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1.
Boundary migration under an electric field was investigated for pure, TiO2 -doped, and Li2 O-doped Al2 O3 specimens. Boundary migration rates in TiO2 -doped and Li2 O-doped Al2 O3 specimens were much faster compared with that of pure Al2 O3 . In all specimens, the migration rate was observed to depend on the applied bias direction. Compared with pure Al2 O3 , the dependence of boundary migration on bias direction became more pronounced in TiO2 -doped Al2 O3 but less pronounced in Li2 O-doped Al2 O3 . The results were explained in terms of the variation of grain sizes, mobility, and electrostatic potential of boundaries because of doping. 相似文献
2.
Compatible phases in the system Li2 O-Al2 O3 -TiO2 at various temperature levels were determined mainly by solid-state reactions for the portion of the ternary system bounded by Li2 O Al2 O2 , Li2 O.TiO2 , Al2 O, and TiO2 . The existence of a ternary compound, Li2 O.Al2 O3 .4TiO2 , and nine joins was established. The ternary compound has a lower limit of stability at 1090°± 15°C. and dissociates and recombines rapidly at 1380°± 15°C. 相似文献
3.
TAKAYASU IKEGAMI KAZUO KOTANI Katsuya Eguchi 《Journal of the American Ceramic Society》1987,70(12):885-890
Sinterability of undoped, MgO-doped, and TiO2 -doped Al2 O3 has been examined by applying reported sintering equations. The order of sinterability was MgO-doped ∼ undoped≪ TiO2 -doped Al2 O3 in the initial and intermediate stages of sintering, but a relative sintered density at 1600°C for 1 h occurred in the order undoped < TiO2 -doped < MgO-doped AI2 O3 . The dispersion of thermal grooving angles increased in the order MgO-doped < undoped < TiO2 -doped Al2 O3 , The change of sinterability by the dopants is explained in terms of mobility of mass transfer estimated from a densification rate in the initial- and intermediate-stage sintering and of dispersed driving forces of densification and grain growth qualitatively evaluated from the width of the dispersion of thermal grooving angles. 相似文献
4.
Direct-Current Field Dependence of Dielectric Properties in Alumina-Doped Barium Strontium Titanate 总被引:7,自引:0,他引:7
Long Wu Yih-Chien Chen Cheng-Liang Huang Yi-Ping Chou Yuan-Tu Tsai 《Journal of the American Ceramic Society》2000,83(7):1713-1719
The dielectric properties of (Ba0.6 Sr0.4 )TiO3 and Al2 O3 -doped (Ba0.6 Sr0.4 )TiO3 have been characterized. The grain size of the specimen is maximum for (Ba0.6 Sr0.4 )TiO3 that has been doped with 1 wt% Al2 O3 . The density and the real part of the relative dielectric constant each decrease as the Al2 O3 content increases. The loss factor is minimum for (Ba0.6 Sr0.4 )TiO3 that has been doped with 2 wt% Al2 O3 . The dielectric constant of the specimens decreases as the applied dc field increases. The influence of the dc field on the loss factor is much less than that on the dielectric constant. The tunability is ∼24% for (Ba0.6 Sr0.4 )TiO3 that has been doped with 1 wt% Al2 O3 . 相似文献
5.
Miaofang Chi Hui Gu Xin Wang Peiling Wang 《Journal of the American Ceramic Society》2003,86(11):1953-1955
A phenomenon of bilevel solubility was observed in a TiO2 -doped (2.0 wt%) alumina with bimodal microstructure sintered in N2 . Surface contributions to dopant signals in individual grains were identified and removed, using a spatially resolved energy dispersive spectroscopy analysis. Two levels of solubility, 1.005 ± 0.166 and 0.504 ± 0.082 mol% of TiO2 in Al2 O3 , were obtained for anisotropic and equiaxed grains, respectively. No grain size dependence of solubility was found, but segregation of SiO2 to boundaries with the anisotropic grains was observed. This phenomenon was explained by the incorporation of Ti3+ into the Al2 O3 lattice during the abnormal grain growth caused by SiO2 liquid under a reducing atmosphere. 相似文献
6.
This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li2 O·9Al2 O3 ·38 TiO2 ·39P2 O5 glass–ceramic and polyethylene. The processing involved tape casting of 14Li2 O·9Al2 O3 ·38TiO2 ·39P2 O5 glass powder with organic additives into tapes, subjecting the green tape to binder burnout and thermal soaking in the temperature range of 950°–1100°C, and finally infiltrating the porous tape with polyethylene solution. The ionic conductivity and microstructure of 150–350 μm thick membranes were characterized and are discussed in this paper. The crystallites of the glass–ceramic show liquid-like conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of five. The lower grain boundary conductivity is explained on the basis of crystallographic mismatch and the existence of AlPO4 at the grain boundary. The polyethylene infiltration in the porous membrane improved mechanical resilience with a minor adverse effect on conductivity. 相似文献
7.
