• 센서학회지
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• 제9권1호
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• pp.9-14
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• 2000

스핀 코팅 방법으로 제조된 P(VDF/TrFE) 막의 유전적 특성을 조사하였다. 막의 결정성과 막질을 개선하기 위해 스핀 코팅 후에 3 단계에 걸친 열처리 공정을 하였다. 상부전극을 마스크로 사용하는 간단한 P(VDF/TrFE) 막의 식각공정과 조건을 확립하였다. 분극을 여러 단계에 걸쳐 하는 정확한 분극공정을 실현하였다. 스핀코팅으로 제조된 막의 두께는 용액농도 10 wt%, 스핀속도 3000 rpm, 스핀시간 30초에서 $1.87\;{\mu}m$였다. 제조된 P(VDF/TrFE) 막의 유전상수와 유전손실을 측정하였다. 1 kHz의 주파수에서 분극전 P(VDF/TrFE) 막의 유전상수는 13.5, 유전 손실은 0.042로 나타났으며 분극후 각각 11.5, 0.037로 나타났다.

• 공업화학
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• 제25권4호
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• pp.386-391
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• 2014

본 연구에서는 상압 저온 코로나 방전 플라즈마를 화산암재(스코리아) 분말의 살균에 적용하였다. 스코리아 분말에 Escherichia coli (E. coli) 배양액을 살포하여 균일하게 혼합한 후, 코로나 방전 플라즈마 특성 인자인 방전전력, 방전시간, 주입기체, 전극간격 등의 조건을 변화시키며 E. coli 살균효율을 조사하였다. 실험 결과 상압 저온 코로나 방전 플라즈마는 분말상의 스코리아 살균에 아주 효과적인 것으로 나타났으며, 방전전력 15 W에서 5 min 동안 살균한 결과 E. coli가 99.9% 이상 사멸하였다. 방전전력, 방전시간, 인가전압이 증가할수록 사멸율이 향상되었다. 반응기에 주입되는 기체의 종류에 따른 살균력 실험 결과, 산소 > 모사공기(산소 20%) > 질소 순으로 나타났다. 코로나 방전 플라즈마에 의한 E. coli 살균은 자외선과 활성산화종(산소라디칼, OH라디칼, 오존 등)에 의한 세포막 침식 및 에칭, 그리고 플라즈마 방전 스트리머에 의한 대장균 세포막 파괴로 설명할 수 있다.

• 한국세라믹학회지
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• 제43권4호
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• pp.235-241
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• 2006

Mullite short fibers have been fabricated by adapting the Kneading-Drying-Calcination (KDC) process and characterized. The effect of the addition of foaming agent and calcination temperature on the formation of mullite fibers from coal fly ash, was examined. In the present work, ammonium alum $NH_4Al(SO_4)_2\;12H_2O$ synthesized trom coal fly ash and sodium phosphate $Na_2HPO_4\;2H_2O$ were used as foaming agents. After calcination at $1300^{\circ}C$ for 10 h and then etching with 20% HF solution at $50^{\circ}C$ for 5 h using a microwave heating source, the alumina-deficient $(AI_2O_3/SiO_2$ = 1.13, molar ratio) orthorhombic mullite fibers with a width of ${\sim}0.8mm$ (aspect ratio >30), were prepared from the coal fly ash with $AI_2O_3/SiO_2$ = 0.32, molar ratio by the addition of $NH_4AI(SO_4)_2\;12H_2O$, and with further addition of 2 wt% sodium phosphate. The excessive addition of sodium phosphate rather decreased the formation of mullite fibers, possibly due to the large amount of liquid phase prior to mullitization reaction.

• Corrosion Science and Technology
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• 제2권3호
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• pp.117-126
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• 2003

