• 한국전기전자재료학회논문지
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• 제37권1호
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• pp.101-105
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• 2024

4H-SiC power metal-oxide-semiconductor field effect transistors (MOSFETs) have been developed to achieve lower specific-on-resistance (R_on,sp), and the gate oxides have been thermally grown. The poor channel mobility resulting from the high interface trap density (D_it) at the SiO₂/4H-SiC interface significantly affects the higher switching loss of the power device. Therefore, the development of novel fabrication processes to enhance the quality of the SiO₂/4H-SiC interface is required. In this paper, NO post-oxidation annealing (POA) by using the conditions of N₂ diluted NO at a high temperature (1,300℃) is proposed to reduce the high interface trap density resulting from thermal oxidation. The NO POA is carried out in various NO ambient (0, 10, 50, and 100% NO mixed with 100, 90, 50, and 0% of high purity N₂ gas to achieve the optimized condition while maintaining a high temperature (1,300℃). To confirm the optimized condition of the NO POA, measuring capacitance-voltage (C-V) and current-voltage (I-V), and time-of-flight secondary-ion mass spectrometry (ToF-SIMS) are employed. It is confirmed that the POA condition of 50% NO at 1,300℃ facilitates the equilibrium state of both the oxidation and nitridation at the SiO₂/4H-SiC interface, thereby reducing the D_it.

• 한국재료학회지
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• 제27권12호
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• pp.710-715
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• 2017

We synthesized YOF(yttirum oxyfluoride) powders through solid state reactions using $Y_2O_3$ and $YF_3$ as raw materials. The synthesis of crystalline YOF was started at $300^{\circ}C$ and completed at $500^{\circ}C$. The atmosphere during synthesis had a negligible effect on the synthesis of the YOF powder under the investigated temperature range. The particle size distribution of the YOF was nearly identical to that of the mixed $Y_2O_3$ and $YF_3$ powders. When the synthesized YOF powders were used as a raw material for the suspension plasma spray(SPS) coating, the crystalline phases of the coated layer consisted of YOF and $Y_2O_3$, indicating that oxidation or evaporation of YOF powders occurred during the coating process. Based on thermogravimetric analysis, the crystalline formation appeared to be affected by the evaporation of fluoride because of the high vapor pressure of the YOF material.

• 한국분말재료학회지
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• 제12권2호
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• pp.112-116
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• 2005

In the present study, the focus is on the analysis of carbothermal reduction of oxide powder prepared from waste WC/Co hardmetal by solid carbon under a stream of argon for the recycling of the WC/Co hard-metal. The oxide powder was prepared by the combination of the oxidation and crushing processes using the waste $WC-8 wt.\%Co$ hardmetal as the raw material. This oxide powder was mixed with carbon black, and then this mixture was carbothermally reduced under a flowing argon atmosphere. The changes in the phase structure and gases discharge of the mixture during carbothermal reduction was analysed using XRD and gas analyzer. The oxide powder prepared from waste $WC-8wt.\%Co$ hardmetal has a mixture of $WO_{3} and CoWO_{4}$. This oxide powder reduced at about $850^{\circ}C$, formed tungsten carbides at about $950^{\circ}C$, and then fully transformed to a mixed state of tungsten carbide (WC) and cobalt at about $1100^{\circ}C$ by solid carbon under a stream of argon. The WC/Co composite powder synthesized at $1000^{\circ}C$ for 6 hours from oxide powder of waste $WC-8wt.\%Co$ hardmetal has an average particle size of $0.3 {\mu}m$.

