• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.677-677
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• 2013

최근 석유에너지의 고갈과 휴대용 전자기기의 사용의 증가로 고효율의 배터리의 개발이 요구되고 있다. 생체칩에서 부터 전기자동차, 에너지 저장체까지 광범위한 산업군에 걸처 배터리의 개발이 되고 있어 시장규모의 계속적인 성장이 있을 것으로 전망하고 있다. 현재 상용되고 있는 음극 재료는 카본재료(이론 용량 372 mAh/g)이다. 이 카본재료의 특징은 값이 싸고, 표준 환원전위가 낮아 비교적 높은 전압을 낼 수 있다. 그러나 낮은 에너지밀도를 갖으므로 높은 에너지를 필요로 하는 차세대 산업군인 전기자동차 등에는 적합하지 않은 것으로 평가되고 있다. 그래서 더 높은 에너지 밀도를 갖는 다른 재료들에 대한 연구들이 활발히 이루어지고 있다. 본 연구에서는 음극 재료로서 주석을 선택해서 연구를 하였다. 카본계열의 음극재료의 질량당 이론 에너지 밀도는 372 mAh/g임에 반해 주석같은 경우는 약 991 mAh/g 정도의 비교적 큰 이론용량을 갖고 있다. 하지만, 주석 등 금속, 혹은 금속 합금을 음극재료로 사용할 경우 많은 양의 리튬이 삽입/탈착되면서 약 300% 이상의 부피변화가 있게 된다. 그러한 과정에서 주석이 분쇄되어 떨어지거나 전자를 제공받는 집전체로부터 떨어지게 되고, 이 과정에서 심각한 에너지 밀도의 손실이 일어나게 된다. 이러한 문제점들을 극복하기 위해 다음과 같은 구조들을 고안하여 도금 공정을 사용하여 음극재료를 제작하여 실험을 진행하게 되었다. 도금법은 대면적을 싼 가격으로 할 수 있으며 원하는 두께 및 모폴로지까지 쉽게 조절할 수 있다. 부피팽창에 의한 스트레스를 최소화하기 위해 도금법을 사용하여 나노구조를 만들어 그에 따른 전기화학적 특성 변화를 측정하였다. 다공성 필름인 AAO 디스크의 한 면에 구리를 sputtering 공정을 사용하여 0.5 um 두께의 seed layer 구리 박막을 형성하고 형성된 구리 박막 위에 도금공정을 이용하여 두껍게 구리를 증착함으로 구리 음극 집전체를 형성한다. 그 후 AAO 구조 안에 주석을 도금하면 AAO의 구조를 따라 주석 나노와이어가 형성이 된다. 마지막으로 NaOH로 AAO를 제거해주면 직경 200 nm, 길이 2 um 정도의 주석 나노와이어를 구리 집전체위에 만들 수 있었다. 배터리의 용량을 측정한 결과 안정한 싸이클 특성과 약 400 mAh/g의 에너지 밀도를 갖는 것으로 나타났다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.1
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• pp.29-36
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• 2014

Hybrid rocket displays many different low frequency pressure oscillations during combustion. Thermal lag between solid and gas phase is the primary mechanism to trigger low frequency pressure oscillations of around 10Hz, and Helmholtz or $L^*$ mode also produces other types of low frequency oscillations above 10 Hz which is associated with the change in combustion volume. Since the flow characteristics in hybrid rocket is very similar to those in solid rocket combustion, it is not surprising to observe similar pressure oscillation behaviors. Experimental test shows that combustion pressure suddenly turns into to a big amplitude oscillation around 10Hz then followed by returning to an original pressure level after a short period combustion. Further investigations show that this instability is independent of the change in O/F ratio at all. One of the possible candidates is the vortex shedding dynamics over the backward step in the post combustion chamber. It is required to investigate the low frequency oscillation mechanism in the future study.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.809-812
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• 2008

