1. The Dispersion Process

The most frequent application of high speed dispersion is to incorporate extremely fine solid particles into fluids, to produce colloidal suspensions.

Colloidal suspensions are characterised by their behaviour that the finely divided small particles do not settle under the force of gravity. A sequence of related steps take place during the dispersing process. 

These are: 

• the wetting of the surface of the solid particles by the fluid components of the millbase
• the mechanical breakdown of associated particles leading to smaller particles (agglomerates and aggregates)
• the smaller particles generated during the dispersion are stabilised, preventing renewed association (flocculation).

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2. The doughnut effect

The dispersion process is characterised by the rolling flow pattern known as the doughnut effect.

The most effective dispersion takes place in concentrated systems where the impeller tip speed is 18-26m/sec.

The dispersion process is typically completed after 20 minutes
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3. Optimising the dispersion process

It is important for the impeller to be no smaller than 1/3 of the container diameter.   It can be varied to achieve the required rolling flow pattern in the millbase.