Characterisation of colloidal dispersions using ultrasound spectroscopy and multiple-scattering theory inclusive of shear-wave effects

Ultrasonic spectrometry measures the attenuation of a sound wave propagating through a sample. In slurries the ultrasound signal becomes highly attenuated as a function of particle size, concentration and density. To monitor these properties in slurries the attenuation requires interpretation using a mathematical model. We examine different sizes of silica suspended in water, at different concentrations, and frequencies up to 100 MHz. We determine that a new multiple scattering theory inclusive of shear-wave reconversion effects (i.e. conversion of compressional wave to shear wave and back to compressional wave at the particle/liquid boundary) is successful for attenuation prediction in the range up to ≈20MHz and 20% (by volume). Beyond this level the model with shear-effects begins to deviate from the real attenuation, but is still more representative of the experimental results than modelling only an incident compressional wave. Thus, shear-wave reconversion modelling is essential to more accurately reflect the attenuation spectra in a solid particle in suspension system, and dictates the ultrasonic attenuation as particle sizes decrease and concentration increases.