Showing papers on "Particle published in 2007"
TL;DR: The crystallization and x-ray structure determination of a p-mercaptobenzoic acid–protected gold nanoparticle, which comprises 102 gold atoms and 44 p-MBAs, is reported, which is chiral, with the two enantiomers alternating in the crystal lattice.
Abstract: Structural information on nanometer-sized gold particles has been limited, due in part to the problem of preparing homogeneous material. Here we report the crystallization and x-ray structure determination of a p-mercaptobenzoic acid (p-MBA)-protected gold nanoparticle, which comprises 102 gold atoms and 44 p-MBAs. The central gold atoms are packed in a Marks decahedron, surrounded by additional layers of gold atoms in unanticipated geometries. The p-MBAs interact not only with the gold but also with one another, forming a rigid surface layer. The particles are chiral, with the two enantiomers alternating in the crystal lattice. The discrete nature of the particle may be explained by the closing of a 58-electron shell.
2,268 citations
TL;DR: Care needs to be taken in toxicity testing in ascribing toxicity to nanoparticles per se when the effects may be related, at least in part, to simple solubility, as this study has shown.
Abstract: Metal oxide nanoparticles are finding increasing application in various commercial products, leading to concerns for their environmental fate and potential toxicity. It is generally assumed that nanoparticles will persist as small particles in aquatic systems and that their bioavailability could be significantly greater than that of larger particles. The current study using nanoparticulate ZnO (ca. 30 nm) has shown that this is not always so. Particle characterization using transmission electron microscopy and dynamic light scattering techniques showed that particle aggregation is significant in a freshwater system, resulting in flocs ranging from several hundred nanometers to several microns. Chemical investigations using equilibrium dialysis demonstrated rapid dissolution of ZnO nanoparticles in a freshwater medium (pH 7.6), with a saturation solubility in the milligram per liter range, similar to that of bulk ZnO. Toxicity experiments using the freshwater alga Pseudokirchneriella subcapitata revealed c...
1,221 citations
TL;DR: Investigation of the rapid aggregation of NZVI from single nanoparticles to micrometer size aggregates, and optical microscopy and sedimentation measurements to estimate the size of interconnected fractal aggregates formed confirm that magnetic attractive forces between particles increase the rate ofNZVI aggregation as compared to nonmagnetic particles.
Abstract: Nanoscale zerovalent iron (NZVI) rapidly transforms many environmental contaminants to benign products and is a promising in-situ remediation agent. To be effective, NZVI should form stable dispersions in water such that it can be delivered in water-saturated porous media to the contaminated area. Limited mobility of NZVI has been reported, however, attributed to its rapid aggregation. This study uses dynamic light scattering to investigate the rapid aggregation of NZVI from single nanoparticles to micrometer size aggregates, and optical microscopy and sedimentation measurements to estimate the size of interconnected fractal aggregates formed. The rate of aggregation increased with increasing particle concentration and increasing saturation magnetization (i.e., the maximum intrinsic magnet moment) of the particles. During diffusion limited aggregation the primary particles (average radius = 20 nm) aggregate to micrometer-size aggregates in only 10 min, with average hydrodynamic radii ranging from 125 nm to 1.2 microm at a particle concentration of 2 mg/L (volume fraction(phi= 3.2 x 10(-7)) and 60 mg/L (phi = 9.5 x 10(-6)), respectively. Subsequently, these aggregates assemble themselves into fractal, chain-like clusters. At an initial concentration of just 60 mg/L, cluster sizes reach 20-70 microm in 30 min and rapidly sedimented from solution. Parallel experiments conducted with magnetite and hematite, coupled with extended DLVO theory and multiple regression analysis confirm that magnetic attractive forces between particles increase the rate of NZVI aggregation as compared to nonmagnetic particles.
