• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.5
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• pp.808-815
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• 2008

The composites were fabricated 61[vol.%] ${\beta}$-SiC and 39[vol.%] $TiB_2$ powders with the liquid forming additives of 8, 12, 16[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid by pressureless annealing at 1650[$^{\circ}C$] for 4 hours. The present study investigated the influence of the content of $Al_2O_3+Y_2O_3$ sintering additives on the microstructure, mechanical and electrical properties of the pressureless annealed SiC-$TiB_2$ electroconductive ceramic composites. Reactions between SiC and transition metal $TiB_2$ were not observed in the microstructure and the phase analysis of the pressureless annealed SiC-$TiB_2$ electroconductive ceramic composites. Phase analysis of SiC-$TiB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), ${\beta}$-SiC(3C), $TiB_2$, and In Situ YAG($Al_2Y_3O_{12}$). The relative density of SiC-$TiB_2$ composites was lowered due to gaseous products of the result of reaction between SiC and $Al_2O_3+Y_2O_3$. There is another reason which pressureless annealed temperature 1650[$^{\circ}C$] is lower $300{\sim}450[^{\circ}C]$ than applied pressure sintering temperature $1950{\sim}2100[^{\circ}C]$. The relative density, the flexural strength, the Young's modulus and the Vicker's hardness showed the highest value of 82.29[%], 189.5[Mpa], 54.60[Gpa] and 2.84[Gpa] for SiC-$TiB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature. Abnormal grain growth takes place during phase transformation from ${\beta}$-SiC into ${\alpha}$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. The electrical resistivity showed the lowest value of 0.0117[${\Omega}{\cdot}cm$] for 16[wt%] $Al_2O_3+Y_2O_3$ additives at 25[$^{\circ}C$]. The electrical resistivity was all negative temperature coefficient resistance (NTCR) in the temperature ranges from $25^{\circ}C$ to 700[$^{\circ}C$]. The resistance temperature coefficient of composite showed the lowest value of $-2.3{\times}10^{-3}[^{\circ}C]^{-1}$ for 16[wt%] additives in the temperature ranges from 25[$^{\circ}C$] to 100[$^{\circ}C$].

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.318-324
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• 2012

Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, $Lu_2O_3-SiO_2$ (US), $La_2O_3$-MgO (AM) and $Y_2O_3-Al_2O_3$ (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the $La_2O_3$-MgO system. Since the $Lu_2O_3-SiO_2$ system has the highest melting temperature, full densification could not be achieved after sintering at $1950^{\circ}C$. However, the system had a reasonably high bending strength of 527 MPa at $1200^{\circ}C$ in air and a high fracture toughness of 9.2 $MPa{\cdot}m^{1/2}$. The $Y_2O_3-Al_2O_3$ system had the highest room temperature bending strength of 1.2 GPa.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.963-967
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• 2001

The effects of the sintering additives such as Bi$_2$O$_3$and V$_2$O$_{5}$ on the microwave dielectric and sintering properties of ZnTiO$_3$system were investigated. Densities of >97% of the theoretical densities have been attained for ZnTiO$_3$at the sintering temperature range of 870~90$0^{\circ}C$ with Bi$_2$O$_3$and V$_2$O$_{5}$ additions of $_3$were obtained with 0.6wt% Bi$_2$O$_3$and 0.5wt% V$_2$O$_{5}$; Qxf$_{o}$ = 48,400 GHz, $\varepsilon$$_{r}$ = 22, and $\tau$$_{f}$ = -43 PPm/$^{\circ}C$. In order to improve temperature coefficient of resonance frequency, TiO$_2$was added to the above system. The optimum amount of TiO$_2$was 15mo1% when sintered at 87$0^{\circ}C$, at which we could obtain following results ; Qxf$_{o}$ = 44,700 GHz, $\varepsilon$$_{r}$ = 26, and $\tau$$_{f}$ = 0 ppm/$^{\circ}C$.EX>.>.EX>.>.>.EX>.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.561-565
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• 2002

The effects of sintering additives such as $Bi_2O_3$ and $V_2O_5$ on the microwave dielectric and sintering properties of (Zn, Mg)$TiO_3$ system were investigated. Highly dense samples were obtained for $(Zn_{0.8}Mg_{0.2})TiO_3$ at the sintering temperature range of $870{\sim}900^{\circ}C$ with $Bi_2O_3$ and $V_2O_5$ additions of <1wt.%, respectively. The microwave dielectric properties of $(Zn_{0.8}Mg_{0.2})TiO_3$ with 0.45 wt.% $Bi_2O_3$ and 0.55 wt.% $V_2O_5$ sintered at $900^{\circ}C$ were as follows: $Q{\times}f_o$=56,800 GHz, ${\varepsilon}_r$=22, and ${\tau}_f=-53ppm/^{\circ}C$. In order to improve temperature coefficient of resonant frequency, $TiO_2$ was added to the above system. The optimum amount of $TiO_2$ was 15 mol.% when sintered at $870^{\circ}C$, at which we could obtain following results: $Q{\times}f_o$ = 32,800 GHz, ${\varepsilon}_r$ = 26, and $\tau_f=0ppm/^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.1
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• pp.30-36
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• 2002

