Polyhedral Particles Research Articles

Newtonian Event-Chain Monte Carlo and Collision Prediction with Polyhedral Particles.

Polyhedral nanocrystals are building blocks for nanostructured materials that find applications in catalysis and plasmonics. Synthesis efforts and self-assembly experiments have been assisted by computer simulations that predict phase equilibria. Most current simulations employ Monte Carlo methods, which generate stochastic dynamics. Collective and correlated configuration updates are alternatives that promise higher computational efficiency and generate trajectories with realistic dynamics. One such alternative involves event-chain updates and has recently been proposed for spherical particles. In this contribution, we develop and apply event-chain Monte Carlo for hard convex polyhedra. Our simulation makes use of an improved computational geometry algorithm XenoSweep, which predicts sweep collision in a particularly simple way. We implement Newtonian event chains in the open-source general-purpose particle simulation toolkit HOOMD-blue for serial and parallel simulation. The speedup over state-of-the-art Monte Carlo is between a factor of 10 for nearly spherical polyhedra and a factor of 2 for highly aspherical polyhedra. Finally, we validate the Newtonian event-chain algorithm by applying it to a current research problem, the multistep nucleation of two classes of hard polyhedra.

The Influence of Particle Size and Shape in Cobalt 2‐Methylimidazolate Polymers on Catalytic Properties

AbstractThe reaction products between in situ generated Co(OH)2 and 2‐methylimidazole were studied and characterized. Using 9 fold excess of ligand, the well studied polyhedral (dodecahedral) particles (1–3 μm diameter) of the zeolitic imidazolate framework were obtained, i. e. ZIF‐67. When a stoichiometric amount of 2‐methylimidazole was employed, amorphous spheres of ca 500 nm diameter were obtained with low dispersion in size. Both samples were pyrolyzed at 700 and 900 °C under inert atmosphere. The external morphology was kept, however TEM images of the spherical particles showed that they were mainly composed of carbon nanotubes. Co nanoparticles embedded in the carbonaceous matrix could be observed in both samples. The activity of the pyrolyzed (700 and 900 °C) acid leached samples towards the Oxygen Reduction Reaction was studied. Upon the same thermal treatment both types of samples showed similar electrokinetic parameters.

Performance prediction of asphalt mixture based on dynamic reconstruction of heterogeneous microstructure

This paper proposed an algorithm to reconstruct the microstructure of asphalt mixture considering dynamic arrangement process of aggregate particles. In this method, asphalt mixture was considered to be composed of dispersed phase including coarse aggregate and air voids, and continuous phase including fine asphalt matrix (FAM). The dispersed phase materials were characterized by high-dimensional polyhedral particles. In order to reconstruct the microstructure by 1:1 in volume fraction, three basic parameters that determine the heterogeneous structure of asphalt mixture were abided in the design of digital specimen. Then, impulse-based rigid collision response was introduced to simulate the rearrangement of aggregate particles in the compaction process of asphalt mixture. In particular, the applicability of the proposed method to typical structural types of asphalt mixture was discussed. For the asphalt mixture with high air void content, the reconstructed specimen may deviate from the real structure. Furthermore, the dynamic modulus and thermal conductivity of the generated specimens were predicted by finite element method (FEM) and compared with the experimental values. The predicted dynamic modulus and thermal conductivity coincide with the experimental results well, which indicates that the proposed method is reliable for reconstructing the heterogeneous structure of asphalt mixture with relatively low content of air voids.

