• The Transactions of the Korean Institute of Electrical Engineers C
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• 제49권11호
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• pp.596-602
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• 2000

Diamond thin films were synthesized on WC-Co substrate at various experimental parameters using 13.56MHz RF PACVD)radio frequency plasma-assisted chemical vapor deposition). In order to increased the nucleation density, the WC-Co substrate was polished with 3${\mu}m$ diamond paste. And the WC-Co substrate was preatreated in $HNO_3\;:\;H_2O$ = 1:1 and $O_2$ plasma. In $H_2-CH_4$ gas mixture, the crystallinity of thin film increased with decreasing $CH_4$ concentration at 800W discharge power and 20torr reaction pressure. In $H_2-CH_4-O_2$ gas mixture, the crystallinity of thin film increased with increasing $O_2$ concentration at 800W discharge power, 200torr reaction pressure and 4% $CH_4$ concentration.

• Korean Journal of Materials Research
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• 제27권9호
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• pp.507-511
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• 2017

An optimum route to fabricate oxide dispersion strengthened ferritic superalloy with desired microstructure was investigated. Two methods of high energy ball milling or polymeric additive solution route for developing a uniform dispersion of $Y_2O_3$ particles in Fe-Cr-Al-Ti alloy powders were compared on the basis of the resulting microstructures. Microstructural observation revealed that the crystalline size of Fe decreased with increases in milling time, to values of about 15-20 nm, and that an FeCr alloy phase was formed. SEM and TEM analyses of the alloy powders fabricated by solution route using yttrium nitrate and polyvinyl alcohol showed that the nano-sized Y-oxide particles were well distributed in the Fe based alloy powders. The prepared powders were sintered at 1000 and $1100^{\circ}C$ for 30 min in vacuum. The sintered specimen with heat treatment before spark plasma sintering at $1100^{\circ}C$ showed a more homogeneous microstructure. In the case of sintering at $1100^{\circ}C$, the alloys exhibited densified microstructure and the formation of large reaction phases due to oxidation of Al.

• Journal of the Korean institute of surface engineering
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• 제34권5호
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• pp.421-428
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• 2001

New WC-CrN superlattice film was deposited on Si substrate (500$\mu\textrm{m}$) using cathodic arc ion plating system. The microstructure and mechanical properties of the film depend on the superlattice period (λ). In the X-ray diffraction analysis (XRD), preferred orientation of microstructure was changed according to various superlattice periods(λ). During the Transmission Electron Microscope analysis (TEM), microstructure and superlattice period (λ) of the WC - CrN superlattice film was confirmed. Hardness and adhesion of the deposited film was evaluated by nanoindentation test and scratch test, respectively. As a result of nanoindentation test, the hardness of WC - CrN superlattice film was gained about 40GPa at superlattice period (λ) with 7nm. Also residual stress with various superlattice period (λ) was measured on Si wafer (100$\mu\textrm{m}$) by conventional beam-bending technique. The residual stress of the film was reduced to a value of 0.2 GPa by introducing Ti - WC buffer layers periodically with a thickness ratio ($t_{buffer}$/$t_{buffer+superlattice}$ ). To the end, for the evaluation of oxidation resistance at the elevated temperature, CrN single layer and WC - CrN superlattice films with various superlattice periods on SKD61 substrate was measured and compared with the oxidation resistance.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.62-62
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• 2018