Bleed test methods currently being specified in KS, ASTM and BS are the methods to read the height of bleed water and volume changes of mortar poured into transparent cylinder. Time for measuring of bleed are specified as 3, 20 hours in KS specification, while bleed is measured at 3 hour and change of volume is measured at 24 hour in ASTM and BS specification. Like these, bleed test takes a lot of time to conduct. Another method to measure the bleed is the pressure filter test. This method predict the bleed by measuring the passed water through the fiber glass filter under pressure. This pressure filter test developed by Schupack in 1971 has an advantage in predicting the bleed in shorter time. However, data correlating the pressure filter test results with amount of bleed are limited. Therefore, this study aims at verifying the availability of pressure filter test as a method to predict the bleed and deriving the relation between this test results and bleed.

• Polymer(Korea)
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• v.36 no.4
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• pp.455-460
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• 2012

Poly(N-isopropylacrylamide) (PNIPAM) hydrogel has been studied as an important drug delivery system due to its volume transition or temperature-responsive swelling properties, whose phase separation temperature is similar to the body temperature. However, because of hydrophilic PNIPAM, hydrophobic drugs are difficult to be uniformly loaded in the networks. Antioxidant alpha-lipoic acid (LA) can be prepared as a polymer(polylipoic acid, PLA) by ring opening polymerization, which is hardly developed as a material due to its low molecular weight and easy depolymerization. To overcome this limitation, a hydrophobic active ingredient, LA was reacted with NIPAM into stable hydrogels. Simple thermal radical reaction successfully resulted in a hydrogel (PNIPAM/PLA), which was confirmed by DSC, FTIR, and Raman spectroscopy. The PNIPAM/PLA showed temperature-responsive properties, and their volume swelling decreased with an increase in lipoic acid content. These hydrogels can carry hydrophobic drugs with PNIPAM and the hydrogels could be useful as final drug delivery systems having lipoic acid as an antioxidant.

• Journal of the Korean GEO-environmental Society
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• v.11 no.12
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• pp.5-11
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• 2010

If the groundwater in rock joint is changed into ice, it induces the stress increment by volume increase. Also, if the ice is changed into groundwater again, the stress in joint decreases by volume decrease. The accumulated displacement and fatigues of joints are increased by the stress-hysterisis, induced from the continuous frost-thawing. Also the shear strength is decreased by them continuously. The stress-hysterisis is affected by the atmospheric temperature changes, whose behavior is visco-elasticity, usually. Therefore, Kelvin model could be used to analyze the frost-thawing behavior in winter. The measured data of total 5 points are examined, which are composed of 3 points of shallow joints and 2 points of deep joints. Because shallow weathered rocks have many joints, a lot of Kelvin model are connected and the behaviors are complicated. In case of deep joints, simple Kelvin model is applied and the behaviors are also simple.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.4
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• pp.35-45
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• 2002

The stresses of the underfill/chip interface due to thermal loading was studied using the finite element method. At first, the effective properties of underfill for several volume fractions of silica particles were calculated by Mori-Tanaka method for three different material sets, and the parameters of singularity for the bimaterial edge and the bimaterial wedge were calculated. Consequently, the stresses at the underfill/chip interface with volume fraction of silica particles were investigated. Five different geometric models of flip-chip assembly involving two kinds of bimaterial strips and three kinds of three-layer models were considered under the assumption that the underfill is homogeneous. It was assumed that all components of the flip-chip assembly were linear elastic and isotropic, and their properties were temperature independent. The analysis was conducted in the context of the uncoupled plane thermo-elasticity under a plane strain assumption.

