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융합소재연구센터 "Enhanced Low-Temperature Power Density of Solid Oxide Fuel Cell by Nickel Nanoparticle Infiltration Into Pre-Fired Ni/Yttria-Stabilized Zirconia Anode"

· 저자

강이승, 박재량, 이성규, 진연호, 홍현선, 이찬기, 김범성


The Ni/yttria-stabilized zirconia (YSZ) anode morphology of an anode-supported solid oxide fuel cell (SOFC) unit cell was improved by nickel nanoparticle infiltration. A colloidal route was selected for efficient fabrication of nickel metal nanoparticles and subsequent infiltration into the Ni/YSZ anode of a pre-fired SOFC unit cell. The power density of the anode-supported SOFC unit cell was measured by the potentiostatic method to investigate the effect of nickel nanoparticle infiltration. The increase in the power density of the Ni/YSZ anode with nickel nanoparticle infiltration became gradually less significant as the SOFC operating temperature increased from 700 to 800 °C. The improved performance of the Ni/YSZ anode with nickel nanoparticle infiltration compared to that of an anode without nickel nanoparticles is tentatively attributed to two factors: The discretely distributed nanoparticles on the nanostructured electrodes exhibited significant catalytic effects on the electrochemical performance of the electrodes, in addition to substantially increasing the triple phase boundary lengths.


융합소재연구센터 Synthesis of CdSe/ZnSe quantum dots passivated with a polymer for oxidation prevention

· 저자

권영태, 최요민, 김가희, 이찬기, 이근재, 김범성, 좌용호


Surface overcoated CdSe/ZnSe core/shell structured quantum dots (QDs) with enhanced stability, narrow size distribution and strong photoluminescence have been successfully synthesized by using a simple poly(methylmethacrylate) (PMMA) coating on nanoparticles. When applied to the surface of QDs, the polymer coating provided ultra-dispersion stability and a high fluorescence quantum yield of above 80% that prevented chemical degradation, such as aggregation and Ostwald ripening. The degree of degradation was measured with respect to storage time (1, 7, 15, and 30 days) in order to provide a comparison between PMMA uncoated and coated QDs, and the oxidation of QDs was confirmed with Fourier transform infrared spectroscopy.


융합소재연구센터 Improvement of Dispersion Stability and Optical Properties of CdSe/ZnSe Structured Quantum Dots by Polymer Coating

· 저자

권영태, Eom Nu Si A, 최요민, 김범성, 김택수, 이찬기, 이근재, 좌용호


In this study, CdSe core and CdSe/ZnSe core/shell quantum dots with a narrow size distribution were synthesized in a micro-reactor. A PMMA coating applied to the surface of CdSe/ZnSe core/shell QDs to prevent degradation gave improved dispersion stability compared to the CdSe core and CdSe/ZnSe core/shell. Many previous approaches to dispersion stability have not been quantitatively assessed. The dispersion stability was confirmed by multiple light scattering measurement. Additionally, the PMMA-coated CdSe/ZnSe QDs showed greatly improved optical properties with a photoluminescence quantum yield up to 80%. This structural motif is expected to prevent the degradation of QDs.


융합소재연구센터 Characteristics of Niobium Powder Used Capacitors Produced by Metallothermic Reduction in Molten Salt

· 저자

윤재식, 이개항, 홍순직, 홍현선, 이찬기, 이지면


The niobium capacitor shows somewhat more unstable characteristics than the commercial tantalum capacitors, but it will be nonetheless considered as an excellent substitute of tantalum capacitors in the future. In this study, niobium powder is fabricated by metallothermic reduction process using K2NbF7 as a raw material, KCl and KF as diluents, and Na as a reducing agent. The niobium particle size greatly decreases from 0.7μm to 0.2μm as the amount of diluent increases. However, when a higher surface area of niobium powder is desired, more amounts of diluents are used in the said method. The niobium powder morphology and particle sizes are very sensitive to the amount of sodium excess, thus the particle size of niobium powder increases with increases in the amount of sodium excess. When more diluent and sodium are used, the niobium powder is contaminated further by impurities such as Fe, Cr, Ni, and others [1,2].


융합소재연구센터 Reflectance Characteristics of Al Alloys Containing Si, Mg, Cu, and Lanthanide (Nd, Sm, Gd) for 3D Printing

· 저자

최광묵, 김대근, 임병용, 채홍준


To fabricate a low-reflectance aluminum alloy, we have analyzed the changes in reflectance according to the morphology, components, and composition of the aluminum alloy. We find that the larger the particle size of the powder, the lower is the reflectance. This is attributed to the fact that the larger the particle size, the greater is the amount of light absorbed into the interparticle space in the powder. In addition, the reflectance decreases with increase in the Si and Mg contents, because of the lower reflectance of the strengthening phase formed in the alloy as compared to that of aluminum. In contrast, lanthanide addition causes an increase in the reflectance, which is attributed to an increase in the electrical conductivity of the alloy.


