Channel Intersections Research Articles

Effect of the quasi-continuous equal-channel angular pressing on the structure and functional properties of Ti–Ni-based shape-memory alloys

The effect of severe plastic deformation by equal-channel angular pressing (ECAP) under normal and quasi-continuous regimes on the structure and the mechanical and functional properties of a Ti–50.2 at % Ni shape-memory alloy (SMA) has been studied. ECAP was carried out at an angle of intersection of channels of 120° in the normal regime with heating between passes at 450°C for 20 passes and in the quasi-continuous regime at the temperature of 400°C for three, five, and seven passes. The hot screw rolling with subsequent annealing at 750°C for 30 min and cooling in water was used as a control treatment (CT). A mixed submicrocrystalline and nanosubgrained structure was formed. The increase in the number of passes from three to seven led to a decrease in the average size of structural elements from 115 ± 5 to 103 ± 5 nm and to an increase in the fraction of grains/subgrains having a size less than 100 nm. After ECAP (seven passes) and post-deformation annealing at the temperature of 400°C for 1 h, a completely recoverable strain was 9.5%; after normal ECAP, 7.2%; after CT, 4.0%.

Synthesis of ZSM-5 and its application in butylene catalytic cracking

The template-free ZSM-5 was prepared by hydrothermal synthesis and then modified by tetramethoxysilane (TMOS). The structure, morphology, and acidity of all samples were studied by various techniques, such as XRD, SEM, 29Si MAS NMR, 27Al MAS NMR, NH3-TPD, BET and UV-vis DRS. Comparing with the zeolites synthesized by traditional method, the template-free ZSM-5 exhibited the analogical acidity, morphology and structure, but obvious difference in acid distribution. Due to the absence of the structure directing agent, the template-free ZSM-5 possessed more acid sites situated at pore channels of catalyst and less acid sites stayed at the intersection of straight and sinusoidal channels. Consequently, the shape selectivity enhanced significantly. After TMOS modification, the non-shape acid sites located at the external surface were covered by a single SiO2 layer. The template-free ZSM-5 achieved the highest total yield of ethylene and propylene, longest working life-span and lowest level of coke deposition among the studied catalysts, ascribing to the suppression of the side reactions.

Analytical solutions of the two-dimensional Dirac equation for a topological channel intersection

Numerical simulations in a tight-binding model have shown that an intersection of topologically protected one-dimensional chiral channels can function as a beam splitter for non-interacting fermions on a two-dimensional lattice \cite{Qiao2011,Qiao2014}. Here we confirm this result analytically in the corresponding continuum $\mathbf{k}\cdot\mathbf{p}$ model, by solving the associated two-dimensional Dirac equation, in the presence of a `checkerboard' potential that provides a right-angled intersection between two zero-line modes. The method by which we obtain our analytical solutions is systematic and potentially generalizable to similar problems involving intersections of one-dimensional systems.

2D CFD description of the kinematic effects of movable inlet and outlet die wall transport motion and punch shape geometry on the dynamics of viscous flow during ECAE through Segal 2θ-dies for a range of channel angles

Minimization of the dead zone (DZA) in the process of material forming is a materials science problem. Geometric and kinematic approaches to the minimization of the DZA during Equal Channel Angular Extrusion (ECAE) have been proposed, developed, analyzed, and documented. The present article is focused on a 2D Computational Fluid Dynamics (CFD) description of the kinematic effects of punch shape geometry and inlet (IDW) and outlet (ODW) die wall motion on the DZA during ECAE of Viscous Incompressible Continuum (VIC) through a Segal 2θ-die for a range of channel angles 60° ≤ 2θ ≤ 135°. Due attention has been given to the independent alternating transport motions of the IDW and ODW. Punch shape geometry and the kinematic modes of IDW and ODW motions for DZA minimization have been determined with a numerical solution of the boundary value problem for the Navier-Stokes equations in curl transfer form for VIC. Experimental verification was accomplished with an introduction of initial circular gridlines-based physical simulation techniques. For the first time, experimental verification of CFD-derived results was made through an additional superposition of empirically-derived digital photos with deformed elliptical gridlines in the channel intersection deformation zones and correspondent 2D numerical plots with CFD-derived flow lines and full flow velocities. An empirical DZA localization was experimentally determined as the location of minimally-deformed near circular markers. The computational DZA localization was numerically determined as a flow-lines-free zone (the first hypothesis) or as a zone with near-zero values of full flow velocities (the second hypothesis). The relative DZA was estimated as a ratio of the measured DZA with respect to the area of the deformation zone in the channel intersection region. A good agreement was obtained between DZA values obtained with the first hypothesis and experimental results.

