Changes In Particle Shape Research Articles

Synthesis of Alternate Layered Structure of Ruthenate Nanosheet-Graphene Oxide for Electrochemical Applications

As a power storage device with performances of rapid charge/discharge, long-life and high power density, electrochemical capacitor is receiving attention. As high power density materials, there are two types of materials: (1) carbon materials such as activated carbon, reduced graphene oxide (rGO), and carbon nanotube and (2) metal oxide materials such as RuO2 and MnO2. Studies have also been conducted to improve specific capacitance by supporting metal oxide on carbon materials.1 We focus on the combination of RuO2 nanosheet which has a high pseudocapacitance, with GO which has a high ion conductivity to enhance electrochemical performance. As combining method of carbon material and ruthenium oxide, we focused on click chemistry. Click chemistry is a method to combine different materials by reacting them with surface functional groups.2 Click chemistry between two-dimensional nanosheets has been used to form alternate layers.3 Since the alternate layered structures are obtained in the form of powder, broader electrochemical applications are expected. Moreover, since the alternate layers are irregularly stacked, improved substance diffusion is expected compared to the regular stacking of nanosheets by Langmuir-Blodgett or Layer-by-Layer methods. In the present study, thiol-ene reaction is considered most useful among click reactions. This is because thiol-ene reaction makes use of a combination of alkene group and thiol group, and since GO has C=C bonds, the reaction with GO is possible by only modification of RuO2 nanosheet with thiol group. We tried modification of layered ruthenium oxide with thiol group. As coupling agent, we used 3-mercaptopropyltrimethoxysilane. SEM-EDX observation results after silane coupling showed no substantial change in particle shape by silane coupling. The presence of S and Si after silane coupling was confirmed from the EDX results, indicating silane coupling was in progress. Following that we tried to exfoliate layered C3SH-RuO2 and synthesize C3SH-RuO2 nanosheet colloids. Figure shows the AFM image of substrate made by immersing silicon substrate in toluene. The AFM image showed a sheet-like morphology of approximately 1 nm thickness and 400 nm width, indicating the formation of the C3SH-RuO2 nanosheet. Alternate layered structures were synthesized by thiol-ene reaction of C3SH-RuO2 nanosheet with GO in the addition of radical initiator. SEM-EDX observation of the product shows stacking of nanosheets. The compounding of ruthenium oxide and GO was confirmed by IR, suggesting the formation of the alternate layered structure after thiol-ene reaction. Figure 1

Inelastic shape changes of silicon particles and stress evolution at binder/particle interface in a composite electrode during lithiation/delithiation cycling

Inelastic shape changes of Si particles and stress evolution at binder/particle interface was modeled using coupled diffusion–stress framework available in finite element software. A simple model that contains two spherical Si particles with and without the polymer binder film was used to represent the composite electrode. The particles were lithiated and delithiated at two different rates: one representing a slow charging case which results in a uniform Li concentration throughout the Si particles and the other representing a fast charging condition which results in non-uniform lithium concentration within the spherical Si particles. The inelastic shape changes and associated contact forces predicted by the model are qualitatively consistent with experimental data. Further, the effect of binder mechanical properties and the binder fraction on the stress evolution in Si particles and at the binder/particle interface was calculated. The proposed model, although simple, can guide a battery design engineer to choose a proper binder, charge/discharge strategy, and binder fraction for a durable electrode design.

Large range localized surface plasmon resonance of Ag nanoparticles films dependent of surface morphology

Noble metal nanoparticles (NPs) have received enormous attention since it displays uniquely optical and electronic properties. In this work, we study localized surface plasmon resonances (LSPR) at different thicknesses and substrate temperatures of Ag NPs films grown by Laser Molecule Beam Epitaxy (LMBE). The LSPR wavelength can be largely tuned in the visible light range of 470nm to 770nm. The surface morphology is characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The average size of Ag NPs increased with the thickness increased which leading to the LSPR band broaden and wavelength red-shift. As the substrate temperature is increased from RT to 200°C, the Ag NPs size distribution becomes homogeneous and particle shape changes from oblate spheroid to sphere, the LSPR band displays sharp, blue-shift and significantly symmetric. Obviously, the morphology of Ag NPs films is important for tuning absorption position. We obtain the cubic crystal structure of Ag NPs with a (111) main diffraction peak from the X-ray diffraction (XRD) spectra. The high resolution TEM (HR-TEM) and selected area electron diffraction (SAED) prove that Ag NPs is polycrystal structure. The Ag NPs films with large range absorption in visible light region can composite with semiconductor to apply in various optical or photoelectric devices.

