Irregular-shaped Particles Research Articles

A facile fabrication of polypropylene composites with excellent low-temperature toughness through tuning interfacial area between matrix and rubber dispersion by silica nanoparticles located at the interface

In order to fabricate super low-temperature tough polymer composites which can withstand extreme environments, hydrophobic silica nanoparticles were incorporated into polypropylene/ethylene propylene rubber (PP/EPR) blends with the hope to tailor the brittle ductile transition temperature (Tbd). Compared with PP/EPR blends, PP/EPR/SiO2 composites presented much lower Tbd, and Tbd decreased with the increase of EPR content and SiO2 content. It was found that PP/EPR/SiO2 composites could present excellent low-temperature toughness with little rigidity loss. Phase morphology showed that the silica nanoparticles were located at the interface of PP and EPR. It was found that silica nanoparticles at the interface could not only suppress the phase coarsening in PP/EPR/SiO2 composites greatly, but also tailor the shape of rubber particles. A detailed investigation on rubber particle size, interparticle distance and interfacial area indicated that the tremendous drop of Tbd should be ascribed to the increased interfacial area between the matrix and rubber phase due to the decreased size and more irregular shape of rubber particles. As a result, a quantitative correlation between Tbd and interfacial area in PP/EPR/SiO2 composites was established. This study provided a facile approach to fabricate polymer composites with super low-temperature toughness or other functions through tuning the size and shape of rubber domains by adding nanoparticles.

Three-Dimensional Microstructure of ε-Fe2O3 Crystals in Ancient Chinese Sauce Glaze Porcelain Revealed by Focused Ion Beam Scanning Electron Microscopy.

Ancient Chinese sauce glaze porcelain has recently received growing attention for the discovery of epsilon iron oxide (ε-Fe2O3) crystals in glaze. In this work, we first confirm the presence of ε-Fe2O3 microcrystals, in large quantiteis, in sauce glaze porcelain fired at the Qilizhen kiln in Jiangxi province during the Southern Song dynasty. We then employed focused ion beam scanning electron microscopy (FIB-SEM) to investigate the three-dimensional microstructure of ε-Fe2O3 microcrystals, which revealed three well-separated layers (labeled, respectively, as LY1, LY2, and LY3 from the glaze surface to inside) under the glaze surface. Specifically, LY1 consists of well-defined dendritic fractal structure with high ordered branches at micrometers scale, LY2 has spherical or irregular-shaped particles at nanometers scale, while LY3 consists of dendrites with four, six, or eight primary branches ranging from several nanometers to around 1 μm. Given these findings, we proposed a process for the possible growth of ε-Fe2O3 microcrystals in ancient Chinese sauce glaze.

Glycine-nitrate solution combustion synthesis of lithium zirconate: Effect of fuel-to oxidant ratio on phase, microstructure and sintering

Pure monoclinic lithium zirconate (Li2ZrO3) powder was synthesized by solution combustion route using glycine as fuel and nitrates as oxidants. Effect of fuel-to-oxidizer ratio (φ = 0.5–1.25) on synthesis condition, phase, powder morphology, sintering and thermodynamic aspects was systematically investigated. Thermodynamic analysis reveals; mode of combustion, adiabatic flame temperature, amount of gases and powder characteristics can be controlled by adjusting φ. The crystallite size of Li2ZrO3 powder was in the range of 18–40 nm. The powders consist of micrometric soft-agglomerates of irregular flake shape particles. The residual Li2O in Li2ZrO3 powder was found to be in the range 155–469 μg/g. The Li2ZrO3 powder synthesized by present method shows significantly enhanced sinter-ability as compared to conventional solid-state method. The Li2ZrO3 pellets were sintered close to 98% of T.D. at 1000 °C with grain size 1–2 μm. Increase of sintering temperature to 1050 °C results abnormal grain growth with large number of closed pores.

Exploring the influence of sphericity on the mechanical behaviors of ballast particles subjected to direct shear

To quantitatively evaluate the influence of shape on the mechanical behaviors of ballast, a series of 2D direct shear simulations were conducted on particles with different sphericities. The particle contours were obtained from the scanning images of 40 ballast particles, based on which the irregular-shaped particles were precisely reconstructed by clumps in the discrete element models. According to the sphericity, five assemblies were prepared for the direct shear simulation. Higher shear strength, vertical relative displacement and apparent angle of shear resistance were observed in assemblies consisting of low-sphericity particles. To explore the mechanism of macro-mechanical behaviors, an in-depth analysis of the mesoscopic responses was conducted. Two parameters were adopted to evaluate the anisotropy of the contact force distribution observed clearly in all samples and stronger anisotropy was found in samples with low-sphericity particles. The translational and rotational displacements of particles were also analyzed. Larger vertical displacements and less rotations were observed in samples with low-sphericity particles. The results suggest that particles with diverse shapes can produce varying particle interlock states and moving behaviors, hence influence the macro-mechanical behaviors.

