고체산화물 연료전지의 공기극으로서 La_1-xSr_xMnO₃ 계의 합성 및 특성

이유기,이영기,Lee, You-Kee,Lee, Young-Ki 한국재료학회 2012 한국재료학회지 Vol.22 No.9

$La_{1-x}Sr_xMnO_3$(LSM,$0{\leq}x{\leq}0.5$) powders as the air electrode for solid oxide fuel cell were synthesized by a glycine-nitrate combustion process. The powders were then examined by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The as-formed powders were composed of very fine ash particles linked together in chains. X-ray maps of the LSM powders milled for 1.5 h showed that the metallic elements are homogeneously distributed inside each grain and in the different grains. The powder XRD patterns of the LSM with x < 0.3 showed a rhombohedral phase; the phase changes to the cubic phase at higher compositions($x{\geq}0.3$) calcined in air at $1200^{\circ}C$ for 4 h. Also, the SEM micrographs showed that the average grain size decreases as Sr content increases. Composite air electrodes made of 50/50 vol% of the resulting LSM powders and yttria stabilized zirconia(YSZ) powders were prepared by colloidal deposition technique. The electrodes were studied by ac impedance spectroscopy in order to improve the performance of a solid oxide fuel cell(SOFC). Reproducible impedance spectra were confirmed using the improved cell, which consisted of LSM-YSZ/YSZ. The composite electrode of LSM and YSZ was found to yield a lower cathodic resistivity than that of the non-composite one. Also, the addition of YSZ to the $La_{1-x}Sr_xMnO_3$ ($0.1{\leq}x{\leq}0.2$) electrode led to a pronounced, large decrease in the cathodic resistivity of the LSM-YSZ composite electrodes.

Structural and Optical Properties of RF Magnetron Sputtered Yttria - Stabilized Zirconia Thin Films

이유기(You-Kee Lee),박종완(Jong-Wan Park) 한국진공학회(ASCT) 1996 Applied Science and Convergence Technology Vol.5 No.2

고주파 마그네트론 스퍼터링법에 의해 제조된 3 mol%와 8 mol% YSZ 박막의 스퍼터링 가스 내의 산소농도, 기판온도 및 Ar 압력에 따른 조직 및 광학적 특성을 조사하였다. 제조된 박막과 타게트의 결정구조는 서로 상이하게 나타났다. 3 mol% YSZ 박막의 경우 스퍼터링 가스 내의 산소농도가 증가함에 따라 grain-like particle의 크기가 감소하였지만 8mol% YSZ 박막의 경우는 증가하는 경향을 보여주었으며, 8 mol% YSZ 박막의 투과율은 3 mol% YSZ 박막의 두께보다 더 두꺼운 두께에도 불구하고 더 높았다. 3 mol% YSZ 박막의 굴절률은 스퍼터링 가스 내의 산소농도가 증가함에 따라 증가하였지만 8 mol% YSZ 박막의 경우는 감소하는 경향을 보여주었다 또한 8 mol% YSZ 박막의 투과율은 기판온도 및 Ar 압력에 크게 영향을 받지 않았지만 굴절률은 큰 영향을 받았다. The effects of the O₂ concentration in the sputtering gas mixture, substrate temperature and Ar pressure on the structural and optical properties of 3 mol% YSZ and 8 mol% YSZ thin films deposited by RF magnetron sputtering were investigated. The films were observed to have various crystal structures with different compositions in accordance with the type of the target materials. The size of fine grain-like particles decreased with increasing the O₂ concentration in the sputtering gas in the case of 3 mol% YSZ, while it increased in the case of 8 mol% YSZ. However, the average optical transmission of 8 mol% YSZ, despite of thicker thickness, was higher than that of 3 mol% YSZ. Furthermore, the values of refractive index of 3 mol% YSZ increased with increasing the O₂ concentration in the sputtering gas on the contrary to those of the 8 mol% YSZ. However, the transmission spectra of 8 mol% YSZ films were not strongly influenced by the substrate temperature and Ar pressure, whereas the refractive index of the YSZ films were strongly affected by the sputtering parameters.

