共查询到20条相似文献,搜索用时 15 毫秒
1.
Silvia Schicker Daniel E. García Igor Gorlov Rolf Janssen Nils Claussen 《Journal of the American Ceramic Society》1999,82(10):2607-2612
Wet milling of Al2 O3 -aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al2 O3 and Fe2 O3 /Al/Al2 O3 powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe2 O3 /Al/Al2 O3 powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al2 O3 powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8. 相似文献
2.
Adiabatic bulk modulus, Bs , of polycrystalline MgO and Al2 O3 was measured from 298° to 1473°K using the resonance technique. The Grüneisen constant, calculated from the measured bulk modulus, was constant over the whole temperature range (1.53 for MgO and 1.34 for Al2 O3 ). Another important parameter, , is constant at high temperature and is 3.1 for MgO and 3.6 for Al2 O3 . The Poisson's ratio increases linearly with temperature for MgO and Al2 O3 . To describe the change of bulk modulus with temperature a theoretical equation was verified by using the foregoing constants. A practical form of this theoretical equation is where Bs 0 is the adiabatic bulk modulus at 0°K, δ is the quantity , γ is the Grüneisen constant, H is the enthalpy. The experimental data are described very well by this equation, which is equivalent to the empirical equation suggested by Wachtman et al., Bs T = Bs 0 - CT exp (-Tc /T) , where C and Tc are empirical constants. 相似文献
3.
Yu Jia Yuji Hotta Kimiyasu Sato Koji Watari 《Journal of the American Ceramic Society》2006,89(3):1103-1106
ZrO2 –Al2 O3 nanocomposite particles were synthesized by coating nano-ZrO2 particles on the surface of Al2 O3 particles via the layer-by-layer (LBL) method. Polyacrylic acid (PAA) adsorption successfully modified the Al2 O3 surface charge. Multilayer coating was successfully implemented, which was characterized by ξ potential, particle size. X-ray diffraction patterns showed that the content of ZrO2 in the final powders could be well controlled by the LBL method. The powders coated with three layers of nano-ZrO2 particles, which contained about 12 wt% ZrO2 , were compacted by dry press and cold isostatically pressed methods. After sintering the compact at 1450°C for 2 h under atmosphere, a sintered body with a low pore microstructure was obtained. Scanning electron microscopy micrographs of the sintered body indicated that ZrO2 was well dispersed in the Al2 O3 matrix. 相似文献
4.
Manuel Belmonte Jose S. Moya Pilar Miranzo 《Journal of the American Ceramic Society》1995,78(6):1661-1667
The sintering behavior of an Al2 O3 compact containing uniformly dispersed Al2 O3 platelets has been investigated. The results reveal a significant decrease in the sintering rate as well as the formation of voids and cracklike defects in the presence of nonsinterable platelets. The addition of a small amount (2 vol%) of tetragonal-ZrO2 particles enhances the sintering rate, increases end-point density (∼99.5% of theoretical density) and prevents formation of sintering defects. 相似文献
5.
The dynamic stress intensity factors, which were determined with newly developed bar impact facilities and a new data reduction procedure, for an Al2 O3 ceramic and 29 vol% SiCw /Al2 O3 composite were virtually identical, thus indicating that the short SiC whiskers were ineffective under dynamic fracture. SEM studies revealed five distinct fracture morphologies with increased percentage area of transgranular fracture in both materials with rapid crack propagation. Also, the high dynamic stress intensity factor caused multiple microscopic crack planes to form and then join as the crack advanced. 相似文献
6.
Shyan-Lung Chung Yu-Cheng Sheu Ming-Shyong Tsai 《Journal of the American Ceramic Society》1992,75(1):117-123
SiO2 , Al2 O3 , and 3Al2 O3 .2SiO2 powders were synthesized by combustion of SiCl4 or/and AlCl3 using a counterflow diffusion flame. The SiO2 and Al2 O3 powders produced under various operation conditions were all amorphous and the particles were in the form of agglomerates of small particles (mostly 20 to 30 nm in diameter). The 3Al2 O3 .2SiO2 powder produced with a low-temperature flame was also amorphous and had a similar morphology. However, those produced with high-temperature flames had poorly crystallized mullite and spinel structure, and the particles, in addition to agglomerates of small particles (20 to 30 nm in diameter), contained larger, spherical particles 150 to 130 nm in diameter). Laser light scattering and extinction measurements of the particle size and number density distributions in the flame suggested that rapid fusion leading to the formation of the larger, spherical particles occurred in a specific region of the flame. 相似文献
7.
