Silica fume is a mineral composed of primary particles < 1 µm of amorphous, non-crystalline, silicon dioxide (SiO2), produced during the manufacture of silicon or ferrosilicon. This tightly controlled electro-metallurgical process involves the carbothermic reduction of quartz in the production of Silicon and FeSi alloys. Silica fume is formed when SiO gas, given off as the quartz is reduced, mixes with oxygen. Here SiO is oxidised to SiO2 condensing into the spherical particles of silica fume, forming the major part of the smoke or fume from the furnace.
At ambient temperature, silica fume is a fine odorless powder with a purity range of 85-98 % depending on raw materials and furnace parameters. The colour varies from white to black, depending on the carbon content.
