High-density Particles Research Articles

Effect of secondary phase particles on thermal stability of ultra-fine grained Mg-4Y-3RE alloy prepared by equal channel angular pressing

As-cast magnesium alloy WE43, containing yttrium and rare earth elements, was processed by equal channel angular pressing (ECAP). The processing led to a significant grain refinement together with a massive precipitation of the secondary phase particles. Thermal stability of the ultra-fine grain (UFG) structure together with microstructural changes due to exposure to elevated temperatures were studied by several complementary techniques in the temperature range of 160–500 °C. It was found that UFG structure consisting of grains with size of ~340 nm and high density of Mg5RE particles is stable up to 280 °C for 1 h of annealing. Moreover, only negligible change of the microstructure occurred after annealing for 16 h at 250 °C. Excellent thermal stability of UFG structure was caused by fine Mg5RE particles, which suppressed the grain growth. Exceeding the limit of thermal stability of these particles above 280 °C resulted in material softening. Moreover, statistically significant hardening of the UFG material occurred in the temperature range of 200–280 °C. Segregation of yttrium and rare earth elements and eventually precipitation at grain boundaries was proved to be responsible for observed hardening by in-situ and ex-situ transmission electron microscope and positron annihilation spectroscopy analysis. Finally, individual effect of particles dissolution and grain growth on the material softening was investigated and discussed.

Stratification of mixtures in evaporating liquid films occurs only for a range of volume fractions of the smaller component.

I model the drying of a liquid film containing small and big colloid particles. Fortini et al. [Phys. Rev. Lett. 116, 118301 (2016)] studied these films with both computer simulation and experiment. They found that at the end of drying, the mixture had stratified with a layer of the smaller particles on top of the big particles. I develop a simple model for this process. The model has two ingredients: arrest of the diffusion of the particles at high density and diffusiophoretic motion of the big particles due to gradients in the volume fraction of the small particles. The model predicts that stratification only occurs over a range of initial volume fractions of the smaller colloidal species. Above and below this range, the downward diffusiophoretic motion of the big particles is too slow to remove the big particles from the top of the film, and so there is no stratification. In agreement with earlier work, the model also predicts that large Péclet numbers for drying are needed to see stratification.

Estimation of diffusion constants from single molecular measurement without explicit tracking

BackgroundTime course measurement of single molecules on a cell surface provides detailed information about the dynamics of the molecules that would otherwise be inaccessible. To extract the quantitative information, single particle tracking (SPT) is typically performed. However, trajectories extracted by SPT inevitably have linking errors when the diffusion speed of single molecules is high compared to the scale of the particle density.MethodsTo circumvent this problem, we develop an algorithm to estimate diffusion constants without relying on SPT. The proposed algorithm is based on a probabilistic model of the distance to the nearest point in subsequent frames. This probabilistic model generalizes the model of single particle Brownian motion under an isolated environment into the one surrounded by indistinguishable multiple particles, with a mean field approximation.ResultsWe demonstrate that the proposed algorithm provides reasonable estimation of diffusion constants, even when other methods suffer due to high particle density or inhomogeneous particle distribution. In addition, our algorithm can be used for visualization of time course data from single molecular measurements.ConclusionsThe proposed algorithm based on the probabilistic model of indistinguishable Brownian particles provide accurate estimation of diffusion constants even in the regime where the traditional SPT methods underestimate them due to linking errors.

Macroscopic‐Oriented Gold Nanorods in Polyvinyl Alcohol Films for Polarization‐Dependent Multicolor Displays

AbstractDue to their abundant optical colors, durable color generation, and high refreshing rate, smart chromic nanomaterials (SCNMs) have been employed in various applications. However, most SCNMs often require multicomponent materials, precise morphology control, and complicated modulation to realize multicolor changes, which limits their widely practical applications. In the present study, a simple and effective strategy is demonstrated to achieve the flexible and cost‐effective multicolor gold nanorods (Au NRs)/polymer hybrid film, by tuning macroscopic‐oriented Au NRs in films and a synergy of polarization‐dependent surface plasmon resonance. Au NRs are first functionalized with methoxypoly(ethylene glycol)thiol to improve the compatibility, ensuring Au NRs can be homogenously dispersed in the polyvinyl alcohol (PVA) matrix with high particle density. The macroscopic‐oriented alignment of Au NRs can be achieved by the elongation of the PVA polymer molecular chains. Under different polarized excitation directions, the same strip of the hybrid film exhibits various colors including red, orange, yellow, and green. Therefore, the strategy provides a simple and powerful approach to achieve macroscopic‐oriented anisotropic nanoparticles in the polymer matrix, and the resultant hybrid films are promising in various practical applications, such as color displays, optical devices, and plasmonic biosensors.

