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pISSN : 1225-1429 / eISSN : 2234-5078

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2014, Vol.24, No.5

  • 1.

    The influence of Co and Fe on the color change of diopside crystals

    변수민 | 이병하 | 2014, 24(5) | pp.183~189 | number of Cited : 0
    Abstract PDF
    This study was conducted to study the influence of Co and Fe on the color of glaze and diopside crystals inthe diopside crystal glaze empirically produced and used by ceramic artists, in case of adding Co3O4 and Fe2O3. As aresult, the color of glaze was blue when Co3O4 was added to the diopside crystal glaze and the diopside crystals appearedpastel violet with Co included. When Fe2O3 was added to the diopside crystal glaze, the color of glaze appeared brownand the color of diopside crystals was goldenrod with Fe included. The crystals precipitated on the surface of diopsideconsisted of diopside crystals and diopside precursors. With longer retention time, the amount of diopside precursorsdecreased and the amount of diopside crystals increased. Also, Co was more easily included by the diopside crystals thanFe was and crystallizability of dispside was improved in case of including Co. Including Fe lowered peak intensity ofproperties and partially dissolved the diopside crystals.
  • 2.

    Structural defects in the multicrystalline silicon ingot grown with the seed at the bottom of crucible

    A-Young Lee | KIM YOUNG KWAN | 2014, 24(5) | pp.190~195 | number of Cited : 2
    Abstract PDF
    Because of the temperature gradient occurring during the growth of the ingot with directional solidificationmethod, defects are generated and the residual stress is produced in the ingot. Changing the growth and cooling rate duringthe crystal growth process will be helpful for us to understand the defects and residual stress generation. The defects andresidual stress can affect the properties of wafer. Generally, it was found that the size of grains and twin boundaries aresmaller at the top area than at the bottom of the ingot regardless of growth and cooling condition. In addition to that, inthe top area of silicon ingot, higher density of dislocation is observed to be present than in the bottom area of the siliconingot. This observation implies that higher stress is imposed to the top area due to the faster cooling of silicon ingot aftersolidification process. In the ingot with slower growth rate, dislocation density was reduced and the TTV (Total ThicknessVariation), saw mark, warp, and bow of wafer became lower. Therefore, optimum growth condition will help us to obtainhigh quality silicon ingot with low defect density and low residual stress.
  • 3.

    Investigation of defects and surface polarity in AlN and GaN using wet chemical etching technique

    홍윤표 | 박재화 | Cheol Woo Park and 5other persons | 2014, 24(5) | pp.196~201 | number of Cited : 3
    Abstract PDF
    We investigated defects and surface polarity in AlN and GaN by using wet chemical etching. Therefore, theeffectiveness and reliability of estimating the single crystals by defect selective etching in NaOH/KOH eutectic alloy havebeen successfully demonstrated. High-quality AlN and GaN single crystals were etched in molten NaOH/KOH eutecticalloy. The etching characteristics and surface morphologies were carried out by scanning electron microscope (SEM) andatomic force microscope (AFM). The etch rates of AlN and GaN surface were calculated by etching depth as a function ofetching time. As a result, two-types of etch pits with different sizes were revealed on AlN and GaN surface, respectively. Etching produced hexagonal pits on the metal-face (Al, Ga) (0001) plane, while hexagonal hillocks formed on the N-face. On etching rate calibration, it was found that N-face had approximately 109 and 15 times higher etch rate than the metalfaceof AlN and GaN, respectively. The size of etch pits increased with an increase of the etching time and they tend tomerge together with a neighbouring etch pits. Also, the chemical mechanism of each etching process was discussed. It wasfound that hydroxide ion (OH−) and the dangling bond of nitrogen play an important role in the selective etching of themetal-face and N-face.
  • 4.

    Temperature-dependent photoluminescence properties of amorphous and crystalline V2O5 films

    강만일 | 추민우 | Sok Won Kim | 2014, 24(5) | pp.202~206 | number of Cited : 0
    Abstract PDF
    In order to investigate the photoluminescence (PL) properties of V2O5 films, amorphous and crystalline filmswere prepared by using RF sputtering system, and the PL spectra of the films were measured at the temperatures rangingfrom 300 K to 10 K. In the amorphous V2O5 film grown at room temperature, a PL peak centered at ~505 nm was onlyobserved, and in the crystalline V2O5 film, two peaks centered at ~505 nm and ~695 nm, which is known to correspond tooxygen defects, were revealed. The position of PL peak centered at 505 nm for both the amorphous and crystalline V2O5films showed a strong dependence on temperature, and the positions were 2.45 eV at 300 K and 2.35 eV at 10 K,respectively. The PL at 505 nm was due to the band energy transition in V2O5, and also, the reduction of the peak positionenergy with decreasing temperature was caused by a decrement of the lattice dilatation effect with reducing electron-phononinteraction.
  • 5.

