Fabrication of porous SiC ceramics using glass beads

Porous SiC ceramics have been fabricated by using SiO₂-Al₂O₃ based glass beads. SiC powder with the average grain size of 0.6 μm was mixed with 5-20 wt.% glass beads by dry mixing. The average particle size of the glass beads was about 45 μm. The mixed powder was compressed into plate form and sintered at 1970°C for 2 hours in Ar atmosphere. The resultant materials had porosities ranging from 25 to 50%. Large spherical pores connecting through micro-sized open pores were observed in their microstructures. It has been concluded that the occurrence of open pores was originated in the formation of gas phase through the reaction, SiC+2SiO₂→3SiO(g)+CO(g), in Ar atmosphere. The alumina element in the glass beads contributed to the densification of SiC matrix through the formation of liquid phase and as a result, the materials had high bending strength in spite of their high porosity.