• Korean Journal of Materials Research
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• v.17 no.8
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• pp.437-441
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• 2007

Preparation and morphology control of $TiO_2$ nano powders for gas sensor applications are investigated. $TiO_2$ nanopowders with rutile and anatase structures were prepared by controlling the pH value of a precursor solution without any heat treatment. The mean particle size of $TiO_2$ powders were below 10nm. The prepared $TiO_2$ nano powders were hydrothermal treated by NaOH solution. The sample was washed in HCl solution. As a result and $TiO_2$ nanotubes were formed. The lengths of $TiO_2$ nanotube were $1{\mu}m$ and the diameters were 10nm. Crystal structure and microstructure of $TiO_2$ nanotube were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). As-prepared $TiO_2$ nanotube powders have several advantages of nano particle size and high surface area and could be a prominent candidate for nano-sensors. The sensitivity of $TiO_2$ nanotube sensor was measured for toluene and NO in this study.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.4
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• pp.625-628
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• 2008

Ba-Zn ferrite powders for electromagnetic insulator were synthesized by self-propagating high-temperature synthesis(SHS) with a reaction of $xBaO_2+(1-x)ZnO+0.5Fe_2O_3+Fe{\rightarrow}Ba_xZn_{1-x}Fe_2O_4$. In this study, phase indentification of SHS products was carried out by using x-ray diffractometry and quasi-nano sized Ba-Zn powders were prepared by a pulverizing process. SHS mechanism was studied by thermodynamical analysis about oxidation reaction among $BaO_2,\;ZnO,\;Fe_2O_3$, and Fe. As oxygen pressure increases from 0.25 MPa to 1.0 MPa, the SHS reactions occur well and make clearly the SHS products. X-ray analysis shows that final SHS products formed with the ratio of $BaO_2/ZnO$ of 0.25, 1.0 and 4.0, are mainly $Ba_xZn_{1-x}Fe_2O_4$. Based on thermodynamical evaluation, the heat of formation increases in the order of $ZnFe_2O_4,\;BaFe_2O_4$, and $Ba_xZn_{1-x}Fe_2O_4$. This supports that $Ba_xZn_{1-x}Fe_2O_4$ phase is predominately formed during SHS reaction. The SHS reactions to form $Ba_xZn_{1-x}Fe_2O_4$ depends on oxygen partial pressure, and the heat of formation during the SHS reaction. The SHS reactions tends to occur well with increasing the oxygen partial pressure and BaO2/ZnO ratio in the reactants This means that the SHS reaction for the formation of Ba-Zn ferrite includes the reduction of BaO2/ZnO and the oxidation of Fe. $Ba_xZn_{1-x}Fe_2O_4$ powders after pulverizing is agglomeratedwith a size of about $50{\mu}m$, in which quasi-nano sized particles with about 300nm are present.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.2
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• pp.108-113
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• 2017

The performance of refrigerant oil at the thrust bearing and at the journal bearing of a scroll compressor is a significant factor. This paper presents the friction and anti-wear characteristics of nano-fluid with a mixture of a refrigerant oil and nano powders. The particle size distribution and oxidation stability of nano powders prepared by the electrical explosion method were analyzed by TEM and BET. It was found that the nanoparticles showed a spherical morphology with sizes ranging of 40-60 nm and were covered with graphite layers of 2-4 nm. The thermal conductivity of POE oil was 0.1-0.5W/mk higher than that of POE oil. The coefficient of friction of Cu-POE was found to be 0.1 higher than that of Al2O3. The cooling capacity of the heat pump with nanofluid increased to 3.67%, and the performance was improved by 5.83%.

• Journal of Powder Materials
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• v.20 no.3
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• pp.191-196
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• 2013

Nano-sized cobalt powder was fabricated by wet chemical reduction method at room temperature. The effects of various experimental variables on the overall properties of fabricated nano-sized cobalt powders have been investigated in detail, and amount of NaOH and reducing agent and dropping speed of reducing agent have been properly selected as experimental variables in the present research. Minitab program which could find optimized conditions was adopted as a statistic analysis. 3D Scatter-Plot and DOE (Design of Experiments) conditions for synthesis of nano-sized cobalt powder were well developed using Box-Behnken DOE method. Based on the results of the DOE process, reproducibility test were performed for nano-sized cobalt powder. Spherical nano-sized cobalt powders with an average size of 70-100 nm were successfully developed and crystalline peaks for the HCP and FCC structure were observed without second phase such as $Co(OH)_2$.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.22.1-22.1
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• 2007

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2004.11a
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• pp.100-101
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• 2004

• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.454-460
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• 2012

The nano-sized zirconia powders were synthesized in an impregnation method using pulp and $ZrOCl_2{\cdot}8H_2O$ as an initial material. The synthesized powders were characterized by XRD and FE-SEM. The particle size of the powder was controlled by preparation conditions, such as drying temperature and time. As a result of the various drying and calcination conditions, 30~50 nm sized homogeneous zirconia particles were obtained at $800^{\circ}C$ for 1 h. Crystallization and the rapid growth of particles were accelerated with increasing calcination temperature and time. Tetragonal phase generated below $800^{\circ}C$ were transferred to monoclinic phase with increasing calcination temperature and time. Moreover, above $800^{\circ}C$, heat treatment time had very large influence on the particle growth, and the change of drying condition also had large influence on the growth of a crystal.

• Journal of Powder Materials
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• v.11 no.4
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• pp.341-347
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• 2004

In the study, a hybrid constitutive model for densification of metallic powders was applied to cold isostatic pressing. The model is based on a pressure-dependent plasticity model for porous materials combined with a dislocation density-based viscoplastic constitutive model considering microstructural features such as grain size and inter-particle spacing. Comparison of experiment and calculated results of microscale and nanoscale Cu powders was made. This theoretical approach is useful for powder densification analysis of various powder sizes, deformation routes and powder processing methods.

• Applied Chemistry for Engineering
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• v.19 no.1
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• pp.27-30
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• 2008

Nano-sized phosphor powders were synthesized by the liquid phase method to confirm the size and morphology. By using the process, red phosphor particles with a size of 80 nm were obtained. The characteristic comparison of $Y_2O_3:Eu^{3+}$ and $YBO_3:Eu^{3+}$ was carried out and, as a result, $YBO_3:Eu^{3+}$ powders using boric salt showed an aggregated morphology and lower PL performance compared to $Y_2O_3:Eu^{3+}$.

• Journal of Powder Materials
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• v.15 no.1
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• pp.53-57
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• 2008

The amorphous $Fe_{73}Si_{16}B_7Nb_3Cu_1$(at%) alloy strip was pulverized using a jet mill and an attrition mill to get flake-shaped powder. The flake powder was mixed with dielectric $BaTiO_3$ powder and its dispersant to increase the permittivity. The powders covered with dielectric powders and its dispersant were mixed with a binder and a solvent and then tape-cast to form sheets. The absorbing properties of the sheets were measured to investigate the roles of the dielectric powder and its dispersant. The results showed that the addition of $BaTiO_3$ powders and its dispersant improved the absorbing properties of the sheets noticeably. The powder sheet mixed with 5 wt% of $BaTiO_3$ powder and 1 wt% of dispersant showed the best electromagnetic wave absorption rate because of the increase of the permittivity and the electrical resistance.