ABSTRACT

The formation of dispersions from powders can be visualized to involve three stages: wetting of the powder, breaking up of aggregates and agglomerates and reduction of particles to a colloidal size and stabilization of the dispersion. The wetting process has to displace air from the internal surfaces between particles to facilitate breaking of their agglomerates during milling or mixing. The wetting of solid particles with porous surfaces is a complex process involving several primary processes: immersion, adhesion, spreading, and capillary penetration. Wetting of powders, the displacement of a solid-vapor interface with a solid-liquid interface, is an essential step in the dispersion process. The contact angle formed by a drop of liquid resting on the surface of a solid is commonly measured as an indication of wettability. The miscellaneous tests attempting to relate the wettability of powders to their surface tension have demonstrated the complexities involved. The penetration methods describe wettability without the need to compact the powder.