A Super-Clustering Approach for Fully Automated Single Particle Picking in Cryo-EM.

Structure determination of proteins and macromolecular complexes by single-particle cryo-electron microscopy (cryo-EM) is poised to revolutionize structural biology. An early challenging step in the cryo-EM pipeline is the detection and selection of particles from two-dimensional micrographs (particle picking). Most existing particle-picking methods require human intervention to deal with complex (irregular) particle shapes and extremely low signal-to-noise ratio (SNR) in cryo-EM images. Here, we design a fully automated super-clustering approach for single particle picking (SuperCryoEMPicker) in cryo-EM micrographs, which focuses on identifying, detecting, and picking particles of the complex and irregular shapes in micrographs with extremely low signal-to-noise ratio (SNR). Our method first applies advanced image processing procedures to improve the quality of the cryo-EM images. The binary mask image-highlighting protein particles are then generated from each individual cryo-EM image using the super-clustering (SP) method, which improves upon base clustering methods (i.e., k-means, fuzzy c-means (FCM), and intensity-based cluster (IBC) algorithm) via a super-pixel algorithm. SuperCryoEMPicker is tested and evaluated on micrographs of β-galactosidase and 80S ribosomes, which are examples of cryo-EM data exhibiting complex and irregular particle shapes. The results show that the super-particle clustering method provides a more robust detection of particles than the base clustering methods, such as k-means, FCM, and IBC. SuperCryoEMPicker automatically and effectively identifies very complex particles from cryo-EM images of extremely low SNR. As a fully automated particle detection method, it has the potential to relieve researchers from laborious, manual particle-labeling work and therefore is a useful tool for cryo-EM protein structure determination.

Particle obstruction and crushing of dredged calcareous soil in the Nansha Islands, South China Sea

The bearing capacity of the dredged calcareous soil in the Nansha Islands, South China Sea typically exceeds that of terrigenous dredger fill. Furthermore, the shear strength of calcareous soil exceeds that of siliceous sand under identical conditions. It is mainly caused by the interparticle obstruction between calcareous soil particles. To explore the obstruction mechanism of calcareous soil particles, a series of triaxial tests were performed on calcareous soils under both consolidated undrained (CU) and consolidated drained (CD) conditions, respectively. Particle shape characteristics and particle crushing were also investigated to study the formation mechanism of obstruction force. Test results indicate that irregular particle shape is the prerequisite for the emergence of particle obstruction in calcareous soils. A simple obstruction-dilatation model was developed to describe the relationship among particle obstruction, dilation and particle crushing. The obstruction force varies greatly during the shearing process, which is mainly influenced by particle size and stress level. Under low confining pressure, particle obstruction results in dilatation and increases internal friction angle. In contrast, obstruction causes particle breakage, increases the apparent cohesion, and ultimately decreases the effective internal friction angle under high confining pressures. The particle obstruction of calcareous soil noticeably improves shear strength. Therefore, the effect of particle obstruction on strength should be considered in coral reef engineering design work.

Green liquor dregs and slaker grits residues characterization of a pulp and paper mill for future application on ceramic products

Abstract Green liquor dregs and slaker grits are pulp and paper mill residues usually landfilled. Whit high calcium carbonate content, its use as alternative raw materials in traditional ceramic products becomes an interesting study field. In order to evaluate its incorporation potential, the residues characterization with diverse approaches was performed and for the first time reunited exploring this eco-friendly intent. Green liquor dregs and slaker grits were characterized by its chemical and mineralogical composition (XRF, XRD, FT-IR); physical and morphological characteristics (particle size, BET surface area, density, SEM) and thermal properties (TGA). Chemical and mineralogical analysis reveals the high calcium carbonate content in calcite form especially on slaker grits, that has less inorganic and organic contaminants than green liquor dregs. Smaller irregular-shaped particles and bigger surface area was found on this last residue, comparing with slaker grits. The thermal analysis indicated a lower calcite decomposition for green liquor dregs (720 °C), while this event on slaker grits occurred 40 °C above (760 °C). Thus, it was observed the residues behavior and characteristics are much alike calcium carbonate itself, especially slaker grits, considering its composition, morphology and thermal events. As conclusion, the potentiality uses of green liquor dregs and slaker grits as alternative raw materials on ceramic products was revealed. Being able to incorporate clay, concrete, glasses and great majority of other ceramic products, these residues use will generate excellent benefit-cost ratio to industries and environment.

