共查询到20条相似文献,搜索用时 46 毫秒
1.
Yasuo Cho Teruaki Kasahara Koichi Fukuda 《Journal of the American Ceramic Society》1999,82(7):1720-1724
Two-dimensional images of the distribution showing the temperature coefficient of the dielectric constant for two types of two-phase composite ceramics composed of TiO2 -Bi2 Ti4 O11 and BaTi4 O9 -BaPr2 Ti4 O12 were obtained using scanning photothermal dielectric microscopy. The images of the TiO2 -Bi2 Ti4 O11 ceramic showed that the TiO2 and Bi2 Ti4 O11 grains had negative and positive temperature coefficients, respectively, and that the macroscopic averaged temperature coefficient of the ceramic was relatively low because of the cancellation of the opposite signs of the coefficients. On the other hand, the images of the BaTi4 O9 -BaPr2 Ti4 O12 ceramic showed that the temperature coefficient of both grains had the same sign (negative), although their absolute values were quite different. 相似文献
2.
Kiyoshi Yamazaki Tadashi Suzuki Naoki Takahashi Kouji Yokota Masahiro Sugiura 《Applied catalysis. B, Environmental》2001,30(3-4):459-468
The NOx storage-reduction catalysis under oxidizing conditions in the presence of SO2 has been investigated on Pt/Ba/Fe/Al2O3, Pt/Ba/Co/Al2O3, Pt/Ba/Ni/Al2O3, and Pt/Ba/Cu/Al2O3 catalysts compared with Pt/Ba/Al2O3, Pt/Fe/Al2O3, Pt/Co/Al2O3, Pt/Ni/Al2O3, Pt/Cu/Al2O3 and Pt/Al2O3 catalysts. The NOx purification activity of Pt/Ba/Fe/Al2O3 catalyst was the highest of all the catalysts investigated in this paper after an aging treatment. That of the aged Pt/Ba/Co/Al2O3 and Pt/Ba/Ni/Al2O3 catalysts was essentially the same as that of the aged Pt/Ba/Al2O3 catalyst, while that of the aged Pt/Ba/Cu/Al2O3 and Pt/Cu/Al2O3 catalysts was substantially lower than the others.
The Fe-compound on the aged Pt/Ba/Fe/Al2O3 catalyst has played a role in decreasing the sulfur content on the catalyst after exposure to simulated reducing gas compared with the Pt/Ba/Al2O3 catalyst without the Fe-compound. XRD and EDX show that the Fe-compound inhibits the growth in the size of BaSO4 particles formed on the Pt/Ba/Fe/Al2O3 catalyst under oxidizing conditions in the presence of SO2 and promotes the decomposition of BaSO4 and desorption of the sulfur compound under reducing conditions. 相似文献
3.
Jalajakumari Nair Padmakumar Nair Fujio Mizukami Jan G. Van Ommen Giel B. M. Doesburg Julian R. H. Ross Anthonie J. Burggraaf 《Journal of the American Ceramic Society》2000,83(8):1942-1946
Pure Al2 O3 and different compositions of La2 O3 –Al2 O3 samples have been prepared through coprecipitation. Even after heating at 1300°C, the compositions La2 O3 ·11Al2 O3 and La2 O3 ·13Al2 O3 had higher surface area compared to the pure Al2 O3 and the La2 O3 ·Al2 O3 composition. Ethanol washing is an effective way for improving the textural stability of pure Al2 O3 and La2 O3 –Al2 O3 samples. The effect of steam on the thermal stability of La2 O3 ·11Al2 O3 has also been studied. La2 O3 ·11Al2 O3 sample is found to be stable in steam. 相似文献
4.
