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1.
Aluminum titanate (Al2 TiO5 ) is an excellent refractory and thermal shock resistant material due to its relatively low-thermal expansion coefficient and high melting point. However, Al2 TiO5 is only thermodynamically stable above 1280°C and undergoes a eutectoid decomposition to α-Al2 O3 and TiO2 (rutile) in the temperature range of 900°–1280°C. In this paper, we describe the use of high-temperature neutron diffraction to study the properties of self-recovery in Al2 TiO5 when it is annealed at ≥1300°C in air. It is shown that the process of decomposition in Al2 TiO5 is reversible and that self-recovery occurs readily when decomposed Al2 TiO5 is reheated above 1300°C. It is further shown that the existence of a temperature range (900°–1280°C) in which Al2 TiO5 is prone to decomposition can be explained by the competing dominance of self-recovery at ≥1280°C and decomposition at ≤1280°C. 相似文献
2.
Alumina–aluminum titanate–titania (Al2 O3 –Al2 TiO5 –TiO2 ) nanocomposites were synthesized using alkoxide precursor solutions. Thermal analysis provided information on phase evolution from the as-synthesized gel with an increase in temperature. Calcination at 700°C led to the formation of an Al2 O3 –TiO2 nanocomposite, while at a higher temperature (1300°C) an Al2 O3 –Al2 TiO5 –TiO2 nanocomposite was formed. The nanocomposites were uniaxially compacted and sintered in a pressureless environment in air to study the densification behavior, grain growth, and phase evolution. The effects of nanosize particles on the crystal structure and densification of the nanocomposite have been discussed. The sintered nanocomposite structures were also characterized for dielectric properties. 相似文献
3.
Hans Wohlfromm Pilar Pena José S. Moya Joaquín Requena 《Journal of the American Ceramic Society》1992,75(12):3473-3476
Al2 TiO5 formation in Al2 O3 /TiO2 multilayer composites obtained by slip casting has been studied in the temperature interval ranging from 1200° to 1450°C. It has been found that nucleation plays a fundamental role in Al2 TiO5 formation. Furthermore, it has been observed that initial growth of Al2 TiO5 is substantially enhanced when in contact with TiO2 . 相似文献
4.
MASAYUKI ISHITSUKA TSUGIO SATO TADASHI ENDO MASAHIKO SHIMADA 《Journal of the American Ceramic Society》1987,70(2):69-71
Aluminum titanate solid solutions with empirical formulas of Al2 Ti1-x Zrx O5 , Al6(2-x)(6+x) Si6x/(6+x) □6x/(6+x) TiO5 , and Al2(1-x) Mgx Ti1+x O5 were synthesized by reaction sintering and annealed at 900° to 1300°C in air to evaluate the thermal stability. Substitution of Al in Al2 TiO5 by Si and 2Al by Mg and Ti ions to form solid solutions such as AI6(2-x)/(6+x)l-Si 6x/(6+x)□6x/(6+x) TiO5 , and Al2(1-x) Mgx Ti1+x O5 was effective in controlling the thermal decomposition, but substitution of Ti by Zr had little effect. 相似文献
5.
Aluminum titanate (Al2 TiO5 ) is a promising engineering material because of its low thermal expansion coefficient, excellent thermal shock resistance, good refractoriness, and nonwetting with most metals. However, it is susceptible to thermal dissociation in the temperature range of 800°–1280°C, which degrades its desirable properties. In this work, the various factors controlling the thermal instability of Al2 TiO5 in the temperature range of 20°–1100°C have been characterized by neutron diffraction to study the temperature- and time-dependence structural changes in real time during the process of thermal decomposition. Results show that the thermal stability of Al2 TiO5 is strongly influenced by temperature, dwell time, heating rate, phase purity, grain size, atmosphere, and additives. Possible mechanisms of structure stabilization and instability in Al2 TiO5 under different conditions are discussed. 相似文献
6.
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
7.
A process for production of near-net-shape mullite-matrix ceramic composites at ≤1300°C has been achieved by reaction-bonding Al2 O3 , silicon, mullite seeds, and eutectics of Al2 O3 –SiO2 –mixed-rare-earth oxide. The fusion temperature of the eutectic composition utilized is 1175°C. This liquid phase facilitates silicon oxidation, mullitization, and sintering. Mullite phase develops with low residual Al2 O3 when 7.5 wt% mixed-rare-earth oxide and 5 wt% mullite seeds are used. The final sinter is >90% of theoretical density, >90% mullite (by quantitative XRD), and suffers 2.2% sintering shrinkage. 相似文献
8.