• Applied Chemistry for Engineering
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• v.17 no.1
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• pp.82-86
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• 2006

When a domestically manufactured floater is used in a general gasoline or LPG car, or a flowmeter is floated long time in the engine oil under above $150^{\circ}C$, the floater will be swelled or its organization will be slackened because weight and volume will be changed due to the osmosis of fuel. In this study, we conducted a research on a manufacturing technique of a foam-floater with the small changse in weight and volume, oil-resistance, and thermal resistance in the high temperature engine oil. When the prepared floater TROF II-3, where Nitrile Butadiene Rubber (NBR) as basic material of the floater was superseded by Hydrogenated Nitrile Butadiene Rubber (HNBR), was floated for 100 h at the engine oil of high temperature ($150^{\circ}C$), the change rates of the weight and the volume were 2.90%, and 2.56%, respectively. These were less than the NBR (TROF I-3) case, where the change rates of the weight and the volume were 10.81% and 3.08%, respectively, Therefore, TROF II-3 was determined to be suitable as an engine-oil floater in high temperature because the change of weight and volume were small, the appearance, and the specific gravity of floater were maintained uniformly in the high temperature.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.1
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• pp.83-91
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• 2018

While using an electrokinetic method to analyze the characteristics of cement solidification of radioactive wastes from decontaminated uranium soil and concrete, the compressive strength, pH, electrical conductivity, irradiation effects, and volume expansion were measured for the solidified cement specimens. The workability of cement solidified from radioactive waste was about 170-190%. After the solidified cement was irradiated, the compressive strength decreased by about 15%, but met the criteria ($34kgf{\cdot}cm^{-2}$) of KORAD (Korea Radioactive Waste Agent). According to the results of SEM-EDS for solidified cement, the aluminum phase was well combined with cement, while the calcium phase was separated from cement. The volume of solidified cement in radioactive wastes was dependent on the waste-to-cement ratio and the amount of water, and increased by about 30% under the conditions used in this study. Therefore, it was concluded that permanent disposal of electrokinetically decontaminated radioactive wastes is appropriate.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.428-428
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• 2012

CIGS 또는 CIS 태양전지는 높은 흡광계수와 조절가능한 밴드갭 특성으로 인해 높은 광전변환효율을 나타내므로 실리콘 태양전지를 대체할 차세대 태양전지로 주목받고 있다. 그러나 태양전지의 저가화를 위해서는 기존의 동시증발법 또는 스퍼터링을 대신할 수 있는 비진공 방식의 박막제조방법이 요구된다. 다양한 비진공 코팅방법 중에서 용액 또는 콜로이드 전구체를 프린팅하는 방법은 batch 조성이 박막의 조성으로 전사되므로, 전착법에 비해 조성 조절이 용이하다는 장점이 있다. 한편, 콜로이드 공정에 속하는 Cu-In 합금 나노 분말법은 셀렌화 또는 황화 과정 중에 부피가 팽창하는 장점을 활용 가능한 반면, 전구체 박막의 충진밀도가 낮을 경우 열처리를 통한 치밀화에 한계가 생길 수 있는 단점이 있다. 본 연구에서는 합성한 Cu-In합금 분말을 이용하여 전구체 박막을 형성한 후 반응기구가 다른 황 및 셀레늄 분위기에서의 열처리를 통해 소결된 박막의 결정상, 미세구조 및 표면 형상의 차이를 비교하였다.

• Korean Journal of Materials Research
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• v.8 no.1
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• pp.23-26
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• 1998

알루미나와 하소된 귤껍질의 소결반응에 의해 A $I_{2}$ $O_{3}$-CaO내화물이 제조되었다. 치밀화과정에서의 CaO의 영향과 A $I_{2}$ $O_{3}$-CaO 소결체의 특성을 고찰하였다. 소결체의 미세구조와 EDS 결과로 A $I_{2}$ $O_{3}$-CaO화합물을 확인하였다. 145$0^{\circ}C$에서 열처리한 소결체는 2.87/㎤의 부피비중과 12.03%의 겉보기 기공율을 가지며 압축강도는 312kg/$\textrm{cm}^2$이였다. 140$0^{\circ}C$에서 서결체의 열팽창 계수는 6.55Kx10$_{-6}$ $K_{-1}$이였다.