• 한국전기전자재료학회논문지
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• 제31권6호
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• pp.417-421
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• 2018

$TiO_2$ has excellent photocatalytic properties and several studies have reported the increase in its specific surface area. The structure of $TiO_2$ nanofibers indicates promising improved photocatalytic properties and these nanofibers can thus potentially be applied in air pollution sensors and pollutant removal filters. In this study, a $TiO_2$ nanofiber was fabricated by the electrospinning method. The fabrication processing factors such as the applied voltage, the distance between nozzle and collector, and the inflow rate of solution were controlled. The precursor was titanium (IV) isopropoxide and as-spun $TiO_2$ nanofibers were heated at $450^{\circ}C$ for 2 h to obtain an anatase crystalline structure. The microstructure was analyzed using field emission scanning electron microscope (FE-SEM) and X-ray diffraction analysis (XRD). The anatase phase was observed in the $TiO_2$ nanofibers after heat treatment. The diameter of $TiO_2$ nanofibers increased with the flow rate, but decreased with decreasing applied voltage and nozzle to collector distance. The diameter of $TiO_2$ nanofibers was controlled in the range of 364 nm to 660 nm. These nanofibers are expected to be very useful in photocatalytic applications.

• 한국미생물·생명공학회지
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• 제42권2호
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• pp.202-206
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• 2014

본 연구에서는 감가공 과정에서 매년 막대한 양으로 발생하는 감껍질을 이용하여 에탄올을 생산하기 위하여 묽은 황산으로 감껍질을 전처리하는 조건을 중심합성계획법과 반응표면분석법을 통하여 최적화하였다. 감껍질의 최적 전처리 조건은 황산농도 1.77%와 열처리 시간 26.4분이었으며 RSM 모델에서 예측한 수준과 비슷한 수율로 환원당을 생성하였다. 감껍질 전처리물을 이용한 효모발효에서 혐기적 배양조건에서 15.52 g/l의 에탄올이 생산되는 것을 확인하였다. 본 연구를 통하여 매년 막대한 양으로 발생하는 감껍질을 활용하는 방안 중의 하나로써 효모를 이용한 에탄올 생산의 가능성을 제시하였다.

• 대한금속재료학회지
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• 제48권11호
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• pp.995-1002
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• 2010

This study investigated the effect of process temperature on the alloying process during synthesis of $Sm_2Fe_{17}$ powder from ball-milled samarium oxide ($Sm_2O_3$) powders and a solid reducing agent of calcium hydrides ($CaH_2$) using iron nanopowder (n-Fe powder) by a reduction-diffusion (R-D) process. The $n-Fe-Sm_2O_3-CaH_2$ mixed powders were subjected to heat treatment at $850{\sim}1100^{\circ}C$ in $Ar-H_2$ for 5 h. It was found that the iron nanopowders in the mixed powders are sintered below $850^{\circ}C$ during the R-D process and the $SmH_2$ is synthesized by a reduced Sm that combines with $H_2$ around $850^{\circ}C$. The results showed that $SmH_2$ is able to separate Sm and $H_2$ respectively depending on an increase in process temperature, and the formed $Sm_2Fe_{17}$ phase on the surface of the sintered Fe nanopowder agglomerated at temperatures of $950{\sim}1100^{\circ}C$ in this study. The formation of the $Sm_2Fe_{17}$ layer is mainly due to the diffusion reaction of Sm atoms into the sintered Fe nanopowder, which agglomerates above $950^{\circ}C$. We concluded that nanoscale $Sm_2Fe_{17}$ powder can be synthesized by controlling the diffusion depth using well-dispersed Fe nanopowders.

• 한국재료학회지
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• 제31권9호
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• pp.532-538
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• 2021

In this study, a spray dryer is used to make granules of Y₂O₃ and YF₃, and then Y₅O₄F₇ is synthesized following heat treatment of them under Ar gas atmosphere at 600 ℃. Single and binary monomer mixtures are compared and analyzed to optimize photocurable monomer system for DLP 3D printing. The mixture of HEA and TMPTA at 8:2 ratio exhibits the highest photocuring properties and low viscosity with shear thinning behavior. The optimized photocurable monomer and synthesized Y₅O₄F₇ are therefore mixed and applied to printing process at variable solid contents (60, 70, 80, & 85 wt.%) and light exposure times. Under optimal light exposure conditions (initial exposure time: 1.2 s, basic exposure time: 5 s), YOF composites at 60, 70 & 80 wt.% solid contents are successfully printed. As a result of measuring the size of the printed samples compared to the dimensions of the designed bar type specimen, the deviation is found to increase as the YOF solid content increases. This shows that it is necessary to maximize the photocuring activity of the monomer system and to optimize the exposure time when printing using a high-solids ceramic slurry.

• 한국약용작물학회지
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• 제27권2호
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• pp.86-95
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• 2019

Background: Depending on the processing method, the raw materials constituents change in various ways. In particular, a heat treatment process, such as steaming, changes the color and aroma of a raw material to increase its palatability and number of physiologically active ingredients. Methods and Results: In the present study, the effects of the steaming temperature and time on the yield, color, proximal composition, and total polyphenol and ginsenoside content of a 4-year-old ginseng root were analyzed. The yield tended to decrease with the increase of steaming time at each temperature and the total ginsenoside content increased with increasing of steaming temperature except at $80^{\circ}C$. Conclusions: These results suggest that steaming at $100^{\circ}C$ for 6 - 9 hours or at $110^{\circ}C$ for 3 - 6 hours is suitable for increasing total polyphenol and ginsenoside content with less yield reduction in a 4-year-old ginseng root.

