Synthetic Amorphous Silica (SAS)
SASs are white, fluffy powders or milky-white dispersions of these powders (usually in water). SASs are hydrophilic, but can be made hydrophobic by surface treatment. SASs are produced by the wet route (precipitated silica, silica gel) or the thermal route (pyrogenic silica).
Silicon ranks next to oxygen in abundance in the earth’s crust in the form of silicate minerals. Crystalline and/or amorphous silicas are ubiquitous on the earth in soils and sediments, and in living organisms (e.g. diatoms), but only the dissolved form is bioavailable. On a global scale, the level of man-made SAS represents up to 2.4% of the dissolved silica naturally present in the aquatic environment. The rate of SAS released into the environment during the product life cycle is negligible in comparison with the natural flux of silica in the environment.
SASs were commercialized in the 1950s and current worldwide production exceeds 1 Mt/y. SASs are used in a wide variety of industrial applications, including reinforcement and thickening agents in various systems such as elastomers, resins and inks. SAS is also used as a flow aid for powdery coatings and dry toners, in various industrial applications (e.g. thickening of elastomers) and in consumer products (e.g. cosmetics and pharmaceuticals) and as direct food and feed additives, and in beer and wine clarification.