Hexagonal Tubes Research Articles

ICONE19-43857 Investigation on Velocity Distribution in an Inner Subchannel of Wire Wrapped Fuel Pin Bundle of Sodium-cooled Fast Reactor

A sodium cooled fast reactor is designed to attain a high burn-up of core fuel in commercialized fast reactor cycle systems. In high burn-up fuel subassemblies, deformation of fuel pin due to the swelling and thermal bowing may decrease local flow velocity via change of flow area in the subassembly and influence the heat removal capability. Therefore, it is important to obtain the detail of flow velocity distribution in a wire wrapped pin bundle. In this study, water experiments were carried out to investigate the detailed velocity distribution in a subchannel of nominal pin geometry as the first step. These basic data are not only useful for understanding of pin bundle thermal hydraulics but also a code validation. A wire-wrapped 3-pin bundle water model was applied to investigate the detailed velocity distribution in the subchannel which is surrounded by 3 pins with wrapping wire. The test section consists of an irregular hexagonal acrylic duct tube and three pins made of fluorinated resin pins which has nearly the same refractive index with that of water and a high light transmission rate. This enables to visualize the central subchannel through the pins. The velocity distribution in the central subchannel with the wrapping wire was measured by PIV (Particle Image Velocimetry) through a side wall of the duct tube. Typical flow velocity conditions in the pin bundle were 0.36m/s (Re=2,700) and 1.6m/s (Re=13,500). Influence of the wrapping wire on the velocity distributions in vertical and horizontal directions was confirmed. A clockwise swirl flow around the wire was found in subchannel. Significant differences were not recognized between the two cases of Re=2,700 and 13,500 concerning flow patterns.

Rich magnesium ternary compound so-called LaCuMg 8 derived from La 2Mg 17. Structure and hydrogenation behavior

The magnesium metal rich composition La 10TM 10Mg 80 (with TM = Ni and Cu) were synthesized from the elements in sealed tantalum tubes in an induction furnace. The results show differences depending on the transition metal used. The sample with Ni demixed into ternary and binary compounds with composition close to LaMgNi 2, La 2Mg 17 and Mg 2Ni. Only the sample with copper forms a ternary compound. Crystal structure of this new compound was determined by X-ray diffraction on single crystals with an exact formulation La 1.744(5)Cu 1.53(5)Mg 15.73(4). It crystallizes with the La 2Mg 17 structure type, space group P6 3/mmc, a = 10.1254(2) Å and c = 10.0751(2) Å. The Mg atoms form hexagonal tubes along the c-axis filled by La and Mg. The Cu atoms are located in these tubes on or around the La and Mg positions, inducing disorder. This compound so-called LaCuMg 8 absorbs around 2 wt% of hydrogen at 603 K, 30 bar and reversibility is possible. Nevertheless, after the first hydrogenation, decomposition into MgH 2, LaH 3 and MgCu 2 have been shown. The pathway of the reaction is described herein.

Cu 22Bi 12S 21Cl 16—A mixed conductor with fast one-dimensional copper(I) ion transport

Melting reactions of Cu, CuCl, S, and Bi 2S 3 yield black, shiny needles of Cu 22(1)Bi 12S 21(1)Cl 16(1). The compound decomposes peritectically at 649(5) K. Oxidation state +I of the copper atoms is supported by Cu– K-XANES. The compound crystallizes in the hexagonal space group P6/ m with a=2116.7(7) pm and c=395.17(5) pm. Seven anions coordinate each of the two independent bismuth cations in the shape of mono-capped trigonal prisms. These polyhedra share edges and faces to form trigonal and hexagonal tubes running along [0 0 1]. The hexagonal tubes are centered by chloride ions, which are surrounded by disordered copper cations. The majority of copper cations are distributed over numerous sites between the tubes. The Joint Probability Density Function (JPDF) reveals a continuous pathway along [0 0 1]. The high mobility of the copper cations along [0 0 1] was demonstrated by impedance spectroscopy and DC polarization measurements on single crystals. The ionic conductivity at 450 K is about σ ion=0.06 S cm −1, and the activation energy for Cu + ion conduction is E a=0.44 eV. The chemical diffusion coefficient of copper is in the order of D cu δ =10 19 cm −3 at 420 K. The electronic band gap (p-type conductor) was determined as E g=0.06 eV. At room temperature the thermal conductivity of a pressed pellet is about κ=0.3 W K −1 m −1 and the Seebeck coefficient is S=43 μV K −1.

