Mechanism Of Particle Formation Research Articles

Investigation of sources and formation mechanisms of fine particles and organic aerosols in cold season in Fenhe Plain, China

Air quality has been improved significantly from 2017 to 2020 in Fenhe Plain, one of the most polluted regions in China. However, severe haze episodes from days to weeks were still frequently observed in cold seasons, and the sources and formation mechanisms especially organic aerosols are poorly understood due to the limited highly time-resolved measurements. Here we have a comprehensive characterization of chemical composition, variations and sources of fine particles in fall and winter in Fenhe Plain mainly using a PM2.5 Aerosol Chemical Speciation Monitor. Our results showed that organics and nitrate were two major species of PM2.5, on average accounting for 35.4% and 27.0%, respectively, and they played consistently important roles across different pollution levels. Positive matrix factorization revealed three primary sources from traffic, biomass burning and coal combustion emissions, and two secondary factors that are associated with photochemical and aqueous-phase processing. While secondary OA (SOA) dominated OA for the entire study (63%), large increases in primary OA from 19% to 41% were observed during heating period. Particularly, we found a high contribution of photochemical OOA (45%) during severely polluted periods in heating season demonstrating the presence of strong photochemical production in winter. Most aerosol species presented similarly pronounced diurnal cycles with low concentrations during daytime indicating the major influences from planetary boundary layer and primary emissions. The bivariate polar plots further illustrated the different sources of primary and secondary species, i.e., local emissions versus regional transport from the south and southeast. By analyzing four case studies, we found three major formation mechanisms of severe haze episodes that were driven by photochemical processing, aqueous-phase production, and local emissions, respectively. Therefore, different mitigating strategies are suggested in Fenhe Plain depending on the types of severe haze episodes.

Experiment-theory hybrid method for studying the formation mechanism of atmospheric new particle formation.

Atmospheric aerosols have a significant influence on climate change through their effect on the cloud lifetime and the radiative balance of the Earth's atmosphere. Despite its importance, the mechanism of aerosol nucleation is still poorly understood. Based on the low-energy structure of cluster molecules, quantum chemical (QC) computations can help us to directly calculate the formation mechanism of atmospheric clusters and formation rates at the molecular level. However, deciphering the formation mechanism of pre-nucleated clusters, especially those close to the critical size (∼1.7 nm), remains extremely challenging because many millions of configuration spaces might need to be explored to find the low-energy structure. We present a new idea that establishes a comprehensive experimental and computational hybrid calculation protocol to integrate experimental data, isomer distributions, hydrogen bond interactions, and interaction sites for exploring the configuration spaces and clarifying the nucleation mechanism of acid-base clusters, whose maximum size can exceed 1.7 nm. This protocol can effectively and accurately explore the configuration space of complex large nucleation clusters on the potential energy surface (PES). The consistency of the cluster concentration and the formation rate between the experiment and the in situ measurement is much better than that of the previous studies and proves its accuracy. In addition, we found that malic acid (MA) can enhance sulfuric acid-dimethylamine (SA-DMA)-based particle formation rates in the atmospheric boundary layer, for example, in Shanghai and Beijing in the summer, with an enhancement of up to 700- and 135-fold, respectively. The enhancement in atmospheric particle formation by MA is critical for new particle formation in the boundary layer with relatively low SA and DMA concentrations and at high temperature. This model greatly improves our understanding of the complex aerosol nucleation mechanism of large-scale multicomponent cluster molecules.

An Analysis of the Formation Mechanisms of Abrasive Particles and Their Effects on Cutting Efficiency

Magnetic induction-free abrasive wire sawing (MIFAWS) is a method that combines magnetic fields with traditional free abrasive wire sawing technologies. Magnetic abrasive particles (MAPs) are attracted on a magnetized wire, thus leading to an increase in their number into the cutting zone. The number of instantaneous-effective abrasive particles (IEAPs) adsorbed on the wire surface has a great influence on the cutting efficiency of the saw wire. In this study, a mathematic model of the movement of the MAP is presented, and the factors influencing the IEAPs number, including slurry-supply speed and slurry dynamic viscosity, are investigated both by means of simulation analysis and experiments. The results indicate that the number of IEAPs decreases with an increase in the slurry supply speed. The cutting efficiency increases gradually with the increase of slurry supply speed, but the growth rate of wire saw cutting efficiency slows down when the slurry supply speed exceeds a given threshold. The number of IEAPs adsorbed by saw wire increases with a decrease in the dynamic viscosity of the cutting fluid, while the cutting efficiency first increases and then decreases. The cutting efficiency attains its highest value when the dynamic viscosity of the cutting fluid is 0.0047 Pa⋅s. The experimental results agree with the simulation results, and provide some guidance for the practical application of the MIFAWS process.

