• Journal of the Korean Society of Safety
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• v.21 no.5 s.77
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• pp.28-33
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• 2006

The rapidly advanced industrial society takes advantage of high-technology, but it also suffered from the side effects such as various diseases by contamination. Of these problems, air pollution is considered as the most important problem nowadays. Air contamination is not only limited outdoors, but it also causes more serious effect in our indoor air environment. Depending on the notion that indoor air effects physical health seriously, the needs of the air cleaner is more earnest. Therefore, the main purpose of this study is to develop the air cleaner to meet the standard and get rid of poisonous and harmful material from the atmosphere by using a Corona Discharge. According to the purpose of this study, We set the negative ion generator, the UV, $TiO_{2}$ optical catalyzer, the electrical dust collector and the air filter in series order. It emits a lot of negative ions. We use these ions to purify harmful factors and contaminated materials. We collect the dust using static power that comes from the discharge of corona. At the same time, we try to develop the air cleaner to keep the air quality to meet the standard and kill the various viruses using UV LED and $TiO_{2}$ optical catalyzer. In this study, we use the UV LED that is smaller and efficient than a existing UV lamp. What is more, the UV LED has a features that a stabilizer occupying much space is not needed any more.

• Journal of the Korean Ceramic Society
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• v.53 no.5
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• pp.500-505
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• 2016

Scandia-stabilized zirconia co-doped with $CeO_2$ is a promising electrolyte for intermediate temperature SOFC, but still shows rapid degradation during a long-term operation. In this study, $CeO_2$ (1 mol%) as a stabilizer is partially substituted with lanthanum oxides ($M_2O_3$, M=Yb, Gd, Sm) to stabilize a cubic phase and thus durability in reducing atmosphere. 0.5M0.5Ce10ScSZ electrolytes were prepared by solid state reaction and sintered at $1450^{\circ}C$ for 10 h to produce dense ceramic specimens. With addition of the lanthanum oxide, 0.5M0.5Ce10ScSZ showed lower degradation rates than 1Ce10ScSZ. Since $Gd_2O_3$ showed the highest ionic conductivity among the co-dopants, an electrolyte-supported cell with 0.5Gd0.5Ce10ScSZ was prepared to compare its long-term performance with that of 1Ce10ScSZ-based cell. Maximum power density of 0.5Gd0.5Ce10ScSZ-based cell was degraded by about 2.3% after 250 h, which was much lower than 1Ce10ScSZ-based cell (4.2%).

• Korean Journal of Environmental Agriculture
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• v.38 no.1
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• pp.17-22
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• 2019

BACKGROUND: Soil contamination of As is a very sensitive environmental issue due to its adverse impact on human health and different characteristics with other heavy metals. With public awareness of As poisoning, there has been growing interest in developing guideline and remediation technologies for As-contaminated soil. The objective of this research was to evaluate the effectiveness of stabilizing amendments and soil dressing methods on the mobility of As in the contaminated rice paddy soils nearby mining area. METHODS AND RESULTS: Different amendments were mixed with surface and subsurface contaminated soils at a ratio of 3% (w/w) and monitored for five months. Three different extractants including 0.01M $CaCl_2$, TCLP, and PBET were used to examine As bioavailability in the soil and the concentration of As in rice grain was also measured with an inductively coupled plasma (ICP) spectroscopy. The results showed that all amendment treatments decreased As concentration compared to the control. Especially, coal mine drainage sludge (CMDS) treatment showed the highest efficiency of decreasing As concentration in the soil and rice grain. The values of Pearson correlation (r) between As concentrations in the soil and rice grain were 0.782, 0.753, and 0.678 for $CaCl_2$, TCLP, and PBET methods, respectively. Especially, $CaCl_2$ method was highly correlated between As concentrations of the soil and soil solution (r=0.719), followed by TCLP (r=0.706), PBET (r=0.561) methods. CONCLUSION: Stabilizing amendments can effectively reduce available As concentration in the soils as well as soil solution, and thereby potentially mitigating risks of crop contamination by As.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.195-195
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• 2016

Titanium and its alloys are widely used as implants in orthopedics, dentistry and cardiology due to their outstanding properties, such as high strength, high level of hemocompatibility and enhanced biocompatibility. 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. The aim of this study is to research Si and Mg doped hydroxyapatite film formation by plasma electrolytic oxidation. 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 $1050^{\circ}C$. Each alloy was anodized in solution containing typically 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate at room temperature. A direct current power source was used for the process of anodization. Anodized alloys was prepared using 270V~300V anodization voltage at room. A Si and Mg coating was produced by RF-magnetron sputtering system. RF power of 100W was applied to the target for 1h 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.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.197-197
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• 2016

Commercially pure titanium (CP Ti) and Ti-6Al-4V 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. Manganese(Mn) 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. Radio frequency(RF) magnetron sputtering in the various PVD methods has high deposition rates, high-purity films, extremely high adhesion of films, and excellent uniform layers for depositing a wide range of materials, including metals, alloys and ceramics like a hydroxyapatite. The aim of this study is to research the Mn coatings on the micro-pore formed Ti-29Nb-xHf alloys by RF-magnetron sputtering for dental applications. 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 $1050^{\circ}C$. Each alloy was anodized in solution containing typically 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate at room temperature. A direct current power source was used for the process of anodization. Anodized alloys was prepared using 270V~300V anodization voltage at room. Mn coatings was produced by RF-magnetron sputtering system. RF power of 100W was applied to the target for 1h at room temperature. The microstructure, phase and composition of Mn coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.