Comparison of the crushing performance of hollow and foam-filled small-scale composite tubes with different geometrical shapes for use in sacrificial cladding structures

This paper presents the quasi-static crushing performance of nine different geometrical shapes of small-scale glass/polyester composite tubes filled with polyurethane closed-cell foam for use in sacrificial cladding structures. The effect of polyurethane foam on the crushing characteristics and the corresponding energy absorption is addressed for each geometrical shape of the composite tube. Composite tubes with two different thicknesses (1 mm and 2 mm) have been considered to study the influence of polyurethane foam on the crushing performance. From the present study, it was found that the presence of polyurethane foam inside the composite tubes suppressed the circumferential delamination process and fibre fracturing; consequently, it reduced the specific energy absorption of composite tubes. Furthermore, the polyurethane foam attributed to a higher peak crush load for each composite tube. However, the presence of polyurethane foam inside the composite tubes significantly increased the stability of the crushing phenomena especially for the square and hexagonal cross-sectional composite tubes with 1 mm wall thickness. The results from this study are compared with our previous results for composite tubes without polyurethane foam [1].

Melting of (MgO)n (n=18, 21, and 24) clusters simulated by molecular dynamics

Molecular dynamics simulations are employed to investigate the melting behavior and thermal stability of magnesium oxide clusters (MgO)(n) (n=18, 21, and 24). The rocksalt and hexagonal tube structures are two dominant low-energy structural motifs for small (MgO)(n) clusters and it results in the magic sizes n=3k (k is an integer). For n=6, 9, 12, and 15, the rocksalt and hexagonal tube structures have the same topological geometry, but for n>or=18, the two isomers are separated by high energy barriers. The simulations show a one-step melting process for the rocksalt structures of (MgO)(18,24) (no perfect rocksalt structure exists for n=21). The melting transition occurs sharply between 1800 and 1950 K for n=24 but gradually from 1400 to 2450 K for n=18. The relative root-mean-square bond length fluctuation reveals a premelting stage from about 700 K to the melting transition for the hexagonal tube structures of all the three clusters. The short-time averages of kinetic energy and a visual molecular dynamics package are used to monitor the structures along the trajectories. The low-energy isomers are identified by the quenching technique and the isomerization processes are traced. The results show that there exists a family of isomers which are only 0.1-0.4 eV higher in energy than the corresponding hexagonal tube structures and separated by low energy barriers. The premelting stage is caused by the isomerizations among these structures. The melting characteristics demonstrated in the simulations are clarified in terms of the energies of the isomers and the energy barriers separating them.

Rapid growth of ZnO hexagonal tubes by direct microwave heating

Zinc oxide hexagonal tubular crystals were synthesized by direct microwave heating from ZnO powders within 5 min without any metal catalysts or transport agents. ZnO source materials were evaporated from the high-temperature zone in an enclosure, and crystals were grown on the self-source substrate in an appropriate condition. The ZnO vapor formed in the high-temperature zone can deposit and grow on the powders located in the low-temperature zone to form crystals. The scanning electron microscopy (SEM) reveals that these products are hexagonal tube crystals with 80 μm in diameter and 250 μm in length, having a well faceted end and side surface. A possible growth mechanism and the influence of reaction temperature on the formation of crystalline ZnO hexagonal tubes were presented. The photoluminescence (PL) exhibits strong ultraviolet emission at room temperature, indicating the potential applications in short-wave light-emitting photonic devices.

