Journal of Powder Materials

Preparation and Characterization of Visible Light-Sensitive N-doped TiO₂ Using a Sol-gel Method: NaRi Lee, Ri Yu, Tae Kwan Kim, Jae-Hwan Pee, YooJin Kim; J Korean Powder Metall Inst. 2017;24(6):477-482. Published online December 1, 2017; DOI: https://doi.org/10.4150/KPMI.2017.24.6.477

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Abstract PDF: Nitrogen-doped titanium dioxide (N-doped TiO₂) is attracting continuously increasing attention as a material for environmental photocatalysis. The N-atoms can occupy both interstitial and substitutional positions in the solid, with some evidence of a preference for interstitial sites. In this study, N-doped TiO₂ is prepared by the sol–gel method using NH₄OH and NH₄Cl as N ion doping agents, and the physical and photocatalytic properties with changes in the synthesis temperature and amount of agent are analyzed. The photocatalytic activities of the N-doped TiO₂ samples are evaluated based on the decomposition of methylene blue (MB) under visible-light irradiation. The addition of 5 wt% NH₄Cl produces the best physical properties. As per the UV-vis analysis results, the N-doped TiO₂ exhibits a higher visible-light activity than the undoped TiO₂. The wavelength of the N-doped TiO₂ shifts to the visible-light region up to 412 nm. In addition, this sample shows MB removal of approximately 81%, with the whiteness increasing to +97 when the synthesis temperature is 600oC. The coloration and phase structure of the N-doped TiO₂ are characterized in detail using UV-vis, CIE Lab color parameter measurements, and powder X-ray diffraction (XRD).

Coloration Study of Red/Yellow β-FeOOH Nanorod using NH₄OH Solution: Ri Yu, IllJoo Kim, JiYeon Yun, Eun-Young Choi, Jae-Hwan Pee, YooJin Kim; J Korean Powder Metall Inst. 2016;23(5):343-347. Published online October 1, 2016; DOI: https://doi.org/10.4150/KPMI.2016.23.5.343

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Abstract PDF: Fe-based pigments have attracted much interest owing to their eco-friendliness. In particular, the color of nanosized pigments can be tuned by controlling their size and morphology. This study reports on the effect of length on the coloration of β-FeOOH pigments prepared using an NH₄OH solution. First, rod-type β-FeOOH is prepared by the hydrolysis of FeCl₃·6H₂O and NH₄OH. When the amount of NH₄OH is increased, the length of the rods decreases. Thus, the length of the nanorods can be adjusted from 10 nm to 300 nm. The color of β-FeOOH changes from orangered to yellow depending on the length of β-FeOOH. The color and phase structure of β-FeOOH is characterized by UVvis spectroscopy, CIE Lab color parameter measurements, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and powder X-ray diffraction (XRD).

Coloration and Chemical Stability of SiO₂ and SnO₂ Coated Blue CoAl₂O₄ Pigment: JiYeon Yun, Ri Yu, Jae-Hwan Pee, YooJin Kim; J Korean Powder Metall Inst. 2014;21(5):377-381. Published online October 1, 2014; DOI: https://doi.org/10.4150/KPMI.2014.21.5.377

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Abstract PDF: This work describes the coloration, chemical stability of SiO₂ and SnO₂-coated blue CoAl₂O₄ pigment. The CoAl₂O₄, raw materials, were synthesized by a co-precipitation method and coated with silica (SiO₂) and tin oxide (SnO₂) using sol-gel method, respectively. To study phase and coloration of CoAl₂O₄, we prepared nano sized CoAl₂O₄ pigments which were coated SiO₂ and SnO₂ using tetraethylorthosilicate, Na₂SiO₃ and Na₂SnO₃ as a coating material. To determine the stability of the coated samples and their colloidal solutions under acidic and basic conditions, colloidal nanoparticle solutions with various pH values were prepared and monitored over time. Blue CoAl₂O₄ solutions were tuned yellow color under all acidic/basic conditions. On the other hand, the chemical stability of SiO₂ and SnO₂-coated CoAl₂O₄ solution were improved when all samples pH values, respectively. Phase stability under acidic/basic condition of the core-shell type CoAl₂O₄ powders were characterized by transmission electron microscope, X-ray diffraction, CIE L*a*b* color parameter measurements.

