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pISSN : 1225-1429 / eISSN : 2234-5078

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2022, Vol.32, No.3

  • 1.

    Effect of low-temperature GaN grown at different temperature on residual stress of epitaxial GaN

    Seung Hoon Lee , Joo Hyung Lee , Oh Nuri and 4 other persons | 2022, 32(3) | pp.83~88 | number of Cited : 0
    Abstract PDF
    To improve the crystallinity of GaN, there are researches on surface treatment to control the difference inphysical properties between GaN and heterogeneous substrate. ‘Low-temperature GaN (LT-GaN)’ is one of the ways tosolve the problem and we investigated the relationship between growth temperature and properties of LT-GaN in ourhomemade vertical type HVPE. The LT-GaN nuclei were formed on the sapphire surface at low growth temperatures andthey presented differences in the density and crystallinity depending on the growth temperature. Significantly, the stressrelaxation effect on the epitaxial GaN (epi-GaN) was affected by the crystallinity of LT-GaN. However, the highcrystallinity of LT-GaN exacerbated the crystal quality of epi-GaN because they worked as a catalyst and seed ofpolycrystalline.
  • 2.

    Morphology control of glassy carbon coating layer to additive ethylene glycol and phenolic resin

    Sang Hyun Joo , Young Jun Joo , Hyuk Jun Lee and 3 other persons | 2022, 32(3) | pp.89~95 | number of Cited : 0
    Abstract PDF
    In this study, glassy carbon coating was performed on the graphite using a phenolic resin and a curing agent was mixed with ethylene glycol as an additive to form the uniform surface. The phenolic resin was dried and cured under the environments of hot air, then converted into a glassy carbon layer by pyrolysis at 500~1,500°C. FTIR, XRD, SEM analysis, and density/porosity/contact angle measurement were performed for characterization of glassy carbon. The pyrolysis temperature for high-quality glassy carbon was optimized to be about 1,000°C. As the content of the additiveincreased, the effect of reducing surface defects on the coated surface, reduction of porosity, increase of contact angle, andincrease of density were investigated in this study. The method of forming a glassy carbon coating layer through an additive is expected to be applicable to graphite coating and other fields.
  • 3.

    Synthesis parameters of hydroxyapatite preparation by a precipitation process

    Sung Wook Moon , Byeong Woo Lee | 2022, 32(3) | pp.96~102 | number of Cited : 0
    Abstract PDF
    Hydroxyapatite (HAp) was synthesized from calcium hydroxide (Ca(OH)2) reacting with phosphoric acid (H3PO4) in aqueous solution. HAp powders were synthesized from extremely high concentration of precursor solutions over 3 M of Ca(OH)2 aqueous suspension using modified process parameters such as phosphoric acid (H3PO4) pouring rate, aging time and post ball milling process. Regardless of phosphoric acid pouring rate, the DCPD (dicalcium phosphate dihydrate) was formed at room temperature and when heated above 700°C, β-TCP (tricalcium phosphate) was synthesized and the amount reached its maximum at 900°C. When the synthesized powder was sintered at 1150°C, β-TCP, a high temperature impurity phase, remained. The single HAp phase without DCPD was obtained from post ball-milled precipitates followed by 3 day aging. For the ball-milled precipitates even without the aging process, the desired single HAp phase without β-TCP could be obtained by heat treatment above 500°C. The post ball milling process provided a convenient route for HAp synthesis.
  • 4.

    The effect of Al2O3 on the isokom temperatures in soda-lime glass

    Seung-Min Kang , Chang-sam Kim | 2022, 32(3) | pp.103~106 | number of Cited : 0
    Abstract PDF
    The effect of Al2O3 on isokom temperatures in soda-lime glass is estimated by comparing calculated isokom temperatures using viscosity model proposed by Lakatos. Substitution of SiO2 with Al2O3 by 0.5 mol% raises the isokom temperatures by 3.1, 3.3, 3.6 and 7.2°C at the viscosity of log η = 12.3, 10, 6.6 and 1 (Pa·s), respectively. Meanwhile, replacing 0.5 mol% of CaO with Al2O3 raises the isokom temperatures by 1.6, 2.3, 4.1 and 17.7°C at the viscosity of log η = 12.3, 10, 6.6 and 1 (Pa·s), respectively.
  • 5.

    Carboxymethyl cellulose/polyethylene glycol superabsorbent hydrogel crosslinked with citric acid

    Deuk Yong Lee , Cheolbyong Chun , Siwon Son and 1 other persons | 2022, 32(3) | pp.107~114 | number of Cited : 0
    Abstract PDF
    Carboxymethyl cellulose/poly(ethylene glycol) (CMC/PEG) hydrogels crosslinked with citric acid (CA) are synthesized to evaluate the effect of CMC molecular weight (Mw), PEG and CA concentration on the optical property, swelling rate (SR), degradation rate (DR), and cytotoxicity and cell proliferation of hydrogels. For crosslinked CMC/PEG hydrogels, the FT-IR peak intensity associated with hydroxyl groups decreases due to PEG intercalation (esterification crosslinking) between CMC chains in a similar manner as the concentration of CA crosslinker increases. Crosslinked CMC (Mw = 90,000)/PEG hydrogels with 10 % CA dissolve regardless of PEG content. However, the SR of the CMC (Mw = 250,000)/PEG hydrogels decrease from 4923 % to 168 % with increasing PEG and CA concentrations from 0 to 20 % and from 0 to 25 %, respectively. As the Mw of CMC increases, the DR of the hydrogel is greatly improved. CMC (Mw = 250,000)/PEG10 hydrogels with 10 % CA exhibit the optimum properties of high absorbing capacity (3,200 %) with moderate DR (54 %), stiffness (1.39 ± 0.19 GPa), and cell viability (94.8 ± 1.3 %). CA-crosslinked CMC/PEG hydrogels are highly suitable for wound dressing or personal care applications due to their non-toxicity, good cell proliferation, SR, and mechanical properties.
  • 6.

    A study on the brownish ring of quartz glass crucible for silicon single crystal ingot

    Yoon Sung Jung , Jae Ho Choi , Kyung Won Min and 5 other persons | 2022, 32(3) | pp.115~120 | number of Cited : 0
    Abstract PDF
    A brown ring (hereinafter referred to as BR) on the inner surface of a quartz glass crucible used in the manufacturing process of a silicon ingot for semiconductor wafers was studied. BR is 20~30 µm in size and has an asymmetric brown ring shape. The size and distribution of BR were different depending on the crucible location, and the size and distribution of BR were the largest and most abundant in the round part with the highest crucible temperature during Si ingot growth. BR contains cristobalite, which has a higher coefficient of thermal expansion than quartz glass, so it is considered that surface cracks appear. The color development of BR and pin holes are presumed to be due to oxygen vacancies.