• 한국세라믹학회지
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• 제44권12호
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• pp.740-746
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• 2007

The potential candidates for IT-SOFCs cathode materials, $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ (BSCF) and $La_{0.6}Ba_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ (LBCF) powders, were synthesized by a EDTA-citrate combined method from $Sr(NO_3)_2$, $Ba(NO_3)_2$, $La(NO_3)_3{\cdot}6H_2O$, $Co(NO_3)_2{\cdot}6H_2O$, $Fe(NO_3)_3{\cdot}9H_2O$, citric acid and $EDTA-NH_3$. The cathode performance of symmetrical electrochemical cells consisting of BSCF-GDC or LBCF-GDC composite electrodes and a GDC electrolyte was investigated using by AC impedance spectroscopy at the temperature range of 500 to $700^{\circ}C$. It was found that a single phase perovskite could be successfully synthesized when the precursor is heated at $850^{\circ}C$ for 2 h. Due to thermal expansion mismatch between BSCF and GDC, the composite cathodes with lower GDC content than 45 wt% were peeled off from the GDC electrolyte and their electrode polarization resistance was estimated to be high. The thermal expansion coefficient of BSCF-GDC composites was decreased with increasing the GDC content and the electrode peeling off did not occur in BSCF-45 and 55 wt% GDC composites. BSCF-45 wt% GDC composite electrode showed the lowest area specific resistances (ASR) of 0.15 and $0.04{\Omega}{\cdot}cm^2$ at 600 and $700^{\circ}C$, respectively. On the other hand, LBCF-GDC composite cathodes showed higher ASR than the BSCF-45 and 55 wt% GDC and their cathode performance were decreased with the GDC content.

• Journal of Biosystems Engineering
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• 제42권4호
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• pp.350-357
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• 2017

Purpose: In-situ monitoring of water quality is fundamental to most environmental applications. The high cost and long delays of conventional laboratory methods used to determine water quality, including on-site sampling and chemical analysis, have limited their use in efficiently managing water sources while preventing environmental pollution. The objective of this study was to develop an on-site water monitoring system consisting mainly of an Arduino board and a sensor array of multiple ion selective electrodes (ISEs) to measure the concentration of $NO_3$ ions. Methods: The developed system includes a combination of three ISEs, double-junction reference electrode, solution container, sampling system consisting of three pumps and solenoid valves, signal processing circuit, and an Arduino board for data acquisition and system control. Prior to each sample measurement, a two-point normalization method was applied for a sensitivity adjustment followed by an offset adjustment to minimize the potential drift that could occur during continuous measurement and standardize the response of multiple electrodes. To investigate its utility in on-site nitrate monitoring, the prototype was tested in a facility where drinking water was collected from a water supply source. Results: Differences in the electric potentials of the $NO_3$ ISEs between 10 and $100mg{\cdot}L^{-1}$ $NO_3$ concentration levels were nearly constant with negative sensitivities of 58 to 62 mV during the period of sample measurement, which is representative of a stable electrode response. The $NO_3$ concentrations determined by the ISEs were almost comparable to those obtained with standard instruments within 15% relative errors. Conclusions: The use of the developed on-site nitrate monitoring system based on automatic sampling and two-point normalization was feasible for detecting abrupt changes in nitrate concentration at various water supply sites, showing a maximum difference of $4.2mg{\cdot}L^{-1}$ from an actual concentration of $14mg{\cdot}L^{-1}$.

• 분석과학
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• 제19권6호
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• pp.482-489
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• 2006

Pediococcus에서 추출된 lactate oxidase(LOD)를 poly(vinyl alcohol)(PVA)에 고정화하여 2전극계로 구성된 lactate 바이오센서를 제조하였다. Lactate는 LOD 효소와의 반응에서 생성되는 $H_2O_2$를 전기화학적으로 금(Au)위에 형성시킨 Pt-black 층에서 산화시켜 정량 할 수 있었다. Pt-black으로 만들어진 센서는 과산화수소에 대해서 낮은 전위(+300 mV vs. Ag/AgCl)에서 큰 산화전류를 보여주었으며, ascorbic acid, acetaminophen, uric acid 등과 같이 산화되기 쉬운 산화 종들의 영향을 감소시켜주었다. 외부보호막으로는 다양한 종류의 친수성 폴리우레탄을 사용하였다. 센서는 in vitro 방식으로 흐름계와 비흐름계 모두에서 성능을 평가하였다. 제작된 센서는 0.05 M NaCl을 포함하는 0.05 M 인산염 완충용액(pH 7.6)에서 성능을 시험하였으며, 0.1 mM에서 9.0 mM의 lactate 농도구간에서 직선적 감응성을 나타내었다. 최적화된 센서는 $4^{\circ}C$ 완충용액에 보관하였으며, 25일 이상 감응도(sensitivity)가 거의 변화하지 않았다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.331-331
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• 2009

