Micro silica (silica fume) is a byproduct from silicon metal or ferrosilicon industries, is an amorphous silicon dioxide – SiO2 which is generated as a gas in submerged electrical arc furnaces during the reduction of very pure quartz. As the molten metal is produced, a silica-based gas is emitted. This gaseous fume, as it rises, cools rapidly and forms extremely minute, amorphous, spherical particles. The micro silica is collected in a bag house, a system for filtering the hot air and gases vented from the furnace. This gas vapor is condensed in bag house collectors as very fine powder of spherical particles that average 0.1 to 0.3 microns in diameter with a surface area of 17 to 30 m2/g.
The main effect of these ultra-fine particles is to greatly improve particle packing and produce a highly pozzolanic reaction in concrete and other cementitious bond systems where the silicon dioxide reacts with calcium hydroxide, heightening performance levels and the strength and durability of these materials.
Additionally, silica fume, because of its amorphous (non-crystalline) structure and its high specific surface area, provides other useful features to various applications, including improved sintering capabilities and enhanced high-temperature performance of refractory castable, resulting in reactions between micro silica and other components of the refractory mix.