Characterization of concentrated dispersions with several dispersed phasesby means of acoustic spectroscopy

Acoustic attenuation spectroscopy can characterize the particle size distri bution (PSD) of mixed concentrated dispersions, i.e., systems having more t han one dispersed phase. In this paper, we will suggest two models that can be particularly helpful for describing such mixed dispersions. The first m ultiphase" model assumes that we can represent the PSD of a real-world disp ersion as a sum of separate log-normal distributions, one for each componen t in the mixed system. For this paper we assume that there are but two comp onents, which reduces the overall PSD to a simple bimodal distribution. The second "effective medium" model further assumes that one needs to determin e the PSD of just one component in an otherwise complex mixed, system. All other disperse phases are lumped together into an effective homogeneous med ium characterized by some composite density, viscosity and acoustic propert ies. By adopting this viewpoint, we significantly reduce a complex real-wor ld mixture to a simpler dispersion of a single pre-selected dispersed phase in a newly defined "effective medium". We need not even define the exact n ature and composition of this new medium since we can simply measure, or pe rhaps calculate, the required composite density, viscosity, attenuation, an d sound speed. The "multiphase" model is most suitable for samples where it is desired to measure the PSD for more than one well-characterized dispers e phase. In contrast, the effective medium model is particularly useful whe re it is desired to measure only one component in a complex poorly defined multicomponent mixture. Experimental results are presented for five differe nt mixtures including alumina, zirconia, silica, and calcium carbonate mate rials. These tests demonstrate that the mathematical complexity of the "mul tiphase" model often leads to the familiar "multiple solution problem" wher eas the "effective medium" approach is more reliable and robust. Furthermor e, the "verification" approach reveals an aggregation phenomena in the PCC- silica mixed dispersion.