Synthesis of tailored porous alumina with a bimodal pore size distribution

Hierarchical channel or well-connected small and large pore networks show multiple advantages for application in catalysis or adsorbent in aqueous condition. Micro- and mesopores provide size or shape selectivity for a guest molecule, while additional macropores reduce transport limitations. In this study, we proposed a novel method to prepare bimodal porous aluminas, which have meso- and macropores with narrow pore size distribution and well defined pore channels. The framework of the porous alumina is prepared via a chemical templating method using alkyl carboxylates. Polystyrene (PS) beads are employed as a physical template for macropores. We examined polydiallyldimethylammonium chloride (PDDA)-treated aluminas as organic adsorbent in aqueous solution. Above 90% of the anionic dye (acid red 44) is removed within 10 min, and the adsorption rate of PDDA/P4 (supported on the bimodal porous alumina) is faster than that of PDDA/P2 (supported on the unimodal porous alumina) because macropore of P4 have reduced transport limitation and enhanced the accessibility to the active site of cationic charge.     

Preparation and characterization of hypercrosslinked resins with bimodal pore size distribution and controllable microporosity

Hypercrosslinked polystyrene resins with bimodal pore size distribution and controllable microporosity were prepared by combining traditional suspension polymerization and post crosslinking technique. The volume ratio of divinylbenzene (DVB) in monomer mixtures was kept at 20%, while vinylbenzyl chloride (VBC) concentration was progressively reduced to investigate effect of post crosslinking degree on the pore structure of the hypercrosslinked species. The results indicated that higher VBC concentration in monomer mixtures led to greater surface area, smaller average pore size and higher microporosity. Moreover, bimodal distribution of pore size could be observed for the final resins. The mesopore fraction should be derived from the pores originally present in precursor resins, while the micropore fraction was originated from the post crosslinking.     

From pore size distribution to an equivalent pore size of cement mortar

An experimental and theoretical study has been performed with the aim of quantifying pore size distribution curves and correlating them with water and oxygen permeability. Twenty mortars have been investigated which contained Portland cement, blast-furnace slag cement and silica fume as a binder. Admixtures have been used as well. The water-cement ratio varied between 0.4 and 0.75 and two curing conditions were applied. By the use of mercury intrusion porosimetry, the pore size distribution was determined. Water and oxygen permeability have been measured in the steady state. Equivalent pore sizes have been calculated which quantify the pore size distribution by a single number. This number is not a constant but depends on the physical transport mechanism. It is shown that equivalent pore size and porosity together are sufficient to predict the physical properties with an acceptable accuracy.     

Fracture mechanism of toughened epoxy resin with bimodal rubber-particle size distribution

A bimodal rubber-particle distributed epoxy resin was made by simultaneous addition of two kinds of liquid rubbers, CTBN1300X9 and CTBN1300X13. These rubbers were added at a constant total rubber content but with varying weight ratios. The microstructure and fracture behaviour of these rubber-modified epoxy resins have been studied. A strong increase in the fracture resistance was found for the bimodal rubber-particle distributed epoxy resin. The role of the small particle is thought to toughen the shear bands between large particles. The role of large particle is thought to induce a large-scale shear deformation in the crack front. The synergistic effect of these particles gives rise to a strong increase in the toughness of these bimodal rubber-particle distributed epoxy systems.     

Numerical investigation of fracture behavior of nanostructured Cu with bimodal grain size distribution

Nanostructured metals with bimodal grain size distribution, composed of coarse grain (CG) and nanograin (NG) regions, have proved to have high strength and good ductility. Here, numerical investigation, based on the mechanism-based strain gradient plasticity theory and the Johnson–Cook failure model, focuses on effects of (1) distribution characteristics of the CG regions and (2) the constitutive relation of the NG with different grain sizes on fracture behavior in a center-cracked tension specimen of bimodal nanostructured Cu. High strain rate simulations show that both of them directly influence load response and energy history, and importantly, they are closely related to the fracture pattern. This study shows that both CG region bridging and crack deflection toughen the bimodal nanostructured Cu significantly, while debonding enhances the overall ductility moderately. Simulations also show that with volume fraction of the CG regions increasing, both structural strength and ductility of the bimodal nanostructured Cu specimen can be improved.     

