• 한국안전학회지
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• 제19권4호
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• pp.141-149
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• 2004

가솔린 엔진을 장착한 자동차는 고전압발생장치인 점화코일을 이용하여 고전압을 발생 연소실 내의 혼합기를 점화 및 연소시킴으로써 동력을 얻고 엔진을 구동하게 된다. 점화코일은 1차측 낮은 전압을 스위칭 작용으로 2차측 높은 전압을 발생시키고, 이를 전극으로 보내는데, 점화코일에 작은 결함이 발생하게 되면 제 성능을 발휘하지 못한다. 본 연구에서는 현재 사용하고 있는 에폭시 성형 점화코일과 절연재료인 에폭시수지를 시료로 선택하여 시료에 전압이 인가될 때 발생하는 부분방전 특성을 측정하여 전압변화에 따른 위상각, 방전전하량 및 발생빈도 수 등의 분포를 연구하고 검토한 결과를 실제 자동차점화장치에 접목시켜 점화코일의 성능향상과 전기장치의 신뢰성 확보에 기여하고자 한다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 추계학술대회
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• pp.478-481
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• 1997

A technique or the preparation of porous polyurethane vascular prostheses was investigated. Small-diameter vessels are not in general clinical use due to their limited long-term biocompatibility and low patency rates in experimental trial. These limits are mainly due to the failure of mechanical unction of the vascular grafts. This failure has been suggested to result partially from compliance mismatch. The long-term patency is considered to depend critically on the properties of the material and the fabrication process of the graft. So the control of pores is very important and main points to develop a available vascular grafts. Two-kind polymer sheets was compared. One was the porous PU-sheet made at room temperature by the solvent/non-solvent exchange. And the other was the porous PU-sheet which was fabricated by thermal phase transition and solvent-/non-solvent exchange using the thermal controller. The polymer sheets had a uniform pore size and pore occupation. According to the result of the above experiments, polyurethane solution was injected into a mold designed or U-type tube. The average pore size and pore occupation were easily changed by changing polyurethane concentration, freezing temperature, and methods. This technique can give a proper pore size ($10{\sim}45\;{\mu}m$) or tissue in growth, and suitable compliances or matching with arteries and veins. Besides, the fabrication of more complicated shaped vessels such as the U-type vascular grafts is easily controlled by using the fixed mold. this method might give a desired compliant graft or artificial implantation with the presently valid medical polymers.

• 한국분말재료학회지
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• 제24권6호
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• pp.437-443
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• 2017

SiC-based composite materials with light weight, high durability, and high-temperature stability have been actively studied for use in aerospace and defense applications. Moreover, environmental barrier coating (EBC) technologies using oxide-based ceramic materials have been studied to prevent chemical deterioration at a high temperature of $1300^{\circ}C$ or higher. In this study, an ytterbium silicate material, which has recently been actively studied as an environmental barrier coating because of its high-temperature chemical stability, is fabricated on a sintered SiC substrate. $Yb_2O_3$ and $SiO_2$ are used as the raw starting materials to form ytterbium disilicate ($Yb_2Si_2O_7$). Suspension plasma spraying is applied as the coating method. The effect of the mixing method on the particle size and distribution, which affect the coating formation behavior, is investigated using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. It is found that the originally designed compounds are not effectively formed because of the refinement and vaporization of the raw material particles, i.e., $SiO_2$, and the formation of a porous coating structure. By changing the coating parameters such as the deposition distance, it is found that a denser coating structure can be formed at a closer deposition distance.

• 대한기계학회논문집B
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• 제38권8호
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• pp.695-700
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• 2014

본 논문에서는 수정된 증발법을 이용하여 제작된 주석(Sn) 나노입자의 녹는점 강하 특성에 대한 연구를 진행하였다. 이를 위해 대량생산이 가능한 수정된 증발법을 이용하여 10nm 급 주석 나노입자를 제조하였다. 주석 나노입자 표면의 산화 방지를 위하여 Benzyl Alcohol 을 기본유체로 사용하였으며, 제작된 주석 나노입자의 형상과 입자크기를 알아보기 위하여 투과전자현미경(TEM)을 사용하였다. 제작된 나노입자의 녹는점은 시차주사열량계(DSC)를 통해 측정하였으며, 광전자분광분석기(XPS)를 사용하여 제작된 주석 나노입자의 성분 분석을 진행 하였다. 주석 나노입자의 녹는점은 주석의 녹는점인 $232^{\circ}C$보다 44% 감소한 $129^{\circ}C$로 측정되었다. 녹는점 측정 결과는 Gibbs-Thomson 식 및 Lai 의 식과 비교하였으며, 그 결과 Lai의 식이 실험결과를 잘 예측함을 확인할 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.342-343
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• 2013

