• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.980-981
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• 2006

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve full density of Carbon nanotube (CNT)/metal matrix composites with superior mechanical properties by improved particle bonding and least grain growth, which were considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (equal channel angular pressing), the most promising method in SPD, was used for the CNT/Cu powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 route C passes was conducted at room temperature.

• Journal of the Korean Ceramic Society
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• v.43 no.9 s.292
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• pp.515-518
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• 2006

The microstructure of $ZrO_2$ toughened $Al_2O_3$ ceramics was carefully controlled so as to obtain dense and fine-grained ceramics, thereby improving the properties and reliability of the ceramics for capillary applications in semiconductor bonding technology. $Al_2O_3-ZrO_2(Y_2O_3)$ composite was produced via Ceramic Injection Molding (CIM) technology, followed by Sinter-HIP process. Room temperature strength, hardness, Young's modulus, thermal expansion coefficient and toughness were determined, as well as surface strengthening induced by the fine grained homogenous microstructure and the thermal treatment. The changes in alumina/zirconia grain size, sintering condition and HIP treatment were found to be correlated.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.221-227
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• 1989

To investigate the development and densification YBa2Cu3O7-x(1-2-3) superconducting phase, the 1-2-3 phase powders have been prepared by citrate and nitrate processes with changing calcination temperature. Nearly pure 1-2-3 phase peaks have been obtained by calcining the precursor in air at 90$0^{\circ}C$ for 2.5h in citrate process but at 95$0^{\circ}C$ for 2.5h in nitrate process. The sintering density of citrate derived sample calcined at 80$0^{\circ}C$ has been about 4% higher than that calcined at 90$0^{\circ}C$, although the compacting density has been lower at 80$0^{\circ}C$ calcination. This can be explained that the 1-2-3 phase particles formed at 80$0^{\circ}C$ have reactive sub-micron size which has good sinterbililty.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.267-275
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• 1989

YBa2Cu3O7-x oxide superconductors were fabricated by sintering and hotisostatic pressing (HIP), and their microstructures and properties were compared with each other. Thougha part of the second phase was observed along grain boundaries, their structures were consisted of single (123) phase and they had many porosities. But, porosities were remakably reduced by Hiping and the densification was brought about. The structure of (123) compound also showed a number of twins, which are typical of high Tc superconductors. The on-set temperature of YBa2Cu3O7-x compound sintered at 96$0^{\circ}C$ in oxygen and hipped at 88$0^{\circ}C$ was highest, but that shwoed 0 resistance at 87$^{\circ}$K, which is a little lower than the compound sintered at 96$0^{\circ}C$. HIP treatment also increased the critical current density of as-sintered compound. However, its value was low, which may be ascribed to the many pores of starting-sintered compact and partially to the second phase along grain boundaries.

• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.646-650
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• 1992

Effect of Li2O.4B2O3 frit addition on microstructural and thermal expansion behaviour of the $\beta$-spodumene ceramics made from kaolinite was investigated. With 2.0~4.0 wt% frit addition, the densification by liquid phase sintering caused low water absorption below 3% and enhancement of beding strength. As the amount of frit addition was increased, thermal expansion coefficient was increased to large scale, but in 2 wt% frit addition, its thermal expansion coefficient was constrained to 1.92$\times$10-6$^{\circ}C$-1.

• Journal of the Korean Ceramic Society
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• v.29 no.2
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• pp.127-135
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• 1992

It has been reported that natural petalite showed a low negative thermal coefficient and wide coefficient and wide coexisting region with liquid phase in Li2O-Al2O3-SiO2 system. Therefore, we investigated variation of microstructure and thermal and mechanical properties when the amount of SiO2 content in petalite compound and MgO addition to it compound were changed. As SiO2 content exceeded 80 wt%, crystal phases of $\beta$-cristobalite and $\beta$-spondumene solid solution were formed. Generally, the densification and bending strength were increased by the addition of MgO, but the positive thermal coefficient was found in the case of MgO 10 wt% addition because of second phase and glassy phase.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.109-110
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• 2006

