Dispersion Behavior Of Particles Research Articles

Scale-independent model of gravitational settling of particulate suspension in a fractal channel

Gravitational settling of solid particles into a fractal-shaped channel was investigated experimentally and theoretically. Previous studies have reported that the settling behavior of particles in liquid-filled channels depends strongly on particle properties and suspension conditions. At small particle size and high concentration, particles settle collectively like an immiscible fluid with respect to the surrounding one. In this study, we examined the gravitational dispersion behavior of solid particles in a three-dimensional fractal-shaped channel under various collective conditions. The experimental results showed that the settling behavior varies with the collectivity of suspended particles. In the case of high collectivity conditions, settling velocity is enhanced by a density-driven instability, which depends not only on the physical properties of the particles and fluid but also on channel geometry. We developed a model of temporal change in the volumetric occupancy ratio of the suspended particles region. This model describes the invasion of particles into a fractal channel. Our model comprises only the fractal characteristics of the channel, such as a homothetic ratio and a bifurcation number. Consequently, This model could provide a rough prediction of the gravity-induced invasion behavior of particles into any fractal-shaped channel.

Clarification of Particle Dispersion Behaviors Based on the Dielectric Characteristics of Cathode Slurry in Lithium-Ion Battery (LIB)

Particle dispersion behaviors in Lithium Ion Battery (LIB) are clarified by Electrochemical Impedance Spectroscopy (EIS) method based on the dielectric characteristics of cathode slurry, which are Carbon Black (CB) aggregation, CB-bare LiCoO2 particles, CB path and CB-coated LiCoO2 particles. The experimental particle dispersion behaviors are evaluated by numerical simulation. In the experiments, cathode slurry is stirred under different rotational speed n; meanwhile, in the simulation, medium conductivities σm and particle conductivities σp in cathode slurry model are changed. Herein, CB aggregation and CB path are verified by σm, while CB-bare LiCoO2 particles and CB-coated LiCoO2 particles are verified by σp. Compared with σp, σm plays important roles in determining particle dispersion behaviors because σm has the similar functions as n to change characteristic resistances RcL and RcH and characteristic frequencies fcL and fcH. Therefore, compared with CB-coated LiCoO2 particles, CB path dominates the conductivity of cathode slurry in LIB. Furthermore, the dielectric characteristics of NMP solution, CB-NMP slurry and LiCoO2-NMP slurry are investigated to clarify how each component of cathode slurry contribute to the whole Nyquist plot. The results show that the straight line is caused by adding CB, while low frequency semi-circle is caused by CB-bare LiCoO2 particles. Electrical impedance spectroscopy (EIS) method, Lithium ion battery (LIB).

Dispersion behavior of TiB2 particles in AISI D2 tool steel surfaces during pulsed laser dispersing and their influence on material properties

AISI D2 is one of the most applied cold-working tool steel for deep drawing operations, due to the materials good toughness and high wear resistance. However, since the lubricant-free deep drawing as well as the processing of high strength and ultra-high strength steel sheets remaining ongoing trends in the automotive industry, the tool surfaces need to be improved regarding their friction and wear behavior. For this purpose elevated micro textures can be applied. Since protruded micro features are predominantly affected by wear, a structuring process enabling the formation of suitable textures with high wear resistance is needed.In this paper surface texturing at microscale was conducted by laser implantation. This technique allows the fabrication of highly wear resistant, separated and elevated features (implants) on steel surfaces via a discontinuous dispersing of ceramic particles by pulsed laser radiation. The aim of this study was to investigate the techniques potential for the creation of wear resistant elevated micro features on AISI D2 tool steel surfaces by the application of TiB2 particles. The laser parameters (pulse power and length) were varied and a comparative material analysis on AISI D2 laser remelted spots and TiB2 localized dispersed zones was examined. High-speed camera recordings allowed the description of the particle insertion mechanism from pre-coatings during laser processing. Mechanical properties were analyzed by (micro-) hardness measurements at top and cross sections. The microstructure was investigated by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The implants geometrical properties (diameter, height, depth) were investigated by white light interferometry and optical microscopy. The experiments reveal that a pulsed laser remelting of AISI D2 leads to a significant hardness drop due to high retained austenite (γR) contents. Contrary, a localized dispersing of TiB2 particles leads to defect free dome- or ring-shaped elevated features with hardness values up to 1800 HV1. The high hardness values result from the dispersed TiB2 particles and an in-situ precipitation of new hard particle phases, which lead to a reduction of the γR content within the matrix.

