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

Abstract
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 CO₂ laser irradiation. At the CEA the first experiments were conducted with hexamethyldisilazane - (CH₃)₃SiNHSi(CH₃)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 CO₂ laser. At laboratory scale up to 100cm³/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).