• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.11
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• pp.1028-1034
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• 1998

Bi-2223 superconductor is known as one of the candidates for practical superconducting wires. Ag-sheathed Bi-2223 superconducting wires were fabricated using the powder-in-tube(PIT) method. When the 19-filaments wire was immersed in liquid nitrogen(77K), maximum critical current density Jc of 62 A/$mm_2$ at 0T was achieved. The critical current density has been shown to depend on the mechanical properties such as tensile stress and bending strain in Ag-sheathed Bi-2223 superconducting wires. The tensile strain for Jc degradation onset was in the range of 0.12~0.3%. In the case of 19-filaments wire, the bending strain is estimated to be smaller than 0.3% for the reasonable Jc value. The observed degradation of the critical current density due to strain effect is inevitable and can be attributed to the formation of microcracks within the superconducting core.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.220-223
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• 2003

High-Tc superconducting(HT S) systems are commercialized by many study on high-Tc superconductor. For the successful commercialization of superconducting systems using Bi-2223 wires, the database on the degradation of critical current is essentially needed. In this paper, critical current variation of Bi-2223 wires according to the transport time was investigated. The degradation rate of critical current was also calculated. Solenoid type specimens have the length of 190cm Bi-2223 wire and double-pancake type specimens have the length of l0m wire were tested. Tested Bi-2223 wires are commercialized products of AMSC (American Superconductor) and Innost. When the transportation current was 95% of critical current, the degradation of critical current was appeared after 5 hours of transport time.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.831-834
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• 2002

Several companies in the world are marketing superconducting wires, films and bulks. High-Tc superconducting systems using these superconductors are begun to commercialize. For the successful realization or commercialization of superconducting system used Bi-2223 wires, the database on the degradation of critical current is essentially needed. In this paper, the electrical degradation of a Bi-2223 wires is measured. The electrical degradation rate was measured after the certain time of continuous current transportation. Specimens have the length of 190cm and double-pancakes coil have the length of 10m were tested. Tested Bi-2223 wires are commercialized product has 115A of Ic. When the transportation current was 95% of Ie, the degradation of Ic was appeared after 5 hours of transportation time. When the transferred current is enough larger than Ic, Bi-2223 double pancake is damaged seriously.

• 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.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.96-98
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• 2003

Many of research efforts have been focused on the improvement of critical current density Jc of silver-sheathed Bi-2223 tapes for practical applications of material. Bi-2223 superconducting wires with 55 filaments were fabricated by stacking, drawing process with different heat-treatment histories. After rolling process, Bi-2223 tapes were heat-treatment at 780~826$^{\circ}C$ with variable mass flow rate of mixed gas. In this study, the effect of changes in the variable mass flow rate of mixed gas during the heat treatment of Bi-2223/Ag tapes has been investigated. Distinct differences were observed in the Bi-2223 phase and critical current as flow rate of mixed gas. We could achieve proper conditions of mass flow rate of mixed gas for Ag-alloy clad Bi-2223 superconducting tapes.

• Progress in Superconductivity and Cryogenics
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• v.6 no.1
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• pp.1-5
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• 2004

Long length of Bi-2223/Ag superconducting wives were fabricated by stacking and drawing process with advanced heat-treatment schedules. Intermediate annealing was carried out to increase the homogeneity and uniformity of the superconducting filaments embedded in the silver matrix. Phase modification from tetragonal to orthorhombic Bi-2212 by pre heat treatment(PHT) was executed to improve the texture and phase transformation of Bi-2223. Drawing stress was measured to predict the sausaging and stress limit. Rolling Parameters such as thickness. width and winding tension were investigated to roll the tape with uniformity. 1 km length of Bi-2223/Ag superconducting wires were fabricated without any breakage. Critical current (Je) of 270 m length of superconducting tapes was measured over than $70 A/cm^2$ continuously after final sintering.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.527-530
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• 2002

A lot of efforts have been focused on the optimization of PIT parameters for Bi-2223/Ag wire. In this paper, initial annealing of Bi-2223/Ag wire to transform Bi-2212 orthorhombic from Bi-2212 tetragonal Precursor was investigated. This initial annealing step at low oxygen partial pressure were to transform Bi-2212 orthorhombic structure and to reduce the formation of second phases at superconducting wire. However Bi-2223 Phases were appeared at higher annealing temperature. Critical currents(Je) of Bi-2223/Ag tapes were sintered at low oxygen Partial pressure were higher than that of the wires sintered at atmosphere condition. In order to investigate the effect of rolling reduction ratio, Bi-2223/Ag HTS tapes were rolled with different reduction ratio. There were no clear difference of Je and filaments shape with various rolling reduction ratio.

• Progress in Superconductivity
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• v.5 no.2
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• pp.124-127
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• 2004

Many of research efforts have been focused on the improvement of critical current density (Jc) of silver-sheathed Bi-2223 tapes far practical applications. In this study, the transformation of Bi-2212 phase was investigated, which was transformed to orthorhombic from tetragonal through pre-annealing during powder packing and drawing process. The relationship between hardness of Bi-2212 orthorhombic phase and workability of Bi-2223/Ag tape was investigated. Bi-2223 superconducting wires with 55 filaments were fabricated by stacking and drawing process with different heat-treatment histories. Before rolling process, round wires were pre-annealing at 76$0^{\circ}C$ and in a low oxygen partial pressure. We confirmed that pre-annealing step was to transform to Bi-2212 orthorhombic structure from Bi-2212 tetragonal structure and to reduce the formation of second phases. However the breakages were created at Ag-alloy clad during rolling for pre-annealed Bi-22231Ag tapes. Several pre-annealing scenarios were introduced to reduce the breakages during rolling process. Microstructure and critical current density of pre-annealed Bi-2223 superconducting tapes were investigated. We could achieve proper pre-annealing conditions for Ag-alloy clad Bi-2223 superconducting tapes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.488-491
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• 2000

Bi-2223/Ag superconducting wires have been mainly prepared by a powder-in-tube method. The drawing and the rolling are main processes to increase the core density and wire length. In the fabrication of long wire, especially, the drawing should be precisely controlled to assure the filament homogeneity. In this paper, the influences of drawing die angle, bearing length and reduction ratio on the sausaging and the critical current density of the wire are investigated. Single cored and multi-filamentary wires are fabricated by PIT method with different conditions. The core densities and sausaging in the wires are investigated and are discussed regarding their relationship to the I$_{c}$. It was made clear that the geometry of drawing die is sensitively dependent on the sausaging. The improvement of I$_{c}$ was achieved by reducing the die angle and high core density.ity.

• 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.