Magnesium

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MELTING POINT: 651°C
BOILING POINT: 1,107°C
DENSITY: 1.738 g/cm ³ at 20°C
MOST COMMON IONS: Mg ²⁺

Magnesium was first recognized as an element by Joseph Black in 1755. In 1808 Sir Humphry Davy isolated the element, and in 1831 H. Bussy devised a method for producing it. Magnesium, in its combined states, is readily abundant and is the eighth most common element in Earth's crust. Magnesium metal is silvery white in color.

The most common method for producing elemental magnesium is in fused salt electrolytic cells, wherein magnesium chloride (MgCl ₂ ) is decomposed by applying a voltage to elemental magnesium and chlorine gas. The magnesium chloride feed is obtained directly from seawater or from magnesium oxide deposits containing magnesite or dolomite. In these cases, the oxide is first chlorinated prior to electrolysis. Another method is to produce magnesium directly from the oxide by reducing the oxide with silicon under vacuum. The resultant Mg vapor is condensed to recover Mg metal. This process is carried out in vacuum retorts and is known as the Pidgeon process.

The principal uses of Mg are for alloying with aluminum, for desulphurizing steel and pig iron, and for nodularizing the graphite in cast irons. Recently, researchers have focused on using Mg alloys to produce lightweight components in automobiles. As a result, Mg usage in vehicles is steadily increasing.

Compounds of magnesium, including the hydroxide, the chloride, the citrate, and the sulfate, are used in the medical field. Magnesium is an important element in both animal and plant life. On average, adults require a daily intake of about 300 milligrams (0.011 ounces) of magnesium.

SEE ALSO Alkaline Earth Metals ; Black, Joseph ; Davy, Humphry ; Inorganic Chemistry .

Frank Mucciardi

Bibliography

Kramer, Deborah A. (2001). "Magnesium, Its Alloys and Compounds." U.S. Geological Survey Open-File Report 01-341. Also available from http://pubs.usgs.gov/of/of01-341/ .

Raloff, J. (1998). "Magnesium: Another Metal to Bone up On." Science News. 154(9):134.