Analiza radnih parametara kočenja pri ispitivanju habanja kočnica i nastanka čestica na inercijalnom kočnom dinamometru

In parallel with the significant reduction of the impact of vehicles on the environment, the development of modern propulsion systems that have less and less harmful impact, new pollutants are being identified on the vehicle. One of the such pollutants is the brakes, which wear out and lead to the formation of particles that are released into the air, i.e. generally into the environment. Investigation of the mechanism of particle formation during braking, and thus the brake wear is today becoming one of the important areas of research. The most common tests in this area are performed using initial brake dynamometers and pin-on-disc machines. An overview of the influence of some operation parameters (initial vehicle speed, braking pressure, and deceleration) that varies frequently during testing on an inertial brake dynamometer is performed in this paper. There are a number of tests and cycles that are applied during research, but they are not specifically prescribed for testing the particle formation during braking. The UNECE (United Nations Economic Commission for Europe) has included it in its plan and is in the development phase of introducing standardized cycles that will prescribe the braking cycle, the purpose of which will be to examine the formation of particles. This kind of review paper can be important for researchers who are engaged in this field, and the develop their own cycles or tests to examine the concentration or mass of particles formed during braking.

Atmospheric particle number size distribution and size-dependent formation rate and growth rate of neutral and charged new particles at a coastal site of eastern China

Coastal new particle formation (NPF) may be complicated due to the influence of both continental and marine air masses. Here we presented the result of particle number size distribution and NPF event measurements at a coastal industrial park of eastern China from 2018 to 2019. The highest nucleation-mode particle number concentration (daytime maximum: 4.9 × 103 cm−3) and NPF frequency (8% of the observation days) were observed in the continental-marine air masses that originated from North China Plain and traveled along the coastline before arriving at the coastal site. The formation rates of 2 nm particles (J2) at this coastal site are similar to those reported in the urban environments around the world, probably due to the influence of local industrial emission. Ion to total particle number concentration ratios in 2–7 nm and 7–20 nm were 1.5% and 12%, respectively, during the NPF periods. Neutral new particle formation pathway thus dominated over ion-mediated pathway at this coastal site. Our observation also showed that number concentration and formation rate of neutral new particles decreased monotonically with particle size, while those of charged new particles increased with particle size. Such difference points to additional formation and loss mechanisms of charged particles, such as ion-aerosol attachment and ion-ion recombination in the atmosphere. The behavior of appearance time-based growth rates, however, are similar for neutral and charged particles.

Energy storage and photosensitivity of in-situ formed silver-copper (Ag-Cu) heterogeneous nanoparticles generated using multi-tool micro electro discharge machining process

The present work focused on the energy storage and photosensitivity of in-situ formed segregated type silver-copper (Ag-Cu) heterogeneous nanoparticles generated by using the developed Micro-Electro Discharge Machining (Micro-EDM) process. The investigation includes analysis of useful heat gain, temperature gain, and thermal efficiencies by the nanofluids using fabricated mini parabolic solar trough collector. Photosensitivity of nanoparticles are studied by evaluating light absorbance and bandgap energies at different light intensities. Theoretical study includes understanding of the effects of the metallic vapor pressure, dielectric temperature, and the material properties on heterogeneous particle formation mechanisms. The experimentation work comprises of conduction of ten experiments by keeping silver plate (workpiece) at anode terminal and varying copper multi-tool pins from 1, 2, 3…10 at cathode terminal submerged in deionized water with 0.7 mM concentration of CTAB surfactant. Particles generated are found to be well dispersed, heterogeneously arranged structures with average particle size ranging from (4.83 ± 3.35 in 3rd experiment) nm to (15.37 ± 5.46 in 5th experiment) nm. XRD crystallographic studies confirmed the presence of the FCC structure of Ag and BCC structure of Cu2O. The maximum particle synthesis is from the 9th experiment producing 5.4 g/L for 30 min of machining with the spark energy of 2.88 mJ. The highest useful heat gain is obtained by the 3rd experiment due to higher silver content whereas highest overall thermal efficiency of 14.5% and bandgap energy of 2.75 eV is obtained by the 7th experiment nanofluid.

