• Applied Chemistry for Engineering
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• v.21 no.6
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• pp.689-693
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• 2010

When natural rubber dissolved in toluene comes into use as a binder of carbon powder, the volatilization of solvent just after the construction of biosensor brought the mechanical robustness on the paste. This characteristic satisfied the pre-requisite condition for the practical use of carbon paste electrode and a biosensor for the determination of hydrogen peroxide was designed. In order to evaluate its electrochemical qualitative and quantitative behaviors, various electrochemical kinetic parameters of the electrode, e.g. the symmetry factor (${\alpha}$, 0.37), the exchange current density ($i_0$, $0.075mAcm^{-2}$), the capacitance of double layer ($C_d$, $9.7{\times}10^{-3}F$), the time constant (${\tau}_A$, 0.92 s), the maximum current ($i_{max}$, $5.92{\times}10^{-7}Acm^{-2}$), the Michaelis constant ($K_M$, $1.99{\times}10^{-3}M$) and others were investigated. Results show that natural rubber is a promising binder of carbon powder.

• Journal of the Korean Society of Safety
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• v.30 no.1
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• pp.14-20
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• 2015

A Large Eddy Simulation(LES) was performed for the prediction of unsteady dispersion behavior of hydrogen fluoride (HF). The HF leakage accident occurred at the Gumi fourth industrial complex was numerically investigated using the Fire Dynamics Simulator (FDS) based on the LES. The accident area was modeled three-dimensionally and time-varying boundary conditions for wind were adopted in the simulation for considering the realistic accident conditions. The Message Passing Interface (MPI) parallel computation technique was used to reduce the computational time. As a result, it was found that the present LES simulation could predict the unsteady dispersion features of HF near the accident area effectively. The dispersion behaviors of the leaked HF was much affected by the unsteady wind direction. The LES could predict the time variation of the HF concentration reasonably and give an useful information for the risk analysis while the prediction with the time-averaging concept of HF concentration had a limitation for the amount of HF concentration at specific location point. It was identified that the LES is very useful to predict the dispersion characteristics of hazardous chemicals.

• Applied Chemistry for Engineering
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• v.20 no.6
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• pp.685-691
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• 2009

Dispersions of fumed silica are made in 6 kinds of mono-solvents and mixed solvents which have hydroxyl group, non hydroxyl group, different polarity, and different molecular size. The viscosity and rheology behaviors of the each dispersion are investigated according to the viewpoint of solvent characteristic. The silica dispersion in polar solvent with hydroxyl group is stable and low viscous sol. The silica dispersion in non-polar solvent with non-hydroxyl group is high viscous gel. When the solvent with hydroxyl group is added to the silica dispersions with non-polar solvents, they show the reduction of viscosity with solvent content. They have minimum critical content which shows no viscosity change. The minimum critical solvent content is decreased according to the polarity of solvents with no hydroxyl group. The solvation layer which is formed on the silica surface through hydrogen bonding between hydroxyl-containing solvent and the silanol group of silica surface is the reason of stable and low viscous sol. In case of non-polar solvent, silanol on adjacent silica particles interacted directly by hydrogen bonding show high viscous and flocculated gel.

• Korean Journal of Materials Research
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• v.11 no.2
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• pp.151-154
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• 2001

The leakage current behaviors of PLZT capacitors with top electrodes of Pt, Ir, and $IrO_2$ are investigated before and after hydrogen forming gas anneal. The P-E hysteresis and fatigue properties of Pt/PLZT/Pt capacitors are almost recovered after recovery anneal in $O_2$ ambient. The leakage current mechanisms of PLZT capacitors with Pt and $IrO_2$ top electrodes are consistent with space-charge influenced injection model showing the strong time dependence irrespective of annealing conditions. On the other hand, the leakage current behavior of Ir/PLZT/Pt capacitor shows steady state independent of time because IrPb, conducting phase, formed at interface between Ir top and PLZT is a high conduction path. Teh leakage current mechanism of Ir/PLZT/Pt capacitor is consistent with Schottky barrier model.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.161-162
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• 2002

This study concerns the tribological behaviors of ultra-thin DLC coating with 3 nm thickness deposited in a mixed gas of argon + 20 % hydrogen as a function of humidity. Reciprocating wear tests employing a micro wear tester were performed under various normal loads and relative humidity in air environment. The chemical composition of the original and worn surfaces were studied by Auger electron spectroscopy (AES). It showed that the ultra-thin DLC coating exhibited low friction with enough wear stability at low normal load (0.18 N) and its tribological behavior was strongly dependent on the humidity. The sample surfaces before and after the test were examined using atomic force microscopy (AFM). Capillary force and meniscus areas were discussed in order to explain the influence of humidity on the friction force.

