• 한국재료학회지
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• 제20권2호
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• pp.55-59
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• 2010

$Na^+$ ion conductivity can be improved by the substitution of an Mg atom for an Al atom to form a nonstoichiometric $Na^+$ $\beta$-alumina. We performed a first principles study to investigate the most stable substitution site of an Mg atom and the resulting structural change of the nonstoichiometric $Na^+$ $\beta$-alumina. Al atoms were classified as four different layers in the spinel block that are separated by conduction planes in the nonstoichiometric $Na^+$ $\beta$-alumina. The substitution of an Mg atom for an Al atom at a tetragonal site was more favorable than that at an octahedral site. The substitution in the spinel block was more favorable than that close to the conduction plane. This result was well explained by the volume changes of the polyhedrons, by the standard deviation of the Mg-O distance, and by the comparison with bulk MgO structure. Our result indicates that the most preferable site for the Mg atom was the tetrahedral site at the spinel block in the nonstoichiometric $Na^+$ $\beta$-alumina.

• 한국세라믹학회지
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• 제53권1호
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• pp.43-49
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• 2016

This analyzed a Young's modulus (E), a thermal expansion coefficient (TEC, ${\beta}$) and a thermal conductivity (${\kappa}$) of the material with simple cubic particulate inclusion using two model structures: a parallel structure and a series structure of laminated layers. The derived ${\beta}$ equations were applied to calculate the ${\beta}$ value of the W-MgO system. The accuracy was higher for the series model structure than for the parallel model structure. Young's moduli ($E_c$) of sintered porous alumina compacts were theoretically related to the development of neck growth of grain boundary between sintered two particles and expressed as a function of porosity. The series structure model with cubic pores explained well the increased tendency of $E_c$ with neck growth rather than the parallel structure model. The thermal conductivity of the three phase system of alumina-mullite-pore was calculated by a theoretical equation developed in this research group, and compared with the experimental results. The pores in the sintered composite were treated as one phase. The measured thermal conductivity of the composite with 0.5-25% porosity (open and closed pores) was in accordance with the theoretical prediction based on the parallel structure model.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.157-161
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• 2000

Blue phosphor of Ba-Mg-Al-O:Eu$^{2+}$ phase was fabricated by conventional firing techniques under reducing atmosphere and its photoluminescence properties are studied with varying Eu concentration and phost-annealing temperature under air atmosphere. This phosphors were well crystallized with particle size in the range of 3~5um and emitted a blue light at a dominent wavelength 450nm for 254nm UV irradiation. The concentration quenching wit Eu$^{2+}$ was that with increasing Eu concentration the energy transfer between the activator ions steadily improves, so that the excitation energy is transported over larger distances through the lattice before luminescence can occur. Thermal quenching also occurred in this phosphor means that in a host lattice with the $\beta$-alumina structure the bond of an Eu$^{2+}$ ion with the nearest-neighbour oxygen ion is much stronger than in a lattice with the magnetoplumbite structure.cture.

• Bulletin of the Korean Chemical Society
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• 제32권4호
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• pp.1310-1314
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• 2011

Sodium beta-alumina (SBA) nano-powders were synthesized by the citrate sol-gel process, and the effects of the cationic surfactant n-cetyltrimethylammonium bromide surfactant (CTAB) were investigated. The structure and morphology of the nano-powders were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques, respectively. The effects of CTAB on the citrate sol-gel process and the SBA formation were investigated by thermo gravimetric/differential thermal analysis (TG/DTA) and Fourier transform infrared spectroscopy (FTIR). The conductivity of ceramic pellets of SBA was measured by electrochemical impedance spectroscopy (EIS). The results showed that the CTAB inhibited the agglomeration of SBA powders effectively and consequently decreased the crystallization temperature of SBA, about $150^{\circ}C$ lower than that of the sample without CTAB. The measured conductivity of SBA was $1.21{\times}10^{-2}S{\cdot}cm^{-1}$ at $300^{\circ}C$.

• 센서학회지
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• 제23권3호
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• pp.170-172
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• 2014

$CO_2$ sensor was used only one solid electrolyte in many cases. To improve the sensing characteristics of $CO_2$ sensors, solid electrolyte $CO_2$ sensor has been developed by bi-electrolyte type sensor using Na-Beta-alumina and YSZ. However, in many further studies, bi-electrolyte type sensor was made by pellet pressed by press machine and additional treatment for formation of interface. In the aspect of mass production, using thick film and additional treatment is not suitable. In this study, $CO_2$ sensor was fabricated by bi-electrolyte structure which was made by an NBA paste layer deposited on YSZ pellet and fired at $1650^{\circ}C$ for 2 hour. The formation of stable interface between YSZ and NBA were confirmed by SEM image. When the type IV electrochemical cell arrangement represented by $CO_2,O_2,Pt{\mid}Li_2CO_3-CaCO_3{\parallel}NBA{\parallel}YSZ{\mid}O_2,Pt$ is used to measure the $CO_2$ concentration in air. This sensor EMF should depend only on the concentration of $CO_2$ by logarithmic. Also, sensor shows $P_{CO_2}$ and EMF relationship like nerstian reaction at a temperature of $450^{\circ}C$.

