Papers by Author: Yung Jen Lin

Abstract: Bio-structured carbon was obtained by carbonization of rattan in Ar. Then, the charcoal was reacted with Si at 1500 °C to form SiC. It was also reacted with Si and 2024 aluminum alloy at 1400°C for various times to form composites. The results showed that the SiC was beta phase and had the structure of rattan. SiC whiskers were also found on the inner surfaces of the pore channels (vessels) of rattan structure. The bulk density of the porous SiC was 1.5 g/cm3 and its open porosity was 44%. On the other hand, the charcoal embedded in Si powder and 2024 alloy was converted into SiC/aluminum-silicon composite after heat treatment. The charcoal was reacted to form SiC first. Then, Al-Si alloy infiltrated into the pores of the porous SiC to form composites. When the alloy composition was Al-20 at% Si, the composite obtained after 5 hours of reaction had bulk density of 2.3 g/cm3, open porosity of 19%, compressive strength of 316 MPa and bending strength of 138 MPa.

Abstract: Copper and 2024 aluminum alloy were melt-infiltrated into porous β-SiC to form SiC/Cu and SiC/Al composites. The porous β-SiC was prepared using Moso bamboo as the bio-template and had structural characteristics of bamboo. The Cu infiltration occurred as low as 1100°C and became significant at 1200°C. After infiltration at 1300°C for 4 h, there was still ~5 % of residual porosity. For the composites with low degree of metal infiltration, the samples fractured like the bamboo-structured porous SiC. For the composites with high degree of infiltration, the sample behaved like monolithic copper. In the infiltration of Al alloy, infiltration occurred at 900°C. Higher Infiltration temperatures would result in significant formation of Al4C3, which gradually decomposed in air.

Abstract: Carbon fibers of ~9 μ m in diameter were used as templates to fabricate alumina and silicon carbide fibers. The carbon fibers were placed in a vacuum furnace with aluminum and heated at 1100°C for 8 h to form aluminum carbide. Then, the aluminum carbide fibers were oxidized in air at 1500°C. The resulted fibers were hollow and the alumina layer was porous in the interior. To fabricate silicon carbide fiber, carbon fibers were reacted with Si at 1300°C -1500°C in Ar. The thickness of silicon carbide layers increased with reaction temperature and reaction time. Solid fibers could be obtained after reaction at 1400°C for 4 h. In contrast to porous alumina layer, the silicon carbide layer/fibers were dense. The porous alumina hollow fibers were fragile while the solid silicon carbide fibers were flexible. BET surface area measurements revealed that the porous alumina had surface area as high as ~100 m2/g.

Abstract: Alumina/glass composites were successfully fabricated by melt-infiltration of glass into porous alumina pellets. Alumina powder was first pressed uniaxially at 100MPa to form disc-shaped pellets, then, heated up to 1200°C for 2 h to form porous pellets with moderate strength for subsequent infiltration. A mixture of calcium aluminosilicate and magnesium borosilicate glass powders were melt-infiltrated into porous alumina at 1200°C ~1250°C by capillary pressure to form composites. The infiltration depths varied with the square root of infiltration time. And the activation energy of the infiltration process was estimated to be 621 KJ/mole. After complete infiltration, the composite had bulk density approaching 3.3 g/cm3 (~ 96% of theoretical density) and open porosity reaching zero, with slight expansion of 0.5% in diameter. Its flexural strength was 150MPa and its Vickers microhardness was about 1000 Kg/mm2.