• Korean Journal of Materials Research
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• v.13 no.11
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• pp.761-768
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• 2003

The corrosion resistance and cytotoxicity behavior of Ti alloys were studied as a function of Nb contents(3wt.%Nb, 20wt.%Nb, 40wt.%Nb). Ti-Nb alloys were melted by vacuum arc furnace and then rolled to 50% reduction ratio after homogenized at 105$0^{\circ}C$ for 24hrs. The corrosion resistance of Ti-Nb alloys were investigated by potentiodynamic polarization test in the 0.9% NaCl and 5% HCI solution. Biocompatibility of Ti-Nb alloys was evaluated by cytotoxicity test. The results can be summarized as follows 1) The microstructure change from equiaxial to acicular and the increased $\beta$ phase in Ti-Nb alloys were obtained as the Nb content increased. 2) For the corrosion test in the solution of 0.9% NaCl and 5% HCI, the corrosion behavior of Ti-Nb alloys was similar to ASTM grade 2 CP Ti. 3) For the cytotoxicity test, Ti-Nb alloys showed excellent biocompatibility compared to ASTM grade 2 CP Ti, 316L STS and Co-Cr alloys.

• Journal of the Korean Ceramic Society
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• v.48 no.2
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• pp.160-167
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• 2011

Plasma sprayed ceramic coatings inherently contain pores and usually also cracks. Post-treatment of the plasma sprayed coatings is a way to close the connected pores and cracks. In this study, post-sealing treatment in plasma sprayed $Al_2O_3$ coatings was employed to overcome the reduction of coating properties. $Al_2O_3$ plasma thermal spray coating was made on aluminum alloys plate, $CrO_3$ post coating and heat treatment at $550^{\circ}C$ was carried out in order for final $Cr_2O_3$ to be saturated through phase transformation. Chromia sealing began at the fine defect in coated microstructure, while larger pores were permeated later. The increase in concentration and treatment frequency of sealing solution resulted in the decrease of porosity of coating layer, while cracks occurred partially after the third treatment. After twice treatment of 10M $CrO_3$ solution, microhardness and breakdown voltage of $Al_2O_3$ coatings were found to increase by ${\fallingdotseq}$ 50% and ${\fallingdotseq}$ 390% respectively than without post-treatment.

• The Korean Journal of Physiology
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• v.16 no.2
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• pp.119-128
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• 1982

The frog truncus arterious were studied with conventional glass microelectrode technique in order to elucidate the underlying mechanism of spontaneous pacemaker activity. The analyses were focussed on the ionic nature of pacemaker current by changing the concentrations of extracellular $K^+$ and, $Na^+$, or by using blockers of K- and Ca-current and chronotropic transmitters. 1) The action potential of the spontaneously active truncus arteriosus has some characteristic feature of maximal distolic potential ranged from -65 to -75 mV, resting potential from -45 to -50 mV and overshoot voltage about +30 mV, respectively. Duration of the action potential taken from rapid upstroke to maximal diastolic potential was about 600 msec. Usual discharge rate was $25{\sim}30/min$ at room temperature $(18{\sim}20^{\circ}C)$. 2) The sensitivity of the resting membrane potential to change extracellular potassium concentrations $(0{\sim}12\;mM)$ was relatively low. Transient hyperpolarization was appeared in the 12 mM K Ringer after 10 min exposure to 0 mM K and it could be related to Na-pump reactivation by high potassium. 3) Reduction of extracellular sodium concetrations diminished the amplitude and frequency of the action potential. In Ringer solution containing 30% Na (substituted by equimolar Tris), spontaneous activity stopped but reappeared as very slow and small action potential. There was no spotaneous activity in zero Na Ringer solution. 4) Caesium(10 mM), K-current blocker decreased the frequency of the action potential and also pacemaker depolarization. Manganese (2 mM) known to be Ca-current antagonist, blocked spontaneous activity completely. 5) Adrenaline and acetylcholine had no chronotropic effect. But adrenaline increased the duration of plateau phase and the magnitude of the action potential in the follower cell. It is concluded that K-, Na-and Ca-current components are involved in the genesis of spontaneous activity of the frog truncus arteriosus like cardiac pacemaker tissues. But the insensitivity of truncus arteriosus to adrenaline and acetylcholine indicates that there are some different control mechanisms of spontaneous rhythm in two tissues.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.201-205
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• 2012

