Rectangular Particles Research Articles

Prediction of thermal conductivity of SiC-filled emulsion-polymerized styrene-butadiene rubber composites by finite element method

A finite element method was developed to predict the thermal conductivity of emulsion-polymerized styrene-butadiene rubber composites filled with silicon carbide (SiC). Two-dimensional finite element method models, which involved the effects of aspect ratio, shape, particle size and mass ratio of silicon carbide, were used to simulate the microstructure of emulsion-polymerized styrene-butadiene rubber composites. An increase in thermal conductivity of the composites with increasing aspect ratio values was predicted by the finite element method models. The shape and particle size of silicon carbide affected the thermal conductivity as predicted by the finite element method models. At silicon carbide loadings of 100 and 200 phr, the thermal conductivity of the composites filled with two kinds of silicon carbide at mass ratio of 1:1 exhibited the highest thermal conductivity as predicted by rectangular particle filler finite element method models. Rectangular particle filler finite element method models (aspect ratio of 4 for SiC 1# and aspect ratio of 5 for SiC 2#) are better than other finite element method models for accurately predicting the thermal conductivity of silicon carbide/emulsion-polymerized styrene-butadiene rubber composites. The thermal conductivities predicted by the rectangular particle filler finite element method models were compared with the experimental results. The trend and particular values of thermal conductivity predicted by the rectangular particle filler finite element method models agreed with the experimental data considerably. Compared with the experimental data, the biggest difference of predicted values is not more than 5%. The proposed finite element method models would provide theoretical foundations and practical methods for tailoring emulsion-polymerized styrene-butadiene rubber composites with specific thermal conductivity.

Comparison of the morphology and structure of WO3 nanomaterials synthesized by a sol-gel method followed by calcination or hydrothermal treatment

Tungsten (VI) oxide (WO3) nanomaterials were synthesized by a sol-gel method using WCl6 and C2H5OH as precursors followed by calcination or hydrothermal treatment. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) equipped with energy dispersive X-ray spectroscopy (EDX) were used to characterize the structure and morphology of the materials. There were significant differences between the WO3 materials that were calcinated and those that were subjected to a hydrothermal process. The XRD results revealed that calcination temperatures of 300°C and 400°C gave hexagonal structures and temperatures of 500°C and 600°C gave monoclinic structures. The SEM images showed that an increase in calcination temperature led to a decrease in the WO3 powder particle size. The TEM analysis showed that several nanoparticles agglomerated to form bigger clusters. The hydrothermal process produced hexagonal structures for holding times of 12, 16, and 20 h and monoclinic structures for a holding time of 24 h. The SEM results showed transparent rectangular particles which according to the TEM results originated from the aggregation of several nanotubes.

Particle Stimulated Nucleation in Coarse-Grained Ferritic Stainless Steel

Particle-stimulated nucleation (PSN) is investigated in Nb-containing ferritic stainless steel. Coarse-grained sheets were cold rolled to 80 pct thickness reduction and annealed from 973 K to 998 K (700 °C to 725 °C) to obtain partially recrystallized microstructures. Electron backscatter diffraction was performed around coarse niobium carbonitride particles (larger than 1 μm) within coarse grains (~1 mm), with different host orientations in both deformed and annealed states. In the deformed state, the deformation zones around both spherical and rectangular particles were investigated. The local lattice rotations about the transverse direction necessary to accommodate the particle-matrix strain incompatibility were observed in all grains investigated. After annealing, recrystallization occurs preferentially around coarse particles at the initial stages of recrystallization. Based on a total number of 130 grains nucleated via PSN, we observe both, randomly oriented and minor {111}〈110〉 oriented texture components. The results also reveal that PSN in this material is not associated with a specific host orientation.

