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Ryu, Hyun Sam,Lim, Tae Seop,Ryu, Jungho,Hong, Seong-Hyeon The Electrochemical Society 2013 Journal of the Electrochemical Society Vol.160 No.1
<P>Yttria stabilized zirconia (YSZ) coating was deposited on AA7075 aluminum alloy by aerosol deposition (AD) at room temperature, and its electrochemical corrosion properties were investigated in 0.5 M H<SUB>2</SUB>SO<SUB>4</SUB>, 3.5 wt% NaCl, and 0.1 M KOH solutions. A crack-free, dense, and ∼5 μm thick YSZ coating on Al alloy was successfully obtained by AD method. The YSZ coating was polycrystalline and composed of ∼10 nm nanocrystallites. Potentiodynamic and electrochemical impedance spectroscopy (EIS) tests indicated that the corrosion behavior in each solution was different, but the corrosion protection of the AA7075 Al alloy was significantly improved by the AD YSZ coating in all three solutions.</P>
Photooxidation of Arsenite under 254 nm Irradiation with a Quantum Yield Higher than Unity
Ryu, Jungho,Monllor-Satoca, Damiá,n,Kim, Dong-hyo,Yeo, Jiman,Choi, Wonyong American Chemical Society 2013 Environmental science & technology Vol.47 No.16
<P>Arsenite (As(III)) in water was demonstrated to be efficiently oxidized to arsenate (As(V)) under 254 nm UV irradiation without needing any chemical reagents. Although the molar absorption coefficient of As(III) at 254 nm is very low (2.49 ± 0.1 M<SUP>–1</SUP>cm<SUP>–1</SUP>), the photooxidation proceeded with a quantum yield over 1.0, which implies a chain of propagating oxidation cycles. The rate of As(III) photooxidation was highly enhanced in the presence of dissolved oxygen, which can be ascribed to its dual role as an electron acceptor of photoexcited As(III) and a precursor of oxidizing radicals. The in situ production of H<SUB>2</SUB>O<SUB>2</SUB> was observed during the photooxidation of As(III) and its subsequent photolysis under UV irradiation produced OH radicals. The addition of <I>tert</I>-butyl alcohol as OH radical scavenger significantly reduced (but not completely inhibited) the oxidation rate, which indicates that OH radicals as well as superoxide serve as an oxidant of As(III). Superoxide, H<SUB>2</SUB>O<SUB>2</SUB>, and OH radicals were all in situ generated from the irradiated solution of As(III) in the presence of dissolved O<SUB>2</SUB> and their subsequent reactions with As(III) induce the regeneration of some oxidants, which makes the overall quantum yield higher than 1. The homogeneous photolysis of arsenite under 254 nm irradiation can be also proposed as a new method of generating OH radicals.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2013/esthag.2013.47.issue-16/es402011g/production/images/medium/es-2013-02011g_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es402011g'>ACS Electronic Supporting Info</A></P>
Ryu, Jungho,Han, Guifang,Lee, Jong-Pil,Lim, Dong-Soo,Park, Yun-Soo,Jeong, Dae-Yong American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.5
<P>Spinel structured highly dense NiMn2O4-based (NMO) negative temperature coefficient (NTC) thermistor thick films were fabricated by aerosol-deposition at room temperature. To enhance the thermistor B constant, which represents the temperature sensitivity of the NMO thermistor material, Co and Co-Fe doping was applied. In the case of single element doping of Co, 5 mol% doped NMO showed a high B constant of over 5000 K, while undoped NMO showed -4000 K. By doping Fe to the 5 mol% Co doped NMO, the B constant was more enhanced at over 5600 K. The aging effect on the NTC characteristics of Co doped and Fe-Co co-doped NMO thick film showed very stable resistivity-time characteristics because of the highly dense microstructure.</P>
Sintering and piezoelectric properties of KNN ceramics doped with KZT
Jungho Ryu,Jong-Jin Choi,Byung-Dong Hahn,Dong-Soo Park,Woon-Ha Yoon,Kun-Young Kim IEEE 2007 and Frequency Control Vol.54 No.12
