• 한국초전도학회:학술대회논문집
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• v.10
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• pp.230-235
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• 2000

The extrusion process for long-length multi-filaments of BSCCO 2223 superconductor tape has been investigated with aids of Finite Element Method and experimental inspection. Since the arrangement of filaments in matrix material has characteristic of rotational symmetry, a 2-dimensional commercial FEM package, DEFORM-2D, was adopted to simulate extrusion process with different variables such as hardness of sheath material, lengths of each filament and arrangement. From the FEM analysis, since the inner filaments move faster than the outer one, distribution of filaments is needed to be optimized. In the case of pure Ag matrix, undesirable non-uniform distribution of filament was obtained due to low hardness of sheath material. Dummy sample(brass (sheath) and talc powder(filament)), however, which has relatively high hardness of sheath material, had been produced with desirable results. Therefore, it is necessary to optimize hardness of sheath material, extrusion temperature and billet design.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.678-682
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• 2004

Generally Bi-2223/Ag tapes have a broad S/N transition region and their sheath is a good electric conductor. In this study, the current distribution between superconductor and metal sheath in HTS tapes were investigated. AC with its peak value above 10 times $I_{c}$ was applied to HTS tapes for around 6 cycles and V-I characteristics were measured. Using the resistance of the sheath and V-I curves, the current distribution between superconductor and metal sheath was calculated. When 150 $A_{p}$ was applied, more than 2/3 of the current flows through superconductor. However, in the case of 304 $A_{p}$, most of the applied current came to flow through the metal sheath at the 6th cycle.e.e.e.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.470-470
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• 2010

Negative ions are generated in fusion edge plasmas, material processing plasmas, ionospheric plasmas. Analytic formulas for the deduction of the absolute density of negative ions was given by using the current-voltage(IV) characteristics of two electric probes at two different pressures [1], and negative ion density has been measured by one electric probe using the current-voltage characteristics of three different pressures [2]. Ratios of ion and electron saturation currents and electron temperatures and sheath areas of different pressures are usually incorporated into two equations with two unknowns for the negative ion density. In the previous publications, the sheath factor(sheath area, sheath density, sheath velocity) and effective masses of background ions with different pressures are qualitatively incorporated for the deduction of negative density. In this presentation, the quantitative and detailed relation of negative ion density with sheath factor and effective masses are going to be given. The effect of these parameters on the change of IV characteristics will be addressed.

• Korean Journal of Materials Research
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• v.23 no.11
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• pp.607-612
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• 2013

A powder in sheath rolling method was applied to the fabrication of a carbon nano tube (CNT) reinforced aluminum composite. A 6061 aluminum alloy tube with outer diameter of 31 mm and wall thickness of 2 mm was used as a sheath material. A mixture of pure aluminum powder and CNTs with a volume content of 5% was filled in the tube by tap filling and then processed to an 85% reduction using multi-pass rolling after heating for 0.5 h at $400^{\circ}C$. The specimen was then further processed at $400^{\circ}C$ by multi-pass hot rolling. The specimen was then annealed for 1 h at various temperatures that ranged from 100 to $500^{\circ}C$. The relative density of the 5vol%CNT/Al composite fabricated using powder in sheath rolling increased with increasing of the rolling reduction, becoming about 97% after hot rolling under 96 % total reduction. The relative density of the composite hardly changed regardless of the increasing of the annealing temperature. The average hardness also had only slight dependence on the annealing temperature. However, the tensile strength of the composite containing the 6061 aluminum sheath decreased and the fracture elongation increased with increasing of the annealing temperature. It is concluded that the powder in sheath rolling method is an effective process for fabrication of CNT reinforced Al matrix composites.

• Journal of the Korean institute of surface engineering
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• v.23 no.1
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• pp.1-7
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• 1990

Ion implantation is a well established superior superior surface modification technique for the improvement of wear resistance, hardenece, hardness, corrosion resistance, biocompaibity, surface friction, as well as for the modification of surface electric conductance. Conventional ion implantaion is a line-of-sight process witch ues the ion beam accelerator techniques. Plasma sheath ion implantation (PSII), as a new technique, is described in this paper. In PSII high voltage pulse is applied to a target material placed directly in a plasma, forming a think ion-matrix sheath around the target. Ions accelerate through the sheath drop and bombard the traget from all sides simultaneosuslyregardless of the target shape. This paper describes the principle of PSII, which has non-line-of sight characteristics, as well as the experimental appratus.

• Proceedings of the KIEE Conference
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• 2002.11a
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• pp.102-105
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• 2002

ADSS(All Dielectirc Self-Supporting) cable installed under high voltage power cable line suffers a variety of environmental influence, rain, wind, snow fall, chemical pollution, salt fog and electrical stress. Its lifetime is required to be at least 20 years with this harsh weathering condition. The electrical stress under high voltage power line gives rise to dry band arcing and tracking, the severest damage, on the outer sheath of cable. Finally tracking might penetrate sheath and cause the break-down of ADSS cable. Tracking resistant sheath material, therefore, should be used to protect the core of ADSS from dry band arcing and to be sure long lifetime. In this work, we discuss various commercial tracking resistant material to investigate the way of track resistance and compare their mechanical, electrical, weathering and tracking properties through serial experiments. We found track resistant material is categorized into two main type : polyethylene with metal hydroxide and polyethylene with reduced carbon black. The Liquid contaminant, Inclined plane Tracking and Erosion test says the time to track of tracking resistant material with metal hydroxide has a little longer time to track in the high applied voltage than that with carbon black, but mechanical and weathering properties were inferior to.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.313-316
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• 1995

In this study, in case the lead sheath of XLPE cable (radius : 15cm, inner conductor radius : 5cm, insulation paper raidius : 6cm, dc voltage : 1MV) is harmed, so that breakdown process by inhomogeneous eletric field is simulated with Finite Element Method. The result of simulation showed that defect of lead sheath layer caused breakdown.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.7
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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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.05a
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• pp.9-19
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• 1999

A clad material is a different type of the typical composites which is composed of two or more materials joined at their interface surface. The advantage of clad material is that the combination of different materials can satisfy both the need of good mechanical properties and the other demand of user such as electrical properties instantaneouly. This paper is concerned with the direct and indirect extrusion process of copper-clad aluminum rod. Extrusion of copper-clad aluminum rod was simulated using a commercially available finite element package of DEFORM. The simulations were performed for copper-clad aluminum rod to predict the distributions of temperature, effective stress, effective strain rate and moan stress for some sheath thicknesses, die exit diameters and die temperatures.