共查询到20条相似文献,搜索用时 32 毫秒
1.
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
2.
Koji Tsukuma 《Journal of the American Ceramic Society》2000,83(12):3219-3221
Composites of β-Ce2 O3 ·11Al2 O3 and tetragonal ZrO2 were fabricated by a reductive atmosphere sintering of mixed powders of CeO2 , ZrO2 (2 mol% Y2 O3 ), and Al2 O3 . The composites had microstructures composed of elongated grains of β-Ce2 O3 ·11Al2 O3 in a Y-TZP matrix. The β-Ce2 O3 ·11Al2 O3 decomposed to α-Al2 O3 and CeO2 by annealing at 1500°C for 1 h in oxygen. The elongated single grain of β-Ce2 O3 ·11Al2 O3 divided into several grains of α-Al2 O3 and ZrO2 doped with Y2 O3 and CeO2 . High-temperature bending strength of the oxygen-annealed α-Al2 O3 composite was comparable to the β-Ce2 O3 ·11Al2 O3 composite before annealing. 相似文献
3.
Synthesis of Titanate Derivatives Using Ion-Exchange Reaction 总被引:3,自引:0,他引:3
Chul-Tae Lee Myeong-Heon Um Hidehiro Kumazawa 《Journal of the American Ceramic Society》2000,83(5):1098-1102
Two types of titanate derivatives, layered hydrous titanium dioxide (H2 Ti4 O9 · n H2 O) and potassium octatitanate (K2 Ti8 O17 ) with a tunnellike structure, were synthesized using an ion-exchange reaction. Fibrous potassium tetratitanate (K2 Ti4 O9 · n H2 O) was prepared by calcination of a mixture of K2 CO3 and TiO2 with a molar ratio of 2.8 at 1050°C for 3 h, followed by boiling-water treatment of the calcined products for 10 h. The material then was transformed to layered H2 Ti4 O9 · n H2 O through an exchange of K+ ions with H+ ions using HCl. K2 Ti8 O17 was formed by a thermal treatment of KHTi4 O9 · n H2 O. Pure KHTi4 O9 · n H2 O phase was effectively produced by a treatment of K2 Ti4 O9 with 0.005 M HCl solution for 30 min. Thermal treatment at 250°–500°C for 3 h resulted in formation of only K2 Ti8 O17 . 相似文献
4.
Dietmar Seyferth Timothy G. Wood Henry J. Tracy Jennifer L. Robison 《Journal of the American Ceramic Society》1992,75(5):1300-1302
Na condensation of CH3 SiHCl2 gives polysilanes of the type ((CH3 SiH) x (CH3 Si) y ) n (where x + y = 1) whose pyrolysis in a stream of Ar gives SiC and a substantial amount of elemental Si. Treatment of such polysilanes with catalytic quantities of group-IV-metal–organometallic complexes, ((η-C5 H5 )2 ZrH2 ) n , (η-C5 H5 )2 Zr(CH3 )2 , (η-C5 H5 )2 ZrHCl, and (η-C5 H5 )2 -Ti(CH3 )2 , results in cross-linking processes such that pyrolysis of these polysilanes gives close to stoichiometric SiC (≥95 wt %) and only very little elemental Si. 相似文献
5.
为提高红色荧光粉的发光强度和色纯度,以硝酸钙、硝酸钠、硝酸铕、磷酸二氢铵、钼酸铵、硝酸钡为原料,采用高温固相法合成了NaCa1-xPO4:xEu3+、NaCa1-x(PO4)1-y(MoO4)y:xEu3+、NaCa1-x-zPO4:xEu3+,zBa2+系列红色荧光粉。探讨了Eu3+单掺杂和Eu3+/MoO42-、Eu3+/Ba2+共掺杂对荧光粉发光性能的影响。用X射线衍射(XRD)、荧光分光光度计、色坐标等对荧光粉的结构进行表征。研究结果表明:掺杂Eu3+、MoO42-、Ba2+后NaCaPO4晶系没有发生变化,但是晶胞参数发生了变化,说明Eu3+、MoO42-、Ba2+进入NaCaPO4晶格中。在393 nm紫外光激发下,荧光粉发射光谱图出现两个Eu3+比较强的特征发射峰,分别属于Eu3+的5D0→7F1和5D0→7F2跃迁。与单掺杂16%Eu3+荧光粉相比,共掺杂16%Eu3+/3%MoO42-或16%Eu3+/6%Ba2+荧光粉的发射光谱中5D0→7F2跃迁产生的发射峰强度均高于单掺杂16%Eu3+荧光粉的发射峰强度,其5D0→7F2与5D0→7F1发射光强度之比(R)分别为1.76(RMo)和1.28(RBa),都大于单掺杂16%Eu3+荧光粉的REu(0.99),共掺杂Eu3+/MoO42-荧光粉的色纯度比单掺杂Eu3+和共掺杂Eu3+/Ba2+荧光粉的色纯度更好。 相似文献
6.
