• Journal of the Korean Electrochemical Society
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• v.3 no.2
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• pp.109-114
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• 2000

The relation between the phase-shift profile fur the intermediate frequencies and the Langmuir adsorption isotherm at the poly-Ir/0.1 M $H_2SO_4$ aqueous electrolyte interface has been studied using ac impedance measurements, i.e., the phase-shift methods. The simplified interfacial equivalent circuit consists of the serial connection of the electrolyte resistance $(R_s)$, the faradaic resistance $(R_F)$, and the equivalent circuit element $(C_P)$ of the adsorption pseudoca-pacitance $(C_\phi)$. The comparison of the change rates of the $\Delta(-\phi)/{\Delta}E\;and\;\Delta{\theta}/{\Delta}E$ are represented. The delayed phase shift $(\phi)$ depends on both the cathode potential (E) and frequency (f), and is given by $\phi=tan^{-1}[1/2{\pi}f(R_s+R_F)C_P]$. The phase-shift profile $(-\phi\;vs.\;E)$ for the intermediate frequency (ca. 1 Hz) can be used as an experimental method to determine the Langmuir adsorption isotherm $(\theta\;vs.\;E)$. The equilibrium constant (K) for H adsorption and the standard free energy $({\Delta}G_{ads})$ of H adsorption at the poly-Ir/0.1 M $H_2SO_4$ electrolyte interface are $2.0\times10^{-4}$ and 21.1kJ/mol, respectively. The H adsorption is attributed to the over-potentially deposited hydrogen (OPD H).

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.447-447
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• 2012

최근 생물전자공학에서 의료 산업 환경 등 많은 분야에 응용 가능한 바이오센서의 연구가 활발해지고 있다. 그 중 의료 분야에서, 수소이온 ($H^+$)의 농도 감지는 인간의 질병을 예측하는데 중요한 지표가 되며 이러한 수소이온 ($H^+$) 농도의 변화를 실시간으로 감지하기 위해 반도체를 기반으로 한 다양한 pH 센서가 제안되었다. Ion sensitive field effect transistor (ISFET), electrolyte-insulator-semiconductor (EIS)는 대표적인 반도체 pH센서로, 작은 소자 크기, 견고한 구조, 빠른 응답속도와 CMOS 공정과의 호환성이 좋다는 장점이 있다. 특히, EIS는 제조공정이 간단하고 감지막의 감지 특성 평가가 용이하기 때문에 지속적으로 연구되고 있는 pH 센서이다. 센서의 감지 특성을 평가함에 있어 감지막의 감지감도와 안정성이 우수해야 하며 이를 위해 high-k 물질이 감지막으로 사용되고 있다. 추가적으로 high-k 물질은 기존의 $SiO_2$와 $Si_3N_4$를 대신하여 높은 유전상수로 인한 고성능, 고감도 센서제작을 가능케 한다. 본 연구에서는, high-k 물질인 $HfO_2$, $Ta_2O_5$, $ZrO_2$, $Al_2O_3$를 각각 $SiO_2$ 완충막에 적층한 이단 감지막을 제작하였고, 그 특성을 기존의 $SiO_2$, $Si_3N_4$ 감지막의 감지특성과 비교하였다. pH 감지 특성을 평가해 본 결과, 기존의 $SiO_2$, $Si_3N_4$ 감지막과 비교했을 때 high-k 물질의 감지막을 갖는 EIS pH 센서에서 감지감도와 안정성 모두 우수하게 나타났다. 특히, high-k 물질 중 $HfO_2$에서 감지감도가 다소 크게 평가되었으나, 화학적 용액에 대한 안정성은 떨어졌다. 반면에 $Al_2O_3$과 $Ta_2O_5$은 화학용액에 대한 안정성 측면에서 최적의 특성을 보임을 확인하였다. 결론적으로, high-k 물질에 대한 전반적인 평가를 통하여 높은 pH 감지감도뿐만 아니라 우수한 안정성의 EIS pH 센서를 제작 할 수 있었다.

