• 센서학회지
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• 제29권6호
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• pp.374-381
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• 2020

Hydrogen gas has attracted considerable attention as a promising candidate for future energy resources because of its eco-friendly characteristics; however, its highly combustible characteristics should be thoroughly examined to preclude potential disasters. In this regard, a highly sensitive method for the selective detection of H₂ is extremely important. To achieve excellent H₂ selectivity, the utilization of a metal-organic framework (MOF) membrane can physically screen interfering gas molecules by restricting the size of kinetic diameters that can penetrate its nanopores. This paper summarizes the various endeavors of researchers to utilize the MOF molecular sieving layer for the development of highly selective H₂ sensors. Further, the review affords useful insights into the development of highly reliable H₂ sensors.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.615-620
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• 2010

During braking of railway vehicles the repetitive thermal shock leads to thermal cracks on disc surface, and the lifetime of brake disc is dependent on the number of trimming works for removing these thermal cracks. Many tries for development of high heat resistant brake disc to extend the disc life and to warrant reliable braking performance has been continued. In present study, we carry out the computational fatigue analysis for thermal fatigue test in three candidate materials which were made to develop new high heat resistant material. Using FEM, we simulate thermal fatigue test in three candidate materials and conventional disc material. We then estimate the number of cycle to thermal crack initiation based on data from mechanical fatigue tests, and the results are compared with each material. For each material, the correction factor for $N_{f-40}$ which is the number of cycles when crack over $40{\mu}m$ was observed in thermal fatigue test is decided. From this study, we can verify the performance of thermal fatigue test system and suggest a qualitatively comparative method for heat resistance by FEM analysis of thermal shocking phenomenon.

• Nuclear Engineering and Technology
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• 제39권4호
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• pp.273-286
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• 2007

This paper presents the research activities performed to date for the development of a supercritical pressure water-cooled reactor (SCWR) in Korea. The research areas include a conceptual design of an SCWR with an internal flow recirculation, a reactor core conceptual design, a heat transfer test with supercritical $CO_2$, an adaptation of an existing safety analysis code to the supercritical pressure condition, and an evaluation of candidate materials through a corrosion study. Methods to reduce the cladding temperature are introduced from two different perspectives, namely, thermal-hydraulics and core neutronics. Briefly described are the results of an experiment on the heat transfer at a supercritical pressure, an experiment that is essential for the analysis of the subchannels of fuel assemblies and the analysis of a system safety. An existing system code has been adapted to SCWR conditions, and the process of a first-hand validation is presented. Finally, the corrosion test results of the candidate materials for an SCWR are introduced.

• Corrosion Science and Technology
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• 제8권2호
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• pp.68-73
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• 2009

An evaluation of underwater - repair coating materials was based on the premise that defective areas of the existent epoxy coating such as blistering and cracking will be repaired on spot under submerged condition. Tests include the clarification as to whether they are compatible between as-built coating and new repair coating on each concrete specimen. Candidate coating materials for repair were tested in a laboratory to scrutinize their suitability to perform the needed function satisfactorily. The qualification tests performed are as a minimum as follows: Integrated radiation tolerance test, chemical resistance test (submerged condition in deionized water), hardness test and adhesion test of the repair materials. The proper repair coating materials were selected and approved from this test results.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.1350-1352
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• 2008

Research on down conversion phosphor materials is the key for the development of solid state lighting (SSL). Especially finding alternative red phosphor for white LEDs based on blue or NUV LEDs are important research task. Under this view, we have synthesized a series of $Eu^{3+}$ substituted $La_2W_{2-x}Mo_xO_9$ (x = 0 ~ 2, insteps of 0.1) red phosphor and characterized by X-ray diffraction (XRD) and photoluminescence. XRD results reveal a phase transition from triclinic to cubic structure for $x\;{\geq}\;0$. All the compositions show broad charge transfer band due to charge transfer from oxygen to tungsten/molybdenum and red emission due to $Eu^{3+}$ ions. Select compositions show high red emission intensity compared to the commercial red phosphor under NUV/blue ray excitation. Hence, this candidate can be possible red emitting phosphors for white LEDs.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.127-131
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• 2008

In the disk braking of the railway trains, kinetic energy of the vehicles is converted into thermal energy by friction between a brake disk and the pad materials. This can be cause of the iterative thermal shock and generates thermal cracks on the brake disk surface. In this study, we show the comparative thermal fatigue test procedures and thermal crack analysis process to evaluate the thermal fatigue characteristics of candidate materials designed for development of heat-resistant brake disk material. We carried out tests on the conventional brake disk materials used for Saemaul and Mugunghwa trains, then we comparatively analyzed the thermal crack initiation and propagation on the surface of a specimen. A thermal fatigue test procedure and a crack analysis process were suggested to evaluate the heat resistance of the developed materials at later studies.