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
7.
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
8.
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
9.
Microstructural changes occurring during oxidation of the reduced form of donor-doped BaTiO3 (Ba1− X D X . Ti1− X 4+ Ti X 3+ O3 ) and during reduction of the oxidized form of donor-doped BaTiO3 (Ba1− X D X . Ti1− X /4 4+ ( V Ti ) X /4 O3 ) were studied using TEM. Samples of both types of solid solutions, containing different La concentrations (from 2 to 20 mol% La), were prepared by sintering under reducing conditions and in air, respectively. The reduced form of donor-doped BaTiO3 was oxidized by annealing at high temperatures (1150° and 1350°C) in air, while the oxidized form was reduced by annealing under reducing conditions. Because of oxidation of the reduced phase of donor-doped BaTiO3 , the Ti-rich phases Ba6 Ti17 O40 and BaLa2 Ti4 O12 were precipitated. Reduction of the oxidized form caused precipitation of the Ba-rich phase Ba2 TiO4 preferentially inside the matrix grains. All precipitates had well-defined orientational relationships with the perovskite matrix. 相似文献
10.
Activity–composition relations of FeCr2 O4 –FeAl2 O4 and MnCr2 O4 –MnAl2 O4 solid solutions were derived from activity–composition relations of Cr2 O3 –Al2 O3 solid solutions and directions of conjugation lines between coexisting spinel and sesquioxide phases in the systems FeO–Cr2 O3 –Al2 O3 and MnO–Cr2 O3 –Al2 O3 . Moderate positive deviations from ideality were observed. 相似文献
11.
Excitation of Tm3+ to 3 H 4 using the 791 nm pump source showed the frequency up-converted blue emission (∼480 nm) due to the Tm3+ :1 G 4 →3 H 6 transition in Tm3+ /Nd3+ codoped CaO·Al2 O3 glasses. Intensity and lifetime changes with rare-earth concentrations suggested the efficient energy transfer of Tm3+ :3 H 4 → Nd3+ :4 F 5/2 and Nd3+ :4 F 3/2 → Tm3+ :1 G 4 . The latter transfer enabled Tm3+ to reach its 1 G 4 level, and the blue emission became possible through the 1 G 4 →3 H 6 transition. Quantitative analysis with rate equations proved that these two transitions were the most efficient among all the possible energy transfer routes between Tm3+ and Nd3+ . Calculated up-conversion efficiency of the Tm3+ /Nd3+ combination in CaO·Al2 O3 glass was 6.6 × 10−3 , and it was ∼4 orders of magnitude larger than those reported for other oxide glasses. 相似文献
12.
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
13.
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
14.
James L. McArdle Gary L. Messing Lisa A. Tietz C. Barry Carter 《Journal of the American Ceramic Society》1989,72(5):864-867
The seeded transformation of boehmite-derived alumina was studied by transmission electron microscopy. Crystallographic analysis confirmed that the growth of α-Al2 O3 on α-Fe2 O3 seed crystals occurs by solid-phase epitaxy, with the orientation relationship [0001]Al2 O3 ||[0001]Fe2 O3 and [11 2 0]Al2 O3 ||[11 2 0Fe2 O3 . 相似文献
15.
Eugene B. Pretorius R. Snellgrove Arnulf Muan 《Journal of the American Ceramic Society》1992,75(6):1378-1381
Equilibrium ratios Cr2+ /Cr3+ of chromium oxide dissolved in CaO–chromium oxide–Al2 O3 –SiO2 melts have been determined by analysis of samples equilibrated at 1500°C under strongly reducing conditions ( p o2 = 10−9.56 to 10−12.50 atm). The majority of the chromium is divalent (Cr2+ ) under these conditions and Cr2+ /Cr3+ ratios at given constant oxygen pressures decrease with increasing basicity of the melts, expressed as CaO/SiO2 ratios. In addition, Cr2+ /Cr3+ ratios, at a given CaO/SiO2 ratio, are relatively unaffected by the amount of Al2 O3 present. 相似文献
16.