Sedimentology and carbonatogenesis of the Upper Campanian limestones in Jebel Berda (south central Tunisia)

The Berda Formation corresponds to an inner-shelf stratigraphic equivalent of the Campanian-Maastrichtian outer-shelf Abiod Formation of Tunisia. The present work aims to carry out a sedimentological study of the lower unit (Upper Campanian) of Berda Formation limestones in order to interpret the limestone depositional environment and the origin of the associated micrite particles. This work is based on the study of a geological section surveyed in the Jebel Berda, typic locality, completed by microscopic observation of thin sections that allowed us identifying different carbonate facies and interpreting their depositional environments. The micrite particles have been examined with the SEM. The mineralogical and geochemical proportions and the magnetic susceptibility of the Berda Formation limestone, have been evaluated using respectively XRD, Atomic Absorption Techniques and KLY-3 Kappabridge susceptometer. The studied succession of Berda Formation includes five carbonate facies that developed within different depositional environments (1) calcisphere-rich bioclastic mudstone-wackestone within a circalittoral environment, (2) echinoderm-rich bioclastic wackestone-packstone within a shallow-marine environment (3) bioclastic rudstone within an open-marine environment, (4) peloid-rich bioclastic grainstone within high energy littoral shallow-water marine environment and (5) bioclastic dolomicrite-dolomicrosparite within a continental to marine transition environment. The studied limestones are composed of two kinds of micrite particles, (1) irregularly shaped particles resulting from fossils and micro-fossils desintegration and (2) regularly shaped polyhedral particles resulting from inorganic chemical precipitation. The carbonate facies are arranged into shallowing-up parasequences. The sedimentary facies variation and carbonate accumulation are controlled by eustatic sea-level fluctuation. In this way the biodetrital micrite occurred mainly during the transgressive intervals whereas the inorganic chemical micrite is related to the regressive intervals.

Shared memory parallelization for high-fidelity large-scale 3D polyhedral particle simulations

Particle shape plays a vital role in granular material behavior, but simulations with realistic particle shapes are uncommon due to significant computational demands of complex particle geometry representation. In this work, BLOKS3D, a polyhedral Discrete Element Method (DEM) and impulse-based DEM (iDEM) codes are parallelized to enable large-scale simulations with realistic particle shapes on readily accessible multi-core machines. Data structures used in the original codes were redesigned and optimized, leading to 15% improved performance of the original serial codes. New parallel algorithms were developed resulting in 28 times performance improvement on a 48-core (quad-CPU) shared memory system over single core serial algorithm. The parallelized 3D polyhedral DEM and iDEM were applied to series of column collapse simulations. The codes successfully reproduced the runout distance in granular column collapse experiments. The particle force data from both parallelized DEM and iDEM matched data from the serial algorithm. The new parallel implementation of iDEM was then demonstrated with unprecedented 52 million 3D polyhedral particles simulations. This work will benefit future granular material studies with the newly introduced capacity to run large-scale simulations with realistic particle shapes on shared memory hardware platforms readily accessible to many engineers and researchers.

Phase evolution, powder morphology and photoluminescence exploration of borohydride derived red-emitting Eu3+-doped ZnO nanophosphors

Deep red-emitting Eu3+-doped ZnO nanostructured materials were successfully prepared considering three different zinc-based precursor salts such as acetate, chloride and nitrate using sodium borohydride. XRD results confirmed the presence of ZnO at 800 °C for all samples. However, the nucleation of impurity phases such as EuBO3 and Eu(BO2)3 were significantly evolved and partly crystalline in nature while using nitrate precursor. When the samples were prepared by acetate and chloride precursors, the nucleation of impurity phases were not properly crystallized. The FTIR analysis confirmed the presence of metal-oxygen bond (M-O), triangular borate (BO3), tetrahedral borate (BO4) and hydroxyl (O–H/B–OH) groups, and thus it helps to form ZnO along with impurity phases. Flower-like morphology along with polyhedral particles was observed for acetate-based sample. In addition, polyhedral and elongated/elliptical shaped particles were found in nitrate and chloride precursor based samples. The Raman spectra suggested the presence of defects such as oxygen vacancy, zinc related defects, and their complexes in all the samples. Emission spectra for all samples exhibit a broad red emission at 613 nm, which corresponds to the electric dipole 5D0→7F2 transition. However, a splitting shoulder peak was significantly observed in the 5D0→7F2 transition for the sample prepared by nitrate precursor, and it was attributed to the existence of impurity phases. Moreover, the impurity phases were not evolved for the sample prepared by chloride and nitrate precursor, and thus the shoulder peak was not considerably noticeable. The presence of impurity phases in nitrate-based samples does not hamper but moderately enhanced the photoluminescence characteristics. The luminescence decay curve was well fitted with the bi-exponential function, and it suggested that the dopant ions have located in two different environments. The quantum yield of acetate-based sample was found to be 3.56%. Further, the results of asymmetric ratio, CIE coordinates and colour purity suggested that the samples can be used in red-emitting indoor lighting application.