The experimental verification of the known flow line models describing local flow during ECAE (ECAP)

In spite of the existence of a number of studies suggesting various models of flow-lines during ECAE, there are few studies dedicated to the experimental visualization of the empirically observable flow-lines. The present research is focused on an experimental verification of the known previously published research results by Han et al (2008), Hasani et al (2008) — Hosseini et al (2009), and Tóth et al (2004) for material flow lines through a die of classical Segal geometry. The experimental research used physical simulation techniques to visualize moving marker trajectories in the vicinity of the channel intersection zone during ECAE of plasticine models. The successive positions of moving markers were recorded with a digital camera with further recognition and digitalization of experimental marker trajectories. This research has shown that experimental flow-lines do not fully fit Toth et al’s and Han et al’s flow models. It was found that the best fit of experimental flow-lines is achieved by using of Hasani et al’s — Hosseini et al’s model. Experimental / theoretical results which were obtained in the current study are of interest to the interdisciplinary SPD mechanics sphere. The experimental verification of the earlier published models quoted in the paper provides the succession, sustainability and academic integrity of the experimental / theoretical results from the SPD mechanics of the various schools of sciences. New results of the study relate to the experimental visualization of the moving markers positions during ECAE physical modeling and the experimental / theoretical determination of corresponding empirical flow-lines.

Microchip electrophoresis utilizing an in situ photopolymerized Phos-tag binding polyacrylamide gel for specific entrapment and analysis of phosphorylated compounds.

A method was developed for the specific entrapment and separation of phosphorylated compounds using a Phos-tag polyacrylamide gel fabricated at the channel crossing point of a microfluidic electrophoresis chip. The channel intersection of the poly(methyl methacrylate)-made microchip was filled with a solution comprising acrylamide, N,N-methylene-bis-acrylamide, Phos-tag acrylamide, and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], which functioned as a photocatalytic initiator. In situ polymerization at the channel crossing point was performed by irradiation with a UV LED laser beam. The fabricated Phos-tag gel (100 × 100 × 30 μm) contains ca. 20 fmol of the Phos-tag group and therefore could entrap phosphorylated compounds at the femtomolar level. The electrophoretically trapped phosphorylated compounds were released from the gel by switching the voltage to deliver high concentrations of phosphate and EDTA in a background electrolyte. The broad sample band eluted from the gel was effectively reconcentrated at the boundary of a pH junction generated by sodium ions delivered from the outlet reservoir. The reconcentrated sample components were then separated and fluorometrically detected at the end of the separation channel. Under the optimized conditions, the phosphorylated compounds were concentrated by a factor of 100-fold, and the peak resolution was comparable to that obtained by pinched injection. This method was successfully utilized to preconcentrate and analyze phosphorylated peptides in a complex peptide mixture.

Effects of Material Rheology and Die Walls Translational Motions on the Dynamics of Viscous Flow during Equal Channel Angular Extrusion through a Segal 2θ-Die: CFD 2D Solution of a Curl Transfer Equation

