• Composites Research
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• v.30 no.2
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• pp.102-107
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• 2017

The preceramic polymer can realize a variety of complex ceramic structures that can not be obtained by conventional ceramic processes. Polycarbosilane, which is a typical preceramic polymer, can control the molecular structure, molecular weight and molecular weight distribution for preparing complex morphology and microstructure of SiC ceramics, including SiC fiber. In this paper, synthesis and molecular structure control technique of polycarbosilane is explained. The silicon carbide fiber prepared by melt spinning, stabilization and heat treatment, and ceramic fiber composites technology made by PIP process are also discussed. In addition, we introduce an example of the development of a complex silicon carbide material such as a silicon carbide hollow fiber having a nanoporous structure.

• Journal of Sensor Science and Technology
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• v.11 no.6
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• pp.327-334
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• 2002

Fine particles of $SnO_2$ were fabricated by the sol-gel powder processing using tine(II) chloride dihydrate($SnCl_2{\cdot}2H_2O$) and ethanol($C_2H_5OH$) as raw materials. The powders were investigated about the properties and electrical sensing. Gel powders were fabricated by drying of sol at $120^{\circ}C$ after aging 72hrs and 168hrs. The amount of $SnO_2$ phase was increased below $600^{\circ}C$ due to the elimination of volatile components, and the $SnO_2$ phase was almost completed by the heat treatment at $700^{\circ}C$ for 30min. The grain sizes were about 30nm below $700^{\circ}C$, and it showed the narrow distribution of the grain sizes. The specimens to measure electrical properties were fabricated by the thick film screen printing technique on the alumina substrates. The conductance of $SnO_2$ was showed the intrinsic behaviour of semiconducting ceramics above at $450^{\circ}C$. The constant conductance was observed in the temperature range of $200{\sim}450^{\circ}C$. The sensing properties of response time, recovery, and sensitivity of CO were improved with aging time.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.23-28
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• 2002

This paper describes the machining characteristics of the $MoSi_2$ based composites by electric discharge drilling with various tubular electrodes, besides, Hardness characteristics and microstructures of $Nb/MoSi_2$ laminate composites were evaluated from the variation of fabricating conditions such as preparation temperature, applied pressure and pressure holding time. $MoSi_2$ -based composites has been developed in new materials for jet engine of supersonic-speed airplanes and gas turbine for high- temperature generator. Achieving this objective may require new hard materials with high strength and high temperature-resistance. However, With the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material, the tool electrode being almost non-unloaded, because there is no direct contact between the tool electrode and the workpiece. By combining a nonconducting ceramics with more conducting ceramic it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and $MoSi_2$ powder was an excellent strategy to improve hardness characteristics of monolithic $MoSi_2$. However, interfacial reaction products like (Nb, Mo)$SiO_2$ and $Nb_2Si_3$ formed at the interface of $Nb/MoSi_2$ and increased with fabricating temperature. $MoSi_2$ composites which a hole drilling was not possible by the conventional machining process, enhanced the capacity of ED-drilling by adding $NbSi_2$ relative to that of SiC or $ZrO_2$ reinforcements.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.888-894
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• 2015

Inorganic composite particles have excellent physical and chemical characteristics and have been applied in various industries. Recently, many studies have examined the optical properties, such as light scattering, refraction, transmission characteristics, by coating organic-inorganic materials on a substrate, such as mica. Mica is widely applied as a pigment, plastics, painted products, and ceramics because of its high chemical stability, durability and non-toxicity. Magnesium oxide has a range of properties, such as high light transmittance, corrosion resistance and non-toxicity, and it is used as an optical material and polymer additives. To use the optical properties of mica and magnesium oxide, mica was coated with magnesium hydroxide by a dissolution and recrystallization process. In this study, the optimal conditions for the haze value of the particles were found by adjusting the amount of precursors and pH. Magnesium hydroxide layers were formed on the surfaces of mica and converted to MgO after calcination at $400^{\circ}C$ for 4 h. The results showed that the value of MgO-coated mica haze can be controlled easily by the amount of the magnesium hydroxide and pH. The optical properties of the inorganic composite powder were analyzed using a hazemeter and the highest haze value was 85.92 % at pH 9. The physicochemical properties of the synthesized composite was analyzed by SEM, XRD, EDS, and PSA.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.260-260
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• 2013