The effects of various manganese precursors for the low-temperature selective catalytic reduction (SCR) of $NO_x$ were investigated in terms of structural, morphological, and physico-chemical analyses. $MnO_x/TiO_2$ catalysts were prepared from three different precursors, manganese nitrate, manganese acetate(II), and manganese acetate(III), by the sol-gel method. The manganese acetate(III)-$MnO_x/TiO_2$ catalyst tended to suppress the phase transition from the anatase structure to the rutile or the brookite after calcination at $500^{\circ}C$ for 2 h. It also had a high specific surface area, which was caused by a smaller particle size and more uniform distribution than the others. The change of catalytic acid sites was confirmed by Raman and FT-IR spectroscopy and the manganese acetate(III)-$MnO_x/TiO_2$ had the strongest Lewis acid sites among them. The highest de-NOx efficiency and structural stability were achieved by using the manganese cetate(III) as a precursor, because of its high specific surface area, a large amount of anatase $TiO_2$, and the strong catalytic acidity.

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.594-599
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• 2011

$SrAl_2O_4:Eu$ green phosphor was prepared by spray pyrolysis and its luminescence properties were controlled by replacing the Al sites with boron and using organic modifier or drying control chemical additive. It was clear that the substitution of B into the Al sites was helpful to obtain pure monoclinic $SrAl_2O_4$ phase and greatly enhance the emission intensity. In terms of the emission intensity, the optimal content of boron was about 1 at% with respect to the aluminum element. The luminescence intensity of $Sr_{0.9}Al_{1.98}B_{0.02}O_4:Eu_{0.1}$ phosphor could be improved by the use of 0.2 M organic additives in the spray solution. Futhermore, using 0.5 M dimethylformamide(DMF) as a drying control chemical with organic additives made it possible to improve about 172% the emission intensity of $Sr_{0.9}Al_{1.98}B_{0.02}O_4:Eu_{0.1}$ phosphor. According to XRD analysis, the organic additive and DMF used enhanced the crystallinity without any change in the crystal phase. When used only the organic additive without DMF, the surface area of the prepared $Sr_{0.9}Al_{1.98}B_{0.02}O_4:Eu_{0.1}$ phosphor became enlarged. The use of DMF with the organic additive resulted in significant reduction in the surface area. It was concluded that the increase of the crystallinity as well as the reduction of surface area mainly contribute to the improvement in the luminescence intensity of $Sr_{0.9}Al_{1.98}B_{0.02}O_4:Eu_{0.1}$ phosphor prepared using DMF and organic additives.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.114-120
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• 1997

Perovskite $BaTiO_3$ thin films on stainless steel substrate were prepared by using electrochemical reduction method in solution of $TiCl_4\;and\;Ba(N0_3)_2$. According to current density and electrolysis time. the morphology and thickness of film were varied. Ra/'Ti atomic ratio in $BaTiO_3$ film was controlled by Ha/Ti atomic ratio in solution. Although the excess $TiO_2{\cdot}nH_2O$ film was coated in initial stage of electrolysis. UiilTi atomic ratio in film was nearly constant in later stage. $BaTiO_3$ film precursor was obtained under the condition of $1OmA/cm^2$ current density and Smin electrolysis time. $BaTiO_2$ thin films with perovskite phase were formed 11,. the heat treatment above $500^{\circ}$.

• 한국해양학회지
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• v.28 no.3
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• pp.229-240
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• 1993

