Manganese (pronounced /ˈmæŋɡəniːz/, MANG-gən-neez) is a chemical element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon,, designated by the symbol Mn. It has the atomic number In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element. In an atom of neutral charge, the atomic number is also equal to the number of 25. It is found as a free element In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by integers, which can be positive, negative, or zero in nature (often in combination with iron), and in many minerals. As a free element, manganese is a metal with important industrial metal alloy uses, particularly in stainless steels.

Manganese phosphating Phosphate coatings are used on steel parts for corrosion resistance, lubricity, or as a foundation for subsequent coatings or painting. It serves as a conversion coating in which a dilute solution of phosphoric acid and phosphate salts is applied via spraying or immersion, chemically reacts with the surface of the part being coated to form a layer is used as a treatment for rust and corrosion prevention on steel. Depending on their oxidation state, manganese ions have various colors and are used industrially as pigments A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light. The permanganates A permanganate is the general name for a chemical compound containing the manganate ion, (MnO4−). Because manganese is in the +7 oxidation state, the manganate(VII) ion is a strong oxidizing agent. The ion has tetrahedral geometry. Permanganate solutions are purple in color and are stable in neutral or slightly alkaline media of alkali The alkali metals are a series of chemical elements forming Group 1 of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). (Hydrogen, although nominally also a member of Group 1, very rarely exhibits behavior comparable to the alkali metals). The alkali metals provide one of the best and alkaline earth metals The alkaline earth metals are a series of elements comprising Group 2 (Group IIA) of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). This specific group in the periodic table owes its name to their oxides that simply give basic alkaline solutions. These elements melt at such high are powerful oxidizers. Manganese dioxide is used as the cathode (electron acceptor) material in standard and alkaline disposable dry cells An electrical battery, first named by Benjamin Franklin in 1748, is a combination of two or more electrochemical cells used to convert stored chemical energy into electrical energy. Since the invention of the first voltaic pile in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial applications and batteries.

Manganese(II) ions function as cofactors A cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes, and cofactors can be considered "helper molecules" that assist in biochemical transformations. Cofactors can also be classified depending on how tightly they bind to an for a number of enzymes in higher organisms, where they are essential in detoxification of superoxide Superoxide is an anion with the chemical formula O2−. It is important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature. With one unpaired electron, the superoxide ion is a free radical, and, like dioxygen, it is paramagnetic free radicals. The element is a required trace mineral for all known living organisms. In larger amounts, and apparently with far greater activity by inhalation, manganese can cause a poisoning syndrome Manganism or manganese poisoning is a toxic condition resulting from chronic exposure to manganese and first identified in 1837 by James Couper in mammals, with neurological damage which is sometimes irreversible.

Contents

Characteristics

Physical

Manganese is a silvery-gray metal A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by resembling iron. It is hard and very brittle, difficult to fuse, but easy to oxidize.[1] Manganese metal and its common ions are paramagnetic Paramagnetism is a form of magnetism that occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields and hence have a relative magnetic permeability of ≥1 . The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a.[2]

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

Naturally occurring manganese is composed of 1 stable isotope Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. In a corresponding manner, isotopes differ in mass number (or number of nucleons) but never in atomic number. The number of protons (the atomic number) is the same because that is what characterizes a chemical element. For example,; 55Mn. 18 radioisotopes A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron . The radionuclide, in this process, undergoes radioactive decay, and emits a gamma ray(s) and/or subatomic particles have been characterized with the most stable being 53Mn with a half-life Half-life is the period of time it takes for a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay of 3.7 million years, 54Mn with a half-life Half-life is the period of time it takes for a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay of 312.3 days, and 52Mn with a half-life of 5.591 days. All of the remaining radioactive Radioactive decay is the process by which an unstable atomic nucleus loses energy by emitting ionizing particles or radiation. The emission is spontaneous in that the nucleus decays without collision with another particle. This decay, or loss of energy, results in an atom of one type, called the parent nuclide, transforming to an atom of a 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 A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons. A nuclear isomer occupies a higher energy state than the corresponding non-excited nucleus, called the ground state. Most nuclear excited states decay by gamma ray emission or internal conversion, though, far from stability, other.[3]

