What is silica ?

Silica, chemically silicon dioxide, SiO2, occurs naturally, in several forms, the most obvious being sand.

Silica polymorphs ?

Silica, independent of its form and method of preparation (including by-products), is found under CAS Nr. 7631-86-9. However, as the different polymorphs of silica differ in their hazards to human health, it is essential, to distinguish carefully between crystalline silica and synthetic amorphous silica (crystalline-free). The situation can be complicated as natural forms of amorphous silica, unlike synthetic versions, often contain crystalline impurities (up to 65 % cristobalite in the case of calcinations). An overview of silica types and CAS numbers is shown in Figure 1:

Silica tree


What is Synthetic Amorphous Silica ?

Synthetic Amorphous Silica (SAS), EINECS No. 231-545-4, is a form of silicon dioxide (SiO2) that is intentionally manufactured. SAS has been produced and marketed for almost a Century without significant changes in its physicochemical properties. SAS as white dry powders or dispersions is used in a multitude of industrial applications. In addition, it is approved for use in food, cosmetics and pharmaceutical applications. All historic physicochemical and toxicology data remain valid for SAS manufactured today.

SAS is highly pure, crystalline-free, silicon dioxide, SiO2, which may be produced as pyrogenic (also called fumed) silica, precipitated silica and silica gel. SAS products are marketed as dry white powders or dispersions. SAS may sometimes be surface-treated to render it hydrophobic but these specialised products are produced at relatively low tonnage levels compared to the untreated material.

SAS such as precipitated silica, silica gels and pyrogenic (fumed) silica are produced by the members of ASASP in a total volume of 500.000 tons per year.