Synopsis from the
CRC Handbook of Chemistry and Physics
92nd Edition 2011-2013
|Manganese — (L. magnes, magnet, from magnetic properties of
pyrolusite; It. manganese, corrupt form of magnesia), Mn; at.
wt. 54.938045(5); at. no. 25; m.p. 1246 °C; b.p. 2061 °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 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
in 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 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
The Elements 4-21
utilization of vitamin B1. Twenty-seven isotopes and isomers
are known. Manganese metal (99.95%) is priced at about $800/
kg. Metal of 99.6% purity is priced at about $80/kg.