Papers by Author: Sea Hoon Lee

Abstract: Single-phase and hexagonal plate-like Al4SiC4 powder was successfully synthesized using a mixture of Al(OH)3, SiO2 and carbon via a carbothermal reduction process. Two-step reaction was compartmentally observed during the calcination; the carbothermal reduction of SiO2 between 1300 and 1600oC and that of Al2O3 above 1500oC. The mechanisms which were responsible for the synthesis of the ternary carbide (Al4SiC4) powder were discussed.

Abstract: Hydrolysis and dispersing behavior of aqueous ZrB2 slurry were investigated. The isoelectric point (IEP) of ZrB2 slurry was measured to be pH 6.3. The acid and base slurry underwent rather rapid change of pH after fabrication for one and three hours, respectively. The oxygen content of the boride powder increased slowly with static ageing time in acid and neutral slurries, while the value decreased in base slurry. Application of poly(ethyleneimine) changed IEP of the boride slurry to pH 10.4. Sedimentation test informed that stability of the slurry was improved when increasing the molecular weight of poly(ethyleneimine) to 70,000 and in acid slurry (pH 3).

Abstract: We report sintering additive systems to decrease the densification temperature of the corrosion resistant AlN-SiC-TiB2 system. Since oxide additives degrade the high temperature properties of the system, and other kinds of metallic additives may affect the formation of protective mullite during oxidation, only the constituent elements were applied as additives. Dense samples ( > 98 % relative density) could be fabricated at 1850 oC and 1900 oC by spark plasma sintering (SPS) and hot pressing method, respectively.