• Korean Journal of Materials Research
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• v.22 no.3
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• pp.155-158
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• 2012

In this work, AlON-$Al_2O_3$ coatings were prepared on Al2021 alloy by the electrolytic plasma processing (EPP) method. The experimental electrolytes include: 2 g/l NaOH as the electrolytic conductive agent, 10 g/l $Na_2AlO_2$ as the alumina formative agent, and 0.5 g/l $NaNO_2$, $NaNO_3$, and $NH_4NO_3$ as the nitride inducing agents. The effects of different nitrogen inducing agents were studied by a combined compositional and structural analyses of the ceramic coatings carried out by Xray diffractometry (XRD) and scanning electron microscopy (SEM) for the specimens EPP-treated at room temperature for 15 min under a hybrid voltage of 260 DC along with an AC 50 Hz power supply (200 V). Microhardness tests and wear tests were carried out to correlate the evolution of the microstructure and the resulting mechanical properties. Potentiodynamic polarizations and immersion corrosion tests were carried out in 3.5wt% NaCl water solutions under static conditions in order to evaluate the corrosion behavior of the coated samples. The results demonstrate that $NaNO_2$ is proven to be a good nitrogen inducing agent to produce high quality AlON-$Al_2O_3$ ceramic coatings.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.153-153
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• 2017

The application of the coating supports the mechanical characteristics of the implant, and various materials and coatings are currently being used in the implant in a way to accelerate adhesion. Especially, plasma electrolytic oxidation (PEO) coating has been proposed continually with good surface treatment of titanium alloys. Also, the PEO process can incorporate Ca and P ions on the titanium surface through variables varied factor. PEO process for bioactive surface has carried out in electrolytes containing Ca and P ions. Natural bone is composed of mineral elements such as Mg, Si, Zn, Sr, and Mn, etc. Especially, Mg and Si of these elements play role in bone formation and growth after clinical implantation of bio-implants. In this study, corrosion charateristics of PEO-treated Ti-6Al-4V alloy in solution containing Si and Mg ions has been investigated using several experimental techniques. The PEO-treated surfaces were identified by X-ray diffraction, using a diffractometer (XRD, Philips X' pert PRO, Netherlands) with Cu $K{\alpha}$ radiation. The morphology was observed by field-emission scanning electron microscopy (FE-SEM, Hitachi 4800, Japan) and energy-dispersive X-ray spectroscopy (EDX, Oxford ISIS 310, England). The potentiodynamic polarization and AC impedance tests for electrochemical degradations were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat with a scan rate of 1.67mV/s and potential range from -1500mV to + 2000mV.

• Journal of Surface Science and Engineering
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• v.55 no.1
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• pp.24-31
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• 2022

This study investigated the effect of pre-treatment on the PEO film formation of AZ91 Mg alloy. The pre-treatment was conducted for 10 min at room temperature in 0.5 M oxalic acid (C₂H₂O₄) solution containing various ammonium fluoride (NH₄F) concentrations. The pre-treated AZ91 Mg specimens were anodized at 100 mA/cm² of 300 Hz AC for 2 min in 0.1 M NaOH + 0.4 M Na₂SiO₃ solution. When AZ91 Mg alloy was pretreated in 0.5 M oxalic acid with NH₄F concentration less than 0.3 M, continuous dissolution of the AZ91 Mg alloy occurred together with the formation of black smuts and arc initiation time for PEO film formation was very late. It was noticed that corrosion rate of the AZ91 Mg alloy became faster if small amount of NH₄F concentration, 0.1 M, is added. The fast corrosion is attributable to fast formation of porous fluoride together with porous oxides in the reaction products. On the other hand, when AZ91 Mg alloy was pretreated in 0.5 M oxalic acid with sufficient NH₄F more than 0.3 M, a thin and dense protective film was formed on the AZ91 Mg alloy surface which resulted in faster initiation of arcs and formation of PEO film.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.93-94
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• 2006

The sheath of a single-conductor cable for ac service acts as a secondary of a transformer, the current in the conductor induces a voltage in the sheath. When the sheaths of single-conductor cables are bonded to each other, as is common practice for multi-conductor cables, the induced voltage causes current to flow in the completed circuit. This current causes losses in the sheath. Various methods of bonding may be used for the purpose of minimizing sheath losses. In korea, sheath cross bonding system was employed for the prevention of sheath losses, the sheaths wire subjected to at voltages, and the bonding was designed to keep the magnitude of the induced voltages within small limits so as to prevent the possibility of sheath corrosion. But, sheath cross bonding system without transposition of cable can not achieve an exact balance of induced sheath voltages unless the cables are lain in trefoil. This paper describes a transposition system with sheath cross bonding using EMTP(Electromagnetic Transient Program). The transposition system with cross bonding can be extended to longer cable circuits for laid in flat as wall as trefoil by the methods described in this paper.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.12
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• pp.1159-1165
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• 2005

New conductor is developed by using high strength nonmagnetic steel(NM) wire as the core of overhead conductor This conductor is called ACNR overhead conductor(Aluminum Conductor Nonmagnetic Steel Reinforced). Formed by the combination of aluminum alloy wire and high strength nonmagnetic steel wire, it has about the same weight and diameter as conventional ACSR overhead conductor. To enhance properties beneficial in an electrical and mechanical conductor during the Process of high strength nonmagnetic steel wire, we made a large number of improvements and modifications in the working process, aluminum cladded method, and other process. ACNR overhead conductor, we successfully developed, has mechanical and electrical properties as good as or even better than conventional galvanized wire. Microstructure of raw material NM wire was austenite and then deformed martensite after drawing process. Strength at room temperature is about $180kgf/mm^2\~200kgf/mm^2$. The conductivity at 0.78 mm thickness of Aluminum cladded M wire is about $7\%$ IACS higher than $20\%$IACS of HC wire used as core of commercial ACSR overhead conductor. The corrosion resistance is about 3 times higher than that of HC wire.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.5
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• pp.360-366
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• 2013

