OXIDATION OF CHEMICALLY VAPOR-DEPOSITED SILICON-NITRIDE IN DRY OXYGENAT 1923-K TO 2003-K

Oxidation of chemically vapor-deposited Si3N4 was studied in dry oxyge n between 1923 and 2003 K under a total pressure of 0.1 MPa using a th ermogravimetric technique. At 1923 to 1953 K, a parabolic rate mechani sm prevailed for the oxidation reaction. From 1973 K, the oxidation re action exhibited a mixed linear-parabolic rate mechanism. At 2003 K, o n the other hand, the oxidation of Si3N4 showed a linear behavior. Bot h amorphous silica and cristobalite were identified as reaction produc ts on the oxidized Si3N4 surface using X-ray diffraction analysis. The percentage of cristobalite in the surface oxide scale was determined from the X-ray diffraction pattern. It was found that, at 2003 K, only amorphous silica was formed. The parabolic rate constants (K(p)) obta ined from this study were close to those obtained in the literature.