• 한국분말재료학회지
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• 제19권6호
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• pp.446-450
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• 2012

In order to fabricate the porous Mo with controlled pore characteristics, unique processing by using $MoO_3$ powder as the source and camphene as the sublimable material is introduced. Camphene-based 15 vol% $MoO_3$ slurries, prepared by milling at $50^{\circ}C$ with a small amount of dispersant, were frozen at $-25^{\circ}C$. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at $750^{\circ}C$, and sintered at $1000-1100^{\circ}C$ for 1 h. After heat treatment in hydrogen atmosphere, $MoO_3$ powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about $150{\mu}m$ which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores due to the difference in the camphene growth rate during freezing process. The size of small pores was decreased with increase in sintering temperature, while that of large pores was unchanged. The results are strongly suggested that the porous metal with required pore characteristics can be successfully fabricated by freeze-drying process using metal oxide powders.

• 전기화학회지
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• 제12권3호
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• pp.239-244
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• 2009

리튬 이차 전지의 전기화학적 특성 및 안전성 향상을 위한 음극 활물질 표면 처리 재료로 $Al_2O_3$와 $nano-Li_4Ti_5O_{12}$등이 사용된다. 표면 처리된 음극 활물질의 형상과 특성을 관찰하기 위해 주사전자현미경(Scanning electron microscopy, SEM), 투과전자현미경(Transmission electron microscopy, TEM)으로 관찰하였으며, 전기화학적 특성 및 안전성 평가를 위해 충방전기 및 가속 율열량계(Accelerating Rate Calorimeter, ARC)를 사용하였다. 각각의 금속 산화물에 따른 초기 효율 및 초기 용량은 82.5%와 350mAh/g로 동일하지만, 충방전 율속에 따른 특성 및 수명, 그리고 열적 안전성은 $nano-Li_4Ti_5O_{12}$로 음극 활물질을 표면 처리 한 활물질이 더 우수하였다.

• 한국전기전자재료학회논문지
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• 제17권12호
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• pp.1356-1361
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• 2004

High temperature superconducting coated conductor has a structure of ///. The buffer layer consists of multi-layer, this study reports the deposition method and optimal deposition conditions of YSZ(Yttria-stabilized zirconia) layer which plays a important part in preventing the elements of substrate from diffusing into the superconducting layer. YSZ layer was deposited by DC reactive sputtering technique using water vapor for oxidizing deposited elements on substrate. To investigate optimal thickness of YSZ film, four YSZ/CeO$_2$/Ni samples with different YSZ thickness(130 nm, 260 nm, 390 nm, and 650 nm) were prepared. The SEM image showed that the surface of YSZ layer was getting to be rougher as YSZ layer was getting thicker and the growth mode of YSZ layer was columnar grain growth. After CeO$_2$ layer was deposited with the same thickness of 18.3 nm on each four samples, YBCO layer was deposited by PLD method with the thickness of 300 nm. The critical currents of four samples were 0, 6 A, 7.5 A, and 5 A respectively. This shows that as YSZ layer is getting thicker, YSZ layer plays a good role as a diffusion barrier but the surface of YSZ layer is getting rougher.

• 전자공학회논문지D
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• 제34D권12호
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• pp.89-100
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• 1997

This paper investigated a new type of low voltage threshold switch (LVTS). As distinguished from the many other types of electronic threshold switches, the LvTS is ; voltage controlled, occurs at low voltages ($V_{2}$ $O_{5}$lV devices. The average low threshold voltage < $V_{LVT}$>=218 mV (standard deviation =24mV~kT/q, where T=300K), and was independent of the device area (x100) and amorphous oxide occurred in an ~22.angs. thick interphase of the V/amorphous- $V_{2}$ $O_{5}$ contacts. At $V_{LVT}$ there was a transition from an initially low conductance (OFF) state into a succession of quantized states of higher conductance (ON). The OFF state was spatically homogeneous and dominated by tunneling into the interphase. The ON state conductances were consistent with the quantized conductances of ballistic transport through a one dimensional, quantum point contact. The temeprature dependence of $V_{LVT}$, and fit of the material parameters (dielectric function, barrier energy, conductivity) to the data, showed that transport in the OFF and ON states occurred in an interphase with the characteristics of, respectively, semiconducting and metallic V $O_{2}$. The experimental results suggest that the LVTS is likely to be observed in interphases produced by a critical event associated with an inelastic transfer of energy.rgy.y.rgy.

