• 한국분말재료학회지
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• 제10권5호
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• pp.333-336
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• 2003

The purpose of this study is the fabrication of nano-sized Fe-Co alloy powders with soft magnetic properties by the slurry mixing and hydrogen reduction (SMHR) process. $FeCl_2$0 and $CoCl_2$ powders with 99.9% purities were used for synthesizing nanostructured Fe-Co alloy powder. Nano-sized Fe-Co alloy powders were successfully fabricated using SMHR, which was performed at 50$0^{\circ}C$ for 1 h in H$_2$ atmosphere. The fabricated Fe-Co alloy powders showed $\alpha$' phase (ordered body centered cubic) with the average particle size of 45 nm. The SMHR powder exhibited low coercivity force of 32.5 Oe and saturation magnetization of 214 emu/g.

• 한국분말재료학회지
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• 제6권3호
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• pp.231-237
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• 1999

In this study, the characteristics of gas atomized Mg-3wt%Al-1wt%Zn-1wt%MM alloy powders under vacuum condition were investigated. In spite of the low fluidity and easy oxidation of the molten magnesium, the spherical powders could be successfully produced by using a modified three pieces nozzle attached to the gas atomization unit. It was found that most of the solidified powders less than 50$\mu$m in diameter were single crystal and the solidified structure showed a typical dendritic morphology due to supercooling prior to nucleation. The secondary dendrite arm spacing decreased as the size of powders decreased. The Mg-Al-Ce intermetallic compounds with chemically stable phase were found in the interdendritic regions of $\alpha$-Mg. It is considered that formation of the chemically stable phase may possibly affect to improve the corrosion resistance. Therefore, it is expected that the materials formed of these Mg-Al-Zn-MM alloy powders shows better mechanical properties and corrosion resistance due to the structural refinement.

• 한국분말재료학회지
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• 제9권5호
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• pp.346-351
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• 2002

Pure and fine, two-component titanate powders (barium titanate, calcium titanate etc.) were synthesized by an ethylene glycol method. Titanium isopropoxide and other metal ionic salts were dissolved in liquid-type ethylene glycol without any precipitation. In non-aqueous system, the amount of ethylene glycol affected the solubility and homogeneity of metal cation sources in the solution. At the optimum amount of the polymer, the metal ions were dispersed effectively in solution and a homogeneous polymeric network was formed. Most of the synthesized powders had sub-micron or nano-size primary particles after calcination and the agglomerated calcined powders were easily ground by ball milling process. All synthesized titanate powders had stable crystallization behavior at low temperature and high specific surface area after ball milling. The crystallization behavior and the microstructures of the calcined powders were affected on the ethylene glycol content.

• 한국재료학회지
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• 제12권6호
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• pp.476-481
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• 2002

In this work, we report on the synthesis of the GaN powders from gallium oxide hydroxide (GaOOH) powders and on the structural and optical properties of them. Simple heat treatment of GaOOH in the flow of $NH_3$ gas leads to the formation of submicron hexagonal GaN powders even at the low reaction temperature of $800^{\circ}C$. XRD measurements show that the powders obtained are the single phase GaN. EDS, FTIR, and PL measurements indicate the oxygen-associated characteristics. It is shown from the low temperature PL measurement on GaN powders synthesized at $1000^{\circ}C$ that the shallow donor-acceptor recombination induced emission is more intense than the near band-edge excitonic emission.

• 한국세라믹학회지
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• 제31권10호
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• pp.1209-1217
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• 1994

Monodispersed alumina-zirconia fine powders were prepared by controlled hydrolysis of alkoxides. These powders and the sintered bodies were characterized. Aluminium alkoxide and zirconium alkoxide were dissolved into complex solvent with butanol and n-propanol, and by acetonitrile added hydrolytic solution, hydrolysis rate was controlled. The oil, as a dispersant, was added in hydrolytic solution, and then prepared powders were nano-sized and well-monodispersed. In the case of hydroxypropyl celluose (HPC) as a dispersant, it was added in complex solution with butanol and iso-propanol, sub-micrometer sized and well-monodispersed powders could be prepared. The value of relative density (R.D.) and tetragonal phase fraction of zirconia in the sintered body made by nano-meter sized powders were respectively higher than those in the case of sub-micrometer sized one.

