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61.
类质同象置换对蒙脱石水化性能的影响 总被引:1,自引:1,他引:1
研究了10个蒙脱石样品在蒸馏水中水化性能——自由膨润量的差异。样品来自不同产地或不同矿层,具有不同的类质同象置换。研究前对样品进行了提纯和钠化处理。实验结果表明,蒙脱石膨润性与其类质同象置换情况有密切的关系,膨润量与由蒙脱石结构成分计算得到的品格常数6有明显的相关性。讨论了膨润量差异的原因。 相似文献
62.
Hansan Liu 《Electrochimica acta》2004,49(7):1151-1159
Multiple substitution compounds with the formula LiNi0.8−yTiyCo0.2O2 (0≤y≤0.1) were synthesized by sol-gel method using citric acid as a chelating agent. The effects of titanium substitution on the structural, electrochemical and thermal properties of the cathode materials are investigated. A solid solution phase (R-3m) is observed in the range of 0≤y≤0.1 for the titanium-doped materials. X-ray photoelectron spectroscopy (XPS) shows that there are Ni3+, Ni2+, Co3+, Co2+ and Ti4+ five transition metal ions in titanium-doped materials. Rietveld refinement of X-ray diffraction (XRD) patterns indicates that titanium substitution changes the materials’ structure with different cationic distribution. An increase of the Ni/Co amount in the 3a Li site is found with the addition of titanium amount. An improved cycling performance is observed for titanium-doped cathode materials, which is interpreted to a significant suppression of phase transitions and lattice changes during cycling. The thermal stability of titanium-doped materials is also improved, which can be attributed to its lower oxidation ability and enhanced structural stability at delithiated state. 相似文献
63.
S. Saggar M. J. Hedley R. E. White P. E. H. Gregg K. W. Perrott I. S. Cornforth 《Nutrient Cycling in Agroecosystems》1993,34(2):141-151
Six phosphate rocks (PRs) of varying reactivities were compared with monocalcium phosphate (MCP) in a glasshouse experiment growing perennial ryegrass (Lolium perenne cv. Nui) as the test plant on four soils of contrasting P sorption capacity and exchangeable Ca. The cumulative dry matter yield over 10 harvests showed a significant response to P application in all soils. Based on relative yield and P uptake, MCP was the most effective P fertilizer followed by the reactive phosphate rocks, which were superior to the unreactive rocks in all soils. The relative agronomic effectiveness (RAE) and substitution ratio (SR) of individual PR fertilizers, calculated with respect to MCP using the methods of vertical and horizontal comparison, respectively, were similar over a range of fertilizer rate. There was a decline or slight increase in the performance of PRs with time in the low P sorption soils but a consistent increase in the high P sorption soils. Some initial influence of exchangeable Ca content of the soils on the relative performance of PRs was also observed. Generally the PRs performed better in high P sorption soils than low P sorption soils and in low exchangeable Ca soils than high exchangeable Ca soils. 相似文献
64.
Combustion characteristics and flame stability at the microscale: a CFD study of premixed methane/air mixtures 总被引:1,自引:0,他引:1
D.G. Norton 《Chemical engineering science》2003,58(21):4871-4882
A two-dimensional elliptic, computational fluid dynamics (CFD) model of a microburner is solved to study the effects of microburner dimensions, conductivity and thickness of wall materials, external heat losses, and operating conditions on combustion characteristics and flame stability. We have found that the wall conductivity and thickness are very important as they determine the upstream heat transfer, which is necessary for flame ignition and stability, and the material's integrity by controlling the existence of hot spots. Two modes of flame extinction occur: a spatially global type for large wall thermal conductivities and/or low flow velocities and blowout. It is shown that there exists a narrow range of flow velocities that permit sustained combustion within a microburner. Large transverse and axial gradients are observed even at these small scales under certain conditions. Periodic oscillations are observed near extinction in cases of high heat loss. Engineering maps that delineate flame stability, extinction, and blowout are constructed. Design recommendations are finally made. 相似文献
65.
Transition of the flow in a periodically grooved channel is numerically investigated for periodicity indices m=1 up to 6 by assuming the two-dimensional and fully developed flow field, where m is defined as a number of grooves in which the flow repeats periodically. Critical Reynolds numbers for the onset of a self-sustained oscillatory flow from a steady-state flow are evaluated by numerical simulations. It is found that the bifurcations occur at the critical Reynolds numbers as a result of Hopf bifurcation, and a period in the streamwise direction of the oscillatory flow is twice as long as the groove pitch of the channel. In addition, flow visualization with the aluminum dust method is carried out to confirm the results obtained from the numerical simulations. The experimental results are in good agreement with the numerical ones. 相似文献
66.
