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pISSN : 1225-1429 / eISSN : 2234-5078

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2020, Vol.30, No.4

  • 1.

    Performance characteristics of AGM lead acid battery with the content of positive plate incorporating nano-size additive material

    Tae Seop Lim , Sung Jun Kim , Sang Dong Kim and 2 other persons | 2020, 30(4) | pp.123~130 | number of Cited : 1
    Abstract PDF
    Nano seed incorporated in micro-sized 4BS (Tetrabasic lead Sulfate) seed was applied to the positive electrodeactive material and compared with Nano 4BS seed (NS). The dispersion of NS decreased due to the aggregationphenomenon, while the nano seed incorporated in micro-sized 4BS seed (INS) could confirm excellent dispersion. As thecontent of INS increased, the particle size of the active material became small and constant, which was confirmed throughSEM and particle size analysis. The specific surface area for the reaction was increased and the high-rate discharge andlifetime characteristics were improved. In order to confirm the variation in particle size distribution in the platemanufacturing process, internal resistance and voltage were measured for 200 AGM lead-acid batteries, and it wasconfirmed that batteries quality variation decreased.
  • 2.

    Synthesis of CaZrO₃ : Eu³⁺ phosphor by skull melting method

    Hyun-Min Choi , Young-Chool Kim , SEOK, JEONG-WON | 2020, 30(4) | pp.131~135 | number of Cited : 0
    Abstract PDF
    Single crystal phased CaZrO3 : Eu3+ phosphor have been synthesized by skull melting method. The crystalstructure, morphology and optical properties of synthesized phosphor were investigated XRD (X-ray diffraction), SEM(scanning electron microscopy), UV (ultraviolet) fluorescence reaction and PL (photo luminescence). The starting materialshaving chemical composition of CaO: ZrO2 : Eu2O3= 0.962 : 1.013 : 0.025 mol% were charged into a cold crucible. The coldcrucible was 120 mm in inner diameter and 150 mm in inner height, and 3 kg of mixed powder (CaO, ZrO2 and Eu2O3)was completely melted within 1 hour at an oscillation frequency of 3.4 MHz, maintained in the molten state for 2 hours,and finally air-cooled. The XRD results show that synthesized phosphor is stabilized in orthorhombic perovskite structurewithout any impurity phases. The synthesized phosphor could be excited by UV light (254 or 365 nm) and the emissionspectra results indicated that bright red luminescence of CaZrO3 : Eu3+ due to magnetic dipole transition ⁵D₀→⁷F₂ at 615nm was dominant.
  • 3.

    The study of recrystallization of willemite crystal in ceramic glaze

    Lee, Hyun Soo | 2020, 30(4) | pp.136~142 | number of Cited : 0
    Abstract PDF
    Crystallization of zinc crystalline glaze requires demanding conditions such as the formation of a nucleating agentand the amount of nucleating agent, and growth of crystalline. Zinc crystalline glaze is hard to utilize in the industry becauseof its narrow range of the firing temperature, and the crystallization’s dependency on the quality of zinc. Stimulation ofzinc crystallization and formation of frit enable zinc crystalline glaze to be reconstituted in a various range of firingschedules, leading to the development of a competitive industrial glaze.
  • 4.

    Synthesis of calcium phosphates from abalone shells via precipitation

    Sung Wook Moon , BYEONG WOO LEE | 2020, 30(4) | pp.143~149 | number of Cited : 0
    Abstract PDF
    Calcium phosphates recognized as important bio-materials have been successfully synthesized by simple precipitationusing waste abalone shells, which are rich mineral sources of calcium. Calcium hydroxide (Ca(OH)2) originated from abalone shells was used as calcium source (precursor) for the preparation. Synthesis of calcium phosphates was performed by reacting calcium hydroxide with phosphoric acid (H3PO4) in aqueous solution. The initial precursor Ca/P ratios were adjusted to 1.50, 1.59 and 1.67, and the effect of the composition and the heat treatment on the synthesized powders and sintered bodies was investigated. The phases of the sintered ceramics prepared at 1150°C were hydroxyapatite (HAp), β-tricalcium phosphate(β-TCP), and biphasic phosphate (HAp with β-TCP)), which were determined by the initial precursor Ca/P ratios. The results demonstrate the possibility for the synthesis of high value-added calcium phosphates from economical starting materials with low cost and high availability.
  • 5.

    Effect of Co₂O₃ addition on liquid phase sintering behavior and mechanical properties of commercial alumina

    Oh BokHyun , Tae-Gyu Yoon , Heon Kong and 2 other persons | 2020, 30(4) | pp.150~155 | number of Cited : 1
    Abstract PDF
    Alumina (Al₂O₃) is mainly used as a structural ceramic material and to have good mechanical properties requires a dense microstructure. In commercial fabrication, the liquid phase sintering process is adjusted to reduce the sintering temperature of alumina. In this study, the effect of added amounts of cobalt oxide as a coloring agent on the microstructureand mechanical properties was investigated in the CaO-SiO₂-MgO-system liquid phase sintering of 92 % alumina at various sintering temperatures. When 11 wt% Co₂O₃ was added, a rearrangement of alumina particles, which is the main densification step in liquid phase sintering, occurred from a sintering temperature of 1200°C. Solution re-precipitation and coalescence steps followed from 1300°C with the grain growth of alumina particles. The addition of excess Co₂O₃ and sintering temperatures above 1400°C resulted in a decrease in sintered density and Vickers hardness, because of the low viscosity of the liquid phase. In 92 % alumina with the addition of 11 wt% Co₂O₃, a sintered density and Vickers hardness of 3.86 g/cm³ and 12.32 GPa, respectively, were obtained at a sintering temperature of 1350°C.
  • 6.

    Color revelation characteristics of color mortar using iron oxide and carbon black

    Hwa-Song Seok , Hong, Chang-woo | 2020, 30(4) | pp.156~161 | number of Cited : 0
    Abstract PDF
    Recently, as there has been growing demand for aesthetic quality in structural materials, the development ofexcellent color cement concrete having good coloration properties has become a requirement. This study is designed toanalyze the basic physical properties of mortar and the properties of keeping the coloration under an ultraviolet rayaccelerated weathering test environment according to changes in the mixing ratio between carbon black and iron oxide usedas colorants. The test results show that the use of carbon black and iron oxide reduces the initial flow by 6.3~17.2 % andthe air content by 3.5~31.5 % but increases the unit volume weight by 3.4~5.5 %, compared to ordinary Portland cement(OPC). In addition, the study shows that the addition of iron oxide increases the self drying shrinkage. So, caution needsto be taken on the workability of the concrete. The brightness value L*represented by black showed the most excellentblack colour when carbon black 3 % and iron oxide 5 % are added. According to UV accelerated weatherproof test, thebrightness value L*was found to increase in all experiment specimens by 4.28~11.97 %, and the color change by UV wasfound to be higher for the case where carbon black colorant was not used. Therefore, in terms of color revelationcharacteristics, the case using carbon black 3 % and iron oxide 5 % was found to show the best black color