Hafnium oxide ($HfO_2$) attracted by one of the potential candidates for the replacement of si-based oxides. For applications of the high-k gate dielectric material, high thermodynamic stability and low interface-trap density are required. Furthermore, the amorphous film structure would be more effective to reduce the leakage current. To search the gate oxide materials, metal-insulator-metal (MIM) capacitors was fabricated by pulsed laser deposition (PLD) on indium tin oxide (ITO) coated glass with different oxygen pressures (30 and 50 mTorr) at room temperature, and they were deposited by Au/Ti metal as the top electrode patterned by conventional photolithography with an area of $3.14\times10^{-4}\;cm^2$. The results of XRD patterns indicate that all films have amorphous phase. Field emission scanning electron microscopy (FE-SEM) images show that the thickness of the $HfO_2$ films is typical 50 nm, and the grain size of the $HfO_2$ films increases as the oxygen pressure increases. The capacitance and leakage current of films were measured by a Agilent 4284A LCR meter and Keithley 4200 semiconductor parameter analyzer, respectively. Capacitance-voltage characteristics show that the capacitance at 1 MHz are 150 and 58 nF, and leakage current density of films indicate $7.8\times10^{-4}$ and $1.6\times10^{-3}\;A/cm^2$ grown at 30 and 50 mTorr, respectively. The optical properties of the $HfO_2$ films were demonstrated by UV-VIS spectrophotometer (Scinco, S-3100) having the wavelength from 190 to 900 nm. Because films show high transmittance (around 85 %), they are suitable as transparent devices.

• Journal of Electrochemical Science and Technology
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• 제11권1호
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• pp.92-98
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• 2020

SnO₂-based high-capacity anode materials are attractive candidate for the next-generation high-performance lithium-ion batteries since the theoretical capacity of SnO₂ can be ideally extended from 781 to 1494 mAh g^-1. Here 3D etched Cu foam is applied as a current collector for electron path and simultaneously a substrate for the SnO₂ coating, for developing an integrated electrode structure. We fabricate the 3D etched Cu foam through an auto-catalytic electroless plating method, and then coat the SnO₂ onto the self-supporting substrate through a simple sol-gel method. The catalytic dissolution of Cu metal makes secondary pores of both several micrometers and several tens of micrometers at the surface of Cu foam strut, besides main channel-like interconnected pores. Especially, the additional surface pores on etched Cu foam are intended for penetrating the individual strut of Cu foam, and thereby increasing the surface area for SnO₂ coating by using even the internal of Cu foam. The increased areal capacity with high structural integrity upon cycling is demonstrated in the SnO₂-coated 3D etched Cu foam. This study not only prepares the etched Cu foam using the spontaneous chemical reactions but also demonstrates the potential for electroless plating method about surface modification on various metal substrates.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 2001년도 춘계학술발표논문집
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• pp.18-25
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• 2001

A new wood-degrading fungus Trichophyton rubrum LKY-7 secretes a high level of laccase in a glucose-peptone liquid medium. The production of laccase by the fungus was barely induced by 2,5-xylidine. The laccase has been purified to homogeneity through three chromatography steps in an overall yield of 40%. The molecular mass of the purified laccase was about 65 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified laccase had the distinct blue color and had basic spectroscopic features of a typical blue laccase: two absorption maxima at 278 and 610 nm and a shoulder at 338 nm. The N-terminus of the laccase has been sequenced, revealing high homology to laccases from wood-degrading white-rot fungi such as Ceriporiopsis subvermispora. The enzyme had a "low" redox potential (0.5 V vs normal hydrogen electrode), yet it was one of the most active laccases in oxidizing a series of representative substrates/mediators. Compared with other fungal laccases, the laccase has a very low Km value with ABTS [2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid] as a substrate and a very high Km value with violuric acid as a substrate. The laccase has the isoelectric point of 4.0. The laccase had very acidic optimal pH values (pH 3-4) while it was more stable at neutral pH than at acidic pH. The laccase oxidized hydroquinone faster than catechol and pyrogallol. The oxidation of tyrosine by the laccase was not detectable under the reaction conditions. The laccase was strongly inhibited by sodium azide and sodium fluoride. fluoride.

• 한국진공학회지
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• 제19권5호
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• pp.331-340
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• 2010

초고주파 다중 중공 음극 방전을 이용한 플라즈마 화학 기상 증착 장치를 3차원 수치 모델링하였다. 기본적인 방전 특성을 파악하기 위하여 알곤 플라즈마를 40 MHz, 100 V, 133.3 Pa (1 Torr)의 조건에 대해서 계산하였다. 6 mm 직경의 홀을 20 mm 간격으로 배열하였고 전극 간격은 10 mm를 가정하였다. 피크 플라즈마 밀도는 홀의 하부 중앙에서 $5{\times}10^{11}#/cm^3$ 였으며 전자 온도는 접지 상태로 가정한 기판과 챔버 벽면 주위에서 가장 높았다. 준안정 상태에 의한 2단 이온화 속도는 전자 충돌에 의한 직접 이온화보다 10배 가량 높았다. 수소에 대한 계산에서는 이온화 이외의 다양한 에너지 소모 경로가 있어서 방전의 국재화가 잘 이루어지지 않았다.

