Magnesium dihydride

As seen from the change in valency of metal and hydrogen, this is a redox reaction because the metal is oxidized (loses n electrons) by the hydrogen, while the valence of hydrogen becomes, formally, -1. Magnesium dihydride, MgH, can be manufactured in ball mills in such a manner, with the reaction yield close to 90%. The reaction of... 

R.A. Varin, T. Czujko, Ch. Chiu, Z. Wronski, Particle size effects on the desorption properties of nanostructured magnesium dihydride (MgH ) synthesized by controlled reactive mechanical milling (CRMM), J. Alloys Compd. 424 (2006) 356-364. 

There are four general methods for preparing magnesium dihydride.1... 

Caution. Magnesium dihydride prepared by this method is pyrophoric and reacts violently with water or other protic compounds. 

Fig. 1. Apparatus for the preparation of magnesium dihydride A, magnetic stirrer B, Teflon-coated stirring bar C, 250-ml, three-necked, round-bottomed flask D, water-cooled condenser E, pinch clamp F, 100-mL dropping funnel G, three-way stopcock H, stopcock to addition funnel I, mineral-oil bubbler J, Tygon tubing.

Magnesium dihydride is a white, granular solid which decomposes at 310° to magnesium metal and hydrogen.11 It is stable indefinitely at room temperature when protected from moisture and oxygen. It is pyrophoric in air and reacts violently with water. The infrared spectrum of magnesium dihydride shows two broad envelopes. One is at 1400-800 cm-1, the other at 800-400 cm-1. The x-ray powder diffraction (nickel-filtered CuKa) pattern shows lines at 3.17 A (s) 2.50 A (m) 2.25 A (m) 1.67 A (w). 

The checkers noted a delay in the formation of solid magnesium dihydride, which did not begin to precipitate until nearly all the lithium tetrahydridoaluminate(l —) had been added, t The diethyl ether was determined by difference in the gravimetric analysis. 

The overall electrochemical reaction cannot explain its corrosion rate in frequent conditions. The electrochemical dissolution of magnesium can be carried out through two successive steps the electrochemical formation of Mg " and its oxidation to a divalent ion through hydrogen ion reduction (chemical reaction) or the electrochemical formation of divalent ion directly or both. The mechanism of dissolution can depend also on the stability of magnesium dihydride as a functiou of pH at the interface. 

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