Aluminum Stabilizer Research Articles

Reconsideration of Evaluation of Balance Voltages During a Normal Zone Propagation in the LHD Helical Coils

One-side propagation and recovery of normal zones were observed more than a few times in a pair of helical coils (H1 and H2) of the large helical device. Each coil is divided into three blocks ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> , and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> ) from the inside. When a normal zone propagates, balance voltages between H1 and H2 are induced in all the blocks because of a shift of current center from the superconducting wires to a pure aluminum stabilizer at the normal zone. The cross-sectional position of the conductor in which the normal zone propagates can be estimated from the difference among the balance voltages of the blocks. In the previous study, the conductor positions were estimated at the first or last turn in the third and fourth layers of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> under the assumption that the resistive voltage is in proportion to the normal zone length. This assumption is not precise because the transient high resistance is induced by slow current diffusion into the stabilizer. Considering the transient resistance of the normal zone, the position of the normal zone propagation is reconsidered. The estimated positions are in the first layer of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> for most of the cases.

Influence of alloying elements on phase stability and elastic properties of aluminum and magnesium studied by first principles

Influence mechanisms of alloying elements Al, Mg, Ti, V, Cr, Fe, Ni, Cu, Zr, Nb, Mo, Sn, Ta, and W on phase stability and elastic properties of magnesium and aluminum were studied by first principles total energy calculations. Calculations show that all systems with impurity satisfy the mechanical stability criteria. However, only Sn could enhance the stability of Mg, but decreases the stability of Al energetically. Mg and Cr also show the same effect as Sn on Al. The electronic structure analysis illustrates that an extra bonding peak appears in the low energy region in Mg–Sn, which increases the stability of Mg. While other alloying elements slightly move the Fermi energy level toward the conduction band causing a decrease on stability of Mg. In Al with impurity systems, the alloying elements except Sn, Mg, and Cr greatly increase the number of bonding peaks in low energy regions and consequently increase the stability of the systems.

Kinetic Stability of Aluminium and Its Alloys: The Role of "Structural" Features

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Comparison of storage stability of odorous VOCs in polyester aluminum and polyvinyl fluoride Tedlar ® bags

Whole air sampling using containers such as flexible bags or rigid canisters is commonly used to collect samples of volatile organic compounds (VOC) in air. The objective of this study was to compare the stability of polyester aluminum (PEA) and polyvinyl fluoride (PVF, brand name Tedlar ®) bags for gaseous VOC sampling. Eight VOC standards (benzene, toluene, p-xylene, styrene, methyl ethyl ketone, methyl isobutyl ketone, butyl acetate, and isobutyl alcohol) were placed into each bag at storage times of 0, 2, and 3 days prior to analyses by gas chromatography/mass spectrometry (GC/MS). From each bag representing each storage day, samples of 3 different mass loadings were withdrawn and analyzed to derive response factors (RF) of each chemical between the slope of the GC response ( y-axis) vs. loaded mass ( x-axis). The relative recoveries (RR) of VOC, if derived by dividing RF value of a given storage day by that of 0 day, varied by time, bag type, and VOC type. If the RR values after three days are compared, those of methyl isobutyl ketone were the highest with 96 (PVF) and 99% (PEA); however, the results of isobutyl alcohol were highly contrasting between the two bags with 31 and 94%, respectively. Differences in RR values between the two bag types increased with storage time, such that RR of PEA bags (88 ± 10%) were superior to those of PVF bags (73 ± 22%) after three days, demonstrating that VOC in PEA bags were more stable than in PVF bags.

Lateral-torsional buckling resistance of aluminium I-beams

This paper presents a detailed investigation into lateral-torsional stability of aluminium extruded I section beams under pure bending. Forty aluminium members of two different alloys 6061-T6 and 6063-T5, representing weak hardening and strong hardening alloys respectively, were tested. Stress–strain relationships were determined by tensile tests with 8 coupons cut from extruded flanges and web. Widths of flanges and lengths of members were herein taken as primary parameters to study lateral-torsional stability of the beams. With rigid lateral-torsional restraint on beam ends, lateral-torsional buckling resistances and load-rotation relationships were obtained by continuous loading. Comparison of numerical predictions with test results indicated that accurate and reliable replication could be achieved by the described finite element (FE) models. By means of measured material behaviour and geometric properties, the corresponding provisions in Eurocode 9 (CEN 2007) and a design method previously proposed by the authors were evaluated by the test results. It was demonstrated that the proposed calculation method could provide cross-section lateral-torsional buckling resistances that are much closer to the test results than design strengths on the basis of the Eurocode 9 provisions are. Therefore, the proposed design method could be an alternative way of predicting the lateral-torsional buckling resistances of aluminium alloy I-beams.

