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spectroscopy (PCS) [32]. PCS measures the diffusion coefficient, which is
subsequently recalculated into the particle size of a solid sphere using the well-known
Stokes-Einstein-Equation. Hence, for irregular pyrogenic silica aggregates a diffusion-
equivalent hydrodynamic solid sphere diameter is obtained. In Fig. 11 the evolution of
hydrodynamic equivalent diameter of pyrogenic silica with increasing specific surface
area is depicted. A clear decrease of aggregates size with increasing specific surface
area can be observed.
Figure 11:
Evolution of hydrodynamic equivalent diameter of pyrogenic silica with
increasing specific surface area. Measurement was performed in epoxy resins RIM
135 at 80 °C.
Pyrogenic silica agglomerates are situated in a size range > 1 μm. A FE-SEM
micrograph of a pyrogenic silica agglomerate is depicted in Fig. 12.
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