|
|
Atomic Number: |
25 |
Melting Point: | 1246 ºC | |
| Atomic Symbol: | Mn | Boiling Point: | 2061 ºC | ||
| Atomic Weight: | 54.9380 amu | Density: | 7470
kg/m 3 |
||
| Atomic Radius: |
124 pm |
Oxidation States: | 7, 4, 3, 2 | ||
| Covalent Radius: | 139 pm | Electron Configuration: | [Ar]4s23d5 | ||
| van der Waals Radius: |
-- |
State of Matter: | solid |
(L. magnes: magnet, from magnetic properties of pyrolusite; Itl. manganese, corrupt form of magnesia)
Recognized by Scheele, Bergman, and others as an element and isolated by Gahn in 1774 by reduction of the dioxide with carbon.
It is gray-white, resembling iron, but is harder and very brittle. The metal is reactive chemically, and decomposes cold water slowly. Manganese is used to form many important alloys. In steel, manganese improves rolling and forging qualities, strength, toughness, stiffness, wear resistance, hardness, and hardenability.
With aluminum and antimony, and 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 said to be flexible, soft, easily cut, and capable of being bent.
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 may become 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 Russia, Brazil, Australia, South Africa, Gabon, and India. Pyrolusite and rhodochrosite are among the most common manganese minerals. The metal is obtained by reduction of the oxide with sodium, magnesium, aluminum, or by electrolysis.
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 utilization of vitamin B1.
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 dioxide is used in dry cells, and can be used to decolorize glass that is colored green by trace amounts of iron. Manganese compounds can color glass an amethyst color, and is responsible for the color of true amethyst. Manganese dioxide is also used in the manufacture of oxygen and chlorine, and in drying black paints.
Naturally occurring manganese is composed of 1 stable isotope; 55-Mn. 18 radioisotopes have been characterized with the most stable being 53-Mn with a half-life of 3.7 million years, 54-Mn with a half-life of 312.3 days, and 52-Mn 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 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.
Parkinson's Disease has been linked to manganese exposure and the welding industry especially. Scientists have reported that welders studied had an average of the onset of Parkinson's Disease 15 years prior to the rest of the general population. Listed on the Hazardous Substance List, manganese is regulated by OSHA due to its high level of toxicity.
