Wide Particle Size Distribution Research Articles

Effects of the Gas-Atomization Pressure and Annealing Temperature on the Microstructure and Performance of FeSiBCuNb Nanocrystalline Soft Magnetic Composites.

FeSiBCuNb powders prepared by the gas atomization method generally exhibit a wide particle size distribution and a high degree of sphericity. In addition, the correspondingly prepared nanocrystalline soft magnetic composites (NSMCs) perform good service stability. In this paper, effects of the gas-atomization pressure and annealing temperature on the microstructure and soft magnetic properties of FeSiBCuNb powders and NSMCs are investigated. The results show that the powders obtained by a higher gas-atomization pressure possess a larger amorphous ratio and a smaller average crystallite size, which contribute to the better soft magnetic performance of the NSMCs. After being annealed at 550 °C for 60 min, the NSMCs show a much better performance than those treated by the stress-relief annealing process under 300 °C, which indicates that the optimization of the soft magnetic properties resulting from the precipitation of the α-Fe(Si) nanocrystalline largely overwhelms the deterioration caused by the grain growth of the pre-existing crystals. In addition, the annealed NSMCs prepared by the powders with the gas-atomization pressure of 4 MPa show the best performance in this work, μe = 33.32 (f = 100 kHz), Hc = 73.08 A/m and Pcv = 33.242 mW/cm3 (f = 100 kHz, Bm = 20 mT, sine wave).

Fabrication of silver nanoparticles-deposited fabrics as a potential candidate for the development of reusable facemasks and evaluation of their performance

Recently, wearing facemasks in public has been raised due to the coronavirus disease 2019 epidemic worldwide. However, the performance and effectiveness of many existing products have raised significant concerns among people and professionals. Therefore, greater attempts have been focused recently to increase the efficacy of these products scientifically and industrially. In this respect, doping or impregnating facemask fabrics with metallic substances or nanoparticles like silver nanoparticles has been proposed. So, in the present study, we aimed to sonochemically coat silver nanoparticles on the non-woven Spunbond substrates at different sonication times and concentrations to develop antibacterial and antiviral facemask. The coated substrates were characterized using Field Emission Scanning Electron Microscope, Energy Dispersive X-Ray, X-ray diffraction, and Thermogravimetry analysis. The amount of silver released from the coated substrates was measured by atomic absorption spectroscopy. The filtration efficiency, pressure drop, and electrical conductivity of the coated samples were also investigated. The antibacterial activity of fabrics was evaluated against Escherichia coli and Staphylococcus aureus. Cellular viability of samples assessed by MTT and brine shrimp lethality tests. The results revealed that the higher sonication times and precursor concentrations result in a higher and more stable coating, larger particle size, wider particle size distribution, and lower content of released silver. Coated fabrics also revealed enhanced filtration efficiency (against nanosize particles), desired pressure drop, and antibacterial activity without significant cytotoxicity toward HEK 293 cells and Artemia nauplii. As a result, the coated fabrics could find potential applications in the development of facemasks for protection against different pathogenic entities.

Fines-controlled drainage in just-saturated, inertial column collapses

The wide particle size distributions, over several orders of magnitude, observed in debris flows leads to a diverse range of rheological behaviours controlling flow outcomes. This study explores the influence of different scale grains by conducting subaerial, fully saturated granular column collapse experiments with extreme, bimodal particle size distributions. The primary particles were of a size where their behaviour was controlled by their inertia while a suspension of kaolin clay particles within the fluid phase acts at spatial scales smaller than the pore space between the primary particles. The use of a geotechnical centrifuge allowed for the systematic variation of gravitational acceleration, inertial particle size and the degree of kaolin fines. Characteristic velocity- and time-scales of the acceleration phase of the collapse were quantified using high-speed cameras. Comparing tests containing fines to equivalent collapses with a glycerol solution mimicking the enhanced viscosity but not the particle behaviour of the fines, it was found that all characteristic dynamic quantities were dependent on the degree of fines, the system size, the grain fluid-density ratio and the column– and grain-scale Bond and Capillary numbers. We introduce a fine-scale Capillary number showing that, although surface tension effects at the column scale are negligible, fines do control the movement of fluid through the pore spaces.

