• Laser Solutions
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• v.17 no.2
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• pp.1-4
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• 2014

With the PEO(Plasma electrolytic oxidation) surface treatment, the oxide film of aluminum alloy is growing in a short time. The reflectance measurement to find the oxygen atoms in the oxide could be investigated. In order to form a thicker oxide film, the PEO surface treatment should be uniformly controlled in processing time.

• Korean Journal of Materials Research
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• v.33 no.7
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• pp.315-322
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• 2023

In the present work, we address the new route for the green synthesis of manganese dioxide (MnO₂) by an innovative method named the solution plasma process (SPP). The reaction mechanism of both colloidal and nanostructured MnO₂ was investigated. Firstly, colloidal MnO₂ was synthesized by plasma discharging in KMnO₄ aqueous solution without any additives such as reducing agents, acids, or base chemicals. As a function of the discharge time, the purple color solution of MnO₄^- (oxidation state +7) was changed to the brown color of MnO₂ (oxidation state +4) and then light yellow of Mn²⁺ (oxidation state +2). Based on the UV-vis analysis we found the optimal discharging time for the synthesis of stable colloidal MnO₂ and also reaction mechanism was verified by optical emission spectroscopy (OES) analysis. Secondly, MnO₂ nanoparticles were synthesized by SPP with a small amount of reducing sugar. The precipitation of brown color was observed after 8 min of plasma discharge and then completely separated into colorless solution and precipitation. It was confirmed layered type of nanoporous birnessite-MnO₂ by X-ray powder diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), and electron microscopes. The most important merits of this approach are environmentally friendly process within a short time compared to the conventional method. Moreover, the morphology and the microstructure could be controllable by discharge conditions for the appropriate potential applications, such as secondary batteries, supercapacitors, adsorbents, and catalysts.

• Journal of the Korean institute of surface engineering
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• v.47 no.4
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• pp.147-154
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• 2014

Formation behavior of PEO (Plasma Electrolytic Oxidation) films on AZ31 Mg alloy was studied in aqueous solutions containing various concentrations of hydroxide ion ($OH^-$) and silicate ion ($SiO_3{^{2-}}$) by voltage-time curves, and corrosion resistance of the PEO film-covered specimen was investigated by immersion test in 0.5 M NaCl solution. From the analyses of the voltage-time curves, it is suggested that two different types of anions are essentially needed for the formation of PEO films on AZ31 Mg alloy: film formation agent and local film breakdown agent. $SiO_3{^{2-}}$ ion acts only as a film formation agent but $OH^-$ ion acts not only as a film formation agent but also film breakdown agent. The PEO films prepared on AZ31 Mg alloy in alkaline silicate solution showed very good corrosion resistance without any pitting or filiform corrosions up to 480 h of immersion in 0.5 M NaCl.

• Journal of the Korean institute of surface engineering
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• v.51 no.6
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• pp.381-386
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• 2018

In this study, plasma electrolytic oxidation (PEO) method was used to from anodic oxide films on Al alloy and their resistance and morphological characteristics were investigated as a function of film formation voltage and treatment time. Cross-sectional morphology and composition of the PEO films were analyzed by SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive Spectroscopy). The PEO films showed increased surface roughness and thickness with of film formation voltage and treatment time. The wear resistance was found to be the best for the PEO film formed for 5 min at 500V which is attributed to be denser structure relatively and lower surface roughness.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.04a
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• pp.124-125
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• 2002

• Journal of the Korean institute of surface engineering
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• v.55 no.5
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• pp.292-298
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• 2022

In this study, PEO (plasma electrolytic oxidation) film formation behavior of AZ31 Mg alloy under application of 300 Hz pulse current was studied by the analyses of V-t curve, arc generation behavior, PEO film thickness and morphology of PEO films with treatment time in 0.05 M NaOH + 0.05 M Na₂SiO₃ + 0.1 M NaF solution. PEO films was observed to grow after 10 s of application of pulse current together with generation of micro-arcs. PEO film grew linearly with treatment time at a growth rate of about 5.58 ㎛/min at 200 mA/cm² of pulse current but increasing rate of film formation voltage became lowered largely with increasing treatment time after passing about 250 V, suggesting that resistivity of PEO films during micro-arc generation decreases with increasing film formation voltage at more than 250 V.

