Magnesium is the chemical element with atomic number 12, symbol Mg.

Magnesium is an alkaline earth metal. Magnesium is the ninth most abundant element in the universe8. It is produced in large aging stars by the sequential addition of three helium nuclei to a carbon nucleus9. When such stars explode as supernovas, much of the magnesium is expelled into the interstellar medium where it can be recycled into new star systems. Magnesium is the eighth most abundant element in the Earth's crust10 and the fourth most common element on Earth (after iron, oxygen and silicon), constituting 13% of the mass of the planet and a large part of the planet coat. It is the third most abundant element dissolved in seawater, after sodium and chlorine11.

Magnesium atoms exist in nature only as combinations with other elements, where it invariably has the +2 oxidation state. The pure element is produced artificially by reduction or electrolysis. It is highly reactive in powder and in chips but, left in the open air, it is quickly coated with a thin layer of waterproof oxide reducing its reactivity (passivation by oxidation). Pure metal burns easily under certain conditions (producing a characteristic bright, white, dazzling light). In mechanics it is mainly used as a component in aluminum-magnesium alloys (sometimes called magnalium). Magnesium is less dense than aluminum and the alloy is appreciated for its lightness and its greater resistance (mechanical and chemical).

Magnesium is the eleventh most abundant element in mass in the human body. It is essential for all cells and some 300 enzymes, notably as a cofactor. Magnesium ions interact with polyphosphate compounds such as ATP, DNA and RNA. Magnesium compounds are used medicinally as laxatives, antacids (for example, milk of magnesia) and to stabilize abnormal excitation of nerves or spasm of blood vessels under conditions such as eclampsia12.

Magnesium is mainly used in the automotive field because it allows for fuel savings of 75% greater than that of aluminum, thanks to its density (the lowest of the structural metals) but also its good mechanical properties (especially for reducing vibrations).

Its production and recycling are, on the other hand, difficult, energy-consuming and polluting (see Deposit and production of metal) 14. It would also lead to significant environmental gains in the aviation sector15.

It is a metal used in mechanics for its lightness.

It is also an important reagent in chemistry, especially used in desulfurization processes, during the manufacture of steels, the purification of metals (debismuthage) or the Grignard reaction. It is flammable and was used as fuel in photographic flashes. It is a chemical agent essential for life, especially during photosynthesis, in bones and in a multitude of biological processes. Its salts have multiple applications (milk of magnesia Mg (OH) 2, magnesium carbonate, MgO, MgCl2)

It is also used to make a multitude of objects as rolled, machined, molded. In specialized mass consumption (bodywork, small resistant cases, laptop cases, high-end photographic equipment, bicycle parts, etc.) because it is one of the easiest metals to machine, especially as some alloys are recyclable by lamination 16.

Magnesium is also used in alloys, notably with aluminum (series 3000, 4000, 5000 and 6000) but also with zinc, zirconium, thorium and several rare earths (lanthanum and cerium) 17.

Another common use is the protection against corrosion of other submerged metals, mainly iron, this is called sacrificial anode (its use is common for the protection of boat hulls or hot water tanks).

Battery project
The stable, abundant, non-toxic, non-corrosive nature of magnesium, which moreover does not produce dendrites as lithium ion does with rechargeable lithium batteries18,19 makes it an attractive material for new rechargeable magnesium-sulfur batteries (Mg / S). The magnesium ion is tested as a charge carrier while the magnesium metal is used for the anodes and sulfur as the cathode18. In 2019, this technology is still emerging but promising20 especially since the Mg / S couple can provide a theoretical energy density of 1722 Wh / kg with a voltage of around 1.7 V18; it could be a safe and inexpensive economical alternative to Li-ion batteries, including for electric vehicles (by storing more electricity). They could also benefit from high capacity cathodes, possibly operating under high voltage, the material of which (based on sulfur, with magnesium borohydride21, magnesium borate22 or magnesium sulfide for example 23,24) would allow a density of higher energy than with lithium-ion batteries25. The conductivity of the sulfur cathode can be doped with carbon (semi-organic cathode composite) 18.

copper     aluminum     lead    Zinc   tin    nickel   iron

   magnesium    bismuth   manganese   chromium    cobalt    titanium

    Tungsten    vanadium   niobium   indium     molybdenum     antimony