Showing papers on "Particle published in 2001"
TL;DR: In this article, the authors present the state-of-the-art in strategies for engineering particle surfaces, such as the layer-by-layer deposition process, which allows fine control over shell thickness and composition.
Abstract: The creation of core–shell particles is attracting a great deal of interest because of the diverse applicability of these colloidal particles; e.g., as building blocks for photonic crystals, in multi-enzyme biocatalysis, and in drug delivery. This review presents the state-of-the-art in strategies for engineering particle surfaces, such as the layer-by-layer deposition process (see Figure), which allows fine control over shell thickness and composition.
2,324 citations
TL;DR: In this paper, gold nanoparticles of diameters 5−40 nm were prepared with 10−15% standard deviation in diameter from 3.5 ± 0.7 nm gold particle seeds.
Abstract: Following a seeding growth approach, gold nanoparticles of diameters 5−40 nm were prepared with 10−15% standard deviation in diameter from 3.5 ± 0.7 nm gold particle seeds. Particle size can be controlled by varying the ratio of seed to metal salt, and thus any size in the range 5−40 nm can be prepared. The method can also be scaled up to produce 10−100 mg of gold nanoparticles.
1,310 citations
TL;DR: In this article, the synthesis and study of so-called "nanoparticles" with diameters in the range of 1−20 nm, has become a major interdisciplinary area of research over the past 10 years.
Abstract: The synthesis and study of so-called “nanoparticles”, particles with diameters in the range of 1−20 nm, has become a major interdisciplinary area of research over the past 10 years. Semiconductor nanoparticles promise to play a major role in several new technologies. The intense interest in this area derives from their unique chemical and electronic properties, which gives rise to their potential use in the fields of nonlinear optics, luminescence, electronics, catalysis, solar energy conversion, and optoelectronics, as well as other areas. The small dimensions of these particles result in different physical properties from those observed in the corresponding macrocrystalline, “bulk”, material. As particle sizes become smaller, the ratio of surface atoms to those in the interior increase, leading to the surface properties playing an important role in the properties of the material. Semiconductor nanoparticles also exhibit a change in their electronic properties relative to that of the bulk material; as th...
1,213 citations
TL;DR: It is demonstrated that only ultrafine polystyrene particles induced a significant increase in cytosolic calcium ion concentration and experiments using dichlorofluorescin diacetate demonstrated greater oxidant activity of the ultrafine particles, which may explain their activity in these assays.
1,181 citations
TL;DR: A survey of published knowledge classified according to the different concepts currently used to manufacture particles, microspheres or microcapsules, liposomes or other dispersed materials (like microfibers) is presented in this article.
Abstract: As particle design is presently a major development of supercritical fluids applications, mainly in the pharmaceutical, nutraceutical, cosmetic and specialty chemistry industries, number of publications are issued and numerous patents filed every year. This document presents a survey (that cannot pretend to be exhaustive!) of published knowledge classified according to the different concepts currently used to manufacture particles, microspheres or microcapsules, liposomes or other dispersed materials (like microfibers):
RESS: This acronym refers to ‘Rapid Expansion of Supercritical Solutions’; this process consists in solvating the product in the fluid and rapidly depressurizing this solution through an adequate nozzle, causing an extremely rapid nucleation of the product into a highly dispersed material. Known for long, this process is attractive due to the absence of organic solvent use; unfortunately, its application is restricted to products that present a reasonable solubility in supercritical carbon dioxide (low polarity compounds).
GAS or SAS: These acronyms refer to ‘Gas (or Supercritical fluid) Anti-Solvent’, one specific implementation being SEDS (‘Solution Enhanced Dispersion by Supercritical Fluids’); this general concept consists in decreasing the solvent power of a polar liquid solvent in which the substrate is dissolved, by saturating it with carbon dioxide in supercritical conditions, causing the substrate precipitation or recrystallization. According to the solid morphology that is wished, various ways of implementation are available:
GAS or SAS recrystallization: This process is mostly used for recrystallization of solid dissolved in a solvent with the aim of obtaining either small size particles or large crystals, depending on the growth rate controlled by the anti-solvent pressure variation rate;
ASES: This name is rather used when micro- or nano-particles are expected; the process consists in pulverizing a solution of the substrate(s) in an organic solvent into a vessel swept by a supercritical fluid;
SEDS: A specific implementation of ASES consists in co-pulverizing the substrate(s) solution and a stream of supercritical carbon dioxide through appropriate nozzles.