The influence of faceted particle shapes on material dynamics in screw conveying

Screw conveyors are widely used in several industries to transport various granular materials needed to manufacture products or components in a product chain. Degradation of the material and variable packing in the screw pitches are some of the significant operational concerns. This paper explores the effect that particle shape has on the material’s behaviour in screw conveyors. Specifically, faceted polyhedral particles are considered and computed on GPUs using the DEM code, Blaze-DEM. Particle shape significantly influences bulk discharge characteristics, in particular, for higher rotation speeds of the screw. Although spheres yield similar bulk discharge rates to symmetric and equiaxed polyhedra at lower rotational speeds, the packing structure and collision dynamics within the screw are shown to be significantly different between the particle shapes. In general polyhedra have a larger fraction of normal impacts between particles and increased abrasion with the screw and enclosing case. On the other hand, spheres have the highest fraction of energy dissipated as shear between particles.

Hierarchical Ni3S2-CoMoSx on the nickel foam as an advanced electrocatalyst for overall water splitting

This work used nickel foam (NF) as a conductive substrate to construct a self-supporting structure catalyst, which exhibited excellent bifunctional catalytic activity for both oxygen evolution reactions (OER) and hydrogen evolution reactions (HER). Through CoMo-MOF and NF sulfuration together, NF surface participates in the reaction and grows uniform needle-shaped Ni3S2 nanorods, while CoMo-MOF transforms into CoMoSx hollow polyhedral particles, which are attached to the surface of Ni3S2 rods and formed Ni3S2-CoMoSx/NF composite. It was found that there is an obvious synergistic effect between CoMoSx, Ni3S2 and NF, thus obtaining excellent catalytic activity for both OER and HER. The overpotential of Ni3S2-CoMoSx/NF catalyst at 10 mA cm−2 is only 234 and 90 mV for HER and OER. In addition, Ni3S2-CoMoSx/NF also exhibits excellent performance in the process of overall water splitting. It can reach 10 mA cm−2 at only 1.52 V and the catalytic performance remain stable for 65 h. Therefore, the self-supporting Ni3S2-CoMoSx/NF can become a highly efficient and long-term durable bifunctional electrocatalyst for overall water splitting.

Numerical modeling for the effects of gravel permeability coefficient based on DEM and CFD method

PurposeThe purpose of this paper is to form a numerical simulation method for permeability coefficient that can consider the characteristics of gravel gradation and further explore the effects of indoor test factors and gradation characteristics on the permeability coefficient of gravel.Design/methodology/approachThe random point method is used to establish the polyhedral gravel particle model, the discrete element method (DEM) is used to construct the gravel permeability test sample with gradation characteristics and the finite element method is used to calculate the permeability coefficient to form a DEM-computational fluid dynamics combined method to simulate the gravel seepage characteristics. Then, verified by the indoor test results. Based on this method, the influence of sample size, treatment method of oversize particles and the content of fine particles on the permeability coefficient of gravel is studied.FindingsFor the gravel containing large particles, the larger size permeameter should be used as far as possible. When the permeameter size is limited, the equal weight substitution method is recommended for the treatment method of oversized particles. Compared with the porosity, the pore connectivity has a higher correlation with the permeability coefficient of the sample.Research limitations/implicationsInsufficient consideration of the movement of gravel particles in the seepage process is also an issue for further study.Originality/valueThe simulation method described in this paper is helpful for qualitative analysis, quantitative expression of pore size and makes up for the defect that the seepage characteristics in pores cannot be observed in laboratory tests.

