Agglomerate Size Distribution Research Articles

Self-preserving size distribution and collision frequency of flame-made nanoparticles in the transition regime

Coagulation of polydisperse primary particles is the dominant agglomerate growth mechanism in flame reactors and in the low-temperature or high-pressure regions of combustion engines. Here, the evolution of agglomerate size distribution (SD) and collision frequency function of coagulating soot and silica primary particles is investigated with simultaneous surface growth or coalescence using discrete element modeling (DEM). The growth of polydisperse soot and silica nanoparticles is captured from the free molecular up to the transition regime in excellent agreement with microscopy and mobility measurements in diffusion flames and flame spray pyrolysis (FSP) reactors. The broad agglomerate size distributions of soot and silica formed in the free molecular regime narrow by coagulation in the transition regime, attaining their mobility-based quasi-self-preserving or signature SD with the same geometric standard deviation of 1.48 ± 0.03, in excellent agreement with soot or silica SDs measured from diffusion flames and the CAST generator or from a FSP reactor, respectively. The coagulation rate of both soot and silica agglomerates is about twice as much higher as that of monodisperse agglomerates in the transition regime, regardless of material or combustion conditions. The DEM-derived collision kernel enhanced by a factor of 1.82 ± 0.35 can be interfaced with method of moments and monodisperse population balance models to improve the design of aerosol flame reactors and combustion engines.

Solvothermal‐assisted green synthesis of hybrid Chi‐Fe3O4nanocomposites: a potential antibacterial and antibiofilm material

In this present study, a hybrid Chi-Fe3O4 was prepared, characterised and evaluated for its antibacterial and antibiofilm potential against Staphylococcus aureus and Staphylococcus marcescens bacterial pathogens. Intense peak around 260 nm in the ultraviolet-visible spectrum specify the formation of magnetite nanoparticles. Spherical-shaped particles with less agglomeration and particle size distribution of 3.78-46.40 nm were observed using transmission electron microscopy analysis and strong interaction of chitosan with the surface of magnetite nanoparticles was studied using field emission scanning microscopy (FESEM). X-ray diffraction analysis exhibited the polycrystalline and spinel structure configuration of the nanocomposite. Presence of Fe and O, C and Cl elements were confirmed using energy dispersive X-ray microanalysis. Fourier transform infrared spectroscopic analysis showed the reduction and formation of Chi-Fe3O4 nanocomposite. The antibacterial activity by deformation of the bacterial cell walls on treatment with Chi-Fe3O4 nanocomposite and its interaction was visualised using FESEM and the antibiofilm activity was determined using antibiofilm assay. In conclusion, this present study shows the green synthesis of Chi-Fe3O4 nanocomposite and evaluation of its antibacterial and antibiofilm potential, proving its significance in medical and biological applications.

Effect of reaction conditions on agglomeration of aluminum hydroxide in the recovery of waste aluminum-catalyst

Water-soluble waste salts, especially those contain harmful ions, are a great threat to soil, water, air, and human health. NaAlCl4 waste salt, containing harmful Al3+ ion, is massively by-produced in the manufacture of dichlorophenylphosphine (DCPP) and remains a big issue to both industry and environment. In this work, we intensively investigated the aluminum hydroxide precipitation process during the recovery of NaAlCl4 waste salt via acid-base reaction. The aluminum hydroxide crystallized under different conditions was monitored and characterized using XRD, TG, SEM, and Zeta potential. The effect of precipitation pH and temperature on crystal form, gel content, agglomerate size distribution, and moisture content of filter cake were studied. Precipitation pH was found to influence both gel-precipitation conversion and agglomerate state, but its effect varied under different temperature, indicating complex gelation and agglomeration processes. Temperature, however, has similar effect at different pH conditions that low gel content and hardened agglomerate can be achieved with increasing temperature due to intensified particle movement and collision. In addition, NaCl has little effect on the crystal form of aluminum hydroxide even though some initial NaCl exists in the solution. Then, the precipitation mechanism was proposed, in which agglomerate void filling process was discovered and verified via porosity analysis. Furthermore, the precipitation process was optimized and a drop of 25.16% in filter cake moisture content was achieved which can lead to a better separation of Al3+ and Na+ and a higher efficient recovery of the waste salts.

