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Ni 나노입자의 전기영동 코팅에 의한 전열관 자가보수 기술 개발
이경자,이민구,이창규,Lee, Gyoung-Ja,Lee, Min-Ku,Rhee, Chang-Kyu 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.4
The electrophoretic deposition process of Ni nano-particles in organic suspension was employed for self-repairing of heat exchanger tubes. For this purpose, Ni nano-particles prepared by levitational gas condensation method were dispersed into the solution of ethanol with the addition of dispersant Hypermer KD2. For electrophoretic deposition of Ni nano-particles on the Ni alloy specimen, constant electric fields of 20 and 100 V $cm^{-1}$ were applied to the specimen in Ni-dispersed solution. It was found that as electrophoretic deposition proceeds, the size of the pit or crack remarkably decreased due to the agglomeration of Ni nano-particles at the pit or crack. This strongly suggests that the electrophoretic mobility of the charged particles is larger for the damaged part with a higher current value rather than outer surfaces with a lower current value.
가스응축장치 캐리어가스 공급속도 및 압력변화를 통한 비스무스 나노분말 입도제어
이경자,김창규,이민구,이창규,Lee, Gyoung-Ja,Kim, Chang-Kyu,Lee, Min-Ku,Rhee, Chang-Kyu 한국분말야금학회 2010 한국분말재료학회지 (KPMI) Vol.17 No.5
In the present work, bismuth nanopowders with various particle size distributions were synthesized by controlling argon (Ar) gas flow rate and chamber pressure of a gas condensation (GC) apparatus. From the analyses of transmission electron microscopy (TEM) images and nitrogen gas adsorption results, it was found that as Ar gas flow rate increased, the specific surface area of bismuth increased and the average particles size decreased. On the other hand, as the chamber pressure increased, the specific surface area of bismuth decreased and the average particles size increased. The optimum gas flow rate and chamber pressure for the maximized electrochemical active surface area were determined to be 8 L/min and 50 torr, respectively. The bismuth nanopowders synthesized at the above condition exhibit 13.47 $m^2g^{-1}$ of specific surface area and 45.6 nm of average particles diameter.
질소가스흡착법을 이용한 금속 나노분말의 프랙탈 차원 결정 및 표면 특성 평가
이경자,엄영랑,이창규,Lee, Gyoung-Ja,Uhm, Young-Rang,Rhee, Chang-Kyu 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.6
The surface roughness of Al, Ag and Ni nano-powders which were prepared by pulsed wire evaporation method was quantified based upon the fractal theory. The surface fractal dimensions of metal nano-powders were determined from the linear relationship between In $V/V_{mono}$ and Inln ($P^o/P$) using multi-layer gas adsorption theory. Moreover, the fractal surface image was realized by computer simulation. The relationship between preparation condition and surface characteristics of metal nano-powders was discussed in detail.
Fe<sub>3</sub>O<sub>4</sub> 나노분말을 이용한 전기화학적 비효소 면역센서 응답특성
김창규,이경자,엄영랑,이민구,이창규,Kim, Chang-Kyu,Lee, Gyoung-Ja,Uhm, Young-Rang,Lee, Min-Ku,Rhee, Chang-Kyu 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.3
In this paper, the electrochemical non-enzyme immunosensor has been developed for the determination of salmonella antigen, using inverse voltammetry. For the estimation of salmonella antigen concentration, the $Fe_3O_4$ nanoparticles synthesized by microemulsion method were conjugated with salmonella antigen. Then, the immunocomplex between antibody immobilized on the transducer surface and antigen containing a magnetic nanoparticles was formed. From the linear relationship between the reduction peak current of Fe(III) and salmonella antigen concentration, it is suggested that the electrochemical non-enzyme biosensor is applicable to detect salmonella antigen in the concentration range of $10^1-10^5$ CFU/ml.
전기선 폭발법을 이용하여 제조된 구리 나노유체의 특성평가
김창규,이경자,이창규,Kim, Chang-Kyu,Lee, Gyoung-Ja,Rhee, Chang-Kyu 한국분말야금학회 2010 한국분말재료학회지 (KPMI) Vol.17 No.4
Ethylene glycol-based Cu nanofluids were prepared by pulsed wire evaporation (PWE) method. The structural properties of Cu nanoparticles were studied by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The average diameter and Brunauer Emmett Teller (BET) surface area of Cu nanoparticles were about 100 nm and $7.46\;m^2/g$, respectively. The thermal conductivity and viscosity of copper nanofluid were measured as functions of Cu concentration and temperature. As the volume fraction of Cu nanoparticles increased, both the enhanced ratios of thermal conductivity and viscosity of Cu nanofluids increased. As the temperature increased, the enhanced ratio of thermal conductivity increased, but that ratio of viscosity decreased.
물리화학적 처리를 통한 극성 용매 내 나노다이아몬드의 탈응집 및 분산성 향상 연구
김창규,이경자,이창규,Kim, Changkyu,Lee, Gyoung-Ja,Rhee, Changkyu 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.6
In the present work, physicochemical treatments were introduced for de-aggregation and stable dispersion of detonation nanodiamonds (DND) in polar solvents. The DNDs in water exhibited a particle size of 138 nm and high dispersion stability without particular treatment. However, the DNDs in ethanol were severely aggregated to several micrometers in size and showed poor dispersion stability with time. To break down aggregates of DNDs and enhance the dispersion stability of them in ethanol, mechanical force and chemical surfactant were introduced as functions of zirconia ball size, kind of surfactant and amount of surfactant added. From the analyses of average particle size and Turbiscan results, it was suggested that the size of DNDs in ethanol can be reduced by only mechanical force; however, the DNDs were re-aggregated due to high surface activity. The long-term dispersion stability can be achieved by applying mechanical force to break down the aggregates of DNDs and by preventing re-aggregation of them using proper surfactant.
