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1.
In the CaO-SiO2-Al2O3-Fe2O3 pseudoquaternary system, the solid solutions of Ca2(AlxFe1−x)2O5, with x<0.7 (ferrite), Ca2SiO4 (belite), Ca3Al2O6 (C3A) and Ca12Al14O33 (C12A7), were crystallized out of a complete melt during cooling at 8.3 °C/min. Upon cooling to 1370 °C, both the crystals of ferrite with x=0.41 and belite would start to nucleate from the melt. During further cooling, the x value of the precipitating ferrite would progressively increase and eventually approach 0.7. At ambient temperature, the ferrite crystals had a zonal structure, the x value of which successively increased from the cores toward the rims. The value of 0.45 was confirmed for the cores by EPMA. The chemical formula of the rims was determined to be Ca2.03[Al1.27Fe0.68Si0.02]Σ1.97O5 (x=0.65). As the crystallization of ferrite and belite proceeded, the coexisting melt would become progressively enriched in the aluminate components. After the termination of the ferrite crystallization, the C3A and belite would immediately crystallize out of the melt, followed by the nucleation of C12A7. The C12A7 accommodated about 2.1 mass% Fe2O3 in the chemical formula Ca12.03[Al13.61Fe0.37]Σ13.98O33, being free from the other foreign oxides (SiO2 and P2O5). 相似文献
2.
Tao Chen Hongli Wang Ting Zhang Guangchang Wang Jifang Zhou Jianwei Zhang Yuhong Liu 《Ceramics International》2014
(Bi0.5Na0.5)0.94Ba0.06TiO3–xHfO2 [BNBT–xHfO2] lead-free ceramics were prepared using the conventional solid-state reaction method. Effects of HfO2 content on their microstructures and electrical properties were systematically studied. A pure perovskite phase was observed in all the ceramics with x=0–0.07 wt%. Adding optimum HfO2 content can induce dense microstructures and improve their piezoelectric properties, and a high depolarization temperature was also obtained. The ceramics with x=0.03 wt% possess optimum electrical properties (i.e., d33~168 pC/N, kp~32.1%, Qm~130, εr~715, tan δ~0.026, and Td~106 °C, showing that HfO2-modified BNBT ceramics are promising materials for piezoelectric applications. 相似文献
3.
A. P. Tang X. Y. Wang S. Y. Yang J. Q. Cao 《Journal of Applied Electrochemistry》2008,38(10):1453-1457
Monoclinic structure Li3V2(PO4)3/C composite powders are synthesized via a novel homogeneous mixing route followed by a one-step heat treatment. The composites
were characterized by X-ray diffraction (XRD) and galvanostatic charge/discharge, CV measurements. The influence of the heat
treatment on the electrochemical properties of Li3V2(PO4)3/C composites was investigated. To examine the effect of residual carbon content on the properties of the composites, six
samples with 1.2, 2.3, 3.4, 4.4, 5.8, and 7.0 wt% carbon were prepared. The sample with 4.4 wt% carbon exhibited good cycling
performance and rate capability in the range of 3.0–4.8 V. 相似文献
4.
Catalytic Production of Carbon Nanotubes by Decomposition of CH4 over the Pre-reduced Catalysts LaNiO3, La4Ni3O10, La3Ni2O7 and La2NiO4 总被引:4,自引:0,他引:4
H. Li Q. Liang L.Z. Gao S.H. Tang Z.Y. Cheng B.L. Zhang Z.L. Yu C.F. Ng C.T. Au 《Catalysis Letters》2001,74(3-4):185-188
A large amount of more graphitic carbon nanotubes with a narrow size distribution was produced from catalytic decomposition of CH4 over pre-reduced LaNiO3, La4Ni3O10, La3Ni2O7 and La2NiO4. The structure and component of fresh and reduced LaNiO3, La4Ni3O10, La3Ni2O7 and La2NiO4 were determined by X-ray diffraction (XRD). The carbon nanotubes obtained were characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Thermal oxidation of carbon nanotubes in air was made by thermogravimetric experiments (TG). The results revealed that the value of La/Ni in different catalyst precursors influences the diameter distribution and graphitic degree of carbon nanotubes. Lower La/Ni leads to wider diameter and higher graphitic degree of carbon nanotubes. 相似文献
5.
