Monodisperse Spherical Particles Research Articles

Подготовка тетраэтоксисилана для получения монодисперсных сферических частиц кремнезема. Часть 3. Влияние элементов-примесей

Nanostructured 3D matrices based on monodisperse spherical silica particles are currently of considerable interest due to the prospects for their widespread use in the synthesis of new nanocomposite materials. At the same time, one of the main problems hindering their large-scale synthesis is associated with the unstable behavior of tetraethoxysilane (TEOS) during its hydrolysis and, as a result, poor reproducibility of the sizes of the formed silica particles under given conditions. In this work, based on the study of the elemental composition of impurities in silica opal matrices obtained from tetraethoxysilane from various manufacturers, we continued to study factors affecting the size of the formed particles. To solve this problem, samples of supramolecular structures obtained from TEOS from various manufacturers were examined by the ICP-MS method for the content of impurity elements in them. It is shown that the content of elements in the initial TEOS correlates with deviations in the size of the formed silica particles. The experiments carried out on the synthesis of spherical particles with the introduction of additives of a number of previously defined elements confirm the obtained dependence. Moreover, it was found that the presence of certain impurity elements in the system increased the monodispersity of the sizes of the formed silica particles, which was a fundamentally important step to solve the problem of obtaining silica particles of a given size with high reproducibility of results. The obtained results are important for understanding the features of the formation of supramolecular structures of silica in nature.

Rotational and translational motions in a homogeneously cooling granular gas

A granular gas composed of monodisperse spherical particles was studied in microgravity experiments in a drop tower. Translations and rotations of the particles were extracted from optical video data. Equipartition is violated, the rotational degrees of freedom were excited only to roughly 2/3 of the translational ones. After stopping the mechanical excitation, we observed granular cooling of the ensemble for a period of three times the Haff time, where the kinetic energy dropped to about 5% of its initial value. The cooling rates of all observable degrees of freedom were comparable, and the ratio of rotational and translational kinetic energies fluctuated around a constant value. The distributions of translational and rotational velocity components showed slight but systematic deviations from Gaussians at the start of cooling.

One-step formation of ZrON thin film on surface of carbon fine particles for membrane electrode assembly

Zirconium nitride and oxynitride films were deposited on alumina or carbon particles by reactive sputtering using a magnetron sputtering apparatus with a Zr hollow cylindrical target and a vibrating equipment with heating capability. The vibrating equipment developed in this study was effective if the particles are spherical and highly monodisperse. Uniform film deposition was achieved over the entire surface of highly monodisperse spherical alumina particles using the vibrating equipment during deposition. Pure ZrN crystalline layers was deposited under Ar and N2 gas flows with heating on XC-72 carbon powder particles removed adsorbed oxygen. Energy dispersive x-ray spectroscopy mapping analysis for deposited XC-72 carbon particles showed ubiquitous film deposition on agglomerated particles regardless of vibration during sputtering. Uniform film deposition with vibrating equipment was achieved on the entire surface of CGB-10 particles with more spherical and monodisperse than XC-72 but precipitated crystalline phase depended on unintentional oxygen chemisorbed on the particles. Addition and increase in flow rate of oxygen to the sputtering gas resulted in the formation of desired crystalline phase, Zr2ON2, Zr7O8N4, and monoclinic ZrO2, precipitated in the film using CGB-10 particles with chemisorbed oxygen removed. Current density for oxygen reduction reaction measured for MEA made from CGB-10 particles with ZrON-based crystals deposited was larger than that for thin film deposited on a carbon plate substrate.

Synchrotron radiation SAXS study of the species structure evolution in the synthesis process of MCM-56 zeolite

