• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.173-176
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• 1999

Crosslinked Decree is an important 7actor to determine dielectric property of crosslinked polyethylene(XLPE) used for the insulation material in Power cables. Recently, though it is necessary to investigate electrical properties according to crosslinked degree as a Part of the whose characterization of cable. it is not examined closely. In this study. crosslinked degree of samples were measured according to temperature and holding time of crosslinking. electrical tree characteristics of these characteristics of these samples were analyzed by crosslinked degree and applied temperature that was chanced from normal temperature to operating temperature of power cables. As a result. when the crosslinked degree was low, dielectric properties were decreased and influence of temperature was increased. but the crosslinked degrees were high, initiation voltages of treeing were increased and dielectric properties were improved. It is proved that the optimum crosslinked degree was one of most important factor for aging time and residual lifetime of Power cable.

• Journal of the Optical Society of Korea
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• 제7권2호
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• pp.84-88
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• 2003

A new method for temperature compensation of fiber Bragg grating (FBG) using hi-metal is proposed and experimentally demonstrated. Bi-metal bends toward the metal of low temperature expansion coefficient as the temperature increases, and this property is utilized to cancel the thermo-optic effect of the fiber. The optimum thickness of the high coefficient metal was empirically found by the trial-and-error method. The temperature sensitivities were 8.1 pm/$^{\circ}C$ and -0.018 pm/$^{\circ}C$ for the uncompensated and compensated FBGs, respectively, which indicates a reduction to a mere 0.22 % of the original sensitivity. No appreciable change in the spectral shape was observed. The packaging technique described in this paper is simple and compact, and it can be used for FBGs in WDM and DWDM communication systems that have stringent requirements on the temperature stability of the components.

• 대한기계학회논문집
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• 제8권2호
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• pp.178-183
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• 1984

본 연구에서는 108개의 아르곤 입자가 Lennard-Jones의 포텐셜함수로 상호작 용하고 있는 고밀도 액체계에 높은 전단율울 작요시켜 외력에 의하여 물성의 변화가 일어나고 있는 비평형상태의 액체가 나타내는 현상을 분자동력학을 이용하여 미시적 인 관점에서 고찰하므로써, 높은 전단하중으로 인하여 윤활유 내부에서 전단응력이 발생하고, 이완되는 과정과 이로 인하여 점성이 저하하는등 비평형상태하의 물성변화 를 예측하는데 도움이 되고자 한다.

• Tribology and Lubricants
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• 제5권1호
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• pp.44-50
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• 1989

High strength steel is similar to carbon steel in its composition. This material is developed originally for special uses such as aerospace and automobile due to its high strength and shock-free property in spite of lightness. But the chemical attraction of high strength steel is serious, which includes comminution of formation, metalization and strengthening. Machining results in built-up edge between this material and the tool. Especially the work hardening behavior results in tool life shortening, which was caused by temperature generation during machining. In this study, cooling system was made in which liquid nitrogen is supplied to circulate in order to make up for these weaknesses. Machining of high strength steels, which is recognized as difficult to machine materials, was conducted after tool is cooled at -195$\circ$C. Experimental results showed that the tool was cooled down rapidly below -195$\circ$C in about 200 seconds. The tool temperature of machining with cooling system was lowered by 60~95$\circ$C than that of machining in room temperature. The hardness of the surface of chip is decreased by machining with cooling system. And the machining using the cooling system made it possible to increase shear angle, to retain smooth surface on chip without built-up-edge and to get a better roughness.

• 한국재료학회지
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• 제19권4호
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• pp.179-185
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• 2009

We fabricated thermally evaporated 30 nm-Ni/(20 nm or 60 nm)a-Si:H/Si films to investigate the energy-saving property of silicides formed by rapid thermal annealing (RTA) at temperatures of $350^{\circ}C$, $450^{\circ}C$, $550^{\circ}C$, and $600^{\circ}C$ for 40 seconds. A transmission electron microscope (TEM) and a high resolution X-ray diffractometer (HRXRD) were used to determine the cross-sectional microstructure and phase changes. A UVVIS-NIR and FT-IR (Fourier transform infrared spectroscopy) were employed for near-IR and middle-IR absorbance. Through TEM and HRXRD analysis, for the nickel silicide formed at low temperatures below $450^{\circ}C$, we confirmed columnar-shaped structures with thicknesses of $20{\sim}30\;nm$ that had ${\delta}-Ni^2Si$ phases. Regarding the nickel silicide formed at high temperatures above $550^{\circ}C$, we confirmed that the nickel silicide had more than 50 nm-thick columnar-shaped structures with a $Ni_{31}Si_{12}$ phase. Through UV-VIS-NIR analysis, nickel silicide showed almost the same absorbance in the near IR region as well as ITO. However, in the middle IR region, the nickel silicides with low temperature showed similar absorbance to those from high temperature silicidation.

