Preparation and Li^＋ storage properties of hierarchical hollow porous carbon spheres

Hollow ordered porous carbon spheres （HOPCS） with a hierarchical structure were prepared by templating with hollow ordered mesoporous silica spheres （HOMSS）. Scanning electron microscopy （SEM） and transmission electron microscopy （TEM） showed that HOPCS exhibited a spherical hollow morphology. High-resolution TEM, small angle X-ray diffraction （SAXRD） and N2 sorption measurements confirmed that HOPCS inversely replicated the unconnected hexagonal-stacked pore structure of HOMSS, and possessed ordered porosity. HOPCS exhibited a higher storage capacity for Li^＋ ion battery （LIB） of 527.6 mA h/g, and good cycling performance. A large capacity loss during the first discharge-charge cycle was found attributed to the high content of micropores. The cycling performance was derived from the hierarchical structure.     

Template-free synthesis and characterization of K-phillipsite for use in potassium extraction from seawater

Kbphillipsite was prepared using a hydrothermal method. Soluble glass and sodium aluminate were used as raw materials in the absence of an organic template. Investigations regarding the K＋ ions were con- ducted at room temperature to determine the ion-exchange capacity in the seawater sample and the selectivity coefficient of the mixed K＋-Na~ solution. The sample was characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and energy dispersion spectroscopy （EDS）. The K＋ ion- exchange capacity is 51 mg/g in seawater and the selectivity coefficient is 75.1 in the mixed K＋-Na＋ solution. The sample has a selectivity preference for K＋, and therefore can be used to selectively extract potassium from seawater. The sample composed of Si, Al, K, Na, and O exhibits a cross-like shape and is a typical K-phillipsite structure.     

PARTICLE COATING BY CHEMICAL VAPOR DEPOSITION IN A FLUIDIZED BED REACTOR

Aluminum coatings were created onto glass beads by chemical vapor deposition in a fluidized bed reactor at different temperatures. Nitrogen was enriched with Triisobutylaluminum (TIBA) vapor and the latter was thermally decomposed inside the fluidized bed to deposit the elemental aluminum. To ensure homogeneous coating on the bed material, the fluidizing conditions necessary to avoid agglomeration were investigated for a broad range of temperatures.The deposition reaction was modeled on the basis of a discrete particle simulation to gain insight into homogeneity and thickness of the coating throughout the bed material. In particular, the take-up of aluminum was traced for selected particles that exhibited a large mass of deposited aluminum.     

Characteristics and efficiency of a new vibrating screen with a swing trace

A new vibration type and motion characteristics were proposed according to the principle of manual sieving.A mechanical model of the new motion was established and the characteristics of the new vibrating screen were analyzed to establish its equation of motion by using the vibration theory,to include as technological parameters,amplitude,movement velocity,and throwing index through theoretical calculation.The efficiency of particle screening was studied at different values of frequency and swing declination angle.The discrete element method(DEM) was used to simulate the screening with the swing trace.The functional relationship between screening efficiency and the parameters was fitted with the least square method.The results show that high frequency and large swing angle are suitable for small particles,while small values are suitable for particles close to the aperture size.Compared to the linear vibration trace,both screening efficiency and processing capacity were effectively improved.     

RESEARCH ON THE MOTION OF PARTICLES IN THE TURBULENT PIPE FLOW OF FIBER SUSPENSIONS

The motion of fibers in turbulent pipe flow was simulated by 3-D integral method based on the slender body theory and simplified model of turbulence. The orientation distribution of fibers in the computational area for different Re numbers was computed. The results which were consistent with the experimental ones show that the fluctuation velocity of turbulence cause fibers to orient randomly. The orientation distributions become broader as the Re number increases. Then the fluctuation velocity and angular velocity of fibers were obtained. Both are affected by the fluctuation velocity of turbulence. The fluctuation velocity intensity of fiber is stronger at longitudinal than at lateral, while it was opposite for the fluctuation angular velocity intensity of fibers. Finally, the spatial distribution of fiber was given. It is obvious that the fiber dispersion is strenghened with the increase of Re numbers.     