Ronald E. Hanson Erich H. Kisi Heather J. Goodshaw Jennifer S. Forrester 《Journal of the American Ceramic Society》2009,92(6):1339-1346
In part I of this work, it was found that titanium (Ti) wire encapsulated within mechanically milled alumina powder and sintered at 1350°C forms potentially useful microcavities due to the consolidation of Kirkendall porosity. Here a series of samples sintered at 1350°C in the range 0–24 h has shown the remarkable way in which these cavities form. The cavity has already started in samples quenched from the top of the heating ramp (0 min at 1350°C). It is surrounded by a diffusion zone ∼300 μm in diameter, which does not change size throughout the firing process although the contents change markedly. The diffusion zone microstructure is initially complex with phase sequence TiO2 /Al2 O3 /TiO2 +Al2 O3 /Al2 TiO5 . Microstructure evolution may be summarized as outward growth of the cavity accompanied by inward growth of the Al2 TiO5 resulting in a ∼190-μm-diameter cavity surrounded by a 50-μm-thick layer of Al2 TiO5 . The formation of the cavity and surrounding microstructure is discussed although some features, such as the nucleation of Al2 TiO5 in the part of the diffusion zone furthest from the Ti source and the ring of Al2 O3 , which persists in between Ti-rich parts of the diffusion zone are still poorly understood. 相似文献
9.
The formation of Al2 TiO5 has been studied in equimolar Al2 O3 -TiO2 powder mixtures of ∼1μm particle sizes and moderate purity (∼99.8 wt%) at temperatures around 1300°C, where the free energy of formation is very small. Micro-structural development and reaction kinetics indicate that different mechanisms operate depending on the advancement of the reaction. The rapid initial reaction stage is interpreted as the nucleation-growth of Al2 TiO5 cells in a virtually non-reacting matrix. The final reaction stage corresponds to the slow diffusion-controlled elimination of Al2 O3 and TiO2 dispersoids trapped during the growth of the initial Al2 TiO5 cells. 相似文献
10.
A type of new low sintering temperature ceramic, Li2 TiO3 ceramic, has been found. Although it is difficult for the Li2 TiO3 compound to be sintered compactly at temperatures above 1000°C for the volatilization of Li2 O, dense Li2 TiO3 ceramics were obtained by conventional solid-state reaction method at the sintering temperature of 900°C with the addition of ZnO–B2 O3 frit. The sintering behavior and microwave dielectric properties of Li2 TiO3 ceramics with less ZnO–B2 O3 frit (≤3.0 wt%) doping were investigated. The addition of ZnO–B2 O3 frit can lower the sintering temperature of the Li2 TiO3 ceramics, but it does not apparently degrade the microwave dielectric properties of the Li2 TiO3 ceramics. Typically, the good microwave dielectric properties of ɛr =23.06, Q × f =32 275 GHz, τf = 35.79 ppm/°C were obtained for 2.5 wt% ZnO–B2 O3 frit-doped Li2 TiO3 ceramics sintered at 900°C for 2 h. The porosity was 0.08%. The Li2 TiO3 ceramic system may be a promising candidate for low-temperature cofired ceramics applications. 相似文献
11.
Nanoparticles of strontium titanates (SrTiO3 , Sr2 TiO4 ) and lead titanate (PbTiO3 ) have been obtained using reverse micelles as nanoreactors. Powder X-ray diffraction studies of the powders after calcining at 800°C show monophasic SrTiO3 , Sr2 TiO4 , and PbTiO3 . X-ray line broadening studies and transmission electron microscopic studies show spherical grains of 30–40 nm size for strontium titanates, while PbTiO3 is obtained in the form of nanorods. The dielectric constant of SrTiO3 and Sr2 TiO4 is found to be 90 and 30, respectively, (at 100 kHz) for samples sintered at 1000°C. PbTiO3 shows a dielectric constant of 160 (at 100 kHz) after sintering at 900°C. The dielectric constant of Sr2 TiO4 (with temperature) is highly stable. The temperature variation studies of the dielectric constant of PbTiO3 show a ferroelectric phase transition at 490°C (1 kHz). The T c varies with frequency and is found to decrease to 470°C at 100 kHz. 相似文献
12.
