Flame synthesis of composite carbon black-fumed silica nanostructured particles

Simultaneous synthesis of SiO2/C nanostructured powders is investigated in a premixed flame aerosol reactor by combustion of acetylene and SiCl4. The powders are found to be composed of SiO2 either encapsulated in or partially covered by carbon black. The effect of fuel equivalence ratio (phi) on carbon black yield and specific surface area is presented. High phi means fuel-rich flames that result in finer fumed silica though the specific surface area of the composite powder remains virtually unchanged with phi. 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. (C) 1998 Elsevier Science Ltd. All rights reserved.