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Polyhedral representation of spinel MgAl 2 O 4. Spinel (/ s p ɪ ˈ n ɛ l, ˈ s p ɪ n əl / [7]) is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl 2 O 4 in the cubic crystal system. Its name comes from the Latin word spinella, a diminutive form of spine, in reference to its pointed crystals. [5]
Magnesium aluminate spinel (MgAl 2 O 4) is a transparent ceramic with a cubic crystal structure with an excellent optical transmission from 0.2 to 5.5 micrometers in its polycrystalline form. Optical quality transparent spinel has been produced by sinter/HIP, hot pressing, and hot press/HIP operations, and it has been shown that the use of a ...
It is four times as hard as fused silica glass, 85% as hard as sapphire, and nearly 115% as hard as magnesium aluminate spinel. It can be fabricated into transparent windows, plates, domes, rods, tubes, and other forms using conventional ceramic powder processing techniques. [citation needed]
The heterogeneity of spinel group members varies based on composition with ferrous and magnesium based members varying greatly as in solid solution, which requires similarly sized cations. However, ferric and aluminium based spinels are almost entirely homogeneous due to their large size difference.
Magnesium aluminide is an intermetallic compound of magnesium and aluminium. Common phases (molecular structures) include the beta phase (Mg 2 Al 3 ) and the gamma phase (Mg 17 Al 12 ), which both have cubic crystal structures.
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.
There are many mixed oxides containing aluminium where there are no discrete or polymeric aluminate ions. The spinels with a generic formula A 2+ B 3+ 2 O 2− 4 that contain aluminium as Al 3+, such as the mineral spinel itself, MgAl 2 O 4 are mixed oxides with cubic close packed O atoms and aluminium Al 3+ in octahedral positions.
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