Direct template-free electrochemical growth of hexagonal CuSn tubes from an ionic liquid

Free standing hexagonal hollow copper-tin tube arrays are formed by direct cathodic electrolysis in the 1-ethyl-3-methylimidazolium dicyanamide ionic liquid containing Cu(I) and Sn(II) without using a template at 313 K.

Theory of the exciton spectrum of an array of widely spaced hexagonal nanotubes

A theory of the exciton spectrum of an individual complex hexagonal nanotube in an array of hexagonal quantum tubes prepared from InP and InAs has been proposed in the framework of the effective-mass and square-potential approximations. It has been demonstrated that the theoretically calculated exciton spectrum agrees well with the experimental emission spectrum of the array of widely spaced hexagonal nanotubes not only in energy positions of the peaks but also in their intensity.

A honeycomb-tube packing medium and its application to column flotation

We address problems in the development of large-scale flotation columns that use short cylinders. As a starting point, we investigated the packing medium to identify a highly efficient internal packing for the flotation column. The chosen packing was a honeycomb structure with an aperture diameter of 80 mm, a web thickness of 0.80 mm, a film height of 1000 mm, packed into a 400 mm diameter space, which completely filled the vessel at optimal cost. The column consisted of a modular ring of single-hole hexagonal honeycomb tube packing made from atactic polyproplene (PP-R). The packing was tested in a cyclonic, static micro-bubble flotation column. Computational fluid dynamic modeling was used to analyze the flotation fluid in a honeycomb tube packed flotation column. Our results show that the fluid axial movement was maximized and that the transverse fluid velocities were zero in the vicinity of axial flow. Using the honeycomb tube packing for copper sulfide flotation we observed that the average concentration in the product was increased to 25.41%, from an average feed concentration of 0.729%, with an average recovery of 92.92%. The demands of on-site industrial production were met.

Cu9Bi9S16Cl8 und Cu7.4Bi6Se12Cl7 – Polyedernetzwerke mit Dichalkogenidbrücken und mobilen Kupfer(I)‐Kationen

AbstractMelting reactions of Cu, CuCl, Q (Q = S, Se), and Bi2Q3 yield black, shiny needles of the chalcogenide chlorides Cu9Bi9S16Cl8 or Cu7.4Bi6Se12Cl7. The compounds decompose peritectically above 612(5) K and 623(5) K. Raman spectra reveal the presence of dichalcogenide groups, whereas for copper the oxidation state +I is supported by Cu‐K‐XANES. Cu9Bi9S16Cl8 crystallizes in the monoclinic space group C2/m with a = 2061.6(3) pm, b = 394.89(3) pm, c = 1194.1(2) pm, β = 102.98(1) °, T = 293(2) K. Three sulfide and four chloride anions coordinate each of the two independent bismuth cations in the shape of monocapped trigonal prisms. The [BiS3Cl4] polyhedra form quadruple rods by sharing edges and faces. Covalent bonds between sulfide anions connect the rods into layers parallel to (001). Disordered copper as well as bismuth cations fill the voids between the layers. The Joint Probability Density Function (JPDF) reveals a continuous pathway along [010], which might be used for ion conduction. Cu7.4Bi6Se12Cl7 crystallizes in the hexagonal space group P6/m with a = 1505.8(1) pm, c = 401.41(3) pm, T = 293(2) K. Monocapped trigonal prisms [BiSe3Cl4] share faces along [001]. Through edge‐sharing these rods form hexagonal tubes, which are filled with disordered copper cations as well as chloride anions. Diselenide bridges link neighboring tubes. The intertubular channels contain stationary copper cations.

