Final Particle Size Distribution Research Articles

Investigations into metallurgical, mechanical, and particulate matter emissions in in situ micropowder alloyed wire arc additive manufacturing process

Wire Arc Additive Manufacturing (WAAM) is an advanced manufacturing technique capable of a high deposition rate and is used for fabricating large-sized and complex components. Of specific interest in the recent past is the in-situ micropowder alloying during filler material deposition to modify the properties of each deposited layer. This study focuses on investigating the metallurgical and mechanical characteristics of the steel produced through powder-added WAAM, using characterization techniques such as optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy and Vickers microhardness testing. Additionally, changes in the size distribution of fine and ultrafine particles (UFP) emitted during WAAM deposition, with and without micropowder addition, were studied using a Scanning-Mobility-Particle-Sizer. Two single-bead multi-layered walls of ER70S6 were deposited in two conditions: as-deposited steel wall and interlayer Titanium micropowder-added steel wall. The results indicate that the microhardness of the Ti micropowder-added steel wall increased by approximately 35% due to the formation of specific microstructures, such as bainitic-ferrite, with retained austenite and mainly due to precipitation strengthening. The emission measurement results suggest that the addition of Ti micropowder during WAAM increases UFP concentration by 20%. The elevated temperature during the deposition process could be a key factor for the rise in particulate matter emissions.

Ultrasonic Atomization as a Method for Testing Material Properties of Liquid Metals.

Ultrasonic atomization is an object of steadily increasing interest from metal powder manufacturers, both for additive manufacturing and powder metallurgy. Based on the analysis of available theoretical studies, simulations and experiments, it was noted that the average particle size after atomization and the final particle size distribution depend on the process parameters (e.g., frequency, amplitude) and the parameters of the atomized fluid (e.g., viscosity, surface tension). The objective of this study is to evaluate the feasibility of using ultrasonic atomization to study the properties of liquid metals. It attempts to close a gap in existing knowledge in searching for a new, possibly simple and cost-effective method to study the properties of liquid metals and clarify the relationship between ultrasonic atomization parameters (amplitude, frequency, metal spill on vibrating surface) and obtained atomization results (average particle size, particle size distribution, atomization time). Utilizing numerical modeling as a methodology, especially the finite element method, the possibilities of using ultrasonic atomization as an instrument to determine properties of liquid metals were considered as an introduction to a series of real experiments. Modeling was applied to liquids with different properties, atomized at a chosen specific constant frequency and amplitude. The results of the simulation are in line with the current state of knowledge about ultrasonic atomization. However, in the existing studies available to the authors, there are no data that can be compared directly, but indirect comparisons confirmed the conclusions of the preliminary literature analysis. The relationship between viscosity and surface tension and the average size of the atomization processes obtained in the simulation of particles was demonstrated, thus providing a tool for the development of the presented concept: ultrasonic atomization as a research method. Research and simulation results led to the final conclusion: ultrasonic atomization can be applied to study the properties of liquid metals and this will be the subject of further research and experimentation.

Rheology and early age evaluation of 3D printable cement-limestone filler pastes with nanoclays and methylcellulose

Nanoclays (NC) are known to increase the structural build-up of cement-based materials (CBM) while methylcellulose (MC) is used to increase open time and workability, helping to prevent cold joints in 3D Printing applications. The combination and compatibility of both NC and MC could lead to the design of new 3D printable CBM able to tackle all the manufacturing process requirements. The aim of the study is to evaluate the effect of sepiolite nanoclay and MC on rheology and early age (EA) parameters of cement-limestone filler pastes for 3D printing applications, identifying fresh structural build up and setting mechanisms. The effect of two cement types with coarser and finer particle size distribution (CEM I 42.5-R and CEM I 52.5-R, respectively) was considered. Pastes rheology was characterized by Cone Penetration Test (CPT) and Dynamic Shear Rheometer (DSR). EA was monitored by P- and S-waves Ultrasonic Pulse Velocity (UPV), internal temperature, capillary pressure and drying shrinkage. Fresh Shear Yield Stress (τ0) and shear elastic modulus (G), effective thixotropy (Athix), critical strain (γcrit) and their evolution over time were calculated form CPT and DSR experimental results. A limit of usability was defined for τ0 up to 20 kPa for CPT with a 30º tip cone. Although pastes with both NC and MC showed thixotropy, NC reduced γcrit while MC strongly increased it. NC significantly increased Athix and ΔG with coarser particle size cement when compared to the finer cement. MC delayed hydration reaction and setting, while NC did not affect early age stages. On the other hand, combining NC and MC increased superplasticiser demand and reduced effective thixotropy (Athix). Finally, an integrated overview of the physical and chemical mechanisms involved in rheology and early age properties of cement-based systems and the key experimental parameters for their identification was proposed.

