• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.284-285
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• 2006

The nano-sized Fe powders were prepared by plasma arc discharge process using pure Fe rod. The microstructure and the sintering behavior of the prepared nanopowders were evaluated. The prepared Fe nanopowders had nearly spherical shapes and consisted of metallic core and oxide shell structures. The higher volume shrinkage at low sintering temperature was observed due to the reduction of surface oxide. The nanopowders showed 6 times higher densification rate and more significant isotropic shrinkage behavior than those of micron sized Fe powders.

• Metals and materials international
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• 제24권6호
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• pp.1327-1332
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• 2018

In this study, a novel approach to the explosive synthesis of titanium carbide (TiC) is discussed. Nonstoichiometric $TiC_x$ powder was produced via the underwater explosion of a Ti powder encapsulated within a spherical explosive charge. The explosion process, bubble formation, and synthesis process were visualized using high-speed camera imaging. It was concluded that synthesis occurred within the detonation gas during the first expansion/contraction cycle of the bubble, which was accompanied by a strong emission of light. The recovered powders were studied using scanning electron microscopy and X-ray diffraction. Submicron particles were generated during the explosion. An increase in the carbon content of the starting powder resulted in an increase in the carbon content of the final product. No oxide byproducts were observed within the recovered powders.

• Elastomers and Composites
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• 제53권4호
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• pp.234-238
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• 2018

The influence of reinforcing UHMWPE powder on the tribological and mechanical properties of HDPE was investigated. The circularizing of UHMWPE powder was improved by high-speed rotation to enhance particle distribution and flowability. HDPE composites reinforced with UHMWPE powder in the range of 0-50 wt% were prepared by co-rotating twin screw extrusion. The abrasion resistance, plane friction coefficient, tensile strengths, and impact strengths of the composites were investigated as a function of the UHMWPE content. An increasing UHMWPE content decreased the plane friction coefficient and increased the abrasion resistance and impact strength. It is expected that HDPE composites reinforced with spherical UHMWPE powder particles can be used to improve the durability of products such as pipes in the future.

• 한국재료학회지
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• 제12권10호
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• pp.784-790
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• 2002

For mass product of nanocrystalline ZnO ultrafine powders, self-sustaining combustion process(SCP) and ultrasonic spray combustion method(USCM) were applied at the same time. Ultrasonic spray gun was attached on top of the vertical type furnace. The droplet was sprayed into reaction zone of the furnace to form SCP which produces spherical shape with soft agglomerate crystalline ZnO particles. To characterize formed particles, fuel and oxidizing agent for SCP were used glycine and zinc nitrate or zinc hydroxide. Respectively, with changing combustion temperature and mixture ratio of oxidizing agent and fuel, the best ultrasonic spray conditions were obtained. To observe ultrasonic spray effect, two types of powder synthesis processes were compared. One was directly sprayed into furnace from the precursor solution (Type A), the other directly was heated on the hot plate without using spray gun (Type B). Powder obtained by type A was porous sponge shape with heavy agglomeration, but powder obtained using type B was finer primary particle size, spherical shape with weak agglomeration and bigger value of specific surface area. 9/ This can be due to much lower reaction temperature of type B at ignition time than type A. Synthesized nanocrystalline ZnO powders at the best ultrasonic spray conditions have primary particle size in range 20~30nm and specific surface area is about 20m$^2$/g.

• 한국재료학회지
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• 제27권9호
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• pp.489-494
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• 2017

ZnS powder was synthesized using a relatively facile and convenient glycothermal method at various reaction temperatures. ZnS was successfully synthesized at temperatures as low as $125^{\circ}C$ using zinc acetate and thiourea as raw materials, and diethylene glycol as the solvent. No mineralizers or precipitation processes were used in the fabrication, which suggests that the spherical ZnS powders were directly prepared in the glycothermal method. The phase composition, morphology, and optical properties of the prepared ZnS powders were characterized using XRD, FE-SEM, and UV-vis measurements. The prepared ZnS powders had a zinc blende structure and showed average primary particles with diameters of approximately 20~30 nm, calculated from the XRD peak width. All of the powders consisted of aggregated secondary powders with spherical morphology and a size of approximately $0.1{\sim}0.5{\mu}m$; these powders contained many small primary nanopowders. The as-prepared ZnS exhibited strong photo absorption in the UV region, and a red-shift in the optical absorption spectra due to the improvement in powder size and crystallinity with increasing reaction temperature. The effects of the reaction temperature on the photocatalytic properties of the ZnS powders were investigated. The photocatalytic properties of the as-synthesized ZnS powders were evaluated according to the removal degree of methyl orange (MO) under UV irradiation (${\lambda}=365nm$). It was found that the ZnS powder prepared at above $175^{\circ}C$ exhibited the highest photocatalytic degradation, with nearly 95 % of MO decomposed through the mediation of photo-generated hydroxyl radicals after irradiation for 60 min. These results suggest that the ZnS powders could potentially be applicable as photocatalysts for the efficient degradation of organic pollutants.