Antonio H. de Aza Juan E. Iglesias Pilar Pena Salvador De Aza 《Journal of the American Ceramic Society》2000,83(4):919-927
Solid-state compatibility and melting relationships in the subsystem Al2 O3 —MgAl2 O4 —CaAl4 O7 were studied by firing and quenching selected samples located in the isopletal section (CaO·MgO)—Al2 O3 . The samples then were examined using X-ray diffractomtery, optical microscopy, and scanning and transmission electron microscopies with wavelength- and energy-dispersive spectroscopies, respectively. The temperature, composition, and character of the ternary invariant points of the subsystem were established. The existence of two new ternary phases (Ca2 Mg2 Al28 O46 and CaMg2 Al16 O27 ) was confirmed, and the composition, temperature, and peritectic character of their melting points were determined. The isothermal sections at 1650°, 1750°, and 1840°C of this subsystem were plotted, and the solid-solution ranges of CaAl4 O7 , CaAl12 O19 , MgAl2 O4 , Ca2 Mg2 Al28 O46 , and CaMg2 Al16 O27 were determined at various temperatures. The experimental data obtained in this investigation, those reported in Part I of this work, and those found in the literature were used to establish the projection of the liquidus surface of the ternary system Al2 O3 —MgO—CaO. 相似文献
17.
Robert J. Sullivan Thallam T. Srinivasan Robert E. Newnham 《Journal of the American Ceramic Society》1990,73(12):3715-3717
The evaporative decomposition of solutions method was used to form V2 O5 . Spraying above the congruent melting temperature of V2 O5 (690°C) resulted in dense spherical particles with a smooth surface. Spraying below the V2 O5 melting temperature yielded porous V2 O5 powder with a rough surface. Reduction of the V2 O5 to V2 O3 was done in a H2 atmosphere. Spherical V2 O3 powder was attained when the reduction temperature was low enough to reduce the V2 O5 surface before partial sintering (necking) between V2 O5 particles occurred. The resulting V2 O3 particle size was smaller than the precursor V2 O5 powder as expected by the differences in densities between V2 O5 ( p = 3.36 g/cm3 ) and V2 O3 ( p = 4.87 g/cm3 ). 相似文献
18.
Satoshi lio Hitoshi Yokoi Masakazu Watanabe Yasushi Matsuo 《Journal of the American Ceramic Society》1991,74(2):296-300
The mechanical and thermal properties of Si2 N2 O/SiC-whisker composites were studied with emphasis on the effect of matrix composition and of whisker content. The fracture toughness of Si2 N2 O was remarkably improved by 90% with a concomitant 70% strength improvement by addition of SiC whiskers of only 10 vol%. Optimum mechanical and thermal properties of Si2 N2 O/SiC-whisker composites were obtained at an equimolar ratio of Si3 N4 /SiO2 , which is the stoichiometric composition for Si2 N2 O. Additional investigation concerning the Si2 N2 O-matrix/SiC-whisker interface by controlling sintering additives is necessary for further improvement of mechanical and thermal properties of Si2 N2 O/SiC-whisker composites. 相似文献
19.
采用等温溶解平衡法研究了298.2 K三元体系Li+, // Cl--H2O和四元体系Li+,K+, // Cl--H2O的相平衡。采用湿渣法和XRD测定了三元体系共饱点处平衡固相组成,发现固溶体(NH4Cl) x (LiCl·H2O)1-x 形成;采用XRD和SEM测定了四元体系共饱点处平衡固相组成,发现固溶体(NH4Cl) x (LiCl·H2O)1-x 、(NH4Cl) x (KCl)1-x 和 (KCl) x (NH4Cl)1-x 形成。研究发现:298.2 K下,三元体系相图由2个共饱点、3条单变量曲线和3个结晶相区组成,结晶区面积按照NH4Cl > (NH4Cl) x (LiCl·H2O)1-x > LiCl·H2O顺序依次减小;四元体系相图包含3个共饱点、8条单变量曲线和6个结晶相区,结晶区面积按 (KCl) x (NH4Cl)1-x > NH4Cl > KCl > (NH4Cl) x (KCl)1-x > (NH4Cl) x (LiCl·H2O)1-x > LiCl·H2O顺序依次减小。结果表明:298.2 K时,在氯化物体系中,锂铵和钾铵均可形成固溶体,且钾铵比锂铵更容易形成固溶体而大量析出,增加了锂钾铵氯化物的分离难度。 相似文献
20.
The decomposition products of YBa2 Cu3 O7-x depend on the composition of the molten chloride salt for exposure at 1173 K in air. The presence of dichloride salts such as CuCl2 , CaCl2 , or MgCl2 promote formation of CuO, Cu2 Y2 O5 , and loss of barium to the chloride salt as BaCl2 . Salts based on BaCl2 or containing LiCl result in YBa2 Cu3 O7-x decomposition products of Y2 BaCuO5 , CuO, and BaCl2 . High barium activity in the salt supports formation of the Y2 BaCuO5 phase and reaction of CO2 with the salt producing BaCO3 . Decomposition is most sluggish in binary NaCl-KCl salts where minimal amounts of reaction or decomposition products are observed. 相似文献