• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.696-702
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• 2007

The family of (Sr,Mg)-doped $LaGaO_3$ compounds, which exhibit high ionic conductivity at $600-800^{\circ}C$ over a wide range of oxygen partial pressure, appears to be promising as the electrolyte for intermediate temperature solid oxide fuel cells. Conventional synthesis routes of (Sr,Mg)-doped $LaGaO_3$ compounds based on solid state reaction have some problems such as the formation of impurity phases, long sintering time and Ga loss during high temperature sintering. Phase stability problem especially, the formation of additional phases at the grain boundary is detrimental to the electrical properties of the electrolyte. From this point of view, we focused to synthesize single phase (Sr,Mg)-doped $LaGaO_3$ electrolyte at the stage of powder synthesis and to apply relatively low heat-treatment temperature using novel synthesis route based on combustion method. The synthesized powder and sintered bulk electrolytes were characterized by XRD, TG-DTA, FT-IR and SEM. AC impedance spectroscopy was used to characterize the electrical transport properties of the electrolyte with the consideration of the contribution of the bulk lattice and grain boundary to the total conductivity. Finally, relationship between synthesis condition and electrical properties of the (Sr, Mg)-doped $LaGaO_3$ electrolytes was discussed with the consideration of phase analysis results.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.6
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• pp.553-561
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• 2012

Existing energy sources convert chemical energy into mechanical energy, while fuel cell directly generates electricity through an electrochemical reaction between hydrogen and oxygen. Therefore, it has a lot of strong points such as high efficiency, zero emission, and etc. In addition, with the development of hydrogen preservation technique, some companies have been researching and releasing portable fuel cell power packs for specific applications like military equipment, automobile, and so on. However, there are some drawbacks to the fuel cell, high cost and slow dynamic response. In order to compensate these weak points, auxiliary energy storages could be applied to the fuel cell system. In this paper, the optimum structure for a 150W portable fuel cell power pack with a battery pack is selected considering the specification of the system, and the design process of main parts is described in detail. Here, main objectives are compact size, simple control, high efficiency, and low cost. Then, an automatic mode change algorithm, which converts the operating mode depending on the states of fuel cell stack, battery pack, and load, is introduced. Finally, performance of the designed prototype using the automatic mode change control is verified through experiments.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.1
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• pp.41-55
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• 2018

General polymer electrolyte fuel cell (PEMFC) operates at less than $80^{\circ}C$. Therefore liquid phase water resulting from electrochemical reaction accumulates and floods the cell which in turn increases the mass transfer loss. To prevent the flooding, it is common to employ serpentine flow channel, which can efficiently export liquid phase water to the outlet. The major drawback of utilizing serpentine flow channel is the large pressure drop that happens between the inlet and outlet. On the other hand, in the high temperature polymer electrolyte fuel cell (HT-PEMFC), since the operating temperature is 130 to $180^{\circ}C$, the generated water is in the state of gas, so the flooding phenomenon is not taken into consideration. In HT-PEMFCs parallel flow channel with lower pressure drop between the inlet and outlet is employed therefore, in order to circulate hydrogen and air in the cell less pumping power is required. In this study we analyzed HT-PEMFC's different flow channels by parallel computation using previously developed 3-D isothermal model. All the flow channels had an active area of $25cm^2$. Also, we numerically compared the performance of HT-PEMFC parallel flow channel with different manifold area and Rib interval against the original serpentine flow channel. Results of the analysis are shown in the form of three-dimensional contour polarization curves, flow characteristics in the channel, current density distribution in the Membrane, overpotential distribution in the catalyst layer, and hydrogen and oxygen concentration distribution. As a result, the performance of a real area fuel cell was predicted.

• Composites Research
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• v.32 no.6
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• pp.342-348
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• 2019

Development of flame retarding polymer based materials has been studied actively due to the increase in use of polymers. The post treatment of manufactured fibers or the introduction of flame retardant into fibers is representative method for the way to improve the flame retardancy. Among the polymers, polyacrylonitrile (PAN), which is a precursor of carbon fiber, has been widely used for clothes. Due to low flame retardancy of PAN fiber (LOI value: 17~18%), the improvement of flame retardancy of PAN fiber is needed. In this review paper, we report preparation methods for the fabrication of post-treated (oxidization or chemical reaction) flame-retarding PAN fibers and composites composed of PAN and organic/inorganic materials (SiO₂, 2D materials or CNT).

