AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Accounting for the Variable Df during Coagulation and Sintering of Fractal-like Particles
Eirini Goudeli, MAX L. EGGERSDORFER, Sotiris E. Pratsinis, ETH Zurich
Abstract Number: 146 Working Group: Nanoparticles and Materials Synthesis
Abstract Nanoparticle formation by coagulation in atmospheric and industrial systems typically results in fractal-like structures. Though the asymptotic form of such structures is described well with the so-called fractal dimension, D$_f, little is known for the D$_f evolution, from that of initially tiny spheres (D$_f=3) to that of large fractal-like aerosol particles (D$_f=1.9-2.1). In simulating such aerosol dynamics, usually the evolution of D$_f is neglected or simplified with a constant D$_f. Here, the effect of evolving structure on primary particle, d$_p, and collision diameters, d$_c, of fractal-like TiO$_2 particles is explored non-isothermally accounting for simultaneous coagulation and sintering over the entire process parameter space, from laboratory to industrial scale conditions by intefacing molecular dynamics, mesocale and continuum models. The evolution of agglomerate morphology is presented for varying D$_f based on mesoscale simulations (Schmid et al. 2006; Eggersdorfer et al. 2011) as well as constant and arbitrarily-varying D$_f (Artelt et al. 2003) using the characteristic sintering time of rutile from molecular dynamics (Buesser et al., 2011). The effect of process conditions, such as maximum temperature, cooling rate and initial precursor volume fraction on d$_p, hard- and soft-dc are investigated. Accounting for the D$_f evolution does not affect the asymptotic d$_p and d$_c compared to those obtained assuming constant D$_f. Neglecting, however, the D$_f evolution overpredicts the d$_c up to 30% during the hard- to soft-agglomerate transformation even though d$_p is not affected. A similar analysis is performed for amorphous SiO$_2 and compared to that of titania.
Artelt, C., Schmid, H-J. and Peukert W. (2003) J. Aerosol Sci. 34:511.
Buesser, B., Gröhn, A. J. and Pratsinis, S. E. (2011) J.Phys. Chem. C 115: 11030.
Eggersdorfer, M.L., Kadau, D., Herrmann, H.J. and Pratsinis, S.E. (2011) Langmuir 27:6358.
Schmid, H-J., Al-Zaitone, B., Artelt, C. and Peukert, W. (2006) Chem. Eng. Sci. 61:293.