Dispersion Of Small Particles Research Articles

A Simplified Two-Fluid Model Based on Equilibrium Closure for a Dilute Dispersion of Small Particles

Two-fluid formalisms that fully account for all complex inter-phase interactions have been developed based on a rigorous ensemble-averaging procedure. Here, we apply equilibrium approximation to particle velocity to simplify two-phase flow equations for the case of a dilute dispersion of particles much smaller than the flow scales. First, we extend an earlier approach to consider the rotational motion of the particles and seek an equilibrium approximation for the angular velocity of the particulate phase. The resulting explicit knowledge of the particulate phase translational and rotational velocities in terms of fluid velocity eliminates the need to consider the momentum equations for the particulate phase. The equilibrium approximations also provide precise scaling for various terms in the governing equations of the two-fluid model, based on which a simplified set of equations is obtained here. Three different regimes based on the relative strength of gravitational settling are identified, and the actual form of the simplified two-phase flow equations depends on the regime. We present two simple examples illustrating the use of the simplified two-fluid formalism.

Effect of Intermediate Annealing on Microstructure and Cold Rolling Hardness of AlFeMn Alloy

The microstructure and texture of an AlFeMn alloy were studied under different intermediate annealing processes, and the changes in microhardness during cold rolling were analyzed. After annealing at 420 °C with a slow heating rate, the alloy showed a high number of small dispersed particles and recrystallization textures dominated by R texture, with deformation textures of 23.5%. Annealing at 610 °C with a rapid heating rate resulted in a significant decrease in the number of small-sized particles and an increase in recrystallization texture contents, with CubeND being the majority. The deformation texture contents decreased to 14.9%. The electrical conductivity of the 420 °C annealed sheet was higher than before annealing, whereas the sheet annealed at 610 °C showed a decrease in electrical conductivity after annealing. This indicated that annealing at 610 °C led to a higher degree of recrystallization and the development of Cube/CubeND due to the dissolution of dispersed particles. During the subsequent cold rolling process, the microhardness of both annealed sheets initially increased and then decreased. However, the microhardness of the 420 °C annealed sheet with varying cold rolling reductions consistently remained lower than that of the 610 °C annealed sheet, as was the cold rolling reduction corresponding to the peak microhardness. The results showed that the precipitation at 420 °C facilitated work softening, while the dissolution at 610 °C promoted work hardening.

MODIFICATION OF PINDIGA BENTONITE CLAY WITH DIDODECYLDIMETHYLAMMONIUM BROMIDES SURFACTANT FOR FOUNDRY USE

Bentonite clay from Pindiga, Gombe State, Nigeria, was surface modified with didodecyldimethylammonium bromides (DDAB) by the Base Exchange (cation exchange capacity) method for its possible use in foundries. The surfaces of the unmodified and modified Pindiga bentonite clay were characterised by means of spectroscopic, diffraction, and scanning methods (X-Ray fluorescence spectrometry (XRF)Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM).XRF showed that unmodified sample was rich of montmorillonite (MMt) with ca +2 as exchangeable cation, FTIR analysis revealed that unmodified water absorption causes stretching and bending vibrations for hydroxyl groups, with the most intense bands in the low-frequency region, while DDAB organo-bentonites showed slight changes in wave bands, with a strong methyl band and a weak methyl band indicative of long-chain linear aliphatic structure. The basal spacing of the unmodified bentonite sample was 1.52 nm, and after modification with DDAB, it improved to 2.1 nm as determined from the X-ray diffraction (XRD) analysis. Results of the SEM images revealed rougher surfaces with uniformly dispersed small particles of grain-like structures characteristic of the unmodified, while theorgano-modified bentoniterevealed clusters of different sizes and shapes, larger Fe 3+ ions replacing smaller Al 3+ ions at octahedral sites, discontinuous layers enveloping large grains, polygonal growth foams with octahedral and tetrahedral shapes, mixed layers of calcium bentonite, and particle sizes less than 200nm. The study concluded that modified bentonite with didodecyldimethylammonium bromides gives good microstructure, increases rigidity, and improve thermal stability, to the organoclays. Therefore, it is recommended that DDAB bentonite be used as binder for foundries.

