• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.225-226
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• 2021

Recently, environmental problems have emerged as a major issue all over the world due to an increase in carbon dioxide(CO₂). The amount of CO₂ generated during cement production accounts for 6% to 8% of domestic CO₂ emissions and a solution to reduce CO₂ emissions the construction industry is trying to use mineral admixtures to reduce cement. Since digestion has no firing process the advantage of it is that there is no air pollution to occur. In this study, we studied the compressive strength of binary non-cement mortar containing rice husk powder extracted from digestion by the ratio of 10%, 20%, 30%, 40%. As a result, the table flow was increased when the mixing rate of rice husk powder extracted from digestion was higher, and the highest compressive strength was shown when the rice husk powder extracted from digestion mixing rate was 10%.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.437-440
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• 2003

This study has focused on the possibility for recycling of tailings from the Sangdong tungsten mine as powder of self-compacting concrete(SCC). The experimental tests for slump-flow, reaching time to the slump-flow of 500mm, V-funnel and U-box were carried out in accordance with the specified by the Japanese Society of Civil Engineering(JSCE). The result of this study, in case of SCC mixed with tailings, slump-flow was decreased with increasing mixing ratio. But reaching time slump-flow of 500mm, V-funnel and U-box were satisfied a prescribed range. The mechanical properties including compressive strength, splitting tensile strength and static modulus of elasticity were checked with the requirements specified by Korean Industrial Standard(KS). The compressive strength of SCC was decreased with increasing replacement, splitting tensile strength and static modulus were similar to those of normal concrete.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.571-575
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• 2011

Graphite-based electrodes were prepared using synthetic graphite (MCMB 1028) or natural graphite (NG) powder using a dimensionally stable anode (DSA) as a substrate. Their electrochemical properties were investigated in vanadiumbased electrolytes to determine how to increase the durability and improve the energy efficiency of redox flow batteries. Cyclic voltammetry (CV) was performed in the voltage range of -0.7 V to 1.6 V vs. SCE at various scan rates to analyze the vanadium redox reaction. The graphite-based electrodes showed a fast redox reaction and good reversibility in a highly concentrated acidic electrolyte. The increased electrochemical activity of the NG-based electrode for the $V^{4+}/V^{5+}$ redox reaction can be attributed to the increased surface concentration of functional groups from the addition of conductive material that served as a catalyst. Therefore, it is expected that this electrode can be used to increase the power density and energy density of redox flow batteries.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.8 no.4
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• pp.1-6
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• 2009

Air drying technology was developed as an equipment for reducing of moisture content from wastewater treatment and waterworks sludge cake and reproducing it by reusable matter. Advantage of cyclone type pneumatic dehydrator is simple and excellent drying performance. The air drying equipment was composed to the air ejector which made high-speed fluid field, and cyclone which made circling fluid field. Dewatered cake was crushed at the high-speed zone as first step, and formed with dried powder of sphere shape by the collision between particles at the circling fluid zone. In this study, a CFD analysis has been performed to predict air-sludge particles flow in cyclone and ejector of pneumatic dehydrator. The computational results showed typical Rankine vortex structure which was frequently found in swirling flow phenomena. And the conical type wedge in lower part of a cyclone prevented accumulation of the sludge particles in the cyclone. Therefore, this technology was effective in drying of dehydrated cake of waterworks sludge.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.528-537
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• 1989

The objective of this paper is to investigate effects of the specific heat and the diameter of suspending particles on the heat transfer coefficient of two phase turbulent flow with suspension of solid particles in a circular tube with constant heat flux. Heat transfer coefficients of two phase turbulent flow in pipe with suspension of graphite powder were measured with variations of particle sizes and solid-gas loading ratio. Measured data were compared with predictions by numerical analysis in which the turbulece models are closed on the first order level. Results show that heat transfer coefficient increases with increasing the solid-gas loading ratio and the specific heat of suspending material, however, it decreases as the average diameter of particles decreases below $24{\mu}m$.

• Resources Recycling
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• v.25 no.5
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• pp.75-83
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• 2016

AlN powder was prepared by carbon reduction and subsequent nitridation method through the scale-up experiments of 0.7 ~ 1.5 kg per batch. AlN powder was synthesized using the mixture of $Al_2O_3$ powder and carbon black at $1,550{\sim}1,750^{\circ}C$ for 0.5 ~ 4 hours under nitrogen atmosphere (flow rate of nitrogen gas: $10{\sim}40{\ell}/min$) at $2.0{\times}10^{-1}Torr$. Experimental results showed that $1,700{\sim}1,750^{\circ}C$ for the reaction temperature, 3 hr for reaction time, and $40{\ell}/min$ for the flow rate of nitrogen gas were the optimal conditions. Also, in order to remove carbon in the synthesized AlN, the remained carbon was removed at $650{\sim}750^{\circ}C$ for 1 ~ 2 hr using horizontal tube furnace. The results showed that 1 : 3.2 mol ratio of $Al_2O_3$ to carbon black, reaction temperature of $750^{\circ}C$, reaction time of 2 hours, rotating speed of 1.5 rpm under atmosphere condition were the optimal conditions. Under these conditions, high-purity AlN powder over 99% could be prepared: carbon and oxygen contents of the AlN powder were 835 ppm and 0.77%, respectively.