PGSS: This acronym refers to ‘Particles from Gas-Saturated Solutions (or Suspensions)’: This process consists in dissolving a supercritical fluid into a liquid substrate, or a solution of the substrate(s) in a solvent, or a suspension of the substrate(s) in a solvent followed by a rapid depressurization of this mixture through a nozzle causing the formation of solid particles or liquid droplets according to the system.
The use of supercritical fluids as chemical reaction media for material synthesis. Two processes are described: thermal decomposition in supercritical fluids and hydrothermal synthesis.
We will successively detail the literature and patents for these four main process concepts, and related applications that have been claimed. Moreover, as we believe it is important to take into account the user's point-of-view, we will also present this survey in classifying the documents according three product objectives: particles (micro- or nano-) of a single component, microspheres and microcapsules of mixtures of active and carrier (or excipient) components, and particle coating.
1,124 citations
TL;DR: In this paper, a parameterization of particle dry deposition has been developed for the Canadian Aerosol Module (CAM) with meteorological input provided by the Canadian Regional Climate Model (RCM) to the eastern North America.
990 citations
TL;DR: The current state of knowledge of the fundamentals of particle formation from homogeneous solution and the effect of solvent and polymer additives on the morphology and supramolecular structure of the nanoparticle will be discussed and the practical implementation of this new formulation technology will be explored in detail.
Abstract: Many active organic compounds and organic effect materials are poorly soluble in water, or even insoluble. Aqueous forms of application thus require special formulation techniques to utilize or optimize the physiological (pharmaceuticals, cosmetics, plant protection, nutrition) or technical (varnishes, printing inks, toners) action. The most interesting properties of nanodispersions of active organic compounds and effect materials include the impressive increase in solubility, the improvement in biological resorption, and the modification of optical, electrooptical, and other physical properties which are achievable only with particle sizes in the middle or lower nanometer range (50-500 nm). Hence in addition to economic and ecological constraints there are also technical demands which appear to urgently require the development of new processes for the production of organic nanoparticles as alternatives to the established mechanical milling processes. In this context attention is drawn to the recent increase in research activities which have as their objective the continuous, automatic preparation of nanodispersed systems by precipitation from molecular solution. In this review the current state of knowledge of the fundamentals of particle formation from homogeneous solution and the effect of solvent and polymer additives on the morphology and supramolecular structure of the nanoparticle will be discussed. The practical implementation of this new formulation technology will be explored in detail for the carotenoids, a class of compounds of both physiological and technical interest.
950 citations
TL;DR: In this article, the influence of particle size on the antibacterial activity of ZnO powders was investigated using powders with different particle sizes ranging from 0.1 to 0.8 μm.
839 citations
TL;DR: The Secondary Organic Aerosol Model (SORGAM) as mentioned in this paper has been developed for use in comprehensive air quality model systems and is capable of simulating secondary organic aerosol (SOA) formation including the production of lowvolatility products and their subsequent gas/particle partitioning.
Abstract: The Secondary Organic Aerosol Model (SORGAM) has been developed for use in comprehensive air quality model systems. Coupled to a chemistry-transport model, SORGAM is capable of simulating secondary organic aerosol (SOA) formation including the production of low-volatility products and their subsequent gas/particle partitioning. The current model formulation assumes that all SOA compounds interact and form a quasi-ideal solution. This has significant impact on the gas/particle partitioning, since in this case the saturation concentrations of the SOA compounds depend on the composition of the SOA and the amount of absorbing material present. Box model simulations have been performed to investigate the sensitivity of the model against several parameters. Results clearly show the importance of the temperature dependence of saturation concentrations on the partitioning process. Furthermore, SORGAM has been coupled to the comprehensive European Air Pollution and Dispersion/Modal Aerosol Dynamics Model for Europe air quality model system, and results of a three-dimensional model application are presented. The model results indicate that assuming interacting SOA compounds, biogenic and anthropogenic contributions significantly influence each other and cannot be treated independently.
