• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.6
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• pp.400-406
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• 2000

The fired Precursor (Y,Gd,Eu)(OH)$CO_3$.$H_2O$$900^{\circ}C$ was used to synthesize the red phosphor $(Y,Gd)_2O_3$: Eu for plasma display panel. Rounded and ~l $\mu\textrm{m}$ diameter phosphor $(Y,Gd)_2O_3$: Eu can be obtained by the reaction of aformentioned powder with a small amount addition of flux at $1350^{\circ}C$ for 2 hours. Emission spectra of these phosphors were measured under excitation wavelength at 254 nm and 147 nm and the optimum concentrations of activator ion were determined at around 15 mo1e % and 10 mole % under these conditions, respectively. $BaCO_3$flux had the best property in emission intensity among the prepared $BaCO_3AlF_3$and $Li_3PO_4$phosphors. The properties of optimized sample were improved in terms of relative luminance and color coordinate comparing with commercial phosphor such as $Y_2O_3$: Eu.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2009.06a
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• pp.435-438
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• 2009

A navigation aid buoy is a kind of safety facility for maritime navigation with a purpose of leading the vessels for navigating, docking and sail off. An advanced rechargeable battery is required for stable power supply for navigation aid buoy as the high magnitude LED lamps, real time location/control for navigation aids and e-Navigation support systems with maritime climate observation equipments have recently been deployed. This study is focused on the lithium battery, especially lithium polymer battery which is believed to be safer than the other types of batteries. The lithium polymer battery reviewed in this study is designed with $LiFePO_4$-based cathode, which has superior safety features to the oxide-based cathodes. Besides, a 3.6kWh battery pack has been built with the above-mentioned unit cells for the purpose of comparative research with lead acid battery system.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4205-4209
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• 2011

The $Li_2Mn_{0.5}Fe_{0.5}SiO_4$ silicate was prepared by blending of $Li_2MnSiO_4$ and $Li_2FeSiO_4$ precursors with same molar ratio. The one of the silicates of $Li_2FeSiO_4$ is known as high capacitive up to ~330 mAh/g due to 2 mole electron exchange, and the other of $Li_2FeSiO_4$ has identical structure with $Li_2MnSiO_4$ and shows stable cycle with less capacity of ~170 mAh/g. The major drawback of silicate family is low electronic conductivity (3 orders of magnitude lower than $LiFePO_4$). To overcome this disadvantage, carbon composite of the silicate compound was prepared by sucrose mixing with silicate precursors and heat-treated in reducing atmosphere. The crystal structure and physical morphology of $Li_2Mn_{0.5}Fe_{0.5}SiO_4$ was investigated by X-ray diffraction, scanning electron microscopy, and high resolution transmission electron microscopy. The $Li_2Mn_{0.5}Fe_{0.5}SiO_4$/C nanocomposite has a maximum discharge capacity of 200 mAh/g, and 63% of its discharge capacity is retained after the tenth cycles. We have realized that more than 1 mole of electrons are exchanged in $Li_2Mn_{0.5}Fe_{0.5}SiO_4$. We have observed that $Li_2Mn_{0.5}Fe_{0.5}SiO_4$ is unstable structure upon first delithiation with structural collapse. High temperature cell performance result shows high capacity of discharge capacity (244 mAh/g) but it had poor capacity retention (50%) due to the accelerated structural degradation and related reaction.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.1055-1059
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• 2001

Porous glass ceramics composed of Li$_2$O.-Ti $O_2$-P$_2$ $O_{5}$ -CaO were prepared by melting and 2 step heat treatment for nucleation at 61$0^{\circ}C$ and crystallization at 78$0^{\circ}C$. subsequently $\beta$-Ca$_3$(P $O_4$)$_2$crystal phase was selectively leached out in 1N-HC1 solution for 3 days, leaving Li $Ti_2$(P $O_4$)$_3$crystal phases. prepared porous glass ceramics were immersed in 1M AgN $O_3$solution for ion exchange. Staphylococcus aureus and salmonella typhi were used in this study. It was found taht the resultant porous glas ceramics show excellent bacteriostatic properties.

• Earthquakes and Structures
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• v.22 no.1
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• pp.15-23
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• 2022

One of the key tools in assessing the seismic vulnerability of the structures is the use of fragile functions, which is the possibility of damage from a particular damage surface for several levels of risk from the seismic movements of the earth. The aim of this study is to investigate the effect of two categories of earthquake events on the fragile curve (FRC) of the steel construction system. In this study, the relative lateral displacement of the structures is considered as a damage criterion. The limits set for modifying the relative lateral position in the HAZUS instruction are used to determine the failure modes, which include: slight, moderate, extensive and complete. The results show, as time strong-motion increases, the probability of exceeding (PoE) increases (for Peak ground acceleration (PGA) less than 0.5). The increase in seismic demand increases the probability of exceeding. In other words, it increases the probability of exceeding, if the maximum earthquake acceleration increases. Also, 7-storey model in extensive mode has 20 and 26.5% PoE larger than 5- and 3-storey models, respectively.

