Particle Shape Characteristics Research Articles

Synthesis, particle shape characterization, magnetic properties and surface modification of superparamagnetic iron oxide nanochains

We report monodisperse, chain-like particles (nanochains) consisted of silica-coated maghemite (γ-Fe2O3) nanoparticle clusters prepared by colloidal chemistry and magnetic field-induced self-assembly of nanoparticle clusters. In order to quantify the shapes of chain-like particles, we have used the measure for shape convexity which is also called solidity. We functionalize the surface of the nanochains with amino (NH2) and carboxyl groups (COOH) in order to modify surface charge. These surfaces of nanochains provide better colloidal stability and their potential for practical applications in biomedicine. The enhanced colloidal stability of the surface modified nanochains is confirmed by Zeta potential (ζ-potential) analysis. Magnetic properties of the nanochains show superparamagnetic state at room temperature since the nanochains are composed of tiny nanoparticles as their building blocks. The measured M(H) data at room temperature have been successfully fitted by the Langevin function and magnetic moment μp = 20,526 μB for sphere-like nanoparticle clusters and μp = 20,767 μB for nanochains are determined. The determined magnetic parameters have revealed that the nanochains show a magnetic moment of the nanoparticles higher than the one of individual nanoparticle clusters. These differences can be attributed to the collective magnetic properties of superparamagnetic iron oxide nanoparticles (SPION) assembled in different morphologies (isotropic and anisotropic morphology).

Hydro-mechanical analysis of calcareous sand with a new shape-dependent fluid-particle drag model integrated into CFD-DEM coupling program

In this study, a new shape-dependent fluid-particle drag model for irregularly shaped particles is integrated into the fluid dynamic program CFD-DEM and used to analyse the behaviour of calcareous sand particles in liquids. The new drag model had been correlated by pervious settling experiments of calcareous sand particles in a static Newtonian Liquid. The new drag model defines the particle-fluid drag coefficient as a function of both the fluid regime and particle shape characteristics which can evaluate how the particle shape deviates from a regular sphere. This study is a follow-up work of the authors' previous experimental research, focusing on the numerical modelling of sand particle-fluid interaction. To validate the integration of the new drag model in program CFD-DEM, the code has been used to reproduce the calcareous sand particle settling and seepage experiments. The comparison with simulations using the existing drag models without considering particle shape effect demonstrates that, by means of the new drag model, a significant improvement in the capability of CFD-DEM program to predict the terminal falling velocity of irregularly shaped particles is obtained. With this implementation, CFD-DEM program is used to simulate seepage flows within calcareous sand sample in which particles are significantly different from regular spheres, as is usually the case of environmental and geological fluid-particle flows.

Stochastic numerical model of stone-based materials with realistic stone-inclusion features

This paper presents a systematic approach for generating a stochastic model with realistic stone-inclusion features for the numerical simulation of stone-based materials. Firstly, the inverse discrete Fourier transform method is employed to randomly generate realistic stones with predetermined particle shape features. Then, an overlapping detection algorithm is proposed to facilitate random and quick allocation of irregularly shaped stones, considering the stone contents, stone size distributions and stone orientations. Finally, several examples are provided to show that the proposed approach can generate stone-based materials with prescribed stone features in a rapid and precise manner.

Algorithms for 3D Particles Characterization Using X-Ray Microtomography in Proppant Crush Test

We present image processing algorithms for a new technique of ceramic proppant crush resistance characterization. To obtain the images of the proppant material before and after the test we used X-ray microtomography. We propose a watershed-based unsupervised algorithm for segmentation of proppant particles, as well as a set of parameters for the characterization of 3D particle size, shape, and porosity. An effective approach based on central geometric moments is described. The approach is used for calculation of particles’ form factor, compactness, equivalent ellipsoid axes lengths, and lengths of projections to these axes. Obtained grain size distribution and crush resistance fit the results of conventional test measured by sieves. However, our technique has a remarkable advantage over traditional laboratory method since it allows to trace the destruction at the level of individual particles and their fragments; it grants to analyze morphological features of fines. We also provide an example describing how the approach can be used for verification of statistical hypotheses about the correlation between particles’ parameters and their crushing under load.

