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pISSN : 1225-1429 / eISSN : 2234-5078

2020 KCI Impact Factor : 0.17
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2021, Vol.31, No.1

  • 1.

    Growth of ε-Ga2O3 film and fabrication of high quality β-Ga2O3 films by phase transition

    Lee Han Sol | KIM SO YOON | 이정복 and 3other persons | 2021, 31(1) | pp.1~7 | number of Cited : 0
    Abstract PDF
    ε-Ga2O3, a metastable phase of Ga2O3, has excellent compatibility with substrates having a hexagonal structureor a quasi-hexagonal structure, so that a film having a relatively lower surface roughness and defect density than β-Ga2O3can be obtained easily. Accordingly, we attempted to fabricate a high-quality β-Ga2O3 film with a low surface rough nessand defect density using the property of phase transition to β-Ga2O3 when ε-Ga2O3 is annealed at a high temperature. Forthis, the growth of high-quality ε-Ga2O3 films must be preceded. In this study, the optimal flow rate was investigated byanalyzing the structural and morphological characteristics of the ε-Ga2O3 film according to the supplied precursor ratio. Inaddition, the annealing condition and the effect of β-Ga2O3 mixed in the ε-Ga2O3 film on the crystallinity of β-Ga2O3 afterphase transition were also investigated.
  • 2.

    The control of TiO2 nanofiber diameters using fabrication variables in electrospinning method

    윤한솔 | 김보성 | 김완태 and 5other persons | 2021, 31(1) | pp.8~15 | number of Cited : 0
    Abstract PDF
    TiO2 has been used in various fields such as solar cells, dental implants, and photocatalysis, because it has high physical and chemical stability and is harmless to the body. TiO2 nanofibers which have a large specific surface area also show a good reactivity in bio-friendly products and excellent photocatalysis in air and water purification. To fabricate TiO2 nanofibers, an electrospinning method was used. To observe the diameter of TiO2 nanofibers with fabrication variables, the fabrication variables was divided into precursor composition variables and process variables and microstructure was analyzed. The concentrations of PVP (Polyvinylpyrrolidone) and TTIP (Titanium(Ⅳ) isopropoxide) were selected as precursor composition variables, and inflow velocity and voltage were also selected as process variables. Microstructure and crystal structure of TiO2 nanofibers were analyzed using FE-SEM (Field emission scanning electron microscope) and XRD (X-ray diffraction), respectively. As-spun TiO2 nanofibers with an average diameter of about 0.27 μm to 1.31 μm were transformed to anatase TiO2 nanofibers with an average diameter of about 0.22 μm to 0.78 μm after heat treatment of 3 hours at 450ºC. Anatase TiO2 nanofibers with an average diameter of 0.22 μm can be expected to improve the photocatalytic properties by increasing the specific surface area. To change the average diameter of TiO2 nanofibers, the control of precursor composition variables such as concentrations of PVP and TTIP is more efficient than the control of electrospinning process variables such as inflow velocity and voltage.
  • 3.

    A study on the fabrication of high purity lithium carbonate by recrystallization of low grade lithium carbonate

    Bo-Ram Kim | Kim Dae Weon | 황성옥 and 2other persons | 2021, 31(1) | pp.16~23 | number of Cited : 0
    Abstract PDF
    Lithium carbonate recovered from the waste solution generated during the lithium secondary battery manufacturingprocess contains heavy metals such as cobalt, nickel, and manganese. In this study, the recrystallization of lithium carbonatewas performed to remove heavy metals contained in the powder and to increase the purity of lithium carbonate. First, theleaching efficiency of lithium carbonate according to pH in the aqueous hydrochloric acid solution was examined, and theeffect on the recrystallization of lithium carbonate according to the equivalent and concentration of sodium carbonate wasconfirmed. As the equivalent and concentration of sodium carbonate increased, the recovery rate of lithium carbonate improved. And the SEM image showed that the crystal shape was changed depending on the reaction conditions with sodium carbonate. Finally, the high purity lithium carbonate of 99.9% or more was recovered by washing with water.
  • 4.

    Effect of vacuum annealing and characterization of diecast ADC12 aluminum alloys

    ChiHoon Cho | Daseul Ham | seongchan oh and 2other persons | 2021, 31(1) | pp.24~31 | number of Cited : 0
    Abstract PDF
    We report structural, mechanical, and thermal properties of diecast ADC12 aluminum alloys characterized using synchrotron X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray (EDX) analysis, thermal conductivity (λ), Vickers hardness (Hv), and stress-strain measurements. We also studied the effect of post-annealing performed in a vacuum atmosphere on the mechanical properties of diecast ADC12 alloys. EDX and XRD results revealed that Al2Cu and AlCu3 grains are formed, well dispersed in Al base and highly crystalline. Ultimate tensile strength (UTS) of 307.9 ± 9.1 MPa and elongation of 2.98 ± 0.62% were estimated. λ was 129.3 ± 0.27 W/mK and Hv was approximately 130. Both values were significantly higher than the reported values. At annealing temperatures ranging from 25 to 200°C, UTS and Hv values remained constant, while as the annealing temperature increased to 500°C, these values gradually decreased. This is because stabilization of the microstructure improves toughness and ductility.
  • 5.