962 citations
TL;DR: In this paper, the influence of both the temperature and the particle size on the dynamic viscosities of two particular water-based nanofluids, namely water-Al2O3 and water-CuO mixtures, was investigated experimentally using a piston-type calibrated viscometer based on the Couette flow inside a cylindrical measurement chamber.
876 citations
TL;DR: In this article, a core-shell nanocomposites (R−Au) bearing well-defined gold nanoparticles as surface atoms of variable sizes (8−55 nm) have been synthesized exploiting polystyrene-based commercial anion exchangers.
Abstract: Core−shell nanocomposites (R−Au) bearing well-defined gold nanoparticles as surface atoms of variable sizes (8−55 nm) have been synthesized exploiting polystyrene-based commercial anion exchangers. Immobilization of gold nanoparticles, prepared by the Frens method, onto the resin beads in the chloride form is possible by the ready exchange of the citrate-capped negatively charged gold particles. The difficulty of nanoparticle loading, avoiding aggregation, has been solved by stepwise operation. Analysis of the gold particles after immobilization and successive elution confirm the unaltered particle morphology while compared to those of the citrate-capped gold particles in colloidal dispersion. It was observed that the rate of the reaction increases with the increase in catalyst loading, which suggests the catalytic behavior of the gold nanoparticles for the reduction of the aromatic nitrocompounds. The rate constant, k, was found to be proportional to the total surface area of the nanoparticles in the sys...
739 citations
TL;DR: Together, these results imply that the geometry, agglomeration state, and surface resistance of nanoparticles are the main variables controlling thermal conductivity enhancement in nanofluids.
Abstract: In recent years many experimentalists have reported an anomalously enhanced thermal conductivity in liquid suspensions of nanoparticles. Despite the importance of this effect for heat transfer applications, no agreement has emerged about the mechanism of this phenomenon, or even about the experimentally observed magnitude of the enhancement. To address these issues, this paper presents a combined experimental and theoretical study of heat conduction and particle agglomeration in nanofluids. On the experimental side, nanofluids of alumina particles in water and ethylene glycol are characterized using thermal conductivity measurements, viscosity measurements, dynamic light scattering, and other techniques. The results show that the particles are agglomerated, with an agglomeration state that evolves in time. The data also show that the thermal conductivity enhancement is within the range predicted by effective medium theory. On the theoretical side, a model is developed for heat conduction through a fluid containing nanoparticles and agglomerates of various geometries. The calculations show that elongated and dendritic structures are more efficient in enhancing the thermal conductivity than compact spherical structures of the same volume fraction, and that surface (Kapitza) resistance is the major factor resulting in the lower than effective medium conductivities measured in our experiments. Together, these results imply that the geometry, agglomeration state, and surface resistance of nanoparticles are the main variables controlling thermal conductivity enhancement in nanofluids.
700 citations
TL;DR: In this article, a set of simulation techniques, ranging from one-dimensional finite difference simulations of spherical particles, to fully three-dimensional (3D) simulations of ellipsoidal particles, were used to systematically study the intercalation-induced stresses developed in particles of various shapes and sizes, with the latter 3D calculations performed using a commercial finite element code.
Abstract: Severe, particle-level strains induced during both production and cycling have been putatively linked to lifetime limiting damage in lithium-ion cells. Because of the presently unknown contributions of manufacturing and intercalation induced stresses in Li cells, this correlation is critical in determining optimal materials and manufacturing methods for these cells. Both global and localized loads must be estimated, in order to select materials able to resist fracture. Here, we select the LiMn 2 O 4 system for study. We present results of a set of simulation techniques, ranging from one-dimensional finite difference simulations of spherical particles, to fully three-dimensional (3D) simulations of ellipsoidal particles, to systematically study the intercalation-induced stresses developed in particles of various shapes and sizes, with the latter 3D calculations performed using a commercial finite element code. Simulations of spherical particles show that larger particle sizes and larger discharge current densities give larger intercalation-induced stresses. Simulations of ellipsoidal particles show that large aspect ratios are preferred to reduce the intercalation-induced stresses. In total, these results suggest that it is desirable to synthesize electrode particles with smaller sizes and larger aspect ratios to reduce intercalation-induced stress during cycling of lithium-ion batteries.