• 한국세라믹학회지
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• 제34권11호
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• pp.1113-1120
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• 1997

The 2, 4, 6 and 8mol% Y2O3 doped-ZrO2 powders (20 kinds) with the addedtion of Al2O3 upto 8wt% were prepared by coprecipitation method using the zirconium oxyacetate, yttrium chloride and aluminum nitrate as starting materials. The coprecipitated powders were characterized by XRD, TG-DTA, FT-IR and SEM. The sintering properties of zirconia-alumina composites prepared by 2YSZ and 8YSZ powders containing various Al2O3 contents were also investigated. With increasing the yttria stabilizer contents, the amount of exothermic heat for zirconia crystallization decreased. And it was confirmed that the crystallizing temperature of coprecipitated zirconia powders increased and the crystallization process occurred in a wide temperature range, as Al2O3 content increased in 8YSZ.

• 대한한방소아과학회지
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• 제9권1호
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• pp.257-278
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• 1995

Experimental studies were done to research the clinical effect of Bojeosodokeum on the Analgesic, Antipyretic, Anti-inflammatory, Antimicrobial and Anti-convulsive effects in mice and rats. The results obtained as follows : 1. The solid extract powders of Bojeosodokeum was revealed significant action on analgesic effect. 2. the solid extract powders of Bojeosodokeum was revealed significant action on Anti-inflammatory effect. 3. The solid extract powders of Bojeosodokeum was revealed significant action on antipyretic effect. 4. Antimicrobial effects of solid extract powders of Bojeosodokeum against Escherichia coli and staphylococcus aureus was observed. 5. The solid extract powders of Bojeosodokeum was revealed significant action on anticonvulsive effect. According to the above results, it is confirmed that analgestic, anti-inflammatory, antipyretic, antimicrobial and anticonvulsive effect were recognized in solid extract powders of Bojeosodokeum.

• 한국세라믹학회지
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• 제28권11호
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• pp.892-896
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• 1991

The cyrstallization behavior of lead titanate powders prepared by sol-gel and coprecipitation techniques was investigated. The lead titanate precursors were derived from a mixed solution of lead nitrate and titanium tetrachloride at 4$0^{\circ}C$ to 43$^{\circ}C$ and pH of 9.00 to 9.75. The X-ray diffraction patterns of the dried gel and coprecipitated powders showed it to be amorphous. DTA runs of the powders indicated crystallization to occur at 475~48$0^{\circ}C$. However, the amorphous powders were partially crystallized at 400~45$0^{\circ}C$ with sufficient annealing time. The room temperature Raman spectra from heat-treated powders changed continuously from amorphous to crystalline state with increasing heat-treating temperature. By annealing coprecipitated powders, a dramatic change in the Raman spectra due to the structural relaxation as the annealing temperatures increased, was clearly visible. i.e., coprecipitated, gel, and crystalline structure, in turn.

• 한국재료학회지
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• 제13권12호
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• pp.806-811
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• 2003

Ultrafine TaC powders were synthesised by spray drying using tantalum oxalate solution. The spray dried powders were spherical shape and less than 30 $\mu\textrm{m}$ in size. The powders calcined at 500 and X$700^{\circ}C$ showed amorphous structures and $Ta_2$$O_{5}$ phase was obtained by calcining at $700^{\circ}C$. The particle size and shape remains constant after calcination. The calcined spherical powders were composed of an agglomerate of primary particles under 50 nm in size. The complete formation of TaC could be achieved by heat treatment at $1050^{\circ}C$ for 6 hrs. The observed size of TaC powders by TEM was less than 200 nm.

• 한국분말재료학회지
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• 제5권3호
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• pp.178-183
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• 1998

Ultrafine WC-10wt.%Co cemented carbides powders were synthesized by direct carburization. W-Co composite powders and carbon black powders were mixed by wet ball milling and dried. The mixed powders were heated to 800 $^{\circ}C$ with heating rate of 8.2$^{\circ}C$/min and held for various times in flowing $H_2$. For carbon addition of 140%, the carburization was completed by heating at 80$0^{\circ}C$ for 4 hours. The carburization time decreased with increasing amount of carbon and carburization was completed by heating at 800 $^{\circ}C$ for 2 hours with carbon addition of 150%. WC-10 wt%Co cemented carbides powders fabricated by direct carburization have nanoscale WC($\/leqq$100 nm) size.