Kinetic Particle Research Articles

Effective thermo-electric-mechanical modeling of capacitively coupled plasma in low-pressure conditions: Modeling and application in dry etching

In semiconductor dry etching process, capacitively coupled plasma (CCP) is widely used in low-pressure environments. However, the kinetics of species particles in low-pressure conditions are different from the general environments. Traditional continuum models are popular in industry due to their simplicity, but they struggle to account for the kinetics of particles in low-pressure conditions. Although particle-in-cell (PIC) modeling is suitable for simulating the behavior of a single particle, it is difficult to perform such industrial simulations due to the high computational cost. To account for both kinetics and engineering applicability, this study presents an effective thermo-electric-mechanical modeling structure of CCP at low-pressure conditions. This modeling structure includes balance laws of continua derived from the global energy equilibrium containing thermal, electric and mechanical energies. The ion momentum, which is ignored in traditional plasma continuum models, is considered in the balance laws, and electron energy distributions are obtained by solving the Boltzmann equation to obtain the properties of electron transport. In addition, the model variables are calculated based on mixed kinetic theory accounting for the fraction of each species. The results of the proposed modeling are compared to those of a PIC model to validate its ability to describe the distribution of electrons with respect to pressure conditions. Based on the proposed numerical formulations, this study built a MATLAB-based program to guide the design of a screen baffle in dry etching equipment. This program captures the critical aspects of the practical application of screen baffle design in the context of the dry etching process. The results of this paper showed that the proposed model can be applied to engineering applications under low-pressure conditions.

Direct solar-driven calcination kinetics for Ca-looping thermochemical energy storage

Ca-looping thermochemical energy storage is considered to be an efficient and low-cost thermal energy storage technology for third-generation concentrated solar thermal power generation. However, the limitation of conventional kinetic studies cannot satisfy the direct solar driven calcination reaction mechanism. Therefore, a direct solar-driven calcination kinetics function of calcium carbonate particles based on multivariate nonlinear regression method is proposed. This scheme driven by full-wavelength solar energy has widely universality and application taking the effects of particle size, porosity, doping composition, temperature and CO2 concentration into account, which intuitively reflects the essence of photothermal conversion characteristics and reveals the mechanisms of photothermal calcination reactions. The heat storage efficiency of Fe:Mn:Al modified calcium carbonate particles after 20 cycles is 93.03%, the spectral absorption rate is 84.27%. This work provides a new idea for the in-depth study of the decomposition kinetics of solar-driven calcium-based particles.

Numerical model of a gaseous inductive discharge in oxygen, taking into account the complete scheme of the vibrational kinetics of O2 molecules

In this work, the two-dimensional model of inductively coupled plasma discharge in oxygen was developed. The model includes hydrodynamic equations in drift-diffusion approximation for describing the kinetics of charged (electrons and ions) and neutral plasma particles, Maxwell’s equations for electromagnetic fields, and equations for the temperature and neutral gas flow as well as a detailed scheme of plasma-chemical reactions. The model was tested against theoretical and experimental data in a simple cylindrical chamber. The electron density and temperature distributions were obtained over a wide range of powers deposited in the plasma (100–500 W) and compared with literature data. Also, the complete scheme of the vibrational kinetics of O2 molecules was included in the model. The vibrational distribution function was calculated in low-pressure inductive discharge as well as spatial distributions of plasma parameters (density and temperature of electrons, excited components, neutral gas temperature, etc.) and flows of charged and active neutral particles at the reactor walls.

Kinetics of suspended particles with different shapes interacting in a fluid channel

Kinetics of suspended particles with different shapes interacting in a fluid channel

Single-Crystal Growth of P2-Type Layered Oxides with Increased Exposure of {010} Planes for High-Performance Sodium-Ion Batteries.

