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101.
A novel anionic surfactant templating route for synthesizing mesoporous silica with unique structure
Che S Garcia-Bennett AE Yokoi T Sakamoto K Kunieda H Terasaki O Tatsumi T 《Nature materials》2003,2(12):801-805
Anionic surfactants are used in greater volume than any other surfactants because of their highly potent detergency and low cost of manufacture. However, they have not been used as templates for synthesizing mesoporous silica. Here we show a templating route for preparing mesoporous silicas based on self-assembly of anionic surfactants and inorganic precursors. We use aminosilane or quaternized aminosilane as co-structure-directing agent (CSDA), which is different from previous pathways. The alkoxysilane site of CSDA is co-condensed with inorganic precursors; the ammonium site of CSDA, attached to silicon atoms incorporated into the wall, electrostatically interacts with the anionic surfactants to produce well-ordered anionic-surfactant-templated mesoporous silicas (AMS). These have new structures with periodic modulations as well as two-dimensional hexagonal and lamellar phases. The periodic modulations may be caused by the coexistence of micelles that differ in size or curvature, possibly owing to local chirality. These mesoporous silicas provide a new family of mesoporous materials as well as shedding light on the structural behaviour of anionic surfactants. 相似文献
102.
Mechanical and thermophysical characteristics of Si-Ti-C-O fibre-bonded ceramic produced by hot-pressing the laminated material of oxidized satin-woven Si-Ti-C-O fibre have been investigated at room and cryogenic temperatures. The fibre element (diameter: 8 m, fibre volume fraction: 85 ± 1%) constructing the Si-Ti-C-O fibre-bonded ceramic showed a close-packed structure of the oxidized Si-Ti-C-O fibre mainly composed of fine SiC crystals, amorphous SiO2-based phase and turbostratic carbon. The Si-Ti-C-O fibre-bonded ceramic with lightweight (density: 2.45 × 103kg/m3) and low porosity (<1 vol%) showed a markedly higher fracture energy (notched, cross-plied specimen: approximately 10kJ/m2) and lower thermal conductivity (1/10 the value of stainless steel). The reason why the fibre- bonded ceramic showed such a low thermal conductivity in spite of very high thermal conductivity of a pure SiC and carbon could be attributed to the complicated microstructure of Si-Ti-C-O fibre-bonded ceramics. 相似文献
103.
A recirculating system of aqueous trichloroethylene (TCE) solutions through the packed bed reactor with TiO2 pellets has been developed in order to mineralize TCE without difficulties for filtration and recovery of catalyst. The TiO2 pellets prepared by sol gel method have photocatalytic activity similar to commercially available PC-101 and PC-102 in the powder form and to ST-B11 pellets. In batch experiments with TiO2 powders, Degussa P-25 is the most active photocatalyst, which indicates that specific surface area is not an important factor controlling the photocatalytic activity in aqueous solutions. The degradation rates of TCE in the recirculating system with TiO2 pellets decreased in the presence of H2O2, while were remarkably accelerated by adding S2O8(2-). The presence of S2O8(2-) ions more than 0.01 mol dm(-3) completely suppressed hole-electron recombination and mineralized 50 ppm TCE with the 2 h irradiation. In a reactor without TiO2 photocatalysts, TCE was photodegraded by SO4- radicals which produced by photodissociation of S2O8(2-). The degradation rates increased with increase of the initial S2O8(2-) concentration. However, TCE was not mineralized but converted to intermediates which were slowly degraded to Cl- by continuing the irradiation. 相似文献
104.
A.J. McEvily S. Ishihara M. Endo H. Sakai H. Matsunaga 《International Journal of Fatigue》2007,29(12):2237-2245
Recent data on short fatigue crack growth in two cast and hot isostatically pressed (hipped) aluminum alloys obtained by Shyam, Allison and Jones have been analyzed in terms of a previously proposed one-parameter short crack model which includes consideration of elastic–plastic effects, the Kitagawa effect and the development of crack closure in the wake of a newly formed crack. The material constants obtained in a prior investigation of short crack growth behavior in a cast aluminum alloy tested under fully reversed loading were used as a basis for the present analysis. The predicted rates of fatigue crack propagation are in accord with the experimental results. In the discussion, aspects of the two-parameter approach presented by Shyam et al. are compared with those of the one-parameter method of analysis used herein. 相似文献
105.