Microscale dispersion behaviors of dust particles during coal cutting at large-height mining face

In order to ensure safe production and occupational health at a large-mining-height fully mechanized mining face in a coal mine, the present study firstly establishes an airflow-dust coupled model based on gas/solid two-phase flow equations and combines numerical simulation and field measurement for analyzing the dispersion pattern of dust particles with various sizes for different coal cutter locations. Results show that, due to the existence of drums, airflow deviates from the original direction and enters the footway. Driven by the airflow, dust particles enter the footway at different locations depending on coal cutter locations. The coal-cutting location (denoted as Prl) and the location where dust particles enter the footway (denoted as Pdt) are correlated as follows: Pdt(Prl) = - 0.0007Prl2 + 1.0343Prl - 3.3536. When Prl < 55m, dust particles produced by the rear drum during coal cutting enter the footway earlier than those produced by the front drum, leading to the first and second dust concentration peaks in respiratory zones of footway. Dust suppression effects are assessed in these regions based on the first and second dust concentration peaks. Due to the superposition of the concentration fields associated with dust particles 2.5, 7, and 20μm in diameter, dust concentration 25m down the leeward side of the coal cutter can reach 1440mg/m3. The concentration of dust particles with a diameter of 40μm drops steadily and approaches 0 at the return corner. The dust particles 80μm in diameter are fully settled within 22m down the leeward side of the coal cutter. A comparison with the field measurement indicates that the present simulation results are highly accurate. Graphical abstract.

Adsorption of Anionic Polyacrylamide onto Coal and Kaolinite Calculated from the Extended DLVO Theory Using the van Oss-Chaudhury-Good Theory.

The dispersion behavior of particles is of great significance in selective flocculation flotation. The interfacial interaction between coal and the main impurity mineral (kaolinite) particles with the effect of an anionic polyacrylamide (PAM A401) was explored by the extended Derjagin–Landau–Verwey–Overbeek (DLVO) theory. The involved surface free energy components of fine mineral particles were estimated using the van Oss-Chaudhury-Good theory and Washburn equation. After adsorption of PAM A401, the range and absolute value of the hydrophobic interaction VHA of the coal particles decreased, the electrostatic repulsive potential increased, and the total potential energy changed from −1.66 × 105 to −4.03 × 104 kT at the separation distance of 5 nm. For interactions between the kaolinite and coal particles after PAM A401 adsorption, the electrostatic repulsive potential increased and the hydrophilic repulsive potential energy decreased. The energy barrier at the separation distance of 0.2 nm decreased from 2.78 × 104 to 2.29 × 104 kT. The total potential energy between the kaolinite and coal particles after PAM A401 adsorption was still repulsive, and the range of the repulsive interaction increased from ~0.05 to 47 nm to ~0.05 to 50 nm. The total potential energy of the coal particles after PAM A401 adsorption was still attractive. This behavior of coal and kaolinite particles with the effect of PAM A401 indicates the possibility of enhanced fine coal separation by the method of selective flocculation flotation.

