Light extinction at agglomerates of spheres--a practical test on the submicroscale

Today's theories applied to the inversion of measurement data from optical measurement devices are restricted to single spherical particles. However, particles formed in industrial processes such as precipitation and crystallization are often nonspherical or agglomerates. Theoretical approaches to describe the optical behavior of such particle systems have already been proposed. The verification of these theories has mostly been done using microwave scattering experiments with agglomerates in the millimeter range. This paper provides a first but surely not all-embracing practical test for a general extension of the Mie theory to agglomerates of submicroscale spheres. For the sake of simplicity and from practical viewpoints of online-sensor development only light extinction of an agglomerated suspension has been examined. The required rigid agglomerates have been produced using a spray-drying method that generates particles with a much higher mechanical stability than can be obtained by the usual procedures. Subsequent fractionation of the suspension delivers systems with only a limited number of agglomerate configurations. Extinction measurements at multiple wavelengths using dynamic extinction spectroscopy have been conducted to determine the extinction cross section of the agglomerated dispersions. These data are compared with computations of agglomerates scattering.