2D-3D conversion method for assessment of multiple characteristics of particle shape and size

Accurate assessment of three-dimensional (3D) particle characteristics, such as particle shape and size distribution, is a basic requirement in various fields. In practice, however, two-dimensional (2D) characteristics are often measured instead of 3D, due to limitations of cost, speed, and so on. A conversion method which simultaneously estimates multiple 3D characteristics from measurable multiple 2D counterparts is here proposed. Briefly, the method consists of the following steps: numerical creation of 3D particle models; computation of 3D and 2D parameter distributions of the model particles to establish a conversion database; and determination of the optimal combination of the 3D particle models to fit the measured 2D parameter distributions, using the genetic algorithm. The proposed method was validated by numerical examination using ellipsoidal particles with three grades of surface roughness. The method is novel in two respects: (i) versatility, as it is applicable to various types of particles, and (ii) convenience, as multiple parameters can be estimated at once; and it has the potential to be a fundamental technique in various fields dealing with particles, whether organic or inorganic, natural or artificial.

Open-source support toward validating and falsifying discrete mechanics models using synthetic granular materials—Part I: Experimental tests with particles manufactured by a 3D printer

This article presents a new test prototype that leverages the 3D printing technique to create artificial particle assembles to provide auxiliary evidences that supports the validation procedure. The prototype test first extracts particle shape features from micro-CT images of a real sand grain and replicates the geometrical features of sand grain using a 3D printer. The quantitative measurements of the particle shape descriptors reveal that the synthetic particles inherit some attributes such as aspect ratio and sparseness of the real materials while exhibiting marked differences for sphericity and convexity. While it is not sufficient to consider the printed particle assembles a replica of the real sand, the repeatable manufacture process provides convention tools to generate additional data that supports the validation procedure for particulate simulations. Oedometric compression tests are conducted on a specimen composed of the printed particles of identical size and shape to create benchmark cases for calibrating and validating discrete element models. Results from digital image correlation on the synthetic sand assemblies reveal that the fracture and fragmentation of the synthetic particles are minor, which in return makes particle position tracking possible. As our prototype test and research data are designed to be open source, the dataset and the prototype work will open doors for modelers to design further controlled experiments using synthetic granular materials such that the individual influence of each morphological feature of granular assemblies (e.g., shape and size distribution, void ratio, fabric orientation) can be individually tested without being simultaneously affected by other variables.

Abundance and Speciation of Surface Oxygen on Nanosized Platinum Catalysts and Effect on Catalytic Activity

Oxygen at the surface of nanosized platinum has a direct effect on catalytic activity of oxidation–reduction chemical reactions. However, the abundance and speciation of oxygen remain uncertain for platinum with different particle size and shape characteristics, which has hindered the development of fundamental property–activity relationships. We have characterized two commercially available platinum nanocatalysts known as Pt black and Pt nanopowder to evaluate the effects of synthesis and heating conditions on the physical and surface chemical properties, as well as on catalytic activity. Characterization using complementary electron microscopy, X-ray scattering, and spectroscopic methods showed that the larger average crystallite size of Pt nanopowder (23 nm) compared to Pt black (11 nm) corresponds with a 70% greater surface oxygen concentration. Heating the samples in air resulted in an increase in surface oxygen concentration for both nanocatalysts. Surface oxygen associated with platinum is in the f...

Hopper flow of irregularly shaped particles (non-convex polyhedra): GPU-based DEM simulation and experimental validation

Numerous practical applications of the Discrete Element Method (DEM) require a flexible description of particles that can account for irregular and non-convex particle shape features. Capturing the particle non-convexity is important since it allows to model the physical interlocking when the particles are in contact. To that end, the most flexible approach to capture the particle shape is via a polyhedron, which provides a faceted representation of any shape, albeit at a significant computational cost. In this study we present a decomposition approach to modeling non-convex polyhedral particles as an extension of an existing open source convex polyhedral discrete element code, BlazeDEM-GPU, which computes using general purpose graphical processing units (GPGPUs). Although the principle of decomposition of non-convex particles into convex particles is not new, its application by the discrete element modeling community has been rather limited. The non-convex extension of BlazeDEM-GPU was validated using a hopper flow experiment with identical convex and identical non-convex 3D printed particles. The experiment was designed around two sensitive flow points, with the convex particles following the intermittent flow and the non-convex particles forming stable arches. It was demonstrated that the DEM simulations can be applied to reproduce both the convex and the non-convex flow behavior using the same parameter set. This study is a significant step towards general computing of non-convex particles for industrial-scale applications using the GPGPUs.

Identification and Characterization of Particle Shapes from Images of Sand Assemblies Using Pattern Recognition

Pattern recognition was used on images of contacting three-dimensional sand particle assemblies to detect foreground sand grains that exhibit full-particle projections. Once identified, the roundness and sphericity of those particles could be determined using previously developed computational geometry image analysis methods. The pattern recognition used cascade and sliding window techniques from the literature with modifications to account for the unique features of sand grains, including variable sizes and a range of elongations and orientations of long axes in an image. A library of over 85,000 images was created to train the pattern recognition program. An example problem illustrated the capabilities of the method to generate particle roundness and sphericity curves.

