• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.288-288
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• 2013

Lithium-ion battery (LIB) is one of the most important rechargeable battery and portable energy storage for the electric digital devices. In particular, study about the higher energy capacity and longer cycle life is intensively studied because of applications in mobile electronics and electric vehicles. Generally, the LIB's capacity can be improved by replacing anode materials with high capacitance. The graphite, common anode materials, has a good cyclability but shows limitations of capacity (~374 mAh/g). On the contrary, silicon (Si) and germanium(Ge), which is same group elements, are promising candidate for high-performance LIB electrodes because it has a higher theoretical specific capacity. (Si:4200 mAh/g, Ge:1600 mAh/g) However, it is well known that Si volume change by 400% upon full lithiation (lithium insertion into Si), which result in a mechanical pulverization and poor capacity retention during cycling. Therefore, variety of nanostructure group IV elements, including nanoparticles, nanowires, and hollow nanospheres, can be promising solution about the critical issues associated with the large volume change. However, the fundamental research about correlation between the composition and structure for LIB anode is not studied yet. Herein, we successfully synthesized various structure of nanowire such as Si-Ge, Ge-Carbon and Si-graphene core-shell types and analyzed the properties of LIB. Nanowires (NWs) were grown on stainless steel substrates using Au catalyst via VLS (Vapor Liquid Solid) mechanism. And, core-shell NWs were grown by VS (Vapor-Solid) process on the surface of NWs. In order to characterize it, we used FE-SEM, HR-TEM, and Raman spectroscopy. We measured battery property of various nanostructures for checking the capacity and cyclability by cell-tester.

• 한국분말재료학회지
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• 제26권1호
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• pp.49-57
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• 2019

Layered $LiNi_{0.83}Co_{0.11}Mn_{0.06}O_2$ cathode materials single- and dual-doped by the rare-earth elements Ce and Nd are successfully fabricated by using a coprecipitation-assisted solid-phase method. For comparison purposes, non-doping pristine $LiNi_{0.83}Co_{0.11}Mn_{0.06}O_2$ cathode material is also prepared using the same method. The crystal structure, morphology, and electrochemical performances are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) mapping, and electrochemical techniques. The XRD data demonstrates that all prepared samples maintain a typical ${\alpha}-NaFeO_2$-layered structure with the R-3m space group, and that the doped samples with Ce and/or Nd have lower cation mixing than that of pristine samples without doping. The results of SEM and EDS show that doped elements are uniformly distributed in all samples. The electrochemical performances of all doped samples are better than those of pristine samples without doping. In addition, the Ce/Nd dual-doped cathode material shows the best cycling performance and the least capacity loss. At a 10 C-rate, the electrodes of Ce/Nd dual-doped cathode material exhibit good capacity retention of 72.7, 58.5, and 45.2% after 100, 200, and 300 cycles, respectively, compared to those of pristine samples without doping (24.4, 11.1, and 8.0%).

• International Journal of Stem Cells
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• 제16권1호
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• pp.93-107
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• 2023

Background and Objectives: Chronic periodontitis can lead to alveolar bone resorption and eventually tooth loss. Stem cells from exfoliated deciduous teeth (SHED) are appropriate bone regeneration seed cells. To track the survival, migration, and differentiation of the transplanted SHED, we used super paramagnetic iron oxide particles (SPIO) Molday ION Rhodamine-B (MIRB) to label and monitor the transplanted cells while repairing periodontal bone defects. Methods and Results: We determined an appropriate dose of MIRB for labeling SHED by examining the growth and osteogenic differentiation of labeled SHED. Finally, SHED was labeled with 25 ㎍ Fe/ml MIRB before being transplanted into rats. Magnetic resonance imaging was used to track SHED survival and migration in vivo due to a low-intensity signal artifact caused by MIRB. HE and immunohistochemical analyses revealed that both MIRB-labeled and unlabeled SHED could promote periodontal bone regeneration. The colocalization of hNUC and MIRB demonstrated that SHED transplanted into rats could survive in vivo. Furthermore, some MIRB-positive cells expressed the osteoblast and osteocyte markers OCN and DMP1, respectively. Enzyme-linked immunosorbent assay revealed that SHED could secrete protein factors, such as IGF-1, OCN, ALP, IL-4, VEGF, and bFGF, which promote bone regeneration. Immunofluorescence staining revealed that the transplanted SHED was surrounded by a large number of host-derived Runx2- and Col II-positive cells that played important roles in the bone healing process. Conclusions: SHED could promote periodontal bone regeneration in rats, and the survival of SHED could be tracked in vivo by labeling them with MIRB. SHED are likely to promote bone healing through both direct differentiation and paracrine mechanisms.

