Distribution Of Primary Particles Research Articles

Collision frequencies across collision regimes in two-component systems

Agglomeration is the most important growth process in particle systems but modelling efforts typically assume mono-disperse primary particle distributions for the closure of the collision frequency that determines the growth rates. Real systems such as sooting flames, however, involve poly-disperse primary particle distributions. Also, systems with multiple components, where primary particles are of distinct but different sizes, cannot be treated as mono-disperse. Here, we introduce bi-disperse primary particle distributions and use Langevin dynamics simulations to develop closures for the collision kernels that are applicable over a wide range of agglomerate characteristics. The simulations cover fractal dimensions from 1.4 to 2.2, primary particle diameters from 5 nm to 50 nm, primary particle size ratios from 2 to 10 and agglomerates of up to a size of 200 primary particles with varying particle compositions. The Langevin dynamics simulations cover all collision regimes from ballistic to diffusive and allow to deduce expressions for the respective collision diameters, the hydrodynamic radii and the projected area as functions of particle characteristics. It is shown that existing expressions for the transition regime that were developed for the modelling of the collision kernel of spherical particles continue to hold for collision kernels of agglomerates in two-component systems under the condition that the collision diameters and drag coefficients are modelled accurately. An example ‘a posteriori’ simulation for a particle size ratio of 6 uses the population balance equation and demonstrates that bi-variate kernels are needed for the accurate prediction of the growth rates. Errors in predicted number density at the end of the simulations are less than 12 % while mono-variate kernels developed for mono-disperse primary particle systems overpredict the growth rate by 46%.

A phenomenological model for predicting the size of soot primary particles emitted from an aero-engine combustor

Soot particles emitted from aero-engines are harmful to airport local air quality, and the adverse impact from soot particles is closely related to particle morphology, microstructure and chemical properties. To understand those properties of aviation soot particles, combustion experiments using conventional aviation fuel RP-3 were conducted on a Rich-Burn/Quick-Quench/Lean-Burn (RQL) aero-engine combustor. The soot emissions from the RQL combustor were analyzed via a high resolution transmission electron microscope (HRTEM), and the size distributions of primary particles at different power levels were determined based on the HRTEM images. Since the primary particle size is strongly related to the power level and follows an S-shaped curve, a phenomenological model with low-computational complexity and general applicability was established. Furthermore, the model was validated by using previously published experimental data of a CFM56–2C1 aero-engine burning four different fuels, including sustainable aviation fuels (SAF), demonstrating the influence of fuel properties on primary particle sizes at different power levels.Novelty and Significance Statement: In this paper, combustion experiments were conducted on an RQL combustor burning RP-3 fuel. Based on the HRTEM observation, the log-normal size distributions of primary particles at different power levels were determined. Furthermore, based on the fact that the relationship between primary particle size and power level followed an S-shaped curve, a phenomenological model linking primary particle size and combustor power was proposed and validated.

Modelling the formation, growth and coagulation of soot in a combustion system using a 2-D population balance model

A 2-D population balance model utilizing carbon mass and surface sites as internal variables was developed for soot formation during hydrocarbon decomposition reactions. The model provides particle properties such as composition and mean polyaromatic hydrocarbon size, enabling the incorporation of cyclization reactions, soot maturation, and a dynamic model of surface reactions. Accompanied by a reduced kinetic model for gas-phase species, this population balance model was then discretized using the fixed-pivot method, to provide predictions of the soot distribution as a function of position within a plug flow reactor. The model predictions of the particle size distribution functions resulting from high-temperature hydrocarbon pyrolysis within a PFTR system provide good comparison with experimental measurements under a variety of conditions. In addition to this, by tracking the changes in particle composition occurring through cyclization reactions, the point of carbon particle maturity could be determined, allowing subsequent predictions of the size distributions of the primary particles comprising soot aggregates. Through comparison with TEM and SEM imaging, these primary particle distributions were found to be accurate for the experimental conditions examined. While the implementation of the second internal variable describing particle composition was not found to provide substantial improvements to the prediction of the overall aggregate distribution from existing models, the additional computational cost that accompanies additional variables is justified in applications where morphological predictions of particle aggregates are of interest, in addition to their size distribution.

Characterization of Fractal Structures by Spray Flame Synthesis Using X-ray Scattering.

