• Journal of Biosystems Engineering
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• v.33 no.6
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• pp.404-409
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• 2008

Excessive presence of heavy metals in environment affects plants and fruits grown in the contaminated area. Rapid on-site monitoring of heavy metals can provide useful information for efficiently characterizing heavy metal-contaminated sites and for minimizing the exposure of the contaminated food crops to humans. This study reports on the evaluation of gold and glassy carbon (GC) electrodes with mercury or bismuth as a coating material for simultaneous determination of cadmium (Cd) and lead (Pb) in 0.1 M $HNO_3$ solution by anodic stripping voltammetry (ASV). The use of a square-wave voltammetric potential between a working electrode and a reference electrode caused Cd and Pb ions deposited on the electrode surface to be oxidized, thereby generating electric currents at different potentials. The mercury-coated gold electrode was not sensitive enough to detect the usable range of Cd concentrations (1 to 100 ppb). The GC electrodes with mercury or bismuth displayed well-defined, sharp and separate current peaks for Cd and Pb ions when the square-wave voltammetric potentials were applied. The peak currents measured with both mercury- and bismuth- coated GC electrodes were linearly proportional to Cd and Pb concentrations in the range of 1 to 200 ppb in 0.1 M $HNO_3$ with strong linear relationships between concentration and peak current ($R^2$ > 0.95), indicating that both of Cd and Pb ions could be quantitatively measured.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.224-224
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• 2012

For decades, carbon fiber has expanded their application fields from reinforced composites to energy storage and transfer technologies such as electrodes for super-capacitors and lithium ion batteries and gas diffusion layers for proton exchange membrane fuel cell. Especially in fuel cell, water repellency of gas diffusion layer has become very important property for preventing flooding which is induced by condensed water could damage the fuel cell performance. In this work, we fabricated superhydrophobic network of carbon fiber with high aspect ratio hair-like nanostructure by preferential oxygen plasma etching. Superhydrophobic carbon fiber surfaces were achieved by hydrophobic material coating with a siloxane-based hydrocarbon film, which increased the water contact angle from $147^{\circ}$ to $163^{\circ}$ and decreased the contact angle hysteresis from $71^{\circ}$ to below $5^{\circ}$, sufficient to cause droplet roll-off from the surface in millimeter scale water droplet deposition test. Also, we have explored that the condensation behavior (nucleation and growth) of water droplet on the superhydrophobic carbon fiber were significantly retarded due to the high-aspect-ratio nanostructures under super-saturated vapor conditions. It is implied that superhydrophobic carbon fiber can provide a passage for vapor or gas flow in wet environments such as a gas diffusion layer requiring the effective water removal in the operation of proton exchange membrane fuel cell. Moreover, such nanostructuring of carbon-based materials can be extended to carbon fiber, carbon black or carbon films for applications as a cathode in lithium batteries or carbon fiber composites.

• Clean Technology
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• v.8 no.4
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• pp.173-180
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• 2002

As a primary material for MLCC, $BaTiO_3$ particles coated with two additives in a core-shell structure were prepared in this study. This composite powder can not only reduce the VOC emission during MLCC manufacture but also increase the density and reliability of electronic products. The additives were $Y_2O_3$ and $MnCO_3$, whose composition information was obtained from domestic companies. It was observed that the surface of $BaTiO_3$ particles was uniformly as well as simultaneously coated by those two materials via urea-decomposition reaction over $70^{\circ}C$ as the reaction temperature. Elemental analysis indicated that the measured content of each additve was quite close to the designated value. The effect of polymeric dispersant such as PVP, on the coating characteristics was not as significant as expected.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.73.1-73.1
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• 2010

