Spherical Particles Of Different Sizes Research Articles

Modelling and Microstructural Characterization of Sintered Metallic Porous Materials.

This paper presents selected characteristics of the metallic porous materials produced by the sintering of metal powders. The authors focus on materials produced from the iron powder (Fe) of ASC 100.29 and Distaloy SE. ASC 100.29 is formed by atomization and has a characteristic morphology. It consists of spherical particles of different sizes forming agglomerates. Distaloy SE is also based on the sponge-iron. The porous material is prepared using the patented method of sintering the mixture of iron powder ASC 100.29, Fe(III) oxide, Distaloy SE and Fe(III) oxide in the reducing atmosphere of dissociated ammonia. As a result, the materials with open pores of micrometer sizes are obtained. The pores are formed between iron particles bonded by diffusion bridges. The modelling of porous materials containing diffusion bridges that allows for three-dimensional (3D) imaging is presented.

Multiple scattering of polarized light in turbid infinite planes: Monte Carlo simulations.

Monte Carlo simulations were performed for infinite plane media containing spherical particles of different sizes. Most of the features of the surface plots for the elements of the effective scattering Mueller matrices are explained by the azimuthal dependence of the matrix predicted according to the theory of Raković et al. [Appl. Opt.38, 3399 (1999)10.1364/AO.38.003399APOPAI1559-128X]. The reduced effective scattering Mueller matrices calculated according to the theory have eight nonzero elements, which are only dependent on the distance from the illumination point. The reduced matrices are factorized approximately into products of a depolarizer and retarding diattenuators. The turbid infinite plane media nearly behave as a pure depolarizer at long distances and become more diattenuating and birefringent with decreasing distance.

Centrifuge-based deterministic lateral displacement separation

This work investigates the migration of spherical particles of different sizes in a centrifuge-driven deterministic lateral displacement (c-DLD) device. Specifically, we use a scaled-up model to study the motion of suspended particles through a square array of cylindrical posts under the action of centrifugation. Experiments show that separation of particles by size is possible depending on the orientation of the driving acceleration with respect to the array of posts (forcing angle). We focus on the fractionation of binary suspensions and measure the separation resolution at the outlet of the device for different forcing angles. We found excellent resolution at intermediate forcing angles, when large particles are locked to move at small migration angles but smaller particles follow the forcing angle more closely. Finally, we show that reducing the initial concentration (number) of particles, approaching the dilute limit of single particles, leads to increased resolution in the separation.

Structural and gas sensing properties of ex-situ oxidized Sn grown by thermal evaporation

SnO2 thin films were obtained by ex-situ oxidation of Sn metal film deposited by thermal evaporation. The oxidation of the Sn film was carried out at 600, 700 and 900°C for 2h in a controlled oxygen atmosphere. GIXRD confirmed the tetragonal rutile phase of SnO2 which was further confirmed by Raman spectroscopy. The RBS measurements provided the thickness and chemical information of the film. Thickness of the film was in the range of 6⿿12nm and the presence of Sn and oxygen in the films are shown. Scanning electron microscopy revealed spherical particles of different sizes for films annealed at different temperatures. The SnO2 thin film oxidized at 900°C was tested for methane gas sensing. A sensing response of 78.46% for 100ppm of methane at an operating temperature of 100°C which is one of lowest reported was obtained.

Material property evaluation of particle reinforced composites using finite element approach

In this work, the elasto-plastic material properties of particle reinforced composites are evaluated using three-dimensional finite element approach. Effective properties of the composite are evaluated using representative volume element and numerical homogenization for kinematic and static boundary conditions. A computer program is developed to generate non-overlapping spherical particles of arbitrary size in an representative volume element. The numerical modeling of representative volume element containing the randomly distributed spherical particles of different sizes is performed by finite element method. Convergence study is performed to determine the suitable size of representative volume element. Homogenization is carried out for two cases i.e. matrix with soft and hard particles for reinforcement volume fraction up to 25%. A numerical comparison of 2-D and 3-D results is presented in terms of material behavior for matrix with soft particles.

