In situ characterization and structure modification of agglomerated aerosol particles

A method based on the combination of differential mobility analysis with inductively coupled plasma optical emission spectrometry, an epiphaniometer and a condensation particle counter is presented to measure simultaneously and in situ mass, exposed surface and mobility diameter of aerosol agglomerates. The technique was applied to silver agglomerates formed by spark discharge in argon and offered the possibility to determine the exponent Df as well as the proportionality factor A in the power-law relation between agglomerate mass and size. Within the same ensemble of agglomerates, structures with Df ≈ 3 were found below a critical size and low-density fractal-like structures (Df ≈ 1.8) above. A substantial increase in the density of the agglomerates occurred by heating, even in the temperature range where the primary particle size remained unchanged. This increase was due to internal rearrangement leading to a more compact packing, as reflected in an increase of A. In the domain of fractal-like structures, heating resulted in a gradual increase from Df ≈ 1.8 to Df ≈ 3. The restructuring rate (indicated by the changing rate of the fractal dimension) was governed by the temperature and the heating time. The results show that the applied methods have the potential to tailor agglomerate shape in order to match special requirements in the production of agglomerated structures.