• Korean Journal of Materials Research
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• v.7 no.4
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• pp.287-294
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• 1997

(NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 합금에 Sn,Mo등을 첨가하여 그에 따른 미세구조와 열적안정성 및 자기적 특성 변화를 조사하였다. Sn과 Mo의 첨가는 (NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 합금리본의 큐리온도를 크게 향상시켰으며 자기특성, 특히 보자력을 1KOe이상 증가시켰다. 그리고 이러한 현저한 보자력 증가는 입계형 defect인 disturbed grain boundary defect에 기인하는 것이라 판단되었다. 또한 Sn과 Mo 첨가원소는 irreversible loss를 각각 4%와 6% 감소시켜 리본자석의 열적안정성을 향상시켰다. 이는 Sn과 Mo의 첨가가 보자력을 크게 증가시켰기 때문이다. 한편 (NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 리본자석들의 열저항온도(heat resistance temperature)는 irreversible loss와 직선관계를 이루었다.

• Membrane Journal
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• v.19 no.1
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• pp.63-71
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• 2009

In this study, polysulfone which has excellent mechanical and thermal stability with low cost was used for preparing a non-conducting polymer matrix as a reinforced composite membrane for fuel cell application. The membranes were prepared by phase separation method. Polymer concentration and retention time were controlled to investigate the effects on the membrane morphology. The resaltant membranes showed all sponge-like structure independent of polymer concentration. The mechanical and thermal stability were improved with increasing polymer concentration in contrast to the membrane porosity. As a result, the membranes prepared with the retention time for 2 mins using 20 wt% of polymer solution was suitable for a fuel cell compositite membrane providing optimum properties such as approximately 80% of high porosity, 1.3 MPa of tensile strength, and less than 1% of thermal shrinkage both machine and transverse direction.

• Tunnel and Underground Space
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• v.23 no.2
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• pp.150-159
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• 2013

It is generally well known that the stratification of thermal energy in heat stores can be improved by increasing the aspect ratio (the height-to-width ratio) of the stores. Accordingly, it will be desirable to apply a high aspect ratio so as to demonstrate the good thermal performance of heat stores. However, as the aspect ratio of a store increases, the height of the store become larger compared to its width, which may be unfavorable for the structural stability of the store. Therefore, to determine an optimum aspect ratio of heat stores, a quantitative mechanical stability assessment should be performed in addition to thermal performance evaluations. In the present study, we numerically investigated the mechanical stability of silo-shaped rock caverns for underground thermal energy storage at different aspect ratios. The applied aspect ratios ranged from 1 to 6 and the mechanical stability was examined based on factor of safety using a shear strength reduction method. The results from the present study showed that the factor of safety of rock caverns tended to decrease with the increase in aspect ratio and the stress ratio of the surrounding rock mass was influential to the stability of the caverns. In addition, the numerical results demonstrated that under the same conditions of rock mass properties and aspect ratio, mechanical stability could be improved by the reduction in cavern size (storage volume), which indicates that one can design high-aspect-ratio rock caverns by dividing a single large cavern into multiple small caverns.

• Applied Chemistry for Engineering
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• v.24 no.2
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• pp.144-147
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• 2013

Sweating, which is the excretion of oil on the surface of a solid product containing several kinds of pigments in oil and is also solidified with wax, is a unique phenomenon often observed on the surface of cover make-up or lipstick. The cause of sweating is an imbalanced formula. Many studies have been conducted to decrease the symptoms of sweating in the field of cosmetics. Differential scanning calorimetry (DSC) is a thermo-analytical technique that measures the amount of heat required to increase the temperature of a sample as a function of temperature or time under certain conditions. DSC has been used to determine the thermal properties of oil/wax structures. This study investigates how the thermal characteristics correlate with the sweating symptoms. An oil/wax formulation with an optimal melting point was studied in an attempt to make a stable product by considering the thermal properties that represent minimal structural changes with temperature variation. In addition, the sweating of the oil/wax formulation was observed over a various temperature range. As a result, it was found that sweating was minimized when the structure remained static or little bit changed over a variety of temperatures.

• Journal of the Korean Magnetics Society
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• v.14 no.4
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• pp.127-130
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• 2004

Magnetic properties and thermal stability by exchange biased perpendicular magnetic anisotropy in (Pd/Co)$_{N}$FeMn multilayer deposited by do magnetron sputtering system are investigated. We measured the perpendicular magnetization curves of (Pd(0.8nm)/Co(0.8nm)$_{5}$FeMn multilayer as function of FeMn thickness and annealing temperature. As FeMn thickness increases from 0 to 21nm, the perpendicular exchange bias(Hex) obtained 127 Oe at FeMn thickness 15nm. As the annealing temperature increases to 24$0^{\circ}C$, the E$_{ex}$ increased from 115 Oe to 190 Oe and disappeared exchange biased perpendicular magnetic anisotropy effect at 33$0^{\circ}C$.

