'Magnesium' has the symbol 'Mg', the
atomic number 12, and an
atomic mass of 24.31. Magnesium is the ninth most abundant element in the universe by mass. It constitutes about 2% of the
Earth's
crust by mass, and it is the third most abundant element dissolved in
seawater. Magnesium ion is essential to all living cells, and is the 4th most abundant element by mass in the human body. The free element (metal) is not found in nature. Once produced from magnesium salts, this
alkaline earth metal is used as an
alloying agent to make
aluminium-magnesium alloys, sometimes called "magnalium" or "magnelium".
Isotopes
Magnesium has three stable
isotopes 24Mg,
25Mg,
26Mg present in significant amounts in purified samples.
28Mg is radioactive and in the 1950's to 1970's was made commercially by several nuclear power plants for use in scientific experiments. This isotope has a relativity short half-life (21 hours) and so its use was limited by shipping times.
26Mg has found application in
isotopic geology, similar to that of
aluminium.
26Mg is a
radiogenic daughter product of
26Al, which has a
half-life of 717,000 years. Large enrichments of stable
26Mg have been observed in the
Ca-Al-rich inclusions of some
carbonaceous chondrite meteorites. The anomalous abundance of
26Mg is attributed to the decay of its parent
26Al in the inclusions. Therefore, the meteorite must have formed in the
solar nebula before the
26Al had decayed. Hence, these fragments are among the oldest objects in the
solar system and have preserved information about its early history.
It is conventional to plot
26Mg/
24Mg against an Al/Mg ratio. In an
isochron dating plot, the Al/Mg ratio plotted is
27Al/
24Mg. The slope of the isochron has no age significance, but indicates the initial
26Al/
27Al ratio in the sample at the time when the systems were separated from a common reservoir.
Notable characteristics
Elemental magnesium is a fairly strong, silvery-white, light-weight metal (two thirds the density of
aluminium). It
tarnishes slightly when exposed to air, although unlike the alkaline metals, storage in an oxygen free environment is unnecessary because magnesium is protected by a thin layer of oxide which is fairly impermeable and hard to remove. Like its lower
periodic table group neighbor
calcium, magnesium reacts with water at room temperature, though it reacts much more slowly than calcium. When it is submerged in water,
hydrogen bubbles will almost unnoticeably begin to form on the surface of the metal, though if powdered it will react much more rapidly. Magnesium also reacts with
hydrochloric acid and produces heat and hydrogen when added to it. The magnesium will begin to bubble and become hot – too hot to touch comfortably. The reaction will occur faster with higher temperatures (see precautions). Magnesium is a highly flammable metal, but while it is easy to ignite when powdered or shaved into thin strips, it is difficult to ignite in mass or bulk. Once ignited it is difficult to extinguish, being able to burn in both
nitrogen (forming magnesium nitride), and
carbon dioxide (forming magnesium oxide and
carbon).
Magnesium, when it burns in air, produces a brilliant white light
(images of burning magnesium). This was used in the early days of
photography when magnesium powder was used as a source of illumination (flash powder). Later, magnesium ribbon was used in electrically ignited flash bulbs. Magnesium powder is still used in the manufacture of
fireworks and marine
flares where a brilliant white light is required.
Magnesium, when glowing white, has many chemical properties that it does not possess at lower temperatures. It also becomes more toxic, although this is of little practical importance, because the high temperature alone generally prevents human contact.
Magnesium compounds are typically white crystals. Most are soluble in water, providing the sour-tasting magnesium ion Mg
2+. Small amounts of dissolved magnesium ion contributes to the tartness and taste of natural waters. Magnesium ion in large amounts is an ionic laxative, and magnesium sulfate (
Epsom salts) is sometimes used for this purpose. So-called "
milk of magnesia" is a water suspension of one of the few insoluble magnesium compounds: magnesium hydroxide. The undissolved particles give rise to its appearance and name. Milk of magnesia is a mild base, and is commonly used as an antacid.
History
The name originates from the
Greek word for a district in
Thessaly called
Magnesia. It is related to
magnetite and
manganese, which also originated from this area, and required differentiation as separate substances. See
manganese for this history.
Magnesium is the eighth most abundant element in the earth's crust. It is found in large deposits of
magnesite,
dolomite, and other
minerals, and in mineral waters, where magnesium ion is soluble. In 1618 a farmer at Epsom in England attempted to give his cows water from a well. This they refused to drink because of the water's bitter taste. However the farmer noticed that the water seemed to heal scratches and rashes. The fame of
Epsom salts spread. Eventually they were recognised to be hydrated magnesium sulphate, MgSO
4.
Sir
Humphry Davy electrolytically isolated pure magnesium metal in 1808 from a mix of magnesia and
HgO, and
A. A. B. Bussy prepared it in coherent form in
1831. Davy's first suggestion for a name was magnium, but the name magnesium is now used.
Sources
Although magnesium is found in over 60
minerals, only
dolomite,
magnesite,
brucite,
carnallite,
talc, and
olivine are of commercial importance.