In the process of synthesizing zeolite, the evolution behavior of aluminosilicate species is crucial for investigating the crystallization mechanism and controlling the structure of desired zeolite. Herein, the synthesis process of MCM-56 zeolite was investigated by using the synchrotron radiation Small Angle X-ray Scattering (SAXS) technique. Based on the distance distribution function curves and Porod analysis, the particle distribution of the sol in the synthesis system transformed from a monodisperse spherical particle to a polydisperse lamellar structure. The results indicated that the particle size distribution, fractal dimension, and the evolution behavior of particles in sol vary with the variation of crystallization time. Specifically, the initial step involves the depolymerization of particles forming small particles approximately 1 nm. Subsequently, these small particles polymerize to form structural units ranging in size from 1 to 5 nm, and finally grow to form MCM-56 zeolite crystal by consuming aluminosilicate species. The SAXS results in conjunction with the XRD, SEM, FT-IR, and N2 adsorption-desorption analysis elucidate the evolution of aluminosilicate species and the crystallization process of MCM-56 zeolite at three stages, including the induction/nucleation period (0–84 h), the crystal growth period (84–108 h) and the crystal stability period (108–168 h). By virtue of the understanding for the structural evolution of the sol species, this work is expected to highlight the controllable synthesis of MCM-56 zeolite.

Toward the Assembly of 2D Tunable Crystal Patterns of Spherical Colloids on a Wafer-Scale.

Entering an era of miniaturization prompted scientists to explore strategies to assemble colloidal crystals for numerous applications, including photonics. However, wet methods are intrinsically less versatile than dry methods, whereas the manual rubbing method of dry powders has been demonstrated only on sticky elastomeric layers, hindering particle transfer in printing applications and applicability in analytical screening. To address this clear impetus of broad applicability, we explore here the assembly on nonelastomeric, rigid substrates by utilizing the manual rubbing method to rapidly (≈20 s) attain monolayers comprising hexagonal closely packed (HCP) crystals of monodisperse dry powder spherical particles with a diameter ranging from 500 nm to 10 μm using a PDMS stamp. Our findings elucidate that the tribocharging-induced electrostatic attraction, particularly on relatively stiff substrates, and contact mechanics force between particles and substrates are critical contributors to attain large-scale HCP structures on conductive and insulating substrates. The best performance was obtained with polystyrene and PMMA powder, while silica was assembled only in HCP structures on fluorocarbon-coated substrates under zero-humidity conditions. Finally, we successfully demonstrated the assembly of tunable crystal patterns on a wafer-scale with great control on fluorocarbon-coated wafers, which is promising in microelectronics, bead-based assays, sensing, and anticounterfeiting applications.

Self‐templated magnesiothermic reduction of ORMOSIL particles to monodisperse hollow spherical SiC composite particles

AbstractHollow silicon carbide (SiC) particles have attracted attention due to their well‐defined morphology, low density, and large surface area that can be leveraged for a wide variety of applications. Here, we report the self‐templated synthesis of monodisperse hollow spherical SiC composite particles with controllable shell thicknesses using magnesiothermic reduction of organically modified silica (ORMOSIL) particles. Monodisperse ORMOSIL particles containing three organic groups of methyl, vinyl, and mercaptopropyl were produced by a simple one‐pot sol–gel process and then converted to hollow spherical SiC composite particles via a magnesiothermic reduction at 700°C under an inert atmosphere. The spherical morphologies of the original ORMOSIL particles were well maintained through this self‐templated conversion process, but the sizes of the hollow SiC particles were slightly reduced by the thermal treatment. Field emission transmission electron microscopy studies revealed that the shell of hollow particles mainly consists of primary β‐SiC particles with nanometer‐scale sizes. The physical and chemical properties of the hollow SiC composite particles were investigated by scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, Brunauer–Emmett–Teller, X‐ray diffraction, Fourier transform infrared spectroscopy, Raman, and solid‐state nuclear magnetic resonance analyses. The shell thickness of hollow spherical SiC composite particles can be controlled by simply changing the duration of the thermal conversion process. This study not only provides a simple and easy approach for the preparation of hollow spherical SiC particles but also opens the possibility of large‐scale manufacturing of such particles for commercial applications.

Precise control of discharge of spherical particles by cone valve configuration: Insert – Converging orifice

The effect of the size and shape of the insert (inverted cone, sphere) when placed axially above an orifice on the mass discharge rate (MDR) of monodisperse spherical particles from a cylindrical silo has been investigated through experiments and DEM simulations. MDR characteristics have been measured for various distances between the insert and the orifice.An important practical finding is that, within a specific range of placement distances, the MDR increases by approximately 10% when a conical insert is used, whereas no such effect was observed when a spherical insert was employed.It was observed that, in some cases, a slight increase in friction coefficient leads to an increase in MDR as result of alterations in the initial grain structure, facilitating faster discharge.In a quasi-2D configuration, significant changes in flow rate occur when the thickness exceeds the natural multiple of dp, allowing the next layer of particles to flow.