LCO flutter of cantilevered woven glass/epoxy laminate in subsonic flow

The paper presents a cantilevered composite wing, aeroelastic characteristics of idealized as a composite flat plate laminate. The composite laminate was made from woven glass fibers with epoxy matrix. The elastic and dynamic properties of the laminate were determined experimentally for aeroelastic calculations. Aeroelastic wind tunnel testing of the laminate was performed and the result showed that flutter, a dynamic instability occurred. The cantilevered laminate also displayed limit cycle amplitude, post-flutter oscillation. The experimental flutter velocity and frequency were verified by our computational analysis.     

Attritor-milling of poly（amide imide） suspensions

The milling behavior of poly(amide imide),which serves as a prototypical hydrophilic high-performance polymer with a high glass transition temperature,was investigated.Various milling conditions(milling times up to 7h,stirrer tip speeds of 3.4-4.9 m/s,and mass concentrations of 5-20%) were tested,and particle sizes as low as d_(50,3) ~3μm were obtained.The milling was performed at 11℃ in an attritor.Differential scanning calorimetry and thermogravimetric analysis were performed before and after milling to investigate the effect of milling on the glass transition temperature and on the decomposition behavior of the polymer.The suspension obtained after milling was observed to be stable without the addition of stabilizers or the adjustment of the pH value,and no negative effect of milling on the polymer properties was observed.The attritor technique proved to be an adequate and efficient milling tool for the production of micrometer-sized high-performance polymer suspensions.     

Preparation of porous polyimide microspheres by thermal degradation of block copolymers

A new preparation method has been developed for thermally stable porous polyimide microspheres. Porous polyimide microspheres were prepared using trib]ock copolymers that consisted of a thermally stable polyimide derived from pyromellitic dianhydride/4,4＇-oxydianiline as the continuous phase and a thermally labile polyether as the dispersed phase. Spheres of copolymers were generated in a nonaqueous emulsion and then gradually heated to complete the imidization to form a microphase-separated structure. Subsequently, thermal treatment at a slightly reduced pressure removed the labile blocks and produced pores. Under suitable decomposition conditions, the pore size of the porous polyimide was in the range of 200-400nm.     

THERMODYNAMIC ANALYSIS AND EXPERIMENTAL VERIFICATION FOR SYNTHESIZING SILICON NITRIDE NANOPARTICLES USING RF PLASMA CVD

Silicon nitride nanoparticles were synthesized by radio-frequency (RF) plasma chemical vapor deposition (PCVD) using silicon tetrachloride and ammonia as precursors, and argon as carrier gas. By assuming chemical thermodynamic equilibrium in the system, a computer program based on chemical thermodynamics was used to calculate the compositions of the system at different initial concentrations and final temperatures. At first, five elements and thirty-four species were considered. The effects of temperatures, and concentrations of ammonia, hydrogen and nitrogen on the equilibrium compositions were analyzed. It was found that the optimal reaction temperature range should be 1200 to 1500 K to obtain the highest conversion and yield of Si3N4. The inlet position of ammonia should be lower than that of silicon tetrachloride, and both should be located at the tail of the plasma torch. The best moleratio of ammonia to silicon tetrachloride was found to be about 6. Later, the influences of water (.and oxygen) were considered, and 17 additional species were included in the computations. It was found that oxygen or water content in the raw materials should be as low as possible in order to have high nitride content in the produced Si3N4. Nitrogen or hydrogen might be used to replace some or even all the argon to improve the yield of silicon nitride and reduce the cost. The ratio of ammonia to silicon tetrachloride should be high enough to obtain high conversion, but not excessively high to reduce the oxygen content due to the existence of water in ammonia. The simulated results were verified bv experiments.     