An increase in the size of single-crystal particles can effectively reduce the interfacial side reactions of layered oxides for sodium-ion batteries at high voltages but may result in sluggish Na+ transport. Herein, single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 with increased proportions of {010} planes is synthesized by adding low-cost NaCl as the molten salt. With the assistance of a NaCl molten salt, the median diameter (D50) of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 increases to 10.46 μm relative to that of the comparison sample without NaCl (6.57 μm). Electrolyte decomposition on the surface of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 is considerably suppressed, owing to a decrease in the specific surface area. Moreover, the increased exposure of {010} planes is favorable for improving the Na+ transport kinetics of single-crystal particles. Therefore, at 100 mA g-1, single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 exhibits a high-capacity retention of 96.6% after 100 cycles, which is considerably greater than that of the comparison sample (86.8%). Moreover, the rate performance of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 (average discharge capacity of 81.2 mAh g-1) is superior to that of the comparison sample (average discharge capacity of 61.2 mAh g-1) at 2000 mA g-1. This work provides a new approach for promoting the single-crystal growth of layered oxides for highly stable interfaces at high voltages without compromising Na+ transport kinetics.

Influence of hydrogen flow rate on multistep kinetics of hematite reduction

Hydrogen ironmaking is the most ideal approach to reduce industrial carbon emissions. In this study, the isothermal reaction characteristics and multistep kinetics of hematite particles with hydrogen are investigated using thermogravimetric analysis (TGA) at 650–725 °C. The two steps of Fe3O4–FeO and FeO–Fe of hematite reduction are discovered to proceed simultaneously. The reduction is divided into three stages according to the derivative thermogravimetry (DTG) curves. For the three stages, the optimal kinetic models are the phase boundary and the 2D growth of nuclei. In the range of 75–130 mL/min, there is a critical hydrogen flow rate below which the apparent activation energy increases and above which it remains constant, which is 30.44 ± 3.30, 77.33 ± 0.41, and 49.56 ± 0.49 kJ/mol, respectively. A significant linear correlation between hydrogen flow rate above the critical value and the pre-exponential factor is found.

Insights into the precipitation kinetics of CaCO3 particles in the presence of polystyrene sulfonate using in situ small-angle X-ray scattering.

The formation of calcium carbonate (CaCO3) nanoparticles (NPs) in the presence of polystyrene sulfonate (PSS) as an additive was examined by time-resolved small-angle X-ray scattering (SAXS) in a flow system that mimics experimental conditions used at home facilities where the precipitation can be achieved in a beaker. The experiments were carried out at low concentrations to remain in the dilute regime. A model-independent analysis was performed using the Porod invariant which defines the scale factor, leaving only the distribution of radii as the adjustable parameter. The presence of the PSS additive strongly retards the precipitation of CaCO3 NPs. The formation of NPs reaches a state of equilibrium after a few minutes. Here, it is shown that the concentration of precursors at a fixed PSS concentration plays a key role in determining the size of the NPs obtained. A full analysis of the SAXS patterns was carried out using the Hurd-Flower model to account for the weaker intensity decay than the classical Porod behaviour. The temporal evolution of the particle radii was determined. Wide-angle X-ray scattering experiments carried out simultaneously show that the particles formed have the structure of vaterite with growth consistent with the evolution of the Porod invariant.

Plasma Astrophysics and Modern Plasma Cosmology

As well known, more than 99% of the observable matter in the universe is plasma, and the plasma astrophysics studies various physical processes and phenomena occurring in cosmic plasmas, from small-scale collective interaction processes and energy transforming mechanisms in particle kinetics to the state of large-scale structure of cosmic objects and their eruptive phenomena. The present paper reviews the important role of the plasma astrophysics in the development of the modern astronomy as well as the formation of the modern plasma cosmology based on the history of the cosmic evolution, the formation of large-scale structures, and eruptive phenomena of cosmic objects. In addition, the unique function of satellite in situ exploring researches in space plasmas to act as the natural laboratory for the plasma astrophysics is further elaborated.

Exploring the influence of particle phase in the ozonolysis of oleic and elaidic acid

