Papers by Author: Byung Hak Choe

Abstract: Dental implant with porous surface has been studied by many researchers because it has a good osseointegration. TiO₂ nanotube arrays on the surface of dental implant could provide the porous surface, the space of drug loading, and better biocompatibility than bare surface. To investigate the effects of TiO₂ nanotube arrays for dental implant, commercial dental implant was used and its surface was anodized to fabricate TiO₂ nanotube arrays. Highly ordered TiO₂ nanotube arrays were grown on the surface of dental implant. Ethylene glycol based electrolyte was used in anodic oxidation process. Anodic oxidation voltage and time were 50V and 15 min, respectively. The micro structure was observed by FE-SEM. The diameter and length of TiO₂ nanotube arrays were ~60 nm and 10μm, respectively. BMP-2 was loaded in TiO₂ nanotube arrays. For in-vivo testing, the dental implant with TiO₂ nanotube arrays was applied to rabbit legs for 8 weeks. In dental implant with TiO₂ nanotube arrays, good osseointegration properties were observed. TiO₂ nanotube arrays fabricated by anodic oxidation will be very useful in the field of bone implants and bone tissue engineering.

Abstract: This paper reports the fabrication of indium oxide (In2O3) films using a triethylindium and oxygen mixture. The deposition has been carried out on TiAlN substrates (200-350°C). We have established the correlation between the substrate temperature and the structural properties. The films deposited at 300-350°C were polycrystalline, whereas those deposited at 200°C was close to amorphous. XRD analysis and SEM images indicated that the films grown at 350°C had grained structures with the (222) preferred orientation. The room-temperature photoluminescence spectra of the In2O3 films exhibited a visible light emission.

Abstract: The embrittlement fracture mechanism caused by microstructural evolution of 17-4 PH stainless steel at long term aging was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The solution treated specimen consists largely of lath martensite with a small fraction of elongated δ-ferrite. The spherical particles existed a little in the martensite matrix, while no precipitates were present in the δ-ferrite at the solution treated specimen as non-aging. The precipitation of Fe-Cu in the δ-ferrite causes the aged hardening after long term aging accormpanied by decreases in elongation and charpy V-notch energy absorption. The increased fraction of brittle fracture on the fractured surface by impact and tensile test reveals that the embrittlement of the 17-4 PH alloys during long term aging is mainly caused by the precipitation hardening in the δ-ferrite matrix.

Abstract: This study presents a probabilistic methodology for estimation of the remaining life of pressurized pipelines containing active corrosion defects. A reliability assessment was carried out using extreme value distribution of the corroded defects instead of the already published failure pressure model like NG18 or ASME B31G. The failure probability of pipelines depends on the number of corroded defects, and it was calculated directly as the area exceeded a defined LV(Limited Value of corrosion depth). The remaining life of pressurized pipelines can also be estimated by the PDF of extreme value distribution as calculating the exceeded area with a defined failure probability.