• 식품과학과 산업
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• 제53권3호
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• pp.284-294
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• 2020

고전압 펄스 전기장 기술은 전기 에너지를 활용한 친환경적 비가열 공정 기술로서 꾸준히 업계의 관심을 받고 있다. 장치에 대한 이해의 부족과 장비가격에 대한 부담으로 실제 상업적 적용이 크게 증가하지 않고 있으나 가열 공정을 대체할 수 있는 기술로서의 가능성은 지속적으로 제기되고 있다. PEF 공정을 이용한 식품의 살균은 지금까지는 대부분 과일 및 야채 주스 등 저점도의 액체 식품의 살균에 대해 적용되어 왔으나 최근에는 고점도의 스무디, 고농도 단백질 음료, 혼합 주스, 알코올 음료 등으로 적용 범위가 확대되었으며, 분말, 생육 등 고체 식품의 살균에 대한 연구도 진행되고 있다. 살균 이외에도 색소, 유용성분의 추출 및 회수, 생리활성물질의 활성화, 건조의 전처리 등의 식품 공정뿐만 아니라 씨앗의 발아율 증가, 육제품의 육질 변화, 전분의 물성 변화 등에 대한 적용이 연구되면서 기존의 식품 공정을 보완 또는 대체할 수 있는 기술로서 기대되고 있다.

• 대한금속재료학회지
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• 제50권12호
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• pp.931-937
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• 2012

The microstructure of Cu-15 wt%Ag composites fabricated by equal channel angular pressing (ECAP) with intermediate heat treatment at $320^{\circ}C$ was investigated by transmission electron microscopy (TEM) observations. Ag precipitates with a thickness of 20-40 nm were observed in the eutectic region of the Cu-15 wt%Ag composite solution treated at $700^{\circ}C$ before ECAP. The Cu matrix and Ag precipitates had a cube on cube orientation relationship. ECAPed composites exhibited ultrafine-grained microstructures with the shape and distribution dependent on the processing routes. For route A in which the sample was pressed without rotation between each pass, the Cu and Ag grains were elongated along the shear direction and many micro-twins were observed in elongated Cu grains as well as in Ag filaments. The steps were observed on coherent twin boundaries in Cu grains. For route Bc in which the sample was rotated by 90 degrees after each pass, a subgrain structure with misorientation of 2-4 degree by fragmentation of the large Cu grains were observed. For route C in which the sample was rotated by 180 degrees after each pass, the microstructure was similar to that of the route A sample. However, the thickness of the elongated grains along the shear direction was wider than that of the route A sample and the twin density was lower than the route A sample. It was found that more microtwins were formed in ECAPed Cu-15 wt%Ag than in the drawn sample. Grain boundaries were observed in relatively thick and long Ag filaments in Cu-15 wt%Ag ECAPed by route C, indicating the multi-crystalline nature of Ag filaments.

• 대한금속재료학회지
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• 제46권4호
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• pp.189-198
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• 2008

The changes in microstructure and mechanical properties of AZ31 alloy subjected hot-rolling process were investigated. The AZ31 plates fabricated by horizontal continuous casting process were prepared and have hot-rolled from 30 mm to 1 mm in thickness under different processing conditions. At the rolling temperature of $400^{\circ}C$, little surface and side crack was observed up to 20% reduction rate. As total reduction and reduction rate increase to more than 75% and 20% pass, respectively, Grains were more uniformly refined through overall thickness, and particularly lots of shear bands were appeared to be inclined at less than $20^{\circ}C$ along the rolling direction. Average grain size of less than $5{\mu}m$ and tensile properties of YS ${\geq}$ 250 MPa, UTS ${\geq}$ 300 MPa and El. ${\geq}$ 13% were acquired for hot-rolled AZ31 sheets without post-heat treatment. Maximum intensity of (0002) pole figure was decreased with an increase in reduction rate, indicating the improvement of texture by means of high reduction rate.

• 소성∙가공
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• 제31권4호
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• pp.207-213
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• 2022

In this study, variations in the microstructure and hardness of a low-carbon SCM415 steel with austenitizing temperature and cooling rate are investigated. When the austenitizing temperature is lower than the A₁ temperature (738.8 ℃) of the SCM415 steel, the microstructures of both the air-cooled and water-cooled specimens consist of ferrite and pearlite, which are similar to the microstructure of the initial specimen. When heat treatment is conducted at temperatures ranging from the A₁ temperature to the A₃ temperature (822.4 ℃), the microstructure of the specimen changes depending on the temperature and cooling rate. The specimens air- and water-cooled from 750 ℃ consist of ferrite and pearlite, whereas the specimen water-cooled from 800 ℃ consists of ferrite and martensite. At a temperature higher than the A₃ temperature, the air-cooled specimens consist of ferrite and pearlite, whereas the water-cooled specimens consist of martensite. At 650 ℃ and 700 ℃, which are lower than the A₁ temperature, the hardness decreases irrespective of the cooling rate due to the ferrite coarsening and pearlite spheroidization. At 750 ℃ or higher, the air-cooled specimens have smaller grain sizes than the initial specimen, but they have lower hardness than the initial specimen owing to the increased interlamellar spacing of pearlite. At 800 ℃ or higher, martensitic transformation occurs during water cooling, which results in a significant increase in hardness. The specimens water-cooled from 850 ℃ and 950 ℃ have a complete martensite structure, and the specimen water-cooled from 850 ℃ has a higher hardness than that water-cooled from 950 ℃ because of the smaller size of prior austenite grains.

• 한국분말재료학회지
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• 제31권2호
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• pp.152-162
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• 2024

The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150℃ under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10^-2/m²) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.