Detection System for Propagating Normal-Zones With Pick-Up Coils in the LHD Helical Coils

Propagation and recovery of normal zones were observed several times in a pair of helical coils, which are H1 and H2 coils, of the Large Helical Device. In order to detect the position of a propagating normal zone, pick-up coils were installed along the helical coils by the pitch of 30 degree of the poloidal angle. The diameter and turn number of the pick-up coil are 99 mm and 10,000, respectively. They detect the change of magnetic field by current transfer between the superconducting strands and an aluminum stabilizer. The position and the velocity of propagating normal-zones were detected successfully 15 times since the pickup coils had been installed. They were induced 12 times in H1 coil and three times in H2 coil. Most of the normal zones were induced at the bottom of the coils, and all of them propagated to one side, which is the downstream of the transport current, with recovery from the opposite side. The propagation velocity can be estimated from the delay time of the peak voltage of the pickup coils. These obtained data are very useful to investigate the cause of the normal-zone propagation and cryogenic stability of the helical coils. Furthermore, this method is applicable for other superconducting magnets made of asymmetrical conductors.

Thermal Stability of Aluminum Doped Zinc Oxide Thin Films

Transparent conductive oxides are key electrode materials for thin film solar cells. Aluminum doped zinc oxide has become one of the most promising transparent conductive oxide (TCO) materials because of its excellent optical and electrical properties. In this work, aluminum doped zinc oxide thin films were prepared using RF magnetron sputtering of a 4 at% ceramic target. The thermal stability of aluminum doped zinc oxide thin films was studied using various physical and structural characterization methods. It was observed that the electrical conductivity of aluminum doped zinc oxide thin films deteriorated rapidly and unevenly when it was heated up to 350 °C. When the aluminum doped zinc oxide thin films were exposed to UV ozone for a short time before heating up, its thermal stability and large area homogeneity were significantly improved. The present work provided a novel method for improving the durability of aluminum doped zinc oxides as transparent conductive electrodes in thin film solar cells.

Local Buckling Analysis of Aluminum I Section Beams

Low elastic modulus of aluminum alloy gives prominence to lateral and local buckling of members, especially when thin walled sections are adopted to save material usage. Under certain conditions of loads and constraint, local buckling would occur in aluminum beams. A numerical study to assess the local stability of aluminum I section beams is presented in this paper. The study focused on two aspects: the local buckling of aluminum flange plate under compression, the local buckling of aluminum web plate under bending and shear. An extensive parameter analysis including width-to-thickness ratio, initial imperfection, material constitutive relation and restriction effect from adjacent plates was carried out with the purpose of extracting several governing parameters and investigating their effects on the local buckling of aluminum plate. Based upon the results of finite element analysis (FEA), a new design method in connection with the local stability of aluminum I section beams has been developed. By virtue of the proposed design method, three key indicators that include the critical value of width-to-thickness ratio to prevent local buckling of aluminum flange plate under compression, the local stability of aluminum web plate under bending/shear and the bearing capacity of aluminum I section beams under the condition that the post buckling strength of web is taken into account, could be obtained to provide more rational and efficient designs. The proposed design method is different from the current Eurocode but acts in accordance with Chinese code for design of steel structures (Chinese steel code) in order to satisfy applicability.

Stability of aluminium in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and ethylene glycol mixtures

The stability of electrochemically passivity aluminium has been investigated in mixtures of ethylene glycol, 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid, Na 2B 4O 7.10H 2O and NaH 2PO 4. The effects of (i) borax and sodium dihydrogen phosphate salts presence, (ii) water absorption and (iii) ethylene glycol content are studied by electrochemical impedance spectroscopy (EIS). The results show a decrease in the polarization resistance and an increase in the capacitance associated with the passive oxide dielectric properties with an increase in the water and/or ethylene glycol content in the mixtures. The presence of Na 2B 4O 7.10H 2O and NaH 2PO 4 salts stabilize the oxide layer.

Overview of LHD Superconducting Magnet System and Its 10-Year Operation

The Large Helical Device (LHD) is one of the world’s largest superconducting systems. It consists of a pair of pool-cooled helical coils, three pairs of forced-flow-cooled poloidal coils, nine superconducting bus lines, a helium liquefier and refrigerator of 10-kW class, and six dc power supplies. Its stored magnetic energy reaches 0.8 GJ. Availability higher than 99% has been achieved in the long-term continuous operation since the first cooldown in February 1998 owing to the robustness of the systems and to efforts of maintenance and operation. One major problem is shortage of cryogenic stability of the helical coil conductor due to the slow current diffusion into a thick pure aluminum stabilizer. To improve its cryogenic stability by lowering the temperature, a subcooling system was installed before the tenth cooldown. The outlet temperature of the coil was successfully lowered to 3.8 K from 4.4 K of the saturated temperature, and its operation current was increased to 11.6 kA from 11.0 kA. These experiences of modification, maintenance, and operation should be useful for next large superconducting systems.

