Effects of salt concentration on the yield stress of sodium montmorillonite suspension

The yield stress of Na-montmorillonite suspension in an electrostatically dispersed state was studied to confirm the validity of previously proposed equation for the dependency of the yield stress on the volume fraction of clay and ionic strength. In the derivation of the equation, it is assumed that (1) clay layers array in parallel, and (2) the yield stress is equivalent to the strength of electrostatic repulsion when it reaches the yield stress. Measurements of the yield stress were performed with the vane method, varying the volume fraction of clay, ϕ, under controlled ionic strength for the region of 0.008<ϕ<0.023 and 10−2