Aerosol particles in the atmosphere undergo heterogeneous transformations due to interactions with various gas-phase oxidants such as ozone. While it is known that these reactions are significantly affected by the phase state of the particle, a direct comparison between the reaction kinetics and product distributions for the same reactive process occurring in the different phases remains elusive. This study uses single particle levitation and flow-tube methods to measure and compare the ozonolysis of particles containing oleic acid and its trans isomer elaidic acid in liquid, supercooled liquid, and solid states. We measure their evolving size, optical properties, phase, and chemical composition during reaction. Both primary reactions and secondary chemistry were explored, along with the influence of particle phase state on reaction kinetics and product formation. Notably, we directly compare the reaction kinetics of supercooled liquid elaidic acid particles with liquid oleic acid particles, revealing similar uptake coefficients indicative of similar inherent reactivity of the C = C moiety. We go on to compare the kinetics of solid elaidic acid particles, formed due to solidification at room temperature and freezing at low temperature. We found a significant slowing in reaction kinetics that may be attributed to the phase of the particle and the influence of slowed molecular diffusion, supported by qualitative agreement with a multilayer kinetic model (KM-SUB). We further explore differences in the product distributions between particles exhibiting different phase states. These results provide important insights into how the chemical aging of ambient aerosol particles may be influenced by their physicochemical characteristics.

Key Modes of Ignition and Maintenance of Corona Discharge in Air

Theoretical and experimental studies of various modes of corona discharge operation in atmospheric pressure air are presented in this short review. The original results of modeling negative corona discharges are presented, taking into account the non-stationary plasma-chemical kinetics of charged particles in air plasma. The space–time evolution of the discharge in needle-to-plane geometry is investigated and analyzed. Several stages of discharge development are revealed from the moment of initiation of a low-negative current corona to the quasi-stationary mode of a glow discharge. Experimental data of the authors are presented. Modern technology and diagnostic equipment with a wide variation of the main parameters (the shape and polarity of the applied voltage, the type of gap, etc.) was used. The measurement of the optical characteristics of the plasma glow was carried out with high spatial resolution. Corona discharge current pulse profiles in the air at atmospheric pressure have been recorded with subnanosecond time resolution. With a positive polarity of the pin electrode and high voltage, a transition from a spherical streamer initiating a corona discharge to a cylindrical streamer is shown. The author’s results are rigorously evaluated through a critical comparison with findings from other research groups.

On the impact of grinding conditions in the flotation of semi-soluble salt-type mineral-containing ores driven by surface or particle geometry effects?

Grinding and flotation processes are often studied independently, despite the well-established grinding influence on flotation performance, which affects not only particle size and thus liberation but also shape and leads to complex changes in pulp chemistry affecting the particle surface properties relevant for selective bubble attachment. Yet, no study jointly investigated these possible causes and many are limited to single mineral flotation. We relate grinding conditions to changes in pulp chemistry and particle surface properties and assess their impact on upgrading. We studied three non-sulfide ores with different feed grades and valuables: scheelite, apatite, and fluorite. These were dry-, wet-, and wet conditioned-ground before flotation in a laboratory mechanical cell. Results were evaluated with bulk- and particle-specific methodologies. The selectivity of the process is higher after dry grinding for the fluorite and apatite ores and irrelevant for the scheelite ore. Variations in flotation kinetics of individual particles associated to their size and shape are not sufficient to explain these results. The higher concentration of Ca2+ and Mg2+ observed in the pulp after wet grinding, altering particle surface properties, better explains the phenomenon. Additionally, we demonstrate how particle shape impacts are system specific and related to both entrainment and true flotation.

The Nonorthogonal X-line in a Small Guide-field Reconnection Event in the Magnetotail

Magnetic reconnection is a fundamental plasma process that has been studied with analytical theory, numerical simulations, in situ observations, and laboratory experiments for decades. The models that have been established to describe magnetic reconnection often assume a reconnection plane normal to the current sheet in which an antiparallel magnetic field annihilates. The annihilation points, also known as the X-points, form an x-line, which is believed to be perpendicular to the reconnection plane. Recently, a new study using Magnetospheric Multiscale mission observations has challenged our understanding of magnetic reconnection by providing evidence that the x-line is not necessarily orthogonal to the reconnection plane. In this study we report a second nonorthogonal x-line event with similar features as that in the previous case study, supporting that the sheared x-line phenomenon is not an aberrant event. We employ a detailed directional derivative analysis to identify the x-line direction and show that the in-plane reconnection characteristics are well maintained even with a nonorthogonal x-line. In addition, we find the x-line tends to follow the magnetic field on one side of the current sheet, which suggests an asymmetry across the current sheet. We discuss the possibility that the nonorthogonal x-line arises from an interplay between the two aspects of reconnection: the macroscopic magnetic field topology and microscopic particle kinetics.