Using Local Concentration to Model the Progress of Acoustophoretic Assembly of Microspheres in Planar Standing Waves

Abstract Acoustophoretic assembly uses a standing acoustic field to move dispersed small particles into a geometric pattern. The technique relies on the acoustic radiation force (ARF), which arises from the interaction between the acoustic field and the particles, and drives the particles toward the pressure nodes or antinodes of the standing wave. Acoustophoretic assembly shows potential for a wide range of applications, including organizing filler materials in composites, creating metamaterials, and fabricating functional biological tissue. However, the method has not yet been incorporated into large-scale manufacturing processes. One barrier is the incomplete understanding of the assembly process. While an ideal final pattern geometry can be calculated from the acoustic field and material properties, there are currently no widespread metrics for measuring the progress of the pattern formation. As a result, it is difficult to know how long the acoustic field should be applied during manufacturing. Our approach uses the local particle concentration to model the acoustophoretic assembly process in bulk acoustic waves. We show that the time-dependent local particle concentration can be derived from the force balance on the particles and a control volume analysis. The analysis is applied to microspheres in a planar standing wave, and an analytical expression is obtained, which yields a time parameter for pattern assembly and suggests a cutoff time. We then use the local concentration to define measurements for the quality of the assembled microsphere pattern. Experiments were carried out using polystyrene microspheres in a glycerol–water mixture to validate the theoretical results.

A Computational Study of Magneto-Convective Heat Transfer Over Inclined Surfaces With Thermodiffusion

In this article, the ocean energy generator system is analysed. The need for sustainable renewable energy systems is continually growing, given the situation of the world’s energy supplies. Numerous similar systems, including photovoltaic solar collectors, biomass, and wind turbines are used for energy generation. The ocean energy generator system uses the magnetohydrodynamics transformation concept to convert kinetic energy to electrical energy. Similar to conventional generators, an ocean generator requires an applied magnetic field to generate current, making it a critical component of the system. To optimize the performance and efficiency of ocean generators, various devices utilizing superconducting magnets have been developed, including Hall current generators, rotating channels, rotating disc magnetohydrodynamics generators, and helicoid generators. However, these systems also involve complex heat, momentum, and mass transfer, which can be better understood through mathematical modeling. The similarity transformation are introduced to transform the mathematical model from partial differential equation system to ordinary differential equation system. By adopting this approach, the numerical solution is significantly simplified while still preserving numerous crucial physical aspects of the studied heat and material transport phenomena. The physical characteristics of sea waves are governed by the three variables of seawater: temperature, salinity, and pressure. Small dispersed particles also affect the generation of hydroelectric power from surface water. The behaviour of velocity, temperature, and salinity profile is observed for the variations of different parameters such as magnetic, Grashof number and heat source. The system is converted into an optimization problem and solved by a neural network procedure. The solutions are compared with reference solutions for validation. The errors, performance, testing and training data are also presented graphically. The data is typically visualized using histograms, line graphs, and other visual aids. This allows for easier comprehension and analysis of the data.

Synthesis of Hard Layer by Titanium Addition During Welding Process and Quenched Directly

Enhance the surface hardness of materials usually conducted through a hardfacing technique. Hardfacing is popular, whereby materials with better properties are deposited over cheaper bulk material. This work fabricated hard layers by adding titanium (Ti) wire during the welding process. This research used low-carbon steel as the base material, wire optime Ti grade 1 for Ti addition, and an HV 600 electrode with a diameter of 3.2 mm for filler metal. A single-layer weld was conducted with SMAW (positive polarity and 90 A). The samples were directly quenched in a different solution after welding. The properties of the weld layer were examined phase, structure, microstructure, macrostructure, and hardness using optical emission spectroscopy (OES), x-ray diffraction (XRD), an optical microscope, a digital camera, and a hardness device, respectively. Adding titanium (Ti) to the weld layer and quenching the samples after welding in the solution enhances the hardness. This phenomenon is attributed to different phase compositions, oxides, and microstructures. A fine dispersion of small particles and oxide amount is important in increasing hardness. There is no cracking in the weld and base metal. In conclusion, samples BNTiO and BNTiM are recommended for lathe-cutting tools.

