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pISSN : 1225-1429 / eISSN : 2234-5078

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2012, Vol.22, No.5

  • 1.

    Geometry variation for as-grown carbon coils under the minimized sulfur additive condition

    Kim Sung-Hoon | Lee Seok Hee | 2012, 22(5) | pp.213~217 | number of Cited : 1
    Abstract PDF
    Carbon coils could be synthesized on nickel catalyst layer-deposited silicon oxide substrate using C2H2 and H2 as source gases under thermal chemical vapor deposition system. By the incorporation of SF6 additive in cyclic modulation manner,the dominant formation of the nanosized carbon coils could be achieved with maintaining the minimized sulfur additive amount. The geometry variation of the as-grown carbon coils, such as linear type, microsized coil type, wavelike nanosized coil type,and nanosized coil type, were investigated according to the different cyclic modulation manner of SF6 flow. SF6 gas incorporation develops the coil-type geometry. Furthermore, the higher flow rate of SF6 gas increased the amount of the nanosized carbon coils. The slightly increased etching ability by SF6 addition seems to be the cause for these results.
  • 2.

    Synthesis and electromagnetic properties of FeNi alloy nanofibers using an electrospinning method

    CHOA, YONGHO | Young-In, Lee | 2012, 22(5) | pp.218~222 | number of Cited : 0
    Abstract PDF
    FeNi alloy nanofibers have been prepared by an electrospinning process followed by air-calcination and H2reduction to develop electromagnetic (EM) wave absorbers in the giga-hertz (GHz) frequency range. The thermal behavior and phase and morphology evolution in the synthetic processes were systematically investigated. Through the heat treatments of calcination and H2 reduction, as-spun PVP/FeNi precursor nanofiber has been stepwise transformed into nickel iron oxide and FeNi phases but the fibrous shape was maintained perfectly. The FeNi alloy nanofiber had the high aspect ratio and the average diameter of approximately 190 nm and primarily composed of FeNi nanocrystals with an average diameter of ~60 nm. The FeNi alloy nanofibers could be used for excellent EM wave absorbing materials in the GHz frequency range because the power loss of the FeNi nanofibers increased up to 20 GHz without a degradation and exhibited the superior EM wave absorption properties compared to commercial FeNi nanoparticles.
  • 3.

    A study on jewelry-making using a multi-casting

    이정수 | 김형성 | 2012, 22(5) | pp.223~226 | number of Cited : 1
    Abstract PDF
    There are many restrictions in conventional ways of Jewelry mass production which are Mokume Gane, Inlaid Technology based on a joining work of dissimilar metals. To overcome this, Multi-Casting using both Jewelry-Casting and CAD/CAM has presented. In experiment on Muti-Casting, second original sample which was produced by CAD/CAM is 5 % smaller than first one. The first and second castings are brass and silver, respectively. When making second sample,the temperature of flask was about 150~200oC higher than the standard temperature of flask when making castings. Through the Multi-Casting, it was found that there was no trouble making dissimilar metals Jewelry which can be mass produced.
  • 4.

    Thermal stability of surface modified Ni-Cr-alloys in molten FLiNaK salt

    Cho, Hyun | Kwang-Hyun Bang | TAE-SUK LEE and 1other persons | 2012, 22(5) | pp.227~232 | number of Cited : 0
    Abstract PDF
    Inconel 617 and Hastelloy X are the most promising candidate materials for the heat exchanger of next generation nuclear reactor. Surface coating and its effects on high temperature properties for the Inconel 617 and Hastelloy X under molten FLiNaK (LiF-NaF-KF) salt environment have been investigated. For TiAlN and Al2O3 overlay coatings, the two different PVD (physical vapor deposition) methods of an arc discharge and a sputtering were applied, respectively. A study for the thermal stability of the surface modified Ni-Cr alloy substrates has been conducted. To evaluate the corrosion mechanism of Ni-Cr alloys in the molten salt, a ruptured Inconel pipe used for the molten salt transportation has been analyzed. The thermal properties of morphological and structural properties each sample were characterized before and after heat-treatment at 600oC in molten FLiNaK salt. The results showed that the TiAlN and Al2O3 overlay coated specimens had the enhanced high temperature stability.
  • 5.