Thermal stability of aluminum, molybdenum, tungsten, and chromium nanopowders and their mixtures

Our experimental studies have revealed that after the mixing of nanopowders and coarsely dispersed powders, the temperature of the start of oxidation of the mixture was not determined by the corresponding temperature of the thermally less stable component, but took a new constant value. This tendency was explained by the mutual effects of the binary electrical layers formed by redox reactions in the surface and subsurface layers of the particles of the powders being mixed.

Structure and stability of aluminium doped lithium clusters (LinAl0/+, n = 1–8): a case of the phenomenological shell model

Quantum chemical calculations are performed on the aluminium doped lithium clusters Li(n)Al at both neutral and cationic states using the DFT/B3LYP and CCSD(T) methods in conjugation with the aug-cc-pVaZ (a = D,T,Q) basis sets. The global minima are located and the growth mechanism is established. The electronic structure, geometrical parameters and energetic properties, such as average binding energy E(b), second difference of energy Δ(2)E, adiabatic and vertical ionization energy, and dissociated enthalpy, are evaluated using the coupled-cluster CCSD(T) method, whose energies are extrapolated to the complete basis set limit (CBS). The high stability of Li(5)Al, Li(7)Al, Li(6)Al(+) and Li(8)Al(+) that have the "magic numbers" of valence electrons, can be understood using the phenomenological shell model.

The Impact of Aluminum and Iron Substitution on the Structure and Electrochemistry of Li ( Ni0.4Co0.2 − yMyMn0.4 ) O2 Materials

and compounds were prepared to investigate the effect of replacement of all or part of the cobalt on the structural and electrochemical properties. The impact of substitution on the structure has been examined by both X-ray and neutron diffraction experiments. The incorporation of aluminum has minimal effect on the antisite defect concentration, but leads to structural changes that affect electrochemical performance. The most important effect is an opening of the lithium slab dimension upon substitution, which results in improved rate performance compared to the parent compound. In contrast, the lithium slab dimension is not affected by iron substitution and no rate enhancement effect is observed. The cycling stability of aluminum containing materials is superior to both the parent material and iron-substituted materials.

Metal Complexation by Humic Substances in Seawater

We determined the complex stability of copper, zinc, cobalt and aluminum with humic acid (HA) and fulvic acid (FA) in pH 8 seawater. The method is based on metal competition against iron, for which the complex stability with humic substances (HS) in seawater had been calibrated previously against EDTA. The conditional stability constants, log K'(Mn+HS) values, were found to decrease in the order of Cu > Zn > Co and Fe > Al. The complex stability of the HA species was greater than the FA species, but all determined complex stabilities are sufficiently high for significant complexation of the examined metals by HS in seawater. Data modeling shows a good data fit over the entire titrations for Cu and Co and for low levels of Zn. A second site on the HS appears to bind higher levels of Zn. The Al data suggest that Fe is exchanged for Al at a ratio different from 1:1. The data suggests that HS may be an important ligand for these metals in seawater.

Enhancement of the stability of microporous silica films in non-aqueous solvents at elevated temperature

The effect of Al incorporation and pH adjustment during hydrolysis of the silica precursor on the thermal and structural stability of ordered microporous silica films with a 2D structure is presented. The structural stability of the films was determined from a combination of LA XRD/TEM data with porosity data obtained from ethanol adsorption isotherms. Thermogravimetric analysis and FTIR data were used to determine the template removal and the thermal stability. Stability of aluminium incorporated silica films has further been examined in several organic solvents with different polarity. A solvent with a higher polarity interacts more strongly with the films; the long-order structure disappeared after exposure to polar solvents. After exposure to non-polar solvents, the pore size uniformity was retained after 48 h. The samples with an Al/Si ratio of 0.007 showed the smallest d-spacing shift after exposure to hexane. The stability was further tested in the hydrogenation of phenylacetylene performed in a batch reactor over 1 wt.% Pd/Si(Al)O 2/Si (Al/Si = 0.007) films at 30 °C and 10 bar H 2 with hexane as solvent. No deactivation was observed in two subsequent hydrogenation runs.

