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Magnesium is a chemical element; it has symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic table), it occurs naturally only in combination with other elements and almost always has an oxidation state of +2. It reacts readily with air to form a thin passivation coating of magnesium oxide that inhibits further corrosion of the metal. The free metal burns with a brilliant-white light. The metal is obtained mainly by electrolysis of magnesium salts obtained from brine. It is less dense than aluminium and is used primarily as a component in strong and lightweight magnesium alloy that contain aluminium.
In the cosmos, magnesium is produced in large, aging by the sequential addition of three Helium nucleus to a carbon nucleus. When such stars explode as , much of the magnesium is expelled into the interstellar medium where it may recycle into new star systems. Magnesium is the eighth most abundant element in the Earth's crust and the fourth most common element in the Earth (after iron, oxygen and silicon), making up 13% of the planet's mass and a large fraction of the planet's mantle. It is the third most abundant element dissolved in seawater, after sodium and chlorine.
This element is the eleventh most abundant element by mass in the human body and is essential to all cells and some 300 enzymes. Magnesium ions interact with polyphosphate compounds such as ATP, DNA, and RNA. Hundreds of enzymes require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives and antacids (such as milk of magnesia), and to stabilize abnormal nerve excitation or blood vessel spasm in such conditions as eclampsia.
Pure polycrystalline magnesium is brittle and easily fractures along . It becomes much more ductility when alloyed with small amounts of other metals, such as 1% aluminium. The malleability of polycrystalline magnesium can also be significantly improved by reducing its grain size to about 1 micrometre or less.
When finely powdered, magnesium reacts with water to produce hydrogen gas:
Direct reaction of magnesium with air or oxygen at ambient pressure forms only the "normal" oxide MgO. However, this oxide may be combined with hydrogen peroxide to form magnesium peroxide, MgO2, and at low temperature the peroxide may be further reacted with ozone to form magnesium superoxide Mg(O2)2.
Magnesium reacts with nitrogen in the solid state if it is powdered and heated to just below the melting point, forming Magnesium nitride Mg3N2.
Magnesium reacts with water at room temperature, though it reacts much more slowly than calcium, a similar group 2 metal. When submerged in water, hydrogen bubbles form slowly on the surface of the metal; this reaction happens much more rapidly with powdered magnesium. The reaction also occurs faster with higher temperatures (see ). Magnesium's reversible reaction with water can be harnessed to store energy and run a magnesium-based engine. Magnesium also reacts exothermically with most acids such as hydrochloric acid (HCl), producing magnesium chloride and hydrogen gas, similar to the HCl reaction with aluminium, zinc, and many other metals. Although it is difficult to ignite in mass or bulk, magnesium metal will ignite.
Magnesium may also be used as an igniter for thermite, a mixture of aluminium and iron oxide powder that ignites only at a very high temperature.
A prominent organomagnesium reagent beyond Grignard reagents is magnesium anthracene, which is used as a source of highly active magnesium. The related butadiene-magnesium adduct serves as a source for the butadiene dianion.
Complexes of dimagnesium(I) have been observed.
Azo violet dye can also be used, turning deep blue in the presence of an alkaline solution of magnesium salt. The color is due to the adsorption of azo violet by Mg(OH)2.
As recently as 2020, magnesium hydride was under investigation as a way to store hydrogen.
The nuclide has found application in isotope geology, similar to that of aluminium. is a radiogenic daughter product of , which has a half-life of 717,000 years. Excessive quantities of stable have been observed in the Ca-Al-rich inclusions of some carbonaceous chondrite . This anomalous abundance is attributed to the decay of its parent in the inclusions, and researchers conclude that such meteorites were formed in the solar nebula before the had decayed. These are among the oldest objects in the Solar System and contain preserved information about its early history.
It is conventional to plot / against an Al/Mg ratio. In an isochron dating plot, the Al/Mg ratio plotted is /. The slope of the isochron has no age significance, but indicates the initial / ratio in the sample at the time when the systems were separated from a common reservoir.
Although magnesium is found in more than 60 , only dolomite, magnesite, brucite, carnallite, talc, and olivine are of commercial importance.
The cation is the second-most-abundant cation in seawater (about the mass of sodium ions in a given sample), which makes seawater and sea salt attractive commercial sources for Mg.
In September 2021, China took steps to reduce production of magnesium as a result of a government initiative to reduce energy availability for manufacturing industries, leading to a significant price increase.
The Pidgeon and the Bolzano process differ in the details of the heating and the configuration of the reactor. Both generate gaseous Mg that is condensed and collected. The Pidgeon process dominates the worldwide production. The Pidgeon method is less technologically complex and because of distillation/vapour deposition conditions, a high purity product is easily achievable. China is almost completely reliant on the silicothermic Pidgeon process.
To extract the magnesium, calcium hydroxide is added to the seawater to precipitate magnesium hydroxide.
Magnesium hydroxide (brucite) is poorly soluble in water and can be collected by filtration. It reacts with hydrochloric acid to magnesium chloride.
