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81.
Preparation and characterization of antibacterial silver-dispersed activated carbon aerogels 总被引:2,自引:0,他引:2
Silver-dispersed carbon aerogels (CAs) were obtained by direct immersion of organic aerogels prepared by ambient pressure drying technique in AgNO3 aqueous solution and then carbonization. The effect of preparation conditions such as the resorcinol/catalyst ratio, the feed AgNO3 concentration, the ratio of aerogel mass/solution volume, immersion time and carbonization temperature on the bulk density and silver content as well as the BET surface area of the dispersed CAs was studied. The dispersion and structure of silver nanoparticles in obtained materials were investigated by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The Ag-dispersed CAs prepared exhibit strong and long-term antibacterial activity. 相似文献
82.
Robert B. White 《加拿大化工杂志》2005,83(1):64-67
An ECT system has been shown to be useful in observing differences in particle behaviour in a bubbling fluidised bed. An image analysis technique is further described that utilises the construction of solids concentration profiles at three key values, x = 0.2, x = 0.5 and x = 0.8, which have been identified as important solids concentrations in a new Bubble Structure Model. Significant differences in the bubble structure are shown to result when the concentration of fine particles is slightly increased in a bubbling fluidised bed. Changes of this type would seriously alter the gas solid contact efficiency in the fluidised bed, which would significantly influence selectivity of in‐bed catalytic reactions and gas residence time. 相似文献
83.
A. Oberlin 《Carbon》1984,22(6):521-541
A review is made of recent electron microscope observations relating to the carbonization and graphitization of a variety of carbonaceous precursors. The different behaviors of graphitizing and non-graphitizing carbons are elucidated, and the effect of sulphur as a cross-linker is determined. The resulting processes are shown to apply to a wide variety of materials ranging from cokes to carbon fibers. 相似文献
84.
Although structural adhesives are becoming widespread in numerous applications, one important limitation at present is the long term behaviour of bonded assemblies under conditions of high humidity, especially at elevated temperatures. This study presents a comparison between bulk properties of a structural epoxy resin and its behaviour in a torsional joint consisting of a hollowed-out cylinder bonded to a plate—both substrates being in stainless steel. Exposure to ca. 100% relative humidity at 70°C leads to modification of the bulk properties of the polymer, notably reduction of its elastic modulus. Although this may explain some differences in behaviour of the torsional joint, premature failure is attributed to weaknesses in the interphase zone.
Auger Electron Spectroscopy (AES) has been employed to investigate both unbonded steel surfaces and fracture zones. Although prolonged exposure to water leads to a more extensive degree of (apparently) adhesive failure at the interface polymer/metal, AES has shown the presence of non-negligible quantities of carbon, attributed to residual polymer. Failure would seem to occur, at least partly, in a weak interphase of the polymer, near, but not at, the interface.
Various possible causes are evoked. For dry failure, residual polymer may be due to the topography of the metal surface and/or local modification of the adhesive during cure. In the case of aged joints, in addition there are potential effects due to swelling and differential stresses, secondary bond failure and molecular chain scission within the polymer, all provoked by the presence of water. 相似文献
Auger Electron Spectroscopy (AES) has been employed to investigate both unbonded steel surfaces and fracture zones. Although prolonged exposure to water leads to a more extensive degree of (apparently) adhesive failure at the interface polymer/metal, AES has shown the presence of non-negligible quantities of carbon, attributed to residual polymer. Failure would seem to occur, at least partly, in a weak interphase of the polymer, near, but not at, the interface.
Various possible causes are evoked. For dry failure, residual polymer may be due to the topography of the metal surface and/or local modification of the adhesive during cure. In the case of aged joints, in addition there are potential effects due to swelling and differential stresses, secondary bond failure and molecular chain scission within the polymer, all provoked by the presence of water. 相似文献
85.
Ji Hoon Yang Min Hyung Yum Eun Jung Kim Myeung Hoi Kwon Cheol Woong Yang Ha-Jin Song Yong-Wan Jin 《Carbon》2006,44(11):2219-2223
Nitrogen molecules have been encapsulated into the central hollows of vertically aligned carbon nitride (CN) multiwalled nanofibers by dc plasma-enhanced chemical vapor deposition with C2H2, NH3, and N2 gases on a Ni/TiN/Si(1 0 0) substrate at 650 °C. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectra showed the existence of nitrogen molecules in CN nanofibers. Elemental mapping images with electron energy loss spectroscopy of the CN nanofiber and catalyst metal, and optical emission spectroscopy spectra of the plasma showed the distribution of nitrogen atoms and molecules in the CN nanofiber, catalyst metal, and gaseous precursor, respectively. These studies showed that atomic nitrogen diffused into the catalytic metal particle because of the concentration gradient and then saturated at the bottom of the particle. Saturated nitrogen atom participated in the formation of the CN nanofiber wall but most of nitrogen was trapped in the central hollow of the nanofiber as molecules. 相似文献
86.