Long-Range Capture and Delivery of Water-Dispersed Nano-objects by Microbubbles Generated on 3D Plasmonic Surfaces.

The possibility of investigating small amounts of molecules, moieties, or nano-objects dispersed in solution constitutes a central step for various application areas in which high sensitivity is necessary. Here, we show that the rapid expansion of a water bubble can act as a fast-moving net for molecules or nano-objects, collecting the floating objects in the surrounding medium in a range up to 100 μm. Thanks to an engineered 3D patterning of the substrate, the collapse of the bubble could be guided toward a designed area of the surface with micrometric precision. Thus, a locally confined high density of particles is obtained, ready for evaluation by most optical/spectroscopic detection schemes. One of the main relevant strengths of the long-range capture and delivery method is the ability to increase, by a few orders of magnitude, the local density of particles with no changes in their physiological environment. The bubble is generated by an ultrafast IR laser pulse train focused on a resonant plasmonic antenna; due to the excitation process, the technique is trustworthy and applicable to biological samples. We have tested the reliabilities of the process by concentrating highly dispersed fluorescence molecules and fluorescent beads. Lastly, as an ultimate test, we have applied the bubble clustering method on nanosized exosome vesicles dispersed in water; due to the clustering effect, we were able to effectively perform Raman spectroscopy on specimens that were otherwise extremely difficult to measure.

A new correlation for minimum spouting velocity for conical spouted beds operating with high density particles

Hydrodynamics of conical spouted beds operating with high density particles was studied by means of measuring the minimum spouting velocity and analysis of pressure signals in time and frequency domains. Three different types of particles, zirconia (dp = 1 mm; ρp = 6050 kg/m3), zirconia toughened alumina (ρp = 3700 kg/m3; dp = 1, 2 and 2.4 mm) and glass beads (ρp = 2460 kg/m3, dp = 1 and 2 mm) were used in the experiments. Experiments were performed in three small scale (γ = 30°, 45° and 60°) and two large scale (γ = 31° and 66°) beds at different gas inlet diameters and static bed heights. It was found by the analysis of pressure signals that the pressure drop in the stable spouting bed increases with increasing bed size, static bed height, gas inlet diameter and density of particles, and decreasing particle size and cone angle. The minimum spouting velocity increases with increasing particle size, cone angle, static bed height and density of particles, and decreasing bed size and gas inlet diameter. Power spectral density of the pressure signals also revealed significant influence of the above mentioned parameters on the hydrodynamics of conical spouted beds. Based on the results of the experiments, a new correlation is proposed for prediction of the minimum spouting velocity in conical spouted beds operating within the density range of 2460–6050 kg/m3 particles. The average relative error and correlation coefficient of the proposed correlation was found to be 10.55% and 0.95, respectively, which shows the potential of the proposed correlation for prediction of the minimum spouting velocity in conical spouted beds with high density particles.

Exploring tarnished daguerreotypes with synchrotron light: XRF and \u03bc-XANES analysis