The present article is focused on a phenomenological description of a polymer workpiece Equal Channel Angular Extrusion (ECAE) through 2θ-dies of Segal and Iwahashi geometries with a channel intersection angle 2θ = 105° with fixed and movable external inlet and outlet die walls. The local flow dynamics, including the formation of macroscopic rotation and a dead zone appearance during the flow of plasticine, paraffin, and wax workpiece models through the subject die configuration was studied using physical simulation techniques. The present article utilizes a Computational Fluid Dynamics (CFD) numerical approach to a theoretical description of 2D viscous flow of incompressible Newtonian continuum through the stated die geometries. The boundary value problem for the Navier-Stokes equations in the curl transfer form for the local viscous flow was formulated and numerically solved with a finite-difference method. Theoretical CFD-derived plots with computational flow lines, dimensionless flow and curl functions, flow velocities, and tangential stresses for viscous material flow through the stated die geometries have been generated and described. As a first rheological approximation the derived computational results provide the theoretical description of physical simulation experiments and visualize the formation of ECAE-induced rotational modes of large deformations like macroscopic rotation and rotational inhomogeneity.

Effect of workpiece viscosity on strain unevenness during equal channel angular extrusion: CFD 2D solution of Navier–Stokes equations for the physical variables ‘flow velocities—punching pressure’

The present article addresses strain unevenness effects during equal channel angular extrusion (ECAE) of physical models of polymer workpieces with viscosity flow features through a Segal die with channel intersection angle of 2θ = 90°. Computational viscous flow lines, flow velocity fields, and material dead zone formation in the physical simulation of ECAE have been numerically derived for planar flow of viscous incompressible continua in an angular die with 2θ = 90°. This is accomplished through the introduction of Navier–Stokes equations with the following dimensionless physical variables: polymer model local flow velocities u, v and punching pressure p. Derived experimental results are grounded on the application of the following physical simulation techniques: marker method, based on harder disperse particles partially forcing into the front faces of soft workpieces; layered model production by assembling the workpiece soft model with different layers, and circular gridlines use with viscous flow of the polymer soft model. Good agreement has been found between the computational and observable physical simulation results. Based on the obtained results, recommendations are made for polymer ECAE technology enhancement and angular die design for polymer workpiece pressure forming.

Dynamics of blood flow and thrombus formation in a multi-bypass microfluidic ladder network.

The reaction dynamics of a complex mixture of cells and proteins, such as blood, in branched circulatory networks within the human microvasculature or extravascular therapeutic devices such as extracorporeal oxygenation machine (ECMO) remains ill-defined. In this report we utilize a multi-bypass microfluidics ladder network design with dimensions mimicking venules to study patterns of blood platelet aggregation and fibrin formation under complex shear. Complex blood fluid dynamics within multi-bypass networks under flow were modeled using COMSOL. Red blood cells and platelets were assumed to be non-interacting spherical particles transported by the bulk fluid flow, and convection of the activated coagulation factor II, thrombin, was assumed to be governed by mass transfer. This model served as the basis for predicting formation of local shear rate gradients, stagnation points and recirculation zones as dictated by the bypass geometry. Based on the insights from these models, we were able to predict the patterns of blood clot formation at specific locations in the device. Our experimental data was then used to adjust the model to account for the dynamical presence of thrombus formation in the biorheology of blood flow. The model predictions were then compared to results from experiments using recalcified whole human blood. Microfluidic devices were coated with the extracellular matrix protein, fibrillar collagen, and the initiator of the extrinsic pathway of coagulation, tissue factor. Blood was perfused through the devices at a flow rate of 2 µL/min, translating to physiologically relevant initial shear rates of 300 and 700 s-1 for main channels and bypasses, respectively. Using fluorescent and light microscopy, we observed distinct flow and thrombus formation patterns near channel intersections at bypass points, within recirculation zones and at stagnation points. Findings from this proof-of-principle ladder network model suggest a specific correlation between microvascular geometry and thrombus formation dynamics under shear. This model holds potential for use as an integrative approach to identify regions susceptible to intravascular thrombus formation within the microvasculature as well as extravascular devices such as ECMO.