Recovery of silver in the form of value-added spherical silver powder from spent Ag-Al2O3 catalyst by a novel clean method

The spent Ag-Al2O3 catalyst is an important silver secondary resource due to its high content of Ag. However, the most commonly used nitric acid leaching method produces toxic and harmful NOx gases. Herein, a novel clean method was proposed to treat the spent Ag-Al2O3 catalyst using the green leaching agent cerium ammonium nitrate instead of nitric acid to effectively avoid the generation of toxic NOx gases. More importantly, value-added monodisperse micro-sized uniform spherical particles were synthesized directly from the leaching solution by a simple chemical reduction method. The influence of leaching conditions on the leaching ratio of Ag and leaching kinetics were discussed in detail. The response surface methodology was applied to optimize the synthesis parameters of silver powder and explore the interactions between the synthesis process parameters. Under the optimal leaching parameters, the leaching ratio of Ag reached 99.69 %. The leaching kinetic analysis of leaching indicated that the leaching reaction of spent Ag-Al2O3 catalyst was controlled by chemical reaction. By the response surface methodology design, a fitted mathematical model of the particle size for silver powder and the optimum synthesis parameters of silver powder were obtained. The optimum synthesis parameters of silver powder were as follows: [Fe2+] = 1.08 mol/L, [Ag+] = 1.01 mol/L, and dispersant dosage of 2.05 wt%. The average experimental particle size of 1.337 μm was very close to the predicted value of 1.343 μm obtained from the fitted model, indicating that the fitted model of particle size for silver powders was very good. This process not only provides a clean and value-added method for recycling the spent Ag-Al2O3 catalyst, but also helps to promote the balanced and high-value utilization of high-abundance cerium.

Kinetic modeling of fluid-induced interactions in compressible, rarefied gas flows for aerodynamically interacting particles

In the study of gas-particulate multiphase systems, the flow of high-speed gas through a distribution of solid particulates is of utmost importance. While these aerodynamically interacting systems have been extensively studied for low-speed gas flows in the gas continuum regime, less attention has been given to high-speed systems where non-continuum effects are significant due to the high flow gradients. To address this, the flow of rarefied gas through an aerodynamically interacting monodisperse spherical particle system is studied using the Direct Simulation Monte Carlo (DSMC) gas-kinetic approach. Since the method provides the best resolution of shocks at supersonic Mach numbers it is used to classify the weak separated shocks and strong collective shocks in these systems based on particle spacing in a two-particulate system at different orientation angles. The study used the two-particle system to help analyze more complex particle distributions of volume fractions, 1%, 5%, and 15%, exposed to gas flows in the slip and transitional gas regime for a free-stream Mach number range of 0.2<Ma∞<2.0. We observe that the weak separated shocks in the 1% distribution allow a higher degree of gas penetration and shock-particle interactions or “hypersonic-surfing”, exposing a major fraction of the particulates to higher force magnitudes. In contrast, the strong collective shock in the 5% and 15% distributions only generates high particulate forces on the flow-facing particles. Finally, a simple stochastic model is proposed for use in large-scale Eulerian–Lagrangian simulations that captures the non-monotonic behavior of average drag and force variability generated by the complicated gas particulate interactions in the compressible gas regime.

Numerical simulations of suspensions of rigid spheres in shear-thinning viscoelastic fluids

In multiphase flows, accurately modeling the interaction between the liquid phase of complex fluids and a porous medium of solid spheres poses a fundamental challenge. The dynamics of moderately dense non-colloidal suspensions constituted by static random arrays of mono-disperse spherical particles in non-linear viscoelastic fluids is studied numerically. This numerical study consists of about 9000 different systems, in which the volume fraction ϕ (0.04≤ϕ≤0.2) of the dispersed solid phase, the Reynolds number Re(5≤Re≤50), the solvent viscosity ratio β(0.05≤β≤0.9), the Weissenberg number Wi(0.5≤Wi≤4), and the mobility parameter of the Giesekus model α (0.1≤α≤0.5) were varied to understand the particle's interactions with the viscoelastic suspending fluid. We aim to investigate the relationship between the volume fraction of the dispersed solid phase and the non-linear rheology of shear-thinning viscoelastic fluids with the normalized average drag force ⟨F⟩. In addition, by assessing the flow patterns predicted numerically, we were able to provide a characterization of the velocity and stress fields as a function of the simulation parameters.