In the
United States this metal is principally obtained by
electrolysis of fused
magnesium chloride from
brines, wells, and
sea water:
:
cathode: Mg
2+ + 2
e- → Mg
:
anode: 2
Cl- → Cl
2 (gas) + 2 e
-
The
United States has traditionally been the major world supplier of this metal, supplying 45% of world production even as recently as 1995. Today, the US market share is at 7%, with a single domestic producer left,
US Magnesium, a company born from now-defunct
Magcorp.
[1] As of 2005
China has taken over as the dominant supplier, pegged at 60% world market share, which increased from 4% in 1995. Unlike the above described
electrolytic process, China is almost completely reliant on a different method of obtaining the metal from its ores, the
silicothermic Pidgeon process (the reduction of the oxide at high temperatures with silicon).
Magnesium from sea water
Sea water frequently contains the Mg
2+ cation, and to extract the magnesium,
calcium carbonate is added to sea water to form
magnesium carbonate precipitate.
MgCl
2 + CaCO
3 → MgCO
3 + CaCl
2
Magnesium carbonate is insoluble in water so it can be filtered out, and reacted with
hydrochloric acid to obtain concentrated
magnesium chloride.
MgCO
3 + 2HCl → MgCl
2 + CO
2 + H
2O
From
magnesium chloride, electrolysis produces magnesium.
Biology
Main articles: Magnesium in biology
Magnesium ions are essential to the basic
nucleic acid chemistry of life, and thus are essential to all cells of all known living organisms.
Plants have an additional use for magnesium in that
chlorophylls are magnesium-centered
porphyrins. Many
enzymes require the presence of magnesium ions for their catalytic action, especially enzymes utilizing
ATP, or those which use other nucleotides to synthesize
DNA and
RNA.
Magnesium is a vital component of a healthy human diet and has been implicated in a number of human diseases. Magnesium is readily available in the food that we eat and magnesium deficiency is therefore relatively rare. It is also difficult to overdose on magnesium. However, both of these conditions do occasionally appear in humans. The major causes are genetic with the inactivation of magnesium transporters in the Kidneys. General failure of the Kidneys may also lead to magnesium imbalance.
Applications
As the metal
Products made of magnesium: firestarter and shavings, sharpener, magnesium band
Magnesium is the third most commonly used structural metal, following steel and aluminium.
Magnesium compounds, primarily
magnesium oxide, are used mainly as
refractory material in
furnace linings for producing
iron,
steel, nonferrous metals,
glass and
cement. Magnesium oxide and other compounds also are used in agricultural, chemical and construction industries. As a metal, this element's principal use is as an alloying additive to
aluminium with these aluminium-magnesium alloys being used mainly for
beverage cans.
Magnesium, in its purest form, can be compared with aluminium, and is strong and light, so it is used in several high volume part manufacturing applications, including automotive and truck components. Specialty, high-grade car wheels of magnesium alloy are called "
mag wheels". In 1957 a
Corvette SS, designed for racing, was constructed with magnesium body panels.
Volkswagen has used magnesium in its engine components for many years. For a long time,
Porsche used magnesium alloy for its
engine blocks due to the weight advantage. There is renewed interest in magnesium engine blocks, as featured in the 2006
BMW 325i and 330i models. The BMW engine uses an aluminium alloy insert for the cylinder walls and cooling jackets surrounded by a high temperature magnesium alloy AJ62A. The application of magnesium AE44 alloy in the 2006 Corvette
Z06 engine cradle has advanced the technology of designing robust automotive parts in magnesium. Both of these alloys are recent developments in high temperature low
creep magnesium alloys. The general strategy for such alloys is to form
intermetallic precipitates at the
grain boundaries, for example by adding
mischmetal or
calcium.
[2] New alloy development and lower costs, which are becoming competitive to aluminium, will further the number of automotive applications.
In December 2005, for the first time on record, the automotive grade magnesium alloy price per cm³ dropped below the A380 aluminum alloy price per cm³.
The second application field of magnesium is electronic devices. Due to low weight, good mechanical and electrical properties, magnesium is widely used for manufacturing of mobile phones, laptop computers, cameras, and other electronic components.
Historically, magnesium was one of the main aerospace construction metals and was used for German military aircraft as early as World War I and extensively for German aircraft in World War II. The Germans coined the name 'Elektron' for magnesium alloy which is still used today. Due to perceived hazards with magnesium parts in the event of fire, the application of magnesium in the commercial aerospace industry was generally restricted to engine related components. Currently the use of magnesium alloys in aerospace is increasing, mostly driven by the increasing importance of fuel economy and the need to reduce weight. The development and testing of new magnesium alloys notably Elektron 21 which has successfully undergone extensive aerospace testing for suitability in both engine, internal and airframe components. European Community runs three R&D magnesium projects in Aerospace priority of Six Framework Program.
