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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]
The first crystalline artificial diamond simulants were synthetic white sapphire (Al 2 O 3, pure corundum) and spinel (MgO·Al 2 O 3, pure magnesium aluminium oxide). Both have been synthesized in large quantities since the first decade of the 20th century via the Verneuil or flame-fusion process, although spinel was not in wide use until the ...
All red gemstones used to be referred to as rubies or "balas rubies". It was not until 1783 that spinels were chemically differentiated from rubies. [5] They both contain aluminium and oxygen, and both derive their colour from chromium(III), but the spinel crystal also contains magnesium, which rubies lack.
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 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. [9]
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.
Cordierite or iolite is a magnesium iron aluminium cyclosilicate. Iron is almost always present, and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe) 2 Al 3 (Si 5 AlO 18) to (Fe,Mg) 2 Al 3 (Si 5 AlO 18). [3]
Aluminium-magnesium alloys are considered to be very corrosion-resistant, making them suitable for marine applications, but this is only true if the -phase exists as a non-contiguous phase. Alloys with Mg contents below 3% are therefore always corrosion-resistant, with higher contents, appropriate heat treatment must ensure that this phase is ...