694 citations
TL;DR: The particle size dependence of insertion reactions has been investigated for lithiated anatase TiO2, revealing progressively increasing Li capacity and Li-ion solubility for decreasing particle sizes, strongly deviating from the expected Li-rich andLi-poor phase separation as occurs in the bulk material.
Abstract: Insertion reactions are of key importance for Li ion and hydrogen storage materials and energy storage devices. The particle size dependence of insertion reactions has been investigated for lithiated anatase TiO2, revealing progressively increasing Li capacity and Li-ion solubility for decreasing particle sizes, strongly deviating from the expected Li-rich and Li-poor phase separation as occurs in the bulk material. The phase diagram alters significantly, changing the materials properties already at sizes as large as 40 nm. A rationale is found in the surface strain that occurs between the different intercalated phases, which becomes energetically too costly in small particles. In particular the observed particle size-induced solid solution behavior is expected to have fundamental and practical implications for two-phase lithium or hydrogen insertion reactions.
682 citations
TL;DR: This method uses routine laboratory chemicals and equipment to make particles with >20 distinct shapes and characteristic features ranging in size from 60 nm to 30 μm, which offers independent control over important particle properties such as size and shape, crucial to the development of nonspherical particles both as tools and products for a variety of fields.
Abstract: Polymeric micro- and nanoparticles play a central role in varied applications such as drug delivery, medical imaging, and advanced materials, as well as in fundamental studies in fields such as microfluidics and nanotechnology. Functional behavior of polymeric particles in these fields is strongly influenced by their shape. However, the availability of precisely shaped polymeric particles has been a major bottleneck in understanding and capitalizing on the role of shape in particle function. Here we report a method that directly addresses this need. Our method uses routine laboratory chemicals and equipment to make particles with >20 distinct shapes and characteristic features ranging in size from 60 nm to 30 μm. This method offers independent control over important particle properties such as size and shape, which is crucial to the development of nonspherical particles both as tools and products for a variety of fields.
681 citations
TL;DR: The results show that free flow acoustophoresis can be used to perform complex separation tasks, thereby offering an alternative to expensive and time-consuming methods currently in use.
Abstract: A novel method, free flow acoustophoresis (FFA), capable of continuous separation of mixed particle suspensions into multiple outlet fractions is presented. Acoustic forces are utilized to separate particles based on their size and density. The method is shown to be suitable for both biological and nonbiological suspended particles. The microfluidic separation chips were fabricated using conventional microfabrication methods. Particle separation was accomplished by combining laminar flow with the axial acoustic primary radiation force in an ultrasonic standing wave field. Dissimilar suspended particles flowing through the 350-μm-wide channel were thereby laterally translated to different regions of the laminar flow profile, which was split into multiple outlets for continuous fraction collection. Using four outlets, a mixture of 2-, 5-, 8-, and 10-μm polystyrene particles was separated with between 62 and 94% of each particle size ending up in separate fractions. Using three outlets and three particle siz...
631 citations
TL;DR: This tutorial review will summarize functions associated with the integration of inorganic nanofillers in polymers with a focus on optical properties.
