Particle Size Evolution Research Articles

Carbon Nanoparticle Oxidation by NO2and O2: Chemical Kinetics andReaction Pathways.

Carbon nanoparticle interactions with gases are central to many environmental and technical processes, but the underlying reaction kinetics and mechanisms are not well understood. Here, we investigate the oxidation and gasification of carbon nanoparticles by NO2and O2under combustion exhaust conditions. We build on a comprehensive experimental data set and use a kinetic multilayer model (KM-GAP-CARBON) to trace the uptake and release of gas molecules alongside the temporal evolution of particle size and surface composition. The experimental results are captured by a model mechanism that involves different types of carbon atoms (edge/plane-like) and the formation of a reactive oxygen intermediate (activated CO complex) as the rate-limiting step. A transition between distinct chemical regimes driven by NO2at lower temperatures and O2at higher temperatures is reflected by an increase in the observable activation energy from ~60 kJ/mol to ~130 kJ/mol. We derive energy profiles for three alternative reaction pathways that involve uni- or bimolecular decomposition of reactive oxygen intermediates.

Carbon Nanoparticle Oxidation by NO2 and O2: Chemical Kinetics and Reaction Pathways

Carbon nanoparticle interactions with gases are central to many environmental and technical processes, but the underlying reaction kinetics and mechanisms are not well understood. Here, we investigate the oxidation and gasification of carbon nanoparticles by NO2 and O2 under combustion exhaust conditions. We build on a comprehensive experimental data set and use a kinetic multilayer model (KM‐GAP‐CARBON) to trace the uptake and release of gas molecules alongside the temporal evolution of particle size and surface composition. The experimental results are captured by a model mechanism that involves different types of carbon atoms (edge/plane‐like) and the formation of a reactive oxygen intermediate (activated CO complex) as the rate‐limiting step. A transition between distinct chemical regimes driven by NO2 at lower temperatures and O2 at higher temperatures is reflected by an increase in the observable activation energy from ~60 kJ/mol to ~130 kJ/mol. We derive energy profiles for three alternative reaction pathways that involve uni‐ or bimolecular decomposition of reactive oxygen intermediates.

Investigation of iron oxide nanoparticle formation in a spray-flame synthesis process using laser-induced incandescence

In this work, iron-oxide nanoparticle formation in the spray-flame synthesis (SFS) process of the standardized SpraySyn 2.0 burner was investigated in situ using laser-induced incandescence (LII). For the evaluation of these measurements, prior LII-experiments within iron-oxide aerosols (Fe3O4 and α-Fe2O3) with known primary particle size distribution and morphological properties were performed to determine the thermal accommodation coefficient (TAC) α, which led to approx. α = 0.08. The applicability of the TAC results within the flame was validated using spectrally and temporally resolved measurements in the flame at 65 mm HAB employing a spectrograph. Data for a bimodal particle size distribution, obtained from Transmission Electron Microscopy (TEM), were used in the LII-evaluation. The validated TAC was then used to evaluate the primary particle size evolution from in situ Time-Resolved (TiRe) LII-measurements using PMTs along the centre axis of the burner, ranging from 10 mm to 50 mm HAB. These measurements reveal a relatively constant effective particle diameter along HAB with dp,eff ≈ 300 nm. To further investigate particle formation in SFS, 2-dimensional time-resolved LII-measurements in the SFS flame were performed, showing a clear particle formation region up to approx. 30 mm HAB, from where on a constant particle mass is observed.

Powder coarsening mechanisms of Ti-6Al-4 V with multiple build cycles in laser powder bed fusion

Laser powder bed fusion (LPBF) is an additive manufacturing process which can produce complex 3D parts from digital models. The performance of parts fabricated by LPBF is largely dependent on the characteristics of the powder feedstock, in particular, the particle size distribution. The coarsening of powder particles may limit the potential for reusing powder in further builds, as consistency in powder quality is crucial for ensuring consistent parts performance when using reused powder, especially in aerospace applications. However, there is a lack of systematic understanding regarding the causes and nature of powder coarsening in LPBF. In this work, the characteristics of powder samples from different locations in the build chamber during LPBF were studied to understand the particle size evolution and determine the origin of coarsening, which has not been previously reported. Meanwhile, powder coarsening was found to have a detrimental effect on the relative density and surface quality of as-built parts, highlighting the importance of exploring the mechanisms of powder coarsening and finding ways to control it in LPBF. The relationship between powder in key locations in the build chamber and its effect on powder coarsening has been established. Layer thickness is identified as a critical factor in causing powder coarsening due to the fine powder size characteristic in the powder bed. Spatter, in its various forms, plays a direct or indirect role in powder coarsening. Sintered powders resulting from spatter and the laser scanning borders of as-built parts were observed to contribute to the powder coarsening. Therefore, three main mechanisms (layer thickness, spatter, sintered powder) associated with the powder coarsening are therefore proposed. This work provides insight and potential solutions to control powder coarsening and maintain consistent parts performance.

