• Korean Journal of Materials Research
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• v.14 no.7
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• pp.489-493
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• 2004

The electrical property of MMC is essentially important to some applications such as power transmission lines and cables, electronic and electrical components as well as electromagnetic shielding equipments. The behavior of electrical resistivity of $SiC_{w}/Al$ alloy composites under as-extruded and annealed conditions has been investigated within the temperature range from room temperature to $450^{\circ}C$. It can be seen that within entire temperature range, the electrical resistivity of composites was higher than that of an unreinforced matrix alloy under the same condition of either as-extrusion or annealing. The temperature dependence of both exhibited positive incline like a typical metal. The variation of electrical resistivity of an unreinforced matrix alloy with temperature from ambient temperature to $450^{\circ}C$ was nearly monotonous, while those of composites increased monotonously at low temperature and rose to a high level after about $250^{\circ}C or 275^{\circ}C$. The difference of these temperature dependences on electrical resistivity can be interpreted as qualitatively the interfaces of $SiC_{w}$ fibers and matrix, where act as nucleation sites.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.6
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• pp.263-270
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• 2001

The mechanical and electrical properties of the hot-pressed and annealed ${\beta}-SiC-TiB_2$,/TEX> electroconductive ceramic composites were investigated as function as functions of the liquid forming additives of $Al_2O_3+Y_2O_3$. The result of phase analysis of composites by XRD revealed ${\alpha}$-SiC(6H), $TiB_2$,/TEX>, and YAG($Al_5Y_3O_{12}$) crystal phase. The relative density and the mechanical properties of composites were increased with increasing $Al_2O_3+Y_2O_3$ contents in pressureless annealing method because YAG of reaction between $Al_2O_3$ was increased. The flexural strength showed the highest value of 458.9 MPa for composites added with 4 wt% $Al_2O_3+Y_2O_3$ additives in pressed annealing method at room temperature. Owing to crack deflection, crack bridging, phase transition and YAG of fracture toughness mechanism, the fracture toughness showed 7.1 MPa ${\cdot}\;m^{1/2}$ for composites added with 12 wt% $Al_2O_3+Y_2O_3$ additives in pressureless annealing method at room temperature. The electrical resistivity and the resistance temperature coefficient showed the lowest value of $6.0{\times}10^{-4}\;{\Omega}\;{\cdot}\;cm(25\'^{\circ}C}$ and $3.0{\times}10^{-3}/^{\circ}C$ for composite added with 12 wt% $Al_2O_3+Y_2O_3$ additives in pressureless annealing method at room temperature, respectively. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature ranges from 25 $^{\circ}C$ to 700 $^{\circ}C$.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.317-323
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• 1999

Si3N4-TiC composites have been known as electrically conductive ceramics. $Si_3N_4-TiC$ composites with 2 wt% $Al_2O_3$ and 4 wt% $Y_2O_3$ were hot pressed in $N_2$ environment. The mechanical properties including hardness, fracture toughness, and flexural strength and tribological properties were investigated as a function of TiC content. $Si_3N_4-40$ vol% TiC composite was hot pressed at $1,750^{\circ}C$, $1,800^{\circ}C$, and $1,850^{\circ}C$ for 1, 3 and 5 hours in $N_2$ gas. Mechanical and tribolgical properties depended on microstructures, which were controlled by hte TiC content, hot press temperature, and hot press holding time. However, mechanical properties and tribological behaviors were degraded by the chemical reaction between TiC and N. The chemically reacted products such as TiCN, SiC, and $SiO_2$ were detered by the X-ray diffraction analysis.

• Journal of Ceramic Processing Research
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• v.21
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• pp.16-22
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• 2020

We fabricated SiC-TiC composites by hot-press sintering with aluminum and yttrium nitrate additive and evaluated crystal phase, relative density, microstructure, electrical resistivity and mechanical properties of the sintered body. And the effect of nitrate additive on the densification of SiC-TiC composites was compared with that of Al₂O₃ and Y₂O₃ additives. Because nitrate additives were uniformly dispersed in SiC and TiC mixture, it inhibited the growth of crystal grain between each other and formed fine and uniform microstructure, thereby improving mechanical properties and electrical resistivity. The electrical resistivity and flexural strength of the SiC-TiC composite with aluminum and yttrium nitrate additive were 2.3 Ω·cm and 652.3 MPa respectively.

• Korean Journal of Materials Research
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• v.17 no.1
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• pp.18-24
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• 2007

Mullite-PSZ composite was prepared by sol-gel method using $Al(sec-OC_4H_9)_3,\;Si(OC_2H_5)_4,\;ZrOCl_2\;8H_2O\;and\;Y_2O_3$. The sinterability ana mechanical properties of powder compacts sintered at $1,650^{\circ}C$ for 4 hrs were investigated for various PSZ contents. In result Al-Si spinel formed at $980^{\circ}C$ from amorphous dried gel, and zirconia as well as mullite crystal formed above $1,200^{\circ}C$. The sintered body was densified to $97{\sim}98%$ except the specimen containing 25vol% PSZ which showed the relative density of about 95% obtained by sintering at $1,650^{\circ}C$ for 4 h. The flexural strength of the sintered body was a maximum value of 290 MPa in 20 vol% PSZ, which was also considerably larger than the value of 200 MPa without PSZ. The value of the fracture toughness increased linearly with increase of PSZ content and showed a maximum value of $4.3MPam^{1/2}$ in 25 vol% PSZ, Namely this value was remarkably larger than the $value(2.6MPam^{1/2})$ of pure mullite without PSZ.

