• 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.

• Bulletin of the Korean Chemical Society
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• v.26 no.10
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• pp.1525-1528
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• 2005

The synthesis and characterization of ${K_3[Ru(C_2O_4)3]{\cdot}4H_2O\;(C_2O_4}^{2-}$ = oxalato anoin) complex are described, and its redox properties (in buffer solution of pH = 12) have been investigated. This complex is used for in situ generation of oxoruthenates complexes which have been characterized by electronic spectroscopy. Reaction of ${K_3[Ru(C_2O_4)3]{\cdot}4H_2O$ with excess ${S_2O_8}^{2-}$ in molar KOH generates trans-${[RuO_3(OH)_2]^{2-}/S_2O_8}^{2-}$ reagent while with excess ${BrO_3}^-$ in molar $Na_2CO_3$ generates ${[RuO_4]^-/BrO_3}^-$ reagent. Avoiding the direct use of [$RuO_4$] the organic-soluble $(n-Pr_4N)^+[RuO_4]^-$, (TPAP) has been isolated by reaction of $K_3[Ru(C_2O_4)3]{\cdot}4H_2O$ with excess ${BrO_3}^-$ in molar carbonate and n-$Pr_4$NOH. In a mixture of $H_2O/CCl_4$ ruthenium tetraoxide can be generated by reaction of $K_3[Ru(C_2O_4)3]{\cdot}4H_2O$ with excess ${IO_4}^-$. The catalytic activities of oxoruthenates that have been made from $K_3[Ru(C_2O_4)3]{\cdot}4H_2O$ towards the oxidation of benzyl alcohol, piperonyl alcohol, benzaldehyde and benzyl amine at room temperature have been studied.

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.3
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• pp.291-302
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• 2004

The CuO/$3AL_2O_3{\cdot}2SiO_2$ catalyst impregnated ceramic candle filters for nitrogen oxides removal were prepared by porous mullite($3AL_2O_3{\cdot}2SiO_2$) support and CuO catalyst deposited on this support to achieve uniformly dispersed CuO deposition, which are impregnated into the pores of available alumino-silicate ceramic candle filter. The CuO/3$AL_2O_3{\cdot}2SiO_2$ catalyst impregnated ceramic candle filters were characterized by XRD, BET, air permeability, pore size, SEM and catalytic tests in the reduction of NOx by NH$_3$. The observed effects of CuO/3$AL_2O_3{\cdot}2SiO_2$ impregnated ceramic candle filters in SCR reaction are as follows : (1) when the content of CuO catalyst increased further, activity of NO increased. (2) NO conversion at first increased with temperature and then decreased at high temperatures (above 40$0^{\circ}C$), possibly due to the occurrence of the ammonia oxidation reaction. (3) In pilot plant test for 3 months, NO conversion was greater than 90%.

• Korean Chemical Engineering Research
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• v.45 no.3
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• pp.298-303
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• 2007

Several combinations of ozone based advanced oxidation processes were tested for the treatment of red water (RW) containing recalcitrant chemical pollutants produced from 2,4,6-trinitrotoluene (TNT) manufacturing process. $O_3$, $UV/O_3$, $UV/O_3/H_2O_2$, $UV/O_3/H_2O_2/Fe^{2+}$ processes were tested for the treatment of RW. The order of organic and color removal efficiency was found to be : $O_3{\leq}UV/O_3$ < $UV/O_3/H_2O_2$ < $UV/O_3/H_2O_2/Fe^{2+}$. The optimum conditions for the removal of organic and color in the $UV/O_3/H_2O_2/Fe^{2+}$ process were 0.053 g/min of ozone flow rate, 10 mM of $H_2O_2$ concentration and 0.1 mM of $FeSO_4$ concentration. Organic and color removal efficiencies were 96 and 100 % respectively in the $UV/O_3/H_2O_2/Fe^{2+}$ process. tert-butyl alcohol (t-buOH) was used as the hydroxyl radical scavenger. Enhancement of hydroxyl radical production was achieved by the combination of ozone with several oxidants such as UV, $H_2O_2$, $Fe^{2+}$.

• Journal of the Korean Ceramic Society
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• v.31 no.6
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• pp.629-636
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• 1994

The ferrimagnetic glass-ceramics in the system Fe2O3-CaO-SiO2 for hyperthermia were investigated. Glasses could be prepared up to the content of 40 wt% of Fe2O3 and below the weight ratio of 1.0 of CaO/SiO2. The maximum saturation magnetization and the maximum coercive force were 29.85 emu/g and 340.1 Oe respectively, for a glass 40Fe2O3.20CaO.40SiO2 composition heat-treated at 95$0^{\circ}C$ for 8 hours. And for a glass 40Fe2O3.30CaO.30SiO2 composition the maximum saturation magnetization and the maximum coercive force were 18.47 emu/g and 374.4 Oe heat-treated at 1,00$0^{\circ}C$ and 90$0^{\circ}C$ for 8 hours respectively. The maximum hysteresis loss was 1,726.3 cal/g for a glass 40Fe2O3.20CaO.40SiO2 composition heat-treated at 95$0^{\circ}C$ for 8 hours. It was found that the ferrimagnetic Fe2O3.CaO.SiO2 glass-ceramics was little injurious to human body as results of biocompatibility test and biotoxicity test.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1209-1216
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• 1996