Experimental Investigation into the Influence of Roundness and Sphericity on the Undrained Shear Response of Silty Sand Soils

AbstractParticle shape represents one of the key parameters that significantly influences the mechanical response, shear strength, deformation, and settlement characteristics of cohesionless soil deposits when subjected to static or dynamic loading conditions. Shear behavior of coarse-grained soils (gravel, gravelly sand, sandy gravel, sand, silty sand, or sandy silt) depends heavily on the two essential particle shape characteristics, which are termed roundness and sphericity. However, there are limited published studies available in the literature that deal solely with the effects of particle shape on shear-strain characteristics and shear behavior of granular soil deposits. Therefore, the veritable role of the particle shape parameter on soil behavior remains incomplete and requires further investigation. The present research work attempts to investigate the effects of particle shape on shear response of different categories of sand-silt mixtures under static triaxial loading conditions. For this purpose, a series of undrained compression triaxial tests was carried out on mixtures of Chlef (Algerian) rounded sand, Fontainebleau (France) subrounded sand, and Hostun (France) subangular sand mixed with low-plastic (Ip=5 %) rounded silty fines. All the sand-silt mixture samples were reconstituted at an initial relative density (Dr=52 %) and subjected to a constant confining pressure (P’c=100 kPa). An evaluation of particle shape characteristics of the tested materials (sand and silt) was performed using a digital microscope device. Two new indexes, termed combined roundness and combined sphericity based on the combination of sand and silt to account for the coupled effects of particle shape and fines content, were proposed. The test results are used to correlate the undrained shear strength of the silty sand soils to the particle shape characteristics. Therefore, particle shape appears to be an important soil index property that needs to be adequately identified, particularly for silty sand–silt mixture soils. The systematic identification of particle shape characteristics leads to a better understanding of silty sand behavior.

DSPC/Cholesterol Nano-formulated 9-Cis-retinoic Acid has Potent Therapeutic Effect on A549 Cell Line

The main objective of the present work was to develop liposomal nano-formulation for 9-cis-retinoic acid using di-stearoylphosphocholin/cholesterol mixture, to characterise and to evaluate its anticancer effect on A549 human lung cancer cell lines. The liposomes were prepared using thin film formulation method and characterization of particle size and shape were carried out employing dynamic light scattering and scanning electron microscopy techniques, respectively. The level of drug entrapment into the liposomes and liposomal stability were analysed using spectrophotometry and expressed in terms of percent entrapment. The level of 9-cis-retinoic acid in treated cells also was assayed using spectrophotometry. In vitro drug release level evaluated using a dialysis bag. The anticancer effect was studied using MTT and trypsin blue assays in human lung cancer cell line. The drug entrapment level achieved was 83.33 %. Viability of cancer cells was significantly reduced after liposomal 9-cis-retinoic acid treatment. From these results it could be concluded that the liposomal 9-cis-retinoic acid was easily taken up by the A549 cells compared to free 9-cis-retinoic acid, which might have enhanced the anticancer activity observed in this study.

Inferring 3D particle size and shape characteristics from projected 2D images: Lessons learned from ellipsoids

This paper investigates the relationship between the 3D size and shape characteristics of ellipsoids and their 2D counterparts obtained from projected images. We found that the average radius of ellipsoids can be satisfactorily estimated from the statistical mean or median of the average radius of the corresponding 2D projected images. However, the shape characteristics evaluated from the images may not always yield reliable quantitative prediction of the corresponding 3D descriptors. The results suggest that quantifying particle shape characteristics from projected 2D images may only work well for particles similar in shape to prolate spheroids.

Image based shape characterization of granular materials and its effect on kinematics of particle motion

Quantification of particle shape features to characterize granular materials remains an open problem till date, owing to the complexity involved in obtaining the geometrical parameters necessary to adequately compute the shape components (sphericity, roundness and roughness). A new computational method based on image analysis and filter techniques is proposed in this paper to overcome this difficulty. In this method, operations are performed on binary images of particles obtained from raster images (collection of pixels) by the process of image segmentation. The boundary of particles captured in 2D images consist of micro, meso and macro scale features on which filter techniques are applied to remove the micro level features for the quantification of particle roughness and to obtain a roughness free boundary. A robust algorithm is then written and implemented in MATLAB to obtain the complete geometry of the particle boundary (free from roughness features) and to identify the precise corner and non-corner regions along the boundary. This information is used to quantify the roundness (as per Wadell in J Geol 40:443–451, 1932) and sphericity of particles. The proposed methodology to measure roundness and sphericity is compared against standard visual charts provided by earlier researchers. Finally, the methodology is demonstrated on real soil particles falling across a wide range of sizes, shapes and mineralogical compositions. Also, an idea to comprehend the kinematics of particle motion based on its concavo-convex features is discussed with two proposed novel descriptors and a visual classification chart.