• 전기학회논문지
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• 제65권12호
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• pp.2014-2018
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• 2016

Transparent, conductive electrode films, showing the particular characteristics of good conductivity and high transparency, are of considerable research interest because of their potential for use in opto-electronic applications, such as smart window, photovoltaic cells and flat panel displays. Multilayer transparent electrodes, having a much lower electrical resistance than widely-used transparent conducting oxide electrodes, were prepared by using RF/DC magnetron sputtering system. The multilayer structure consisted of three layers, [NiInZnO(NIZO)/Ag/NIZO]. The optical and electrical properties of the multilayered NIZO/Ag/NIZO structure were investigated in relation to the thickness of each layer. The optical and electrical characteristics of multilayer structures have been investigated as a function of the Ag and NIZO film thickness. High-quality transparent conductive films have been obtained, with sheet resistance of $9.8{\Omega}/sq$ for Ag film thickness of 8 nm. Also the multilayer films of inserted Ag 8 nm thickness showed a high optical transmittance above 93% in the visible range. The electrical and optical properties of the new multilayer films were mainly dependent on the thickness of Ag insertion layer.

• 지구물리와물리탐사
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• 제10권3호
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• pp.203-210
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• 2007

자연전위 측정에 의한 산사태나 사면 안정성 모니터링의 기본 연구로 일축 압축에 의한 암석의 파괴 시 수반되는 미소 전위를 측정하였다. 측정시스템은 24 bit의 분해능을 가지며 동시에 8채널 측정이 가능한 A/D 변환기와 일축 압축 시험기, 일축 압축 시 암석의 변형률 측정 장치, 4조의 전위 전극으로 구성된다. 구축된 시스템을 이용하여 화강암, 석회암, 사암의 암석시료와 균질한 시료 상태에서 미소 전위 발생을 모니터링하기 위해 제작한 모르타르 시료에 대하여 실험하였다. 포화된 암석 시료에서는 압력이 가해짐에 따라 모든 시료에서 미소 전위의 발생이 관측되었으며, 하중이 증가함에 따라 발생되는 전위의 세기가 증가하는 것을 확인하였다. 발생 전위의 세기는 사암, 석회암, 화강암의 순으로 크게 나타났는데, 이는 공극률과 비례관계가 있음을 알 수 있었고, 전기동역학적인 관점에서 발생 메커니즘을 설명할 수 있다. 반면, 건조 시료에서는 사암에서만 전위 발생이 관측되었는데 이는 사암에 석영 함량이 많아 발생한 압전 전위에 의한 것으로 이론을 통해 알 수 있었다. 시료에 부착된 4조의 전위전극에서의 측정된 전위세기를 비교한 결과 파괴면에 인접한 전극에서의 전위세기가 다른 전극에 비해 크게 나타나는 것을 확인했다. 이는 다채널 SP 모니터링을 통해 산사태나 사면 붕괴 지점을 미리 예측할 수 있는 긍정적인 결과로서 향후 음향방사(acoustic emission)와 동시에 측정하여 정확한 파괴면과 미소 전위세기와의 정량적 상관관계를 규명할 예정이다.

• The Journal of Advanced Prosthodontics
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• 제12권3호
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• pp.114-123
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• 2020

PURPOSE. The aim of this study was to evaluate the corrosion resistance of the specimens produced by five different commercial metal laser sintering (MLS) systems with their recommended Co-Cr alloy powders. MATERIALS AND METHODS. The MLS machines and the alloy powders used were, ProX 100-ST2724G (St-Pro), Mysint 100-EOS SP2 (SP2-Mys), EOSINT 270-EOS SP2 (SP2-EOS), SLM 100-Starbond CoS (SB-SLM), and MLab Cusing-Remanium^® Star (RS-MLab), respectively. Eight specimens from each group were prepared. Open circuit potential (E_ocp) and electrochemical impedance spectroscopy (EIS) measurements of polished surfaces of the specimens were conducted in a three-electrode cell using a potentiostat-galvanostat in Fusayama-Meyer artificial saliva (AS). Specimens from each group were immersed in AS and de-ionized water for seven days. E_ocp, charge transfer resistance (R_ct) values, and released ions (㎍/㎠ × 7d) in different solutions were determined. The specimen surfaces were observed with SEM/EDS. Results were analyzed statistically. RESULTS. E_ocp values have shifted to potentials that are more positive over time. Steady-state E_ocp values were from high to low as follows, SB-SLM, SP2-Mys, SP2-EOS, RS-MLab, and ST-Pro, respectively. After 60 mins, RS-MLab specimens had the highest R_ct value, followed by SP2-Mys, SB-SLM, SP2-EOS, and ST-Pro. In all groups, ion release was higher in AS than that in de-ionized water. CONCLUSION. There were small differences among the corrosion resistances of the Co-Cr alloy specimens produced with MLS systems; meanwhile, the corrosion resistances were quite high for all specimens.