We report on the elemental and chemical characterization of tarnish on a historic daguerreotype plate. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy reveal the presence of C, O, Na, K, P, Cl, Hg, Ag, Cu, S and Au. Synchrotron based X-ray absorption near edge structure (XANES) spectroscopy, together with two-dimensional X-ray fluorescence (XRF) microscopy, provide information beyond the elemental distribution and speciation of the daguerreian tarnish features, revealing the presence of NaCl, KCl, HgCl2, HgSO4, CuS, and Ag2S on the surface. Through the application of synchrotron XRF, the distributions of Ag and S were found to be inversely correlated. This suggests a preferential accumulation of S within high-density particle regions. Spectroscopic investigation at different regions within the XRF image showed that blemish regions contained degradation products such as NaCl and KCl with AgCl noted in the surrounding regions. The observation of Cu on the surface, in the form of CuS, may either be a result of Cu diffusing through grain boundaries and/or holes in the Ag, or from the accretion of Cu salts, such as basic sodium copper carbonate, from the deterioration of the above cover glass. Silver halides (AgCl, AgBr and AgI) were also detected with XANES. This may be the result of either environmental conditions or from residual products from the production process of the plate. These results point to the interaction between deterioration products from the cover glass with the daguerreotype surface as one, but not the only, source of the tarnish.

Hydrodynamics of high solids anaerobic reactor: Characterization of solid segregation and liquid mixing pattern in a pilot plant VALORGA facility under different reactor geometry

One of the main problems of dry anaerobic digestion plants treating urban solid waste is the loss of useful volume by the sedimentation of solids (inerts) into the bottom of the digester, or by accumulation of floating materials in its upper part. This entails a periodic cost of emptying and cleaning the digesters, a decrease in biogas production and complications in maintenance. Usually the sedimentation is a consequence of the heterogeneity of waste that, in addition to organic matter, drags particles of high density that end up obstructing the digesters. To reduce this bottleneck, URBASER has designed a new configuration of VALORGA reactor. That is, the VALORGA central wall has been removed and an inclined bottom has been added. To test the sedimentability and the overall performance of both configurations (current and new design), hydrodynamic tests have been carried out in a pilot digester (digester of 95 m3 capacity). To simulate the liquid phase and the solid phase of the reactor, lithium tracers and tags of different densities with RFID (radio frequency identification reader) have been used respectively. The results of the study showed an improvement in the performance of the new reactor design at pilot level.

Polypyrrole-Fe2O3 Nanocomposites with High Dielectric Constant: In Situ Chemical Polymerisation

Novel nanocomposites of polypyrrole (PPy) dispersed with iron oxide (Fe2O3) particles have been synthesised by in situ chemical oxidative polymerisation of pyrrole in the presence of ammonium persulfate (APS) as an oxidising agent. The concentration of Fe2O3 was varied between 10-50wt% of PPy. The simultaneous polymerisation of pyrrole and oxide addition led to the complete synthesis of nanocomposites. A maximum dielectric constant of ∼28500 was observed at 20wt% of Fe2O3. The nanocomposites were characterised by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD analysis confirmed the structure and crystallinity of the nanocomposites, and a strong interaction between PPy and Fe2O3 particles was observed by FTIR technique. SEM and TEM images showed that Fe2O3 particles had been coated with PPy by establishing a network during the polymerisation process. The values of dielectric constant were obtained from capacitance measurements. The value of dielectric constant for nanocomposites with 20wt% of Fe2O3 was observed to be almost 12 times that of the pure PPy matrix. The high value of dielectric constant indicated a high packing density of Fe2O3 particles in PPy matrix. These nanocomposites have potential applications in electronic or biomedical devices.

Pre-ingestive selection capacity and endoscopic analysis in the sympatric bivalves Mulinia edulis and Mytilus chilensis exposed to diets containing toxic and non-toxic dinoflagellates.

