Papers by Author: Soo Wohn Lee

Abstract: Ni-SiC nano composite coatings were fabricated using electrodeposition technique with the aid of ultrasound. The properties of the nano composite were investigated using SEM and Vicker’s microhardness tester. The results demonstrated that the microhardness of composite coatings under ultrasonic vibrations was improved significantly as compared to conventional electrodeposition techniques without ultrasound. The nano particles were found to be distributed homogeneously with reduced agglomeration due to the ultrasonic vibration.

Abstract: The ceramic channel is very important in SRL hot dipping system. High strength and fracture toughness of ceramic channel materials can improve the quality, productivity and economic feasibility of zinc plated steel. The purpose of this research was to find out the most suitable conditions of the ceramic channel that have best fracture strength and fracture toughness. The hot pressed composite materials was carried out by hot pressing Al2O3 with different content of ZrO2. The composite contained from 0-20 wt.% ZrO2. Hot pressed composite materials were observed for mechanical properties (density, hardness, fracture toughness and flexural strength) and microstructure.

Abstract: Solid lubricants were suited for the applications of high temperature parts. Recently, researches for self-lubricating ceramic matrix composites using solid lubricants, such as MoS2, WS2, h-BN, and graphite etc., became active. This work is to use the spark plasma sintering (SPS) technique in order to make self-lubricating Al2O3/15wt% ZrO2 nanocomposites with higher mechanical properties. To optimize the self-lubricating Al2O3/15wt% ZrO2 nanocomposite systems were added with different solid lubricants (CaF2, BaF2, MoS2, WS2, h-BN, and graphite). The coefficient of friction of CaF2, h-BN and graphite added composites in steady-state at room temperature are below 0.3.

Abstract: Nano-technology is a super microscopic technology to deal with the structures of 100 nm or smaller. This technology also involves the developing of TiO2 materials or TiO2 devices within that size. The aim of the present paper is to synthesize the silver doped nano-TiO2 by Sonochemistry method and to evaluate the effect of different percentages (0.2-1.5%) of silver load on TiO2 in the algae inactivation, The sample were characterized by using different techniques as XPS, TEM, SEM. Photo-catalytic activity of Silver doped TiO2 were evaluated through the inactivation of red tide (Cochlodinium) using UV-irradiation (315-400nm). The best result was found with silver doped TiO2.

Abstract: In this paper, antibacterial silver-containing hydroxyapatite coating was prepared by vacuum plasma spraying method and osteoblasts were seeded onto the surface of the coating to evaluate its cytocompatibility. The results indicated that the cells proliferated well on the samples, and the proliferation rate on the silver-containing hydroxyapatite coating was a little bit higher than that on the silver-free hydroxyapatite coating. The contact angle of water drop on the coating was measured, and it was found that the contact angles of the silver-containing hydroxyapatite coatings were smaller than the hydroxyapatite coating. The improvement of hydrophilicity for the silver-containing hydroxyapatite coating could be beneficial to the cells proliferation on its surface. It can be concluded that the addition of silver in the hydroxyapatite coating endowed the coating with antibacterial property while maintaining its excellent cytocompatibility.

Abstract: The in vitro attachment, spread, and proliferation behavior of osteoblast cells on the plasma-sprayed composite coating with 70wt% zirconia and 30wt% dicalcium silicate were studied. The composite coating shows good cytocompatibility. The human osteoblast cells attached, spread and proliferate well on the surface. The cytocompatibility of the coating was attributed to the incongruent dissolution of dicalcium silicate and the large amount of Si-OH functional groups produced on the surface. The released calcium and silicon ions are also positive to the proliferation of cells. All our results show that the composite coating possesses good cytocompatibility.

Abstract: High-purity aluminum oxide is potentially an attractive implante material for total hip joint replacement, because its biocompatibility, excellent wear resistance, high strength and corrosion resistance. The main problem of alumina is relatively low fracture toughness. Thus, this study is the introduction of ZrO2 as second ceramic phase homogeneously dispersed wihtin an alumina matix. Al2O3/ZrO2 nanocomposites disk is prepared by spark plasma sintering (SPS) method at 1500°C and 50MPa, in vacuum for 5min. Then, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the microstucture and phases of this nanocomposite. Moreover, frexual sthrength of the nanocomposites was meausured as well as hardness and fracture toughness. When the content of ZrO2 is up to 15wt%, the fracture toughness value (8.4MPam1/2), and strength (527MPa) are achieved. This Al2O3/ZrO2 nanocomposites may be served as a tatal hip joint replacement.

Abstract: Carbon nanotubes reinforced alumina was fabricated by spark plasma sintering method. When adding 0.2wt% nanotubes, the fracture toughness of the composites prepared increases 19% compared with the pure alumina ceramics. The effect of sintering schedule on microstructure and mechanical properties is investigated systematically. Microstructure studies reveal that at high sintering temperature, the nanotubes tend to gather in the gaps surrounded by three or more grains in a flocculent state, which leads to poor mechanical properties. Raman spectrum indicates that long sintering duration may cause serious nanotubes destruction and lower the mechanical properties.

Abstract: Dense nanocrystalline Y2O3 ceramics without grain growth have been successfully obtained by a new method, which is based on the self-propagating high temperature synthesis and quick pressing. A suitable self-propagating system with a maximum combustion temperature of 1350 °C and a heating rate of 1300 °C/min was chosen as a chemical furnace to supply the heat to densify nanocrystalline Y2O3. Dense samples without grain growth were obtained when the applied pressure was 120 MPa.

Abstract: Nano-hydroxyapatite (n-HA)/chitosan (CS)/konjac glucomannan (KGM) composite was prepared by integrating composition and molding. Then, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the physical, chemical and degradable properties of the composite before and after in simulated body fluid (SBF). Moreover, study in vitro test for drug delivery revealed that the amount of released pentoxifylline (1-[5-oxohexyl]-3,7-dimethylxanthine)(PTX) reached a plateau and equaled 80% of the drug loaded in an implant. The newly develop n-HA/CS/KGM composite may serve as a good degradable biomaterial for implantable drug delivery system (IDDS) in bone tissue engineering.