Due to excellent corrosion resistance and mechanical properties, austenitic stainless steel is widely used as the material for chemical plants. nuclear power plants, and food processing facilities. But, the zone affected by heat in the range of 400 to $800^{\circ}C$ during welding loses corrosion resistance and tensile strength since Cr-carbide precipitation like $Cr_{23}C_6$ forms at the grain boundary and thereby takes place the intergranular corrosion. In this study, AISI 304 stainless steel with the added Nb of 0.3 to 0.7 wt% was solutionized at $1050^{\circ}C$ and sensitized at $650^{\circ}C$. Specimen was welded by MIG. The phase and the microstructure of the specimens were examined by an optical microscope, a scanning electron microscope, and a x-ray diffractometer. The corrosion characteristics of specimens were tested by electrolytic etching and by double loop electrochemical potentiokinetic reactivation method(EPR) in the mixed solution of 0.5M $H_2SO_4$ + 0.01M KSCN. The melting zone had dendritic structure constituted of austenitic phase and $\delta$-ferrite phase. Cr carbide at the matrix did not appear, as Nb content increased. At the grain boundaries of the heat affected zone, the precipitates decreased and the twins appeared. The hardness increased, as Nb content increased. The hardness was highest in the order of the heat affected zone>melted zone>matrix. According to EPR curve, as the Nb content decreased, the reactivation current density(Ir) and the activation current density(la) were highest in the order of the melted zone

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.153-153
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• 2016

Aluminum alloys have poor corrosion resistance compared to the pure aluminum due to the additive elements. Thus, anodizing technology artificially generating thick oxide films are widely applied nowadays in order to improve corrosion resistance. Anodizing is one of the surface modification techniques, which is commercially applicable to a large surface at a low price. However, most studies up to now have focused on its commercialization with hardly any research on the assessment and improvement of the physical characteristics of the anodized films. Therefore, this study aims to select the optimum temperature of sulfuric electrolyte to perform excellent corrosion resistance in the harsh marine environment through electrochemical experiment in the sea water upon generating porous films by variating the temperatures of sulfuric electrolyte. To fabricate uniform porous film of 5083 aluminum alloy, we conducted electro-polishing under the 25 V at $5^{\circ}C$ condition for three minutes using mixed solution of ethanol (95 %) and perchloric (70 %) acid with volume ratio of 4:1. Afterward, the first step surface modification was performed using sulfuric acid as an electrolyte where the electrolyte concentration was maintained at 10 vol.% by using a jacketed beaker. For anode, 5083 aluminum alloy with thickness of 5 mm and size of $2cm{\times}2cm$ was used, while platinum electrode was used for cathode. The distance between the two was maintained at 3 cm. Afterward, the irregular oxide film that was created in the first step surface modification was removed. For the second step surface modification process (identical to the step 1), etching was performed using mixture of chromic acid (1.8 wt.%) and phosphoric acid (6 wt.%) at $60^{\circ}C$ temperature for 30 minutes. Anodic polarization test was performed at scan rate of 2 mV/s up to +3.0 V vs open circuit potential in natural seawater. Surface morphology was compared using 3D analysis microscope to observe the damage behavior. As a result, the case of surface modification presented a significantly lower corrosion current density than that without modification, indicating excellent corrosion resistance.

• 전기화학회지
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• 제9권2호
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• pp.59-63
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• 2006

전해코팅 법과 dip-coating 법을 이용해 산화주석(IV)을 티타늄 지지체에 코팅하여, 코팅 방법에 따른 코팅 전극의 물성과 전기화학적 특성에 대해여 연구하였다. HCl 로 전극 에칭 후, nitrate 용액에 $SnCl_2{\cdot}2H_2O$을 용해시켜 pulse technique를 이용하여 전해코팅 하였으며, dip-coating 법 또한 $SnCl_2{\cdot}2H_2O$를 사용하여 1:1V% HCl 용액에 용해시켜 코팅 소결 후 산화주석(IV)코팅 전극을 제작하였다. 두 가지 코팅 방법을 통해 제작된 산화주석(IV)코팅 전극은 전극의 물성을 비교하기 위해 x-ray diffraction (XRD), scanning election microscopy (SEM)를 관찰해보았고, 전기화학적 특성을 평가하기 위해 cyclic voltammetry (CV)를 측정하여 전위창을 비교해 보았다.

• 한국세라믹학회지
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• 제50권6호
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• pp.423-428
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• 2013

Porous YSZ ceramics are fabricated using 3 mol% yittria-stabilized zirconia (3YSZ) and NiO with different particlesizes (0.6 and 7 ${\mu}m$). Nickel oxide (NiO) is added to the YSZ powder as a pore former with different amounts(40, 50, and 60 vol%) and at different sintering temperatures (1350 and $1400^{\circ}C$) are applied in order to evaluate the temperature effects on the pore and mechanical properties. Heat treatment is conducted after sintering at $700^{\circ}C$ in $H_2$ for the NiO reduction process; then, Ni is removed using a $HNO_3$ etchant solution. According to the NiO contentand sintering temperatures, 41-67% porous YSZ ceramic is obtained and the flexural strength increases, while the porosity decreases with an increasing sintering temperature. The optimum flexural strength ($136.5{\pm}13.4MPa$) and porosity (47%) for oxygen transport porous YSZ membrane can be obtained with 40 vol% of 7 ${\mu}m$ NiO particle at a sintering temperature of $1350^{\circ}C$.