Insights and Applications of Composite Electroplating

Composite electroplating is the process of particle incorporation during the electrolytic deposition of metal. This process produces composite films consisting of a metallic matrix containing a dispersion of small particles. The advantages of composite electrodeposition over other coating methods are the uniformity of deposition even for complex shapes, the strong adhesion to the substrate, reduction of waste compared to dipping or spraying techniques, low levels of contamination, the ability to produce functionally-gradient material and to continuously process parts. In addition, this process avoids the problems associated with high temperature or vacuum processing.There are many contradictory experimental results in literature concerning the effects of the electrocodeposition process variables on particle incorporation. The effects of some of the process variables also vary for different particle-electrolyte combinations and cell configurations. Some of the reported contradictions are a direct consequence of incomparable hydrodynamics. The bulk of experimental electrocodeposition research has been conducted using a vertical parallel plate electrode set-up. In this configuration, the particles are maintained in suspension by either stirring the solution, vibrating a perforated plate at the bottom of the cell, bubbling gas, or pumping the suspension through the cell, all of which result in uncontrollable, and hence incomparable hydrodynamics. Other contradictions are due to the fact that the process parameters were evaluated only for a narrow range of experimental parameters and to differences in particle size and purity.This talk discusses the experimental results and mathematical modeling of electrocodeposition of particles in a metallic matrix. The effects of several key parameters, such as current density, particle loading, electrolyte composition, particle surface charge and polarity, on particle incorporation in electrodeposited composite coatings were studied and modeled. All experiments were done utilizing rotating disk electrodes over a wide range of experimental conditions in which the incorporation behavior changes appreciably, yielding reproducible data for better interpretation of process effects and modeling. These studies were combined with colloidal probe AFM experiments and process archeology using pulse plating which helped to understand the codeposition mechanism.

Stabilizer-free Vitamin E Nanovehicle for Biological Research.

In molecular biology research, a vitamin E (VE) vehicle (VE dissolved in organic solvent) is often added to water media without a stabilizer. However, the detailed behavior of VE colloids in water media is unclear. In this study, we reveal that VE nanoemulsion readily forms in water-based media through the existing protocol. The colloid size was changed from 39 nm to the submicron scale by adjusting the initial concentration of the VE solution and adding a buffer. The radical scavenging effect of the dispersed nanosized VEs is comparable to that of the water-soluble antioxidant Trolox, providing excellent antioxidant performance in colloid form. The cytoprotection effect of the VE colloids under a lipid oxidation condition largely depends on the size of the nanodispersion. Smaller dispersed particles are more efficient radical scavengers than larger particles for a constant VE amount owing to sophisticated uptake behavior of cell. This unveiled fundamental knowledge pave the way for a preparative protocol of stabilizer-free VE vehicles, which are expected to become widely used in molecular biology research.

Quick microwave assembling nitrogen-regulated graphene supported iron nanoparticles for Fischer-Tropsch synthesis

Facile preparation of highly efficient iron-based catalysts is vital to improve the performance of Fischer-Tropsch synthesis (FTS), a sustainable process for converting non-petroleum carbon resources to valuable hydrocarbons. In this work, a convenient preparation for nitrogen-regulated graphene supported iron nanoparticles, with the assistant of microwave treatment, was developed. Thereinto, the nitrogen-containing groups in graphene support were introduced by NH3·H2O treatment. By comparison with ordinary calcination, microwave treatment could significantly shorten the heating time to few seconds, and promote the reduction of iron species. The existence of a small number of nitrogen-containing groups could effectively anchor iron species, and improve the dispersion of iron species. Meanwhile, the duration length of NH3·H2O treatment time could regulate the content of N configuration (pyridinic-N and pyrrolic-N). The size of supported iron species from 120 nm to 10 nm could be well controlled via increasing microwave time from 0 to 14 s. For N-regulated graphene supported iron catalysts, evenly dispersed small particles of iron species, improved surface reduction behavior and reasonable N configuration all promoted FTS. Under relevant industrial conditions (320 °C, 2.0 MPa, 5 g h mol−1), the optimized 15%Fe/AG(12 h)-W(10) catalyst achieved CO conversion as high as 97.2% and C5+ selectivity of 40.0% while maintaining a mild CO2 selectivity (28.2%). The superior preparation and catalytic performance disclosed that the catalyst could be one of ideal candidates for industrial iron-based FTS catalysts in future.