Controlled regulation of the transformation of carbon nanomaterials under H2 mixture atmosphere by arc plasma

Hydrogen plays a pivotal role in carbon nanomaterials synthesis by arc plasma. However, the effect of hydrogen on morphological regulation of carbon nanomaterials has received little attention. In this paper, carbon nanomaterials synthesized under mixed H2/Ar, H2/N2, and Ar/N2 atmospheres with different ratios were investigated in detail to tackle the issue. Graphene, carbon nanocages, polyhedral graphite particles, amorphous carbon nanoballs, and carbon nanohorns underwent structural transformation as hydrogen content reduced. As a result of varying hydrogen concentration, the number of C-H bond sites at the edge of graphene islands differed, leading to the structural transformation of carbon nanomaterials originating from the formation of various types of precursors. Meanwhile, X-ray photoelectron spectroscopy results revealed that hydrogen impeded nitrogen doping because it tended to bond with electronegative nitrogen. Moreover, morphology control capability followed the order of H2 > N2 > Ar during the preparation of carbon nanomaterials through arc plasma under a mixed atmosphere.

Growth and aggregation micromorphology of natural gas hydrate particles near gas-liquid interface under stirring condition

To investigate the morphological evolution of the whole growth and aggregation processes of hydrate crystals near the gas–liquid interface, we used a high-pressure visual reactor with high-speed camera to capture the micromorphology of hydrate particles in a natural gas + pure water system with pressure from 2.6 to 3.6 MPa and sub-cooling from 4.7 to 6.23 °C. The results showed that under low sub-cooling conditions, the amount and size of particles increased first and then decreased in the range of 0–330 μm, and the small particles always dominated. These particles can be roughly classified into two categories: planar flake particles and polyhedral solid particles. Then, the concept of maximum growth dominant particle size was proposed to distinguish the morphological boundary of growth and aggregation. In addition, the micro model was established to better reflect the effects of particle formation process and evolution mechanism near the gas–liquid interface under stirring condition. The results of this study can provide a guidance for flow assurance in multiphase pipeline.

Inversion of force lines in fiber-reinforced jammed granular material

Freestanding columns, built out of nothing but loose gravel and continuous strings can be stable even at several meters in height and withstand vertical loads high enough to severely fragment grains of the column core. We explain this counter-intuitive behavior through dynamic simulations with polyhedral rigid particles and elastic wire chains. We evaluate the fine structure of the particle contact networks, as well as confining forces and reveal fundamental intrinsic differences to the well-studied case of confining silos.Graphic abstract

DEM investigation of SAG mill with spherical grinding media and non-spherical ore based on polyhedron-sphere contact model

In the ore milling process, the ore particles are usually irregular polyhedrons, and the grinding media are often spherical. The need for accurate simulation of this process calls for a contact algorithm between the polyhedron and sphere, achieving a balance of accuracy, stability, and efficiency. For this purpose, we propose a polyhedron-sphere contact model based on the deepest point method. Experiments and simulation studies by discrete element method (DEM) are conducted to test this model's accuracy in a hexahedral box and a lab-scale horizontal drum with lifters. Then, systematic research is carried out for an industrial semi-automatic grinding (SAG) mill to explore the effect of particle shape. To reveal the advantage over the traditional spherical DEM model, the polyhedron-sphere (PH-SP) grinding system is compared with a pure spherical grinding system. Results are discussed from the motion behavior particles, power consumption, collision energy on ore and liner, and liner wear. The results show that the charging of particles in the PH-SP grinding system is blocked to a certain extent by polyhedral particles, both the power consumption and energy utilization efficiency increase somewhat, the large energy collision between ore and liner has increased significantly. The liner wear of the PH-SP grinding system is more severe than the pure spherical grinding system, which indicates that the new model is necessary for more accurate prediction of the grinding process.

