Low-temperature fabrication of porous β-SiC ceramics in sodium vapor

β-silicon carbide (SiC) porous ceramics were synthesized from pelletized powder mixtures of silicon (Si) and fullerene or Si and amorphous carbon (carbon black) at 1000 K for 24 h in sodium (Na) vapor. The relative density of the ceramics was 29%-34% of the theoretical density of SiC. Scanning electron microscopic observation of the fracture surface showed that the ceramics prepared with fullerene were agglomerates of submicrometer-sized SiC particles and open spaces. The samples prepared with carbon black had a smooth fracture surface with cavities and voids. Using transmission electron microscopy, grains of over 250 nm and a diffuse electron diffraction ring pattern of β-SiC were observed for the sample prepared with fullerene, and grains of 10-20 nm with a β-SiC spot ring pattern for the sample prepared with carbon black. A surface area of 11-17 m²/g and a mesopore size distribution in the range of 2-10 nm were shown by a nitrogen adsorption technique. Energy-dispersive X-ray analysis detected 1-5 at.% of Na against Si on the fracture surface of the ceramics.