• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2011년도 춘계학술대회 및 Fine pattern PCB 표면 처리 기술 워크샵
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• pp.47-48
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• 2011

The effect of solution acidity and organic additives, polyethylene glycol (PEG), on the trivalent chromium electroplating was systematically investigated in the view point of solution stability, electroreduction of trivalent chromium ions and characterization of deposition layer. It was found that, the concentration of fraction chromium complexes in the trivalent chromium bath containing formic acid is strongly depended on pH value. PEG molecules were stable in trivalent chromium bath containing formic acid via studies on electrospray ionization mass spectrometry (ESI-MS) and UV-Vis. However, the presence of PEG molecules decreased the reductive current of hydrogen evolution, increasing of current efficiency higher about 10 % compared with solutions without PEG. Moreover, PEG additives developed the nodular morphology during electroreduction of trivalent chromium ions with the increase of solution acidity and enhanced its current efficiency by maintaining the consumption of complexant, formic acid, at a low speed. In this study, the effect of solution acidity was emphasized important, there, it controlled the formation of complexes in the solution, cathodic film (CF) during deposition, and properties of deposited layer. By electrochemical quartz crystal microbalance (EQCM), studies show that chromium electrodeposition occurs via the formation of intermediate complexes and adsorption on the cathode surface, which hinder the penetration of ions from bulk solution to the cathode surface.

• Metals and materials international
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• 제24권6호
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• pp.1232-1240
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• 2018

Corrosion properties of dissimilar friction stir welded 6061 aluminum and HT590 steel were investigated to understand effects of galvanic corrosion. As cathode when coupled, HT590 was cathodically protected. However, the passivation of AA6061 made the aluminum alloy cathode temporarily, which leaded to corrosion of HT590. From the EIS analysis showing Warburg diffusion plot in Nyquist plots, it can be inferred that the stable passivation layer was formed on AA6061. However, the weld as well as HT590 did not show Warburg diffusion plot in Nyquist plots, suggesting that there was no barrier for corrosion or even if it exists, the barrier had no function for preventing and/or retarding charge transport through the passivation layer. The open circuit potential measurements showed that the potential of the weld was similar to that of HT590, which lied in the pitting region for AA6061, making the aluminum alloy part of the weld keep corrosion state. That resulted in the cracked oxide film on AA6061 of the weld, which could not play a role of corrosion barrier.

• 분석과학
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• 제22권2호
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• pp.152-158
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• 2009

본 연구에서는 유기화합물의 효과적인 소프트 이온화를 위하여 기존의 SPI장치를 개선한 새로운 형태의 방전 장치를 제작하였다. 새로 제작된 소프트 플라스마 이온화 장치는 반 원통 형태의 메쉬 음극과 속빈 원통 형태의 양극으로 구성하였다. 이온화원으로 사용하기에 앞서, 특정압력에서 전극간격에 따른 전압 전류 특성곡선을 조사하여 장치의 구성을 최적화 하였으며, 그 결과 넓은 전압 전류 영역에서 안정한 플라스마를 생성하는 조건을 결정하여 다양한 이온화 패턴을 기대 할 수 있게 하였다. 최적화된 이온화장치를 사중극자 질량분석기와 연결하여 디클로로메탄의 질량 스펙트럼을 관찰하였고, 분석결과 디클로로메탄은 전자충격이온화에 의한 분리 패턴과 비슷하게 나타나는 것을 확인하였다.

• Journal of Microbiology and Biotechnology
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• 제21권6호
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• pp.590-598
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• 2011

Bacterial assimilation of $CO_2$ into stable biomolecules using electrochemical reducing power may be an effective method to reduce atmospheric $CO_2$ without fossil fuel combustion. For the enrichment of the $CO_2$-fixing bacteria using electrochemical reducing power as an energy source, a cylinder-type electrochemical bioreactor with a built-in anode compartment was developed. A graphite felt cathode modified with neutral red (NR-graphite cathode) was used as a solid electron mediator to induce bacterial cells to fix $CO_2$ using electrochemical reducing power. Bacterial $CO_2$ consumption was calculated based on the variation in the ratio of $CO_2$ to $N_2$ in the gas reservoir. $CO_2$ consumed by the bacteria grown in the electrochemical bioreactor (2,000 ml) reached a maximum of approximately 1,500 ml per week. Time-coursed variations in the bacterial community grown with the electrochemical reducing power and $CO_2$ in the mineral-based medium were analyzed via temperature gradient gel electrophoresis (TGGE) of the 16S rDNA variable region. Some of the bacterial community constituents noted at the initial time disappeared completely, but some of them observed as DNA signs at the initial time were clearly enriched in the electrochemical bioreactor during 24 weeks of incubation. Finally, Alcaligenes sp. and Achromobacter sp., which are capable of autotrophically fixing $CO_2$, were enriched to major constituents of the bacterial community in the electrochemical bioreactor.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 전자세라믹스 센서 및 박막재료 반도체재료 일렉트렛트 및 응용기술
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• pp.117-120
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• 2000

