• 한국세라믹학회지
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• 제48권5호
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• pp.418-425
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• 2011

In this study, a high energy ball milling process was introduced in order to improve the densification of direct nitrided AlN powder. The sintering behavior and thermal conductivity of the AlN milled powder was investigated. The mixture of AlN powder and 5 wt% $Y_2O_3$ as a sintering additive was pulverized and dispersed by a bead mill with very small $ZrO_2$ bead media. The milled powders were sintered at $1700^{\circ}C-1800^{\circ}C$ for 4 h under $N_2$ atmosphere. The results showed that the sintered density was enhanced with increasing milling time due to the particle refinement as well as the increase in oxygen contents. Appropriate milling time was effective for the improvement of thermal conductivity, but the extensive millied powder formed more fractions of secondary phase during sintering, resulted in the decrease in thermal conductivity. The AlN powder milled for 10min after sintering at $1800^{\circ}C$ revealed the highest thermal conductivity, of 164W/$m{\cdot}K$ in tne densified AlN sintered at $1800^{\circ}C$.

• 한국분말재료학회지
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• 제19권1호
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• pp.25-31
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• 2012

In this study, a high energy ball milling process was employed in order to improve the densification of direct nitrided AlN powder. The densification behavior and the sintered microstructure of the milled AlN powder were investigated. Mixture of AlN powder doped with 5 wt.% $Y_2O_3$ as a sintering additive was pulverized and dispersed up to 50 min in a bead mill with very small $ZrO_2$ beads. Ultrafine AlN powder with a particle size of 600 nm and a specific surface area of 9.54 $m^2/g$ was prepared after milling for 50 min. The milled powders were pressureless-sintered at $1700^{\circ}C-1800^{\circ}C$ for 4 h under $N_2$ atmosphere. This powder showed excellent sinterability leading to full densification after sintering at $1700^{\circ}C$ for 4 h. However, the sintered microstructure revealed that the fraction of yitttium aluminate increased with milling time and sintering temperature and the newly-secondary phase of ZrN was observed due to the reaction of AlN with the $ZrO_2$ impurity.

• 한국분말재료학회지
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• 제3권3호
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• pp.153-158
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• 1996

The exhaust gas from vehicle engines and industrial boilers contains considerable amount of harmful nitrogen monoxide(NO) which causes air pollusion and acid rain. To remove NO catalytic reduction processes using Cu ion exchanged ZSM-5 zeolite have been widely studied. In this study, an attempt was made to fabricate Cu/zeolite catalyst by using high energy ball mill. The catalytic performance of ball milled Cu/ZSM-5 zeolites is analyzed and optimum copper contents was determined. The processing variables were reaction temperature and copper contents. Complete removal of NO gas was obtained at the temperature of 553 K on 10wt.% CU/ZSM-5 mechanically alloyed composite powders. Mechanically alloyed CU/ZSM-5 catalyst showed homogeneous distribution of Cu in ZSM-5.

• 한국세라믹학회지
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• 제42권10호
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• pp.685-690
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• 2005

Pb(Zr,Ti)$O_{3}$Pb($Mn_{1/3}$$Nb_{2/3}$)$O_{3}$ powder was successfully synthesised by high-energy milling method, and the behavior of low­temperature sintering and piezoelectrical properties of Pb(Zr,Ti)$O_{3}$-Pb($Mn_{1/3}$$Nb_{2/3}$)$O_{3}$ ceramics were investigated as a function of mechanical alloying time. In order to confirm whether the Perovskite phase in this composition was formed by mechanical activation technique or not, we performed X-Ray Diffraction pattern analysis (XRD). The microstructure for the sintered samples were characterized using a Scanning Electronic Microscope (SEM). And the piezoelectrical properties ($k_{p}$ and $Q_{m}$) of the sintered samples was measured using HP 4194A impedance analyzer.

• 한국분말재료학회지
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• 제22권4호
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• pp.283-288
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• 2015

Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-TiC composite powders which are fabricated by high-energy ball-milling. A powder mixture of Fe and TiC is prepared in a planetary ball mill at a rotation speed of 500 rpm for 1h. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts show incomplete densification with a relative denstiy of 86.1% after sintering at $1300^{\circ}C$ for 3h. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly complete densification of 98.6% relative density under the sintering pressure of 50 MPa.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.24-25
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• 2006

High-Speed Centrifugal Compaction Process is one of slip-using compacting method originally developed for processing of oxide ceramics. In this study, we apply the HCP to ultra-fine (0.1 micron) WC powder. Organic liquid of heptane was chosen as dispersing media to avoid possible oxidation of WC. The mixing apparatus was a key to obtain dense compacts. Only the slips mixed by high energy planetary ball mill were packed up to 55% by the HCP, and sintered to almost full density at 1673 K without any sintering aids. This sintered compact marked Vickers hardness of Hv 2750 at maximum.