The Study of the Electrochemical Corrosion Behavior of Cu-30%Fe Nanoalloy

In this work, we have developed Cu-Fe alloys with a nanometric structure through the process of mechanosynthesis. We then followed the formation mechanism of these alloys and proceeded with a crucial step, which is cold compaction. We have elaborated Cu-Fe alloys with a nanometric structure by mechanosynthesis and following the mechanism of formation of these alloys, the we employed various analytical techniques to characterize the structural and microstructural properties of our powders. The X-ray diffraction method (XRD) was used to calculate the structural parameters, while laser granulometry was employed to study the evolution of particle size. Scanning electron microscopy (SEM) was then utilized to examine the morphology of the powders. Additionally, we investigated the electrochemical behavior of our alloys, focusing on their corrosion resistance. Electrochemical impedance spectroscopy (EIS) was performed in the frequency range of 10 kHz to 15 mHz to evaluate the corrosion performance.

Evolution of Morphology, Particle Size and Oxidation Resistance of Recycled Ti-6Al-4V Powders Prepared by Planetary Ball Milling

AbstractPlanetary ball milling is a high-energy ball milling technique that is widely used for the synthesis of alloy and composite powders with micrometer or nanometer particle sizes. The effect of process control agent (PCA) content (wt%) and milling time on the morphology, particle size and distribution, crystallite structure, apparent density and oxidation resistance of recycled T-6Al-4V alloy powders from lathe chips is investigated in this study. To investigate the effect of the PCA on the properties of the Ti-6Al-4V alloy particles, methanol is used as the PCA in various amounts of 0.5, 1 and 2 wt%. The milling is carried out using 20:1 of ball-to-powder ratio (BPR) and 400 rpm of milling speed. A morphological change from scrap form to flake-like shape, from flake-like morphology to irregular and semispherical shape and finally from semispherical form to spherical morphology is observed with increase in milling time for all PCA ratios. The results showed that the average particle sizes (D50) are 20, 18.1 and 21.8 μm after milling of 360 min with 0.5 wt%, 1 wt% and 2 wt% PCA, respectively. Results show that the most suitable recycled Ti-6Al-4V powders for powder-based manufacturing techniques are produced between 180 and 360 min of milling with 2 wt% PCA.

Real-Time Monitoring of Particle Size in Emulsion Polymerization: Simultaneous Turbidity and Photon Density Wave Spectroscopy.

Particle size evolution in seeded semibatch emulsion polymerization is monitored by two real-time monitoring techniques: online turbidity spectroscopy (TUS) and inline photon density wave spectroscopy (PDWS). An automatic dilution system that withdraws a sample from the reactor and upon dilution transfers to the measurement cell is used for the online TUS analysis. A PDWS probe is immersed in the reactor and collects inline the scattered light directly from the reacting latex. The particle sizes retrieved from TUS and PDWS are compared to offline dynamic light scattering (DLS) values. The particle size obtained by TUS is close to the intensity-average particle size obtained offline by DLS, while the particle size obtained by PDWS lies closer to the number-average particle size from DLS.

Artificial aging behavior of SiCP/AA2009 composite by electric heating: Mechanisms and modelling

SiCP/Al composite is regarded as a superior alternative material in the aerospace industry due to its excellent properties. Meanwhile, electrically-assisted aging (EAA) heat treatment has emerged as a promising method for artificial aging to obtain better aging performances. This study explores the potential of EAA heat treatment to enhance the aging kinetics of SiCP/Al composite. The impact of EAA on the aging behavior of SiCP/AA2009 composites is investigated and compared with conventional furnace aging treatment, ranging from microstructure to macroscopic properties. The electric current has few effects on the evolution trend of aging strength, but can enhance the aging process of SiCP/AA2009 with higher yield strength (about 13.7 MPa improvement) and ultimate tensile strength (about 9.7 MPa improvement). Analysis of microstructures demonstrates that EAA can generate more nucleation sites and reduce consumption of Cu atoms by Cu–Mg co-clusters near SiCP interface, resulting in more θ’ phases compared to conventional aging (CA). Additionally, more fine precipitates and dislocations contribute to higher strength under EAA condition. Subsequently, a precipitation kinetic model based on the Lagrange-like approach is employed to predict the particular electric current effects on the particle size distribution and evolution during aging, and to calculate yield strength by establishing a relationship between microstructural characteristics and macroscopic performance, providing a model basis for the design of potential EAA processes.

