• Bulletin of the Korean Chemical Society
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• v.29 no.9
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• pp.1705-1710
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• 2008

Imidazolium based zwitterions, 1,2-dimethylimidazolium-3-n-propanesulfonate (DMIm-3S) and 1-Butylimidazolium-3-n-butanesulphonate (BIm-4S), were synthesized, and utilized them as additive for Li ion cell comprising of graphite anode and $LiCoO_2$ cathode. The use of 10 wt% of DMIm-3S in 1 M $LiPF_6$, EC-EMCDMC (1:1:1 (v/v)) resulted in the increased high rate charge-discharge performance. The low temperature performance of the Li ion cells at about −20 ${^{\circ}C}$ was also enhanced by these zwitterion additives. The DMIm- 3S additive resulted in the better capacity retention by the Li-ion cells even after 120 cycles with 100% depth of discharge (DOD) at 1 C rate in room temperature. Surface morphology of both graphite and $LiCoO_2$ electrode before and after 300 cycles was studied by scanning electron microscopy. An analogous study was performed using liquid electrolyte without any additive.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.113-118
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• 2019

In this study, we investigated the growth of single-crystallinity α-Ga₂O₃ thin films on c-plane sapphire substrates using halide vapor pressure epitaxy. We also found the optimal growth conditions to suppress the phase transition of α-Ga₂O₃. Our results confirmed that the growth temperature and partial pressure of the reactive gas greatly influenced the crystallinity. The optimal growth temperature range was about 460~510℃, and the α-Ga₂O₃ thin films with the highest crystallinity were obtained at a III/VI ratio of 4. The thickness and surface morphology of the thin films was observed by scanning electron microscopy. The film thickness was 6.938 ㎛, and the full width at half maximum of the ω-2θ scan rocking curve was as small as 178 arcsec. The optical band gap energy obtained was 5.21 eV, and the films were almost completely transparent in the near-ultraviolet and visible regions. The etch pit density was found to be as low as about 6.0 × 10⁴ cm^-2.

• Nuclear Engineering and Technology
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• v.50 no.2
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• pp.246-252
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• 2018

A series of simulated reactivity-initiated accident (RIA) tests on irradiated fully recrystallized boiling water reactor Zircaloy-2 cladding has been performed by means of the expansion-due-to-compression (EDC) test method. The EDC method reproduces fuel pellet-clad mechanical interaction (PCMI) conditions for the cladding during RIA transients with respect to temperature and loading rates by out-of-pile mechanical testing. The tested materials had a large variation in burnup and hydrogen content (up to 907 wppm). The results of the EDC tests showed variation in the PCMI resistance of claddings with similar burnup and hydrogen content, making it difficult to clearly identify ductile-to-brittle transition temperatures. The EDC-tested samples of the present and previous work were investigated by light optical and scanning electron microscopy to study the influence of factors such as azimuthal variation of the Zr-hydrides and the presence of hydride rims and radially oriented hydrides. Two main characteristics were identified in samples with low ductility with respect to hydrogen content and test temperature: hydride rims and radial hydrides at the cladding outer surface. Crack propagation and failure modes were also studied, showing two general modes of crack propagation depending on distribution and amount of radially oriented hydrides. It was concluded that the PCMI resistance of irradiated cladding under normal conditions with homogenously distributed circumferential hydrides is high, with good margin to the RIA failure limits. To further improve safety, focus should be on conditions causing nonfavorable hydride distribution, such as hydride reorientation and formation of hydride blisters at the cladding outer surface.