• Journal of Electrochemical Science and Technology
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• 제9권3호
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• pp.202-211
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• 2018

In this work, Fe-Pd alloy films have been electrodeposited on different substrates using an electrolyte containing $[Pd(NH_3)_4]^{2+}$ (0.02 M) and $[Fe-Citrate]^{2+}$ (0.2 M). The influences of substrate and overpotential on chemical composition, nucleation and growth kinetics as well as the electrodeposited films morphology have been investigated using energy dispersive X-ray spectroscopy (EDS), current-time transients, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) patterns. In all substrates - brass, copper and sputtered fluorine doped tin oxide on glass (FTO/glass) - Fe content of the electrodeposited alloys increases by increasing the overpotential. Also the cathodic current efficiency is low due to high rate of $H_2$ co-reduction. Regarding the chronoamperometry current-time transients, it has been demonstrated that the nucleation mechanism is instantaneous with a typical three dimensional (3D) diffusion-controlled growth in the case of brass and copper substrates; while for FTO, the growth mode changes to 3D progressive. At a constant overpotential, the calculated number of active nucleation sites for metallic substrates is much higher than that of FTO/glass; however by increasing the overpotential, the number of active nucleation sites increases. The SEM micrographs as well as the XRD patterns reveal the formation of Fe-Pd alloy thin films with nanostructure arrangement and ultra-fine grains.

• 조명전기설비학회논문지
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• 제18권3호
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• pp.27-33
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• 2004

우리가 생활하는 거의 모든 곳에서 발생하는 슬러지(sludge)는 악취, 토양오염 등 많은 문제점을 가지고 있으며, 대부분의 폐기물은 매립 또는 소각에 의해 처리되고 있으나 슬러지의 경우 두 가지 방법 모두 심각한 문제점을 가지고 있어, 대체 처리방법의 개발이 시급한 실정이다. 본 연구에서는 그 슬러지를 NOx제거용 촉매 펠렛(Pellet)재료로 재활용하기 위한 가능성을 타진하기 위하여 수돗물 정수장에서 발생되는 슬러지로 펠렛을 제작하여 $BaTiO_3$ 펠렛과 하이브리드 구조로 NOx제거용 플라즈마 반응기를 제작하였고, specific energy, 전압인가 방법, 슬러지의 양, 산소농도 변화에 따른 NOx제거 특성을 측정하고 슬러지 펠렛의 영향을 측정하고 분석하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.165-165
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• 2014

In this study, we demonstrated that the soft lithographic patterning processing of chemical vapor deposition (CVD) graphene and rGO sheets as large scale, low cost, high quality and simplicity for future industrial applications. Recently, a previous study has reported that single layer graphene grown via CVD was patterned and transferred to a target surface by controlling the surface energy of the polydimethylsiloxane (PDMS) stamp [1]. Using this approach, the surface of a relief-patterned elastomeric stamp was functionalized with hydrophilic dimethylsulfoxide (DMSO) molecules to enhance the surface energy of the stamp and to remove the graphene-based layer from the initial substrate and transfer it to a target surface [2]. Further, we developed a soft lithographic patterning process via surface energy modification for advanced graphene-based flexible devices such as transistors or simple and efficient chemical sensor consisting of reduced graphene oxide (rGO) and a metallic nanoparticle composite. A flexible graphene-based device on a biocompatible silk fibroin substrate, which is attachable to an arbitrary target surface, was also successfully fabricated.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.79-79
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• 2017

