Micron-sized Particles Research Articles

Study on the mechanical properties, microstructure and hydration mechanism of phosphogypsum-based geopolymer cement with added micron-sized silica particles

Phosphogypsum (PG) is a solid waste product that is generated during the manufacture of phosphoric acid. In this study, beta-hemihydrate phosphogypsum (β-HPG), slag, sodium metasilicate (SM), citric acid (CA) and micron-sized silica particles (MSSP) were mixed to form a phosphogypsum-based geopolymer (PBG) cement. The results revealed that by adding 3 % MSSP, the 28-day unconfined compressive strength (UCS) reached its highest level of 59.2 MPa. Furthermore, adding 2 % MSSP resulted in the greatest water resistance, with a softening coefficient of 0.92. Additionally, X-ray diffractometry (XRD) Rietveld analysis, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) imaging, thermogravimetry-differential scanning calorimetry (TG-DSC) analysis, high-temperature XRD analysis, and mercury intrusion porosimetry (MIP) testing were employed to analyse the PBG cement. Results indicated that dihydrate gypsum (CaSO4·2H2O), ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)26), and polymers (Nan{−(SiO2)zAlO2}n·ωH2O) were the principal hydration products in the PBG cement system. Also, the addition of MSSP led to reduced porosity, lower pore-specific surface area, and fewer cracks in the cement structure. After exceeding temperatures of 990.9 °C, these polymers gradually decomposed into Na6(AlSiO4)6, Al2O3, and SiO2. PBG cement is characterized by its easy processing, high strength, eco-friendly nature, and high PG incorporation. It shows promise as a potential substitute for traditional Portland cement in certain sectors, thereby facilitating the consumption of waste gypsum.

Time-resolved characteristics of oscillatory particle-laden air flow in a realistic human airway model

Human airways represent a complex flow system with a spatially and temporally variable character of air flow during respiration. In this paper, we experimentally studied the oscillatory flow of air with monodispersed micron-sized liquid particles in a transparent, anatomically realistic model of human upper airways and several bronchi generations using phase-Doppler anemometry (PDA). The PDA provided point-wise high-frequency measurements of axial velocities of individual aerosol particles in multiple positions of the airways (in the trachea and the upper bronchi) for three breathing regimes with a sinusoidal course. Typical time-resolved velocity plots at several positions within the model were documented and analysed using dimensionless criteria. Local mean air velocity and turbulence time-lines disclosed specific flow dynamic features in the multiple bifurcation system, namely the transit of vortical structures, oscillations induced by flow reversals, and inspiratory flow separations behind bifurcations. The results elucidated the laminar, transitional and turbulent flows during inspiratory and expiratory breathing phases. The character of the flow varies significantly with position in the airways, while the breathing regime has a generally low effect on the flow character. Inspection of the flow in the terminal branches indicated the need to add further branches for more realistic results there.

Fast-facile synthesis of single-phase nanocrystalline β-Ca2P2O7 powder by an aerosol synthesis method

Recently, β-phase of calcium pyrophosphate has gained wide attention for potential in different applications. In this communication, we report for the first time an ultra-fast, cost-effective, and facile one-step synthesis of single-phase β-CPP powder without post-heat treatment by applying liquid flame spray (LFS). LFS is a scalable, continuous, and adjustable one-step flame-based aerosol synthesis method. The effect of Ca/P ratio on structural properties was investigated. β-Ca2P2O7 could be successfully synthesized in spherical nano-and micron-sized particles, as well as plate-like particles. The synthesized single-phase powder exhibited high thermal stability and relatively high specific surface area with different (nano)porous structures.

Ultrahigh-Throughput, Real-Time Flow Cytometry for Rare Cell Quantification from Whole Blood.

We present an ultrahigh-throughput, real-time fluorescence cytometer comprising a viscoelastic microfluidic system and a complementary metal-oxide-semiconductor (CMOS) linear image sensor-based detection system. The flow cytometer allows for real-time quantification of a variety of fluorescence species, including micrometer-sized particles and cells, at analytical throughputs in excess of 400,000 species per second. The platform integrates a custom C++ control program and graphical user interface (GUI) to allow for the processing of raw signals, adjustment of processing parameters, and display of fluorescence intensity histograms in real time. To demonstrate the efficacy of the platform for rare event detection and its utility as a basic clinical tool, we measure and quantify patient-derived circulating tumor cells (CTCs) in peripheral blood, realizing that detection has a sensitivity of 6 CTCs per million blood cells (0.000006%) with a volumetric throughput of over 3 mL/min.

