Nb Tubes Research Articles

ChemInform Abstract: Ca3[BN2]I3: The First Halide‐Rich Alkaline Earth Nitridoborate with Isolated [BN2]3‐ Units.

AbstractThe title compound is prepared from a mixture of Ca3[BN2]2 and CaI2 in a molar 1:4 ratio (Nb tube, 1223 K, 24 h).

ChemInform Abstract: Two Hexagonal Series of Lanthanoid(III) Oxide Fluoride Selenides: M6O2F8Se3 (M: La—Nd) and M2OF2Se (M: Nd, Sm, Gd—Ho).

AbstractThe two series of title compounds are prepared from mixtures of MF3 (M: La—Nd, Sm, Gd—Ho), M2O3, M, and Se using excess CsI as a flux (Nb tubes, 850 °C, 10 d).

Dynamics of the Abrikosov Vortices on Cylindrical Microtubes

We consider the special features at nano- and microscales of the vortex dynamics on superconducting cylindrical Nb tubes produced by the roll-up (self-rolling) technique. A transport current enters the tube through electrodes placed on both sides of a cut (in the paraxial direction) of the tube. The system is in the magnetic field perpendicular to the tube axis. The vortex dynamics is described by means of characteristic times: time (Δt1) needed for a vortex to move from one edge of the tube to another and time (Δt2) between two consecutive vortex nucleation events at one edge of the tube. A range of magnetic field values is analyzed where Δt1 as a function of the magnetic field has a highly nonlinear and non-monotonic behavior. For certain values of the magnetic field, two different trajectories are possible for a moving vortex, i.e., a bifurcation phenomenon occurs. We explain the reason of this bifurcation.

Ca3[BN2]I3: The First Halide‐Rich Alkaline Earth Nitrido­borate with Isolated [BN2]3– Units

AbstractThe title compound Ca3[BN2]I3 was obtained from reactions of mixtures of the starting materials Ca3[BN2]2 and CaI2 in a 1:4 ratio in sealed Nb tubes at 1223 K. The crystal structure was solved from powder synchrotron diffraction data. Ca3[BN2]I3 is the first example of a halide‐rich nitridoborate crystallizing in the rhombohedral space group R32 [no. 155, Pearson code: hR96; Z = 12; a = 16.70491(2) Å, c = 12.41024(2) Å]. The crystal structure is built up by two interpenetrating networks of condensed edge‐sharing [BN2]@Ca6 and [□]@I6 trigonal antiprisms (□ = void). In Ca3[BN2]I3 two crystallograhically distinct [BN2]3– anions are present with d(B1–N) = 1.393(2) Å and d(B2–N) = 1.369(9) Å. Their bond angles are practically linear, varying only slightly: N–B1–N = 179(1)° and N–B2–N = 180°. Vibrational spectra were interpreted based on the D∞h symmetry of the discrete linear [N–B–N]3– moieties, considering the site symmetry reduction and the presence of two distinct [BN2]3– groups.

ChemInform Abstract: Ternary Aurides RE4Mg3Au10 (RE: Y, Nd, Sm, Gd—Dy) and Their Silver Analogues.

AbstractThe title compounds are prepared by induction melting of the elements in sealed Nb tubes (rapidly heating to about 1500 K, 1300 K for 30 min, and 900 K for 2 h).

ChemInform Abstract: Yb14MgSb11 and Ca14MgSb11 — New Mg‐Containing Zintl Compounds and Their Structures, Bonding, and Thermoelectric Properties.

AbstractThe Zintl phases Yb14MgSb11 (I) and Ca14MgSb11 (II) are prepared by annealing mixtures of the elements in the molar ratio Yb(Ca):Mg:Sb of 14:2:11 (Nb tube in evacuated silica tubes, 1275 K for (I) and 1225 K for (II)).

