• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.245-251
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• 2015

We have applied mechanical alloying (MA) to produce soft magnetic composite material using a mixture of elemental $Fe_2O_3$-Mg powders. An optimal milling and heat treatment conditions to obtain soft magnetic ${\alpha}$-Fe/MgO composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that ${\alpha}$-Fe/MgO composite powders in which MgO is dispersed in ${\alpha}$-Fe matrix are obtained by MA of $Fe_2O_3$ with Mg for 30 min. The saturation magnetization of ball-milled powders increases with increasing milling time and reaches to a maximum value of 69.5 emu/g after 5 h MA. The magnetic hardening due to the reduction of the ${\alpha}$-Fe grain size by MA was also observed. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at $800{\sim}1000^{\circ}C$ under 60 MPa. X-ray diffraction result shows that the average grain size of ${\alpha}$-Fe in ${\alpha}$-Fe/MgO nanocomposite sintered at $800^{\circ}C$ is in the range of 110 nm.

• Food Engineering Progress
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• v.21 no.3
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• pp.225-232
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• 2017

Most of the red ginseng (RG) products contain active substances derived from hot water or alcohol extraction. Since active substances of RG are divided into two types - water-soluble and liposoluble - water or alcohol is needed as an extraction solvent and this leads the different extraction yields and components of the active substances. To overcome the limit, whole red ginseng powder can be used and consumed by consumers. In this study, the physicochemical properties and extractable active substance contents of variable-sized RG powder ($158.00{\mu}m$, $8.45{\mu}m$, and $6.33{\mu}m$) were analyzed, and dispersion stability was measured to investigate the suitable size of RG powder for industrial processing. In the results, no significant difference was found from the changes in color intensity and thiobarbutric acid tests at $4^{\circ}C$, $25^{\circ}C$, and $40^{\circ}C$ for 4 weeks. There was no significant difference on the production of antioxidants and ginsenoside among the samples (p>0.05). In dispersion stability, $RG-158.00{\mu}m$ was precipitated immediately, and the dispersion stabilities between $RG-8.45{\mu}m$ and $RG-6.33{\mu}m$ showed no significant difference. It implies that fine RG is suitable for the production process. With further study, it seemed that the physicochemical effects of RG particle sizes can be clearly revealed.

• Korean Journal of Materials Research
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• v.24 no.5
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• pp.249-254
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• 2014

Due to their unique properties, tungsten borides are good candidates for the industrial applications where certain features such as high hardness, chemical inertness, resistance to high temperatures, thermal shock and corrosion. In this study, conditions were investigated for producing tungsten boride powder from tungsten oxide($WO_3$) by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques. In the first stage of the study, the exothermicity of the $WO_3$-Mg reaction was investigated by computer simulation. Based on the simulation experimental study was conducted and the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of $WO_3$, Mg and $B_2O_3$. It was found that $WO_3$, Mg and $B_2O_3$ reaction system produced high combustion temperature and radical reaction so that diffusion between W and B was not properly occurred. Addition of NaCl and replacement of $B_2O_3$ with B successfully solved the diffusion problem. From the optimum condition tungsten boride($W_2B$ and WB) powders which has 0.1~0.9 um particle size were synthesized.

• Korean Journal of Metals and Materials
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• v.49 no.7
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• pp.565-569
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• 2011

Nanopowders of MgO, $Al_2O_3$ and $SiO_2$ were made by high-energy ball milling. The fast sintering of nanostructured $Al_2O_3-MgSiO_3-SiO_2$ composites was investigated from mechanically activated powders of MgO, $Al_2O_3$ and $SiO_2$ by a pulsed-current activated sintering process. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties; in particular greater strength, hardness, excellent ductility and toughness. Highly dense nanostructured $Al_2O_3- MgSiO_3-SiO_2$ composites were produced with simultaneous application of 80 MPa and pulsed output current of 2800A within 2 minutes. The sintering behavior, grain size and mechanical properties of $Al_2O_3-MgSiO_3-SiO_2$ composites were investigated.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.3981-3986
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• 2012

Anatase nanocrystalline and its tungsten-doped (0.4, 2, and 4 mol %) powders have been synthesized by microwave irradiation through hydrolysis of titanium tetra-isopropoxide (TIP) in aqueous solution. The materials are characterized by XRD, Raman, SEM-EDX, TEM, FT-IR and UV-vis techniques. The nanocrystalline $TiO_2$ particles are 30 nm in nature and doping of tungsten ion decreases their size. As seen in TEM images, the crystallites of W (4 mol %) doped $TiO_2$ are small with a size of about 10 nm. The photocatalytic activity was tested on the degradation of 4-nitrophenol (4-NP). Catalytic activities of W-doped and pure $TiO_2$ were also compared. The results show that the photocatalytic activity of the W-doped $TiO_2$ photocatalyst is much higher than that of pure $TiO_2$. Degradation decreases from 96 to 50%, during 115 min, when the initial 4-NP concentration increases from 10 to 120 ppm. Maximum degradation was obtained at 35 mg of photocatalyst.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.2
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• pp.19-25
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• 2002

