Evolution Of Particle Morphology Research Articles

Particle morphology control for spherical powder fabrication using the ball milling process with DEM simulation

Characteristics of spherical particles on copper powder and changing sizes were studied in a ball mill under various experimental conditions, such as different ball diameters, high rotation speeds, and milling times, using a discrete element method (DEM) simulation. This experiment has investigated the characteristics of spherical particle morphology evolution involved in the mechanical alloying of copper powder. The morphological evolution of the copper particle was analyzed using scanning electron microscopy (SEM). A spherical copper particle was shown with a roundness value using imageJ software. The DEM was used to simulate the ball motion in a planetary ball mill, and the impact energy and shear energy generated during the collision were analyzed to estimate the contact number between the ball and the ball wall. Therefore, as the size of the ball decreased, the number of ball-to-ball and ball-to-wall contacts increased accordingly, and the spherical shape of the copper powder changed.

Electric sampling of soot particles in spreading non-premixed flames: methodology and influence of gravity

Finer strategies of spacecraft fire mitigation require more experimental data related to fire detection. Fire detection systems developed on Earth rely massively on the optical detection of soot particles, which are present in the smoke. To detect the fire correctly, it is thus important to know how the optical properties of these particles are affected in reduced gravity. With different transport processes and increased residence time, soot in reduced gravity can be different from those produced at normal gravity. As their optical properties are related to their morphological properties, a better understanding about the evolution of soot particle morphology in flames under microgravity conditions is required. Within this context, a novel technique of soot sampling using electric field is applied to a spreading non-premixed flame at normal and micro-gravity. The soot particles sampled are observed subsequently under Transmission Electron Microscopy (TEM). Density, soot particle projected area, radius of gyration, fractal dimension, and primary particle size are extracted and the influence of gravity is investigated with the evolution of these morphological properties within the flame. Though the present study cannot be conclusive in itself, the similarity between the evolution of the optical density measured throughout the flame just before the electric perturbation required by the sampling technique and the evolution of the amount of soot deposited due to the electric perturbation along the sampling plates supports the future works that need to be devoted to further assess the consistency of the technique.

Impact of Solution {Ba2+}:{SO42-} on Charge Evolution of Forming and Growing Barite (BaSO4) Crystals: A ζ-Potential Measurement Investigation.

The impact of solution stoichiometry on formation of BaSO4 (barite) crystals and the development of surface charge was investigated at various predefined stoichiometries (raq = 0.01, 0.1, 1, 10, and 100, where raq = {Ba2+}:{SO42-}). Synthesis experiments and zeta potential (ζ-potential) measurements were conducted at a fixed initial degree of supersaturation (Ωbarite = 1000, where Ωbarite = {Ba2+}{SO42-}/Ksp), at circumneutral pH of ∼6, 0.02 M NaCl, and ambient temperature and pressure. Mixed-mode measurement-phase analysis light scattering (M3-PALS) showed that the particles stayed negative for raq < 1 during barite crystal formation and positive for raq > 1. At raq = 1, two populations with a positive or negative ζ-potential prevailed for ∼2.5 h before a population with a circumneutral ζ-potential (-10 to +10 mV) remained. We relate the observations of particle charge evolution to particle size and morphology evolution under the experimental conditions. Furthermore, we showed that the ζ-potential became more negative when the pH was increased for every raq. In addition, our results demonstrated that the type of monovalent background electrolyte did not influence the ζ-potential of barite crystals significantly, although NaCl showed slightly different behavior compared to KCl and NaNO3. Our results show the important role of surface charge (evolution) during ionic crystal formation under nonstoichiometric conditions. Moreover, our combined scanning electron microscopy and ζ-potential results imply that the surface charge during particle formation can be influenced by solution stoichiometry, besides the pH and ionic strength, and may aid in predicting the fate of barite in environmental settings and in understanding and improving industrial barite (surface chemistry) processes.

