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1.
The solid phases formed at 1400°C. in air in the three-component systems BaO-SrO-TiO2 , BaO-CaO-TiO2 , and SrO-CaO-TiO2 are described. Besides solid solutions of components with known structures, some new ternary compounds have been studied. The dielectric constants and loss factors of a number of specimens are given. Crystallographic data of the compounds BaCaTiO4 , Ba3 Ca2 Ti2 O9 , and Ca3 Ti2 O7 and of the solid solution series (Ba, Sr), TiO4 are presented. The preparation of the new compounds is described in detail. 相似文献
2.
RAM A. SHARMA 《Journal of the American Ceramic Society》1988,71(4):272-276
Partial equilibrium phase diagrams for the systems MgF2 -MgO, MgF2 -CaO, and MgF2 -Al2 O3 were determined by differential thermal analysis. Simple eutectics were observed at 8.5 mol% MgO and 1228°± 3°C in the MgF2 -MgO system, at 7.5 mol% CaO and 1208°± 3°C in the MgF2 -CaO system, and at 2.5 mol% Al2 O3 and 1250°± 3°C in the MgF2 -Al2 O3 system. On the basis of agreements between the activities calculated by the Clausius-Clapeyron equation and Temkin's model using the present data, the eutectic melt consists of Mg2+ , F- , and O2- ions in the MgF2 -MgO system; Mg2+ , Ca2+ , F- , and O2- ions in the MgF2 -CaO system; and Mg2+ , Al3+ , F- , and AlO2¯ ions in the MgF2 -Al2 O3 system. Well-defined long needles of MgO in the MgF2 -MgO system, less defined needles of CaO in the MgF2 -CaO system, and Al2 O3 grains in the MgF2 -Al2 O3 system were observed by optical microscopy. 相似文献
3.
O3/UV,O3/TiO2/UV,O3/VO2/TiO2降解磺基水杨酸 总被引:1,自引:0,他引:1
实验利用O3/UV,O3/TiO2/UV,O3/VO2/TiO2降解了磺基水杨酸.结果表明,在这三种高级氧化技术中,O3/VO2/TiO2的氧化效果最好,如在相同的条件下,30 min后取样表明三者COD的去除率分别为47%,55%和70%.在不同pH条件下研究表明O3/TiO2/UV对水体pH的影响较为敏感.通过加入自由基猝灭剂研究表明三者产生羟基自由基的活性顺序是O3/VO2/TiO2>O3/TiO2/UV>O3/UV. 相似文献
4.
The mechanism of parahydrogen conversion was studied on Gd2 O3 and Y2 O3 powders and on Gd and Y evaporated metal films at low and high temperatures (77° to 90°K and 298° to 418°K). Absolute rates of conversion are compared to theoretical values for 3 possible reaction mechanisms, and it is concluded that a paramagnetic vibrational mechanism is operative on Gd2 O3 , Gd, and Y. On Y2 O3 the reaction rate is enhanced by additional surface paramagnetic sites. The portion of the surface which is active is ∼1 for the metals and ∼0.01 for the oxides. 相似文献
5.
R. E. CARTER 《Journal of the American Ceramic Society》1959,42(7):324-327
The thermal expansion of magnesium ferrite, wüstite, and magnesio-wüstite has been measured up to 1000°C. Good agreement has been found with published data obtained at lower temperatures, but the reported extrapolations have been shown to be low. The thermal expansion of MgFe2 O4 has been interpreted to support Gilleo's hypothesis that the super-exchange energy for Fe3+ -O2- -Fe3+ linkages is independent of the Fe3+ -O2- distance. This conclusion is supported by the fact that the energy per linkage is the same as that for Fe3+ -O2- Fe3+ linkages in a variety of crystal structures. 相似文献
6.
