Approximation of the light scattering cross section for aggregated non absorbent spherical particles

Powders of metallic oxides (ZrO2, TiO2, Al2O3, SiO2 ...) are used as precursors in ceramic industry or as pigments in paints. Aggregation occurs in the suspension of such particles in water. The most often, the formed aggregates contain few primary particles. The on-line characterization of the suspension is made by spectral turbidimetry, i.e attenuation of a light beam by particles scattering and absorption. In order to analyse the corresponding signal, i.e turbidity, the scattering cross section and anisotropy factor of aggregates are needed. It exists an important literature about the calculation of the light scattering of aggregates. For instance, Xu [1] proposed an exact calculation based on a generalization of the Mie theory. In a previous work [2] we compare the exact value of scattering cross section (Csca) got from Xu’s theory to the corresponding one from the following approximations: Effective Refractive Index (ERI) method, Percival-Berry-Khlebtsov (PBK) method, Anomalous Diffraction (AD) approximation for different aggregates morphology. We conclude that ERI method is the most conclusive over all the size parameter range α∈[0.01; 10] and for the 3 materials. Tested materials are the ones with low (SiO2, m=1.08), intermediate (Al2O3, m=1.32) and high (TiO2, m=1.94) optical contrast in water. In turbidimetry, another relevant parameter is the radiation pressure cross section (Cpr).The topic of this paper is, to extend this work by comparing the Cpr obtained with the exact theory and the one calculated with ERI method.