Manganese

Manganese, ₂₅Mn

Pure manganese cube and oxidized manganese chips
Manganese
Pronunciation	/ˈmæŋɡəniːz/ ​(MANG-gə-neez)
Appearance	silvery metallic
Standard atomic weight Ar°(Mn)
	54.938043±0.000002 54.938±0.001 (abridged)
Manganese in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson – ↑ Mn ↓ Tc chromium ← manganese → iron
Atomic number (Z)	25
Group	group 7
Period	period 4
Block	d-block
Electron configuration	[Ar] 3d5 4s2
Electrons per shell	2, 8, 13, 2
Physical properties
Phase at STP	solid
Melting point	1519 K ​(1246 °C, ​2275 °F)
Boiling point	2334 K ​(2061 °C, ​3742 °F)
Density (at 20° C)	7.476 g/cm3
when liquid (at m.p.)	5.95 g/cm3
Heat of fusion	12.91 kJ/mol
Heat of vaporization	221 kJ/mol
Molar heat capacity	26.32 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1228 1347 1493 1691 1955 2333
Atomic properties
Oxidation states	−3, −1, 0, +1, +2, +3, +4, +5, +6, +7 (depending on the oxidation state, an acidic, basic, or amphoteric oxide)
Electronegativity	Pauling scale: 1.55
Ionization energies	1st: 717.3 kJ/mol 2nd: 1509.0 kJ/mol 3rd: 3248 kJ/mol (more)
Atomic radius	empirical: 127 pm
Covalent radius	Low spin: 139±5 pm High spin: 161±8 pm
Spectral lines of manganese
Other properties
Natural occurrence	primordial
Crystal structure	α-Mn: ​body-centered cubic (bcc) (cI58)
Lattice constant	a = 891.16 pm (at 20 °C)
Thermal expansion	23.61×10−6/K (at 20 °C)
Thermal conductivity	7.81 W/(m⋅K)
Electrical resistivity	1.44 µΩ⋅m (at 20 °C)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	(α) +529.0×10−6 cm3/mol (293 K)
Young's modulus	198 GPa
Bulk modulus	120 GPa
Speed of sound thin rod	5150 m/s (at 20 °C)
Mohs hardness	6.0
Brinell hardness	196 MPa
CAS Number	7439-96-5
History
Discovery	Carl Wilhelm Scheele (1774)
First isolation	Johann Gottlieb Gahn (1774)
Isotopes of manganese
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 52Mn synth 5.591 d β+ 52Cr 53Mn trace 3.7×106 y ε 53Cr 54Mn synth 312.081 d ε 54Cr β− 54Fe β+ 54Cr 55Mn 100% stable

Manganese (Template:PronEng) is a chemical element that has the symbol Mn and atomic number 25. It is found as the free element in nature (often in combination with iron), and in many minerals. The free element is a metal with important industrial metal alloy uses. Manganese ions are variously colored, and are used industrially as pigments and as oxidation chemicals. Manganese (II) ions function as cofactors for a number of enzymes and the element is thus a required trace mineral for all known living organisms.

Notable chemical characteristics

Manganese

Manganese is a gray-white metal resembling iron. It is a hard metal and is very brittle, fusible with difficulty, but easily oxidized. Manganese metal and its common ions are paramagnetic. This means that, while manganese metal does not form a permanent magnet, it does exhibit strong magnetic properties in the presence of an external magnetic field.

The most common oxidation states of manganese are +2, +3, +4, +6 and +7, though oxidation states from +1 to +7 are observed. Mn²⁺ often competes with Mg²⁺ in biological systems, and manganese compounds where manganese is in oxidation state +7 are powerful oxidizing agents.

Compounds

Methylcyclopentadienyl manganese tricarbonyl is used as an additive in unleaded gasoline to boost octane rating and reduce engine knocking.

Manganese dioxide is also used as a reagent in organic chemistry for the oxidation of benzylic alcohols (i.e. adjacent to an aromatic ring). Manganese(IV) oxide (manganese dioxide, MnO₂) is used in dry cells. Manganese can be used to neutralize the greenish tinge in glass caused by trace amounts of iron contamination. Manganese compounds in larger amounts can color glass an amethyst color, and are responsible for the purple color of true amethyst. MnO₂ is also used in the manufacture of oxygen and chlorine, and in drying black paints. Manganese oxide is a brown pigment that can be used to make paint and is a constituent of natural umber. Potassium permanganate, sodium permanganate and barium permanganate are all potent oxidizers. 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). Solutions of potassium permanganate were among the first stains and fixatives to be used in the preparation of biological cells and tissues for electron microscopy.

Manganese phosphating is used as a treatment for rust and corrosion prevention on steel.

Manganese(IV) oxide (manganese dioxide) was used in the original type of dry cell battery, and is the black material found when opening carbon-zinc type flashlight cells. The same material also functions in newer alkaline batteries (usually battery cells), which use the same basic reaction but a different electrolyte.

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.

Substitutes: Manganese has no satisfactory substitute in its major applications, which are related to metallurgical alloy use. In minor applications, (e.g., manganese phosphating), zinc and sometimes vanadium are viable substitutes. In disposable battery manufacture, standard and alkaline cells using manganese will probably eventually be mostly replaced with lithium battery technology.

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.

Metal alloys

The Pourbaix diagram for manganese in pure water, perchloric acid or sodium hydroxide

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% to 90% of the total demand. Among a variety of other uses, manganese is a key component of low-cost stainless steel formulations and certain widely used aluminium alloys.

The metal is very occasionally used in coins; the only United States coins to use manganese were the "Wartime" nickel from 1942–1945, and, since 2000, dollar coins. The EU uses manganese in 1 and 2 Euro coins due to greater and cheaper availability.

