• 한국분말재료학회지
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• 제12권6호
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• pp.406-412
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• 2005

This work is to present a new synthesis of metallic glass (MG)/metallic glass (MG) composites using gas atomization and spark plasma sintering (SPS) processes. The MG powders of $Cu_{54}Ni_6Zr_{22}Ti_{18}$ (CuA) and $Ni_{59}Zr_{15}Ti_{13}Nb_7Si_3Sn_2Al_1$(NiA) as atomized consist of fully amorphous phases and present a different thermal behavior; $T_g$ (glass transition temperature) and $T_x$ (crystallization temperature) are 716K and 765K for the Cu base powder, but 836K and 890K for the Ni base ones, respectively. SPS process was used to consolidate the mixture of each amorphous powder, being $CuA/10\%NiA\;and\;NiA/10\%CuA$ in weight. The resultant phases were Cu crystalline dispersed NiA matrix composites as well as NiA phase dispersed CuA matrix composites, depending on the SPS temperatures. Effect of the second phases embedded in the MG matrix was discussed on the micro-structure and mechanical properties.

• 한국분말재료학회지
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• 제12권4호
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• pp.273-278
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• 2005

Nanostructured TiN/$TiB_2$/$TiSi_2$ and TiN/$TiB_2$/$Ti_5Si_2$ composite powders have been prepared by mechanochemical reaction from mixtures of Ti, BN, and $Si_3N_4$ powders. The raw materials have reacted to form a uniform mixture of TiN, $TiB_2$ and $TiSi_2$ or $Ti_5Si_3$ depending on the amount of $Si_3N_4$ used in the starting mixtures, and the reaction proceeded through so-called mechanically activated self-sustaining reaction (MSR). Fine TiN and $TiB_2$ crystallites less than a few tens of nanometer were homogeneously dispersed in the amorphous $TiSi_2$ or $Ti_5Si_3$ matrix after milling for 12 hours. These amorphous matrices became crystalline phases after annealing at high temperatures as expected, but the original microstructure did not change significantly.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.851-854
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• 2001

Europium-activated Ga$_2$O$_3$powders were prepared by modified "Pechini method" from mixed aqueous solutions of gallium nitrate, europium nitrate, ethylene glycol and citric acid. The formation process and structure of the phosphor powders were investigated by means of TG/DTA, XRD and SEM. It has been found that the phosphor powders were amorphous up to 50$0^{\circ}C$ and changed into crystalline $\beta$-Ga$_2$O$_3$phase above $600^{\circ}C$. The resulting nano-sized powders were obtained. Red luminescence in emission spectra were observed at room temperature.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.648-649
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• 2006

The dry-milling technique was used for mixing and crushing oxides and graphite powders. The ratio of ball-to-powder was 30:1 and argon gas was filled in jar. The excess carbon was $10{\sim}20wt%$ of the stoichiometric amount. The dry-milling was carried for 20 hours. The mixed powders were reduced and carburized at $900{\sim}980^{\circ}C$ for 3 hours flowing Ar gas in tube furnace. The dry-milled powders showed the wide diffraction patterns of X-ray. The reactions of reduction and carburization were completed in 3 hours at $980^{\circ}C$. After the reactions, the mean size of WC particles was about 200 nm. The content of free carbon in WC/Co mixed powders was less as the reaction temperature increased.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
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• pp.311-313
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• 2004

WC-12-17%Co powders with nano- and micro-structures were deposited by cold spray process using nitrogen and helium gases. The results show that there is no detrimental phase transformation and/or decarburization of WC by cold spray deposition as expected. It is also observed that nano-sized WC in the feedstock powder is maintained in the cold spray deposition. It is demonstrated that it is possible to fabricate the nano-structured WC-Co coating with low porosity and very high hardness (-2050 HV) by cold spray deposition with reasonable powder preheating.

