X-RAY-INDUCED AES STUDY OF THE EFFECT OF CHEMICALLY BOUND HYDROGEN ONTHE OXIDATION-KINETICS OF AN SI3N4 POWDER

Silicon nitride powders manufactured by the pyrolysis of silane and am monia were found to contain chemically bound hydrogen. Most of this hy drogen could be removed by vacuum annealing at 1000-degrees-C. In the present study, x-ray-induced AES has been used to determine the oxidat ion kinetics for vacuum-annealed Si3N4 powders that were heated in air at temperatures between 850 and 975-degrees-C. The average oxide thic kness on the surface of the powder particles for each temperature and oxidation time was calculated from the ratio of the SiO2 to Si3N4 Si K LL peak intensities. The results are compared with those for the as-ma nufactured powder, which contained the hydrogen impurity. For both ann ealed and unannealed powder, the oxidation rate was linear within the temperature range 850-1000-degrees-C. Within this temperature range, t he oxidation rate was significantly higher for the vacuum-annealed Si3 N4 powder.