• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.302-307
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• 2000

The objective of this study was to investigate the sintering behavior, crystallization characteristic of glass-ceramic and optimal sintering condition on the glass/ceramic composite for fabricating substrate of LTCC. Glass/ceramic composite was made from alumina powder and glass frit, which was composed of SiO2-TiO2-RO-PbO/(R: Ba, Sr, Ca), and was sintered for 0, 30, 60minutes in the temperature range from 700$^{\circ}C$ to 1000$^{\circ}C$. Properties of frit and glass/ceramic compsoite were analyzed by DTA, XRD, SEM and Network Analyzer and so on. Main sintering mechanism was densification occurred above 730$^{\circ}C$ by viscous flow and crystallization starting about 780$^{\circ}C$ affected sintering also. So viscous flow was affected by sintering temperature, duration time, and creation of crystallization phase etc. From this study, it was possible to fabricate glass/ceramic composite by changing sintering temperature and duration time.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1379-1384
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• 2014

${\alpha}-Fe_2O_3$ spherical particles having an average diameter of ca. 420 nm and ${\alpha}-Fe_2O_3$ fine particles (< 10 ${\mu}m$ particle size) were prepared to examine as catalysts for CO oxidation. Kinetic studies on the catalytic reactions were performed in a flow reactor using an on-line gas chromatography system operated at 1 atm. The apparent activation energies and the partial orders with respect to CO and $O_2$ were determined from the rates of CO disappearance in the reaction stage showing a constant catalytic activity. In the temperature range of $150-275^{\circ}C$, the apparent activation energies were calculated to be 13.7 kcal/mol on the ${\alpha}-Fe_2O_3$ spherical submicron clusters and 15.0 kcal/mol on the ${\alpha}-Fe_2O_3$ fine powder. The Pco and $Po_2$ dependencies of rate were investigated at various partial pressures of CO and $O_2$ at $250^{\circ}C$. Zero-order kinetics were observed for $O_2$ on both the catalysts, but the reaction order for CO was observed as first-order on the ${\alpha}-Fe_2O_3$ fine powder and 0.75-order on the ${\alpha}-Fe_2O_3$ spherical submicron clusters. The catalytic processes including the inhibition process by $CO_2$ on the ${\alpha}-Fe_2O_3$ spherical submicron powder are discussed according to the kinetic results. The catalysts were characterized using XRD (X-ray powder diffraction), FE-SEM (field emission-scanning electron microscopy), HR-TEM (high resolution-transmission electron microscopy), and $N_2$ sorption measurements.

• Applied Chemistry for Engineering
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• v.24 no.2
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• pp.126-131
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• 2013

BGsome coating on the surface of illite powder was attempted to impart skin affinity and improve various characteristics of the powder for makeup cosmetics. BGsome is a type of hydrated liquid crystalline vesicles prepared by the hydration of 1,3-butylene glycol (BG) dissolved lecithin. BGsome droplets were coated through wet process and the coated powders were analyzed by TGA, SEM, and particle size measurements. Effect of BGsome coating on the physical properties, such as flow-ability, dispersibility, spreadability, and adhesion, were examined. The repose angle of BGsome-coated illite was decreased, which means that BGsome coating improves the flowability of the powder. Dispersibility, spreadability, and adhesion of the coated illite were also improved remarkably. The result of adhesion tests showed that the BGsome-coated illite was evenly adhered onto artificial leather surface with almost no lumps. The flowability, dispersibility, spreadability and adhesion of face powders containing the BGsome-coated illite were also improved.

• Journal of Powder Materials
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• v.27 no.1
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• pp.37-43
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• 2020

The Fe-22wt.%Cr-6wt.%Al foams were fabricated via the powder alloying process in this study. The structural characteristics, microstructure, and mechanical properties of Fe-Cr-Al foams with different average pore sizes were investigated. Result of the structural analysis shows that the average pore sizes were measured as 474 ㎛ (450 foam) and 1220 ㎛ (1200 foam). Regardless of the pore size, Fe-Cr-Al foams had a Weaire-Phelan bubble structure, and α-ferrite was the major constituent phase. Tensile and compressive tests were conducted with an initial strain rate of 10^-3/s. Tensile yield strengths were 3.4 MPa (450 foam) and 1.4 MPa (1200 foam). Note that the total elongation of 1200 foam was higher than that of 450 foam. Furthermore, their compressive yield strengths were 2.5 MPa (450 foam) and 1.1 MPa (1200 foam), respectively. Different compressive deformation behaviors according to the pore sizes of the Fe-Cr-Al foams were characterized: strain hardening for the 450 foam and constant flow stress after a slight stress drop for the 1200 foam. The effect of structural characteristics on the mechanical properties was also discussed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.365-371
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• 2020

In this study, in order to recycle the stems of opuntia cactus discarded after harvesting the fruit, the cactus stems were powdered and applied as a cement-based admixture. The powder of cactus stem was mixed into the mortar, and its effect on the fresh properties and strength of the mortar was studied. The results were compared with the properties of mortars produced by mixing with a retarder sugar and a viscosity agent methyl-cellulose, which are conventional saccharide-based admixtures. Based on the test results, the cactus stem powder did not clearly show the effect as a retarding agent, whereas the flow and the air content were similar to those of the mortar mixed with methyl-cellulose. This indicated that the cactus stem powder can be used as a viscosity agent. It was found that the strength of the mortar tended to increase when the mixing ratio of the cactus stem powder was lower than 0.3%.