Full-flow surface defect identification method based on spot scanning scattering for unpatterned wafer

As the critical dimensions of semiconductor manufacturing processes gradually decrease, the requirements for production yield management become increasingly stringent. During the manufacturing process, there are many different types of defects, such as micron-sized particles, millimeter-sized scratches, etc. Multiple categories and different scales bring great challenges to the detection and identification of defects. This paper provides a full-flow surface defect identification method based on spot scanning scattering for unpatterned wafers. First, an adaptive threshold method with dynamic kernel windows is used to perform line-by-line scanning inspection of the wafer Mercator image. The 3σ decision strategy is used to avoid the impact of defects on background estimation and to improve detection sensitivity. After morphological processing, connected domain analysis is performed to obtain the defect mask, and feature information such as the shape, size, and distribution of the defect is extracted. Finally, the defect identification is performed by rules based binning, and the identified defects are converted into wafer polar coordinate image for display and analysis. In the experiments, the proposed method is used to identify micron-scale particles as well as large scratches on the millimeter scale for SiC wafers. Relative to the actual production rate requirement of 20 wafers per hour, the analysis time for a 6-inch wafer is 24.4 s, which can meet the requirement. Meanwhile, the test results illustrate the effectiveness of the method. The proposed method is recommended for early-stage defect detection and identification of unpatterned wafers.

From molecular salt to layered network: cation-driven tuning of band gap, structure, and charge transport in A3Bi2I9 (A = Cs, Rb) perovskites.

The increasing demand for eco-friendly and stable optoelectronic materials has led to interest in all-inorganic lead-free halide perovskites. This study reports the synthesis of A3Bi2I9 (A = Cs, Rb) perovskites via a solvothermal technique. The materials crystallize in hexagonal and monoclinic structures, with micrometer-sized particles. Optical investigations reveal direct band-gaps of 2.03 eV for Cs3Bi2I9 and 1.90 eV for Rb3Bi2I9. Raman spectroscopy highlights distinct vibrational modes, influenced by their structural differences. Space charge limited current (SCLC) measurements indicate varying threshold voltages and trap densities. Impedance spectroscopy and Jonscher's power law analysis reveal different polaron tunneling mechanisms in each compound. Ultrafast transient absorption spectroscopy shows the formation of self-trapped states upon photoexcitation, linked to lattice distortion and the formation of small polarons, which affect electrical conductivity.

The empty world - a view from the free volume concept and Eyring's rate process theory.

The many-body problem is a common issue, irrespective of the scale of entities under consideration. From electrons to atoms, small molecules like simple inorganic or organic structures, large molecules like proteins or polymers, nanometer- or micrometer-sized particles, granular matter, and even galaxies, the precise determination or estimation of geometrical locations and momentum energy of individual entities, and interaction forces between these millions of entities, is impossible but unfortunately important for understanding the collective physical properties like mechanical and electrical characteristics of the whole system. Despite foreseeable difficulties and complexities, attempts to estimate "interparticle" forces have never stopped using traditional Newtonian models, quantum mechanical approaches, and density functional theory. In this review, a simple approach integrating the free volume and Eyring's rate process theory is summarized and its application across a wide range of scales from electrons to the universe is presented in a unified manner. The focus is on comparisons between theoretical predictions and experimental results.

Convolutional neural networks applied to differential dynamic microscopy reduces noise when quantifying heterogeneous dynamics.

Differential dynamic microscopy (DDM) typically relies on movies containing hundreds or thousands of frames to accurately quantify motion in soft matter systems. Using movies much shorter in duration produces noisier and less accurate results. This limits the applicability of DDM to situations where the dynamics are stationary over extended times. Here, we investigate a method to denoise the DDM process, particularly suited to when a limited number of imaging frames are available or when dynamics are quickly evolving in time. We use a convolutional neural network encoder-decoder (CNN-ED) model to reduce the noise in the intermediate scattering function that is computed via DDM. We demonstrate this approach of combining machine learning and DDM on samples containing diffusing micron-sized colloidal particles. We quantify how the particles' diffusivities change over time as the fluid they are suspended in gels. We also quantify how the diffusivity of particles varies with position in a sample containing a viscosity gradient. These test cases demonstrate how studies of non-equilibrium dynamics and high-throughput screens could benefit from a method to denoise the outputs of DDM.