We have studied the effect of C/Ti atomic ratio of TiCx (x=0.5, 0.75 and 1.0) raw powder on the properties of the Ti-Mo-WTiC sintered hard alloy. The decrease of C/Ti atomic ratio accelerated the densification in the sintering process. The hardness was remarkably improved up to 1350HV with decreasing the C/Ti atomic ratio because of increase of TiCx phase volume content and its fine dispersion. From the results of electro-chemical tests in acid and 3% NaCl solutions, it was obvious that every alloy had excellent corrosion resistance, which meant about 200 times better than that of WC-Co cemented carbide.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.555-556
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• 2006

The study examines hardness pattern of SH737-2Cu-.9C samples transient liquid phase sintered at different temperatures viz. $1120^{\circ}C$, $1180^{\circ}C$ and $1250^{\circ}C$, heat treated by various methods and then tempered at different temperatures. Sintered samples were characterized for density and densification parameter, and austenitized at $900^{\circ}C$, subsequently cooled by four different methods viz. annealing, normalizing, oil and brine quenching. Hardness pattern was found minimum for air cooled and maximum for brine quenched, and samples sintered at $1250^{\circ}C$ had relatively higher hardness. The O.Q and B.Q samples were then tempered at $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$ and $700^{\circ}C$. Hardness pattern typically showed secondary hardness taking place, with maximum around $600^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.1
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• pp.33-38
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• 2009

The effect of ${Y_2}{O_3}$ as a sintering additive on thermal conductivity and microstructure of pressureless sintered AIN ceramics was investigated at sintering temperature range from 1,700 to $1,900^{\circ}C$. ${Y_2}{O_3}$ added AIN specimens showed higher densification rate than pure AIN because of the formation of the yttrium aluminates secondary phase by reaction of ${Y_2}{O_3}$ and ${Al_2}{O_3}$ of AIN surface. The thermal conductivity of AIN specimens was promoted by the addition of ${Y_2}{O_3}$ in spite of the formation of secondary phase in AIN gram boundaries and grain boundary triple junction, because ${Y_2}{O_3}$ addition could reduced the oxygen contents in AIN lattice which is primary factor of thermal conductivity. The them1al conductivity of AIN specimens was promoted by increasing sintering time because the increases of average grain size and the elimination of secondary phases from the grain boundary due to the evaporation. Particularly. the thermal conductivity of AIN specimen sintered at $1,900^{\circ}C$ for 5 hours improved over 20 %. $141\;Wm^{-1}K^{-1}$, compared with the specimen sintered at $1,900^{\circ}C$ for 1 hour.

• Journal of the Korean Ceramic Society
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• v.49 no.2
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• pp.197-203
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• 2012

In this study, in order to improve densification of $La_{0.8}Ca_{0.2}Cr_{0.9}Co_{0.1}O_{3-\delta}$ (LCCC), which is known for one of the most proper candidate interconnector materials in the solid oxide fuel cells, $CaCrO_4$ was prepared via solid oxide synthesis route and added to the LCCC with different amount and particle sizes. As the amount of the $CaCrO_4$ increased, porosity of the sintered samples increased, and the pore size was proportional to the particle size of the $CaCrO_4$. This supports the fact that the $CaCrO_4$ phase forms liquid during sintering and permeate into the matrix leaving behind large pores. Then the liquid reacts with the matrix through the solid solution. However, when the samples were sintered with a slow ramp up rates, the porosity decreased. This is thought to be caused by the progressive solid solution of $CaCrO_4$ before the temperature reach to the melting temperature and forms a fluent amount of liquids. The sintering behavior of the LCCC with the addition of $CaCrO_4$ was analyzed through the transient liquid phase sintering on the basis of the microstructure observation and phase identification by x-ray diffraction.