Papers by Author: Sung Goon Kang

Abstract: Thermal behavior and microstructural characterization of the CNTs/Al2O3 nanocomposites with different relative densities were studied by TGA and SEM. The onset temperature for weight loss corresponded to a decomposition of CNTs in TGA increased with an increase of relative density. The activation energy for CNTs decomposition obtained by the Kissinger method increased with increasing relative density. The difference in thermal behavior was explained by the porosity effect on the oxidation and decomposition of CNTs.

Abstract: The separator of the molten carbonate fuel cells (MCFC) has the major corrosion problems, especially wet-seal area, because this part contacts directly with the corrosive molten carbonate electrolyte. For the protection of the wet-seal area, aluminization method is developed recently. Coated aluminum reacts with the molten carbonate and forms the LiAlO2 having high corrosion resistance, high melting point, no electrical conductivity and no dissolution in molten carbonate. In this study, 50㎛ thickness aluminum foil was applied to form the Al-Fe coating layer on the AISI316L by using the laminating method. Laminating of aluminum foil on AISI 316L was performed at 630°C for 5h in Ar atmosphere using a jig and diffusion heat treatment was carried out at 700°C, 750°C and 800°C for 3h in Ar atmosphere respectively. This method simplified the existing complicated process and has a great advantage of low-cost mass production compared to other methods like PVD, CVD and spray coating.

Abstract: Ag deposited Si/C composite was studied as the anode. In order to enhance the electrochemical properties of Si electrodes, which show poor cyclability as an anode in lithium ion secondary battery, the deposition of Ag prepared by electroless deposition method on the surface of the Si/C composite powder produced by high energy ball milling. Si/C composite shows overall fade in capacity which is caused by Si pulverization. However, The Ag deposited Si/C composite improves cyclability and exhibits capacity of ~590mAh/g after 30th cycle. Scanning electron microscopy(SEM) and X-ray diffraction(XRD) measurement are adapted to inspect the deposition process.

Abstract: The influence of relative density on the thermal stability of CNTs-dispersed Al2O3 nanocomposites has been investigated by using thermogravimetric analysis (TGA). TGA revealed that the onset temperature for weight loss increased with an increasing sintering temperature and CNT content. By taking account of the XRD and SEM results, it is suggested that the weight loss is caused by a decomposition of CNTs phase by oxidative atmosphere. The difference in thermal stability was explained by the porosity effect on the oxidation and decomposition behavior of CNTs, because the open pores promote the chemical reaction and gas flow of reactants.

Abstract: The microstructure and electrical conductivity of CNTs dispersed Al2O3 nancomposites depending on the powder processing and CNTs content were demonstrated. The composite powders with homogeneous dispersion of CNTs could be synthesized by a catalytic route for direct formation of CNTs on nano-sized Fe dispersed Al2O3 powders. The sintered nanocomposite using the composite powder with directly synthesized CNTs showed homogeneous microstructure and enhanced elelctrical conductivity. The influence of powder processing on the properties of sintered nanocomposites was discussed by the observed microstructural features.

Abstract: CNTs/Fe/Al2O3 nanocomposites were prepared by thermal CVD and SPS methods. The dispersion of CNTs in the Fe/Al2O3 matrix were controlled by an attrition milling process. FESEM analysis revealed that the CNTs of 5 vol.% were homogeneously dispersed in the Fe/Al2O3. The effects of CNTs dispersion on the mechanical and electrical properties of the specimens were investigated. Fracture strength and electrical conductivity of 5 vol.% CNTs/Fe/Al2O3 specimen were measured at 641 MPa and 2.93
10-11 mS/m, whereas that of a 20 vol.% CNTs/Fe/Al2O3 specimen were 208 MPa and 8.46
10-7 mS/m, respectively. In comparison with an Al2O3 monolith, the specimen with 5 vol.% CNTs showed enhanced fracture strength and increased electrical conductivity.

Abstract: Platinum/Palladium modified aluminide coatings prepared by aluminide pack cementation on the nickel base superalloy Inconnel 738. The platinum/palladium modified aluminide coating of cyclic oxidation behavior at 1200°C was investigated by TGA, XRD and SEM/EDS. Platinum/Palladium modified aluminide coatings showed better cyclic oxidation resistance than Platinum modified aluminide coating and palladium modified aluminide coating compared. Pt and Pd alloy played an enough role in alumina stabilization and in delaying the degradation of β-phase.

Abstract: In this work, we made micromolds using SU-8 photoresist and adopted electroless Ni-P deposition, well known as a hard coating material, to improve the rigidity and durability of SU-8 micromolds. After a micromold using SU-8 was defined by conventional lithography, Ni-P layer was electrolessly deposited on SU-8. By means of electroless Ni-P deposition, it was possible to increase the hardness of a micromold as much as about 17 times. In addition, it will be able to make various sized micromolds with one photomask by regulating the thickness of Ni-P layer.

Abstract: The effects of deformation on corrosion behavior of galvanized steel were investigated. Accelerated corrosion test was conducted under the conditions of 30oC and 90% relative humidity with flowing 200ppm sulfur dioxide gas for five weeks. Surface morphologies and corrosion products were analyzed by SEM/EDS and XRD. The corrosion products were composed of hydrates of ZnSO4. And corrosion rates of each part, bottom, bended and wall, were increased with growing strain due to surface damage and enlargement of naked surface for corrosion.

Abstract: Silicon to silicon wafer bonding at low temperature of 300 °C using residual stress controlled evaporated 2 ㎛ thick Pyrex glass thin film (briefly, glass thin film) on silicon wafer was investigated. It was found that residual stresses of 2 ㎛ thick glass films on silicon wafers were strongly dependent upon moisture contents and annealing processes. Residual stresses of asdeposited glass films with compressive stress of -150 MPa could be changed to more compressive stress of -230 MPa by moisture absorption. However, after annealing process at 200 °C to 400 °C for 30 min, residual stresses were remarkably changed to tensile stresses of about 75 MPa to 130 MPa, respectively. For the reliable wafer bonding process, the evaporated glass thin films should be annealed in the range of 200 °C to 500 °C for 30 min. So, bare silicon to bare silicon and bare silicon to patterned silicon were bonded at 300 °C and 30 V ~ 60 V for 15 min using 2 ㎛ thick glass film with residual stress of 130 MPa which were generated after the annealing process of 400 °C for 30 min. These results could be used for low temperature silicon to silicon wafer bondings for applications of micro sensors, micro actuators and micro fluidics devices.