In vitro gastrointestinal digestion of cow’s and sheep’s dairy products: Impact of species and structure

Sheep’s milk (SM) is known to differ from cow’s milk (CM) in nutritional composition and physicochemical properties, which may lead to different digestion behaviours. This work aimed to investigate the impact of the species (cow vs sheep) and the structure (milk vs yogurt) on the digestion of dairy products. Using an in vitro static gastrointestinal digestion model, CM, SM, cow’s milk yogurt (CY) and sheep’s milk yogurt (SY) were compared on particle size evolution, microscopic observations, degree of lipolysis, degree of proteolysis, specific protein degradation and calcium bioaccessibility. Species and structure affected particle size evolution during the gastric phase resulting in smaller particles for yogurts compared to milks as well as for CM products compared to SM products. Species impacted lipid composition and lipolysis, with SM products presenting higher short/medium-chain fatty acids content and higher intestinal degree of lipolysis. Proteolysis was influenced by structure, with milks showing higher intestinal degree of proteolysis compared to yogurts. Caseins were digested faster in CM, ⍺-lactalbumin was digested faster in SM despite its higher concentration, and during gastric digestion β-lactoglobulin was more degraded in CM products compared to SM products and more in yogurts compared to milks. Lastly, SM products released more bioaccessible calcium than CM products. In conclusion, species (cow vs sheep) impacted more the digestion compared to the structure (milk vs yogurt). In fact, SM was different from CM mainly due to a denser protein network that might slow down the accessibility of the enzyme to its substrate which induce a delay of gastric disaggregation and thus lead to slower the digestion of the nutrients.

A Refined Thin-Film Model for Drug Dissolution Considering Radial Diffusion - Simulating Powder Dissolution.

We aim to present a refined thin-film model describing the drug particle dissolution considering radial diffusion in spherical boundary layer, and to demonstrate the ability of the model to describe the dissolution behavior of bulk drug powders. The dissolution model introduced in this study was refined from a radial diffusion-based model previously published by our laboratory (So et al. in Pharm Res. 39:907-17, 2022). The refined model was created to simulate the dissolution of bulk powders, and to account for the evolution of particle size and diffusion layer thickness during dissolution. In vitro dissolution testing, using fractionated hydrochlorothiazide powders, was employed to assess the performance of the model. Overall, there was a good agreement between the experimental dissolution data and the predicted dissolution profiles using the proposed model across all size fractions of hydrochlorothiazide. The model over-predicted the dissolution rate when the particles became smaller. Notably, the classic Nernst-Brunner formalism led to an under-estimation of the dissolution rate. Additionally, calculation based on the equivalent particle size derived from the specific surface area substantially over-predicted the dissolution rate. The study demonstrated the potential of the radial diffusion-based model to describe dissolution of drug powders. In contrast, the classic Nernst-Brunner equation could under-estimate drug dissolution rate, largely due to the underlying assumption of translational diffusion. Moreover, the study indicated that not all surfaces on a drug particle contribute to dissolution. Therefore, relying on the experimentally-determined specific surface area for predicting drug dissolution is not advisable.

Optoelectronic properties of BiCuOSe p-type oxychalcogenides

BiCuOSe systems are proposed as candidates to develop transparent p-type semiconductors in the visible region. This work reports the characterization results obtained for the BiCuOSe powders, synthesized by the solid-state reaction (SSR) method through mechanical milling, and nanostructured thin films deposited from the same processed powders using the pulsed laser deposition (PLD) technique. Structural characterization through X-ray diffraction (XRD) showed that the material presents a tetragonal structure with an average crystallite size of 21 nm and a preferential orientation in the (1 0 2) plane. The morphological and particle size evolution of BiCuOSe powders is presented as a function of the milling time. Transmission and scanning electron microscopies confirmed the spherical geometry of the particles in the powders and nanosheets like structure for the films. Particle sizes were also estimated, ranging from 10 to 100 nm for powders and 60 to 70 nm for films. The bandgap values, EG, for BiCuOSe powders were estimated from diffuse reflectance spectra using the Kubelka–Munk method, yielding values close to 0.7 eV. For thin films, EG values were estimated using the Tauc method, obtaining values in the range of 0.8–3.5 eV, depending on the annealing treatment. Additionally, electrical properties were measured in all deposited thin films, confirming the p-type conductivity, a minimal resistivity of 0.0735 Ω cm, hole mobility on the order of 88 cm2/Vs, and carrier concentration of 9.7 × 1018 cm−3.

