• Journal of the Korean Society for Nondestructive Testing
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• v.7 no.2
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• pp.16-26
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• 1988

In the in-service inspections for the steam generator tubing of the nuclear power plants by the Eddy Current Testing, the ECT signals are evaluated by their phase. If oxidized copper sludge is piled up in the secondary side, however, big sludge signals occur in large quantities which originate from copper layers forming in the sludge piles due to the pitting mechanism of the steam generator tubing by $Cu^{2+}$, and modulate the defect signals, causing the difficulty in the defect detection. In this research, sludge specimens were prepared considering the formations of the sludge signal sources and multi-frequency ECT mixing experiments by different choices of the mixing standards were performed. The results were found to be 5 to 30% of the tube wall thickness over-estimated. Experiments using the ring-type mixing standards showed the least errors of all, while those with the mixing standards nearing the sludge conditions brought larger errors as a result of the influence of the interference between the defect and the copper layers.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1660-1662
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• 1996

Superconducting current lead is one of the promising applications of the oxide high-Tc superconductors, because they have the advantage of decreasing heat conduction to low temperature region, comparing with a conventional cooper alloy lead. High critical current density is a key factor for the applications such as current lead. $(Bi,Pb)_{2}Sr_{2}Ca_{2}Cu_{3}O_{x}$ high Tc superconductor hase been investigated in terms of critical current density. Bi-2223 superconducting current lead made by CIP and solid state sintering process. Bi-2223 current lead that heat treated at $836\;^{\circ}C$ for 240 h in 1/13 $PO_2$ had over $500\;A/cm^2$ of critical current density at 77K. We knew that the superconducting properties of tube type current leads were better than rods type of them. And we investigated the relation of Bi-2223 formation and heat treatment condition by XRD and SEM analysis.

• Progress in Superconductivity
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• v.8 no.1
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• pp.119-121
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• 2006

We studied the mechanical and magnetic properties of Y-Ba-Cu-O superconductor with and without resin and Ag impregnation. Bulk YBCO superconductor was manufactured with the top-seeded melt-growth method. Typical sample of 40mm X 20mm X 3mm was made and then 8 holes with 0.5mm diameter were drilled arbitrally. Epoxy resin and $AgNO_3$ were systematically added into the holes to compare the mechanical and magnetic properties of YBCO superconductor before and after reinforcement of resin and Ag. Based on the result of 3 point bending, bending strength increased with increasing amounts of resin and carbon nano-tube. However, it was found that the levitation force decreased after making hole, compared with virgin sample without hole.

• Corrosion Science and Technology
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• v.19 no.2
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• pp.89-99
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• 2020

The inhibition of pitting corrosion failure of copper sprinkler tubes in wet sprinkler systems was studied. First, an apparatus and technology for removing air in the sprinkler tubes by vacuum pumping and then filling the tubes with water were developed. Using this apparatus and technology, three methods for inhibiting the pitting corrosion of the copper sprinkler tubes installed in several apartment complexes were tested. The first one was filling the sprinkler tubes with water bubbled by high-pressure nitrogen gas to reduce the dissolved oxygen concentration to lower than 2 ppm. In the second method, the dissolved oxygen concentration of water was further reduced to lower than 0.01 ppm by sodium sulfite. In the third method, the sprinkler tubes were filled with benzotriazole (BTAH) dissolved in water. The third method was the most effective, reducing the failure frequency of the sprinkler tubes due to pitting corrosion by more than 80%. X-ray photoelectron spectroscopy analyses confirmed that a Cu-BTA layer was well coated on the inside surface of the corrosion pit, protecting it from corrosion. A potentiodynamic polarization test showed that BTAH should be very effective in reducing the corrosion rate of copper in the acidic environment of the corrosion pit.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.82-84
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• 1998

The normal zone propagation velocity and minimum quench energy (MQE) of cable-in-conduit conductors (CICC) has been investigated at the different background magnetic fields and supercritical helium pressures. The sample CICC of 2 m in length was fabricated with triplet NbTi/Cu strands inserting into a round stainless-steel tube. The heat pulse disturbance with duration time about 400 ms was acted on the center region of the CICC to quench the strands. The normal zone propagation velocity increased with operating current of the CICC. The measured velocity with respect to operation current could be fitted with numerical results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.3
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• pp.254-258
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• 2000

Current leads of high $T_{c}$ superconductor were fabricated with Bi excess B $i_{2.2}$/S $r_{1.8}$/C $a_{1}$/C $u_{2}$/ $O_{x}$ composition by rapid cooling method. The dimensions of final samples were fixed 3 mm and 8 mm diameter with 50 mm length each To control uniform density the samples were preformed by CIP(Cold Isostatic Press) process and followed by partial or full melting process after raising up to 90$0^{\circ}C$ for 30min. Plate shaped microstructure was clearly observed adjacent to the Ag tube wall and the size of plate was about 100$\mu$m. However the severe destruction of growth orientation was shown in the inner growth part. critical temperature ( $T_{c}$) was about 53~71K after directional growth while Tc was decreased about 77~80 K before directional growth. After directional growth critical current( $I_{c}$) and critical current density( $J_{c}$) in the specimen of 8 mm diameter at 50 K were about 110 A and 280 A/c $m^2$ respectively.pectively.ely.

