Magnesium nitride

Magnesium nitride, Mg₃N₂, is an inorganic compound of magnesium and nitrogen. At room temperature and pressure it is a greenish yellow powder. It reacts with water to produce ammonia gas, as do many metal nitrides.

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Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃

Magnesium Nitride can be produced by burning magnesium metal in a pure nitrogen atmosphere.

3Mg + N₂ → Mg₃N₂

In fact, when magnesium is burned in air, some magnesium nitride is formed in addition to the principal product, magnesium oxide.

Uses

Magnesium nitride was the catalyst in the first practical synthesis of borazon (cubic boron nitride).^[1]

Robert H. Wentorf, Jr. was trying to convert the hexagonal form of boron nitride into the cubic form by a combination of heat, pressure, and a catalyst. He had already tried all the logical catalysts (for instance, those that catalyze the synthesis of diamond), but with no success.

Out of desperation and curiosity (he called it the "make the maximum number of mistakes" approach^[2]), he added some magnesium wire to the hexagonal boron nitride and gave it the same pressure and heat treatment. When he examined the wire under a microscope, he found tiny dark lumps clinging to it. These lumps could scratch a polished block of boron carbide, something only diamond was known to do.

From the smell of ammonia, caused by the reaction of magnesium nitride with the moisture in the air, he deduced that the magnesium metal had reacted with the boron nitride to form magnesium nitride, which was the true catalyst.

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