• 전기화학회지
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• 제13권4호
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• pp.246-250
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• 2010

In this study, nano-crystallized $Al_2O_3$ was coated on the surface of $LiFePO_4$ powders via a novel dry coating method. The influence of coated $LiFePO_4$ upon electrochemical behavior was discussed. Surface morphology characterization was achieved by transmission electron microscopy (TEM), clearly showing nano-crystallized $Al_2O_3$ on $LiFePO_4$ surfaces. Furthermore, it revealed that the $Al_2O_3$-coated $LiFePO_4$ cathode exhibited a distinct surface morphology. It was also found that the $Al_2O_3$ coating reduces capacity fading especially at high charge/discharge rates. Results from the cyclic voltammogram measurements (2.5-4.2 V) showed a significant decrease in both interfacial resistance and cathode polarization. This behavior implies that $Al_2O_3$ can prevent structural change of $LiFePO_4$ or reaction with the electrolyte on cycling. In addition, the $Al_2O_3$ coated $LiFePO_4$ compound showed highly improved area-specific impedance (ASI), an important measure of battery performance. From the correlation between these characteristics of bare and coated $LiFePO_4$, the role of $Al_2O_3$ coating played on the electrochemical performance of $LiFePO_4$ was probed.

• 한국환경과학회지
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• 제18권11호
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• pp.1225-1234
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• 2009

The aim of this research was to apply experimental design methodology in the optimization condition of electrochemical oxidation of Rhodamine B(RhB). The reactions of electrochemical oxidation were mathematically described as a function of parameters amounts of current, NaCl dosage, pH and time being modeled by the use of the central composite design, which was used for fitting quadratic response surface model. The application of response surface methodology using central composite design(CCD) technique yielded the following regression equation, which is an empirical relationship between the removal efficiency of RhB and test variable in actual variables: RhB removal (%) = 3.977 + 23.279$\cdot$Current + 49.124$\cdot$NaCI - 5.539$\cdot$pH - 8.863$\cdot$time - 22.710$\cdot$Current$\cdot$NaCl + 5.409$\cdot$Current$\cdot$time + 2.390$\cdot$NaCl$\cdot$time + 1.061$\cdot$pH$\cdot$time - $0.570{\cdot}time^2$. The model predicted also agree with the experimentally observed result($R^2$ = 91.9%).

• 열처리공학회지
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• 제35권6호
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• pp.337-342
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• 2022

In metal cutting, water-soluble cutting oil is used for cooling the surface of the workpiece and improving the surface roughness. However, waste cutting oil contains preservatives and surfactants, and if it is discarded as it is, it has an great influence on environmental pollution. For this reason, regulations on the use of cutting oil are being stricter. Hence, the development of eco-friendly treatment technologies is required. In this study, a diamond electrode doped with boron on a niobium substrate was deposited by thermal filament chemical vapor deposition and waste cutting oil was treated using an electrochemical method. Compared to the total amount of organic carbon contained in the waste cutting oil, it was confirmed that the boron-doped diamonds developed from this study showed much better performance than electrodes that has been widely used before.

• 한국전기화학회:학술대회논문집
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• 한국전기화학회 2003년도 연료전지심포지움 2003논문집
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• pp.279-282
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• 2003

• 전기학회논문지
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• 제65권4호
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• pp.628-634
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• 2016

This paper demonstrates a microfluidic electrochemical sensor for detecting endocrine disruptor such as estradiol at a very low concentration by using preconcentration technique. In addition, self-assembled monolayer(SAM) was also employed on the working electrode of the electrochemical sensor in order to increase the estradiol capture efficiency of the sensor. SAM treatment on the working electrode enhanced the specific binding between the surface of the working electrode and the estradiol antibody. The estradiol antibody was applied on the working electrode at different concentrations(10, 20, 50, 100, 200 pg/ml) for observing the concentration dependency. The measured electrochemical redox current changed with the amount of the bound estradiol on the Au working electrode surface and the sensor can detect all the target material when the immobilized antibody amount is more than the estradiol amount in the water. The elecrochemical estradiol sensor without SAM treatment showed a low current of 7.79 nA, while the sensor treated with SAM resulted in 339 nA at 200 pg/ml, which is more than 40 fold higher output current. When combining the preconcentration technique and the SAM-treated electrode, the measured current became more than 100 fold higher than that of the sensor without neither SAM treatment nor preconcentration technique. The combination of these two techniques can would enable the proposed microfluidic electrochemical sensor to detect a very low concentration endocrine disruptor.

• 한국표면공학회지
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• 제41권5호
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• pp.194-198
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• 2008

Several methods for improving dispersion of carbon nanotubes (CNTs) have been investigated. CNTs modified by acids and hydrogen peroxide ($H_2O_2$) showed improved dispersion. From SEM micrographs and photos of dispersion, CNTs modified with nitric acid and $H_2O_2$, showed no agglomeration in solution even standing for 4 months, which means successfully improved dispersion property. TEM micrographs of surface modified single CNT treated with 69% $HNO_3$ in boiling acid solution as the optimum method were obtained. For confirmation of CNTs' application to EDLC electrode materials, characteristics of EDLC have been analyzed by cyclic voltammetry curve, specific capacitance of unit cell, electrode discharge curves and AC impedance curve. From the results, it could be confirmed that electrochemical properties of CNTs were enhanced after surface modification with 69% $HNO_3$ acid treatment.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.49-54
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• 2007

Electropolishing, the anodic dissolution process without contact with tools, is a surface treatment method to make a surface planarization using an electrochemical reaction with low current density. Nitinol is a metal alloy composed of Ni and Ti around 50% respectively which has shape memory effect. Nitinol can be put various applications which require purity and high pricision surface of products. The aim of this study is to investigate the characteristic of electropolishing effect for nitinol workpieces. In order to analyze the characteristics of electropolishing effect, surface roughness and micro-burr size were measured in terms of machining conditions such as current density, machining time and electrode gap. The tendencies about improvement of surface roughness and deburring effect by electropolishing for nitinol workpieces were determined.