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

Synthesis of LiCoO₂ Powders using Recycled Cobalt Precursors from Waste WC-Co Hard Metal: Hee-Seung Yang, Jae-Hwan Pee, Yoo-Jin Kim; J Korean Powder Metall Inst. 2011;18(3):277-282.; DOI: https://doi.org/10.4150/KPMI.2011.18.3.277

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[ LiCoO_2 ] a cathode material for lithium rechargeable batteries, was prepared using recycled Co_3O_4. First, the cobalt hydroxide powders were separated from waste WC-Co hard metal with acid-base chemical treatment, and then the impurities were eliminated by centrifuge method. Subsequently, Co_3O_4 powders were prepared by thermal treatment of resulting Co(OH)_2. By adding a certain amount of Li_2CO_3 and LiOHcdotH_2O, the LiCoO_2 was obtained by sintering for 10 h in air at 800°C. The synthesized LiCoO_2 particles were characterized by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analysis.

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Fabrication of Flake-like LiCoO2Nanopowders using Electrospinning
Bon-Ryul Koo, Geon-Hyoung An, Hyo-Jin Ahn
Journal of Korean Powder Metallurgy Institute.2014; 21(2): 108. 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.

Effects of Chemical Composition and Particle Size of Starting Aluminum Source on the Spheroidization in the Flame Fusion Process: Sun-Hui Eom, Jae-Hwan Pee, Jong-Keun Lee, Kwang-Taek Hwang, Woo-Seok Cho, Kyeong-Ja Kim; J Korean Powder Metall Inst. 2009;16(6):431-437.; DOI: https://doi.org/10.4150/KPMI.2009.16.6.431

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Various inorganic fillers improve the thermal conductivity and physical properties of organic products. Alumina has been used a representative filler in the heat radiation sheet for the heat radiation of electric device. The high filling rate of alumina increases the thermal conductivity and properties of products. We successfully developed the spherical alumina by flame fusion process using the oxygen burner with LPG fuel. In the high temperature flame (2500sim3000°C) of oxygen burner, sprayed powders were melting and then rotated by carrier gas. This surface melting and rotation process made spherical alumina. Especially effects of chemical composition and particle size of stating materials on the melting behavior of starting materials in the flame and spheroidization ratio were investigated. As a result, spheroidization ratio of boehmite and aluminum hydroxide with endothermic reaction of dehydration process was lower than that of the sintered alumina without dehydration reaction.

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Comparative Analysis of Commercial Al2O3 Powders and the Dispersion Characteristics of Slurries Produced Using Them
Mo-Se Kwon, Seung-Joon Yoo, Jin-Ho Kim, Kyoung-Hoon Jeong, Jong-Keun Lee, Ung-Soo Kim
Korean Journal of Materials Research.2024; 34(1): 27. CrossRef
Fabrication and Characterization of Al2O3-Siloxane Composite Thermal Pads for Thermal Interface Materials
Seul-Ki Kim, Yeong-Jin Koo, Hyun Sik Kim, Jong-Keun Lee, Kyounghoon Jeong, Younki Lee, Eun Young Jung
Materials.2024; 17(4): 914. CrossRef

Effects of Doping Elements and the Amounts of Oxygen/Nitrogen Contents in Final Nitrides on the Characteristics of Red Pigment of Tantalum Nitrides (Ta₃N₅): Eun-Young Park, Jae-Hwan Pee, Yoo-Jin Kim, Woo-Seok Cho, Kyeong-Ja Kim; J Korean Powder Metall Inst. 2009;16(6):396-402.; DOI: https://doi.org/10.4150/KPMI.2009.16.6.396