• Journal of Powder Materials
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• v.23 no.2
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• pp.91-94
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• 2016

High-quality colloidal CdSe/ZnS (core/shell) is synthesized using a continuous microreactor. The particle size of the synthesized quantum dots (QDs) is a function of the precursor flow rate; as the precursor flow rate increases, the size of the QDs decreases and the band gap energy increases. The photoluminescence properties are found to depend strongly on the flow rate of the CdSe precursor owing to the change in the core size. In addition, a gradual shift in the maximum luminescent wave (${\lambda}_{max}$) to shorter wavelengths (blue shift) is found owing to the decrease in the QD size in accordance with the quantum confinement effect. The ZnS shell decreases the surface defect concentration of CdSe. It also lowers the thermal energy dissipation by increasing the concentration of recombination. Thus, a relatively high emission and quantum yield occur because of an increase in the optical energy emitted at equal concentration. In addition, the maximum quantum yield is derived for process conditions of 0.35 ml/min and is related to the optimum thickness of the shell material.

• Journal of Powder Materials
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• v.22 no.2
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• pp.100-104
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• 2015

The porous metals are known as relatively excellent characteristic such as large surface area, light, lower heat capacity, high toughness and permeability. The Fe-Cr-Al alloys have high corrosion resistance, heat resistance and chemical stability for high temperature applications. And then many researches are developed the Fe-Cr-Al porous metals for exhaust gas filter, hydrogen reformer catalyst support and chemical filter. In this study, the Fe-Cr-Al porous metals are developed with Fe-22Cr-6Al(wt) powder using powder compaction method. The mean size of Fe-22Cr-6Al(wt) powders is about $42.69{\mu}m$. In order to control pore size and porosity, Fe-Cr-Al powders are sintered at $1200{\sim}1450^{\circ}C$ and different sintering maintenance as 1~4 hours. The powders are pressed on disk shapes of 3 mm thickness using uniaxial press machine and sintered in high vacuum condition. The pore properties are evaluated using capillary flow porometer. As sintering temperature increased, relative density is increased from 73% to 96% and porosity, pore size are decreased from 27 to 3.3%, from 3.1 to $1.8{\mu}m$ respectively. When the sintering time is increased, the relative density is also increased from 76.5% to 84.7% and porosity, pore size are decreased from 23.5% to 15.3%, from 2.7 to $2.08{\mu}m$ respectively.

• Journal of fish pathology
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• v.23 no.3
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• pp.409-420
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• 2010

Effects of various concentrations of garlic powder and garlic extract in the diets on growth, serum chemistry and immune response of olive flounder were determined. Thirty-five juvenile fish averaging 5.1 g were randomly distributed into 21 of 180 L flow-through tanks. Seven experimental diets with various concentrations of garlic powder (GP) and garlic extract (GE) were prepared in triplicate: GP-0 without garlic supplementation, GP-0.5, GP-1, GP-2, GP-3 and GP-5 diets containing garlic powder at the concentrations of 0.5, 1, 2, 3 and 5%, respectively at the expense of wheat flour and finally, GE-0.4 diet containing 0.4% garlic extract were prepared. At the end of the 8-week feeding trial, serum chemistry of fish was measured. In addition, twenty fish from each tank were artificially infected with E. tarda for the following 96 h to monitor cumulative mortality. Weight gain of fish fed GP-0 diet was higher than that of fish fed GP-1, GP-2, GP-3 and GP-5 diets. No difference in serum criteria (total protein, glucose, glutamate oxaloacetate transaminase, cholesterol and triglyceride levels) of olive flounder was found among the experimental diets except for glutamate pyruvate transaminase. Lysozyme activity of fish fed GP-0, GP-1, GP-3 and GE-0.4 diets was higher than that of fish fed GP-5 diet. The highest cumulative mortality was 93.3% in fish fed GP-0 diet at 96 h after E. tarda infection, followed by GP-3, GP-1, GP-5, GP-2, GP-0.5 and GE-0.4 diets. In considering these results, dietary inclusion of garlic powder and garlic extract has no distinctive positive effect on improvement in growth, serum chemistry and immune response of olive flounder in this experimental conditions, therefore, its application should be carefully considered.

• Journal of the Korean Magnetics Society
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• v.25 no.3
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• pp.67-73
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• 2015

This is a basic research for improving soft magnetic property of Fe based nano crystalline alloy powder core. The main study is done around characteristics of permeability, core loss, and DC bias depending on amount of insulation coating agent and particle size. First, $Fe_{73.5}Si_{13.5}B_9Nb_3Cu_1$ amorphous alloy ribbon was fabricated by using the planar flow casting (PFC) device. Then, heat treatment and ball milling were done to obtain alloy powder. The amount of polyether imide (PEI) added to it was varied by 0.5, 1.0, 2.0, 2.5 wt% to have compression molding into $16ton/cm^2$. After going through crystalline heat treatment, the made toroidal nano crystalline powder core ($OD12.7mm^*ID7.62mm^*H4.75mm$) had smaller permeability as amount of insulation coating agent decreases. However, it was found out that core loss and DC bias characteristics have been improved. The reason for this results were expected to be because green density of power core decreases as amorphous alloy powder particles become smaller as amount of alloy powder insulation coating agent increases, it was determined that 1 wt% of insulation coating agent is appropriate. Also, for powder core made based on alloy powder size with amount of insulation coating agent fixed at 1 wt%, effective permeability and core loss were outstanding as particle size became bigger. However, characteristics of DC bias became worse as applied DC field increases. This is expected to be due to insulation effect, residual pores, or molding density of powder core resulting from thickness of coating on surface of alloy powder.