Ki Gang Lee

Preparation of ZrO2 coated graphite powders

Graphite powders were coated with ZrO2 by the controlled hydrolysis of a zirconium oxychloride aqueous solution. Thehydrolysis process was carried out with temperature control because of the low wettability of ZrO2 to the surface of thegraphite. PVA was added to the solution for the enhancement of Zr ion adsorption. The surface of the graphite particles coatedwith ZrO2 was observed by TEM. There are two types of ZrO2 particles; (a) primary particles a few nm in size and (b) secondary particles with ∼0.1 μm size were obtained. The data of oxidation weight loss and surface potentialshow that the graphite surface was successfully modified by the forced hydrolysis of the zirconium chloride aqueous solution.

Growth and luminescent characteristics of ZnGa2O4 thin film phosphor prepared by radio frequency magnetron sputtering

ZnGa2O4 and doped ZnGa2O4 thin film phosphors were prepared by the rf magnetron sputtering method. Deposition parameters were controlled to characterize the deposition mechanism and structural changes. And then the relation between the structure and luminous properties was characterized. To observe the effects of the substrates, thin films were deposited on Si(100), Si(111), and indium–tin–oxide (ITO) coated glass substrates. The orientational transition was observed by varying the substrate temperature. The grain size of ZnGa2O4:Mn thin film deposited on a Si wafer was smaller than that on an ITO/glass substrate, which resulted in higher photoluminescence (PL) intensity. By heat treatment, PL intensity was increased because it eliminated the defects in films and improved the crystallinity.

Efflorescence and Leaching Behavior of Metal Ions for EAF Dust-Clay Based Bricks

Brick samples were prepared through vitrification process with two different kinds of EAF dust. Leaching concentrations of various metal ions and anions for the bricks(20wt% EAF dust-80wt% clay) were evaluated by ICP and IC analysis. The results of leaching test showed that the concentration of ions leached from bricks were proportional to the square root of time and saturated with leaching time. The saturated concentrations of alkali and alkali-earth metal ions were 0.1-250ppm; on the other hand, the heavy metal ions were 0-0.084ppm. The efflorescence mechanism of EAF dust-clay bricks was studied by quantitative analysis for the effects of various metal ions and anions. Efflorescence formed on the brick surfaces which were immersed in DI water and dried slowly in the air were characterized by SEM, EDS and XRD. The results of EDS and XRD showed that the main component of the efflorescence was water soluble Na2SO4 .

Microwave dielectric properties of Bi(Nb1-xTax)O4 ceramics with Cu2V2O7

Abstract Microwave dielectric properties of Bi(Nb1-xTax)O4 with 0.8 wt.% Cu2V2O7 were investigated as a function of Ta content and sintering temperature. X-ray powder diffraction patterns of the specimens sintered at 775°C for 3h showed the orthorhombic single phase throughout the entire composition range. Dielectric constant was not changed drastically, however, Qf value strongly depended on the composition and sintering temperature. The temperature coefficient of the resonant frequency (TCF) could be controlled with Ta content. Typically, K of 45, Qf of 8900 GHz and TCF of +4 ppm/°C were obtained in the Bi(Nb0.6Ta0.4)O4 specimens with 0.8 wt.% Cu2V2O7 sintered at 775°C for 3h.

Characteristics of Artificial Lightweight Aggregate by Using Magnetic Separated Desulfurized Fly Ash and Dredged Soil

This research concerns the characteristics of ALA made of magnetically separated desulfurized fly ash (DFA) generated from the coal power plant having fluidized bed type boiler. Being believed that these alkali-rich components could be separated by magnetic separation, desulfurized fly ash was separated by using 10,000 Gauss magnets as magnetic desulfurized fly ash (MDFA) and non-magnetic desulfurized fly ash (DFA). The dependence of composition and sintering temperature on physical property of ALA was studied. It seems to be apparent that the glass phase which is one of the main problems in the ALA manufacturing process could not be controlled by the magnetic separation only, but the formation of pores could be considerably controlled by the magnetic separation. It is also clear that neither DFA nor MDFA can be used as raw materials for making ALA; however, magnetic separation of desulfurized fly ash from fluidized bed type boiler is effective to collect bloating components for self-bloating of ALA without addition of an extra bloating agent.

Thermal and Leaching Behaviors of EAF Dust-Clay Systems

Thermal behaviors of EAF dust, water-washed EAF dust, and EAF dust/heavy clay mixtures with wet mixing process were characterized by TG/ DTA analysis. The ionic concentrations of some metal ions and anions in the supernatant from water-washing process were evaluated by ICP and IC analysis. Weight loss of water-washed EAF dust above the temperature range of 1000°C was significantly decreased because of the washing effect of chloride and sulfate compounds. The variation of volatile ZnO and PbO contents were not detected in 20wt% D dust-80wt% clay sample. The wet mixing process not only enhanced the homogeneous mixing of EAF dust and clay particles, but also reduced the volatilization of heavy metals(Zn, Pb, etc.) at the high temperature range.