Aerosol Science 34 (2003) 275–287 www.elsevier.com/locate/jaerosci Impact fragmentation of nanoparticle agglomerates Sonja Froeschke * , Stefanie Kohler, Alfred P. Weber, Gerhard Kasper Institut f ur Mechanische Verfahrenstechnik und Mechanik, Universit at Karlsruhe, Karlsruhe 76128, Germany Received 7 May 2002; received in revised form 8 November 2002; accepted 11 November 2002 Abstract A method of fragmenting nanoparticle agglomerates by impaction from the aerosol phase in a single-stage impactor is described. The degree of fragmentation as a function of impaction velocity is determined by TEM image analysis of impacted agglomerates. Images of unfragmented particles are obtained by diusional deposition in the same apparatus but operated in a dierent way. As an illustration, the method was applied to aerosols of silver, nickel and titanium dioxide agglomerates with primary particle diameters of between 3 and 8:3 nm (Ag), 4 nm (Ni) and 95 nm (TiO 2 ), respectively, for which we determined the inuence of impact energy and primary particle size on fragmentation. For silver, the degree of fragmentation at a given impact energy decreased with primary particle size; at 3 nm hardly any fragmentation was observed. At a given primary particle size, however, the range of energies required for complete fragmentation was found to be relatively narrow, indicating a fairly uniform bond struc- ture. These trends are reected by a model that was devised to calculate bond strength distributions between polydisperse primary particles assuming there are only van-der-Waals interactions. Some measurements were also carried out to investigate potential eects of impact energy on primary particle size. ? 2003 Elsevier Science Ltd. All rights reserved. Keywords: Nanoparticles; Agglomerates; Fragmentation; Impaction; Interparticle forces 1. Introduction The “strength” of an agglomerate particle is mainly determined by the internal coordination num- bers and bond energies between its constituent primaries. These will aect its resistance to break-up under stress and ultimately also determines bulk material properties such as cohesiveness and redispersion of powders. ∗ Corresponding author. Tel.: +49-721-608-6559; fax: +49-721-608-6563. E-mail address: sonja.froeschke@mvm.uni-karlsruhe.de (S. Froeschke). 0021-8502/03/$ - see front matter ? 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0021-8502(02)00185-4