• Korean Journal of Materials Research
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• v.20 no.9
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• pp.467-471
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• 2010

Composites of ceramic powders and an elastomer-based matrix were prepared by mixing $CaCO_3$ powders with polyethylene and polypropylene elastomers, and their mechanical and sound insulation properties were measured. $CaCO_3$ powders with 0.7 ${\mu}m$ and 35 ${\mu}m$ particle size were added to elastomers up to 80 wt%. Scanning electron microscopy photographs showed uniform distribution of the $CaCO_3$ powders in the matrix. While density and surface hardness increased, melt index, tensile strength and elongation of the composites decreased as the amount of added $CaCO_3$ powders increased. As more $CaCO_3$ powders were added sound transmission loss of the composites increased owing to the increase of density. Addition of 0.7 ${\mu}m$ sized $CaCO_3$ powders resulted in a slightly higher transmission loss than the addition of 35 ${\mu}m$ sized powders because of the increased interface area between the elastomer matrix and the $CaCO_3$ powders. Composites with a polyethylene matrix showed higher transmission loss than those with a polypropylene matrix because the tensile strength and hardness of the polyethylene-based composites were low and their elongation was high.

• Journal of the Korean Society of Food Science and Nutrition
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• v.30 no.1
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• pp.48-55
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• 2001

This study investigated the quality characteristics of sponge cakes with addition of yam (Dioscorea) powders prepared by different drying methods, hot air (HDYP : hot air dried yam powder) and freeze drying (FDYP: freeze dried yam powder), using several physical and sensory examinations. For the foam forming ability and foam stability, the specific gravities of egg foams containing 5% yam powders were measured by drainage using funnels for 78 hrs. The results showed that HDYP and FDYP did not affect the foam forming ability but FDYP increased foam stability due to increased viscosity. When the strength of 8% gels composed of wheat starch and HDYP/FDYP was measured to predict the setting of cake structure, the strengths of starch gels containing yam powders were higher than those of control without yam powders. The volume of sponge cake containing 5% HDYP increased whereas those containing FDYP decreased at the levels of 5, 7%. From the texture profile analysis data, hardness, gumminess and chewiness of cakes containing yam powders increased. The color of cake crust and crumb became darker as the amount of yam powders increased. The results of sensory evaluation by QDA (quantitative descriptive analysis) to compare two different drying methods showed that appearance and texture of cakes containing 5% HDYP were closer to those of control than cakes containing 5% FDYP but overall acceptability of sponge cakes containing yams were comparable to the control cakes regardless of drying methods. The addition of yam powders to sponge cakes increased yam flavor and decreased egg smell. Therefore, it can be suggested that HDYP and FDYP can be added to the sponge cake formula up to 7% and 5%, respectively.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.550-557
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• 2020

Used in the ceramic tile market as a representative building material, relief ceramic tile is showing increased demand recently. Since ceramic tiles are manufactured through a sintering process at over 1,000 ℃ after uniaxial compression molding by loading granule powders into a mold, it is very important to secure the flowability of granular powders in a mold having a relief pattern. In this study, kaolin, silica, and feldspar are used as starting materials to prepare granule powders by a spray dryer process; the surface of the granule powders is subject to hydrophobic treatment with various concentrations of stearic acid. The effect on the flowability of the granular powder according to the change of stearic acid concentration is confirmed by measuring the angle of repose, tap density, and compressibility, and the occurrence of cracks in the green body produced in the mold with the relief pattern is observed. Then, the green body is sintered by a fast firing process, and the water absorption, flexural strength, and durability are evaluated. The surface treatment of the granule powders with stearic acid improves the flowability of the granule powders, leading to a dense microstructure of the sintered body. Finally, the hydrophobic treatment of the granule powders makes it possible to manufacture relief ceramic tiles having a flexural strength of 292 N/cm, a water absorption of 0.91 %, and excellent mechanical durability.

• Korean Journal of Materials Research
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• v.27 no.9
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• pp.489-494
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• 2017

