• 한국분말재료학회지
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• 제7권1호
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• pp.12-18
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• 2000

Effects of the microstrucrure of rapidy solidified Al-Pb-Cu-Mg alloys on the wear investigated. In order to overcome the miscility gap between Al and pb under equilibrium conditions, both in the solid and the liquid states, the alloy were rapidy solidifies to produce them in a segregation-free condition. Although the Pb particles showed relatively fine dispersion in the Al matrix in all the alloys by this process. the Al-16Pb alloy was found to have the most favorable microstructure with discretre with discrete Pb particles of abount 0.5 ${\mu}$m in size. With the addition of Cu and Cu-Mg to Al-16Pb, cellular structures were newly formed; not seen in the binary Al-Pb alloy. Wear properties of the Al-Pb binary alloys measured as a function of the sliding speen, sliding distance, and applied load showed that the Al-16Pb alloy has the best wear resistance, as expected from the fine microstructural features in this alloy. The were resistance of the alloy containing Cu-and Cu-Mg was higher than that of the Al-16Pvb alloy, due to matrix strengthening by precipitation hardeing. The wear mechanism was identified by examining the traces and wear debris.

• Progress in Superconductivity
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• 제10권2호
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• pp.79-86
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• 2009

We successfully fabricated C-doped ex-situ $MgB_2$ wires using two different methods such as mechanical alloying(MA) and combined process(CP) of in-situ and ex-situ. In the MA, the precursor powder was prepared with a mixture of $MgB_2$ and 1 at% C powders by planetary ball milling for 0-100 h. In the CP, on the other hand, C-doped $MgB_2$ powder was prepared with Mg, B, and C powders by in-situ process via compaction, sintering, and crushing. The powders prepared by two methods were loaded into Fe tube and then the assemblages were drawn by a conventional powder-in-tube technique. The MA treatment of C-added $MgB_2$ decreased the particles/grains size and resulted in C-doping into $MgB_2$ after sintering, improving the critical current density($J_c$) in high external magnetic field. For the C-doped $MgB_2$ wire by MA for 25 h, the $J_c$ was $4.1{\times}10^3A/cm^2$ at 5 K and 6.4 T, which was 5.9 times higher than that of pure and untreated $MgB_2$ wire. The CP also provided C-doping into $MgB_2$ and improved the $J_c$ in high magnetic field; the C-doped $MgB_2$ wire fabricated by CP exhibited a $J_c$ being 2.3 times higher than that of the ex-situ wire used commercial $MgB_2$ powder at 5 K and 6.0 T($2.7{\times}10^3A/cm^2\;vs.\;1.2{\times}10^3A/cm^2$).

• 한국세라믹학회지
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• 제46권1호
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• pp.53-57
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• 2009

The h-BN powder was synthesized by amorphous $B_2O_3$ and activated carbon at $1550^{\circ}C$ in nitrogen atmosphere, whose properties were examined according to $MgB_6$ addition. Amount of $MgB_6$ addition was varied in the range of $0{\sim}$10\;wt% of the initial mixture. It was observed that $MgB_6$ addition led to an increase in the amount and the grain size of h-BN and decrease in the amount of $B_4C$ forming. When $MgB_6$ added 5 wt%, the amount and crystallinity of h-BN increased as the holding time at the synthesis temperature was prolonged. It was also confirmed that the regularity of three-dimensional ordering of h-BN increases.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3749-3754
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• 2012

Nanoporous carbons with a high specific surface area were prepared directly from thermoplastic acrylic resin as carbon precursor and MgO powder as template by carbonization over the temperature range, $500-1000^{\circ}C$. The effect of the carbonization temperature on the pore structure and $CO_2$ adsorption capacity of the obtained porous carbon was examined. The textural properties and morphology of the porous carbon materials were analyzed by $N_2/-196^{\circ}C$ and $CO_2/0^{\circ}C$ adsorption/desorption isotherms, SEM and TEM. The $CO_2$ adsorption capacity of the prepared porous carbon was measured at $25^{\circ}C$ and 1 bar and 30 bar. The specific surface area increased from 237 to $1251m^2/g$, and the total pore volumes increased from 0.242 to $0.763cm^3/g$ with increasing the carbonization temperature. The carbonization temperature acts mainly by generating large narrow micropores and mesopores with an average pore size dependent on the level of carbonization of the MgO-templated nanoporous carbons. The results showed that the MgO-templated nanoporous carbons at $900^{\circ}C$ exhibited the best $CO_2$ adsorption value of 194 mg/g at 1 bar.

