SYNTHESIS AND CHARACTERIZATION OF NANOCOMPOSITE SI/C/N POWDERS BY LASER SPRAY-PYROLYSIS OF HEXAMETHYLDISILAZANE

Ultrafine amorphous Si/C/N powders are obtained using ultrasonic injection of a liquid precursor (hexamethyldisilazane: HMDS) into the beam of a high power industrial cw-CO2 laser. Up to 100 cm3/h of liquid are displaced with a conversion efficiency (liquid --> powder) of about 45%. The chemical composition is controlled by varying the synthesis conditions. Nitrogen-rich powders are produced by adding ammonia in the reaction zone. These pre-ceramic powders are nanosized and monodispersed. The improvements due to the use of liquid precursors are discussed (in particular safely). The effect of annealing under nitrogen atmosphere has been studied by various diagnostics (chemical analysis, BET, XRD).