Micron-sized iron particles as energy carrier: Cycling experiments in a fixed-bed reactor

Iron is a promising energy carrier with the potential to store substantial amounts of energy over extended time periods with minimal losses. For instance, the energy from green hydrogen sources can be used to reduce iron oxides, be stored or transported, and thus be regained by exothermic oxidation of the iron. This work explores the influence of oxygen partial pressure and temperature on the oxidation process in a fixed-bed reactor. Furthermore, the analysis extends to the reduction of oxidized iron particles at varying temperatures. The experimental findings highlight that both oxidation and reduction progress through the fixed-bed reactor as distinct reaction fronts. In the oxidation process, the speed of the reaction front increases with rising oxygen content and temperature, resulting in a higher reaction rate and a correspondingly increased heat release. Conversely, the reaction rate for reduction experiences a notable decrease for 600°C and 700°C. The reprocessability of the iron powder was validated for up to 16 cycles under the optimal reaction conditions established. Furthermore, it was demonstrated that the performance improves with an increasing number of cycles. This improvement is attributed to the formation of pores due to density changes and the subsequent creation of a larger surface area, mitigating the negative effects of sintering and agglomeration.

Utilization of Coal Fly-Ash derived Silicon (Si) as Capacity Enhancer of Li-Ion Batteries Anode Material

The increasing demand for energy has caused a rise in coal usage, resulting in high fly ash generation. The high SiO2, Al2O3, and Fe2O3 content in fly ashes (FAs) allow them to be processed in electrical energy storage technology, such as lithium-ion-based secondary batteries. The research aims to develop silicon from FAs for Li-ion battery applications. The fabrication of silicon materials employed in this study are (i) extraction of SiO2 from FA, (ii) gelation of SiO2, (iii) magnesiothermic reduction of SiO2 to Si under N2 flow, (iv) purification of silicon, (v) the solid-state composite fabrication of Si/C. The as-prepared Si was characterized. XRD test showed the presence of silicon phase and minor impurities in Mg. SEM analysis of the Si showed that the material has a polymorph shape with a rough surface of micron-sized secondary particles. EDX test showed the presence of impurities in the form of O and Mg atoms; meanwhile, the EDX mapping confirmed the dominant distribution of Si in the sample. Galvanostatic charge-discharge analysis of a battery with 5%Si/C anode and LiNi0.8Co0.1Mn0.1O2 or NCM811 cathode resulted in a specific charge and discharge capacity of 600 mAh/g and 473.6 mAh/g, respectively, which is greater than the graphite theoretical capacity of 372 mAh/g.

Concentration-polarization electroosmosis for particle fractionation.

Concentration-polarization electroosmosis (CPEO) refers to steady-state electroosmotic flows around charged dielectric micro-particles induced by low-frequency AC electric fields. Recently, these flows were shown to cause repulsion of colloidal particles from the wall of a microfluidic channel when an electric field is applied along the length of the channel. In this work, we exploit this mechanism to demonstrate fractionation of micron-sized polystyrene particles and bacteria in a flow-focusing device. The results are in agreement with predictions of the CPEO theory. The ease of implementation of CPEO-based fractionation in microfluidics makes it an ideal candidate for combining with current techniques commonly used to generate particle lift, such as inertial or viscoelastic focusing, requiring no extra fabrication steps other than inserting two electrodes.

Design of gum Arabic/gelatin composite microcapsules and their cosmetic applications in encapsulating tea tree essential oil.

Microencapsulation has been widely used to protect essential oils, facilitating their application in cosmetics. In this study, gelatin, gum arabic and n-butyl cyanoacrylate were used as wall materials, and composite microcapsules of tea tree essential oil (TTO) were prepared using a combination of composite coagulation and in situ polymerization methods. When the ratio of gelatin to gum arabic is 1 : 1, the ratio of TTO to n-butyl cyanoacrylate is 4 : 1, the curing time is 10 h, and the encapsulation efficiency (EE) under these conditions is 73.61%. Morphological observation showed that the composite capsule was a micron-sized spherical particle with an average particle size of 10.51 μm, and Fourier transform infrared spectroscopy (FT-IR) confirmed a complex coagulation reaction between gelatin and gum arabic, and the disappearance of the n-butyl cyanoacrylate peak indicated that the film was formed in a condensation layer. The thermogravimetric analysis (TGA) results showed that the composite capsule greatly improved the thermal stability of TTO. Rheological testing showed that the viscosity and viscoelasticity of the surface composite capsules have been improved. In addition, the composite capsule showed good stability in the osmotic environment and has good sustained-release performance and antioxidant capacity in the average human skin environment.