The basic reaction is as follows:
The temperatures at which this reaction is operated is between 680 and 750 °C.
The magnesium chloride can be obtained using the Dow process, a process that mixes sea water and dolomite in a flocculator or by dehydration of magnesium chloride brines. The electrolytic cells are partially submerged in a molten salt electrolyte to which the produced magnesium chloride is added in concentrations between 6–18%. This process does have its share of disadvantages including production of harmful chlorine gas and the overall reaction being very energy intensive, creating environmental risks. The Pidgeon process is more advantageous regarding its simplicity, shorter construction period, low power consumption and overall good magnesium quality compared to the electrolysis method.
In the United States, magnesium was once obtained principally with the Dow process in Corpus Christi TX, by electrolysis of fused magnesium chloride from brine and sea water. A saline solution containing ions is first treated with Calcium oxide (calcium oxide) and the precipitated magnesium hydroxide is collected:
The hydroxide is then converted to magnesium chloride by treatment with hydrochloric acid and heating of the product to eliminate water:
The salt is then electrolyzed in the molten state. At the cathode, the ion is reduced by two to magnesium metal:
At the anode, each pair of ions is oxidized to chlorine gas, releasing two electrons to complete the circuit:
A disadvantage of this method is that slow cooling the vapour can cause the reaction to quickly revert. To prevent this from happening, the magnesium can be dissolved directly in a suitable metal solvent before reversion starts happening. Rapid quenching of the vapour can also be performed to prevent reversion.
In 1618, a farmer at Epsom in England attempted to give his cows water from a local well. The cows refused to drink because of the water's bitter taste, but the farmer noticed that the water seemed to heal scratches and rashes. The substance obtained by evaporating the water became known as Epsom salts and its fame spread. It was eventually recognized as hydrated magnesium sulfate, ·7.
The metal itself was first isolated by Humphry Davy in England in 1808. He used electrolysis on a mixture of magnesia alba and mercuric oxide. Antoine Bussy prepared it in coherent form in 1831. Davy's first suggestion for a name was 'magnium', but the name magnesium is now used in most European languages.
Further discoveries about magnesium were made by the father of physical chemistry in Imperial Russia, Nikolai Beketov (1827-1911), who established that magnesium and zinc displaced other metals from their salts under high temperatures.
Magnesium is used in lightweight materials and alloys. For example, when infused with silicon carbide , it has extremely high specific strength.
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, a term which is still used today. In the commercial aerospace industry, magnesium was generally restricted to engine-related components, due to fire and corrosion hazards. Magnesium alloy use in aerospace is increasing in the 21st century, driven by the importance of fuel economy. Magnesium alloys can act as replacements for aluminium and steel alloys in structural applications.
Magnesium powder (flash powder) was used for subject illumination in the early days of photography. (2025). 9781135873271, Routledge. ISBN 9781135873271 Magnesium filament used in electrically ignited single-use photography flashbulbs replaced this usage eventually. Magnesium powder is used in fireworks and marine where a brilliant light is required, and in trick self-relighting birthday candles. It was also used for various theatrical effects, such as lightning, (2025). 9780231116633, Columbia University Press. ISBN 9780231116633 pistol flashes, (2025). 9780595347667, iUniverse. ISBN 9780595347667 and supernatural appearances. (2025). 9780521616157, Cambridge University Press. ISBN 9780521616157
Magnesium is often used to ignite thermite or other materials that require a high ignition temperature. Magnesium continues to be used as an incendiary element in warfare. and flint to create sparks that ignite the shavings]]
Flame temperatures of magnesium and magnesium alloys can reach , although flame height above the burning metal is usually less than . Once ignited, such fires are difficult to extinguish because they resist several substances commonly used to put out fires; combustion continues in nitrogen (forming magnesium nitride),
Magnesium reacts with to give , which are used for a wide variety of forming carbon–carbon bonds.
Magnesium salts are included in various , (magnesium is a component of chlorophyll), and culture medium.
Magnesium sulfite is used in the manufacture of paper (sulfite process).
Magnesium phosphate is used to fireproof wood used in construction.
Magnesium hexafluorosilicate is used for moth-proofing .
In the U.S. the Recommended Dietary Allowances (RDAs) are for men ages 19–30 and for older; for women for ages 19–30 and for older.
Magnesium concentrations in plasma or serum may be monitored for efficacy and safety in those receiving the drug Therapy, to confirm the diagnosis in potential poisoning victims. The newborn children of mothers who received parenteral magnesium sulfate during labor may exhibit toxicity with normal serum magnesium levels.
Magnesium is capable of reducing water and releasing highly flammable hydrogen gas:
Therefore, water cannot extinguish magnesium fires. The hydrogen gas produced intensifies the fire. Dry sand is an effective smothering agent, but only on relatively level and flat surfaces.
Magnesium reacts with carbon dioxide exothermically to form magnesium oxide and carbon:
Hence, carbon dioxide fuels rather than extinguishes magnesium fires.
Burning magnesium can be quenched by using a Class D dry chemical fire extinguisher, or by covering the fire with sand or magnesium foundry flux to remove its air source.
