What is silica (and what are the differences between the various types of silica)?

Silica is the common name for silicon dioxide (SiO2). In German, it is often called “Kieselsäure” (silicic acid). SiO2 is very common in nature, it gives plants like field horsetail and grass its stability, for example. Evonik produces only synthetic amorphous silica, or SAS. The various types of silica produced by Evonik differ in terms of their characteristic features, such as particle size or surface treatment. This creates different properties for many different applications.

Generally, silica grades that are used as flow and anti-caking agents have very fine particles. They ensure that powders can flow evenly and do not clump together. As opposed to this, carrier silica types are used to absorb liquids and make them powdery. These are usually made from coarse, free flowing particles. These are just two examples – if you look closer, you will realize that silica is part of our everyday lives.

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Silica types with crystalline and amorphous structure are found in nature and are also produced synthetically.
Quartz as it is in rocks or as grains of sand e.g. is a crystalline silica, whereas the silica which is incorporated in plants is amorphous. The structure of this incorporated silica can look very similar to the structure of Synthetic Amorphous Silica (SAS). While crystalline silica has an orderly lattice structure, amorphous silica has a randomized structure. Consequently, it differs from crystalline SiO2 not only in physical terms but also as regards its toxicological properties. There are no hazards associated with amorphous silica.