This study investigates the effects of toxic and non-toxic dinoflatellates on two sympatric bivalves, the clam Mulinia edulis and the mussel Mytilus chilensis. Groups of bivalves were fed one of three diets: (i) the toxic paralytic shellfish producing (PSP) Alexandrium catenella + Isochrysis galbana; (ii) the non-toxic Alexandrium affine + Isochrysis galbana and (iii) the control diet of Isochrysis galbana. Several physiological traits were measured, such as, clearance rate, pre-ingestive selection efficiency and particle transport velocity in the gill. The clearance rates of both M. chilensis and M. edulis showed a significant reduction when fed a mixed toxic diet of 50% Alexandrium catenella: 50% Isochrysis galbana. Similarly, when both species of bivalves were fed with the non-toxic diet (50% A. affine: 50% I. galbana), clearance rate was significantly lower compared with a diet of 100% I. galbana. Under all the experimental diets, M. chilensis showed higher clearance rate values, slightly more than double that of M. edulis. M. edulis and M. chilensis have the ability to select particles at the pre-ingestive level, thus eliminating a larger proportion of the toxic dinoflagellate A. catenella as well as the non-toxic A. affine in the form of pseudofaeces. Higher values of selection efficiency were registered in M. edulis than in M. chilensis when exposed to the toxic diet. Similar results were observed when these two species were exposed to the diet containing the non-toxic dinoflagellate, explained by the fact that the infaunal Mulinia edulis is adapted to dealing with larger particle sizes and higher particle densities (Navarro et al., 1993). The lower transport particle velocity observed in the present work for both species, is related to the reduced clearance rate, the higher particle concentration, and the presence of larger, toxic dinoflagellates. In addition, the species differ in their feeding responses to diets, with and without A. catenella or A. affine, largely reflecting their adaptations to different environmental conditions. The results suggest that the presence of a dinoflagellate bloom, whether toxic or non-toxic spp in Yaldad Bay, is likely to have a greater impact on the Mytilus chilensis than the infaunal Mulinia edulis, based on the combined effects on clearance rate, selection efficiency and particle transport velocity.

On the microstructure and mechanical property of as-extruded Mg–Sn–Zn alloy with Cu addition

This work explored the effect of Cu addition on the microstructure characteristics and tensile properties of as-extruded Mg–8Sn–2Zn alloys. Results indicated that adding Cu caused the formation of MgZnCu phase with a face-center cubic structure (α = 0.7169 nm) and exhibited subtle grain refinement effect of the as-cast alloys. Moreover, the volume fraction of MgZnCu phase increased as Cu content increased. Appropriate Cu addition could refine the precipitates and increase the number density of precipitate of as-extruded alloys, which resulted in the refinement of grains and weakening of texture intensity. However, extensive addition of Cu increased the size of secondary phases, thereby resulted in weak grain boundary pinning effect and growth of dynamic recrystallized grains. Such grain growth might cause the growth selection of grains with the predominant orientation of extruded fiber texture. The as-extruded Mg–8Sn–2Zn–0.5Cu alloy exhibited the optimal yield strength of 365.9 MPa and ultimate tensile strength of 388.4 MPa. High strength values were expected due to the high number density of micron-sized broken MgZnCu and Mg2Sn particles, as well as nano-sized Mg2Sn precipitates and fine grains.

Size-resolved effective density of submicron particles during summertime in the rural atmosphere of Beijing, China

Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer (CPMA) combined with a differential mobility analyzer (DMA) was deployed to determine the size-resolved effective density of 50 to 350nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55g/cm3, on average. The effective particle density distributions were dominated by a mode peaked at around 1.5g/cm3 for 50 to 350nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6g/cm3 for 150, 240, and 350nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation (NPF) event decreased considerably, indicating the significant contribution of organics to new particle growth.

Chemically reacting hypersonic flows over 3D cavities: Flowfield structure characterisation

In this paper, a computational investigation of hypersonic rarefied gas flows in the transitional flow regime over 3D cavities is carried out by using the direct simulation Monte Carlo method. Such cavities give rise to geometric discontinuities that are often present at the surface of reentry vehicles. This work is focused on the flowfield structure characterisation under a rarefied environment and in the presence of chemical reactions. The cavities are investigated with different length-to-depth ratios, and the different flow structures are studied. In particular, for length-to-depth ratios of 1 and 2, a single recirculation is observed inside the cavities and the main flow is not able to enter the cavity due to the recirculation structure and high particle density. In the case of length-to-depth ratio 3, the flow is able to partially enter the cavity resulting in an elongated recirculation and the beginning of a secondary recirculation core is noticed. For the case of values 4 and 5, the main flow is able to penetrate deeper into the cavities and two recirculation zones are observed; however, for the length-to-depth ratio 5 the flow impinges directly on the bottom surface, which is a behaviour that is only observed in the continuum regime with a cavity length-to-depth ratio greater than 14.