Metallic biomaterials have been mainly used for the fabrication of medical devices for the replacement of hard tissue such as artificial hip joints, bone plates, and dental implants. Because they are very reliable on the viewpoint of mechanical performance. This trend is expected to continue. Especially, Ti and Ti alloys are bioinert. So, they do not chemically bond to the bone, whereas they physically bond with bone tissue. For their poor surface biocompatibility, the surface of Ti alloys has to be modified to improve the surface osteoinductivity. Recently, ceramic-like coatings on titanium, produced by plasma electrolytic oxidation (PEO), have been developed with calciumand phosphorus-enriched surfaces. A lso included the influences of coatings, which can accelerate healing and cell integration, as well as improve tribological properties. However, the adhesions of these coatings to the Ti surface need to be improved for clinical use. Particularly Silicon (Si) has been found to be essential for normal bone, cartilage growth and development. This hydroxyapatite, modified with the inclusion of small concentrations of silicon has been demonstrating to improve the osteoblast proliferation and the bone extracellular matrix production. Strontium-containing hydroxyapatite (Sr-HA) was designed as a filling material to improve the biocompatibility of bone cement. In vitro, the presence of strontium in the coating enhances osteoblast activity and differentiation, whereas it inhibits osteoclast production and proliferation. The objective of this work was to study Morphology of bone-like apatite formation on Sr and Si-doped hydroxyapatite surface of Ti-6Al-4V alloy after plasma electrolytic oxidation. Anodized alloys was prepared at 270V~300V voltages with various concentrations of Si and Sr ions. Bone-like apatite formation was carried out in SBF solution. The morphology of PEO, phase and composition of oxide surface of Ti-6Al-4V alloys were examined by FE-SEM, EDS, and XRD.

• 한국주조공학회지
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• 제23권3호
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• pp.137-146
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• 2003

The main purpose of this study is to investigate the effects of process parameter on alpha-case formation of Ti and TiAl castings. The previous studies showed that the molten titanium is excessively reactive to the refractory oxide mold, resulting in alpha-caes of the titanium castings regardless of composition of titanium alloys. However, the behavior of the alpha-case formation of TiAl alloy is not consistent with conventional titanium alloy. In order to investigate the alpha-case formation of Ti and TiAl castings with process parameter, especially the associated factors of investment mold such as mold material, binder and mold preheating temperature. An attempt has been made to characterize the alpha-case of titanium casting by using optical microscope, EDS, XRD, EMPA and hardness profiles. The formation of the alpha-case on the surface of pure titanium during investment casting was rather by that of solid solution with metallic element from mold material. The required mold strength was obtained with $CaZrO_3$ because of the possibility of using water soluble binder. However, the separation phenomenon between facing and back-up mold materials should be considered. The interfacial reaction of TiAl alloy showed different behavior from that of pure titanium and $Al_2O_3$ was best mold materials. The effect of binder as well as mold material on the formation of alpha-case was significant.

• 자원환경지질
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• 제29권1호
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• pp.87-103
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• 1996

The purposes of this research are to investigate the pollution level of heavy metals due to the urbanization and industrialization in the satellite cities of Seoul, and to assess the chemical species and the sources of heavy metals in highly contaminated soils and dusts. Soil and dust samples were collected from the Uijeongbu and the Koyang cities, which are northern and the northwestern satellite cities of Seoul metropolitan city, respectively. Relatively high pH values($6.3{\sim}9.9$) were found in roadside soils compared with agricultural and forest soils. Difference in pH values of soils was not identified between before and after rainy seasons. In spite of no specific pollution sources in the above cities, the contents of Cu, Pb, and Zn in soils and dusts were much higher than the world average contents. The metal levels in dusts were higher than those in soils, but the metal concentration in dusts was significantly decreased after rainy season. Pollution index was high(> 1.0) in the areas of heavy traffic, industrial complex, and city centres. There is an appreciable proportion of total Zn in exchangeable/water-acid soluble fraction. Copper is predominantly associated with reducible and oxidizable phases, whereas Pb is largely in reducible association. It is concluded that the mobility and bioavailability of metals are high in the order of Zn >> Cu > Pb, on the basis of characteristic particle morphology and chemical composition, Pb-containing particles are originated probably from the automobile exhaust, particularly in heavy traffic areas. The metallic forms and iron-oxide associated forms of Cr, Ni, Cu, Zn, and Pb can be assessed as industrial origin.