Ag Tapes Research Articles

E–I characteristics and critical currents of small Bi-2223/Ag coil thermally stabilized by solid and liquid nitrogen compared to water ice

A small-sized coil of helically wound Bi-2223/Ag tape was measured in liquid/solid nitrogen (LN2/SN2), and also in water (H2O) ice at external fields of 0–8 T and in a temperature range of 10–77 K. This work is especially focused on the coil stability for current amplitudes above the critical current criterion of 1 µV cm−1. While the E–I characteristics measured under the critical current criterion did not show any substantial variances at these different cooling conditions, significant differences were observed above the critical current magnitude, mainly upon cooling by solid nitrogen and water ice. The results confirm improved thermal stability for the coil measured in sub-cooled water ice compared to solid nitrogen. Consequently, cooling by water ice could be interesting for future applications of high-temperature superconducting coils.

Research on current carrying capacity of Bi-2223/Ag superconducting tape in the temperature range of 75–105 K

In order to study the feasibility of the co-transmission of electricity and liquefied natural gas (LNG) based energy fluid, we carried out a project supported by a grant from Chinese national key research and development program, Basic Research on Superconducting DC Energy Pipeline. In this project, a superconducting cable cooled by LNG based mixed energy fluid at temperature around 90 K is proposed. As the first commercial high-temperature superconducting wire, the silver-sheathed (Bi, Pb)2Sr2Ca2Cu3O10 tape is the only choice for the conductors of superconducting cable in this project due to its superiorities such as high critical temperature and high cost performance. Current carrying capacity is one of the important properties for applications of practical superconductors. However, there has been no systematic data on the current carrying capacity and characteristic of this kind of HTS wire above liquid nitrogen temperature available in literature up to date. In this study, we systematically measured the critical current of Bi-2223/Ag tape samples in a temperature range of 75–105 K, at different magnetic field and field angles. In this paper, experimental details and measurement results are reported. Some practical suggestions are proposed for the applications of this kind of HTS wire in this temperature region. The experimental results obtained in this study will make up the lack of the critical current data of Bi-2223/Ag tape above liquid nitrogen temperature in literature, and provide some fundamental information for the applications of Bi-2223/Ag tape in this temperature region.

Adhesion properties of CeO2 films produced from different precursors using sol-gel process

CeO2 films were deposited on Ni and Ag tapes by sol–gel process using nitrate, ammonium nitrate, colloidal, alkoxide, acetate, and oxalate based precursors and a detailed characterization of adhesion properties were performed in relation with structural features. The structural, microstructural and adhesion properties of the films heat-treated at 500 °C for 60 min in air were determined via XRD, ESEM and a mini tensile testing machine. The results showed that homogeneous films with cubic structure can be deposited on Ni and Ag tapes. The microstructure of the CeO2 films could also be tailored by altering precursor type, solvent, chelating agent and modifying liquid. The CeO2 joint samples with Ag tapes prepared from cerium(III)2,4 pentanedionate based solution exhibited the best adhesive properties because of polymeric sol and gel. The observed results in joint samples indicate a correlation between the failure types and the choice of solution from which CeO2 films prepared.

Effects of different directional rolling on the fabrication of 7-filament Ba1-xKxFe2As2 tapes

The transport performance of iron-based superconductor has been raised rapidly for the past few years, and the critical current density of single-core tape has surpassed 1.5 × 105 A/cm2 at 4.2 K and 10 T. In this work, 7-filament Ba1-xKxFe2As2/Ag tapes were prepared by adopting the conventional power-in-tube method. Unidirectional and bidirectional rolling experiments were designed to investigate the effect of rolling direction on the tapes. It is found that unidirectional rolling will easily break the superconducting filaments; while the bidirectional rolling can achieve the integrity and uniformity of each superconducting filament with tape thinning. Moreover, a critical current (Ic) of 157.5 A was obtained in bidirectional rolled 0.3 mm thick tape, which realized a 104 A/cm2 of engineering critical current density (Je) at 4.2 K and 10 T. In the long run, the bidirectional rolling method shows significant advantages in fabricating multi-filamentary and long tapes.