MoSi2-Al2O3 composites were prepared by thermal explosion mode of self-propagating high temperature syn-thesis (SHS) using element powders of MoO3 Mo Si and Al. The combustion products of MoSi2 which have 10, 20, 30 and 40 wt% Al2O3 showed the molten state in the range of Mo to MoO3 6:1-9.5:1, 2:1-8:1, 1:1-5:1, and 1:1-3:1 (molar ratio) respectively. The combustion products which made least seperation the molten phase from the slag phase were in Mo/MoO3=9, 5:1, 8:1, 5:1 and 3:1 (molar ratio) respectively. Particles size of MoSi2 and Al2O3 in the combustion product were decreased as the molar ratio of Mo to MoO3 increase. By XRD analysis only MoSi2 and $\alpha$-Al2O3 peaks were identified in the combusion products, In case of MoSi2 containing 20wt% Al2O3 5.1wt% Al existed into MoSi2 grains and 30.7wt% Si and 7.7wt% Mo existed into Al2O3 grains. The relative density of MoSi2 containing 10, 20, 30 and 40 wt% Al2O3 were 82.7, 85.2, and 81.9% respectively. The fracture strength of MoSi2-Al2O3 composites increased with increasing Al2O3 and that of MoSi2-20wt% Al2O3 composite was 195 MPa.

• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.139-145
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• 1989

An eutectic melt in the system(Bi2O3)0.85·(Nb2O5)0.15-6Bi2O3·SiO2 was unidirectionally solidfield at a rate of 0.5mm/h under a thermal gradient of 100℃/cm. Double crucibles and seed crystal plate were used in order to botain the composite crystals which had uniform microstructure throughout the ingot. The obtained composite crystals showed uniform microstructure, in which needle-like δ-(Bi2O3)0.85·(Nb2O5)0.15 crystals were arrayed in parallel in a matrix of γ-6Bi2O3·SiO2 single crystal. It was found that the <110> direction of δ-(Bi2O3)0.85·(Nb2O5)0.15 crystal was essentially parallel to the <111> direction of γ-6Bi2O3·SiO2 crystal in the composite crystals. A transverse thin plate of the composite crystals showed a high resolution optical transmission like an optical fiber array, and sharp chatoyancy was observed in the cabochon shaped composite crystals. Then, this may be useful for applications such as screen of a cathode ray tube or artificial cat's eye gem stones.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.435-435
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• 2011

The electronic structure and various physical properties of CeO2, Ce2O3, PrO2, and Pr2O3 have been studied from the framework of Ab-initio by the all-electron projector-augmented-wave (PAW) method, as implemented VASP (Vienna Ab-initio Simulation Package). The generalized gradient approximation (GGA) with effective U (Ueff) has been used to explain the strong on-site Coulomb repulsion among the localized Ce 4f electrons. The dependence of selected observables of these materials on the Ueff parameter has been scrutinized. The studied properties contain lattice constants, density of states, and reaction energies of CeO2, Ce2O3, PrO2, and Pr2O3. For CeO2 and PrO2, the GGA(PBE)+U results are in good agreement with experimental data whereas for the computational calculationally more demanding Ce2O3 and Pr2O3 both approaches give comparable accuracy. This results represent that by choosing an appropriate Ueff it is possible to reliably describe structural and electronic properties of CeO2, Ce2O3, PrO2, and Pr2O3, which enables modeling of oxygen reduction reaction processes involving ceria-based materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.37-40
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• 2003

Amorphous $Al_2O_3$ nanotubes have been fabricated by utilizing the ZnO nanowires as template with wet etching method. ZnO nanowires synthesized by thermal evaporation are conformally coated with $Al_2O_3$ by atomic-layer deposition(ALD) method. The $Al_2O_3$-coated ZnO nanowires are of core-shell structure; ZnO core nanowires and $Al_2O_3$ shells. When the $ZnO/Al_2O_3$ core-shell structure is dipped in $H_3PO_4$ solution at $25^{\circ}C$ for a 6 min, the core ZnO materials are completely etched, and only $Al_2O_3$ nanotubes are remained. This nanotube fabrication is technically easier than others, and simply approachable. Transmission electron microscopy shows that the $Al_2O_3$ nanotubes have various thicknesses that can be controlled.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1331-1336
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• 1995

The glass-ceramics for ferro-electric were made from compositions of 70PbO.16TiO2.8SiO2.4B2O3.2AlPO4 (wt%) and 67.5PbO.20TiO2.8.5SiO2.2B2O3.2AlPO4 (wt%). The crystallization kinetics for PbTiO3 crystalline phase formation from glass was studied using non-isothermal DSC techniques. The values of activation energy, ΔE using variables of heating rate and temperature were calculated at various reaction fractions obtained from peak area over DSC. The results indicated that activation energy was lowest at 60% reaction fractions and the activation energy of glass containing 20.0 wt% TiO2 is higher than that of glass containing 16.0 wt% TiO2. The crystallization mechanism was three dimensional growth (n=4).