Abstract: The integration of inorganic nanoparticles into polymers has been used for the functionalization of polymer materials with great success. Whereas in traditional polymer composites, micron sized particles or agglomerates typically cause significant light scattering hampering optical applications, in nanocomposites the particle dimensions are small enough for the production of highly transparent composites. A challenge for the generation of such materials is to develop an integrated synthesis strategy adapting particle generation, surface modification and integration inside the polymer. Surface grafting using polymerizable surfactants or capping agents allows for linking the particles to the polymer. Novel techniques such as in situ polymerization and in situ particle processing are beneficial to avoid aggregation of inorganic particles inside the polymer matrix. The functions associated with inorganic fillers are widespread. Layered silicates and related materials are nowadays commercially available for improving mechanical and barrier properties in packaging. With the availability of highly transparent materials, the focus has shifted towards optical functions such as luminescence and UV-protection in transparent polymers. IR-active fillers are used in laser-holography for transparent poly(methyl methacrylate) (PMMA) nanocomposites. Refractive index modulation and ultrahigh refractive index films were developed based on inorganic materials such as PbS. The integration of magnetic nanoparticles has a great potential for applications such as electromagnetic interference shielding and magneto-optical storage.This tutorial review will summarize functions associated with the integration of inorganic nanofillers in polymers with a focus on optical properties.
TL;DR: In this article, the authors investigated the behavior and heat transfer enhancement of a particular nanofluid, Al2O3 nanoparticle-water mixture, flowing inside a closed system that is destined for cooling of microprocessors or other electronic components.
TL;DR: In this paper, the particles have been suspended in non-aqueous and aqueous media by coating the particles with a single layer and a bilayer of oleic acid, respectively.
TL;DR: In this paper, an experimental investigation of rheological properties of copper oxide nanoparticles suspended in 60:40 (by weight) ethylene glycol and water mixture was presented.
TL;DR: An instrumental setup to measure atmospheric concentrations of both neutral and charged nanometer-sized clusters concludes that a pool of numerous neutral clusters in the sub–3 nanometer size range is continuously present and neutral nucleation dominates over the ion-induced mechanism, at least in boreal forest conditions.
Abstract: Atmospheric aerosol formation is known to occur almost all over the world, and the importance of these particles to climate and air quality has been recognized. Although almost all of the processes driving aerosol formation take place below a particle diameter of 3 nanometers, observations cover only larger particles. We introduce an instrumental setup to measure atmospheric concentrations of both neutral and charged nanometer-sized clusters. By applying the instruments in the field, we come to three important conclusions: (i) A pool of numerous neutral clusters in the sub–3 nanometer size range is continuously present; (ii) the processes initiating atmospheric aerosol formation start from particle sizes of ∼1.5 nanometers; and (iii) neutral nucleation dominates over the ion-induced mechanism, at least in boreal forest conditions.
TL;DR: A simple model is developed that captures the dependence of the time required to stop the flow on geometric parameters such as the height, length and width of the microchannel, as well as on the externally imposed pressure.
Abstract: Polymeric particles in custom designed geometries and with tunable chemical anisotropy are expected to enable a variety of new technologies in diverse areas such as photonics, diagnostics and functional materials. We present a simple, high throughput and high resolution microfluidic method to synthesize such polymeric particles. Building off earlier work that we have done on continuous flow lithography (CFL) (D. Dendukuri, D. C. Pregibon, J. Collins, T. A. Hatton, P. S. Doyle, Nat. Mater., 2006, 5, 365–369; ref. 1), we have devised and implemented a new setup that uses compressed air driven flows in preference to syringe pumps to synthesize particles using a technique that we call stop-flow lithography (SFL). A flowing stream of oligomer is stopped before polymerizing an array of particles into it, providing for much improved resolution over particles synthesized in flow. The formed particles are then flushed out at high flow rates before the cycle of stop-polymerize-flow is repeated. The high flow rates enable orders-of-magnitude improvements in particle throughput over CFL. However, the deformation of the PDMS elastomer due to the imposed pressure restricts how quickly the flow can be stopped before each polymerization event. We have developed a simple model that captures the dependence of the time required to stop the flow on geometric parameters such as the height, length and width of the microchannel, as well as on the externally imposed pressure. Further, we show that SFL proves to be superior to CFL even for the synthesis of chemically anisotropic particles with sharp interfaces between distinct sections.