Dissolution kinetics of phosphate ore particles in excessive phosphoric acid

Dissolution kinetics of phosphate ore particles in excessive phosphoric acid

Effect of Na+ on the Adsorption Behavior of Polystyrene Nanoparticles onto Coal and Quartz Surfaces

The recovery of difficult-to-float coal using traditional nonpolar hydrocarbon oil collectors can be challenging, particularly for low-rank or oxidized coal. Thus, there is a need for more efficient flotation agents. Nanoparticle flotation collector technology has become increasingly popular in the field of mineral processing, and the presence of various ions in the slurry can significantly affect the interaction between collectors and mineral surfaces. In this study, cationic polystyrene (PS) nanoparticles were prepared using an emulsion polymerization method, and the effects of Na+ ion concentration on the in situ adsorption and desorption processes, adsorption layer configuration, and adsorption kinetics of PS particles on amorphous carbon (coal model) and SiO2 sensors (quartz mineral model) were analyzed using the quartz crystal microbalance with dissipation (QCM-D) technique. Our results showed that the hydrophobic PS nanoparticles irreversibly adsorbed onto both amorphous carbon and SiO2 sensors under different environmental conditions, and their adsorption capacity decreased gradually with increasing Na+ ion concentration. Increasing Na+ ion concentration from 0 M to 1.0 M resulted in a 24.4% and 30.9% decrease in equilibrium adsorption capacities of PS nanoparticles onto amorphous carbon and SiO2 surfaces, respectively. The adsorption rate of PS nanoparticles onto the SiO2 surface was much greater than that on the amorphous carbon surface. The adsorption rate constant of PS nanoparticles onto SiO2 surfaces was 0.782 at 0.1 M Na+ ion concentration, while its adsorption rate constant onto amorphous carbon surfaces was only 0.060. Moreover, the adsorption process was found to be more in line with the quasi-primary kinetic model. These findings suggest that PS nanoparticles may serve as promising flotation collectors for the recovery of difficult-to-float coal, and highlight the importance of considering the effect of dissolved ions on the adsorption properties of flotation collectors.

Physicochemical Analysis of Particle Matter from a Gasoline Direct Injection Engine Based on the China Light-Duty Vehicle Test Cycle

This paper investigated the physical and chemical properties of gasoline direct injection (GDI) engine particulate matter (PM). The physical properties mainly included the particulate aggregate morphology, primary particle size, and internal nanostructure. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) were used to obtain particle morphology information and to conduct image processing and analysis. The chemical characterization tests included X-ray photoelectron spectroscopy (XPS), energy dispersive scanning (EDS), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA). XPS can be used to observe the content of carbon and oxygen components and the surface carbon chemistry status, EDS can be used to obtain the elemental composition of particles, and TGA is used to analyze the oxidative kinetics of particles. Samples were collected from the exhaust emissions of a passenger vehicle compliant with China’s VI emission standards under China Light-Duty Vehicle Test Cycle (CLTC) test conditions. The study found that the particle morphology mainly comprised primary particles stacked on top of each other to form agglomerate structures, and the primary particles exhibited a core–shell structure. Analysis showed that carbon and oxygen were the predominant components of the particles, with other metallic elements also present. The XPS observations agreed with the FTIR results, indicating a small amount of oxygen was present on the particle surface and that the carbon components consisted mainly of sp2 hybridized graphite and sp3 hybridized organic carbon. The TGA results indicated high characteristic temperatures and low oxidation activity.

Drying Kinetics of a Single Biomass Particle Using Fick’s Second Law of Diffusion

Drying has been widely studied as a necessary process in biomass utilization. The steam diffusion law plays an important role in drying kinetics. The drying kinetics of a single biomass particle using Fick’s second law of diffusion was studied in this paper. A parabolic relationship appeared between the critical moisture content and temperature. The critical moisture content decreased with the increase in drying temperature and the initial moisture content. The drying temperature had a significant effect on the effective diffusivity and coefficient of mass transfer during the dramatically falling period of the biomass drying process. However, it was affected by the effective diffusivity and coefficient of mass transfer during the slowly falling period. The initial moisture caused the opposite effect during the different periods. The normalized biomass moisture content generally increased with the increase in drying temperature, and decreased with the increase in initial moisture content. The initial moisture content had an effect on the normalized biomass moisture during the slowly rising period. Meanwhile, the drying temperature had an effect on the normalized biomass moisture during the whole period. The critical moisture content and the normalized biomass moisture content had negative relevant relationship. This study provides some valuable conclusions regarding the biomass drying process.