In this work, we take on an in-depth characterization of the complex particle structures made by spray flame synthesis. Because of the resulting hierarchical aggregates, very few measurement techniques are available to analyze their primary particle and fractal properties. Therefore, we use small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) to investigate the influence of the precursor concentration on the fractal structures of zirconia nanoparticles. The combination of information gained from these measurement results leads to a detailed description of the particle system, including the polydispersity and size distribution of the primary particles. Based on our findings, unstable process conditions could be identified at low precursor concentrations resulting in the broadest size distribution of primary particles with rough surfaces. Higher precursor concentrations lead to reproducible primary particle sizes almost independent of the initial precursor concentration. Regarding the fractal properties, the typical shape of aggregates for aerosols is present for the investigated range of precursor concentrations. In conclusion, the consistent results for SAXS and TEM show a conclusive characterization of a complex particle system, allowing for the identification of the underlying particle formation mechanism.

Some control mechanisms of spatial solidification in light alloys

Abstract Two unconventional approaches of controlling the size and distribution of primary particles in aluminium and magnesium alloys are suggested. The first approach uses the ultrasonic cavitation treatment for multiplication of solidification sites for primary crystals by activating catalytic impurities that are present in the melt. The second way, on the contrary, involves elimination of active solidification nuclei by melt overheating with subsequent nucleation of primary particles at a higher undercooling. Both approaches result in refinement of primary crystals.

Investigation of Proton Beam-Driven Fusion Reactions Generated by an Ultra-Short Petawatt-Scale Laser Pulse

We present results from a pitcher-catcher experiment utilizing a proton beam generated with nanostructured targets at a petawatt-class, short-pulse laser facility to induce proton-boron fusion reactions in a secondary target. A 45-fs laser pulse with either 400 nm wavelength and 7 J energy, or 800 nm and 14 J, and an intensity of up to 5 × 1021 W/cm2 was used to irradiate either thin foil targets or near-solid density, nanostructured targets made of boron nitride (BN) nanotubes. In particular, for 800 nm wavelength irradiation, a BN nanotube target created a proton beam with about five times higher maximum energy and about ten times more protons than a foil target. This proton beam was used to irradiate a thick plate made of boron nitride placed in close proximity to trigger 11B (p, α) 2α fusion reactions. A suite of diagnostics consisting of Thomson parabola ion spectrometers, postshot nuclear activation measurements, neutron time-of-flight detectors, and differentially filtered solid-state nuclear track detectors were used to measure both the primary proton spectrum and the fusion products. From the primary proton spectrum, we calculated (p, n) and (α,n) reactions in the catcher and compare with our measurements. The nuclear activation results agree quantitatively and neutron signals agree qualitatively with the calculations, giving confidence that primary particle distributions can be obtained from such measurements. These results provide new insights for measuring the ion distributions inside of proton-boron fusion targets.

Characteristic of TiO2&Ag0 nanocomposites formed via transformation of metatitanic acid and titanium (IV) isopropoxide

Composite nanoparticles TiO2&Ag0 were synthesized by coprecipitationin a weakly alkaline medium in the presence of various precursors - metatitanic acid and titanium (IV) isopropoxide. Comparative study of TiO2&Ag0 included analysis of morphology (SEM), phase (XRD) and chemical compositions (EDS). The formation of anatase structures was confirmed at a relatively low concentration of silver (0–8 wt% for metatitanic acid and 0–4 wt% for Ti (IV) isopropoxide). An increase in the Ag fraction to 8 wt% led to the appearance of the Ti2O3 and β-TiO2 phases in the Ti(IV) isopropoxide system. The size distribution of primary particles is 8.3–10.6 nm (Ti(IV) isopropoxide system) and 12.3–14.0 nm (metatitanic acid system). The anatase lattice parameters decrease with Ag wt% increasing in Ti(IV) isopropoxide system and do not change for the metatitanic acid system. TG-DTA study showed the effects corresponding to the removal of structural water (210 °C), destruction of isopropoxide and combustion of organic matter (300–410 °C), crystallization of anatase (510 °C) and the anatase transformation into the rutile phase (720–760 °C), but in the presence silver, the anatase structure did not change to 1000 °C. Morphological study shows high crystallinity of both kinds of structures but less aggregative stability composites formed in the metatitanic acid solution. All type nanocomposites include four chemical elements – Ti, Ag, O, and Na as well as a small number of various admixtures - S or Cl and K depending on precursor species. At the same time, a relatively high concentration of argentum in the initial solution led to obtaining chemically pure composite nanoparticlesandcore&shell type structures.

