FABRICATION OF FIBER-REINFORCED POROUS CERAMICS OF AL2O3-MULLITE AND SIC-MULLITE SYSTEMS

Ceramic fibers and whiskers have been used for modification of toughne ss because they increase fracture energy due to their high elastic mod ulus and strength. The mechanism of this increase is well known to be pull-out, crack deflection and a bridging mechanism. This study focuse d on the increase in toughness, strength and thermal shock resistance when using ceramic fibers in a gas filter for high temperatures. The b asic systems studied were clay bonded SiC-mullite and Al2O3-mullite wi th carbon black (to improve filtering efficiency). The Al2O3-mullite s ystem showed lower porosity (27.45%) and higher strength (131 kg/cm(2) ) than the same system fired in air. The strength was higher than for the SiC-mullite system with the same treatment because df the high sin tering rate. Also, the hot strength at 1000 degrees C was higher than for the SiC-mullite system. Strength degradation was only 14% and 5% a fter thermal shock tests. Resistance to thermal shock was better than the Al2O3-mullite system owing to better thermal shock resistant raw m aterials (like SiC) and the fibrous microstructure. Both systems fired in air showed broader pore size distributions than when fired in a co ke bed.