This study investigated the behaviour of sulfur species after the early diegenetic reduction of sulfate from pore solution in an anoxic intertidal flat deposit in the Banweol area of Kyeong-gi Bay, west coast of Korea. A total of seven sediment cores were collected during 1990∼1992 and were analyzed for their solid-phase sulfur species (acid-volatile sulfur, element sulfur, pyrite sulfur) as well as for chemical components in the pore solution, such as sulfate, ammonium, hydrogen sulfide, phosphate and Fe ion. The pore water sulfate oncentration was found to decrease rapidly downward from the sediment surface, while that of hydrogen sulfide, ammonium and phosphate showed and increase. The dissolved iron concentration in pore water, on the other hand, was found high in the surface layer of sediment, but fell sharply below this layer. these characteristic profiles of pore water sulfide and iron concentrations suggest that some reaction occurs between dissolved iron and sulfide ions, leading to the formation of various sulfide minerals in the sedimentary phase. The amount of inorganic sulfur species in the sediment increased downward, and showed a maximum of up to 7.9 mg/g. among the three species analyzed, acid-volatile sulfur (AVS) was dominant comprising more than 50% of the total. The amount of pyrite sulfur was greater than that of element sulfur. This implies that the formation of pyrite was restricted in this environment. the limited amount of element sulfur in this deposit may have discouraged the active formation of pyrite.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.3
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• pp.51-56
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• 2016

To fabricate a copper (Cu)-based fine conductive filler having antioxidation property, submicron silver (Ag)-coated Cu particles were fabricated and their antioxidation property was evaluated. After synthesizing the Cu particles of $0.705{\mu}m$ in average diameter by a wet-reduction process, Ag-coated Cu particles were fabricated by successive Ag plating using ethylene grycol solvent. Main process parameters in the Ag plating were the concentration of reductant (ascorbic acid), the injection rate of Ag precursor solution, and the stirring rate in mixed solution. Thus, Ag plating characteristics and the formation of separate fine pure Ag phase were observed with different combinations of process parameters. As a result, formation of the separate pure Ag phase and aggregation between Ag-coated Cu particles could be suppressed by optimization of the process parameters. The Ag-coated Cu particles which were fabricated using optimal conditions showed slight aggregation, but excellent antioxidation property. For example, the particles indicated the weight gain not exceeding 0.1% until $225^{\circ}C$ when they were heated in air at the rate of $10^{\circ}C/min$ and no weight gain until 75 min when they were heated in air at $150^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.41 no.5
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• pp.410-416
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• 2004

In this study, we fabricated magnetite coated on a cordierite honeycomb which has complex shape by ultrasound-enhanced ferrite plating. The effects of the plating condition on the formation of the magnetite and its microstructure were investigated. The magnetite coated on the honeycomb became an oxygen-deficient ferrite by H$_2$ gas reduction, then the effects of the molar concentrations of ammonium acetate for $CO_2$ gas decomposition have been studied. As the molar concentration of a pH buffer($CH_3$COONH$_4$, 0.1946∼0.3892 M) solution increased, the average particle size increased about 200∼250 nm. The magnetite coated on the honeycomb was reduced by H$_2$ gas for 2 h at 30$0^{\circ}C$. The inner pressure change in the cell began to occur at 315∼34$0^{\circ}C$. The H$_2$-Reduced magnetite coated on the honeycomb at 35$0^{\circ}C$ contained an oxygen deficient magnetite and $\alpha$-Fe phase. The thermogravimetric analysis with H$_2$ reduction and $CO_2$ decomposition were carried out with the magnetite coated on the honeycomb. A weight loss in process of H$_2$ reduction occurred between 32$0^{\circ}C$ and 34$0^{\circ}C$, while a weight gain was observed during the $CO_2$ decomposition.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.3
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• pp.523-533
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• 2000

A two-phase anaerobic reactor with submerged membrane system was developed for increasing acidogen concentration and methane recovery. The membrane used was mixed esters of cellulose of $0.5{\mu}m$ pore size and $0.8m^2$ of effective surface area. The methanogenic reactor comprised of UASB (Upflow Anaerobic Sludge Blanket) and AF (Anaerobic Filter). COD removal efficiency was 70~80% and the methane content in the biogas increased up to 90% for the submerged membrane system in the anaerobic reactor. As the cake resistance of membrane caused a serious problem, stainless steal prefilters (40, 53, $63{\mu}m$) and air backwashing methods were applied to minimize the cake resistance effectively. Among the tested prefilters. the $63{\mu}m$ prefilter showed the best performance for reduction of cake resistance and a successful long-tern operation. By cleaning with alkali first and acidic solution later. the permeate flux decreased by long term operation was recovered to 89% of that with a new membrane.