• 한국수소및신에너지학회논문집
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• 제24권1호
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• pp.29-35
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• 2013

A dense mixed ionic and electronic conducting ceramic membrane is one of the most promising materials because it can be used for separation of oxygen from the mixture gas. The $ABO_3$ perovskite structure shows high chemical stability at high temperatures under reduction and oxidation atmospheres. $BaCo_{1-x-y}Fe_xZr_yO_{3-{\delta}}$ (BCFZ) was well-known material as high mechanical strength, low thermal conductivity and stability in the high valence state. Glycine Nitrate Process (GNP) is rapid and effective method for powder synthesis using glycine as a fuel and show higher product crystallinity compared to solid state reaction and citrate-EDTA method. BCFZ was fabricated by modified glycine nitrate process. In order to control the burn-up reaction, $NH_4NO_3$ was used as extra nitrate. According to X-Ray Diffraction (XRD) results, BCFZ was single phase regardless of Zr dopants from y=0.1 to 0.3 on B sites. The green compacts were sintered at $1200^{\circ}C$ for 2 hours. Oxygen permeability, methane partial oxidation rate and hydrogen production ability of the membranes were characterized by using Micro Gas Chromatography (Micro GC) under various condition. The high oxygen permeation flux of BCFZ 1-451 was about $1ml{\cdot}cm^{-2}s^{-1}$. Using the humidified Argon gas, BCFZ 1-433 produced hydrogen about $1ml{\cdot}cm^{-2}s^{-1}$.

• 대한화학회지
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• 제49권1호
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• pp.78-82
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• 2005

• 센서학회지
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• 제19권3호
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• pp.176-183
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• 2010

It is considered that the urea injection DeNOx SCR(selective catalytic reduction) system is the only promising method to satisfy the worldwide NOx emission standards. As for the theoretical aspect, reactants of NO and $NO_2$ with $NH_3$ produce $H_2O$, $N_2$ and $O_2$ which do not harm human beings and environmental as well. The realization of maximum NOx conversion (without using a post oxidation catalyst) is only possible with closed loop controlled urea dosing. It means built-in $NH_3$ gas sensor have to be developed for detecting accurate $NH_3$ concentration for the feedback system. Using YSZ(yttria-stabilized zirconia) as a solid state electrolyte and $In_2O_3$ as a sensing material, this paper aims to study dependable $NH_3$ gas sensor for the promising solution of DeNOx technology, which have a reproducible electric output signal, a high sensitivity and fast response.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.260-265
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• 2006

An experimental study on the catalytic reformer adopted in the auxiliary power unit system of solid oxide fuel cell was conducted. A 3-fluid nozzle, by which liquid fuel such as diesel, water and air are sprayed and uniformed mixed, was designed and used in this study. An electrically heated monolith inserted in the reformer was used for the vaporization of fuel and water in the transient state of reformer. The reformer uses the partial oxidizing reaction at the catalyst and the supply of water prevents the flame combustion in the spraying zone and lessens the deactivation of catalyst. The result showed that the reforming of liquid fuel can be started by the electrically heated monolith and the 3-fluid nozzle can give the uniform mixing of fuel, water and air. It was also found that the reformer fueled by n-hexadecane can make the reformate, at best, containing $H_2$ at 15.5% and CO at 11.5% that are used as fuel in the solid oxide fuel cell.

• Journal of Applied Biological Chemistry
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• 제42권4호
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• pp.175-179
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• 1999

Grape seed oil was extracted using different preparatory treatments as follows: (1) grinding, (2) grinding and roasting, (3) grinding and wet- roasting, (4) grinding, roasting, and wet-roasting, and (5) grinding, wet-roasting, and wet-roasting. The highest antioxidant activity was obtained from the sample with the method (2). Initial states of oxidation were similar except method (1) that showed more oxidized state, being P.O.V.8. Acid values were observed in the range from 1.42 to 1.89. The lowest acid value was found as 1.42 in method (1) and those of others were somewhat higher, indicating that heating process of roasting produced some free fatty acids. From the results of sensory evaluation, the best odor and taste were obtained from the methods (2) and (3). Repetitive procedure of wet-roasting, like method 5, caused some loss of flavor components and decrease in the sensory evaluation score. Addition of grape seed oil (method 2) to soybean and perilla oil at the level of 20% retained considerable antioxidant activities as much as 4.3 and 5 times, respectively, than 100% soybean or perilla oil stored for 12 weeks. When soybean or perilla oil was mixed with 20% grape seed oils, P.O.V. decreased to half of that of unmixed oils.

