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pISSN : 1225-1429 / eISSN : 2234-5078

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2018, Vol.28, No.5

  • 1.

    Influence of relative distance between heater and quartz crucible on temperature profile of hot-zone in Czochralski silicon crystal growth

    김광훈 | 권세진 | 김일환 and 3other persons | 2018, 28(5) | pp.179~184 | number of Cited : 0
    Abstract PDF
    To lessen oxygen concentrations in a wafer through modifying the length of graphite heaters, we investigated the influence of relative distance from heater to quartz crucible on temperature profile of hot-zone in Czochralski siliconcrystal growth by simulation. In particular, ATC temperature and power profiles as a function of different ingot body positions were investigated for five different heater designs; (a) typical side heater (SH), (b) short side heater-up (SSH-up), (c) short side heater-low (SSH-low), (d) bottom heater without side heater (Only-BH), and (e) side heater with bottom heater (SH + BH). It was confirmed that lower short side heater exhibited the highest ATC temperature, which was attributed to the longest distance from triple point to heater center. In addition, for the viewpoint of energy efficiency, it was observed that the typical side heater showed the lowest power because it heated more area of quartz crucible than that of others. This result provides the possibility to predict the feed-forward delta temperature profile as a function of various heater designs.
  • 2.

    Behavior of ultrasonic transducer in air by using finite element method simulation

    채연화 | Kyoon Choi | 이호용 | 2018, 28(5) | pp.185~190 | number of Cited : 0
    Abstract PDF
    The Tonpilz transducer was implemented using the structural module of COMSOL which is a FEM simulation tool. In order to compare the sound pressure characteristics of the transducer with the simulated results, the spacial distribution of the sound pressure level (SPL) was simulated by the acoustic module of COMSOL and then compared with the SPL distribution measured by a microphone. As a result, the resonance frequency and the peak in SPL for the simulation were predicted to be 28 kHz and 163.5 dB, respectively. And the resonance frequency and the peak in SPL for the actual transducer were measured to be 28.84 kHz and 137.8 dB, respectively. It is also confirmed that the simulated SPL distribution and the actually measured one are formed in a similar pattern.
  • 3.

    Synthesis of SnSb alloys using high energy ball-miiling and its lithium electrochemical behavior

    김대경 | Hyukjae Lee | 2018, 28(5) | pp.191~198 | number of Cited : 0
    Abstract PDF
    SnSb alloy powders with excess Sn or Sb are fabricated by the high energy ball-milling of pure Sn and Sb powders with different Sn/Sb molar ratios, and then their material properties and lithium electrochemical performances are investigated. It is revealed by X-ray diffraction that SnSb alloys are successfully synthesized, and the powder size is decreased via ball-milling. Charge-discharge test using a coin-cell shows that the best result, in terms of the cyclability and the capacity after 50 cycles, comes from the electrode composed of Sn : Sb = 4 : 6, i.e. the capacity of 580 mAh g−1 after 50 cycles. When the electrode is composed of Sn : Sb = 3 : 7, however, the capacity is noticeably decreased by the restrained Sn reaction with Li-ion. The pure SnSb alloy powders (Sn : Sb = 5 : 5) results in the second best performance. In the case of Sn-rich SnSb alloys, the initial capacity is relatively high, but the capacity is quickly fading after 20 cycles.
  • 4.

    Study on the immersion test of geopolymers made by recycling of coal ash

    John J. Bang | KANG SEUNG GU | 2018, 28(5) | pp.199~205 | number of Cited : 1
    Abstract PDF
    A geopolymer was produced from coal ash generated from an integrated gasification combined cycle (IGCC) plant and its water resistance was evaluated. For this purpose, the geopolymer specimens were immersed in water for 30 days to measure changes in microstructure and alkalinity of the immersion liquid. Particularly, the experiment was carried out with foaming status of the geopolymers and parameters of room temperature aging condition, and immersion time. The foamed geopolymer containing 0.1 wt% Si-sludge had pores with a diameter of 1 to 3 mm and exhibited excellent foamability. Also, the calcium-silicate-hydrate crystal phase appeared in the foamed geopolymer. In the geopolymer immersion experiment, the pH of the immersion liquid increased with time, because the un-reacted alkali activator remained was dissolved in the immersion liquid. From the pH change of the immersion liquid, it was found that geopolymer reaction in the foamed specimen was completed faster than the non-foamed specimen. Through this study, it was possible to successfully produce foamed and non-foamed geopolymers recycled from IGCC coal ash. Also the necessary data for the safe application of IGCC coal ash-based geopolymers to areas where water resistance is needed were established; for example, the process conditions for room temperature aging time, effect of foaming status, immersion time and so on.
  • 5.

