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41.
Lithium-doped sulfated-zirconia catalysts for oxidative coupling of methane to give ethylene and ethane 总被引:1,自引:0,他引:1
Li-doped sulfated-zirconia catalysts were found to be effective for oxidative coupling of methane (OCM). The catalyst performances depend on the sulfate content and calcination temperature. A maximum C2 yield is attained over the catalysts, which contain 6 wt.% sulfate and calcined at 923–973 K, being closely related to the preparation conditions of sulfated-ZrO2 as solid super-acids. When the performances of the Li-doped sulfated-ZrO2 (Li/SZ) catalysts were tested at 1023 K as a function of reaction time, both the C2 and COx selectivities remained constant over the range of 8 h, but the CH4 conversion decreased from 17.5% to 11.9%. The nature of Li/SZ catalysts for the OCM was investigated by X-ray diffraction, XPS, and NH3 and CO2 TPD measurements. It could be postulated that the sulfated-ZrO2 surface could play an important role in the formation of a catalytically active structure by Li-doping. 相似文献
42.
Rare-earth (RE: Lu, Gd, Nd, 0.10 mol%)-doped alumina nanopowders were prepared by a new sol-gel route using polyhydroxoaluminum (PHA) and RECl3 solutions under α-alumina (∼ 75 nm) seeding. Among the rare-earth dopants studied, Lu yields the most suitable nanopowders for low-temperature densification. The 0.10 mol% Lu-doped nanopowders, which were obtained at a calcination temperature of 900 °C under 5 mass% α-alumina seeding, consisted of ∼ 80-nm α-alumina particles and γ-alumina nanoparticles. Using these Lu-doped alumina nanopowders, fully densified alumina ceramics with a uniform microstructure composed of fine grains with an average size of 0.61 μm could be obtained at 1400 °C by pressureless sintering. Clearly, the Lu-doped nanopowders obtained here represent a viable option for fabricating dense, finer-grained alumina ceramics because an undoped sample with 5 mass% seeds gave a microstructure with an average grain size of 1.78 μm at 1400 °C. 相似文献
43.
Atsushi Odaka Tomohiro Yamaguchi Masahiro Hida Seiichi Taruta Kunio Kitajima 《Ceramics International》2009,35(5):1845-1850
Dense submicron-grained alumina ceramics were fabricated by pulse electric current sintering (PECS) using M2+(M: Mg, Ca, Ni)-doped alumina nanopowders at 1250 °C under a uniaxial pressure of 80 MPa. The M2+-doped alumina nanopowders (0–0.10 mass%) were prepared through a new sol–gel route using high-purity polyhydroxoaluminum (PHA) and MCl2 solutions as starting materials. The composite gels obtained were calcined at 900 °C and ground by planetary ball milling. The powders were re-calcined at 900 °C to increase the content of α-alumina particles, which act as seeding for low-temperature densification. Densification and microstructural development depend on the M2+ dopant species. Dense alumina ceramics (relative density ≥99.0%) thus obtained had a uniform microstructure composed of fine grains, where the average grain size developed for non-doped, Ni-doped, Mg-doped and Ca-doped samples was 0.67, 0.67, 0.47 and 0.30 μm, respectively, showing that Ca-doping is the most promising method for tailoring of nanocrystalline alumina ceramics. 相似文献
44.
Tomohiro Yamaguchi Teruyoshi Yoshimura Tomohiko Yamakami Seiichi Taruta Kunio Kitajima 《Microporous and mesoporous materials》2008,111(1-3):285-291
New porous solids from alumina-pillared fluorine micas (APMs), which were obtained from synthetic Na-tetrasilicic fluorine mica [NaMg2.5Si4O10F2], were prepared by sulfuric acid-treatment under mild conditions at 25 °C. The products were investigated by XRD, ICP, SEM, TEM and N2 adsorption–desorption isotherm at 77 K. XRD measurements indicated that the interlayer pillared structure having a large basal spacing collapsed during the early stages of the acid-treatment. ICP analyses indicated that Al3+ and Mg2+ ions were leached out from the pillared micas during the acid-treatment. The pore properties of the leached products were found to differ from those of the mother pillared micas: the acid leaching of the pillared micas leads to the formation of mesopores around 3.2 nm in diameter. The correlation between the change in pore properties and cation elution behavior suggests that the mesopore formation results from the leaching of Mg2+ ions from the octahedral sheet of the pillared micas. The leached products thus obtained retained the flaky morphology of the mother pillared micas. These results show that the mild acid-treatment using APMs provides a novel route for obtaining unique mesopore solids having the large particle sizes of the mother micas. 相似文献
45.