• Resources Recycling
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• v.26 no.3
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• pp.39-46
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• 2017

AlN powder was prepared by carbon reduction and subsequent nitridation method through lab- scale experiments. AlN powder was synthesized using the mixture of high purity $Al_2O_3$ powder and carbon black at $1,600{\sim}1,700^{\circ}C$ for 0.5~6 hours under nitrogen atmosphere (flow rate of nitrogen gas: $4.7{\times}10^{-6}{\sim}20{\times}10^{-6}m^3/sec$) with variation of charged height of the mixture powder. Experimental results showed that size of the synthesized particles grows with increasing of temperature. The reaction activation energy was calculated as 382 kJ/mol at the temperature range, and it was considered that chemical reaction is the rate determining step. Content of oxygen and nitrogen of the prpared samples were 0.71~0.96 wt% and 30.7~35.1 wt%. The results was similar with those of the commercial AlN product.

• Food Engineering Progress
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• v.13 no.1
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• pp.44-49
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• 2009

Angelicae gigantis Radix (dried root of Angelica gigas) including major bioactives such as decursin and decursinol angelate provides rich flavors and several healthy benefits. Recent studies have shown that ultrafine powders of herbal medicines provide better physical properties and biological activities. Thus, ultrafine Angelica powder was added into the oligosaccharide syrup to provide flavors and healthy benefits in this study. Angelicae gigantis Radix was pulverized into d(0.1) = 3.220, d(0.5) = 7.822, and d(0.9) = 7.817 $\mu$m respectively using an air-flow mill. The ultrafine Angelica powder was added into the oligosaccharide syrup process with different ratios of water to oligosaccharide syrup at 1:5, 1:8, 1:11, and 1:14. The physicochemical properties such as viscosity and bulk density were measured. The Stokes' law was applied to predict the sedimentation velocity of the added Angelica powder in the syrup. The Angelica syrup prepared in this experiment showed good stability since the Angelica particles precipitated down slowly. The ratio of water to oligosaccharide syrup at 1:11 showed the optimal preparation in terms of the stability and the viscosity. The ultrafine-sized herbal powders such as Angelicae gigantis Radix have potentials for various food and pharmaceutical applications.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.88-94
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• 2012

This study is conducted to utilize waste concrete powder made as a by-product manufacturing high quality recycled aggregate. The blaine fineness of the used waste concrete powder was 928 and $1,360cm^2/g$. As the main characteristic of waste concrete powder, it showed an angular type similar to cement, but hydrated products were attached on the surface of particles. In addition, the size of the particles of waste concrete powder was larger than OPC and in terms of chemical components it had higher $SiO_2$ contents. The viscosity of the paste that mixed waste concrete power decreased by 62% at the most, compared to the paste that only used OPC, and the final set time was delayed about two hours. As composition rates of waste concrete powder increased, the flow value decreased by 30% at the most according to the comparison with mortar that only used OPC, and sorptivity coefficients increased by 70%. The compressive strength of mortar decreased by 73% at the most as composition rates of waste concrete powder increased. According to the test results, it is desirable to use waste concrete powder by combining OPC appropriately(below 15%).

• Journal of Pharmaceutical Investigation
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• v.31 no.2
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• pp.81-87
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• 2001

The purpose of this study was to investigate the effect of additives on the powder characteristics of peonja dry elixir. Peonja dry elixirs were prepared with various amounts of dextrin using a spray-dryer, and their powder characteristics such as flow, cohesion and compressibility were evaluated as an angle of repose, cohesion index and compressibility index, respectively. Their powder characteristics were not significantly different from one another, indicating that the hydrophilic dextrin, a base of dry elixir hardly affected their powder characteristics. Peonja dry elixirs were prepared with 10% dextrin and various amounts of additives such as mannitol (hydrophilic excipient), sodium lauryl sulfate (surfactant), colloidal silica (hydrophobic excipient) and HPMC (polymer), respectively, and their angle of repose, cohesion index and compressibility index were measured. The powder characteristics of peonja dry elixirs prepared with mannitol were not significantly different from one another, indicating that the mannitol scarcely improved the powder characteristics of peonja dry elixirs. The angle of repose and cohesion index of peonja dry elixirs significantly decreased with increasing amount of sodium lauryl sulfate to 0.3% followed by no significant changes in them. The cohesion index of peonja dry elixir significantly decreased with increasing amount of colloidal silica. The angle of repose and cohesion index of peonja dry elixir significantly decreased with increasing amount of HPMC to 0.3% followed by an abrupt increase in them. However, the compressibility index of peonja dry elixir significantly increased with increasing amount of HPMC to 0.3% followed by an abrupt decrease in them. Our results suggested that a small amount of sodium lauryl sulfate, colloidal silica and HPMC improved markedly the powder characteristics of peonja dry elixirs due to forming stronger and less hygroscopic shell of peonja dry elixirs. Among the peonja dry elixirs studied, the peonja dry elixir prepared with 0.3% sodium lauryl sulfate and 0.3% HPMC had the lowest angle of repose of $27^{\circ}$ and cohesion index of 37.8%, and the highest compressibility index of 38.7%, respectively. Thus, sodium lauryl sulfate and HPMC appear to be promising additives for peonja dry elixir, if used in adequate amounts.

• Journal of Sensor Science and Technology
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• v.3 no.3
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• pp.3-8
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• 1994

Flow sensor was fabricated with PTC thermistor usually operating as thermostats. The PTC thermistor was manufactured with $(Ba_{0.7}Sr_{0.3})TiO_{3}$ powder and its resistivity as a function of flow velocity was investigated. The resistivity changed from 4.45 $k{\Omega}{\cdot}cm$ to 3.95 $k{\Omega}{\cdot}cm$ as flow velocity varied 0 cm/s to 5 cm/s The sensitivities of the PTC thermistor were -204 (${\Omega}{\cdot}cm$)/(cm/s) and -24 (${\Omega}{\cdot}cm$)/(cm/s) at the flow velocity of 1 cm/s and 5 cm/s, respectively.