Fabrication of Porous Si3N4-Lu2Si2O7 Composite Ceramics

To improve the corrosion resistance of porous Si3N4 used in the high temperature environments, which contain water vapor and volatile species, porous Si3N4-Lu2Si2O7 composite ceramics were fabricated by a process of oxidation bonding and pressureless sintering in flowing N-2 atmosphere at the temperatures lower than 1550 degrees C. The pores in ceramics were formed by removing the pore-forming agent (phenolic resin). SiO2 derived by the oxidation of Si3N4 at 1250 degrees C in air reacted with Lu2O3 at various sintering temperatures, leading to the formation of Lu2Si2O7 with excellent oxidation and corrosion resistance. The phase composition, microstructure, and mechanical properties of the porous ceramics depended on the sintering temperatures. Si3N4-Lu2Si2O7 composite ceramics with the porosity of 52% and the pore size of 0.2 mu m were obtained by oxidation bonding at 1250 degrees C for 1 h and pressureless sintering at 1550 degrees C for 2 h using 4 wt pct Lu2O3 additive.