• 대한약학회:학술대회논문집
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• 대한약학회 2003년도 Proceedings of the Convention of the Pharmaceutical Society of Korea Vol.2-2
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• pp.234.2-234.2
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• 2003

Recently, the need for ultra-fine particles, especially nano-sized particles has increased in the fields preparing raw powders such as pharmaceutical additive and high value added products in the Nano-Technology processes. Therefore, the research in ultra-fine grinding is very important, especially, in nanometer grinding. In the previous paper, a series of wet grinding experiments using grinding aids using a stirred ball mill have been performed on grinding rate constant based on grinding kinetics. (omitted)

• 한국전기전자재료학회논문지
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• 제25권12호
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• pp.974-978
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• 2012

The effect of Cu coating on the sensing properties of nano $SnO_2:Cu$ based sensors for the $CH_4$, $CH_3CH_2CH_3$ gas was studied. This work was focussed on investigating the change of sensitivity of nano $SnO_2:Cu$ based sensors for $CH_4$, $CH_3CH_2CH_3$ gas by Cu coating. Nano sized $SnO_2$ powders were prepared by solution reduction method using stannous chloride($SnCl_2{\cdot}2H_2O$), hydrazine($N_2H_2$) and NaOH and subsequent heat treatment. XRD patterns showed that nano $SnO_2$ powders with rutile structure were grown with (110), (101), (211) dominant peak. The particle size of nano $SnO_2:Cu$ powders at 8 wt% Cu was about 50 nm. $SnO_2$ particles were found to contain many pores, according to SEM analysis. The sensitivity of nano $SnO_2:Cu$ based sensors was measured for 5 ppm $CH_4$ gas and $CH_3CH_2CH_3$ gas at room temperature by comparing the resistance in air with that in target gases. The sensitivity for both $CH_4$ and $CH_3CH_2CH_3$ gases was improved by Cu coating on the nano $SnO_2$ surface. The response time and recovery time of the $SnO_2:Cu$ gas sensors for the $CH_4$ and $CH_3CH_2CH_3$ gases were 18~20 seconds, and 13~15 seconds, respectively.

• 한국재료학회지
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• 제19권9호
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• pp.504-509
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• 2009

The Zr-based bulk metallic glass matrix composites of a mixture of gas-atomized metallic glass powders and Fe-based nanostructured powders were fabricated by spark plasma sintering. The Fe-based nanostructured powders adopted for the enhancement of plasticity were well distributed in the matrix after consolidation, and the matrix remains as a fully amorphous phase. The successful consolidation of metallic glass matrix composite with high density was attributed to viscous flow in the supercooled liquid state during spark plasma sintering. Unlike other amorphous matrix composites, in which improved ductility could be obtained at the expense of their strength, the developed composite exhibited improvement both in strength and ductility. The ductility improvement in the composite was considered to be due to the formation of multiple shear bands under the presence of the Fe-based nanostructured particles.

• 한국세라믹학회지
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• 제45권7호
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• pp.380-386
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• 2008

Optimized volume production of nanoscale phosphor powders synthesized by radio frequency (RF) plasma process was developed for the application to plasma display panels. The nano powders were synthesized by feeding the both solid and liquid type precursors, and nanoparticle phosphors were characterized in terms of particle size, shape, and photoluminescence (PL) intensities. Computer simulation was performed in advance to determine the process parameters, and nano phosphors were evaluated by comparing with current commercial micron-sized phosphor powders. Practical feeding of both solid and liquid type precursor was proved to be effective for volume production.The developed process showed a potential as a production method for red, blue and green phosphor although the PL intensity still needs further improvement.

• 한국세라믹학회지
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• 제50권6호
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• pp.489-494
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• 2013

Nano-sized titanium oxide powders were synthesized by a polymer matrix technique using pulp and Titanium tetraisopropoxide (TTIP) as starting materials. The synthesized powders were characterized by XRD and FE-SEM. The particle size of the powders was controlled by preparation conditions, such as heat treatment temperature and time. After investigating various drying and heat treatment conditions, 50-100 nm sized homogeneous titanium oxide particles were obtained by treating at $600^{\circ}C$ for 1 h. The crystallization and rapid growth of particles was accelerated by increasing heat treatment temperature and time. Anatase phase generated below $600^{\circ}C$ transformed to the rutile phase with increasing heat treatment temperature. Moreover, above $800^{\circ}C$, heat treatment time had a very large influence on particle growth, and changing the heating condition also had a large influence on crystal growth.