Experiment of Current Limiting Behavior Based on Air-Core Superconducting Transformer and Inductor-Capacitor Series Resonant Limiter

This paper studies the current limiting behavior based on an air-core high-temperature superconducting transformer (HTST) and a group of inductor-capacitor series resonant limiters. The air-core HTST is composed of four same double-pancake type high-temperature superconducting coils made up of Bi-2333/Ag tape, and both of primary and secondary windings include two series superconducting coils. It plays the roles of inductive fault current limiting and transformation impedance; in addition, the magnetic flux saturation can also be avoided. Meanwhile, the inductor and capacitor series with the secondary winding of the air-core HTST in series resonance state are the conventional devices. The influence of them on the circuit can almost be ignored, because they are in series resonant state in normal operation. While the fault current appeared in the primary circuit, it will be limited by the impedance of the air-core HTST and the inductor without quench (the inductor and capacitor would quit the series resonant state). According to the preliminary experiment carried out in our laboratory, this superconducting current limiting module can operate as expected, and its behavior is satisfactory.

The Frequency Dependence of AC Susceptibility for Bi-2223/Ag Tapes With Varying Lengths

An experimental investigation on ac susceptibility χ = χ′ − j χ′′ of Bi-2223/Ag superconducting tapes with different lengths L is carried out under a perpendicular ac magnetic field. A series of n -value is deduced from the ac susceptibility scaling law, which is used to systematically analyze the induced current in Bi-2223/Ag superconducting tapes. Based on the experiment results, a critical length L c is defined for the tapes as ten times the width of them. AC susceptibility χ shows conspicuous frequency dependence when the length L is smaller than L c. This phenomenon is attributed to the induced transverse current in silver. In addition, the proportion of transverse current to total induced current increases with the decreasing length dimension in our research. The results help understand the electromagnetic properties of Bi-2223/Ag superconducting tapes better and lay down important experimental foundation for practical applications.

Investigation of the melt-growth process of YbBa2Cu3O7−δ powder in Ag-sheathed tapes

We investigate the reaction mechanism of the melting and regrowth of Yb123 in Ag tape, which provides a starting point to fabricate Ag-sheathed Yb123 wires by PIT.

Critical Current Density and Flux Pinning Mechanism in Flat-Rolled Sr-122/Ag Tapes

We fabricate Ag sheathed Sr-122 superconducting tapes via a scalable rolling process. The critical current density and its homogeneity are studied by electrical and magnetic measurements. At 4.2 K and 10 T, the transport critical current density J c achieves 3.3×10 4 A/cm 2 . The magneto-optical images of the superconducting core indicate a global supercurrent throughout the sample. A scaling analysis reveals a universal behavior of normalized pinning force as a function of reduced field, suggesting that grain boundary is the prevailing pinning source. Combined with the scanning electron microscope images of the superconducting core, we conclude that the pores and the relatively low c -axis texture are the main factors that limit the critical current density.

Experimental Investigation of Bi-2223/Ag Superconducting Tape Joints

We have developed a manufacturing method for superconducting joints for Bi-2223/Ag tapes (DI-BSCCO Type-H, Sumitomo Electric Industries Ltd., Yokosuka, Japan). The tapes' superconducting joints were fabricated under pressure and heat treatment processes. The critical currents of these joints under relevant temperature conditions were measured to investigate their applicability to superconducting devices such as magnetic shields and superconducting magnets using current transport tests. In addition, the critical currents were investigated in a parallel magnetic field to the tape surface up to 5 T at 4 and 20 K. We will report the results of these experiments.

Thermal Conductivity and Dilatation of Bi-2223/Ag (DI-BSCCO) Superconducting Wire Laminated With Various Thin Alloy Tapes

A Bi-2223/Ag wire laminated with Ni-alloy tapes offered the high critical tensile strength over 400 MPa with a high critical current of about 200 A, which has just started to be equipped in high-field facilities. To design such a practical superconducting apparatus, we must know the heat leakage through the wires and the elasticity among the constitutional materials. In this paper, we report on the thermal conductivity and dilatation of this new Bi-2223/Ag/Ni-alloy tape, compared to those of other Bi-2223/Ag tapes, and discuss the contribution of the lamination alloy to the thermal properties.

