• Korean Journal of Materials Research
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• v.9 no.11
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• pp.1075-1082
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• 1999

Composite air electrodes of 50/50 vol% LSM- YSZ where LSM =$\textrm{La}_{1-x}\textrm{Sr}_{x}\textrm{MnO}_{3}$(0$\leq$x$\leq$0.5) were prepared by colloidal deposition technique. The electrodes were then examined by scanning electron microscopy (SEM) and studied by ac impedance spectroscopy in order to improve the performance of a solid oxide fuel cell (SOFC). Reproducible impedance spectra were confirmed by using the improved cell, consisting of LSM- YSZ/YSZ/LSM-YSZ. These spectra were a strong function of operating temperature and the stable conditions for the cells were typically reached at $900^{\circ}C$. The typical spectra measured for an air//air cell at $900^{\circ}C$ were composed of two arcs. Addition of YSZ to the LSM electrode led to a pronounced decrease in cathodic resistivity of LSM-YSZ composite electrodes. Polishing the electrolyte surface to eliminate the influences of surface impurities could further reduce cathode resistivity. The cathodic resistivity of the LSM-YSZ electrodes with catalytic interlayer (Ni or Sr) was much smaller than that of LSM-YSZ electrodes without catalytic interlayer. In addition, the cathodic resistivity of the LSM-YSZ electrodes was a strong function of composition of electrode materials, the electrolyte geometry, and applied current.

• Economic and Environmental Geology
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• v.56 no.4
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• pp.409-419
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• 2023

Acid mine drainage(AMD) treatment is classified as both passive and active treatment. During the treatment, about 5,000 tons of neutralization sludge is generated as a by-product per year in Korea. This study was conducted to evaluate the characteristics of sludge generated from physico·chemical treatment processes as an active treatment from 5 different sources (D, H, S, T, Y) and the possibility of the sludges being recycled. The sludges have a pH range of 5.86 ~ pH 7.89, and a water content range of 51% ~ 82%. Most of particle sizes were less than 25 ㎛. In analysis of inorganic elements, the concentration of Al, Fe, and Mn were between 1,189 mg/kg ~ 129,344 mg/kg, 106,132 mg/kg ~ 338,011 mg/kg, and 3,472 mg/kg ~ 11,743 mg/kg, respectively. The concentration of As and Zn in sludge-T, Cd in sludge-D, Ni in sludge-H, Zn in sludge-S, and Cd in sludge-Y exceeded the soil contamination standards of Korea. The results from 2 separate kinds of leaching test, the Korea Standard Leaching Test(KSLT) and Toxicity Characteristic Leaching Procedure(TCLP), showed that all the sludges met the Korea groundwater standards. From the XRD and SEM-EDS analysis, the peaks of calcite and quartz were found in the sludges. The sludge also had a high proportion of Fe and O, and the majority of the composition was amorphous iron hydroxide.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.51-51
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• 2009

Ni 기 초내열합금은 원자력 발전설비의 열교환기용 재료를 비롯한 발전용 가스터빈, 제트엔진, 화학공장용 튜브 및 파이프재료 등 우수한 고온 기계적 특성 및 고온 내식성을 요구하는 각종 부품재에 광범위하게 이용되고 있다. Al 확산침투처리는 Ni기 초내열합금에 Al 혼합분말을 이용하여 금속간합화물을 코팅함으로써 고온산화특성 향상에 효과적인 방법이다. 본 연구에서는 Al 확산침투처리를 통하여 Inconel 617 표면에 Aluminide 코팅층을 형성함으로써 고온 내산화특성을 향상시키고자 하였다. Al 확산침투처리는 Al :$Al_2O_3$ : $NH_4Cl$ = 15g : 83g : 2g(wt.%)의 비율의 혼합분말을 사용하여 $900^{\circ}C$에서 1 시간 동안 Ar 분위기에서 수행되었다. Al 확산침투처리 후 $950^{\circ}C$에서 1000 시간 동안 air 분위기에서 열화시험을 수행하였다. Al 확산침투처리 후 고온열화를 통해 고온산화특성을 평가였으며, 고온 열화에 의해 형성된 코팅층의 석출물과 계면상의 상분석을 수행하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.6
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• pp.714-720
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• 2003

