Showing papers on "Particle-size distribution published in 2021"

Nanofragmentation of Expanded Polystyrene Under Simulated Environmental Weathering (Thermooxidative Degradation and Hydrodynamic Turbulence)

Abstract: Fragmentation of macroplastics into microplastics in the marine environment is probably one of the process that has generated most drive for the development of the microplastics research field. It is thus surprising that the level of scientific knowledge on the combinative effect of oxidative degradation and mechanical stressors on fragmentation is relatively limited. Furthermore, it has been hypothesized that plastic fragmentation continues into the nanoplastic size domains, but environmentally realistic studies are lacking. Here the effects of thermooxidative degradation and hydrodynamic conditions relevant for the shoreline environment on the fragmentation of expanded polystyrene (EPS) were tested in laboratory simulations. The pre-degraded EPS was cut into pieces and subjected to mechanical, hydrodynamic simulations during four-day stirring experiments. Subsamples were filtered and subsequently analyzed with light microscopy with automated image analysis particle size distribution determinations, polymer identification with Raman spectroscopy, Scanning Electron Microscopy (SEM) with automated image analysis particle size distribution, and the nanoplastic size fraction was measured using nanoparticle tracking analysis. In addition, the degree of polymer oxidation was spectroscopically characterized with Fourier transform infrared (FTIR) spectroscopy, and the surface changes were analyzed with SEM. The results illustrate that fragmentation of the mesoplastic objects is observed already after two days, but that is more distinct after four days, with higher abundances for the smaller size fractions, which imply more release of smaller sizes or fragmentation in several steps. The nanoplastic fractions show very high abundances released or fragmented the polymer and higher for day four than day two. The conclusions are that nanofragmentation is an important and understudied process and that standardized test protocols for both thermooxidative degradation and mechanical treatments mimicking realistic environmental conditions are needed and then further testing of the most common macro- and mesoplastic materials to assess the rates and fluxes of fragmenting particles to micro- and nanoplastic fractions should be conducted.

The effects of particle size distribution on the rheological properties of the powder and the mechanical properties of additively manufactured 17-4 PH stainless steel.

Abstract: It is well known that changes in the starting powder can have a significant impact on the laser powder bed fusion process and subsequent part performance. Relationships between the powder particle size distribution and powder performance such as flowability and spreadability are generally known; however, links to part performance are not fully established. This study attempts to more precisely isolate the effect of particle size by using three customized batches of 17-4 PH stainless steel powders with small shifts in particle size distributions having non-intersecting cumulative size distributions, designated as Fine, Medium, and Coarse. It is found that the Fine powder has the worst overall powder performance with poor flow and raking during spreading while the Coarse powder has the best overall flow. Despite these differences in powder performance, the microstructures (i.e., porosity, grain size, phase, and crystallographic texture) of the built parts using the same process parameters are largely the same. Furthermore, the Medium powder produced parts with the highest mechanical properties (i.e., hardness and tensile strength) while the Fine and Coarse powders produced parts with effectively identical mechanical properties. Parts with good static mechanical properties can be produced from powders with a wide range of powder performance.

Effect of powder milling routes on the sinterability and optical properties of transparent Y2O3 ceramics

Abstract: In ceramic processing, the size distribution of the starting powder to a certain degree is inevitable. It is prerequisite to control the size distribution, which influences the fabrication of a sound green body featuring both smaller pores and a narrower pore structure for full-density sintering facilitated by the easier elimination of pores. The milling process was systematically investigated here to elucidate the effect of powder characteristics on the sinterability and transmittance of Y2O3 ceramics. Three types of powder sets having different width of particle size distribution (WPSD) while keeping the same median size (D50) were prepared by changing the milling condition. By means of narrowing the WPSD in this research, pore free transparent polycrystalline Y2O3 with average grain size of 730 nm was successfully fabricated by hot-pressing at 1500℃, which is 100℃ lower than the previously lowest known sintering temperature.