Comparative discrete element modelling of a vibratory sieving process with spherical and rounded polyhedron particles

Current spherical particle usage in discrete element modelling (DEM) is not able to accurately reflect the particle shape effect in some specific industrial applications. This study specifically investigated the effect of particle shape in discrete element modelling of a vibratory sieving process, with the focus on comparing results from spherical and non-spherical modelling methods. The particle size distribution of an iron ore material was initially obtained experimentally through vibratory sieving tests. An identical process was replicated in DEM with both spheres and non-spherical particles, and resulting particle size distributions were subsequently compared against the experimental results. A rounded polyhedron shape was utilised to calibrate and generate non-spherical particles based on a 2D particle shape characterisation process. Modelling results suggested that the rounded polyhedron method was able to accurately reflect the particle-sieve contacts without excessive rolling resistance tuning, which was required by the spheres.

Formation mechanism of bead-chain-like ZnO nanostructures from oriented attachment of Zn/ZnO nanocomposites prepared via DC arc discharge in liquid

Bead-chain-like ZnO nanoparticles (NPs) formed in colloidal solution from oriented attachment (OA) of spherical nanoparticles. Arc discharge in liquid is a cost-effective method for quick mass production of nanostructured materials without considerable environmental footprints. Applying voltage across two zinc rods as electrodes, which were immersed in water cause explosion of electrodes and plasma generation. Zn/ZnO nanocomposites produced by interaction of different active species in high-pressure and high-temperature plasma at the solid-liquid interface. Different sized nanoparticles with diameters of 26, 35, 40 and 60nm at applied discharge currents of 150, 100, 50 and 20A respectively, were fabricated in water without any chemical additives. The results showed bead-like oriented attachments appeared with increasing the applied current during synthesis. Length of aggregates increases from 114nm to 120nm with the applied current of the arc discharge. The mechanism of OA of ZnO NPs was investigated by calculating the attractive and repulsive forces based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed for characterization of particle size, shape, and investigation of bead-like aggregates. X-ray diffraction (XRD) analysis was used to study the crystal structure and phase composition of the bead-chain like nanostructures. Finally, zeta potential analysis was used to measure surface charges and study the mechanism of oriented attachment. The results provide a simple and flexible method for synthesis of Zn/ZnO bead-chain like nanostructures.

Reconstruction of granular railway ballast based on inverse discrete Fourier transform method

This paper presents a particle shape characterization and reconstruction method to describe the geometrical information of granular railway ballast. The outline of a real granular particle is segmented and transformed as discrete time domain signals based on Fourier transform method. Then, the discrete Fourier transform algorithm is developed and applied to convert discrete time domain signals into a discrete Fourier spectrum. Meanwhile, the normalized amplitudes are defined as Fourier descriptors, which is found to be applicable to characterize and reconstruct particle contour. Further, the proposed method is validated by comparing the contours of the real particle with that of reconstructed particle. Moreover, the shape indexes of particles Fourier descriptors and reconstruction of ballasted gravel are illustrated and the the results show that the geometrical parameters can be classified as three levels which can represent the geometrical characteristics in terms of macroscopical and microscopic structure. The inverse discrete Fourier transform can quantitatively control the shape of reconstructed particles by controlling the value and distribution of Fourier descriptors, which matchs the three levels of shape indexes. Furthermore, it can be found that a large number of virtual particles with similar geometrical features can be reconstructed using the proposed Fourier descriptors in a rapid and convenient manner, which is beneficial for providing a virtual test sample for the numerical modeling of realistic granular materials.