The creep characteristics and related evolution of particle morphology for calcareous sand

In the study, the creep characteristics and meso-mechanism of calcareous sand under different stresses are explored through triaxial creep tests. The influence of particle size on calcareous sand creep is also considered. Furthermore, the particularity of calcareous sand creep is revealed by comparing with the creep behavior of silica sand. The results show that during creep, the calcareous sand is more stable than silica sand due to the interlocking of irregular particles. When creep deviatoric stress is small, the creep of calcareous sand is manifested as nonlinear attenuation creep (primary creep), and the creep deformation is smooth without creep failure. With the increase of creep deviatoric stress, the creep deformation is concentrated, resulting in a strain concentration zone similar to the shear band, and the associated creep rate first decreases and then suddenly increases, finally, creep failure occurs. With increasing particle size of calcareous sand, the particle crushing increases, which induces a higher creep deformation, however, the overall creep failure is not generated. During the graded creep of calcareous sand, an obvious creep structural effect is observed, which is temporary and results in a significantly reduction of creep rate. Only after the previous creep structure effect is destroyed by the continuously creep process, the creep response can restore to its original behavior. The meso-behavior is represented by particle morphology, i.e., the fractal dimension and aspect ratio. It is found that both confining pressure and particle size can influence the evolution of particle morphology during creep. With the increase of confining pressure, the fractal dimension of calcareous sand decreases which means that particle grinding is always existent, while the aspect ratio of small-sized calcareous sand after creep decreases first and then stabilizes (slightly increases), suggesting that the overall particle breakage is the main cause of deformation. However, the aspect ratio of large-sized calcareous sand continually decreases, indicating that the main contribution for its deformation is angular cracking. The mesoscopic behavior of silica sand is basically unaffected by creep, and its creep deformation is mainly caused by particle rearrangement.

Particle Morphology Evolution and Its Enhancement for Lignite Gasification in Supercritical Water

Particle Morphology Evolution and Its Enhancement for Lignite Gasification in Supercritical Water

Evolution of particle morphology of quartz sand during one-dimensional compression

Particle breakage alters particle size, shape, surface roughness, and co-ordination number, which in turn changes macro-mechanical behaviour including compressibility and shear strength. This study conducted a series of one-dimensional (1D) compression tests on quartz sands with different initial void ratios, ending the tests at various stress levels up to 13.5 MPa. The size and shape of particles were quantified using a dynamic particle shape analyser, while the surface roughness of thirty randomly selected particles for each sample was measured by an optical interferometer and quantified using flattened root-mean-square roughness (RMSf). The results demonstrate that a unique normal compression line is defined due to extensive particle breakage, with denser sample exhibiting a higher yield stress. Prior to yielding (vertical stress < 6 MPa), the changes in the three shape descriptors are limited, as the primary particle damage modes are abrasion and grinding. Conversely, at high stress level, a greater number of particles undergo splitting or explosive damage, leading to the creation of more irregularly shaped particles. The occurrence of plastic deformation at particle asperities under one-dimensional compression is identified, resulting in a decrease in surface roughness. This study highlights the significant role of the initial void ratio in shaping the evolution of surface roughness of particles under 1D compression.

Combining Langevin dynamics and CFD-PBM model to predict TiO2 nanoparticle evolution during aerosol synthesis

The computational fluid dynamics coupled with the population balance model (CFD-PBM) based on the monodisperse model is widely used for the design of aerosol synthesis nanoparticles. Due to the monodisperse assumption, it is insufficient to accurately describe the particle polydispersity and morphology during particle evolution in the reactor. To solve these limitations, we employed the mesoscale Langevin dynamics (LD) simulation for particle coagulation and combined it with CFD-PBM to investigate the particle evolution in a tubular aerosol reactor. Particle coagulation is simulated by LD simulations, which is split into two separate stages including the pure coalescence stage at high temperatures and the subsequent pure agglomeration stage at low temperatures. The evolution function of morphology (Df) and the in-real-time coagulation rate (β) are derived from LD and then applied for the PBM calculation. CFD-PBM model estimates the primary and agglomerate nanoparticle diameters in a tubular aerosol reactor within 90% and 75% accuracy, respectively, compared to the experimental measurements in the literature. By this LD-combined CFD-PBM model, the evolution of particle morphology along the axis can also be evaluated.

Evolution of particle size and morphology in plasma synthesis of few-layer graphene and soot

This paper examines the evolution of particle size and morphology of plasma-synthesized carbonaceous nanoparticles for various reactants, reactant concentrations, reactor temperatures, and positions within the reactor. Aerosol particles were characterized at various positions downstream from the plasma zone by spatially-resolved thermophoretic sampling and transmission electron microscopy, Raman spectroscopy, and by in situ time-resolved laser-induced incandescence. Depending on the carbon-bearing reactant (ethanol or toluene) and its concentration, either pure few-layer graphene (FLG) or soot-like particles, or a mixture of both, were generated. The initial carbon nucleation has been found to commence less than 12.4 cm downstream from the plasma nozzle. In the case of FLG formation, particles show an increasing level of crumpling with increasing distance downstream from the plasma zone. The process was numerically simulated with a 1D plug-flow reactor model employing a joint population balance model for graphitic and amorphous-like particles (FLG and soot-like, respectively). The simulation includes modified versions of inception, hydrogen-abstraction-carbon-addition (HACA), and polycyclic-aromatic hydrocarbon (PAH) adsorption models adapted from a pre-existing soot model. The simulations showed that the ratio of HACA/PAH adsorption determined by post-plasma C2H2 is the main factor that affects the soot-to-FLG ratio. This is also consistent with experimental observations as reducing the rate at which carbon precursor is supplied to the reactor leads to less C2H2 in the post-plasma zone, which results in less PAH adsorption, and consequently suppressed soot formation in favor of FLG synthesis.

