Free flow with AEROSIL® fumed silica

The flowability of a powder is determined by interparticular attractive forces on the one hand and gravity on the other hand. In all powders so-called Van-der-Waals-forces are present, attracting the particles to each other. These forces are the more important the smaller the particles are. Therefore fine powders usually show inferior flow properties than coarse granules.

Besides this there are some more possible reasons for a bad flow: Liquid on the surface of powder particles, which may be water or oil (e.g. in hygroscopic or fatty powders) keeps them together by surface tension. In the worst case, the powder particles even may glue together. Uneven particle shapes may lead to hooking, and some powders may stick to the walls of a pipe or blender by electrostatic charging.

AEROSIL^® fumed silica consists of extremely fine silica particles that can cover the particles of the powder which is treated. The silica acts as a distance holder between the particles of the treated powder, keeping them apart and, thus, reducing the attractive forces. Furthermore hydrophilic AEROSIL^® fumed silica can absorb moisture from the surface and avoid liquid bridging.

For extremely hygroscopic powders hydrophobic AEROSIL^® grades are even more effective. Due to their water repellence they float on the powder particles with the water layer. Thus, they build a barrier between the individual particles avoiding water bridging.

Especially AEROXIDE^® Alu C can reduce significantly electrostatic charging of a powder.