Mixed convection from a spheroid in Bingham plastic fluids: Effect of buoyancy-assisted flow

ABSTRACTIn this work, laminar mixed convection from an isothermal spheroidal particle immersed in a Bingham plastic fluid is studied numerically in the buoyancy-assisted regime. The results reported herein encompass the following ranges of conditions: Reynolds number, 0.1 ≤ Re ≤ 100; Prandtl number, 10 ≤ Pr ≤ 100; Bingham number, 0 ≤ Bn ≤ 100; Richardson number, 0 ≤ Ri ≤ 8; and aspect ratio of the spheroid, 0.2 ≤ e ≤ 5. In particular, consideration is given to the effect of shape and orientation of the particle on the detailed flow and temperature fields (in terms of streamlines, iso-vorticity, and isotherm contours), morphology of the yielded–unyielded regions, and the local and surface-averaged Nusselt number. All else being equal, the propensity for flow separation is seen to be greater for oblates (e < 1) than that for prolates (e > 1). In both cases, this reduces with the increasing Bingham number and/or the Richardson number. Both drag coefficient and the Nusselt number show a positive dependence on the Bingham number as well as on the Richardson number. Overall, the drag coefficient increases as the particle shape changes from an oblate to prolate, whereas the reverse trend is obtained for the average Nusselt number, which is in line with the general inference that more drag corresponds to more heat transfer. Finally, the average Nusselt number is correlated with the pertinent dimensionless parameters (Re, Pr, Bn, Ri, e) via a simple correlation, thereby enabling its prediction for intermediate values of the parameters and/or in a new application.

3D quantitative shape analysis on form, roundness, and compactness with μCT

Particle shape plays an important role in determining the engineering behaviour of granular materials. In this regard, characterisation and quantification of particle shape are essential for understanding the behaviour of granular materials. X-ray micro-computed tomography (μCT) enables observation of particle morphology at ever-greater resolutions. The challenge has thus become extracting quantified shape parameters from these rich three-dimensional (3D) images. In this paper, we implement X-ray μCT to obtain 3D particle morphology and utilize image processing and analysis techniques to quantify it at different scales. A novel framework is proposed to measure 3D shape parameters of form, roundness, and compactness. New 3D roundness indexes were formulated from the local curvature on reconstructed triangular surface mesh. Subsequently, this method is utilized to study the change of particle shape by single particle crushing tests on Leighton Buzzard sand (LBS) particles. It is found that compactness value (i.e., sphericity) could be influenced by both form and roundness. Then, the distributions of shape parameters are characterised by Weibull statistics. It shows that single particle crushing tests generate more irregular fragments which have smaller shape parameters with larger variance for the measured shape parameters.

Enhanced ferromagnetism in Cr doped SrMoO4 scheelite structured compounds

Wide band gap semiconductors of pure and Cr (5, 10, 15 and 20 %) doped SrMoO4 compounds were synthesized by chemical precipitation method. Powder X-ray diffraction analysis confirms scheelite type tetragonal crystal structure of the compounds. Metal oxide vibrations of the prepared compounds were identified by Fourier transform infra red spectroscopy. Laser Raman spectral studies elucidated the presence of local order- disorder parameters in Cr doped SrMoO4 compounds. Oxidation state of elements present in a compound, chemical composition and the presence of oxygen vacancy were analyzed by X-ray photoelectron spectroscopy. Electron microscopy studies reveal the high degree of agglomeration and change in shape of particles while increasing dopant concentration in SrMoO4 system. Optical absorption spectra evidence the distinctive shift in absorption peak and exhibit red shift. The presence of paramagnetic Cr3+ ion in the host lattice was identified with electron paramagnetic resonance analysis. The magnetization studies reveal the effect of carrier doping on SrMoO4 compounds by exhibiting paramagnetic to saturated ferromagnetic phase transition. The presence of excess carriers by doping leads to Cr–Cr interactions and results in antiferromagnetic ordering in highly doped compounds and the enhancement of magnetic moment have been explained in terms of RKKY interaction theory. The inducement of ferromagnetic behavior by doping Cr in SrMoO4 compounds reveal the possibility of multifunctional behaviour and showing their prompt candidature for the fabrication of optoelectronic and spintronics devices.