Chayene G. Anchieta Daniela Sallet Edson L. Foletto Syllos S. da Silva Osvaldo Chiavone-Filho Claudio A.O. do Nascimento 《Ceramics International》2014
Ternary zinc spinel oxides such as Zn2SnO4, ZnAl2O4 and ZnFe2O4 were synthesized and characterized, and their activities in the photodegradation of phenol molecules were investigated. Zn2SnO4, ZnAl2O4 and ZnFe2O4 powders were synthesized by hydrothermal, metal–chitosan complexation and solvothermal routes, respectively. The face-centered cubic spinel structure of each material was confirmed by powder X-ray diffractometry (XRD) and its porous structure by N2 adsorption–desorption isotherms. The characterization of spinels was complemented with Fourier transform infrared spectroscopy (FTIR) and X-rays fluorescence (XRF), revealing the formation of spinel structures with high purity. The photocatalytic activity in the degradation of phenol was observed only with Zn2SnO4 oxide. Mineralization degree of phenol molecules by Zn2SnO4 photocatalyst determined by total organic carbon analysis (TOC) reached 80% at 360 min under sunlight. 相似文献
6.
Soo Chool Lee Chun Yong Ryu Dhanusuraman Ragupathy Joong Beom Lee Jae Chang Kim 《Fuel》2011,90(4):1465-3842
A new regenerable alumina-modified sorbent was developed for CO2 capture at temperatures below 200 °C. The CO2 capture capacity of a potassium-based sorbent containing Al2O3 (KAlI) decreased during multiple CO2 sorption (60 °C) and regeneration (200 °C) tests due to the formation of the KAl(CO3)(OH)2 phase, which could be converted into the original K2CO3 phase above 300 °C. However, the new regenerable potassium-based sorbent (Re-KAl(I)) maintained its CO2 capture capacity during multiple tests even at a regeneration temperature of 130 °C. In particular, the CO2 capture capacity of the Re-KAl(I)60 sorbent which was prepared by the impregnation of Al2O3 with 60 wt.% K2CO3 was about 128 mg CO2/g sorbent. This excellent CO2 capture capacity and regeneration property were due to the characteristics of the Re-KAl(I) sorbent producing only a KHCO3 phase during CO2 sorption, unlike the KAlI30 sorbent which formed the KHCO3 and KAl(CO3)(OH)2 phases even at 60 °C. This result was explained through the structural effect of the support containing the KAl(CO3)(OH)2 phase which was prepared by impregnation of Al2O3 with K2CO3 in the presence of CO2. 相似文献
7.
E. Minor-Pérez R. Mendoza-Serna J. Méndez-Vivar R. C. Pless D. Quintana-Zavala R. Torres-Robles 《Journal of Porous Materials》2006,13(1):13-19
An experimental strategy was developed to obtain transparent Si-Al-Ti-Ni-Mo and Si-Zr-Ti-Ni-Mo sols via the sol-gel process.
The sol was prepared from Si(OEt)4 (TEOS), Al(OBus)3 (OBus: C2H5CH(CH3)O), Ti(OEt)4 (OEt: OCH2CH3), Zr(OPrn)4 (OPrn: OCH2CH2CH3). In both cases nickel nitrate hexahydrate (Ni(NO3)2 · 6H2O) and ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24 · 4H2O) were the Ni and Mo sources, respectively. The sols were characterized by Fourier Transform Infrared Spectroscopy (FTIR).
Assignments of the simultaneous formation of the Si-O-Al, Si-O-Ti, Si-O-Ni, and Si-O-Zr bonds were done. The sols were polymerized
at room temperature (293 K) to obtain gels, and these were dried at 423 K and calcined at 573, 853 and 893 K in air. The characterization
techniques used were small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and
29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR). The density of the solids was measured following ASTM method
D-4892 and the porosity and surface area were determined by N2 adsorption/desorption isotherms. The corresponding average pore diameters were evaluated using the BJH, HK, and DA methods. 相似文献
8.
This work investigates the improvement of Ni/Al2O3 catalyst stability by ZrO2 addition for H2 gas production from CH4/CO2 reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO2 loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH4:CO2 ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al2O3 was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO2, as it enhances dissociation of CO2 forming oxygen intermediates near the contact between ZrO2 and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO2–Al2O3 composite and the plugging of Al2O3 pore by ZrO2. The 15% Ni/10% ZrO2/Al2O3 co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made. 相似文献
9.