Quantitative analysis of wear particles generated by cavitation erosion in glycerol-water mixtures

PurposeThis paper aimed to analyze removed particles from stationary specimen-aluminum (Al-99.92) produced by vibratory cavitation erosion tests in distilled water and glycerol-water mixtures.Design/methodology/approachThe particle morphology which include particle surface topography, size distribution, particle size parameters and particle shape parameters were examined for distilled water and glycerol-water mixtures having different viscosities.FindingsThe results showed that the variation of size parameters with viscosity was very similar to the variation of weight loss with viscosity. Both the size parameters and weight losses show a monotonic decrease in going from distilled water to glycerol-water mixtures having viscosity about 10.1 cSt, beyond which the change is very small. On the other hand, the shape parameters were much less sensitive to distinguish between the particles produced in water and glycerol-water mixtures. The mechanism of cavitation erosion is investigated in detail through observations of the removed particles. The particle surfaces topography demonstrated that the mechanism in water and glycerol-water mixtures was fatigue failure.Originality/valueCavitation often occurs in almost all machines that handle liquids, especially at high speeds, leading to irreparable damage of the components of these machines. Elucidation of such complex phenomenon demands full characterization of the erosion mechanism and controlling parameters inherent to it, so that cavitation erosion can be prevented or at least be reduced through adequate information and collection of relevant data under different operating conditions. Very few studies have been made to approach the viscosity effect upon cavitation erosion from the particle analysis standpoint. The aim of the present work is to identify the effect of liquid viscosity on the size, shape characteristics of the erosion particles and their morphological features. The prevailed mechanisms of wear and particle generation have been proposed based on the acquired information from particle analysis.

Fine grinding: How mill type affects particle shape characteristics and mineral liberation

In minerals beneficiation applications, the main function of comminution circuits is to liberate valuable minerals to facilitate downstream separation processes such as flotation. Traditionally, design and optimisation of comminution circuits was based on the production of a target particle size distribution at an optimised throughput with consideration of energy efficiency and equipment wear rates. However, research in flotation and process mineralogy is leading to queries as to whether more should be demanded from the comminution circuit in terms of particle preparation. For example – if particle shape affects hydrophobicity, can mill operating conditions be adjusted to produce particles with shape characteristics which are more amenable to flotation? For this work UG2 ore (a South African platinum group mineral ore) was milled in a laboratory ball mill and stirred mill. To supplement the laboratory study, samples were taken from the fine grinding circuit of an operational UG2 concentrator. Automated Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (Auto-SEM-EDS) was used for mineralogical and particle shape analysis of feed and product samples. Although the laboratory test work indicated a significant difference in product particle shape characteristics for the two mill types, the difference was not evident in the plant data.

Particle shape quantification using rotation-invariant spherical harmonic analysis

A three-dimensional particle surface can be mathematically represented by a spherical harmonic (SH) coefficient matrix through surface parameterisation and SH expansion. However, this matrix depends not only on the particle shape, but also on the size, position and orientation. This study adopts a rotation-invariant analysis to explore the relationship between SH coefficient matrices and particle shape characteristics. Particle shapes are quantified at different scales (i.e. form, roundness and compactness). These methods are applied to two groups of particles [i.e. Leighton Buzzard sand (LBS) particles and LBS fragments] with distinct shape features. Using rotation invariants, the multi-scale nature of the particle shape is illustrated, and two novel shape descriptors are defined. The results in this paper serve as a starting point for the generation of particle shapes with the prescribed shape features using SHs.

Accurate particle speed prediction by improved particle speed measurement and 3-dimensional particle size and shape characterization technique

Accurate particle mass and velocity measurement is needed for interpreting test results in erosion tests of materials and coatings. The impact and damage of a surface is influenced by the kinetic energy of a particle, i.e. particle mass and velocity. Particle mass is usually determined with optical methods, e.g. laser light scattering, and velocity by the double disk (DD) method. In this article we present two novel techniques, which allow a more accurate measurement of mass, velocity and shape, and we later compare the experimentally obtained flow velocities of particles with a simulation that also includes the particle's shape parameter, known as sphericity. Mass and sphericity are obtained from 3-dimensional data with an industrial X-ray computed tomography (CT) scanner. CT data can be used to accurately determine the volume-basis median of the particles (using the volume-equivalent particle diameter). Velocity is measured with a fast 2-dimensional particle imaging method using a pulsed LED. Good agreement of the measured and simulated particle velocity was found when including the sphericity from CT results. 2-dimensional optical particle size measurements in the jet of an erosion rig are compared with detailed 3-dimensional CT measurements and a low angle laser light scattering (LALLS) measurement system for six different samples of particles. It is shown that the particle volume or mass is usually overestimated by 16–22% when using 2-dimensional methods or LALLS. For CT allows additionally the surface-equivalent diameter to be calculated by using 2-dimensional projections of each particle, these results can be used to correct particle diameters measured with the particle imaging method using a pulsed LED.