• Korean Journal of Materials Research
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• v.5 no.8
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• pp.953-959
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• 1995

It was investigated that reinforced species, billet condition and extrusion variation in Al 6061 composite material effected on extrusion process of particulate reinforced composite material. The strength of composite material with reinforcement species revealed SiC$\sub$w/> A1$_2$O$\sub$3f/ > A1$_2$O$\sub$3f/ > A1$_2$O$\sub$3f/ orderly. K$\sub$w/ increased as volute fraction increased in all composite material. The composite materials reinforced by A1$_2$ $O_3$required the larger pressure in hot extrusion process than those by SiC$\sub$p/ at all condition. Extrusion process tended to decrease as the semi-angle of extrusion dies increased because larger contact area caused larger shear friction. Extrusion temperature went up about 50$^{\circ}C$ in low elevated deformation temperature. In extrusion temperature above 500$^{\circ}C$, severe tearing occurred on extrusion surface. More reinforcement in volume fraction, more hot tearing.

• Journal of the Korean Society of Safety
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• v.32 no.3
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• pp.1-7
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• 2017

Particle reinforced composites are materials that have enhanced physical properties by adding particle reinforcements to polymer materials and have been applied to a wide range of fields such as the aerospace, bio-technology and automative industry. In this study, particle reinforced composites were prepared by mixing $SiC/Al_2O_3$ to the vinyl ester as the thermoset resin. The purpose of this study is to evaluate mechanical properties and fracture behavior by the tensile test and single edge notch specimen according to the addition ratio of reinforcement. Addition of 1 and 2 wt% of the particle reinforcement to the vinyl-ester resin was effective for the strength improvement. However, when it was more than 3 wt%, its strength was decreased. Also the highest elastic modulus obtained as 3.19 GPa was found at the 2 wt% addition of reinforcement. Futhermore the fracture toughness was evaluated by the energy release rate and the maximum critical energy release rate was obtained when 1 wt% reinforcement. The results show that the limit of adding of $SiC/Al_2O_3$ for improvement of the mechanical and fracture performance is 2 wt% reinforcement particles.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.204-209
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, $SiC_f/SiC$ composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of $SiC_f/SiC$ composites by hot pressing method. In the present work, Monolithic LPS-SiC was fabricated by hot pressing method in Ar atmosphere at 1760 $^{\circ}C$, 1780 $^{\circ}C$, 1800 $^{\circ}C$ and 1820 $^{\circ}C$ under 20 MPa using $Al_2O_3-Y_2O_3$ system as sintering additives in order to low sintering temperature. The starting powder was high purity ${\beta}-SiC$ nano-powder with an average particle size of 30 nm. Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the sintering temperature. In the micro-structure of this specimen, it was found that grain of sintered body was grown from 30 nm to 200 nm.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.558-564
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• 1992

The effect of composed phase in the hot pressed CaO-MgO-Al2O3-SiO2 glass-ceramic has been investigated through microstructure studies, thermal, physical and mechanical properties. Sintering was done in the condition at the temperature range 900~95$0^{\circ}C$ for 20~120 mins under 7.5 MPa unilateral pressure. Sintered ceramics were composed of diopside, anorthite, residual glass and the portion of each phase was dependent on the sintering temperature and the holding time: as the temperature increases, the amount of diopside increased and then the rate of increase of diopside reduced with increasing anorthite. The thermal expansion coefficient of hot pressed was reduced with increasing crystallinity of hot pressed and was in the range of 6.69~7.46$\times$10-6 K-1 below $600^{\circ}C$. The elastic constant of hot pressed increased with increasing crystallinity up to about 80%, but after that was reduced due to the change of microstructure. The flexural strength of sintered ceramics was decreased with higher temperature and holding time, while the fracture toughness of those increased. It was shown that the physical and mechanical properties of hot pressed ceramic were related to the fraction of composed sintered ceramics, similar to a particulate composite, to the crystallinity of 80% of the glass-ceramic.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.281-281
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• 2007

Low Temperature Co-fired Ceramic (LTCC) technology has been used in electronic device for various functions. LTCC technology is to fire dielectric ceramic and a conductive electrode such as Ag or Cu thick film below the temperature of $900^{\circ}C$ simultaneously. The glass-ceramic has been widely used for LTCC materials due to its low sintering temperature, high mechanical properties and low dielectric constants. To obtain the high strength, addition of filler, the microstructure should have various crystals and low pores in a composite. In this study, two glass frits were mixed with different alumina size(0.5, 2, 3.7um) and sintered at the range of $850{\sim}950^{\circ}C$. The microstructure, crystal phases, thermal and mechanical properties of the composites were investigated using FE-SEM, XRD, TG-DTA, Dilatomer. When the particle size of $Al_2O_3$ filler increased, the starting temperatures for the densification of the sintered bodies, onset point of crystallization, peak crystallization temperature in the glass-ceramic composites decreased gradually. After sintered at $900^{\circ}C$, the glass frits were crystallized as $CaAl_2Si_2O_8\;and\;CaMgSi_2O_6$. The purpose of our study is to understand the relationship between the $Al_2O_3$ particle size and thermal properties in composites.