• Composites Research
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• v.32 no.6
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• pp.368-374
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• 2019

Basalt fiber reinforced epoxy composites with inorganic filler (BFRP-F) such as Mg(OH)₂ (magnesium hydroxide), Al(OH)₃ (aluminum hydroxide), Al₂O₃ (aluminum oxide) and AlOOH (boehmite) were prepared by hand lay-up and hot pressing. The combustive properties of BFRP-F were improved comparing with basalt fiber reinforced epoxy composite (BFRP) without inorganic filler. At a 30 wt% resin content, the limited oxygen index (LOI) of BFRP is 28.9, which is higher than that of epoxy (21.4), and the LOI of BFRP-F is higher than that of BFRP. The BFRP-F showed the lower peak heat release rate (PHRR), total heat release (THR) and total smoke release rate (TSR) than those of BFRP. We confirmed that the flame retardant properties of the composite were improved by the addition of inorganic filler through the dehydration reaction and oxide film formation.

• Toxicological Research
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• v.11 no.2
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• pp.247-252
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• 1995

To evaluate the effect of xanthine oxidase on liver injury by $CCl_4$, liver damage was induced both in allopurinol pretreated rats (500 mg/kg. ip) and control group by twice intraperitoneal injection of $CCl_4$ (0.1 ml/100 g body wt. 50% in olive oil) at interval of one day. Increases in the levels of serum alanine aminotransferase and liver weight/body weight (%) by $CCl_4$ were significantly smaller inallopurinol pretreated rats than in control whereas the hepatic microsomal glucose-6-pholphatase activities were significantly higher in allopurinol pretreated rats than control group by $CCl_4$ treatment. These results indicates that allopurinol pretreatment may reduce the liver damage in $CCl_4$ intoxicated rats. In rats either with $CCl_4$or not, hepatic type O xanthine oxidase activities were significantly reduced by allopurinol pretreatment and the increasing rate of these enzymes to each control was remarkably lower in allopurinol pretreated rats than control. Liver cytosolic protein contents and aniline hydroxylase, aminopyrine demethylase activities were higher in allopurinol pretreated rats than coirol rats when animals were treated with $CCl_4$. On the other hand, neither allopurinol pretreated nor $CCl_4$ treatment caused any significant changes in hepatic superoxide dismutase and catalase activities. Hepatic glutathione contents were higher in $CCl_4$-treated rats than control, but no significant changes were found in both between the allopurinol treated rats and $CCl_4$-treated rats pretreated with allopurinol, and glutathione and glutathione S-transferase activities were significantly reduced in $CCl_4$-treated rats than control whereas these enzyme activities showed on significant change in both between allopurinel treated and $CCl_4$-treated rats pretreated with allopurinol. It is concluded that xanthine oxidase reaction system augment $CCl_4$ induced liver injury via even oxygen free radical system.

• Toxicological Research
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• v.26 no.4
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• pp.321-327
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• 2010