• Journal of Powder Materials
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• v.15 no.2
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• pp.95-100
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• 2008

The investigation is to modify the mechanical and chemical properties of Mg alloys using a combination of rapid solidification and surface treatment. As the first approach, $Mg_{95}Zn_{4.3}Y_{0.7}$ was gas atomized and pressure sintered by spark plasma sintering process (SPS), showing much finer microstructure and higher strength than the alloys as cast. Further modification was performed by treating the surface of PM Mg specimen using Plasma electrolytic oxidation (PEO) process. During the PEO processing, MgO layer was initiated to form on the surface of Mg powder compacts, and the thickness and the density of MgO layer were varied with the reaction time. The thickening rate became low with the reaction time due to the limited diffusion rate of Mg ions. The surface morphology, corrosion behavior and wear resistance were also discussed.

• Journal of the Korean institute of surface engineering
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• v.52 no.6
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• pp.283-288
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• 2019

MCrAlY overaly coatings are used as oxidation barrier coatings to prevent degradation of the underlying substrate in high temperature and oxidizing environment of the hot section of gas turbines. Therefore, oxidation resistance in high temperature is important property of MCrAlY coatings. Also, coefficients of thermal expansion (CTE) of MCrAlY have middle value of that of Ni-based superalloys and oxides, which have the effect of preventing the delamination of the surface oxides. Cyclic oxidation test is one of the most useful methods for evaluating the high temperature durability of coatings used in gas turbines. In this study, NiCoCrAlY overlay coatings were formed on Inconel 792(IN 792) substrates by vacuum plasma spraying process. Vacuum plasma sprayed NiCoCrAlY coatings and IN 792 susbstrates were exposed to 1000℃ one-hour cyclic oxidation environment. NiCoCrAlY coatings showed lower weight gain in short-term oxidation. In long-term oxidation, IN 792 substrates showed higher weight loss due to delamination of surface oxide but NiCoCrAlY coatings showed lower weight loss. X-ray diffraction (XRD) analysis showed α-Al2O3 and NiCr₂O₄ was formed during the cyclic oxidation test. Through cross-section observation using scanning electron microscopy (SEM) and electron back scatter diffraction (EBSD) analysis, thermally grown oxide (TGO) layer composed of α-Al₂O₃ and NiCr₂O₄ was formed and the thickness of TGO increased during 1000℃ cyclic oxidation test. β phase in upper side of NiCoCrAlY coating was depleted due to oxidation of Al and outer beta depletion zone thickness also increased as the cyclic oxidation time increased.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.33-40
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• 2010

In this research, the effects for surface Improvement of plasma ion implanted carbide endmill tools were observed by measuring cutting forces and tools wear affecting surface roughness in high speed cutting. From the 2nd ion mass analysis, the oxidation layer was found to be built up by sputtering. The residual gas contamination of oxygen was found to be contained impurities in nitrogen gas. The plasma implanted ion was found to be spreaded, especially the nitrogen was implanted up to 150nm depth as impressed voltage and ion implanting time. It is analyzed as bring surface improvement by spreading deeply forming oxidation on surface. The factors in Analysis of Variance(ANOVA) about mutuality cause reference of cutting force. The cutting force Fx is affected by the interaction of spindle rpm and federate, the cutting force Fy is influenced by spindle rpm and time injected ion, and cutting force Fz is affected by the interaction of impressed voltage and feedrate. Also, it was found that the cutting forces of implanted tools become lower and the surface roughness is improved by the effect of nitrogen according to the implantation.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.193.2-193.2
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• 2016

We evaluate the change in defects in the oxidized SiO2 grown on 4H-SiC (0001) by plasma assisted oxidation, by comparing with that of conventional thermal oxide. In order to investigate the changes in the electronic structure and electrical characteristics of the interfacial reaction between the thin SiO2 and SiC, x-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), DFT calculation and electrical measurements were carried out. We observed that the direct plasma oxide grown at the room temperature and rapid processing time (300 s) has enhanced electrical characteristics (frequency dispersion, hysteresis and interface trap density) than conventional thermal oxide and suppressed interfacial defect state. The decrease in defect state in conduction band edge and stress-induced leakage current (SILC) clearly indicate that plasma oxidation process improves SiO2 quality due to the reduced transition layer and energetically most stable interfacial state between SiO2/SiC controlled by the interstitial C.