• Progress in Superconductivity
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• 제3권1호
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• pp.91-94
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• 2001

By varying fabricating process, precursor powders with different initial conditions were prepared. Subsequently, Bi-2223/Ag tapes were made through these powders. The effects of precursor powders on the phase evolution and Jr properties of Bi-2223/Ag tapes were studied along with several thermomechanical cycles. Our results showed that the initial conditions of precursor powders could strongly influence the phase formation rate and $J_{c}$ value in final tapes. The factors of precursor powders that influence the phase formation and $J_{c}$ of Bi-2223/Ag tapes must be studied and optimized in combination.ion.

• Progress in Superconductivity
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• 제3권2호
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• pp.247-251
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• 2002

In general, the bubbling, generated during the fabrication of the tapes, breaks the superconducting filament, and critical current of the tapes will be decreased. Heat-treatment schemes of Bi-2223/Ag HTS tapes were modified, such as pre-annealing of multi-stacked billet, 2-step main sintering and ramp rate etc. The generation of bubbling was drastically decreased from 20 bubbles/m to 0 ~ 1 bubble/m by the modified heat-treatment. Therefore, the value of critical current of the tapes without bubbling was increased almost twice higher than that of already existing tapes. Critical current up to 42 A in 40 m length Bi-22231Ag tapes have been measured at 77K, self-field, 1$mutextrm{V}$/cm criterion. It could be confirmed that elimination of bubbling is effective to maintain the superconducting property along the tape length.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.101-104
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• 2003

Influences of transverse compressive stress on the critical current ( $I_{c}$) in AgMg and AgMn alloy sheathed Bi-2223 tapes were investigated at 77 K and 0 T. The $I_{c}$ degradation behavior depending on sample specifications was discussed in viewpoints of n-value and damage morphology. As a result, Bi-2223 tapes showed a significant drop in $I_{c}$ for stresses greater than 50MPa. The AgMg sheathed Bi-2223 tapes representing higher $I_{c}$ showed a lower $\sigma$$_{irr}$ and a significant $I_{c}$ degradation with increase in compressive stress. There existed a voltage tap separation dependency of the $I_{c}$ degradation behavior caused by the transverse compressive stress.sive stress.s.

• Progress in Superconductivity
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• 제5권2호
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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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 초전도 자성체
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• pp.50-54
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• 2002

Influences of bending strain on the critical current ($I_c$) in Ag-sheathed Bi-2223 superconducting tapes at 77K were investigated. The effect of bending mode on the bending strain characteristics was discussed in viewpoints of sample geometry, n-value and damage morphology. Especially, in this paper, we reported the $I_c$ behavior in Ag alloy sheathed Bi-2223 multifilamentary superconducting tapes under hard bending. As a result, $I_c$ degradation behavior of the hard bending appeared remarkably than the case of easy bending, but it did not influence greatly on the n-value.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 초전도 자성체 연구회
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• pp.69-72
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• 2003

Bi-2223 superconducting wires were fabricated by stacking, drawing process with different precursor powders 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. XRD and DC magnetization analysis were performed in order to investigate the fraction of Bi-2223 phase in Bi-2223/Ag HTS tape. We could achieve best Ic of 70 A class at the Bi-2223/Ag tape using low Pb content of precursor powder and experienced pre-annealing process. DC magnetization analysis was useful to investigate the fraction of Bi-2223 phase in the Bi-2223/Ag tape.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.1240-1242
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• 2005

In this study, we estimate the transport current loss of Bi-2223/Ag tapes with non-uniform current distribution. The conductor was consisted of three Bi-2223/Ag tapes and the each tapes were attached in parallel. The loss of conductor was investigated both numerical and experimental methods. The numerical code to predict ac loss was developed, and finite element method was introduced. It contained intrinsic properties of superconducting tape, which was obtained from nonlinear current voltage relation with external magnetic field and its orientation. Two results were compared and discussed. They showed good agreements with each other.

• 한국전기전자재료학회논문지
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• 제14권4호
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• pp.345-350
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• 2001

Normal zone propagaton(NZP) properties were investigated on Bi-223/Ag tapes and prototype HTS cable. NZP experiments in tape were conducted in temperatures from 45K to 77K in zero field. Prototype HTS cable was molded using epoxy and the experiments were carried out under adiabatic condition in LN$_2$. NZP velocities in tapes with tow conditions of DC and AC currents were almost same at each temperature. NZP velocity in prototype HTS cable was 1.9-2.4 cm/sec in LN$_2$. Numerical analysis was carried out by a one-dimensional equation of heat balance. The simulation results of NZP velocity in Bi-2223/Ag tapes were similar to the experimental results.

• 한국재료학회지
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• 제7권2호
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• pp.140-144
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• 1997

은 튜브에 장입되기 전의 초기 분말의 입자 크기가 Ag/Bi-2223초전도 선재의 미세구조와 상전이, 임계 전류 밀도등에 미치는 영향에 대해 고찰하였다. 분말의 입자 크기는 하소 분말을 볼밀을 이용하여 0-48 시간 동안 분쇄하여 조절하였다. 열처리 후 최종 초전도 선재의 전기적 성질은 초기 분말의 입자 크기에 영향을 받는 것으로 나타났으며 분말의 분쇄에 의한 반응성의 증가에 의해 열처리시 2223 상으로의 상전이가 빠르게 일어났고 이차상의 크기와 분율이 감소된 미세구조를 얻을 수 있었다. 그러나 과다한 분쇄에 의한 반응성의 증가에 의해 열처리시 2223상으로의 상전이가 빠르게 일어났고 이차상의 크기와 분율이 감소된 미세구조를 얻을 수 있었다. 그러나 과다한 분쇄는 분말의 비정질화를 유발하여 2223 상으로의 전이를 방해함으로써 선재의 임계 전류 밀도를 감소시키는 결과를 나타내었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.235-238
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• 2000

There have been a lot of studies to improve the characteristic of Bi-2223 tape by PIT method which is considered as one of the best way for applying superconductor. These improved characteristic of Bi-2223 tape is able to be acqured by control of mechanical deformation and heat treatment. In this work, we studied HTS tapes with the sheath(Ag and Ag-alloy)of tapes that affect mechenical strength and critical current, with each two kind of purity(99.9% and 99.999%) and with two kind of tapes(single and double concentric). These charateristics affect Jc of tapes seriously that is the most important factor of superconductor tapes.