Magnesium diboride

Magnesium boride

Odorless dark gray to black powder

Fixed

800 ° C ( decomposition)

Insoluble in water

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Magnesium diboride is a metallic chemical compound which has the current highest critical temperature (39 K ) under the metallic superconductors. This is almost double to the previously known leader ( Niobgermanium, Nb3Ge, at 23 K). This property was discovered in 2001 by Japanese scientists in June Akimitsu, although magnesium diboride been known for over 50 years and easy to produce (but not in pure form).

Production and representation

In 1914, it was reported on the appearance of a magnesium boride, which was created in a hydrogen flow through the heating amorphous, finely divided boron with magnesium powder to red heat. The same compound was observed in the reaction of boron oxide with magnesium in addition magnesium oxide.

The preparation of pure magnesium diboride

The production of pure magnesium diboride as it is needed for the superconductor is expensive. However, since magnesium melt at 650 ° C, boron only at about 2000 ° C ( there is already magnesium in gaseous form ), a production of magnesium diboride by melting is not possible. Instead, the two starting materials at 900 ° C are brought together, that is, at a temperature not in boiling magnesium. The still occurring magnesium vapor diffuses into the boron, which form readily releasable magnesium diboride beads. In a procedure similar thin wires can be made.

Also possible is the deposition of thin films of magnesium diboride by the reaction of magnesium vapor in a hydrogen atmosphere with diborane.

Properties

Magnesium diboride is an odorless dark gray to black powder. Studies on magnesium diboride was first published in 1954 by Jones and March. This hitherto largest magnesium metal boride ( beside are, to date in the literature with MgB4, MgB7, MgB12 and MgB20 four other binary Magnesiumboride known) crystallizes in the aluminum diboride - type in the space group P6/mmm and the lattice constants a = 3.0834 ( 3) Å and c = 3.522 (2) Å. The boron atoms form in the ab plane graphite- like network of planar edge-sharing six-membered rings, wherein the magnesium atoms each above and below the ring centers and the boron atoms are trigonal prismatic surrounded by them.