• 한국초전도ㆍ저온공학회논문지
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• 제19권1호
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• pp.42-46
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• 2017

The effects of the heat treatment temperature ($600^{\circ}C-1050^{\circ}C$) on the formation of $MgB_2$ and the superconducting properties have been examined. The self-synthesized $MgB_4$ and commercial Mg powders were used as raw materials for the formation of $MgB_2$. The superconducting critical temperatures ($T_cs$) of $MgB_2$ bulk superconductors prepared at $600^{\circ}C-850^{\circ}C$ were as high as 37-38 K regardless of the heat treatment temperature. However, because $MgB_4$ is more stable than $MgB_2$ at above $850^{\circ}C$, no superconducting signals were detected in the susceptibility-temperature curves of the samples prepared above $850^{\circ}C$. As for the critical current density ($J_c$), the sample heat-treated at a low temperature ($600^{\circ}C$) for a prolonged period (40 h) showed a Jc higher than those prepared at $650^{\circ}C-850^{\circ}C$ for a short period (1 h). The FWHM (full width at half maximum) result showed that the grain size of $MgB_2$ of the $600^{\circ}C$ sample was smaller than that of the other samples. The high $J_c$ of the $600^{\circ}C$sample is attributed to the presence of large numbers of grain boundaries, which can act as flux pinning centers of $MgB_2$.

• 한국분말재료학회지
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• 제11권1호
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• pp.69-73
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• 2004

The sintering characteristics of commercial 7xxx series Al-Zn-Mg-Cu alloy have been investigated. Sintering system of this blended elemental powder has aspects of both transient and supersolidus liquid phase sintering. Transient liquids occur when the constitution point during sintering lies in a solid phase region but where the sintering temperature is greater than either the melting point of one of the constituent or a eutectic temperature. Supersolidus liquid phase sintering occurs when a preblended powder is heated to a temperature between the solidus and liquids. However, these reaction were restrained their inter diffusion due to the appearance of the oxide film. Thus, 7xxx series Al alloy is extremely sensitive to process variables, including particle size, holding time and sintering temperature. Therefore, above phenomenons were observed formation and behaviour of the liquid by using SEM and DSC.

• 한국분말재료학회지
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• 제18권4호
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• pp.359-364
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• 2011

Zr-Ti alloy powders were successfully synthesized by magnesium thermal reduction of metal chlorides. The evaporated and mixed gasses of $ZrCl_4+TiCl_4$ were injected to liquid magnesium and the chloride components were reduced by magnesium leading to the formation of $MgCl_2$. The released Zr and Ti atoms were then condensed to particle forms inside the mixture of liquid magnesium and magnesium chloride, which could be dissolved fully in post process by 1~5% HCl solution at room temperature. By the fraction-control of individually injected $ZrCl_4$ and $TiCl_4$ gasses, the final compositions of produced alloy powders were changed in the ranges of Zr-0 wt.%~20 wt.%Ti and their purity and particle size were about 99.4% and the level of several micrometers, respectively.

• 한국세라믹학회지
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• 제19권2호
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• pp.127-132
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• 1982

This experiment has been carried out for the purpose of investigating the effect of additives on densification and grain growth in magnesium oxide by a two-step process; hot pressing and heat treating. MgO powder has been obtained by calcining extra reagent grade MgCO3 at 90$0^{\circ}C$ for 30 minutes, and additives have been added to $MgCO_3$ in the form of soluble salts-Al$(NO_3)_3$$. $9H_2O$ and $Cr(NO_3)_3$.9H_2O$. The hot pressing has been carried out with changes of soaking time at 125$0^{\circ}C$ under the pressure of 250kg/$\textrm{cm}^2$, and the heat treating also at same temperature. The initial particle size of MgO measured by particle size analyzer was 0.86 microns. Densification rate obeyed the equation D=K lnt + C, and grain growth rate obeyed the equation G-G0=kt1/2. It was vaporization of some $Cr_2O_3$ and formation of solid solution that had an influence on desification of MgO containing $Cr_2O_3$. Activation energy for grain growth of pure MgO was 62.4 kcal/mole, therefore grain growth was supposed to be diffusioncontrolled process. But after heat treatmeat, excess additives were expected to slow down the grain growth by the formation of second phase or the solute atoms at grainboundary.

• 한국식품조리과학회지
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• 제14권5호
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• pp.584-588
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• 1998

Red pepper powders with variuos seed contents (0%, 10%, 20%) and particle sizes were stored at 0$^{\circ}C$, 20$^{\circ}C$, and 30$^{\circ}C$ for 90 days, and the changes in their characteristics were monitored. The initial moisture content was about 13%, and the powders were packed in 0.1 mm-thick polypropylene (PP) bags. Moisture content of each power remained constantly, so PP bags appeared to be effective to prevent moisture transmission. All the values of L＊, a＊ and b＊ were higher in fine particles than in coarse particles. Storage at 0$^{\circ}C$ did not change any color values, however, overall color values devreased apparently when stored at 30$^{\circ}C$ for 90 days. Capsanthin contents decreased gradually at all storage temperatures and more rapidly at higher temperature. The contents of capsaicinoids in fine particles (49∼59 mg%) were twic as much as those in coarse particles (15∼36 mg%), and they did not change throughout the storage.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.736-739
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• 2009

We have studied that the secondary electron emission characteristics of functional layers which have different kinds of MgO sub-micrometer size powder in AC-PDP. We used cathodoluminescence(CL) and gamma focused ion beam (${\gamma}$-FIB) system for measurement of secondary electron emission characteristics. Also we made 6 inch test panel which applied functional layers for evaluation of discharge characteristics.