Effect of polysaccharide polymer on sedimentation and rheological behavior of aqueous BaTiO3 suspensions

The gravity-settling and rheological behavior of aqueous barium titanate (BaTiO3) suspensions with a polysaccharide derivative (concentration ranging from 0.5 to 2 wt.% of the powder weight) as a gelling additive have been investigated over a range of solids concentrations (phi = 0.005-0.1). The polysaccharide polymer served as a floc-forming agent for the suspensions when both the polymeric concentration and solids loading exceeded critical levels. As phi greater than or equal to 0.03 at polysaccharide concentration 0.5 wt.%, the particles formed clusters in liquid, resulting in increased settling velocities at initial stage of settling. Collective settling of the particles followed the cluster deposition, in compliance with the formation of a continuous gelled suspension structure as phi was further increased. Strength of the gelled network eventually prevailed over gravity force imposed on the network as phi was increased towards a critical concentration (phi(c)) at which the network ceased to settle. This phi(c) appeared to decrease from 0.1 to 0.03 as the polysaccharide concentration was increased from 0.5 to 2 wt.%. The suspensions showed shear-thinning flow character at low shear rate range (gamma = 1 to similar to100s(-1)), indicative of breakdown of the particle clusters into smaller flow units as shear rate was increased; whilst, the suspensions then changed toward shear thickening as shear rate was further increased (gamma greater than or similar to 100s(-1)). Suspension viscosity was found to increase linearly with the polysaccharide concentration. (C) 2003 Elsevier B.V. All rights reserved.