In this paper a theoretical investigation into the basis of the reduced efficiency of a conical cyclone is performed. By considering the flow in a region where viscosity is unimportant an analytical solution to the problem is obtained. From this model the performance of the cyclone is evaluated and this can be expressed in terms of three operating and design parameters. One of these parameters is the split ratio, that is the proportion of the volume of fluid entering the cyclone which goes to the underflow. It is demonstrated mathematically that the empirical formula for the reduced efficiency at present in common use is a very good absolute measure of the separating ability of a cyclone. 相似文献
67.
This paper discusses the simulation of bubbling gas-solid flows by using the Eulerian two-fluid approach. Predictions of particle motion, bed expansion, bubble size and bubble velocity in bubbling beds containing Geldart B particles are compared with experimental results and correlations found in the literature. In addition, gas mixing in a bed of Geldart A particles is investigated.An in-house code has been developed based on the finite-volume method and the time-splitting approach using a staggered grid arrangement. The velocities in both phases are obtained by solving the 2D Reynolds-averaged Navier/Stokes equations using a partial elimination algorithm (PEA) and a coupled solver. The k-ε turbulence model is used to describe the turbulent quantities in the continuous phase.In general, the model predictions are in good agreement with experimental data found in the literature. Most important observations are: the level of the restitution coefficient was found to be crucial in order to obtain successful results from 2D axisymmetric simulations of a system containing Geldart B particles. Bubble size and bubble rise velocities are not as sensitive to the restitution coefficient. The turbulence model is of outmost importance concerning gas mixing in a fluidized bed of Geldart A particles.From these numerical analyzes an optimized granular flow two-fluid model can be designed for the purpose of simulating reactive systems in fluidized bed reactors. 相似文献
68.
Continuous-velocity lattice gas cellular automata (CVLGA) is extended to miscible binary fluid systems. A new parameter is introduced in order to control the diffusivity of the fluids. The correlation between the diffusivity and the new parameter proves that there exists the maximum value of the diffusivity. Quantitative verifications of the model are carried out with numerical simulations of the diffusion phenomena across a falling fluid film. The model is then applied to the simulations of Rayleigh-Taylor instability during the gravitational mixing phenomena. The qualitative tendency of the growth of the interface instability is the same as that obtained in conventional numerical methods. 相似文献
69.
Alaa?S.?Abd-El-AzizEmail author Sarrah?A.?Carruthers Pedro?M.?Aguiar Scott?Kroeker 《Journal of Inorganic and Organometallic Polymers and Materials》2005,15(3):349-359
A number of hyperbranched polymers containing cyclopentadienyliron moieties were prepared using the A2+B3 method. The A2 compounds used were common diols, dithiols or dichloroarenecomplexes. B3 compounds included either prepared star-shaped molecules or a purchased triol. The effect of the reaction conditions on the
properties of the products was probed. Analysis of the prepared polymers was conducted using 1H and 13C NMR, viscometry, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Viscometry values were generally
found to be low, in the range of 0.175–0.300 dl/g. TGA showed losses starting at approximately 230°C and ending at 280°C,
corresponding to the decomposition of the cyclopentadienyliron moiety. Degradation of the polyether backbone was found to
occur starting at 390–567°C. Glass transition temperatures were found to be between 60 and 134°C, whereas melting temperatures
ranged from 155 to 190°C. 相似文献
70.
Kojiro Nakai Yasunori Oumi Haruyuki Horie Tsuneji Sano Hideaki Yoshitake 《Microporous and mesoporous materials》2007,100(1-3):328-339
Bromination and subsequent ethylenediamine substitution of the CC double bond in mesoporous ethylenesilica were carried out to explore the characteristics of this periodic mesoporous organosilica. The structures of the products (BrPMO and EDA–BrPMO, respectively) were analysed by IR, Br K-edge EXAFS and NMR spectroscopies, as well as X-ray diffraction and nitrogen adsorption. We showed (1) that the formulae of the two products that formed were [CHBrSiO1.5]0.45[CHSiO1.5]0.55 and [NH2CH2CH2NHCHSiO1.5]0.05 [CHBrSiO1.5]0.40[CHSiO1.5]0.55, respectively, (2) that the addition of Br2 at room temperature occurred on the CC double bonds with disturbing the framework structure, (3) that IR absorption band of CC bonds that reacted with Br2 is significantly different from that of inactive CC bond, (4) that the length of the C–Br bond was considerably longer than in conventional alkyl bromides, and (5) that a large proportion of the ν(C–Br) band remained at the same position in the IR absorption spectrum after the ethylenediamine (EDA) substitution, while a new ν(C–Br) absorption also appeared. The mechanisms of these reactions are discussed at both the micro and mesoscopic levels.
Arsenate adsorption on EDA–BrPMO, in which the EDA is directly bound to the “surface” of the mesopores, was compared with adsorption on EDA–Pr–PMO, which was prepared by the direct synthesis of 3-chloropropyl-functionalized mesoporous ethanesilica followed by the substitution of Cl with EDA. The strength of the adsorption, as measured with the distribution coefficient, was greater for the former adsorbent than the latter. The origin of this difference was attributed to the distance between amino group and the surface. 相似文献