Bingbing Tian 《Electrochimica acta》2010,55(19):5453-14416
Niobium doped lithium titanate with the composition of Li4Ti4.95Nb0.05O12 has been prepared by a sol-gel method. X-ray diffraction (XRD) and scanning electron microscope (SEM) are employed to characterize the structure and morphology of Li4Ti4.95Nb0.05O12. The Li4Ti4.95Nb0.05O12 electrode presents a higher specific capacity and better cycling performance than the Li4Ti5O12 electrode prepared by the similar process. The Li4Ti4.95Nb0.05O12 exhibits an excellent rate capability with a reversible capacity of 135 mAh g−1 at 10 C, 127 mAh g−1 at 20 C and even 80 mAh g−1 at 40 C. Electrical resistance measurement and electrochemical impedance spectra (EIS) reveal that the Li4Ti4.95Nb0.05O12 exhibits a higher electronic conductivity and faster lithium-ion diffusivity than the Li4Ti5O12, which indicates that niobium doped lithium titanate (Li4Ti4.95Nb0.05O12) is promising as a high rate anode for the lithium-ion batteries. 相似文献
10.
11.
Silicon nitride ceramics were sintered using Y2O3–Al2O3 or E2O3–Al2O3 (E2O3 denotes a mixed oxide of Y2O3 and rare-earth oxides) as sintering additives. The intergranular phases formed after sintering was investigated using high-resolution X-ray diffraction (HRXRD). The use of synchrotron radiation enabled high angular resolution and a high signal to background ratio. Besides the appearance of β-Si3N4 phase the intergranular phases Y3Al5O12 (YAG) and Y2SiO5 were identified in both samples. The refinement of the structural parameters by the Rietveld method indicated similar crystalline structure of β-Si3N4 for both systems used as sintering additive. On the other hand, the intergranular phases Y3Al5O12 and Y2SiO5 shown a decrease of the lattice parameters, when E2O3 was used as additive, indicating the formation of solid solutions of E3Al5O12 and E2SiO5, respectively. 相似文献
12.
Annemarieke Maltha Thomas L. F. Favre Benoit Brunet Clarisse J. C. Gaudin Vladimir Ponec 《Catalysis Letters》1994,28(1):17-23
The catalytic behaviour of the PbO-Mn3O4 and the Bi2O3-MoO3 systems was investigated in the selective reduction of nitrobenzene to nitrosobenzene. Lead compounds appeared to be good catalysts, and co-catalysts when used with Mn3O4. Different from oxidations by di-oxygen, Bi3O3 alone is a good catalyst and formation of mixed Bi-Mo-O compounds does not enhance the catalytic activity. It is suggested that the difference between these catalysts in the mentioned reaction is related to the way in which the oxygen vacancy is represented by the oxygen donor. 相似文献
13.
S.M. Lakiza Ja.S. TyschenkoL.M. Lopato 《Journal of the European Ceramic Society》2011,31(7):1285-1291
The phase diagram of the Al2O3-HfO2-Y2O3 system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al2O3 + HfO2 + Y3Al5O12. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al2O3-HfO2-Y2O3 system. 相似文献
14.
Columbite MgNb2O6 (MN) and ZnNb2O6 (ZN) ceramics produced by the reaction-sintering process were investigated. Secondary phases Mg0.652Nb0.598O2.25 and Mg0.66Nb11.33O29 were found in MgNb2O6 pellets. After 1250 °C sintering for 2 h, a density 4.85 g/cm3 (97.1% of the theoretical value) was obtained in MgNb2O6 pellets. In ZnNb2O6 pellets, no secondary phase formed. The maximum density 5.55 g/cm3 (98.7% of the theoretical value) occurs at 1200 and 1180 °C sintering for 2 and 4 h, respectively. 相似文献
15.
The acid-base properties of -Al2O3 and alumina-supported B2O3, Ga2O3 and In2O3 have been determined by microcalorimetry of ammonia and sulfur dioxide adsorption. From the adsorption of NH3, it was found that the addition of B2O3 on alumina leads to an increase of the number of acid sites, while Ga2O3 and In2O3 additives caused a decrease in the acidity of alumina. Using SO2 as a probe molecule to study the basicity, the number of surface basic sites on alumina was found to be strongly decreased by the addition of boron oxide, while it was only slightly affected by the addition of gallium oxide and decreased by the addition of indium oxide. The differential heats of adsorption are discussed as a function of the coverage by the probe molecules. The electronic properties of the oxides are examined in order to explain the acid-base properties of the supported oxides. 相似文献
16.