Co73Cr27 씨앗층이 CoCr 박막의 결정배향성 및 미세구조에 미치는 영향

이유기(You-Kee Lee),이택동(Taek-Dong Lee),이계완(Kye-Wan Lee) 한국진공학회(ASCT) 1994 Applied Science and Convergence Technology Vol.3 No.1

CoCr 박막에 있어서 C축 결정배향성과 미세구조 변화에 대한 Co_(73)Cr_(27) 씨앗층의 영향이 조사되었다. 기록밀도가 높고 재생전압도 높은 CoCr 수직기록매체를 개발하기 위해서는 CoCr층의 두께가 엷으면서 결정배향성이 우수하고 결정립 크기가 적고 균일한 자성기록막 제조가 필요하다. CoCr 단층막 또는 CoCr/퍼말로이 이중막 제조에서 500Å 정도의 Co_(73)Cr_(27)층을 씨앗층으로 만들어 줌으로써 기록층인 CoCr 박막이 0.2 ㎛의 두께에서도 천이층이 거의 없고 결정배향성이 우수한 자성막을 제조할 수 있었다. 또한 Co_(73)Cr_(27) 씨앗층은 비록 결정립 크기는 증가시켰지만 기록층의 에피택시 성장에 보다 바람직한 것으로 조사되었다. The effects of Co_(73)Cr_(27) seed layer on crystallographic C-axis alignment and microsturctural changes in CoCr films were studied. To develop the CoCr perpendicular media of high density recording capabiblity with highly reproducing voltage, it is necessary to study how to make highly aligned, and uniform and fine grained CoCr films from the early stage of film growth. Co_(73)Cr_(27) seed layer with the thickness of 500Å served as an excellent seed layer for CoCr single layer and CoCr/permalloy double layer. This seed layer effectively suppressed the formation of the transition layer and significantly improved C-axis alignment of the CoCr recording layer with the thickness of 0.2 ㎛. Furthermore, Co_(73)Cr_(27) seed layer is also found to be favorable for epitaxial growth of recording layer, although it increases the column size.

SrAl₂O₄:Eu⁺², Dy⁺³ 장잔광 형광체 합성에 있어서 알루미늄 화합물에 따른 열적거동 및 발광특성 변화

이영기,이유기,Lee, Young-Ki,Lee, You-Kee 한국재료학회 2007 한국재료학회지 Vol.17 No.11

Both photoluminescence and thermal characteristics for $SrAl_2O_4:Eu^{+2},\;Dy^{+3}$ phosphors synthesized with various aluminum compounds (${\alpha}-Al_2O_3$, ${\gamma}-Al_2O_3$, amorphous-$Al_2O_3$ and $Al(OH)_3)$ were investigated in this study. The formation temperature of the host $SrAl_2O_4$ crystal is changed by these various aluminum compounds, as a result of the different thermal decomposition temperature of $SrCO_3$ phase. Among these compounds, the amorphous-$Al_2O_3$ phase shows the lowest formation temperature of the host $SrAl_2O_4$ crystal. The PL emission and excitation spectra of $SrAl_2O_4:Eu^{+2},\;Dy^{+3}$ phosphor are not affected by these aluminum compounds. After the removal of the Xenon lamp excitation (360 nm), however, the excellent longphosphorescent property of the phosphor is obtained by the amorphous-$Al_2O_3$ phase, although the decay time for all phosphors decrease exponentially.