Numerical study of heat transfer for gravity-driven binary size particle flow around circular tube

As the primary working medium in moving bed heat exchangers, solid bulk materials are composed of multiple size particles. To clarify the effect of particle size distribution (PSD) on heat transfer, the discrete element method (DEM) is used to study the flow and heat transfer of binary size particle flow around a circular tube. The heat transfer model for multiple size particles is developed and coupled with DEM method. The particle flow characteristics with PSD width are analyzed in detail. The results show that particle size segregation, competitive flow and flow instability are the unique characteristics of binary size particle flow around a tube. Wider PSD will enhance these characteristics and have a positive effect on particle renewal in the stagnation zone, which could decrease the local heat resistance. The total heat transfer coefficient between particle flow and tube wall increases at most by 9.73% as PSD is wider. • Binary size particle flow around a circular tube is studied with DEM method. • Binary size particle flow can form local particle size segregation around tube. • Binary size particles can decrease the stagnation zone above the tube. • A wider binary particle size distribution can increase the flow instability. • A wider binary particle size distribution can enhance heat transfer performance.

Preliminary characteristics of non-starch polysaccharide from chayote (Sechium edule)

Chayote is rich in non-starch polysaccharides. The physicochemical properties of non-starch polysaccharide from chayote were not study extensively. In the present research, non-starch polysaccharide of chayote (CP-CHE) extracted by conventional heating extraction method was obtained, and the preliminary physicochemical and functional properties of CP-CHE had been carried out. The results indicated that the CP-CHE was rich in galactan, glucoses and galacturonic acid. Also, CP-CHE had the negatively charged, a wide distribution of molecular weight and particle size. Additionally, CP-CHE solutions had shear thinned fluid property when the concentrations between 1% to 4%. The results of this study would be beneficial to the application of CP-CHE in food and improve the economic value of chayote.

Sustainable and Efficacy Approach of Green Synthesized Cobalt Oxide (Co3O4) Nanoparticles and Evaluation of Their Cytotoxicity Activity on Cancerous Cells

In this study, rosemary leaf extract was effectively used to synthesize cobalt oxide nanoparticles (Co3O4 NPs) using a rapid, low-cost, and environmentally friendly approach. The prepared Co3O4 NPs were examined using various analytical techniques. However, UV spectrum analysis displayed two sharp absorption peaks at ~350 and 745 nm. The dynamic light scattering and zeta potential measurements were used to evaluate the particle size and the effective stabilization of the synthetic nanoparticles in the suspensions. A semi-triangular pyramidal shape of the Co3O4 NPs with a wide particle-size distribution could be observed in the scanning electron microscopy images. The energy-dispersive X-ray spectrum confirmed their successful synthesis, as the experimental atomic percentages agreed with the theoretical values. Moreover, X-ray diffraction analysis revealed that the synthesized Co3O4 NPs had a cubic crystalline structure corroborating that of theoretical Co3O4. Additionally, the Co3O4 NPs were not toxic at ≤62.5 µg/mL for Hep G2 and at ≤31.25 µg/mL for Mcf7. Therefore, these unique environmentally friendly Co3O4 NPs at this safe concentration could be studied in the future for their therapeutic activity.

Coarse-grained CFD-DEM simulation of coal and biomass co-gasification process in a fluidized bed reactor: Effects of particle size distribution and operating pressure

The co-gasification of coal and biomass through fluidized bed gasifier is a promising technology for the improvement of the utilization efficiency of fossil fuels and the development of renewable energy. In this work, a coarse-grained computational fluid dynamics-discrete element method (CFD-DEM) simulation is performed to investigate the co-gasification process in a bubbling fluidized bed gasifier. The effects of particle size distribution and operating pressure on the hydrodynamics, heat transfer, and co-gasification performance are analyzed. The results show that the increase of sand particle size distribution (PSD) width slightly affects the particle concentration distribution, particle residence time distribution, and co-gasification performance. The heat transfer rate of convection is an order of magnitude higher than those of conduction and radiation. At higher PSD width, the formation of the vertical solid temperature gradient at the bed bottom is attributed to the deteriorated solid mixing. As the operating pressure increases, the bed temperature decreases apparently. In addition, the variation of the convective heat transfer rate dominates the heat transfer efficiency as the operating pressure changes. The application of elevated operating pressure benefits to the thermal-chemical conversion of blend fuel since the char conversion reaction is accelerated.

