A proposed new characterization of particle shape and its application

In order to identify particles morphologically nine new shape indices, using three kinds of powder particles which include circularity and elongation as reltionships between characteristic diameters, have been defined. Shape indices have been examined on their numerical lines. The nine shape indices were divided into three groups which characterize the concavities and/or convexities of a particle, mainly characterize slimless and do not characterize specific shape. Shape identification has been tried on two kinds of diagrams which were obtained by combining shape indices of different character.Particle shape without surface texture is characterized on the diagrams and it is also suggested that morphological identification of powder particles is possible with statistical treatment.     

Characterization of packing structure of tape cast with non-spherical natural graphite particles

A three-dimensional microstructure of green and pressed tapes cast with graphite particles of non-spherical shape were examined quantitatively on the basis of the distribution of void sizes among the packed particles. The distributions measured over the cross-sections of the tape in three directions were expressed by the theoretical ones deduced for non-spherical particles. Particle shape was characterized by shape indices defined by Fourier analysis of particle outlines measured over the corresponding cross-sections of the green tape. The relationships were totally established between the limiting packing density, characterizing the void size distribution at the same section voidage, and the shape index of particle over the section. As a result, the normalized median void diameter as well as the limiting packing density of the pressed tape was found to increase with the particle shape index, corresponding to wider void size distribution. Therefore, based on developed correlations, the optimization of packing microstructure of the cast tape can be expected to result in high performance battery by using shape-modified graphite particles.     

Visualization of the shear region in a cohesive powder by scanning with a polarized neutron beam

The flow of cohesive powder occurs by the formation of shear planes or zones. How these form and how particles microscopically behave in a shear zone is fundamental for understanding powder flow. In this work Neutron Depolarization has been used to study in-line particles in a powder sample. The Neutron Depolarization technique gives a unique insight in the particle rotations and width of the shear zone. It has been shown that rotation of particles during a normal consolidation becomes less when the sample is more compacted. Shear displacement experiments showed that particles rotate in a preferred direction. The width of the region in which the preferred rotation takes place is found to be at least 1000 to 2000 particle diameters.     

The use of the ring gap sizer for characterization of particle shape in the sieve range

The ring gap sizer sorts particles by their minimum dimension, i.e. thickness. This new instrument has been used to establish particle shape factors and distributions of powders in the sieve range.The powders investigated were quartz and tablet granules, i.e. powders consisting of non-equidimensional particles. It is shown that the combination of results obtained by the ring gap sizer, dry sieving and microscopy gave log-normal distributions of particle flakiness. This was in good agreement with results obtained by a microscopical reference method.For the quartz powder the variation of particle elongation with changing particle size was also determined, using the ring gap sizer to obtain samples of varying particle size, which were then measured on length and breadth by microscopy.Additionally, the two average values of flakiness and elongation have been used to calculate the Heywood surface and volume shape coefficients.     

Determination of Dispersion in Anisotropic Mica and Wollastonite Particles Using the Layer Sedimentation Method

The results of studying the dispersion composition of muscovite mica and wollastonite, whose particle shape is significantly anisometric, are described. A simple method for sedimentation analysis is proposed, which makes it possible quickly and with great accuracy to determine the particle distribution based on their sedimentation diameters. Relationships are obtained which can be used to estimate the geometrical sizes of particles for the considered materials.     

Radiative transfer simulation of dust-like aerosols: Uncertainties from particle shape and refractive index

The composition, particle shape, number concentration, size distribution, and spatial and temporal distributions of dust aerosols cause significant uncertainties in relevant radiative transfer simulations. The spherical particle approximation has been generally recognized to introduce errors in radiative transfer calculations involving dust aerosols. Although previous studies have attempted to quantify the effect of non-spherical particles, no consensus has been reached as to the significance of the dust aerosols non-spherical effect on flux calculations. For this study, we utilize a newly developed ultra-violet-to-far-infrared spectral database of the single-scattering properties of tri-axial ellipsoidal, mineral dust-like aerosols to study the non-spherical effect on radiative forcing. The radiance and flux differences between the spherical and ellipsoidal models are obtained for various refractive indices and particle size distributions. The errors originating from using the spherical model and the uncertainties in the refractive indices are quantified at both the top and bottom of the atmosphere. The dust non-spherical effect on the net flux and heating rate profile is obtained over the entire range of the solar spectrum. The particle shape effect is found to be related to the dust optical depth and the surface albedo and can be an important uncertainty source in radiative transfer simulation. The particle shape effect is largest over water surfaces and can cause up to a 30% difference in dust forcing at the top of the atmosphere.     

