• Journal of Sensor Science and Technology
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• v.9 no.1
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• pp.9-14
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• 2000

Dielectric characteristics of P(VDF/TrFE) film manufactured using spin coating technique have been investigated. To improve the crystallinity and quality of film, the film was three step annealed. Simple etching process and conditions for P(VDF/TrFE) film were established using top electrode as a mask. Poling is performed by several steps. $1.87\;{\mu}m$ thick P(VDF/TrFE) films were obtained with conditions such that the solution of 10 wt% concentration was spun at 3000rpm for 30 seconds. Before poling, dielectric constant and dielectric loss of P(VDF/TrFE) film were 13.5 and 0.042, respectively. After poling, dielectric constant and dielectric loss of P(VDF/TrFE) film were 11.5 and 0.037, respectively.

• Applied Chemistry for Engineering
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• v.25 no.4
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• pp.386-391
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• 2014

Atmospheric-pressure nonthermal corona discharge plasma was applied to the sterilization of biologically contaminated scoria powder. Escherichia coli (E. coli) culture solution was uniformly sprayed throughout the scoria powder for artificial inoculation, which was well mixed to ensure uniformity of the batch. The effect of the key parameters such as discharge power, treatment time, type of gas and electrode distance on the sterilization efficiency was examined and discussed. The experimental results revealed that the plasma treatment was very effective for the sterilization of scoria powder; 5-min treatment at 15 W could sterilize more than 99.9% of E. coli inoculated into the scoria powder. Increasing the discharge power, treatment time or applied voltage led to an improvement in the sterilization efficiency. The effect of type of gas on the sterilization efficiency was in order of oxygen, synthetic air (20% oxygen) and nitrogen from high to low. The inactivation of E. coli under the influence of corona discharge plasma can be explained by cell membrane erosion or etching resulting from UV and reactive oxidizing species (oxygen radical, OH radical, ozone, etc.), and the destruction of E. coli cell membrane by the physical action of numerous corona streamers.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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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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• v.2 no.3
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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

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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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.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.59-63
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• 2006

The study is coated tin(IV) oxide coated on the titanium substrate electrodes by electrodepositon and dip-coating method and studied about that physical and electrochemical characterization by coating methods. After titanium substrate is etched in HCl, electrodespotion is coated $SnCl_2{\cdot}2H_2O$ in nitrate solution by pulse technique, dip-coating method is also used $SnCl_2{\cdot}2H_2O$ in 1;1V% HCl and coated by dipping and annealing process. tin(IV) oxide coated on titanium substrate electrodes by two coating methods are studied x-ray diffraction (XRD), scanning electron microscopy (SEM) to compare physical characterization of electrode and potential window by cyclic voltammetry (CV) to observe electrochemical characterization.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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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 $1350^{\circ}C$.

• Journal of the Korean institute of surface engineering
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• v.42 no.4
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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.

• Proceedings of the KIEE Conference
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• 1999.07g
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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.

• Proceedings of the KIEE Conference
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• 2005.07c
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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