• Korean Journal of Materials Research
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• v.21 no.6
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• pp.299-302
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• 2011

[ $WO_3$ ]powders were ball-milled with an alumina ball for 0-72 hours. $In_2O_3$ doped $WO_3$ was prepared by soaking ball-milled $WO_3$ in an $InCl_3$ solution. The mixed powder was annealed at $700^{\circ}C$ for 30 min in an air atmosphere. A paste for screen-printing the thick film was prepared by mixing the $WO_3$:In2O3 powders with ${\alpha}$-terpinol and glycerol. $In_2O_3$ doped $WO_3$ thick films were fabricated into a gas sensor by a screen-printing method on alumina substrates. The structural properties of the $WO_3$:$InO_3$ thick films were a monoclinic phase with a (002) dominant orientation. The particle size of the $WO_3$:$InO_3$ decreased with the ball-milling time. The sensing characteristics of the $In_2O_3$ doped $WO_3$ were investigated by measuring the electrical resistance of each sensor in the test-box. The highest sensitivity to 5 ppm $CH_4$ gas and 5 ppm $CH_3CH_2CH_3$ gas was observed in the ball-milled $WO_3$:$InO_3$ gas sensors at 48 hours. The response time of $WO_3$:$In_2O_3$ gas sensors was 7 seconds and recovery time was 9 seconds for the methane gas.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.483-490
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• 1997

Al2O3/metal composites were fabricated by oxidation and reaction of molten Al-alloy into two types of commercial Al2O3-SiO2 fibrous insulation board. The growth rate, composition and microstructure of these materials were described. An AlZnMg(7075) alloy was selected as a parent alloy. Mixed polycrystalline fiber and glass phase fiber were used as a filler. The growth surface of an alloy was covered with and without SiO2. SiO2 powder was employed as a surface dopant to aid initial oxidation of Al-alloy. Al-alloy, SiO2, fiber block and growth inhibitor CaSiO3 were packed sequentially in a alumina crucible and oxidized in air at temperature range 90$0^{\circ}C$ to 120$0^{\circ}C$. The growth rate of composite layer was calculated by measuring the mass increasement(g) per unit surface($\textrm{cm}^2$). XRD and optical microscope were used to investigate the composition and phase of composites. The composite grown at 120$0^{\circ}C$ and with SiO2 dopant showed rapid growth rate. The growth behavior differed a little depending on the types of fiber used. The composites consist of $\alpha$-Al2O3, Al, Si and pore. The composite grown at 100$0^{\circ}C$ exhibited better microstructure compared to that grown at 120$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.45 no.5
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• pp.297-302
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• 2008

To direct the evolution of nanostructure and immobilize ${\gamma}-Al_2O_3$ catalyst, nanocrystalline La-doped-$Al_2O_3$ powder were prepared by the sol-gel process with addition of an amphiphilic block copolymer template (pluronic P123: $(poly(ethyleneoxide)_{20}-poly(propyleneoxide)_{70}-poly(ethyleneoxide)_{20})$. The dried gel is amorphous, whereas heating at temperature above $700^{\circ}C$ leads to the formation of nanocrystalline ${\gamma}$ and ${\delta}-Al_2O_3$ and these two phases is kept until $1100^{\circ}C$. ${\alpha}-A1_2O_3 $starts to form at $1200^{\circ}C$ with $LaAl_{11}O_{18}$. The surface morphology and crystal structure has been observed by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). Solid state $^{27}Al$ MAS NMR indicates two types of local environment, i.e. octahedral and tetrahedral sites. The surface area and pore size was compared among these powders using the BET nitrogen adsorption measurements.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.9
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• pp.776-780
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• 2009

In this study, the opto-electric properties of EL devices with PMN dielectric layer with variation of firing tempereature were investigated. For the PMN dielectric layer process, the paste was prepared by optimization of quantitative mixing of PMN powder, $BaTiO_3$, Glass Frit, $\alpha$-Terpineol and ethyl cellulose. The EL device stack consists of Alumina substrate ($Al_2O_3$), metallic electrode (Au), insulating layer (manufactured PMN paste), phosphor layer (ELPP- 030, ELK) and transparent electrode (ITO), which is well structure as a thick film EL device. The phase transformation properties of PMN dielectric with various firing temperatures of $150^{\circ}C$ to $850^{\circ}C$ was characterized by XRD. Also the opto-electric properties of EL devices with different firing temperature were investigated by LCR meter and spectrometer. We found the best opto-electric property was obtained at the condition of $550^{\circ}C$ firing which is 3432.96 $cd/m^2$ at 1948.3 pF Capacitance, 40 kHz Frequency, 40% Duty, Vth+330 V voltage.

• Journal of the Korean Ceramic Society
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• v.41 no.4
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• pp.284-288
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• 2004

To improve mechanical properties of $Al_2$O$_3$/ZrO$_2$composites have been controlled dispersion of ultra low size ZrO$_2$ particles in $Al_2$O$_3$ ceramics by polymeric precursor method (Pechini process). In case of coprecipitation or mechanical mixing of ZrO$_2$ powders with $Al_2$O$_3$, homogeneous dispersion and controlling the ZrO$_2$ size were relatively difficult due to high sintering temperature. So the polyesterization process of Zr/Y(NO$_3$)$_3$-citric acid solution in ethylene glycol with the commercial sub-micron sized o(-alumina powder (Sumitomo AES-11(0.4 ${\mu}{\textrm}{m}$)) was adopted in order to obtain homogeneous dispersion of ZrO$_2$ in A1203. By this partial polyesterization process, the homogeneous dispersion of relatively low sized ZrO$_2$in $Al_2$O$_3$/ZrO$_2$composites was achieved at 1450∼1$600^{\circ}C$ of sintering temperature range and their mechanical properties were measured.

• Korean Chemical Engineering Research
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• v.44 no.3
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• pp.307-313
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• 2006

In order to improve the efficiency of methane steam reforming process, a part of the system which produces hydrogen from heavy hydrocarbon resources such as coal, we combined metal catalyst with CaO sorbent and fabricated catalyst/sorbent. To increase the porosity and the compressive strength of sorbent, carbon black and ${\alpha}-alumina$ were mixed with CaO powder during preparation. The effects of sorbent composition on the physical properties were investigated by SEM, TGA, BET, XRD, abrasion strength measuring device and adsorption-desorption instrument. Sorbent with 5 wt％ $Al_2O_3$ and 10 wt％ carbon black showed the best physical features with $7.61kg_f$ strength and 47％ $CO_2$ adsorption capability. Various metal catalysts such as Ni, Co and Fe were supported on the sorbent developed and 10 wt％ Ni/sorbent was selected for methane steam reforming process based on the result of reaction experiment. The reaction system using the catalyst/sorbent showed better $H_2$ productivity compared to the detached system with catalyst and sorbent, indicating the effectiveness of the system developed in this study.