Manganese is part of the iron Iron is the most common element in the earth as a whole, and the fourth most common in the Earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used group of elements, which are thought to be synthesized in large stars A star is a massive, luminous ball of plasma held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun. Historically, the most prominent stars on the celestial sphere were grouped together into constellations shortly before the supernova A supernova is a stellar explosion that is more energetic than a nova. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this short interval a supernova can radiate as much energy as the Sun is expected to emit over its entire explosion. 53Mn decays to 53Cr Chromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρώμα), meaning color, with a half-life Half-life is the period of time it takes for a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay of 3.7 million years. Because of its relatively short half-life, 53Mn occurs only in tiny amounts due to the action of cosmic rays Cosmic rays are energetic particles originating from outer space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are simple protons, with nearly 10% being helium nuclei , and slightly under 1% are heavier elements, electrons (beta particles), or gamma ray photons. The term ray is a misnomer, as cosmic on iron Iron is the most common element in the earth as a whole, and the fourth most common in the Earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used in rocks [4]. Manganese isotopic contents are typically combined with chromium Chromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρώμα), meaning color, isotopic contents and have found application in isotope geology Isotope geochemistry is an aspect of geology based upon study of the relative and absolute concentrations of the elements and their isotopes in the Earth. Variations in the abundance of these isotopes, typically measured with an isotope ratio mass spectrometer or an accelerator mass spectrometer, can reveal information about the age of a rock or and radiometric dating Radiometric dating is a technique used to date materials, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. It is the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth. Mn–Cr isotopic ratios reinforce the evidence from 26Al Aluminium (UK: /ˌæljʉˈmɪniəm/ AL-yew-MIN-ee-əm) or aluminum (US: /əˈluːmɨnəm/ ( listen) ə-LOO-mi-nəm) is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth' and 107Pd Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. Palladium is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it after the asteroid Pallas, which was named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas for the early history of the solar system The Solar System[a] consists of the Sun and those celestial objects bound to it by gravity, all of which were formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets[e] whose orbits are almost circular and. Variations in 53Cr/52Cr and Mn/Cr ratios from several meteorites A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids. When it enters the atmosphere, impact pressure causes the body to heat up indicate an initial 53Mn/55Mn ratio that suggests Mn–Cr isotopic composition must result from in–situ decay of 53Mn in differentiated planetary bodies. Hence 53Mn provides additional evidence for nucleosynthetic Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark-gluon plasma from the Big Bang as it cooled below two trillion degrees. A few minutes afterward, starting with only protons and neutrons, nuclei up to lithium and beryllium (both processes immediately before coalescence of the solar system The Solar System[a] consists of the Sun and those celestial objects bound to it by gravity, all of which were formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets[e] whose orbits are almost circular and.[3]

The isotopes of manganese range in atomic weight Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element (from a given source) to 1/12 of the mass of an atom of carbon-12 (known as the unified atomic mass unit). The term is usually used, without further qualification, to refer to the standard atomic weights published at regular intervals by the from 46 u The unified atomic mass unit or atomic mass unit , or dalton (Da) or, sometimes, universal mass unit (u), is a unit of mass used to express atomic and molecular masses. It is the approximate mass of a hydrogen atom, a proton, or a neutron (46Mn) to 65 u (65Mn). The primary decay mode Radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, named the daughter nuclide. For example: a carbon-14 atom emits radiation before the most abundant stable isotope, 55Mn, is electron capture Electron capture is a decay mode for isotopes that will occur when there are too many protons in the nucleus of an atom and insufficient energy to emit a positron; however, it continues to be a viable decay mode for radioactive isotopes that can decay by positron emission. If the energy difference between the parent atom and the daughter atom is and the primary mode after is beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus (β⁻), while in the case of a positron emission as beta plus (β+). Kinetic energy of beta particles has continuous spectrum ranging from 0 to maximal available energy (Q), which.[3]

Chemical

Oxidation states of manganese[note 1][5]
0 Mn2(CO)10 Dimanganese decacarbonyl is the chemical compound with the formula Mn210. This metal carbonyl is an important reagent in the organometallic chemistry of manganese
+1 K5[Mn(CN)6NO]
+2 MnCl2
+3 MnF3 Manganese trifluoride is the chemical compound with the formula MnF3. This purplish solid is highly reactive, being unstable in moist air and liberating F2 upon heating. MnF3 is useful for converting hydrocarbons into fluorocarbons; i.e., it is a fluorination agent
+4 MnO2 Manganese dioxide is the inorganic compound with the formula MnO2. This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese. It is also present in manganese nodules. The principal use for MnO2 is for dry-cell batteries, such as the alkaline battery and the zinc-carbon battery. In 1976 this
+5 Na3MnO4
+6 K2MnO4 Potassium manganate is the chemical compound with the formula K2MnO4. This purple salt is an intermediate in the industrial synthesis of potassium permanganate, KMnO4, a common chemical. Occasionally, potassium manganate and potassium permanganate are confused, but they are different compounds with distinctly different properties
+7 KMnO4 Potassium permanganate is the inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4– ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intense purple solutions, the evaporation of which gives prismatic purplish-black glistening