The effects of powder reuse on the mechanical response of electron beam additively manufactured Ti6Al4V parts

Abstract: High cost of metal powders has increased the demand for recycling of unmelted powder in electron beam powder bed fusion additive manufacturing process. However, powder characteristics are likely to change during manufacturing, recovery and reuse. It is important to track the evolution of powder characteristics at different stages of recycling to produce components with consistent properties. The present work evaluates the changes in Ti6Al4V powder properties during manufacturing by characterising powder particles at different locations in the powder bed; recovery and reuse, through evaluating the effects of the powder recovery system and sieving for 10 build cycles. Heterogeneous powder degradation occurred during manufacturing with the particles closer to the melt zone showing higher oxygen content and thicker α laths with β phase boundaries. Most of them had a hard-sintered and agglomerated powder morphology in contrast to particles at the edges of the powder bed. Recovery and reuse resulted in a refined particle size distribution, but only marginal change in powder morphology. The increased oxygen caused a slight increase in the yield and tensile strengths of the build. The effect of powder reuse on material elongation, hardness and Charpy impact energy was negligible. The high cycle fatigue performance deteriorated with reuse due to the increased lack-of-fusion defects. This might be attributed to the voids formed in the powder bed due to decrease in the number of fine particles coupled with an increase in the number of high-aspect ratio particles.

Particle Size Distribution of Various Soil Materials Measured by Laser Diffraction—The Problem of Reproducibility

Abstract: Particle size distribution is an important soil parameter—therefore precise measurement of this characteristic is essential. The application of the widely used laser diffraction method for soil analysis continues to be a subject of debate. The precision of this method, proven on homogeneous samples, has been implicitly extended to soil analyses, but this has not been sufficiently well confirmed in the literature thus far. The aim of this study is to supplement the information available on the precision of the method in terms of reproducibility of soil measurement and whether the reproducibility of soil measurement is characterized by a normal distribution. To estimate the reproducibility of the laser diffraction method, thirteen various soil samples were characterized, and results were analysed statistically. The coefficient of variation acquired was lowest (3.44%) for silt and highest for sand (23.28%). Five of the thirteen tested samples were characterized by a normal distribution. The fraction content of eight samples was not characterized by normal distribution, but the extent of this phenomenon varied between soils. Although the laser diffraction method is repeatable, the measurement of soil particle size distribution can have limited reproducibility. The main cause seems to be small amounts of sand particles. The error can be amplified by the construction of the dispersion unit. Non-parametric statistical tests should be used by default for soil laser diffraction method analysis.

Spray-flame synthesis of LaMO3 (M = Mn, Fe, Co) perovskite nanomaterials: Effect of spray droplet size and esterification on particle size distribution

Abstract: Perovskite nanomaterials such as LaMnO3, LaFeO3, and LaCoO3 were synthesized in a spray flame from metal nitrates dissolved in combustible liquids. The addition of low-boiling solvents such as 2-ethylhexanoic acid (2-EHA) to the ethanol-based solutions supports the formation of phase-pure particles with unimodal particle-size distribution in the 10-nm range attributed to enhanced evaporation through micro-explosions. Nevertheless, in many cases, a second particle mode with sizes of a few hundred nanometers is formed. In this paper, we investigate two possible reasons for the appearance of large particles. Firstly, we analyze the effect of the oxygen dispersion gas flow applied in the two-fluid nozzle on the droplet size distributions of burning sprays using phase Doppler anemometry. We identified that an increase of the dispersion gas flow significantly decreases the number concentration of large droplets (>30 μm), which causes a significant increase of the BET surface area of as-synthesized LaMnO3 and LaCoO3 with increasing dispersion gas flow from 60 m2/g (5 slm dispersion gas) to 100 m2/g (8 slm). Secondly, the esterification in the mixture of solvents towards ethyl-2-ethylhexanoate, which is associated with the release of water as a byproduct, was analyzed by GC/MS. The ester concentration in the iron-containing solution was found to be up to nine times higher than in cobalt or manganese precursor solutions. Simultaneously, the produced LaFeO3 materials show lower BET surface areas and the increasing dispersion gas flow has a minor effect on this material than on the cobalt and manganese perovskite cases. We attribute this to the fact that water formed during esterification forces the hydrolysis of iron nitrate and the formation of large particles within the droplets.

