• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.128-128
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• 2013

Fabrication of heterogeneous catalysts using Atomic Layer Deposition (ALD) has recently been attracting attention of surface chemists and physicists. In this talk, I will present recent results about structures and chemical activities of various catalysts prepared by ALD, particularly focusing on Ni-based catalysts. Ni has been considered as potential catalysts for $CO_2$ reforming of methane (CRM); however, Ni often undergoes rapid decrease in catalytic activity with time, and therefore, application of Ni as catalysts for CRM has been regarded as difficult so far. Deactivation of Ni catalysts during CRM reaction is from either coke formation on Ni surface or sintering of Ni particles during reaction. Two different strategies have been used for enhancing stability of Ni-based catalysts; $TiO_2$ nanoparticles were deposited on micrometer-size Ni particles by ALD, which turned out to reduce coke formation on Ni surfaces. Ni nanoparticles deposited by ALD on mesoporous silica showed high activity and long-term stability from CRM without coke deposition and sintering during CRM reaction. Ni-based catalysts have been also used for oxidation of toluene, which is one of the most notorious gases responsible for sick-building syndrome. It was shown that onset-temperature of Ni catalysts for toluene oxidation is as low as $120^{\circ}C$. At $250\circ}C$, total oxidation of toluene to $CO_2$ with a 100% conversion was found.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.04a
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• pp.77-78
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• 2006

급속소결방법인 고주파유도가열 소결법과 펄스전류활성 소결법을 이용하여 습식 볼밀링으로 혼합한 WC-8wt.%Ni분말에 60MPa의 압력과 고주파유도가열장치의 경우 전체 용량 (15kw)의 90%에 해당하는 고주파출력을, 펄스전류활성 소결장치의 경우 2800A의 펄스전류를 가하여 치밀한 소결체를 2분이내의 짧은 시간에 제조하였다. WC 초기입자크기가 증가함에 따라 제조된 소결체의 입자크기와 평균자유행로는 증가하였다. 또한 WC 결정립 크기가 증가함에 따라 경도는 증가하였으며, 파괴인성은 감소함을 알 수 있었다. $0.5{\mu}m$의 분말을 60MPa의 압력하에서 고주파유도가열 소결법에 의해 얻어진 소결체의 파괴인성과 경도는 각각 $1813kg/mm^2$과 $8.9MPa{\cdot}m^{1/2}$ 이었고, 펄스전류활성 소결법에 의해 제조된 소결체의 경도와 파괴인성은 각각 $1839kg/mm^2$과 $8.5MPa{\cdot}m^{1/2}$ 이었다.

• Journal of Powder Materials
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• v.15 no.3
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• pp.196-203
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• 2008

The densification behavior of Al-20Si-5.5Fe-1.2Mg-0.5Mn powders was investigated through micro-structure analysis of sintered specimens. The specimens sintered in vacuum or in high purity (99.999%) nitrogen showed porous near-surface microstructures. The densification of near-surface part was enhanced by means of ultra-high purity (99.9999%) nitrogen atmosphere. The relationship between slow densification and oxide surfaces of Al alloy powders was discussed. And the effects of Mg addition, nitrogen gas, and humidity on densification were discussed. In addition, the rapid growth of primary Si crystals above the critical temperature was reported.

• Journal of Powder Materials
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• v.13 no.3 s.56
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• pp.172-177
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• 2006

Aging characteristics and mechanical properties of commercial 7xxx series Al composites were investigated from viewpoint of ceramic contents. After sintering process, sintered densities of blended and composite powder were 95 and 97%, respectively. Each part was solution-treated at $475^{\circ}C$ for 60 min and aged $175^{\circ}C$. And two-step aging was also performed form $120^{\circ}C$ to $175^{\circ}C$. The aging behavior of the sintered composite pow-der was different from that of sintered blended powder. The peak aging time of the composite was rapid as well due to strain. Before aging, mechanical properties of sintered composite powder was significantly higher than that of sintered blended powder. These increments of properties were directly affected by ceramic particles. However, after aging, incremental rate of mechanical properties was slowed in the composite.

• Journal of Powder Materials
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• v.27 no.1
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• pp.31-36
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• 2020

Phosphorus is an element that plays many important roles in powder metallurgy as an alloy element. The purpose of this study is to investigate the influence of phosphorus addition on the microstructures and mechanical properties of sintered low-alloy steel. The sintered low-alloy steels Fe-0.6%C-3.89%Ni-1.95%Cu-1.40%Mo-xP (x=0, 0.05, 0.10, 0.15, 0.20%) were manufactured by compacting at 700 MPa, sintering in H₂-N₂ at 1260 ℃, rapid cooling, and low-temperature tempering in Ar at 160 ℃. The microstructure, pore, density, hardness, and transverse rupture strength (TRS) of the sintered low-alloy steels were evaluated. The hardness increased as the phosphorus content increased, whereas the density and TRS showed maximum values when the content of P was 0.05%. Based on microstructure observation, the phase of the microstructure changed from bainite to martensite as the content of phosphorus is increased. Hence, the most appropriate addition of phosphorus in this study was 0.05%.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2175-2178
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• 2005