TL;DR: This work has developed a novel printing process that enables positioning of sub-100-nm particles individually with high placement accuracy and can create a variety of particle arrangements including lines, arrays and bitmaps, while preserving the catalytic and optical activity of the individual nanoparticles.
Abstract: Bulk syntheses of colloids efficiently produce nanoparticles with unique and useful properties. Their integration onto surfaces is a prerequisite for exploiting these properties in practice. Ideally, the integration would be compatible with a variety of surfaces and particles, while also enabling the fabrication of large areas and arbitrarily high-accuracy patterns. Whereas printing routinely meets these demands at larger length scales, we have developed a novel printing process that enables positioning of sub-100-nm particles individually with high placement accuracy. A colloidal suspension is inked directly onto printing plates, whose wetting properties and geometry ensure that the nanoparticles only fill predefined topographical features. The dry particle assembly is subsequently printed from the plate onto plain substrates through tailored adhesion. We demonstrate that the process can create a variety of particle arrangements including lines, arrays and bitmaps, while preserving the catalytic and optical activity of the individual nanoparticles.
TL;DR: The systematic approach presented in this study demonstrates that a substantial improvement of the photocatalytic activity of TiO2 can be achieved by a careful design of the particle morphology and the control of the surface chemistry.
Abstract: The possibility of controlling the photocatalytic activity of TiO2 nanoparticles by tailoring their crystalline structure and morphology is a current topic of great interest. In this study, a broad variety of well-faceted particles with different phase compositions, sizes, and shapes have been obtained from concentrated TiOCl2 solutions by systematically changing temperature, pH, and duration of the hydrothermal treatment. The guide to select the suitable experimental conditions was provided by thermodynamic modeling based on available thermochemical data. By combining the results of TEM, HRTEM, XRD, density, and specific surface area measurements, a complete structural and morphological characterization of the particles was performed. Correlation between the photocatalytic activity in the UV photodegradation of phenol solutions and the particle size was established. Prismatic rutile particles with length/width ratio around 5 and breadth of 60−100 nm showed the highest activity. The surface chemistry of t...
TL;DR: In this article, it was shown that in LiFePO4-based cathode materials, the electrode resistance depends solely on the mean particle size and the effect of carbon coating is marginal, it suffices that each particle is point-contacted with a reasonable number of carbon black particles usually added in the course of electrode preparation.
TL;DR: In this article, the authors present complete, closed-form expressions for random relative velocities between colliding particles of arbitrary size in nebula turbulence, which are exact for very small particles (those with stopping times much shorter than the large eddy overturn time).
Abstract: In this note we present complete, closed-form expressions for random relative velocities between colliding particles of arbitrary size in nebula turbulence. These results are exact for very small particles (those with stopping times much shorter than the large eddy overturn time) and are also surprisingly accurate in complete generality (that is, also apply for particles with stopping times comparable to, or much longer than, the large eddy overturn time). We note that some previous studies may have adopted previous simple expressions, which we find to be in error regarding the size dependence in the large particle regime.
TL;DR: Finite-difference time-domain (FDTD) calculations were employed to study the distribution of electric field near the metal monomer and dimer and revealed that the single-molecule fluorescence was enhanced 7-fold and 13-fold on the metal dimer relative to the free Cy5-labeled oligonucleotide in the absence of metal.
Abstract: We prepared silver particle dimers with single Cy5 molecules localized between coupled metal particles. The silver particles with a 20 nm diameter were chemically bound with single-stranded oligonucleotides. The dimers were formed by hybridization with double-length single-stranded oligonucleotides that contained single Cy5 molecules. The image analysis revealed that the single-molecule fluorescence was enhanced 7-fold on the metal monomer and 13-fold on the metal dimer relative to the free Cy5-labeled oligonucleotide in the absence of metal. The lifetimes were shortened on the silver monomers and further shortened on the silver dimers, demonstrating the near-field interaction mechanism of fluorophore with the metal substrate. Finite-difference time-domain (FDTD) calculations were employed to study the distribution of electric field near the metal monomer and dimer. The coupling effect of metal particle on the fluorescence enhancement was discussed.
