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pISSN : 1225-1429 / eISSN : 2234-5078

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2010, Vol.20, No.4

  • 1.

    The ionization energy and lattice parameters of Co- and Ce-doped cubic zirconia (YSZ) single crystal

    SEOK, JEONG-WON | 2010, 20(4) | pp.159~163 | number of Cited : 2
    Abstract PDF
    Co-(0.5 mol%) and Ce-(0~0.3 mol%) doped cubic zirconia (ZrO2 : Y2O3 = 64 : 36 mol%) single crystals grown by a skull melting method were heat-treated in N2 at 1200oC for 3 hrs. The brown-colored as-grown single crystals were changed into either green or blue color after the heat treatment. Before and after the heat treatment, the YSZ (yttriastabilized zirconia) single crystals were cut for wafer form (φ7 mm × t2 mm) and round brilliant cut (φ12 mm). The optical and structural properties were examined by UV-VIS spectrophotometer and X-ray diffraction. Absorption by Ce3+(2F5/2, 7/2(4f)→2Tg(5d1)), Co2+(4A2(4F)→4T1(4F) or 4T1(4P)) and Co3+, change of ionization energy and lattice parameter were confirmed.
  • 2.

    Fabrication and characterization of GaN substrate by HVPE

    오동근 | Bonggeun Choi | 방신영 and 5other persons | 2010, 20(4) | pp.164~167 | number of Cited : 2
    Abstract PDF
    Bulk GaN single crystal with 1.5 mm thickness was successfully grown by hydride vapor phase epitaxy (HVPE)technique. Free-standing GaN substrates of 10 × 10, 15 × 15 mm size were fabricate after lift-off of sapphire substrate and their optical properties were characterized properties for device applications. X-ray diffraction patterns showed (002) and (004) peak, and the FWHM of the X-ray rocking curve (XRC) measurement in (002) was 98 arcsec. A sharp photoluminescence spectrum at 363 nm was observed and defect spectrum at visible range was not detected. The hexagonal-shaped etch-pits are formed on the GaN surface in 200oC H3PO4 at 5 minutes. The defect density calculated from observed etch-pits on surface was around 5 × 106/cm 2. This indicates that the fabricated GaN substrates can be used for applications in the field of optodevice, and high power electronics.
  • 3.

    Characterization of superhydrophilic thin films fabricated by a layer-bylayer self-assembly method

    김진호 | 황종회 | Tae-Young Lim and 2other persons | 2010, 20(4) | pp.168~172 | number of Cited : 1
    Abstract PDF
    Superhydrophilic thin film consisted of positively charged poly (allylamine hydrochloride) (PAH) and negatively charged poly (acrylic acid) (PAA) was fabricated by a layer-by-layer (LBL) self-assembly. Glutaraldehyde (GA) was used in order to increase an adhesion hardness by amine-aldehyde reaction. The surface morphology, thickness, transmittance,water contact angle and adhesion hardness of PAH/PAA thin film with or without GA were measured. The adhesion hardness of PAH/PAA thin film with GA deposition increased over 2 times although the film thickness of PAH/GA/PAA decreased than that of PAH/PAA thin film. The increase of adhesion hardness by amine-aldehyde reaction between PAH and GA was measured by fourier transform infrared (FT-IR) spectroscopy. Fabricated PAH/PAA and PAH/GA/PAA thin films showed water contact angel under 5oand high transmittance over 91.3 % at 550 nm.
  • 4.

    Thermal stabilizing effect of Yb 3+ Er 3+ codoping into TiO2 powder prepared by sol-gel method and its upconversion characteristic

    은종원 | 오동근 | 김광진 and 4other persons | 2010, 20(4) | pp.173~177 | number of Cited : 2
    Abstract PDF
    Thermal stabilizing effect of Yb 3+, Er 3+codoping into TiO2 powder prepared by sol-gel method and its upconversion characteristics were analyzed. The effect of TiO2 : Yb 3+, Er 3+ions on crystallinity and phase transition was studied by X-ray diffraction (XRD). The change of band-gap energy induced from Yb and Er codoping was analyzed by UV-Vis. The band-gap energy of TiO2 have been slightly narrowed by Yb 3+, Er 3+codoping, which indicated that the Yb 3+,Er 3+ions can enhance the photo-catalytic property of TiO2. green and red up-conversions of Yb 3+and Er 3+co-doped Y2O3 :Yb 3+, Er 3+phosphor were analyzed by PL equipped with 980 nm laser.
  • 5.

    Transition of 12CaO · 7Al2O3 electrical insulator to the permanent semiconductor using via thermo-chemical reduction treatment

    정준호 | 은종원 | 오동근 and 5other persons | 2010, 20(4) | pp.178~184 | number of Cited : 0
    Abstract PDF
    The 12CaO · 7Al2O3(C12A7) powders were successfully synthesized using combustion method with microwaveassistant and C12A7:H were fabricated by post-annealed process in Ar/H atmosphere. X-ray diffraction patterns and TGDSC were used for investigating to the precursors of crystalline and reaction depending on temperature. C12A7:H that was treated post-annealed process were investigated TG-MS and Hall-measurement for confirming H ions doping and checking electrical resistivity of C12A7:H. H ion substituted to O 2− ions in the C12A7 cages were confirmed at 289.5oC by TG-MS and C12A7:H calcined at 1000oC in Ar/H = 8 : 2 atmosphere for 8~10 h has low electrical resistivity about 102Ω · cm at room temperature.
  • 6.

    A study on the characteristics of eological lightweight aggregates containing reject ash from the power plant

    KIM, YOOTAEK | 류유광 | 2010, 20(4) | pp.185~191 | number of Cited : 4
    Abstract PDF
    To effectively utilize resources of reject ash and dredged soil, globular shape-formed artificial lightweight aggregate were manufactured in 8~10 mm size. Starting materials were changed various grading and composition, sintered at 1050~1250oC. The specific gravity, water absorptance of artificial lightweight aggregates were measured on the basis of the KS. In this study could make a prediction about application of bloating mechanism by ferrous materials and alkali/alkali-earth oxide at high temperature
  • 7.

    Properties of portland cement concrete with the addition of a modified sulfur polymer

    Seunggun Yu | HEON JIN CHOI | 권혁 and 2other persons | 2010, 20(4) | pp.192~196 | number of Cited : 4
    Abstract PDF
    This paper describes the effects of modified sulfur polymer content on the compressive strength and chemical resistance of Portland cement concrete with and without the modified sulfur polymer. The Portland cement concrete which contained modified sulfur had much higher strength than the Portland cement concrete without modified sulfur, workability is stabled at 55oC. Alkali tolerance test was evaluated by immersing these concrete specimens in 13 % CaCl2 solutions. In the alkali tolerance test, the resistance of Portland cement concrete with modified sulfur to CaCl2 increased compared with Portland cement concrete without modified sulfur.