Ferrosilicon

Ferrosilicons with silicon content up to about 15% are made in blast furnaces lined with acid fire bricks.

The melting point and density of ferrosilicon depends on its silicon content, with two nearly-eutectic areas, one near Fe2Si and second spanning FeSi2-FeSi3 composition range.

Ferrosilicon is used as a source of silicon to reduce metals from their oxides and to deoxidize steel and other ferrous alloys.

This prevents the loss of carbon from the molten steel (so called blocking the heat); ferromanganese, spiegeleisen, calcium silicides, and many other materials are used for the same purpose.

Magnesium ferrosilicon is instrumental in the formation of nodules, which give ductile iron its flexible property.

Prior to this, the process and purity of hydrogen generation relying on steam passing over hot iron was difficult to control.

While in the "silicol" process, a heavy steel pressure vessel is filled with sodium hydroxide and ferrosilicon, and upon closing, a controlled amount of water is added; the dissolving of the hydroxide heats the mixture to about 200 °F (93 °C) and starts the reaction; sodium silicate, hydrogen and steam are produced.