AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Rebound Behavior of Nanoparticle-Agglomerates
MANUEL GENSCH, Alfred P. Weber, TU Clausthal
Abstract Number: 645 Working Group: Aerosol Physics
Abstract The rebound behaviour is described by the coefficient of restitution (COR) which is defined as the ratio of the rebound velocity to the impaction velocity. The COR depends on the adhesion and mechanical properties of the particles and substrate. First, the COR increases when the onset velocity for rebound (v$_(cr)) is exceeded where the kinetic impaction energy is mostly converted to rebound energy, until the particles start to deform plastically which leads to a decrease of the COR. While the understanding of the rebound behavior of single spherical nanoparticles has progressed substantially over the last few years, the rebound characteristics of nanoparticle agglomerates are scarcely studied so far. The aim of this work is to investigate the rebound of differently structured agglomerates and compare it to single particles.
The fraction of bouncing particles is used to determine v$_(cr) and the inset velocity for plastic deformation (i.e. the yield pressure), where the bounced fractions as a function of the impaction velocity are measured in a low pressure impactor.
The experimental results show that for a mica substrate v$_(cr) of single spherical particles scales with the particle size in agreement with theoretical predictions, whereas for a copper substrate a stronger size dependence was found indicating a size dependent COR.
The v$_(cr) of openly structured agglomerates is independent of the agglomerate size and determined by the primary particles. However, absence of rebound is observed when the fragmentation starts before v$_(cr) is reached where the impaction energy is consumed by fragmentation. Closely structured agglomerates show a similar rebound behavior as single spherical particles. But, the maximum bounced fraction occurs at lower impaction energies caused by fragmentation and not by plastic deformation as confirmed TEM analysis.