• Journal of the Korean Ceramic Society
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• v.25 no.2
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• pp.136-142
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• 1988

β-Al2O3, which is used for solid electrolyte membrances in sodium-sulfur batteries, was prepared by sol-gel process. Sodium-n-propoxide NaOC3H7 and aluminum-isopropoxide Al(OC3H7)3 were hydrolyzated in the solution at pH 3, pH 7, pH 9 and pH 11, respectively. The sol-gel processed samples were calcined at several temperature steps, respectively and analysed by thermal analyser(DT-TGA), infrared spectrum analyser and X-ray diffraction analyser. The gelling rate of solution at pH 7 was much higher than that of the solution at pH 3. Thermal exchanging behavior of the gels at pH 3 were similar to Na2O·Al2O3·6H2O and, above pH 7, were similar to Na2O·Al2O3·3H2O. When samples' composition ratio was 9.13 : 90.87 [NaOC3H7:Al(OC3H7)3] at pH 7, β-Al2O3 was formed at 1100℃.

• Journal of Soil and Groundwater Environment
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• v.8 no.3
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• pp.56-60
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• 2003

The optimal operation conditions of electrofloatation for oil-water separation of soil flushing effluent including electrolyte and pH were investigated. The reactor (200 ${\times}$ 10 ${\times}$ 15 cm) for the experiment was constructed by using acrylic plate. Diesel concentration was 1,000 mg/L in the 1 % mixed surfactant solution ($POE_5$: $POE_{14}$ 1: 1). Titanium coated electrode was used as cathode and stainless steel electrode as anode. Reaction time was 62 minutes (reaction time: 60 min., flotation time: 2 min.) and voltage was 6 V. The separation efficiency of electrofloatation was improved to 40% by electrolyte addition. Furthermore, NaCl (1N) added as electrolyte was showed enhanced efficiency compared to NaOH (1N). While, the effect of both NaCl and NaOH was sequentially increased in the range of 0.2∼1.0% (0.02∼0.1 M). The equilibrium time was found as 20 min. in the range of 0.4∼1.0% (0.04∼0.1M) for both of them.

• Journal of Environmental Science International
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• v.19 no.9
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• pp.1143-1152
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• 2010

The purpose of this study is to degradation of Rhodamine B (RhB, dye) and N, N-Dimethyl-4-nitrosoaniline (RNO, indicator of the electro-generation of OH radical) in solution using boron doped diamond (BDD) electrode. The effects of applied current (0.2~1.0 A), electrolyte type (NaCl, KCl, and $Na_2SO_4$) and electrolyte concentration (0.5~3.0 g/L), solution pH (3~11) and air flow rate (0~4 L/min) were evaluated. Experimental results showed that RhB and RNO removal tendencies appeared with the almost similar thing, except of current. Optimum current for RhB degradation was 0.6 A, however, RNO degradations was increased with increase of applied current. The RhB and RNO degradation of Cl type electrolyte were higher than that of the sulfate type. The RhB and RNO degradation were increased with increase of NaCl concentration and optimum NaCl dosage was 2.5 g/L. The RhB and RNO concentrations were not influenced by pH under pH 7. Optimum air flow rate for the oxidants generation and RhB and RNO degradation were 2 L/min. Initial removal rate of electrolysis process was expressed Langmuir - Hinshelwood equation, which is used to express the initial removal rate of UV/$TiO_$2 process.

• Journal of Electrical Engineering and Technology
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• v.10 no.6
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• pp.2364-2367
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• 2015

In this study, we fabricated an electrolyte-insulator-metal (EIM) device incorporating a high-k Al₂O₃ sensing membrane using a porous anodic aluminum oxide (AAO) through a two-step anodizing process for pH detection. The structural properties were observed by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction patterns (XRD). Electrochemical measurements taken consisted of capacitance-voltage (C-V), hysteresis voltage and drift rates. The average pore diameter and depth of the AAO membrane with a pore-widening time of 20 min were 123nm and 273.5nm, respectively. At a pore-widening time of 20 min, the EIM device using anodic aluminum oxide exhibited a high sensitivity (56mV/pH), hysteresis voltage (6.2mV) and drift rate (0.25mV/pH).