Magnetization Reversal of Rectangular Particles: Closure States and Effect of Dipolar Coupling

We have investigated the magnetization configurations of ferromagnetic rectangular particles with lateral dimensions 1025 × 450 nm2 and two different thicknesses: 10 and 40 nm. For each thickness, we analyzed both an array consisting of isolated particles and a second one where the nanomagnets are put head-to-tail, with 85 nm interdot spacing, forming long chains of closely-spaced elements. Magneto-optical Kerr effect measurements and in-field magnetic force microscopy experiments were performed to achieve a deep comprehension of the magnetization reversal process. It is shown that inter-particle dipolar coupling substantially modifies the reversal mechanism in the case of the largest thickness, where it can delay or even suppress the occurrence of closure configurations of the magnetization (with one or more vortices), that are typical of isolated nanomagnets.

Non-Prestonian Behavior of Rectangular Shaped Ceria Slurry in Shallow Trench Isolation Chemical Mechanical Planarization

Rectangular ceria particles were synthesized using the flash creation method. The influence of the morphology of ceria particles and the surfactant concentration on the removal rate was systematically investigated. These ceria slurries with polymeric surfactant molecules as the passivation agents of Si3N4 film, shows an exceptional non-Prestonian behaviors. The non-Prestonian behavior can be attributed to the increase in the contact area of the ceria particles with the SiO2 film, which is dominated by the morphology of the ceria particles. Force measurements using an atomic force microscope (AFM) at different concentrations of polymeric surfactant molecules was used to identify the interactions between the polymeric molecules and the oxide film and analyze the non-Prestonian behavior of ceria slurry having rectangular abrasives.

Numerical homogenization of polymer/clay nanocomposites by the boundary element method

The paper deals with the numerical homogenization of polymer/clay nanocomposites by using the boundary element method (BEM). The reinforcement has the form of stacks of parallel clay sheets modelled by effective isotropic particles. Two-dimensional representative volume elements (RVEs), containing randomly distributed parallel rectangular particles, are modelled and five plane-strain elastic constants of the orthotropic composite are analysed: two Young’s moduli, shear modulus and two Poisson’s ratios. The results are compared to experimental data, finite element method (FEM) results, and analytical models as well. The positive-definiteness and symmetry of the apparent compliance matrix are verified. All the comparisons and tests confirm validity of the applied method.

Numerical simulation of sedimentation of rectangular particle in Newtonian fluid

The sedimentation of a rectangular particle falling in a two-dimensional channel filled with Newtonian fluid was simulated with finite element arbitrary Lagrangian–Eulerian domain method. The numerical procedure was validated by comparison of the simulation results with existing numerical work. Moreover, good agreement was obtained between the simulation results and experimental measurements performed in the current study. The equilibrium position, stable orientation and drag coefficient of a rectangular particle for different particle Reynolds numbers (Rep) were studied. The results show that there is a critical particle Reynolds number for the preferred orientation of a rectangular particle falling in a Newtonian fluid. When Rep is smaller than the critical value, the particle falls with its long side parallel to gravity; otherwise the particle falls with its long side perpendicular to gravity. The critical particle Reynolds number is a decreasing function of the blockage ratio and aspect ratio. The distributions of pressure and shear stress on rectangular particle surface were analyzed. Moreover, the drag coefficient of the rectangular particle decreases as Rep or the blockage ratio increases; however, it appears to be independent of aspect ratio.

A geometric-based method for recognizing overlapping polygonal-shaped and semi-transparent particles in gray tone images

A geometric-based method is proposed to recognize the overlapping particles of different polygonal shapes such as rectangular, regular and/or irregular prismatic particles in a gray tone image. The first step consists in extracting the salient corners, identified by their locations and orientations, of the overlapping particles. Although there are certain difficulties like the perspective geometric projection, out of focus, transparency and superposition of the studied particles. Then, a new clustering technique is applied to detect the shape by grouping its correspondent salient corners according to the geometric properties of each shape. A simulation process is carried out for evaluating the performance of the proposed method. Then, it is particularly applied on a real application of batch cooling crystallization of the ammonium oxalate in pure water. The experimental results show that the method is efficient to recognize the overlapping particles of different shapes and sizes.

