General Information

Manganese(Mn), chemical element, one of the silvery-white, hard, brittle metals of Group VIIb of the periodic table. It was recognized as an element (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.

As in the case of titanium, vanadium, and chromium, the highest oxidation state (+7) of manganese corresponds to the total number of 3d and 4s electrons. That state occurs only in the oxo species manganate (VII) (MnO4-), manganese(VII) oxide (Mn2O7), and manganese(VII) trioxide fluoride (MnO3F), which show some similarity to corresponding compounds of the halogens--for example, in the instability of the oxide. Manganese in oxidation state +7 is powerfully oxidizing, usually being reduced to divalent manganese. The intermediate oxidation states are known, but, except for some compounds in the +3 and +4 states, they are not particularly important.

Manganese, first recognized as an element by the Swedish chemist Carl Wilhelm Scheele in 1774, is second only to iron among the transition elements in its abundance in the Earth's crust and is roughly similar to iron in its physical and chemical properties but is harder and more brittle. Although it is widely distributed, manganese occurs in a number of substantial deposits, mainly the oxides, of which the mineral pyrolusite (manganese(IV) oxide, MnO2) is the most important. Manganese is quite electropositive, dissolving very readily in dilute non-oxidizing 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) and (III) fluorides, MnF2 and MnF3; and burns in nitrogen at about 1,200 C to give manganese(II) nitride, Mn3N2, and in oxygen to give trimanganese tetroxide, Mn3O4. Manganese also combines directly with boron, carbon, sulfur, silicon, or phosphorus, but not with hydrogen. The most important oxidation states for manganese are +2, +3, +7.

Occurrence, uses, and properties.

Manganese combined with other elements is widely distributed in the Earth's crust. The most important ores consist primarily of manganese dioxide (MnO2) in the form of pyrolusite, psilomelane, and wad. Manganese is essential to plant growth and is involved in the reduction 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.

More than 95 percent 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, also called Hadfield steel, is used for very rugged service; containing 12-14 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.

All natural manganese is 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 divalent salts.

History