Understanding the effects of process parameters and material properties on the breakage mechanisms and regimes of a milling process

Milling is an important unit operation used as a particle design process in solid drug manufacturing processes. The size reduction process, where granules break into smaller fragments, governs the operation of the mill. The breakage behavior in a mill can be described through its breakage mechanisms, which are described using the critical screen size, breakage mode, and breakage rate. Breakage mechanisms are important because they determine the output quality attributes of the mill, such as the particle size distribution (PSD) and mass throughput. This study investigates the effect of process parameters and material properties on breakage mechanisms and determines its correlation to the output quality attributes. Additionally, dynamic data was collected and analyzed to determine the effect of process parameters and material properties on the transition of regimes and the evolvement of breakage modes. The findings in this study indicate that stronger granules undergo solely impact-attrition breakage mode, whereas weaker granules first undergo impact breakage mode and then transition into impact-attrition mode. Mass throughput is observed to be higher for impact mode than impact-attrition mode. Moreover, impact mode produces a wide and unimodal PSD, while impact-attrition mode produces a bimodal distribution.

Measuring adhesion of microparticles in lunar regolith simulant BHLD1000 by centrifugal technique

The adhesion of lunar material is strong and harmful to the functional surfaces of spacecraft systems. Using lunar regolith simulant instead of rare real one to understand the adhesive property of lunar regolith is an economical approach. In this work, we firstly introduced a theoretical model of the adhesive behavior between lunar regolith simulant micro-particle and different aerospace materials. In this model, total adhesion force is determined by Van der Waals force, electrostatic force and capillary force. Surface energy, surface potential, particle size and inertia force are the key factors affecting adhesion. Then we designed an experimental method using centrifugal technique and image processing to quantify and visualize the adhesion effect. By using a newly developed lunar regolith simulant BHLD1000 and four types of aerospace functional surfaces, we found the size of adhesive micro-particles are a few micrometers and the adhesion forces on them are a few nN on average. This experimental value is three orders of magnitude smaller than the theoretical one (several μN) due to particle irregularity and surface roughness. The adhesion model, the experimental approach and measurement results developed here are useful in understanding the real adhesion of lunar regolith on the moon as well as designing dust-proof tools for future lunar explorations. • An adhesion model between lunar regolith simulant and typical aerospace materials is proposed. • Lunar regolith simulant BHLD1000 with a wide particle size distribution is developed for experimental study. • High Speed centrifuge technology with specially-made accessories is used to help quantify the adhesion indirectly. • Optical microscopy with picture processing is discussed to embody the particles detaching manner statistically. • Adhesion force between BHLD1000 and typical aerospace materials is evaluated in laboratory environment.

Catalyst-scale investigation of polydispersity effect on thermophysical properties in a commercial-scale catalytic MTO fluidized bed reactor

The methanol-to-olefin (MTO) process is commercialized worldwide, yet the understanding of in-furnace phenomena is still lacking. Accordingly, this work explores the multiphase flow and thermochemical characteristics in a commercial-scale MTO fluidized bed reactor using a three-dimensional multiphase particle-in-cell model. After model validations, the intrinsic relationship of solid transportation and thermochemical properties is elucidated together with the study of the polydispersity effect on reactor performance. The non-uniform gas-solid distribution in the reactor demonstrates the turbulent fluidization regime. Heat transfer coefficients (HTCs) of about 300 and 200 W/(m2·K) are observed in the medium and upper regions, respectively. The small velocity, particle Reynolds number, temperature, and HTC correspond to those large-size catalysts in the dense region where particles are nearly close packing with a large solid volume fraction. Increasing particle size distribution (PSD) width increases the catalyst HTCs and the mass fraction of C2H4, promoting reactor performance. Besides, increasing the PSD width enlarges gas viscosity, gas specific heat capacity, and gas thermal conductivity but decreases gas density.