Volume expansion and micro-explosion of combusting iron particles analyzed using magnified holographic imaging

In-situ characterization of combusting iron particles is of great importance for understanding the combustion mechanism. Here, magnified holographic imaging is employed to investigate the transient morphology and dynamics of iron particles during combustion. The volume expansion behavior of combusting particles (mean diameter: 85 μm) is observed in situ. The particle volume increases to eight times of its initial volume within 0.14 ms, indicating that a hollow structure is generated due to bubbles formation inside the particle. In addition, the micro-explosion behaviors of expanded and unexpanded particles are resolved with high spatiotemporal resolutions. The ratio between the overall volume of the fragments (after explosion) and the volume of the expanded particle (before explosion) is around 0.2, which further validates the existence of the gas bubbles. Finally, based on the observed evolution of particle morphology, a hypothesis exploring the release of gases dissolved in burning particles as affecting combustion is supported experimentally.

Particle structure development during spray drying from a single droplet to pilot-scale perspective

Crucial for achieving premium agglomerated powder products through spray drying is that the primary particle morphology and the degree of agglomeration can be controlled. However, the costs of trial runs and the wide range of products properties complicate achieving this control of particle structure during spray drying. Single droplet drying approaches are employed to study the development of the primary particle morphology and the collision behavior of droplets under well-defined conditions. These studies shed light on the underlying mechanisms but have been related less often to realistic drying and especially agglomeration. This review focuses on the potential and limitations of single droplet drying approaches to unravel the evolution of primary particle morphology and nozzle-zone agglomeration phenomena during spray drying. We discuss advances in single droplet drying approaches and how to combine these with pilot-scale spray drying to obtain the desired particle structures. • A wide range of SDD techniques exist, each providing their own benefit. • Collision behavior of droplets can be studied by modified SDD approaches. • Particle morphology development can only be studied for individual particles. • Pilot scale equipment is required to study full nozzle zone agglomeration.

Swelling-Induced Fragmentation and Polymer Leakage of Nanoplastics in Seawater.

Nanoplastics (NPs) have been successively detected in different environmental matrixes and have aroused great concern worldwide. However, the fate of NPs in real environments such as seawater remains unclear, impeding their environmental risk assessment. Herein, multiple techniques were employed to monitor the particle number concentration, size, and morphology evolution of polystyrene NPs in seawater under simulated sunlight over a time course of 29 days. Aggregation was found to be a continuous process that occurred constantly and was markedly promoted by light irradiation. Moreover, the occurrence of NP swelling, fragmentation, and polymer leaching was evidenced by both transmission electron microscopy and scanning electron microscopy techniques. The statistical results of different transformation types suggested that swelling induces fragmentation and polymer leakage and that light irradiation plays a positive but not decisive role in this transformation. The observation of fragmentation and polymer leakage of poly(methyl methacrylate) and poly(vinyl chloride) NPs suggests that these transformation processes are general for NPs of different polymer types. Facilitated by the increase of surface functional groups, the ions in seawater could penetrate into NPs and then stretch the polymer structure, leading to the swelling phenomenon and other transformations.

Particle breakage and morphology changes of calcareous sands under one-dimensional compression loading

Particle breakage and the corresponding change of morphology are two key factors governing the mechanical behavior of calcareous sands in offshore geotechnical engineering constructions. To reveal the characteristics of these two factors, oedometer tests on calcareous sands have been performed in this study. The materials were sampled from the South China Sea with a homogenous composition but different particle size ranges and relative densities. In these tests, the dynamic imaging analysis (DIA) by Microtrac PartAn3D and acoustic emission (AE) techniques were employed to investigate the evolution of particle morphology and characteristics of AE signaling associated with the material deformations, respectively. The compressive deformation of calcareous sands was mainly induced by the particle rearrangement and particle breakage which are effectively irreversible plastic deformations. The irregular particle shape has led to strong interparticle filling and interlocking effects, which affected the particle slippage and rearrangement significantly during the deformation. The intensity and type of AE-triggering micro-mechanical behaviors were characterized by AE ringdown counts (RDC) and peak frequency, respectively. The RDC values concentrated primarily in the compression stage and increased rapidly under the normal stress of 400–3200 kPa. The RDC values increased with the increase of particle size but decreased with the increase of initial relative density. The compressive deformation and breakage characteristics of calcareous sands are consistent with the existing acoustic emission laws.