• 한국수소및신에너지학회논문집
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• 제31권2호
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• pp.177-183
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• 2020

To utilize hydrogen energy, high-yield, high-purity hydrogen needs to be produced; therefore, hydrogen separation membrane studies are being conducted. The membrane reactor that fabricates hydrogen needs to have high hydrogen permeability, selective permeability, heatresistant and a stable mechanical membrane. Dense membranes of Pd and Pd alloys are usually used, but these have drawbacks associated with high cost and durability. Therefore, many researchers have studied replacing Pd and Pd alloys. Dense TiN membrane is highly selective and can separate high-purity hydrogen. The porous alumina has a high permeation rate but low selectivity; therefore, separating high-purity hydrogen is difficult. To overcome this drawback, the two materials are combined as composite reclamations to produce a separation membrane with a high penetration rate and high selectivity. Accordingly, TiN-alumina was manufactured using a high-energy ball mill. The TiN-alumina membrane was characterized by X-ray diffraction analysis, scanning electron microscopy, and energy dispersive spectroscopy. The hydrogen permeability of the TiN-alumina membrane was estimated by a Sievert-type hydrogen permeation membrane apparatus. Due to the change in the diffusion mechanism, the transmittance value was lower than that of the general TiN ceramic separator.

• 한국분말재료학회지
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• 제15권2호
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• pp.101-106
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• 2008

The objective of the present study is to investigate the increase in the functional characteristics of a substrate by the formation of a thin coating layer. Thin coating layers of $Ti_5Si_3$ have high potential because $Ti_5Si_3$ exhibits high hardness. Shock induced reaction synthesis is an attractive fabrication technique to synthesize uniform coating layer by controlling the shock wave. Ti and Si powders to form $Ti_5Si_3$ using shock induced reaction synthesis, were mixed using high-energy ball mill into small scale. The positive effect of this technique is highly functional coating layer on the substrate due to ultra fine substructure, which improves the bonding strength. These materials are in great demand as heat resisting, structural and corrosion resistant materials. Thin $Ti_5Si_3$ coating layer was successfully recovered and showed high Vickers' hardness (Hv=1183). Characterization studies on microstructure revealed a fairly uniform distribution of powders with good interfacial integrity between the powders and the substrate.

• 한국분말재료학회지
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• 제9권6호
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• pp.441-448
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• 2002

Dispersions of non-soluble ceramic particles in a metallic matrix can enhance the strength and heat resistance of materials. With the advent of mechanical alloying it became possible to put the theoretical concept into practice by incorporating very fine particles in a flirty uniform distribution into often oxidation- and corrosion- resistant metal matrices. e.g. superalloys. The present paper will give an overview about the mechanical alloying technique as a dry, high energy ball milling process for producing composite metal powders with a fine controlled microstructure. The common way is milling of a mixture of metallic and nonmetallic powders (e.g. oxides. carbides, nitrides, borides) in a high energy ball mill. The heavy mechanical deformation during milling causes also fracture of the ceramic particles to be distributed homogeneously by further milling. The mechanisms of the process are described. To obtain a homogeneous distribution of nano-sized dispersoids in a more ductile matrix (e.g. aluminium-or copper based alloys) a reaction milling is suitable. Dispersoid can be formed in a solid state reaction by introducing materials that react with the matrix either during milling or during a subsequent heat treatment. The pre-conditions for obtaining high quality materials, which require a homogeneous distribution of small dis-persoids, are: milling behaviour of the ductile phase (Al, Cu) will be improved by the additives (e.g. graphite), homogeneous introduction of the additives into the granules is possible and the additive reacts with the matrix or an alloying element to form hard particles that are inert with respect to the matrix also at elevated temperatures. The mechanism of the in-situ formation of dispersoids is described using copper-based alloys as an example. A comparison between the in-situ formation of dispersoids (TiC) in the copper matrix and the milling of Cu-TiC mixtures is given with respect to the microstructure and properties, obtained.

• 한국분말재료학회지
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• 제16권5호
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• pp.316-325
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• 2009

Fe based (Fe$_{68.2}$C$_{5.9}$Si$_{3.5}$B$_{6.7}$P$_{9.6}$Cr$_{2.1}$Mo$_{2.0}$Al$_{2.0}$) amorphous powder, which is a composition of iron blast cast slag, were produced by a gas atomization process, and sequently mixed with ductile Cu powder by a mechanical ball milling process. The experiment results show that the as-prepared Fe amorphous powders less than 90 $\mu$m in size has a fully amorphous phase and its weight fraction was about 73.7%. The as-atomized amorphous Fe powders had a complete spherical shape with very clean surface. Differential scanning calorimetric results of the as-atomized Fe powders less than 90 $\mu$m showed that the glass transition, T$_g$, onset crystallization, T$_x$, and super-cooled liquid range $\Delta$T=T$_x$-T$_g$ were 512, 548 and 36$^{\circ}C$, respectively. Fe amorphous powders were mixed and deformed well with 10 wt.% Cu by using AGO-2 high energy ball mill under 500 rpm.