Bimodal Particle Size Distribution Research Articles

Sensitivities of Spectral Optical Properties of Dust Aerosols to Their Mineralogical and Microphysical Properties

AbstractDust aerosol is a key component in global radiative forcing and climate modeling. We developed a mineralogy‐resolved spectral optical property model for dust aerosols. The model incorporates nine mineral groups and applies the effective medium methods to obtain the spectral complex refractive indices of inhomogeneous dust particles. This study considers 5,000 sets of dust mineral composition mixtures along with the use of the bimodal particle size distribution. We calculate the bulk properties of these samples in a wide spectral range from 0.2 to 50 μm using a comprehensive database of hexahedral dust single‐scattering properties. Through sensitivity analyses, this study reveals that the illite and hematite components substantially affect the optical properties of dust. Furthermore, the effective radii of both the fine‐mode and the coarse‐mode dust particles have significant impacts on the bulk optical properties, albeit to varying degrees.

Measurement and Analysis of Brake and Tyre Particle Emissions from Automotive Series Components for High-Load Driving Tests on a Wheel and Suspension Test Bed

A current challenge in realising clean road transport is non-exhaust emissions. Important advances regarding measurement systems, including well-defined characterisation techniques, as well as regulation, will be made in the next few years. In this work, we present the detailed results of particle emission analyses, consisting of aerosol (size distribution, particle number (PN), and mass (PM)) and electron microscopy (EM) measurements, under different load conditions on a test bed for a wheel suspension and brakes. Standard tyres and brakes from serial production were tested with a high-load driving cycle, while particle measurements were conducted by gravimetric measurements and with a TSI SMPS, a TSI APS, and a GRIMM OPS. Furthermore, samples were analysed by electron microscopy. A bimodal particle size distribution (PSD) was obtained with an SMPS, with peaks at 20 nm and around 400 nm. The results of an EM analysis of >1400 single particles from the electrostatic sampler match the PSD results. The EM analysis also showed ultrafine particles, mainly containing O, Fe, Si, Ba, Mg, and S, and also fractal particles with high-C fractions. Our results suggest, in agreement with the previously published literature, that particulate emissions are related to the brake disc temperature and occur in significant amounts above a threshold temperature.

Innovative ceramic paste for stereolithography additive manufacturing alumina core applied in turbine blade casting

AbstractCeramic stereolithography 3D printing technology has demonstrated great potential in alumina core manufacturing for advanced turbine blade casting. However, there have been very few photosensitive material formulas specifically designed for alumina core fabrications. Herein, we present the design of a 3D printable ceramic paste based on bimodal particle size distributions for additive manufacturing of high‐quality alumina cores. The coarse particles in the paste remain in their original shape while the fine particles transform into platelet‐like particles during sintering. The effects of coarse particles, platelet‐like particles, and grain growth on maintaining porosity and limiting shrinkage rates are studied. Furthermore, the vacuum sintering process is found to be beneficial for core material properties. The physical properties tests verify that the newly designed alumina paste in this work can meet the application requirement, which is superior to the previous research.

The role of fines in espresso extraction dynamics

The impact of particle size distribution of coffee grounds on espresso extraction was explored. Finely ground coffee for espresso has a characteristically bimodal particle size distribution. For a given median grind size, different grinding technologies can yield a different share of fines (particles < 100 µm). We performed espresso extractions for a range of median particle sizes and systematically varying the share of fines by adding sieved fines to the coffee grounds. Dynamic beverage weights, extraction percentage, extraction time and dynamic headspace PTR-MS (proton-transfer mass spectrometer) analysis and sensory evaluation of the resulting brews were measured. We show that the share of fines plays a key role in the espresso extraction flow rate. An increase of share of fines decreases coffee bed permeability, leads to reduced flow rates and longer extraction times. A statistical model using partial least squares regression of the particle size distributions of coffee grounds confirms that fines decrease the coffee bed permeability. The PTR-MS analysis shows a non-linear increase of aroma compounds in the cup with increasing extraction yield. Our hypothesis is that both extraction efficiency and post-extraction evaporative losses of aroma compounds influence the final aroma compound concentrations in the cup.