The most common oxidation states In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by integers, which can be positive, negative, or zero of manganese are +2, +3, +4, +6 and +7, though oxidation states from -3 to +7 are observed. Mn2+ often competes with Mg2+ in biological systems. Manganese compounds where manganese is in oxidation state +7, which are restricted to the unstable oxide Mn2O7 and compounds of the intensely purple permanganate anion MnO4−, are powerful oxidizing agents Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the.[1] Compounds with oxidation states +5 (blue) and +6 (green) are strong oxidizing agents and are vulnerable to disproportionation This was examined using tartrates by Johan Gadolin in 1788. In the Swedish version of his paper he called it 'söndring'..

The most stable oxidation state for manganese is +2, which has a pale pink color, 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 +2 oxidation state is the state used in living organisms for essential functions; other states are toxic for the human body. The +2 oxidation of Mn results from removal of the two 4s electrons, leaving a "high spin" ion in which all five of the 3d orbitals contain a single electron. Absorption of visible light by this ion is accomplished only by a spin-forbidden transition in which one of the d electrons must pair with another, to give the atom a change in spin of two units. The unlikeliness of such a transition is seen in the uniformly pale and almost colorless nature of Mn(II) compounds relative to other oxidation states of manganese.[6]

The +3 oxidation state is known, in compounds such as manganese(III) acetate, but these are quite powerful oxidizing agents and also prone to disproportionation in solution to Mn(II) and Mn(IV). Solid compounds of Mn(III) are characterized by their preference for distorted octahedral coordination due to the Jahn-Teller effect and its strong purple-red color.

The oxidation state 5+ can be obtained if manganese dioxide is dissolved in molten sodium nitrite.[7] Manganate (VI) salts can also be produced by dissolving Mn compounds, such as manganese dioxide, in molten alkali while exposed to air.

Permanganate (+7 oxidation state) compounds are purple, and can give glass a violet color. 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.[8]

Mineral rhodochrosite (manganese(II) carbonate). The red color is due to impurities, as the pure compound is only faintly pink.
Manganese(II) chloride
Aqueous solution of KMnO4

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 lodestone 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. Neither this mineral nor manganese itself is magnetic. In the 16th century, manganese dioxide was called manganesum (note the two n's instead of one) by glassmakers, possibly as a corruption and concatenation 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). Michele 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.[9]

Some of the cave painting in Lascaux, France use manganese-based pigments.[10]

Several oxides of manganese, for example manganese dioxide, are abundant in nature and due to color these oxides have been used as since the Stone Age. The cave paintings in Gargas contain manganese as pigments and these cave paintings are 30,000 to 24,000 years old.[11]

Manganese compounds were used by Egyptian and Roman glassmakers, to either remove color from glass or add color to it.[12] The use as glassmakers soap continued through the middle ages until modern times and is evident in 14th century glass from Venice.[13]

Credit for first isolating manganese is usually given to Johan Gottlieb Gahn

Because of the use in glassmaking, manganese dioxide was available to alchemists, the first chemists, and was used for experiments. Ignatius Gottfried Kaim (1770) and Johann Glauber (17th century) discovered that manganese dioxide could be converted to permanganate, a useful laboratory reagent.[14] By the mid-18th century the Swedish chemist Carl Wilhelm Scheele used manganese dioxide to produce chlorine. First hydrochloric acid, or a mixture of dilute sulfuric acid and sodium chloride was reacted with manganese dioxide, later hydrochloric acid from the Leblanc process was used and the manganese dioxide was recycled by the Weldon process. The production of chlorine and hypochlorite containing bleaching agents was a large consumer of manganese ores.

Scheele and other chemists were aware that manganese dioxide contained a new element, but they were not able to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, by reducing the dioxide with carbon.

The manganese content of some iron ores used in Greece led to the speculations that the steel produced from that ore contains inadvertent amounts of manganese making the Spartan steel exceptionally hard.[15] Around the beginning of the 19th century, manganese was used in steelmaking and several patents were granted. 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 exposures to manganese in mines with a form of Parkinson's Disease.[16] 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.[17]

The invention of the Leclanché cell in 1866 and the subsequent improvement of the batteries containing manganese dioxide as cathodic depolarizer increased the demand of manganese dioxide. Until the introduction of the nickel-cadmium battery and lithium containing batteries, most batteries contained manganese. The zinc-carbon battery and the alkaline battery normally use industrially produced manganese dioxide, because natural occurring manganese dioxide contains impurities. 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 (zinc-carbon) and alkaline types.[18]

Occurrence and production

See also: Category:Manganese minerals

Manganese makes up about 1000 ppm (0.1%) of the Earth's crust, making it the 12th most abundant element there.[19] Soil contains 7–9000 ppm of manganese with an average of 440 ppm.[19] Seawater has only 10 ppm manganese and the atmosphere contains 0.01 µg/m3.[19] Manganese occurs principally as pyrolusite (MnO2), braunite, (Mn2+Mn3+6)(SiO12),[20] psilomelane (Ba,H2O)2Mn5O10, and to a lesser extent as rhodochrosite (MnCO3).