Binder Jetting Additive Manufacturing: Effect of Particle Size Distribution on Density

Abstract: This paper reports a study on the effects of particle size distribution (tuned by mixing different-sized powders) on density of a densely packed powder, powder bed density, and sintered density in binder jetting additive manufacturing. An analytical model was used first to study the mixture packing density. Analytical results showed that multimodal (bimodal or trimodal) mixtures could achieve a higher packing density than their component powders and there existed an optimal mixing fraction to achieve the maximum mixture packing density. Both a lower component particle size ratio (fine to coarse) and a larger component packing density ratio (fine to coarse) led to a larger maximum mixture packing density. A threshold existed for the component packing density ratio, below which the mixing method was not effective for density improvement. Its relationship to the component particle size ratio was calculated and plotted. In addition, the dependence of the optimal mixing fraction and maximum mixture packing density on the component particle size ratio and component packing density ratio was calculated and plotted. These plots can be used as theoretical tools to select parameters for the mixing method. Experimental results of tap density were consistent with the above-mentioned analytical predictions. Also, experimental measurements showed that powders with multimodal particle size distributions achieved a higher tap density, powder bed density, and sintered density in most cases.

Effect of Particle size of monomodal 316L powder on powder layer density in powder bed fusion

Abstract: Powder layer density is an important measure for understanding the effect of powder on part quality in powder bed fusion. The density of thin layers, as they are deposited in powder bed fusion, differs from the density of powder in large containers. This study investigates this difference. Therefore, six monomodal powders with different particle size distributions, from coarse to fine, are spread in an 84.5 µm deep cavity to determine their powder layer densities for a single layer. A linear dependence of powder layer density on the D50 of powder is discovered for monomodal powders with good flowability. This dependence can be explained by the wall effect. Fine powders with low flowability show an increase in the standard deviation of the powder layer density. These findings suggest the existence of a particle size distribution that is sufficiently small to minimize the wall effect in a thin layer while still being sufficiently large to guarantee a good flowability of the powder.

Microfluidic ultrafine particle dosimeter using an electrical detection method with a machine-learning-aided algorithm for real-time monitoring of particle density and size distribution

Abstract: Growing concerns related to the adverse health effects of airborne ultrafine particles (UFPs; particles smaller than 300 nm) have highlighted the need for field-portable, cost-efficient, real-time UFP dosimeters to monitor individual exposure. These dosimeters must measure both the particle density and size distribution as these parameters are essential to the determination of where and how many UFPs will be deposited in human lungs. However, though various kinds of laboratory-grade instruments and hand-held monitors have been developed, they are expensive and only capable of measuring particle size distribution. A microfluidic UFP dosimeter is proposed in this study to address these limitations. The proposed sensor, based on an electrical detection method with a machine-learning-aided algorithm, can simultaneously measure the size distribution (number concentration, mean mobility diameter, geometric standard deviation) and particle density, and is compact owing to the microelectromechanical systems (MEMS) technology. In a comparison test using physically synthesised Ag and di-ethyl-hexyl sebacate (DEHS) aerosols, the mean measurement errors of the proposed sensor compared to the reference system were 6.1%, 4.5%, and 7.3% for number concentration, mean mobility diameter, and particle density, respectively. Moreover, when the machine-learning aided algorithm was operated, the geometric standard deviation could be deduced with a 7.6% difference. These results indicate that the proposed device can be successfully used as a field-portable UFP sensor to assess individual exposure, an on-site monitor for ambient air pollution, an analysis tool in toxicological studies of inhaled particles, for quality assurance of nanomaterials engineered via aerosol synthesis, etc.

Ultrahigh hardness in Y2O3 dispersed ferrous multicomponent nanocomposites

Abstract: Oxide dispersion strengthened Fe-based steels are one of the candidate materials for applications in future nuclear reactors, an operation that needs superior mechanical properties and long-term microstructural stability at elevated temperatures. The effects of milling time on the hardness of nano-Y2O3 dispersed [Fe:(Cr-Mo-W-Ni-Nb-V)] nanocomposites were studied. The nanostructure, microstructure and crystallographic structure of the nanocomposites were evaluated using scanning electron microscopy (SEM), particle size analysis, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HR-TEM) and energy dispersive spectroscopy (EDS). The nanocomposites’ hardness was assessed by Vickers microhardness (HV). Milling up to 6 h yielded textured plate-like particles of 200 nm thickness and 117 µm mean particle size due to particle-particle welding. Milling for 24 h resulted in a bimodal particle size distribution of 6 µm mean particle size due to strain hardening induced particle fracture. X-ray crystallite size of 24 h milled powder was 30 nm, corresponding to a dislocation density of 1.30 × 1015 /m2. Peak shift of (110) reflection with increasing milling time indicated that α-Fe matrix was under a compressive state of stress. Compositional fluctuations of alloying elements in the α-Fe matrix was detected even in 24 h milled powder by x-ray diffraction. Per TEM, uniformly dispersed ~ 20 nm Y2O3 particles of ~ 10 nm mean separation form an incoherent interface with the α-Fe matrix. The Vickers hardness of the nanocomposite increased from 185 to 537 -a ~ 300% after 24 h of milling. Such colossal increase in hardness was attributed to concurrent size effects associated with fracture, surface effects, solid solution strengthening in multicomponent alloys, and the Orowan mechanism.