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
8.
Shimin Liu Gaoling Zhao Wangle Ruan Zhiwang Yao Tingting Xie Ji Jin Hao Ying Jianxun Wang Gaorong Han 《Journal of the American Ceramic Society》2008,91(8):2740-2742
Eu2 O3 -doped aluminoborosilicate glasses were prepared in air at high temperature. Luminescence measurements were used to investigate a valence change from Eu3+ to Eu2+ ions in the aluminoborosilicate glasses. The results showed that the doped Eu3+ ions were partially reduced to Eu2+ in the Eu2 O3 :RO–Al2 O3 –B2 O3 –SiO2 (RO=CaO, SrO, BaO, Li2 O) glasses, but not in the Eu2 O3 :RO–Al2 O3 –B2 O3 –SiO2 (RO=Na2 O, K2 O) glasses. The changes of Eu reduction with different RO components were discussed with the variation of optical basicity of RO and with different valency of R cations. The effects of co-doping BaO and ZnO in aluminoborosilicate glasses on Eu reduction were also investigated and discussed. 相似文献
9.
Koji Watari Maria Cecilia Valecillos Manuel E. Brito Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》1996,79(12):3103-3108
Small amounts of Li2 O result in sintering in the AIN-Y2 O3 -CaO and AIN-CaO systems at firing temperatures <1600°C. The effect is ascribed to reduction of the liquidus temperature. Furthermore, Li2 O is removed by volatization at temperatures from 1300° to 1600°C, and its content decreases several ppm from the initial 0.3 wt%. Li2 O-doped AIN specimens containing Y2 O3 and CaO additives are well densified by firing at 1600°C for 6 h, and their thermal conductivity is 135 W. m−1. K−1 .The effect of Li2 O addition on sintering and thermal conductivity also is discussed through thermo-dynamic considerations. 相似文献
10.
Solid-state reactions between Li2 O and Al2 O3 were studied in the region between Li2 O.Al2 O 3 and Al2 O 3 . The compound Li2 O Al2 O 3 melts at 1610°± 15°C. and undergoes a rapid reversible inversion between 1200° and 1300°C. Vaporization of Li2 O from compositions in the system proceeds at an appreciable rate at 1400°C, as shown by fluorescence. Lithium spinel, Li2 O -5Al2 O3 , was the only other compound observed. The effect of Li2 O on the sintering of alumina was investigated. 相似文献
11.
Microstructure and Mechanical Properties of Porous Alumina Ceramics Fabricated by the Decomposition of Aluminum Hydroxide 总被引:3,自引:0,他引:3
Zhen-Yan Deng Takayuki Fukasawa Motohide Ando Guo-Jun Zhang Tatsuki Ohji 《Journal of the American Ceramic Society》2001,84(11):2638-2644
The mechanical properties of Al2 O3 -based porous ceramics fabricated from pure Al2 O3 powder and the mixtures with Al(OH)3 were investigated. The fracture strength of the porous Al2 O3 specimens sintered from the mixture was substantially higher than that of the pure Al2 O3 sintered specimens because of strong grain bonding that resulted from the fine Al2 O3 grains produced by the decomposition of Al(OH)3 . However, the elastic modulus of the porous Al2 O3 specimens did not increase with the incorporation of Al(OH)3 , so that the strain to failure of the porous Al2 O3 ceramics increased considerably, especially in the specimens with high porosity, because of the unique pore structures related to the large original Al(OH)3 particles. Fracture toughness also increased with the addition of Al(OH)3 in the specimens with higher porosity. However, fracture toughness did not improve in the specimens with lower porosity because of the fracture-mode transition from intergranular, at higher porosity, to transgranular, at lower porosity. 相似文献
12.
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
13.
CECIL M. JONES II 《Journal of the American Ceramic Society》1971,54(7):347-349
A technique for growing α-Al2 O3 crystals is described in which Na2 O·11Al2 O3 is dissolved in a liquid of composition Na2 O·4TiO2 ·3Al2 O3 . Alpha Al2 O3 is precipitated as Na2 O evaporates from the system; Na2 O·11Al2 O3 serves as a source of Al2 O3 , and Na2 O in the liquid. The content of solids in the mixture is always such that it does not melt completely. The size of the α-Al2 O3 crystals grown is related to the Na2 O content of the composition. Crystals as large as 4000 by 3000 μm in the α-axis direction and 500 μm in the c -axis direction have been grown. 相似文献
14.
