• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.131-133
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• 2003

The effect of axial strain and thermal cycling on the critical current is investigated for the Bi-2223/Ag PIT tapes. The axial strain was applied to the tapes by the U-shape sample holder. Two kinds of Bi-2223/Ag tapes with different Ag sheath are used to know the effect of sheath alloying for the tensile strain. The influence of thermal cycling between room temperature and 77 K on critical current are examined. Critical current is drastically decreased for Ag/alloy and Ag/alloy/alloy sheathed tapes at tensile strain above 0.22％ and 0.3％, respectively.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.5
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• pp.204-210
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• 2005

Alternating current (AC) losses of two Bi-2223 ([Bi, Pb]: Sr: Ca: Cu: O = 2:2:2:3) tapes [(Tape I, un-twist-pitch) and the other with a twist-pitch of 10 mm (Tape II)] were measured and compared. These samples, produced by the powder-in-(Ag) tube (PIT) method, are multi-filamentary. Also, it's produced by non-twist and different twist pitch (8, 10, 13, 30, 50 and 70 mm). The critical current measurement was carried out under the environment in liquid Nitrogen and in zero-field by 4-probe method. Susceptibility measurements were conducted while cooling in a magnetic field. Flux loss measurements were conducted as a function of ramping rate, frequency and field direction. The AC flux loss increases as the twist-pitch of the tapes decreased, in agreement with the Norris Equation. Neutron-diffraction measurements have been carried out investigate the crystal structure, magnetic structures, and magnetic phase transitions in Bi-2223([Bi, Pb]:Sr:Ca:Cu:O)

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.262-267
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• 2000

To tap the possibility of exploiting the precipitates as flux-pinning center in the Bi-2223 superconducting system, as-received Bi-2223/Ag tapes with the starting composition of Bi$_{1.8}$Pb$_{0.4}$Sr$_2$Ca$_{2.2}$Cu$_3$O$_8$ were post-annealed at various temperature, oxygen partial pressure, and annealing time. The 2$^{nd}$ phases in the annealed specimen were analysed with XRD, SEM, TEM, and EDS. The size and the distribution of the precipitates such as (Ca,Sr)$_2$(Pb,Bi)O$_4$ and Bi$_{0.5}$Pb$_3$Sr$_2$Ca$_2$CuO$_{12+{\delta}}$ (3221) in the Bi-2223 matrix was controllable by varying heat-treatment condition without breaking the connectivity of the 2223 grains. The nano-size precipitates within the 2223 grains are conjectured as working as flux-pinning sites, resulting in increased J$_c$ value.

• Progress in Superconductivity
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• v.4 no.2
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• pp.180-183
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• 2003

We evaluated the effect of alloying-element additions to Ag sheath on thermal conductivity of Bi-2223 superconductor tapes. In order to evaluate the effect of sheath alloys and their configuration on the properties of tape, various combinations of Ag and Ag alloys were selected as inner and outer sheath. Thermal conductivity of the tapes was measured by using thermal integral method at 10∼120 K. It is observed that the presence of alloying-elements such as Mg, Sb, and Au in Ag sheath results in decreased thermal conductivity at low temperature. Specifically, the thermal conductivity of AgMg, AgSb, and AgAu at 40 K were 411.4, 142.3, and 109.7 W/(m·K), respectively, which is about 2∼9 times lower than that of Ag (1004.6 W/(m·K)). In addition, the thermal conductivity of alloy-sheathed tape was significantly dependent on their values of constituent sheath materials.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.105-108
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• 2003

Long length of Bi-2223 superconducting wires were fabricated by stacking, drawing process with different precursor owders and different heat-treatment histories. The precursor powders were 2 kinds of Pb content. And a part of the tapes were experienced pre-annealing process which caused tetragonal structure of Bi-2212 phase to orthorhombic structure of it was during drawing process. We confirmed the transformation of Bi-2212 phase from tetragonal structure to orthorhombic structure and reduction of second phases. We designed and made a continuous Ic measurement system for Bi-2223/Ag HTS tape. We could achieve best Ic of 65 A at the Bi-2223/Ag tape using low Pb content of precursor powder and experienced pre-annealing process.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.40-44
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• 2002

Influences of bending strain on the critical current (Ic) were investigated in Bi-2223 superconducting tapes at 77K. The effect of bending mode on the Ic degradation behavior was discussed in viewpoints of test procedure, n-value and damage morphology Especially, in this paper, we reported the Ic behavior in Ag alloy/Bi-2223 multifilamentary superconducting tapes under bending occurred within a width plane of the tape which was called as a hard bending. The Ic degradation under hard bending appeared significantly as compared with that under easy bending. The n-value decreased slightly with the increase in bending strain under the hard bending.