Impact of Particle Size Polydispersity on Chemical Looping Combustion of Biomass under a Continuous Injection Mode

Particle size polydispersity considerably influences the chemical looping combustion (CLC) of solid fuels. In the present work, a three-dimensional multiphase particle-in-cell (MP-PIC) method was established and applied to study the full-loop CLC of biomass under a continuous injection mode. After model validation, the gas–solid flow characteristics, solid circulation rate (SCR), particle mixing in a fuel reactor (FR), and biomass leakage at different oxygen carrier (OC) particle size distribution (PSD) widths and biomass densities were systematically explored. The results showed that OC particles significantly stratified within the FR and both loop seals. Moreover, the fluctuation amplitude of the SCR decreased as the OC PSD width increased. Small biomass particles were more likely to leak. The number fraction of total leaked biomass particles first decreased and then increased as the OC PSD width increased. In the FR, small OC particles were primarily distributed in the upper part of the bed, and large particles were mainly distributed in the lower part. In addition, within the test range, the magnitude of the density difference between biomass and OC particles positively correlated with the likelihood of biomass leaking. These observations are all beneficial for the design and optimization of the CLC process of biomass.

Large-scale frictionless jamming with power-law particle size distributions.

Due to significant computational expense, discrete element method simulations of jammed packings of size-dispersed spheres with size ratios greater than 1:10 have remained elusive, limiting the correspondence between simulations and real-world granular materials with large size dispersity. Invoking a recently developed neighbor binning algorithm, we generate mechanically stable jammed packings of frictionless spheres with power-law size distributions containing up to nearly 4000000 particles with size ratios up to 1:100. By systematically varying the width and exponent of the underlying power laws, we analyze the role of particle size distributions on the structure of jammed packings. The densest packings are obtained for size distributions that balance the relative abundance of large-large and small-small particle contacts. Although the proportion of rattler particles and mean coordination number strongly depend on the size distribution, the mean coordination of nonrattler particles attains the frictionless isostatic value of six in all cases. The size distribution of nonrattler particles that participate in the load-bearing network exhibits no dependence on the width of the total particle size distribution beyond a critical particle size for low-magnitude exponent power laws. This signifies that only particles with sizes greater than the critical particle size contribute to the mechanical stability. However, for high-magnitude exponent power laws, all particle sizes participate in the mechanical stability of the packing.

Coupled discrete phase model and Eulerian wall film model for numerical simulation of respiratory droplet generation during coughing

Computational fluid dynamics is widely used to simulate droplet-spreading behavior due to respiratory events. However, droplet generation inside the body, such as the number, mass, and particle size distribution, has not been quantitatively analyzed. The aim of this study was to identify quantitative characteristics of droplet generation during coughing. Airflow simulations were performed by coupling the discrete phase model and Eulerian wall film model to reproduce shear-induced stripping of airway mucosa. An ideal airway model with symmetric bifurcations was constructed, and the wall domain was covered by a mucous liquid film. The results of the transient airflow simulation indicated that the droplets had a wide particle size distribution of 0.1–400 µm, and smaller droplets were generated in larger numbers. In addition, the total mass and number of droplets generated increased with an increasing airflow. The total mass of the droplets also increased with an increasing mucous viscosity, and the largest number and size of droplets were obtained at a viscosity of 8 mPa s. The simulation methods used in this study can be used to quantify the particle size distribution and maximum particle diameter under various conditions.

Effect of reuse times on H13 powder properties processed by selective electron beam melting

ABSTRACT The inconsistency of high material cost and powder properties are the primary barriers to widespread adoption of metal additive manufacturing. Obviously, powder reuse without affecting the properties of the parts can reduce the cost burden. In this study, the properties of H13 (4Cr5MoSiV1) powder were evaluated 16 build cycles in selective electron beam melting. Results show that the crystal plane spacing and particle size of the powder increased with reuse. With the increase i reuse times, more irregular particles appeared and the flowability decreased. The oxygen and nitrogen content of powder gradually increases from 149 to 250 ppm and 237 ppm to 394 ppm, respectively, with reuse. The simulation results show that the wider particle size distribution, the better the relative packing performance of the powder layer. Powder reuse has no negative effect on the hardness of the as-built samples.

