The relationship between blend ratio and rheological properties of concentrated suspensions is of great importance since it is the key to get high solid suspensions. The rheological properties of bidisperse aqueous suspensions made of two SiC powders with different particle size [ d (0.5)=1.63 and 18.43 μm, respectively] has been studied as a function of blend ratio ξ (the volume fraction of larger particle size). The results showed that the value of critical blend ratio ξ, at which the viscosity is minimized, is in close relation to the shear rate applied. At shear rates below 10 S −1, the critical ξ was greater than 70%. But at shear rates from 10 to 500 S −1, ξ turned to be 50%. The change of shear region from shear-thinning behavior to shear-thickening behavior may be used to account for the variation of critical ξ. Dynamic oscillatory tests showed that the moduli and the linear viscoelastic region of suspensions with higher ξ are smaller than those with low ξ and the increment of blend ratio ξ leads to the change of suspension from nearly an elastic response to a liquid like response.

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