Fatty Acids Can Induce the Formation of Proteinaceous Particles in Monoclonal Antibody Formulations

The presence of subvisible or visible particles in mAb formulations can pose significant challenges to pharmaceutical development as it can lead to reduced shelf life, batch rejection, and recalls. Among all type of particles, proteinaceous particles are the most concerning due to their potential role in immunogenicity. Nevertheless, the underlying mechanism for protein particle formation remains poorly understood. Past research highlighted the importance of interfaces and mechanical agitation in causing protein particle formation. Current research suggests that fatty acids, as impurities present in excipients or as a result of polysorbate degradation, can also induce protein assembly and promote particle formation. In this work, we assessed oleic and lauric acid for their impact on particle formation as each represents the main hydrolysis product of PS80 or PS20, respectively. It was found that co-existence of either fatty acids with 10 mg/mL mAb A can cause protein particles, with a similar morphology to those observed previously in mAb formulations. FTIR spectra showed that the particles are proteinaceous, heterogeneous in its composition, but contain corresponding fatty acids. Interestingly, it was found that oleic acid is significantly more effective in causing protein particles than lauric acid in these experiments. This suggests that PS20 containing formulations might have a lower likelihood to have protein particles compared to PS80 containing mAb formulations if hydrolysis of polysorbate were to occur. Lastly, the presence of 0.01% polysorbate in the mAb A formulation was able to fully mitigate the effect of fatty acids and reduce the protein particles significantly, suggesting a potential mechanism where interfacial action is involved. The present study can help to understand the root cause for protein particles in a mAb formulation where fatty acids are introduced because of polysorbate hydrolysis. With further work, it will help to shed light into product control strategy as well as design approaches for robust mAb products.

Custom Design of Protein Particles as Multifunctional Biomaterials

AbstractAssembled protein particles, as emerging biomaterials, have broad applications ranging from vaccines and drug delivery to biocatalysis and particle tracking, but to date these require trial‐and‐error rational design experimentation and/or intensive computational methods to generate. Here, the authors describe an easy‐to‐implement engineering strategy to generate customized protein particles as multifunctional biomaterials. They utilize protein–peptide modules to generate functional nanoparticles whose assembly and size is controlled by the addition of mild stimuli. The protein assembling method is versatile, as exemplified through particle formation with 7 distinct protein modules, using a variety of assembly conditions tailored by the chemistries of 3 peptide partners. They have generated customized protein particles using enzymes, binding and reporter proteins, and their functions and utilities are demonstrated using biocatalysis, sensing, and labelling applications, respectively. Furthermore, co‐assembly with two functional proteins within one particle has been successfully achieved and demonstrated. Physical insights into the kinetics and molecular mechanisms of particle formation are revealed by small angle X‐ray scattering and mass photometry, providing fundamental knowledge to guide design and manufacture these interesting biomaterials in future. Their protein assembling strategy is a reliable method for fabricating a protein particle to deliver new functionalities on‐demand.

Modelling the phenomenon of elements separation in GSR particles containing aluminum using information theory analysis and molecular dynamics simulation

In the field of forensic science, detecting gunshot residue (GSR) particles on an individual or his belongings can connect him to a firearm discharge. One of the most important aspects in research into primer discharge residue analysis is the mechanism of residue particle formation. Understanding the particle formation mechanism should help the forensic scientist to differentiate GSR from particles originating from other sources. The elemental composition of GSR particles depends upon the type of ammunition used. Modern Western ammunition all contain a very similar priming composition, the basic elements found being Lead (Pb), Barium (Ba) and Antimony (Sb). However, some manufacturers add Aluminum (Al) to the primer mixture, this addition may result in GSR particles composition of PbBaSbAl. Our experience in analyzing GSR particles derived from ammunition containing Al suggests that the addition of Al to the primer often causes elements separation forming particles with regions of distinct composition instead of one homogenous particle type. One particle-region-type predominantly includes the elements Pb and Sb, with a small amount of Ba, and the other particle-region-type predominantly contains Al and Ba. We replicated and explained this phenomenon using information theory analysis as well as running a molecular dynamic simulation, both on large-scale systems.