Preparation of polyamide 6 and its titanium dioxide photocatalytic composite powders for laser powder bed fusion

Laser powder bed fusion (LPBF) additive manufacturing is an effective method to prepare three-dimensional ordered network titanium dioxide (TiO2) photocatalytic materials, therefore enhancing the absorption intensity of incident light and improving the photocatalytic efficiency. However, TiO2 is difficult to be directly sintered by LPBF due to the high melting point and brittleness. In this study, we prepared a polyamide 6 (PA6)-coated TiO2 photocatalytic composite powder for LPBF based on the dissolution precipitation polymer coating (DPPC) method and evaluated its LPBF processability. In the precipitation process of PA6, there was a significant crystallization exotherm with temperature recovery. Effective temperature control of this precipitation process had a significant effect on the morphology and particle size distribution of the precipitated powder. The increase of the dissolved concentration of PA6 to 150 g/L produced an obvious temperature gradient of the reactor, resulting in a wide particle size distribution and a powder with a characteristic porous surface. The prepared PA6/TiO2 composite powder presents a near-spherical porous-surfaced morphology, a high specific surface area of 240.5 m2/kg, an appropriate Dv(50) of 48.8 μm, and a wide sintering window of 26.6°C, indicating a good LPBF processability and potential of the photocatalytic application.

Fabrication of Highly Compacted Green Body Using Multi-Sized Al Powder under a Centrifugal Force

This study investigates the application of centrifugal force for the compaction of metal powder. Previous studies using the centrifugal force for manufacturing the green bodies were focused on fine powders with narrow particle size distribution or binary mixtures. This study explores the particle packing of multi-sized powder. Aluminum alloy powder with a particle size less than 100 µm and polymer binder were admixed and compacted in the centrifugal casting with ranging magnitudes of centripetal acceleration. Three different centrifugal forces were tested: 700, 1800, and 3700 G. The microstructure of the green bodies was then observed on the SEM micrographs. The obtained green bodies had high packing densities ranging from 62 to 69%. The packing density and median particle size increase at the positions further away from the center of rotation of the centrifuge with an increase of centrifugal force. The effect of centrifugal force on the segregation of particles was investigated through the quasi-binary segregation index. The segregation phenomena was not observed at 700 G, but clear particle segregation was found at higher centrifugal forces. The increase of the centrifugal force resulted in higher segregation with finer particles moving to the inner part of the spinning mold, with a significant change in the size of particles located closer to the center of rotation. Overall, the centrifugal process was found to produce highly compacted green bodies while yielding a segregation effect due to wide particle size distribution.

CFD Analysis and Life Cycle Assessment of Continuous Synthesis of Magnetite Nanoparticles Using 2D and 3D Micromixers

Magnetite nanoparticles (MNPs) have attracted basic and applied research due to their immense potential to enable applications in fields as varied as drug delivery and bioremediation. Conventional synthesis schemes led to wide particle size distributions and inhomogeneous morphologies and crystalline structures. This has been attributed to the inability to control nucleation and growth processes under the conventional conditions of bulk batch processes. Here, we attempted to address these issues by scaling down the synthesis process aided by microfluidic devices, as they provide highly controlled and stable mixing patterns. Accordingly, we proposed three micromixers with different channel configurations, namely, serpentine, triangular, and a 3D arrangement with abrupt changes in fluid direction. The micromixers were first studied in silico, aided by Comsol Multiphysics® to investigate the obtained mixing patterns, and consequently, their potential for controlled growth and the nucleation processes required to form MNPs of uniform size and crystalline structure. The devices were then manufactured using a low-cost approach based on polymethyl methacrylate (PMMA) and laser cutting. Testing the micromixers in the synthesis of MNPs revealed homogeneous morphologies and particle size distributions, and the typical crystalline structure reported previously. A life cycle assessment (LCA) analysis for the devices was conducted in comparison with conventional batch co-precipitation synthesis to investigate the potential impacts on water and energy consumption. The obtained results revealed that such consumptions are higher than those of the conventional process. However, they can be reduced by conducting the synthesis with reused micromixers, as new PMMA is not needed for their assembly prior to operation. We are certain that the proposed approach represents an advantageous alternative to co-precipitation synthesis schemes, in terms of continuous production and more homogeneous physicochemical parameters of interest such as size, morphologies, and crystalline structure. Future work should be directed towards improving the sustainability indicators of the micromixers’ manufacturing process.

