共查询到20条相似文献,搜索用时 31 毫秒
1.
Ken-ichi Tajima † Hae Jin Hwang Mutsuo Sando Koichi Niihara 《Journal of the American Ceramic Society》2000,83(3):651-653
Hard lead zirconate titanate (PZT) and PZT/Al2 O3 composites were prepared and the alternating-electric-field-induced crack growth behavior of a precrack above the coercive field was evaluated via optical and scanning electron microscopy. The crack extension in the 1.0 vol% Al2 O3 composite was significantly smaller than that in monolithic PZT and the 0.5 vol% Al2 O3 composite. Secondary-phase Al2 O3 dispersoids were found both at grain boundaries and within grains in the composites. A large number of dispersoids were observed at the grain boundaries in the 1.0 vol% Al2 O3 composite. It appears that the Al2 O3 dispersoids reinforce the grain boundaries of the PZT matrix as well as act as effective pins against microcrack propagation. 相似文献
2.
J. P. COUTURES 《Journal of the American Ceramic Society》1985,68(3):105-107
A tentative phase diagram for the system Al2 03 -Nd2 O3 is presented. Three compounds were obtained: a β -A12 O3 -type compound, the perovskite NdAlO3 , and Nd4 Al2 O9 . The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al2 O3 , mp 1900°C; Nd4 Al2 O9 , mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al2 O3 , 1750°C; 23 mol% Al2 O3 ,1800°C. Nd4 Al2 O9 decomposes in the solid state at 1780°C. 相似文献
3.
The composite sol—gel (CSG) technology has been utilized to process SiC—Al2 O3 ceramic/ceramic particulate reinforced composites with a high content of SiC (up to 50 vol%). Alumina sol, resulting from hydrolysis of aluminum isopropoxide, has been utilized as a dispersant and sintering additive. Microstructures of the composites (investigated using TEM) show the sol-originating phase present at grain boundaries, in particular at triple junctions, irrespective of the type of grain (i.e., SiC or Al2 O3 ). It is hypothesized that the alumina film originating from the alumina sol reacts with SiO2 film on the surface of SiC grains to form mullite or alumina-rich mullite-glass mixed phase. Effectively, SiC particles interconnect through this phase, facilitating formation of a dense body even at very high SiC content. Comparative sinterability studies were performed on similar SiC—Al2 O3 compositions free of alumina sol. It appears that in these systems the large fraction of directly contacting SiC—SiC grains prevents full densification of the composite. The microhardness of SiC—Al2 O3 sol—gel composites has been measured as a function of the content of SiC and sintering temperature. The highest microhardness of 22.9 GPa has been obtained for the composition 50 vol% SiC—50 vol% Al2 O3 , sintered at 1850°C. 相似文献
4.
Philippe Boch Thierry Chartier Muriel Huttepain 《Journal of the American Ceramic Society》1986,69(8):191-C
Fracture toughness of ZrO2 -toughened alumina could he increased by macroscopic interfaces, such as those existing in laminated composites. In this work, tape casting was used to produce A/A or A/B laminates, where A and B can be Al2 O3 , Al2 O3 /5 vol% ZrO2 , and Al2 O3 /l0 vol% ZrO2 . An increase of toughness is observed, even in the Al2 O3 /Al2 O3 laminates. 相似文献
5.
Chunfeng Hu Yanchun Zhou Yiwang Bao Detian Wan 《Journal of the American Ceramic Society》2006,89(11):3456-3461
Tribological properties of Ti3 SiC2 and Al2 O3 -reinforced Ti3 SiC2 composites (10 and 20 vol% Al2 O3 ) were investigated by using an AISI-52100 bearing steel ball dryly sliding on a linear reciprocating athletic specimen. The friction coefficients were found varying only in a range of 0.1 under the applied loads (2.5, 5, and 10 N), and the wear rates of the composites decreased with increasing Al2 O3 content. The enhanced wear resistance is mainly attributed to the hard Al2 O3 particles nail the surrounding soft matrix and decentrale the shear stresses under the sliding ball to reduce the wear losses. 相似文献
6.
