• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.199-199
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• 2003

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.55-58
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• 2003

[ $YBa_2Cu_3Ox$ ](YBCO) oxide superconductor was prepared by sol-gel method to improve its superconducting properties, and it was made to be a fine powder, which has the same property of solid state reacted powder. $BaPbO_3$ was synthesized with $BaCO_3$, BaO, PbO, and $PbO_2$ and analyzed by XRD. YBCO superconductor was prepared by use of sol-gelled YBCO powder and additive $BaPbO_3$ and its critical temperature and transition temperature were shown as 91.9 K, 3.7 K respectively in case 20 wt.% $BaPbO_3$ was added to pure sol-gelled YBCO powder.

• Journal of Power System Engineering
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• v.12 no.3
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• pp.50-54
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• 2008

Various Sialon ceramics were fabricated by hot-pressing mixtures of $Si_3N_4$ with additive $Y_2O_3$ and $Al_2O_3$. The polished specimen of SiAlON $I{\sim}III$ went on increasing in strength by heat treatment, heat treated non-polished specimen were similar or up to polished specimen in strength. The polished specimen of both SiAlON IV and V showed a very high strength, but were not Increasing of strength by heat treatment. All specimens were fractured on the surface and at the inner flaws. Surface fractures were initiated from the polished surface flaw and corner flaw. Inner fractures were initiated from an internal defect.

• Korean Journal of Materials Research
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• v.3 no.3
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• pp.207-214
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• 1993

Glass-ceramic monoliths with an ultra-low thermal expansion coefficient have been synthesized by the sol-gel technique using metal alkoxides as starting materials and dimethyl formamide as a drying control chemical additive. The ternary gels: $Li_2O\cdot Al_2O_3\cdot 2, 4 or $6SiO_2$ were obtained by hydrolysis and polycondensation reactions of metal alkoxides of silicon, aluminum and lithium. To produce cylindrical crack-free gel monoliths, excess water was used to the starting solutions and drying rates were controlled precisely to prevent cracking. In conversion process ,${\beta}$-eucryptite, $Li_2O\cdot Al_2O_3\cdot 3SiO_2$ and P-spodumene with ,${\beta}$-quartz solid solution phase were obtained by heating at the range of 750 ~$1000^{\circ}C$. Above $800^{\circ}C$, the ,${\beta}$-spodumene phase increased while ,${\beta}$-eucryptite phase decreased. The thermal expansion coefficient of the crystallized specimens were -15~ $+5{\times}{10^{-7}}/{\circ}C$ over the temperature range from room temperature to $600^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.35 no.7
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• pp.726-732
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• 1998

• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.829-837
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• 1993

Chemically and geometrically homogeneous mixing of Si3N4 powders with sintering additives(YAG, 3Y2O3$.$5Al2O3) was attempted via coprecipitation method. X-ray dot maps for the additive elements(Al and Y) showed that the additives are evenly distributed in the powder mixture prepared by coprecipitation method(CP). TEM observation of the coprecipittion-treated Si3N4 powders revealed that they are covered with extremely fine crystallites of additive. The shift in isoelectric point(IEP) of Si3N4 powders from pH 6.7 to pH 7.9 after coprecipitation mixing gave another evidence for coating of Si3N4 powders with YAG additives. SIMS analysis for composition on the surface and in the matrix of mixed powders showed that the YAG additives are highly enriched on the surface of coprecipitation-treated Si3N4 powders. Especially when a small amount of additive was used, the effect of homogeneous additive distribution on densification was preceptible: After pressureless-sintering of powder compacts containing 5 mol% YAG at 1800$^{\circ}C$ for 0.5h, a sintered density of 96.5% theoretical was obtained from the specimens prepared bycoprecipitation in comparison with 93.8% from the mechanically-mixed one.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.3
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• pp.214-220
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• 1998

ZnO varistors are characterized by the features of excellent nonlinearity and surge withstand capability. In this paper, in order to investigate the use of ZnO varistor as surge absorption device in low voltage, metal oxide material($TiO_2$) was selected as control material of grain growth. Samples of ZnO varistors were fabricated with varying the contents, and then the microstructures and V-I characteristics were measured. It was observed by SEM that the mean grain size increased with the increase of the additive. From the measurement of V-I characteristics, it was observed that according to the increase of the quantity of $TiO_2$ as additive, the operating voltage was lowered.

• Journal of the Korea Safety Management & Science
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• v.15 no.3
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• pp.127-132
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• 2013

This study shows an air-purification test by the UV lamp on which TiO2 catalyst is deposited with glass fiber in the reactor chamber. This test was based on the fundamental data of air-purifier as assessing a removing ability on various contaminants such as CH3COOH, NH3, NO and SO2 as variation of the TiO2 coating, the wave of UV lamp, and the additive CaO. As a result, the highest decomposing removal ratio was shown when 5-times coated glass fiber was used. It can be due to the recombination reaction of electrons and electron-hole in the loaded CaO. Thus, the decomposing removal ratio increased as the recombination ratio decreased. In addition, it was confirmed that the decomposing removal ratio lowered when CaO was considerably deposited because it hided the lamp of OH-1 radical.

• Korean Journal of Materials Research
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• v.23 no.2
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• pp.104-111
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• 2013

In this study, GaN powders were synthesized from gallium oxide-hydroxide (GaOOH) through an ammonification process in an $NH_3$ flow with the variation of $B_2O_3$ additives within a temperature range of $300-1050^{\circ}C$. The additive effect of $B_2O_3$ on the hexagonal phase GaN powder synthesis route was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transformation infrared transmission (FTIR) spectroscopy. With increasing the mol% of $B_2O_3$ additive in the GaOOH precursor powder, the transition temperature and the activation energy for GaN powder formation increased while the GaN synthesis limit-time ($t_c$) shortened. The XPS results showed that Boron compounds of $B_2O_3$ and BN coexisted in the synthesized GaN powders. From the FTIR spectra, we were able to confirm that the GaN powder consisted of an amorphous or cubic phase $B_2O_3$ due to bond formation between B and O and the amorphous phase BN due to B-N bonds. The GaN powder synthesized from GaOOH and $B_2O_3$ mixed powder by an ammonification route through ${\beta}-Ga_2O_3$ intermediate state. During the ammonification process, boron compounds of $B_2O_3$ and BN coated ${\beta}-Ga_2O_3$ and GaN particles limited further nitridation processes.

• Proceedings of the Korean Ceranic Society Conference
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• 2002.10a
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• pp.79.2-79
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• 2002