共查询到20条相似文献,搜索用时 31 毫秒
1.
Tsugio Sato Tadashi Endo Masahiko Shimada 《Journal of the American Ceramic Society》1989,72(5):761-764
Ceria-doped tetragonal zirconia (Ce-TZP)/alumina (Al2 O3 ) composites were fabricated by sintering at 1450° to 1600°C in air, followed by hot isostatic pressing (postsintering hot isostatic pressing) at 1450°C and 100 MPa in an 80 vol% Ar–20 vol% O2 gas atmosphere. Dispersion of Al2 O3 particles into Ce-TZP was useful in increasing the relative density and suppressing the grain growth of Ce-TZP before hot isostatic pressing, but improvement of the fracture strength and fracture toughness was limited. Postsintering hot isostatic pressing was useful to densify Ce-TZP/Al2 O3 composites without grain growth and to improve the fracture strength and thermal shock resistance. 相似文献
2.
Kyoung Hun Kim Seung Hwan Shim Kwang Bo Shim Koichi Niihara Junichi Hojo 《Journal of the American Ceramic Society》2005,88(3):628-632
M-doped zinc oxide (ZnO) (M=Al and/or Ni) thermoelectric materials were fully densified at a temperature lower than 1000°C using a spark plasma sintering technique and their microstructural evolution and thermoelectric characteristics were investigated. The addition of Al2 O3 reduced the surface evaporation of pure ZnO and suppressed grain growth by the formation of a secondary phase. The addition of NiO promoted the formation of a solid solution with the ZnO crystal structure and caused severe grain growth. The co-addition of Al2 O3 and NiO produced a homogeneous microstructure with a good grain boundary distribution. The microstructural characteristics induced by the co-addition of Al2 O3 and NiO have a major role in increasing the electrical conductivity and decreasing the thermal conductivity, resulting from an increase in carrier concentration and the phonon scattering effect, respectively, and therefore improving the thermoelectric properties. The ZnO specimen, which was sintered at 1000°C with the co-addition of Al2 O3 and NiO, exhibited a ZT value of 0.6 × 10−3 K−1 , electrical conductivity of 1.7 × 10−4 Ω−1 ·m−1 , the thermal conductivity of 5.16 W·(m·K)−1 , and Seebeck coefficient of −425.4 μV/K at 900°C. The ZT value obtained respects the 30% increase compared with the previously reported value, 0.4 × 10−3 K−1 , in the literature. 相似文献
3.
Preparation of Nanometer-Sized α-Alumina Powders by Calcining an Emulsion of Boehmite and Oleic Acid
Chih-Peng Lin Shaw-Bing Wen Ting-Tai Lee 《Journal of the American Ceramic Society》2002,85(1):129-133
This study proposes a method to form ultrafine α-Al2 O3 powders. Oleic acid is mixed with Al(OH)3 gel. The gel is the precursor of the Al2 O3 . After it is mixed and aged, the mixture is calcined in a depleted oxygen atmosphere between 25° and 1100°C. Oleic acid evaporates and decomposes into carbon during the thermal process. Residual carbon prevents the growth of agglomerates during the formation of α-Al2 O3 . The phase transformation in this process is as follows: emulsion →γ-Al2 O3 →δ-Al2 O3 →θ-Al2 O3 →α-Al2 O3 . This process has no clear θ phase. Aging the mixed sample lowers the formation temperature of α-Al2 O3 from 1100° to 1000°C. The average crystallite diameter is 60 nm, measured using Scherrer's equation, which is consistent with TEM observations. 相似文献
4.
Lianjun Wang Ting Wu Wan Jiang Jianlin Li Lidong Chen 《Journal of the American Ceramic Society》2006,89(5):1540-1543
A novel method for the preparation of Al2 O3 –TiN nanocomposites was developed. A mixture of TiO2 , AlN, and Ti powder was used as the starting material to synthesize the Al2 O3 –TiN nanocomposite under 60 MPa at 1400°C for 6 min using spark plasma sintering. X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy were used for detailed microstructural analysis. Dense (up to 99%) nanostructured Al2 O3 –TiN composites were successfully fabricated, the average grain size being less than 400 nm. The fracture toughness ( K I C ) and bending strength (σb ) of the nanostructured Al2 O3 –TiN composites reached 4.22±0.20 MPa·m1/2 and 746±28 MPa, respectively. 相似文献
5.