Formation of two-dimensional diamond-like colloidal crystals using layer-by-layer electrostatic self-assembly.

We report here that a two-dimensional (2D) diamond-like structure of micron-sized colloidal particles can be obtained by layer-by-layer self-assembly. Positively and negatively charged silica particles, 1 μm in diameter, were used in the experiments. On a positively charged, flat glass substrate, the first layer of negatively charged particles was prepared to form a non-close-packed 2D crystal. Then the second and third layers were fabricated using electrostatic adsorption. The positions of adsorbed particles were controllable by tuning the zeta-potential of the particles and the salt concentration of the medium. The FDTD calculations show that the 2D diamond structures of particles with higher refractive index (titania) have an absorption band in the wavelength range corresponding to the photonic band gap of the 3D bulk crystal. We expect these findings to be useful for the fabrication of novel photonic materials.

Restoration kinetics and microstructural evolution of moderately warm-rolled yttria dispersion-strengthened tungsten plate during annealing at high temperatures

The thermal stability of an yttria particle dispersion strengthening tungsten (W-2vol%Y2O3) plate with 67 % rolling thickness reduction (WY67) fabricated by powder metallurgy and warm rolling is investigated through isochronous annealing and isothermal annealing. Hardness testing of annealed specimens allows tracking the degradation of the mechanical properties and electron backscatter diffraction (EBSD) was used to characterize the corresponding microstructure. Isochronous annealing for 1 hour between 1150 °C and 1450 °C indicates that the recrystallization temperature of WY67 is about 1400 °C. Herein, the recovery kinetics, recrystallization kinetics, and the evolution of microstructure and texture of WY67 during isothermal annealing at temperatures ranging from 1300 ℃ to 1450 ℃ were investigated in detail. The effect of both the heterogeneity of the deformed microstructure and the yttria particles on the recovery and recrystallization was further studied. The results show that the stored energy of the deformed grains of yttria dispersion strengthened tungsten is texture-dependent and the grain with γ-fiber (normal direction // <111>) texture has the largest stored energy of 546 KJ/m3. The grains with higher stored energy are conducive to recrystallized nucleus/grain growth rather than nucleation during subsequent annealing. The recrystallized texture inherits the deformed texture and is mainly composed of γ-fiber texture. There are more pre-existing potential recrystallization nuclei in the elongated grains with larger deformation in the as-rolled microstructure. Micron-sized yttria particles can stimulate the formation of recrystallization nuclei through particle-stimulated nucleation mechanism, nevertheless, this is not the dominant nucleation mode for WY67 during recrystallization in this study. Fine (submicron) yttria particles hinder the recovery and recrystallization processes through the Smith–Zener pinning effect.

Porous hybrid encapsulation enables high-rate lithium storage for a micron-sized SiO anode.

Establishing a durable interfacial layer between an electrode and electrolyte to enable micron-sized silicon-based lithium-ion battery (LIB) anodes to achieve superior electrochemical performance is highly desired. Recent studies have shown that heterogeneous encapsulation with enhanced ion/electron transport is an effective strategy. However, the structural design of the existing hetero-coated interface lacks a reasonable ion/electron transport channel, resulting in high interfacial impedance. Herein, we designed a heterogenous MXene-mesoporous polypyrrole (mPPy) encapsulation layer onto micron-sized SiO particles. The MXene coating layer functions as a bridging interface that can build a strong chemical link to internal SiO via covalent bonding, thus reinforcing interfacial charge transfer rate. Meanwhile, it forms a dynamic connection with the outer mPPy through hydrogen bonding, which contributes to high interfacial Li+ concentration and ion/electron coupling transport rate. Accordingly, the as-prepared SiO@MXene@mPPy anode delivers a boosted specific capacity of 673.9 mA h g-1 at 2 A g-1 after 1000 cycles and high-rate capability of 777.4 mA h g-1 at 5 A g-1. Further, electrochemical kinetic analysis indicates that the MXene@mPPy coating layer shows a pseudocapacitance controlled Li storage mechanism, thereby displaying improved high-rate capability. This porous hybrid encapsulation strategy offers new possibilities for a micron-sized SiO anode to achieve an excellent performance.

Effects of salinity on the flow of dense colloidal suspensions.

