논문현황

INSTITUTE FOR ADVANCED ENGINEERING

에너지융복합팀 Catalytic application of metallic iron on dyeing sludge ash for steam reforming reaction

· 저자

남성방, 박영수, 윤영식, 구재회, 성호진, Masayuki Horio


Because it is the most promising method for reforming tar in a gasification system, a catalytic steam reforming reaction of tar using a dyeing sludge ash catalyst that contains mostly iron oxide has been modeled using benzene to investigate whether a steam reforming catalyst produced from waste is viable. The catalytic activity of the ash catalyst is similar to that of the commercially available iron-chrome-based catalyst for the same equivalent total amount of Fe2O3. The activity over the ash catalyst has been examined in terms of the weight hour space velocity (WHSV) and the reaction temperature to develop a model for the reaction kinetics. Using a power law model, the reaction order coefficients of the benzene and steam were estimated to be 0.43 and 0, respectively. The activation energy required for the ash catalyst was approximately 187.6 kJ mol−1. In addition, the reductive properties of the iron oxide in the ash catalyst were also examined via XRD and H2-TPR analyses.


신소재공정센터 플라즈마 전해산화법에 의해 형성된 알루미늄 합금의 양극산화피막 내마모특성에 관한 연구

· 저자

정우철, 진연호, 최진주, 양재교


In this study, plasma electrolytic oxidation (PEO) method was used to from anodic oxide films on Al alloy and their resistance and morphological characteristics were investigated as a function of film formation voltage and treatment time. Cross-sectional morphology and composition of the PEO films were analyzed by SEM and EDS. The PEO films showed increased surface roughness and thickness with of film formation voltage and treatment time. The wear resistance was found to be the best for the PEO film formed for 5 min at 500V which is attributed to be denser structure relatively and lower surface roughness


신소재공정센터 Thermodynamics of fluoride-based molten fluxes for extraction of magnesium through the low temperature solid oxide membrane (LT-SOM) process

· 저자

Y. Lee, J.K. Yang and J.H. Park


The melt quenching experiments and thermodynamic calculations of phase diagrams were carried out to investigate potential additives for the low temperature solid oxide membrane (LT-SOM) magnesium extraction process. The solubility of MgO, which is a major source of magnesium extraction, was also measured in the molten fluoride fluxes. The solubility of MgO in the 46.5MgF2-46.5CaF2-7LiF and 45MgF2-45CaF2-10NaF (wt%) systems reached 3.4 and 1.9 wt% at 1473 K, respectively, and 1.5 wt% MgO in both fluxes at 1223 K. In addition, the 45MgF2-55CaF2 binary eutectic flux, which has been widely used in SOM process, could dissolve up to 2.3 wt% MgO at 1473 K. This value is significantly lower than the literature value, i.e. 10 wt% MgO. From the evaluation of the activity coefficient of MgO in the 46.5MgF2-46.5CaF2-7LiF and 45MgF2-45CaF2-10NaF fluxes under MgO saturation, it was confirmed that the stability of MgO in the 7LiF flux is greater than that in the 10NaF flux. Hence, the driving force of MgO dissolution into the 7LiF flux is higher than that into the 10NaF flux. The newly developed molten flux for magnesium extraction using the LT-SOM process with an operating temperature lower than 1273 K is the 46.5MgF2-46.5CaF2-7LiF system.


신소재공정센터 The oxygen-permeation property of doped-zirconia membrane at high temperature and in reduced condition

· 저자

Hee Jung Park, Jae-kyo Yang, Yun-Ho Jin, K.H. Lee


Doped zirconia with fast oxygen ionic conduction can be applied to an oxygen ion transport membrane for the deoxidation from metal melts and the production of metals from molten metal oxides. For the application, an oxygen-permeation study is required in low-oxygen partial pressure and high temperature. In this study, the electrical conductivity of the zirconia at high temperature (above 1200 °C) was estimated with a 4-probe DC method in order to estimate the theoretical oxygen-permeation flux. The oxygen permeation was investigated with two types of apparatus: a permeation concentration cell and a common permeation structure. As a result, the measured oxygen flux was much lower than the value expected from the electrical conductivity, indicating that the oxygen permeation was mostly limited by the surface-exchange kinetics in spite of the very high temperature. The rate-determining elementary step of the surface-exchange kinetics was the surface ionic diffusion and the charge transfer of minor charge carriers. To enhance the oxygen permeation of the zirconia, a surface-coating strategy using a double layer of ceria and lanthanum-chromate was applied with various coating thickness. The oxygen-permeation flux was maximized by the surface modification with optimal coating thickness.


