• 한국결정성장학회지
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• 제21권6호
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• pp.246-252
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• 2011

반도성 $MnSi_{1.73}$ 화합물은 고온 특성이 우수하고 뛰어난 내산화성을 가진 열전재료로서 알려져 있다. 본 연구에서는 순 Mn 및 Si 분말재료를 출발 원료로 기계적 합금화법(MA)을 적용하여 $MnSi_{1.73}$ 화합물 합성을 실시하였다. MA 처리는 P-5 유성형 볼밀장치를 이용하여 Ar 중에서 행하였다. MA 분말재료의 X선 회절, 열분석 및 전자현미경 분석을 통하여 고상반응을 관찰하였다. MA 공정 중 Si의 손실을 고려하여 화학양론 조성에서 Si 양을 증가시켜 $MnSi_{1.73}$ 화합물 합성을 시도하였다. 그 결과 $MnSi_{1.73}$ 화합물 단상은 $MnSi_{1.88}$ 조성의 혼합 분말을 200시간 볼밀 처리함으로써 얻을 수 있었다. 또한 200시간 볼밀 처리에 의하여 제조된 $MnSi_{1.73}$ 화합물의 평균결정립 크기는 40 nm 임을 X 선 회절피크의 Hall plot으로 부터 알 수 있었다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.100-105
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• 2003

25Cr-20Ni series strainless steel have an excellent high temperature strength, high oxidation and high corrosion resistance. However, further improvement can be creep strength by work hardening prior creep. In the present study, the effect of prestraining at room temperature on the creep behavior of a Class M(STS310S) and a Class A(STS310J1TB) alloy containing precipitates have been examined. Prestraining was carried out at room temperature and range of prestrain was $0.5{\sim}2.5$ % at STS310J1TB and $2.0{\sim}7.0$ % at STS310S. Creep behavior and creep rate of pre-strained specimens were compared with that of virgin specimens. Room temperature prestraining produced the creep life that is longer than that of a virgin specimen both for STS310J1TB and STS310S when creep test carried out at the temperature lower than recrystallization temperature. The reason for this improvement of creep life was ascribable to the interaction between dislocations and precipitates in addition to the dislocation-dislocation interaction in STS310J1TB and the dislocation-dislocation interaction in STS310S. The beneficial effect of prestraining in STS310J1TB was larger than that of STS310S.

• 한국수소및신에너지학회논문집
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• 제17권1호
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• pp.62-68
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• 2006

High temperature electrolysis is a promising technology to produce massively hydrogen using renewable and nuclear energy. Solid oxide fuel cell materials are candidates as the components of steam electrolysers. However, the polarization characteristics of the typical electrode materials during the electrolysis have not been intensively investigated. In this study, NiO electrode was deposited on YSZ electrolyte by spin coat process and firing at $1300^{\circ}C$. Pt electrode was applied on the other side of the electrolyte to compare the polarization characteristics with those by NiO during electrolysis. The $H_2$ evolution rate was also monitored by measuring the electromotive force of Lambda probe and calculated by thermodynamic consideration. At low current density, Pt showed lower cathodic polarization and thus higher current efficiency than Ni, but the oxidation of Ni into NiO caused the increase of anodic resistance with increasing current density. High overpotential induced high power consumption to produce hydrogen by electrolysis.

• 한국재료학회지
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• 제28권6호
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• pp.324-329
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• 2018

Needle-like NiO protecting layers on NiCrAl alloy foam, used as support for hydrogen production, are introduced through electroplated Ni and subsequent microwave annealing. To improve the stability of the NiCrAl alloy foam, oxygen concentration of microwave annealing to form a needle-like NiO layer with good chemical stability and corrosion resistance is controlled in a range of 20 and 50 %. As the oxygen concentration increases to 50 %, needle-like NiO forms a dense coating layer on the NiCrAl alloy foam; this layer formation can be attributed to accelerated growth of the (200) plane. In addition, the increased oxygen concentration causes increased NiO/Ni ratio of the resultant coating layer on NiCrAl alloy foam due to improved rate of the oxidation reaction. As a result, the introduction of dense needle-like NiO layers formed at 50 % oxygen concentration improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the electrolyte and the foam. Thus, needle-like NiO can be proposed as a superb protecting layer to improve the chemical stability of NiCrAl alloy form.

