Microstructural development of Si3N4-SiC-Y2O3 ceramics derived from polymeric precursors

[Si-Y-O-C-N] amorphous powders were synthesized by the pyrolysis at 1000 degrees C in N-2 of chemically modified perhydropolysilazane using n-decyl alcohol and yttrium tri-methoxide. [Si-Y-O-C-N] amorphous powders yielded a unique fibrous microstructure by heat treatment in N-2 at 1800 degrees C. The fibrous microstructure was composed of beta-Si3N4 whiskers of submicron in diameter and more than 10 mu m in length. Fully dense Si3N4-SiC-Y2O3 ceramics were also fabricated by heat treatment at 1800 degrees C followed by powder-vehicle hot pressing at 1700 degrees C. After these two-step processings, [Si-Y-O-C-N] amorphous powders yielded a unique fine-grained microstructure composed of submicron grains with high aspect ratio.