NANOMETRIC SI-BASED OXIDE POWDERS - SYNTHESIS BY LASER SPRAY-PYROLYSIS AND CHARACTERIZATION

The versatility of the laser synthesis method has been improved during the last few years. In this paper we present the synthesis of amorpho us, nanosized Si/C/O powders obtained via ultrasonic injection of aero sol droplets into the beam of a high-power tunable CO2 laser, using (C H3)(2)Si(OC2H5)(4-x) (0 less than or equal to x less than or equal to 3) and hexamethyldisiloxane as alkoxysilane precursors. All these prec ursors strongly absorb the CO2 laser emission between 9 and II mu m. T he addition of precursors containing Al or Ti in tetraethoxysilane (x = 0) leads to Si,AI or Si,Ti oxide composite powders. The evolution of the powders (chemical composition, crystallization, morphology) durin g heat treatment under air, argon or nitrogen is studied by infra-red absorption, thermogravimetric analysis, transmission electron microsco py and X-ray disfunction. Silica powders with specific surface area up to 500 m(2) g(-1) are obtained when heating in air. (C) 1996 Elsevier Science Limited.