• Journal of the Korean Ceramic Society
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• v.41 no.6
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• pp.481-484
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• 2004

TiO$_2$ and TiO$_2$-CdS powders which were expected to be highly activated photocatalysts were prepared using supercritical fluid method (SCF). The prepared photocatalyst TiO$_2$ powders were crystalline of anatase and ultrafine spherical powders with large specific surface area. When photodecompositoion reaction was done with TiO$_2$ powders prepared by SCF as a photocatalyst in DCA (Dichloroactic Acid) solution, a hazardous organic compound, the photocatlyst, properties of TiO$_2$ powders prepared by SCF were better than that of commercial TiO$_2$ powders.

• Journal of the Korean Ceramic Society
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• v.30 no.4
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• pp.316-324
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• 1993

Three types of dispersed, coated and mechanically mixed SiC reinforced Al2O3 composite powders were used to investigate the effect of composite powder type on sintering characteristics and properties of Al2O3-SiC composites. Sinterability of coated type composite powders was superior to that of other composite powders when they were pressureless sintered at 1500~1$700^{\circ}C$ for 2h in Ar atmosphere. However, sinterabilities (>98% TD) of each type of composite powders were similar when they were hot pressed at 180$0^{\circ}C$ for 1h under 30MPa in N2 atmosphere. SiC powders were randomly distributed in the specimen prepared from dispersed type composite powders, whereas homogeneously distributed for coated type specimens. It was found that SiC powders inhibited the grain growth of Al2O3, and fracture toughness was increased by the increment of crack growth resistance due to residual stress by secondary SiC particles within Al2O3 grains.

• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.7-10
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• 2005

[ $TiO_{2}-ZrO_{2}$ ] powders were successfully synthesized by the sol-gel process using titanium iso-propoxide as a precursor. The amorphous $TiO_{2}$ particles, 70 nm in size, homogenously adhered to the surface of $ZrO_{2}$ the powders. After calcination at $450^{circ}C$, most of the $TiO_{2}$ powders appeared as an anatase type, whereas they changed to a rutile phase at $750^{circ}C$. For comparison of photocata­lytic activity, $TiO_{2}-ZrO_{2}$ nano-sized powders calcined at $450^{circ}C,\;600^{circ}C,\;and\;750^{circ}C$ were used. In the $TiO_{2}-20wt\%$ $ZrO_{2}$ powders cal­cined at $450^{circ}C$, there was excellent removal efficiency of Methyl Orange (MO). For the calcination temperature increased, $TiO_{2}­ZrO_{2}$ nano-sized powders increased $ZrO_{2}$ contents showed the good photoactivity for the photooxidation of MO.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.168.2-168
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• 2003

• Proceedings of the Korean Ceranic Society Conference
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• 1986.12a
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• pp.87-113
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• 1986

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1376-1383
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• 2006

Densification behavior of various metal and ceramic powders was investigated under cold compaction. The Cap model was proposed by using the parameters involved in the yield function for sintered metal powder and volumetric strain evolution under cold isostatic pressing. The parameters for ceramic powder can also be obtained from experimental data under triaxial compression. The Cap model was implemented into a finite element program (ABAQUS) to compare with experimental data for densification behavior of various metal and ceramic powders under cold compaction. The agreement between finite element calculations from the Cap model and experimental data is very good for metal and ceramic powder under cold compaction.

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.688-693
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• 2008

This paper presents a study on the photocatalytic reaction about the composite particles of $TiO_2$-coated phosphors under visible light irradiation. Nanocrystalline titanium dioxide layers were directly coated on the alkaline earth aluminate phosphor, $CaAl_2O_4:Eu^{2+},\;Nd^{3+}$ particles by an sol-gel processing method. The photocatalytic reaction was analyzed with the degradation of methylene blue (MB) aqueous solution under UV and visible light irradiations. $TiO_2$-coated phosphor powders showed different photocatalytic mechanism, compared with pure $TiO_2$ (P-25, Degussa). Under UV-irradiation, $TiO_2$-coated phosphor powders showed slow photocatalytic reactivity in the early stage and fast in the latter, compared with that of pure $TiO_2$. However, $TiO_2$-coated phosphor powders showed much faster photocatalytic reactivity than that of pure $TiO_2$ under visible irradiation. In addition, the characterizations of the $TiO_2$-coated phosphor powders were conducted by a X-ray diffractometer (XRD), transmission electron microscope (TEM), and energy dispersive spectroscopy (EDS).

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.551-557
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• 1992

X-ray diffraction patterns, IR spectra and zeta-potentials of silicon nitride and $\beta$-Sialon powders were investigated before and after surface manipulations. $\beta$-Sialon powder was produced from Hadong Kaolin by the carbothermic reduction and simulataneous nitridation. Isoelectric points of as-prepared Si3N4 and $\beta$-Sialon powders were 8.4 and 7.4, respectively. After both silicon nitride and $\beta$-Sialon powders were oxidized at 80$0^{\circ}C$ for 24 h in air, the isoelectric points of these powders corresponded to that of silica (pH=3). I case of the addition of Darvan C as deflocculant, its isoelectric point was 3 and zeta-potential was nearly constant in the range of pH 5~12. When SN 7347 was used as deflocculant, its isoelectric point was 8.3 and zeta-potential over -156 mV was measured above pH 11.

• Journal of the Korean Ceramic Society
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• v.27 no.1
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• pp.127-135
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• 1990

Characteristics of the sol-gel derived (Ba1-xPbx)TiO3 powders are compared with those of powders prepared by the calcining ofmixed oxides method (CMO) and molten salt synthesis method(MSS). The sol-gel derived powder has a higher surface area (50$m^2$/g) than those of CMO(3.8$m^2$/g) and MSS(11.5$m^2$/g) derived powders. In the sol-gel method, the (Ba1-xPbx)TiO3 was synthesized at $600^{\circ}C$ for 1hr, indicating that this method has a crystalline temperature 20$0^{\circ}C$-30$0^{\circ}C$ lowr than those of the CMO and MSS methods.

• Journal of the Korean Ceramic Society
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• v.28 no.7
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• pp.503-508
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• 1991

High pure and fine mullite powders were synthesized from Al-secbutoxide[Al(OC4H9)3] and TEOS[Si(OC2H5)4] (SiO2/Al2O3=2/3 mole). Sol-Gel process by partial hydrolysis technique, as it were, first, TEOS was partially hydrolysized and then mixed with Al-secbutoxide for complete hydrolysis was used. The mullite precursor was synthesized within 30 hrs, which was reduced about a half of synthetic time in comparison with the other's study. Al-Si spinel was formed at 980℃ and mullite crystal was formed at 1200℃. Mullite powders synthesized in this study was spherical type like those of the other studies and particle sizes were very fine. Also mullite powders calcined at 1,600℃ had a stoichiometric composition (3Al2O3·2SiO2) and lattice constants were coincided with known theoretical values.