• Journal of the Korean Electrochemical Society
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• v.15 no.4
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• pp.207-215
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• 2012

Soft carbons are prepared by heat-treatment of cokes with different amounts of phosphoric acid (2, 4.5, and 10 wt% vs. cokes) at $900^{\circ}C$ to be used as anode materials for lithium ion batteries. From electrochemical measurements combined with structural analyses, we confirm that abundant nano-pores are existed in the microstructure of soft carbons prepared with the phosphoric acid, which are responsible for further lithium ion storage. Significant increase in reversible capacity of soft carbon is attained in proportion to added amount of the phosphoric acid. We also demonstrate the effect of structural modification with phosphoric acid on electrochemical performance of soft carbon to elucidate the origin of additional capacity.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.219-222
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• 1996

수열법은 밀폐용기중에서 10$0^{\circ}C$이상의 가열, 가압된 수용액이 반응에 관여하는 것으로써, 수정, CaCO3, AlPO4, GaPO4 등과 같은 단결정의 육성 뿐만 아니라 균일분산계로부터 균일한 결정성의 미립자 합성에도 폭넓게 이용되고 있다. 세라믹분말의 합성에 있어서, 이 방법은 특히 형상, 입자크기의 제어가 용이할 뿐만 아니라 고상법, 졸-겔법, 공침법에서와 같은 열처리, 분쇄과정이 필요없기 때문에 고순도의 초미립자를 얻을 수 있는 장점이 있다. 근년 미국, 일본에서는 수열법을 이용한 유전, 압전체 등 세라믹분말의 일부가 공업적인 규모로 대량 생산되고 있다. 그러나 이에 대한 국내 기술은 아직 초기단계에 이르고 있는 실정이다. 따라서 본 연구실에서는 수열법에 의한 단결정 육성 (예; 자수정, CaCO3, AlPO4, GaPO4, KTP, Emerald 등), 박막제조 (예; GaP, PbTiO3, BaTiO3 등), 정제 (고령토, 장석, 도석 등), 원석처리 (진주, 인공 emerald, 비취 등) 그리고 각종 세라믹분말의 합성 등과 같은 다양한 기반기술의 축적과 동시에 공업화에 대응한 수열장치를 위하여 반응용기의 대형화, 엄밀한 밀폐방식, 실용적인 수열조건 등을 개발해 오고 있다. 본 발표에서는 현재까지의 연구개발 내용 중에서 결정성 미립자에 관련한 세라믹분말의 합성에 대한 일부의 결과들을 보고한다. 일반적으로 수열장치는 전기로, 반응용기, 온도 및 압력제어계 등을 기본으로 하고 있으며 시판용의 대부분이 교반기가 부착된 수직형 (vertical type)이다. 이와 같은 방식에 있어서는 엄밀한 밀폐가 곤란, 반응온도의 한계성 (25$0^{\circ}C$ 이하), 증진율의 한계성 (소량생산) 등과 같은 점이 있기 때문에 본 연구실에서는 개폐식 전기로내에 엄밀한 밀폐가 가능한 수평식(horizontal type)의 반응용기를 채택한 뒤 이를 회전 또는 시이소(seesaw)식으로 움직일 수 있도록 하여 연속공정화, 온도구배의 자율조절 그리고 보다 저온에서도 인위적인 이온의 확산을 효율적으로 유도할 수 있도록 하였다. 이와 같은 방식은 기존의 방식과 비교하여 반응용기 내에 응집현상과 미반응물이 존재하지 않으며 또한 단분산으로 결정성 미립자를 대량적으로 얻을 수 있는 장점이 있었다. 다음은 이상과 같이 본 연구실에서 자체 개발한 수열장치를 이용하여 PbTiO3, (Pb,La)TiO3Mn, BaTiO3, ZnSiO4:Mn, CaWO4 등과 같은 세라믹분말에 대한 합성 실험의 결과이다. 압전성, 초전성이 우수한 PbTiO3 및 (Pb,La)TiO3:Mn 분말의 수열합성은 PbO, TiO2, La2O3 등의 분말을 출발원료로 하여 합성도도 25$0^{\circ}C$부근의 알카리성 용액중에서 결정성 PbTiO3 및 (Pb,La)TiO3:Mn 미립자를 단상으로 얻었으며 입자의 형상 및 크기는 합성온도와 수열용매의 종류에 의존하였다. 유전체로서 폭넓게 응용되고 있는 BaTiO3 분말은 Ba(OH)2.8H2O, TiO2와 같은 최적의 출발원료를 선택함으로써 15$0^{\circ}C$ 부근의 저온영역에서도 용이하게 합성할 수 있었다. 특히 본 연구에서는 수용성인 Ba(OH)2.8H2O를 사용함으로써 host-guest적인 반응을 유도시키는데 있어 물의 가장 실용적이고 효과적인 수열용매임도 알았다. ZnSiO4:Mn, CaWO4, MgWO4와 같은 형광체 분말은 공업적으로 고상반응 또는 습식법에 의해 얻어지고 있으나 이들 방법에 있어서는 분쇄공정으로 인한 형광특성의 저하와 같은 문제점이 있다. 따라서 본 연구에서는 수열법을 이용하여 이들 화합물의 합성을 시도하였으며 그 결과 합성온도 30$0^{\circ}C$ 부근의 알칼리성 용액중에서 수열적으로 얻어짐을 알았다. 여기서의 합성분말을 이용하여 실제 조명램프로 제조한 결과 녹색, 청색 발광용 형광체로서 우수한 형광특성을 나타내었다. 천연에서 소량 산출되고 있는 고가의 (Li,Al)MnO2(OH)2:Co 분말은 도자기의 전사지용 청색안료로써 이용되고 있다. 본 연구실에서는 LiOH.H2O, Al(OH)3, MnO2 등의 분말을 출발원료로 하고 24$0^{\circ}C$ 온도 부근 그리고 물을 수열용매로 하여 천연산에 필적하는 (Li,Al)MnO2(OH)2:Co 분말을 인공적으로 합성하였다.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.145-145
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• 1997