ChemInform Abstract: Surfactant Assisted Ball Milling: A Simple Top Down Approach for the Synthesis of Controlled Structure Nanoparticle

AbstractReview: 20 refs.

Influence of shape on the optical properties of hematite aerosol

AbstractMineral dust particles are the second highest emitted aerosol type by mass. Due to changes in particle size, composition, and shape that are caused by physical processes and reactive chemistry, optical properties vary during transport, contributing uncertainty in the calculation of radiative forcing. Hematite is the major absorbing species of mineral dust. In this study, we analyzed the extinction cross sections of nigrosin and hematite particles using cavity ring‐down aerosol extinction spectroscopy (CRD‐AES) and have measured particle shape and size distributions using transmission electron microscopy. Nigrosin was also used in this study as a spherical standard for absorbing particles. The size‐selected nigrosin particles have a narrow size distribution, with extinction cross sections that are described by Mie theory. In contrast, the size distribution of size‐selected hematite particles is more polydisperse. The extinction cross sections were modeled using Mie theory and the discrete dipole approximation (DDA). The DDA was used to model more complex shapes that account for the surface roughness and particle geometry. Of the four models used, Mie theory was the simplest to implement, but had significant error with a 26.1% difference from the CRD‐AES results. By increasing the complexity of the models using the DDA, we determined that spheroids had a 14.7% difference, roughened spheres a 12.8% difference, and roughened spheroids a 11.2% difference from the experimental results. Using additional parameters that account for particle shape is necessary to model the optical properties of hematite particles and leads to improved extinction cross sections for modeling aerosol optical properties.

Implicit frictional-contact model for soft particle systems

We introduce a novel numerical approach for the simulation of soft particles interacting via frictional contacts. This approach is based on an implicit formulation of the Material Point Method, allowing for large particle deformations, combined with the Contact Dynamics method for the treatment of unilateral frictional contacts between particles. This approach is both precise due to the treatment of contacts with no regularization and artificial damping parameters, and robust due to implicit time integration of both bulk degrees of freedom and relative contact velocities at the nodes representing the contact points. By construction, our algorithm is capable of handling arbitrary particle shapes and deformations. We illustrate this approach by two simple 2D examples: a Hertz contact and a rolling particle on an inclined plane. We also investigate the compaction of a packing of circular particles up to a solid fraction well above the jamming limit of hard particles. We find that, for the same level of deformation, the solid fraction in a packing of frictional particles is above that of a packing of frictionless particles as a result of larger particle shape change.

The obtainment of particle shape factor by the combination of experimental data and fluid–particle reaction model

A new approach to calculate the shape factor of the solid particle(s) was introduced using the experimental data and fluid–particle reaction model. In fluid–particle reactions, the solid particle reactants have complex shapes, rather than standard sphere in theory. In order to evaluate the influence of particle shape changes during the reaction process, we established a fluid–particle reaction model incorporating a parameter called the shape factor. Combining the model and experimental data by mathematical method, we can obtain the shape factor and the comprehensive reaction coefficient. The results show that the shape factor is larger than 1 in the early stage, then begins to decline rapidly and gradually comes near to constant 1. It agrees well with the experimental observation, indicating that the shapes of limestone particles are changing from irregular shapes to sphere during the reaction progress. The fluid–particle reaction model with the shape factor can describe the reaction well, which demonstrates the validity of our work. Using this method, the particle shape factor and the comprehensive reaction coefficient of any fluid–particle reaction can be acquired, which has great value on the precise prediction and control of fluid–particle reaction.

