• 항공우주기술
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• 제10권2호
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• pp.114-120
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• 2011

인공위성의 효율적인 열제어를 위해 알루미늄으로 만들어진 하니콤 패널과 OSR로 구성된 방열판을 사용한다. 또한 추가적으로 발열량이 많은 부품의 경우, 알루미늄으로 만들어진 더블러와 히트파이프 등을 이용하여 열제어를 수행한다. 최근 위성 전장 부품의 발열량의 증가로 정해진 위성의 크기, 발사 중량 및 비용으로 더 많은 열을 외부로 효율적으로 방출할 수 있는 방열 능력향상에 대한 필요성으로 새로운 열제어 물질에 대한 연구가 진행 중이다. 특히, 탄소 복합재는 일반적으로 열전도가 매우 높고, 가볍고, 기계적 강성에 좋은 특성이 있어 차세대 열제어를 위한 물질로 많은 연구가 진행되고 있다. 본 논문에서는 차세대 탄소 복합재인, APG(Annealed Pyrolytic Graphite)와 탄소-탄소 복합재(carbon-carbon composites)를 이용하여 통신패널의 열제어를 수행하는 경우와 기존의 열제어 방식과의 차이를 수치적으로 비교하였다.

• Journal of Ceramic Processing Research
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• 제19권6호
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• pp.504-508
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• 2018

Diopside is a ceramic material with excellent physical and chemical properties. However, when it is applied as an LED packaging material, heat dissipation of the LED element is not sufficient due to its relatively lower thermal conductivity, which may cause degradation of the LED function. In this study, glass-ceramics based on a $ZrO_2-CaO-MgO-SiO_2$ system, in which diopside is the main crystal phase, were prepared by heat-treating the glass, which was composed of zircon ($ZrO_2-SiO_2$) powders and diopside ($CaO-MgO-2SiO_2$) powders. The possibility of using the glass-ceramics as a packaging material for LEDs was then investigated by analyzing the density, shrinkage, thermal conductivity, and phases generated according to the amount of zircon powder added. The density and shrinkage of specimens decreased slightly and then increased again with the amount of $ZrO_2-SiO_2$ added within a range of 0~0.38 mol. Even though the crystal phase of zircon does not appear in the $ZrO_2-CaO-MgO-SiO_2$ system, the glass containing 0.38 mol zircon powder showed the highest thermal conductivity, 1.85 W/mK, among the specimens fabricated in this study: this value was about 23% higher than that of pure diopside. It was found that the thermal conductivity of the glass-ceramics based on a $ZrO_2-CaO-MgO-SiO_2$ system was closely related to the density, but not to the phase type. Zirconia ($ZrO_2$), a component oxide of zircon, plays an important role in increasing the density of the specimen. Furthermore the thermal conductivity of glass-ceramics based on a $ZrO_2-CaO-MgO-SiO_2$ system showed a nearly linear relationship with thermal diffusivity.

• 한국결정성장학회지
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• 제30권2호
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• pp.73-77
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• 2020

본 연구에서는 차세대 자동차 레이저 헤드램프 적용을 위하여 분무건조법을 통하여 가넷 구조를 갖는 구형의 YAG : Ce 형광체를 합성하였으며 이를 기반으로 형광체 세라믹을 제조하고 광학적 특성을 분석하였다. 분무건조법 기반으로 합성된 구형의 YAG : Ce 형광체를 이용한 형광체 세라믹의 두께를 100 ㎛, 150 ㎛, 200 ㎛로 조절하여 두께에 따른 광변환 효율, 열 소광, 휘도 및 색온도의 광학적 특성을 비교하였다. 연구 결과, 양자효율 및 광속 값은 두께가 150 ㎛ 일 때, 가장 높게 나타났다. 본 연구 결과는 기존의 액상법을 기반으로 한 YAG : Ce 나노 형광체 제조의 고 비용, 저 수율 등의 문제점을 개선한 방법으로 향 후, 형광체 세라믹 제조에 큰 역할을 할 수 있을 것이라 기대된다.

