• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.1
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• pp.27-32
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• 2001

The 0.9PMN-0.1PT powders was prepared by the sol-gel process, and the effect amounts of ${Mg(OC_{2}H_{5})}_2$ and ${Pb(CH_{3}COO)}_2.3H_{2}O$ as starting materials was studied. As a result the percent of perovskite phase of the calcined powders increased with increased calcination temperatures. Maximum of perovskite phase was at $850^{\circ}C$ for 4 hrs. 0.9PMN-0.1PT powder by addition of 5 wt% excess ${Mg(OC_{2}H_{5})}_2$ crystallized to perovskite phase with a ${\fallingdotseq}100%$ yield.

• Journal of Powder Materials
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• v.19 no.3
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• pp.226-231
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• 2012

In this research, the coating behavior of Mg and Fe desulfurization powder fabricated by low energy and conventional planetary mill equipment was investigated as a function of milling time, which produces uniform Fe coated powders due to milling energy. Since high energy ball milling results in breaking the Fe coated Mg powders into coarse particles, low energy ball milling was considered appropriate for this study, and can be implemented in desulfurization industry widely. XRD and FE-SEM analyses were carried out to investigate the microstructure and distribution of the coating material. The thickness of the Fe coating layer reaches a maximum of 14 ${\mu}m$ at 20 milling hours. The BCC structures of Fe particles are deformed due to the slip system of Fe coated Mg particles.

• Progress in Superconductivity and Cryogenics
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• v.25 no.3
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• pp.22-27
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• 2023

Magnetic properties of MgB₂ superconducting powder were investigated. M(H), the magnetic field H dependence of magnetization M, was measured and analyzed using a PPMS instrument. The MgB₂ superconducting powder showed high critical current density J_c > ~ 10⁷ A/cm² and clean limit superconducting properties. The equilibrium magnetization M_eq properties of MgB₂ powders exhibiting various superconducting properties were studied. We find that the equilibrium magnetization M_eq(H) properties of MgB₂ powders showing conventional BCS properties deviate from the predictions of the standard local-London theory at temperatures below T = 19 K and are in good agreement with the generalized nonlocal-London theory. Nonlocal-London analysis was used to determine and analyze the nonlocal parameters. The temperature dependence of the London penetration depth values λ(T) was studied.

• Journal of Powder Materials
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• v.20 no.1
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• pp.43-47
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• 2013

The extraction of metallic pure vanadium powder from raw oxide has been tried by Mg-reduction. In first stage, $V_2O_5$ powders as initial raw material was reduced by hydrogen gas into $V_2O_3$ phase. $V_2O_3$ powder was reduced in next stage by magnesium gas at 1,073K for 24 hours. After reduction reaction, the MgO component mixed with reduced vanadium powder were dissolved and removed fully in 10% HCl solution for 5 hours at room temperature. The oxygen content and particle size of finally produced vanadium powders were 0.84 wt% and 1 ${\mu}m$, respectively

• Journal of the Korean Ceramic Society
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• v.29 no.6
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• pp.451-458
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• 1992

Dense glass-ceramics for low firing temperature substrate were prepared by addition of CeO2 flux to the glass of MgO-Al2O3-SiO2 system. Glass powders were fabricated by melting at 150$0^{\circ}C$ and ball milling. Glass powder compacts were sintered at 800~100$0^{\circ}C$ for 3h. The crystallization and the shrinkage behaviors of glass powder compacts were analyzed by XRD, DTA and TMA. The shrinkage of glass powder compact increased with increasing the amount of CeO2. Because the softening temperature decreased and the crystallization temperature increased with increasing the amount of CeO2. Apparently, addition of CeO2 prevented formation of $\mu$-cordierite phase from the glass-ceramics and improved formation of $\alpha$-cordierite phase. Therefore crystallization properties were enhanced.