Abnormal grain growth of tetragonal tungsten bronze structured ferroelectric ceramics

Microstructures of tetragonal tungsten bronze-structured ferroelectric ceramics vary owing to abnormal grain growth. Control of the grain microstructure stability is a critical aspect in the electrical properties. In this study, the grain growth behavior was meticulously explored through a combination of experiments and numerical simulations. Effects of the liquid phase and initial particle-size distribution on the microstructural evolution were investigated under different grain boundary energy anisotropy conditions. The grain area and edge number were calculated to investigate the grain growth kinetics and shape variation. The results revealed that the presence of a large amount of the liquid phase contributed to rapid grain growth and a duplex structure formation. The grain-size inhomogeneity can be eliminated by using initial particles with a bimodal particle-size distribution. The grain shape was mainly determined by the degree of anisotropy of the grain boundary energy and was nearly unaffected by the process parameters. The findings of this study afford theoretical guidance for microstructure regulation and stable preparation of high-performance ferroelectric ceramics.

Important roles of coarse particles in pasting and gelling performance of different pulse flours under high-temperature heating

Dehulled pea, lentil, and faba bean grains were milled into flours with 0.5- to 2.5-mm sieves. As the particle size decreased, damaged-starch contents of the flours from the same pulse crop increased. At a holding temperature of 95 °C in RVA, peak and final viscosities and gelling ability of the flours generally increased as the particle size decreased. When the holding temperature increased from 95 to 140 °C, pasting viscosities of pea and lentil flours and gel hardness of lentil flours gradually decreased. In contrast, pasting viscosities and gel hardness of faba bean flours reached the highest values at 120 °C. The comparison of the pulse flours varying in particle size across the three market classes revealed that coarse particles comprising agglomerated starch, protein, and dietary fiber (i.e., particles of the second peak in the bimodal particle-size distribution curves) showed significant correlations with certain important functional properties of pulse flours.

Influence of particle size gradation on the preparation of highly concentrated coal-water slurry and the development of a gradation model

ABSTRACT Aiming at the problem that low-rank coal is unsuitable for making CWS (coal-water slurry) and lacks an accurate particle size gradation prediction model. This paper expounds on the effects of ball milling time and speed on the concentration and rheology of CWS under different grinding conditions. After size grading, the slurry’s bimodal parameters and particle size distribution are studied. Based on the BP neural network, a particle size distribution model more suitable for low-rank coal is established in this paper. The results show that the slurry concentration in the graded coal sample increases by 4% higher than that of the ungraded coal sample. The BP neural network model accurately predicts the relationship between bimodal parameters and slurry concentration based on bimodal parameters. In the context of grain size gradation, the optimized particle size cumulative distribution model, denoted as y = x n − x K n x 100 n − x K n + K { ( K + 10 % > x > K% } , demonstrates enhanced alignment with the attributes of low-rank coal. This underscores the paper’s contribution in providing a more fitting particle size distribution model for low-rank coal in the context of CWS production.

Bi-modal particle size distribution for high energy product hybrid Nd–Fe–B—Sm–Fe–N bonded magnets

In this work, we have demonstrated high energy product bonded magnet by leveraging the variation in sizes between Nd-Fe-B and Sm-Fe-N, as well as their hard magnetic properties. The hybrid anisotropic bonded magnets contain 70 vol% of magnet powder (Dy-free Nd-Fe-B and Sm-Fe-N) and 30 vol% of nylon. The objective of the work was to create bi-modal and bi-compositional bonded magnets in which the fine (3μm) particles of Sm-Fe-N would be used to fill the voids between the bigger Nd-Fe-B (105μm) particles, thus improve packing density. The magnetic hysteresis loop did not show significant signs of decoupled interactions between the magnetic phases. It was also found that the performance of the bonded magnet was most enhanced at 1:4 ratio of Nd-Fe-B and Sm-Fe-N. At that ratio, maximum density of 5 g/cm3 and the highest (BH)max value of 18.5 MGOe were obtained, although the intrinsic coercivity decreased, relative to the trend seen for other ratios. This work advances the opportunity to expand the use of Sm-Fe-N in bonded magnet applications.

