Development of high critical current density in multifilamentary round-wire Bi2Sr2CaCu2O8+x by strong overdoping

Bi2Sr2CaCu2O8+x is the only cuprate superconductor that can be made into a round-wire conductor form with a high enough critical current density Jc for applications. Here we show that the Jc(5 T,4.2 K) of such Ag-sheathed filamentary wires can be doubled to more than 1.4x10^5 A/cm^2 by low temperature oxygenation. Careful analysis shows that the improved performance is associated with a 12 K reduction in transition temperature Tc to 80 K and a significant enhancement in intergranular connectivity. In spite of the macroscopically untextured nature of the wire, overdoping is highly effective in producing high Jc values.Comment: 4 figure

Evidence for length-dependent wire expansion, filament dedensification and consequent degradation of critical current density in Ag-alloy sheathed Bi-2212 wires

It is well known that longer Bi-2212 conductors have significantly lower critical current density (Jc) than shorter ones, and recently it has become clear that a major cause of this reduction is internal gas pressure generated during heat treatment, which expands the wire diameter and dedensifies the Bi-2212 filaments. Here we report on the length-dependent expansion of 5 to 240 cm lengths of state-of-the-art, commercial Ag alloy-sheathed Bi-2212 wire after full and some partial heat treatments. Detailed image analysis along the wire length shows that the wire diameter increases with distance from the ends, longer samples often showing evident damage and leaks provoked by the internal gas pressure. Comparison of heat treatments carried out just below the melting point and with the usual melt process makes it clear that melting is crucial to developing high internal pressure. The decay of Jc away from the ends is directly correlated to the local wire diameter increase, which decreases the local Bi-2212 filament mass density and lowers Jc, often by well over 50%. It is clear that control of the internal gas pressure is crucial to attaining the full Jc of these very promising round wires and that the very variable properties of Bi-2212 wires are due to the fact that this internal gas pressure has so far not been well controlled

Fragmentation of carbohydrate anomeric alkoxy radicals. A new general method for the synthesis of alduronic acid lactones

11 pages, 2 tables, 7 schemes.Alduronic acid 4,1-, 5,1-, and 5,2-lactones can be specifically obtained when hexuronic and penturonic acids belonging to the erythrose and threose carbohydrate series undergo a tandem β-fragmentation−intramolecular cyclization reaction. In this way, γ-lactones such as 3-O-formyl-1,2-O-isopropylidene-d-threurono-4,1-lactone (38), 3-O-formyl-1,2-di-O-methyl-d-threurono-4,1-lactones (39), or 3-O-formyl-1,2-O-isopropylidene-d-erythrurono-4,1-lactone (41), and δ-lactones such as 1-O-(tert-butyldimethylsilyl)-4-O-formyl-2,3-O-isopropylidene-d-lyxurono-5,1-lactones (40), or 4-O-formyl-1,2,3-tri-O-methyl-d-arabinurono-5,1-lactones (42), or 3-O-benzyl-4-O-formyl-1,2-O-isopropylidene-d-arabinurono-5,1-lactone (43), were obtained. Alternatively, an intermolecular reaction took place when the carboxyl group was lactonized. Thus, 1,4-di-O-acetyl-3-formyl-1-iodo-d-arabinurono-5,2-lactone (45) was prepared from 2,5-di-O-acetyl-d-glucurono-6,3-lactone (37). The reaction is promoted by two different systems: (diacetoxyiodo)benzene (DIB)−iodine, under mild conditions, or diphenylhydroxyselenium acetate (DHSA)−iodine under visible light irradiation. With this new strategy, nor-aldopyranosuronic and aldofuranosuronic acid lactones are formed via 1,5 and 1,6 intramolecular cyclization.This work was supported by the Investigation Program no. PB96-1461 of the Dirección General de Investigación Científica y Técnica. C.G.M. thanks the Ministerio de Educación y Ciencia, Spain, for a fellowship

Microstructural development and superconducting properties of BaO{sub 2}-added Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}.

Investigations on the effects of Ba additions in Bi-2212 superconductors are focused on compositional, microstructural, and magnetization studies. In previous studies, we showed that BaO{sub 2} reacts with Bi-2212 to form second phases. Zero-field and in-field transport properties in Ag-clad BaO{sub 2} added Bi-2212 tapes had been improved at 4.2 K [1]-[3]. SEM micrographs, pole figures, and transport critical currents versus magnetic field orientation suggest that BaO{sub 2} has a strong influence on the microstructural properties. Magnetization studies revealed that BaO{sub 2} does not affect the pinning properties of optimally added Bi-2212. To estimate the potential of BaO{sub 2} additions in creating possible pinning sites, TEM investigations were carried out focusing on sub-micrometer inclusions and growth defects in the superconducting phase

Process to densify Bi2_2Sr2_2CaCu2_2OX_X round wire with overpressure before coil winding and final overpressure heat treatment

