Silica fume, also known as
microsilica, (CAS number 69012-64-2, EINECS number 273-761-1) is an
amorphous (non-crystalline) polymorph of
silicon dioxide,
silica. It is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production and consists of spherical particles with an average particle diameter of 150 nm. The main field of application is as
pozzolanic material for high performance concrete.