811 citations
TL;DR: In this paper, a water-in-oil microemulsion method has been applied for the preparation of silica-coated iron oxide nanoparticles, and their effects on the particle size, crystallinity, and the magnetic properties have been studied.
Abstract: A water-in-oil microemulsion method has been applied for the preparation of silica-coated iron oxide nanoparticles. Three different nonionic surfactants (Triton X-100, Igepal CO-520, and Brij-97) have been used for the preparation of microemulsions, and their effects on the particle size, crystallinity, and the magnetic properties have been studied. The iron oxide nanoparticles are formed by the coprecipitation reaction of ferrous and ferric salts with inorganic bases. A strong base, NaOH, and a comparatively mild base, NH4OH, have been used in each surfactant to observe whether the basicity has some influence on the crystallization process during particle formation. Transmission electron microscopy, X-ray electron diffraction, and superconducting quantum interference device magnetometry have been employed to study both uncoated and silica-coated iron oxide nanoparticles. All these particles show magnetic behavior close to that of superparamagnetic materials. By use of this method, magnetic nanoparticles ...
772 citations
TL;DR: The microfabrication and characterisation of an on-chip flow-cytometer is described as the first building block of a complete cell-sorting device and the signal conditioning technique and impedance measurements of cells and particles of different sizes and types are discussed to demonstrate the differentiation of subpopulations in a mixed sample.
Abstract: A new cytological tool, based on the micro Coulter particle counter (μCPC) principle, aimed at diagnostic applications for cell counting and separation in haematology, oncology or toxicology is described. The device measures the spectral impedance of individual cells or particles and allows screening rates over 100 samples s−1 on a single-cell basis. This analyzer is intended to drive a sorting actuator producing a subsequent cell separation. Size reduction and integration of functions are essential in achieving precise measurements and high throughput. 3D finite element simulations are presented to compare various electrode geometries and their influence on cell parameters estimation. The device is based on a glass-polyimide microfluidic chip with integrated channels and electrodes microfabricated at the length scale of the particles to be investigated (1–20 μm). A laminar liquid flow carries the suspended particles through the measurement area.
Each particle’s impedance signal is recorded by a differential pair of microelectrodes using the cell surrounding media as a reference. The micromachined chip and processing electronic circuit allow simultaneous impedance measurements at multiple frequencies, ranging from 100 kHz to 15 MHz. In this paper, we describe the microfabrication and characterisation of an on-chip flow-cytometer as the first building block of a complete cell-sorting device. We then discuss the signal conditioning technique and finally impedance measurements of cells and particles of different sizes and types to demonstrate the differentiation of subpopulations in a mixed sample.
TL;DR: In this article, the use of several analytical techniques, including X-ray absorption spectroscopy (XAS), electron microscopy, and electron diffraction, as tools for characterizing the structural dynamics of supported Pt nanoscale particles was described.
Abstract: In this report, we describe the use of several analytical techniques, including X-ray absorption spectroscopy (XAS), electron microscopy, and electron diffraction, as tools for characterizing the structural dynamics of supported Pt nanoscale particles. We examined several carbon-supported samples. Electron microscopy shows that the particles in these samples (S1−S3) have average particle diameters of roughly 20, 40, and 60 A respectively, while electron microdiffraction data for these particles provided evidence of long-ranged ordering in the form of face centered cubic structures. This study highlights the use of advanced synchrotron X-ray absorption spectroscopies (XAS), in particular extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), as powerful tools for studying the structural habits and dynamics of these prototypical nanoscale materials. Using state-of-the-art methods of measurement and computational modeling, we demonstrate that it is possible to deve...
TL;DR: In this paper, a three-dimensional, incompressible, multiphase particle-in-cell method for dense particle flows is presented, which solves the governing equations of the fluid phase using a continuum model and those of the particle phase using Lagrangian model.
TL;DR: In this paper, the optical properties of the resulting thin Au@SiO2 particles have been analyzed as a function of the particle volume fraction, which is controlled through the silica shell thickness, and the surface plasmon peak position in films with volume fractions up to φ > 0.5 is accurately predicted by the Maxwell−Garnett model.
