• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.198-198
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• 2016

An ideal orthopedic implant should provide an excellent bone-implant connection, less implant loosening and minimum adverse reactions. Commercial pure titanium (CP-Ti) and Ti alloys have been widely utilized for biomedical applications such as orthopedic and dental implants. However, being bioinert, the integration of such implant in bone was not in good condition to achieve improved osseointegraiton, there have been many efforts to modify the composition and topography of implant surface. These processes are generally classified as physical, chemical, and electrochemical methods. Plasma electrolytic oxidation (PEO) as an electrochemical route has been recently utilized to produce this kind of composite coatings. Mg ion plays a key role in bone metabolism, since it influences osteoblast and osteoclast activity. From previous studies, it has been found that Mg ions improve the bone formation on Ti alloys. PEO is a promising technology to produce porous and firmly adherent inorganic Mg containing $TiO_2$($Mg-TiO_2$ ) coatings on Ti surface, and the amount of Mg introduced into the coatings can be optimized by altering the electrolyte composition. In this study, a series of $Mg-TiO_2$ coatings are produced on Ti-6Al-4V ELI dental implant using PEO, with the substitution degree, respectively, at 0, 5, 10 and 20%. Based on the preliminary analysis of the coating structure, composition and morphology, a bone like apatite formation model is used to evaluate the in vitro biological responses at the bone-implant interface. The enhancement of the bone like apatite forming ability arises from $Mg-TiO_2$ surface, which has formed the reduction of the Mg ions. The promising results successfully demonstrate the immense potential of $Mg-TiO_2$ coatings in dental and biomaterials applications.

• Korean Journal of Materials Research
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• v.26 no.10
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• pp.513-520
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• 2016

The effect of NaOH concentration on the properties of electrolytic plasma processing (EPP) coating formed on AZ61A Mg alloy is studied. Various types of EPP were employed on magnesium alloy AZ61A in a silicate bath with different concentrations of NaOH additive. Analysis of the composition and structure of the coating layers was carried out using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The results showed that the oxide coating layer mainly consisted of MgO and $Mg_2SiO_4$; its porosity and thickness were highly dependent on the NaOH concentration. The Vickers hardness was over 900 HV for all the coatings. The oxide layer with 3 g/l of NaOH concentration exhibited the highest hardness value (1220 HV) and the lowest wear rate. Potentiodynamic testing of the 3 g/l NaOH concentration showed that this concentration had the highest corrosion resistance value of $2.04{\times}10^5{\Omega}cm^2$; however, the corrosion current density value of $5.80{\times}10^{-7}A/cm^2$ was the lowest such value.

• Journal of Soil and Groundwater Environment
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• v.15 no.4
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• pp.46-52
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• 2010

Acid mine drainage occurs when sulfide minerals are exposed to an oxidizing environment. The objective of this study was to inhibit the oxidation of pyrite by applying various coating agent such as $KH_2PO_4$, MgO and $KMnO_4$ over its surface as an oxidation inhibitors. Experiments were conducted for 8 days to test the feasibility of oxidation inhibitors. The optimal condition of coating agent for standard pyrite and IK mine was the combination of 0.01M $KH_2PO_4$, 0.01M NaOAc and 0.01M NaClO. Otherwise, for YD mine the combination of 0.01M $KMnO_4$, 0.01M NaOAc and 0.01M NaClO. The $SO_4^{2-}$ reduction efficiency of pyrite, IK and YD mine samples was 70, 92 and 84%, respectively. For 8 days, no significant increase of $SO_4^{2-}$ from pyrite sample coated with inhibitor was observed. The pH of solution remains in between 4 to 6 for the reaction conditions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.43-46
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• 2002

Ferroelectric Mg-doped SBT and Ti-doped SBT were successfully deposited on Pt/Ti/$SiO_2/Si$ substrate by using a sol-gel solution coating method. The solutions were prepared through out adding the metal alkoxide solutions to SBT solution. The typical hysteresis loop of the films was obtained at 5V. The measured $2P_r$ value were $16.50{\mu}C/cm^2$ for SBT, $18.98{\mu}C/cm^2$ and for Mg-doped SBT, and $17.10{\mu}C/cm^2$ for Ti-doped SBT at an applied voltage of 5V, respectively. And it is found that the leakage current densities are less than $10^{-7}A/cm^2$ when applied voltage is less than 10.8MV/cm, which indicates the excellent insulating characteristics.

