• 한국재료학회지
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• 제31권7호
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• pp.409-419
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• 2021

The effect of solidification rate on micro-segregation in investment casting of IN738LC superalloy was studied. In Ni-based superalloys, the micro-segregation of solute atoms is formed due to limited diffusion during cast and solidification. The microstructure of cast Ni-based superalloys is largely divided into dendrite core of initial solidification and interdendrite of final solidification. In particular, mosaic shaped eutectic γ/γ' and carbides are formed in the interdendrite of the final solidification region in some cases. The micro-segregation phenomena formed in regions of dendrite core and interdendrite including eutectic γ/γ' and carbides were analyzed using OM, SEM/EDS and micro Vickers hardness. As a result of analysis, the lack of (Cr, W) and the accumulation of Ti were measured in the eutectic γ/γ', and the accumulation of (Cr, Mo) and the lack of Ti were measured in the interdendrite between dendrite and eutectic. Carbides formed in interdendritic region were composed of (Ti, W, Mo, C). The segregation applied to each microstructure is mainly due to the formation of γ' with Ni₃(Al,Ti) composition. The Ni accumulation accompanied by Cr depletion, and the Ti accumulated in the eutectic region as a γ' forming elements. The Mo tends to diffuse out from the dendrite core to the interdendrite, and the W diffuse out from the interdendrite to the dendrite core. Therefore, the accumulation of Mo in the interdendrite and the deficiency of W occur in the eutectic region located in the interdendrite. Heat treatment makes the degree of the micro-segregation decrease due to the diffusion during solid solution. This study could be applied to the heat treatment technology for the micro-segregation control in cast Ni-based superalloys.

• Asian Journal of Atmospheric Environment
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• 제8권3호
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• pp.154-161
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• 2014

The present study was undertaken to evaluate the chemical characteristics of Asian dust (hereafter called "AD") particles with the aid of the most advanced micro-PIXE (Particle-induced X-ray emission) analytical technique. To this end, size-selected particles were sampled on a rural peninsula of Korea (Byunsan, 35.37N; 126.27E) during AD and non-AD periods in 2004. The coarse particle (> $2{\mu}m$) number density during an AD event were 170 times higher than those of the non-AD counterpart. The average net-count of silica in individual particles collected on AD event was roughly 11 times higher than that of non-AD counterpart. The X-ray net-counts of trace elements (Zn, Co, Mn, and V) were also considerably high in AD relative to the non-AD day. Particle classification based on the inter ratio analysis of elemental net-count suggests that a large portion of the coarse particles collected during AD event underwent chemical transformation to a certain degree. The visual interpretation of micro-PIXE elemental maps and elemental localization data in and/or on individual AD particles clarified the internal mixture of AD particles with sea-salt and artificial metallic particles.

• 펄프종이기술
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• 제41권5호
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• pp.26-32
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• 2009

As a part of utilizing the nanocellulose (NC) from lignocellulosic components of wood biomass, this paper reports preliminary results on the products of sulfuric acid hydrolysis. The purpose of this study was to investigate the morphology of both NC and micro-sized cellulose fiber (MCF) isolated by acid hydrolysis from commercial microcrystalline cellulose (MCC). Field emission.scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were employed to observe the acid hydrolysis suspension, NC, and MCF. The electron microscopy observations showed that the acid hydrolysis suspension, before separation into NC and MCF by centrifugation, was composed of nano-sized NCs and micro-sized MCFs. The morphology of isolated NCs was a whisker form of rod-like NCs. Measurements of individual NCs using TEM indicated dimensions of 6.96$\pm$0.87 nm wide by 178$\pm$55 nm long. Observations of the MCFs showed that most of the MCC particles had de-fibered into relatively long fibers with a diameter of 3-9 ${\mu}m$, depending on the degree of acid hydrolysis. These results suggest that proper technologies are required to effectively realize the potentials of both NCs and MCFs.

• 한국전기전자재료학회논문지
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• 제14권7호
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• pp.557-561
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• 2001

Chemical mechanical polishing (CMP) process has been widely used to planarize dielectric layers, which can be applied to the integraded circuits for sub-micron technology. Despite the increased use of CMP process, it is difficult to accomplish the global planarization of in the defect-free inter-level dielectrics (ILD). Especially, defects such as micro-scratch lead to severe circuit failure which affect yield. CMP slurries can contain particles exceeding 1㎛ in size, which could cause micro-scratch on the wafer surface. The large particles in these slurries may be caused by particles agglomeration in slurry supply line. To reduce these defects, slurry filtration method has been recommended in oxide CMP. In this work, we have studied the effects of filtration and the defect trend as a function of polished wafer count using various filters in inter-metal dielectrics(IMD)-CMP process. The filter installation in CMP polisher could reduce defects after IMD-CMP process. As a result of micro-scratch formation, it is shown that slurry filter plays an important role in determining consumable pad lifetime. The filter lifetime is dominated by the defects. We have concluded that slurry filter lifetime is fixed by the degree of generating defects.

• 한국기계가공학회지
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• 제19권8호
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• pp.81-87
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• 2020

A stable rotational-to-linear motion transformation structure using a driving mechanism with 2 degrees of freedom was developed for an orthogonal mechanism to prevent the interference of each axis in 2D motion. In this mechanism, a step motor was used for precise position control. This structure was developed to maneuver workparts in micro particle blast machining experiments. To determine the real-time performance of micro particle blast machining, the control, input, and output were operated simultaneously and precise position control was implemented, using a timer interrupt with multiple execution codes. The two step motors obtained precise position control by removing backlash with a ball-screw mechanism. The device has menu-type control codes for user-friendliness, and real-time sequence control was simultaneously adopted for user control input.