The effects of hydration on the DC breakdown strength of polyethylene composites employing oxide and nitride fillers

Particle dispersion, water absorption/desorption and electrical breakdown behavior were studied in a range of polyethylene composites having a common matrix morphology. Three different conditioning routes (dry, ambient and wet) were used to vary the absorbed water content. Systems employing oxide fillers (silica and alumina) were found to have poor or intermediate levels of particle dispersion and could absorb/desorb significant amounts of water. Consequently, they required drying to provide breakdown strengths comparable to that of the host matrix. Systems based on calcined silica exhibited reduced water absorption and provided improved breakdown strength after ambient conditioning, despite having an identical dispersion to those utilizing untreated silica. Composites employing nitride fillers (silicon nitride and aluminum nitride) were found to have good or intermediate levels of particle dispersion. These absorbed far less water and hence provided breakdown strength values comparable to that of the host matrix following ambient conditioning. Their breakdown strength was degraded after wet conditioning with both exhibiting similar breakdown strengths despite there being a large difference in the level of particle dispersion between the two fillers. In composites based upon a hydrophobic host matrix, water absorption is largely determined by particle surface chemistry and, although the above results are presented in terms of water absorption, we suggest that changes in this characteristic can be interpreted as a proxy for changed surface chemistry. The results suggest that surface chemistry is at least as important as particle dispersion in determining the electrical breakdown strength.

Comparison of dispersion behavior of agglomerated particles in liquid between ultrasonic irradiation and mechanical stirring

The particle dispersion behavior was compared for ultrasonic irradiation and mechanical stirring. The experiment and calculation were carried out with polymethylmethacrylate (PMMA) particles. The dispersion rate of the agglomerated particles increased with the decreasing ultrasonic frequency and the increasing electric power, whereas it increased with the increasing rotation speed for the mechanical stirring. The temporal change in the particle dispersion proceeded stably after passage of a long time. The dispersion of the ultrasonic irradiation was suggested to occur by the erosion from the surface of the cluster one by one due to the bulk cavitation as well as the division into smaller particles because of the inner cavitation, and that of the mechanical stirring mainly by the division into smaller clusters due to the shear stress flow. Based on the experimental results, mathematical models for the ultrasonic irradiation and mechanical stirring were developed with the dispersion and agglomeration terms and the calculation of the temporal change in the total cluster number at the different operational factors agreed with the experiments. The dispersion efficiency of the ultrasonic irradiation was larger than that of the mechanical stirring at the lower input power, but it was reversed at the higher input power.

Analysis for the Mechanism for the Dispersion Behaviors of Particles in Mixing Processes

Analysis for the Mechanism for the Dispersion Behaviors of Particles in Mixing Processes

The Effect of Ca2+ and Mg2+ on the Dispersion and Flocculation Behaviors of Muscovite Particles

The dispersion and flocculation behavior of muscovite suspensions in the presence of Ca2+ and Mg2+ are relevant for industrial processing of pre-concentrated muscovite from stone coal, a primary source of vanadium. In this study, the dispersion and flocculation behavior were investigated by means of sedimentation, zeta potential, and ion absorption experiments, as well as the force between particles and ion speciation calculations. The results indicated that the dispersion and flocculation behavior of muscovite particles without excess ions were in qualitative agreement with the classical DLVO theory. The muscovite particles aggregated mainly due to basal surface-edge interactions in acidic suspensions but were dispersed in alkaline suspension by electrostatic repulsion of the total particle surface. In acidic suspensions, the ability of muscovite to form dispersions of muscovite was increased with the decrease in the electrostatic attraction between the basal surface and the edge caused by the compression of the electric double layers withCa2+ and Mg2+. In alkaline suspension, the main adsorption form of Ca2+ and Mg2+ on muscovite surface was the ion-hydroxy complexes. The flocculation behavior of muscovite was affected by the static bridge effect of the ion-hydroxy complexes.

