Deagglomerating wetted clumps

The next stage in the dispersion process is the breakdown of agglomerates. For easily wetted material, penetration of liquid into the voids between particles may provide sufficient force to bring about disintegration. Often however, mechanical energy is required and this is usually introduced by spatulation or stirring, though the use of ultrasonics is now widely practiced. 

For powders that are difficult to disperse, the dispersing liquid (e.g. 0.1% sodium hexametaphosphate in distilled water) may be added to the powder to form a paste. More liquid is added to this paste while it is sheared using a flexible spatula so that it becomes a sluny and eventually a suspension. Care needs to be taken, with this procedure, to ensure that aggregates and particles are not fractured. 

Clumps of particle may contain occluded air that is difficult to displace this is best dealt with by adding the liquid whilst the powder is under vacuum. 

The effect, on dispersion and de-agglomeration in water, of electrostatic repulsion force arising from the surface potential and the double layer 1/x around particles has been investigate. Several suspensions of polystyrene latex in an agglomerated state were prepared where j/ and 1 x were controlled by the pH and electrolyte concentration respectively. These were accelerated in a convergent nozzle to give an external force and the resulting dispersions were examined by optical microscopy. It was found that the dispersion was enhanced with an increase in y/and 1/x. 

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Fig. 3. Typical design elements for wet-in (a)a spinning disk deagglomerates powder just prior to wet-in (b) a rotor breaks clumps as they wet-in, andcentrifugal force helps submerge nonbuoyant powders and (c) a disk impeller provides a rapidly refreshedHquid surface. In (a) and (c), the system may...

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