Monte Carlo Aggregation Code (MCAC) Part 2: Application to soot agglomeration, highlighting the importance of primary particles

During the agglomeration of nanoparticles and in particular, soot, a change in both the flow regime (from free molecular to near continuum) as well as the change of agglomeration regime (from ballistic to diffusive) is expected. However, these effects are rarely taken into account in numerical simulations of particle agglomeration and yet, they are suspected to have an important impact on the agglomeration kinetics, particle morphologies, and size distributions. This work intends to study these properties by using the Monte Carlo Aggregation Code (MCAC) presented in the preceding work (part 1), focusing on the physical impacts of varying the particle volume fraction and monomers size and polydispersity. The results show an important sensitivity of the kinetics of agglomeration, coagulation homogeneity, and agglomerate morphology to the size of monomers. First, for smaller monomer diameters, the agglomeration kinetic is enhanced and agglomerates are characterized by larger fractal dimensions. Second, for large monomer diameters, fractal dimensions down to 1.67 can be found being smaller than the classical 1.78 for Diffusion Limited Cluster Agglomeration (DLCA) mechanism. One important conclusion is that variation in time of both regimes has to be considered for a more accurate simulation of the agglomerate size distribution and morphology.

Promoting the removal of fine particles by turbulent agglomeration with the coupling of different-scale vortexes

To improve the particle agglomeration and removal effect by turbulent agglomeration, the coupling of different-scale vortexes in turbulent flow field was proposed and a turbulent agglomerator containing different types of vortex sheets was constructed and applied. The particle agglomeration efficiency, size distribution and removal effect by ESP through it were investigated experimentally. The results demonstrated that the coupling of different-scale vortexes in turbulent flow field can further promote the agglomeration and removal of fine particles. The particle agglomeration efficiency was improved and the particle number and mass concentrations at the outlet of ESP were reduced. Besides, to explore the coupling promotion mechanism, the flow field distribution, as well as the particle motion trajectory, residence time and fluctuation range in y-axis direction in three turbulent agglomerators were simulated using CFD method, and a turbulent agglomeration model for fine particles with different sizes was put forward.

Study on hydrocyclone separation enhancement of micro Si/SiC from silicon-sawing waste by selective comminution

ABSTRACT Particle agglomeration and close particle size distribution is the main limitation for effective recycling of Si and SiC. In this study, selective comminution was used to liberate fine particles from agglomerated ones before hydrocyclone separation. Furthermore, difference in particle size distribution between Si and SiC was enlarged by milling for 30 min. Compared with other milling time, pre-milling for 30 min showed the best hydrocyclone separation result (from 24 wt% to 8.1 wt%). Silicon with purity of 99.98 wt% was obtained by further treatment. SiC with purity of 99.2 wt% was obtained by washing off the impurities in the underflow.

A Simple Model for the High Temperature Oxidation Kinetics of Silicon Nanoparticle Aggregates

Silicon nanoparticles are an emerging and promising material in many fields including electronics, catalysis, and biomaterial engineering. Synthesis in the gas phase via aerosol routes allows tuning and engineering material features such as primary particle size distribution, agglomerate size distribution, crystallite size, and morphology. Proper control of these features as well as post-synthesis processing such as surface oxidation is very relevant for making the nanoparticles chemically stable. Therefore, a kinetic expression for determining the extent of oxidation in silicon nanoparticles is necessary. Significant work has been devoted to understanding the kinetics of monocrystalline silicon, and generally accepted models such as the one by Deal and Grove provide a very accurate description of bulk silicon oxidation. However, these models are not as accurate for the first hundreds of angstroms of the oxidation. While this might be acceptable for bulk wafers, it has critical results for silicon nanoparticles with diameters around such range. Furthermore, many applications involve silicon nanoparticle aggregates with a shape far away from perfect spheres. For this reason, in this work, we propose an expression for the parabolic oxidation kinetics of polycrystalline silicon nanoparticle aggregates at 1000 °C with surface area in the range of 3 to 19 m2/g. and crystallite sizes from 50 to 70 nm. The activation energy of the process is also reported to be linked to the crystallite size.

Mathematical Modeling of Emulsion Solvent Diffusion for Spherical Crystallization: How To Deconvolute Primary Crystal Size Distribution from Agglomerate Size Distribution?

