Abstract

Amorphous silica, a three-dimensional, inorganic polymeric silicon dioxide, SiO₂, does not have a crystalline structure as defined by the absence of definitive lines in X-ray diffraction measurements. Amorphous silica can be naturally occurring or synthetic, and either anhydrous or surface-hydrated with silanol groups. Synthetic amorphous silica can be divided into microamorphous silica and vitreous silica (glass) made by fusing quartz at temperatures greater than ~ 1700°C. A discussion of microamorphous silica is presented, including colloidal silica, ie, sol or stable dispersion of discrete particles; silicas gelled or precipitated from solution; and pyrogenic and fused silica. Amorphous silica is characterized by chemical composition, physical properties, and characteristics of its particles, with exact analytical procedures depending on the type and application. Various methods to prepare and characterize each type of amorphous silica, commercial applications including principal global manufacturers, and health and safety issues are discussed.