The Development and Application of a Kinetic Theory for Modeling Dispersed Particle Flows

Abstract This Freeman Scholar article reviews the formulation and application of a kinetic theory for modeling the transport and dispersion of small particles in turbulent gas-flows. The theory has been developed and refined by numerous authors and now forms a rational basis for modeling complex particle laden flows. The formalism and methodology of this approach are discussed and the choice of closure of the kinetic equations involved ensures realizability and well posedness with exact closure for Gaussian carrier flow fields. The historical development is presented and how single-particle kinetic equations resolve the problem of closure of the transport equations for particle mass, momentum, and kinetic energy/stress (the so-called continuum equations) and the treatment of the dispersed phase as a fluid. The mass fluxes associated with the turbulent aerodynamic driving forces and interfacial stresses are shown to be both dispersive and convective in inhomogeneous turbulence with implications for the build-up of particles concentration in near wall turbulent boundary layers and particle pair concentration at small separation. It is shown how this approach deals with the natural wall boundary conditions for a flowing particle suspension and examples are given of partially absorbing surfaces with particle scattering and gravitational settling; how this approach has revealed the existence of contra gradient diffusion in a developing shear flow and the influence of the turbulence on gravitational settling (the Maxey effect). Particular consideration is given to the general problem of particle transport and deposition in turbulent boundary layers including particle resuspension. Finally, the application of a particle pair formulation for both monodisperse and bidisperse particle flows is reviewed where the differences between the two are compared through the influence of collisions on the particle continuum equations and the particle collision kernel for the clustering of particles and the degree of random uncorrelated motion (RUM) at the small scales of the turbulence. The inclusion of bidisperse particle suspensions implies the application to polydisperse flows and the evolution of particle size distribution.

DISCRETE DISLOCATION DYNAMICS SIMULATIONS FOR COMPRESSION OF PARTICLE REINFORCED COMPOSITES

Particle reinforced copper matrix composites have high strength, elastic modulus, excellent electrical and thermal conductivity and wear resistance, they are widely used in aerospace, rail transit, equipment manufacturing and other fields. In particle reinforced composites, the dislocation movement is prevented by small dispersed particles in the alloy, thus effectively improving the mechanical properties of metallic materials and enhancing their service safety. In this paper, the three-dimensional discrete dislocation dynamics (3D-DDD) method was used to simulate the compression of particles reinforced copper matrix composites micro-pillar. The influence of the dislocation-precipitate interaction on the mechanical response of the material was analyzed to reveal the microscopic mechanism of the precipitation strengthening. In this study, the precipitate was regarded as a spherical particle with an impenetrable surface. The dislocation bypass mechanism was used to simulate the interaction between the precipitates and the dislocations. By changing the relative distance of dislocation slip plane against the center of spherical particle, it is found that when the distance is zero, the yield strength and the subsequent strain hardening rate are the highest. As the slip plane is far away from the center of spherical particle, the yield strength and the strain hardening rate decreases. The study also found that the higher the Schmid factor, the lower the yield strength and the lower strain hardening rate. In the simulation of multiple dislocations, it was found that the reaction of dislocations in same slip planes and the interaction of dislocations in different slip systems may be responsible for the reduction of the yield strength and the strain hardening rate.

Effect of D-Mannitol on the Microstructure and Rheology of Non-Aqueous Carbopol Microgels.