• 항공우주산업기술동향
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• 제7권2호
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• pp.76-84
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• 2009

본 논문에서는 우주비행체에 사용하는 세라믹 복합재료의 기술개발에 대한 외국의 현황을 검토하였다. 우주선진국에서는 세라믹 복합재료의 경량 및 우수한 고온 특성을 이용하기 위해 최첨단 엔진구조물에 적용하여 우주비행체의 성능을 향상시키기 위하여 많이 사용해왔다. 특히 내열성, 내산화성 그리고 고온에서의 높은 강도가 요구되는 우주비행체에 적합하여, 로켓엔진챔버, 노즐, 태양판, 레이더안테나, 우주반사경 구조물, 초음속비행체 선단부, 재진입비행체의 노즈팁, 그리고 우주비행체의 방열판등에 사용하고 있다. 이러한 부품을 제작하기 위한 공정기술과 현재의 응용사례를 제시되어 향후 국내의 우주개발사업에 적용될 수 있도록 하였다.

• 한국전기전자재료학회논문지
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• 제23권9호
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• pp.681-684
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• 2010

The $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ multilayered structure for the transparent electrodes in plasma display panel was designed by essential macleod program (EMP) and the multilayered film was deposited on a glass substrate by direct-current (DC)/radio-frequency (RF) magnetron sputtering system. During film deposition process, the Ag layer in $TiO_2$/Ag/$TiO_2$ structure became oxidized and the filter characteristic was degraded easily. In this study, ZnS layer was adopted as a diffusion blocking layer between $TiO_2$ and Ag to prevent the oxidation of Ag layer efficiently in $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ structure. Based on the AES depth profiling analysis, the Ag layer was effectively protected by the ZnS layer as compared with the $TiO_2$/Ag/$TiO_2$ multilayered films without ZnS as an antioxidant layer. The 3 times stacked $TiO_2$/ZnS/Ag/ZnS/$TiO_2$ films have low sheet resistance of $1.22{\Omega}/{\square}$ and luminous transmittance was as high as 62% in the visible ranges.

• 한국전기전자재료학회논문지
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• 제23권9호
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• pp.696-700
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• 2010

We fabricated red and blue organic light emitting display (OLEDs) which had the two kinds of multi-structure of ITO/HIL/HTL/EML/ETL/LiF/Al and ITO/HIL/HTL/EML/ETL/LiF/Al/LiF. In the case of red OLED that had LiF/Al/LiF structure compared to LiF/Al structure, the current density increased from 4.3 mA/$cm^2$ to 7.3 mA/$cm^2$, and the brightness increased from 488 cd/$m^2$ to 1,023 cd/$m^2$ at 7.0 V, and as a result the current efficiency was improved from 11.28 cd/A to 13.95 cd/A. Also in the case of blue OLED that had LiF on Al cathode layer, the current density increased from 1.2 mA/$cm^2$ to 1.8 mA/$cm^2$, and the brightness increased from 45 cd/$m^2$ to 85 cd/$m^2$ at 7.0 V, and as a result the current efficiency was improved from 3.69 cd/A to 4.82 cd/A. Through these experimental results it could be suggested that the LiF layer formed on Al prevents the oxidation of Al surface, and the electrode resistance become low with increase of supplied electrons, therefore the brightness and the efficiency are improved from the influence to the well-balanced bonding of electron and hole at emitting layer.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1232_1233
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• 2009

Paraquat is well-known to cause hepatotoxic responses in human and other mammal species. In solution, it forms free radicals and charge-transfer complex of which formation plays an important role in determination of its biological activity in the presence of various anions. The HepG2 cells were cultured onto a quartz crystal sensor which is possible to detect the density and a viscosity changes using the resonance frequency (F) and the resonance resistance (R). The plot of F-R diagram is able to explain the rheological change of cells onto the surface of the quartz crystal sensor. In this paper, we investigated the physical properties of the HepG2 cells cultured onto a ITO electrode of the quartz crystal sensor according to the paraquat injection at various concentrations (100 mM, 10 mM, 1 mM). We also observed the morphological changes with a micro CCD camera, simultaneously. The HepG2 cells were cultured onto the ITO electrode surface of the quartz crystal modified a collagen film in $CO_2$ incubator. After the paraquat injection, we observed the changes of the morphologies by the micro CCD camera depending on time and analyzed the physical changes of cells on the electrode surface of quartz crystal using F-R diagram. From all results, we proved the effect of paraquat at various concentrations which is led to an apoptosis such as weakening and death of the cells by oxidation and reduction reaction that were produced the superoxide anions and other free radicals.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.438-439
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• 2013