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
8.
David B. Marshall Peter E. D. Morgan Robert M. Housley Jeffrey T. Cheung 《Journal of the American Ceramic Society》1998,81(4):951-956
The compatibility of Al2 O3 and LaPO4 at temperatures up to 1600°C is examined. Provided the ratio of La to P was close to 1:1, no reactions were observed after 200 h at 1600°C. Moreover, the Al2 O3 /LaPO4 interface remained sufficiently weakly bonded to cause deflection of cracks, as reported previously. In the presence of excess P or La, reactions occurred as expected, forming AlPO4 in the case of excess P, and LaAlO3 and LaAl11 O18 in the case of excess La. 相似文献
9.
Ryan K. Roeder Kevin P. Trumble Keith J. Bowman' 《Journal of the American Ceramic Society》1997,80(1):27-36
Composites containing Ce-ZrO2 , Al2 O3 , and aligned Al2 O3 platelets were produced by centrifugal consolidation and pressureless sintering, followed by heat treatments at 1600°C for varied duration. Constituents in the consolidated microstructures were either uniformly distributed throughout or segregated into gradient layers, depending critically on platelet content. Quantitative image analysis was used to examine microstructure development with heat treatment. Changes in the volume fraction, dimensional anisotropy, and gradient of pores and platelets, as well as changes in the phase gradient, were quantified. Microstructure development was strongly dependent on the initial microstructure design attained from suspension processing. 相似文献
10.
The transformation of ultrafine powders (particle size, 0.01 to 0.04 μm) of the system ZrO2– Al2 O3 , prepared by spraying their corresponding nitrate solutions into an inductively coupled plasma (ICP) of ultrahigh temperature, was investigated. The powders were composed of metastable tetragonal ZrO2 ( mt- ZrO2 ) and γ-Al2 O3 . On heating, the mt- ZrO2 (or tetragonal ZrO2 , t -ZrO2 ) was retained up to 1200°C. At 1380°C the transformation to monoclinic ZrO2 ( m -ZrO2 ) occurred and the amount of the m -ZrO2 decreased with the increase in Al2 O3 content, thus indicating the stabilization of the t -ZrO2 by the Al2 O3 , which seems to be explained in terms of the retardation of grain growth. 相似文献
11.
Mamoun Medraj Robert Hammond William T. Thompson Robin A. L. Drew 《Journal of the American Ceramic Society》2003,86(4):717-26
The importance of aluminum nitride (AlN) stems from its application in microelectronics as a substrate material due to high thermal conductivity, high electrical resistance, mechanical strength and hardness, thermal durability, and chemical stability. Yttria (Y2 O3 ) is the best additive for AlN sintering. AlN densifies by a liquid-phase mechanism, where the surface oxide, Al2 O3 , reacts with Y2 O3 to form an Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is essential for optimizing the properties of AlN. The ternary phase diagram of the AlN–Al2 O3 –Y2 O3 was developed by Gibbs energy minimization using interpolation procedures based on modeling the binary subsystems. This paper aims at testing the resultant understanding experimentally at selected compositions using in situ high-temperature neutron diffractometry. These experimental results agree with the thermodynamic calculations of AlN–Al2 O3 –Y2 O3 . The ternary phase diagram has been constructed for the first time in this work. High-temperature neutron diffractometry has permitted real time measurement of the reactions involved in this ternary system, especially to determine the temperature range for each reaction, which would have been difficult to establish by other means. 相似文献
12.
Oxide crystallite formation and growth from freeze-dried sulfates were studied for the representative materials Al2 O3 and Fe2 O3 . Transmission and scanning electron micrographs showed the formation and growth of chainlike aggregates of crystallites. Aggregation occurred as part of the nucleation and growth of the oxide, and discrete oxide particles were never present. Orientation of the chain aggregates was related to the ice structure formed during freezing. X-ray line broadening data showed that crystallite size is a function of the 1/5 to 1/7 power of time for isothermal treatments. A qualitative analysis of material transport favored the surface diffusion mechanism. 相似文献
13.