Proton proximity – New key parameter controlling adsorption, desorption and activity in propene oligomerization over H-ZSM-5 zeolites

The proximity of protons (∼5Å) derived from the distribution of Al atoms in the H-ZSM-5 framework has been shown to substantially affect the rate of propene oligomerization. Two sets of H-ZSM-5 zeolites (Si/Al 13–30) greatly differing in the occurrence of Al pairs (AlSiSiAl sequences in 6MRs) or distant Al atoms in the framework (both located prevailingly at the channel intersections) were synthesized to analyze the effect of the proton proximity. Propene adsorption and formation of oligomeric alkoxides is faster over distant isolated protons, while the close (5Å) positive charges of proximate protons result in faster olefin(s) release from H-bonded propene and oligomeric alkoxides. As the steady-state TOF of propene oligomerization to C4–C9 olefins at 473–533K over close protons exceeds 2–10 fold (with increasing Si/Al) those over isolated protons, the release of olefins from alkoxides is suggested to be an important reaction step. The distribution of framework Al atoms determining the mutual distances of protons represents a new parameter for evaluating rates of acid-catalyzed reactions and individual steps over H-zeolites.

Computer Simulation of the Combined Process "Helical Rolling-Pressing"

In this work a simulation of the innovation process "helical rolling – pressing" in the software package Simufact.Formingwas performed. The result is several models of this process. To analyze the feasibility of the process various key parameters that have a significant impact on the implementation processwere carried out. As a result, the optimal values of friction coefficients in the rolls and in the matrix, the angle of intersection of channels in the matrix and the distance of matrix from the deformation zone of the rollswere obtained.

Conversion of Methanol to Olefins over H-ZSM-5 Zeolite: Reaction Pathway Is Related to the Framework Aluminum Siting

As the conversion of methanol to olefins (MTO) over a zeolite catalyst is conducted on acid sites derived from framework aluminum (AlF), it is possible to enhance the catalytic performance by altering the siting of AlF if one knows the catalytic behavior of specified AlF located at certain sites. In this work, two series of H-ZSM-5 zeolites, viz., S-HZ-m and T-HZ-m, were synthesized with silica sol and tetraethyl orthosilicate, respectively, as the silicon source. Both series of H-ZSM-5 zeolites exhibit similar acidity, morphology, and textual properties. However, they are quite different with respect to AlF siting, as determined by UV–vis–DRS of Co(II) ions and 27Al MAS NMR; AlF of S-HZ-m is enriched in the sinusoidal and straight channels, whereas AlF of T-HZ-m is concentrated in the channel intersections. When they are used as the catalyst in MTO, T-HZ-m gives higher selectivity to ethene and aromatics and a larger hydrogen transfer index (HTI) than S-HZ-m, whereas S-HZ-m exhibits higher selectivity to...

Diffusion of Aromatics in Silicalite-1: Experimental and Theoretical Evidence of Entropic Barriers

A specific computational methodology based on transition state theory (Kolokathis, P. D. et al. Mol. Simul., 2014, 40, 80–100) is evolved and applied for calculation of the self-diffusion coefficients of p-xylene and benzene in silicalite-1 at infinite dilution. In addition, we study the orientational distributions of phenyl rings and methyl stems of p-xylene and benzene sorbed in the zeolite and check for the existence of entropic barriers to translational motion. A new reduction method for the states appearing in the free energy profiles is presented and used for calculation of transition rate constants for elementary jumps. Quasi-elastic neutron scattering measurements are also conducted and compared with the simulation results. A major conclusion from both experiments and simulations is that p-xylene diffuses roughly 100 times faster than benzene when sorbed at low occupancy in silicalite. Benzene encounters strong entropic barriers to translational motion at channel intersections, where it can adopt ...

