논문현황

INSTITUTE FOR ADVANCED ENGINEERING

융합소재연구센터 Optical Properties of Nano–Structured ZnO : Sn Powders Prepared in a Micro Drop Fluidized Reactor

· 저자

유동준, 임대호, 강용, 이찬기, 강경민


Optical properties of nano–structured ZnO : Sn powders prepared by means of a one–step micro drop fluidized reactor continuously were investigated. The band–gap edge of ZnO : Sn powder was extended to the visible region due to the formation of the extrinsic levels of interstitial oxygen and oxygen vacancy in the band structure of ZnO. The BET surface area of ZnO : Sn powders increased by up to 300%. The fluidization of micro drops of precursors during thermal decomposition contributed to the formation of porous surface morphology and modification of band gap structure of the ZnO : Sn powders by generating micro shear force and strain at the surface of micro drops. The doping of Sn4+ ions into ZnO reduced the electrical resistivity by generating extra free electrons at the surface of ZnO : Sn powders.


융합소재연구센터 Effect of controlled Mn doping on transition of oxygen vacancies in Bi2Ti2O7 thin films: An electrochemical study

· 저자

강이승, 안혜란, 김태형, 이덕희, 박경수, Basudev swain, 이찬기, Nahm sahn


Crystalline pyrochlore Bi2Ti2O7 (B2T2) thin films were well formed at 300 °C under 740 mTorr of oxygen partial pressure using pulsed laser deposition. In order to improve the electrical properties of the dielectric B2T2 films, Mn ions were doped into the films and their influence was investigated. Improvement in electrical behavior, especially leakage current density were revealed via impedance spectroscopy and electrochemical studies. Mn doping at an appropriate level improved the electrical properties of the films by affording extrinsic oxygen vacancies that reduced the number of intrinsic oxygen vacancies acting as electron trap sites at the interface between the Pt electrode and the B2T2 film. Schottky emission was posited as the leakage current mechanism in the 10 mol% Mn doped B2T2 (Mn:B2T2) films. The barrier height between the Pt electrode and the Mn:B2T2film was approximately 1.46 eV, but decreased to 0.51 eV for the non-doped film due to large numbers of intrinsic oxygen vacancies.


융합소재연구센터 A validation experiment on indium recovery by electrowinning of aqueous electrolytes: Optimization of electrolyte composition

· 저자

이성규, 이수영, Basudev swain, 조성수, 이찬기


A batch-type and lab-scale indium recovery method was developed via electrowinning (EW) to prove mass production-capability and economic recovery of indium from InCl3 crystals precipitated from the solvent extraction using a suitable phosphoric acid-based extractant. More precisely, the InCl3 crystals thus precipitated were further dissolved in three different aqueous electrolyte mixtures for subsequent electrowinning experiments: 0.05 M InCl3 – 0.7 M LiCl; 0.05M InCl3; 0.05 M InCl3 – 0.7 M NaCl. The effect of adding LiCl and NaCl supporting electrolytes to InCl3 on overall EW efficiency was thus comprehensibly investigated. Direct electroreduction of InCl3 using 0.05 M InCl3 aqueous electrolyte resulted in the highest indium metal purity of 99.996 % deposited on the copper cathode. Thus, metallic contents obtained from the validation experiments were further characterized using various analytical tools such as inductively coupled plasma/atomic emission spectroscopy (ICP/AES), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence (XRF).


융합소재연구센터 Opto-electrical properties of ZnO:Al powders prepared in a micro drop fluidized reactor

· 저자

유동준, 임대호, 강용, 이찬기, 강경민


Optical and electrical properties of ZnO:Al powders prepared in a continuous and one-step micro drop fluidized reactor were investigated. The shift of main peaks in XRD patterns and crystallite size of ZnO:Al powders increased with increasing flow rate of micro bubbles (UMB), indicating that the fluidization of micro drops during the formation of powders could help the doping of Al3+ ions into the lattice of ZnO. The band gap energy of ZnO:Al powders became narrow by forming the extrinsic donor levels to the conduction band more easily, with increasing UMB. The surface morphology of ZnO:Al powders became more wrinkled and furrowed with increasing UMB, due to the increase of micro shear force and strain acting on the surface of ZnO:Al during the formation in the fluidization field of the reactor. The room temperature photoluminescence indicated that the doping effects of as-prepared ZnO:Al powders were getting better with increasing UMB. The electrical resistivity of ZnO:Al decreased considerably due to the active generation of extra free electrons at the surface of the powder, with increasing UMB.