Development of a Semi-Mechanistic Modeling Framework for Wet Bead Milling of Pharmaceutical Nanosuspensions.

This study aimed to develop a practical semi-mechanistic modeling framework to predict particle size evolution during wet bead milling of pharmaceutical nanosuspensions over a wide range of process conditions and milling scales. The model incorporates process parameters, formulation parameters, and equipment-specific parameters such as rotor speed, bead type, bead size, bead loading, active pharmaceutical ingredient (API) mass, temperature, API loading, maximum bead volume, blade diameter, distance between blade and wall, and an efficiency parameter. The characteristic particle size quantiles, i.e., x10, x50, and x90, were transformed to obtain a linear relationship with time, while the general functional form of the apparent breakage rate constant of this relationship was derived based on three models with different complexity levels. Model A, the most complex and general model, was derived directly from microhydrodynamics. Model B is a simpler model based on a power-law function of process parameters. Model C is the simplest model, which is the pre-calibrated version of Model B based on data collected from different mills across scales, formulations, and drug products. Being simple and computationally convenient, Model C is expected to reduce the amount of experimentation needed to develop and optimize the wet bead milling process and streamline scale-up and/or scale-out.

The impact of stoichiometry on the initial steps of crystal formation: Stability and lifetime of charged triple-ion complexes.

Minerals form in natural systems from solutions with varying ratios of their lattice ions, yet non-stoichiometric conditions have generally been overlooked in investigations of new formation (nucleation) of ionic crystals. Here, we investigated the influence of cation:anion ratio in the solution on the initial steps of nucleation by studying positively and negatively charged triple ion complexes and subsequent particle size evolution. Our model systems are carbonates and sulfates of calcium and barium, as it was recently shown that solution stoichiometry affects the timing and rate of their nucleation. Molecular dynamics (MD) simulations and dynamic light scattering (DLS) flow experiments show that nucleation correlates with the stability and lifetime of the initial complexes, which were significantly impacted by the cation:anion stoichiometry and ion type. Specifically, was found to have higher association constants and its lifetime was twofold longer than . Similar trends were observed for and . Contrastingly, for , was found to have lower association constants and its lifetime was shorter than . These trends in stability and lifetime follow the same asymmetrical behaviour as observed experimentally for particle formation using techniques like DLS. This suggests a causal relationship between the stability and lifetime of the initial charged complexes and the nucleation under non-stoichiometric conditions.

In-situ iron oxide particle size and shape evolution during the dissolution in oxalic acid

In this study, the influence of temperature (40, 60 and 80∘C) and light exposure on the dissolution of ▪ particles in aqueous, oxalic acid (0.45 mol/l) is experimentally investigated. A novel experimental setup, consisting of a vessel with undistorted optical access, allows the recording of dissolving particles using a video system. During post-processing, particles are automatically identified and their size and morphology are determined. Binning particles into discrete time-steps during the reaction yields heavy-tailed distributions characterized by a single parameter estimated through a maximum-likelihood estimation of a doubly truncated power-law fit. For the first time, up to three consecutive phases could be identified during the dissolution process of iron oxide particles. The contribution of each phase to the overall dissolution process is determined by a complex interplay between particle fragmentation, different reaction mechanisms and solid product formation. The initial phase is characterized by the fragmentation of larger particles with a more complex morphology, resulting in greater surface area available for reaction. In the second phase, fragmentation is less apparent and the available particle surface area is reduced. The transition to the third phase relies primarily on the supply of short wavelength light, which leads to the formation of a solid product that can increase the tracked particle diameter.

Maghemite nanoparticles synthesis via spray flame synthesis and particle characterization by hole in a tube sampling and scanning mobility particle sizing (HIAT-SMPS)