• 대한화학회지
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• 제36권1호
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• pp.147-156
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• 1992

${\alpha}-{\beta}-,{\gamma}$-알루미나 및 MgO를 담체로 사용하여 담지된 납산화물 촉매를 제조하였다. 담지된 납산화물 촉매상에서 메탄의 $C^{2+}$ 탄화수소로의 전환반응은 MgO 담지촉매에서 $C^{2+}$ 선택도가 최대로 얻어졌으며, ${\gamma}$-알루미나 담지 PbO 촉매에서는 $CO_2$ 선택도가 높았다. 그리고 ${\alpha}$-알루미나 담지촉매에서는 중간정도의 활성이 얻어졌으며, ${\beta}$-알루미나 담지촉매에서는 활성이 거의 나타나지 않았다. 이러한 반응특성은 촉매의 격자산소의 활성에 크게 의존하였으며, 또한 격자 산소의 활성은 담체와 산화물간의 상호작용과 담체의 성질에 영향받았다. 특히 MgO 담지 촉매에서는 X-선 회절분석에서 여타의 담체에서보다 PbO 산화물의 (002)면의 피크 세기가 (111)면의 세기에 비해 훨씬 크게 나타난 것으로 볼 때 메탄의 Oxidative Coupling 반응에서의 표면산화물-담체 상호작용(SOSI)의 한 예로 여겨졌다.

• 한국전기전자재료학회논문지
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• 제15권1호
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• pp.67-74
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• 2002

A phosphor for Plasma Display Panel, BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$, showing a blue emission band at about 450nm was prepared by a solid-state reaction using BaCO$_3$, $Al_2$O$_3$, MgO, Eu$_2$O$_3$ as starting materials wish flux AlF$_3$. The study of the behaviour of Eu in BAM phosphor was carried out by the photoluminescence spectra and the Rietveld method with X-ray and neutron powder diffraction data to refine the structural parameters such as lattice constants, the valence state of Eu, the preferential site of Mg atom and the site fraction of each atom. The phenomenon of the concentration quenching was abound 2.25~2.3wt% of Eu due to a decrease in the critical distance for energy transfer of inter-atomic Eu. Through the combined Rietveld refinement, R-factor, R$_{wp}$, was 8.11%, and the occupancy of Eu and Mg was 0.0882 and 0.526 at critical concentration. The critical distance of Eu$^{2+}$ in BAM was 18.8$\AA$ at 2.25% Eu of the concentration quenching. Furthermore, c/a ratio was decreased to 3.0wt% and no more change was observed over that concentration. The maximum entropy electron density was found that the modeling of $\beta$-alumina structure in BaMgAl$_{10}$ O$_{17}$ :Eu$^{2+}$correct coincided showing Ba, Eu, O atoms of z= 1/4 mirror plane.e.ane.e.

• 전기화학회지
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• 제15권3호
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• pp.124-134
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• 2012

최근 화석에너지 위기와 지구환경문제 등으로 신재생 에너지에 대한 관심이 높아지고 있으며, 여기에서 발전되는 전력을 저장할 수 있는 에너지저장장치의 수요가 증가하고 있다. Na/$NiCl_2$ 전지는 에너지효율이 높고, 환경친화적이며, 저가 등 우수한 장점들로 인하여 전력 저장용뿐만 아니라 전기자동차에도 응용 가능하다. 그러나, 본격적인 상용화를 위해서는 재료 및 부품, 셀 설계 및 제조 분야에서 개선이 필요한 부분이 많이 남아 있다. 본 논문에서는 Na/$NiCl_2$ 전지의 구조, 전기화학, 핵심 재료, 셀 설계 및 제작, 응용분야에 대하여 현재까지의 개발 동향에 대하여 서술하고자 한다.

• 한국전기전자재료학회논문지
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• 제16권12호
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• pp.1103-1109
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• 2003

Crystalline carbon nitride films have been deposited by RF reactive magnetron sputtering system with negative DC bias. The carbon nitride films deposited on various substrates showed ${\alpha}$- C$_3$N$_4$,${\beta}$-C$_3$N$_4$ and lonsdaleite structures through XRD and FTIR We can find the grain growth of hexagonal structure from SEMI photographs, which is coincident with the theoretical carbon nitride unit cell. When nitrogen gas ratio is 70 % and RF power is 200 W, the growth rate of carbon nitride film on quartz substrate is about 2.1 $\mu\textrm{m}$/hr.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.956-961
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• 2000

This paper describes the design of a small size Alkali Metal Thermal to Electric Converter (AMTEC) which employs a capillary structure for recirculating sodium working fluid. The cycle is based on the simple and small capillary type ${\beta}"$ -alumina and wick tube element. The proposed cell consists of the 37 conversion elements with capillary tube of $50{\mu}m$ in diameter and the sealed cylindrical vessel of 22mm in outer diameter. Results on the cycle analysis of sodium flow and heat transfer in the cell showed that the expected power output was 4.65W and the conversion efficiency was 19% for the source temperature of 900K.