융합소재연구센터 Low-voltage operating solution-processed CdS thin-film transistor with Ca2Nb3O10 nanosheets deposited by Langmuir–Blodgett method for the gate insulator

· 저자

강이승, 안혜란, 정승민, 김세열, Nahm sahn, 김대근, 이찬기


One of the most demanding challenges in next-generation thin-film transistors (TFTs) is the development of new materials for high-performance devices with higher speed and lower operation voltage. To drive a TFT at a low power, it is important to form an insulating layer as a thin film with good characteristics. Langmuir–Blodgett (LB) technique is one of the most suitable methods for controlling and developing two-dimensional nanomaterials. In the LB method, a layer only one molecule thick (Langmuir monolayer) is spread at the air/water interface and transferred onto the surface of a solid substrate and the process can be repeated several times with the same substrate to deposit multilayer films. In this study, a Ca2Nb3O10 (CNO) dielectric layer was fabricated using the LB method, and a CdS active layer was fabricated using the chemical bath deposition (CBD) method to obtain the final structure of CdS-TFTs. CNO dielectric layers have low leakage current density (7.26 × 10−7 A cm−2) and a high capacitance density of 944 nF cm−2 at 100 kHz. Therefore, it is considered that the CNO films produced using the LB method are suitable as an insulating layer material. Furthermore, the CdS-TFTs exhibited good performance with a low threshold voltage of 0.596 V, Ion/Ioff current ratio of 106, subthreshold slope of 0.05 V dec−1, and high mobility of 0.428 cm2 V−1 s−1at operating voltages less than 2 V.


융합소재연구센터 La-doped p-type ZnO nanowire with enhanced piezoelectric performance for flexible nanogenerators

· 저자

강이승, 안혜란, 박지영, 홍명환, Nahm sahn, 이찬기


In recent years, energy harvesting has attracted considerable attention as a promising method to convert waste energy to useful energy. In particular, piezoelectric energy harvesters are of significant interest, because they have a simple structure and can be used to harvest energy regardless of weather or other environmental conditions. In accordance with the miniaturization trend of electronic devices driven by low power, piezoelectric nanogenerators (PENGs) using various nanostructured materials are being developed. Among them, ZnOnanowires (NWs) are most widely used for the use of PENGs. However, while research on n-type ZnO NWs is extensive, studies on p-type ZnO NWs are insufficient owing to their poor stability. In this study, La-doped p-type ZnO (La:ZnO) NWs were synthesized by a hydrothermal method to expand the applications of p-type ZnO and determine their potential as PENGs. XRD analysis showed that La3+ ions was well doped without the formation of any secondary phases and caused a change in the lattice parameter when compared to that of undoped ZnO. XPS analysis was performed to investigate the surface elemental compositions of La:ZnO NWs, and the morphology of La:ZnO NWs was investigated using SEM and TEM. We further studied the piezoelectric output performance of undoped and La-doped ZnO NWs, and found that La:ZnO NWs showed improved piezoelectric output performance as a result of electron screening effect of the p-type semiconductor.


융합소재연구센터 Commercial indium recovery processes development from various e-(industry) waste through the insightful integration of valorization processes: A perspective

· 저자

Basudev swain, 이찬기


Recycling of the waste LCD and recovery of indium which is an important classified critical raw material rarely have been industrially valorized for the circular economy due to lack of technology. Waste specific technology development is a cost-intensive and time-consuming process for the recycling industry. Hence, integrating existing technology for the purpose can address the e-waste issue in general and waste LCD in particular. Waste LCD and LCD industry itching wastewater are two important challenges can be addressed through an insightful combination of two. Hence, here possible integration of waste LCD leaching process with ITO wastewater treatment has been focused on indium recovery purpose. From our perspective process integration can be managed in two different ways, i.e., waste-to-waste mix stream process and integration of two different valorization processes for complete recovery of indium. With reference to indium recovery and context of e-waste recovery the process integration can be managed in two different ways, i.e., (i) waste LCD leaching with ITO etching industry wastewater then valorized (Waste-to-waste mix stream), (ii) Integration of waste LCD leaching process with ITO wastewater treatment process (integration of two valorization processes).Through proposed process semiconductor manufacturing industry and ITO recycling industry can address various issues like; (i) waste disposal, as well as indium recovery, (ii) brings back the material to production stream and address the circular economy, (ii) can be closed-loop process with industry and (iii) can be part of cradle-to-cradle technology management and lower the futuristic carbon economy, simultaneously.


