• 한국분말재료학회지
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• 제12권3호
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• pp.214-219
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• 2005

In order to investigate the formation of AlN, mechanical alloying was carried out in $N_2$ and $NH_3$ atmosphere. Differential thermal analysis (DTA), x-ray diffraction (XRD) and chemical analysis were carried out to examine the formation behavior of aluminum nitrides. No diffraction pattern of AlN was observed in XRD analysis of the as-milled powders in $NH_3\;or\;N_2$ atmosphere. However, DTA and chemical analysis indicated that the precursors for AlN were formed in the Al powders milled in $NH_3$ atmosphere. The AlN precursors transformed to AlN after heat treatment at and above $600^{\circ}C$. It was considered that the reaction between Al and $NH_3$ was possible by the formation of fresh Al surface during mechanical alloying of Al powders.

• 한국세라믹학회지
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• 제26권1호
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• pp.100-108
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• 1989

Aluminum hydroxides were prepared by the alkoxide hydrolysis method using Al-isopropoxide as a starting material and NH4OH as a catalytic agent. When Al-isopropoxide was hydrolyzed in a H2O-NH3 system, only Al(OH)3 was obtained over all pH values. However, AlOOH was formed besides Al(OH)3 when Al-isopropoxide was hydrolyzed in a H2O-NH3-isopropyl alcohol system. The AlOOH/Al(OH)3 ratio was increased as the isopropyl alcohol content was increased. The hydroxides, Al(OH)3 and AlOOH, obtained in this study and the commerical products, $\alpha$-Al2O3 and AlOOH were subjected to the carbothermal reduction and nitridation reaction to product AlN powder, using carbon black as a reducing agent under N2 atmosphere at various temperatures. AlN was synthesized from the obtained Al(OH)3 and the commercial AlOOH at 145$0^{\circ}C$, however, synthesized from the obtained AlOOH and the commercial alpha-alumina at 135$0^{\circ}C$. The temperature difference is assumed to be attributed to the reactivity of those powders. AlN powder prepared from the Al-isopropoxide was observed to have the narrower particle size distribution than that prepared from the commercial $\alpha$-Al2O3 or AlOOH.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1703-1707
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• 2018

Ferromagnetic ${\tau}-phase$ $Mn_{54}Al_{46}C_{2.44}$ particles were synthesized, and its composites with commercial $Sm_2Fe_{17}N_3$ and synthesized $Fe_{65}Co_{35}$ powders were fabricated. Smaller grain size than the single domain size of the $Mn_{54}Al_{46}C_{2.44}$ without obvious grain boundaries and secondary phases is the origin for the low intrinsic coercivity. It was confirmed that the magnetic properties of the $Mn_{54}Al_{46}C_{2.44}$ can be enhanced by magnetic exchange coupling with the hard magnetic $Sm_2Fe_{17}N_3$ and soft magnetic $Fe_{65}Co_{35}$. The high degrees of the exchange coupling were verified by calculating first derivative curves. Thermo-magnetic stabilities of the composites from 100 to 400 K were measured and compared. It was demonstrated that the $Mn_{54}Al_{46}C_{2.44}$ based composites containing $Sm_2Fe_{17}N_3$ and $Fe_{65}Co_{35}$ could be promising candidates for future permanent magnetic materials with the proper control of purity, magnetic properties, etc.

• 한국분말재료학회지
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• 제18권3호
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• pp.238-243
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• 2011

Al/AlN composites were synthesized by mechanical alloying using process control agents(PCAs). Three different PCAs which contain N element, were examined to see the effectiveness of ball-milling and the nitridation during sintering. Among examined PCAs, $C_8H_6N_4O_5$ was the most effective to facilitate ball-milling and to form nitrides during a subsequent sintering. By a proper control of ball-milling and sintering, we could obtained surface-hardened Al-based composites.

• 한국세라믹학회지
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• 제51권5호
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• pp.498-504
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• 2014

Particulate nitride composites have been fabricated by sintering the compacted powder of AlN and 5 - 64.3 mol% $Al_2O_3$, with a small addition of $Y_2O_3$ ($Y_2O_3$/AlN, 1 wt%), in 1-atm nitrogen gas at $1650-1900^{\circ}C$. The composites were characterized in terms of sintering behavior, phase relations, microstructure and thermal shock resistance. AlN, 27R AlN pseudopolytype, and alminium oxynitride (AlON, $5AlN{\cdot}9Al_2O_3$) were found to existin the sintered material. Regardless of batch composition, the AlN-$Al_2O_3$ powder compacts exhibited similar sintering behavior; however, the degree of shrinkage commonly increased with increasing $Al_2O_3$ content, consequently giving high sintered bulk density. By increasing the $Al_2O_3$ addition up to ${\geq}50 mol%$, the matrix phase in the sintered material was converted from AlN or 27R to AlON. Above $1850^{\circ}C$, a liquid phase was formed by the reaction of $Al_2O_3$ with AlN, aided by $Y_2O_3$ and mainly existed at the grain boundaries of AlON. Thermal shock resistance was superior in the sintered composite consisting of AlON with dispersed AlN or AlN matrix phase.