Hideshi Suzuki Masahiro Ogawa Kenji Hironaka Kunio Ito Hisakazu Sunada 《Drug development and industrial pharmacy》2001,27(9):951-958
Nifedipine is a poorly water soluble drug that demonstrates low bioavailability. In a previous study, a coground mixture of nifedipine with sodium deoxycholate (DCNa), a bile salt, immediately produced colloidal particles when dispersed in water. In this study, the effect of the weight fraction of DCNa, grinding time, dissolution media, and storage conditions on colloidal particle formation in solution was investigated. The coground mixture was prepared with a vibration rod mill, and its solid state was characterized using powder X-ray diffraction. A laser diffraction particle size analyzer was used to determine the particle size distribution curve in water. The size of particles formed in solution decreased with an increase in the weight fraction of DCNa and grinding time. A nifedipine-DCNa (1 : 2 w/w) mixture coground for 30 min was used in the experiments. Colloidal particle formation from the coground mixture was also observed in dissolution media of water and a pH 6.8 buffer solution at 37°C. Most precipitates passed through a filter with a pore size of 0.8 μm, but the particle size distribution in water was different from that in the pH 6.8 buffer solution. DCNa exhibited not only micellar solubilization for drug crystals, but also a retarding effect on drug crystal growth in a supersaturated solution. The latter effect could serve to form colloidal particles in solution. When stored under 75% relative humidity at 40°C for 1 month, the amorphous coground mixture crystallized, and the particle size in water markedly increased. Therefore, the weight fraction of DCNa, grinding time, dissolution media, and humidity during storage influence the dissolution characteristics of nifedipine from a coground mixture. 相似文献
46.
A self-consistent simulation using the Monte Carlo ensemble particle technique for analysis of heterojunction bipolar transistor (HBT) transient behavior, such as switching performance, is presented. The transient Monte Carlo method has been applied to a self-consistent simulation of two HBT designs with improved collector structures for high-speed and high-frequency applications, and the results are compared with the characteristics of conventional HBTs. The simulation results indicate that the two new collector structures, the inverted field collector and the undoped collector, have better switching performance than the conventional HBT. The study of the switching characteristics' dependence on collector-base bias voltage and collector current suggests that the inverted field HBT is the best approach in terms of switching properties. The results are supported and explained by examining electron transport properties such as overshoot velocity and energy valley occupation, as well as band bending in the collector space-charge region at different current levels 相似文献
47.
Shigeru Okada Toetsu Shishido Takao Mori Kiyokata Iizumi Kunio Kudou Kazuo Nakajima 《Journal of Alloys and Compounds》2008,458(1-2):297-301
LEAlB14 (orthorhombic, Imam) (LE = Li, Mg) crystals were grown using metal salts (Li2CO3, LiF, LiI, MgO, MgF2, MgI2) and crystalline boron from a high-temperature aluminium metal flux. The growth conditions for growing LEAlB14 were established using the starting mixtures of B/LE = 2.0, and Al metal was added to each mixture at a mass ratio of 1:15–20. LEAlB14 crystals from the Al-self flux using metal salts could be obtained from all the different salts. The maximum dimensions of LiAlB14 and MgAlB14 crystals were approximately 18 and 12 mm for the crystals obtained from LiF and MgF2. The unit-cell parameters of as-grown LEAlB14 are as follows: for LiAlB14, obtained from LiF, a = 0.5846 (2) nm, b = 0.8144 (2) nm, c = 1.0355 (3) nm, V = 0.4930 (2) nm3: for MgAlB14, obtained from MgF2, a = 0.5845 (2) nm, b = 0.8114 (2) nm, c = 1.0330 (3) nm, V = 0.4899 (3) nm3. Microhardness, oxidation resistance and magnetic susceptibility of these materials are described in detail. 相似文献
48.
Kunio Matsui Jun Kikuma Masamichi Tsunashima Tetsuji Ishikawa Shin-ya Matsuno Akihiro Ogawa Masugu Sato 《Cement and Concrete Research》2011,(5):510-519
The hydrothermal formation of tobermorite during the processing of autoclaved aerated concrete was investigated by in situ X-ray diffraction (XRD) analysis. High-energy X-rays from a synchrotron radiation source in combination with a newly developed autoclave cell and a photon-counting pixel array detector were used.To investigate the effects of the silica source, reactive quartz from chert and less-reactive quartz from quartz sand were used as starting materials. The effect of Al addition on tobermorite formation was also studied. In all cases, C-S-H, hydroxylellestadite and katoite were clearly observed as intermediates.Acceleration of tobermorite formation by Al addition was clearly observed. However, Al addition did not affect the dissolution rate of quartz. Two pathways, via C-S-H and katoite, were also observed in the Al-containing system. These results suggest that the structure of initially formed C-S-H is important for the subsequent tobermorite formation reactions. 相似文献
49.
Atsushi Tsutsumi Hidehiko Suzuki Yasushi Saito Kunio Yoshida Ryohei Yamazaki 《Powder Technology》1998,100(2-3):237-241
The granulation of multi-component particles was conducted in a fast fluidized bed with an atomizing binder solution. The effects of gas velocity and binder droplet diameter on granulation rate, granule size distribution and granule composition were studied. The granulation rate and granule yield were determined by the balance between the agglomeration rate of feed particles and the disintegration rate of granules because there was no secondary granulation. With the increase in gas velocity and the reduction in binder droplet size, the agglomeration rate of feed particles decreased but the disintegration rate of granules increased, resulting in a reduced granule yield. Despite the larger fraction of small particles in the granules, the homogenous granulation of multi-component particles was achieved. 相似文献
50.
Kunio Yoshikawa 《中国科学:信息科学(英文版)》2010,(1)
Drying of sewage sludge is an effective way for treatment and utilization of sewage sludge,where reduction of energy consumption is one of the major technical challenges.So we experimentally investigated the possibility of the hydrothermal treatment.We have found that treatment of sewage sludge by saturated steam with the temperature of 190°C and pressure of 20 bar can dramatically improve the dehydration performance of the slurry like product.And the water content can be reduced down to about 55% by a mech... 相似文献