• Bulletin of the Korean Chemical Society
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• v.25 no.5
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• pp.625-628
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• 2004

Ceruloplasmin (CP), the blue oxidase present in all vertebrates, is the major copper-containing protein of plasma. It has been proposed that oxidation of L-3,4-dihydroxyphenylalanine (DOPA) may contribute to the pathogenesis of neurodegenerative disorders. The effect of the oxidized products of DOPA on the modification of human CP was investigated. When CP was incubated with the oxidized L-DOPA, the protein was induced to be aggregated and ferroxidase activity was decreased in a time-dependent manner. Radical scavengers and catalase significantly inhibited the oxidized DOPA-mediated CP aggregation. Copper chelatrors, Diethylenetriaminepenta acetic acid (DTPA) and Diethyldithiocarbamic acid (DDC), also inhibited the oxidative modification of CP. The results suggested that DOPA oxidation led to the formation of free radical and induced the CP aggregation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.152-152
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• 2017

Titanium and its alloys have been widely used for biomedical applications. However, the use of the Ti-6Al-4V alloy in biomaterial is then a subject of controversy because aluminum ions and vanadium oxide have potential detrimental influence on the human body due to vanadium and aluminum. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element,such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}$-stabilizer and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Silicon (Si) and magnesium (Mg) has a beneficial effect on bone. Si in particular has been found to be essential for normal bone and cartilage growth and development. In vitro studies have shown that Mg plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. Therefore, in this study, Si and Mg coatings on the hydroxyapatite film formed Ti-29Nb-xHf alloys by plasma electrolyte oxidation has been investigated using several experimental techniques. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. The electrolyte was Si and Mg ions containing calcium acetate monohydrate + calcium glycerophosphate at room temperature. The microstructure, phase and composition of Si and Mg coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.

• Journal of the Korean institute of surface engineering
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• v.49 no.3
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• pp.280-285
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• 2016

In this study, we investigated the influences of potassium fluoride(KF) addition on the surface characteristics of plasma electrolytic oxidation(PEO) coating produced on Al alloy. The PEO of marine grade Al alloy(5083 grade) was conducted in KOH 1g/L solution adding different concentrations of KF(0, 1 and 2 g/L) under a galvanostatic regime. With KF addition, unusual behavior was observed on the voltage-time characteristic curves, which can be characterized by the following process: (i) initial rapid increase in voltage (ii) a short plateau after 1st breakdown (iii) gradual increase in voltage (iv) intermittent fluctuation of voltage after 2nd breakdown. The SEM observation revealed irregular surface morphology with KF addition, as compared with one formed without KF addition, which had a reticulate structure. The XRD analysis detected the formation of aluminium hydroxide fluoride hydrate($H_{4.76}Al_2F_{3.24}O_{3.76}$) on surface grown by PEO process with KF. Particularly, at very early stage of the process (~ 120 s), thin film was formed having nanoporous structure, and F element was confirmed on surface by EDS analysis. The thickness and surface roughness of the coating increased with increasing KF concentration. As a result, KF addition was found to be less beneficial influences on PEO of marine grade Al alloy, and therefore needs further research to improve its capability.

• Journal of the Korean institute of surface engineering
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• v.51 no.6
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• pp.415-420
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• 2018

The possibility of an improvement in heat dissipation performance of aluminum alloy heat sink for shipboard LED luminaries through plasma electrolytic oxidation (PEO) was investigated. Four different PEO coatings were produced on aluminum alloy 5052 in silicate based alkaline solution by varying current density ($50{\sim}200mA/cm^2$). On voltage-time response curves, three stages were clearly distinguished at all current densities, namely an initial linear increase, slowdown of increase rate, and steady state(constant voltage). It was found that the increase in current density caused the breakdown voltage to increase. Two different surface morphologies - coralline porous structure and pancake structure - were confirmed by SEM examination. The coralline porous structure was predominant in the coatings produced at lower current densities (50 and $100mA/cm^2$) while under high current densities(150 and $200mA/cm^2$) the pancake structure became dominant. The coating thickness was measured and found to be in a range between about $13{\mu}m$ and $44{\mu}m$, showing increasing thickness with increasing current density. As a result, $100mA/cm^2$ was proposed as an effective process parameter to improve the heat dissipation performance of aluminum alloy heat sink, which could lower the LED operating temperature by about 30%.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.9
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• pp.1614-1618
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• 2007