The ability of 80% ethanol extracts from five medicinal plants, Aralia continentalis, Paeonia suffruticosa, Magnolia denudata, Anemarrhena asphodeloides, and Schizonepeta tenuifolia, to neutralize hydroxyl radical, peroxyl radical and peroxynitrite was examined using the total oxyradical scavenging capacity (TOSC) assay. Peroxyl radical was generated from thermal homolysis of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (ABAP); hydroxyl radical by an iron-ascorbate Fenton reaction; peroxynitrite by spontaneous decomposition of 3-morpholinosydnonimine N-ethylcarbamide (SIN-1). The oxidants generated react with $\alpha$-keto-$\gamma$-methiolbutyric acid (KMBA) to yield ethylene, and the TOSC of the substances tested is quantified from their ability to inhibit ethylene formation. Extracts from P. suffruticosa, M. denudata, and S. tenuifolia were determined to be potent peroxyl radical scavenging agents with a specific TOSC (sTOSC) being at least six-fold greater than that of glutathione (GSH). These three plants also showed sTOSCs toward peroxynitrite markedly greater than sTOSC of GSH, however, only P. suffruticosa revealed a significant hydroxyl radical scavenging capacity. Seven major active constituents isolated from P. suffruticosa, quercetin, (+)-catechin, methyl gallate, gallic acid, benzoic acid, benzoyl paeoniflorin and paeoniflorin, were determined for their antioxidant potential toward peroxynitrite, peroxyl and hydroxyl radicals. Quercetin, (+)-catechin, methyl gallate, and gallic acid exhibited sTOSCs 40~85 times greater than sTOSC of GSH. These four components also showed a peroxynitrite scavenging capacity higher than at least 10-fold of GSH. For antioxidant activity against hydroxyl radical, methyl gallate was greatest followed by gallic acid and quercetin. Further studies need to be conducted to substantiate the significance of scavenging a specific oxidant in the prevention of cellular injury and disease states caused by the reactive free radical species.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2003.11a
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• pp.65-65
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• 2003

The aim of this study was to investigate the effect of resveratrol on the oxidative stress-induced inhibition of gap junctional intercellular communication (GJIC) in HaCaT keratinocyte. Anti-oxidative activity of resveratrol was measured by a,a-diphenyl-b-picrylhydrazyl (DPPH) assay and dichlorodihydrofluorescein diacetate oxidation assay. GJIC of HaCaT keratinocyte was assessed using the scrape loading/dye transfer technique. Western blots and reverse transcription-polymerase chain reaction were also analyzed for Connexin 43 protein and mRNA expression, respectively. Resveratrol scavenged directly the stable DPPH radical over a concentration range of 4 mg/$\mell$ (78.2 $\pm$ 2.7% of control) to 500 mg/$\mell$ (29.9 $\pm$ 4.2% of control) and prevent to increase the intracellular fluorescence induced by oxidative stress significantly. Ultraviolet A irradiation (UVA) and 12-O-tetradecanoylphorbol-13-acetate markedly reduced GJIC, which was restored by resveratrol. There were no significant differences in the level of Connexin 43 protein and mRNA expression among any of the experimental groups. Our data suggests that resveratrol has the protective effect on the oxidative stress-induced inhibition of gap junctional intercellular communication in HaCaT keratinocyte and this protection is likely due to the scavenging of reactive oxygen species.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.7
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• pp.721-727
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• 2010

The spontaneous ignition of coal stockpile causes serious safety and economic problems. Such spontaneous ignition occurs in coal stockpile when the rate of heat released by the oxidation of coal is greater than the rate of heat lost to the surroundings. In this study, a two-dimensional unsteady model is adopted for studying spontaneous ignition and the numerical results are compared with experimental results. The numerical results are in a good agreement with the experimental ones. Depending on the porosity, the internal maximum temperature, pressure, and oxygen mass fraction during spontaneous ignition are investigated. On the basis of the numerical results, the transient temperature variations for several shapes of coal stockpiles are analyzed. Further, the physical mechanisms of hot-spot formation and spontaneous ignition are analyzed.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.382-388
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• 1997

Reforming of propane by carbon dioxide using NiO/${\gamma}$-$A1_2O_3$ was carried out in a pulse or continuous kid bed reactor. NiO/${\gamma}$-$Al_2O_3$ showed higher dissociation ability of $CO_2$ than NiO/${\gamma}$-$Al_2O_3$, and the former exhibited higher conversion of propane than the latter. The presence of oxygen in the reaction mixture of propane and $CO_2$ increased the conversion of propane and reduced the amount of carbon deposit on the catalyst surface. Mechanical mixture catalyst of NiO/${\gamma}$-$Al_2O_3$ and $Ga_2O_3$ showed higher stability to deactivation than NiO/${\gamma}$-$Al_2O_3$ itself. The synergistic effect between NiO/${\gamma}$-$Al_2O_3$ and $Al_2O_3$ was also observed in this study.