Influence of Shear Rate on Thixotropic Suspensions

Abstract

The thixotropic type of a suspension can be specified by first shearing the suspension at high shear rate to destroy the structure of the suspension, then monitoring the change of the viscosity or stress with time under low shear (D l), i.e., to study the process of structure recovery. The shear history and D l can influence the recovery process, so they have an influence on the thixotropic type of a suspension. In this paper, the influence of D l on the thixotropy of Fe–Al–Mg‐mixed metal hydroxide (MMH for short)/Na‐montmorillonite (MT for short) suspensions is reported. The system with a weight ratio (R) of MMH/MT of 0 and with R = 0.013 both show positive thixotropy in the D 1 range of 10–1022 s−1, i.e., D l does not change the thixotropic type of the suspensions. The suspension with R = 0.051 shows complex thixotropy under lower D l values (10 and 170 s−1), but shows positive thixotropy under higher D l values (511 and 1022 s−1). The system with R = 0.091 shows negative thixotropy at lower D l values (10 and 170 s−1), but shows complex thixotropy at higher D l values (511 and 1022 s−1). With increasing D l, the viscosity of these suspensions decreases gradually, and the degree of change in η ∼ t slows down, i.e., the thixotropic strength becomes weak. The mechanism for these changes is discussed.