Charge Distribution of Incipient Flame-Generated Particles

We report the size and electrical charge distributions of incipient nanoparticles generated in atmospheric pressure hydrocarbon/air premixed flames in conditions prior to the onset of soot particles. The particle size and charge distributions are measured by Differential Mobility Analysis (DMA) and compared to theoretical charge distributions predicted for flame conditions. The results show that the charge distribution attained in flames is well predicted by Boltzmann theory for all particles, including even the smallest incipient particles with diameters in the 1–3 nm size range. In flame conditions that produce only particles smaller than 3 nm, the charge fraction of particles agrees with that predicted by Boltzmann theory near the flame temperature (1700 K). In flame conditions with ‘bimodal’ particle size distributions, the charge fraction of the smallest particles agrees with the Boltzmann prediction at maximum flame temperature, while the charge fractions of larger particles agree with Boltzmann theory at temperatures that coincide with the local temperature near the probe surface (1000–1200 K). The results of this paper show that the temperature of the Boltzmann charge fraction that best agrees with the measured charge fraction for each particle size gives the local temperature of their last coagulation event. The smaller particles, which retain their charge fraction predicted by Boltzmann at the maximum flame temperature, do not thermalize by coagulation in the cool region near the probe evidencing low probability for charge transfer as well as for coagulation.     

A Thermophoretic Precipitator for the Representative Collection of Atmospheric Ultrafine Particles for Microscopic Analysis

In this article, the potential of a thermophoretic sampling device to derive quantitative particle size distributions and number concentrations of aerosols based on microscopic single particle analysis is explored. For that purpose a plate-to-plate thermophoretic precipitator to collect ultrafine atmospheric particles for TEM (transmission electron microscopy) analysis has been calibrated and characterized. The representativeness of the samples has been verified in a series of experiments. Results show that, for particles with diameters of 15 nm to 300 nm, the precipitator's collection efficiency is independent of size, shape, and composition of the particles. Hence, its samples accurately represent the original aerosol.

A numerical model of thermophoretic deposition within the device has been developed and tailored to the specifications of the precipitator. The model has been used to derive the particle number density and size distribution of several calibration aerosols using the TEM analysis of the samples taken with the thermophoretic precipitator as input parameters. The results agree very well with the on-line measurements of the calibration aerosols. This work demonstrates that our thermophoretic sampling device can be used to derive quantitative particle size distributions and number concentrations of ultrafine particles based on microscopic single particle analysis.     

Partikelform und Porosität von biogenen Pyrolysekoksen

Char particles from pyrolyzed biomass vary in particle size and shape. On average, the particles are more elongated the larger their size. The average size‐specific elongation is almost alike for all investigated samples, i.e. independent from their source material and process. The particle collectives cannot be characterized accurately with classical particle size distributions, which assume spherical particle shape. Accounting for their shape, they can be described more accurately with particle size distributions that are based on an ellipsoid model. The high bulk porosity is mainly attributed to the spaces between particles.     

Spherical particles for automotive powder coatings

Clear powder coatings that consist of spherical particles with a narrow particle size distribution were produced via a suspension method that involves the agglomeration and unification of smaller particles. These powder coatings have the advantages of excellent powder flowability and high transfer efficiency. This behavior is attributable to the spherical particle shape and absence of finer particles. This production method has been developed for thinner film build clear coats with improved surface smoothness as compared to powder coatings produced by conventional methods.     

Impact of powder morphology on quality of low-pressure injection moulded reaction-bonded net shape oxide ceramics

Low-pressure injection moulding is a very efficient process for net shape manufacturing of ceramic micro parts. In order to obtain sintered ceramic specimens without shape distortion or damages, density gradients in the green bodies have to be avoided. Especially feedstocks with a solid loading near the critical powder volume content often tend to segregate the binder while flowing. However, the value of critical powder content can be significantly influenced by particle size, particle size distribution and particle morphology. This paper compares two powder mixtures of identical chemical compositions with different specific surfaces and morphology and evaluates their workability for low-pressure injection moulding. The aim of this paper is to identify the influence of morphology on feedstock rheology as well as on accuracy, mechanical properties and microstructure of net shape manufactured reaction-bonded zircon ceramics.     