Microstructural and magnetic properties of BiFeO3/Bi2Fe4O9 binary nanoparticles with a bimodal size distribution

Binary nanoparticles composed of BiFeO3 and Bi2Fe4O9 have attracted considerable interest due to their magnetic properties and exchange bias effect. In this paper, two samples of well-crystallized BiFeO3/Bi2Fe4O9 binary nanoparticles with varying compositions, containing approximately 3 % and 32 % of the Bi2Fe4O9 crystalline phase, were investigated to understand the impact of microstructural variations on the magnetic behavior of the samples. Both BiFeO3 and Bi2Fe4O9 phases of binary nanoparticles were synthesized in the same synthesis process by calcining amorphous precursors obtained after solvent evaporation from aqueous solutions containing iron and bismuth nitrates and tartaric acid. The identification and quantification of crystalline phases of the produced samples were performed using the X-ray diffraction technique and multiphase Rietveld refinement, respectively. The structure and microstructures of the synthesized BiFeO3/Bi2Fe4O9 nanoparticles were carried out using transmission electron microscopy techniques. The atomic composition of the samples was investigated by energy-dispersive X-ray. The magnetic properties were studied by the DC magnetization technique. Transmission electron microscopy analyses showed that both samples exhibit a bimodal particle size distribution, with average particle sizes of ∼ 116 nm and ∼ 6.5 nm for the ∼ 3 % Bi2Fe4O9 sample. In contrast, for the ∼ 32 % Bi2Fe4O9 sample the average particle sizes were ∼ 108 nm and ∼ 7 nm, respectively. Energy-dispersive X-ray analyses revealed a Fe-rich impurity phase in both samples. Temperature-dependent zero-field-cooled and field-cooled magnetization curves present a large separation between them below 300 K and zero-field-cooled curves are consistent with a broad (bimodal) size distribution of the nanoparticles for both samples. Magnetic hysteresis loops measured at 5 K after the samples are cooled from 400 K in a zero magnetic field show weak ferromagnetism for the ∼ 3 % Bi2Fe4O9 sample, whereas the ∼ 32 % Bi2Fe4O9 sample presents an improved ferromagnetism. An exchange bias-type effect was observed in both samples. The results suggest that the increase of ultrasmall Bi2Fe4O9 nanoparticles leads to an improvement in the coercivity and remanence of BiFeO3/Bi2Fe4O9 binary nanoparticles.

A New Methodology to Evaluate the Sealing Process Based on Pressure Drop and Fluid Loss in Fractures during the Drilling Operation

Summary Natural or artificial fractures are common in the wellbore during drilling operations. These fractures allow the flow of drilling fluid into the rock formation. The loss of circulation increases the operation’s cost and nonproductive time, which may threaten the well’s structural integrity. To overcome this problem, it is necessary to understand the flow of fluids through fractures and develop methods to mitigate the loss of circulation. This work’s main contributions are expanding the knowledge on the flow of drilling fluids through fractured channels, conducting an experimental study on the flow of suspensions of lost circulation materials (LCM) in fractures, and performing a theoretical analysis to obtain mathematical models describing fractured channels’ sealing. This work proposes a correlation between the pressure drop and the volumetric flow rate of fluid through fractures. To validate the model, a physical simulator collected fluid flow data and pressure drop in fractures with 2-mm, 5-mm, and 10-mm apertures and 1.02-m length. A blend of polymers and calcium borate was used in suspension in water viscosified with xanthan gum (XG). Density and rheological behavior tests were performed to characterize the studied fluids. The LCM had a bimodal particle-size distribution, and the formulated fluids had a Herschel-Bulkley rheological behavior. Pressure drop, flow rate, and rheological data were used to propose a correlation between pressure drop and volumetric flow rate through the fracture. The proposed correlation was used to monitor the sealing of fractures by calculating their hydraulic diameter throughout the sealing process. The LCM suspensions underwent filtration tests to observe the effects of sealing particles on the mudcake and filtrate volume. The proposed correlation fitted the experimental data with less than 10% deviation. The fracture hydraulic diameter was estimated using experimental data of volumetric flow rate and pressure drop, which made it possible to monitor the sealing process of fractures through time. The sealing and filtration tests showed that the borate and polymer blends are effective as filtration control agents and LCM.