• 열처리공학회지
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• 제33권2호
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• pp.65-71
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• 2020

To study the effects of tempering on microstructure and mechanical property of Cu-22 wt.%Sn alloy, tempering was carried out for 30 sec, 1 min, 5 min, 30 min, 3 h, 5 h, and 10 h at 325, 370, 500, and 570℃, which are in the (α+ε), lower (α+δ), higher (α+δ), and (α+γ) region of Cu-Sn phase diagram, respectively. Overall, the hardness value increased and decreased over time at all tempering temperatures, and the time to reach the maximum hardness value beccame shorter as the tempering temperature increases. At the beginning of tempering at each temperature, a portion of the β' phase was decomposed into a fine (α+δ) phase or (α+γ) phase, so that the Cu-22Sn alloy had a high hardness value. However, as the tempering time increases, the hardness value of the alloy decreased due to the growth of the decomposed phases.

• 한국주조공학회지
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• 제28권2호
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• pp.79-84
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• 2008

Metal foam is one of the most interesting materials with various multi-functional properties such as light weight, energy absorption, high stiffness and damping capability. Among them, energy absorption property has keen interests in the field of automotives for passenger protection. Nowadays, researches about pore size and porosity control of the foam are increased to correspond them. However, though energy absorption properties are improved, these results are not cost-effective process. In present research, however, as a part of improving the energy absorption property of metallic foams, 606X aluminum alloy was used for cell wall material which has higher strength than pure aluminum. And its morphological features are characterized. As a results, porosity and pore size are uniformity distribution with increasing foaming temperature in the case of 6061 alloy foams. 6063 alloy foam specimens have opposite tendency because of the influence of alloying element and viscosity of the molten melt.

• 한국초전도ㆍ저온공학회논문지
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• 제16권4호
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• pp.7-16
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• 2014

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes have already been commercialized but still possess some issues in terms of manufacturing cost, anisotropic in-field performance, $I_c$ response to mechanical loads such as delamination, homogeneity of current transport property, and production length. Development on improving its performance properties to meet the needs in practical device applications is underway and simplification of the tape's architecture and manufacturing process are also being considered to enhance the performance-cost ratio. As compared to low temperature superconductors (LTS), high temperature superconductor (HTS) REBCO CC tapes provide a much wider range of operating temperature and a higher critical current density at 4.2 K making it more attractive in magnet and coil applications. The superior properties of the REBCO CC tapes under magnetic field have led to the development of superconducting magnets capable of producing field way above 23.5 T. In order to achieve its optimum performance, the electromechanical properties under different deformation modes and magnetic field should be evaluated for practical device design. This paper gives an overview of the effects of mechanical stress/strain on $I_c$ in HTS CC tapes due to uniaxial tension, bending deformation, transverse load, and including the electrical performance of a CC tape joint which were performed by our group at ANU in the last decade.

• 한국전기전자재료학회논문지
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• 제14권11호
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• pp.904-911
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• 2001

High-density lead zirconate titanate(Pb(Zr$\_$0.53/Ti$\_$0.47/)O$_3$, PZT) ceramics were fabricated by a new milling-precipitation(MP) process improved from the conventional solid state process. This process was progressed by a milling impregnation through mixing ZrO$_2$ and TiO$_2$ powders with lead nitrate(Pb(NO$_3$)$_2$) water solution in zirconia ball media, and then milling precipitation was induced from precipitation of PbC$_2$O$_4$ by adding ammonium of oxalate monohydrate((NH$_4$)$_2$C$_2$O$_4$$.$H$_2$O) as a precipitant. As a result of this process, single-phase perovskite structure was formed at the calcination temperature of 750$\^{C}$ for Pb(Zr$\_$0.53/Ti$\_$0.47/)O$_3$ powders. In addition, the highest density at the sintering temperature of 1100$\^{C}$ was obtained, because of the highly sinterable PZT Powders ground through the re-milling process. Piezoelectric and dielectric properties of sintered sample were improved by MP process.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.253-253
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• 2012

Low temperature SiOx film process has being required for both silicon and oxide (IGZO) based low temperature thin film transistor (TFT) for application of flexible display. In recent decades, from low density and high pressure such as capacitively coupled plasma (CCP) type plasma enhanced chemical vapor deposition (PECVD) to the high density plasma and low pressure such as inductively coupled plasma (ICP) and electron cyclotron resonance (ECR) have been used to researching to obtain high quality silicon oxide (SiOx) thin film at low temperature. However, these plasma deposition devices have limitation of controllability of process condition because process parameters of plasma deposition such as RF power, working pressure and gas ratio influence each other on plasma conditions which non-leanly influence depositing thin film. In compared to these plasma deposition devices, neutral beam assisted chemical vapor deposition (NBaCVD) has advantage of independence of control parameters. The energy of neutral beam (NB) can be controlled independently of other process conditions. In this manner, we obtained NB dependent high crystallized intrinsic and doped silicon thin film at low temperature in our another papers. We examine the properties of the low temperature processed silicon oxide thin films which are fabricated by the NBaCVD. NBaCVD deposition system consists of the internal inductively coupled plasma (ICP) antenna and the reflector. Internal ICP antenna generates high density plasma and reflector generates NB by auger recombination of ions at the surface of metal reflector. During deposition of silicon oxide thin film by using the NBaCVD process with a tungsten reflector, the energetic Neutral Beam (NB) that controlled by the reflector bias believed to help surface reaction. Electrical and structural properties of the silicon oxide are changed by the reflector bias, effectively. We measured the breakdown field and structure property of the Si oxide thin film by analysis of I-V, C-V and FTIR measurement.