Production of Thermal-Resistant Cornstarch-Alginate Beads by Dripping Agglomeration

Abstract This work investigated the agglomeration of native cornstarch and production of microcapsules by dripping of sodium alginate suspensions into calcium chloride solution. The crosslinking reaction formed a calcium alginate that worked as an encapsulation matrix and coated the cornstarch granules. The spherical beads produced were rigid and compact, and resistant to mechanical handling. The differential scanning calorimetry (DSC) computed the thermal resistance of the cornstarch-alginate beads. Particles containing 50 % w/w calcium alginate showed an increased gelatinization peak compared to particles with a higher starch content. The increase in alginate fraction resulted in beads with a higher particle density. Scanning electron micrographs showed the coating of cornstarch by the calcium alginate matrix. The beads were compact and with no superficial pores. DSC thermograms of native cornstarch showed a gelatinization temperature of 70.0 °C, and the gelatinization range was 64.6–80.4 °C, while beads containing 50 % alginate had an increased peak at 79.5 °C and the gelatinization interval was 71.0–90.2 °C. When compared with the native cornstarch, cornstarch-alginate beads had a lower water absorption, and the gelatinization occurred at a higher temperature and over a wider temperature range.

Simultaneous location and size measurement of particles using extended glare-point imaging technique.

Interferometric particle imaging (IPI) is a robust and popular technique for measuring particle size and velocity. A method based on a template matching algorithm and an auto-correlation method is proposed to simultaneously extract the location and the separation of doublet images of a particle from an IPI focused image. The position coordinate (x,y) of the particle can be determined with high accuracy, as evaluated by using a serial particle mask. Furthermore, the method can be employed to achieve sub-pixel spacing extraction when combined with Gaussian interpolation. The algorithm is tested using synthetic and experimental data. The results suggest that the method presented here is promising for its application to a high-density particle field, in accurately measuring both the particle size and its location.

CFD simulation of the preheater cyclone of a cement plant and the optimization of its performance using a combination of the design of experiment and multi-gene genetic programming

Hurriclon cyclone is a specially designed preheater cyclone with two outlet connector pipes of cleaned gas in the cement industry. In Kerman cement plant, Iran, the initial structure of this cyclone was changed. This caused a decrease in the cyclone efficiency. In this study, to optimize the changed cyclone performance, one of the twin cyclones in the first-stage of the preheater tower, which had the most significant effect on particle separation from gas was simulated and validated by computational fluid dynamics. Using the design of experiment based on the simulation results, the effects of three dimensions (vortex-finder length, cylinder height, and cone tip diameter) were investigated on cyclone performance. The turbulent gas flow inside the cyclone was modelled using the Reynolds stress model due to the swirling flow inside the cyclones. The discrete phase model was used to calculate the trajectory of particles. It was observed that because of high gas inlet velocity and particle density as well as the geometry of the preheater cyclone, particles larger than the critical diameter continue spinning in the cyclone. The Multi-Gene Genetic Programming (MGGP) was used to obtain two equations for efficiency and pressure drop in order to optimize the preheater cyclone performance. For this purpose, two-objective optimization using the Genetic Algorithm (GA) was performed. The optimization results showed that by using the optimized dimensions for the preheater cyclone, the pressure drop decreases by 2.2% and the efficiency increases by 13.4%.

К ВОПРОСУ ОБ ИННОВАЦИОННЫХ СПОСОБАХ ПОЛУЧЕНИЯ МАТЕРИАЛОВ ДЛЯ ПОКРЫТИЙ ПОВЕРХНОСТЕЙ ТЕХНОЛОГИЧЕСКОГО ОБОРУДОВАНИЯ НА ПРЕДПРИЯТИЯХ ПИЩЕВОЙ ИНДУСТРИИ