Due to the electric power shortage in summer season and regulation of freon refrigerant, the application of gas absorption refrigeration and hot water systems are considerably increasing trend. But, this system consists of condenser, heat exchanger, supply pipe and radiator etc. which are easily corroded by acidity and dissolved oxygen and gases. In result, this system occurs scale attachment and corrosion damage like pitting and crevice corrosion. In this study, electrochemical polarization test of heat exchanger tubing material (copper, aluminium brass, 30% cupronickel(30% Cu-Ni)) was carried out in 60% lithium bromide solution at $95^{\circ}C$. As a result of polarization test, corrosion behavior by impressed potential and local corrosion. such as galvanic corrosion, pitting corrosion behavior, of tubing materials was investigated. The main results obtained are as follows: (1) The effect of pitting and crevice corrosion control of 30% cupronickel in 60% LiBr solution at $95^{\circ}C$ is very excellent. (2) Dissimilar metal corrosion of 30% cupronickel coupling to aluminium bronze is the most sensitive. (3) Current density behavior of tube materials by impressed potential is high in order of copper > aluminium brass > 30% cupronickel.

• Journal of Hydrogen and New Energy
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• v.18 no.4
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• pp.406-412
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• 2007

An experimental study on the design of a catalytic combustor for 1.6 kW MCFC system has been performed. The roles of the catalytic combustor are to completely burn anode off-gas and to supply sufficient $CO_2$ to cathode channels. In order to avoid hot spot or fuel slippage, flow uniformity at the catalyst inlet was achieved by installing two crossing perforated plates between the catalyst and the mixing chamber with minimal pressure drop. A Pd/Ce/Ni-$Al_2O_3$ catalyst was used for complete combustion of the off-gas at GHSV=36,000.

• Corrosion Science and Technology
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• v.2 no.1
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• pp.53-57
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• 2003

The MarM247 based superalloy (8wt.%Cr- 9wt.%Co- 3wt.%Ta- 1.5wt.%Hf- 5.6%wt.Al- 9.5wt.%W- Bal. Ni) specimens were diffusion aluminized by for types of pack cementation methods, and their coating structure and their high temperature oxidation resistance were investigated. The coated specimens treated at 973K in high aluminum concentration pack had a coating layer containing large hafunium rich precipitates, which were originally included in substrate alloy. After the high temperature oxidation test in air containing 30 vol.% $H_2O$ at 1273K ~ 323K, the deep localized corrosion which reached to the substrate were observed along with these hafnium rich precipitates. On the other hand, the coated specimens treated at 1323K using low aluminum concentration pack showed the coating layer without the large hafunium rich precipitates, and after the high temperature oxidation test at 1273K for 1800 ksec, it did not show the deep localized corrosion. The nickel electroplating before the aluminizing forms thick hafnium free area, and its high temperature oxidation resistance were comparable to platinum modified aluminizing coatings at 1273K.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.148-148
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• 2011

일반적으로 LED 제작에 사용되는 c-plane GaN는 c축 방향으로 발생하는 분극의 영향을 받게 된다. 분극은 LED내 양자우물의 밴드를 기울게 하여 그 결과 전자와 홀의 재결합 확률을 감소시켜 낮은 내부양자효율을 가지게 된다. 이러한 문제를 해결하기 위한 여러 가지 방법들이 제시되었는데 그 중에서도 특히 a-plane 혹은 m-plane면과 같은 무분극 면을 사용하는 GaN LED가 주목받고 있다. 그 이유는 무분극 면은 분극이 발생하는 c축과 수직이기 때문에 분극의 영향을 받지 않아 높은 내부 양자효율을 가질수 있다. 본 연구에서는 MOCVD 장비를 사용하여 2인치 r-plane 사파이어 기판위에 3um두께의 a-plane GaN을 성장하였다. 그위에 2um정도로 Si을 도핑하여 n-type GaN 형성한후 단일 양자우물, 그리고 Mg을 도핑하여 p-type GaN을 성장하였다. 장파장대역의 a-plane LED의 특성을 알아보기 위해서 양자우물 형성시 In의 조성비를 높였다. 일반적인 포토리소그래피 공정과 Dry etching 공정을 사용하여 메사구조를 형성하였으며 Ti/Al/Pt/Au와 Ni/Au를 각각 n-type과 p-type의 전극 물질로 사용하였다. 제작된 LED의 특성을 파악하기 위해서 인가전류를 0부터 100mA까지 출력 스펙트럼을 측정하였으며 orange대역의 파장을 갖는 LED를 얻었다. 인가전류별 Peak 파장의 변화와 반측폭의 변화를 파악하여 장파장 대역의 a-plane LED의 특성을 확인하였다.