Selective Laser Sintering(SLS) method is one of Rapid Prototyping(RP) technologies. It has been used to fabricate desirable part to sinter powder and stack the fabricated layer. Since the sintering process occurs using infrared laser having high thermal energy, shrinkage and curling of the fabricated part occurs according to thermal distribution. Therefore, the fast scanning path generation is necessary to eliminate the factors of quality deterioration. In case of fabricating larger size parts, the unique scanning device and scanning path generation should be considered. In this paper, the development of SLS machines being capable of large size fabrication(800${\times}$1000${\times}$800 mm, W${\times}$D${\times}$H) will be addressed. The dual laser system and the unique scanning device have been designed and built, which employ CO2 lasers and dynamic 3-axis scanners. The developed system allows scanning a larger planar surface with the desired laser spot size. Also, to generate the fast scanning paths, adaptive path generation is needed with respect to the shape of each layer, and not simply x, y scanning, but the scanning of arbitrary direction should be enabled. To evaluate the suggested method, the complex part will be used for the experiment fabrication.

• Journal of the Korean Ceramic Society
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• v.48 no.1
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• pp.106-109
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• 2011

In order to fabricate 8YSZ thick film by silk screen printing, YSZ(yttria-stabilized zirconia) commercial powder was used as starting materials. Paste for screen printing was made by mixing 8YSZ powder and organic vehicles. 8YSZ thick film was formed on $Al_2O_3$ substrate. The crystal structure, and microstructure were investigated. Grain size of 8YSZ was increased with increasing calcination temperature and rapid grain growth was shown after calcination at $1300^{\circ}C$. Microstructure showed the mixture of large and small grain size after $1400^{\circ}C$ sintering. Shrinkage rate of 8YSZ thick film sintered at $1400^{\circ}C$ was more than 40%.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.9
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• pp.773-779
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• 2015

The laser Powder Bed Fusion (PBF) system is currently recognized as a leading process. Due to the various materials employed such as thermoplastic, metal and ceramic composite powder, the application's use extends to machinery, automobiles, and medical devices. The PBF system's surface quality of prototypes and processing time are significantly affected by several parameters such as laser power, laser beam size, heat temperature and laminate thickness. In order to develop a more elaborate and rapid system, this study developed a new PBF system and sintering process. It contains a 3-axis dynamic focusing scanner system that maintains a uniform laser beam size throughout the system unlike the $f{\theta}$ lens. In this study, experiments were performed to evaluate the effects of various laser scanning parameters and fabricating parameters on the fusion process, in addition to fabricating various 3D objects using a PA-12 starting material.

• Journal of Korea Foundry Society
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• v.23 no.5
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• pp.244-250
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• 2003

The aim of this study is fabricating of composite filler metal (CFM) by a combination of selective laser sintering (SLS) of stainless steel powders (RapidSteel $2.0^{TM}$ and liquid phase infiltration of Ag-28 wt.%Cu alloy. Porous stainless steel body with inter-connected pore channels was fabricated by SLS, binder decomposing and densification processes. By the direct contact infiltration, the narrow inter-particle channels of the porous body were completely filled with the Ag-28 wt.%Cu alloy infiltrant. During infiltration, the dissolved elements of Fe, Ni and Cr from the porous body were solved into copper solid solution phases, which consist of eutectic structure of composite metal matrix. The S10C/CFM/S10C joints, which have narrow clearance gaps between them up to 10 micrometers, were joined successfully by self-feeding of filler metal from the matrix of CFM. The CFM kept its original thickness and microstructure after brazing. The tensile strength of brazed specimen was higher than 30 kgf/$mm^2$ and showed a typical ductile fracture mode in the CFM.

• The Korean Journal of Ceramics
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• v.1 no.4
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• pp.179-184
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• 1995

Sodium superionic conductor (NASICON) compounds were prepared. The effects of sintering temperature and cooling rate on the formation and the distribution of crystalline NASICON and $ZrO_3$ second phase were investigated. In the von Alpen-type composition, the $ZrO_2$ second phase is in thermal equilibrium with the crystalline NASICON above $1320^{\circ}C$, but when cooled through 1260-$1320^{\circ}C$ crystalline NASICON was formed by reaction between $ZrO_2$ and liquid phase. Very slow cooling ($1^{\circ}C$/hr) to $1260^{\circ}C$ from sintering temperature decreased the amount of sodium which prevents the formation of the crystalline NASICON resulted high number of $ZrO_2$ grains near the surface of some sintered bodies. Maximum electrical conductivity of 0.200 ohm-1cm-1 was obtained at $300^{\circ}C$ for well-sintered samples with little $ZrO_3$. On the other hand, low conductivities were obtained for rapid-cooled samples which have less dense microstructure.