Influence of Seeding on the Reaction Sintering of Silicon Oxynitride

Abstract

The relationships among reaction rate, densification behavior and microstructure development were examined for seeded or unseeded silicon oxynitride ceramics prepared from Si3N4, SiO2 and a small amount of CeO2. The reaction rate of silicon oxynitride without seed crystals was very low during the initial stage, because the nucleation was the rate-determining step for lack of favorable nucleation sites. The formation of silicon oxynitride was promoted by seeding. With the addition of seed crystals, the nucleation was almost terminated at the beginning of the reaction. Therefore, the formation of silicon oxynitride proceeded only by the growth of the nuclei originated at the beginning. The addition of a large amount of seed crystals, however, resulted in suppressed densification, because too many rod-shaped silicon oxynitride grains were formed in the initial stage.