History

The origin of the name manganese is complex. In ancient times, two black minerals from Magnesia in what is now modern Greece were both called magnes, but were thought to differ in gender. The male magnes attracted iron, and was the iron ore we now know as loadstone or magnetite, and which probably gave us the term magnet. The female magnes ore did not attract iron, but was used to decolorize glass. This feminine magnes was later called magnesia, known now in modern times as pyrolusite or manganese dioxide. This mineral is never magnetic (although manganese itself is paramagnetic). In the 16th century, it was called manganesum by glassmakers, possibly as a corruption of two words since alchemists and glassmakers eventually had to differentiate a magnesia negra (the black ore) from magnesia alba (a white ore, also from Magnesia, also useful in glassmaking). Mercati called magnesia negra Manganesa, and finally the metal isolated from it became known as manganese (German: Mangan). The name magnesia eventually was then used to refer only to the white magnesia alba (magnesium oxide), which provided the name magnesium for that free element, when it was eventually isolated, much later.

Manganese compounds were in use in prehistoric times; paints that were pigmented with manganese dioxide 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 17th century, German chemist Johann Glauber first produced permanganate, a useful laboratory reagent (although some people believe that it was discovered by Ignites Kaim in 1770). By the mid-18th century, manganese dioxide was in use in the manufacture of chlorine (which it produces when mixed with hydrochloric acid, or commercially with a mixture of dilute sulfuric acid and sodium chloride). The Swedish chemist 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 19th century, scientists began exploring the use of manganese in steelmaking, with patents being 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, manganese phosphating electrochemical conversion coatings for protecting firearms against rust and corrosion were patented in the United States, and have seen widespread use ever since.

In the 20th century, manganese dioxide has seen wide commercial use as the chief cathodic material for commercial disposable dry cells and dry batteries of both the standard (carbon-zinc) and alkaline type.

Biological role

Manganese is an essential trace nutrient in all forms of life.

The classes of enzymes that have manganese cofactors are very broad and include such classes as oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The best known manganese-containing polypeptides may be arginase, the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD), which is the enzyme typically present in eukaryotic mitochondria, and also in many bacteria (this fact is in keeping with the bacterial-origin theory of mitochondria). The Mn-SOD enzyme is probably one of the most ancient, for nearly all organisms living in the presence of oxygen use it to deal with the toxic effects of superoxide, formed from by the 1-electron reduction of dioxygen. Exceptions include a few kinds of bacteria such as Lactobacillus plantarum and related lactobacilli, which use a different non-enzymatic mechanism, involving manganese (Mn²⁺) ions complexed with polyphosphate directly for this task, indicating how this function possibly evolved in aerobic life. Manganese is also important in photosynthetic oxygen evolution.

Occurrence

Manganese ore

Manganese occurs principally as pyrolusite (MnO₂), and to a lesser extent as rhodochrosite (MnCO₃). Land-based resources are large but irregularly distributed; those of the United States are very low grade and have potentially high extraction costs. Over 80% of the known world manganese resources are found in South Africa and Ukraine. Other important manganese deposits are in China, Australia, Brazil, Gabon, India, and Mexico.

US 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%.

Manganese is mined in Burkina Faso and Gabon.

Vast quantities of manganese exist in manganese nodules on the ocean floor. Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.

See also manganese minerals.

Isotopes

Main article: Isotopes of manganese

Naturally occurring manganese is composed of 1 stable isotope; ⁵⁵Mn. 18 radioisotopes have been characterized with the most stable being ⁵³Mn with a half-life of 3.7 million years, ⁵⁴Mn with a half-life of 312.3 days, and ⁵²Mn with a half-life of 5.591 days. All of the remaining radioactive isotopes have half lives that are less than 3 hours and the majority of these have half lives that are less than 1 minute. This element also has 3 meta states.

Manganese is part of the iron group of elements which are thought to be synthesized in large stars shortly before supernova explosion. ⁵³Mn decays to ⁵³Cr with a half-life of 3.7 million years. Because of its relatively short half-life, ⁵³Mn is an extinct radionuclide. 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 ²⁶Al and ¹⁰⁷Pd for the early history of the solar system. Variations in ⁵³Cr/⁵²Cr and Mn/Cr ratios from several meteorites indicate an initial ⁵³Mn/⁵⁵Mn ratio that suggests Mn-Cr isotopic systematics must result from in-situ decay of ⁵³Mn in differentiated planetary bodies. Hence ⁵³Mn provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system.

The isotopes of manganese range in atomic weight from 46 u (⁴⁶Mn) to 65 u (⁶⁵Mn). The primary decay mode before the most abundant stable isotope, ⁵⁵Mn, is electron capture and the primary mode after is beta decay.

Precautions

Manganese compounds are less toxic than those of other widespread metals such as iron, nickel and copper. However, manganese is toxic in excess. Exposure to manganese dusts and fumes should not exceed the ceiling value of 5 mg/m³ even for short periods because of its toxicity level. Manganese poses a particular risk for children due to its propensity to bind to CH-7 receptors. Manganese poisoning has been linked to impaired motor skills and cognitive disorders.

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. 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 neurodegeneration similar to Parkinson's Disease 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 Occupational Safety and Health Administration.

See also

• Parkerize
• Potassium permanganate
• Magnet
• Chemical element
• Periodic table
• Manganism

References

• Los Alamos National Laboratory – Manganese

External links

• National Pollutant Inventory - Manganese and compounds Fact Sheet
• WebElements.com – Manganese
• International Manganese Institute
• Neurotoxicity of inhaled manganese: Public health danger in the shower?