FLOW PROPERTIES AND YIELD STRESSES OF DILUTE SODIUM-MONTMORILLONITE SUSPENSIONS

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Montmorillonite is noted for its expansive properties and characteristics that whose suspension exhibit a certain yield stress even in dilute state. In general, yield stress is regarded as a criterion whether continuous network of particles arise or not, and its strength is the measure of an interaction between clay particles and their flocs. In this study, flow curves, namely, relationships between shear rates and shear stresses of montmorillonite suspensions were observed with use of cone-plate viscometer.Then a slight yield stress was confirmed for suspension whose solid ratio was 1.0% on the volume basis. When estimating yield stresses τ_0 [Pa] as a function of solid ratio φ_s [%], their dependence proved to be markedly high, and expressed as τ_0 ∝ φ_s^<7.24>. However, usual uniform floc models fail to explain this high dependence, because this model leads to the power law approximately as τ_0 ∝ φ_s^5 at most. In order to solve this discrepancy, self-similar floc model is newly proposed. This model is based on the assumption that each n th order spherical floc is composed of the same L pieces of (n-1)th order flocs. Here diameter ratio of n th to (n-1)th is m, shown in Fig. 4. When compared with the calculated values on this model, experimental tendencies of yield stresses would be realized by the step up of the order of self-similar degree from two to three, with increase in solid ratio from 1% to 2%.
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