Fumed silica has a chemical formula SiO2. Silicon Dioxide is a natural compound of silicon and oxygen found mostly in sand. Silica has three main crystalline varieties: quartz, tridymite, and cristobalite. SiO2 are transparent, tasteless crystals found in nature as agate, amethyst, chalcedony, cristobalite, flint, sand, quartz, and tridymite. The compound is insoluble in water or acids except hydrofluoric acid. Silica is most commonly found in nature as sand or quartz, as well as in the cell walls of diatoms. Silica is the most abundant mineral in the Earth's crust.
2H2 + O2 → 2H2O
SiCl4 + 2 H2O → SiO2 + 4HCl
2H2 + O2 + SiCl4 → SiO2 + 4HCl
Fumed silica is manufactured using the reactions above and a continuous flame hydrolysis process of silicon tetrachloride SiCl4. This process converts SiCl4 into the gas phase and reacts quantitatively and spontaneously with the water formed intermediately in an oxyhydrogen flame in order to obtain silicon dioxide.
Fumed silica is generally used as a universal thickening agent and an anticaking agent (free-flow agent) in powders. Like silica gel, it also functions as a desiccant. In the cosmetics industry, it is used for its light-diffusing properties.
Fumed silica is widely used in the paint industry to control rheological characteristics, as anti-setting agent, as thixotropic agent, and to help in the prevention of corrosion and rust.
In dental hygiene product such as toothpaste, it is used as a light abrasive. It is also used in the plastic industry to improve plastics tenacity and strength and also to prevent water absorption.