• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1071-1077
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• 2000

Recently, several attempts have been made to apply high Tc superconductor bearings of thrust type to flywheel energy storage system (FESS) throughout the world. Radial type superconductor bearings, however, have never been tried to the real FESS. KEPRI has developed its own radial type bearings and is now currently applying them to a FESS designed by KIMM, for the first time. In this paper preliminary test results of bearing performance and dynamic behavior of the flywheel rotor system mounted on them are presented. The dynamic properties, i.e, stiffness and damping, of the superconductor bearings were experimentally estimated using the static loading test as well as the impact test. The test revealed that stiffness value of the present superconductor bearings is about 67,700N/m and the damping value 29Ns/m. It was also found out that these bearings have some levitation drift problems due to excessive vibrations encountered while passing through the critical speeds. With recommend backup bearings to limit the vibration amplitudes of the rotor it is predicted that the flywheel rotor will show stable operations in the design speed range.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.561-561
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• 2012

Graphene, two dimensional single layer of carbon atoms, has tremendous attention due to its superior property such as fast electron mobility, high thermal conductivity and optical transparency, and also found many applications such as field-effect transistors (FET), energy storage and conversion, optoelectronic device, electromechanical resonators and chemical sensors. Several techniques have been developed to form the graphene. Especially chemical vapor deposition (CVD) is a promising process for the large area graphene. For the electrically isolated devices, the graphene should be transfer to insulated substrate from Cu or Ni. However, transferred graphene has serious drawback due to remaining polymeric residue during transfer process which induces the poor device characteristics by impurity scattering and it interrupts the surface functionalization for the sensor application. In this study, we demonstrate the characteristics of solution-gated FET depending on the removal of polymeric residues. The solution-gated FET is operated by the modulation of the channel conductance by applying a gate potential from a reference electrode via the electrolyte, and it can be used as a chemical sensor. The removal process was achieved by several solvents during the transfer of CVD graphene from a copper foil to a substrate and additional annealing process with H2/Ar environments was carried out. We compare the properties of graphene by Raman spectroscopy, atomic force microscopy(AFM), and X-ray Photoelectron Spectroscopy (XPS) measurements. Effects of residual polymeric materials on the device performance of graphene FET will be discussed in detail.

• Bulletin of the Korean Chemical Society
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• 제33권1호
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• pp.243-247
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• 2012

Photocatalysis has been applied to decompose the waste and toxic materials produced in daily life and in the global environment. Pure $TiO_2$ (Zn-$TiO_2$-0) and Zn-doped $TiO_2$ (Zn-$TiO_2$-x, x = 3-10 mol %) samples were synthesized using a novel sol-gel and ammonia-evaporation method. The Zn-doped $TiO_2$ samples showed high photocatalytic activity for the degradation of methylene blue (MB). The physicochemical properties of the samples were investigated using XRD, SEM, ICP, DLS and BET methods. In addition, the most important measurement of photocatalytic ability was investigated by a UV-vis spectrophotometer. The effects of the mol % of zinc ion doping in $TiO_2$ on photocatalytic activity were studied. Among the mol % Zn ions investigated, the Zn-$TiO_2$-9 sample showed the highest photoreactivity. This sample removed 91.4% of the MB after 4 h, while the pure $TiO_2$ only removed 46.4% of the MB.

• 한국세라믹학회지
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• 제52권3호
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• pp.209-214
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• 2015

Silicon nitride films were deposited at $100^{\circ}C$ by using the catalytic chemical vapor deposition technique. The source gas mixing ratio, $R_N=[NH_3]/[SiH_4]$, was varied from 10 to 30, and the hydrogen dilution ratio, $R_H=[H_2]/[SiH_4]$, was varied from 20 to 100. The breakdown field strength reached a maximum value at $R_N=20$ and $R_H=20$, whereas the resistivity decreased in the same sample. The relative permittivity had a positive correlation with the breakdown field strength. The capacitance-voltage threshold curve showed an asymmetric hysteresis loop, which became more squared as $R_H$ increased. The width of the hysteresis window showed a negative correlation with the slope of the transition region, implying that the combined effect of $R_N$ and $R_H$ overides the interface defects while creating charge storage sites in the bulk region.

• 한국전기전자재료학회논문지
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• 제16권8호
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• pp.744-751
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• 2003

Co-Pd alloy thin films prepared by a DC-sputter that have self-organized nano structure(SONS), are promising for high-density information storage media in information era. We prepared the samples by varying Pd contents of 0~8.1 wt% at the substrate temperatures of room temperature (RT) and 200 $^{\circ}C$, respectively Microstructure and Pd contents of the Co$_{1-x}$ Pd$_{x}$ films are probed by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and an energy dispersive spectrometer (EDS). We also investigated the saturation magnetization (Ms), remanence and coercivity of the Co$_{1-x}$ Pd$_{x}$ films. Surface roughness are measured by an atomic force microscope (AFM). We revealed that self-organized nano size Co-enriched phase and Pd-enriched phase existed with Pd contents at the substrate temperatures of RT and 20$0^{\circ}C$ through microstructure characterization. SONS helped to keep the saturation magnetization and enhance the perpendicular anisotropy with Pd contents. Out result implies that we may tune the perpendicular magnetic properties with keeping the saturation magnetization by varying substrate temperatures and Pd contents for high density magnetic recording.rding.