On-chip intermediate potential measurements for the control of electromigration in multi-channel networks in case of time-dependent potential changes

One of the greatest challenges in multi-channel networks for electromigrative separation techniques is the control of the leakage of sample constituents and band broadening at the channel intersections in microfluidic devices or capillary-chip interfaces, which can be achieved using fixed bias or pullback potentials. These may be implemented as the first separation dimension in a 2D setup, where the electric potential at the interface to the second dimension changes with time. Thus, a dynamic control via on-line potential measurement in combination with a feedback system is needed to control electromigration into the side channels. We here present for the first time a prototype for in-channel potential measurements using a low working current in combination with a Si3N4 passivated Ti/Pt electrode at the intersection of the channels in a microfluidic interface. Exemplarily we chose capillary electrophoresis and isotachophoresis as model applications with constant vs. dynamic potential. Parallel on-chip intersection potential measurements were successfully conducted without disturbing capillary zone electrophoretic and isotachophoretic analysis regarding separation and peak performance of amino acids chosen as model analytes. This was possible due to a Si3N4 passivation layer, but also due to an ad-hoc developed high impedance instrumentation, resulting in a very low measuring electric current. Simulations of the detected isotachophoretic cross-section potential allowed a deeper understanding of the potential development during the separation.

Control of Hydroid Colony Form by Surface Heterogeneity.

The colonial hydroid Podocoryna carnea grows adherent to surfaces progressing along them by a motile stolon tip. We here ask whether the stolon tip grows preferentially within grooves etched in silicon wafers. In a series of pilot experiments, we varied the dimensions of grooves and found that stolons did not utilize grooves with a width:depth of 5:5 μm or 10:10 μm, occasionally followed grooves 25:25 μm in size, and preferentially grew within grooves of a width:depth of 50:50 μm and 100:50 μm. We then grew colonies in grids, with fixed 50:50 μm width:depth channels intersecting at 90° every 950, 700, 450, or 150 μm. We find that stolons grew within grooves early in colony ontogeny, but remained restricted to them only in the grid pattern with channel intersections every 150 μm. Finally, we created a grid in the shape of the Yale Y logo, with channels of 50:50 μm width:depth and intersections every 100 μm. The resulting colonies conformed to that of the logo. Our findings demonstrate that stolons respond to surface heterogeneity and that surface etching can be used to fabricate microfluidic circuits comprised of hydroid perisarc.

CFD 2D Description of Local Flow of Polymer Workpiece through a modified U-Shaped Die During Equal Channel Multiple Angular Extrusion

The present article is focused on a 2D computational fluid mechanics study of local viscous flow dynamics and the formation character of rotary modes of deformation during Equal Channel Multiple Angular Extrusion (ECMAE) of a polymer workpiece fluid model through a U-shaped die with parallel slants in channel intersection zones. The present local flow problem was experimentally analyzed using physical simulation methods and theoretically studied with numerical fluid mechanics techniques. The computational approach has been grounded on the numerical finite difference solution of the boundary value problem for the Navier-Stokes equations in the curl transfer form for the local viscous flow of incompressible Newtonian fluid through a U-shaped rectangular die with parallel slants. The derived research results allow us to draw a conclusion that the implementation of a geometric design of parallel slants within a 2-turn U-shaped die results in localization of the maximum tangential stresses within the workpiece volume to the vicinity of these parallel slants during ECMAE.

Location of Framework Al Atoms in the Channels of ZSM‐5: Effect of the (Hydrothermal) Synthesis

(27) Al 3Q MAS NMR and UV/Vis spectroscopy with bare Co(II) ions as probes of Al pairs in the zeolite framework were employed to analyze the location of framework Al atoms in the channel system of zeolite ZSM-5. Furthermore, the effect of Na(+) ions together with tetrapropylammonium cation (TPA(+)) in the ZSM-5 synthesis gel on the location of Al in the channel system was investigated. Zeolites prepared using exclusively TPA(+) as a structure-directing agent (i.e., in the absence of Na(+) ions) led to 55-90% of Al atoms located at the channel intersection, regardless the presence or absence of Al pairs [Al-O-(Si-O)2 -Al sequences in one ring] in the zeolite framework. The presence of Na(+) ions in the synthesis gel did not modify the Al location at the channel intersection (55-95% of Al atoms) and led only to changes in i) the distribution of framework Al atoms between Al pairs (decrease) and single isolated Al atoms (increase), and ii) the siting of Al in distinguishable framework tetrahedral sites.