The technologies involving the use of different modern nano-sized food additives are relevant in the food industry. All methods for obtaining systems containing nano-sized particles are divided into dispersion and aggregation methods. The dispersion methods as widely known in the food production are well-studied and formalised in terms of equipment. The main disadvantage of mechanical dispersion methods is a possibility of mixing the grinding powder with milling agents. The basic approach to minimization is the production or facing of working areas by wear-resistant materials. The recent studies of fire-proof materials focus on the properties of sintered alumina, which has a high density of particles due to their small size and as a result the increase in mechanical resistance and stability to wear and tear. In this context, this material is favourable to facing the working areas of grinding aggregates, including in the food industry. The nanotechnology analysis proved the technology of selective laser melting of fine powders to be desirable. This technology is multi-functional, and as an innovative decision can be used to get wear-resistant materials when producing the food nanosystems by dispersion. As one of the promising areas for further development is the study on grinding capacity of food systems ensuring the energy-saving production of nano-sized food additives in the context of optimization of their preparation as an element of system approach to the problem solving.

Combination of Magnetic Lignocellulosic Particles, High-Density Polyethylene, and Carbon Black for the Construction of Composites with Tunable Functionalities.

Biocomposites with unique functionalities for tailored applications are promising products for a sustainable future. In this work, a process concept of forming functional composites by combining of high-density polyethylene, carbon black, and magnetic lignocellulosic particles (wood flour) was demonstrated. The impacts of process parameters on morphologies, crystalline phase, and magnetic intensity of wood flour were identified. Magnetic, antistatic and mechanical properties of biocomposites were also evaluated. Lignocellulosic particles were encapsulated with magnetic nanoparticles, and the resulting composites exhibited tunable magnetic and antistatic properties. A noticeable feature is that magnetic nanoparticles were uniformly distributed in the matrices as a result of anchorage to lignocellulosic particles. Magnetic lignocellulosic particles and polymer resin had good compatibility. The resulting composites provided another opportunity for shielding materials, which could reduce the radiation in the living environment. These findings could provide a tunable strategy of the tailored use of lignocellulose-based composites in functional applications.

Numerical investigation of a cold bubbling bed throughout a dense discrete phase model with KTGF collisional closure

Abstract A hybrid Euleran-Lagrangian Dense Discrete Particle Model (DDPM) was used to numerically simulate the bubbling behavior of a fluidized bed reactor. The model exploits the parcels concept to reduce the number of particles to simulate while exploiting the Kinetic Theory of Granular Flow (KTGF) to account for their repulsive interactions. The DDPM-KTGF was explored throughout a model sensitivity analysis to identify the most influent parameters impacting on the numerical accuracy and performances to ultimately assess its potential use for industrial purposes. Because of the measurement simplicity as well as its strong connection with the bed fluid-dynamic, pressure-drop data was used and processed to obtain the power spectral density (PSD) distribution to empirically and numerically characterize the behavior of this system under a bubbling fluidization regime. The DDPM-KTGF model was found to be sensitive to mesh size, restitution coefficients but mostly to the drag law. However, poor sensitivity to the kinetic viscosity, solid pressure, radial distribution function as well as to the number of parcels was revealed. Besides having an effect on the physical outputs, the mesh refinement was also required to numerically verify the model which also had a significant impact on the simulation time-performance. Moreover, a major barrier was found when using this model to simulate fixed bed regime, showing the limitation of the KTGF approach to high particle density regions as a result of a poor estimation of particles force interactions.

Boosting the Photoluminescence of Monolayer MoS2 on High‐Density Nanodimer Arrays with Sub‐10 nm Gap

AbstractPatterned plasmonic nanodimers are fabricated exploiting an ultrathin porous anodic aluminum oxide membrane as a mask during angle‐resolved shadow deposition. The fabricated nanodimer arrays exhibit consistent sub‐10 nm gaps and a high particle density up to 1.0 × 1010 cm−2 over a large area. The ultrasmall dimer gaps provide highly confined electromagnetic fields, which strongly enhance the photoluminescence (PL) emission and Raman scattering from the surrounding monolayer molybdenum disulphide (MoS2). The ensemble PL intensity from MoS2/dimers is enhanced by up to a factor of ≈160 by resonant excitation of the dimer modes. Anisotropic polarization‐dependent characteristics of PL and Raman from the MoS2/dimers confirm that the dominant enhancement originates from the dimer configuration. These experiments demonstrate a facile approach for the fabrication of low‐cost high‐performance 2D material‐based optoelectronic devices.