Pt is still considered as one of the most active electrocatalysts for ORR in alkaline fuel cells. However, the high cost and scarcity of Pt hamper the widespread commercialization of fuel cells. As a strong candidate for the replacement of Pt catalyst, silver (Ag) has been extensively studied due to its high activity, abundance, and low cost. Ag is more stable than Pt in the pH range of 8~14 as the equilibrium potential of Ag/Ag+ being ${\approx}200mV$ higher than that of Pt/PtO. However, Ag is the overall catalytic activity of Ag for oxygen reduction reaction(ORR) is still not comparable to Pt catalyst since the surface Ag atoms are approximately 10 times less active than Pt atoms. Therefore, further enhancement in the ORR activity of Ag catalysts is necessary to be competitive with current cutting-edge Pt-based catalysts. We demonstrate the architectural design of Ag catalysts, synthesized using plasma discharge in liquid phase, for enhanced ORR kinetics in alkaline media. An attractive feature of this work is that the plasma status controlled via electric-field could form the Ag nanowires or dendrites without any chemical agents. The plasma reactor was made of a Teflon vessel with an inner diameter of 80 mm and a height of 80 mm, where a pair of tungsten(W) electrodes with a diameter of 2 mm was placed horizontally. The stock solutions were made by dissolving the 5-mM AgNO3 in DI water. For the synthesis of Agnanowires, the electricfield of 3.6kVcm-1 in a 200-ml AgNO3 aqueous solution was applied across the electrodes using a bipolar pulsed power supply(Kurita, Seisakusyo Co. Ltd). The repetition rate and pulse width were fixed at 30kHz and 2.0 us, respectively. The plasma discharge was carried out for a fixed reaction time of 60 min. In case of Ag nanodendrites, the electric field of 32kVcm-1 in a 200-ml AgNO3 aqueous solution was applied and other conditions were identical to the plasma discharge in water in terms of electrode configuration, repetition rate and discharge time. Using SEM and STEM, morphology of Ag nanowires and dendrites were investigated. With 3.6 kV/cm, Ag nanowire was obtained, while Ag dendrite was constructed with 32 kV/cm. The average diameter and legth of Ag nanowireses were 50 nm and 3.5 um, and thoes values of Ag dendrites were 40 nm and 3.0 um. As a results of XPS analysis, the surface defects in the Ag nanowires facilitated O2 incorporation into the surface region via the interaction between the oxygen and the electron cloud of the adjacent Ag atoms. The catalytic activity of Ag for oxygen reduction reaction(ORR) showed that the catalytic ORR activity of Ag nanowires are much better than Ag nanodendrites, and electron transfer number of Ag nanowires is similar to that of Pt (${\approx}4$).

• Applied Chemistry for Engineering
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• 제19권3호
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• pp.270-276
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• 2008

$N_2$ doped $TiO_2$ nano-sized powder was prepared using a DC arc plasma jet and investigated with XRD, BET, SEM, TEM, and photo-catalytic decomposition. Recently the research interest about the nano-sized $TiO_2$ powder has been increased to improve its photo-catalytic activity for the removal of environmental pollutants. Nitrogen gas, reacting gas, and titanium tetrachloride ($TiCl_4$) were used as the raw materials and injected into the plasma reactor to synthesize the $N_2$ doped $TiO_2$ power. The particle size and XRD peaks of the synthesized powder were analyzed as a function of the flow rate of the nitrogen gas. Also, the characteristics of the photo-catalytic decomposition using the prepared powder were studied. For comparing the photo-catalytic decomposition performance of $TiO_2$ powder with that of $TiO_2$ coating, $TiO_2$ thin films were prepared by the spin coating and the pulsed laser deposition. For the results of the acetaldehyde decomposition, the photo-catalytic activity of $TiO_{2-x}N_x$ powder was higher than that of the pure $TiO_2$ powder in the visible light region. For the methylene blue decomposition, the decomposition efficiency of $TiO_2$ powder was also higher than that of $TiO_2$ film.

• Journal of Korean Society of Environmental Engineers
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• 제28권3호
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• pp.323-328
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• 2006

The purpose of this paper was to investigate the reforming characteristics and optimum operating condition of the GlidArc-assisted $C_3H_8$ reforming reaction for the synthesis gas(SynGas) production without formation of carbon black from propane using GildArc plasma reforming. Also, in order to increase the hydrogen production and the propane conversion rate, 13 wt % nickel catalyst was filled into the catalytic reactor and parametric screening studies were conducted, in which there were the variations of vapor mole ratio$(H_2O/C_3H_8),\;CO_2$ mole ratio($CO_2/C_3H_8$), input power and injection flow rate. When the variations of vapor mole ratio, $CO_2$ mole ratio, input power and injection flow rate were 1.86, 0.48, 1.37 kW and 14 L/min, respectively, the conversion rate of the propane reached its most optimal condition, or 62.6%. Under the condition mentioned above, the dry basic concentrations of the SynGas were $H_2\;44.4%,\;CO\;18.2%,\;CH_4\;11.2%,\;C_2H_2\;2.0%,\;C_3H_6\;1.6%,\;C_2H_4\;0.6%\;and\;C_3H_4$ 0.4%. The conversion rate of carbon dioxide was 29.2% and the concentration ratio of hydrogen to carbon monoxide($H_2/CO$) in the SynGas was 2.4.