TL;DR: Spatial distributions of heavy particles suspended in an incompressible isotropic and homogeneous turbulent flow are investigated by means of high resolution direct numerical simulations and it is shown that particles form fractal clusters with properties independent of the Reynolds number.
Abstract: Spatial distributions of heavy particles suspended in an incompressible isotropic and homogeneous turbulent flow are investigated by means of high resolution direct numerical simulations. In the dissipative range, it is shown that particles form fractal clusters with properties independent of the Reynolds number. Clustering is there optimal when the particle response time is of the order of the Kolmogorov time scale � � . In the inertial range, the particle distribution is no longer scale invariant. It is, however, shown that deviations from uniformity depend on a rescaled contraction rate, which is different from the local Stokes number given by dimensional analysis. Particle distribution is characterized by voids spanning all scales of the turbulent flow; their signature in the coarse-grained mass probability distribution is an algebraic behavior at small densities.
TL;DR: In this paper, an experimental investigation into the viscosity and specific heat of silicon dioxide nanoparticles with various diameters (20, 50 and 100 nm) suspended in a 60:40 (by weight) ethylene glycol and water mixture is presented.
Abstract: Results of an experimental investigation into the viscosity and specific heat of silicon dioxide (SiO
2
) nanoparticles with various diameters (20, 50 and 100 nm) suspended in a 60:40 (by weight) ethylene glycol and water mixture are presented. Nanofluids with particle volume percentages ranging from 0 to 10% were examined. Viscosity experiments were carried out over wide temperature ranges, from -35 to 50degC, to demonstrate their applicability in cold regions. The nano- particle diameter effect on the rheology of the SiO
2
nanofluid is explored. Non-Newtonian behaviour was observed for the particle volume concentrations of these nanofluids at sub-zero temperatures. A new correlation was developed from experimental data, which related viscosity with particle volume percent and nanofluid temperature. The specific heats of the SiO
2
nanofluids for various particle volume concentrations are presented.
IBM1
TL;DR: It is demonstrated for the first time that the velocity and direction of particles in the suspension can be controlled to perform assembly or disassembly of particles, and a mechanism is proposed that takes into account the relative influences of these parameters on the motion of particles and that describes the influence of temperature on the assembly efficiency.
Abstract: A wide variety of methods are now available for the synthesis of colloidal particle having controlled shapes, structures, and dimensions. One of the main challenges in the development of devices that utilize micro- and nanoparticles is still particle placement and integration on surfaces. Required are engineering approaches to control the assembly of these building blocks at accurate positions and at high yield. Here, we investigate two complementary methods to create particle assemblies ranging from full layers to sparse arrays of single particles starting from colloidal suspensions of gold and polystyrene particles. Convective assembly was performed on hydrophilic substrates to create crystalline mono- or multilayers using the convective flow of nanoparticles induced by the evaporation of solvent at the three-phase contact line of a solution. On hydrophobic surfaces, capillary assembly was investigated to create sparse arrays and complex three-dimensional structures using capillary forces to trap and organize particles in the recessed regions of a template. In both methods, the hydrodynamic drag exerted on the particle in the suspension plays a key role in the assembly process. We demonstrate for the first time that the velocity and direction of particles in the suspension can be controlled to perform assembly or disassembly of particles. This is achieved by setting the temperature of the colloidal suspension above or below the dew point. The influence of other parameters, such as substrate velocity, wetting properties, and pattern geometry, is also investigated. For the particular case of capillary assembly, we propose a mechanism that takes into account the relative influences of these parameters on the motion of particles and that describes the influence of temperature on the assembly efficiency.