융합소재연구센터 Prediction of Diffusion Behaviors Between Liquid Magnesium and Neodymium-Iron-Boron Magnets

· 저자

김용수, 채홍준, 서석준, 박경태, 김범성, 김택수


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 α-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.


융합소재연구센터 Sn doped In2O3 nanowires for enhanced photocurrent generation for photoelectrodes

· 저자

박경수, 이찬기, 홍현선, 이일석, 권석준, 박재관


High-quality single-crystalline Sn-doped In2O3 (ITO) nanowires (NWs) with diameters of about 60–80 nm and lengths of several tens of micrometers were produced using a simple thermal co-evaporation method at a substrate temperature of ~540 °C. The electrical conductivity of as-synthesized ITO NW was ~115.9 S/cm at room temperature. Photocurrent generation devices were prepared by self-assembling di(3-aminopropyl)viologen and Ru(2,2′-bipyridine-4,4′-dicarboxylic acid)2(NCS)2 on the surface of ITO NWs. The maximum photocurrent density of the device with an ITO NW electrode under illumination of 100 mW/cm2 was 11.05 μA/cm2, which is about three orders of magnitude larger than that of the device with a bare ITO thin film electrode. The high photocurrent density could be attributed to the large surface area, high crystallinity, and electrical conductivity of the ITO NW electrode.


융합소재연구센터 Temperature-dependent Ta hydride formation for recycling of Ta scraps: Experimental and thermodynamic investigations

· 저자

박경태, 박지환, 윤진호, 이지은, 박일규


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 °C 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.


융합소재연구센터 Synthesis of uniform-sized zeolite from windshield waste

· 저자

김재찬, 최민구, 송희조, 박정은, 윤진호, 박경수, 이찬기, 김동완


We demonstrate the synthesis of A-type zeolite from mechanically milled windshield waste via acid treatment and a low-temperature hydrothermal method. As-received windshield cullet was crushed to a fine powder and impurities were removed by HNO3 treatment. The resulting glass powder was used as the source material for the hydrothermal synthesis of A-type zeolite. Crystal structure, morphology, and elemental composition changes of the windshield waste were evaluated at each step of the process through scanning electron microscopy, X-ray diffraction, X-ray fluorescence spectrometry, etc. After a high-energy milling process, the glass had an average particle size of 520 nm; after acid treatment, its composition was over 94% silica. Zeolite was successfully synthesized in the A-type phase with a uniform cubic shape.


융합소재연구센터 Synthesis of submicron silver powder from scrap low-temperature co-fired ceramic an e-waste: Understanding the leaching kinetics and wet chemistry

· 저자

Basudev Swain, 신동윤, 주소영, 안낙균, 이찬기, 윤진호


The current study focuses on the understanding of leaching kinetics of metal in the LTCC in general and silver leaching in particular along with wet chemical reduction involving silver nanoparticle synthesis. Followed by metal leaching, the silver was selectively precipitated using HCl as AgCl. The precipitated AgCl was dissolved in ammonium hydroxide and reduced to pure silver metal nanopowder (NPs) using hydrazine as a reductant. Polyvinylpyrrolidone (PVP) used as a stabilizer and Polyethylene glycol (PEG) used as reducing reagent as well as stabilizing reagent to control size and shape of the Ag NPs. An in-depth investigation indicated a first-order kinetics model fits well with high accuracy among all possible models. Activation energy required for the first order reaction was 21.242 kJ mol−1 for Silver. PVP and PEG 1% each together provide better size control over silver nanoparticle synthesis using 0.4 M hydrazine as reductant, which provides relatively regular morphology in comparison to their individual application. The investigation revealed that the waste LTCC (an industrial e-waste) can be recycled through the reported process even in industrial scale. The novelty of reported recycling process is simplicity, versatile and eco-efficiency through which waste LTCC recycling can address various issues like; (i) industrial waste disposal (ii) synthesis of silver nanoparticles from waste LTCC (iii) circulate metal economy within a closed loop cycle in the industrial economies where resources are scarce, altogether.


융합소재연구센터 Spark plasma sintering of WC–Co tool materials prepared with emphasis on WC core–Co shell structure development

· 저자

이성규, 홍현선, 김효섭, 홍순직, 윤진호


Quasi-nano-sized WC core–Co shell structure composites were successfully fabricated by the wet chemical reduction method by introducing uniformly dispersed WC powders of 300-nm size into the Co(OH)2, which was subsequently reduced to Co shell structure by drop-wise titration of H3PO2. X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) identified WC core–Co shell phases which were subsequently ball-milled, compacted and finally densified at 1400–1450 °C by spark plasma sintering. WC–Co sintered composites thus prepared were analyzed to examine densification, hardness and fracture behavior: reasonably adequate post-sintering properties are attributable to improved WC core–Co shell structure afforded by the optimized mechanical alloying and SPS sintering processes.


