• 한국표면공학회지
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• 제43권3호
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• pp.132-141
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• 2010

NiTi alloy has been used for orthodontic wire due to good mechanical properties, such as elastic strength and frictional resistance, combined with a high resistance to corrosion. Recently, these wire were coated by polymer and ceramic materials for aesthetics. The purpose of this study was to investigate surface characteristics of polymer coated NiTi alloy wire for orthodontics using various instruments. Wires (round type and rectangular type) were used, respectively, for experiment. Polymer coating was carried out for wire. Specimen was investigated with field emission scanning electron microscopy(FE-SEM), energy dispersive x-ray spectroscopy(EDS) and atomic force microscopy(AFM). The phase transformation of non-coated NiTi wire from martensite to austenite occurred at the range of $14{\sim}15^{\circ}C$, in the case of coated wire, it occurred at the range of $16{\sim}18^{\circ}C$. Polymer coating on NiTi wire surface decreased the surface defects such as scratch which was formed at severe machined surface. From the AFM results, the average surface roughness of non-coated and coated NiTi wire was 13.1 nm, and 224.5 nm, respectively. From convetional surface roughness test, the average surface roughness of non-coated and coated NiTi wire was $0.046{\mu}m$, and $0.718{\mu}m$, respectively.

• 한국표면공학회지
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• 제50권5호
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• pp.366-372
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• 2017

Plasma electrolytic oxidation(PEO) has attracted attention as a surface treatment which has high wear resistance and corrosion resistance. PEO is generally considered as cost-effective, environmentally friendly and superior in terms of coating performance. Most of studies about the PEO processes have been applied to light metals such as Al and Mg. Because the strength of Al and Mg is weaker than that of steel, there is a limit to the application. In this study, PEO process was used to form oxide coatings on Hot dipped aluminized(HDA) steel and the characteristics of the coating film according to the PEO current density were studied. The morphology was observed by SEM and component was analyzed by using EDS. The corrosion behaviors of PEO coating films were estimated by exposing salt spray test at 5 wt.% NaCl solution and measuring polarization curves in deaerated 3 wt.% NaCl solution. With the increase of PEO process current density, the pore size of the coating surface and the thickness of coating increased. It was confirmed that no Fe component was present on the coating surface. PEO coating films obviously showed good corrosion resistance compared with HDA. It is considered that the PEO coating acts as a barrier to protect the base material from external factors causing corrosion.

• Tribology and Lubricants
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• 제31권2호
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• pp.42-49
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• 2015

Because of the growing need for high-speed transport options such as trains and aircraft, there is increasing demand for technology related to high-speed trains. Among them, braking systems are important in high-speed trains in terms of reliability. Especially, the disk brake system, in use in most high-speed trains, transforms kinetic energy into thermal energy and noise. Therefore, the material properties of both the friction materials and disks are expected to influence the tribological characteristics. In this paper, the tribological characteristics depend on the hardness of the brake disks between the Cu-based sintered metallic friction material and the heat-treated heat-resisting steel disks. A lab-scale dynamometer used to perform braking tests at a variety of braking speeds using dry conditions. The test results revealed that the hardness of the disks affects the friction coefficients, friction stabilities, and wear rates. Thus, the brake system using the heat-resisting steel disk requires proper heat-treatment. These differences are considered to be caused by the change in tribological mechanisms and the generation of an oxide layer on the friction surfaces. The oxide layers on the friction surfaces are confirmed to Fe₂O₃ by x-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) analysis.

• 한국환경과학회지
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• 제29권12호
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• pp.1213-1222
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• 2020

In the current study, a Cu2O/TiO2 photoinduced nanocomposite materials prepared by ultrasonification method was evaluated the photocatalytic oxidation efficiency of volatile organic compounds (BTEX) under visible-light irradiation. The results of XRD confirmed the successful preparation of photoinduced nanocomposite materials. However, diffraction peaks belonging to TiO2 were not confirmed for the Cu2O/TiO2. The possible reason for the absence of Cu2O peak is their low content and small particle size. The result of uv-vis spectra exhibited that the fabricated Cu2O/TiO2 can be activated under visible light irradiation. The FE-SEM/EDS and TEM showed the formation of synthesized nanocomposites and componential analysis in the undoped TiO2 and Cu2O/TiO2. The photocatalytic oxidation efficiencies of benzene, toluene, ethylbenzene, and o-xylene with Cu2O/TiO2 were higher than undoped TiO2. According to light sources, the average oxidation efficiencies for BTEX by Cu2OT-0.5 were exhibited in the orer of 8 W day light > violet LEDs > white LEDs. However, the photocatalytic oxidation efficiencies normalized to supplied electric power were calculated to be in the following order of violet LEDs > white LEDs > 8 W day light, indicating that the LEDs could be a much more energy efficient light source for the photo-oxidation of gaseous BTEX using Cu2O/TiO2.

