• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2767-2774
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• 2024

In this study, investment casting shell waste successfully utilized to produce cordierite/mullite/zircon composites. Green pellets, consisting of investment casting shell waste, alumina, and magnesia, were prepared and sintered at temperatures between 1250 and 1350 ℃. The influence of the sintering temperature on the crystalline phase composition, densification behavior, flexural strength, microstructure, and radiation shielding properties of the cordierite/mullite/zircon composites is investigated. Phase analysis showed that characteristic cordierite peaks appear at 1250 ℃, but the complete conversation of silica from investment casting shell waste into cordierite requires a sintering temperature of at least 1300 ℃. Notably, the cordierite/mullite/zircon composite sintered at 1350 ℃ exhibited a sixfold increase in flexural strength compared to the ceramic composite directly fabricated from investment casting shell waste at the same sintering temperature. Furthermore, the effect of Y₂O₃ addition on composites' radiation shielding properties is investigated. The results show that the Y₂O₃ addition improves densification behavior, enhancing the shielding capabilities of the composites against fast neutron and gamma radiation. Our findings suggest that the developed ceramic composites show significant potential for gamma-ray and neutron shielding applications.

• Journal of the Korean Ceramic Society
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• v.49 no.3
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• pp.247-252
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• 2012

Crystal structure and chemical compositions of Plasma electrolytic oxidized layer of A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for plasma electrolytic oxidation was mixture of distilled water, $Na_2P_2O_7$, Cu, Cr metal salts and KOH. ${\eta}$-Alumina, as well as ${\alpha}$-alumina, was main crystal phase. Another crystals such as $(Al_{0.948}Cr_{0.052})_2O_3$ and $(Al_{0.9}Cr_{0.1})_2O_3$ were also formed in the oxide layer. It was thought that the effect of electrolyte compositions on the physical properties and crystal system of PEO layers was greater than the effect of Al alloy composition variation.

• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1083-1089
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• 2002

Densification and grain growth behavior of MgO and -doped alumina ceramics were investigated. MgO was found to inhibit grain growth and to promote densification, but acted to promote grain growth more than densification. The density which showed the maximum shrinkage rate was investigated in the plot of shrinkage rate versus density. The data suggests that the maximum shrinkage rate separates the two kinetic regimes, below the density of maximum shrinkage, the regime associated with densification and above the maxima, the regime associated with the grain growth. The plot exhibits a maximum which shifts to higher temperatures with MgO doping and to lower with doping.

• Journal of the Korean Ceramic Society
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• v.41 no.6
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• pp.471-475
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• 2004

TiO$_2$, SiO$_2$, and PBA(Pseudo Boehemite Alumina) sol were prepared by sol-gel process. The particle sizes of these sol exhibited uniform 10∼30 nm. As the amount of SiO$_2$ sol increased, the temperature of phase transition (from anatase phase to rutile phase) was raised temperature than $600^{\circ}C$, which attributed to the enhanced photocatalyst properties. Also, the anatase phase was obtained with very small amount of the rutile phase from the addition of SiO$_2$ (10∼30 wt%) at annealing temperature of 120$0^{\circ}C$. The specimen with 20 wt% SiO$_2$ sol exhibited the maximum photocatalyst properties. But, the specimen with PBA sol did not affect photocatalytic activity due to the presence of rutile phase.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.311-318
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• 1998

The reaction bonded alumina ceramics with reinforced particles which have low shrinkage were pro-duced by blending of SiC or TiC or ZrO2 powders to the mixture of Al metal and Al2O3 powder. The powd-ers were attrition milled isostantically pressed and preheated tio 110$0^{\circ}C$ with a heating rate of $1.5^{\circ}C$/min The specimens were then sintered at the temperature range 1500 to 1$600^{\circ}C$ for 5 hours with a heating rate of 5$^{\circ}C$/min. The specimens showed 5-9% weight gain and 2-9% dimensional expansion through the complete oxidation of Al after preheating up to 11--$^{\circ}C$ the overall dimensional change of the specimens after the reaction sintering at 1500-1$600^{\circ}C$ was 6-12% The maximum densities were 92% theoretical. The fine grain-ed(average grain size :0.4 ${\mu}{\textrm}{m}$) microstructure were observed in the specimen with ZrO2 and SiC. But the microstructure of specimen with TiC was relatively coarse.(average grain size : 2.1 ${\mu}{\textrm}{m}$) The mullite phase was formed by the reaction of Al2O3 and SiO2 in a specimen with SiC. In the TiC contained specimen TiC was oxidized into TiO2 and finally reacted with Al2O3 to form Al2TiO5 during sintering.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1076-1086
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• 1994