Particle Size Distributions and Extinction Coefficients of Aerosol Particles in Land Battlefield Environments

In land battlefield environments, aerosol particles can cause laser beams to undergo attenuation, thus deteriorating the operational performance of military laser devices. The particle size distribution (PSD) and extinction coefficient are key optical properties for assessing the attenuation characteristics of laser beams caused by aerosol particles. In this study, we employed the laser diffraction method to measure the PSDs of graphite smoke screen, copper powder smoke screen, iron powder smoke screen, ground dust, and soil explosion dust. We evaluated the goodness of fit of six common unimodal PSD functions and a bimodal lognormal PSD function employed for fitting these aerosol particles using the root mean square error (RMSE) and adjusted R2, and selected the optimal PSD function to evaluate their extinction coefficients in the laser wavelength range of 0.249~12 μm. The results showed that smoke screens, ground dust, and soil explosion dust exhibited particle size ranges of 0.7~50 µm, 1~400 µm, and 1.7~800 μm, respectively. The lognormal distribution had the best goodness of fit for fitting the PSDs of these aerosol particles in the six unimodal PSD functions, followed by the gamma and Rosin–Rammler distributions. For the bimodal aerosol particles with a lower span, the bimodal lognormal PSD functions exhibited the best goodness of fit. The graphite smoke screen exhibited the highest extinction coefficient, followed by the copper and iron powder smoke screens. In contrast, the ground dust and soil explosion dust exhibited the lowest extinction coefficients, reaching their minimum values at a wavelength of approximately 8.2 μm. This study provides a basis for analyzing and improving the detection and recognition performance of lasers in land battlefield environments.

Lentil protein stabilized emulsion - Impact of lecithin addition on emulsions properties

Plant-based proteins are currently the focus of a lot of product development research, as they have proved to be a potential replacement of animal-based ingredients and safeguard environmental and human health. However, most of the studies focus on soy and pea based food whereas lentil proteins have received only little attention. The aim of this work is to elucidate the behavior of different lentil protein sources (isolate, concentrate and flour) in stabilizing emulsions and to study their interaction with food emulsifiers such as lecithin. We study the adsorption kinetics at the oil water interface of both, the different protein sources as well as their combination with lecithin. Lentil protein-based emulsions (with 1%wt protein content) reveal bimodal particle size distribution and the emulsion shows various dispersion states (aggregated or well dispersed) depending on the protein sources and processing conditions. The addition of lecithin (with 0.25%wt) reduces aggregation phenomenon and reduce the average droplet size for lentil flour based emulsion. The adsorption kinetic at the oil water interface, suggest the formation of a surface active protein-lecithin complex and a mixed interfaces. Moreover, the mixture of lentil proteins and lecithin can reduce the interfacial tension by up to 12 mN/m compared to lentil protein alone. This demonstrates the presence of synergistic effects at interfaces and potential interactions between lecithin and proteins.

Properties of Packed Bed Structures Formed during Filtration: A Two and Three-Dimensional Model.