Dispersion and agglomeration mechanism of flaky graphite particles in aqueous solution

ABSTRACTThe dispersion and agglomeration behavior of flaky graphite particles in an aqueous solution was studied. The small particles of flaky graphite naturally formed a large and compact agglomeration in an aqueous solution at pH 7.0 and 9.0, respectively. The theoretical calculation result based on typical DLVO theory was opposite the phenomenon observed by optical microscope, indicating that the interaction force between the flaky graphite particles exceeded the van der Waals and electrostatic double-layer forces. When the extended DLVO theory was used, the total interaction energy (UT = UA + UR + UHI) was negative over most of the distance range, indicating that the agglomeration of the small particles was attributed to the attraction. This result indicated that hydrophobic interactions dominated the dispersion and agglomeration behavior of the hydrophobic flaky graphite particles.

Particle dispersion in a partially filled rotating cylindrical tank

Particles-liquid flow involving a free surface in partially filled rotating cylindrical tank is common in chemical engineering, which attracts numerical studies on it in an effort to provide useful information for the design and optimization of operational conditions in the real application. However, the dynamics of particles dispersion in partially filled rotating cylindrical tank under small particles-liquid density ratio has not been fully understood by performing a reasonable 3D numerical simulation. A three-dimensional unsteady model of a solid–liquid dispersed flow involving a free surface has been developed and numerically analyzed to investigate the particle dispersion in a partially filled rotating cylindrical tank. In the model, the discrete element method (DEM) and the volume of fluid (VOF) method have been applied. The flow field and the particle dispersion process in a rotational cylindrical tank have been presented. The effects of the tank rotation speed and the liquid height on the dispersion behaviors of particles are examined and analyzed. The results indicate that vortexes have formed in the liquid phase that entrain the particles and induce their gradual dispersion throughout the entire region of the liquid phase. The average mass concentration of particles is high in the rotating-out side of the liquid phase and in the liquid–wall contact region, while it is low in the rotating-in side of the liquid phase and in the vortex generation region. In addition, as the rotation speed increases, the entrainment capability of the liquid phase has been enhanced, which improves the dispersion performance of the particles. The selection of an appropriate liquid height is beneficial for the enhancement of particle dispersion in a partially filled rotating cylindrical tank.

Measurement of the axial dispersion coefficient of powders in a rotating cylinder: dependence on bulk flow properties

Rotating drums are encountered in numerous industrial applications, including blenders, rotary calciners, impregnators, coaters, granulators, and cement mixers. In all of these devices, the rotation of the drum is used to engender mixing of the granular material in the radial direction. Axial mixing, because of its significantly lower rate, can also have an impact on the process performance, especially when control of residence time is important. Typically, the particle dynamics in rotating drums are quantified as a function of process conditions, such as rotation speed, fill level, and cylinder size. Particle properties are also important, but previous studies have largely been limited to the effects of particle size. In this work, the quantification of the axial particle dynamics has been expanded to include the effect of bulk flow properties by studying a number of cohesive powders. Fick's second law was found to describe the axial dispersion behavior of cohesive particles. Therefore, changes in behavior can be characterized using the axial dispersion coefficient. The effect of material flow properties was found to be statistically significant; the flowability of the material (as measured using bulk flow properties) correlated significantly to the axial dispersion coefficient. Partial least squares was used to determine that 95% of the variation observed in the axial dispersion coefficient measurement can be explained using particle size, compressibility, and shear cell measurements.

Role of water in TiO2 screen-printing inks for dye-sensitized solar cells

This work deeply investigated the effect of water in terpineol-based TiO2 screen-printing inks, commonly used for the deposition of photoanodes for dye-sensitized solar cells. The study involved all the different phases necessary for the photoanode production and the final device characterization. Firstly, inks modified with different amounts of water were produced and analyzed considering particle dispersion (DLS) and rheological behavior, while the deposited layers were analyzed in terms of morphology (FE–SEM), roughness (profilometry) transmittance (UV–Vis spectroscopy) and dye adsorption capability. Finally, the observed properties were correlated to the performance and the electrochemical behavior (EIS) of a complete DSC. The extensive study allowed to understand the real role played by the water in the ink formulation and, as a consequence, the identification of the optimal amount to be introduced in the system. Water was showed to increase the dispersion and time stability of the particle suspensions, leading to an optimized flow behavior of the inks. The ceramic films so obtained exhibited improved morphologies and enhanced optical properties and dye uptake. However, the optimal concentration for DSC application was found to be not the one that allows the best dispersability of the ceramic particles but the one that best compromised the homogeneity of the film with the highest dye uptake. This key result could not be obtained analyzing just the film morphology but necessitate a thorough analyses of all the different properties (morphological, electrochemical and photovoltaic) related to the final application. The best-performing device recorded an increase in efficiency of the 12% compared to the un-modified system.