Reaction kinetics in a coarse equimolar powder mixture were slow enough to allow for the different stages to be identified, notably in the lower and higher temperature ranges, respectively. In the former ( T ≤ 1600 K), Al2 TiO5 nucleation was hindered by the strain energy contribution to the overall driving force. The setting up of metastable layer sequences Al2 TiO5 /TiO2 /Al2 O3 was found to occur generally during subsequent growth. The high Al mobility in the TiO2 provided a rapid aluminum transport from the metastable Al2 O3 /TiO2 interface to the TiO2 /Al2 TiO5 front. At temperatures above ∼1700 K the Al2 O3 /TiO2 interface was very rapidly sealed off by Al2 TiO5 formation. Reactant transport across the Al2 TiO5 was slow because of the low mobilities in the product phase. Therefore, much lower product growth velocities were observed at higher temperatures than at lower temperatures. 相似文献
15.
Jin-Wook Jeong Joo-Hwan Han Doh-Yeon Kim 《Journal of the American Ceramic Society》2000,83(4):915-918
The effect of an external electric field on the grain-boundary migration in Al2 O3 ceramics has been investigated. The boundary migration is dependent on the direction and magnitude of the applied bias, and the observed boundary migration behavior is attributed to the presence of an electrostatic potential that inherently forms at the grain boundaries of Al2 O3 ceramics. The results give experimental evidence that the boundary phenomena in oxide ceramics are related to the grain-boundary potential. 相似文献
16.
Measurements of electrical resistance in the composition systems Al2 O3 –SiO2 , SiO2 –TiO2 , Al2 O3 –Cr2 O3 , and MgO–NiO were made using, in general, dry-pressed disks about 3 cm. in diameter and 0.4 cm. thick and fired to 1500°C. In the Al2 O3 –SiO2 series minimum resistance was shown by the samples containing 50% SiO2 , 50% Al2 O3 . The resistance of Al2 O3 was increased by the addition of small amounts of Cr2 O3 . The same effect was observed in the higher temperature range with small additions of NiO to MgO. In other instances the addition of the relatively inert SiO2 , Al2 O3 , and MgO to the semiconductors TiO2 , Cr2 O3 , and NiO resulted in a dilution effect. The resistance of Cr2 O3 was decreased by the addition of a slight amount of MgO. 相似文献
17.
Heromichi Okamura Eric A. Barringer H. Kent Bowen 《Journal of the American Ceramic Society》1986,69(2):22-C-
An unagglomerated, monosized Al2 O3 TiO2 composite powder was prepared by the stepwise hydrolysis of titanium alkoxide in an Al2 O3 dispersion. Particle size was controlled by selecting the particle size of the starting Al2 O3 powder; TiO2 content was determined by the amount of alkoxide hydrolyzed. A composite-powder compact containing 50 mol% TiO2 , when fired at 1350°C for 30 min, showed nearly theoretical density with aluminum titanate phase formation. 相似文献
18.
Mullite transformation kinetics of sol-gel-derived diphasic mullite gels doped with P2 O5 , TiO2 , and B2 O3 were studied using quantitative X-ray diffraction and differential thermal analysis (DTA). The mullite transformation temperature initially increased with P2 O5 doping because of phase separation and formation of α-alumina and cristobalite. In TiO2 -doped samples, the mullite transformation temperature decreased with TiO2 doping, and the transformation rate increased with decreasing TiO2 particle size. Kinetic studies showed that titania reduced the activation energy for both nucleation and growth relative to pure diphasic mullite gels by lowering the glass viscosity and/or enhancing the solid-state mass transport through lattice defects. B2 O3 doping decreased the mullite transformation temperature and lowered the activation energy for both nucleation and growth but especially affected the mullite nucleation process, as indicated by the much smaller grain size. 相似文献
19.
Cheng-Kuei Jen Christian Neron Alain Shang Koich Abe Lee Bonnell Junichi Kushibiki 《Journal of the American Ceramic Society》1993,76(3):712-716
Acoustic characterization of doped silica glasses with a GeO2 , P2 O5 , F, TiO2 , Al2 O3 , or B2 O3 dopant having different concentrations is presented. Quantitative measurements were performed with a 225-MHz line-focus-beam scanning acoustic microscope. The acoustic velocity variation due to different dopant concentrations is given. It has been found that the Al2 O3 dopant increases, but the other dopants decrease, the acoustic velocity as compared with that of the pure fused silica. We have also found that the fractional change in acoustic velocity is greater than that in refractive index for a given dopant concentration. 相似文献
20.
In the system TiO2 —Al2 O3 , TiO2 (anatase, tetragonal) solid solutions crystallize at low temperatures (with up to ∼ 22 mol% Al2 O3 ) from amorphous materials prepared by the simultaneous hydrolysis of titanium and aluminum alkoxides. The lattice parameter a is relatively constant regardless of composition, whereas parameter c decreases linearly with increasing Al2 O3 . At higher temperatures, anatase solid solutions transform into TiO2 (rutile) with the formation of α-Al2 O3 . Powder characterization is studied. Pure anatase crystallizes at 220° to 360°C, and the anatase-to-rutile phase transformation occurs at 770° to 850°C. 相似文献