• Proceedings of the Korean Fiber Society Conference
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• 2001.10a
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• pp.37-40
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• 2001

Aromatic polyimides는 다른 고분자 재료에 비해 고온에서의 열 안정성 및 기계적 물성, 내화학성, 전기 절연성, 난연성 등이 매우 탁월하기 때문에, 최근 들어서 고성능 구조재료, 전자재료(microelectronics devices, electrical insulators of semiconduntor packages), 내열성 접착제, 코팅제 등 그 응용 범위가 점차 확대되고 있는 추세이다. (중략)

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.403-408
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• 2000

The Al-Cr-Zr composite metal powders were prepared by mechanical alloying and consolidated by vacuum hot pressing. The microstructural characteristics and the thermal stability of the MA Al-Cr-Zr alloys were evaluated by means of microhardness measurement, XRD and TEM in order to develop high temperature, high strength aluminum alloys. The mechanical alloying was conducted in attritor with 300rpm for 20 hours. The density of the vacuum hot pressed Al-Cr-Zr alloy reached at 97% of theoretical one. After exposing at $300^{\circ}C$ for 100 hours, there is almost no variation in hardness change of the MA alloys. Even after exposing at $ 500^{\circ}C$ for 100 hours, the hardness of the alloy was decreased within 6% of the initial value. The fine stable $Al_3Zr\;and\; Al_{13}Cr_2$ intermetallics were formed at the stage of consolidation and heat treatment in aluminum matrix. The good thermal stability of the MA Al-Cr-Zr alloy can ab attributed to the role of the dispersoids, inhibiting grain growth of nanocrystalline, and the final grain size after heat treatment was less than 150nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.130-130
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• 2010

고출력 레이저 다이오드는 광 디스크, 고체 레이저 여기, 광섬유 증폭기, 레이저 프린터, 위성 간 통신 등의 여러분야에 응용되고 있고. 고효율, 저가격, 초소형등과 같은 장점으로 수요가 점점 증가하고 있다. 최근 레이저 다이오드의 광출력 향상 및 열적 안성성를 위해 양자점(Quantum Dot) 응용에 대해 많은 연구가 진행되고 있다. 양자점 기반 레이저 다이오드는 전자가 3차원으로 구속되어 있어 열적 안정성이 우수할 뿐만 아니라 낮은 문턱전류밀도로 인해 열 발생이 적어 광출력 감소 현상을 지연시킬 수 있다. 또한 발광면에서의 재결합 확률이 낮아 표면재결합에 의한 신뢰성 열화 문제를 해결할 수 있어 고신뢰성의 레이저 다이오드를 개발할 수 있다. 고출럭 808 nm 양자점 레이저 다이오드 개발을 위해서는 레이저 다이오드의 활성 영역인 양자점 구조에 대한 연구가 필수적이다. 본 연구에서는 최적화된 고출력 808 nm 양자점 레이저 다이오드 에피 성장을 위해 에피 구조에 대한 2D 시뮬레이션을 수행하였고, 양자점 밀도 및 에피층 변화에 따른 최적 양자점 구조에 대한 연구를 수행하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.176-176
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• 2012

본 연구는 GaN 기반의 전자소자의 표면 패시베이션 방법으로 열산화 공정을 이용한 알루미늄산화막 패시베이션 공정에 대하여 연구하였다. 결정질의 알루미늄산화물은 경도가 크고 화학적으로 안정적이기 때문에 외부 오염에 대한 소자 표면을 효과적으로 보호할 수 있으며, 열적안정성이 뛰어나 공정중 또는 공정 후의 고온 환경에서의 열 손상이 적은 장점을 가진다. 결정질 알루미늄산화막($Al_2O_3$)을 소자 표면에 형성하기 위해서 일반적으로 TMA (trimethlyaluminium)와 오존($O_3$)가스를 이용한 ALD 공정법이 사용되고 있으나 공정 비용이 비싸고 열산화막에 비해 전자 trapping이 많이 발생하여 전자이동도가 저하되는 단점이 있어, 본 연구에서는 열산화 공정을 이용하여 소자의 전기적 특성 저하를 발생시키지 않는 알루미늄산화막 패시베이션을 수행하였다. 실험에 사용된 기판은 AlGaN/GaN 이종접합 구조가 증착된 HEMT 제작용 기판을 사용하였으며 TLM 구조를 제작하여 소자의 채널 면저항 및 절연영역간 누설전류 특성을 확인하였다. TLM 구조가 제작된 샘플 위에 알루미늄을 100 ${\AA}$ 두께로 소자위에 증착하고 $O_2$ 분위기에서 약 $525{\sim}675^{\circ}C$ 온도로 3분간 열처리하여 알루미늄 산화막을 형성한 후 $950^{\circ}C$ 온도로 $N_2$ 분위기에서 30초간 안정화열처리 하여 안정한 알루미늄 산화막 패시베이션을 형성하였다. 알루미늄산화막 패시베이션 후 소자의 절연영역 사이의 누설전류는 패시베이션 전과 비슷한 크기를 나타냈고 패시베이션 후 채널의 면저항이 패시베이션 전에 비해 약 20% 감소한 것을 확인하였다. 또한 패시베이션된 소자와 패시베이션되지않은 소자에 대해 $900^{\circ}C$ 온도로 30초간 열처리한 결과 패시베이션 되지 않은 소자는 74%만큼 채널 면저항이 증가하였으며, 절연영역 누설전류가 다섯오더 크기로 증가한 반면 알루미늄산화막 패시베이션한 소자는 단지 13%의 채널 면저항의 증가를 나타내었고 절연영역 누설전류는 100배 감소한 값을 보여 알루미늄산화막 패시베이션이 소자의 열적 안정성을 향상시키는 것을 확인하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.99-104
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• 2005

The major role of a spacecraft structure is to keep and support the spacecraft safely in all the launch environment, on-orbit condition and during ground-transportation and handling. In a satellite development, a structural and thermal model (STM) is developed for two goals ; demonstration of a structural and a thermal stability. In the structure point of view, STM is used to verify the static/dynamic characteristics of structure in the initial stage of development. In this paper, the structure design/analysis of high resolution LEO earth observation satellite STM is described. Also, a low level sine vibration test is performed and compared to the results of finite element analysis.