Charged Solid Particles Research Articles

Magnetized dusty plasma: On issues of its complexity and magnetization of charged dust particles

AbstractIt is possible to excite various linear and nonlinear low‐frequency modes in dusty plasma, which is an admixture of electrons, ions, gas atoms, and negatively charged solid particles. The experimental as well as theoretical study of these low‐frequency dynamical modes in dusty plasma is very complex because of the involvement of dynamics of electrons, ions, and neutrals. If the external magnetic field is introduced to dusty plasma, then the dynamics of it will be more complex. The complexity of magnetized dusty plasma where plasma species (electrons and ions) are magnetized is discussed in detail by keeping the experimental findings in mind. The requirement of theoretical modeling, as well as computation experiments in understanding the dynamics of dusty plasma in the presence of a strong magnetic field, is suggested in the context of experimental findings. The major challenges to magnetizing the massive charged particles in plasma experiments and some proposed solutions are discussed in this review report.

TRIC EXPLOSION OF AEROSOLS. TO THE 115TH ANNIVERSARY OF THE TUNGUSKA METEORITE

A hypothesis has been proposed according to which the preserved traces of the impact on the nature caused by the explosion of the Tunguska meteorite are the result of electrical discharges in a cloud of solid particles, which, when moving at the space velocity in the upper atmosphere, were heated up to a high temperature and, due to thermionic emission, acquired large positive charges. The released thermo-electrons attached to air molecules and lagged behind the charged particles. The separation of the charges in the cloud caused powerful discharges similar to horizontal lightnings in clouds. The consequences of the discharges in the cloud of highly charged solid particles, which gave rise to the generation of hard ionizing radiation, are discussed.

Ion induced nucleation based-generator of strictly singly charged (solid - liquid) polydisperse particles up to 1 μm

Abstract: Calibration of optical counters, condensation particle counters, electrical impactors, filtration efficiency measurement, heterogeneous condensation (and many other laboratory applications in aerosol science and technology) are widely used with singly charged particles classified by a differential mobility analyzer with particles smaller than 1 μm. Nevertheless the method presents an ambiguity because of the presence of multi charged large particles of the same mobility than singly ones. This ambiguity results in uncertainty in the concentration regarded as a reference. The present paper reports a generation method of strictly singly (positive and negative) charged liquid and solid particles up to 1 μm. The generation-method is based on ion-induced nucleation of singly charged atmospheric ions. The method uses evaporation and controlled condensation of liquids or solid on seed ions. The ions grow and form wide continuum polydisperse distributions of positive or negative liquid/solid polydisperse particles up to 1 μm. The ions are produced with a corona or radioactive or soft X ray or UV source in filtered dry stream air. The final formed droplets or spheres around the ions keep the positive or negative initial charge of the ions. Vapors from low meting point solids or high boiling point and low vapor pressure liquids are used in this vaporizer-condenser generator. The paper focuses on particles with diameters up to 1 μm dedicated to classical differential mobility analyzers (DMA). The results with larger particles produced with the same generator design using heterogeneous condensation of vapors on sub 10 nm singly charged particles from melting NiCr (Kanthal) wires in air will be published in a second paper (manuscript in preparation). A companion paper on the saturation ratio profiles modeling with Comsol and comparison theory-experiments is in preparation. • Polydisperse aerosol generator based on ion induced nucleation is presented and characterized in this paper. • The generator produces particles from low melting points solids or low vapor pressure liquids. • The generator is based on evaporation-condensation method used in the widely used Sinclair Lamer generators. • Atmospheric ions produced by a corona source are used as seed residues. • Singly charged spherical particles (solid or liquid) up to 1 μm are produced by the generator without neutralizer.

Electrokinetics of spherical colloidal particles with a slip surface in a concentrated suspension

A theory is developed of the electrophoresis of a spherical colloidal particle with a slip surface in a concentrated suspension on the basis of Kuwabara’s cell model. We introduce the slipping length on the particle surface, which is the measure of the particle surface hydrophobicity. We derive the general expression of the particle electrophoretic mobility and its approximate analytic expressions for a particle carrying a low zeta potential. Expressions for other electrokinetics, that is, electrical conductivity, sedimentation velocity, and potential in concentrated suspensions, are also derived. Furthermore, it is shown that as in the case of a dilute suspension, a similarity is found between the electrokinetics of charged spherical solid particles with a slip surface in a concentrated suspension and that for liquid drops.