HIGH TEMPERATURE VACUUM CARBURIZATION BEHAVIORS AND PHASE EVOLUTION MECHANISMS OF Cr35Ni45Nb ALLOY UNDER SERVICE CONDITION

Carburization in Ni-Cr-Fe-based alloys is an important phenomenon, especially in ethylene cracking tubes which serve at high temperatures under highly carburizing environment. In this work, the Cr35Ni45 Nb tube subjected to service condition for 6 a was carburized by low-pressure vacuum carburizing(LPVC) at 1080 ℃.The carburization behaviors and corresponding mechanisms of phase evolution in the inner wall were comprehensively analyzed through SEM, XRD and EPMA. The results showed that oxidation behaviors of the tube at high temperature were consisted of external oxidation of Cr and internal oxidation of Si, resulting in formation of com-posite oxide scales. Depletion of Cr in the subsurface caused by surface Cr2O3 leaded to carbide dissolution and formation of carbide free zone and carburized zone. The critical concentration of Cr for carbide dissolution is about19.0%(mass fraction). By comparing carburization behaviors of specimens whose oxide scales were retained or removed, the carburization resistance of the composite oxide scales in carburizing environment was systematically investigated. The results showed that the composite oxide scales formed previously acted as an effective barrier to carbon infiltration. However, the outermost Cr2O3 scale tended to be carbonized to form carbide scale to spall from the surface in the strongly reducing environment with low oxygen partial pressure, while the Si O2 kept stable all along due to its excellent thermodynamic stability. However, a certain amount of carbon was still capable to penetrate the alloy interior through gaps of the Si O2 scale due to its discontinuity. Therefore, continuity, density and high-temperature stability of the oxide scales were crucial for the alloy to achieve excellent anti-carburizing performance. Once the oxide layers were removed or carbonized adequately, inconceivable internal carburization occured widely. Large amounts of secondary carbides precipitated again in the previous carbide free zone due to high carbon activity. Widespread precipitations of graphite called metal dusting in the range of about 0.5 mm in depth occurred after long exposure of specimens to the carburizing environment. The carbon activity gradually decreased with increasing distance from the surface. The primary carbides within the deeper carburized region were transformed from M23C6 to M7C3in situ, which were accompanied by precipitation of vermicular g phase in the primary carbides, phase transition from h to Nb C and decomposition of intragranular secondary carbides. Severe coalescing and coarsening of carbides and metal dusting caused the serious degradation of microstructure, formation of macrocracks and final thinning of the Cr35Ni45 Nb tube wall.

Nb<sub>3</sub>Sn 超電導線材の特徴と諸外国の開発動向

Multifilamentary Nb3Sn wires are fabricated starting from Nb/Cu-Sn or Nb/Cu/Sn composites, which facilitates their mass production. Nb3Sn superconducting wires are now one of the key materials in modern science and technology, such as NMR, fusion and refrigerator cooled magnets. Present volume is the special issue on the recent status of mass productionscaled Nb3Sn conductors in Japan. Then this article describes aspects of Nb3Sn conductors, and overviews recent activities in foreign industries. Bronze process and internal tin process are common fabrication process of Nb3Sn multifilamentary wires, whose features are briefly described in this article. The former process is dominantly used in Japan and Europe including Russia, while the latter is rather frequently used in USA, Korea and China. Thus countries are divided into roughly two groups with respect to the major fabrication technology of Nb3Sn. Beside these, Nb tube process and powder-in-tube process are being proceeded in foreign industries. Nb3Sn conductors still have a possibility of improvement in their fabrication technologies, and will continue to contribute for the application of superconductivity.

ChemInform Abstract: Ternary Bismuthides Li3REBi2 (RE: Ce, Pr, Sm, Gd) with Li3LaSb2‐Type Structure.

AbstractThe title compounds are prepared from the elements (Nb tubes, 1273 K for 6 h and 923 K for 72 h) and characterized by powder XRD.