Effect of nano-sized TiC particle addition on microstructure and mechanical properties of SA-106B carbon steel

The dispersion behavior of nano-sized TiC particles treated by different processes and its influence on microstructural and mechanical modification has been investigated in SA-106B carbon steel with different TiC contents. It was found that mechanically-activated TiC nanoparticles introduced into a carbon steel matrix were dissolved during hot rolling and re-precipitated vigorously during subsequent normalizing treatment at 920°C. The dispersed TiC particles were very fine (<20nm), giving a suppressing effect on the growth of recrystallized austenite to promote considerable grain refinement of final ferrite–pearlite structure. This fine microstructure (grain size: ~10μm) with a homogeneous distribution of TiC particles offers a higher strength level (yield strength: 372MPa, tensile strength: 544MPa) without sacrificing ductility (>30%) and impact energy (>250J) at the TiC content of 0.1wt%. Theoretical calculations showed that grain refinement plays a dominant role in enhancing the yield strength of TiC-bearing carbon steel, together with nanoparticle strengthening interacting on the solid solution strengthening and dislocation strengthening.

Electrokinetic Research on the Dispersion Behavior of Nano-Ceria Particles in Concentrated Suspensions

A multi-scale method was developed, which utilized intrinsic relationships among zeta potential of particles, rheological properties of suspensions and particle size distribution (PSD), to analyze dispersion behavior of nanoparticles in concentrated suspensions. It was found that PSD of a kind of nanoceria particles by dynamic light scattering (DLS) method in solution A with concentration 5 wt% accorded well with that by direct TEM analysis, which meant the particles had been dispersed well. However, there had a significant difference when the concentration was increased to 20 wt%. When particles concentration increased from 5 wt% to 20 wt%, zeta potential in solution A changed from-150 mV to-100 mV, while zeta potential in solution B changed from-35mV to-45 mV. Variations of zeta potential of particles accorded well with rheological properties of suspensions too, from phenomenological models. When the suspensions composed by solution A and the nanoparticles with concentration about 20 wt% was diluted with its original solution to 5 wt%, the PSD of nanoceria could be measured indirectly, which accorded well with both that of a suspension prepared directly with near concentration and that from TEM images. Then a method to measure PSD of nanoparticles in concentrated suspension was brought forward.

Numerical Analysis on the Vortex Pattern and Flux Particle Dispersion in KR Method Using MPS Method

The mechanically-stirring vessel is widely used in many fields, such as chemical reactor, bioreactor, and metallurgy, etc. The type of vortex mode that formed during impeller stirring has great effect on stirring efficiency, chemical reacting rate and air entrapment. Many efforts have been made to numerically simulate the fluid flow in the stirring vessel with classical Eulerian method. However, it is difficult to directly investigate the vortex mode and flux particle dispersion. Therefore, moving particle semi-implicit (MPS) method, which is based on Lagrangian method, is applied to simulate the fluid flow in a KR method in this practice. Top height and bottom heights of vortex surface in a steady state under several rotation speed was taken as key parameters to compare the results of numerical and published results. Flux particle dispersion behaviour under a rotation speed range from 80 to 480 rpm was also compared with the past study. The result shows that the numerical calculation has high consistency with experimental results. It is confirmed that the calculation using MPS method well reflected the vortex mode and flux particle dispersion in a mechanically-stirring vessel.