• 한국분말재료학회지
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• 제20권2호
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• pp.114-119
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• 2013

In the DBC (direct bonding of copper) process the oxygen partial pressure surrounding the AlN/Cu bonding pairs has been controlled by Ar gas mixed with oxygen. However, the direct bonding of Cu with sound interface and good adhesion strength is complicated process due to the difficulty in the exact control of oxygen partial pressure by using Ar gas. In this study, we have utilized the in-situ equilibrium established during the reaction of $2CuO{\rightarrow}Cu_2O$ + 1/2 $O_2$ by placing powder bed of CuO or $Cu_2O$ around the Cu/AlN bonding pair at $1065{\sim}1085^{\circ}C$. The adhesion strength was relatively better in case of using CuO powder than when $Cu_2O$ powder was used. Microstructural analysis by optical microscopy and XRD revealed that the interface of bonding pair was composed of $Cu_2O$, Cu and small amount of CuO phase. Thus, it is explained that the good adhesion between Cu and AlN is attributed to the wetting of eutectic liquid formed by reaction of Cu and $Cu_2O$.

• 대한금속재료학회지
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• 제48권11호
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• pp.1003-1008
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• 2010

In this study, the effect of the reinforcement on the wear behaviour and mechanical properties of hypereutectic Al-Si alloys was investigated. The Gas atomized hypereutectic Al-20Si alloy powders were mixed with 1, 3, and 5 wt.% AlN and TiC ceramic particles and consolidated by hotpress. The Al-20Si powder has both finely dispersed primary Si phases and eutectic structures. The Al-20Si-AlN, TiC composites showed that the reinforcements were distributed along the boundary of the Al-20Si alloy. The UTS increased with increasing the AlN, TiC contents. At a lower load, with an increasing weight fraction of reinforcements, the wear rate decreased in both composites and the wear mechanism was adhesive wear. At a higher load, the shape of the debris changes the mechanism of the AlN composites to abrasive-adhesion wear and this resulted in an increase of the wear rate.

• 대한금속재료학회지
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• 제50권11호
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• pp.839-845
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• 2012

The effect of an AlN additive on the thermoelectric properties of SiC ceramics was studied. Porous SiC ceramics with 48-54% relative density were fabricated by sintering the pressed ${\alpha}-SiC$ powder compacts with AlN at $2100-2200^{\circ}C$ for 3 h in an Ar atmosphere. In the undoped specimens, the Seebeck coefficients were positive (p-type semiconducting) possibly due to a dominant effect of the acceptor impurities (Al, Fe) contained in the starting powder. With AlN addition, the reverse phase transformation of 6H-SiC to 4H-SiC was observed during the sintering process. The electrical conductivity of the AlN doped specimen was larger than that of the undoped specimen under the same conditions, which might be due to a reverse phase trans-formation. The Seebeck coefficient of the AlN doped specimen was also larger than that of the undoped specimen. The density of specimen and the amount of addition had significant effects on the thermoelectric properties.

• 한국재료학회지
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• 제17권10호
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• pp.560-566
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• 2007

AlN plates were fabricated by hot pressing at $1700-1900^{\circ}C$ using yttria and alumina (3 and $10\;{\mu}m$ particle size) powders as additives and characterized: density, thermal conductivity, transverse rupture strength, and grain size measurement by SEM and EDS. Density values of $3.31-3.34\;g/cm^3$ are largely attributed to hot pressing of powder mixtures in carbon mold under $N_2$ atmosphere which caused effective degree of oxygen removal from yttrium-aluminate phase expected to form at $1100^{\circ}C$. The grain size of hot pressed AlN was almost homogeneous, with size approximately from 3.2 to $4.0\;{\mu}m$ after hot pressing. $Al_2O_3$ powder of $3\;{\mu}m$ particle size resulted in better transverse rupture strength and finer grain size compared to $10\;{\mu}m$ $Al_2O_3$ powder. The thermal conductivity of AlN ranged between $83-92.7\;W/m{\cdot}K$ and decreased with $Al_2O_3$ addition. Fine grain size is preferred for better mechanical properties and thermal conductivity.

• 한국세라믹학회지
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• 제25권2호
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• pp.184-190
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• 1988

ZrN powder was prepared from the powder mixture of ZrCl4 and Al by the halogenide process in nitrogen gas flow (100-150ml/min) at the temperatures from 200$^{\circ}$to 1050$^{\circ}C$. ZrN powder was formed about 600$^{\circ}C$ and in the slow nitriding reaction, however, an intermediate product of Al3Zr was formed. The fine powder (0.1-10$\mu\textrm{m}$) of single phase ZrN was obtained at 1050$^{\circ}C$ after 1 hour. The lattice parameter and crystallite size of ZrN were 4.5787A and 360A, respectively. According to SEM observation, the particles were apt to agglomerates. The apparent activation energy for the formation of ZrN was approximately 13.2kcal/mole(750$^{\circ}$-1000$^{\circ}C$).