• Bulletin of the Korean Chemical Society
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• v.24 no.1
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• pp.86-90
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• 2003

Reverse-Water-Gas-Shift reaction (RWGSR) was carried out over the ZnO, $Al_2O_3,\;and\;ZnO/Al_2O_3$ catalysts at the temperature range from 400 to 700 ℃. The ZnO showed good specific reaction activity but this catalyst was deactivated. All the catalysts except the $ZnO/Al_2O_3$ catalyst (850 ℃) showed low stability for the RWGSR and was deactivated at the reaction temperature of 600 ℃. The $ZnO/Al_2O_3$ catalyst calcined at 850 ℃ was stable during 210 hrs under the reaction conditions of 600 ℃ and 150,000 GHSV, showing CO selectivity of 100% even at the pressure of 5 atm. The high stability of the $ZnO/Al_2O_3$ catalyst (850 ℃) was attributed to the prevention of ZnO reduction by the formation of $ZnAl_2O_4$ spinel structure. The spinel structure of $ZnAl_2O_4$ phase in the $ZnO/Al_2O_3$ catalyst calcined at 850 ℃ was confirmed by XRD and electron diffraction.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.423-423
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• 2011

Zinc oxide is metal oxide semiconductor with the 3.37 eV bandgap energy. Zinc oxide is very attractive materials for many application fields. Zinc Oxide has many advantages such as high conductivity and good transmittance in visible region. Also it is cheaper than other semiconductor materials such as indium tin oxide (ITO). Therefore, ZnO is alternative material for ITO. ZnO is attracting attention for its application to transparent conductive oxide (TCO) films, surface acoustic wave (SAW), films bulk acoustic resonator (FBAR), piezoelectric materials, gas-sensing, solar cells and photocatalyst. In this study, we synthesized ZnO nanoparticles and defined their physical and chemical properties. Also we studied about the application of ZnO nanoparticles as a photocatalyst and try to find a enhancement photocatalytic activity of ZnO nanorticles.. We synthesized ZnO nanoparticles using spray-pyrolysis method and defined the physical and optical properties of ZnO nanoparticles in experiment I. When the ZnO are exposed to UV light, reduction and oxidation (REDOX) reaction will occur on the ZnO surface and generate O2- and OH radicals. These powerful oxidizing agents are proven to be effective in decomposition of the harmful organic materials and convert them into CO2 and H2O. Therefore, we investigated that the photocatalytic activity was increased through the surface modification of synthesized ZnO nanoparticles. In experiment II, we studied on the stability of ZnO nanoparticles in water. It is well known that ZnO is unstable in water in comparison with TiO2. Zn(OH)2 was formed at the ZnO surface and ZnO become inactive as a photocatalyst when ZnO is present in the solution. Therefore, we prepared synthesized ZnO nanoparticles that were immersed in the water and dried in the oven. After that, we measured photocatalytic activities of prepared samples and find the cause of their photocatalytic activity changes.

• Korean Journal of Materials Research
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• v.15 no.10
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• pp.678-682
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• 2005

We studied the possibility of $Zn_4O(Ac)_2(OH)$ formation as a precursor for ZnO nano particles in sol-gel method. Four different additives such as tetra methyl ammonium hydroxide, mono ethanol amine (MEA), LiOH, and $H_2O$ were used for zinc acetate dissolved in 2-methoxy ethanol. ZnO particles of 5-6 nm in size were observed. Existence of $Zn_4O(Ac)_6$ was not verified. $Zn_4O(Ac)_2(OH)$ molecules were observed and they were believed to be the precursors of ZnO. A peak at 275nm in UV-Vis analysis was observed In the case of MEA and $H_2O$ but no ZnO particles were detected in transmission electron microscopy.

• Electrical & Electronic Materials
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• v.9 no.9
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• pp.925-932
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• 1996

Using the d.c. 2-probe method, we have examined the temperature dependence of CO gas sensitivity of pure ZnO and ZnO CuO thick films prepared by the acqueous precipitation. At 200ppm CO gas, pure ZnO thick film shows the maximum sensitivity of -6.5 at 300.deg. C. On the other hand, the maximum sensitivity of 1-5 mol% and 10-15 mol% CuO added ZnO thick films are 2.8-2.5 and 1.6, respectively. Therefore, the sensitivity of pure ZnO thick film is about three times larger than those of ZnO-CuO thick films. We suggest that the promotion of maximum sensitivity is caused by low packing and the increase of chemical adsorptions for $O_{2}$ gas.