Sub-Micrometric MCM-41 Particles as Support to Design Efficient and Regenerable Maghemite-Based Sorbent for H₂S Removal.

In this work, highly dispersed maghemite (λ-Fe₂O₃) in form of ultrasmall nanoparticles (about 2 nm) was embedded into a mesostructured silica MCM-41 (about 600 nm) featuring regular submicrometric hexagonal shaped particles via the two-solvent incipient wetness impregnation strategy. The obtained nanocomposite was then tested as H₂S sorbent in the mid-temperature range. When compared with a commercial sorbent (KatalkoJM 32-5), it showed superior performances after the first sulfidation which remained steady over three repeated sulfidation cycles, highlighting the regenerability properties of the composite. In order to evaluate the effect of the length of the pore channels on the accessibility of H₂S to the active phase, an analogous micrometric λ-Fe₂O₃@MCM-41, featuring micrometric channels and particles of irregular shape was used as reference.

Study of morphological characteristics and elemental composition of respirable particulate matter in an opencast coal mineusing FESEM-EDX

Atmospheric aerosol consists of both natural and anthropogenic origin. Studies have shown that continuous exposure to these particles is associated with a high percentage of death from respiratory and cardiovascular disease. In the present study, the PM10 samples were collected from eight sampling stations around a highly mechanised opencast coal mine in Talcher, India. Identification of the probable sources of PM10 was carried out through morphological analysis using FESEM, and elemental analysis was performed by using EDX analysis. Based on the FESEM-EDX analysis, the seasonal behaviour of PM10 was studied. The FESEM study revealed that the monitoring stations, which were mostly affected by mining activities were found dominated by the big-sized and irregular-shaped particles. On the other hand, monitoring stations mostly affected by transportation activities were affected by small-sized and regular-shaped particles. The EDX analyses showed that elements like C, O, Si, Al, Hg and Fe were the major elemental constituents of PM10 in the study area.

Two-dimensional particle shapes modelling for DEM simulations in engineering: a review

The Discrete Element Method/Modelling (DEM) is a well-elaborated method for modelling the dynamical behaviour of particulate systems. The term “DEM” refers to a family of numerical methods for computing the motion of a large number of particles such as molecules, grains, and rocks. Despite it was originally pioneered for rock mechanics, DEM is being developed for wide-range of applications in most engineering domains. The representation of particle shape geometry in DEM is crucial, which has a direct impact on the computational performance of the methods and on the dynamical behaviour of particulate systems. Most applications are limited in time of simulation to simple particle shapes due to the increase in computation with increasing complexity of geometry. Currently, many methods for particle shape representation are proposed due to irregular shape of the real particles. This paper reviews the research and methods of particle shapes modelling for 2D-DEM over the last three decades. This includes classification of particle shapes models in the different categories, applicable to numerous engineering disciplines that use DEM.

Improved method to measure the strength and elastic modulus of single aggregate particles

The standard methods used to determine the mechanical properties of single aggregate particles have shortcomings. Indeed, methods that are commonly used to measure the strength of irregular particles do not provide their elastic modulus and are also only semi-quantitative. The aim of this work is to determine more accurately both the tensile strength and the elastic modulus of single coarse aggregate particles using the point load test fitted with tungsten carbide semi-spheres and coupled with a linear transducer. In the experiment, the poles of the particles are made flat and parallel at the points of contact with the semi-spheres of the apparatus, allowing to estimate the elastic modulus of aggregates in accordance to Hertz contact theory. Glass particles of different shapes (spheres, cubes, and prisms) were used as reference material to validate the experimental method and establish the optimal conditions to conduct the test. These conditions consisted of a deformation rate of 0.2 mm/min, a blunt 4.0-mm diameter cylinder piston for spherical particles, while two 14.0-mm diameter semi-spheres in the case of rectangular particles (cubes/prisms). It is also hereby proposed to measure the tensile strength of irregularly-shaped particles by a modified version of Hiramatsu and Oka’s formula using the equivalent core diameter. The proposed method was then applied to measure the strength and modulus of coarse granite aggregate particles (25.0 to 9.5 mm). It demonstrated that the variability of the elastic modulus and tensile strengths of the individual aggregate particles was quite significant, confirming the importance of using the proposed improved method to qualify materials for structural (high strength) concrete, or to simulate/predict the mechanical behavior of concrete.