Effects of solid particles with various charging states and oil aerosols on the filtration characteristics of electret media

In this study, electret media were loaded with neutralized and charged potassium chloride (KCl) to examine the effect of charged solid particles on loading behaviour. The media were then loaded with diethylhexyl sebacate (DEHS), dipropylene glycol (DPG) and glycerol to obtain a correlation between the efficiency degradation and liquid aerosol. The results indicated that the efficiency of electret media decreased from 72% to 46% under the neutralized KCl loading whilst the efficiency decreased from 96% to 82% under the positively charged KCl loading. Particle charging increased the initial efficiency and also effectively minimized the efficiency degradation. Given the increase in efficiency via chargers, the deposition morphology of the solid particles on the fibres was changed to mitigate the efficiency degradation. With respect to electret media loaded with DEHS, DPG and glycerol, the decrease in efficiency was associated with the solubility difference between the fibres and oil aerosols. Given sufficient affinity between the oil particles and fibres, oil molecules permeated the chain segments of the fibres and produced swelling that damaged the charge traps and decreased efficiency. The results of this study can guide practical electret filter operations and provide a better indoor environment.

Effect of charging solid particles on their growth process and parameters of microwave discharge in liquid n-heptane

A zero-dimensional non-stationary model of a microwave discharge in liquid n-heptane at atmospheric pressure with continuous argon injection into the plasma region is presented. The model includes equations for the kinetics of neutral and charged plasma components, equations describing the formation and growth of solid particles from the decomposition products of n-heptane, and an equation for the microwave field strength in plasma. The description of the coagulation process takes into account the electrostatic repulsion of solid particles due to their charge. The kinetics of charged particles is described taking into account their death on the surface of negatively charged solid particles formed in plasma. To determine the coefficients of the reaction rates in mechanisms of direct electron impact, the electron energy distribution function obtained by solving the Boltzmann equation is used. Calculations have shown that the plasma quasineutrality is mainly supported by the charge of solid particles, and the electron concentration is 1–2 orders of magnitude less than the total ion concentration. An increase in the averaged microwave field was noted in comparison with the case that does not take into account charging. Charging of the solid particles does not affect the composition of the main gas-phase products, but leads to the suppression of the coagulation process for large solid particles, which leads to a change in the size distribution function of the solid particles formed in the plasma.

Analytically solvable model of scattering of relativistic charged particles in solids

We propose an analytically solvable model of the differential and total inelastic cross sections, mean free paths, and energy losses of charged projectiles (electrons, positrons, protons, ions, etc) within a unified framework. It is applicable within a broad range of incident energies (from 30–50 eV up to GeV in a case of an electron). Only the optical data are used as an input, without any ad-hoc correction terms, splitting into close and distant collisions, or fitting and adjustable parameters. We demonstrate that the derived expressions are in a very good agreement with other more complex numerical models and experimental data. Application of the derived formulae greatly saves computational time of evaluation of cross sections with respect to the numerical integration required by other models.

МАТЕМАТИЧЕСКОЕ ИССЛЕДОВАНИЕ СКОРОСТНОГО СКОЛЬЖЕНИЯ ФАЗ ПРИ ВЗАИМОДЕЙСТВИИ УДАРНОЙ ВОЛНЫ ПРЕДЕЛЬНО МАЛОЙ ИНТЕНСИВНОСТИ С ЭЛЕКТРИЧЕСКИ ЗАРЯЖЕННОЙ ГАЗОВЗВЕСЬЮ

The paper presents a mathematical model of an electrically charged suspension of particles, as well as numerical calculations related to the dynamics of the dispersed component of a mixture moving both under the influence of aerodynamic forces and under the influence of the Coulomb force. The author used a mathematical model of a nonequilibrium multiphase medium motion to describe the aerodynamics of suspensions. The mathematical model took into account the force interaction of the carrier and dispersed phases and interphase heat transfer, as well as the internal electric field generated by electrically charged solid particles. Using the software implementation of the mathematical model, a numerical study of the velocity slip of phases was carried out.