• Journal of Environmental Health Sciences
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• v.34 no.3
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• pp.226-232
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• 2008

A feasibility study for the application of the photoelectrocatalytic decolorization of Rhodamine B (RhB) was performed in a photoelectrochemical reactor with immobilized $TiO_2$ particle. The effects of operating conditions, such as current, electrolyte and pH were evaluated. The experimental results showed that optimum $TiO_2$ dosage and current in the photoelectrocatalytic process were 83.3 g/l and 0.5 A, respectively. It was found that the RhB could be degraded more efficiently by this photoelectrocatalytic process than the sum of the two individual oxidation processes (photocatalytic and electrolytic process). The addition of NaCl increased the initial decolorization rate and reduced reaction time. The optimum dosage of NaCl was 0.15 g/l. The decolorization rate of the photoelectrocatalytic process increased sharply with a decrease in pH value. However when the NaCl was added, the pH effect was not high.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.5
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• pp.571-579
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• 2013

The aggregation behaviors of silver nanoparticles (AgNPs) and titanium dioxide ($TiO_2$) nanoparticles were investigated. Time-resolved dynamic light scattering (DLS) was used to study the initial aggregation of AgNPs and $TiO_2$ over a range of mono (NaCl) and divalent ($CaCl_2$) electrolyte concentrations. The effects of pH, initial concentration of NPs and natural organic matters (NOM) on the aggregation of NPs were also investigated. The aggregation of both nanoparticles showed classical Derjaguin-Landau-Verwey-Overbeek (DLVO) type behavior. Divalent electrolyte was more efficient in destabilize the AgNPs and $TiO_2$ than monovalent electrolyte. The effect of pH on the aggregation of AgNPs was not significant. But the aggregation rate of $TiO_2$ was much higher with increasing pH. Higher NPs concentration leads to faster aggregation. Natural organic matter (NOM) was found to substantially hinder the aggregation of both AgNPs and $TiO_2$. This study found that the aggregation behavior of AgNPs and $TiO_2$ are closely associated with environmental factors such as ionic strength, pH, initial concentration of NPs and NOM.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.7
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• pp.1042-1048
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• 1990

The approximations of charge relationships at normally doped semiconductor interfaces were qualitatively derived basis on electrical neutrality conditions. Effects of ion adsorptions, activation processes, interfacial structures, rectifying phenomena, and effects of surface potential barriers at the p- and n-Si/CsNO3 aqueous electrolytes, and the p-Si/(1HF:3HNO3:6H2O) electrolyte solutions were investigated using a cyclic voltammetric method. The space charge acts the most important role for the pn junction structures, the rectifying phenomena, and the activation processes. The Current-Voltage (I-V) characteristics curves significantly depend on developing of the Helmholtz double layers and charging of the show surface states during the activation processes. A linear Current-Voltage characteristics region was observed at the p-Si/(1HF:3HNO3: 6H2O) electrolyte solution interface.

• Journal of Surface Science and Engineering
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• v.23 no.1
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• pp.34-43
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• 1990

Al-Si piston alloys such as AlS10CuMg have been anodized to examine apossibility of forming a hard film aat relatively higher temperatures compard with those in conventional sulfuric acid processes. Three types of electrolytes have been employed in this study ; electrolyte A(15% H2SO4, $0^{\circ}C$), electrolyte B(12% H2SO4, 1% oxalic, $10^{\circ}C$), electrolyte C(tartaric acid 125g/L+oxalic 75g/L+aluminum sulfate 225g/L, $25^{\circ}C$). Hard anodisine process in electrolyte B at a current density of 1.54A/dm2 produced a harder film of VHN 396 at a relatibely low film forming voltage compared with those obtained in other electrolyte at equivalent current density. A liner relationship between hardness and abrasion resistance exists for Al-Si piston alloys. The hardness of anodized film decreasees with increasing silicon content in Al-Si alloys and also with bath temperature. The film hardeness of Na-modified alloy os higher than that of P-modified alloy due to its finer microstructre. The film on the silicon phase in Al-Si alloys is observed to be formed by lateral growth of oxide film nucleated at surroundings.