D-mannitol is a common polyol that is used as additive in pharmaceutical and personal care product formulations. We investigated its effect on the microstructure and rheology of novel non-aqueous Carbopol dispersions employing traditional and time-resolved rheological analysis. We considered two types of sample, (i) fresh (i.e., mannitol completely dissolved in solution) and aged (i.e., visible in crystalline form). The analysis of the intracycle rheological transitions that were observed for different samples revealed that, when completely dissolved in solution, mannitol does not alter the rheological behaviour of the Carbopol dispersions. This highlights that the chemical similarity of the additive with the molecules of the surrounding solvent allows preserving the swollen dimension and interparticle interactions of the Carbopol molecules. Conversely, when crystals are present, a hierarchical structure forms, consisting of a small dispersed phase (Carbopol) agglomerated around a big dispersed phase (crystals). In keeping with this microstructural picture, as the concentration of Carbopol reduces, the local dynamics of the crystals gradually start to control the integrity of the microstructure. Rheologically, this results in a higher elasticity of the suspensions at infinitesimal deformations, but a fragile yielding process at intermediate strains.

Enhanced catalytic performance of highly mesoporous hydrotalcite/SBA-15 composites involved in chromene multicomponent synthesis

Abstract A series of highly porous hydrotalcite/SBA-15 composites were synthesized and used as catalysts, for the first time, in the multicomponent synthesis of chromenes, from 2-hydroxybenzaldehydes and cyano compounds, with enolizable hydrogens, under solvent-free and mild conditions. The composites were prepared by ultrasound irradiation in the crystallization step, as non-conventional energy source, using different hydrotalcite/SBA-15 proportions. HT30-SBA composite, with lower hydrotalcite loading and high developed porosity, presented superior catalytic performance affording the corresponding chromenes in excellent conversions with total selectivity, after considerably decreased reaction times. The observed reactivity was mainly attributed to the high dispersion of small particles of hydrotalcite on the SBA-15 component, contributing to a great enhancement of the mesoporosity. The high dispersion promoted the increase of the surface area given rise to a high concentration of superficial hydroxyls as more accessible catalytic sites, responsible to the catalytic activity. Therefore, our results demonstrate that percentage of hydrotalcite component, dispersion of hydrotalcite nanoparticles and texture of the composites strongly influence the catalytic performance.

Modification of Ashaka and Tango Bentonites with Tetraphenyl Phosphonium and Hexadecyl Pyridinium Bromides for Possible Use in Polymer-Clay Nanocomposite Preparation

Bentonites from Ashaka (GA) and Tango (GT) of Gombe State, Nigeria were surface modified with Tetraphenyl phosphonium (TPP) and Hexadecyl pyridinium bromides (HDP) by cation exchange method for their possible use in Clay/polymer nanocomposite preparation. The surfaces of the modified products were characterized by means of spectroscopic, diffraction and scanning methods [Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM)]. The basal spacing of the unmodified bentonite samples was 1.52nm and 1.29nm and after modification with TPP + and HDP + it increased to 1.86nm, 1.74nm and 2.15nm, 2.11nm respectively as determined from the X-ray diffraction (XRD) analysis. Results of the SEM images revealed rougher surfaces with uniformly dispersed small particles of grain-like structures characteristic of the organomodified bentonites. Bentonites from Ashaka (GA) and Tango (GT) of Gombe State, Nigeria were surface modifiedwith Tetraphenyl phosphonium (TPP) and Hexadecyl pyridinium bromides (HDP) by cationexchange method for their possible use in clay/polymer nanocomposite preparation. Thesurfaces of the modified products were characterized by means of spectroscopic, diffractionand scanning methods (Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction(XRD) and scanning electron microscopy (SEM)). The basal spacing of the unmodifiedbentonite samples was 1.52 and 1.29 nm and after modification with TPP+ and HDP+ itincreased to 1.86 and 1.74 nm; and 2.15 and 2.11 nm respectively as determined from the Xraydiffraction (XRD) analysis. Results of the SEM images revealed rougher surfaces withuniformly dispersed small particles of grain-like structures characteristic of theorganomodified bentonites.

Combined Electromagnetic and Mechanical Ultrasound for Particle Dispersion in Liquid Metals

It is known that acoustic cavitation is one of the mechanisms resulting in the dispersion of small particles in liquid metallic alloys. Previous research has shown that the contactless electromagnetic method can be used to induce such cavitation and disperse particles in metals, where the application of a high-frequency alternating magnetic field plus a static magnetic field results in pressure oscillations that can become strong enough to disperse particles. Promising results have been obtained on the laboratory scale for some metal/particle pairs such as tin/silicon carbide (Sn/SiC) and chrome steel/titanium nitride (FeCr/TiN). We present herein the idea of combining such electromagnetically induced ultrasound with the application of mechanical ultrasound to a liquid melt to achieve enhanced particle mixing and dispersion. This combined method allows the achievement of a strong oscillating pressure with simultaneous significant stirring of the melt. This approach has the potential to stir and disperse particles in a single-stage process.