Abstract: Homogeneous films of Au@SiO2 particles have been deposited on glass as a prototype 3D “artificial solid” using the LBL method. The film thickness is controlled by the number of dipping cycles and is measured by AFM. Each cycle results in approximately one monolayer of particles being deposited. The particle films are dense, but disordered. The optical properties of the resulting thin films have been analyzed as a function of the particle volume fraction, which is controlled through the silica shell thickness. We find that the surface plasmon peak position in films with volume fractions up to φ > 0.5 is accurately predicted by the Maxwell−Garnett model. The films exhibit remarkably uniform, transmitted colors and display metallic reflection at low angles of incidence, even at low volume fractions. The films can be annealed at T > 500 K to provide extremely stable, optical films.
TL;DR: In this article, the authors present an analysis of particle production yields measured in central Au-Au collisions at RHIC in the framework of the statistical thermal model. And they demonstrate that the model extrapolated from previous analyses at SPS and AGS energy is in good agreement with the available experimental data at s =130 GeV implying a high degree of chemical equilibration.
TL;DR: In this paper, the authors consider the adsorption at an oil−water interface of spherical particles of two types: homogeneous and non-homogeneous particles, and show that increasing the amphiphilicity of the particles produces a maximum of a 3-fold increase in surface activity for average contact angles around 90°.
Abstract: We consider the adsorption at an oil−water interface of spherical particles of two types. The first type has a homogeneous surface of uniform wettability. The second type, so-called “Janus” particles, has two surface regions of differing wettabilities. Homogeneous particles are strongly surface active but are not amphiphilic, whereas Janus particles are both surface active and amphiphilic. We present calculations to show how the particle amphiphilicity, tuned by variation of either the relative surfaces areas or the different wettabilities of the two surface regions on the particles, influences the strength of particle adsorption. Increasing the amphiphilicity of the particles produces a maximum of a 3-fold increase in surface activity for average contact angles around 90°. Unlike homogeneous surface particles, Janus particles remain strongly surface active for average contact angles approaching either 0 or 180°.
TL;DR: In this article, the authors used aluminum nitride whiskers (and/or particles) and/or silicon carbide whiskers as fillers(s) and polyvinylidene fluoride (PVDF) or epoxy as matrix.
Abstract: Thermally conducting, but electrically insulating, polymer-matrix composites that exhibit low values of the dielectric constant and the coefficient of thermal expansion (CTE) are needed for electronic packaging. For developing such composites, this work used aluminum nitride whiskers (and/or particles) and/or silicon carbide whiskers as fillers(s) and polyvinylidene fluoride (PVDF) or epoxy as matrix. The highest thermal conductivity of 11.5 W/(m K) was attained by using PVDF, AlN whiskers and AlN particles (7 μm), such that the total filler volume fraction was 60% and the AlN whisker–particle ratio was 1:25.7. When AlN particles were used as the sole filler, the thermal conductivity was highest for the largest AlN particle size (115 μm), but the porosity increased with increasing AlN particle size. The thermal conductivity of AlN particle epoxy-matrix composite was increased by up to 97% by silane surface treatment of the particles prior to composite fabrication. The increase in thermal conductivity is due to decrease in the filler–matrix thermal contact resistance through the improvement of the interface between matrix and particles. At 60 vol.% silane-treated AlN particles only, the thermal conductivity of epoxy-matrix composite reached 11.0 W/(m K). The dielectric constant was quite high (up to 10 at 2 MHz) for the PVDF composites. The change of the filler from AlN to SiC greatly increased the dielectric constant. Combined use of whiskers and particles in an appropriate ratio gave composites with higher thermal conductivity and low CTE than the use of whiskers alone or particles alone. However, AlN addition caused the tensile strength, modulus and ductility to decrease from the values of the neat polymer, and caused degradation after water immersion.
TL;DR: In this article, the interfacial effect on properties of epoxy composites was investigated by using infrared and raman spectroscopy, differential scanning calorimetry (DSC), and particle size analyzer.
TL;DR: In this article, a modified ver- sion of a particle size magnifier (Okuyama et al. 1984) is employed to activate and grow particles comprising the fine aerosol mass.