• Journal of Ceramic Processing Research
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• v.19 no.6
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• pp.504-508
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• 2018

Diopside is a ceramic material with excellent physical and chemical properties. However, when it is applied as an LED packaging material, heat dissipation of the LED element is not sufficient due to its relatively lower thermal conductivity, which may cause degradation of the LED function. In this study, glass-ceramics based on a $ZrO_2-CaO-MgO-SiO_2$ system, in which diopside is the main crystal phase, were prepared by heat-treating the glass, which was composed of zircon ($ZrO_2-SiO_2$) powders and diopside ($CaO-MgO-2SiO_2$) powders. The possibility of using the glass-ceramics as a packaging material for LEDs was then investigated by analyzing the density, shrinkage, thermal conductivity, and phases generated according to the amount of zircon powder added. The density and shrinkage of specimens decreased slightly and then increased again with the amount of $ZrO_2-SiO_2$ added within a range of 0~0.38 mol. Even though the crystal phase of zircon does not appear in the $ZrO_2-CaO-MgO-SiO_2$ system, the glass containing 0.38 mol zircon powder showed the highest thermal conductivity, 1.85 W/mK, among the specimens fabricated in this study: this value was about 23% higher than that of pure diopside. It was found that the thermal conductivity of the glass-ceramics based on a $ZrO_2-CaO-MgO-SiO_2$ system was closely related to the density, but not to the phase type. Zirconia ($ZrO_2$), a component oxide of zircon, plays an important role in increasing the density of the specimen. Furthermore the thermal conductivity of glass-ceramics based on a $ZrO_2-CaO-MgO-SiO_2$ system showed a nearly linear relationship with thermal diffusivity.

• Progress in Superconductivity
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• v.12 no.2
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• pp.88-92
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• 2011

[ $MgB_2$ ]superconducting sheets have been fabricated using powder roll compaction method. Sheet-type $MgB_2$ bulk samples were successfully fabricated using the pre-reacted $MgB_2$ powders. In this work, $MgB_2$ powders were compacted by two rotating rolls and squeezed out as a form of $MgB_2$ sheets of ~1 mm thickness. The rolling speed of 0.3-0.7 rpm and the gap distance of 0.3-0.8 mm between the two rollers were carefully controlled to get a full compaction of the powders into bulk $MgB_2$ sheets. The densities of $MgB_2$ sheets were 1.98-2.05 g/$cm^3$, which is 75.44-77.99 % of the theoretical value of 2.63 g/$cm^3$. And the density comparison was made compared to those of typical $MgB_2$ bulks from uni-axial pressing and $MgB_2$ wires from Powder-In-Tube processing.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.4
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• pp.207-212
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• 2012

A single phase $Mg_3Sb_2$ alloy was synthesized by melting the mixture of Mg and Sb metal powders at 1173 K. The figure of merit of the $Mg_3Sb_2$ prepared by melting method increased with temperature and showed a value of $2.39{\times}10^{-2}$ at 593 K. When the $Mg_3Sb_2$ powders were milled at high speed in a planetary ball mill for 12~48 h, Zintle phase ($Mg_3Sb_2$) was maintained as a main phase, but its crystallinity became deteriorated and elemental Sb phase appeared. Sb phase free $Mg_3Sb_2$ could be obtained by the mechanical alloying of high speed ball milling for 24 h using elemental Mg and Sb powder mixtures.

• 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 the Korean Society of Food Science and Nutrition
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• v.41 no.6
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• pp.870-874
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• 2012

The objective of this study was to determine the content of capsaicinoids in different commercial pepper powders and pepper-containing products in the Korean market. The two major capsaicinoids in the samples, capsaicin and dihydrocapsaicin, were analyzed using reversed-phase HPLC. The levels of capsaicin and dihydrocapsaicin in pepper powders and pepper-containing products ranged from 0.21 to 78.24 and 0.20 to 38.82 mg/100 g sample, respectively. Pepper powders contained generally higher amounts of capsaicin and dihydrocapsaicin than pepper- containing products. In addition, the analytical method validation parameters including accuracy, precision, and specificity were provided to ensure the validity of the extraction procedure for capsaicinoid analysis. Overall recovery from pepper powder and pepper paste was close to 100% (n=3). The results of validation parameters indicated that the present method was reliable and reproducible for the HPLC analyses of capsaicin and dihydrocapsaicin in commercial pepper products.