JENQ-GONG DUH HSING-TAO DAI BI-SHIOU CHIOU 《Journal of the American Ceramic Society》1988,71(10):813-819
A wet-chemical approach is applied to derive fine powders with compositions 11 mol% CeO2 -ZrO2 , 1 mol% YO1.5 -10 mol% CeO2 -ZrO2 , 12 mol% CeO2 -ZrO2 , and 2 mol% YO1.5 -10 mol% CeO2 -ZrO2 by the coprecipitation method. The characteristics of the as-derived powders are evaluated through thermal analysis and electron microscopy. The sintering behavior of the calcined powders is carried out at 1400° and 1500°C for 1 to 10 h. Sintered density higher than 98% of theoretical is achieved for sintering at 1400°C for several hours. The as-sintered density dependence on the sintering condition is related to the extent of tetragonal-to-monoclinic phase transformation as well as the associated microcracks. Partial substitution by Y2 O3 in CeO2 -ZrO2 results in reduced grain size and tends to stabilize the tetragonal structure. Y2 O3 is more effective than CeO2 with respect to the grain size refinement and tetragonal stability. In addition, Y2 O3 substitution in CeO2 -ZrO2 increases the hardness, while it decreases the fracture toughness. 相似文献
7.
OLAF MULLER RUSTUM ROY WILLIAM B. WHITE 《Journal of the American Ceramic Society》1968,51(12):693-699
Phase equilibria were determined for the systems NiO-Cr2 O3 −O2 , MgO-Cr2 O3 ,-O2 , and CdO-Cr2 O3 −O2 from 450° to above 850° C and at oxygen pressures of from 2 to 3500 atm. Only two intermediate phases were found in the nickel system: NiCrO., (CrVO4 structure) and the spinel NiCr2 O4 . The magnesium and cadmium systems are similar in that they have three analogous phases: the low-temperature α-MgCrO4 and α-CdCrO4 (both with the CrVO4 structure), the high-temperature β-MgCrO4 and β-CdCrO4 (both with the α-MnMoO4 structure), and the spinels MgCr2 O4 and CdCr2 O4 . The cadmium system contains an additional phase, Cd2 CrO5 , which is primitive monoclinic. 相似文献
8.
The phase equilibrium relations in the systems Y2 O3 -Al2 O3 and Gd2 O3 -Fe2 O3 were examined. Each system has two stable binary compounds. A 3:s molar ratio garnet-type compound exists in both systems. The 1:1 distorted perovskite structure is stable in the system Gd2 O3 -Fe2 O3 but only metastable in the system Y2 O3 -AI2 O3 . This interesting example of metastable formation and persistence of a compound with ions of high Z/r values explains the discrepancies in the literature on the structure of the composition YA1O3 . A new 2:1 molar ratio cubic phase has been found in the system Y2 O3 -A12 O3 . Since silicon can be completely substituted for aluminum in this compound, the aluminum ions are presumably in fourfold coordination. 相似文献
9.
PETER TAYLOR ALLAN B. CAMPBELL DERREK G. OWEN 《Journal of the American Ceramic Society》1983,66(5):347-351
The limits of miscibility at 650°C were determined for compositions with the mole ratio SiO2 /B2 O3 =1.07 in the systems X2 O-MO-B2 O3 -SiO2 (X = Na,K; M = Mg,Ca,Ba) and Na2 O-MgO-BaO-B2 O3 -SiO2 . The form of the miscibility gaps in the quaternary systems is similar to that previously described for the system Na2 O-ZnO-B2 O3 -SiO2 . The topography of miscibility gaps in systems of this type is discussed in detail. The extent of the miscibility gap is correlated with the polarizing power of each cation, X and M (Na > K and Zn ≅ Mg > Ca > Ba) both among the seven quaternary systems and within the single five-component system examined. The possibility of using empirical correlations observed among the quaternary systems to predict the behavior of other compositions, or of more complex systems, is explored. 相似文献
10.