Nanodispersive aluminum boride prepared by a plasma recondensation of aluminum and boron micron powders

This work presents investigations into the composition and some properties of nanodispersive powders of aluminum boride prepared by the plasma-recondensation technique. It is shown that, under a strictly determined aluminum: boron ratio in the starting mixture and with the complete observance of technological processing parameters, aluminum boride (n-AB) nanopowders of the required composition and dispersivity can be obtained. SEM investigations of the aluminum boride samples reveal that aluminum boride powders are mixtures of spherical particles of different sizes and a significant agglomeration of the particles is observed. In general, the sizes of particles are varied from several dozens of nanometers up to 500 nm and more. Investigations into the thermal-oxidative activity of synthesized aluminum boride using thermogravimetric and differential thermal analysis show that these compounds are more active towards air than nanodispersive aluminum. The highest rate of oxidation of aluminum borides was observed in the temperature range of 680–700°C.

Simple way to analyze Brillouin spectra from turbid liquids.

The shape of the Brillouin light-scattering spectrum recorded from turbid liquids is distinctly distorted compared to that from a transparent sample. The reason for this is the multiple scattering of light within the medium. The usual expression for the Brillouin spectrum does not apply to the multiple scattering situation. In this Letter, we consider a Brillouin spectrum from opaque samples composed of a distribution of spectra resulting from elementary scattering events, each occurring in single scattering vector conditions. We introduce a one-parameter test function to define the probability distribution of scattering events occurring at a given value of the scattering vector. The proposed procedure was tested on model liquids that consisted of suspensions of sub-micrometer spherical particles of different size and concentration, dispersed in different carrier liquids and studied as a function of temperature. Our analysis made it possible to account for the effect of multiple scattering and to recover the values of mechanical parameters describing the pure solvents.

Model of Heat and Mass Transfer in Random Packing Layer of Powder Particles in Selective Laser Melting

Abstract Discretegrid model of heat transfer in granular porous mediumto describe the processes of selective laser melting of powdersis developed. The thermal conductivity in this mediumis performed through thecontact surfaces between the particles. The calculation method of morphology of random packing layer of powder considering the adhesive interaction between the particles is proposed. The internal structure of the obtained loose powder layer is a granular medium where spherical particles of different sizes are arranged in contact with each other randomly. Analytical models of powder balling process and formation of the remelted track are proposed.

Al2O3 and ZrO2 powders formed by centrifugal compaction using the ultra HCP method

The influence of high speed centrifugal compaction process, the HCP method, on the properties of green compacts and sintered samples of Al2O3 and ZrO2 micropowders was investigated. This method may reduce friction between particles and prevent bridging of particles during compaction. The properties of the sintered materials strongly depend on the conditions of the centrifugal process: i.e. duration, rotation speed, solid content and dispersive liquids. The centrifugal compaction process of powder forming often results in gradient phase composition. An algorithm describing sedimentation of a group of spherical particles of different sizes and of different materials was used. Calculations for Al2O3 and ZrO2 deposition for the real conditions of the high-speed centrifugal compaction process have been carried out using the Barnea–Mizrahi equation. Deposition was carried out using an ultra-centrifuge with rotational speeds of 10,000, 20,000 and 30,000rpm for various pH of dispersive liquids. Pore size and pore size distribution of Al2O3 and ZrO2 green compacts were measured by the mercury porosimetry method. Densities, Young's moduli and Vickers hardness distribution of sintered compacts prepared in various conditions are reported.

Simulation of Vibrating Forming Process of Concrete Brick Based on DEM

The forming compact process of the concrete brick in vibration is simulated based on three-dimensional discrete element method (3D-DEM) where the crude granular materials of the concrete brick are simplified into two spherical particles of different sizes. There are three zones affecting compactness in vibration including porous zone, compact zone, and compact stable zone. The compactness's variation of the different heights and the above three zone are analyzed when both the amplitude and the frequency are different. By orthogonal experiment the result is showed that the average compactness is best when the amplitude is about 4 mm and the frequency is 100 Hz.

Monte Carlo simulation of fluorescence correlation spectroscopy data

We employed the Monte Carlo simulation methodology to emulate the diffusion of fluorescently labeled particles and understand the source of differences between values of diffusion coefficients (and consequently hydrodynamic radii) of fluorescently labeled nanoparticles measured by fluorescence correlation spectroscopy (FCS) and dynamic light scattering (DLS). We used the simulation program developed in our laboratory and studied the diffusion of spherical particles of different sizes, which are labeled on their surface. In this study, we focused on two complicating effects: (i) multiple labeling and (ii) rotational diffusion which affect the fluorescence signal from large particles and hinder the analysis of autocorrelation functions according to simple analytical models. We have shown that the fluorescence fluctuations can be well fitted using the analytical model for small point-like particles, but the obtained parameters deviate in some cases significantly from the real ones. It means that the current data treatment yields apparent values of diffusion coefficients and other parameters only and the interpretation of experimental results for systems of particles with sizes comparable to the size of the active illuminated volume requires great care and precaution.

