Papers by Author: Hyung Sun Kim

Abstract: As one of the most important parts of the generator, Epoxy/mica insulation system has the direct effect on the reliability of generator operation. The accelerated aging of insulation system was taking place under the complex operation condition, and resulting in the insulation system breakdown. It had always been the target for the researchers to find an efficient way to evaluate the state of generator insulation system. According to the real operation situation, the multi-factor aging test sequence with electric field, temperature field, mechanical vibration and thermal cycling was developed, and the test platform with multi-factor aging was built in this research. The partial discharge test was conducted at the end of each cycle. The result showed that, with the insulation aging time prolonged, the maximum partial discharge quantity decreased first then increased while skewness and kurtosis varied the opposite way. And the phase range of partial discharge began to expand. This research provided a new way to evaluate the state of generator insulation system.

Abstract: AlN single crystal can be grown by physical vapor transport (PVT) method. The purity and particle size of the source material are important factors for single crystal growth to obtain good quality of AlN single crystal. The aim of this study was purification of AlN powder and growth of its particle size through thermocyclic treatment. The initial particle size was about 1.0 μm and the purity was 98.4% containing 1.6% oxygen and metallic impurities such as Fe, Sn, Ca, Na and Mg etc. which were analyzed based on KSL1612. For purification of AlN powder, it was performed using a thermocycle process with various thermocyclic numbers. After the thermocycle treatment, it is able to obtain large particle size AlN powder as much as 30μm and purity was increased to 99.6% based on chemical analysis.

Abstract: The formation of organic-inorganic hybrid composite with ceramic platelets and polymeric compound can have the higher strength and higher elasticity than metal, which is a nanocomposite with high strength and light weight. Ceramic platelet such as Al₂O₃ has been used to form organic-inorganic composite material using PMMA as an organic polymer. Bending strength and density of the composites prepared by infiltration and post-warm pressing were measured. FE-SEM and TG analysis were carried out to determine the microstructure of the organic-inorganic composite materials. Bending strengths and densities of the composites prepared by Al₂O₃ ceramic plate and PMMA after post-warm pressing were ~70MPa and ranged from 2.4 to 2.6, respectively.

Abstract: In our study, the dielectric properties of SiOC low k thin film derived from polyphenylcarbosilane were investigated as a potential interlayer dielectrics for Cu interconnect technology. A SiOC low k thin film was fabricated onto a n-type silicon wafer by dip coating using 30wt % polyphenylcarbosilane in cyclohexane. Curing of the film was performed in air at 300°C for 2h. The thickness of the film ranges from 1 μm to 1.7 μm. The dielectric constant was determined from the capacitance data obtained from metal/polyphenylcarbosilane/conductive Si MIM capacitors and shows a dielectric constant as low as 3.26 without porosity added. The SiOC low k thin film derived from polyphenylcarbosilane shows promising application as an interlayer dielectrics for Cu interconnect technology.

Abstract: Photolithographic process is one of the eco-friendly processes for forming the pattern of the barrier ribs in PDP. Controlling the refractive index of glass is important to develop a photosensitive paste for photolithographic process. We studied the refractive index and the structural transition of these glasses by measuring the refractive index, reflectance, density and dielectric constant with changing the SiO2/B2O3 ratio in the SiO2-B2O3-Al2O3 glass system. The refractive index was investigated to the relationship between the thermal and optical properties depending on the composition. It suggests that the thermal and optical properties in borosilicate glasses should be correlated to the glass structure with the SiO2/B2O3 ratio.

Abstract: Indium oxide (In2O3) films were successfully grown on LiAlO2 substrates using the triethylindium (TEI) as a precursor in the presence of oxygen in the metalorganic chemical vapor deposition process. We have established the correlation between the substrate temperature and the structural properties. The grain structures were clearly shown on the surface of the films deposited at 350°C. The root mean square (RMS) surface roughness of the In2O3 films increased with increasing the substrate temperature. A photoluminescence measurement at room temperature exhibited a yellow-green emission band centered at 585 nm.

Abstract: The chemical reaction between water and frit surface was determined using pH meter, ICP-MS, zeta-potential analyzer and FT-IR. With increasing the content of barium and boron of glass composition, the difference of water pH increased with different glass systems. During wet milling in aqueous solution, boron and barium of glasses dissolved. The values of zeta potential of lead and bismate frits were negative in water solution. Based on the results, when wet milling is used in water solution, the contents of barium and boron in a glass should be less than 10mol%.

Abstract: The present study is mainly focused on the evaluation of interface reaction between ceramic fillers and phosphate glass matrix for barrier ribs in PDP. The samples were prepared by dry milling for frits with a mean particle size(d50) of 1-2㎛. The frit was mixed with ceramic fillers (Al2O3, ZnO) and was fired at 550°C for 30 minutes. Interface reaction was observed by measuring the weight change of fired samples as a function of immersion time in 90°C de-ionized water and in 60°C acid solution. Fired samples were characterized by differential thermal analyzer, scanning electron microscopy, X-ray diffraction and ion dissolution was analyzed by inductive coupled plasma measurement. The results suggest that properties of barrier rib depend on the crystallization behavior and interface reaction between the fillers and the glass matrix.

Abstract: For low temperature co-fired ceramics (LTCC) materials, BaO-B2O3-MgO-Al2O3 glass system was tested. The starting temperature for densification of a sintered body was at 700°C and the onset temperature for crystallization of a sintered body was 820°C. With the sintering temperature, the sintered body was investigated with shrinkage, crystal phases, thermal properties, and mechanical properties. The glass transition temperature was constant with increasing frit size. However, the onset point of crystallization increased with increasing frit size. The formation of crystal phase was celsian (BaAl2Si2O8). From our results, it is possible to achieve the glass-ceramic having the high strength and the ability of sintering at low temperature using controlling the sintering temperature of BaO-B2O3-MgO-Al2O3 system glass frit.

Abstract: We investigated the mechanism of chemical reaction between Bi2O3 glass and water solution during milling. As a result, the frit condition affected discoloration with crystallization. After milling, there was a deposited layer on the frit surface. The layer was composed of leached ions, contaminates of metal oxides, and hydroxides. Bismate glass frit is reacted to the milling solution so that the frit surface is formed with a gel layer. In milling, contaminates contained in milling solution is contributed to the formation of deposed layer on frit surface.