Manganese

Vapor pressure
25	chromium ← manganese → iron
	periodic table
General
Name, Symbol, Number	manganese, Mn, 25
Chemical series	transition metals
Group, Period, Block	7, 4, d
Appearance	silvery metallic ;
Atomic mass	54.938045(5) g/mol
Electron configuration	[Ar] 3d5 4s2
Electrons per shell	2, 8, 13, 2
Physical properties
Phase	solid
Density (near r.t.)	7.21 g/cm³
Liquid density at m.p.	5.95 g/cm³
Melting point	1519 K; (1246 °C, 2275 °F)
Boiling point	2334 K; (2061 °C, 3742 °F)
Heat of fusion	12.91 kJ/mol
Heat of vaporization	221 kJ/mol
Heat capacity	(25 °C) 26.32 J/(mol·K)
Atomic properties
Crystal structure	cubic body centered
Oxidation states	7, 6, 4, 2, 3; (strongly acidic oxide)
Electronegativity	1.55 (Pauling scale)
Ionization energies; (more)	1st: 717.3 kJ/mol
	2nd: 1509.0 kJ/mol
	3rd: 3248 kJ/mol
Atomic radius	140 pm
Atomic radius (calc.)	161 pm
Covalent radius	139 pm
Miscellaneous
Magnetic ordering	nonmagnetic
Electrical resistivity	(20 °C) 1.44 µΩ·m
Thermal conductivity	(300 K) 7.81 W/(m·K)
Thermal expansion	(25 °C) 21.7 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 5150 m/s
Speed of sound (thin rod)	(r.t.) 198 m/s
Bulk modulus	120 GPa
Mohs hardness	6.0
Brinell hardness	196 MPa
CAS registry number	7439-96-5
Notable isotopes

Previous (Mangabey)

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Manganese (chemical symbol Mn, atomic number 25) is a gray-white metal, resembling iron.

a chemical element in the periodic table.

Occurrence

Manganese ore

Manganese occurs principally as the mineral pyrolusite (manganese(IV) oxide, MnO₂), and to a lesser extent as rhodochrosite (manganese(II) carbonate, MnCO₃). Land-based resources are large but irregularly distributed; those of the United States are very low grade and have potentially high extraction costs. South Africa and Ukraine account for more than 80% of the world's identified resources. In addition, manganese is mined in Burkina Faso and Gabon. Vast quantities of manganese exist in manganese nodules on the ocean floor, but attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.

U.S. import sources (1998-2001):

Manganese ore: Gabon, 70%; South Africa, 10%; Australia, 9%; Mexico, 5%; and other, 6%.
Ferromanganese: South Africa, 47%; France, 22%; Mexico, 8%; Australia, 8%; and other, 15%.
Manganese contained in all manganese imports: South Africa, 31%; Gabon, 21%; Australia, 13%; Mexico, 8%; and other, 27%.

History

Manganese (from the Latin word magnes, meaning "magnet") was in use in prehistoric times, in the form of its compounds. Paints that were pigmented with manganese dioxide (manganese(IV) oxide) can be traced back 17,000 years. The Egyptians and Romans used manganese compounds in glass-making, to either remove color from glass or add color to it. Manganese can be found in the iron ores used by the Spartans. Some speculate that the exceptional hardness of Spartan steels derives from the inadvertent production of an iron-manganese alloy.

In the seventeenth century, German chemist Johann Glauber first produced permanganate, a useful laboratory reagent. (Some, however, believe that it was discovered by Ignites Kaim in 1770). By the mid-eighteenth century, manganese dioxide was in use in the manufacture of chlorine. Swedish chemist Carl Wilhelm Scheele was the first to recognize that manganese was an element, and his colleague, Johan Gottlieb Gahn, isolated the pure element in 1774 by reduction of the dioxide with carbon.

Around the beginning of the nineteenth century, scientists began exploring the use of manganese in steelmaking, and patents were granted for its use at the time. In 1816, it was noted that adding manganese to iron made it harder, without making it any more brittle. In 1837, British academic James Couper noted an association between heavy exposure to manganese in mines with a form of Parkinson's disease. In 1912, patents were issued in the United States for methods of using manganese for "Parkerizing" (electrochemical conversion coating of) firearms to protect them from rust and corrosion, and these methods have been in widespread use ever since.

Notable characteristics

Manganese

Manganese is a metallic element placed in period 4 and group 7 (former group 7B) of the periodic table. In period 4, it lies between chromium (Cr) and iron (Fe), and in group 7, it is positioned above technetium (Tc) and rhenium (Re). Manganese is very brittle, fusible with difficulty, but easily oxidized. After special treatment, manganese metal becomes ferromagnetic.

Manganese combines with various other elements in different proportions. The oxidation states* of manganese are known to range from +1 to +7, but the most common ones are +2, +3, +4, +6, and +7. Mn²⁺ often competes with Mg²⁺ in biological systems, and compounds in which manganese is in oxidation state +7 are powerful oxidizing agents.

