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Atomic Number: 25
Atomic Symbol: Mn
Atomic Weight: 54.9380
Electron Configuration: [Ar]4s23d5
History
(L. magnes, magnet, from magnetic properties of pyrolusite; It.
manganese, corrupt form of magnesia) Recognized by Scheele, Bergman, and others
as an element and isolated by Gahn in 1774 by reduction of the dioxide with
carbon.
Sources
Manganese minerals are widely distributed; oxides, silicates, and
carbonates are the most common. The discovery of large quantities of manganese
nodules on the floor of the oceans may become a source of manganese. These
nodules contain about 24% manganese together with many other elements in lesser
abundance.
Most manganese today is obtained from ores found in Russia,
Brazil, Australia, Republic of S. Africa, Gabon, and India. Pyrolusite and
rhodochrosite are among the most common manganese minerals. The metal is
obtained by reduction of the oxide with sodium,
magnesium, aluminum,
or by electrolysis.
Properties
It is gray-white, resembling iron, but
is harder and very brittle. The metal is reactive chemically, and decomposes
cold water slowly. Manganese is used to form many important alloys. In steel,
manganese improves the rolling and forging qualities, strength, toughness,
stiffness, wear resistance, hardness, and hardenability.
With aluminum and
antimony, especially with small amounts of
copper, it forms highly ferromagnetic alloys.
Manganese metal is ferromagnetic only after special treatment.
The pure metal exists in four allotropic forms. The alpha form is stable at
ordinary temperature; gamma manganese, which changes to alpha at ordinary
temperatures, is said to be flexible, soft, easily cut, and capable of being
bent.
Uses
The dioxide (pyrolusite) is used as a depolarizer in dry cells, and
is used to "decolorize" glass that is colored green by impurities of iron.
Manganese by itself colors glass an amethyst color, and is responsible for the
color of true amethyst. The dioxide is also used in the preparation of oxygen
and chlorine, and in drying black paints. The permanganate is a powerful
oxidizing agent and is used in quantitative analysis and in medicine.
Manganese is widely distributed throughout the animal kingdom.
It is an important trace element and may be essential for utilization of vitamin
B1.
Handling
Exposure to manganese dusts, fume, and compounds should not exceed
the ceiling value of 5 mg/m3 for even short periods because of the
element's toxicity level.
Sources: CRC Handbook of Chemistry and
Physics and the American Chemical Society.
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