ZnS powder was synthesized using a relatively facile and convenient glycothermal method at various reaction temperatures. ZnS was successfully synthesized at temperatures as low as $125^{\circ}C$ using zinc acetate and thiourea as raw materials, and diethylene glycol as the solvent. No mineralizers or precipitation processes were used in the fabrication, which suggests that the spherical ZnS powders were directly prepared in the glycothermal method. The phase composition, morphology, and optical properties of the prepared ZnS powders were characterized using XRD, FE-SEM, and UV-vis measurements. The prepared ZnS powders had a zinc blende structure and showed average primary particles with diameters of approximately 20~30 nm, calculated from the XRD peak width. All of the powders consisted of aggregated secondary powders with spherical morphology and a size of approximately $0.1{\sim}0.5{\mu}m$; these powders contained many small primary nanopowders. The as-prepared ZnS exhibited strong photo absorption in the UV region, and a red-shift in the optical absorption spectra due to the improvement in powder size and crystallinity with increasing reaction temperature. The effects of the reaction temperature on the photocatalytic properties of the ZnS powders were investigated. The photocatalytic properties of the as-synthesized ZnS powders were evaluated according to the removal degree of methyl orange (MO) under UV irradiation (${\lambda}=365nm$). It was found that the ZnS powder prepared at above $175^{\circ}C$ exhibited the highest photocatalytic degradation, with nearly 95 % of MO decomposed through the mediation of photo-generated hydroxyl radicals after irradiation for 60 min. These results suggest that the ZnS powders could potentially be applicable as photocatalysts for the efficient degradation of organic pollutants.

• Journal of Powder Materials
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• v.23 no.2
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• pp.136-142
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• 2016

As precursors of cathode materials for lithium ion batteries, $Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$ powders are prepared in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH in the presence of $NH_4OH$ in air or nitrogen ambient. Calcination of the precursors with $Li_2CO_3$ for 8 h at $1,000^{\circ}C$ in air produces dense spherical cathode materials. The precursors and final powders are characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analysis, tap density measurement, and thermal gravimetric analysis. The precursor powders obtained in air or nitrogen ambient show XRD patterns identified as $Ni_{1/3}Co_{1/3}Mn_{1/3}(OH)_2$. Regardless of the atmosphere, the final powders exhibit the XRD patterns of $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ (NCM). The precursor powders obtained in air have larger particle size and lower tap density than those obtained in nitrogen ambient. NCM powders show similar tendencies in terms of particle size and tap density. Electrochemical characterization is performed after fabricating a coin cell using NCM as the cathode and Li metal as the anode. The NCM powders from the precursors obtained in air and those from the precursors obtained in nitrogen have similar initial charge/discharge capacities and cycle life. In conclusion, the powders co-precipitated in air can be utilized as precursor materials, replacing those synthesized in the presence of nitrogen injection, which is the usual industrial practice.

• Journal of Powder Materials
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• v.21 no.3
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• pp.207-214
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• 2014

In this study, nano-scale copper powders were reduction treated in a hydrogen atmosphere at the relatively high temperature of $350^{\circ}C$ in order to eliminate surface oxide layers, which are the main obstacles for fabricating a nano/ultrafine grained bulk parts from the nano-scale powders. The changes in composition and microstructure before and after the hydrogen reduction treatment were evaluated by analyzing X-ray diffraction (XRD) line profile patterns using the convolutional multiple whole profile (CMWP) procedure. In order to confirm the result from the XRD line profile analysis, transmitted electron microscope observations were performed on the specimen of the hydrogen reduction treated powders fabricated using a focused ion beam process. A quasi-statically compacted specimen from the nano-scale powders was produced and Vickers micro-hardness was measured to verify the potential of the powders as the basis for a bulk nano/ultrafine grained material. Although the bonding between particles and the growth in size of the particles occurred, crystallites retained their nano-scale size evaluated using the XRD results. The hardness results demonstrate the usefulness of the powders for a nano/ultrafine grained material, once a good consolidation of powders is achieved.

• Journal of Technologic Dentistry
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• v.23 no.1
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• pp.9-19
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• 2001

Microstructure and phase transformation of Ti-Ni-Cu alloy powders produced by using attrition milling method were studied. Mixed powders of Ti-(50-X)Ni-XCu ($X=0{\sim}20$ at%) in composition range were mechanically alloyed for maximum 20 hours by using SUS 1/4" ball in argon atmosphere. Ball to powder ratio was 50: 1 and impeller speed was 350rpm. Mechanically alloyed with attrition millimg method. powder was heat treated at the temperature up to $850^{\circ}C$ for 1 hour in the $10^{-6}$ torr vacuum. Ti-Ni-Cu alloy powders have been fabricated by attrition milling method. and then phase transformation behaviours and microstructual properties of the alloy powders were investigated to assist in improving the the high damping capacity of Ti-Ni-Cu shape memory alloy powders. The results obtained are as follows: 1. After heat treating of fully mechanically alloyed powder at $850^{\circ}C$ for 1hour. most of the B2 and B 19' phases was formed and $TiNi_3$ were coexisted. 2. The B 19' martensite were formed in Ti-Ni-Cu alloy powders whose Cu-content is less than 5a/o. where as the B19 martensite in those whose Cu-content is more than 10at%. 3. The powders of as-milled Ti-Ni-Cu alloys whose Cu-contents is less than 5at% are amorphous. whereas those of as-milled Ti-Ni-Cu alloys whose Cu-content is more than 10at% are crystalline. This means that Cu addition tends to suppress amorphization of Ti-Ni alloy powders.