We experimentally study the effects of salt concentration on the flowing dynamics of dense suspensions of micrometer-sized silica particles in microfluidic drums. In pure water, the particles are fully sedimented under their own weight, but do not touch each other due to their negative surface charges, which results in a "frictionless" dense colloidal suspension. When the pile is inclined above a critical angle θc ∼ 5° a fast avalanche occurs, similar to what is expected for classical athermal granular media. When inclined below this angle, the pile slowly creeps until it reaches flatness. Adding ions in solution screens the repulsive forces between particles, and the flowing properties of the suspension are modified. We observe significant changes in the fast avalanche regime: a time delay appears before the onset of the avalanche and increases with the salt concentration, the whole dynamics becomes slower, and the critical angle θc increases from ∼5° to ∼20°. In contrast, the slow creep regime does not seem to be heavily modified. These behaviors can be explained by considering an increase in both the initial packing fraction of the suspension Φ0, and the effective friction between the particles μp. These observations are confirmed by confocal microscopy measurements to estimate the initial packing fraction of the suspensions, and AFM measurements to quantify the particles surface roughness and the repulsion forces, as a function of the ionic strength of the suspensions.

Investigation of direct simultaneous uranium isotopic determination and age dating of micrometer-sized uranium particles by laser ablation – multi-collector ICPMS

The proposed method offers to the analytical community an alternative technique for uranium particle aged dating more widely available than LG SIMS. Moreover, working on μm-sized particles reduces issues with laser-induced fractionation.

Charged hollow microgel capsules.

Responsive hollow microgels are a fascinating class of soft model systems at the crossover between polymer capsules and microgels. The presence of the cavity makes them promising materials for encapsulation and controlled release applications but also confers them an additional softness that is reflected by their peculiar behaviour in bulk and at interfaces. Their responsivity to external stimuli, such as temperature, pH, and ionic strength, can be designed from their synthesis conditions and the choice of functional moieties. So far most studies have focused on "small" hollow microgels that were mostly studied with scattering or atomic force microscopy techniques. In our previous study, we have shown that large fluorescent hollow poly(N-isopropylacrylamide) (PNIPAM) microgels could be synthesized using micrometer-sized silica particles as sacrificial templates allowing their investigation in situ via confocal microscopy. In this work, we extend this approach to charged large hollow microgels based on poly(N-isopropylacrylamide-co-itaconic acid) (P(NIPAM-co-IA)). Hereby, we compare the structure and responsivity of "neutral" (PNIPAM) and "charged" (P(NIPAM-co-IA)) hollow microgel systems synthesized under similar conditions with the same sacrificial template using confocal and atomic force microscopy and light scattering techniques. In particular, we could demonstrate the extremely soft character of the swollen charged hollow microgels and their responsivity to pH, ionic strength, and temperature. To conclude this study, the buckling behavior of the different capsules was investigated illustrating the potential of such systems to change its conformation by varying the osmotic pressure and pH conditions.

Melting of a single ice microparticle on exposure to focused near-IR laser beam to yield a supercooled water droplet.

We observed for the first time that a single ice microparticle supported on a substrate melted photothermally to form a supercooled water droplet on exposure to tightly focused illumination with a 1064-nm laser beam that generated a point heat source. In situ Raman micro-spectroscopy clearly showed the formation of liquid water at the expense of ice. The observation of this melting is only possible when the experiment is performed with micrometer-sized ice particles. A previous attempt to melt millimeter-sized ice through photothermal heating of gold nanoaggregates fell short of expectations because only vapor formation, rather than liquid water formation, has been postulated. Our observation is significant because thermal confinement in a microscale compartment using a water-air interface as a heat-insulated wall can achieve particle temperatures above the melting point of water, whereas, in an unlimited space of ice, heat transfer from the heating center to the surroundings causes steep temperature decays, resulting in limited temperature increase.

Physical phase field model for phagocytosis

We propose and study a simple, physical model for phagocytosis, i.e. the active, actin-mediated uptake of micron-sized particles by biological cells. The cell is described by the phase field method and the driving mechanisms of uptake are actin ratcheting, modeled by a dynamic vector field, as well as cell-particle adhesion due to receptor-ligand binding. We first test the modeling framework for the symmetric situation of a spherical cell engulfing a fixed spherical particle. We then exemplify its versatility by studying various asymmetric situations like different particle shapes and orientations, as well as the simultaneous uptake of two particles. In addition, we perform a perturbation theory of a slightly modified model version in the symmetric setting, allowing to derive a reduced model, shedding light on the effective driving forces and being easier to solve. This work is meant as a first step in describing phagocytosis and we discuss several effects that are amenable to future modeling within the same framework.