Assessing the thermal maturity of black shales using vitrinite reflectance: Insights from Devonian black shales in the eastern United States

Thermal maturity of source rocks indicated by vitrinite reflectance (Ro) is an important and reliable parameter to determine the petroleum potential of sedimentary basins. Originally, Ro was used to characterize the degree of coalification of coals and thus works well for coal seams, but it has limitations when used to determine the thermal maturity of black shale successions. A suite of six coal-shale pairs from the Upper Devonian black shale formations in the eastern United States (New Albany Shale, Ohio Shale, Dunkirk Shale, and Rhinestreet Shale) was selected to study the applicability of Ro in assessing the thermal maturity of black shale successions. The results show that vitrinite in the studied coal samples is dominated by collotelinite, whereas vitrinite in black shales occurs as small dispersed particles (~5 μm) in the mineral matrix. When comparing the size and morphology of dispersed vitrinite particles in shales and collotelinite fragments in coals, vitrinite in shales and adjacent coals should have the same origin. The measured mean random Ro of vitrinite in coals ranges from 0.51–0.68%, and is 0.04–0.11% (average 0.07%) lower than that of dispersed vitrinite particles in enclosing shales. This observation contrasts with previously reported Ro suppression in liptinite-rich black shales. A high standard deviation of Ro measurements indicates a highly heterogeneous nature of vitrinite in black shales.Three mechanisms can be envisioned to contribute to the higher Ro of dispersed vitrinite particles in black shales relative to enclosed coals. First, small vitrinite particles may become more oxidized because small particles are more frequently suspended during transport to the site of deposition and reworking of bottom sediments after deposition than large pieces of driftwood that will turn into enclosed coal lenses during burial diagenesis. Second, misidentification of zooclast (e.g., chitinozoan) fragments as vitrinite due to loss of diagnostic morphology. Third, various macerals in the vitrinite group (e.g., corpogelinite and collotelinite) may have had different original reflectance values. Based on the petrographic characteristics of vitrinite and vitrinite-like particles, caution should be applied when using the Ro values of dispersed vitrinite and vitrinite-like particles in black shales as indicators of thermal maturity.

Surface grafted agents with various molecular lengths and photochemically active benzophenone moieties.

Homologues of benzophenone silane, a covalently graftable, photochemically active surface functionalizing agent, are investigated as surface functionalization agents for both small particles and planar substrates. In these homologues, a chlorosilane functional group and a photochemically active benzophenone oxo moiety are separated with an aliphatic spacer of varying length. The species obtained are first investigated by surface grafting on substrates (Si wafers, glass plates, and indium tin oxide coated glass plates). Si wafer samples are investigated with ellipsometry clearly indicating monolayer formation. The monolayer thickness can be controlled by the size of the aliphatic spacer group and also by the doping concentration of the solution used in the spin-casting step. The functionalized surfaces are further investigated by measuring the contact angle of a suitable organic fluid, a nematic liquid crystal. Photo exposure of these samples results in a drastically varied contact angle: The surface grafted species are still photochemically active and photo exposure leads to the addition of a nearby organic molecule (from the liquid crystalline phase) to each activated surface agent molecule. The synthesized species are then investigated as (covalently binding) surfactants in the wet planetary ball milling process aimed to fabricate solid-liquid dispersions (of Fe doped lithium niobate particles). It was found that the use of species with higher molecular length results in dispersions of small particles, functionalized with photochemically active surface agents. Indeed, they show better performance than conventional surfactants.