• 한국초전도ㆍ저온공학회논문지
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• 제16권1호
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• pp.32-35
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• 2014

Recently, many researches on the system of superconducting power supply and superconducting magnetic energy storage (SMES) using high temperature superconducting (HTS) tapes has been progressed. Those kinds of superconducting devices use the heater trigger switches that have a control delay problem at moments of heating up and cooling down. One way to reduce the time delay is using a different HTS tape at trigger part. For example, HTS tape having lower critical temperature can reduce time delay of heating up and heating down stage for heater trigger operation. This paper deals with resistances joint with different kinds of HTS tapes which have different properties to verify usefulness of the suggested method. Three kinds of commercial HTS tapes with different specifications are selected as samples and two kinds of solders are used for comparison. Joint is performed with temperature and pressure controllable joint machine and the joint characteristics are analyzed under the repeatable conditions.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.413-417
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• 2018

The $Li_4Ti_5O_{12}$ of anode material for the hybrid capacitor was coated using $CePO_4$, $M_3(PO_4)_2$ (M=Mg, Zn). The capacitance of phosphate coated $Li_4Ti_5O_{12}$ was found to be lower than that of $Li_4Ti_5O_{12}$, whereas the equivalent series resistance was higher than that of $Li_4Ti_5O_{12}$. With an increase in cycle number, the base of cylindrical cell exhibited swelling due to gas generated from the reaction between $Li_4Ti_5O_{12}$ and electrolyte. The swelling cycle number of phosphate coated $Li_4Ti_5O_{12}$ was higher than that of $Li_4Ti_5O_{12}$ due to improvement in electrochemical stability. Based on the results, it is proposed that phosphate coating can be employed as a barrier layer to control the gassing reaction by isolating the $Li_4Ti_5O_{12}$ particle from electrolyte solution.

• 폴리머
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• 제35권3호
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• pp.196-202
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• 2011

비즈페놀 A 에폭시 수지와 폴리옥시프로필렌 디아민 경화제계의 경화 반응속도를 시차주사열량계을 이용하여 승온 및 등온 경화조건에서 조사하였다. 승온실험에서는 Ozawa와 Kissinger법을 이용하여 다양한 가열속도에서 얻어진 발열피크의 이동으로부터 활성화 에너지를 구하였다. 또한 등온실험에서 얻어진 데이터는 자촉매 효과를 고려한 Kamal의 속도모델로 분석하였으며, 그 결과 경화반응 초기의 속도우세 구간에서 실험데이터와 잘 맞았다. 반응 후기의 확산우세 구간에서는 확산효과를 적용하여 경화의 전체과정을 기술하였다. 또한 동역학분석을 이용하여 경화 후 저장 탄성률과 가교점간의 평균분자량을 측정하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.1184-1187
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• 2003

Electrochemical capacitors are becoming attractive energy storage systems particularly for applications involving high power requirements such as hybrid systems consisting of batteries and electrochemical capacitors for electric vehicle propulsion. A new type electric double layer capacitor (EDLC) was constructed by using carbon nanofibers (CNFs) and DAAQ(1,5-diaminoanthraquinone) electrode. Carbonaceous materials are found in variety forms such as graphite, diamond, carbon fibers etc. While all the carbon nanofibers include impurities such as amorphous carbon, nanoparticles, catalytic metals and incompletely grown carbons. We have eliminated of Ni particles and some carbonaceous particles in nitric acid. Nitric acid treated CNFs could be covered with very thin DAAQ oligomer from the results of CV and TG analyses and SEM images. DAAQ oligomer film exhibited a specific capacity as 45-50 Ah/kg in 4M $H_2SO_4$. We established Process Parameters of the technique for the formation of nano-structured materials. Furthermore, improved the capacitive properties of the nano structured CNFs electrodes using controlled solution chemistry. As a result, CNFs coated by DAAQ composite electrode showed relatively good electrochemical behaviors in acidic electrolyte system with respect to specific capacity and scan rate dependency.

• 대한금속재료학회지
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• 제49권12호
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• pp.989-994
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• 2011

Samples with compositions of 80 wt% Mg-14 wt% Ni-6 wt% $Fe_2O_3$ (named $Mg-Ni-Fe_2O_3$), and 78 wt% Mg-14 wt% Ni-6 wt% $Fe_2O_3-2$ wt% CNT (named $Mg-Ni-Fe_2O_3-CNT$ ) were prepared by reactive mechanical grinding. Hydriding and dehydriding properties and effects of CNT addition on the hydriding and dehydriding rates of $Mg-Ni-Fe_2O_3$ were then investigated. Activation of the $Mg-14Ni-6Fe_2O_3$ sample was completed after three hydriding (under 12 bar $H_2$)-dehydriding (under 1.0 bar $H_2$) cycles at 573 K. The addition of CNT to the $Mg-14Ni-6Fe_2O_3$ sample made the activation process unnecessary, with a small decrease in the hydrogen-storage capacity.