Spherical crystallization (SC) is a novel process intensification strategy, which can substantially reduce the manufacturing cost for solid oral dosage forms. However, although the manufacturabilit...

Fluidization of nanoparticle agglomerates assisted by combining vibration and stirring methods

Fluidization of nanoparticle agglomerates is a promising technology to process nanoparticles, where the nanoparticles always exist in complex agglomerates due to strong interparticle forces. In this study, we propose an assisted method by combing vibration and stirring to improve the fluidization quality of nanoparticle agglomerates. The fluidization behaviors are evaluated in terms of minimum fluidization velocity, bed expansion ratio, and the size distribution of agglomerates, for three kinds nanoparticles of SiO2, Al2O3 and TiO2. The results show that, both vibration and stirring can improve the fluidization quality of nanoparticle agglomerates. However, the fluidization quality is no longer improved, or even worsen when the vibration or stirring parameter exceeds a critical value. Compared with fluidization assisted by vibration or stirring separately, the combination of the two methods can further decrease the minimum fluidization velocity, and increase the bed expansion ratio. More importantly, the segregation of the agglomerate sizes can be significantly reduced by using the combined method. This study provides a new reliable method to assist the fluidization of nanoparticle agglomerates.

Agglomeration of stoichiometric hydroxyapatite: Impact on particle size distribution and purity in the precipitation and maturation steps

Stoichiometric hydroxyapatite (HAP) is a prominent biomaterial, notably used as coating on metal bone prostheses. High chemical purity and a specific particle size distribution are the main properties for such an application. Based on industrial practice, a reference synthesis was first performed in a lab-scale stirred reactor. Improvements were then suggested by varying the physicochemical and hydrodynamic conditions. The shear rate within the reactor, characterized by the mean Kolmogorov micro-scale, has a strong impact on the final agglomerate size distribution. By maintaining a rather high mixing rate and a high temperature, the duration of the synthesis can be reduced considerably without affecting the HAP purity provided the pH is properly regulated. This consists of imposing acidic conditions during a short period just after the initial formation of large aggregates and then setting the pH at above 7.5 to ensure the production of pure stoichiometric HAP.

The effect of solvent and ionomer on agglomeration in fuel cell catalyst inks: Simulation by the Discrete Element Method

We simulate agglomeration in different fuel cell catalyst ink solutions using Discrete Element Method. Carbon support is modelled as particles in various inks with ionomer and various solvents. The particles interact with particle-pair forces resulting in agglomerate build-up. The classical colloidal theory with van der Waals and electric double layer forces underestimates the ink stability, which motivates the development of a new model of polymer force between particles. The force is activated when there is a bridging of polymer between the carbon black particles, and the strength is dependent on the ionomer interaction with the solvent by the dielectric constant. A critical dielectric constant was defined for which ionomer form a web-like polymer network that increases the ink stability. This modification can explain the trend of the ink stability, and the model can simulate the effect of different solvents on the agglomerate size distribution with good agreement with experimental results.

Pore-scale and multiscale study of effects of Pt degradation on reactive transport processes in proton exchange membrane fuel cells

Understanding catalyst degradation mechanisms and their effects on reactive transport in proton exchange membrane fuel cell (PEMFC) is critical for prolonging cell lifetime. In this study, for the first time pore-scale numerical studies are conducted to explore effects of catalyst degradation on transport and electrochemical reactions in catalyst layers (CLs) of PEMFCs. High-resolution nanoscale structures of pristine and degraded CLs are reconstructed, in which detailed distributions of carbon, Pt, electrolyte and pores are resolved. Different particle size distributions of Pt agglomerates are also considered during the reconstruction. Based on the lattice Boltzmann method, pore-scale models for oxygen diffusion, interfacial dissolution, and electrochemical reaction are developed. Pore-scale modeling is then conducted to evaluate effects of Pt degradation on Pt utilization, active surface area, limiting current density and local transport resistance. It is found that total reaction rate is reduced by approximately 10–30% due to Pt degradation. Such negative effects are more prominent when Pt loading is low or more Pt is distributed in the CL interior, causing 25% and 45% increased transport resistance, respectively. Further, a multi-scale simulation strategy is proposed, and upscaling schemes for integrating pore-scale results into cell-scale models are proposed. The present study demonstrates that pore-scale simulation is a useful tool for understanding coupled mechanisms between Pt degradation and reactive transport phenomena within CLs, and is helpful for providing practical guidance for CL fabrication.

