Ferrosilicon is an alloy of iron and

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

. It has a typical silicon content of 15–90% by weight and a high proportion of iron

silicide A silicide is a type of chemical compound that combines silicon and a usually more electropositive element. Silicon is more electropositive than carbon. In terms of their physical properties, silicides are structurally closer to borides than t ...

Production and reactions

Ferrosilicon is produced by reduction of

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

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 furnace A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being supplied above atmospheric pressure. In a ...

s lined with acid

fire brick A fire brick, firebrick, fireclay brick, or refractory brick is a block of ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. Made of primarily oxide materials like silica and alumina in varying ratios, these insulati ...

s. Ferrosilicons with higher silicon content are made in

electric arc furnace An electric arc furnace (EAF) is a Industrial furnace, furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundry, foundries for producin ...

s. 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 Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...

. 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 Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

. The reaction, which is accelerated in the presence of base, is used for

hydrogen production Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Article in press. Most hydrogen is ''gray hydrogen'' made through steam methane reforming. In this process, ...

. The melting point and

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

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

Uses

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 Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

from the molten steel (so called ''blocking the heat'');

ferromanganese Ferromanganese is an alloy of iron and manganese, with other elements such as silicon, carbon, sulfur, nitrogen and phosphorus. The primary use of ferromanganese is as a type of processed manganese source to add to different types of steel, such ...

spiegeleisen Spiegeleisen (literally "mirror-iron", —mirror or specular; —iron) is a ferromanganese alloy containing approximately 15% manganese and small quantities of carbon and silicon. Spiegeleisen is sometimes also referred to as ''specular pig iron' ...

, 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 Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

for

electromotor An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate Laplace force i ...

s and

transformer In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...

cores. In the manufacture of

cast iron Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...

, ferrosilicon is used for inoculation of the iron to accelerate

graphitization Graphitization is a process of transforming a carbonaceous material, such as coal or the carbon in certain forms of iron alloys, into graphite. Process The graphitization process involves a restructuring of the molecular structure of the carbon ...

. In

arc welding Arc welding is a welding process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals, when cool, result in a joining of the metals. It is a type of welding that uses a welding power ...

, ferrosilicon can be found in some electrode coatings. Ferrosilicon is a basis for manufacture of prealloys like magnesium ferrosilicon (MgFeSi), used for production of

ductile iron Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron and SG iron, is a type of graphite-rich cast iron discovered in 1943 by Keith Millis. While most varieties of cast iron are ...

. MgFeSi contains 3–42%

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

and small amounts of

rare-earth elements The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set of ...

. Ferrosilicon is also important as an additive to cast irons for controlling the initial content of silicon. Magnesium ferrosilicon is instrumental in the formation of nodules, which give

its flexible property. Unlike gray cast iron, which forms

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

flakes, ductile iron contains graphite nodules, or pores, which make cracking more difficult. Ferrosilicon is also used in the

Pidgeon process The Pidgeon process is a practical method for smelting magnesium. The most common method involves the raw material, dolomite being fed into an externally heated reduction tank and then thermally reduced to metallic magnesium using 75% ferrosilicon ...

to make magnesium from dolomite.

Silanes

Treatment of high-silicon ferrosilicon with

hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...

is the basis of the industrial synthesis of

trichlorosilane Trichlorosilane (TCS) is an inorganic compound with the formula HCl3Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes ...

. Ferrosilicon is also used in a ratio of 3–3.5% in the manufacture of sheets for the magnetic circuit of electrical transformers.

Hydrogen production

The method has been in use since

World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

. Prior to this, the process and purity of hydrogen generation relying on

steam Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...

passing over hot iron was difficult to control. The chemical reaction uses

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

(NaOH), ferrosilicon, and water (H₂O). While in the "silicol" process, a heavy steel

pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

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 and starts the reaction;

sodium silicate Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate (), sodium orthosilicate (), and sodium pyrosilicate (). The anions are often polymeric. These compounds are generally colorless tra ...

, hydrogen and steam are produced. The overall reaction of the process is believed to be: : 2NaOH + Si + H₂O → Na₂SiO₃ + 2H₂ Ferrosilicon is used by the military to quickly produce hydrogen for

balloons A balloon is a flexible membrane bag that can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, or air. For special purposes, balloons can be filled with smoke, liquid water, granular media (e.g. sand, flour or rice), ...

by the ferrosilicon method. The generator may be small enough to fit in a truck and requires only a small amount of electric power, the materials are stable and not combustible, and they do not generate hydrogen until mixed.Report No 40: The ferrosilicon process for the generation of hydrogen
/ref> One report notes that this method of hydrogen production wasn't thoroughly investigated for about century despite being reported by the US military in the beginning of 20th century.

Production and reactions

Uses

Silanes

Hydrogen production

Footnotes

References

Further reading