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Magnesium oxide (Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg 2+ ions and O 2− ions held together by ionic bonding .
In aluminium alloys containing magnesium, magnesium oxides (MgO), cuboids (MgAl 2 O 4-cuboid) and metallurgical spinel (MgAl 2 O 4-spinel) can form. They result from the reaction between magnesium and oxygen in the melt. More of them will form with time and temperature. Spinel can be highly detrimental because of its big size and high hardness.
The temperature of firing has a greater influence on reactivity than grind size as excess energy goes into lattice energy. Crystalline magnesium oxide, or periclase, has a calculated lattice energy of 3795 kJ mol-1 which must be overcome for it to go into solution or for reaction to occur.
In both, magnesium oxide is the precursor to magnesium metal. The magnesium oxide is produced as a solid solution with calcium oxide by calcining the mineral dolomite, which is a solid solution of calcium and magnesium carbonates: CaCO 3 ·MgCO 3 → MgO·CaO + 2 CO 2. Reduction occurs at high temperatures with silicon.
Vapor-deposited magnesium crystals from the Pidgeon process. The Pidgeon process is a practical method for smelting magnesium.The most common method involves the raw material, dolomite being fed into an externally heated reduction tank and then thermally reduced to metallic magnesium using 75% ferrosilicon as a reducing agent in a vacuum. [1]
The solubility of Mg decreases sharply with falling temperature, i.e., at 100 °C it is still 2%, at room temperature 0.2%. The elimination of the -phase occurs with pure AlMg alloys after a four-stage process. With technically used alloys with other alloying elements and impurities, the process is much more complicated: [4]
Magnesium is highly flammable, burning at a temperature of approximately 3,100 °C (3,370 K; 5,610 °F), [2] and the autoignition temperature of magnesium ribbon is approximately 473 °C (746 K; 883 °F). [3] It produces intense, bright, white light when it burns.
The binary magnesium-manganese alloy (AM505) is readily extruded at low pressures in the temperature range 250 to 350 °C (482 to 662 °F)., the actual temperature used depending upon the reduction and billet length rather than the properties desired, which are relatively insensitive to extrusion conditions.