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IAE 고등기술연구원 : Institute for Advanced Engineering
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Understanding the Isothermal Growth Kinetics of Cdse Quantum Dots Through Microfluidic Reactor Assisted Combinatorial Synthesis
저자명_  Basudev Swain, Myung Hwan Hong, Lee-Seung Kang and Chan Gi Lee
With the use of a microfluidic-assisted combinatorial reactor, the synthesis of CdSe quantum dots was optimized by varying one parameter at a time, and the isothermal growth kinetics of CdSe quantum dots using various models was analyzed. To understand precisely the nucleation and growth characteristics of CdSe quantum dots (QDs), we synthesized the CdSe QDs using various experimental conditions. Different model equations, like acceleratory growth-time curves, sigmoidal growth-time curves or Johnson-Mehl-Avrami-Kolmogorov (JMAK), acceleratory growthtime curves based on diffusion, geometric model growth-time curves, and nth order growth-time curves were fitted. Among all growth models, the JMAK model with α = 1 − e−(kt)n , and n = 1 was the best fitting model with the MATLAB interactive curve-fitting procedure were used. Errors associated with the best-fitting model and statistics for the goodness of fit were analyzed. Most of the models were not as good as the other than the proposed model. The errors associated with the proposed model were minimal, and the growth kinetics and other associated statistical factors are very similar, for all the variables investigated. The minimal error associated with the reproducibility and the similar data for growth kinetics for all studied parameters indicated that microfluidic-assisted combinatorial synthesis can be used in the industrial production of QDs. By using the proposed model to obtain an understanding of growth of QDs, their size and properties can be managed and simulated.
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Optimization of CdSe nanocrystals synthesis with a microfluidic reactor and development of combinatorial synthesis process for industrial production
저자명_  Basudev Swain, Myung Hwan Hong, Leeseung Kang, Bum Sung Kim, Nam-Hoon Kim, Chan Gi Lee
A lab scale microfluidic reactor with computer-controlled programmable isocratic pumps and online detectors was employed to syntheses CdSe nanocrystal and operational parameters for lab scale microfluidic reactor were optimized. Three reaction parameters, viz. the reaction time, the [Cd]/[Se] molar concentration ratio, and the precursor concentrations, were optimized for optical characteristics, the particle diameter, and product yield. The average time corresponding to each reaction condition for obtaining the ultraviolet–visible (UV–vis) absorbance and photoluminescence spectra was approximately 10 min. Based on lab scale microfluidic reactor a combinatorial reactor for synthesis CdSe on commercial interest has been redesigned and reproducibility of the CdSe synthesis, diameter size, and product yield were verified at the obtained condition from the lab scale synthesis. Using the data from the combinatorial synthesis system, the effects of the reaction conditions on the synthesized CdSe nanocrystals and their yield were elucidated. Further, the data were used to determine the relationships between the reaction conditions, the CdSe particle diameter, and the product yield. Advantages of reported synthesis are, unlikely, other reported processes instead of batch scale operation, the combinatorial synthesis system can be used for continuous production, if required. Through the process, controlling the precursor concentration, flow rate, and other physical and instrumental parameter, desired sized NCs can be synthesized precisely, which is a remarkable aspect of the combinatorial synthesis reported here. Depending upon the requirement, automation can be done for preciseness, reproducibility and mass production of the NCs.
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Recycling of GaN, a Refractory eWaste Material: Understanding the Chemical Thermodynamics
저자명_  Basudev Swain, Chinmayee Mishra, Kyung-Soo Park, and Chan Gi Lee
South Korea is a major producer of light-emitting diode (LED) material, contributing 31% of total LED demand worldwide, and also a major consumer of electronic devices. During manufacturing and after end of life (EOL) of the consumer electronics, significant amount of GaN-bearing waste is being generated. As the Republic of Korea depends upon the import of all mineral commodities, under the national policy of securing a stable supply, much attention has been paid to the notion of “urban mining.” The stringent international environmental directive for recycling of waste electrical and electronic equipment (WEEE), United Nations Environment Programme (UNEP) E-Waste Management goal, restriction of the use of hazardous substances in EEE (RoHS), and extended producer responsibility (EPR) have made recycling an important responsibility. Recovery of the gallium from GaN-bearing waste can be a promising feasible option; simultaneously from the waste, the wealth can be generated. As GaN is a refractory material, which is hard to leach in the recovery process, hence, needs a chemical pretreatment. In this study, thermodynamics of GaN oxidation and oxidative roasting using Na2CO3 has been studied. Thermodynamic feasibility for leaching of oxidized GaN either through acidic leaching or through alkali leaching has been explored.