Electrostatic spraying for fine-tuning particle dimensions to enhance oral bioavailability of poorly water-soluble drugs

While spray-drying has been widely utilized to improve the bioavailability of poorly water-soluble drugs, the outcomes often exhibit suboptimal particle size distribution and large particle sizes, limiting their effectiveness. In this study, we introduce electrostatic spraying as an advanced technology tailored for poorly water-soluble drugs, enabling the fabrication of nanoparticles with fine and uniform particle size distribution. Regorafenib (1 g), as a model drug, copovidone (5 g), and sodium dodecyl sulfate (0.1 g) were dissolved in 200 ml ethanol and subjected to conventional-spray-dryer and electrostatic spray dryer. The electrostatic spray-dried nanoparticles (ESDN) showed smaller particle sizes with better uniformity compared to conventional spray-dried nanoparticles (CSDN). ESDN demonstrated significantly enhanced solubility and rapid release in water. In vitro studies revealed that ESDN induced apoptosis in HCT-116 cells to a greater extent, exhibiting superior cytotoxicity compared to CSDN. Furthermore, ESDN substantially improved oral bioavailability and antitumor efficacy compared to CSDN. These findings suggest that ESD shows potential in developing enhanced drug delivery systems for poorly water-soluble drugs, effectively addressing the limitations associated with CSD methods.

Finer Particle Size Distribution and Potential Higher Toxicity of Elemental Carbon and Polycyclic Aromatic Hydrocarbons Emitted by Ships after Fuel Oil Quality Improvement.

Ship emissions are a significant source of air pollution, and the primary policy to control is fuel oil quality improvement. However, the impact of this policy on particle size distribution and composition characteristics remains unclear. Measurements were conducted on nine different vessels (ocean-going vessels, coastal cargo ships, and inland cargo ships) to determine the impact of fuel upgrading (S < 0.1% m/m marine gas oil (MGO) vs S < 0.5% m/m heavy fuel oil (HFO)) on elemental carbon (EC) and polycyclic aromatic hydrocarbons (PAHs) emitted by ships. (1) Fuel improvement significantly reduced EC and PAH emission, by 31 ± 25 and 45 ± 38%, respectively. However, particle size distributions showed a trend toward finer particles, with the peak size decreasing from DP = 0.38-0.60 μm (HFO) to DP = 0.15-0.25 μm (MGO), and the emission factor of DP < 100 nm increased. (2) Changes in emission characteristics led to an increase in the toxicity of ultrafine particulate matter. (3) Ship types and engine conditions affected the EC and PAH particle size distributions. Inland ships have a more concentrated particle size distribution. Higher loads result in higher emissions. (4) The composition and engine conditions of fuel oils jointly affected pollutant formation mechanisms. MGO and HFO exhibited opposite EC emissions when emitting the same level of PAHs.

Encapsulation of organic ultraviolet photoprotective actives into poly(methyl methacrylate) nanoparticles for sunscreen formulations

AbstractSkin cancer is the most common of all cancers worldwide. This way, it is mandatory to adopt an adequate sun protection routine, including sunscreen lotions. However, despite the proven effectiveness of numerous chemical filters, many of them are also known for their allergenic and carcinogenic potential effects, which can be mitigated by exploring some encapsulation routes. Thus, the present work evaluates the influence of seven distinct ultraviolet (UV) organic filters on the final particle size and molecular weight distributions of poly(methyl methacrylate) (PMMA) beads. Moreover, the sun protection factors (SPF) of the loaded nanoparticles are also evaluated when used for preparation of sunscreen formulations. The UV filters did not affect the course of MMA miniemulsion polymerizations significantly, enabling the synthesis of loaded nanoparticles. Nevertheless, adding the filters shifted the particle size distributions toward larger diameters, which are appropriate for cosmetic formulations. Based on the SPF analyses, it was also possible to observe a 12‐fold increase in the SPF values of the prepared formulations and an increase in the critical wavelength. Therefore, the in situ incorporation of distinct UV filters during miniemulsion MMA polymerizations constitutes a robust and versatile technology to produce PMMA nanoparticles loaded with UV filters for preparation of sunscreen formulations.