Robust synthesis of coal bottom ash-based geopolymers using additional microwave heating and curing for high compressive strength properties

While coal bottom ash (CBA) contains an amount of amorphous silica and alumina as high as coal fly ash (CFA), its irregular particle shapes and excess unburnt carbon content compared to CFA are known to decrease the compressive strength of CBA-based geopolymers. Hence, we propose an advanced synthetic method of high-strength CBA-based geopolymer by appending microwave heating to conventional oven curing process without pretreatments for carbon removal. First, we blended finely crushed CBA with a moderate amount of 14 M NaOH alkali activator to make a mixture in a slightly wet state. Then, we fabricated precast samples by casting the mixture against 5-cm cubic molds with the help of a hand press. Next, the samples were hardened through the two-stage process of pre-dry-oven curing (12, 24 and 36 hr at 75 °C) and post-microwave-oven heating (up to 7 min under 700 W power). In essence, the specimens cured for 36 hr in the dry oven showed a considerable improvement in compressive strength just after being heated for 3 min in the microwave oven (from 12.8 to 40.5 MPa). This newly proposed synthetic method is proven to be very cost-effective for producing CBA-based geopolymer with high compressive strength.

Reaping the remarkable benefits of a ‘burst nucleation’ approach for a ceria doped zirconia system

Through this work, we show the efficacy of a novel processing step (during co-precipitation synthesis) that ensured a ‘burst nucleation’ scenario and yielded crucial benefits for a stabilized zirconia (Ce0.2Zr0.8O2) system. In addition to the high surface area and near-spherical morphology of the Ce0.2Zr0.8O2 nanoparticles, high temperature (≥1350 °C) tetragonal phase stability was noted for both Ce0.2Zr0.8O2 powders and ceramics. Ce0.2Zr0.8O2 powders produced near-theoretical density (∼97%) ceramic with equiaxed grain size (0.17 ± 0.05 μm) via conventional sintering at 1250 °C. Significant improvement was noted for the hardness values (∼14.5 GPa) for the Ce0.2Zr0.8O2 ceramic compared to all previously published literature. Tetragonal→monoclinic transformation (for synthesis plan without burst nucleation approach) was correlated to anisotropic and irregular particle shapes, wide dispersion in particle sizes that induced internal stress in ZrO2 matrix.

Photo-Electrochemical Oxygen Evolution Reaction by Biomimetic CaMn2O4 Catalyst

Calcium manganese oxide catalysts are a new class of redox catalysts with significant importance because of their structural similarity to natural oxygen-evolving complex in plant cells and the earth-abundant elemental constituents. In the present study, the photo-electrocatalytic properties of CaMn2O4 in water-splitting were investigated. CaMn2O4 powders with irregular shapes and nanowire shapes were synthesised using mechanochemical processing and a hydrothermal method, respectively. The anode in a photo-electrochemical cell was fabricated by embedding CaMn2O4 powders within polypyrrole. The results showed that CaMn2O4 induced a higher dark and light current in comparison to the control sample (polypyrrole alone). CaMn2O4 nanowires exhibited higher dark and light current in comparison to irregular-shaped CaMn2O4 powders. The difference was attributable to the higher surface area of nanowires compared to the irregular-shaped particles, rather than the difference in exposed crystal facets.

Effect of nickel acetylacetonate addition on soot inception and growth in an ethylene flame studied by using in situ small-angle X-ray scattering

Small-angle X-ray scattering (SAXS) technique has been used to study soot formation and growth in an ethylene flame doped with Ni(acac)2 (nickel acetylacetonate) at atmospheric pressure. An undoped flame under the same conditions was also studied to compare with the doped flame. The results show that the Ni(acac)2 addition affects particle size, shape and morphology significantly at certain flame heights. It has reducing effect on the primary soot particle size at the flame heights between 17 and 34 mm. It delays the growth of primary soot particles at soot growth region. The soot volume fraction in the doped flame is smaller than that in the undoped flame by factors of 1.5–4 at different heights above the burner. In the most heights of the soot surface growth region (HAB=13–30 mm), the Porod exponents for the doped flame are smaller than those in the undoped flame, suggesting that the addition of Ni(acac)2 in the ethylene flame induces a rougher surface and more irregular shape of the soot primary particles.

Characterization of dynamic morphological changes of tin anode electrode during (de)lithiation processes using in operando synchrotron transmission X-ray microscopy

The morphological evolution of tin particles with different sizes during the first lithiation and delithiation processes has been visualized by an in operando synchrotron transmission X-ray microscope (TXM). The in operando lithium ion battery cell was operated at constant current condition during TXM imaging. Two-dimensional projection images with 40 nm resolution showing morphological evolution were obtained and analyzed. The analysis of relative area change shows that the morphology of tin particles with different sizes changed simultaneously. This phenomenon is mainly due to a negative feedback mechanism among tin particles in the battery electrode at a constant current operating condition. For irregular-shaped tin particles, the contour analysis shows that the regions with higher curvature started volume expansion first, and then the entire particle expanded almost homogeneously. This study provides insights for understanding the dynamic morphological change and the particle-particle interactions in high capacity lithium ion battery electrodes.

