Abstract : Many industrial processes involve solid-liquid suspensions (i.e.:paintings). These suspensions, initially made up of solid primary particles, contain many aggregates which modify their properties of use. The characterization methods of these suspensions use the scattering light (Mie theory). However, the Mie theory (1908) is seldom applicable to the practical problems since the scattering object must be a sphere. The traditional granulometers which use this theory do not make it possible to measure the aggregates. An extension of the latter, to the aggregates, was given by Xu (1995-2003): GMM (Generalized Multiparticle Mie solution). But the computing times of the optical properties via this exact theory do not make it possible to consider a use in real time in the immediate future. The PhD subject was thus directed towards the search of approximated methods for the optical properties of spherical non-absorbent aggregated particles.
Initially, the study of the parameters influencing, scattering (Csca) and the radiation pressure (Cpr), cross section of aggregates obtained with the exact method, revealed that:
- various aggregate configurations, following its form or the number of primary particles which it contains, are perfectly discernible,
- the number of primary particles is the relevant parameter in the case of the weak size parameters ( )
- there exists, for an aggregate made up of a given number of primary particles, two extreme configurations (linear and compacts) between which the cross sections of the others evolve.
Thereafter, it was evaluated with respect to the exact method, seven approximated methods (selected according to the preceding remarks) making it possible to obtain the scattering cross section:
- the methods assimilating the aggregate to a compact sphere (CS) or porous (PS) are inappropriate
- the methods using a fractal dimension are as for them not very conclusive on aggregates containing a low number of primary particles.
- the PBK (Percival-Berry-Khlebtsov) method is valid for 0