• Korean Journal of Materials Research
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• v.22 no.4
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• pp.207-210
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• 2012

The preparation of $Sm_2O_3$ doped $CeO_2$ in Igepal CO-520/cyclohexane reverse micelle solutions has been studied. In the present work, we synthesized nanosized $Sm_2O_3$ doped $CeO_2$ powders by reverse micelle process using aqueous ammonia as the precipitant; hydroxide precursor was obtained from nitrate solutions dispersed in the nanosized aqueous domains of a micro emulsion consisting of cyclohexane as the oil phase, and poly (xoyethylene) nonylphenylether (Igepal CO-520) as the non-ionic surfactant. The synthesized and calcined powders were characterized by Thermogravimetry-differential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD), and Transmission electron microscopy (TEM). The crystallite size was found to increase with increase in water to surfactant (R) molar ratio. Average particle size and distribution of the synthesized $Sm_2O_3$ doped $CeO_2$ were below 10 nm and narrow, respectively. TG-DTA analysis shows that phase of $Sm_2O_3$ doped $CeO_2$ nanoparticles changed from monoclinic to tetragonal at approximately $560^{\circ}C$. The phase of the synthesized $Sm_2O_3$ doped $CeO_2$ with heating to $600^{\circ}C$ for 30 min was tetragonal $CeO_2$. This study revealed that the particle formation process in reverse micelles is based on a two step model. The rapid first step is the complete reduction of the metal to the zero valence state. The second step is growth, via reagent exchanges between micelles through the inter-micellar exchange.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.200-201
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• 2007

The SBT($SrBi_2Ta_2O_9$) thin films with $Bi_2O_3$ buffer layer were deposited on Pt/Ti/$SiO_2$/Si substrate by R.F. magnetron sputtering method in order to improve the ferroelectric characteristics. In SBT thin films, the deficiency of bismuth during the process due to its volatility results in an obvious non stoichiometry of the films and the presence of secondary phases. $Bi_2O_3$ buffer layer was found to be effective to achieve the low temperature crystallization and improve the ferroelectric properties of SBT thin films. Ferroelectric properties and crystallinities of SBT thin films with various post annealing of $Bi_2O_3$ buffer layer were observed as various annealing temperature, using X-Ray Diffraction (XRD), scanning electron microscopy (SEM), Keithley 237 and HP 4192A Impedance Analyzer.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.9-17
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• 2017

$K_2Ti_6O_{13}$ whisker have been synthesized by hydrothermal process at low temperature and pressure condition. The average length of the synthesized $K_2Ti_6O_{13}$ whisker was about in the range of 300 nm to $1.5{\mu}m$. The average diameter of the synthesized $K_2Ti_6O_{13}$ whisker was 15 nm to 60 nm. The aspect ratio of the synthesized $K_2Ti_6O_{13}$ whisker was below 12. The average length and diameter of the synthesized $K_2Ti_6O_{13}$ whisker can be controlled by reaction temperature and time, KOH molar ratio. $K_2Ti_6O_{13}$ whisker was synthesized from more than $210^{\circ}C$ and 4 h at reaction temperature and time. The length of the whisker is increased with increasing reaction temperature. Characterization of the synthesized $K_2Ti_6O_{13}$ whisker was carried out using the XRD and FE-SEM.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.195-195
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• 2008

CAS계 유리에 $CaCO_3-Al_2O_3$ 혼합물 및 화합물을 10, 30 wt% 첨가하여 저온 소걸 및 마이크로파 유전 특성을 고찰하였다. CAS계 유리의 연화온도는 $841^{\circ}C$ 이며, CAS계 유리에 $CaCO_3$ 와 30 wt%의 $CaCO_3-Al_2O_3$ 혼합물을 melting되며, 10 wt%의 $CaCO_3$, $Al_2O_3$, $1CaCO_3-1Al_2O_3$ 혼합물 및 $CaAl_2O_4$ 화합물를 10 wt% 첨가하였을 때 $900^{\circ}C$ 이하에서 소걸이 가능하였다. 복합체의 XRD 상 분석 결과, CaCO3를 첨가하였을 때에는 모든 조성이 비정질을 나타내었고, $Al_2O_3$와 $1CaCO_3-1Al_2O_3$ 혼합물은 $Al_2O_3$ 결정상이 생성되었고, $CaAl_2O_4$ 화합물은 $CaAl_2Si_2O_8$의 hexagonal와 anorthite 결정상이 생성되었다. 따라서 CAS-10 (A, C-A, CA) 복합체는 $900^{\circ}C$에서 각각 유전율 ($\varepsilon_r$) 6.4, 6.9, 5.15 와 품질계수 ($Q^*f$) 2,400, 1,500, 3,000의 마이크로파 유전 특성을 나타내어 LTCC 기판 재료로 사용이 가능하며, 특히 $CaAl_2O_4$ 화합물을 사용하였을 때 가장 우수한 유전 특성을 나타내는 것을 확인하였다.