Direct Numerical Simulation of Particle Migration in a Simple Shear Flow

Motion of a rectangular particle in a two-dimensional vertical shear flow of Newtonian fluid and viscoelastic fluid with different parameters is studied using the finite element arbitrary Lagrangian—Eulerian domain method. The results show that the centerline of the channel is a stable equilibrium position for the neutrally buoyant rectangular particle in a vertical shear flow. Inertia causes the particle to migrate towards the centerline of the channel. In addition, a critical elasticity number exists. When the elasticity number is below the critical value, the rectangular particle migrates to the centerline; otherwise the centerline of the channel is apparently no longer a global attractor of trajectories of the particle.

Surface collision theory for suspension-based cleaning of particle-contaminated solid substrates

To quantify removal kinetics of contaminant particles on solid surfaces, we study collisions between nonspherical particles when one particle is suspended in laminar shear flow while the second is adhered to a solid surface. Based on kinetic theory of rigid nonspherical particles, we outline a theoretical framework for our previously developed binary-collision contaminant-removal model. We show that a distribution of adhered contaminant particles over orientation, size, and shape results in multiexponential decay of surface concentration of particles with time, in agreement with experimental findings [Andreev et al., J. Electrochem. Soc. 158, H55 (2011)]. Theory predicts a linear increase of removal rate constant with shear rate and with suspended solids concentration near the substrate surface, also in agreement with experiment [Andreev et al., J. Electrochem. Soc. 158, H55 (2011); Ind. Eng. Chem. Res. 49, 12461 (2010)]. To reveal the effect of geometry and size of colliding entrained particles on removal rates, an approximate singlet distribution function is derived for particles in flow at the level of the Smoluchowski theory for orthocoagulation. Two shapes of flow-suspended particles are considered: spheres and cuboids with high aspect ratio, while contaminant particles on the surface are small and spherical. Removal kinetic rate constants scale with contaminant particle size, aA, as aA3/2 for spheres and as aA for cuboids. Thus, rectangular platelet particles are effective for removal of small contaminant particles, confirming experimental observation [Andreev et al., J. Electrochem. Soc. 158, H55 (2011)]. The influence of platelet aspect ratio on removal rates is analyzed. Due to interplay between solids velocity and collision cross section, small aspect ratios improve cleaning efficiency when the size ratio of the entrained to contaminant particles is large.

Effect of dipolar interaction on the magnetization state of chains of rectangular particles located either head-to-tail or side-by-side

Magnetostatic coupling in arrays of closely spaced magnetic elements is becoming an important issue in the path to the fabrication of spintronic devices. Dense chains of rounded-corners rectangular particles (dots) of lateral size 1025 × 450 nm2, with interdot spacing variable in the range between 55 and 700 nm, have been patterned by deep UV lithography, followed by the lift-off of two permalloy films of thickness 20 and 40 nm. Magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM) experiments, together with micromagnetic simulations, were performed to study the dependence of the magnetization configuration on the dipolar coupling. Both MOKE measurements and MFM images clearly show that, at remanence, the magnetic state of isolated particles of thickness 20 nm takes the form of a distorted single domain (C-state or S-State configurations). Instead, when the particle thickness is double (40 nm), closure states characterized by one, two or three vortices occur at remanence. However, when the 40 nm thick dots are placed in chains along the easy axis (head to tail), as the separation is progressively reduced, the single domain state is stabilized at remanence. On the other hand, when the 40 nm thick particles are placed side by side in chains the effect of dipolar interactions is to favour the nucleation of vortex states. For small inter-element separation, there is only one vortex per particle and it has the same chirality in adjacent particles, due to the dipolar interaction. Different from this, for the 20 nm thick samples and sub-100 nm separation, adjacent particles are single-domain but with antiparallel magnetization in neighbour elements, like in an artificial antiferromagnet.