Investigation of the Dispersion Behavior of Inertial Particles within Accelerated Domain

Investigation of the Dispersion Behavior of Inertial Particles within Accelerated Domain

Effects of Soybean Oil Modified Cellulose Fibril and Organosilane Modified Cellulose Fibril on Crystallization of Polypropylene

Soybean oil modified cellulose fibril (Oil-g-CF) and organosilane modified cellulose fibril (Silane-g-CF) were prepared using maleinized soybean oil and hexadecyltrimethoxysilane, respectively. Thus obtained modified cellulose fibril was added to polypropylene by a simple melt mixing on a hotplate. PP/modified CF composites with 4.0 wt% filler content were prepared. The composites were subject to a polarized optical microscope to investigate particle dispersion, supramolecular morphology, and crystallization behavior. It was found that Silane-g-CF exhibited smaller particle sizes with better particle distribution when compared to Oil-g-CF. In addition, the etched composite samples unveiled an increase in a number of spherulite crystals as well as a decrease in the spherulite size. The nonisothermal crystallization study of composites revealed that both Oil-g-CF and Silane-g-CF were capable of nucleating PP by facilitating faster crystallization process and raising the number of spherulites. The DSC results indicated that Silane-g-CF was able to perform a more effective nucleation than Oil-g-CF, judged by a higher crystallization temperature. Moreover, PP composites containing Oil-g-CF and Silane-g-CF had higher crystallinity by 7% and 10%, for the first and the latter, respectively, when compared to neat PP.

Aggregation and Dispersion Behavior in the 0- to 2- µm Fraction of Luvisols

The migration of particles smaller than 2 µm in soil pores is responsible for the preferential transfer of various contaminants and for soil textural differentiation in Luvisols. Aggregation vs. dispersion mechanisms of clay particles are suspected to play a major role in this migration process. However, these mechanisms have mostly been studied with respect to pure and well-crystallized clay minerals rather than pedogenetic particles and have often been performed under physicochemical conditions, which are poorly representative of soil conditions. We studied the respective impacts of pH and Ca concentration on aggregation and dispersion behavior of clay particles in a Luvisol under conditions encountered in the soil solution. Both static and dynamic approaches were followed in studying particle interactions and dynamics under transient phenomena. Based on these experiments, we have drawn a phase diagram for soil clays as a function of pH and Ca concentrations and have identified mechanisms associated with the formation of these different phases. We find that soil particle behavior in suspensions is similar to that recorded for model clays in that they are driven by both pH and Ca concentrations. These two parameters are interrelated and tend to favor aggregation at higher Ca concentrations and/or lower pH. These effects are reversible over the gravitational water time scale, with the exception of dilution-induced dispersion. In situating these physicochemical mechanisms within a literature review of rainwater and soil solution chemistries, we determine the expected role of these mechanisms on the transport of particles in gravitational soil water.

Analysis of dispersion and aggregation behavior of carbon black particles in aqueous suspension by colloid probe AFM method

To clarify the role of polymer dispersants at the carbon black (CB) nanoparticle/liquid interface, the adsorbed structure of the dispersants and the interactions between particle surfaces was evaluated using colloid probe AFM. As it is difficult to prepare stable spherical granules consisting of CB nanoparticles with diameters on the scale of several microns, for a colloidal probe by spray drying and sintering, CB nanoparticles were uniformly coated on the surface of spherical resin particles using a physical composing process. In order to establish the mechanism of action of the CB polymer dispersant by using the prepared colloid probe, polyethyleneimine (PEI) and PEI functionalized with a hydrophobic toluoyl group (T-PEI) were compared. It was found that on the adsorption of T-PEI, the viscosity of the aqueous CB suspension and the size of the aggregates were remarkably decreased in acidic conditions. Although the amounts of PEI and T-PEI adsorbed onto the CB were almost the same, a larger repulsive interaction was observed in the case of the T-PEI. CB nanoparticle dispersion was promoted by the increase in steric repulsion due to the structure of the adsorbed T-PEI.