Design sensitivity and mixing uniformity of a micro-fluidic mixer

We consider a particular hydrodynamic focusing microfluidic mixer used to initiate the folding process of individual proteins, which has been designed in a previous work and exhibited a mixing time of 0.1 μs. The aim of the current paper is twofold. First, we explore the sensitivity of mixing time to key geometric and flow parameters. In particular, we study the angle between inlets, the shape of the channel intersections, channel widths, mixer depth, mixer symmetry, inlet velocities, working fluid physical properties, and denaturant concentration thresholds. Second, we analyze the uniformity of mixing times as a function of inlet flow streamlines. We find the shape of the intersection, channel width, inlet velocity ratio, and asymmetries have strong effects on mixing time; while inlet angles, mixer depth, fluid properties, and concentration thresholds have weaker effects. Also, the uniformity of the mixing time is preserved for most of the inlet flow and distances of down to within about 0.4 μm of the mixer wall. We offer these analyses of sensitivities to imperfections in mixer geometry and flow conditions as a guide to experimental efforts which aim to fabricate and use these types of mixers. Our study also highlights key issues and provides a guide to the optimization and practical design of other microfluidic devices dependent on both geometry and flow conditions.

Structure-Directing Behaviors of Tetraethylammonium Cations toward Zeolite Beta Revealed by the Evolution of Aluminosilicate Species Formed during the Crystallization Process.

Organic structure-directing agents (OSDAs) have been widely used for the synthesis of zeolites. In most cases, OSDAs are occluded in zeolites as an isolated cation or molecule geometrically fitted within the zeolite cavities. This is not the case for zeolite beta synthesized by using tetraethylammonium (TEA(+)) cation as an OSDA, in which a cluster/aggregate of ca. six TEA(+) cations is occluded intact in the cavity (i.e., the channel intersection) of zeolite beta. The structure direction of TEA(+) in such a nontypical, clustered mode has remained elusive. Here, zeolite beta was hydrothermally synthesized using TEA(+) in the absence of other alkali metal cations in order to focus on the structure-directing behaviors of TEA(+) alone. The solid products formed throughout the hydrothermal synthesis were analyzed by an array of characterization techniques including argon adsorption-desorption, high-energy X-ray total scattering, Raman and solid-state NMR spectroscopy, and high-resolution transmission electron microscopy. It was revealed that the formation of amorphous TEA(+)-aluminosilicate composites and their structural, chemical, and textural evolution toward the amorphous zeolite beta-like structure during the induction period is vital for the formation of zeolite beta. A comprehensive scheme of the formation of zeolite beta is proposed paying attention to the clustered behavior of TEA(+) as follows: (i) the formation of the TEA(+)-aluminosilicate composites after heating, (ii) the reorganization of aluminosilicates together with the conformational rearrangement of TEA(+), yielding the formation of the amorphous TEA(+)-aluminosilicate composites with the zeolite beta-like structure, (iii) the formation of zeolite beta nuclei by solid-state reorganization of such zeolite beta-like, TEA(+)-aluminosilicate composites, and (iv) the subsequent crystal growth. It is anticipated that these findings can provide a basis for broadening the utilization of OSDAs in the clustered mode of structure direction in more effective ways.

Two-parameter Rigid Block Approach to Upper Bound Analysis of Equal Channel Angular Extrusion Through a Segal 2θ-die

This article deals with a phenomenological description of experimentally determined complex geometric shape of material dead zone during Equal Channel Angular Extrusion (ECAE) through a Segal 2θ-die with a channel intersection angle of 2θ>0°and 2θ<180°. Taking into account the complex dead zone geometry in a 2θ-die, a two-parameter Rigid Block Method (RBM) approach to a two-parameter Upper Bound Method (UBM) has been introduced with Discontinuous Velocity Field (DVF) for planar flow of plastic incompressible continua. The two-parameter UBM has allowed us to derive the numerical estimations for such energy-power parameters of ECAE as punching pressure and accumulated plastic strain for 2θ-dies. The obtained computational data have been compared with the one-parameter analytic UBM solution. Good agreement between the two computational results has been found.