Sang-Kee Lee Koji Takahashi § Masahiro Yokouchi Hiroyoshi Suenaga Kotoji Ando 《Journal of the American Ceramic Society》2004,87(7):1259-1264
Al2 O3 reinforced by SiC whiskers (Al2 O3 /SiC-W) was hot-pressed to investigate the fatigue strength of crack-healed specimens at high temperature. Semielliptical surface cracks of 100 μm surface length were introduced on each specimen surface. These specimens were crack-healed at 1300°C for 1 h in air, and static and cyclic fatigue strengths were systematically investigated at room temperature, 900° and 1100°C by three-point bending. The static and cyclic fatigue limits of the crack-healed specimens were more than 70% of the average bending strength at each testing temperature. Crack-healed specimens of Al2 O3 /SiC-W were not sensitive to static and cyclic fatigue at room temperature and high temperatures. Therefore, the combination of crack-healing and whisker reinforcement can play an important role in increasing static and cyclic fatigue strengths at high temperature. 相似文献
14.
15.
16.
Crystallographic notation for Al2 O3 is reviewed, with particular reference to the correct basis to be used in describing slip systems. A Groves-and-Kelly calculation showed that the combination of pyramidal slip on {11¯02}<11¯01> and basal slip on (0001){112¯0} will allow homogeneous deformation of Al2 O3 polycrystals. Furthermore, operation of either the {101¯1}<1¯011> or the {011¯2}<2¯021> slip system will also satisfy the Von Mises criterion, since each system is capable of 5 independent deformation modes. Electron microscopy of an Al2 O3 polycrystal deformed ≅5% at 1150°C under a hydrostatic confining pressure confirmed that pyramidal slip had occurred. 相似文献
17.
18.
Tai-Il Mah Kristin A. Keller Sankar Sambasivan Ronald J. Kerans 《Journal of the American Ceramic Society》1997,80(4):874-878
Heat treatments in several environments were performed on a series of compounds in the Al2 O3 and Y2 O3 system: Al2 O3 Y3 Al5 O12 eutectic, Y3 Al5 O12 , YAlO3 , Y4 Al2 O9 , and Y2 O3 . The yttrium aluminates were found to be stable at high temperatures under vacuum and in air. However, when they were heat-treated under vacuum in proximity to SiC, degradation was observed. This was found to be primarily a result of carbothermal reduction. In a similarly reducing environment without Si, the yttrium aluminates, and Al2 O3 and Y2 O3 , all exhibited degradation by carbothermal reduction. Based upon the experimental results, a degradation mechanism for yttrium aluminates was proposed. 相似文献
19.
Mamoru Omori Toshinori Isobe Toshio Hirai 《Journal of the American Ceramic Society》2000,83(11):2878-2880
A eutectic solid of Al2 O3 –GdAlO3 was prepared by arc discharge and crushed to a eutectic powder of 3–125 μm. The powder was consolidated by the spark plasma system (SPS). The consolidated powder duplicated the eutectic structure: Al2 O3 and GdAlO3 were joined to each crystal. There were no flaws such as cracks or pores in the eutectic composite. The bending strength was half that of the eutectic composite prepared by unidirectional solidification. 相似文献
20.
Paste samples of tricalcium aluminate alone, with CaCl2 , with gypsum, and with gypsum and CaCl2 were hydrated for up to 6 months and the hydration products characterized by SEM, XRD, and DTA. Tricalcium aluminate hydrated initially to a hexagonal hydroaluminate phase which then changed to the cubic form; the transformation rate depended on the size and shape of the sample and on temperature. The addition of CaCl2 to tricalcium aluminate resulted in the formation of 3CaO · Al2 O3 · CaCl2 ·10H2 O and 4CaO · Al2 O3 · 13H2 O, or a solid solution of the two. The chloride retarded the formation of the cubic phase 3CaO · Al2 O3 · 6H2 O; the addition of gypsum resulted in the formation of monosulfoaluminate with a minor amount of ettringite. When chloride was added to tricalcium aluminate and gypsum, more ettringite was formed, although 3CaO · Al2 O3 · CaSO4 · 12H2 O and 3CaO · Al2 O3 · CaCl2 · 10H2 O were the main hydration products. 相似文献