Simultaneous shape and size measurements of irregular rough particles by an IPI system with double receivers

ABSTRACTThis paper proposes a method of obtaining the shape and the size of irregular rough particles, which are abundant in particle fields. The approach uses the infocused image of the particle to determine its size, and an improved relation between the central peak of the 2D-autocorrelation of its defocused image and its size to obtain the shape. An interferometric particle imaging system with double receivers is established to simultaneously collect the infocused image and defocused image. Experiments confirm the effectiveness of the proposed algorithm with a measurement relative error on the sample particles not exceeding 10.4%. In general, this method can offer significant perspectives on the characterization of particle fields.

Statistical size scaling of breakage strength of irregularly-shaped particles

The microdefects in a material responsible for fracture initiation in particle breakage may not always have a uniform spatial distribution. This work applies the power-law spatial flaw distribution based weakest link formulation of cumulative failure probability for statistical size scaling of breakage strength of irregularly-shaped particles. Four sets of published breakage strength data of different sized grains made of different materials including rock, basalt, sugar, and potash are adopted to validate the power-law spatial flaw distribution based weakest link model. Since the power-law spatial flaw distribution based weakest link model encompasses the uniform spatial flaw distribution based weakest link model as its subordinate member, while the Weibull statistical strength theory is a special case of the uniform spatial flaw distribution based weakest link model, this work extends the capability to investigate size scaling of particle breakage strength.

Ingestion of small-sized and irregularly shaped polyethylene microplastics affect Chironomus riparius life-history traits

Microplastics (MPs) are emerging contaminants of freshwater ecosystems. Once in aquatic systems, most of these plastic particles undergo processes of fragmentation, biofouling, and sedimentation, resulting in increased concentrations of smaller sized and irregularly-shaped particles in the sediment. High levels of MPs in freshwater sediments can denote a potential threat to benthic and sediment-dwelling organisms such as dipteran larvae. This study evaluates the ecotoxicological effect of three pools of irregularly-shaped polyethylene (PE) microplastics (pools containing 90% of the particles within 32–63 μm (size-class A), 63–250 μm (size-class B) and 125–500 μm (size-class C)), with concentrations ranging from 1.25 to 20 g Kg−1 sediment, on the dipteran Chironomus riparius life-history traits. After ten days of exposure, larvae ingested PE particles typically in the 32–63 μm range, even when 90% of the particles possessed higher size (i.e., in size-classes B and C) and the larvae mandible allowed the ingestion of such bigger-sized particles. Thus, the number of ingested particles was higher in size-class A, followed by B and C, and led to a significant reduction with similar magnitude on larval growth (Lowest Observed Effect Concentrations (LOEC) = 2.5 g Kg−1 sediment DW) and a significant delay on imagoes emergence (e.g., LOEC = 1.5 g Kg−1 sediment DW for females).The results from this study show that the ingestion and persistence of small-sized polyethylene microplastics caused significant impairments on life-history traits of C. riparius. Considering their role on freshwater food-webs and the potential persistence of small-sized PE particles in their larval gut, these results also point for the potential adverse effects of small-sized microplastics at the community and ecosystem level.

Cytotoxicity of Pharma Grade ZnO with Higher Surficial Oxygen on L929 Mouse Cell

Apart from being a promising optoelectronic devices such as photodetector and sensors, ZnO has many dental and biomedical applications. ZnO has been known to possess strong toxicity towards bacteria, cancer and fungi. Cytotoxicity test of pharmaceutical grade of ZnO on L929 mouse fibroblast cell lines was carried out using trypan blue assay. ZnO was characterized for its morphology, structure and optical properties using FESEM, EDS, UV-Vis and XRD. ZnO exhibited various morphologies like rod, platelet, slab and irregular-shaped particles. EDS data showed the ZnO powder possessed relatively higher oxygen atomic percentage if compared to zinc atoms with an oxygen-to-zinc ratio of 1.219. The average crystallite size obtained was about 39 nm. The percentage of cell viability on L929 cell was decreased with increasing ZnO concentrations. The cells viability after 72h were achieved and the concentration of ZnO below 1 mM was summarized as non-toxic after treated with ZnO. The higher surficial oxygen on ZnO particle surface could have promoted higher generation of reactive oxygen species that caused lower L929 cell viability.