융합소재연구센터 Understanding the isothermal growth kinetics of CdSe quantum dots through the microfluidic reactor assisted combinatorial synthesis

· 저자

Basudev swain, 홍명환, 강이승, 이찬기


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)nα=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.


융합소재연구센터 Optimization of CdSe nanocrystals synthesis with a microfluidic reactor and development of combinatorial synthesis process for industrial production

· 저자

Basudev swain, 홍명환, 강이승, 김범성, 김남훈, 이찬기


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.


융합소재연구센터 Effect of Amine Additive for the Synthesis of Cadmium Selenide Quantum Dots in a Microreactor

· 저자

정다원, Basudev swain, 성태연, 박경태, 이찬기, 김범성


The effect of octylamine flow rate on the structure and morphology of CdSe quantum dots synthesized in a microreactor was studied. The flow rate of octylamine was varied from 0.005 ml/min to 0.030 ml/min, and the optical properties of the synthesized particles were analyzed by UV–vis and photoluminescence spectroscopy. The particle size of the quantum dots was found to increase with an increasing octylamine flow rate. Further, UV–vis and photoluminescence bands were found to be red‐shifted with an increasing flow rate. We determined that, by controlling octylamine flow rate, the particle size of the quantum dots could be controlled. This method will help to determine the optimal octylamine flow conditions for synthesizing nanoparticles for use in a diverse range of applications.


융합소재연구센터 Fischer-Tropsch Synthesis of the Promoted Co/ZSM-5 Hybrid Catalysts for the Production of Gasoline Range Hydrocarbons

· 저자

강석환, 류재홍, 김진호, 김효식, 이찬기, 이연조, 전기원


Fischer-Tropsch synthesis (FTS) reaction for the direct production of gasoline range hydrocarbons (C5-C9) from syngas was investigated on Ru, Pt, and La promoted Co/ZSM-5 (Si/Al = 25) catalysts. The hybrid catalysts were characterized by BET surface area, XRD, H2-TPR, NH3-TPD and XPS analyses. These physico-chemical properties were correlated with activity and selectivity of the catalysts. The promoted Co/ZSM-5 hybrid catalysts were found to be superior to the unpromoted Co/ZSM-5 catalyst in terms of better C5-C9 selectivity. Pt-Co/ZSM-5 exhibited the highest catalytic activity because of the small cobalt particle size.


융합소재연구센터 Bubble and Heat Transfer Phenomena in Viscous Slurry Bubble Column

· 저자

김효식, 김진호, 이찬기, 강석환, 우광재, 정호진, 김동욱


Heat transfer and bubble phenomena were investigated by adopting the drift flux model in a viscous slurry bubble column reactor (SBCR), having a diameter of 0.0508 m (ID) and height 1.5 m. The effects of superficial gas velocity (0.002 - 0.164 m/s), solid concentration (0 - 20 wt%) and liquid viscosity (paraffin oil; 16.9 mPa∙s and squalane; 25.9 mPa∙s) on the gas holdup and heat transfer characteristics were examined. It was observed that the gas holdup increased with increasing superficial gas velocity (UG), but decreased with increasing solid concentration (SC) or slurry viscosity. The degree of non-uniformity in a SBCR could be determined by the modified drift flux model at the heterogeneous flow regime. The local heat transfer coefficient (h) between the immersed heater and the bed decreased with increasing liquid viscosity and SC, but it increased with increasing UG. The modified Nusselt number including the gas holdup and local heat transfer coefficient was well correlated in terms of dimensionless groups such as Reynolds and Prandtl numbers.


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.