Preparation of Metal Nitride Particles Using Arc Discharge in Liquid Nitrogen.

A simple process to synthesize metal nitride particles was proposed using submerged arc discharge plasma in liquid nitrogen. Gibbs standard free energy was considered for the selection of the nitride-forming materials. In this study, titanium (Ti) and aluminum (Al) electrodes were used as raw materials for nitride particle preparation. Liquid nitrogen acted as a dielectric medium as well as a nitridation source in this process. A copper electrode was also used as a non-reactive material for comparison with the reactive Ti and Al electrodes. As the operating conditions of the experiments, the arc discharge current was varied from 5 A (low-power mode) to 30 A (high-power mode). The formation of titanium nitride (TiN) and aluminum nitride (AlN) was confirmed in the particles prepared in all experimental conditions by X-ray powder diffraction (XRD). The observation using a field emission scanning electron microscope (FE-SEM) and a field emission transmission electron microscope (FE-TEM) indicated that the synthesized TiN particles showed a cubic morphology, whereas AlN particles containing unreacted Al showed a spherical morphology. The experiments using different metal electrode configurations showed that the anode generated most of the particles in this process. Based on the obtained results, a particle formation mechanism was proposed.

Characterizing the Chemical Profile of Incidental Ultrafine Particles for Toxicity Assessment Using an Aerosol Concentrator.

Incidental ultrafine particles (UFPs) constitute a key pollutant in industrial workplaces. However, characterizing their chemical properties for exposure and toxicity assessments still remains a challenge. In this work, the performance of an aerosol concentrator (Versatile Aerosol Concentration Enrichment System, VACES) was assessed to simultaneously sample UFPs on filter substrates (for chemical analysis) and as liquid suspensions (for toxicity assessment), in a high UFP concentration scenario. An industrial case study was selected where metal-containing UFPs were emitted during thermal spraying of ceramic coatings. Results evidenced the comparability of the VACES system with online monitors in terms of UFP particle mass (for concentrations up to 95 µg UFP/m3) and between filters and liquid suspensions, in terms of particle composition (for concentrations up to 1000 µg/m3). This supports the applicability of this tool for UFP collection in view of chemical and toxicological characterization for incidental UFPs. In the industrial setting evaluated, results showed that the spraying temperature was a driver of fractionation of metals between UF (<0.2 µm) and fine (0.2–2.5 µm) particles. Potentially health hazardous metals (Ni, Cr) were enriched in UFPs and depleted in the fine particle fraction. Metals vaporized at high temperatures and concentrated in the UF fraction through nucleation processes. Results evidenced the need to understand incidental particle formation mechanisms due to their direct implications on particle composition and, thus, exposure. It is advisable that personal exposure and subsequent risk assessments in occupational settings should include dedicated metrics to monitor UFPs (especially, incidental).

The Mechanism for Coarse Nb-Rich Particle Formation in Steel

The Mechanism for Coarse Nb-Rich Particle Formation in Steel

Morphological evolution of boron carbide particles: Sol-gel synthesis of nano/micro B4C fibers

Herein we present a novel non-catalytic sol-gel route to synthesize nano/micro boron carbide fibers. By in-situ decoration of the precursor surface with boric acid crystals during the thermal decomposition stage, the growth kinetics of boron carbide particles was manipulated. Therefore, the formation of anisotropic crystals instead of polyhedral-equiaxed ones was successfully enabled. The results indicated that highly crystalline boron carbide (B4C) particles with a low amount (<1 ± 5 wt%) of free carbon were obtained. The SEM and HR-FESEM micrographs revealed that B4C particles with fully polyhedral-equiaxed morphology were obtained from the precursors, which were thermally decomposed with 2 h holding time at 675 °C. As a result of increased thermal decomposition duration of precursor, B4C particles with various morphologies, such as rhomboid-plate, nanobelt, and fiber were formed beside the polyhedral-equiaxed particles. The yield of boron carbide fiber formation was increased, and polyhedral-equiaxed particles were decreased in the final products by tailoring the structure of the preceramic precursor. The products containing at least 50% of boron carbide fiber were achieved using 12 h of thermally decomposed precursors. The formation and growth mechanisms of boron carbide particles were speculated and comprehensively discussed.

