SILICON-29 MAS-NMR AND ESR STUDY ON THE EFFECT OF HEAT TREATMENT ON THE STRUCTURE OF SiC−Si₃N₄ COMPOSITE ULTRAFINE PARTICLES

The effect of heat treatment on the structure of SiC−Si 3 N 4 composite ultrafine particles was studied by 29 Si MAS-NMR and ESR. 29 Si MAS-NMR and ESR results showed that the local structure changed a little below 1573 K, at which the XRD pattern did not change significantly, but slight increase in crystalline size were observed. When the SiC−Si 3 N 4 powder was heat-treated at 1773 K, most nitrogen atoms dissolved into β-SiC lattice were removed from the β- SiC lattice, and the remaining nitrogens were considered to exist in the boundary layer between SiC crystals as SiC 3 N unit in the particle.