H2O2-Responsive Nanocarriers Prepared by RAFT-Mediated Polymerization-Induced Self-Assembly of N-(2-(Methylthio)ethyl)acrylamide for Biomedical Applications

H2O2-sensitive block copolymer nanoparticles (NPs) composed of a hydrophilic macro-chain transfer agent (macro-CTA) and a hydrophobic thioether-bearing block were prepared by polymerization-induced self-assembly (PISA) approach. The PISA process first involved the chain extension of poly((poly(ethylene glycol) methyl ether methacrylate)-co-(poly(ethylene glycol) methacrylate)) macro-CTA with a H2O2-responsive N-(2-(methylthio)ethyl)acrylamide (MTEAM) monomer, which self-assembled into P((PEGMA-co-PEGMAOH)-b-PMTEAM) block copolymer NPs. The polymerization kinetics indicated the evolution of particle size and morphology from spherical micelles, fused micelles, to vesicles over time. Upon incubation with 0.1 to 10 mM H2O2, spheres were fragmented due to the oxidation of the PMTEAM cores, thus transforming the hydrophobic thioethers into hydrophilic sulfoxides and disassociating the nanocarriers. 43% of the hydrophobic Nile red dye was encapsulated into the spherical micelles and demonstrated a controlled release in H2O2 incubation. Spherical micelles and vesicles displayed no cytotoxicity in MCF-7, DU145, and 22Rv1 cells. Both spheres and vesicles were efficiently internalized into MCF-7 cells, with spheres showing a higher level of uptake than vesicles due to the smaller sizes. In summary, PISA of P((PEGMA-co-PEGMAOH)-b-PMTEAM) allowed the direct formation and loading of hydrophobic dye into spherical micelles, which showed a controlled drug release in H2O2.

Formation and growth of cerium (III) oxalate nanocrystals by liquid-cell transmission electron microscopy

Using rare earth elements as analogs for actinide series elements enables studying the chemistry of these radioactive materials without the inherent risks. A fundamental understanding of the nucleation and growth of actinide oxalates is crucial for processing nuclear waste. Using in-situ liquid cell TEM (LC-TEM), we show particle attachment processes occurring during the nucleation and growth of cerium oxalate. The early stages of the observed non-classical growth mechanisms have important implications for particle evolution and predictions of final particle morphology. We observed particle formation via monomer-by-monomer addition or the particle aggregation pathway depending on the selected precursor concentration. At the highest precursor concentration at a high dose rate, we observed particle alignment in a branch structure is due to the interfacial instability. It was demonstrated that in-situ LC-TEM is an invaluable tool in studying the cerium oxalate formation and ultimately a path to understanding actinide chemistry.

Polymer particle growth and morphology evolution during dispersion polymerization through optical microscopy

Polymer particle growth and morphology evolution during dispersion polymerization through optical microscopy

Investigation into La(Fe/Mn)O3 Perovskites Formation over Time during Molten Salt Synthesis.

Molten salt synthesis (MSS) of complex oxides is generally investigated by characterization of the product phases with no insight into evolution of particle morphology. In this work, LaFeO3 and LaMnO3 MSS was investigated in KF-KCl and LiCl-KCl at 850 °C using a "feeding-and-sampling" procedure. By feeding the oxide reagents into a molten salt, the reaction starting point was clearly defined, while subsequent sampling of the melt provided means for tracking the phase composition along with the shape and size of product particles during MSS. Samples taken just after 1 min contained perovskite particles along with reagents and intermediates, which were consumed over time to yield a pure product within 10-30 min. The shape and size of perovskite particles sampled at different times during MSS were virtually unchanged, revealing a lack of notable growth. The observed fast MSS along with prevailing nucleation provided means to control perovskite particle size by varying the extent of reagent dissolution. Thus, increasing the salt/reagent ratio (from 10:1 to 25:1) strikingly reduced the duration required to obtain a pure product, along with decreasing the size of product particles (from 0.5-1.5 μm to 80-200 nm). Furthermore, performing MSS in KF-KCl, which exhibits greater oxide solubility compared to LiCl-KCl, resulted in a shorter duration and smaller perovskite particles (80-200 nm and 0.6-2.0 μm, respectively). This insight into perovskite formation and growth during MSS and its kinetics provides valuable guidelines for tuning MSS conditions to better control synthesis duration and particle size.