For the successful cold starting of a fuel cell engine, either internal of external heat supply must be made to overcome the formation of ice from water below the freezing point of water. In the present study, switchable vanadium oxide compounds as variable temperature-electrical resistance materials onto the surface of flat metallic bipolar plates have been prepared by a dip-coating technique via an aqueous sol-gel method. Subsequently, the chemical composition and micro-structure of the polycrystalline solid thin films were analyzed by X-ray diffraction, X-ray fluorescence spectroscopy, and field emission scanning electron microscopy. In addition, it was carefully measured electrical resistance hysteresis loop over a temperature range from $-20^{\circ}C$ to $80^{\circ}C$ using the four-point probe method. The experimental results revealed that the thin films was mainly composed of Karelianite $V_2O_3$ which acts as negative temperature coefficient materials. Also, it was found that thermal dissipation rate of the vanadium oxide thin films partially satisfy about 50% saving of the substantial amount of energy required for ice melting at $-20^{\circ}C$. Moreover, electrical resistances of the vanadium-based materials converge on an extremely small value similar to that of pure flat metallic bipolar plates at higher temperature, i.e. $T{\geq}40^{\circ}C$. As a consequence, experimental studies proved that it is possible to apply the variable temperature-electrical resistance material based on vanadium oxides for the cold starting enhancement of a fuel cell vehicle and minimize parasitic power loss and eliminate any necessity for external equipment for heat supply in freezing conditions.

• Journal of the Korean Vacuum Society
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• v.13 no.1
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• pp.39-45
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• 2004

Ultraviolet-nanoimprint lithography (UV-NIL) is a promising method for cost-effectively defining nanoscale structures at room temperature and low pressure. A 5${\times}$5${\times}$0.09 in. quartz stamp is fabricated using the etch process in which a Cr film was employed as a hard mask for transferring nanostructures onto the quartz plate. FAS(Fluoroalkanesilane) is used as a material for anti-adhesion surface treatment on the stamp and a thin organic film to improve adhesion on a wafer is formed by spin-coating. The low viscosity resin droplets with a nanometer scale volume are dispensed on the whole area of the coated wafer. The UV-NIL experiments have been performed using the EVG620-NIL. 370 nm - 1 m features on the stamp have been transferred to the thin resin layer on the wafer using the multi-dispensing method and UV-NIL process. We have measured the imprinted patterns and residual layer using SEM and AFM to evaluate the potential of the process.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.37 no.3
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• pp.23-32
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• 2005

A change of z-directional structural and surface properties by calendering has a great influence on liquid penetration into a sheet. It could be also important for multi-ply sheet because it contacts liquid dunhg coating or converting process. Therefore, this study was aimed to evaluate of a change of z-directional structure in multi-ply sheet by calendering. To do this, multi-ply sheets were prepared with various raw materials and calendered at the different pressure and temperature conditions. In multi-ply sheet which consisted of one kind of pulp fiber, thickness reductions were higher in top and bottom plies than in middle plies. And in the case of soft nip calender treatment with high temperature, top layer which was in contact with heating roll showed the highest reduction of thickness. Hard nip calender treatment showed U-shaped density profile in z-direction, but compression profile by SNC treatment was dependent on calendering condition. To examine z-directional structure of multi-ply sheet which was composed of different raw material for each layer, CLSM (Confocal Laser Scanning Microscopy) analyses were carried out on cross direction of sheet. It turned out to be a useful tool for investigating z-directional analysis. As a result, variation of thickness reduction in z-direction is dependent on ply structure, compressibility of pulp fiber, and calendering condition.

• Korean Journal of Materials Research
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• v.24 no.6
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• pp.310-318
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• 2014

In this experiment, a highly porous scaffold of biphasic calcium phosphate (BCP) was prepared using the spongereplica method. The BCP scaffold was coated with 58S bioactive glass (BG) and sintered for a second time. The resulting scaffold was coated with gelatin (Gel) and cross-linked with [3-(3-dimethyl aminopropyl) carbodiimide] and N-Hydroxysuccinamide (EDC-NHS). The initial average pore size of the scaffold ranged from 300 to $700{\mu}m$, with more than 85 % porosity. The coating of BG and Gel had a significant effect on the scaffold-pore size, decreasing scaffold porosity while increasing mechanical strength. The material and surface properties were evaluated by means of several experiments involving scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-ray diffraction (XRD). Cytotoxicity was evaluated using MTT assay and confocal imaging of MC3T3-E1 pre-osteoblast cells cultured in vitro. Three types of scaffold (BCP, BCP-BG and BCP-BG-Gel) were implanted in a rat skull for in vivo evaluation. After 8 weeks of implantation, bone regeneration occurred in all three types of sample. Interestingly, regeneration was found to be greater (geometrically and physiologically) for neat BCP scaffolds than for two other kinds of composite scaffolds. However, the other two types of scaffolds were still better than the control (i.e., defect without treatment).