Catalytic Meerwein-Ponndorf-Verley reductions over mesoporous silica supports: Rational design of hydrophobic mesoporous silica for enhanced stability of aluminum doped mesoporous catalysts

A series of aluminum isopropoxide-grafted mesoporous organosilica having ethane (–CH 2–CH 2–) and ethene (–CH CH–) groups in the frame wall positions (ethane–silica, ethene–silica) as well as mesoporous silicas (MCM-41, MCM-48, SBA-15) through siloxide linkages were fabricated. The samples were used as catalysts in the Meerwein-Ponndorf-Verley reduction of ketones and aldehydes of different nature and size using secondary alcohols as the hydrogen transfer agents. Aluminum isopropoxide supported mesoporous silica samples show higher catalytic conversion and among them, the one-dimensionally channel oriented Si-MCM-41 supported aluminum isopropoxide shows better results than the three-dimensional Si-MCM-48 and the large pore Si-SBA-15. Compared to aluminum isopropoxide-grafted mesoporous silica samples, aluminum alkoxide-grafted organosilica samples shows better catalytic activity even in the presence of 10% of water and the better stability is attributed to the presence of integrated hydrophobic organic groups in the frame wall positions.

Transient Stability Analysis of Large Scale Aluminum Stabilized Superconductor Cooled by He II

Large-scale aluminum stabilized superconductors are applied to accelerator magnets, SMES, fusion magnets and so on. Authors have investigated transient stability of large helical device (LHD) conductor, which consists of a NbTi/Cu Rutherford cable, a pure aluminum stabilizer, and a copper sheath, cooled by saturated He I, sub-cooled He I and pressurized He II. The peculiar phenomena, such as normal and asymmetrical propagation of normal were observed in the original LHD helical coil and also in small test coils wound with the LHD conductor. These phenomena appeared with He I cooling and were emphasized with He II cooling. In order to investigate the transient stability of LHD composite superconductors against a thermal disturbance and the electromagnetic behavior inside the conductor, the tests with numerical simulations were carried out. In this paper, the effects of the polarity of the external field and the transport current on the direction of the traveling normal zone and the propagation velocity were discussed based on the experimental and simulation results. The hall current distributions in the longitudinal area around the normal zone and their effects on the transient stability were discussed. Important factors in the design of a large-scale aluminum stabilized superconductor were discussed.

Thermodynamics of chemical and electrochemical stability of aluminum, silicon, and tin bronzes

Phase diagrams copper-element-oxygen and potential-pH diagrams are plotted for alloys of the Cu-Al, Cu-Si, and Cu-Sn systems at 25°C. Thermodynamic peculiarities of the corrosion and electrochemical behavior of phase components of aluminum, silicon, and tin bronzes are analyzed. The surface activity of alloying elements is assessed.

Mesoporous beta zeolite obtained by desilication

Zeolite beta crystals (Si/Al = 35) synthesized in fluoride medium were treated in aqueous 0.2 M NaOH solution for mesopore formation by selective extraction of framework silicon. A 16 parallel-batch reactor was used to study the influence of the treatment time and temperature on the physico-chemical properties of the zeolites, which were characterized by ICP-OES, XRD, N 2 adsorption at 77 K, SEM, TEM, DRIFTS, and in situ ATR-IR. Alkaline treatment of H-beta within the optimal window of Si/Al ratios identified for other zeolite families leads to extensive silicon extraction at mild treatment conditions. This originates substantial mesoporosity and presumably improved transport, but negatively impacts on the microporous and acidic properties of the resulting sample. Consequently, the alkaline-treated beta zeolites show lower catalytic activity in the acid-catalyzed liquid-phase benzene alkylation than the purely microporous parent material. The relatively low stability of framework aluminum in BEA, compared to MFI and MOR, is detrimental for the controlled mesopore formation by Si dissolution, since aluminum cannot optimally exert its pore-directing role.

Influence of Nanosized Silicon Carbide on Dimensional Stability of Al/SiC Nanocomposite

This study concentrated on the role of particle size of silicon carbide (SiC) on dimensional stability of aluminum. Three kinds of Al/SiC composite reinforced with different SiC particle sizes (25 μm, 5 μm, and 70 nm) were produced using a high-energy ball mill. The standard samples were fabricated using powder metallurgy method. The samples were heated from room temperature up to500∘Cin a dilatometer at different heating rates, that is, 10, 30, 40, and60∘C/min. The results showed that for all materials, there was an increase in length change as temperature increased and the temperature sensitivity of aluminum decreased in the presence of both micro- and nanosized silicon carbide. At the same condition, dimensional stability of Al/SiC nanocomposite was better than conventional Al/SiC composites.