Lithium nitride is an inorganic compound with the chemical formula . It is the only stable alkali metal nitride. It is a reddish-pink solid with a high melting point.
Preparation and handling
Lithium nitride is prepared by direct reaction of elemental
lithium with
nitrogen gas:
[E. Döneges "Lithium Nitride" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, New York. Vol. 1. p. 984.]
Instead of burning lithium metal in an atmosphere of nitrogen, a solution of lithium in liquid
sodium metal can be treated with .
Lithium nitride is an extremely strong base, so it must be protected from moisture as it reacts violently with water to produce ammonia:
Structure and properties
-
alpha- (stable at room temperature and pressure) has an unusual crystal structure that consists of two types of layers: one layer has the composition contains 6-coordinate N centers and the other layer consists only of lithium cations.
Two other forms are known:
-
beta-, formed from the alpha phase at 0.42 GPa has the sodium arsenide () structure;
-
gamma- (same structure as lithium bismuthide ) forms from the beta form at 35 to 45 GPa.
Lithium nitride shows ionic conductivity for , with a value of c. 2×10−4 Ω−1cm−1, and an (intracrystal) activation energy of c. 0.26 eV (c. 24 kJ/mol). Hydrogen doping increases conductivity, whilst doping with metal ions (Aluminium, Copper, Magnesium) reduces it.
Reactions
Reacting lithium nitride with
carbon dioxide results in amorphous carbon nitride (), a
semiconductor, and lithium
cyanamide (), a precursor to
, in an exothermic reaction.
Under hydrogen at around 200°C, Li3N will react to form lithium amide.
At higher temperatures it will react further to form ammonia and lithium hydride.
Lithium imide can also be formed under certain conditions. Some research has explored this as a possible industrial process to produce ammonia since lithium hydride can be thermally decomposed back to lithium metal.
Lithium nitride has been investigated as a hydrogen storage for hydrogen gas, as the reaction is reversible at 270 °C. Up to 11.5% by weight absorption of hydrogen has been achieved.
See also
