• Korean Journal of Materials Research
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• v.17 no.12
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• pp.669-675
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• 2007

Hydroxyapatite (HAp) and biphasic calcium phosphate (BCP) nano powders were synthesized using the microwave-assisted synthesis process dependent on pH and microwave irradiation time. The average size of a powder was less than 100 nm in diameter. Through in-vitro cytotoxicity tests by an extract dilution method, the HAp and BCP nano powders have shown to be cytocompatible for L-929 fibroblast cells, osteoblastlike MG-63 cells and osteoclast-like Raw 264.7 cells. The activation of osteoblast was estimated by alkaline phosphatase (ALP) activity. When the HAp and BCP were treated to MG-63 cells, alkaline phosphatase activities increased on day 3, compared with those of the untreated cells. Also, the collagen fibers increased when the HAp and BCP powders suspension were treated to MG-63 cells, compared to those of the untreated cells. Quantitative alizarin red S mineralization assays showed a trend toward increasing mineralization in osteoblast cultured with powder suspension. In conclusion, hydroxyapatite and biphasic calcium phosphate appeared to be a bone graft substitute material with optimal biocompatibility and could be further applied to clinical use as an artificial bone graft substitute.

• Journal of Powder Materials
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• v.23 no.5
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• pp.353-357
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• 2016

In this study, $TiO_2$ powders are synthesized from ammonium hexafluoride titanate (AHFT, $(NH_4)_2TiF_6$) as a precursor by heat treatment. First, we evaluate the physical properties of AHFT using X-ray diffraction (XRD), particle size analysis (PSA), thermogravimetric analysis (TGA), and field-emission scanning electron microscopy (FE-SEM). Then, to prepare the $TiO_2$ powders, is heat-treated at $300-1300^{\circ}C$ for 1 h. The ratio of anatase to rutile phase in $TiO_2$ is estimated by XRD. The anatase phase forms at $500^{\circ}C$ and phase transformation to the rutile phase occurs at $1200^{\circ}C$. Increase in the particle size is observed upon increasing the reaction temperature, and the phase ratio of the rutile phase is determined from a comparison with the calculated XRD data. Thus, we show that anatase and rutile $TiO_2$ powders could be synthesized using AHFT as a raw material, and the obtained data are utilized for developing a new process for producing high-quality $TiO_2$ powder.

• Korean Journal of Materials Research
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• v.26 no.10
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• pp.561-569
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• 2016

$SrAl_2O_4$: $Eu^{2+}$ and $Dy^{3+}$ phosphorescent phosphors were synthesized using the polymerized complex method. Generally, phosphorescent phosphors synthesized by conventional solid state reaction show a micro-sized particle diameter; thus, this process is restricted to applications such as phosphorescent ink and paint. However, it is possible to synthesize homogeneous multi-component powders with fine particle diameter by wet process such as the polymerized complex method. The characteristics of $SrAl_2O_4$: $Eu^{2+}$ and $Dy^{3+}$ powders prepared by polymerized complex method with one and two step calcination processes were comparatively analyzed. Temperatures of organic material removal and crystallization were observed through TG-DTA analysis. The crystalline phase and crystallite size of the $SrAl_2O_4$: $Eu^{2+}$ and $Dy^{3+}$ phosphorescent phosphors were analyzed by XRD. Microstructures and afterglow characteristics of the $SrAl_2O_4$: $Eu^{2+}$ and $Dy^{3+}$ phosphors were measured by SEM and spectrofluorometry, respectively.

• Journal of the Korean Ceramic Society
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• v.55 no.2
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• pp.160-165
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• 2018

This paper investigates the reaction rate of $CO_2$ storing carbonation hybrid reaction by comparing the behavior of carbonation between $Ca(OH)_2$ and fly ash with that of CFBC (Circulating Fluidized Bed Combustion) containing plenty of Free-CaO. Because fly ash with CFBC contains a lot of unreacted CaO, it cannot be used as a raw material for concrete admixtures and its usages are limited. To reuse such material, we stabilized unreacted CaO by carbonation and investigated the carbonation rate. We used a pH meter and a thermometer to check the rate of the carbonization. Also, we set the contents of fly ash with CFBC, $Ca(OH)_2$, flow and fluid of $CO_2$, respectively, to 100 g, 50 g, 100 ~ 1000 cc/min and 400 g based on the content of Free-CaO. We used carbonated water instead of water, and added an alkaline activator to promote the carbonation rate. As a result, the addition of the alkaline activator and carbonated water promoted the rate of carbonation via a hybrid reaction.

• Journal of Powder Materials
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• v.14 no.1 s.60
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• pp.63-69
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• 2007

The present study was focused on the synthesis of a zirconium-based alloyed nanopowder by the plasma arc discharge process. The chemical composition, phase structure, particle size and hydrogen sorption property of the synthesized powders under various synthesis conditions were analyzed using XRF, XRD, SEM, XPS and the ASTM-F798 method. The chemical composition of the synthesized Zr-V-Fe-based powders approached that of the raw material with an increasing hydrogen fraction in the powder synthesis atmosphere. The synthesized $Zr_{55}V_{29}Fe_{16}$ powder consist of a mixed phase structure of the $Zr,\;ZrH_2,\;FeV\;and\;Zr(V_{1-x}Fe_{x})_2$ phases. This powder has an average particle size of about 20 nm. The synthesized $Zr_{55}V_{29}Fe_{16}$ nanopowder showed getter characteristics, even though it had a lower hydrogen sorption speed than the $Zr_{57}\;V{36}\;Fe_7$ getter powder. However, the synthesized Zr nanopowder with an average particle size of 20 nm showed higher hydrogen sorption speed than the $Zr_{57}\;V{36}\;Fe_7$ getter powder.