Kentaro Terashima Sae-Hoon Kim Toshinobu Yoko 《Journal of the American Ceramic Society》1995,78(6):1601-1605
The third-order nonlinear optical susceptibilities χ(3) of M2 O-B2 O3 (M = Li, Na, K, Rb, Cs, and Ag) binary borate glasses have been measured by the third harmonic generation (THG) method. It is found that the enhancement of χ(3) by the structural change of BO3 units to BO4 units is small, while the enhancement of χ(3) due to the formation of non- bridging oxygen is rather significant. The effects of alkali cations on the χ(3) of alkali borate glasses are discussed in terms of the M-O bond character, focusing on the covalency of Li2 O-B2 O3 glasses. Comparison of the χ(3) values for Cs2 O-B2 O3 and Ag2 O-B2 O3 glasses which contain cations of comparable polarizability reveals that the χ(3) value is much greater for Ag2 O-B2 O3 glasses than for Cs2 O-B2 O3 glasses, which is possibly due to the great contribution of Ag(4 dz2 + 5 s + 5 pz ) hybrid orbitals to the nonlinear optical response. 相似文献
11.
Previous studies on glass formation involving GeO2 with Bi2 O3 , TI2 O, and PbO were extended by the use of Sb2 O3 . Wide areas of glass formation occur in the systems GeO2 -PbO-Sb2 O3 and GeO2 -Bi2 O3 -Sb2 O3 at all but the lowest GeO2 contents; the region of single-phase glasses in the system GeO2 -Tl2 O-Sb2 O3 is severely restricted. Glasses were examined by powder X-ray diffraction, differential thermal analysis, thermomechanical analysis, and Archimedes'technique to obtain glass transition and crystallization exotherm temperatures, thermal expansion coefficients, and densities; these properties are presented in diagrams for the GeO2 -Sb2 O3 binary and for two ternary systems. Based on calculated values of Δo ,the waveleneth for zero material dispersion. and dM/dΔ . the material disiersion slope at Δo , compositions in these systems may be useful for the construction of ultralow-loss optical waveguides in the 3 to 4 μm region. 相似文献
12.
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
13.
AKIO MAKEHIMA YOSHIAKI TAMURA TERUO SAKAINO 《Journal of the American Ceramic Society》1978,61(5-6):247-249
Glasses in the system Al2 O3 -Y2 O3 -SiO2 , containing TiO2 and La2 O3 , were investigated. Glasses of high refractive index and elastic modulus were developed. The observed Young's and shear moduli of these glasses show good agreement with theoretical values. Agreement was also found between the observed and calculated values of refractive index when the Appen's empirical coefficients were used. 相似文献
14.
Reforming of methane with carbon dioxide into syngas over Ni/γ-Al2O3 catalysts modified by potassium, MnO and CeO2 was studied. The catalysts were prepared by impregnation technique and were characterized by N2 adsorption/desorption isotherm, BET surface area, pore volume, and BJH pore size distribution measurements, and by X-ray diffraction and scanning electron microscopy. The performance of these catalysts was evaluated by conducting the reforming reaction in a fixed bed reactor. The coke content of the catalysts was determined by oxidation conducted in a thermo-gravimetric analyzer. Incorporation of potassium and CeO2 (or MnO) onto the catalyst significantly reduced the coke formation without significantly affecting the methane conversion and hydrogen yield. The stability and the lower amount of coking on promoted catalysts were attributed to partial coverage of the surface of nickel by patches of promoters and to their increased CO2 adsorption, forming a surface reactive carbonate species. Addition of CeO2 or MnO reduced the particle size of nickel, thus increasing Ni dispersion. For Ni–K/CeO2–Al2O3 catalysts, the improved stability was further attributed to the oxidative properties of CeO2. Results of the investigation suggest that stable Ni/Al2O3 catalysts for the carbon dioxide reforming of methane can be prepared by addition of both potassium and CeO2 (or MnO) as promoters. 相似文献
15.
The crystallization kinetics and mechanism of low-dielectric, low-temperature, cofirable CaO-B2 O3 -SiO2 glass-ceramics were investigated. Crystalline phases formed during firing included calcium silicates (CaSiO3 , Ca3 Si2 O7 , Ca2 SiO4 ) and calcium borate (CaB2 O4 ), with crystalline wollastonite (CaSiO3 ) the major phase. The crystallization kinetics of wollastonite followed an Avrami equation. The results of the present study showed an apparent activation energy of 200-260 kJ/mol. Combined with the results of reduced growth rate (growth rate × viscosity) and thermal analysis, the rate-controlling mechanism of crystallization appeared to be a two-dimensional surface nucleation growth. As the amount of crystalline wollastonite increased, the dielectric constant decreased, but the thermal expansion coefficient remained relatively unchanged. 相似文献
16.