• Current Photovoltaic Research
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• 제8권4호
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• pp.124-128
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• 2020

Output power of photovoltaic (PV) modules installed outdoors decreases every year due to environmental conditions such as temperature, humidity, and ultraviolet irradiations. In order to promote the installation of PV modules, the reliability must be guaranteed. One of the important factors affecting reliability is intermetallic compounds (IMC) layer formed in ribbon solder joint. For this reason, various studies on soldering properties between the ribbon and cell have been performed to solve the reliability deterioration caused by excessive growth of the IMC layer. However, the IMC layer of the PV module interconnected by multi-wires has been studied less than using the ribbon. It is necessary to study soldering characteristics of the multi-wire module for improvement of its reliability. In this study, we analyzed the growth of IMC layer of the PV module with multi-wire and the degradation of output power through damp-heat test. The fabricated modules were exposed to damp-heat conditions (85 ºC and 85 % relative humidity) for 1000 hours and the output powers of the modules before and after the damp-heat test were measured. Then, the process of dissolving ethylene vinyl acetate (EVA) as an encapsulant of the modules was performed to observe the IMC layer. The growth of IMC layer was evaluated using OM and FE-SEM for cross-sectional analysis and EDS for elemental mapping. Based on these results, we investigated the correlation between the IMC layer and output power of modules.

• 한국분말재료학회지
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• 제30권3호
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• pp.249-254
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• 2023

The influence of MgO addition on the densification and microstructure of alumina (Al₂O₃) was studied. Compacted alumina specimens were manufactured using ball-milling and one-directional pressing followed by sintering at temperatures below 1700℃. Relative density, shrinkage, hardness, and microstructure were investigated using analytical tools such as FE-SEM, EDS, and XRD. When the MgO was added up to 5.0 wt% and sintered at 1500℃ and 1600℃, the relative density exhibited an average value of 97% or more at both temperatures. The maximum density of 99.2% was with the addition of 0.5 wt% MgO at 1500℃. Meanwhile, the specimens showed significantly lower density values when sintered at 1400℃ than at 1500℃ and 1600℃ owing to the relatively low sintering temperature. The hardness and shrinkage data also showed a similar trend in the change in density, implying that the addition of approximately 0.5 wt% MgO can promote the densification of Al₂O₃. Studying the microstructure confirmed the uniformity of the sintered alumina. These results can be used as basic compositional data for the development of MgO-containing alumina as high-dielectric insulators.

• 소성∙가공
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• 제32권6호
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• pp.344-351
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• 2023

The use of Zn-Al-Mg alloy coatings for enhancing the corrosion resistance of steel sheets is gaining prominence over traditional Zn coatings. There is a growing demand for the development of thermal spray wires made from Zn-Al-Mg alloys, as a replacement for the existing wires produced using Al and Zn. This is particularly crucial to secure corrosion resistance and durability in the damaged areas of coated steel sheets caused by deformation and welding. This study focuses on the casting and extrusion processes of Zn-2Al-1Mg alloy for the fabrication of such spray wires and analyzes the changes in microstructure during the extrusion process. The Zn-2Al-1Mg alloy, cast in molds, was subjected to a heat treatment at 250 ℃ for 3 hours prior to extrusion. The extrusion process was carried out by heating both the material and the mold up to 300 ℃. Microstructural analysis was conducted using FE-SEM and EDS to differentiate each phase. The mechanical properties of the cast specimen were evaluated through compression tests at temperatures ranging from 200 to 300 ℃, with strain rates of 0.1 to 5 sec^-1. Vickers hardness testing was utilized to assess the inhomogeneity of mechanical properties in the radial direction of the extruded material. Finite Element Analysis (FEA) was employed to understand the inhomogeneity in stress and strain distribution during extrusion, which aids in understanding the impact of heterogeneous deformation on the microstructure during the process.

