NMR AND X-RAY DIFFRACTION STUDIES OF AMORPHOUS AND CRYSTALLIZED PYROLYSIS RESIDUES FROM PRE-CERAMIC POLYMERS

摘要

Si-29 MAS NMR and X-ray diffraction studies are presented of black and white pyrolysis residues obtained by initial 1100 degrees C pyrolyses in N-2 and NH3 atmospheres followed by 1550 degrees C pyrolyses in Ar, N-2 or vacuum atmospheres of a polycarbosilane and four polysilazane precursors to SIC and SI,N, ceramics. Amorphous white pyrolysis residues crystallized under the various conditions to give not only Si3N4 but also Si2N2O, SiC, SiO2 and Si, while black amorphous pyrolysis residues crystallized to form only Si3N4 or SiC. In general, the crystalline ceramic products observed depended on a variety of factors, i.e. moisture sensitivity of polymer, the initial 1100 degrees C pyrolysis gas (N-2/NH3), the dryness of the 1100 degrees C-NH3 pyrolysis gas and the 1550 degrees C pyrolysis atmosphere (N-2, Ar, vacuum). An additional factor of interest affecting product distribution was the choice of crucible (alumina/graphite) employed in the 1550 degrees C pyrolysis. The combined studies suggest that the white amorphous pyrolysis residues are complex silicon oxycarbonitrides (SixNyOzCa),while the amorphous black residues are silicon carbonitrides (SixNyCz). [References: 41]