• 한국재료학회지
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• 제25권10호
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• pp.537-542
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• 2015

One-dimensional (1D) silver nanostructures, which possess the highest conductivity among all room-temperature materials, moderate flexibility and high transmittance, are one of the most promising candidate materials to replace conventional indium tin oxide transparent electrodes. However, the short length and large diameter of 1D silver nanostructures cause a substantial decrease in the optical transparency or an increase in the sheet resistance. In this work, ultra-long silver nanofiber networks were synthesized with a low-cost and scalable electrospinning process, and the diameter of the nanofibers were finetuned to achieve a higher aspect ratio. The decrease in the diameter of the nanofibers resulted in a higher optical transparency at a lower sheet resistance: 87 % at $300{\Omega}/sq$, respectively. It is expected that an electrospun silver nanofiber based transparent electrode can be used as a key component in various optoelectronic applications.

• 한국철도학회논문집
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• 제11권2호
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• pp.188-194
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• 2008

철도차량의 기계제동에 사용되는 제동 디스크의 표면에는 반복적인 마찰제동에 의해 열피로에 기인한 열균열이 발생하게 된다. 이러한 열균열은 제동성능 저하, 제동장치 유지보수비용 증가를 발생시키고 심지어는 대규모 열차사고의 원인으로 작용할 수도 있다. 본 연구에서는 우리나라의 새마을 및 무궁화 열차를 대상으로 고내열성을 지닌 제동 디스크 재질을 개발하기 위하여 FC280, FC250, NCM 등의 후보 재질을 선별하여 각 재질의 화학원소 성분과 비율을 결정하였다. 선별된 후보 재질로 주물 공시재를 제작하여 화학적 성분 분석, 결정 및 흑연조직 분석을 하였고 후보재질 시편에 대한 기계적 특성 시험 및 마찰특성 시험을 실시하여 현재 사용되는 제동 디스크 재질 특성과 비교하였다. 기계적 특성시험 결과 NCM이 가장 큰 인장강도를 보이나 마찰계수는 가장 작았다. 소형 다이나모 시험기에서 마찰제동 시 제동 속도 및 제동압력 변화에 대해 가장 안정적인 마찰계수를 나타내는 것은 현재의 사용품인 것으로 나타났다.

• International Journal of Concrete Structures and Materials
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• 제6권2호
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• pp.87-100
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• 2012

The process of selecting a repair material is a typical one of multi-criteria decision-making (MCDM) problems. In this study Analytical Hierarch Process was applied to solve this MCDM problem. Many factors affecting a process to select an optimal repair material can be classified into quantitative and qualitative requirements and this study handled only quantitative items. Quantitative requirements in the optimal selection model for repair material were divided into two parts, namely, the required chemical performance and the required physical performance. The former is composed of alkali-resistance, chloride permeability and electrical resistivity. The latter is composed of compressive strength, tensile strength, adhesive strength, drying shrinkage, elasticity and thermal expansion. The result of the study shows that this method is the useful and rational engineering approach in the problem concerning the selection of one out of many candidate repair materials even if this study was limited to repair material only for chloride-deteriorated concrete.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.1099-1102
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• 2004

For the development of Pb-free low temperature sintering glass frits, $BaO-B_2O_3-SiO_2$ system was examined. The content of BaO and $B_2O_3$ was changed when the content of $SiO_2$ was fixed to 10 mol%. When the content of BaO was more than 60 mol% devitrification was observed. In the sintering temperature range between 520${\sim}$620 $^{\circ}C$, the optimum sintering temperature decreased as the content of BaO increased. When BaO ${\geq}$45 mol%, the glasses were crystallized after sintering. Candidate compositions are suggested in $BaO-B_2O_3-SiO_2$ system, which can replace the PbO containing glass system.