COPLANAR METAMATERIAL MICRO-RESONATOR

We propose a metamaterial coplanar stop-band fllter made of multi-turn rectangular spiral particles. Numerical and experimental results show the feasibility of devices with dimensions more than 10 times smaller than those in the literature and with good performances.

Characterization of Wood Dust from Furniture by Scanning Electron Microscopy and Energy-dispersive X-ray Analysis

Study characterized and analyzed form factor, elementary composition and particle size of wood dust, in order to understand its harmful health effects on carpenters in Quindío (Colombia). Once particle characteristics (size distributions, aerodynamic equivalent diameter (D(α)), elemental composition and shape factors) were analyzed, particles were then characterized via scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray analysis (EDXRA). SEM analysis of particulate matter showed: 1) cone-shaped particle ranged from 2.09 to 48.79 µm D(α); 2) rectangular prism-shaped particle from 2.47 to 72.9 µm D(α); 3) cylindrically-shaped particle from 2.5 to 48.79 µm D(α); and 4) spherically-shaped particle from 2.61 to 51.93 µm D(α). EDXRA reveals presence of chemical elements from paints and varnishes such as Ca, K, Na and Cr. SEM/EDXRA contributes in a significant manner to the morphological characterization of wood dust. It is obvious that the type of particles sampled is a complex function of shapes and sizes of particles. Thus, it is important to investigate the influence of particles characteristics, morphology, shapes and D(α) that may affect the health of carpenters in Quindío.

Spline Subdomain Approach to Thermal Conduction Problem for Composite with Rectangular Shape Particle

In this paper the spline subdomain approach is applied to the 2D simulations of the temperature distributions for composites containing a single rectangular particle with an interfacial thermal resistance at the interface between the particle and matrix. The bicubic B-splines are used to construct the trial functions for the approximations of the potential fields of composites. Applying the weighted residual point collocation method inside each subdomain and also on the boundaries between different subdomains, a system of linear algebraic equations is set up to determine the unknowns of the trial functions. The temperature distributions both inside the rectangular particle and along the interfaces under different interfacial contact conditions can be simulated approximately. Numerical results which are compared with the available solutions obtained by FEM method illustrate the accuracy and suitability of the present approach for steady-state conduction. Even in the adjacent areas of corners in the rectangular particle, the simulation results are also satisfactory.

Long-time decay of the translational/rotational velocity autocorrelation function for colloidal particles in two dimensions

In this work, the previously developed LB-DF/FD method has been extended to non-spherical particle suspensions in two dimensions. The calculated translational/rotational velocity autocorrelation function (VCF/RVCF) for the circular particles completely reproduces the theoretical predictions, i.e. the long-time decay of ( t √ ln t ) − 1 for the VCF and the long-time decay of t − 2 for the RVCF. Extensive numerical simulations of the elliptical and rectangular particles also confirm the theoretical results. On the basis of the reduced RVCFs and VCFs for the three kinds of particles, we conclude that the coefficients of the long-time tails of the RVCF and VCF are independent of the particle shape.

Reorientation phase transitions in planar arrays of dipolarly interacting ferromagnetic particles

Reorientation phase transitions (RPT) taking place in regular arrays of rectangular submicron-size ferromagnetic particles due to the competition between the external magnetic field of arbitrary direction and internal dipolar fields are analysed in this article. Dipolar interaction between particles is taken into account via real-space calculations of magnetometric demagnetizing factors. Long stripe arrays are also under consideration. I find that the direction of the external magnetic field determines the kind of the phase transition, while the dipolar interaction between particles can significantly change the values of RPT critical field. Calculations were presented for a set of submicron particles/stripe arrays, which were under experimental investigations recently.