    A review on inorganic phosphor materials for white LEDs

    Ryu, Jeong-ho | 황석민 | 이재빈 and 1other persons | 2012, 22(5) | pp.233~240 | number of Cited : 5
    Abstract PDF
    White LEDs (light-emitting diodes) are promising new-generation light sources which can replace conventional lamps due to their high reliability, low energy consumption and eco-friendly effects. This paper briefly reviews recent progress of oxy/nitride host phosphor and quantum dot materials with broad excitation band characteristics for phosphorconverted white LEDs. Among oxy/nitride host materials, M2Si5N8 : Eu2+, MAlSiN3 : Eu2+ M-SiON (M = Ca, Sr, Ba), α/β-SiAlON : Eu2+ are excellent phosphors for white LED using blue-emitting chip. They have very broad excitation bands in the range of 440~460 nm and exhibit emission from green to red. In this paper, In this review we focus on recent developments in the crystal structure, luminescence and applications of the oxy/nitride phosphors for white LEDs. In addition, the application prospects and current trends of research and development of quantum dot phosphors are also discussed.
  • 6.

    Analysis of upconversion luminescence from Yb3+, Er3+ co-doped SrMoO4

    정준호 | 허태형 | 이정훈 and 6other persons | 2012, 22(5) | pp.241~246 | number of Cited : 0
    Abstract PDF
    Yb3+, Er3+ co-doped SrMoO4 (SrMoO4 : Yb3+/Er3+) specimens have been successfully synthesized via the complex citrate-gel method and their structural and optical properties were investigated in detail. Under 980 nm excitation,SrMoO4 : Yb3+/Er3+ UC phosphors have been emitted strong green luminescence at 530 and 550 nm with weak red emission around 670 nm corresponding to the intra 4f transitions of Er3+ (4F9/2, 2H11/2, 4S3/2) → Er3+ (4I15/2). The optimal doping concentrations of Er3+ and Yb3+ ions were verified to 2/16 mol% and a possible upconversion mechanism depending on pump power dependence is studied in detail.
  • 7.

    Effects of particle size and oxygen contents on ZrB2 powder for densification

    정세혁 | Sungchurl Choi | 2012, 22(5) | pp.247~253 | number of Cited : 0
    Abstract PDF
    In this study, two pretreatment methods were used to improve the sinterability of zirconium diboride (ZrB2). As a mechanical treatment, as-received ZrB2 powder was crushed using SPEX mill from an average size of 2.61 μm to 0.35 μm. As a chemical treatment, oxygen contents of ZrB2 powder were decreased from 4.20 wt% to 2.22 wt% using a dilute hydrofluoric solution. The relative density of sintered ZrB2 increased with decreasing particle size and oxygen contents. But it is considered that particle size is more effective than oxygen contents for ZrB2 densification. Through the two pretreatment processes, we produced sintered ZrB2 ceramic with a full density without sintering additives. The sinterability of ZrB2 was improved by using mechanical and chemical pretreatment methods.
  • 8.

    Property enhancement of lightweight aggregate by carbonation processing

    박준영 | KIM, YOOTAEK | 최윤재 | 2012, 22(5) | pp.254~259 | number of Cited : 2
    Abstract PDF
    The mechanical property enhancement was studied using fly ash produced from fluidized bed type boiler in power plant, which contains a lot of Ca component being used to carbonate for CO2 fixation in the lightweight aggregates made of cement and some portion of fly ash as a cement substitution under the supercritical condition. Specimens having various fly ash substitution rates and curing periods were carbonated under the supercritical condition at 40oC. The weight change rate, carbonation rate by TG/DTA analysis, 1% Phenolphthalein test, specific gravity and mechanical compression strength test were performed to observe the mechanical property enhancement of the cemented materials after carbonation under the supercritical condition and to make sure those could be classified as lightweight aggregates having specific gravity under 2.0.