• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.272-277
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• 2002

Aluminum nitride (AlN) powders and whiskers were synthesized by a modified carbothermal reduction and nitridation where a ($NH_4)[Al(ethylenediaminetetraacetate)]{\cdot}2H_2O$ complex is used as precursor. The AlN powders were obtained by calcining the complex without mixing any carbon source under a flow of nitrogen in the temperature range 1200∼1500$^{\circ}$C and then burning out the residual carbon. The nitridation process was investigated by $^{27}Al$ magic-angle spinning (MAS) unclear magnetic resonance, infrared spectroscopy and X-ray diffraction. The complex is pyrolyzed, converted to ${\rho}$- and ${\gamma}$- alumina and then nitridated to AlN without ${\gamma}-{\alpha}$ alumina transition. The morphology of ${\gamma}$-alumina, when it was converted to AlN, was retained, strongly indicating that ${\gamma}$-alumina is converted to AlN through solid-state $AlO_xN_y$, not through gaseous intermediates such as aluminum and aluminaum suboxides. AlN whiskers were obtained, when a (0001) sapphire was used as a catalyst.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.201-209
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• 1989

Fine Si-Al-OH coprecipitate powders were prepared from Si- and Al-alkoxides by the hydrolysis method. $\beta$-Sialon powder was obtained from prepared Si-Al-OH coprecipitate by the simultaneous reduction and nitridation method. The syntehsized Sialon powder was pressureless sintered at 175$0^{\circ}C$ for 90 min in N2 atmosphere. The characterization of the Sialon powder was performed with XRD, BET, SEM, TEM and particle size analysis. The sinterability and mechanical properties of sintered bodies were investigated in terms of relative density, M.O.R., fracture toughness, hardness and the morphology of microstructure. The highest values of their mechanical properties were obtained for the $\beta$-Sialon ceramics at Z=1 and those values are as follows : M.O.R., KIC and HV of $\beta$-Sialon ceramics(Z=1) are 499.1 MPa, 5.9MN/m3/2 and 18.7GPa, respectively.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.387-390
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• 2009

This study was designed to fabricate the micro-electro-mechanical systems (MEMS) parts such as micro spur gears using hot extrusion of gas atomized Al-78Zn powders. For this purpose, it is important to develop new methods to fabricate micro-dies and choose suitable extrusion conditions for a micro-forming. Micro-dies with Ni were fabricated by LIGA technology. LIGA technology was capable to produce micro-extrusion dies with close tolerances, thick bearing length and adequate surface quality. Superplastic Al-78Zn powders have the great advantage in achieving deformation under low stresses and exhibiting good micro formability with average strain rates ranging from $10^{-3}$ to $10^{-2}\;s^{-1}$ and constant temperatures ranging from 503 to 563K. Al-78Zn powders were compacted into a cylindrical shape (${\Phi}3{\times}h10$) under compressive force of 10kN and, subsequently, the compacted powders were extruded at 563k in a hot furnace. Micro-extrusion has succeeded in forming micro-gear shafts.

• Journal of the Korean Ceramic Society
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• v.27 no.7
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• pp.916-924
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• 1990

The preparatin of the fine TiN powders by reduction-nitridation of TiCl3-Al-N2 system was attempted in the temperature range from 350$^{\circ}$to 100$0^{\circ}C$. The formation mechanism and kinetics of TiN were examined, and the resultant TiN powder was characterized by means of XRD, PSA and SEM-EPMA methods. TiN was formed at temperatrue higher than $600^{\circ}C$. As an intermediate phase, AlTi was obtained. The apparent activation energy for the formation of TiN was approximately 4.2kcal/mole(600$^{\circ}$~90$0^{\circ}C$). The crystallite size and lattice constnat of TiN powder obtained in the temperature range from 600$^{\circ}$to 100$0^{\circ}C$ for 2h at the Al/TiCl3 molar ratio of 1.0 were 160~255A and 4.231~4.239A, respectively. According to PSA measurement, the mean particle size ranged from 14.0 to 14.8${\mu}{\textrm}{m}$.

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.05a
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• pp.22-22
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• 1996

• Journal of the Korean Ceramic Society
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• v.33 no.9
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• pp.961-968
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• 1996

The aluminum nitride was synthesized by the self-propagating high-temperature synthesis(SHS). The synthe-sis was used aluminum powder mixed with AlN powder as reactant and the control factors affected to synthesis were considered compact density pressure of reaction gas AlN diluent content and aluminum powder size. The SHS reaction conducted with a reactant containing 50% AlN diluent under 0.8MPa nitrogen gas pressure yielded a complete conversion of aluminum powder to AlN powders. The size and purity of AlN produced were found to be comparable with that of AlN produced by the carbothermal nitrogen method.

• Journal of the Microelectronics and Packaging Society
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• v.5 no.2
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• pp.53-58
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• 1998

Sintering and dielectric characteristics of substrates were estimated by mixing rate of alumina and potashborosilicate glass(PBSG) powders. PBSG powders were used 7761(corning code)and alumina powders were used in extra pure rate(99.9%) and had 0.1 ${\mu}$m mean size. After ball milling with organic additives green sheets which were casted by doctor blade machine were sintered at 800$^{\circ}C$ for 1∼3hrs. Microstructure, linear shrinkage and dielectric constant of substrates were surveyed in order to fabricate low-dielectric and low tem-perature sintering substrate.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.224-228
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• 2000

Using a small amount of additives and amorphous Si₂N₂O powders, O-SiAlON ceramics have been hot-pressed and its microstructure and mechanical properties were investigated. Scandium oxide was demonstrated to be an effective densification additive for O-SiAlON. Amorphous Si₂N₂O was densified at relatively low temperatures and a microstructure with acicular grains was developed. Fine grains found in materials obtained from amorphous powders suggest that nucleation and crystallization of O-SiAlOH is relatively easy compared with the Si₃N₄-SiO₂reaction.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1063-1064
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• 2006

Mechanical properties of 7xxx series Al metal matrix composite (MMC) powders containing different amounts of ceramic were investigated. The ceramic contents of the starting powders were 5 wt.% or 10 wt.%. The powders were uniaxially cold compacted using a cylindrical die with a compacting pressure of 250 MPa and were sintered at $620^{\circ}C$ in a dry $N_2$ atmosphere for 60 min. For the heat treatment, sintered parts were solution treated at $475^{\circ}C$ and aged at $175^{\circ}C$. Compression tests were conducted to reveal the effect of $Al_2O_3$ particle content on the mechanical properties of the composites. Fractography was examined using a scanning electron microscope.

• Korean Journal of Materials Research
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• v.11 no.10
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• pp.863-868
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• 2001

The present study was carried out to investigate the effect of MA processing variables on the microstructural properties of composite powders and the coefficient of thermal expansion of pulse electric current sintered AlN-Cu powder compacts. The AlN-Cu powders had a size of less than 15 $\mu\textrm{m}$ with 25 nm size of copper crystallite after MA 32 hours. The finely distributed AlN-Cu powder compacts were completely achieved after PECS. The residual oxygen was considerably removed after hydrogen reduction treatment. The residual carbon was completely removed to 97%. The CTE of AlN-Cu powder compacts showed a good consistency with Kingery-Tuner model when the volume fraction of copper was less than 60%. When it was more than 60%, the CTE had a good agreement with Series model.