Preparation of Titanium Nitride/Alumina Laminate Composites 总被引:2,自引:0,他引:2
Jing-Xian Zhang Zheng-Ren Huang Dong-Liang Jiang Shouhong H. Tan Zhijian Shen Mats Nygren 《Journal of the American Ceramic Society》2002,85(5):1133-1138
A preparation route for TiN/Al2 O3 laminate composites has been described. A water-based process using Al2 O3 and TiN slurries with solids contents of 40 and 35 vol%, respectively, was used to make TiN and Al2 O3 tapes. The removal of the binder was monitored by weight-loss measurements in a thermogravimetry unit. Bodies composed of Al2 O3 and TiN tapes were densified at temperatures of 1400° and 1500°C using the Spark Plasma Sintering® (SPS) technique. Densities of >98% of the theoretical densities were approached. Crack-free and almost fully densified TiN/Al2 O3 compacts were prepared by heating the burned-out green bodies to the final sintering temperature (1500°C) at a rate of 100°C/min, and with a holding time of 5–10 min, under a pressure of 75 MPa. The microstructures of the obtained compacts were studied using scanning electron microscopy. Grain sizes in the sintered Al2 O3 and TiN compacts were similar to those of the precursor powders. Hardness and indentation fracture toughness were measured at room temperature, and the monolithic compacts as well as the laminate composites exhibited anisotropic mechanical behavior; i.e., the cracks propagated much more easily in a direction parallel to the laminas than perpendicular to them. 相似文献
13.
Ki-Woong Chae† Doh-Yeon Kim Koichi Niihara 《Journal of the American Ceramic Society》1995,78(1):257-259
The results obtained from the sintering of Al2 O3 –50TiC (in weight percent) composite in the temperature range from 1650° to 1800°C with addition of Y2 O3 are presented. Densification is accelerated by the formation of liquid at temperatures above 1750°C, and 99% of theoretical density can be achieved by vacuum sintering at 1800°C for 15 min. The liquid presented at the sintering temperature is crystallized to YAG (Y3 Al5 O12 ) during cooling. 相似文献
14.
Mark I. Pownceby Keri K. Constanti-Carey Michael J. Fisher-White 《Journal of the American Ceramic Society》2003,86(6):975-980
Subsolidus phase equilibria in the system Fe2 O3 –Al2 O3 –TiO2 were investigated between 1000° and 1300°C. Quenched samples were examined using powder X-ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M3 O5 solid solution series between end members Fe2 TiO5 and Al2 TiO5 , (b) a miscibility gap along the Fe2 O3 –Al2 O3 binary, (c) an α-M2 O3 ( ss ) ternary solid-solution region based on mutual solubility between Fe2 O3 , Al2 O3 , and TiO2 , and (d) an extensive three-phase region characterized by the assemblage M3 O5 +α-M2 O3 ( ss ) + Cor( ss ). A comparison of results with previously established phase relations for the Fe2 O3 –Al2 O3 –TiO2 system shows considerable discrepancy. 相似文献
15.
By a combination of solid-state sintering and quenching experiments the validity of calcium hexaluminate as a stable phase and the extent of its primary field in the system CaO–Al2 O3 –SiO2 have been established. The size of the primary field is considerably reduced from that suggested by earlier work. The anorthite-corundum-calcium hexaluminate invariant point has been relocated at 28.0% CaO, 39.7% Al2 O2 , and 32.3% SiO2 and at 1405°± 5°C. 相似文献
16.
The preparation of near stoichiometric spinel and alumina-rich spinel composites from Al2 O3 and MgO powders with the addition of Na3 AlF6 up to 4 wt% in the temperature range 700°–1600°C was studied; 98 wt% spinel containing 72 wt% Al2 O3 can be produced from the mixture of 72 wt% (50 at.%) Al2 O3 + 28 wt% (50 at.%) MgO powders with the addition of 1 wt% Na3 AlF6 fired at 1300°C for 1 h. Spinels containing 81–85 wt% Al2 O3 can be produced from either the mixture of 90 wt% (78 at.%) Al2 O3 + 10 wt% (22 at.%) MgO or the mixture of 95 wt% (88 at.%) Al2 O3 + 5 wt% (12 at.%) MgO powders with the addition of 4 wt% Na3 AlF6 in the temperature range 1300°–1600°C by using a torch-flame firing for 3 min, followed by quenching in water, while the same system under slow cooling in a furnace results in spinel containing 74–76 wt% Al2 O3 . Microscopic studies indicate that the alumina-rich spinel composites consist of a continuous majority spinel phase and an isolated minority corundum phase, regardless of slow cooling in a furnace or quenching in water. 相似文献
17.