Structure and electrochemical properties of nanocarbon-coated Li3V2(PO4)3 prepared by sol-gel method
A liquid-based sol-gel method was developed to synthesize nanocarbon-coated Li3V2(PO4)3. The products were characterized by XRD, SEM and electrochemical measurements. The results of Rietveld refinement analysis indicate that single-phase Li3V2(PO4)3 with monoclinic structure can be obtained in our experimental process. The discharge capacity of carbon-coated Li3V2(PO4)3 was 152.6 mAh/g at the 50th cycle under 1C rate, with 95.4% retention rate of initial capacity. A high discharge capacity of 184.1 mAh/g can be obtained under 0.12C rate, and a capacity of 140.0 mAh/g can still be held at 3C rate. The cyclic voltammetric measurements indicate that the electrode reaction reversibility is enhanced due to the carbon-coating. SEM images show that the reduced particle size and well-dispersed carbon-coating can be responsible for the good electrochemical performance obtained in our experiments. 相似文献
17.
Sang-Woo Park Oh-Shim Joo Kwang-Deog Jung Hyo Kim Sung-Hwan Han 《Korean Journal of Chemical Engineering》2000,17(6):719-722
The stability and the activity of Fe2O3/Cr2O3 and ZnO/Cr2O3 catalysts were examined for a reverse-watergas-shift reaction (RWReaction). The initial activities of those catalysts were
quite high so that the conversion reached close to equilibrium. The activity of Fe2O3/Cr2O3 catalyst decreased from 33.5 to 29.8% during the RWReaction for 75 h at 873 K with GHSV (ml/gcat · h) of 100,000. Moreover,
the coke formation on the Fe2O3/Cr2O3 catalyst caused clogging in the RWReactor of the CAMERE process. On the other hand, the ZnO/Cr2O3 catalyst showed no coke formation and no deactivation for the RWReaction at 873 K with GHSV (ml/gcat · h) of 150,000. The
ZnO/Cr2O3 was a good catalyst for the RWReaction of the CAMERE process. 相似文献
18.
K. J. W. Atkinson Robin W. Grimes Mark R. Levy Zoe L. Coull Tim English 《Journal of the European Ceramic Society》2003,23(16):3059-3070
Atomic scale computer simulation was used to predict the mechanisms and energies associated with the accommodation of aliovalent and isovalent dopants in three host oxides with the corundum structure. Here we consider a much more extensive range of dopant ions than has previously been the case. This enables a rigorous comparison of calculated mechanism energetics. From this we predict that divalent ions are charge compensated by oxygen vacancies and tetravalent ions by cation vacancies over the full range of dopant radii. When defect associations are included in the model these conclusions remain valid. At equilibrium, defects resulting from extrinsic dopant solution dominate intrinsic processes, except for the largest dopant cations. Solution reaction energies increase markedly with increasing dopant radius. The behaviour of cluster binding energies is more complex. 相似文献
19.
C Z Zhao M Werner S Taylor P R Chalker A C Jones Chun Zhao 《Nanoscale research letters》2011,6(1):48-6
La-doped zirconia films, deposited by ALD at 300°C, were found to be amorphous with dielectric constants (k-values) up to
19. A tetragonal or cubic phase was induced by post-deposition annealing (PDA) at 900°C in both nitrogen and air. Higher k-values
(~32) were measured following PDA in air, but not after PDA in nitrogen. However, a significant dielectric relaxation was
observed in the air-annealed film, and this is attributed to the formation of nano-crystallites. The relaxation behavior was
modeled using the Curie–von Schweidler (CS) and Havriliak–Negami (HN) relationships. The k-value of the as-deposited films
clearly shows a mixed CS and HN dependence on frequency. The CS dependence vanished after annealing in air, while the HN dependence
disappeared after annealing in nitrogen. 相似文献
20.
《应用陶瓷进展》2013,112(8):466-472
ABSTRACTMCo2O4 (M?=?Mn,Ni) microparticles were synthesised by a simple hydrothermal solvothermal method. The samples were characterised by X-ray diffraction, X-ray energy dispersive spectroscopy and scanning electron microscopy, which showed that MnCo2O4 microparticles with spherical particles aggregated by a large number of small cubes and cubic shaped NiCo2O4 microcubes were obtained. The microwave absorption properties of these products were systematically investigated by vector network analysis. Results indicated that the minimum reflection loss value of MnCo2O4 microparticles was ?26.34?dB at 11.04?GHz with the absorber thickness of 2.5?mm, which was much lower than that of NiCo2O4 microcubes with the same absorber thickness. The possible mechanism was analysed, indicating that the geometry and size of MCo2O4 (M?=?Mn,Ni) microparticles played a key role in microwave absorption. 相似文献