Multi-scale particle morphology evolution in rotating drum tests: Role of particle shape and pore fluid

During the downslope long-distance movement of debris avalanches, particles interact with each other in various modes, by rolling, sliding and colliding with each other. During transport, grains may undergo breakage, changing in size and shape. However, research on debris avalanches at the grain scale remains limited, in particular, the evolution of grain morphology at different scales, from the overall form down to surface roughness, with runout distance. This paper investigates the evolution of particle morphology of granite gravel particles during long distance travel using a rotating drum, Micro-Deval apparatus, together with three-dimensional (3D) image analysis with a 3D laser scanner. The effects of particle shape and pore fluid (dry, saturated with water or slurry) on the evolution of particle morphology during transport were investigated. It was found that while the gravel was strong enough to resist the fragmentation that could be induced by the inter-particle actions during testing, the corners and edges became rounded, and the general form and surface roughness remained unaffected by the particle interactions. The more angular the grains, the easier the corners to be abraded during interaction. The change of local roundness of the grains was amplified in water-saturated conditions and suppressed in a slurry-saturated medium. The viscosity of the pore fluid, rather than initial particle shape, was critical in controlling the particle morphology evolution.

The Importance of Surface Oxygen for Lithiation and Morphology Evolution during Calcination of High‐Nickel NMC Cathodes

AbstractNanoscale morphology has a direct impact on the performance of materials for electrochemical energy storage. Despite this importance, little is known about the evolution of primary particle morphology nor its effect on chemical pathways during synthesis. In this study, operando characterization is combined with atomic‐scale and continuum simulations to clarify the relationship between morphology of cathode primary particles and their lithiation during calcination of LiNi0.8Mn0.1Co0.1O2 (NMC‐811). This combined approach reveals a key role for surface oxygen adsorption in facilitating the lithiation reaction by promoting metal diffusion and oxidation, and simultaneously providing surface sites for lithium insertion. Furthermore, oxygen surface termination is shown to increase the activation energy for sintering, leading to smaller primary particle sizes at intermediate temperatures. Smaller particles provide both shorter diffusion lengths for lithium incorporation and increased surface site density for lithium insertion. These insights provide a foundation for more tailored syntheses of cathode materials with optimized performance characteristics.

(Invited) Synthesis Design Strategies of Faceted Cerium Oxide Nanoparticles and its Properties

Cerium oxide nanoparticles (CNP or nano-ceria) are widely studied for their use in catalysis, energy, environmental protection, and bio-medical applications. Recently CNP is used as additives for Chemical Mechanical Planarization (CMP) slurries. The chemical performance of ceria in many of these applications depends on the ability of cerium to switch between +3 and +4 oxidation states. Our research involves examination of the synthesis design strategies of CNP with various shape and sizes and their effect on the surface chemistry. In most catalytic applications, highly reduced ceria surfaces play an active role and very similar observation is also noted in increased CMP removal rates. While high resolution TEM (HRTEM) is used to follow the particle morphology evolution, the surface effects are studied using high resolution X-ray photoelectron spectroscopy (XPS) of the Ce 3d spectrum. Atomistic computer simulations were used to help rationalize how the synthetic conditions impact upon the morphology of the nanomaterial. Further we provide understanding of the adsorption Interface of Polyelectrolyte Coating on Redox Active CNP Using Soft Particle Electro kinetics, which is relevant to CMP and biomedical applications. This talk summarizes some of our observations of the impact that synthesis route, storage and environmental conditions have on the properties of CNPs.

Effect of particle characteristics on the evolution of particle size, particle morphology, and fabric of sands loaded under uniaxial compression

This paper presents the results and analyses of uniaxial compression experiments performed on three silica sands. The sands have comparable particle-size distributions, but their particles differ in morphology and strength. Cylindrical samples of the three sands were compressed in a loading device placed inside an X-ray microscope (XRM) and scanned at multiple stress levels during uniaxial compression. 3D tomography data of the samples obtained from the XRM at different stress levels were then analyzed to obtain the distributions of particle size, particle morphology, and interparticle contact normals within the sample. Results indicate that: (1) the compressibility of the sands loaded under uniaxial compression is closely tied to particle morphology and strength and (2) the anisotropy in the orientations of interparticle contact normals generally increases with axial stress; however, this increase is limited by the occurrence of particle crushing in the sample.