J. Aerosol Sci. Vol. 29, No. 5/6, pp. 647—659, 1998  1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0021-8502/98 $19.00#0.00 PII: S0021-8502(97)10023-4 FLAME SYNTHESIS OF COMPOSITE CARBON BLACK-FUMED SILICA NANOSTRUCTURED PARTICLES Patrick T. Spicer,* Christian Artelt, Steffen Sanders and Sotiris E. Pratsinis  Department of Chemical Engineering, University of Cincinnati, Cincinnati, OH 45221-0171, U.S.A. * Currently at the Procter and Gamble Company, Este Process Technology Center, 4530 Este Avenue, Cincinnati, OH 45232-1732, U.S.A.  Currently at Hosokawa-Mikron, Welserstr. 9-11, 51149 Koln, Germany  Currently at TU Bergakademic Freiberg, Institut fur Mechanische Verfahrenstechnik, Agricolastr. 1, 0999 Freiberg, Germany (First received 1 April 1997; and in final form 20 October 1997) Abstract—Simultaneous synthesis of SiO  /C nanostructured powders is investigated in a premixed flame aerosol reactor by combustion of acetylene and SiCl  . The powders are found to be composed of SiO  either encapsulated in or partially covered by carbon black. The effect of fuel equivalence ratio () on carbon black yield and specific surface area is presented. High  means fuel-rich flames that result in finer fumed silica though the specific surface area of the composite powder remains virtually unchanged with . The presence of silica enhances the carbon black yield 2—3 times. Applying external electric fields across the flame allows synthesis of nanostructured powders with closely controlled specific surface area and composition. Making composite powders permits application of much higher electric fields than with pure carbon black before field breakdown. Increasing the electric field intensity decreases the specific surface area of the product powder in contrast to that of electrically assisted flame synthesis of pure silica and other oxides.  1998 Elsevier Science Ltd. All rights reserved INTRODUCTION The nearly molecular scale of nanoparticles and their uniquely active surfaces provide a potential basis for the development of innovative engineering technology and consumer applications. As nanoparticle synthesis techniques improve, practical considerations of nanoparticle applications become increasingly important. For example, the simultaneous production of two different nanoparticle materials is a potential pathway for synthesis of nanocomposite particles with unique properties. This type of process could provide new engineering materials as well as eliminate difficult processing steps like powder mixing. Two representative nanostructured particle systems with such potential are also two of the largest volume particulate materials produced in flames by the chemical process industry: carbon black and fumed silica. Formation of carbon black and fumed silica in flames has been studied in detail by Donnet et al. (1993) and Ulrich and Riehl (1982), respectively. In summary, carbon black is formed by nuclei inception and surface growth while fumed silica is formed by chemical reaction and coagulation. Fumed silica and carbon blacks are routinely made in flames on an industrial scale. Carbon black is used, among other applications, to increase the wear resistance of automobile tires. Silica particles also reinforce the structure of rubber, signifi- cantly increasing its strength by forming silica networks within the rubber structure (Hashim et al., 1995; Mandal et al., 1995). Silicas with high specific surface area result in stronger networks (Cochrane and Lin, 1993). The combination of carbon black and silica particles is more effective at reinforcing rubber than carbon black alone, although silica does not disperse as well as carbon black and some carbon black is required for static electricity dissipation (Bomal et al., 1993; Waddell et al., 1993). Carbon black and silica are also precursors for the production of silicon carbide (Murukawa et al., 1987; Vlasova et al., 1993) and opaque silica aerogels (Lee et al., 1995).  Author to whom correspondence should be addressed. 647