Some effects of CaO, Na2 O, Sb2 O3 , and ZrO2 additions on Li0.3 Zn0.4 Fe2.3 O4 ferrite were studied to improve its density and other material properties. The densification behavior of the ferrite depended on the amount and type of additive. A relative density of ∼98.5% was achieved with the addition of CaO. The grain size decreased with the addition of Na2 O, CaO, and Sb2 O3 . The permeability and electrical resistivity increased with additives. CaO remarkably increased resistvity, whereas, ZrO2 increased permeability. Na2 O and Sb2 O3 increased the Curie temperature, whereas CaO and ZrO2 decreased it. These effects were attributed to mainly additive segregation on the grain boundaries, which suppressed grain-size development during the sintering of lithium zinc ferrite. 相似文献
17.
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
18.
A study of the solid solution of TiO2 , Fe2 O3 , and Cr2 03 in mullite was made by measuring the changes in lattice parameters and unit-cell volume. Synthetic mullite (3O3 -2SiO2 ) was reacted with up to 12 weight % of the oxides at temperatures ranging from 1000° to 17000C. The approximate minimum temperature required for the formation of solid solution was 12000C. for Fe2 03 and 1400°C. for Cr2 O3 and TiO3 . The maximum amount of solid solution found was 2 to 4% TiO2 at 1600°C., 10 to 12% Fe2 Os at 1300°C., and 8 to 10% CrZ O3 at 1600OC. Lattice parameters and unit-cell volumes for each solid solution series increased with increasing amounts of foreign oxide. There was good agreement between the calculated and observed increase in cell dimensions for the iron oxide series. Except in the case of titania, there was good agreement between X-ray data and petrographic observations. 相似文献
19.
MADELEINE H. WARZEE MARCEL MAURICE FRANZ HALLA WALTER R. RUSTON 《Journal of the American Ceramic Society》1965,48(1):15-17
In the binary system PbO–Laz O3 only one compound, 4PbO.La2 O3 , exists; it is flanked by two eutectics. The structure of the compound, although of lower symmetry, is intimately related to the C modification of the rare earths. Below 800° to 1000°C, metastable solid solutions are formed from oxide mixtures coprecipitated from mixed solutions of the nitrates, the cubic parameter a = 5.66 A, if extrapolated to pure La2 O3 , corresponding to half the a parameter of the C form of La2 O3 . The solid solutions existing between the compositions La2 O3 –2Pb0 and pure La2 O3 have a cubic face–centered lattice and obey Vegard's rule. The systems of PbO with Sm2 O3 and Gd2 O8 are quite similar to that with La2 O3 . The compound Sm2 O3 .4Pb0 decomposes at 1000°C with evaporation of PbO; Sm2 O3 remains in the B modification. 相似文献
20.
Jie Fu 《Journal of the American Ceramic Society》2000,83(4):1004-1006
Glasses with compositions Li1.2 M0.2 Ge1.8 (PO4 )3 (M = Al, Ga, Y, Gd, Dy, and La) were prepared and converted to glass-ceramics by heat treatment. The effects of the M3+ ions on the conductivity of the glasses and glass-ceramics were studied. The main phase present in the glass-ceramics was the conductive phase LiGe2 (PO4 )3 . Al3+ and Ga3+ ions entered the LiGe2 (PO4 )3 structure by replacing Ge4+ ions, but lanthanide ions did not. The glass-ceramics exhibited much higher conductivity than the glasses. With increased ionic radius of the M3+ ions, the conductivity remained almost unchanged at ∼3 × 10−12 S/cm for the glasses, but it decreased from 1.5 × 10−5 to 8 × 10−9 S/cm for the glass-ceramics at room temperature. The higher conductivity for Al3+ - and Ga3+ -containing glass-ceramics was suggested to result from the substitutions of Al3+ and Ga3+ ions for Ge4+ ions in the LiGe2 (PO4 )3 structure. 相似文献