• Proceedings of the Korean Magnestics Society Conference
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• 2016.05a
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• pp.76-77
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• 2016

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.2
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• pp.74-79
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• 2018

To increase corrosion resistance of Mg alloy, AZ31 and AZ91 were PEO treated with different applied voltage and time conditions. We used Na-P and Na-Si system electrolyte. Crystalline phase and morphology were investigated. MgO was Most common crystal phase and vitreous phase could be found. Crystalline phase of $Na_{3.59}Mg_{2.71}(PO_4)_3$ and $Mg_2SiO_4$ also could be found. Porosity of oxidized surface tends to decrease with increasing PEO applied voltage, treat time and concentration of electrolyte, after then, size of pore increased and total number of pore decreased, distinctly.

• Bulletin of the Korean Chemical Society
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• v.33 no.8
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• pp.2523-2528
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• 2012

Green phosphors $(Zn_{1-a-b}M_aM^{\prime}_b)_xGa_yS_{x+3y/2}:Eu^{2+}$ (M, M' = alkali earth ions) with x = 2 and y = 2-5 were prepared, starting from ZnO, MgO, $SrCO_3$, $Ga_2O_3$, $Eu_2O_3$, and S with a flux $NH_4F$ using a conventional solidstate reaction. A phosphor with the composition of $(Zn_{0.6}Sr_{0.3}Mg_{0.1})_2Ga_2S_5:Eu^{2+}$ produced the strongest luminescence at a 460-nm excitation. The observed XRD patterns indicated that the optimized phosphor consisted of two components: zinc thiogallate and zinc sulfide. The characteristic green luminescence of the $ZnS:Eu^{2+}$ component on excitation at 460 nm was attributed to the donor-acceptor ($D_{ZnGa_2S_4}-A_{ZnS}$) recombination in the hybrid boundary. The optimized green phosphor converted 17.9% of the absorbed blue light into luminescence. For the fabrication of light-emitting diode (LED), the optimized phosphor was coated with MgO using magnesium nitrate to overcome their weakness against moisture. The MgO-coated green phosphor was fabricated with a blue GaN LED, and the chromaticity index of the phosphor-cast LED (pc-LED) was investigated as a function of the wt % of the optimized phosphor. White LEDs were fabricated by pasting the optimized green (G) and the red (R) phosphors, and the commercial yellow (Y) phosphor on the blue chips. The three-band pc-WLED resulted in improved color rendering index (CRI) and corrected color temperature (CCT), compared with those of the two-band pc-WLED.

• Korean Journal of Metals and Materials
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• v.49 no.8
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• pp.601-607
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• 2011

The study investigated the influence of current density on the corrosion-protection properties of an AZ91 Mg alloy subjected to plasma electrolytic oxidation coating. The present coatings were carried out under an AC condition at three different current densities, i.e., 100, 150, and $200mA/cm^2$. From microstructural observations, the micro cracks connecting each micro pore were pronounced on the oxide surface of the samples coated at current densities higher than $150mA/cm^2$ since increasing the current density in this study led to an increment in the relative volume fraction of the MgO compound. Based on potentio dynamic polarization and immersion tests, the sample coated at a current density of $100mA/cm^2$ showed superior corrosion resistance.

• 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.

• Environmental Engineering Research
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• v.13 no.4
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• pp.197-202
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• 2008

This study evaluated the photocatalytic oxidation of BPA using the RPOD reactor under various conditions. This study found that the RPOD was effective for BPA degradation. It could reduce 1 mg/L of BPA by half within 5 min under the optimum conditions. According to the study results, $TiO_2$ coating was important for the BPA oxidation. As the coating thickness increased, the removal efficiency improved. The light source, the light intensity and the drum rotating speed were important for the oxidation. The UV light was more effective for the BPA degradation than the visible light. The removal efficiency improved with increasing intensity. As the drum speed increased, the removal efficiency improved. The maximum speed was 240 rpm in this study. Addition of air and nitrogen was not beneficial for the BPA degradation in this study probably due to enough oxygen in the water.