The effect of the particle size distribution on the mechanics of fibre-reinforced sands under one-dimensional compression

Seven reconstituted sands of different mineralogies and different particle size distributions, from uniform to well-graded and coarse to fine, were tested under one-dimensional compression, with and without reinforcement by discrete fibres. The compressibility, the particle breakage and the associated change in particle shape were examined in the sands with and without reinforcement. Each reconstituted sand was found to have a unique normal compression line. The compressibility increased with increasing uniformity and with larger mean diameters, thus coarse uniform sands were found to be the most compressible. They also underwent more breakage of particles, which was more significant in the weaker carbonate sands. At the grain scale, the addition of fibres seemed to reduce the amount of particle breakage in the soil, more significantly in well-graded sands. A unique NCL was found for each fibre-reinforced sand, parallel to that of the corresponding non-reinforced sand. A strong correlation was found between the ability of the fibres to prevent particle breakage and their ability to limit changes in particle shape.

On titanium dioxide thin films growth from the direct current electric field assisted chemical vapour deposition of titanium (IV) chloride in toluene

Titanium dioxide thin films were deposited from the aerosol assisted chemical vapour deposition reaction of titanium tetrachloride in toluene (1M) at 600°C and 5Lmin−1. Direct current electric fields were applied and increased in a range of 0 to 30V during the reaction. Changes in particle size, agglomeration and particle shape were observed. Raman spectroscopy analysis revealed different composition of anatase and rutile and crystal phase depending on the field strength applied. The photocatalytic activity was calculated from the half-life or time needed by the films to degrade 50% Resazurin dye-ink initial concentration. High photocatalytic performance with high anatase content (98.3%) was observed with half-life values of 3.9min. Deposited films with pure content in rutile showed better photocatalytic performance than films with mix of crystal phases with anatase content below 40%.

Micronizing ceramic pigments for inkjet printing: Part I. Grindability and particle size distribution

Inkjet printing is increasingly used to decorate ceramic tiles, with pigmented inks in most cases. These inks are manufactured by micronizing conventional ceramic pigments down to median diameters of 0.2–0.6µm. Although such a size reduction theoretically offers significant advantages in terms of the optical and fluid mechanical properties of the pigment particles, still unanswered questions concern color strength and the efficiency of the milling process. The present study aimed to elucidate how micronizing influences the pigments’ particle size and shape, and the specific surface area. For this purpose, industrial pigments were selected to represent crystal structures of different density, hardness, cleavage and fracture toughness, i.e. rutile, spinel and zircon. The pigments were micronized in a pilot plant, controlling carrier, solid load, dispersant type and concentration, rotation speed, amount and size of grinding media, temperature and milling time. The pigments were characterized by particle size distribution (laser diffraction and dynamic light scattering) and morphology (SEM). The results revealed a different behavior of the pigments during micronization, with changes in particle size and shape partially consistent with the literature. The pigments’ grindability differed: zircon>rutile≥spinel.

Simulation of radiation transfer properties of polarized light in non-spherical aerosol using Monte Carlo method

The shape of atmospheric aerosol is an important factor that influences radiation transfer. In this paper, a vector radiation transfer model based on Monte Carlo method is systematically introduced, and its accuracy is validated against the published results. and the sensitivity of Stokes vectors of transmitted and reflected light to aerosol shape is discussed when polarized light incidents. In addition, the influence of the particle shape on the depolarization ratio, transmission rate and the reflection rate is analyzed for incident light with different polarization states. Simulation results show that for the incident light in different polarization states, the sensitivity of the Stokes vectors of the diffuse light to different aerosol shapes is not the same in different viewing directions, and the Q, U, V elements of Stokes vector are all insensitive to the change of particle shape near the direction of the zenith angle 0°. It is evident that the aerosol shapes have a stronger influence on the depolarization ratio for reflected diffuse light compared with that for transmitted diffuse light, and there are also remarkable differences between the degree of depolarization of the diffuse light when the polarization states of the incident light are different. Results also show that the aerosol shape has a significant influence on the whole transmission rate and the reflection rate, and with the increasing of propagation distance, the influence also becomes more remarkable. Compared with particle shape, the influence of polarization states of incident light is relatively small, the transmission rate of horizontally-polarized light is slightly larger than that of unpolarized light, while for perpendicularly-polarized light, its results is opposite. For circularly polarized light, the results is almost the same as that of unpolarized light.