热孔法表征特种高分子合金超滤膜的孔径

用热分析方法（ＤＳＣ）对磺化聚砜（ＳＰＳＦ）与聚醚酮（ＰＥＫ）高分子合金超滤膜的孔径和孔结构进行了研究。由实验得到热谱图，经计算得到不同合金比（ＳＰＳＦ／ＰＥＫ）的超滤膜孔径及孔径体积分布。研究结果表明，在一定条件下，ＳＰＳＦ／ＰＥＫ以不同的比例混合时，其膜的孔径分布范围在５￣１５ｎｍ，平均孔径在６￣９ｎｍ之间；当合金比（ＳＰＳＦ／ＰＥＫ）等于或大于４：６时，所制得的超滤膜对聚乙二醇（ＰＥＧ，Ｍｗ     

Determination of pore size distribution by suction prosimetry

The theory and practice of suction porosimetry methods (suction plate, pressure membrane and centrifuge) are reviewed together with related methods based on the rate of penetration of wetting liquids, and on static and dynamic fluid/fluid displacement measurements.

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Résumé La porosimétrie par succion repose sur la mesure de la dépression capillaire que suscite un liquide mouillant retenu dans un milieu poreux. C’est donc une méthode complémentaire à celle de la porosimétrie par pression (par ex. pénétration de mercure) où l’on opère avec des liquides mouillants. On expose la théorie et la pratique des méthodes par succion, entre autres les méthodes de la plaque, de la membrane et de la centrifugation. Un groupe de méthodes voisines découle de la vitesse de pénétration des liquides mouillants sous l’action des forces capillaires (par ex. la méthode d’Astbury), et de l’observation dans les conditions statique et dynamique des mouvements gaz/liquide et liquide/liquide.

     

Porous hydroxyapatite ceramics of bi-modal pore size distribution

A route for the fabrication of porous hydroxyapatite ceramics having two populations of open pores is reported. The bodies are prepared by sintering the spherical gelatin/hydroxyapatite granules. As the result, ceramics containing intragranular small-size pores and intergranular large-size interconnecting pores are obtained. The pore size and content are dependent on the route. Ceramics can generally be applied as bone replacement materials where the interconnections in the intergranular pores are the pathway to conduct cells and vessels for the bone ingrowth, whereas the intragranular pores can be filled with a drug, e.g. to eliminate infections.     

Frost resistance and pore size distribution in bricks

Correlation between frost resistance, porosity and pore size distribution was examined. Different test methods were used to evaluate the frost resistance. Porosity and pore size distribution were examined in mercury intrusion porosimeter (MIP). Scanning electron microscopy gave a visual view of the pore geometry, pore size and porosity. A linear correlation was found between frost resistance and the inverse value of the intruded pore volume. A linear correlation was also found between frost resistance and percentage of pores with diameter bigger than 3 μm. The test results were analysed using statistical methods. From the MIP-test a frost resistance number can be calculated which indicates the frost resistance of the brick.     

Effect of media pore size distribution on deep-bed filtration

One important parameter of filtration, the media pore size distribution, has not been explicitly considered in modeling deep-bed filtration models by previous investigators. In this study, we propose, based on the hypothesis of O'Melia-Ali and the use of the effective medium approximation theory, a new transient-state model and examine the effect of the media pore size distribution on filter performance. From the simulation results based on six different pore size distribution functions, it is clear that the pore size distribution plays an important role in determining the removal efficiency as well as headloss development.     