The role of metallic nickel nanoparticles to remove dispersed oil from produced water in Sudan oil field plant

Abstract In this study, nickel nanoparticles (NiNPs) were synthesized and utilized for removing dispersed oil from oilfield-produced water in Sudan. The synthesis process involved using two concentration of hydrazine as a reducing agent and sodium hydroxide as solvent. Physiochemical characterizations, such as X-ray diffraction (XRD) and transmission electron microscopy (TEM), confirmed the successful preparation of NiNPs. The TEM analysis revealed an average particle size ranging from 70 to 90 nm, with a change in morphology from star-shaped to monodispersed spherical particles. The crystal structure analysis confirmed the face-centered-cubic (FCC) configuration of the NiNPs, validating their structural properties. Significantly, the NiNPs demonstrated an impressive capability to remove oil form produced water, achieving a remarkable efficiency of 98% in eliminating dispersed oil from produced water. The oil removal process followed Freundlich isotherms, as evidenced by the high value of the linear regression coefficient. Additionally, the kinetics of the oil removal process conformed well to the pseudo-second-order model, indicating a rapid reaction. This study successfully demonstrated the efficient removal of dispersed oil from produced water using nickel nanoparticles, which interacted physically with the oil particles. These findings highlight the potential of NiNPs as an effective adsorbent for treating oilfield-produced water and mitigating environmental contamination.

Evolution of particle deposits at communicating membrane pores during crossflow filtration

Understanding the influence of operating conditions on fouling is a great challenge in crossflow membrane filtration since it is determined by a complex interplay between the shear force of the crossflow and the drag toward the membrane arising from the applied trans-membrane pressure. This study uses a coupled CFD-DEM approach to simulate the motion and deposition behavior of monodisperse spherical particles within a membrane-mimicking geometry. Trans-membrane pressure and crossflow velocity are varied to reveal their respective influence on different aspects of fouling at a pore scale. A visual analysis of the simulation results demonstrates distinct behavior regarding the initial deposition of particles and the resulting filter cake morphology, which can be attributed to defined phenomena. Additionally, quantitative data reveals that the dynamic fouling behavior is dominated by the applied crossflow velocity, while the resistance to the removal of particles by crossflow and the level of flux decline is mainly influenced by the trans-membrane pressure. This study links visual pore-scale phenomena to macroscopic filtration quantities, not only underlining the importance of pore-scale investigations but also narrowing the gap between pore-scale events and the filtration process.

Подготовка тетраэтоксисилана для получения сферических частиц кремнезема. Часть 2. Примеси и их влияние на размеры формирующихся глобул

Monodisperse spherical silica particles, as a basis for creating supramolecular 3D matrices, are currently of increasing interest due to the prospects for their wide application in the synthesis of new nanocomposite materials. At the same time, one of main problems of their large-scale synthesis is associated with the unstable behavior of tetraethoxysilane (TEOS) during hydrolysis, which leads both to the deviation of the particles from a given size and their shape from a spherical one. In this paper, on the basis of the study of tetraethoxysilane from various manufacturers, we continued to work on determining factors that can influence the process of hydrolysis of tetraethoxysilane and, as a result, the monodispersity and size of the formed particles, and also other factors. To solve this task, all TEOS samples were studied by various physicochemical methods of analysis, including Fourier IR and Raman spectroscopy, gas chromatography-mass spectrometry. As a result of the studies, we showed that the presence of di- and trisiloxanes in the system did not significantly affect the size of the formed silica particles, while significantly accelerating the rate of formation of silica spheres. Moreover, the presence of methoxyl groups in the initial silane, and an insignificant content of ethanol in the system did not affect the size stability of the formed particles. At the same time, the replacement of part of the ethoxy groups in the initial TEOS by methyl or ethyl groups, as they are not capable of participating in the hydrolysis reaction, largely contribute to the deviation of sizes of the formed silica particles from each other. The results obtained on the effect of impurities on the size of the formed silica globules are important, among other things, for understanding the processes of formation of natural supramolecular structures of silica.

