Papers by Author: Sang Whan Park

Abstract: In this study, we carried out a sol-gel processing to synthesize two types of phenol resin and TEOS sol with fluoric acid as the catalysts, and fabricated the β-SiC powder by carbothermal reduction of the obtained precursor gels. The gels were observed to be cross linked between TEOS and phenol resins by FT-IR and TG-DTA. After pyrolyzed at 1000oC in Ar to obtain the precursor, to confirm the phase transition and morphologies by XRD, and SEM were measured. Finally, the light green colored SiC powder was obtained after carbothermal reduction process up to 1800oC. The residual condensed SiO(v) phase and free carbons as a role of impurities for final products using the solid type phenol resin was observed in the surface of powder by BSE.

Abstract: Bulk Ti3(Al1-nGen)C2 (n=0, 0.3, 0.5, 0.7, 1.0)were synthesized by a reactive hot pressing of TiCX (x=0.6), Al and Ge powder mixture at 1400 °C for 1 h under 25 MPa. A series of Ti3(Al1-nGen)C2 was successfully synthesised by a hot pressing through a direct liquid-solid reaction between Al-Ge melt and TiCx, and simultaneous densification. Synthesized bulk Ti3(Al1-nGen)C2 was maintained a typical layered structure as shown in other ternary carbide such as Ti3AlC2 and Ti3GeC2. With increasing Al or Ge contents in Ti3(Al1-nGen)C2, both of Vickers hardness and flexural strength of Ti3(Al1-nGen)C2 were increased compared to those of pure Ti3AlC2 and Ti3GeC2 . The maximum flexural strength of Ti3(Al1-nGen)C2 (n=0.3) was about 600 MPa, which was about 3 times higher than that of pure Ti3GeC2. The Vickers hardnesses of Ti3(Al1-nGen)C2 and Ti3AlC2 were slightly decreased with increasing an indentation load.

Abstract: In this paper, we present results of an investigation on the physical, mechanical, chemical properties and processing ability of the Cr2AlC ternary carbide bulk material synthesized by hot pressing technique. The combination of excellent properties indicated that Cr2AlC ternary carbide alloy could be potential candidate materials as bipolar plates in polymer membrane fuel cell (PEMFC).

Abstract: Cr2AlC, one of the ternary carbide families, was synthesized by a reactive hot pressing of CrCx (x=0.5) and Al powder mixture used as starting materials at the temperature range of 1200 oC~1400 oC under 25 MPa in Ar atmosphere. Fully dense Cr2AlC with high purity was synthesized by hot pressing CrCx and Al powder mixture at the temperature as low as 1200 oC. After synthesizing the bulk Cr2AlC, it was found that it has a typical layered structure as found in other ternary carbides such as Ti3AlC2 and Ti3SiC2. The average grain size of synthesized bulk Cr2AlC was varied in the range of 10-100 ㎛ depending on hot pressing temperatures. The Vickers hardness of bulk Cr2AlC was less than 4 GPa under the loading of 10N and this decreased with increasing indentation load. The maximum flexural strength of synthesized bulk Cr2AlC exceeded 600 MPa. Also, it was found that synthesized Cr2AlC was readily machinable by a conventional WC tool bit due to its low hardness as well as damage tolerance properties upon fracture.

Abstract: The Ti3SiC2 materials were synthesized by hot pressing TiCx and Si powder mixtures. The matrix grains were lamellar, having a small amount of TiCx. The high-temperature stability was investigated by subjecting Ti3SiC2 to high-temperature oxidation up to 1200oC in air. Ti3SiC2 began to oxidize appreciably above 850oC. The oxidation resulted in the formation of the oxide layer that consisted of TiO2 and SiO2. The scales formed were adherent.

Abstract: Boron carbide is a very hard material with high abrasive wear resistance. It requires a very high sintering temperature of above 2200 oC to fabricate a monolithic B4C close to the theoretical density. However, the mechanical property of monolithic B4C is not good enough to use it directly to industrial applications. In this investigation, B4C based ceramic composites were fabricated by in-situ reaction hot pressing using B4C, TiC and SiC powder as starting materials. The reaction synthesized composites by hot pressing at 1950 oC was found to posses very high relative density. The reaction synthesized B4C composites comprise B4C, TiB2, SiC and graphite by the reaction between TiC and B4C. The newly formed TiB2 and graphite was embedded both inside grain and at grain boundary of B4C. The mechanical properties of reaction synthesized B4C-TiB2- SiC-graphite composites were more enhanced compared to those of monolithic B4C. The flexural strength and fracture toughness of these in-situ B4C synthesized composites were 400-570 MPa and 6-9.5 MPam1/2, respectively.

Abstract: Using the hot pressing method, the Ti3SiC2 materials having fine and coarse grains were synthesized from TiC0.6 and Si powders, and the Ti3AlC2 materials having fine and coarse grains were also synthesized from TiC0.6 and Al powders. The cyclic oxidation between 900 and 1200oC for 40 hr in air resulted in the formation of an outer TiO2 layer and an inner (TiO2+ amorphous SiO2) mixed layer for Ti3SiC2, and the formation of an outer TiO2 layer and an inner (TiO2+ Al2O3) mixed layer for Ti3AlC2. The effect of the grain size on the cyclic oxidation resistance was not significant.

Abstract: Nanosized ITO(indium tin oxide) powders were prepared in ethylene glycol solution under mild temperature and pressure conditions by precipitation from metal nitrates with aqueous potassium hydroxide. The average size and distribution of the synthesized ITO powders were about 20 ㎚ and broad, respectively. The phase of synthesized particles was crystalline reacted at 230 0C for 6 h.. The optical properties of the synthesized ITO powders were transparent.

Abstract: Nanosized ZnxMn1-xFe2O4 powders were prepared in ethylene glycol solution under mild temperature and pressure conditions by precipitation from metal nitrates. The average size and distribution of the synthesized ZnxMn1-xFe2O4 powders were 10- 20 ㎚ and narrow, respectively. The magnetic property of the synthesized ZnxMn1- xFe2O4 powder was of superparamagnetic character at room temperature.

Abstract: The contact fracture behaviors of fine-grained Ti3SiC2 and coarse-grained high purity Ti3SiC2 are examined by the Hertzian indentation and Vickers indentation technique. The Vickers hardness of bulk Ti3SiC2 is as low as 5.3~6.3 Gpa, and the Hertzian contact stress-strain curves for Ti3SiC2 deviate much from linearity, which resembles the fracture behavior of a ductile metal rather than a brittle ceramic. The contact damages by both Vickers indentation and Hertzian indentation reveal a fairly good plastic deformation nature of Ti3SiC2. Un-reacted TiCx in fine-grained Ti3SiC2 may impede the plastic deformation by slip along basal plan inside Ti3SiC2 grain, making Ti3SiC2 less plastic under loading.