This study covers synthetic effect of the various hydrothermal treatments on formation of artificially made kaolinite mineral. The hydrothermal treatment includes the temperature treatment with time duration, addition of seeds, particle size of the starting material used, pH variation and the different types of organic acids. A colloidal silica and alumina sol which are commercially available are used for this study. A colloidal silica and alumina sol are mixed by the atomic ratio of Al/Si = 1, based on the theoretical kaolinite composition and calcined at $600^{\circ}C$ for 8 hours duration. It was found that the kaolinitic clay mineral was well developed; thereby, the different patterns of crystalline mineral are appeared. Spherical type as a crystal form was distinctively formed at the temperature of 20$0^{\circ}C$ to 25$0^{\circ}C$ with short duration time, while platy type as a crystal was highly yielded at 300~35$0^{\circ}C$. Moreover, by adding more than 20 wt% of seed as the natural kaolinitic clay to the starting material is widely distributed and developed when 2 ${\mu}{\textrm}{m}$ or less particle size of the starting material is used; also, when they are heat-treated at the temperature of 25$0^{\circ}C$ with 5 hours duration. With respect of the effect of pH variation on formation of the synthetic kaolinite minerals, the crystalline minerals are highly yielded at less than pH 2 and gradually diminished at more than pH9. Regarding to the effect of different acids on development of the kaolinite mineral, the organic acids with high chelating capacity produces good formation of crystalline minerals; whereas, amine radical-(NH2) is not an effective agent to generate the crystalline minerals.

• Journal of the Korean Ceramic Society
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• v.40 no.2
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• pp.128-131
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• 2003

Formation of$B_4C/Al$composite by pressureless infiltration was investigated by lowering wetting angle via surface modification of $B_4C$powder with alumina precursor. Surface modification was confirmed by zeta potential analysis. The$B_4C/Al$composite was prepared by placing an Al 6061 disk on the$B_4C$preform and heating at $1030{\circ}C$/20 min under a flowing argon, but no infiltration took place for a bare $B_4C$ preform even at$1250{\circ}C$/30 min. Analysis of XRD and SEM showed the $Al_3BC$phase besides$B_4C$and Al, but no trace of deteriorative$A1_4C_3$.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1213-1219
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• 2003

Porous ceramics for microoganism carriers were prepared with amorphous alumina and pore formers by hydrothermal reaction, burn-out and wash-out method. Activated carbon with average size of 67,222, and 405 $\mu\textrm{m}$, organic polymer and inorganic salt were used as pore formers. Specimens were hydrothermally treated at 200$^{\circ}C$ for 24 h, heat-treated at 650$^{\circ}C$ for 5 h, and washed out at 80$^{\circ}C$ for 48 h. The formation of crystalline phase, porosity, pore size distribution and compressive strength were measured. The specimen with activated carbon was transformed to boehmite phase, but organic polymer and inorganic salt inhibited the aquohydroxoy complex gel and crystalline formation. The porous ceramics for microoganism carriers using activated carbon as a pore formers was successfully prepared, which is composed of ${\gamma}$-alumina phase with porosity of above 70 vol% and the compressive strength of 40 kgf/$\textrm{cm}^2$.

• Resources Recycling
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• v.14 no.4 s.66
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• pp.41-46
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• 2005

Waste aluminum dross is a major waste in the aluminum scrap smelters and its major components are alumina and metallic aluminum. In this study, waste aluminum dross was leached with sodium hydroxide solution to extract the remained aluminum into the solution, and aluminum hydroxide was recovered from the leached solution. The dross residue generated at the leaching step was recycled into alumina base ceramic materials through a series of treatments such as washing, drying and roasting. Also, a pilot plant was constructed and tested to demonstrate the developed technology. Four tons of waste aluminum dross could be processed per day. From the test run of the pilot plant, it was confirmed that the developed technology could be applied to commercialization.

• Transactions on Electrical and Electronic Materials
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• v.8 no.6
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• pp.241-245
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• 2007

[ $(Ba_{0.9-x}Sr_xCa_{0.10})TiO_3$ ] (x=0.33, 0.36) powders were prepared by sol-gel method. $(Ba,Sr,Ca)TiO_3$(BSCT) thick films, undoped and doped with $MnCO_3$ and $Yb_2O_3(0.1{\sim}0.7mol%)$, were fabricated by the screen printing method on the alumina substrate. The coating and drying procedure was repeated 6-times. The Pt bottom electrode was screen printing method on the alumina substrate. These BSCT thick films were annealed at $1420^{\circ}C$ for 2 hr in atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at $590^{\circ}C$ for 10 min. And then the structured and dielectric properties as a function of the doping amount of $Yb_2O_3$ were studied. As a result of the TG-DTA, exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All BSCT thick films showed XRD patterns of typical cubic peroveskite structure. The average thickness of BSCT thick films was about $70^{\mu}m$. The curie temperature and the dielectric constant decreased with increasing $Yb_2O_3$ doped content and the relative dielectric constant of the specimen, doped with 0.5 mol% $Yb_2O_3$ at BSCT(54/36/10), showed a best value of 5018 at curie temperature.