• Journal of Powder Materials
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• v.2 no.2
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• pp.135-141
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• 1995

As the first step of study on fabrication of ceramic powders from phytoliths in rice, especially in rice husks, pulverization method of rice husks and the properties of milled rice husks were investigated. Impact methods, such as ball milling, were not meaningful for pulverizing elastic and thin fabric structure of rice husks. The most effective one was cutting method. In the present work, a rotating knife cutting method was applied to pulverizing rice husks. A 40-mesh screen was inserted under the rotating knives. The most portion of the milled powder was found in -50/+100 mesh section. Morphology of the milled rice husks revealed that the husks larger than 70 mesh were flake-like shape, at -70/+100 mesh section relatively equi-axed shape, at -170/+325 mesh section rod-like shape, and below 325 mesh section dust-like shape. Tap density of raw rice husks was about 0.1 $g/cm^3$, while those of milled rice husks were over $0.4 g/cm^3$. This meant that, for a given volume of reactor, raw material charge can be increased more that 4 times when using milled rice husks than unmilled one. True densities of unmilled and milled rice husks were higher than $1.4 g/cm^3$, and increased with decreasing milled sizes.

• Journal of Powder Materials
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• v.15 no.1
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• pp.1-5
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• 2008

ZnS-$SiO_2$ composite is normally used for sputtering target. In recent years, high sputtering power for higher deposition rate often causes crack formation of the target. Therefore the target material is required that the sintered target material should have high crack resistance, excellent strength and a homogeneous microstructure with high sintered density. In this study, raw ZnS and ZnS-$SiO_2$ powders prepared by a 3-D mixer or high energy ball-milling were successfully densified by spark plasma sintering, the effective densification method of hard-to-sinter materials in a short time. After sintering, the fracture toughness was measured by the indentation fracture (IF) method. Due to the effect of crack deflection by the residual stress occurred by the second phase of fine $SiO_2$, the hardness and fracture toughness reached to 3.031 GPa and $1.014MPa{\cdot}m^{1/2}$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.3
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• pp.122-129
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• 2017

For the production of a high-density ITO target, $In_2O_3$ powders with a small particle size and low agglomeration should be synthesized. The purpose of this study is to control the size and shape of the Indium hydroxide precursor which affects the properties of the $In_2O_3$ powder. As a starting raw material, Indium metal was dissolved in a Nitric acid ($HNO_3$) solution. The effect of concentration, pH, and temperature on the properties of Indium hydroxide was investigated using ammonium hydroxide as a precipitant. Crystallite size of each sample was analyzed by X-ray diffraction and the shape and the size of the powder was analyzed by transmission electron microscopy. As a result, the particle size of Indium hydroxide was increased with increase in the concentration of $In(NO_3)_3$ and the particle size and shape of the Indium hydroxide remained unchanged with increase in the pH of the solution. The particle size increased with increase in the precipitation temperature during precipitation.

• Journal of Powder Materials
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• v.15 no.5
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• pp.352-358
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• 2008

The present study focused on the synthesis of a bismuth-antimony-tellurium-based thermoelectric nanopowders using plasma arc discharge process. The chemical composition, phase structure, particle size of the synthesized powders under various synthesis conditions were analyzed using XRF, XRD and SEM. The powders as synthesized were sintered by the plasma activated sintering. The thermoelectric properties of sintered body were analyzed by measuring Seebeck coefficient, specific electric resistivity and thermal conductivity. The chemical composition of the synthesized Bi-Sb-Te-based powders approached that of the raw material with an increasing DC current of the are plasma. The synthesized Bi-Sb-Te-based powder consist of a mixed phase structure of the $Bi_{0.5}Sb_{1.5}Te_{3}$, $Bi_{2}Te_{3}$ and $Sb_{2}Te_{3}$ phases. This powder has homogeneous mixing state of two different particles in an average particle size; about 100nm and about 500nm. The figure of merit of the sintered body of the synthesized 18.75 wt.%Bi-24.68 wt.%Sb-56.57 wt.%Te nanopowder showed higher value than one of the sintered body of the mechanically milled 12.64 wt.%Bi-29.47 wt.%Sb-57.89 wt.%Te powder.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.395-402
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• 2015

The suspension plasma spray (SPS) technique has been used to obtain dense $Y_2O_3$ coatings and to overcome the drawbacks of the conventional air plasma spray (APS). SPS uses suspensions containing micrometer or sub-micrometer sized powders dispersed in liquid media. In this study, microstructure developments and mechanical properties have been investigated as functions of particle size of source material and plasma processing parameters such as plasma power and stand-off distance. The microstructure of the coating was found to be highly related to the particle size and the plasma processing parameters, and it was directly reflected in the hardness and the adhesion strength. When fine powder (BET $16.4m^2/g$) was used as a raw material in the suspension, there was, with increasing stand-off distance, a change from a dense structure with a slightly bumpy surface to a porous structure with a cauliflower-like surface. On the other hand, when a coarse powder (BET $2.8m^2/g$) was used, the coating density was lower, with microscopic splats on the surface. Using fine $Y_2O_3$ powders, the coating layer with an optimum short stand-off distance showed a high hardness of approximately 90% of that of sintered $Y_2O_3$ and an adhesion strength several times higher than that of the coating by conventional APS.