• 한국재료학회지
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• 제12권7호
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• pp.528-532
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• 2002

Anodic $TiO_2$film on Ti substrate was fabricated at 180V in sulfuric acid solutions containing phosphoric acid and hydrogen peroxide. Effects of the anodizing conditions on the morphology of the oxide layers, and chemical states of the component elements of the layers were studied primarily using SEM, XRD, AFM, and XPS. The pores in the oxide layer was not uniform in size, shape, and growth direction particularly near the interface between the substrate and the oxide layer, compared with those of the surface layer. The formation of irregular type of pores seemed to be attributed to spark discharge phenomena which heavily occurred during increasing the anodic voltage. The pore diameter and the cell size increased, and the number of cells per unit area decreased with the increasing time. From the XPS results, it was shown that component elements of the electrolytes, P and S, existed in the chemical states of $PO_4^{-3}$ , $P_2$$O_{5}$, $SO_4^{-2}$ , $SO_3^{-2}$ , P, S, etc., which were penetrated from the electrolytes into the oxide layer during anodization.

• 한국표면공학회지
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• 제51권4호
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• pp.243-248
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• 2018

All solid state thin film batteries with two types of cell structure, Pt / $LiCoO_2$ / LiPON / Cu and Pt / $LiCoO_2$ / LiPON / $LiCoO_2$ / Cu, are prepared and their electrochemical performances are investigated to evaluate the effect of $LiCoO_2$ interlayer at the interface of LiPON / Cu. The crystallinity of the deposited $LiCoO_2$ thin films is confirmed by XRD and Raman analysis. The crystalline $LiCoO_2$ cathode thin film is obtained and $LiCoO_2$ as the interlayer appears to be amorphous. The surface morphology of Cu current collector after cycling of the batteries is observed by AFM. The presence of a 10 nm-thick layer of $LiCoO_2$ at the interface of LiPON / Cu enhances the interfacial adhesion and reduces the interfacial resistance. As a result, Li plating / stripping at the interface of LiPON / Cu during charge/discharge reaction takes place more uniformly on Cu current collector, while without the interlayer of $LiCoO_2$ at the interface of LiPON / Cu, the Li plating / stripping is localized on current collector. The thin film batteries with the interlayer of $LiCoO_2$ at the interface of LiPON / Cu exhibits enhanced initial coulombic efficiency, reversible capacity and cycling stability. The thickness of the anode current collector Cu also appears to be crucial for electrochemical performances of all solid state thin film batteries.

• 폴리머
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• 제36권1호
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• pp.93-97
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• 2012

본 연구에서는 리튬 이차전지용 분리막을 80, 100, $120^{\circ}C$의 온도에서 각각 1시간 동안 열처리하여 형상 및 물성의 변화에 미치는 영향을 평가하였다. 열처리는 전자빔처리에 의한 사슬절단 산화반응과 달리 화학적 반응을 수반하지 않았으며, 흥미롭게도 인장강도 및 탄성계수가 향상되는 효과를 보여주었다. 하지만 $100^{\circ}C$ 및 $120^{\circ}C$에서 처리된 분리막의 경우 PE 섬유사에 상당량의 주름이 형성되었으며 각각 7.5 및 15%의 면적수축이 관찰되었다. 결과적으로 $80^{\circ}C$, 1시간의 처리 조건을 통하여 5%의 면적 수축이 발생되었지만 일반 분리막대비 향상된 전지특성을 유지하면서 최대 1.3배의 인장강도 및 2.3배의 탄성계수를 확보할 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제19권1호
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• pp.39-44
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• 1998

$LiCoO_2$ powder was synthesized in an aqueous solution by a sol-gel method and used as a cathode active material for a lithium ion rechargeable battery. The layered $LiCoO_2$ powders were prepared by igniting in air for 12 hrs at 600 ℃ $(600-LiCoO_2)$ and 850 ℃ $(850-LiCoO_2)$. The structure of the $LiCoO_2$ powder was assigned to the space group R bar 3 m (lattice parameters a=2.814 Å and c=14.04Å). The SEM pictures of $600-LiCoO_2$ revealed homogeneous and fine particles of about 1 μm in diameter. Cyclic voltammograms (CVs) of $600-LiCoO_2$ electrode displayed a set of redox peaks at 3.80/4.05 V due to the intercalation/deintercalation of the lithium ions into/out of the $LiCoO_2$ structure. CVs for the $850-LiCoO_2$ electrode had a major set of redox peaks at 3.88/4.13 V, and two small set of redox peaks at 4.18/4.42 V and 4.05/4.25 V due to phase transitions. The initial charge-discharge capacity was 156-132 mAh/g for the $600-LiCoO_2$ electrode and 158-131 mAh/g for the $850-LiCoO_2$ electrode at the current density of 0.2 mA/cm2. The cycleability of the cell consisting of the $600-LiCoO_2$ electrode was better than that of the $850-LiCoO_2$. The diffusion coefficient of the $Li^+$ ion in the $600-LiCoO_2$ electrode was calculated as $4.6{\times}10^{-8}\; cm^2/sec$.

• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.161-167
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• 2018

In this study, transition metal coated carbon nanofibers (CNFs) were synthesized and applied as anode materials of Li secondary batteries. CNFs/Ni foam was immersed into 0.01 M transition metal solutions after growing CNFs on Ni foam via chemical vapor deposition (CVD) method. Transition metal coated CNFs/Ni foam was dried in an oven at $80^{\circ}C$. Morphologies, compositions, and crystal quality of CNFs-transition metal composites were characterized by scanning electron microscopy (SEM), Raman spectroscopy (Raman), and X-ray photoelectron spectroscopy (XPS), respectively. Electrochemical characteristics of CNFs-transition metal composites as anodes of Li secondary batteries were investigated using a three-electrode cell. Transition metal/CNFs/Ni foam was directly employed as a working electrode without any binder. Lithium foil was used as both counter and reference electrodes while 1 M $LiClO_4$ was employed as the electrolyte after it was dissolved in a mixture of propylene carbonate:ethylene carbonate (PC:EC) at 1:1 volume ratio. Galvanostatic charge/discharge cycling and cyclic voltammetry measurements were taken at room temperature using a battery tester. In particular, the capacity of the synthesized CNFs-Fe was improved compared to that of CNFs. After 30 cycles, the capacity of CNFs-Fe was increased by 78%. Among four transition metals of Fe, Cu, Co and Ni coated on carbon nanofibers, the retention rate of CNFs-Fe was the highest at 41%. The initial capacity of CNFs-Fe with 670 mAh/g was reduced to 275 mAh/g after 30 cycles.

• Korean Chemical Engineering Research
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• 제57권4호
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• pp.531-538
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• 2019

고분자전해질 연료전지(PEMFC)의 성능이 개선됨에 따라 생성물인 물과 열의 발생이 증가하고 이를 처리하기 위한 관리기법이 중요해지고 있다. 본 연구에서는 물 관리 기법으로 수소 재순환을 적용하였고, 수소 재순환 유량(flow rate)과 퍼지 간격(purge interval) 및 지속 시간(duration)이 연료전지의 성능에 미치는 영향에 대한 실험을 수행하였다. Purge 조건의 영향을 해석하기 위하여 수소극의 압력, 연료의 습도, 운전 간의 연료 이용 효율과 물 배출 양을 측정하였다. 수소 재순환 유량이 증가할수록 수소극 출구의 압력 저하로 인하여 스택 성능이 낮아졌다. Purge 조건에 따라서 물을 효과적으로 배출하지 못해 순간적인 전압 강하가 발생하거나 혹은 잦은 purge로 인해 수소극의 습도를 유지하지 못하여 성능이 점차적으로 감소하는 것을 확인하였다. Purge 조건 실험을 통하여 수소극의 습도를 유지하고 응축된 물을 충분히 배출할 수 있는 purge interval과 duration을 선정하였고, 이를 통하여 스택의 성능과 연료 이용 효율을 향상시킬 수 있었다.

• 한국재료학회지
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• 제29권9호
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• pp.519-524
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• 2019

Spherical $Li_3V_2(PO_4)_3$ (LVP) and carbon-coated LVP with a monoclinic phase for the cathode materials are synthesized by a hydrothermal method using $N_2H_4$ as the reducing agent and saccharose as the carbon source. The results show that single phase monoclinic LVP without impurity phases such as $LiV(P_2O_7)$, $Li(VO)(PO_4)$ and $Li_3(PO_4)$ can be obtained after calcination at $800^{\circ}C$ for 4 h. SEM and TEM images show that the particle sizes are $0.5{\sim}2{\mu}m$ and the thickness of the amorphous carbon layer is approximately 3~4 nm. CV curves for the test cell are recorded in the potential ranges of 3.0~4.3 V and 3.0~4.8 V at a scan rate of $0.01mV\;s^{-1}$ and at room temperature. At potentials between 3.0 and 4.8 V, the third $Li^+$ ions from the carbon-coated LVP can be completely extracted, at voltages close to 4.51 V. The carbon-coated LVP exhibits an initial specific discharge capacity of $118mAh\;g^{-1}$ in the voltage region of 3.0 to 4.3 V at a current rate of 0.2 C. The results indicate that the reducing agent and carbon source can affect the crystal structure and electrochemical properties of the cathode materials.

