Nanosized Si/C/N composite powders formed by laser-aerosol coupling

Recently it has been shown that ultrafine preceramic Si/C/N powders in the nanometric range can be obtained by combining the ultrasonic injection of a liquid precursor with the CO 2 laser irradiation. At the CEA the first experiments were conducted with hexamethyldisilazane-(CH 3 ) 3 SiNHSi(CH 3 ) 3 - (or HMDS) as the precursor. The aerosol droplets formed by the Pyrosol process are carried out with a flow of argon or argon ammonia mixture into the beam of a high powered industrial continuous wave CO 2 laser. At laboratory scale up to 100cm 3 /hr of liquid are displaced with a conversion efficiency (liquid→powder) of about 45%. The chemical composition is controlled by varying the synthesis conditions. The C/N atomic ratio changes from 3 (under argon) to 0.35 (under argon+ammonia). The as-formed powders are amorphous, monodispersed and nanosized (<100nm). The effect of heating under nitrogen atmosphere has been studied by various diagnostics (chemical analysis, BET, XRD)