Simultaneous Roadside and Urban Background Measurements of Submicron Aerosol Number Concentration and Size Distribution (in the Range 20–800 nm), along with Chemical Composition in Strasbourg, France

Abstract: The adverse health impact of particles and ultrafine particles (UFP) is proven, highlighting the need of measuring the particle number concentration (PNC) dominated by UFP. So far, PNC had never been measured in the Strasbourg urban area (France). The present study on particle size distribution and PNC measurements by an UFP-3031 analyzer was conducted during winter 2019 on a background and a roadside multi-instrumented sites (Black Carbon, chemical speciation, particulate matter 10 μm or less in diameter—PM10 mass). This paper shows significantly higher particle number concentrations of particles below 100 nm at the traffic site compared to the background site. The presence of a road axis thus mainly influences UFP, contrary to larger particles whose levels are more homogeneous over the agglomeration. During the measurement period, the nature of the particles (particle size contribution and chemical composition) was different between periods of high PM10 mass concentrations and periods of high PNC. High PM10 mass concentrations were associated with a high contribution of particles larger than 100 nm but they did not show specific chemical signature. On the other hand, during the periods with high PNC, the chemical composition was modified with an increase of the primary carbonaceous fraction compared to the periods with low PNC, but there was then no clear change in size distribution. Overall, this study illustrates that PM10 mass concentrations were barely representative of UFP and PNC variations, confirming that the monitoring of the latter metrics is necessary to better evaluate the particles toxicity, knowing that this toxicity also depends on the particle’s chemical composition.

Characterization of Particle Size and Composition of Respirable Coal Mine Dust

Abstract: Respirable coal mine dust (RCMD) particles, particularly the nano-sized fraction ( 1 μm) of RCMD particles collected at the miner location, from an underground coal mine, contained more coal particles, while those collected at the bolter location contained more rock dust particles. Two image processing procedures were developed to determine the size of individual RCMD particles. The particle size distribution (PSD) results showed that a significant amount (~80% by number) of nano-sized particles were present in the RCMD sample collected in an underground coal mine. The presence of nano-sized RCMD particles was confirmed by bulk sample analysis, using both DLS and AsFIFFF. The mode particle size at the peak frequency of the size distribution was found to be 300–400 nm, which was consistent with the result obtained from SEM analysis. The chemical composition data of the nano-sized RCMD showed that not only diesel particles, but also both coal and rock dust particles were present in the nano-sized fraction of the RCMD. The presence of the nano-sized fraction of RCMD particles may be site and location dependent, and a detailed analysis of the entire size range of RCMD particles in different underground coal mines is needed.

Effect of particle size distribution on the evolution of porous, microstructural, and dimensional characteristics during sinter-crystallisation of a glass-ceramic glaze

Abstract: Glass-ceramic test pieces, obtained from three different particle size distributions of a frit, were fired at temperatures between 800°C and 1200°C. Evolution of porous characteristics of the test pieces with firing temperature enabled the mechanisms responsible for the microstructural changes and the temperature range in which each mechanism predominated to be identified. Induced anorthoclase and diopside crystallisation porosity was observed to increase, after which it decreased at high temperatures by solution–reprecipitation of these phases, until a minimum was reached. The process caused crystal size, mean pore size, and pore size distribution uniformity to rise. Models were developed that appropriately describe the combined effect of firing temperature and glaze particle mean volume diameter on open porosity, linear shrinkage, mean pore size, and pore size distribution uniformity. Effect of glaze particle size distribution on pore size distribution, in the solution-reprecipitation stage, was perfectly described by mean pore size at solution-reprecipitation onset.