Ultrasonic velocity and attenuation in aqueous kaolin dispersions

Abstract

Near field measurements of ultrasonic compressional wave attenuation (α) and velocity ( c) in aqueous kaolin clay dispersions are presented. The dependence of these parameters on the clay volume fraction (in the range 0 to 0.3) and frequency (in the range 1 to 5 MHz) is examined. The velocity measured has been compared with the theoretical expressions due to Urick, Ament, and Gibson and Toksőz. It is shown that when particle size and ultrasonic viscous skin depth are of similar magnitude, the particle eccentricity must be taken into account to reconcile theory and experiment. Predictions for the volume fraction dependence of attenuation due to Urick, Hovem, and Gibson and Toksőz have been compared with the experimental data. The Urick theory and the low frequency approximation of Hovem's expression show qualitative agreement with the experimental data up to a solid volume fraction of about 0.1 and 0.3, respectively. At high frequencies, when the viscous skin depth is small relative to particle size, the application of a correction function to the Stokes' drag force on the suspended particles greatly improves the agreement between experiment and the Gibson and Toksőz theory.