Facile fabrication of monodispersed α- and γ-Al2O3 microspheres through controlled calcination of alumina precursors synthesized by homogeneous precipitation

Monodispersed spherical particles of γ- and α-alumina were synthesized by urea-based homogeneous precipitation, using potassium sulfate and aluminum nitrate as the precursor and urea as a precipitating agent. The influence of various synthesis parameters like concentration of reactants, temperature, and reaction time, on the morphological features of alumina were investigated. Results showed that all the experimental parameters had a considerable effect on the morphology of the synthesized alumina, and control of these parameters resulted in monodispersed spherical particles with good dispensability and filtering performance. Extensive optimization of the experimental parameters led to produced alumina precursors with spherical morphology and an average particle size of 610 nm. The precipitated solids were characterized by various techniques and it was noted that the as-prepared particles were amorphous. Relatively well-dispersed and crystalline γ- and α-Al2O3 with higher sintering activity were obtained by calcining the as-synthesized precursors at 1000 and 1200 °C, respectively. The crystallographic results showed that crystallite size increased with an increase in annealing temperature. It was observed that the crystallite size of γ-Al2O3 was much smaller (5.71 nm ± 7.21%) than α-Al2O3 (35.40 nm) ± 4.58%. The Scanning electron microscopic analysis of the calcined alumina showed that the particle morphology was retained to a greater extent after calcination. The synthesized alumina particles can be used as a reinforcement filler in the Ni/Al2O3 composite coatings to enhance the tribological and mechanical properties of Ni-composite coating on a steel surface. The incorporated alumina particles in the composite may improve the properties of the coatings.

Stabilization of Iron (0) in plasma treated semi porous polylactic acid based particles for in situ groundwater remediation

This study aims at incorporating reactive zero valent iron (ZVI) nanoparticles into water dispersible, biodegradable polymeric particles acting as a slow release reservoir of ZVI for targeting groundwater contaminants in situ. In order to accomplish the goal, three simple steps were adopted such as: 1) electrojetting of PLA (polylactic acid) with FeCl3 (∼17 wt%) to yield ∼700 nm sized monodisperse spherical particles (PLA_FeCl3) 2) surface modification of PLA_FeCl3 particles using oxygen plasma to enhance surface hydrophilicity and porosity (∼ 75%) 3) reduction of plasma treated PLA_FeCl3 particles in presence of NaBH4 to produce ZVI (size: 20–50 nm) entrapped PLA particles (PLA_ZVI) with high encapsulation efficiency of iron (∼85%). The plasma treated semi-porous PLA_ZVI particles exhibited slow and sustain release of iron (∼90% in ∼100 hrs) that were further employed to completely decontaminate both methyl orange (hydrophilic dye) and trichloroethylene (hydrophobic waste). Interestingly, the plasma treated particles were recyclable up to fourth batch, whereas the non-plasma treated one hardly show any recyclability due to burst release of surface entrapped iron from the latter. Moreover, the plasma treated hydrophilic particles provided stable dispersion (96 hrs) and prolonged reactivity (∼10 days in sand column) in water as opposed to non-plasma treated particles displaying 1 min dispersion stability in water. As a result, the plasma treated particles displayed smooth transportability through sand column (>80%) with negligible attachment efficiency (α = 1.1) onto sand particles. These attributes make them a potential alternative to bare ZVI (transportability <20%) for targeting hazardous pollutants by injecting them in groundwater.

Quantification of Very Low Concentrations of Colloids with Light Scattering Applied to Micro(Nano)Plastics in Seawater

The detection and quantification of micro(nano)plastics in the marine environment are essential requirements to understand the full impacts of plastic pollution on the ecosystem and human health. Here, static light scattering (SLS) and dynamic (DLS) light scattering techniques are assessed for their capacity to detect colloidal particles with diameters between d = 0.1 and 0.8 µm at very low concentrations in seawater. The detection limit of the apparatus was determined using model monodisperse spherical polystyrene latex particles with diameters of 0.2 µm and 0.5 µm. It is shown that the concentration and size of colloids can be determined down to about 10−6 g/L. Light scattering measurements on seawater obtained from different locations in Western Europe show that colloidal particles were detected with DLS in seawater filtered through 0.8 µm pore size filters. The concentration of these particles was not higher than 1 µg/L, with an average diameter of about 0.6 µm. We stress that these particles are not necessarily plastic. No particles were detected after filtration through 0.45 µm pore size filters.

