Papers by Author: Deug Joong Kim

Abstract:
The formation, microstructure and electrical property of conductive ceramic composites derived from polymer pyrolysis were investigated. Methylpolysiloxane was mixed with TiH2 as a filler and pyrolyzed in nitrogen, argon and vacuum atmosphere at a temperature of 1600oC for 1 hour after the preheat treatment at 850oC in N2 atmosphere. Depending on the atmosphere conditions, TiN and Ti5Si3 phases were formed by reaction of TiH2 as reactive filler and atmospheric gas or pyrolytic product such as SiO2. Consequently, the microstructures of the ceramic composites with 70 vol.%TiH2 pyrolyzed at 1600oC for 1 hour in vacuum were composed of TiN and Ti5Si3 particles. The density and electrical conductivity of the ceramic composites were 97.3 TD% and 6200 ohm-1⋅cm-1, respectively. These composites pyrolyzed by polymer were considered as superior conductive material with a value of 103 ~ 104 in log scale at room temperature.

Abstract: Hardening of blood vessels has steeply increased every year, and implantation stent was used to solve that the conditions of illness. However, in-stent restenosis continues to make problem. To overcome the problem of in-stent restenosis, the concept of local delivery of antiproliferative or immunosuppressive drugs has been introduced into interventional cardiology. Local drug delivery system was demonstrated by using drug-eluting stents coated with nanoporous anodic aluminum oxide (AAO) used for controlled drug release. Effects of diameter and depth of AAO on the diffusion characteristics of drug were investigated. 2-deoxyadenosine was tested. AAO pore diameter and depth showed image by SEM and characterization of diffusion of drug from the AAO nanoporous pore diameter and depth was carried out using by HPLC (high performance liquid chromatography).

Abstract: Polymer derived ceramic composites have been developed for SOFC seals. The formation and properties of the ceramic composite derived from a mixture with polysiloxane and filler were investigated. In the presence of filler materials such as ZrO2 and AlCo, the thermal properties of the ceramic composite could be controlled. The mixtures with polymethylsiloxane and fillers were prepared and their conversions to ceramic composites by annealing in N2 atmosphere were studied. The microcrystalline composites with filler embedded in a silicon-boron-oxycarbide glass matrix were formed. The thermal expansion behaviors were measured and discussed.

Abstract: The carbothermal reduction synthesis process of titanium diboride (TiB2) particles was studied. In the synthesis of TiB2 using carbothermal reduction from a mixture of TiO2, B2O3 and carbon, solid-solid reactions occur. TiO2 particles rapidly react with carbon to TiC, which then reacts with boron oxide and carbon to TiB2. In the vacuum condition, TiB2 particles were formed within 10 minutes at temperature of 1300oC. It seems that a high exothermic reaction eventually results in the increase of reaction rate. In flowing argon atmosphere, TiB2 particles were formed at temperature of 1550oC after a reaction of 0 minute and it showed a finer particle size than that in the vacuum condition. This is attributed to the faster heat elimination due to the flowing argon. In high atmospheric pressure of argon gas such as 20 atm in reaction or cooling state, the synthesized TiB2 particles shows a mixture of diverse sized particles.

Abstract: Synthesis of nano TiC powder by carbothermal reduction procedure of TiO2 was investigated. TiO2 was mixed with resin or carbon powder as reduction agent and was reacted at 1500oC for 0 ~ 45 minutes under Ar atmosphere. Conglomeration of the powders mixed with TiO2 and resin were observed in the initial stage of the reduction and the unreacted TiO2 was not found even after 5 minutes elapsed. The fine TiC particles with a size of 80 nm were formed by complete reaction between Ti, a reduction product, and C after 15 minutes. However, the conglomerated particles were not the powders added with carbon powder as carbon source in the initial stage. The unreacted TiO2 particles were kept for 15 minutes. Finally, TiC particles were formed and were partially grown after 20 minutes.

Abstract: Ceramic foams containing MoSi2 were prepared by a self-blowing process of poly-silsesquioxane with MoSi2 as filler. Ceramic foams prepared by polymer pyrolysis were composed of MoSi2 and silicon oxycarbide glass matrix. Densities, pore sizes and mechanical properties of ceramic foams were depended on the filler content and heating rate for curing of polymer. Depending on the foaming condition, ceramic foams with a density of 1.2∼0.4 and a compressive strength of 3∼30 MPa were obtained.

Abstract: The sintering of TiB2 was limited due to its high degree of covalent bonding and low self diffusion coefficient. To solve this problem, hot pressing has been used for fabricating TiB2 ceramics, but this process was expensive and limited to the production of simple shapes. Pressureless sintering has also been studied, but its sintering temperatures is, as high as more than 2000°C, resulting in exaggerated grain growth and decrease of mechanical properties. The addition of SiC was found to be effective in improving the densification. However, a supplementary HIP process was needed to enhance the mechanical properties. In this study, the densification behavior and microstructural change of TiB2 ceramics infiltrated by the polycarbosilane of SiC precusor were investigated. The infiltrated polycarbosilane was converted to SiC during heating and densification was accelerated.