Analysis of the Mechanism of Cholesterol Particle Formation by Liquid Antisolvent Crystallization

Analysis of the Mechanism of Cholesterol Particle Formation by Liquid Antisolvent Crystallization

Theoretical and Experimental Evaluation of the Reduction Potential of Straight-Chain Alcohols for the Designed Synthesis of Bimetallic Nanostructures.

Recently, the development of bimetallic nanoparticles with functional properties has been attempted extensively but with limited control over their morphological and structural properties. The reason was the inability to control the kinetics of the reduction reaction in most liquid-phase syntheses. However, the alcohol reduction technique has demonstrated the possibility of controlling the reduction reaction and facilitating the incorporation of other phenomena such as diffusion, etching, and galvanic replacement during nanostructure synthesis. In this study, the reduction potential of straight-chain alcohols has been investigated using molecular orbital calculations and experimentally verified by reducing transition metals. The alcohols with a longer chain exhibited higher reduction potential, and 1-octanol was found to be the strongest among alcohols considered. Furthermore, the experimental evaluation carried out via the synthesis of metallic Cu, Ni, and Co particles was consistent with the theoretical predictions. The reaction mechanism of metallic particle formation was also studied in detail in the Ni-1-octanol system, and the metal ions were confirmed to be reduced via the formation of nickel alkoxide. The results of this investigation were successfully implemented to synthesize Cu-Ni bimetallic nanostructures (core-shell, wire, and tube) via the incorporation of diffusion and etching besides the reduction reaction. These results suggest that the designed synthesis of a wide range of bimetallic nanostructures with more refined control has become possible.

Synthesis of High Specific Surface Area Macroporous Pectin Particles by Template-Assisted Spray Drying.

Many types of porous particles containing inorganic and organic substances, such as carbon, metals, metal oxides, inorganic-organic hybrids, and polymers, have been developed. However, natural polymer-derived particles are relatively rare. To our knowledge, this report describes the first synthetic method for obtaining meso-/macroporous particles made from pectin, which is a natural polymer with a wide range of biological activities suitable for active substance support applications. These porous particles were prepared using a template-assisted spray-drying method, followed by a chemical etching process. An organic template [i.e., poly(methyl methacrylate) (PMMA)] or an inorganic template [i.e., calcium carbonate (CaCO3)] was used to evaluate the resulting formation of macroporous structures in the pectin particles. Furthermore, the concentration of the templates in the precursor solution was varied to better understand the mechanism of porous pectin particle formation. The results showed that the final porous particles maintained the characteristic properties of pectin. The differences between the two templates resulted in two distinct types of porous particles that differed in their particle morphologies (i.e., spherical or wrinkled), particle sizes (ranging from 3 to 8 μm), pore sizes (ranging from 80 to 350 nm), and pore volume (ranging from 0.024 to 1.40 cm3 g-1). Especially, the porous pectin particles using the CaCO3 template have a significantly high specific surface area of 171.2 m2 g-1, which is 114 times higher than that of nonporous pectin particles. These data demonstrated the potential for using PMMA and CaCO3 templates to control and design desired porous materials.

Competitive formation of HSO4- and HSO5- from ion-induced SO2 oxidation: Implication in atmospheric aerosol formation