Agglomeration is an issue that causes many problems during secondary processing for pharmaceutical companies, causing material to need further processing and costing additional time and resources to ensure a satisfactory outcome. A potential source of agglomeration arises from the particle contacts established during filtration that lead to robust agglomerates forming during drying, so that a necessary first step toward understanding agglomeration is to study the packing properties of filtration beds. Here, we present two and three-dimensional models simulating the formation of packed bed structures during filtration. The models use circular and spherical particles of different sizes, mimicking the bimodal particle size distributions sometimes encountered in industrial practice. The statistics of packing and void formation, along with the distribution of interparticle contacts and percolation structures, are presented and discussed in the context of filtration, drying, and agglomeration. The model paves the way for predictive capabilities that can lead to the rational design of processes to minimize the impact of agglomeration.

Effect of bimodal particle size distribution on the performance of SiC slurry for maskless vat photopolymerization

To address the concerns associated with the difficulties of the very limited light curing depth in the pure silicon carbide (SiC) printing slurry, a bimodal particle size distribution was investigated systematically. Powder mixtures of 1 µm SiC particles and 10.5 µm SiC particles with specific ratios were prepared for making the printing slurries of 55 vol% solid load. A comprehensive investigation was conducted on the rheological stability and photopolymerization properties of coarse and fine powders at different proportions, along with an exploration of the impact of powder proportion on the quality of sintering. It was observed that at a 40% proportion of fine powder in the mixed powder, the viscosity of the slurry reached its minimum value (4.7 Pa.s) at a shear rate of 10 s–1. Meanwhile, the settlement ratio V1/V0 reached the lowest value of 1.2%. The printed sample size closely matched the design size and the quality of ceramic samples obtained after sintering was excellent (134.78 MPa).

DC conductivity mechanism in La0.7Sr0.3MnO3 (LSMO)-ZnO nanocomposites

La0.7Sr0.3MnO3 (LSMO)-ZnO nanocomposites with varying concentrations of ZnO have been synthesized using the solution combustion method. A bimodal particle size distribution has been formed in all the samples. The crystallite size increases in the composites as compared to LSMO. The study on electrical resistivity reveals that LSMO exhibits a metal-to-insulator transition at 359 K, while the inclusion of ZnO suppresses the metallic behavior in the composites and increases the resistivity. Transport behavior of the samples in metallic and semiconducting regions has been explained with a known polynomial equation and a two-channel conduction model obeying the small polaron hopping mechanism, respectively. A very low activation energy in the range of 10–12 meV is observed due to smaller-sized particles. The presence of ZnO drives the hopping mechanism from adiabatic in LSMO to become non-adiabatic in the composites and enhances the maximum temperature coefficient of resistance. 80% LSMO-20% ZnO (by weight ratio) composite shows a maximum TCR of −29.81%/K at 248 K, which makes it a potential candidate for several applications in sensing devices. The Curie temperature of the material decreases with the increase in ZnO content in the sample. The results of this study also confirm the existence of correlation between the electrical and magnetic properties of LSMO.

A discrete element method to model coating layer mechanical properties with bimodal and pseudo-full particle size distributions

The mechanical properties of paper coating layers are important in converting operations such as calendering, printing, and folding. While several experimental and theoretical studies have advanced our knowledge of these systems, a particle level understanding of issues like crack-at-the-fold are lacking. A discrete element method (DEM) model is used to describe bending and tension deformations of a coating layer. The particles in the model are either bimodal distributions or pseudo-full particle size distributions of spherical particles. The impact of particle size distribution on the predicted mechanical properties of the coating layer is reported. Inputs to the model include properties of the binder film and the binder concentration. The model predicts crack formation as a function of these parameters and also calculates the modulus, the maximum stress, and the strain-to-failure. The simulation results are compared to previous experimental results. Reasonable predictions were obtained for both tensile and bending for a range of latex-starch ratios and at various binder concentrations. The influence of particle packing density on mechanical properties is reported.

Emergence of Power-Law Particle Size Distribution in Microfluidic Calcium Carbonate Precipitation: An Extended Yule Process with a Ripening Effect.