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Synthesis of Cu3(MoO4)2(OH)2 nanostructures by simple aqueous precipitation: understanding the fundamental chemistry and growth mechanism
저자명_  Basudev Swain, Duk-Hee Lee, Jae Ryang Park, Chan-Gi Lee, Kun-Jae Lee, Dong-Wan Kim and Kyung-Soo Park
Lindgrenite (Cu3(MoO4)2(OH)2) nanoflowers were synthesized through the simplest possible route by an aqueous chemical precipitation technique at room temperature without using any surfactants, template, expensive chemicals, complex instrumentation or tedious multistage synthesis process. Their morphology, structure, thermal properties, surface area, synthesis chemistry, and structural and growth mechanisms involved in the synthesis process were analyzed. Using XRD, FE-SEM, HR-TEM and FT-IR spectroscopy, their structure and morphology were analyzed. The thermal stability, surface area and porosity of the Cu3(MoO4)2(OH)2 nanoflowers were analyzed by TGA and BET. XRD analysis showed that the Cu3(MoO4)2(OH)2 nanoflowers have a pure monoclinic structure. The morphological analysis showed that the Cu3(MoO4)2(OH)2 nanoflowers are ∼10 μm in size, which are formed from self-assembly of thin nanosheets with a thickness of ∼20 nm. TGA indicated that the Cu3(MoO4)2(OH)2 nanoflowers are stable materials up to 328 ℃ and the isotherm from BET analysis indicated that the Cu3(MoO4)2(OH)2 nanoflowers are non-porous materials. The BET surface area of the synthesized Cu3(MoO4)2(OH)2 nanoflowers was found to be 21.357 m2 g−1. Moreover, the effects of the pH value and reaction time on the morphology of the Cu3(MoO4)2(OH)2 nanoflowers were studied and their optimization was performed. The results of the optimization study indicated that the reaction time and pH are two important parameters influencing the nucleation, growth, morphology, and synthesis mechanism. These flower-shaped Cu3(MoO4)2(OH)2 nanostructures are promising precursors for preparing molybdenum oxide materials which have various applications and can be synthesized in a very simple one-pot reaction system using commonly available chemicals without using a complex route.
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Temperature-dependent Ta hydride formation for recycling of Ta scraps: Experimental and thermodynamic investigations
저자명_  Kyoung-Tae Park, Ji-Hwan Park, Jin-Ho Yoon, Ji-Eun Lee, Il-Kyu Park
We report on the theoretical and experimental investigations about the Ta-hydride formation depending on the temperature for recycling of Ta scraps. The structural investigations based on scanning electron microscope and X-ray diffraction (XRD) showed that the amount of hydrogen incorporated into the Ta matrix varied with hydridation temperature. The XRD measurement showed that the H/Ta mole ratio in Ta-hydride increased with increasing the hydridation temperature up to 700 ℃ and then decreased with increasing the temperature furthermore. Depending on the hydridation temperature, various phase of Ta-hydride, such as TaH0.93 and Ta2H were formed and this hydride process was verified by thermodynamic analysis.
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Prediction of Diffusion Behaviors Between Liquid Magnesium and Neodymium-Iron-Boron Magnets
저자명_  Hong Jun Chae, Kyoung-Tae Park, Seok-Jun Seo, Bum Sung Kim, and Taek-Soo Kim
The extraction behavior of the rare earth metal Nd from Nd–Fe–B alloy was investigated using Mg, a typical  low-melting-point element. Among the alloy components, Nd has a selective affinity with Mg; thus, Nd was  successfully diffused into the Mg at a temperature of 1023 K. This is significantly above the Mg melting point. The Nd diffusion sequence during the solid (Nd–Fe–B)–liquid (Mg) reaction was examined using scanning and  transmission electron microscopy, while energy dispersive spectroscopy and X-ray diffractometry were used  for the phase characterization. As the liquid Mg encountered the solid Nd–Fe–B, the Nd began to diffuse into  the Mg; this was followed by the formation of Nd–Mg compounds within the -Mg matrix. In addition, the Nd-deficient solid was converted to Fe2B. The Mg infiltration sequence and the reaction mechanism between the phases were also examined. This investigation presents a proposed pyro-metallurgical method for recycling critical rare earths in an energy-conserving and environmentally friendly manner, as an alternative to the conventionally used hydro-metallurgy.
