• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05b
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• pp.98-101
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• 2005

BSCCO thin films fabricated by using the evaporation method. As a result, although the composition of Bi2212 was set up, the phase of Bi2201, Bi2212 and Bi2223 was formed. The formation area of these stable phases is indicated as inclined line in the direction of the right lower end from the Arrhenius plot of the substrate temperature-oxidation gas pressure, and are distributed in very small area. The activation energy for the phase transformation from the Bi2201 to the Bi2212 is estimated in terms of the Avrami equation.

• 연구논문집
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• s.33
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• pp.123-135
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• 2003

Using the residence time calculated by computer simulation for temperature and gas velocity distribution in CVC reactor, the kinetics on the formation of $TiO_2$ nano powder was analyzed for coagulation process, After abrupt increase of particle size at initial growth stage (< 0.2 $\mus$ ), the particle grew in proportion of cubic root to time. The numerically calculated particle sizes well agreed with the experimental results. However, the coarse rutile $TiO_2$ powders having the particle size of over 40 nm were formed on the surface of quratz rod in the reactor. it is thought that the fine anatase particles condensed on quratz rod were sintered in a heated CVC reactor to grow and transform to coarse rutile phase, and the critical size for phase transformation anstase-to-rutile was around 25 nm tn this study.

• The Korean Journal of Ceramics
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• v.1 no.4
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• pp.214-218
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• 1995

Partially stabilized zironia with magnesia (Mg-PSZ) is known as one of the toughest monolithic ceramics. However, the very large grain sizes obtained after sintering at a high solution-heat treatment temperature in the cubic region of the phase diagram limit the strength of this material rather modest. In this study fine-grained Mg-PSZ materials were fabricated by adding TiC particles as a dispersed phase. Samples were hot-pressed at $1750^{\circ}C$ and then annealed at $1420^{\circ}C$ for various times. Grain growth was retarded severely by the TiC particles resulting in grain sizes smaller by more than one order of magnitude than those of PSZ without TiC. The fine-grained microstructure lead to doubly-increased fracture strength while maintaining the same level of high fracture toughness as that of conventional Mg-PSZ without TiC particles.

• Journal of Magnetics
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• v.6 no.3
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• pp.94-100
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• 2001

Fe-Co-Ni particles with an average size of 45 and 135 nm are characterized in terms of magnetic phase transformation and magnetic properties at room temperature. BCC structure of Fe-Co-Ni spherical particles can be synthesized from Fe-Co-Ni-Al-Cu precursor films by heating at 600-80$0^{\circ}C$ for the phase separation of Fe-Co rich Fe-Co-Ni particles, followed by a post heating at $600^{\circ}C$ for 5 hours. The average size of nanoparticles was directly determined by the thickness of precursor films. Exchange interactive hysteresis was observed for the nano-composite (Fe-Co-Ni)+(Fe-Ni-Al) films resulting from the short exchange interface between ferromagnetic Fe-Co-Ni particles surrounded by almost papramagnetic Ni-Al-Fe matrix. Arraying the isolated Fe-Co-Ni nano-particles in a random arrangement on $Al_2O_3$substrate the particle assembly showed a behavior of dipole interactive ferromagnetic clusters depending on their volume and inter-particle distance.

• Journal of Magnetics
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• v.7 no.2
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• pp.51-54
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• 2002

The crystallization of amorphous Ba-ferrite/sapphire(001) thin films was studied in real-time synchrotron x-ray scattering experiments. In the sputter-grown amorphous films, we found the existence of epitaxial $Fe_3O_4$ interfacial crystallites (50-${\AA}$-thick), well aligned $[0.03^circ$full-width at half-maximum (FWHM)] to the sapphire [001] direction. The amorphous precursor was crystallized to epitaxial Ba-ferrite and \alpha-Fe_2O_3$grains in two steps; i) the nucleation of crystalline \alpha-Fe_2O_3$ phase started at $300^circ{C}$ together with the transformation of the $Fe_3O_4$ crystallites to the \alpha-Fe_2O_3$ crystallites, ii) the nucleation of Ba-ferrite phase occurred at temperature above $600^circ{C}$. In the crystallized films irrespective of the film thickness, the crystal domain size of the \alpha-Fe_2O_3$grains was about 250 ${\AA}$ in the film plane, similar to that of the Ba-ferrite grains.

• Journal of the Korean Ceramic Society
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• v.27 no.5
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• pp.613-618
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• 1990

The pure and 6mol% MgO-doped ZrO2 powders were prepared by hot petroleum drying method. The power characterization of homogeneous fine powder was indentified by the method of thermal analysis, BET and electron microscope. The transformation, content of t-ZrO2, crystallite size and apparent strain were measured by X-ray diffraction technique. The prepared powders were transformed in order of amorphouslongrightarrowmetastable cubic ZrO2longrightarrowmetastable tetragonal ZrO2longrightarrowstable monoclinic ZrO2 by a adequate heat treatment. The stabilization of metastable phase can be discussed in terms of energetial concept ; the difference of surface energy and internal strain in particle.