Numerical Simulations of AC Losses in Multifilamentary Superconducting Tapes Under Bending Strain

AC loss has become a key problem for practical applications of high-temperature superconductors. It is well known that mechanical deformation will affect the critical current and ac loss as the superconductor is subjected to the magnetic field or transport current. In this paper, the ac losses in Bi2Cr2Ca2Cu 3O10 (Bi2223)/Ag tapes under bending deformation are investigated. Bi2223 tape consists of Ag matrix and Bi2223 filaments, and the ac losses are generated by transport current and external field. By considering the plastic deformation of Ag matrix and residual strain, the simplified mechanical fracture model is established. Then, the finite element method analysis is used to investigate the relation of critical current and ac loss with bending deformations, and the losses are presented for different transport current and external magnetic field conditions. The influences of filament fracture on the ac loss are discussed for transport current and external magnetic field cases, respectively.

Numerical investigation of residual stresses in high temperature ZrO2 insulation coatings on Ag tape substrate for magnet technologies

In this research, the numerical investigation of residual stresses was carried out in high temperature ZrO2 insulation coatings on Ag tape substrate for magnet technologies. ZrO2 coatings were fabricated on Ag substrate using a reel-to-reel sol–gel system. The microstructural observation of ZrO2 coatings was performed through an environmental scanning electron microscope (ESEM). ESEM micrograph revealed that ZrO2 coatings with crack had mosaic structure which is suitable for high temperature insulation fields. The thermal stresses in the each layer were determined by the means of the lamination theory for both elastic solution and the finite element method (FEM) for elastoplastic solution in the temperature range of 298 to 50 K in liquid helium. The residual stresses happened throughout the production are neglected because of gradually cooling process. As a result of this, all of the residual stresses at the 298 K are accepted to be zero. Difference of thermal expansion coefficients and elasticity modulus cause the thermal stresses in the layers.

Observation of reversible critical current performance under large compressive strain in Sr0.6K0.4Fe2As2 tapes

Iron-based superconductors have caused great interest regarding high-field applications due to their good properties. A common fabrication route for 122-type wires and tapes is the ex situ powder-in-tube (PIT) process. From the point of application in the high magnetic field, where high electromagnetic forces are present, the conductor strength and its tolerance to the mechanical load are important issues. In order to understand the comparatively integrated critical current characterization of the Sr-122 tape under axial strain, the so-called U-spring setup was used to test a silver-sheathed Sr0.6K0.4Fe2As2 tape sample with a single core over a wide range of applied axial strain (−0.6% ∼ 0.3%). It was found that when the sample was compressed, the critical current performance showed reversiblity; meanwhile the irreversible tensile strain limit was quite low. The Sr-122/Ag tape shows very good performance under compression, and a possible conductor design should be considered to make the superconductor work at proper compressive strain states for future applications.

Fabrication of new high temperature Gd2O3-ZrO2 insulation coatings on Ag tapes by sol-gel technique for magnet technology

Cost-effective and easy-to-apply materials are necessary for magnet technologies. This research covers a fabrication development of high temperature insulation coatings for magnet technologies. With this context, gel coatings were successfully deposited on Ag tapes using sol-gel technique by preparing transparent solutions from Gd- and Zr-based precursor materials, methanol and glacial acetic acid, and subsequently 0, 5, 8, and 12 mol% Gd2O3-ZrO2 coatings were heat treated at 300, 500, and 800 °C which respectively indicate drying, heat treatment, and annealing processes. Prior to coating process, Gd2O3 effect on thermal, structural and microstructural, and electrical properties were observed and extensively discussed in the present study. FTIR revealed that when increasing heat treatment temperature from 25 to 800 °C, the frequencies of O-H, C-H, and C=O bands decreased. According to XRD results, Gd2O3 additive has a propensity to generate tetragonal ZrO2 and help to stabilize it. It was also observed that the regular surface morphology generally forms when Gd2O3 content increase in ZrO2 from 0 to 12 mol%. The film thicknesses increased from 0.5 to 1.8 μm as a function of number of dipping. The porosities of the insulation coatings can be estimated to be in the range of 25 and 40 vol%. Besides, as insulative layers, Gd2O3 additive improved ZrO2 coatings. As a result, commercial Ag and AgMg sheathed Bi-2212 long length tapes can be insulated with pure ZrO2 and Gd2O3–ZrO2 coatings and then the coated tapes can be wound to fabricate an electromagnet.