YPSZ/Al2 O3 -platelet composites were fabricated by conventional and tape-casting techniques followed by sintering and HIPing. The room-temperature fracture toughness increased, from 4.9 MPa·m1/2 for YPSZ, to 7.9 MPa·m1/2 (by the ISB method) for 25 mol% Al2 O3 platelets with aspect ratio = 12. The room-temperature fiexural strength decreased 21% and 30% (from 935 MPa for YPSZ) for platelet contents of 25 vol% and 40 vol%, respectively. Al2 O3 platelets improved the high-temperature strength (by 110% over YPSZ with 25 vol% platelets at 800°C and by 40% with 40 vol% platelets at 1300°C) and fracture toughness (by 90% at 800°C and 61% at 1300°C with 40 vol% platelets). An amorphous phase at the Al2 O3 -platelet/YPSZ interface limited mechanical property improvement at 1300°C. The influence of platelet alignment was examined by tape casting and laminating the composites. Platelet alignment improved the sintered density by >1% d th , high-temperature strength by 11% at 800°C and 16% at 1300°C, and fracture toughness by 33% at 1300°C, over random platelet orientation. 相似文献
6.
Mullite ceramics were fabricated according to the recently developed reaction-bonded Al2 O3 (RBAO) technology. Green compacts consisting of mechanically alloyed Al, SiC, and Al2 O3 were heat-treated in two steps. During the first hold at 1200°C, Al and SiC were oxidized to form Al2 O3 and SiO2 . On further heating, mullite was formed which then sintered during the second hold at 1550°C. All reactions involved in the process were associated with volume expansions that almost compensated for the shrinkage on sintering. Processing details and microstructure development are discussed. Reaction-bonded mullite ceramics exhibit high fracture strength, e.g., 290 MPa at a density of 97% of theoretical density. 相似文献
7.
Ling-Feng He Yi-Wang Bao Yan-Chun Zhou 《Journal of the American Ceramic Society》2009,92(11):2751-2758
ZrO2 –Al2 O3 nanocrystalline powders have been synthesized by oxidizing ternary Zr2 Al3 C4 powders. The simultaneous oxidation of Al and Zr in Zr2 Al3 C4 results in homogeneous mixture of ZrO2 and Al2 O3 at nanoscale. Bulk nano- and submicro-composites were prepared by hot-pressing as-oxidized powders at 1100°–1500°C. The composition and microstructure evolution during sintering was investigated by XRD, Raman spectroscopy, SEM, and TEM. The crystallite size of ZrO2 in the composites increased from 7.5 nm for as-oxidized powders to about 0.5 μm at 1500°C, while the tetragonal polymorph gradually converted to monolithic one with increasing crystallite size. The Al2 O3 in the composites transformed from an amorphous phase in as oxidized powders to θ phase at 1100°C and α phase at higher temperatures. The hardness of the composite increased from 2.0 GPa at 1100°C to 13.5 GPa at 1400°C due to the increase of density. 相似文献
8.
Yosuke Matsumoto Ken Hirota Osamu Yamaguchi Suguru Inamura Hiroki Miyamoto Nobuaki Shiokawa Kazuhiro Tsuji 《Journal of the American Ceramic Society》1993,76(10):2677-2680
Amorphous Al2 O3 –ZrO2 composite powders with 5–30 mol% ZrO2 have been prepared by adding aqueous ammonia to the mixed solution of aqueous aluminum sulfate and zirconium alkoxide containing 2-propanol. Simultaneous crystallization of γ-Al2 O3 and t -ZrO2 occurs at 870°–980°C. The γ-Al2 O3 transforms to α-Al2 O3 at 1160°–1220°C. Hot isostatic pressing has been performed for 1 h at 1400°C under 196 MPa using α-Al2 O3 – t -ZrO2 composite powders. Dense ZrO2 -toughened Al2 O3 (ZTA) ceramics with homogeneous-dispersed ZrO2 particles show excellent mechanical properties. The toughening mechanism is discussed. The microstructures and t / m ratios of ZTA are examined, with emphasis on the relation between strength and fracture toughness. 相似文献
9.