Heat and fluid flow in electro-osmotically driven systems

A numerical investigation of heat and fluid flow in electro-osmotically driven systems is presented, by considering plain channels and channels packed with charged solid particles. The results show that the introduction of charged solid particles a_ects the internal potential distribution, fluid flow and temperature distribution in the channel. Under the analysed conditions, the effect on heat transfer is confined to the centre of the channel. This topic needs to be further investigated since it is of interest in practical applications.

Pickering emulsions stabilized by charged nanoparticles.

The stabilization of o/w Pickering emulsions in cases of weak adsorption of solid particles at the surface of oil droplets is addressed. Though the adsorption is usually very strong and irreversible when partial wetting conditions are fulfilled, electrostatic repulsions between charged solid particles act against the adsorption. The regime of weak adsorption was reached using charged silica nanoparticles at high pH and low ionic strength. O/w Pickering emulsions of the diisopropyl adipate oil were stabilized by colloidal nanoparticles of Ludox® AS40 consisting of non-aggregated particles of bare silica (hydrophilic). The combination of stability assessment, droplet size and electrokinetic potential measurements at various pH values, adsorption isotherms and cryo-SEM observations of the adsorbed layers disclosed the specificities of the stabilization of Pickering emulsions by adsorption of solid nanoparticles against strong electrostatic repulsions. Not only the long-term stability of emulsions was poor under strong electrostatic repulsions at high pH, but emulsification failed since full dispersion of oil could not be achieved. Emulsion stability was ensured by decreasing electrostatic repulsions by lowering the pH from 9 to 3. Stable emulsions were stabilized by a monolayer of silica particles at 54% coverage of the oil droplet surface at low silica content and an adsorption regime as multilayers was reached at higher concentrations of silica although there was no aggregation of silica in the bulk aqueous phase.

Streaming-potential phenomena in the thin-Debye-layer limit. Part 3. Shear-induced electroviscous repulsion

We employ the moderate-Péclet-number macroscale model developed in part 2 of this sequence (Schnitzer et al., J. Fluid Mech., vol. 704, 2012, pp. 109–136) towards the calculation of electroviscous forces on charged solid particles engendered by an imposed relative motion between these particles and the electrolyte solution in which they are suspended. In particular, we are interested in the kinematic irreversibility of these forces, stemming from the diffusio-osmotic slip which accompanies the salt-concentration polarisation induced by that imposed motion. We illustrate the electroviscous irreversibility using two prototypic problems, one involving side-by-side sedimentation of two spherical particles, and the other involving a force-free spherical particle suspended in the vicinity of a planar wall and exposed to a simple shear flow. We focus on the pertinent limit of near-contact configurations, where use of lubrication approximations provides closed-form expressions for the leading-order lateral repulsion. In this approximation scheme, the need to solve the advection–diffusion equation governing the salt-concentration polarisation is circumvented.

Numerical model of the electro-gas-dynamics of a gas–particle system based on the equations of motion of a two-velocity two-temperature gas–particle mixture

A mathematical model of the electro-gas-dynamics of a gas–particle system is described. A numerical method for solving the system of equations is proposed, and an analysis is made of the motion of charged solid aerosol particles in gas–particle flow in the electric field produced by the corona electrode of the atomizer, the grounded surface on which deposition is performed, and the charge of the aerosol particles in the interelectrode space. The solution is based on the two-velocity two-temperature model of a monodisperse medium without phase transitions and coagulation assuming that only the carrier medium, described by the Navier–Stokes equations for a compressible gas, has viscosity. The dispersed phase is defined by the equation of conservation of mass, the equations of conservation of momentum components taking into account the Coulomb force and aerodynamic friction, and the equation of conservation of internal energy. The system is written in generalized coordinates in dimensionless form and solved using the explicit McCormack method with splitting over the spatial coordinates and a conservative correction scheme. The velocity and density fields of the gas–particle mixture were investigated in the interelectrode space and near the surface on which solid aerosol particles in the gas–particle flow are deposited.