Experimental investigations of adipic acid agglomeration behavior under different operating conditions using image analysis technique QICPIC software

The agglomeration behavior in adipic acid crystallization from aqueous solution was experimentally studied under different crystallization conditions. The QICPIC software, which uses image analysis technique, was implemented to evaluate the agglomeration behavior of adipic acid crystals. Primary experimental investigations indicated an important role of cooling rate on the agglomeration and crystal size distribution (CSD) of adipic acid. At slower cooling rates of 17.5 K/h and 6 K/h, larger size particles (80% agglomerates) with bimodal and wide CSD were produced while at a higher cooling rate of 30 K/h a narrower unimodal PSD and smaller size particles with the ratio of agglomerated particles of about 80% were produced. The influence of pH was found to be an important factor when studying the agglomeration behavior of adipic acid. A larger size of the product was measured in the strong acidic medium, indicating enhanced agglomeration. Changing the solvent composition and its effect on the agglomeration of adipic acid were studied. A bimodal and larger size agglomerates are obtained in a pure water solvent while adding ethanol will change the CSD to unimodal shape (no nucleation) with smaller sized agglomerates.

Effect of engine operating conditions on soot layer permeability and density in diesel particulate filters

Understanding the variation of soot deposit properties in diesel particulate filters is necessary for their real-life modeling and onboard control. In this study, the effect of exhaust mass flow rate and particle agglomerate size on the soot layer permeability and density was investigated experimentally and analyzed using a well-validated model. A bare and a coated diesel particulate filter were loaded at five different engine operating points, specially selected to explore these effects in a heavily used part of the diesel engine map. Particle emissions were characterized in terms of particle agglomerate size distribution and primary particle diameter, while soot layer permeability and density were estimated indirectly by fitting the model to the pressure drop recordings. To this end, an automatic calibration procedure was applied to obtain values in a consistent and repeatable manner. The results showed considerable variation in both permeability and density. Furthermore, some trends could be identified after depicting the particle characterization data and soot layer properties in contour plots. Increased permeability appeared at the engine operating point with high flow rate and large particle agglomerate size. Lower density was obtained at the operating points with large particle agglomerate diameter.

Microstructure Characterization of PGM-Free Catalyst Ink Using in-Situ Ultra Small Angle X-Ray Scattering

Platinum-group metal (PGM)-free cathode catalysts have been widely studied to cut down a production cost of the fuel cell stack, which is one of main challenges to enable the widespread use of fuel cell vehicles. Transition metal-nitrogen-carbon (TM-N-C) such as Fe, Co, Mn or Ni catalysts are now regarded as the most promising PGM-free catalyst due to its stable ORR activity [1]. A high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate framework (ZIF) has recently reported to be a wide range from 20 to 1000 nm after only one-step thermal activation [2]. The microstructure evolution of PGM-free catalysts and ionomer-catalyst interactions during the ink mixing and processing procedure have not yet been identified. This presentation will describe both PGM-free catalyst ink compositions and processing techniques for efficient preparation steps of the electrode while optimizing fuel cell performance and minimizing ink processing time and cost. The electron microscopy technique is widely used to identify the carbon particle size distribution, however, it may not represent the whole catalyst ink. This study uses the in situ measurement of ultra-small angle X-ray scattering (USAXS) combined with SAXS to examine the PGM-free catalyst agglomerate size distribution during ink mixing/processing. The sonicated catalyst ink is circulated through a thin-walled capillary tube situated in the beamline using a peristaltic pump. The ideal ink composition and processing method that facilitate the break-up of primary particle agglomerates with the minimum amount of sonication time are determined in different solvents, ionomer-carbon ratios, and sonication method/time. The microstructure characterization of PGM-free catalyst inks will also be correlated with the fuel cell performance. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). This research used the resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.