Other uses include:
★ Removal of
sulfur from iron and steel.
★ Production of
Titanium
★
Photoengraved plates in the printing industry.
★ Combined in alloys, this metal is essential for
airplane and
missile construction.
★ When used as an alloying agent, this metal improves the mechanical,
fabrication and
welding characteristics of aluminium.
★ Additive agent for conventional propellants and used in producing nodular graphite in cast iron.
★ Reducing agent for the production of pure
uranium and other metals from their
salts.
★ Magnesium turnings or ribbon are used to prepare
Grignard reagents, which are useful in
organic synthesis
★ Easily reacting with water, it can serve as a
desiccant
★ Magnesium is also flammable, burning at a temperature of approximately 2500 K (2200 °C, 4000 °F).
★ The
autoignition temperature of magnesium is approximately 744 K (473 °C, 883 °F).
★ The extremely high temperature at which magnesium burns makes it a handy tool for starting emergency fires during outdoor recreation.
★ Other uses include flashlight
photography, flares,
pyrotechnics, sparklers, and incendiary bombs.
In magnesium compounds
★ Magnesium's
hydroxide is used in
milk of magnesia, its
chloride and
citrate used as oral magnesium supplements, and its
sulfate (
Epsom salts) for various purposes in medicine, and elsewhere.
★
Epsom salt (magnesium sulfate) is used to treat aches and sore throats.
★ Dead-burned magnesite is used for refractory purposes such as brick and liners in furnaces and converters.
★
Magnesium carbonate (Mg
CO3) powder is also used by athletes, such as
gymnasts and
weightlifters, to improve the grip on objects – the apparatus or lifting bar.
★
Magnesium stearate is a slightly
flammable white
powder with
lubricative properties. In
pharmaceutical technology it is used in the manufacturing of
tablets, to prevent the tablets from sticking to the equipment during the tablet compression process (i.e., when the tablet's substance is pressed into tablet form).
★ Magnesium borate, magnesium salicylate and magnesium sulfate are used as
antiseptics to kill germs.
★
Magnesium bromide is used as a mild
sedative.
★ Magnesium in the forms of magnesium oxide and magnesium gluconate are used in dietary supplement tablets. These have been shown to be an effective therapy for some individuals who suffer from
Restless Leg Syndrome (
RLS).
★
Magnesium sulfite is used in the manufacture of
paper.
★ Magnesium phosphate is used to fireproof wood for construction.
★ Magnesium hexafluorosilicate is used in mothproofing of
textiles.
★ The magnesium ion is necessary for all life (see
magnesium in biological systems), so magnesium salts are an additive for foods, fertilizers (Mg is a component of chlorophyll), and culture media.
★ Magnesium is even used to make some higher end
yo-yos such as the Duncan Freehand Mg (priced at $450).
Precautions
Magnesium metal and alloys are highly flammable in their pure form when molten, as a powder, or in ribbon form. Burning or molten magnesium metal reacts violently with water. Magnesium powder is an explosive hazard. One should wear safety glasses while working with magnesium, and if burning it, these should include a heavy U.V. filter, similar to welding eye protection. The bright white light (including
ultraviolet) produced by burning magnesium can permanently damage the retinas of the eyes, similar to welding arc burns.
[3]
Water should not be used to extinguish magnesium fires, because it can actually feed the fire, according to the reaction:
[4]
:Mg
(s) + 2 H
2O
(g) → Mg(OH)
2 (aq) + H
2 (g)
:or in words:
:Magnesium
(solid) + steam → Magnesium hydroxide
(aqueous) + Hydrogen
(gas)
Carbon dioxide
fire extinguishers should not be used either, because magnesium can burn in carbon dioxide (forming
magnesium oxide, MgO, and
carbon).
[5] A
Class D dry chemical fire extinguisher should be used if available, or else the fire should be covered with
sand or magnesium foundry flux. An easy way to put out small metal fires is to place a polyethene bag filled with dry sand on top of the fire. The heat of the fire will melt the bag and the sand will flow out onto the fire.
See also
★
★
References
1. Man With Many Enemies
2.
3. Science Safety: Chapter 8
4. Chemistry : Periodic Table : magnesium : chemical reaction data
5. Demo Lab: Reaction Of Magnesium Metal With Carbon Dioxide
External links
★
Magnesium Industry Professional’s corner
★
WebElements.com – Magnesium
★
Magnesium online resource center
★
The Magnesium Website – Includes full text papers and textbook chapters by leading magnesium authorities Mildred Seelig, Jean Durlach, Burton M. Altura and Bella T. Altura. Links to over 300 articles discussing magnesium and magnesium deficiency.
★
Computational Chemistry Wiki
★
Humorous story of burning a magnesium NeXT computer.
★
Info.
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