TL;DR: In this article, a detailed kinetic model is developed on the basis of these steps and is combined with population balance to predict particle-size distribution, which is able to explain the unusual dependence of the mean particle size on the ratio of citrate to gold salt concentration, while subsequent increases in the ratio hardly have any effect on the size.
Abstract: Properties of nanoparticles are size dependent, and a model to predict particle size is of importance. Gold nanoparticles are commonly synthesized by reducing tetrachloroauric acid with trisodium citrate, a method pioneered by Turkevich et al (Discuss. Faraday Soc. 1951, 11, 55). Data from several investigators that used this method show that when the ratio of initial concentrations of citrate to gold is varied from 0.4 to similar to 2, the final mean size of the particles formed varies by a factor of 7, while subsequent increases in the ratio hardly have any effect on the size. In this paper, a model is developed to explain this widely varying dependence. The steps that lead to the formation of particles are as follows: reduction of Au3+ in solution, disproportionation of Au+ to gold atoms and their nucleation, growth by disproportionation on particle surface, and coagulation. Oxidation of citrate results in the formation of dicarboxy acetone, which aids nucleation but also decomposes into side products. A detailed kinetic model is developed on the basis of these steps and is combined with population balance to predict particle-size distribution. The model shows that, unlike the usual balance between nucleation and growth that determines the particle size, it is the balance between rate of nucleation and degradation of dicarboxy acetone that determines the particle size in the citrate process. It is this feature that is able to explain the unusual dependence of the mean particle size on the ratio of citrate to gold salt concentration. It is also found that coagulation plays an important role in determining the particle size at high concentrations of citrate.
29 Jul 2007
TL;DR: A sampling condition based on geometric local feature size that allows focusing computational resources in geometrically complex regions, while reducing the number of particles deep inside the fluid or near thick flat surfaces is introduced.
Abstract: We present novel adaptive sampling algorithms for particle-based fluid simulation We introduce a sampling condition based on geometric local feature size that allows focusing computational resources in geometrically complex regions, while reducing the number of particles deep inside the fluid or near thick flat surfaces Further performance gains are achieved by varying the sampling density according to visual importance In addition, we propose a novel fluid surface definition based on approximate particle-to-surface distances that are carried along with the particles and updated appropriately The resulting surface reconstruction method has several advantages over existing methods, including stability under particle resampling and suitability for representing smooth flat surfaces We demonstrate how our adaptive sampling and distance-based surface reconstruction algorithms lead to significant improvements in time and memory as compared to single resolution particle simulations, without significantly affecting the fluid flow behavior
TL;DR: LiMnPO4 was synthesized using a sol-gel method and tested as a cathode material for lithium ion batteries as discussed by the authors, achieving a reversible capacity of 156 mAh g−1 at C/100 and 134 mAh G−1 in C/10.
TL;DR: Size-resolved indicators of aerosol acidity, including H+ ion concentrations (H+Aer) and the ratio of stoichiometric neutralization and the mass concentrations and size distributions of oxygenated organic aerosol (00A--surrogate for SOA in Pittsburgh) are evaluated, suggesting that the chemical nature of SOA is similar during acidic and neutralized periods and that there is no significant enhancement of SoA oligomer formation during acidic particle periods in Pittsburgh.