Multiferroic materials have attracted much attention due to their fascinating fundamental physical properties and technological applications in magnetic/ferroelectric data-storage systems, quantum electromagnets, spintronics, and sensor devices. Among single-phase multiferroic materials, $BiFeO_3 $ is a typical multiferroic material with a room temperature magnetoelectric coupling in view of high magnetic-and ferroelectric-ordering temperatures (Neel temperature $T_N$~647 K and Curie temperature $T_C$~1,103 K). Rare-earth ion substitution at the Bi sties is very interesting, which induces suppressed volatility of Bi ion and improved ferroelectric properties. At the same time, Fe-site substitution with magnetic ions is also attracting, and the enhanced ferromagnetism was reported. In this study, $Bi_{1-x}Dy_xFe_{0.95}Co_{0.05}O_3$ (x=0, 0.05 and 0.1) bulk ceramic compounds were prepared by solid-state reaction and rapid sintering. High-purity $Bi_2O_3$, $Dy_2O_3$, $Fe_2O_3$ and $Co_3O_4$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ or 24 h to produce $Bi_{1-x}Dy_xFe_{0.95}Co_{0.05}O_3$. The samples were immediately put into an oven, which was heated up to $800^{\circ}C$ nd sintered in air for 30 min. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent magnetization measurements were performed with a vibrating-sample magnetometer. The electric polarization was measured at room temperature by using a standard ferroelectric tester (RT66B, Radiant Technologies).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.270-276
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• 2020

3D printing is an additive manufacturing technology that can produce complex shapes in a single process for a range of materials, such as polymers, ceramics, and metals. Recent 3D printing technology has developed to a level that enables the mass-production through an improvement of the printing speed and the continuous development of applicable materials. In this study, 3D printing technology using a laser was applied to manufacture a heat exchanger for an air compressor in a railway vehicle. First, the optimal design of the heat exchanger was carried out by focusing on weight reduction and compactness as a shape suitable for 3D printing. Based on the design derived, heat exchanger prototypes were made of AlSi10Mg alloy material by applying the SLM technique. Moreover, the manufactured prototypes were attached to an existing air compressor, and the heat exchange performance of the compressed air was tested. The test results of the 3D printed prototypes showed a heat exchange performance of approximately 80% and 85% at low and high-pressure, respectively, compared to the existing heat exchanger. From the 𝓔-NTU method results with an external cooling air condition similar to that of the existing heat exchanger, the calculated heat transfer amount of 3D printed parts showed similar performance compared to the existing heat exchanger. As a result, the 3D printed heat exchanger is lightweight with good performance.

• Journal of the Korean Applied Science and Technology
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• v.29 no.3
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• pp.478-485
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• 2012

Polymers are widely used as membrane material for performing the separation of various gaseous mixtures due to their attractive permselective properties and high processability. The separation characteristics of $CH_4$ and $CO_2$ mixed gas using polyamide composite membrane has been studied in this work. The sample gas was prepared by mixing pure methane and carbon dioxide. Permeation tests were carried out at different operation conditions. Feed flow rates were varied between 800~1000 $cm^3/min$, and the stage cuts were varied between 50~60%. The gas inlet pressure and the temperature were varied as 6 bar and $30{\sim}70^{\circ}C$, respectively. The effects of the above mentioned parameters were investigated to estimate the permeability of $CH_4$ and $CO_2$, and the selectivity of $CO_2$ was also calculated for all conditions. The Arrhenius plots were also performed to obtaine the activation energies of $CH_4$ and $CO_2$ permeabilities.