Production of the matrix protein of Nipah virus in Escherichia coli: Virus-like particles and possible application for diagnosis

The broad species tropism of Nipah virus (NiV) coupled with its high pathogenicity demand a rapid search for a new biomarker candidate for diagnosis. The matrix (M) protein was expressed in Escherichia coli and purified using a Ni-NTA affinity column chromatography and sucrose density gradient centrifugation. The recombinant M protein with the molecular mass ( M r) of about 43 kDa was detected by anti-NiV serum and anti- myc antibody. About 50% of the M protein was found to be soluble and localized in cytoplasm when the cells were grown at 30 °C. Electron microscopic analysis showed that the purified M protein assembled into spherical particles of different sizes with diameters ranging from 20 to 50 nm. The purified M protein showed significant reactivity with the swine sera collected during the NiV outbreak, demonstrating its potential as a diagnostic reagent.

Modeling of Structure Evolution of Filled Elastomers under Uniaxial Elongation

The evolution of filler network structure in elastomers during elongation is investigated on the basis of computer modeling. The filler network is represented by spherical particles of different sizes, which are randomly filling a prismatic volume. No physical interaction forces between the particles on the molecular level are considered. The modeling is based on geometrical obstructions of particle ensembles. Interpenetrations of rigid particles during modeling of filling and subsequent stretching are forbidden, and only a minimal finite distance between the particles is allowed. The material is assumed to be incompressible. It was found that the number of nearest neighbors (coordination number) in a loosely filled material increases during stretching; however, in a densely filled material, this value decreases. The analysis of the size of unfilled spaces in the matrix has shown the occurrence of essential structural heterogeneities in the filler network. Stretching of a densely filled material results in appreciable mixing of particles whereby changes of the distances between originally neighboring particles exceed the macroscopic elongation of the material by several times. An analytical relation between the elongation of the composite and polymer chains via transmission ratio is proposed.

Conditions for entrainment into a FeO x containing slag for a carbon-containing particle in an entrained coal gasifier

When incompletely gasified coal particles impact the slag layer in an entrained slagging gasifier, a situation will arise where the particles will either get engulfed by the slag or re-entrained into the circulating gas. This will be determined by a balance of forces acting on the particle which in turn is governed by the slag and particle properties, and pertinent gasifier conditions, namely temperature, and particle impact velocity. In this paper a model is introduced that takes into account, the drag-, capillary-, and added mass-forces and predicts the behavior of spherical particles of different sizes and slags of different FeO x contents. The model predicts that particles either get completely submerged, settle at an incompletely separated position, or oscillate at the interface. A sensitivity analysis was performed showing that for a particle of certain size and impact velocity, submersion is most strongly promoted by a low slag viscosity (largely influenced by FeO x content) and contact angle (determined by whether or not-reactive wetting and liquid Fe formation occurs).

Sintering of particles of different sizes

A computer simulation study of the sintering process of cylindrical particles is presented following an earlier work by Pan et al. [Pan J, Le H, Kucherenko S, Yeomans JA. A model for the sintering of spherical particles of different sizes by solid state diffusion. Acta Metall 1998;46:4671–90]. The current paper focuses on the effect that the size of the particles has on the sintering kinetics. The computer simulation revealed a sophisticated behaviour for this apparently well-understood problem. Firstly, it is shown that a smaller particle can grow temporarily at the expense of its larger neighbours, in contradiction to conventional wisdom. There are two conditions for this to happen: (a) the particles must be nano-sized and (b) the smaller particle must be placed between two larger neighbours. Secondly, a pair of nanoparticles of different size can separate from each other in the later stage of their co-sintering process. Thirdly, the extent to which particles approach each other is strongly influenced by degree of constraint that the particles are subjected to by the neighbouring particles. This sophisticated behaviour revealed by the computer simulation questions the relevance of the oversimplistic sintering models to a real powder compact.

Coarsening and grain growth in sintering of two particles of different sizes

Coarsening during sintering results from surface motion, while grain growth results from grain boundary motion. The sintering of two spherical particles of different sizes, and subsequent coarsening and grain growth, were studied until the smaller particle disappeared. When the grain boundary mobility M gb was comparable to the surface mobility M s, the curved grain boundary migrated out of the smaller particle in a shorter time with increasing ratio of grain boundary energy γ gb to surface energy γ s. As long as the grain boundary was anchored to the surface triple junction, the grain boundary was approximated to be flat at the limit of M gb ≫ M s. The motion of flat grain boundary was affected by γ gb/ γ s in a different way to that of the curved grain boundary.

