CONVERSION MECHANISM OF PERHYDROPOLYSILAZANE INTO SILICON NITRIDE-BASED CERAMICS

The pyrolysis of perhydropolysilazane in anhydrous ammonia has been st udied up to 1000 degrees C through the analysis of the gas phase and t he characterization of the solid residue by thermogravimetric analysis , Fourier transform-infrared analysis, X-ray photoelectron spectroscop y, X-ray diffraction and Si-29 cross-polarization magic angle spinning -nuclear magnetic resonance. The pyrolysis mechanism involves three ma in steps: (1) below 400 degrees C, evaporation of residual solvent; (2 ) from 400-600 degrees C, reaction with ammonia leading to an increase of nitrogen content and formation of preceramic polymer-ceramics inte rmediate solid with a three-dimensional network; (3) from 600-1000 deg rees C, completion of the formation of an amorphous hydrogenated solid with composition close to silicon nitride.