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Pourable or “flowable” powders are easier to dose precisely, handle, and process, a phenomenon familiar to us through our day-to-day use of table salt, which should flow freely from the saltshaker. The effect is especially important in automated processes, where a spice blend, for instance, can be improved to such an extent through the addition of less than 1% AEROSIL® 200 F that it can be dispensed evenly on potato chips. In many instances, flowability at any given moment is not the only issue—preventing clumps while in storage is a concern as well, and in these cases we also speak of anticaking. Evonik has the right flow enhancer for virtually any powder. Our applied technology will be glad to assist you further.
The flowability of powders is influenced by cohesive forces between the powder particles—the finer the powder, the more powerful the cohesive forces. For this reason, finely divided powders do not flow as well as coarse ones. A film of liquid on the surface of powder particles (as occurs in damp or oil-containing powders) can also hold particles together via surface tension. SIPERNAT® and AEROSIL® products consist of fine silica agglomerates that form an envelope surrounding the particles of the powder being treated. Their function here is to preserve some distance between individual powder particles, separating them from each other and thereby minimizing the cohesive forces. They can also absorb any liquid film that may be present.
Finely divided SIPERNAT® and AEROSIL® products can be worked into the powder to be treated—referred to as the “host powder”—through a simple mixing process. Suitable mixers include plowshare mixers, paddle mixers, and ribbon blenders. Whereas we recommend a quick but intense mixing process for dry host powders, damp host powders need to be blended especially gently. This will retain the porous structure of the silica and optimize the absorption of liquid from the powder.
Examples can be found in the food and animal feed industries, where powdered ingredients need to be dispensed evenly. Other examples include processing for industrial chemicals, polymer powders processed using automated methods, the pharmaceutical industry, where the tableting process has to be uniform, and many others.
Detailed information on this subject can be found in the following technical information sheets: TI 1213, TI 1351, TI 1360, and TI 1365. more