• Journal of the Korean Ceramic Society
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• v.25 no.4
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• pp.341-348
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• 1988

Thin films of tin-oxide were prepared by chemical vapor deposition technique using the direct of SnCl4. Resistivity and carrier concentration of deposited SnO2 thin film were measured by 4-point probe method and Hall effect measurement. The results showed the remarkable dependence of electrical properties on the deposition temperature. As the deposition temperature increased, resistivity of deposited film initially decreased to a minimum value of ~10-3$\Omega$cm at 50$0^{\circ}C$, and then rapidly increased to ~10$\Omega$cm at $700^{\circ}C$. Electrical conductance of these films was measured in exposure to H2 gas. It was found that gas sensitivity was affected combination of film thickness and intrinsic resistivity of deposited film. Gas sensitivity increased with decrease of film thickness. Fairly high sensitivity to H2 gas was obtained for the film deposited at $700^{\circ}C$. Optimum operation temperature of sensing was 30$0^{\circ}C$ for H2 gas.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2012.03a
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• pp.51-51
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• 2012

Cellulose is extremely difficult to dissolve cellulose in water and most common organic solvents due to their stiff molecular structure, close chain packing and intermolecular hydrogen bonds. Recently, cellulose solutions using ionic liquids (ILs) as a green solvent have been known to form cholesteric liquid crystalline phase at high cellulose concentration. In this study, the phase transition and rheological behaviors of concentrated cellulose/[AMIM]Cl solution were investigated using polarized optical microscopy and rheometry. Studies were conducted to characterize the influence of cellulose concentration on the phase transition of the cellulose solution and the mechanical properties of the regenerated fibers spun from the anisotropic cellulose/[AMIM]Cl solutions.

• Journal of Powder Materials
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• v.10 no.5
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• pp.337-343
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• 2003

Nanostructured Cu-$Al_2O_3$ composite powders were synthesized by thermochemical process. The synthesis procedures are 1) preparation of precursor powder by spray drying of solution made from water-soluble copper and aluminum nitrates, 2) air heat treatments to evaporate volatile components in the precursor powder and synthesis of nano-structured CuO + $Al_2O_3$, and 3) CuO reduction by hydrogen into pure Cu. The suggested procedures stimulated the formation of the gamma-$Al_2O_3$, and different alumina formation behaviors appeared with various heat treating temperatures. The mean particle size of the final Cu/$Al_2O_3$ composite powders produced was 20 nm, and the electrical conductivity and hardness in the hot-extruded bulk were competitive with Cu/$Al_2O_3$ composite by the conventional internal oxidation process.

• Journal of the Korean Professional Engineers Association
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• v.14 no.4
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• pp.15-25
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• 1981

Electrical behaviors of the divalent silver oxide-zinc cell were analyzed for imporving capacity and keeping electrodes from passivation or sharp increases of cell internal resistance in the course of discharge. One of primary factors in relation to lowering performance can be depicted by cell internal resistance increase being created by various routes, first by insufficiency and/or the carbonation of the electrolyte, secondly by barrier blockage, thirdly by electrode passivation which are due to improper material use of wrong processing, and by gassing as fourth cause. The carbonation causes electrobyte to have impedance up as well as poor amalgamation, resulting in vigorous corrosion reaction of copper plated inner top, evolving hydrogen gas. Electrical characteristics of the cell was reviewed to elucidate relationships between the discharge capacity and the cell internal resistance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1123-1130
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• 2006

This study discusses about research efforts of hydrogen generation from hydrocarbon(e.g., diesel, gasoline, natural gas, and LPG), especially, butane reforming by using Autothermal Reforming Reaction (ATR) technology. Several catalysts were selected for butane ATR. Thermodynamic reactor conditions (temperature, $O_2$/C, S/C) are varied and reforming characteristics of 2 catalysts (Pt and Rh on ceramic supports) and 1 commercial catalyst (FCR-HC35) have been examined. To understand reaction behaviors in an ATR reactor comprehensively, temperature profiles of reactor were observed. By mass transfer limitation, fuel conversion decreases when GHSV increases. Significant temperature variation along the reactor was observed and it was mainly due reaction kinetics difference between exothermic oxidation and endothermic reforming reaction.