• Journal of the Korean Solar Energy Society
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• v.33 no.1
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• pp.73-78
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• 2013

Hexadecane and exfoliated graphite nanoplate (xGnP)composite was prepared as a shape-stabilized phase change material (SSPCM) in a vacuum to develope thermal energy storage. The Hexadecane as an organic phase change material (PCM) is very stable against phase separation of PCM and has a melting point at $18^{\circ}C$ that is under the thermally comfortable temperature range in buildings. The xGnP is a porous carbon nanotube material with high thermal conductivity. Scanning electron microscope (SEM) and Fourier transformation infrared spectrophotometer (FT-IR)were used to confirm the chemical and physical stability of Hexadecane/xGnP SSPCM. In addition, thermal properties were determined by Deferential scanning calorimeter(DSC) and Thermogravimetric analysis (TGA). The specific heat of Hexadecane/xGnPSSPCM was $10.0J/g{\cdot}K$ at $21.8^{\circ}C$. The melting temperature range of melting and freezing were found to be $16-25^{\circ}C$ and $17-12^{\circ}C$. At this time, the laten heats of melting and freezing were 96.4J/g and 94.8J/g. The Hexadecane was impregnated into xGnP as much about 48.8% of Hexadecane/xGnP SSPCM's mass fraction.

• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1222-1228
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• 1999

The effects of Sn and Nb content on the characteristics of ${\beta}$ to ${\alpha}$ phase transformation for Zr were studied by optical microscopy and transmission electron microscopy. The basketweave structures consisted of fine ${\alpha}$-laths were shown in all the air-cooled specimens. As the Nb content increased, the ${\beta}{\to}{\alpha}$+${\beta}$ transformation temperature decreased thus allowing the width of ${\alpha}$-lath, however, did not change with Sn content. While water-quenched pure Zr and Zr-xSn alloys were found to be mailny slipped martensite, water-quenched Zr-xNb alloys showed predominantly a twinned martensite. The transition of slipped martensite to twinned martensite was contributed to the decrease of Ms temperature.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.9
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• pp.1602-1608
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• 2007

The composites were fabricated, respectively, using 61[vol.%] SiC-39[vol.%] $TiB_2$ and using 61[vol.%] SiC-39[vol.%] $ZrB_2$ powders with the liquid forming additives of 12[wt%] $Al_2O_3+Y_2O_3$ by hot pressing annealing at $1650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, $ZrB_2$ were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H, 3C), $TiB_2$, $ZrB_2$ and $YAG(Al_5Y_3O_{12})$ crystal phase on the Liquid-Phase-Sintered(LPS) $SiC-TiB_2$, and $SiC-ZrB_2$ composite. $\beta\rightarrow\alpha-SiC$ phase transformation was occurred on the $SiC-TiB_2$ and $SiC-ZrB_2$ composite. The relative density, the flexural strength and Young's modulus showed the highest value of 98.57[%], 249.42[MPa] and 91.64[GPa] in $SiC-ZrB_2$ composite at room temperature respectively. The electrical resistivity showed the lowest value of $7.96{\times}10^{-4}[\Omega{\cdot}cm]$ for $SiC-ZrB_2$ composite at $25[^{\circ}C]$. The electrical resistivity of the $SiC-TiB_2$ and $SiC-ZrB_2$ composite was all positive temperature coefficient resistance (PTCR) in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$. The resistance temperature coefficient of composite showed the lowest value of $1.319\times10^{-3}/[^{\circ}C]$ for $SiC-ZrB_2$ composite in the temperature ranges from $100[^{\circ}C]$ to $300[^{\circ}C]$ Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.3
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• pp.179-185
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• 1992

The shape memory effect results from the martensite transfomation of each individual grain. Thus it is necessary to study the texture and its variation. In this study the change of texture during thermal cycling and it's effect on shape memory ability are investigated. The major component of the rolling texture in the parent phase is identified (001) [110], and minor components are (112) [110], (111) [112], {hkl}<100> fiber texture is developed at $45^{\circ}$ from rolling direction. In the case of martensite phase, it is estimated that the major component is (011) [100] and the minor components are (105) [501], (010) [101] and (100) [001]. According to thermal cycling. severity of texture, especially (001) [110] component in parent phase and (011) [100] component in martensite phase are increased. The shape memory ability is increased with increase of thermal cycles and also increased as the direction of specimen approach to $45^{\circ}$ from rolling direction. After first thermal cycling the temperature of transformation can be define clearly and Ms and As are raised by thermal cycling.