• 청정기술
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• 제19권3호
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• pp.243-248
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• 2013

열전도성 복합재료는 방열특성이 요구되는 다양한 분야에 응용되고 있다. 그래핀은 우수한 전기전도성, 기계적 특성, 열전도 특성을 가지는 잠재성이 높은 물질이다. 그러나 기존의 그래핀 입자를 사용한 경우에서는 유기용매를 이용하여 분산을 하게 되어 청정생산공정측면에서 이를 개선하는 연구가 필요하다. 본 연구에서는 마이크로플루이딕(microfluidic)으로 균일한 미립자를 제조하는데 있어 계면안정제를 도입하여 수분산을 통한 그래핀 용액을 연속상(water phase)으로 사용하여 표면에 그래핀이 분포된 폴리메틸메타크릴레이트(Poly(methyl methacrylate), PMMA)미립자를 제조하였다. 본 연구의 제조방법은 소량의 그래핀으로 열전도 특성이 향상되어 열전도성 복합재료로 사용이 가능하다.

• 전기전자학회논문지
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• 제26권4호
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• pp.671-680
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• 2022

본 논문에서는 현재 출시되어 있는 전기차의 구동모터 사양을 대부분 포괄하는 200kW급 구동용 모터드라이버를 개발하였다. 고효율ㆍ고전력밀도를 달성하기 위해 기존 전력반도체(Insulated-gate bipolar transistor, IGBT)대신에 차세대 전력반도체(Silicon carbide, SiC)를 적용하였으며 SiC를 최적사용하기 위해 하드웨어에 대한 분석을 통해, 예상되는 효율 및 방열특성을 구하여 최적 설계를 하였다. 전기차 구동모터에 대부분 활용되는 매입형 영구자석 동기모터(Interior permanent-magnet synchronous machine, IPMSM)를 위한 벡터 제어 알고리즘을 DSP를 활용하여 구현하였다. 본 논문에서는 SiC기반 전기차 구동용 모터드라이버 시작품을 설계ㆍ제작하였으며 실험을 통해 성능을 검증하였다.

• 한국분말재료학회지
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• 제23권6호
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• pp.414-419
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• 2016

Much attention has been paid to thermally conductive materials for efficient heat dissipation of electronic devices to maintain their functionality and to support lifetime span. Hexagonal boron nitride (h-BN), which has a high thermal conductivity, is one of the most suitable materials for thermally conductive composites. In this study, we synthesize h-BN nanocrystals by pyrolysis of cost-effective precursors, boric acid, and melamine. Through pyrolysis at $900^{\circ}C$ and subsequent annealing at $1500^{\circ}C$, h-BN nanoparticles with diameters of ~80 nm are synthesized. We demonstrate that the addition of small amounts of Eu-containing salts during the preparation of melamine borate precursors significantly enhanced the crystallinity of h-BN. In particular, addition of Eu assists the growth of h-BN nanoplatelets with diameters up to ~200 nm. Polymer composites containing both spherical $Al_2O_3$ (70 vol%) and Eu-doped h-BN nanoparticles (4 vol%) show an enhanced thermal conductivity (${\lambda}{\sim}1.72W/mK$), which is larger than the thermal conductivity of polymer composites containing spherical $Al_2O_3$ (70 vol%) as the sole fillers (${\lambda}{\sim}1.48W/mK$).

• 조명전기설비학회논문지
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• 제29권4호
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• pp.1-10
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• 2015

The light emitting diodes(LED) package of new structure is proposed to promote the reliability and lifespan by maximize heat dissipation occurred on the chip. We designed and fabricated the LED packages mixing the advantages of chip on board(COB) based on conventional metal printed circuit board(PCB) and the merits of Si sub-mount using base as a substrate. The proposed LED package samples were selected for the superior efficiency of the material through the sealant properties, chip characteristics, and phosphor properties evaluations. Reliability test was conducted the thermal shock test and flux rate according to the usage time at room temperature, high-temperature operation, high-temperature operation, high-temperature storage, low-temperature storage, high-temperature and high-humidity storage. Reliability test result, the average flux rate was maintained at 97.04% for each items. Thus, the Si sub-mount based LED package is expected to be applicable to high power down-light type LED light sources.