Effect of the distribution of anisotropy constants on the magnetic properties of iron oxide nanoparticles

The distribution of shape anisotropy constants in two colloids of iron oxide nanoparticles has been measured from the distribution of particle elongations within each system. The results are in good agreement with the values calculated from a temperature decay of remanence measurement. For a fluid with a saturation magnetisation of 420 emu/cc and an average particle elongation of ∼ 1.3, the distribution of energy barriers is controlled by both the distribution of particle sizes and particle elongations. For a fluid with a saturation magnetisation of 320 emu/cc and a wide distribution of particle sizes, the energy barrier to reversal can be assumed to be controlled by the distribution of particle volumes. These results highlight the need to take into account the distribution of anisotropy constants when making predictions of the heating properties of assemblies of magnetic nanoparticles for hyperthermia applications.

Quasi-Shell-Growth Strategy Achieves Stable and Efficient Green InP Quantum Dot Light-Emitting Diodes.

Indium phosphide (InP) based quantum dots (QDs) have been known as an ideal alternative to heavy metals including QDs light emitters, such as cadmium selenium (CdSe) QDs, and show great promise in the next‐generation solid‐state lighting and displays. However, the electroluminescence performance of green InP QDs is still inferior to their red counterparts, due to the higher density of surface defects and the wider particle size distribution. Here, a quasi‐shell‐growth strategy for the growth of highly luminescent green InP/ZnSe/ZnS QDs is reported, in which the zinc and selenium monomers are added at the initial nucleation of InP stage to adsorb on the surface of InP cores that create a quasi‐ZnSe shell rather than a bulk ZnSe shell. The quasi‐ZnSe shell reduces the surface defects of InP core by passivating In‐terminated vacancies, and suppresses the Ostwald ripening of InP core at high temperatures, leading to a photoluminescence quantum yield of 91% with a narrow emission linewidth of 36 nm for the synthesized InP/ZnSe/ZnS QDs. Consequently, the light‐emitting diodes based on the green QDs realize a maximum luminance of 15606 cd m−2, a peak external quantum efficiency of 10.6%, and a long half lifetime of > 5000 h.

The quantitative assessment of clogging and cleaning effects on the permeability of pervious concrete

Portland Cement Pervious Concrete (PCPC) is a unique and effective mean to solve the important environmental issues and support green, sustainable growth, by reducing stormwater and providing treatment of pollutants contained within. However, clogging of PCPC leading to potential problems in serviceability has been regarded as one of the primary drawbacks of PCPC applications. In order to quantitatively assess the effects of clogging mechanisms on the permeability of pervious concrete, the clogging potential of three void ratios of pervious concrete, 15%, 20% and 25%, were examined using three different soil types: sand, clay silt and clay silty sand. Pervious concrete cylindrical specimens were exposed to sediments mixed in water to simulate runoff with small and large load of soil sediments. Pressure washing, vacuuming and a combination of both were applied as rehabilitation methods to clean the clogged specimens. The clogging tests were conducted using falling head permeability apparatus by allowing the “dirty water” to flow through the specimen and the permeability was determined during the clogging and after the cleaning process in each clogging cycle. Totally 20 clogging cycles were repeated on each sample to simulate the 20 years of pavement service life. The results indicated that clay silty sand had a greater chance of clogging the specimen than sand and clay because of the cohesiveness and the wider particle size distribution. Residual permeability and permeability recoveries increased with increasing porosity of the specimens. Pressure washing followed by vacuuming was demonstrated to be the most efficient method of rehabilitation. The results of simulated sedimentation tests and the quantitative relationship between the permeability reduction and recovery of PCPC have the potential to optimize the pervious concrete mix design and maintenance strategies for rational soil characteristics and working condition scenarios.