On reinforcing the friction stir weld joints of AA5086-H116 using the plasma spray coatings

The fatigue properties of friction stir weld joints of AA5086-H116 alloy, reinforced with Al2O3 particles using the plasma spray coating method, were investigated after single and double weld passes. A relatively uniform distribution of reinforced particles was achieved with superior properties, even higher than that of the parent alloy. The reinforced joints had enhanced hardness as well as joint efficiency, the double pass being superior to the single pass, but at the cost of reduced total elongation. Furthermore, the reinforced double-pass joints exhibited a remarkable ∼ 55%, ∼ 14%, and ∼ 89% increase in fatigue strength compared to the as-weld, the base material, and single-pass joints, respectively. The fractographic examination mainly revealed a defect-free crack initiation mechanism with a few cases of the ones induced by defects. The superior fatigue performance was mainly attributed to the uniform spatial and size distribution of fine Al2O3 particles within the weld nugget zone, thanks to the novel weld reinforcement method used in this study, which provides a promising avenue for improving the fatigue properties of weld joints.

Induction heating-based pulsed spray drier for dewatering of alkali metal halide salts: Numerical model and its experimental validation

Dewatering of alkali metal halide salts in conventional co-current or counter-current spray driers to obtain low moisture content and agglomeration in resultant dried powders is difficult owing to their hygroscopic nature. Co-current spray driers offer the advantage of good heat transport characteristics in spray zone while counter-current spray driers offer better thermal utilization throughout the drying chamber. In the present work, modified prototype of a conventional counter-current spray drier is developed to obtain both these advantages in the drying chamber by employing induction heating and mechanical pulsation techniques. After carrying out several experiments in this prototype viz. Induction heating-based pulsed spray drier (IH-PSD), the optimal process parameters are obtained which maximize thermal utilization throughout the drying chamber and minimize both moisture content and agglomeration in resultant dried powders of sodium and potassium halide salts. The initial droplet and final particle size distributions are obtained using laser diffraction analyzer and sieve shaker experiments respectively. An experimentally validated numerical model implemented using open-source computational solvers is utilized to obtain average drying rates in IH-PSD. It is observed that the average drying rate lies between 0.03 and 0.18 mg/s and 0.04 and 0.14 mg/s for sodium and potassium metal halide salts respectively.

A numerical modeling framework for predicting the effects of operational parameters on particle size distribution in the gas atomization process for Nickel-Silicon alloys

Gas atomization is utilized to produce good-quality metal powders. A numerical modeling framework is developed to simulate the gas atomization process. A two-phase VOF flow model in OpenFOAM is applied to track the primary breakup of the melt stream by a high-speed gas flow. The generation of primary melt droplets is extracted from the VOF field. A Lagrangian-Eulerian multiphase flow model in Ansys Fluent is adopted to track the secondary breakup of the primary melt droplets under the high-speed gas flow. The final particle size distribution is obtained by analyzing the particles sampled at the outlet of the atomization chamber. The process of gas atomization can be affected by many factors such as the atomization equipment, operating parameters, and material properties. Sensitivity analysis is conducted through modeling to investigate the effects of these factors on particle size distribution. The model predictions are validated by specially designed gas-atomization experiments.

