• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.811-818
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• 2020

Y-containing CLAM steels were melted via vacuum induction melting and electroslag remelting. In this study, the evolution, microstructure, and mechanical properties of the alloy inclusions (ESR-1 (0 wt.% Y), ESR-2 (0.016 wt.% Y) and ESR-3 (0.042 wt.% Y)) were investigated. Further, the number of inclusions in ESRed steel was observed to obviously decrease, and the distributions were more uniform. The fine Y-Al-O inclusions (1-2 ㎛) were the main inclusions in ESR-2. The addition of Y affected the prior austenite grain size (PAGZ), increasing the tensile strength at test temperature. Low ductile-brittle transition temperature (DBTT) was obtained because of the fine PAGZ and dispersive inclusions. For the ESRed CLAM steel with 0.016 wt.% Y, the yield strengths were 621 MPa at 20 ℃ and 354 MPa at 600 ℃ in air. Further, the uniform elongation and elongation of the ESR-2 alloy were 5.5% and 20.1% at 20 ℃, respectively. Meanwhile, the DBTT tested using full-size Charpy impact specimen (55 cm × 10 cm × 10 cm) was reduced to -83 ℃.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.589-596
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• 2020

Many components in the assembly section of Sodium-cooled Fast Reactor are made of good corrosionresistant 316 LN Stainless Steel material. To avoid self-welding of the components with the coolant sodium at elevated temperature, hardfacing is inevitable. Ni-based colmonoy-5 is used for hardfacing due to its lower dose rate by Plasma Transferred Arc process due to its low dilution. Since Ni-Cr-B-Si alloy becomes very fluidic while depositing, the major height of the weld overlay rests inside the groove. Hardfacing is also done over the plain surface where grooving is not possible. Therefore, grooved and ungrooved hardfaced specimens were prepared at different travel speeds. Fe content at every 100 ㎛ of the weld overlay was studied by Energy Dispersive Spectroscopy and also the micro hardness was determined at those locations. A correlation between iron dilution from the base metal and the micro hardness was established. Therefore, if the Fe content of the weld overlay is known, the hardness at that location can be obtained using the correlation and vice-versa. A new correlation between micro hardness and dilution coefficient is obtained at different locations. A comparative study between those specimens is carried out to recommend the optimum travel speed for lower dilution.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.136-141
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• 2010

ACF/ZnO photocatalyst was synthesized by a sol-gel method using activated carbon fiber (ACF) and Zn $(NO_3)_2$ as precursors. Samples were characterized by Brunauer-Emmett-Teller measurements (BET), scanning electron microscope (SEM), X-ray diffraction (XRD), and energy dispersive X-ray (EDX). The XRD results showed that ACF/ZnO composites only included a hexagonal phase by heat-treated temperature at $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, and $700^{\circ}C$. The SEM analysis revealed that the ACF/ZnO composites did not exhibit any morphological changes of the catalyst surface according to the different heat-treated temperatures. The photocatalytic activity of the samples was tested for degradation of methylene blue (MB) solutions under ultraviolet (UV) light and ultrasonication respectively. The results showed that the photocatalytic activity of ACF/ZnO composites heat-treated at $500^{\circ}C$ was higher than other samples, which is ascribed to the fine distribution of ZnO particles on the surface of the ACF. In addition, an ultrasound of low power (50 W) was used as an irradiation source to successfully induce ACF/ZnO composites to perform sonocatalytic degradation of MB. Results indicated that the sonocatalytic method in the presence of ACF/ZnO composites is an advisable choice for the treatments of organic dyes.

• Journal of Electrochemical Science and Technology
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• v.2 no.2
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• pp.116-123
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• 2011

Herein, a novel preparation method of highly homogeneous carbon-silicon composite materials was presented. In contrast to conventional solvent evaporation method, a milled silicon-graphite or its oxidized material were directly reacted with petroleum-derived pitch precursor. After thermal reaction under high pressure, pitch-graphite-silicon composite was prepared. Carbon-graphite-silicon composite were prepared by an air-oxidization and following carbonization. From energy dispersive spectroscopy, it was observed that small Si particles were highly embedded within carbon, which was confirmed by disappearance of Si peaks in Raman spectra. Furthermore, X-ray diffraction and Raman spectra revealed that carbon crystallinity decreased when the strongly oxidized silicon-graphite was added, which was probably due to oxygen-induced cross-linking. From the anode application in lithium ion batteries, carbon-graphite-silicon composite anode displayed a high capacity ($565\;mAh\;g^{-1}$), a good initial efficiency (68%) and an good cyclability (88% retention at 50 cycles), which were attributed to the high dispersion of Si particles within cabon. In case of the strongly oxidized silicongraphite addtion, a decrease of reversible capacity was observed due to its low crystallinity.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.509-515
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• 2005

Interfacial reactions at LSGM electrolyte and NiO-GDC anode interfaces were thoroughly investigated with Environmental Scanning Electron Microscopy (ESEM-PHlLIPS XL-30) and Energy Dispersive X-ray (EDX-Link XL30). According to the analysis, serious reaction zone was observed at LSGM/NiO-GDC interface. It was found that the reaction layer was originated from the chemical reaction between NiO and LSGM. The reaction products were identified as La deficient form of LSGM based perovskite and Ni-La-O compounds such as LaSrGa$_{3}$O$_{7}$ and LaNiO$_{3}$ from the X-Ray Diffraction (XRD, Philips) analysis. According to the electrical characterization, interfacial layer was very electrically resistive which would be the cause of high internal resistance and low power generating characteristic of the unit cell.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.102-102
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• 2008