煤基活性炭孔径分布的调控

提出并研究了一种煤基活性炭孔径分布的调控方法及调控机理.将煤样与不同质量的KOH混合后炭化,分别对炭化料进行酸洗,以控制其中的钾含量,然后对酸洗料进行蒸汽活化,制成活性炭.通过对所制活性炭进行氮气吸附实验、扫描电镜及能谱分析和吸附能力表征实验后发现:改变KOH加入量和采用质量浓度为5%的盐酸对炭化料进行酸洗,能够改变炭化料中的钾含量;随着KOH含量的提高,活性炭的口发附能力逐渐增强,平均孔径从2.379 nm逐渐增大到2.636nm,同时孔径分布由以微孔为主逐渐向以中孔为主转移,其中孔含量由30.9%提高到46.1%.     

Thermal conductivity of Al–SiC composites with monomodal and bimodal particle size distribution

The thermal conductivity of aluminum matrix composites having a high volume fraction of SiC particles is investigated by comparing data for composites fabricated by infiltrating liquid aluminum into preforms made either from a single particle size, or by mixing and packing SiC particles of two largely different average sizes (170 and 16 μm). For composites based on powders with a monomodal size distribution, the thermal conductivity increases steadily from 151 W/m K for particles of average diameter 8 μm to 216 W/m K for 170 μm particles. For the bimodal particle mixtures the thermal conductivity increases with increasing volume fraction of coarse particles and reaches a roughly constant value of 220 W/m K for mixtures with 40 or more vol.% of coarse particles. It is shown that all present data can be accounted for by the differential effective medium (DEM) scheme taking into account a finite interfacial thermal resistance.     

Carbon-coated material with bimodal pore-size distribution

Carbon-coated material was prepared by impregnation of a polymer and successive thermal treatment. Polymers such as phenol resin, polyacrylonitrile, polyvinylchloride and polivinylidene dichloride were used for impregnation and inorganic oxides such as SiO₂, Al₂O₃, ZrO₂ and TiO₂ were used as supports. The amount of carbon coating was varied arbitrarily by changing the amount of polymer dissolved in the solvent for impregnation. Carbon-coated materials were characterized by TG/DTA, N₂ adsorption, mercury porosimetry and elemental analysis. Properties and structure of carbon-coated materials were discussed.     

Ethylcellulose nanoparticles with bimodal size distribution as precursors for the production of very small nanoparticles

A common technique for the preparation of polymeric nanoparticles (NPs) from preformed polymers is the emulsification solvent evaporation (ESE) method. However, the particle size of such carriers can typically not reduced below 100?nm. A bimodal distribution of particle size when applying ESE to the preparation of ethylcellulose (EC) NPs was intended to obtain very small particles in a size range below 50?nm. The proportion and size of the small particle fraction (SPF) depended on the surfactant as well as on the EC type and concentration. The preparation was conducted with different pharmaceutically relevant surfactants (polyoxyethylene (23) lauryl ether, sodium dodecyl sulfate, cetyltrimethylammonium bromide, polyvinyl alcohol and polysorbate 20) and all permitted obtaining very small NPs. After purification from excess surfactant by diafiltration and separation of the SPF by centrifugation, monodispersed particles with mean sizes between 20.6?±?2.3?nm and 49.7?±?4.8?nm could be isolated. The entrapment of a lipophilic model drug led to encapsulation rates between 34.0?±?2.4% and 78.2?±?12.6%, which were size and surfactant dependent. The preparation of polymeric NPs in a size below 50?nm by a simple centrifugation step holds promise for therapeutic applications where larger particles would be inefficient.     

Porous carbon nanofibers with narrow pore size distribution from electrospun phenolic resins

Phenolic resin-based porous carbon nanofibers (PCNFs) with large surface area and narrow pore size distribution have been successfully prepared using novolac-type phenolic resin as precursor. The high molecular weight precursor was first synthesized in this study, then was dissolved in methanol. The PCNFs were finally obtained through electrospinning the phenolic resin polymer solution followed by successive curing and carbonization without activation. The N₂ adsorption/desorption isotherms reveal that the PCNFs have high specific surface area about 812 m²/g, the pore size falls in the range of 0.4-0.7 nm and the pore volume is 0.91 cm³/g. The vapor adsorption testing demonstrated that PCNFs exhibited different adsorption performance for ethanol and water.     