Abstract: We report on a new instrument developed for rapid automated on-line and continuous measurement of ambient aerosol bulk com- position.The general approach is based on earlier devices (Khlystov et al. 1995; Simon and Dasgupta 1995) in which ambient particles are mixed with saturated water vapor to produce droplets easily collected by inertial techniques. The resulting liquid stream is analyzed with an ion chromatograph to quantitatively measure the bulk aerosol ionic components. In this instrument, a modified ver- sion of a particle size magnifier (Okuyama et al. 1984) is employed to activate and grow particles comprising the fine aerosol mass. A single jet inertial impactor is used to collect the droplets onto a vertical glass plate that is continually washed with a constant water diluent flow of nominally 0.10 ml min-1
01 Oct 2001
TL;DR: In this paper, the authors describe the technology used to produce the particles and deposit them, and discuss the details of the landing on the surface and subsequent surface kinetics, as well as the equilibrium structures and morphologies of the particles as also how the organisation of the particle assemblies is influenced by the particle-surface and interparticle interactions.
Abstract: Recently, films produced by depositing pre-formed mass-selected atomic clusters in the size range 1–10 nm have generated a great deal of attention. The ability to control the size, density and in some cases the morphology of the deposited particles allows unprecedented flexibility in the creation of new types of nanostructure. The technique enables research on the fundamental behaviour of matter at mesoscopic length scales and in addition has enormous potential in the creation of new materials whose properties can be widely varied. This review will describe the technology used to produce the particles and deposit them, and discuss the details of the landing on the surface and subsequent surface kinetics. The equilibrium structures and morphologies of the particles will be reviewed as also how the organisation of the particle assemblies is influenced by the particle–surface and inter-particle interactions. As a result of the reduced average atomic coordination, the quantum size effect and the modified screening response in nanoscale systems, the clusters display novel electronic and magnetic properties and these will be described for a range of elements including transition metals, noble and simple metals, and rare-earths. In addition to the native properties, the effect of the interaction with the substrate and other deposited particles will be explored. Finally, the work on coated particles and particles embedded in matrices will be reviewed and the potential to create new materials and devices will be discussed.
TL;DR: In this paper, the shape and structure of nanometer-sized particles are discussed, such as the octahedron and truncated octahedral, the icosahedron, the marks decahedric, the truncated “star-like” decahedral and the regular decahingric.
Abstract: Nanoparticles are a state of matter that has properties different from either molecules or bulk solids. In the present work, we review the shape and structure of nanometer-sized particles; several shapes are discussed, such as the octahedron and truncated octahedron, the icosahedron, the Marks decahedron, the truncated “star-like” decahedron, the rounded decahedron and the regular decahedron. Experimental high-resolution transmission electron microscopy (TEM) images of each type of particle are presented together with the Fast Fourier Transform and a model of the particle. We consider only gold particles grown by vapor deposition or by colloidal methods. High-resolution TEM images of the particles in different orientations are shown. We discuss two basic types of particles uncapped and capped. Data for other metals and semiconductors are reviewed. We have also performed very extensive simulations obtaining the total energy and pair correlation functions for each cluster under study. Furthermore, distributions of single atom energy for every cluster are displayed in order to reveal the effect of surface on the stability of different types and sizes of clusters. We discuss the structure of the particles from ∼1 to ∼100 nm. The mechanisms for stress release as the particles grow larger are reviewed and a mechanism is suggested. Finally, we discuss the parameters that define the shape of a nanoparticle and the possible implications in technological applications.Nanoparticles are a state of matter that has properties different from either molecules or bulk solids. In the present work, we review the shape and structure of nanometer-sized particles; several shapes are discussed, such as the octahedron and truncated octahedron, the icosahedron, the Marks decahedron, the truncated “star-like” decahedron, the rounded decahedron and the regular decahedron. Experimental high-resolution transmission electron microscopy (TEM) images of each type of particle are presented together with the Fast Fourier Transform and a model of the particle. We consider only gold particles grown by vapor deposition or by colloidal methods. High-resolution TEM images of the particles in different orientations are shown. We discuss two basic types of particles uncapped and capped. Data for other metals and semiconductors are reviewed. We have also performed very extensive simulations obtaining the total energy and pair correlation functions for each cluster under study. Furthermore, distribut...
TL;DR: An overview of recent advances in the synthesis of nanoparticles by flame aerosol processes is given in this paper, where a wide spectrum of new nanosized powders can be synthesized.