Toughness improvement of novel biobased aromatic polyamide/SEBS/organoclay ternary hybrids

ABSTRACTBiobased aromatic polyamide/organoclay (Cloisite30B, C30B) nanocomposites were melt‐compounded with reactive and nonreactive styrene–ethylene–butylene–styrene (SEBS) rubbers at different weight contents to form ternary and quaternary blends. The mechanical properties were investigated as a function of the blend composition. The elongation at break and the impact strength increase with increasing SEBS rubber content, whereas the Young's modulus logically decreases proportionally to SEBS amount. Extra addition of SEBS grafted maleic anhydride (SEBS‐g‐MA) induces a synergistic effect. The SEBS‐g‐MA makes it possible to limit the aforementioned rigidity loss and to greatly increase the impact strength. The critical strain energy release rate increases significantly when both reactive and nonreactive rubbers are combined. Three types of microstructures appear depending on the blend composition: (1) small and numerous well‐dispersed particles when reactive rubber is used, (2) about 10 times bigger and less numerous well‐dispersed particles in the case of nonreactive rubber, and (3) a flocculated dispersion of small particles when both reactive and nonreactive rubber are added. Finally, the polyamide performances were significantly increased when the flocculated morphology was noticed due to a better PAXD/SEBS interfacial adhesion given by the SEBS‐g‐MA compatibilization and to a thinner rubber distribution in the matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48888.

A population balance model for large eddy simulation of polydisperse droplet evolution

In the context of many applications of turbulent multi-phase flows, knowledge of the dispersed phase size distribution and its evolution is critical to predicting important macroscopic features. We develop a large eddy simulation (LES) model that can predict the turbulent transport and evolution of size distributions, for a specific subset of applications in which the dispersed phase can be assumed to consist of spherical droplets, and occurring at low volume fraction. We use a population dynamics model for polydisperse droplet distributions specifically adapted to a LES framework including a model for droplet breakup due to turbulence, neglecting coalescence consistent with the assumed small dispersed phase volume fractions. We model the number density fields using an Eulerian approach for each bin of the discretized droplet size distribution. Following earlier methods used in the Reynolds-averaged Navier–Stokes framework, the droplet breakup due to turbulent fluctuations is modelled by treating droplet–eddy collisions as in kinetic theory of gases. Existing models assume the scale of droplet–eddy collision to be in the inertial range of turbulence. In order to also model smaller droplets comparable to or smaller than the Kolmogorov scale we extend the breakup kernels using a structure function model that smoothly transitions from the inertial to the viscous range. The model includes a dimensionless coefficient that is fitted by comparing predictions in a one-dimensional version of the model with a laboratory experiment of oil droplet breakup below breaking waves. After initial comparisons of the one-dimensional model to measurements of oil droplets in an axisymmetric jet, it is then applied in a three-dimensional LES of a jet in cross-flow with large oil droplets of a single size being released at the source of the jet. We model the concentration fields using $N_{d}=15$ bins of discrete droplet sizes and solve scalar transport equations for each bin. The resulting droplet size distributions are compared with published experimental data, and good agreement for the relative size distribution is obtained. The LES results also enable us to quantify size distribution variability. We find that the probability distribution functions of key quantities such as the total surface area and the Sauter mean diameter of oil droplets are highly variable, some displaying strong non-Gaussian intermittent behaviour.

Characterization and oxidation resistance of B-modified Mo3Si coating on Mo substrate

A B-modified Mo3Si coating was fabricated on a pure Mo substrate by the plasma transferred arc (PTA) cladding process. The microstructure, phase constitution, and oxidation resistance of the coating were studied to determine the effect of B addition. The microstructure characterization shows that the coarse Mo3Si dendrites and few small dispersed Mo5Si3 particles are uniformly distributed in the Mo3Si/Mo5SiB2 eutectics matrix. Compared to both the pure Mo and Mo3Si reference materials, the B-modified Mo3Si coating exhibits a drastic improvement in oxidation resistance, which can be ascribed to a complete surface coverage by a borosilicate glass scale produced during the high temperature oxidation exposure to air at 1300 °C. Upon oxidation small additions of B into Mo3Si compound promotes the rapid formation of a dense and continuous borosilicate glass scale and improves its viscous flow on the coating surface, restricting the inward oxygen diffusion to the oxidation interface, and thereby enhancing its oxidation resistance.