Corrosion Behavior of Alumina Ceramics in Caustic Alkaline Solutions at High Temperatures 总被引:2,自引:0,他引:2
Tsugio Sato Shigeki Sato Akitsugu Okuwaki Syun-ichiro Tanaka 《Journal of the American Ceramic Society》1991,74(12):3081-3084
The corrosion rate and changes in the microstructure and fracture strength of alumina ceramics (93.0% Al2 O3 and 99.5% Al2 O3 ) were studied in 0.1 m to 25 m NaOH solutions at 150°C to 200°C, where m = mol/(kg of H2 O). The attack of the caustic alkaline solution started at the grain boundaries. Consequently, the corrosion resistance increased with decreasing SiO2 content in Al2 O3 ceramics, and the corrosion resistance of 99.5% pure Al2 O3 was similar to that of Si3 N4 ceramics. Since large pits are formed by corrosion, the surface area increased first and the apparent corrosion rate increased with time in the initial stage of the corrosion. The corrosion rate of Al2 O3 increased linearly with increasing NaOH concentration, and the activation energy was 102 kJ/mol. The fracture strength of corroded Al2 O3 decreased monotonically as the degree of dissolution of alumina increased. 相似文献
10.
Yury G. Gogotsi Franz Porz Viktor P. Yaroshenko 《Journal of the American Ceramic Society》1992,75(8):2251-2259
The study examines the effect which the composition of hot-pressed electroconductive ceramics has on their structure, mechanical properties, and oxidation behavior, for ceramics of the type AIN–Al2 O3 –42 wt% TiN, differing in the AIN/Al2 O3 ratio. The results are physico-mechanical property data, including density, hardness, strength, fracture toughness, and wear resistance. A correlation was found between the wear resistance and fracture toughness. The analysis of oxidation products revealed the formation of α-Al2 O3 and rutile in the temperature range from 600° to 1100°C and aluminum titanate above 1200°C. The spallation of the oxide layer caused low oxidation resistance of Al2 O3 -rich composites above 1250°C. The oxidation of composites was compared with the oxidation of pure TiN. The relationship is discussed between material properties, composition, phases, and processing parameters. 相似文献
11.
Akira Kato Hisao Yamashita Hiroshi Kawagoshi Shimpei Matsuda 《Journal of the American Ceramic Society》1987,70(7):157-C
Mixtures of La2 O3 and Al2 O3 with various La contents were prepared by co-precipitation from La(NO3 )3 and Al(NO3 )3 solutions and calcined at 800° to 1400°C. The addition of small amounts of La2 O3 (2 to 10 mol%) to Al2 O3 gives rise to the formation of lanthanum β-alumina (La 2 O3 ·11–14Al2 O3 ) upon heating to above 1000°C and retards the transformation of γ-Al2 O3 to α-Al2 O3 and associated sintering. 相似文献
12.
Robert Günther Thomas Klassen Birte Dickau Frank Gärtner Arno Bartels Rüdiger Bormann 《Journal of the American Ceramic Society》2001,84(7):1509-1513
New (inter)metallic-ceramic composites for high-temperature structural and functional applications are prepared via high-energy ball milling. During compaction by pressureless sintering, dense Al2 O3 /Ti-based alloy composites are formed that consist of inter-connected networks of the ceramic and the (inter)metallic phases. Ti-Al-V/Al2 O3 and Ti-Al-Nb/Al2 O3 composites show enhanced damage tolerance over monolithic Al2 O3 , i.e ., fracture toughnesses up to 5.6 MPa·m0.5 and bending strengths up to 527 MPa. The resistance against abrasive wear is almost doubled with respect to monolithic Al2 O3 ceramic. Electrical resistivity scales with the ceramic volume fraction and ranges between 0.3 mΩ·cm and 55.1 mΩ·cm, with only a weak temperature dependence ≤700°C. 相似文献
13.