• Korean Chemical Engineering Research
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• 제57권3호
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• pp.408-412
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• 2019

본 연구에서는 urea를 이용해 질소 도핑된 카본 펠트 전극을 제조하고 이를 바나듐 레독스 흐름 전지용 전극으로 적용하였다. Urea는 암모니아 보다 취급이 용이할 뿐 아니라 고온 열분해를 통해 $NH_2$ 라디칼이 발생하여 탄소 표면에 질소 작용기를 만들고 이는 바나듐 이온의 산화/환원 반응을 향상시키는 활성점(active site)로 작용한다. Urea로 활성화된 카본 펠트 전극은 $150mA/cm^2$의 전류 밀도에서 14.9 Ah/L의 방전 용량을 보였으며 이는 산소작용기로 활성화된 카본 펠트(OGF) 및 비활성화 카본 펠트(GF)보다 각각 23% 및 187% 더 높았다. 이러한 결과는 urea로 활성화된 카본 펠트 전극이 레독스 흐름 전지용 전극 소재로 사용될 수 있는 가능성을 보여준다.

• 한국인터넷방송통신학회논문지
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• 제21권2호
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• pp.137-142
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• 2021

태양광발전 가로등은 태양광에너지를 사용하여 2차전지에 충전 후 램프를 통해 야간조명에 활용하는 시스템으로서 부하 단 LED 가로등을 설치하여 독립형 또는 계통연계형으로 구성할 수 있다. 태양전지모듈을 통해 발전된 에너지는 충방전 제어장치를 통해 2차전지에 충전 후 일사량 감시에 따른 발전전압과 충전전압의 비교, 또는 일몰, 일출 후 특정시간 설정으로 LED 가로등을 점등 소등을 할 수 있다. 따라서 이러한 내용을 기반으로 본 논문에서는 신재생에너지 활용 및 저장기능을 이용한 교육용 모의 태양광발전 가로등 설계 및 제작을 통해 대학의 학생들에게 1) 태양광을 포함한 신재생에너지를 이용하여 전기에너지로 활용하는 에너지 변화의 흐름 이해, 2) 신재생에너지 이해 및 관련 제품의 기초설계와 제작 응용력 함양, 3) 전력변환을 통한 신재생에너지 활용과 하드웨어 제작을 통한 실습과 분석력 강화를 심어줄 수 있다.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제47권3호
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• pp.197-208
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• 2021

Objectives: The purpose of this retrospective study was to evaluate the variables associated with length of stay (LOS), hospital costs, intensive care unit (ICU) use, and treatment outcomes in patients hospitalized for maxillofacial infections at a tertiary medical center in South Korea. Materials and Methods: A retrospective chart review was conducted for patients admitted for treatment of maxillofacial infections at Dankook University Hospital from January 1, 2011 through September 30, 2020. A total of 390 patient charts were reviewed and included in the final statistical analyses. Results: Average LOS and hospital bill per patient of this study was 11.47 days, and ₩4,710,017.25 ($4,216.67), respectively. Of the 390 subjects, 97.3% were discharged routinely following complete recovery, 1.0% expired following treatment, and 0.8% were transferred to another hospital. In multivariate linear regression analyses to determine variables associated with LOS, admission year, infection side, Flynn score, deep neck infection, cardiovascular disease, admission C-reactive protein (CRP) and glucose levels, number and length of surgical interventions, tracheostomy, time elapsed from admission to first surgery, and length of ICU stay accounted for 85.8% of the variation. With regard to the total hospital bill, significantly associated variables were age, type of insurance, Flynn score, number of comorbidities, admission CRP, white blood cell, and glucose levels, admission temperature, peak temperature, surgical intervention, the length, type, and location of surgery, tracheostomy, time elapsed from admission to first surgery, and length of ICU use, which accounted for 90.4% of the variation. Age and ICU use were the only variables significantly associated with unfavorable discharge outcomes in multivariate logistic regression analysis. Conclusion: For successful and cost-effective management of maxillofacial infections, clinicians to be vigilant about the decision to admit patients with maxillofacial infections, perform appropriate surgery at an adequate time, and admit them to the ICU.