• Journal of Conservation Science
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• v.33 no.2
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• pp.131-147
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• 2017

The purpose of this study is to analyze the characteristics of Punchong and Whiteware pottery excavated from the kiln site in Dongkok-Town, Gimge. Scientific analysis is carried out to evaluate the physical and chemical properties of the body and glaze. The physical properties indicate the gradual development of the production technology with respect to the kiln operating conditions and period. In chemical properties, the ceramic body is found to be made of raw materials from the same source, but the mixing method depends on the type of Punchong and Whiteware pottery, the production kiln, and period. Whiteware pottery is manufactured with less over 1.3% of the colorant content and more about 1.2% of the $K_2O$ flux content than Punchong pottery. This compositions allow easier vitrification at the same temperature. These characteristics which is low colorant content and high flux content become more prominent as lately. The ceramic glaze is likely to have changed the type of raw materials used after 16~17C, as the contents of MgO, $TiO_2$, MnO, $P_2O_5$ are less three to ten times than 15C.

• Electrical & Electronic Materials
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• v.4 no.2
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• pp.150-158
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• 1991

본 연구에서는 0.80Pb(F $e_{1}$2/N $b_{1}$2/) $O_{3}$-(0.20-x)Pb(F $e_{2}$3/ $W_{1}$3/) $O_{3-x}$Ba(C $u_{1}$2/ $W_{1}$2/) $O_{3}$ (x=0.01, 0.02, 0.03) 세라믹을 소결온도 및 시간을 각각 860~960[.deg.C], 2시간으로 하여 일반 소성법으로 제작하였다. 시편의 조성비와 소결온도에 따른 구조적, 유전적 특성을 조사하였으며 유전손실 특성의 개선을 위해 조성 0.80Pb(F $e_{1}$2/N $b_{1}$2/) $O_{3}$-0.18Pb (F $e_{2}$3/ $W_{1}$3/) $O_{3}$-0.02Ba(C $u_{1}$2/ $W_{1}$2/) $O_{3}$시편에 Mn $O_{2}$를 0~1.25[wt%]로 첨가한 후 유전특성의 변화를 관찰하였다. Mn $O_{2}$의 첨가량이 증가함에 따라 결정립의 크기와 유전상수는 점차 감소하였다. 소결밀도는 900[.deg.C]에서 소결시킨 시편의 경우 최대값을 나타내었다. Ba(C $u_{1}$2/ $W_{1}$2/) $O_{3}$의 양이 0.01에서 0.03[mol]로 증가함에 따라 상전이온도는 38[.deg.C]에서 2[.deg.C]로 감소하였다. 조성 0.80Pb(F $e_{1}$2/N $b_{1}$2/) $O_{3}$0.18Pb(F $e_{2}$3/ $W_{1}$3/) $O_{3}$-0.02Ba(C $u_{1}$2/ $W_{1}$2/) $O_{3}$에 Mn $O_{2}$가 0.25[wt%] 첨가된 시편의 20[.deg.C]에서의 유전상수는 16,700으로 최대값을 유전손실을 1.28[%]로 최소값을 나타내었다. 또한 모든 시편은 온도 및 주파수에 따라 유전상수가 완만하게 변화하는 유전이완 특성을 나타내었다.다.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.3
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• pp.1-6
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• 2007

In this study, the pentacene thin films were prepared by the soluble process, and characterized fur the application of the organic thin film transistor(OTFT) device. To dissolve the pentacene material, two kinds of solvents such as toluene and chloroform were used, and the effects of these solvents on the properties of pentacene thin films coated on ITO/Glass substrate were investigated. Pentacene thin films were prepared by using spin-coating methode and characterized the surface morphology, crystalline and electrical properties. From the AFM measurement, the surface morphology of the pentacene film dissolved with chloroform was improved compared with the one dissolved with toluene solvent. XRD measurement showed that all prepared pentacene film samples were amorphous crystal phases without crystallization of the films. The electrical properties of the pentacene film dissolved with chloroform showed better results than the ones using toluene solvent by hall measurement system. The carrier concentration and the mobility values of pentacene films using chloroform solvent were found to be $-3.225{\times}10^{14}\;cm^{-3}$ and $3.5{\times}10^{-1}\;cm^2{\cdot}V^{-1}{\cdot}S^[-1}$, respectively. The resistivity was about $2.5{\times}10^2\;{\Omega}{\cdot}cm$.