Abstract: An overview of recent advances in the synthesis of nanoparticles by flame aerosol processes is given. In flame processes with gaseous precursors emphasis is placed on reactant mixing and composition, additives, and external electric fields for control of product characteristics. Thermophoretic sampling can monitor the formation and growth of nanoparticles, while the corresponding temperature history can be obtained by non-intrusive Fourier transform infrared spectroscopy. Furthermore, synthesis of composite nanoparticles for various applications is addressed such as in reinforcement or catalysis as well as for scale-up from 1 to 700 g/h of silica-carbon nanostructured particles. In flame processes with liquid precursors using the so-called flame spray pyrolysis (FSP), emphasis is placed on reactant and fuel composition. The FSP processes are quite attractive as they can employ a wide array of precursors, so a broad spectrum of new nanosized powders can be synthesized. Computational fluid dynamics (CFD) in combination with gas-phase particle formation models offer unique possibilities for improvement and possible new designs for flame reactors.
TL;DR: In this paper, the approach and rebound of a particle colliding with a wall in a viscous fluid was monitored using a high-speed video camera, and a coefficient of restitution was defined from the ratio of the velocity just prior to and after impact.
Abstract: This paper presents experimental measurements of the approach and rebound of a particle colliding with a wall in a viscous fluid. The particle's trajectory was controlled by setting the initial inclination angle of a pendulum immersed in a fluid. The resulting collisions were monitored using a high-speed video camera. The diameters of the particles ranged from 3 to 12 mm, and the ratio of the particle density to fluid density varied from 1.2 to 7.8. The experiments were performed using a thick glass or Lucite wall with different mixtures of glycerol and water. With these parameters, the Reynolds number defined using the velocity just prior to impact ranged from 10 to approximately 3000. A coefficient of restitution was defined from the ratio of the velocity just prior to and after impact.
The experiments clearly demonstrate that the rebound velocity depends on the impact Stokes number (defined from the Reynolds number and the density ratio) and weakly on the elastic properties of the material. Below a Stokes number of approximately 10, no rebound of the particle occurred. For impact Stokes number above 500 the coefficient of restitution appears to asymptote to the values for dry collisions. The coefficients of restitution were also compared with previous experimental studies. In addition, the approach of the particle to the wall indicated that the particle slowed prior to impacting the surface. The distance at which the particle's trajectory varied due to the presence of the wall was dependent on the impact Stokes number. The particle surface roughness was found to affect the repeatability of some measurements, especially for low impact velocities.
TL;DR: In this article, the authors examined the relationship between the curvature and slope of the compression line and the statistics of individual particle crushing taking into account particle size and overall grading, high pressure one-dimensional compression tests on silica sand samples seeded with marked particles were carried out.
TL;DR: In this article, the effect of inter-particle collisions on the two-phase flow field was investigated and the shape and scale of particle concentrations calculated considering interparticle collision were in good agreement with experimental observations.
Abstract: The interaction between a turbulent gas flow and particle motion was investigated by numerical simulations of gas–particle turbulent downward flow in a vertical channel. In particular the effect of inter-particle collision on the two-phase flow field was investigated. The gas flow field was obtained by large-eddy simulation (LES). Particles were treated by a Lagrangian method, with inter-particle collisions calculated by a deterministic method. The spatial resolution for LES of gas–solid two-phase turbulent flow was examined and relations between grid resolution and Stokes number are presented. Profiles of particle mean velocity, particle wall-normal fluctuation velocity and number density are flattened as a result of inter-particle collisions and these results are in good agreement with experimental measurements. Calculated turbulence attenuation by particles agrees well with experimental measurements for small Stokes numbers, but not for large Stokes number particle. The shape and scale of particle concentrations calculated considering inter-particle collision are in good agreement with experimental observations.
TL;DR: In this paper, the particle size dependence of the reversible shear thickening transition in dense colloidal suspensions is explored, and a simplified two particle force balance between the interparticle repulsive forces and the hydrodynamic compressive forces is used to derive a scaling relationship between this critical shear stress and the suspension properties.