For conventional electrical actuators, the materials are mainly made up of metals, which mean they are prone to corrosion and electrical sparking. Replacing these systems with polymer metal composite based materials can be solved both problems. Considering their excellent electromechanical property, low device fabrication cost, light weight, and good electrical conductivity, the actuator based on ionic polymer metal composite (IPMC) was fabricated using Nafion film, NaOH 0.1 molar solution, and Au electrode. IPMCs exhibit good electrostatic property which means they can in principle be used in making actuators based on electromechanical motions. The resistance measurements of Nafion film after soaking in NaOH and deionized water were demonstrated and compared each other. The result of sample soaked in NaOH showed better electrical conductivity than in deionized water. The fabricated IPMC actuator exhibits a large deformation of bending displacement of approximately 9 mm with applied low AC voltage 6.89 V at 2.84 Hz. The result of computer simulation was also very similar and shown as a bending displacement of 8.6085 mm.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1060-1068
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• 1994

Stable zirconia sol was prepared from zirconium butoxide Zr(OC4O9)4 as a precursor and ethylacetoacetate(EAcAc) or diethylene glycol(DEG) as a chelating agent under ambient agent under ambient atmosphere by Sol-Gel process. The sythesized sol was coated on 304 stainless steel substrate by dip coating, thereafter zirconia film could be obtained by heat-treatment at $600^{\circ}C$. The characteristics of coating film were determined by FT-IR, XRD, and ellipsometion peak represented Zr-O-Zr bonding of tetragonal phase was shown at 470cm-1. Crystallization of zirconia gel and film from amorphous state to tetragonal phase started at 40$0^{\circ}C$, and then transformed into monoclinic phase around $700^{\circ}C$. Zirconia film coated on 304 stainless steel substrate showed relatively low porosity of 16% when it was coated with 0.4M zirconia sol and thereafter heat-treated at 80$0^{\circ}C$ and the film was densified continuously up to 90$0^{\circ}C$. The zirconia film of 10 nm thick acted as a protective layer against oxidation up to $700^{\circ}C$.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.356-361
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• 2005

Earth brush for electrical multiple units(EMUs) is a device through which the current of the EMU load's consumed power fed from the DC 1,500V overhead line (or from the AC 25.000V catenary) flows via axle to the rail(ground) and which prevents the electric corrosion of the axle bearings by preventing the current flow to the axle bearings caused by electric potential from the magnetic field when the bearings rotate together with the earthing function when a thunderbolt falls or a surge comes. The earth brush wear rates among cars, however, shows quite differences when the earth brushes after being separated from the holders are measured with vernier callipers every 6 months of maintenance period. Main causes of the earth brush wear are divided as mechanical, electric arc and electrical one, and the factors can be running speed, current, harmonics, connection state. spring tension, earth brush material, lubricant and so on. but only the earth brushes of the motor(M1) car show the highest wear rate and moreover maintenance difficulty occurs because of the wear rate differences among e earth brushes in one holder. The reason for these preponderant wear comes from the design concept of making preponderant current flow to some particular earth brushes and moreover the heat generated by the harmonics when the inverter starts to operate accelerate the wear. By defining these causes through experiments. I hope that the found results would be helpful for the future EMU design, safety, economy and maintenance.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.379-381
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• 2003

The sharing of common corridors by electric power transmission lines and pipelines is becoming more common place. However, such corridor sharing can result in undesired coupling of electromagnetic energy from the power lines to the near facilities. This causes induced voltages on underground metallic pipelines due to the power line currents. This could cause AC corrosion in the pipeline, which could in turn lead to disastrous accidents, such as gas explosion or oil leakage. This paper investigates for the limitation of induced voltage on the buried metal structures which is used in the inside and outside of the country. And then we measure the earth resistance and leakage current of 22.9kV distribution lines and pipe to soil potential of near pipelines in Seoul Korea. Hereby we can see the leakage current flowing through the earthing electrode have an effect on near pipelines.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.11
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• pp.715-719
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• 2012

We investigated the effects of electrochemical characteristics and generation of chlorine by the different amount of Ru coating which was prepared for $RuO_2$/Ti electrode coated with 1.5 mg, 2.5 mg, 5.5 mg, 8.5 mg Ru per unit area ($cm^2$). As a Result of the cycle voltammetry experiments, chlorine overvoltage of Ru-coated electrodes showed to be the nearly sustained value of approximately 1.15V (vs. Ag/AgCl). By contrary, According to the results of the AC impedance spectroscopy and potentiodynamic polarization tests, the amount of Ru per unit area ($cm^2$) included 2.5 mg, 3.5 mg as $RuO_2$/Ti offered the highest levels of durability which was electrode resistance and corrosion rate appeared to be $0.4582{\Omega}$, $0.5267{\Omega}$ and 0.082 mm/yr, 0.058 mm/yr, respectively. It was also observed that generation of chlorine coated with 3.5 mg per unit area ($cm^2$) was the highest value of 15.2 mg/L.