• Analytical Science and Technology
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• v.12 no.2
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• pp.125-129
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• 1999

Portable-type two electrode system for the determination of highly concentrated hydrogen peroxide (10-75%) has been studied. The electrode body was made with teflon rod (length=10 cm, diameter=1.5 cm) to withstand the highly corrosive power of hydrogen peroxide. Glass carbon rod (diameter=3 mm) was used as the working electrode and a carbon cylinder (i.d.=5 mm; o.d.=9 mm) was used as counter electrode. The applied voltage for the determination of $H_2O_2$ was 0.8 V. Diluting the highly concentrated samples taken from the industrial batch to 10% or less, it was possible to make quantitative determinations, while eliminating the interference from the stabilizer contained in the sample and preventing the surface of the electrode from oxidative corrosion. Employing hydrogen peroxide permeable membrane (teflon membrane${\leq}100{\mu}m$) for the electrode system, it was possible to measure the content of $H_2O_2$ in highly concentrated samples directly, quantitatively and reproducibly with no extra dilution step. However, it was necessary to change the internal electrolyte frequently to maintain the analytical performance of the electrode.

• Journal of the Korean GEO-environmental Society
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• v.21 no.9
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• pp.25-32
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• 2020

The underground utilities installed under the ground is an important civil engineering structure, such as water supply and sewerage pipes, underground power lines, various communication lines, and city gas pipes. Such underground utilities can be exposed to risk due to external factors such as concentrated rainfall and vehicle load, and it is important to select and construct an appropriate backfill material. Currently, a method mainly used is to fill the soil around the underground utilities and compact it. But it is difficult to compact the lower part of the buried pipe and the compaction efficiency decreases, reducing the stability of the underground utilities and causing various damages. In addition, there are disadvantages such as a decrease in ground strength due to disturbance of the ground, a complicated construction process, and construction costs increase because the construction period becomes longer, and civil complaints due to traffic restrictions. One way to solve this problem is to use a liquid filler. The liquid filler has advantages such as self-leveling ability, self-compaction, fluidity, artificial strength control, and low strength that can be re-excavated for maintenance. In this study, uniaxial compression strength test and fluidity test were performed to characterize the mixed soil using marine clay, stabilizer, and in-situ soil as backfill material. A freezing-thawing test was performed to understand the strength characteristics of the liquid filler by freezing, and in order to examine the effect of the filling materials on the corrosion of the underground pipe, an electrical resistivity test and a pH test were performed.

• Journal of the Mineralogical Society of Korea
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• v.14 no.2
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• pp.99-110
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• 2001

A gem-quality yttria-stabilized zirconium oxide crystals were synthesized by the skull-melting method, using the RF electrical apparatus. Principal raw materials used were $ZrO_2$and 25 wt.% $Y_2O_3$as stabilizer and 0.03~0.05 wt.% $Nd_2O_3$decolorizing agent were added to it. The single crystals were approximately 20$\times$63 mm in size with chemical composition $Zr_{0.73}$ $Y_{0.27}$ $O_{1.87}$ . The crystals are isotropic with no appreciable anisotropism under a polarizing microscope. Their refractive indices are in the range of 2.15~2.18, specific gravity 5.85, Mohs' hardness 8~8.5, and reflectivity 13.47%. The zirconia crystals were confirmed to have cubic structure with Face-centered lattice(Z=4), space group Fm3m ($CaF_2$-type structure) and unit cell parameters are a=5.157 $\AA$. The optimal growing conditions for yttria-stabilized zirconia are 50 kW, 2.94 MHz in power and to use a crucible with 105 mm $\times$ 135 mm in size. When the lowering speed of the crucible was set 16mm/hr gave the best yield, 42%. Since the refractive index(2.15~2.18) of cubic zirconia is smaller than that of diamond, the angle between crown and pavilion should be fashioned to make it smaller than $40.5^{\circ}$ to show the maximum brilliancy and fire.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.3
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• pp.214-218
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• 2020

In this study, Mg_xZn_1-xO thin films, which can be applied not only to active layers of light-emitting devices (LEDs), such as UV-LEDs, but also to solar cells, high mobility field-effect transistors, and power semiconductor devices, are fabricated using the sol-gel method. ZnO and Mg_0.3Zn_0.7O solution synthesized by the sol-gel method and the thin film were grown by spin coating on a Si (100) substrate and sapphire substrate. The solutions are synthesized by dissolving precursor materials in 2-methoxyethanol (2-ME) solvent, and then monoethanolamine (MEA) was added to the mixed solution as a sol stabilizer. Zinc acetate dihydrate is used as a ZnO precursor, while Mg nitrate hexahydrate and Mg acetate tetrahydrate are used as an MgO precursor. Then, the optical and structural characteristics of the fabricated thin films are compared. The molar concentration of the Zn precursor in the solvent is fixed at 0.3 M, and the amount of the Mg precursor is 30% of Mg²⁺/Zn²⁺. The optical characteristics are measured using an UV-vis spectrophotometer, and the transmittance of each wavelength is measured. Structural characteristics are measured using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Composition analyses are performed using energy dispersive X-ray spectroscopy (EDS). The Mg_0.3Zn_0.7O thin film was well formed at the ratio of the Mg precursor added regardless of the type of Mg precursor, and the c-axis of the thin film was decreased, while the band gap was increased to 3.56 eV.