• Journal of Powder Materials
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• v.20 no.6
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• pp.474-478
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• 2013

The most general photocatalyst, $TiO_2$ and $WO_3$, are acknowledged to be ineffective in range of visible light. Therefore, many efforts have been directed at improving their activity such as: band-gap narrowing with non-metal element doping and making composites with high specific surface area to effectively separate electrons and holes. In this paper, the method was introduced to prepare a photo-active catalyst to visible irradiation by making a mixture with $TiO_2$ and $WO_3$. In the $TiO_2-WO_3$ composite, $WO_3$ absorbs visible light creating excited electrons and holes while some of the excited electrons move to $TiO_2$ and the holes remain in $WO_3$. This charge separation reduces electron-hole recombination resulting in an enhancement of photocatalytic activity. Added Ag plays the role of electron acceptor, retarding the recombination rate of excited electrons and holes. In making a mixture of $TiO_2-WO_3$ composite, the mixing route affects the photocatalytic activity. The planetary ball-mill method is more effective than magnetic stirring route, owing to a more effective dispersion of aggregated powders. The volume ratio of $TiO_2(4)$ and $WO_3(6)$ shows the most effective photocatalytic activity in the range of visible light in the view point of effective separation of electrons and holes.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.347-360
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• 2021

Currently, the demand for eco-friendly energy sources is high, which has prompted research on polymer electrolyte membrane fuel cells. Both aluminum alloys and nickel alloys, which are commonly considered as materials of bipolar plates in fuel cells, oxide layers formed on the metal surface have excellent corrosion resistance. In this research, the electrochemical characteristics of 6061-T6 aluminum alloy and Inconel 600 were investigated with chloride concentrations in an acid environment that simulated the cathode condition of the PEMFC. After potentiodynamic polarization experiments, Tafel analysis and surface analysis were performed. Inconel 600 presented remarkably good corrosion resistance under all test conditions. The corrosion current density of 6061-T6 aluminum alloy was significantly higher than that of Inconel 600 under all test conditions. Also, 6061-T6 aluminum alloy and Inconel 600 presented uniform corrosion and intergranular corrosion, respectively. The Ni, Cr, and Fe, which are the main chemical compositions of Inconel 600, are higher than Al in the electromotive force series. And a double oxide film of NiO-Cr₂O₃, which is more stable than Al₂O₃, is formed. Thus, the corrosion resistance of Inconel 600 is better.

• Korean Journal of Materials Research
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• v.27 no.6
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• pp.339-344
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• 2017

A series of $CaNb_2O_6:Dy^{3+}$, $CaNb_2O_6$:$Eu^{3+}$ and $CaNb_2O_6:Dy^{3+}$, $Eu^{3+}$ phosphors were prepared by solid-state reaction process. The effects of activator ions on the structural, morphological and optical properties of the phosphor particles were investigated. XRD patterns showed that all the phosphors had an orthorhombic system with a main (131) diffraction peak. For the $Dy^{3+}$-doped $CaNb_2O_6$ phosphor powders, the excitation spectra consisted of one broad band centered at 267 nm in the range of 210-310 nm and three weak peaks; the main emission band showed an intense yellow band at 575 nm that corresponded to the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transition of $Dy^{3+}$ ions. For the $Eu^{3+}$-doped $CaNb_2O_6$ phosphor, the emission spectra under ultraviolet excitation at 263 nm exhibited one strong reddish-orange band centered at 612 nm and four weak bands at 536, 593, 650, and 705 nm. For the $Dy^{3+}$ and $Eu^{3+}$-codoped $CaNb_2O_6$ phosphor powders, blue and yellow emission bands due to the $^4F_{9/2}{\rightarrow}^6H_{15/2}$ and $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transitions of $Dy^{3+}$ ions and a main reddish-orange emission line at 612 nm resulting from the $^5D_0{\rightarrow}^7F_2$ transition of $Eu^{3+}$ ions were observed. As the concentration of $Eu^{3+}$ ions increased from 1 mol% to 10 mol%, the intensities of the emissions due to $Dy^{3+}$ ions rapidly decreased, while those of the emission bands originating from the $Eu^{3+}$ ions gradually increased, reached maxima at 10 mol%, and then slightly decreased at 15 mol% of $Eu^{3+}$. These results indicate that white light emission can be achieved by modulating the concentrations of the $Eu^{3+}$ ions incorporated into the $Dy^{3+}$-doped $CaNb_2O_6$ host lattice.

• Analytical Science and Technology
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• v.20 no.1
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• pp.61-69
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• 2007

The geometrical parameters, total and relative energies, vibrational frequencies, the HOMO-LUMO energy gap, and reorganization energies for the neutral molecule, anion, and cation of $C_{16}H_{16}O_3$ have been determined using density functional method (DFT). The highest level of theory employed in this study is $B3LYP/6-311G^{**}$. Harmonic vibrational frequencies were determined at the $B3LYP/6-311G^{**}$ level of theory. All positive vibrational frequencies were obtained to confirm minimum structures. The HOMO-LUMO energy gap and reorganization energies were calculated to predict the charge transport property of liquid-crystal.

• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.554-559
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• 2014

Gadolinium zirconate, $Gd_2Zr_2O_7$, is one of the most promising candidates for replacing yttira-stabilized zirconia (YSZ) in thermal barrier coating (TBC) applications due to its low thermal conductivity and chemical stability at high temperature. In this study, rare-earth zirconate ceramics in the $GdO_{1.5}-ZrO_2$ system with reduced gadolinia contents were fabricated via solid-state reaction as well as hot-pressing at $1800^{\circ}C$. The phase formation, microstructure, and thermo-physical properties of these oxides were examined. The potential application of $GdO_{1.5}-ZrO_2$ ceramics for TBC was also discussed.

• Journal of Powder Materials
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• v.22 no.6
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• pp.413-419
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• 2015

Lanthanum zirconate, $La_2Zr_2O_7$, is one of the most promising candidates for next-generation thermal barrier coating (TBC) applications in high efficient gas turbines due to its low thermal conductivity and chemical stability at high temperature. In this study, bulk specimens and thermal barrier coatings are fabricated via a variety of sintering processes as well as suspension plasma spray in lanthanum zirconates with reduced rare-earth contents. The phase formation, microstructure, and thermo-physical properties of these oxide ceramics and coatings are examined. In particular, lanthanum zirconates with reduced rare-earth contents in a $La_2Zr_2O_7-4YSZ$ composite system exhibit a single phase of fluorite or pyrochlore after fabricated by suspension plasma spray or spark plasma sintering. The potential of lanthanum zirconate ceramics for TBC applications is also discussed.

• Journal of Powder Materials
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• v.20 no.6
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• pp.445-452
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• 2013

Yttria-stabilized zirconia (YSZ) coatings are fabricated via suspension plasma spray (SPS) for thermal barrier applications. Three different suspension sets are prepared by using a planetary mill as well as ball mill in order to examine the effect of starting suspension on the phase evolution and the microstructure of SPS prepared coatings. In the case of planetary-milled commercial YSZ powder, a deposited thick coating turns out to have a dense, vertically-cracked microstructure. In addition, a dense YSZ coating with fully developed phase can be obtained via suspension plasma spray with suspension from planetary-milled mixture of $Y_2O_3$ and $ZrO_2$.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.471-478
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• 2011

Investigations of crystal structure and phase transition of $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramics doped with A-site substitution impurity (La, Nd) or B-site substitution impurity (Sb, Nb) at 2 mol% concentration were carried out. X-ray diffraction patterns of impurities doped $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramics have been measured at pressures up to ~5 GPa with diamond anvil cell and synchrotron radiation. The patterns were obtained at room temperature using methanol-ethanol mixture as pressure-transmitting media. In order to refine the crystal structure, Rietveld analysis has been performed. The structures of impurities doped $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramics are tetragonal in space group P4mm at ambient pressure and are transformed into a cubic phase in space group Pm$\bar{3}$m as the pressure increases. In this study, when A-site substitution donor $La^{3+}$ or $Nd^{3+}$ ion was added to $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramics, the phase transition phenomena showed up at the pressure of 2.5~4.6 GPa, but when B-site substitution donor $Nb^{5+}$ or $Sb^{5+}$ ion was added to it, the phase transition appeared at relatively lower pressure of 1.7~2.6 GPa.

• Resources Recycling
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• v.31 no.4
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• pp.49-55
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• 2022

In this study, the heavy metal ions (of Pb, Cd, Cr, and Hg) in wastewater were removed using a spent Li₂O-Al₂O₃-SiO₂-based crystallized glass previously used as an induction top plate material. Changes in the removal efficiency of heavy metals according to different reaction parameters, such as the amount of zeolite used as a heavy-metal adsorbent, adsorption time, initial concentration of the heavy metals, and pH of the initial solution, were investigated. As the amount of zeolite added increased, the heavy-metal removal efficiency also increased. Adsorption time had a considerable influence on adsorption characteristics, and the removal efficiency of all heavy metals increased with increasing adsorption time. In the case of Cd, the removal efficiency was greatly improved depending on the adsorption time. The initial concentration of the heavy-metal solution did not affect the removal efficiency; however, the initial pH of the heavy-metal solution affected the removal efficiency. More specifically, the removal efficiency of Cd increased while that of Pb and Cr decreased with increasing pH. The adsorption characteristics of Hg were not significantly affected by pH.

• Resources Recycling
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• v.30 no.2
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• pp.46-52
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• 2021

Off-grade Ti generated from smelting and mechanical processing has a high oxygen content. In this work, off-grade Ti was deoxidized using Mg and a chloride mixture as the reductant and flux, respectively. The experiments were conducted in the α-Ti temperature range (1,023~1,123 K) and the effects of the reaction time, reaction temperature, quantitiy of Mg and chloride ratio on deoxidation were investigated. Notably, when YCl3 is used as the flux to react with MgO, it is possible to reduce the activity of MgO. Therefore Ti can be deoxidized using Mg. In this study, the O content was decreased from 0.5 wt% to 0.1004 wt% at 1073 K, for 6 hours, with Mg=3.6 g and $X_{YCl_3}=0.22$.