융합소재연구센터 Selective recovery of silver from waste low-temperature co-fired ceramic and valorization through silver nanoparticle synthesis

· 저자

Basudev Swain, 신동윤, 주소영, 안낙균, 이찬기, 윤진호


Considering the value of silver metal and silver nanoparticles, the waste generated during manufacturing of low temperature co-fired ceramic (LTCC) were recycled through the simple yet cost effective process by chemical-metallurgy. Followed by leaching optimization, silver was selectively recovered through precipitation. The precipitated silver chloride was valorized though silver nanoparticle synthesis by a simple one-pot greener synthesis route. Through leaching-precipitation optimization, quantitative selective recovery of silver chloride was achieved, followed by homogeneous pure silver nanoparticle about 100 nm size were synthesized. The reported recycling process is a simple process, versatile, easy to implement, requires minimum facilities and no specialty chemicals, through which semiconductor manufacturing industry can treat the waste generated during manufacturing of LTCC and reutilize the valorized silver nanoparticles in manufacturing in a close loop process. Our reported process can address issues like; (i) waste disposal, as well as value-added silver recovery, (ii) brings back the material to production stream and address the circular economy, and (iii) can be part of lower the futuristic carbon economy and cradle-to-cradle technology management, simultaneously.


융합소재연구센터 Hydridation and oxidation behaviors of tantalum hydride during milling process

· 저자

이지은, 윤진호, 이찬기, 박지환, 박일규


The effect of ethanol addition during milling on the milling performances of Ta-hydride powders was investigated for hydride and dehydride processes during Ta recycling process. As the Ta-hydride was milled in a conventional dry atmosphere, Ta2O was dominantly formed due to the increased temperature of the Ta-hydride pieces because they were rubbed against each other and crushed by the ring mill system. However, with the addition of ethanol solvent, the ratio of the Ta2H phase increased compared to the Ta2O phase, and the size of the powders reduced and became more uniform. These were attributed to the enhanced hydride formation and reduced contact between the Ta-hydride powders and air by wetting them. Therefore, an optimum amount of ethanol addition and milling time can enhance the formation of additional Ta-hydrides, while preventing oxidation during milling.


융합소재연구센터 Enhanced Tantalum Hydride Formation by the Catalytic Effect of Tungsten for Hydrogen Dissociation

· 저자

이지은, 윤진호, 이찬기, 박지환, 박일규


We investigated enhanced tantalum (Ta) hydride formation by using the catalytic effect of tungsten (W) to reduce the hydrogen dissociation energy. Ta turning scrap was hydrated at various temperatures by using a W crucible and conventional Al2O3 crucible, and the structural and chemical properties of the hydrated powders were compared. Structural investigation by X-ray diffraction and chemical analysis using an oxygen–nitrogen–hydrogen determinator showed that the Ta hydride was formed at temperatures lower than 500 °C, while the dehydride formation process occurs at temperatures higher than 600 °C in conventional Al2O3 crucibles. However, when the W crucible is used, the hydrogen incorporation into the Ta lattice was enhanced at both low and high temperatures. This enhancement was attributed to the reduced energy of dissociation of H2 into mono-atomic H because of the catalytic effect of W, finally resulting in enhanced Ta hydride formation.


융합소재연구센터 Development of High-Strength Glass–Ceramic Materials by Utilization of Slag Discharged from Steel-Making Industry in Korea

· 저자

신동윤, 이덕희, 윤미정, 박현서, 서성보, 윤진호


Every year 25 million tons of slag is generated as an industrial by-product by the steel-making industry in Korea. Using slag to manufacture high-strength glass–ceramic materials is increasingly becoming a feasible option, and recently several types of slag have been used in combination to manufacture glass–ceramic materials such as basalt-based glass–ceramics. Glass–ceramic materials with two different chemical compositions were prepared using Fe–Ni slag, basic oxygen furnace slag, dephosphorization slag, and fly ash by melting and casting and a subsequent heat treatment. X-ray diffraction analyses confirmed that clinopyroxene and CaAl2SiO8 were the primary phases in the formed glass–ceramics, while thermogravimetry and differential thermal analyses showed that their glass-transition points were 709–724 °C and crystallization temperatures were 888–918 °C. The morphologies and constituent components were also examined using field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The stable phases were calculated as functions of the temperature using FactSage. Finally, the compressive strength, Vickers hardness, and wear rate values of the glass–ceramics were evaluated in order to elucidate their physical properties.