• Journal of Welding and Joining
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• v.23 no.3
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• pp.76-82
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• 2005

Recently the application of laser welding technology has been considered to shipbuilding structure. However, when this technology is applied to primer coated steel, good quality weld beads are not easily obtained. Because the primer-coated layer caused the spatter, humping bead and porosity which are main part of the welding defect attributed to the powerful vaporizing pressure of zinc. So we performed experiment with objectives of understanding spatter and porosity formation mechanism and producing sound weld beads in 6mmt primer coated steels by a $CO_2$ CW laser. The effects of welding parameters; defocused distance, welding speed, coated thickness and coated position; were investigated in the bead shape and penetration depth on bead and lap welding. Alternative idea was suggested to suspend the welding defect by giving a reasonable gap clearance for primer coated thickness. The zinc of primer has a boiling point that is lower than melting point of steel. Zinc vapor builds up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Significant effects of primer coated position was lap side rather than surface. Therefore introducing a small gap clearance in the lap position, the zinc vapor could escape through it and sound weld beads can be acquired. In conclusion, formation and suspension mechanism of the welding defects was suggested by controling the factors.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.193-202
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• 2008

This paper investigates experimentally the confining effect, strengthening capacity and rebound rate of sprayed Fiber-Reinforced-Polymer (SFRP). From the method, resin and chopped fibers are sprayed separately from the nozzle with high pressure, and then they are attached to the concrete surface, so structure could be repaired. To evaluate the strengthening effect of sprayed FRP, cylindrical specimens and beam specimens were strengthening with SFRP. As main material of FRP, glass fiber and polyester resin are used. To investigate the optimum condition of sprayed FRP, the effects of fiber length, coating thickness, fiber volume ratio and concrete strength were examined. Capacities of sprayed FRP method were also compared to the FRP sheet method. In case of the sprayed FRP, rebound rate is important parameter considering economical efficiency and constructibility, so rebound rate of was discussed. From the test results, optimum conditions of sprayed FRP were determined. SFRP method showed superior strengthening capacities than FRP sheet method.

• Journal of the Korean Society of Industry Convergence
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• v.8 no.1
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• pp.47-55
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• 2005

Infrared heating has been traditionally used in industrial applications for processes such as dehydration of food industrial. This heating method involves the application of radiation in the wavelength range of 2 to 50 micrometers. In this work, simultaneous heat balance equations were developed to simulate the infrared radiation heating of agricultural products. The equations assume that moisture diffuses to the outer boundaries of the material in liquid form and evaporation occurs at the surface of the agricultural products. Energy for moisture evaporation is supplied by the infrared radiant energy. The optimum temperature and drying time for the best drying conditions of changing the red peppers with the moisture content of 18% and the restore rate of 80~85% are $80^{\circ}C$ and 44 hours. The performance of radiation tubes coating with the radiation paint developed in this research has the energy of $2.27{\times}103W/m^2{\mu}m$, $150^{\circ}C$ within the scope of radiation wave length of $2{\sim}30{\mu}m$ and has the radiation 0.92~0.93, which is superior to the general radiation tubes. The extinction coefficient according to the band pass filter using the 4 flux theory ha higher dependability on wave length, accounting for $2{\sim}17{\mu}m$ and $5{\times}105{\sim}106m-1$. A comparison between the theoretical energy transfer whose figures are interpreted according to 4 flux theory and the experimental energy transfer of far infrared dryer leads to the findings of the agreement less than 5%.