Combined continuous nanoparticle synthesis with chromatographic size classification

In this paper, we report a combination of the continuous flow synthesis of gold nanoparticles (AuNPs) with subsequent purification and narrowing of the particle size distribution (PSD) by size-exclusion chromatography (SEC) by adapting the flow rates of synthesis and classification. First, we show scalability of chromatographic classification with respect to column dimension and the absence of irreversible nanoparticle adhesion on the column material. Two different syntheses lead to a large and widely distributed and a small and narrowly distributed AuNP dispersion, which are classified by a semipreparative column. The PSDs of individual fractions are characterized by analytical SEC. The broadly distributed AuNP dispersion was classified into three fractions with distinct PSDs. For the narrowly distributed AuNPs, the separation is almost independent of the mobile phase flow rate: coarse and fine fractions with almost identical PSDs and separation efficiency curves are observed irrespective of the flow rate. Even NP samples with narrow PSDs can be classified into multiple fractions with tailored PSDs while simultaneously removing dissolved impurities from the dispersion. With our study, we demonstrate the potential of a direct combination of continuous NP synthesis with chromatographic classification for the optimization of final PSDs and the simultaneous purification of nanoparticulate dispersions.

Process intensification of microplasma nanoparticle synthesis enabled by gas flow design

The wide range of practical uses for nanometer-size metal particles has motivated many lab-scale aerosol synthesis processes. It is well known that the aggregation dynamics of aerosol particles impose a trade-off between particle size and concentration: methods that achieve sub-10 nm particles without aggregation are generally limited by low concentration and low flow rates of order 100 cm3/min. Thus, the intensification of aerosol nanoparticle synthesis and its development for industrial use remains a unique and important manufacturing challenge. We present a microplasma reactor system that has been developed to improve process intensification and reliability. The system utilizes an atmospheric pressure DC microplasma to synthesize iron-carbon particles from a ferrocene vapor precursor. The microplasma incorporates a novel focusing technique using a spatial gradient in gas composition to stabilize short-term fluctuations in performance, achieving an iron yield of up to 0.93. We identify the build-up of deposits between the plasma electrodes as the primary cause of reduced performance over time, and eliminate this build-up by indirectly supplying ferrocene to avoid dissociation in this region of the reactor. Further, we show that the design and conditions downstream of the microplasma have a similar influence on the final particle size distribution as those of the microplasma itself. By tuning the coupled process variables of both the microplasma and this downstream region, we synthesize aerosols with mean diameter from 2 to 7 nm and number concentration of 2 to 8×109 #/cm3 at the system outlet.

Characterization, kinetics and thermodynamic evaluation of struvite produced using ferrochrome slag as a magnesium source

There is limited data on studies that have focused on the kinetics, thermodynamics, and characterization of struvite crystallization from alternative magnesium sources. This study focused on thermal analysis of struvite (produced using ferrochrome slag as a magnesium source) and the results indicated that the residual quantities of struvite were lower than the theoretical mass loss of struvite of 51.42%. When using ferrochrome slag (FCS) as the magnesium source, 47.9%, 47.4%, and 46.9% losses in mass were observed for heating rates of 5°C/min; 10°C/min and 15°C/min respectively. The mean activation energies for struvite produced using FCS were deduced using isoconversional kinetic methods and ranged from 49.81to 56.20 kJ/mol which is very similar to the activation energies deduced using MgCl2. The study also focused on the surface morphology, and particle size of the final product at different pH and N:P ratios. The final particle size distribution of the product was significantly influenced by the solution pH. To improve the crystal growth kinetics for both MgCl2 and FCS, a high ratio of N:P molar ratios should be adopted. The product's highest median particle size was obtained using FCS as the magnesium source at a low pH. Median particle size increased with decrease in pH, at a pH of 7.5 the recorded median particle size was 96 µm whilst, the lowest was 31 µm at a pH of 9.5. The highest percent of fines (<10 µm) was recorded at a pH of 9.5 using FCS as magnesium source in the metastable region of struvite precipitation whereas at a pH of 7.5 no fines (<10 µm) were recorded. SEM images confirmed that the struvite underwent morphological changes when prepared with FCS in comparison to that produced using MgCl2. The surface morphology of the finished product demonstrated the presence of irregular shaped particles, due to presence of impurities. The kinetic data showed that struvite precipitation was limited by the chemical reaction step. Model fitting was used to determine the reaction control mechanism and the average activation energies obtained by four model free methods were FWO (56.2), KAS (51.67) Starink (49.61) and Tang (49.81) kJ/mol, indicating that the FWO method was the least accurate method. The thermodynamic data indicated that the thermal degradation of struvite crystals has a high degree of disorder, and the process is endothermic, irreversible, and non-spontaneous.