Analysis of Silicon Carbide and Silicon Nitride Precipitates in Block Cast Multicrystalline Silicon

We report on the optical and mechanical properties of Si3N4 inclusions, formed in the upper part of mc-Si blocks during the crystallization process. Those inclusions usually appear as crystalline hexagonal tubes or rods. Here we show that in many cases the Si3N4 inclusions contain crystalline Si in their core. The presence of the Si phase in the centre was proven by means of cathodoluminescence spectroscopy and imaging, electron beam induced current measurements and Raman spectroscopy. The crystalline Si3N4 phase was identified as β-Si3N4. Residual stress was revealed at the particles. While the stress is compressive in the Si material surrounding the Si3N4 particles tensile stress is found in the Si core. We assume that the stress is formed during cool down of the Si block and is a consequence of the larger thermal expansion coefficient of Si in comparison to that of β-Si3N4. Iron assisted nitridation of Si at temperatures below 1400 °C is considered a possible mechanism of Si3N4 formation.

Inside Cover: Self‐Template‐Directed Formation of Coordination‐Polymer Hexagonal Tubes and Rings, and their Calcination to ZnO Rings (Angew. Chem. Int. Ed. 8/2009)

AbstractHexagonal tubes and rings with unusual shapes were generated through a unique self‐template‐directed growth mechanism. As described by M. Oh and co‐workers in the Communication on page 1459 ff., initially formed solid coordination polymer particles (CPPs) act as templates for the growth of the final hexagonal tubes and rings. Simple calcination of these unusually shaped CPPs results in the spontaneous formation of ZnO particles while the unique shape is maintained.magnified image

Self‐Template‐Directed Formation of Coordination‐Polymer Hexagonal Tubes and Rings, and their Calcination to ZnO Rings

AbstractSelbstzerstörerisches Templat: Bei einem einzigartigen Partikelwachstumsmechanismus wachsen neue Koordinationspolymere auf der Oberfläche ursprünglich gebildeter hexagonaler Blöcke, und zugleich lösen sich die Blöcke unter Bildung hexagonaler Röhren auf (siehe Schema und Rasterelektronen‐, optische und Fluoreszenzmikroskopiebilder). Durch Kalzinieren werden die Röhren in ZnO‐Partikel der gleichen Form umgewandelt.magnified image

Self‐Template‐Directed Formation of Coordination‐Polymer Hexagonal Tubes and Rings, and their Calcination to ZnO Rings

This template will self-destruct: A unique particle-growth mechanism involves growth of new coordination polymers on the surface of initially formed hexagonal blocks and concomitant dissolution of the blocks to form hexagonal tubes (see scheme and scanning electron, optical, and fluorescence microscopy images). Calcination of the tubes yields ZnO particles of the same shape.

Novel sonochemical assisted hydrothermal approach towards the controllable synthesis of ZnO nanorods, nanocups and nanoneedles and their photocatalytic study

ZnO nanovariants possessing different morphologies have been synthesized via a sonochemical as well as a sonochemical assisted hydrothermal (SAH) method. The synthesis process variables such as concentration of the precursors, ultrasonic irradiation period and duty cycle are observed to influence the resultant morphology of the ZnO nanostructures. Novel and significant morphologies of the ZnO nanostructures such as nanoneedles, tetrapods, nanowires, nanopetals, self assembled hexagonal rods and nanocups have been successfully obtained by controlling the process parameters. The surface morphology of the ZnO nanostructures was investigated using a scanning electron microscope (SEM). The SEM investigations showed that the nanoneedles originate from the hexagonal tube. Transmission electron microscope (TEM) analysis clearly demonstrates the nanocrystalline nature of the ZnO structures with unique morphologies like hexagonal nanocups. The ZnO nanostructures were characterized by UV-visible and photoluminescence spectrometers and a possible growth mechanism of the ZnO nanostructures is proposed. The photocatalytic activity of these nanostructures has also been presented. The ZnO nanostructures like nanocups and nanoneedles exhibit an excellent photocatalytic activity. Being a wide band gap semiconductor, these unique nanostructures will have a prospective application in ZnO based dye sensitized solar cells.