Manganese ore
Psilomelane (manganese ore)
Spiegeleisen is an iron alloy with a manganese content of approximately 15%
Manganese oxide dendrites on a limestone bedding plane from Solnhofen, Germany—a kind of pseudofossil. Scale is in mm
Percentage of manganese output in 2006 by countries[21]

The most important manganese ore is pyrolusite (MnO2). Other economically important manganese ores usually show a close spatial relation to the iron ores.[1] Land-based resources are large but irregularly distributed. Over 80% of the known world manganese resources are found in South Africa and Ukraine, other important manganese deposits are in Australia, India, China, Gabon and Brazil.[21] In 1978 it was estimated that 500 billion tons of manganese nodules exist on the ocean floor.[22] Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.[23]

Manganese is mined in South Africa, Australia, China, Brazil, Gabon, Ukraine, India and Ghana and Kazakhstan. 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%.[21][24]

For the production of ferromanganese, the manganese ore are mixed with iron ore and carbon and then reduced either in a blast furnace or in an electric arc furnace.[25] The resulting ferromanganese has a manganese content of 30 to 80%.[1] Pure manganese used for the production of non-iron alloys is produced by leaching manganese ore with sulfuric acid and a subsequent electrowinning process.[26]

Applications

Manganese has no satisfactory substitute in its major applications, which are related to metallurgical alloy use.[21] 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.

Steel

British Brodie helmet

Manganese is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties. Steelmaking,[27] including its ironmaking component, has accounted for most manganese demand, presently in the range of 85% to 90% of the total demand.[26] Among a variety of other uses, manganese is a key component of low-cost stainless steel formulations.[24][28]

Small amounts of manganese improve the workability of steel at high temperatures, because it forms a high melting sulfide and therefore prevents the formation of a liquid iron sulfide at the grain boundaries. If the manganese content reaches 4% the embrittlement of the steel becomes a dominant feature. The embrittlement decreases at higher manganese concentrations and reaches an acceptable level at 8%. Steel containing 8 to 15% of manganese is cold hardening and can obtain a high tensile strength of up to 863 MPa,[29][30]. Steel with 12% manganese was used for the British steel helmets. This steel composition was discovered in 1882 by Robert Hadfield and is still known as Hadfield steel.[31]

Aluminium alloys

Main article: Aluminium alloy

The second large application for manganese is as alloying agent for aluminium. Aluminium with a manganese content of roughly 1.5% has an increased resistance against corrosion due to the formation of grains absorbing impurities which would lead to galvanic corrosion.[32] The corrosion resistant aluminium alloy 3004 and 3104 with a manganese content of 0.8 to 1.5% are the alloy used for most of the beverage cans.[33] Before year 2000, in excess of 1.6 million metric tons have been used of those alloys, with a content of 1% of manganese this amount would need 16,000 metric tons of manganese.[33]

Other uses

World War II-time nickel made from a copper-silver-manganese alloy

Methylcyclopentadienyl manganese tricarbonyl is used as an additive in unleaded gasoline to boost octane rating and reduce engine knocking. The manganese in this unusual organometallic compound is in the +1 oxidation state.[34]

Manganese(IV) oxide (manganese dioxide, MnO2) is used as a reagent in organic chemistry for the oxidation of benzylic alcohols (i.e. adjacent to an aromatic ring). Manganese dioxide has been used since antiquity to oxidatively neutralize the greenish tinge in glass caused by trace amounts of iron contamination.[13] MnO2 is also used in the manufacture of oxygen and chlorine, and in drying black paints. In some preparations it is a brown pigment that can be used to make paint and is a constituent of natural umber.