• 한국분말재료학회지
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• 제22권5호
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• pp.331-336
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• 2015

We report on the succesful fabrication of ZnO nanorod (NR)-based robust piezoelectric nanogenerators (PNGs) by using Cu foil substrate. The ZnO NRs are successfully grown on the Cu foil substrate by using all solution based method, a two step hydrothermal synthesis. The ZnO NRs are grown along c-axis well with an average diameter of 75~80 nm and length of $1{\sim}1.5{\mu}m$. The ZnO NRs showed abnormal photoluminescence specrta which is attributed from surface plasmon resonance assistant enhancement at specific wavelength. The PNGs on the SUS substrates show typical piezoelectric output performance which showing a frequency dependent voltage enhancement and polarity dependent charging and discharging characteristics. The output voltage range is 0.79~2.28 V with variation of input strain frequency of 1.8~3.9 Hz. The PNG on Cu foil shows reliable output performance even at the operation over 200 times without showing degradation of output voltage. The current output from the PNG is $0.7{\mu}A/cm^2$ which is a typical out-put range from the ZnO NR-based PNGs. These performance enhancement is attributed from the high flexibility, high electrical conductivity and excellent heat dissipation properties of the Cu foil as a substrate.

• 한국지진공학회논문집
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• 제16권6호
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• pp.1-12
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• 2012

The researches related to active control systems utilizing superelastic shape memory alloys (SMA) have been recently conducted to reduce critical damage due to lateral deformation after severe earthquakes. Although Superelastic SMAs undergo considerable inelastic deformation, they can return to original conditions without heat treatment only after stress removal. We can expect the mitigation of residual deformation owing to inherent recentering characteristics when these smart materials are installed at the part where large deformation is likely to occur. Therefore, the primary purpose of this research is to develop concentrically braced frames (CBFs) with superelastic SMA bracing systems and to evaluate the seismic performance of such frame structures. In order to investigate the inter-story drift response of CBF structures, 3- and 6-story buildings were design according to current design specifications, and then nonlinear time-history analyses were performed on numerical 2D frame models. Based on the numerical analysis results, it can be comparatively verified that the CBFs with superelastic SMA bracing systems have more structural advantages in terms of energy dissipation and recentering behavior than those with conventional steel bracing systems.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.159-159
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• 2016

Vertically-aligned carbon nanotubes (VCNT) have attracted much attention due to their unique structural, mechanical and electronic properties, and possess many advantages for a wide range of multifunctional applications such as field emission displays, heat dissipation and potential energy conversion devices. Surface modification of the VCNT plays a fundamental role to meet specific demands for the applications and control their surface property. Recent studies have been focused on the improvement of the electron emission property and the structural modification of CNTs to enable the mass fabrication, since the VCNT considered as an ideal candidate for various field emission applications such as lamps and flat panel display devices, X-ray tubes, vacuum gauges, and microwave amplifiers. Here, we investigate the effect of surface morphology of the VCNT by water vapor exposure and coating materials on field emission property. VCNT with various height were prepared by thermal chemical vapor deposition: short-length around $200{\mu}m$, medium-length around $500{\mu}m$, and long-length around 1 mm. The surface morphology is modified by water vapor exposure by adjusting exposure time and temperature with ranges from 2 to 10 min and from 60 to 120oC, respectively. Thin films of SiO2 and W are coated on the structure-modified VCNT to confirm the effect of coated materials on field emission properties. As a result, the surface morphology of VCNT dramatically changes with increasing temperature and exposure time. Especially, the shorter VCNT change their surface morphology most rapidly. The difference of field emission property depending on the coating materials is discussed from the point of work function and field concentration factor based on Fowler-Nordheim tunneling.