• 한국분말재료학회지
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• 제23권6호
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• pp.414-419
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• 2016

Much attention has been paid to thermally conductive materials for efficient heat dissipation of electronic devices to maintain their functionality and to support lifetime span. Hexagonal boron nitride (h-BN), which has a high thermal conductivity, is one of the most suitable materials for thermally conductive composites. In this study, we synthesize h-BN nanocrystals by pyrolysis of cost-effective precursors, boric acid, and melamine. Through pyrolysis at $900^{\circ}C$ and subsequent annealing at $1500^{\circ}C$, h-BN nanoparticles with diameters of ~80 nm are synthesized. We demonstrate that the addition of small amounts of Eu-containing salts during the preparation of melamine borate precursors significantly enhanced the crystallinity of h-BN. In particular, addition of Eu assists the growth of h-BN nanoplatelets with diameters up to ~200 nm. Polymer composites containing both spherical $Al_2O_3$ (70 vol%) and Eu-doped h-BN nanoparticles (4 vol%) show an enhanced thermal conductivity (${\lambda}{\sim}1.72W/mK$), which is larger than the thermal conductivity of polymer composites containing spherical $Al_2O_3$ (70 vol%) as the sole fillers (${\lambda}{\sim}1.48W/mK$).

• 한국세라믹학회지
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• 제35권11호
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• pp.1171-1181
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• 1998

$SrZr_{0.95}$$Y_{0.05}$$O_{2.975}$ powder was synthesized by ultrasonic spray pyrolysis using a solution that Sr carbonate and Zr and Y nitrates were dissolved in a citric acid solution. The processes of particle formation were in-vestigated with respect to solution properties and pyrolysis temperature. With changing the solution con-centration form 0.1M to 0.01M there was a tendency that average sizes of droplets and particles were de-creased and their size distributions were narrowed. Citrate functional groups converted the droplets into gel particles which prevented an inhomogeneous precipitation of the metal ions and facilitated the diffusion of gases during thermal decomposition. As a result the powder having spherical particles without hollow par-ticles could be prepared. Low pyrolysis temperature led to amorphous particles due to incomplete pyrolysis and made the particles difficult to maintain spherical shape due to retarded gelation of the droplets. Whereas higher pyrolysis temperature produced hollow and broken particles because the droplets un-derwent rapid gelationand decomposition. The particles obtained at two pyrolysis temperature $500^{\circ}$and $1000^{\circ}C$ consisted of a perovskite phase and a very small amount of $SrCO_3$ However after calcination at $1000^{\circ}C$ the particles contained a single perovskite phase having an average particle size of 0.63${\mu}{\textrm}{m}$ and an apparent density near to the theoretical density.

• 한국분말재료학회지
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• 제12권5호
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• pp.325-331
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• 2005

Implant prototypes with various porosities were fabricated by electro-discharge-sintering of atomized spherical Ti-6Al-4V powders. Single pulse of 0.75 to 2.0 kJ/0.7 g-powder, using 150, 300, and $450{\mu}F$ capacitors was applied to produce a fully porous and porous surfaced implant compact. The solid core formed in the center of the compact after discharge was composed of acicular ${\alpha}+{\beta}$ grains and porous layer consisted of particles connected in three dimensions by necks. The solid core and neck sizes increased with an increase in input energy and capacitance. On the other hand, pore volume decreased with increased capacitance and input energy due to the formation of solid core. Capacitance and input energy are the only controllable discharge parameters even though the heat generated during a discharge is the unique parameter that determines the porosity of compact. It is known that electro-discharge-sintering of spherical Ti-6Al-4V powders can efficiently produce fully-porous and porous surfaced Ti-6Al-4V implants with various porosities in a short time less then 400 isec by manipulating the discharging condition such as input energy and capacitance including powder size.

• 한국분말재료학회지
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• 제18권4호
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• pp.365-371
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• 2011

In this study, gradient porous Al-Cu sintered body was fabricated by powder metallurgy processing. Al-Cu powder mixtures were prepared by low energy ball milling with various milling time. After ball milling for 3h, the shape of powder mixtures changed to spherical type with size of 100~500 ${\mu}m$. Subsequently, Al-Cu powder mixtures were classified (under 150, 150~300 and over 300 ${\mu}m$) and compacted (20, 50 and 100 MPa). Then, they were sintered at $600^{\circ}C$ for various holding time (10, 30, 60 and 120 min) in $N_2$ atmosphere. The sintered bodies had 32~45% of porosity. As a result, the optimum holding time was determined to be 60 min at $600^{\circ}C$ and sintered bodies with various porosity were obtained by controlling the compacting pressure.

• 한국분말재료학회지
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• 제12권1호
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• pp.56-63
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• 2005

Ag powder was prepared from $AgNO_3$ by wet chemical reduction method using various reduction agent system involving $AgNO_3$, $AgNO_2$(AgCl) and Ag complex ion aqueous solution. The pure Ag powder could be prepared regardless of reaction system but the particle shape and distribution were affected very much according to the kind of reduction agents and reaction systems. The optimum reaction system for the preparation of the silver powder having the uniform particle shape and size distribution was Ag complex ion aqueous solution-reduction agent system and in particular, $H_2O_2$ and $C_6H_8O_6$as a reduction agent leaded the more uniform particle shape and size distribution.