Satoshi Uda Etsuro Asakura Masahisa Nagashima 《Journal of the American Ceramic Society》1998,81(3):725-729
The influence of the additive SO3 on the phase relationships in the quaternary system CaO-SiO2 -Al2 O3 -Fe2 O3 was investigated by observing the change of volume ratio of 3CaOSiO2 (C3 S) to 2CaOSiO2 (C2 S) + CaO (C) in the sintered material with the increase of SO3 content. The primary phase volume of C3 S in the quaternary phase diagram shrank with the increase of SO3 and disappeared when the SO3 content exceeded 2.6 wt% in the sintered material. Changes in the peritectic reaction relationship between CaO (C), 2CaOSiO2 (C2 S), 3CaOSiO2 (C3 S), 3CaOAl2 O3 (C3 A), 4CaOAl2 O3 Fe2 O3 (C4 AF), and liquid were also observed and discussed. 相似文献
5.
Y.J. Mergler A. van Aalst J. van Delft B.E. Nieuwenhuys 《Applied catalysis. B, Environmental》1996,10(4):245-261
A study of CO oxidation by O2 over Pt catalysts, promoted by MnOx and CoOx, is described. The activities of Pt/SiO2, Pt/MnOx/SiO2 and Pt/CoOx/SiO2 are compared with commercial Pt/Al2O3, Pt/Rh/Al2O3 and Pt/CeOx/Al2O3 catalysts. Since these catalysts differ in dispersion and weight loading of platinum, the turnover frequencies are also compared. The following order in activity in CO oxidation after a reductive pretreatment is found: Pt/CoOx/SiO2 > Pt/MnOx/SiO2, Pt/CeOx/Al2O3 > Pt/Al2O3, Pt/Rh/Al2O3, Pt/SiO2. Over Pt/CoOx/SiO2 CO is already oxidised at room temperature. Possible models to account for the high activity of Pt/CoOx/SiO2 in the CO/O2 reaction are presented and discussed. Partially reduced metal oxides are necessary to increase the activity of the Pt/CoOx/SiO2, Pt/MnOx/SiO2 or Pt/CeOx/Al2O3 catalysts. It was shown that mild ageing treatments did not affect the activity of the Pt/CoOx/SiO2 catalyst in CO oxidation. 相似文献
6.
Dielectric and piezoelectric properties of 0.02Pb(Y2/3 W1/3 )O3 0.98Pb(Zr0.52Ti0.48)O3 ceramics doped with additives (Nb2 O5 , La2 O3 , MnO2 , and Fe2 O3 ) were investigated. The grain sizes of these ceramics decreased with increasing amounts of additives. For additions of MnO2 and Fe2 O3 , dielectric losses decreased, while for Nb2 O5 and La2 O3 , these values increased. The maximum values of the mechanical quality factor Qm were found to be 956 and 975 for additions of 0.9 wt% Fe2 O3 and 0.7 wt% MnO2 , respectively, but donor dopants (Nb2 O5 and La2 O3 ) did not change the values of Qm . On the other hand, the piezoelectric constant d33 and the electromechanical coupling factor kp decreased with additions of MnO2 and Fe2 O3 , but improved with additions of Nb2 O5 and La2 O3 . 相似文献
7.
Sea-Fue Wang Chiang-Chuang Chung Chai-Hui Wang Jinn P. Chu 《Journal of the American Ceramic Society》2002,85(6):1619-1621
Preparation of dense and phase-pure Ba2 Ti9 O20 is generally difficult using solid-state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition and a curvature of Ba2 Ti9 O20 equilibrium phase boundary in the BaO–TiO2 system at high temperatures. In this study, the effects of B2 O3 on the densification, microstructural evolution, and phase stability of Ba2 Ti9 O20 were investigated. It was found that the densification of Ba2 Ti9 O20 sintered with B2 O3 was promoted by the transient liquid phase formed at 840°C. At sintering temperatures higher than 1100°C, the solid-state sintering became dominant because of the evaporation of B2 O3 . With the addition of 5 wt% B2 O3 , the ceramic yielded a pure Ba2 Ti9 O20 phase at sintering temperatures as low as 900°C, without any solid solution additive such as SnO2 or ZrO2 . The facilities of B2 O3 addition to the stability of Ba2 Ti9 O20 are apparently due to the eutectic liquid phase which accelerates the migration of reactant species. 相似文献
8.