• Korean Membrane Journal
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• 제9권1호
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• pp.34-42
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• 2007

A perovskite-type ($La_{0.6}Sr_{0.4}Ti_{0.2}Fe_{0.8}O_{3-{\delta}}$) dense ceramic membrane was prepared by polymerized complex method, using citric acid as a chelating agent and ethylene glycol as an organic stabilizer. Effect of Ti addition on lanthanum-strontium ferrite mixed conductor was investigated by evaluating the thermal expansion coefficient, the oxygen flux, the electrical conductivity, and the phase stability. The thermal expansion coefficient in air was $21.19\;{\times}\;10^{-6}/K$ at 473 to 1,223 K. At the oxygen partial pressure of 0.21 atm ($20%\;O_2$), the electrical conductivity increased with temperature and then decreased after 973 K. The decrement in electrical conductivity at high temperatures was explained by a loss of the lattice oxygen. The oxygen flux increased with temperature and was $0.17\;mL/cm^2{\cdot}min$ at 1,223 K. From the temperature-dependent oxygen flux data, the activation energy of oxygen ion conduction was calculated and was 80.5 kJ/mol at 1,073 to 1,223 K. Also, the Ti-added lanthanum-strontium ferrite mixed conductor was structurally and chemically stable after 450 hours long-term test at 1,173 K.

• Journal of Magnetics
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• 제7권3호
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• pp.63-71
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• 2002

Three fabrication techniques for forming thin barrier layer with uniform thickness and large barrier height in magnetic tunnel junction (MTJ) are discussed. First, the effect of immiscible element addition to Cu layer, a high conducting layer generally placed under the MTJ, is investigated in order to reduce the surface roughness of the bottom ferromagnetic layer, on which the barrier is formed. The Ag addition to the Cu layer successfully realizes the smooth surface of the ferromagnetic layer because of the suppression of the grain growth of Cu. Second, a new plasma source, characterized as low electron energy of 1 eV and high density of $10^{12}$ $cm^{-3}$, is introduced to the Al oxidation process in MTJ fabrication in order to reduce damages to the barrier layer by the ion-bombardment. The magnetotransport properties of the MTJs are investigated as a function of the annealing temperature. As a peculiar feature, the monotonous decrease of resistance area product (RA) is observed with increasing the annealing temperature. The decrease of the RA is due to the decrease of the effective barrier width. Third, the influence of the mixed inert gas species for plasma oxidization process of metallic Al layer on the tunnel magnetoresistance (TMR) was investigated. By the use of Kr-O$_2$ plasma for Al oxidation process, a 58.8 % of MR ratio was obtained at room temperature after annealing the junction at $300{^{\circ}C}$, while the achieved TMR ratio of the MTJ fabricated with usual Ar-$0_2$ plasma remained 48.4%. A faster oxidization rate of the Al layer by using Kr-O$_2$ plasma is a possible cause to prevent the over oxidization of Al layer and to realize a large magnetoresistance.

• 한국식품조리과학회지
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• 제12권4호
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• pp.506-510
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• 1996

제주도에서 생산된 선인장 열매의 적색 betanine 색소를 천연착색료로 사용하기 위하여 pH, 금속이온, 당 및 산의 영향을 조사하였다. 선인장 열매 색소액을 음료의 천연착색료로 사용할 때의 색소농도는 2.5% 가장 선호되었다. pH 영향에서 산성범위인 pH 4와 5에서 색소액이 비교적 안정하였으며 Fe 및 Cu 이온이 색소의 변화에 큰 영향을 주었으나 Sn이온에 의하여 색소의 안정성이 감소되지 않았다. 선인장 열매 색소액에 0.15M, 0.3 M의 포도당과 과당 및 자당 0.075 M, 0.15 M을 첨가하였을 때 대조군에 비하여 안정성이 감소되지 않았으며 과당 0.15 M 첨가군은 고유한 붉은색을 안정화시키는 결과를 가져왔다 또 한 tartaric, phophoric, citric acid 100, 500 ppm을 첨가 한 경우에도 대조군에 비하여 색소안정성의 변화를 보이지 않았으나 100, 500ppm의 ascorbic acid는 항산화 효과를 보여 색소의 안정성을 상승시켰다. 이상에서 제시한 바와 같이 선인장 열매의 적색색소가 합성색소에 비하여 안정성이 비교적 약하므로 색소의 안정성을 증가시키기 위한 많은 연구가 수행되어야 하며, 현재까지의 결과로 미루어 보아 제한된 조건에 서 선인장 열매를 음료의 천연착색료로 사용하여야 하겠다.

