Magnesium is the 12th element on the periodic table of Mendeleev, where it is designated by the symbol Mg. It is a silvery-white, extremely light metal. Under normal conditions it is practically unchanged in air - it is protected from oxidation by a thin surface oxide layer.
|Atomic number||Atomic (molar) mass g/mol||Oxidation state||Density [g/cm3]||Melting point t°C||Boiling point t ° C||Melting point kJ/kg|
The discovery of magnesium is associated with the mineral waters of Epsom Spring in England. In 1695 a salt with a bitter taste and laxative effect was boiled out of the water (it was magnesia sulphate). Pharmacists immediately dubbed it English salt. The pure form of the metal was only isolated two centuries later, at the beginning of the twentieth century.
Magnesium is most abundant in the United States, Norway and China. Brusite and magnesite are 1/3 of magnesium salts, while kieserite, epsomite, dolomite are 1/6. The magnesium salts are easily soluble. Up to 0.13% of Mg is contained in seawater. Magnesite is brought out of the bowels by geothermal waters. The sediments of sedimentary lakes are especially rich in magnesium salts. Deposits of sedimentary carnallite salts are found everywhere. Deposits of dolomite are also associated with hot springs. Their reserves are enormous Most of them were formed millions of years ago by sedimentation.
Magnesium is an important electrolyte in the regulation of metabolism. As physicians have found out, applications of bischofit treat disorders of the musculoskeletal system, first of all, of the spine and joints, and are indispensable for rehabilitation of the consequences of injuries.
Technical magnesium is obtained by electrolysis of the molten salt mixture of magnesium, sodium and potassium chlorides. Such metal is contaminated with impurities and requires additional purification by electrolytic refining, remelting in a vacuum, together with special fluxes. Often sublimation in a vacuum is used. The purity of refined magnesium is 99.999% or higher. Another, thermal method, is based on the reduction of MgO with silicon or coke at high temperature. This is how silicon makes it easy to separate magnesium from dolomite. The price of magnesium in ingots is about $3/kg.
Mg readily dissolves in acids with the release of hydrogen. Alkalis have no effect on it. It corrodes quickly in seawater and 3% sodium chloride solution, forming hydroxide... Mg is stable in alcohols (except methyl), gasoline, kerosene, freon and mineral oils. It is a vigorous reducing agent, it displaces less active elements from compounds. It reduces other metals from salt solutions at room temperature. When heated, it takes oxygen away from alkalis and oxides, and simple compounds can be made with magnesium powder. This valuable property allows it to be used to produce titanium.
Mg is very light, its density at 20 °C is about 1.7 g/cm³, melting point 651 °C, boiling point: 1103 °C. Its surface is covered by a film of oxide, which breaks down at 623 °C, after which magnesium combusts. Mg foil and powder ignite with an ordinary match and burn not only in air but also in carbon dioxide. The bright magnesium flash, which has even ultraviolet rays in its spectrum, was used in photography until the beginning of the twentieth century. This property of burning with blindingly bright flame is indispensable in flares and signal rockets, tracer bullets and projectiles, and incendiary bombs. In pioneer camps it was added to the fires that were lit at the closing or opening of a shift. Such fires scattered a sheaf of sparks. A mixture of magnesium and potassium permanganate powders is an explosive.
Magnesium is a very light and ductile metal. It can be bent, stamped, rolled, drilled and cut well. However, in its pure form it is brittle and unsuitable for heavy-duty construction. Magnesium alloys with zinc, aluminum, beryllium, manganese, titanium or rare-earth elements are used for this purpose... They are corrosion-resistant and have considerable specific strength. Such alloys are produced by flux-free melting in an inert atmosphere. This produces a homogeneous structure that is physically and mechanically stable. Such alloys have an exceptionally wide range of applications.
Magnesium alloys percentage composition (GOST 2581-78)
|Mark of the alloy||Al||Zn||Mn||Other||Al||Si||Fe||Ni||Cu|
|MCr1H3||-||-||0,2-0,5||0,4-1,1 Zr - 2,6-3,2 Nd||0,02||0,02||0,01||0,004||0,01|
Today, magnesium has become the basis for the lightest construction materials. The alloy of aluminum and magnesium has a significant specific strength and is essential in today's aviation and automotive industry. The lightest parts of airplanes, helicopters and dirigibles are made of this alloy. It gives a serious advantage when developing new models. This alloy is now the basis for parts of airframes, fairings, ailerons, cockpit doors, landing gear, control levers, instrument and pump housings, oxygen and fuel tanks. Parts made of magnesium alloys reduce fuel consumption by reducing weight and increase fuel efficiency of modern automobiles. Magnesium alloys are used in the manufacture of automotive crankcases, shock absorber parts, pump and instrumentation parts, and tank covers. Magnesium wheel rims give not only lightness and durability, but also a stylish look. In instrumentation, rolled magnesium is required for instrument housings, binoculars, cell phones and video cameras. Rolled magnesium is used in the manufacture of electric batteries and the negligible absorption of thermal neutrons is the basis of magnesium used in the manufacture of fuel element cladding.
Magnesium salts (magnesium bromide and perchlorate) are used in modern high-power batteries, which have considerable capacity and discharge voltage. Magnesium-sulfur batteries are still at a promising stage of development. Magnesium perchlorate is also used for deep drying of gases. MgO is part of refractories for production of crucibles and lining of industrial furnaces. Synthetic single crystals of MgF2 are the basis of special optics.
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