Emission and capture characteristics of Chinese cooking-related fine particles.

Cooking can emit high concentrations of particles and gaseous pollutants. Cooking has contributed to the major source of indoor air pollutants, especially for particle pollutants in residential buildings. Many studies already analyzed the emission characteristics of Chinese cooking-related UFPs and PM2.5, while less for the fine particle size distributions. Currently, the fine particle emission characteristics of Chinese cooking need to be further investigated, since the mass size distribution of Chinese cooking is dominated by fine particles. This study determined the emission characteristics of PM1 and fine particles from three Chinese cooking methods. The capture efficiencies of particles were also measured by a modified indirect approach, including the impact of particle decay. The results showed that stir-fried vegetable and pan-fried meat dishes generated more fine particles at 0.542-1.5 μm. Besides, pan-fried and deep-fried meat dishes produce a higher generation of PM1. The fine particles (0.542-10 μm) number-based and volume-based size distributions of six dishes both presented a monodisperse behavior. The cooking methods are not a sensitive factor to the volume frequency of fine particle ranging from 0.542 to 10 μm. The averaged volume median and mode diameter for six typical Chinese dishes are 2.5 μm and 3.3 μm, respectively. The Sauter and DeBroukere mean diameter is 4.7 μm and 5.6 μm, respectively. The decay of fine particles increases with the particle diameter. The impact of particle decay on capture efficiency for 2-3 μm particles is about 5%. The capture efficiencies of pan-fried and deep-fried meat dishes are lower than that of vegetable dishes. In contrast, the capture efficiency for stir-fried meat dishes is higher than that of vegetable dishes. The capture efficiency for PM1 and 0.542-5 μm particles from six typical Chinese dishes were 60-90% on the IEC recommended exhaust flowrate.

Effect of stirring speed and particle size on couscous powder reconstitution

Couscous powders require to be reconstituted with water or steam to be used. Wetting, swelling, and dispersion occur during couscous powder reconstitution with water. Fine couscous was the least wettable, with a clearly apparent swelling step and depended on the stirring speed: increased stirring led to a decrease in swelling time and a lower maximal particle diameter reached during the swelling step. Dispersion lasted longer than the wetting step and it was shortened at higher stirring speed. For the medium couscous, the swelling step was not observed due to its high wettability. Dispersion was its limiting reconstitution mechanism and was faster for medium couscous whatever the stirring speed. Based on SEM analysis, this could be explained by the more dispersible structure of the medium couscous, as it is composed of more agglomerates. Although the reconstitution kinetics of medium and fine couscous powders differed, the final particle size distributions were similar.

Cemented waste rock backfill enhancement via fly ash-graphene oxide hybrid under different particle size distribution

Cemented waste rock backfill (CWRB) is an important composite in supporting technology for safe and green production in mining. However, the mechanical performance of CWRB is highly correlated to cement consumption. This study utilized industrial graphene oxide (GO) and fly ash (FA) to create a high-performance, low-cost, and environment-friendly material for backfill. The results show that the GO-FA hybrid improves the microstructural matrix of hydrated cement by generating nucleation effects that refine the microstructure to a denser state and promote pore-filling effects that form barriers at pore throat junctions. This significantly reinforced the compressive strength (up to 53.6%) of the CWRB specimens. The reinforcing efficiency is more pronounced when using fine particle size distributions due to the lack of skeleton effect of gangue aggregates. By monitoring the acoustic emission and analyzing fractal properties, it can be further revealed that GO improves the integrity of CWRB material during loading. Compared to traditional backfill materials, the study found that 0.008 wt% industrial GO can assist FA to lower the consumption of cement by over 20% and improve the engineering properties by 2.6–53.6% at the same time. This research further proves that GO is promising for CWRB composites reinforcement and solid waste recycling.