    Coating of two kinds of bioactive glass on Ti6Al4V alloy

    EuntaeKang | 이남영 | 최현빈 | 2018, 28(5) | pp.206~210 | number of Cited : 0
    Abstract PDF
    Two kinds of bioactive glass were coated on the Ti6Al4V alloy by the enameling technique. In order to reduce the thermal stress due to the difference in expansion coefficient with the alloy with the secondary coating forming hydroxyapatite, the difference in expansion coefficient between the alloy and the two glasses was adjusted at 2 × 10−6 / o C intervals. FE-SEM and EDS analysis showed that good adhesion was formed between the Ti6Al4V alloy and the primary coating by diffusion bonding. After immersion in SBF solution, it was confirmed from FT-IR that hydroxycarbonate apatite formed in the secondary coating was not different from bulk bioactive glass.
  • 6.

    A study on the synthesis of lanthanum oxide (La2O3) from NaLa(SO4)2 · H2O by metathesis reaction

    Kim Dae Weon | Nak-Kyoon Ahn | Hyun-Woo Shim and 3other persons | 2018, 28(5) | pp.211~216 | number of Cited : 0
    Abstract PDF
    The recovery of rare earth elements (REE) including La, Nd and Ce from spent batteries is important issues to reuse scarce resources. Herein, we present a simple recovery process to obtain lanthanum oxide (La2O3) from spent Ni-MH batteries, and demonstrate the conversion mechanism from NaLa(SO4)2 · H2O to La2O3. This strategy requires the initial preparation of NaLa(SO4)2 · H2O and subsequent metathesis reaction with Na2CO3 at 70 o C. This metathesis reaction resulted in the crystalline lanthanum carbonate hydrate (La2(CO3)3 · xH2O) powder with plate-like morphology. On the basis of TGA result, the La2(CO3)3 · xH2O powder was calcined in air at three different temperatures, that is, 300 o C, 500 o C, and 1000 o C. As the calcination temperature increased, the morphology of powder was changed; prism-like (NaLa(SO4)2 · H2O)→platelike (La2(CO3)3 · xH2O)→aggregated irregular shape (La2O3). Futhermore, XRD results indicated that the crystalline La2O3 could be synthesized after the metathesis reaction with Na2CO3, followed by heat-treatment at 1000 o C, along with a change of crystallographic structures; NaLa(SO4)2 · H2O→La2(CO3)3 · xH2O→La2O3.
  • 7.

    Optimization for high speed manufacturing of Ti-6Al-4V alloy by a selective laser melting technique

    이강표 | Kangmin Kim | 강석현 and 2other persons | 2018, 28(5) | pp.217~221 | number of Cited : 0
    Abstract PDF
    Selective laser melting (SLM) technique is one of the additive manufacturing processes, in which functional, complex parts can be directly manufactured by selective melting layers of powder. SLM technique has received great attention due to offering a facile part-manufacturing route and utilizing a hard-to-manufacturing material (e.g. Ti6Al4V). The SLM process allows the accurate fabrication of near-net shaped parts and the significant reduction in the consumption of raw materials when compared to the traditional manufacturing processes such as casting and/or forging. In this study, we focus the high-speed additive manufacturing of Ti6Al4V parts in the aspect of manufacturing time, controlling various process parameters.
  • 8.

    Zn/Co ZIF derived synthesis of Co-doped ZnO nanoparticles and application as high-performance trimethylamine sensors

    Yoon, Ji-Wook | 2018, 28(5) | pp.222~227 | number of Cited : 0
    Abstract PDF
    Zn1 − xCox Zeolitic Imidazolate Framework (ZIF) (x = 0~0.05) were prepared by the co-precipitation of Zn 2+ and Co 2+ using 2-methylimidazole, which were converted into pure and Co-doped ZnO nanoparticles by heat treatment at 600 o C for 2 h. Homogeneous Zn/Co ZIFs were achieved at x < 0.05 owing to the strong coordination of the imidazole linker to Zn 2+ and Co 2+ , facilitating atomic-scale doping of Co into ZnO via annealing. By contrast, heterogeneous Zn/Co ZIFs were formed at x ≥ 0.05, resulting in the formation of Co3O4 second phase. To investigate the potential as high-performance gas sensors, the gas sensing characteristics of pure and Co-doped ZnO nanoparticles were evaluated. The sensor using 3 at% Co-doped ZnO exhibited an unprecedentedly high response and selectivity to trimethylamine, whereas pure ZnO nanoparticles did not. The facile, bimetallic ZIF derived synthesis of doped-metal oxide nanoparticles can be used to design high-performance gas sensors.