The relation of crystal phase and charge/discharge capacity of $Li[Li_yMn_{2-y}]O_4$ were studied for different degrees of Li substitution (y). All cathode material showed spinel phase based on cubic phase in X-ray diffraction. Other peaks didn't show in spite of the increase of y value in $Li[Li_yMn_{2-y}]O_4$. Ununiform of $Li[Li_yMn_{2-y}]O_4$ which calcinated by (111) face and (222) face was more stable than that of pure $LiMn_2O_4$. In addition, At TG analysis, calcined $Li[Li_{0.1}Mn_{1.9}]O_4$ exhibited much mass loss at $800{\mu}m$. The cycle performance of the $Li(Li_yMn_{2-y}]O_4$ was improved by the substitution of $Li^{1+}$ for $Mn^{3+}$ in the octahedral sites. Specially, $Li[Li_{0.08}Mn_{1.92}]O_4$ and $Li[Li_{0.1}Mn_{1.9}]O_4$ cathode materials showed the charge and discharge capacity of about 125mAh/g at first cycle, and about 95mAh/g after 70th cycle. It is excellent than that of pure $LiMn_2O_4$, which 125mAh/g at first cycle, 65mAh/g at 70th.

• Corrosion Science and Technology
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• 제6권6호
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• pp.291-296
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• 2007

The corrosion of metals and alloys in flowing liquids can be classified into uniform corrosion and localized corrosion which may be categorized as follows. (1) Localized corrosion of the erosion-corrosion type: the protective oxide layer is assumed to be removed from the metal surface by shear stress or turbulence of the fluid flow. A macro-cell may be defined as a situation in which the bare surface is the macro-anode and the other surface covered with the oxide layer is the macro-cathode. (2) Localized corrosion of the differential flow-velocity corrosion type: at a location of lower fluid velocity, a thin and coarse oxide layer with poor protective qualities may be produced because of an insufficient supply of oxygen. A macro-cell may be defined as a situation in which this surface is the macro-anode and the other surface covered with a dense and stable oxide layer is the macro-cathode. (3) Localized corrosion of the active/passive-cell type: on a metal surface a macro-cell may be defined as a situation in which a part of it is in a passivation state and another in an active dissolution state. This situation may arise from differences in temperature as well as in the supply of the dissolved oxygen. Compared to uniform corrosion, localized corrosion tends to involve a higher wall thinning rate (corrosion rate) due to the macro-cell current as well as to the ratio of the surface area of the macro-anode to that of the macro-cathode, which may be rationalized using potential vs. current density diagrams. The three types of localized corrosion described above can be reproduced in a Jet-in-slit test by changing the flow direction of the test liquid and arranging environmental conditions in an appropriate manner.

• 한국세라믹학회지
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• 제47권1호
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• pp.26-38
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• 2010

Degradation in Solid Oxide Fuel Cell performance can be ascribed to the following fundamental processes from the materials chemical point of view; that is, diffusion in solids and reaction with gaseous impurities. For SOFC materials, diffusion in solids is usually slow in operation temperatures $800\sim1000^{\circ}C$. Even at $800^{\circ}C$, however, a few processes are rapid enough to lead to some degradations; namely, Sr diffusion in doped ceria, cation diffusion in cathode materials, diffusion related with metal corrosion, and sintering of nickel anodes. For gaseous impurities, chromium containing vapors are important to know how the chemical stability of cathode materials is related with degradation of performance. For LSM as the most stable cathode among the perovskite-type cathodes, electrochemical reduction reaction of $CrO_3$(g) at the electrochemically active sites is crucial, whereas the rest of the cathodes have the $SrCrO_4$ formation at the point where cathodes meet with the gases, leading to rather complicated processes to the degradations, depending on the amount and distribution of reacted Cr component. These features can be easily generalized to other impurities in air or to the reaction of nickel anodes with gaseous impurities in anode atmosphere.