In order to standardize spray flame synthesis (SFS) studies, intensive work has been done in recent years on the design of burner types. Thus, in 2019, the so-called SpraySyn1 burner was introduced (SS1), which was subsequently characterized in numerical and experimental studies. Based on this research, a modification of the nozzle design was proposed, which has now been considered in the successor model, SpraySyn2 (SS2). As little is known about the effect of the nozzle adaptation on the particle formation, we operated both burners under identical operating conditions to produce maghemite. The final powder comparison showed that SS2 yielded considerable higher specific surface areas (associated with smaller primary particle sizes), lower polydispersity, and higher phase purity. To obtain further information on the size distributions of aggregates and agglomerates generated by SS2, aerosol samples were extracted by hole in a tube (HIAT) sampling and characterized by scanning mobility particle sizing (SMPS). Samples were extracted along the centerline at different heights above the burner (HAB) above the visible flame tip (>7 cm), and quenching experiments were performed to extract the aerosol samples at different dilution rates. Thereby, it was demonstrated that performing detailed quenching experiments is crucial for obtaining representative HIAT-SMPS data. In particular, agglomerates/aggregate sizes were overestimated by up to ∼70 % if samples were not sufficiently diluted. If sufficient dilution was applied, distribution widths and mean particle mobility diameters were determined with high accuracy (sample standard derivation <5 %). Our data suggested the evolution of primary particle sizes was mostly completed <7 cm HAB and it was shown aggregates/agglomerates present above the visible flame were compact in structure (non-fractal). The mean diameter of the particle ensemble grew along the centerline from 6.9 nm (7 cm) to 11.4 nm (15 cm), while distribution widths grew from 1.42 to 1.52.

Experimental investigation and optimization of morphological characteristics in mechanically agitated aluminium 6061‐fly ash cenosphere composite

AbstractThe current work examines the results of an experimental study for the liquid casting of an aluminum‐6061‐5 weight % fly ash cenosphere composite by employing stir casting. The studies were conducted using the response surface methodology (central composite design L16 experiments) with three process factors (stirring temperature, stirring speed, and stirring time) at three different levels. An attempt has been made to determine the impact of process variables on the degree of sphericity and particle size. The optimal processing conditions for the best degree of sphericity (0.765) and particle size (93.227 μm) are identified as A−1, B+1, and C+1, corresponding to a stirring temperature of 670 °C, a stirring speed of 600 min−1, and 15 min stirring time. Based on the analysis of variance analysis, the degree of sphericity and particle size evolution is significantly influenced by stirring time followed by temperature and speed. Additionally, a mathematical model for the evaluation of the degree of sphericity and particle size in the primary‐aluminium phase has been developed and it shows good consensus with the experiments.

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.

Insight to evolution of particle size and penetration resistance of Ca(OH)2/CaO powder bed for thermochemical energy storage

During the Ca(OH)2/CaO thermochemical energy storage process, the cyclability of reactions and the consolidation properties of powder storage are important issues to consider. In this study, experiments were conducted to assess the evolution of reaction conversion, particle size and penetration resistance of Ca(OH)2/CaO powder fixed bed. The results revealed that the final conversions of both the hydration and dehydration reactions stabilized between 70 and 80%. The particle size distributions of Ca(OH)2 increased initially and then decreased with the increasing cycle number and degree of dehydration. The dehydration conversion was the dominant factor for changing Ca(OH)2 bed penetration resistance force. The particle size and penetration resistance of the CaO bed remained stable during long-term storage at high temperatures. The theoretical analysis of the inter-particle forces agreed with the trend of the experimental results, with particle size and moisture content being the main factors affecting cohesion.

Distribution and evolution of particles in flash converting furnace under different operational conditions

A series of industrial experiments were conducted, not only to reveal the distribution and evolution of particle mass and size inside the flash converting furnace, but also to investigate the influence of airflows on the particle distribution. The results showed that the average size of particles grows 2–3 times when falling through the reaction shaft, and large aggregated particles were mainly distributed in the center and outer part of the material cone. This phenomenon was attributed to the collision and aggregation of molten particles caused by the high turbulent intensity of airflow, high particle mass concentration, and positions of natural gas combusting. Moreover, increasing the momentum ratio of the distribution air to the process air helped the particles to be distributed more uniformly, which could be beneficial to matte oxidation. Compared with changing process air, adjusting the distribution air could improve the particle spatial distribution more efficiently.

Curcuma particle size evolution by application of bead milling process and curcuminoids content determination

SummaryThe aim of this research was to investigate the effect of curcuma dispersion bead milling on particle size evolution over time. The study of 10 wt.% and 20 wt.% curcuma dispersions revealed that dispersions' polydispersity was decreasing up to 180 min which was found to be the optimum milling time with the volume mean diameter (d4,3) of (11.47 ± 0.85) μm. This diameter was the most effective with respect to the curcuma powder coagulation process attributed to the effect of curcuma oils after the milling time of 180 min. The mechanochemically atomized curcuma was used as a potential source of curcuminoids. By differential scanning calorimetry (DSC), two endothermic peaks were observed and related to curcuma melting effects. Curcumin powder exhibited one broad melting peak at 176 °C. Obtained data indicated that effective mechanochemical treatment makes curcuma powder a highly beneficial supplement applicable in food matrices of the human diet.