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pISSN : 1225-1429 / eISSN : 2234-5078

2020 KCI Impact Factor : 0.17
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2021, Vol.31, No.4

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  • 1.

    Growth of Ga2O3 films on 4H-SiC substrates by metal organic chemical vapor deposition and their characteristics depend on crystal phase

    KIM SO YOON | 이정복 | Hyung Soo Ahn and 2other persons | 2021, 31(4) | pp.149~153 | number of Cited : 0
    Abstract PDF
    ε-Ga2O3 thin films were grown on 4H-SiC substrates by metal organic chemical vapor deposition (MOCVD) andcrystalline quality were evaluated depend on growth conditions. It was found that the best conditions of the ε-Ga2O3 were grown at a growth temperature of 665°C and an oxygen flow rate of 200 sccm. Two-dimensional growth was completed after the merge of hexagonal nuclei, and the arrangement direction of hexagonal nuclei was closely related to the crystal direction of the substrate. However, it was confirmed that crystal structure of the ε-Ga2O3 had an orthorhombic rather than hexagonal. Crystal phase transformation was performed by thermal treatment. And a β-Ga2O3 thin film was grown directly on 4H-SiC for the comparison to the phase transformed β-Ga2O3 thin film. The phase transformed β-Ga2O3 film showed better crystal quality than directly grown one.
  • 2.

    Effect of O2/Ar+O2 concentration on phase stability of transparent Mn doped SnO2 monolayer film

    김태근 | Jang, Gun-eik | 2021, 31(4) | pp.154~158 | number of Cited : 0
    Abstract PDF
    The optical transmittance of Mn-doped SnO2 monolayer film increased gradually from 80.9 to 85.4 % at 550 nm wavelengths upon increasing the O2/Ar+O2 concentration rate from 0 to 7.9 % and the band gap energy changed from 3.0 to 3.6 eV. The resistivity tended to decrease from 3.21 Ω·cm to 0.03 Ω·cm, reaching a minimum at 2.7 %, and then gradually increased from 0.03 to 52.0 Ω·cm at higher O2/Ar+O2 gas concentration ratio. Based on XPS spectra analysis, the Sn 3d5/2 peak of Mn-doped SnO2 single layer shifted slightly from 486.40 to 486.58 and O1s peak a lso shifted f rom 530.20 to 530.33 eV with increase the O2/Ar+O2 concentration ratio. Therefore, the XPS spectra results indicate that a multiphase with SnO and SnO2 coexisted in the sputtered Mn-doped SnO2 monolayer film.
  • 3.

    Fabrication of carbon nano tube reinforced grass fiber composite and investigation of fracture surface of reinforced composites

    김형태 | 이도현 | Woo-Jin An and 5other persons | 2021, 31(4) | pp.159~165 | number of Cited : 0
    Abstract PDF
    The fiber composites have been investigated as lightweight structure material platforms for aerospace applications because their strength can be enhanced by adding reinforcement without a significant increase in weight. In this study, thefabrication and characterization of carbon nanotube (CNT) reinforced glass fiber composites are demonstrated to enhance the tensile strength of longitudinal direction along the glass fibers. Due to the reinforcement of CNT in epoxy layers, the yield strength of fiber/epoxy composites is enhanced by about 10 %. Furthermore, using scanning electron microscopy, analysis of fracture surfaces shows that mixed CNT in epoxy layers acts as necking agents between fractured surfaces of fiber/epoxy; thereby, initiation and evolution of crack across fiber composite can be suppressed by CNT necking between fractured surfaces.
  • 4.

    Phase stability of TiO2 synthesized by Sol-gel Method at various pH and calcination temperatures

    LEEJAEYEON | Yong Jin Kim | Dae Sung Kim and 3other persons | 2021, 31(4) | pp.166~173 | number of Cited : 0
    Abstract PDF
    The rutile phase of TiO2 forms a stable phase at high temperatures compared to anatase phase, but the stable temperature range of anatase changes depending on the synthesis conditions. In this study, nano-sized TiO2 was synthesized by the Sol-gel method using TiOSO4 and a mixed solvent of ethanol and distilled water, and the phase change of anatase and rutile according to pH and heat treatment temperature was investigated. Changes in the ratio of anatase and rutile wereobserved by changing the pH (3, 5, 7, 9) and heat treatment temperature (500, 600, 700, 800, 900°C) conditions of the prepared TiO2. As a result of observing these changes through XRD and FE-SEM analysis, anatase TiO2 at 500°C and rutile TiO2 at 900°C were observed. According to the pH, at these intermediate temperatures of 600, 700 and 800°C, the ratio of anatase and rutile changes. At 700°C, it was concluded that pH = 3~5 had a larger ratio of anatase TiO2, andpH = 7~9 had a larger ratio of rutile TiO2.
  • 5.