(1963). 9780121266011, Academic Press. ISBN 9780121266011 in carbon dioxide (forming magnesium oxide and carbon), and in water (forming magnesium oxide and hydrogen, which also combusts due to heat in the presence of additional oxygen). This property was used in incendiary weapons during the firebombing of cities in World War II, where the only practical civil defense was to smother a burning flare under dry sand to exclude atmosphere from the combustion.
Chemical reagent
In the form of turnings or ribbons, to prepare , which are useful in organic synthesis.
Other
Compounds
Magnesium compounds, primarily magnesium oxide (MgO), are used as a refractory material in furnace linings for producing iron, steel, , glass, and cement. Magnesium oxide and other magnesium compounds are also used in the agricultural, chemical, and construction industries. Magnesium oxide from calcination is used as an electrical insulator in fire-resistant cables.
Biological roles
Mechanism of action
The important interaction between phosphate and magnesium ions makes magnesium essential to the basic nucleic acid chemistry of all cells of all known living organisms. More than 300 require magnesium ions for their catalytic action, including all enzymes using or synthesizing ATP and those that use other nucleotides to synthesize DNA and RNA. The ATP molecule is normally found in a Chelation with a magnesium ion.
(2025). 9789400774995, Springer. ISBN 9789400774995
Nutrition
Diet
Spices, nuts, cereals, cocoa and vegetables are good sources of magnesium. Green leafy vegetables such as spinach are also rich in magnesium.
Dietary recommendations
In the United Kingdom, the recommended daily values by the Dietary Reference Intake for magnesium are for men and for women.
Supplementation
Numerous pharmaceutical preparations of magnesium and dietary supplements are available. In two human trials magnesium oxide, one of the most common forms in magnesium dietary supplements because of its high magnesium content per weight, was less bioavailable than magnesium citrate, chloride, lactate or aspartate.
Metabolism
An adult body contains of magnesium, with 60% in the skeleton, 39% intracellular (20% in skeletal muscle), and 1% extracellular. Serum levels are typically or . Serum magnesium levels may be normal even when intracellular magnesium is deficient. The mechanisms for maintaining the magnesium level in the serum are varying gastrointestinal absorption and renal excretion. Intracellular magnesium is correlated with intracellular potassium. Increased magnesium lowers calcium and can either prevent hypercalcemia or cause hypocalcemia depending on the initial level. Both low and high protein intake conditions inhibit magnesium absorption, as does the amount of phosphate, phytate, and fat in the gut. Unabsorbed dietary magnesium is excreted in feces; absorbed magnesium is excreted in urine and sweat.
Detection in serum and plasma
Magnesium status may be assessed by measuring serum and erythrocyte magnesium concentrations coupled with Urinary system and Feces magnesium content, but intravenous magnesium loading tests are more accurate and practical. A retention of 20% or more of the injected amount indicates deficiency. As of 2004, no biomarker has been established for magnesium.
Deficiency
Low plasma magnesium (hypomagnesemia) is common: it is found in 2.5–15% of the general population. From 2005 to 2006, 48 percent of the United States population consumed less magnesium than recommended in the Dietary Reference Intake. Other causes are increased renal or gastrointestinal loss, an increased intracellular shift, and proton-pump inhibitor antacid therapy. Most are asymptomatic, but symptoms referable to neuromuscular, cardiovascular, and metabolic dysfunction may occur. Alcoholism is often associated with magnesium deficiency. Chronically low serum magnesium levels are associated with metabolic syndrome, diabetes mellitus type 2, fasciculation, and hypertension.
Therapy
Other medical applications
Sorted by type of magnesium salt, other therapeutic applications include:
Overdose
Overdose from dietary sources alone is unlikely because excess magnesium in the blood is promptly filtered by the . Overdose is more likely in the presence of impaired renal function. Overdose is likely in cases of excessive intake of supplements. Megavitamin therapy has caused death in a child, and severe hypermagnesemia in a woman and a young girl who had healthy kidneys. The most common symptoms of overdose are nausea, vomiting, and diarrhea; other symptoms include hypotension, confusion, slowed heart and respiratory rates, deficiencies of other minerals, coma, cardiac arrhythmia, and death from cardiac arrest.
Function in plants
Plants require magnesium to synthesize chlorophyll, essential for photosynthesis. Magnesium in the center of the porphyrin ring in chlorophyll functions in a manner similar to the iron in the center of the porphyrin ring in heme. Magnesium deficiency in plants causes late-season yellowing between leaf veins, especially in older leaves, and can be corrected by either applying epsom salts (which is rapidly leached), or crushed dolomitic limestone, to the soil.
Safety precautions
Magnesium metal and its alloys can be explosive hazards; they are highly flammable in their pure form when molten or in powder or ribbon form. Burning or molten magnesium reacts violently with water. When working with powdered magnesium, safety glasses with eye protection and UV filters (such as welders use) are employed because burning magnesium produces ultraviolet light that can permanently damage the retina of a human eye.
See also
Notes
Cited sources
External links
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