기수지역 선박평형수의 염소 생성 효율에 미치는 전기화학 처리의 영향

최용선,이유기,Choi, Yong-Sun,Lee, You-Kee 한국재료학회 2019 한국재료학회지 Vol.29 No.1

Indirect oxidation using chlorine species oxidizing agents is often effective in wastewater treatment using an electrochemical oxidation process. When chlorine ions are contained in the wastewater, oxidizing agents of various chlorine species are produced during electrolysis. In a ballast water management system, it is also used to treat ballast water by electrolyzing seawater to produce a chlorine species oxidizer. However, ballast water in the brackish zone and some wastewater has a low chlorine ion concentration. Therefore, it is necessary to study the chlorine generation current efficiency at various chlorine concentration conditions. In this study, the chlorine generating current efficiency of a boron-doped diamond(BDD) electrode and insoluble electrodes are compared with various chloride ion concentrations. The results of this study show that the current efficiency of the BDD electrode is better than that of the insoluble electrodes. The chlorine generation current efficiency is better in the order of BDD, MMO(mixed metal oxide), $Ti/RuO_2$, and $Ti/IrO_2$ electrodes. In particular, when the concentration of sodium chloride is 10 g/L or less, the current efficiency of the BDD electrode is excellent.

Al-Ti 혼합 분말 슬러리를 이용한 강의 알루미나이징처리 방법

이영기,김정열,이유기,Lee, Young-Ki,Kim, Jung-Yeul,Lee, You-Kee 한국재료학회 2009 한국재료학회지 Vol.19 No.4

In this study, we attempted to develop a convenient aluminizing process, using Al-Ti mixed slurry as an aluminum source, to control the Al content of the aluminized layer as a result of a one-step process and can be widely adopted for coating complex-shaped components. The aluminizing process was carried out by the heat treatment on disc and rod shaped S45C steel substrates with Al-Ti mixed slurries that were composed of various mixed ratios (wt%) of Al and Ti powders. The surface of the resultant aluminized layer was relatively smooth with no obvious cracks. The aluminized layers mainly contain an Fe-Al compound as the bulk phase. However, the Al concentration and the thickness of the aluminized layer gradually decrease as the Ti proportion among Al-Ti mixed slurries increases. It has also been shown that the Al-Ti compound layer, which formed on the substrate during heat treatment, easily separates from the substrate. In addition, the incorporation of Ti into the substrate surface during heat treatment was not observed.

글리신-질산염 연소법으로 합성된 SrAl₂O₄:Eu²⁺,Dy³⁺ 형광체의 발광 및 장잔광 특성

이영기,김정열,이유기,Lee, Young-Ki,Kim, Jung-Yeul,Lee, You-Kee 한국재료학회 2010 한국재료학회지 Vol.20 No.7

A $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor powder with stuffed tridymite structure was synthesized by glycine-nitrate combustion method. The luminescence, formation process and microstructure of the phosphor powder were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). The XRD patterns show that the as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor was an amorphous phase. However, a crystalline $SrAl_2O_4 $ phase was formed by calcining at $1200^{\circ}C$ for 4h. From the SEM analysis, also, it was found that the as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor was in irregular porous particles of about 50 ${\mu}m$, while the calcined phosphor was aggregated in spherical particles with radius of about 0.5 ${\mu}m$. The emission spectrum of as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor did not appear, due to the amorphous phase. However, the emission spectrum of the calcined phosphor was observed at 520 nm (2.384eV); it showed green emission peaking, in the range of 450~650 nm. The excitation spectrum of the $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor exhibits a maximum peak intensity at 360 nm (3.44eV) in the range of 250~480 nm. After the removal of the pulse Xe-lamp excitation (360 nm), also, the decay time for the emission spectrum was very slow, which shows the excellent longphosphorescent property of the phosphor, although the decay time decreased exponentially.

폴리 실리콘을 이용한 금속-반도체-금속 광 검출기의 열처리에 따른 전기적 특성

김경민,김정열,이유기,최용선,이재성,이영기,Kim, Kyeong-Min,Kim, Jung-Yeul,Lee, You-Kee,Choi, Yong-Sun,Lee, Jae-Sung,Lee, Young-Ki 한국재료학회 2018 한국재료학회지 Vol.28 No.4