Yoshiho Ito Shiro Shimada Michio Inagaki 《Journal of the American Ceramic Society》1995,78(10):2695-2699
Ba1– x Pb x TiO3 powder with a fixed composition was prepared by the reaction of BaTiO3 powders with molten PbCl2 at various PbCl2 /BaTiO3 molar ratios at 600° and 800°C in a nitrogen atmosphere. When 0.1 μm powder was used, the reaction was finished when x = 0.9. Two phases of BaTiO3 and a solid solution of Ba1– x Pb x TiO3 coexisted, but the final phase gave a solid solution of Ba1– x Pb x TiO3 at 800°C. When 0.5 μm powder was used, the two phases coexisted in the products at 600°C at PbCl2 /BaTiO3 = 1.0. A sintered compact of Ba1– x Pb x TiO3 powders solid solution was prepared by hot isostatic pressing, and its dielectric constant was measured in the temperature range 20°–550°C. 相似文献
18.
Xianran Xing Jun Luo Guirong Liu Lijie Qiao 《Journal of the American Ceramic Society》2006,89(3):1125-1128
A multi-component substitution of Co and Ni was incorporated into ZnTiO3 to form pure hexagonal Zn1− x (Co1/2 Ni1/2 ) x TiO3 ( x =0,0.8,0.9,1.0) dielectric ceramic powders by a modified sol–gel route, following heat treatments at 600°C for 3 h and at 800°C for 6 h. Differential scanning calorimetry measurements revealed that the order of increasing thermal stability of solid solution compound Zn1− x (Co1/2 Ni1/2 ) x TiO3 was ZnTiO3 (945°C), Zn0.1 Ni0.9 TiO3 (1346°C), Zn0.1 (Co1/2 Ni1/2 )0.9 TiO3 (1390°C), and Zn0.1 Co0.9 TiO3 (>1400°C). Both the dielectric constant and loss tangent reached a maximum at x =0.8 and then decreased with solubility, x , and measurement frequency. 相似文献
19.
Yoshihiro Hirata Kazuyoshi Sakeda Yumi Matsushita Kinji Shimada Yoshimi Ishihara 《Journal of the American Ceramic Society》1989,72(6):995-1002
Submicrometer SiO2 -Al2 O3 powders with compositions of 46.5 to 76.6 wt% Al2 O3 were prepared by hydrolysis of mixed alkoxides. Phase change, mullite composition, and particle size of powders with heating were analyzed by DTA, XRD, IR, BET, and TEM. As-produced amorphous powders partially transformed to mullite and Al-Si spinel at around 980°C. The compositions of mullite produced at 1400° and 1550°C were richer in Al2 O3 than the compositions of stable mullite solid solutions predicted from the phase diagram of the SiO2 -Al2 O3 system. Particle size decreased with increasing Al2 O3 content. The sintered densities depended upon the amount of SiO2 -rich glassy phase formed during sintering and the green density expressed as a function of particle size. 相似文献
20.
Kiyoshi Itatani Minoru Hasegawa Mamoru Aizawa F. Scott Howell Akira Kishioka Makio Kinoshita 《Journal of the American Ceramic Society》1995,78(3):801-804
Ultrafine aluminum carbide (Al4 C3 ) powders with crystallite sizes of <40 nm were prepared by the pyrolyses of alkylaluminums, i.e., trimethylaluminum (Al(CH3 )3 : TMAL), triethylaluminum (Al(C2 H5 )3 : TEAL), triisobutylaluminum (Al(i-C4 H9 )3 : TIBAL) at a temperature between 950° and 1100°C. Although the pyrolysis of TMAL produced Al4 C3 at 950°C, the pyrolysis temperature of TEAL to produce Al4 C3 was raised up to 1100°C. The pyrolysis of TIBAL at 1100°C produced not only crystalline Al4 C3 but also amorphous oxycarbide. The TEAL-derived powder had the highest true density (2.89 g. cm−3 or 97% of the theoretical density) among the three kinds of powders. 相似文献