Peridynamics-based discrete element method (PeriDEM) model of granular systems involving breakage of arbitrarily shaped particles

Usage, manipulation, transport, delivery, and mixing of granular or particulate media, comprised of spherical or polyhedral particles, is commonly encountered in industrial sectors of construction (cement and rock fragments), pharmaceutics (tablets), and transportation (ballast). Elucidating particulate media’s behavior in concert with particle attrition (i.e., particle wear and subsequent particle fragmentation) is essential for predicting the performance and increasing the efficiency of engineering systems using such media. Discrete element method (DEM) based techniques can describe the interaction between particles but cannot model intra-particle deformation, especially intra-particle fracture. On the other hand, peridynamics provides the means to account for intra-particle deformation and fracture due to contact forces between particles. The present study proposes a hybrid model referred to as PeriDEM that combines the advantages of peridynamics and DEM. The model parameters can be tuned to achieve desired DEM contact forces, damping effects, and intra-particle stiffness. Two particle impacts and compressive behavior of multi-particle systems are thoroughly investigated. The model can account for any arbitrarily shaped particle in general. Spherical, hexagonal, and non-convex particle shapes are simulated in the present study. The effect of mesh resolution on intra-particle peridynamics is explicitly studied. The proposed hybrid model opens a new avenue to explore the complicated interactions encountered in discrete particle dynamics that involve the formation of force chains, particle interlocking, particle attrition, wear, and the eventual breakage.

Phase-field simulation of γʹ coarsening behavior in cobalt-based superalloy

Because the microstructure characteristics of γʹ strengthened cobalt-based superalloys are critical for anticipated next generation superalloys, the morphological evolution and coarsening behavior of γʹ precipitates during isothermal aging in Co-Al-W ternary alloys are investigated using the phase-field method. Accurate γʹ evolution over the entire aging process is simulated through coupling with the antiphase domain and the elastic energy. With a change in γʹ volume fraction from 38% to 66%, the coarsening rate of γʹ precipitates shows an approximately linear increase, primarily due to the increased diffusion potential difference between the γ matrix and γʹ precipitate. The coalescence between adjacent precipitates is promoted in the high γʹ volume fraction, resulting in polyhedral precipitates and particle size distribution (PSD), which agrees with MLSW theory. The morphology transition mechanism of γʹ is showed through the evolutions of interfacial energy and elastic energy, and the effects of microstructure features on the coarsening rate and coarsening mode are discussed. Results of this study provide guidance for the development of Co-based superalloys with optimized microstructures.

Tailoring pore structures and morphologies of highly ordered cubic mesoporous silica prepared in mild conditions: the effects of reaction parameters

In this study, we report on a novel and reactive synthesis of highly ordered cubic mesoporous silica that is able to tailor different symmetries of pores and morphologies through a two-step procedure carried out in relatively low temperatures (20–60 °C) using a single type of surfactant. We systematically examined the effects of reaction parameters such as pH, times of hydrolysis and condensation, concentration of Pluronic F-127 surfactant, and aging temperature, by using characterization techniques such as small-angle X-ray scattering (SAXS), analysis of surface area and porosity by adsorption of N2 (BET isotherms), and scanning and transmission electron microscopy (SEM and TEM). Our investigations found that, at 20 °C, the shape of particles is sensitive to changes in surfactant concentration which means that it is possible to tune spherical to polyhedral particles by simply increasing the amount of surfactant. In addition, at low concentrations of F-127, the size of the particles is temperature-dependent, with an inversely proportional pattern of behavior. The protocol also enables the production of well-ordered pores, particularly with 3D-cubic symmetries Fm3m and Im3m, and some hexagonal, as well as to control the sizes of the pores.

