AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Mesoscale Simulations of Nanoparticle Growth by Coagulation and Sintering in the Free Molecular Regime
MAX L. EGGERSDORFER, Sotiris E. Pratsinis, ETH Zurich
Abstract Number: 144 Working Group: Aerosol Physics
Abstract Aerosol technology is used routinely in large scale production of commodities like pigmentary titania, carbon black and fumed silica and recently also for sophisticated materials from catalysts to devices and even biomaterials and nutritional products (Strobel and Pratsinis, 2007). The dynamics of aerosol reactors and product nanoparticle characteristics span 10-15 orders of magnitude in length and time scale and require interconnected models for systematic design that can be distinguished into continuum, mesoscale, molecular dynamics and quantum mechanics (Buesser and Pratsinis, 2012). One important, if not the most important, design criterion is the high temperature particle residence time. It determines the nanoparticle growth by gas and surface reaction, coagulation and sintering. Typically the chemistry is so rapid that coagulation and sintering control particle growth.
Here, the formation of nanoparticles by coagulation and sintering is simulated in the free molecular regime by a discrete element method (DEM, mesoscale) at volume fraction, phi=10$^(-7), following the trajectories of up to 16x10$^6 particles. The formation of agglomerates is traced in time to extract the detailed collision frequency. Aggregate sintering is modeled by a multiparticle viscous flow sintering mechanism intrinsically accounting for the primary particle polydispersity and aggregate structure (Eggersdorfer et al., 2011). So the relation between structure, coagulation and sintering rate is fully resolved. It is found that the ratio of characteristic sintering, tau$_s, to collision time, tau$_c, solely defines the aggregate structure independent of process conditions. Modified collision kernels are proposed and applied with continuum models (monodisperse and sectional). Furthermore, detailed aggregate size distributions are studied quantitatively to determine the fractions of spherical particles, aggregates and agglomerates.
Buesser, B. and Pratsinis, S.E. (2012) Annu. Rev. Chem. Biomol. Eng. 3, 103-127.
Eggersdorfer, M.L., Kadau, D., Herrmann, H.J. and Pratsinis, S.E. (2011) Langmuir 27, 6358-6367.
Strobel, R. and Pratsinis, S.E. (2007) J. Mater. Chem. 17, 4743-4756.