Effect of oleic acid content on manganese-zinc ferrite properties

One step hydrothermal synthesis of Mn-Zn ferrite was processed using different contents of ionic manganese, ionic zinc and oleic acid as an anti-agglomeration. In this research, magnetic nanoparticles are soft agglomeration and narrow size distribution. Oleic acid can promote anisotropic growth of particles. The modified Mn-Zn ferrite nanoparticles were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). A vibrating sample magnetometer (VSM) certified that the modified nanoparticles showed the superparamagnetic properties.

Exponential scaling in early-stage agglomeration of adhesive particles in turbulence

We carry out direct numerical simulation together with an adhesive discrete element method calculation (DNS-DEM) to investigate agglomeration of particles in homogeneous isotropic turbulence (HIT). We report an exponential-form scaling for the size distribution of early-stage agglomerates, which is valid across a wide range of particle inertia and inter-particle adhesion values. Such scaling allows one to quantify the state of agglomeration using a single scale parameter. An agglomeration kernel is then constructed containing the information of agglomerate structures and the sticking probability. An explicit relationship between the sticking probability and microscale particle properties is also proposed based on the scaling analysis of the equation for head-on collisions. Our results extend Smoluchowski's theory to the condition of non-coalescing solid adhesive particles and can reproduce DNS-DEM results with a simple one-dimensional simulation.

1P4-6 Characteristics of particle size distribution of agglomerates in an ultrasonic source with a cylindrical rigid wall

1P4-6 Characteristics of particle size distribution of agglomerates in an ultrasonic source with a cylindrical rigid wall

Improved micromeritics, packing properties and compressibility of high dose drug, Cycloserine, by spherical crystallization

Cycloserine, a high dose anti-tuberculosis agent, possesses poor flow properties and compression behaviour. The present study was aimed at improving the flowability, packing properties and compressibility of Cycloserine by spherical crystallization. Cycloserine was dissolved in a water and crystallised by pouring into anti-solvent, 1-Butanol, in presence of ethyl acetate which acts as a bridging liquid for formation of agglomeration. Further, spherical agglomeration process for Cycloserine was statistically optimized using the central composite design, keeping the ‘rate of stirring’ and ‘amount of bridging liquid’ as an independent factors and average particle size as the response. Optimized batch of Cycloserine spherical agglomerates (Cyc-SA) was further evaluated for sieve analysis, solid state characterization studies and compaction behaviour (Kawakita analysis and Heckel study). The uniform spherical agglomerates were revealed in microphotographs of scanning electron microscopy while no chemical alteration in the Cycloserine was indicated by X-Ray powder diffraction, differential scanning calorimetry and Fourier-transform infrared spectroscopy during the crystallization. The excellent flow properties of Cyc-SA were demonstrated by Carr's index, Hausner ratio and Kawakita parameters as compare to plain drug. The enhanced particle size and uniform distribution of agglomerates have also contributed to improve flow properties of Cycloserine. Similarly, Heckel parameters like mean yield pressure and yield strength displayed superior compressibility of Cyc-SA. Thus, spherical crystallization would be interesting technique for improving processability of high dose drug like Cycloserine.

Monte Carlo Simulation Modeling of Nanoparticle-Polymer Cosuspensions.

Creation of high-quality and novel polymer-particle nanocomposites to a large extent depends on understanding the behaviors of individual polymer chains and particles, especially at the mixing state in a liquid solvent. Simulations can help identify critical parameters and equations that govern the suspension behaviors. This study is the first attempt to understand the agglomeration processes of ZnO nanoparticle and poly(methyl methacrylate) polymer cosuspensions through a constant number Monte Carlo simulation. A modified Derjaguin-Landau-Verwey-Overbeek theory is used to describe the particle-particle interactions that lead to agglomeration. The average agglomerate size and number are measured as a function of suspension resting time, particle to polymer volume ratio, polymer chain length, and suspension drying. The agglomerate size increases persistently with the resting time and particle content increase, ranging from 1.2 μm for the 1 vol % particle content suspension to 4.6 μm for the 20 vol % particle content suspension after 30 min of suspension resting. The agglomerate size distribution for all of the particle contents follows a lognormal distribution. As the polymer chain length increases, agglomeration also becomes more severe. If drying is accounted for and thus the solids loading continually increases, the suspension becomes much more stable because of increases in viscosity and depletion stabilization.