Isotopes

The isotopes of manganese range in atomic weight from 46 atomic mass units (amu) (⁴⁶Mn) to 65 amu (⁶⁵Mn). Naturally occurring manganese consists of one stable isotope: ⁵⁵Mn. In addition, 18 radioisotopes have been characterized, of which the most stable is ⁵³Mn, with a half-life of 3.7 million years. The isotope ⁵⁴Mn has a half-life of 312.3 days, and ⁵²Mn has a half-life of 5.591 days. The remaining radioactive isotopes have half-lives under 3 hours, and most of these have half-lives less than 1 minute.

Manganese is part of the iron group of elements that are thought to be synthesized in large stars shortly before supernova explosion. Given that ⁵³Mn decays to ⁵³Cr, manganese isotopic contents are typically combined with chromium isotopic contents and have found application in isotope geology and radiometric dating. Mn-Cr isotopic ratios reinforce the evidence from isotopic ratios of other elements (²⁶Al and ¹⁰⁷Pd) for the early history of the solar system.

Applications

Manganite, a manganese oxide

Manganese is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties. Steelmaking, including its ironmaking component, has accounted for most manganese demand—presently in the range of 85–90% of the total demand. Among its other uses, manganese is a key component of low-cost stainless steel formulations and certain widely used aluminum alloys. It is also added to gasoline to reduce engine knock. At low concentrations, manganese is used to decolorize glass, as it removes the greenish tinge generated by the presence of iron; at higher concentrations, it is used to make violet-colored glass.

Manganese dioxide is a catalyst and is also used in the original type of dry cell battery. Manganese oxide, a component of natural umber, is a brown pigment that is useful for paint. Potassium permanganate is a potent oxidizer used in chemical reactions; it is also used in medicine as a disinfectant. The technique known as manganese phosphating (or Parkerizing) is used to prevent the rusting and corrosion of steel. It is very occasionally used in coins; the only U.S. coins to use manganese were the "wartime" nickel from 1942–1945, and the Sacagawea Dollar (2000–present).

The overall level and nature of manganese use in the United States is expected to remain about the same in the near term. No practical technologies exist for replacing manganese with other materials or for using domestic deposits or other accumulations to reduce the complete dependence of the United States on other countries for manganese ore.

Manganese has no satisfactory substitute in its major applications. In minor applications, (such as manganese phosphating), zinc and sometimes vanadium are viable substitutes.

Biological role

Manganese (in the form of manganese ions) is an essential trace nutrient in all known forms of life. Many classes of enzymes have manganese cofactors. They include oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The best-known manganese-containing polypeptides (protein-like chains) may be arginase, Mn-containing superoxide dismutase, and the diphtheria toxin.

Compounds

Potassium permanganate, also called Condy's crystals, is a commonly used laboratory reagent because of its oxidizing properties and finds use as a topical medicine (for example, in the treatment of fish diseases).

Manganese(IV) oxide (manganese dioxide) is used in dry cells, and can be used to decolorize glass that is polluted by trace amounts of iron. Manganese compounds can color glass an amethyst color, and are responsible for the color of true amethyst. Manganese dioxide is also used in the manufacture of oxygen and chlorine, and in drying black paints.

The most stable oxidation state for manganese is +2, and many manganese(II) compounds are known, such as manganese(II) sulfate (MnSO₄) and manganese(II) chloride (MnCl₂). This oxidation state is also seen in the mineral rhodochrosite, (manganese(II) carbonate). The +3 oxidation state is also known, in compounds such as manganese(III) acetate, but these are quite powerful oxidizing agents.

See also manganese compounds.

Precautions

Manganese in excess is toxic. Exposure to manganese dusts and fumes should not exceed the ceiling value of 5 mg/m³ for even short periods because of its toxicity level.

Acidic permanganate solutions will oxidize any organic material they come into contact with. The oxidation process can generate enough heat to ignite some organic substances.

In 2005, a study suggested a possible link between manganese inhalation and central nervous system toxicity in rats.^[1] It is hypothesized that long-term exposure to the naturally-occurring manganese in shower water puts up to 8.7 million Americans at risk.

A form of Parkinson's Disease-type neurodegeneration called "Manganism" has been linked to manganese exposure amongst miners and smelters since the early 19th Century. Allegations of inhalation-induced manganism have been made regarding the welding industry. Manganese exposure is regulated by OSHA.^[2]

References
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Los Alamos National Laboratory – Manganese

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Manganese

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[1] ttp://dx.doi.org/10.1016/j.mehy.2005.01.043

[2] ttp://www.osha.gov/dts/chemicalsampling/data/CH_250190.html

[1]

[2]

Manganese

Occurrence

History

Notable characteristics

Isotopes

Applications

Biological role

Compounds

Precautions

See also

ReferencesISBN links support NWE through referral fees

External links

Credits

References
ISBN links support NWE through referral fees