• Asian-Australasian Journal of Animal Sciences
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• 제12권4호
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• pp.585-589
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• 1999

Six crossbred goats in their 2nd or 3rd lactation, were administered bromocryptine at 5 mg/day during early lactation of 15-20 days (period I) and thereafter again at an interval of 13 days, bromocryptine was given for 5 days (period II). Blood samples were collected before (-5, -4, -3, -2, -1) during (1, 2, 3, 4, 5) and after (+1, +2, +3, +4, +5) administration of bromocryptine in both the periods of study. In period I, administration of bromocryptine resulted in a decrease in milk yield to the extent of 16..8% in comparison to before treatment, and 28.5% after the cessation of treatment. The glucose content of blood increased (p<0.01) as the milk yield decreased without any change in NEFA concentration. During period II of bromocryptine treatment the milk yields did not change in spite of a decline in prolactin level, perhaps the effect of previous treatment was prolonged. A decline in protein and lactose content of milk after bromocryptine treatment in both the periods of study, when prolactin level also declined suggests a role of prolactin in protein synthesis and also a depressing effect on lactose synthesis.

• Journal of Pharmaceutical Investigation
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• 제24권4호
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• pp.265-271
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• 1994

Cefazolin ethoxycarbonylethyl ester (CFZ-ET) was synthesized to improve oral absorption and bioavailability of the parent drug by esterification of sodium cefazolin (CFZ-Na). The successful synthesis of CFZ-ET was identified with analysis of UV spectra, FT-lR spectra and NMR spectra. Partition coefficient studies showed that CFZ-ET was more lipophilic than CFZ-Na and the ester was hydrolyzed into the parent drug in vivo. Although CFZ-ET did not have antimicrobial activity in vitro, the plasma taken after the oral administration of CFZ-ET had antimicrobial activity. Based on above observations, CFZ-ET might be rapidly hydrolyzed to CFZ in the body. Therefore, it may be concluded that CFZ-ET could be a novel prodrug of CFZ which can improve the bioavailability of CFZ-Na.

• Korean Journal of Pharmacognosy
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• 제33권4호통권131호
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• pp.312-318
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• 2002

Effect of the acid hydrolysate of silk fibroin on obesity was investigated in obese(057BL/KsJ-db/db) mice. After 8 weeks feeding of 1%(w/w) or 3%(w/w) fibroin hydrolysate, the extents of reduction in body weight were significantly higher than that of obese control. The weight reduction in female mice was higher than that in male mice. Plasma leptin in male mice increased up to 1.8-fold higher level than obese control by feeding hydrolysate. In case of female mice, however, it rather decreased with increased feeding concentration of hydrolysate. From the results of high glycine and serine contents of peptide fractions contained in fibroin hydrolysate, it was inferred that fibroin peptides might affect xylosyltransferase(XT) activity on chondroitin sulfate synthesis causing to change susceptibility of adipocytes to hormones such as insulin followed by the reduced leptin synthesis in female mice. The result of the higher lipolysis in hydrolysate-fed group than obese control indicated that the reduction in body weight was due to the increased lipolytic activities in male and female mice in common.

• Journal of Powder Materials
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• 제17권4호
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• pp.336-341
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• 2010

The present study focused on the synthesis of Bi-Sb-Te-based thermoelectric powder by an oxidereduction process. The phase structure, particle size of the synthesized powders were analyzed using XRD and SEM. The synthesized powder was sintered by the spark plasma sintering method. The thermoelectric property of the sintered body was evaluated by measuring the Seebeck coefficient and specific electric resistivity. The $Bi_{0.5}Sb_{1.5}Te_3$ powder had been synthesized by a combination of mechanical milling, calcination and reduction processes using mixture of $Bi_2O_3$, $Sb_2O_3$ and $TeO_2$ powders. The sintered body of the $Bi_{0.5}Sb_{1.5}Te_3$ powder synthesized by an oxide-reduction process showed p-type thermoelectric characteristics, even though it had lower thermoelectric properties than the sintered body of the $Bi_{0.5}Sb_{1.5}Te_3$ thermoelectric powder synthesized by the conventional melting-crushing method.