Manganese(IV) oxide was used in the original type of dry cell battery as an electron acceptor from zinc, and is the blackish material found when opening carbon–zinc type flashlight cells. The manganese dioxide is reduced to the manganese oxide-hydroxide MnO(OH) during discharging, preventing the formation of hydrogen at the anode of the battery.[35]

MnO2 + H2O + e− → MnO(OH) + OH−

The same material also functions in newer alkaline batteries (usually battery cells), which use the same basic reaction, but a different electrolyte mixture. In 2002 more than 230,000 tons of manganese dioxide was used for this purpose.[18][35]

The metal is very occasionally used in coins; until 2000 the only United States coin to use manganese was the "wartime" nickel from 1942–1945.[36] An alloy of 75% copper and 25% nickel was traditionally used for the production of nickel coins. However, because of shortage of nickel metal during the war, it was substituted by more available silver and manganese, thus resulting in an alloy of 56% copper, 35% silver and 9% manganese. Since 2000, dollar coins, for example the Sacagawea dollar and the Presidential $1 Coins, are made from a brass containing 7% of manganese with a pure copper core.[37]

Manganese compounds have been used as pigments and for the coloring of ceramics and glass. The brown color of ceramic is sometimes based on manganese compounds.[38] In the glass industry manganese compounds are used for two effects. Manganese(III) reacts with iron(II). The reaction induces a strong green color in glass by forming less-colored iron(III) and slightly pink manganese(II), compensating the residual color of the iron(III).[13] Larger amounts of manganese are used to produce pink colored glass.

Biological role

Reactive center of arginase with boronic acid inhibitor. The manganese atoms are shown in yellow.

Manganese is an essential trace nutrient in all forms of life.[19] The classes of enzymes that have manganese cofactors are very broad and include oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The reverse transcriptases of many retroviruses (though not lentiviruses such as HIV) contain manganese. The best known manganese-containing polypeptides may be arginase, the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD).[39]

Mn-SOD is the type of SOD present in eukaryotic mitochondria, and also in most 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 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.

The human body contains about 10 mg of manganese, which is stored mainly in the liver and kidneys. In the human brain the manganese is bound to manganese metalloproteins most notably glutamine synthetase in astrocytes.[40]

Manganese is also important in photosynthetic oxygen evolution in chloroplasts in plants. The oxygen evolving complex (OEC) is a part of Photosystem II contained in the thylakoid membranes of chloroplasts; it is responsible for the terminal photooxidation of water during the light reactions of photosynthesis and has a metalloenzyme core containing four atoms of manganese.[41] For this reason, most broad-spectrum plant fertilizers contain manganese.

Precautions

Manganese compounds are less toxic than those of other widespread metals such as nickel and copper.[42] However, 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.[43] Manganese poisoning has been linked to impaired motor skills and cognitive disorders.[44]

The permanganate exhibits a higher toxicity than the manganese(II) compounds. The fatal dose is about 10 g, and several fatal intoxications have occurred. The strong oxidative effect leads to necrosis of the mucous membrane. For example, the esophagus is affected if the permanganate is swallowed. Only a limited amount is absorbed by the intestines, but this small amount shows severe effects on the kidneys and on the liver.[45][46]

In 2005, a study suggested a possible link between manganese inhalation and central nervous system toxicity in rats.[47] It is hypothesized that long-term exposure to the naturally occurring manganese in shower water puts up to 8.7 million Americans at risk.[47][48][49]

A form of neurodegeneration[50] similar to Parkinson's Disease called "manganism" has been linked to manganese exposure amongst miners and smelters since the early 19th century.[51] Allegations of inhalation-induced manganism have been made regarding the welding industry. Manganese exposure in United States is regulated by Occupational Safety and Health Administration.[52]

Clinical toxicity

Manganism has occurred in persons employed in the production or processing of manganese alloys, patients receiving total parenteral nutrition, workers exposed to manganese-containing fungicides such as maneb, and abusers of drugs such as methcathinone made with potassium permanganate. Excessive exposure may be confirmed by measurement of blood or urine manganese concentrations.[53]

See also

Notes

  1. ^ Common oxidation states are in bold.

References

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External links

Wikimedia Commons has media related to: Manganese
Look up manganese in Wiktionary, the free dictionary.
Periodic table
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Uuq Uup Uuh Uus Uuo
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Manganese compounds
+2 oxidation state MnBr2 · MnCO3 · MnCl2 · MnF2 · MnO · MnS · MnSO4 · Mn3O4 · MnSe2 ·
+3 oxidation state MnF3 · Mn2O3 · Mn3O4
+4 oxidation state MnO2 · MnF4
+7 oxidation state

Mn2O7 ·

Categories: Chemical elements | Dietary minerals | Transition metals | Manganese | Deoxidizers | Occupational safety and health | Biology and pharmacology of chemical elements | Reducing agents

 

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Q. Hey does anyone know what the most stable oxidation state of Manganese is? Thanks :)
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A. I believe it's Mn+2. It will lose its two 4s-electrons, and keep five 3d electrons, which gives it a half-full d-orbital.
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