• 열처리공학회지
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• 제14권1호
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• pp.27-34
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• 2001

The effects of pre-heat treatment(Q/T) on microstructure and hardness of STD11 and STD61 tool steel nitrided by micro-pulse plasma were investigated. The quenching temperature for obtaining matrix hardness of STD11 and STD61 steel on range of HRC 50 to HRC 60 desired for machine parts is about $1070^{\circ}C$ and $1020^{\circ}C$ respectively. The hardness of STD11 and STD61 quenched at the temperature was HRC 63 and HRC 56 respectively. The nitrided case depth of STD11 and STD61 nitrided at $550^{\circ}C$ for 5 hours was independent of pre-heat treatment condition and the depth was approximately $100{\mu}m$. However, hardness and compactness of nitrided layer on Q/T treated specimen were higher than the annealed specimen. The case depth increased linearly with the increase of nitriding temperature, however, the hardness of nitrided layer decreased with the increase of temperature. Phase mixture of ${\gamma}-Fe_4N$ and ${\varepsilon}-Fe_{2-3}N$ was detected by XRD analysis in the nitrided layer formed at the optimum nitriding condition. The optimum nitriding temperature was approximately $490^{\circ}C$ which was $10^{\circ}C$ lower than the tempering temperature for preventing softening behavior of STD11 and STD61 matrix during nitriding process and the surface hardness of nitrided layer obtained by optimum pre-heat treatment condition was about Hv1400.

• 한국지반환경공학회 논문집
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• 제13권11호
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• pp.11-17
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• 2012

본 연구에서는 탄산화 반응을 이용하여 아민기를 가지는 다양한 친 이산화탄소 흡착제들을 모르타르에 적용함으로써 모르타르 내에 이산화탄소의 포집능을 증대시키는 연구를 하였다. 모르타르 내에 포집된 이산화탄소의 정도를 평가하기 위하여 열중량 분석, 페놀프탈레인법, FT-IR, XRD 및 FE-SEM의 분석법을 이용하여 연구를 진행하였다. 이산화탄소 흡착제를 사용하였을 때, 이산화탄소 흡수효율은 최대 58.5% 개선되었으며, 탄산화 깊이는 일반 모르타르에 비해 3배 더 증가하였다. 이는 대기 중의 이산화탄소가 친 이산화탄소 흡착제 수용액의 아민기와 반응하여 생성된 중탄산염 이온과 시멘트에서 용해되어 나온 칼슘 이온과 화학반응이 일어나면서 탄산칼슘의 형태로 모르타르 내에 저장된 것으로 확인되었다. 또한 함침에 의한 모르타르의 표면에 흡착제의 고정화는 이산화탄소의 흡착량을 증대시키는 것이 가능한 것으로 나타났다.

• Corrosion Science and Technology
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• 제12권1호
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• pp.40-49
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• 2013

Effects of magnesium and pH on corrosion of aluminum galvanically coupled to iron have studied by using potentio- dynamic and static tests for polarization curves, Mott-Schottky test for analysis of semiconductor property, and GD-AES and XPS for film analysis. Pitting potential was sensitive to magnesium as an alloying element but not to pH, while passive current was sensitive to pH but not to magnesium. It was explained with, instead of point defect model (PDM), surface charge model describing that the ingression of chloride depends on the state of surface charge and passive film at film/solution interface is affected by pH. In addition, galvanic current of aluminum electrically coupled to iron was not affected by magnesium in pH 8.4, 0.2M citrate solution but was increased by magnesium at the solution of pH 9.1. The galvanic current at pH 9.1 increased with time at the initial stage and after the exposure of about 200 minute, decreased and stabilized. The behavior of the galvanic current was related with the concentration of magnesium at the surface. It agreed with the depletion of magnesium at the oxide surface by using glow discharge atomic emission spectroscopy (GD-AES). In addition, pitting potential of pure aluminum was reduced in neutral pH solution where chloride ion maybe are competitively adsorbed on pure aluminum. It was confirmed by the exponential decrease of pitting potential with log of [$Cl^-$] around 0.025 M of [$Cl^-$] and linear decrease of the pitting potential. From the above results, unlike magnesium, alloying elements with higher electron negativity, lowering isoelectric point (ISE), are recommended to be added to improve pitting corrosion resistance of aluminum and its alloys in neutral solutions as well as their galvanic corrosion resistance in weakly basic solutions.

• 공업화학
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• 제27권4호
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• pp.415-420
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• 2016

음극소재의 전기화학적 성능을 향상시키기 위해, 인산의 화학처리를 통한 헤테로 원자를 도입함으로써 석탄계 피치의 표면 개질을 수행하였다. 제조된 표면 개질 피치 음극소재의 물리적 특성은 XRD, FE-SEM, XPS 분석을 통하여 수행되었으며, 전기화학적 특성은 $LiPF_6$ (EC : DMC = 1 : 1 vol% + VC 3 wt%) 전해액을 사용하여 충 방전 테스트, 율속 테스트, 순환 전압 전류 테스트와 임피던스 테스트를 통해 조사하였다. 인산 3 wt% 첨가된 표면 개질 피치 전지의 초기 충전 용량 및 초기효율은 489 mAh/g, 82%로 다른 조성의 음극소재보다 우수하였다. 또한 3 wt% 인산으로 표면개질된 CTP 음극소재의 용량 보존율은 30사이클 후에 86%를 나타냈으며, 2 C/0.1 C에서 87%의 우수한 율속 특성을 보여줌을 알 수 있었다.