• Resources Recycling
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• v.25 no.3
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• pp.49-54
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• 2016

In this study, zircon sand is separated into zirconia and silica by using the Ar-$H_2$ arc plasma refining. And then silica is removed from it by the microwave leaching method to produce a high pure zirconia. Plasma melting consist of two sequential processes; reduction process with Ar gas only followed by refining process with Ar-$H_2$ gas. After cooling in chamber. The solid phase obtained at $240^{\circ}C$ were found to be composed of 20% sulfuric acid solution. The solution was used as a leaching solution with microwave irradiation to obtain a high purity zirconia.

• Journal of Environmental Science International
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• v.12 no.7
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• pp.801-807
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• 2003

This work aims the search of environmentally friendly pre-treatment technologies to develop chromate replacements for metal finishing industries due to its toxicological properties. Since the corrosion resistance of steel was strongly related to water permeation, galvanized steel sheets were treated with various hydrophobic silane compounds and water-suspended polymer solution. Also, plasma gas discharge was applied to modify the surface of a polymer coated-steel sheet to be hydrophobic. The surface hydrophobicity of materials was introduced by CF$_3$H plasma exposure. The corrosion property before and after the plasma treatment was investigated in a slat spray tester with 3.5 wt.% NaCl at 35$^{\circ}C$. The results showed that both silane/polymer double coatings and plasma treatment of the galvanized steel exhibited significant retardation of corrosion.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.5
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• pp.702-711
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• 1998

The characteristics of corrosion resistance for the surface of medium high carbon steels and low alloy steels utilizing as manufacturing the machinery structures and machining tools and treating by plasma/ion nitriding process have been studied in terms of electrochemical polarization behav-iors including corrosion potential(Ecorr) anodic polarization trends and polarization resistance(Rp) The seven base materials showed a clear passivation behavior for the polarization tests in the ASTM standard solution 1N ${H_2){SO_4}$ Although the treated surface by plasma nitriding for the seven test materials showed a significant increase in hardness the treatment gave a detri-mental effect in corrosion resistance. The various characteristics including corrosion potential polarization curves microstructures corrosion current polarization resistance among non-treat-ed nitriding and/or soft-nitriding treated specimens have been investigated and some of the mechanisms discussed.

• Macromolecular Research
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• v.12 no.1
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• pp.71-77
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• 2004

We have synthesized various types of poly(ethylene glycol) (PEG)-ibuprofen conjugates by nucleophilic substitution of bromo-terminated PEG with ibuprofen-Cs salt. The conversion of the terminal hydroxyl groups to bromo-termini was quantitative, as was the drug conjugation process, which suggests that the present synthetic method is very useful for the preparation of PEG-based prodrugs from pharmaceuticals having carboxyl functionalities. The drug-release behavior of the prodrugs was examined in both phosphate buffer (PBS, pH 7.4) and rat plasma. From the drug-release behavior in PBS, we determined that each prodrug has high storage stability. The drug-release rate was observed to be much faster in rat plasma than in buffer solution as a result of the acceleration effect provided by enzymes present in the plasma. The drug-release rate in rat plasma depends on the degree of molecular aggregation of the prodrugs, which can be changed effectively by the nature of their spacer groups or by the use of Pluronic as the polymer carrier.

• Journal of Environmental Science International
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• v.33 no.5
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• pp.323-332
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• 2024

Circulating hydroponic cultivation has the advantage of reducing soil and water pollution problems caused by discharge of fertilizer components because the nutrient solution is reused. However, cyclic hydroponic cultivation has a low biological buffering capacity and can cause outbreaks of infectious root pathogens. Therefore, it is necessary to develop technologies or disinfection systems to control them. This study used dielectric barrier discharge plasma, which generates various persistent oxidants, to treat Fusarium oxysporum f. sp., a pathogen that causes wilt disease. Batch and intermittent continuous inactivation experiments were conducted, and the results showed that the total residual oxidant was persistent in intermittent plasma treatment at intervals of 2-3 days, and F. oxysporum was treated efficiently. Intermittent plasma treatment did not inhibit the growth of tomatoes.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.175.1-175.1
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• 2016

In recent, tract infections such as atopic dermatitis, allergic rhinitis and a respiratory disease are increasing, giving rise to the atmospheric pollution, inflow of micro-size dust and side effect of humidifier disinfectant. In this context, the environment-friendly technology is required to eliminate airborne pathogens. We propose solution of the previous problems, making use of Radical Mist Generator (RMG). Existing technologies of air purification using a gas discharge produce harmful substances such as ozone, NOx, etc. However, the RMG uses a pure water as a plasma forming material. The RMG sprays the water mist, which contains reactive radicals to sterilize microorganisms. RMG is comprised of a power supply, plasma electrodes and a nozzle. In order to analyze the electrical characteristic and concentrations of reactive radicals, we employ an oscilloscope and a titration method. To test the sterilization effect of RMG, we used E.coli. We confirmed that E.coli was killed over 90%. Eventually, we expect that RMG can be promising tool for a purified system.

