• Journal of the Korean institute of surface engineering
• /
• v.50 no.6
• /
• pp.432-438
• /
• 2017

AZ91D casting alloy requires an advanced plasma anodizing processing because large amount of defects are liable to generate during anodization. In this study, plasma electrolytic oxidation (PEO) of AZ91D Mg alloy was conducted by the application of either constant voltage or current using a pulse mode and its effects on pore formation, surface roughness and corrosion resistance were investigated. The PEO films showed a three-layer structure. The PEO film thickness was found to increase linearly with voltage. The surface roughness, Ra, ranged between $0.2{\mu}m$ and $0.3{\mu}m$. The corrosion resistance increased from RN 3.5 to 9.5 by the PEO treatment when evaluated according to the 72 hour salt spray test. The PEO-treated surface exhibited higher pitting potential than the raw material.

• 한국연소학회:학술대회논문집
• /
• 2006.04a
• /
• pp.144-148
• /
• 2006

Characteristics of a plasma reactor for partial oxidation of methane, especially focused on the role and effectiveness of plasma chemistry, is investigated. Partial oxidation of methane is investigated using a rotating arc which is a three dimensional version of a typical glidingarc. The rotating arc has both the characteristics of equilibrium and non-equilibrium plasma. Non-equilibrium characteristics of the rotating gliding arc can be increased by rotating an elongated arc string attached at both the tip of inner electrode and the edge of outer electrode. In this way, plasma chemistry can be enhanced and hydrogen selectivity can reach almost 100% that is much higher than thermal equilibrium condition. As a result, the present study enables the strategic approach of the plasma reforming process by means of appropriate reactor design to maximize plasma effect and resulting in maximized reaction efficiency.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.261-261
• /
• 2013

The smart design of nanocatalysts can improve the catalytic activity of transition metals on reducible oxide supports, such as titania, via strong metal-support interactions. In this work, we investigatedtwo-dimensional Pt nanoparticle/titania catalytic systems under the CO oxidation reaction. Arc plasma deposition (APD) and metal impregnation techniques were employed to achieve Pt nanoparticle deposition on titania supports, which were prepared by multitarget sputtering and sol-gel techniques. APD Pt nanoparticles with an average size of 2.7 nm were deposited on sputtered and sol-gel-prepared titania films to assess the role of the titania support on the catalytic activity of Pt under CO oxidation. In order to study the nature of the dispersed metallic phase and its effect on the activity of the catalytic CO oxidation reaction, Pt nanoparticles were deposited in varying surface coverages on sputtered titania films using arc plasma deposition. Our results show an enhanced activity of Pt nanoparticles when the nanoparticle/titania interfaces are exposed. APD Pt shows superior catalytic activity under CO oxidation, as compared to impregnated Pt nanoparticles, due to the catalytically active nature of the mild surface oxidation and the active Pt metal, suggesting that APD can be used for large-scale synthesis of active metal nanocatalysts.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2007.11a
• /
• pp.106.1-106.1
• /
• 2007

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2007.11a
• /
• pp.147-148
• /
• 2007

The compound, Ti3(Al,Si)C2, was synthesized by hot pressing a powder mixture of TiCX, Al and Si. Its oxidation at 900 and 1000 oC in air for up to 50 h resulted in the formation of rutile-TiO2, -Al2O3 and amorphous SiO2. During oxidation, Ti diffused outwards to form the outer TiO2 layer, and oxygen was transported inwards to form the inner mixed layer.

• Journal of Korean Medicine Rehabilitation
• /
• v.21 no.1
• /
• pp.23-33
• /
• 2011

Objectives : The present study investigated effects of Artemisia Capillaris Thunberg ethanol extract(EtOH ext). on lowering lipid, anti-oxidation and concentration of plasma inflammatory mediators using rat fed on high oxidized fat. Methods : We divided fat sprague-dawley rats fed on high oxidized into 4 groups. They were normal group, feed with 100 mg/kg Artemisia Capillaris Thunberg group, feed with 200 mg/kg Artemisia Capillaris Thunberg group and feed with 300 mg/kg Artemisia capilaris Thunberg group. They were administered for 4 weeks. We measured concentration of plasma free fatty acid(FFA), plasma triglyceride, plasma total cholesterol, and plasma low density lipoprotein-cholesterol(LDL-cholesterol), plasma high density lipoprotein-cholesterol(HDL-cholesterol), concentration of liver total cholesterol and liver triglyceride (TG), concentration of plasma thiobarbituric acid reactive substance(TBARS) and liver thiobarbituric acid reactive substance(TBARS), glutathione peroxidase (GSH-Px) activity, superoxide dismutase(SOD) activity and catalase(CAT) activity, plasma nitric oxide(NO), ceruloplasmin and ${\alpha}-glycoprotein$. Results : 1. The Artemisia Capillaris Thunberg EtOH ext. groups showed low concentration of plasma FFA, plasma triglyceride, plasma total cholesterol and plasma LDL-cholesterol compared to control group. However, concentration of plasma HDL-cholesterol was increased in the Artemisia Capillaris Thunberg EtOH ext. groups. 2. Concentration of liver total cholesterol and liver TG showed a significantly decrement in all Artemisia Capillaris Thunberg EtOH ext. groups than that of control group. 3. The Artemisia Capillaris Thunberg EtOH ext. groups showed lower values in concentration of plasma TBARS and liver TBARS than that of control group. The values of GSH-Px activity, SOD activity and CAT activity were increased in the Artemisia Capillaris Thunberg EtOH ext. groups. 4. The values of plasma NO, ceruloplasmin and ${\alpha}-glycoprotein$ were decreased in Artemisia Capillaris Thunberg EtOH ext. groups. Conclusions : Based on the results in this study, the Artemisia Capillaris Thunberg EtOH ext. showed a positive effect in lowering lipid, anti-oxidation and decrement of plasma inflammatory mediators.