Differential particle and ion kinetics of silver nanoparticles in the lungs and biotransformation to insoluble silver sulfide

The measurement of nanoparticles (NPs) in a biological matrix is essential in various toxicity studies. However, the current knowledge has limitations in differentiating particulate and ionic forms and further identification of their biotransformation. Herein, we evaluate the biotransformation and differential lung clearance kinetics of particulate and ionic forms using PEGylated silver NPs (AgNP-PEGs; 47.51 nm) and PEGylated gold NPs (AuNP-PEGs; 11.76 nm). At 0, 3, and 6 h and 1, 3, 7, and 14 days after a single pharyngeal aspiration in mice at 25 μg/mouse, half of the lung is digested by proteinase K (PK) to separate particulates and ions, and the other half is subjected to the acid digestion method for comparison. The quantitative and qualitative evaluation of lung clearance kinetics suggests that AgNP-PEGs are quickly dissolved and transformed into insoluble silver sulfide (Ag2S), which shows a fast-clearing early phase (0 −6 h; particle T1/2: 4.8 h) and slow-clearing late phase (1 −14 days; particle T1/2: 13.20 days). In contrast, AuNP-PEGs were scarcely cleared or biotransformed in the lungs for 14 days. The lung clearance kinetics of AgNPs and biotransformation shown in this study can be informed by the PK digestion method and cannot be obtained using the acid digestion method.

Understanding the mechanism of microcrack-enhanced bioleaching of copper

Investigations on the microcrack distribution characteristics and bioleaching behaviors of particles were conducted to obtain better bioleaching efficiency and deepen the mechanism understanding. Results indicate that comminution by high-pressure grinding roll (HPGR) is the desirable method for obtaining particles with more abundant and wider microcracks. Fixing the HPGR pressure at 4 MPa results in the highest bioleaching efficiency for copper extraction, namely 86% for the shaking flask bioleaching (particle size: <1.7 mm) and 52% for the column bioleaching of particles (particle size: 3.35–6.7 mm). The suggested model for reaction kinetics of microcrack-containing particles implies that more abundant and wider microcracks can promote the exposure of both Cu-containing phases and ferrous iron as well as solution infiltration, as evidenced by the COMSOL simulation results and bacteria proliferation analysis. The results highlight the importance of microcracks for enhancing the bioleaching process and provide insights for the mechanism understanding.

On the oxidation kinetics of aging magnesium particles

On the oxidation kinetics of aging magnesium particles

Heterostructure charge transfer dynamics on self-assembled ZnO on electronically different single-walled carbon nanotubes

The charge transfer kinetics of the catalyst particles play a key role in advanced oxidation processes (AOP) for the complete destruction of recalcitrant and persistent contaminants in water. Here, a significant improvement in the photocatalytic performance is observed in the Single-Walled Carbon Nanotube (SWCNT)-ZnO heterostructure photocatalyst. The charge transfer dynamics and factors affecting AOP are studied using ZnO nanoparticles self-assembled onto three electronically different SWCNTs (metallic, semiconducting, and pristine) via the precipitation method, introducing a heterojunction interface. The creation of the SWCNT/ZnO heterostructure interface improves charge transfer and separation, resulting in a charge carrier lifetime of 7.37 ns. Also, surface area, pore size, and pore volumes are increased by 4.2 times compared to those of ZnO. The nanoparticles-coated face-mask fabric used as the floating photocatalyst exhibited high stability and recyclability with 99% RhB degradation efficiency under natural sunlight and 94% under UV light after the 5th cycle. The surface and crystal defects-oxygen or zinc defects/interstitials open new reaction active sites that assist in charge carrier transfer and act as pollutant absorption and interaction sites for enhanced performance. The ideal band edge positions of the valence band and conduction band favor the generation of H2O/OH•, OH·/OH, and O2/HO2• reactive oxygen species. OH• radicals are found to play a vital role in this AOP by using ethanol as an OH• scavenger.