Nomenclature
CAS number: 7439-96-5
Description and references
Mn; at. wt 54.938045; at. no. 25; valences
2, 4, 7; 1, 3, 5, 6 rare. Group VIIB (7). One stable isotope: 55;
artificial radioactive isotopes 49-54; 56-58. Widely-distributed,
abundant element; constitutes 0.085% of earth's crust. Occurs in
the minerals pyrolusite, hausmannite, manganite, braunite (3Mn2O3.MnSiO3), manganosite (MnO), and in several others; occurs in minute quantities
in water, plants and animals. Essential dietary nutrient. First
isolated by Gahn in 1774. Prepn of the metal: John et al., cited by Mellor, A Comprehensive Treatise
on Inorganic and Theoretical Chemistry 12, 163
(1932); A. H. Sully, Manganese (Academic Press, New York, 1955) 305 pp. Review of physical properties:
Meaden, Met. Rev. 13, 97-114 (1968). Review of manganese and its compds: Kemmitt in Comprehensive Inorganic Chemistry vol.
3, J. C. Bailar Jr. et al., Eds. (Pergamon Press,
Oxford, 1973) pp 771-876; L. R. Matricardi, J. H. Downing in Kirk-Othmer Encyclopedia of Chemical Technology vol. 14, (Wiley-Interscience, New York, 3rd ed., 1981)
pp 824-843. Review of toxicology and human exposure: Toxicological Profile for Manganese (PB2000-108025,
2000) 504 pp.
Properties
Steel gray, lustrous, hard, brittle metal. Exists
in four allotropic forms: α-form, body-centered cubic, stable below
710° (approx), d20 7.47; β-form, cubic, stable in the range 710-1079°, d20 7.26; γ-form or electrolytic
Mn, face-centered cubic, stable in the range 1079-1143°C, d1100 6.37; δ-form, body-centered
cubic, stable from 1143° to mp, d1143 6.28. γ-Mn when stabilized at room temp is
face-centered tetragonal, d20 7.21. mp 1244°. bp 2095°. Sp heat 0.115 cal/g/°C; latent heat of fusion: 3.5 kcal/g-atom.
Mohs' hardness 5.0. Superficially oxidized on exposure to air.
Burns with an intense white light when heated in air. Dec water
slowly in the cold, rapidly on heating; pure electrolytic manganese
is not attacked by water at ordinary temp; slightly attacked by steam.
Reacts with dil mineral acids with evolution of hydrogen and formation
of divalent manganous salts. Reacts with aq solns of sodium or potassium
bicarbonate. When heated in nitrogen above 2000° burns to form a
nitride. Converted by fluorine into the di- and trifluoride, by chlorine
into the dichloride. In form of powder reduces most metallic oxides
on heating. On heating, reacts directly with carbon, phosphorus,
antimony or arsenic.Caution
Potential symptoms of overexposure
are parkinsonism; asthenia, insomnia and mental confusion; metal fume
fever (dry throat, coughing, tight chest, dyspnea, rales and flu-like
fever); lower back pain; vomiting; malaise; fatigue; kidney damage.
See NIOSH Pocket Guide to Chemical
Hazards (DHHS/NIOSH 97-140, 1997) p 190.Use
In manuf of steel; for rock crushers, railway points
and crossings, wagon buffers; as a constituent of several alloys,
e.g., ferromanganese, copper manganese, Manganin.