Glass composed of $Li_2$O.MgO. $MgF_2$.$SiO_2$.$B_2O_3$ for the fabrication of green sheet was prepared by melting process, and glass ceramics was prepared by the process of nucleation and grystal growth for the glass of $Li_2$O.MgO. $MgF_2$.$SiO_2$.$B_2O_3$ system with Lithium fluorhectorite and Lithium boron fluorphlogopite crystal phase. Powderization of the glass ceramics was carried out by water swelling. The average particle size at this point was 2.574 $\mu\textrm{m}$. Slurry was prepared for green sheet using high viscous sol fabricated by water swelling, which shows cleavage phenomenon in prepared glass ceramics. The optimum ratio of powder to water for the tape casting was 18:100, and its viscosity was 11,000~14,000 cps.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.65-73
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• 2000

Casting of metal matrix composites is an attractive process since it offers a wide selection of materials and processing conditions. Among the casting methods, melt-stirring technology is much attractive route in industrial application because it is more simple and inexpensive compared to squeeze casting or powder metallurgy. In the present work, effects of particle size, volume fraction of particles and mg addition on mechanical properties and thermal expansion coefficients of $\alpha$ -$Al_2O_{3(p)}$/LXA composites were studied. It is shown that $\alpha$ -$Al_2O_3$ particles formed at the interface of $\alpha$ -$Al_2O_3$ particles and matrix made an important role on mechanical properties. Ultimate tensile strength of most composite materials was not increased. But in the case of 5vol% addition of 16$\mu\textrm{m}$ $\alpha$ -$Al_2O_3$ Particle, Ultimate tensile strength of composite materials with 3wt.% Mg was increased. Volume fraction of reinforcements and mg content were thermal expansion coefficients of composite materials were decreased.

• The Korean Journal of Community Living Science
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• v.27 no.3
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• pp.343-350
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• 2016

The antioxidant activity was examined on ultra-fine powdered (UFP) Ulmus davidiana (U. davidiana) var. japonica. The average particle size of UFP or commercial powdered (CP) was $1-3{\mu}m$ or $100{\mu}m$. The extraction was performed using either ethanol (EtOH) or hot-water. Contents of phenolic compound of CP and UFP U. davidiana extracts in EtOH was 40.38 and 65.61 mg/g, respectively. In DPPH, EtOH extract of UFP U. davidiana showed a significantly greater activity than hot-water extract at 40 and $200{\mu}g/mL$. At $200{\mu}g/mL$, the activity was over 90% in all groups. The reducing power of UFP U. davidiana var. japonica in EtOH extraction was 74.3%, which was significantly greater than in other samples (p<0.05). In addition, reducing powder was significantly higher in UFP-EtOH than in other samples at all concentrations except for $0.32{\mu}g/mL$. The above results suggest that EtOH extraction of U. davidiana showed slightly higher DPPH radical scavenging activity, and ultra-fine powder of U. davidiana extracts may show higher antioxidative activities based on reducing power.

• Journal of Powder Materials
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• v.1 no.1
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• pp.42-51
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• 1994

6061Al-SiCP metal matrix composite materials(MMCs) were fabricated by injecting SiCP particles directly into the atomized spray. The main attraction of this technique is the rapid fabrication of semi-finished, composite products in a combined atomization, particulate injection(10 $\mu\textrm{m}$, 40 $\mu\textrm{m}$, SiCP) and deposition operation. Conclusions obtained are as follows; The microstructure of the unreinforced spray formed 6061Al alloy consisted of relatively fine(50 $\mu\textrm{m}$) equiaxed grains. By comparision, the microstructure of the I/M materials was segregated and consisted of relatively coarse(150 $\mu\textrm{m}$) grains. The probability of clustering of SiCP particles in co-sprayed metal matrix composites increased it ceramic particle size(SiCP) was reduced and the volume fraction was held constant. Analysis of overspray powders collected from the spray atomization and deposition experiments indicated that morphology of powders were nearly spherical and degree of powders sphercity was deviated due to composite with SiCp particles. Interfacial bonding between matrix and ceramics was improved by heat treatment and addition of alloying elements(Mg). Maximum hardness values [Hv: 165 kg/mm2 for Al-10 $\mu\textrm{m}$ SiCp Hv--159 kg/mm2 for Al-40 $\mu\textrm{m}$SiCp] were obtained through the solution heat treatment at $530^{\circ}C$ for 2 hrs and aging at $178^{\circ}C$, and there by the resistance were improved.

• Journal of Powder Materials
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• v.17 no.5
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• pp.404-408
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• 2010

The effects of high energy ball-milling (HEBM) on the sintering behavior and piezoelectric properties of 0.1 wt% $Li_2CO_3$ doped 0.8Pb($Mg_{1/3}Nb_{2/3}$)$O_3$-0.2Pb($Zr_{0.475}Ti_{0.525}$)$O_3$ (PMN-PZT) ceramics were investigated. It was found that HEBM treatment was quite effective to reduce the average particle size down to 300 nm, leading to increased density as well as enhanced piezoelectric properties of a sintered specimen even though prolonged HEBM resulted in unwanted secondary phases that caused a degradation of piezoelectric properties. The dielectric constant ($\varepsilon_r$), piezoelectric coupling factor ($k_p$) and piezoelectric constant $d_{33}$ of 0.1 wt% $Li_2CO_3$ doped PMN-PZT ceramics prepared via HEBM for 10 h reached 2040, 0.68 and 554 pC/N, respectively.