Toshiyuki Nishimura Xin Xu Koji Kimoto Naoto Hirosaki Hidehiko Tanaka 《Science and Technology of Advanced Materials》2007,8(7-8):635
Fine-grained silicon nitride ceramics were investigated mainly for their high-strain-rate plasticity. The preparation and densification of fine silicon nitride powder were reviewed. Commercial sub-micrometer powder was used as raw powder in the “as-received” state and then used after being ground and undergoing classification operation. Chemical vapor deposition and plasma processes were used for fabricating nanopowder because a further reduction in grain size caused by grinding had limitations. More recently, nanopowder has also been obtained by high-energy milling. This process in principle is the same as conventional planetary milling. For densification, primarily hot pressing was performed, although a similar process known as spark plasma sintering (SPS) has also recently been used. One of the advantages of SPS is its high heating rate. The high heating rate is advantageous because it reduces sintering time, achieving densification without grain growth. We prepared silicon nitride nanopowder by high-energy milling and then obtained nanoceramics by densifying the nanopowder by SPS. 相似文献
106.
Takanori Takeno Shingo Abe Koshi Adachi Hiroyuki Miki Toshiyuki Takagi 《Diamond and Related Materials》2010,19(5-6):548-552
In this study we developed composite coatings consisting of amorphous hydrogenated carbon (a-C:H) and molybdenum-disulfide (MoS2), and clarified their microstructure. In addition, we interpreted the tribological properties of the composite coatings in the viewpoint of a deposition-induced microstructural modification. The coatings were produced by the hybrid deposition technique of RF-generated methane and argon plasma and DC magnetron co-sputtering of MoS2 target. The deposition parameter investigated in this study was methane flow rate. Structural analyses were performed using a transmission electron microscope (TEM) and an atomic force microscope (AFM). Friction tests were conducted using a ball-on-disk type tribometer. From an electron micrograph, it was confirmed that nano-clusters were embedded into an amorphous carbon host matrix. Surface roughness of the composite coating was ~ 0.25 nm in Ra compared to 5.0 nm in Ra of sputtered MoS2. The concentration measurements were performed, and the results show that the sulfur and molybdenum concentration ratio, [S]/[Mo], is ~ 0.9, which indicates that the amount of sulfur was reduced due to the discharged plasma. In friction tests, composite coatings showed high friction in a vacuum condition. It was considered that lubricant MoS2 lamellar structures showing super-low friction in a vacuum condition during friction could not be formed between ball and coating during friction because of the lack of sulfur in embedded clusters. 相似文献
107.
An N*N self-routing planar network suitable for fabricating optical space switches on lithium niobate substrate is presented. The network has O(N/sup 2/) cross points, good modularity and expandability. It also has no waveguide crossovers and no differential attenuation between any of the input and output pairs. A self-routing control can be applied to this network, which is indispensable for ATM switching systems.<> 相似文献
108.
Toshiyuki Miyamoto Tomohiro Kitayama Sadatoshi Kumagai Kazuyuki Mori Syoichi Kitamura Seiichi Shindo 《Electrical Engineering in Japan》2008,162(4):54-63
Abatement of CO2 emission is one of the most important issues in the 21st century regarding preservation of the earth environment. This paper addresses a utility operations planning problem for distributed energy management systems (DEMSs), where we are to obtain optimal plans that minimize both costs and CO2 emissions. A DEMS consists of multiple entities that seek their own economic profits. In this paper, we give a mathematical formulation of the utility operations planning problem for each entity, and propose an energy trading market, which utlizes a multi‐attribute auction protocol in order to deal with both a price and a CO2 emission rate. Experimental results show that collaboration among entities through the market provides a more profitable plan for each entity and abatement of CO2 emission is also achieved. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 54–63, 2008; Published online in Wiley InterScience ( www.interscience.wiley. com ). DOI 10.1002/eej.20418 相似文献
109.
Katsuyuki Matsunaga Fumiyasu Oba Isao Tanaka Hirohiko Adachi 《Journal of Electroceramics》1999,4(1):69-80
Discrete variational (DV) Xα cluster method has been employed in calculating electronic structures of ZnO. Electronic structures of the bulk and the non-polar surface model clusters are calculated with inclusion of electrostatic potentials in the bulk and near the surface, and the electronic origins of experimental spectra and chemical bonds at the surface are examined in detail. The valence band structure constructed by Zn-3d and O-2p bands is much influenced by electrostatic potentials in ZnO. It is found that the reduction of an electrostatic potential near the surface gives rise to the difference of the valence band structures between in the bulk and at the surface. The calculated density of states at the non-polar surface of ZnO, where the Zn-3d and O-2p bands are more widely separated than in the bulk, is in good agreement with the experimental UPS. In addition, a Zn-O bond at the surface is found to show stronger covalency than that in the bulk, as a result of the change of the valence band structure due to the effect of the electrostatic potential. 相似文献
110.