This study presents a theoretical investigation of the ion-induced SO2 oxidation by the hydroxyl (OH) and hydroperoxyl (HO2) radicals. Initiated by the superoxide ion (O2-), the reaction with HO2 to form the SO5- and HSO4− ions from two different mechanisms is prevented by high energy barriers, 30.20 and 33.42 kcal mol−1, respectively, whereas the reaction with OH to form HSO5- is highly exergonic and takes place through a barrierless process. The latter reaction, hereby, not only highlights the formation mechanism of the HSO5- ion in the gas-phase, but closes a mechanism for SO2 oxidation initiated by O2-. Giving the suspected role of HSO5- to drive aerosol formation besides HSO4- that was brought up in earlier studies, we calculated the formation energies and the thermodynamics of its clustering with 1–3 sulfuric acid molecules with and without one ammonia molecule. The results showed that the formation of HSO5--based clusters is highly exergonic and that they are more stabilized by ammonia than HSO4--based clusters in the cluster size range considered. Assuming thermal equilibrium, the abundance of the largest HSO5--containing cluster, namely NH3⋅(H2SO4)3⋅HSO5−, is determined to be higher than that of the corresponding HSO4--containing cluster at ambient conditions, in agreement with a previous experimental result. This indicates the important role the NH3⋅(H2SO4)3⋅HSO5− cluster might play in the early stages of aerosol formation, and highlights the necessity to consider larger HSO5− – sulfuric acid – bases clusters not only to clarify their implication in the mechanism of atmospheric particle formation but also to quantify their effect on aerosol formation rates.

Impact of Urban Pollution on Organic-Mediated New-Particle Formation and Particle Number Concentration in the Amazon Rainforest.

A major challenge in assessing the impact of aerosols on climate change is to understand how human activities change aerosol loading and properties relative to the pristine/preindustrial baseline. Here, we combine chemical transport simulations and field measurements to investigate the effect of anthropogenic pollution from an isolated metropolis on the particle number concentration over the preindustrial-like Amazon rainforest through various new-particle formation (NPF) mechanisms and primary particle emissions. To represent organic-mediated NPF, we employ a state-of-the-art model that systematically simulates the formation chemistry and thermodynamics of extremely low volatility organic compounds, as well as their roles in NPF processes, and further update the model to improve organic NPF simulations under human-influenced conditions. Results show that urban pollution from the metropolis increases the particle number concentration by a factor of 5-25 over the downwind region (within 200 km from the city center) compared to background conditions. Our model indicates that NPF contributes over 70% of the total particle number in the downwind region except immediately adjacent to the sources. Among different NPF mechanisms, the ternary NPF involving organics and sulfuric acid overwhelmingly dominates. The improved understanding of particle formation mechanisms will help better quantify anthropogenic aerosol forcing from preindustrial times to the present day.

Differing Mechanisms of New Particle Formation at Two Arctic Sites

AbstractNew particle formation in the Arctic atmosphere is an important source of aerosol particles. Understanding the processes of Arctic secondary aerosol formation is crucial due to their significant impact on cloud properties and therefore Arctic amplification. We observed the molecular formation of new particles from low‐volatility vapors at two Arctic sites with differing surroundings. In Svalbard, sulfuric acid (SA) and methane sulfonic acid (MSA) contribute to the formation of secondary aerosol and to some extent to cloud condensation nuclei (CCN). This occurs via ion‐induced nucleation of SA and NH3 and subsequent growth by mainly SA and MSA condensation during springtime and highly oxygenated organic molecules during summertime. By contrast, in an ice‐covered region around Villum, we observed new particle formation driven by iodic acid but its concentration was insufficient to grow nucleated particles to CCN sizes. Our results provide new insight about sources and precursors of Arctic secondary aerosol particles.

Hf metal powder synthesis via a chemically activated combustion-reduction process

The present study demonstrates the synthesis of fine hafnium (Hf) metal powders via a chemically activated combustion synthesis (CS) approach, which develops temperatures in the range of 1000–1600 °C. The current CS approach can be employed to obtain Hf powders with a single-crystalline hexagonal close-packed (hcp) structure in addition to high compositional uniformity and average particle sizes ranging from 0.05 to 2.0 μm. The mechanism of Hf particle formation can be understood by analyzing the process thermodynamics, including adiabatic temperatures and equilibrium reaction phases. In addition, analytical methods, including X-ray diffraction, SEM/TEM BET, FTIR, and oxygen analysis, were employed to characterize the synthesized Hf powders. Theoretical analysis was also conducted to predict the oxygen content according to Hf particle size. To the author's best knowledge, this work is the first known report demonstrating the preparation of hafnium micro- and nanopowders by the combustion synthesis method.