Keisuke Kageyama 《Journal of the American Ceramic Society》1992,75(7):1767-1771
The microwave dielectric properties and crystal structure of Ba(Zn1/3 Ta2/3 )O3 – (Sr,Ba)(Ga1/2 Ta1/2 )O3 ceramics were investigated in the present study. The Q value of Ba(Zn1/3 Ta2/3 )O3 was improved by adding 5 mol% Sr(Ga1/2 Ta1/2 )O3 . The maximum Q value of Q × f = 162000 GHz was obtained at 0.95Ba(Zn1/3 Ta2/3 )O3 . 0.05Sr(Ga1/2 Ta1/2 )O3 . For this composition, a lattice super structure caused by hexagonal ordering was observed. A further improvement in the Q value was attained when some Sr was replaced with Ba, and 0.95Ba(Zn1/3 Ta2/3 )O3 · 0.05(Sr0.25 Ba0.75 )(Ga1/2 Ta1/2 )O3 exhibited a maximum Q value such that Q × f = 210000 GHz. Despite the increased Q value with the replacement of Sr by Ba, the c/a value, which indicates the degree of lattice distortion, remained constant near 3/2. The Q value thus improved without lattice distortion in the system Ba(Zn1/3 Ta2/3 )O3 -(Sr,Ba)(Ga1/2 Ta1/2 )O3 , whereas the improvement of Q value increased with lattice distortion in the solid solution system with Ba(Zn1/3 Ta2/3 )O3 as an end member. 相似文献
9.
Jian Zhang Shiwei Wang Tianjun Rong Lidong Chen 《Journal of the American Ceramic Society》2004,87(6):1072-1075
Y1.9 Er0.1 O3 and Y1.7 Yb0.2 Er0.1 O3 nanocrystalline powders were prepared via a reverse-strike coprecipitation method using nitrates and ammonia as raw materials. The obtained powders were of cubic-phase structure of Y2 O3 and the particle size was in the range of ∼60–80 nm. Strong red (4 F9/2 –4 I15/2 ) and green (2 H11/2 /4 S3/2 –4 I15/2 ) upconversion luminescence were observed in all the samples when excited with a 980-nm continuous wave diode laser. The possible upconversion mechanisms in Y1.9 Er0.1 O3 and Y1.7 Yb0.2 Er0.1 O3 were discussed. Power studies indicated that two-photon processes are responsible for the green and red upconversion luminescence in these systems. The codoping of Yb3+ greatly enhanced the red (4 F9/2 –4 I15/2 ) upconversion emission. 相似文献
10.
The glass-forming regions in the ternary systems M2 O-In2 O3 -GeO2 (M = Li,Na,K) were determined. The region in each of the three ternaries is less extensive than in either of the analogous systems M2 O-Al2 O3 -GeO2 and M2 O-Ga2 O3 -GeO2 ; this behavior reflects the restrictive coordination requirements of the larger In ion. The In2 O3 -containing glasses exhibit higher densities and refractive indices than the corresponding Al2 O3 and Ga2 O3 -containing glasses. Refractive index and density maxima are observed along lines of constant In2 O3 in each of the three alkali indogermanate systems. 相似文献
11.
Water-Based Gelcasting of Surface-Coated Silicon Nitride Powder 总被引:1,自引:0,他引:1
Yong Huang Longjie Zhou Qiang Tang Zhipeng Xie Jinglong Yang 《Journal of the American Ceramic Society》2001,84(4):701-707
A layer of Y2 O3 –Al2 O3 , used as a sintering aid, was coated onto the surface of Si3 N4 particles by the precipitation of inorganic salts from a water-based solution containing Al(NO3 )3 , Y(NO3 )3 , and urea. The electrokinetic and colloidal characteristics of the Si3 N4 powder were changed significantly by the coating layer. As a result, dispersion of the Y2 O3 –Al2 O3 -coated Si3 N4 powder was significantly greater than that of the original powder. Furthermore, the Y2 O3 –Al2 O3 coating layer prevented the hydrogen-gas-discharging problem that occurred during gelcasting of the original Si3 N4 powder because of reaction between the uncoated powder and the basic aqueous solution in suspension. Surface coating, as well as the gelcasting process, significantly improved the microstructure, room-temperature bending strength, and Weibull modulus of the resulting ceramic bodies. 相似文献
12.