Thermal Shock Resistance of Sintered Alumina/Silicon Carbide Nanocomposites Evaluated by Indentation Techniques 总被引:1,自引:0,他引:1
The thermal shock resistance of sintered Al2 O3 /1, 2.5, and 5 vol% SiC nanocomposites was studied using two indentation techniques. In the first technique, "indentation thermal shock" measurements were made of the extension of median/radial cracks around Vickers indentations after quenching from various temperatures (up to 480°C) into a bath of boiling water. This technique allowed a critical thermal shock temperature, Δ T C Ind , to be quantitatively evaluated. In the second technique, "indentation fatigue" tests were conducted on the thermally shocked specimens; repeated indentations were made at the same site, and the number of load cycles needed to initiate lateral fracture was measured. The results showed that nanocomposites with an addition of SiC nanophase as low as 1 vol% had a thermal shock resistance superior to that of pure Al2 O3 . 相似文献
14.
Osamu Yamaguchi Daijo Tomihisa Tatsuji Uegaki Kiyoshi Shimizu 《Journal of the American Ceramic Society》1987,70(11):335-C
In the system Ta2 O3 -Al2 O5 solid solutions of metastable δ-Ta2 O5 (hexagonal) are formed up to 50 mol% Al2 O3 from amorphous materials prepared by the simultaneous hydrolysis of tantalum and aluminum alkoxides. The values of the lattice parameters decrease linearly with increasing Al2 O3 , content. The to β-Ta2 O5 (orthorhombic, low-temperature form) transformation occurs at ∼950°C. The solid solution containing 50 mol% Al2 O3 transforms at 1040° to 1100°C to orthorhombic TaAlO4 . Orthorhombic TaAlO4 contains octahedral TaO6 groups in the structure. 相似文献
15.
High-purity aluminum foil was used to join alumina substrates directly in air at temperatures ranging from 800° to 1200°C and soak times of 1–100 h. It was found that the bend strengths of the resulting Al2 O3 /Al/Al2 O3 joints generally increase with increasing brazing temperature and time, with a maximum bend strength of 135 MPa on average achieved in samples joined at 1200°C for 100 h. Additionally it was determined that measurable ductility is retained in the joint even after exposure under extended high-temperature conditions. During joining, an Al2 O3 scale forms along the interface between the aluminum and adjacent substrates. An increase in brazing temperature and/or time leads to intergrowth and sintering between this thermally grown oxide layer and the substrate surface, which appears to be the primary source of improved joint strength. Fracture analysis indicates that the Al2 O3 /Al/Al2 O3 joints generally fail via one of three mechanisms, (1) by de-bonding along the foil/substrate interface in specimens that were joined at low temperature or held at temperature for an insufficient period of time; (2) by ductile rupture in specimens that were joined at conditions that promoted sintering between the oxidized foil and adjacent alumina faying surfaces, but left behind a continuous residual aluminum layer within the joint; or (3) by mixed-mode fracture in specimens joined at high temperature and long exposure times, in which the thermally grown alumina that forms between the two substrates is interrupted by dispersed pockets of residual aluminum metal. 相似文献
16.
Yoshihiko Takano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》2001,84(10):2445-2447
Intermetallic CoAl powder has been prepared via self-propagating high-temperature synthesis (SHS). Dense CoAl materials (99.6% of theoretical) with the combined additions of ZrO2 (3Y) and Al2 O3 have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The microstructures are such that tetragonal ZrO2 (0.3 μm) and Al2 O3 (0.5 μm) particles are located at the grain boundaries of the CoAl (8.5 μm) matrix. Improved mechanical properties are obtained; especially the fracture toughness and the bending strength of the materials with ZrO2 (3Y)/Al2 O3 = 16/4 mol% are 3.87 MPa·m1/2 and 1080 MPa, respectively, and high strength (>600 MPa) can be retained up to 1000°C. 相似文献
17.