A 3D semi-digital model for the placing of granular materials

A 3D semi-digital model has been developed in order to simulate the gravitational placing of granular mixtures composed of spherical particles of different sizes allowing the optimization of mixtures proportions. The aim is to control concrete placing in formworks particularly in the presence of reinforcement bars. In this case, the representation of a large number of particles is necessary and segregation or wall effects have to be taken into account. Moreover, an easy representation of complex geometries and obstacles of arbitrary shapes should be possible. In order to respect these conditions, the used 3D semi-digital model is based on the digitization of a calculation volume and on the representation of spherical particles with real numbers. The model takes into account only steric repulsion between particles and simulates their collisions during placing by random displacements. The simplicity of the model allows the simulation of up to 2 million spherical particles without spending too much computational time. The model can therefore be used for the simulation of granular materials having a spread granulometry-like concrete. The packing density of binary mixtures of spherical particles with different size ratios and varying proportions of small and big particles is first studied. The results are compared successfully with theoretical packing density of binary mixtures without interactions. It is therefore demonstrated that the semi-digital model can be used for the simulation of binary mixtures having low size ratios (0.1), which corresponds approximately to the size ratio of fine and coarse aggregates in concrete. Secondly, digitized cylindrical obstacles are added in the systems with the aim to represent reinforcement bars in a formwork. The influence of small and big particles proportioning on the local packing density and the homogeneity of the mixture is studied. The results show that in the presence of obstacles, the optimum placing is obtained when the proportion of small particles in the mixture is higher than that without obstacles. This is due principally to the looser packing of big particles around obstacles.

The effect of multiple scattering in disperse media on polarization characteristics of scattered light

The effect of scattering of different multiplicity on polarization characteristics of scattered light is studied by the Monte Carlo computer simulation technique. The scattering multiplicity distribution versus the direction of scattering and dimensions of the scattering system is obtained for monodisperse systems of spherical particles of different size. The angular dependences of the elements of the light-scattering matrix (LSM) are calculated. It is shown that in a system of spherical particles, specific features of the LSM structure associated with multiple scattering have much in common with similar features of the LSM in systems of nonspherical particles under conditions of single scattering. The angular dependences of the degree of depolarization of the scattered light are studied.

Study of dispersion and absorption of an ensemble of spherical particles inside an optical cavity and new possibilities of predicting the optical characteristics of biological media by intracavity laser spectroscopy

Optical characteristics, namely, dispersion and absorption spectra of an ensemble of spherical particles randomly oriented inside an optical cavity are investigated. The study is based on the self-consistent matching of new data from the inhomogeneous optical cavity with data from the scattering of an ensemble of spherical particles of different size, randomly oriented in free space. As a result, a new model, which self-consistently accounts for multiple scattering in the optical cavity, has been developed to predict absorption and dispersion of ensembles of spherical particles. This model is supposed to enhance potentiality of the intracavity method for plotting wavelength dependences of optical characteristics of media. A specific calculation of dispersion and absorption dependences on the wavelength shows that this method can be used for investigation of biological media consisting of spherical particles, in particular, erythrocyte suspension.

Emulsion polymerization of aniline with ionic dispersants containing ionic poly(vinylpyridinium methanesulfonate) segments

Ionic polymer prepared from acid–base interaction between methanesulfonic acid (MSA) and poly(4-vinylpyridine) (P4VP) or poly(styrene- co-4-vinylpyridine) (PS-P4VP) was served as dispersant for the emulsion polymerization of aniline. Dependent on the dispersants (as P4VP(MSA) or PS-P4VP(MSA)) used, the maximum amounts of polyaniline incorporated without premature precipitation during polymerization are different. A 3 wt.% of aniline in relative to P4VP(MSA) dispersant resulted in precipitation during polymerization; however, the aniline/PS-P4VP(MSA) ratio can reach 10 wt.% without the undesired precipitation if PS-P4VP(MSA) was used as dispersant. The inner PS block in PS-P4VP(MSA) can serve as a stabilizer to prevent the expansion of the outer P4VP(MSA) block and provided a more stable micelle system as compared with the aniline/P4VP(MSA) system. Spherical particles of different sizes were observed in products of low polyaniline contents (<3 wt.%). With increasing polyaniline contents, the conductive polyaniline phases tended to aggregated and separated from the dispersant matrix.