Abstract: The particle size dependence of the reversible shear thickening transition in dense colloidal suspensions is explored. Five suspensions of monodisperse silica are synthesized via the Stober synthesis. The physicochemical properties of the dispersions are quantified using transmission electron microscopy, dynamic light scattering, small angle light scattering, electrophoresis, and viscometry. Rheology measurements indicate a critical stress marking the onset of reversible shear thickening that depends on the dispersion’s particle size, concentration, polydispersity, and interparticle interactions. A simplified two particle force balance between the interparticle repulsive forces and the hydrodynamic compressive forces is used to derive a scaling relationship between this critical shear stress and the suspension properties. The scaling is tested against the fully characterized silica dispersions, which span nearly a decade in particle size. Furthermore, bimodal mixtures of the dispersions are employed to ev...
TL;DR: In this article, a simulation of high-concentration sheet flow transport in oscillatory flows quantifies the effect of fluid acceleration on bed load transport in highly unsteady flows typical of nearshore marine environments.
Abstract: Fully three-dimensional discrete particle computer simulations of high-concentration sheet flow transport in oscillatory flows quantify the effect of fluid acceleration on bed load transport in highly unsteady flows typical of nearshore marine environments. A simple impulse-momentum approach explains simulation results and forms the basis for adding an acceleration-related term to widely used energetics sediment transport formulae. Transport predicted by the acceleration term becomes increasingly significant as wave shape approaches the sawtooth profile characteristic of surf zone bores. Simulations integrate F = ma and a corresponding set of equations for the torques for each sphere. Normal and tangential forces between contacting particles are linear functions of the distance between sphere centers and the relative tangential displacement at the contact point, respectively; particle interactions are both inelastic and frictional. Pressure gradient forces generated by the passage of surface gravity waves drive fluid and particle motion in a stack of thin horizontal fluid layers that exchange momentum and exert fluid drag, added mass, and buoyancy forces on particles. Transport properties of the simulated granular-fluid assemblage are robust to large variations in material properties of the particles. Simulated transport rates agree with available experimental data for unsteady transport of coarse sands; the mode of bed load motion, dispersion of bed load particles, and particle segregation by size and density are qualitatively consistent with available particle-scale observations of bed load transport of natural particles.
TL;DR: In this article, the authors used transmission FT-IR spectroscopy to probe changes in the spectrum of the oxide particle surface following adsorption of HNO3 on SiO 2, α-Al2O3, TiO2, γ-Fe 2 O 3, CaO, and MgO.
Abstract: In this study, the heterogeneous reactivity of nitric acid on oxide particles of some of the most abundant crustal elements is investigated at 296 K. The oxide particles are used as models for mineral dust aerosol found in the atmosphere. Transmission FT-IR spectroscopy is used to probe changes in the spectrum of the oxide particle surface following adsorption of HNO3 on SiO2, α-Al2O3, TiO2, γ-Fe2O3, CaO, and MgO. It is found that HNO3 molecularly and reversibly adsorbs on SiO2. For the other oxides investigated, HNO3 dissociatively and irreversibly adsorbs to form surface nitrate. There is also a small amount of molecularly adsorbed nitric acid (<10% of the adsorbed nitrate) on the oxide particle surface in the presence of gas-phase nitric acid. Because adsorbed water may play a role in the heterogeneous uptake of nitric acid in the atmosphere, transmission FT-IR spectroscopy is used to investigate H2O adsorption on SiO2, α-Al2O3, TiO2, γ-Fe2O3, CaO, and MgO particles as well. Uptake of water on the oxid...
TL;DR: A review of available information on factors which contribute to poor wetting between ceramic phases, and liquid metals is presented in this article, focusing on aluminium, a common MMC matrix material.
TL;DR: In this article, a new type of composite particles consisting of a zinc sulfide (ZnS) core and a silica (SiO2) shell or vice versa was reported.
Abstract: We report on a new type of composite particles consisting of a zinc sulfide (ZnS) core and a silica (SiO2) shell or vice versa. We developed and optimized these particles for photonic applications, because ZnS has a large refractive index and does not absorb light in the visible and both ZnS and SiO2 can be easily doped with fluorophores. Both kinds of morphologies were created using a seeded growth procedure using monodisperse seeds on which homogeneous layers with a well-defined thickness were grown. Moreover, the ZnS and SiO2 cores could be completely dissolved leaving SiO2 and ZnS shells, respectively, filled with solvent or air after drying. The particle morphology was investigated by electron microscopy. The optical properties were studied by extinction measurements and angle resolved light scattering and compared to scattering theory.