Reaction-bonded Al2 O3 (RBAO) ceramics were fabricated starting from mechanically alloyed Al2 O3 /Al, Al2 O3 / Al/ZrO2 , and Al2 O3 /Al/ZrO2 /Zr mixtures. Isopressed compacts were heat-treated in air up to 1550°C. Reaction-bonding mechanisms, kinetics, and the influence of ZrO2 and Zr additions are investigated. Independent of additive, oxidation of Al proceeds both as solid/gas and liquid/gas reaction, and the reaction kinetics follow a parabolic rate law. The reaction rate depends strongly on the particle size of Al. The activation energy of the reaction depends essentially on green density. Below the melting temperature of Al, in samples containing 45 vol% Al and 55 vol% Al2 O3 , it is 112 and 152 kJ/mol at ∼64% and ∼74% TD, respectively, while above the melting temperature, it lies in the range ∼ 26–33 kJ/mol. Zr additions reduce the activation energy to some extent. Samples with only ZrO2 additions exhibit nearly the same activation energies as ZrO2 -free samples, though ZrO2 has a very positive effect on the microstructural development in RBAO ceramics. Microstructure evolution and some strength data of RBAO bodies are also reported. 相似文献
18.
Reaction-Bonded Mullite/Zirconia Composites 总被引:4,自引:0,他引:4
Srinivasarao Lathabai David G. Hay Florian Wagner Nils Claussen 《Journal of the American Ceramic Society》1996,79(1):248-256
The feasibility of fabricating dense, low-shrinkage, mullite/ ZrO2 composites based on the reaction bonding of alumina (RBAO) process and the reaction sintering of zircon is examined. Compacts pressed from an attrition-milled powder mixture of Al, A12 O3 and zircon were heated in air according to a two-step heating cycle. The phase evolution and microstructural development during reaction bonding were traced by X-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy on samples extracted from various points along the heating cycle. It is seen that, as in conventional RBAO, AI oxidizes to γ-Al2 O3 which then transforms to α-AI2 O3 between 1100° and 1200°C. The zircon dissociation commences at ∼1400°C and is practically complete by 1500°C. Mullite enriched in Al2 O3 forms initially, but 3:2 stoichiometry is attained in the final product which consists of mullite, t - and m-ZrO2 , and residual α-AI2 O3 . The flexure strength of the composite is superior to that of pure mullite, and ∼80% of the strength is retained up to 1200°C. Although there was no toughness enhancement relative to mullite, this should be achievable by optimizing the fabrication procedure. 相似文献
19.
Phase Transformation of Diphasic Aluminosilicate Gels 总被引:1,自引:0,他引:1
Aluminosilicate gels with compositions Al2 O2 /SiO2 and 2 were prepared by gelling a mixture of colloidal pseudo-boehmite and a silica sol prepared from acid-hydrolyzed Si(OC2 H5 )4 . Upon heating the pseudo-boehmite transforms to γ-Al2 O3 around 400°C, then to δ-Al2 O3 at 1050°C, and at 1200°C reacts with amorphous SiO2 to form mullite. Some twinned θ-Al2 O3 forms before mullite. Nonstoichiometric specimens have a similar transformation sequence, but form mullite grains with inclusions of either Al2 O3 or cristobalite, often associated with dislocation networks or micropores. Mullite grains are formed by nucleation and growth and have equiaxed shape. 相似文献
20.
Preparation and Characterization of Aluminum Borate 总被引:2,自引:0,他引:2
Siba P. Ray 《Journal of the American Ceramic Society》1992,75(9):2605-2609
Aluminum borate, 9Al2 O3 ·2B2 O3 or Al18 B4 O33 , was synthesized by the reaction of stoichiometric amounts of α-Al2 O3 and B2 O3 . The Al18 B4 O33 material was formed into a dense ceramic by pressureless sintering with CaO, MgO, or CaAl2 B2 O7 additives. The material was characterized by low bulk density, moderate coefficient of thermal expansion (3 × 10−6 /°C to 5 × 10−6 /°C), moderate strength (210 to 324 MPa), and low dielectric constant. 相似文献