Magnesium hydride

Magnesium hydride is the chemical compound MgH₂. It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium.

Preparation

In 1951 preparation from the elements was first reported involving direct hydrogenation of Mg metal at high pressure and temperature (200 atmospheres, 500 °C) with MgI₂ catalyst:

Lower temperature production from Mg and H₂ using nano crystalline Mg produced in ball mills has been investigated. Other preparations include:

Structure and bonding

The room temperature form α-MgH₂ has a rutile structure. There are at least four high pressure forms: γ-MgH₂ with α-PbO₂ structure, cubic β-MgH₂ with Pa-3 space group, orthorhombic HP1 with Pbc2₁ space group and orthorhombic HP2 with Pnma space group. Additionally a non stoichiometric MgH_(2-δ) has been characterised, but this appears to exist only for very small particles
(bulk MgH₂ is essentially stoichiometric, as it can only accommodate very low concentrations of H vacancies).

MGH

MGH may refer to:

Magnesium monohydride

Magnesium monohydride is a molecular gas with formula MgH that exists at high temperatures, such as the atmospheres of the Sun and stars. It was originally known as magnesium hydride, although that name is now more commonly used when referring to the similar chemical magnesium dihydride.

History

George Downing Liveing and James Dewar are claimed to be the first to make and observe a spectral line from MgH in 1878. However they did not realise what the substance was.

Formation

A laser can evaporate magnesium metal to form atoms that react with molecular hydrogen gas to form MgH and other magnesium hydrides.

An electric discharge through hydrogen gas at low pressure (20 pascals) containing pieces of magnesium can produce MgH.

Thermally produced hydrogen atoms and magnesium vapour can react and condense in a solid argon matrix. This process does not work with solid neon, probably due to the formation of MgH₂ instead.

A simple way to produce some MgH is to burn magnesium in a bunsen burner flame, where there is enough hydrogen to form MgH temporarily. Magnesium arcs in steam also produce MgH, but also produce MgO.