<P>This paper investigates the effect of K<SUB>1.94</SUB> Zn<SUB>1.06</SUB>Ta<SUB>5.19</SUB>O<SUB>15</SUB> (KZT) addition on the sintering behavior and piezoelectric properties in lead-free piezoelectric ceramics of (K<SUB>0.5</SUB>Na<SUB>0.5</SUB>)NbO<SUB>3</SUB> (KNN). The apparent density of sintered KNN ceramics was increased with KZT addition, and a relative density of above 96.3% was obtained with the doping of over 0.5 mol% KZT. The maximum dielectric and piezoelectric properties of epsiv<SUB>3</SUB> <SUP>T</SUP>/epsiv<SUB>0</SUB> = 590, d<SUB>33</SUB> = 126 pC/N, k<SUB>p</SUB> = 0.42, and P<SUB>tau</SUB>, = 18 muC/cm<SUP>2</SUP> were obtained from 0.5 mol% KZT-doped KNN ceramics. A small amount of KZT (~0.5 mol%) was effective for improving the sintering behavior and piezoelectric properties, but KZT addition exceeding 1.0 mol% was effective only for den-siflcation. A small amount of KZT was effective for den-siflcation of KNN ceramics by promoting K<SUB>5.75</SUB>Nb<SUB>10.8</SUB>O<SUB>30</SUB> liquid phase formation. However, even though KNN with 1.0~2.0 mol% KZT had a relative density of > 98.5%, the piezoelectric properties were inferior to those of 0.5 mol% KZT-doped KNN, presumably due to the smaller grain size and excess liquid phase of the KNN ceramics doped with higher amounts of KZT. It is believed that a small amount of KZT could be one of the suitable sintering aids to obtain highly dense KNN based piezoelectric.</P>
Enhanced domain contribution to ferroelectric properties in freestanding thick films
Ryu, Jungho,Priya, Shashank,Park, Chee-Sung,Kim, Kun-Young,Choi, Jong-Jin,Hahn, Byung-Dong,Yoon, Woon-Ha,Lee, Byoung-Kuk,Park, Dong-Soo,Park, Chan American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.106 No.2
Ryu, Jungho,Kim, Soonhyun,Hong, Hye-Jin,Hong, Jeongsik,Kim, Minsun,Ryu, Taegong,Park, In-Su,Chung, Kang-Sup,Jang, Jum Suk,Kim, Byoung-Gyu Elsevier 2016 Chemical engineering journal Vol.304 No.-
<P><B>Abstract</B></P> <P>Strontium ion (Sr<SUP>2+</SUP>) separation from seawater has attracted attention for radioactive pollutants removal and for Sr<SUP>2+</SUP> recovery. Herein, we synthesized titanate nanotubes (TiNTs) via a simple hydrothermal reaction, characterized their physicochemical properties, and systematically evaluated Sr<SUP>2+</SUP> sorption behavior under various reaction conditions corresponding to seawater environments. The synthesized TiNTs exhibited a fibril-type nanotube structure with a high specific surface area (260m<SUP>2</SUP>/g). Sr<SUP>2+</SUP> adsorption on TiNTs rapidly occurred following a pseudo-second-order kinetic model and was in good agreement with the Langmuir isotherm model, indicating a maximum adsorption capacity of 97mg/g. Based on the Sr<SUP>2+</SUP> uptake and Na<SUP>+</SUP> release with a stoichiometric balance, the Sr<SUP>2+</SUP> sorption mechanism on TiNTs was ion exchange between Na<SUP>+</SUP> in the TiNT lattice and Sr<SUP>2+</SUP> in the solution phase, as confirmed by XRD and Raman analysis. Among the competitive ions, Ca<SUP>2+</SUP> significantly hindered Sr<SUP>2+</SUP> sorption on TiNTs, whereas Na<SUP>+</SUP> only slightly affected Sr<SUP>2+</SUP> sorption, despite the Na<SUP>+</SUP> exchange sorption mechanism. The effect of Ca<SUP>2+</SUP> on Sr<SUP>2+</SUP> sorption was evaluated by introducing a distribution coefficient (<I>K<SUB>d</SUB> </I>) as a critical factor in determining the selectivity, which revealed a slightly higher selectivity for Sr<SUP>2+</SUP>. The Sr<SUP>2+</SUP> adsorption-desorption test in a real seawater medium enabled the determination of <I>K<SUB>d</SUB> </I> and the concentration factor (CF) for co-existing matrix ions in seawater; these values were evaluated for Sr<SUP>2+</SUP> removal and recovery from seawater. TiNTs were regenerated by acid treatment and reused through consecutive adsorption-desorption experiments. While most studies addressing Sr<SUP>2+</SUP> sorption using TiNTs aimed for extraction from wastewater and radioactive wastewater, this study elucidated Sr<SUP>2+</SUP> sorption behavior under seawater conditions and provided insights into developing the removal and recovery processes from seawater.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Titanate nanotubes (TiNTs) were synthesized by a simple hydrothermal reaction. </LI> <LI> The sorption of strontium (Sr) on TiNTs rapidly occurred, achieving Sr uptake 97mg/g. </LI> <LI> Na had little effect on Sr sorption despite the sorption mechanism of the Na exchange. </LI> <LI> Ca significantly hindered Sr sorption on TiNTs among co-existing cations in seawater. </LI> <LI> TiNTs could be easily regenerated by acid treatment and reused for repeated cycles. </LI> </UL> </P>