Microelectronic devices의 접촉저항의 향상을 위해 Metal silicides의 형성 mechanism과 전기적 특성에 대한 연구가 많이 이루어지고 있다. 지난 수십년에 걸쳐, Ti silicide, Co silicide, Ni silicide 등에 대한 개발이 이루어져 왔으나, 계속적인 저저항 접촉 소재에 대한 요구에 의해 최근에는 Rare earth silicide에 관한 연구가 시작되고 있다. Rare-earth silicide는 저온에서 silicides를 형성하고, n-type Si과 낮은 schottky barrier contact (~0.3 eV)를 이룬다. 또한, 비교적 낮은 resistivity와 hexagonal AlB2 crystal structure에 의해 Si과 좋은 lattice match를 가져 Si wafer에서 high quality silicide thin film을 성장시킬 수 있다. Rare earth silicides 중에서 ytterbium silicide는 가장 낮은 electric work function을 갖고 있어 낮은 schottky barrier 응용에서 쓰이고 있다. 이로 인해, n-channel schottky barrier MOSFETs의 source/drain으로써 주목받고 있다. 특히 ytterbium과 molybdenum co-deposition을 하여 증착할 경우 thin film 형성에 있어 안정적인 morphology를 나타낸다. 또한, ytterbium silicide와 마찬가지로 낮은 면저항과 electric work function을 갖는다. 그러나 ytterbium silicide에 molybdenum을 화합물로써 높은 농도로 포함할 경우 높은 schottky barrier를 형성하고 epitaxial growth를 방해하여 silicide film의 quality 저하를 야기할 수 있다. 본 연구에서는 ytterbium과 molybdenum의 co-deposition에 따른 silicide 형성과 전기적 특성 변화에 대한 자세한 분석을 TEM, 4-probe point 등의 다양한 분석 도구를 이용하여 진행하였다. Ytterbium과 molybdenum을 co-deposition하기 위하여 기판으로 $1{\sim}0{\Omega}{\cdot}cm$의 비저항을 갖는 low doped n-type Si (100) bulk wafer를 사용하였다. Native oxide layer를 제거하기 위해 1%의 hydrofluoric (HF) acid solution에 wafer를 세정하였다. 그리고 고진공에서 RF sputtering 법을 이용하여 Ytterbium과 molybdenum을 동시에 증착하였다. RE metal의 경우 oxygen과 높은 반응성을 가지므로 oxidation을 막기 위해 그 위에 capping layer로 100 nm 두께의 TiN을 증착하였다. 증착 후, 진공 분위기에서 rapid thermal anneal(RTA)을 이용하여 $300{\sim}700^{\circ}C$에서 각각 1분간 열처리하여 ytterbium silicides를 형성하였다. 전기적 특성 평가를 위한 sheet resistance 측정은 4-point probe를 사용하였고, Mo doped ytterbium silicide와 Si interface의 atomic scale의 미세 구조를 통한 Mo doped ytterbium silicide의 형성 mechanism 분석을 위하여 trasmission electron microscopy (JEM-2100F)를 이용하였다.

• The Korean Journal of Physiology and Pharmacology
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• 제21권3호
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• pp.317-325
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• 2017

Non-alcoholic fatty liver disease (NAFLD) has become the most prevalent liver disease in parallel with worldwide epidemic of obesity. Reactive oxygen species (ROS) contributes to the development and progression of NAFLD. Peroxisomes play an important role in fatty acid oxidation and ROS homeostasis, and catalase is an antioxidant exclusively expressed in peroxisome. The present study examined the role of endogenous catalase in early stage of NAFLD. 8-week-old male catalase knock-out (CKO) and age-matched C57BL/6J wild type (WT) mice were fed either a normal diet (ND: 18% of total calories from fat) or a high fat diet (HFD: 60% of total calories from fat) for 2 weeks. CKO mice gained body weight faster than WT mice at early period of HFD feeding. Plasma triglyceride and ALT, fasting plasma insulin, as well as liver lipid accumulation, inflammation (F4/80 staining), and oxidative stress (8-oxo-dG staining and nitrotyrosine level) were significantly increased in CKO but not in WT mice at 2 weeks of HFD feeding. While phosphorylation of Akt (Ser473) and $PGC1{\alpha}$ mRNA expression were decreased in both CKO and WT mice at HFD feeding, $GSK3{\beta}$ phosphorylation and Cox4-il mRNA expression in the liver were decreased only in CKO-HF mice. Taken together, the present data demonstrated that endogenous catalase exerted beneficial effects in protecting liver injury including lipid accumulation and inflammation through maintaining liver redox balance from the early stage of HFD-induced metabolic stress.