융합소재연구센터 Electrochemical Performances of Li2MnSiO4 Cathodes Synthesized by Mechanical Alloying Process

· 저자

진연호, 박경수, 강이승, 김범성, 홍현선


We report the fabrication and electrochemical properties of Li2MnSiO4 powders produced by various solid-state reactions, such as ball-, attrition-, and bead-milling. Li2MnSiO4 powders prepared by bead-milling had the smallest particle sizes (∼100 nm) and the largest amount of surface carbon (∼20 wt%), which were produced by adding sucrose during milling process. The surface carbon layer can improve electronic/ionic conductivity of Li2MnSiO4 as cathode material for lithium ion battery. As expected, the bead-milled Li2MnSiO4 powder electrode showed the best electrochemical performance of the electrode materials obtained by the various solid-state reactions. This is attributed to the small particle size and facile electronic transport through the conductive carbon layer on each Li2MnSiO4 particle.


융합소재연구센터 Recycling of GaN, a Refractory eWaste Material: Understanding the Chemical Thermodynamics

· 저자

Basudev Swain, Chinmayee Mishra, 이근재, 홍현선, 박경수, 이찬기


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.


융합소재연구센터 Synthesis of Flower‐like Cu3[MoO4]2O from Cu3(MoO4)2(OH)2 and Its Application for Lithium‐Ion Batteries: Structure‐Electrochemical Property Relationships

· 저자

Basudev Swain, 이덕희, 김준식, 이찬기, 김동완, 박경수


Flower‐like Cu3[MoO4]2O microspheres have been synthesized by using a sequential process from lindgrenite (Cu3(MoO4)2(OH)2). Lindgrenite nanoflowers were synthesized through a simpler route by using an aqueous chemical precipitation technique at room temperature without any surfactants or template. Subsequently, 3D flower‐like Cu3[MoO4]2O microspheres have been synthesized by annealing at 300 °C for 2 h from lindgrenite (Cu3(MoO4)2(OH)2). From the XRD pattern, FTIR spectrum, SEM and TEM analysis, flower‐like Cu3[MoO4]2O (ca. 5 μm) microspheres have been obtained, which were assembled from 3–4 nm thick nanosheets with an orthorhombic structure. Application of 3D flower‐like microspheres as an anode material for lithium‐ion batteries (LIBs) has been investigated and the possible electrochemical mechanism is analyzed. Electrochemical characterization of the Cu3[MoO4]2O nanoflowers as an anode material for LIBs has exhibited good cycle stability and a high coulombic efficiency during operation. The electrochemical activity was attributed to the unique structure of the Cu3[MoO4]2O microspheres, which provide more active sites for Li‐ion storage as well as a reduced transfer resistance. This work has explored a simple synthesis strategy for the synthesis of flower‐like Cu3[MoO4]2O microspheres without templates, additives, or surfactants, which exhibit a basis for not only high electrochemical performance in reversible Li storage, but also cycle stability.


융합소재연구센터 Enhanced electrochemical performance of carbon-coated Li2MnSiO4 nanoparticles synthesized by tartaric acid-assisted sol–gel process

· 저자

박경수, 진연호, 강이승, 이광희, 이남희, 김동완, 홍현선


A tartaric acid-assisted sol–gel process was used to synthesize Li2MnSiO4 (SG-LMS) nanopowders with orthorhombic structures (Pmn21 space group). The Li-active SG-LMS nanoparticles were fully surrounded by a conducting amorphous carbon layer/matrix that was formed by carbonization of the tartaric acid during post-annealing of the dry gel. The SG-LMS electrode exhibited higher specific capacity and superior cycle retention as compared to the LMS electrode prepared by a conventional solid-state reaction. Such high electrochemical performance originated from the presence of a high-purity phase, a large surface area, and an efficient electron transport path facilitated by the conductive carbon coating of the SG-LMS electrode.


융합소재연구센터 Recycling of waste automotive laminated glass and valorization of polyvinyl butyral through mechanochemical separation

· 저자

Basudev Swain, 박재량, 신동윤, 박경수, 홍명환, 이찬기


Due to strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility polyvinyl butyral (PVB) resin films are commonly used in the automotive and architectural application as a protective interlayer in the laminated glass. Worldwide million tons of PVB waste generated from end-of-life automotive associated with various environmental issues. Stringent environmental directive, higher land cost eliminates land filling option, needs a study, we have developed a mechanochemical separation process to separate PVB resins from glass and characterized the separated PVB through various techniques, i.e., scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), infrared spectroscopy (IR) and nuclear magnetic resonance spectroscopy (NMR). Commercial nonionic surfactants D201 used for the mechanochemical separation purpose. Through parameter optimization following conditions are considered to be the optimum condition; 30 vol% D201, stirring speed of 400 rpm, 35 °C temperature, operation time 1 h, and dilute D201 volume to waste automotive laminated glass weight ratio of ≈25. The technology developed in our laboratory is sustainable, environmentally friendly, techno-economical feasible process, capable of mass production (recycling).