Darko Makovec Irena Priboic Zoran Samardija Miha Drofenik 《Journal of the American Ceramic Society》2001,84(11):2702-2704
The solid solubility of the aliovalent dopants Fe3+ and Nb5+ in the BaBi4 Ti4 O15 compound, a member of the family of Aurivillius bismuth-based layer-structure perovskites, has been studied using quantitative wavelength-dispersive spectroscopic microanalysis (SEM/EPMA) in combination with X-ray powder diffractometry (XRPD). The samples with nominal (starting) compositions corresponding to the chemical formulas BaBi4 Ti4–4 X Fe4 X O15 and BaBi4 Ti4–4 X Nb4 X O15 were prepared by hot forging a mixture of BaTiO3 and Bi4 Ti3 O12 with additions of Fe2 O3 or Nb2 O5 followed by a long annealing at 1100°C. The study showed that an excess charge introduced into the structure by the substitution of Ti4+ ions with aliovalent dopants was preferentially compensated by a change in the ratio of Ba2+ to Bi3+ ions in the host structure according to the general formulas of the solid solutions Ba1–4 X Bi4+4 X Ti4–4 X Fe' 4 X O15 and Ba1+4 X Bi4–4 X Ti4–4 X Nb· 4 X O15 . 相似文献
13.
Quadrupole interactions of 11 B and 27 Al in SiO2 -B2 O3 -Al2 O3 -R2 O glass systems were investigated to determine the structure of these glasses, which should be amenable to chemical strengthening. The ratio of BO4 units to BO3 units approached unity as the R2 O/Al2 O3 ratio for compounds having fixed B2 O3 contents approached unity. Nuclear quadrupole coupling constants ( e2 Qq/h =2.73 to 2.93 MHz) were measured for the NMR spectra of 11 B triangles. The line shapes of 27 Al spectra varied with chemical composition, but a few glasses exhibited 27 Al line shapes similar to those of the AlO4 triclusters in SiO2 -Al2 O3 -Na2 O glasses. Compositional trends in the formation of BO4 and AlO4 were deduced from the NMR spectra. 相似文献
14.
Emission properties and energy transfer of PbO–Bi2 O3 –Ga2 O3 –GeO2 glasses codoped with Tm3+ and Tb3+ ions were investigated. The 1.48-μm emission due to the Tm3+ :3 H4 →3 F4 transition can be used to amplify the S-band (1460–1530-nm) signal light. With Tb3+ addition, the lifetime and emission intensity of the Tm3+ :3 F4 level decreased sharply via the Tm3+ :3 F4 →Tb3+ :7 F0,1,2 energy transfer. Population densities of the 3 F4 and 3 H4 levels in Tm3+ calculated from rate equations clearly verified that population inversion in Tm3+ ions became possible with as little as 0.1 mol% of Tb3+ addition. 相似文献
15.
A. Audzijonis L.
igas G. Gaigalas V. Paulikas R.
altauskas A. er kus D. Balnionis 《Ferroelectrics Letters Section》2004,31(5):113-118
The ferroelectric phase transition temperature has different dependence upon the mixture composition x in mixed SbOxS1-xI and SbSexS1-xI crystals. From dependence of potential energy V(z) upon normal coordinates of the B1u soft mode at a Sb site of SbOxS1-xI and SbSexS1-xI crystals we proved that main reason for the growth of TC in SbOxS1-xI crystals is that atomic formfactor VI decrease with increasing x and decrease of TC in SbSexS1-xI crystals is caused by the increase of VI with increasing x. 相似文献
16.
