Synopsis
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Manganese - (L. magnes, magnet, from magnetic properties
of pyrolusite; It. manganese, corrupt form of magnesia), Mn; at. wt. 54.93805(l);
at. no. 25; m.p. 1246 +/- 3 deg C; b.p. 2061 deg C; sp. gr. 7.21 to 7.44,
depending on allotropic form; valence 1, 2, 3, 4, 6, or 7. Recognized by
Scheele, Bergman, and others as an element and isolated by Gahn in 1774
by reduction of the dioxide with carbon. 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 holds promise as 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 the Ukraine, Brazil, Australia,
Republic of So. Africa, Gabon, China, and India. Pyrolusite (MnO2) and
rhodochrosite (MnCO3) are among the most common manganese minerals. The
metal is obtained by reduction of the oxide with sodium, magnesium, aluminum,
or by electrolysis. 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. 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. Twenty three isotopes and isomers are known. Manganese metal
(99.95%) is priced at about $400/kg. Metal of 99.6% purity is priced at
about $60/kg. |