• Korean Journal of Materials Research
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• v.26 no.2
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• pp.84-89
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• 2016

We present the rectifying and nitrogen monoxide (NO) gas sensing properties of an oxide semiconductor heterostructure composed of n-type zinc oxide (ZnO) and p-type copper oxide thin layers. A CuO thin layer was first formed on an indium-tin-oxide-coated glass substrate by sol-gel spin coating method using copper acetate monohydrate and diethanolamine as precursors; then, to form a p-n oxide heterostructure, a ZnO thin layer was spin-coated on the CuO layer using copper zinc dihydrate and diethanolamine. The crystalline structures and microstructures of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy. The observed current-voltage characteristics of the p-n oxide heterostructure showed a non-linear diode-like rectifying behavior at various temperatures ranging from room temperature to $200^{\circ}C$. When the spin-coated ZnO/CuO heterojunction was exposed to the acceptor gas NO in dry air, a significant increase in the forward diode current of the p-n junction was observed. It was found that the NO gas response of the ZnO/CuO heterostructure exhibited a maximum value at an operating temperature as low as $100^{\circ}C$ and increased gradually with increasing of the NO gas concentration up to 30 ppm. The experimental results indicate that the spin-coated ZnO/CuO heterojunction structure has significant potential applications for gas sensors and other oxide electronics.

• Journal of Electrochemical Science and Technology
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• v.13 no.3
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• pp.390-397
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• 2022

The use of microwaves as the energy source for synthesis and sintering of ceramics offers substantial advantages compared to conventional gas-fired and electric resistance furnaces. Benefits include much shorter processing times and reaching the sintering temperature more quickly, resulting in superior final product quality. Most oxide ceramics poorly interact with microwave irradiation at low temperatures; thus, a more complex setup including a susceptor is needed, which makes the whole process very complicated. This investigation pursued a new approach, which enabled us to use microwave irradiation directly in poorly coupled oxides. In many solid-state electrochemical devices, the support is either metal or can be reduced to metal. Metal powders in the support can act as an internal susceptor and heat the entire cell. Then sufficient interaction of microwave irradiation and ceramic material can occur as the sample temperature increases. This microwave heating and exothermic reaction of oxidation of the support can sinter the ceramic very efficiently without any external susceptor. In this study, yttria stabilized zirconia (YSZ) and a Ni-YSZ cermet support were used as an example. The cermet was used as the support, and a YSZ electrolyte was coated and sintered directly using microwave irradiation without the use of any susceptor. The results were compared to a similar cell prepared using a conventional electric furnace. The leakage test and full cell power measurement results revealed a fully leak-free electrolyte. Scanning electron microscopy and density measurements show that microwave sintered samples have lower open porosity in the electrode support than conventional heat treatment. This technique offers an efficient way to directly use microwave irradiation to sinter thin film ceramics without a susceptor.

• The Plant Pathology Journal
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• v.27 no.4
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• pp.333-341
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• 2011

Two antifungal bacteria were selected from forest soils during the screening of microorganisms antagonistic to Cylindrocarpon destructans, a cause of ginseng root rot. The antifungal bacteria were identified as Bacillus subtilis (I4) and B. amyloliquefaciens (yD16) based on physiological and cultural characteristics, the Biolog program, and 16S rRNA gene sequencing analyses. Antagonistic activity of both bacterial isolates to C. destructans increased with increasing temperature. More rapid starch hydrolytic activity of the bacteria was seen on starch agar at higher temperatures than at lower temperatures, and in the higher density inoculum treatment than in the lower density inoculum treatment. The bacterial isolates failed to colonize ginseng root the root tissues inoculated with the bacteria alone at an inoculum density of $1{\times}10^6$ cfu/ml, but succeeded in colonizing the root tissues co-inoculated with the bacteria and C. destructans. Scanning electron microscopy showed that the pathogen was damaged by the low-density inoculum treatment with the bacterial isolates as much as by the high-density inoculum treatment. Both bacterial isolates were more effective in reducing root rot when they were treated at a concentration of $1{\times}10^6$ cfu/ml than at $1{\times}10^8$ cfu/ml. Also, only the former treatment induced prominent wound periderm formation, related to structural defense against pathogen infection. The results suggest that the bacterial antagonists may have high potential as biocontrol agents against ginseng root rot at relatively low-inoculum concentrations.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.11
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• pp.683-687
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• 2017

