AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Gravity-induced Trapping and Aerogelation of Nanoparticles in Flame Reactors
RAJAN K. CHAKRABARTY, Igor Novosselov, Nicholas Beres, Hans Moosmuller, Chris Sorensen, Christopher Stipe, Desert Research Institute
Abstract Number: 526 Working Group: Aerosol Physics
Abstract Aerogels are volume spanning, semirigid networks of solid nanoparticles (NPs). Owing to their unique material properties such as ultralow density and high surface area, these mesoporous materials have found extensive applications ranging from catching space dusts to purifying air and water supplies. However, aerogel synthesis via the sol-gel process is non-continuous and requires supercritical point drying, hence is time-consuming and expensive. This has prevented their mass production and widespread application. Cost-effective and continuous synthesis routes using gas-phase flame aerosol reactors (FARs), which have been widely adopted by industries for production of nanostructured materials, are yet to be demonstrated as viable options for producing gels. The buoyancy-assisted convection of upward rising (+g) flames in these reactors has prevented achieving sustained high, cluster-dense NP volume fractions fv and greater than millisecond residence time tres as needed for gel synthesis. Here, we report the first experimental realization of continuous aerogel production using a FAR by operating it in negative gravity (-g; up-side-down configuration). Buoyancy opposes the fuel and air flow forces in –g, which eliminates convectional outflow of NPs from the flame and traps them in a distinctive non-tipping, flicker-free, cylindrical flame body, where they grow to millimeter-size aerogel particles and gravitationally fall out. Computational fluid dynamics simulations show that a closed-loop recirculation zone–a deeply metastable state–is set up in the flame wherein NPs experience cluster-dense fv and very long tres. These conditions reduce the time to gel by ≈106 s, compared to +g flames, and facilitate continuous gelation on a millisecond time scale. Our results open up opportunities for continuous and catalyst-free synthesis of a wide variety of aerogels on an industrial scale.