• Journal of Sensor Science and Technology
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• v.10 no.1
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• pp.24-32
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• 2001

High temperature platinum resistance thermometers(HTPRTs) were designed and fabricated using a synthetic sapphire single crystal as sensor former, insulation and protection tube, and its characteristics was investigated. Several fixed points measurement showed that the sapphire HTPRTs were satisfied with the ITS-90 criteria as the interpolating thermometer. The temperature-resistance characteristics of HTPRT was fitted to the quadratic relationship in the temperature range from $500^{\circ}C$ to $1500^{\circ}C$. The reproducibility of Cu freezing point realized using the sapphire HTPRT was ${\pm}19.2\;mK$. The insulation resistance of the HTPRT exponentially decreased as temperature increased, and showed to $63\;k{\Omega}({\sim}31.5\;mK)$ at $1500^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.38-38
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• 2010

Ever since the experimental discovery of graphene exfoiliated from the graphite flakes by Geim et at., this area has drawn a lot of attention for its possible application in IT industry. For the growth of graphene, chemical vapor deposition (CVD) has been widely used to fabricate the large area graphene. The lateral size of this graphene can be easily controlled by the size of the metal substrate though the chemical etching to remove this substrate is somewhat troublesome. Another problem which is hard to avoid is the folding at the grain boundary. We will discuss the origin of the folding first and introduce the way to avoid this folding. To solve this problem, we have used the various types of micro-thin metal foils. The precise control of hydro-carbon and the carrier gas results in the formation of the graphene on top of substrate. The thickness of graphene layers can be controlled with the control of gas flow on top of Cu substrate in contrast to the previously reported self-limiting growth $behavior^1$. Uniformity of this graphene layer has been checked by micro-raman spectroscopy and SEM. The size of grain can be enhanced by thermal treatment or use of other metal substrate. The dependence of grain size on the lattice size of the substrate will be discussed. By selecting the shape of substrate, we can grow various types of graphene. We will introduce the micron size graphene tube and its application.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.99-99
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• 2010

최근 집속이온빔을 이용한 미세회로 교정, MEMS 공정 및 이온 도핑 등에 대한 연구개발이 활발히 이루어지고 있다. 기존에 널리 사용되었던 액체 금속 이온 소스의 경우 비교적 큰 angular divergence 및 Ga 이온 소스에 의한 오염이 문제시 되고 있어 이를 대체할 수 있는 가스 이온 소스에 대한 연구를 진행하였다. 본 연구에서 사용된 가스 이온 소스는 2 turn 안테나(1/4 inch Cu tube)가 감긴 반경 4 cm 석영관 내부에 Ar 가스를 주입 후 RF(13.56MHz)-ICP 타입 방전을 이용하였다. 운전 압력은 $10^{-5}\;Torr$ 범위이며 인가된 RF 전력은 최대 150 W이다. 석영관 내 발생된 플라즈마로부터 Ar 이온을 인출하기 위해 2단 인출 전극 구조가 사용되었으며 상단 전극에 고전압이 인가되고 하단 전극이 접지되는 형태이다. 2단 인출 전극의 최대 인출 전압은 10 kV, 상단 및 하단 전극의 구멍 크기는 각각 0.3 mm, 2 mm이다. 이온빔의 퍼짐을 최소화하기 위해 전극 간 공간 내 이온 거동 전산모사를 통해 전극 구조를 설계하였으며 이를 통해 최대 $30\;mA/cm^2$의 이온 전류 밀도 값을 얻을 수 있었다.

• Steel and Composite Structures
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• v.32 no.3
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• pp.411-422
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• 2019

Six shear-critical square tubed steel reinforced concrete (TSRC) columns using the high-strength concrete ($f_{cu,150}=86.6MPa$) were tested under constant axial and lateral cyclic loads. The height-to-depth ratio of the short column specimens was specified as 2.6, and the axial load ratio and the number of shear studs on the steel shape were considered as two main parameters. The shear failure mode of short square TSRC columns was observed from the test. The steel tube with diagonal stiffener plates provided effective confinement to the concrete core, while welding shear studs on the steel section appeared not significantly enhancing the seismic behavior of short square TRSC columns. Specimens with higher axial load ratio showed higher lateral stiffness and shear strength but worse ductility. A modified ACI design method is proposed to calculate the nominal shear strength, which agrees well with the test database containing ten short square TSRC columns with shear failure mode from this study and other related literature.