Sensitivity of sodium kaolinite flocs to weak shearing forces.

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Suspensions of sodium kaolinite flocs were sheared in a rotary-type, programmableviscometer. A sudden, irreversible, loss of shear stress, as recorded by a torsion spring attached to a bell-shaped rotor, indicated that a sensitivity to shearing forces occurred at low rates of shear (-25 s<SUP>-1</SUP>). This sensitivity was at a maximumfor a 10% w/w concentration at pH 5.5 and could be reduced by: change of pH or concentration, treatment with ultrasonic vibration, successive cycles of shearing or addition of sodium chloride.<BR>Scanning electron micrographs of flocs revealed a clustering of particles comprised of fine-sized kaolinite plates aggregated face to face. The combination of permanent charge on plate faces and pH dependent charge on edges of the aggregate led to the establishment of a network of clusters that entrained water. This clustering of particles was sensitive to weak shearing forces, much stronger forces would have been required to separate kaolinite plates that were aggregated face to face.
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