• Korean Journal of Materials Research
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• v.21 no.10
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• pp.568-572
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• 2011

The preparation of $Y_2O_3$-doped $ZrO_2$ nanoparticles in Igepal CO-520/cyclohexane reverse micelle solutions is studied here. In this work, we synthesized nanosized $Y_2O_3$-doped $ZrO_2$ powders in a reverse micelle process using aqueous ammonia as the precipitant. In this way, a hydroxide precursor was obtained from nitrate solutions dispersed in the nanosized aqueous domains of a microemulsion consisting of cyclohexane as the oil phase, with poly (oxyethylene) nonylphenylether (Igepal CO-520) as the non-ionic surfactant. The synthesized and calcined powders were characterized by thermogravimetrydifferential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The crystallite size was found to nearly identical with an increase in the water-to-surfactant (R) molar ratio. A FTIR analysis was carried to monitor the elimination of residual oil and surfactant phases from the microemulsion-derived precursor and the calcined powder. The average particle size and distribution of the synthesized $Y_2O_3$-doped $ZrO_2$ were below 5 nm and narrow, respectively. The TG-DTA analysis showed that the phase of the $Y_2O_3$-doped $ZrO_2$ nanoparticles changes from the monoclinic phase to the tetragonal phase at temperatures close to $530^{\circ}C$. The phase of the synthesized $Y_2O_3$-doped $ZrO_2$ when heated to $600^{\circ}C$ was tetragonal $ZrO_2$.

• Bulletin of the Korean Chemical Society
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• v.33 no.8
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• pp.2523-2528
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• 2012

Green phosphors $(Zn_{1-a-b}M_aM^{\prime}_b)_xGa_yS_{x+3y/2}:Eu^{2+}$ (M, M' = alkali earth ions) with x = 2 and y = 2-5 were prepared, starting from ZnO, MgO, $SrCO_3$, $Ga_2O_3$, $Eu_2O_3$, and S with a flux $NH_4F$ using a conventional solidstate reaction. A phosphor with the composition of $(Zn_{0.6}Sr_{0.3}Mg_{0.1})_2Ga_2S_5:Eu^{2+}$ produced the strongest luminescence at a 460-nm excitation. The observed XRD patterns indicated that the optimized phosphor consisted of two components: zinc thiogallate and zinc sulfide. The characteristic green luminescence of the $ZnS:Eu^{2+}$ component on excitation at 460 nm was attributed to the donor-acceptor ($D_{ZnGa_2S_4}-A_{ZnS}$) recombination in the hybrid boundary. The optimized green phosphor converted 17.9% of the absorbed blue light into luminescence. For the fabrication of light-emitting diode (LED), the optimized phosphor was coated with MgO using magnesium nitrate to overcome their weakness against moisture. The MgO-coated green phosphor was fabricated with a blue GaN LED, and the chromaticity index of the phosphor-cast LED (pc-LED) was investigated as a function of the wt % of the optimized phosphor. White LEDs were fabricated by pasting the optimized green (G) and the red (R) phosphors, and the commercial yellow (Y) phosphor on the blue chips. The three-band pc-WLED resulted in improved color rendering index (CRI) and corrected color temperature (CCT), compared with those of the two-band pc-WLED.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.2
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• pp.98-103
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• 1999