Abstract: Size-resolved indicators of aerosol acidity, including H+ ion concentrations (H+Aer) and the ratio of stoichiometric neutralization are evaluated in submicrometer aerosols using highly time-resolved aerosol mass spectrometer (AMS) data from Pittsburgh. The pH and ionic strength within the aqueous particle phase are also estimated using the Aerosol Inorganics Model (AIM). Different mechanisms that contribute to the presence of acidic particles in Pittsburgh are discussed. The largest H+Aer loadings and lowest levels of stoichiometric neutralization were detected when PM1 loadings were high and dominated by SO4(2-). The average size distribution of H+Aer loading shows an accumulation mode at Dva approximately 600 nm and an enhanced smaller mode that centers at Dva approximately 200 nm and tails into smaller sizes. The acidity in the accumulation mode particles suggests that there is generally not enough gas-phase NH3 available on a regional scale to completely neutralize sulfate in Pittsburgh. The lack of stoichiometric neutralization in the 200 nm mode particles is likely caused by the relatively slow mixing of gas-phase NH3 into SO2-rich plumes containing younger particles. We examined the influence of particle acidity on secondary organic aerosol (SOA) formation by comparing the mass concentrations and size distributions of oxygenated organic aerosol (00A--surrogate for SOA in Pittsburgh) during periods when particles are, on average, acidic to those when particles are bulk neutralized. The average mass concentration of ODA during the acidic periods (3.1 +/- 1.7 microg m(-3)) is higher than that during the neutralized periods (2.5 +/- 1.3 microg m(-3)). Possible reasons for this enhancement include increased condensation of SOA species, acid-catalyzed SOA formation, and/or differences in air mass transport and history. However, even if the entire enhancement (approximately 0.6 microg m(-3)) can be attributed to acid catalysis, the upperbound increase of SOA mass in acidic particles is approximately 25%, an enhancement that is much more moderate than the multifold increases in SOA mass observed during some lab studies and inferred in SO2-rich industrial plumes. In addition, the mass spectra of OOA from these two periods are almost identical with no discernible increase in relative signal intensity at larger m/z's (>200 amu), suggesting that the chemical nature of SOA is similar during acidic and neutralized periods and that there is no significant enhancement of SOA oligomer formation during acidic particle periods in Pittsburgh.
TL;DR: Wang et al. as mentioned in this paper reported on laboratory experiments carried out to investigate PPG transport mechanisms through porous media, and they demonstrated that PPG propagation exhibits six patterns of behavior: direct pass, adsorption, deform and pass, snap-off-and-pass, shrink and pass and trap.
Abstract: Preformed particle gel (PPG) has been successfully synthesized and applied to control excess water production in most of the mature, waterflooded oil fields in China. This paper reports on laboratory experiments carried out to investigate PPG transport mechanisms through porous media. Visual observations in etchedglass micromodels demonstrate that PPG propagation through porous media exhibits six patterns of behavior: direct pass, adsorption, deform and pass, snap-off and pass, shrink and pass, and trap. At the macroscopic scale, PPG propagation through porous media can be described by three patterns: pass, broken and pass, and plug. The dominant pattern is determined by the pressure change with time along a tested core (as measured at specific points), the particle-size ratio of injected and produced particles from the core outlet, and the residual resistance factor of each segment along the core. Measurements from micromodel and routine coreflooding experiments show that a swollen PPG particle can pass through a pore throat with a diameter that is smaller than the particle diameter owing to the elasticity and deformability of the swollen PPG particle. The largest diameter ratio of a PPG particle and a pore throat that the PPG particle can pass through depends on the swollen PPG strength. PPG particles can pass through porous media only if the driving pressure gradient is higher than the threshold pressure gradient. The threshold pressure depends on the strength of the swollen PPG and the ratio of the particle diameter and the average pore diameter.
TL;DR: In this article, the influence of silicon carbide (SiC) particle size on the microstructure and mechanical properties of Zirconium diboride-silicon carbide-SiC ceramics was investigated.
Abstract: The influence of silicon carbide (SiC) particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide (ZrB2–SiC) ceramics was investigated. ZrB2-based ceramics containing 30 vol.% SiC particles were prepared from four different α-SiC precursor powders with average particle sizes ranging from 0.45 to 10 μm. Examination of the dense ceramics showed that smaller starting SiC particle sizes led to improved densification, finer grain sizes, and higher strength. For example, ceramics prepared from SiC with the particle size of 10 μm had a strength of 389 MPa, but the strength increased to 909 MPa for ceramics prepared from SiC with a starting particle size of 0.45 μm. Analysis indicates that SiC particle size controls the strength of ZrB2–SiC.