Fumed silica, also known as pyrogenic silica, is prepared by burning SiCl₄ in an oxygen-rich hydrogen flame to produce a "smoke" of SiO₂. 
It can also be produced by vaporizing quartz sand in a 3000 °C electric arc.
Both processes result in microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles, a white powder with extremely low bulk density (0.03-.15 g/cm³) and thus high surface area.
The particles act as a thixotropic thickening agent, or as an anti-caking agent, and can be treated to make them hydrophilic or hydrophobic for either water or organic liquid applications  
Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production.
It consists of amorphous (non-crystalline) spherical particles with an average particle diameter of 150 nm, without the branching of the pyrogenic product.
The main use is as pozzolanic material for high performance concrete.
Fumed silica, also known as pyrogenic silica, is prepared by burning SiCl₄ in an oxygen-rich hydrogen flame to produce a "smoke" of SiO₂. 
It can also be produced by vaporizing quartz sand in a 3000 °C electric arc. Both processes result in microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles, a white powder with extremely low bulk density (0.03-.15 g/cm³) and thus high surface area. The particles act as a thixotropic thickening agent, or as an anti-caking agent, and can be treated to make them hydrophilic or hydrophobic for either water or organic liquid applications  
Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. It consists of amorphous (non-crystalline) spherical particles with an average particle diameter of 150 nm, without the branching of the pyrogenic product. The main use is as pozzolanic material for high performance concrete.
Silicon dioxide