Investigations on thermal reactivity of Si/C/N nanopowders produced by laser aerosol or gas interactions

Ultrafine SiCN particles with various compositions, synthesised by laser pyrolysis in interaction either with gaseous or liquid reactant, were heat treated at temperatures between 300 and1773 K. Thermogravimetric measurements performed under inert (helium) atmosphere, showed that the best thermal stability was exhibited by nanopowders prepared from gaseous precursors (SiH4, CH3NH2, NH3). Mass spectrometry analysis data revealed that nanopowders derived from a mixture with ammonia and hexamethyldisilazane (HMDS) contained more N-H and C-N groups than those obtained without ammonia. The loss of hydrogen clearly dominated amongst the observed losses in all the examined samples at all temperatures. This study indicates that thermal degradation of such silicon based systems is not a single reaction but the net result of a number of reactions.