Sapphire (${\alpha}-Al_2O_3$) has been used as the substrate of opto-electronic device because of characteristics of thermal stability, comparatively low cost, large diameter, optical transparency and chemical compatibility. However, there is difficulty in the etching and patterning due to the physical stability of sapphire and the selectivity with sapphire and mask materials [1,2]. Therefore, sapphire has been studied on the various fields and need to be studied, continuously. In this study, the etching properties of sapphire substrate were investigated with various $CH_4$/Ar gas combination, radio frequency (RF) power, DC-bias voltage and process pressure. The characteristics of the plasma were estimated for mechanism using optical emission spectroscopy (OES). The chemical compounds on the surface of sapphire substrate were investigated using energy dispersive X-ray (EDX). The chemical reaction on the surface of the etched sapphire substrate was observed by X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) was used to investigate the vertical and slope profiles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.163-163
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• 2008

반도체 소자가 고집적화 되고 고속화를 필요로 하게 됨에 따라, 기존에 사용되었던 알루미늄이나 텅스텐보다 낮은 전기저항, 높은 electro-migration resistance으로 미세한 금속배선 처리가 가능한 Cu가 주목받게 되었다. 하지만 과잉 디싱 현상과 에로젼을 유도하여 메탈라인 브리징과 단락을 초래할 있고 Cu의 단락인 islands를 남김으로서 표면 결함을 제거하는데 효과적이지 못다는 단점을 가지고 있었다. 특히 평탄화 공정시 높은 압력으로 인하여 Cu막의 하부인 ILD막의 다공성의 low-k 물질의 손상을 초래 할 수 있는 문제점을 해결하기 위하여 기존의 CMP에 전기화학을 결합시킴으로서 낮은 하력에서의 Cu 평탄화를 달성 할 수 있는 기존의 CMP 기술에 전기화학을 접목한 새로운 개념의 ECMP (electrochemical-mechanical polishing) 기술이 생겨나게 되었다. 따라서 본 논문에서는 최적화된 ECMP 공정을 위하여 I-V곡선과 CV법을 이용하여 active. passive. trans-passive 영역의 전기화학적 특징을 알아보았고. Cu막의 표면 형상을 알아보기 위해 Scanning Electron Microscopy (SEM) 측정과 Energy Dispersive Spectroscopy (EDS) 분석을 통해 금속 화학적 조성을 조사하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.985-990
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• 2004

Leak noise is a good source to identify the exact location of a leak point of underground water pipelines. Water leak generates broadband noise from a leak location and can be propagated to both directions of water pipes. This sound propagation due to leak in water pipelines is not a non-dispersive wave any more because of the surrounding pipes and soil. However, the necessity of long-range detection of this leak location makes to identify low-frequency acoustic waves rather than high frequency ones. Acoustic wave propagation coupled with surrounding boundaries including cast iron pipes is theoretically analyzed and the wave velocity was confirmed with experiment. The leak locations were identified both by the acoustic emission (AE) method and the cross-correlation method. In a short-range distance, both the AE method and cross-correlation method are effective to detect leak position. However, the detection for a long-range distance required a lower frequency range accelerometers only because higher frequency waves were attenuated very quickly with the increase of propagation paths. Two algorithms for the cross-correlation function were suggested, and a long-range detection has been achieved at real underground water pipelines longer than 300m.

• Tribology and Lubricants
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• v.31 no.3
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• pp.86-94
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• 2015

We perform lacquer formation experiments with various combinations of marine fuel oils and lubricant oils. We also investigate the influences of base number (BN) in lubricant oil and sulfur content in fuel oil. A dissolution test with 10% dilute sulfuric acid and pull-off force test are accomplished to distinguish whether the residual layers are lacquering or not. The lacquering layers are dissolved by dilute sulfuric acid and have a strong pull-off force. Moreover, the calcium content detected in the residual layers is compared by energy dispersive x-ray spectroscopy (EDS). More calcium is detected in the lacquer layers than in other residual layers. Distillate fuels containing low sulfur levels are more prone to lacquering when mixed with lubricant oil with a high BN. On the other hand, residual fuels with a high sulfur content do not form lacquer. We investigate the effect of mixture volume ratio. The mixture with higher fuel oil content is more prone to generate lacquer. These experiments indicate that a lubricant with an appropriate BN should be used to prevent lacquer forming on the surfaces such as cylinder liners depending on the sulfur content of fuel oil.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.612-615
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• 2015

In this work, on-site corrosion behavior of heat resistant tubes of T91, used as components of a superheater in a power plant for up to 25,762 h, has been investigated using scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDS), and electron backscattered diffraction(EBSD), with the objectives of studying the composition, phase distribution, and evolution during service. A multi-layer structure of oxide scale was found on both the steamside and the fireside of the tube surface; the phase distribution was in the order of hematite/magnetite/spinel from the outer to the inner matrix on the steamside, and in the order of slag/magnetite/spinel from the outer to the inner matrix on the fireside. The magnetite layer was found to be rich in pores and cracks. The absence of a hematite layer on the fireside was considered to be due to the low oxygen partial pressure in the corrosion environment. The thicknesses of the hematite and of the slag-deposit layer were found to exhibit no significant change with the increase of the service time.