Determination of the pore size distribution of correlated mesoporous networks

In the present work we study how the adsorption desorption hysteresis loop of a mesoporous disordered medium represented by a 3-dimensional Dual Site-Bond Model (DSBM) is affected by percolation. Site and bond distributions are assumed to be gaussians. The behavior of the threshold pressure for the evaporation processe suggests a method to determine the site and bond distributions from experimental adsorption-desorption hysteresis curves. Traditional methods developed for non-correlated networks are tested and evaluated against our simulation results showing the discrepancy mainly for highly correlated networks. Results of the prediction capability of our method are shown. Received: 30 March 2000     

Effect of rubber particle size on the impact tensile fracture behavior of MBS resin with a bimodal particle size distribution

We performed impact tensile fracture experiments on methylmethacrylate–butadiene–styrene (MBS) resin with small and large particles in a bimodal size distribution, and examined the effects of particle size on fracture behavior by fixing the total rubber content (28 wt%) and the small particle size (about 140 nm), and varying the size of large particles (about 490 nm or 670 nm). Dynamic load P′ and displacement δ′ of single-edge-cracked specimens were measured using a Piezo sensor and a high-speed extensometer, respectively. A P′−δ′ diagram was used to determine external work U _ex applied to the specimen, elastic energy E _e stored in the specimen, and fracture energy E _f for creating a new fracture surface A _s. Energy release rate was then estimated using G _f = E _f/A _s. Values of G _f were correlated with fracture loads and mean crack velocity v _m determined from load and time relationships. We then examined the effect of particle size on G _f and v _m, and results indicated that particle size plays an important role in changing the values of G _f and v _m.     

Inversion of multiwavelength Raman lidar data for retrieval of bimodal aerosol size distribution

We report on the feasibility of deriving microphysical parameters of bimodal particle size distributions from Mie-Raman lidar based on a triple Nd:YAG laser. Such an instrument provides backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm. The inversion method employed is Tikhonov's inversion with regularization. Special attention has been paid to extend the particle size range for which this inversion scheme works to approximately 10 microm, which makes this algorithm applicable to large particles, e.g., investigations concerning the hygroscopic growth of aerosols. Simulations showed that surface area, volume concentration, and effective radius are derived to an accuracy of approximately 50% for a variety of bimodal particle size distributions. For particle size distributions with an effective radius of < 1 microm the real part of the complex refractive index was retrieved to an accuracy of +/- 0.05, the imaginary part was retrieved to 50% uncertainty. Simulations dealing with a mode-dependent complex refractive index showed that an average complex refractive index is derived that lies between the values for the two individual modes. Thus it becomes possible to investigate external mixtures of particle size distributions, which, for example, might be present along continental rims along which anthropogenic pollution mixes with marine aerosols. Measurement cases obtained from the Institute for Tropospheric Research six-wavelength aerosol lidar observations during the Indian Ocean Experiment were used to test the capabilities of the algorithm for experimental data sets. A benchmark test was attempted for the case representing anthropogenic aerosols between a broken cloud deck. A strong contribution of particle volume in the coarse mode of the particle size distribution was found.     

甘氨酸衍生的双介孔掺氮有序介孔炭用于超级电容器和氧气还原

掺氮多孔炭材料在电化学能量储存和转化方面具有良好的应用前景.可控的氮原子掺杂与孔结构设计对提高其性能起着重要作用.本工作利用无溶剂纳米铸造法,以甘氨酸(Gly)为单一前驱体、以SBA-15为硬模板,制备了掺氮有序介孔炭材料(N-OMCs).甘氨酸在SBA-15孔道内的限域热解对提高碳产率、氮掺杂量以及构筑双介孔结构非常...