Multisphere Representation of Convex Polyhedral Particles for DEM Simulation

The representation of particles of complex shapes is one of the key challenges of numerical simulations based on the discrete element method (DEM). A novel algorithm has been developed by the authors to accurately represent 2D arbitrary particles for DEM modelling. In this paper, the algorithm is extended from 2D to 3D to model convex polyhedral particles based on multisphere methods, which includes three steps: the placement of spheres at the corners, along the edges, and on the facets in sequence. To give a good representation of a polyhedral particle, the spheres are placed tangent to the particle surface in each step. All spheres placed in the three steps are clumped together into a clump in DEM. In addition, the mass properties of the clump are determined based on the corresponding polyhedral particle to obtain accurate simulation results. Finally, an example is used to validate the robust and automatic performance of the algorithm in generating a sphere clump model for an assembly of polyhedral particles. A current FORTRAN version of the algorithm is available by contacting the authors.

Preparation of the regular polyhedral single-crystalline SrTiO3 particles with exposing different crystal facets

Strontium titanate (SrTiO3) has risen and drawn more and more attention of the researchers duo to its excellent photocatalytic activity based on the anisotropic charge transport theory. In this work, we first produced the regular polyhedral single-crystalline SrTiO3 particles with multiple crystal facets exposing include the {100}, {110} and {111} by one-step hydrothermal method. This SrTiO3 exhibited improved photocatalytic activity compared with that only exposing {100} crystal facet. Simultaneously, the SrTiO3 crystal growing process had been discussed. The single-crystalline SrTiO3 particles may provide a new basic material for the SrTiO3 application in photocatalysis.

Spinel type Fe3O4 polyhedron supported on nickel foam as an electrocatalyst for water oxidation reaction

An efficient, cost-effective, and more readily available electrocatalysts that can lower the overpotential associated with oxygen evolution reaction (OER) is a prerequisite for the application of water splitting for hydrogen production at a larger scale. Herein, we demonstrate a composite electrode obtained by anchoring polyhedral Fe3O4 particles on nickel foam (NF) is a highly active catalyst for OER. Notably, this catalyst was able to achieve a current density of 10 mA cm−2 and 100 mA cm−2 at a low overpotential of 251 and 310 mV. Also, Fe3O4-NF displayed a low Tafel slope of 45 mV dec−1. Moreover, at an overpotential of 300 mV Fe3O4-NF showed a turnover frequency (TOF) of 3.12 × 10−3 s−1 suggesting that Fe3O4-NF has a high intrinsic catalytic activity which is on par with commercial RuO2 catalyst. Furthermore, due to the close contact and strong adhesion between Fe3O4 and NF, the Fe3O4-NF displayed good stability during OER. The post-activity characterizations indicate that iron oxyhydroxide (Fe(O)OH) formed due to in-situ oxidation of Fe3O4 surface functions as the active catalytic phase whereas, bulk of the catalyst acts as a conducting scaffold.

Independence of shear strength with particle size dispersity still valid in polyhedral particle assemblies

A very staggering result that has been constantly highlighted in granular media is that the shear strength of granular assemblies is independent of the particle size dispersity. In other words, a packing composed of monodisperse particles has similar strength properties to those of polydisperse systems. This has been shown numerically for the simplified case of disc and polygon assemblies in 2D and spheres in 3D. In this paper, we use three-dimensional contact dynamics simulations to revisit these results for the more complex case of assemblies composed of highly polydisperse rigid polyhedra. Although non-spherical shapes induce more intricated spatial correlations than spherical shapes because of the multiple contact types (i.e., vertex-face, edge-edge, edge-face, face-face), our numerical data provide evidence that the shear strength independence as the particle size dispersity increases still holds up for assemblies of polyhedra. We explain this finding from compensation mechanisms at the micro-scale between geometrical and mechanical anisotropies developed within the assemblies.