• 전기화학회지
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• 제7권1호
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• pp.1-8
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• 2004

This paper deals with the recent development of high-voltage cathode materials of mono- and di- metal ions substituted spinel $LiMn_2O_4$ for lithium batteries. $LiCu_xMn_{2-x}O_4(0{\leq}x{\leq}0.5)$ shows reversible intercalation/deintercalation in two potential regions, $3.9\~43\;and\;4.8-5.0V$ and stable electrochemical cycling behavior but with low capacity. $LiNi_{0.5}Mn_{1.5}O_4$ obtained by a sol-gel process delivers a capacity of 127mAh $g^{-1}$ on the first cycle and sustains a value of 124 mAh $g^{-1}$ even after the 60th cycle. The $Li_xCr_yMn_{2-y}O_4(0{\leq}x{\leq}0.5)$ solid-solutions exhibit enhanced specific capacity, larger average voltage, and improved cycling behaviors for low Cr content. $LiCr_yMn_{2-y}O_4$ presents a reversible Li deintercalation process at 4.9V, whose capacity is proportional to the Cr content in the range of $0.25{\leq}x{\leq}0.5$ and delivers higher capacities. $LiM_yCr_{0.5-y}Mn_{1.5}O_4(M=Fe\;or\;Al)$ shows that the capacity retention is lowered compared with lithium manganate. The cumulative capacities obtainable with Al-substitutted materials are less than those with Fe-substituted materials. $LiCr_xNi_{0.5-x}Mn_{1.5}O_4(x=0.1)$ delivers a high initial capacity of 1$152mAh\;g^{-1}$ with excellent cycleability.

• Journal of Electrochemical Science and Technology
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• 제12권4호
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• pp.406-414
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• 2021

Electrochemical devices are constructed for continuous syngas (CO + H₂) production with controlled selectivity between CO₂ and proton reduction reactions. The ratio of CO to H₂, or the faradaic efficiency toward CO generation, was mechanically manipulated by adjusting the space volume between the cathode and the polymer gas separator in the device. In particular, the area added between the cathode and the ion-conducting polymer using 0.5 M KHCO₃ catholyte regulated the solution acidity and proton reduction kinetics in the flow cell. The faradaic efficiency of CO production was controlled as a function of the distance between the polymer separator and cathode in addition to that manipulated by the electrode potential. Further, the electrochemical CO₂ reduction device using Au NPs presented a stable operation for more than 23 h at different H₂:CO production levels, demonstrating the functional stability of the flow cell utilizing the mechanical variable as an important operational factor.

• 전기화학회지
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• 제16권3호
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• pp.169-176
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• 2013

현재 이차전지에서 사용중인 양극활물질은 구조 안정성이 높은 층상구조(Layered Structure)의 리튬 금속 산화물(Solid State Lithium Oxide Compounds)이 주로 사용된다. 최근에는 리튬이차전지의 성능향상을 위해서 음극활물질과 전해질 사이의 계면뿐만 아니라, 양극활물질과 전해질 사이의 계면에 관한 연구가 활발히 진행되고 있으며, 이러한 계면의 연구를 위해서는 음극활물질 뿐만 아니라, 양극활물질의 표면에 관한 연구도 선행적으로 이루어져야 하는 상황이다. 대표적인 리튬금속 산화물질인 니켈산리튬($LiNiO_2$)과 코발트산리튬($LiCoO_2$)은 서로 매우 유사한 구조를 갖는 층상구조의 양극활물질이다. 코발트산리튬이 다양한 실험적, 이론적 연구가 진행된 반면에, 니켈산 리튬은 실험적 연구에 비해서 이론적 연구가 부족하다. 따라서, 본 연구에서는 니켈산리튬의 X-선 회절계 측정 결과(XRD data)에 나오는9개의 표면 방향을 범밀도함수이론(Density Functional Theory)을 이용하여 니켈산리튬 표면의 표면 에너지를 계산하였다. 니켈산리튬의 X-선 회절계 측정 결과(XRD data)에서는 (003), (104), (101), (110) 결정 등등이 순차적으로 주요하게 존재하는 것으로 확인되었다. 그러나 시뮬레이션을 이용한 각각의 표면 에너지 계산 결과, X-선 회절계 측정 결과와 다른 순서로 안정한 표면 에너지가 나타나는 결과를 얻었다. 따라서 에너지적으로 안정한 표면이자, X-선 회절계에서 주요하게 나타나는 (104)와 (101) 방향의 니켈산리튬 표면이 많이 노출되어 Li 이온의 충방전시 리튬의 삽입 탈리에 영향을 줄 것으로 예상된다.