Papers by Author: Hae Jin Hwang

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Authors: Kazuki Tajima, Hae Jin Hwang, Mutsuo Sando, Koichi Niihara
Authors: Kazuki Tajima, Hae Jin Hwang, Mutsuo Sando, Koichi Niihara
Authors: Tatsuzo Nagai, Hae Jin Hwang, Masaki Yasuoka, Mutsuo Sando, Koichi Niihara
Authors: Geun Hee Kim, Jae Hwan Pee, Yoo Jin Kim, Lada Punsukumtana, Hae Jin Hwang
Abstract: LBP has six steps, which are charging, exposure, development, transfer, fusing, cleaning and discharge, for the printing product. In these steps, we focused on the development step for the source of submicron inorganic pigments. The toner is a negatively charged combination of inorganic particles. A control blade holds the toner at a micro size distance from the drum. The inorganic pigment then moves from the control blade to the more positively charged latent image on the drum. The image in static electricity needs to be developed – made visible. The developer introduces small particles of toner onto the static-charged surface of the drum. In this study inorganic pigments were coated by functional silanes to provide particles with the electrostatic charge. The coating thickness and kinds of silanes were changed to evaluate the electrostatic charge of coated pigments. After coating process, the electrostatic charge of inorganic pigments coated with silanes were evaluated by the Faraday’s device. We will introduce the effect of 3-(N-phenylamino) propyltrimethoxy silane and phenyl tris (methylethylketoxime) silane coating on the electrostatic charge of inorganic pigments.
Authors: Hae Jin Hwang, Ji Woong Moon, Yong Ho Lim, Seung Hun Lee, Eun A Lee
Abstract: Lanthanum strontium chromite (LSC) thin films were prepared from the solution of La, Sr, Cr nitrates, acetylacetone and 2-methoxyethanol. Dip-coating technique was used to decompose La0.8Sr0.2CrO3, LSC thin films. The obtained precursor solution was sufficiently spinable and dried gel films were crystallized after heat-treating above 500°C for 2 h. The oxidation at 800°C for 40 hr resulted in no Fe3O4 surface-insulating phase, which means that the LSC thin film would be an effective oxidation-protecting layer of SUS430 substrate. The carbon deposited on an uncoated SUS430 substrate was amorphous with spherical morphology. The obtained LSC thin film was found to be very effective on preventing carbon deposition under dry hydrocarbon atmosphere.
Authors: Hae Jin Hwang, Do Yeon Kim, Ji Woong Moon
Abstract: Porous clay materials with columnar type pore channels were fabricated from water-based clay slurry and a specially designed mold by using a freeze casting technique. Ice was stimulated to grow vertical direction, and aligned macro pores were formed to the same direction. The phase separation between the ice and clay particles might be responsible for the formation of the columnar type pores. It appears that it is possible to control the size and morphology of pores by modifying a freezing mold, refrigerant temperature, and the weight fraction of clay in slurry.
Authors: Hae Jin Hwang, Kazuki Tajima, Mutsuo Sando, Koichi Niihara
Authors: Hae Jin Hwang, Motohiro Toriyama, Mutsuo Sando, Koichi Niihara
Authors: Chin Myung Whang, J.G. Kim, Hae Jin Hwang
Abstract: Transition metal-doped TiO2 powders as a photocatalyst were prepared by sol-gel process and Sb, Bi and Nb were introduced into them as dopants. The photocatalytic behaviors of the doped TiO2 powder were studied as a function of dopant, doping concentration and preparation conditions. X-ray diffraction, FT-Raman, B.E.T. and scanning electron microscopy were applied for structural and microstructural studies. Optical properties of the doped TiO2 powders were studied by UV-Visible Spectrometer and photocatalytic activity of the doped TiO2 was characterized in terms of the degradation of 1,4-dichlorobenzene. X-ray difraction analysis showed that doping with a transition metal ion suppresses anatase-to-rutile phase transition compared with the pure TiO2. The Sb and Nb-doped TiO2 powders did not exhibit any other diffraction peaks except those belonging to TiO2. On the other hand, a diffraction peak of Bi4Ti3O12 appears for 5 at.% Bi-doped samples. All of the doped TiO2 powders had higher specific surface area than undoped TiO2. Surface area increased with increasing dopant concentration depending on the dopant, from 33.9 m2/g to 55.4m2/g. The UV-visible absorption spectra of doped samples were red-shifted by 20~50nm according to the doping level. Also transition metal doped TiO2 powders exhibited better photocatalytic activity than the undoped TiO2. The increase in photoactivity is probably due to the increase in the interfacial electron transfer, red shifts, and better crystallinity.
Authors: Hyoun Woo Kim, S.H. Shim, Hae Jin Hwang, Jae Hyun Shim, Nam Hee Cho, Mi Kyoung Park, Hyuck Mo Lee, Byung Tae Ahn, Hyeong Tag Jeon, Jong Wan Park, Jin Ho Ahn, Bo Young Hur
Abstract: This study reported the fabrication of tin oxide (SnO2) nanostructures on Co-coated Si substrates by the thermal heating of Sn powders. The microstructures and morphologies of the resultant nanostructures were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning electron microscopy (SEM). The product mainly comprised the tangled nanowires with average diameters in the range of 50-180 nm. The nanostructures were single-crystalline rutile structure of SnO2. The PL measurement with the Gaussian fitting exhibited visible light emission bands centered at 576 nm and 638 nm, respectively. We have discussed the possible growth mechanism of the nanostructures.
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