• Bulletin of the Korean Chemical Society
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• v.11 no.2
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• pp.150-154
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• 1990

The structures of $Tl_{12-2x}Zn_x-A$ (x = 4.3 and 3.25), vacuum dehydrated zeolite A with all $Na^+$ ions replaced by $Tl^+$ and $Zn^{2+}$ as indicated, have been determined by single-crystal X-ray diffraction techniques in cubic space group Pm3m at 21(1) $^{\circ}C$ (a=12.100(2) ${\AA}$ for $Tl_{3.4}Zn_{4.3}-A$ and a=12.092(2) ${\AA}$ for $Tl_{5.5}Zn_{3.25}-A$). The crystals of $Tl_{3.4}Zn_{4.3}-A$ and $Tl_{5.5}Zn_{3.25}-A$ were prepared by flow method using exchange solutions in which mole ratios of $TlNO_3$,/TEX> and $Zn(NO_3)_2$ were 1:50 and 1:1, respectively, with total concentration of 0.05 M. The structures of the dehydrated $Tl_{3.4}Zn_{4.3}-A$ and $Tl_{5.5}Zn_{3.25}-A$ were refined to yield the final error indices $R_1$ = 0.075 and $R_2$ = 0.075 with 236 reflections, and $R_1$ = 0.057 and $R_2$ = 0.064 with 202 reflections, respectively, for which I > 3$\sigma$(I). Both structures indicate that Zn(II) ions are coordinated by three framework oxygens: the Zn(II) to O(3) distances are 2.08(1) ${\AA}$ for $Tl_{3.4}Zn_{4.3}-A$ and 2.07(1) ${\AA}$ for $Tl_{5.5}Zn_{3.25}-A$, respectively. In each structure, the angle subtended at Zn(II), O(3)-Zn(II)-O(3) is 119.9(3)$^{\circ}$ for $Tl_{3.4}Zn_{4.3}-A$, and 120.0(3)$^{\circ}$ for $Tl_{5.5}Zn_{3.25}-A$, respectively, close to the idealized trigonal-planar value. Zn(II) ions prefer to 6-ring sites. $Tl^+$ ions do not have any preference to a particular site but occupy simultaneously both at the 6-ring sites and 8-ring sites.

• Journal of the Korean Ceramic Society
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• v.30 no.1
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• pp.25-33
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• 1993

Formation reaction of Mn-Zn ferrite depending on various synthetic conditions of wet process was investigated using FeCl2.nH2O(n≒4), MnCl2.4H2O, ZnCl2 as starting materials. A stable intermediate precipitate was formed by the addition of H2O2. And the precipitate was hard to transform to spinel phase of Mn-Zn Fe2O4. Single phase of Mn-Zn Fe2O4 spinel was obtained above 8$0^{\circ}C$ reaction temperature. The powder had spherical particle shape and 0.02~0.05${\mu}{\textrm}{m}$ particle size. Fe(OH)2 solid solution, -FeO(OH) solid solution, -FeOOH, Mn-Zn Fe2O4 spinel were formed with air flow rate 180$\ell$/hr. However, single phase of Mn-Zn Fe2O4 spinel with cubic particle shape and 0.1~0.2${\mu}{\textrm}{m}$ particle size was formed with synthetic conditions of 8$0^{\circ}C$ and 90 munutes. The particle shape of the -FeOOH was needle-like.