Recent progress of electric technology requires new piezoelectric crystals having superior properties such as zero temperature coefficients and large electromechanical coupling factors. We have developed a series of new leading chandidates, La$_3$Ga5SiO14(langasite, LGS), La3Nb0.5Ga5.5O14(LNG), La3Ta0.5O14(LTG), to satisfy those requirements. High quality LGS, LNG and LTG single crystals, with dimensions of 2 inches in diameter, were successfully grown by the Czochralski method at a pulling rate of 1mm/h. Since no variation of chemical composition was observed when whole melt in a crucible was crystallized, congruency of these compositions was confirmed. Physical constants such as elastic constants, dielectric constants and piezoelectric constants were measured. Filters and oscillators made of grown LGS, LNG and LTG single crystals showed superior properties such as three times wider passband than that of quartz, low insertion loss and easy processing, Langasite family crystals were shown to be superior materials to other known materials such as quartz, LiTaO$_3$, $\alpha$-AlPO$_4$ and Li$_2$B$_4$O7.

• Journal of Environmental Health Sciences
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• v.22 no.2
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• pp.10-18
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• 1996

Experiments were carried out to find the possibility of an economic production of single cell protein(SCP) in mixed culture by Cellulomonas sp. KL-6 and a second organism. The second organism, strain LI-10, was isolated from the large intestines of a mouse. 1. When these strains were mixed, cell growth and carboxymethyl cellulase (CMCase) activity were increased to about 63% and 161%, respectively compared with that of single culture of strain KL-6. We found the mixed culture as a proper method of degradation of cellulose in our study. 2. Strain LI-10 was identified as E. coli. 3. This strain produced trace amounts of cellobiose, but glucose was not found in detectable amounts in the filter paper(FP) medium. 4. $CaCO_3$ injected in the medium at the ratio of 0.1% not only enhanced cell growth but also was effective as an acid neutralizing agent. 5. When this organism was cultured under the optimal medium (glucose 0.1%, $NH_4Cl$ 0.1%, yeast extract 2.0%, $KH_2PO_4$ 0.1%, KCl 0.05%, pH 7.2 and a temperature 30$\circ$C) for 5 days, a cell mass produced 1.18 g/l. The results showed the increase of cell mass up to 300% compared to 0.28 g/l produced in CMC medium.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12B
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• pp.809-814
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• 2007

In this paper, we proposed new method of a bidirectional WDM-PON transmission using suppressed optical carreir(SOC) and reflective semi-conductor optical amplifier(RSOA) based on WDM-PON. while LiNbO3 mach zehnder modulator(LN-MZM) generates 5GHz modulated SOC for uplink at central office(CO), RSOA at CO modulates the downstream data. At optical network units(ONUs), Another RSOA modulates the SOC light source for uplink at ONU and uplink data are up-converted to the 5 GHz already modulated SOC using LN-MZM.