The effects of the sintering additives such as B $i_2$ $O_3$ and $V_2$ $O_{5}$ on the microwave dielectric and sintering properties of ZnTi $O_3$ system were investigated. Highly dense samples were obtained for ZnTi $O_3$ at the sintering temperature range of 870~90$0^{\circ}C$ with B $i_2$ $O_3$ and $V_2$ $O_{5}$ additions of <1 wt.%, respectively. The microwave dielectric properties of ZnTi $O_3$ with 0.6 wt.% B $i_2$ $O_3$ and 0.5 wt.% $V_2$ $O_{5}$ were as follows: Qx $f_{o}$ = 48,400 GHz, $\varepsilon$$_{r}$= 22, and $\tau$$_{f}$ = -43 ppm/$^{\circ}C$. In order to improve temperature coefficient of resonant frequency, Ti $O_2$ was added to the abode system. The optimum amount of Ti $O_2$was 15 mol.% when sintered at 87$0^{\circ}C$, at which Ive could obtain following results: Qx $f_{O}$ = 44,700GHz, $\varepsilon$$_{r}$ = 26, and $\tau$$_{f}$ = 0 PPm/$^{\circ}C$.>.EX>.>.>.EX>.>.>.

• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.777-783
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• 1994

Oxidation behavior of hot-pressed silicon nitride ceramics with various sintering additives has been investigated. The weight gain of each specimens has shown in the range of 0.11 mg/$\textrm{cm}^2$ ~3.4 mg/$\textrm{cm}^2$ at 140$0^{\circ}C$ for 192 h and eleven compositions have shown good oxidation resistance with the weight gain below 0.5 mg/$\textrm{cm}^2$. The oxidation rate has been shown to obey the parabolic rate law and the oxidized surface has consisted of $\alpha$-cristobalite and M2Si2O7 or MSiO3 (M=rare earth or transition metals) phase. The oxidation rate of each specimens has related to the eutectic temperature between additive oxide and SiO2, and ionic radius of additive oxides, respectively. From the above results, it could be concluded that the oxidation behavior of hot pressed silicon nitride is dominated by the high temperature properties of grain boundary glassy phase and the high temperature properties of grain boundary glassy phase are affected by the ionic radius of additive oxides.

• Journal of the Korean Ceramic Society
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• v.28 no.5
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• pp.359-364
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• 1991

The effects of Pb5Ge3O11 on the sinterbility and lattice variation of the semiconducting 0.15 mol% Y2O3 doped BaTiO3 have been investigated as functions of additive contents (from 0.25 mol% to 2.5 mol%) and sintering temperatures (from 110$0^{\circ}C$ to 130$0^{\circ}C$). As the amount of Pb5Ge3O11 increases, the sinterbility of BaTiO3 increases abruptly at around 115$0^{\circ}C$. During the sintering, the most of Pb+2 ions in additives penetrate into BaTiO3 lattices and Ge+4 ions present at grain boundaries. Therefore the c lattice of the BaTiO3 increases largely and then the tetragonality increases due to the diffusion of the Pb+2 ions.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.210-219
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• 1999

The fundamental dispersion property of Si2N4 and a combination of AlN and Nd2O3 as sintering additives in a variety of organic solvents such as alcohols, hydrocarbons, ketones, and ethers was investigated. The stabilization mechanism and interaction between organic functional groups of the various organic additives were studied to clarify the dispersibility of the ceramic particles in the nonaqueous suspending medium. characterization of the suspensions was based mainly on electrokinetic sonic amplitude(ESA) measurements and the flow curves obtained from the rheological studies as well as estimated Hamaker constants. It was found that the contribution of electrostatic repulsive forces to the Si3N4, AlN and Nd2O3 stabilization in organic media is appreciably greater than anticipated and is dependent on the physicochemical properties of organic solvents.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1405-1407
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• 2001

It was studied to prepare high temperature heating elements using molybdenum disilicide($MoSi_2$). Molybdenum disilicide is widely used as material for manufacturing high temperature heating elements. $MoSi_2$ heating elements could be used at 1700-1900$^{\circ}C$. However, it is relatively expensive, and its demand depends on import. $MoSi_2$ powders was mixed with 4-5wt% of montmorillonites type bentonite as plasticizer and a small amount of $Si_3N_4$, $ThO_2$, and B as additives to prepare specimen of heating elements. Then, it was extruded, dried, sintered and machined followed by heating test. Effects of sintering conditions and amount of additives were investigated, It was sintered effectively at 1,350$^{\circ}C$ for five hours. Electrical resistivity was decreased with increasing of sintering temperature and time, and related with apparent density of the specimens. It was linealy decreased with increasing of sintered density. The heating elements thus prepared was stable at 1700$^{\circ}C$ and the physical properties such as specific electrical resistivity, hardness, apparent density, thermal expansion coefficient, and bending strength were almost identical with those of commercial heating elements.

• Journal of the Korean Ceramic Society
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• v.28 no.7
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• pp.525-530
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• 1991

The effects of 0.15mol% Y2O3 doped semiconducting (Ba1-xPbx)TiO3 ceramics with 0.5 mol% Pb5Ge3O11 as sintering additives have been investigated as function of Pb contents (from 0.05 mol to 0.3 mol) and sintering temperatures (from 1050$^{\circ}C$ to 1200$^{\circ}C$). As the Pb content increases in the (Ba1-xPbx)TiO3 system, the size and resistance of the grain increase but the capacitance of the grain boundary decreases due to the formation of liquid phase during the sintering. And with increasing the sintering temperatures, the resistance of the grain decreases but the capacitance of the grain boundary increases. The PTCR effects decrease with increasing the Pb content and the sintering temperature.