Ferrosilicon, or ferrosilicium, is a ferroalloy an alloy of
iron and silicon with between 15 and 90% silicon. It
contains a high proportion of iron silicides. Its melting point is
about 1200 °C to 1250 °C with a boiling point of 2355 °C. It also
contains about 1 to 2% of calcium and aluminium.
Ferrosilicon is produced by reduction of silica or sand
with coke in presence of scrap iron, millscale, or other source of
iron. Ferrosilicons with silicon content up to about 15% are made
in blast furnaces lined with acid fire bricks.
Ferrosilicons with higher silicon content are made in electric arc
furnaces. An overabundance of silica is used to prevent formation
of silicon carbide. Microsilica is a useful byproduct. The usual
formulations on the market are ferrosilicons with 15, 45, 75, and
90% of silicon. The remainder is iron, with about 2% of other
elements like aluminium and calcium.