Investigation of an electrogasdynamic energy conversion process in a gas expanding nozzle with heat addition

An electrogasdynamic (EGD) generator produces electricity by using a moving gas stream to transport charged particles from a low electric potential region to a high electric potential region. EGD electric conversion combined with the acceleration of gas expansion in a de laval nozzle is one of the methods of converting heat directly into electricity. A two-dimensional axis-symmetric model was developed to explore the effect of heat addition to the two phase flow acceleration process of air and charged solid particle inside the EGD gas expander nozzle. The results indicate that heat addition can effectively change the characteristics of the two phase flow. The added heat energy can be considerably converted into the kinetic energy of the air and the charged particles. Consequently, the heat to electricity efficiency of the energy conversion process in EGD gas expanding nozzle with heat addition can be further improved by the increasing of particle flow rate.

Dynamics of Two Charged Particles in a Creeping Flow

We study the interaction of two charged solid particles in a viscous fluid. It is assumed that the particles move either side-by-side or one after another along the same vertical line under the influence of the buoyancy/gravity force, Coulomb electrostatic force or its modification, and viscous drag force. The drag force consists of two components: the quasi-stationary Stokes drag force and Boussinesq–Basset drag force resulting from the unsteady motion. Solutions of the governing equations are analysed analytically and numerically for the cases of perfect fluid and viscous fluid; the comparison of these two cases is presented.

Effect of solution salinity on settling of mineral tailings by polymer flocculants

Understanding the interaction mechanism between polymeric flocculants and solid particles in solutions of high salinity and the associated flocculation mechanism is of great practical and fundamental importance in mineral processing and colloid and interface science. In this work, the effects of three polymers, polyacrylamide (PAM), Magnafloc 1011 (MF) and Al(OH)3-polyacrylamide (Al-PAM), on the settling of mineral tailings in freshwater and in saline solution were investigated. The settling of tailings significantly depends on solution salinity, type and dosage of polymer flocculants. MF showed the best settling performance among the three polymers in both freshwater and saline solutions. The tailings settling was found to be largely dependent on the various interactions among negatively charged clay particles and polymers including van der Waals attractions, electrostatic repulsion, and polymer bridging. The increased solution salinity significantly reduces the electrostatic repulsion among the negatively charged solid particles and negatively charged polymer flocculants (i.e. for MF, but not for PAM and Al-PAM), leading to more effective polymer bridging interactions, which enhances the settling of mineral tailings. Our results provide some new insight into the understanding of the effects of solution salinity on the settling of mineral tailings and the development of novel polymer flocculants.

Removal possibilities of colloidal chromium (III) oxide from water using polyacrylic acid

The lack of water is the most serious threat to humanity that leads to more efficient water and sewage treatment. Currently, many scientists are looking for new coagulants, flocculants and physicochemical methods allowing for sufficient removal of pollutants from water. The presence of various types of pigments, including chromium (III) oxide, poses the major problem. Even small amounts of these substances inhibit life processes in water. In this paper, the stability of Cr2O3 suspension in the absence and the presence of polyacrylic acid (PAA) was determined. To explain the changes in the system stability, the adsorption and electrokinetic measurements were performed. The chromium (III) oxide suspension not containing PAA is the most stable at pH = 3. Under these conditions, each positively charged solid particle is surrounded by a negatively charged diffusion layer which protects from particle collision and aggregates formation (electrostatic stabilization). In turn, the Cr2O3 suspension containing the PAA is most unstable also at pH = 3. In this case, the polymer causes destabilization of the colloidal suspension, which results from charge neutralization of solid particles by adsorbed PAA.

The modified Thomson equation in the theory of heterogeneous vapor nucleation on charged solid particles

Thermodynamic theory of heterogeneous vapor nucleation on charged nanosized solid particles is considered and formulas for the condensate chemical potential in the droplet and the nucleation activation barrier are derived. A modified Thomson equation for the pressure of vapor saturated over a liquid droplet formed around the spherical charged particle is proposed. This equation determines the saturated vapor pressure as a function of the particle size, charge magnitude and sign, and the droplet radius. The approach assumes that the droplet liquid film between the particle and the vapor phase is polarized in the central electric field of the charged particle and is thin, i.e., surface layers of the film at the boundaries with the particle and the vapor phase are overlapped and the arising disjoining pressure affects the droplet state. It is shown that the film disjoining pressure, the Maxwell stress of the film in the central electric field of the particle, the degree of the particle wetting, and the particle size interplay in determination of the threshold value of vapor supersaturation ratio at barrierless nucleation. The threshold values of the vapor supersaturation ratio were found for different model isotherms of the disjoining pressure and different relations between size and charge of the solid particles.