융합소재연구센터 Poly(methylmethacrylate) coating on quantum dot surfaces via photo-chemical reaction for defect passivation

· 저자

김도연, 주소영, 이찬기, 김범성, 김우병


An effective poly(methylmethacrylate) (PMMA) coating process via photo-chemical reaction for quantum dots (QDs) was investigated. Various concentrations of PMMA were tested and the optimal concentration was confirmed to be 0.1 mM. The quantum yield (QY%) of the 0.1 mM PMMA-coated sample showed a 27% increase in efficiency relative to the as-synthesized CdSe/ZnS QDs due to the passivation of defect states on the surface. The QY% enhanced by PMMA was further increased by light irradiation because of the strong interactions and bonding between the surface atoms and functional groups of PMMA (acrylic groups). The excitation and formation of electron-hole pairs generated by light irradiation lead to strong interactions and chemical bonding on the surface; this is applicable to other cadmium QDs. When the QDs were passivated by a photo-chemical method, the QY% increased by approximately 20% for CdSe, CdSe/ZnS, and CdSe/ZnSe QDs. In order to evaluate the long-term stability depending on the PMMA coating, the QDs were stored for 12 months. The efficiency of as-synthesized bare QDs, initially 90%, drastically decreased to 17% after 12 months, but the PMMA-coated QDs with our coating method maintained a high efficiency of over 75%.


융합소재연구센터 A Novel Synthetic Method for N Doped TiO2 Nanoparticles Through Plasma-Assisted Electrolysis and Photocatalytic Activity in the Visible Region

· 저자

김태형, 고광명, 조홍백, 송요셉, 이찬기, 좌용호


Nitrogen doped TiO2 (N-TiO2) nanoparticles were synthesized via a novel plasma enhanced electrolysis method using bulk titanium (Ti) as a source material and nitric acid as the nitrogen dopant. This method possesses remarkable merits with regard to the direct-metal synthesis of nanoparticles with its one-step process, eco-friendliness, and its ability to be mass produced. The nanoparticles were synthesized from bulk Ti metal and dipped in 5–15 mmol of a nitric acid electrolyte under the application of AC 500 V, the minimum range of voltage to generate plasma. By controlling the electrolyte concentration, the nanoparticle size distribution could be tuned between 12.1 and 24.7 nm using repulsion forces via variations in pH. The prepared N-TiO2 nanoparticles were calcined at between 100 and 300°C to determine their photocatalytic efficiency within the visible-light region, which depended on their crystal structure and N doping content. Analysis showed that the temperature treatment yielded an anatase TiO2 crystalline structure when the N doping content was varied from 0.4 to 0.54 at.%. In particular, the 0.4 at.% N doped TiO2 catalyst exhibited the highest catalytic performance with quadruple efficiency compared to the P-25 standard TiO2 nanoparticles, which featured a 91% degradation of methyl orange organic dye within 300 min. This solid-liquid reaction based on plasma enhanced electrolysis could open new pathways with regard to high purity mass producible ceramic nanoparticles with advanced properties.


융합소재연구센터 Facile Synthesis of Carbon-Coated LiFeBO 3 Microspheres by Spray Drying and Their Structural Properties

· 저자

강이승, 안혜란, 정승민, Nahm sahn, 이찬기


Spherical LiFeBO3 (LFB) powder was successfully synthesized by a commercially available spray drying process. The powders were coated with a layer of carbon through a calcination step. This simple method allowed for fabrication of the powder with spherical particles and a homogeneous carbon coating. The crystal configuration, microstructure, and nature of the carbon coating were investigated by Rietveld refinement, Mössbauer spectroscopy, scanning electron microscopy, and transmission electron microscopy. The characterized structure had a monoclinic phase and belonged to the C2/c space group. The synthesized particles had a radius of 5 μm and were covered by a 6.5-nm-thick carbon coating. The spherical geometry of LFB with a well-encapsulated carbon coating layer is expected to enhanced powder density and result in good electrical performance. This preliminary study are expected to contribute to a deeper understanding of the novel LFB and aid the development of an effective method to fabricate cathode materials for Li-ion batteries.