• 한국표면공학회지
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• 제42권4호
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• pp.157-160
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• 2009

Many fundamental studies have been carried out regarding waste water and hazardous gas treatments technologies using the photolysis effect of $TiO_2$. However, a permanent use of $TiO_2$ particles immobilized using organic or organic-inorganic binders is impossible. In this study, Ni-$TiO_2$ composite coating was produced by electroless plating to trap $TiO_2$ particles in the Ni coating layer. The electroless plating was performed in the bath solutions with three different concentrations of $TiO_2$ particles : 10 g/l, 20 g/l, and 40 g/l. The surface and photolytic characteristics of the coating layer was investigated by the use of SEM, a scratch tester, and an UV-Visible spectrophotometer. The results showed that the amounts of immobilized $TiO_2$ particles and the photolytic rate of the coating increased with the initial content of $TiO_2$ particles in the electroless bath. In addition, the photolytic rate of the Ni-$TiO_2$ composite coating was remarkably promoted by etching process in 10% HCl solution.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 G
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• pp.3310-3312
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• 1999

We have studied the method of silicon direct bonding using the mixture of $HNO_$, $H_2O_2$, and HF chemicals called the controlled slight etch (CSE) solution for the effective wafer cleaning. CSE, two combinations of oxidizing and etching agents, have been used to clean the silicon surfaces prior to wafer bonding. Two wafers of silicon and silicon dioxide were contacted each other at room temperature and postannealed at $300{\sim}1100^{\circ}C$ in $N_2$ ambient for 2.5 h. We have cleaned silicon wafers with the various HF concentrations and characterized the parameters with regard to surface roughness, chemical nature, chemical oxide thickness, and bonding energy. It was observed that the chemical oxide thickness on silicon wafer decreased with increasing HF concentrations. The initial interfacial energy and final energy postannealed at $1100^{\circ}C$ for 2.5h measured by the crack propagation method was 122 $mJ/m^2$ and 2.96 $mJ/m^2$, respectively.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2410-2412
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• 2005

In this study, two types of PS substrate were fabricated for sensing of chemical and biological substances. For sensing of the humidity and chemical analyzes such as $CH_3OH$ or $C_2H_5OH$, PS layers are prepared by photoelectrochemical etching of silicon wafer in aqueous hydrofluoric acid solution. To evaluate their sensitivity, we measured the resistance variation of the PS diaphragm. As the amplitude of applied voltage increases from 2 to 6Vpp at constant frequency of 5kHz, the resistance variation for humidity sensor rises from 376.3 to $784.8{\Omega}$/%RH. And the sensitivities for $CH_3OH$ and $C_2H_5OH$ were 0.068 uA/% and 0.212 uA/%, respectively. For biological sensing application, amperometric urea sensors were fabricated based on porous silicon(PS), and planar silicon(PLS) electrode substrates by the electrochemical methods. Pt thin film was sputtered on these substrates which were previously formed by electrochemical anodization. Poly (3-methylthiophene) (P3MT) were used for electron transfer matrix between urease(Urs) and the electrode phase, and Urs also was by electrochemically immobilized. Effective working area of these electrodes was determined for the first time by using $Fe(CN)_6^{3-}/Fe(CN)_6^{4-}$ redox couple in which nearly reversible cyclic voltammograms were obtained. The $i_p$ vs $v^{1/2}$ plots show that effective working electrode area of the PS-based Pt thin film electrode was 1.6 times larger than the PLS-based one and we can readily expect the enlarged surface area of PS electrode would result in increased sensitivity by ca. 1.6 times. Actually, amperometric sensitivity of the Urs/P3MT/Pt/PS electrode was ca 0.91uA/$mM{\cdot}cm^2$, and that of the Urs/P3MT/Pt/PLS electrode was ca. 0.91uA/$mM{\cdot}cm^2$ in a linear range of 1mmol/L to 100mmol/L urea concentrations