Relaxation of charged and neutral particles in doped atomic solids: TSL, OSL, TSEE, OSEE and their interconnection

Relaxation processes in nitrogen-containing Ar solids pre-irradiated by an electron beam are studied with the focus on the interconnection of relaxation channels in system of charged and neutral species. The results of correlated in real time measurements of thermally stimulated phenomena are presented. The experiments have been performed using activation spectroscopy methods – thermally stimulated exoelectron emission (TSEE), spectrally resolved thermally stimulated luminescence (TSL) measured in visible, NUV and VUV ranges. Solid evidence of the charge relaxation cascades triggering via radiative recombination of neutral species is presented.

The modified Thomson equation in the theory of heterogeneous vapor nucleation on charged solid particles

Thermodynamic theory of heterogeneous vapor nucleation on charged nanosized solid particles is considered and formulas for the condensate chemical potential in the droplet and the nucleation activation barrier are derived. A modified Thomson equation for the pressure of vapor saturated over a liquid droplet formed around the spherical charged particle is proposed. This equation determines the saturated vapor pressure as a function of the particle size, charge magnitude and sign, and the droplet radius. The approach assumes that the droplet liquid film between the particle and the vapor phase is polarized in the central electric field of the charged particle and is thin, i.e., the surface layers of the film at the boundaries with the particle and the vapor phase are overlapped and the arising disjoining pressure affects the droplet state. It is shown that the film disjoining pressure, the Maxwell stress of the film in the central electric field of the particle, the degree of the particle wetting, and the particle size interplay in determination of the threshold value of vapor supersaturation ratio at barrierless nucleation. The threshold values of the vapor supersaturation ratio are found for different model isotherms of the disjoining pressure and different relations between size and charge of the solid particles.

Dynamic Electrophoretic Mobility of Spherical Colloidal Particles in Realistic Aqueous Salt-Free Concentrated Suspensions

In this contribution, the dynamic (or alternating current (AC)) electrophoretic mobility of spherical colloidal particles in a realistic salt-free concentrated suspension subjected to an oscillating electric field is studied theoretically using a cell model approach. Such a suspension is a concentrated one (in charged solid particles) in an aqueous solution without any electrolyte added during the preparation. The ionic species in solution can solely be: (i) the "added counterions" stemming from the particles (for example, by ionization of particle surface ionizable groups), (ii) the H(+) and OH(-) ions from water dissociation, and (iii) the ions produced by the atmospheric CO(2) contamination. The corrections related to water dissociation and CO(2) contamination in suspensions open to the atmosphere have turned out to be tremendous in many of the experimental situations of interest in direct current (DC) electric fields. Thus, it is mandatory to explore their influence in the more complex situation of AC electrophoresis. The results confirm the importance of ions produced by water dissociation and those originated by the acidification of the aqueous solution in suspensions contaminated with atmospheric CO(2), for low to moderate particle volume fractions, where the role of the added counterions is screened by the other ionic species. It is worth mentioning that, for high particle charges, two Maxwell-Wagner processes develop in the mobility frequency spectrum, respectively linked to the diffuse layer relaxation and to the relaxation of a condensed layer of counterions located very close to the particle surface. This is the so-called ionic condensation effect for highly charged particles, already described in the literature, and which for the first time will be studied in detail in realistic salt-free systems. The dynamic electrophoretic mobility will be numerically computed throughout a wide frequency range and compared with the cases of pure and realistic salt-free conditions. In addition, the competition between different relaxation processes associated to the complex electric dipole moment induced on the particles by the field, the particle inertia, as well as their influence on the dynamic response, will be explored for pure and realistic cases.