• Korean Chemical Engineering Research
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• v.46 no.4
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• pp.806-812
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• 2008

The ammonia decomposition reaction has been of increasing interest as a means of treating ammonia in flue gas in the presence of precious metal catalyst. Various catalysts, $Pt-Rh/Al_2O_3$, $Pt-Rh/TiO_2$, $Pt-Rh/ZrO_2$, $Pt-Pd/Al_2O_3$, $Pd-Rh/Al_2O_3$, $Pd-Rh/TiO_2$, $Pd-Rh/ZrO_2$, $Pt-Pd-Rh/Al_2O_3$, $Pd/Ga-Al_2O_3$, $Rh/Ga-Al_2O_3$, and Ru/Ga-$Al_2O_3$, were synthesized by using excess wet impregnation method. Using a homemade 1/4" reactor at $10,000{\sim}50,000hr^{-1}$ of space velocity in the presence of precious metal catalyst ammonia decomposition reactions were carried out to investigate the catalyst activity. The inlet ammonia concentration was maintained at 2,000 ppm, with an air balance. Both $T_{50}$ and $T_{90}$, defined as the temperatures where 50% and 90% of ammonia, respectively, are converted, decreased significantly when alumina-supported catalysts were applied. In terms of catalytic performance on the ammonia conversion in the presence of hydrogen sulfide, $Pt-Rh/Al_2O_3$ catalyst showed no effect on the poisoning caused by hydrogen sulfide. These results indicate that platinum-rhodium bimetallic catalyst is a useful catalyst for ammonia decomposition.

• Journal of the Korean Ceramic Society
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• v.25 no.4
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• pp.364-372
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• 1988

The mechanical properties and microstructure of ceramics of the system Al2O3-ZrO2-Y2O3 sintered at 1$650^{\circ}C$ for 2h after powder preparation by the precipitation method from Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were investigated. The Al2O3-ZrO2-Y2O3 ceramics sintered at 1$650^{\circ}C$ for 2h after mixing alpha-Al2O3 and ZrO2-Y2O3 powders, both were separately precipitated and calcined, were found to have the relative density higher than 97.5% so that the strengthening and toughening mechanisms could be explained mainly as the stress-induced phase transformation. On the other hand, the sintered bodies prepared by co-precipitating the three starting materials were measured to have the relative density lower than 85% so that the degradation of strength were observed above 15 vol% ZrO2 contents due to the high porosity by which the effect of stress-induced phase transformation was assumed to be depressed.

• Journal of the Korean Ceramic Society
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• v.22 no.1
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• pp.11-18
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• 1985

The effect of stress induced phase transformation on $Al_2 O_3$ matrix dispersed with $ZrO_2-Y_2O_3$ has been studied. In order to determinate the mechanical properties three $Al_2O_3-ZrO_2$ composite series containing 1, 3 and 5 mole% $Y_2O_3$ were prepared. The starting materials were $Al_2O_3$ and $ZrO_2-Y_2O_3$ which was prepared from the aqueous solution of high purity $YCl_3$.$6H_2O$ and $ZrOCl_2$.$8H_2O$. Powder mixtures of $Al_2O_3-ZrO_2$ containing $Y_2O_3$ have been prepared by ball-milling with methanol and the samples were formed by isostatic press and sintered at 150$0^{\circ}C$ for 2hrs. After sintering. the specimens were polished for mechanical determination. The relative density of sintered specimens were also measured. It was found that the addition of 1, 3mole% to {{{{ { ZrO}_{2 } }} allowed full retention of the tetragonal phase in $Al_2O_3-ZrO_2$ but partially stabilized zirconia (PSZ) was produced by additions of 5 mole% $Y_2O_3$.The critical stress-intensity factor KIc of $A_2O_3-ZrO_2$ (containing 1 mole% $Y_2O_3$) composite materials increased with increasing $ZrO_2$ content, The maximum value of KIC=7Mn/$m^3$/2 at 20 mole% $ZrO_2$ exhibited about twice that of the $Al_2 O_3$ The modulus of rupture exhibited a trend similiar to KIC The maximum value of MOR was 580MN/m2. As the amount of Y2O3 increase it was observed that the maximum of KIC and MOR decreased : Additions of 3 mole% $Al_2O_3$ $Y_2O_3$ allowed the maximum of KIC 6MN/$m^3$/2 MOR 540MN/$m^2$ at 15 mole% $ZrO_2$ additions of 5 mole% $Y_2O_3$ allowed the maximum of KIC 5MN/$m^3$/2 MOR 410MN/$m^2$ at 10 mole% $ZrO_2$.

• Journal of the Korean Ceramic Society
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• v.27 no.1
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• pp.55-61
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• 1990

Effect of Al2O3 addition on the mechanical properties and microstructure of Ce-TZP were studied. 12, 14, 16Ce-TZP containing 0-40wt% Al2O3 were prepared by sintering at 155$0^{\circ}C$ for 2h. in air. Density, linear shrinkage, bending strength, Vickers hardness, microstructuer and the amount of stress induced phase transformation were examined. Vickers hardness increased linearly with increasing amounts of Al2O3. The amount of transformation and fracture toughness decreased linearly with increasing amount of Al2O3. Linear shrinkage and relative density decreased with increasing Al2O3 content in all composition of Ce-TZP. Grain growth of Ce-TZP was inhibited by Al2O3 dispersion and fracture mode of Ce-TZP/Al2O3 composites transformed from intergranular to transgranular fracture as the amount of Al2O3 increased. TEM observation revealed that Al2O3 particles were located mainly at grain boundaries of ZrO2.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.836-839
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• 2003

We have synthesized some phosphors in the system $CaO-Y_{2}O_3-Al_{2}O_{3}$ by combinatorial polymerized-complex method. Composition and synthetic temperature of phosphors in the liblary was screened from the emission intensities of individual samples under VUV excitation. In $Tb^{3+}$-activated $CaO-Y_{2}O_3-Al_{2}O_{3}$, green phosphors showing good intensity were found to be $CaYAl_{3}O_{7}$, $CaYalO_{4}$, $YAlO_{3}$, $Y_{3}Al_{5}O_{12}$, $Y_{4}Al_{2}O_{9}$, $Ca_{3}Al_{2}O6$.