융합소재연구센터 Synthesis and Characterization of TiO2/CuS Nanocomposite Fibers as a Visible Light-Driven Photocatalyst

· 저자

안혜란, 강이승, 안효진, 좌용호, 이찬기


TiO2/CuS nanocomposites were fabricated by precipitation of nanosized CuS via sonochemical method on electrospun TiO2 nanofibers, and their structure, chemical bonding states, optical properties, and photocatalytic activity were investigated. In the TiO2/CuS nanocomposite, the position of the conduction band for CuS was at a more negative than that of TiO; meanwhile, the position of the valence band for CuS was more positive than those for TiO, indicating a heterojunction structure belonging to type-II band alignment. Photocatalytic activity, measured by decomposition of methylene blue under visible-light irradiation (λ > 400 nm) for the TiO2/CuS nanocomposite, showed a value of 85.94% at 653 nm, which represented an improvement of 52% compared to that for single TiO2nanofiber (44.97% at 653 nm). Consequently, the photocatalyst with TiO2/CuS nanocomposite had excellent photocatalytic activity for methylene blue under visible-light irradiation, which could be explained by the formation of a heterojunction structure and improvement of the surface reaction by increase in surface area.


융합소재연구센터 Valorization of cobalt from waste lib cathode through cobalt oxalate and cobalt oxide synthesis by leaching-solvent extract-precipitation stripping

· 저자

Basudev swain, LEE, J. C., 이찬기


An ecoefficient, economical and sustainable valorization process for the synthesis of Co3O4 from waste lithium-ion battery (LIB) by leaching-solvent extract-scrubbing-precipitation stripping route has been developed. Through an optimization, the waste LIB cathode was leached using 2000 mole/m3 of H2SO4 and 5 Vol. % of the H2O2 at a pulp density of 100 kg/m3 under leaching time 60 minutes and temperature 75°C. From the separated leach liquor, cobalt was purified by saponified Cyanex 272. From cobalt, loaded Cyanex 272 impurities were scrubbed and the CoC2O4·2H2O was recovered through precipitation stripping. Finally, the precipitate was calcined to synthesize Co3O4, which is a precursor for LIB cathode materials manufacturing. From TGA-DTA, followed by XRD analysis it was confirmed that at 200°C the CoC2O4·2H2O can be converted to anhydrous CoC2O4 and at 350°C the anhydrous can be converted to Co3O4 and at 1100°C the Co3O4 can be converted to CoO. Through reported route waste LIB can back to LIB manufacturing process through a versatile and flexible industrial approach.


융합소재연구센터 An investigation into the effective surface passivation of quantum dots by a photo-assisted chemical method

· 저자

주소영, 박현수, 김도연, 김범성, 이찬기, 김우병


In this study, we have developed an effective amino passivation process for quantum dots (QDs) at room temperature and have investigated a passivation mechanism using a photo-assisted chemical method. As a result of the reverse reaction of the H2O molecules, the etching kinetics of the photo-assisted chemical method increased upon increasing the 3-amino-1-propanol (APOL)/H2O ratio of the etching solution. Photon-excited electron-hole pairs lead to strong bonding between the organic and surface atoms of the QDs, and results in an increase of the quantum yield (QY%). This passivation method is also applicable to CdSe/ZnSe core/shell structures of QDs, due to the passivation of mid-gap defects states at the interface. The QY% of the as-synthesized CdSe QDs is dramatically enhanced by the amino passivation from 37% to 75% and the QY% of the CdSe/ZnSe core/shell QDs is also improved by ∼28%.


융합소재연구센터 Bulk-Direct Synthesis of TiO 2 Nanoparticles by Plasma-Assisted Electrolysis with Enhanced Photocatalytic Performance

· 저자

김태형, 정승재, 임효령, 조홍백, 이찬기, 좌용호


A new plasma-assisted electrolysis method has been developed to synthesize amorphous TiO2 nanoparticles and exploited for the enhanced photocatalytic performance. The method is simple, environmentally friendly, produces nanoparticles directly from bulk metal, and is suitable for mass production. The process was conducted in low-concentration nitric acid electrolyte under a voltage of 450 V, the minimum necessary to produce plasma on the anode surface. The average nanoparticle size was tuned between 16 and 28 nm by controlling electrolyte concentration within the range of 5 to 15 mM. The production rate increased with time, with the maximum of 11.27 g/h. The amorphous TiO2 nanoparticles were calcined at various temperatures to determine the crystalline structures and to compare their photocatalytic effects. The structure ranged from pure anatase to rutile under various calcination temperatures; the anatase–rutile mixed phase produced at 600°C showed the highest catalytic performance, with 94% degradation of methylene blue within 30 min owing to a synergetic effect between the phases. This liquid-phase plasma-assisted electrolysis method can pave the way for large-scale synthesis of highly pure metal-based ceramic nanoparticles with narrow size distributions.


