Preparation of silicon nitride fibers by pyrolysis nitridation of polycarbosilance

In this work, PCS cured fibers were pyrolysis nitridation in the ammonia atmosphere for carbon removal and amination, and then condensation/nitridation reaction at high temperature in the nitrogen to produce Si₃N₄ fibers. Results showed that as-prepared Si₃N₄ fibers were colorless and transparent. What was more, the skin of the fiber was smooth and the cross section was rather dense without identifiable defects. This paper also discussed the mechanism of nitridation and the influence of pyrolysis conditions on the structure and properties of Si₃N₄ fibers. The results of FT-IR spectra and elemental analysis showed that the carbon content was extremely low after amination and pyrolysis, which was less than 1%, while the nitrogen content increased with the elevated pyrolysis temperature, and the oxygen content first increased and then decreased with the elevated pyrolysis temperature. The fibers were amorphous when the pyrolysis temperature was less than 1500°C, while the tensile strength reached a maximum at 1300°C. The processes of pyrolysis nitridation were a process of decarburization and ammonification, and then condensation/nitridation at high temperature in the nitrogen, finally producing Si₃N₄ fibers.