Neutrino production in Population III microquasars

Microquasars (MQs) are binary systems composed by a star feeding mass to a compact object through an accretion disk. The compact object, usually a black hole, launches oppositely directed jets which are typically observed in our galaxy through their broadband electromagnetic emission. These jets are considered potential galactic neutrino sources. MQs can also have been formed by the first generations of stars in the universe, i.e., Population III (Pop III) stars, which are considered essential contributors to the ionization processes that took place during the period of ãcosmic reionizationå. In the present work, we develop a model that accounts for the main particle processes occurring within Pop III MQ jets, with the aim to obtain the diffuse neutrino flux at the Earth. We define different zones within the jets of Pop III MQs where particle interactions occur, and primary particles (i.e protons and electrons) are injected. We solve a transport equation for each zone, including the relevant cooling and escape processes, which include pγ and pp interactions. Once we obtain the primary particle distributions, we compute the pion and muon distributions, as well as the neutrino output produced by their decays. Finally, we obtain the diffuse neutrino flux by integration over the redshift, the line-of-sight angle, and the MQs lifetime. We find that, for a range of parameters suitable for Pop III MQ jets, the most relevant site for neutrino production in the jets is the base of the inner conical jet. Additionally, if protons accelerated at the forward shock formed at terminal jet region can escape from the outer shell, they would produce further neutrinos via pγ interactions with the cosmic microwave background (CMB). The latter contribution to the diffuse neutrino flux turns out to be dominant in the range 107GeV≲Eν≲109GeV, while the neutrinos produced in the inner jet could only account for a small fraction of the IceCube flux for Eν∼105 GeV. The co-produced multiwavelength photon background is also computed and it is checked to be in agreement with observations.

A review of contact force models between nanoparticles in agglomerates, aggregates, and films

A desire to optimise the production and performance of nanoparticle structured materials has driven the development of increasingly accurate and fundamental models that describe their underlying physical and chemical mechanisms of interaction. In processes where particles form by nucleation and growth, such as aerosol synthesis processes, the primary nanoparticles can form complex assemblies referred to as aggregates, agglomerates and particle films. These materials typically consist of a distribution of primary particles in the nanoscale range (5–50 nm) which form chemically bonded aggregates (typical size range 200–300 nm) during their production. Aggregates in turn form larger structures called agglomerates which are held together by weaker forces arising from electrostatics, van der Waals, solvation or capillary effects. Extended particle assemblies with thicknesses in the order of 1–50 μm over substrate areas of the order of several square centimetre are referred to as particle films. These systems present a particularly challenging modelling problem due to their multiscale nature. Many classical models hold on the mesoscale and macroscale, while on the primary particle level many continuum laws break down and new contact models are required. In these particle-particle contact models, ambient conditions such as humidity have a large effect on the long-range capillary and solvation forces and thus on the final structure of the materials. This publication reviews the work that has been conducted in deducing the discrete physical laws that govern particle-particle contacts as well as their use in practical industrial processes and applications.

Nanostructural and morphological characteristics of single soot aggregates during low-temperature oxidation

In this paper the evolution of morphological and nanostructural properties of soot primary particles during low-temperature oxidation with oxygen is presented. Soot primary particles and aggregates from three soot samples with varying morphological and nanostructural initial properties were investigated by high-resolution transmission electron microscopy (HRTEM) at consecutive steps of oxidation. Soot samples were deposited on a TEM grid and then oxidized repetitively. After each oxidation step labelled identical aggregates were scanned and reanalyzed by HRTEM. Size distributions of primary particles and their nanostructure was tracked using an image analysis algorithm. The oxidation conditions (temperature 850 K, O2 concentration 5% by volume) correspond to those of the real application, e.g. for regeneration of particle filters.The tracking of different aggregates revealed that the morphological changes of the primary particles are determined by the predominant oxidation mode, which is governed by the nanostructure of the primary particles. Extended graphene layers favor internal oxidation, while bent, short and reactive layers favor both, external and internal oxidation. In surface oxidation mode, primary particles do not shrink homogeneously, but rather form a blackberry-like cluster of smallest nucleated particles.While a partly expansion of graphene layers is detected in the early stages of oxidation, the number density of graphene layers gradually decreases with increasing oxidation time. Additionally, graphene layers are oxidized by fragmentation until final degradation. Tracking of selected primary particles at different positions within the aggregate brought about that each primary particle is subjected to its own oxidation history. Therefore, each observed and analyzed primary particle possibly exhibits a different oxidation stage at the same oxidation time.