Robert J. Moon Matthew Tilbrook Mark Hoffman Achim Neubrand 《Journal of the American Ceramic Society》2005,88(3):666-674
The effective Young's moduli of co-continuous Al–Al2 O3 composites over the 5–97 vol% Al2 O3 composition range were experimentally measured and compared with theoretical composite modulus values predicted using the methods of Ravichandran, Tuchinskii, Hashin-Shtrikman, and the effective medium approximation (EMA). The influence of phase morphology and the modulus ratio ( E 1 / E 2 ) of the constituent phases on the resulting experimental and calculated Young's modulus is discussed. For two-phased co-continuous composites with a modulus ratio greater than 5, the EMA, with an appropriate microstructural shape factor, was the most consistent method for approximating the composite Young's modulus over the entire composition range. 相似文献
7.
F. G. BUTTLER L. S. DENT GLASSER H. F. W. TAYLOR 《Journal of the American Ceramic Society》1959,42(3):121-126
Single-crystal X-ray and electron-diffraction studies show the existence in one polymorph of 4CaO.Al2 O3 . 13H2 O of a hexagonal structural element with α= 5.74 a.u., c = 7.92 a. u. and atomic contents Ca2 (OH)7 - 3H2 O. These structural elements are stacked in a complex way and there are probably two or more poly-types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A12 O3 .13H2 O, from which it is derived by substitution of CO3 2- for 20H- + 3H2 O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al2 O3 .Ca Y 2 - xH2 O and 3CaO Al2 O3 Ca Y xH2 O. On dehydration, 4CaO.Al2 O3 .13H2 O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)2 and 4CaO.3Al2 O3 .3H2 O are formed and, by 1000°C., CaO and 12CaO.7Al2 O8 . The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al2 O3 .3H2 O is formed. 相似文献
8.
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
9.
DAVID J. GREEN 《Journal of the American Ceramic Society》1982,65(12):610-614
The internal strains asSociated with the martensitic phase transformation of zirconia were used to introduce microcracks into Al2 O3 /ZrO2 composites. The degree of transformation was found to be dependent on the volume fraction of ZrO2 and its size, the latter of which could be controlled by suitable heat treatments. The microstructural changes that occurred during the heat treatments were studied using quantitative microscopy and X-ray diffraction. For materials containing more than 7.5 vol% Zr02 , the ZrO2 particles were found to pin the Al2 O3 grain boundaries, thus limiting the Al2 O3 grain growth. The limiting grain size was found to be dependent on size and volume fraction of ZrO2 . Heat treatments for the higher volume fraction materials (>7.5 vol% ZrO2 ) caused micro-structural changes which resulted in increased amounts of monoclinic ZrO2 at room temperature; elastic modulus measurements indicated that this was occurring concurrently with microcracking. By combining the ZrO2 grain-size distributions with the X-ray analysis it was possible to calculate the critical ZrO2 size required for the transformation. The critical size was found to decrease with increasing amounts of ZrO2 . Hardness and indentation fracture toughness were measured on the composites. Grain fragmentation was observed at the edge of the indentations and microcracks were observed directly, using an AgNO3 decoration technique, near the indentations. 相似文献
10.
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
11.
The mechanical behavior of reaction-sintered alumina: 30 vol% calcium hexaluminate (Al2 O3 :CaAl12 O19, or A12 O3 : CA6 ) composites was evaluated using the indentation strength in bending technique. A composite in which the hexaluminate (CA6 ) phase possessed a platelike morphology showed more-pronounced R -curve behavior than a composite in which the CA6 phase consisted of equiaxed grains. Toughness curves derived from the indentation-strength data exhibited a "crossover," such that the platelet composite exhibited the lower toughness at small flaw sizes, but the higher toughness at large flaw sizes. Incorporation of the platelet CA6 resulted in enhanced toughening, compared to single-phase alumina of comparable grain size, thus demonstrating the viability of the in-situ -toughening approach. A simple grain-pullout model was used to estimate the toughening increment due to bridging by the platelet grains; the value obtained was in good agreement with toughness curves derived from indentation-strength measurements. Finally, fabrication of trilayer specimens, whereby outer layers of equiaxed A12 O3 :CA6 composite were strongly bonded to the platelet A12 O3 :CA6 composite, demonstrated high strength over the range of tested flaw sizes. 相似文献
12.
