• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.551-554
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• 2004

Bi-2223 HTS tapes are used widely for application of superconducting power systems. However there are need the properties of high strength and low AC loss. Two kinds of Bi-2223 HTS tapes with different Ag sheath were used to know the effect of sheath alloying for the strength and the resistivity. The workability and reaction degree of superconducting phase at Bi-2223 HTS tapes were investigated. We designed conventional type-Ag/alloy and double sheathed mono filament type-Ag/alloy/alloy in order to increase the strength and resistivity of matrix in Bi-2223 HTS tapes. The effect of axial strain and thermal cycling on the critical current was investigated for the Bi-2223 HTS tapes. Because the workability of double sheath Bi-2223 HTS tape was lower than one sheath Bi-2223 HTS tape, it was need additional softening treatment. Bi-2223 formation reaction was decreased by Ag alloy matrix during sintering process. Two kinds of Bi-2223/Ag tapes with different Ag sheath were used to know the effect of sheath alloying for the tensile strain. Critical current is drastically decreased for Ag/alloy and Ag/alloy/alloy sheathed tapes at tensile strain above 0.24 % and 0.34 %, respectively. This result showed that mechanical strength was increased over than 40 % by introduce double sheath at mono filament stage.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.351-354
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• 2002

In most of electrical applications using Bi-2223/Ag HTS tapes, bending and tension stresses are essentially applied to the tape. Therefore, the critical current of the Bi-2223/Ag tape is degraded by increasing the deformation stress, though brittle superconducting filaments are embedded in the reinforced Ag alloy sheath. It is needed to understand bending and tension properties of HTS tapes at room temperature and cryogen to make superconducting magnet, cable and etc. using Bi-2223/Ag HTS tapes. Actually, bending and tension stress applied to the tapes simultaneously, when winding the tapes on former for applications. In this study, the effect of mechanical deformations, bending and tension, on the critical current of Bi-2223/Ag tape was investigated.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1489-1491
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• 1996

The effect of Ag alloy sheath have been investigated in terns of critical current density and mechanical property. Nevertheless the continuous improvement of critical current density($J_c$) of Ag sheathed Bi2223 oxide superconducting wire processed with powder in tube(PIT) method, poor mechanical strength is still considered to be demerits for power application. In this study, we prepared two kinds of Ag- x wt% Cu alloy and pure Ag sheathed Bi2223 superconducting tapes. The hardness and tensile strength of prepared tapes has been measured. Their mechanical propertes were improved by Ag alloying.

• Progress in Superconductivity
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• 제4권2호
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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.

• 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.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.276-279
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• 2000

When high temperature superconducting tapes is fabricated using the PIT (Powder In Tube) method, the length of HTS tapes is increased more than 500 ${\sim}$ 1,000 times of initial powder packed billet. On mechanical processing, heterogeneous properties between the ceramic superconducting core and Ag/Ag alloy sheath occur the non-uniformity deformation as like sausaging that deteriorate the critical current properties of HTS tapes. In this study, we investigated the workability of Bi-2223/Ag/Ag alloy sheath tapes fabricated by the PIT method involving a number of different mechanical processes, multi drawing and rolling. In order to obtain the high critical current density and high uniformity of Bi-2223/Ag sheath tapes, the influences of powder packing density, drawing die angle and rolling parameters were studied. We found that the roll diameter is an important variable in the rolling process, as critical current of tapes rolled using 250 mm rolls was higher than that using 150 mm rolls.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 초전도 자성체 연구회
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• pp.25-29
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• 2003

Pre-treatment of Bi-2223/Ag tapes has been investigated to improve the superconducting property and grain alignment. However, rolling deformability of Bi-2223/Ag wires was degraded by the breakage of Ag alloy sheath after pre-treatment. Various pre-treatment conditions were tried to prevent the problem of sliver sheath and improve the superconducting property of Bi-2223/Ag tapes. Filament precursor of Bi-2223/Ag tapes was modified to be textured easily during main sintering by the optimum pre-treatment with low oxygen pressure and up to $800^{\circ}C$. Critical current was also increased up to 20% than that of no pre-treated tape.

• 한국전기전자재료학회논문지
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• 제16권7호
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• pp.627-633
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• 2003

The effects of alloying-element additions to Ag sheath on thermal conductivity and mechanical properties of Bi-2223 superconductor tapes have been evaluated. In order to evaluate the effects of sheath alloys and their configuration on the properties of tape, various combinations of Ag and Ag alloys were selected as the inner and outer sheath. Thermal conductivity of the tapes was evaluated by using thermal integral method at 10 ∼120 K. It was observed that the addition of Mg, Sb, and Au to Ag sheath significantly decreased the thermal conductivity at low temperature probably due to the alloying effect. Specifically, the thermal conductivity of AgMg, AgSb, and AgAu at 40 K were 411.4, 142.3, and 109.7 W/(m·K), respectly, 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 thermal conductivities of constituent sheath materials. The mechanical properties of alloy-sheathed tapes were also evaluated. Yield strength and tensile strength were improved but workability decreased for alloy-sheathed 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.

• 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.