• Journal of Hydrogen and New Energy
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• v.12 no.1
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• pp.65-73
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• 2001

Carbon nanotubes were prepared by catalytic decomposition of $CH_4$ using Ni-MgO catalyst at various temperatures. $H_2$ effect on crystallinity and morphology during the synthesis of carbon nanotubes was investigated. The crystallinity and morphology were characterized by SEM, TEM, XRD, TGA, and Raman spectroscopy. In addition, the hydrogen adsorption properties were evaluated by PCT measurement in a hydrogen pressure range between 1 and 120 bar. The optimal synthesis temperature of carbon nanotubes was elevated in the presence of $H_2$, although significant difference of carbon nanotube morphology was not found. It is believed that hydrogen served as self-cleaner mops the amorphous carbon on the catalyst surface. It is proved that the carbon nanotubes have multi-walled structure, short length with a outer diameter of 20 ~40nm and open tips after elimination of the catalyst. The amount of hydrogen adsorbed in carbon nanotubes is increased as the pressure of hydrogen is increased and reaches 1.3 wt % under the hydrogen pressure of 120 bar at room temperature.

• Journal of Industrial Technology
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• v.42 no.1
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• pp.7-12
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• 2022

High nickel layered oxide cathodes are gaining increasing attention for lithium-ion batteries due to their higher energy density and lower cost compared to LiCoO₂. However, they suffer from the formation of residual lithium on the surface in the form of LiOH and Li₂CO₃ on exposure to ambient air. The residual lithium causes notorious issues, such as slurry gelation during electrode preparation and gas evolution during cell cycling. In this review, we investigate the residual lithium issues through its impact on cathode slurry instability based on deformed polyvinylidene fluoride (PVdF) as well as its formation and reduction mechanism in terms of inherently off-stoichiometric synthesis of high nickel cathodes. Additionally, new analysis method with anhydrous methanol was introduced to exclude Li⁺/H⁺ exchange effect during sample preparation with distilled water. We hope that this review would contribute to encouraging the academic efforts to consider practical aspects and mitigation in global high-energy-density lithium-ion battery manufacturers.

• New & Renewable Energy
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• v.20 no.3
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• pp.20-27
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• 2024

A Li-rich cathode material, Li_1.167Mn_0.548Ni_0.18Co_0.105O₂, with a spherical shape and high crystallinity, is prepared using flame spray pyrolysis. The post-heat treatment condition influences the properties of the prepared material, such as its structure, morphology, and chemical composition, and optimum performance is achieved at 900℃. Various excess Li contents (0-12 wt.%) are introduced in the precursor solution to compensate for volatilized Li during synthesis, bringing it close to the target composition. Compensation for volatilized Li enhances the electrochemical performance, i.e., the Li-compensated sample shows a good discharge capacity of 247 mAh g^-1 at a current density of 20 mA g^-1 in a potential window of 4.6-2.5 V. In addition, the prepared Li-rich cathode material supplemented with 9 wt.% of the Li source shows increased discharge capacity of 175 and 148 mAh g^-1 at 200 and 400 mA g^-1, respectively, compared with those of a bare sample (164 and 127 mAh g^-1, respectively).