パウダー・イン・チューブ (PIT) 法による (Ba(Sr),K)Fe<sub>2</sub>As<sub>2 </sub>超電導線材の開発

The iron-based superconductors of K-doped Ba(Sr)Fe2As2(Ba(Sr)-122) are most potentially useful for high-field applications as a result of their high upper critical fields of over 50T and their small anisotropies. For Ba(Sr)-122, a powder-intube(PIT) method using an Ag sheath has been developed for tape and wire fabrications. Two important factors that greatly influence the transport Jc of PIT Ba(Sr)-122 tape are the density and c-axis grain orientation of the Ba(Sr)-122 core. The Jc of our PIT Ba-122/Ag tapes approach 4×104 A/cm2 at 4.2 K and 10 T for flat-rolled thin tapes. Alloying Ag with Sn is effective for improving the density and grain orientation of the Ba-122 core, and hence the Jc values. The application of uniaxial pressing in the final stage of deformation significantly enhanced Jc values up to ~7×104 A/cm2. This is also due to improving the density and grain orientation of the Ba-122 core. Another effective method to increase the density and grain orientation is double sheathing with an Ag or Ag-Sn inner sheath and stainless steel (SUS) outer sheath. This double-sheath architecture brings about much improved packing density and c-axis grain orientation in the Ba-122 core. The flat-rolled SUS/(Ag-Sn) sheathed Ba-122 tapes show Jc values of 1×105 A/cm2 at 4.2 K and 10 T with high homogeneity. The application of uniaxial pressing to this doublesheathed tape further increased Jc up to 1.4×105 A/cm2. The Jc values of both rolled and pressed Ba-122 tapes show extremely small magnetic field dependence up to 28 T, indicating that Ba-122 is a promising candidate as a conductor for high-field magnets.

Design, Fabrication, and Test of an HTS Magnetic Suspension Experimental System

Aiming at a number of disadvantages in the current normal-conductive electromagnetic suspension (EMS) system, particularly considerable energy consumption and high precision requirement for rail processing, this paper compared three types of suspension schemes, taking advantage of superconducting wire, i.e., electrodynamic suspension, hybrid suspension (HTS+EMS), and HTS EMS. An HTS magnetic suspension experimental system was designed and built on the basis of Bi-2223/Ag tape. A few of the concerns with respect to the HTS coils were discussed, including insulation, stabilization, current leads, fixation, and cooling condition. The 3-D simulation of electromagnetic field based on finite element analysis was executed to validate the theoretical design and parameter calculation of the HTS suspension electromagnet. In addition, some other major components of the experimental system were briefly introduced, i.e., sensors, digital signal processing control circuit, power amplifier, suspension program, and measuring instruments. In contrast to the previous preliminary test, a significant progress was that a superconducting and steady state of dynamic suspension had been successfully achieved when the experimental system was suffering from a larger alternating current in real-time control operation. The results of the suspension test would be of great reference value for the practical maglev train making use of the HTS EMS in the future.

Influences of Pb content on the critical current of Bi-2223 multi-filamentary tapes

Multifilament Bi-2223/Ag tapes with different Pb contents in precursor powders were fabricated by powder in tube (PIT) method. The influence of Pb contents on the phase formation, microstructure and critical current density of Bi-2223/Ag tapes were systematically investigated. X-ray photoelectron spectroscopy (XPS) demonstrated that the content and oxidation states change of Pb ions can influence the carrier concentration of superconducting phase. Scanning electron microscopy (SEM) revealed that the variation of Pb content can lead to the difference in microstructure due to the change of thermodynamic properties. The results showed that with the Pb content of x=0.35 in the nominal composition of Bi2−xPbxSr2Ca2Cu3Oy, proper content of liquid phase can be formed during the sintering process, thus maximum critical current (Ic) was obtained. The correlation between the transport property, carrier concentration and Pb content was discussed.

