Amorphous silicon dioxide, or micro silica, or silicon fume, is a byproduct of the silicon metal and ferrosilicon industries. It is produced as a gas in submerged electrical arc furnaces during the reduction of extremely pure quartz. A silica-based gas is released as the metal becomes molten. As this gaseous fume rises, it rapidly cools and condenses into incredibly tiny, amorphous, spherical particles. A bag house, a mechanism for filtering the hot air and gases discharged from the furnace, is where the microsilica is gathered. This gas vapour condenses into a very fine powder with spherical particles that range in size from 0.1 to 0.3 microns and have a surface area of 17 to 30 m2/g in bag house collectors.
Micro silica is added to Portland cement concrete to improve its properties, particularly its compressive strength, bond strength, and abrasion resistance. These advantages result from pozzolanic interactions between the free calcium hydroxide and silica fume in the paste as well as from the addition of a very fine powder, which improves the cement paste's mechanical properties.