• Journal of Welding and Joining
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• v.22 no.2
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• pp.59-68
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• 2004

Plasma transferred arc welding (PTAW) has been taken into consideration for repairing Ni-based superalloy components used gas turbine blades. Various cracks has been generally reported to be found in the base metal heat affected zone(HAZ) along grain boundary. Thus, hot cracking susceptibility of Ni-based superalloys was evaluated according to heat treatments. Hot ductility test was conducted on specimens with solution treated at 112$0^{\circ}C$ for 2 hours and aging treated at 845$^{\circ}C$ for 24hours after solution treatment. The results of the hot ductility test appeared that solution treated specimens were the highest ductility recovery rate among three conditions. The loss of ductility at high temperature in Ni-based superalloy was mainly controlled by the degree of pain boundary wetting due to constitutional liquation of MC carbide precipitates. Meanwhile, the highest ductility recovery rate in solution-treated alloys seems to be lack of M23C6, which can be dissolved during heating and then result in the local enrichment of Cr in the vicinity of the grain boundary.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.157-157
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• 2017

Titanium and its alloys that have a good biocompatibility, corrosion resistance, and mechanical properties such as hardness and wear resistance are widely used in dental and orthopedic implant applications. They can directly connect to bone. However, they do not form a chemical bond with bone tissue. Plasma electrolytic oxidation (PEO) that combines the high voltage spark and electrochemical oxidation is a novel method to form ceramic coatings on light metals such as titanium and its alloys. This is an excellent reproducibility and economical, because the size and shape control of the nano-structure is relatively easy. Silicon (Si), manganese (Mn), and magnesium (Mg) has a useful to bone. Particularly, Si has been found to be essential for normal bone, cartilage growth and development. Manganese influences regulation of bone remodeling because its low content in body is connected with the rise of the concentration of calcium, phosphates and phosphatase out of cells. Insufficience of Mn in human body is probably contributing cause of osteoporosis. Pre-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. The objective of this work was to study nucleation and growth of bone-like apatite formation on Ti-6Al-4V in solution containing Mn, Mg, and Si ions after plasma electrolytic oxidation. Anodized alloys was prepared at 270V~300V voltages. And bone-like apatite formation was carried out in SBF solution for 1, 3, 5, and 7 days. The morphologies of PEO-treated Ti-6Al-4V alloy in containing Mn, Mg, and Si ions were examined by FE-SEM, EDS, and XRD.

• Korean Journal of Materials Research
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• v.27 no.9
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• pp.495-500
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• 2017

Oxide layers were formed by an environmentally friendly plasma electrolytic oxidation (PEO) process on AZ91 Mg alloy. PEO treatment also resulted in strong adhesion between the oxide layer and the substrate. The influence of the KF electrolytic solution and the structure, composition, microstructure, and micro-hardness properties of the oxide layer were investigated. It was found that the addition of KF instead of KOH to the $Na_2SiO_3$ electrolytic solution increased the electrical conductivity. The oxide layers were mainly composed of MgO and $Mg_2SiO_4$ phases. The oxide layers exhibited solidification particles and pancake-shaped oxide melting. The pore size and surface roughness of the oxide layer decreased considerably with an increase in the concentration of KF, while densification of the oxide layers increased. It is shown that the addition of KF to the basis electrolyte resulted in fabricating of an oxide layer with higher surface hardness and smoother surface roughness on Mg alloys by the PEO process. The uniform thickness of the oxide layer formed on the Mg alloy substrates was largely determined by the electrolytic solution with KF, which suggests that the composition of the electrolytic solution is one of the key factors controlling the uniform thickness of the oxide layer.

• Membrane Journal
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• v.19 no.1
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• pp.54-62
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• 2009

Pervaporation membrane for butanol separation was prepared by hybrid process. Plasma treatment of commercial poly(dimethylsiloxane) (PDMS) membrane was attempted and combination of plasma treatment and PDMS solution coating on polysulfone, poly(ether imide) supports were also performed. Plasma treatment of PDMS membrane with hexane and silane group compounds was performed to increase the hydrophobicity of the surface, which enhanced the separation factor upto 12.5 at the expense of flux decrease down to $1.15kg/m^2{\cdot}hr$. Contact angle and relative sorption ratio were also related with hydrophobicity of the memrbane. Increase of PDMS prepolymer composition resulted in dense structure of coating layer with better separation factor. Effects of sequence of PDMS coating vs. plasma treatment were examined. It was found that plasma treatment with butanol and n-hexane plasma followed by PDMS coating showed better performance and vice versa for plasma treatment with hexamethyldisilane and hexamethyldisilazane.