융합소재연구센터 Structural and Optical Properties of ZnSe:Eu/ZnS Quantum Dots depending on Interfacial Residual Europium

· 저자

박지영, 이찬기, 서한욱, 정다원, 김민영, 김우병, 김범성


A multimodal emitter comprising of ZnSe:Eu/ZnS (core/shell) quantum dots (QDs) by adding a ZnS precursor in situ during synthesis. ZnSe/Eu2+/Eu3+/ZnS actives both core and core/shell. QDs prepared with the ZnS precursor displayed a luminescence intensity three times that of ZnSe QDs due to the passivation effect of the Shell. While the core QDs display the 450–550 nm emission of Eu2+ (4F65D1 → 4F7), the core/shell system showed no Eu2+ emission but only the sharp peaks in the red at 579, 592, 615, 651, and 700 nm due to the electronic transitions of 5D0 → 7Fn (n = 0–4) depending on leisurely decreased with increased reaction time. These results are in agreement with Eu 3d spectra of XPS analysis results. Microscopic analyses show that the core and core/shell QDs both have a zinc blende structure, and their respective sizes were about 3.19 and 3.44 nm. The lattice constant in the central portion of the core/shell QDs are around d111 = 3.13 Å, which is between the outside and inside ring patterns (d111 = 3.27 and 3.07 Å, respectively). This shows the effective over-capping of shell onto the core QDs. The core/shell structure may contain Eu2O3 bonding the over-coated ZnS surface on the Eu3+-doped ZnSe core.


융합소재연구센터  Size-Distribution Effects of TiO2 Nanopowders Synthesized by Chemical Vapor Condensation Method for Dye-Sensitized Solar Cells

· 저자

주소영, 박현수, 이찬기, 김우병


The size distribution effects of TiO2 nanoparticles synthesized by chemical vapor condensation (CVC) have been investigated. Nanoparticles of sizes 3–5 nm, 10–400 nm and 30–400 nm were synthesized at synthesis pressures of 5 kPa, 40 kPa and 100 kPa, respectively. Anodes of the dye-sensitized solar cell (DSSC), when doped with 3–5 nm nanoparticle (synthesized at 5 kPa) exhibited the highest photoconversion efficiency (5.04%), which is attributed to (1) narrow size-distribution of nanoparticle and pore, (2) high specific surface area and (3) high transmission of the dye absorption wavelength. However, anodes fabricated with 10–400 nm TiO2 nanoparticles (synthesized at 40 kPa) produced the lowest photo-current. This could be due to sintering of bi-size nanoparticle, because the bi-size of nanoparticles produced the smaller pore size and lower concentration of pore volume during sintering and which results in the poor penetration of electrolyte into the porous TiO2.


융합소재연구센터 Carbon Co-Deposition during Gas Reduction of Water-Atomized Fe-Cr-Mo Powder

· 저자

Basit ali, 최상훈, 서석준, 맹덕영, 이찬기, 김택수, 박경태


The water atomization of iron powder with a composition of Fe-3Cr-0.5Mo (wt.%) at 1600°C and 150 bar creates an oxide layer, which in this study was reduced using a mixture of methane (CH4) and argon (Ar) gas. The lowest oxygen content was achieved with a 100 cc/min flow rate of CH4, but this also resulted in a co-deposition of carbon due to the cracking of CH4. This carbon can be used directly to create high-quality, sinter hardenable steel, thereby eliminating the need for an additional mixing step prior to sintering. An exponential relationship was found to exist between the CH4 gas flow rate and carbon content of the powder, meaning that its composition can be easily controlled to suit a variety of different applications.


융합소재연구센터 Room-temperature processing of CdSe quantum dots with tunable sizes

· 저자

주소영, 정다원, 이찬기, 김범성, 박현수, 김우병


In this work, CdSe quantum dots (QDs) with tunable sizes have been fabricated via photo-induced chemical etching at room temperature, and the related reaction mechanism was investigated. The surface of QDs was oxidized by the holes generated through photon irradiation of oxygen species, and the obtained oxide layer was dissolved in an aqueous solution of 3-amino-1-propanol (APOL) with an APOL:H2O volume ratio of 5:1. The generated electrons promoted QD surface interactions with amino groups, which ultimately passivated surface defects. The absorption and photoluminescence emission peaks of the produced QDs were clearly blue-shifted about 26 nm with increasing time, and the resulting quantum yield for an 8 h etched sample was increased from 20% to 26%, as compared to the initial sample.


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.