We investigated the structure of an ultra-thin insulating board with low thermal conductivity along z-axis, which was based on the idea of void layers created during the glass infiltration process for the zero-shrinkage low-temperature co-fired ceramic (LTCC) technology. An alumina and four glass powders were chosen and prepared as green sheets by the tape casting method. After comparison of the four glass powders, bismuth glass was selected for the experiment. Since there is no notable reactivity between alumina and bismuth glass, alumina was selected as the supporting additive in glass layers. With 2.5 vol% of alumina powder, glass green sheets were prepared and stacked alternately with alumina green sheet to form the 'alumina/glass (including alumina additive)/alumina' structure. The stacked green sheets were sintered into an insulating substrate. Scanning electron microscopy revealed that the additive alumina formed supporting bridges in void layers. The depth and number of the stacking layers were varied to examine the insulating property. The lowest thermal conductivity obtained was 0.23 W/mK with a $500-{\mu}m-thick$ substrate.

• Journal of Powder Materials
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• v.11 no.4
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• pp.308-313
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• 2004

An experimental study on the combustion of superfine aluminum powders (average particle diameter, a$_{s}$: ∼0.1 ${\mu}{\textrm}{m}$) in air is reported. The formation of aluminum nitride during the combustion of aluminum in air and the influence of the combustion scenario on the structures and compositions of the final products are in the focus of this study. The experiments were conducted in an air (pressure: 1 atm). Superfine aluminum powders were produced by the wire electrical explosion method. Such superfine aluminum powder is stable in air but once ignited it can burn in a self-sustaining way due to its low bulk: density (∼0.1 g/㎤) and a low thermal conductivity. During combustion, the temperature and radiation were measured and the actual burning process was recorded by a video camera. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and chemical analysis were performed on the both initial powders and final products. It was found that the powders, ignited by local heating, burned in a two-stage self-propagating regime. The products of the first stage consisted of unreacted aluminum (-70 mass %) and amorphous oxides with traces of AlN. After the second stage the AlN content exceeded 50 mass % and the residual Al content decreased to ∼10 mass %. A qualitative discussion is given on the kinetic limitation for AlN oxidation due to rapid condensation and encapsulation of gaseous AlN.N.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.755-759
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• 2008

New cathode materials $LaNi_{1-x}{Cu_x}{O_3}$ (typically $LaNi_{0.8}Cu_{0.2}O_3$) were synthesized using a co-precipitation method. The structure and morphology of the powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composite material [$Ce_{0.8}Sm_{0.2}O_{2-\ddot{a}}$(SDC) and carbonate (${Na_2}{CO_3},{Li_2}{CO_3}$)], NiO and $LaNi_{1-x}{Cu_x}{O_3}$ were used as the electrolyte, anode and cathode, respectively. The electrochemical performance of La-Ni-Cu-O perovskite oxide at low temperatures ($400{\sim}550^{\circ}C$) was studied. The results showed that $LaNi_{0.8}Cu_{0.2}O_3$ precursor powder prepared through a co-precipitation method and calcined at $860^{\circ}C$ for 2 h formed uniform grains with diameters in the range of $400{\sim}500\;nm$. The maximum power density and the short circuit current density of the single cell unit at $550^{\circ}C$ were found to be $390\;mW/cm^2$ and $968\;mA/cm^2$, respectively.

• Applied Chemistry for Engineering
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• v.20 no.5
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• pp.511-516
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• 2009

Photodegradation characteristics of polyolefin composites were studied. Thermogravimetric analysis results suggest that the polyolefin blends used in this study have different amounts of talc. The mechanical behaviors of polyolefin blends, which experienced UV-irradiation in accordance with SAE J1960, are investigated using tensile and Izod impact tests. These results show that as the UV-exposure time increases, a significant drop in the elongation at break and impact strength at a low temperature are observed. This may be explained by the decreases in elastic energy derived from the scission of polymer molecular chains and the low density of entanglement after UV- photodegradation. Scanning electron microscopy observations indicate that no crack and surface damage are observed, while the additional talc particles are exposed, on the UV-exposed surfaces. The exposure of talc particles may be responsible for the discoloration of UV-exposed polyolefin blend surface. Observation using Fourier transform infrared spectroscopy (FT-IR) confirms the presence of photodegradation on the surface of UV-exposed polyolefin blend.