• Korean Journal of Materials Research
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• v.12 no.6
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• pp.493-498
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• 2002

$Al_2O_3$ is a promising gate dielectric because of its high dielectric constant, high resistivity and low leakage current. Since $OH^-$ radical in $Al_2O_3$ films deposited by ALD using TMA and $H_2O$ degrades the good properties of $Al_2O_3$, TMA and $O_3$ were used to deposite $Al_2O_3$ films and the effects of $O_3$ on the properties of the $Al_2O_3$ films were investigated. The growth rate of the $Al_2O_3$ film under the optimum condition was 0.85 $\AA$/cycle. According to the XPS analysis results the $OH^-$ concentration in the $Al_2O_3$ film deposited using $O_3$ is lower than that using $H_2O$. RBS analysis results indicate the chemical formula of the film is $Al_{2.2}O_{2.8}$. The carbon concentration in the film detected by AES is under 1 at%. SEM observation confirms that the step coverage of the $Al_2O_3$ film deposited by ALD using $O_3$ is nearly 100%.

• Bulletin of the Korean Chemical Society
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• v.28 no.4
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• pp.647-651
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• 2007

In order to investigate the excited-state intramolecular proton transfer (ESIPT) process of dihydroxyanthraquinones (DHAQ; 1,5-DHAQ and 1,8-DHAQ) in organic-inorganic hybrid matrices, transparent SiO2, SiO2- Al2O3, and Al2O3 matrices chemically bonded with DHAQ were prepared using a sol-gel technique. The absorption maxima of 1,5- and 1,8-DHAQ in SiO2 matrices are observed at around 420 nm, whereas those of DHAQ in both SiO2-Al2O3 and Al2O3 matrices are markedly shifted to longer wavelength compared with those in SiO2 matrix. This indicates that DAHQ forms a chemical bond with an Al atom of Al2O3. The DHAQ in SiO2 matrix shows a markedly Stokes-shifted emission which is originated from the ESIPT in DHAQ. Based on the emission lifetimes of DHAQ, the ESIPT of DHAQ was found to be strongly affected by the chemical interaction with Al atom in the Al2O3-related matrices.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.73-80
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• 1999

The effect of alloy compositions of the bond coating on the plasma sprayed-thermal barrier coatings was investigated. The performance of the coating composed of Rene80/NiCrAl/ZrO$_2$-CeO$_2$-Y$_2$O$_3$ and Rene80/CoNiCrAlY/ZrO$_2$-CeO$_2$-Y$_2$O$_3$was evaluated by isothermal and thermal cyclic test in an ambient atmosphere at 115$0^{\circ}C$. The failure of Rene80/NiCrAl/ZrO$_2$-CeO$_2$-Y$_2$O$_3$ coatings was occurred at the bond coating/ceramic coating interface while Rene80/CoNiCrAlY/ZrO$_2$-CeO$_2$-Y$_2$O$_3$ coating was failed at the substrate/bond coating interface after thermal cyclic test. The lifetime of Rene80/NiCrAl/ZrO$_2$-CeO$_2$-Y$_2$O$_3$coatings was longer than Rene80/CoNiCrAlY/ZrO$_2$-CeO$_2$-Y$_2$O$_3$coating. The oxidation rate of the NiCrAl bond coating examined by TGA was lower than CoNiCrAlY bond coatings. In summary, these results suggest that Rene80/CoNiCrAlY/ZrO$_2$-CeO$_2$-Y$_2$O$_3$system as thermal barrier coating be not suitable considering the durability of the coating layer for high temperature oxidation and thermal stress.

• Proceedings of the Korean Ceranic Society Conference
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• 2002.10a
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• pp.30.1-30
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• 2002

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.7
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• pp.394-399
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• 2000

The mechanical and electrical properties of pressed and annealed $\beta-SiC-TiB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of $Al_2O_3+Y_2O_3$. Phase analysis of composites by XRD revealed $\alpha$-SiC(6H), TiB2, and (Al5Y3O12). Reaction between Al2O3 and $Y_2O_3$ formed YAG but the relative density decreased with increasing $Al_2O_3+Y_2O_3$ contents. The Flexural strength showed the value of 458.9 MPa for composites added with 4 wt% $Al_2O_3+Y_2O_3$ additives at room temperatures. Owing to crack deflection and crack bridging, the fracture toughness showed 6.2, 6.0 and 6.6 MPa.m1/2 for composites added with 4, 8 and 12 wt% Al2O3+Y2O3 additives respectively at room temperature. The resistance temperature coefficient showed the value of $3.6\times10^{-3},\; 2.9\times10^{-3}\; and\; 3.0\times10^{-3} /^{\circ}C$$^{\circ}C$ for composite added with 4, 8 and 12 wt% $Al_2O_3+Y_2O_3$additives respectively at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25^{\circ}C\; to\; 700^{\circ}$.