Masayuki Nogami Naoya Hayakawa Naoya Sugioka Yoshihiro Abe 《Journal of the American Ceramic Society》1996,79(5):1257-1261
Samarium ions (Sm2+ ) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na2 O-Al2 O3 SiO2 synthesized by the hydrolysis of Si(OC2 H5 )4 , Al(OC4 H9 )3 , CH3 COONa, and SmCl3 ·6H2 O were heated in air at 500°C, then reacted with H2 gas to form Sm2+ ions. Whereas Al3+ ions effectively dispersed the Sm3+ ions in the glass structure, Na+ ions were not effective. The Al2 O3 -SiO2 glasses proved appropriate for reacting the Sm3+ ions with H2 gas and exhibited the intense photoluminescence of Sm2+ ions. The reaction of Sm3+ ions with H2 in the Al2 O2 -SiO2 glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm2+ ions was achieved within 20 min. 相似文献
13.
Hyun M. Jang Jong H. Moon Cheol W. Jang 《Journal of the American Ceramic Society》1992,75(12):3369-3376
Al2 O3 –ZrO2 –SiC whisker composites were prepared by surface-induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2 O3 and SiC whisker. The fabricated composites were characterized by a uniform spatial distribution of ZrO2 and SiC whisker phases throughout the Al2 O3 matrix. The fracture toughness values of the Al2 O3 –15 vol% ZrO2 –20 vol% SiC whisker composites (∼12 MPa.m1/2 ) are substantially greater than those of comparable Al2 O3 –SiC whisker composites, indicating that both the toughening resulting from the process zone mechanism and that caused by the reinforced SiC whiskers work simultaneously in hot-pressed composites. 相似文献
14.
Silvia Schicker Daniel E. Garcia Jorn Bruhn Rolf Janssen Nils Claussen 《Journal of the American Ceramic Society》1997,80(9):2294-2300
Different Fe-Al2 O3 and FeAl-Al2 O3 composites with metallic contents up to 30 vol% have been fabricated via reaction processing of Al2 O3 , Fe, and Al mixtures. Low Al contents (<∼10 vol%) within the starting mixture lead to composites consisting of Fe embedded in an Al2 O3 matrix, whereas aluminide-containing Al2 O3 composites result from powder mixtures with higher Al contents. In both cases, densification up to 98% TD can be achieved by pressureless sintering in inert atmosphere at moderate temperatures (1450°-1500°C). The proposed reaction sintering mechanism includes the reduction of native oxide layers on the surface of the Fe particles by Al and, in the case of mixtures with high Al contents, aluminide formation followed by sintering of the composites. Density and bending strengths of the reaction-sintered composites depend strongly on the Al content of the starting mixture. In the case of samples containing elemental Fe, crack path observations indicate the potential for an increase of fracture toughness, even at room temperature, by crack bridging of the ductile Fe inclusions. 相似文献
15.
Jingxian Zhang Qiang Xu Hideaki Tanaka Mikio Iwasa Dongliang Jiang 《Journal of the American Ceramic Society》2006,89(4):1440-1442
Polyacrylic acid (PAA) is known to be an effective dispersant for Al2 O3 powder in aqueous media. However, at high solid loading (>55 vol%), the dispersion of the Al2 O3 suspensions became difficult with only PAA as a dispersant. In this paper, ethylenediaminetetraacetic acid, tetrasodium salt, dihydrate (EDTA-4Na) was introduced to improve the dispersion of the Al2 O3 suspensions. With the aid of EDTA-4Na, the adsorption amount of sodium polyacrylic acid (PAA-Na) increased, while the apparent viscosity of 60 vol% Al2 O3 slurries decreased significantly. Particle size measurements showed that EDTA-4Na could help to reduce larger agglomerates, possibly by modifying the adsorbed layer thickness. The interactions between EDTA-4Na and PAA-Na were studied using Fourier-transform infrared spectroscopy analysis. Results showed that it was possible to introduce EDTA-4Na as the second dispersant to improve the dispersion of high solid content Al2 O3 slurries. 相似文献
16.