SYNTHESIS OF SILVER NANOPARTICLES BY CHEMICAL REDUCTION METHOD: EFFECT OF REDUCING AGENT AND SURFACTANT CONCENTRATION

Uniform, well-dispersed, silver nanoparticles (AgNPs) were prepared by a simple chemical reduction method. The particles were synthesized via the reduction of AgNO3 by trisodium citrate and ascorbic acid as a surfactant. The resulting AgNPs were characterized by X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy. It was found that the size of the AgNPs ranged from 35– 80 nm, with an average of 50 nm. In this study, the effects of trisodium citrate and ascorbic acid, which act as reducing agent and surfactant respectively on the morphology of the silver nanoparticles, were investigated. It was found that the increasing concentration of trisodium citrate resulted in decreasing size of silver nanoparticles, while increasing the concentration of ascorbic acid shows the opposite effect. Moreover, the quasi-spherical shape of as-synthesized silver nanoparticles is also more uniform with the increase of trisodium citrate. Meanwhile, a slight change in particle shape from quasi-spherical to polygonal was observed as the concentrations of ascorbic acid were increased. Keywords: Chemical synthesis; silver nanoparticles; reducing agent; surfactant.

Large-scale plasmonic-SERS templates by successive growth steps

This work presents the fabrication of large-scale tunable-plasmonic surface-enhanced Raman scattering (SERS) templates and investigates their Raman enhancement. Substrates for SERS were prepared by deposition of gold nanoparticles on a glass slide followed by their growth. A plasmon shift was observed upon growing due to the formation of elongated nanoparticles and their mutual coupling. The changes in particle size, shape and interparticle distances were indicated by SEM measurements. Surface-enhanced Raman spectra of Nile blue A at a very low concentration on top of a blocking layer were measured. The overall Raman enhancement is correlated with the number of growth steps. For excitation at 532 nm four growth steps lead to maximum enhancement. Better overlap of excitation laser and the plasmon resonances upon growing increased the enhancement until four steps while further growing decreased the enhancement. At longer wavelengths excitation (633 and 785 nm) the enhancement further increased beyond the fourth growth step. This enhancement is caused by the plasmon excitation of narrower gap sizes. The proposed procedure for the SERS substrates is simple, allows covering large surface areas and plasmon band tuning from 530 nm to the near infrared in order to increase overall Raman enhancement.

Influence of post-treatment operations on structural properties and photocatalytic activity of octahedral anatase titania particles prepared by an ultrasonication-hydrothermal reaction.

The influence of changes in structural and physical properties on the photocatalytic activity of octahedral anatase particles (OAPs), exposing eight equivalent {101} facets, caused by calcination (2 h) in air or grinding (1 h) in an agate mortar was studied with samples prepared by ultrasonication (US; 1 h)–hydrothermal reaction (HT; 24 h, 433 K). Calcination in air at temperatures up to 1173 K induced particle shape changes, evaluated by aspect ratio (AR; d001/d101 = depth vertical to anatase {001} and {101} facets estimated by the Scherrer equation with data obtained from X-ray diffraction (XRD) patterns) and content of OAP and semi-OAP particles, without transformation into rutile. AR and OAP content, as well as specific surface area (SSA), were almost unchanged by calcination at temperatures up to 673 K and were then decreased by elevating the calcination temperature, suggesting that calcination at a higher temperature caused dull-edging and particle sintering, the latter also being supported by the analysis of particle size using XRD patterns and scanning electron microscopic (SEM) images. Time-resolved microwave conductivity (TRMC) showed that the maximum signal intensity (Imax), corresponding to a product of charge-carrier density and mobility, and signal-decay rate, presumably corresponding to reactivity of charge carriers, were increased with increase in AR, suggesting higher photocatalytic activity of OAPs than that of dull-edged particles. Grinding also decreased the AR, indicating the formation of dull-edged particles. The original non-treated samples showed activities in the oxidative decomposition of acetic acid (CO2 system) and dehydrogenation of methanol (H2 system) comparable to and lower than those of a commercial anatase titania (Showa Denko Ceramics FP-6), respectively. The activities of calcined and ground samples for the CO2 system and H2 system showed almost linear relations with AR and Imax, respectively, suggesting that those activities may depend on different properties.

