Observation of Superaggregates from a Reversed Gravity Low-Sooting Flame

摘要

Superaggregates (SAs) are formed due to late stage aggregation occurring near the gelling point of an aggregating system (Dhaubhadel et al. 2006). Percolation theory best describes their formation mechanism (Sorensen and Chakrabarti 2011). SAs have a long-range overall structure described by a fractal dimension D_f ≈ 2.6 and a short-range local structure described by D_f ≈ 1.8 (Sorensen et al. 1998; Sorensen and Chakrabarti 2011). Recently, based on the mechanism of SA formation in an aggregating system, Dhaubhadel and co-workers (Dhaubhadel et al. 2007) carried out enclosed-chamber aerosol aggregation to create "aerosol gels"-a novel material similar in properties to aerogels (Akimov 2003; Lerner 2004). Flame synthesis-which has been shown to be a cost-effective, scalable, and versatile route for large-scale production of nanoscale materials (Ulrich 1984)-is yet to be established as a viable method for production of aerosol gels. An upward-pointing flame system cannot facilitate steady and consistent formation of SAs in its product outflow upstream because of the aggregate fragmentation effects associated with buoyancy-driven flickering and shear stress of the flame's "tipping" front (Shaddix and Smyth 1996).