The fracture toughness of 3 mol% Y2 O3 -ZrO2 (3Y-PSZ) composites containing 10–30 vol% Al2 O3 with different particle sizes was investigated. It was found that Al2 O3 dispersion of up to 30 vol% increased the fracture toughness by 17% to 30%, and the toughness increase was more remarkable in the composite dispersed with Al2 O3 particles of larger sizes. By combining the effects of the dispersion toughening and phase transformation toughening, the toughness change in the present materials was theoretically predicted, which was in good agreement with the experimental data. 相似文献
17.
P. L. ROEDER F. P. GLASSER† E. F. OSBORN 《Journal of the American Ceramic Society》1968,51(10):585-593
Liquidus phase equilibrium data are presented for the system Al2 O3 -Cr2 O3 -SiO2 . The liquidus diagram is dominated by a large, high-temperature, two-liquid region overlying the primary phase field of corundum solid solution. Other important features are a narrow field for mullite solid solution, a very small cristobalite field, and a ternary eutectic at 1580°C. The eutectic liquid (6Al2 O3 -ICr2 O3 -93SiO2 ) coexists with a mullite solid solution (61Al2 O3 -10Cr2 O3 -29SiO2 ), a corundum solid solution (19Al2 O3 -81Cr2 O3 ), and cristobalite (SO2 ). Diagrams are presented to show courses of fractional crystallization, courses of equilibrium crystallization, and phase relations on isothermal planes at 1800°, 1700°, and 1575°C. Tie lines were sketched to indicate the composition of coexisting mullite and corundum solid solution phases. 相似文献
18.
Polycrystalline Al2 O3 was chemically vapor-deposited onto sintered Al2 O3 substrates by reaction of AlCl3 with (1) H2 O, (2) CO:H2 , and (3) O2 at 1000° and 1500°C and 0.5 and 5.0 torr. Although the thermodynamics of all these reactions predict the formation of solid Al2 O3 , the deposition rate of the first reaction was considerably greater than that of the second. The third reaction was so slow that no measurable deposit was formed in 6 h at 1500°C. Formation of dense deposits of α-Al2 O3 was favored by increasing temperature and decreasing pressure. Microstructural examination of the dense deposits showed long columnar grains, the largest of which extended through the deposit from the substrate to the surface. 相似文献
19.
Haiyan Liu Morris E. Fine H. S. Cheng Alan L. Geiger 《Journal of the American Ceramic Society》1994,77(1):179-185
Lubricated rolling wear studies of SiC-whisker (SiCw ) reinforced A12 O3 composites and monolithic A12 O3 against M2 tool steel were conducted using a cylinder-on-cylinder apparatus. The composites wore considerably less than A12 O3 . The wear of the tool steel against the composites was also considerably less than against A12 O3 . Microfracture occurred on a smaller scale in the composites than in the Al2 O3 . This was attributed to the differences in microstruc-ture and fracture toughness. The worn surfaces of the steel and the composites were polished, possibly due to fine, hard wear debris circulating with the lubricant to the contact area. 相似文献
20.
Byong-Taek Lee Rajat Kanti Paul Hyun-Jin Hong Kap-Ho Lee 《Journal of the American Ceramic Society》2009,92(4):911-915
Using a multipass extrusion process, continuous porous Al2 O3 body (∼41% porosity) was produced and used as a substrate to fabricate continuous porous TiO2 /Al2 O3 composite membrane. The diameter of the continuous pores of the porous Al2 O3 body was about 150 μm. The TiO2 nanopowders dip coated on the continuous pore-surface Al2 O3 body existed as rutile and anatase phases after calcination at 520°C in air. However, after aging of the fabricated continuous porous TiO2 /Al2 O3 composite membrane in 20% NaOH at 60°C for 24 h, a large number of TiO2 fibers frequently observed on the pore surface. The diameter of the TiO2 fibers was about 150 nm having a high specific surface area. However, after 48-h aging period, the diameter of the TiO2 fibers increased, which was about 3 μm. Most of the TiO2 fibers had polycrystalline structure having nanosized rutile and anatase crystals of about 20 nm. 相似文献