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 inje ction of a liquid precursor with the CO2 laser irradiation. At the CEA the first experiments were conducted with hexamethyldisilazane - (CH3 )(3)SiNHSi(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 conti nuous wave CO2 laser. At laboratory scale up to 100cm(3)/hr of liquid are displaced with a conversion efficiency (liquid --> powder) of abou t 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, monodis persed and nanosized (<100nm). The effect of heating under nitrogen at mosphere has been studied by various diagnostics (chemical analysis, B ET, XRD).