• Progress in Superconductivity and Cryogenics
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• v.3 no.2
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• pp.1-4
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• 2001

For the practical use of a superconducting wire to magnet application, it is important to assess the Young modulus and other mechanical properties of HTS tapes. In order to establish a test method of mechanical properties for oxide composite superconductors. tensile tests of Bi-2223 multi- filamentary tapes were carried out at room temperature, as an activity of the International round robin test proposed by the committee of VAMAS/TWA 16-Subrgroup. The tapes consisting of mutli-filamentary showed a three stage tensile behavior. At the initial stage of the stress-streain curve. The elastic deformation existed in a quite nattrow strain region. But the plastic deformation was observed in a wide strain region due to the platic flow of the Ag alloy matrix. The results of RRT were also reported and discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.25-28
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• 2002

Contact type Ic measurement system is needed to measure Ic continuously for long Bi-2223 tapes. Voltage and current terminals were designed several shapes for 4-probe method Ic measurement. Voltage terminals were made with brass and current terminals were made with Cu. We used 2 kinds of Bi-2223 tapes with different strength. When we measured Ic of Bi-2223 tape with Ag-Mg sheath, The proper weight was 0.3 kg and sharp pin type was better. according to voltage terminal shape and load. In case of Bi-2223 tape with Ag-Mn sheath, the proper terminal weight was 4 kg and sharp pin type was bad. It was possible to make continuous contact type Ic measurement system because We could get proper data - terminal shapes and loads - through these experiments.

• Progress in Superconductivity
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• v.4 no.2
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• pp.176-179
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• 2003

A lot of efforts have been focused on the optimization of PIT parameters for Bi-2223/Ag wire. Bi-2223 superconducting wires with 55 filaments were fabricated by stacking, drawing process. Before rolling process, round wires were pre -annealed at 760 - 820 $^{\circ}C$ and low oxygen partial pressure. We confirmed that pre-annealing step was to transform Bi-2212 orthorhombic structure from Bi-2212 tetragonal structure and to reduce the formation of second phases. However Bi-2223 phases also were formed at higher than 76$0^{\circ}C$ of pre-annealing temperature. The engineering critical current densities (Je) of Bi-22231Ag tapes were sintered at low oxygen partial pressure were higher than t hat of the wires sintered at air. We could achieve 6500 A/${cm}^2$ of Je for the tape that was initially kept at slightly higher temperature than that of normal heat treatment.

• Progress in Superconductivity
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• v.3 no.1
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• pp.130-133
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• 2001

A multifilamentary Bi-2223 HTS tape for superconducting power applications was studied through the fabrication of 250-meter long tapes by the PIT(powder in tube) process. To fabricate continuous long wire, a drawing machine, a two-drum bull block and a rolled tape winding machine were developed. Especially, 250-meter long tapes were heat treated in the shape of pancake coil to reduce the heat affect zone and to achieve the high critical current. Engineering critical current density was improved through both the enhancements of critical current density by control of thermal process and the increase of filling factor by using thin Ag alloy sheath tubes less than 1.5 mm in thickness. We have made successfully 250-meter long 37 filamentary tapes with high filling factor up to 31 % employing the modified drawing and rolling technique. The critical current of 250-meter long tapes with pancake coil type was measured by transport method at self-field up to 250 gauss of center field. The measured values, based on the transport critical current at self-field, $I_{c}$ -B characteristics and magnetic field analysis, are 34 A of I$_{c}$ and 4.0 $kA/\textrm{cm}^2$ of $J_{e}$ at 250 m, 77 K, and 0 T. We also have achieved the 56 A of I$_{c}$ and 7.0 $0 kA/\textrm{cm}^2$ of$ J_{e}$ in short tapes at 77K, self-field, and 1$mutextrm{V}$/cm.