    Carbon diffusion behavior and mechanical properties of carbon-doped TiZrN coatings by laser carburization

    유현조 | Kim Taewoo | Seonghoon Kim and 2other persons | 2021, 31(1) | pp.32~36 | number of Cited : 0
    Abstract PDF
    This study was investigated in carbon diffusion behavior of laser-carburized TiZrN coating layer and the changesof mechanical properties. The carbon paste was deposited on TiZrN coatings, and the laser was irradiated to carburize intothe coatings. The XRD peak corresponding to the (111) plane shifted to a lower angle after the carburization, showing thelattice expansion by doped carbon. The decreased grain size implied the compression by the grain boundary diffusion ofcarbon. The XPS spectra for the bonding states of carbon was analyzed that carbon was substitute to nitrogen atoms inTiZrN, as carbide, through the thermal energy of laser. In addition, the combination of sp2 and sp3 hybridized bondsrepresented the formation of an amorphous carbon. The cross-sectional TEM image and the inverse FFT of the TiZrNcoating after carburizing were observed as the wavy shape, confirming the amorphous phase located in grain boundaries. After the carburization, the hardness increased from 34.57 GPa to 38.24 GPa, and the friction coefficient decreased by83 %. In particular, the ratio of hardness and elastic modulus (H/E) which is used as an index of the elastic recovery,increased from 0.11 to 0.15 and the wear rate improved by 65 %.
  • 6.

    Effect of composition on the structural and thermal properties of TiZrN thin film

    Choi ByoungSu | UM JI HUN | 석민준 and 3other persons | 2021, 31(1) | pp.37~42 | number of Cited : 0
    Abstract PDF
    The effect of chemical composition on the structural and thermal properties of TiZrN thin films was studied. Asthe Zr fraction in the deposited TixZr1-xN (x = 0.87, 0.82, 0.7, 0.6, and 0.28) increased, microstructural changes consisted ofreduction in the grain size and a gradual transition from columnar structure to granular structure were observed. In addition,it was also confirmed that a gradual crystal phase transition from TiN to TiZrN has occurred as the Zr fraction increasedup to 0.4. After heat t reatment a t 900°C, Ti0.82Zr0.18N and Ti0.7Zr0.3N layers were converted to a form in which rutile phaseTiO2 and TiZrO4 oxides coexist, while Ti0.6Zr0.4N layer was converted to TiZrO4 oxide. Among the five compositions ofTiZrN films, the Ti0.6Zr0.4N showed the best high temperature stability and produced a significant enhancement in thethermal oxidation resistance of Inconel 617 through suppressing the surface diffusion of Cr caused by thermal oxidation of the Inconel 617 substrate.
  • 7.

    A study on the application of sports wheelchair materials based on emotional materials

    SONG SUNG IL | 2021, 31(1) | pp.43~54 | number of Cited : 0
    Abstract PDF
    This work proposes a process to derive elements of emotional materials based on trend research in the application of materials in product development. It was intended to be applied to the development of a case model, a Korean sports wheelchair, and focused on the material portion of CMF-based research. Through research methodologies such as megatrends,competitor product and part-by-part analysis, and psychological color analysis, we studied optimization, verification, andDBization of materials, and drew the final application plan through FGI verification.
  • 8.

    Improvement of charging efficiency of AGM lead acid battery through formation pattern research

    Sung Jun Kim | Jeong Hun Son | Bong Gu Kim and 1other persons | 2021, 31(1) | pp.55~62 | number of Cited : 0
    Abstract PDF
    In order to improve fuel economy and reduce CO2, HEV adopts ISG system as a standard. This ISG systemincreased the electric load that the battery had to bear, and the number of starting increased rapidly. AGM Lead Acidbatteries have been developed and used, but the charging time is about three times longer as the electrolyte amount controlduring formation must be maintained at a higher level compared to conventional lead-acid batteries. In this study, we triedto shorten the charging time by increasing the charging efficiency through the optimization of the formation pattern. Inorder to optimize the Formation Pattern, 10 charging steps and 6 discharging steps were applied to 16 multi steps, and thecharging current for each step was controlled, and the test was conducted under 4 conditions (21 hr, 24 hr, 27 hr, 30 hr). Asa result of simultaneous application of multi-step and discharge step, it was verified that minimizing the current loss andeliminating the sudden polarization during charging contributes to the improvement of charging efficiency. As a result, itshowed excellent results in reducing the charging time by about 30 % with improved charging efficiency compared to theprevious one.