Mechanistic insight into size-dependent activity and durability in Pt/CNT catalyzed hydrolytic dehydrogenation of ammonia borane.

We report a size-dependent activity in Pt/CNT catalyzed hydrolytic dehydrogenation of ammonia borane. Kinetic study and model calculations revealed that Pt(111) facet is the dominating catalytically active surface. There is an optimized Pt particle size of ca. 1.8 nm. Meanwhile, the catalyst durability was found to be highly sensitive to the Pt particle size. The smaller Pt particles appear to have lower durability, which could be related to more significant adsorption of B-containing species on Pt surfaces as well as easier changes in Pt particle size and shape. The insights reported here may pave the way for the rational design of highly active and durable Pt catalysts for hydrogen generation.

Fe(II)-catalyzed recrystallization of goethite revisited.

Results from enriched (57)Fe isotope tracer experiments have shown that atom exchange can occur between structural Fe in Fe(III) oxides and aqueous Fe(II) with no formation of secondary minerals or change in particle size or shape. Here we derive a mass balance model to quantify the extent of Fe atom exchange between goethite and aqueous Fe(II) that accounts for different Fe pool sizes. We use this model to reinterpret our previous work and to quantify the influence of particle size and pH on extent of goethite exchange with aqueous Fe(II). Consistent with our previous interpretation, substantial exchange of goethite occurred at pH 7.5 (≈ 90%) and we observed little effect of particle size between nanogoethite (average size of 81 × 11 nm; ≈ 110 m(2)/g) and microgoethite (average size of 590 × 42 nm; ≈ 40 m(2)/g). Despite ≈ 90% of the bulk goethite exchanging at pH 7.5, we found no change in mineral phase, average particle size, crystallinity, or reactivity after reaction with aqueous Fe(II). At a lower pH of 5.0, no net sorption of Fe(II) was observed and significantly less exchange occurred accounting for less than the estimated proportion of surface Fe atoms in the particles. Particle size appears to influence the amount of exchange at pH 5.0 and we suggest that aggregation and surface area may play a role. Results from sequential chemical extractions indicate that (57)Fe accumulates in extracted Fe(III) goethite components. Isotopic compositions of the extracts indicate that a gradient of (57)Fe develops within the goethite with more accumulation of (57)Fe occurring in the more easily extracted Fe(III) that may be nearer to the surface.

Development on Silicon Rubber Elastic Composite Magnetic Abrasive and Research on Internal Polishing

With the use of Magnetic Abrasive Finishing (MAF) to polish surfaces of the parts, roughness on the surfaces can reach a level like a mirror. We have devoted to the study of MAF for many years; the magnetic abrasive particle we have developed can yield a value of Ra 0.008μm (Rmax0.1μm), which is similar to the surface of a mirror. However, there is no way to absorb charging of abrasive particle during polishing for conventional stiff abrasive materials. Therefore, it is difficult to obtain the nanolevel mirror surface. The study is based on silicon rubber and mix Sic and pure iron powder to develop elastic magnetic abrasive particles. During the process, employing the micro elastic of the polymer elastic magnetic abrasive particle to make the particle shape change and increase the contact area, therefore to improve the surface roughness by micro polishing to achieve a nanolevel mirror polishing demand。 The particle could be made easily in a short time, therefore it could reduce production cost and achieve environmental protection simultaneously.