Overpressure (OP) processing of wind-and-react Bi$_2$Sr$_2$CaCu$_2$O$_X$ (2212) round wire compresses the wire to almost full density, decreasing its diameter by about 4% without change in wire length and substantially raising its JC. However, such shrinkage can degrade coil winding pack density and magnetic field homogeneity. To address this issue, we here present an overpressure predensification (OP-PD) heat treatment process performed before melting the 2212, which greatly reduces wire diameter shrinkage during the full OP heat treatment (OP-HT). We found that about 80% of the total wire diameter shrinkage occurs during the 50 atm OP-PD before melting. We successfully wound such pre-densified 1.2 mm diameter wires onto coil mandrels as small as 10 mm diameter for Ag–Mg-sheathed wire and 5 mm for Ag-sheathed wire, even though such small diameters impose plastic strains up to 12% on the conductor. A further ∼20% shrinkage occurred during a standard OP-HT. No 2212 leakage was observed for coil diameters as small as 20 mm for Ag–Mg-sheathed wire and 10 mm for Ag-sheathed wire, and no JC degradation was observed on straight samples and 30 mm diameter coil

Автотранспортне законодавство : основні законодавчі акти ( за станом на 15 березня 2013 р.). Ч. 1.

Наведено основні законодавчі акти, що визначають правові, економічні та організаційні засади діяльності на автомобільному транспорті. Видання призначено для фахівців, діяльність яких пов’язана з організацією перевезень і управління на автомобільному транспорті, студентів юридичних навчальних закладів, а також для студентів спеціальностей “Організація перевезень і управління на транспорті (автомобільний)”, “Автомобілі та автомобільне господарство”

Correlation of critical current density to quasi-biaxial texture and grain boundary cleanliness in fully dense Bi-2212 wires

The distinctive quasi-biaxial texture of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{x}$ (Bi-2212) plays an important role in enabling high critical current density (J$_{c}$) in Bi-2212 round wires (RWs). Here we studied three over pressure heat treated wires with J$_{c}$ varying by a factor of ∼10, all being fully dense. Using electron backscatter diffraction, we observed the differences in biaxial texture in these three wires. Transmission electron microscopy also revealed differences in grain boundary (GB) cleanliness and connectivity. These analyses showed that high J$_{c}$ is unambiguously correlated to the best biaxial texture, which is in turn correlated to slow cooling from the liquid melt into solid Bi-2212. However, at 4.2 K, there is a negligible difference in intragrain pinning in the three wires, suggesting that the J$_{c}$ variation by a factor of ∼10 is primarily due to variable filament and intergrain connectivity. The principal determinants of intergrain connectivity is the quasi-biaxial texture and GB cleanliness. Overall, J$_{c}$ optimization of the Bi-2212 RW is a complex multi-variable process, but this study shows that maximizing the biaxial texture quality is an important first step in such an optimization process

Isotropic round-wire multifilament cuprate superconductor for generation of magnetic fields above 30 T

Magnets are the principal market for superconductors, but making attractive conductors out of the high-temperature cuprate superconductors (HTSs) has proved difficult because of the presence of high-angle grain boundaries that are generally believed to lower the critical current density, J$_c$. To minimize such grain boundary obstacles, HTS conductors such as REBa$_2$Cu$_3$O$_{7−x}$ and (Bi, Pb)$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10−x}$ are both made as tapes with a high aspect ratio and a large superconducting anisotropy. Here we report that Bi$_2$2Sr$_2$CaCu$_2$O$_{8−x}$ (Bi-2212) can be made in the much more desirable isotropic, round-wire, multifilament form that can be wound or cabled into arbitrary geometries and will be especially valuable for high-field NMR magnets beyond the present 1 GHz proton resonance limit of Nb$_3$Sn technology. An appealing attribute of this Bi-2212 conductor is that, being without macroscopic texture, it contains many high-angle grain boundaries but nevertheless attains a very high J$_c$ of 2,500 A mm$^{−2}$ at 20 T and 4.2 K. The large potential of the conductor has been demonstrated by building a small coil that generated almost 2.6 T in a 31 T background field. This demonstration that grain boundary limits to high J$_c$ can be practically overcome underlines the value of a renewed focus on grain boundary properties in non-ideal geometries

A transformative superconducting magnet technology for fields well above 30 T using isotropic round wire multifilament Bi2Sr2CaCu2O8−xBi_2Sr_2CaCu_2O_{8-x} conductor

We report here that magnetic fields of almost 34 T, far above the upper 24 T limit of Nb$_{3}$Sn, can be generated using a multifilament round wire conductor made of the high temperature cuprate superconductor Bi2Sr2CaCu2O8-x (Bi-2212). A remarkable attribute of this Bi-2212 conductor is that it does not exhibit macroscopic texture and contains many high angle grain boundaries but nevertheless attains very high superconducting critical current densities Jc of 2500 A/mm2 at 20 T and 4.2 K. This Bi-2212 conductor does not possess the extreme texture that high Jc coated conductors of REBa2Cu3O7-x (REBCO) require, avoiding also its high aspect ratio, large superconducting anisotropy and the inherent sensitivity to defects of a single filament conductor. Bi-2212 wires can be wound or cabled into almost any type of superconducting magnet and will be especially valuable for very high field NMR magnets beyond the present 1 GHz proton resonance limit of Nb$_{3}$Sn technology. This demonstration that grain boundary limits to high Jc can be practically overcome suggests the huge value of a renewed focus on grain boundary properties in non-ideal geometries, especially with the goal of translating the lessons of this Bi-2212 conductor into fabrication of multifilament round wire REBCO or Fe-based superconductors