|
|
www.mineralgallery.co.za Minerals K-O |
|
|
Manganese |
||
Name
Manganese group
Uses
In the steel industry
Color
Black
The Earth's crust contains 850 ppm manganese in chemically bonded form. By far the most important manganese mineral is pyrolusite, which consists largely of manganese dioxide.
Pyrolusite is brown black in color and often somewhat magnetic; the name manganese is a corrupted form of the Latin word for a form of magnetic stone, magnesia. Although manganese ores are not scarce, extraction is economically feasible only with open-cast mining. In addition, extensive deposits of manganese nodules are found at many sites on the ocean floor.
Biological Significance
Trace amounts of manganese are essential for plant growth, because the element is involved in nitrogen and iron metabolism and in the function of some of the enzymes involved in photosynthesis and respiration. Higher animals also require trace amounts of the element for activating many of the metabolic enzymes, for good bone structure, and for central nervous system functions.
Uses
Pure manganese is rarely used, as it is a moderately reactive and brittle metal. About 95% of the world's annual production of manganese is used by the iron and steel industry to purify iron and to make alloys. Manganese is added to iron because it reduces iron oxide to form manganese oxide, which dissolves well in molten slag and is easily separated from the iron. In alloys, manganese increases the durability and corrosion resistance of iron and steel and makes steel more malleable when forged. Manganese steel, or Hadfield manganese steel, contains 11-14% manganese and 1-1.5% carbon. This nonmagnetic, tough, durable, and shockproof alloy is used in grinding machinery, wrecking equipment, caterpillar trucks, and mechanical pounding equipment used in heavy-duty construction. The iron manganese alloys, which are used for making other alloys, are ferromanganese (about 80% Mn) and spiegeleisen (15-30% Mn); they contain some carbon and silicon.
Other important manganese alloys that do not contain iron include the Heusler alloys (18-25% manganese plus copper and aluminum or zinc), which are the strongest nonferrous metals; manganese copper (approximately 75% copper and 25% manganese), which has great electrical resistance; and manganin (about 83% copper, 14% manganese, and 3% nickel), which has a very slight heat-expansion coefficient and an electrical resistance nearly independent of temperature. Alloys very rich in manganese and containing nickel and copper have a high heat-expansion coefficient, however, and are used in the expanding part of bimetal thermostats.
The most important manganese compound, pyrolusite or manganese dioxide, is also an oxidizing agent. Pyrolusite is used extensively in the electrodes of dry batteries, where it absorbs liberated hydrogen gas and then chemically bonds it. It is also used as an oxygen source in fireworks and as a chemical catalyst. All other manganese compounds are made from pyrolusite.