Structural transition of hexagonal tube to rocksalt for (MgO)3n, 2≤n≤10

The structures of (MgO)(3n) (2<or=n<or=10) clusters are studied using density functional theory (DFT). The starting structures are generated from empirical genetic algorithm simulations. The lowest-energy structures of (MgO)(3n) are then obtained from a number of structural isomers by using DFT optimization. It is found that when n<or=5 hexagonal tube is the most stable structure, and when n>or=6 (except 7) the rocksaltlike structure is favored, which is the same as that of the bulk. The n=7 is an interesting case, where the structure again is the hexagonal tube as the most stable structure. However, from the second order difference of the average atomization energy, we find that the n=7 case is thermodynamically unstable with respect to disproportionation to the smaller and larger clusters. The result may be the reason that it is not observed in the experiment. Therefore, we can conclude that the geometry transition really takes place at n=6. The rocksalt is the most stable structure for a large range of n numbers, from the (MgO)(3x6) cluster to bulk magnesium oxide. The result is different from Wilson's previous prediction because of the use of the ionic potential.

NaYF4:Eu2+ Microcrystals: Synthesis and Intense Blue Luminescence

In this work, NaYF4:Eu2+ microcrystals with an intense blue luminescence were successfully fabricated via a solution-based route. During the sample preparation, oleic acid and cetyltrimethylammonuim bromide were used as the surfactants to tune the morphology, while citric acid was taken as a ligand to stabilize the β-phase NaYF4 and to completely reduce Eu3+ to Eu2+ for activation of blue luminescence. As confirmed by transmission electron microscopy and scanning electron microscopy measurements, all as-prepared samples crystallized in hexagonal rods or tubes, depending on the types of surfactants used. The rod samples had a diameter of about 1.7 µm and a length in the range of 2.6−3 µm, while the tube samples showed an external diameter in the range of 0.8−1 µm and a length in the range of 2.5−3.5 µm with an internal diameter of about 0.5 µm. Both rods and tubes were capped with surfactants, which enabled them to stably disperse in glycol to form transparent solutions. This work seems to be the first exa...

Dynamic Material Properties of Stainless Steel and Multiphase High Strength Steels

This work presents results of tensile testing of H400 stainless steel, DP600 and TRIP600 at different strain rates. Mechanical properties were determined from tensile test using flat sheet specimens and recurring to different test techniques: servo-hydraulic machine and a tensile-loading Hopkinson bar. The test results were used to compare different mechanical properties of the tested steels and to validate constitutive equations intended to provide a mathematical description of strain rate dependence, namely the Cowper-Symonds equation. Following previous research work in dynamic material proprieties of multiphase and stainless steel grades, the energy absorption in quasi-static crushing of thin walled section made of the tested materials was subsequently investigated. Crush tests were performed in top-hat and hexagonal section tubes manufactured using laser welding. The experimental results were compared in order to assess the efficiency of the different steel grades for energy absorption.

Structures and electronic transport of water molecular nanotubes embedded in carbon nanotubes

In this paper, ice nanotubes confined in carbon nanotubes are investigated by molecular dynamics. The trigonal, square, pentagonal, and hexagonal water tubes are obtained, respectively. The current-voltage (I-V) curves of water nanotubes are found to be nonlinear, and fluctuations of conductance spectra of these ice nanotubes show that the transport properties of ice nanotubes are quite different from those of bulk materials. Our studies indicate that the conductance gap of ice nanotube is related to the difference value from the Fermi energy EF to the nearest molecular energy level E0. Increasing the diameter of a water molecular nanostructure results in the increase of the conductance.

Uncommon hexagonal microtubule based gel from a simple trimesic amide

A small molecule of N,N′,N″-tris(3-methylpyridyl)-trimesic amide was assembled into a novel hexagonal microtube through intermolecular hydrogen bonds, and simultaneously formed a gel system in H2O–THF mixed solvent. Tuning gelator concentration or the preparation method can effectively control the size of the hexagonal tubes.