Acoustic behavior at the fluid/solid transition of kaolinite suspensions

Abstract

Anomalously high ultrasonic attenuation is observed in kaolinite/water suspensions near 40% solid‐volume concentrations. Within the range of frequencies used (3–7 MHz), the concentration of this loss maximum is nearly independent of wave frequency. Velocity extrema are observed near this same concentration. This behavior is attributed to viscous losses in the oscillating fluid between adjacent particles. At low concentrations (<40%), this mechanism becomes stronger with decreasing interparticle separation and therefore with increasing concentration as well. As particles begin to touch at high concentrations, their oscillatory motion is inhibited and the wave damping decreases. Thus, the loss maximum can be used as a signature of the onset of rigidity in suspensions and colloids. The 40% concentration is consistent with water contents of published Atterberg liquid limits for kaolinite/water mixtures. Full elastic rigidity is not likely to be realized until the two‐phase material achieves a dense particle packing, such as close packing (62% concentration) for well‐sorted particles.

Geophysics at the interface: Response of geophysical properties to solid-fluid, fluid-fluid, and solid-solid interfaces

“…The resulting increase in velocity is generally small at this stage. In contrast, in experiments conducted by Green and Esquivel‐Sirvent [1999] on kaolinite particles suspensions, a peak in P wave attenuation was observed at the point interpreted as corresponding to the transition from a suspension (solid‐fluid interfaces dominate) to a fluid‐saturated granular solid with finite rigidity (solid‐solid interfaces dominate). Because the hydrodynamic coupling depends on the fluid viscosity, the magnitude of the attenuation and the grain concentration at which the peak attenuation occurs are frequency dependent.…”

Acoustic measurements of clay-size particles

“…The mechanical failures in rocks and unconsolidated materials frequently involve clay-rich lithologies. 10 In the sea floor, clays represent 40%-80% of silicate minerals in pelagic sediments. 11 There is also a strong effect of kaolinite content on the acoustic properties in sedimentary rocks and unconsolidated mixtures.…”