Technological and economical investigation of glaze preparation using dry stirred media mill

Ceramic tiles are the most common building material for floor and wall coverings in many countries. Glazed tiles are produced from mixture of frits and some additional raw materials applied on the surface of green tiles and subjected to a firing process. A new method of processing of glaze that is dry stirred media mill was investigated in a pilot grinding plant. The produced glaze particle size, shape and surface area are measured. The comparison was made with the product of conventional wet discontinue ball mills using the same wall tile glaze recipes. The results indicated that dry stirred media mill can provide product that have finer particle size distribution, more stable product compared to the conventional wet ball milling. The glaze thermal expansion and optical properties such as colour (L, a and b parameters) of the produced glazes were measured and comparison was also made in details. Finally, the microstructural characteristics of the produced glazes were determined using scanning electron microscopy (SEM). The results have shown that dry stirred media mill enhances glaze properties and process economy considerably.

Source Apportionment of Ambient Fine Particle Size Distribution Using Positive Matrix Factorisation and Conditional Bivariate Probability Function in a Coastal Urban Area

Source Apportionment of Ambient Fine Particle Size Distribution Using Positive Matrix Factorisation and Conditional Bivariate Probability Function in a Coastal Urban Area

Modeling of Particle Size Distributions in Industrial Poly(vinyl chloride) Suspension Polymerization Reactors

In the present paper, a mathematical model is built and implemented to describe the trajectories of mass inventories, pressures and polymer properties with emphasis on final particle size distributions of industrial scale poly(vinyl chloride) suspension polymerization reactors. The model comprises the mass balances, statistical moment balances, equilibrium relationships and population balance equations. A discretization scheme is employed to transform the integro-differential equations resulting from the population balance model into a system of differential equations. The obtained results show, for the first time, that classical breakage and coalescence kernels described in the literature can provide very good fittings of actual industrial scale data when coupled with proper parameter estimation procedures, so that the proposed model is able to represent the available operation data with good accuracy at distinct conditions. Particularly, it is also shown that the use of a top condenser for control of the reactor temperature can lead to changes of parameters that control the particle size distributions.

The effect of liquid grinding aids on the dry fine grinding of muscovite

This paper investigates the production of a micronized muscovite to a target product size of d50~15 µm with a minimum energy consumption to suit the product requirements of the paint industry by a dry grinding process in a laboratory-scale vertical stirred ball mill. A series of batch dry grinding tests were conducted without and with two commonly used industrial liquid grinding aids, ethylene glycol (EG, C2H6O2) and triethanolamine (TEA, C6H15NO3). The results were evaluated based on particle size distribution (PSD), specific energy consumption, span value, and aspect ratio. The results showed that using liquid grinding aids resulted in a finer PSD, lower specific energy consumption, a narrower size distribution, lower span values, and a higher aspect ratio, which meant better delamination and improved grinding efficiency to that of no grinding aid. The interaction between grinding aids and ground muscovite surfaces was investigated by Fourier Transform Infrared Spectroscopy (FTIR). FTIR measurements revealed that EG and TEA were physically adsorbed on muscovite surfaces. Scanning Electron Microscopy (SEM) was also employed to determine differences between ground muscovite surfaces with and without grinding aids. SEM images indicated that grinding aids could prevent the agglomeration of ground muscovite particles while improving delamination. Adding grinding aids led to a decrease in muscovite agglomeration and an improvement in lamination owing to the adsorption of grinding aids on the particle surfaces.

Thiol‐ene emulsion polymerization using a semi‐continuous approach

AbstractThe thermally initiated thiol‐ene emulsion polymerization of diallyl phthalate (DAP) diene and ethylenedioxy diethanthiol (EDDT) dithiol monomers in batch and semibatch emulsion polymerization is investigated. The batch process leads to larger and broader particle sizes than when the polymerization is carried out in semibatch. The evolution of the particle size and the final particle size distribution indicate that the stability of the latexes is limited and, hence, aggregation phenomena occurred in both processes. In particular, the evolution of the particle size distribution (PSD) in the semibatch process indicates nucleation, growth, and aggregation occurring simultaneously that produced a bimodal particle size. When the diene monomer was changed to diallyl terephthalate (DATP), the semibatch polymerization yielded smaller particles and narrow distribution without any indication of aggregation. The partial substitution of the dithiol by a trithiol monomer that is substantially more water insoluble affected nucleation of the particles, yielding for both systems smaller particles. The polythioether polymers synthesized present low glass transition temperatures (~ −30/−40°C) and those containing the therephthalate yield crystalline films. The potential application of the polymers as pressure sensitive adhesives (PSAs) was preliminarily assessed.