Papers by Author: Chang Yeoul Kim

Abstract: The paper presents studies of influences of platelet-shape alumina content on the morphology, mechanical and thermal properties of Al₂O₃/epoxy composites. The alumina particles were pre-treated with surface modifier, and its addition contents were ranged from 17 to 40vol.%. It was found that tensile strength and thermal conductivity increased with the increase of the alumina contents. The fracture surface investigation showed that several strengthening mechanisms, including particles pull-out, crack pinning, plastic void growth and deformation were the main factors for the increments of the tensile strength of the Al₂O₃/epoxy composites. Comparing with pure epoxy polymer, the creep strain values at 70 °C for 1800 s and recovery strain after 3600 s of 40vol.%Al₂O₃/epoxy composites was lower as 0.23% and 70%, respectively. It was due to effective prohibition of the slippage and disentanglement of epoxy polymer molecules by the rigid Al₂O₃.

Abstract: Capacitive deionization (CDI) is a water desalination technique in which salt ions are removed from brackish water by flowing through a spacer channel with porous electrodes on each side. Upon applying a small voltage difference between the two electrodes, cations move to and are accumulated in electrostatic double layers inside the negatively charged cathode and the anions are removed by the positively charged anode. Therefore, one of the advanced merits of CDI is the low driven energy by compared to other desalination technologies. Inspired this, we have performed the calculation on energy consumption of activated carbon based CDI in different operation conditions. The results show that the energy consumptions are significantly related to cell voltage as well as solution concentration. Furthermore, the round trip efficiency as a vital indication in terms of energy consumption have been introduced and discussed as well.

Abstract: Al2O3-SiO2 nanoparticles have been synthesized by a sol-gel processing. Size and composition of the synthesized particles can be controlled by manipulating the relative rates of the hydrolysis and condensation reaction of precursor. The average size of synthesized Al2O3-SiO2 nanoparticles was about in the size range of 50~100nm. The effects of synthesis parameters, such as the molar ratio of water to precursor, the molar ratio of water to surfactant and stirring rate, are discussed.

Abstract: Electrochromic WO3 thin film was prepared by using tungsten metal solution in hydrogen peroxide as a starting solution and by a sol-gel dip coating method. The thermal analysis was conducted by DSC/TG method. A DSC/TG analysis and the XRD patterns showed that a tungsten oxide crystal phase was formed at 400oC. WO3 thin film when heat-treated at 300oC was amorphous and had a better electrochemical property than that of the crystalline phase. Crystallization of tungsten oxide decreased active sites of ion intercalation so that the current density decreased with heat-treatment temperature.

Abstract: Color sol was fabricated and coated it on glass substrate using sol-gel method. Silicate sol prepared by the use of commercially available tetraethoxysilane(TEOS), tetramethoxysilane (TMOS), methoxysilane(MTSO), phenytrimethoxysilane(PTMS) as a raw material of alkoxysilane family, and C.I. solvent red 122 and C.I. solvent yellow 82 as a organic dye, and C.I. pigment blue 28 and C.I. pigment red 26 as a pigment. Colored thin films were fabricated with changing the withdrawal speed by dip coating method, and heat treatment at 100~400°C. The visible light transmittance of colored thin film was measured with UV/VIS spectrophotometer, the surface hardness measured by pencil test, the surface turbidity measured by haze meter, and the film thickness was measureded by Alpha-step surface profiler.

Abstract: Aerogel has its advantages of light density of 0.003-0.35 g/cm3 and its high specific surface area, 600-1000m2/g, mean pore diameter ~20nm. However, aerogel has its disadvantages of fragility and high cost. To overcome the mechanical fragility, we synthesized aerogel composite blankets with glass wools by drying at ambient atmosphere. Colloidal silica sol was first prepared by ion exchanging sodium silicate through amberlite column. Then, glass wool was soaked into the pH-controlled silica aerogel and then gelated. Ageing of silica aerogel composite was conducted in purified water and solvent exchange/surface modification was simultaneously processed in hexane and TMCS solution. After drying at 60oC and heat-treatment at 230oC, we evaluated the properties of aerogel composite, its apparent density and specific surface area.

Abstract: Electrochromic WO3 thin film was prepared by using tungsten metal solution in hydrogen peroxide as a starting solution and by sol-gel dip coating method. XRD pattern showed that tungsten oxide crystal phase formed at 400
. In the view of electrochemical property, WO3 thin film which was heat-treated at 300
and was amorphous had better than that of the crystalline phase.

Abstract: The porous ceramic panel using glass powder as a main raw material can be applied for the thermal insulator in architecture and industry since it is noncombustible and chemically stable as well as eco-friendly unlike the organic thermal insulators. For the study of fabrication and characterization of this material, we used grinded glass powder with grain size smaller than 150
, and Calcium carbonate(CaCO3) and Calcium phosphate(Ca3(PO4)2, CaHPO4·2H2O) as foaming agent. The shape and size of pore cell in porous glass structure with the change of additives and sintering temperature were studied. The physical properties as like density, thermal conductivity and compressive strength of materials are also studied. It was possible to make a porous ceramic panel with multi-layered which has the form of sandwich with layer of low density and high density in one body by adjusting the foaming characteristics.

Abstract: The effect of RO components variation on some properties was studied in Pb free glass frit for PDP (Plasma Display Panel). One of the main components, BaO, was replaced progressively at fixed concentration of alkaline earth oxides. We studied the transparency, thermal expansion, softening point, and the high temperature microscopic behaviors of glass frits and TG(thermal gravimetry) of raw material. The compositional dependence of those properties was discussed from the view points of compositional diversity and production process of Pb free glass frit.