• Journal of the Korean Ceramic Society
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• v.35 no.6
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• pp.543-550
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• 1998

A process for the preparation of spherical tungsten oxide powders by the emulsion evaporation method was developed. The characteristics of the powders thus prepared were examined by means of TGA X-ray diffraction SEM and image analysis. The emulsion was prepared by fast mixing of tungsten containing aque-ous phase and the organic phase which contained kerosene surfactant and paraffin oil. The precursor was made by evaporating the emulsion in the kerosene bath at $160^{\circ}C$ and then calcined at $650^{\circ}C$ in order to pro-duce tungsten oxide powders. The average particle size of the tungsten oxide powders was $0.5\;\mu\textrm{m}$ and their shapes were spherical. Water-in-oil type emulsion wasmore advantageous to make less agglmerated. $W_{3}$ powders than the oil-in-water type emulsion for the emulsion evaporation experiments. As the HLB value of the surfactant increased and the concentration of tungsten ions in the aqueous phase decreased the mean particle size of tungsten oxide powders decreased whereas agglomeration increased. The optimum con-centration of Span 80 was 8 percent by volume and the optimum stirring speed in the emulsion formation was 5000 rpm in order to obtain find less agglomerated $W_{3}$ powders.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1340-1345
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• 2018

Mo-10 at.% Cu nanocomposite powders were fabricated by using planetary ball-milling (PBM), a mechanical alloying technique for preparing nanocomposite alloy powders of metals with mutual insolubility, and the variations in the physical and the chemical characteristics with the process conditions were investigated. We observed that Mo-10 at.% Cu was an appropriate composition to ensure a good alloying grade and minimal welding between particles. The influences of the temperature and the milling conditions on the mechanical alloying process and the phase change of Mo-10 at.% Cu composite powders were investigated, and the particle and the grain sizes of the powders after mechanical alloying were confirmed. The Mo-10 at.% Cu powders showed homogeneous elemental distributions and no phase changes up to $1200^{\circ}C$; their compositions were retained after the mechanical alloying process. The finest grain size obtained was about 5 nm for powders processed using optimum PBM processing conditions: ball-to-powder weight ratio of 5 : 1, ambient air atmosphere, a milling time of 20 h, a rotation speed of 200 rpm, and a stearic acid content of 4 wt.% produced superfine-grained Mo-10 at.% Cu nanocomposite powders with an average grain size of 5 nm (which is smaller than that of other similar materials reported in the literature). The analytical results confirmed that the PBM technique presented here is a promising method for preparing superfine-grained Mo-10 at.% Cu powders with improved properties.

• Journal of the Korean Home Economics Association
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• v.44 no.3 s.217
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• pp.163-169
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• 2006

The effects of adding Angelica plant (Bakluncho) and Angelica gigas (Senggumcho) powders on the quality characteristics of bread were investigated. The moisture, crude protein, ash, reducing sugar and vitamin C contents of Angelica plant (Bakluncho) powder were 7.78%, 6.07%, 7.37%, 6.13% and 50.10mg%, respectively, and of Angelica gigas (Senggumcho) powder were 8.69%, 12.28%, 5.15%, 2.21% and 108.00mg%, respectively. The lightness value decreased but the redness and yellowness values increased with the addition of Angelica plant (Bakluncho) and Angelica gigas (Senggumcho) powders. The mechanical hardness of bread decreased with the addition of 3% of Angelica plant (Bakluncho) powder, but increased with the addition of 1% and 5% of Angelica plant (Bakluncho) powder. The mechanical hardness of bread decreased with the addition of 1%, 3% and 5% of Angelica gigas (Senggumcho) powder. In sensory characteristics, the crust color, crumb color, moistness and springiness decreased, but aroma and hardness increased with the addition of Angelica plant (Bakluncho) and Angelica gigas (Senggumcho) powders. The savory taste and overall quality of breads with 1% Angelica plant (Bakluncho) and 1% Angelica gigas (Senggumcho) powders were higher than without either powder. A negative correlation was observed between mechanical hardness and overall bread quality with the addition of Angelica plant (Bakluncho) powder, while a positive correlation (p<0.01) was observed with the addition of Angelica gigas (Senggumcho) powder.