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A study on the synthesis of tin oxide crystalline by the liquid reduction precipitation method and hydrothermal process
저자명_  Il-Jeong Park, Geon-Hong Kim, Dae-Weon Kim, Hee-Lack Choi
In this work, tin oxides were obtained by the liquid reduction precipitation method and hydrothermal process  using SnCl2 · 2H2O, N2H4, and NaOH. Tin oxide crystals having different sizes and morphologies could be achieved. The powders were characterized by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM). Depending on the molar ratio of the raw materials, tin oxide crystalline with the spherical and rectangular plate-like shape could be obtained, the crystal phase was SnO and Sn6O4(OH)4. And the obtained SnO crystals by a hydrothermal reaction showed various shapes, such as, spherical, plate-like and flower-like architectures depending on the temperature conditions.
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지르코니아 전해질을 이용한 단실형 고체산화물 연료전지의 전기화학 특성
저자명_  박희정, 주종훈, 양재교, 진연호, 이규형
Single-chamber solid oxide fuel cells (SC-SOFCs) consist of only one gas chamber, in which both the anode and the cathode are exposed to the same fuel-oxidant mixture. Thus, this configuration shows good thermal and mechanical resistance and allows rapid start-up and -down. In this study, the unit cell consisting of La0.8Sr0.2MnO3 (cathode) / Zr0.84Y0.16O2-x (electrolyte) / Ni-Zr0.84Y0.16O2-x (anode) was fabricated and its electrochemical property was investigated as a function of temperature and the volume ratio of fuel and oxidant for  SC-SOFCs. Impedance spectra were also investigated in order to figure out the electrical characteristics of the cell. As a result, the cell performance was governed by the polarization resistances of the electrodes. The cell exhibited an acceptable cell-performance of 86 mW/cm2 at 800℃ and stable performance for 3 hs under 0.7 V.
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Synthesis of Gd-doped CeO2 by ultrasonic spray pyrolysis with salt-assisted decomposition and its electrical and mechanical properties
저자명_  Hee Jung Park, Gyung Bok Kim, Seng Jae Jung, Young-In Lee, Jae-Kyo Yang, Yun Ho Jin and Yong Ho Choa
Much attention has been paid to acceptor doped-ceria as a promising solid electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to its high oxygen-ion conductivity. However, poor sinterability leading to high grain boundary resistance and weak mechanical properties have limited its commercialization. In this work, ceria nanoparticles were synthesized via ultrasonic spray pyrolysis using salt-assisted decomposition (SA-USP) to enhance the sinterabililty of the ceria. The effects of the quantity of added salt on the nanoparticle-characteristics were examined. Highly dense ceria (relative density~ 97.5%) was obtained by sintering the nanoparticles at a temperature as low as 1300 oC and its mechanical and electrical properties were investigated. The hardness and the oxygen-ion conductivity of the ceria with high density were reasonably good, ~ 14 GPa and above 10−3 S/cm at the IT-SOFC operating temperatures.
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유동층 환원공정을 활용한 동 드로스 및 분진 부산물 재활용
저자명_  공만식, 양재교, 진연호
Copper is the third most recycled metal after iron and aluminum because of high price. Copper which has been widely used in various fields such as electrical wires, roofing and plumbing and industrial machinery. Copper by-products produced while smelting process which usually discarded or exported to the oversea. However, the by-products are consists of a lot of valuable metal such as copper and zinc etc. Here in, we studied development and optimization of reduction process for copper by-product. LNG were used as reduction gas. Copper by-product were completely reduced in one hour with fluidized bed reaction.
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