Coffee-ring deposits of polydisperse particles

The coffee-ring phenomenon has attracted attention for spontaneously concentrating suspended inclusions at the tri-phase contact line. Yet, little is known about how the size distribution of particle mixtures affects the annular structure. Here, instead of the classic power-law relation between the ring width and the initial volume fraction for monodisperse spherical particles in evaporative droplets, a logarithmic function is observed for polydisperse particle mixtures mimicking the size distribution of matters in material and biological research (e.g., Gamma distribution). The effect of particle size distribution on the evolution of ring deposits would inspire strategies for diagnostics, assembly, and manufacturing processes.

Influence of NH4BF4 on the alumina phase transition and morphology

The spherical alumina powders including regular morphology, uniform particle size, smooth surface, and reduced particle wear generally give the finished products with the excellent performances. This research presents a novel method to produce the spherical alumina by employing gibbsite precipitated by the Bayer process as raw material mixed with NH4BF4 at 1000 °C, nano α-Al2O3 was characterized by the well-crystallized and monodispersed spherical alumina single crystal particles. The results provide a novel economical method to prepare the spherical alumina from gibbsite.

Ordering analysis of SiO&lt;sub&gt;2&lt;/sub&gt; particle-accumulated films by small-angle X-ray scattering

The ordered arrangement of particles and holes in SiO2 particle-accumulated films by small-angle X-ray scattering (SAXS) was investigated. The SAXS profiles of SiO2 particles exhibited the typical oscillation shown by monodisperse spherical particles. On the other hand, the SAXS profile of the ordered SiO2 particle-accumulated film showed an additional oscillation suggesting that another scattering component existed except for SiO2 particles. Furthermore, considering two components: “SiO2 in an air matrix” and “air holes in a SiO2 matrix”, we successfully reproduced the SAXS profile of the ordered particle-accumulated film. The additional oscillation shows the existence of the tetrahedral holes, suggesting that this SiO2 particle-accumulated film forms a close-packed structure. The intensity of the additional oscillation increased with the regularity of the particle arrangement in the SiO2 particle-accumulating film. These results suggest that SAXS measurements using synchrotron radiation can provide information on the order of particle arrangement in composite films.

Voronoi tessellation-based algorithm for determining rigorously defined classical and generalized geometric pore size distributions.

The geometric pore size distribution (PSD) P(r) as function of pore radius r is an important characteristic of porous structures, including particle-based systems, because it allows us to analyze adsorption behavior, the strength of materials, etc. Multiple definitions and corresponding algorithms, particularly in the context of computational approaches, exist that aim at calculating a PSD, often without mentioning the employed definition and therefore leading to qualitatively very different and apparently incompatible results. Here, we analyze the differences between the PSDs introduced by Torquato etal. and the more widely accepted one provided by Gelb and Gubbins, here denoted as T-PSD and G-PSD, respectively, and provide rigorous mathematical definitions that allow us to quantify the qualitative differences. We then extend G-PSD to incorporate the ideas of coating, which is significant for nanoparticle-based systems, and of finite probe particles, which is crucial to micro and mesoporous particles. We derive how the extended and classical versions are interrelated and how to calculate them properly. We next analyze various numerical approaches used to calculate classical G-PSDs and may be used to calculate the generalized G-PSD. To this end, we propose a simple yet sufficiently complicated benchmark for which we calculate the different PSDs analytically. This approach allows us to completely rule out a recently proposed algorithm based on radical Voronoi tessellation. Instead, we find and prove that the output of a grid-free classical Voronoi tessellation, namely, the properties of its triangulated faces, can be used to formulate an algorithm, which is capable of calculating the generalized G-PSD for a system of monodisperse spherical particles (or points) to any precision, using analytical expressions. The Voronoi-based algorithm developed and provided here has optimal scaling behavior and outperforms grid-based approaches.