and can be rationalized in terms of R-curve behavior. 相似文献