We have demonstrated the experimental results to obtain the immunity of FN (Fowler Nordheim) stress for S-RCAT (Spherical-Recess Cell Array Transistor) which has been employed to meet the requirements of data retention time and propagation delay time for sub-100-nm mobile DRAM (Dynamic Random Access Memory). Despite of the same S-RCAT structure, the immunity of FN stress of S-RCAT depends on the process condition of gate oxidation. The S-RCAT using DPN (decoupled plasma nitridation) process showed the different degradation of device properties after FN stress. This paper gives the mechanism of FN-stress degradation of S-RCAT and introduces the improved process to suppress the FN-stress degradation of mobile DRAM.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.4
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• pp.191-196
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• 2003

For improvement of the wear performance of Ti alloy, vacuum-carburizing technique was tried for the first time using propane atmosphere. During the low pressure carburizing carbide was formed at the surface and carbon transfer was occurred from the carbide to the matrix. It was found that: (i) surface hardness increased with the reduction of operating pressure and time; (ii) optimum hardness distribution could be obtained with the proper choice of temperature and carbon flux control; and, (iii) case depth was largely influenced not by time but by temperature. The two steps process was recommended for obtaining thick case depth and high surface hardness of Ti alloy. For the low oxygen partial pressure, it was necessary to introduce additional CO gas to the atmosphere.Grain boundary oxidation and non-uniformity could be prevented.

• Journal of Environmental Science International
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• v.21 no.3
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• pp.363-368
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• 2012

The influence of plasma discharge on the nutrient components ($NO_3$-N, $NH_4$-N, $PO_4$-P, K, Ca, and Mg) and water quality [pH, ORP (oxidation-reduction potential) and electric conductivity] of hydroponic water were investigated. It was observed that the $NH_4$-N, $PO_4$-P, K, Ca, and Mg were kept at the constant concentrations for plasma discharging of 90 min. On the other hand, $NO_3$-N concentration was increased with proceeding of the plasma discharge. The increase of $NO_3$-N concentration was considered with the fact that nitric acid was created from nitrogen among supplying air for the insulation of inside of dielectric barrier. ORP and electric conductivity was increased with plasma discharging time. However, pH was decrease with what because of the generation of the nitric acid. When adjusting the hydroponic ingredients, pH and conductivity must to be considered because of the change of pH and conductivitiy with the discharging.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.1
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• pp.41-45
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• 2014

We have investigated the passivation property of $SiN_x$ and $SiO_2$ thin films formed using various process conditions for the application of crystalline Si solar cells. An increase in the thickness of $SiN_x$ deposited using plasma enhanced chemical vapor deposition (PECVD) led to the improvement of passivation quality. This could be associated with the passivation of Si dangling bonds by hydrogen atoms which were supplied during PECVD deposition. The $SiO_2$ thin films grown using dry oxidation process exhibited better passivation behavior than those using wet oxidation process, implying the dry oxidation process was more effective in the formation of high quality $SiO_2$ thin films. The relative effective life time gradually decreased with increasing dry oxidation temperature. Such a degradation of passivation behavior could be attributed to the increase in interface trap density caused by thermal damages.

• Korean Journal of Metals and Materials
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• v.46 no.1
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• pp.39-43
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• 2008

PSII (Plasma Source Ion Implantation) using high density pulsed ICP source was employed to implant oxygen ions in Si wafer. The PSII technique can achieve a nominal oxygen dose of $3 {\times}10^{17}atoms/cm^2$ in implantation time of about 20min. In order to prevent oxidation of SOI layer during high temperature annealing, the wafer was capped with $2,000{\AA}$ $Si_3N_4 $ by PECVD. Cross-sectional TEM showed that continuous $500{\AA}$ thick buried oxide layer was formed with $300{\AA}$ thick top silicon layer in the sample. This study showed the possibility of SOI fabrication using the plasma source ion implantation with pulsed ICP source.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.10
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• pp.888-893
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• 2016

In this study, the solution plasma process was utilized with the aim of degrading synthetic dyes in water at atmospheric pressure. The experiments were conducted in a batch-type reactor consisting of a symmetric wire-wire electrode configuration with rhodamine B (RhB) as the target synthetic dye. The effects of the plasma treatment time and initial dye concentration on the RhB degradation were investigated by monitoring the change in absorbance of RhB solutions. The RhB solutions turned lighter in color and finally colorless with prolonged plasma treatment time, indicating the destruction of dye molecules. The RhB solutions were found to have degraded, following the first-order kinetic process. However, for high initial RhB concentrations, another kinetic process or factor seems to play a dominant role at the initial degradation stage. The fitted first-order rate constant decreased as the initial concentration increased. This result suggests that the degradation behavior and kinetic process of the RhB solution strongly depends on its initial concentration. The RhB degradation is considered to be due to a combination of factors, including the formation of chemically oxidative species, as well as the emission of intense UV radiation and high-energy electrons from the plasma. We believe that the solution plasma process may prove to be an effective and environment-friendly method for the degradation or remediation of synthetic dye in wastewater.