Precipitation of calcium carbonate in bulk solutions is well known to result in a bell-shaped or bimodal particle size distribution. However, it is unclear how the distribution behaves if precipitation occurs in a small, confined volume. In this Letter, we conduct microfluidic experiments where sodium carbonate and calcium chloride solutions are continuously injected into a microchannel to precipitate calcium carbonate particles. Results show that, regardless of the variations in reagent concentrations, mixing schemes, flow rates, and precipitation time, sizes of precipitated particles in the channel are power law distributed, with an exponent of 1.4. The data are described by an extended Yule process with the introduction of a ripening term. Since the Yule process is a general mechanism for power law generation, the extended Yule process proposed here provides a general model for systems where growth and ripening simultaneously present.

A study of biochar physiochemistry and particle size distribution influencing the properties of water-based slurry fuels

Biochar-based slurry is a fossil-free-liquid fuel derived from a renewable source, biomass. This study aims to examine the properties of this fuel as an alternative to coal-water slurries. The slurries were produced by suspending 40 wt% biochar in a solution made of water and a surfactant. Two biochar types from chemically treated and untreated rice straw (RS) were utilized to assess the impact of particle-particle interactions and biochar physicochemical composition on slurry properties, including stability, rheology, and heating value. Additionally, three particle size distributions (PSD), two unimodal and a bimodal, were used to analyze the effect of PSD on the abovementioned properties.All slurries had an average energy content of 7.32 ± 0.27 MJ/kg. The stability of the slurry was higher for fine particles from treated RS with unimodal PSD (Dv50 8.8 ± 0.68 μm). However, slurries containing fine and coarse particles with bimodal PSD (Dv50 15.8 ± 0.64 μm) had relatively lower apparent viscosities of 342.1 and 336.55 mPa.s at a shear rate of 100 s−1 for slurries made of biochar from treated and untreated RS, respectively. Slurries containing coarse particles from treated and untreated RS with unimodal PSD (Dv50 18.6 ± 0.32 μm) led to higher viscosities and particle settling rates. Biochar morphology and chemical surface constitution significantly influenced slurry stability, while PSD greatly impacted rheological results.

Film formation of high poly(vinyl chloride) content latex particles

Although poly(vinyl chloride) (PVC) is produced on a large scale industrially by emulsion and suspension polymerization, it is usually processed from the dry state and is seldom directly used as an aqueous polymer dispersion. In this work we demonstrate that by control of particle morphology and particle size distribution it is possible to produce latexes with high PVC content from which polymer films can be cast directly. A series of hybrid PVC/acrylic latexes with a core-shell structure are produced by semi-batch emulsion polymerization using a preformed PVC latex as a seed. Although monomodal particles of this type have a minimum film formation temperature in excess of 80 °C when the content of PVC is high, it is shown that through the use of a bimodal particle size distribution the packing efficiency of the spherical PVC domains is increased such that room temperature film formation is possible with PVC content up to 80 wt%.

Interfacial Interactions in Particle‐Induced Abnormal Grain Growth

The presence of secondary particles to polycrystalline alloys results in kinetic stabilization of the grain boundaries, which maintains desirable fine microstructures. In some instances, secondary particles trigger abnormal grain growth. The mechanisms influencing abnormal grain growth are still a subject of conjecture. As dispersed fine particles can contribute to abnormal grain growth, it is necessary to clarify the governing mechanism by which this occurs. The current work employs a multiphase field modeling approach to shed light onto abnormal grain growth. Particular attention is placed on understanding the role of grain boundary–particle interactions on abnormal grain growth. The results show that, in the presence of particles, normal grain growth occurs until a pinned state is achieved. In the pinned state, some grains overcome the pinning pressure exerted by some particles by piercing through the particles, which results in abnormal grain growth. The piercing events appear to be entirely random and not related to the size of the interacting particles. None‐the‐less, a bimodal particle size distribution is observed to lead to abnormal grain growth. A pinning parameter is introduced as a metric to identify the transition from normal to abnormal grain growth.