Transport critical current density of (Bi1.6Pb0.4)Sr2Ca2Cu3O10/Ag superconductor tapes with addition of nanosized CoFe2O4

The effect of nanosized CoFe2O4 (60 nm) addition on the transport critical current density, Jc, of (Bi1.6Pb0.4)Sr2Ca2Cu3O10(CoFe2O4)x (x = 0–0.05 wt%) superconductor prepared by the co-precipitation method was investigated. The optimal Jc (measured using the four-point probe method) was observed in the x = 0.01 wt% pellets. Using this optimal wt%, Ag-sheathed (Bi1.6Pb0.4)Sr2Ca2Cu3O10(CoFe2O4)0.01 superconductor tapes were fabricated using the powder-in-tube method. The tapes were sintered for 50 and 100 h at 845 °C. The phase and microstructure of the samples were determined using the powder X-ray diffraction method and scanning electron microscopy, respectively. The temperature dependence of Jc for the tapes in various applied magnetic fields was also measured. Jc of (Bi1.6Pb0.4)Sr2Ca2Cu3O10(CoFe2O4)0.01/Ag tapes sintered for 100 h was 22,420 A/cm2 at 30 K. The non-added tapes sintered for 100 h showed a much lower Jc (8280 A/cm2 at 30 K). This study showed that addition of CoFe2O4 nanoparticles enhanced the transport critical current density in the (Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor tapes. This result is consistent with the previous calculations on frozen flux superconductor in a nanomagnet–superconductor hybrid system.

Effect of Nanosized NiF2Addition on the Transport Critical Current Density of Ag-Sheathed (Bi1.6Pb0.4)Sr2Ca2Cu3O10Superconductor Tapes

We report the effect of NiF2(10 nm) additions on the transport critical current density,Jcof (Bi1.6Pb0.4)Sr2Ca2Cu3O10/Ag sheathed superconductor tapes. Pellets of (Bi1.6Pb0.4)Sr2Ca2Cu3O10(NiF2)x(x=0–0.05 wt.%) superconductor were prepared using the acetate coprecipitation method. The sample with 0.04 wt.% addition of NiF2exhibited the highestJc. Ag-sheathed (Bi1.6Pb0.4)Sr2Ca2Cu3O10(NiF2)0.04superconductor tapes were fabricated using the powder-in-tube (PIT) method and sintered at 845°C for 50 and 100 h.Jcof nonadded tapes at 30 K sintered for 50 and 100 h was 6370 and 8280 A/cm2, respectively.Jcof (Bi1.6Pb0.4)Sr2Ca2Cu3O10(NiF2)0.04/Ag tape at 30 K sintered for 50 and 100 h was 14390 and 17270 A/cm2, respectively. In magnetic fields (0 to 0.7 T),Jcof the NiF2added tapes was also higher compared with the nonadded tape indicating that NiF2nanoparticles can act as effective flux pinning centers and longer sintering time improved the microstructure. A steeper increase inJcwas observed below 60 K in the NiF2added tapes which coincided with the Neel temperature,TNof nanosized NiF2(60 K). The pronounced enhancement ofJcwas attributed to the strong interaction between flux line network and the antiferromagnetic NiF2belowTN.

High critical current density in textured Ba-122/Ag tapes fabricated by a scalable rolling process

The industrial manufacturing of the long-length iron-pnictide wires and tapes requires simple and low-cost technology. Although the transport critical current density of the FeAs-122 tapes has already achieved the practical application level, their fabrication procedures are relatively complicated or required specialized instruments. Ag-sheathed Ba0.6K0.4Fe2As2 superconducting tapes were fabricated by the scalable rolling process. At 4.2 K and 10 T, the critical current density Jc has achieved 5.4x10^4 A/cm2. We ascribe the excellent performance to the high purity and homogeneity of the superconducting phase, high density and high c-axis texture of the superconducting core. Our method provides a simple way to scale up the production of the long-length iron-based superconducting tapes with high Jc.