    Synthesis of carbon nanosheets using RF thermal plasma

    이승용 | Sang-Min Ko | Sang Man Koo and 3other persons | 2014, 24(5) | pp.207~212 | number of Cited : 0
    Abstract PDF
    An ultrathin sheet-like carbon nanostructure provides an important model of a two-dimensional graphite structurewith strong anisotropy in physical properties. As an easy and cheap route for mass production, RF thermal plasmasynthesis of freestanding carbon nanosheet from CH4 (Methane) and C3H8 (Propane) is presented. Using vapor synthesisprocess with RF inductively thermal plasma, carbon nanosheets were obtained without catalysts and substrates. Thesynthesized carbon nanosheets were characterized using transmission electron microscopy (TEM), Raman spectroscopy, Xraydiffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis. The carbon nanosheets synthesized using methane andpropane generally showed 5~6 and 15~16 layers with a wrinkled morphology and size of approximately 100 nm.
  • 6.

    Synthesis of WO3/TiO2 catalysts from different tungsten precursors and their catalytic performances in the SCR

    BYEONG WOO LEE | 이진희 | 2014, 24(5) | pp.213~218 | number of Cited : 1
    Abstract PDF
    An investigation of the influence of WO3 addition with different precursors and preparation methods on thephase formation and selective catalytic reduction (SCR) efficiency of anatase-TiO2 powders has been carried out. Ananatase-TiO2 synthesized by precipitation process was used as a catalyst support. For WO3(10 wt%)/TiO2, the W loading tothe TiO2 support led to the lower in anatase to rutile transition temperature to ~900oC from 1200oC of the TiO2 supportalone. In the case of WO3(10 wt%)/TiO2 SCR powders obtained from a wet process with ammonium meta-tungstate (AMT)precursor, the highest NOX conversion efficiency was achieved at 450oC remaining high efficiency at 500oC, while thesame composition prepared from a dry process with WO3 addition showed the lowered efficiency with temperature afterreaching the efficiency maximum at 350oC. The same tendency has been found that the V2O5(5 wt%)-WO3(10 wt%)/TiO2SCR powders obtained from the wet process with AMT precursor has shown the superior NOX conversion efficiency over90 % in a wider temperature range of 300~500oC.
  • 7.

    Pulsed laser ablation of hydroxyapatite in ethanol

    Lee, Jung-il | Ryu, Jeong-ho | 2014, 24(5) | pp.219~223 | number of Cited : 0
    Abstract PDF
    Pulsed laser ablation in liquid medium was successfully employed to synthesize hydroxyapatite colloidal nanoparticles. The crystalline phase, particle morphology, size distribution and microstructure of the hydroxyapatite nanoparticles wereinvestigated in detail. The obtained hydroxyapatite nanoparticles had spherical shape with sizes ranging from 5 to 20 nm. Thelaser ablation and the nanoparticle forming process were discussed with explosive ejection mechanism by investigating changeof surface morphology on target. The analytical results of XPS, FT-IR and Raman spectroscopy confirms that the stoichiometryand bonding properties of the hydroxyapatite nanoparticles are in good agreement with reported bulk hydroxyapatite materials.
  • 8.

    Separation of Nickel and Tin from copper alloy dross

    Lee, Jung-il | Hong, Chang-woo | Ryu, Jeong-ho | 2014, 24(5) | pp.224~228 | number of Cited : 3
    Abstract PDF
    Recently, the demands for separation/recovery of valuable metals such as nickel or tin from copper based alloyshas been attracting much attention from the viewpoints of environmental protection and resource utilization. In this report,experimental results on concentration increasement of nickel and tin compared to the previous report are investigated. Ni issuccessfully separated by a organic solvent and reduced to the metal powder whose concentration is over 98 %. Sn isseparated by a selective solution method and its concentration is increased to 97.5 % by three consecutive solution andreduction process. Crystal structure, surface morphology and microstructure of the separated samples are studied.