    Change in compressive strength of lightweight geopolymers after immersion

    kimhakmin | KIM, YOOTAEK | 2021, 31(4) | pp.174~181 | number of Cited : 0
    Abstract PDF
    Lightweight geopolymers were fabricated by using IGCC (integrated gasification combined cycle) slag and Si sludge which are classified as general wastes (recyclable resources). Three curing methods were tried to investigate thechanges in compressive strength and density according to the curing method and immersion time. Immersion period was tried up to 21 days to observe long-term performance in water. Compressive strength of the specimens cured in ovendecreased abruptly with an increase in immersion time. Compressive strength of the specimen cured in autoclave was low after 3 and 7 day immersion; however, increased rapidly after 21 day immersion. On the contrary, compressive strength of the specimen cured in autoclave and oven was high but substantially decreased after 21 day immersion. Conclusively, it was speculated that oven curing is effective for the compressive strength development at early age; however, autoclave curing is more desirable for the long-term performance in water.
  • 6.

    Thermal properties of silica fume-SiO2 based porous ceramic fabricated by using foaming method

    하태완 | KANG SEUNG GU | Kangduk Kim | 2021, 31(4) | pp.182~189 | number of Cited : 0
    Abstract PDF
    Porous ceramics were manufactured using the foaming method for the development of inorganic insulating materials. Silica fume and SiO2 were used as main raw materials, and bentonite was used as a rapid setting agent for uniform structure formation of porous ceramics. The porous ceramics were sintered at 1200°C, and porosity, density, compressive strength, microstructure and thermal conductivity were analyzed. As the content of silica fume to SiO2 of the porous ceramics increased 70 to 90 %, the specific gravity increased from 0.63 to 0.69, and the compressive strength increased from 9.41 Mpa to 12.86 Mpa. But, the porosity showed a tendency to decrease from 72.07 % to 70.82 %, contrary to the specific gravity. As a result of measuring the thermal conductivity, the porous ceramic with a silica fume content of 70 % showed a thermal conductivity o f 0.75 to 0 .72W/m∙K at 25 t o 800°C, respectively, and, another that a silica fume content of 90 % showed a 0.66~0.86W/m∙K. So the l ower t he s ilica f ume content, t he l ower t he t hermal c onductivity, which w as c onfirmed to b econsistent with porosity result. As a result of microstructure analysis using SEM (Scanning Electron Microscope), pores in the range of tens to hundreds µm were observed inside and outside the porous ceramic, and it was confirmed that the pore distribution was relatively uniform.
  • 7.

    Figure of merit and bending characteristics of Mn-SnO2/Ag/Mn-SnO2 tri-layer film

    Young-Su Jo | Jang, Gun-eik | 2021, 31(4) | pp.190~195 | number of Cited : 0
    Abstract PDF
    Typical Mn-SnO2/Ag/Mn-SnO2 tri-layer films were prepared on a PET substrate by RF/DC magnetron sputtering method at room temperature. Based on EMP simulation, the thicknesses of the top and bottom Mn-doped SnO2 layers werekept at 40 nm and the Ag layer was maintained at 13 nm for continuous electrical conduction. The experimentally measured optical transmittances at 550 nm wavelength were ranged from 82.9 to 88.1 % and sheet resistances were variedfrom 5.9 to 6.9 Ω/□. The highest value of figure of merit, фTC was 48.1 × 10-3Ω-1. Based on bending test under 4 and 5 mm of inner and outer curvature radius condition, tri-layer film resistance varies only by approximately 1.5 % after 10,000 bending cycles, showing excellent mechanical flexibility.