Concept

Ferrosilicon

Summary
Ferrosilicon is an alloy of iron and silicon with a typical silicon content by weight of 15–90%. It contains a high proportion of iron silicides. Ferrosilicon is produced by reduction of silica or sand with coke in the presence of iron. Typical sources of iron are scrap iron or millscale. 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. The usual formulations on the market are ferrosilicons with 15%, 45%, 75%, and 90% silicon. The remainder is iron, with about 2% consisting of other elements like aluminium and calcium. An overabundance of silica is used to prevent formation of silicon carbide. Microsilica is a useful byproduct. A mineral perryite is similar to ferrosilicon, with its composition Fe5Si2. In contact with water, ferrosilicon may slowly produce hydrogen. The reaction, which is accelerated in the presence of base, is used for hydrogen production. 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. {| class="wikitable" style="text-align:center;" |+ Physical properties of ferrosilicon |- ! Si mass fraction (%) | 0 || 20 || 35 || 50 || 60 || 80 || 100 |- ! Solidus point (°C) | 1538 || 1200 || 1203 || 1212 || 1207 || 1207 || 1414 |- ! Liquidus point (°C) | 1538 || 1212 || 1410 || 1220 || 1230 || 1360 || 1414 |- ! Density (g/cm3) | 7.87 || 6.76 || 5.65 || 5.1 || 4.27 || 3.44 || 2.33 |} 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. It can be used to make other ferroalloys. Ferrosilicon is also used for manufacture of silicon, corrosion-resistant and high-temperature-resistant ferrous silicon alloys, and silicon steel for electromotors and transformer cores.
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