Advanced Porous Electrode Modelling Framework Based on More Consistent Virtual Representation of the Electrode Topology

The paper proposes an advanced continuum level modelling framework characterized by a more consistent virtual representation of electrode topology to enhance prediction capability and generality of porous electrode theory based models. The proposed modelling framework, therefore, establishes the missing link between the mesoscopic scale with a detailed 3D representation of electrode topology and the continuum single cell scale, where interrelation to the real electrode topology was missing. This link is established by elaborating a unified approach for modelling materials with significantly different topologies of active material by virtually creating agglomerates, representing secondary particles, from primary particles. Proposed approach relies on multi-particle size distribution of primary particles and particle-to-particle connectivity. Generality of the proposed modelling framework is demonstrated by simulating LFP and NMC materials featuring significantly different electrode topologies by the same modelling framework while adapting only virtual representation of electrode topologies and intrinsic material properties. Credibility of the proposed modelling framework is confirmed through good agreement with experimental results for various discharge tests. Insightful simulation results also reveal background of the topologically driven low Li utilization at high current densities of the LFP material and topologically driven voltage response difference during the memory effect of different LFP materials.

Effect of high hydrostatic pressure on formation and rheological properties of inulin gels

The aim of the study was to determine the possibility of using high hydrostatic pressure (HHP) for induction of inulin gels and to compare properties of the obtained gels with gels induced traditionally by thermal or shear force treatment. HHP (500 MPa) induced inulin gelation regardless of the time treatment (5–20 min) and inulin concertation (20–25 g/100 g). Obtained by HHP gels differ from traditional gels, had different microstructure and distribution of primary particles. In consequences HHP gels, comparing with thermally and mechanically induced ones, were less firm and spreadable and were characterized by a higher yield stress and lower L* colour parameter. Those properties may allow using inulin gels for creating new, innovative products, than those made with traditionally induced inulin gels. It was also found that exposure time to HHP was not deteriorating physical properties of inulin gels, what gives opportunity to preserved product with inulin gels by HHP.

General method of specimen preparation for the quantitative microscopic characterization of nano- and microparticles

Nano-materials are a subject of current research and development due to their special characteristics, based on the size of their constituent particles. A major hurdle is the reliable analysis of the particle size and particle size distribution. This article introduces a new method of specimen preparation for the quantitative analysis of particle systems. Selected examples show the capabilities of computer-assisted image analysis of microscopic images. The problem of agglomeration and aggregation of primary particles is discussed and a strategy for calculating the primary particle distribution based on a mathematical model is presented. The successful, highly controlled deposition of deagglomerated nanoparticles on a microscope carrier enables a reliable particle size distribution measurement, even with strong interacting nanoparticles.

Particle-Size, Microaggregate-Size, and Aggregate-Size Distributions in Humus Horizons of the Zonal Sequence of Soils in European Russia

Experimental data on size distribution of micro- and macroaggregates and primary soil particles were obtained by laser diffraction analysis of the samples of humus horizons of the zonal soil sequence (from Retisols to Kastanozems) in European Russia. Both undisturbed native soils and agricultural soils were analyzed. The relationships between the parameters of the size distribution of aggregates, microaggregates, and primary particles were valuated. The parameters of the size distribution (content of the particles and their mean-weight diameter) were compared with data on the contents of water-stable aggregates, organic carbon, nitrogen, phosphorus, potassium, and pH. Size distribution of primary particles in the humus horizons of Endocalcic Chernozems had a bimodal pattern. A positive linear correlation between the contents of microaggregates and organic carbon was found to occur only when the latter exceeded 2–3%. An index of the size distribution of microaggregates—the minimum size of stable microaggregates—was proposed; it can be determined as an intersection point of differential curves of size distribution of microaggregates and primary particles. For this index, a negative correlation with the soil pH was found. It was supposed that the observed correlation reflects the coagulation of soil colloids, when their electric charge is compensated.

Hierarchically Structured Core-Shell Design of a Lithium Transition-Metal Oxide Cathode Material for Excellent Electrochemical Performance.

Tuning geometrical parameters of lithium-mixed transition-metal oxide (LiTM) cathode materials is a promising strategy for resource-efficient design of high-performance Li-ion batteries. In this paper, we demonstrate that simple and facile geometrical tailoring of the secondary microstructure of LiTM cathode materials without complex chemical modification or heterostructure engineering can significantly improve overall electrochemical performance of the active cathode materials. An optimized LiTM with a bimodal size distribution of primary particles inside the secondary particles exhibits a 53.8% increase in capacity at a high discharge rate (10 C) compared to a commerciallyavailable reference and comparable rate capability after 100charge/discharge cycles. The key concept of this approach is to maximize the beneficial effects arising from the controlled sizes of primary particles. Multimodal/multiscale microscopic characterizations based on electron tomography and scanning transmission electron microscopy, combined with electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy from the atomic level to the microscale level, were employed to elucidate structural origins of enhanced battery performance. This study paves the way for the resource-efficient microstructure design of LiTM cathode materials to maximize capacity and stability via simple adjustment of processing conditions, which is advantageous for mass-production applications.