Mechanical properties and phase composition of potential biodegradable Mg–Zn–Mn–base alloys with addition of rare earth elements

Mechanical properties and creep resistance of the MgY4Zn1Mn1 alloy in the as cast as well as in the T5 condition were compared to those of the MgCe4Zn1Mn1 alloy in the same conditions. Yield tensile stress and ultimate tensile strength of the MgY4Zn1Mn1 alloy are slightly better in the temperature range 20 °C–400 °C than these of the MgCe4Zn1Mn1 alloy. Better thermal stability of ultimate tensile strength was observed in the T5 treated MgCe4Zn1Mn1 alloy than in this material in the as cast condition. An outstanding creep resistance at 225 °C–350 °C found in the MgY4Zn1Mn1 alloy is due to the existence of the 18R long period stacking structure persisting in this alloy even a long heat treatment of 500 °C/32 h. No similar stacking effects happen when Ce substitutes Y in approximately the same concentration. The creep resistance deteriorates considerably in the MgCe4Zn1Mn1 alloy. Rectangular particles of the equilibrium Mg 12Ce phase dominate in the microstructure of as cast as well as of high temperature heat-treated MgCe4Zn1Mn1 alloy. A population of small oval particles containing Mg and Zn develops additionally during annealing of this alloy. These particles pin effectively dislocations and can be responsible for the better thermal stability of the T5 treated material.

HYDROTHERMAL SYNTHESIS OF SILVER EMBEDDED LIFEPO4/C¹

Silver embedded LiFePO4/C were preparad by direct hydrothermal synthesis of Li2CO3 FeSO4 and H3PO4 in mixed solution of Glucose and Ag(NH3)2OH Samples were characterized by XRD, SEM and galvanostatic charge-discharge test. Results show that silver particles are located in the inner part of synthesized diamond-like and rectangular particles. The reversible capacities of prepared samples are 141.3 mAh g-1 and no capacity loss are detected after 800 cycles at 1C.

Competition between capillarity, layering and biaxiality in a confined liquid crystal

The effect of confinement on the phase behaviour and structure of fluids made of biaxial hard particles (cuboids) is examined theoretically by means of Onsager second-order virial theory in the limit where the long particle axes are frozen in a mutually parallel configuration. Confinement is induced by two parallel planar hard walls (slit-pore geometry), with particle long axes perpendicular to the walls (perfect homeotropic anchoring). In bulk, a continuous nematic-to-smectic transition takes place, while shape anisotropy in the (rectangular) particle cross-section induces biaxial ordering. As a consequence, four bulk phases, uniaxial and biaxial nematic and smectic phases, can be stabilised as the cross-sectional aspect ratio is varied. On confining the fluid, the nematic-to-smectic transition is suppressed, and either uniaxial or biaxial phases, separated by a continuous transition, can be present. Smectic ordering develops continuously from the walls for increasing particle concentration (in agreement with the supression of nematic-smectic second-order transition at confinement), but first-order layering transitions, involving structures with n and n + 1 layers, arise in the confined fluid at high concentration. Competition between layering and uniaxial-biaxial ordering leads to three different types of layering transitions, at which the two coexisting structures can be both uniaxial, one uniaxial and another biaxial, or both biaxial. Also, the interplay between molecular biaxiality and wall interactions is very subtle: while the hard wall disfavours the formation of the biaxial phase, biaxiality is against the layering transitions, as we have shown by comparing the confined phase behaviour of cylinders and cuboids. The predictive power of Onsager theory is checked and confirmed by performing some calculations based on fundamental-measure theory.

Facile Morphological Control of Cyclodextrin Nano- and Microstructures and Their Unique Organogelation Ability

We successfully fabricated γ-cyclodextrin (γ-CD) nano- and microstructures of various morphologies, such as cubes, rods, and rectangular particles, simply by modifying the preparation method for channel-type γ-CD assemblies. These γ-CD structures formed organogels in oils and organic solvents, and the morphologies of the γ-CD structures remarkably affected their organogelation ability.