Charge transfer and bipolar charging of particles in a bubbling fluidized bed

Particle-particle and particle-wall collisions in gas-solid fluidized beds lead to charge accumulation on particles.This work evaluated the effect of fluidization time on charge transfer and bipolar charging(charge separation)and their influence on hydrodynamic structures in a fluidized bed.Experiments were performed with glass beads and polyethylene particles in a glass column.The pressure fluctuations and net electrostatic charge of particles were measured during fluidization.Wavelet and short-time Fourier transforms were used to analyze pressure fluctuations.The results revealed that bipolar charging is the dominant tribocharging mechanism in a bed of glass beads.Bipolar charging in a bed of particles with a narrow size distribution does not affect either hydrodynamic structures or the transition velocity to the turbulent regime.A large difference between the work functions of the wall and particle in the bed of polyethylene particles leads to high charge transfer.Formation of a stagnant particle layer on the wall eventually causes the energy of macro-structures to increase to its maximum.At longer fluidization times,the macro-structural energy decreases and bubbles shrink until the electrostatic charge reaches the equilibrium level.These results well describe the effect of fluidization time on hydrodynamic structures.     

Preparation and Li+ storage properties of hierarchical hollow porous carbon spheres

Hollow ordered porous carbon spheres (HOPCS) with a hierarchical structure were prepared by templating with hollow ordered mesoporous silica spheres (HOMSS). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that HOPCS exhibited a spherical hollow morphology. High-resolution TEM, small angle X-ray diffraction (SAXRD) and N₂ sorption measurements confirmed that HOPCS inversely replicated the unconnected hexagonal-stacked pore structure of HOMSS, and possessed ordered porosity. HOPCS exhibited a higher storage capacity for Li⁺ ion battery (LIB) of 527.6 mA h/g, and good cycling performance. A large capacity loss during the first discharge–charge cycle was found attributed to the high content of micropores. The cycling performance was derived from the hierarchical structure.     

Multi-scale Optical Analyses of Dynamic Gas Saturation During Air Sparging into Glass Beads

A multi-scale optical imaging technique was developed allowing for the 2D observation of two phase flow in porous media at two different scales simultaneously: Using two coupled cameras, a 2D flow cell (0.5 × 0.5m²) is recorded entirely at the bench scale and at the pore scale with a spatial resolution of 0.5 and 0.01 mm, respectively. The technique is applied to study channelized gas flow in saturated glass beads. We analyze the phase distribution at the pore scale and derive a pixel-based method for the measurement of saturation at the larger scale. This method assumes linearity between the mean reflected light intensity and the local gas saturation if averaging is performed over representative areas (REV). The REV depends on the irregularity of the local pore structure and has a lower limit at the correlation length of the porous medium (somewhat above the size of the glass beads) and an upper limit which correlates with the width of gas channels. These limits could be quantified through optical analysis. The optical approach to estimate phase saturations was validated by gravimetric analysis where a characteristic ratio between the optically observed flow cell wall and the saturation within the bulk material was identified, which corresponds to the expectation based on geometrical considerations of the glass bead packing. Considering a transient flow experiment the optical method is demonstrated to be able to quantify the temporal evolution of the residual and the convective gas phase. We conclude that the new technique provides a valuable tool to improve our quantitative understanding of multiphase phenomena across different scales.     

Stress-induced interfacial failure in filled polymer melts

We study a dynamic interfacial slip phenomenon in filled polymer melts. When a poly(dimethyl siloxane) melt of weight average molecular weight M _w = 93 700 is mixed with glass beads of diameter up to 45 m, the sample shows some evidence of breakdown of interfacial adhesion between the glass beads and the PDMS matrix at a level of oscillatory stress under which the pure PDMS melt exhibits no decay. The decay of viscoelastic properties with time is essentially independent of the amplitude of shear strain as long as the magnitude of the oscillating stress is sufficiently high. It is suggested that much higher local stress than the apparent applied stress may be generated between the narrowly spaced beads. The interfacial slip was observable because it was measured against a natural length scale d in the filled polymer melts which is the filler size or the inter-filler distance and is much smaller than the dimensions of the flow cell. The decay under high stress and healing of interfacial adhesion upon a large reduction in stress may be related to the de-bonding and reformation of hydrogen bonds between the PDMS chains and the glass bead surfaces.     