数字成像颗粒分析仪在聚乙烯粉料测试中的应用

采用CAMSIZER数字成像颗粒分析仪对聚乙烯粉料样品的粒度分布进行了测试,考察了测试结果的重复性,并对该仪器在粒度分布测试同时获得颗粒球形度数据和颗粒照片的功能进行了验证。结果表明,粒度分布测试自动化程度高,结果重复性较好,与筛分法比较,工作量大大降低,但测试速度有待提高;在进行粒度分布测试的同时,可获得颗粒的球形度数据和颗粒投影照片。     

Assessment of adhesion and autoadhesion forces between particles and surfaces

A centrifuge technique has been used to investigate the autoadhesion force between particles and a plane surface of the same material compacted into a disk, which is resistant to the centrifugal force. When measured by profilemetry, these compact surfaces are rougher than metal or plastic surfaces used in previous studies. This results in a change of the detachment force distribution from a log-normal to a right-shifted distribution. The relationship between press-on force and median autoadhesion force depends on particle size, shape and particle surface morphology of the powder particles autoadhered. The lower the autoadhesion force, the greater the possibility that the substance can be used in a single-component powder application. The bulk properties of the powders such as cohesiveness or free powder flow were found to be related to the autoadhesion force. Estimation of the distance between the particles and surfaces has been made based on the Lifshitz-van der Waals constant derived from low frequency dielectric measurements. There was a decrease in distance of separation with increase in press-on force for both sets of particles. The contact between angular lactose monohydrate particles and a lactose monohydrate surface can be increased by more than that between irregular or spherical salmeterol xinafoate particles and their equivalent compact surface.     

Handling properties of cereal materials in the presence of moisture and oil

A powder flow analyzer attached to a Texture Analyser (Stable Micro Systems, UK) was used to compare the flow behaviour of four cereals systems: maize and wheat (in both starch and flour forms), as functions of particle size and distribution, water content and the addition of different types of oil. It was expected that the smaller the particle size the higher the tendency to stick (because of less free volume between the particles), but that was not the case. The results showed that wheat starch used, with bigger particle size than maize starch, had higher cohesion properties and as water content increases the cohesion increases by the same magnitude. This was attributed to the differences in granular shape as well as protein quantity and quality. Caking strength for both starches was influenced by the water content; in particular at 30% water content (w/w), neither cohesion nor caking indices could be measured for wheat starch because of the high stickiness of the particles.Although the two flours had particles of very similar sizes, with differences in the distributions only, maize showed higher cohesion indices compared to wheat flour. These values decreased with increasing water content. The caking property for maize was not significantly affected by water content with values of approximately 100 ± 5. The caking strength increased for wheat flour from 8 to 500 as moisture increased from 12.5 to 30%. This was ascribed to the differences in hydration properties of the two flours. For wheat flour and as the water content increased, gluten started to form and would require more than 30% to form a homogenous, visco-elastic mass.Generally, cohesivity and cake forming ability were affected by water content as well as the physical state of the oil i.e. by the solid/liquid ratios. As water content increases, wheat starch showed the greatest packing and cohesive behaviour, with and without the oil, while maize flour exhibited the weakest packing and cohesive properties.     

Reference materials of defined particle size certified recently by the community bureau of reference of the european economic community

Some results from an international projects, supported by the Community Bureau of Reference of the European Economic Community, on the certification of five reference materials of defined particle size covering the overall range 0.35 – 650 μm are presented and discussed. Four of the reference materials were certified with respect to the mass distributions of the Stokes' diameters measured by an agreed gravitational sedimentation (Andreasen pipette) method. The coarsest of the reference materials was certified with respect to the mass distribution of the volume diameters of the particles using sieves, the ‘cut sizes’ of which were calibrated with respect to their equivalent volume diameters.Data were also obtained using several other methods, including X-ray gravitational sedimentation, sedimentation balance, centrifugal sedimentation, electrical sensing zone and photo-sedimentation methods. These were not used for certification but are presented for comparison purposes and to indicate the usefulness of the certified reference materials for the checking and calibration of many particle sizing techniques.     

Discrete particle simulations for flow of binary particle mixture in a bubbling fluidized bed with a transport energy weighted averaging scheme

Flow behavior of small and big particles with the same particle density in a bubbling fluidized bed is modeled by a combined approach of discrete particle method and computational fluid dynamics (CFD-DPM). The collision time of a collision pair is computed by a quartic equation in which the effect of acceleration due to the different diameters is considered. A transport energy weighted averaging approach is proposed to determine the local gas velocity at a particle. The fluidization behavior of binary mixture differing in size is experimentally and numerically studied in the gas bubbling fluidized bed. The distributions of mass fraction of small and big particles along the bed height are simulated, and the profiles of the mean particle diameters of binary mixture are determined. The numerical results are in agreement with experimental data. The distributions of granular temperature, stresses, and shear viscosities of small and big particles are compared.     

