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Jai Ganesh

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Manganese

Manganese

Gist

Manganese (Mn) is a chemical element, a silvery-gray, hard, and brittle transition metal with atomic number 25. It's essential for various industrial applications, particularly in steelmaking, and is also a vital trace element for both plants and animals, including humans.

It is mainly used in alloys, such as steel. Steel contains about 1% manganese, to increase the strength and also improve workability and resistance to wear. Manganese steel contains about 13% manganese. This is extremely strong and is used for railway tracks, safes, rifle barrels and prison bars.

Summary

Manganese is a chemical element; it has symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition metal with a multifaceted array of industrial alloy uses, particularly in stainless steels. It improves strength, workability, and resistance to wear. Manganese oxide is used as an oxidising agent, as a rubber additive, and in glass making, fertilisers, and ceramics. Manganese sulfate can be used as a fungicide.

Manganese is also an essential human dietary element, important in macronutrient metabolism, bone formation, and free radical defense systems. It is a critical component in dozens of proteins and enzymes. It is found mostly in the bones, but also the liver, kidneys, and brain. In the human brain, the manganese is bound to manganese metalloproteins, most notably glutamine synthetase in astrocytes.

Manganese is commonly found in laboratories in the form of the deep violet salt potassium permanganate where it is used as an oxidizer. Potassium permanganate is also used as a biocide in water treatment.

It occurs at the active sites in some enzymes. Of particular interest is the use of a Mn–O cluster, the oxygen-evolving complex, in the production of oxygen by plants.

Details

Manganese (Mn), chemical element, one of the silvery white, hard, brittle metals of Group 7 (VIIb) of the periodic table. It was recognized as an element in 1774 by the Swedish chemist Carl Wilhelm Scheele while working with the mineral pyrolusite and was isolated the same year by his associate, Johan Gottlieb Gahn. Although it is rarely used in pure form, manganese is essential to steelmaking.

Element Properties

atomic number  :  25
atomic weigh  :  54.938
melting point  :  1,246 °C (2,275 °F)
boiling point  :  2,062 °C (3,744 °F)
density  :  7.21–7.44 gram/{cm}^{3} at 20 °C (68 °F)
oxidation states  :  +2, +3, +4, +5, +6, +7

Occurrence, uses, and properties

Manganese combined with other elements is widely distributed in Earth’s crust. Manganese is second only to iron among the transition elements in its abundance in Earth’s crust; it is roughly similar to iron in its physical and chemical properties but is harder and more brittle. It occurs in a number of substantial deposits, of which the most important ores (which are mainly oxides) consist primarily of manganese dioxide (MnO2) in the form of pyrolusite, romanechite, and wad. Manganese is essential to plant growth and is involved in the assimilation of nitrates in green plants and algae. It is an essential trace element in higher animals, in which it participates in the action of many enzymes. Lack of manganese causes testicular atrophy. An excess of this element in plants and animals is toxic.

Manganese ores are primarily produced by Australia, South Africa, China, Gabon, and Brazil. Large areas of the ocean floor are covered with manganese nodules, also called polymetallic nodules, concretions of manganese with some iron, silicon, and aluminum. The amount of manganese in the nodules is estimated to be much more than that in land reserves.

Most of the manganese produced is used in the form of ferromanganese and silicomanganese alloys for iron and steel manufacture. Manganese ores containing iron oxides are first reduced in blast furnaces or electric furnaces with carbon to yield ferromanganese, which in turn is used in steelmaking. Adding manganese, which has a greater affinity for sulfur than does iron, converts the low-melting iron sulfide in steel to high-melting manganese sulfide. Produced without manganese, steel breaks up when hot-rolled or forged. Steels generally contain less than 1 percent manganese. Manganese steel is used for very rugged service; containing 11–14 percent manganese, it provides a hard, wear-resistant, and self-renewing surface over a tough unbreakable core. Pure manganese produced electrolytically is used mostly in the preparation of nonferrous alloys of copper, aluminum, magnesium, and nickel and in the production of high-purity chemicals. Practically all commercial alloys of aluminum and magnesium contain manganese to improve corrosion resistance and mechanical properties. Aluminum cans contain about 1.5 percent manganese.

All natural manganese is the stable isotope manganese-55. It exists in four allotropic modifications; the complex cubic structure of the so-called alpha phase is the form stable at ordinary temperatures. Manganese somewhat resembles iron in general chemical activity. The metal oxidizes superficially in air and rusts in moist air. It burns in air or oxygen at elevated temperatures, as does iron; decomposes water slowly when cold and rapidly on heating; and dissolves readily in dilute mineral acids with hydrogen evolution and the formation of the corresponding salts in the +2 oxidation state.

Manganese is quite electropositive, dissolving very readily in dilute nonoxidizing acids. Although relatively unreactive toward nonmetals at room temperature, it reacts with many at elevated temperatures. Thus, manganese burns in chlorine to give manganese(II) chloride (MnCl2), reacts with fluorine to give manganese(II) fluoride (MnF2) and manganese(III) fluoride (MnF3), burns in nitrogen at about 1,200 °C (2,200 °F) to give manganese(II) nitride (Mn3N2), and burns in oxygen to give manganese(II,III) oxide (Mn3O4). Manganese also combines directly with boron, carbon, sulfur, silicon, or phosphorus but not with hydrogen.

Additional Information

Appearance

A hard, brittle, silvery metal.

Uses

Manganese is too brittle to be of much use as a pure metal. It is mainly used in alloys, such as steel.

Steel contains about 1% manganese, to increase the strength and also improve workability and resistance to wear.

Manganese steel contains about 13% manganese. This is extremely strong and is used for railway tracks, safes, rifle barrels and prison bars.

Drinks cans are made of an alloy of aluminium with 1.5% manganese, to improve resistance to corrosion. With aluminium, antimony and copper it forms highly magnetic alloys.

Manganese(IV) oxide is used as a catalyst, a rubber additive and to decolourise glass that is coloured green by iron impurities. Manganese sulfate is used to make a fungicide. Manganese(II) oxide is a powerful oxidising agent and is used in quantitative analysis. It is also used to make fertilisers and ceramics.
Biological role
Manganese is an essential element in all known living organisms. Many types of enzymes contain manganese. For example, the enzyme responsible for converting water molecules to oxygen during photosynthesis contains four atoms of manganese.

Some soils have low levels of manganese and so it is added to some fertilisers and given as a food supplement to grazing animals.

The average human body contains about 12 milligrams of manganese. We take in about 4 milligrams each day from such foods as nuts, bran, wholegrain cereals, tea and parsley. Without it, bones grow spongier and break more easily. It is also essential for utilisation of vitamin B1.

Natural abundance

Manganese is the fifth most abundant metal in the Earth’s crust. Its minerals are widely distributed, with pyrolusite (manganese dioxide) and rhodochrosite (manganese carbonate) being the most common.

The main mining areas for manganese are in China, Africa, Australia and Gabon. The metal is obtained by reducing the oxide with sodium, magnesium or aluminium, or by the electrolysis of manganese sulfate.

Manganese nodules have been found on the floor of the oceans. These nodules contain about 24% manganese, along with smaller amounts of many other elements.

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