Nonaxisymmetric compressive failure of a circular crack parallel to a surface of halfspace

Considered in this work is the fracture stability of a circular crack parallel to the surface of a halfspace subjected to around applied compression. A state of subcritical initial strain is assumed. The failure criterion is based on the loss of local stability and quantified in terms of a critical eigen value. Analysis involves reducing the problem to a system of Fredholm equations of the second kind where the solutions are identified with harmonic potential functions. Critical loads are determined for nonaxisymmetric forms of loss in stability in the region local to the crack; their values would depend on the material properties and geometric parameters. Numerical results are displayed graphically for a crack in an elastic solid and a composite made of aluminum/boron/silicate glass with epoxy-maleimic resin. They depend on the number of angularly dependent harmonies that introduce the nonaxisymmetry in the problem.     

Direct Observation of Trapped Gas Bubbles by Capillarity in Sandy Porous Media

We investigated the mechanism of residual gas trapping at a microscopic level. We imaged trapped air bubbles in a Berea sandstone chip after spontaneous imbibition at atmospheric pressure. The pore structure and trapped bubbles were observed by microfocused X-ray computed tomography. Distributions of trapped bubbles in Berea and Tako sandstone were imaged in coreflooding at a capillary number of 1.0 × 10⁻⁶. Trapped bubbles are of two types, those occupying the center of the pore with a pore-scale size and others having a pore-network scale size. In low-porosity media such as sandstone, connected bubbles contribute greatly to trapped gas saturation. Effects of capillary number and injected water volume were investigated using a packed bed of glass beads 600μm in diameter, which had high porosity (38%). The trapped N₂ bubbles are stable against the water flow rate corresponding to a capillary number of 1.0 × 10⁻⁴.     

Boiling dryout on flat surfaces covered with bead-packed structures

Visual observations were conducted to focus on the dynamic interfacial behavior associated with dryout and rewetting during boiling on surfaces covered with porous structures made of staggered glass beads. Associated interfacial behavior was significantly affected by the bead-packed structure. Intensive wetting of the liquid replenishment protected heated surface from full dryout. Even at extremely high heat fluxes, intermittent rewetting of heated surface can also be established due to rather unsteady behavior of dry areas. Based on these unique characteristics, an introductory model was proposed to perform a theoretical analysis and explore the dryout process inside the pore structure. The theoretical results were compared with experimental data, and the present model provides a good explanation of the fundamental mechanisms and predicts the important influences of the bead-packed structure on dryout behavior.     

应力调整对石英玻璃珠低速冲击破碎行为的影响

结合高速摄影技术,应用SHPB加载装置,分别使用钢制、铝制和有机玻璃制3种透射杆,对直径约7.90、11.80、15.61 mm 3种尺寸的石英玻璃珠进行了低速冲击实验。根据不同透射杆条件下的玻璃珠破碎过程中的载荷-位移曲线,结合有限元软件计算玻璃珠在冲击作用下载荷的变化情况以及实验过程中玻璃珠的应变,探讨了应力调整对玻璃珠破碎过程的影响。结果表明:相同冲击条件作用下,改变透射杆的材料,会改变玻璃珠破碎过程中的载荷分布,即透射端边界波阻抗的改变会导致反射波发生改变,从而导致玻璃珠内部载荷发生变化;透射杆为铝材和有机玻璃材质时,玻璃珠在破碎过程中的载荷明显下降,在加载过程中伴随着垫块的变形,玻璃珠内部的应力调整时间变长;透射杆为钢杆时,玻璃珠的应变主要表现为两端最大,越靠近中间应变越小,对于透射杆为铝杆和有机玻璃杆的玻璃珠,透射端局部出现了卸载行为。采用有机玻璃透射杆之后,局部应力和变形降低的结果使得玻璃珠在经受较大的变形之后发生破碎,表明玻璃珠的破碎行为由局部变形和局部变形梯度共同控制。     

Flow behaviour in the presence of wettability heterogeneities

The physical processes occurring during fluid flow and displacement within porous media having wettability heterogeneities have been investigated in specially designed heterogeneous visual models. The models were packed with glass beads, areas of which were treated with a water repellent to create wettability variations. Immiscible displacement experiments show visually the effect of wettability heterogeneities on the formation of residual oil and recovery due to capillary trapping. This work demonstrates by experiment the importance of incorporating reservoir heterogeneity into pore displacement analysis, essential for the correct interpretation of core data and for directing the route for scale-up of the processes to reservoir scale.