Y.T. Makkawi 《Chemical engineering science》2003,58(10):2035-2051
Here, an experimental investigation on the effective drag force in a conventional fluidized bed is presented. Two beds of different particle size distribution belonging to group B and group B/D powders were fluidized in air in a diameter column. The drag force on a particle has been calculated based on the measurement of particle velocity and concentration during pulse gas tests, using twin-plane electrical capacitance tomography. The validity of the voidage function “correction function”, (1−εs)n, for the reliable estimation of the effective drag force has been investigated. The parameter n shows substantial dependence on the relative particle Reynolds number , and the spatial variation of the effective static and hydrodynamic forces. It is also illustrated that, a simple correlation for the effective drag coefficient as function of the particle Reynolds number (Rep), expressed implicitly in terms of the interstitial gas velocity, can serve in estimating the effective drag force in a real fluidization process. Analysis shows that, the calculated drag force is comparable to the particle weight, which enables a better understanding of the particle dynamics, and the degree of spatial segregation in a multi-sized particle bed mixture. The analogy presented in this paper could be extended to obtain a generalized correlation for the effective drag coefficient in a fluidized bed in terms of Rep and the particle physical properties. 相似文献
87.
It has been shown in a previous paper in this series that important dilatation is produced by plastic deformation under tension of neat PP and PP/PA6/POE blends, for which the POE to PA6 concentration ratio equals 1/2. In this work, the detailed mechanisms of this volume change are investigated from electron micrographs (SEM and TEM) obtained in the deformed state. At low alloy content, it is thus observed that dilatation results from decohesion of the PA6 particles from the PP matrix. As the amount of PA6 and POE increases, voids are nucleated preferentially in the thicker POE interphase making a shell around the PA6 particles, and secondarily in isolated POE particles. Unexpectedly, it has been found that the overall volume dilatation decreases with total alloying content. This is interpreted by: (i) the increasing contribution of PA6 that intrinsically deforms with less cavitation than PP, (ii) the post-cavitation rubber-like stretching of POE particles and, (iii) the early formation of a percolating network of shear bands from the diffuse array of voids formed after the yield point. These mechanisms explain the gradual increase of the resistance to impact of the PP/PA6/POE as their alloying content is increased. 相似文献
88.
89.
Qin Kuang Shui-Chao Lin Xian-Hua Zhang Su-Yuan Xie Rong-Bin Huang Lan-Sun Zheng 《Carbon》2006,44(7):1166-1172
A simple and efficient approach for coating multiwalled carbon nanotubes (MWCNTs) with size-controllable SnO2 nanoparticles by chemical vapor deposition has been developed using tin hydride (SnH4) gas as the source of SnO2 at 550 °C. The size and coverage of SnO2 nanoparticles can be adjusted by simply controlling the deposition time and the flow rate of the SnH4/N2 mixture gas during the CVD procedure. In addition, by using the MWCNTs as a sacrificial template, a kind of one-dimensional chain-like SnO2 nanostructure has been synthesized by increasing the deposition temperature to 730 °C. This technique may provide a good way to produce tunable SnO2-MWCNT composites. 相似文献
90.
Garima Lakhanpal Jay R. Black Roser Casas-Mulet Meenakshi Arora Michael J. Stewardson 《河流研究与利用》2023,39(4):734-744
Fine particle clogging and faunal bioturbation are two key processes co-occurring in the hyporheic zone that potentially affect hyporheic exchange through modifications in the sediment structure of streambeds. Clogging results from excessive fine sediment infiltration and deposition in rivers, and it is known to decrease matrix porosity and potentially reduce permeability. Faunal bioturbation activity may compensate for the negative effect of clogging by reworking the sediment, increasing porosity, and preventing further infiltration of fines. Although both processes of clogging and bioturbation have received significant attention in the literature separately, their combined effects on streambed sediment structure are not well understood, mostly due to the lack of a standard methodology for their assessment. Here, we illustrate a novel methodology using X-ray computed tomography (CT), as proof of concept, to investigate how, together, clogging and bioturbation affect streambed porosity in a controlled flow-through flume. By visualising gallery formations of an upward conveyor macroinvertebrate; Lumbriculus variegatus as a model species, we quantified bioturbation activity in a clogged streambed, focusing on orientation, depth, and volume at downwelling and upwelling areas of the flume. Gallery creation increased the porosity of the streambed sediment, suggesting a potential improvement in permeability and a possible offset of clogging effects. We illustrate the promising use of X-ray CT as a tool to assess bioturbation in clogged streambeds, and the potential role of bioturbation activity supporting hyporheic exchange processes in streambeds, warranting further studies to understand the extent of bioturbation impacts in natural systems. 相似文献