Wei-Heng Shih David Kisailus Wan Y. Shih Yung-Haw Hu Jerry Hughes 《Journal of the American Ceramic Society》1996,79(5):1155-1162
In an attempt to improve the colloidal processing of Si3 N4 ceramics, we studied the rheology and consolidation of colloidal suspensions of Si3 N4 particles (average particle size 0.7 μm) with small Al2 O3 particles (average particle size 20 nm). It was found that at pH >7, the viscosity of the mixtures increased and then decreased with an increasing concentration of Al2 O3 . λpotential measurements, optical micrographs, and visible light absorptance measurement suggest that such viscosity behavior is due to clustering of Si3 N4 particles bridged by the small Al2 O3 particles. This is also supported by the Derjaquin-Landau-Verwey-Overbeek (DLVO) potential calculations that show the barrier height in the DLVO potential between Al2 O3 and Si3 N4 is small. The small barrier height under current experimental conditions stems from the small size of the Al2 O3 particles. The small barrier height allows the thermal motion of the two kinds of particles to overcome the barrier and attach to each other. The adsorption of small Al2 O3 particles on Si3 N4 can occur even when both Al2 O3 and Si3 N4 carry the same sign of charges. The adsorption of Al2 O3 on Si3 N4 also increases the density of consolidated compacts. 相似文献
17.
Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li1+ x Ti2− x Al x (PO4 )3 (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li2 O─CaO─TiO2 ─Al2 O3 –P2 O5 system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li1+ x Ti2− x Al x (PO4 )3 and β-Ca3 (PO4 )2 phases. The median pore diameter and surface area of the resulting porous Li1+ x Ti2− x Al x (PO4 )3 glass-ceramics were approximately 0.2 μm and 50 m2 /g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO3 aqueous solution was 8 × 10−5 S/cm at 300 K or 2 × 10−2 S/cm at 600 K. 相似文献
18.
Results are presented of a study of phase equilibria among crystalline and liquid phases in the quaternary system CaO–MgO-Al2 O3 –SiO2 at Al2 O3 contents greater than 35%. Equilibrium diagrams shown are for the five triangular joins CaAl2 Si2 O3 -Ca2 Al2 SiO7 -MgAl2 O4 , Ca2 Al2 SiO7 -MgAl2 O4 -Al2 O3 , CaAl2 Si2 O8 -MgO-Al2 O3 , CaAl2 Si2 O8 -Mg2 SiO4 -MgAl2 O4 , and CaAl2 Si2 O8 -MgO-Mg2 SiO4 . The composition and nature of the four quaternary peritectic points and the relationships of univariant lines and primary phase volumes are discussed. 相似文献
19.
Piezoelectric Properties of Pb(Mg1/3 Nb2/3 )O3 PbTiO3 -PbZrO3 Ceramics Modified with Certain Additives
HIROMU OUCHI MASAMITSU NISHIDA SHIGERU HAYAKAWA 《Journal of the American Ceramic Society》1966,49(11):577-582
Effects of additives on the piezoelectric properties of Pb(Mg1/3 Nb2/3 )O3 -PbTiO3 -PbZrO3 ceramics in a perovskite-type structure are described. The tetragonality of Pb(Mg1/3 Nb2/3 )0.375 -Ti0.375 Zr0.25 O3 ceramics increased with the addition of NiO, Cr2 O3 , or Fe2 O3 but decreased with the addition of MnO2 or CoO. The dielectric and piezoelectric properties of the base composition were improved markedly through selection of additives in proper amounts. Addition of NiO yielded a high dielectric constant and planar coupling coefficient for compositions at the morphotropic transition boundary. High mechanical Q -factors and low electrical dissipation factors were obtained by addition of MnO2 . Addition of both NiO and MnO2 produced a mechanical Q -factor of 2051 and a planar coupling coefficient of 0.553. The resonant frequency of Pb(Mg1/2 Nb2/3 )0.4375 Ti0.4375 zr0.125 O3 containing MnO2 had very low temperature and time dependence. The microstructure indicated that ceramics with a high mechanical Q -factor had a fine, uniform grain structure. Addition of Cr2 O3 retarded grain growth and addition of MnO2 , NiO, CoO, or Fe2 O3 promoted grain growth in the ternary system. 相似文献
20.
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