• Wind and Structures
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• 제19권2호
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• pp.199-217
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• 2014

Reported experimental and computational fluid dynamic (CFD) studies have demonstrated significant power augmentation of diffuser shrouded horizontal axis micro wind turbine compared to bare turbine. These studies also found the degree of augmentation is strongly dependent on the shape and geometry of the diffuser such as length and expansion angle. However study flow field over the rotor blades in shrouded turbine has not received much attention. In this paper, CFD simulations of an experimental diffuser shrouded micro wind turbine have been carried out with the aim to understand the mechanisms underpinning the power augmentation phenomenon. The simulations provide insight of the flow field over the blades of bare wind turbine and of shrouded one elucidating the augmentation mechanisms. From the analysis, sub-atmospheric back pressure leading to velocity augmentation at the inlet of diffuser and lowering the static pressure on blade suction sides have been identified as th dominant mechanisms driving the power augmentation. And effective augmentation was achieved for ${\lambda}$ above certain value. For the case turbine it is ${\lambda}$ greater than ${\approx}2$.

• 한국식품영양과학회지
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• 제35권4호
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• pp.507-509
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• 2006

미량확산법에 의한 휘발성 염기질소 분석에서 고체소자센서가 부착된 마이크로 pH 전극을 사용하여 적정 과정을 자동화하기 위하여 자동적정시스템을 구성하고 자동적정 프로그램을 작성하였다. 자동적정시스템으로 돈육시료의 휘발성염기질소 분석을 수행한 결과 부패도가 서로 다른 모든 시료에서 자동적정과 수동적정의 평균들 간에 유의수준 15%에서도 유의차가 인정되지 않았으며, 두 방법의 평균치들 사이에 높은 상관성이 확인되었다.

• 동력기계공학회지
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• 제20권5호
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• pp.5-13
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• 2016

This study is on wear damage of the material for a molding machine that be used at finally cutting of metal beam made in roll forming process of vehicle bump beam process line. SKD11 steel was used with the material for cutting mold jig. In the cutting mold jig, Ti diffusion heat treatment after vacuum heat treatment was carried out for upgrade of surface hardness and anti-wear. Also, the heat treatments by various methods were performed to compare the wear damage degree against above the existing heat treatment. Wear loss and friction coefficient were obtained from wear test. And, micro Vickers hardness values were compared with damaged parts or not of cutting mold jig. Micro Vickers hardness value appeared higher at the undamaged part by Ti diffusion heat treatment. The micro Vickers hardness well followed a two-parameter Weibull probability distribution.

• 한국염색가공학회지
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• 제33권4호
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• pp.288-301
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• 2021

The purpose of this study was to verify the degree of visibility of FOLED (fiber optic light-emitting diode) materials applied to safety-enhancing clothes of micro-mobility users during the day and night by conducting an empirical test targeting 50 people in their teens, 20's, 30's, 40's, and 50's or older. First, the results of the visibility test at 10 m-intervals from 10 to 70 m based on the clothes sample showed that the light detection of FOLED material was very good without daytime or night-time distinction. Second, the results of directional sign detection of FOLED were confirmed to be very high without any daytime or night. Third, the results of identifying a pictogram design showed that the distance was shorter than that of light detection or directional indication. However, the FOLED pictogram design could be confirmed at a distance of 50 m or less. Therefore, if a clothes product using FOLED material is worn and micro-mobility is used, the experimental results indicate that safety will be sufficiently secured due to the excellent visibility.

• 한국응용곤충학회지
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• 제32권3호
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• pp.354-371
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• 1993

컴퓨터와 자동감지장치를 이용하여 먹바퀴 성충 암컷의 행동을 사육상에서 10~15일간 연속 관찰하였다. 대체적으로 12L~12D의 광조건하에서 각 미소서식처에서의 출현율과 활동성에는 개체의 변이가 컸고 일주기성이 낮게 나타났다. 먹이, 물 타개체가 공급되었을 경우 휴식처, 타개체, 먹이 및 물이 있는 것에서 각각 하루 평균 20.42, 11.50, 6.31, 2.66% 출현했다. 먹이, 물 타개체를 공급하지 않았을 경우 휴식처에서 하루중 20.29% 출현하였다. 출현 시간당 방문 횟수는 다른 미소서식처에서보다 먹이 먹는 곳과 물 마시는 곳에서 많았고 먹바퀴의 활동성은 먹이, 물, 타개체를 공급했을 때가 공급하지 않았을 때 보다 높았다. 미소서식처 출현에 대한 Principal Component Analysis (PCA) 결과 각 개체들의 출현 양상은 다양하게 나타났으나 (Q모드), 각 시간대는 명, 암기로 유형화 되어 나타났다(R모드). 먹이, 물, 타개체 공급시 휴식처에서의 출현이 먹이를 먹는 곳과 물을 마시는 곳에서의 출현보다 명, 암기의 유형성이 강하게 나타났다. 각 미소서식처에서의 출현율과 활동을 종합적으로 고려하여 PCA한 결과 먹바퀴의 활동은 먹이 및 타개체가 있는 것의 출현율과 관련 되었다.