ChemInform Abstract: Experimental and Theoretical Investigations for Site Preference and Anisotropic Size Change of RE11Ge4In6‐xMx (RE: La, Ce; M: Li, Ge; x = 1, 1.96).

AbstractLa11Ge4In5.00Li1.00 and Ce11Ge5.96In4.04 are prepared from the elements (Nb tubes, 1080 °C for 5 h and 750 °C for 2 d) and characterized by powder and single crystal XRD, and TB‐LMTO‐ASA computations.

ChemInform Abstract: Evidence of a Mixed Magnetic Phase in EuMgGe: A Semimetallic Zintl Compound with TiNiSi Structure Type.

AbstractEuMgGe is prepared by melting and annealing the elements (Nb tube, 1.

ChemInform Abstract: Framework Structures of Interconnected Layers in Calcium Iron Arsenides.

AbstractThe new compounds Can(n+1)/2(Fe1‐xM1x) (2+3n) M2n(n‐1)/2As(n+1)(n+2)/2 (n = 1—3; M1: Nb, Pd, Pt; M2: □, Pd, Pt) and (Ca,Na)3(Fe,Nb)8As6 are synthesized by solid state reaction of stoichiometric mixtures of the elements (alumina or Nb tubes, 900—1000 °C) and their crystal structures are determined by single crystal XRD.

Structure and stability of superconducting core of single-core MgB2/Cu,Nb tube composite with a high critical current

The core of a single-core MgB2/Cu,Nb composite, which has been prepared by the ex-situ technique and exhibits a high critical current equal to 427 A (at 0 T and 4.2 K, j c ≥ 105 A/cm2), has been studied using various structural methods. Two kinds of MgB2 crystals were observed; those of the first kind is large, highly dense crystals characterized by a low oxygen content (2–8 at %) and the others are fine, weakly coupled crystallites characterized by high oxygen content (4–21 at %). To perform a comparative analysis of the structures, we have also studied an MgB2 bulk sample synthesized at 1000°C. It was found that two phases with the same lattice are formed; they differ in the magnesium and boron contents (within the homogeneity range), impurity oxygen content and microstructure as well but differ slightly in the lattice parameters. The two-phase state of MgB2 bulk sample is due to the mechanism of its formation, which includes the melting of magnesium, the dissolution of solid boron in it, and the crystallization of MgB2 from the melt with the formation of dendrite-like structure characterized by corresponding redistribution of components and impurities. To a certain degree, the two-phase structure of MgB2 bulk sample is inherited by the MgB2/Cu,Nd composite prepared by ex-situ technique (annealing of composite at 700°C). It was shown that oxygen in the MgB2 compound is the destabilizing factor and leads to the transformation of the superconductor into MgO.

The Effects of Ti Addition and High Cu/Sn Ratio on Tube Type <formula formulatype="inline"> <tex Notation="TeX">$(\hbox{Nb}, \hbox{Ta})_{3}\hbox{Sn}$</tex></formula> Strands, and a New Type of Strand Designed to Reduce Unreacted Nb Ratio

In this paper, we report the properties of two tube type Ta doped Nb3Sn strands: one strand was additionally Ti doped by way of a Sn-Ti alloy core, and the other had high Cu/Sn ratio within the filaments. Higher irreversibility field (Birr) was obtained on the quaternary strand with respect to the (Nb-7.5 wt.%Ta)3Sn strand. High Cu/Sn ratio decreased the amount of coarse grain formation, but also degraded the layer Jc of the tube type strand by depressing the Sn content in the fine grain (FG) layer. A new type of strand, the subelement of which is composed of seven bare Cu-Sn cored Nb tube filaments, was designed with the aim to reduce the unreacted Nb area fractions. The test results of the first experimental strand are reported. The unreacted Nb ratio is reduced relative to normal tube type strands and the FG area fraction is improved. The unique structure of this strand makes it also possible to improve the stoichiometry of FG and reduce the effective diameter (deff) .

