Papers by Author: Geum Chan Hwang

Abstract: The Na-bentonite compact with absorbent polymer was fabricated in order to observe their absorption and preservation about water. Absorption of fabricated specimens in the water and preservation of absorbed samples in the drying machine at 323 K was measured. It was obtained that the absorption had been increasing with inhancing absorbent polymer. Absorption of As-received Na-bentonite was lower than absorption of As-received absorbent polymer. The preservation had been also increased with absorbent polymer was obtained. Na-bentonite compact with absorbent polymer ware investigated the good absorption and preservation when the Na-bentonite compact with absorbent polymer 40 mass %.

Abstract: The Na-bentonite with contained smectite was fabricated in order to observe their absorption and preservation about water. Absorption of fabricated specimens in the water and preservation of absorbed samples in the drying machine at 323 K was measured. It was obtained that absorption had been decreasing with increasing smectite. Absorption of As-received Na-bentonite was higher than absorption of As-received smectite. The preservation has been also decreased with increasing smectite was obtained. Na-bentonite with contained smectite were investigated the good absorption and preservation when the Na-bentonite containing smectite 5 mass %.

Abstract: The oxidation behavior of tantalum diboride (TaB2) powder at high temperature was investigated in order to determine the possibility of the use of advanced high temperature structural materials. Unfortunately, monolithic TaB2 were known to be chemical stability up to high temperatures. To date, there have been few reports regarding the properties of TaB2 ceramics. The samples were oxidized at room temperature to 1273 K for 5 minutes to 25 hours in air. The weight changes were measured to estimate the oxidation resistance. The oxidation of samples oxidized for short oxidation time of 5 minutes started at 873 K, and the weight gain increased with increasing oxidation temperature. On the other hand, at the oxidation time of above 1 hour, a maximum weight gain value at 973 to 1073 K was observed. However, even if the oxidation temperature was increased an additional weight change slightly occurred. The weight gain of the sample oxidized at 1273 K for 5 minutes to 25 hours was about 40 to 20 % of the theoretical oxidation mass change. According to the powder X-ray diffraction date, the oxidized TaB2 sample was changed to Ta2O5 at 873 K. Finally, the TaB2 showed a good oxidation resistance at high temperature, because the surface film of tantalum oxide (Ta2O5) formed by oxidation acted as an oxidation resistant layer.

Abstract: Boron carbide composites in Si-B-C System have been widely studied and applied in excellent engineering materials. These materials are usually used at high temperature. Unfortunately, amorphous Si-B-C ceramics have been few reports regarding the properties of Si-B-B4C ceramics. In this study, the preparation of crystallized Si-B-C system compounds using Si, B, and B4C powders was investigated to determine their potentially for applications as high hardness composites. The samples were prepared at 1673 K for 2 hours in Ar atmosphere. The sintered bodies were cut into 5 х 5 х 10 mm blocks and polished with diamond disk for Vickers hardness. The samples were subjected to X-ray diffraction (XRD) analysis for phase evolution using a powder X-ray diffractometer. The fracture surfaces of the specimens were observed using a scanning electron microscope (SEM) included an energy dispersive X-ray fluorescence spectrometer (EDX) system to estimate the microstructures.