AlSb is a promising material for optical devices, particularly for high-frequency and nonlinear-optical applications. And AlSb offers significant potential for devices such as quantum-well lasers, laser diodes, and heterojunction bipolar transistors. In this work we study molecular beam epitaxy (MBE) growth of an unstrained AISb film on a GaAs substrate and identify the real-time monitoring capabilities of in situ spectroscopic ellipsometry (SE). The samples were fabricated on semi-insulating (0 0 1) GaAs substrates using MBE system. A rotating sample stage ensured uniform film growth. The substrate was first heated to $620^{\circ}C$ under As2 to remove surface oxides. A GaAs buffer layer approximately 200 nm- thick was then grown at $580^{\circ}C$. During the temperature changing process from $580^{\circ}C$ to $530^{\circ}C$, As2 flux is maintained with the shutter for Ga being closed and the reflection high-energy electron diffraction (RHEED) pattern remaining at ($2{\times}4$). Upon reaching the preset temperature of $530^{\circ}C$, As shutter was promptly closed with Sb shutter open, resulting in the change of RHEED pattern from ($2{\times}4$) to ($1{\times}3$). This was followed by the growth of AlSb while using a rotating-compensator SE with a charge-coupled-device (CCD) detector to obtain real-time SE spectra from 0.74 to 6.48 eV. Fig. 1 shows the real time measured SE spectra of AlSb on GaAs in growth process. In the Fig. 1 (a), a change of ellipsometric parameter ${\Delta}$ is observed. The ${\Delta}$ is the parameter which contains thickness information of the sample, and it changes in a periodic from 0 to 180o with growth. The significant change of ${\Delta}$ at~0.4 min means that the growth of AlSb on GaAs has been started. Fig. 1b shows the changes of dielectric function with time over the range 0.74~6.48 eV. These changes mean phase transition from pseudodielectric function of GaAs to AlSb at~0.44 min. Fig. 2 shows the observed RHEED patterns in the growth process. The observed RHEED pattern of GaAs is ($2{\times}4$), and the pattern changes into ($1{\times}3$) with starting the growth of AlSb. This means that the RHEED pattern is in agreement with the result of SE measurements. These data show the importance and sensitivity of SE for real-time monitoring for materials growth by MBE. We performed the real-time monitoring of AlSb growth by using SE measurements, and it is good agreement with the results of RHEED pattern. This fact proves the importance and the sensitivity of SE technique for the real-time monitoring of film growth by using ellipsometry. We believe that these results will be useful in a number of contexts including more accurate optical properties for high speed device engineering.

• 에너지공학
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• 제16권4호
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• pp.170-180
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• 2007

본 연구에서는 증기개질 방식으로 천연가스와 납사를 연료로 하여 수소를 생산하는 국내 분산형 수소충전소의 규모의 경제성 문제를 다루었다. 분산형 수소충전소의 수소 생산규모는 $30\;Nm^3/hr,\;100\;Nm^3/hr,\;300\;Nm^3/hr$ 등을 분석대상으로 하였다. 분산형 수소충전소의 초기투자비 및 연간운영비, 수소 판매가격 등을 주요변수로 하는 전통적인 경제성 분석모형을 수립하였으며 수소 판매가격과 할인율을 대상으로 민감도 분석을 수행하였다. 천연가스를 원료로 하는 수소충전소의 수소가격은 $30\;Nm^3/hr,\;100\;Nm^3/hr,\;300\;Nm^3/hr$ 등의 생산규모에 대하여 각기 18,472원/kg, 10,686원/kg, 7,758원/kg이며, 천연가스 대신에 납사를 사용하여도 거의 비슷한 수소 가격을 갖는 것으로 추정되었다. 현 시점에서 $300\;Nm^3/hr$ 이하의 수소충전소는 경제성이 부족한 것으로 나타났으며, 이러한 경제성 분석결과는 향후에 분산형 수소충전소를 건설할 때 중대형 생산규모 이상의 수소충전소를 중심으로 보급하는 것이 바람직한 방안인 것을 시사하고 있다.