This study investigated the effects of the post annealing temperatures on the electrical and interfacial properties of a metal-semiconductor-metal photodetector(MSM-PD) device. The interdigitate type MSM-PD devices had the structure Al(500 nm) / Ti(200 nm) / poly-Si(500 nm). Structural analyses of the MSM-PD devices were performed by employing X-ray diffraction(XRD), scanning electron microscopy(SEM) and transmission electron microscope(TEM). Electrical characteristics of the MSM-PD were also examined using current-voltage(I-V) measurements. The optimal post annealing condition for the Schottky contact of MSM-PD devices are $350^{\circ}C$-30minutes. However, as the annealing temperature and time are increased, electrical characteristics of MSM-PD device are degraded. Especially, for the annealing conditions of $400^{\circ}C$-180minutes and $500^{\circ}C$-30minutes, the I-V measurement itself was impossible. These results are closely related to the solid phase reactions at the interface of MSM-PD device, which result in the formation of intermetallic compounds such as $Al_3Ti$ and $Ti_7Al_5Si_{12}$.

금 증착 적외선 반사판의 반사율 및 수명에 미치는 제조공정 변수의 영향

최용선,이영기,이유기,Choi, Yong-Sun,Lee, Young-Ki,Lee, You-Kee 한국재료학회 2018 한국재료학회지 Vol.28 No.4

Infrared(IR) heating has many advantages, such as energy efficiency, reduced heating time, cleanliness, equipment compactness, high drying rate and easy automation. These features of IR heating provide widely industrial applications, such as surface heat treatment in semiconductor fabrication, thermoforming of polymers, drying and disinfection of food products, heating to metal forging, and drying of wet materials. In this study, the characteristics of a protected gold mirror were examined by spectrophotometer and the lifetime of the coating layers were evaluated by a cross-cutting method and salt spray test. The effects of manufacturing conditions on the protected gold mirror were seen and remedies for these effects were noted in order to improve the properties of the protected gold mirror in the drying process. The reflectance and lifetime of the protected gold mirror was influenced by manufacturing conditions, such as surface roughness and forming conditions of the anti-oxide layer, the adhesion layer, the reflecting layer and the protection layer. The results of this study showed that the protected gold mirror manufactured using a buffing method for pre-treatment resulted in the most effective reflectance. In addition, $Al_2O_3$ coating on an Al substrate as an anti-oxide layer was more effective than the anodizing process in the test of reflectance. Furthermore, the protected gold mirror manufactured by layers forming of various materials resulted in the most effective reflectance and lifetime when coated with $Al_2O_3$ as the anti-oxide layer, coated Cr as the adhesion layer, and coated $MgF_2$ as the protection layer.

아르곤 가스의 주입이 붕소 도핑 다이아몬드 전극의 특성에 미치는 효과

최용선,이영기,김정열,이유기,Choi, Yong-Sun,Lee, Young-Ki,Kim, Jung-Yuel,Lee, You-Kee 한국재료학회 2018 한국재료학회지 Vol.28 No.5

A boron-doped diamond(BDD) electrode is attractive for many electrochemical applications due to its distinctive properties: an extremely wide potential window in aqueous and non-aqueous electrolytes, a very low and stable background current and a high resistance to surface fouling. An Ar gas mixture of $H_2$, $CH_4$ and trimethylboron (TMB, 0.1 % $C_3H_9B$ in $H_2$) is used in a hot filament chemical vapor deposition(HFCVD) reactor. The effect of argon addition on quality, structure and electrochemical property is investigated by scanning electron microscope(SEM), X-ray diffraction(XRD) and cyclic voltammetry(CV). In this study, BDD electrodes are manufactured using different $Ar/CH_4$ ratios ($Ar/CH_4$ = 0, 1, 2 and 4). The results of this study show that the diamond grain size decreases with increasing $Ar/CH_4$ ratios. On the other hand, the samples with an $Ar/CH_4$ ratio above 5 fail to produce a BDD electrode. In addition, the BDD electrodes manufactured by introducing different $Ar/CH_4$ ratios result in the most inclined to (111) preferential growth when the $Ar/CH_4$ ratio is 2. It is also noted that the electrochemical properties of the BDD electrode improve with the process of adding argon.