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Abstract PDF: Tantalum nitrides (Ta_3N_5) have been developed to substitute the Cd based pigments for non-toxic red pigment. Various doping elements were doped to reduce the amount of high price Tantalum element used and preserve the red color tonality. Doping elements were added in the synthesizing process of precursor of amorphous tantalum oxides and then Tantalum nitrides doped with various elements were obtained by ammonolysis process. The average particle size of final nitrides with secondary phases was larger than the nitride without the secondary phases. Also secondary phases reduced the red color tonality of final products. On the other hand, final nitrides without secondary phase had orthorhombic crystal system and presented good red color. In other words, in the case of nitrides without secondary phases, doping elements made a solid solution of tantalum nitride. In this context, doping process controlled the ionic state of nitrides and the amount of oxygen/nitrogen in final nitrides affected the color tonality.

Synthesis of Nano-size Aluminum Nitride Powders by Chemical Vapor Process: Jae-Hwan Pee, Jong-Chul Park, Yoo-Jin Kim, Kwang-Taek Hwang, So-Ryong Kim; J Korean Powder Metall Inst. 2008;15(6):496-502.; DOI: https://doi.org/10.4150/KPMI.2008.15.6.496

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Aluminum nitride (AlN) powders were prepared by the chemical vapor synthesis (CVS) process in the AlCl_3-NH_3-N_2 system. Aluminum chloride (AlCl_3) as the starting material was gasified in the heating chamber of 300°C. Aluminum chloride gas transported to the furnace in NH_3-N_2 atmosphere at the gas flow rate of 200-400ml/min. For samples synthesized between 700 and 1200°C, the XRD peaks corresponding to AlN were comparatively sharp and also showed an improvement of crystallinity with increasing the reaction temperature. In additions, the average particle size of the AlN powders decreased from 250 to 40 nm, as the reaction temperature increased.

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A Scale-Up Test for Preparation of AlN by Carbon Reduction and Subsequent Nitridation Method
Hyung-Kyu Park, Sung-Don Kim, Chul-Woo Nam, Dae-Woong Kim, Moon-Soo Kang, Gwang-Hee Shin
Journal of the Korean Institute of Resources Recycling.2016; 25(5): 75. CrossRef
Synthesis of High Purity Aluminum Nitride Nanopowder in Ammonia and Nitrogen Atmosphere by RF Induction Thermal Plasma
Kyung-In Kim, Sung-Churl Choi, Jin-Ho Kim, Kwang-Taek Hwang, Kyu-Sung Han
Journal of the Korean Ceramic Society.2014; 51(3): 201. CrossRef
Synthesis of an aluminum nitride–yttria (AlN–Y2O3) composite from nano-sized porous AlN and YCl3
Jae-Hwan Pee, Jong-Chul Park, Kwang-Taek Hwang, SooRyong Kim, Woo-Seok Cho
Research on Chemical Intermediates.2010; 36(6-7): 801. CrossRef

Synthesis of Tantalum Oxy-nitride and Nitride using Oxygen Dificiency Tantalum Oxides: Jong-Chul Park, Jae-Hwan Pee, Yoo-Jin Kim, Eui-Seock Choi; J Korean Powder Metall Inst. 2008;15(6):489-495.; DOI: https://doi.org/10.4150/KPMI.2008.15.6.489

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Abstract PDF: Colored tantalum oxy-nitride (TaON) and tantalum nitride (Ta_3N_5) were synthesized by ammonolysis. Oxygen deficient tantalum oxides (TaO_1.7) were produced by a titration process, using a tantalum chloride (TaCl_5) precursor. The stirring speed and the amount of NH_4OH were important factors for controling the crystallinity of tantalum oxides. The high crystallinity of tantalum oxides improved the degree of nitridation which was related to the color value. Synthesized powders were characterized by XRD, SEM, TEM and Colorimeter.

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