액상/기상중 전기선 폭발법을 이용한 은 나노유체의 제조 및 특성평가에 관한 연구
김창규,이경자,이창규,Kim, Chang-Kyu,Lee, Gyoung-Ja,Rhee, Chang-Kyu 한국재료학회 2009 한국재료학회지 Vol.19 No.9
The silver nanofluids were synthesized by the pulsed wire evaporation (PWE) method in a liquid-gas mixture. The size and microstructure of nanoparticles in the deionized water were investigated by a particle size analyzer (PSA), transmission electron microscope (TEM), and scanning electron microscope (SEM). Also, the synthesized nanofluids were investigated in order to assess the stability of dispersion of nanofluid by the zetapotential analyzer and dispersion stability analyzer. The results showed that the spherical silver nanoparticle formed in the deionized water and mean particle size was about 50 nm. Also, when explosion times were in the range of 20$\sim$200 times, the absolute value of zeta potential was less than -27 mV and the dispersion stability characteristic of low concentration silver nanofluid was better than the high concentration silver nanofluid by turbiscan.
산화구리 나노분말을 포함하는 에틸렌글리콜 용액의 열전특성에 관한 연구
김창규,이경자,이창규,Kim, Chang-Kyu,Lee, Gyoung-Ja,Rhee, Chang-Kyu 한국분말야금학회 2010 한국분말재료학회지 (KPMI) Vol.17 No.4
In the present work, ethylene glycol-based (EG) copper oxide nanofluids were synthesized by pulsed wire evaporation method. In order to explode the pure copper wire, high voltage of 23 kV was applied to the both ends of wire and argon/oxygen gas mixture was used as reactant gas. EG-based copper oxide nanofluids with different volume fraction were prepared by controlling explosion number of copper wire. From the transmission electron microscope (TEM) image, it was found that the copper oxide nanoparticles exhibited an average diameter about 100 nm with the oxide layer of 2~3 nm. The synthesized copper oxide consists of CuO/$Cu_2O$ phases and the Brunauer Emmett Teller (BET) surface area was estimated to be $6.86\;m^2\;g^{-1}$. From the analyses of thermal properties, it is suggested that viscosity and thermal conductivity of EG-based copper oxide nanofluids do not show temperature-dependent behavior over the range of 20 to $90^{\circ}C$. On the other hand, the viscosity and thermal conductivity of EG-based copper oxide nanofluids increase with volume fraction due to the active Brownian motion of the nanoparticles, i.e., nanoconvection.
플래시광 열처리를 통한 압전 고분자의 결정성 향상 연구
이동훈 ( Donghun Lee ),정성민 ( Seongmin Jeong ),장학수 ( Hak Su Jang ),하동주 ( Dongju Ha ),현동열 ( Dong Yeol Hyeon ),우유미 ( Yu Mi Woo ),백창연 ( Changyeon Baek ),이민구 ( Min-ku Lee ),이경자 ( Gyoung-ja Lee ),박정환 ( Jung Hw 한국전기전자재료학회 2024 전기전자재료학회논문지 Vol.37 No.4
The polymer crystallization process, promoting the formation of ferroelectric β-phase, is essential for developing polyvinylidene fluoride (PVDF)-based high-performance piezoelectric energy harvesters. However, traditional high-temperature annealing is unsuitable for the manufacture of flexible piezoelectric devices due to the thermal damage to plastic components that occurs during the long processing times. In this study, we investigated the feasibility of introducing a flash lamp annealing that can rapidly induce the β-phase in the PVDF layer while avoiding device damage through selective heating. The flash lightirradiated PVDF films achieved a maximum β-phase content of 76.52% under an applied voltage of 300 V and an on-time of 1.5 ms, a higher fraction than that obtained through thermal annealing. The PVDF-based piezoelectric energy harvester with the optimized irradiation condition generates a stable output voltage of 0.23 V and a current of 102 nA under repeated bendings. These results demonstrate that flash lamp annealing can be an effective process for realizing the mass production of PVDF-based flexible electronics.
탄소층으로 캡슐화된 Ni나노입자 촉매의 CO<sub>2</sub> 메탄화 반응
김혜정,김승보,김동현,윤재랑,김민재,전상구,이경자,이규복,Kim, Hye Jeong,Kim, Seung Bo,Kim, Dong Hyun,Youn, Jae-Rang,Kim, Min-Jae,Jeon, Sang Goo,Lee, Gyoung-Ja,Lee, Kyubock 한국재료학회 2021 한국재료학회지 Vol.31 No.9
Carbon-encapsulated Ni catalysts are synthesized by an electrical explosion of wires (EEW) method and applied for CO<sub>2</sub> methanation. We find that the presence of carbon shell on Ni nanoparticles as catalyst can positively affect CO<sub>2</sub> methanation reaction. Ni@5C that is produced under 5 % CH<sub>4</sub> partial pressure in Ar gas has highest conversions of 68 % at 350 ℃ and 70 % at 400 ℃, which are 73 and 75 % of the thermodynamic equilibrium conversion, respectively. The catalyst of Ni@10C with thicker carbon layer shows much reduced activity. The EEW-produced Ni catalysts with low specific surface area outperform Ni catalysts with high surface area synthesized by solution-based precipitation methods. Our finding in this study shows the possibility of utilizing carbon-encapsulated metal catalysts for heterogeneous catalysis reaction including CO<sub>2</sub> methanation. Furthermore, EEW, which is a highly promising method for massive production of metal nanoparticles, can be applied for various catalysis system, requiring scaled-up synthesis of catalysts.