The powder properties of poly(vinyl chloride) resins

The properties of powders depend mainly upon the characteristics of the individual particles and their interactions. In the case of PVC resins, particle characteristics vary broadly depending upon the manufacturing process used or variables within a given process. In this paper, the effects of grain size, size distribution, grain shape, degree of compaction and static on the bulk density and flow properties of PVC resins are studied. Results indicate that grain shape mainly affects bulk density while grain size and distribution mainly affect powder flow. The degree of compaction and the amount of static on the resin grains are variables which can overwhelm other powder properties.     

Photomicrographic size distribution determination of non-spherical objects

Equations have been developed for calculating the size distribution of non-spherical objects by using photomicrographs prepared of sections or projections of samples. The equations contain the shape function characteristic of the shape of the objects in the sample which is also determined from the photomicrographs. The equations have been applied to the void size distribution determination in various sandstones and packed beds of beads, as well as to the particle size distribution determination of a sample of common salt. It has been found that the new equations resulted in plausible calculated size distributions in the case of highly anisotropic objects, whereas this was not the case when the sphere model was used as a basis for the calculations. In the case of the salt particles, however, the sphere model was almost equally adequate as the shape function method, because the shape function was, in this case, very nearly spherical.     

A new method for identifying the modes of particulate matter from pulverized coal combustion

Knowledge of the modality of the size distribution of particulate matter (PM) from pulverized coal combustion is of great significance from the viewpoint of exposure and risk assessment. Mass or number size distributions are usually used in modality analyses, but sometimes the central particle mode fails to be detected due to overlapping. This work provides a new method for identifying particle modes using mass fraction size distributions of the aluminum (Al). Five Chinese pulverized coals of different ranks were burnt in a laboratory drop tube furnace at 1673 K. The produced PM was size segregated by a low pressure impactor and subjected to elemental composition analysis by X-ray fluorescence (XRF). Particle mass size distributions, mass fraction size distributions of the Al and sulfur (S) were obtained for all the particle samples. The mass size distributions of four coal ash samples all show three distinct particle modes, with a central mode at approximately 2 µm, while the mass size distribution of the LPS coal ash sample only indicates two particle modes. However, the mass fraction size distributions of the Al for all ash samples, including the LPS coal ash sample, generally show three particle modes. The obscurity of the central mode in the mass size distribution of the LPS coal ash sample is expected to be a consequence of the merging of it into the coarse mode. The formation of the central mode is attributed to the more pronounced heterogeneous condensation or adsorption of vaporized species on fine residual ash particles, whose origins are still unclear at present. This is further confirmed by examination of the mass fraction size distributions of the S. These results show that mass fraction size distributions of the Al seem to be more effective in identifying particle modes and their size boundaries than particle mass size distributions.     

Simulating Particle Size Distributions over California and Impact on Lung Deposition Fraction

Reliable simulations of particle mass size distributions by regional photochemical air quality models are needed in regulatory applications because the U.S. EPA's National Ambient Air Quality Standards specify limits on the mass concentration of particles in a specific size range (i.e., aerodynamic diameter <2.5 μm). Considering the associations between adverse health effects and exposure to ultrafine particles, air quality models may need to accurately simulate particle number size distributions in addition to mass size distributions in future applications. In this study, predictions of particle number and mass size distributions by the Community Multiscale Air Quality model with the standard and an updated emission size distribution are evaluated using wintertime observations in California. Differences in modeled lung deposition fraction for simulated and observed particle number size distributions are also evaluated. Simulated mass size distributions are generally broader and shifted to larger diameters than observations, and observed differences in inorganic and carbon (elemental and organic) distributions are not captured by the model. These model limitations can be reasonably accounted for in regulatory modeling applications. Simulated number size distributions are considerably less accurate than mass size distributions and are difficult to represent in air quality models due to large sub-grid-scale concentration gradients. However, modeled number size distributions are responsive to updates of the emission size distribution, and reasonable simulation of background number size distributions might be possible with an improved treatment of emission size distributions. Modeled lung deposition fractions for simulated number size distributions peak in the same lung region as those for number size distributions observed in the background. However, differences in modeled and observed total number concentrations generally suggest large differences in the total number of deposited particles. Future model development on simulating particle mass size distributions should focus on improving predictions of the mass fraction of particles <2.5 μm. Model development for particle number size distributions should focus on reducing differences in modeled lung deposition for modeled and observed distributions.