• Applied Biological Chemistry
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• v.49 no.4
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• pp.281-286
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• 2006

Tolaasin, a pore-forming toxin, is a 1,985 Da peptide produced by Pseudomonas tolaasii and causes a brown blotch disease on cultivated mushrooms. Tolaasin forms pores on the plasma membrane of various cells including fungi, bacteria, plant as well as erythrocytes, and destroys cell structure. $Zn^{+2}$ has been known to block the tolaasin activity by an unknown mechanism. Thus, we investigated the inhibitory effects of $Zn^{+2}$ on the tolaasin-induced hemolysis to understand the molecular mechanism of tolaasin-induced pore formation. $Zn^{+2}$ and $Cd^{+2}$ inhibited the tolaasin-induced hemolysis in a dose-dependent manner and their Ki values were 170 ${\mu}M$ and 20 mM, respectively. The effect of $Zn^{+2}$ was reversible since the subsequent addition of EDTA chelates $Zn^{+2}$ and removes the inhibitory effect of $Zn^{+2}$. When an osmotic protectant, PEG 2000, was added, the tolaasin-induced hemolysis was not observed. After the removal of osmotic protectant by centrifugation, resuspended erythrocytes with fresh medium were immediately hemolyzed, while the addition of $Zn^{+2}$ prevented from hemolysis, implying that tolaasin-induced pores on the membrane were already formed in the medium containing osmotic protectant. These results suggest that $Zn^{+2}$ inhibits the activity of tolaasin pores and it has minor effects on the membrane binding of tolaasin and the formation of pore.

• Applied Chemistry for Engineering
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• v.17 no.3
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• pp.274-279
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• 2006

To synthesize ZnO colloidal solution by a sol-gel process, zinc acetate ($C_{4}H_{6}O_{4}Zn{\cdot}2H_{2}O{\cdot}0.2\;mol$) and lithium hydroxide ($LiOH{\cdot}H_{2}O{\cdot}0.14\;mol$) in the ethanol were added to the solution containing a dispersing agent, hydroxypropyl cellulose (HPC). The nanosize and physical shape of the synthesized ZnO particles were determined by HPC acting as the dispersing agent. Nanosized ZnO particles were also obtained by a precipitation method based on zinc-2-ethylhexagonate. The precipitates were characterized by DLS, XRD, FE-SEM, and UV-vis. As the results, the ZnO colloids tend to self-assemble into a well-ordered hexagonal close-packed structure. The ZnO nanoparticles have an average diameter of nearly 40 nm with a narrow size distribution.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.4
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• pp.79-85
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• 2009

This paper describes the degradation properties of ZnO surge arresters impressed by lightning impulse currents. To investigate the deterioration behaviors of ZnO surge arresters due to lightning surges, the 8/20[${\mu}s$], 2.5[kA] standard lightning impulse currents were injected to the ZnO surge arrester under test. The power frequency AC and DC leakage currents flowing through the ZnO surge arresters with and without the injection of lightning impulse currents were measured. As a result, the leakage currents are increased and the asymmetry of the AC leakage current is pronounced as the number of injection of the impulse current increases. The ZnO grain of the surge arrester without the injection of lightning surges are uniform but the ZnO grain of the ZnO surge arrester with the injection of lightning impulse currents are deformed. Also, it was found that the decrease of the $Bi_2O_3$ due to the lightning impulse current leads to the lack of grain boundary layer and the current concentrated by the lack of grain boundary layer play an important role to degrade nonlinear property of ZnO surge arrester blocks.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.6
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• pp.309-314
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• 2010

Microstructures and grain growth behaviors at elevated temperatures have been investigated for extruded Mg-2%Zn and Mg-2%Zn-0.3%Zr alloys, in order to clarify the role of Zr in grain stability of Mg-Zn alloy. The grain size of Zr-free alloy increased continuously with an increase in annealing temperature, when isochronally annealed for 60 min from 573 to 723K, while the grains of the Zr-containing alloy were relatively stable up to 723 K. The activation energies for grain growth ($E_g$) between 573 and 723 K were calculated as 77.8 and 118.6 kJ/mole for the Mg-2%Zn and Mg-2%Zn-0.3%Zr alloys, respectively, which indicates that grains in the Zr-added alloy possess higher thermal stabilities at elevated temperatures. TEM observations on the annealed Mg-2%Zn and Mg-2%Zn-0.3%Zr alloys revealed that enhanced grain stability resulting from Zr addition into Mg-Zn alloy would be ascribed to the restriction of grain growth by stable Zn-Zr nano-precipitates distributed in the microstructure.