Spatial morphology of maltodextrin agglomerates from X-ray microtomographic data: Real structure evaluation vs. spherical primary particle model

The morphology of agglomerates has been investigated mainly by approximating constituent primary particles with equivalent spheres. However, this simplified spherical primary particle model (SPPM) is questionable, because most agglomerates in food, pharmaceutical and chemical industry are made of irregularly shaped primary particles. Therefore, in the present work the SPPM is compared with a model that is based on complete data of the real structure (real structure model, RSM). Individual agglomerates of different sizes, produced from maltodextrin powder in a spray fluidized bed, have been scanned in an X-ray microtomographic device. After a series of image processing steps, the data has been used to derive various 3D morphological descriptors (such as coordination number, coordination angle, radial distribution of primary particles and open porosity) by both the SPPM and the RSM. The results of the two models delineate noticeable differences, indicating that the SPPM may not provide a precise characterization of maltodextrin agglomerates. Therefore, the RSM is the more appropriate method to study the morphology of agglomerates that consist of soft and deformable primary particles of varying size and irregular shape.

The Influence of Casting Methods on Microstructure of Al-Mg-Sc-Zr Alloy

Two methods of fabrication of Al-Mg-Sc alloy are compared - conventional casting followed by cold-rolling and twin-roll casting. To the advantages of twin-roll casting belong the lower material and energy requirements during the production. However, twin-roll cast material exhibits different initial microstructure and routes established for conventionally cast materials cannot be applied. In twin-roll cast material the distribution of primary particles is more inhomogeneous - they form segregation near the center and edges of the sheet and their average size is smaller. On the contrary, the average sub-grain size is much higher in the twin-roll cast material.

Oxidation Activity Restoration of Diesel Particulate Matter by Aging in Air

Diesel particulate matter (PM) was collected at different tailpipe positions where the sampling temperature was different. The PM samples were pre-treated in air at high temperature until 40% mass loss. Then, the partially oxidized PM samples were aged in air for 40 days, and the physicochemical properties of partially oxidized PM before and after aging in air were tested. The results showed that the oxidation activity of partially oxidized PM was appreciably restored by aging in air. The morphology, diameter distribution of primary particles and nanostructures of partially oxidized PM changed slightly after aging in air. The amorphous carbon adsorbing on PM surface were faintly observed through high resolution transmission electron microscope (HRTEM) images. The adsorption of oxygen-containing functional groups (carbonyl and hydroxy) and organic compounds were evidenced through Fourier transform infrared spectroscopy (FTIR) and Raman parameter AD3/AG. The crystallite size calculated using Raman parameter decreased slightly after aging in air.

Disorientation angle distribution of primary particles in potash alum aggregates

In order to fully characterize crystal aggregates, the orientation of primary particles has to be analyzed. A procedure for extracting this information from three-dimensional microcomputed tomography (μCT) images was recently published by our group. We here extend this method for asymmetrical crystals and apply it for studying the disorientation angle distribution of four potash alum crystal samples that were obtained under various experimental conditions. The results show that for all considered supersaturation profiles, primary particle pairs tend to have the same orientation significantly more often than in theoretical considerations, in which the orientations of primary particles are assumed to be distributed randomly.

Effect of lubricant sulfur on the morphology and elemental composition of diesel exhaust particles

This work investigates the effects of lubricant sulfur contents on the morphology, nanostructure, size distribution and elemental composition of diesel exhaust particle on a light-duty diesel engine. Three kinds of lubricant (LS-oil, MS-oil and HS-oil, all of which have different sulfur contents: 0.182%, 0.583% and 1.06%, respectively) were used in this study. The morphologies and nanostructures of exhaust particles were analyzed using high-resolution transmission electron microscopy (TEM). Size distributions of primary particles were determined through advanced image-processing software. Elemental compositions of exhaust particles were obtained through X-ray energy dispersive spectroscopy (EDS). Results show that as lubricant sulfur contents increase, the macroscopic structure of diesel exhaust particles turn from chain-like to a more complex agglomerate. The inner cores of the core-shell structure belonging to these primary particles change little; the shell thickness decreases, and the spacing of carbon layer gradually descends, and amorphous materials that attached onto outer carbon layer of primary particles increase. Size distributions of primary particles present a unimodal and normal distribution, and higher sulfur contents lead to larger size primary particles. The sulfur content in lubricants directly affects the chemical composition in the particles. The content of C (carbon) decreases as sulfur increases in the lubricants, while the contents of O (oxygen), S (sulfur) and trace elements (including S, Si (silicon), Fe (ferrum), P (phosphorus), Ca (calcium), Zn (zinc), Mg (magnesium), Cl (chlorine) and Ni (nickel)) all increase in particles.