• Journal of Electrochemical Science and Technology
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• 제2권1호
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• pp.1-7
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• 2011

Nanocomposites of reduced graphene oxide and manganese (II,III) oxide can be synthesized by the freeze-drying process of the mixed colloidal suspension of graphene oxide and manganese oxide, and the subsequent heat-treatment. The calcined reduced graphene oxide-manganese (II,III) oxide nanocomposites are X-ray amorphous, suggesting the formation of homogeneous and disordered mixture without any phase separation. The reduction of graphene oxide to reduced graphene oxide upon the heat-treatment is evidenced by Fourier-transformed infrared spectroscopy. Field emission-scanning electronic microscopy and energy dispersive spectrometry clearly demonstrate the formation of porous structure by the house-of-cards type stacking of reduced graphene oxide nanosheets and the homogeneous distribution of manganese ions in the nanocomposites. According to Mn K-edge X-ray absorption spectroscopy, manganese ions in the calcined nanocomposites are stabilized in octahedral symmetry with mixed Mn oxidation state of Mn(II)/Mn(III). The present reduced graphene oxide-manganese oxide nanocomposites show characteristic pseudocapacitance behavior superior to the pristine manganese oxide, suggesting their applicability as electrode material for supercapacitors.

• 한국지하수토양환경학회지:지하수토양환경
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• 제13권1호
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• pp.24-31
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• 2008

혼합균에서 분리 배양한 황환원균에 의해 발생되는 황화수소가 염소계유기오염물질인 트리클로로에틸렌의 환원에 어떠한 영향을 미치는지, 또한 염소계유기오염물질에 대한 환원력이 있다고 알려진 2가철은 황화수소가 존재할 경우 트리클로로에틸렌의 환원과 어떠한 관계에 있는지를 알아보기 위하여 본 실험을 수행하였다. 황환원균에 독성을 나타내지 않는 수준의 트리클로로에틸렌의 농도에서 황화수소 발생 및 트리클로로에틸렌의 분해 실험을 수행한 결과 황산염의 환원으로 발생한 황화수소의 농도는 4.38 mM, 트리클로로에틸렌의 농도는 큰 변화가 없는 것으로 관찰되었으며 이를 통하여 황환원균에 의해 발생되는 황화수소의 농도가 트리클로로에틸렌을 환원시키기에는 부족하다는 것을 알 수 있었다. 그러나 황화수소의 농도가 위 실험에서 발생된 농도보다 100배 정도 높을 경우(438 mM)에는 트리클로로에틸렌에 대한 환원력이 있음을 확인하였다. 대표적인 산화철인 $Fe_2O_3$(3가철)를 첨가하였을 경우, 황환원균의 생장에 따라 황화수소, 2가철 및 트리클로로에틸렌의 농도변화를 관찰하였으며 이를 통하여 황환원균에 의해서 발생된 황화수소가 산화되면서 3가의 산화철을 2가철로 환원시키고 황화수소에 의하여 환원된 2가철이 트리클로로에틸렌을 분해하여 농도를 감소시키는 것을 확인하였다. 위의 실험결과를 바탕으로 낮은 농도의 황화수소는 트리클로로에틸렌의 환원에 영향을 미치지 못하며 다만, 황화수소에 의해 환원된 2가철이 트리클로로에틸렌을 분해시키는 주요한 요인임을 알 수 있었다. 또한 실제 해수중에서 황환원균과 $Fe_2O_3$가 공존할 경우의 트리클로로에틸렌의 제거 효과를 살펴보기 위한 실험을 한 결과 황환원균이 황화수소를 생성하여 트리클로로에틸렌의 제거에 영향을 줄 수 있는 반응들은 황환원균 생장에 필수적인 탄소원의 농도가 확보될 때 가능하다는 결론을 얻을 수 있었다.