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In-situ carbon content adjustment in polymer-derived Si/C/N ceramics by reactive heat treatment

Calculations of the pyrolysis product composition
: Galusek, D.; Reschke, S.; Riedel, R.

Silicates industriels 64 (1999), No.1-2, pp.3-7
ISSN: 0037-5225
Journal Article
Fraunhofer INT ()
precursor; polymer pyrolysis; NH3; Si/N(/C); amorphous ceramics; calculations; poly(hydridomethyl)silazanes; polyvinylsilazanes; polymethyldisilazanes

A simplified mechanistic approach has been developed to estimate the range of compositional changes during the reactive heat treatment of different preceramic organosilicon precursors resulting in their conversion to amorphous Si/C/N ceramics. The calculations use the compositions of the respective crosslinked polyilazanes as starting values and combine the conversion degrees of chemical reactions with the highest thermodynamical probability taking part during heat treatment. This approach allows to estimate a processing-dependend stoichiometry of the Si/C/N ceramics, assuming the reactions yield thermodynamically stable equilibrium products. Calculated data are consistent with experimental results and indicate, that the stoichiometry of the product is determined by structure and chemical composition of the polymer rather than by the conditions applied during heat treatment. However, within the restrictions through the chemistry of the polymer, the stoichiometry of the product can be controlled by proper adjustment of the experimental conditions.