Journal of Powder Materials

Ri Yu

4 Articles

Size Control and Optical Properties of ZnO nanoparticles by Zinc-Lithium-Acetate System: Ri Yu, YooJin Kim; J Korean Powder Metall Inst. 2013;20(5):371-375.; DOI: https://doi.org/10.4150/KPMI.2013.20.5.371

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Abstract PDF: ZnO nanoparticles in the size range from 5 to 15 nm were prepared by zinc-lithium-acetate system. The morphologies and structures of ZnO were characterized by TEM, XRD and FT-IR spectra. UV-visible results shows that the absorption of ZnO nanoparticles is blue shifted with decrease in particles size. Furthermore, photoluminescence spectra of the ZnO nanoparticles were also investigated. The ZnO nanoparticles have strong visible-emission intensity and their intensities depend upon size of ZnO nanoparticles.

Color Evolution and Phase Transformation of α-FeOOH@SiO₂ and β-FeOOH@SiO₂ pigments: Ri Yu, Kyoon Choi, Jae-Hwan Pee, YooJin Kim; J Korean Powder Metall Inst. 2013;20(3):210-214.; DOI: https://doi.org/10.4150/KPMI.2013.20.3.210

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This manuscript reports on compared color evolution about phase transformation of alpha-FeOOH@SiO_2 and beta-FeOOH@SiO_2 pigments. Prepared alpha-FeOOH and beta-FeOOH were coated with silica for enhancing thermal properties and coloration of both samples. To study phase and color of alpha-FeOOH and beta-FeOOH, we prepared nano sized iron oxide hydroxide pigments which were coated with SiO_2 using tetraethylorthosilicate and cetyltrimethyl-ammonium bromide as a surface modifier. The silica-coated both samples were calcined at high temperatures (300, 700 and 1000°C) and characterized by scanning electron microscopy, CIE L*a*b* color parameter measurements, transmission electron microscopy and UV-vis spectroscopy. The yellow alpha-FeOOH and beta-FeOOH was transformed to alpha-Fe_2O_3 with red, brown at 300, 700°C, respectively.

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Coloration and Chemical Stability of SiO2and SnO2Coated Blue CoAl2O4Pigment
JiYeon Yun, Ri Yu, Jae-Hwan Pee, YooJin Kim
Journal of Korean Powder Metallurgy Institute.2014; 21(5): 377. CrossRef

Effect of MgO and NH₄OH on Formation of 5Mg(OH)₂·MgSO₄·3H₂O Whiskers: Ri Yu, Jae-Hwan Pee, Hyung-Tae Kim, Kyung-Ja Kim, Young-Woong Kim, Woong Kim, Yoo-Jin Kim; J Korean Powder Metall Inst. 2011;18(3):283-289.; DOI: https://doi.org/10.4150/KPMI.2011.18.3.283

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Magnesium hydroxide sulfate hydrate whiskers (5Mg(OH)_2cdotMgSO_4cdot3H_2O, abbreviated 513 MHSH) were prepared using hydrothermal reaction with magnesium oxide (MgO) and magnesium sulfate (MgSO_4cdot7H_2O) as the starting materials. The effects of the molar ratio of MgSO_4/MgO and amount of NH_4OH were studied. As a result, 513 MHSH whiskers co-existed with hexagonal plate Mg(OH)_2 at low concentration of SO_42-. The molar ratio of MgSO_4cdot7H_2O/MgO was 7:1, uniform 513 MHSH whiskers were formed without impurity such as Mg(OH)_2. Appropriate amount of NH_4OH has affected to formation of high quality MHSH. Their morphologies and structures were determined by powder X-ray diffraction (XRD) scanning electron microscopy (SEM) and thermo-gravimetric analyzer (TGA).

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Effect of sulfate ion on synthesis of 5 Mg(OH)2·MgSO4·3H2O whiskers using non-hydrothermal method with acid catalyst
Areum Choi, Nuri Oh, YooJin Kim
Journal of the Korean Ceramic Society.2022; 59(2): 224. CrossRef
Effect of H₂SO₄ and Reaction Time on Synthesis of 5Mg(OH)₂∙MgSO₄∙3H₂O Whiskers using Hydrothermal Reaction
Areum Choi, Nuri Oh, YooJin Kim
Journal of Korean Powder Metallurgy Institute.2020; 27(5): 401. CrossRef
Study of Fabrication and Improvement of Mechanical Properties of Mg-based Inorganic Fiber using Reflux Process and Silica Coating
Ri Yu, YooJin Kim
Journal of Korean Powder Metallurgy Institute.2019; 26(3): 195. CrossRef
Effect of MgSO4/MgO on the Synthesis of 5Mg(OH)2·MgSO4·3H2O Whiskers using One-step Ambient Pressure
Ri Yu, Jae-Hwan Pee, Hyung Tae Kim, YooJin Kim
Journal of the Korean Ceramic Society.2013; 50(3): 201. CrossRef

Thickness Control of Core Shell type Nano CoFe₂O₄@SiO₂ Structure: Ri Yu, Yoo-Jin Kim, Jae-Hwan Pee, Kyung-Ja Kim; J Korean Powder Metall Inst. 2010;17(3):230-234.; DOI: https://doi.org/10.4150/KPMI.2010.17.3.230

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Abstract PDF: Homogenous silica-coated CoFe_2O_4 samples with controlled silica thickness were synthesized by the reverse microemulsion method. First, 7 nm size cobalt ferrite nanoparticles were prepared by thermal decomposition methods. Hydrophobic cobalt ferrites were coated with controlled SiO_2 using polyoxyethylene(5)nonylphenylether (Igepal) as a surfactant, NH_4OH and tetraethyl orthosilicate (TEOS). The well controlled thickness of the silica shell was found to depend on the reaction time and the amount of surfactant used during production. Thick shell was prepared by increasing reaction time and small amount of surfactant.

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