IN-SITU CHARACTERIZATION AND STRUCTURE MODIFICATION OF AGGLOMERATED AEROSOL-PARTICLES

A method based on the combination of differential mobility analysis wi th inductively coupled plasma optical emission spectrometry, an epipha niometer and a condensation particle counter is presented to measure s imultaneously and in situ mass, exposed surface and mobility diameter of aerosol agglomerates. The technique was applied to silver agglomera tes formed by spark discharge in argon and offered the possibility to determine the exponent D-f as well as the proportionality factor A in the power-law relation between agglomerate mass and size. Within the s ame ensemble of agglomerates, structures with D-f approximate to 3 wer e found below a critical size and low-density fractal-like structures (D-f approximate to 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 r eflected in an increase of A. In the domain of fractal-like structures , heating resulted in a gradual increase from Df approximate to 1.8 to D-f approximate to 3. The restructuring rate (indicated by the changi ng rate of the fractal dimension) was governed by the temperature and the heating time. The results show that the applied methods have the p otential to tailor agglomerate shape in order to match special require ments in the production of agglomerated structures. Copyright (C) 1996 Elsevier Science Ltd