• 한국표면공학회지
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• 제56권5호
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• pp.299-308
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• 2023

In this study, phosphorus (P)-doped nickel cobaltite (P-NiCo₂O₄) and nickel-cobalt layered double hydroxide (P-NiCo-LDH) were synthesized on nickel (Ni) foam as a conductive support using hydrothermal synthesis. The thermal properties, crystal structure, microscopic surface morphology, chemical distribution, electronic state of the constituent elements on the sample surface, and electrical properties of the synthesized P-NiCo₂O₄ and P-NiCo-LDH samples were analyzed using thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The P-NiCo₂O₄ electrode exhibited a specific capacitance of 1,129 Fg^-1 at a current density of 1 Ag^-1, while the P-NiCo-LDH electrode displayed a specific capacitance of 1,012 Fg^-1 at a current density of 1 Ag-1. When assessing capacity changes for 3,000 cycles, the P-NiCo₂O₄ electrode exhibited a capacity retention rate of 54%, whereas the P-NiCo-LDH electrode showed a capacity retention rate of 57%.

• 한국표면공학회지
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• 제56권6호
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• pp.437-442
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• 2023

This research aims to enhance the efficiency of Pt/C catalysts due to the limited availability and high cost of platinum in contemporary fuel cell catalysts. Nano-sized platinum particles were distributed onto a carbon-based support via the polyol process, utilizing the metal precursor H₂PtCl₆·6H₂O. Key parameters such as pH, temperature, and RPM were carefully regulated. The findings revealed variations in the particle size, distribution, and dispersion of nano-sized Pt particles, influenced by temperature and pH. Following sodium hydroxide treatment, heat treatment procedures were systematically executed at diverse temperatures, specifically 120, 140, and 160 ℃. Notably, the thermal treatment at 140 ℃ facilitated the production of Pt/C catalysts characterized by the smallest platinum particle size, measuring at 1.49 nm. Comparative evaluations between the commercially available Pt/C catalysts and those synthesized in this study were meticulously conducted through cyclic voltammetry, X-ray diffraction (XRD), and field-emission scanning electron microscopy-energy dispersive X-ray spectroscopy (FE-SEM EDS) methodologies. The catalyst synthesized at 160 ℃ demonstrated superior electrochemical performance; however, it is imperative to underscore the necessity for further optimization studies to refine its efficacy.

• 자원환경지질
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• 제35권3호
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• pp.241-255
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• 2002

이 연구는 호남탄전지역 폐탄광에서 배출된 산성광산배수와 하상퇴적물에 대한 환경지구화학적 특성을 밝히기 위해 수행되었다. 화학적 분석을 위해 54곳에서 하천수를 채취하였고, 광물학적-화학적 분석을 위해 34개의 하상퇴적물을 채취하였다. 하천수의 물리화학적 특성은 현장에서 바로 측정하였고, ICP-AES, ICP-MS 와 IC를 이용하여 화학조성을 측정하였으며, 하상퇴적물의 광물학적 특성은 XRD, SEM 그리고 EDS를 이용하였다. 하천수의 물리화학적 특성은 pH 2.85~8.12, Eh -62~215 mV, EC 0.205~146 ms/m, ER 0.234~255 {$\Omega}{\cdot}$m, DO 0.03~1068 mg/L 그리고 TDS 10.96~1420 mg/L 이었고, 화학조성에서 K 0.118~3.184 mg/L, Mg 2.1~114.48 mg/L, Ca 2.59~125.02 mg/L, Al 0.01~44.72 mg/L, Fe 0.108~89.49 mg/L, Na 5.45~125.41 mg/L를 함유한 것으로 분석되었다. 하상퇴직물에 대한 XRD분석에서 석영, 일라이트, 괴사이트 등의 피크가 보였으며, 98$0^{\circ}C$로 가열하였더니 헤마타이트의 피크가 관찰되었다. 하상퇴적물의 중금속에 대한 고찰에서 Fe 22575~34713 ppm, Zn 41.66~970.3 ppm, Cd 0.52~52.07 ppm, Cu 1.25~198.50 ppm, Pb 0.43~77.35 ppm이 각각 검출되었다.