• 전기화학회지
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• 제10권3호
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• pp.184-189
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• 2007

전자 산업의 발전과 함께 휴대폰, 노트북, PDA등과 같은 휴대 정보 전자 기기의 고성능 에너지 공급원으로서 이차전지 산업의 중요성이 높아지고 있다. 이에 따라 리튬이차전지의 핵심부품인 양극재료의 고성능화 및 안전성 확보에 대해 많은 관심이 증대되고 있다. 현재 사용되고 있는 양극재료에는 $LiCoO_2,\;LiMn_2O_4,\;LiNi_xCo_yMn_zO_2,\;LiNi_xCo_yM_zO_2$ (M=Al, Zr, Mg 등) 등이 있으며, 그중 가장 대표적으로 사용되고 있는 물질은 $LiCoO_2$이다. 그러나 $LiCoO_2$가 가지고 있는 용량적 한계 및 안전성 문제로 인하여 $LiCoO_2$의 성능 개선 및 3성분계, 올리빈계와 같은 대체물질의 개발에 대한 연구가 활발히 진행중이다. 특히 산화물($M_xO_3$)을 이용한 활물질 표면처리와 같은 성능개선 및 안전성 확보연구는 국내 및 국외에서 활발히 진행되고 있다. 본 연구에서는 $LiCoO_2$의 표면처리 과정에서 불균일 코팅된 산화물의 탈리 및 이의 응집에 의한 침전물 생성 및 표면처리량의 증가에 따른 전지에서의 부작용에 대하여 분석하고, 이와 같은 문제점을 개선하기 위해 코팅량 조정 및 표면처리 공정의 혼합, 건조, 소성 조건 등과 같은 신공정에 대한 연구와 전기화학적 특성 고찰을 실시하였다.

• 한국표면공학회지
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• 제51권2호
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• pp.87-94
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• 2018

Various sealing techniques were applied to the anodized 5083 aluminum alloy for marine environment to reduce corrosion and cavitation erosion damage. Electrochemical experiments and cavitation erosion tests were conducted to evaluate the corrosion resistance and cavitation resistance of the anodic oxide film treated with sealing in natural seawater solution. Then, damaged surface morphology was analyzed by scanning electron microscope(SEM) and 3D microscope. As the results of the electrochemical experiments, it was observed that the surface damage of all the experimental conditions in the anodic polarization experiment was locally grown by the combination of crack and corrosion damage. In the Tafel analysis, the corrosion resistance of all sealing treatment conditions was improved compared to the anodizing. On the other hand, cavitation erosion tests showed that the anodizing and all the sealing treatment conditions generated local pit damage by cavitation erosion attack and grew to crater damage in the observation of damaged surface by SEM. Also, the weight loss and the surface damage depth measured with the experiment time presented that most of the sealing treatment conditions showed better cavitation erosion resistance than the anodizing, and they had an incubation period at the beginning of the experiment.

• Korean Chemical Engineering Research
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• 제46권1호
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• pp.118-123
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• 2008

본 연구에서는 multi-walled nanotubes(MWNTs)를 산소-불소 혼합가스로 처리하여, 표면 관능기를 분석하고, 그 처리효과를 조사하였다. 산소-불소 처리된 MWNTs의 표면특성은 FT-IR 그리고 XPS로 분석하였다. 처리된 탄소지지체에 백금 나노입자를 담지시킨 후, 입자 결정성크기와 담지함량을 조사하였다. 위 탄소지지체에 담지된 촉매의 전기화학적 특성은 전류-전압 곡선을 측정하여 분석하였다. 표면분석의 결과로부터, 산소 및 불소를 포함한 화학관능기가 탄소지지체에 도입된 사실을 알 수 있었다. 산소-불소 함량은 처리온도가 $100^{\circ}C$ 일때 최고값을 나타냈다. Pt/100-MWNTs 샘플의 경우, 3.5 nm의 최소의 결정성 크기를 보였고, 9.4%의 가장 높은 담지율을 나타냈다. 그러나, 이보다 높은 온도에서 처리된 샘플의 경우, 결정성 크기가 증가하였고, 담지율은 감소하였다. 이러한 결과를 통해, 결정성 크기와 담지율을 산소-불소 처리온도를 변화시켜 제어할 수 있었음을 제시하였다. 이와 연관되어, 촉매의 전기화학적 활성이 $100^{\circ}C$ 처리까지는 증가하다가, $200^{\circ}C$와 $300^{\circ}C$의 경우에는 감소하였다. Pt/100-MWNTs 샘플은 비교샘플 중에서 최고의 비전류밀도(specific current density)인 120 mA/mg 수치를 나타냈다.