• Journal of the Korean Society of Combustion
• /
• v.11 no.3
• /
• pp.1-7
• /
• 2006

A reaction mechanism of methane partial oxidation, which consists of thermal and plasma chemistry reaction pathways, has been investigated using with an arc-jet reactor. The reaction zone of the arc-jet reactor is spatially separated into thermal and non-thermal plasma zone. Methane conversion rates, selectivity of $H_2$ and $C_2$ chemicals in each zone are obtained, which reveals clearly different characteristics of reaction pathways depending on the temperature conditions. The conversion rates obtained in thermal plasma zone is higher than those in non-thermal plasma zone. The selectivity, however, obtained in non-thermal plasma zone is significantly higher than those in thermal plasma zone. Further parametric study on $O_2/C$ ratio, arc length and SED shows that the present process is mainly governed by thermal chemistry pathways.

• Journal of Electrical Engineering and Technology
• /
• v.10 no.4
• /
• pp.1746-1751
• /
• 2015

In this study low voltage Plasma Electrolytic Oxidation (PEO) was utilized to eliminate high voltage PEO drawbacks such as high cost, dimensional deformation and porosity. Low voltage PEO produces a thin coating which causes low corrosion resistance. In order to solve such problem, 0.1~0.6M pyrophosphates were added in a bath containing 1.4M NaOH, and 0.35M Na₂SiO₃. 70 V PEO was conducted at 25℃ for 3 minutes. Chemical composition, morphology and corrosion resistance of the anodized coating were analyzed. The anodized film was composed of MgO, Mg₂SiO₄, and Mg₂O₇P₂. The morphology of film showed appropriately dense structure and low porosity in the anodized layers. It is found that low voltage Plasma Electrolytic Oxidation in cooperation with phosphating treatment can provide a good corrosion protection for the AZ31B magnesium alloy.

• Journal of the Korean Society of Combustion
• /
• v.12 no.4
• /
• pp.39-46
• /
• 2007

The technique of $NH_3$ SCR (selective catalytic reduction) assisted by plasma oxidation has been applied to a 2,000 cc diesel engine. The present combined $deNO_x$ process consists of two steps. The first step is that about 50% of emitted NO from the engine is oxidized to $NO_2$ in a plasma oxidation process. The second step is that NO and $NO_2$ are simultaneously reduced to $N_2$ in the $NH_3$ SCR process. The engine test results showed that the $deNO_x$ rates of the present combined process are higher than those of conventional SCR process by 20%. Such a high performance of the combined process is noticeable especially, when the exhaust temperature are relatively low, i.e., $170-220^{\circ}C$. To provide a feasibility of the present technique the effects of operating conditions, such as an electrical input energy, an exhaust gas temperature, an initial NO concentration, and the amount of hydrocarbon addition, were discussed.

• Corrosion Science and Technology
• /
• v.17 no.3
• /
• pp.91-100
• /
• 2018

Development of biodegradable implants for treatment of complex bone fractures has recently become one of the priority areas in biomedical materials research. Multifunctional corrosion resistant and bioactive coatings containing hydroxyapatite $Ca_{10}(PO_4)_6(OH)_2$ and magnesium oxide MgO were obtained on Mg-Mn-Ce magnesium alloy by plasma electrolytic oxidation. The phase and elemental composition, morphology, and anticorrosion properties of the coatings were investigated by scanning electron microscopy, energy dispersive spectroscopy, potentiodynamic polarization, and electrochemical impedance spectroscopy. The PEO-layers were post-treated using superdispersed polytetrafluoroethylene powder. The duplex treatment considerably reduced the corrosion rate (>4 orders of magnitude) of the magnesium alloy. The use of composite coatings in inducing bioactivity and controlling the corrosion degradation of resorbable Mg implants are considered promising. We also applied the plasma electrolytic oxidation method for the formation of the composite bioinert coatings on the titanium nickelide surface in order to improve its electrochemical properties and to change the morphological structure. It was shown that formed coatings significantly reduced the quantity of nickel ions released into the organism.