Interparticle bond energy and rheological properties of clay suspensions

Abstract

A new method was developed for measuring the heat released when the interparticle bonds in a clay suspension reform after being broken by a shearing stress. In this method, the rotor and cup of a Stormer viscometer were located within one of the microcalorimetric elements of a Calvet microcalorimeter. After filling the annulus between the rotor and cup with a clay suspension and establishing thermal equilibrium, a brake was released and the rotor was activated for a few seconds by a falling weight. The weight was attached to a string that was wound around a drum geared to the rotor. A stopwatch was used to measure the time of shear, i.e., the rotation time, and the microcalorimeter was used to measure the heat generated. In a related experiment, the rheological properties of the suspension were determined with a Fann viscometer. The product of shear stress, shear rate, and time of shear equals the heat dissipated by viscous flow. When the value of this product was substracted from the corresponding value fo the total heat dissipated, the result was the heat dissipated by the formation of bonds that were broken in the process of shear. We calculated an average value for the latter quantity by averaging the results obtained at various combinations of shear stress, shear rate, and time of shear. The procedure-described above was repeated for several suspensions of different clay and electrolyte concentrations. It was found that the heat of bond formation increased in magnitude as the clay concentration increased but decreased in magnitude as the electrolyte concentration increased. Also, it was found that the heat of bond formation was correlated with the extrapolated shear stress of the suspension.