The effect of $Al_2O_3$ additives to $\beta-SiC+39vol.%ZrB_2$ electroconductive ceramic composites by pressureless sintering on microstructural, mechanical and electrical properties were investigated. The $\beta-SiC+39vol.%ZrB_2$ ceramic composites were pressureless sintered by adding 4, 8, 12wt.% $Al_2O_3$ powder as a liquid forming additives at $1950^{\cire}C$ for 1h. Phase analysis of composites by XRD revealed mostly of $\alpha-SiC(6H), ZrB_2$ and weakly $\alpha-SiC(4H), \beta-SiC (15R)$ phase. The relative density of composites was lowered by gaseous products of the result of reaction between \beta-SiC and Al_2O_3$, therefore, porosity was increased with increasing $Al_2O_3$ contents, and showed the maximum value of 1.4197MPa.$m^{1/2}$ for composite with 4wt.% $Al_2O_3$ additives. The electrical resistivity of $\beta-SiC+39vol.%ZrB_2$ electroconductive ceramic composite was increased with increasing $Al_2O_3$ contents, and showed positive temperature coefficient resistance (PTCR) in the temperature range of $25^{\cire}C$ to $700^{\cire}C$.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.847-849
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• 1998

The effect of $Al_{2}O_{3}$ additives on the microstructure, mechanical and electrical properties of ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites by pressureless sintering were investigated. The ${\beta}$-SiC+39vol.%$ZrB_2$ ceramic composites were pressureless sintered by adding 4, 8, 12wt.% $Al_{2}O_{3}$ powder as a liquid forming additives at $1950^{\circ}C$ for 1h. Phase analysis of composites by XRD revealed mostly of $\alpha$-SiC(6H), $ZrB_2$ and weakly $\alpha$-SiC(4H), $\beta$-SiC(15R) phase. The relative density of composites was lowered by gaseous products of the result of reaction between $\beta$-SiC and $Al_{2}O_{3}$ therefore, porosity was increased with increased $Al_{2}O_{3}$ contents. The fracture toughness of composites was decreased with increased $Al_{2}O_{3}$ contents, and showed the maximum value of $1.4197MPa{\cdot}m^{1/2}$ for composite added with 4wt.% $Al_{2}O_{3}$ additives. The electrical resistivity of ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composite was increased with increased $Al_{2}O_{3}$ contents, and showed positive temperature coefficient resistance (PTCR) in the temperature from $25^{\circ}C$ to $700^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.30 no.11
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• pp.2603-2607
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• 2009

$LiNi_{0.5-x}Co_{2x}Mn_{0.5-x}O_{2}$ (x = 0, 0.1, 1/6, 1.2, 0.3) were synthesized by the solid-state reaction method. The crystal structure was analyzed by X-ray powder diffraction and Rietveld refinement. $LiNi_{0.5-x}Co_{2x}Mn_{0.5-x}O_{2}$ samples give single phases of hexagonal layered structures with a space group of R-3m for x = 0.1, 1/6, 0.2, and 0.3. The lattice constants of a and c-axis were decreased with the increase in Co contents in samples. The thickness of MO2 slab was decreased and inter-slab distance was increased with the increase in Co contents in $LiNi_{0.5-x}Co_{2x}Mn_{0.5-x}O_{2}$. According to XPS analysis, the valence states of Mn, Co, and Ni in the sample are mainly +4, +3, and +3, respectively. The discharge capacity of 202 mAh/g at 0.1C-rate in the potential range of 4.7 - 3.0 V was obtained in $LiNi_{0.3}Co_{0.4}Mn_{0.3}O_2$ sample, and $LiNi_{0.4}Co_{0.2}Mn_{0.4}O_2$ gives excellent cycle performance in the same potential range.

• Polymer(Korea)
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• v.29 no.2
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• pp.177-182
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• 2005

Montmorillonite (MMT) modified with siloxane diamine was reacted with a reactant obtained from 4,4'-diphenyl methane diisocyanate (MDI) and polyester type polyol, $Nippollan4010(\bar{M}_n2000)$. Finally, polyurethane (PU)/MMT composites were prepared by using 1,4-butane diol as a chain extender in $25\;wt\%$ solution of N,N-dimethyl acetamide (DMAc). It was expected that these nanocomposites had superior exfoliation property to that of MMT dispersed polyurethanes produced by simple mixing due to insertion of siloxane main chain to the silicate interlayer of MMT. Extent of reaction and formation of final products were analysed by using FT-IR spectroscopy. Dispersion into the PU and intercalation of MMT were identified by applying X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile data were acquired by universal test machine (UTM). Thermal stability and variation of surface energy were characterized by thermal gravimetric analysis (TGA) method and measurement of contact angle on the synthesized composites, respectively. As the results the organo-MMT modified with siloxane diamine in the PU composites has an intercalated structure relatively well-expanded rather than a completely exfoliated structure. The tensile strengths and the moduli for the PU/organo-MMT composites were drastically enhanced in comparison to those of $PU/Na^+-MMT$ composites.