ChemInform Abstract: Superconductivity in Ba1‐xKxTi2Sb2O (0 ≤ x ≤ 1) Controlled by the Layer Charge.

AbstractThe title solid solution is synthesized by solid state reaction of stoichiometric mixtures of Ba, BaO2, K, Sb, and Ti for x ≤ 0.5 and Ba, K, Sb, Ti, and TiO2 for x < 0.5 (Nb tubes, 600 °C, 15 h, sintering at 900 °C, 3 d).

ChemInform Abstract: Magnesium‐rich Intermetallics RE3RuMg7 (RE: Y, Nd, Dy, Ho) — Rows of Condensed Ru@RE6/2 Octahedra in Magnesium Matrices.

AbstractThe title compounds are synthesized from the elements (Nb tubes, 1273 K for 2 h, 673 K for 5 h) and characterized by powder XRD, and single crystal XRD for the Dy compound.

ChemInform Abstract: The Layered Antimonides RELi3Sb2 (RE: Ce—Nd, Sm, Gd—Ho). Filled Derivatives of the CaAl2Si2 Structure Type.

AbstractThe title compounds are prepared from stoichiometric mixtures of the elements (Nb tubes, 900 °C for 24 h and 800 °C for 96 h) and characterized by powder and single crystal XRD, magnetic susceptibility measurements, and TB‐LMTO electronic band structure calculations.

ChemInform Abstract: Site‐Preference Among Three Anions in the Quaternary BaAl4‐Type Structure: Experimental and Computational Investigations for BaLi1.09(1)In0.91Ge2.

AbstractBaLi1.09In0.91Ge2 is synthesized from a mixture of Ba, Li, In, and Ge in a ratio of 1:2:2:2 (Nb tube, 950 °C, 5 h) and characterized by single crystal XRD and TB‐LMTO‐ASA quantum chemical calculations.

ChemInform Abstract: A Lithium‐Rich Compound Li7Mn(BO3)3 Containing Mn2+ in Tetrahedral Coordination: A Cathode Candidate for Lithium‐Ion Batteries.

AbstractCrystals of the title compound are synthesized from stoichiometric mixtures of Li2O, MnO, and B2O3 (sealed Nb tube, 850 °C, 24 h).

A model for phase evolution and volume expansion in tube type Nb3Sn conductors

In this work, an analytic model for phase formation and volume expansion during heat treatment in tube type Nb3Sn strands is presented. Tube type Nb3Sn conductors consist of Nb or Nb–Ta alloy tube with a simple Cu/Sn binary metal insert to form the basic subelement (filament). A number of these elements, each with an outer Cu jacket, are restacked to form a multifilamentary strand. The present tube type conductors, with 4.2 K, 12 T non-Cu critical current density (Jc) in the 2000–2500 A mm−2 range and effective subelement diameters (deff) in the 12–36 μm range, are of interest for a number of applications. During the reaction of typical tube type strands, the Sn–Cu becomes molten and reacts with the Nb tube first to form NbSn2, then Nb6Sn5. At later times in the reaction sequence, all of the NbSn2 and Nb6Sn5 is converted to Nb3Sn. Some of the Nb3Sn is formed by a Nb–Sn reaction and has a fine grain (FG) structure, while some is converted from Nb6Sn5, which results in a coarse grain (CG) region. The fractions of FG and CG A15 are important in determining the final conductor properties. In this work we develop an analytic model to predict the radial extents of the various phases, and in particular the final FG and CG fractions based on the starting Nb, Cu, and Sn amounts in the subelements. The model is then compared to experimental results and seen to give reasonable agreement. By virtue of this model we outline an approach to minimize the CG regions in tube type and PIT strands and maximize the final FG area fractions. Furthermore, the volume change during the various reaction stages was also studied. It is proposed that the Sn content in the Cu–Sn alloy has a crucial influence on the radial expansion.